Science.gov

Sample records for metallicity galaxy ic

  1. Irregular Dwarf Galaxy IC 1613

    NASA Technical Reports Server (NTRS)

    2005-01-01

    Ultraviolet image (left) and visual image (right) of the irregular dwarf galaxy IC 1613. Low surface brightness galaxies, such as IC 1613, are more easily detected in the ultraviolet because of the low background levels compared to visual wavelengths.

  2. SN 2010ay Is a Luminous and Broad-Lined Type Ic Supernova Within a Low-Metallicity Host Galaxy

    NASA Technical Reports Server (NTRS)

    Sanders, N. E.; Soderberg, A. M.; Valenti, S.; Foley, R. J.; Chornock, R.; Chomiuk, L.; Berger, E.; Smartt, S.; Hurley, K.; Barthelmy, S. D.; Levesque, E. M.; Narayan, G.; Botticella, M. T.; Briggs, M. S.; Connaughton, V.; Terada, Y.; Gehrels, N.; Golenetskii, S.; Mazets, E.; Cline, T.; von Kienlin, A.; Boynton, W.; Chambers, K. C.; Grav, T.; Heasley, J. N.

    2012-01-01

    We report on our serendipitous pre-discovery detection and follow-up observations of the broad-lined Type Ic supernova (SN Ic) 2010ay at z = 0.067 imaged by the Pan-STARRS1 3pi survey just approximately 4 days after explosion. The supernova (SN) had a peak luminosity, MR approx. -20.2 mag, significantly more luminous than known GRB-SNe and one of the most luminous SNe Ib/c ever discovered. The absorption velocity of SN 2010ay is v Si (is) approx. 19×10(exp 3) km s-1 at approximately 40 days after explosion, 2-5 times higher than other broad-lined SNe and similar to the GRB-SN 2010bh at comparable epochs. Moreover, the velocity declines approximately 2 times slower than other SNe Ic-BL and GRB-SNe. Assuming that the optical emission is powered by radioactive decay, the peak magnitude implies the synthesis of an unusually large mass of 56Ni, MNi = 0.9 solar mass. Applying scaling relations to the light curve, we estimate a total ejecta mass, Mej (is) approx. 4.7 solar mass, and total kinetic energy, EK (is) approx. 11 × 10(exp 51) erg. The ratio of MNi to Mej is approximately 2 times as large for SN 2010ay as typical GRB-SNe and may suggest an additional energy reservoir. The metallicity (log(O/H)PP04 + 12 = 8.19) of the explosion site within the host galaxy places SN 2010ay in the low-metallicity regime populated by GRB-SNe, and (is) approximately 0.5(0.2) dex lower than that typically measured for the host environments of normal (broad-lined) SNe Ic. We constrain any gamma-ray emission with E(gamma) (is) approximately less than 6 × 10(exp 48) erg (25-150 keV), and our deep radio follow-up observations with the Expanded Very Large Array rule out relativistic ejecta with energy E (is) approximately greater than 10(exp 48) erg. We therefore rule out the association of a relativistic outflow like those that accompanied SN 1998bw and traditional long-duration gamma-ray bursts (GRBs), but we place less-stringent constraints on a weak afterglow like that seen from XRF

  3. SN 2010ay is a Luminous and Broad-lined Type Ic Supernova within a Low-metallicity Host Galaxy

    NASA Technical Reports Server (NTRS)

    Sanders, N. E.; Soderberg, A. M.; Valenti, S.; Chomiuk, L.; Berger, E.; Smartt, S.; Hurley, K.; Barthelmy, S. D.; Chornock, R.; Foley, R. J.; Levesque, E. M.; Narayan, G.; Botticella, M. T.; Briggs, M. S.; Connaughton, V.; Terada, Y.; Gehrels, N.; Golenetskii, S.; Mazets, E.; Cline, T.; von Kienlin, A.; Boynton, W.; Chambers, K. C.; Grav, T.; Heasley, J. N.

    2011-01-01

    We report on our serendipitous pre-discovery detection and detailed follow-up of the broad-lined Type Ic supernova SN2010ay at z approx 0.067 imaged by the Pan-STARRS1 3pi survey just approx 4 days after explosion. Combining our photometric observations with those available in the literature, we estimate the explosion date and the peak luminosity of the SN, M(sub R) approximately equals 20.2 mag, significantly brighter than known GRB-SNe and one of the most luminous SNe Ibc ever discovered. We measure the photospheric expansion velocity of the explosion from our spectroscopic follow-up observations, v(sub ph) approximately equals 19.2 X 10 (exp 3) km/s at approx 40 days after explosion. In comparison with other broad-lined SNe, the characteristic velocity of SN2010ay is 2 - 5 X higher and similar to the measurements for GRB-SNe at comparable epochs. Moreover the velocity declines two times slower than other SNe Ic-BL and GRB-SNe. Assuming that the optical emission is powered by radioactive decay, the peak magnitude implies the synthesis of an unusually large mass of Ni-56, M(sub Ni) = 0.9(+0.1/-0.1) solar mass. Our modeling of the light-curve points to a total ejecta mass, M(sub ej) approx 4.7 Solar Mass, and total kinetic energy, E(sub K,51) approximately equals 11. Thus the ratio of M(sub Ni) to M(sub ej) is at least twice as large for SN2010ay than in GRB-SNe and may indicate an additional energy reservoir. We also measure the metallicity (log(O/H) + 12 = 8.19) of the explosion site within the host galaxy using a high S/N optical spectrum. Our abundance measurement places this SN in the low-metallicity regime populated by GRB-SNe, and approx 0.2(0.5) dex lower than that typically measured for the host environments of normal (broad-lined) Ic supernovae. Despite striking similarities to the recent GRB-SN100316D/2010bh, we show that gamma-ray observations rule out an associated GRB with E(sub gamma) approx < 6 X 10(exp 48) erg (25-150 keV). Similarly, our deep

  4. Spectroscopic study of the peculiar galaxy IC 883

    NASA Astrophysics Data System (ADS)

    Yakovleva, V. A.; Merkulova, O. A.; Karataeva, G. M.; Shalyapina, L. V.; Yablokova, N. V.; Burenkov, A. N.

    2016-04-01

    We analyze new optical spectroscopic observations obtained at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences with the SCORPIO focal reducer (in the modes of a Fabry-Perot interferometer (FPI) and long-slit spectroscopy) and the Multi-Pupil Fiber Spectrograph for the galaxy IC 883. We have confirmed that the main body of the galaxy rotates around its minor axis. The positions of the dynamical axes of the stellar and gaseous components have been found to differ by ~10°. The velocities in the SE tail do not correspond to the circular rotation around the galaxy's minor axis. This structure is probably a fragment of an unwound curved spiral arm. Regions with high velocity dispersions and peculiarities in the velocity fields have been found along the minor axis. Our study of the age and metallicity of the galaxy's stellar population has shown that the mean values of these parameters in the stellar disk, except for the central region ( r ≤ 5"), are ≈1 Gyr and ≈-0.4 dex, respectively. Both young (2-5 × 108 yr) and old (5-10 × 109 yr) stellar populations are present in the circumnuclear region. Our analysis of the spectroscopic data for the bright feature 8" south of the nucleus coincident in position with a compact X-ray source has shown that this is apparently a dwarf galaxy or a remnant of a companion galaxy. Our FPI observations in the Hα emission line and direct images have revealed a region of ionized gas that together with the already known structures along the minor axis forms a clumpy tidal structure of ionized gas pulled from the companion galaxy. The results of our study confirm the previously proposed hypothesis that the observed peculiar structures were formed by the merger of two galaxies. However, it can be said that IC 883 does not belong to the class of polar-ring galaxies.

  5. First Stellar Abundances in the Dwarf Irregular Galaxy IC 1613

    NASA Astrophysics Data System (ADS)

    Tautvaišienė, Gražina; Geisler, Doug; Wallerstein, George; Borissova, Jura; Bizyaev, Dmitry; Pagel, Bernard E. J.; Charbonnel, Corinne; Smith, Verne

    2007-12-01

    Chemical abundances in three M supergiants in the Local Group dwarf irregular galaxy IC 1613 have been determined using high-resolution spectra obtained with the UVES spectrograph on the ESO 8.2 m Kueyen telescope. A detailed synthetic-spectrum analysis has been used to determine the atmospheric parameters and abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Fe, Co, Ni, La, and Eu. We find the overall metallicity of the stars to be [Fe/H] = -0.67 ± 0.09 and the age 9-13 Myr, which is in excellent agreement with the present-day values in the age-metallicity relationship model of IC 1613 by Skillman et al. We have found that the three supergiants investigated have a mean [α/Fe] equal to about -0.1, which is lower than seen in Galactic stars at the same metallicity and is in agreement with the results obtained in other dwarf irregular galaxies. The oxygen abundances are in agreement with the upper values of the nebular oxygen determinations in IC 1613. The abundance ratios of s- and r-process elements to iron are enhanced relative to solar by about 0.3 dex. The abundance pattern of the elements studied is similar to that of the Small Magellanic Cloud, except for Co and Ni, which are underabundant in the SMC. The observed elemental abundances are generally in very good agreement with the recent chemical evolution model of Yuk and Lee. Based on observations collected with the Very Large Telescope and the 2.2 m Telescope of the European Southern Observatory within the Observing Programs 70.B-0361(A) and 072.D-0113(D).

  6. ASKAP H I imaging of the galaxy group IC 1459

    NASA Astrophysics Data System (ADS)

    Serra, P.; Koribalski, B.; Kilborn, V.; Allison, J. R.; Amy, S. W.; Ball, L.; Bannister, K.; Bell, M. E.; Bock, D. C.-J.; Bolton, R.; Bowen, M.; Boyle, B.; Broadhurst, S.; Brodrick, D.; Brothers, M.; Bunton, J. D.; Chapman, J.; Cheng, W.; Chippendale, A. P.; Chung, Y.; Cooray, F.; Cornwell, T.; DeBoer, D.; Diamond, P.; Forsyth, R.; Gough, R.; Gupta, N.; Hampson, G. A.; Harvey-Smith, L.; Hay, S.; Hayman, D. B.; Heywood, I.; Hotan, A. W.; Hoyle, S.; Humphreys, B.; Indermuehle, B.; Jacka, C.; Jackson, C. A.; Jackson, S.; Jeganathan, K.; Johnston, S.; Joseph, J.; Kamphuis, P.; Leach, M.; Lenc, E.; Lensson, E.; Mackay, S.; Marquarding, M.; Marvil, J.; McClure-Griffiths, N.; McConnell, D.; Meyer, M.; Mirtschin, P.; Neuhold, S.; Ng, A.; Norris, R. P.; O'Sullivan, J.; Pathikulangara, J.; Pearce, S.; Phillips, C.; Popping, A.; Qiao, R. Y.; Reynolds, J. E.; Roberts, P.; Sault, R. J.; Schinckel, A. E. T.; Shaw, R.; Shimwell, T. W.; Staveley-Smith, L.; Storey, M.; Sweetnam, A. W.; Troup, E.; Tzioumis, A.; Voronkov, M. A.; Westmeier, T.; Whiting, M.; Wilson, C.; Wong, O. I.; Wu, X.

    2015-09-01

    We present H I imaging of the galaxy group IC 1459 carried out with six antennas of the Australian Square Kilometre Array Pathfinder equipped with phased-array feeds. We detect and resolve H I in 11 galaxies down to a column density of ˜1020 cm-2 inside a ˜6 deg2 field and with a resolution of ˜1 arcmin on the sky and ˜8 km s-1 in velocity. We present H I images, velocity fields and integrated spectra of all detections, and highlight the discovery of three H I clouds - two in the proximity of the galaxy IC 5270 and one close to NGC 7418. Each cloud has an H I mass of ˜109 M⊙ and accounts for ˜15 per cent of the H I associated with its host galaxy. Available images at ultraviolet, optical and infrared wavelengths do not reveal any clear stellar counterpart of any of the clouds, suggesting that they are not gas-rich dwarf neighbours of IC 5270 and NGC 7418. Using Parkes data, we find evidence of additional extended, low-column-density H I emission around IC 5270, indicating that the clouds are the tip of the iceberg of a larger system of gas surrounding this galaxy. This result adds to the body of evidence on the presence of intragroup gas within the IC 1459 group. Altogether, the H I found outside galaxies in this group amounts to several times 109 M⊙, at least 10 per cent of the H I contained inside galaxies. This suggests a substantial flow of gas in and out of galaxies during the several billion years of the group's evolution.

  7. Mass modelling of superthin galaxies: IC5249, UGC7321 and IC2233

    NASA Astrophysics Data System (ADS)

    Banerjee, Arunima; Bapat, Disha

    2017-04-01

    Superthin galaxies are low surface brightness (LSB) disc galaxies, characterized by optical discs with strikingly high values of planar-to-vertical axes ratios (>10), the physical origin and evolution of which continue to be a puzzle. We present mass models for three superthin galaxies: IC5249, UGC7321 and IC2233. We use high-resolution rotation curves and gas surface density distributions obtained from H I 21 cm radiosynthesis observations, in combination with their two-dimensional structural surface brightness decompositions at Spitzer 3.6 μm band, all of which were available in the literature. We find that while models with the pseudo-isothermal (PIS) and the Navarro-Frenk-White (NFW) dark matter density profiles fit the observed rotation curves of IC5249 and UGC7321 equally well, those with the NFW profile do not comply with the slowly rising rotation curve of IC2233. Interestingly, for all of our sample galaxies, the best-fitting mass models with a PIS dark matter density profile indicate a compact dark matter halo, i.e. Rc/RD < 2, where Rc is the core radius of the PIS dark matter halo and RD is the radial scalelength of the exponential stellar disc. The compact dark matter halo may be fundamentally responsible for the superthin nature of the stellar disc, and therefore our results may have important implications for the formation and evolution models of superthin galaxies in the universe.

  8. Exploring Dwarf Galaxy Evolution through Metallicity Distributions

    NASA Astrophysics Data System (ADS)

    Ross, Teresa

    2015-01-01

    As the most numerous type of galaxy, dwarf galaxies are ideal for examining galactic evolution on small scales. Additional clues to galactic evolution come from the metallicity distribution function (MDF), which is influenced by the star formation, accretion, outflows and galaxy interactions. We derived stellar MDFs for the Leo I, Leo II, IC 1613, and Phoenix dwarf galaxies using HST images in order to examine how their evolution compares as a function of various galaxy properties. These galaxies span a range of different morphologies, masses, SFHs and distances from the MW. We fit a simple evolution model and an accretion model to the MDFs in order to quantify the effect of gas flows and enrichment within the galaxies. The MDFs of Leo II (dSph), Phoenix (dTrans) and IC 1613 (dIr) have similar shapes, though their peak metallicities differ. Additionally, we find the accretion model, over the simple model, is a better fit chemical evolution model for these three galaxies. However these best fit accretion models do not require a significant amount of additional gas to explain the MDF shapes. In contrast the chemical evolution model that best fits the narrow MDF of Leo I implies twice the additional gas accretion. The similarities in the MDF shapes of Leo II, Phoenix and IC 1613, even though these galaxies all have different morphologies, implies that the current morphology is not the driving factor in shaping the MDF of these galaxies.

  9. Neutral hydrogen in the starburst galaxy NGC3690/IC694

    NASA Technical Reports Server (NTRS)

    Tolstoy, E.; Dickey, John M.; Israel, F. P.

    1990-01-01

    Researchers made observations of the neutral hydrogen (HI) emission structure surrounding the very deep absorption peak (observed earlier by Dickey (1986)) in the galaxy pair NGC3690/IC694. This galaxy pair is highly luminous in the far infrared, and known to exhibit extensive star formation as well as nuclear activity. Knowledge of the spatial distribution and velocity structure of the HI emission is of great importance to the understanding of the dynamics of the interaction and the resulting environmental effects on the galaxies.

  10. IC 1689: S0 galaxy with inner polar disk.

    NASA Astrophysics Data System (ADS)

    Hagen-Thorn, V. A.; Reshetnikov, V. P.

    1997-03-01

    The results of spectroscopic observations of the S0 galaxy IC 1689 are given. The radial velocity curves constructed from the measurements of Hα and [NII]λ6583 lines show that in the galaxy interior there is a gas disk (r=~3kpc) rotating around the axis placed in the main plane of the galaxy (polar disk). Active star formation occurs in the outer part of the disk (in the ring). Both Hα and [NII]λ6583 emission lines are observed here. Only collisionally excited [NII] radiates in the inner regions of the disk.

  11. The remarkable infrared galaxy Arp 220 = IC 4553

    NASA Technical Reports Server (NTRS)

    Soifer, B. T.; Neugebauer, G.; Helou, G.; Lonsdale, C. J.; Hacking, P.; Rice, W.; Houck, J. R.; Low, F. J.; Rowan-Robinson, M.

    1984-01-01

    IRAS observations of the peculiar galaxy Arp 220 = IC 4553 show that it is extremely luminous in the far-infrared, with a total luminosity of 2 x 10 to the 12th solar luminosities. The infrared-to-blue luminosity ratio of this galaxy is about 80, which is the largest value of the ratio for galaxies in the UGC catalog, and places it in the range of the 'unidentified' infrared sources recently reported by Houck et al. in the IRAS all-sky survey. Other observations of Arp 220, combined with the luminosity in the infrared, allow either a Seyfert-like or starburst origin for this luminosity.

  12. A nonthermal superbubble in the irregular galaxy IC 10

    NASA Technical Reports Server (NTRS)

    Yang, Hui; Skillman, Evan D.

    1993-01-01

    We present synthesis radio continuum observations of the nearby irregular galaxy IC 10. These observations, at 6, 20, and 49 cm, allow us to measure the flux and spectral index of a number of resolved sources in IC 10. While most of these are easily identified as thermal emission from H II regions and a few are nonthermal background sources, one extended, nonthermal source appears to be a superbubble in IC 10. Its large size (about 250 pc) implies that it is most likely the product of several supernovae. Comparisons of these radio observations with Halpha, H I, and optical imaging observations reveal that the large nonthermal superbubble is associated with a region of star formation containing two of the most luminous H II regions and the most massive H I cloud in IC 10. We tentatively identify a stellar cluster with two Wolf-Rayet stars in the center of the superbubble. We propose that this superbubble in IC 10 represents a bridge between the giant H II regions and the H I shells and supershells observed in our Galaxy and external galaxies.

  13. Ocular Shock Front in the Colliding Galaxy IC 2163

    NASA Astrophysics Data System (ADS)

    Kaufman, Michele; Elmegreen, Bruce G.; Struck, Curtis; Elmegreen, Debra Meloy; Bournaud, Frédéric; Brinks, Elias; Juneau, Stephanie; Sheth, Kartik

    2016-11-01

    ALMA observations in the 12CO J=1\\to 0 line of the interacting galaxy pair IC 2163 and NGC 2207 at 2″ × 1.″5 resolution reveal how the encounter drives gas to pile up in narrow, ∼1 kpc wide, “eyelids” in IC 2163. IC 2163 and NGC 2207 are involved in a grazing encounter, which has led to the development in IC 2163 of an eye-shaped (ocular) structure at mid-radius and two tidal arms. The CO data show that there are large velocity gradients across the width of each eyelid, with a mixture of radial and azimuthal streaming of gas at the outer edge of the eyelid relative to its inner edge. The sense of the radial streaming in the eyelids is consistent with the idea that gas from the outer part of IC 2163 flows inward until its radial streaming slows down abruptly and the gas piles up in the eyelids. The radial compression at the eyelids causes an increase in the gas column density by direct radial impact and also leads to a high rate of shear. A linear regression of the molecular column density N({{{H}}}2) on the magnitude of | {dv}/{dR}| across the width of the eyelid at fixed values of azimuth finds a strong correlation between N({{{H}}}2) and | {dv}/{dR}| . Substantial portions of the eyelids have high velocity dispersion in CO, indicative of elevated turbulence there.

  14. 1 Mpc giant radio galaxy IC 711 - 3 km Westerbork observations at 92 cm

    SciTech Connect

    Vallee, J.P.; Strom, R.G.

    1988-05-01

    New Westerbork obsevations at 92 cm of the galaxy IC 711 show a radio trail that extends 1 Mpc long, much farther out than previously observed at shorter wavelengths. These new observations confirm IC 711 as the longest head-tail galaxy known, and move IC 711 to the fifth rank among galaxies with the largest radio extension from an optical galaxy nucleus (after the classical double sources 3C 236, 3C 326, HB 13, and MSH 05-22). 20 references.

  15. Feeding IC 342: The nuclear spiral of a starburst galaxy

    NASA Technical Reports Server (NTRS)

    Levine, D.; Turner, J. L.; Hurt, Robert L.

    1993-01-01

    IC 342 is a large nearby (1.8 Mpc, Turner and Hurt, 1991, hereafter T&H) spiral galaxy undergoing a moderate nuclear starburst. T&H have previously mapped the inner arcminute in CO-13(1-0) using the Owens Valley Millimeter Interferometer and found evidence that the nuclear molecular gas takes the form of spiral arms in a density wave pattern. They suggest that radial streaming along the arms may channel gas from the exterior of the galaxy into the nucleus, feeding the starburst. We have mapped the CO-12(1-0) emission of the inner 2 kpc of IC 342 at 2.8 inch resolution using the Owens Valley Radio Observatory (OVRO) Millimeter Interferometer. The greater sensitivity of CO-12 observations has allowed us to trace the spiral pattern out to a total extent of greater than 1 kpc. The CO-12 observations extend considerably the structure observed at CO-13 and offer further evidence that a spiral density wave may extend from the disk into the nucleus of IC 342.

  16. X-ray Emission from Megamaser Galaxy IC 2560

    SciTech Connect

    Madejski, Greg; Done, Chris; Zycki, Piotr; Greenhill, Lincoln; /KIPAC, Menlo Park /Harvard-Smithsonian Ctr. Astrophys.

    2005-09-12

    Observation of the H{sub 2}O megamaser galaxy IC 2560 with the Chandra Observatory reveals a complex spectrum composed of soft X-ray emission due to multi-temperature thermal plasma, and a hard continuum with strong emission lines. The continuum is most likely a Compton reflection (reprocessing) of primary emission that is completely absorbed at least up to 7 keV. The lines can be identified with fluorescence from Si, S and Fe in the lowest ionization stages. The equivalent widths of the Si and S lines are broadly compatible with those anticipated for reprocessing by optically thick cold plasma of Solar abundances, while the large equivalent width of the Fe line requires some overabundance of iron. A contribution to the line from a transmitted component cannot be ruled out, but the limits on the strength of the Compton shoulder make it less likely. From the bolometric luminosity of the nuclear region, we infer that the source radiates at 1-10% of its Eddington luminosity, for an adopted central mass of 3 x 10{sup 6} M{sub {circle_dot}}. The overall spectrum is consistent with the hypotheses that the central engines powering the detected megamsers in accretion disks are obscured from direct view by the associated accretion disk material itself, and that there is a correlation between the occurrence of megamaser emission and Compton-thick absorption columns. For the 11 known galaxies with both column density measurements and maser emission believed to arise from accretion disks, eight AGN are Compton thick.

  17. The red extended structure of IC 10, the nearest blue compact galaxy

    NASA Astrophysics Data System (ADS)

    Gerbrandt, Stephanie A. N.; McConnachie, Alan W.; Irwin, Mike

    2015-11-01

    The Local Group starburst galaxy IC 10 is the closest example of a blue compact galaxy. Here, we use optical gi imaging from Canada-France-Hawaii Telescope/MegaCam and near infrared JHK imaging from United Kingdom Infrared Telescope/Wide Field Camera to conduct a comprehensive survey of the structure of IC 10. We examine the spatial distribution of its resolved young, intermediate and old stellar populations to large radius and low effective surface brightness levels. Akin to other dwarfs with multiple populations of different ages, stellar populations of decreasing average age are increasingly concentrated in this galaxy. We find that the young, starbursting population and the asymptotic giant branch population are both offset from the geometric centre of the older red giant branch (RGB) population by a few hundred parsecs, implying that the younger star formation occurred significantly away from the centre of the galaxy. The RGB population traces an extended structure that is typical of blue compact galaxies, with an effective radius of ˜5.75 arcmin (˜1.25 kpc). These measurements show that IC 10 is much more extended than has previously been realized, and this blue compact galaxy is one of the most extended dwarf galaxies in the Local Group. The outermost isophotes of this galaxy are very regular in shape and essentially circular in morphology. Based on this analysis, we do not find any evidence to suggest that IC 10 has undergone a recent, significant, interaction with an unknown companion.

  18. METALLICITY DISTRIBUTION FUNCTIONS OF FOUR LOCAL GROUP DWARF GALAXIES

    SciTech Connect

    Ross, Teresa L.; Holtzman, Jon; Saha, Abhijit; Anthony-Twarog, Barbara J. E-mail: holtz@nmsu.edu

    2015-06-15

    We present stellar metallicities in Leo I, Leo II, IC 1613, and Phoenix dwarf galaxies derived from medium (F390M) and broad (F555W, F814W) band photometry using the Wide Field Camera 3 instrument on board the Hubble Space Telescope. We measured metallicity distribution functions (MDFs) in two ways, (1) matching stars to isochrones in color–color diagrams and (2) solving for the best linear combination of synthetic populations to match the observed color–color diagram. The synthetic technique reduces the effect of photometric scatter and produces MDFs 30%–50% narrower than the MDFs produced from individually matched stars. We fit the synthetic and individual MDFs to analytical chemical evolution models (CEMs) to quantify the enrichment and the effect of gas flows within the galaxies. Additionally, we measure stellar metallicity gradients in Leo I and II. For IC 1613 and Phoenix our data do not have the radial extent to confirm a metallicity gradient for either galaxy. We find the MDF of Leo I (dwarf spheroidal) to be very peaked with a steep metal-rich cutoff and an extended metal-poor tail, while Leo II (dwarf spheroidal), Phoenix (dwarf transition), and IC 1613 (dwarf irregular) have wider, less peaked MDFs than Leo I. A simple CEM is not the best fit for any of our galaxies; therefore we also fit the “Best Accretion Model” of Lynden-Bell. For Leo II, IC 1613, and Phoenix we find similar accretion parameters for the CEM even though they all have different effective yields, masses, star formation histories, and morphologies. We suggest that the dynamical history of a galaxy is reflected in the MDF, where broad MDFs are seen in galaxies that have chemically evolved in relative isolation and narrowly peaked MDFs are seen in galaxies that have experienced more complicated dynamical interactions concurrent with their chemical evolution.

  19. Ionized gas in the Irr galaxy IC 10: The emission spectrum and ionization sources

    NASA Astrophysics Data System (ADS)

    Arkhipova, V. P.; Egorov, O. V.; Lozinskaya, T. A.; Moiseev, A. V.

    2011-02-01

    We present the observations of the Irr galaxy IC 10 at the 6-m SAO telescope with the panoramic Multi-Pupil Fiber Spectrograph (MPFS). Based on the results of these observations and our long-slit spectroscopy performed previously, we have investigated the ionized-gas emission spectrum in the region of intense star formation and refined the gas metallicity estimates. We show that the “diagnostic diagrams” constructed from our observations agree best with the new improved ionization models by Martin-Manjon et al. Using these models, we have determined the electron density and gas ionization parameter and ionizing-cluster characteristics, the age and mass, from the spectra of the investigated HII regions. The cluster ages and masses are shown to be within the ranges 2.5-5 Myr and (0.2-1) × 105 M ⊗, respectively.

  20. Winds of low-metallicity OB-type stars: HST-COS spectroscopy in IC 1613

    SciTech Connect

    Garcia, Miriam; Najarro, Francisco; Herrero, Artemio; Urbaneja, Miguel Alejandro

    2014-06-10

    We present the first quantitative ultraviolet spectroscopic analysis of resolved OB stars in IC 1613. Because of its alleged very low metallicity (≲1/10 Z {sub ☉}, from H II regions), studies in this Local Group dwarf galaxy could become a significant step forward from the Small Magellanic Cloud (SMC) toward the extremely metal-poor massive stars of the early universe. We present HST-COS data covering the ∼1150-1800 Å wavelength range with resolution R ∼ 2500. We find that the targets do exhibit wind features, and these are similar in strength to SMC stars. Wind terminal velocities were derived from the observed P Cygni profiles with the Sobolev plus Exact Integration method. The v {sub ∞}-Z relationship has been revisited. The terminal velocity of IC 1613 O stars is clearly lower than Milky Way counterparts, but there is no clear difference between IC 1613 and SMC or LMC analog stars. We find no clear segregation with host galaxy in the terminal velocities of B-supergiants, nor in the v {sub ∞}/v {sub esc} ratio of the whole OB star sample in any of the studied galaxies. Finally, we present the first evidence that the Fe-abundance of IC 1613 OB stars is similar to the SMC, which is in agreement with previous results on red supergiants. With the confirmed ∼1/10 solar oxygen abundances of B-supergiants, our results indicate that IC 1613's α/Fe ratio is sub-solar.

  1. Evolved stars in the Local Group galaxies - I. AGB evolution and dust production in IC 1613

    NASA Astrophysics Data System (ADS)

    Dell'Agli, F.; Di Criscienzo, M.; Boyer, M. L.; García-Hernández, D. A.

    2016-08-01

    We used models of thermally pulsing asymptotic giant branch (AGB) stars, which also describe the dust-formation process in the wind, to interpret the combination of near- and mid-infrared photometric data of the dwarf galaxy IC 1613. This is the first time that this approach is extended to an environment different from the Milky Way and the Magellanic Clouds (MCs). Our analysis, based on synthetic population techniques, shows nice agreement between the observations and the expected distribution of stars in the colour-magnitude diagrams obtained with JHK and Spitzer bands. This allows a characterization of the individual stars in the AGB sample in terms of mass, chemical composition and formation epoch of the progenitors. We identify the stars exhibiting the largest degree of obscuration as carbon stars evolving through the final AGB phases, descending from 1-1.25 M⊙ objects of metallicity Z = 10-3 and from 1.5-2.5 M⊙ stars with Z = 2 × 10-3. Oxygen-rich stars constitute the majority of the sample (˜65 per cent), mainly low-mass stars (<2 M⊙) that produce a negligible amount of dust (≤10-7 M⊙ yr-1). We predict the overall dust-production rate from IC 1613, mostly determined by carbon stars, to be ˜6 × 10-7 M⊙ yr-1 with an uncertainty of 30 per cent. The capability of the current generation of models to interpret the AGB population in an environment different from the MCs opens the possibility to extend this kind of analysis to other Local Group galaxies.

  2. An HI and Optical Study of Interacting Galaxies NGC 672 and IC 1727

    NASA Astrophysics Data System (ADS)

    Stanchfield, Sara; Wilcots, E.; Prescott, M.

    2012-05-01

    We present VLA HI radio data and WIYN broadband optical observations of NGC 672 and IC 1727, two nearby, late-type, spiral galaxies. In the optical NGC 672 appears as a symmetric barred spiral with defined spiral arms and a scale length of 1.2 kpc. IC 1727 is asymmetric, lacks a true bar, and has a scale length of 2. 4 kpc. In the HI, we see tidal bridge, indicating interaction between the two galaxies. We map the distribution and kinematics of the neutral hydrogen gas in order to understand the nature of the true distribution of mass in these systems and present the resulting mass models.

  3. Dense gas in low-metallicity galaxies

    NASA Astrophysics Data System (ADS)

    Braine, J.; Shimajiri, Y.; André, P.; Bontemps, S.; Gao, Yu; Chen, Hao; Kramer, C.

    2017-01-01

    Stars form out of the densest parts of molecular clouds. Far-IR emission can be used to estimate the star formation rate (SFR) and high dipole moment molecules, typically HCN, trace the dense gas. A strong correlation exists between HCN and far-IR emission, with the ratio being nearly constant, over a large range of physical scales. A few recent observations have found HCN to be weak with respect to the far-IR and CO in subsolar metallicity (low-Z) objects. We present observations of the Local Group galaxies M 33, IC 10, and NGC 6822 with the IRAM 30 m and NRO 45 m telescopes, greatly improving the sample of low-Z galaxies observed. HCN, HCO+, CS, C2H, and HNC have been detected. Compared to solar metallicity galaxies, the nitrogen-bearing species are weak (HCN, HNC) or not detected (CN, HNCO, N2H+) relative to far-IR or CO emission. HCO+ and C2H emission is normal with respect to CO and far-IR. While 13CO is the usual factor 10 weaker than 12CO, C18O emission was not detected down to very low levels. Including earlier data, we find that the HCN/HCO+ ratio varies with metallicity (O/H) and attribute this to the sharply decreasing nitrogen abundance. The dense gas fraction, traced by the HCN/CO and HCO+/CO ratios, follows the SFR but in the low-Z objects the HCO+ is much easier to measure. Combined with larger and smaller scale measurements, the HCO+ line appears to be an excellent tracer of dense gas and varies linearly with the SFR for both low and high metallicities.

  4. EVIDENCE FOR AN INTERACTION IN THE NEAREST STARBURSTING DWARF IRREGULAR GALAXY IC 10

    SciTech Connect

    Nidever, David L.; Slater, Colin T.; Bell, Eric F.; Ashley, Trisha; Simpson, Caroline E.; Ott, Jürgen; Johnson, Megan; Stanimirović, Snežana; Putman, Mary; Majewski, Steven R.; Jütte, Eva; Oosterloo, Tom A.; Burton, W. Butler

    2013-12-20

    Using deep 21 cm H I data from the Green Bank Telescope we have detected an ≳18.3 kpc long gaseous extension associated with the starbursting dwarf galaxy IC 10. The newly found feature stretches 1.°3 to the northwest and has a large radial velocity gradient reaching to ∼65 km s{sup –1} lower than the IC 10 systemic velocity. A region of higher column density at the end of the extension that possesses a coherent velocity gradient (∼10 km s{sup –1} across ∼26') transverse to the extension suggests rotation and may be a satellite galaxy of IC 10. The H I mass of IC 10 is 9.5 × 10{sup 7} (d/805 kpc){sup 2} M {sub ☉} and the mass of the new extension is 7.1 × 10{sup 5} (d/805 kpc){sup 2} M {sub ☉}. An IC 10-M31 orbit using known radial velocity and proper motion values for IC 10 show that the H I extension is inconsistent with the trailing portion of the orbit so that an M31-tidal or ram pressure origin seems unlikely. We argue that the most plausible explanation for the new feature is that it is the result of a recent interaction (and possible late merger) with another dwarf galaxy. This interaction could not only have triggered the origin of the recent starburst in IC 10, but could also explain the existence of previously found counter-rotating H I gas in the periphery of the IC 10 which was interpreted as originating from primordial gas infall.

  5. Metallicity Distribution Functions of Four Local Group Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Ross, Teresa L.; Holtzman, Jon; Saha, Abhijit; Anthony-Twarog, Barbara J.

    2015-06-01

    We present stellar metallicities in Leo I, Leo II, IC 1613, and Phoenix dwarf galaxies derived from medium (F390M) and broad (F555W, F814W) band photometry using the Wide Field Camera 3 instrument on board the Hubble Space Telescope. We measured metallicity distribution functions (MDFs) in two ways, (1) matching stars to isochrones in color-color diagrams and (2) solving for the best linear combination of synthetic populations to match the observed color-color diagram. The synthetic technique reduces the effect of photometric scatter and produces MDFs 30%-50% narrower than the MDFs produced from individually matched stars. We fit the synthetic and individual MDFs to analytical chemical evolution models (CEMs) to quantify the enrichment and the effect of gas flows within the galaxies. Additionally, we measure stellar metallicity gradients in Leo I and II. For IC 1613 and Phoenix our data do not have the radial extent to confirm a metallicity gradient for either galaxy. We find the MDF of Leo I (dwarf spheroidal) to be very peaked with a steep metal-rich cutoff and an extended metal-poor tail, while Leo II (dwarf spheroidal), Phoenix (dwarf transition), and IC 1613 (dwarf irregular) have wider, less peaked MDFs than Leo I. A simple CEM is not the best fit for any of our galaxies; therefore we also fit the “Best Accretion Model” of Lynden-Bell. For Leo II, IC 1613, and Phoenix we find similar accretion parameters for the CEM even though they all have different effective yields, masses, star formation histories, and morphologies. We suggest that the dynamical history of a galaxy is reflected in the MDF, where broad MDFs are seen in galaxies that have chemically evolved in relative isolation and narrowly peaked MDFs are seen in galaxies that have experienced more complicated dynamical interactions concurrent with their chemical evolution. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is

  6. A High-Resolution Radio Continuum Study Of The Dwarf Irregular Galaxy IC 10

    NASA Astrophysics Data System (ADS)

    Westcott, J.; Brinks, E.; Beswick, R. J.; Heesen, V.; Argo, M. K.; Baldi, R. D.; Fenech, D. M.; McHardy, I. M.; Smith, D. J. B.; Williams, D. R. A.

    2017-01-01

    We present high-resolution e-MERLIN radio continuum maps of the Dwarf Irregular galaxy IC 10 at 1.5 GHz and 5 GHz. We detect 11 compact sources at 1.5 GHz, 5 of which have complementary detections at 5 GHz. We classify 3 extended sources as compact HII regions within IC 10, 5 sources as contaminating background galaxies and identify 3 sources which require additional observations to classify. We do not expect that any of these 3 sources are Supernova Remnants as they will likely be resolved out at the assumed distance of IC 10 (0.7 Mpc). We correct integrated flux densities of IC 10 from the literature for contamination by unrelated background sources and obtain updated flux density measurements of 354 ± 11 mJy at 1.5 GHz and 199 ± 9 mJy at 4.85 GHz. The background contamination does not contribute significantly to the overall radio emission from IC 10, so previous analysis concerning its integrated radio properties remain valid.

  7. Metallic Winds in Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Robles-Valdez, F.; Rodríguez-González, A.; Hernández-Martínez, L.; Esquivel, A.

    2017-02-01

    We present results from models of galactic winds driven by energy injected from nuclear (at the galactic center) and non-nuclear starbursts. The total energy of the starburst is provided by very massive young stellar clusters, which can push the galactic interstellar medium and produce an important outflow. Such outflow can be a well or partially mixed wind, or a highly metallic wind. We have performed adiabatic 3D N-Body/Smooth Particle Hydrodynamics simulations of galactic winds using the gadget-2 code. The numerical models cover a wide range of parameters, varying the galaxy concentration index, gas fraction of the galactic disk, and radial distance of the starburst. We show that an off-center starburst in dwarf galaxies is the most effective mechanism to produce a significant loss of metals (material from the starburst itself). At the same time, a non-nuclear starburst produces a high efficiency of metal loss, in spite of having a moderate to low mass loss rate.

  8. Blue Supergiant X-Ray Binaries in the Nearby Dwarf Galaxy IC 10

    NASA Astrophysics Data System (ADS)

    Laycock, Silas G. T.; Christodoulou, Dimitris M.; Williams, Benjamin F.; Binder, Breanna; Prestwich, Andrea

    2017-02-01

    In young starburst galaxies, the X-ray population is expected to be dominated by the relics of the most massive and short-lived stars, black hole and neutron-star high-mass X-ray binaries (XRBs). In the closest such galaxy, IC 10, we have made a multi-wavelength census of these objects. Employing a novel statistical correlation technique, we have matched our list of 110 X-ray point sources, derived from a decade of Chandra observations, against published photometric data. We report an 8σ correlation between the celestial coordinates of the two catalogs, with 42 X-ray sources having an optical counterpart. Applying an optical color–magnitude selection to isolate blue supergiant (SG) stars in IC 10, we find 16 matches. Both cases show a statistically significant overabundance versus the expectation value for chance alignments. The blue objects also exhibit systematically higher {f}x/{f}v ratios than other stars in the same magnitude range. Blue SG-XRBs include a major class of progenitors of double-degenerate binaries, hence their numbers are an important factor in modeling the rate of gravitational-wave sources. We suggest that the anomalous features of the IC 10 stellar population are explained if the age of the IC 10 starburst is close to the time of the peak of interaction for massive binaries.

  9. Kinematics of the ionized gas in the Local Group irregular galaxy IC 1613

    NASA Astrophysics Data System (ADS)

    Valdez-Gutiérrez, M.; Rosado, M.; Georgiev, L.; Borissova, J.; Kurtev, R.

    2001-01-01

    We present Hα and [S Ii] observations for the Local Group irregular galaxy IC 1613 using the PUMA scanning Fabry-Perot interferometer. Our goal is to analyze the kinematics of the ionized gas in the complex sample of superbubbles located in the whole extension of our field (10\\arcmin ), which includes most of the optical emission of this galaxy, and to study the inter-relationship between young stellar associations and nebulae based on a previous study that we have made on the stellar associations of the central region of this galaxy. The ionized gas in this galaxy is distributed in classical H Ii regions and in a series of superbubbles (also called giant shells) covering a large fraction of the optical extent of the galaxy. We present a catalog of kinematical properties of both the H Ii regions of this galaxy and the superbubbles. We have also compared the kinematics of the ionized gas in H Ii regions to search for possible dynamic differences between neutral and ionized gas.

  10. Efficiency of Metal Mixing in Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Hirai, Yutaka; Saitoh, Takayuki R.

    2017-04-01

    Metal mixing plays a critical role in the enrichment of metals in galaxies. The abundance of elements such as Mg, Fe, and Ba in metal-poor stars helps us understand the metal mixing in galaxies. However, the efficiency of metal mixing in galaxies is not yet understood. Here we report a series of N-body/smoothed particle hydrodynamics simulations of dwarf galaxies with different efficiencies of metal mixing using a turbulence-induced mixing model. We show that metal mixing apparently occurs in dwarf galaxies from Mg and Ba abundances. We find that a scaling factor for metal diffusion larger than 0.01 is necessary to reproduce the measured abundances of Ba in dwarf galaxies. This value is consistent with the value expected from turbulence theory and experiments. We also find that the timescale of metal mixing is less than 40 Myr. This timescale is shorter than the typical dynamical times of dwarf galaxies. We demonstrate that the determination of a degree of scatters of Ba abundance by the observation will help us to better constrain the efficiency of metal mixing.

  11. IC 4767 (the X-galaxy) - the missing link for understanding galaxies with peanut-shaped bulges

    SciTech Connect

    Whitmore, B.C.; Bell, M.

    1988-01-01

    Photometric and kinematic observations of the peculiar S0 galaxy IC 4767, the X-galaxy, are presented. At various intensities the bulge of this galaxy looks like a normal spheroidal system with elliptical isophotes, a well-defined rectangle, and a peanut-shaped or X-shaped structure with components aligned at oblique angles to the major axis. The observations reveal a rapidly rotating inner disk of gas and dust which is nearly aligned with the major axis. The presence of gaseous emission alone suggests an accretion event. The stars in the outer regions of the X-component are rotating nearly as rapidly as the gas in the main disk, indicating that they are in relatively circular orbits. The five most prominent peanut-shaped bulges all have several nearby companions, evidence that the peanut deformity is due to interaction between galaxies. An analogy with the formation mechanism proposed for polar-ring galaxies suggests how an X-shaped component could develop from the accretion of gaseous material during an inclined encounter. 29 references.

  12. Choirs H I galaxy groups: The metallicity of dwarf galaxies

    SciTech Connect

    Sweet, Sarah M.; Drinkwater, Michael J.; Meurer, Gerhardt; Bekki, Kenji; Dopita, Michael A.; Nicholls, David C.; Kilborn, Virginia

    2014-02-10

    We present a recalibration of the luminosity-metallicity relation for gas-rich, star-forming dwarfs to magnitudes as faint as M{sub R} ∼ –13. We use the Dopita et al. metallicity calibrations to calibrate the relation for all the data in this analysis. In metallicity-luminosity space, we find two subpopulations within a sample of high-confidence Sloan Digital Sky Survey (SDSS) DR8 star-forming galaxies: 52% are metal-rich giants and 48% are metal-medium galaxies. Metal-rich dwarfs classified as tidal dwarf galaxy (TDG) candidates in the literature are typically of metallicity 12 + log(O/H) = 8.70 ± 0.05, while SDSS dwarfs fainter than M{sub R} = –16 have a mean metallicity of 12 + log(O/H) = 8.28 ± 0.10, regardless of their luminosity, indicating that there is an approximate floor to the metallicity of low-luminosity galaxies. Our hydrodynamical simulations predict that TDGs should have metallicities elevated above the normal luminosity-metallicity relation. Metallicity can therefore be a useful diagnostic for identifying TDG candidate populations in the absence of tidal tails. At magnitudes brighter than M{sub R} ∼ –16, our sample of 53 star-forming galaxies in 9 H I gas-rich groups is consistent with the normal relation defined by the SDSS sample. At fainter magnitudes, there is an increase in dispersion of the metallicity of our sample, suggestive of a wide range of H I content and environment. In our sample, we identify three (16% of dwarfs) strong TDG candidates (12 + log(O/H) > 8.6) and four (21%) very metal-poor dwarfs (12 + log(O/H) < 8.0), which are likely gas-rich dwarfs with recently ignited star formation.

  13. Characterization Of Deformation Properties Of Metals In 3D ICs

    NASA Astrophysics Data System (ADS)

    Wittler, Olaf; Mroßko, Raul; Huber, Saskia; Dowhan, Lukasz; Lang, Klaus-Dieter

    2011-09-01

    The properties of the materials involved in the set-up of 3D ICs need to be known, when the occurring mechanical stresses are to be modeled. Especially elastic-plastic properties are relevant for the metal layers, which form redistribution layers and the through silicon vias. These can be characterized by the nanoindentation experiment, which is an established technique for the determination of Hardness and Young's modulus of thin films. But this standard data set is not sufficient to be used as input to finite element simulations, because stress strain curves are required for the analysis of reliability of metal layers. These stress-strain curves can be obtained by fitting the force displacement curves of the experiment with a finite-element model. This approach enables additionally a solution for the so called substrate effect, because the stiffness of the substrate can be considered in the fitting model. This known approach is being applied and tested on thin (300 nm) gold layers deposited on silicon. It is shown that a good sensitivity for Young's Modulus can be reached even for indents that exceed 10% of the film thickness, but for the plastic data the results are not unique and a range of plastic properties can be fitted.

  14. Exploring stellar metallicities in dwarf galaxies and their implications

    NASA Astrophysics Data System (ADS)

    Ross, Teresa Lynn

    In this thesis I discuss issues involving stellar metallicities in dwarf galaxies. Stars reflect the gas composition at the time they formed, thereby making the metallicity distribution function (MDF -- the relative number of stars as a function of metallicity) a record of the chemical evolution within a galaxy. I measure photometric metallicities using Wide Field Camera 3 (WFC3) observations aboard the Hubble Space Telescope. Advantages of photometric metallicities include measuring every star in the field down to fainter magnitudes than allowed by spectroscopy. I quantified and calibrated the metallicity and temperature sensitivities of colors derived from nine WFC3 filters using Dartmouth isochrones and Kurucz model atmospheres. The photometric metallicities were tested and calibrated with five well studied Galactic clusters spanning three orders of magnitude in metallicity: M92, NGC 6752, NGC 104, NGC 5927, and NGC 6791. The greatest accuracy in assigning metallicity was found using the (F390M--F555W) color, with the main advantage being the increased color sensitivity at low metallicity. MDFs for a population, along with chemical evolution models provide evolutionary information about gas flows and enrichment within that galaxy. I measured photometric metallicities in Leo I, Leo II, IC 1613, and Phoenix, and analytical chemical evolution models were fit to their MDFs. The MDF shapes, chemical evolution models and dynamic histories suggest that the galactic conditions during periods of star formation influenced the metallicities. I find that the narrower MDFs are indicative of interactions occurring in concert with star formation, while a broader MDF indicates a passive evolution. Additionally, I explore ways to combine chemical evolution models and star formation histories (SFH), to quantify the metallicity evolution with time. The SFHs of Weisz et al. (2014) are assessed for their potential to determine MDFs for 40 Local Group dwarf galaxies. The SFH

  15. Modeling the spectral energy distribution of the radio galaxy IC310

    NASA Astrophysics Data System (ADS)

    Fraija, N.; Marinelli, A.; Galván-Gámez, A.; Aguilar-Ruiz, E.

    2017-03-01

    The radio galaxy IC310 located in the Perseus Cluster is one of the brightest objects in the radio and X-ray bands, and one of the closest active galactic nuclei observed in very-high energies. In GeV - TeV γ-rays, IC310 was detected in low and high flux states by the MAGIC telescopes from October 2009 to February 2010. Taking into account that the spectral energy distribution (SED) up to a few GeV seems to exhibit a double-peak feature and that a single-zone synchrotron self-Compton (SSC) model can explain all of the multiwavelength emission except for the non-simultaneous MAGIC emission, we interpret, in this work, the multifrequency data set of the radio galaxy IC310 in the context of homogeneous hadronic and leptonic models. In the leptonic framework, we present a multi-zone SSC model with two electron populations to explain the whole SED whereas for the hadronic model, we propose that a single-zone SSC model describes the SED up to a few GeVs and neutral pion decay products resulting from pγ interactions could describe the TeV - GeV γ-ray spectra. These interactions occur when Fermi-accelerated protons interact with the seed photons around the SSC peaks. We show that, in the leptonic model the minimum Lorentz factor of second electron population is exceedingly high γe ∼ 105 disfavoring this model, and in the hadronic model the required proton luminosity is not extremely high ∼1044 erg/s, provided that charge neutrality between the number of electrons and protons is given. Correlating the TeV γ-ray and neutrino spectra through photo-hadronic interactions, we find that the contribution of the emitting region of IC310 to the observed neutrino and ultra-high-energy cosmic ray fluxes are negligible.

  16. ON THE RADIAL EXTENT OF THE DWARF IRREGULAR GALAXY IC10

    SciTech Connect

    Sanna, N.; Bono, G.; Buonanno, R.; Stetson, P. B.; Ferraro, I.; Caputo, F.; Iannicola, G.; Monelli, M.; Nonino, M.; Prada Moroni, P. G.; Degl'Innocenti, S.; Bresolin, R.; Cignoni, M.; Matsunaga, N.; Pietrinferni, A.; Romaniello, M.; Storm, J.; Walker, A. R.

    2010-10-20

    We present new deep and accurate space (Advanced Camera for Surveys-Wide Field Planetary Camera 2 on board the Hubble Space Telescope) and ground-based (Suprime-Cam at Subaru Telescope, Mega-Cam at Canada-France-Hawaii Telescope) photometric and astrometric data for the Local Group dwarf irregular IC10. We confirm the significant decrease of the young stellar population when moving from the center toward the outermost regions. We find that the tidal radius of IC10 is significantly larger than previous estimates of r{sub t} {approx_lt} 10'. By using the I, V-I color-magnitude diagram based on the Suprime-Cam data, we detect sizable samples of red giant (RG) stars up to radial distances of 18'-23' from the galactic center. The ratio between observed star counts (Mega-Cam data) across the tip of the RG branch and star counts predicted by Galactic models indicates a star count excess at least at a 3{sigma} level up to 34'-42' from the center. This finding supports the hypothesis that the huge H I cloud covering more than 1{sup 0} across the galaxy is associated with IC10. We also provide new estimates of the total luminosity (L{sub V} {approx} 9 x 10{sup 7} L {sub sun}, M{sub V} {approx} -15.1 mag) that agree with similar estimates available in the literature. If we restrict our study to the regions where rotational velocity measurements are available (r {approx} 13'), we find a mass-to-light ratio ({approx}10 M {sub sun}/L {sub sun}) that is at least one order of magnitude larger than previous estimates. The new estimate should be cautiously treated, since it is based on a minimal fraction of the body of the galaxy.

  17. A Journey In The Radio Galaxy IC 1531: Through The Linear Scale, Across The Electromagnetic Spectrum

    NASA Astrophysics Data System (ADS)

    Bassi, Tiziana; Migliori, G.; Grandi, P.; Vignali, C.

    2016-10-01

    We present a multi-scale and multi-frequency study of the radio galaxy IC1531 (z=0.026) with Chandra, XMM-Newton and Fermi. The Chandra image shows an X-ray core and 5 extended emission with the radio jet. The X-ray spectrum of the core is well fitted by a power law (Γ=2.2). The X-ray emission of the large scale jet is most-likely synchrotron emission, further confirming the low-power source classication. The gamma-ray analisys shows a 5-days variability, from which it is possible to estimate the size of the emitting region. We present a study of the spectral energy distribution of the core of IC1531 from radio to gamma-ray emission. The models allowed us to determine the nature of the gamma-ray emission and infer the jet kinetic power at sub-pc scales. The jet power at kpc scales is estimated from the total radio luminosity at 151 MHz. Finally, we compare the jet power with the disk luminosity. We discuss our results in terms of the formation and evolution of the jet.

  18. Shock-induced star formation in IC2153 - A colliding pair of galaxies

    NASA Astrophysics Data System (ADS)

    Olofsson, K.; Bergvall, N.; Ekman, A.

    1984-08-01

    Direct photographic, photometric and spectroscopic observations of the interacting galaxy-pair IC2153 = ESO 364-IG 22 are reported. The observations were performed with the ESO 3.6-m, 1.5 m and 1-m telescopes at La Silla, Chile. The mean radial velocity of the system is 2630 km/s ( = or 30 km/s), corresponding to a distance of 35 Mpc. The system is aobut nine kpc across, and its UBV colors are consistent with those found in irregular galaxies. The absolute magnitude of the system is -18.4 mag. Spectral tracings of the main components show an early-type absorption spectrum and an emission spectrum. Spectra in the intermediate region of the pair have pure emission-line characteristics. Evidence of shock-heating in the galactic H-II regions, and it is estimated that about 7 percent of the light in H-beta originates from shock-heating and that the remainder arises from photoionization by hot stars. From a stellar population model, it is found that the UBV Johnson colors in the pair represent a burst of star formation with an age of 150 million years.

  19. Spectrophotometry of the central region of the galaxy Markaryan 298 = IC 1182-4

    NASA Astrophysics Data System (ADS)

    Metik, L. P.; Pronik, I. I.

    1981-10-01

    An analysis of spectra obtained with an approximately 95 A/mm-dispersion spectrograph has yielded new data on the structure of the central region of the Seyfert galaxy Markaryan 298 = IC 1182-4. The central region's gaseous formation has a diameter of 6.5 kpc, an electron density of 0.2-0.5/cu cm, and a mass ratio (M/solar-M) ranging from 0.6 x 10 to the 7th to 7 x 10 to the 8th. The data further suggests that this gas formation is associated with condensations of blue stars, and interacts with both the nucleus and the eastern elongated structure of the galaxy. The nucleus of Markaryan 298 is found to be a type 1 Seyfert which is distorted by dust absorption, with a hydrogen envelope that is opaque in the Balmer lines and inhomogeneous in its physical conditions. Gas condensations in the forbidden line emission region are found to be of the densities 20, 10,000 and 200,000/cu cm

  20. THE METALLICITY EVOLUTION OF INTERACTING GALAXIES

    SciTech Connect

    Torrey, Paul; Hernquist, Lars; Cox, T. J.; Kewley, Lisa

    2012-02-10

    Nuclear inflows of metal-poor interstellar gas triggered by galaxy interactions can account for the systematically lower central oxygen abundances observed in local interacting galaxies. Here, we investigate the metallicity evolution of a large set of simulations of colliding galaxies. Our models include cooling, star formation, feedback, and a new stochastic method for tracking the mass recycled back to the interstellar medium from stellar winds and supernovae. We study the influence of merger-induced inflows, enrichment, gas consumption, and galactic winds in determining the nuclear metallicity. The central metallicity is primarily a competition between the inflow of low-metallicity gas and enrichment from star formation. An average depression in the nuclear metallicity of {approx}0.07 is found for gas-poor disk-disk interactions. Gas-rich disk-disk interactions, on the other hand, typically have an enhancement in the central metallicity that is positively correlated with the gas content. The simulations fare reasonably well when compared to the observed mass-metallicity and separation-metallicity relationships, but further study is warranted.

  1. A Radio Study of the Seyfert Galaxy IC 5063: Evidence for Fast Gas Outflow

    NASA Astrophysics Data System (ADS)

    Morganti, R.; Oosterloo, T.; Tsvetanov, Z.

    1998-03-01

    We present new radio continuum (8 and 1.4 GHz) and H i 21 cm line observations of the Seyfert 2 galaxy IC 5063 (PKS 2048-572), obtained with the Australia Telescope Compact Array. The high-resolution 8 GHz image reveals a linear triple structure ~4" (1.3 kpc) in size. This small-scale radio emission shows a strong morphological association with the narrow-line region (NLR), the inner part of the optical emission-line region. It is aligned with the inner dust lane and is oriented perpendicularly to the position angle of the optical polarization. We identify the radio nucleus as the central blob of the radio emission. At 21 cm, very broad (~700 km s^-1) H i absorption is observed against the strong continuum source. This absorption is almost entirely blueshifted, indicating a fast net outflow, but a faint and narrow redshifted component is also present. In IC 5063 we see clear evidence, both morphological and kinematic, of strong shocks resulting from the interaction between the radio plasma and the interstellar medium (ISM) in the central few kiloparsecs. However, we estimate the energy flux in the radio plasma to be an order of magnitude smaller than the energy flux emitted in emission lines. Thus, although strong shocks associated with the jet/ISM interaction occur, and could contribute locally to the ionization of the NLR, they are unlikely to account solely for the global ionization of the emission-line region, particularly at large distances. The main structure of the H i emission is a warped disk associated with the system of dust lanes of R ~ 2' (~38 kpc, corresponding to ~5 effective radii). The lack of kinematically disturbed gas (both neutral and ionized) outside the central few kiloparsecs, the warped structure of the large-scale disk, and the close morphological connection between the inner dust lanes and the large-scale ionized gas all support the idea that the gas at large radii is photoionized by the central region, while shadowing effects are

  2. The fast molecular outflow in the Seyfert galaxy IC 5063 as seen by ALMA

    NASA Astrophysics Data System (ADS)

    Morganti, Raffaella; Oosterloo, Tom; Oonk, J. B. Raymond; Frieswijk, Wilfred; Tadhunter, Clive

    2015-08-01

    We use high-resolution (0.5 arcsec) CO(2-1) observations performed with the Atacama Large Millimetre/submillimetre Array to trace the kinematics of the molecular gas in the Seyfert 2 galaxy IC 5063. The data reveal that the kinematics of the gas is very complex. A fast outflow of molecular gas extends along the entire radio jet (~1 kpc), with the highest outflow velocities about 0.5 kpc from the nucleus, at the location of the brighter hot spot in the western lobe. The ALMA data show that a massive, fast outflow with velocities up to 650kms-1 of cold molecular gas is present, in addition to the outflow detected earlier in warm H2, H i and ionized gas. All phases of the gas outflow show similar kinematics. IC 5063 appears to be one of the best examples of the multi-phase nature of AGN-driven outflows. Both the central AGN and the radio jet could energetically drive the outflow, however, the characteristics of the outflowing gas point to the radio jet being the main driver. This is an important result because IC 5063, although one of the most powerful Seyfert galaxies, is a relatively weak radio source (P1.4 GHz = 3 × 1023 W Hz-1). All the observed characteristics can be described by a scenario of a radio plasma jet expanding into a clumpy medium, interacting directly with the clouds and inflating a cocoon that drives a lateral outflow into the interstellar medium. This model is consistent with results obtained by recent simulations. A stronger, direct interaction between the jet and a gas cloud is present at the location of the brighter western lobe. This interaction may also be responsible for the asymmetry in the radio brightness of the two lobes. Even assuming the most conservative values for the conversion factor CO-to-H2, we find that the mass of the outflowing gas is between 1.9 and 4.8 × 107 M⊙, of which between 0.5 and 1.3 × 107 M⊙ is associated with the fast outflow at the location of the western lobe. These amounts are much larger than those of the

  3. The optical and near-infrared distribution of light in the edge-on galaxy IC 2531

    NASA Technical Reports Server (NTRS)

    Wainscoat, R. J.; Freeman, K. C.; Hyland, A. R.

    1989-01-01

    Optical and near-IR imaging of the edge-on galaxy IC 2531 is presented, and an attempt is made to derive the true distributions of stars and dust in this galaxy. The results suggest that the z dependence of the light distribution is better fitted by an exponential than by the isothermal sech-squared distribution. The dynamical implication of such a distribution is that the vertical velocity dispersion near the galactic plane should increase with z. A simple model for the light and dust distribution in IC 2531 employing three exponential components is constructed: an old disk, a young disk, and dust. Vertical scale heights of h(zd) = h(z)/4 and h(zy) = h(z)/8 and an absorption equivalent to about half of that in the Galaxy are found to produce the best fits.

  4. LOCAL TADPOLE GALAXIES: DYNAMICS AND METALLICITY

    SciTech Connect

    Sanchez Almeida, J.; Munoz-Tunon, C.; Mendez-Abreu, J.; Elmegreen, D. M.; Elmegreen, B. G. E-mail: cmt@iac.es E-mail: elmegreen@vassar.edu

    2013-04-10

    Tadpole galaxies, with a bright peripheral clump on a faint tail, are morphological types unusual in the nearby universe but very common early on. Low mass local tadpoles were identified and studied photometrically in a previous work, which we complete here analyzing their chemical and dynamical properties. We measure H{alpha} velocity curves of seven local tadpoles, representing 50% of the initial sample. Five of them show evidence for rotation ({approx}70%), and a sixth target hints at it. Often the center of rotation is spatially offset with respect to the tadpole head (three out of five cases). The size and velocity dispersion of the heads are typical of giant H II regions, and three of them yield dynamical masses in fair agreement with their stellar masses as inferred from photometry. In four cases the velocity dispersion at the head is reduced with respect to its immediate surroundings. The oxygen metallicity estimated from [N II] {lambda}6583/H{alpha} often shows significant spatial variations across the galaxies ({approx}0.5 dex), being smallest at the head and larger elsewhere. The resulting chemical abundance gradients are opposite to the ones observed in local spirals, but agrees with disk galaxies at high redshift. We interpret the metallicity variation as a sign of external gas accretion (cold-flows) onto the head of the tadpole. The galaxies are low-metallicity outliers of the mass-metallicity relationship. In particular, two of the tadpole heads are extremely metal poor, with a metallicity smaller than a tenth of the solar value. These two targets are also very young (ages smaller than 5 Myr). All these results combined are consistent with the local tadpole galaxies being disks in early stages of assembling, with their star formation sustained by accretion of external metal-poor gas.

  5. THE ACS LCID PROJECT. II. FAINT VARIABLE STARS IN THE ISOLATED DWARF IRREGULAR GALAXY IC 1613

    SciTech Connect

    Bernard, Edouard J.; Monelli, Matteo; Gallart, Carme; Aparicio, Antonio; Drozdovsky, Igor; Hidalgo, Sebastian L.; Cassisi, Santi; Skillman, Evan D.; Stetson, Peter B. E-mail: monelli@iac.e E-mail: antapaj@iac.e E-mail: slhidalgo@iac.e E-mail: skillman@astro.umn.ed

    2010-04-01

    We present the results of a new search for variable stars in the Local Group (LG) isolated dwarf galaxy IC 1613, based on 24 orbits of F475W and F814W photometry from the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope. We detected 259 candidate variables in this field, of which only 13 (all of them bright Cepheids) were previously known. Out of the confirmed variables, we found 90 RR Lyrae stars, 49 classical Cepheids (including 36 new discoveries), and 38 eclipsing binary stars for which we could determine a period. The RR Lyrae include 61 fundamental (RRab) and 24 first-overtone (FO, RRc) pulsators, and five pulsating in both modes simultaneously (RRd). As for the majority of LG dwarfs, the mean periods of the RRab and RRc (0.611 and 0.334 days, respectively) as well as the fraction of overtone pulsators (f{sub c} = 0.28) place this galaxy in the intermediate regime between the Oosterhoff types. From their position on the period-luminosity diagram and light-curve morphology, we can unambiguously classify 25 and 14 Cepheids as fundamental and FO mode pulsators, respectively. Another two are clearly second-overtone Cepheids, the first ones to be discovered beyond the Magellanic Clouds. Among the remaining candidate variables, five were classified as delta-Scuti and five as long-period variables. Most of the others are located on the main sequence, the majority of them likely eclipsing binary systems, although some present variations similar to pulsating stars. We estimate the distance to IC 1613 using various methods based on the photometric and pulsational properties of the Cepheids and RR Lyrae stars. The values we find are in very good agreement with each other and with previous estimates based on independent methods. When corrected to a common reddening of E(B - V) = 0.025 and true Large Magellanic Cloud (LMC) distance modulus of (m-M){sub LMC,0} = 18.515 +- 0.085, we find that all the distance determinations from the literature converge

  6. Multi-Wavelength Observations of the Supernova Remnant Populations in the Nearby Spiral Galaxies IC 342 and NGC 4258

    NASA Astrophysics Data System (ADS)

    Pannuti, Thomas; Chomiuk, L.; Grimes, C. K.; Staggs, W. D.; Tussey, J. M.; Laine, S.; Schlegel, E.

    2011-01-01

    Supernova remnants (SNRs) are intimately tied to many crucial processes associated with the interstellar medium of galaxies, such as the acceleration of cosmic-ray particles and the deposition of vast amounts of kinetic energy and chemically-enriched material. Well-known observational challenges in the study of SNRs located in the Milky Way Galaxy (for example, formidable extinction along Galactic lines of sight and considerable uncertainties in the distances to these sources) have motivated searches for SNRs in nearby galaxies at such characteristic wavelengths as X-ray, optical and radio. These searches have revealed a considerable number of SNRs and led to new insights into their properties, but the SNR populations in only a handful of nearby galaxies have been adequately surveyed at multiple wavelengths. To help remedy this situation, we are conducting a multi-wavelength study of the SNR population of selected nearby galaxies. To illustrate our work, we present the results of studies of the SNR population in two nearby spiral galaxies, IC 342 and NGC 4258. Our results draw upon the analysis of pointed archival radio and X-ray observations of these two galaxies. Initial results will be presented and discussed.

  7. The ACS LCID Project. II. Faint Variable Stars in the Isolated Dwarf Irregular Galaxy IC 1613

    NASA Astrophysics Data System (ADS)

    Bernard, Edouard J.; Monelli, Matteo; Gallart, Carme; Aparicio, Antonio; Cassisi, Santi; Drozdovsky, Igor; Hidalgo, Sebastian L.; Skillman, Evan D.; Stetson, Peter B.

    2010-04-01

    We present the results of a new search for variable stars in the Local Group (LG) isolated dwarf galaxy IC 1613, based on 24 orbits of F475W and F814W photometry from the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope. We detected 259 candidate variables in this field, of which only 13 (all of them bright Cepheids) were previously known. Out of the confirmed variables, we found 90 RR Lyrae stars, 49 classical Cepheids (including 36 new discoveries), and 38 eclipsing binary stars for which we could determine a period. The RR Lyrae include 61 fundamental (RRab) and 24 first-overtone (FO, RRc) pulsators, and five pulsating in both modes simultaneously (RRd). As for the majority of LG dwarfs, the mean periods of the RRab and RRc (0.611 and 0.334 days, respectively) as well as the fraction of overtone pulsators (f c = 0.28) place this galaxy in the intermediate regime between the Oosterhoff types. From their position on the period-luminosity diagram and light-curve morphology, we can unambiguously classify 25 and 14 Cepheids as fundamental and FO mode pulsators, respectively. Another two are clearly second-overtone Cepheids, the first ones to be discovered beyond the Magellanic Clouds. Among the remaining candidate variables, five were classified as δ-Scuti and five as long-period variables. Most of the others are located on the main sequence, the majority of them likely eclipsing binary systems, although some present variations similar to pulsating stars. We estimate the distance to IC 1613 using various methods based on the photometric and pulsational properties of the Cepheids and RR Lyrae stars. The values we find are in very good agreement with each other and with previous estimates based on independent methods. When corrected to a common reddening of E(B - V) = 0.025 and true Large Magellanic Cloud (LMC) distance modulus of (m-M)LMC,0 = 18.515 ± 0.085, we find that all the distance determinations from the literature converge to a common

  8. The Relativistic Iron Line Profile in the Seyfert 1 Galaxy IC4329a

    NASA Technical Reports Server (NTRS)

    Done, C.; Madejski, G. M.; Zycki, P. T.

    2000-01-01

    We present simultaneous ASCA and RXTE data on the bright Seyfert 1 galaxy IC4329a. The iron line is significantly broadened, but not to the extent expected from an accretion disk which extends down to the last stable orbit around a black hole. We marginally detect a narrow line component, presumably from the molecular torus, but, even including this gives a line profile from the accretion disk which is significantly narrower that that seen in MCG-6-30-15, and is much more like that seen from the low/hard state galactic black hole candidates. This is consistent with the inner disk being truncated before the last stable orbit, forming a hot flow at small radii as in the ADAF models. However. we cannot rule out the presence of an inner disk which does not contribute to the reflected spectrum. either because of extreme ionisation suppressing the characteristic atomic features of the reflected spectrum or because the X-ray source is intrinsically anisotropic, so it does not illuminate the inner disk. The source was monitored by RXTE every 2 days for 2 months, and these snapshot spectra show that there is intrinsic spectral variability. The data are good enough to disentangle the power law from the reflected continuum and we see that the power law softens as the source brightens. The lack of a corresponding increase in the observed reflected spectrum implies that either the changes in disk inner radial extent/ionization structure are small, or that the variability is actually driven by changes in the seed photons which are decoupled from the hard X-ray mechanism.

  9. INTEGRAL FIELD SPECTROSCOPY OF SUPERNOVA EXPLOSION SITES: CONSTRAINING THE MASS AND METALLICITY OF THE PROGENITORS. I. TYPE Ib AND Ic SUPERNOVAE

    SciTech Connect

    Kuncarayakti, Hanindyo; Maeda, Keiichi; Doi, Mamoru; Morokuma, Tomoki; Hashiba, Yasuhito; Aldering, Greg; Arimoto, Nobuo; Pereira, Rui

    2013-08-01

    Integral field spectroscopy of 11 Type Ib/Ic supernova (SN Ib/Ic) explosion sites in nearby galaxies has been obtained using UH88/SNIFS and Gemini-N/GMOS. The use of integral field spectroscopy enables us to obtain both spatial and spectral information about the explosion site, enabling the identification of the parent stellar population of the SN progenitor star. The spectrum of the parent population provides metallicity determination via strong-line method and age estimation obtained via comparison with simple stellar population models. We adopt this information as the metallicity and age of the SN progenitor, under the assumption that it was coeval with the parent stellar population. The age of the star corresponds to its lifetime, which in turn gives the estimate of its initial mass. With this method we were able to determine both the metallicity and initial (zero-age main sequence) mass of the progenitor stars of SNe Ib and Ic. We found that on average SN Ic explosion sites are more metal-rich and younger than SN Ib sites. The initial mass of the progenitors derived from parent stellar population age suggests that SN Ic has more massive progenitors than SN Ib. In addition, we also found indication that some of our SN progenitors are less massive than {approx}25 M{sub Sun }, indicating that they may have been stars in a close binary system that have lost their outer envelope via binary interactions to produce SNe Ib/Ic, instead of single Wolf-Rayet stars. These findings support the current suggestions that both binary and single progenitor channels are in effect in producing SNe Ib/Ic. This work also demonstrates the power of integral field spectroscopy in investigating SN environments and active star-forming regions.

  10. Carbon monoxide in an extremely metal-poor galaxy.

    PubMed

    Shi, Yong; Wang, Junzhi; Zhang, Zhi-Yu; Gao, Yu; Hao, Cai-Na; Xia, Xiao-Yang; Gu, Qiusheng

    2016-12-09

    Extremely metal-poor galaxies with metallicity below 10% of the solar value in the local universe are the best analogues to investigating the interstellar medium at a quasi-primitive environment in the early universe. In spite of the ongoing formation of stars in these galaxies, the presence of molecular gas (which is known to provide the material reservoir for star formation in galaxies such as our Milky Way) remains unclear. Here we report the detection of carbon monoxide (CO), the primary tracer of molecular gas, in a galaxy with 7% solar metallicity, with additional detections in two galaxies at higher metallicities. Such detections offer direct evidence for the existence of molecular gas in these galaxies that contain few metals. Using archived infrared data, it is shown that the molecular gas mass per CO luminosity at extremely low metallicity is approximately one-thousand times the Milky Way value.

  11. Carbon monoxide in an extremely metal-poor galaxy

    PubMed Central

    Shi, Yong; Wang, Junzhi; Zhang, Zhi-Yu; Gao, Yu; Hao, Cai-Na; Xia, Xiao-Yang; Gu, Qiusheng

    2016-01-01

    Extremely metal-poor galaxies with metallicity below 10% of the solar value in the local universe are the best analogues to investigating the interstellar medium at a quasi-primitive environment in the early universe. In spite of the ongoing formation of stars in these galaxies, the presence of molecular gas (which is known to provide the material reservoir for star formation in galaxies such as our Milky Way) remains unclear. Here we report the detection of carbon monoxide (CO), the primary tracer of molecular gas, in a galaxy with 7% solar metallicity, with additional detections in two galaxies at higher metallicities. Such detections offer direct evidence for the existence of molecular gas in these galaxies that contain few metals. Using archived infrared data, it is shown that the molecular gas mass per CO luminosity at extremely low metallicity is approximately one-thousand times the Milky Way value. PMID:27934880

  12. Transformation of a Virgo Cluster dwarf irregular galaxy by ram pressure stripping: IC3418 and its fireballs

    SciTech Connect

    Kenney, Jeffrey D. P.; Geha, Marla; Jáchym, Pavel; Dague, William; Crowl, Hugh H.; Chung, Aeree; Van Gorkom, Jacqueline; Vollmer, Bernd

    2014-01-10

    We present optical imaging and spectroscopy and H I imaging of the Virgo Cluster galaxy IC 3418, which is likely a 'smoking gun' example of the transformation of a dwarf irregular into a dwarf elliptical galaxy by ram pressure stripping. IC 3418 has a spectacular 17 kpc length UV-bright tail comprised of knots, head-tail, and linear stellar features. The only Hα emission arises from a few H II regions in the tail, the brightest of which are at the heads of head-tail UV sources whose tails point toward the galaxy ('fireballs'). Several of the elongated tail sources have Hα peaks outwardly offset by ∼80-150 pc from the UV peaks, suggesting that gas clumps continue to accelerate through ram pressure, leaving behind streams of newly formed stars which have decoupled from the gas. Absorption line strengths, measured from Keck DEIMOS spectra, together with UV colors, show star formation stopped 300 ± 100 Myr ago in the main body, and a strong starburst occurred prior to quenching. While neither Hα nor H I emission are detected in the main body of the galaxy, we have detected 4 × 10{sup 7} M {sub ☉} of H I from the tail with the Very Large Array. The velocities of tail H II regions, measured from Keck LRIS spectra, extend only a small fraction of the way to the cluster velocity, suggesting that star formation does not happen in more distant parts of the tail. Stars in the outer tail have velocities exceeding the escape speed, but some in the inner tail should fall back into the galaxy, forming halo streams.

  13. Investigating the Processes Driving Low-Mass Galaxy Evolution with Gas Metallicities of Starburst Galaxies

    NASA Astrophysics Data System (ADS)

    Ly, Chun; Malkan, Matthew; Nagao, Tohru; Hayashi, Masao; Kashikawa, Nobunari; Shimasaku, Kazuhiro; Motohara, Kentaro

    2013-02-01

    There appears to be a ``fundamental" relationship that links the stellar masses, star-formation rates (SFRs), and gas metallicities of local galaxies. It has been used to constrain the major processes in galaxy evolution. However, it is unclear whether (1) this observed relation holds at earlier cosmic time, and (2) if it applies to low-mass galaxies and/or those with relatively higher specific SFRs (sSFRs). We request follow-up Hectospec spectroscopy %and DEIMOS spectroscopy to obtain gas metallicity measurements in key unexplored domains of galaxy parameter space. We will target Ntarget low-mass high equivalent width (EW) emission-line galaxies at zrange in the Subaru Deep Field (SDF). This sample is a factor of almost 4 larger than the existing data for galaxies with similar redshifts, SFRs and stellar masses. The SDF is ideal for such a survey because of its unique multi-wavelength imaging data that allow us to (1) identify a much higher surface density of high-EW star-forming galaxies over a wide redshift range than in any other survey, and (2) determine stellar masses and SFRs for individual galaxies. With the largest spectroscopic sample of low mass and/or high sSFR galaxies, we will determine the relationships between metallicity, stellar mass, and SFRs for dwarf galaxies. We will examine if the same galaxy evolution processes in massive galaxies also hold for lower mass galaxies over the past six billion years.

  14. Metallicity evolution in mergers of disk galaxies with black holes

    NASA Astrophysics Data System (ADS)

    Rantala, Antti; Johansson, Peter H.

    2016-10-01

    We use the TreeSPH simulation code Gadget-3 including a recently improved smoothed particle hydrodynamics (SPH) module, a detailed metallicity evolution model and sophisticated subresolution feedback models for supernovae and supermassive black holes in order to study the metallicity evolution in disk galaxy mergers. In addition, we examine the simulated morphology, star formation histories, metallicity gradients and kinematic properties of merging galaxies and merger remnants. We will compare our simulation results with observations of the early-type Centaurus A galaxy and the currently colliding Antennae galaxies.

  15. Quasar Metallicities and Host Galaxy Evolution

    NASA Astrophysics Data System (ADS)

    Leah, Simon E.; Hamann, F. W.

    2006-12-01

    From studies of galaxies in the local Universe we find the masses of the galactic spheroidal component corresponds with the mass of the central supermassive black hole (SMBH). This relation is known as the M(gal) M(BH) relation, and suggests a close relationship between the formation of the galaxy and the black hole. We study the metallicities near quasars at high redshift to observe this formation process in action. Associated absorption lines (AALs) provide us with a unique tool for this study, because these lines have a high probability of forming close to the quasar. Most of the work so far, using the emission lines, suggests that quasar environments are typically metal rich, with gas-phase metallicities near solar or higher at all observed redshifts. However, other independant abundance checks, such as AALs, are essential in order to confirm these results. We use very high resolution echelle spectra from VLT-UVES for 8 high redshift (z of 2 to z of 4.6) quasars, selected to contain candidate intrinsic absorbers, and ecompassing a typical rest-frame spectral range from approximatly 900 Angstroms to 2500 Angstroms, designed to include at least Lyman alpha and C IV spectral features. We perform one of the first analyses of absorption line metallicities in high redshift quasars and present lower limits on column densities, as well as estimates for the absorber locations relative to the quasar. We place rough estimates on the abundances where possible. We find covering fractions which vary with velocity, and a significant fraction of absorption lines which exhibit variability, indicating their intrinsic nature. Saturated lines inhibit concrete abundance analysis, but present excellent opportunities for future research proposals.

  16. Quasar Metallicities and Host Galaxy Evolution

    NASA Astrophysics Data System (ADS)

    Simon, Leah; Hamann, F.

    2007-12-01

    From studies of galaxies in the local Universe we find the masses of the galactic spheroidal component corresponds with the mass of the central supermassive black hole (SMBH). This relation is known as the M(gal) - M(BH) relation, and suggests a close relationship between the formation of the galaxy and the black hole. We study the metallicities near quasars at high redshift to observe this formation process in action. Associated absorption lines (AALs) provide us with a unique tool for this study, because these lines have a high probability of forming close to the quasar. Most of the work so far, using the emission lines, suggests that quasar environments are typically metal rich, with gas-phase metallicities near solar or higher at all observed redshifts. However, other independent abundance checks, such as AALs, are essential in order to confirm these results. We use very high resolution echelle spectra from VLT-UVES, Keck-HIRES and Magellan-MIKE for 18 high redshift (z of 2 to z of 4.6) quasars, selected to contain candidate intrinsic absorbers, and encompassing a typical rest-frame spectral range from approximately 900 Angstroms to 2500 Angstroms, designed to include at least Lyman alpha and C IV spectral features. We perform one of the first analyses of absorption line metallicities in high redshift quasars and present column densities, as well as estimates for the absorber locations relative to the quasar. We place solid limits on the C/H abundances, and find a wide range of values, from one hundredth solar to several times solar. We find covering fractions which vary with velocity, indicating the intrinsic nature of the absorbing gas. Saturated lines inhibit concrete abundance analysis in some systems, but are still useful for placing limits based on Gaussian fits to the lines.

  17. The origin of the enhanced metallicity of satellite galaxies

    NASA Astrophysics Data System (ADS)

    Bahé, Yannick M.; Schaye, Joop; Crain, Robert A.; McCarthy, Ian G.; Bower, Richard G.; Theuns, Tom; McGee, Sean L.; Trayford, James W.

    2017-01-01

    Observations of galaxies in the local Universe have shown that both the ionized gas and the stars of satellites are more metal-rich than of equally massive centrals. To gain insight into the connection between this metallicity enhancement and other differences between centrals and satellites, such as their star formation rates, gas content, and growth history, we study the metallicities of >3600 galaxies with Mstar > 1010 M⊙ in the cosmological hydrodynamical EAGLE 100 Mpc `Reference' simulation, including ˜1500 in the vicinity of galaxy groups and clusters (M200 ≥ 1013 M⊙). The simulation predicts excess gas and stellar metallicities in satellites consistent with observations, except for stellar metallicities at Mstar ≲ 1010.2 M⊙ where the predicted excess is smaller than observed. The exact magnitude of the effect depends on galaxy selection, aperture, and on whether the metallicity is weighted by stellar mass or luminosity. The stellar metallicity excess in clusters is also sensitive to the efficiency scaling of star formation feedback. We identify stripping of low-metallicity gas from the galaxy outskirts, as well as suppression of metal-poor inflows towards the galaxy centre, as key drivers of the enhancement of gas metallicity. Stellar metallicities in satellites are higher than in the field as a direct consequence of the more metal-rich star-forming gas, whereas stripping of stars and suppressed stellar mass growth, as well as differences in accreted versus in situ star formation between satellites and the field, are of secondary importance.

