Radio Jets Clearing the Way Through a Galaxy: Watching Feedback in Action in the Seyfert Galaxy IC 5063

NASA Astrophysics Data System (ADS)

Morganti, R.; Oosterloo, T. A.; Oonk, J. B. R.; Frieswijk, W.; Tadhunter, C. N.

2015-12-01

High-resolution (0.5 arcsec) CO(2-1) observations performed with the Atacama Large Millimetre/submillimetre Array have been used to trace the kinematics of the molecular gas in the Seyfert 2 galaxy{IC 5063}. Although one of the most radio-loud Seyfert galaxy, IC 5063 is a relatively weak radio source (P1.4GHz=3 ×1023 W Hz-1). 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 W lobe. 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 suggests that most of the observed cold molecular outflow is due to fast cooling of the gas after the passage of a shock and that it is the end product of the cooling process.

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.

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

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.

Metal Abundances of KISS Galaxies. VI. New Metallicity Relations for the KISS Sample of Star-forming Galaxies

NASA Astrophysics Data System (ADS)

Hirschauer, Alec S.; Salzer, John J.; Janowiecki, Steven; Wegner, Gary A.

2018-02-01

We present updated metallicity relations for the spectral database of star-forming galaxies (SFGs) found in the KPNO International Spectroscopic Survey (KISS). New spectral observations of emission-line galaxies obtained from a variety of telescope facilities provide oxygen abundance information. A nearly fourfold increase in the number of KISS objects with robust metallicities relative to our previous analysis provides for an empirical abundance calibration to compute self-consistent metallicity estimates for all SFGs in the sample with adequate spectral data. In addition, a sophisticated spectral energy distribution fitting routine has provided robust calculations of stellar mass. With these new and/or improved galaxy characteristics, we have developed luminosity–metallicity (L–Z) relations, mass–metallicity (M *–Z) relations, and the so-called fundamental metallicity relation (FMR) for over 1450 galaxies from the KISS sample. This KISS M *–Z relation is presented for the first time and demonstrates markedly lower scatter than the KISS L–Z relation. We find that our relations agree reasonably well with previous publications, modulo modest offsets due to differences in the strong emission line metallicity calibrations used. We illustrate an important bias present in previous L–Z and M *–Z studies involving direct-method (T e ) abundances that may result in systematically lower slopes in these relations. Our KISS FMR shows consistency with those found in the literature, albeit with a larger scatter. This is likely a consequence of the KISS sample being biased toward galaxies with high levels of activity.

The new semi-analytic code GalICS 2.0 - reproducing the galaxy stellar mass function and the Tully-Fisher relation simultaneously

NASA Astrophysics Data System (ADS)

Cattaneo, A.; Blaizot, J.; Devriendt, J. E. G.; Mamon, G. A.; Tollet, E.; Dekel, A.; Guiderdoni, B.; Kucukbas, M.; Thob, A. C. R.

2017-10-01

GalICS 2.0 is a new semi-analytic code to model the formation and evolution of galaxies in a cosmological context. N-body simulations based on a Planck cosmology are used to construct halo merger trees, track subhaloes, compute spins and measure concentrations. The accretion of gas on to galaxies and the morphological evolution of galaxies are modelled with prescriptions derived from hydrodynamic simulations. Star formation and stellar feedback are described with phenomenological models (as in other semi-analytic codes). GalICS 2.0 computes rotation speeds from the gravitational potential of the dark matter, the disc and the central bulge. As the rotation speed depends not only on the virial velocity but also on the ratio of baryons to dark matter within a galaxy, our calculation predicts a different Tully-Fisher relation from models in which vrot ∝ vvir. This is why, GalICS 2.0 is able to reproduce the galaxy stellar mass function and the Tully-Fisher relation simultaneously. Our results are also in agreement with halo masses from weak lensing and satellite kinematics, gas fractions, the relation between star formation rate (SFR) and stellar mass, the evolution of the cosmic SFR density, bulge-to-disc ratios, disc sizes and the Faber-Jackson relation.

Survey of Water and Ammonia in Nearby Galaxies (SWAN): Resolved Ammonia Thermometry and Water and Methanol Masers in IC 342, NGC 6946, and NGC 2146

NASA Astrophysics Data System (ADS)

Gorski, Mark; Ott, Jürgen; Rand, Richard; Meier, David S.; Momjian, Emmanuel; Schinnerer, Eva

2018-04-01

The Survey of Water and Ammonia in Nearby galaxies (SWAN) studies atomic and molecular species across the nuclei of four star-forming galaxies: NGC 253, IC 342, NGC 6946, and NGC 2146. As part of this survey, we present Karl G. Jansky Very Large Array molecular line observations of three galaxies: IC 342, NGC 6946, and NGC 2146. NGC 253 is covered in a previous paper. These galaxies were chosen to span an order of magnitude in star formation rates and to select a variety of galaxy types. We target the metastable transitions of ammonia NH3(1, 1) to (5, 5), the 22 GHz water (H2O) (616–523) transition, and the 36.1 GHz methanol (CH3OH) (4‑1–30) transition. We use the NH3 metastable lines to perform thermometry of the dense molecular gas. We show evidence for uniform heating across the central kiloparsec of IC 342 with two temperature components for the molecular gas, similar to NGC 253, of 27 and 308 K, and that the dense molecular gas in NGC 2146 has a temperature <86 K. We identify two new water masers in IC 342, and one new water maser in each of NGC 6946 and NGC 2146. The two galaxies NGC 253 and NGC 2146, with the most vigorous star formation, host H2O kilomasers. Lastly, we detect the first 36 GHz CH3OH masers in IC 342 and NGC 6946. For the four external galaxies the total CH3OH luminosity in each galaxy suggests a correlation with galactic star formation rate, whereas the morphology of the emission is similar to that of HNCO, a weak shock tracer.

Origin of the Galaxy Mass-Metallicity-Star Formation Relation

NASA Astrophysics Data System (ADS)

Harwit, Martin; Brisbin, Drew

2015-02-01

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 × 109 to 6 × 1010 M ⊙. 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.

The beautiful side of IC 335

NASA Image and Video Library

2017-12-08

Hubble sees a galaxy 60 million light-years away This new NASA/ESA Hubble Space Telescope image shows the galaxy IC 335 in front of a backdrop of distant galaxies. IC 335 is part of a galaxy group containing three other galaxies, and located in the Fornax Galaxy Cluster 60 million light-years away. As seen in this image, the disk of IC 335 appears edge-on from the vantage point of Earth. This makes it harder for astronomers to classify it, as most of the characteristics of a galaxy’s morphology — the arms of a spiral or the bar across the center — are only visible on its face. Still, the 45 000 light-year-long galaxy could be classified as an S0 type. These lenticular galaxies are an intermediate state in galaxy morphological classification schemes between true spiral and elliptical galaxies. They have a thin stellar disk and a bulge, like spiral galaxies, but in contrast to typical spiral galaxies they have used up most of the interstellar medium. Only a few new stars can be created out of the material that is left and the star formation rate is very low. Hence, the population of stars in S0 galaxies consists mainly of aging stars, very similar to the star population in elliptical galaxies. As S0 galaxies have only ill-defined spiral arms they are easily mistaken for elliptical galaxies if they are seen inclined face-on or edge-on as IC 335 here. And indeed, despite the morphological differences between S0 and elliptical class galaxies, they share some common characteristics, like typical sizes and spectral features. Both classes are also deemed "early-type" galaxies, because they are evolving passively. However, while elliptical galaxies may be passively evolving when we observe them, they have usually had violent interactions with other galaxies in their past. In contrast, S0 galaxies are either aging and fading spiral galaxies, which never had any interactions with other galaxies, or they are the aging result of a single merger between two spiral galaxies

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.

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.

LOCAL TADPOLE GALAXIES: DYNAMICS AND METALLICITY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sanchez Almeida, J.; Munoz-Tunon, C.; Mendez-Abreu, J.

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 velocitymore » 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.« less

Metallicity of Young and Old Stars in Irregular Galaxies

NASA Astrophysics Data System (ADS)

Tikhonov, N. A.

2018-01-01

Based on archived images obtained with the Hubble Space Telescope, stellar photometry for 105 irregular galaxies has been conducted. We have shown the red supergiant and giant branches in the obtained Hertzsprung-Russel diagrams. Using the TRGB method, distances to galaxies and metallicity of red giants have been determined. The color index ( V - I) of the supergiant branch at the luminosity level M I = -7 was chosen as the metallicity index of red supergiants. For the galaxies under study, the diagrams have been built, in which the correlation can be seen between the luminosity of galaxies ( M B ) and metallicity of red giants and supergiants. The main source of variance of the results in the obtained diagrams is, in our opinion, uncertainty inmeasurements of galaxy luminosities and star-forming outburst. The relation between metallicity of young and old stars shows that main enrichment of galaxies with metals has taken place in the remote past. Deviations of some galaxies in the obtained relation can possibly be explained with the fall of the intergalactic gas on them, although, this inconsiderably affects metallicities of the stellar content.

“Direct” Gas-phase Metallicity in Local Analogs of High-redshift Galaxies: Empirical Metallicity Calibrations for High-redshift Star-forming Galaxies

NASA Astrophysics Data System (ADS)

Bian, Fuyan; Kewley, Lisa J.; Dopita, Michael A.

2018-06-01

We study the direct gas-phase oxygen abundance using the well-detected auroral line [O III]λ4363 in the stacked spectra of a sample of local analogs of high-redshift galaxies. These local analogs share the same location as z ∼ 2 star-forming galaxies on the [O III]λ5007/Hβ versus [N II]λ6584/Hα Baldwin–Phillips–Terlevich diagram. This type of analog has the same ionized interstellar medium (ISM) properties as high-redshift galaxies. We establish empirical metallicity calibrations between the direct gas-phase oxygen abundances (7.8< 12+{log}({{O}}/{{H}})< 8.4) and the N2 (log([N II]λ6584/Hα))/O3N2 (log(([O III]λ5007/Hβ)/([N II]λ6584/Hα))) indices in our local analogs. We find significant systematic offsets between the metallicity calibrations for our local analogs of high-redshift galaxies and those derived from the local H II regions and a sample of local reference galaxies selected from the Sloan Digital Sky Survey (SDSS). The N2 and O3N2 metallicities will be underestimated by 0.05–0.1 dex relative to our calibration, if one simply applies the local metallicity calibration in previous studies to high-redshift galaxies. Local metallicity calibrations also cause discrepancies of metallicity measurements in high-redshift galaxies using the N2 and O3N2 indicators. In contrast, our new calibrations produce consistent metallicities between these two indicators. We also derive metallicity calibrations for R23 (log(([O III]λλ4959,5007+[O II]λλ3726,3729)/Hβ)), O32(log([O III]λλ4959,5007/[O II]λλ3726,3729)), {log}([O III]λ5007/Hβ), and log([Ne III]λ3869/[O II]λ3727) indices in our local analogs, which show significant offset compared to those in the SDSS reference galaxies. By comparing with MAPPINGS photoionization models, the different empirical metallicity calibration relations in the local analogs and the SDSS reference galaxies can be shown to be primarily due to the change of ionized ISM conditions. Assuming that temperature structure

Evolved stars in the Local Group galaxies - II. AGB, RSG stars and dust production in IC10

NASA Astrophysics Data System (ADS)

Dell'Agli, F.; Di Criscienzo, M.; Ventura, P.; Limongi, M.; García-Hernández, D. A.; Marini, E.; Rossi, C.

2018-06-01

We study the evolved stellar population of the Local Group galaxy IC10, with the aim of characterizing the individual sources observed and to derive global information on the galaxy, primarily the star formation history and the dust production rate. To this aim, we use evolutionary sequences of low- and intermediate-mass (M < 8 M⊙) stars, evolved through the asymptotic giant branch phase, with the inclusion of the description of dust formation. We also use models of higher mass stars. From the analysis of the distribution of stars in the observational planes obtained with IR bands, we find that the reddening and distance of IC10 are E(B - V) = 1.85 mag and d = 0.77 Mpc, respectively. The evolved stellar population is dominated by carbon stars, that account for 40% of the sources brighter than the tip of the red giant branch. Most of these stars descend from ˜1.1 - 1.3 M⊙ progenitors, formed during the major epoch of star formation, which occurred ˜2.5 Gyr ago. The presence of a significant number of bright stars indicates that IC10 has been site of significant star formation in recent epochs and currently hosts a group of massive stars in the core helium-burning phase. Dust production in this galaxy is largely dominated by carbon stars; the overall dust production rate estimated is 7 × 10-6 M⊙/yr.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morales-Luis, A. B.; Almeida, J. Sánchez; Muñoz-Tuñón, C.

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 overestimatemore » 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.« less

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

2017-04-01

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 project, which include physically motivated models of the multiphase interstellar medium, 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 disc, 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 disc, 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.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kenney, Jeffrey D. P.; Geha, Marla; Jáchym, Pavel

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 peaksmore » 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.« less

The Shape of Extremely Metal-Poor Galaxies

NASA Astrophysics Data System (ADS)

Putko, Joseph; Sánchez Almeida, Jorge; Muñoz-Tuñón, Casiana; Elmegreen, Bruce; Elmegreen, Debra

2018-01-01

This work is the first study on the 3D shape of starbursting extremely metal-poor galaxies (XMPs; a galaxy is said to be an XMP if its ionized gas-phase metallicity is less than 1/10 the solar value). A few hundred XMPs have been identified in the local universe primarily through mining the spectroscopic catalog of the Sloan Digital Sky Survey (SDSS), and follow-up observations have shown that metallicity drops significantly at the starburst (compared to the quiescent component of the galaxy). As the timescale for gas mixing is short, the metal-poor gas triggering the starburst must have been accreted recently. This is strong observational evidence for the cold flow accretion predicted by cosmological models of galaxy formation, and, in this respect, XMPs seem to be the best local analogs of the very first galaxies.The ellipsoidal shape of a class of galaxies can be inferred from the observed axial ratio (q) distribution (q = minor axis/major axis) of a large sample of randomly-oriented galaxies. Fitting ellipses to 200 XMPs using r-band SDSS images, we observe that the axial ratio distribution falls off at q < ~0.4 and q > ~0.8, and we determine that these falloffs are not due to biases in the data. The falloff at low axial ratio indicates that the XMPs are thick for their size, and the falloff at high axial ratio suggests the vast majority of XMPs are triaxial. We also observe that smaller XMPs are thicker in proportion to their size, and it is expected that for decreasing galaxy size the ratio of random to rotational motions increases, which correlates with increasing relative thickness. The XMPs are low-redshift dwarf galaxies dominated by dark matter, and our results are compatible with simulations that have shown dark matter halos to be triaxial, with triaxial stellar distributions for low-mass galaxies and with triaxiality increasing over time. We will offer precise constraints on the 3D shape of XMPs via Bayesian analysis of our observed axial ratio

The Star Cluster System in the Local Group Starburst Galaxy IC 10

NASA Astrophysics Data System (ADS)

Lim, Sungsoon; Lee, Myung Gyoon

2015-05-01

We present a survey of star clusters in the halo of IC 10, a starburst galaxy in the Local Group, based on Subaru R-band images and NOAO Local Group Survey UBVRI images. We find five new star clusters. All of these star clusters are located far from the center of IC 10, while previously known star clusters are mostly located in the main body. Interestingly, the distribution of these star clusters shows an asymmetrical structure elongated along the east and southwest directions. We derive UBVRI photometry of 66 star clusters, including these new star clusters, as well as previously known star clusters. Ages of the star clusters are estimated from a comparison of their UBVRI spectral energy distribution with the simple stellar population models. We find that the star clusters in the halo are all older than 1 Gyr, while those in the main body have various ages, from very young (several Myr) to old (\\gt 1 Gyr). The young clusters (\\lt 10 Myr) are mostly located in the Hα emission regions and are concentrated on a small region at 2\\prime\\prime in the southeast direction from the galaxy center, while the old clusters are distributed in a wider area than the disk. Intermediate-age clusters (∼100 Myr) are found in two groups. One is close to the location of the young clusters and the other is at ∼ 4\\prime\\prime from the location of the young clusters. The latter may be related to past mergers or tidal interaction.

A New Approach for Simulating Galaxy Cluster Properties

NASA Astrophysics Data System (ADS)

Arieli, Y.; Rephaeli, Y.; Norman, M. L.

2008-08-01

We describe a subgrid model for including galaxies into hydrodynamical cosmological simulations of galaxy cluster evolution. Each galaxy construct—or galcon—is modeled as a physically extended object within which star formation, galactic winds, and ram pressure stripping of gas are modeled analytically. Galcons are initialized at high redshift (z ~ 3) after galaxy dark matter halos have formed but before the cluster has virialized. Each galcon moves self-consistently within the evolving cluster potential and injects mass, metals, and energy into intracluster (IC) gas through a well-resolved spherical interface layer. We have implemented galcons into the Enzo adaptive mesh refinement code and carried out a simulation of cluster formation in a ΛCDM universe. With our approach, we are able to economically follow the impact of a large number of galaxies on IC gas. We compare the results of the galcon simulation with a second, more standard simulation where star formation and feedback are treated using a popular heuristic prescription. One advantage of the galcon approach is explicit control over the star formation history of cluster galaxies. Using a galactic SFR derived from the cosmic star formation density, we find the galcon simulation produces a lower stellar fraction, a larger gas core radius, a more isothermal temperature profile, and a flatter metallicity gradient than the standard simulation, in better agreement with observations.

The Near-infrared Tip of the Red Giant Branch. I. A Calibration in the Isolated Dwarf Galaxy IC 1613

NASA Astrophysics Data System (ADS)

Madore, Barry F.; Freedman, Wendy L.; Hatt, Dylan; Hoyt, Taylor J.; Monson, Andrew J.; Beaton, Rachael L.; Rich, Jeffrey A.; Jang, In Sung; Lee, Myung Gyoon; Scowcroft, Victoria; Seibert, Mark

2018-05-01

Based on observations from the FourStar near-infrared camera on the 6.5 m Baade-Magellan telescope at Las Campanas, Chile, we present calibrations of the JHK luminosities of stars defining the tip of the red giant branch (TRGB) in the halo of the Local Group dwarf galaxy IC 1613. We employ metallicity-independent (rectified) T-band magnitudes—constructed using J-, H-, and K-band magnitudes and both (J ‑ H) and (J ‑ K) colors to flatten the upward-sloping red giant branch tips as otherwise seen in their apparent color–magnitude diagrams. We describe and quantify the advantages of working at these particular near-infrared wavelengths, which are applicable to both the Hubble Space Telescope (HST) and the James Webb Space Telescope (JWST). We also note that these same wavelengths can be accessed from the ground for an eventual tie-in to Gaia for absolute astrometry and parallaxes to calibrate the intrinsic luminosity of the TRGB. Adopting the color terms derived from the IC 1613 data, as well as the zero points from a companion study of the Large Magellanic Cloud, whose distance is anchored to the geometric distances of detached eclipsing binaries, we find a true distance modulus of 24.32 ± 0.02 (statistical) ±0.05 mag (systematic) for IC 1613, which compares favorably with the recently published multi-wavelength, multi-method consensus modulus of 24.30 ± 0.05 mag by Hatt et al.

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.

AGB stars as tracers to IC 1613 evolution.

NASA Astrophysics Data System (ADS)

Hashemi, S. A.; Javadi, A.; van Loon, J. Th.

We are going to apply AGB stars to find star formation history for IC 1613 galaxy; this a new and simple method that works well for nearby galaxies. IC 1613 is a Local Group dwarf irregular galaxy that is located at distance of 750 kpc, a gas rich and isolated dwarf galaxy that has a low foreground extinction. We use the long period variable stars (LPVs) that represent the very final stage of evolution of stars with low and intermediate mass at the AGB phase and are very luminous and cool so that they emit maximum brightness in near-infrared bands. Thus near-infrared photometry with using stellar evolutionary models help us to convert brightness to birth mass and age and from this drive star formation history of the galaxy. We will use the luminosity distribution of the LPVs to reconstruct the star formation history-a method we have successfully applied in other Local Group galaxies. Our analysis shows that the IC 1613 has had a nearly constant star formation rate, without any dominant star formation episode.

Metallicity inhomogeneities in local star-forming galaxies as a sign of recent metal-poor gas accretion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sánchez Almeida, J.; Morales-Luis, A. B.; Muñoz-Tuñón, C.

2014-03-01

We measure the oxygen metallicity of the ionized gas along the major axis of seven dwarf star-forming galaxies. Two of them, SDSSJ1647+21 and SDSSJ2238+14, show ≅0.5 dex metallicity decrements in inner regions with enhanced star formation activity. This behavior is similar to the metallicity drop observed in a number of local tadpole galaxies by Sánchez Almeida et al., and was interpreted as showing early stages of assembling in disk galaxies, with the star formation sustained by external metal-poor gas accretion. The agreement with tadpoles has several implications. (1) It proves that galaxies other than the local tadpoles present the samemore » unusual metallicity pattern. (2) Our metallicity inhomogeneities were inferred using the direct method, thus discarding systematic errors usually attributed to other methods. (3) Taken together with the tadpole data, our findings suggest a threshold around one-tenth the solar value for the metallicity drops to show up. Although galaxies with clear metallicity drops are rare, the physical mechanism responsible for them may sustain a significant part of the star formation activity in the local universe. We argue that the star formation dependence of the mass-metallicity relationship, as well as other general properties followed by most local disk galaxies, is naturally interpreted as side effects of pristine gas infall. Alternatives to the metal-poor gas accretion are examined as well.« less

Nebular Metallicities in Two Isolated Local Void Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Nicholls, David C.; Jerjen, Helmut; Dopita, Michael A.; Basurah, Hassan

2014-01-01

Isolated dwarf galaxies, especially those situated in voids, may provide insight into primordial conditions in the universe and the physical processes that govern star formation in undisturbed stellar systems. The metallicity of H II regions in such galaxies is key to investigating this possibility. From the SIGRID sample of isolated dwarf galaxies, we have identified two exceptionally isolated objects, the Local Void galaxy [KK98]246 (ESO 461-G036) and another somewhat larger dwarf irregular on the edge of the Local Void, MCG-01-41-006 (HIPASS J1609-04). We report our measurements of the nebular metallicities in these objects. The first object has a single low luminosity H II region, while the second is in a more vigorous star forming phase with several bright H II regions. We find that the metallicities in both galaxies are typical for galaxies of this size, and do not indicate the presence of any primordial gas, despite (for [KK98]246) the known surrounding large reservoir of neutral hydrogen.

Estimating precise metallicity and stellar mass evolution of galaxies

NASA Astrophysics Data System (ADS)

Mosby, Gregory

2018-01-01

The evolution of galaxies can be conveniently broken down into the evolution of their contents. The changing dust, gas, and stellar content in addition to the changing dark matter potential and periodic feedback from a super-massive blackhole are some of the key ingredients. We focus on the stellar content that can be observed, as the stars reflect information about the galaxy when they were formed. We approximate the stellar content and star formation histories of unresolved galaxies using stellar population modeling. Though simplistic, this approach allows us to reconstruct the star formation histories of galaxies that can be used to test models of galaxy formation and evolution. These models, however, suffer from degeneracies at large lookback times (t > 1 Gyr) as red, low luminosity stars begin to dominate a galaxy’s spectrum. Additionally, degeneracies between stellar populations at different ages and metallicities often make stellar population modeling less precise. The machine learning technique diffusion k-means has been shown to increase the precision in stellar population modeling using a mono-metallicity basis set. However, as galaxies evolve, we expect the metallicity of stellar populations to vary. We use diffusion k-means to generate a multi-metallicity basis set to estimate the stellar mass and chemical evolution of unresolved galaxies. Two basis sets are formed from the Bruzual & Charlot 2003 and MILES stellar population models. We then compare the accuracy and precision of these models in recovering complete (stellar mass and metallicity) histories of mock data. Similarities in the groupings of stellar population spectra in the diffusion maps for each metallicity hint at fundamental age transitions common to both basis sets that can be used to identify stellar populations in a given age range.