  18. Inefficient star formation in extremely metal poor galaxies.

    PubMed

    Shi, Yong; Armus, Lee; Helou, George; Stierwalt, Sabrina; Gao, Yu; Wang, Junzhi; Zhang, Zhi-Yu; Gu, Qiusheng

    2014-10-16

    The first galaxies contain stars born out of gas with few or no 'metals' (that is, elements heavier than helium). The lack of metals is expected to inhibit efficient gas cooling and star formation, but this effect has yet to be observed in galaxies with an oxygen abundance (relative to hydrogen) below a tenth of that of the Sun. Extremely metal poor nearby galaxies may be our best local laboratories for studying in detail the conditions that prevailed in low metallicity galaxies at early epochs. Carbon monoxide emission is unreliable as a tracer of gas at low metallicities, and while dust has been used to trace gas in low-metallicity galaxies, low spatial resolution in the far-infrared has typically led to large uncertainties. Here we report spatially resolved infrared observations of two galaxies with oxygen abundances below ten per cent of the solar value, and show that stars formed very inefficiently in seven star-forming clumps in these galaxies. The efficiencies are less than a tenth of those found in normal, metal rich galaxies today, suggesting that star formation may have been very inefficient in the early Universe.

  19. ALMA CO Observations of Shocks and Star Formation in the Interacting Galaxies IC 2163 and NGC 2207

    NASA Astrophysics Data System (ADS)

    Elmegreen, Debra M.; Elmegreen, Bruce; Kaufman, Michele; Brinks, Elias; Struck, Curtis; Bournaud, Frederic; Sheth, Kartik; Juneau, Stephanie

    2017-01-01

    The spiral galaxies IC 2163 and NGC 2207 are a well-studied pair undergoing a grazing collision. ALMA CO observations of masses, column densities, and velocities are combined with HI, Hα, optical, and 24 micron data to study the star formation rates and efficiencies. The close encounter of the galaxies produced in-plane tidal forces in IC 2163, resulting in a large shock with high molecular velocity gradients and both radial and azimuthal streaming (100 km/s) that formed a pile-up of molecular gas in the resulting cuspy-oval or ``eyelid'' structure at mid-radius. The encounter also produced forces nearly orthogonal to the plane of NGC 2207, resulting in a warp. By comparing with the Kennicutt-Schmidt relation for star formation, we find that some regions of NGC 2207 with unusually high turbulent speeds (40-50 km/s) and high star formation rates (>0.01 Mo/pc2/Myr) have gas that is predominantly atomic with high density cores. Half of the CO mass is in 300 clouds each more massive than 4.0x105 Mo. The mass distribution functions for the CO clouds and star complexes in the eyelid in IC 2163 both have a slope similar to what is observed in Milky Way clouds; the CO slope is steeper in NGC 2207. The CO distribution in NGC 2207 also includes a nuclear ring, a mini-bar, and a mini-starburst region that dominates the 24 micron, radio, and Hα emission in both galaxies. Dust extinction, molecular column densities, and slightly negative molecular velocities indicate the mini-starburst region has ejected a jet of molecular gas nearly perpendicular to the plane of NGC 2207 on the near side with a kinetic energy of 1052 ergs. The large scale star formation efficiency, measured as the ratio of the summed masses of the star complexes near molecular clouds to the combined star complex and cloud masses, is 7% overall; it is 23% in the mini-starburst. The maximum age of star complexes in the galactic-scale shock front at the eyelid is about the same as the time since closest

  20. Joint ROSAT-Compton GRO observations of the X-ray bright Seyfert galaxy IC 4329A

    NASA Technical Reports Server (NTRS)

    Madejski, G. M.; Zdziarski, A. A.; Turner, T. J.; Done, C.; Mushotzky, R. F.; Hartman, R. C.; Gehrels, N.; Connors, A.; Fabian, A. C.; Nandra, K.

    1995-01-01

    We report a simultaneous ROSAT and Gamma Ray Observatory (GRO) observation of the X-ray-bright Seyfert galaxy IC 4329A. For the GRO Oriented Scintillation Spectrometer Experiment (OSSE) detector, we also present the sum of the data for this and earlier observations. The overall spectrum is very well described as a power law with an energy spectral index of approximately 1 absorbed at low energies plus a strong Compton reflection component, typical for Seyfert 1 galaxies. The low energy absorption can be well described by a sum of a neutral column density of approximately 3 x 10(exp 21)sq cm, most of which is associated with the edge-on galactic disk of IC 4329A, plus an edgelike feature at approximately 700 eV; this feature implies either complex absorption (due to additional ionized material, or due to a partial covering), or a soft excess. The data only weakly constrain the presence of a high-energy cutoff in the underlying power law; they are compatible with an exponential cutoff at any energy E(sub c) approximately greater than 100 keV. The relative steepness of the OSSE data, with the power-law energy index of 1.6 +/- 0.2, can be accounted for entirely by the contribution of the high-energy tail of the reflection component when E(sub c) approaches infinity. (We find that the definite cutoff at an energy E(sub c)approximately 130 keV suggested in the recently published analysis of the OSSE data for this subject is due to a data reduction error.) Including nonsimultaneous Ginga observations with 2 keV fluxes matching well that of ROSAT gives us likely broad-band X-ray/gamma-ray spectra of the object from approximately 0.1 keV up to several hundred keV. We also report the ROSAT spectrum of the companion object to the Seyfert galaxy, the elliptical galaxy IC 4329.

  1. Shocks and metallicity gradients in normal star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Ho, I.-Ting

    Gas flow is one of the most fundamental processes driving galaxy evolution. This thesis explores gas flows in local galaxies by studying metallicity gradients and galactic-scale outflows in normal star-forming galaxies. This is made possible by new integral field spectroscopy data that provide simultaneously spatial and spectral information of galaxies. First, I measure metallicity gradients in isolated disk galaxies and show that their metallicity gradients are remarkably simple and universal. When the metallicity gradients are normalized to galaxy sizes, all the 49 galaxies studied have virtually the same metallicity gradient. I model the common metallicity gradient using a simple chemical evolution model to understand its origin. The common metallicity gradient is a direct result of the coevolution of gas and stellar disk while galactic disks build up their masses from inside-out. Tight constraints on the mass outflow rates and inflow rates can be placed by the chemical evolution model. Second, I investigate galactic winds in normal star-forming galaxies using data from an integral field spectroscopy survey. I demonstrate how to search for galactic winds by probing emission line ratios, shocks, and gas kinematics. Galactic winds are found to be common even in normal star-forming galaxies that were not expected to host winds. By comparing galaxies with and without hosting winds, I show that galaxies with high star formation rate surface densities and bursty star formation histories are more likely to drive large-scale galactic winds. Finally, lzifu, a toolkit for fitting multiple emission lines simultaneously in integral field spectroscopy data, is developed in this thesis. I describe in detail the structure of the toolkit and demonstrate the capabilities of lzifu.

  2. Submillimeter continuum emission from galaxies - Star formation and the interstellar medium in the local group dwarf IC 10

    SciTech Connect

    Thronson, H.A. Jr.; Hunter, D.A.; Casey, S.; Harper, D.A. Lowell Observatory, Flagstaff, AZ Yerkes Observatory, Williams Bay, WI )

    1990-05-01

    Far-infrared (95 and 160 micron) maps and visual broad-band and line images of the nearby, luminous irregular galaxy IC 10 are discussed. Observations of the dust emission make it possible to constrain the total mass of gas and the rate of star formation derived for the galaxy. The total star-formation rate is estimated to be about 0.15 solar mass/yr, and the e-folding time for exhaustion of the interstellar gas due to the star formation is only a few billion years. To determine the source of the cool dust in emission at approximately 100-250 microns from many galaxies, 60, 100, and 160 micron photometry, obtained previously, is compared; and CO, H I, and dust emission is correlated. Based on the correlation between the various cool components of the interstellar medium, it is concluded that the likely location of the dust that dominates the emission at about 160, and possibly 100, microns is within both the diffuse atomic gas and in surface layers of molecular clouds. 57 refs.

  3. ORIGIN OF THE GALAXY MASS-METALLICITY-STAR FORMATION RELATION

    SciTech Connect

    Harwit, Martin; Brisbin, Drew

    2015-02-20

    We describe an equilibrium model that links the metallicity of low-redshift galaxies to stellar evolution models. It enables the testing of different stellar initial mass functions and metal yields against observed galaxy metallicities. We show that the metallicities of more than 80,000 Sloan Digital Sky Survey galaxies in the low-redshift range 0.07 ≤ z ≤ 0.3 considerably constrain stellar evolution models that simultaneously relate galaxy stellar mass, metallicity, and star formation rates to the infall rate of low-metallicity extragalactic gas and outflow of enriched matter. A feature of our model is that it encompasses both the active star forming phases of a galaxy and epochs during which the same galaxy may lie fallow. We show that the galaxy mass-metallicity-star formation relation can be traced to infall of extragalactic gas mixing with native gas from host galaxies to form stars of observed metallicities, the most massive of which eject oxygen into extragalactic space. Most consequential among our findings is that, on average, extragalactic infall accounts for one half of the gas required for star formation, a ratio that is remarkably constant across galaxies with stellar masses ranging at least from M* = 2 × 10{sup 9} to 6 × 10{sup 10} M {sub ☉}. This leads us to propose that star formation is initiated when extragalactic infall roughly doubles the mass of marginally stable interstellar clouds. The processes described may also account quantitatively for the metallicity of extragalactic space, though to check this the fraction of extragalactic baryons will need to be more firmly established.

  4. The metal enrichment of passive galaxies in cosmological simulations of galaxy formation

    NASA Astrophysics Data System (ADS)

    Okamoto, Takashi; Nagashima, Masahiro; Lacey, Cedric G.; Frenk, Carlos S.

    2017-02-01

    Massive early-type galaxies have higher metallicities and higher ratios of α elements to iron than their less massive counterparts. Reproducing these correlations has long been a problem for hierarchical galaxy formation theory, both in semi-analytic models and cosmological hydrodynamic simulations. We show that a simulation in which gas cooling in massive dark haloes is quenched by radio-mode active galactic nuclei (AGNs) feedback naturally reproduces the observed trend between α/Fe and the velocity dispersion of galaxies, σ. The quenching occurs earlier for more massive galaxies. Consequently, these galaxies complete their star formation before α/Fe is diluted by the contribution from Type Ia supernovae. For galaxies more massive than ˜1011 M⊙, whose α/Fe correlates positively with stellar mass, we find an inversely correlated mass-metallicity relation. This is a common problem in simulations in which star formation in massive galaxies is quenched either by quasar- or radio-mode AGN feedback. The early suppression of gas cooling in progenitors of massive galaxies prevents them from recapturing enriched gas ejected as winds. Simultaneously reproducing the [α/Fe]-σ relation and the mass-metallicity relation is, thus, difficult in the current framework of galaxy formation.

  5. THE METALLICITY OF VOID DWARF GALAXIES

    SciTech Connect

    Kreckel, K.; Groves, B.; Croxall, K.; Pogge, R. W.; Van de Weygaert, R.

    2015-01-01

    The current ΛCDM cosmological model predicts that galaxy evolution proceeds more slowly in lower density environments, suggesting that voids are a prime location to search for relatively pristine galaxies that are representative of the building blocks of early massive galaxies. To test the assumption that void galaxies are more pristine, we compare the evolutionary properties of a sample of dwarf galaxies selected specifically to lie in voids with a sample of similar isolated dwarf galaxies in average density environments. We measure gas-phase oxygen abundances and gas fractions for eight dwarf galaxies (M{sub r} > –16.2), carefully selected to reside within the lowest density environments of seven voids, and apply the same calibrations to existing samples of isolated dwarf galaxies. We find no significant difference between these void dwarf galaxies and the isolated dwarf galaxies, suggesting that dwarf galaxy chemical evolution proceeds independent of the large-scale environment. While this sample is too small to draw strong conclusions, it suggests that external gas accretion is playing a limited role in the chemical evolution of these systems, and that this evolution is instead dominated mainly by the internal secular processes that are linking the simultaneous growth and enrichment of these galaxies.

  6. A COMPREHENSIVE X-RAY AND MULTIWAVELENGTH STUDY OF THE COLLIDING GALAXY PAIR NGC 2207/IC 2163

    SciTech Connect

    Mineo, S.; Rappaport, S.; Levine, A.; Homan, J.; Pooley, D.; Steinhorn, B. E-mail: sar@mit.edu E-mail: jeroen@space.mit.edu E-mail: bsteinho@mit.edu

    2014-12-20

    We present a comprehensive study of the total X-ray emission from the colliding galaxy pair NGC 2207/IC 2163, based on Chandra, Spitzer, and GALEX data. We detect 28 ultraluminous X-ray sources (ULXs), 7 of which were not detected previously because of X-ray variability. Twelve sources show significant long-term variability, with no correlated spectral changes. Seven sources are transient candidates. One ULX coincides with an extremely blue star cluster (B – V = –0.7). We confirm that the global relation between the number and luminosity of ULXs and the integrated star-formation rate (SFR) of the host galaxy also holds on local scales. We investigate the effects of dust extinction and age on the X-ray binary (XRB) population on subgalactic scales. The distributions of N {sub X} and L {sub X} are peaked at L {sub IR}/L {sub NUV} ∼ 1, which may be associated with an age of ∼10 Myr for the underlying stellar population. We find that approximately one-third of the XRBs are located in close proximity to young star complexes. The luminosity function of the XRBs is consistent with that typical for high-mass XRBs and appears unaffected by variability. We disentangle and compare the X-ray diffuse spectrum with that of the bright XRBs. The hot interstellar medium dominates the diffuse X-ray emission at E ≲ 1 keV and has a temperature kT=0.28{sub −0.04}{sup +0.05} keV and intrinsic 0.5-2 keV luminosity of 7.9×10{sup 40} erg s{sup −1}, a factor of ∼2.3 higher than the average thermal luminosity produced per unit SFR in local star-forming galaxies. The total X-ray output of NGC 2207/IC 2163 is 1.5×10{sup 41} erg s{sup −1}, and the corresponding total integrated SFR is 23.7 M {sub ☉} yr{sup –1}.

  7. Probing Globular Cluster Formation in Low Metallicity Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Johnson, Kelsey E.; Hunt, Leslie K.; Reines, Amy E.

    2008-12-01

    The ubiquitous presence of globular clusters around massive galaxies today suggests that these extreme star clusters must have been formed prolifically in the earlier universe in low-metallicity galaxies. Numerous adolescent and massive star clusters are already known to be present in a variety of galaxies in the local universe; however most of these systems have metallicities of 12 + log(O/H) > 8, and are thus not representative of the galaxies in which today's ancient globular clusters were formed. In order to better understand the formation and evolution of these massive clusters in environments with few heavy elements, we have targeted several low-metallicity dwarf galaxies with radio observations, searching for newly-formed massive star clusters still embedded in their birth material. The galaxies in this initial study are HS 0822+3542, UGC 4483, Pox 186, and SBS 0335-052, all of which have metallicities of 12 + log(O/H) < 7.75. While no thermal radio sources, indicative of natal massive star clusters, are found in three of the four galaxies, SBS 0335-052 hosts two such objects, which are incredibly luminous. The radio spectral energy distributions of these intense star-forming regions in SBS 0335-052 suggest the presence of ~12,000 equivalent O-type stars, and the implied star formation rate is nearing the maximum starburst intensity limit.

  8. The Thermal Pressure in Low Metallicity Galaxies

    NASA Astrophysics Data System (ADS)

    Wolfire, Mark; McKee, Christopher; Ostriker, Eve C.; Bolatto, Alberto; Jenkins, Edward

    2015-08-01

    The thermal pressure in the diffuse interstellar medium (ISM) is a relatively small fraction of the total ISM pressure yet it is extremely important for the evolution of the ISM phases. A multi-phase medium can exist between a range of thermal pressures Pmin < Pth < Pmax. The phase separation is driven by thermal instability and produces a cold (T ˜ 100 K) neutral atomic gas and a warm (T ˜ 8000 K) neutral atomic gas separated by thermally unstable gas. At thermal pressures greater than Pmax only the cold phase can exist and at thermal pressures less than Pmin only the warm phase can exist. The ISM is also highly turbulent and turbulence can both initiate the thermal phase transition and be produced in a rapid phase transition. Hydrodynamic modeling also points to a strong two-phase distribution (.e.g., Kim et al. 2011; Audit & Hennebelle 2010) with a median thermal pressure in the cold gas very near the expected two-phase pressure. Global, theoretical models including star-formation feedback have been developed for the molecular fraction in galactic disks using, at their core, the paradigm that thermal pressure determines the phase transitions to warm, cold, or multiphase medium (e.g., Krumholz et al. 2009; Ostriker et al. 2010).Here we present a phase diagram for a low metallicity galaxy using the Small Magellanic Clouds as an example. We find that although the heating rates and metallicities can differ by factors of 5 to 10 from the Milky Way, the resulting two-phase pressure and physical conditions of the phases are not very different from Galactic. We also confirm that a widely used fitting function for Pmin presented in Wolfire et al. 2003 provides an accurate prediction for the new results. We demonstrate how the variation in input parameters determine the final pressures and physical conditions.

  9. THE METALLICITIES OF LOW STELLAR MASS GALAXIES AND THE SCATTER IN THE MASS-METALLICITY RELATION

    SciTech Connect

    Zahid, H. J.; Bresolin, F.; Kewley, L. J.; Coil, A. L.; Dave, R.

    2012-05-10

    In this investigation, we quantify the metallicities of low-mass galaxies by constructing the most comprehensive census to date. We use galaxies from the Sloan Digital Sky Survey (SDSS) and DEEP2 survey and estimate metallicities from their optical emission lines. We also use two smaller samples from the literature that have metallicities determined by the direct method using the temperature sensitive [O III]{lambda}4363 line. We examine the scatter in the local mass-metallicity (MZ) relation determined from {approx}20,000 star-forming galaxies in the SDSS and show that it is larger at lower stellar masses, consistent with the theoretical scatter in the MZ relation determined from hydrodynamical simulations. We determine a lower limit for the scatter in metallicities of galaxies down to stellar masses of {approx}10{sup 7} M{sub Sun} which is only slightly smaller than the expected scatter inferred from the SDSS MZ relation and significantly larger than what has been previously established in the literature. The average metallicity of star-forming galaxies increases with stellar mass. By examining the scatter in the SDSS MZ relation, we show that this is mostly due to the lowest metallicity galaxies. The population of low-mass, metal-rich galaxies have properties that are consistent with previously identified galaxies that may be transitional objects between gas-rich dwarf irregulars and gas-poor dwarf spheroidals and ellipticals.

  10. Numerical Simulations of the Metallicity Distribution in Dwarf Spheroidal Galaxies

    SciTech Connect

    Ripamonti, Emanuele; Tolstoy, E.; Helmi, A.; Battaglia, G.; Abel, T.; /KIPAC, Menlo Park

    2006-12-12

    Recent observations show that the number of stars with very low metallicities in the dwarf spheroidal satellites of the Milky Way is low, despite the low average metallicities of stars in these systems. We undertake numerical simulations of star formation and metal enrichment of dwarf galaxies in order to verify whether this result can be reproduced with ''standard'' assumptions. The answer is likely to be negative, unless some selection bias against very low metallicity stars is present in the observations.

  11. METAL PRODUCTION IN GALAXY CLUSTERS: THE NON-GALACTIC COMPONENT

    SciTech Connect

    Bregman, Joel N.; Anderson, Michael E.; Dai Xinyu E-mail: michevan@umich.ed

    2010-06-10

    The metallicity in galaxy clusters is expected to originate from the stars in galaxies, with a population dominated by high-mass stars likely being the most important stellar component, especially in rich clusters. We examine the relationship between the metallicity and the prominence of galaxies as measured by the star-to-baryon ratio, M{sub *}/M{sub bary}. Counter to expectations, we rule out a metallicity that is proportional to M{sub *}/M{sub bary}, where the best fit has the gas-phase metallicity decreasing with M{sub *}/M{sub bary}, or the metallicity of the gas plus the stars being independent of M{sub *}/M{sub bary}. This implies that the population of stars responsible for the metals is largely proportional to the total baryonic mass of the cluster, not to the galaxy mass within the cluster. If generally applicable, most of the heavy elements in the universe were not produced within galaxies.

  12. METALS REMOVED BY OUTFLOWS FROM MILKY WAY DWARF SPHEROIDAL GALAXIES

    SciTech Connect

    Kirby, Evan N.; Martin, Crystal L.; Finlator, Kristian

    2011-12-15

    The stars in the dwarf spheroidal satellite galaxies (dSphs) of the Milky Way are significantly more metal-poor than would be expected from a closed box model of chemical evolution. Gas outflows likely carried away most of the metals produced by the dSphs. Based on previous Keck/DEIMOS observations and models, we calculate the mass in Mg, Si, Ca, and Fe expelled from each of eight dSphs. Essentially, these masses are the differences between the observed amount of metals present in the dSphs' stars today and the inferred amount of metals produced by supernovae. We conclude that the dSphs lost 96% to >99% of the metals their stars manufactured. We apply the observed mass function of Milky Way dSphs to the ejected mass function to determine that a single large dSph, like Fornax, lost more metals over 10 Gyr than all smaller dSphs combined. Therefore, small galaxies like dSphs are not significant contributors to the metal content of the intergalactic medium. Finally, we compare our ejected mass function to previous X-ray measurements of the metal content of the winds from the post-starburst dwarf irregular galaxy NGC 1569. Remarkably, the most recent starburst in that galaxy falls exactly on the ejected-mass-stellar-mass relation defined by the Milky Way dSphs.

  13. SPIRITS 15c and SPIRITS 14buu: Two Obscured Supernovae in the Nearby Star-forming Galaxy IC 2163

    NASA Astrophysics Data System (ADS)

    Jencson, Jacob E.; Kasliwal, Mansi M.; Johansson, Joel; Contreras, Carlos; Castellón, Sergio; Bond, Howard E.; Monson, Andrew J.; Masci, Frank J.; Cody, Ann Marie; Andrews, Jennifer E.; Bally, John; Cao, Yi; Fox, Ori D.; Gburek, Timothy; Gehrz, Robert D.; Green, Wayne; Helou, George; Hsiao, Eric; Morrell, Nidia; Phillips, Mark; Prince, Thomas A.; Simcoe, Robert A.; Smith, Nathan; Tinyanont, Samaporn; Williams, Robert

    2017-03-01

    SPitzer InfraRed Intensive Transients Survey—SPIRITS—is an ongoing survey of nearby galaxies searching for infrared (IR) transients with Spitzer/IRAC. We present the discovery and follow-up observations of one of our most luminous (M [4.5] = ‑17.1 ± 0.4 mag, Vega) and reddest ([3.6] ‑ [4.5] = 3.0 ± 0.2 mag) transients, SPIRITS 15c. The transient was detected in a dusty spiral arm of IC 2163 (D ≈ 35.5 Mpc). Pre-discovery ground-based imaging revealed an associated, shorter-duration transient in the optical and near-IR (NIR). NIR spectroscopy showed a broad (≈8400 km s‑1), double-peaked emission line of He i at 1.083 μm, indicating an explosive origin. The NIR spectrum of SPIRITS 15c is similar to that of the Type IIb SN 2011dh at a phase of ≈200 days. Assuming an A V = 2.2 mag of extinction in SPIRITS 15c provides a good match between their optical light curves. The NIR light curves, however, show some minor discrepancies when compared with SN 2011dh, and the extreme [3.6]–[4.5] color has not been previously observed for any SN IIb. Another luminous (M 4.5 = ‑16.1 ± 0.4 mag) event, SPIRITS 14buu, was serendipitously discovered in the same galaxy. The source displays an optical plateau lasting ≳80 days, and we suggest a scenario similar to the low-luminosity Type IIP SN 2005cs obscured by A V ≈ 1.5 mag. Other classes of IR-luminous transients can likely be ruled out in both cases. If both events are indeed SNe, this may suggest that ≳18% of nearby core-collapse SNe are missed by currently operating optical surveys.

  14. FE K EMISSION AND ABSORPTION FEATURES IN THE XMM-EPIC SPECTRUM OF THE SEYFERT GALAXY IC 4329A

    NASA Technical Reports Server (NTRS)

    Markowitz, A.; Reeves, J. N.; Braito, V.

    2001-01-01

    We present a re-analysis of the XMM-Newton long-look of the X-ray bright Seyfert galaxy IC 4329a. The Fe K bandpass is dominated by two peaks, consistent with emission from neutral or near-neutral Fe Ka and KP. A relativistic diskline model whereby both peaks are the result of one doubly-peaked diskline profile is found to be a poor description of the data. Models using two relativistic disklines are found to describe the emission profile well. A low-inclination, moderately-relativistic dual-diskline model is possible if the contribution from narrow components, due to distant material, is small or absent. A high-inclination, moderately relativistic profile for each peak is possible if there are roughly equal contributions from both the broad and narrow components. Upper limits on Fe XXV and Fe XXVI emission and absorption at the systemic velocity of IC 4329a are obtained. We also present the results of RXTE monitoring of this source obtained so far; the combined XMM-Newton and RXTE data sets allow us to explore the time-resolved spectral behavior of this source on time scales ranging from hours to 2 years. We find no strong evidence for variability of the Fe Ka emission line on any time scale probed, likely due to the minimal level of continuum variability. We detect a narrow absorption line, at a energy of 7.68 keV in the rest frame of the source; its significance has been confirmed using Monte Carlo simulations. This feature is most likely due to absorption from Fe XXVI blueshifted to approximately 0.1c relative to the systemic velocity, making IC 4329a the lowest-redshift AGN known with a high-velocity, highly-ionized outflow component. As is often the case with similar outflows seen in high-luminosity quasars, the estimated mass outflow rate is larger than the inflow accretion rate, signaling that the outflow represents a substantial portion of the total energy budget of the AGN. The outflow could arise from a radiatively-driven disk wind, or it may be in the

  15. A framework for empirical galaxy phenomenology: the scatter in galaxy ages and stellar metallicities

    NASA Astrophysics Data System (ADS)

    Muñoz, Joseph A.; Peeples, Molly S.

    2015-04-01

    We develop a theoretical framework that extracts a deeper understanding of galaxy formation from empirically derived relations among galaxy properties by extending the main-sequence integration method for computing galaxy star formation histories. We properly account for scatter in the stellar mass-star formation rate relation and the evolving fraction of passive systems and find that the latter effect is almost solely responsible for the age distributions among z ˜ 0 galaxies with stellar masses above ˜1010 M⊙. However, while we qualitatively agree with the observed median stellar metallicity as a function of stellar mass, we attribute our inability to reproduce the distribution in detail largely to a combination of imperfect gas-phase metallicity and α/Fe ratio calibrations. Our formalism will benefit from new observational constraints and, in turn, improve interpretations of future data by providing self-consistent star formation histories for population synthesis modelling.

  16. FURTHER DEFINITION OF THE MASS-METALLICITY RELATION IN GLOBULAR CLUSTER SYSTEMS AROUND BRIGHTEST CLUSTER GALAXIES

    SciTech Connect

    Cockcroft, Robert; Harris, William E.; Wehner, Elizabeth M. H.; Whitmore, Bradley C.; Rothberg, Barry E-mail: harris@physics.mcmaster.ca E-mail: whitmore@stsci.edu

    2009-09-15

    We combine the globular cluster (GC) data for 15 brightest cluster galaxies and use this material to trace the mass-metallicity relations (MMRs) in their globular cluster systems (GCSs). This work extends previous studies which correlate the properties of the MMR with those of the host galaxy. Our combined data sets show a mean trend for the metal-poor subpopulation that corresponds to a scaling of heavy-element abundance with cluster mass Z {approx} M {sup 0.30{+-}}{sup 0.05}. No trend is seen for the metal-rich subpopulation which has a scaling relation that is consistent with zero. We also find that the scaling exponent is independent of the GCS specific frequency and host galaxy luminosity, except perhaps for dwarf galaxies. We present new photometry in (g',i') obtained with Gemini/GMOS for the GC populations around the southern giant ellipticals NGC 5193 and IC 4329. Both galaxies have rich cluster populations which show up as normal, bimodal sequences in the color-magnitude diagram. We test the observed MMRs and argue that they are statistically real, and not an artifact caused by the method we used. We also argue against asymmetric contamination causing the observed MMR as our mean results are no different from other contamination-free studies. Finally, we compare our method to the standard bimodal fitting method (KMM or RMIX) and find our results are consistent. Interpretation of these results is consistent with recent models for GC formation in which the MMR is determined by GC self-enrichment during their brief formation period.

  17. Environmental Effects on the Metallicities of Early-Type Galaxies

    NASA Technical Reports Server (NTRS)

    Jones, Christine; Oliversen, Ronald (Technical Monitor)

    2004-01-01

    We completed and published two papers in the Astrophysical Journal based on research from grant. In the first paper we analyzed nine X-ray-bright Virgo early-type galaxies observed by both ASCA and ROSAT. Through spatially resolved spectroscopy, we determined the radial temperature profiles and abundances of Mg, Si, and Fe for six galaxies. The temperature profiles are consistent with isothermal temperatures outside of cooler regions at the galaxies' centers. We present new evidence for iron abundance gradients in NGC 4472 and NGC 4649 and confirm the previous results on NGC 4636. Mg and Si abundance gradients on average are flatter than those of iron and correspond to an underabundance of α-process elements at high Fe values, while at low iron the element ratios favor enrichment by Type II supernovae (SNe). We explain the observed trend using the metallicity dependence of SN Ia metal production and present constraints on the available theoretical modeling for low-metallicity inhibition of SNe Ia. In the second paper We analyzed nine X-ray-bright Virgo early-type galaxies observed by both ASCA and ROSAT. Through spatially resolved spectroscopy, we determined the radial temperature profiles and abundances of Mg, Si, and Fe for six galaxies. The temperature profiles are consistent with isothermal temperatures outside of cooler regions at the galaxies' centers. We present new evidence for iron abundance gradients in NGC 4472 and NGC 4649 and confirm the previous results on NGC 4636. Mg and Si abundance gradients on average are flatter than those of iron and correspond to an underabundance of α-process elements at high Fe values, while at low iron the element ratios favor enrichment by Type I1 supernovae (SNe). We explain the observed trend using the metallicity dependence of SN Ia metal production and present constraints on the available theoretical modeling for low-metallicity inhibition of SNe Ia.

  18. The Extremely Metal-Poor Dwarf Galaxy AGC 198691

    NASA Astrophysics Data System (ADS)

    Hirschauer, Alec S.; Salzer, John Joseph; Cannon, John M.; Skillman, Evan D.; SHIELD II Team

    2016-01-01

    We present spectroscopic observations of the nearby dwarf irregular galaxy AGC 198691. This object is part of the Survey of HI in Extremely Low-Mass Dwarfs (SHIELD) sample, which consists of ultra-low HI mass galaxies discovered by the Arecibo Legacy Fast-Acting ALFA (ALFALFA) survey. SHIELD is a multi-configuration Expanded Very Large Array (EVLA) study of the neutral gas content and dynamics of galaxies with HI masses in the range of 106-107 M⊙. Our spectral data were obtained using the new high-throughput KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m telescope as part of a systematic study of the nebular abundances in the SHIELD galaxy sample. These observations enable measurement of the temperature sensitive [OIII]λ4363 line and hence the determination of a "direct" oxygen abundance for AGC 198691. We find this system to be an extremely metal-deficient (XMD) galaxy with an oxygen abundance comparable to such objects as I Zw 18, SBS 0335-052W, Leo P, and DDO 68 - the lowest metallicity star-forming systems known. It is worth noting that two of the five lowest-abundance galaxies currently recognized were discovered via the ALFALFA blind HI survey. These XMD galaxies are potential analogues to the first star-forming systems, which through hierarchical accretion processes built up the large galaxies we observe today in the local Universe. Detailed analysis of such XMD systems offers observational constraint to models of galactic evolution and star formation histories to allow a better understanding of the processes that govern the chemical evolution of low-mass galaxies.

  19. Understanding The Baryonic Cycle: Confronting Galaxy Physics With The Mass; Metallicity Relation And Dust Content Of Galaxies Over Cosmic Time

    NASA Astrophysics Data System (ADS)

    Popping, Gergö; Somerville, Rachel; Galametz, Maud

    2016-09-01

    The mass-metallicity relation combines the star formation, metal enrichment, feedback, and baryon accretion history of galaxies and acts as a superb probe of the cycle of baryons through galaxies. Reproducing its cosmic evolution is a stringent constraint on models of galaxy formation. I will present new cosmological models of galaxy formation that include various ejective and preventive feedback schemes and detailed chemical evolution and dust chemistry models. I will present the impact of the different feedback schemes on the evolution of the mass;metallicity relation, compare my predictions with observations, and discuss how this comparison helps us constrain the galaxy physics acting on the baryonic cycle. I will further show that proper accounting for dust emphasizes a serious caveat in our understanding of galaxy formation. Galaxies are too metal enriched at early times.

  20. Exploring the Metal Retention Fractions of Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Morris, Melissa Elizabeth; McQuinn, Kristen B.; Cannon, John M.; Dalcanton, Julianne; Dolphin, Andrew E.; Skillman, Evan D.; Williams, Benjamin F.; van Zee, Liese

    2017-01-01

    Using a novel technique that combines star formation and chemical evolution histories from resolved stellar populations, nebular abundances, and gas masses, McQuinn et al. 2015 measured that only 5% of the oxygen produced by stellar nucleosynthesis was retained in the gas and stars in the very low-mass (stellar mass = 6x105 Msun) galaxy Leo P. In contrast to expectations, metal production and metal loss for spirals in the mass range ~109 - 1011 Msun show that these galaxies retain 20-25% of their metals, independent of mass (Peeples et al. 2014). This suggests there is only a factor of ~5 difference in the ability of galaxies to retain metals, despite a factor of 106 difference in mass. In this prototype study, we explore using the same technique from McQuinn et al. on a small sample of dwarfs with HST archival data, with particular attention to understanding the uncertainties in the approach. Our results will provide a measurement in the intervening mass range between Leo P and more massive spirals. This will allow us to test theoretical predictions of metal loss as a function of galaxy mass.

  1. Tidal dwarf galaxies and the luminosity-metallicity relation .

    NASA Astrophysics Data System (ADS)

    Sweet, S. M.; Drinkwater, M. J.; Meurer, G.; Bekki, K.; Dopita, M. A.; Kilborn, V.; Nicholls, D.

    We present a recalibration of the luminosity-metallicity relation for gas-rich, star-forming dwarfs to magnitudes as faint as M_R˜ -13. We use the \\citet{Dopita2013} metallicity calibrations to calibrate the relation for all of the data in this analysis. Metal-rich dwarfs classified as tidal dwarf galaxy (TDG) candidates in the literature are typically of metallicity 12 + log(O/H) = 8.70 ± 0.05, while SDSS dwarfs fainter than M_R = -16 have a mean metallicity of 12 + log(O/H) = 8.28 ± 0.10, regardless of their luminosity. Our hydrodynamical simuations predict that TDGs should have metallicities elevated above the normal luminosity-metallicity relation. Metallicity can therefore be a useful diagnostic for identifying TDG candidate populations in the absence of tidal tails. At magnitudes brighter than M_R˜ -16 our sample of 53 star-forming galaxies in 9 HI gas-rich groups is consistent with the normal relation defined by the SDSS sample. At fainter magnitudes there is an increase in dispersion in metallicity of our sample. In our sample we identify three (16% of dwarfs) strong TDG candidates (12 + log(O/H) > 8.6), and four (21%) very metal poor dwarfs (12 + log(O/H) < 8.0), which are likely gas-rich dwarfs with recently ignited star formation. Further details of this analysis are available in Sweet et al. (2013, ApJ submitted).

  2. SPATIALLY RESOLVED POLYCYCLIC AROMATIC HYDROCARBON EMISSION FEATURES IN NEARBY, LOW METALLICITY, STAR-FORMING GALAXIES

    SciTech Connect

    Haynes, Korey; Cannon, John M.; Skillman, Evan D.; Gehrz, Robert; Jackson, Dale C. E-mail: khaynes5@gmu.ed E-mail: gehrz@astro.umn.ed

    2010-11-20

    Low-resolution, mid-infrared Spitzer/IRS spectral maps are presented for three nearby, low-metallicity dwarf galaxies (NGC 55, NGC 3109, and IC 5152) for the purpose of examining the spatial distribution and variation of polycyclic aromatic hydrocarbon (PAH) emission. The sample straddles a metallicity of 12 + log(O/H) {approx} 8, a transition point below which PAH intensity empirically drops and the character of the interstellar medium changes. We derive quantitative radiances of PAH features and atomic lines on both global and spatially resolved scales. The Spitzer spectra, combined with extensive ancillary data from the UV through the mid-infrared, allow us to examine changes in the physical environments and in PAH feature radiances down to a physical scale of {approx}50 pc. We discuss correlations between various PAH emission feature and atomic line radiances. The (6.2 {mu}m)/(11.3 {mu}m), (7.7 {mu}m)/(11.3 {mu}m), (8.6 {mu}m)/(11.3 {mu}m), (7.7 {mu}m)/(6.2 {mu}m), and (8.6 {mu}m)/(6.2 {mu}m) PAH radiance ratios are found to be independent of position across all three galaxies, although the ratios do vary from galaxy to galaxy. As seen in other galaxies, we find no variation in the grain size distribution as a function of local radiation field strength. Absolute PAH feature intensities as measured by a ratio of PAH/(24 {mu}m) radiances are seen to vary both positionally within a given galaxy and from one galaxy to another when integrated over the full observed extent of each system. We examine direct comparisons of CC mode PAH ratios (7.7 {mu}m)/(6.2 {mu}m) and (8.6 {mu}m)/(6.2 {mu}m) to the mixed (CC/CH) mode PAH ratio (7.7 {mu}m)/(11.3 {mu}m). We find little variation in either mode and no difference in trends between modes. While the local conditions change markedly over the observed regions of these galaxies, the properties of PAH emission show a remarkable degree of uniformity.

  3. The multifrequency parsec-scale structure of PKS 2254-367 (IC 1459): a luminosity-dependent break in morphology for the precursors of radio galaxies?

    NASA Astrophysics Data System (ADS)

    Tingay, S. J.; Edwards, P. G.

    2015-03-01

    We present the first multifrequency very long baseline interferometry (VLBI) images of PKS 2254-367, a gigahertz-peaked spectrum (GPS) radio source hosted by the nearby galaxy IC 1459 (D = 20.5 Mpc). PKS 2254-367 and the radio source in NGC 1052 (PKS 0238-084; D = 17.2 Mpc) are the two closest GPS radio sources to us, far closer than the next closest example, PKS 1718-649 (D = 59 Mpc). As such, IC 1459 and NGC 1052 offer opportunities to study the details of the parsec-scale radio sources as well as the environments that the radio sources inhabit, across the electromagnetic spectrum. Given that some models for the origin and evolution of GPS radio sources require a strong connection between the radio source morphology and the gaseous nuclear environment, such opportunities for detailed study are important. Our VLBI images of PKS 2254-367 show that the previously identified similarities between IC 1459 and NGC 1052 continue on to the parsec-scale. Both compact radio sources appear to have symmetric jets of approximately the same luminosity, much lower than typically noted in compact double GPS sources. Similarities between PKS 2254-367 and NGC 1052, and differences with respect to other GPS galaxies, lead us to speculate that a sub-class of GPS radio sources, with low luminosity and with jet-dominated morphologies, exists and would be largely absent from radio source surveys with ˜1 Jy flux density cut-offs. We suggest that this possible low-luminosity, jet-dominated population of GPS sources could be an analogue of the Fanaroff-Riley type I (FR I) radio galaxies, with the higher luminosity lobe-dominated GPS sources being the analogue of the FR II radio galaxies.

  4. Metal enrichment in a semi-analytical model, fundamental scaling relations, and the case of Milky Way galaxies

    NASA Astrophysics Data System (ADS)

    Cousin, M.; Buat, V.; Boissier, S.; Bethermin, M.; Roehlly, Y.; Génois, M.

    2016-05-01

    Context. Gas flows play a fundamental role in galaxy formation and evolution, providing the fuel for the star formation process. These mechanisms leave an imprint in the amount of heavy elements that enrich the interstellar medium. Thus, the analysis of this metallicity signature provides additional constraint on the galaxy formation scenario. Aims: We aim to discriminate between four different galaxy formation models based on two accretion scenarios and two different star formation recipes. We address the impact of a bimodal accretion scenario and a strongly regulated star formation recipe on the metal enrichment process of galaxies. Methods: We present a new extension of the eGalICS model, which allows us to track the metal enrichment process in both stellar populations and in the gas phase. Based on stellar metallicity bins from 0 to 2.5 Z⊙, our new chemodynamical model is applicable for situations ranging from metal-free primordial accretion to very enriched interstellar gas contents. We use this new tool to predict the metallicity evolution of both the stellar populations and gas phase. We compare these predictions with recent observational measurements. We also address the evolution of the gas metallicity with the star formation rate (SFR). We then focus on a sub-sample of Milky Way-like galaxies. We compare both the cosmic stellar mass assembly and the metal enrichment process of such galaxies with observations and detailed chemical evolution models. Results: Our models, based on a strong star formation regulation, allow us to reproduce well the stellar mass to gas-phase metallicity relation observed in the local Universe. The shape of our average stellar mass to stellar metallicity relations is in good agreement with observations. However, we observe a systematic shift towards high masses. Our M⋆ - Zg -SFR relation is in good agreement with recent measurements: our best model predicts a clear dependence with the SFR. Both SFR and metal enrichment

  5. Chemical abundances in metal-poor stars in Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Venn, Kim; Norris, John; Shetrone, Matthew

    2015-08-01

    Stars in low-mass dwarf galaxies show a larger range in their chemical properties than those in the Milky Way halo. Not only are alpha-poor stars found at lower metallicities, but also r-process challenged stars, and a disparate fraction of carbon-enhanced metal-poor stars. A more pristine and chemically inhomogeneous interstellar medium, combined with stoichastic star formation in a metal-poor environment, is thought to cause these detectable differences in the early SN II contributions. We are also now finding stars in dwarf galaxies that appear to be iron-enhanced, i.e., stars that have formed in pockets of SN Ia enriched gas. A comparison of their chemical abundances with individual SN Ia models can provide unique constraints on the SN Ia progenitors.

  6. WISE DISCOVERY OF LOW-METALLICITY BLUE COMPACT DWARF GALAXIES

    SciTech Connect

    Griffith, Roger L.; Tsai, Chao-Wei; Jarrett, Thomas H.; Wu Yanling; Yan Lin; Stern, Daniel; Eisenhardt, Peter R. M.; Wu Jingwen; Blain, Andrew; Harrison, Fiona; Madsen, Kristin; Stanford, Spencer A.; Wright, Edward L.

    2011-07-20

    We report two new low-metallicity blue compact dwarf galaxies (BCDs), WISEP J080103.93+264053.9 (hereafter W0801+26) and WISEP J170233.53+180306.4 (hereafter W1702+18), discovered using the Wide-field Infrared Survey Explorer (WISE). We identified these two BCDs from their extremely red colors at mid-infrared wavelengths and obtained follow-up optical spectroscopy using the Low Resolution Imaging Spectrometer on Keck I. The mid-infrared properties of these two sources are similar to the well-studied, extremely low metallicity galaxy SBS 0335-052E. We determine metallicities of 12 + log (O/H) = 7.75 and 7.63 for W0801+26 and W1702+18, respectively, placing them among a very small group of very metal deficient galaxies (Z {<=} 1/10 Z{sub sun}). Their >300 A H{beta} equivalent widths, similar to SBS 0335-052E, imply the existence of young (<5 Myr) star-forming regions. We measure star formation rates of 2.6 and 10.9 M{sub sun} yr{sup -1} for W0801+26 and W1702+18, respectively. These BCDs, showing recent star formation activity in extremely low metallicity environments, provide new laboratories for studying star formation in extreme conditions and are low-redshift analogs of the first generation of galaxies to form in the universe. Using the all-sky WISE survey, we discuss a new method to identify similar star-forming, low-metallicity BCDs.

  7. The mass-metallicity relation of absorption selected high-redshift galaxies

    NASA Astrophysics Data System (ADS)

    Christensen, Lise; Møller, P.; Rhodin, Henrik; Krogager, Jens-Kristian; Fynbo, Johan P. U.

    2017-03-01

    Strong absorption lines in quasar spectra primarily probe low-mass galaxies and detecting these in emission has previously been difficult. Dedicated surveys for the host galaxies of damped Lyman-α (DLA) systems have often resulted in non-detections and upper limits. Targeting the most metal-rich absorbers has proven to be a viable method, because these galaxies are brighter. By combining DLA metallicities and deriving host galaxy stellar masses, we find that metal-rich DLAs (with >10% solar metallicity) and their host galaxies follow the same redshift-dependent scaling relation between stellar mass and metallicity as luminosity-selected galaxies. We derive a prediction for an absorber galaxy mass that depends on the DLA metallicity.

  8. THE METALLICITY BIMODALITY OF GLOBULAR CLUSTER SYSTEMS: A TEST OF GALAXY ASSEMBLY AND OF THE EVOLUTION OF THE GALAXY MASS-METALLICITY RELATION

    SciTech Connect

    Tonini, Chiara

    2013-01-01

    We build a theoretical model to study the origin of the globular cluster metallicity bimodality in the hierarchical galaxy assembly scenario. The model is based on empirical relations such as the galaxy mass-metallicity relation [O/H]-M {sub star} as a function of redshift, and on the observed galaxy stellar mass function up to redshift z {approx} 4. We make use of the theoretical merger rates as a function of mass and redshift from the Millennium simulation to build galaxy merger trees. We derive a new galaxy [Fe/H]-M {sub star} relation as a function of redshift, and by assuming that globular clusters share the metallicity of their original parent galaxy at the time of their formation, we populate the merger tree with globular clusters. We perform a series of Monte Carlo simulations of the galaxy hierarchical assembly, and study the properties of the final globular cluster population as a function of galaxy mass, assembly and star formation history, and under different assumptions for the evolution of the galaxy mass-metallicity relation. The main results and predictions of the model are the following. (1) The hierarchical clustering scenario naturally predicts a metallicity bimodality in the galaxy globular cluster population, where the metal-rich subpopulation is composed of globular clusters formed in the galaxy main progenitor around redshift z {approx} 2, and the metal-poor subpopulation is composed of clusters accreted from satellites, and formed at redshifts z {approx} 3-4. (2) The model reproduces the observed relations by Peng et al. for the metallicities of the metal-rich and metal-poor globular cluster subpopulations as a function of galaxy mass; the positions of the metal-poor and metal-rich peaks depend exclusively on the evolution of the galaxy mass-metallicity relation and the [O/Fe], both of which can be constrained by this method. In particular, we find that the galaxy [O/Fe] evolves linearly with redshift from a value of {approx}0.5 at redshift

  9. Artificial neural network to search for metal-poor galaxies

    NASA Astrophysics Data System (ADS)

    Shi, Fei; Liu, Yu-Yan; Kong, Xu; Chen, Yang

    2014-02-01

    Aims: To find a fast and reliable method for selecting metal-poor galaxies (MPGs), especially in large surveys and huge databases, an artificial neural network (ANN) method is applied to a sample of star-forming galaxies from the Sloan Digital Sky Survey (SDSS) data release 9 (DR9) provided by the Max Planck Institute and the Johns Hopkins University (MPA/JHU). Methods: A two-step approach is adopted: (i) The ANN network must be trained with a subset of objects that are known to be either MPGs or metal rich galaxies (MRGs), treating the strong emission line flux measurements as input feature vectors in n-dimensional space, where n is the number of strong emission line flux ratios. (ii) After the network is trained on a sample of star-forming galaxies, the remaining galaxies are classified in the automatic test analysis as either MPGs or MRGs. We consider several random divisions of the data into training and testing sets; for instance, for our sample, a total of 70 percent of the data are involved in training the algorithm, 15 percent are involved in validating the algorithm, and the remaining 15 percent are used for blind testing the resulting classifier. Results: For target selection, we have achieved an acquisition rate for MPGs of 96 percent and 92 percent for an MPGs threshold of 12 + log (O/H) = 8.00 and 12 + log (O/H) = 8.39, respectively. Running the code takes minutes in most cases under the Matlab 2013a software environment. The ANN method can easily be extended to any MPGs target selection task when the physical property of the target can be expressed as a quantitative variable. The code in the paper is available on the web (http://fshi5388.blog.163.com).

  10. Metallicity and the level of the ultraviolet rising branch in elliptical galaxies

    NASA Technical Reports Server (NTRS)

    Faber, S. M.

    1986-01-01

    This final report concerns a project to study the systematics of the ultraviolet flux level in elliptical galaxies. Prior to the inception of this work, the systematic behavior of the ultraviolet flux level was basically unknown and ultraviolet fluxes were observed to vary greatly from galaxy to galaxy. There was a suggestion, however, that there might be a dependence of ultraviolet flux on galaxy metallicity, but the correlation was based on just six galaxies. IUE spectra of elliptical galaxies have been reanalyzed and placed on a consistent, homogenous flux system. The major conclusion is a confirmation of the original hypothesis: galaxies with stronger Mg2 lines show enhanced ultraviolet flux.

  11. Theoretical Modeling of Star-Forming Galaxies. I. Emission-Line Diagnostic Grids for Local and Low-Metallicity Galaxies

    NASA Astrophysics Data System (ADS)

    Levesque, Emily M.; Kewley, Lisa J.; Larson, Kirsten L.

    2010-02-01

    We use the newest generation of the Starburst99/Mappings code to generate an extensive suite of models to facilitate detailed studies of star-forming galaxies and their interstellar medium properties, particularly at low metallicities. The new models used include a rigorous treatment of metal opacities in the population synthesis modeling and more detailed dust physics in the photoionization code. These models span a wide range of physical parameters including metallicity, ionization parameter, and the adoption of both an instantaneous burst and continuous star formation history (SFH). We examine the agreement between our models and local (z < 0.1) star-forming galaxy populations from several large data sets, including the Sloan Digital Sky Survey, the Nearby Field Galaxy Survey, and samples of blue compact galaxies and metal-poor galaxies. We find that models adopting a continuous SFH reproduce the metallicity-sensitive line ratios observed in the local population of star-forming galaxies, including the low-metallicity sample. However, we find that the current codes generate an insufficiently hard ionizing radiation field, leading to deficiencies in the [S II] fluxes produced by the models. We consider the advantages and shortcomings of this suite of models, and discuss future work and improvements that can be applied to the modeling of star-forming galaxies.

  12. The rarity of dust in metal-poor galaxies.

    PubMed

    Fisher, David B; Bolatto, Alberto D; Herrera-Camus, Rodrigo; Draine, Bruce T; Donaldson, Jessica; Walter, Fabian; Sandstrom, Karin M; Leroy, Adam K; Cannon, John; Gordon, Karl

    2014-01-09

    Galaxies observed at redshift z > 6, when the Universe was less than a billion years old, thus far very rarely show evidence of the cold dust that accompanies star formation in the local Universe, where the dust-to-gas mass ratio is around one per cent. A prototypical example is the galaxy Himiko (z = 6.6), which--a mere 840 million years after the Big Bang--is forming stars at a rate of 30-100 solar masses per year, yielding a mass assembly time of about 150 × 10(6) years. Himiko is thought to have a low fraction (2-3 per cent of the Sun's) of elements heavier than helium (low metallicity), and although its gas mass cannot yet be determined its dust-to-stellar mass ratio is constrained to be less than 0.05 per cent. The local dwarf galaxy I Zwicky 18, which has a metallicity about 4 per cent that of the Sun's and is forming stars less rapidly (assembly time about 1.6 × 10(9) years) than Himiko but still vigorously for its mass, is also very dust deficient and is perhaps one of the best analogues of primitive galaxies accessible to detailed study. Here we report observations of dust emission from I Zw 18, from which we determine its dust mass to be 450-1,800 solar masses, yielding a dust-to-stellar mass ratio of about 10(-6) to 10(-5) and a dust-to-gas mass ratio of 3.2-13 × 10(-6). If I Zw 18 is a reasonable analogue of Himiko, then Himiko's dust mass must be around 50,000 solar masses, a factor of 100 below the current upper limit. These numbers are quite uncertain, but if most high-z galaxies are more like Himiko than like the very-high-dust-mass galaxy SDSS J114816.64 + 525150.3 at z ≈ 6, which hosts a quasar, then our prospects for detecting the gas and dust inside such galaxies are much poorer than hitherto anticipated.

  13. New fully empirical calibrations of strong-line metallicity indicators in star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Curti, M.; Cresci, G.; Mannucci, F.; Marconi, A.; Maiolino, R.; Esposito, S.

    2017-02-01

    We derive new empirical calibrations for strong-line diagnostics of gas-phase metallicity in local star-forming galaxies by uniformly applying the Te method over the full metallicity range probed by the Sloan Digital Sky Survey (SDSS). To measure electron temperatures at high metallicity, where the auroral lines needed are not detected in single galaxies, we stacked spectra of more than 110 000 galaxies from the SDSS in bins of log[O II]/Hβ and log[O III]/Hβ. This stacking scheme does not assume any dependence of metallicity on mass or star formation rate, but only that galaxies with the same line ratios have the same oxygen abundance. We provide calibrations which span more than 1 dex in metallicity and are entirely defined on a consistent absolute Te metallicity scale for galaxies. We apply our calibrations to the SDSS sample and find that they provide consistent metallicity estimates to within 0.05 dex.

  14. A search for Wolf-Rayet stars in active star forming regions of low mass galaxies - GR8, NGC 2366, IC 2574, and NGC 1569

    NASA Astrophysics Data System (ADS)

    Drissen, Laurent; Roy, Jean-Rene; Moffat, Anthony F. J.

    1993-10-01

    We report the detection, via narrow-band 4686 A filter imagery, of possible new Wolf-Rayet stars in the most massive giant H II regions of the irregular galaxies NGC 2366 and IC 2574. One stellar knot in the post-starburst galaxy NGC 1569 also appears to contain a weak excess of light at 4686 A. A similar search yielded negative results in the very low mass galaxy GR8. The strongest 4686 A excess is located close to the secondary eastern knot in the core of NGC 2366-I (NGC 2363). If this excess is of stellar origin, about five Wolf-Rayet stars of the luminous late-type can account for the excess emission. Nebular emission wraps around this cluster in the form of a shell. The putative Wolf-Rayet stars appear to be close to the center of the large expanding H II bubble discovered by Roy et al. (1991). A possible nebular origin of the 4686 A excess is also discussed.

  15. Searching for metal-deficient emission-line galaxy candidates: the final sample of the SDSS DR12 galaxies

    NASA Astrophysics Data System (ADS)

    Guseva, N. G.; Izotov, Y. I.; Fricke, K. J.; Henkel, C.

    2017-03-01

    We present a spectroscopic study of metal-deficient dwarf galaxy candidates, selected from the SDSS DR12. The oxygen abundances were derived using the direct method in galaxies with the electron temperature-sensitive emission line [O iii]λ4363 Å measured with an accuracy better than 30%. The oxygen abundances for the remaining galaxies with larger uncertainties of the [O iii]λ4363 Å line fluxes were calculated using a strong-line semi-empirical method by Izotov and Thuan. The resulting sample consists of 287 low-metallicity candidates with oxygen abundances below 12 + log O/H = 7.65 including 23 extremely metal-deficient (XMD) candidates with 12 + log O/H ≤ 7.35. Ten out of sixteen XMDs known so far (or 60%) have been discovered by our team using the direct method. Three XMDs were found in the present study. We study relations between global parameters of low-metallicity galaxies, including absolute optical magnitudes, Hβ luminosities (or equivalently star formation rates), stellar masses, mid-infrared colours, and oxygen abundances. Low-metallicity and XMD galaxies strongly deviate to lower metallicities in L-Z, L(Hβ)-Z and M∗-Z diagrams than in relations obtained for large samples of low-redshift, star-forming galaxies with non-restricted metallicities. These less chemically evolved galaxies with stellar masses ≈106-108M⊙, Hβ luminosities ≈1038-1041 erg s-1, SFR ≈ 0.01-1.0 M⊙ yr-1, and sSFR 50 Gyr-1 have physical conditions which may be characteristic of high-redshift low-mass star-forming galaxies which are still awaiting discovery.

  16. ALFALFA DISCOVERY OF THE NEARBY GAS-RICH DWARF GALAXY LEO P. III. AN EXTREMELY METAL DEFICIENT GALAXY

    SciTech Connect

    Skillman, Evan D.; Berg, Danielle A.; Olive, Keith A.; McQuinn, Kristen B. W. E-mail: berg@astro.umn.edu E-mail: kmcquinn@astro.umn.edu; and others

    2013-07-01

    We present KPNO 4 m and LBT/MODS spectroscopic observations of an H II region in the nearby dwarf irregular galaxy Leo P discovered recently in the Arecibo ALFALFA survey. In both observations, we are able to accurately measure the temperature sensitive [O III] {lambda}4363 line and determine a ''direct'' oxygen abundance of 12 + log(O/H) = 7.17 {+-} 0.04. Thus, Leo P is an extremely metal deficient (XMD) galaxy, and, indeed, one of the most metal deficient star-forming galaxies ever observed. For its estimated luminosity, Leo P is consistent with the relationship between luminosity and oxygen abundance seen in nearby dwarf galaxies. Leo P shows normal {alpha} element abundance ratios (Ne/O, S/O, and Ar/O) when compared to other XMD galaxies, but elevated N/O, consistent with the ''delayed release'' hypothesis for N/O abundances. We derive a helium mass fraction of 0.2509{sup +0.0184}{sub -0.0123}, which compares well with the WMAP + BBN prediction of 0.2483 {+-} 0.0002 for the primordial helium abundance. We suggest that surveys of very low mass galaxies compete well with emission line galaxy surveys for finding XMD galaxies. It is possible that XMD galaxies may be divided into two classes: the relatively rare XMD emission line galaxies which are associated with starbursts triggered by infall of low-metallicity gas and the more common, relatively quiescent XMD galaxies like Leo P, with very low chemical abundances due to their intrinsically small masses.

  17. Deep Imaging of Extremely Metal-Poor Galaxies

    NASA Astrophysics Data System (ADS)

    Corbin, Michael

    2006-07-01

    Conflicting evidence exists regarding whether the most metal-poor and actively star-forming galaxies in the local universe such as I Zw 18 contain evolved stars. We propose to help settle this issue by obtaining deep ACS/HRC U, narrow-V, I, and H-alpha images of nine nearby {z < 0.01} extremely metal-poor {12 + O/H < 7.65} galaxies selected from the Sloan Digital Sky Survey. These objects are only marginally resolved from the ground and appear uniformly blue, strongly motivating HST imaging. The continuum images will establish: 1.} If underlying populations of evolved stars are present, by revealing the objects' colors on scales 10 pc, and 2.} The presence of any faint tidal features, dust lanes, and globular or super star clusters, all of which constrain the objects' evolutionary states. The H-alpha images, in combination with ground-based echelle spectroscopy, will reveal 1.} Whether the objects are producing "superwinds" that are depleting them of their metals; ground-based images of some of them indeed show large halos of ionized gas, and 2.} The correspondence of their nebular and stellar emission on scales of a few parsecs, which is important for understanding the "feedback" process by which supernovae and stellar winds regulate star formation. One of the sample objects, CGCG 269-049, lies only 2 Mpc away, allowing the detection of individual red giant stars in it if any are present. We have recently obtained Spitzer images and spectra of this galaxy to determine its dust content and star formation history, which will complement the proposed HST observations. [NOTE: THIS PROPOSAL WAS REDUCED TO FIVE ORBITS, AND ONLY ONE OF THE ORIGINAL TARGETS, CGCG 269-049, AFTER THE PHASE I REVIEW

  18. Carbon and Oxygen Abundances in Low Metallicity Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Berg, Danielle A.; Skillman, Evan D.; Henry, Richard B. C.; Erb, Dawn K.; Carigi, Leticia

    2016-08-01

    The study of carbon and oxygen abundances yields information on the time evolution and nucleosynthetic origins of these elements, yet they remain relatively unexplored. At low metallicities, (12+log(O/H) < 8.0), nebular carbon measurements are limited to rest-frame UV collisionally excited emission lines. Therefore, we present the UV spectrophotometry of 12 nearby low-metallicity high-ionization H ii regions in dwarf galaxies obtained using the Cosmic Origins Spectrograph on the Hubble Space Telescope. We present the first analysis of the C/O ratio in local galaxies based solely on simultaneous significant detections of the UV {{{O}}}+2 and {{{C}}}+2 collisionally excited lines in seven of our targets and five objects from the literature to create a final sample of 12 significant detections. Our sample is complemented by optical SDSS spectra, from which we measured the nebular physical conditions and oxygen abundances using the direct method. At low metallicity, (12+log(O/H) < 8.0), no clear trend is evident in C/O versus O/H for the present sample given the large dispersion observed. When combined with recombination line observations at higher values of O/H, a general trend of increasing C/O with increasing O/H is also viable but with some significant outliers. Additionally, we find the C/N ratio appears to be constant (but with significant scatter) over a large range in oxygen abundance, indicating that carbon is predominantly produced by similar nucleosynthetic mechanisms as nitrogen. If true, and our current understanding of nitrogen production is correct, this would indicate that primary production of carbon (a flat trend) dominates at low metallicity, but quasi-secondary production (an increasing trend) becomes prominent at higher metallicities. A larger sample will be needed to determine the true nature and dispersion of the relation.

  19. THE INFLUENCE OF GALAXY SURFACE BRIGHTNESS ON THE MASS–METALLICITY RELATION

    SciTech Connect

    Wu, Po-Feng; Kudritzki, Rolf-Peter; Tully, R. Brent; Neill, J. D.

    2015-09-10

    We study the effect of surface brightness on the mass–metallicity relation using nearby galaxies whose gas content and metallicity profiles are available. Previous studies using fiber spectra indicated that lower surface brightness galaxies have systematically lower metallicities for their stellar mass, but the results were uncertain because of aperture effects. With stellar masses and surface brightnesses measured at Wide-field Infrared Explorer W1 and W2 bands, we re-investigate the surface brightness dependence with spatially resolved metallicity profiles and find similar results. We further demonstrate that the systematical difference cannot be explained by the gas content of galaxies. For two galaxies with similar stellar and gas masses, the one with lower surface brightness tends to have a lower metallicity. Using chemical evolution models, we investigate the inflow and outflow properties of galaxies of different masses and surface brightnesses. We find that, on average, high mass galaxies have lower inflow and outflow rates relative to the star formation rate. On the other hand, galaxies with a lower surface brightness experience stronger inflow than galaxies with a higher surface brightness of a similar mass. The surface brightness effect is more significant for low-mass galaxies. We discuss implications on the different inflow properties between low and high surface brightness galaxies, including star formation efficiency, environment, and mass assembly history.

  20. ON THE USE OF THE INDEX N2 TO DERIVE THE METALLICITY IN METAL-POOR GALAXIES

    SciTech Connect

    Morales-Luis, A. B.; Almeida, J. Sánchez; Muñoz-Tuñón, C.; Pérez-Montero, E. E-mail: cmt@iac.es E-mail: epm@iaa.es

    2014-12-20

    The N2 index ([N II] λ6584/Hα) is used to determine emission line galaxy metallicities at all redshifts, including high redshift, where galaxies tend to be metal-poor. The initial aim of this work was to improve the calibrations used to infer oxygen abundance from N2 by employing updated low-metallicity galaxy databases. We compare N2 and the metallicity determined using the direct method for the set of extremely metal-poor galaxies compiled by Morales-Luis et al. To our surprise, the oxygen abundance presents a tendency to be constant with N2, with a very large scatter. Consequently, we find that the existing N2 calibrators overestimate the oxygen abundance for most low-metallicity galaxies, and can therefore only be used to set upper limits to the true metallicity in low-metallicity galaxies. An explicit expression for this limit is given. In addition, we try to explain the observed scatter using photoionization models. It is mostly due to the different evolutionary state of the H II regions producing the emission lines, but it also arises due to differences in N/O among the galaxies.

  1. Why do high-redshift galaxies show diverse gas-phase metallicity gradients?

    NASA Astrophysics Data System (ADS)

    Ma, Xiangcheng; Hopkins, Philip F.; Feldmann, Robert; Torrey, Paul; Faucher-Giguère, Claude-André; Kereš, Dušan

    2017-01-01

    Recent spatially resolved observations of galaxies at z ˜ 0.6-3 reveal that high-redshift galaxies show complex kinematics and a broad distribution of gas-phase metallicity gradients. To understand these results, we use a suite of high-resolution cosmological zoom-in simulations from the Feedback in Realistic Environments (FIRE) project, which include physically motivated models of the multi-phase ISM, star formation, and stellar feedback. Our simulations reproduce the observed diversity of kinematic properties and metallicity gradients, broadly consistent with observations at z ˜ 0-3. Strong negative metallicity gradients only appear in galaxies with a rotating disk, but not all rotationally supported galaxies have significant gradients. Strongly perturbed galaxies with little rotation always have flat gradients. The kinematic properties and metallicity gradient of a high-redshift galaxy can vary significantly on short time-scales, associated with starburst episodes. Feedback from a starburst can destroy the gas disk, drive strong outflows, and flatten a pre-existing negative metallicity gradient. The time variability of a single galaxy is statistically similar to the entire simulated sample, indicating that the observed metallicity gradients in high-redshift galaxies reflect the instantaneous state of the galaxy rather than the accretion and growth history on cosmological time-scales. We find weak dependence of metallicity gradient on stellar mass and specific star formation rate (sSFR). Low-mass galaxies and galaxies with high sSFR tend to have flat gradients, likely due to the fact that feedback is more efficient in these galaxies. We argue that it is important to resolve feedback on small scales in order to produce the diverse metallicity gradients observed.

  2. The evolution of galaxies. III - Metal-enhanced star formation

    NASA Technical Reports Server (NTRS)

    Talbot, R. J., Jr.; Arnett, W. D.

    1973-01-01

    The problem of the paucity of low-metal-abundance low-mass stars is discussed. One alternative to the variable-initial-mass-function (VIMF) solution is proposed. It is shown that this solution - metal-enhanced star formation - satisfies the classical test which prompted the VIMF hypothesis. Furthermore, with no additional parameters it provides improved fits to other tests - e.g., inhomogeneities in the abundances in young stars, concordance of all nucleo-cosmochronologies, and a required yield of heavy-element production which is consistent with current stellar evolution theory. In this model the age of the Galaxy is 18.6 plus or minus 5.7 b.y.

  3. Galaxy And Mass Assembly (GAMA): the mass-metallicity relationship

    NASA Astrophysics Data System (ADS)

    Foster, C.; Hopkins, A. M.; Gunawardhana, M.; Lara-López, M. A.; Sharp, R. G.; Steele, O.; Taylor, E. N.; Driver, S. P.; Baldry, I. K.; Bamford, S. P.; Liske, J.; Loveday, J.; Norberg, P.; Peacock, J. A.; Alpaslan, M.; Bauer, A. E.; Bland-Hawthorn, J.; Brough, S.; Cameron, E.; Colless, M.; Conselice, C. J.; Croom, S. M.; Frenk, C. S.; Hill, D. T.; Jones, D. H.; Kelvin, L. S.; Kuijken, K.; Nichol, R. C.; Owers, M. S.; Parkinson, H. R.; Pimbblet, K. A.; Popescu, C. C.; Prescott, M.; Robotham, A. S. G.; Lopez-Sanchez, A. R.; Sutherland, W. J.; Thomas, D.; Tuffs, R. J.; van Kampen, E.; Wijesinghe, D.

    2012-11-01

    Context. The mass-metallicity relationship (MMR) of star-forming galaxies is well-established, however there is still some disagreement with respect to its exact shape and its possible dependence on other observables. Aims: We measure the MMR in the Galaxy And Mass Assembly (GAMA) survey. We compare our measured MMR to that measured in the Sloan Digital Sky Survey (SDSS) and study the dependence of the MMR on various selection criteria to identify potential causes for disparities seen in the literature. Methods: We use strong emission line ratio diagnostics to derive oxygen abundances. We then apply a range of selection criteria for the minimum signal-to-noise in various emission lines, as well as the apparent and absolute magnitude to study variations in the inferred MMR. Results: The shape and position of the MMR can differ significantly depending on the metallicity calibration and selection used. After selecting a robust metallicity calibration amongst those tested, we find that the mass-metallicity relation for redshifts 0.061 ≲ z ≲ 0.35 in GAMA is in reasonable agreement with that found in the SDSS despite the difference in the luminosity range probed. Conclusions: In view of the significant variations of the MMR brought about by reasonable changes in the sample selection criteria and method, we recommend that care be taken when comparing the MMR from different surveys and studies directly. We also conclude that there could be a modest level of evolution over 0.06 ≤ z ≤ 0.35 within the GAMA sample.

  4. Does star formation proceed differently in metal-poor galaxies?

    NASA Astrophysics Data System (ADS)

    Lebouteiller, Vianney

    2014-10-01

    The importance of molecular gas in the star-formation process has been questioned by recent theoretical studies. When metals are scarce, star formation could proceed before the molecular fraction becomes significant, making cold atomic gas the key pre-requisite for star formation. The best case studies are blue compact dwarf galaxies (BCDs), with their prominent star-formation episode and yet with little or no evidence of molecular gas. Current observations do not provide strong constraints on the presence of dense atomic gas in BCDs nor on the fraction of molecular gas.We propose to examine the HI region of 9 nearby BCDs selected from the Herschel Dwarf Galaxy Survey. Our program relies on the synergy of Hubble and Herschel, by calculating the gas cooling rate from the fine-structure level of ionized carbon, a parameter that can be determined both in the FUV with COS (probing the diffuse gas through the 1335.7A CII* absorption) and in the FIR with Herschel (probing the denser gas through the [CII] 157um emission). This comparison allows us to constrain the volume filling factor of dense vs. diffuse gas. The program we propose will allow us to examine how this fraction varies with metallicity, star-formation rate, and total gas mass. We will also be able to quantify the mass of molecular gas and evaluate its actual importance for star formation. Finally, a secondary objective is to characterize the main gas heating mechanisms in the HI region of BCDs and in particular the validity of the photoelectric effect paradigm in sources with a low dust-to-gas ratio, with potential implications for high-redshift galaxies.

  5. The X-Ray Binary Population of the Nearby Dwarf Starburst Galaxy IC 10: Variable and Transient X-Ray Sources

    NASA Astrophysics Data System (ADS)

    Laycock, Silas; Cappallo, Rigel; Williams, Benjamin F.; Prestwich, Andrea; Binder, Breanna; Christodoulou, Dimitris M.

    2017-02-01

    We have monitored the Cassiopeia dwarf galaxy (IC 10) in a series of 10 Chandra ACIS-S observations to capture its variable and transient X-ray source population, which is expected to be dominated by High Mass X-ray Binaries (HMXBs). We present a sample of 21 X-ray sources that are variable between observations at the 3σ level, from a catalog of 110 unique point sources. We find four transients (flux variability ratio greater than 10) and a further eight objects with ratios >5. The observations span the years 2003–2010 and reach a limiting luminosity of >1035 erg s‑1, providing sensitivity to X-ray binaries in IC 10 as well as flare stars in the foreground Milky Way. The nature of the variable sources is investigated from light curves, X-ray spectra, energy quantiles, and optical counterparts. The purpose of this study is to discover the composition of the X-ray binary population in a young starburst environment. IC 10 provides a sharp contrast in stellar population age (<10 My) when compared to the Magellanic Clouds (40–200 My) where most of the known HMXBs reside. We find 10 strong HMXB candidates, 2 probable background Active Galactic Nuclei, 4 foreground flare-stars or active binaries, and 5 not yet classifiable sources. Complete classification of the sample requires optical spectroscopy for radial velocity analysis and deeper X-ray observations to obtain higher S/N spectra and search for pulsations. A catalog and supporting data set are provided.

  6. How surface density of galaxy disks affects metallicity? Outflow and Accretion

    NASA Astrophysics Data System (ADS)

    Wu, Po-Feng; Kudritzki, Rolf-Peter; Tully, R. Brent; Neill, J. D.

    2015-08-01

    The surface density of disk is considered as a second parameter affecting the evolution of disk galaxies other than mass. Several physical and chemical properties of galaxies are found to be correlated with surface density of disk galaxies. However, the surface density, or surface brightness, is also strongly correlated with mass. It's not clear whether surface density really plays a role, or those correlations simply reflect the effect from stellar mass. To ask the question properly, one should take away the dependence on mass of galaxies, i.e., compare galaxies with the same mass but different surface densities.In this study, we ask, besides stellar mass, whether the surface density of disks also affects chemical evolution of galaxies. We demonstrate that, after removing the dependence on stellar mass and gas mass, the metallicity of galaxy still correlates with surface density of the galaxy disk. At the same stellar and gas mass, higher surface brightness galaxies on average possess both higher stellar and gas-phase metallicity, inferred from broadband color and spectrosopy of HII regions, respectively.We use an analytical model of chemical evolution involving gas outflow and accretion to explore possible reasons causing the difference in metallicity. Accroding to the model, at the same mass, lower metallicity galaxies should have experienced severer mass loss during star-formation events, and/or be inert to gas accretion. Both scenarios are consistent with general expections from properties of low surface density disks of shallow potential wells and dynamical stability.

  7. The gas-phase metallicity of central and satellite galaxies in the Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

    Pasquali, Anna; Gallazzi, Anna; van den Bosch, Frank C.

    2012-09-01

    We exploit the galaxy groups catalogue of Yang et al. and the galaxy properties measured in the Sloan Digital Sky Survey Data Releases 4 and 7 to study how the gas-phase metallicities of star-forming galaxies depend on environment. We find that satellite and central galaxies follow a qualitatively similar stellar mass (M★)-gas-phase metallicity relation, whereby their gas-phase metallicity increases with M★. Satellites, though, have higher gas-phase metallicities than equally massive centrals, and this difference increases with decreasing stellar mass. We find a maximum offset of 0.06 dex at log(M★/h-2 M⊙) ≃ 8.25. At fixed halo mass, centrals are more metal rich than satellites by ˜0.5 dex on average. This is simply due to the fact that, by definition, centrals are the most massive galaxies in their groups, and the fact that gas-phase metallicity increases with stellar mass. More interestingly, we also find that the gas-phase metallicity of satellites increases with halo mass (Mh) at fixed stellar mass. This increment is more pronounced for less massive galaxies, and, at M★ ≃ 109 h-2 M⊙, corresponds to ˜0.15 dex across the range 11 < log (Mh/h-1 M⊙) < 14. We also show that low-mass satellite galaxies have higher gas-phase metallicities than central galaxies of the same stellar metallicity. This difference becomes negligible for more massive galaxies of roughly solar metallicity. We demonstrate that the observed differences in gas-phase metallicity between centrals and satellites at fixed M★ are not a consequence of stellar mass stripping (advocated by Pasquali et al. in order to explain similar differences but in stellar metallicity), nor to the past star formation history of these galaxies as quantified by their surface mass density or gas mass fraction. Rather, we argue that these trends probably originate from a combination of three environmental effects: (i) strangulation, which prevents satellite galaxies from accreting new, low-metallicity

  8. Measuring the Radius of a Neutron Star; Origin of High X-Ray Luminosities in Optically Passive Galaxies; Resolving the Source of X-Rays in IC 1613"

    NASA Technical Reports Server (NTRS)

    Helfand, David J.

    1998-01-01

    This recently expired grant has supported the work of the PI, his students, and his collaborators on a variety of ROSAT projects over the past three years. Annual reports have summarized much of the work accomplished; here we provide a brief review of the work resulting from this effort, and a summary of the personnel who have benefited from its support. A high resolution ROSAT HRI X-ray image of the Local Group dwarf IC1613 revealed that the principal source of X-ray emission in this direction arises in a background cluster of galaxies, as first suggested by Eskridge (1995). In addition, however, we found a bright X-ray source coincident with the only known supernova remnant in this galaxy, S # 8. Extensive ground-based follow-up observations in the radio and optical regimes were conducted. We confirmed the nonthermal radio spectral index of the source and measured its extent to be approx. 3 sec at 20 cm. Imaging spectrophotometric observations taken with the multi-pupil spectrograph of the Special Astrophysical Observatory in the FSU allowed us to determine the density and velocity distribution of the gas in the remnant. The simultaneous presence of luminous X-ray and optical emission suggests a relatively young remnant in which the outward-moving shock has recently encountered dense material. Many of this object's properties are similar to those of the brightest optical remnant in the Large Magellanic Cloud, N49. Another potential source of X-rays in this galaxy which featured prominently in our original proposal, an Oxygen Wolf-Rayet star with a large surrounding wind-blown bubble, was not detected.

  9. The galaxy population of Abell 1367: the stellar mass-metallicity relation

    NASA Astrophysics Data System (ADS)

    Mouhcine, M.; Kriwattanawong, W.; James, P. A.

    2011-04-01

    Using wide baseline broad-band photometry, we analyse the stellar population properties of a sample of 72 galaxies, spanning a wide range of stellar masses and morphological types, in the nearby spiral-rich and dynamically young galaxy cluster Abell 1367. The sample galaxies are distributed from the cluster centre out to approximately half the cluster Abell radius. The optical/near-infrared colours are compared with simple stellar population synthesis models from which the luminosity-weighted stellar population ages and metallicities are determined. The locus of the colours of elliptical galaxies traces a sequence of varying metallicity at a narrow range of luminosity-weighted stellar ages. Lenticular galaxies in the red sequence, however, exhibit a substantial spread of luminosity-weighted stellar metallicities and ages. For red-sequence lenticular galaxies and blue cloud galaxies, low-mass galaxies tend to be on average dominated by stellar populations of younger luminosity-weighted ages. Sample galaxies exhibit a strong correlation between integrated stellar mass and luminosity-weighted stellar metallicity. Galaxies with signs of morphological disturbance and ongoing star formation activity, tend to be underabundant with respect to passive galaxies in the red sequence of comparable stellar masses. We argue that this could be due to tidally driven gas flows towards the star-forming regions, carrying less enriched gas and diluting the pre-existing gas to produce younger stellar populations with lower metallicities than would be obtained prior to the interaction. Finally, we find no statistically significant evidence for changes in the luminosity-weighted ages and metallicities for either red-sequence or blue-cloud galaxies, at fixed stellar mass, with location within the cluster. We dedicate this work to the memory of our friend and colleague C. Moss who died suddenly recently.

  10. Evaluation of surface analysis methods for characterization of trace metal surface contaminants found in silicon IC manufacturing

    SciTech Connect

    Diebold, A.C.; Maillot, P.; Gordon, M.; Baylis, J.; Chacon, J.; Witowski, R. ); Arlinghaus, H. ); Knapp, J.A.; Doyle, B.L. )

    1991-01-01

    A major topic at recent silicon-based integrated circuit (IC) manufacturing symposia is the pursuit of decreased contamination levels. The aim is to remove contamination from both processes and materials. In conjunction with this effort, characterization methods are being pushed to lower and lower detection limits. In this paper, we evaluate surface analysis methods used to determine the concentration of inorganic contamination on unpatterned Si wafers. We compare sampling depths, detection limits, and applicability of each method for use in support of Si IC manufacturing. This comparison is further limited to Fe and Cu which are transition metal contaminants associated with manufacturing yield loss. The surface analysis methods included in this evaluation are: Total Reflection X-Ray Fluorescence (TXRF or TRXRF); Secondary Ion Mass Spectrometry (SIMS); two post-ionization'' methods Surface Analysis by Laser Ionization (SALI) and Sputter Initiated Resonant Ionization Spectroscopy (SIRIS); Heavy Ion Backscattering Spectroscopy (HIBS); and Vapor Phase Phase Decomposition (VPD) based methods Atomic Absorption (VPD-AA) along with VPD-TXRF. Sets of 6 in. Si wafers with concentration levels between 10{sup 9} atoms/cm{sup 2} and 10{sup 12} atoms/cm{sup 2} Fe and Cu were characterized by TXRF, SIMS, SIRIS, and HIBS. This data allows estimation of detection limits (DLs) and relative method accuracy. In Section 1 we describe each surface analysis method and the circumstance under which it would be used to support Si IC manufacturing. The equipment used for this comparison and the 150 mm Si wafer set are described in Section 2. Results from each method are contrasted in Section 3. Finally, a conclusion is presented in Section 4.

  11. Charting the evolution of the ages and metallicities of massive galaxies since z = 0.7

    SciTech Connect

    Gallazzi, Anna; Zibetti, Stefano; Bell, Eric F.; Brinchmann, Jarle; Kelson, Daniel D.

    2014-06-10

    Detailed studies of the stellar populations of intermediate-redshift galaxies can shed light onto the processes responsible for the growth of the massive galaxy population in the last 8 billion years. We here take a step toward this goal by means of deep, multiobject rest-frame optical spectroscopy, performed with the Inamori Magellan Areal Camera and Spectrograph on the Magellan telescope, of a sample of ∼70 galaxies in the Extended Chandra Deep Field South survey with redshift 0.65 ≤ z ≤ 0.75, apparent R > 22.7 mag{sub Vega}, and stellar mass >10{sup 10} M {sub ☉}. We measure velocity dispersion and stellar absorption features for individual sources. We interpret them by means of a large Monte Carlo library of star formation histories, following the Bayesian approach adopted for previous low redshift studies, and derive constraints on the stellar mass, mean stellar age, and stellar metallicity of these galaxies. We characterize for the first time the relations between stellar age and stellar mass and between stellar metallicity and stellar mass at z ∼ 0.7 for the galaxy population as a whole and for quiescent and star-forming galaxies separately. These relations of increasing age and metallicity with galaxy mass for the galaxy population as a whole have a similar shape as the z ∼ 0.1 analog derived for Sloan Digital Sky Survey galaxies but are shifted by –0.28 dex in age and by –0.13 dex in metallicity, at odds with simple passive evolution. Considering z = 0.7 quiescent galaxies alone, we find that no additional star formation and chemical enrichment are required for them to evolve into the present-day quiescent population. However, other observations require the quiescent population to grow from z = 0.7 to the present day. This growth could be supplied by the quenching of a fraction of z = 0.7 M {sub *} > 10{sup 11} M {sub ☉} star-forming galaxies with metallicities already comparable to those of quiescent galaxies, thus leading to the

  12. Toward Gas Chemistry in Low Metallicity Starburst Galaxies

    NASA Astrophysics Data System (ADS)

    Meier, David S.; Anderson, Crystal N.; Turner, Jean; Ott, Juergen; Beck, Sara C.