Metallic Winds in Dwarf Galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

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, andmore » 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.« less

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

Environmental Effects on the Metallicities of Early-Type Galaxies

NASA Technical Reports Server (NTRS)

Oliversen, Ronald J. (Technical Monitor); Jones, Christine

2004-01-01

In this multi-year project to investigate the metal enrichment of early-type galaxies, we have used ROSAT, ASCA and now Chandra observations to study samples of galaxies. We have published two papers and a third paper that incorporates Chandra archival observations is nearing completion. Below, we briefly describe our findings. Our first paper "SN IA Enrichment in Virgo Early-type Galaxies from ROSAT and ASCA Observations" was published in the Astrophysical Journal (vol 539, 603) reported on the properties of nine X-ray bright elliptical galaxies in the Virgo cluster observed by ROSAT and ASCA. We measured iron abundance gradients as a function of radius in three galaxies. We found that the magnesium and silicon abundance gradients were in general flatter than those of iron. We suggest this is due to a metallicity dependence in the metal production rates of SN Ia's. We calculate SN Ia rates in the center of these galaxies that are comparable to those measured optically. Our second paper "ASCA Observations of Groups at Radii of Low Overdensity: Implications for Cosmic Preheating" also was published in the Astrophysical Journal (vol 578, 74). This paper reported on the ASCA spectroscopy of nine groups of galaxies. We found that the entropy profile in groups is driven by nongravitational heating processes, and could be explained by a short period of preheating by galactic winds. The third paper (in preparation) uses a sample of about 200 galaxies from both ROSAT and Chandra observations. In this paper we characterize both the nuclear and the extended X-ray emission for this sample. We will use these observations to determine the "on-time" of the X-ray emitting AGN and the fraction of "fossil groups" as well as to investigate how large AGN outbursts can sweep the galaxy of its hot ISM, thus leading to changes in the ISM metal enrichment.

The host of the Type I SLSN 2017egm. A young, sub-solar metallicity environment in a massive spiral galaxy

NASA Astrophysics Data System (ADS)

Izzo, L.; Thöne, C. C.; García-Benito, R.; de Ugarte Postigo, A.; Cano, Z.; Kann, D. A.; Bensch, K.; Della Valle, M.; Galadí-Enríquez, D.; Hedrosa, R. P.

2018-02-01

Context. Type I superluminous supernova (SLSN) host galaxies are predominantly low-metallicity, highly star-forming (SF) dwarfs. One of the current key questions is whether Type I SLSNe can only occur in such environments and hosts. Aims: Here we present an integral-field study of the massive, high-metallicity spiral NGC 3191, the host of SN 2017egm, the closest Type I SLSN known to date. We use data from PMAS/CAHA and the public MaNGA survey to shed light on the properties of the SLSN site and the origin of star formation in this non-starburst spiral galaxy. Methods: We map the physical properties of different H II regions throughout the galaxy and characterise their stellar populations using the STARLIGHT fitting code. Kinematical information allows us to study a possible interaction with its neighbouring galaxy as the origin of recent star formation activity which could have caused the SLSN. Results: NGC 3191 shows intense star formation in the western part with three large SF regions of low metallicity. Taking only the properties of emitting gas, the central regions of the host have a higher metallicity, a lower specific star formation rate, and lower ionisation. Modelling the stellar populations gives a different picture: the SLSN region has two dominant stellar populations with different ages, the younger one with an age of 2-10 Myr and lower metallicity, likely the population from which the SN progenitor originated. Emission line kinematics of NGC 3191 show indications of interaction with its neighbour MCG+08-19-017 at 45 kpc, which might be responsible for the recent starburst. In fact, this galaxy pair has hosted a total of four SNe, 1988B (Type Ia), SN 2003ds (Type Ic in MCG+08-19-017), PTF10bgl (Type II), and 2017egm, underlying the enhanced SF in both galaxies due to interaction. Conclusions: Our study shows that care should be taken when interpreting global host and even gas properties without looking at the stellar population history of the region

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

Galaxy And Mass Assembly (GAMA): the connection between metals, specific SFR and H I gas in galaxies: the Z-SSFR relation

NASA Astrophysics Data System (ADS)

Lara-López, M. A.; Hopkins, A. M.; López-Sánchez, A. R.; Brough, S.; Colless, M.; Bland-Hawthorn, J.; Driver, S.; Foster, C.; Liske, J.; Loveday, J.; Robotham, A. S. G.; Sharp, R. G.; Steele, O.; Taylor, E. N.

2013-06-01

We study the interplay between gas phase metallicity (Z), specific star formation rate (SSFR) and neutral hydrogen gas (H I) for galaxies of different stellar masses. Our study uses spectroscopic data from Galaxy and Mass Assembly and Sloan Digital Sky Survey (SDSS) star-forming galaxies, as well as H I detection from the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) and Galex Arecibo SDSS Survey (GASS) public catalogues. We present a model based on the Z-SSFR relation that shows that at a given stellar mass, depending on the amount of gas, galaxies will follow opposite behaviours. Low-mass galaxies with a large amount of gas will show high SSFR and low metallicities, while low-mass galaxies with small amounts of gas will show lower SSFR and high metallicities. In contrast, massive galaxies with a large amount of gas will show moderate SSFR and high metallicities, while massive galaxies with small amounts of gas will show low SSFR and low metallicities. Using ALFALFA and GASS counterparts, we find that the amount of gas is related to those drastic differences in Z and SSFR for galaxies of a similar stellar mass.

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.

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.

Mass-metallicity relation for AKARI-FMOS infrared luminous galaxies at z ~ 0.9

NASA Astrophysics Data System (ADS)

Oi, Nagisa; Matsuhara, Hideo; Goto, Tomotsugu; Pearson, Chris; Buat, Véronique; Malkan, Matthew A.

We study the mass-metallicity relation and fundamental relation (FMR) for infrared bright galaxies (IR galaxies) at z ~ 0.9 discovered by AKARI NEP-Deep survey. The main result of this work is that metallicity of IR galaxies surprisingly match optical selected galaxies at a given mass even their star formation rates are different, which may imply that optical and IR selected galaxies follow similar star formation histories, and the starbursts in the IR galaxies do not give a strong impact in changing metallicity because of the short duration time.

The Universal Stellar Mass-Stellar Metallicity Relation for Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Kirby, Evan N.; Cohen, Judith G.; Guhathakurta, Puragra; Cheng, Lucy; Bullock, James S.; Gallazzi, Anna

2013-12-01

We present spectroscopic metallicities of individual stars in seven gas-rich dwarf irregular galaxies (dIrrs), and we show that dIrrs obey the same mass-metallicity relation as the dwarf spheroidal (dSph) satellites of both the Milky Way and M31: Z_* \\propto M_*^{0.30+/- 0.02}. The uniformity of the relation is in contradiction to previous estimates of metallicity based on photometry. This relationship is roughly continuous with the stellar mass-stellar metallicity relation for galaxies as massive as M * = 1012 M ⊙. Although the average metallicities of dwarf galaxies depend only on stellar mass, the shapes of their metallicity distributions depend on galaxy type. The metallicity distributions of dIrrs resemble simple, leaky box chemical evolution models, whereas dSphs require an additional parameter, such as gas accretion, to explain the shapes of their metallicity distributions. Furthermore, the metallicity distributions of the more luminous dSphs have sharp, metal-rich cut-offs that are consistent with the sudden truncation of star formation due to ram pressure stripping. 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 Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Metallicities of z ~2 Galaxies From the 3D-HST Survey

NASA Astrophysics Data System (ADS)

Hernandez, Betsy; Momcheva, Ivelina; 3D-HST team

2018-01-01

The metal content of the gas in galaxies as a function of cosmic time is a measure of the exchange of gas between the galaxy and its environment. Understanding its evolution is central to understanding the physical processes that govern the efficiency and timing of star formation in galaxies. Our sample consists of 127 galaxies from the 3D-HST survey with individually detected spectral lines at z~2. We perform a comparison of line ratios that serve as proxies for the ionization parameter and oxygen abundance (O32 and R23 respectively) between the 3D-HST sample and SDSS galaxies at z~0. We examine the mass-metallicity relation of the 3D-HST sample, deriving the metallicity using O32 and R23, based on the Kobulnicky & Kewley models. Results from the O32 versus R23 comparison in the 3D-HST sample yield a similar distribution to recent high redshift samples. The mass-metallicity (MZ) relation shows the majority of 3D-HST metallicity values fall within previous MZ relation results.

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.

The Origin of the Relation between Metallicity and Size in Star-forming Galaxies

NASA Astrophysics Data System (ADS)

Sánchez Almeida, J.; Dalla Vecchia, C.

2018-06-01

For the same stellar mass, physically smaller star-forming galaxies are also metal richer. What causes the relation remains unclear. The central star-forming galaxies in the EAGLE cosmological numerical simulation reproduce the observed trend. We use them to explore the origin of the relation assuming that the physical mechanism responsible for the anticorrelation between size and gas-phase metallicity is the same in the simulated and the observed galaxies. We consider the three most likely causes: (1) metal-poor gas inflows feeding the star formation (SF) process, (2) metal-rich gas outflows particularly efficient in shallow gravitational potentials, and (3) enhanced efficiency of the SF process in compact galaxies. Outflows (cause 2) and enhanced SF efficiency (cause 3) can be discarded. Metal-poor gas inflows (cause 1) produce the correlation in the simulated galaxies. Galaxies grow in size with time, so those that receive gas later are both metal poorer and larger, giving rise to the observed anticorrelation. As expected within this explanation, larger galaxies have younger stellar populations. We explore the variation with redshift of the relation, which is maintained up to, at least, redshift 8.

The jet-ISM interactions in IC 5063

NASA Astrophysics Data System (ADS)

Mukherjee, Dipanjan; Wagner, Alexander Y.; Bicknell, Geoffrey V.; Morganti, Raffaella; Oosterloo, Tom; Nesvadba, Nicole; Sutherland, Ralph S.

2018-05-01

The interstellar medium of the radio galaxy IC 5063 is highly perturbed by an AGN jet expanding in the gaseous disc of the galaxy. We model this interaction with relativistic hydrodynamic simulations and multiphase initial conditions for the interstellar medium and compare the results with recent observations. As the jets flood through the intercloud channels of the disc, they ablate, accelerate, and disperse clouds to velocities exceeding 400 km s-1. Clouds are also destroyed or displaced in bulk from the central regions of the galaxy. Our models with jet powers of 1044 and 1045 erg s-1 are capable of reproducing many of the observed features in the position velocity diagram of IC 5063, and confirm the notion that the jet is responsible for the strongly perturbed gas dynamics seen in the ionized, neutral, and molecular gas phases. In our simulations, we also see strong venting of the jet plasma perpendicular to the disc, which entrains clumps and diffuse filaments into the halo of the galaxy. Our simulations are the first 3D hydrodynamic simulations of the jet and interstellar matter of IC 5063.

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).

Revealing the nebular properties and Wolf-Rayet population of IC10 with Gemini/GMOS

NASA Astrophysics Data System (ADS)

Tehrani, Katie; Crowther, Paul A.; Archer, I.

2017-12-01

We present a deep imaging and spectroscopic survey of the Local Group irregular galaxy IC10 using Gemini North and GMOS to unveil its global Wolf-Rayet (WR) population. We obtain a star formation rate (SFR) of 0.045 ± 0.023 M⊙ yr-1, for IC10 from the nebular H α luminosity, which is comparable to the Small Magellanic Cloud. We also present a revised nebular oxygen abundance of log(O/H) + 12 = 8.40 ± 0.04, comparable to the LMC. It has previously been suggested that for IC10 to follow the WR subtype-metallicity dependance seen in other Local Group galaxies, a large WN population awaits discovery. Our search revealed three new WN stars, and six candidates awaiting confirmation, providing little evidence to support this claim. The new global WR star total of 29 stars is consistent with the Large Magellanic Cloud population when scaled to the reduced SFR of IC10. For spectroscopically confirmed WR stars, the WC/WN ratio is lowered to 1.0; however, including all potential candidates, and assuming those unconfirmed to be WN stars, would reduce the ratio to ∼0.7. We attribute the high WC/WN ratio to the high star formation surface density of IC10 relative to the Magellanic Clouds, which enhances the frequency of high-mass stars capable of producing WC stars.

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.

First gas-phase metallicity gradients of 0.1 ≲ z ≲ 0.8 galaxies with MUSE

NASA Astrophysics Data System (ADS)

Carton, David; Brinchmann, Jarle; Contini, Thierry; Epinat, Benoît; Finley, Hayley; Richard, Johan; Patrício, Vera; Schaye, Joop; Nanayakkara, Themiya; Weilbacher, Peter M.; Wisotzki, Lutz

2018-05-01

Galaxies at low-redshift typically possess negative gas-phase metallicity gradients (centres more metal-rich than their outskirts). Whereas, it is not uncommon to observe positive metallicity gradients in higher-redshift galaxies (z ≳ 0.6). Bridging these epochs, we present gas-phase metallicity gradients of 84 star-forming galaxies between 0.08 < z < 0.84. Using the galaxies with reliably determined metallicity gradients, we measure the median metallicity gradient to be negative (-0.039^{+0.007}_{-0.009} dex/kpc). Underlying this, however, is significant scatter: (8 ± 3)% [7] of galaxies have significantly positive metallicity gradients, (38 ± 5)% [32] have significantly negative gradients, (31 ± 5)% [26] have gradients consistent with being flat. (The remaining (23 ± 5)% [19] have unreliable gradient estimates.) We notice a slight trend for a more negative metallicity gradient with both increasing stellar mass and increasing star formation rate (SFR). However, given the potential redshift and size selection effects, we do not consider these trends to be significant. Indeed, once we normalize the SFR relative to that of the main sequence, we do not observe any trend between the metallicity gradient and the normalized SFR. This is contrary to recent studies of galaxies at similar and higher redshifts. We do, however, identify a novel trend between the metallicity gradient of a galaxy and its size. Small galaxies (rd < 3 kpc) present a large spread in observed metallicity gradients (both negative and positive gradients). In contrast, we find no large galaxies (rd > 3 kpc) with positive metallicity gradients, and overall there is less scatter in the metallicity gradient amongst the large galaxies. These large (well-evolved) galaxies may be analogues of present-day galaxies, which also show a common negative metallicity gradient.

Cosmic evolution and metal aversion in superluminous supernova host galaxies

NASA Astrophysics Data System (ADS)

Schulze, S.; Krühler, T.; Leloudas, G.; Gorosabel, J.; Mehner, A.; Buchner, J.; Kim, S.; Ibar, E.; Amorín, R.; Herrero-Illana, R.; Anderson, J. P.; Bauer, F. E.; Christensen, L.; de Pasquale, M.; de Ugarte Postigo, A.; Gallazzi, A.; Hjorth, J.; Morrell, N.; Malesani, D.; Sparre, M.; Stalder, B.; Stark, A. A.; Thöne, C. C.; Wheeler, J. C.

2018-01-01

The SUperluminous Supernova Host galaxIES survey aims to provide strong new constraints on the progenitors of superluminous supernovae (SLSNe) by understanding the relationship to their host galaxies. We present the photometric properties of 53 H-poor and 16 H-rich SLSN host galaxies out to z ∼ 4. We model their spectral energy distributions to derive physical properties, which we compare with other galaxy populations. At low redshift, H-poor SLSNe are preferentially found in very blue, low-mass galaxies with high average specific star formation rates. As redshift increases, the host population follows the general evolution of star-forming galaxies towards more luminous galaxies. After accounting for secular evolution, we find evidence for differential evolution in galaxy mass, but not in the B band and the far-ultraviolet luminosity (3σ confidence). Most remarkable is the scarcity of hosts with stellar masses above 1010 M⊙ for both classes of SLSNe. In case of H-poor SLSNe, we attribute this to a stifled production efficiency above ∼0.4 solar metallicity. However, we argue that, in addition to low metallicity, a short-lived stellar population is also required to regulate the SLSN production. H-rich SLSNe are found in a very diverse population of star-forming galaxies. Still, the scarcity of massive hosts suggests a stifled production efficiency above ∼0.8 solar metallicity. The large dispersion of the H-rich SLSNe host properties is in stark contrast to those of gamma-ray burst, regular core-collapse SN, and H-poor SLSNe host galaxies. We propose that multiple progenitor channels give rise to this subclass.

Rapid and multiband variability of the TeV bright active nucleus of the galaxy IC 310

DOE PAGES

Aleksić, J.; Antonelli, L. A.; Antoranz, P.; ...

2014-03-14

Recently the radio galaxy IC 310 was identified as a γ-ray emitter based on observations at GeV energies with Fermi-LAT and at very high energies (VHE, E > 100 GeV) with the MAGIC telescopes. Originally classified as a head-tail radio galaxy, the nature of this object is subject of controversy since its nucleus shows blazar-like behavior. In order to understand the nature of IC 310 and the origin of the VHE emission, we studied the spectral and flux variability of IC 310 from the X-ray band to the VHE γ-ray regime. The light curve of IC 310 above 300 GeVmore » has been measured with the MAGIC telescopes from 2009 October to 2010 February. Contemporaneous Fermi-LAT data (2008-2011) in the 10-500 GeV energy range were also analyzed. In the X-ray regime, archival observations from 2003 to 2007 with XMM-Newton, Chandra, and Swift-XRT in the 0.5-10 keV band were studied. The VHE light curve reveals several high-amplitude and short-duration flares. Day-to-day flux variability is clearly present (>5σ). The photon index between 120 GeV and 8 TeV remains at the value Γ ~ 2.0 during both low and high flux states. The VHE spectral shape does not show significant variability, whereas the flux at 1 TeV changes by a factor of ~7. Fermi-LAT detected only eight γ-ray events in the energy range 10 GeV–500 GeV in three years of observation. Moreover, the measured photon index of Γ = 1.3 ± 0.5 in the Fermi-LAT range is very hard. The X-ray measurements show strong variability in both flux and photon index. The latter varied from 1.76 ± 0.07 to 2.55 ± 0.07. The rapid variability measured in γ-rays and X-rays confirms the blazar-like behavior of IC 310. The multi-TeV γ-ray emission seems to originate from scales of less than 80 Schwarzschild radii (for a black hole mass of 2 × 10 8 M⊙) within the compact core of its FR I radio jet with orientation angle 10°-38°. The spectral energy distribution resembles that of an extreme blazar, albeit the luminosity is more than

X-ray binary formation in low-metallicity blue compact dwarf galaxies

NASA Astrophysics Data System (ADS)

Brorby, M.; Kaaret, P.; Prestwich, A.

2014-07-01

X-rays from binaries in small, metal-deficient galaxies may have contributed significantly to the heating and reionization of the early Universe. We investigate this claim by studying blue compact dwarfs (BCDs) as local analogues to these early galaxies. We constrain the relation of the X-ray luminosity function (XLF) to the star formation rate (SFR) using a Bayesian approach applied to a sample of 25 BCDs. The functional form of the XLF is fixed to that found for near-solar metallicity galaxies and is used to find the probability distribution of the normalization that relates X-ray luminosity to SFR. Our results suggest that the XLF normalization for low-metallicity BCDs (12+log(O/H) < 7.7) is not consistent with the XLF normalization for galaxies with near-solar metallicities, at a confidence level 1-5 × 10- 6. The XLF normalization for the BCDs is found to be 14.5± 4.8 ({M}_{⊙}^{-1} yr), a factor of 9.7 ± 3.2 higher than for near-solar metallicity galaxies. Simultaneous determination of the XLF normalization and power-law index result in estimates of q = 21.2^{+12.2}_{-8.8} ({M}_{⊙}^{-1} yr) and α = 1.89^{+0.41}_{-0.30}, respectively. Our results suggest a significant enhancement in the population of high-mass X-ray binaries in BCDs compared to the near-solar metallicity galaxies. This suggests that X-ray binaries could have been a significant source of heating in the early Universe.

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.

Broad-line Type Ic supernova SN 2014ad

NASA Astrophysics Data System (ADS)

Sahu, D. K.; Anupama, G. C.; Chakradhari, N. K.; Srivastav, S.; Tanaka, Masaomi; Maeda, Keiichi; Nomoto, Ken'ichi

2018-04-01

We present optical and ultraviolet photometry and low-resolution optical spectroscopy of the broad-line Type Ic supernova SN 2014ad in the galaxy PGC 37625 (Mrk 1309), covering the evolution of the supernova during -5 to +87 d with respect to the date of maximum in the B band. A late-phase spectrum obtained at +340 d is also presented. With an absolute V-band magnitude at peak of MV = -18.86 ± 0.23 mag, SN 2014ad is fainter than supernovae associated with gamma ray bursts (GRBs), and brighter than most of the normal and broad-line Type Ic supernovae without an associated GRB. The spectral evolution indicates that the expansion velocity of the ejecta, as measured using the Si II line, is as high as ˜33 500 km s-1 around maximum, while during the post-maximum phase it settles at ˜15 000 km s-1. The expansion velocity of SN 2014ad is higher than that of all other well-observed broad-line Type Ic supernovae except for the GRB-associated SN 2010bh. The explosion parameters, determined by applying Arnett's analytical light-curve model to the observed bolometric light-curve, indicate that it was an energetic explosion with a kinetic energy of ˜(1 ± 0.3) × 1052 erg and a total ejected mass of ˜(3.3 ± 0.8) M⊙, and that ˜0.24 M⊙ of 56Ni was synthesized in the explosion. The metallicity of the host galaxy near the supernova region is estimated to be ˜0.5 Z⊙.

The Leoncino Dwarf: The Lowest Metallicity Star-Forming Galaxy in the Nearby Universe

NASA Astrophysics Data System (ADS)

McQuinn, Kristen

2017-08-01

Extremely metal-poor (XMP) galaxies are dwarf irregular galaxies with very low metallicities, traced by their gas-phase oxygen abundance. Galaxy evolution scenarios suggest three pathways to form an XMP: (1) secular evolution at low galaxy masses, (2) slow evolution in voids, or (3) dilution of measured abundances from infall of pristine gas. These scenarios have proven challenging to test because, despite concerted efforts, XMP galaxies in the nearby universe have proven hard to find. A notable exception is the recently discovered dwarf galaxy Leoncino. Leoncino has the lowest gas-phase oxygen abundance ever measured in a galaxy in the local Universe. From optical spectroscopy, the oxygen abundance is 12+log(O/H)=7.02+/-0.03, more than 40% lower than the iconic low-metallicity galaxy I Zw 18 and less than 2% Z_sun. Despite a precision oxygen abundance measurement, the evolutionary context of Leoncino remains uncertain without a secure distance. We propose HST WFC3 high-resolution optical imaging of Leoncino to accurately measure the distance to the galaxy using the tip of the red giant branch (TRGB) method. The distance will determine whether Leoncino is located in a typical field environment or in a void, and whether the galaxy is consistent with the luminosity-metallicity relation at low galaxy masses. The detailed study of Leoncino will provide benchmark results for future XMP discoveries in the nearby Universe, and an exceptionally timely comparison for studies of chemically primitive, high-redshift galaxies that will be observable in the JWST era.

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

On the Kennicutt-Schmidt Relation of Low-Metallicity High-Redshift Galaxies

NASA Astrophysics Data System (ADS)

Gnedin, Nickolay Y.; Kravtsov, Andrey V.

2010-05-01

We present results of self-consistent, high-resolution cosmological simulations of galaxy formation at z ~ 3. The simulations employ a recently developed recipe for star formation based on the local abundance of molecular hydrogen, which is tracked self-consistently during the course of simulation. The phenomenological H2 formation model accounts for the effects of dissociating UV radiation of stars in each galaxy, as well as self-shielding and shielding of H2 by dust, and therefore allows us to explore effects of lower metallicities and higher UV fluxes prevalent in high-redshift galaxies on their star formation. We compare stellar masses, metallicities, and star formation rates of the simulated galaxies to available observations of the Lyman break galaxies (LBGs) and find a reasonable agreement. We find that the Kennicutt-Schmidt (KS) relation exhibited by our simulated galaxies at z ≈ 3 is substantially steeper and has a lower amplitude than the z = 0 relation at ΣH <~ 100 M odot pc-2. The predicted relation, however, is consistent with existing observational constraints for the z ≈ 3 damped Lyα and LBGs. Our tests show that the main reason for the difference from the local KS relation is lower metallicity of the interstellar medium in high-redshift galaxies. We discuss several implications of the metallicity-dependence of the KS relation for galaxy evolution and interpretation of observations. In particular, we show that the observed size of high-redshift exponential disks depends sensitively on their KS relation. Our results also suggest that significantly reduced star formation efficiency at low gas surface densities can lead to strong suppression of star formation in low-mass high-redshift galaxies and long gas consumption time scales over most of the disks in large galaxies. The longer gas consumption time scales could make disks more resilient to major and minor mergers and could help explain the prevalence of the thin stellar disks in the local

Stars and gas in the most metal-deficient galaxies in the Universe.