    2017-01-01

    Dense gas, which is intimately connected with star formation, is key to understanding star formation. Though challenging to study, dense gas in low metallicity starbursts is important given these system's often extreme star formation and their potential implications for high redshift analogs. High spatial resolution (~50 pc) ALMA observations of several key probes of gas chemistry, including HCN(1-0), HCO+(1-0), CS(2-1), CCH(1-0;3/2-1/2) and SiO(2-1), towards the nearby super star-cluster (SSC) forming, sub-solar metallicity galaxy NGC 5253 are discussed. Dense gas is observed to be extended well beyond the current compact starburst, reaching into the apparently infalling molecular streamer. The faintness of HCN, the standard dense gas tracer, is extreme both in an absolute sense relative to high metallicity starbursts of a similar intensity and in a relative sense, with the HCO+/HCN ratio being one of the most elevated observed. UV-irradiated molecular gas, traced by CCH, is also extended over the mapped region, not being strongly correlated with the SSC. Despite the accretion of molecular gas from the halo and the intense burst of star formation, chemical signatures of shocked gas, traced by SiO (and HNCO), are not obvious. By placing NGC 5253 in context with other local starbursts, like 30 Doradus in the Large Magellanic Clouds and the high metallicity proto-typical starburst NGC 253, it is suggested that a combination of gas excitation and abundance changes associated with the sub solar metallicity may explain these anomalous dense gas properties.

  13. Rest-UV Absorption Lines as Metallicity Estimator: The Metal Content of Star-forming Galaxies at z ~ 5

    NASA Astrophysics Data System (ADS)

    Faisst, A. L.; Capak, P. L.; Davidzon, I.; Salvato, M.; Laigle, C.; Ilbert, O.; Onodera, M.; Hasinger, G.; Kakazu, Y.; Masters, D.; McCracken, H. J.; Mobasher, B.; Sanders, D.; Silverman, J. D.; Yan, L.; Scoville, N. Z.

    2016-05-01

    We measure a relation between the depth of four prominent rest-UV absorption complexes and metallicity for local galaxies and verify it up to z˜ 3. We then apply this relation to a sample of 224 galaxies at 3.5\\lt z\\lt 6.0 (< z> =4.8) in the Cosmic Evolution Survey (COSMOS), for which unique UV spectra from the Deep Imaging Multi-object Spectrograph (DEIMOS) and accurate stellar masses from the Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH) are available. The average galaxy population at z˜ 5 and {log}(M/{M}⊙ )\\gt 9 is characterized by 0.3-0.4 dex (in units of 12+{log}({{O/H}})) lower metallicities than at z ˜ 2, but comparable to z˜ 3.5. We find galaxies with weak or no Lyα emission to have metallicities comparable to z ˜ 2 galaxies and therefore may represent an evolved subpopulation of z˜ 5 galaxies. We find a correlation between metallicity and dust in good agreement with local galaxies and an inverse trend between metallicity and star-formation rate consistent with observations at z ˜ 2. The relation between stellar mass and metallicity (MZ relation) is similar to z˜ 3.5, but there are indications of it being slightly shallower, in particular for the young, Lyα-emitting galaxies. We show that, within a “bathtub” approach, a shallower MZ relation is expected in the case of a fast (exponential) build-up of stellar mass with an e-folding time of 100-200 Myr. Because of this fast evolution, the process of dust production and metal enrichment as a function of mass could be more stochastic in the first billion years of galaxy formation compared to later times.

  14. Star Formation at Low Metallicity in Local Dwarf Irregular Galaxies

    NASA Astrophysics Data System (ADS)

    Elmegreen, Bruce; Hunter, Deidre Ann; Rubio, Monica; Brinks, Elias; Cortés, Juan R.; Cigan, Phil

    2016-01-01

    The radial profiles of star formation rates and surface mass densities for gas and stars have been compiled for 20 local dwarf irregular galaxies and converted into disk scale heights and Toomre Q values. The scale heights are relatively large compared to the galaxy sizes (~0.6 times the local radii) and generally increase with radius in a flare. The gaseous Q values are high, ~4, at most radii and even higher for the stars. Star formation proceeds even with these high Q values in a normal exponential disk as viewed in the far ultraviolet. Such normal star formation suggests that Q is not relevant to star formation in dIrrs. The star formation rate per unit area always equals approximately the gas surface density divided by the midplane free fall time with an efficiency factor of about 1% that decreases systematically with radius in approximate proportion to the gas surface density. We view this efficiency variation as a result of a changing molecular fraction in a disk where atomic gas dominates both stars and molecules. In a related study, CO observations with ALMA of star-forming regions at the low metallicities of these dwarfs, which averages 13% solar, shows, in the case of the WLM galaxy, tiny CO clouds inside much larger molecular and atomic hydrogen envelopes. The CO cloud mass fraction within the molecular region is only one percent or so. Nevertheless, the CO clouds have properties that are similar to solar neighborhood clouds: they satisfy the size-linewidth relation observed in the LMC, SMC, and other local dwarfs where CO has been observed, and the same virial mass versus luminosity relation. This uniforming of CO cloud properties seems to be the result of a confining pressure from the weight of the overlying molecular and atomic shielding layers. Star formation at low metallicity therefore appears to be a three dimensional process independent of 2D instabilities involving Q, in highly atomic gas with relatively small CO cores, activated at a rate

  15. Hot, Massive Stars in the Extremely Metal-Poor Galaxy, I Zw 18

    NASA Technical Reports Server (NTRS)

    Heap, Sara R.; Malumuth, Eliot M.

    2010-01-01

    The extremely metal-poor galaxy I Zw 18, is the Rosetta Stone for understanding z=7-8 galaxies now being discovered by Hubb|e's Wide Field Camera 3 (HST/WFC3). Using HST/STIS images and recently obtained HST/COS ultraviolet spectra, we derive information about the hot, massive stars in this galaxy including stellar abundances, constraints on the stellar IMF and mass distribution of young clusters containing hot, massive stars.

  16. A Semi-Analytic Study of Feedback Processes and Metallicity Profiles in Disc Galaxies

    NASA Astrophysics Data System (ADS)

    Sandford, Nathan Ross; Lu, Yu

    2016-01-01

    The metallicity gradients of disc galaxies contain valuable information about the physics governing their formation and evolution. The observed metallicity profiles have negative gradients that are steeper at high redshifts, indicating an inside-out formation of disc galaxies. We improve on our semi-analytic galaxy formation model (Lu, Mo & Wechsler 2015) by incorporating the radial distribution of metals into the model. With the improved model, we explore how feedback scenarios affect metallicity gradients. The model features 3 feedback scenarios: An Ejective (EJ) model, which includes ejective supernova (SN) feedback, a PRe-Heating (PR) model, which assumes that the intergalactic medium is preheated, preventing it from collapsing onto galaxies, and a Re-Incorporation (RI) model, which also includes strong outflows but allows ejected gas to re-accrete onto the galaxies. We compare the models with observations from Ho et al. (2015) and find that while all models struggle to match the observed metallicity gradient-stellar mass relationship, the PR model predicts metallicity gradients that best match observations. We also find that the RI model predicts a flat gradient because its outflow and re-accretion replenish the disc uniformly with newly accreted enriched gas, erasing the mark of inside-out formation. Our findings suggest feedback plays a key role in shaping the metallicity gradients of disc galaxies and require more detailed theoretical modeling to understand them.

  17. Spatially resolved dust emission of extremely metal-poor galaxies*

    NASA Astrophysics Data System (ADS)

    Zhou, Luwenjia; Shi, Yong; Diaz-Santos, Taino; Armus, Lee; Helou, George; Stierwalt, Sabrina; Li, Aigen

    2016-05-01

    We present infrared (IR) spectral energy distributions (SEDs) of individual star-forming regions in four extremely metal-poor (EMP) galaxies with metallicity Z ≲ Z⊙/10 as observed by the Herschel Space Observatory. With the good wavelength coverage of the SED, it is found that these EMP star-forming regions show distinct SED shapes as compared to those of grand design Spirals and higher metallicity dwarfs: they have on average much higher f70μm/f160 μm ratios at a given f160 μm/f250 μm ratio; single modified blackbody (MBB) fittings to the SED at λ ≥ 100 μm still reveal higher dust temperatures and lower emissivity indices compared to that of Spirals, while two MBB fittings to the full SED with a fixed emissivity index (β = 2) show that even at 100 μm, about half of the emission comes from warm (50 K) dust, in contrast to the cold (˜20 K) dust component. Our spatially resolved images furthermore reveal that the far-IR colours including f70 μm/f160 μm, f160 μm/f250 μm and f250 μm/f350 μm are all related to the surface densities of young stars as traced by far-UV, 24 μm and star formation rates (SFRs), but not to the stellar mass surface densities. This suggests that the dust emitting at wavelengths from 70 to 350 μm is primarily heated by radiation from young stars.

  18. Witnessing Gas Mixing in the Metal Distribution during a Galaxy Merger.

    NASA Astrophysics Data System (ADS)

    Amram, Philippe

    2015-08-01

    I will present direct evidence that in a merger of disk galaxies, the pre-existing central metallicities will mix as a result of gas being transported in the merger interface region along the line that joins the two coalescing nuclei. In focusing on the emission line gas, this is shown using detailed two-dimensional kinematics as well as metallicity measurements for the nearby ongoing merger in the center of the compact group HCG 31. The two coalescing cores display similar oxygen abundances, while in between the two nuclei, the metallicity changes smoothly from one nucleus to the other indicating a mix of metals in this region. This nearby system involves the merging of two fairly low-mass and clumpy galaxies (LMC-like galaxies), making it an important system for comparison with high-redshift galaxies.

  19. How does metallicity affect the gas and dust properties of galaxies?

    NASA Astrophysics Data System (ADS)

    Madden, Suzanne C.; Cormier, Diane; Rémy-Ruyer, Aurélie

    Comparison of the ISM properties of a wide range of metal poor galaxies with normal metal-rich galaxies reveals striking differences. We find that the combination of the low dust abundance and the active star formation results in a very porous ISM filled with hard photons, heating the dust in dwarf galaxies to overall higher temperatures than their metal-rich counterparts. This results in photodissociation of molecular clouds to greater depths, leaving relatively large PDR envelopes and difficult-to-detect CO cores. From detailed modeling of the low-metallicity ISM, we find significant fractions of CO-dark H2 - a reservoir of molecular gas not traced by CO, but present in the [CII] and [CI]-emitting envelopes. Self-consistent analyses of the neutral and ionized gas diagnostics along with the dust SED is the necessary way forward in uncovering the multiphase structure of galaxies.

  20. On the evolution of simulated galaxies: the mass dependence in metallicity gradients

    NASA Astrophysics Data System (ADS)

    Miranda, Maider; Sánchez-Blázquez, Patricia; Brook, Chris B.; Gibson, Brad K.

    2017-03-01

    Making use of a fiducial set of simulated disc galaxies spanning a wide range of mass, we examine the influence of stellar mass in the radial metallicity gradients and compare to observational trends from Ho et al. (2015).

  1. Galaxies

    SciTech Connect

    Not Available

    1981-01-01

    Normal galaxies, radio galaxies, and Seyfert galaxies are considered. The large magellanic cloud and the great galaxy in Andromedia are highlighted. Quasars and BL lacertae objects are also discussed and a review of the spectral observations of all of these galaxies and celestial objects is presented.

  2. Metallicity gradients in local Universe galaxies: Time evolution and effects of radial migration

    NASA Astrophysics Data System (ADS)

    Magrini, Laura; Coccato, Lodovico; Stanghellini, Letizia; Casasola, Viviana; Galli, Daniele

    2016-04-01

    Context. Our knowledge of the shape of radial metallicity gradients in disc galaxies has recently improved. Conversely, the understanding of their time evolution is more complex, since it requires analysis of stellar populations with different ages or systematic studies of galaxies at different redshifts. In the local Universe, H ii regions and planetary nebulae (PNe) are important tools to investigate radial metallicity gradients in disc galaxies. Aims: We present an in-depth study of all nearby spiral galaxies (M33, M31, NGC 300, and M81) with direct-method nebular abundances of both populations, aiming at studying the evolution of their radial metallicity gradients. For the first time, we also evaluate the radial migration of PN populations. Methods: For the selected galaxies, we analysed H ii region and PN properties to: determine whether oxygen in PNe is a reliable tracer for past interstellar medium (ISM) composition; homogenise published datasets; estimate the migration of the oldest stellar populations; and determine the overall chemical enrichment and slope evolution. Results: We confirm that oxygen in PNe is a reliable tracer for past ISM metallicity. We find that PN gradients are flatter than or equal to those of H ii regions. When radial motions are negligible, this result provides a direct measurement of the time evolution of the gradient. For galaxies with dominant radial motions, we provide upper limits on the gradient evolution. Finally, the total metal content increases with time in all target galaxies, and early morphological types have a larger increment Δ(O/H) than late-type galaxies. Conclusions: Our findings provide important constraints to discriminate among different galactic evolutionary scenarios, favouring cosmological models with enhanced feedback from supernovae. The advent of extremely large telescopes allows us to include galaxies in a wider range of morphologies and environments, thus putting firmer constraints on galaxy formation

  3. Velocity-metallicity correlation for high-z DLA galaxies: evidence of a mass-metallicity relation?

    NASA Astrophysics Data System (ADS)

    Ledoux, C.; Petitjean, P.; Fynbo, J. P. U.; Møller, P.; Srianand, R.

    2006-10-01

    We used our database of VLT-UVES quasar spectra to build up a sample of 70 Damped Lyman-α (DLA) or strong sub-DLA systems with total neutral hydrogen column densities of log N(H i)⪆ 20 and redshifts in the range 1.7metallicities relative to solar in an homogeneous manner, [X/H] (with X=Zn, or S or Si), and the velocity widths of low-ionization line profiles, Δ V. For the first time, we provide evidence for a correlation between DLA metallicity and line profile velocity width, which is detected at the 6.1σ significance level. This confirms the trend previously observed in a much smaller sample by Wolfe & Prochaska (1998). The best-fit linear relation is [X/H]=1.55(± 0.12)logΔ V -4.33(± 0.23), with Δ V expressed in km s-1. The slope of the DLA velocity-metallicity relation is the same within uncertainties between the higher (z_abs>2.43) and the lower (z_abs≤ 2.43) redshift halves of our sample. However, the two populations of systems are statistically different. There is a strong redshift evolution in the sense that the median metallicity and median velocity width increase with decreasing redshift. We argue that the existence of a DLA velocity-metallicity correlation, over more than a factor of 100 spread in metallicity, is probably the consequence of an underlying mass-metallicity relation for the galaxies responsible for DLA absorption lines. Assuming a simple linear scaling of the galaxy luminosity with the mass of the dark-matter halo, we find that the slope of the DLA velocity-metallicity relation is consistent with that of the luminosity-metallicity relation derived for local galaxies. If the galaxy dynamical mass is indeed the dominant factor setting up the observed DLA velocity-metallicity correlation, then the DLA systems exhibiting the lowest metallicities among the DLA population should, on average, be associated with galaxies of lower masses (e.g., gas-rich dwarf galaxies). In turn

  4. UV Absorption Lines as Metallicity Estimator and the Metal Content of Star-forming Galaxies at z=5

    NASA Astrophysics Data System (ADS)

    Faisst, Andreas; Capak, Peter L.; Davidson, Iary; Kakazu, Yuko; Salvato, Mara; Laigle, Clotilde; Onodera, Masato; Masters, Daniel; COSMOS Team

    2016-01-01

    Probing the metal content of high redshift galaxies is essential to study their formation and evolution in the early universe. However, the spectral features used to measure the metallicity are shifted out of the wavelength range of current spectrographs at high-z and therefore alternative methods must be used.We measure the relation between four prominent UV absorption complexes and metallicity for more than 50 local galaxies and, by using a sample of more than 20 galaxies at z ~ 2 - 3, verify that this relation holds up to z ˜ 3. We then apply this method to a sample of ˜ 220 galaxies at 3.5 < z < 6.0 in COSMOS, for which unique UV spectra from DEIMOS and accurate stellar mass estimates from SPLASH are available. The z ~ 5 galaxies at 9 < log(m/M⊙) < 11 are characterized by 0.3 - 0.4 dex (in units of 12 + log(O/H)) lower metallicities than galaxies at z ˜ 2 but comparable to z ˜ 3 - 3.5 galaxies. In the same stellar mass range, we do not find a significant relation between stellar mass and metallicity (MZ relation), suggesting that the MZ relation at z ~ 5 is very shallow or breaking down. Since we verify a correlation between dust obscuration (measured by β) and UV absorption strength (i.e., metallicity), we argue that the process of dust production and metal enrichment in the first billion years of galaxy formation is more stochastic than at later times. Using a "bathtub" model approach, we find that an exponential build up of stellar mass within a short time of several 100 Myr can explain a shallow MZ relation at z ˜ 5. Furthermore, we find a weak anti-correlation between star-formation rates and UV absorption strength (i.e., metallicity), indicative of these galaxies being fueled by the inflow of pristine (metal-poor) gas. The galaxy sample presented in this work is unique to further test these scenarios using ALMA and the upcoming James Webb Space Telescope.

  5. Linking dust emission to fundamental properties in galaxies: the low-metallicity picture

    NASA Astrophysics Data System (ADS)

    Rémy-Ruyer, A.; Madden, S. C.; Galliano, F.; Lebouteiller, V.; Baes, M.; Bendo, G. J.; Boselli, A.; Ciesla, L.; Cormier, D.; Cooray, A.; Cortese, L.; De Looze, I.; Doublier-Pritchard, V.; Galametz, M.; Jones, A. P.; Karczewski, O. Ł.; Lu, N.; Spinoglio, L.

    2015-10-01

    Aims: In this work, we aim to provide a consistent analysis of the dust properties from metal-poor to metal-rich environments by linking them to fundamental galactic parameters. Methods: We consider two samples of galaxies: the Dwarf Galaxy Survey (DGS) and the Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel (KINGFISH), totalling 109 galaxies, spanning almost 2 dex in metallicity. We collect infrared (IR) to submillimetre (submm) data for both samples and present the complete data set for the DGS sample. We model the observed spectral energy distributions (SED) with a physically-motivated dust model to access the dust properties: dust mass, total-IR luminosity, polycyclic aromatic hydrocarbon (PAH) mass fraction, dust temperature distribution, and dust-to-stellar mass ratio. Results: Using a different SED model (modified black body), different dust composition (amorphous carbon in lieu of graphite), or a different wavelength coverage at submm wavelengths results in differences in the dust mass estimate of a factor two to three, showing that this parameter is subject to non-negligible systematic modelling uncertainties. We find half as much dust with the amorphous carbon dust composition. For eight galaxies in our sample, we find a rather small excess at 500 μm (≤1.5σ). We find that the dust SED of low-metallicity galaxies is broader and peaks at shorter wavelengths compared to more metal-rich systems, a sign of a clumpier medium in dwarf galaxies. The PAH mass fraction and dust temperature distribution are found to be driven mostly by the specific star formation rate, sSFR, with secondary effects from metallicity. The correlations between metallicity and dust mass or total-IR luminosity are direct consequences of the stellar mass-metallicity relation. The dust-to-stellar mass ratios of metal-rich sources follow the well-studied trend of decreasing ratio for decreasing sSFR. The relation is more complex for low-metallicity galaxies with high

  6. LOCALIZED STARBURSTS IN DWARF GALAXIES PRODUCED BY THE IMPACT OF LOW-METALLICITY COSMIC GAS CLOUDS

    SciTech Connect

    Sánchez Almeida, J.; Muñoz-Tuñón, C.; Filho, M. E.; Elmegreen, B. G.; Elmegreen, D. M.; Pérez-Montero, E.; Vílchez, J. M.; Amorín, R.; Ascasibar, Y.; Papaderos, P.

    2015-09-10

    Models of galaxy formation predict that gas accretion from the cosmic web is a primary driver of star formation over cosmic history. Except in very dense environments where galaxy mergers are also important, model galaxies feed from cold streams of gas from the web that penetrate their dark matter halos. Although these predictions are unambiguous, the observational support has been indirect so far. Here, we report spectroscopic evidence for this process in extremely metal-poor galaxies (XMPs) of the local universe, taking the form of localized starbursts associated with gas having low metallicity. Detailed abundance analyses based on Gran Telescopio Canarias optical spectra of 10 XMPs show that the galaxy hosts have metallicities around 60% solar, on average, while the large star-forming regions that dominate their integrated light have low metallicities of some 6% solar. Because gas mixes azimuthally in a rotation timescale (a few hundred Myr), the observed metallicity inhomogeneities are only possible if the metal-poor gas fell onto the disk recently. We analyze several possibilities for the origin of the metal-poor gas, favoring the metal-poor gas infall predicted by numerical models. If this interpretation is correct, XMPs trace the cosmic web gas in their surroundings, making them probes to examine its properties.

  7. On the Dearth of Ultra-faint Extremely Metal-poor Galaxies

    NASA Astrophysics Data System (ADS)

    Sánchez Almeida, J.; Filho, M. E.; Dalla Vecchia, C.; Skillman, E. D.

    2017-02-01

    Local extremely metal-poor galaxies (XMPs) are of particular astrophysical interest since they allow us to look into physical processes characteristic of the early universe, from the assembly of galaxy disks to the formation of stars in conditions of low metallicity. Given the luminosity–metallicity relationship, all galaxies fainter than Mr ≃ ‑13 are expected to be XMPs. Therefore, XMPs should be common in galaxy surveys. However, they are not common, because several observational biases hamper their detection. This work compares the number of faint XMPs in the SDSS-DR7 spectroscopic survey with the expected number, given the known biases and the observed galaxy luminosity function (LF). The faint end of the LF is poorly constrained observationally, but it determines the expected number of XMPs. Surprisingly, the number of observed faint XMPs (∼10) is overpredicted by our calculation, unless the upturn in the faint end of the LF is not present in the model. The lack of an upturn can be naturally understood if most XMPs are central galaxies in their low-mass dark matter halos, which are highly depleted in baryons due to interaction with the cosmic ultraviolet background and to other physical processes. Our result also suggests that the upturn toward low luminosity of the observed galaxy LF is due to satellite galaxies.

  8. Hot, Massive Stars in the Extremely Metal-Poor Galaxy, I Zw 18

    NASA Technical Reports Server (NTRS)

    Heap, Sara R.; Malumuth, Eliot M.

    2010-01-01

    The carbon-enhanced metal-poor galaxy, I Zw 18, is the Rosetta Stone for understanding galaxies in the early universe by providing constraints on the IMF of massive stars, the role of galaxies in reionization of the universe, mixing of newly synthesized material in the ISM, and gamma-ray bursts at low metallicity, and on the earliest generations of stars producing the observed abundance pattern. We describe these constraints as derived from analyses of HST/COS spectra of I Zw 18 including stellar atmosphere analysis and photo-ionization modeling of both the emission and absorption spectra of the nebular material and interstellar medium.

  9. Determining the Large-scale Environmental Dependence of Gas-phase Metallicity in Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Douglass, Kelly A.; Vogeley, Michael S.

    2017-01-01

    We study how the cosmic environment affects galaxy evolution in the universe by comparing the metallicities of dwarf galaxies in voids with dwarf galaxies in more dense regions. Ratios of the fluxes of emission lines, particularly those of the forbidden [O iii] and [S ii] transitions, provide estimates of a region’s electron temperature and number density. From these two quantities and the emission line fluxes [O ii] λ3727, [O iii] λ4363, and [O iii] λλ4959, 5007, we estimate the abundance of oxygen with the direct Te method. We estimate the metallicity of 42 blue, star-forming void dwarf galaxies and 89 blue, star-forming dwarf galaxies in more dense regions using spectroscopic observations from the Sloan Digital Sky Survey Data Release 7, as reprocessed in the MPA-JHU value-added catalog. We find very little difference between the two sets of galaxies, indicating little influence from the large-scale environment on their chemical evolution. Of particular interest are a number of extremely metal-poor dwarf galaxies that are less prevalent in voids than in the denser regions.

  10. THE ACS NEARBY GALAXY SURVEY TREASURY. IX. CONSTRAINING ASYMPTOTIC GIANT BRANCH EVOLUTION WITH OLD METAL-POOR GALAXIES

    SciTech Connect

    Girardi, Leo; Williams, Benjamin F.; Gilbert, Karoline M.; Rosenfield, Philip; Dalcanton, Julianne J.; Marigo, Paola; Boyer, Martha L.; Dolphin, Andrew; Weisz, Daniel R.; Skillman, Evan; Melbourne, Jason; Olsen, Knut A. G.; Seth, Anil C.

    2010-12-01

    In an attempt to constrain evolutionary models of the asymptotic giant branch (AGB) phase at the limit of low masses and low metallicities, we have examined the luminosity functions and number ratios between AGB and red giant branch (RGB) stars from a sample of resolved galaxies from the ACS Nearby Galaxy Survey Treasury. This database provides Hubble Space Telescope optical photometry together with maps of completeness, photometric errors, and star formation histories for dozens of galaxies within 4 Mpc. We select 12 galaxies characterized by predominantly metal-poor populations as indicated by a very steep and blue RGB, and which do not present any indication of recent star formation in their color-magnitude diagrams. Thousands of AGB stars brighter than the tip of the RGB (TRGB) are present in the sample (between 60 and 400 per galaxy), hence, the Poisson noise has little impact in our measurements of the AGB/RGB ratio. We model the photometric data with a few sets of thermally pulsing AGB (TP-AGB) evolutionary models with different prescriptions for the mass loss. This technique allows us to set stringent constraints on the TP-AGB models of low-mass, metal-poor stars (with M < 1.5 M{sub sun}, [Fe/H]{approx}< -1.0). Indeed, those which satisfactorily reproduce the observed AGB/RGB ratios have TP-AGB lifetimes between 1.2 and 1.8 Myr, and finish their nuclear burning lives with masses between 0.51 and 0.55 M{sub sun}. This is also in good agreement with recent observations of white dwarf masses in the M4 old globular cluster. These constraints can be added to those already derived from Magellanic Cloud star clusters as important mileposts in the arduous process of calibrating AGB evolutionary models.

  11. Exploring the Role of Galaxy Morphology in the Mass-Metallicity-Star Formation Rate Relation

    NASA Astrophysics Data System (ADS)

    Pahl, Anthony; Rafelski, Marc; Scarlata, Claudia; Pacifici, Camilla; Henry, Alaina L.; Gardner, Jonathan P.; Elmegreen, Debra M.

    2017-01-01

    The Mass-Metallicity-Star Formation Rate (M-Z-SFR) fundamental relation reveals the underlying physics behind galaxy evolution: the mechanics of gas inflow, outflow, and the formation of stars are intimately connected. At higher redshift, we observe galaxies which are believed to be more actively accreting from the cosmic web, and as a result bright star-forming clumps are expected to form due to the increased gravitational instability of the galactic medium. We investigate these “clumpy” galaxies in context of their location on the M-Z-SFR plane to search for evidence of metal-poor gas inflows as predicted by theoretical models, and to help us understand how galaxies form and change at a higher redshift (1.3 < z < 2.2). We use the CANDELS survey to examine the morphological structure of star forming regions utilizing the high resolution of space-based HST imaging. We create stamps in their rest-frame UV light to investigate recent star formation and visually classify the morphology of the galaxies. We also utilize stellar population fits of the photometric data to determine properties such as mass and star formation rate. From the grism data of the 3D-HST survey, we select 1861 galaxies based on the strong detection of the [OIII_5007] line, and determine metallicity through the line-diagnostic R_23 using [OIII_5007], [OII_3727] and H_beta. We improve these results through the stacking of spectra to remove a sample bias of requiring strong detections on weak emission lines. Using mass, star formation rate, and metallicity we compare the location of clumpy galaxies on the fundamental plane to investigate possible diminished metallicity and heightened star formation rate compared to the remainder of the sample. This will enable us to better understand the theoretical underpinnings of gas accretion and galaxy evolution at high redshift.

  12. Galaxy evolution in cosmological simulations with outflows - II. Metallicities and gas fractions

    NASA Astrophysics Data System (ADS)

    Davé, Romeel; Finlator, Kristian; Oppenheimer, Benjamin D.

    2011-09-01

    We use cosmological hydrodynamic simulations to investigate how inflows, star formation and outflows govern the gaseous and metal content of galaxies within a hierarchical structure formation context. In our simulations, galaxy metallicities are established by a balance between inflows and outflows as governed by the mass outflow rate, implying that the mass-metallicity relation reflects how the outflow rate varies with stellar mass. Gas content, meanwhile, is set by a competition between inflow into and gas consumption within the interstellar medium, the latter being governed by the star formation law, while the former is impacted by both wind recycling and preventive feedback. Stochastic variations in the inflow rate move galaxies off the equilibrium mass-metallicity and mass-gas fraction relations in a manner correlated with the star formation rate, and the scatter is set by the time-scale to re-equilibrate. The evolution of both relations from z= 3 → 0 is slow, as individual galaxies tend to evolve mostly along the relations. Gas fractions at a given stellar mass slowly decrease with time because the cosmic inflow rate diminishes faster than the consumption rate, while metallicities slowly increase as infalling gas becomes more enriched. Observations from z˜ 3 → 0 are better matched by simulations employing momentum-driven wind scalings rather than constant wind speeds, but all models predict too low gas fractions at low masses and too high metallicities at high masses. All our models reproduce observed second-parameter trends of the mass-metallicity relation with the star formation rate and environment, indicating that these are a consequence of equilibrium and not feedback. Overall, the analytical framework of our equilibrium scenario broadly captures the relevant physics establishing the galaxy gas and metal content in simulations, which suggests that the cycle of baryonic inflows and outflows centrally governs the cosmic evolution of these properties

  13. Constraining Metallicity and Age for Massive Quiescent Galaxies in a Redshift Range of 1

    NASA Astrophysics Data System (ADS)

    Estrada-Carpenter, Vicente; Papovich, Casey J.; Momcheva, Ivelina G.; Brammer, Gabriel; Bridge, Joanna; Dickinson, Mark; Closson Ferguson, Henry; finlator, kristian; Finkelstein, Steven L.; Giavalisco, Mauro; Gosmeyer, Catherine; Livermore, Rachael C.; Long, James; Lotz, Jennifer M.; Kawinwanichakij, Lalitwadee; Pirzkal, Norbert; Quadri, Ryan; Salmon, Brett W.; Tilvi, Vithal; Trump, Jonathan R.; Weiner, Benjamin J.

    2017-01-01

    Using HST/WFC3 grism spectroscopy from the CANDELS Lyman-alpha Emission at Reionization (CLEAR) survey, we constrain the metallicities and ages of massive quiescent galaxies, at z ~ 1.5. CLEAR provides deep spectroscopy (12 HST orbits per pointing) with the WFC3/G102 grism over the wavelength range ~ 7,500 < λ < 12,000 Å, at a spectral resolution of R ~ 200, within the GOODS-N and GOODS-S Deep regions of CANDELS. These data cover important age and metallicity sensitive spectral features for galaxies at 1 < z < 2, including the redshifted Ca HK lines, 4000 Å break, Balmer-series lines, and Hg+G features. We stack the G102 spectra of a stellar-mass limited sample of 34 quiescent galaxies, with log(M*/M⊙) > 10 and 1 < z < 2, and fit the spectra using two sets of stellar population synthesis models, BC03 (Bruzual & Charlot 2003) and FSPS (Flexible Stellar Population Synthesis, Conroy & Gunn 2010). From these fits, we construct probability distribution functions of age and metallicity for these galaxies, separated into two mass bins, 10 < log(M*/M⊙) < 10.9 and log(M*/M⊙) > 10.9. The model fits favor higher metallicity for the more massive quiescent galaxies, with Z/Z⊙ ~ 1, with some systematics possibly leading from differences in the stellar population models. Therefore, there is no evidence for significant evolution in metallicity for the most massive quiescent galaxies since z ~ 1.5. The model fits to the lower mass quiescent galaxies favor lower metallicites, Z/Z⊙ ~ 0.4, with an offset of ~ 0.3 dex from the present-day relation (e.g., Galazzi et al. 2005). For quiescent galaxies in this mass range, 10.0 < log(M*/M⊙) < 10.9, this requires evolution in metallicity, either as a result of continued chemical enrichment of current galaxies, or the formation of additional quiescent galaxies (presumably quenching of star-forming galaxies at z > 1), or a combination of the two.

  14. Inside-Out or Outside-In? Metallicity Gradients in Low Surface Brightness Galaxies in the MUSCEL Program

    NASA Astrophysics Data System (ADS)

    Young, Jason; Kuzio de Naray, Rachel; Xuesong Wang, Sharon

    2016-01-01

    We present the metallicity profiles of three low surface brightness (LSB) galaxies as clues to the formation of these galaxies. This easily overlooked class of galaxy comprises up to half of the galaxy population with masses spanning that of the Milky Way, making them cosmologically significant baryon repositories. LSB galaxies are also very different from the more familiar archetypal galaxies in that they have unusually high gas fractions, up to 95%. Yet, they do not represent a distinct class of galaxy, but are simply on the low surface brightness end of a continuum.We have observed a sample of low surface brightness galaxies with the VIRUS-P integral field spectrograph as part of the MUSCEL program (MUltiwavelength observations of the Structure, Chemistry, and Evolution of LSB galaxies). Our program aims to fully characterize the formation histories of these galaxies by using these data in tandem with Spitzer, Galex, and Swift observations.Optical emission lines contained within the VIRUS-P spectra have allowed us to determined the metallicities of HII regions within these galaxies via emission-line ratio diagnostics. Because ISM metallicities are directly linked to the competing effects of star formation and gas accretion, the distribution of metals is a significant clue to the formation of these galaxies.

  15. Chemical abundances in Virgo cluster spirals - what drives the environmental dependence of galaxy metallicity?

    NASA Astrophysics Data System (ADS)

    Ellison, Sara; Skillman, Evan; Chung, Aeree

    2009-08-01

    The Virgo cluster is not only our nearest massive cluster, but its dynamical infancy also renders it an ideal laboratory for studies of cluster formation and galaxy evolution. Given the intense interest in Virgo, it is astounding that only 9 out of over 100 spirals in its firmament have chemical abundance measurements. We propose to simultaneously address this gap in our fundamental knowledge of Virgo cluster spirals and investigate how the metallicity and abundance gradients of star forming galaxies are sensitive to environment. Our sample consists of 13 Virgo cluster spiral galaxies, preferentially gas-poor early types, which complement the existing metallicity measurements. We also sample a range of clustercentric distances (0.3 -- 3 Mpc from M87), local densities and include several galaxies which exhibit evidence for interactions with the intra-cluster medium.

  16. MUFASA: Galaxy star formation, gas, and metal properties across cosmic time

    NASA Astrophysics Data System (ADS)

    Davé, Romeel; Rafieferantsoa, Mika H.; Thompson, Robert J.; Hopkins, Philip F.

    2017-01-01

    We examine galaxy star formation rates (SFRs), metallicities, and gas contents predicted by the MUFASA cosmological hydrodynamic simulations, which employ meshless hydrodynamics and novel feedback prescriptions that yield a good match to observed galaxy stellar mass assembly. We combine 50, 25, and 12.5h-1Mpc boxes with a quarter billion particles each to show that MUFASA broadly reproduces a wide range of relevant observations, including SFR and specific SFR functions, the mass-metallicity relation, H I and H2 fractions, H I (21 cm) and CO luminosity functions, and cosmic gas density evolution. There are mild but significant discrepancies, such as perhaps too many high-SFR galaxies, overly metal-rich and H I-poor galaxies at M_* ≳ 2× 10^{10} M_⊙, and sSFRs that are too low at z ˜ 1 - 2. The H I mass function increases by × 2 out to z ˜ 1 then steepens to higher redshifts, while the CO luminosity function computed using the Narayanan et al. conversion factor shows a rapid increase of CO-bright galaxies out to z ˜ 2 in accord with data. ΩHI and ΩH2 both scale roughly as ∝(1 + z)0.7 out to z ˜ 3, comparable to the rise in H I and H2 fractions. MUFASA galaxies with high SFR at a given M★ have lower metallicities and higher H I and H2 fractions, following observed trends; we make quantitative predictions for how fluctuations in the baryon cycle drive correlated scatter around galaxy scaling relations. Most of these trends are well converged with numerical resolution. These successes highlight MUFASA as a viable platform to study many facets of cosmological galaxy evolution.

  17. Dense cloud cores revealed by CO in the low metallicity dwarf galaxy WLM.

    PubMed

    Rubio, Monica; Elmegreen, Bruce G; Hunter, Deidre A; Brinks, Elias; Cortés, Juan R; Cigan, Phil

    2015-09-10

    Understanding stellar birth requires observations of the clouds in which they form. These clouds are dense and self-gravitating, and in all existing observations they are molecular, with H2 the dominant species and carbon monoxide (CO) the best available tracer. When the abundances of carbon and oxygen are low compared with that of hydrogen, and the opacity from dust is also low, as in primeval galaxies and local dwarf irregular galaxies, CO forms slowly and is easily destroyed, so it is difficult for it to accumulate inside dense clouds. Here we report interferometric observations of CO clouds in the local group dwarf irregular galaxy Wolf-Lundmark-Melotte (WLM), which has a metallicity that is 13 per cent of the solar value and 50 per cent lower than the previous CO detection threshold. The clouds are tiny compared to the surrounding atomic and H2 envelopes, but they have typical densities and column densities for CO clouds in the Milky Way. The normal CO density explains why star clusters forming in dwarf irregulars have similar densities to star clusters in giant spiral galaxies. The low cloud masses suggest that these clusters will also be low mass, unless some galaxy-scale compression occurs, such as an impact from a cosmic cloud or other galaxy. If the massive metal-poor globular clusters in the halo of the Milky Way formed in dwarf galaxies, as is commonly believed, then they were probably triggered by such an impact.

  18. Quantitative spectroscopy of blue supergiants in metal-poor dwarf galaxy NGC 3109

    SciTech Connect

    Hosek, Matthew W. Jr.; Kudritzki, Rolf-Peter; Bresolin, Fabio; Urbaneja, Miguel A.; Przybilla, Norbert; Evans, Christopher J.; Pietrzyński, Grzegorz; Gieren, Wolfgang; Carraro, Giovanni E-mail: kud@ifa.hawaii.edu E-mail: Miguel.Urbaneja-Perez@uibk.ac.at E-mail: chris.evans@stfc.ac.uk E-mail: wgieren@astro-udec.cl

    2014-04-20

    We present a quantitative analysis of the low-resolution (∼4.5 Å) spectra of 12 late-B and early-A blue supergiants (BSGs) in the metal-poor dwarf galaxy NGC 3109. A modified method of analysis is presented which does not require use of the Balmer jump as an independent T {sub eff} indicator, as used in previous studies. We determine stellar effective temperatures, gravities, metallicities, reddening, and luminosities, and combine our sample with the early-B-type BSGs analyzed by Evans et al. to derive the distance to NGC 3109 using the flux-weighted gravity-luminosity relation (FGLR). Using primarily Fe-group elements, we find an average metallicity of [ Z-bar ] = –0.67 ± 0.13, and no evidence of a metallicity gradient in the galaxy. Our metallicities are higher than those found by Evans et al. based on the oxygen abundances of early-B supergiants ([ Z-bar ] = –0.93 ± 0.07), suggesting a low α/Fe ratio for the galaxy. We adjust the position of NGC 3109 on the BSG-determined galaxy mass-metallicity relation accordingly and compare it to metallicity studies of H II regions in star-forming galaxies. We derive an FGLR distance modulus of 25.55 ± 0.09 (1.27 Mpc) that compares well with Cepheid and tip of the red giant branch distances. The FGLR itself is consistent with those found in other galaxies, demonstrating the reliability of this method as a measure of extragalactic distances.

  19. Leo P: A very low-mass, extremely metal-poor, star-forming galaxy

    NASA Astrophysics Data System (ADS)

    McQuinn, Kristen B.; Leo P Team

    2017-01-01

    Leo P is a low-luminosity dwarf galaxy just outside the Local Group with properties that make it an ideal probe of galaxy evolution at the faint-end of the luminosity function. Using combined data from 2 Hubble Space Telescope (HST) observing campaigns, the Very Large Array, the Spitzer Space telescope, as well as ground based data, we have constructed a robust evolutionary picture of Leo P. Leo P is one the most metal-poor, gas-rich galaxies ever discovered, has a stellar mass of a 5x105 Msun, comparable gas mass, and a single HII region. The star formation history reconstructed from the resolved stellar populations in Leo P shows it is unquenched, despite its very low mass. Based on the star formation history and metallicity measurements, the galaxy has lost 95% of its oxygen produced via nucleosynthesis, presumably to outflows. The neutral gas in the galaxy shows signs of rotation, although the velocity dispersion is comparable to the rotation velocity. Thus, Leo P bridges the gap between more massive dwarf irregular and less massive dwarf spheroidals on the baryonic Tully-Fisher relation. Furthermore, the galaxy hosts several, extremely dusty AGB candidates which will be probed with new HST and Spitzer observations. If confirmed as AGB stars, these may be our best local proxies for studying chemically unevolved star formation and subsequent dust production in metallicity environments comparable to the early universe.

  20. Metallicity gradients and newly created star-forming systems in interacting galaxies

    NASA Astrophysics Data System (ADS)

    Mendes de Oliveira, Claudia L.

    2015-08-01

    Interactions play an extremely important role in the evolution of galaxies, changing their morphologies and kinematics. Galaxy collisions may result in the formation of intergalactic star-forming objects, such as HII regions, young clusters and/or tidal dwarf galaxies. Several studies have found a wealth of newly created objects in interacting systems. We will exemplify the problems and challenges in this field and will describe observations of the interacting group NGC 6845, which contains four bright galaxies, two of which have extended tidal tails. We obtained Gemini/GMOS spectra for 28 of the regions located in the galaxies and in the tails. All regions in the latter are star-forming objects according to their line ratios, with ages younger than 10 Myr. A super luminous star forming complex is found in the brightest member of the group, NGC 6845A. Its luminosity reveals a star formation density of 0.19 solar masses, per year, per kpc^2, suggesting that this object is a localized starburst. We derived the gas-phase metallicity gradients across NGC 6845A and its two tails and we find that these are shallower than those for isolated galaxies. We speculate that the observed metallicity gradient may be related to one or more of the following mechanisms: (1) interaction induced inflow of fresh gas to the galaxy center, as seen in simulations, which is expected to dilute the metallicity of the central burst, (2) the formation of young metal-rich star forming regions in the tidal tails, which were born out of enriched gas expelled from the central regions of the system during the interaction and (3) the incremental growth of metals accumulated over time, due to the successful generations of star forming regions along the tails. Finally we will describe our plans to do a search for such objects on Halpha images that will soon be available for 17.5k degrees of the sky, with the A-PLUS survey.

  1. Metal-line absorption at Zabs approximately Zem from associated galaxies

    NASA Astrophysics Data System (ADS)

    Ellingson, E.; Yee, H. K. C.; Bechtold, Jill; Dobrzycki, Adam

    1994-04-01

    For a preliminary study of whether C IV absorption at Zabs approximately Zem is related to associated galaxy companions, we have collected data from a sample of 10 quasars with 0.15 less than z less than 0.65 for which high-resolution optical and UV spectroscopy is available from the literature, and for which we have deep optical images and limited spectroscopy. We also present new optical spectra for two of our samples. Four of these quasars have associated C IV absorption systems. In thes four fields, there are eight galaxies with Mr less than -19.0 mag within 35 kpc of the quasar (projected distance, assuming they are at the quasar redshift), which may be candidates for the associated C IV absorption. This observed density of galaxies near quasars with associated C IV absorption is significantly greater than that for a control sample of quasars chosen from the literature. This result suggests that galaxies near the quasar line of sight may be linked with associated C IV absorption. None of these quasars show associated Mg II absorption, despite the presence of galaxies very near the line of sight, suggesting a Mg II 'proximity effect,' where ionizing flux from the quasar destroys the Mg(+) from at least the outer parts of the galaxies. Three quasars are located in rich galaxy clusters, but none of these quasars are found to have associated C IV absorption. This suggests that galaxies in rich clusters associated with quasars are less likely to be metal-line absorbers. It is plausible that the extended galaxy halos which may be responsible for the absorptions are stripped from galaxies in these dense environments. While it seems that at Z approximately 0.6 rich clusters do not cause them, associated C IV absorption systems at higher redshift may be explained by associated clusters if there has been evolution in the properties of galaxy halos in dense environments.

  2. Low-Metallicity Star Formation: From the First Stars to Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Hunt, Leslie K.; Madden, Suzanne C.; Schneider, Raffaella

    2008-12-01

    Preface; SOC and LOC; Participants; Life at the conference; Conference photo; Session I. Population III and Metal-Free Star Formation: 1. Open questions in the study of population III star formation S. C. O. Glover, P. C. Clark, T. H. Greif, J. L. Johnson, V. Bromm, R. S. Klessen and A. Stacy; 2. Protostar formation in the early universe Naoki Yoshida; 3. Population III.1 stars: formation, feedback and evolution of the IMF Jonathan C. Tan; 4. The formation of the first galaxies and the transition to low-mass star formation T. H. Greif, D. R. G. Schleicher, J. L. Johnson, A.-K. Jappsen, R. S. Klessen, P. C. Clark, S. C. O. Glover, A. Stacy and V. Bromm; 5. Low-metallicity star formation: the characteristic mass and upper mass limit Kazuyuki Omukai; 6. Dark stars: dark matter in the first stars leads to a new phase of stellar evolution Katherine Freese, Douglas Spolyar, Anthony Aguirre, Peter Bodenheimer, Paolo Gondolo, J. A. Sellwood and Naoki Yoshida; 7. Effects of dark matter annihilation on the first stars F. Iocco, A. Bressan, E. Ripamonti, R. Schneider, A. Ferrara and P. Marigo; 8. Searching for Pop III stars and galaxies at high redshift Daniel Schaerer; 9. The search for population III stars Sperello di Serego Alighieri, Jaron Kurk, Benedetta Ciardi, Andrea Cimatti, Emanuele Daddi and Andrea Ferrara; 10. Observational search for population III stars in high-redshift galaxies Tohru Nagao; Session II. Metal Enrichment, Chemical Evolution, and Feedback: 11. Cosmic metal enrichment Andrea Ferrara; 12. Insights into the origin of the galaxy mass-metallicity relation Henry Lee, Eric F. Bell and Rachel S. Somerville; 13. LSD and AMAZE: the mass-metallicity relation at z > 3 F. Mannucci and R. Maiolino; 14. Three modes of metal-enriched star formation at high redshift Britton D. Smith, Matthew J. Turk, Steinn Sigurdsson, Brian W. O'Shea and Michael L. Norman; 15. Primordial supernovae and the assembly of the first galaxies Daniel Whalen, Bob Van Veelen, Brian W. O

  3. AN INFRARED CENSUS OF DUST IN NEARBY GALAXIES WITH SPITZER (DUSTiNGS). II. DISCOVERY OF METAL-POOR DUSTY AGB STARS

    SciTech Connect

    Boyer, Martha L.; Sonneborn, George; McQuinn, Kristen B. W.; Gehrz, Robert D.; Skillman, Evan; Barmby, Pauline; Bonanos, Alceste Z.; Gordon, Karl D.; Meixner, Margaret; Groenewegen, M. A. T.; Lagadec, Eric; Lennon, Daniel; Marengo, Massimo; McDonald, Iain; Zijlstra, Albert; Sloan, G. C.; Van Loon, Jacco Th.

    2015-02-10

    The DUSTiNGS survey (DUST in Nearby Galaxies with Spitzer) is a 3.6 and 4.5 μm imaging survey of 50 nearby dwarf galaxies designed to identify dust-producing asymptotic giant branch (AGB) stars and massive stars. Using two epochs, spaced approximately six months apart, we identify a total of 526 dusty variable AGB stars (sometimes called ''extreme'' or x-AGB stars; [3.6]-[4.5] > 0.1 mag). Of these, 111 are in galaxies with [Fe/H] < –1.5 and 12 are in galaxies with [Fe/H] < –2.0, making them the most metal-poor dust-producing AGB stars known. We compare these identifications to those in the literature and find that most are newly discovered large-amplitude variables, with the exception of ≈30 stars in NGC 185 and NGC 147, 1 star in IC 1613, and 1 star in Phoenix. The chemical abundances of the x-AGB variables are unknown, but the low metallicities suggest that they are more likely to be carbon-rich than oxygen-rich and comparisons with existing optical and near-IR photometry confirm that 70 of the x-AGB variables are confirmed or likely carbon stars. We see an increase in the pulsation amplitude with increased dust production, supporting previous studies suggesting that dust production and pulsation are linked. We find no strong evidence linking dust production with metallicity, indicating that dust can form in very metal-poor environments.

  4. Ultraviolet to near-infrared spectral distributions of star-forming galaxies: Metallicity and age effects

    NASA Technical Reports Server (NTRS)

    Storchi-Bergmann, Thaisa; Calzetti, Daniela; Kinney, Anne L.

    1994-01-01

    Spectral distributions from the UV to the near-IR of a sample of 44 star-forming galaxies are used to calculate the metallicity (O/H), star-formation rate (SFR) and age of the starbursts. The oxygen abundance covers the range 8.3 less than O/H less than 9.4 and nitrogen (N) is found to be mostly a product of secondary nucleosynthesis for O/H greater than 8.4. Due to its secondary origin, N/O ratios up to approximately equals 4 times the solar value can be obtained for metal-rich starbursts. The SFR ranges 0.01 to 100 solar mass/year. The lower metallicity galaxies seem to be experiencing an instantaneous burst of star formation, with ages ranging from under 5 x 10(exp 6) to 10(exp 7) yr. The highest metallicity galaxies are most probably experiencing a continuous burst. Correlations between the calculated quantities and several spectral features are investigated. We found a highly significant correlation between the equivalent width W(C IV lambda 1550)-a stellar (absorption) feature- and the oxygen abundance of the emitting gas (O/H). Thus we show for the first time that the stellar metallicity is well correlated with the gas metallicity in star-bursting galaxies. The equivalent width W(Si IV lambda 1400) and the emission line ratio (N II) lambda lambda 6548.84/H(sub alpha) also correlate well with O/H, and all three features can be used as metallicity indicators for star-forming galaxies. The continuum color between lambda 1400 and lambda 3500 (C(14 - 35)) is shown to correlate with O/H, although it is better correlated with E(B - V). It was not possible to disentangle the metallicity from the reddening effect in C(14- 35). We estimate that the reddening affecting the UV continuum is about half the one derived from the Balmer decrement of the emitting gas. The SFR correlates well with the galaxy luminosity and there is no dependence of the continuum color on the SFR. The higher metallicities are only found in the more luminous galaxies, while low metallicities are

  5. Observationally Constrained Metal Signatures of Galaxy Evolution in the Stars and Gas of Cosmological Simulations

    NASA Astrophysics Data System (ADS)

    Corlies, Lauren N.

    The halos of galaxies - consisting of gas, stars, and satellite galaxies - are formed and shaped by the most fundamental processes: hierarchical merging and the flow of gas into and out of galaxies. While these processes are hard to disentangle, metals are tied to the gas that fuels star formation and entrained in the wind that the deaths of these stars generate. As such, they can act as important indicators of the star formation, the chemical enrichment, and the outflow histories of galaxies. Thus, this thesis aims to take advantage of such metal signatures in the stars and gas to place observational constraints on current theories of galaxy evolution as implemented in cosmological simulations. The first two chapters consider the metallicities of stars in the stellar halo of the Milky Way and its surviving satellite dwarf galaxies. Chapter 2 pairs an N-body simulation with a semi-analytic model for supernova-driven winds to examine the early environment of a Milky Way-like galaxy. At z = 10, progenitors of surviving z = 0 satellite galaxies are found to sit preferentially on the outskirts of progenitor halos of the eventual main halo. The consequence of these positions is that main halo progenitors are found to more effectively cross-pollute each other than satellite progenitors. Thus, inhomogeneous cross-pollution as a result of different high-z spatial locations of different progenitors can help to explain observed differences in abundance patterns measured today. Chapter 3 expands this work into the analysis of a cosmological, hydrodynamical simulation of dwarf galaxies in the early universe. We find that simple assumptions for modeling the extent of supernova-driven winds used in Chapter 2 agree well with the simulation whereas the presence of inhomogeneous mixing in the simulation has a large effect on the stellar metallicities. Furthermore, the star-forming halos show both bursty and continuous SFHs, two scenarios proposed by stellar metallicity data

  6. DUST EXTINCTION AND METALLICITIES OF STAR-FORMING Ly{alpha} EMITTING GALAXIES AT LOW REDSHIFT

    SciTech Connect

    Finkelstein, Steven L.; Papovich, Casey; Cohen, Seth H.; Malhotra, Sangeeta; Rhoads, James E.; Moustakas, John

    2011-06-01

    We present the results of an optical spectroscopic study of 12 GALEX-discovered star-forming Ly{alpha} emitting galaxies (LAEs) at z {approx} 0.3. We measure the emission-line fluxes from these galaxies by fitting their observed spectra to stellar population models in order to correct for underlying stellar absorption. We revisit earlier stellar population model fitting results, finding that excluding now-known active galactic nuclei lowers the typical stellar population age and stellar mass of this sample to {approx}300 Myr and {approx}4 x 10{sup 9} M{sub sun}, respectively. We calculate their dust extinction using the Balmer decrement, and find a typical visual attenuation of A{sub V} {approx} 0.3 mag, similar to that seen in some high-redshift LAEs. Comparing the ratios of Ly{alpha}/H{alpha} and the Ly{alpha} equivalent widths to the measured dust extinction, we find that the interstellar media (ISMs) in these objects appear to be neither enhancing nor seriously attenuating the Ly{alpha} equivalent widths, as would be the case in a quasi-clumpy ISM. Lastly, we perform a detailed analysis of the gas-phase metallicities of these galaxies, and we find that most galaxies in our sample have Z {approx}< 0.4 Z{sub sun}. We find that at a fixed stellar mass, these low-redshift LAE analogs are offset by {approx}0.3-0.6 dex lower metallicity from the general galaxy population at similar redshifts based on the local mass-metallicity relationship. This implies that galaxies with Ly{alpha} in emission may be systematically more metal-poor than star-forming galaxies at the same stellar mass and redshift, similar to preliminary results at z {approx} 2.

  7. THE WHIQII SURVEY: METALLICITIES AND SPECTROSCOPIC PROPERTIES OF LUMINOUS COMPACT BLUE GALAXIES

    SciTech Connect

    Tollerud, Erik J.; Barton, Elizabeth J.; Cooke, Jeff; Van Zee, Liese

    2010-01-10

    As part of the WIYN High Image Quality Indiana-Irvine (WHIQII) survey, we present 123 spectra of faint emission-line galaxies, selected to focus on intermediate redshift (0.4 approx< z approx< 0.8) galaxies with blue colors that appear physically compact on the sky. The sample includes 15 true Luminous Compact Blue Galaxies (LCBGs) and an additional 27 slightly less extreme emission-line systems. These galaxies represent a highly evolving class that may play an important role in the decline of star formation since z approx 1, but their exact nature and evolutionary pathways remain a mystery. Here, we use emission lines to determine metallicities and ionization parameters, constraining their intrinsic properties and state of star formation. Some LCBG metallicities are consistent with a 'bursting dwarf' scenario, while a substantial fraction of others are not, further confirming that LCBGs are a highly heterogeneous population but are broadly consistent with the intermediate redshift field. In agreement with previous studies, we observe overall evolution in the luminosity-metallicity relation at intermediate redshift. Our sample, and particularly the LCBGs, occupies a region in the empirical R{sub 23}-O{sub 32} plane that differs from luminous local galaxies and is more consistent with dwarf irregulars at the present epoch, suggesting that cosmic 'downsizing' is observable in even the most fundamental parameters that describe star formation. These properties for our sample are also generally consistent with lying between local galaxies and those at high redshift, as expected by this scenario. Surprisingly, our sample exhibits no detectable correlation between compactness and metallicity, strongly suggesting that at these epochs of rapid star formation, the morphology of compact star-forming galaxies is largely transient.

  8. On the Mass-Metallicity-Star Formation Rate Relation for Galaxies at z˜2

    NASA Astrophysics Data System (ADS)

    Salim, Samir; Lee, Janice C.; Davé, Romeel; Dickinson, Mark

    2015-07-01

    Recent studies have shown that the local mass-metallicity (M*-Z) relation depends on the specific star formation rate (sSFR). Whether such a dependence exists at higher redshifts, and whether the resulting M*-Z-SFR relation is redshift invariant, is debated. We re-examine these issues by applying the non-parametric techniques of Salim et al. to ˜130 z˜ 2.3 galaxies with N2 and O3 measurements from Keck Baryonic Structure Survey (KBSS). We find that the KBSS M*-Z relation depends on sSFR at intermediate masses where such dependence exists locally. KBSS and SDSS galaxies of the same mass and sSFR (“local analogs”) are similarly offset in the BPT diagram relative to the bulk of local star-forming galaxies, and thus we posit that metallicities can be compared self-consistently at different redshifts as long as the masses and sSFRs of the galaxies are similar. We find that the M*-Z-SFR relation of z˜ 2 galaxies is consistent with the local one at {log}{M}*\\lt 10, but is offset up to -0.25 dex at higher masses, so it is altogether not redshift invariant. This high-mass offset could arise from a bias that [O iii]-based, high-redshift spectroscopic surveys have against high-metallicity galaxies, but additional evidence disfavors this possibility. We identify three causes for the reported discrepancy between N2 and O3N2 metallicities at z˜ 2: (1) a smaller offset that is also present for SDSS galaxies, which we remove with new N2 calibration, (2) a genuine offset due to differing ISM condition, which is also present in local analogs, and (3) an additional offset due to unrecognized active galactic nucleus contamination.

  9. ALFALFA Discovery of the Most Metal-poor Gas-rich Galaxy Known: AGC 198691

    NASA Astrophysics Data System (ADS)

    Hirschauer, Alec S.; Salzer, John J.; Skillman, Evan D.; Berg, Danielle; McQuinn, Kristen B. W.; Cannon, John M.; Gordon, Alex J. R.; Haynes, Martha P.; Giovanelli, Riccardo; Adams, Elizabeth A. K.; Janowiecki, Steven; Rhode, Katherine L.; Pogge, Richard W.; Croxall, Kevin V.; Aver, Erik

    2016-05-01

    We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part of the Survey of H i in Extremely Low-Mass Dwarfs project, which is a multi-wavelength study of galaxies with H i masses in the range of 106-107.2 M ⊙, discovered by the Arecibo Legacy Fast ALFA (ALFALFA) survey. We have obtained spectra of the lone H ii region in AGC 198691 with the new high-throughput KPNO Ohio State Multi-Object Spectrograph on the Mayall 4 m, as well as with the Blue Channel spectrograph on the MMT 6.5 m telescope. These observations enable the measurement of the temperature-sensitive [O iii]λ4363 line and hence the determination of a “direct” oxygen abundance for AGC 198691. We find this system to be an extremely metal-deficient (XMD) system with an oxygen abundance of 12+log(O/H) = 7.02 ± 0.03, making AGC 198691 the lowest-abundance star-forming galaxy known in the local universe. Two of the five lowest-abundance galaxies known have been discovered by the ALFALFA blind H i survey; this high yield of XMD galaxies represents a paradigm shift in the search for extremely metal-poor galaxies.

  10. What shapes stellar metallicity gradients of massive galaxies at large radii?

    NASA Astrophysics Data System (ADS)

    Hirschmann, Michaela

    2017-03-01

    We investigate the differential impact of physical mechanisms, mergers and internal energetic phenomena, on the evolution of stellar metallicity gradients in massive, present-day galaxies employing sets of high-resolution, cosmological zoom simulations. We demonstrate that negative metallicity gradients at large radii (>2Reff) originate from the accretion of metal-poor stellar systems. At larger radii, galaxies become typically more dominated by stars accreted from satellite galaxies in major and minor mergers. However, only strong galactic, stellar-driven winds can sufficiently reduce the metallicity content of the accreted stars to realistically steepen the outer metallicity gradients in agreement with observations. In contrast, the gradients of the models without winds are inconsistent with observations. Moreover, we discuss the impact of additional AGN feedback. This analysis greatly highlights the importance of both energetic processes and merger events for stellar population properties of massive galaxies at large radii. Our results are expected to significantly contribute to the interpretation of current and up-coming IFU surveys (e.g. MaNGA, CALIFA).

  11. Prolate rotation and metallicity gradient in the transforming dwarf galaxy Phoenix

    NASA Astrophysics Data System (ADS)

    Kacharov, Nikolay; Battaglia, Giuseppina; Rejkuba, Marina; Cole, Andrew A.; Carrera, Ricardo; Fraternali, Filippo; Wilkinson, Mark I.; Gallart, Carme G.; Irwin, Mike; Tolstoy, Eline

    2017-04-01

    Transition type dwarf galaxies are thought to be systems undergoing the process of transformation from a star-forming into a passively evolving dwarf, which makes them particularly suitable to study evolutionary processes driving the existence of different dwarf morphological types. Here we present results from a spectroscopic survey of ∼200 individual red giant branch stars in the Phoenix dwarf, the closest transition type with a comparable luminosity to 'classical' dwarf galaxies. We measure a systemic heliocentric velocity Vhelio = -21.2 ± 1.0 km s-1. Our survey reveals the clear presence of prolate rotation that is aligned with the peculiar spatial distribution of the youngest stars in Phoenix. We speculate that both features might have arisen from the same event, possibly an accretion of a smaller system. The evolved stellar population of Phoenix is relatively metal-poor (<[Fe/H] > = -1.49 ± 0.04 dex) and shows a large metallicity spread (σ[Fe/H] = 0.51 ± 0.04 dex), with a pronounced metallicity gradient of -0.13 ± 0.01 dex arcmin-1 similar to luminous, passive dwarf galaxies. We also report a discovery of an extremely metal-poor star candidate in Phoenix and discuss the importance of correcting for spatial sampling when interpreting the chemical properties of galaxies with metallicity gradients. This study presents a major leap forward in our knowledge of the internal kinematics of the Phoenix transition type dwarf galaxy and the first wide area spectroscopic survey of its metallicity properties. A table containing the measured velocities, metallicities, and CaT equivalent widths of all spectroscopic targets is available online at the CDS.

  12. LEO P: HOW MANY METALS CAN A VERY LOW MASS, ISOLATED GALAXY RETAIN?

    SciTech Connect

    McQuinn, Kristen B. W.; Skillman, Evan D.; Dolphin, Andrew; Cannon, John M.; Salzer, John J.; Rhode, Katherine L.; Adams, Elizabeth A. K.; Berg, Danielle; Giovanelli, Riccardo; Haynes, Martha P.

    2015-12-20

    Leo P is a gas-rich dwarf galaxy with an extremely low gas-phase oxygen abundance (3% solar). The isolated nature of Leo P enables a quantitative measurement of metals lost solely due to star formation feedback. We present an inventory of the oxygen atoms in Leo P based on the gas-phase oxygen abundance measurement, the star formation history (SFH), and the chemical enrichment evolution derived from resolved stellar populations. The SFH also provides the total amount of oxygen produced. Overall, Leo P has retained 5% of its oxygen; 25% of the retained oxygen is in the stars while 75% is in the gas phase. This is considerably lower than the 20%–25% calculated for massive galaxies, supporting the trend for less efficient metal retention for lower-mass galaxies. The retention fraction is higher than that calculated for other alpha elements (Mg, Si, Ca) in dSph Milky Way satellites of similar stellar mass and metallicity. Accounting only for the oxygen retained in stars, our results are consistent with those derived for the alpha elements in dSph galaxies. Thus, under the assumption that the dSph galaxies lost the bulk of their gas mass through an environmental process such as tidal stripping, the estimates of retained metal fractions represent underestimates by roughly a factor of four. Because of its isolation, Leo P provides an important datum for the fraction of metals lost as a function of galaxy mass due to star formation.

  13. Leo P: How Many Metals Can a Very Low Mass, Isolated Galaxy Retain?

    NASA Astrophysics Data System (ADS)

    McQuinn, Kristen B. W.; Skillman, Evan D.; Dolphin, Andrew; Cannon, John M.; Salzer, John J.; Rhode, Katherine L.; Adams, Elizabeth A. K.; Berg, Danielle; Giovanelli, Riccardo; Haynes, Martha P.

    2015-12-01

    Leo P is a gas-rich dwarf galaxy with an extremely low gas-phase oxygen abundance (3% solar). The isolated nature of Leo P enables a quantitative measurement of metals lost solely due to star formation feedback. We present an inventory of the oxygen atoms in Leo P based on the gas-phase oxygen abundance measurement, the star formation history (SFH), and the chemical enrichment evolution derived from resolved stellar populations. The SFH also provides the total amount of oxygen produced. Overall, Leo P has retained 5% of its oxygen; 25% of the retained oxygen is in the stars while 75% is in the gas phase. This is considerably lower than the 20%-25% calculated for massive galaxies, supporting the trend for less efficient metal retention for lower-mass galaxies. The retention fraction is higher than that calculated for other alpha elements (Mg, Si, Ca) in dSph Milky Way satellites of similar stellar mass and metallicity. Accounting only for the oxygen retained in stars, our results are consistent with those derived for the alpha elements in dSph galaxies. Thus, under the assumption that the dSph galaxies lost the bulk of their gas mass through an environmental process such as tidal stripping, the estimates of retained metal fractions represent underestimates by roughly a factor of four. Because of its isolation, Leo P provides an important datum for the fraction of metals lost as a function of galaxy mass due to star formation. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  14. High Resolution Studies Of Lensed z ∼ 2 Galaxies: Kinematics And Metal Gradients

    NASA Astrophysics Data System (ADS)

    Leethochawalit, Nicha

    2016-09-01

    We use the OSIRIS integral field unit (IFU) spectograph to secure spatially-resolved strong emission lines of 15 gravitationally-lensed star-forming galaxies at redshift z ∼ 2. With the aid of gravitational lensing and Keck laser-assisted adaptive optics, the spatial resolution of these sub-luminous galaxies is at a few hundred parsecs. First, we demonstrate that high spatial resolution is crucial in diagnosing the kinematic properties and dynamical maturity of z ∼ 2 galaxies. We observe a significantly lower fraction of rotationally-supported systems than what has been claimed in lower spatial resolution surveys. Second, we find a much larger fraction of z ∼ 2 galaxies with weak metallicity gradients, contrary to the simple picture suggested by earlier studies that well-ordered rotation develops concurrently with established steep metal gradients in all but merging systems. Comparing our observations with the predictions of hydronamical simulations, strong feedback is likely to play a key role in flattening metal gradients in early star-forming galaxies.

  15. Linking dwarf galaxies to halo building blocks with the most metal-poor star in Sculptor.

    PubMed

    Frebel, Anna; Kirby, Evan N; Simon, Joshua D

    2010-03-04

    Current cosmological models indicate that the Milky Way's stellar halo was assembled from many smaller systems. On the basis of the apparent absence of the most metal-poor stars in present-day dwarf galaxies, recent studies claimed that the true Galactic building blocks must have been vastly different from the surviving dwarfs. The discovery of an extremely iron-poor star (S1020549) in the Sculptor dwarf galaxy based on a medium-resolution spectrum cast some doubt on this conclusion. Verification of the iron-deficiency, however, and measurements of additional elements, such as the alpha-element Mg, are necessary to demonstrate that the same type of stars produced the metals found in dwarf galaxies and the Galactic halo. Only then can dwarf galaxy stars be conclusively linked to early stellar halo assembly. Here we report high-resolution spectroscopic abundances for 11 elements in S1020549, confirming its iron abundance of less than 1/4,000th that of the Sun, and showing that the overall abundance pattern follows that seen in low-metallicity halo stars, including the alpha-elements. Such chemical similarity indicates that the systems destroyed to form the halo billions of years ago were not fundamentally different from the progenitors of present-day dwarfs, and suggests that the early chemical enrichment of all galaxies may be nearly identical.

  16. The stellar metallicity gradients in galaxy discs in a cosmological scenario

    NASA Astrophysics Data System (ADS)

    Tissera, Patricia B.; Machado, Rubens E. G.; Sanchez-Blazquez, Patricia; Pedrosa, Susana E.; Sánchez, Sebastián F.; Snaith, Owain; Vilchez, Jose

    2016-08-01

    Context. The stellar metallicity gradients of disc galaxies provide information on disc assembly, star formation processes, and chemical evolution. They also might store information on dynamical processes that could affect the distribution of chemical elements in the gas phase and the stellar components. Understanding their joint effects within a hierarchical clustering scenario is of paramount importance. Aims: We studied the stellar metallicity gradients of simulated discs in a cosmological simulation. We explored the dependence of the stellar metallicity gradients on stellar age and on the size and mass of the stellar discs. Methods: We used a catalogue of galaxies with disc components selected from a cosmological hydrodynamical simulation performed including a physically motivated supernova feedback and chemical evolution. Disc components were defined based on angular momentum and binding energy criteria. The metallicity profiles were estimated for stars with different ages. We confront our numerical findings with results from the Calar Alto Legacy Integral Field Area (CALIFA) Survey. Results: The simulated stellar discs are found to have metallicity profiles with slopes in global agreement with observations. Low stellar mass galaxies tend to have a larger variety of metallicity slopes. When normalized by the half-mass radius, the stellar metallicity gradients do not show any dependence and the dispersion increases significantly, regardless of the galaxy mass. Galaxies with stellar masses o f around 1010M⊙ show steeper negative metallicity gradients. The stellar metallicity gradients correlate with the half-mass radius. However, the correlation signal is not present when they are normalized by the half-mass radius. Stellar discs with positive age gradients are detected to have negative and positive metallicity gradients, depending on the relative importance of recent star formation activity in the central regions. Conclusions: Our results suggest that inside

  17. A CANDIDATE MASSIVE BLACK HOLE IN THE LOW-METALLICITY DWARF GALAXY PAIR MRK 709

    SciTech Connect

    Reines, Amy E.; Condon, James J.; Plotkin, Richard M.; Russell, Thomas D.; Mezcua, Mar; Sivakoff, Gregory R.; Johnson, Kelsey E.

    2014-06-01

    The incidence and properties of present-day dwarf galaxies hosting massive black holes (BHs) can provide important constraints on the origin of high-redshift BH seeds. Here we present high-resolution X-ray and radio observations of the low-metallicity, star-forming, dwarf-galaxy system Mrk 709 with the Chandra X-ray Observatory and the Karl G. Jansky Very Large Array. These data reveal spatially coincident hard X-ray and radio point sources with luminosities suggesting the presence of an accreting massive BH (M {sub BH} ∼ 10{sup 5-7} M {sub ☉}). Based on imaging from the Sloan Digital Sky Survey (SDSS), we find that Mrk 709 consists of a pair of compact dwarf galaxies that appear to be interacting with one another. The position of the candidate massive BH is consistent with the optical center of the southern galaxy (Mrk 709 S), while no evidence for an active BH is seen in the northern galaxy (Mrk 709 N). We derive stellar masses of M {sub *} ∼ 2.5 × 10{sup 9} M {sub ☉} and M {sub *} ∼ 1.1 × 10{sup 9} M {sub ☉} for Mrk 709 S and Mrk 709 N, respectively, and present an analysis of the SDSS spectrum of the BH host Mrk 709 S. At a metallicity of just ∼10% solar, Mrk 709 is among the most metal-poor galaxies with evidence for an active galactic nucleus. Moreover, this discovery adds to the growing body of evidence that massive BHs can form in dwarf galaxies and that deep, high-resolution X-ray and radio observations are ideally suited to reveal accreting massive BHs hidden at optical wavelengths.

  18. Galaxy assembly, stellar feedback and metal enrichment: the view from the GAEA model

    NASA Astrophysics Data System (ADS)

    Hirschmann, Michaela; De Lucia, Gabriella; Fontanot, Fabio

    2016-09-01

    One major problem of current theoretical models of galaxy formation is given by their inability to reproduce the apparently `anti-hierarchical' evolution of galaxy assembly: massive galaxies appear to be in place since z ˜ 3, while a significant increase of the number densities of low-mass galaxies is measured with decreasing redshift. In this work, we perform a systematic analysis of the influence of different stellar feedback schemes, carried out in the framework of GAEA, a new semi-analytic model of galaxy formation. It includes a self-consistent treatment for the timings of gas, metal and energy recycling, and for the chemical yields. We show this to be crucial to use observational measurements of the metallicity as independent and powerful constraints for the adopted feedback schemes. The observed trends can be reproduced in the framework of either a strong ejective or preventive feedback model. In the former case, the gas ejection rate must decrease significantly with cosmic time (as suggested by parametrizations of the cosmological `FIRE' simulations). Irrespective of the feedback scheme used, our successful models always imply that up to 60-70 per cent of the baryons reside in an `ejected' reservoir and are unavailable for cooling at high redshift. The same schemes predict physical properties of model galaxies (e.g. gas content, colour, age, and metallicity) that are in much better agreement with observational data than our fiducial model. The overall fraction of passive galaxies is found to be primarily determined by internal physical processes, with environment playing a secondary role.

  19. The Metallicity Evolution of Low Mass Galaxies: New Contraints at Intermediate Redshift

    NASA Technical Reports Server (NTRS)

    Henry, Alaina; Martin, Crystal L.; Finlator, Kristian; Dressler, Alan

    2013-01-01

    We present abundance measurements from 26 emission-line-selected galaxies at z approx. 0.6-0.7. By reaching stellar masses as low as 10(exp 8) M stellar mass, these observations provide the first measurement of the intermediate-redshift mass-metallicity (MZ) relation below 10(exp 9)M stellar mass. For the portion of our sample above M is greater than 10(exp 9)M (8/26 galaxies), we find good agreement with previous measurements of the intermediate-redshift MZ relation. Compared to the local relation, we measure an evolution that corresponds to a 0.12 dex decrease in oxygen abundances at intermediate redshifts. This result confirms the trend that metallicity evolution becomes more significant toward lower stellar masses, in keeping with a downsizing scenario where low-mass galaxies evolve onto the local MZ relation at later cosmic times. We show that these galaxies follow the local fundamental metallicity relation, where objects with higher specific (mass-normalized) star formation rates (SFRs) have lower metallicities. Furthermore, we show that the galaxies in our sample lie on an extrapolation of the SFR-M* relation (the star-forming main sequence). Leveraging the MZ relation and star-forming main sequence (and combining our data with higher-mass measurements from the literature), we test models that assume an equilibrium between mass inflow, outflow, and star formation.We find that outflows are required to describe the data. By comparing different outflow prescriptions, we show that momentum, driven winds can describe the MZ relation; however, this model underpredicts the amount of star formation in low-mass galaxies. This disagreement may indicate that preventive feedback from gas heating has been overestimated, or it may signify a more fundamental deviation from the equilibrium assumption.

  20. Carbon monoxide in clouds at low metallicity in the dwarf irregular galaxy WLM.

    PubMed

    Elmegreen, Bruce G; Rubio, Monica; Hunter, Deidre A; Verdugo, Celia; Brinks, Elias; Schruba, Andreas

    2013-03-28

    Carbon monoxide (CO) is the primary tracer for interstellar clouds where stars form, but it has never been detected in galaxies in which the oxygen abundance relative to hydrogen is less than 20 per cent of that of the Sun, even though such 'low-metallicity' galaxies often form stars. This raises the question of whether stars can form in dense gas without molecules, cooling to the required near-zero temperatures by atomic transitions and dust radiation rather than by molecular line emission; and it highlights uncertainties about star formation in the early Universe, when the metallicity was generally low. Here we report the detection of CO in two regions of a local dwarf irregular galaxy, WLM, where the metallicity is 13 per cent of the solar value. We use new submillimetre observations and archival far-infrared observations to estimate the cloud masses, which are both slightly greater than 100,000 solar masses. The clouds have produced stars at a rate per molecule equal to 10 per cent of that in the local Orion nebula cloud. The CO fraction of the molecular gas is also low, about 3 per cent of the Milky Way value. These results suggest that in small galaxies both star-forming cores and CO molecules become increasingly rare in molecular hydrogen clouds as the metallicity decreases.

  1. THE METALLICITY EVOLUTION OF BLUE COMPACT DWARF GALAXIES FROM THE INTERMEDIATE REDSHIFT TO THE LOCAL UNIVERSE

    SciTech Connect

    Lian, Jianhui; Hu, Ning; Ye, Chengyun; Kong, Xu; Fang, Guanwen E-mail: xkong@ustc.edu.cn

    2016-03-01

    We present oxygen abundance measurements for 74 blue compact dwarf (BCD) galaxies in the redshift range of [0.2, 0.5] using the strong-line method. The spectra of these objects are taken using Hectospec on the Multiple Mirror Telescope. More than half of these BCDs had dust attenuation corrected using the Balmer decrement method. For comparison, we also selected a sample of 2023 local BCDs from the Sloan Digital Sky Survey (SDSS) database. Based on the local and intermediate-z BCD samples, we investigated the cosmic evolution of the metallicity, star formation rate (SFR), and D{sub n}(4000) index. Compared with local BCDs, the intermediate-z BCDs had a systematically higher R23 ratio but a similar O32 ratio. Interestingly, no significant deviation in the mass–metallicity (MZ) relation was found between the intermediate-z and local BCDs. Besides the metallicity, the intermediate-z BCDs also exhibited an SFR distribution that was consistent with local BCDs, suggesting a weak dependence on redshift. The intermediate-z BCDs seemed to be younger than the local BCDs with lower D{sub n}(4000) index values. The insignificant deviation in the mass–metallicity and mass–SFR relations between intermediate-z and local BCDs indicates that the relations between the global parameters of low-mass compact galaxies may be universal. These results from low-mass compact galaxies could be used to place important observational constraints on galaxy formation and evolution models.

  2. The metallicity and dust content of a redshift 5 gamma-ray burst host galaxy

    SciTech Connect

    Sparre, M.; Krühler, T.; Fynbo, J. P. U.; Watson, D. J.; De Ugarte Postigo, A.; Hjorth, J.; Malesani, D.; Hartoog, O. E.; Kaper, L.; Wiersema, K.; D'Elia, V.; Afonso, P. M. J.; Covino, S.; Flores, H.; Goldoni, P.; Jakobsson, P.; Klose, S.; Levan, A. J.; and others

    2014-04-20

    Observations of the afterglows of long gamma-ray bursts (GRBs) allow the study of star-forming galaxies across most of cosmic history. Here we present observations of GRB 111008A, from which we can measure metallicity, chemical abundance patterns, dust-to-metals ratio (DTM), and extinction of the GRB host galaxy at z = 5.0. The host absorption system is a damped Lyα absorber with a very large neutral hydrogen column density of log N(H I)/cm{sup −2}=22.30±0.06 and a metallicity of [S/H] = –1.70 ± 0.10. It is the highest-redshift GRB with such a precise metallicity measurement. The presence of fine-structure lines confirms the z = 5.0 system as the GRB host galaxy and makes this the highest redshift where Fe II fine-structure lines have been detected. The afterglow is mildly reddened with A{sub V} = 0.11 ± 0.04 mag, and the host galaxy has a DTM that is consistent with being equal to or lower than typical values in the Local Group.

  3. The distribution of star formation and metals in the low surface brightness galaxy UGC 628

    NASA Astrophysics Data System (ADS)

    Young, J. E.; Kuzio de Naray, Rachel; Wang, Sharon X.

    2015-09-01

    We introduce the MUSCEL Programme (MUltiwavelength observations of the Structure, Chemistry and Evolution of LSB galaxies), a project aimed at determining the star-formation histories of low surface brightness galaxies. MUSCEL utilizes ground-based optical spectra and space-based UV and IR photometry to fully constrain the star-formation histories of our targets with the aim of shedding light on the processes that led low surface brightness galaxies down a different evolutionary path from that followed by high surface brightness galaxies, such as our Milky Way. Here we present the spatially resolved optical spectra of UGC 628, observed with the VIRUS-P IFU at the 2.7-m Harlen J. Smith Telescope at the McDonald Observatory, and utilize emission-line diagnostics to determine the rate and distribution of star formation as well as the gas-phase metallicity and metallicity gradient. We find highly clustered star formation throughout UGC 628, excluding the core regions, and a log(O/H) metallicity around -4.2, with more metal-rich regions near the edges of the galactic disc. Based on the emission-line diagnostics alone, the current mode of star formation, slow and concentrated in the outer disc, appears to have dominated for quite some time, although there are clear signs of a much older stellar population formed in a more standard inside-out fashion.

  4. Why do disk galaxies present a common gas-phase metallicity gradient?

    NASA Astrophysics Data System (ADS)

    Chang, R.; Zhang, Shuhui; Shen, Shiyin; Yin, Jun; Hou, Jinliang

    2017-03-01

    CALIFA data show that isolated disk galaxies present a common gas-phase metallicity gradient, with a characteristic slope of -0.1dex/re between 0.3 and 2 disk effective radius re (Sanchez et al. 2014). Here we construct a simple model to investigate which processes regulate the formation and evolution.

  5. LONG GRBs ARE METALLICITY-BIASED TRACERS OF STAR FORMATION: EVIDENCE FROM HOST GALAXIES AND REDSHIFT DISTRIBUTION

    SciTech Connect

    Wang, F. Y.; Dai, Z. G. E-mail: dzg@nju.edu.cn

    2014-07-01

    We investigate the mass distribution of long gamma-ray burst (GRB) host galaxies and the redshift distribution of long GRBs by considering that long GRBs occur in low-metallicity environments. We calculate the upper limit on the stellar mass of a galaxy which can produce long GRBs by utilizing the mass-metallicity (M-Z) relation of galaxies. After comparing with the observed GRB host galaxies masses, we find that the observed GRB host galaxy masses can fit the predicted masses well if GRBs occur in low-metallicity 12 + log (O/H){sub KK04} < 8.7. GRB host galaxies have low metallicity, low mass, and high star formation rate compared with galaxies of seventh data release of the Sloan Digital Sky Survey. We also study the cumulative redshift distribution of the latest Swift long GRBs by adding dark GRBs and 10 new GRBs redshifts from the TOUGH survey. The observed discrepancy between the GRB rate and the star formation history can be reconciled by considering that GRBs tend to occur in low-metallicity galaxies with 12 + log (O/H){sub KK04} < 8.7. We conclude that the metallicity cutoff that can produce long GRBs is about 12 + log (O/H){sub KK04} < 8.7 from the host mass distribution and redshift distribution.

  6. IC Treatment: Antidepressants

    MedlinePlus

    ... a “black box warning” regarding the potential for suicide and suicidal thinking in children and adolescents taking ... Flares Women & IC Pregnancy & IC Intimacy & IC Pelvic Exam Tips Men & IC Intimacy & IC Support for Men ...

  7. The growth of discs and bulges during hierarchical galaxy formation - II. Metallicity, stellar populations and dynamical evolution

    NASA Astrophysics Data System (ADS)

    Tonini, C.; Mutch, S. J.; Wyithe, J. S. B.; Croton, D. J.

    2017-03-01

    We investigate the properties of the stellar populations of model galaxies as a function of galaxy evolutionary history and angular momentum content. We use the new semi-analytic model presented in Tonini et al. This new model follows the angular momentum evolution of gas and stars, providing the base for a new star formation recipe, and treatment of the effects of mergers that depends on the central galaxy dynamical structure. We find that the new recipes have the effect of boosting the efficiency of the baryonic cycle in producing and recycling metals, as well as preventing minor mergers from diluting the metallicity of bulges and ellipticals. The model reproduces the stellar mass-stellar metallicity relation for galaxies above 1010 solar masses, including Brightest Cluster Galaxies. Model discs, galaxies dominated by instability-driven components, and merger-driven objects each stem from different evolutionary channels. These model galaxies therefore occupy different loci in the galaxy mass-size relation, which we find to be in accord with the ATLAS 3D classification of disc galaxies, fast rotators and slow rotators. We find that the stellar populations' properties depend on the galaxy evolutionary type, with more evolved stellar populations being part of systems that have lost or dissipated more angular momentum during their assembly history.

  8. Probing the History of Galaxy Clusters with Metallicity and Entropy Measurements

    NASA Astrophysics Data System (ADS)

    Elkholy, Tamer Yohanna

    Galaxy clusters are the largest gravitationally bound objects found today in our Universe. The gas they contain, the intra-cluster medium (ICM), is heated to temperatures in the approximate range of 1 to 10 keV, and thus emits X-ray radiation. Studying the ICM through the spatial and spectral analysis of its emission returns the richest information about both the overall cosmological context which governs the formation of clusters, as well as the physical processes occurring within. The aim of this thesis is to learn about the history of the physical processes that drive the evolution of galaxy clusters, through careful, spatially resolved measurements of their metallicity and entropy content. A sample of 45 nearby clusters observed with Chandra is analyzed to produce radial density, temperature, entropy and metallicity profiles. The entropy profiles are computed to larger radial extents than in previous Chandra analyses. The results of this analysis are made available to the scientific community in an electronic database. Comparing metallicity and entropy in the outskirts of clusters, we find no signature on the entropy profiles of the ensemble of supernovae that produced the observed metals. In the centers of clusters, we find that the metallicities of high-mass clusters are much less dispersed than those of low-mass clusters. A comparison of metallicity with the regularity of the X-ray emission morphology suggests that metallicities in low-mass clusters are more susceptible to increase from violent events such as mergers. We also find that the variation in the stellar-to-gas mass ratio as a function of cluster mass can explain the variation of central metallicity with cluster mass, only if we assume that there is a constant level of metallicity for clusters of all masses, above which the observed galaxies add more metals in proportion to their mass. (Copies available exclusively from MIT Libraries, libraries.mit.edu/docs - docs mit.edu)

  9. The H I content of extremely metal-deficient blue compact dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Thuan, T. X.; Goehring, K. M.; Hibbard, J. E.; Izotov, Y. I.; Hunt, L. K.

    2016-12-01

    We have obtained new H I observations with the 100 m Green Bank Telescope (GBT) for a sample of 29 extremely metal-deficient star-forming blue compact dwarf (BCD) galaxies, selected from the Sloan Digital Sky Survey (SDSS) spectral data base to be extremely metal-deficient (12 + log O/H ≤ 7.6). Neutral hydrogen was detected in 28 galaxies, a 97 per cent detection rate. Combining the H I data with SDSS optical spectra for the BCD sample and adding complementary galaxy samples from the literature to extend the metallicity and mass ranges, we have studied how the H I content of a galaxy varies with various global galaxian properties. There is a clear trend of increasing gas mass fraction with decreasing metallicity, mass and luminosity. We obtain the relation M(H I)/Lg∝ L_g^{-0.3}, in agreement with previous studies based on samples with a smaller luminosity range. The median gas mass fraction fgas for the GBT sample is equal to 0.94 while the mean gas mass fraction is 0.90±0.15, with a lower limit of ˜0.65. The H I depletion time is independent of metallicity, with a large scatter around the median value of 3.4 Gyr. The ratio of the baryonic mass to the dynamical mass of the metal-deficient BCDs varies from 0.05 to 0.80, with a median value of ˜0.2. About 65 per cent of the BCDs in our sample have an effective yield larger than the true yield, implying that the neutral gas envelope in BCDs is more metal-deficient by a factor of 1.5-20, as compared to the ionized gas.

  10. The X-ray source population of IC 10

    NASA Astrophysics Data System (ADS)

    Kilgard, Roy; Placek, Ben; Prestwich, Andrea

    2009-09-01

    The Local Group dwarf galaxy IC 10 is the nearest starburst to the Milky Way. Its proximity and low metallicity make it an ideal candidate for the study of high-mass X-ray binaries in quiescence. IC 10 presents an unique case for studying a complete sample of such objects, something made difficult in the Milky Way by absorption in the Galactic disc and in other galaxies by their distances.We present results from a set of Chandra/ACIS-S imaging observations of IC 10, including spectra, lightcurves, X-ray colors, and X-ray luminosity functions. The XLF is steeper than for the more luminous HMXBs observed in other galaxies, thus implying that the ``universal'' luminosity function for HMXBs does not extend below 1e36 erg/s. We also present initial results from a search for optical counterparts to the X-ray sources using archival HST/ACS observations. Approximately 10% of the sources have strong optical counterpart candidates, all of which appear to be high-mass stars.

  11. The X-ray Source Population of IC 10

    NASA Astrophysics Data System (ADS)

    Placek, Ben; Kilgard, R. E.; Prestwich, A. H.

    2010-01-01

    The Local Group dwarf galaxy IC 10 is the nearest starburst to the Milky Way. Its proximity and low metallicity make it an ideal candidate for the study of high-mass X-ray binaries in quiescence.  IC 10 presents an unique case for studying a complete sample of such objects, something made difficult in the Milky Way by absorption in the Galactic disc and in other galaxies by their distances. We present results from a set of Chandra/ACIS-S imaging observations of IC 10, including spectra, X-ray colors, and X-ray luminosity functions. The XLF is steeper than for the more luminous HMXBs observed in other galaxies, thus implying that the "universal" luminosity function for HMXBs does not extend below 1e36 erg/s.  We also present initial results from a search for optical counterparts to the X-ray sources using archival HST/ACS observations.  Approximately 15% of the sources have strong optical counterpart candidates, all of which appear to be high-mass stars.

  12. THE FOSSIL RECORD OF TWO-PHASE GALAXY ASSEMBLY: KINEMATICS AND METALLICITIES IN THE NEAREST S0 GALAXY

    SciTech Connect

    Arnold, Jacob A.; Romanowsky, Aaron J.; Brodie, Jean P.; Spitler, Lee R.; Forbes, Duncan A.; Benson, Andrew J.

    2011-08-01

    We present a global analysis of kinematics and metallicity in the nearest S0 galaxy, NGC 3115, along with implications for its assembly history. The data include high-quality wide-field imaging from Suprime-Cam on the Subaru telescope, and multi-slit spectra of the field stars and globular clusters (GCs) obtained using Keck-DEIMOS/LRIS and Magellan-IMACS. Within two effective radii, the bulge (as traced by the stars and metal-rich GCs) is flattened and rotates rapidly (v/{sigma} {approx}> 1.5). At larger radii, the rotation declines dramatically to v/{sigma} {approx} 0.7, but remains well aligned with the inner regions. The radial decrease in characteristic metallicity of both the metal-rich and metal-poor GC subpopulations produces strong gradients with power-law slopes of -0.17 {+-} 0.04 and -0.38 {+-} 0.06 dex dex{sup -1}, respectively. We argue that this pattern is not naturally explained by a binary major merger, but instead by a two-phase assembly process where the inner regions have formed in an early violent, dissipative phase, followed by the protracted growth of the outer parts via minor mergers with typical mass ratios of {approx}15-20:1.

  13. NEAR-INFRARED IMAGING OF SIX METAL-RICH QUASAR ABSORBER GALAXY FIELDS

    SciTech Connect

    Straka, Lorrie A.; Kulkarni, Varsha P.; York, Donald G.

    2011-06-15

    Absorption lines in quasar spectra allow us to locate and study intervening galaxies. In order to obtain a clearer picture of these absorber galaxies, we have used the Near-Infrared Camera Fabry-Perot System at Apache Point Observatory to obtain near-infrared broadband images in one or more filters (J and K{sub s} ) of six quasar fields containing metal-rich low-z damped or sub-damped Ly{alpha} systems. These data allow us to search for the galaxies and constrain their luminosities. Candidate absorber galaxies are detected at 2.''01-7.''38 separation from the quasar in three out of six fields in the J and K{sub s} bands at >3{sigma} level with luminosities ranging from log(L/L{sub sun}) = 10.44-10.36 in the J band (for E-Sc type galaxies) and log(L/L{sub sun}) = 11.59-10.03 in the K{sub s} band for our detections. We place limits on the remaining fields with no detections of log(L/L{sub sun}) <10.83-9.75 for the J band and log(L/L{sub sun}) <10.43-10.05 for the K{sub s} band. We are also able to utilize Sloan Digital Sky Survey spectra for each field to calculate optical fluxes and limits as well as limits on star formation rate via [O II]{lambda}3727 emission in spectra. Our data, combined with other recent imaging results for metal-rich absorbers, suggest a possible positive correlation between absorber metallicity and galaxy luminosity, although the samples are still small.

  14. Ages and metallicities for quiescent galaxies in the Shapley supercluster: driving parameters of the stellar populations

    NASA Astrophysics Data System (ADS)

    Smith, Russell J.; Lucey, John R.; Hudson, Michael J.

    2009-12-01

    We use high signal-to-noise spectroscopy for a sample of 232 quiescent galaxies in the Shapley supercluster, to investigate how their stellar populations depend on velocity dispersion (σ), luminosity and stellar mass. The sample spans a large range in velocity dispersion (30-300kms-1) and in luminosity (MR from -18.7 to -23.2). Estimates of age, total metallicity (Z/H) and α-element abundance ratio (α/Fe) were derived from absorption-line analysis, using single-burst models of Thomas and collaborators. Using the Rose CaII index, we conclude that recent star formation (frosting) events are not responsible for the intermediate ages observed in some of the galaxies. Age, Z/H and α/Fe are correlated positively with velocity dispersion, but we also find significant residual trends with luminosity: at given σ, the brighter galaxies are younger, less α-enriched and have higher Z/H. At face value, these results might suggest that the stellar populations depend on stellar mass as well as on velocity dispersion. However, we show that the observed trends can be reproduced by models in which the stellar populations depend systematically only on σ, and are independent of stellar mass M*. For age, the observed luminosity correlation arises because young galaxies are brighter, at fixed M*. For metallicity, the observed luminosity dependence arises because metal-rich galaxies, at fixed mass, tend also to be younger, and hence brighter. We find a good match to the observed luminosity correlations with age ~σ+0.40, Z/H~σ+0.35,α/Fe ~σ+0.20, where the slopes are close to those found when fitting traditional scaling relations. We conclude that the star formation and enrichment histories of galaxies are determined primarily by the depth of their gravitational potential wells. The observed residual correlations with luminosity do not imply a corresponding dependence on stellar mass.

  15. Kinematics of Extremely Metal-poor Galaxies: Evidence for Stellar Feedback

    NASA Astrophysics Data System (ADS)

    Olmo-García, A.; Sánchez Almeida, J.; Muñoz-Tuñón, C.; Filho, M. E.; Elmegreen, B. G.; Elmegreen, D. M.; Pérez-Montero, E.; Méndez-Abreu, J.

    2017-01-01

    The extremely metal-poor (XMP) galaxies analyzed in a previous paper have large star-forming regions with a metallicity lower than the rest of the galaxy. Such a chemical inhomogeneity reveals the external origin of the metal-poor gas fueling star formation, possibly indicating accretion from the cosmic web. This paper studies the kinematic properties of the ionized gas in these galaxies. Most XMPs have a rotation velocity around a few tens of km s‑1. The star-forming regions appear to move coherently. The velocity is constant within each region, and the velocity dispersion sometimes increases within the star-forming clump toward the galaxy midpoint, suggesting inspiral motion toward the galaxy center. Other regions present a local maximum in velocity dispersion at their center, suggesting a moderate global expansion. The Hα line wings show a number of faint emission features with amplitudes around a few per cent of the main Hα component, and wavelength shifts between 100 and 400 km s‑1. The components are often paired, so that red and blue emission features with similar amplitudes and shifts appear simultaneously. Assuming the faint emission to be produced by expanding shell-like structures, the inferred mass loading factor (mass loss rate divided by star formation rate) exceeds 10. Since the expansion velocity far exceeds the rotational and turbulent velocities, the gas may eventually escape from the galaxy disk. The observed motions involve energies consistent with the kinetic energy released by individual core-collapse supernovae. Alternative explanations for the faint emission have been considered and discarded.

  16. Modeling the Destruction and Survival of PAHs in Astrophysical Regions: from Low-metallicity Galaxies to Elliptical Galaxies and Galactic Halos

    NASA Astrophysics Data System (ADS)

    Li, Aigen

    2006-05-01

    The 3.3, 6.2, 7.7, 8.6 and 11.3 micron emission features of polycyclic aromatic hydrocarbon (PAH) molecules have been seen in a wide variety of Galactic and extragalactic objects. However, the PAH features are weak or absent in low-metallicity galaxies and AGN, as generally interpreted as the destruction of PAHs by hard UV photons in metal-poor galaxies or by extreme UV and soft X-ray photons in AGN. On the other hand, the PAH emission features have recently been detected in elliptical galaxies, tidal dwarf galaxies, galaxy halos, and distant galaxies at redshift >=2. However, it is not clear how PAHs can survive in elliptical galaxies containing X-ray emitting hot gas where PAHs are expected to be easily destroyed through sputtering by hot plasma ions. It is also not clear how PAHs get ``levitated'' and survive from galactic plane to galaxy halo where the physical conditions are similar to those of elliptical galaxies. We propose to study the destruction of PAHs (1) by UV photons in low-metallicity galaxies, (2) by extreme UV and X-ray photons in AGN, (3) by intense UV radiation in regions with strong star-forming activities, and (4) through sputtering by plasma ions in hot gas. This will allow us, by the first time, to quantitatively investigate the deficiency or lack of PAHs in AGN and low-metallicity galaxies, as well as the survivability of PAHs in elliptical galaxies, galaxy halo, and superwind, and the method of using the IRAC 8 micron photometry as a tracer of star formation rates. This program will create a web-based ``library'' of the destruction rates of PAHs by UV and X-ray photons as a function of size, intensity and hardness of the radiation field, and the sputtering rates of PAHs by plasma ions as a function of size, gas density and temperature. This library will be made publicly available to the astronomical community by May 2007 on the internet at http://www.missouri.edu/~lia/.

  17. Dust-to-gas ratio and metallicity variations in nearby galaxies

    NASA Astrophysics Data System (ADS)

    Issa, M. R.; MacLaren, I.; Wolfendale, A. W.

    1990-09-01

    The dependence of the dust-to-gas ratio on Galacto-centric radius and its relation to the known metallicity gradient in the Galaxy and nearby galaxies is investigated. Despite the large degree of uncertainty associated with both quantities, there is evidence for a correlation, with dust-to-gas ratio and metallicity decreasing at roughly the same rate with increasing radius. Such a result has important implications. For example, attempts using FIR surveys to estimate the conversion between observed CO emission and molecular hydrogen column density should allow for the varying dust-to-gas ratio. Broadbent et al. (1989) used a dust-to-gas ratio that varied in proportion to metallicity, following the approach used by Cox et al. (1986), and confirmed the previously estimated low value for the conversion factor; there is thus support for this result.

  18. Relative abundances in the low-metallicity dwarf irregular galaxy UGC 4483

    NASA Technical Reports Server (NTRS)

    Skillman, Evan D.

    1991-01-01

    UGC 4483 is a dwarf irregular galaxy in the M 81 group. Narrow-band optical imaging has revealed an H II region in UGC 4483 with an H-alpha flux of about 2 x 10 to the -13th erg/sq cm per A per s. Optical, UV and NIR spectroscopy of this H II region yield He, C, N, O, Ne, and S abundances for the ISM in this galaxy. With an oxygen abundance of 0.000021 12 + log(O/H) = 7.3, this galaxy is among the most metal-poor dwarf irregulars known to date. A comparison of the S/O abundance ratio in this galaxy with that in I Zw 18 supports the claim by Garnett (1990) that the S/O ratio is consistent with the solar ratio for low-metallicity dwarf irregulars. The C/O ratio in UGC 4483 is lower than that derived for I Zw 18 and, therefore, more in line with the trend seen in higher metallicity H II regions. The derived helium abundance is He/H = 0.075, which converts to a He mass fraction of 0.23, consistent with earlier determinations of the primordial He abundance.

  19. Long gamma-ray Bursts and Type Ic Core CollapseSupernovae have Similar Environments

    SciTech Connect

    Kelly, P.L.; Kirshner, R.P.; Pahre, M.

    2007-12-04

    When the afterglow fades at the site of a long-duration {gamma}-ray burst (LGRB), Type Ic supernovae (SN Ic) are the only type of core collapse supernova observed. Recent work found that a sample of LGRB had different environments from a collection of core-collapse supernovae identified in a high-redshift sample from colors and light curves. LGRB were in the brightest regions of their hosts, but the core-collapse sample followed the overall distribution of the galaxy light. Here we examine 263 fully spectroscopically-typed supernovae found in nearby (z < 0.06) galaxies for which we have constructed surface photometry from the Sloan Digital Sky Survey (SDSS). The distributions of the thermonuclear supernovae (SN Ia) and some varieties of core-collapse supernovae (SN II and SN Ib) follow the galaxy light, but the SN Ic (like LGRB) are much more likely to erupt in the brightest regions of their hosts. The high-redshift hosts of LGRB are overwhelmingly irregulars, without bulges, while many low redshift SN Ic hosts are spirals with small bulges. When we remove the bulge light from our low-redshift sample, the SN Ic and LGRB distributions agree extremely well. If both LGRB and SN Ic stem from very massive stars, then it seems plausible that the conditions necessary for forming SN Ic are also required for LGRB. Additional factors, including metallicity, may determine whether the stellar evolution of a massive star leads to a LGRB with an underlying broad-lined SN Ic, or simply a SN Ic without a {gamma}-ray burst.

  20. Metal-Poor, Strongly Star-Forming Galaxies in the DEEP2 Survey: The Relationship Between Stellar Mass, Temperature-Based Metallicity, and Star Formation Rate

    NASA Technical Reports Server (NTRS)

    Ly, Chun; Rigby, Jane R.; Cooper, Michael; Yan, Renbin

    2015-01-01

    We report on the discovery of 28 redshift (z) approximately equal to 0.8 metal-poor galaxies in DEEP2. These galaxies were selected for their detection of the weak [O (sub III)] lambda 4363 emission line, which provides a "direct" measure of the gas-phase metallicity. A primary goal for identifying these rare galaxies is to examine whether the fundamental metallicity relation (FMR) between stellar mass, gas metallicity, and star formation rate (SFR) holds for low stellar mass and high SFR galaxies. The FMR suggests that higher SFR galaxies have lower metallicity (at fixed stellar mass). To test this trend, we combine spectroscopic measurements of metallicity and dust-corrected SFR with stellar mass estimates from modeling the optical photometry. We find that these galaxies are 1.05 plus or minus 0.61 dex above the redshift (z) approximately 1 stellar mass-SFR relation and 0.23 plus or minus 0.23 dex below the local mass-metallicity relation. Relative to the FMR, the latter offset is reduced to 0.01 dex, but significant dispersion remains dex with 0.16 dex due to measurement uncertainties). This dispersion suggests that gas accretion, star formation, and chemical enrichment have not reached equilibrium in these galaxies. This is evident by their short stellar mass doubling timescale of approximately equal to 100 (sup plus 310) (sub minus 75) million years which suggests stochastic star formation. Combining our sample with other redshift (z) of approximately 1 metal-poor galaxies, we find a weak positive SFR-metallicity dependence (at fixed stellar mass) that is significant at 94.4 percent confidence. We interpret this positive correlation as recent star formation that has enriched the gas but has not had time to drive the metal-enriched gas out with feedback mechanisms.

  1. THE KENNICUTT–SCHMIDT RELATION IN EXTREMELY METAL-POOR DWARF GALAXIES

    SciTech Connect

    Filho, M. E.; Almeida, J. Sánchez; Muñoz-Tuñón, C.; Amorín, R.; Elmegreen, B. G.; Elmegreen, D. M.

    2016-04-01

    The Kennicutt–Schmidt (KS) relation between the gas mass and star formation rate (SFR) describes the star formation regulation in disk galaxies. It is a function of gas metallicity, but the low-metallicity regime of the KS diagram is poorly sampled. We have analyzed data for a representative set of extremely metal-poor galaxies (XMPs), as well as auxiliary data, and compared these to empirical and theoretical predictions. The majority of the XMPs possess high specific SFRs, similar to high-redshift star-forming galaxies. On the KS plot, the XMP H i data occupy the same region as dwarfs and extend the relation for low surface brightness galaxies. Considering the H i gas alone, a considerable fraction of the XMPs already fall off the KS law. Significant quantities of “dark” H{sub 2} mass (i.e., not traced by CO) would imply that XMPs possess low star formation efficiencies (SFE{sub gas}). Low SFE{sub gas} in XMPs may be the result of the metal-poor nature of the H i gas. Alternatively, the H i reservoir may be largely inert, the star formation being dominated by cosmological accretion. Time lags between gas accretion and star formation may also reduce the apparent SFE{sub gas}, as may galaxy winds, which can expel most of the gas into the intergalactic medium. Hence, on global scales, XMPs could be H i-dominated, high-specific-SFR (≳10{sup −10} yr{sup −1}), low-SFE{sub gas} (≲10{sup −9} yr{sup −1}) systems, in which the total H i mass is likely not a good predictor of the total H{sub 2} mass, nor of the SFR.

  2. OUTFLOW VERSUS INFALL IN SPIRAL GALAXIES: METAL ABSORPTION IN THE HALO OF NGC 891

    SciTech Connect

    Bregman, Joel N.; Seitzer, Patrick; Cowley, C. R.; Miller, Matthew J.; Miller, Eric D.

    2013-03-20

    Gas accreting onto a galaxy will be of low metallicity while halo gas due to a galactic fountain will be of near-solar metallicity. We test these predictions by measuring the metal absorption line properties of halo gas 5 kpc above the plane of the edge-on galaxy NGC 891, using observations taken with HST/STIS toward a bright background quasar. Metal absorption lines of Fe II, Mg II, and Mg I in the halo of NGC 891 are clearly seen, and when combined with recent deep H I observations, we are able to place constraints on the metallicity of the halo gas for the first time. The H I line width defines the line broadening, from which we model opacity effects in these metal lines, assuming that the absorbing gas is continuously distributed in the halo. The gas-phase metallicities are [Fe/H] = -1.18 {+-} 0.07 and [Mg/H] = -0.23 + 0.36/ - 0.27 (statistical errors) and this difference is probably due to differential depletion onto grains. When corrected for such depletion using Galactic gas as a guide, both elements have approximately solar or even supersolar abundances. This suggests that the gas is from the galaxy disk, probably expelled into the halo by a galactic fountain, rather than from accretion of intergalactic gas, which would have a low metallicity. The abundances would be raised by significant amounts if the absorbing gas lies in a few clouds with thermal widths smaller than the rotational velocity of the halo. If this is the case, both the abundances and [Mg/Fe] would be supersolar.

  3. THE ORIGIN OF METALS IN THE CIRCUMGALACTIC MEDIUM OF MASSIVE GALAXIES AT z = 3

    SciTech Connect

    Shen Sijing; Madau, Piero; Aguirre, Anthony; Guedes, Javiera; Mayer, Lucio; Wadsley, James

    2012-11-20

    We present a detailed study of the metal-enriched circumgalactic medium (CGM) of a massive galaxy at z = 3 using results from 'ErisMC', a new cosmological hydrodynamic 'zoom-in' simulation of a disk galaxy with mass comparable to the Milky Way. The reference run adopts a blast wave scheme for supernova feedback that generates galactic outflows without explicit wind particles, a star formation recipe based on a high gas density threshold and high-temperature metal cooling. ErisMC's main progenitor at z = 3 resembles a 'Lyman break' galaxy of total mass M {sub vir} = 2.4 Multiplication-Sign 10{sup 11} M {sub Sun }, virial radius R {sub vir} = 48 kpc, and star formation rate 18 M {sub Sun} yr{sup -1}, and its metal-enriched CGM extends as far as 200 (physical) kpc from its center. Approximately 41%, 9%, and 50% of all gas-phase metals at z = 3 are locked in a hot (T > 3 Multiplication-Sign 10{sup 5} K), warm (3 Multiplication-Sign 10{sup 5} K > T > 3 Multiplication-Sign 10{sup 4} K), and cold (T < 3 Multiplication-Sign 10{sup 4} K) medium, respectively. We identify three sources of heavy elements: (1) the main host, responsible for 60% of all the metals found within 3 R {sub vir}; (2) its satellite progenitors, which shed their metals before and during infall, and are responsible for 28% of all the metals within 3 R {sub vir}, and for only 5% of those beyond 3 R {sub vir}; and (3) nearby dwarfs, which give origin to 12% of all the metals within 3 R {sub vir} and 95% of those beyond 3 R {sub vir}. Late (z < 5) galactic 'superwinds'-the result of recent star formation in ErisMC-account for only 9% of all the metals observed beyond 2 R {sub vir}, the bulk having been released at redshifts 5 {approx}< z {approx}< 8 by early star formation and outflows. In the CGM, lower overdensities are typically enriched by 'older', colder metals. Heavy elements are accreted onto ErisMC along filaments via low-metallicity cold inflows and are ejected hot via galactic outflows at a few

  4. Dense Cloud Cores revealed by ALMA CO observations in the low metallicity dwarf galaxy WLM

    NASA Astrophysics Data System (ADS)

    Rubio, M.; Elmegreen, B.; Hunter, D.; Cortes, J.; Brinks, E.; Cigan, P.

    2017-03-01

    Understanding stellar birth requires observations of the clouds in which they form. These clouds are dense and self-gravitating, and in all existing observations, they are molecular with H2 the dominant species and CO the best available. When the abundances of carbon and oxygen are low compared to hydrogen, and the opacity from dust is also low, as in primeval galaxies and local dwarf irregular galaxies CO forms slowly and is easily destroyed, so it cannot accumulate inside dense clouds. Then we lose our ability to trace the gas in regions of star formation and we lose critical information on the temperatures, densities, and velocities of the material that collapses. I will report on high resolution observations with ALMA of CO clouds in the local group dwarf irregular galaxy WLM, which has a metallicity that is 13% of the solar value and 50% lower than the previous CO detection threshold and the properties derived of very small dense CO clouds mapped..

  5. Metallicity Distribution Functions of Dwarf Galaxies: A Probe of Star Formation History and Baryonic Physics

    NASA Astrophysics Data System (ADS)

    Escala, Ivanna; Kirby, Evan N.; Wetzel, Andrew R.; Hopkins, Philip F.

    2016-06-01

    We examine the metallicity distribution functions (MDFs) of simulated, isolated dwarf galaxies (M_{star} = 4 × 10^{4} - 3 × 10^{8} M_{⊙}) from the Feedback in Realistic Environments (FIRE) project to quantify the impact of star formation history (SFH) and baryonic physics. These high-resolution cosmological simulations include realistic treatments of stellar evolution and complex gas dynamics and do not require the usual approximations (e.g., instantaneous recycling and instantaneous mixing) of analytic chemical evolution models. The evolution of the MDF with redshift informs which processes drive the dominant contributions to the distribution at z = 0, thus enabling a reconstruction of the SFH and gas loss/accretion history. We then compare the theoretical MDFs to the observed MDFs of Local Group dwarf galaxies to infer plausible SFHs for each matched galaxy.

  6. AGES AND METALLICITIES OF CLUSTER GALAXIES IN A779 USING MODIFIED STROeMGREN PHOTOMETRY

    SciTech Connect

    Sreedhar, Yuvraj Harsha; Rakos, Karl D.; Hensler, Gerhard; Zeilinger, Werner W.; Odell, Andrew P.

    2012-03-01

    In the quest for the formation and evolution of galaxy clusters, Rakos and co-workers introduced a spectrophotometric method using modified Stroemgren photometry, but with the considerable debate toward the project's abilities, we re-introduce the system by testing for the repeatability of the modified Stroemgren colors and compare them with the Stroemgren colors, and check for the reproducibility of the ages and metallicities (using the Principle Component Analysis (PCA) technique and the GALEV models) for the six common galaxies in all three A779 data sets. As a result, a fair agreement between two filter systems was found to produce similar colors (with a precision of 0.09 mag in (uz - vz), 0.02 mag in (bz - yz), and 0.03 mag in (vz - vz)) and the generated ages and metallicities are also similar (with an uncertainty of 0.36 Gyr and 0.04 dex from PCA and 0.44 Gyr and 0.2 dex using the GALEV models). We infer that the technique is able to relieve the age-metallicity degeneracy by separating the age effects from the metallicity effects, but it is still unable to completely eliminate it. We further extend this paper to re-study the evolution of galaxies in the low mass, dynamically poor A779 cluster (as it was not elaborately analyzed by Rakos and co-workers in their previous work) by correlating the luminosity (mass), density, and radial distance with the estimated age, metallicity, and the star formation history. Our results distinctly show the bimodality of the young, low-mass, metal-poor population with a mean age of 6.7 Gyr ({+-} 0.5 Gyr) and the old, high-mass, metal-rich galaxies with a mean age of 9 Gyr ({+-} 0.5 Gyr). The method also observes the color evolution of the blue cluster galaxies to red (Butcher-Oemler phenomenon), and the downsizing phenomenon. Our analysis shows that modified Stroemgren photometry is very well suited for studying low- and intermediate-z clusters, as it is capable of observing deeper with better spatial resolution at

  7. DISCOVERY OF A GAS-RICH COMPANION TO THE EXTREMELY METAL-POOR GALAXY DDO 68

    SciTech Connect

    Cannon, John M.; Alfvin, Erik D.; Johnson, Megan; Koribalski, Baerbel; McQuinn, Kristen B. W.; Skillman, Evan D.; Bailin, Jeremy; Ford, H. Alyson; Girardi, Léo; Hirschauer, Alec S.; Janowiecki, Steven; Salzer, John J.; Van Sistine, Angela; Dolphin, Andrew; Elson, E. C.; Marigo, Paola; Rosenfield, Philip; Rosenberg, Jessica L.; Venkatesan, Aparna; Warren, Steven R.

    2014-05-20

    We present H I spectral-line imaging of the extremely metal-poor galaxy DDO 68. This system has a nebular oxygen abundance of only ∼3% Z {sub ☉}, making it one of the most metal-deficient galaxies known in the local volume. Surprisingly, DDO 68 is a relatively massive and luminous galaxy for its metal content, making it a significant outlier in the mass-metallicity and luminosity-metallicity relationships. The origin of such a low oxygen abundance in DDO 68 presents a challenge for models of the chemical evolution of galaxies. One possible solution to this problem is the infall of pristine neutral gas, potentially initiated during a gravitational interaction. Using archival H I spectral-line imaging obtained with the Karl G. Jansky Very Large Array, we have discovered a previously unknown companion of DDO 68. This low-mass (M{sub H} {sub I} = 2.8 × 10{sup 7} M {sub ☉}), recently star-forming (SFR{sub FUV} = 1.4 × 10{sup –3} M {sub ☉} yr{sup –1}, SFR{sub Hα} < 7 × 10{sup –5} M {sub ☉} yr{sup –1}) companion has the same systemic velocity as DDO 68 (V {sub sys} = 506 km s{sup –1}; D = 12.74 ± 0.27 Mpc) and is located at a projected distance of ∼42 kpc. New H I maps obtained with the 100 m Robert C. Byrd Green Bank Telescope provide evidence that DDO 68 and this companion are gravitationally interacting at the present time. Low surface brightness H I gas forms a bridge between these objects.

  8. Extreme Star Formation in Low-Metallicity Dusty Compact Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Thuan, Trinh; Hunt, Leslie; Izotov, Yuri

    2008-03-01

    Dusty star formation plays a key role in the early universe. ISOCAM, MIPS and submillimeter surveys have found significant populations of dusty luminous galaxies which dominate the cosmic infrared background at z >= 1. Some of these galaxies host starbursts with high star formation rates (SFRs) in such compact regions that they approach the maximum starburst intensity limit. Similar extreme conditions can occur in star clusters within nearby starburst galaxies, but these clusters generally do not dominate the light. We propose here to study extreme SF in the local universe in systems where most of the SF occurs in massive star clusters, the light of which does dominate the galaxy light. These systems are 23 low-metallicity dusty compact dwarf galaxies (DCDs) selected from the Sloan Digital Sky Survey to have a high SFR/area, potentially near the starburst intensity limit, and significant warm dust emission, a good indicator of extreme SF in massive star clusters. These DCDs will allow us to study the physics of extreme SF with a sensitivity and spatial and spectral resolution that high-z starbursts do not allow. We wish to use IRAC, IRS and MIPS to investigate how the spectral energy distributions of the DCDs, the dust properties, and the SFR/area change as a function of various physical parameters such as metallicity, the hardness of the ionizing radiation, and the compactness of the starburst region. Combining our proposed DCD observations with other data will allow us to quantify the amount of dust-enshrouded SF over a wide range of metallicities and dust properties and derive true SFRs, which are crucial for deriving the SFR as a function of cosmic epoch.

  9. The Origin of the Heaviest Metals in Most Ultra-faint Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Roederer, Ian U.

    2017-01-01

    The heaviest metals found in stars in most ultra-faint dwarf (UFD) galaxies in the Milky Way halo are generally underabundant by an order of magnitude or more when compared with stars in the halo field. Among the heavy elements produced by n-capture reactions, only Sr and Ba can be detected in red giant stars in most UFD galaxies. This limited chemical information is unable to identify the nucleosynthesis process(es) responsible for producing the heavy elements in UFD galaxies. Similar [Sr/Ba] and [Ba/Fe] ratios are found in three bright halo field stars, BD‑18°5550, CS 22185–007, and CS 22891–200. Previous studies of high-quality spectra of these stars report detections of additional n-capture elements, including Eu. The [Eu/Ba] ratios in these stars span +0.41 to +0.86. These ratios and others among elements in the rare Earth domain indicate an r-process origin. These stars have some of the lowest levels of r-process enhancement known, with [Eu/H] spanning ‑3.95 to ‑3.32, and they may be considered nearby proxies for faint stars in UFD galaxies. Direct confirmation, however, must await future observations of additional heavy elements in stars in the UFD galaxies themselves.

  10. The Metallicity of the Circumgalactic Medium of z<1 Galaxies: How low can you go?

    NASA Astrophysics Data System (ADS)

    Wotta, Christopher; Lehner, Nicolas; Howk, J. Christopher; O'Meara, John; Prochaska, Jason X.

    2017-01-01

    Accretion from the intergalactic medium and large-scale outflows are thought to drive a galaxy's evolution, including its star formation rate and its metal content. Studying the circumgalactic medium (CGM), the host of these processes, provides insights into the balance of these competing mechanisms. The cool, dense CGM has integrated H I column densities typical of optically-thick Lyman limit systems (LLSs, 17.2 <= log N(H I) < 19.0) and optically-thin partial-LLSs (pLLSs, 16 < log N(HI) < 17.2). With our Cosmic Origins Spectrograph (COS) survey of 44 pLLSs and 11 LLSs at z<1, we show that the metallicity distribution of the pLLSs is bimodal, with peaks at 1.3% and 48% of the solar metallicity. This strengthens our earlier findings and demonstrates unambiguously that low-metallicity gas is prevalent around z<1 galaxies, which provides the best-yet observational evidence for cold accretion flows like those present in numerical simulations of galaxies. For the LLSs, the sample is still small but there is a hint that the metallicity distribution changes to a unimodal distribution. It is also in this N(HI) regime that we found the lowest metallicity LLS at z<1, with <0.3% solar metallicity. Here I will present briefly these early results as well as our ongoing follow-up survey of ~40 strong pLLSs/LLSs (16.9 <= log N(H I) < 18.5) where we are systematically estimating the metallicity with COS and ground-based MgII spectra. With this new sample, we will robustly determine the metallicity distribution of the LLSs and how frequently extremely low-metallicity gas (<0.3% solar metallicity) is present at z<1. This extremely low-metallicity gas could be possible evidence for remnants of Population III enrichment at low redshift, and only in the LLS regime is the HI absorption strong enough to be sensitive to <0.3% solar metallicity.

  11. Metal-Poor, Strongly Star-Forming Galaxies in the DEEP2 Survey: The Relationship Between Stellar Mass, Temperature-Based Metallicity, and Star Formation Rate

    NASA Technical Reports Server (NTRS)

    Ly, Chun; Rigby, Jane R.; Cooper, Michael; Yan, Renbin

    2015-01-01

    We report on the discovery of 28 redshift (z) approximately 0.8 metal-poor galaxies in DEEP2. These galaxies were selected for their detection of the weak [O (sub III)] lambda 4363 emission line, which provides a "direct" measure of the gas-phase metallicity. A primary goal for identifying these rare galaxies is to examine whether the fundamental metallicity relation (FMR) between stellar mass, gas metallicity, and star formation rate (SFR) extends to low stellar mass and high SFR. The FMR suggests that higher SFR galaxies have lower metallicity (at fixed stellar mass). To test this trend, we combine spectroscopic measurements of metallicity and dust-corrected SFRs, with stellar mass estimates from modeling the optical photometry. We find that these galaxies are 1.05 plus or minus 0.61 decimal exponent (dex) above the redshift (z) approximately equal to 1 stellar mass-SFR relation, and 0.23 plus or minus 0.23 decimal exponent (dex) below the local mass-metallicity relation. Relative to the FMR, the latter offset is reduced to 0.01 decimal exponent (dex), but significant dispersion remains (0.29 decimal exponent (dex) with 0.16 decimal exponent (dex) due to measurement uncertainties). This dispersion suggests that gas accretion, star formation and chemical enrichment have not reached equilibrium in these galaxies. This is evident by their short stellar mass doubling timescale of approximately 100 (sup plus 310) (sub minus 75) million years that suggests stochastic star formation. Combining our sample with other redshift (z) of approximately 1 metal-poor galaxies, we find a weak positive SFR-metallicity dependence (at fixed stellar mass) that is significant at 97.3 percent confidence. We interpret this positive correlation as recent star formation that has enriched the gas, but has not had time to drive the metal-enriched gas out with feedback mechanisms.

  12. Metal enriched gaseous halos around distant radio galaxies: Clues to feedback in galaxy formation

    SciTech Connect

    Reuland, M; van Breugel, W; de Vries, W; Dopita, A; Dey, A; Miley, G; Rottgering, H; Venemans, B; Stanford, S A; Lacy, M; Spinrad, H; Dawson, S; Stern, D; Bunker, A

    2006-08-01

    We present the results of an optical and near-IR spectroscopic study of giant nebular emission line halos associated with three z > 3 radio galaxies, 4C 41.17, 4C 60.07 and B2 0902+34. Previous deep narrow band Ly{alpha} imaging had revealed complex morphologies with sizes up to 100 kpc, possibly connected to outflows and AGN feedback from the central regions. The outer regions of these halos show quiet kinematics with typical velocity dispersions of a few hundred km s{sup -1}, and velocity shears that can mostly be interpreted as being due to rotation. The inner regions show shocked cocoons of gas closely associated with the radio lobes. These display disturbed kinematics and have expansion velocities and/or velocity dispersions >1000 km s{sup -1}. The core region is chemically evolved, and we also find spectroscopic evidence for the ejection of enriched material in 4C 41.17 up to a distance of {approx} 60 kpc along the radio-axis. The dynamical structures traced in the Ly{alpha} line are, in most cases, closely echoed in the Carbon and Oxygen lines. This shows that the Ly{alpha} line is produced in a highly clumped medium of small filling factor, and can therefore be used as a tracer of the dynamics of HzRGs. We conclude that these HzRGs are undergoing a final jet-induced phase of star formation with ejection of most of their interstellar medium before becoming 'red and dead' Elliptical galaxies.

  13. Local Group Galaxy Emission-line Survey

    NASA Astrophysics Data System (ADS)

    Blaha, Cindy; Baildon, Taylor; Mehta, Shail; Garcia, Edgar; Massey, Philip; Hodge, Paul W.

    2015-01-01

    We present the results of the Local Group Galaxy Emission-line Survey of Hα emission regions in M31, M33 and seven dwarf galaxies in (NGC6822, IC10, WLM, Sextans A and B, Phoenix and Pegasus). Using data from the Local Group Galaxy Survey (LGGS - see Massey et al, 2006), we used continuum-subtracted Ha emission line images to define emission regions with a faint flux limit of 10 -17 ergs-sec-1-cm-2above the background. We have obtained photometric measurements for roughly 7450 Hα emission regions in M31, M33 and five of the seven dwarf galaxies (no regions for Phoenix or Pegasus). Using these regions, with boundaries defined by Hα-emission flux limits, we also measured fluxes for the continuum-subtracted [OIII] and [SII] images and constructed a catalog of Hα fluxes, region sizes and [OIII]/ Hα and [SII]/ Hα line ratios. The HII region luminosity functions and size distributions for the spiral galaxies M31 and M33 are compared with those of the dwarf galaxies NGC 6822 and IC10. For M31 and M33, the average [SII]/ Hα and [OIII]/ Hα line ratios, plotted as a function of galactocentric radius, display a linear trend with shallow slopes consistent with other studies of metallicity gradients in these galaxies. The galaxy-wide averages of [SII]/ Hα line ratios correlate with the masses of the dwarf galaxies following the previously established dwarf galaxy mass-metallicity relationship. The slope of the luminosity functions for the dwarf galaxies varies with galaxy mass. The Carleton Catalog of this Local Group Emission-line Survey will be made available on-line.

  14. Hitomi observations of the Perseus Cluster / Constant metallicity in the outskirts of galaxy clusters

    NASA Astrophysics Data System (ADS)

    Werner, Norbert; Simionescu, Aurora; Urban, Ondrej; Allen, Steven

    2016-07-01

    X-ray observations with the Suzaku satellite reveal a remarkably homogeneous distribution of iron out to the virial radii of nearby galaxy clusters. Observations of the Virgo Cluster, that also allow us to measure the abundances of Si, S, and Mg out to the outskirts, show that the chemical composition of the intra-cluster medium is constant on large scales. These observations require that most of the metal enrichment and mixing of the intergalactic medium occurred before clusters formed, probably more than ten billion years ago, during the period of maximal star formation and black hole activity. We estimate the ratio between the number of SN Ia and the total number of supernovae enriching the intergalactic medium to be between 15-20%, generally consistent with the metal abundance patterns in our own Galaxy.

  15. Stellar kinematics and metallicities in the ultra-faint dwarf galaxy Reticulum II

    SciTech Connect

    Simon, J. D.

    2015-07-23

    With this study, we present Magellan/M2FS, Very Large Telescope/GIRAFFE, and Gemini South/GMOS spectroscopy of the newly discovered Milky Way satellite Reticulum II. Based on the spectra of 25 Ret II member stars selected from Dark Energy Survey imaging, we measure a mean heliocentric velocity of $62.8\\pm 0.5\\;\\mathrm{km}\\;{\\rm{s}}^{-1}$ and a velocity dispersion of $3.3\\pm 0.7\\;\\mathrm{km}\\;{\\rm{s}}^{-1}$. The mass-to-light ratio of Ret II within its half-light radius is $470\\pm 210\\ {M}_{\\odot }/{L}_{\\odot }$, demonstrating that it is a strongly dark matter-dominated system. Despite its spatial proximity to the Magellanic Clouds, the radial velocity of Ret II differs from that of the LMC and SMC by 199 and 83 $\\mathrm{km}\\ {{\\rm{s}}}^{-1}$, respectively, suggesting that it is not gravitationally bound to the Magellanic system. The likely member stars of Ret II span 1.3 dex in metallicity, with a dispersion of 0.28 ± 0.09 dex, and we identify several extremely metal-poor stars with ${\\rm{[Fe/H]}}\\lt -3$. In combination with its luminosity, size, and ellipticity, these results confirm that Ret II is an ultra-faint dwarf galaxy. With a mean metallicity of ${\\rm{[Fe/H]}}=-2.65\\pm 0.07$, Ret II matches Segue 1 as the most metal-poor galaxy known. Although Ret II is the third-closest dwarf galaxy to the Milky Way, the line-of-sight integral of the dark matter density squared is ${\\mathrm{log}}_{10}(J)=18.8\\pm 0.6\\;\\;\\mathrm{GeV}{\\;}^{2}\\;{\\mathrm{cm}}^{-5}\\;$ within 0fdg2, indicating that the predicted gamma-ray flux from dark matter annihilation in Ret II is lower than that of several other dwarf galaxies.

  16. Stellar Kinematics and Metallicities in the Ultra-faint Dwarf Galaxy Reticulum II

    NASA Astrophysics Data System (ADS)

    Simon, J. D.; Drlica-Wagner, A.; Li, T. S.; Nord, B.; Geha, M.; Bechtol, K.; Balbinot, E.; Buckley-Geer, E.; Lin, H.; Marshall, J.; Santiago, B.; Strigari, L.; Wang, M.; Wechsler, R. H.; Yanny, B.; Abbott, T.; Bauer, A. H.; Bernstein, G. M.; Bertin, E.; Brooks, D.; Burke, D. L.; Capozzi, D.; Carnero Rosell, A.; Carrasco Kind, M.; D'Andrea, C. B.; da Costa, L. N.; DePoy, D. L.; Desai, S.; Diehl, H. T.; Dodelson, S.; Cunha, C. E.; Estrada, J.; Evrard, A. E.; Fausti Neto, A.; Fernandez, E.; Finley, D. A.; Flaugher, B.; Frieman, J.; Gaztanaga, E.; Gerdes, D.; Gruen, D.; Gruendl, R. A.; Honscheid, K.; James, D.; Kent, S.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Maia, M. A. G.; March, M.; Martini, P.; Miller, C. J.; Miquel, R.; Ogando, R.; Romer, A. K.; Roodman, A.; Rykoff, E. S.; Sako, M.; Sanchez, E.; Schubnell, M.; Sevilla, I.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thaler, J.; Tucker, D.; Vikram, V.; Walker, A. R.; Wester, W.; DES Collaboration

    2015-07-01

    We present Magellan/M2FS, Very Large Telescope/GIRAFFE, and Gemini South/GMOS spectroscopy of the newly discovered Milky Way satellite Reticulum II. Based on the spectra of 25 Ret II member stars selected from Dark Energy Survey imaging, we measure a mean heliocentric velocity of 62.8+/- 0.5 {km} {{{s}}}-1 and a velocity dispersion of 3.3+/- 0.7 {km} {{{s}}}-1. The mass-to-light ratio of Ret II within its half-light radius is 470+/- 210 {M}⊙ /{L}⊙ , demonstrating that it is a strongly dark matter-dominated system. Despite its spatial proximity to the Magellanic Clouds, the radial velocity of Ret II differs from that of the LMC and SMC by 199 and 83 {km} {{{s}}}-1, respectively, suggesting that it is not gravitationally bound to the Magellanic system. The likely member stars of Ret II span 1.3 dex in metallicity, with a dispersion of 0.28 ± 0.09 dex, and we identify several extremely metal-poor stars with {{[Fe/H]}}\\lt -3. In combination with its luminosity, size, and ellipticity, these results confirm that Ret II is an ultra-faint dwarf galaxy. With a mean metallicity of {{[Fe/H]}}=-2.65+/- 0.07, Ret II matches Segue 1 as the most metal-poor galaxy known. Although Ret II is the third-closest dwarf galaxy to the Milky Way, the line-of-sight integral of the dark matter density squared is {{log}}10(J)=18.8+/- 0.6 {GeV}{ }2 {{cm}}-5 within 0.°2, indicating that the predicted gamma-ray flux from dark matter annihilation in Ret II is lower than that of several other dwarf galaxies. Based on data obtained from the ESO Science Archive Facility under request number 157689.

  17. METAL DEFICIENCY IN CLUSTER STAR-FORMING GALAXIES AT Z = 2

    SciTech Connect

    Valentino, F.; Daddi, E.; Strazzullo, V.; Gobat, R.; Bournaud, F.; Juneau, S.; Zanella, A.; Renzini, A.; Arimoto, N.

    2015-03-10

    We investigate the environmental effect on the metal enrichment of star-forming galaxies (SFGs) in the farthest spectroscopically confirmed and X-ray-detected cluster, CL J1449+0856 at z = 1.99. We combined Hubble Space Telescope/WFC3 G141 slitless spectroscopic data, our thirteen-band photometry, and a recent Subaru/Multi-object InfraRed Camera and Spectrograph (MOIRCS) near-infrared spectroscopic follow-up to constrain the physical properties of SFGs in CL J1449+0856 and in a mass-matched field sample. After a conservative removal of active galactic nuclei, stacking individual MOIRCS spectra of 6 (31) sources in the cluster (field) in the mass range 10 ≤ log(M/M{sub ⊙}) ≤ 11, we find a ∼4σ lower [N ii]/Hα ratio in the cluster than in the field. Stacking a subsample of 16 field galaxies with Hβ and [O iii] in the observed range, we measure an [O iii]/Hβ ratio fully compatible with the cluster value. Converting these ratios into metallicities, we find that the cluster SFGs are up to 0.25 dex poorer in metals than their field counterparts, depending on the adopted calibration. The low metallicity in cluster sources is confirmed using alternative indicators. Furthermore, we observe a significantly higher Hα luminosity and equivalent width in the average cluster spectrum than in the field. This is likely due to the enhanced specific star formation rate; even if lower dust reddening and/or an uncertain environmental dependence on the continuum-to-nebular emission differential reddening may play a role. Our findings might be explained by the accretion of pristine gas around galaxies at z = 2 and from cluster-scale reservoirs, possibly connected with a phase of rapid halo mass assembly at z > 2 and of a high galaxy merging rate.

  18. The galaxy counterpart of the high-metallicity and 16 kpc impact parameter DLA towards Q 0918+1636 - a challenge to galaxy formation models?

    NASA Astrophysics Data System (ADS)

    Sommer-Larsen, J.; Fynbo, J. P. U.

    2017-01-01

    The quasar Q0918+1636 (z = 3.07) has an intervening high-metallicity damped Lyman α absorber (DLA) along the line of sight, at a redshift of z = 2.58. The DLA is located at a large impact parameter of 16.2 kpc, and despite this large impact parameter, it has a very high metallicity (consistent with solar). In this paper, it is investigated whether a novel type of galaxy formation models, based on hydrodynamical/gravitational TreeSPH simulations invoking a new Supernova Type II feedback prescription, the Haardt & Madau most recent ultraviolet background radiation (UVB) field and explicit treatment of UVB self-shielding effects, can reproduce the observed characteristics of the DLA. Effects of UV radiation from young stellar populations in the galaxy, in particular in the photon energy range 10.36-13.61 eV (relating to Sulphur II abundance), are also considered in the analysis. It is found that (a) for L ˜ L⋆ galaxies (at z = 2.58), about 10 per cent of the sight-lines through the galaxies at impact parameter b = 16.2 kpc will display a Sulphur II column density of N({S II)} ≥ 10^{15.82} cm-2 (the observed value for the DLA), and (b) considering only cases where a near-solar metallicity will be detected at 16.2 kpc impact parameter, the (Bayesian) probability distribution of galaxy star formation rate peaks near the value observed for the DLA galaxy counterpart of 27^{+20}_{-9} { M_{⊙}} yr-1. It is argued that the bulk of the α-elements, like Sulphur, traced by the high metal column density, b = 16.2 kpc absorption lines, have been produced by evolving stars in the inner galaxy, and subsequently transported outwards by galactic winds.

  19. LOW-METALLICITY STAR FORMATION IN HIGH-REDSHIFT GALAXIES AT z {approx} 8

    SciTech Connect

    Taniguchi, Y.; Shioya, Y.; Trump, J. R.

    2010-12-01

    Based on the recent very deep near-infrared imaging of the Hubble Ultra Deep Field with WFC3 on the Hubble Space Telescope, five groups published the most probable samples of galaxies at z {approx} 8, selected by the so-called dropout method or photometric redshift; e.g., Y{sub 105}-dropouts (Y{sub 105} - J{sub 125} > 0.8). These studies are highly useful for investigating both the early star formation history of galaxies and the sources of cosmic re-ionization. In order to better understand these issues, we carefully examine whether there are low-z interlopers in the samples of z {approx} 8 galaxy candidates. We focus on the strong emission-line galaxies at z {approx} 2 in this paper. Such galaxies may be selected as Y{sub 105}-dropouts since the [O III] {lambda}5007 emission line is redshifted into the J{sub 125} band. We have found that the contamination from such low-z interlopers is negligibly small. Therefore, all objects found by the five groups are free from this type of contamination. However, it remains difficult to extract real z {approx} 8 galaxies because all the sources are very faint and the different groups have found different candidates. With this in mind, we construct a robust sample of eight galaxies at z {approx} 8 from the objects found by the five groups: each of these eight objects has been selected by at least two groups. Using this sample, we discuss their UV continuum slope. We also discuss the escape fraction of ionizing photons adopting various metallicities. Our analysis suggests that massive stars forming in low-metallicity gas (Z {approx} 5 x 10{sup -4} Z{sub sun}) can be responsible for the completion of cosmic re-ionization if the escape fraction of the ionizing continuum from galaxies is as large as 0.5, and this is consistent with the observed blue UV continua.

  20. The Low-Metallicity Galaxy, I Zw 18 (Z=1/50 Z(circle dot))

    NASA Technical Reports Server (NTRS)

    Heap, Sara R.

    2003-01-01

    Both observations and evolutionary models indicate that rotation becomes a more important factor at lower metallicities. Some important effects of rotation include: increasing the rate of mass-loss; lowering the effective gravity; altering the evolutionary track on the Hertzsprung-Russell Diagram (HRD); extending the main-sequence phase (both on the HR diagram and in time); and mixing of CNO-processed elements up to the stellar surface. We discuss these effects for massive stars in the low-metallicity galaxy, I Zw 18 (Z=1/50 Z(circle dot)) and their implications for the first stars.

  1. The Metallicity Evolution of Low-mass Galaxies: New Constraints at Intermediate Redshift

    NASA Astrophysics Data System (ADS)

    Henry, Alaina; Martin, Crystal L.; Finlator, Kristian; Dressler, Alan

    2013-06-01

    We present abundance measurements from 26 emission-line-selected galaxies at z ~ 0.6-0.7. By reaching stellar masses as low as 108 M ⊙, these observations provide the first measurement of the intermediate-redshift mass-metallicity (MZ) relation below 109 M ⊙. For the portion of our sample above M > 109 M ⊙ (8/26 galaxies), we find good agreement with previous measurements of the intermediate-redshift MZ relation. Compared to the local relation, we measure an evolution that corresponds to a 0.12 dex decrease in oxygen abundances at intermediate redshifts. This result confirms the trend that metallicity evolution becomes more significant toward lower stellar masses, in keeping with a downsizing scenario where low-mass galaxies evolve onto the local MZ relation at later cosmic times. We show that these galaxies follow the local fundamental metallicity relation, where objects with higher specific (mass-normalized) star formation rates (SFRs) have lower metallicities. Furthermore, we show that the galaxies in our sample lie on an extrapolation of the SFR-M * relation (the star-forming main sequence). Leveraging the MZ relation and star-forming main sequence (and combining our data with higher-mass measurements from the literature), we test models that assume an equilibrium between mass inflow, outflow, and star formation. We find that outflows are required to describe the data. By comparing different outflow prescriptions, we show that momentum, driven winds can describe the MZ relation; however, this model underpredicts the amount of star formation in low-mass galaxies. This disagreement may indicate that preventive feedback from gas heating has been overestimated, or it may signify a more fundamental deviation from the equilibrium assumption. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National

  2. Revealing the cold dust in low-metallicity environments. I. Photometry analysis of the Dwarf Galaxy Survey with Herschel

    NASA Astrophysics Data System (ADS)

    Rémy-Ruyer, A.; Madden, S. C.; Galliano, F.; Hony, S.; Sauvage, M.; Bendo, G. J.; Roussel, H.; Pohlen, M.; Smith, M. W. L.; Galametz, M.; Cormier, D.; Lebouteiller, V.; Wu, R.; Baes, M.; Barlow, M. J.; Boquien, M.; Boselli, A.; Ciesla, L.; De Looze, I.; Karczewski, O. Ł.; Panuzzo, P.; Spinoglio, L.; Vaccari, M.; Wilson, C. D.

    2013-09-01

    Context. We present new photometric data from our Herschel guaranteed time key programme, the Dwarf Galaxy Survey (DGS), dedicated to the observation of the gas and dust in low-metallicity environments. A total of 48 dwarf galaxies were observed with the PACS and SPIRE instruments onboard the Herschel Space Observatory at 70, 100, 160, 250, 350, and 500 μm. Aims: The goal of this paper is to provide reliable far-infrared (FIR) photometry for the DGS sample and to analyse the FIR/submillimetre (submm) behaviour of the DGS galaxies. We focus on a systematic comparison of the derived FIR properties (FIR luminosity, LFIR, dust mass, Mdust, dust temperature, T, emissivity index, β) with more metal-rich galaxies and investigate the detection of a potential submm excess. Methods: The data reduction method is adapted for each galaxy in order to derive the most reliable photometry from the final maps. The derived PACS flux densities are compared with the Spitzer MIPS 70 and 160 μm bands. We use colour-colour diagrams to analyse the FIR/submm behaviour of the DGS galaxies and modified blackbody fitting procedures to determine their dust properties. To study the variation in these dust properties with metallicity, we also include galaxies from the Herschel KINGFISH sample, which contains more metal-rich environments, totalling 109 galaxies. Results: The location of the DGS galaxies on Herschel colour-colour diagrams highlights the differences in dust grain properties and/or global environments of low-metallicity dwarf galaxies. The dust in DGS galaxies is generally warmer than in KINGFISH galaxies (TDGS ~ 32 K and TKINGFISH ~ 23 K). The emissivity index, β, is ~1.7 in the DGS, however metallicity does not make a strong effect on β. The proportion of dust mass relative to stellar mass is lower in low-metallicity galaxies: Mdust/Mstar ~ 0.02% for the DGS versus 0.1% for KINGFISH. However, per unit dust mass, dwarf galaxies emit about six times more in the FIR/submm than

  3. CARBON-RICH DUST PRODUCTION IN METAL-POOR GALAXIES IN THE LOCAL GROUP

    SciTech Connect

    Sloan, G. C.; Matsuura, M.; Lagadec, E.; Van Loon, J. Th.; Kraemer, K. E.; McDonald, I.; Zijlstra, A. A.; Groenewegen, M. A. T.; Wood, P. R.; Bernard-Salas, J.

    2012-06-20

    We have observed a sample of 19 carbon stars in the Sculptor, Carina, Fornax, and Leo I dwarf spheroidal galaxies with the Infrared Spectrograph on the Spitzer Space Telescope. The spectra show significant quantities of dust around the carbon stars in Sculptor, Fornax, and Leo I, but little in Carina. Previous comparisons of carbon stars with similar pulsation properties in the Galaxy and the Magellanic Clouds revealed no evidence that metallicity affected the production of dust by carbon stars. However, the more metal-poor stars in the current sample appear to be generating less dust. These data extend two known trends to lower metallicities. In more metal-poor samples, the SiC dust emission weakens, while the acetylene absorption strengthens. The bolometric magnitudes and infrared spectral properties of the carbon stars in Fornax are consistent with metallicities more similar to carbon stars in the Magellanic Clouds than in the other dwarf spheroidals in our sample. A study of the carbon budget in these stars reinforces previous considerations that the dredge-up of sufficient quantities of carbon from the stellar cores may trigger the final superwind phase, ending a star's lifetime on the asymptotic giant branch.

  4. A support vector machine to search for metal-poor galaxies

    NASA Astrophysics Data System (ADS)

    Shi, Fei; Liu, Yu-Yan; Kong, Xu; Chen, Yang; Li, Zhong-Hua; Zhi, Shu-Teng

    2014-10-01

    To develop a fast and reliable method for selecting metal-poor galaxies (MPGs), especially in large surveys and huge data bases, a support vector machine (SVM) supervized learning algorithms is applied to a sample of star-forming galaxies from the Sloan Digital Sky Survey data release 9 provided by the Max Planck Institute and the Johns Hopkins University (http://www.sdss3.org/dr9/spectro/spectroaccess.php). A two-step approach is adopted: (i) the SVM must be trained with a subset of objects that are known to be either MPGs or metal-rich galaxies (MRGs), treating the strong emission line flux measurements as input feature vectors in n-dimensional space, where n is the number of strong emission line flux ratios. (ii) After training on a sample of star-forming galaxies, the remaining galaxies are classified in the automatic test analysis as either MPGs or MRGs using a 10-fold cross-validation technique. For target selection, we have achieved an acquisition accuracy for MPGs of ˜96 and ˜95 per cent for an MPG threshold of 12 + log(O/H) = 8.00 and 12 + log(O/H) = 8.39, respectively. Running the code takes minutes in most cases under the MATLAB 2013a software environment. The code in the Letter is available on the web (http://fshi5388.blog.163.com). The SVM method can easily be extended to any MPGs target selection task and can be regarded as an efficient classification method particularly suitable for modern large surveys.

  5. Missing metals and baryons in galaxies: Clues from our Milky Way

    NASA Astrophysics Data System (ADS)

    Gupta, Anjali; Mathur, Smita

    2016-06-01

    It is well-known that most galaxies are missing most of their baryonic mass. Perhaps more surprisingly, they also seem to be missing most of their metals. Our Milky Way galaxy, like other nearby galaxies, is missing most of its baryons. Cosmological simulations of galaxy formation suggest that the missing baryonic mass should reside in the circum-galactic medium (CGM), in a warm-hot gas phase at temperatures between one million and 10 million K. Although theoretical models predict the existence of the warm-hot gas in the CGM, detecting and characterizing the diffuse CGM has been difficult. At the expected temperatures the baryons are in the form of highly ionized plasma, observable in soft X-rays. A combination of absorption and emission studies at soft X-ray energies is required to fully characterize this warm-hot CGM. Recently, combining the Chandra observations of OVII and OVIII absorption lines and XMM-Newton and Suzaku measurements of the Galactic halo emission measure, we found that there is a huge reservoir of ionized gas around the Milky Way, with the mass of over 2 billion solar masses and the radius of over 100 kpc.I will present Chandra, XMM-Newton and Suzaku observations probing our Milky Way halo in absorption and emission. Our results show that the Milky Way halo contains a huge reservoir of warm-hot gas that may account for a large fraction of missing baryons and metals. I'll review current status of this field, discuss implications of our results to models of galaxy formation and evolution and outline paths for future progress.

  6. Missing metals and baryons in galaxies: Clues from our Milky Way

    NASA Astrophysics Data System (ADS)

    Gupta, Anjali

    2016-04-01

    It is well-known that most galaxies are missing most of their baryonic mass. Perhaps more surprisingly, they also seem to be missing most of their metals. Our Milky Way galaxy, like other nearby galaxies, is missing most of its baryons. Cosmological simulations of galaxy formation suggest that the missing baryonic mass should reside in the circum-galactic medium (CGM), in a warm-hot gas phase at temperatures between one million and 10 million K. Although theoretical models predict the existence of the warm-hot gas in the CGM, detecting and characterizing the diffuse CGM has been difficult. At the expected temperatures the baryons are in the form of highly ionized plasma, observable in soft X-rays. A combination of absorption and emission studies at soft X-ray energies is required to fully characterize this warm-hot CGM. Recently, combining the Chandra observations of OVII and OVIII absorption lines and XMM-Newton and Suzaku measurements of the Galactic halo emission measure, we found that there is a huge reservoir of ionized gas around the Milky Way, with the mass of over 2 billion solar masses and the radius of over 100 kpc.I will present Chandra, XMM-Newton and Suzaku observations probing our Milky Way halo in absorption and emission. Our results show that the Milky Way halo contains a huge reservoir of warm-hot gas that may account for a large fraction of missing baryons and metals. I'll review current status of this field, discuss implications of our results to models of galaxy formation and evolution and outline paths for future progress.

  7. The Deep2 Galaxy Redshift Survey: Mean Ages and Metallicities ofRed Field Galaxies at Z ~; 0.9 from Stacked Keck/Deimos Spectra

    SciTech Connect

    Schiavon, Ricardo P.; Faber, S.M.; Konidaris, Nicholas; Graves,Genevieve; Willmer, Christopher N.A.; Weiner, Benjamin J.; Coil, AlisonL.; Cooper, Michael C.; Davis, Marc; Harker, Justin; Koo, David C.; Newman, Jeffrey A.; Yan, Renbin

    2006-10-19

    As part of the DEEP2 galaxy redshift survey, we analyze absorption line strengths in stacked Keck/DEIMOS spectra of red field galaxies with weak to no emission lines, at redshifts 0.7 {approx}< z {approx}< 1. Comparison with models of stellar population synthesis shows that red galaxies at z {approx} 0:9 have mean luminosity-weighted ages of the order of only 1 Gyr and at least solar metallicities. These ages cannot be reconciled with a scenario where all stars evolved passively after forming at very high z. Rather, a significant fraction of stars can be no more than 1 Gyr old, which means that some star formation in the stacked populations continued to at least z {approx} 1:2. Furthermore, a comparison of these distant galaxies with a local SDSS sample, using stellar populations synthesis models, shows that the drop in the equivalent width of H{delta} from z {approx} 0:9 to 0.1 is less than predicted by passively evolving models. This admits of two interpretations: either each individual galaxy experiences continuing low-level star formation, or the red-sequence galaxy population from z {approx} 0:9 to 0.1 is continually being added to by new galaxies with younger stars.

  8. The SAMI Galaxy Survey: the discovery of a luminous, low-metallicity H II complex in the dwarf galaxy GAMA J141103.98-003242.3

    NASA Astrophysics Data System (ADS)

    Richards, S. N.; Schaefer, A. L.; López-Sánchez, Á. R.; Croom, S. M.; Bryant, J. J.; Sweet, S. M.; Konstantopoulos, I. S.; Allen, J. T.; Bland-Hawthorn, J.; Bloom, J. V.; Brough, S.; Fogarty, L. M. R.; Goodwin, M.; Green, A. W.; Ho, I.-T.; Kewley, L. J.; Koribalski, B. S.; Lawrence, J. S.; Owers, M. S.; Sadler, E. M.; Sharp, R.

    2014-12-01

    We present the discovery of a luminous unresolved H II complex on the edge of dwarf galaxy GAMA J141103.98-003242.3 using data from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. This dwarf galaxy is situated at a distance of ˜100 Mpc and contains an unresolved region of H II emission that contributes ˜70 per cent of the galaxy's Hα luminosity, located at the top end of established H II region luminosity functions. For the H II complex, we measure a star formation rate of 0.147 ± 0.041 M⊙ yr-1and a metallicity of 12+log(O/H) = 8.01 ± 0.05 that is lower than the rest of the galaxy by ˜0.2 dex. Data from the H I Parkes All-Sky Survey (HIPASS) indicate the likely presence of neutral hydrogen in the galaxy to potentially fuel ongoing and future star-forming events. We discuss various triggering mechanisms for the intense star formation activity of this H II complex, where the kinematics of the ionized gas are well described by a rotating disc and do not show any features indicative of interactions. We show that SAMI is an ideal instrument to identify similar systems to GAMA J141103.98-003242.3, and the SAMI Galaxy Survey is likely to find many more of these systems to aid in the understanding of their formation and evolution.

  9. Spectral Line Survey toward a Molecular Cloud in IC10

    NASA Astrophysics Data System (ADS)

    Nishimura, Yuri; Shimonishi, Takashi; Watanabe, Yoshimasa; Sakai, Nami; Aikawa, Yuri; Kawamura, Akiko; Yamamoto, Satoshi

    2016-10-01

    We have conducted a spectral line survey observation in the 3 mm band toward the low-metallicity dwarf galaxy IC10 with the 45 m radio telescope of the Nobeyama Radio Observatory to explore its chemical composition at a molecular-cloud scale (∼80 pc). The CS, SO, CCH, HCN, HCO+, and HNC lines are detected for the first time in this galaxy in addition to the CO and 13CO lines, while the c-C3H2, CH3OH, CN, C18O, and N2H+ lines are not detected. The spectral intensity pattern is found to be similar to those observed toward molecular clouds in the Large Magellanic Cloud (LMC), whose metallicity is as low as IC10. Nitrogen-bearing species are deficient in comparison with the Galactic molecular clouds due to a lower elemental abundance of nitrogen. CCH is abundant in comparison with Galactic translucent clouds, whereas CH3OH may be deficient. These characteristic trends for CCH and CH3OH are also seen in the LMC, and seem to originate from photodissociation regions more extended in the peripheries of molecular clouds due to the lower metallicity condition.

  10. FORMATION OF METAL-POOR GLOBULAR CLUSTERS IN Ly{alpha} EMITTING GALAXIES IN THE EARLY UNIVERSE

    SciTech Connect

    Elmegreen, Bruce G.; Malhotra, Sangeeta; Rhoads, James

    2012-09-20

    The size, mass, luminosity, and space density of Ly{alpha} emitting (LAE) galaxies observed at intermediate to high redshift agree with expectations for the properties of galaxies that formed metal-poor halo globular clusters (GCs). The low metallicity of these clusters is the result of their formation in low-mass galaxies. Metal-poor GCs could enter spiral galaxies along with their dwarf galaxy hosts, unlike metal-rich GCs, which form in the spirals themselves. Considering an initial GC mass larger than the current mass to account for multiple stellar populations, and considering the additional clusters that are likely to form with massive clusters, we estimate that each GC with a mass today greater than 2 Multiplication-Sign 10{sup 5} M{sub Sun} was likely to have formed among a total stellar mass {approx}> 3 Multiplication-Sign 10{sup 7} M{sub Sun }, a molecular mass {approx}> 10{sup 9} M{sub Sun }, and 10{sup 7} to 10{sup 9} M{sub Sun} of older stars, depending on the relative gas fraction. The star formation rate would have been several M{sub Sun} yr{sup -1} lasting for {approx}10{sup 7} yr, and the Ly{alpha} luminosity would have been {approx}> 10{sup 42} erg s{sup -1}. Integrating the LAE galaxy luminosity function above this minimum, considering the average escape probability for Ly{alpha} photons (25%), and then dividing by the probability that a dwarf galaxy is observed in the LAE phase (0.4%), we find agreement between the comoving space density of LAEs and the average space density of metal-poor GCs today. The local galaxy WLM, with its early starburst and old GC, could be an LAE remnant that did not get into a galaxy halo because of its remote location.

  11. Spatially resolved optical and near-infrared spectroscopy of the low-metallicity galaxy UGC 4483

    NASA Technical Reports Server (NTRS)

    Skillman, Evan D.; Televich, Roberto J.; Kennicutt, Robert C., Jr.; Garnett, Donald R.; Terlevich, Elena

    1994-01-01

    UGC 4483 is a dwarf irregular galaxy in the M81 group. Narrow-band imaging has revealed an H II region in UGC 4483 with an H alpha flux approximately = 1 x 10 (exp - 13) ergs/sq cm/s. Optical and near-infrared spectroscopy of this H ll region yields He, N, O, Ne, and S abundances for the interstellar matter (ISM) in this galaxy. The spectra were acquired with several different telescope/instrument combinations in order to assess the quality of the derived uncertainties. With oxygen abundance of 3.3 x 10 (exp -5) (12 + log (O/H) = 7.5), this galaxy is similar to GR 8 and among the most metal poor dwarf irregulars known to date. However, the H II region in UGC 4483 has high excitation and higher surface brightness than GR 8, allowing very accurate abundance estimates. The N/O ratio is 3%, in good agreement with other low-metallicity dwarf galaxies. The S/O abundance ratio in UGC 4483 is close to the solar ratio, consistent with results for I Zw 18 and other low-metallicity dwarf irregulars. A He/H abundance of 0.079 +/- 0.002 is derived from observations of the lambda 6678 He ll emission line. A comparison of observations obtained with different telescopes and with the same telescope on different nights supports our relatively small estimated uncertainty in this measurement. We determine that the neutral helium fraction is insignificant through both direct observations of the He(+)/H(+) ratio across the nebula and through photoionization modeling. This results in a helium mass fraction of 0.239 +/- 0.006, consistent with the most recent theoretical and observational determinations of the primordial helium abundance. We also discuss remaining systematic uncertainties in the calculation of the primordial helium abundance

  12. On the Metal Aversion of LGRBs

    NASA Astrophysics Data System (ADS)

    Graham, John; Fruchter, A.; Levesque, E.; L., K.; J., B.; Levan, A.; Tanvir, N.; Patel, S.; Aldering, G.; Perlmutter, S.; Misra, K.; Huang, K.; Reichart, D.; Nysewander, M.

    2012-01-01

    We discuss recent observations of several high metallicity LGRBs hosts. We then compare the entire population of LGRB hosts with measured metallicities to the hosts of Type II and broad-lined Type Ic SNe as well as the star-forming SDSS galaxy population using several methods of analysis. We argue that even though a few LGRBs do lie in fairly metal rich hosts, the general population of LGRB hosts is surprisingly metal poor, and that metallicity must be an important factor in the formation of LGRBs. Finally we conclude with a discussion of the potential importance and practicality of obtaining spatiality resolved metallicity measurement of LGRB host galaxies.

  13. Detailed Abundances of Two Very Metal-poor Stars in Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Kirby, Evan N.; Cohen, Judith G.

    2012-12-01

    The most metal-poor stars in dwarf spheroidal galaxies (dSphs) can show the nucleosynthetic patterns of one or a few supernovae (SNe). These SNe could have zero metallicity, making metal-poor dSph stars the closest surviving links to Population III stars. Metal-poor dSph stars also help to reveal the formation mechanism of the Milky Way (MW) halo. We present the detailed abundances from Keck/HIRES spectroscopy for two very metal-poor stars in two MW dSphs. One star, in the Sculptor dSph, has [Fe I/H] = -2.40. The other star, in the Ursa Minor dSph, has [Fe I/H] = -3.16. Both stars fall in the previously discovered low-metallicity, high-[α/Fe] plateau. Most abundance ratios of very metal-poor stars in these two dSphs are largely consistent with very metal-poor halo stars. However, the abundances of Na and some r-process elements lie at the lower end of the envelope defined by inner halo stars of similar metallicity. We propose that the metallicity dependence of SN yields is the cause. The earliest SNe in low-mass dSphs have less gas to pollute than the earliest SNe in massive halo progenitors. As a result, dSph stars at -3 < [Fe/H] < -2 sample SNe with [Fe/H] Lt -3, whereas halo stars in the same metallicity range sample SNe with [Fe/H] ~ -3. Consequently, enhancements in [Na/Fe] and [r/Fe] were deferred to higher metallicity in dSphs than in the progenitors of the inner halo. Data herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  14. A CENSUS OF OXYGEN IN STAR-FORMING GALAXIES: AN EMPIRICAL MODEL LINKING METALLICITIES, STAR FORMATION RATES, AND OUTFLOWS

    SciTech Connect

    Zahid, H. J.; Dima, G. I.; Kewley, L. J.; Erb, D. K.; Dave, R.

    2012-09-20

    In this contribution, we present the first census of oxygen in star-forming galaxies in the local universe. We examine three samples of galaxies with metallicities and star formation rates (SFRs) at z = 0.07, 0.8, and 2.26, including the Sloan Digital Sky Survey (SDSS) and DEEP2 survey. We infer the total mass of oxygen produced and mass of oxygen found in the gas-phase from our local SDSS sample. The star formation history is determined by requiring that galaxies evolve along the relation between stellar mass and SFR observed in our three samples. We show that the observed relation between stellar mass and SFR for our three samples is consistent with other samples in the literature. The mass-metallicity relation is well established for our three samples, and from this we empirically determine the chemical evolution of star-forming galaxies. Thus, we are able to simultaneously constrain the SFRs and metallicities of galaxies over cosmic time, allowing us to estimate the mass of oxygen locked up in stars. Combining this work with independent measurements reported in the literature, we conclude that the loss of oxygen from the interstellar medium of local star-forming galaxies is likely to be a ubiquitous process with the oxygen mass loss scaling (almost) linearly with stellar mass. We estimate the total baryonic mass loss and argue that only a small fraction of the baryons inferred from cosmological observations accrete onto galaxies.

  15. ON THE DEPENDENCE OF TYPE Ia SNe LUMINOSITIES ON THE METALLICITY OF THEIR HOST GALAXIES

    SciTech Connect

    Moreno-Raya, Manuel E.; Mollá, Mercedes; López-Sánchez, Ángel R.; Galbany, Lluís; Vílchez, José Manuel; Rosell, Aurelio Carnero; Domínguez, Inmaculada

    2016-02-10

    The metallicity of the progenitor system producing a type Ia supernova (SN Ia) could play a role in its maximum luminosity, as suggested by theoretical predictions. We present an observational study to investigate if such a relationship exists. Using the 4.2 m William Herschel Telescope (WHT) we have obtained intermediate-resolution spectroscopy data of a sample of 28 local galaxies hosting SNe Ia, for which distances have been derived using methods independent of those based on SN Ia parameters. From the emission lines observed in their optical spectra, we derived the gas-phase oxygen abundance in the region where each SN Ia exploded. Our data show a trend, with an 80% of chance not being due to random fluctuation, between SNe Ia absolute magnitudes and the oxygen abundances of the host galaxies, in the sense that luminosities tend to be higher for galaxies with lower metallicities. This result seems likely to be in agreement with both the theoretically expected behavior and with other observational results. This dependence M{sub B}–Z might induce systematic errors when it is not considered when deriving SNe Ia luminosities and then using them to derive cosmological distances.

  16. On the Dependence of Type Ia SNe Luminosities on the Metallicity of Their Host Galaxies

    NASA Astrophysics Data System (ADS)

    Moreno-Raya, Manuel E.; Mollá, Mercedes; López-Sánchez, Ángel R.; Galbany, Lluís; Vílchez, José Manuel; Carnero Rosell, Aurelio; Domínguez, Inmaculada

    2016-02-01

    The metallicity of the progenitor system producing a type Ia supernova (SN Ia) could play a role in its maximum luminosity, as suggested by theoretical predictions. We present an observational study to investigate if such a relationship exists. Using the 4.2 m William Herschel Telescope (WHT) we have obtained intermediate-resolution spectroscopy data of a sample of 28 local galaxies hosting SNe Ia, for which distances have been derived using methods independent of those based on SN Ia parameters. From the emission lines observed in their optical spectra, we derived the gas-phase oxygen abundance in the region where each SN Ia exploded. Our data show a trend, with an 80% of chance not being due to random fluctuation, between SNe Ia absolute magnitudes and the oxygen abundances of the host galaxies, in the sense that luminosities tend to be higher for galaxies with lower metallicities. This result seems likely to be in agreement with both the theoretically expected behavior and with other observational results. This dependence MB-Z might induce systematic errors when it is not considered when deriving SNe Ia luminosities and then using them to derive cosmological distances.

  17. THE DYNAMICS AND METALLICITY DISTRIBUTION OF THE DISTANT DWARF GALAXY VV124

    SciTech Connect

    Kirby, Evan N.; Cohen, Judith G.; Bellazzini, Michele

    2012-05-20

    VV124 (UGC 4879) is an isolated, dwarf irregular/dwarf spheroidal (dIrr/dSph) transition-type galaxy at a distance of 1.36 Mpc. Previous low-resolution spectroscopy yielded inconsistent radial velocities for different components of the galaxy, and photometry hinted at the presence of a stellar disk. In order to quantify the stellar dynamics, we observed individual red giants in VV124 with the Keck/Deep Extragalactic Imaging Multi-Object Spectrograph (DEIMOS). We validated members based on their positions in the color-magnitude diagram, radial velocities, and spectral features. Our sample contains 67 members. The average radial velocity is (v{sub r} ) = -29.1 {+-} 1.3 km s{sup -1} in agreement with the previous radio measurements of H I gas. The velocity distribution is Gaussian, indicating that VV124 is supported primarily by velocity dispersion inside a radius of 1.5 kpc. Outside that radius, our measurements provide only an upper limit of 8.6 km s{sup -1} on any rotation in the photometric disk-like feature. The velocity dispersion is {sigma}{sub v} = 9.4 {+-} 1.0 km s{sup -1}, from which we inferred a mass of M{sub 1/2} = (2.1 {+-} 0.2) Multiplication-Sign 10{sup 7} M{sub Sun} and a mass-to-light ratio of (M/L{sub V} ){sub 1/2} = 5.2 {+-} 1.1 M{sub Sun }/L{sub Sun }, both measured within the half-light radius. Thus, VV124 contains dark matter. We also measured the metallicity distribution from neutral iron lines. The average metallicity, ([Fe/H]) = -1.14 {+-} 0.06, is consistent with the mass-metallicity relation defined by dSph galaxies. The dynamics and metallicity distribution of VV124 appear similar to dSphs of similar stellar mass.

  18. CORE-COLLAPSE SUPERNOVAE AND HOST GALAXY STELLAR POPULATIONS

    SciTech Connect

    Kelly, Patrick L.; Kirshner, Robert P.

    2012-11-10

    We have used images and spectra of the Sloan Digital Sky Survey to examine the host galaxies of 519 nearby supernovae (SN). The colors at the sites of the explosions, as well as chemical abundances, and specific star formation rates (SFRs) of the host galaxies provide circumstantial evidence on the origin of each SN type. We examine separately SN II, SN IIn, SN IIb, SN Ib, SN Ic, and SN Ic with broad lines (SN Ic-BL). For host galaxies that have multiple spectroscopic fibers, we select the fiber with host radial offset most similar to that of the SN. Type Ic SN explode at small host offsets, and their hosts have exceptionally strongly star-forming, metal-rich, and dusty stellar populations near their centers. The SN Ic-BL and SN IIb explode in exceptionally blue locations, and, in our sample, we find that the host spectra for SN Ic-BL show lower average oxygen abundances than those for SN Ic. SN IIb host fiber spectra are also more metal-poor than those for SN Ib, although a significant difference exists for only one of two strong-line diagnostics. SN Ic-BL host galaxy emission lines show strong central specific SFRs. In contrast, we find no strong evidence for different environments for SN IIn compared to the sites of SN II. Because our SN sample is constructed from a variety of sources, there is always a risk that sampling methods can produce misleading results. We have separated the SN discovered by targeted surveys from those discovered by galaxy-impartial searches to examine these questions and show that our results do not depend sensitively on the discovery technique.