NASA Astrophysics Data System (ADS)

Wofford, Aida

2017-08-01

Improving our understanding of star formation at low metallicity is of large relevance for a variety of fields in astrophysics since it relates to multiple topical questions. These range from understanding the properties of galaxies that contributed to cosmic reionization to the evolution of metal poor massive stars that give rise to the formation of heavy binary black holes. Crucial are observational constraints for the theoretical predictions, which can be obtained from rest-frame UV spectra of local star-forming dwarf galaxies with ionized-gas oxygen abundances at the low-metallicity threshold of the nearby Universe.While samples of UV spectra exist for galaxies in the metallicity range above 1/20 solar, only two useful spectra covering from H I Lyman-alpha (LyA, 1216 Ang) to C III] 1909 are available at lower metallicites. We propose COS G140L observations of eight extremely-metal poor galaxies (XMPGs) with He II emission that will: i) provide three more spectra with 12+log(O/H)=<7.4 (suitable targets at such low Z are hard to find), and ii) leverage existing WFC3 and Chandra images which are useful for discrimintating among different sources of ionization. Combining this dataset with existing spectra at similar and higher metallicity will allow us to address three questions: 1) How does metallicity determine galaxy properties?, 2) Is narrow He II emission a good tracer of peculiar massive stars?, and 3) Can we probe star-formation at high redshift with UV lines other than LyA? Our study will provide valuable clues for interpreting rest-frame UV spectra of high-z galaxies that will challenge our understanding of star formation at low Z.

Environmental Effects on the Metallicities of Early-Type Galaxies

NASA Technical Reports Server (NTRS)

Jones, Christine; Oliversen, Ronald J. (Technical Monitor)

2003-01-01

We have completed and published two papers based on research from this grant. Our first paper "SN IA Enrichment in Virgo Early-type Galaxies from ROSAT and ASCA Observations" was published in the Astrophysical Journal (vol 539,603) reported on the properties of nine X-ray bright elliptical galaxies in the Virgo cluster observed by ROSAT and ASCA. We measured iron abundance gradients as a function of radius in three galaxies. We found that the magnesium and silicon abundance gradients were in general flatter than those of iron. We suggest this is due to a metallicity dependence in the metal production rates of SN Ia's. We calculate SN Ia rates in the center of these galaxies that are comparable to those measured optically. Our second paper "ASCA Observations of Groups at Radii of Low Overdensity: Implications for Cosmic Preheating" also was published in the Astrophysical Journal (vol 578, 74). This paper reported on the ASCA spectroscopy of nine groups of galaxies. We found that the entropy profile in groups is driven by nongravitational heating processes, and could be explained by a short period of preheating by galactic winds.

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

The metallicity and elemental abundance gradients of simulated galaxies and their environmental dependence

NASA Astrophysics Data System (ADS)

Taylor, Philip; Kobayashi, Chiaki

2017-11-01

The internal distribution of heavy elements, in particular the radial metallicity gradient, offers insight into the merging history of galaxies. Using our cosmological, chemodynamical simulations that include both detailed chemical enrichment and feedback from active galactic nuclei (AGN), we find that stellar metallicity gradients in the most massive galaxies (≳3 × 1010M⊙) are made flatter by mergers and are unable to regenerate due to the quenching of star formation by AGN feedback. The fitting range is chosen on a galaxy-by-galaxy basis in order to mask satellite galaxies. The evolutionary paths of the gradients can be summarized as follows: (I) creation of initial steep gradients by gas-rich assembly, (II) passive evolution by star formation and/or stellar accretion at outskirts, and (III) sudden flattening by mergers. There is a significant scatter in gradients at a given mass, which originates from the last path, and therefore from galaxy type. Some variation remains at given galaxy mass and type because of the complexity of merging events, and hence we find only a weak environmental dependence. Our early-type galaxies (ETGs), defined from the star formation main sequence rather than their morphology, are in excellent agreement with the observed stellar metallicity gradients of ETGs in the SAURON and ATLAS3D surveys. We find small positive [O/Fe] gradients of stars in our simulated galaxies, although they are smaller with AGN feedback. Gas-phase metallicity and [O/Fe] gradients also show variation, the origin of which is not as clear as for stellar populations.

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.

HERSCHEL SPECTROSCOPIC OBSERVATIONS OF LITTLE THINGS DWARF GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cigan, Phil; Young, Lisa; Cormier, Diane

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 usmore » 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.« less

DETERMINING THE LARGE-SCALE ENVIRONMENTAL DEPENDENCE OF GAS-PHASE METALLICITY IN DWARF GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Douglass, Kelly A.; Vogeley, Michael S., E-mail: kelly.a.douglass@drexel.edu

2017-01-10

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] λ 3727, [O iii] λ 4363, and [O iii] λλ 4959, 5007, we estimate the abundance of oxygen with the direct T{sub e}  method. We estimate the metallicity of 42 blue, star-forming voidmore » 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.« less

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.

The evolution of the metallicity gradient and the star formation efficiency in disc galaxies

NASA Astrophysics Data System (ADS)

Sillero, Emanuel; Tissera, Patricia B.; Lambas, Diego G.; Michel-Dansac, Leo

2017-12-01

We study the oxygen abundance profiles of the gas-phase components in hydrodynamical simulations of pre-prepared disc galaxies including major mergers, close encounters and isolated configurations. We analyse the evolution of the slope of oxygen abundance profiles and the specific star formation rate (sSFR) along their evolution. We find that galaxy-galaxy interactions could generate either positive or negative gas-phase oxygen profiles, depending on the state of evolution. Along the interaction, galaxies are found to have metallicity gradients and sSFR consistent with observations, on average. Strong gas inflows produced during galaxy-galaxy interactions or as a result of strong local instabilities in gas-rich discs are able to produce both a quick dilution of the central gas-phase metallicity and a sudden increase of the sSFR. Our simulations show that, during these events, a correlation between the metallicity gradients and the sSFR can be set up if strong gas inflows are triggered in the central regions in short time-scales. Simulated galaxies without experiencing strong disturbances evolve smoothly without modifying the metallicity gradients. Gas-rich systems show large dispersion along the correlation. The dispersion in the observed relation could be interpreted as produced by the combination of galaxies with different gas-richness and/or experiencing different types of interactions. Hence, our findings suggest that the observed relation might be the smoking gun of galaxies forming in a hierarchical clustering scenario.

Biases in Metallicity Measurements from Global Galaxy Spectra: The Effects of Flux Weighting and Diffuse Ionized Gas Contamination

NASA Astrophysics Data System (ADS)

Sanders, Ryan L.; Shapley, Alice E.; Zhang, Kai; Yan, Renbin

2017-12-01

Galaxy metallicity scaling relations provide a powerful tool for understanding galaxy evolution, but obtaining unbiased global galaxy gas-phase oxygen abundances requires proper treatment of the various line-emitting sources within spectroscopic apertures. We present a model framework that treats galaxies as ensembles of H II and diffuse ionized gas (DIG) regions of varying metallicities. These models are based upon empirical relations between line ratios and electron temperature for H II regions, and DIG strong-line ratio relations from SDSS-IV MaNGA IFU data. Flux-weighting effects and DIG contamination can significantly affect properties inferred from global galaxy spectra, biasing metallicity estimates by more than 0.3 dex in some cases. We use observationally motivated inputs to construct a model matched to typical local star-forming galaxies, and quantify the biases in strong-line ratios, electron temperatures, and direct-method metallicities as inferred from global galaxy spectra relative to the median values of the H II region distributions in each galaxy. We also provide a generalized set of models that can be applied to individual galaxies or galaxy samples in atypical regions of parameter space. We use these models to correct for the effects of flux-weighting and DIG contamination in the local direct-method mass-metallicity and fundamental metallicity relations, and in the mass-metallicity relation based on strong-line metallicities. Future photoionization models of galaxy line emission need to include DIG emission and represent galaxies as ensembles of emitting regions with varying metallicity, instead of as single H II regions with effective properties, in order to obtain unbiased estimates of key underlying physical properties.

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.

An Infrared Census of DUST in Nearby Galaxies with Spitzer (DUSTiNGS). IV. Discovery of High-redshift AGB Analogs

NASA Astrophysics Data System (ADS)

Boyer, M. L.; McQuinn, K. B. W.; Groenewegen, M. A. T.; Zijlstra, A. A.; Whitelock, P. A.; van Loon, J. Th.; Sonneborn, G.; Sloan, G. C.; Skillman, E. D.; Meixner, M.; McDonald, I.; Jones, O. C.; Javadi, A.; Gehrz, R. D.; Britavskiy, N.; Bonanos, A. Z.

2017-12-01

The survey for DUST in Nearby Galaxies with Spitzer (DUSTiNGS) identified several candidate Asymptotic Giant Branch (AGB) stars in nearby dwarf galaxies and showed that dust can form even in very metal-poor systems ({\\boldsymbol{Z}}∼ 0.008 {Z}ȯ ). Here, we present a follow-up survey with WFC3/IR on the Hubble Space Telescope (HST), using filters that are capable of distinguishing carbon-rich (C-type) stars from oxygen-rich (M-type) stars: F127M, F139M, and F153M. We include six star-forming DUSTiNGS galaxies (NGC 147, IC 10, Pegasus dIrr, Sextans B, Sextans A, and Sag DIG), all more metal-poor than the Magellanic Clouds and spanning 1 dex in metallicity. We double the number of dusty AGB stars known in these galaxies and find that most are carbon rich. We also find 26 dusty M-type stars, mostly in IC 10. Given the large dust excess and tight spatial distribution of these M-type stars, they are most likely on the upper end of the AGB mass range (stars undergoing Hot Bottom Burning). Theoretical models do not predict significant dust production in metal-poor M-type stars, but we see evidence for dust excess around M-type stars even in the most metal-poor galaxies in our sample (12+{log}({{O}}/{{H}})=7.26{--}7.50). The low metallicities and inferred high stellar masses (up to ∼10 {M}ȯ ) suggest that AGB stars can produce dust very early in the evolution of galaxies (∼30 Myr after they form), and may contribute significantly to the dust reservoirs seen in high-redshift galaxies. Based on observations made 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, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-14073.

Metallicity gradients in local field star-forming galaxies: insights on inflows, outflows, and the coevolution of gas, stars and metals

NASA Astrophysics Data System (ADS)

Ho, I.-Ting; Kudritzki, Rolf-Peter; Kewley, Lisa J.; Zahid, H. Jabran; Dopita, Michael A.; Bresolin, Fabio; Rupke, David S. N.

2015-04-01

We present metallicity gradients in 49 local field star-forming galaxies. We derive gas-phase oxygen abundances using two widely adopted metallicity calibrations based on the [O III]/Hβ, [N II]/Hα, and [N II]/[O II] line ratios. The two derived metallicity gradients are usually in good agreement within ± 0.14 dex R_{25}^{-1} (R25 is the B-band iso-photoal radius), but the metallicity gradients can differ significantly when the ionization parameters change systematically with radius. We investigate the metallicity gradients as a function of stellar mass (8 < log (M*/M⊙) < 11) and absolute B-band luminosity (-16 > MB > -22). When the metallicity gradients are expressed in dex kpc-1, we show that galaxies with lower mass and luminosity, on average, have steeper metallicity gradients. When the metallicity gradients are expressed in dex R_{25}^{-1}, we find no correlation between the metallicity gradients, and stellar mass and luminosity. We provide a local benchmark metallicity gradient of field star-forming galaxies useful for comparison with studies at high redshifts. We investigate the origin of the local benchmark gradient using simple chemical evolution models and observed gas and stellar surface density profiles in nearby field spiral galaxies. Our models suggest that the local benchmark gradient is a direct result of the coevolution of gas and stellar disc under virtually closed-box chemical evolution when the stellar-to-gas mass ratio becomes high (≫0.3). These models imply low current mass accretion rates ( ≲ 0.3 × SFR), and low-mass outflow rates ( ≲ 3 × SFR) in local field star-forming galaxies.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

McQuinn, Kristen B. W.; Skillman, Evan D.; Dolphin, Andrew

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. Thismore » 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.« less

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.

Measuring the High-Mass IMF in Low-Metallicity Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Weisz, Daniel

2017-08-01

We propose to measure the stellar initial mass function above >1-2 Msun in 46 nearby dwarf galaxies with archival HST observations. This novel approach leverages the redundant age information provided by the main sequence and blue core helium burning stars <500 years old to break the well-known degeneracy between the IMF and star formation history (SFH), enabling a direct measurement of the high-mass IMF in dwarf galaxies. We will be able to constrain the high-mass IMF slope to a precision better than 0.1 to 0.3 dex in each galaxy. Our sample spans a factor of 6 in metallicity ( 5-30% Zsun), 4 decades in star formation rate, and 3 decades in both stellar and gas mass, allowing us to explore the IMF over a wide range of extreme environments.Current observational evidence suggests that nearby dwarf galaxies are the most likely candidates to host significant and systematic variations in the high-mass IMF (e.g., Halpha/UV ratios). However, to date there have been no direct measurements of the high-mass IMF in environments with lower star formation rates and/or more metal poor than the Magellanic Clouds. Our program remedies this shortcoming allowing us to (1) make the first-ever measurement of the high-mass IMF in extremely metal-poor environments; (2) empirically quantify environmental the (lack of) variations in the high-mass IMF; (3) directly test the integrated galactic mass initial mass function (IGIMF), which predicts environmental sensitivity of the IMF in dwarf galaxies.

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

Mass and metallicity scaling relations of high-redshift star-forming galaxies selected by GRBs

NASA Astrophysics Data System (ADS)

Arabsalmani, M.; Møller, P.; Perley, D. A.; Freudling, W.; Fynbo, J. P. U.; Le Floc'h, E.; Zwaan, M. A.; Schulze, S.; Tanvir, N. R.; Christensen, L.; Levan, A. J.; Jakobsson, P.; Malesani, D.; Cano, Z.; Covino, S.; D'Elia, V.; Goldoni, P.; Gomboc, A.; Heintz, K. E.; Sparre, M.; de Ugarte Postigo, A.; Vergani, S. D.

2018-01-01

We present a comprehensive study of the relations between gas kinematics, metallicity and stellar mass in a sample of 82 gamma-ray burst (GRB)-selected galaxies using absorption and emission methods. We find the velocity widths of both emission and absorption profiles to be a proxy of stellar mass. We also investigate the velocity-metallicity correlation and its evolution with redshift. Using 33 GRB hosts with measured stellar mass and metallicity, we study the mass-metallicity relation for GRB host galaxies in a stellar mass range of 108.2-1011.1 M⊙ and a redshift range of z ∼ 0.3-3.4. The GRB-selected galaxies appear to track the mass-metallicity relation of star-forming galaxies but with an offset of 0.15 towards lower metallicities. This offset is comparable with the average error bar on the metallicity measurements of the GRB sample and also the scatter on the mass-metallicity relation of the general population. It is hard to decide whether this relatively small offset is due to systematic effects or the intrinsic nature of GRB hosts. We also investigate the possibility of using absorption-line metallicity measurements of GRB hosts to study the mass-metallicity relation at high redshifts. Our analysis shows that the metallicity measurements from absorption methods can significantly differ from emission metallicities and assuming identical measurements from the two methods may result in erroneous conclusions.

SDSS IV MaNGA - metallicity and nitrogen abundance gradients in local galaxies

NASA Astrophysics Data System (ADS)

Belfiore, Francesco; Maiolino, Roberto; Tremonti, Christy; Sánchez, Sebastian F.; Bundy, Kevin; Bershady, Matthew; Westfall, Kyle; Lin, Lihwai; Drory, Niv; Boquien, Médéric; Thomas, Daniel; Brinkmann, Jonathan

2017-07-01

We study the gas phase metallicity (O/H) and nitrogen abundance gradients traced by star-forming regions in a representative sample of 550 nearby galaxies in the stellar mass range 109-1011.5 M⊙ with resolved spectroscopic data from the Sloan Digital Sky Survey IV Mapping Nearby Galaxies at Apache Point Observatory survey. Using strong-line ratio diagnostics (R23 and O3N2 for metallicity and N2O2 for N/O) and referencing to the effective (half-light) radius (Re), we find that the metallicity gradient steepens with stellar mass, lying roughly flat among galaxies with log (M⋆/M⊙) = 9.0 but exhibiting slopes as steep as -0.14 dex R_e^{-1} at log (M⋆/M⊙) = 10.5 (using R23, but equivalent results are obtained using O3N2). At higher masses, these slopes remain typical in the outer regions of our sample (R > 1.5Re), but a flattening is observed in the central regions (R < 1Re). In the outer regions (R > 2.0Re), we detect a mild flattening of the metallicity gradient in stacked profiles, although with low significance. The N/O ratio gradient provides complementary constraints on the average chemical enrichment history. Unlike the oxygen abundance, the average N/O profiles do not flatten out in the central regions of massive galaxies. The metallicity and N/O profiles both depart significantly from an exponential form, suggesting a disconnect between chemical enrichment and stellar mass surface density on local scales. In the context of inside-out growth of discs, our findings suggest that central regions of massive galaxies today have evolved to an equilibrium metallicity, while the nitrogen abundance continues to increase as a consequence of delayed secondary nucleosynthetic production.

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.

Hubble Spotlight on Irregular Galaxy

NASA Image and Video Library

2017-12-08

This delicate blue group of stars — actually an irregular galaxy named IC 3583 — sits some 30 million light-years away in the constellation of Virgo (The Virgin). It may seem to have no discernable structure, but IC 3583 has been found to have a bar of stars running through its center. These structures are common throughout the Universe, and are found within the majority of spiral, many irregular, and some lenticular galaxies. Two of our closest cosmic neighbors, the Large and Small Magellanic Clouds, are barred, indicating that they may have once been barred spiral galaxies that were disrupted or torn apart by the gravitational pull of the Milky Way. Researchers at the University of Leicester, England note there are two types of irregular galaxy. Type I's are usually single galaxies of peculiar appearance. They contain a large fraction of young stars, and show the luminous nebulae that are also visible in spiral galaxies. Type II irregulars include the group known as interacting or disrupting galaxies, in which the strange appearance is due to two or more galaxies colliding, merging or otherwise interacting gravitationally. Something similar might be happening with IC 3583. This small galaxy is thought to be gravitationally interacting with one of its neighbors, the spiral Messier 90. Together, the duo form a pairing known as Arp 76. It’s still unclear whether these flirtations are the cause of IC 3583’s irregular appearance — but whatever the cause, the galaxy makes for a strikingly delicate sight in this NASA/ESA Hubble Space Telescope image, glimmering in the blackness of space. Image Credit: ESA/Hubble & NASA NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on

KINEMATICS OF EXTREMELY METAL-POOR GALAXIES: EVIDENCE FOR STELLAR FEEDBACK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Olmo-García, A.; Sánchez Almeida, J.; Muñoz-Tuñón, C.

2017-01-10

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{sup −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 galaxymore » 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 H α line wings show a number of faint emission features with amplitudes around a few per cent of the main H α component, and wavelength shifts between 100 and 400 km s{sup −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.« less

The Little Cub: Discovery of an Extremely Metal-poor Star-forming Galaxy in the Local Universe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hsyu, Tiffany; Prochaska, J. Xavier; Bolte, Michael

We report the discovery of the Little Cub, an extremely metal-poor star-forming galaxy in the local universe, found in the constellation Ursa Major (a.k.a. the Great Bear). We first identified the Little Cub as a candidate metal-poor galaxy based on its Sloan Digital Sky Survey photometric colors, combined with spectroscopy using the Kast spectrograph on the Shane 3 m telescope at Lick Observatory. In this Letter, we present high-quality spectroscopic data taken with the Low Resolution Imaging Spectrometer at Keck Observatory, which confirm the extremely metal-poor nature of this galaxy. Based on the weak [O iii] λ 4363 Å emissionmore » line, we estimate a direct oxygen abundance of 12 + log(O/H) = 7.13 ± 0.08, making the Little Cub one of the lowest-metallicity star-forming galaxies currently known in the local universe. The Little Cub appears to be a companion of the spiral galaxy NGC 3359 and shows evidence of gas stripping. We may therefore be witnessing the quenching of a near-pristine galaxy as it makes its first passage about a Milky Way–like galaxy.« less

The Little Cub: Discovery of an Extremely Metal-poor Star-forming Galaxy in the Local Universe

NASA Astrophysics Data System (ADS)

Hsyu, Tiffany; Cooke, Ryan J.; Prochaska, J. Xavier; Bolte, Michael

2017-08-01

We report the discovery of the Little Cub, an extremely metal-poor star-forming galaxy in the local universe, found in the constellation Ursa Major (a.k.a. the Great Bear). We first identified the Little Cub as a candidate metal-poor galaxy based on its Sloan Digital Sky Survey photometric colors, combined with spectroscopy using the Kast spectrograph on the Shane 3 m telescope at Lick Observatory. In this Letter, we present high-quality spectroscopic data taken with the Low Resolution Imaging Spectrometer at Keck Observatory, which confirm the extremely metal-poor nature of this galaxy. Based on the weak [O III] λ4363 Å emission line, we estimate a direct oxygen abundance of 12 + log(O/H) = 7.13 ± 0.08, making the Little Cub one of the lowest-metallicity star-forming galaxies currently known in the local universe. The Little Cub appears to be a companion of the spiral galaxy NGC 3359 and shows evidence of gas stripping. We may therefore be witnessing the quenching of a near-pristine galaxy as it makes its first passage about a Milky Way-like galaxy.

METAL DIFFUSION IN SMOOTHED PARTICLE HYDRODYNAMICS SIMULATIONS OF DWARF GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williamson, David; Martel, Hugo; Kawata, Daisuke, E-mail: david-john.williamson.1@ulaval.ca

2016-05-10

We perform a series of smoothed particle hydrodynamics simulations of isolated dwarf galaxies to compare different metal mixing models. In particular, we examine the role of diffusion in the production of enriched outflows and in determining the metallicity distributions of gas and stars. We investigate different diffusion strengths by changing the pre-factor of the diffusion coefficient, by varying how the diffusion coefficient is calculated from the local velocity distribution, and by varying whether the speed of sound is included as a velocity term. Stronger diffusion produces a tighter [O/Fe]–[Fe/H] distribution in the gas and cuts off the gas metallicity distributionmore » function at lower metallicities. Diffusion suppresses the formation of low-metallicity stars, even with weak diffusion, and also strips metals from enriched outflows. This produces a remarkably tight correlation between “metal mass-loading” (mean metal outflow rate divided by mean metal production rate) and the strength of diffusion, even when the diffusion coefficient is calculated in different ways. The effectiveness of outflows at removing metals from dwarf galaxies and the metal distribution of the gas is thus dependent on the strength of diffusion. By contrast, we show that the metallicities of stars are not strongly dependent on the strength of diffusion, provided that some diffusion is present.« less

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.

Ionized and Molecular Gas in IC 860: Evidence for an Outflow

NASA Astrophysics Data System (ADS)

Adams, Carson; Alatalo, Katherine; Medling, Anne M.

2018-01-01

Galaxies at present-day fall predominantly in two distinct populations, as either blue, star-forming spirals or red, quiescent early-type galaxies. Blue galaxies appear to evolve onto the red sequence as star formation is quenched. The absence of a significant population falling in the intermediate ‘green valley’ implies that these transitions must occur rapidly. Identifying the initial properties of and pathways taken by these ‘dying galaxies’ is essential to building a complete understanding of galactic evolution. In this work, we investigate these phenomena in action within IC860 — a nearby, early-type spiral in the initial stages of undergoing a rapid transition in the presence of a powerful AGN-driven molecular outflow. As a shocked, post-starburst galaxy with an intermediate-age stellar population which lies on the blue end of the green valley, IC860 provides a window into the early stages of galaxy transition and AGN feedback. We present Hubble Space Telescope imaging of IC860 showing a violent, dusty outflow originating from a compact core. We find that the mean velocity map of the CO(1-0) from CARMA suggests a dynamically excited bar funneling molecular gas into the galactic center. Finally, we present kinematic maps of ionized gas emission lines as well as sodium D absorption tracing neutral winds obtained by the Wide-Field Spectrograph.

A remarkably large depleted core in the Abell 2029 BCG IC 1101

NASA Astrophysics Data System (ADS)

Dullo, Bililign T.; Graham, Alister W.; Knapen, Johan H.

2017-10-01

We report the discovery of an extremely large (Rb ˜2.77 arcsec ≈ 4.2 kpc) core in the brightest cluster galaxy, IC 1101, of the rich galaxy cluster Abell 2029. Luminous core-Sérsic galaxies contain depleted cores - with sizes (Rb) typically 20-500 pc - that are thought to be formed by coalescing black hole binaries. We fit a (double nucleus) + (spheroid) + (intermediate-scale component) + (stellar halo) model to the Hubble Space Telescope surface brightness profile of IC 1101, finding the largest core size measured in any galaxy to date. This core is an order of magnitude larger than those typically measured for core-Sérsic galaxies. We find that the spheroid's V-band absolute magnitude (MV) of -23.8 mag (˜25 per cent of the total galaxy light, I.e. including the stellar halo) is faint for the large Rb, such that the observed core is 1.02 dex ≈ 3.4σs (rms scatter) larger than that estimated from the Rb-MV relation. The suspected scouring process has produced a large stellar mass deficit (Mdef) ˜4.9 × 1011 M⊙, I.e. a luminosity deficit ≈28 per cent of the spheroid's luminosity prior to the depletion. Using IC 1101's black hole mass (MBH) estimated from the MBH-σ, MBH-L and MBH-M* relations, we measure an excessive and unrealistically high number of 'dry' major mergers for IC 1101 (I.e. N ≳ 76) as traced by the large Mdef/MBH ratios of 38-101. The large core, high mass deficit and oversized Mdef/MBH ratio of IC 1101 suggest that the depleted core was scoured by overmassive SMBH binaries with a final coalesced mass MBH ˜ (4-10) × 1010 M⊙, I.e. ˜ (1.7-3.2) × σs larger than the black hole masses estimated using the spheroid's σ, L and M*. The large core might be partly due to oscillatory core passages by a gravitational radiation-recoiled black hole.