  19. First Detection of a Cluster-scale Gradient in the ISM metallicity of the Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Gupta, Anshu; Yuan, Tiantian; Tran, Kim-Vy; Martizzi, Davide; Taylor, Philip; Kewley, Lisa J.

    2017-01-01

    Understanding the effect of cluster environment on galaxy formation and evolution is a central topic in extragalactic astronomy. The interstellar medium (ISM) metallicity provides a powerful constraint on the complex interplay of star formation and the galactic inflow/outflow. Disentangling the effect of internal (stellar mass) and external (environment) processes on galaxy evolution is difficult because high mass galaxies tend to exist in dense environments. For the past decade, the difference between mass-metallicity relations in the cluster and field environment have been used to disentangle the effect of internal/external processes. Current observations of the mass-metallicity relation show minimal dependence on the large-scale environment. In this talk, I will present the radial distribution of ISM metallicity in galaxy clusters as an alternative method to study the impact of environment on galaxy evolution. I will present the first observation of cluster-scale negative abundance gradients in two CLASH clusters at z~0.35: MACS1115+0129 and RXJ1532+3021. Our observation presents the highest metallicity enhancement observed in a galaxy cluster on the mass-metallicity relation to date. Most strikingly, we discover that neither the radial metallicity gradient nor the offset on the mass-metallicity relation show any obvious dependence on the stellar mass of cluster members. I will discuss the different physical processes in the cluster environment such as disk truncation due to ram-pressure stripping and self-enrichment due to strangulation that can lead to the observed cluster-scale negative abundance gradient in ISM metallicity.In our follow-up work, we have performed simulations of the disk-truncation in cluster environment using a sample of CALIFA galaxies. Our analytical model of disk-truncation is based on the ram-pressure stripping of the cold gas component of the infalling galaxy in the cluster environment. I will present the simulated radial metallicity

  20. The metallicity dependence of the long-duration gamma-ray burst rate from host galaxy luminosities

    NASA Astrophysics Data System (ADS)

    Wolf, Christian; Podsiadlowski, Philipp

    2007-03-01

    We investigate the difference between the host galaxy properties of core-collapse supernovae (CC SNe) and long-duration gamma-ray bursts (LGRBs), and quantify a possible metallicity dependence of the efficiency of producing LGRBs. We use a sample of 16 CC SNe and 16 LGRBs from Fruchter et al. which have similar redshift distributions to eliminate galaxy evolution biases. We make a forward prediction of their host galaxy luminosity distributions from the overall cosmic metallicity distribution of star formation. The latter is based on luminosity functions, star formation rates (SFRs) and luminosity-metallicity (L-Z) relations of galaxies. This approach is supported by the finding that LGRB hosts follow the L-Z relations of star-forming galaxies. We then compare predictions for metallicity-dependent event efficiencies with the observed host data. We find that ultraviolet-based SFR estimates predict the host distribution of CC SNe perfectly well in a metallicity-independent form. In contrast, LGRB hosts are on average fainter by one magnitude, almost as faint as the Large Magellanic Cloud. Assuming this to be a metallicity effect, the present data are insufficient to discriminate between a sharp cut-off and a soft decrease in efficiency towards higher metallicity. For a sharp cut-off, however, we find a best value for the cut-off metallicity, as reflected in the oxygen abundance, 12 + log(O/H)lim ~= 8.7 +/- 0.3 at 95 per cent confidence including systematic uncertainties, in the calibration of Asplund, Grevesse & Sauval. This value is somewhat lower than the traditionally quoted value for the Sun, but is comparable to the revised solar oxygen abundance. LGRB models that require sharp metallicity cut-offs well below approximately one-half the revised solar metallicity appear to be effectively ruled out, as they would require fainter LGRB hosts than those that are observed. We also discuss the likely implications of the still ongoing metallicity `calibration debate'.

  1. The GRB 030329 host: a blue low metallicity subluminous galaxy with intense star formation

    NASA Astrophysics Data System (ADS)

    Gorosabel, J.; Pérez-Ramírez, D.; Sollerman, J.; de Ugarte Postigo, A.; Fynbo, J. P. U.; Castro-Tirado, A. J.; Jakobsson, P.; Christensen, L.; Hjorth, J.; Jóhannesson, G.; Guziy, S.; Castro Cerón, J. M.; Björnsson, G.; Sokolov, V. V.; Fatkhullin, T. A.; Nilsson, K.

    2005-12-01

    We present broad band photometry and spectroscopic observations of the host galaxy of GRB 030329. Analysis of the spectral emission lines shows that the host is likely a low metallicity galaxy (Z˜0.004). The spectral energy distribution (SED) constructed with the photometric points has been fitted using synthetic and observational templates. The best SED fit is obtained with a starburst template with an age of 150 Myr and an extinction Av ˜ 0.6. We find that the GRB 030329 host galaxy is a subluminous galaxy (L ˜ 0.016 Lstar) with a stellar mass of ≳ 108 M⊙. Three independent diagnostics, based on the restframe UV continuum, the [O II], and the Balmer emission lines, provide a consistent unextinguished star formation rate of ˜ 0.6 M⊙ yr-1, implying a high unextinguished specific star formation rate ( 34 M⊙ yr-1 (L/Lstar)-1). We estimate that the unextinguished specific star formation rate of the GRB 030329 host is higher than 93.5% of the galaxies at a similar redshift. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. Based on data taken at the 2.2-m and 3.5-m telescopes of the Centro Astronómico Hispano Alemán de Calar Alto, operated by the Max Planck institute of Heidelberg and Centro Superior de Investigaciones Científicas. The spectral observations were obtained at the European Southern Observatory, Cerro Paranal (Chile), under the Director's Discretionary Time programme 271.D-5006(A).

  2. Gravitational Wave Background from Binary Mergers and Metallicity Evolution of Galaxies

    NASA Astrophysics Data System (ADS)

    Nakazato, Ken'ichiro; Niino, Yuu; Sago, Norichika

    2016-12-01

    The cosmological evolution of the binary black hole (BH) merger rate and the energy density of the gravitational wave (GW) background are investigated. To evaluate the redshift dependence of the BH formation rate, BHs are assumed to originate from low-metallicity stars, and the relations between the star formation rate, metallicity and stellar mass of galaxies are combined with the stellar mass function at each redshift. As a result, it is found that when the energy density of the GW background is scaled with the merger rate at the local universe, the scaling factor does not depend on the critical metallicity for the formation of BHs. Also taking into account the merger of binary neutron stars, a simple formula to express the energy spectrum of the GW background is constructed for the inspiral phase. The relation between the local merger rate and the energy density of the GW background will be examined by future GW observations.

  3. Children and IC

    MedlinePlus

    ... well as his or her teachers, principal, school nurse, gym teacher, etc. Your child’s symptoms may be ... Out IC How to Schedule an IC Advocacy District Visit IC Advocates in Action Spur Research Funding ...

  4. Pregnancy and IC

    MedlinePlus

    ... hospital personnel (such as medical students or student nurses) to observe your birth process Whether you will ... Out IC How to Schedule an IC Advocacy District Visit IC Advocates in Action Spur Research Funding ...

  5. DETECTION OF A DISTINCT METAL-POOR STELLAR HALO IN THE EARLY-TYPE GALAXY NGC 3115

    SciTech Connect

    Peacock, Mark B.; Strader, Jay; Romanowsky, Aaron J.; Brodie, Jean P.

    2015-02-10

    We present the resolved stellar populations in the inner and outer halo of the nearby lenticular galaxy NGC 3115. Using deep Hubble Space Telescope observations, we analyze stars 2 mag fainter than the tip of the red giant branch (TRGB). We study three fields along the minor axis of this galaxy, 19, 37, and 54 kpc from its center—corresponding to 7, 14, and 21 effective radii (r{sub e} ). Even at these large galactocentric distances, all of the fields are dominated by a relatively enriched population, with the main peak in the metallicity distribution decreasing with radius from [Z/H] ∼ –0.5 to –0.65. The fraction of metal-poor stars ([Z/H] < –0.95) increases from 17% at 16-37 kpc to 28% at ∼54 kpc. We observe a distinct low-metallicity population (peaked at [Z/H] ∼ –1.3 and with total mass 2 × 10{sup 10} M {sub ☉} ∼ 14% of the galaxy's stellar mass) and argue that this represents the detection of an underlying low-metallicity stellar halo. Such halos are generally predicted by galaxy formation theories and have been observed in several late-type galaxies, including the Milky Way and M31. The metallicity and spatial distribution of the stellar halo of NGC 3115 are consistent with the galaxy's globular cluster system, which has a similar low-metallicity population that becomes dominant at these large radii. This finding supports the use of globular clusters as bright chemodynamical tracers of galaxy halos. These data also allow us to make a precise measurement of the magnitude of the TRGB, from which we derive a distance modulus of NGC 3115 of 30.05 ± 0.05 ± 0.10{sub sys} (10.2 ± 0.2 ± 0.5{sub sys} Mpc)

  6. The physical conditions, metallicity and metal abundance ratios in a highly magnified galaxy at z = 3.6252

    SciTech Connect

    Bayliss, Matthew B.; Rigby, Jane R.; Sharon, Keren; Johnson, Traci; Wuyts, Eva; Florian, Michael; Gladders, Michael D.; Oguri, Masamune

    2014-08-01

    We present optical and near-IR imaging and spectroscopy of SGAS J105039.6+001730, a strongly lensed galaxy at z = 3.6252 magnified by >30×, and derive its physical properties. We measure a stellar mass of log(M{sub *}/M{sub ☉}) = 9.5 ± 0.35, star formation rates from [O II] λλ3727 and Hβ of 55 ± 25 and 84 ± 24 M{sub ☉} yr{sup –1}, respectively, an electron density of n{sub e} ≤ 10{sup 3} cm{sup –2}, an electron temperature of T{sub e} ≤ 14,000 K, and a metallicity of 12 + log(O/H) = 8.3 ± 0.1. The strong C III] λλ1907,1909 emission and abundance ratios of C, N, O, and Si are consistent with well-studied starbursts at z ∼ 0 with similar metallicities. Strong P Cygni lines and He II λ1640 emission indicate a significant population of Wolf-Rayet stars, but synthetic spectra of individual populations of young, hot stars do not reproduce the observed integrated P Cygni absorption features. The rest-frame UV spectral features are indicative of a young starburst with high ionization, implying either (1) an ionization parameter significantly higher than suggested by rest-frame optical nebular lines, or (2) differences in one or both of the initial mass function and the properties of ionizing spectra of massive stars. We argue that the observed features are likely the result of a superposition of star forming regions with different physical properties. These results demonstrate the complexity of star formation on scales smaller than individual galaxies, and highlight the importance of systematic effects that result from smearing together the signatures of individual star forming regions within galaxies.

  7. Radial metallicity gradients in spiral galaxies from H II regions and planetary nebulae: probing galactic chemical evolution

    NASA Astrophysics Data System (ADS)

    Stanghellini, Letizia

    2015-08-01

    Radial metallicity gradients, typically observed in spiral galaxies, are excellent constraints for chemical evolution models. The contemporary studies of the two stellar populations, whose progenitors have formed at different times, yield to the chemical and time constraining of the models. In this context, planetary nebula and HII region analysis proved to be ideal two-epochs test populations. We present an assortment of galaxies whose oxygen abundances have been determined both with weak- and strong-line methods, and whose radial metallicity gradients and their evolution in time have disclosed very interesting correlations with the galaxy characteristics. New results from our Gemini/GMOS observations, and a review of the best literature data, set the stage for a better understanding of spiral galaxy evolution.

  8. Deep Hubble Space Telescope Imaging of IC 1613. II. The Star Formation History

    NASA Astrophysics Data System (ADS)

    Skillman, Evan D.; Tolstoy, Eline; Cole, Andrew A.; Dolphin, Andrew E.; Saha, Abhijit; Gallagher, J. S.; Dohm-Palmer, R. C.; Mateo, Mario

    2003-10-01

    We have taken deep images of an outlying field in the Local Group dwarf irregular galaxy IC 1613 with the WFPC2 aboard the Hubble Space Telescope in the standard broadband F555W (V, 8 orbits) and F814W (I, 16 orbits) filters. The photometry reaches to V=27.7 (MV=+3.4) and I=27.1 (MI=+2.8) at the 50% completeness level, the deepest to date for an isolated dwarf irregular galaxy. We analyze the resulting color-magnitude diagram (CMD) and compare it with CMDs created from theoretical stellar models using three different methods to derive a star formation history (SFH) as well as constrain the chemical evolution for IC 1613. All three methods find an enhanced star formation rate (SFR), at roughly the same magnitude (factor of 3), over roughly the same period (from 3 to 6 Gyr ago). Additionally, all three methods were driven to similar age-metallicity relationships (AMR) that show an increase from [Fe/H]~-1.3 at earliest times to [Fe/H]~-0.7 at present. Good agreement is found between the AMR which is derived from the CMD analysis and that which can be inferred from the derived SFH at all but the earliest ages. The agreement between the three models and the self-consistency of the derived chemical enrichment history support the reality of the derived SFH of IC 1613 and, more generally, are supportive of the practice of constructing galaxy SFHs from CMDs. A comparison of the newly observed outer field with an earlier studied central field of IC 1613 shows that the SFR in the outer field has been significantly depressed during the last Gyr. This implies that the optical scale length of the galaxy has been decreasing with time and that comparison of galaxies at intermediate redshift with present-day galaxies should take this effect into account. Comparing the CMD of the outer field of IC 1613 with CMDs of Milky Way dSph companions, we find strong similarities between IC 1613 and the more distant dSph companions (Carina, Fornax, Leo I, and Leo II) in that all are dominated

  9. VARIATIONS OF MID- AND FAR-INFRARED LUMINOSITIES AMONG EARLY-TYPE GALAXIES: RELATION TO STELLAR METALLICITY AND COLD DUST

    SciTech Connect

    Mathews, William G.; Brighenti, Fabrizio

    2013-05-01

    The Hubble morphological sequence from early to late galaxies corresponds to an increasing rate of specific star formation. The Hubble sequence also follows a banana-shaped correlation between 24 and 70 {mu}m luminosities, both normalized with the K-band luminosity. We show that this correlation is significantly tightened if galaxies with central active galactic nucleus (AGN) emission are removed, but the cosmic scatter of elliptical galaxies in both 24 and 70 {mu}m luminosities remains significant along the correlation. We find that the 24 {mu}m variation among ellipticals correlates with stellar metallicity, reflecting emission from hot dust in winds from asymptotic giant branch stars of varying metallicity. Infrared surface brightness variations in elliptical galaxies indicate that the K - 24 color profile is U-shaped for reasons that are unclear. In some elliptical galaxies, cold interstellar dust emitting at 70 and 160 {mu}m may arise from recent gas-rich mergers. However, we argue that most of the large range of 70 {mu}m luminosity in elliptical galaxies is due to dust transported from galactic cores by feedback events in (currently IR-quiet) AGNs. Cooler dusty gas naturally accumulates in the cores of elliptical galaxies due to dust-cooled local stellar mass loss and may accrete onto the central black hole, releasing energy. AGN-heated gas can transport dust in cores 5-10 kpc out into the hot gas atmospheres where it radiates extended 70 {mu}m emission but is eventually destroyed by sputtering. This, and some modest star formation, defines a cycle of dust creation and destruction. Elliptical galaxies evidently undergo large transient excursions in the banana plot in times comparable to the sputtering time or AGN duty cycle, 10 Myr. Normally regarded as passive, elliptical galaxies are the most active galaxies in the IR color-color correlation.

  10. SDSS-IV MaNGA: environmental dependence of stellar age and metallicity gradients in nearby galaxies

    NASA Astrophysics Data System (ADS)

    Zheng, Zheng; Wang, Huiyuan; Ge, Junqiang; Mao, Shude; Li, Cheng; Li, Ran; Mo, Houjun; Goddard, Daniel; Bundy, Kevin; Li, Hongyu; Nair, Preethi; Lin, Lihwai; Long, R. J.; Riffel, Rogério; Thomas, Daniel; Masters, Karen; Bizyaev, Dmitry; Brownstein, Joel R.; Zhang, Kai; Law, David R.; Drory, Niv; Roman Lopes, Alexandre; Malanushenko, Olena

    2017-03-01

    We present a study on the stellar age and metallicity distributions for 1105 galaxies using the STARLIGHT software on MaNGA (Mapping Nearby Galaxies at APO) integral field spectra. We derive age and metallicity gradients by fitting straight lines to the radial profiles, and explore their correlations with total stellar mass M*, NUV - r colour and environments, as identified by both the large-scale structure (LSS) type and the local density. We find that the mean age and metallicity gradients are close to zero but slightly negative, which is consistent with the inside-out formation scenario. Within our sample, we find that both the age and metallicity gradients show weak or no correlation with either the LSS type or local density environment. In addition, we also study the environmental dependence of age and metallicity values at the effective radii. The age and metallicity values are highly correlated with M* and NUV - r and are also dependent on LSS type as well as local density. Low-mass galaxies tend to be younger and have lower metallicity in low-density environments while high-mass galaxies are less affected by environment.

  11. ANISOTROPIC METAL-ENRICHED OUTFLOWS DRIVEN BY ACTIVE GALACTIC NUCLEI IN CLUSTERS OF GALAXIES

    SciTech Connect

    Kirkpatrick, C. C.; McNamara, B. R.; Cavagnolo, K. W.

    2011-04-20

    We present an analysis of the spatial distribution of metal-rich gas in 10 galaxy clusters using deep observations from the Chandra X-ray Observatory. The brightest cluster galaxies (BCGs) have experienced recent active galactic nucleus activity in the forms of bright radio emission, cavities, and shock fronts embedded in the hot atmospheres. The heavy elements are distributed anisotropically and are aligned with the large-scale radio and cavity axes. They are apparently being transported from the halo of the BCG into the intracluster medium along large-scale outflows driven by the radio jets. The radial ranges of the metal-enriched outflows are found to scale with jet power as R{sub Fe} {proportional_to} P {sup 0.42}{sub jet}, with a scatter of only 0.5 dex. The heavy elements are transported beyond the extent of the inner cavities in all clusters, suggesting that this is a long-lasting effect sustained over multiple generations of outbursts. Black holes in BCGs will likely have difficulty ejecting metal-enriched gas beyond 1 Mpc unless their masses substantially exceed 10{sup 9} M{sub sun}.

  12. Effects of Metallicity and AGN Activity on the Mid-Infrared Dust Emission of Galaxies

    NASA Astrophysics Data System (ADS)

    Wu, Hong; Zhu, Yi-Nan; Cao, Chen; Qin, Bo

    2007-10-01

    Using a sample of the Spitzer SWIRE-field galaxies whose optical spectra are taken from Data Release 4 of the Sloan Digital Sky Survey, we study possible correlations between the mid-infrared (MIR) dust emission from these galaxies and both their metallicities and AGN activities. We find that both metallicity and AGN activity are well correlated with the following ratios: PAH-to-star, VSG-to-star, and PAH-to-VSG, which can be characterized by νLν[8 μm(dust)]/νLν[3.6 μm], νLν[24 μm]/νLν[3.6 μm], and νLν[8 μm(dust)]/νLν[24 μm], respectively. We argue that our MIR-metallicity correlation could be explained by either the amount of dust (ongoing dust formation) or dust destruction (PAHs and VSGs could be destroyed by hard and intense radiation fields), and that the MIR-AGN correlation could arise due to either PAH destruction or an enhanced VSG continuum by the central AGN.

  13. A DIRECT STELLAR METALLICITY DETERMINATION IN THE DISK OF THE MASER GALAXY NGC 4258

    SciTech Connect

    Kudritzki, Rolf-Peter; Gazak, Zachary; Hosek, Matthew W. Jr.; Bresolin, Fabio; Urbaneja, Miguel A.; Przybilla, Norbert

    2013-12-20

    We present the first direct determination of a stellar metallicity in the spiral galaxy NGC 4258 (D = 7.6 Mpc) based on the quantitative analysis of a low-resolution (∼5 Å) Keck Low Resolution Imaging Spectrograph spectrum of a blue supergiant star located in its disk. A determination of stellar metallicity in this galaxy is important for the absolute calibration of the Cepheid period-luminosity relation as an anchor for the extragalactic distance scale and for a better characterization of its dependence as a function of abundance. We find a value 0.2 dex lower than solar metallicity at a galactocentric distance of 8.7 kpc, in agreement with recent H II region studies using the weak forbidden auroral oxygen line at 4363 Å. We determine the effective stellar temperature, gravity, luminosity, and line-of-sight extinction of the blue supergiant being studied. We show that it fits well on the flux-weighted gravity-luminosity relation, strengthening the potential of this method as a new extragalactic distance indicator.

  14. Ultraviolet ISM Diagnostics for Star-forming Galaxies. I. Tracers of Metallicity and Extinction

    NASA Astrophysics Data System (ADS)

    Zetterlund, Erika; Levesque, Emily M.; Leitherer, Claus; Danforth, Charles W.

    2015-06-01

    We have observed a sample of 14 nearby (z˜ 0.03) star-forming blue compact galaxies (BCGs) in the rest-frame far-UV (˜1150-2200 Å) using the Cosmic Origins Spectrograph on the Hubble Space Telescope. We have also generated a grid of stellar population synthesis models using the Starburst99 evolutionary synthesis code, allowing us to compare observations and theoretical predictions for the Si iv_1400 and C iv_1550 UV indices; both are comprised of a blend of stellar wind and interstellar lines and have been proposed as metallicity diagnostics in the UV. Our models and observations both demonstrate that there is a positive linear correlation with metallicity for both indices, and we find generally good agreement between our observations and the predictions of the Starburst99 models (with the models slightly under-estimating the value of the indices due to contributions from interstellar lines not simulated by a stellar population synthesis code). By combining the rest-frame UV observations with pre-existing rest-frame optical spectrophotometry of our BCG sample, we also directly compare the predictions of metallicity and extinction diagnostics across both wavelength regimes. This comparison reveals a correlation between the UV absorption and optical strong-line diagnostics, offering the first means of directly comparing interstellar medium (ISM) properties determined across different rest-frame regimes. Finally, using our Starburst99 model grid, we determine theoretical values for the short-wavelength UV continuum slope, {{β }18}, which can be used for determining extinction in rest-frame UV spectra of star-forming galaxies. We consider the implications of these results and discuss future work aimed at parameterizing these and other environmental diagnostics in the UV (a suite of diagnostics that could offer particular utility in the study of star-forming galaxies at high redshift) as well as the development of robust comparisons between ISM diagnostics across a

  15. Stellar metallicity of the extended disk and distance of the spiral galaxy NGC 3621

    SciTech Connect

    Kudritzki, Rolf-Peter; Bresolin, Fabio; Hosek, Matthew W. Jr.; Urbaneja, Miguel A.; Przybilla, Norbert E-mail: bresolin@ifa.hawaii.edu E-mail: Miguel.Urbaneja-Perez@uibk.ac.at

    2014-06-10

    Low resolution (∼4.5 Å) ESO VLT/FORS spectra of blue supergiant stars are analyzed to determine stellar metallicities (based on elements such as iron, titanium, and magnesium) in the extended disk of the spiral galaxy, NGC 3621. Mildly subsolar metallicity (–0.30 dex) is found for the outer objects beyond 7 kpc, independent of galactocentric radius and compatible with the absence of a metallicity gradient, confirming the results of a recent investigation of interstellar medium H II region gas oxygen abundances. The stellar metallicities are slightly higher than those from the H II regions when based on measurements of the weak forbidden auroral oxygen line at 4363 Å but lower than the ones obtained with the R {sub 23} strong line method. It is shown that the present level of metallicity in the extended disk cannot be the result of chemical evolution over the age of the disk with the present rate of in situ star formation. Additional mechanisms must be involved. In addition to metallicity, stellar effective temperatures, gravities, interstellar reddening, and bolometric magnitudes are determined. After the application of individual reddening corrections for each target, the flux-weighted gravity-luminosity relationship of blue supergiant stars is used to obtain a distance modulus of 29.07 ± 0.09 mag (distance D = 6.52 ± 0.28 Mpc). This new distance is discussed in relation to Cepheid and the tip of the red giant branch distances.

  16. Stellar kinematics and metallicities in the ultra-faint dwarf galaxy Reticulum II

    DOE PAGES

    Simon, J. D.

    2015-07-23

    With this study, we present Magellan/M2FS, Very Large Telescope/GIRAFFE, and Gemini South/GMOS spectroscopy of the newly discovered Milky Way satellite Reticulum II. Based on the spectra of 25 Ret II member stars selected from Dark Energy Survey imaging, we measure a mean heliocentric velocity ofmore » $$62.8\\pm 0.5\\;\\mathrm{km}\\;{\\rm{s}}^{-1}$$ and a velocity dispersion of $$3.3\\pm 0.7\\;\\mathrm{km}\\;{\\rm{s}}^{-1}$$. The mass-to-light ratio of Ret II within its half-light radius is $$470\\pm 210\\ {M}_{\\odot }/{L}_{\\odot }$$, demonstrating that it is a strongly dark matter-dominated system. Despite its spatial proximity to the Magellanic Clouds, the radial velocity of Ret II differs from that of the LMC and SMC by 199 and 83 $$\\mathrm{km}\\ {{\\rm{s}}}^{-1}$$, respectively, suggesting that it is not gravitationally bound to the Magellanic system. The likely member stars of Ret II span 1.3 dex in metallicity, with a dispersion of 0.28 ± 0.09 dex, and we identify several extremely metal-poor stars with $${\\rm{[Fe/H]}}\\lt -3$$. In combination with its luminosity, size, and ellipticity, these results confirm that Ret II is an ultra-faint dwarf galaxy. With a mean metallicity of $${\\rm{[Fe/H]}}=-2.65\\pm 0.07$$, Ret II matches Segue 1 as the most metal-poor galaxy known. Although Ret II is the third-closest dwarf galaxy to the Milky Way, the line-of-sight integral of the dark matter density squared is $${\\mathrm{log}}_{10}(J)=18.8\\pm 0.6\\;\\;\\mathrm{GeV}{\\;}^{2}\\;{\\mathrm{cm}}^{-5}\\;$$ within 0fdg2, indicating that the predicted gamma-ray flux from dark matter annihilation in Ret II is lower than that of several other dwarf galaxies.« less

  17. THE QUEST FOR CRADLES OF LIFE: USING THE FUNDAMENTAL METALLICITY RELATION TO HUNT FOR THE MOST HABITABLE TYPE OF GALAXY

    SciTech Connect

    Dayal, Pratika; Cockell, Charles; Rice, Ken; Mazumdar, Anupam

    2015-09-01

    The field of astrobiology has made huge strides in understanding the habitable zones around stars (stellar habitable zones) where life can begin, sustain its existence and evolve into complex forms. A few studies have extended this idea by modeling galactic-scale habitable zones (galactic habitable zones) for our Milky Way (MW) and specific elliptical galaxies. However, estimating the habitability for galaxies spanning a wide range of physical properties has so far remained an outstanding issue. Here, we present a “cosmobiological” framework that allows us to sift through the entire galaxy population in the local universe and answer the question, “Which type of galaxy is most likely to host complex life in the cosmos?” Interestingly, the three key astrophysical criteria governing habitability (total mass in stars, total metal mass and ongoing star formation rate) are found to be intricately linked through the “fundamental metallicity relation” as shown by Sloan Digital Sky Survey observations of more than a hundred thousand galaxies in the local universe. Using this relation we show that metal-rich, shapeless giant elliptical galaxies at least twice as massive as the MW (with a tenth of its star formation rate) can potentially host ten thousand times as many habitable (Earth-like) planets, making them the most probable “cradles of life” in the universe.

  18. The Quest for Cradles of Life: Using the Fundamental Metallicity Relation to Hunt for the Most Habitable Type of Galaxy

    NASA Astrophysics Data System (ADS)

    Dayal, Pratika; Cockell, Charles; Rice, Ken; Mazumdar, Anupam

    2015-09-01

    The field of astrobiology has made huge strides in understanding the habitable zones around stars (stellar habitable zones) where life can begin, sustain its existence and evolve into complex forms. A few studies have extended this idea by modeling galactic-scale habitable zones (galactic habitable zones) for our Milky Way (MW) and specific elliptical galaxies. However, estimating the habitability for galaxies spanning a wide range of physical properties has so far remained an outstanding issue. Here, we present a “cosmobiological” framework that allows us to sift through the entire galaxy population in the local universe and answer the question, “Which type of galaxy is most likely to host complex life in the cosmos?” Interestingly, the three key astrophysical criteria governing habitability (total mass in stars, total metal mass and ongoing star formation rate) are found to be intricately linked through the “fundamental metallicity relation” as shown by Sloan Digital Sky Survey observations of more than a hundred thousand galaxies in the local universe. Using this relation we show that metal-rich, shapeless giant elliptical galaxies at least twice as massive as the MW (with a tenth of its star formation rate) can potentially host ten thousand times as many habitable (Earth-like) planets, making them the most probable “cradles of life” in the universe.

  19. Metal-line absorption at Z(sub abs) approximately Z(sub em) from associated galaxies

    NASA Technical Reports Server (NTRS)

    Ellingson, E.; Yee, H. K. C.; Bechtold, Jill; Dobrzycki, Adam

    1994-01-01

    For a preliminary study of whether C IV absorption at Z(sub abs) approximately Z(sub em) is related to associated galaxy companions, we have collected data from a sample of 10 quasars with 0.15 less than z less than 0.65 for which high-resolution optical and UV spectroscopy is available from the literature, and for which we have deep optical images and limited spectroscopy. We also present new optical spectra for two of our samples. Four of these quasars have associated C IV absorption systems. In thes four fields, there are eight galaxies with M(sub r) less than -19.0 mag within 35 kpc of the quasar (projected distance, assuming they are at the quasar redshift), which may be candidates for the associated C IV absorption. This observed density of galaxies near quasars with associated C IV absorption is significantly greater than that for a control sample of quasars chosen from the literature. This result suggests that galaxies near the quasar line of sight may be linked with associated C IV absorption. None of these quasars show associated Mg II absorption, despite the presence of galaxies very near the line of sight, suggesting a Mg II 'proximity effect,' where ionizing flux from the quasar destroys the Mg(+) from at least the outer parts of the galaxies. Three quasars are located in rich galaxy clusters, but none of these quasars are found to have associated C IV absorption. This suggests that galaxies in rich clusters associated with quasars are less likely to be metal-line absorbers. It is plausible that the extended galaxy halos which may be responsible for the absorptions are stripped from galaxies in these dense environments. While it seems that at Z approximately 0.6 rich clusters do not cause them, associated C IV absorption systems at higher redshift may be explained by associated clusters if there has been evolution in the properties of galaxy halos in dense environments.

  20. Do galaxy global relationships emerge from local ones? The SDSS IV MaNGA surface mass density-metallicity relation

    NASA Astrophysics Data System (ADS)

    Barrera-Ballesteros, Jorge K.; Heckman, Timothy M.; Zhu, Guangtun B.; Zakamska, Nadia L.; Sánchez, Sebastian F.; Law, David; Wake, David; Green, Jenny E.; Bizyaev, Dmitry; Oravetz, Daniel; Simmons, Audrey; Malanushenko, Elena; Pan, Kaike; Roman Lopes, Alexandre; Lane, Richard R.

    2016-12-01

    We present the stellar surface mass density versus gas metallicity (Σ*-Z) relation for more than 500 000 spatially resolved star-forming resolution elements (spaxels) from a sample of 653 disc galaxies included in the SDSS IV MaNGA survey. We find a tight relation between these local properties, with higher metallicities as the surface density increases. This relation extends over three orders of magnitude in the surface mass density and a factor of 4 in metallicity. We show that this local relationship can simultaneously reproduce two well-known properties of disc galaxies: their global mass-metallicity relationship and their radial metallicity gradients. We also find that the Σ*-Z relation is largely independent of the galaxy's total stellar mass and specific star formation rate (sSFR), except at low stellar mass and high sSFR. These results suggest that in the present-day universe local properties play a key role in determining the gas-phase metallicity in typical disc galaxies.

  1. Very metal-poor galaxies: ionized gas kinematics in nine objects

    NASA Astrophysics Data System (ADS)

    Moiseev, A. V.; Pustilnik, S. A.; Kniazev, A. Y.

    2010-07-01

    The study of ionized gas morphology and kinematics in nine extremely metal-deficient (XMD) galaxies with the scanning Fabry-Perot interferometer on the Special Astrophysical Observatory (SAO) 6-m telescope is presented. Some of these very rare objects (with currently known range of O/H of 7.12 < 12 + log(O/H) < 7.65, or ) are believed to be the best proxies of `young' low-mass galaxies in the high-redshift Universe. One of the main goals of this study is to look for possible evidence of star formation (SF) activity induced by external perturbations. Recent results from HI mapping of a small subsample of XMD star-forming galaxies provided confident evidence for the important role of interaction-induced SF. Our observations provide complementary or new information that the great majority of the studied XMD dwarfs have strongly disturbed gas morphology and kinematics or the presence of detached components. We approximate the observed velocity fields by simple models of a rotating tilted thin disc, which allows us the robust detection of non-circular gas motions. These data, in turn, indicate the important role of current/recent interactions and mergers in the observed enhanced SF. As a by-product of our observations, we obtained data for two Low Surface Brightness (LSB) dwarf galaxies: Anon J012544+075957 that is a companion of the merger system UGC 993, and SAO 0822+3545 which shows off-centre, asymmetric, low star formation rate star-forming regions, likely induced by the interaction with the companion XMD dwarf HS 0822+3542. Based on observations obtained with the Special Astrophysical Observatory RAS 6-m telescope. E-mail: moisav@gmail.com (AVM); sap@sao.ru (SAP); akniazev@saao.ac.za (AYK)

  2. The Subaru FMOS Galaxy Redshift Survey (FastSound): The Mass-Metallicity Relation and the Fundamental Metallicity Relation at z˜1.4

    NASA Astrophysics Data System (ADS)

    Yabe, K.; Ohta, K.; Akiyama, M.; Tamura, N.; Iwamuro, F.; Totani, T.; Dalton, G.; Bunker, A.; FastSound Team

    2016-10-01

    We present results from a large NIR spectroscopic survey (FastSound) with Subaru/FMOS, consisting of ˜4,000 galaxies at z˜1.4 with significant Hα detection. The resulting mass-metallicity relation generally agrees with those obtained previously in a similar redshift range to our sample. No clear dependence on the mass-metallicity relation on star-formation rate is found, which is not in agreement with the extrapolation of the local fundamental metallicity relation. We estimate the nitrogen-to-oxygen abundance ratio (N/O) from the N2S2 index, and find that the N/O in galaxies at z˜1.4 is significantly higher than the local values at a fixed metallicity and stellar mass. The metallicity derived by using the N2 method calibrated in the local universe decreases by ˜0.2 dex if we correct the N/O enhancement.

  3. New metallicity calibration for Seyfert 2 galaxies based on the N2O2 index

    NASA Astrophysics Data System (ADS)

    Castro, C. S.; Dors, O. L.; Cardaci, M. V.; Hägele, G. F.

    2017-01-01

    We derive a new relation between the metallicity of Seyfert 2 Active Galactic Nuclei (AGNs) and the intensity of the narrow emission-lines ratio N2O2=log([N II]λ6584/[O II]λ3727). The calibration of this relation was performed determining the metallicity (Z) of a sample of 58 AGNs through a diagram containing the observational data and the results of a grid of photoionization models obtained with the CLOUDY code. We find the new Z/Z⊙-N2O2 relation using the obtained metallicity values and the corresponding observational emission line intensities for each object of the sample. Estimations derived through the use of this new calibration indicate that narrow line regions of Seyfert 2 galaxies exhibit a large range of metallicities (0.3 ≲ Z/Z_{⊙} ≲ 2.0), with a median value Z ≈ Z⊙. Regarding the possible existence of correlations between the luminosity L(Hβ), the electron density, and the color excess E(B-V) with the metallicity in this kind of objects, we do not find correlations between them.

  4. A uniform metal distribution in the intergalactic medium of the Perseus cluster of galaxies.

    PubMed

    Werner, Norbert; Urban, Ondrej; Simionescu, Aurora; Allen, Steven W

    2013-10-31

    Most of the metals (elements heavier than helium) produced by stars in the member galaxies of clusters currently reside within the hot, X-ray-emitting intra-cluster gas. Observations of X-ray line emission from this intergalactic medium have suggested a relatively small cluster-to-cluster scatter outside the cluster centres and enrichment with iron out to large radii, leading to the idea that the metal enrichment occurred early in the history of the Universe. Models with early enrichment predict a uniform metal distribution at large radii in clusters, whereas those with late-time enrichment are expected to introduce significant spatial variations of the metallicity. To discriminate clearly between these competing models, it is essential to test for potential inhomogeneities by measuring the abundances out to large radii along multiple directions in clusters, which has not hitherto been done. Here we report a remarkably uniform iron abundance, as a function of radius and azimuth, that is statistically consistent with a constant value of ZFe = 0.306 ± 0.012 in solar units out to the edge of the nearby Perseus cluster. This homogeneous distribution requires that most of the metal enrichment of the intergalactic medium occurred before the cluster formed, probably more than ten billion years ago, during the period of maximal star formation and black hole activity.

  5. SPECTRUM OF THE SUPERNOVA RELIC NEUTRINO BACKGROUND AND METALLICITY EVOLUTION OF GALAXIES

    SciTech Connect

    Nakazato, Ken’ichiro; Mochida, Eri; Suzuki, Hideyuki; Niino, Yuu

    2015-05-01

    The spectrum of the supernova relic neutrino (SRN) background from past stellar collapses including black hole formation (failed supernovae) is calculated. The redshift dependence of the black hole formation rate is considered on the basis of the metallicity evolution of galaxies. Assuming the mass and metallicity ranges of failed supernova progenitors, their contribution to SRNs is quantitatively estimated for the first time. Using this model, the dependences of SRNs on the cosmic star formation rate density (CSFRD), shock revival time, and equation of state (EOS) are investigated. The shock revival time is introduced as a parameter that should depend on the still unknown explosion mechanism of core collapse supernovae. The dependence on EOS is considered for failed supernovae, whose collapse dynamics and neutrino emission are certainly affected. It is found that the low-energy spectrum of SRNs is mainly determined by the CSFRD. These low-energy events will be observed in the Super-Kamiokande experiment with gadolinium-loaded water.

  6. Gas-phase Oxygen Abundances and Radial Metallicity Gradients in the Two nearby Spiral Galaxies NGC 7793 and NGC 4945

    NASA Astrophysics Data System (ADS)

    Stanghellini, Letizia; Magrini, Laura; Casasola, Viviana

    2015-10-01

    Gas-phase abundances in H ii regions of two spiral galaxies, NGC 7793 and NGC 4945, have been studied to determine their radial metallicity gradients. We used the strong-line method to derive oxygen abundances from spectra acquired with GMOS-S, the multi-object spectrograph on the 8 m Gemini South telescope. We found that NGC 7793 has a well-defined gas-phase radial oxygen gradient of -0.321 ± 0.112 dex {R}25-1 (or -0.054 ± 0.019 dex kpc-1) in the galactocentric range 0.17 < RG/R25 < 0.82, not dissimilar from gradients calculated with direct abundance methods in galaxies of similar mass and morphology. We also determined a shallow radial oxygen gradient in NGC 4945, -0.253 ± 0.149 dex {R}25-1 (or -0.019 ± 0.011 dex kpc-1) for 0.04 < RG/R25 < 0.51, where the larger relative uncertainty derives mostly from the larger inclination of this galaxy. NGC 7793 and NGC 4945 have been selected for this study because they are similar, in mass and morphology, to M33 and the Milky Way, respectively. Since at zeroth order we expect the radial metallicity gradients to depend on mass and galaxy type, we compared our galaxies in the framework of radial metallicity models best suited for M33 and the Galaxy. We found a good agreement between M33 and NGC 7793, pointing toward similar evolution for the two galaxies. We notice instead differences between NGC 4945 and the radial metallicity gradient model that best fits the Milky Way. We found that these differences are likely related to the presence of an active galactic nucleus combined with a bar in the central regions of NGC 4945, and to its interacting environment.

  7. Coevolution of metallicity and star formation in galaxies to z ≃ 3.7 - II. A theoretical model

    NASA Astrophysics Data System (ADS)

    Hunt, Leslie; Dayal, Pratika; Magrini, Laura; Ferrara, Andrea

    2016-12-01

    Recent work suggests that galaxy evolution, and the build-up of stellar mass (M*) over cosmic time, is characterized by changes with redshift of star formation rate (SFR) and oxygen abundance (O/H). In a companion paper, we have compiled a large data set to study Metallicity Evolution and Galaxy Assembly (MEGA), consisting of ˜1000 galaxies to z ≃ 3.7 with a common O/H calibration. Here we interpret the MEGA scaling relations of M*, SFR, and O/H with an updated version of the model presented by Dayal et al. This model successfully reproduces the observed O/H ratio of ˜80 000 galaxies selected from the Sloan Digital Sky Survey to within 0.05-0.06 dex. By extending the model to the higher redshift MEGA sample, we find that although the specific mass loading of outflows does not change measurably during the evolution, the accretion rate and gas content of galaxies increase significantly with redshift. These two effects can explain, either separately or possibly in tandem, the observed lower metal abundance of high-z galaxies.

  8. NEW PERSPECTIVE ON GALAXY OUTFLOWS FROM THE FIRST DETECTION OF BOTH INTRINSIC AND TRAVERSE METAL-LINE ABSORPTION

    SciTech Connect

    Kacprzak, Glenn G.; Cooke, Jeff; Martin, Crystal L.; Ho, Stephanie H.; Bouché, Nicolas; LeReun, Audrey; Schroetter, Ilane; Churchill, Christopher W.; Klimek, Elizabeth

    2014-09-01

    We present the first observation of a galaxy (z = 0.2) that exhibits metal-line absorption back-illuminated by the galaxy (down-the-barrel) and transversely by a background quasar at a projected distance of 58 kpc. Both absorption systems, traced by Mg II, are blueshifted relative to the galaxy systemic velocity. The quasar sight line, which resides almost directly along the projected minor axis of the galaxy, probes Mg I and Mg II absorption obtained from the Keck/Low Resolution Imaging Spectrometer as well as Lyα, Si II, and Si III absorption obtained from the Hubble Space Telescope/Cosmic Origins Spectrograph. For the first time, we combine two independent models used to quantify the outflow properties for down-the-barrel and transverse absorption. We find that the modeled down-the-barrel deprojected outflow velocities range between V {sub dtb} = 45-255 km s{sup –1}. The transverse bi-conical outflow model, assuming constant-velocity flows perpendicular to the disk, requires wind velocities V {sub outflow} = 40-80 km s{sup –1} to reproduce the transverse Mg II absorption kinematics, which is consistent with the range of V {sub dtb}. The galaxy has a metallicity, derived from Hα and N II, of [O/H] = –0.21 ± 0.08, whereas the transverse absorption has [X/H] = –1.12 ± 0.02. The galaxy star formation rate is constrained between 4.6-15 M {sub ☉} yr{sup –1} while the estimated outflow rate ranges between 1.6-4.2 M {sub ☉} yr{sup –1} and yields a wind loading factor ranging between 0.1-0.9. The galaxy and gas metallicities, the galaxy-quasar sight-line geometry, and the down-the-barrel and transverse modeled outflow velocities collectively suggest that the transverse gas originates from ongoing outflowing material from the galaxy. The ∼1 dex decrease in metallicity from the base of the outflow to the outer halo suggests metal dilution of the gas by the time it reached 58 kpc.

  9. INVESTIGATING THE POTENTIAL DILUTION OF THE METAL CONTENT OF HOT GAS IN EARLY-TYPE GALAXIES BY ACCRETED COLD GAS

    SciTech Connect

    Su, Yuanyuan; Irwin, Jimmy A.

    2013-03-20

    The measured emission-weighted metal abundance of the hot gas in early-type galaxies has been known to be lower than theoretical expectations for 20 years. In addition, both X-ray luminosity and metal abundance vary significantly among galaxies of similar optical luminosities. This suggests some missing factors in the galaxy evolution process, especially the metal enrichment process. With Chandra and XMM-Newton, we studied 32 early-type galaxies (kT {approx}< 1 keV) covering a span of two orders of L{sub X,gas}/L{sub K} to investigate these missing factors. Contrary to previous studies that X-ray faint galaxies show extremely low Fe abundance ({approx}0.1 Z{sub Sun }), nearly all galaxies in our sample show an Fe abundance at least 0.3 Z{sub Sun }, although the measured Fe abundance difference between X-ray faint and X-ray bright galaxies remains remarkable. We investigated whether this dichotomy of hot gas Fe abundances can be related to the dilution of hot gas by mixing with cold gas. With a subset of 24 galaxies in this sample, we find that there is virtually no correlation between hot gas Fe abundances and their atomic gas content, which disproves the scenario that the low metal abundance of X-ray faint galaxies might be a result of the dilution of the remaining hot gas by pristine atomic gas. In contrast, we demonstrate a negative correlation between the measured hot gas Fe abundance and the ratio of molecular gas mass to hot gas mass, although it is unclear what is responsible for this apparent anti-correlation. We discuss several possibilities including that externally originated molecular gas might be able to dilute the hot gas metal content. Alternatively, the measured hot gas Fe abundance may be underestimated due to more complex temperature and abundance structures and even a two-temperature model might be insufficient to reflect the true value of the emission weighted mean Fe abundance.

  10. Stellar Populations and Star Formation History of the Metal-poor Dwarf Galaxy DDO 68

    NASA Astrophysics Data System (ADS)

    Sacchi, E.; Annibali, F.; Cignoni, M.; Aloisi, A.; Sohn, T.; Tosi, M.; van der Marel, R. P.; Grocholski, A. J.; James, B.

    2016-10-01

    We present the star formation history (SFH) of the extremely metal-poor dwarf galaxy DDO 68, based on our photometry with the Advanced Camera for Surveys. With a metallicity of only 12+{log}({{O}}/{{H}})=7.15 and a very isolated location, DDO 68 is one of the most metal-poor galaxies known. It has been argued that DDO 68 is a young system that started forming stars only ˜0.15 Gyr ago. Our data provide a deep and uncontaminated optical color-magnitude diagram (CMD) that allows us to disprove this hypothesis since we find a population of at least ˜1 Gyr old stars. The star formation activity has been fairly continuous over all the look-back time. The current rate is quite low, and the highest activity occurred between 10 and 100 Myr ago. The average star formation rate over the whole Hubble time is ≃0.01 M ⊙ yr-1, corresponding to a total astrated mass of ≃1.3 × 108 M ⊙. Our photometry allows us to infer the distance from the tip of the red giant branch, D = 12.08 ± 0.67 Mpc; however, to let our synthetic CMD reproduce the observed ones, we need a slightly higher distance, D = 12.65 Mpc, or (m - M)0 = 30.51, still inside the errors of the previous determination, and we adopt the latter. DDO 68 shows a very interesting and complex history, with its quite disturbed shape and a long tail, probably due to tidal interactions. The SFH of the tail differs from that of the main body mainly for enhanced activity at recent epochs likely triggered by the interaction. Based on observations obtained with the NASA/ESA Hubble Space Telescope at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy under NASA Contract NAS5-26555.

  11. Redshift, metallicity and size of two extended dwarf Irregular galaxies. A link between dwarf Irregulars and ultra diffuse galaxies?

    NASA Astrophysics Data System (ADS)

    Bellazzini, M.; Belokurov, V.; Magrini, L.; Fraternali, F.; Testa, V.; Beccari, G.; Marchetti, A.; Carini, R.

    2017-01-01

    We present the results of the spectroscopic and photometric follow-up of two field galaxies that were selected as possible stellar counterparts of local high velocity clouds. Our analysis shows that the two systems are distant (D>20 Mpc) dwarf irregular galaxies unrelated to the local H I clouds. However, the newly derived distance and structural parameters reveal that the two galaxies have luminosities and effective radii very similar to the recently identified ultra diffuse galaxies (UDGs). At odds with classical UDGs, they are remarkably isolated, having no known giant galaxy within ˜2.0 Mpc. Moreover, one of them has a very high gas content compared to galaxies of similar stellar mass, with a H I to stellar mass ratio MHI/M⋆ ˜ 90, typical of almost-dark dwarfs. Expanding on this finding, we show that extended dwarf irregulars overlap the distribution of UDGs in the MV vs. log re plane and that the sequence including dwarf spheroidals, dwarf irregulars and UDGs appears as continuously populated in this plane. This may suggest an evolutionary link between dwarf irregulars and UDGs.

  12. The mass-metallicity and fundamental metallicity relations at z > 2 using very large telescope and Subaru near-infrared spectroscopy of zCOSMOS galaxies

    SciTech Connect

    Maier, C.; Ziegler, B. L.; Lilly, S. J.; Peng, Y.; Contini, T.; Pérez Montero, E.; Balestra, I.

    2014-09-01

    In the local universe, there is good evidence that, at a given stellar mass M, the gas-phase metallicity Z is anti-correlated with the star formation rate (SFR) of the galaxies. It has also been claimed that the resulting Z(M, SFR) relation is invariant with redshift—the so-called 'fundamental metallicity relation' (FMR). Given a number of difficulties in determining metallicities, especially at higher redshifts, the form of the Z(M, SFR) relation and whether it is really independent of redshift is still very controversial. To explore this issue at z > 2, we used VLT-SINFONI and Subaru-MOIRCS near-infrared spectroscopy of 20 zCOSMOS-deep galaxies at 2.1 < z < 2.5 to measure the strengths of up to five emission lines: [O II] λ3727, Hβ, [O III] λ5007, Hα, and [N II] λ6584. This near-infrared spectroscopy enables us to derive O/H metallicities, and also SFRs from extinction corrected Hα measurements. We find that the mass-metallicity relation (MZR) of these star-forming galaxies at z ≈ 2.3 is lower than the local Sloan Digital Sky Survey (SDSS) MZR by a factor of three to five, a larger change than found by Erb et al. using [N II]/Hα-based metallicities from stacked spectra. We discuss how the different selections of the samples and metallicity calibrations used may be responsible for this discrepancy. The galaxies show direct evidence that the SFR is still a second parameter in the MZR at these redshifts. However, determining whether the Z(M, SFR) relation is invariant with epoch depends on the choice of extrapolation used from local samples, because z > 2 galaxies of a given mass have much higher SFRs than the local SDSS galaxies. We find that the zCOSMOS galaxies are consistent with a non-evolving FMR if we use the physically motivated formulation of the Z(M, SFR) relation from Lilly et al., but not if we use the empirical formulation of Mannucci et al.

  13. The Mass-Metallicity and Fundamental Metallicity Relations at z > 2 Using Very Large Telescope and Subaru Near-infrared Spectroscopy of zCOSMOS Galaxies

    NASA Astrophysics Data System (ADS)

    Maier, C.; Lilly, S. J.; Ziegler, B. L.; Contini, T.; Pérez Montero, E.; Peng, Y.; Balestra, I.

    2014-09-01

    In the local universe, there is good evidence that, at a given stellar mass M, the gas-phase metallicity Z is anti-correlated with the star formation rate (SFR) of the galaxies. It has also been claimed that the resulting Z(M, SFR) relation is invariant with redshift—the so-called "fundamental metallicity relation" (FMR). Given a number of difficulties in determining metallicities, especially at higher redshifts, the form of the Z(M, SFR) relation and whether it is really independent of redshift is still very controversial. To explore this issue at z > 2, we used VLT-SINFONI and Subaru-MOIRCS near-infrared spectroscopy of 20 zCOSMOS-deep galaxies at 2.1 < z < 2.5 to measure the strengths of up to five emission lines: [O II] λ3727, Hβ, [O III] λ5007, Hα, and [N II] λ6584. This near-infrared spectroscopy enables us to derive O/H metallicities, and also SFRs from extinction corrected Hα measurements. We find that the mass-metallicity relation (MZR) of these star-forming galaxies at z ≈ 2.3 is lower than the local Sloan Digital Sky Survey (SDSS) MZR by a factor of three to five, a larger change than found by Erb et al. using [N II]/Hα-based metallicities from stacked spectra. We discuss how the different selections of the samples and metallicity calibrations used may be responsible for this discrepancy. The galaxies show direct evidence that the SFR is still a second parameter in the MZR at these redshifts. However, determining whether the Z(M, SFR) relation is invariant with epoch depends on the choice of extrapolation used from local samples, because z > 2 galaxies of a given mass have much higher SFRs than the local SDSS galaxies. We find that the zCOSMOS galaxies are consistent with a non-evolving FMR if we use the physically motivated formulation of the Z(M, SFR) relation from Lilly et al., but not if we use the empirical formulation of Mannucci et al. AND SUBARU

  14. VizieR Online Data Catalog: Metal abundances of KISS galaxies. V. (Hirschauer+, 2015)

    NASA Astrophysics Data System (ADS)

    Hirschauer, A. S.; Salzer, J. J.; Bresolin, F.; Saviane, I.; Yegorova, I.

    2016-01-01

    Our spectroscopic targets for this project were potentially metal-rich galaxies identified by KPNO International Spectroscopic Survey (KISS; Salzer et al., 2000AJ....120...80S). KISS used low-dispersion objective-prism spectra to identify emission-line galaxy (ELG) candidates via detection of line emission in galaxies with redshifts of less than 0.095. The "red" survey (Salzer et al. 2001, cat. J/AJ/121/66; Gronwall et al. 2004, cat. J/AJ/127/1943; Jangren et al. 2005, cat. J/AJ/130/2571) cataloged objects by means of the Hα line, while the "blue" survey (Salzer et al. 2002, cat. J/AJ/123/1292) distinguished objects through strong [OIII]λ5007 line emission. The 15 galaxies discussed in this paper were chosen from the KISS Hα-selected catalog. Spectra of 15 KISS ELGs were obtained using the Keck I 10m telescope on 2006 May 25 with the Low-Resolution Imaging Spectrometer (LRIS), a double spectrograph that includes a dichroic that directs light toward a red and a blue side. The use of two distinct dispersion elements and cameras enables simultaneous spectral coverage spanning from ~3000 to ~10000Å with good dispersion. Blue side exposures used the 600/400 grism, with a dispersion of 0.63Å/pixel, a resolution of ~6Å, and wavelength coverage between ~3000 and ~5600Å. Red side exposures used the 900/5500 grating, with a dispersion of 0.53Å/pixel, a resolution of ~3Å, and wavelength coverage between ~5700 and ~7300Å. Each galaxy was first observed using the blue and red sides simultaneously to determine if further observations would yield usable spectra. If the raw spectra were of substantially high quality, the red side grating was switched to observe near-infrared (NIR) lines. This was completed for ten of the fifteen galaxies. For NIR exposures, the red side was switched to the 400/8500 grating, with a dispersion of 1.16Å/pixel, a resolution of ~6Å, and wavelength coverage between ~6300 and ~10000Å in order to observe the NIR [SIII] nebular lines at λ9069

  15. Men and IC

    MedlinePlus

    ... Body-based Practices Energy Medicine Bringing Treatments to Market IC Healthcare Provider Toolkit Join the Provider Registry ... Body-based Practices Energy Medicine Bringing Treatments to Market IC Healthcare Provider Toolkit Join the Provider Registry ...

  16. IC Associated Conditions

    MedlinePlus

    ... Body-based Practices Energy Medicine Bringing Treatments to Market IC Healthcare Provider Toolkit Join the Provider Registry ... Body-based Practices Energy Medicine Bringing Treatments to Market IC Healthcare Provider Toolkit Join the Provider Registry ...

  17. IC Treatment: Surgical Procedures

    MedlinePlus

    ... Body-based Practices Energy Medicine Bringing Treatments to Market IC Healthcare Provider Toolkit Join the Provider Registry ... Body-based Practices Energy Medicine Bringing Treatments to Market IC Healthcare Provider Toolkit Join the Provider Registry ...

  18. IC Treatment: Antihistamines

    MedlinePlus

    ... Body-based Practices Energy Medicine Bringing Treatments to Market IC Healthcare Provider Toolkit Join the Provider Registry ... Body-based Practices Energy Medicine Bringing Treatments to Market IC Healthcare Provider Toolkit Join the Provider Registry ...

  19. General IC Symptoms

    MedlinePlus

    ... Body-based Practices Energy Medicine Bringing Treatments to Market IC Healthcare Provider Toolkit Join the Provider Registry ... Body-based Practices Energy Medicine Bringing Treatments to Market IC Healthcare Provider Toolkit Join the Provider Registry ...

  20. IC: Frequently Asked Questions

    MedlinePlus

    ... Management of IC Pain Complementary Therapies Complementary vs. Alternative Herbs, Dietary Supplements, & Biologicals Mind-body Medicine Massage, Manipulation, & Body-based Practices Energy Medicine Bringing Treatments to Market IC Healthcare Provider ...

  1. THE MOST METAL-POOR DAMPED Lyα SYSTEMS: AN INSIGHT INTO DWARF GALAXIES AT HIGH-REDSHIFT

    SciTech Connect

    Cooke, Ryan J.; Pettini, Max; Jorgenson, Regina A.

    2015-02-10

    In this paper we analyze the kinematics, chemistry, and physical properties of a sample of the most metal-poor damped Lyα systems (DLAs), to uncover their links to modern-day galaxies. We present evidence that the DLA population as a whole exhibits a ''knee'' in the relative abundances of the α-capture and Fe-peak elements when the metallicity is [Fe/H] ≅ –2.0, assuming that Zn traces the buildup of Fe-peak elements. In this respect, the chemical evolution of DLAs is clearly different from that experienced by Milky Way halo stars, but resembles that of dwarf spheroidal galaxies in the Local Group. We also find a close correspondence between the kinematics of Local Group dwarf galaxies and of high-redshift metal-poor DLAs, which further strengthens this connection. On the basis of such similarities, we propose that the most metal-poor DLAs provide us with a unique opportunity to directly study the dwarf galaxy population more than ten billion years in the past, at a time when many dwarf galaxies were forming the bulk of their stars. To this end, we have measured some of the key physical properties of the DLA gas, including their neutral gas mass, size, kinetic temperature, density, and turbulence. We find that metal-poor DLAs contain a warm neutral medium with T {sub gas} ≅ 9600 K predominantly held up by thermal pressure. Furthermore, all of the DLAs in our sample exhibit a subsonic turbulent Mach number, implying that the gas distribution is largely smooth. These results are among the first empirical descriptions of the environments where the first few generations of stars may have formed in the universe.

  2. Low-metallicity Young Clusters in the Outer Galaxy. II. Sh 2-208

    NASA Astrophysics Data System (ADS)

    Yasui, Chikako; Kobayashi, Naoto; Saito, Masao; Izumi, Natsuko

    2016-05-01

    We obtained deep near-infrared images of Sh 2-208, one of the lowest-metallicity H ii regions in the Galaxy, [O/H] = -0.8 dex. We detected a young cluster in the center of the H ii region with a limiting magnitude of K = 18.0 mag (10σ), which corresponds to a mass detection limit of ˜0.2 M⊙. This enables the comparison of star-forming properties under low metallicity with those of the solar neighborhood. We identified 89 cluster members. From the fitting of the K-band luminosity function (KLF), the age and distance of the cluster are estimated to be ˜0.5 Myr and ˜4 kpc, respectively. The estimated young age is consistent with the detection of strong CO emission in the cluster region and the estimated large extinction of cluster members (AV ˜ 4-25 mag). The observed KLF suggests that the underlying initial mass function (IMF) of the low-metallicity cluster is not significantly different from canonical IMFs in the solar neighborhood in terms of both high-mass slope and IMF peak (characteristic mass). Despite the very young age, the disk fraction of the cluster is estimated at only 27% ± 6%, which is significantly lower than those in the solar metallicity. Those results are similar to Sh 2-207, which is another star-forming region close to Sh 2-208 with a separation of 12 pc, suggesting that their star-forming activities in low-metallicity environments are essentially identical to those in the solar neighborhood, except for the disk dispersal timescale. From large-scale mid-infrared images, we suggest that sequential star formation is taking place in Sh 2-207, Sh 2-208, and the surrounding region, triggered by an expanding bubble with a ˜30 pc radius.

  3. A very deep Chandra view of metals, sloshing and feedback in the Centaurus cluster of galaxies

    NASA Astrophysics Data System (ADS)

    Sanders, J. S.; Fabian, A. C.; Taylor, G. B.; Russell, H. R.; Blundell, K. M.; Canning, R. E. A.; Hlavacek-Larrondo, J.; Walker, S. A.; Grimes, C. K.

    2016-03-01

    We examine deep Chandra X-ray observations of the Centaurus cluster of galaxies, Abell 3526. Applying a gradient magnitude filter reveals a wealth of structure, from filamentary soft emission on 100 pc (0.5 arcsec) scales close to the nucleus to features 10 s of kpc in size at larger radii. The cluster contains multiple high-metallicity regions with sharp edges. Relative to an azimuthal average, the deviations of metallicity and surface brightness are correlated, and the temperature is inversely correlated, as expected if the larger scale asymmetries in the cluster are dominated by sloshing motions. Around the western cold front are a series of ˜7 kpc `notches', suggestive of Kelvin-Helmholtz instabilities. The cold front width varies from 4 kpc down to close to the electron mean free path. Inside the front are multiple metallicity blobs on scales of 5-10 kpc, which could have been uplifted by AGN activity, also explaining the central metallicity drop and flat inner metallicity profile. Close to the nucleus are multiple shocks, including a 1.9-kpc-radius inner shell-like structure and a weak 1.1-1.4 Mach number shock around the central cavities. Within a 10 kpc radius are nine depressions in surface brightness, several of which appear to be associated with radio emission. The shocks and cavities imply that the nucleus has been repeatedly active on 5-10 Myr time-scales, indicating a tight balance between heating and cooling. We confirm the presence of a series of linear quasi-periodic structures. If they are sound waves, the ˜5 kpc spacing implies a period of 6 Myr, similar to the ages of the shocks and cavities. Alternatively, these structures may be Kelvin-Helmholtz instabilities, their associated turbulence or amplified magnetic field layers.

  4. 3D-HST GRISM SPECTROSCOPY OF A GRAVITATIONALLY LENSED, LOW-METALLICITY STARBURST GALAXY AT z = 1.847

    SciTech Connect

    Brammer, Gabriel B.; Sanchez-Janssen, Ruben; Labbe, Ivo; Franx, Marijn; Fumagalli, Mattia; Patel, Shannon; Da Cunha, Elisabete; Rix, Hans-Walter; Schmidt, Kasper B.; Van der Wel, Arjen; Erb, Dawn K.; Lundgren, Britt; Momcheva, Ivelina; Nelson, Erica; Skelton, Rosalind E.; Van Dokkum, Pieter G.; Wake, David A.; Whitaker, Katherine E.; Marchesini, Danilo; Quadri, Ryan

    2012-10-10

    We present Hubble Space Telescope (HST) imaging and spectroscopy of the gravitational lens SL2SJ02176-0513, a cusp arc at z = 1.847. The UV continuum of the lensed galaxy is very blue, which is seemingly at odds with its redder optical colors. The 3D-HST WFC3/G141 near-infrared spectrum of the lens reveals the source of this discrepancy to be extremely strong [O III] {lambda}5007 and H{beta} emission lines with rest-frame equivalent widths of 2000 {+-} 100 and 520 {+-} 40 A, respectively. The source has a stellar mass {approx}10{sup 8} M{sub Sun }, sSFR {approx} 100 Gyr{sup -1}, and detection of [O III] {lambda}4363 yields a metallicity of 12 + log (O/H) = 7.5 {+-} 0.2. We identify local blue compact dwarf analogs to SL2SJ02176-0513, which are among the most metal-poor galaxies in the Sloan Digital Sky Survey. The local analogs resemble the lensed galaxy in many ways, including UV/optical spectral energy distribution, spatial morphology, and emission line equivalent widths and ratios. Common to SL2SJ02176-0513 and its local counterparts is an upturn at mid-IR wavelengths likely arising from hot dust heated by starbursts. The emission lines of SL2SJ02176-0513 are spatially resolved owing to the combination of the lens and the high spatial resolution of HST. The lensed galaxy is composed of two clumps with combined size r{sub e} {approx}300 pc, and we resolve significant differences in UV color and emission line equivalent width between them. Though it has characteristics occasionally attributed to active galactic nuclei, we conclude that SL2SJ02176-0513 is a low-metallicity star-bursting dwarf galaxy. Such galaxies will be found in significant numbers in the full 3D-HST grism survey.

  5. LSD: Lyman-break galaxies Stellar populations and Dynamics - I. Mass, metallicity and gas at z ~ 3.1

    NASA Astrophysics Data System (ADS)

    Mannucci, F.; Cresci, G.; Maiolino, R.; Marconi, A.; Pastorini, G.; Pozzetti, L.; Gnerucci, A.; Risaliti, G.; Schneider, R.; Lehnert, M.; Salvati, M.

    2009-10-01

    We present the first results of a project, Lyman-break galaxies Stellar populations and Dynamics (LSD), aimed at obtaining spatially resolved, near-infrared (IR) spectroscopy of a complete sample of Lyman-break galaxies at z ~ 3. Deep observations with adaptive optics resulted in the detection of the main optical lines, such as [OII] λ3727, Hβ and [OIII] λ5007, which are used to study sizes, star formation rates (SFRs), morphologies, gas-phase metallicities, gas fractions and effective yields. Optical, near-IR and Spitzer/Infrared Array Camera photometry are used to measure stellar mass. We obtain that morphologies are usually complex, with the presence of several peaks of emissions and companions that are not detected in broad-band images. Typical metallicities are 10-50 per cent solar, with a strong evolution of the mass-metallicity relation from lower redshifts. Stellar masses, gas fraction and evolutionary stages vary significantly among the galaxies, with less massive galaxies showing larger fractions of gas. In contrast with observations in the local universe, effective yields decrease with stellar mass and reach solar values at the low-mass end of the sample. This effect can be reproduced by gas infall with rates of the order of the SFRs. Outflows are present but are not needed to explain the mass-metallicity relation. We conclude that a large fraction of these galaxies is actively creating stars after major episodes of gas infall or merging. Based on observations collected with European Southern Observatory/Very Large Telescope (ESO/VLT) (proposals 075.A-0300 and 076.A-0711), with the Italian TNG, operated by FGG (INAF) at the Spanish Observatorio del Roque de los Muchachos, and with the Spitzer Space Telescope, operated by JPL (Caltech) under a contract with NASA.

  6. LOW-METALLICITY YOUNG CLUSTERS IN THE OUTER GALAXY. I. Sh 2-207

    SciTech Connect

    Yasui, Chikako; Kobayashi, Naoto; Izumi, Natsuko; Tokunaga, Alan T.; Saito, Masao

    2016-03-15

    To study star formation in low-metallicity environments ([M/H] ∼ −1 dex), we obtained deep near-infrared (NIR) images of Sh 2-207 (S207), which is an H ii region in the outer Galaxy with a spectroscopically determined metallicity of [O/H] ≃ −0.8 dex. We identified a young cluster in the western region of S207 with a limiting magnitude of K{sub S} = 19.0 mag (10σ) that corresponds to a mass detection limit of ≲0.1 M{sub ⊙} and enables the comparison of star-forming properties under low metallicity with those of the solar neighborhood. From the fitting of the K-band luminosity function (KLF), the age and distance of the S207 cluster are estimated at 2–3 Myr and ∼4 kpc, respectively. The estimated age is consistent with the suggestion of small extinctions of stars in the cluster (A{sub V} ∼ 3 mag) and the non-detection of molecular clouds. The reasonably good fit between the observed KLF and the model KLF suggests that the underlying initial mass function (IMF) of the cluster down to the detection limit is not significantly different from the typical IMFs in the solar metallicity. From the fraction of stars with NIR excesses, a low disk fraction (<10%) in the cluster with a relatively young age is suggested, as we had previously proposed.

  7. The Host Galaxies of Fast-Ejecta Core-Collapse Supernovae

    NASA Technical Reports Server (NTRS)

    Kelly, Patrick L.; Filippenko, Alexei V.; Modjaz, Maryam; Kocevski, Daniel

    2014-01-01

    Spectra of broad-lined Type Ic supernovae (SN Ic-BL), the only kind of SN observed at the locations of long-duration gamma-ray bursts (LGRBs), exhibit wide features indicative of high ejecta velocities ((is) approximately 0.1c). We study the host galaxies of a sample of 245 low-redshift (z (is) less than 0.2) core-collapse SN, including 17 SN Ic-BL, discovered by galaxy-untargeted searches, and 15 optically luminous and dust-obscured z (is) less than 1.2 LGRBs. We show that, in comparison with SDSS galaxies having similar stellar masses, the hosts of low-redshift SN Ic- BL and z (is) is less than 1.2 LGRBs have high stellar-mass and star-formation-rate densities. Core-collapse SN having typical ejecta velocities, in contrast, show no preference for such galaxies. Moreover, we find that the hosts of SN Ic-BL, unlike those of SN Ib/Ic and SN II, exhibit high gas velocity dispersions for their stellar masses. The patterns likely reflect variations among star-forming environments, and suggest that LGRBs can be used as probes of conditions in high-redshift galaxies. They may be caused by efficient formation of massive binary progenitors systems in densely star-forming regions, or, less probably, a higher fraction of stars created with the initial masses required for a SN Ic-BL or LGRB. Finally, we show that the preference of SN Ic-BL and LGRBs for galaxies with high stellar-mass and star-formation-rate densities cannot be attributed to a preference for low metal abundances but must reflect the influence of a separate environmental factor.

  8. The host galaxies of fast-ejecta core-collapse supernovae

    SciTech Connect

    Kelly, Patrick L.; Filippenko, Alexei V.; Modjaz, Maryam; Kocevski, Daniel

    2014-07-01

    Spectra of broad-lined Type Ic supernovae (SNe Ic-BL), the only kind of SN observed at the locations of long-duration gamma-ray bursts (LGRBs), exhibit wide features indicative of high ejecta velocities (∼0.1c). We study the host galaxies of a sample of 245 low-redshift (z < 0.2) core-collapse SNe, including 17 SNe Ic-BL, discovered by galaxy-untargeted searches, and 15 optically luminous and dust-obscured z < 1.2 LGRBs. We show that, in comparison with Sloan Digital Sky Survey galaxies having similar stellar masses, the hosts of low-redshift SNe Ic-BL and z < 1.2 LGRBs have high stellar mass and star formation rate densities. Core-collapse SNe having typical ejecta velocities, in contrast, show no preference for such galaxies. Moreover, we find that the hosts of SNe Ic-BL, unlike those of SNe Ib/Ic and SNe II, exhibit high gas velocity dispersions for their stellar masses. The patterns likely reflect variations among star-forming environments and suggest that LGRBs can be used as probes of conditions in high-redshift galaxies. They may be caused by efficient formation of massive binary progenitor systems in densely star-forming regions, or, less probably, a higher fraction of stars created with the initial masses required for an SN Ic-BL or LGRB. Finally, we show that the preference of SNe Ic-BL and LGRBs for galaxies with high stellar mass and star formation rate densities cannot be attributed to a preference for low metal abundances but must reflect the influence of a separate environmental factor.

  9. Dust-to-gas Ratio in the Extremely Metal-poor Galaxy I Zw 18

    NASA Astrophysics Data System (ADS)

    Herrera-Camus, Rodrigo; Fisher, David B.; Bolatto, Alberto D.; Leroy, Adam K.; Walter, Fabian; Gordon, Karl. D.; Roman-Duval, Julia; Donaldson, Jessica; Meléndez, Marcio; Cannon, John M.

    2012-06-01

    The blue compact dwarf galaxy I Zw 18 is one of the most metal-poor systems known in the local universe (12+log(O/H) = 7.17). In this work we study I Zw 18 using data from Spitzer, Herschel Space Telescope, and IRAM Plateau de Bure Interferometer. Our data set includes the most sensitive maps of I Zw 18, to date, in both the far-infrared and the CO J = 1 → 0 transition. We use dust emission models to derive a dust mass upper limit of only M dust <= 1.1 × 104 M ⊙ (3σ limit). This upper limit is driven by the non-detection at 160 μm, and it is a factor of 4-10 times smaller than previous estimates (depending on the model used). We also estimate an upper limit to the total dust-to-gas mass ratio of M Dust/M gas <= 5.0 × 10-5. If a linear correlation between the dust-to-gas mass ratio and metallicity (measured as O/H) were to hold, we would expect a ratio of 3.9 × 10-4. We also show that the infrared spectral energy distribution is similar to that of starbursting systems.

  10. The IC 342-Maffei 1 Group Revealed

    NASA Astrophysics Data System (ADS)

    McCall, M. L.; Buta, R.

    1996-12-01

    Deep wide-field CCD images of thirteen members of the IC 342-Maffei 1 Group in the Northern Milky Way have been acquired in the Johnson V and Cousins I photometric systems. The observations were obtained with the Kitt Peak Burrell-Schmidt telescope in Arizona during six nights in November 1995. Almost none of these galaxies was effectively studied in the past because of the heavy foreground extinction and significant foreground star contamination in the direction of the group. The tens of thousands of foreground stars included on the Schmidt images have been successfully subtracted using DAOPHOT, revealing the true extent and total brightness of most of the galaxies for the first time. In the absence of galactic extinction, Maffei 1, Maffei 2, and IC 342 would be among the five brightest galaxies in the northern sky, and both Maffei 1 and IC 342 would subtend angles as large as the full Moon. The results are critical for assessing the degree to which the group influenced the dynamical evolution of the Local Group. In this poster, we will present deep photographs, total magnitudes and color indices, luminosity profiles, and distance estimates for the member galaxies.

  11. Strongly time-variable ultraviolet metal-line emission from the circum-galactic medium of high-redshift galaxies

    NASA Astrophysics Data System (ADS)

    Sravan, Niharika; Faucher-Giguère, Claude-André; van de Voort, Freeke; Kereš, Dušan; Muratov, Alexander L.; Hopkins, Philip F.; Feldmann, Robert; Quataert, Eliot; Murray, Norman

    2016-11-01

    We use cosmological simulations from the Feedback In Realistic Environments project, which implement a comprehensive set of stellar feedback processes, to study ultraviolet (UV) metal-line emission from the circum-galactic medium of high-redshift (z = 2-4) galaxies. Our simulations cover the halo mass range Mh ˜ 2 × 1011-8.5 × 1012 M⊙ at z = 2, representative of Lyman break galaxies. Of the transitions we analyse, the low-ionization C III (977 Å) and Si III (1207 Å) emission lines are the most luminous, with C IV (1548 Å) and Si IV (1394 Å) also showing interesting spatially extended structures. The more massive haloes are on average more UV-luminous. The UV metal-line emission from galactic haloes in our simulations arises primarily from collisionally ionized gas and is strongly time variable, with peak-to-trough variations of up to ˜2 dex. The peaks of UV metal-line luminosity correspond closely to massive and energetic mass outflow events, which follow bursts of star formation and inject sufficient energy into galactic haloes to power the metal-line emission. The strong time variability implies that even some relatively low-mass haloes may be detectable. Conversely, flux-limited samples will be biased towards haloes whose central galaxy has recently experienced a strong burst of star formation. Spatially extended UV metal-line emission around high-redshift galaxies should be detectable by current and upcoming integral field spectrographs such as the Multi Unit Spectroscopic Explorer on the Very Large Telescope and Keck Cosmic Web Imager.

  12. The metal-poor knee in the Fornax dwarf spheroidal galaxy

    SciTech Connect

    Hendricks, Benjamin; Koch, Andreas; Lanfranchi, Gustavo A.; Boeche, Corrado; Walker, Matthew; Johnson, Christian I.; Peñarrubia, Jorge; Gilmore, Gerard

    2014-04-20

    We present α-element abundances of Mg, Si, and Ti for a large sample of field stars in two outer fields of the Fornax dwarf spheroidal (dSph) galaxy, obtained with Very Large Telescope/GIRAFFE (R ∼ 16, 000). Due to the large fraction of metal-poor (MP) stars in our sample, we are able to follow the α-element evolution from [Fe/H] ≈ –2.5 continuously to [Fe/H] ≈ –0.7. For the first time we are able to resolve the turnover from the Type II supernovae (SNe) dominated, α-enhanced plateau down to subsolar [α/Fe] values, due to the onset of SNe Ia, and thus to trace the chemical enrichment efficiency of the galaxy. Our data support the general concept of an α-enhanced plateau at early epochs, followed by a well-defined 'knee' caused by the onset of SNe Ia, and finally a second plateau with sub-solar [α/Fe] values. We find the position of this knee to be at [Fe/H] ≈ –1.9 and therefore significantly more MP than expected from comparison with other dSphs and standard evolutionary models. Surprisingly, this value is rather comparable to the knee in Sculptor, a dSph ∼10 times less luminous than Fornax. Using chemical evolution models, we find that the position of the knee and the subsequent plateau at the sub-solar level can hardly be explained unless the galaxy experienced several discrete star formation (SF) events with a drastic variation in SF efficiency, while a uniform SF can be ruled out. One possible evolutionary scenario is that Fornax experienced one or several major accretion events from gas-rich systems in the past, so that its current stellar mass is not indicative of the chemical evolution environment at ancient times. If Fornax is the product of several smaller buildings blocks, this may also have implications for the understanding of the formation process of dSphs in general.

  13. The Metal-poor Knee in the Fornax Dwarf Spheroidal Galaxy

    NASA Astrophysics Data System (ADS)

    Hendricks, Benjamin; Koch, Andreas; Lanfranchi, Gustavo A.; Boeche, Corrado; Walker, Matthew; Johnson, Christian I.; Peñarrubia, Jorge; Gilmore, Gerard

    2014-04-01

    We present α-element abundances of Mg, Si, and Ti for a large sample of field stars in two outer fields of the Fornax dwarf spheroidal (dSph) galaxy, obtained with Very Large Telescope/GIRAFFE (R ~ 16, 000). Due to the large fraction of metal-poor (MP) stars in our sample, we are able to follow the α-element evolution from [Fe/H] ≈ -2.5 continuously to [Fe/H] ≈ -0.7. For the first time we are able to resolve the turnover from the Type II supernovae (SNe) dominated, α-enhanced plateau down to subsolar [α/Fe] values, due to the onset of SNe Ia, and thus to trace the chemical enrichment efficiency of the galaxy. Our data support the general concept of an α-enhanced plateau at early epochs, followed by a well-defined "knee" caused by the onset of SNe Ia, and finally a second plateau with sub-solar [α/Fe] values. We find the position of this knee to be at [Fe/H] ≈ -1.9 and therefore significantly more MP than expected from comparison with other dSphs and standard evolutionary models. Surprisingly, this value is rather comparable to the knee in Sculptor, a dSph ~10 times less luminous than Fornax. Using chemical evolution models, we find that the position of the knee and the subsequent plateau at the sub-solar level can hardly be explained unless the galaxy experienced several discrete star formation (SF) events with a drastic variation in SF efficiency, while a uniform SF can be ruled out. One possible evolutionary scenario is that Fornax experienced one or several major accretion events from gas-rich systems in the past, so that its current stellar mass is not indicative of the chemical evolution environment at ancient times. If Fornax is the product of several smaller buildings blocks, this may also have implications for the understanding of the formation process of dSphs in general. This article is based on observations made with ESO Telescopes at the Paranal Observatory under program 082.B-0940(A).

  14. A Study of Low-Metallicity Red Giant Stars in the Ursa Minor Dwarf Spheroidal Galaxy Using APOGEE Survey Data

    NASA Astrophysics Data System (ADS)

    Fu, Wanying; Simon, Joshua D.; APOGEE-2

    2017-01-01

    Studying the chemical evolution of stars in the Milky Way’s faint dwarf galaxy satellites can provide valuable insight into the formation of the Galaxy and its companions. Past chemical abundance studies of the Ursa Minor dwarf spheroidal galaxy contain a maximum of sixteen stars, but large surveys such as APOGEE (Apache Point Observatory Galactic Evolution Experiment), which perform high-resolution spectroscopy (R ˜ 22,500) for hundreds of stars at a time, have the potential to vastly expand the amount of available stellar chemical abundance data and provide a more comprehensive view of the dSph’s chemical evolution. However, the APOGEE reduction and analysis pipelines were designed for high S/N observations of bright stars, and have not been tested in the lower S/N regime of dSph stars. We evaluate the performance of the APOGEE pipeline for low S/N spectra taken from faint, low-metallicity stars in the galaxy. We compare APOGEE metallicities against those found in literature, and examine the spectra for elemental absorption lines. We also attempt to constrain the population of binary stars in the dSph.

  15. CORE-COLLAPSE SUPERNOVAE FROM THE PALOMAR TRANSIENT FACTORY: INDICATIONS FOR A DIFFERENT POPULATION IN DWARF GALAXIES

    SciTech Connect

    Arcavi, Iair; Gal-Yam, Avishay; Kasliwal, Mansi M.; Quimby, Robert M.; Ofek, Eran O.; Kulkarni, Shrinivas R.; Law, Nicholas; Cooke, Jeff; Nugent, Peter E.; Poznanski, Dovi; Cenko, S. Bradley; Bloom, Joshua S.; Filippenko, Alexei V.; Sullivan, Mark; Hook, Isobel; Joensson, Jakob; Blake, Sarah; Howell, D. Andrew; Dekany, Richard; Rahmer, Gustavo

    2010-09-20

    We use the first compilation of 72 core-collapse supernovae (SNe) from the Palomar Transient Factory (PTF) to study their observed subtype distribution in dwarf galaxies compared to giant galaxies. Our sample is the largest single-survey, untargeted, spectroscopically classified, homogeneous collection of core-collapse events ever assembled, spanning a wide host-galaxy luminosity range (down to M{sub r} {approx} -14 mag) and including a substantial fraction (>20%) of dwarf (M{sub r} {>=} -18 mag) hosts. We find more core-collapse SNe in dwarf galaxies than expected and several interesting trends emerge. We use detailed subclassifications of stripped-envelope core-collapse SNe and find that all Type I core-collapse events occurring in dwarf galaxies are either SNe Ib or broad-lined SNe Ic (SNe Ic-BL), while 'normal' SNe Ic dominate in giant galaxies. We also see a significant excess of SNe IIb in dwarf hosts. We hypothesize that in lower metallicity hosts, metallicity-driven mass loss is reduced, allowing massive stars that would have appeared as 'normal' SNe Ic in metal-rich galaxies to retain some He and H, exploding as Ib/IIb events. At the same time, another mechanism allows some stars to undergo extensive stripping and explode as SNe Ic-BL (and presumably also as long-duration gamma-ray bursts). Our results are still limited by small-number statistics, and our measurements of the observed N(Ib/c)/N(II) number ratio in dwarf and giant hosts (0.25{sup +0.3}{sub -0.15} and 0.23{sup +0.11}{sub -0.08}, respectively; 1{sigma} uncertainties) are consistent with previous studies and theoretical predictions. As additional PTF data accumulate, more robust statistical analyses will be possible, allowing the evolution of massive stars to be probed via the dwarf-galaxy SN population.