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.

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.

NONLINEAR COLOR-METALLICITY RELATIONS OF GLOBULAR CLUSTERS. III. ON THE DISCREPANCY IN METALLICITY BETWEEN GLOBULAR CLUSTER SYSTEMS AND THEIR PARENT ELLIPTICAL GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoon, Suk-Jin; Lee, Sang-Yoon; Cho, Jaeil

2011-12-20

One of the conundrums in extragalactic astronomy is the discrepancy in observed metallicity distribution functions (MDFs) between the two prime stellar components of early-type galaxies-globular clusters (GCs) and halo field stars. This is generally taken as evidence of highly decoupled evolutionary histories between GC systems and their parent galaxies. Here we show, however, that new developments in linking the observed GC colors to their intrinsic metallicities suggest nonlinear color-to-metallicity conversions, which translate observed color distributions into strongly peaked, unimodal MDFs with broad metal-poor tails. Remarkably, the inferred GC MDFs are similar to the MDFs of resolved field stars in nearbymore » elliptical galaxies and those produced by chemical evolution models of galaxies. The GC MDF shape, characterized by a sharp peak with a metal-poor tail, indicates a virtually continuous chemical enrichment with a relatively short timescale. The characteristic shape emerges across three orders of magnitude in the host galaxy mass, suggesting a universal process of chemical enrichment among various GC systems. Given that GCs are bluer than field stars within the same galaxy, it is plausible that the chemical enrichment processes of GCs ceased somewhat earlier than that of the field stellar population, and if so, GCs preferentially trace the major, vigorous mode of star formation events in galactic formation. We further suggest a possible systematic age difference among GC systems, in that the GC systems in more luminous galaxies are older. This is consistent with the downsizing paradigm whereby stars of brighter galaxies, on average, formed earlier than those of dimmer galaxies; this additionally supports the similar nature shared by GCs and field stars. Although the sample used in this study (the Hubble Space Telescope Advanced Camera for Surveys/Wide Field Channel, WFPC2, and WFC3 photometry for the GC systems in the Virgo galaxy cluster) confines

Diffuse gas properties and stellar metallicities in cosmological simulations of disc galaxy formation

NASA Astrophysics Data System (ADS)

Marinacci, Federico; Pakmor, Rüdiger; Springel, Volker; Simpson, Christine M.

2014-08-01

We analyse the properties of the circumgalactic medium and the metal content of the stars comprising the central galaxy in eight hydrodynamical `zoom-in' simulations of disc galaxy formation. We use these properties as a benchmark for our model of galaxy formation physics implemented in the moving-mesh code AREPO, which succeeds in forming quite realistic late-type spirals in the set of `Aquarius' initial conditions of Milky-Way-sized haloes. Galactic winds significantly influence the morphology of the circumgalactic medium and induce bipolar features in the distribution of heavy elements. They also affect the thermodynamic properties of the circumgalactic gas by supplying an energy input that sustains its radiative losses. Although a significant fraction of the heavy elements are transferred from the central galaxy to the halo, and even beyond the virial radius, enough metals are retained by stars to yield a peak in their metallicity distributions at about Z⊙. All our default runs overestimate the stellar [O/Fe] ratio, an effect that we demonstrate can be rectified by an increase of the adopted Type Ia supernova rate. Nevertheless, the models have difficulty in producing stellar metallicity gradients of the same strength as observed in the Milky Way.

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.

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.

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

Probing galaxy growth through metallicity scaling relations over the past 12 Gyr of cosmic history

NASA Astrophysics Data System (ADS)

Sanders, Ryan; MOSDEF team

2018-01-01

A primary goal of galaxy evolution studies is to understand the processes governing the growth of the baryonic content of galaxies over cosmic history. Observations of galaxy metallicity scaling relations and their evolution with redshift, in combination with chemical evolution models, provide unique insight into the interplay between star formation, gas accretion, and feedback/outflows. I present measurements of the stellar mass-gas phase metallicity relation and its evolution over the past 12 Gyr from z~0 to z~3.5, utilizing data from the Mosfire Deep Evolution Field survey that uniquely provides rest-frame optical spectra of >1000 uniformly-selected galaxies at z=1.3-3.8. We find evolution towards lower metallicity at fixed stellar mass with increasing redshift that is consistent with current cosmological simulations including chemical evolution, with a large evolution of ~0.3 dex from z~0 to z~2.5 and minor evolution of <0.1 dex from z~2.5 to z~3.5. We unambiguously confirm the existence of star-formation rate dependence of the mass-metallicity relation at high redshift for the first time. A clear view of cosmic chemical evolution requires accounting for systematic biases in galaxy metallicity measurements at both low and high redshifts. We use a set of empirically-based models to correct for diffuse ionized gas contamination that biases metallicity estimates from z~0 global galaxy spectra. Evolving properties of ionized gas such as electron density, ionization parameter, hardness of the ionizing spectrum, and chemical abundance patterns may render locally-calibrated metallicity estimators unreliable at high redshifts. Using strong-line ratios alone, it is extremely difficult to break degenerate solutions between pure metallicity evolution and additional evolution of the ionization parameter and/or shape of the ionizing spectrum. Temperature-sensitive auroral-line measurements provide a way to directly and independently measure metallicities, breaking these

New insights into the interstellar medium of the dwarf galaxy IC 10: connection between magnetic fields, the radio-infrared correlation and star formation

NASA Astrophysics Data System (ADS)

Basu, Aritra; Roychowdhury, Sambit; Heesen, Volker; Beck, Rainer; Brinks, Elias; Westcott, Jonathan; Hindson, Luke

2017-10-01

We present the highest sensitivity and angular resolution study at 0.32 GHz of the dwarf irregular galaxy IC 10, observed using the Giant Metrewave Radio Telescope, probing ˜45 pc spatial scales. We find the galaxy-averaged radio continuum spectrum to be relatively flat, with a spectral index α = -0.34 ± 0.01 (Sν ∝ να), mainly due to a high contribution from free-free emission. At 0.32 GHz, some of the H II regions show evidence of free-free absorption as they become optically thick below ˜0.41 GHz with corresponding free electron densities of ˜ 11-22 cm- 3. After removing the free-free emission, we studied the radio-infrared (IR) relations on 55, 110 and 165 pc spatial scales. We find that on all scales the non-thermal emission at 0.32 and 6.2 GHz correlates better with far-infrared (FIR) emission at 70 μm than mid-IR emission at 24 μm. The dispersion of the radio-FIR relation arises due to variations in both magnetic field and dust temperature, and decreases systematically with increasing spatial scale. The effect of cosmic ray transport is negligible as cosmic ray electrons were only injected ≲5 Myr ago. The average magnetic field strength (B) of 12 μG in the disc is comparable to that of large star-forming galaxies. The local magnetic field is strongly correlated with local star formation rate (SFR) as B ∝ SFR0.35 ± 0.03, indicating a starburst-driven fluctuation dynamo to be efficient (˜10 per cent) in amplifying the field in IC 10. The high spatial resolution observations presented here suggest that the high efficiency of magnetic field amplification and strong coupling with SFR likely sets up the radio-FIR correlation in cosmologically young galaxies.

The WiggleZ Dark Energy Survey: final data release and the metallicity of UV-luminous galaxies

NASA Astrophysics Data System (ADS)

Drinkwater, Michael J.; Byrne, Zachary J.; Blake, Chris; Glazebrook, Karl; Brough, Sarah; Colless, Matthew; Couch, Warrick; Croton, Darren J.; Croom, Scott M.; Davis, Tamara M.; Forster, Karl; Gilbank, David; Hinton, Samuel R.; Jelliffe, Ben; Jurek, Russell J.; Li, I.-hui; Martin, D. Christopher; Pimbblet, Kevin; Poole, Gregory B.; Pracy, Michael; Sharp, Rob; Smillie, Jon; Spolaor, Max; Wisnioski, Emily; Woods, David; Wyder, Ted K.; Yee, Howard K. C.

2018-03-01

The WiggleZ Dark Energy Survey measured the redshifts of over 200 000 ultraviolet (UV)-selected (NUV < 22.8 mag) galaxies on the Anglo-Australian Telescope. The survey detected the baryon acoustic oscillation signal in the large-scale distribution of galaxies over the redshift range 0.2 < z < 1.0, confirming the acceleration of the expansion of the Universe and measuring the rate of structure growth within it. Here, we present the final data release of the survey: a catalogue of 225 415 galaxies and individual files of the galaxy spectra. We analyse the emission-line properties of these UV-luminous Lyman-break galaxies by stacking the spectra in bins of luminosity, redshift, and stellar mass. The most luminous (-25 maggalaxies have very broad Hβ emission from active nuclei, as well as a broad second component to the [O III] (495.9 nm, 500.7 nm) doublet lines that is blueshifted by 100 km s-1 , indicating the presence of gas outflows in these galaxies. The composite spectra allow us to detect and measure the temperature-sensitive [O III] (436.3 nm) line and obtain metallicities using the direct method. The metallicities of intermediate stellar mass (8.8 < log (M*/M⊙) < 10) WiggleZ galaxies are consistent with normal emission-line galaxies at the same masses. In contrast, the metallicities of high stellar mass (10 < log (M*/M⊙) < 12) WiggleZ galaxies are significantly lower than for normal emission-line galaxies at the same masses. This is not an effect of evolution as the metallicities do not vary with redshift; it is most likely a property specific to the extremely UV-luminous WiggleZ galaxies.

VizieR Online Data Catalog: Metallicity of MPA-JHU SDSS-DR7 dwarf galaxies (Douglass+, 2017)

NASA Astrophysics Data System (ADS)

Douglass, K. A.; Vogeley, M. S.

2017-07-01

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 [OIII] and [SII] transitions, provide estimates of a region's electron temperature and number density. From these two quantities and the emission line fluxes [OII]λ3727, [OIII]λ4363, and [OIII]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. (1 data file).

Watching AGN feedback at its birth: HST observations of nascent outflow host IC860

NASA Astrophysics Data System (ADS)

Alatalo, Katherine

2016-10-01

IC860 is a nearby IR-luminous early-type spiral with a unique set of properties: it is a shocked, poststarburst galaxy that hosts an AGN-driven neutral wind and a compact core of molecular gas. IC860 can serve as a rosetta stone for the early stages of triggering AGN feedback. We propose to use WFC3 on HST to obtain NUV, optical and near-IR imaging of IC860. We will create a spatially-resolved history of star formation quenching through SED-fitting of 7 requested broadband filters, and compare the spatially resolved star formation histories to in different positions within the underlying stellar features (such as spiral structure) that might define a narrative of how star formation is quenching in IC860. These observations will also resolve the super-star cluster sites to trace the most recent star formation. Finally, these observations will trace the mass of the outflow by building an absorption map of the dust. IC860 presents a unique opportunity to study a galaxy at an early stage of transitioning from blue spiral to red early-type galaxy, that also hosts an AGN-driven neutral wind and a compact, turbulent molecular gas core.

Exploring the making of a galactic wind in the starbursting dwarf irregular galaxy IC 10 with LOFAR

NASA Astrophysics Data System (ADS)

Heesen, V.; Rafferty, D. A.; Horneffer, A.; Beck, R.; Basu, A.; Westcott, J.; Hindson, L.; Brinks, E.; ChyŻy, K. T.; Scaife, A. M. M.; Brüggen, M.; Heald, G.; Fletcher, A.; Horellou, C.; Tabatabaei, F. S.; Paladino, R.; Nikiel-Wroczyński, B.; Hoeft, M.; Dettmar, R.-J.

2018-05-01

Low-mass galaxies are subject to strong galactic outflows, in which cosmic rays may play an important role; they can be best traced with low-frequency radio continuum observations, which are less affected by spectral ageing. We present a study of the nearby starburst dwarf irregular galaxy IC 10 using observations at 140 MHz with the Low-Frequency Array (LOFAR), at 1580 MHz with the Very Large Array (VLA), and at 6200 MHz with the VLA and the 100-m Effelsberg telescope. We find that IC 10 has a low-frequency radio halo, which manifests itself as a second component (thick disc) in the minor axis profiles of the non-thermal radio continuum emission at 140 and 1580 MHz. These profiles are then fitted with 1D cosmic ray transport models for pure diffusion and advection. We find that a diffusion model fits best, with a diffusion coefficient of D = (0.4-0.8) × 1026(E/GeV)0.5 cm2 s-1, which is at least an order of magnitude smaller than estimates both from anisotropic diffusion and the diffusion length. In contrast, advection models, which cannot be ruled out due to the mild inclination, while providing poorer fits, result in advection speeds close to the escape velocity of ≈ 50 km s- 1, as expected for a cosmic ray-driven wind. Our favoured model with an accelerating wind provides a self-consistent solution, where the magnetic field is in energy equipartition with both the warm neutral and warm ionized medium with an important contribution from cosmic rays. Consequently, cosmic rays can play a vital role for the launching of galactic winds in the disc-halo interface.

HIGH STAR FORMATION RATES IN TURBULENT ATOMIC-DOMINATED GAS IN THE INTERACTING GALAXIES IC 2163 AND NGC 2207

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elmegreen, Bruce G.; Kaufman, Michele; Bournaud, Frédéric

CO observations of the interacting galaxies IC 2163 and NGC 2207 are combined with HI, H α , and 24 μ m observations to study the star formation rate (SFR) surface density as a function of the gas surface density. More than half of the high-SFR regions are HI dominated. When compared to other galaxies, these HI-dominated regions have excess SFRs relative to their molecular gas surface densities but normal SFRs relative to their total gas surface densities. The HI-dominated regions are mostly located in the outer part of NGC 2207 where the HI velocity dispersion is high, 40–50 kmmore » s{sup −1}. We suggest that the star-forming clouds in these regions have envelopes at lower densities than normal, making them predominantly atomic, and cores at higher densities than normal because of the high turbulent Mach numbers. This is consistent with theoretical predictions of a flattening in the density probability distribution function for compressive, high Mach number turbulence.« less

Andromeda IV: A new local volume very metal-poor galaxy

NASA Astrophysics Data System (ADS)

Pustilnik, S. A.; Tepliakova, A. L.; Kniazev, A. Y.; Burenkov, A. N.

2008-06-01

And IV is a low surface brightness (LSB) dwarf galaxy at a distance of 6.1 Mpc, projecting close to M 31. In this paper the results of spectroscopy of the And IV two brightest HII regions with the SAO 6-m telescope (BTA) are presented. In spectra of both of them the faint line [OIII] λ4363 Å was detected and this allowed us to determine their O/H by the classical Te method. Their values for 12+log(O/H) are equal to 7.49±0.06 and 7.55±0.23, respectively. The comparison of the direct O/H calculations with the two most reliable semi-empirical and empirical methods shows the good consistency between these methods. For And IV absolute blue magnitude, MB = -12.6, our value for O/H corresponds to the ‘standard’ relation between O/H and LB for dwarf irregular galaxies (DIGs). And IV appears to be a new representative of the extremely metal-deficient gas-rich galaxies in the Local Volume. The very large range of M(HI) for LSB galaxies with close metallicities and luminosities indicates that simple models of LSBG chemical evolution are too limited to predict such striking diversity.

Stellar metallicity variations across spiral arms in disk galaxies with multiple populations

NASA Astrophysics Data System (ADS)

Khoperskov, S.; Di Matteo, P.; Haywood, M.; Combes, F.

2018-03-01

This Letter studies the formation of azimuthal metallicity variations in the disks of spiral galaxies in the absence of initial radial metallicity gradients. Using high-resolution N-body simulations, we model composite stellar discs, made of kinematically cold and hot stellar populations, and study their response to spiral arm perturbations. We find that, as expected, disk populations with different kinematics respond differently to a spiral perturbation, with the tendency for dynamically cooler populations to show a larger fractional contribution to spiral arms than dynamically hotter populations. By assuming a relation between kinematics and metallicity, namely the hotter the population, the more metal-poor it is, this differential response to the spiral arm perturbations naturally leads to azimuthal variations in the mean metallicity of stars in the simulated disk. Thus, azimuthal variations in the mean metallicity of stars across a spiral galaxy are not necessarily a consequence of the reshaping, by radial migration, of an initial radial metallicity gradient. They indeed arise naturally also in stellar disks which have initially only a negative vertical metallicity gradient.

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

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.

Using photometrically selected metal-poor stars to study dwarf galaxies and the Galactic stellar halo

NASA Astrophysics Data System (ADS)

Youakim, Kris; Starkenburg, Else; Martin, Nicolas; Pristine Team

2018-06-01

The Pristine survey is a narrow-band photometric survey designed to efficiently search for extremely metal-poor (EMP) stars. In the first three years of the survey, it has demonstrated great efficiency at finding EMP stars, and also great promise for increasing the current, small sample of the most metal-poor stars. The present sky coverage is ~2500 square degrees in the Northern Galactic Halo, including several individual fields targeting dwarf galaxies. By efficiently identifying member stars in the outskirts of known faint dwarf galaxies, the dynamical histories and chemical abundance patterns of these systems can be understood in greater detail. Additionally, with reliable photometric metallicities over a large sky coverage it is possible to perform a large scale clustering analysis in the Milky Way halo, and investigate the characteristic scale of substructure at different metallicities. This can reveal important details about the process of building up the halo through dwarf galaxy accretion, and offer insight into the connection between dwarf galaxies and the Milky Way halo. In this talk I will outline our results on the search for the most pristine stars, with a focus on how we are using this information to advance our understanding of dwarf galaxies and their contribution to the formation of the Galactic stellar halo.

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)

Metal Deficiency in Two Massive Dead Galaxies at z ∼ 2

NASA Astrophysics Data System (ADS)

Morishita, T.; Abramson, L. E.; Treu, T.; Wang, X.; Brammer, G. B.; Kelly, P.; Stiavelli, M.; Jones, T.; Schmidt, K. B.; Trenti, M.; Vulcani, B.

2018-03-01

Local massive early-type galaxies are believed to have completed most of their star formation ∼10 Gyr ago and evolved without having substantial star formation since that time. If so, their progenitors should have roughly solar stellar metallicities (Z *), comparable to their values today. We report the discovery of two lensed massive ({log}{M}* /{M}ȯ ∼ 11), z ∼ 2.2 dead galaxies that appear markedly metal deficient given this scenario. Using 17-band HST+K s +Spitzer photometry and deep Hubble Space Telescope (HST) grism spectra from the Grism Lens Amplified Survey from Space (GLASS) and supernova (SN) Refsdal follow-up campaigns covering features near λ rest ∼ 4000 Å, we find these systems to be dominated by A-type stars with {log}{Z}* /{Z}ȯ =-0.40+/- 0.02 and ‑0.49 ± 0.03 (30%–40% solar) under standard assumptions. The second system’s lower metallicity is robust to isochrone changes, though this choice can drive the first system’s from {log}{Z}* /{Z}ȯ =-0.6 to 0.1. If these two galaxies are representative of larger samples, this finding suggests that evolutionary paths other than dry minor merging are required for these massive galaxies. Future analyses with direct metallicity measurements—e.g., by the James Webb Space Telescope—will provide critical insight into the nature of such phenomena.

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.

Impact of Lyman alpha pressure on metal-poor dwarf galaxies

NASA Astrophysics Data System (ADS)

Kimm, Taysun; Haehnelt, Martin; Blaizot, Jérémy; Katz, Harley; Michel-Dansac, Léo; Garel, Thibault; Rosdahl, Joakim; Teyssier, Romain

2018-04-01

Understanding the origin of strong galactic outflows and the suppression of star formation in dwarf galaxies is a key problem in galaxy formation. Using a set of radiation-hydrodynamic simulations of an isolated dwarf galaxy embedded in a 1010 M⊙ halo, we show that the momentum transferred from resonantly scattered Lyman-α (Lyα) photons is an important source of stellar feedback which can shape the evolution of galaxies. We find that Lyα feedback suppresses star formation by a factor of two in metal-poor galaxies by regulating the dynamics of star-forming clouds before the onset of supernova explosions (SNe). This is possible because each Lyα photon resonantly scatters and imparts ˜10-300 times greater momentum than in the single scattering limit. Consequently, the number of star clusters predicted in the simulations is reduced by a factor of ˜5, compared to the model without the early feedback. More importantly, we find that galactic outflows become weaker in the presence of strong Lyα radiation feedback, as star formation and associated SNe become less bursty. We also examine a model in which radiation field is arbitrarily enhanced by a factor of up to 10, and reach the same conclusion. The typical mass-loading factors in our metal-poor dwarf system are estimated to be ˜5-10 near the mid-plane, while it is reduced to ˜1 at larger radii. Finally, we find that the escape of ionizing radiation and hence the reionization history of the Universe is unlikely to be strongly affected by Lyα feedback.

'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.

Surface density: a new parameter in the fundamental metallicity relation of star-forming galaxies

NASA Astrophysics Data System (ADS)

Hashimoto, Tetsuya; Goto, Tomotsugu; Momose, Rieko

2018-04-01

Star-forming galaxies display a close relation among stellar mass, metallicity, and star formation rate (or molecular-gas mass). This is known as the fundamental metallicity relation (FMR) (or molecular-gas FMR), and it has a profound implication on models of galaxy evolution. However, there still remains a significant residual scatter around the FMR. We show here that a fourth parameter, the surface density of stellar mass, reduces the dispersion around the molecular-gas FMR. In a principal component analysis of 29 physical parameters of 41 338 star-forming galaxies, the surface density of stellar mass is found to be the fourth most important parameter. The new 4D fundamental relation forms a tighter hypersurface that reduces the metallicity dispersion to 50 per cent of that of the molecular-gas FMR. We suggest that future analyses and models of galaxy evolution should consider the FMR in a 4D space that includes surface density. The dilution time-scale of gas inflow and the star-formation efficiency could explain the observational dependence on surface density of stellar mass.

The NIR Ca ii triplet at low metallicity. Searching for extremely low-metallicity stars in classical dwarf galaxies

NASA Astrophysics Data System (ADS)

Starkenburg, E.; Hill, V.; Tolstoy, E.; González Hernández, J. I.; Irwin, M.; Helmi, A.; Battaglia, G.; Jablonka, P.; Tafelmeyer, M.; Shetrone, M.; Venn, K.; de Boer, T.

2010-04-01

The NIR Ca ii triplet absorption lines have proven to be an important tool for quantitative spectroscopy of individual red giant branch stars in the Local Group, providing a better understanding of metallicities of stars in the Milky Way and dwarf galaxies and thereby an opportunity to constrain their chemical evolution processes. An interesting puzzle in this field is the significant lack of extremely metal-poor stars, below [Fe/H] = -3, found in classical dwarf galaxies around the Milky Way using this technique. The question arises whether these stars are really absent, or if the empirical Ca ii triplet method used to study these systems is biased in the low-metallicity regime. Here we present results of synthetic spectral analysis of the Ca ii triplet, that is focused on a better understanding of spectroscopic measurements of low-metallicity giant stars. Our results start to deviate strongly from the widely-used and linear empirical calibrations at [Fe/H] < -2. We provide a new calibration for Ca ii triplet studies which is valid for -0.5 ≥ [Fe/H] ≥ -4. We subsequently apply this new calibration to current data sets and suggest that the classical dwarf galaxies are not so devoid of extremely low-metallicity stars as was previously thought. Using observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile proposal 171.B-0588.

Eight luminous early-type galaxies in nearby pairs and sparse groups. I. Stellar populations spatially analysed

NASA Astrophysics Data System (ADS)

Rosa, D. A.; Milone, A. C.; Krabbe, A. C.; Rodrigues, I.

2018-06-01

We present a detailed spatial analysis of stellar populations based on long-slit optical spectra in a sample of eight luminous early-type galaxies selected from nearby sparse groups and pairs, three of them may have interaction with another galaxy of similar mass. We have spatially measured luminosity-weighted averages of age, [M/H], [Fe/H], and [α /Fe] in the sample galaxies to add empirical data relative to the influence of galaxy mass, environment, interaction, and AGN feedback in their formation and evolution. The stellar population of the individual galaxies were determined through the well-established stellar population synthesis code starlight using semi-empirical simple stellar population models. Radial variations of luminosity- weighted means of age, [M/H], [Fe/H], and [α /Fe] were quantified up to half of the effective radius of each galaxy. We found trends between representative values of age, [M/H], [α /Fe], and the nuclear stellar velocity dispersion. There are also relations between the metallicity/age gradients and the velocity dispersion. Contributions of 1-4 Gyr old stellar populations were quantified in IC 5328 and NGC 6758 as well as 4-8 Gyr old ones in NGC 5812. Extended gas is present in IC 5328, NGC 1052, NGC 1209, and NGC 6758, and the presence of a LINER is identified in all these galaxies. The regions up to one effective radius of all galaxies are basically dominated by α -enhanced metal-rich old stellar populations likely due to rapid star formation episodes that induced efficient chemical enrichment. On average, the age and [α /Fe] gradients are null and the [M/H] gradients are negative, although discordant cases were found. We found no correlation between the stellar population properties and the LINER presence as well as between the stellar properties and environment or gravitational interaction, suggesting that the influence of progenitor mass cannot be discarded in the formation and evolution of early-type galaxies.

Modelling chemical abundance distributions for dwarf galaxies in the Local Group: the impact of turbulent metal diffusion

NASA Astrophysics Data System (ADS)

Escala, Ivanna; Wetzel, Andrew; Kirby, Evan N.; Hopkins, Philip F.; Ma, Xiangcheng; Wheeler, Coral; Kereš, Dušan; Faucher-Giguère, Claude-André; Quataert, Eliot

2018-02-01

We investigate stellar metallicity distribution functions (MDFs), including Fe and α-element abundances, in dwarf galaxies from the Feedback in Realistic Environment (FIRE) project. We examine both isolated dwarf galaxies and those that are satellites of a Milky Way-mass galaxy. In particular, we study the effects of including a sub-grid turbulent model for the diffusion of metals in gas. Simulations that include diffusion have narrower MDFs and abundance ratio distributions, because diffusion drives individual gas and star particles towards the average metallicity. This effect provides significantly better agreement with observed abundance distributions in dwarf galaxies in the Local Group, including small intrinsic scatter in [α/Fe] versus [Fe/H] of ≲0.1 dex. This small intrinsic scatter arises in our simulations because the interstellar medium in dwarf galaxies is well mixed at nearly all cosmic times, such that stars that form at a given time have similar abundances to ≲0.1 dex. Thus, most of the scatter in abundances at z = 0 arises from redshift evolution and not from instantaneous scatter in the ISM. We find similar MDF widths and intrinsic scatter for satellite and isolated dwarf galaxies, which suggests that environmental effects play a minor role compared with internal chemical evolution in our simulations. Overall, with the inclusion of metal diffusion, our simulations reproduce abundance distribution widths of observed low-mass galaxies, enabling detailed studies of chemical evolution in galaxy formation.

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.

ALFALFA DISCOVERY OF THE MOST METAL-POOR GAS-RICH GALAXY KNOWN: AGC 198691

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirschauer, Alec S.; Salzer, John J.; Rhode, Katherine L., E-mail: ash@astro.indiana.edu, E-mail: slaz@astro.indiana.edu, E-mail: krhode@indiana.edu

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 10{sup 6}–10{sup 7.2} M {sub ⊙}, 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 enablemore » the measurement of the temperature-sensitive [O iii] λ 4363 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.« less

Properties of the molecular gas in the fast outflow in the Seyfert galaxy IC 5063

NASA Astrophysics Data System (ADS)

Oosterloo, Tom; Raymond Oonk, J. B.; Morganti, Raffaella; Combes, Françoise; Dasyra, Kalliopi; Salomé, Philippe; Vlahakis, Nektarios; Tadhunter, Clive

2017-12-01

We present a detailed study of the properties of the molecular gas in the fast outflow driven by the active galactic nucleus (AGN) in the nearby radio-loud Seyfert galaxy IC 5063. By using ALMA observations of a number of tracers of the molecular gas (12CO(1-0), 12CO(2-1), 12CO(3-2), 13CO(2-1) and HCO+(4-3)), we map the differences in excitation, density and temperature of the gas as function of position and kinematics. The results show that in the immediate vicinity of the radio jet, a fast outflow, with velocities up to 800 km s-1, is occurring of which the gas has high excitation with excitation temperatures in the range 30-55 K, demonstrating the direct impact of the jet on the ISM. The relative brightness of the 12CO lines, as well as that of 13CO(2-1) vs. 12CO(2-1), show that the outflow is optically thin. We estimate the mass of the molecular outflow to be at least 1.2 × 106 M⊙ and likely to be a factor between two and three larger than this value. This is similar to that of the outflow of atomic gas, but much larger than that of the ionised outflow, showing that the outflow in IC 5063 is dominated by cold gas. The total mass outflow rate we estimated to be 12 M⊙ yr-1. The mass of the outflow is much smaller than the total gas mass of the ISM of IC 5063. Therefore, although the influence of the AGN and its radio jet is very significant in the inner regions of IC 5063, globally speaking the impact will be very modest. We used RADEX non-LTE modelling to explore the physical conditions of the molecular gas in the outflow. Models with the outflowing gas being quite clumpy give the most consistent results and our preferred solutions have kinetic temperatures in the range 20-100 K and densities between 105 and 106 cm-3. The resulting pressures are 106-107.5 K cm-3, about two orders of magnitude higher than in the outer quiescent disk. The highest densities and temperatures are found in the regions with the fastest outflow. The results strongly suggest that

Supernovae in Early-Type Galaxies: Directly Connecting Age and Metallicity with Type Ia Luminosity

NASA Astrophysics Data System (ADS)

Gallagher, Joseph S.; Garnavich, Peter M.; Caldwell, Nelson; Kirshner, Robert P.; Jha, Saurabh W.; Li, Weidong; Ganeshalingam, Mohan; Filippenko, Alexei V.

2008-10-01

We have obtained optical spectra of 29 early-type (E/S0) galaxies that hosted Type Ia supernovae (SNe Ia). We have measured absorption-line strengths and compared them to a grid of models to extract the relations between the supernova properties and the luminosity-weighted age/composition of the host galaxies. Such a direct measurement is a marked improvement over existing analyses that tend to rely on general correlations between the properties of stellar populations and morphology. We find a strong correlation suggesting that SNe Ia in galaxies whose populations have a characteristic age greater than 5 Gyr are ~1 mag fainter at Vmax than those found in galaxies with younger populations. We find that SN Ia distance residuals in the Hubble diagram are correlated with host-galaxy metal abundance with higher iron abundance galaxies hosting less-luminous supernovae. We thus conclude that the time since progenitor formation primarily determines the radioactive Ni production while progenitor metal abundance has a weaker influence on peak luminosity, but one not fully corrected by light-curve shape and color fitters. This result, particularly the secondary dependence on metallicity, has significant implications for the determination of the equation-of-state parameter, w = P/(ρ c2) , and could impact planning for future dark-energy missions such as JDEM. Assuming no selection effects in discovering SNe Ia in local early-type galaxies, we find a higher specific SN Ia rate in E/S0 galaxies with ages below 3 Gyr than in older hosts. The higher rate and brighter luminosities seen in the youngest E/S0 hosts may be a result of recent star formation and represents a tail of the "prompt" SN Ia progenitors.

THE HOST GALAXY OF THE SUPER-LUMINOUS SN 2010gx AND LIMITS ON EXPLOSIVE {sup 56}Ni PRODUCTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Ting-Wan; Smartt, Stephen J.; Kotak, Rubina

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)more » = 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).« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maier, C.; Ziegler, B. L.; Lilly, S. J.

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 galaxiesmore » 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.« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sreedhar, Yuvraj Harsha; Rakos, Karl D.; Hensler, Gerhard

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 colorsmore » (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

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.

Hubble’s Hidden Galaxy

NASA Image and Video Library

2017-12-08

IC 342 is a challenging cosmic target. Although it is bright, the galaxy sits near the equator of the Milky Way’s galactic disk, where the sky is thick with glowing cosmic gas, bright stars, and dark, obscuring dust. In order for astronomers to see the intricate spiral structure of IC 342, they must gaze through a large amount of material contained within our own galaxy — no easy feat! As a result IC 342 is relatively difficult to spot and image, giving rise to its intriguing nickname: the “Hidden Galaxy.” Located very close (in astronomical terms) to the Milky Way, this sweeping spiral galaxy would be among the brightest in the sky were it not for its dust-obscured location. The galaxy is very active, as indicated by the range of colors visible in this NASA/ESA Hubble Space Telescope image, depicting the very central region of the galaxy. A beautiful mixture of hot, blue star-forming regions, redder, cooler regions of gas, and dark lanes of opaque dust can be seen, all swirling together around a bright core. In 2003, astronomers confirmed this core to be a specific type of central region known as an HII nucleus — a name that indicates the presence of ionized hydrogen — that is likely to be creating many hot new stars. Credit: ESA/Hubble & NASA NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

A 3D analysis of the metal distribution in the compact group of galaxies HCG 31

NASA Astrophysics Data System (ADS)

Torres-Flores, Sergio; Mendes de Oliveira, Claudia; Alfaro-Cuello, Mayte; Rodrigo Carrasco, Eleazar; de Mello, Duilia; Amram, Philippe

2015-02-01

We present new Gemini/GMOS integral field unit observations of the central region of the merging compact group of galaxies HCG 31. Using this data set, we derive the oxygen abundances for the merging galaxies HCG 31A and HCG 31C. We found a smooth metallicity gradient between the nuclei of these galaxies, suggesting a mixing of metals between these objects. These results are confirmed by high-resolution Fabry-Perot data, from which we infer that gas is flowing between HCG 31A and HCG 31C.

The mass-metallicity relation of AKARI-FMOS infrared galaxies at z ∼ 0.88 in the AKARI North Ecliptic Pole Deep Survey Field

NASA Astrophysics Data System (ADS)

Oi, Nagisa; Goto, Tomotsugu; Malkan, Matthew; Pearson, Chris; Matsuhara, Hideo

2017-08-01

The mass, metallicity, and star formation rate (SFR) of a galaxy are crucial parameters in understanding galaxy formation and evolution. However, the relation between these parameters, (i.e., the fundamental relation) is still a matter of debate for luminous infrared (IR) galaxies, which carry a bulk of the SFR budget of the universe at z ∼ 1. We have investigated the relation among stellar mass, gas-phase oxygen abundance, and SFR of the Japanese infrared satellite AKARI-detected mid-IR galaxies at z ∼ 0.88 in the AKARI north ecliptic pole deep field. We observed ∼350 AKARI sources with Subaru/Fiber Multi Object Spectrograph near-IR spectrograph, and detected confirmed Hα emission lines from 25 galaxies and expected Hα emission lines from 44 galaxies. The SFRHα, IR of our sample is almost constant (〈SFRHα, IR〉 = ∼ 25 M⊙ yr - 1) over the stellar mass range of our sample. Compared with main-sequence (MS) galaxies at a similar redshift range (z ∼ 0.78), the average SFR of our detected sample is comparable for massive galaxies ( ∼ 1010.58 M⊙), while higher by ∼0.6 dex for less massive galaxies ( ∼ 1010.05 M⊙). We measure metallicities from the [N II]/Hα emission line ratio. We find that the mass-metallicity relation of our individually measured sources agrees with that for optically-selected star-forming galaxies at z ∼ 0.1, while metallicities of stacked spectra agree with that of MS galaxies at z ∼ 0.78. Considering the high SFR of individually measured sources, the fundamental metallicity relation (FMR) of the IR galaxies is different from that at z ∼ 0.1. However, on the mass-metallicity plane, they are consistent with the MS galaxies, highlighting the higher SFR of the IR galaxies. This suggests that the evolutionary path of our infrared galaxies is different from that of MS galaxies. A possible physical interpretation includes that the star-formation activities of IR galaxies at z ∼ 0.88 in our sample are enhanced by

The mass-metallicity relations for gas and stars in star-forming galaxies: strong outflow versus variable IMF

NASA Astrophysics Data System (ADS)

Lian, Jianhui; Thomas, Daniel; Maraston, Claudia; Goddard, Daniel; Comparat, Johan; Gonzalez-Perez, Violeta; Ventura, Paolo

2018-02-01

We investigate the mass-metallicity relations for the gaseous (MZRgas) and stellar components (MZRstar) of local star-forming galaxies based on a representative sample from Sloan Digital Sky Survey Data Release 12. The mass-weighted average stellar metallicities are systematically lower than the gas metallicities. This difference in metallicity increases towards galaxies with lower masses and reaches 0.4-0.8 dex at 109 M⊙ (depending on the gas metallicity calibration). As a result, the MZRstar is much steeper than the MZRgas. The much lower metallicities in stars compared to the gas in low-mass galaxies imply dramatic metallicity evolution with suppressed metal enrichment at early times. The aim of this paper is to explain the observed large difference in gas and stellar metallicity and to infer the origin of the mass-metallicity relations. To this end we develop a galactic chemical evolution model accounting for star formation, gas inflow and outflow. By combining the observed mass-metallicity relation for both gas and stellar components to constrain the models, we find that only two scenarios are able to reproduce the observations. Either strong metal outflow or a steep initial mass function (IMF) slope at early epochs of galaxy evolution is needed. Based on these two scenarios, for the first time we successfully reproduce the observed MZRgas and MZRstar simultaneously, together with other independent observational constraints in the local Universe. Our model also naturally reproduces the flattening of the MZRgas at the high-mass end leaving the MZRstar intact, as seen in observational data.

Dust Evolution in Low-Metallicity Environments: Bridging the Gap Between Local Universe and Primordial Galaxies

NASA Astrophysics Data System (ADS)

Galliano, Frederic; Barlow, Mike; Bendo, George; Boselli, Alessandro; Buat, Veronique; Chanial, Pierre; Clements, David; Davies, Jon; Eales, Steve; Gomez, Haley; Isaak, Kate; Madden, Suzanne; Page, Mathew; Perez Fournon, Ismael; Sauvage, Marc; Spinoglio, Luigi; Vaccari, Mattia; Wilson, Christine

2008-03-01

The local galaxy Science Advisory Group (SAG 2) in the Herschel/SPIRE consortium, has constructed a Guaranteed Time Key Program using the PACS and SPIRE insruments to obtain 60 to 550 micron photometry of a statistically significant sample of 51 dwarf galaxies in our local universe chosen to cover an impressivly broad range of physical conditions. Here we propose the necessary complementary IRAC, MIPS and IRS Spitzer observations which together with the Herschel GT database will provide a rich database to the community to perform the dust and gas analyses in unprecedented detail in low metallicity galaxies ranging between 1/50 to 1 solar metallicity. Due to their chemical youth, and to the extreme conditions they experience, low metallicity environments constitute a keystone to understand dust evolution. The primary goal of this combined Herschel and Spitzer project is to study in details the physical processes at play within the ISM of these galaxies. We will take advantage of the powerful combination of Spitzer, Herschel and ancillary data to decompose the SED into the emission coming from the main phases of the ISM. Such a decomposition will provide reliable estimate of the abundances of the principal dust species, as a fonction of metallicity and physical conditions. These results will be exploited to compare the various evolutionary processes affecting the dust content of galaxies. All these outstanding scientific advances will be the true legacy value that this project brings to the community.

Galaxy And Mass Assembly (GAMA): The M-Z relation for galaxy groups

NASA Astrophysics Data System (ADS)

Lara-López, M. A.; Hopkins, A. M.; Robotham, A.; Owers, M. S.; Colless, M.; Brough, S.; Norberg, P.; Steele, O.; Taylor, E. N.; Thomas, D.

2013-04-01

The stellar mass and metallicity are among the fundamental parameters of galaxies. An understanding of the interplay between those properties as well as their environmental dependence will give us a general picture of the physics and feedback processes ongoing in groups of galaxies. We study the relationships and environmental dependencies between the stellar mass, and gas metallicity for more than 1900 galaxies in groups up to redshift 0.35 using the Galaxy And Mass Assembly (GAMA) survey. Using a control sample of more than 28 000 star-forming field galaxies, we find evidence for a decrement of the gas metallicity for galaxies in groups.

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

Active galactic nuclei feedback, quiescence and circumgalactic medium metal enrichment in early-type galaxies

NASA Astrophysics Data System (ADS)

Eisenreich, Maximilian; Naab, Thorsten; Choi, Ena; Ostriker, Jeremiah P.; Emsellem, Eric

2017-06-01

We present three-dimensional hydrodynamical simulations showing the effect of kinetic and radiative active galactic nuclei (AGN) feedback on a model galaxy representing a massive quiescent low-redshift early-type galaxy of M* = 8.41 × 1010 M⊙, harbouring an MBH = 4 × 108 M⊙ black hole surrounded by a cooling gaseous halo. We show that, for a total baryon fraction of ˜20 per cent of the cosmological value, feedback from the AGN can keep the galaxy quiescent for about 4.35 Gyr and with properties consistent with black hole mass and X-ray luminosity scaling relations. However, this can only be achieved if the AGN feedback model includes both kinetic and radiative feedback modes. The simulation with only kinetic feedback fails to keep the model galaxy fully quiescent, while one with only radiative feedback leads to excessive black hole growth. For higher baryon fractions (e.g. 50 per cent of the cosmological value), the X-ray luminosities exceed observed values by at least one order of magnitude, and rapid cooling results in a star-forming galaxy. The AGN plays a major role in keeping the circumgalactic gas at observed metallicities of Z/Z⊙ ≳ 0.3 within the central ˜30 kpc by venting nuclear gas enriched with metals from residual star formation activity. As indicated by previous cosmological simulations, our results are consistent with a model for which the black hole mass and the total baryon fraction are set at higher redshifts z > 1 and the AGN alone can keep the model galaxy on observed scaling relations. Models without AGN feedback violate both the quiescence criterion as well as circumgalactic medium metallicity constraints.

NOEMA Observations of a Molecular Cloud in the Low-metallicity Galaxy Kiso 5639

NASA Astrophysics Data System (ADS)

Elmegreen, Bruce G.; Herrera, Cinthya; Rubio, Monica; Elmegreen, Debra Meloy; Sánchez Almeida, Jorge; Muñoz-Tuñón, Casiana; Olmo-García, Amanda

2018-06-01

A giant star-forming region in a metal-poor dwarf galaxy has been observed in optical lines with the 10 m Gran Telescopio Canarias (GTC) and in the emission line of CO(1–0) with the Northern Extended Millimeter Array (NOEMA) mm-wave interferometer. The metallicity was determined to be 12+{log}({{O}}/{{H}})=7.83+/- 0.09, from which we estimate a conversion factor of α CO ∼ 100 M ⊙ pc‑2(K km s‑1)‑1 and a molecular cloud mass of ∼2.9 × 107 M ⊙. This is an enormous concentration of molecular mass at one end of a small galaxy, suggesting a recent accretion. The molecular cloud properties seem normal: the surface density, 120 M ⊙ pc‑2, is comparable to that of a standard giant molecular cloud; the cloud’s virial ratio of ∼1.8 is in the star formation range; and the gas consumption time, 0.5 Gyr, at the present star formation rate is typical for molecular regions. The low metallicity implies that the cloud has an average visual extinction of only 0.8 mag, which is close to the threshold for molecule formation. With such an extinction threshold, molecular clouds in metal-poor regions should have high surface densities and high internal pressures. If high pressure is associated with the formation of massive clusters, then metal-poor galaxies such as dwarfs in the early universe could have been the hosts of metal-poor globular clusters.

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.

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.

UV spectroscopy of the most metal-poor galaxies: clues for interpreting distant galaxy observations

NASA Astrophysics Data System (ADS)

Wofford, A.; Vidal-García, A.; Feltre, A.; Chevallard, J.; Herenz, E.; Charlot, S., Stark, D. P.; Hayes, M.

2017-11-01

Among the most metal-poor galaxies known, SBS 0335-052E is on one of the most well-studied. For this galaxy, we present Hubble Space Telescope (HST) / Cosmic Origins Spectrograph (COS) detections of the C IV λλ1549, 1551, He II λ1640, O III] λλ1661, 1666, [C III] λ1907, and C III] λ1909 UV emission lines; and a Very Large Telescope (VLT) / Multi Unit Spectroscopic Explorer (MUSE) spectrum covering from 4600 to 9400 Å, which is co-spatial with the UV data and integrated over the same area. Using these datasets we test: a) the latest Charlot & Bruzal spectral synthesis models with very massive (300 M_⊙) single non-rotating stars; b) the ability of the tool, BayEsian Analysis of GaLaxy sEds (BEAGLE) to reproduce the observed emission line fluxes; and c) the extent to which physical properties of the gas and dust derived independently from the UV and optical with BEAGLE are constrained. The UV observations are part of a pilot program where we also observed UGC 5340-1 and I Zw 18 SE, whose spectra we also present in this contribution.

First multi-wavelength campaign on the gamma-ray-loud active galaxy IC 310

NASA Astrophysics Data System (ADS)

Ahnen, M. L.; Ansoldi, S.; Antonelli, L. A.; Arcaro, C.; Babić, A.; Banerjee, B.; Bangale, P.; Barres de Almeida, U.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Bernardini, E.; Berti, A.; Biasuzzi, B.; Biland, A.; Blanch, O.; Bonnefoy, S.; Bonnoli, G.; Borracci, F.; Bretz, T.; Carosi, R.; Carosi, A.; Chatterjee, A.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; Cumani, P.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Lotto, B.; de Oña Wilhelmi, E.; Di Pierro, F.; Doert, M.; Domínguez, A.; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Eisenacher Glawion, D.; Elsaesser, D.; Engelkemeier, M.; Fallah Ramazani, V.; Fernández-Barral, A.; Fidalgo, D.; Fonseca, M. V.; Font, L.; Fruck, C.; Galindo, D.; García López, R. J.; Garczarczyk, M.; Gaug, M.; Giammaria, P.; Godinović, N.; Gora, D.; Guberman, D.; Hadasch, D.; Hahn, A.; Hassan, T.; Hayashida, M.; Herrera, J.; Hose, J.; Hrupec, D.; Hughes, G.; Idec, W.; Ishio, K.; Kodani, K.; Konno, Y.; Kubo, H.; Kushida, J.; Lelas, D.; Lindfors, E.; Lombardi, S.; Longo, F.; López, M.; Majumdar, P.; Makariev, M.; Mallot, K.; Maneva, G.; Manganaro, M.; Mannheim, K.; Maraschi, L.; Mariotti, M.; Martínez, M.; Mazin, D.; Menzel, U.; Mirzoyan, R.; Moralejo, A.; Moretti, E.; Nakajima, D.; Neustroev, V.; Niedzwiecki, A.; Nievas Rosillo, M.; Nilsson, K.; Nishijima, K.; Noda, K.; Nogués, L.; Nöthe, M.; Paiano, S.; Palacio, J.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Paredes-Fortuny, X.; Pedaletti, G.; Peresano, M.; Perri, L.; Persic, M.; Poutanen, J.; Prada Moroni, P. G.; Prandini, E.; Puljak, I.; Garcia, J. R.; Reichardt, I.; Rhode, W.; Ribó, M.; Rico, J.; Saito, T.; Satalecka, K.; Schroeder, S.; Schweizer, T.; Shore, S. N.; Sillanpää, A.; Sitarek, J.; Snidaric, I.; Sobczynska, D.; Stamerra, A.; Strzys, M.; Surić, T.; Takalo, L.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Tescaro, D.; Teshima, M.; Torres, D. F.; Torres-Albà, N.; Toyama, T.; Treves, A.; Vanzo, G.; Vazquez Acosta, M.; Vovk, I.; Ward, J. E.; Will, M.; Wu, M. H.; Krauß, F.; Schulz, R.; Kadler, M.; Wilms, J.; Ros, E.; Bach, U.; Beuchert, T.; Langejahn, M.; Wendel, C.; Gehrels, N.; Baumgartner, W. H.; Markwardt, C. B.; Müller, C.; Grinberg, V.; Hovatta, T.; Magill, J.