  16. The H II regions of IC 1613

    SciTech Connect

    Price, J.S.; Mason, S.F.; Gullixson, C.A. Prime Computer, Inc., Bedford, MA Lowell Observatory, Flagstaff, AZ )

    1990-08-01

    New H-alpha images are presented of IC 1613, a small irregular galaxy in the Local Group. The images, obtained with a CCD on the 42-in telescope at Lowell Observatory, have been calibrated and used to produce an H-alpha luminosity function and a size distribution for the H II regions in IC 1613. The results are compared to results for NGC 6822 and the Magellanic Clouds. The size distribution is found to be Poissonian over a limited range. 24 refs.

  17. 'Direct' Gas-Phase Metallicities, Stellar Properties, and Local Environments of Emission-Line Galaxies at Redshifts Below 0.90

    NASA Technical Reports Server (NTRS)

    Ly, Chun; Malkan, Matthew A.; Nagao, Tohru; Kashikawa, Nobunari; Shimasaku, Kazuhiro; Hayashi, Masao

    2013-01-01

    Using deep narrow-band (NB) imaging and optical spectroscopy from the Keck telescope and the Multi Mirror Telescope (MMT), we identify a sample of 20 emission-line galaxies (ELGs) at z = 0.065-0.90 where the weak auroral emission line, [O iii] lambda4363, is detected at >=3sigma. These detections allow us to determine the gas-phase metallicity using the "direct" method. With electron temperature measurements, and dust attenuation corrections from Balmer decrements, we find that 4 of these low-mass galaxies are extremely metal-poor with 12+log(O/H) <= 7.65 or one-tenth solar. Our most metal-deficient galaxy has 12+log(O/H)= 7.24(+0.45 / -0.30) (95% confidence), similar to some of the lowest metallicity galaxies identified in the local universe. We find that our galaxies are all undergoing significant star formation with average specific star formation rate (SFR) of (100 Myra)(exp -1), and that they have high central SFR surface densities (average of 0.5 Solar M / yr/ sq. kpc). In addition, more than two-thirds of our galaxies have between one and four nearby companions within a projected radius of 100 kpc, which we find is an excess among star-forming galaxies at z =0.4 -- 0.85. We also find that the gas-phase metallicities for a given stellar mass and SFR lie systematically lower than the local stellar M-Z-(SFR) relation by approx. = 0.2 dex (2 sigma significance). These results are partly due to selection effects, since galaxies with strong star formation and low metallicity are more likely to yield [O iii] lambda4363 detections. Finally, the observed higher ionization parameter and high electron density suggest that they are lower redshift analogs to typical z approx. > 1 galaxies.

  18. High resolution radio and optical observations of the central starburst in the low-metallicity dwarf galaxy II Zw 40

    SciTech Connect

    Kepley, Amanda A.; Reines, Amy E.; Johnson, Kelsey E.; Walker, Lisa May E-mail: areines@nrao.edu E-mail: lisamay@virginia.edu

    2014-02-01

    The extent to which star formation varies in galaxies with low masses, low metallicities, and high star formation rate surface densities is not well constrained. To gain insight into star formation under these physical conditions, this paper estimates the ionizing photon fluxes, masses, and ages for young massive clusters in the central region of II Zw 40—the prototypical low-metallicity dwarf starburst galaxy—from radio continuum and optical observations. Discrete, cluster-sized sources only account for half the total radio continuum emission; the remainder is diffuse. The young (≲ 5 Myr) central burst has a star formation rate surface density that significantly exceeds that of the Milky Way. Three of the 13 sources have ionizing photon fluxes (and thus masses) greater than R136 in 30 Doradus. Although isolating the effects of galaxy mass and metallicity is difficult, the H II region luminosity function and the internal extinction in the center of II Zw 40 appear to be primarily driven by a merger-related starburst. The relatively flat H II region luminosity function may be the result of an increase in interstellar medium pressure during the merger and the internal extinction is similar to that generated by the clumpy and porous dust in other starburst galaxies.

  19. HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS IN THE LEAST EVOLVED GALAXIES: BOÖTES II

    SciTech Connect

    Ji, Alexander P.; Frebel, Anna; Simon, Joshua D.; Geha, Marla

    2016-01-20

    We present high-resolution Magellan/MIKE spectra of the four brightest confirmed red giant stars in the ultra-faint dwarf galaxy Boötes II (Boo II). These stars all inhabit the metal-poor tail of the Boo II metallicity distribution function. The chemical abundance pattern of all detectable elements in these stars is consistent with that of the Galactic halo. However, all four stars have undetectable amounts of neutron-capture elements Sr and Ba, with upper limits comparable to the lowest ever detected in the halo or in other dwarf galaxies. One star exhibits significant radial velocity variations over time, suggesting it to be in a binary system. Its variable velocity has likely increased past determinations of the Boo II velocity dispersion. Our four stars span a limited metallicity range, but their enhanced α-abundances and low neutron-capture abundances are consistent with the interpretation that Boo II has been enriched by very few generations of stars. The chemical abundance pattern in Boo II confirms the emerging trend that the faintest dwarf galaxies have neutron-capture abundances distinct from the halo, suggesting the dominant source of neutron-capture elements in halo stars may be different than in ultra-faint dwarfs.

  20. Molecular gas in low-metallicity starburst galaxies:. Scaling relations and the CO-to-H2 conversion factor

    NASA Astrophysics Data System (ADS)

    Amorín, R.; Muñoz-Tuñón, C.; Aguerri, J. A. L.; Planesas, P.

    2016-04-01

    Context. Tracing the molecular gas-phase in low-mass star-forming galaxies becomes extremely challenging due to significant UV photo-dissociation of CO molecules in their low-dust, low-metallicity ISM environments. Aims: We aim to study the molecular content and the star-formation efficiency of a representative sample of 21 blue compact dwarf galaxies (BCDs), previously characterized on the basis of their spectrophotometric properties. Methods: We present CO (1-0) and (2-1) observations conducted at the IRAM-30m telescope. These data are further supplemented with additional CO measurements and multiwavelength ancillary data from the literature. We explore correlations between the derived CO luminosities and several galaxy-averaged properties. Results: We detect CO emission in seven out of ten BCDs observed. For two galaxies these are the first CO detections reported so far. We find the molecular content traced by CO to be correlated with the stellar and Hi masses, star formation rate (SFR) tracers, the projected size of the starburst, and its gas-phase metallicity. BCDs appear to be systematically offset from the Schmidt-Kennicutt (SK) law, showing lower average gas surface densities for a given ΣSFR, and therefore showing extremely low (≲0.1 Gyr) H2 and H2 +Hi depletion timescales. The departure from the SK law is smaller when considering H2 +Hi rather than H2 only, and is larger for BCDs with lower metallicity and higher specific SFR. Thus, the molecular fraction (ΣH2/ ΣHI) and CO depletion timescale (ΣH2/ ΣSFR) of BCDs is found to be strongly correlated with metallicity. Using this, and assuming that the empirical correlation found between the specific SFR and galaxy-averaged H2 depletion timescale of more metal-rich galaxies extends to lower masses, we derive a metallicity-dependent CO-to-H2 conversion factor αCO,Z ∝ (Z/Z⊙)- y, with y = 1.5(±0.3)in qualitative agreement with previous determinations, dust-based measurements, and recent model

  1. The Ages, Metallicities, and Element Abundance Ratios of Massive Quenched Galaxies at z ≥ 1.6

    NASA Astrophysics Data System (ADS)

    Onodera, M.; Carollo, C. M.; Renzini, A.; Cappellari, M.; Mancini, C.; Arimoto, N.; Daddi, E.; Gobat, R.; Strazzullo, V.; Tacchella, S.; Yamada, Y.

    2015-08-01

    We investigate the stellar population properties of a sample of 24 massive quenched galaxies at 1.25< zspec< 2.09 identified in the COSMOS field with our Subaru/Multi-object Infrared Camera and Spectrograph near-IR spectroscopic observations. Tracing the stellar population properties as close to their major formation epoch as possible, we try to put constraints on the star formation history, post-quenching evolution, and possible progenitor star-forming populations for such massive quenched galaxies. By using a set of Lick absorption line indices on a rest-frame optical composite spectrum, the average age, metallicity [Z/H], and α-to-iron element abundance ratio [α/Fe] are derived as log(age/Gyr)=0.04-0.08+0.10, [Z/H]=0.24-0.14+0.20, and [α /Fe]=0.31-0.12+0.12, respectively. If our sample of quenched galaxies at < z≥1.6 is evolved passively to z = 0, their stellar population properties will align in excellent agreement with local counterparts at similar stellar velocity dispersions, which qualifies them as progenitors of local massive early-type galaxies. Redshift evolution of stellar population ages in quenched galaxies combined with low redshift measurements from the literature suggests a formation redshift of zf∼ 2.3, around which the bulk of stars in these galaxies have been formed. The measured [α/Fe] value indicates a star formation timescale of ≲ 1 Gyr, which can be translated into a specific star formation rate of ≃ 1 Gyr-1 prior to quenching. Based on these findings, we discuss identifying possible progenitor star-forming galaxies at z≃ 2.3. We identify normal star-forming galaxies, i.e., those on the star-forming main sequence, followed by a rapid quenching event, as likely precursors of the quenched galaxies at < z≥1.6 presented here. Based on data collected at the Subaru telescope, which is operated by the National Astronomical Observatory of Japan. (Proposal IDs: S09A-043, S10A-058, and S11A-075.)

  2. THE GAS PHASE MASS METALLICITY RELATION FOR DWARF GALAXIES: DEPENDENCE ON STAR FORMATION RATE AND HI GAS MASS

    SciTech Connect

    Jimmy; Tran, Kim-Vy; Saintonge, Amélie; Accurso, Gioacchino; Brough, Sarah; Oliva-Altamirano, Paola

    2015-10-20

    Using a sample of dwarf galaxies observed using the VIMOS IFU on the Very Large Telescope, we investigate the mass–metallicity relation (MZR) as a function of star formation rate (FMR{sub SFR}) as well as HI-gas mass (FMR{sub HI}). We combine our IFU data with a subsample of galaxies from the ALFALFA HI survey crossmatched to the Sloan Digital Sky Survey (SDSS) to study the FMR{sub SFR} and FMR{sub HI} across the stellar mass range 10{sup 6.6}–10{sup 8.8} M{sub ⊙}, with metallicities as low as 12 + log(O/H) = 7.67. We find the 1σ mean scatter in the MZR to be 0.05 dex. The 1σ mean scatter in the FMR{sub SFR} (0.02 dex) is significantly lower than that of the MZR. The FMR{sub SFR} is not consistent between the IFU observed galaxies and the ALFALFA/SDSS galaxies for SFRs lower than 10{sup −2.4} M{sub ⊙} yr{sup −1}, however, this could be the result of limitations of our measurements in that regime. The lowest mean scatter (0.01 dex) is found in the FMR{sub HI}. We also find that the FMR{sub HI} is consistent between the IFU observed dwarf galaxies and the ALFALFA/SDSS crossmatched sample. We introduce the fundamental metallicity luminosity counterpart to the FMR, again characterized in terms of SFR (FML{sub SFR}) and HI-gas mass (FML{sub HI}). We find that the FML{sub HI} relation is consistent between the IFU observed dwarf galaxy sample and the larger ALFALFA/SDSS sample. However, the 1σ scatter for the FML{sub HI} relation is not improved over the FMR{sub HI} scenario. This leads us to conclude that the FMR{sub HI} is the best candidate for a physically motivated fundamental metallicity relation.

  3. SINFONI-HiZELS: the dynamics, merger rates and metallicity gradients of 'typical' star-forming galaxies at z = 0.8-2.2

    NASA Astrophysics Data System (ADS)

    Molina, J.; Ibar, Edo; Swinbank, A. M.; Sobral, D.; Best, P. N.; Smail, I.; Escala, A.; Cirasuolo, M.

    2017-04-01

    We present adaptive optics (AO) assisted SINFONI integral field unit (IFU) spectroscopy of 11 Hα emitting galaxies selected from the High-Z Emission Line Survey (HiZELS). We obtain spatially resolved dynamics on ∼kpc-scales of star-forming galaxies [stellar mass M⋆ = 109.5 - 10.5 M⊙ and star formation rate (SFR) = 2-30 M⊙ yr-1] near the peak of the cosmic star formation rate history. Combining these observations with our previous SINFONI-HiZELS campaign, we construct a sample of 20 homogeneously selected galaxies with IFU AO-aided observations - the 'SHiZELS' survey, with roughly equal number of galaxies per redshift slice, at z = 0.8, 1.47 and 2.23. We measure the dynamics and identify the major kinematic axis by modelling their velocity fields to extract rotational curves and infer their inclination-corrected rotational velocities. We explore the stellar mass Tully-Fisher relationship, finding that galaxies with higher velocity dispersions tend to deviate from this relation. Using kinemetry analyses, we find that galaxy interactions might be the dominant mechanism controlling the star formation activity at z = 2.23 but they become gradually less important down to z = 0.8. Metallicity gradients derived from the [N II]/Hα emission line ratio show a median negative gradient for the SHiZELS survey of Δlog(O/H)/ΔR = -0.026 ± 0.008 dex kpc-1. We find that metal-rich galaxies tend to show negative gradients, whereas metal-poor galaxies tend to exhibit positive metallicity gradients. This result suggests that the accretion of pristine gas in the periphery of galaxies plays an important role in replenishing the gas in 'typical' star-forming galaxies.

  4. Peanut-shaped metallicity distributions in bulges of edge-on galaxies: the case of NGC 4710

    NASA Astrophysics Data System (ADS)

    Gonzalez, Oscar A.; Debattista, Victor P.; Ness, Melissa; Erwin, Peter; Gadotti, Dimitri A.

    2017-03-01

    Bulges of edge-on galaxies are often boxy/peanut-shaped (B/PS), and unsharp masks reveal the presence of an X shape. Simulations show that these shapes can be produced by dynamical processes driven by a bar which vertically thickens the centre. In the Milky Way, which contains such a B/PS bulge, the X-shaped structure is traced by the metal-rich stars but not by the metal-poor ones. Recently, Debattista et al. interpreted this property as a result of the varying effect of the bar on stellar populations with different starting kinematics. This kinematic fractionation model predicts that cooler populations at the time of bar formation go on to trace the X shape, whereas hotter populations are more uniformly distributed. As this prediction is not specific to the Milky Way, we test it with Multi Unit Spectroscopic Explorer (MUSE) observations of the B/PS bulge in the nearby galaxy NGC 4710. We show that the metallicity map is more peanut-shaped than the density distribution itself, in good agreement with the prediction. This result indicates that the X-shaped structure in B/PS bulges is formed of relatively metal-rich stars that have been vertically redistributed by the bar, whereas the metal-poor stars have a more uniform, box-shaped distribution.

  5. DISCOVERY OF MIRA VARIABLE STARS IN THE METAL-POOR SEXTANS DWARF SPHEROIDAL GALAXY

    SciTech Connect

    Sakamoto, Tsuyoshi; Matsunaga, Noriyuki; Nakada, Yoshikazu; Hasegawa, Takashi

    2012-12-10

    We report the discovery of two Mira variable stars (Miras) toward the Sextans dwarf spheroidal galaxy (dSph). We performed optical long-term monitoring observations for two red stars in the Sextans dSph. The light curves of both stars in the I{sub c} band show large-amplitude (3.7 and 0.9 mag) and long-period (326 {+-} 15 and 122 {+-} 5 days) variations, suggesting that they are Miras. We combine our own infrared data with previously published data to estimate the mean infrared magnitudes. The distances obtained from the period-luminosity relation of the Miras (75.3{sup +12.8}{sub -10.9} and 79.8{sup +11.5}{sub -9.9} kpc, respectively), together with the radial velocities available, support memberships of the Sextans dSph (90.0 {+-} 10.0 kpc). These are the first Miras found in a stellar system with a metallicity as low as [Fe/H] {approx} -1.9 than any other known system with Miras.

  6. The Herschel Virgo Cluster Survey. IX. Dust-to-gas mass ratio and metallicity gradients in four Virgo spiral galaxies

    NASA Astrophysics Data System (ADS)

    Magrini, L.; Bianchi, S.; Corbelli, E.; Cortese, L.; Hunt, L.; Smith, M.; Vlahakis, C.; Davies, J.; Bendo, G. J.; Baes, M.; Boselli, A.; Clemens, M.; Casasola, V.; De Looze, I.; Fritz, J.; Giovanardi, C.; Grossi, M.; Hughes, T.; Madden, S.; Pappalardo, C.; Pohlen, M.; di Serego Alighieri, S.; Verstappen, J.

    2011-11-01

    Context. Using Herschel data from the open time key project the Herschel Virgo Cluster Survey (HeViCS), we investigated the relationship between the metallicity gradients expressed by metal abundances in the gas phase as traced by the chemical composition of HII regions, and in the solid phase, as traced by the dust-to-gas mass ratio. Aims: We derived the radial gradient of the dust-to-gas mass ratio for all galaxies observed by HeViCS whose metallicity gradients are available in the literature. They are all late type Sbc galaxies, namely NGC 4254, NGC 4303, NGC 4321, and NGC 4501. Methods: We fitted PACS and SPIRE observations with a single-temperature modified blackbody, inferred the dust mass, and calculated two dimensional maps of the dust-to-gas mass ratio, with the total mass of gas from available HI and CO maps. HI moment-1 maps were used to derive the geometric parameters of the galaxies and extract the radial profiles. We examined different dependencies on metallicity of the CO-to-H2 conversion factor (XCO), used to transform the 12CO observations into the amount of molecular hydrogen. Results: We found that in these galaxies the dust-to-gas mass ratio radial profile is extremely sensitive to choice of the XCO value, since the molecular gas is the dominant component in the inner parts. We found that for three galaxies of our sample, namely NGC 4254, NGC 4321, and NGC 4501, the slopes of the oxygen and of the dust-to-gas radial gradients agree up to ~0.6-0.7 R25 using XCO values in the range 1/3-1/2 Galactic XCO. For NGC 4303 a lower value of XCO ~ 0.1 × 1020 is necessary. Conclusions: We suggest that such low XCO values might be due to a metallicity dependence of XCO (from close to linear for NGC 4254, NGC 4321, and NGC 4501 to superlinear for NGC 4303), especially in the radial regions RG < 0.6-0.7 R25 where the molecular gas dominates. On the other hand, the outer regions, where the atomic gas component is dominant, are less affected by the choice of

  7. THE X-RAY LUMINOSITY FUNCTION OF LOW MASS X-RAY BINARIES IN EARLY-TYPE GALAXIES, THEIR METAL-RICH, AND METAL-POOR GLOBULAR CLUSTERS

    SciTech Connect

    Peacock, Mark B.; Zepf, Stephen E.

    2016-02-10

    We present the X-ray luminosity function (XLF) of low-mass X-ray binaries (LMXBs) in the globular clusters (GCs) and fields of seven early-type galaxies. These galaxies are selected to have both deep Chandra observations, which allow their LMXB populations to be observed to X-ray luminosities of 10{sup 37}–10{sup 38} erg s{sup −1}, and Hubble Space Telescope optical mosaics that enable the X-ray sources to be separated into field LMXBs, GC LMXBs, and contaminating background and foreground sources. We find that at all luminosities the number of field LMXBs per stellar mass is similar in these galaxies. This suggests that the field LMXB populations in these galaxies are not effected by the GC specific frequency, and that properties such as binary fraction and the stellar initial mass function are either similar across the sample or change in a way that does not affect the number of LMXBs. We compare the XLF of the field LMXBs to that of the GC LMXBs and find that they are significantly different with a p-value of 3 × 10{sup −6} (equivalent to 4.7σ for a normal distribution). The difference is such that the XLF of the GC LMXBs is flatter than that of the field LMXBs, with the GCs hosting relatively more bright sources and fewer faint sources. A comparison of the XLF of the metal-rich and metal-poor GCs hints that the metal-poor clusters may have more bright LMXBs, but the difference is not statistically significant.

  8. Semiconductor/High-Tc-Superconductor Hybrid ICs

    NASA Technical Reports Server (NTRS)

    Burns, Michael J.

    1995-01-01

    Hybrid integrated circuits (ICs) containing both Si-based semiconducting and YBa(2)Cu(3)O(7-x) superconducting circuit elements on sapphire substrates developed. Help to prevent diffusion of Cu from superconductors into semiconductors. These hybrid ICs combine superconducting and semiconducting features unavailable in superconducting or semiconducting circuitry alone. For example, complementary metal oxide/semiconductor (CMOS) readout and memory devices integrated with fast-switching Josephson-junction super-conducting logic devices and zero-resistance interconnections.

  9. High Rate for Type IC Supernovae

    SciTech Connect

    Muller, R.A.; Marvin-Newberg, H.J.; Pennypacker, Carl R.; Perlmutter, S.; Sasseen, T.P.; Smith, C.K.

    1991-09-01

    Using an automated telescope we have detected 20 supernovae in carefully documented observations of nearby galaxies. The supernova rates for late spiral (Sbc, Sc, Scd, and Sd) galaxies, normalized to a blue luminosity of 10{sup 10} L{sub Bsun}, are 0.4 h{sup 2}, 1.6 h{sup 2}, and 1.1 h{sup 2} per 100 years for SNe type la, Ic, and II. The rate for type Ic supernovae is significantly higher than found in previous surveys. The rates are not corrected for detection inefficiencies, and do not take into account the indications that the Ic supernovae are fainter on the average than the previous estimates; therefore the true rates are probably higher. The rates are not strongly dependent on the galaxy inclination, in contradiction to previous compilations. If the Milky Way is a late spiral, then the rate of Galactic supernovae is greater than 1 per 30 {+-} 7 years, assuming h = 0.75. This high rate has encouraging consequences for future neutrino and gravitational wave observatories.

  10. The Herschel Virgo Cluster Survey. V. Star-forming dwarf galaxies - dust in metal-poor environments

    NASA Astrophysics Data System (ADS)

    Grossi, M.; Hunt, L. K.; Madden, S.; Vlahakis, C.; Bomans, D. J.; Baes, M.; Bendo, G. J.; Bianchi, S.; Boselli, A.; Clemens, M.; Corbelli, E.; Cortese, L.; Dariush, A.; Davies, J. I.; De Looze, I.; di Serego Alighieri, S.; Fadda, D.; Fritz, J.; Garcia-Appadoo, D. A.; Gavazzi, G.; Giovanardi, C.; Hughes, T. M.; Jones, A. P.; Pierini, D.; Pohlen, M.; Sabatini, S.; Smith, M. W. L.; Verstappen, J.; Xilouris, E. M.; Zibetti, S.

    2010-07-01

    We present the dust properties of a small sample of Virgo cluster dwarf galaxies drawn from the science demonstration phase data set of the Herschel Virgo Cluster Survey. These galaxies have low metallicities (7.8 < 12 + log(O/H) < 8.3) and star-formation rates ≲10-1 M⊙ yr-1. We measure the spectral energy distribution (SED) from 100 to 500 μm and derive dust temperatures and dust masses. The SEDs are fitted by a cool component of temperature T ≲ 20 K, implying dust masses around 105 M⊙ and dust-to-gas ratios D within the range 10-3-10-2. The completion of the full survey will yield a larger set of galaxies, which will provide more stringent constraints on the dust content of star-forming dwarf galaxies. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

  11. Stellar Kinematics and Metallicities in the Draco and Ursa Minor Dwarf Spheroidal Galaxies from WHT/AF2-WYFFOS

    NASA Astrophysics Data System (ADS)

    Jin, S.; Irwin, M.; Tolstoy, E.; Lewis, J.; Hartke, J.

    2016-10-01

    We present preliminary results from our chemo-dynamical survey of two Milky Way dwarf spheroidal (dSph) galaxies, Draco and Ursa Minor. The two galaxies have similar radial velocities and reside in close proximity in the outskirts of the Milky Way halo, yet exhibit noteworthy differences in their morphologies. We obtained spectroscopic data with AF2-WYFFOS on the WHT for several hundred red-giant-branch (RGB) candidates in each galaxy out to its tidal radius, from which we have identified approximately 100 velocity members in each system. Metallicities are determined for the individual RGB stars using the Ca II triplet lines. Whereas Ursa Minor shows an RGB population of well-mixed metallicities, a clear gradient is observed in Draco, in which the outer regions host stars of lower [Fe/H]. Such differences may be a reflection of their differing morphologies, with Ursa Minor having been tidally stirred to give rise to both its highly elongated shape and a more mixed [Fe/H] distribution.

  12. The Swift GRB Host Galaxy Legacy Survey. II. Rest-frame Near-IR Luminosity Distribution and Evidence for a Near-solar Metallicity Threshold

    NASA Astrophysics Data System (ADS)

    Perley, D. A.; Tanvir, N. R.; Hjorth, J.; Laskar, T.; Berger, E.; Chary, R.; de Ugarte Postigo, A.; Fynbo, J. P. U.; Krühler, T.; Levan, A. J.; Michałowski, M. J.; Schulze, S.

    2016-01-01

    We present rest-frame near-IR (NIR) luminosities and stellar masses for a large and uniformly selected population of gamma-ray burst (GRB) host galaxies using deep Spitzer Space Telescope imaging of 119 targets from the Swift GRB Host Galaxy Legacy Survey spanning 0.03 < z < 6.3, and we determine the effects of galaxy evolution and chemical enrichment on the mass distribution of the GRB host population across cosmic history. We find a rapid increase in the characteristic NIR host luminosity between z ˜ 0.5 and z ˜ 1.5, but little variation between z ˜ 1.5 and z ˜ 5. Dust-obscured GRBs dominate the massive host population but are only rarely seen associated with low-mass hosts, indicating that massive star-forming galaxies are universally and (to some extent) homogeneously dusty at high redshift while low-mass star-forming galaxies retain little dust in their interstellar medium. Comparing our luminosity distributions with field surveys and measurements of the high-z mass-metallicity relation, our results have good consistency with a model in which the GRB rate per unit star formation is constant in galaxies with gas-phase metallicity below approximately the solar value but heavily suppressed in more metal-rich environments. This model also naturally explains the previously reported “excess” in the GRB rate beyond z ≳ 2 metals stifle GRB production in most galaxies at z < 1.5 but have only minor impact at higher redshifts. The metallicity threshold we infer is much higher than predicted by single-star models and favors a binary progenitor. Our observations also constrain the fraction of cosmic star formation in low-mass galaxies undetectable to Spitzer to be small at z < 4.

  13. THE SWIFT GRB HOST GALAXY LEGACY SURVEY. II. REST-FRAME NEAR-IR LUMINOSITY DISTRIBUTION AND EVIDENCE FOR A NEAR-SOLAR METALLICITY THRESHOLD

    SciTech Connect

    Perley, D. A.; Tanvir, N. R.; Hjorth, J.; Fynbo, J. P. U.; Krühler, T.; Laskar, T.; Berger, E.; Chary, R.; Postigo, A. de Ugarte; Michałowski, M. J.; Schulze, S.

    2016-01-20

    We present rest-frame near-IR (NIR) luminosities and stellar masses for a large and uniformly selected population of gamma-ray burst (GRB) host galaxies using deep Spitzer Space Telescope imaging of 119 targets from the Swift GRB Host Galaxy Legacy Survey spanning 0.03 < z < 6.3, and we determine the effects of galaxy evolution and chemical enrichment on the mass distribution of the GRB host population across cosmic history. We find a rapid increase in the characteristic NIR host luminosity between z ∼ 0.5 and z ∼ 1.5, but little variation between z ∼ 1.5 and z ∼ 5. Dust-obscured GRBs dominate the massive host population but are only rarely seen associated with low-mass hosts, indicating that massive star-forming galaxies are universally and (to some extent) homogeneously dusty at high redshift while low-mass star-forming galaxies retain little dust in their interstellar medium. Comparing our luminosity distributions with field surveys and measurements of the high-z mass–metallicity relation, our results have good consistency with a model in which the GRB rate per unit star formation is constant in galaxies with gas-phase metallicity below approximately the solar value but heavily suppressed in more metal-rich environments. This model also naturally explains the previously reported “excess” in the GRB rate beyond z ≳ 2; metals stifle GRB production in most galaxies at z < 1.5 but have only minor impact at higher redshifts. The metallicity threshold we infer is much higher than predicted by single-star models and favors a binary progenitor. Our observations also constrain the fraction of cosmic star formation in low-mass galaxies undetectable to Spitzer to be small at z < 4.

  14. Definitive Measurements of the Mass-Metallicity-SFR Relation at z=0.2--1 with Low-Mass Starbursting Galaxies

    NASA Astrophysics Data System (ADS)

    Ly, Chun

    2014-02-01

    The gas-phase metallicity of galaxies--and how it depends on stellar mass, star formation rate, and redshift--is the key test of galaxy evolution models based on accretion and star-formation 'feedback'. It is even possible that metallicity, M* and SFR all obey a single 'fundamental relation', which could be universal from z=0--3. However, there are hardly any metallicity measurements to test these relations beyond the local Universe, especially in low-mass galaxies with extreme star formation. We request one DEIMOS night to obtain gas metallicity measurements in the key unexplored parameter space. We will prioritize 300 low-mass, and/or high-EW emission-line galaxies at z=0.2-1 (the last half of cosmic history), in the Subaru Deep Field (SDF). The SDF is ideal for such a survey because of its unique imaging data, which allow us to identify a much higher surface density of known high-EW line-emitting galaxies, all of which have well-determined stellar masses. This sam! ple is roughly 10 times larger than the existing data for similar properties of galaxies.

  15. METAL-POOR, COOL GAS IN THE CIRCUMGALACTIC MEDIUM OF A z = 2.4 STAR-FORMING GALAXY: DIRECT EVIDENCE FOR COLD ACCRETION?

    SciTech Connect

    Crighton, Neil H. M.; Hennawi, Joseph F.; Prochaska, J. Xavier

    2013-10-20

    In our current galaxy formation paradigm, high-redshift galaxies are predominantly fueled by accretion of cool, metal-poor gas from the intergalactic medium. Hydrodynamical simulations predict that this material should be observable in absorption against background sightlines within a galaxy's virial radius, as optically thick Lyman limit systems (LLSs) with low metallicities. Here we report the discovery of exactly such a strong metal-poor absorber at an impact parameter R = 58 kpc from a star-forming galaxy at z = 2.44. Besides strong neutral hydrogen (N{sub H{sup 0}}=10{sup 19.50±0.16} cm{sup -2}) we detect neutral deuterium and oxygen, allowing a precise measurement of the metallicity: log{sub 10}(Z/Z {sub ☉}) = –2.0 ± 0.17, or (7-15) × 10{sup –3} solar. Furthermore, the narrow deuterium linewidth requires a cool temperature <20,000 K. Given the striking similarities between this system and the predictions of simulations, we argue that it represents the direct detection of a high-redshift cold-accretion stream. The low-metallicity gas cloud is a single component of an absorption system exhibiting a complex velocity, ionization, and enrichment structure. Two other components have metallicities >0.1 solar, 10 times larger than the metal-poor component. We conclude that the photoionized circumgalactic medium (CGM) of this galaxy is highly inhomogeneous: the majority of the gas is in a cool, metal-poor and predominantly neutral phase, but the majority of the metals are in a highly ionized phase exhibiting weak neutral hydrogen absorption but strong metal absorption. If such inhomogeneity is common, then high-resolution spectra and detailed ionization modeling are critical to accurately appraise the distribution of metals in the high-redshift CGM.

  16. The molecular gas reservoir of 6 low-metallicity galaxies from the Herschel Dwarf Galaxy Survey. A ground-based follow-up survey of CO(1-0), CO(2-1), and CO(3-2)

    NASA Astrophysics Data System (ADS)

    Cormier, D.; Madden, S. C.; Lebouteiller, V.; Hony, S.; Aalto, S.; Costagliola, F.; Hughes, A.; Rémy-Ruyer, A.; Abel, N.; Bayet, E.; Bigiel, F.; Cannon, J. M.; Cumming, R. J.; Galametz, M.; Galliano, F.; Viti, S.; Wu, R.

    2014-04-01

    Context. Observations of nearby starburst and spiral galaxies have revealed that molecular gas is the driver of star formation. However, some nearby low-metallicity dwarf galaxies are actively forming stars, but CO, the most common tracer of this reservoir, is faint, leaving us with a puzzle about how star formation proceeds in these environments. Aims: We aim to quantify the molecular gas reservoir in a subset of 6 galaxies from the Herschel Dwarf Galaxy Survey with newly acquired CO data and to link this reservoir to the observed star formation activity. Methods: We present CO(1-0), CO(2-1), and CO(3-2) observations obtained at the ATNF Mopra 22-m, APEX, and IRAM 30-m telescopes, as well as [C ii] 157μm and [O i] 63μm observations obtained with the Herschel/PACS spectrometer in the 6 low-metallicity dwarf galaxies: Haro 11, Mrk 1089, Mrk 930, NGC 4861, NGC 625, and UM 311. We derived their molecular gas masses from several methods, including using the CO-to-H2 conversion factor XCO (both Galactic and metallicity-scaled values) and dust measurements. The molecular and atomic gas reservoirs were compared to the star formation activity. We also constrained the physical conditions of the molecular clouds using the non-LTE code RADEX and the spectral synthesis code Cloudy. Results: We detect CO in 5 of the 6 galaxies, including first detections in Haro 11 (Z ~ 0.4 Z⊙), Mrk 930 (0.2 Z⊙), and UM 311 (0.5 Z⊙), but CO remains undetected in NGC 4861 (0.2 Z⊙). The CO luminosities are low, while [C ii] is bright in these galaxies, resulting in [C ii]/CO(1-0) ≥ 10 000. Our dwarf galaxies are in relatively good agreement with the Schmidt-Kennicutt relation for total gas. They show short molecular depletion timescales, even when considering metallicity-scaled XCO factors. Those galaxies are dominated by their H i gas, except Haro 11, which has high star formation efficiency and is dominated by ionized and molecular gas. We determine the mass of each ISM phase in

  17. High-z QSO Absorption Systems: Metal-Poor Cold Flows and Mg II Absorber Host Galaxies

    NASA Astrophysics Data System (ADS)

    Cooper, Thomas; Simcoe, R. A.; Cooksey, K.; O'Meara, J.

    2014-01-01

    Cosmological simulations have suggested a new model for gas accretion in young galaxies, in which baryons flow into the star-forming disk along filamentary streams without shock heating at the dark matter halo virial radius. Observationally, these cold flows manifest as Lyman Limit Systems with low heavy element abundances. To search for cold flows in the early Universe, we have obtained echellette-resolution spectra of an HI-selected sample of LLS at z>3.5 from the Sloan Digital Sky Survey. The sightlines were selected to exhibit no heavy element absorption at the resolution afforded by SDSS, and the higher resolution data provides metallicity measurements precise enough to determine if they exhibit cold flow accretion characteristics. In a parallel program, we use the Magellan Telescopes and HST/WFC-3 to investigate the connection between Mg II absorbers and proximate galaxies at 3, extending fruitful studies of the circumgalactic medium to larger redshift.

  18. Removing Cool Cores and Central Metallicity Peaks in Galaxy Clusters with Powerful Active Galactic Nucleus Outbursts

    NASA Astrophysics Data System (ADS)

    Guo, Fulai; Mathews, William G.

    2010-07-01

    Recent X-ray observations of galaxy clusters suggest that cluster populations are bimodally distributed according to central gas entropy and are separated into two distinct classes: cool core (CC) and non-cool core (NCC) clusters. While it is widely accepted that active galactic nucleus (AGN) feedback plays a key role in offsetting radiative losses and maintaining many clusters in the CC state, the origin of NCC clusters is much less clear. At the same time, a handful of extremely powerful AGN outbursts have recently been detected in clusters, with a total energy ~1061-1062 erg. Using two-dimensional hydrodynamic simulations, we show that if a large fraction of this energy is deposited near the centers of CC clusters, which is likely common due to dense cores, these AGN outbursts can completely remove CCs, transforming them to NCC clusters. Our model also has interesting implications for cluster abundance profiles, which usually show a central peak in CC systems. Our calculations indicate that during the CC to NCC transformation, AGN outbursts efficiently mix metals in cluster central regions and may even remove central abundance peaks if they are not broad enough. For CC clusters with broad central abundance peaks, AGN outbursts decrease peak abundances, but cannot effectively destroy the peaks. Our model may simultaneously explain the contradictory (possibly bimodal) results of abundance profiles in NCC clusters, some of which are nearly flat, while others have strong central peaks similar to those in CC clusters. A statistical analysis of the sizes of central abundance peaks and their redshift evolution may shed interesting insights on the origin of both types of NCC clusters and the evolution history of thermodynamics and AGN activity in clusters.

  19. Properties of the most metal-poor gas-rich LSB dwarf galaxies SDSS J0015+0104 and J2354-0005 residing in the Eridanus void

    NASA Astrophysics Data System (ADS)

    Pustilnik, S. A.; Martin, J.-M.; Lyamina, Y. A.; Kniazev, A. Y.

    2013-07-01

    SDSS J0015+0104 is the lowest metallicity low surface brightness dwarf (LSBD) galaxy known. The oxygen abundance in its H II region SDSS J001520.70+010436.9 (at ˜1.5 kpc from the galaxy centre) is 12+log (O/H) = 7.07 (Guseva et al.). This galaxy, at the distance of 28.4 Mpc, appears to reside deeply in the volume devoid of luminous massive galaxies, known as the Eridanus void. SDSS J235437.29-000501.6 is another Eridanus void LSBD galaxy, with parameter 12+log (O/H) = 7.36 (also Guseva et al.). We present the results of their H I observations with the Nançay Radio Telescope revealing their high ratios of M(H I)/LB ˜ 2.3. Based on the Sloan Digital Sky Survey images, we derived for both galaxies their radial surface brightness profiles and the main photometric parameters. Their colours and total magnitudes are used to estimate the galaxy stellar mass and ages. The related gas mass fractions, fg ˜ 0.98 and ˜0.97, and the extremely low metallicities (much lower than for their more typical counterparts with the same luminosity) indicate their unevolved status. We compare these Eridanus void LSBDs with several extreme LSBD galaxies residing in the nearby Lynx-Cancer void. Based on the combination of all their unusual properties, the two discussed LSBD galaxies are similar to the unusual LSBDs residing in the closer void. This finding presents additional evidence for the existence in voids of a sizeable fraction of low-mass unevolved galaxies. Their dedicated search might result in the substantial increase of the number of such objects in the local Universe and in the advancement of understanding their nature.

  20. The nature of extreme emission line galaxies at z = 1-2: kinematics and metallicities from near-infrared spectroscopy

    SciTech Connect

    Maseda, Michael V.; Van der Wel, Arjen; Rix, Hans-Walter; Da Cunha, Elisabete; Meidt, Sharon E.; Pacifici, Camilla; Momcheva, Ivelina; Van Dokkum, Pieter; Nelson, Erica J.; Brammer, Gabriel B.; Ferguson, Henry C.; Koekemoer, Anton M.; Franx, Marijn; Fumagalli, Mattia; Bell, Eric F.; Förster-Schreiber, Natascha M.; Koo, David C.; Marchesini, Danilo; Patel, Shannon G.; and others

    2014-08-10

    We present near-infrared spectroscopy of a sample of 22 Extreme Emission Line Galaxies at redshifts 1.3 < z < 2.3, confirming that these are low-mass (M{sub *} = 10{sup 8}-10{sup 9} M{sub ☉}) galaxies undergoing intense starburst episodes (M{sub *}/SFR ∼ 10-100 Myr). The sample is selected by [O III] or Hα emission line flux and equivalent width using near-infrared grism spectroscopy from the 3D-HST survey. High-resolution NIR spectroscopy is obtained with LBT/LUCI and VLT/X-SHOOTER. The [O III]/Hβ line ratio is high (≳ 5) and [N II]/Hα is always significantly below unity, which suggests a low gas-phase metallicity. We are able to determine gas-phase metallicities for seven of our objects using various strong-line methods, with values in the range 0.05-0.30 Z{sub ☉} and with a median of 0.15 Z{sub ☉}; for three of these objects we detect [O III] λ4363, which allows for a direct constraint on the metallicity. The velocity dispersion, as measured from the nebular emission lines, is typically ∼50 km s{sup –1}. Combined with the observed star-forming activity, the Jeans and Toomre stability criteria imply that the gas fraction must be large (f{sub gas} ≳ 2/3), consistent with the difference between our dynamical and stellar mass estimates. The implied gas depletion timescale (several hundred Myr) is substantially longer than the inferred mass-weighted ages (∼50 Myr), which further supports the emerging picture that most stars in low-mass galaxies form in short, intense bursts of star formation.

  1. THE 21 cm 'OUTER ARM' AND THE OUTER-GALAXY HIGH-VELOCITY CLOUDS: CONNECTED BY KINEMATICS, METALLICITY, AND DISTANCE

    SciTech Connect

    Tripp, Todd M.; Song Limin

    2012-02-20

    Using high-resolution ultraviolet spectra obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph and the Far Ultraviolet Spectroscopic Explorer, we study the metallicity, kinematics, and distance of the gaseous 'outer arm' (OA) and the high-velocity clouds (HVCs) in the outer Galaxy. We detect the OA in a variety of absorption lines toward two QSOs, H1821+643 and HS0624+6907. We search for OA absorption toward eight Galactic stars and detect it in one case, which constrains the OA Galactocentric radius to 9 kpc metallicity is Z = 0.2-0.5 Z{sub Sun }, but nitrogen is underabundant and some species are possibly mildly depleted by dust. The similarity of the OA metallicity, Galactocentric location, and kinematics to those of the adjacent outer-Galaxy HVCs, including high velocities that are not consistent with Galactic rotation, suggests that the OA and outer-Galaxy HVCs could have a common origin.

  2. The roles of atomic and molecular gas on the redshift evolution of star formation and metallicity in galaxy formation models

    NASA Astrophysics Data System (ADS)

    Fu, Jian; Kauffmann, Guinevere

    2013-03-01

    We study the redshift evolution of neutral and molecular gas in the interstellar medium with the results from semi-analytic models of galaxy formation and evolution, which track the cold gas related physical processes in radially resolved galaxy disks. Two kinds of prescriptions are adopted to describe the conversion between molecular and neutral gas in the ISM: one is related to the gas surface density and gas metallicity based on the model results by Krumholz, Mckee & Tumlinson; the other is related the pressure of ISM. We try four types of star formation laws in the models to study the effect of the molecular gas component and the star formation time scale on the model results, and find that the H2 dependent star formation rate with constant star formation efficiency is the preferred star formation law. We run the models based on both Millennium and Millennium II Simulation haloes, and the model parameters are adjusted to fit the observations at z = 0 from THINGS/HERACLES and ALFALFA/COLD GASS. We give predictions for the redshift evolution of cosmic star formation density, H2 to HI cosmic ratios, gas to star mass ratios and gas metallicity vs stellar mass relation. Based on the model results, we find that: (i) the difference in the H2 to HI ratio at z > 3 between the two H2 fraction prescriptions can help future observations to test which prescription is better; (ii) a constant redshift independent star formation time scale will postpone the star formation processes at high redshift and cause obvious redshift evolution for the relation between gas metallicity and stellar mass in galaxies at z < 3.

  3. Kinematics around a non thermal superbubble in IC 10

    NASA Astrophysics Data System (ADS)

    Bullejos, A.; Rosado, M.

    2000-11-01

    IC 10 has long recognized as a peculiar object (Hubble 1936). Among Local Gr oup dwarf galaxies, IC 10 has the highest surface density of WR stars and the highest current rate of star formation (Mateo 1998). The presence of so many WR stars and the high H alpha luminosity emphasize that IC 10 is undergoing a strong burst of star formation that began at least 10 Myr ago. Based upon radio continuum observations, Yang & Skillman (1993) found a non thermal superbubble in this galaxy. This large superbubble (about 250pc) seems to be associated with a region of star formation containing two of the most luminous H II regions and the most massive H I cloud in IC 10. In this work, we study the kinematics of this non-thermal supperbubble. We present our H alpha and [S II] images as well as the radial velocity field.

  4. Physical properties of galaxies and their evolution in the VIMOS VLT Deep Survey. I. The evolution of the mass-metallicity relation up to z ~ 0.9

    NASA Astrophysics Data System (ADS)

    Lamareille, F.; Brinchmann, J.; Contini, T.; Walcher, C. J.; Charlot, S.; Pérez-Montero, E.; Zamorani, G.; Pozzetti, L.; Bolzonella, M.; Garilli, B.; Paltani, S.; Bongiorno, A.; Le Fèvre, O.; Bottini, D.; Le Brun, V.; Maccagni, D.; Scaramella, R.; Scodeggio, M.; Tresse, L.; Vettolani, G.; Zanichelli, A.; Adami, C.; Arnouts, S.; Bardelli, S.; Cappi, A.; Ciliegi, P.; Foucaud, S.; Franzetti, P.; Gavignaud, I.; Guzzo, L.; Ilbert, O.; Iovino, A.; McCracken, H. J.; Marano, B.; Marinoni, C.; Mazure, A.; Meneux, B.; Merighi, R.; Pellò, R.; Pollo, A.; Radovich, M.; Vergani, D.; Zucca, E.; Romano, A.; Grado, A.; Limatola, L.

    2009-02-01

    Aims: We want to derive the mass-metallicity relation of star-forming galaxies up to z ~ 0.9, using data from the VIMOS VLT Deep Survey. The mass-metallicity relation is commonly understood as the relation between the stellar mass and the gas-phase oxygen abundance. Methods: Automatic measurement of emission-line fluxes and equivalent widths have been performed on the full spectroscopic sample of the VIMOS VLT Deep Survey. This sample is divided into two sub-samples depending on the apparent magnitude selection: wide (IAB < 22.5) and deep (IAB < 24). These two samples span two different ranges of stellar masses. Emission-line galaxies have been separated into star-forming galaxies and active galactic nuclei using emission line ratios. For the star-forming galaxies the emission line ratios have also been used to estimate gas-phase oxygen abundance, using empirical calibrations renormalized in order to give consistent results at low and high redshifts. The stellar masses have been estimated by fitting the whole spectral energy distributions with a set of stellar population synthesis models. Results: We assume at first order that the shape of the mass-metallicity relation remains constant with redshift. Then we find a stronger metallicity evolution in the wide sample as compared to the deep sample. We thus conclude that the mass-metallicity relation is flatter at higher redshift. At z ~ 0.77, galaxies at 109.4 solar masses have -0.18 dex lower metallicities than galaxies of similar masses in the local universe, while galaxies at 1010.2 solar masses have -0.28 dex lower metallicities. By comparing the mass-metallicity and luminosity-metallicity relations, we also find an evolution in mass-to-light ratio: galaxies at higher redshifts being more active. The observed flattening of the mass-metallicity relation at high redshift is analyzed as evidence in favor of the open-closed model. Based on data obtained with the European Southern Observatory Very Large Telescope

  5. Neutral Hydrogen Observations of the Extremely Metal-Poor Blue Compact Dwarf Galaxy SBS 0335-052

    NASA Astrophysics Data System (ADS)

    Brinks, E.; Pustilnik, S.; Thuan, T. X.; Izotov, Y. I.

    2002-02-01

    We present VLA H I observations of one of the most metal-deficient blue compact dwarf (BCD) galaxies known, SBS 0335-052, which sports an oxygen abundance of only 1/40 that of the Sun. We study the structure and dynamics of the neutral gas in this chemically young object at a spatial resolution of 20''×15'' ( 5.4×3.9 kpc at a distance of 54 Mpc), and a velocity resolution of 21.2 kms-1.

  6. Neutral Hydrogen Observations of the Extremely Metal-Poor Blue Compact Dwarf Galaxy SBS 0335-052

    NASA Astrophysics Data System (ADS)

    Brinks, E.; Pustilnik, S.; Thuan, T. X.; Lipovetsky, V.; Izotov, Yu. I.

    2000-11-01

    We present VLA HI observations of one of the most metal-deficient blue compa ct dwarf (BCD) galaxies known, SBS 0335-052, which sports an oxygen abundance of only 1/40th that of the Sun. We study the structure and dynamics of the neutral gas in this chemically young object at a spatial resolution of 20'' x 15'' (5.4 x 3.9 kpc at an assumed distance of 54 Mpc), and a velocity resolution of 21.2 km/s. We detected a large HI complex associated with this object with an overall size of about 64 x 21 kpc and elongated in the East-West direction. There are two prominent, slightly resolved peaks visible which are separated by 22 kpc (84''). The eastern peak is nearly coincident with the position of the optical galaxy SBS 0335-052. The western peak is about a factor of 1.3 brighter in the HI line and is identified with a faint blue compact galaxy, SBS 0335-052W, which has an mV = 19, and a metallicity close to the lowest values known for BCDs, about 1/50th that of the Sun. The radial velocities of both systems are similar, suggesting that the two BCDs form a pair of dwarf galaxies embedded in a common HI envelope. Alternatively, the BCDs could be the nuclei of two distinct interacting primordial HI clouds. The estimated total dynamical mass, assuming the BCDs form a bound system, is larger than 7 x 109 Mo. This is to be compared to a total gaseous mass Mgas = 2.0 x 109 Mo, and a total stellar mass Mstar < 108 Mo. Hence, the mass of the SBS 0335-052 system is dominated by dark matter. Because of the disturbed HI velocity field and the presence of what might be tidal tails at either end of the system, we favor the hypothesis that the star formation trigger in this system was provided by a tidal interaction, either with the nearby giant galaxy NGC 1376 or as a result of the mutual gravitational interaction of the two HI clouds proper.

  7. THE OPTICAL COLORS OF GIANT ELLIPTICAL GALAXIES AND THEIR METAL-RICH GLOBULAR CLUSTERS INDICATE A BOTTOM-HEAVY INITIAL MASS FUNCTION

    SciTech Connect

    Goudfrooij, Paul; Diederik Kruijssen, J. M. E-mail: kruijssen@mpa-garching.mpg.de

    2013-01-10

    We report a systematic and statistically significant offset between the optical (g - z or B - I) colors of seven massive elliptical galaxies and the mean colors of their associated massive metal-rich globular clusters (GCs) in the sense that the parent galaxies are redder by {approx}0.12-0.20 mag at a given galactocentric distance. However, spectroscopic indices in the blue indicate that the luminosity-weighted ages and metallicities of such galaxies are equal to that of their averaged massive metal-rich GCs at a given galactocentric distance, to within small uncertainties. The observed color differences between the red GC systems and their parent galaxies cannot be explained by the presence of multiple stellar generations in massive metal-rich GCs, as the impact of the latter to the populations' integrated g - z or B - I colors is found to be negligible. However, we show that this paradox can be explained if the stellar initial mass function (IMF) in these massive elliptical galaxies was significantly steeper at subsolar masses than canonical IMFs derived from star counts in the solar neighborhood, with the GC colors having become bluer due to dynamical evolution, causing a significant flattening of the stellar MF of the average surviving GC.

  8. Metal enrichment of the neutral gas of blue compact dwarf galaxies: the compelling case of Pox 36

    NASA Astrophysics Data System (ADS)

    Lebouteiller, V.; Kunth, D.; Thuan, T. X.; Désert, J. M.

    2009-02-01

    Context: Evidence has grown over the past few years that the neutral phase of blue compact dwarf (BCD) galaxies may be metal-deficient as compared to the ionized gas of their H ii regions. These results have strong implications for our understanding of the chemical evolution of galaxies, and it is essential to strengthen the method, as well as to find possible explanations. Aims: We present the analysis of the interstellar spectrum of Pox 36 with the Far Ultraviolet Spectroscopic Explorer (FUSE). Pox 36 was selected because of the relatively low foreground gas content that makes it possible to detect absorption-lines weak enough that unseen components should not be saturated. Methods: Interstellar lines of H i, N i, O i, Si ii, P ii, Ar i, and Fe ii are detected. Column densities are derived directly from the observed line profiles except for H i, whose lines are contaminated by stellar absorption, thus needing the stellar continuum to be removed. We used the TLUSTY models to remove the stellar continuum and isolate the interstellar component. The best fit indicates that the dominant stellar population is B0. The observed far-UV flux agrees with an equivalent number of ~300 B0 stars. The fit of the interstellar H i line gives a column density of 1020.3±0.4 cm-2. Chemical abundances were then computed from the column densities using the dominant ionization stage in the neutral gas. Our abundances are compared to those measured from emission-line spectra in the optical, probing the ionized gas of the H ii regions. Results: Our results suggest that the neutral gas of Pox 36 is metal-deficient by a factor ~7 as compared to the ionized gas, and they agree with a metallicity of ≈1/35 Z_⊙. Elemental depletion is not problematic because of the low dust content along the selected lines of sight. In contrast, the ionized gas shows a clear depletion pattern, with iron being strongly depleted. Conclusions: The abundance discontinuity between the neutral and ionized phases

  9. IC Fabrication Methods Improve Laser Diodes

    NASA Technical Reports Server (NTRS)

    Miller, M.; Pickhardt, V.

    1984-01-01

    Family of high-performance, tunable diode lasers developed for use as local oscillators in passive laser heterodyne spectrometer. Diodes fabricated using standard IC processes include photolithography, selective etching and vacuum deposition of metals and insulators. Packaging refinements improved thermal-cycling characteristics of diodes and increased room-temperature shelf life.

  10. The low-extinction afterglow in the solar-metallicity host galaxy of γ-ray burst 110918A

    NASA Astrophysics Data System (ADS)

    Elliott, J.; Krühler, T.; Greiner, J.; Savaglio, S.; Olivares, F.; Rau, E. A.; de Ugarte Postigo, A.; Sánchez-Ramírez, R.; Wiersema, K.; Schady, P.; Kann, D. A.; Filgas, R.; Nardini, M.; Berger, E.; Fox, D.; Gorosabel, J.; Klose, S.; Levan, A.; Nicuesa Guelbenzu, A.; Rossi, A.; Schmidl, S.; Sudilovsky, V.; Tanvir, N. R.; Thöne, C. C.

    2013-08-01

    Galaxies selected through long γ-ray bursts (GRBs) could be of fundamental importance when mapping the star formation history out to the highest redshifts. Before using them as efficient tools in the early Universe, however, the environmental factors that govern the formation of GRBs need to be understood. Metallicity is theoretically thought to be a fundamental driver in GRB explosions and energetics, but it is still, even after more than a decade of extensive studies, not fully understood. This is largely related to two phenomena: a dust-extinction bias, which prevented high-mass and thus likely high-metallicity GRB hosts from being detected in the first place, and a lack of efficient instrumentation, which limited spectroscopic studies, including metallicity measurements, to the low-redshift end of the GRB host population. The subject of this work is the very energetic GRB 110918A (Eγ,iso = 1.9 × 1054 erg), for which we measure a redshift of z = 0.984. GRB 110918A gave rise to a luminous afterglow with an intrinsic spectral slope of β = 0.70, which probed a sight-line with little extinction (AGRBV = 0.16 mag) and soft X-ray absorption (NH,X = (1.6 ± 0.5) × 1021 cm-2) typical of the established distributions of afterglow properties. However, photometric and spectroscopic follow-up observations of the galaxy hosting GRB 110918A, including optical/near-infrared photometry with the Gamma-Ray burst Optical Near-infrared Detector and spectroscopy with the Very Large Telescope/X-shooter, reveal an all but average GRB host in comparison to the z ~ 1 galaxies selected through similar afterglows to date. It has a large spatial extent with a half-light radius of R1/2 ~ 10 kpc, the highest stellar mass for z < 1.9 (log (M∗/M⊙) = 10.68 ± 0.16), and an Hα-based star formation rate of SFRHα = 41+28-16M⊙ yr-1. We measure a gas-phase extinction of AgasV ~ 1.8 mag through the Balmer decrement and one of the largest host-integrated metallicities ever of around solar

  11. Origins of the thick disk of the Milky Way Galaxy as traced by the elemental abundances of metal-poor stars

    NASA Astrophysics Data System (ADS)

    Ruchti, Gregory Randal

    2010-12-01

    Understanding the formation and evolution of disks in galaxies in the early universe is very important for understanding the forms of galaxies today. Recent studies of the Milky Way Galaxy, an ideal galaxy for analyzing individual stars within its disk, indicate that the formation of the Galactic disk is very complex. Most of these studies, however, contain very few stars at low metallicities. Metal-poor stars are important, because they are potential survivors of the earliest star formation in the disk of the Milky Way Galaxy. I therefore measured elemental abundances of a statistically significant sample of metal-poor ([Fe/H] ≲ - 1.0) stars in the disk of the Galaxy, chosen from the RAVE survey in order to study the early formation history of the Galactic disk. I report on a sample of 214 red giant branch, 31 red clump/horizontal branch, and 74 dwarf/sub-giant metal-poor thick-disk candidate stars. I found that the [alpha/Fe] ratios are enhanced implying that enrichment proceeded by purely core-collapse supernovae. This requires that star formation in each star forming region had a short duration. The relative lack of scatter in the [alpha/Fe] ratios implies good mixing in the interstellar medium prior to star formation. In addition, the ratios resemble that of the halo, indicating that the halo and thick disk share a similar massive star initial mass function. I further looked for radial or vertical gradients in metallicity or alpha-enhancement for the metal-poor thick disk, never before done for such a sample. I found no radial gradient and a moderate vertical gradient in my derived iron abundance, and only minimal-amplitude gradients in [alpha/Fe]. In addition, I show that the distribution of orbital eccentricities for my metal-poor thick-disk stars requires that the thick disk was formed primarily in situ, with direct accretion being extremely minimal. I conclude that the alpha-enhancement of the metal-poor thick disk, and the lack of obvious radial or

  12. DIRECT FORMATION OF SUPERMASSIVE BLACK HOLES IN METAL-ENRICHED GAS AT THE HEART OF HIGH-REDSHIFT GALAXY MERGERS

    SciTech Connect

    Mayer, Lucio; Fiacconi, Davide; Bonoli, Silvia; Quinn, Thomas; Roškar, Rok; Shen, Sijing; Wadsley, James

    2015-09-01

    We present novel 3D multi-scale smoothed particle hydrodynamics (SPH) simulations of gas-rich galaxy mergers between the most massive galaxies at z ∼ 8–10, designed to scrutinize the direct collapse formation scenario for massive black hole seeds proposed in Mayer et al. The simulations achieve a resolution of 0.1 pc, and include both metallicity-dependent optically thin cooling and a model for thermal balance at high optical depth. We consider different formulations of the SPH hydrodynamical equations, including thermal and metal diffusion. When the two merging galaxy cores collide, gas infall produces a compact, optically thick nuclear disk with densities exceeding 10{sup −10} g cm{sup 3}. The disk rapidly accretes higher angular momentum gas from its surroundings reaching ∼5 pc and a mass of ≳10{sup 9} M{sub ⊙} in only a few 10{sup 4} years. Outside ≳2 pc it fragments into massive clumps. Instead, supersonic turbulence prevents fragmentation in the inner parsec region, which remains warm (∼3000–6000 K) and develops strong non-axisymmetric modes that cause prominent radial gas inflows (>10{sup 4} M{sub ⊙} yr{sup −1}), forming an ultra-dense massive disky core. Angular momentum transport by non-axisymmetric modes should continue below our spatial resolution limit, quickly turning the disky core into a supermassive protostar which can collapse directly into a massive black hole of mass 10{sup 8}–10{sup 9} M{sub ⊙} via the relativistic radial instability. Such a “cold direct collapse” explains naturally the early emergence of high-z QSOs. Its telltale signature would be a burst of gravitational waves in the frequency range of 10{sup −4}–10{sup −1} Hz, possibly detectable by the planned eLISA interferometer.

  13. SURVEYING THE AGENTS OF GALAXY EVOLUTION IN THE TIDALLY STRIPPED, LOW METALLICITY SMALL MAGELLANIC CLOUD (SAGE-SMC). I. OVERVIEW

    SciTech Connect

    Gordon, K. D.; Meixner, M.; Boyer, M. L.; Lawton, B.; Meade, M. R.; Whitney, B.; Babler, B.; Bracker, S.; Engelbracht, C.; Block, M.; Misselt, K.; Bot, C.; Sewilo, M.; Bernard, J.-P.; Blum, R.; Harris, J.; Bolatto, A.; Bonanos, A.; Hora, J. L.; Indebetouw, R.

    2011-10-15

    The Small Magellanic Cloud (SMC) provides a unique laboratory for the study of the lifecycle of dust given its low metallicity ({approx}1/5 solar) and relative proximity ({approx}60 kpc). This motivated the SAGE-SMC (Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud) Spitzer Legacy program with the specific goals of studying the amount and type of dust in the present interstellar medium, the sources of dust in the winds of evolved stars, and how much dust is consumed in star formation. This program mapped the full SMC (30 deg{sup 2}) including the body, wing, and tail in seven bands from 3.6 to 160 {mu}m using IRAC and MIPS on the Spitzer Space Telescope. The data were reduced and mosaicked, and the point sources were measured using customized routines specific for large surveys. We have made the resulting mosaics and point-source catalogs available to the community. The infrared colors of the SMC are compared to those of other nearby galaxies and the 8 {mu}m/24 {mu}m ratio is somewhat lower than the average and the 70 {mu}m/160 {mu}m ratio is somewhat higher than the average. The global infrared spectral energy distribution (SED) shows that the SMC has approximately 1/3 the aromatic emission/polycyclic aromatic hydrocarbon abundance of most nearby galaxies. Infrared color-magnitude diagrams are given illustrating the distribution of different asymptotic giant branch stars and the locations of young stellar objects. Finally, the average SED of H II/star formation regions is compared to the equivalent Large Magellanic Cloud average H II/star formation region SED. These preliminary results will be expanded in detail in subsequent papers.

  14. A CANDELS WFC3 Grism Study of Emission-Line Galaxies at Z approximates 2: A mix of Nuclear Activity and Low-Metallicity Star Formation

    NASA Technical Reports Server (NTRS)

    Trump, Jonathan R.; Weiner, Benjamin J.; Scarlata, Claudia; Kocevski, Dale D.; Bell, Eric F.; McGrath, Elizabeth J.; Koo, David C.; Faber, S. M.; Laird, Elise S.; Mozena, Mark; Rangel, Cyprian; Yan, Renbin; Yesuf, Hassen; Atek, Hakim; Dickinson, Mark; Donley, Jennifer L.; Dunlop, James S.; Ferguson, Henry C.; Finkelstein, Steven L.; Grogin, Norman A.; Hathi, Nimish P.; Juneau, Stephanie; Kartaltepe, Jeyhan S.; Koekemoer, Anton M.; Nandra, Kirpal

    2011-01-01

    We present Hubble Space Telescope Wide Field Camera 3 slitless grism spectroscopy of 28 emission-line galaxies at z approximates 2, in the GOODS-S region of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). The high sensitivity of these grism observations, with > 5-sigma detections of emission lines to f > 2.5 X 10(exp -18( erg/s/ square cm, means that the galaxies in the sample are typically approximately 7 times less massive (median M(star). = 10(exp 9.5)M(solar)) than previously studied z approximates 2 emission-line galaxies. Despite their lower mass, the galaxies have [O-III]/H-Beta ratios which are very similar to previously studied z approximates 2 galaxies and much higher than the typical emission-line ratios of local galaxies. The WFC3 grism allows for unique studies of spatial gradients in emission lines, and we stack the two-dimensional spectra of the galaxies for this purpose. In the stacked data the [O-III] emission line is more spatially concentrated than the H-Beta emission line with 98.1% confidence. We additionally stack the X-ray data (all sources are individually undetected), and find that the average L(sub [O-III])/L(sub 0.5.10keV) ratio is intermediate between typical z approximates 0 obscured active galaxies and star-forming galaxies. Together the compactness of the stacked [O-III] spatial profile and the stacked X-ray data suggest that at least some of these low-mass, low-metallicity galaxies harbor weak active galactic nuclei.

  15. A CANDELS WFC3 GRISM STUDY OF EMISSION-LINE GALAXIES AT z {approx} 2: A MIX OF NUCLEAR ACTIVITY AND LOW-METALLICITY STAR FORMATION

    SciTech Connect

    Trump, Jonathan R.; Kocevski, Dale D.; McGrath, Elizabeth J.; Koo, David C.; Faber, S. M.; Mozena, Mark; Yesuf, Hassen; Scarlata, Claudia; Bell, Eric F.; Laird, Elise S.; Rangel, Cyprian; Yan Renbin; Atek, Hakim; Dickinson, Mark; Donley, Jennifer L.; Ferguson, Henry C.; Grogin, Norman A.; Dunlop, James S.; Finkelstein, Steven L.; and others

    2011-12-20

    We present Hubble Space Telescope Wide Field Camera 3 (WFC3) slitless grism spectroscopy of 28 emission-line galaxies at z {approx} 2, in the GOODS-S region of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey. The high sensitivity of these grism observations, with >1{sigma} detections of emission lines to f > 2.5 Multiplication-Sign 10{sup -18} erg s{sup -1} cm{sup -2}, means that the galaxies in the sample are typically {approx}7 times less massive (median M{sub *} = 10{sup 9.5} M{sub Sun }) than previously studied z {approx} 2 emission-line galaxies. Despite their lower mass, the galaxies have [O III]/H{beta} ratios which are very similar to previously studied z {approx} 2 galaxies and much higher than the typical emission-line ratios of local galaxies. The WFC3 grism allows for unique studies of spatial gradients in emission lines, and we stack the two-dimensional spectra of the galaxies for this purpose. In the stacked data the [O III] emission line is more spatially concentrated than the H{beta} emission line with 98.1% confidence. We additionally stack the X-ray data (all sources are individually undetected), and find that the average L{sub [OIII]}/L{sub 0.5-10keV} ratio is intermediate between typical z {approx} 0 obscured active galaxies and star-forming galaxies. Together the compactness of the stacked [O III] spatial profile and the stacked X-ray data suggest that at least some of these low-mass, low-metallicity galaxies harbor weak active galactic nuclei.

  16. The chemical evolution of local star-forming galaxies: radial profiles of ISM metallicity, gas mass, and stellar mass and constraints on galactic accretion and winds

    NASA Astrophysics Data System (ADS)

    Kudritzki, Rolf-Peter; Ho, I.-Ting; Schruba, Andreas; Burkert, Andreas; Zahid, H. Jabran; Bresolin, Fabio; Dima, Gabriel I.

    2015-06-01

    The radially averaged metallicity distribution of the interstellar medium (ISM) and the young stellar population of a sample of 20 disc galaxies is investigated by means of an analytical chemical evolution model which assumes constant ratios of galactic wind mass-loss and accretion mass gain to star formation rate. Based on this model, the observed metallicities and their gradients can be described surprisingly well by the radially averaged distribution of the ratio of stellar mass to ISM gas mass. The comparison between observed and model-predicted metallicity is used to constrain the rate of mass-loss through galactic wind and accretion gain in units of the star formation rate. Three groups of galaxies are found: galaxies with either mostly winds and only weak accretion, or mostly accretion and only weak winds, and galaxies where winds are roughly balanced by accretion. The three groups are distinct in the properties of their gas discs. Galaxies with approximately equal rates of mass-loss and accretion gain have low metallicity, atomic-hydrogen-dominated gas discs with a flat spatial profile. The other two groups have gas discs dominated by molecular hydrogen out to 0.5 to 0.7 isophotal radii and show a radial exponential decline, which is on average steeper for the galaxies with small accretion rates. The rates of accretion ( ≲ 1.0 × SFR) and outflow ( ≲ 2.4 × SFR) are relatively low. The latter depend on the calibration of the zero-point of the metallicity determination from the use of H II region strong emission lines.

  17. Interaction/merger-induced starbursts in local very metal-poor dwarfs: link to the common SF in high-z young galaxies

    NASA Astrophysics Data System (ADS)

    Pustilnik, S. A.; Ekta; Kniazev, A. Y.; Chengalur, J. N.; Vanzi, L.

    Introduction. Widespread galaxy formation from pregalactic gas took place in the first 1-3 Gyr after the Big Bang, with most of them forming in low-mass halos (i.e., M in the range of 10^7-10^10 Mo). Observations at high redshifts (z=4-7) are, however, mainly limited to the rare massive "tip of the iceberg" objects. Detailed studies of the properties and the evolution of more common lower-mass young galaxies will have to await the next generation mega telescopes. Although the properties of early galaxies are poorly constrained, it seems reasonable to assume that they should share the following three attributes, viz. a) they should be much more metal-poor than typical local galaxies; b) they should be very gas-rich, and c) due to the much higher galaxy density in the early Universe, interaction/merger induced galaxy-wide SF should be one of the main SF modes. Fortunately, there exist in the local Universe a few good analogs of low-mass young galaxies whose properties can serve as a first approximation for understanding those of the main population of high-redshift galaxies. These are the so-called eXtremely Metal-Deficient (XMD, Z = 1/30 - 1/10 Zo) blue compact galaxies (BCGs). Method. We have conducted a multi-wavelength (including optical/NIR morphology/ photometry, HI imaging, and H-alpha-line kinematics) of a sample of such XMD BCGs and find in a large fraction of them clear evidences that strong interactions or mergers with low-mass objects, provide a trigger mechanism for their observed starbursts. Results. We present about 20 such XMD BCGs arranged in a Toomre-like sequence and also the first results of detailed studies of several individual objects from this sample. Discussion. Since both SF (through cooling rate and the IMF) and its feedback (through the massive star evolution and interaction with the ISM) depend substantially on the ISM metallicity, comprehensive multiwavelength studies of local XMD galaxy mergers, coupled with theoretical modelling

  18. Spectral Energy Distribution Mapping of Two Elliptical Galaxies on Sub-kpc Scales

    NASA Astrophysics Data System (ADS)

    Amblard, A.; Temi, P.; Gaspari, M.; Brighenti, F.

    2017-01-01

    We use high-resolution Herschel-PACS data of two nearby elliptical galaxies, IC 1459 and NGC 2768, to characterize their dust and stellar content. IC 1459 and NGC 2768 have an unusually large amount of dust for elliptical galaxies ((1–3) × 105 {M}ȯ ); this dust is also not distributed along the stellar content. Using data from GALEX (ultra-violet) to PACS (far-infrared, FIR), we analyze the spectral energy distribution (SED) of these galaxies with CIGALEMC as a function of the projected position, binning images in 7.″2 pixels. From this analysis, we derive maps of SED parameters, such as the metallicity, the stellar mass, the fraction of young stars, and the dust mass. The larger amount of dust in FIR maps seems related in our model to a larger fraction of young stars which can reach up to 4% in the dustier area. The young stellar population is fitted as a recent (∼0.5 Gyr) short burst of star formation for both galaxies. The metallicities, which are fairly large at the center of both galaxies, decrease with the radial distance with a fairly steep gradient for elliptical galaxies.

  19. VizieR Online Data Catalog: Photometry and Metallicity in ABCG 209 galaxies (Mercurio+, 2004)

    NASA Astrophysics Data System (ADS)

    Mercurio, A.; Busarello, G.; Merluzzi, P.; La Barbera, F.; Girardi, M.; Haines, C.

    2004-06-01

    Photometric data (table1.dat) were collected on November 1999 using the CFH12K mosaic camera and spectroscopic data (table2.dat) have been obtained in the multi-object spectroscopy (MOS) mode of ESO Multi Mode Instrument at the ESO New Technology Telescoe (NTT) for 102 galaxies belonging to the cluster ABCG 209. (2 data files).

  20. Star formation in the first galaxies - III. Formation, evolution, and characteristics of the first metal-enriched stellar cluster

    NASA Astrophysics Data System (ADS)

    Safranek-Shrader, Chalence; Montgomery, Michael H.; Milosavljević, Miloš; Bromm, Volker

    2016-01-01

    We simulate the formation of a low-metallicity (10-2 Z⊙) stellar cluster at redshift z ˜ 14. Beginning with cosmological initial conditions, the simulation utilizes adaptive mesh refinement and sink particles to follow the collapse and evolution of gas past the opacity limit for fragmentation, thus resolving the formation of individual protostellar cores. A time- and location-dependent protostellar radiation field, which heats the gas by absorption on dust, is computed by integration of protostellar evolutionary tracks. The simulation also includes a robust non-equilibrium chemical network that self-consistently treats gas thermodynamics and dust-gas coupling. The system is evolved for 18 kyr after the first protostellar source has formed. In this time span, 30 sink particles representing protostellar cores form with a total mass of 81 M⊙. Their masses range from ˜0.1 to 14.4 M⊙ with a median mass ˜0.5-1 M⊙. Massive protostars grow by competitive accretion while lower mass protostars are stunted in growth by close encounters and many-body ejections. In the regime explored here, the characteristic mass scale is determined by the cosmic microwave background temperature floor and the onset of efficient dust-gas coupling. It seems unlikely that host galaxies of the first bursts of metal-enriched star formation will be detectable with the James Webb Space Telescope or other next-generation infrared observatories. Instead, the most promising access route to the dawn of cosmic star formation may lie in the scrutiny of metal-poor, ancient stellar populations in the Galactic neighbourhood. The observable targets corresponding to the system simulated here are ultra-faint dwarf satellite galaxies such as Boötes II and Willman I.

  1. Metal-enriched, subkiloparsec gas clumps in the circumgalactic medium of a faint z = 2.5 galaxy

    NASA Astrophysics Data System (ADS)

    Crighton, Neil H. M.; Hennawi, Joseph F.; Simcoe, Robert A.; Cooksey, Kathy L.; Murphy, Michael T.; Fumagalli, Michele; Prochaska, J. Xavier; Shanks, Tom

    2015-01-01

    We report the serendipitous detection of a 0.2 L*, Lyα emitting galaxy at redshift 2.5 at an impact parameter of 50 kpc from a bright background QSO sightline. A high-resolution spectrum of the QSO reveals a partial Lyman-limit absorption system ({N}_H I=10^{16.94± 0.10} cm-2) with many associated metal absorption lines at the same redshift as the foreground galaxy. Using photoionization models that carefully treat measurement errors and marginalize over uncertainties in the shape and normalization of the ionizing radiation spectrum, we derive the total hydrogen column density {N}_H=10^{19.4± 0.3} cm^{-2}, and show that all the absorbing clouds are metal enriched, with Z = 0.1-0.6 Z⊙. These metallicities and the system's large velocity width (436 km s- 1) suggest the gas is produced by an outflowing wind. Using an expanding shell model we estimate a mass outflow rate of ˜5 M⊙ yr-1. Our photoionization model yields extremely small sizes (<100-500 pc) for the absorbing clouds, which we argue is typical of high column density absorbers in the circumgalactic medium (CGM). Given these small sizes and extreme kinematics, it is unclear how the clumps survive in the CGM without being destroyed by hydrodynamic instabilities. The small cloud sizes imply that even state-of-the-art cosmological simulations require more than a 1000-fold improvement in mass resolution to resolve the hydrodynamics relevant for cool gas in the CGM.

  2. EVIDENCE OF VERY LOW METALLICITY AND HIGH IONIZATION STATE IN A STRONGLY LENSED, STAR-FORMING DWARF GALAXY AT z = 3.417

    SciTech Connect

    Amorín, R.; Grazian, A.; Castellano, M.; Pentericci, L.; Fontana, A.; Sommariva, V.; Merlin, E.; Van der Wel, A.; Maseda, M.

    2014-06-10

    We investigate the gas-phase metallicity and Lyman continuum (LyC) escape fraction of a strongly gravitationally lensed, extreme emission-line galaxy at z = 3.417, J1000+0221S, recently discovered by the CANDELS team. We derive ionization- and metallicity-sensitive emission-line ratios from H+K band Large Binocular Telescope (LBT)/LUCI medium resolution spectroscopy. J1000+0221S shows high ionization conditions, as evidenced by its enhanced [O III]/[O II] and [O III]/Hβ ratios. Strong-line methods based on the available line ratios suggest that J1000+0221S is an extremely metal-poor galaxy, with a metallicity of 12+log (O/H) < 7.44 (Z < 0.05 Z {sub ☉}), placing it among the most metal-poor star-forming galaxies at z ≳ 3 discovered so far. In combination with its low stellar mass (2 × 10{sup 8} M {sub ☉}) and high star formation rate (5 M {sub ☉} yr{sup –1}), the metallicity of J1000+0221S is consistent with the extrapolation of the mass-metallicity relation traced by Lyman-break galaxies at z ≳ 3 to low masses, but it is 0.55 dex lower than predicted by the fundamental metallicity relation at z ≲ 2.5. These observations suggest a rapidly growing galaxy, possibly fed by massive accretion of pristine gas. Additionally, deep LBT/LBC photometry in the UGR bands are used to derive a limit to the LyC escape fraction, thus allowing us to explore for the first time the regime of sub-L* galaxies at z > 3. We find a 1σ upper limit to the escape fraction of 23%, which adds a new observational constraint to recent theoretical models predicting that sub-L* galaxies at high-z have high escape fractions and thus are the responsible for the reionization of the universe.

  3. Radial Distribution of ISM Gas-phase Metallicity in CLASH Clusters at z ~ 0.35: A New Outlook on Environmental Impact on Galaxy Evolution

    NASA Astrophysics Data System (ADS)

    Gupta, Anshu; Yuan, Tiantian; Tran, Kim-Vy H.; Martizzi, Davide; Taylor, Philip; Kewley, Lisa J.

    2016-11-01

    We present the first observation of cluster-scale radial metallicity gradients from star-forming galaxies. We use DEIMOS on the Keck II telescope to observe two CLASH clusters at z ˜ 0.35: MACS J1115+0129 and RX J1532+3021. Based on our measured interstellar medium properties of star-forming galaxies out to a radius of 2.5 Mpc from the cluster center, we find that the galaxy metallicity decreases as a function of projected cluster-centric distance (-0.15 ± 0.08 dex/Mpc) in MACS 1115+01. On the mass-metallicity relation (MZR), star-forming galaxies in MACS J1115+01 are offset to higher metallicity (˜0.2 dex) than the local Sloan Digital Sky Survey galaxies at a fixed mass range. In contrast, the MZR of RX J1532+30 is consistent with the local comparison sample. RX J1532+30 exhibits a bimodal radial metallicity distribution, with one branch showing a similar negative gradient to MACS J1115+01 (-0.14 ± 0.05 dex/Mpc) and the other branch showing a positive radial gradient. The positive gradient branch in RX J1532+30 is likely caused by either interloper galaxies or an in-plane merger, indicating that cluster-scale abundance gradients probe cluster substructures and thus the dynamical state of a cluster. Most strikingly, we discover that neither the radial metallicity gradient nor the offset from the MZR is driven by the stellar mass. We compare our observations with Rhapsody-G cosmological hydrodynamical zoom-in simulations of relaxed galaxy clusters and find that the simulated galaxy cluster also exhibits a negative abundance gradient, albeit with a shallower slope (-0.04 ± 0.03 dex/Mpc). Our observations suggest that the negative radial gradient originates from ram pressure stripping and/or strangulation processes in the cluster environments.

  4. 30 CFR 57.22102 - Smoking (I-C mines).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Smoking (I-C mines). 57.22102 Section 57.22102... Methane in Metal and Nonmetal Mines Fire Prevention and Control § 57.22102 Smoking (I-C mines). (a) Persons shall not smoke or carry smoking materials, matches, or lighters underground or within 50 feet...

  5. 30 CFR 57.22102 - Smoking (I-C mines).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Smoking (I-C mines). 57.22102 Section 57.22102... Methane in Metal and Nonmetal Mines Fire Prevention and Control § 57.22102 Smoking (I-C mines). (a) Persons shall not smoke or carry smoking materials, matches, or lighters underground or within 50 feet...

  6. 30 CFR 57.22102 - Smoking (I-C mines).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Smoking (I-C mines). 57.22102 Section 57.22102... Methane in Metal and Nonmetal Mines Fire Prevention and Control § 57.22102 Smoking (I-C mines). (a) Persons shall not smoke or carry smoking materials, matches, or lighters underground or within 50 feet...

  7. 30 CFR 57.22102 - Smoking (I-C mines).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Smoking (I-C mines). 57.22102 Section 57.22102... Methane in Metal and Nonmetal Mines Fire Prevention and Control § 57.22102 Smoking (I-C mines). (a) Persons shall not smoke or carry smoking materials, matches, or lighters underground or within 50 feet...

  8. 30 CFR 57.22102 - Smoking (I-C mines).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Smoking (I-C mines). 57.22102 Section 57.22102... Methane in Metal and Nonmetal Mines Fire Prevention and Control § 57.22102 Smoking (I-C mines). (a) Persons shall not smoke or carry smoking materials, matches, or lighters underground or within 50 feet...

  9. NGC 2207/IC 2163: Grazing Encounter with Large Scale Shocks

    NASA Astrophysics Data System (ADS)

    Kaufman, M.; Struck, C.; Brinks, E.; Thomasson, M.; Elmegreen, B. G.; Elmegreen, D. M.

    2005-05-01

    The galaxy pair NGC 2207/IC 2163 has an unusually high ratio of radio continuum/IRAS far-IR flux, yet neither galaxy contains an AGN. We present a 4.86 GHz radio continuum image of this pair from VLA observations with 2.5'' resolution. Much of the excess radio emission arises from apparent shock fronts in the outer parts of the companion sides of the galaxies and along the rim of the ocular oval of IC 2163. With a SFR deduced from Hα emission, each galaxy has a SFR/M(HI) typical of normal spiral disks. Unlike the radio continuum emission, the Hα emission is not enhanced on the companion side of NGC 2207. We also present the results of a detailed, hydrodynamic numerical simulation of the encounter, modelling the responses of the stars and gas in both galaxies in three dimensions. The short-lived ocular phase and other features, such as the HI kinematics, set strict constraints on the encounter model. In the model, shocks generated by disk scraping and mass transfer from IC 2163 to NGC 2207 occur and may account for the excess radio emission on the companion sides. Comparison with Spitzer observations of this pair will be made.