2017-07-01

Context. The extragalactic very-high-energy gamma-ray sky is rich in blazars. These are jetted active galactic nuclei that are viewed at a small angle to the line-of-sight. Only a handful of objects viewed at a larger angle are so far known to emit above 100 GeV. Multi-wavelength studies of such objects up to the highest energies provide new insights into the particle and radiation processes of active galactic nuclei. Aims: We aim to report the results from the first multi-wavelength campaign observing the TeV detected nucleus of the active galaxy IC 310, whose jet is observed at a moderate viewing angle of 10°-20°. Methods: The multi-instrument campaign was conducted between 2012 November and 2013 January, and involved observations with MAGIC, Fermi, INTEGRAL, Swift, OVRO, MOJAVE and EVN. These observations were complemented with archival data from the AllWISE and 2MASS catalogs. A one-zone synchrotron self-Compton model was applied to describe the broadband spectral energy distribution. Results: IC 310 showed an extraordinary TeV flare at the beginning of the campaign, followed by a low, but still detectable TeV flux. Compared to previous measurements in this energy range, the spectral shape was found to be steeper during the low emission state. Simultaneous observations in the soft X-ray band showed an enhanced energy flux state and a harder-when-brighter spectral shape behavior. No strong correlated flux variability was found in other frequency regimes. The broadband spectral energy distribution obtained from these observations supports the hypothesis of a double-hump structure. Conclusions: The harder-when-brighter trend in the X-ray and VHE emission, observed for the first time during this campaign, is consistent with the behavior expected from a synchrotron self-Compton scenario. The contemporaneous broadband spectral energy distribution is well described with a one-zone synchrotron self-Compton model using parameters that are comparable to those found for

The luminous, massive and solar metallicity galaxy hosting the Swift γ-ray burst GRB 160804A at z = 0.737

NASA Astrophysics Data System (ADS)

Heintz, K. E.; Malesani, D.; Wiersema, K.; Jakobsson, P.; Fynbo, J. P. U.; Savaglio, S.; Cano, Z.; Covino, S.; D'Elia, V.; Gomboc, A.; Hammer, F.; Kaper, L.; Milvang-Jensen, B.; Møller, P.; Piranomonte, S.; Selsing, J.; Rhodin, N. H. P.; Tanvir, N. R.; Thöne, C. C.; de Ugarte Postigo, A.; Vergani, S. D.; Watson, D.

2018-02-01

We here present the spectroscopic follow-up observations with VLT/X-shooter of the Swift long-duration gamma-ray burst GRB 160804A at z = 0.737. Typically, GRBs are found in low-mass, metal-poor galaxies that constitute the sub-luminous population of star-forming galaxies. For the host galaxy of the GRB presented here, we derive a stellar mass of log (M*/ M⊙) = 9.80 ± 0.07, a roughly solar metallicity (12 + log (O/H) = 8.74 ± 0.12) based on emission line diagnostics, and an infrared luminosity of M3.6/(1 + z) = -21.94 mag, but find it to be dust-poor (E(B - V) < 0.05 mag). This establishes the galaxy hosting GRB 160804A as one of the most luminous, massive and metal-rich GRB hosts at z < 1.5. Furthermore, the gas-phase metallicity is found to be representative of the physical conditions of the gas close to the explosion site of the burst. The high metallicity of the host galaxy is also observed in absorption, where we detect several strong Fe II transitions as well as Mg II and Mg I. Although host galaxy absorption features are common in GRB afterglow spectra, we detect absorption from strong metal lines directly in the host continuum (at a time when the afterglow was contributing to < 15 per cent). Finally, we discuss the possibility that the geometry and state of the absorbing and emitting gas are indicative of a galactic scale outflow expelled at the final stage of two merging galaxies.

The Galics Project: Virtual Galaxy: from Cosmological N-body Simulations

NASA Astrophysics Data System (ADS)

Guiderdoni, B.

The GalICS project develops extensive semi-analytic post-processing of large cosmological simulations to describe hierarchical galaxy formation. The multiwavelength statistical properties of high-redshift and local galaxies are predicted within the large-scale structures. The fake catalogs and mock images that are generated from the outputs are used for the analysis and preparation of deep surveys. The whole set of results is now available in an on-line database that can be easily queried. The GalICS project represents a first step towards a 'Virtual Observatory of virtual galaxies'.

Variations in Metallicity and Gas Content in Spiral Galaxies: Accidents of Infall

NASA Astrophysics Data System (ADS)

Shields, Gregory A.; Robertson, P.; Dave, R.; Blanc, G. A.; Wright, A.

2013-01-01

Oxygen abundances are elevated in hydrogen deficient spirals in the Virgo and Pegasus clusters (Robertson et al. 2012, ApJ 748:48, and references therein). We confirm the relationship between O/H and H I deficiency "DEF" for an additional set of cluster spirals. In addition, we find that field spirals show a similar increase in O/H with DEF. Thus, the relationship is not uniquely the result of environmental processes in clusters. Cosmological simulations of galaxy formation predict a qualitatively similar trend of O/H with DEF for field spirals. This reflects excursions of gas content and metallicity above and below the mean mass-metallicity relationship as galaxies evolve. These excursions result from the stochastic effects of mergers and merger-free periods during the evolution.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laycock, Silas; Cappallo, Rigel; Williams, Benjamin F.

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 3 σ 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 >10{sup 35} erg s{sup −1}, providingmore » 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.« less

Galaxy And Mass Assembly (GAMA): a deeper view of the mass, metallicity and SFR relationships

NASA Astrophysics Data System (ADS)

Lara-López, M. A.; Hopkins, A. M.; López-Sánchez, A. R.; Brough, S.; Gunawardhana, M. L. P.; Colless, M.; Robotham, A. S. G.; Bauer, A. E.; Bland-Hawthorn, J.; Cluver, M.; Driver, S.; Foster, C.; Kelvin, L. S.; Liske, J.; Loveday, J.; Owers, M. S.; Ponman, T. J.; Sharp, R. G.; Steele, O.; Taylor, E. N.; Thomas, D.

2013-09-01

A full appreciation of the role played by gas metallicity (Z), star formation rate (SFR) and stellar mass (M*) is fundamental to understanding how galaxies form and evolve. The connections between these three parameters at different redshifts significantly affect galaxy evolution, and thus provide important constraints for galaxy evolution models. Using data from the Sloan Digital Sky Survey-Data Release 7 (SDSS-DR7) and the Galaxy and Mass Assembly (GAMA) surveys, we study the relationships and dependences between SFR, Z and M*, as well as the Fundamental Plane for star-forming galaxies. We combine both surveys using volume-limited samples up to a redshift of z ≈ 0.36. The GAMA and SDSS surveys complement each other when analysing the relationships between SFR, M* and Z. We present evidence for SFR and metallicity evolution to z ˜ 0.2. We study the dependences between SFR, M*, Z and specific SFR (SSFR) on the M*-Z, M*-SFR, M*-SSFR, Z-SFR and Z-SSFR relations, finding strong correlations between all. Based on those dependences, we propose a simple model that allows us to explain the different behaviour observed between low- and high-mass galaxies. Finally, our analysis allows us to confirm the existence of a Fundamental Plane, for which M* = f(Z, SFR) in star-forming galaxies.

Metal distributions out to 0.5 r {sub 180} in the intracluster medium of four galaxy groups observed with Suzaku

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sasaki, Toru; Matsushita, Kyoko; Sato, Kosuke, E-mail: j1213703@ed.tus.ac.jp, E-mail: matusita@rs.kagu.tus.ac.jp

2014-01-20

We studied the distributions of metal abundances and metal-mass-to-light ratios in the intracluster medium (ICM) of four galaxy groups, MKW 4, HCG 62, the NGC 1550 group, and the NGC 5044 group, out to ∼0.5 r {sub 180} observed with Suzaku. The iron abundance decreases with radius and is about 0.2-0.4 solar beyond 0.1 r {sub 180}. At a given radius in units of r {sub 180}, the iron abundance in the ICM of the four galaxy groups was consistent with or smaller than those of clusters of galaxies. The Mg/Fe and Si/Fe ratios in the ICM are nearly constantmore » at the solar ratio out to 0.5 r {sub 180}. We also studied systematic uncertainties in the derived metal abundances, comparing the results from two versions of atomic data for astrophysicists (ATOMDB) and single- and two-temperature model fits. Since the metals have been synthesized in galaxies, we collected K-band luminosities of galaxies from the Two Micron All Sky Survey catalog and calculated the integrated iron-mass-to-light-ratios (IMLR), or the ratios of the iron mass in the ICM to light from stars in galaxies. The groups with smaller gas-mass-to-light ratios have smaller IMLR values and the IMLR is inversely correlated with the entropy excess. Based on these abundance features, we discussed the past history of metal enrichment processes in groups of galaxies.« less

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.

Young, metal-enriched cores in early-type dwarf galaxies in the Virgo cluster based on colour gradients

NASA Astrophysics Data System (ADS)

Urich, Linda; Lisker, Thorsten; Janz, Joachim; van de Ven, Glenn; Leaman, Ryan; Boselli, Alessandro; Paudel, Sanjaya; Sybilska, Agnieszka; Peletier, Reynier F.; den Brok, Mark; Hensler, Gerhard; Toloba, Elisa; Falcón-Barroso, Jesús; Niemi, Sami-Matias

2017-10-01

Early-type dwarf galaxies are not simply featureless, old objects, but were found to be much more diverse, hosting substructures and a variety of stellar population properties. To explore the stellar content of faint early-type galaxies, and to investigate in particular those with recent central star formation, we study colours and colour gradients within one effective radius in optical (g - r) and near-infrared (I - H) bands for 120 Virgo cluster early-type galaxies with - 19 mag galaxies turn out to have blue cores, when defined as g - r colour gradients larger than 0.10 mag/Reff, which represents the positive tail of the gradient distribution. For these galaxies, we find that they have the strongest age gradients, and that even outside the blue core, their mean stellar population is younger than the mean of ordinary faint early-type galaxies. The metallicity gradients of these blue-cored early-type dwarf galaxies are, however, in the range of most normal faint early-type galaxies, which we find to have non-zero gradients with higher central metallicity. The blue central regions are consistent with star formation activity within the last few 100 Myr. We discuss whether these galaxies could be explained by environmental quenching of star formation in the outer galaxy regions while the inner star formation activity continued.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cannon, John M.; Alfvin, Erik D.; Johnson, Megan

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 amore » 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.« less

The Mass-Metallicity Relation with the Direct Method on Stacked Spectra of SDSS Galaxies

NASA Astrophysics Data System (ADS)

Andrews, Brett H.; Martini, Paul

2013-03-01

The relation between galaxy stellar mass and gas-phase metallicity is a sensitive diagnostic of the main processes that drive galaxy evolution, namely cosmological gas inflow, metal production in stars, and gas outflow via galactic winds. We employed the direct method to measure the metallicities of ~200,000 star-forming galaxies from the Sloan Digital Sky Survey that were stacked in bins of (1) stellar mass and (2) both stellar mass and star formation rate (SFR) to significantly enhance the signal-to-noise ratio of the weak [O III] λ4363 and [O II] λλ7320, 7330 auroral lines required to apply the direct method. These metallicity measurements span three decades in stellar mass from log(M sstarf/M ⊙) = 7.4-10.5, which allows the direct method mass-metallicity relation to simultaneously capture the high-mass turnover and extend a full decade lower in mass than previous studies that employed more uncertain strong line methods. The direct method mass-metallicity relation rises steeply at low mass (O/H vprop M sstarf 1/2) until it turns over at log(M sstarf/M ⊙) = 8.9 and asymptotes to 12 + log(O/H) = 8.8 at high mass. The direct method mass-metallicity relation has a steeper slope, a lower turnover mass, and a factor of two to three greater dependence on SFR than strong line mass-metallicity relations. Furthermore, the SFR-dependence appears monotonic with stellar mass, unlike strong line mass-metallicity relations. We also measure the N/O abundance ratio, an important tracer of star formation history, and find the clear signature of primary and secondary nitrogen enrichment. N/O correlates tightly with oxygen abundance, and even more so with stellar mass.

Searching for intermediate-mass black holes in extremely-metal poor galaxies

NASA Astrophysics Data System (ADS)

Mezcua, Mar

2016-09-01

Extremely metal-poor dwarf galaxies (XMPs) are star-forming, low-mass galaxies with metallicites highly sub-solar. Their regions of star formation could be triggered by the accretion of pristine gas from the cosmic web and harbour Population III stars. XMPs are thus ideal laboratories for searching for the seed black holes or intermediate-mass black holes (IMBHs) that populated the early Universe. The combination of X-ray, radio and optical observations offer the best tool for detecting such IMBHs in the local Universe. We propose Chandra observations of a sample of XMPs whose optical spectra indicate the possible presence of an active black hole of 1e4 - 1e6 Msun. The Chandra data could confirm this and yield the first detection of an IMBH in these type of galaxies.

Metal enrichment in the neutral gas of star-forming galaxies

NASA Astrophysics Data System (ADS)

Lebouteiller, V.; Kunth, D.; Désert, J.-M.; Thuan, T. X.

2009-05-01

We derive the chemical composition of the neutral gas in the blue compact dwarf (BCD) Pox 36 observed with FUSE. Metals (N, O, Ar, and Fe) are underabundant as compared to the ionized gas associated with H II regions by a factor ~7. The neutral gas, although it is not pristine, is thus probably less chemically evolved than the ionized gas. This could be due to different dispersal and mixing timescales. Results are compared to those of other BCDs observed with FUSE. The metallicity of the neutral gas in BCDs seems to reach a lower threshold of ~1/50Zsolar for extremely-metal poor galaxies.

Local anticorrelation between star formation rate and gas-phase metallicity in disc galaxies

NASA Astrophysics Data System (ADS)

Sánchez Almeida, J.; Caon, N.; Muñoz-Tuñón, C.; Filho, M.; Cerviño, M.

2018-06-01

Using a representative sample of 14 star-forming dwarf galaxies in the local Universe, we show the existence of a spaxel-to-spaxel anticorrelation between the index N2 ≡ log ([N II]λ 6583/H α ) and the H α flux. These two quantities are commonly employed as proxies for gas-phase metallicity and star formation rate (SFR), respectively. Thus, the observed N2 to H α relation may reflect the existence of an anticorrelation between the metallicity of the gas forming stars and the SFR it induces. Such an anticorrelation is to be expected if variable external metal-poor gas fuels the star-formation process. Alternatively, it can result from the contamination of the star-forming gas by stellar winds and SNe, provided that intense outflows drive most of the metals out of the star-forming regions. We also explore the possibility that the observed anticorrelation is due to variations in the physical conditions of the emitting gas, other than metallicity. Using alternative methods to compute metallicity, as well as previous observations of H II regions and photoionization models, we conclude that this possibility is unlikely. The radial gradient of metallicity characterizing disc galaxies does not produce the correlation either.

SPICA and the Chemical Evolution of Galaxies: The Rise of Metals and Dust

NASA Astrophysics Data System (ADS)

Fernández-Ontiveros, J. A.; Armus, L.; Baes, M.; Bernard-Salas, J.; Bolatto, A. D.; Braine, J.; Ciesla, L.; De Looze, I.; Egami, E.; Fischer, J.; Giard, M.; González-Alfonso, E.; Granato, G. L.; Gruppioni, C.; Imanishi, M.; Ishihara, D.; Kaneda, H.; Madden, S.; Malkan, M.; Matsuhara, H.; Matsuura, M.; Nagao, T.; Najarro, F.; Nakagawa, T.; Onaka, T.; Oyabu, S.; Pereira-Santaella, M.; Pérez Fournon, I.; Roelfsema, P.; Santini, P.; Silva, L.; Smith, J.-D. T.; Spinoglio, L.; van der Tak, F.; Wada, T.; Wu, R.

2017-11-01

The physical processes driving the chemical evolution of galaxies in the last 11Gyr cannot be understood without directly probing the dust-obscured phase of star-forming galaxies and active galactic nuclei. This phase, hidden to optical tracers, represents the bulk of the star formation and black hole accretion activity in galaxies at 1 < z < 3. Spectroscopic observations with a cryogenic infrared observatory like SPICA, will be sensitive enough to peer through the dust-obscured regions of galaxies and access the rest-frame mid- to far-infrared range in galaxies at high-z. This wavelength range contains a unique suite of spectral lines and dust features that serve as proxies for the abundances of heavy elements and the dust composition, providing tracers with a feeble response to both extinction and temperature. In this work, we investigate how SPICA observations could be exploited to understand key aspects in the chemical evolution of galaxies: the assembly of nearby galaxies based on the spatial distribution of heavy element abundances, the global content of metals in galaxies reaching the knee of the luminosity function up to z 3, and the dust composition of galaxies at high-z. Possible synergies with facilities available in the late 2020s are also discussed.

The Metallicity of Void Dwarf Galaxies

NASA Astrophysics Data System (ADS)

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

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 (Mr > -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.

A giant stream of metal-rich stars in the halo of the galaxy M31.

PubMed

Ibata, R; Irwin, M; Lewis, G; Ferguson, A M; Tanvir, N

2001-07-05

Recent observations have revealed streams of gas and stars in the halo of the Milky Way that are the debris from interactions between our Galaxy and some of its dwarf companion galaxies; the Sagittarius dwarf galaxy and the Magellanic clouds. Analysis of the material has shown that much of the halo is made up of cannibalized satellite galaxies, and that dark matter is distributed nearly spherically in the Milky Way. It remains unclear, however, whether cannibalized substructures are as common in the haloes of galaxies as predicted by galaxy-formation theory. Here we report the discovery of a giant stream of metal-rich stars within the halo of the nearest large galaxy, M31 (the Andromeda galaxy). The source of this stream could be the dwarf galaxies M32 and NGC205, which are close companions of M31 and which may have lost a substantial number of stars owing to tidal interactions. The results demonstrate that the epoch of galaxy building still continues, albeit at a modest rate, and that tidal streams may be a generic feature of galaxy haloes.

Massive Star Cluster Populations in Irregular Galaxies as Probable Younger Counterparts of Old Metal-rich Globular Cluster Populations in Spheroids

NASA Astrophysics Data System (ADS)

Kravtsov, V. V.

2006-09-01

Peak metallicities of metal-rich populations of globular clusters (MRGCs) belonging to early-type galaxies and spheroidal subsystems of spiral galaxies (spheroids) of different mass fall within the somewhat conservative -0.7<=[Fe/H]<=-0.3 range. Indeed, if possible age effects are taken into account, this metallicity range might become smaller. Irregular galaxies such as the Large Magellanic Cloud (LMC), with longer timescales of formation and lower star formation (SF) efficiency, do not contain old MRGCs with [Fe/H]>-1.0, but they are observed to form populations of young/intermediate-age massive star clusters (MSCs) with masses exceeding 104 Msolar. Their formation is widely believed to be an accidental process fully dependent on external factors. From the analysis of available data on the populations and their hosts, including intermediate-age populous star clusters in the LMC, we find that their most probable mean metallicities fall within -0.7<=[Fe/H]<=-0.3, as the peak metallicities of MRGCs do, irrespective of signs of interaction. Moreover, both the disk giant metallicity distribution function (MDF) in the LMC and the MDFs for old giants in the halos of massive spheroids exhibit a significant increase toward [Fe/H]~-0.5. That is in agreement with a correlation found between SF activity in galaxies and their metallicity. The formation of both the old MRGCs in spheroids and MSC populations in irregular galaxies probably occurs at approximately the same stage of the host galaxies' chemical evolution and is related to the essentially increased SF activity in the hosts around the same metallicity that is achieved very early in massive spheroids, later in lower mass spheroids, and much later in irregular galaxies. Changes in the interstellar dust, particularly in elemental abundances in dust grains and in the mass distribution function of the grains, may be among the factors regulating star and MSC formation activity in galaxies. Strong interactions and mergers

J0811+4730: the most metal-poor star-forming dwarf galaxy known

NASA Astrophysics Data System (ADS)

Izotov, Y. I.; Thuan, T. X.; Guseva, N. G.; Liss, S. E.

2018-01-01

We report the discovery of the most metal-poor dwarf star-forming galaxy (SFG) known to date, J0811+4730. This galaxy, at a redshift z = 0.04444, has a Sloan Digital Sky Survey (SDSS) g-band absolute magnitude Mg = -15.41 mag. It was selected by inspecting the spectroscopic data base in the Data Release 13 (DR13) of the SDSS. Large Binocular Telescope/Multi-Object Double spectrograph (LBT/MODS) spectroscopic observations reveal its oxygen abundance to be 12 + log O/H = 6.98 ± 0.02, the lowest ever observed for an SFG. J0811+4730 strongly deviates from the main sequence defined by SFGs in the emission line diagnostic diagrams and the metallicity-luminosity diagram. These differences are caused mainly by the extremely low oxygen abundance in J0811+4730, which is ∼10 times lower than that in main-sequence SFGs with similar luminosities. By fitting the spectral energy distributions of the SDSS and LBT spectra, we derive a stellar mass of M⋆ = 106.24-106.29 M⊙, and we find that a considerable fraction of the galaxy stellar mass was formed during the most recent burst of star formation.

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.

EVOLUTION OF THE MASS-METALLICITY RELATIONS IN PASSIVE AND STAR-FORMING GALAXIES FROM SPH-COSMOLOGICAL SIMULATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Romeo Velona, A. D.; Gavignaud, I.; Meza, A.

2013-06-20

We present results from SPH-cosmological simulations, including self-consistent modeling of supernova feedback and chemical evolution, of galaxies belonging to two clusters and 12 groups. We reproduce the mass-metallicity (ZM) relation of galaxies classified in two samples according to their star-forming (SF) activity, as parameterized by their specific star formation rate (sSFR), across a redshift range up to z = 2. The overall ZM relation for the composite population evolves according to a redshift-dependent quadratic functional form that is consistent with other empirical estimates, provided that the highest mass bin of the brightest central galaxies is excluded. Its slope shows irrelevantmore » evolution in the passive sample, being steeper in groups than in clusters. However, the subsample of high-mass passive galaxies only is characterized by a steep increase of the slope with redshift, from which it can be inferred that the bulk of the slope evolution of the ZM relation is driven by the more massive passive objects. The scatter of the passive sample is dominated by low-mass galaxies at all redshifts and keeps constant over cosmic times. The mean metallicity is highest in cluster cores and lowest in normal groups, following the same environmental sequence as that previously found in the red sequence building. The ZM relation for the SF sample reveals an increasing scatter with redshift, indicating that it is still being built at early epochs. The SF galaxies make up a tight sequence in the SFR-M{sub *} plane at high redshift, whose scatter increases with time alongside the consolidation of the passive sequence. We also confirm the anti-correlation between sSFR and stellar mass, pointing at a key role of the former in determining the galaxy downsizing, as the most significant means of diagnostics of the star formation efficiency. Likewise, an anti-correlation between sSFR and metallicity can be established for the SF galaxies, while on the contrary more

The H I chronicles of little things BCDs II: The origin of IC 10's H I structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ashley, Trisha; Simpson, Caroline E.; Pokhrel, Nau Raj

In this paper we analyze Very Large Array (VLA) telescope and Green Bank Telescope (GBT) atomic hydrogen (H I) data for the LITTLE THINGS (Local Irregulars That Trace Luminosity Extremes, The H I Nearby Galaxy Survey; https://science.nrao.edu/science/surveys/littlethings) blue compact dwarf galaxy IC 10. The VLA data allow us to study the detailed H I kinematics and morphology of IC 10 at high resolution while the GBT data allow us to search the surrounding area at high sensitivity for tenuous H I. IC 10's H I appears highly disturbed in both the VLA and GBT H I maps with a kinematicallymore » distinct northern H I extension, a kinematically distinct southern plume, and several spurs in the VLA data that do not follow the general kinematics of the main disk. We discuss three possible origins of its H I structure and kinematics in detail: a current interaction with a nearby companion, an advanced merger, and accretion of intergalactic medium. We find that IC 10 is most likely an advanced merger or a galaxy undergoing accretion.« less

METALLICITY AND AGE OF THE STELLAR STREAM AROUND THE DISK GALAXY NGC 5907

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laine, Seppo; Grillmair, Carl J.; Capak, Peter

2016-09-01

Stellar streams have become central to studies of the interaction histories of nearby galaxies. To characterize the most prominent parts of the stellar stream around the well-known nearby ( d  = 17 Mpc) edge-on disk galaxy NGC 5907, we have obtained and analyzed new, deep gri Subaru/Suprime-Cam and 3.6 μ m Spitzer /Infrared Array Camera observations. Combining the near-infrared 3.6 μ m data with visible-light images allows us to use a long wavelength baseline to estimate the metallicity and age of the stellar population along an ∼60 kpc long segment of the stream. We have fitted the stellar spectral energy distributionmore » with a single-burst stellar population synthesis model and we use it to distinguish between the proposed satellite accretion and minor/major merger formation models of the stellar stream around this galaxy. We conclude that a massive minor merger (stellar mass ratio of at least 1:8) can best account for the metallicity of −0.3 inferred along the brightest parts of the stream.« less

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.

The Metallicity Dependence of the CO → H2 Conversion Factor in z >= 1 Star-forming Galaxies

NASA Astrophysics Data System (ADS)

Genzel, R.; Tacconi, L. J.; Combes, F.; Bolatto, A.; Neri, R.; Sternberg, A.; Cooper, M. C.; Bouché, N.; Bournaud, F.; Burkert, A.; Comerford, J.; Cox, P.; Davis, M.; Förster Schreiber, N. M.; Garcia-Burillo, S.; Gracia-Carpio, J.; Lutz, D.; Naab, T.; Newman, S.; Saintonge, A.; Shapiro, K.; Shapley, A.; Weiner, B.

2012-02-01

We use the first systematic samples of CO millimeter emission in z >= 1 ''main-sequence'' star-forming galaxies to study the metallicity dependence of the conversion factor αCO, from CO line luminosity to molecular gas mass. The molecular gas depletion rate inferred from the ratio of the star formation rate (SFR) to CO luminosity, is ~1 Gyr-1 for near-solar metallicity galaxies with stellar masses above M S ~ 1011 M ⊙. In this regime, the depletion rate does not vary more than a factor of two to three as a function of molecular gas surface density or redshift between z ~ 0 and 2. Below M S the depletion rate increases rapidly with decreasing metallicity. We argue that this trend is not caused by starburst events, by changes in the physical parameters of the molecular clouds, or by the impact of the fundamental-metallicity-SFR-stellar mass relation. A more probable explanation is that the conversion factor is metallicity dependent and that star formation can occur in ''CO-dark'' gas. The trend is also expected theoretically from the effect of enhanced photodissociation of CO by ultraviolet radiation at low metallicity. From the available z ~ 0 and z ~ 1-3 samples we constrain the slope of the log(αCO)-log (metallicity) relation to range between -1 and -2, fairly insensitive to the assumed slope of the gas-SFR relation. Because of the lower metallicities near the peak of the galaxy formation activity at z ~ 1-2 compared to z ~ 0, we suggest that molecular gas masses estimated from CO luminosities have to be substantially corrected upward for galaxies below M S. Based on observations with the Plateau de Bure millimetre interferometer, operated by the Institute for Radio Astronomy in the Millimetre Range (IRAM), which is funded by a partnership of INSU/CNRS (France), MPG (Germany), and IGN (Spain).

Metal distribution in the intracluster medium: a comprehensive numerical study of twelve galaxy clusters

NASA Astrophysics Data System (ADS)

Höller, Harald; Stöckl, Josef; Benson, Andrew; Haider, Markus; Steinhauser, Dominik; Lovisari, Lorenzo; Pranger, Florian

2014-09-01

We present a simulation setup for studying the dynamical and chemical evolution of the intracluster medium (ICM) and analyze a sample of 12 galaxy clusters that are diverse both kinetically (pre-merger, merging, virialized) and in total mass (Mvir = 1.17 × 1014 - 1.06 × 1015 M⊙). We analyzed the metal mass fraction in the ICM as a function of redshift and discuss radial trends as well as projected 2D metallicity maps. The setup combines high mass resolution N-body simulations with the semi-analytical galaxy formation model Galacticus for consistent treatment of the subgrid physics (such as galactic winds and ram-pressure stripping) in the cosmological hydrodynamical simulations. The interface between Galacticus and the hydro simulation of the ICM with FLASH is discussed with respect to observations of star formation rate histories, radial star formation trends in galaxy clusters, and the metallicity at different redshifts. As a test for the robustness of the wind model, we compare three prescriptions from different approaches. For the wind model directly taken from Galacticus, we find mean ICM metallicities between 0.2-0.8 Z⊙ within the inner 1 Mpc at z = 0. The main contribution to the metal mass fraction comes from galactic winds. The outflows are efficiently mixed in the ICM, leading to a steady homogenization of metallicities until ram-pressure stripping becomes effective at low redshifts. We find a very peculiar and yet common drop in metal mass fractions within the inner ~200 kpc of the cool cores, which is due to a combination of wind suppression by outer pressure within our model and a lack of mixing after the formation of these dense regions. Appendix A is available in electronic form at http://www.aanda.org

Extended Narrow-Line Region in Seyfert Galaxies

NASA Astrophysics Data System (ADS)

Congiu, Enrico; Contini, Marcella.; Ciroi, Stefano; Cracco, Valentina; Di Mille, Francesco; Berton, Marco; Frezzato, Michele; La Mura, Giovanni; Rafanelli, Piero

2017-10-01

We present our recent results about the extended narrow-line region (ENLR) of two nearby Seyfert 2 galaxies (IC 5063 and NGC 7212) obtained by modelling the observed line profiles and spectra with composite models (photoionization+shocks) in the different regions surrounding the AGN. Then, we compare the Seyfert 2 ENLRs with the very extended one recently discovered in the narrow-line Seyfert 1 (NLS1) galaxy Mrk 783. We have found several evidences of interaction between the ISM of the galaxies and their radio jets, such as a) the contribution of shocks in ionizing the high velocity gas, b) the complex kinematics showed by the profile of the emission lines, c) the high fragmentation of matter, etc. The results suggest that the ENLR of IC 5063 have a hollow bi-conical shape, with one edge aligned to the galaxy disk, which may cause some kind of dependence on velocity of the ionization parameter. Regarding the Mrk 783 properties, it is found that the extension of the optical emission is almost twice the size of the radio one and it seems due to the AGN activity, although there is contamination by star formation around 12 arcsec from the nucleus. Diagnostic diagrams excluded the contribution of star formation in IC 5063 and NGC 7212, while the shock contribution was used to explain the spectra emitted by their high velocity gas.

Detecting metal-poor gas accretion in the star-forming dwarf galaxies UM 461 and Mrk 600

NASA Astrophysics Data System (ADS)

Lagos, P.; Scott, T. C.; Nigoche-Netro, A.; Demarco, R.; Humphrey, A.; Papaderos, P.

2018-06-01

Using VIsible MultiObject Spectrograph (VIMOS)-integral field unit (IFU) observations, we study the interstellar medium (ISM) of two star-forming dwarf galaxies, UM 461 and Mrk 600. Our aim was to search for the existence of metallicity inhomogeneities that might arise from infall of nearly pristine gas feeding ongoing localized star formation. The IFU data allowed us to study the impact of external gas accretion on the chemical evolution as well as the ionized gas kinematics and morphologies of these galaxies. Both systems show signs of morphological distortions, including cometary-like morphologies. We analysed the spatial variation of 12 + log(O/H) abundances within both galaxies using the direct method (Te), the widely applied HII-CHI-mistry code, as well as by employing different standard calibrations. For UM 461, our results show that the ISM is fairly well mixed, at large scales; however, we find an off-centre and low-metallicity region with 12 + log(O/H) < 7.6 in the SW part of the brightest H II region, using the direct method. This result is consistent with the recent infall of a metal-poor H I cloud into the region now exhibiting the lowest metallicity, which also displays localized perturbed neutral and ionized gas kinematics. Mrk 600 in contrast, appears to be chemically homogeneous on both large and small scales. The intrinsic differences in the spatially resolved properties of the ISM in our analysed galaxies are consistent with these systems being at different evolutionary stages.

The Metallicity Evolution of Blue Compact Dwarf Galaxies from the Intermediate Redshift to the Local Universe

NASA Astrophysics Data System (ADS)

Lian, Jianhui; Hu, Ning; Fang, Guanwen; Ye, Chengyun; Kong, Xu

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 Dn(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 Dn(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.

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.

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.

The size and structure of the spheroid of IC 1613

NASA Astrophysics Data System (ADS)

Battinelli, P.; Demers, S.; Artigau, É.

2007-05-01

Context: Nearby galaxies, spirals as well as irregulars, have been found to be much larger than previously believed. The structure of the huge spheroid surrounding dwarf galaxies could give clues to their past gravitational history. Thanks to wide field imagers, nearby galaxies with diameter of dozens of arcmin can be effectively surveyed. Aims: We obtain, from the CFHT archives, a series of i' and g' MegaCam images of IC 1613 in order to determine the stellar surface density of the field and determine the shape of its spheroid. Methods: From the colour magnitude diagram we select some 36 000 stars, in the first three magnitudes of the red giant branch. The spatial distribution of these stars is used to establish the structure of the spheroid. Results: The position angle of the major axis of the stellar spheroid is found to be ≈90°, some 30° from the major axis of the HI cloud surrounding IC 1613. The surface density profile of the spheroid is not exponential over all the length of the major axis. A King profile, with a core radius of 4.5' and a tidal radius of 24' fits the data. The tidal truncation of the spheroid suggests that IC 1613 is indeed a satellite of M 31. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institute National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

VizieR Online Data Catalog: OGLE-II. Cepheids in IC 1613 (Udalski+, 2001)

NASA Astrophysics Data System (ADS)

Udalski, A.; Wyrzykowski, L.; Pietrzynski, G.; Szewczyk, O.; Szymanski, M.; Kubiak, M.; Soszynski, I.; Zebrun, K.

2003-01-01

We present results of the search for Cepheids in the galaxy IC 1613 carried out as a sub-project of the OGLE-II microlensing survey. 138 Cepheids were found in the 14.2'x14.2' region in the center of the galaxy. We present light curves, VI photometry and basic data for all these objects, as well as color-magnitude diagram of the observed field. (4 data files).

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

Evidence of enrichment by individual SN from elemental abundance ratios in the very metal-poor dSph galaxy Boötes I

NASA Astrophysics Data System (ADS)

Feltzing, S.; Eriksson, K.; Kleyna, J.; Wilkinson, M. I.

2009-12-01

Aims. We establish the mean metallicity from high-resolution spectroscopy for the recently found dwarf spheroidal galaxy Boötes I and test whether it is a common feature for ultra-faint dwarf spheroidal galaxies to show signs of inhomogeneous chemical evolution (e.g. as found in the Hercules dwarf spheroidal galaxy). Methods: We analyse high-resolution, moderate signal-to-noise spectra for seven red giant stars in the Boötes I dSph galaxy using standard abundance analysis techniques. In particular, we assume local thermodynamic equilibrium and employ spherical model atmospheres and codes that take the sphericity of the star into account when calculating the elemental abundances. Results: We confirm previous determinations of the mean metallicity of the Boötes I dwarf spheroidal galaxy to be -2.3 dex. Whilst five stars are clustered around this metallicity, one is significantly more metal-poor, at -2.9 dex, and one is more metal-rich at, -1.9 dex. Additionally, we find that one of the stars, Boo-127, shows an atypically high [Mg/Ca] ratio, indicative of stochastic enrichment processes within the dSph galaxy. Similar results have previously only been found in the Hercules and Draco dSph galaxies and appear, so far, to be unique to this type of galaxy. 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 Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.

HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS IN THE LEAST EVOLVED GALAXIES: LEO IV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simon, Joshua D.; McWilliam, Andrew; Thompson, Ian B.

2010-06-10

We present high-resolution Magellan/MIKE spectroscopy of the brightest star in the ultra-faint dwarf galaxy Leo IV. We measure an iron abundance of [Fe/H] = -3.2, adding to the rapidly growing sample of extremely metal-poor (EMP) stars being identified in Milky Way satellite galaxies. The star is enhanced in the {alpha} elements Mg, Ca, and Ti by {approx}0.3 dex, very similar to the typical Milky Way halo abundance pattern. All of the light and iron-peak elements follow the trends established by EMP halo stars, but the neutron-capture elements Ba and Sr are significantly underabundant. These results are quite similar to thosemore » found for stars in the ultra-faint dwarfs Ursa Major II, Coma Berenices, Booetes I, and Hercules, suggesting that the chemical evolution of the lowest-luminosity galaxies may be universal. The abundance pattern we observe is consistent with predictions for nucleosynthesis from a Population III supernova explosion. The extremely low metallicity of this star also supports the idea that a significant fraction ({approx}>10%) of the stars in the faintest dwarfs have metallicities below [Fe/H] = -3.0.« less

THE OPTICAL COLORS OF GIANT ELLIPTICAL GALAXIES AND THEIR METAL-RICH GLOBULAR CLUSTERS INDICATE A BOTTOM-HEAVY INITIAL MASS FUNCTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goudfrooij, Paul; Diederik Kruijssen, J. M., E-mail: goudfroo@stsci.edu, 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 parentmore » 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.« less

CHEMODYNAMIC EVOLUTION OF DWARF GALAXIES IN TIDAL FIELDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williamson, David; Martel, Hugo; Romeo, Alessandro B., E-mail: david-john.williamson.1@ulaval.ca

The mass–metallicity relation shows that the galaxies with the lowest mass have the lowest metallicities. As most dwarf galaxies are in group environments, interaction effects such as tides could contribute to this trend. We perform a series of smoothed particle hydrodynamics simulations of dwarf galaxies in external tidal fields to examine the effects of tides on their metallicities and metallicity gradients. In our simulated galaxies, gravitational instabilities drive gas inwards and produce centralized star formation and a significant metallicity gradient. Strong tides can contribute to these instabilities, but their primary effect is to strip the outer low-metallicity gas, producing amore » truncated gas disk with a large metallicity. This suggests that the effect of tides on the mass–metallicity relation is to move dwarf galaxies to higher metallicities.« less

Search for very high energy gamma-ray emission from the peculiar radio galaxy IC 310 with TACTIC during 2012 to 2015

NASA Astrophysics Data System (ADS)

Ghosal, B.; Singh, K. K.; Yadav, K. K.; Tickoo, A. K.; Rannot, R. C.; Chandra, P.; Kothari, M.; Gaur, K. K.; Goyal, H. C.; Goyal, A.; Kumar, N.; Marandi, P.; Chanchalani, K.; Agarwal, N. K.; Dhar, V. K.; Koul, M. K.; Koul, R.; Venugopal, K.; Bhat, C. K.; Chouhan, N.; Borwankar, C.; Kaul, S. R.; Bhatt, H.; Agarwal, A.; Gupta, A. C.

2018-04-01

Non-blazar active galactic nuclei like radio galaxies have emerged as a new class of γ-ray sources in the sky. Observations of very high energy (VHE) γ-rays from radio galaxies with misaligned jets offer a unique tool to understand the physical processes involved in these type of objects. In this work, we present the results of our observations of the nearby peculiar radio galaxy IC 310 (z = 0.0189) with TACTIC telescope for nearly 95.5 hours from 03 December, 2012 to 19 January, 2015 (MJD 56265 - 57041). Detailed analysis of the data reveals absence of a statistically significant γ-ray signal from the source direction (both on the overall period and on yearly basis). Our results suggest that the source was possibly in a low-TeV emission state (below the TACTIC sensitivity level) during the above mentioned observation period and the resulting 3σ upper limit on the integral flux above 850 GeV has been estimated to be 4.99 ×10-12phcm-2s-1 (23% of the Crab Nebula flux). Analysis of the contemporaneous data collected by Fermi-LAT in the 30 - 300 GeV energy range, also indicate the absence of a statistically significant γ-ray signal, therefore 2σ upper limit on the integral flux above 30 GeV has been estimated on yearly basis. We also report the results from dedicated optical observations in B, V and R bands from ARIES observatory carried out from December, 2014 to March, 2015.

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

THE EFFECT OF SECOND-GENERATION POPULATIONS ON THE INTEGRATED COLORS OF METAL-RICH GLOBULAR CLUSTERS IN EARLY-TYPE GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chung, Chul; Lee, Sang-Yoon; Yoon, Suk-Jin

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 bymore » 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.« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perley, D. A.; Tanvir, N. R.; Hjorth, J.

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 withmore » 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.« less

Inverse Compton X-Ray Halos Around High-z Radio Galaxies: A Feedback Mechanism Powered by Far-Infrared Starbursts or the Cosmic Microwave Background?

NASA Technical Reports Server (NTRS)

Small, Ian; Blundell, Katherine M.; Lehmer, B. D.; Alexander, D. M.

2012-01-01

We report the detection of extended X-ray emission around two powerful radio galaxies at z approx. 3.6 (4C 03.24 and 4C 19.71) and use these to investigate the origin of extended, inverse Compton (IC) powered X-ray halos at high redshifts. The halos have X-ray luminosities of L(sub X) approx. 3 x 10(exp 44) erg/s and sizes of approx.60 kpc. Their morphologies are broadly similar to the approx.60 kpc long radio lobes around these galaxies suggesting they are formed from IC scattering by relativistic electrons in the radio lobes, of either cosmic microwave background (CMB) photons or far-infrared photons from the dust-obscured starbursts in these galaxies. These observations double the number of z > 3 radio galaxies with X-ray-detected IC halos. We compare the IC X-ray-to-radio luminosity ratios for the two new detections to the two previously detected z approx. 3.8 radio galaxies. Given the similar redshifts, we would expect comparable X-ray IC luminosities if millimeter photons from the CMB are the dominant seed field for the IC emission (assuming all four galaxies have similar ages and jet powers). Instead we see that the two z approx. 3.6 radio galaxies, which are 4 fainter in the far-infrared than those at z 3.8, also have approx.4x fainter X-ray IC emission. Including data for a further six z > or approx. 2 radio sources with detected IC X-ray halos from the literature, we suggest that in the more compact, majority of radio sources, those with lobe sizes < or approx.100-200 kpc, the bulk of the IC emission may be driven by scattering of locally produced far-infrared photons from luminous, dust-obscured starbursts within these galaxies, rather than millimeter photons from the CMB. The resulting X-ray emission appears sufficient to ionize the gas on approx.100-200 kpc scales around these systems and thus helps form the extended, kinematically quiescent Ly(alpha) emission line halos found around some of these systems. The starburst and active galactic nucleus

PopIII-star siblings in IZw18 and metal-poor WR galaxies unveiled from integral field spectroscopy

NASA Astrophysics Data System (ADS)

Kehrig, C.; Vílchez, J. M.; Pérez-Montero, E.; Iglesias-Páramo, J.; Brinchmann, J.; Crowther, P. A.; Durret, F.; Kunth, D.

Here, we highlight our recent results from the IFS study of Mrk178, the closest metal-poor WR galaxy, and of IZw18, the most metal-poor star-forming galaxy known in the local Universe. The IFS data of Mrk178 show the importance of aperture effects on the search for WR features, and the extent to which physical variations in the ISM properties can be detected. Our IFS data of IZw18 reveal its entire nebular HeIIλ4686-emitting region, and indicate for the very first time that peculiar, hot (nearly) metal-free ionizing stars (called here PopIII-star siblings) might hold the key to the HeII-ionization in IZw18.

The Star Formation Reference Survey - II. Activity demographics and host-galaxy properties for infrared-selected galaxies

NASA Astrophysics Data System (ADS)

Maragkoudakis, A.; Zezas, A.; Ashby, M. L. N.; Willner, S. P.

2018-04-01

We present activity demographics and host-galaxy properties of infrared-selected galaxies in the local Universe, using the representative Star Formation Reference Survey (SFRS). Our classification scheme is based on a combination of optical emission-line diagrams (BPT) and infrared (IR)-colour diagnostics. Using the weights assigned to the SFRS galaxies based on its parent sample, a far-IR-selected sample comprises 71 per cent H II galaxies, 13 per cent Seyferts, 3 per cent transition objects (TOs), and 13 per cent low-ionization nuclear emission-line regions (LINERs). For the SFRS H II galaxies, we derive nuclear star formation rates and gas-phase metallicities. We measure host-galaxy metallicities for all galaxies with available long-slit spectroscopy and abundance gradients for a subset of 12 face-on galaxies. The majority of H II galaxies show a narrow range of metallicities, close to solar, and flat metallicity profiles. Based on their host-galaxy and nuclear properties, the dominant ionizing source in the far-infrared selected TOs is star-forming activity. LINERs are found mostly in massive hosts (median of 1010.5 M⊙), median L(60 μm) = 109 L⊙, median dust temperatures of F60/F100 = 0.36, and median LH α surface density of 1040.2 erg s-1kpc-2, indicating older stellar populations as their main ionizing source rather than active galactic nucleus activity.

CS in nearby galaxies: Distribution, kinematics, and multilevel studies

NASA Technical Reports Server (NTRS)

Mauersberger, R.; Henkel, Christian

1990-01-01

As a result of observations at the Institute for Radio Astronomy in the Millimeter Range (IRAM) 30-m telescope, maps of the distribution of the J = 2-1 transition of CS toward the galaxies IC 342 and NGC 253 are presented. The distribution of the CS emission from NGC 253 is consistent with the CO 1-0 line. The distribution of the CS emission from IC 342, however, resembles more that seen in the CO 3-2 line. For the first time, the detection of the isotopic substitution C-34S is reported toward an external galaxy: The C-34S 2-1 line has been detected toward NGC 253 and M 82 and the C-34S line has been detected tentatively toward M 82. Also for the first time, extragalactic CS has been observed in the 3-2 (toward NGC 253, IC 342 and M 82) and 5-4 (NGC 253 and IC 342) transitions.

LOSS Revisited. I. Unraveling Correlations between Supernova Rates and Galaxy Properties, as Measured in a Reanalysis of the Lick Observatory Supernova Search

DOE Office of Scientific and Technical Information (OSTI.GOV)

Graur, Or; Bianco, Federica B.; Huang, Shan

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.more » 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.« less

30 CFR 57.22102 - Smoking (I-C mines).

Code of Federal Regulations, 2010 CFR

2010-07-01

... Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards for Methane in Metal and Nonmetal Mines Fire Prevention and Control § 57.22102 Smoking (I-C mines). (a...

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.

No breakdown of the radiatively driven wind theory in low-metallicity environments

NASA Astrophysics Data System (ADS)

Bouret, J.-C.; Lanz, T.; Hillier, D. J.; Martins, F.; Marcolino, W. L. F.; Depagne, E.

2015-05-01

We present a spectroscopic analysis of Hubble Space Telescope/Cosmic Origins Spectrograph observations of three massive stars in the low metallicity dwarf galaxies IC 1613 and WLM. These stars, were previously observed with Very Large Telescope (VLT)/X-shooter by Tramper et al., who claimed that their mass-loss rates are higher than expected from theoretical predictions for the underlying metallicity. A comparison of the far ultraviolet (FUV) spectra with those of stars of similar spectral types/luminosity classes in the Galaxy, and the Magellanic Clouds provides a direct, model-independent check of the mass-loss-metallicity relation. Then, a quantitative spectroscopic analysis is carried out using the non-LTE (NLTE) stellar atmosphere code CMFGEN. We derive the photospheric and wind characteristics, benefiting from a much better sensitivity of the FUV lines to wind properties than Hα. Iron and CNO abundances are measured, providing an independent check of the stellar metallicity. The spectroscopic analysis indicates that Z/Z⊙ = 1/5, similar to a Small Magellanic Cloud-type environment, and higher than usually quoted for IC 1613 and WLM. The mass-loss rates are smaller than the empirical ones by Tramper et al., and those predicted by the widely used theoretical recipe by Vink et al. On the other hand, we show that the empirical, FUV-based, mass-loss rates are in good agreement with those derived from mass fluxes computed by Lucy. We do not concur with Tramper et al. that there is a breakdown in the mass-loss-metallicity relation.

A New Scaling Relation for H II Regions in Spiral Galaxies: Unveiling the True Nature of the Mass-Metallicity Relation

NASA Astrophysics Data System (ADS)

Rosales-Ortega, F. F.; Sánchez, S. F.; Iglesias-Páramo, J.; Díaz, A. I.; Vílchez, J. M.; Bland-Hawthorn, J.; Husemann, B.; Mast, D.

2012-09-01

We demonstrate the existence of a local mass, metallicity, star formation relation using spatially resolved optical spectroscopy of H II regions in the local universe. One of the projections of this distribution—the local mass-metallicity relation—extends over a wide range in this parameter space: three orders of magnitude in mass and a factor of eight in metallicity. We explain the new relation as the combined effect of the differential distributions of mass and metallicity in the disks of galaxies, and a selective star formation efficiency. We use this local relation to reproduce—with a noticeable agreement—the mass-metallicity relation seen in galaxies, and conclude that the latter is a scale-up integrated effect of a local relation, supporting the inside-out growth and downsizing scenarios of galaxy evolution. Based on observations collected at the Centro Astronómico Hispano-Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).

MASSIV: Mass Assembly Survey with SINFONI in VVDS. III. Evidence for positive metallicity gradients in z ~ 1.2 star-forming galaxies

NASA Astrophysics Data System (ADS)

Queyrel, J.; Contini, T.; Kissler-Patig, M.; Epinat, B.; Amram, P.; Garilli, B.; Le Fèvre, O.; Moultaka, J.; Paioro, L.; Tasca, L.; Tresse, L.; Vergani, D.; López-Sanjuan, C.; Perez-Montero, E.