  10. The Carnegie Hubble Program: The Infrared Leavitt Law in IC 1613

    NASA Technical Reports Server (NTRS)

    Scowcroft, Victoria; Freedman, Wendy L.; Madore, Barry F.; Monson, Andrew J.; Persson, S. E.; Seibert, Mark; Rigby, Jane R.; Melbourne, Jason

    2013-01-01

    We have observed the dwarf galaxy IC 1613 at multiple epochs in the midinfrared using Spitzer and the in the near-infrared using the new FourStar near-IR camera on Magellan. We have constructed Cepheid period luminosity relations in the J, H, Ks, [3.6] and [4.5] bands and have used the run of their apparent distance moduli as a function of wavelength to derive the line of sight reddening and distance to IC 1613. Using a nineband fit, we find E(BV ) = 0.050.01 mag and an extinction corrected distance modulus of 0 = 24.29 0.03statistical 0.03systematic mag. By comparing our multiband and [3.6] distance moduli to results from the tip of the red giant branch and red clump distance indicators, we find that metallicity has no measurable effect on Cepheid distances at 3.6 m in the metallicity range 1.0 [Fe/H] 0.2, hence derivations of the Hubble constant at this wavelength require no correction for metallicity.

  11. VizieR Online Data Catalog: Properties of OB associations in IC 1613 (Garcia+, 2010)

    NASA Astrophysics Data System (ADS)

    Garcia, M.; Herrero, A.; Castro, N.; Corral, L.; Rosenberg, A.

    2014-06-01

    To understand the structure and evolution of massive stars, systematic surveys of the Local Group galaxies have been undertaken, to find these objects in environments of different chemical abundances. We focus on the metal-poor irregular galaxy IC 1613 to analyze the stellar and wind structure of its low-metallicity massive stars. We ultimately aim to study the metallicity-dependent driving mechanism of the winds of blue massive stars and use metal-poor massive stars of the Local Volume as a proxy for the stars in the early Universe. In a previous paper we produced a list of OB associations in IC 1613. Their properties are not only a powerful aid towards finding the most interesting candidate massive stars, but also reveal the structure and recent star formation history of the galaxy. We characterize these OB associations and study their connection with the galactic global properties. The reddening-free Q parameter is a powerful tool in the photometric analysis of young populations of massive stars, since it exhibits a smaller degree of degeneracy with OB spectral types than the B-V color. The color-magnitude diagram (Q vs. V) of the OB associations in IC 1613 is studied to determine their age and mass, and confirm the population of young massive stars. We identified more than 10 stars with M>=50M⊙. Spectral classification available for some of them confirm their massive nature, yet we find the common discrepancy with the spectroscopically derived masses. There is a general increasing trend of the mass of the most massive member with the number of members of each association, but not with the stellar density. The average diameter of the associations of this catalog is 40pc, half the historically considered typical size of OB associations. Size increases with the association population. The distribution of the groups strongly correlates with that of neutral and ionized hydrogen. We find the largest dispersion of association ages in the bubble region of the galaxy

  12. Constraining the Metallicity and Escape Fraction of Two z≈3.1 Lyman-Alpha Emitting Galaxies

    NASA Astrophysics Data System (ADS)

    Richardson, Mark L. A.; McLinden, E. M.; Malhotra, S.; Rhoads, J. E.; Levesque, E. M.

    2012-05-01

    We observed two z≈3.1 Lyman-α emitting galaxies (LAE) using the Near-infrared Integral Field Spectrometer (NIFS) at Gemini North, specifically looking for [OIII] 4960 & 5008Å, [OII] 3727Å, and H-β 4863Å. We detected the [OIII] doublet in both objects, determined upper limits for [OII] for both objects, and determined upper limits for H-β for one object. With the detections and upper limits we use the [OIII]/[OII] and R23 line diagnostic to attempt to constrain the metallicity and escape fraction of Ly-α. These metallicity constraints are needed to explore the behaviour of the Mass-Metallicty relation in the low-mass regime and also give insight into the star formation histories of LAE which are known to host young stellar populations. The escape fraction, when combined with an extinction correction, gives insight into the presence of neutral gas. This neutral gas is responsible for resonantly scattering any escaped Ly-α photons, increasing its optical depth to dust. For one object we constrain the metallicity to be Z≤ 0.4Z⊙ and constrain the escape fraction of Ly-α to be Fesc ≤ 30%. For the second object we are only able to constrain its escape fraction, finding 6% ≤ Fesc ≤ 40%. We would like to thank the Natural Sciences and Engineering Research Council of Canada for their financial support through a post-graduate fellowship.

  13. PS1-10bzj: A FAST, HYDROGEN-POOR SUPERLUMINOUS SUPERNOVA IN A METAL-POOR HOST GALAXY

    SciTech Connect

    Lunnan, R.; Chornock, R.; Berger, E.; Milisavljevic, D.; Drout, M.; Sanders, N. E.; Challis, P. M.; Czekala, I.; Foley, R. J.; Fong, W.; Kirshner, R. P.; Leibler, C.; Marion, G. H.; Narayan, G.; Huber, M. E.; McCrum, M.; Smartt, S. J.; Rest, A.; Roth, K. C.; Scolnic, D.; and others

    2013-07-10

    We present observations and analysis of PS1-10bzj, a superluminous supernova (SLSN) discovered in the Pan-STARRS Medium Deep Survey at a redshift z = 0.650. Spectroscopically, PS1-10bzj is similar to the hydrogen-poor SLSNe 2005ap and SCP 06F6, though with a steeper rise and lower peak luminosity (M{sub bol} {approx_equal} -21.4 mag) than previous events. We construct a bolometric light curve, and show that while PS1-10bzj's energetics were less extreme than previous events, its luminosity still cannot be explained by radioactive nickel decay alone. We explore both a magnetar spin-down and circumstellar interaction scenario and find that either can fit the data. PS1-10bzj is located in the Extended Chandra Deep Field South and the host galaxy is imaged in a number of surveys, including with the Hubble Space Telescope. The host is a compact dwarf galaxy (M{sub B} Almost-Equal-To -18 mag, diameter {approx}< 800 pc), with a low stellar mass (M{sub *} Almost-Equal-To 2.4 Multiplication-Sign 10{sup 7} M{sub Sun }), young stellar population ({tau}{sub *} Almost-Equal-To 5 Myr), and a star formation rate of {approx}2-3 M{sub Sun} yr{sup -1}. The specific star formation rate is the highest seen in an SLSN host so far ({approx}100 Gyr{sup -1}). We detect the [O III] {lambda}4363 line, and find a low metallicity: 12 + (O/H) = 7.8 {+-} 0.2 ({approx_equal} 0.1 Z{sub Sun }). Together, this indicates that at least some of the progenitors of SLSNe come from young, low-metallicity populations.

  14. VLT/GIRAFFE spectroscopic observations of the metal-poor blue compact dwarf galaxy SBS 0335-052E

    NASA Astrophysics Data System (ADS)

    Izotov, Y. I.; Schaerer, D.; Blecha, A.; Royer, F.; Guseva, N. G.; North, P.

    2006-11-01

    Aims.We present two-dimensional spectroscopy of the extremely metal-deficient blue compact dwarf (BCD) galaxy SBS 0335-052E to study physical conditions, element abundances and kinematical properties of the ionised gas in this galaxy. Methods: .Observations were obtained in the spectral range λ3620-9400 Å with the imaging spectrograph GIRAFFE on the UT2 of the Very Large Telescope (VLT). These observations are the first ones carried out so far with GIRAFFE in the ARGUS mode which allows one to simultaneously obtain 308 spectra covering a 11.4 arcsec×7.3 arcsec region. Results: .We produced images of SBS 0335-052E in the continuum and in emission lines of different stages of excitation. While the maximum of emission in the majority of lines, including the strong lines Hβ 4861 Å, Hα 6563 Å, [O iii] 4363,5007 Å, [O ii] 3726,3729 Å, coincides with the youngest south-eastern star clusters 1 and 2, the emission of He II 4686 Å line is offset to the more evolved north-west clusters 4, 5. This suggests that hard ionising radiation responsible for the He II λ4686 Å emission is not related to the most massive youngest stars, but rather is related to fast radiative shocks. This conclusion is supported by the kinematical properties of the ionised gas from the different emission lines as the velocity dispersion in the He II λ4686 Å line is systematically higher, by ~50-100%, than that in other lines. The variations of the emission line profiles suggest the presence of an ionised gas outflow in the direction perpendicular to the galaxy disk. We find a relatively high electron number density Ne of several hundred cm-3 in the brightest part of SBS 0335-052E. There is a small gradient of the electron temperature Te and oxygen abundance from the East to the West with systematically higher Te and lower 12+log O/H in the western part of the galaxy. The oxygen abundances for the whole H II region and its brightest part are 12 + log O/H = 7.29 ± 0.02 and 7.31 ± 0

  15. MUSE searches for galaxies near very metal-poor gas clouds at z ˜ 3: new constraints for cold accretion models

    NASA Astrophysics Data System (ADS)

    Fumagalli, Michele; Cantalupo, Sebastiano; Dekel, Avishai; Morris, Simon L.; O'Meara, John M.; Prochaska, J. Xavier; Theuns, Tom

    2016-10-01

    We report on the search for galaxies in the proximity of two very metal-poor gas clouds at z ˜ 3 towards the quasar Q0956+122. With a 5-hour Multi-Unit Spectroscopic Explorer (MUSE) integration in a ˜500 × 500 kpc2 region centred at the quasar position, we achieve a ≥80 per cent complete spectroscopic survey of continuum-detected galaxies with mR ≤ 25 mag and Lyα emitters with luminosity LLyα ≥ 3 × 1041 erg s- 1. We do not identify galaxies at the redshift of a z ˜ 3.2 Lyman limit system (LLS) with log Z/Z⊙ = -3.35 ± 0.05, placing this gas cloud in the intergalactic medium or circumgalactic medium of a galaxy below our sensitivity limits. Conversely, we detect five Lyα emitters at the redshift of a pristine z ˜ 3.1 LLS with log Z/Z⊙ ≤ -3.8, while ˜0.4 sources were expected given the z ˜ 3 Lyα luminosity function. Both this high detection rate and the fact that at least three emitters appear aligned in projection with the LLS suggest that this pristine cloud is tracing a gas filament that is feeding one or multiple galaxies. Our observations uncover two different environments for metal-poor LLSs, implying a complex link between these absorbers and galaxy haloes, which ongoing MUSE surveys will soon explore in detail. Moreover, in agreement with recent MUSE observations, we detected a ˜ 90 kpc Lyα nebula at the quasar redshift and three Lyα emitters reminiscent of a `dark galaxy' population.

  16. SMC west halo: a slice of the galaxy that is being tidally stripped?. Star clusters trace age and metallicity gradients

    NASA Astrophysics Data System (ADS)

    Dias, B.; Kerber, L.; Barbuy, B.; Bica, E.; Ortolani, S.

    2016-06-01

    Context. The evolution and structure of the Magellanic Clouds is currently under debate. The classical scenario in which both the Large and Small Magellanic Clouds (LMC, SMC) are orbiting the Milky Way has been challenged by an alternative in which the LMC and SMC are in their first close passage to our Galaxy. The clouds are close enough to us to allow spatially resolved observation of their stars, and detailed studies of stellar populations in the galaxies are expected to be able to constrain the proposed scenarios. In particular, the west halo (WH) of the SMC was recently characterized with radial trends in age and metallicity that indicate tidal disruption. Aims: We intend to increase the sample of star clusters in the west halo of the SMC with homogeneous age, metallicity, and distance derivations to allow a better determination of age and metallicity gradients in this region. Positions are compared with the orbital plane of the SMC from models. Methods: Comparisons of observed and synthetic V(B-V) colour-magnitude diagrams were used to derive age, metallicity, distance, and reddening for star clusters in the SMC west halo. Observations were carried out using the 4.1 m SOAR telescope. Photometric completeness was determined through artificial star tests, and the members were selected by statistical comparison with a control field. Results: We derived an age of 1.23 ± 0.07 Gyr and [Fe/H] = -0.87 ± 0.07 for the reference cluster NGC 152, compatible with literature parameters. Age and metallicity gradients are confirmed in the WH: 2.6 ± 0.6 Gyr/° and -0.19 ± 0.09 dex/°, respectively. The age-metallicity relation for the WH has a low dispersion in metallicity and is compatible with a burst model of chemical enrichment. All WH clusters seem to follow the same stellar distribution predicted by dynamical models, with the exception of AM-3, which should belong to the counter-bridge. Brück 6 is the youngest cluster in our sample. It is only 130 ± 40 Myr old and

  17. Fracture mechanics characterization of welds: Fatigue life analysis of notches at welds: J(sub Ic) fracture toughness tests for weld metal

    NASA Astrophysics Data System (ADS)

    Underwood, John H.

    1995-03-01

    In this report two methods of fracture analysis of welds will be emphasized, one addressing fatigue life testing and analysis of notches at welds, and the other addressing the final fracture of the welded component and the fracture toughness tests used to characterize final fracture. These fatigue and fracture methods will be described by referring to recent work from the technical literature and from the U.S. Army Armament Research, Development, and Engineering Center, primarily fracture case study and fracture test method development investigations. A brief general summary will be given of fatigue and fracture methods and concepts that have application to welded structures. Specific fatigue crack initiation tests and analysis methods will be presented, using example results from a welded stainless steel box beam of a cannon carriage. Recent improvements and simplifications in J.integral fracture toughness tests will be described, particularly those related to welds. Fracture toughness measurements for various stainless steel weld metals and heat treatments will also be described.

  18. Are the Effects of Structure Formation Seen in the Central Metallicity of Galaxy Clusters?

    NASA Astrophysics Data System (ADS)

    Elkholy, Tamer Y.; Bautz, Mark W.; Canizares, Claude R.

    2015-05-01

    A sample of 46 nearby clusters observed with Chandra is analyzed to produce radial density, temperature, entropy, and metallicity profiles, as well as other morphological measurements. The entropy profiles are computed to larger radii than in previous Chandra cluster sample analyses. We find that the iron mass fraction measured in the inner 0.15{{R}500} shows a larger dispersion across the sample of low-mass clusters than it does for the sample of high-mass clusters. We interpret this finding as the result of the mixing of more halos in large clusters than in small clusters, leading to an averaging of the metallicity in the large clusters, and thus less dispersion of metallicity. This interpretation lends support to the idea that the low-entropy, metal-rich gas of merging halos reaches the clusters’ centers, which explains observations of core-collapse supernova product metallicity peaks, and which is seen in hydrodynamical simulations. The gas in these merging halos would have to reach cluster centers without mixing in the outer regions. On the other hand, the metallicity dispersion does not change with mass in the outer regions of the clusters, suggesting that most of the outer metals originate from a source with a more uniform metallicity level, such as during pre-enrichment. We also measure a correlation between the metal content in low-mass clusters and the morphological disturbance of their intracluster medium, as measured by centroid shift. This suggests an alternative interpretation, whereby transitional metallicity boosts in the center of low-mass clusters account for the larger dispersion of their metallicities.

  19. THE EFFECT OF SECOND-GENERATION POPULATIONS ON THE INTEGRATED COLORS OF METAL-RICH GLOBULAR CLUSTERS IN EARLY-TYPE GALAXIES

    SciTech Connect

    Chung, Chul; Lee, Sang-Yoon; Yoon, Suk-Jin; Lee, Young-Wook

    2013-05-20

    The mean color of globular clusters (GCs) in early-type galaxies is in general bluer than the integrated color of halo field stars in host galaxies. Metal-rich GCs often appear more associated with field stars than metal-poor GCs, yet show bluer colors than their host galaxy light. Motivated by the discovery of multiple stellar populations in Milky Way GCs, we present a new scenario in which the presence of second-generation (SG) stars in GCs is responsible for the color discrepancy between metal-rich GCs and field stars. The model assumes that the SG populations have an enhanced helium abundance as evidenced by observations, and it gives a good explanation of the bluer optical colors of metal-rich GCs than field stars as well as strong Balmer lines and blue UV colors of metal-rich GCs. Ours may be complementary to the recent scenario suggesting the difference in stellar mass functions (MFs) as an origin for the GC-to-star color offset. A quantitative comparison is given between the SG and MF models.

  20. The effects of metallicity, UV radiation and non-equilibrium chemistry in high-resolution simulations of galaxies

    NASA Astrophysics Data System (ADS)

    Richings, A. J.; Schaye, Joop

    2016-05-01

    We present a series of hydrodynamic simulations of isolated galaxies with stellar mass of 109 M⊙. The models use a resolution of 750 M⊙ per particle and include a treatment for the full non-equilibrium chemical evolution of ions and molecules (157 species in total), along with gas cooling rates computed self-consistently using the non-equilibrium abundances. We compare these to simulations evolved using cooling rates calculated assuming chemical (including ionization) equilibrium, and we consider a wide range of metallicities and UV radiation fields, including a local prescription for self-shielding by gas and dust. We find higher star formation rates and stronger outflows at higher metallicity and for weaker radiation fields, as gas can more easily cool to a cold (few hundred Kelvin) star-forming phase under such conditions. Contrary to variations in the metallicity and the radiation field, non-equilibrium chemistry generally has no strong effect on the total star formation rates or outflow properties. However, it is important for modelling molecular outflows. For example, the mass of H2 outflowing with velocities {>}50 {km} {s}^{-1} is enhanced by a factor ˜20 in non-equilibrium. We also compute the observable line emission from C II and CO. Both are stronger at higher metallicity, while C II and CO emission are higher for stronger and weaker radiation fields, respectively. We find that C II is generally unaffected by non-equilibrium chemistry. However, emission from CO varies by a factor of ˜2-4. This has implications for the mean XCO conversion factor between CO emission and H2 column density, which we find is lowered by up to a factor ˜2.3 in non-equilibrium, and for the fraction of CO-dark molecular gas.

  1. GAS REGULATION OF GALAXIES: THE EVOLUTION OF THE COSMIC SPECIFIC STAR FORMATION RATE, THE METALLICITY-MASS-STAR-FORMATION RATE RELATION, AND THE STELLAR CONTENT OF HALOS

    SciTech Connect

    Lilly, Simon J.; Carollo, C. Marcella; Pipino, Antonio; Peng Yingjie; Renzini, Alvio

    2013-08-01

    A very simple physical model of galaxies is one in which the formation of stars is instantaneously regulated by the mass of gas in a reservoir with mass loss scaling with the star-formation rate (SFR). This model links together three different aspects of the evolving galaxy population: (1) the cosmic time evolution of the specific star-formation rate (sSFR) relative to the growth of halos, (2) the gas-phase metallicities across the galaxy population and over cosmic time, and (3) the ratio of the stellar to dark matter mass of halos. The gas regulator is defined by the gas consumption timescale ({epsilon}{sup -1}) and the mass loading {lambda} of the wind outflow {lambda}{center_dot}SFR. The simplest regulator, in which {epsilon} and {lambda} are constant, sets the sSFR equal to exactly the specific accretion rate of the galaxy; more realistic situations lead to an sSFR that is perturbed from this precise relation. Because the gas consumption timescale is shorter than the timescale on which the system evolves, the metallicity Z is set primarily by the instantaneous operation of the regulator system rather than by the past history of the system. The metallicity of the gas reservoir depends on {epsilon}, {lambda}, and sSFR, and the regulator system therefore naturally produces a Z(m{sub star}, SFR) relation if {epsilon} and {lambda} depend on the stellar mass m{sub star}. Furthermore, this relation will be the same at all epochs unless the parameters {epsilon} and {lambda} themselves change with time. A so-called fundamental metallicity relation is naturally produced by these conditions. The overall mass-metallicity relation Z(m{sub star}) directly provides the fraction f{sub star}(m{sub star}) of incoming baryons that are being transformed into stars. The observed Z(m{sub star}) relation of Sloan Digital Sky Survey (SDSS) galaxies implies a strong dependence of stellar mass on halo mass that reconciles the different faint-end slopes of the stellar and halo mass

  2. Measuring the Evolution of Stellar Populations And Gas Metallicity in Galaxies with Far-Infrared Space Spectroscopy

    NASA Astrophysics Data System (ADS)

    Stacey, Gordon

    We propose a study of the evolution of stellar populations and gas metallicities in about 80 nearby star forming galaxies based on mining the NASA data archives for observations of the [NIII] 57 µm, [OIII] 52 µm and/or 88 µm, [NII] 122 and [CII] 158 µm far-infrared (FIR) fine- structure lines and other archives for thermal radio continuum. These lines are powerful probes of both stellar populations and gas properties and our primary science derives from these tracers. For sources that show both signs of active galactic nuclei (AGN) and star formation, we will take advantage of the readily available NASA Spitzer IRS data base that includes mid-IR [NeII] 12.8 µm, [NeIII] 15.6 µm and [NeV] 14.3 µm, [OIV] 25.9 µm and PAH observations. These complementary data reveal the relative fractions of the FIR line emission that might arise from star formation and the narrow line regions (NLR) associated with an AGN, thereby providing a robust set of observations to compare with star formation models. Subsets of the FIR lines have been detected from hundreds of nearby galaxies. From both theoretical studies and the results of these pioneering observations we know that these lines can be powerful probes of stellar populations and star formation in galaxies. Here we plan to use various combinations of the lines to constrain (1) the age of the stellar populations (through lines that trace the hardness of the stellar radiation fields, hence stellar spectral type), (2) the degree of processing of the interstellar medium (through lines that trace growth of secondary to primary element abundances for example, the N/O ratio), (3) the efficiency of star formation (through growth in absolute abundances of N and O, the N/H and O/H ratios), and (4) the current day mass function of upper main sequence stars. Surprisingly, there has been no systematic study of the large sample of these line detections made with PACS on Herschel in order to truly assess and calibrate their diagnostic

  3. A Multiwavelength Study of IC 63 and IC 59

    NASA Astrophysics Data System (ADS)

    Karr, J. L.; Noriega-Crespo, A.; Martin, P. G.

    2005-02-01

    IC 63 and IC 59 are two nearby arc-shaped nebulae with relatively simple geometries and minimal obscuring material. The two regions, in spite of a similar projected distance from their ionizing star, have very different observational properties, both in continuum emission and in the presence and strength of line emission from molecular species. This paper conducts a multiwavelength study of the two regions using archived data from a variety of sources, including the Canadian Galactic Plane Survey and the Infrared Space Observatory. The multiwavelength morphology and structure of the two nebulae are studied in detail, particularly the ionization fronts in IC 63. The possibility of triggered star formation in IC 63 is investigated and determined to be spurious. H2 and polycyclic aromatic hydrocarbon emission is detected in both IC 63 and IC 59, confirming the presence of molecular hydrogen in IC 59. The averaged line ratios are similar in the two regions, but variations are seen within each region. Temperatures and densities were calculated from the S(3) and S(5) pure rotational lines of molecular hydrogen. We derived a temperature of 630 K in IC 63, comparable to previous results, and a column density of 5.8×1017 cm-2, somewhat lower than previous values. New results for IC 59 show values of 590 K and 3.4×1017 cm-2, slightly cooler and with lower column density than IC 63. The contrast in appearance between IC 63 and IC 59 is consistent with a difference in actual (rather than projected) distances and a small variation in temperature and column density.

  4. TYPE Ibc SUPERNOVAE IN DISTURBED GALAXIES: EVIDENCE FOR A TOP-HEAVY INITIAL MASS FUNCTION

    SciTech Connect

    Habergham, S. M.; James, P. A.; Anderson, J. P.

    2010-07-01

    We compare the radial locations of 178 core-collapse supernovae (CCSNe) to the R-band and H{alpha} light distributions of their host galaxies. When the galaxies are split into 'disturbed' and 'undisturbed' categories, a striking difference emerges. The disturbed galaxies have a central excess of CCSNe and this excess is almost completely dominated by supernovae of types Ib, Ic, and Ib/c, whereas type II supernovae dominate in all other environments. The difference cannot easily be explained by metallicity or extinction effects, and thus we propose that this is direct evidence for a stellar initial mass function that is strongly weighted toward high-mass stars, specifically in the central regions of disturbed galaxies.

  5. BOO-1137-AN EXTREMELY METAL-POOR STAR IN THE ULTRA-FAINT DWARF SPHEROIDAL GALAXY BOOeTES I

    SciTech Connect

    Norris, John E.; Yong, David; Gilmore, Gerard; Wyse, Rosemary F. G.

    2010-03-01

    We present high-resolution (R {approx} 40,000), high-signal-to-noise ratio (20-90) spectra of an extremely metal-poor giant star Boo-1137 in the 'ultra-faint' dwarf spheroidal galaxy (dSph) Booetes I, absolute magnitude M{sub V} {approx} -6.3. We derive an iron abundance of [Fe/H] = -3.7, making this the most metal-poor star as yet identified in an ultra-faint dSph. Our derived effective temperature and gravity are consistent with its identification as a red giant in Booetes I. Abundances for a further 15 elements have also been determined. Comparison of the relative abundances, [X/Fe], with those of the extremely metal-poor red giants of the Galactic halo shows that Boo-1137 is 'normal' with respect to C and N, the odd-Z elements Na and Al, the iron-peak elements, and the neutron-capture elements Sr and Ba, in comparison with the bulk of the Milky Way halo population having [Fe/H] {approx}<-3.0. The alpha-elements Mg, Si, Ca, and Ti are all higher by DELTA[X/Fe] {approx} 0.2 than the average halo values. Monte Carlo analysis indicates that DELTA[alpha/Fe] values this large are expected with a probability {approx}0.02. The elemental abundance pattern in Boo-1137 suggests inhomogeneous chemical evolution, consistent with the wide internal spread in iron abundances we previously reported. The similarity of most of the Boo-1137 relative abundances with respect to halo values, and the fact that the alpha-elements are all offset by a similar small amount from the halo averages, points to the same underlying galaxy-scale stellar initial mass function, but that Boo-1137 likely originated in a star-forming region where the abundances reflect either poor mixing of supernova (SN) ejecta, or poor sampling of the SN progenitor mass range, or both.

  6. Detection of hot, metal-enriched outflowing gas around z ≈ 2.3 star-forming galaxies in the Keck Baryonic Structure Survey

    NASA Astrophysics Data System (ADS)

    Turner, Monica L.; Schaye, Joop; Steidel, Charles C.; Rudie, Gwen C.; Strom, Allison L.

    2015-06-01

    We use quasar absorption lines to study the physical conditions in the circumgalactic medium of redshift z ≈ 2.3 star-forming galaxies taken from the Keck Baryonic Structure Survey. In Turner et al. we used the pixel optical depth technique to show that absorption by H I and the metal ions O VI, N V, C IV, C III, and Si IV is strongly enhanced within |Δv| ≲ 170 km s-1 and projected distances |d| ≲ 180 proper kpc from sightlines to the background quasars. Here we demonstrate that the O VI absorption is also strongly enhanced at fixed H I, C IV, and Si IV optical depths, and that this enhancement extends out to ˜350 km s-1. At fixed H I the increase in the median O VI optical depth near galaxies is 0.3-0.7 dex and is detected at 2-3σ confidence for all seven H I bins that have log _{10}τ_{H I} ≥ -1.5. We use ionization models to show that the observed strength of O VI as a function of H I is consistent with enriched, photoionized gas for pixels with τ_{H I} ≳ 10. However, for pixels with τ_{H I} ≲ 1 this would lead to implausibly high metallicities at low densities if the gas were photoionized by the background radiation. This indicates that the galaxies are surrounded by gas that is sufficiently hot to be collisionally ionized (T > 105 K) and that a substantial fraction of the hot gas has a metallicity ≳10-1 of solar. Given the high metallicity and large velocity extent (out to ˜1.5 vcirc) of this gas, we conclude that we have detected hot, metal-enriched outflows arising from star-forming galaxies.

  7. RE-EXAMINING HIGH ABUNDANCE SLOAN DIGITAL SKY SURVEY MASS-METALLICITY OUTLIERS: HIGH N/O, EVOLVED WOLF-RAYET GALAXIES?

    SciTech Connect

    Berg, Danielle A.; Skillman, Evan D.; Marble, Andrew R. E-mail: skillman@astro.umn.edu

    2011-09-01

    We present new MMT spectroscopic observations of four dwarf galaxies representative of a larger sample observed by the Sloan Digital Sky Survey and identified by Peeples et al. as low-mass, high oxygen abundance outliers from the mass-metallicity relation. Peeples showed that these four objects (with metallicity estimates of 8.5 {<=} 12 + log(O/H) {<=} 8.8) have oxygen abundance offsets of 0.4-0.6 dex from the M{sub B} luminosity-metallicity relation. Our new observations extend the wavelength coverage to include the [O II] {lambda}{lambda}3726, 3729 doublet, which adds leverage in oxygen abundance estimates and allows measurements of N/O ratios. All four spectra are low excitation, with relatively high N/O ratios (N/O {approx}> 0.10), each of which tend to bias estimates based on strong emission lines toward high oxygen abundances. These spectra all fall in a regime where the 'standard' strong-line methods for metallicity determinations are not well calibrated either empirically or by photoionization modeling. By comparing our spectra directly to photoionization models, we estimate oxygen abundances in the range of 7.9 {<=} 12 + log (O/H) {<=} 8.4, consistent with the scatter of the mass-metallicity relation. We discuss the physical nature of these galaxies that leads to their unusual spectra (and previous classification as outliers), finding their low excitation, elevated N/O, and strong Balmer absorption are consistent with the properties expected from galaxies evolving past the 'Wolf-Rayet galaxy' phase. We compare our results to the 'main' sample of Peeples and conclude that they are outliers primarily due to enrichment of nitrogen relative to oxygen and not due to unusually high oxygen abundances for their masses or luminosities.

  8. Hunting for extremely metal-poor emission-line galaxies in the Sloan Digital Sky Survey: MMT and 3.5 m APO observations

    NASA Astrophysics Data System (ADS)

    Izotov, Y. I.; Thuan, T. X.; Guseva, N. G.

    2012-10-01

    We present 6.5-m MMT and 3.5 m APO spectrophotometry of 69 H ii regions in 42 low-metallicity emission-line galaxies, selected from the data release 7 of the Sloan Digital Sky Survey to have mostly [O iii]λ4959/Hβ ≲ 1 and [N ii]λ6583/Hβ ≲ 0.1. The electron temperature-sensitive emission line [O iii] λ4363 is detected in 53 H ii regions allowing a direct abundance determination. The oxygen abundance in the remaining 16 H ii regions is derived using a semi-empirical method. The oxygen abundance of the galaxies in our sample ranges from 12 + log O/H ~ 7.1 to ~7.9, with 14 H ii regions in 7 galaxies with 12 + log O/H ≤ 7.35. In 5 of the latter galaxies, the oxygen abundance is derived here for the first time. Including other known extremely metal-deficient emission-line galaxies from the literature, e.g. SBS 0335-052W, SBS 0335-052E and I Zw 18, we have compiled a sample of the 17 most metal-deficient (with 12 + log O/H ≤ 7.35) emission-line galaxies known in the local universe. There appears to be a metallicity floor at 12 + log O/H ~ 6.9, suggesting that the matter from which dwarf emission-line galaxies formed was pre-enriched to that level by e.g. Population III stars. Based on observations with the Multiple Mirror telescope (MMT) and the 3.5 m Apache Point Observatory (APO). The MMT is operated by the MMT Observatory (MMTO), a joint venture of the Smithsonian Institution and the University of Arizona. The Apache Point Observatory 3.5-m telescope is owned and operated by the Astrophysical Research Consortium.Figures 1-3 and Tables 2-8 are available in electronic form at http://www.aanda.org

  9. The HK-II Survey: Kinematics of Metal-Poor Stars in the Galaxy

    NASA Astrophysics Data System (ADS)

    Rhee, J.; Beers, T. C.

    2003-12-01

    The digitized HK-II survey (Rhee 2000, Ph.D. thesis, MSU) was originated as a follow-on to the HK-I survey of Beers and colleagues (e.g., Beers et al. 1992, AJ, 103, 1987). HK-I was based on visually-selected candidate metal-poor stars from objective-prism plates. Unfortunately, in the absence of color information, this selection technique introduced a rather severe temperature-related bias. As a result, the HK-I candidates do not include large numbers of metal-deficient giants. In HK-II, candidate metal-poor stars are quantitatively selected from digitized objective-prism spectra with JHK color information from the recently completeted 2MASS catalog. This approach eliminates much of the temperature bias. We have begun to survey candidate very metal-poor ([Fe/H] ≤ -2.0) giants from HK-II, over the magnitude range 11.0 ≤ B ≤ 16.0, covering some ˜7000 deg2 of intermediate to high Galactic-latitudes. Ongoing medium-resolution ( ˜ 1-2Å ) spectroscopic follow-up using NOAO observing facilities has allowed us to obtain, to date, some 1000 spectra (400, 450, and 150 spectra for red giants, subgiants near the main-sequence turnoff, and FHB/A stars, respectively) for the HK-II metal-poor star candidates. In particular, the detection rate of bona fide very metal-poor giants is about 45 %, which is quite encouraging. Most of the "mistakes" are slightly more metal-rich giants, with -2.0 < [Fe/H] < -1.0. Metallicities and radial velocities are determined from our spectroscopy, and proper motions for most of the program stars are obtained from the recently released UCAC2 astrometric survey catalog. Here we present an analysis of the full space motions for numerous metal-poor stars from the HK-II survey. A comparision of the chemical and kinematic properties between high- and low-halo populations (that is, giants vs. sub-giants) will aid us in understanding the formation history of the Milky Way. J.R. acknowledges partial support for this work by NASA through the AAS

  10. Discovering extremely compact and metal-poor, star-forming dwarf galaxies out to z ~ 0.9 in the VIMOS Ultra-Deep Survey

    NASA Astrophysics Data System (ADS)

    Amorín, R.; Sommariva, V.; Castellano, M.; Grazian, A.; Tasca, L. A. M.; Fontana, A.; Pentericci, L.; Cassata, P.; Garilli, B.; Le Brun, V.; Le Fèvre, O.; Maccagni, D.; Thomas, R.; Vanzella, E.; Zamorani, G.; Zucca, E.; Bardelli, S.; Capak, P.; Cassará, L. P.; Cimatti, A.; Cuby, J. G.; Cucciati, O.; de la Torre, S.; Durkalec, A.; Giavalisco, M.; Hathi, N. P.; Ilbert, O.; Lemaux, B. C.; Moreau, C.; Paltani, S.; Ribeiro, B.; Salvato, M.; Schaerer, D.; Scodeggio, M.; Talia, M.; Taniguchi, Y.; Tresse, L.; Vergani, D.; Wang, P. W.; Charlot, S.; Contini, T.; Fotopoulou, S.; López-Sanjuan, C.; Mellier, Y.; Scoville, N.

    2014-08-01

    We report the discovery of 31 low-luminosity (-14.5 ≳ MAB(B) ≳ -18.8), extreme emission line galaxies (EELGs) at 0.2 ≲ z ≲ 0.9 identified by their unusually high rest-frame equivalent widths (100 ≤ EW[O iii] ≤ 1700 Å) as part of the VIMOS Ultra Deep Survey (VUDS). VIMOS optical spectra of unprecedented sensitivity (IAB ~ 25 mag) along with multiwavelength photometry and HST imaging are used to investigate spectrophotometric properties of this unique sample and to explore, for the first time, the very low stellar mass end (M⋆ ≲ 108M⊙) of the luminosity-metallicity (LZR) and mass-metallicity (MZR) relations at z < 1. Characterized by their extreme compactness (R50 < 1 kpc), low stellar mass and enhanced specific star formation rates (sSFR = SFR/M⋆ ~ 10-9-10-7 yr-1), the VUDS EELGs are blue dwarf galaxies likely experiencing the first stages of a vigorous galaxy-wide starburst. Using Te-sensitive direct and strong-line methods, we find that VUDS EELGs are low-metallicity (7.5 ≲ 12 + log (O/H) ≲ 8.3) galaxies with high ionization conditions (log (qion) ≳ 8 cm s-1), including at least three EELGs showing Heiiλ 4686 Å emission and four extremely metal-poor (≲10% solar) galaxies. The LZR and MZR followed by VUDS EELGs show relatively large scatter, being broadly consistent with the extrapolation toward low luminosity and mass from previous studies at similar redshift. However, we find evidence that galaxies with younger and more vigorous star formation - as characterized by their larger EWs, ionization and sSFR - tend to be more metal poor at a given stellar mass. Based on data obtained with the European Southern Observatory Very Large Telescope, Paranal, Chile, under Large Program 185.A-0791.Figure A.1 is available in electronic form at http://www.aanda.orgTables 1 and 2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/568/L8

  11. A SEARCH FOR UNRECOGNIZED CARBON-ENHANCED METAL-POOR STARS IN THE GALAXY

    SciTech Connect

    Placco, Vinicius M.; Rossi, Silvia; Kennedy, Catherine R.; Beers, Timothy C.; Lee, Young Sun; Christlieb, Norbert; Sivarani, Thirupathi; Reimers, Dieter; Wisotzki, Lutz

    2010-03-15

    We have developed a new procedure to search for carbon-enhanced metal-poor (CEMP) stars from the Hamburg/ESO (HES) prism-survey plates. This method employs an extended line index for the CH G band, which we demonstrate to have superior performance when compared to the narrower G-band index formerly employed to estimate G-band strengths for these spectra. Although CEMP stars have been found previously among candidate metal-poor stars selected from the HES, the selection on metallicity undersamples the population of intermediate-metallicity CEMP stars (-2.5 {<=} [Fe/H] {<=} -1.0); such stars are of importance for constraining the onset of the s-process in metal-deficient asymptotic giant branch stars (thought to be associated with the origin of carbon for roughly 80% of CEMP stars). The new candidates also include substantial numbers of warmer carbon-enhanced stars, which were missed in previous HES searches for carbon stars due to selection criteria that emphasized cooler stars. A first subsample, biased toward brighter stars (B< 15.5), has been extracted from the scanned HES plates. After visual inspection (to eliminate spectra compromised by plate defects, overlapping spectra, etc., and to carry out rough spectral classifications), a list of 669 previously unidentified candidate CEMP stars was compiled. Follow-up spectroscopy for a pilot sample of 132 candidates was obtained with the Goodman spectrograph on the SOAR 4.1 m telescope. Our results show that most of the observed stars lie in the targeted metallicity range, and possess prominent carbon absorption features at 4300 A. The success rate for the identification of new CEMP stars is 43% (13 out of 30) for [Fe/H] < -2.0. For stars with [Fe/H] < -2.5, the ratio increases to 80% (four out of five objects), including one star with [Fe/H] < -3.0.

  12. The large, oxygen-rich halos of star-forming galaxies are a major reservoir of galactic metals.

    PubMed

    Tumlinson, J; Thom, C; Werk, J K; Prochaska, J X; Tripp, T M; Weinberg, D H; Peeples, M S; O'Meara, J M; Oppenheimer, B D; Meiring, J D; Katz, N S; Davé, R; Ford, A B; Sembach, K R

    2011-11-18

    The circumgalactic medium (CGM) is fed by galaxy outflows and accretion of intergalactic gas, but its mass, heavy element enrichment, and relation to galaxy properties are poorly constrained by observations. In a survey of the outskirts of 42 galaxies with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope, we detected ubiquitous, large (150-kiloparsec) halos of ionized oxygen surrounding star-forming galaxies; we found much less ionized oxygen around galaxies with little or no star formation. This ionized CGM contains a substantial mass of heavy elements and gas, perhaps far exceeding the reservoirs of gas in the galaxies themselves. Our data indicate that it is a basic component of nearly all star-forming galaxies that is removed or transformed during the quenching of star formation and the transition to passive evolution.

  13. Age-Metallicity Relationships Across the Milky Way Galaxy with APOGEE

    NASA Astrophysics Data System (ADS)

    Casados-Medve, Colton; Bird, Jonathan C.; APOGEE Team (Sloan Digital Sky Survey)

    2017-01-01

    The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has measured the infrared spectrum of over 160,000 stars. The unique combination of high resolution (R~20,000) and infrared wavelength coverage allows APOGEE to determine precise abundances for ~15 elements in stars located across the Galactic midplane, from ~3 kpc to ~15 kpc. The observed metallicity gradient over this radial range is also accompanied by a change in the shape of the metallicity distribution function (MDF) as a function of galactocentric radius (Hayden et al. 2015). Here, we combine the APOGEE sample with stellar age determinations (Ness et al. 2016) to measure how the distribution of stellar metals changes as a function of both galactocentric radius and age. We determine the age-metallicity relationship (AMR) in several radial zones, allowing comparison with the AMR measured in the local solar neighborhood. In addition, our analysis shows the skewness of the MDF changes as a function of radius even for the youngest (age < 1 gigayear) stars. These stars are too young to have migrated far from their birth radii. Our results suggest that the changing skew of the MDF with radius does not require substantial radial migration in the disk as recent studies contend.

  14. SURVEYING THE AGENTS OF GALAXY EVOLUTION IN THE TIDALLY STRIPPED, LOW METALLICITY SMALL MAGELLANIC CLOUD (SAGE-SMC). II. COOL EVOLVED STARS

    SciTech Connect

    Boyer, Martha L.; Meixner, Margaret; Gordon, Karl D.; Shiao, Bernie; Srinivasan, Sundar; Van Loon, Jacco Th.; McDonald, Iain; Kemper, F.; Zaritsky, Dennis; Block, Miwa; Engelbracht, Charles W.; Misselt, Karl; Babler, Brian; Bracker, Steve; Meade, Marilyn; Whitney, Barbara; Hora, Joe; Robitaille, Thomas; Indebetouw, Remy; Sewilo, Marta

    2011-10-15

    We investigate the infrared (IR) properties of cool, evolved stars in the Small Magellanic Cloud (SMC), including the red giant branch (RGB) stars and the dust-producing red supergiant (RSG) and asymptotic giant branch (AGB) stars using observations from the Spitzer Space Telescope Legacy program entitled 'Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity SMC', or SAGE-SMC. The survey includes, for the first time, full spatial coverage of the SMC bar, wing, and tail regions at IR wavelengths (3.6-160 {mu}m). We identify evolved stars using a combination of near-IR and mid-IR photometry and point out a new feature in the mid-IR color-magnitude diagram that may be due to particularly dusty O-rich AGB stars. We find that the RSG and AGB stars each contribute {approx}20% of the global SMC flux (extended + point-source) at 3.6 {mu}m, which emphasizes the importance of both stellar types to the integrated flux of distant metal-poor galaxies. The equivalent SAGE survey of the higher-metallicity Large Magellanic Cloud (SAGE-LMC) allows us to explore the influence of metallicity on dust production. We find that the SMC RSG stars are less likely to produce a large amount of dust (as indicated by the [3.6] - [8] color). There is a higher fraction of carbon-rich stars in the SMC, and these stars appear to reach colors as red as their LMC counterparts, indicating that C-rich dust forms efficiently in both galaxies. A preliminary estimate of the dust production in AGB and RSG stars reveals that the extreme C-rich AGB stars dominate the dust input in both galaxies, and that the O-rich stars may play a larger role in the LMC than in the SMC.

  15. Oxygen abundances of zCOSMOS galaxies at z ~ 1.4 based on five lines and implications for the fundamental metallicity relation

    NASA Astrophysics Data System (ADS)

    Maier, Christian; Lilly, Simon J.; Ziegler, Bodo L.

    2015-02-01

    A relation between the stellar mass M and the gas-phase metallicity Z of galaxies, the MZR, is observed up to higher redshifts. It is a matter of debate, however, if the SFR is a second parameter in the MZR. To explore this issue at z > 1, we used VLT-SINFONI near-infrared (NIR) spectroscopy of eight zCOSMOS galaxies at 1.3 < z < 1.4 to measure the strengths of four emission lines: Hβ, [OIII]λ5007, Hα, and [NII]λ6584, additional to [OII]λ3727 measured from VIMOS. We derive reliable O/H metallicities based on five lines, and also SFRs from extinction corrected Hα measurements. We find that the MZR of these star-forming galaxies at z ~ 1.4 is lower than the local SDSS MZR by a factor of three to five, a larger change than reported in the literature using [NII]/Hα-based metallicities from individual and stacked spectra. Correcting N2-based O/Hs using recent results by Newman et al. (2014), also the larger FMOS sample at z ~ 1.4 of Zahid et al. (2014) shows a similar evolution of the MZR like the zCOSMOS objects. These observations seem also in agreement with a non-evolving FMR using the physically motivated formulation of the FMR from Lilly et al. (2013).

  16. HERSCHEL SPECTROSCOPIC OBSERVATIONS OF LITTLE THINGS DWARF GALAXIES

    SciTech Connect

    Cigan, Phil; Young, Lisa; Cormier, Diane; Lebouteiller, Vianney; Madden, Suzanne; Brinks, Elias; Elmegreen, Bruce; Schruba, Andreas; Heesen, Volker; Collaboration: LITTLE THINGS Team

    2016-01-15

    We present far-infrared (FIR) spectral line observations of five galaxies from the Little Things sample: DDO 69, DDO 70, DDO 75, DDO 155, and WLM. While most studies of dwarfs focus on bright systems or starbursts due to observational constraints, our data extend the observed parameter space into the regime of low surface brightness dwarf galaxies with low metallicities and moderate star formation rates. Our targets were observed with Herschel at the [C ii] 158 μm, [O i] 63 μm, [O iii] 88 μm, and [N ii] 122 μm emission lines using the PACS Spectrometer. These high-resolution maps allow us for the first time to study the FIR properties of these systems on the scales of larger star-forming complexes. The spatial resolution in our maps, in combination with star formation tracers, allows us to identify separate photodissociation regions (PDRs) in some of the regions we observed. Our systems have widespread [C ii] emission that is bright relative to continuum, averaging near 0.5% of the total infrared (TIR) budget—higher than in solar-metallicity galaxies of other types. [N ii] is weak, suggesting that the [C ii] emission in our galaxies comes mostly from PDRs instead of the diffuse ionized interstellar medium (ISM). These systems exhibit efficient cooling at low dust temperatures, as shown by ([O i]+[C ii])/TIR in relation to 60 μm/100 μm, and low [O i]/[C ii] ratios which indicate that [C ii] is the dominant coolant of the ISM. We observe [O iii]/[C ii] ratios in our galaxies that are lower than those published for other dwarfs, but similar to levels noted in spirals.

  17. IC5063: A merger with a hidden luminous active nucleus

    NASA Technical Reports Server (NTRS)

    Colina, L.; Sparks, W. B.; Macchetto, F. D.

    1990-01-01

    IC5063 is a nearby galaxy classified as an SO and containing a system of dust lanes parallel to its major optical axis (Danziger, Goss and Wellington, 1981; Bergeron, Durret and Boksenberg, 1983). Extended emission line regions with high excitation properties have been detected over distances of up to 19 kpc from the nucleus. This galaxy has been classified as Seyfert 2 on the basis of its emission line spectrum. These characteristics make IC5063 one of the best candidates for a merger remnant and an excellent candidate for a hidden luminous active nucleus. Based on new broad and narrow band images and long-slit spectroscopy obtained at the ESO 3.6 m telescope, the authors present some preliminary results supporting this hypothesis.

  18. Physical properties of simulated galaxy populations at z = 2 - I. Effect of metal-line cooling and feedback from star formation and AGN

    NASA Astrophysics Data System (ADS)

    Haas, Marcel R.; Schaye, Joop; Booth, C. M.; Dalla Vecchia, Claudio; Springel, Volker; Theuns, Tom; Wiersma, Robert P. C.

    2013-11-01

    We use hydrodynamical simulations from the OverWhelmingly Large Simulations (OWLS) project to investigate the dependence of the physical properties of galaxy populations at redshift 2 on metal-line cooling and feedback from star formation and active galactic nuclei (AGN). We find that if the sub-grid feedback from star formation is implemented kinetically, the feedback is only efficient if the initial wind velocity exceeds a critical value. This critical velocity increases with galaxy mass and also if metal-line cooling is included. This suggests that radiative losses quench the winds if their initial velocity is too low. If the feedback is efficient, then the star formation rate is inversely proportional to the amount of energy injected per unit stellar mass formed (which is proportional to the initial mass loading for a fixed wind velocity). This can be understood if the star formation is self-regulating, i.e. if the star formation rate (and thus the gas fraction) increases until the outflow rate balances the inflow rate. Feedback from AGN is efficient at high masses, while increasing the initial wind velocity with gas pressure or halo mass allows one to generate galaxy-wide outflows at all masses. Matching the observed galaxy mass function requires efficient feedback. In particular, the predicted faint-end slope is too steep unless we resort to highly mass loaded winds for low-mass objects. Such efficient feedback from low-mass galaxies (M* ≪ 1010 M⊙) also reduces the discrepancy with the observed specific star formation rates, which are higher than predicted unless the feedback transitions from highly efficient to inefficient just below M* ˜ 5 × 109 M⊙.

  19. The extremely metal-poor galaxy DDO 68: the luminous blue variable, Hα shells and the most luminous stars

    NASA Astrophysics Data System (ADS)

    Pustilnik, S. A.; Makarova, L. N.; Perepelitsyna, Y. A.; Moiseev, A. V.; Makarov, D. I.

    2017-03-01

    This paper presents new results from the ongoing study of the unusual Lynx-Cancer void galaxy DDO 68, which has star-forming regions of record low metallicity [12+log (O/H) ∼7.14]. The results include the following. (i) A new spectrum and photometry have been obtained with the 6-m SAO RAS telescope (BTA) for the luminous blue variable (LBV = DDO68-V1). Photometric data sets were complemented with others based on the Sloan Digital Sky Survey (SDSS) and the Hubble Space Telescope (HST) archive images. (ii) We performed an analysis of the DDO 68 supergiant shell (SGS) and the prominent smaller Hα arcs/shells visible in the HST image coupled with kinematic maps in Hα obtained with the Fabry-Perot interferometer (FPI) at the BTA. (iii) We compiled a list of about 50 of the most luminous stars (-9.1 mag < MV < -6.0 mag) identified from the HST images associated with the star-forming regions with known extremely low O/H. This is intended to pave the path for the current science to be investigated with the next generation of giant telescopes. We have confirmed earlier hints of significant variation of the LBV optical light, deriving its amplitude as ΔV ≳ 3.7 mag for the first time. New data suggest that in 2008-2010 the LBV reached MV = -10.5 mag and probably underwent a giant eruption. We argue that the structure of star-forming complexes along the SGS ('Northern Ring') perimeter provides evidence for sequential induced star-formation episodes caused by the shell gas instabilities and gravitational collapse. The variability of some luminous extremely metal-poor stars in DDO 68 can currently be monitored with medium-size telescopes at sites with superb seeing.

  20. Envelope overshooting in low-metallicity intermediate- and high-mass stars: a test with the Sagittarius dwarf irregular galaxy

    NASA Astrophysics Data System (ADS)

    Tang, Jing; Bressan, Alessandro; Slemer, Alessandra; Marigo, Paola; Girardi, Leo; Bianchi, Luciana; Rosenfield, Phil; Momany, Yazan

    2016-01-01

    We check the performance of the Padova TRieste Stellar Evolution Code (PARSEC) tracks in reproducing the blue loops of intermediate age and young stellar populations at very low metallicity. We compute new evolutionary PARSEC tracks of intermediate- and high-mass stars from 2 to 350 M⊙ with enhanced envelope overshooting (EO), EO = 2HP and 4HP, for very low metallicity, Z = 0.0005. The input physics, including the mass-loss rate, has been described in PARSEC, version V1.2. By comparing the synthetic colour-magnitude diagrams (CMDs) obtained from the different sets of models with EO = 0.7HP (the standard PARSEC tracks), 2HP and 4HP, with deep observations of the Sagittarius dwarf irregular galaxy (SagDIG), we find that the overshooting scale EO = 2HP best reproduces the observed loops. This result is consistent with that obtained by Tang et al. for Z in the range 0.001-0.004. We also discuss the dependence of the blue loop extension on the adopted instability criterion. Contrary to what has been stated in the literature, we find that the Schwarzschild criterion, instead of the Ledoux criterion, favours the development of blue loops. Other factors that could affect the CMD comparisons, such as differential internal extinction or the presence of binary systems, are found to have negligible effects on the results. Thus, we confirm that, in the presence of core overshooting during the H-burning phase, a large EO is needed to reproduce the main features of the central He-burning phase of intermediate- and high-mass stars.

  1. The low-metallicity QSO HE 2158 - 0107: a massive galaxy growing by accretion of nearly pristine gas from its environment?

    NASA Astrophysics Data System (ADS)

    Husemann, B.; Wisotzki, L.; Jahnke, K.; Sánchez, S. F.

    2011-11-01

    The metallicities of active galactic nuclei (AGN) are usually well above solar in their narrow-line regions, often reaching up to several times solar in their broad-line regions independent of redshift. Low-metallicity AGN are rare objects that have so far always been associated with low-mass galaxies hosting low-mass black holes (MBH106M⊙). We present integral field spectroscopy data of the low-redshift (z = 0.212) quasi-stellar object (QSO) HE 2158 - 0107 for which we find strong evidence of sub-solar NLR metallicities associated with a massive black hole (MBH ~ 3 × 108M⊙). The QSO is surrounded by a large extended emission-line region reaching out to 30 kpc from the QSO in a tail-like geometry. We present optical and near-infrared images and investigate the properties of the host galaxy. The host of HE 2158 - 0107 is most likely a very compact bulge-dominated galaxy with a size of re ~ 1.4 kpc. The multi-colour spectral energy distribution (SED) of the host is quite blue, indicative of a significant young age stellar population formed within the last 1 Gyr. A 3σ upper limit of Lbulge,H < 4.5 × 1010L ⊙ ,H for the H-band luminosity and a corresponding stellar mass upper limit of Mbulge < 3.4 × 1010M⊙ show that the host is offset from the local black hole-bulge relations. This is independently supported by the kinematics of the gas. Although the stellar mass of the host galaxy is lower than expected, it cannot explain the exceptionally low metallicity of the gas. We suggest that the extended emission-line region and the galaxy growth are caused by the infall of nearly pristine gas from the environment of the QSO host. Minor mergers of low-metallicity dwarf galaxies or the theoretically predicted smooth accretion of cold (~ 104 K) gas are both potential drivers behind that process. Because the metallicity of the gas in the QSO narrow-line region is much lower than expected, we suspect that the external gas has already reached the galaxy centre and may

  2. Outskirts of spiral galaxies

    NASA Astrophysics Data System (ADS)

    Bresolin, Fabio

    2017-03-01

    I present an overview of the recent star formation activity in the outer disks of spiral galaxies, from the observational standpoint, with emphasis on the gas content, the star formation law, the metallicity and the stellar populations.

  3. Metallicities in long gamma-ray burst host galaxies at z < 0.5 calculated by the detailed modelling of optical and infrared line ratios

    NASA Astrophysics Data System (ADS)

    Contini, M.

    2017-04-01

    We revisit the line spectra emitted from long gamma-ray burst (LGRB) host galaxies at z ≤ 0.5 in order to calculate, through the detailed modelling of line ratios, the physical conditions and relative abundances in LGRB hosts in this redshift range. We have found lower metallicities than in LGRB hosts at higher z. New results regarding the metallicities and physical conditions in different regions throughout the LGRB 980425 host at z = 0.0085 are presented. In particular, we have found that the effective starburst temperature in the supernova (SN) region is the highest in the entire host galaxy. The low ionization parameter reveals that the radiation source is far away, or is somehow prevented from reaching the emitting gas in the SN region. Models constrained by a few oxygen, nitrogen and sulphur line ratios to Hβ in the LGRB 980425 host reproduce the He II/Hβ and [Ar III]/Hβ line ratios satisfactorily. Modelling of the observed [S IV]10.51 μm/[S III]18.71 μm and [Ne III]10.6 μm/[Ne II]12.81 μm line ratios from the LGRB 031203 host galaxy at z = 0.105 shows that the mid-infrared lines are emitted from geometrically thin shock-dominated filaments that are not reached by photoionizing flux, while the optical lines are emitted from radiation-dominated outflowing clouds.

  4. MS 1512 cB58: A case study of star formation, metal enrichment and superwinds in Lyman break galaxies

    NASA Astrophysics Data System (ADS)

    Pettini, Max; Rix, Samantha A.; Steidel, Chuck C.; Hunt, Matthew P.; Shapley, Alice E.; Adelberger, Kurt L.

    2002-07-01

    Recent advances in instrumentation and observing techniques have made it possible to begin to study in detail the stellar populations and the interstellar media of galaxies at redshift z = 3, when the universe was still in its ‘teen years’. I illustrate recent progress in this field with the latest observations of the gravitationally lensed galaxy MS 1512- cB58.

  5. A SINFONI integral field spectroscopy survey for galaxy counterparts to damped Lyman α systems - VI. Metallicity and geometry as gas flow probes

    NASA Astrophysics Data System (ADS)

    Péroux, Céline; Quiret, Samuel; Rahmani, Hadi; Kulkarni, Varsha P.; Epinat, Benoit; Milliard, Bruno; Straka, Lorrie A.; York, Donald G.; Rahmati, Alireza; Contini, Thierry

    2016-03-01

    The use of background quasars provides a powerful tool to probe the cool gas in the circumgalactic medium of foreground galaxies. Here, we present new observations with SINFONI and X-Shooter of absorbing-galaxy candidates at z = 0.7-1. We report the detection with both instruments of the Hα emission line of one sub-damped Lyman α (sub-DLA) at zabs = 0.941 87 with log N(H I) = 19.38^{+0.10}_{-0.15} towards SDSS J002133.27+004300.9. We estimate the star formation rate: SFR = 3.6 ± 2.2 M⊙ yr-1 in that system. A detailed kinematic study indicates a dynamical mass Mdyn = 109.9±0.4 M⊙ and a halo mass Mhalo = 1011.9±0.5 M⊙. In addition, we report the [O II] detection with X-Shooter of another DLA at zabs = 0.7402 with log N(H I) = 20.4 ± 0.1 towards Q0052+0041 and an estimated SFR of 5.3 ± 0.7 M⊙ yr-1. Three other objects are detected in the continuum with X-Shooter but the nature and redshift of two of these objects are unconstrained due to the absence of emission lines, while the third object might be at the redshift of the quasar. We use the objects detected in our whole N(H I)-selected SINFONI survey to compute the metallicity difference between the galaxy and the absorbing gas, δ _{H I}(X), where a positive (negative) value indicates infall (outflow). We compare this quantity with the quasar line-of-sight alignment with the galaxy's major (minor) axis, another tracer of infall (outflow). We find that these quantities do not correlate as expected from simple assumptions. Additional observations are necessary to relate these two independent probes of gas flows around galaxies.

  6. INTEGRAL FIELD SPECTROSCOPY AND MULTI-WAVELENGTH IMAGING OF THE NEARBY SPIRAL GALAXY NGC 5668 : AN UNUSUAL FLATTENING IN METALLICITY GRADIENT

    SciTech Connect

    Marino, R. A.; Gil de Paz, A.; Castillo-Morales, A.; Perez-Gonzalez, P. G.; Gallego, J.; Zamorano, J.; Sanchez, S. F.

    2012-07-20

    We present an analysis of the full bidimensional optical spectral cube of the nearby spiral galaxy NGC 5668, observed with the Pmas fiber PAcK Integral Field Unit (IFU) at the Calar Alto observatory 3.5 m telescope. We make use of broadband imaging to provide further constraints on the evolutionary history of the galaxy. This data set will allow us to improve our understanding of the mechanisms that drive the evolution of disks. We investigated the properties of 62 H II regions and concentric rings in NGC 5668 and derived maps in ionized-gas attenuation and chemical (oxygen) abundances. We find that while inward of r {approx}36'' {approx} 4.4 kpc {approx} 0.36 (D{sub 25}/2) the derived O/H ratio follows the radial gradient typical of spiral galaxies, the abundance gradient beyond r {approx} 36'' flattens out. The analysis of the multi-wavelength surface brightness profiles of NGC 5668 is performed by fitting these profiles with those predicted by chemo-spectrophotometric evolutionary models of galaxy disks. From this, we infer a spin and circular velocity of {lambda} = 0.053 and v{sub c} = 167 km s{sup -1}, respectively. The metallicity gradient and rotation curve predicted by this best-fitting galaxy model nicely match the values derived from the IFU observations, especially within r {approx}36''. The same is true for the colors despite some small offsets and a reddening in the bluest colors beyond that radius. On the other hand, deviations of some of these properties in the outer disk indicate that a secondary mechanism, possibly gas transfer induced by the presence of a young bar, must have played a role in shaping the recent chemical and star formation histories of NGC 5668.

  7. The relationship between stellar mass, gas metallicity, and star formation rate for Hα-selected galaxies at z ≈ 0.8 from the NewHα survey

    SciTech Connect

    Reyes, Mithi A. de los; Ly, Chun; Lee, Janice C.; Peeples, Molly S.; Feddersen, Jesse; Salim, Samir; Momcheva, Ivelina; Dale, Daniel A.; Ouchi, Masami; Ono, Yoshiaki; Finn, Rose

    2015-02-01

    Using a sample of 299 Hα-selected galaxies at z≈0.8, we study the relationship between galaxy stellar mass, gas-phase metallicity, and star formation rate (SFR), and compare to previous results. We use deep optical spectra obtained with the IMACS spectrograph at the Magellan telescope to measure strong oxygen lines. We combine these spectra and metallicities with (1) rest-frame UV-to-optical imaging, which allows us to determine stellar masses and dust attenuation corrections, and (2) Hα narrowband imaging, which provides a robust measurement of the instantaneous SFR. Our sample spans stellar masses of ∼10{sup 9}–6 × 10{sup 11} M{sub ⊙}, SFRs of 0.4–270 M{sub ⊙} yr{sup −1}, and metal abundances of 12+log(O/H)≈8.3–9.1 (≈0.4–2.6 Z{sub ⊙}). The correlations that we find between the Hα-based SFR and stellar mass (i.e., the star-forming “main sequence”) and between the stellar mass and metallicity are both consistent with previous z∼1 studies of star-forming galaxies. We then study the relationship between the three properties using various plane-fitting techniques and a curve-fitting projection. In all cases, we exclude strong dependence of the M{sub ⋆}–Z relation on SFR, but are unable to distinguish between moderate and no dependence. Our results are consistent with previous mass–metallicity–SFR studies. We check whether data set limitations may obscure a strong dependence on the SFR by using mock samples drawn from the Sloan Digital Sky Survey. These experiments reveal that the adopted signal-to-noise ratio cuts may have a significant effect on the measured dependence. Further work is needed to investigate these results, and to test whether a “fundamental metallicity relation” or a “fundamental plane” describes star-forming galaxies across cosmic time.

  8. Opacity, metallicity, and Cepheid period ratios in the galaxy and Magellanic Clouds

    NASA Technical Reports Server (NTRS)

    Simon, Norman R.; Kanbur, Shashi M.

    1994-01-01

    Linear pulsation calculations are employed to reproduce the bump Cepheid resonance (P(sub 2)/P(sub 0) = 0.5 at P(sub 0) approximately equal to 10 days) and to model, individually, the P(sub 1)/P(sub 0) period ratios for the dozen known Galactic beat Cepheids. Convection is ignored. The results point to a range of metallicity among the Cepheids, perhaps as large as 0.01 approximately less than Z approximately less than 0.02, with no evidence for any star exceeding Z = 0.02. We find masses and luminosities which range from M approximately less than 4 solar mass, log(base 10) approximately less than 3.0 at P(sub 0) approximately equal to 3 days to M approximately less than 6 solar mass, log(base 10) L approximately greater than 3.5 at P(sub 0) approximately equal to 10 days. Similar parameters are indicated for the P(sub 0) approximately equal to 10 days Cepheids in the LMC and SMC, provided that the resonance for these stars occurs at a slightly longer period, P(sub 0) days, as has been suggested in the literature. Our calculations were performed mainly using OPAL opacities, but also with new opacities from the Opacity project (OP). Only small differences were found between the OPAL results and those from OP. Finally, some suggestions are made for possible future work, including evolution and pulsation calculations, and more precise observations of Cepheids in the Magellanic Clouds.

  9. Physical Properties of Molecular Clouds at 2 pc Resolution in the Low-metallicity Dwarf Galaxy NGC 6822 and the Milky Way

    NASA Astrophysics Data System (ADS)

    Schruba, Andreas; Leroy, Adam K.; Kruijssen, J. M. Diederik; Bigiel, Frank; Bolatto, Alberto D.; de Blok, W. J. G.; Tacconi, Linda; van Dishoeck, Ewine F.; Walter, Fabian

    2017-02-01

    We present the Atacama Large Millimeter/submillimeter Array survey of CO(2–1) emission from the 1/5 solar metallicity, Local Group dwarf galaxy NGC 6822. We achieve high (0\\buildrel{\\prime\\prime}\\over{.} 9≈ 2 pc) spatial resolution while covering a large area: four 250 pc × 250 pc regions that encompass ∼ 2/3 of NGC 6822's star formation. In these regions, we resolve ∼ 150 compact CO clumps that have small radii (∼2–3 pc), narrow line width (∼ 1 km s‑1), and low filling factor across the galaxy. This is consistent with other recent studies of low-metallicity galaxies, but here shown with a 15× larger sample. At parsec scales, CO emission correlates with 8 μ {{m}} emission better than with 24 μ {{m}} emission and anticorrelates with Hα, so that polycyclic aromatic hydrocarbon emission may be an effective tracer of molecular gas at low metallicity. The properties of the CO clumps resemble those of similar-size structures in Galactic clouds except of slightly lower surface brightness and with CO-to-H2 ratio ∼1–2× the Galactic value. The clumps exist inside larger atomic–molecular complexes with masses typical for giant molecular clouds. Using dust to trace H2 for the entire complex, we find the CO-to-H2 ratio to be ∼ 20{--}25× the Galactic value, but with strong dependence on spatial scale and variations between complexes that may track their evolutionary state. The H2-to-H i ratio is low globally and only mildly above unity within the complexes. The ratio of star formation rate to H2 is ∼ 3{--}5× higher in the complexes than in massive disk galaxies, but after accounting for the bias from targeting star-forming regions, we conclude that the global molecular gas depletion time may be as long as in massive disk galaxies.

  10. Radio Galaxies.

    ERIC Educational Resources Information Center

    Downes, Ann

    1986-01-01

    Provides background information on radio galaxies. Topic areas addressed include: what produces the radio emission; radio telescopes; locating radio galaxies; how distances to radio galaxies are found; physics of radio galaxies; computer simulations of radio galaxies; and the evolution of radio galaxies with cosmic time. (JN)

  11. Using Galaxy Winds to Constrain Galaxy Evolution

    NASA Astrophysics Data System (ADS)

    Churchill, Christopher W.; Klypin, A.; Ceverino, D.; Kacprzak, G.; Klimek, E.

    2010-01-01

    Analysis of mock quasar spectra of metal absorption lines in the proximity of formed galaxies in cosmological simulation is a highly promising for understanding the role of galaxies in IGM physics, or IGM physics in the role of galaxy formation in context of the cosmic web. Such analysis using neutral hydrogen in the cosmic web has literally revolutionized our understanding of the Lyman alpha forest. We are undertaking a wholesale approach to use powerful Lambda-CDM simulations to interpret absorption line data from redshift 1-3 starbursting galaxies e.g. Lyman break galaxies, etc) The data with which direct quantitative comparison is made are from the DEEP survey (Weiner et al.) and the collective work of Steidel et al. and collaborators. The simulations are performed using the Eulerian Gasdynamics plus N-body Adaptive Refinement Tree (ART) code, which has gas cell resolutions of 20-50 pc. Physical processes implemented in the code include realistic radiative cooling, star formation, metal enrichment and thermal feedback due to type II and type Ia supernovae. We quantitatively compare the spatial and kinematic distribution of HI, MgII, CIV, and OVI of absorption lines over a range of impact parameters for various simulated galaxies as a function of redshift, and discuss key insights for interpreting the underlying temperature, density, and ionization structure of the halo/cosmic-web interface, and the influence of galaxies on its chemical enrichment.

  12. The Evolution of the Intracluster Medium Metallicity in Sunyaev Zel’dovich-selected Galaxy Clusters at 0 < z < 1.5

    NASA Astrophysics Data System (ADS)

    McDonald, M.; Bulbul, E.; de Haan, T.; Miller, E. D.; Benson, B. A.; Bleem, L. E.; Brodwin, M.; Carlstrom, J. E.; Chiu, I.; Forman, W. R.; Hlavacek-Larrondo, J.; Garmire, G. P.; Gupta, N.; Mohr, J. J.; Reichardt, C. L.; Saro, A.; Stalder, B.; Stark, A. A.; Vieira, J. D.

    2016-08-01

    We present the results of an X-ray spectral analysis of 153 galaxy clusters observed with the Chandra, XMM-Newton, and Suzaku space telescopes. These clusters, which span 0 < z < 1.5, were drawn from a larger, mass-selected sample of galaxy clusters discovered in the 2500 square degree South Pole Telescope Sunyaev Zel’dovich (SPT-SZ) survey. With a total combined exposure time of 9.1 Ms, these data yield the strongest constraints to date on the evolution of the metal content of the intracluster medium (ICM). We find no evidence for strong evolution in the global (r < R 500) ICM metallicity (dZ/dz = ‑0.06 ± 0.04 Z ⊙), with a mean value at z = 0.6 of < Z> =0.23+/- 0.01 Z ⊙ and a scatter of σ Z = 0.08 ± 0.01 Z ⊙. These results imply that the emission-weighted metallicity has not changed by more than 40% since z = 1 (at 95% confidence), consistent with the picture of an early (z > 1) enrichment. We find, in agreement with previous works, a significantly higher mean value for the metallicity in the centers of cool core clusters versus non-cool core clusters. We find weak evidence for evolution in the central metallicity of cool core clusters (dZ/dz = ‑0.21 ± 0.11 Z ⊙), which is sufficient to account for this enhanced central metallicity over the past ∼10 Gyr. We find no evidence for metallicity evolution outside of the core (dZ/dz = ‑0.03 ± 0.06 Z ⊙), and no significant difference in the core-excised metallicity between cool core and non-cool core clusters. This suggests that strong radio-mode active galactic nucleus feedback does not significantly alter the distribution of metals at r> 0.15{R}500. Given the limitations of current-generation X-ray telescopes in constraining the ICM metallicity at z > 1, significant improvements on this work will likely require next-generation X-ray missions.

  13. The evolution of the intracluster medium metallicity in Sunyaev Zel'dovich-selected galaxy clusters at 0 < z < 1.5

    DOE PAGES

    McDonald, M.; Bulbul, E.; Haan, T. de; ...

    2016-07-27

    Here, we present the results of an X-ray spectral analysis of 153 galaxy clusters observed with the Chandra, XMM-Newton, and Suzaku space telescopes. These clusters, which span 0 < z < 1.5, were drawn from a larger, mass-selected sample of galaxy clusters discovered in the 2500 square degree South Pole Telescope Sunyaev Zel'dovich (SPT-SZ) survey. With a total combined exposure time of 9.1 Ms, these data yield the strongest constraints to date on the evolution of the metal content of the intracluster medium (ICM). We find no evidence for strong evolution in the global (r < R 500) ICM metallicity (dZ/dz = –0.06 ± 0.04 Z ⊙), with a mean value at z = 0.6 ofmore » $$\\langle Z\\rangle =0.23\\pm 0.01$$ Z ⊙ and a scatter of σ Z = 0.08 ± 0.01 Z ⊙. These results imply that the emission-weighted metallicity has not changed by more than 40% since z = 1 (at 95% confidence), consistent with the picture of an early (z > 1) enrichment. We find, in agreement with previous works, a significantly higher mean value for the metallicity in the centers of cool core clusters versus non-cool core clusters. We find weak evidence for evolution in the central metallicity of cool core clusters (dZ/dz = –0.21 ± 0.11 Z ⊙), which is sufficient to account for this enhanced central metallicity over the past ~10 Gyr. We find no evidence for metallicity evolution outside of the core (dZ/dz = –0.03 ± 0.06 Z ⊙), and no significant difference in the core-excised metallicity between cool core and non-cool core clusters. This suggests that strong radio-mode active galactic nucleus feedback does not significantly alter the distribution of metals at $$r\\gt 0.15{R}_{500}$$. Given the limitations of current-generation X-ray telescopes in constraining the ICM metallicity at z > 1, significant improvements on this work will likely require next-generation X-ray missions.« less

  14. The evolution of the intracluster medium metallicity in Sunyaev Zel'dovich-selected galaxy clusters at 0 < z < 1.5

    SciTech Connect

    McDonald, M.; Bulbul, E.; Haan, T. de; Miller, E. D.; Benson, B. A.; Bleem, L. E.; Brodwin, M.; Carlstrom, J. E.; Chiu, I.; Forman, W. R.; Hlavacek-Larrondo, J.; Garmire, G. P.; Gupta, N.; Mohr, J. J.; Reichardt, C. L.; Saro, A.; Stalder, B.; Stark, A. A.; Vieira, J. D.

    2016-07-27

    Here, we present the results of an X-ray spectral analysis of 153 galaxy clusters observed with the Chandra, XMM-Newton, and Suzaku space telescopes. These clusters, which span 0 < z < 1.5, were drawn from a larger, mass-selected sample of galaxy clusters discovered in the 2500 square degree South Pole Telescope Sunyaev Zel'dovich (SPT-SZ) survey. With a total combined exposure time of 9.1 Ms, these data yield the strongest constraints to date on the evolution of the metal content of the intracluster medium (ICM). We find no evidence for strong evolution in the global (r < R 500) ICM metallicity (dZ/dz = –0.06 ± 0.04 Z ⊙), with a mean value at z = 0.6 of $\\langle Z\\rangle =0.23\\pm 0.01$ Z ⊙ and a scatter of σ Z = 0.08 ± 0.01 Z ⊙. These results imply that the emission-weighted metallicity has not changed by more than 40% since z = 1 (at 95% confidence), consistent with the picture of an early (z > 1) enrichment. We find, in agreement with previous works, a significantly higher mean value for the metallicity in the centers of cool core clusters versus non-cool core clusters. We find weak evidence for evolution in the central metallicity of cool core clusters (dZ/dz = –0.21 ± 0.11 Z ⊙), which is sufficient to account for this enhanced central metallicity over the past ~10 Gyr. We find no evidence for metallicity evolution outside of the core (dZ/dz = –0.03 ± 0.06 Z ⊙), and no significant difference in the core-excised metallicity between cool core and non-cool core clusters. This suggests that strong radio-mode active galactic nucleus feedback does not significantly alter the distribution of metals at $r\\gt 0.15{R}_{500}$. Given the limitations of current-generation X-ray telescopes in constraining the ICM metallicity at z > 1, significant improvements on this work will likely require next-generation X-ray missions.

  15. Results from KMOS: Unravelling the origin of the counter-rotating core in IC 1459

    NASA Astrophysics Data System (ADS)

    Prichard, Laura

    2015-08-01

    IC 1459 is the archetype of a massive early-type galaxy with a rapidly counter-rotating core. Previous studies of IC 1459 have revealed the outer part of the galaxy and the ionized gas in the central region are rotating in one direction, while the central stellar component is rapidly rotating in the opposite direction. We present new NIR integral field spectroscopic data from the K-band Multi-Object Spectrograph (KMOS) on the VLT. NIR observations help probe through the dense gas and dust at the centre of this E3 galaxy to study the kinematically distinct stellar core. By combining the 24 integral field units of KMOS to make a 67” by 44” mosaic, we generate over 4500 spectra spanning this bright galaxy. We use this data to trace the kinematics and study the stellar populations of IC 1459 to better understand the origin of the counter-rotating core. In particular, we study dwarf-sensitive absorption features to place constraints on the spatial variation of the initial mass function. Investigating IC 1459 provides insights into how early-type galaxies evolve from high redshift to the local Universe. We present results from this work and demonstrate the science capabilities and potential of KMOS.

  16. Dust and Ionized Gas in Elliptical Galaxies

    NASA Astrophysics Data System (ADS)

    Goudfrooij, Paul

    1995-05-01

    The thesis presents results of a study of the optical and far-infrared properties of dust and ionized gas in a complete, blue magnitude-limited (B_T^0 < 12) sample of 56 luminous elliptical (E) galaxies. The main aim is to investigate the origin and fate of this interstellar material and possible implications for scenarios of galaxy formation and evolution. To ensure consistency in the assignment of morphological types, the galaxy sample was drawn exclusively from the Revised Shapley-Ames Catalog of Bright Galaxies. A deep, systematic optical survey has been performed, including CCD imaging through both broad-band filters and narrow-band filters. For each galaxy we have constructed colour index (B-V, B-I) images and images of the H-alpha+ [N II]-emitting gas to derive the distributions of dust features and ionized gas. Long-slit spectra have also been obtained in two resolutions. Low-resolution spectra (covering the whole optical region) are used to study the properties of the underlying stellar populations (e.g., metallicity gradients), and to study the excitation mechanism of the ionized gas. Additional medium-resolution (~2A) spectra in the wavelength region around H-alpha have been obtained for all sample elliptical galaxies containing ionized gas to study the kinematics of the gas, and derive pure H-alpha luminosities. In this thesis, analysis of the extensive imaging data and of the medium-resolution spectra is reported. In Chapter 1 we report an early result of our survey: The galaxy IC 1459 is found to exhibit a large (15 Kpc diameter) H-alpha+[N II] emission-line region, showing spiral structure. Patchy dust absorption is also found in the inner part of the emission-line region. This galaxy was already shown to contain a massive stellar core which counter-rotates rapidly with respect to the stellar body of the galaxy. Interestingly, the sense of rotation of the spiral "arms" of the ionized gas distribution is the same as that of the rapidly rotating

  17. THE STAR FORMATION HISTORY AND METAL CONTENT OF THE GREEN PEAS. NEW DETAILED GTC-OSIRIS SPECTROPHOTOMETRY OF THREE GALAXIES

    SciTech Connect

    Amorin, R.; Perez-Montero, E.; Vilchez, J. M.

    2012-04-20

    We present deep broadband imaging and long-slit spectroscopy of three compact, low-mass starburst galaxies at redshift z {approx} 0.2-0.3, also referred to as Green Peas (GP). We measure physical properties of the ionized gas and derive abundances for several species with high precision. We find that the three GPs display relatively low extinction, low oxygen abundances, and remarkably high nitrogen-to-oxygen ratios. We also report on the detection of clear signatures of Wolf-Rayet (W-R) stars in these galaxies. We carry out a pilot spectral synthesis study using a combination of both population and evolutionary synthesis models. Their outputs are in qualitative agreement, strongly suggesting a formation history dominated by starbursts. In agreement with the presence of W-R stars, these models show that these GPs currently undergo a major starburst producing between {approx}4% and {approx}20% of their stellar mass. However, as models imply, they are old galaxies that formed most of their stellar mass several Gyr ago. The presence of old stars has been spectroscopically verified in one of the galaxies by the detection of Mg I {lambda}{lambda}5167, 5173 absorption lines. Additionally, we perform a surface photometry study based on Hubble Space Telescope data, which indicates that the three galaxies possess an exponential low surface brightness envelope. If due to stellar emission, the latter is structurally compatible with the evolved hosts of luminous blue compact dwarf (BCD)/H II galaxies, suggesting that GPs are identifiable with major episodes in the assembly history of local BCDs. These conclusions highlight the importance of these objects as laboratories for studying galaxy evolution at late cosmic epochs.

  18. Reliability in CMOS IC processing

    NASA Technical Reports Server (NTRS)

    Shreeve, R.; Ferrier, S.; Hall, D.; Wang, J.

    1990-01-01

    Critical CMOS IC processing reliability monitors are defined in this paper. These monitors are divided into three categories: process qualifications, ongoing production workcell monitors, and ongoing reliability monitors. The key measures in each of these categories are identified and prioritized based on their importance.

  19. The FMOS-COSMOS survey of star-forming galaxies at z ∼ 1.6. II. The mass-metallicity relation and the dependence on star formation rate and dust extinction

    SciTech Connect

    Zahid, H. J.; Sanders, D. B.; Chu, J.; Hasinger, G.; Kashino, D.; Silverman, J. D.; Kewley, L. J.; Daddi, E.; Renzini, A.; Rodighiero, G.; Nagao, T.; Arimoto, N.; Kartaltepe, J.; Lilly, S. J.; Carollo, C. M.; Maier, C.; Geller, M. J.; Capak, P.; Ilbert, O.; Kajisawa, M.; Collaboration: COSMOS Team; and others

    2014-09-01

    We investigate the relationships between stellar mass, gas-phase oxygen abundance (metallicity), star formation rate (SFR), and dust content of star-forming galaxies at z ∼ 1.6 using Subaru/FMOS spectroscopy in the COSMOS field. The mass-metallicity (MZ) relation at z ∼ 1.6 is steeper than the relation observed in the local universe. The steeper MZ relation at z ∼ 1.6 is mainly due to evolution in the stellar mass where the MZ relation begins to turnover and flatten. This turnover mass is 1.2 dex larger at z ∼ 1.6. The most massive galaxies at z ∼ 1.6 (∼10{sup 11} M {sub ☉}) are enriched to the level observed in massive galaxies in the local universe. The MZ relation we measure at z ∼ 1.6 supports the suggestion of an empirical upper metallicity limit that does not significantly evolve with redshift. We find an anti-correlation between metallicity and SFR for galaxies at a fixed stellar mass at z ∼ 1.6, which is similar to trends observed in the local universe. We do not find a relation between stellar mass, metallicity, and SFR that is independent of redshift; rather, our data suggest that there is redshift evolution in this relation. We examine the relation between stellar mass, metallicity, and dust extinction, and find that at a fixed stellar mass, dustier galaxies tend to be more metal rich. From examination of the stellar masses, metallicities, SFRs, and dust extinctions, we conclude that stellar mass is most closely related to dust extinction.

  20. R&D100: IC ID

    SciTech Connect

    Hamlet, Jason; Pierson, Lyndon; Bauer, Todd

    2015-11-19

    Supply chain security to detect, deter, and prevent the counterfeiting of networked and stand-alone integrated circuits (ICs) is critical to cyber security. Sandia National Laboratory researchers have developed IC ID to leverage Physically Unclonable Functions (PUFs) and strong cryptographic authentication to create a unique fingerprint for each integrated circuit. IC ID assures the authenticity of ICs to prevent tampering or malicious substitution.

  1. R&D100: IC ID

    ScienceCinema

    Hamlet, Jason; Pierson, Lyndon; Bauer, Todd

    2016-07-12

    Supply chain security to detect, deter, and prevent the counterfeiting of networked and stand-alone integrated circuits (ICs) is critical to cyber security. Sandia National Laboratory researchers have developed IC ID to leverage Physically Unclonable Functions (PUFs) and strong cryptographic authentication to create a unique fingerprint for each integrated circuit. IC ID assures the authenticity of ICs to prevent tampering or malicious substitution.

  2. Metallicities of Emission-Line Galaxies from HST ACS PEARS and HST WFC3 ERS Grism Spectroscopy at 0.6 is less than z is less than 2.4

    NASA Technical Reports Server (NTRS)

    Xia, Lifang; Malhotra, Sangetta; Rhoads, James; Pirzkal, Nor; Straughn, Amber; Finkelstein, Steven; Cohen, Seth; Kuntschner, Harald; Walsh, Jeremy; Windhorst, Rogier A.; O'Connell, Robert; Kuemmel, Martin

    2012-01-01

    Galaxies selected on the basis of their emission line strength. show low metallicities, regardless of their redshifts. We conclude this from a sample of faint galaxies at redshifts between 0.6 < z < 2.4, selected by their prominent emission lines in low resolution grism spectra in the optiCa.i with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST) and in the near-infrared using Wide-Field Camera 3 (WFC3). Using a sample of 11 emission line galaxies (ELGs) at 0.6 < z < 2.4 with luminosities of -22 approx < MB approx -19 which have [OII], H-Beta, and [OIII] line flux measurements from the combination of two grism spectral surveys, we use the R23 method to derive the gas-phase oxygen abundances: 7.5 <12+log(0/H)<8.5. The galaxy stellar masses are derived using Bayesian based Markov Chain Monte Carlo (pi MC(exp 2)) fitting of their Spectral Energy Distribution (SED), and span the mass range 8.1 < log(M(stellar)/M(solar)) < 10.1. These galaxies show a mass-metal1icity (M-L) and Luminosity-Metallicity (LZ) relation, which is offset by -galaxies, as well as continuum selected DEEP2 samples at similar redshifts. The emission-line selected galaxies most resemble the local "green peas" galaxies and Lyman-alpha galaxies at z approx = 0.3 and z approx = 2.3 in the M-Z and L-Z relations and their morphologies. The G - M(sub 20) morphology analysis shows that 10 out of 11 show disturbed morphology, even as the star-forming regions are compact. These galaxies may be intrinsically metal poor, being at early stages of formation, or the low metallicities may be due to gas infall and accretion due to mergers.

  3. Are long gamma-ray bursts biased tracers of star formation? Clues from the host galaxies of the Swift/BAT6 complete sample of bright LGRBs. II. Star formation rates and metallicities at z < 1

    NASA Astrophysics Data System (ADS)

    Japelj, J.; Vergani, S. D.; Salvaterra, R.; D'Avanzo, P.; Mannucci, F.; Fernandez-Soto, A.; Boissier, S.; Hunt, L. K.; Atek, H.; Rodríguez-Muñoz, L.; Scodeggio, M.; Cristiani, S.; Le Floc'h, E.; Flores, H.; Gallego, J.; Ghirlanda, G.; Gomboc, A.; Hammer, F.; Perley, D. A.; Pescalli, A.; Petitjean, P.; Puech, M.; Rafelski, M.; Tagliaferri, G.

    2016-05-01

    Aims: Long gamma-ray bursts (LGRBs) are associated with the deaths of massive stars and might therefore be a potentially powerful tool for tracing cosmic star formation. However, especially at low redshifts (z< 1.5) LGRBs seem to prefer particular types of environment. Our aim is to study the host galaxies of a complete sample of bright LGRBs to investigate the effect of the environment on GRB formation. Methods: We studied host galaxy spectra of the Swift/BAT6 complete sample of 14 z< 1 bright LGRBs. We used the detected nebular emission lines to measure the dust extinction, star formation rate (SFR), and nebular metallicity (Z) of the hosts and supplemented the data set with previously measured stellar masses M⋆. The distributions of the obtained properties and their interrelations (e.g. mass-metallicity and SFR-M⋆ relations) are compared to samples of field star-forming galaxies. Results: We find that LGRB hosts at z< 1 have on average lower SFRs than if they were direct star formation tracers. By directly comparing metallicity distributions of LGRB hosts and star-forming galaxies, we find a good match between the two populations up to 12 +log ≤ft( frac{OHright)} 8.4-8.5, after which the paucity of metal-rich LGRB hosts becomes apparent. The LGRB host galaxies of our complete sample are consistent with the mass-metallicity relation at similar mean redshift and stellar masses. The cutoff against high metallicities (and high masses) can explain the low SFR values of LGRB hosts. We find a hint of an increased incidence of starburst galaxies in the Swift/BAT6 z< 1 sample with respect to that of a field star-forming population. Given that the SFRs are low on average, the latter is ascribed to low stellar masses. Nevertheless, the limits on the completeness and metallicity availability of current surveys, coupled with the limited number of LGRB host galaxies, prevents us from investigating more quantitatively whether the starburst incidence is such as expected

  4. Physical properties of galaxies and their evolution in the VIMOS VLT Deep Survey. II. Extending the mass-metallicity relation to the range z ≈ 0.89-1.24

    NASA Astrophysics Data System (ADS)

    Pérez-Montero, E.; Contini, T.; Lamareille, F.; Brinchmann, J.; Walcher, C. J.; Charlot, S.; Bolzonella, M.; Pozzetti, L.; Bottini, D.; Garilli, B.; Le Brun, V.; Le Fèvre, O.; Maccagni, D.; Scaramella, R.; Scodeggio, M.; Tresse, L.; Vettolani, G.; Zanichelli, A.; Adami, C.; Arnouts, S.; Bardelli, S.; Cappi, A.; Ciliegi, P.; Foucaud, S.; Franzetti, P.; Gavignaud, I.; Guzzo, L.; Ilbert, O.; Iovino, A.; McCracken, H. J.; Marano, B.; Marinoni, C.; Mazure, A.; Meneux, B.; Merighi, R.; Paltani, S.; Pellò, R.; Pollo, A.; Radovich, M.; Vergani, D.; Zamorani, G.; Zucca, E.

    2009-02-01

    Aims: We present a continuation of our study about the relation between stellar mass and gas-phase metallicity in the VIMOS VLT Deep Survey (VVDS). In this work we extend the determination of metallicities up to redshift ≈1.24 for a sample of 42 star-forming galaxies with a mean redshift value of 0.99. Methods: For a selected sample of emission-line galaxies, we use both diagnostic diagrams and empirical calibrations based on [Oii] emission lines along with the empirical relation between the intensities of the [Oiii] and [Neiii] emission lines and the theoretical ratios between Balmer recombination emission lines to identify star-forming galaxies and to derive their metallicities. We derive stellar masses by fitting the whole spectral energy distribution with a set of stellar population synthesis models. Results: These new methods allow us to extend the mass-metallicity relation to higher redshift. We show that the metallicity determinations are consistent with more established strong-line methods. Taken together this allows us to study the evolution of the mass-metallicity relation up to z ≈ 1.24 with good control of systematic uncertainties. We find an evolution with redshift of the average metallicity of galaxies very similar to those reported in the literature: for a given stellar mass, galaxies at z ~ 1 have, on average, a metallicity ~ 0.3 dex lower than galaxies in the local universe. However we do not see any significant metallicity evolution between redshifts z ~ 0.7 (Paper I) and z ~ 1.0 (this paper). We find also the same flattening of the mass-metallicity relation for the most massive galaxies as reported in Paper I at lower redshifts, but again no apparent evolution of the slope is seen between z ~ 0.7 and z ~ 1.0. Based on data obtained with the European Southern Observatory Very Large Telescope, Paranal, Chile, program 070.A-9007, and on data obtained at the Canada-France-Hawaii Telescope, operated by the CNRS in France, CNRC in Canada and the

  5. ESD evaluation of radiation-hardened, high-reliability CMOS and MNOS ICs

    NASA Astrophysics Data System (ADS)

    Soden, J. M.; Stewart, H. D.; Pastorek, R. A.

    Standard human-body-equivalent circuit electrostatic discharge (ESD) tests were performed on the inputs of high-reliability, radiation-hardened integrated circuits (ICs) designed with seven different technologies. Metal and silicon gate complementary metal oxide semiconductors (CMOS) and metal-nitride-oxide-semiconductor (MNOS) ICs with design rules ranging from 10 microns down to 2 microns were evaluated. The ESD hardness of these ICs ranged from 1 kV to greater than 9 kV. The low-range ESD hardness ICs were fabricated with a masking polysilicon ring that defined the input protection diodes. Tests on commercial equivalent ICs demonstrated that the ESD hardness of the radiation-hardened ICs was not significantly less than the ESD hardness of the commercial equivalent ICs. The failure modes and mechanisms of the ICs were evaluated. Most of the ICs that did not have the making polysilicon ring failed because of input to V sub DD or V sub SS shorts due to degraded protection diodes. ESD tests with the pulse applied between the package metal lid and the package pins were also performed. These lid tests produced permanent input damage, the same as occurred during tests with the pulse applied to the package input, but the damage occurred at lower voltages. ESD pulses with peak voltages as low as 250 volts produced arcs from the lid to the input bond wires, resulting in degraded inputs.

  6. QUALITATIVE INTERPRETATION OF GALAXY SPECTRA

    SciTech Connect

    Sanchez Almeida, J.; Morales-Luis, A. B.; Terlevich, R.; Terlevich, E.; Cid Fernandes, R. E-mail: abml@iac.es E-mail: eterlevi@inaoep.mx

    2012-09-10

    We describe a simple step-by-step guide to qualitative interpretation of galaxy spectra. Rather than an alternative to existing automated tools, it is put forward as an instrument for quick-look analysis and for gaining physical insight when interpreting the outputs provided by automated tools. Though the recipe is for general application, it was developed for understanding the nature of the Automatic Spectroscopic K-means-based (ASK) template spectra. They resulted from the classification of all the galaxy spectra in the Sloan Digital Sky Survey data release 7, thus being a comprehensive representation of the galaxy spectra in the local universe. Using the recipe, we give a description of the properties of the gas and the stars that characterize the ASK classes, from those corresponding to passively evolving galaxies, to H II galaxies undergoing a galaxy-wide starburst. The qualitative analysis is found to be in excellent agreement with quantitative analyses of the same spectra. We compare the mean ages of the stellar populations with those inferred using the code STARLIGHT. We also examine the estimated gas-phase metallicity with the metallicities obtained using electron-temperature-based methods. A number of byproducts follow from the analysis. There is a tight correlation between the age of the stellar population and the metallicity of the gas, which is stronger than the correlations between galaxy mass and stellar age, and galaxy mass and gas metallicity. The galaxy spectra are known to follow a one-dimensional sequence, and we identify the luminosity-weighted mean stellar age as the affine parameter that describes the sequence. All ASK classes happen to have a significant fraction of old stars, although spectrum-wise they are outshined by the youngest populations. Old stars are metal-rich or metal-poor depending on whether they reside in passive galaxies or in star-forming galaxies.

  7. Automatic Identification, Classification, and Abundance Estimation for Metal-Poor Stars in the Galaxy from Objective-Prism Spectroscopy via Artificial Neural Network Analysis

    NASA Astrophysics Data System (ADS)

    Rhee, J.; Beers, T. C.; Irwin, M. J.

    1999-05-01

    The HK prism survey of Beers and collaborators has been extremely successful in the identification of large numbers of metal-deficient stars in the thick disk and halo of the Galaxy. Such stars provide vital clues for unraveling the chemical and dynamical history of the Milky Way, and large spiral galaxies in general. The original selection of candidate metal-poor stars from the HK prism plates was carried out using visual inspection, which introduces a number of (avoidable) biases in the resulting target lists (in particular a tendency to overlook metal-poor stars of low temperature). We are in the process of selecting new candidate metal-poor stars based on automated scans of the HK survey plates with the APM facility in Cambridge. Here we present the results of an artificial neural network analysis of this data, which enables us to objectively select, to classify by color and metallicity class, and to predict the metallicities of stars on the prism plates directly from the extracted spectra. The training set consists of about 370 stars with abundances obtained from previous HK survey follow-up efforts, chosen from some of the 320,000 stars in the ``digital'' HK survey to date (over 1,500,000 stars are expected in the final sample). For first-pass classification, external estimates of the broadband color index, (B-V)_o, and equivalent widths of the CaII H and K lines from the extracted prism spectra are used as input variables to separate the prism spectra into regions of similar (B-V)_o and [Fe/H]. Currently, a correct classification rate is achieved for more than 70% of the stars. In the prediction step, these same quantities are used as input variables to predict stellar [Fe/H]. We presently obtain correlation coefficients between the predicted and known [Fe/H] for stars in our test sample of greater than 0.75, with an rms error of 0.1 dex, which is extremely encouraging. We discuss steps that are underway to improve on these results, primarily by obtaining

  8. ESD evaluation of radiation-hardened, high-reliability CMOS and MNOS ICs

    SciTech Connect

    Soden, J.M.; Stewart, H.D.; Pastorek, R.A.

    1983-01-01

    Standard human-body-equivalent circuit electrostatic discharge (ESD) tests were performed on the inputs of high-reliability, radiation-hardened integrated circuits (ICs) designed with seven different technologies. Metal and silicon gate complementary MOS (CMOS) and metal-nitride-oxide-semiconductor (MNOS) ICs with design rules ranging from 10 microns down to 2 microns were evaluated. The ESD hardness of these ICs ranged from 1 kV to greater than 9 kV. The low-range ESD hardness ICs were fabricated with a masking polysilicon ring that defined the input protection diodes. Tests on commercial equivalent ICs demonstrated that the ESD hardness of the radiation-hardened ICs was not significantly less than the ESD hardness of the commercial equivalent ICs. The failure modes and mechanisms of the ICs were evaluated. Most of the ICs that did not have the masking polysilicon ring failed because of input to V/sub DD/ or V/sub SS/ shorts due to degraded protection diodes. ESD tests with the pulse applied between the package metal lid and the package pins were also performed. These lid tests produced permanent input damage, the same as occurred during tests with the pulse applied to the package input, but the damage occurred at lower voltages. ESD pulses with peak voltages as low as 250 volts produced arcs from the lid to the input bond wires, resulting in degraded inputs.

  9. ESD evaluation of radiation-hardened, high reliability CMOS and MNOS ICs

    SciTech Connect

    Soden, J.M.; Pastorek, R.A.; Stewart, H.D.

    1984-02-01

    Standard human body equivalent circuit electrostatic discharge (ESD) tests were performed on the inputs of high-reliability, radiation-hardened integrated circuits (ICs) designed with seven different technologies. Metal and silicon gate complementary MOS (CMOS) and metal-nitrideoxide-semiconductor (MNOS) ICs with design rules ranging from 10 microns down to 2 microns were evaluated. The ESD hardness of these ICs ranged from 1 kV to greater than 9 kV. The low range ESD hardness ICs were fabricated with a masking polysilicon ring that defined the input protection diodes. Tests on commercial equivalent ICs demonstrated that the ESD hardness of the radiation-hardened ICs was not significantly less than the ESD hardness of the commercial equivalent ICs. The failure modes and mechanisms of the ICs were evaluated. Most of the ICs that did not have the masking polysilicon ring failed because of input to V/sub DD/ or V/sub SS/ shorts due to degraded protection diodes. ESD tests with the pulse applied between the package metal lid and the package pins were also performed. These lid tests produced permanent input damage, the same as occurred during tests with the pulse applied to the package input, but the damage occurred at lower voltages. ESD pulses with peak voltages as low as 250 volts produced arcs from the lid to the input bond wires, resulting in degraded inputs.

  10. 75 FR 54940 - Agency Information Collection (IC) Activities; Revision of an Approved IC; Accident Recordkeeping...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-09-09

    ... Federal Motor Carrier Safety Administration Agency Information Collection (IC) Activities; Revision of an Approved IC; Accident Recordkeeping Requirements AGENCY: Federal Motor Carrier Safety Administration (FMCSA... revision of the Information Collection (IC) entitled, ``Accident Recordkeeping Requirements,''...

  11. The VIRUS-P Exploration of Nearby Galaxies (VENGA): spatially resolved gas-phase metallicity distributions in barred and unbarred spirals

    NASA Astrophysics Data System (ADS)

    Kaplan, Kyle F.; Jogee, Shardha; Kewley, Lisa; Blanc, Guillermo A.; Weinzirl, Tim; Song, Mimi; Drory, Niv; Luo, Rongxin; van den Bosch, Remco C. E.

    2016-10-01

    We present a study of the excitation conditions and metallicity of ionized gas (Zgas) in eight nearby barred and unbarred spiral galaxies from the VIRUS-P Exploration of Nearby Galaxies (VENGA) survey, which provides high spatial sampling and resolution (median ˜387 pc), large coverage from the bulge to outer disc, broad wavelength range (3600-6800 Å), and medium spectral resolution (˜120 km s-1 at 5000 Å). Our results are: (1) We present high resolution gas excitation maps to differentiate between regions with excitation typical of Seyfert, LINER, or recent star formation. We find LINER-type excitation at large distances (3-10 kpc) from the centre, and associate this excitation with diffuse ionized gas (DIG). (2) After excluding spaxels dominated by Seyfert, LINER, or DIG, we produce maps with the best spatial resolution and sampling to date of the ionization parameter q, star formation rate, and Zgas using common strong line diagnostics. We find that isolated barred and unbarred spirals exhibit similarly shallow Zgas profiles from the inner kpc out to large radii (7-10 kpc or 0.5-1.0 R25). This implies that if profiles had steeper gradients at earlier epochs, then the present-day bar is not the primary driver flattening gradients over time. This result contradicts earlier claims, but agrees with recent IFU studies. (3) The Zgas gradients in our z ˜ 0 massive spirals are markedly shallower, by ˜0.2 dex kpc-1, than published gradients for lensed lower mass galaxies at z ˜ 1.5-2.0. Cosmologically motivated hydrodynamical simulations best match this inferred evolution, but the match is sensitive to adopted stellar feedback prescriptions.

  12. 30 CFR 57.22313 - Explosion-protection systems (I-C mines).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Explosion-protection systems (I-C mines). 57... MINES Safety Standards for Methane in Metal and Nonmetal Mines Equipment § 57.22313 Explosion-protection systems (I-C mines). Pressure-relief systems including vents, or explosion suppression systems, shall...

  13. 30 CFR 57.22104 - Open flames (I-C mines).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Open flames (I-C mines). 57.22104 Section 57... Standards for Methane in Metal and Nonmetal Mines Fire Prevention and Control § 57.22104 Open flames (I-C mines). (a) Open flames, including cutting and welding, shall not be used underground. (b) Welding...

  14. 30 CFR 57.22104 - Open flames (I-C mines).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Open flames (I-C mines). 57.22104 Section 57... Standards for Methane in Metal and Nonmetal Mines Fire Prevention and Control § 57.22104 Open flames (I-C mines). (a) Open flames, including cutting and welding, shall not be used underground. (b) Welding...

  15. 30 CFR 57.22104 - Open flames (I-C mines).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Open flames (I-C mines). 57.22104 Section 57... Standards for Methane in Metal and Nonmetal Mines Fire Prevention and Control § 57.22104 Open flames (I-C mines). (a) Open flames, including cutting and welding, shall not be used underground. (b) Welding...

  16. 30 CFR 57.22104 - Open flames (I-C mines).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Open flames (I-C mines). 57.22104 Section 57... Standards for Methane in Metal and Nonmetal Mines Fire Prevention and Control § 57.22104 Open flames (I-C mines). (a) Open flames, including cutting and welding, shall not be used underground. (b) Welding...

  17. 30 CFR 57.22233 - Actions at 0.5 percent methane (I-C mines).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Actions at 0.5 percent methane (I-C mines). 57... MINES Safety Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22233 Actions at 0.5 percent methane (I-C mines). If methane reaches 0.5 percent in the mine atmosphere, ventilation...

  18. 30 CFR 57.22241 - Advance face boreholes (I-C mines).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Advance face boreholes (I-C mines). 57.22241... Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22241 Advance face boreholes (I-C mines). (a) Boreholes shall be drilled at least 25 feet in advance of a face whenever the work place...

  19. 30 CFR 57.22241 - Advance face boreholes (I-C mines).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Advance face boreholes (I-C mines). 57.22241... Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22241 Advance face boreholes (I-C mines). (a) Boreholes shall be drilled at least 25 feet in advance of a face whenever the work place...

  20. 30 CFR 57.22241 - Advance face boreholes (I-C mines).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Advance face boreholes (I-C mines). 57.22241... Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22241 Advance face boreholes (I-C mines). (a) Boreholes shall be drilled at least 25 feet in advance of a face whenever the work place...

  1. 30 CFR 57.22241 - Advance face boreholes (I-C mines).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Advance face boreholes (I-C mines). 57.22241... Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22241 Advance face boreholes (I-C mines). (a) Boreholes shall be drilled at least 25 feet in advance of a face whenever the work place...

  2. 30 CFR 57.22241 - Advance face boreholes (I-C mines).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Advance face boreholes (I-C mines). 57.22241... Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22241 Advance face boreholes (I-C mines). (a) Boreholes shall be drilled at least 25 feet in advance of a face whenever the work place...

  3. 30 CFR 57.22233 - Actions at 0.5 percent methane (I-C mines).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Actions at 0.5 percent methane (I-C mines). 57... MINES Safety Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22233 Actions at 0.5 percent methane (I-C mines). If methane reaches 0.5 percent in the mine atmosphere, ventilation...

  4. Institutional computing (IC) information session

    SciTech Connect

    Koch, Kenneth R; Lally, Bryan R

    2011-01-19

    The LANL Institutional Computing Program (IC) will host an information session about the current state of unclassified Institutional Computing at Los Alamos, exciting plans for the future, and the current call for proposals for science and engineering projects requiring computing. Program representatives will give short presentations and field questions about the call for proposals and future planned machines, and discuss technical support available to existing and future projects. Los Alamos has started making a serious institutional investment in open computing available to our science projects, and that investment is expected to increase even more.

  5. IC and Component Selection for Space Systems

    NASA Technical Reports Server (NTRS)

    Label, Kenneth A.; Cohn, Lewis M.

    2007-01-01

    This viewgraph presentation reviews the integrated circuit (IC) and selections of the IC components for space systems. Included in the discussion are a overview of semiconductors and the evolution of integrated circuit. It also reviews the three different viewpoints of the IC selection: technical, programmatic, and risk. From a radiation perspective there are four criteria for selecting ICs for space systems: guaranteed hardness, historical ground-based data, historical flight usage, and unknown assurance.

  6. Rocket Observations of IC 405

    NASA Astrophysics Data System (ADS)

    France, K.; McCandliss, S. R.; Feldman, P. D.; Burgh, E. B.

    2001-12-01

    We present the preliminary results from a NASA/JHU sounding rocket mission (36.198 UG), launched on 09 February 2001 at 21:00 MST, to obtain a long slit (200\\arcsec x 12\\arcsec) spectrum of the reflection nebula IC 405 in the 900 -- 1400 Å wavelength region. Several pointings within the nebula were obtained, including a high quality (S/N ≈ 10-15 at R = 300) spectrum of the central star, HD 34078, which clearly shows absorption from molecular hydrogen (H2). Observations of the nebula reveal a surface brightness to stellar flux ratio that rises by two orders of magnitude between 1400 and 900 Å. This is in contrast with the relatively flat nebular dust scattering observed during a prior sounding rocket observation of the reflection nebula NGC 2023. We will also present additional nebular pointings within IC 405, including a region observed by the Hopkins Ultraviolet Telescope showing evidence of H2 fluorescent emission. These observations were supported by NASA grant NAG5-5122 to the Johns Hopkins University.

  7. Some stars are totally metal: a new mechanism driving dust across star-forming clouds, and consequences for planets, stars, and galaxies

    SciTech Connect

    Hopkins, Philip F.

    2014-12-10

    Dust grains in neutral gas behave as aerodynamic particles, so they can develop large local density fluctuations entirely independent of gas density fluctuations. Specifically, gas turbulence can drive order-of-magnitude 'resonant' fluctuations in the dust density on scales where the gas stopping/drag timescale is comparable to the turbulent eddy turnover time. Here we show that for large grains (size ≳ 0.1 μm, containing most grain mass) in sufficiently large molecular clouds (radii ≳ 1-10 pc, masses ≳ 10{sup 4} M {sub ☉}), this scale becomes larger than the characteristic sizes of prestellar cores (the sonic length), so large fluctuations in the dust-to-gas ratio are imprinted on cores. As a result, star clusters and protostellar disks formed in large clouds should exhibit significant abundance spreads in the elements preferentially found in large grains (C, O). This naturally predicts populations of carbon-enhanced stars, certain highly unusual stellar populations observed in nearby open clusters, and may explain the 'UV upturn' in early-type galaxies. It will also dramatically change planet formation in the resulting protostellar disks, by preferentially 'seeding' disks with an enhancement in large carbonaceous or silicate grains. The relevant threshold for this behavior scales simply with cloud densities and temperatures, making straightforward predictions for clusters in starbursts and high-redshift galaxies. Because of the selective sorting by size, this process is not necessarily visible in extinction mapping. We also predict the shape of the abundance distribution—when these fluctuations occur, a small fraction of the cores may actually be seeded with abundances Z ∼ 100 (Z) such that they are almost 'totally metal' (Z ∼ 1)! Assuming the cores collapse, these totally metal stars would be rare (1 in ∼10{sup 4} in clusters where this occurs), but represent a fundamentally new stellar evolution channel.

  8. Isolated ellipticals and their globular cluster systems. III. NGC 2271, NGC 2865, NGC 3962, NGC 4240, and IC 4889

    NASA Astrophysics Data System (ADS)

    Salinas, R.; Alabi, A.; Richtler, T.; Lane, R. R.

    2015-05-01

    As tracers of star formation, galaxy assembly, and mass distribution, globular clusters have provided important clues to our understanding of early-type galaxies. But their study has been mostly constrained to galaxy groups and clusters where early-type galaxies dominate, leaving the properties of the globular cluster systems (GCSs) of isolated ellipticals as a mostly uncharted territory. We present Gemini-South/GMOS g'i' observations of five isolated elliptical galaxies: NGC 3962, NGC 2865, IC 4889, NGC 2271, and NGC 4240. Photometry of their GCSs reveals clear color bimodality in three of them, but remains inconclusive for the other two. All the studied GCSs are rather poor with a mean specific frequency SN ~ 1.5, independently of the parent galaxy luminosity. Considering information from previous work as well, it is clear that bimodality and especially the presence of a significant, even dominant, population of blue clusters occurs at even the most isolated systems, which casts doubts on a possible accreted origin of metal-poor clusters, as suggested by some models. Additionally, we discuss the possible existence of ultra-compact dwarfs around the isolated elliptical NGC 3962. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência, Tecnologia e Inovação (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).Globular cluster photometry is available in electronic form at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/577/A59Appendices are available in

  9. HUNTING FOR YOUNG DISPERSING STAR CLUSTERS IN IC 2574

    SciTech Connect

    Pellerin, Anne; Meyer, Martin M.; Calzetti, Daniella; Harris, Jason E-mail: martin.meyer@uwa.edu.au E-mail: jharris@30doradus.org

    2012-12-01

    Dissolving stellar groups are very difficult to detect using traditional surface photometry techniques. We have developed a method to find and characterize non-compact stellar systems in galaxies where the young stellar population can be spatially resolved. By carrying out photometry on individual stars, we are able to separate the luminous blue stellar population from the star field background. The locations of these stars are used to identify groups by applying the HOP algorithm, which are then characterized using color-magnitude and stellar density radial profiles to estimate age, size, density, and shape. We test the method on Hubble Space Telescope Advanced Camera for Surveys archival images of IC 2574 and find 75 dispersed stellar groups. Of these, 20 highly dispersed groups are good candidates for dissolving systems. We find few compact systems with evidence of dissolution, potentially indicating that star formation in this galaxy occurs mostly in unbound clusters or groups. These systems indicate that the dispersion rate of groups and clusters in IC 2574 is at most 0.45 pc Myr{sup -1}. The location of the groups found with HOP correlate well with H I contour map features. However, they do not coincide with H I holes, suggesting that those holes were not created by star-forming regions.

  10. Kinematics of Metal-poor Stars in the Galaxy. III. Formation of the Stellar Halo and Thick Disk as Revealed from a Large Sample of Nonkinematically Selected Stars

    NASA Astrophysics Data System (ADS)

    Chiba, Masashi; Beers, Timothy C.

    2000-06-01

    We present a detailed analysis of the space motions of 1203 solar-neighborhood stars with metal abundances [Fe/H]<=-0.6, on the basis of a catalog, of metal-poor stars selected without kinematic bias recently revised and supplemented by Beers et al. This sample, having available proper motions, radial velocities, and distance estimates for stars with a wide range of metal abundances, is by far the largest such catalog to be assembled to date. We show that the stars in our sample with [Fe/H]<=-2.2, which likely represent a ``pure'' halo component, are characterized by a radially elongated velocity ellipsoid (σU,σV,σW)=(141+/-11, 106+/-9, 94+/-8) km s-1 and small prograde rotation =30 to 50 km s-1, consistent with previous analysis of this sample by Beers and Sommer-Larsen based on radial velocity information alone. In contrast to the previous analysis, we find a decrease in with increasing distance from the Galactic plane for stars that are likely to be members of the halo population (Δ/Δ|Z|=-52+/-6 km s-1 kpc-1), which may represent the signature of a dissipatively formed flattened inner halo. Unlike essentially all previous kinematically selected catalogs, the metal-poor stars in our sample exhibit a diverse distribution of orbital eccentricities, e, with no apparent correlation between [Fe/H] and e. This demonstrates, clearly and convincingly, that the evidence offered in 1962 by Eggen, Lynden-Bell, & Sandage for a rapid collapse of the Galaxy, an apparent correlation between the orbital eccentricity of halo stars with metallicity, is basically the result of their proper-motion selection bias. However, even in our nonkinematically selected sample, we have identified a small concentration of high-e stars at [Fe/H]~-1.7, which may originate, in part, from infalling gas during the early formation of the Galaxy. We find no evidence for an additional thick disk component for stellar abundances [Fe/H]<=-2.2. The kinematics of the intermediate

  11. HC3N observations of nearby galaxies

    NASA Astrophysics Data System (ADS)

    Jiang, Xue-Jian; Wang, Jun-Zhi; Gao, Yu; Gu, Qiu-Sheng

    2017-03-01

    Aims: We aim to systematically study the properties of the different transitions of the dense molecular gas tracer HC3N in galaxies. Methods: We have conducted single-dish observations of HC3N emission lines towards a sample of nearby gas-rich galaxies. HC3N(J = 2-1) was observed in 20 galaxies with the Effelsberg 100-m telescope. HC3N(J = 24-23) was observed in nine galaxies with the 10-m Submillimeter Telescope (SMT). Results: HC3N 2-1 is detected in three galaxies: IC 342, M 66, and NGC 660 (> 3σ). HC3N 24-23 is detected in three galaxies: IC 342, NGC 1068, and IC 694. These are the first measurements of HC3N 2-1 in a relatively large sample of external galaxies, although the detection rate is low. For the HC3N 2-1 non-detections, upper limits (2σ) are derived for each galaxy, and stacking the non-detections is attempted to recover the weak signal of HC3N. The stacked spectrum, however, does not show any significant signs of HC3N 2-1 emission. The results are also compared with other transitions of HC3N observed in galaxies. Conclusions: The low detection rate of both transitions suggests low abundance of HC3N in galaxies, which is consistent with other observational studies. The comparison between HC3N and HCN or HCO+shows a large diversity in the ratios between HC3N and HCN or HCO+. More observations are needed to interpret the behavior of HC3N in different types of galaxies.

  12. Dust-depletion sequences in damped Lyman-α absorbers. A unified picture from low-metallicity systems to the Galaxy

    NASA Astrophysics Data System (ADS)

    De Cia, A.; Ledoux, C.; Mattsson, L.; Petitjean, P.; Srianand, R.; Gavignaud, I.; Jenkins, E. B.

    2016-12-01

    We study metal depletion due to dust in the interstellar medium (ISM) to infer the properties of dust grains and characterize the metal and dust content of galaxies down to low metallicity and intermediate redshift z. We provide metal column densities and abundances of a sample of 70 damped Lyman-α absorbers (DLAs) towards quasars, observed at high spectral resolution with the Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES). This is the largest sample of phosphorus abundances measured in DLAs so far. We use literature measurements for Galactic clouds to cover the high-metallicity end. We discover tight (scatter ≲ 0.2 dex) correlations between [Zn/Fe] and the observed relative abundances from dust depletion. This implies that grain growth in the ISM is an important process of dust production. These sequences are continuous in [Zn/Fe] from dust-free to dusty DLAs, and to Galactic clouds, suggesting that the availability of refractory metals in the ISM is crucial for dust production, regardless of the star formation history. We observe [S/Zn] up to 0.25 dex in DLAs, which is broadly consistent with Galactic stellar abundances. Furthermore, we find a good agreement between the nucleosynthetic pattern of Galactic halo stars and our observations of the least dusty DLAs. This supports recent star formation in low-metallicity DLAs. The derived depletions of Zn, O, P, S, Si, Mg, Mn, Cr, and Fe correlate with [Zn/Fe], with steeper slopes for more refractory elements. P is mostly not affected by dust depletion. We present canonical depletion patterns to be used as reference in future studies of relative abundances and depletion. We derive the total (dust-corrected) metallicity, typically -2 ≲ [M/H] tot ≲ 0 for DLAs, and scattered around solar metallicity for the Galactic ISM. The dust-to-metal ratio (mathcal{{DTM}}) increases with metallicity, again supporting the importance of grain growth for dust production. The dust extinction AV

  13. LOSS Revisited. I. Unraveling Correlations Between Supernova Rates and Galaxy Properties, as Measured in a Reanalysis of the Lick Observatory Supernova Search

    NASA Astrophysics Data System (ADS)

    Graur, Or; Bianco, Federica B.; Huang, Shan; Modjaz, Maryam; Shivvers, Isaac; Filippenko, Alexei V.; Li, Weidong; Eldridge, J. J.

    2017-03-01

    Most types of supernovae (SNe) have yet to be connected with their progenitor stellar systems. Here, we reanalyze the 10-year SN sample collected during 1998–2008 by the Lick Observatory Supernova Search (LOSS) in order to constrain the progenitors of SNe Ia and stripped-envelope SNe (SE SNe, i.e., SNe IIb, Ib, Ic, and broad-lined Ic). We matched the LOSS galaxy sample with spectroscopy from the Sloan Digital Sky Survey and measured SN rates as a function of galaxy stellar mass, specific star formation rate, and oxygen abundance (metallicity). We find significant correlations between the SN rates and all three galaxy properties. The SN Ia correlations are consistent with other measurements, as well as with our previous explanation of these measurements in the form of a combination of the SN Ia delay-time distribution and the correlation between galaxy mass and age. The ratio between the SE SN and SN II rates declines significantly in low-mass galaxies. This rules out single stars as SE SN progenitors, and is consistent with predictions from binary-system progenitor models. Using well-known galaxy scaling relations, any correlation between the rates and one of the galaxy properties examined here can be expressed as a correlation with the other two. These redundant correlations preclude us from establishing causality—that is, from ascertaining which of the galaxy properties (or their combination) is the physical driver for the difference between the SE SN and SN II rates. We outline several methods that have the potential to overcome this problem in future works.

  14. Thackeray's Globules in IC 2944

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Strangely glowing dark clouds float serenely in this remarkable and beautiful image taken with NASA's Hubble Space Telescope. These dense, opaque dust clouds - known as 'globules' - are silhouetted against nearby bright stars in the busy star-forming region, IC 2944. These globules were first found in IC 2944 by astronomer A.D. Thackeray in 1950. Although globules like these have been known since Dutch-American astronomer Bart Bok first drew attention to such objects in 1947, little is still known about their origin and nature, except that they are generally associated with areas of star formation, called 'HII regions' due to the presence of hydrogen gas. The largest of the globules in this image is actually two separate clouds that gently overlap along our line of sight. Each cloud is nearly 1.4 light-years (50 arcseconds) along its longest dimension, and collectively, they contain enough material to equal over 15 solar masses. IC 2944, the surrounding HII region, is filled with gas and dust that is illuminated and heated by a loose cluster of O-type stars. These stars are much hotter and much more massive than our Sun. IC 2944 is relatively close by, located only 5900 light-years (1800 parsecs) away in the constellation Centaurus. Thanks to the remarkable resolution offered by the Hubble Space Telescope, astronomers can for the first time study the intricate structure of these globules. The globules appear to be heavily fractured, as if major forces were tearing them apart. When radio astronomers observed the faint hiss of molecules within the globules, they realized that the globules are actually in constant, churning motion, moving supersonically among each other. This may be caused by the powerful ultraviolet radiation from the luminous, massive stars, which also heat up the gas in the HII region, causing it to expand and stream against the globules, leading to their destruction. Despite their serene appearance, the globules may actually be likened to clumps

  15. THE HOST GALAXY OF THE SUPER-LUMINOUS SN 2010gx AND LIMITS ON EXPLOSIVE {sup 56}Ni PRODUCTION

    SciTech Connect

    Chen, Ting-Wan; Smartt, Stephen J.; Kotak, Rubina; McCrum, Matt; Fraser, Morgan; Bresolin, Fabio; Kudritzki, Rolf-Peter; Pastorello, Andrea; Valenti, Stefano

    2013-02-01

    Super-luminous supernovae have a tendency to occur in faint host galaxies which are likely to have low mass and low metallicity. While these extremely luminous explosions have been observed from z = 0.1 to 1.55, the closest explosions allow more detailed investigations of their host galaxies. We present a detailed analysis of the host galaxy of SN 2010gx (z = 0.23), one of the best studied super-luminous type Ic supernovae. The host is a dwarf galaxy (M{sub g} = -17.42 {+-} 0.17) with a high specific star formation rate. It has a remarkably low metallicity of 12 + log (O/H) = 7.5 {+-} 0.1 dex as determined from the detection of the [O III] {lambda}4363 line. This is the first reliable metallicity determination of a super-luminous stripped-envelope supernova host. We collected deep multi-epoch imaging with Gemini + GMOS between 240 and 560 days after explosion to search for any sign of radioactive {sup 56}Ni, which might provide further insights on the explosion mechanism and the progenitor's nature. We reach griz magnitudes of m{sub AB} {approx} 26, but do not detect SN 2010gx at these epochs. The limit implies that any {sup 56}Ni production was similar to or below that of SN 1998bw (a luminous type Ic SN that produced around 0.4 M{sub Sun} of {sup 56}Ni). The low volumetric rates of these supernovae ({approx}10{sup -4} of the core-collapse population) could be qualitatively matched if the explosion mechanism requires a combination of low-metallicity (below 0.2 Z{sub Sun }), high progenitor mass (>60 M{sub Sun }) and high rotation rate (fastest 10% of rotators).

  16. Mod 1 ICS TI Report: ICS Conversion of a 140% HPGe Detector

    SciTech Connect

    Bounds, John Alan

    2016-07-05

    This report evaluates the Mod 1 ICS, an electrically cooled 140% HPGe detector. It is a custom version of the ORTEC Integrated Cooling System (ICS) modified to make it more practical for us to use in the field. Performance and operating characteristics of the Mod 1 ICS are documented, noting both pros and cons. The Mod 1 ICS is deemed a success. Recommendations for a Mod 2 ICS, a true field prototype, are provided.

  17. A Chandra Archival Study of the Temperature and Metal Abundance Profiles in Hot Galaxy Clusters at 0.1 <~ z <~ 0.3

    NASA Astrophysics Data System (ADS)

    Baldi, A.; Ettori, S.; Mazzotta, P.; Tozzi, P.; Borgani, S.

    2007-09-01

    We present an analysis of the temperature and metallicity profiles of 12 galaxy clusters in the redshift range 0.1-0.3 selected from the Chandra archive with at least ~20,000 net ACIS counts and kT>6 keV. We divide the sample between seven cooling-core (CC) and five non-cooling-core (NCC) clusters according to their central cooling time. We find that single power laws can properly describe both the temperature and metallicity profiles at radii larger than 0.1r180 in both CC and NCC systems, with NCC objects showing steeper profiles outward. A significant deviation is present only in the inner 0.1r180. We perform a comparison of our sample with the De Grandi & Molendi BeppoSAX sample of local CC and NCC clusters, finding a complete agreement in the CC cluster profile and a marginally higher value (at ~1 σ) in the inner regions of the NCC clusters. The slope of the power law describing kT(r) within 0.1r180 correlates strongly with the ratio between the cooling time and the age of the universe at the cluster redshift, with a slope >0 and τc/τage<~0.6 in CC systems.

  18. Carbon-enhanced metal-poor star frequencies in the galaxy: corrections for the effect of evolutionary status on carbon abundances

    SciTech Connect

    Placco, Vinicius M.; Frebel, Anna; Beers, Timothy C.; Stancliffe, Richard J.

    2014-12-10

    We revisit the observed frequencies of carbon-enhanced metal-poor (CEMP) stars as a function of the metallicity in the Galaxy, using data from the literature with available high-resolution spectroscopy. Our analysis excludes stars exhibiting clear overabundances of neutron-capture elements and takes into account the expected depletion of surface carbon abundance that occurs due to CN processing on the upper red giant branch. This allows for the recovery of the initial carbon abundance of these stars, and thus for an accurate assessment of the frequencies of carbon-enhanced stars. The correction procedure we develop is based on stellar-evolution models and depends on the surface gravity, log g, of a given star. Our analysis indicates that for stars with [Fe/H] ≤–2.0, 20% exhibit [C/Fe] ≥+0.7. This fraction increases to 43% for [Fe/H] ≤–3.0 and 81% for [Fe/H] ≤–4.0, which is higher than have been previously inferred without taking the carbon abundance correction into account. These CEMP star frequencies provide important inputs for Galactic and stellar chemical evolution models, as they constrain the evolution of carbon at early times and the possible formation channels for the CEMP-no stars. We also have developed a public online tool with which carbon corrections using our procedure can be easily obtained.

  19. Boo-1137—an Extremely Metal-Poor Star in the Ultra-Faint Dwarf Spheroidal Galaxy Boötes I

    NASA Astrophysics Data System (ADS)

    Norris, John E.; Yong, David; Gilmore, Gerard; Wyse, Rosemary F. G.

    2010-03-01

    We present high-resolution (R ~ 40,000), high-signal-to-noise ratio (20-90) spectra of an extremely metal-poor giant star Boo-1137 in the "ultra-faint" dwarf spheroidal galaxy (dSph) Boötes I, absolute magnitude M V ~ -6.3. We derive an iron abundance of [Fe/H] = -3.7, making this the most metal-poor star as yet identified in an ultra-faint dSph. Our derived effective temperature and gravity are consistent with its identification as a red giant in Boötes I. Abundances for a further 15 elements have also been determined. Comparison of the relative abundances, [X/Fe], with those of the extremely metal-poor red giants of the Galactic halo shows that Boo-1137 is "normal" with respect to C and N, the odd-Z elements Na and Al, the iron-peak elements, and the neutron-capture elements Sr and Ba, in comparison with the bulk of the Milky Way halo population having [Fe/H] lsim-3.0. The α-elements Mg, Si, Ca, and Ti are all higher by Δ[X/Fe] ~ 0.2 than the average halo values. Monte Carlo analysis indicates that Δ[α/Fe] values this large are expected with a probability ~0.02. The elemental abundance pattern in Boo-1137 suggests inhomogeneous chemical evolution, consistent with the wide internal spread in iron abundances we previously reported. The similarity of most of the Boo-1137 relative abundances with respect to halo values, and the fact that the α-elements are all offset by a similar small amount from the halo averages, points to the same underlying galaxy-scale stellar initial mass function, but that Boo-1137 likely originated in a star-forming region where the abundances reflect either poor mixing of supernova (SN) ejecta, or poor sampling of the SN progenitor mass range, or both. Observations obtained for ESO program P383.B-0038, using VLT-UT2/UVES.

  20. STELLAR LIFETIME AND ULTRAVIOLET PROPERTIES OF THE OLD METAL-RICH GALACTIC OPEN CLUSTER NGC 6791: A PATHWAY TO UNDERSTAND THE ULTRAVIOLET UPTURN OF ELLIPTICAL GALAXIES

    SciTech Connect

    Buzzoni, Alberto; Bertone, Emanuele; Carraro, Giovanni; Buson, Lucio

    2012-04-10

    The evolutionary properties of the old metal-rich Galactic open cluster NGC 6791 are assessed based on deep UB photometry and Two Micron All Sky Survey JK data. For the 4739 stars in the cluster, bolometric luminosity and effective temperature have been derived from theoretical (U - B) and (J - K) color fitting. The derived H-R diagram has been matched with the UVBLUE grid of synthetic stellar spectra to obtain the integrated spectral energy distribution (SED) of the system, together with a full set of UV (Fanelli) and optical (Lick) narrowband indices. The total bolometric magnitude of NGC 6791 is M{sup bol}{sub 6791} = -6.29, with a color (B - V){sub 6791} = 0.97. The cluster appears to be a fairly good proxy of standard elliptical galaxies, although with significantly bluer infrared colors, a shallower 4000 A Balmer break, and a lower Mg{sub 2} index. The confirmed presence of a dozen hot stars along their extreme horizontal-branch evolution leads the cluster SED to consistently match the properties of the most active UV-upturn galaxies, with 1.7% {+-} 0.4% of the total bolometric luminosity emitted shortward of 2500 Angstrom-Sign . The cluster helium abundance results in Y{sub 6791} = 0.30 {+-} 0.04, while the post-main-sequence (PMS) implied stellar lifetime from star number counts fairly agrees with the theoretical expectations from both the PADOVA and BASTI stellar tracks. A PMS fuel consumption of 0.43 {+-} 0.01 M{sub Sun} is found for NGC 6791 stars, in close agreement with the estimated mass of cluster He-rich white dwarfs. Such a tight figure may lead one to suspect that a fraction of the cluster stellar population does not actually reach the minimum mass required to effectively ignite He in the stellar core.

  1. Stellar Lifetime and Ultraviolet Properties of the Old Metal-rich Galactic Open Cluster NGC 6791: A Pathway to Understand the Ultraviolet Upturn of Elliptical Galaxies

    NASA Astrophysics Data System (ADS)

    Buzzoni, Alberto; Bertone, Emanuele; Carraro, Giovanni; Buson, Lucio

    2012-04-01

    The evolutionary properties of the old metal-rich Galactic open cluster NGC 6791 are assessed based on deep UB photometry and Two Micron All Sky Survey JK data. For the 4739 stars in the cluster, bolometric luminosity and effective temperature have been derived from theoretical (U - B) and (J - K) color fitting. The derived H-R diagram has been matched with the UVBLUE grid of synthetic stellar spectra to obtain the integrated spectral energy distribution (SED) of the system, together with a full set of UV (Fanelli) and optical (Lick) narrowband indices. The total bolometric magnitude of NGC 6791 is M bol 6791 = -6.29, with a color (B - V)6791 = 0.97. The cluster appears to be a fairly good proxy of standard elliptical galaxies, although with significantly bluer infrared colors, a shallower 4000 Å Balmer break, and a lower Mg2 index. The confirmed presence of a dozen hot stars along their extreme horizontal-branch evolution leads the cluster SED to consistently match the properties of the most active UV-upturn galaxies, with 1.7% ± 0.4% of the total bolometric luminosity emitted shortward of 2500 Å. The cluster helium abundance results in Y 6791 = 0.30 ± 0.04, while the post-main-sequence (PMS) implied stellar lifetime from star number counts fairly agrees with the theoretical expectations from both the PADOVA and BASTI stellar tracks. A PMS fuel consumption of 0.43 ± 0.01 M ⊙ is found for NGC 6791 stars, in close agreement with the estimated mass of cluster He-rich white dwarfs. Such a tight figure may lead one to suspect that a fraction of the cluster stellar population does not actually reach the minimum mass required to effectively ignite He in the stellar core. Based on observations carried out at the Italian Telescopio Nazionale Galileo, operated by INAF at the Roque de los Muchachos Observatory (La Palma, Spain).

  2. Electromigration of damascene copper of IC interconnect

    NASA Astrophysics Data System (ADS)

    Meyer, William Kevin

    Copper metallization patterned with multi-level damascene process is prone to electromigration failure, which affects the reliability and performance of IC interconnect. In typical products, interconnect that is not already constrained by I·R drop or Joule self-heating operates at 'near threshold' conditions. Measurement of electromigration damage near threshold is very difficult due to slow degradation requiring greatly extended stress times, or high currents that cause thermal anomalies. Software simulations of the electromigration mechanism combined with characterization of temperature profiles allows extracting material parameters and calculation of design rules to ensure reliable interconnect. Test structures capable of demonstrating Blech threshold effects while allowing thermal characterization were designed and processed. Electromigration stress tests at various conditions were performed to extract both shortline (threshold) and long-line (above threshold) performance values. The resistance increase time constant shows immortality below Je·L (product of current density and segment length) of 3200 amp/cm. Statistical analysis of times-to-failure show that long lines last 105 hours at 3.1 mA/mum2 (120°C). While this is more robust than aluminum interconnect, the semiconductor industry will be challenged to improve that performance as future products require.

  3. Validating IC early-failure simulation

    NASA Astrophysics Data System (ADS)

    Moosa, Mohamod S.; Poole, Kelvin F.; Grams, Michael L.

    1995-09-01

    Early failures are the dominant concern as integrated circuit technology matures into consistently producing systems of high reliability. These failures are attributed to the presence of randomly occurring defects in elementary objects (contacts, vias, metal runs, gate oxides, bonds etc.) that result in extrinsic rather than intrinsic (wearout-related) mortality. A model relating system failure to failure at the elementary objective level has been developed. Reliability is modeled as a function of circuit architecture, mask layout, material properties, life-test data, worst-case use-conditions and the processing environment. The effects of competing failure mechanisms and the presence of redundant sub-systems are accounted for. Hierarchy is exploited in the analysis, allowing large scale designs to be simulated. Experimental validation of the modeling of oxide leakage related failure, based on correlation between actual failures reported for a production integrated circuit and Monte Carlo simulations that incorporate wafer-level test results and process defect monitor data, is presented. The state of the art in IC reliability simulation is advanced in that a methodology that provides the capability to design-in reliability while accounting for early failures has been developed; applications include process qualification, design assessment and fabrication monitoring.

  4. PROGENITOR DIAGNOSTICS FOR STRIPPED CORE-COLLAPSE SUPERNOVAE: MEASURED METALLICITIES AT EXPLOSION SITES

    SciTech Connect

    Modjaz, M.; Bloom, J. S.; Filippenko, A. V.; Perley, D.; Silverman, J. M.; Kewley, L.

    2011-04-10

    Metallicity is expected to influence not only the lives of massive stars but also the outcome of their deaths as supernovae (SNe) and gamma-ray bursts (GRBs). However, there are surprisingly few direct measurements of the local metallicities of different flavors of core-collapse SNe (CCSNe). Here, we present the largest existing set of host-galaxy spectra with H II region emission lines at the sites of 35 stripped-envelope CCSNe. We derive local oxygen abundances in a robust manner in order to constrain the SN Ib/c progenitor population. We obtain spectra at the SN sites, include SNe from targeted and untargeted surveys, and perform the abundance determinations using three different oxygen-abundance calibrations. The sites of SNe Ic (the demise of the most heavily stripped stars, having lost both H and He layers) are systematically more metal rich than those of SNe Ib (arising from stars that retained their He layer) in all calibrations. A Kolmogorov-Smirnov test yields the very low probability of 1% that SN Ib and SN Ic environment abundances, which are different on average by {approx}0.2 dex (in the Pettini and Pagel scale), are drawn from the same parent population. Broad-lined SNe Ic (without GRBs) occur at metallicities between those of SNe Ib and SNe Ic. Lastly, we find that the host-galaxy central oxygen abundance is not a good indicator of the local SN metallicity; hence, large-scale SN surveys need to obtain local abundance measurements in order to quantify the impact of metallicity on stellar death.

  5. The Kinematics of the Ionized Gas in IC 10

    NASA Astrophysics Data System (ADS)

    Thurow, Joshua C.; Wilcots, Eric M.

    2005-02-01

    We present the results of a WIYN integral field unit study of the kinematics of the ionized gas in IC 10, a dwarf irregular starburst galaxy in the Local Group. Though the velocity field of the ionized gas closely matches that of the H I, there are several kinematically interesting features in the galaxy. The diffuse ionized gas in the galaxy exhibits larger Hα line widths than the bright complexes. In one case this is due to an infusion of energy into the gas associated with the radio superbubble discovered by Yang & Skillman. We find that the amount of energy in this region is consistent with their hypothesis that the region contains 10 supernova remnants. We also detect a high-velocity (70 km s-1) expanding shell in the ionized gas, which is likely driven by three confirmed Wolf-Rayet stars that are located within the shell. Extrapolating from Hunter's initial mass function, we find that the central starburst region contains approximately equal energy contributions from stellar winds and supernovae (SNe), suggesting that SNe are just beginning to play a significant role in shaping the kinematics of the ionized gas. However, all of this energy cannot be easily accounted for in the kinematics of the gas. We detect an energetic flow of gas (3×1052 ergs), which we believe originates from the starburst region. We also detect a high-velocity (70 km s-1) feature not coincident with any structure in our Hα image. This feature, along with the flow and shell, can account for the energy produced by stellar wind and SNe. The flow resembles one discovered by Wilcots & Thurow in NGC 4214; together they suggest that the porosity of the interstellar medium contributes significantly to the high velocity of some portion of the ionized gas in irregular galaxies.

  6. THE OBSERVED PROPERTIES OF DWARF GALAXIES IN AND AROUND THE LOCAL GROUP

    SciTech Connect

    McConnachie, Alan W.

    2012-07-15

    Positional, structural, and dynamical parameters for all dwarf galaxies in and around the Local Group are presented, and various aspects of our observational understanding of this volume-limited sample are discussed. Over 100 nearby galaxies that have distance estimates reliably placing them within 3 Mpc of the Sun are identified. This distance threshold samples dwarfs in a large range of environments, from the satellite systems of the MW and M31, to the quasi-isolated dwarfs in the outer regions of the Local Group, to the numerous isolated galaxies that are found in its surroundings. It extends to, but does not include, the galaxies associated with the next nearest groups, such as Maffei, Sculptor, and IC 342. Our basic knowledge of this important galactic subset and their resolved stellar populations will continue to improve dramatically over the coming years with existing and future observational capabilities, and they will continue to provide the most detailed information available on numerous aspects of dwarf galaxy formation and evolution. Basic observational parameters, such as distances, velocities, magnitudes, mean metallicities, as well as structural and dynamical characteristics, are collated, homogenized (as far as possible), and presented in tables that will be continually updated to provide a convenient and current online resource. As well as discussing the provenance of the tabulated values and possible uncertainties affecting their usage, the membership and spatial extent of the MW sub-group, M31 sub-group, and the Local Group are explored. The morphological diversity of the entire sample and notable sub-groups is discussed, and timescales are derived for the Local Group members in the context of their orbital/interaction histories. The scaling relations and mean stellar metallicity trends defined by the dwarfs are presented, and the origin of a possible 'floor' in central surface brightness (and, more speculatively, stellar mean metallicity) at

  7. Size Distribution of Star Clusters and Stellar Groups in IC2574

    NASA Astrophysics Data System (ADS)

    Pellerin, Anne; Meyer, Martin J.; Calzetti, Daniela

    2017-01-01

    We present an HST/ACS archival study of compact and dispersed star clusters and stellar groups found in the nearby galaxy IC 2574. In this work, we identified and characterized the properties of clusters with spatially unresolved stars. We combined these properties with those found in a companion work on the dispersed stellar groups in IC 2574 with spatially resolved stars. We find that the size distribution of all young stellar groups, sparse and compact together, is consistent with the hierarchical model of star formation.

  8. VLT/X-shooter observations of the low-metallicity blue compact dwarf galaxy PHL 293B including a luminous blue variable star

    NASA Astrophysics Data System (ADS)

    Izotov, Y. I.; Guseva, N. G.; Fricke, K. J.; Henkel, C.

    2011-09-01

    Context. We present VLT/X-shooter spectroscopic observations in the wavelength range λλ3000-23 000 Å of the extremely metal-deficient blue compact dwarf (BCD) galaxy PHL 293B containing a luminous blue variable (LBV) star and compare them with previous data. Aims: This BCD is one of the two lowest-metallicity galaxies where LBV stars were detected, allowing us to study the LBV phenomenon in the extremely low metallicity regime. Methods: We determine abundances of nitrogen, oxygen, neon, sulfur, argon, and iron by analyzing the fluxes of narrow components of the emission lines using empirical methods and study the properties of the LBV from the fluxes and widths of broad emission lines. Results: We derive an interstellar oxygen abundance of 12+log O/H = 7.71 ± 0.02, which is in agreement with previous determinations. The observed fluxes of narrow Balmer, Paschen and Brackett hydrogen lines correspond to the theoretical recombination values after correction for extinction with a single value C(Hβ) = 0.225. This implies that the star-forming region observed in the optical range is the only source of ionisation and there is no additional source of ionisation that is seen in the NIR range but is hidden in the optical range. We detect three v = 1-0 vibrational lines of molecular hydrogen. Their flux ratios and non-detection of v = 2-1 and 3-1 emission lines suggest that collisional excitation is the main source producing H2 lines. For the LBV star in PHL 293B we find broad emission with P Cygni profiles in several Balmer hydrogen emission lines and for the first time in several Paschen hydrogen lines and in several He i emission lines, implying temporal evolution of the LBV on a time scale of 8 years. The Hα luminosity of the LBV star is by one order of magnitude higher than the one obtained for the LBV star in NGC 2363 ≡ Mrk 71 which has a slightly higher metallicity 12+logO/H = 7.87. The terminal velocity of the stellar wind in the low-metallicity LBV of PHL293

  9. Quality control during IC processing

    NASA Technical Reports Server (NTRS)

    1979-01-01

    Manual gives detailed test procedures for controlling silicon-wafer processing in manufacture of integrated circuits. Included among 43 test procedures are: ionic, bacterial, and solids contamination of high-purity water needed for wafer processing; crystallographic reflection, purity, and orientation; substrate dimensions and finish; thickness of deposited epitaxial films; oxide quality; photoresist characteristics; pinholes in insulating layers; metallized adhesion; and quality of ohmic contact.

  10. EVIDENCE THAT GAMMA-RAY BURST 130702A EXPLODED IN A DWARF SATELLITE OF A MASSIVE GALAXY

    SciTech Connect

    Kelly, Patrick L.; Filippenko, Alexei V.; Fox, Ori D.; Zheng Weikang; Clubb, Kelsey I.

    2013-09-20

    GRB 130702A is a nearby long-duration gamma-ray burst (LGRB) discovered by the Fermi satellite whose associated afterglow was detected by the Palomar Transient Factory. Subsequent photometric and spectroscopic monitoring has identified a coincident broad-lined Type Ic supernova (SN), and nebular emission detected near the explosion site is consistent with a redshift of z = 0.145. The SN-GRB exploded at an offset of {approx}7.''6 from the center of an inclined r = 18.1 mag red disk-dominated galaxy, and {approx}0.''6 from the center of a much fainter r = 23 mag object. We obtained Keck-II DEIMOS spectra of the two objects and find a 2{sigma} upper limit on their line-of-sight velocity offset of {approx}<60 km s{sup -1}. If we calculate the inclination angle of the massive red galaxy from its axis ratio and assume that its light is dominated by a very thin disk, the explosion would have a {approx}60 kpc central offset, or {approx}9 times the galaxy's half-light radius. A significant bulge or a thicker disk would imply a higher inclination angle and greater central offset. The substantial offset suggests that the faint source is a separate dwarf galaxy. The star-formation rate of the dwarf galaxy is {approx}0.05 M{sub Sun} yr{sup -1}, and we place an upper limit on its oxygen abundance of 12 + log(O/H) < 8.16 dex. The identification of an LGRB in a dwarf satellite of a massive, metal-rich primary galaxy suggests that recent detections of LGRBs spatially coincident with metal-rich galaxies may be, in some cases, superpositions.

  11. The Local Dwarf GALAXIES:BUILDING Blocks of Massive Ones? I.THE Fornax Dwarf Galaxy

    NASA Astrophysics Data System (ADS)

    Nykytyuk, T. V.

    A chemical evolution of the Local Group dwarf galaxy Fornax is considered in the framework of the merger scenario. We suppose a galactic stellar halo to be formed as separate fragments which then merge; thus, we can calculate the set of such the fragments to reproduce the observed metallicity distribution function of a galaxy. Accordingly, if dwarf galaxies were such the systems, which, once merged, have formed massive galaxies, we need to obtain only one fragment to reproduce the observed metallicity distribution function of a dwarf galaxy. To test this assumption, the stellar metallicity distribution functions of Fornax was calculated in the framework of the merger scenario. The more than one fragment was obtained for galaxy under consideration; thus, it is unlikely the systems similar to Fornax to be building blocks of massive galaxies.

  12. Evolution of the dust-to-metals ratio in high-redshift galaxies probed by GRB-DLAs

    NASA Astrophysics Data System (ADS)

    Wiseman, P.; Schady, P.; Bolmer, J.; Krühler, T.; Yates, R. M.; Greiner, J.; Fynbo, J. P. U.

    2017-02-01

    Context. Several issues regarding the nature of dust at high redshift remain unresolved: its composition, its production and growth mechanisms, and its effect on background sources. Aims: We provide a more accurate relation between dust depletion levels and dust-to-metals ratio (DTM), and to use the DTM to investigate the origin and evolution of dust in the high-redshift Universe via gamma-ray burst damped Lyman-alpha absorbers (GRB-DLAs). Methods: We use absorption-line measured metal column densities for a total of 19 GRB-DLAs, including five new GRB afterglow spectra from VLT/X-Shooter. We use the latest linear models to calculate the dust depletion strength factor in each DLA. Using these values we calculate total dust and metal column densities to determine a DTM. We explore the evolution of DTM with metallicity, and compare it to previous trends in DTM measured with different methods. Results: We find significant dust depletion in 16 of our 19 GRB-DLAs, yet 18 of the 19 have a DTM significantly lower than the Milky Way. We find that DTM is positively correlated with metallicity, which supports a dominant ISM grain-growth mode of dust formation. We find a substantial discrepancy between the dust content measured from depletion and that derived from the total V-band extinction, AV, measured by fitting the afterglow SED. We advise against using a measurement from one method to estimate that from the other until the discrepancy can be resolved. Based on observations collected at the European Southern Observatory, Paranal, Chile, Program IDs: 088.A-0051(B), 089.A-0067(B), 091.C-0934, 094.A-0134(A).

  13. Where stellar halos coexist with intracluster light: a case study of the giant Virgo-central galaxy M87

    NASA Astrophysics Data System (ADS)

    Longobardi, Alessia

    2016-01-01

    What is the role that accretion events play in the evolution of galaxies in dense environments, such as galaxy clusters? Cosmological simulations allow us to study in detail the evolution of galaxies' halos in cluster environments and have shown that the formation of extended halos around central cluster galaxies and intracluster light (ICL) is closely correlated to the morphological transformation of galaxies in clusters. However, the extremely low surface brightness of these components makes it difficult to gather observational constraints. Planetary nebulas (PNs) offer a unique tool to investigate these environments owing to their strong [OIII] emission line. I will present a study of the light and stellar motion in the halo of the giant elliptical galaxy M87 and its surrounding IC component at the centre of the Virgo cluster, prime targets to shed light on the hierarchical assembly of structure in the Universe. We make use of a deep and extended PN sample (~ 300 objects) to study out to ~150 kpc in radius M87. We show that at all distance the galaxy halo overlap with theVirgo ICL. However, they are dynamically distinct components with different density profiles, and parent stellarpopulations, consistent with the halo of M87 being redder and more metal rich than the ICL. Moreover, the synergy between PN kinematical information and deep V/B-band photometry made it possible to unveal an ongoing accretion process in the outskirt of M87, that has caused a non-negligible modification of the halo properties. The ongoing assembly of this galaxy at distances R>60 kpc is also shown by the overall PN halo kinematics, reflecting the dynamical complexity of a still growing system.

  14. ABC: Aging-Based IC Configuration

    DTIC Science & Technology

    2014-04-01

    TERMS IP protection, active hardware metering, unclonability, hardware Trojans 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT UU 18... IP ) protection technique that offers universal protection to both application-specific integrated circuits (ASICs) and field-programmable gate...address several aspects of IC intellectual property ( IP ) protection such as prevention of use of non-authorized ICs, they have significant limitations

  15. Population studies. XIII. A new analysis of the Bidelman-Macconnell 'weak-metal' stars - confirmation of metal-poor stars in the thick disk of the galaxy

    SciTech Connect

    Beers, Timothy C.; Norris, John E.; Placco, Vinicius M.; Lee, Young Sun; Rossi, Silvia; Carollo, Daniela; Masseron, Thomas E-mail: jen@mso.anu.edu.au E-mail: youngsun@cnu.ac.kr E-mail: daniela.carollo@mq.edu.au

    2014-10-10

    A new set of very high signal-to-noise (S/N > 100/1), medium-resolution (R ∼ 3000) optical spectra have been obtained for 302 of the candidate 'weak-metal' stars selected by Bidelman and MacConnell. We use these data to calibrate the recently developed generalization of the Sloan Extension for Galactic Exploration and Understanding and Exploration (SEGUE) Stellar Parameter Pipeline, and obtain estimates of the atmospheric parameters (T {sub eff}, log g, and [Fe/H]) for these non-Sloan Digital Sky Survey/SEGUE data; we also obtain estimates of [C/Fe]. The new abundance measurements are shown to be consistent with available high-resolution spectroscopic determinations, and represent a substantial improvement over the accuracies obtained from the previous photometric estimates reported in Paper I of this series. The apparent offset in the photometric abundances of the giants in this sample noted by several authors is confirmed by our new spectroscopy; no such effect is found for the dwarfs. The presence of a metal-weak thick-disk (MWTD) population is clearly supported by these new abundance data. Some 25% of the stars with metallicities –1.8 < [Fe/H] ≤–0.8 exhibit orbital eccentricities e < 0.4, yet are clearly separated from members of the inner-halo population with similar metallicities by their location in a Lindblad energy versus angular momentum diagram. A comparison is made with recent results for a similar-size sample of Radial Velocity Experiment stars from Ruchti et al. We conclude, based on both of these samples, that the MWTD is real, and must be accounted for in discussions of the formation and evolution of the disk system of the Milky Way.

  16. The nature of the interstellar medium of the starburst low-metallicity galaxy Haro 11: a multi-phase model of the infrared emission

    NASA Astrophysics Data System (ADS)

    Cormier, D.; Lebouteiller, V.; Madden, S. C.; Abel, N.; Hony, S.; Galliano, F.; Baes, M.; Barlow, M. J.; Cooray, A.; De Looze, I.; Galametz, M.; Karczewski, O. Ł.; Parkin, T. J.; Rémy, A.; Sauvage, M.; Spinoglio, L.; Wilson, C. D.; Wu, R.

    2012-12-01

    Context. The low-metallicity interstellar medium (ISM) is profoundly different from that of normal systems, being clumpy with low dust abundance and little CO-traced molecular gas. Yet many dwarf galaxies in the nearby universe are actively forming stars. As the complex ISM phases are spatially mixed with each other, detailed modeling is needed to understand the gas emission and subsequent composition and structure of the ISM. Aims: Our goal is to describe the multi-phase ISM of the infrared bright low-metallicity galaxy Haro 11, dissecting the photoionised and photodissociated gas components. Methods: We present observations of the mid-infrared and far-infrared fine-structure cooling lines obtained with the Spitzer/IRS and Herschel/PACS spectrometers. We use the spectral synthesis code Cloudy to methodically model the ionised and neutral gas from which these lines originate. Results: We find that the mid- and far-infrared lines account for ~1% of the total infrared luminosity LTIR, acting as major coolants of the gas. Haro 11 is undergoing a phase of intense star formation, as traced by the brightest line, [O iii] 88 μm, with L [O III] /LTIR ~ 0.3%, and high ratios of [Ne iii]/[Ne ii] and [S iv]/[S iii]. Due to their different origins, the observed lines require a multi-phase modeling comprising: a compact H ii region, dense fragmented photodissociation regions (PDRs), a diffuse extended low-ionisation/neutral gas which has a volume filling factor of at least 90%, and porous warm dust in proximity to the stellar source. For a more realistic picture of the ISM of Haro 11 we would need to model the clumpy source and gas structures. We combine these 4 model components to explain the emission of 17 spectral lines, investigate the global energy balance of the galaxy through its spectral energy distribution, and establish a phase mass inventory. While the ionic emission lines of Haro 11 essentially originate from the dense H ii region component, a diffuse low

  17. 30 CFR 57.22104 - Open flames (I-C mines).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Open flames (I-C mines). 57.22104 Section 57.22104 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL... mine opening is covered. The cover shall be a substantial material, such as metal or wood, topped...

  18. Color-Magnitude Diagram Constraints on the Metallicities, Ages, and Star Formation History of the Stellar Populations in the Carina Dwarf Spheroidal Galaxy

    NASA Astrophysics Data System (ADS)

    VandenBerg, Don A.; Stetson, Peter B.; Brown, Thomas M.

    2015-06-01

    Victoria-Regina isochrones for -0.4{\\mkern 1mu} ≤slant [α/Fe] ≤slant +0.4 and a wide range in [Fe/H], along with complementary zero-age horizontal branch (ZAHB) loci, have been applied to the color-magnitude diagram (CMD) of Carina. The color transformations that we have used have been “calibrated” so that isochrones provide excellent fits to the [{{(B-V)}0},{{M}V}] diagrams of M3 and M92 when well supported estimates of the globular cluster (GC) reddenings and metallicities are assumed. The adopted distance moduli, for both the GCs and Carina, are based on our ZAHB models, which are able to reproduce the old horizontal branch (HB) component (as well as the luminosity of the HB clump) of the dwarf spheroidal galaxy quite well—even if it spans a range in [Fe/H] of ˜1.5 dex, provided that [α/Fe] varies with [Fe/H] in approximately the way that has been derived spectroscopically. Ages derived here agree reasonably well with those found previously for the old and intermediate-age turnoff (TO) stars, as well as for the period of negligible star formation (SF) activity (˜6-10 Gyr ago). CMD simulations have been carried out for the faintest TO and subgiant stars. They indicate a clear preference for SF that lasted several Gyr instead of a short burst, with some indication that ages decrease with increasing [Fe/H]. In general, stellar models that assume spectroscopic metallicities provide satisfactory fits to the observations, including the thin giant branch of Carina, though higher oxygen abundances than those implied by the adopted values of [α/Fe] would have favorable consequences.

  19. The latest eruption of planetary nebula IC 2165

    NASA Astrophysics Data System (ADS)

    Bohigas, J.; Rodríguez, M.; Dufour, R. J.

    2013-10-01

    Open slit high dispersion spectroscopic observations of the inner region of planetary nebula (PN) IC 2165 indicate that the object has a relatively uniform and high electron temperature, with its density being much larger close to the PN nucleus. Abundances imply that it is a non-type I PN. Calcium and iron have been heavily depleted into grains. The ionized mass is at least ˜ 0.05 M_⊙. A photoionization model (CLOUDY, version 10.00) assuming an inverse square law for the density and abundances typical of a non-type I PN, produced a fair replica of the spectrum and of all electron density and temperature sensitive line ratios, but not of the global properties of this object. All evidence indicates that IC 2165 was produced by a metal poor 2 M_⊙ A5 V star that took off some 2×10^9 yr ago.

  20. HII regions in dwarf irregular galaxies of the local group

    NASA Technical Reports Server (NTRS)

    Hodge, Paul; Lee, Myung Gyoon

    1990-01-01

    Deep, narrowband H alpha Charge Coupled Device (CCD) surveys of HII regions were carried out in several dwarf irregular galaxies in and near the local group. Data are now complete for these galaxies: NGC 6822, GR 8, IC 10, IC 1613, Sextans A, Sextans B, and Sag Irr. Observations are complete for DDO 47, 53, 167, 168 and 187. Details of some of the results for the surveys completed so far are discussed. For NGC 6822, CCD survey at H alpha resulted in the detection of 145 HII regions in the local group irregular galaxy NGC 6822. Most of them are newly detected, faint surface-brightness objects. Positions, maps and dimensions are being published elsewhere. For GR 8, a deep narrowband H alpha imaging of the nearby dwarf irregular galaxy GR 8 revealed a total of 32 HII regions. Positions, H alpha luminosities, and sizes of these objects were determined. The H alpha luminosity function has the same shape as that for more luminous galaxies, except for size of sample effects. Most HII regions detected are at the very low luminosity end of the general luminosity function. For IC 10, a deep CCD narrowband H alpha imaging of the local group dwarf irregular galaxy IC 10 revealed a total of 144 HII regions. Positions, H alpha luminosities, and sizes of these objects were determined. The H alpha luminosity function has the same shape as that for more luminous galaxies.

  1. VizieR Online Data Catalog: Extremely metal-poor (XMP) galaxies in SDSS. II. (Almeida+, 2016)

    NASA Astrophysics Data System (ADS)

    Sanchez Almeida, J.; Perez-Montero, E.; Morales-Luis, A. B.; Munoz-Tunon, C.; Garcia-Benito, R.; Nuza, S. E.; Kitaura, F. S.

    2016-05-01

    First, we search for XMP candidates using the algorithm k-means (Sanchez Almeida et al. 2010ApJ...714..487S; Ordovas-Pascual & Sanchez Almeida 2014A&A...565A..53O). It leads to 1281 candidates. Then, we use the SDSS-DR7 spectra of the candidates to measure their integrated metallicity, which narrows down the list to 196 XMPs. We also include a second list (Table 2) with 332 potential XMPs that are selected under less restrictive noise constraints. (2 data files).

  2. I&C Modeling in SPAR Models

    SciTech Connect

    John A. Schroeder

    2012-06-01

    The Standardized Plant Analysis Risk (SPAR) models for the U.S. commercial nuclear power plants currently have very limited instrumentation and control (I&C) modeling [1]. Most of the I&C components in the operating plant SPAR models are related to the reactor protection system. This was identified as a finding during the industry peer review of SPAR models. While the Emergency Safeguard Features (ESF) actuation and control system was incorporated into the Peach Bottom Unit 2 SPAR model in a recent effort [2], various approaches to expend resources for detailed I&C modeling in other SPAR models are investigated.

  3. High performance MPEG-audio decoder IC

    NASA Technical Reports Server (NTRS)

    Thorn, M.; Benbassat, G.; Cyr, K.; Li, S.; Gill, M.; Kam, D.; Walker, K.; Look, P.; Eldridge, C.; Ng, P.

    1993-01-01

    The emerging digital audio and video compression technology brings both an opportunity and a new challenge to IC design. The pervasive application of compression technology to consumer electronics will require high volume, low cost IC's and fast time to market of the prototypes and production units. At the same time, the algorithms used in the compression technology result in complex VLSI IC's. The conflicting challenges of algorithm complexity, low cost, and fast time to market have an impact on device architecture and design methodology. The work presented in this paper is about the design of a dedicated, high precision, Motion Picture Expert Group (MPEG) audio decoder.

  4. SPROC: A multiple-processor DSP IC

    NASA Technical Reports Server (NTRS)

    Davis, R.

    1991-01-01

    A large, single-chip, multiple-processor, digital signal processing (DSP) integrated circuit (IC) fabricated in HP-Cmos34 is presented. The innovative architecture is best suited for analog and real-time systems characterized by both parallel signal data flows and concurrent logic processing. The IC is supported by a powerful development system that transforms graphical signal flow graphs into production-ready systems in minutes. Automatic compiler partitioning of tasks among four on-chip processors gives the IC the signal processing power of several conventional DSP chips.

  5. Local Group dwarf galaxies: nature and nurture

    NASA Astrophysics Data System (ADS)

    Sawala, Till; Scannapieco, Cecilia; White, Simon

    2012-02-01

    We investigate the formation and evolution of dwarf galaxies in a high-resolution, hydrodynamical cosmological simulation of a Milky Way sized halo and its environment. Our simulation includes gas cooling, star formation, supernova feedback, metal enrichment and ultraviolet heating. In total, 90 satellites and more than 400 isolated dwarf galaxies are formed in the simulation, allowing a systematic study of the internal and environmental processes that determine their evolution. We find that 95 per cent of satellite galaxies are gas free at z= 0, and identify three mechanisms for gas loss: supernova feedback, tidal stripping and photoevaporation due to re-ionization. Gas-rich satellite galaxies are only found with total masses above ˜5 × 109 M⊙. In contrast, for isolated dwarf galaxies, a total mass of ˜109 M⊙ constitutes a sharp transition; less massive galaxies are predominantly gas free at z= 0, more massive, isolated dwarf galaxies are often able to retain their gas. In general, we find that the total mass of a dwarf galaxy is the main factor which determines its star formation, metal enrichment and its gas content, but that stripping may explain the observed difference in gas content between field dwarf galaxies and satellites with total masses close to 109 M⊙. We also find that a morphological transformation via tidal stripping of infalling, luminous dwarf galaxies whose dark matter is less concentrated than their stars cannot explain the high total mass-to-light ratios of the faint dwarf spheroidal galaxies.

  6. Tidal Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Houck, James R.; Higdon, Sarah

    2004-09-01

    Tidal Dwarf Galaxies (TDG's) are formed from material stripped from the disks of spiral galaxies, which are undergoing tidal interactions with a nearby companion. These galaxies provide important clues to our understanding of galaxy formation, evolution and cosmic recycling. Using the IRS we will measure the star formation activity in 6 TDG candidates. We will measure the ionization state ( [NeII] 12.8 um, [NeIII] 15.6 um and [NeV] 14.3um and [OIV] 25.9 um), the density in the ionized gas ([SIII] 18.7um/33.5um), the PAH fractions at 5.5-9um and 11-12.2um and possibly (optimistic here!) molecular hydrogen emission form PDRs at H2 (S0) 28um and H2 (S1) at 17um. In addition to the IRS observations we will map both the Guitar and Stephan's Quintet with IRAC. This will enable us to compare the PAH fraction in the dwarf galaxy to that of its parent. Similarly we will compare our observation of the proposed TDG at the southern tip of NGC 4038 with the GT observations of the central region of the Antennae. This program compliments two existing GT programmes: 1) the high-Z program - these observations enable us to observe in fine detail the nearby/present day analogs of galaxy formation in the early universe. 2) Blue Compact Dwarf programme - On first inpsection BCD's and TDG's appear the same: BCDs are similar in size to TDG's, but TDG's may not have a large dark matter halo component (affecting the long term stability of an object) and BCD's typically have a much lower metallicity. We will be able to compare the star formation activity in terms of the ionization state and PAH fraction in the two galaxy types.

  7. Evidence for axisymmetric halos: The case of IC 2006

    NASA Astrophysics Data System (ADS)

    Franx, Marijn; van Gorkom, J. H.; de Zeeuw, Tim

    1994-12-01

    We present a new method to derive the shape of the potential from the velocity field of a gas ring, or a gas disk with a flat rotation curve. The method is an extension of previous work by Binney and Teuben, and it can detect deviations from axisymmetry at the level of a few percent. The velocity field of the ring or disk is expanded into harmonics, and we present analytic expressions which relate these harmonic terms to the intrinsic parameters, and the viewing angles. We show that both the velocity field and the geometry of the ring are necessary to give complete information on the shape of the potential in the plane of the ring. The velocity field alone gives incomplete information for small ellipticities. We present new neutral hydrogen data on the H I ring around the early-type galaxy IC 2006, which was discovered by Schweizer, van Gorkom, & Seitzer (1989). The new data show that the ring is filled and has a remarkably regular velocity field. Application of our method to this gas ring shows that the halo must be close to perfectly axisymmetric. We detect a nonsignificant ellipticity of the potential of 0.012 +/- 0.026. The 95% confidence limit on the ellipticity is 0.05. This implies that the potential is nearly circular in the plane of the ring. The analysis indicates that the circular velocity is nearly constant from 0.5 Re to 6.5 Re. We confirm that the M/L ration in the outer parts increases (Schweizer et al. 1989). The stellar component probably has a strong disk. The data demonstrate that galaxies other than spiral galaxies have massive halos. The inferred shape of the halo can be contrasted to the strongly triaxial halos found in simulations of dissipationless halo formation. As suggested by Katz & Gunn (1991), the inclusion of baryonic matter in the simulations may be necessary to resolve this issue.

  8. Galaxies on Top of Quasars: Probing Dwarf Galaxies in the SDSS

    NASA Astrophysics Data System (ADS)

    Straka, Lorrie; York, D. G.; Noterdaeme, P.; Srianand, R.; Bowen, D. V.; Khare, P.; Bishof, M.; Whichard, Z.; Kulkarni, V. P.

    2013-07-01

    Absorption lines from galaxies at intervening redshifts in quasar spectra are sensitive probes of metals and gas that are otherwise invisible due to distance or low surface brightness. However, in order to determine the environments these absorption lines arise in, we must detect these galaxies in emission as well. Galaxies on top of quasars (GOTOQs) are low-z galaxies found intervening with background quasars in the SDSS. These galaxies have been flagged for their narrow galactic emission lines present in quasar spectra in the SDSS. Typically, the low-z nature of these galaxies allows them to be easily detected in SDSS imaging. However, a number of GOTOQs (about 10%), despite being detected in spectral emission, are NOT seen in SDSS imaging. This implies that these may be dark galaxies, dwarf galaxies, or similarly low surface brightness galaxies. Additionally, about 25% of those detected in imaging are dwarf galaxies according to their L* values. Dwarf galaxies have long been underrepresented in observations compared to theory and are known to have large extents in dark matter. Given their prevalence here in our sample we must ask what role they play in quasar absorption line systems (QSOALS). Recent detections of 21-cm galaxies with few stars imply that aborted star formation in dark matter sub halos may produce QSOALS. Thus, this sub sample of galaxies offers a unique technique for probing dark and dwarf galaxies. The sample and its properties will be discussed, including star formation rates and dust estimates, as well as prospects for the future.