2012-03-01

Aims: The estimate of radial abundance gradients in high-redshift galaxies allows to constrain their star formation history and their interplay with the surrounding intergalactic medium. Methods: We present VLT/SINFONI integral-field spectroscopy of a first sample of 50 galaxies at z ~ 1.2 in the MASSIV survey. Using the N2 ratio between the [N ii]6584 and Hα rest-frame optical emission lines as a proxy for oxygen abundance in the interstellar medium, we measured the metallicity of the sample galaxies. We developed a tool to extract spectra in annular regions, leading to a spatially resolved estimate of the oxygen abundance in each galaxy. We were able to derive a metallicity gradient for 26 galaxies in our sample and discovered a significant fraction of galaxies with a "positive" gradient. Using a simple chemical evolution model, we derived infall rates of pristine gas onto the disks. Results: Seven galaxies display a positive gradient at a high confidence level. Four out of these are interacting, and one is a chain galaxy. We suggest that interactions might be responsible for shallowing and even inverting the abundance gradient. We also identify two interesting correlations in our sample: a) galaxies with higher gas velocity dispersion have shallower/positive gradients; and b) metal-poor galaxies tend to show a positive gradient, whereas metal-rich ones tend to show a negative one. This last observation can be explained by the infall of metal-poor gas into the center of the disks. We address the question of the origin of this infall under the influence of gas flows triggered by interactions and/or cold gas accretion. All the data published in this paper are publicly available at the time of publication following this link: http://cosmosdb.lambrate.inaf.it/VVDS-SINFONI. This work is based on observations collected at the European Southern Observatory (ESO) Very

X-ray Emission from Early Universe Analog Galaxies

NASA Astrophysics Data System (ADS)

Brorby, Matthew; Kaaret, Philip; Prestwich, Andrea H.; Mirabel, I. Felix; Feng, Hua

2016-01-01

Around 300,000 years after the Big Bang, the Universe had cooled enough to combine and form neutral atoms. This signified the beginning of a time known as the Dark Ages. Neutral matter began to fall into the dark matter gravitational wells that were seeded after the initial moments of the Big Bang. As the first stars and galaxies formed within these gravitational wells, the surrounding baryonic matter was heated and started to ionize. The source of energetic photons that heated and reionized the early Universe remains uncertain. Early galaxies had low metallicity and recent population synthesis calculations suggest that the number and luminosity of high-mass X-ray binaries are enhanced in star-forming galaxies with low metallicity, offering a potentially important and previously overlooked source of heating and reionization. Here we examine two types of local galaxies that have been shown to be good analogs to the early galaxies in the Universe: Blue compact dwarf galaxies (BCDs) and Lyman Break Analogs (LBAs).A BCD is defined by its blue optical colors, low metallicities, and physically small size. This makes BCDs the best available local analogs for early star formation. We analyzed data from a sample of 25 metal-poor BCDs and compared our results with those of near-solar metallicity galaxies. Using a Bayesian approach, we showed that the X-ray luminosity function for the low-metallicity BCDs is significantly elevated relative to the XLF for near-solar metallicity galaxies.Larger, gas-rich galaxies may have formed shortly after these first galaxies. These larger galaxies would be similar in their properties to the high-redshift Lyman break galaxies (LBGs). LBAs provide the best local comparison to the LBGs. We studied a sample of 10 LBAs in order to measure the relation between star formation rate and X-ray luminosity for these galaxies. We found that for LBAs with intermediate sub-solar metallicities, there is enhanced X-ray emission relative to the expected

Stellar Absorption Line Analysis of Local Star-forming Galaxies: The Relation between Stellar Mass, Metallicity, Dust Attenuation, and Star Formation Rate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jabran Zahid, H.; Kudritzki, Rolf-Peter; Ho, I-Ting

We analyze the optical continuum of star-forming galaxies in the Sloan Digital Sky Survey by fitting stacked spectra with stellar population synthesis models to investigate the relation between stellar mass, stellar metallicity, dust attenuation, and star formation rate. We fit models calculated with star formation and chemical evolution histories that are derived empirically from multi-epoch observations of the stellar mass–star formation rate and the stellar mass–gas-phase metallicity relations, respectively. We also fit linear combinations of single-burst models with a range of metallicities and ages. Star formation and chemical evolution histories are unconstrained for these models. The stellar mass–stellar metallicity relationsmore » obtained from the two methods agree with the relation measured from individual supergiant stars in nearby galaxies. These relations are also consistent with the relation obtained from emission-line analysis of gas-phase metallicity after accounting for systematic offsets in the gas-phase metallicity. We measure dust attenuation of the stellar continuum and show that its dependence on stellar mass and star formation rate is consistent with previously reported results derived from nebular emission lines. However, stellar continuum attenuation is smaller than nebular emission line attenuation. The continuum-to-nebular attenuation ratio depends on stellar mass and is smaller in more massive galaxies. Our consistent analysis of stellar continuum and nebular emission lines paves the way for a comprehensive investigation of stellar metallicities of star-forming and quiescent galaxies.« less

Constraining the Star-Formation and Metal-Enrichment Histories of Galaxies with the Next Generation Spectral Library

NASA Astrophysics Data System (ADS)

Heap, Sara

2009-07-01

Hubble's Next Generation Spectral Library {NGSL} comprises intermediate-resolution {R 1000} STIS spectra of 378 stars having a wide range in metallicity and age. Unique features of the NGSL include its broad wavelength coverage {1,800-10,100 ?} and high-S/N, absolute spectrophotometry. When incorporated in modern stellar population synthesis codes, the NGSL should enable us to constrain simultaneously the star-formation history and metal-enrichment history of galaxies over a wide redshift interval {z= 0-2}. In AR10659, we laid the foundation for tracing the spectral evolution of galaxies by putting the NGSL in order. We now propose to derive the atmospheric and fundamental parameters of the program stars, generate integrated spectra of stellar populations of different metallicities and initial mass functions, and derive spectral diagnostics of the age, metalllicity and E{B-V} of stellar populations.

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 of...

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 of...

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 of...

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 of...

LOW CO LUMINOSITIES IN DWARF GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schruba, Andreas; Walter, Fabian; Sandstrom, Karin

2012-06-15

We present maps of {sup 12}COJ = 2-1 emission covering the entire star-forming disks of 16 nearby dwarf galaxies observed by the IRAM HERACLES survey. The data have 13'' angular resolution, {approx}250 pc at our average distance of D = 4 Mpc, and sample the galaxies by 10-1000 resolution elements. We apply stacking techniques to perform the first sensitive search for CO emission in dwarf galaxies outside the Local Group ranging from individual lines of sight, stacking over IR-bright regions of embedded star formation, and stacking over the entire galaxy. We detect five galaxies in CO with total CO luminositiesmore » of L{sub CO2-1} = (3-28) Multiplication-Sign 10{sup 6} K km s{sup -1} pc{sup 2}. The other 11 galaxies remain undetected in CO even in the stacked images and have L{sub CO2-1} {approx}< (0.4-8) Multiplication-Sign 10{sup 6} K km s{sup -1} pc{sup 2}. We combine our sample of dwarf galaxies with a large sample of spiral galaxies from the literature to study scaling relations of L{sub CO} with M{sub B} and metallicity. We find that dwarf galaxies with metallicities of Z Almost-Equal-To 1/2-1/10 Z{sub Sun} have L{sub CO} of 2-4 orders of magnitude smaller than massive spiral galaxies and that their L{sub CO} per unit L{sub B} is 1-2 orders of magnitude smaller. A comparison with tracers of star formation (FUV and 24 {mu}m) shows that L{sub CO} per unit star formation rate (SFR) is 1-2 orders of magnitude smaller in dwarf galaxies. One possible interpretation is that dwarf galaxies form stars much more efficiently: we argue that the low L{sub CO}/SFR ratio is due to the fact that the CO-to-H{sub 2} conversion factor, {alpha}{sub CO}, changes significantly in low-metallicity environments. Assuming that a constant H{sub 2} depletion time of {tau}{sub dep} = 1.8 Gyr holds in dwarf galaxies (as found for a large sample of nearby spirals) implies {alpha}{sub CO} values for dwarf galaxies with Z Almost-Equal-To 1/2-1/10 Z{sub Sun} that are more than one order of

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jimmy; Tran, Kim-Vy; Saintonge, Amélie

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 bemore » 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.« less

Galaxy NGC 1448 with Active Galactic Nucleus

NASA Image and Video Library

2017-01-07

NGC 1448, a galaxy with an active galactic nucleus, is seen in this image combining data from the Carnegie-Irvine Galaxy Survey in the optical range and NuSTAR in the X-ray range. This galaxy contains an example of a supermassive black hole hidden by gas and dust. X-ray emissions from NGC 1448, as seen by NuSTAR and Chandra, suggests for the first time that, like IC 3639 in PIA21087, there must be a thick layer of gas and dust hiding the active black hole in this galaxy from our line of sight. http://photojournal.jpl.nasa.gov/catalog/PIA21086

Physical conditions of the molecular gas in metal-poor galaxies

NASA Astrophysics Data System (ADS)

Hunt, L. K.; Weiß, A.; Henkel, C.; Combes, F.; García-Burillo, S.; Casasola, V.; Caselli, P.; Lundgren, A.; Maiolino, R.; Menten, K. M.; Testi, L.

2017-10-01

Studying the molecular component of the interstellar medium (ISM) in metal-poor galaxies has been challenging because of the faintness of carbon monoxide emission, the most common proxy of H2. Here we present new detections of molecular gas at low metallicities, and assess the physical conditions in the gas through various CO transitions for 8 galaxies. For one, NGC 1140 (Z/Z⊙ 0.3), two detections of 13CO isotopologues and atomic carbon, [Ci](1-0) and an upper limit for HCN(1-0) are also reported. After correcting to a common beam size, we compared 12CO(2-1)/12CO(1-0) (R21) and 12CO(3-2)/12CO(1-0) (R31) line ratios of our sample with galaxies from the literature and find that only NGC 1140 shows extreme values (R21 R31 2). Fitting physical models to the 12CO and 13CO emission in NGC 1140 suggests that the molecular gas is cool (kinetic temperature Tkin ≲ 20 K), dense (H2 volume density nH2 ≳ 106 cm-3), with moderate CO column density (NCO 1016 cm-2) and low filling factor. Surprisingly, the [12CO]/[13CO] abundance ratio in NGC 1140 is very low ( 8-20), lower even than the value of 24 found in the Galactic Center. The young age of the starburst in NGC 1140 precludes 13CO enrichment from evolved intermediate-mass stars; instead we attribute the low ratio to charge-exchange reactions and fractionation, because of the enhanced efficiency of these processes in cool gas at moderate column densities. Fitting physical models to 12CO and [Ci](1-0) emission in NGC 1140 gives an unusually low [12CO]/[12C] abundance ratio, suggesting that in this galaxy atomic carbon is at least 10 times more abundant than 12CO. Based on observations carried out with the IRAM 30 m and the Atacama Pathfinder Experiment (APEX). IRAM is supported by the INSU/CNRS (France), MPG (Germany), and IGN (Spain), and APEX is a collaboration between the Max-Planck-Institut fur Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mathews, William G.; Brighenti, Fabrizio; Temi, Pasquale

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 branchmore » 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.« less

A Radio Jet Drives a Molecular and Atomic Gas Outflow in Multiple Regions within One Square Kiloparsec of the Nucleus of the nearby Galaxy IC5063

NASA Astrophysics Data System (ADS)

Dasyra, K. M.; Bostrom, A. C.; Combes, F.; Vlahakis, N.

2015-12-01

We analyzed near-infrared data of the nearby galaxy IC5063 taken with the Very Large Telescope SINFONI instrument. IC5063 is an elliptical galaxy that has a radio jet nearly aligned with the major axis of a gas disk in its center. The data reveal multiple signatures of molecular and atomic gas that has been kinematically distorted by the passage of the jet plasma or cocoon within an area of ˜1 kpc2. Concrete evidence that the interaction of the jet with the gas causes the gas to accelerate comes from the detection of outflows in four different regions along the jet trail: near the two radio lobes, between the radio emission tip and the optical narrow-line-region cone, and at a region with diffuse 17.8 GHz emission midway between the nucleus and the north radio lobe. The outflow in the latter region is biconical, centered 240 pc away from the nucleus, and oriented perpendicularly to the jet trail. The diffuse emission that is observed as a result of the gas entrainment or scattering unfolds around the trail and away from the nucleus with increasing velocity. It overall extends for ≳700 pc parallel and perpendicular to the trail. Near the outflow starting points, the gas has a velocity excess of 600-1200 km s-1 with respect to ordered motions, as seen in [Fe ii], {Pa}α , or {{{H}}}2 lines. High {{{H}}}2 (1-0) S(3)/S(1) flux ratios indicate non-thermal excitation of gas in the diffuse outflow.

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

ALMA Maps of Dust and Warm Dense Gas Emission in the Starburst Galaxy IC 5179

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao Yinghe; Lu, Nanyao; Xu, C. Kevin

We present our high-resolution (0.″15 × 0.″13, ∼34 pc) observations of the CO (6−5) line emission, which probes the warm and dense molecular gas, and the 434 μ m dust continuum emission in the nuclear region of the starburst galaxy IC 5179, conducted with the Atacama Large Millimeter Array (ALMA). The CO (6−5) emission is spatially distributed in filamentary structures with many dense cores and shows a velocity field that is characteristic of a circumnuclear rotating gas disk, with 90% of the rotation speed arising within a radius of ≲150 pc. At the scale of our spatial resolution, the COmore » (6−5) and dust emission peaks do not always coincide, with their surface brightness ratio varying by a factor of ∼10. This result suggests that their excitation mechanisms are likely different, as further evidenced by the southwest to northeast spatial gradient of both CO-to-dust continuum ratio and Pa- α equivalent width. Within the nuclear region (radius ∼ 300 pc) and with a resolution of ∼34 pc, the CO line flux (dust flux density) detected in our ALMA observations is 180 ± 18 Jy km s{sup −1} (71 ± 7 mJy), which accounts for 22% (2.4%) of the total value measured by Herschel .« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

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. Itsmore » 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.« less

Gas and Dust Properties in Dwarf Irregular Galaxies

NASA Technical Reports Server (NTRS)

Jones, A. P.; Madden, S. C.; Colgan, S. W. J.; Geis, N.; Haas, M.; Maloney, P.; Nikola, T.; Poglitsch, A.

1997-01-01

We present a study of the 158 (micron)meter [C II] fine structure emission line from a sample of 11 low metallicity irregular galaxies using the NASA Kuiper Airborne Observatory (KAO). Our preliminary results demonstrate that the ratio of the 158 (micron)meter [C II] emission to the CO-12(1 yields 0) emission ranges from 6,000 to 46,000. These ratios are significantly enhanced relative to clouds within the Galaxy and to normal metallicity galaxies, which typically have values in the range 2,000 to 6,300. We also find that the [C II] emission in dwarf irregular galaxies can be up to 5% of the far-infrared (FIR) emission, a higher fraction of the FIR than in normal metallicity galaxies. We discuss these results for the dwarf irregular galaxies and compare them to those observed in normal metallicity galaxies. The enhanced 158 (micron)meter [C II] emission relative to CO-12(1 yields 0) emission can be understood in terms of the increased penetration depth of ultraviolet (UV) photons into the clouds in low metallicity environments.

The Fossil Record of Two-phase Galaxy Assembly: Kinematics and Metallicities in the Nearest S0 Galaxy

NASA Astrophysics Data System (ADS)

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

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/σ >~ 1.5). At larger radii, the rotation declines dramatically to v/σ ~ 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-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 ~15-20:1.

Detection of a Population of Carbon-enhanced Metal-poor Stars in the Sculptor Dwarf Spheroidal Galaxy

NASA Astrophysics Data System (ADS)

Chiti, Anirudh; Simon, Joshua D.; Frebel, Anna; Thompson, Ian B.; Shectman, Stephen A.; Mateo, Mario; Bailey, John I., III; Crane, Jeffrey D.; Walker, Matthew

2018-04-01

The study of the chemical abundances of metal-poor stars in dwarf galaxies provides a venue to constrain paradigms of chemical enrichment and galaxy formation. Here we present metallicity and carbon abundance measurements of 100 stars in Sculptor from medium-resolution (R ∼ 2000) spectra taken with the Magellan/Michigan Fiber System mounted on the Magellan-Clay 6.5 m telescope at Las Campanas Observatory. We identify 24 extremely metal-poor star candidates ([Fe/H] < ‑3.0) and 21 carbon-enhanced metal-poor (CEMP) star candidates. Eight carbon-enhanced stars are classified with at least 2σ confidence, and five are confirmed as such with follow-up R ∼ 6000 observations using the Magellan Echellette Spectrograph on the Magellan-Baade 6.5 m telescope. We measure a CEMP fraction of 36% for stars below [Fe/H] = ‑3.0, indicating that the prevalence of carbon-enhanced stars in Sculptor is similar to that of the halo (∼43%) after excluding likely CEMP-s and CEMP-r/s stars from our sample. However, we do not detect that any CEMP stars are strongly enhanced in carbon ([C/Fe] > 1.0). The existence of a large number of CEMP stars both in the halo and in Sculptor suggests that some halo CEMP stars may have originated from accreted early analogs of dwarf galaxies. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

30 CFR 57.22104 - Open flames (I-C mines).

Code of Federal Regulations, 2010 CFR

2010-07-01

....22104 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards for Methane in Metal and Nonmetal Mines Fire Prevention and Control § 57.22104 Open flames (I-C...

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

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.

Low Metallicities and Old Ages for Three Ultra-diffuse Galaxies in the Coma Cluster

NASA Astrophysics Data System (ADS)

Gu, Meng; Conroy, Charlie; Law, David; van Dokkum, Pieter; Yan, Renbin; Wake, David; Bundy, Kevin; Merritt, Allison; Abraham, Roberto; Zhang, Jielai; Bershady, Matthew; Bizyaev, Dmitry; Brinkmann, Jonathan; Drory, Niv; Grabowski, Kathleen; Masters, Karen; Pan, Kaike; Parejko, John; Weijmans, Anne-Marie; Zhang, Kai

2018-05-01

A large population of ultra-diffuse galaxies (UDGs) was recently discovered in the Coma cluster. Here we present optical spectra of three such UDGs, DF 7, DF 44, and DF 17, which have central surface brightnesses of μ g ≈ 24.4–25.1 mag arcsec‑2. The spectra were acquired as part of an ancillary program within the SDSS-IV MaNGA Survey. We stacked 19 fibers in the central regions from larger integral field units (IFUs) per source. With over 13.5 hr of on-source integration, we achieved a mean signal-to-noise ratio in the optical of 9.5 Å‑1, 7.9 Å‑1, and 5.0 Å‑1, respectively, for DF 7, DF 44, and DF 17. Stellar population models applied to these spectra enable measurements of recession velocities, ages, and metallicities. The recession velocities of DF 7, DF 44, and DF 17 are {6599}-25+40 km s‑1, {6402}-39+41 km s‑1, and {8315}-43+43 km s‑1, spectroscopically confirming that all of them reside in the Coma cluster. The stellar populations of these three galaxies are old and metal-poor, with ages of {7.9}-2.5+3.6 Gyr, {8.9}-3.3+4.3 Gyr, and {9.1}-5.5+3.9 Gyr, and iron abundances of [Fe/H] -{1.0}-0.4+0.3, -{1.3}-0.4+0.4, and -{0.8}-0.5+0.5, respectively. Their stellar masses are (3–6) × 108 M ⊙. The UDGs in our sample are as old or older than galaxies at similar stellar mass or velocity dispersion (only DF 44 has an independently measured dispersion). They all follow the well-established stellar mass–stellar metallicity relation, while DF 44 lies below the velocity dispersion-metallicity relation. These results, combined with the fact that UDGs are unusually large for their stellar masses, suggest that stellar mass plays a more important role in setting stellar population properties for these galaxies than either size or surface brightness.

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.

Blueberry Galaxies: The Lowest Mass Young Starbursts

NASA Astrophysics Data System (ADS)

Yang, Huan; Malhotra, Sangeeta; Rhoads, James E.; Wang, Junxian

2017-09-01

Searching for extreme emission line galaxies allows us to find low-mass metal-poor galaxies that are good analogs of high redshift Lyα emitting galaxies. These low-mass extreme emission line galaxies are also potential Lyman-continuum leakers. Finding them at very low redshifts (z≲ 0.05) allows us to be sensitive to even lower stellar masses and metallicities. We report on a sample of extreme emission line galaxies at z≲ 0.05 (blueberry galaxies). We selected them from SDSS broadband images on the basis of their broadband colors and studied their properties with MMT spectroscopy. From the entire SDSS DR12 photometric catalog, we found 51 photometric candidates. We spectroscopically confirm 40 as blueberry galaxies. (An additional seven candidates are contaminants, and four remain without spectra.) These blueberries are dwarf starburst galaxies with very small sizes (<1 kpc) and very high ionization ([O III]/[O II] ˜ 10-60). They also have some of the lowest stellar masses ({log}(M/{M}⊙ )˜ 6.5{--}7.5) and lowest metallicities (7.1< 12+{log}({{O}}/{{H}})< 7.8) of starburst galaxies. Thus, they are small counterparts to green pea galaxies and high redshift Lyα emitting galaxies.

EVIDENCE THAT GAMMA-RAY BURST 130702A EXPLODED IN A DWARF SATELLITE OF A MASSIVE GALAXY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kelly, Patrick L.; Filippenko, Alexei V.; Fox, Ori D.

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 andmore » 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.« less

RE-EXAMINING HIGH ABUNDANCE SLOAN DIGITAL SKY SURVEY MASS-METALLICITY OUTLIERS: HIGH N/O, EVOLVED WOLF-RAYET GALAXIES?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berg, Danielle A.; Skillman, Evan D.; Marble, Andrew R., E-mail: berg@astro.umn.edu, E-mail: skillman@astro.umn.edu, E-mail: amarble@nso.edu

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 aremore » 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.« less

3D-HST Grism Spectroscopy of a Gravitationally Lensed, Low-metallicity Starburst Galaxy at z = 1.847

NASA Astrophysics Data System (ADS)

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

2012-10-01

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] λ5007 and Hβ emission lines with rest-frame equivalent widths of 2000 ± 100 and 520 ± 40 Å, respectively. The source has a stellar mass ~108 M ⊙, sSFR ~ 100 Gyr-1, and detection of [O III] λ4363 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 re ~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. Based on observations made with the NASA/ESA Hubble Space Telescope, program 12328, obtained 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.

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.

Carbon and oxygen abundances from recombination lines in low-metallicity star-forming galaxies. Implications for chemical evolution

NASA Astrophysics Data System (ADS)

Esteban, C.; García-Rojas, J.; Carigi, L.; Peimbert, M.; Bresolin, F.; López-Sánchez, A. R.; Mesa-Delgado, A.

2014-09-01

We present deep echelle spectrophotometry of the brightest emission-line knots of the star-forming galaxies He 2-10, Mrk 1271, NGC 3125, NGC 5408, POX 4, SDSS J1253-0312, Tol 1457-262, Tol 1924-416 and the H II region Hubble V in the Local Group dwarf irregular galaxy NGC 6822. The data have been taken with the Very Large Telescope Ultraviolet-Visual Echelle Spectrograph in the 3100-10420 Å range. We determine electron densities and temperatures of the ionized gas from several emission-line intensity ratios for all the objects. We derive the ionic abundances of C2+ and/or O2+ from faint pure recombination lines in several of the objects, permitting to derive their C/H and C/O ratios. We have explored the chemical evolution at low metallicities analysing the C/O versus O/H, C/O versus N/O and C/N versus O/H relations for Galactic and extragalactic H II regions and comparing with results for Galactic halo stars and damped Lyα systems. We find that H II regions in star-forming dwarf galaxies occupy a different locus in the C/O versus O/H diagram than those belonging to the inner discs of spiral galaxies, indicating their different chemical evolution histories, and that the bulk of C in the most metal-poor extragalactic H II regions should have the same origin than in halo stars. The comparison between the C/O ratios in H II regions and in stars of the Galactic thick and thin discs seems to give arguments to support the merging scenario for the origin of the Galactic thick disc. Finally, we find an apparent coupling between C and N enrichment at the usual metallicities determined for H II regions and that this coupling breaks in very low metallicity objects.

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

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 and...

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 and...

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 and...

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 and...

From Galaxies to the Intergalactic Medium

NASA Astrophysics Data System (ADS)

Peeples, Molly S.

2010-07-01

Deep in dark matter halos, galaxies are large factories that convert gas into stars. Gas is accreted from the expansive intergalactic medium (IGM); stars process this gas by fusing lighter elements into heavier ones. In this Dissertation, I combine both observations and theories from a variety of subfields of astrophysics with analytic and numerical models in an aim for a comprehensive understanding of the underlying physics of star formation feedback, galaxy chemical evolution, and the IGM. The mass-metallicity relation is an observed tight correlation between the stellar masses and gas-phase oxygen abundances of star-forming galaxies. I show that while the intrinsic scatter in this relation is small, extreme outliers do exist; I argue that these outliers have unusual metallicities for their masses because they have unusual gas fractions for their masses. The low-mass high-metallicity galaxies appear to be nearing the end of their star formation, and thus should have abnormally small gas reservoirs with which to dilute their metals. On the other hand, the high-mass low-metallicity galaxies appear to be undergoing gas-rich galaxy mergers, implying that they have larger-than-normal amounts of gas diluting their metals. I then show through analytic arguments that while gas fractions can have a large impact on observed metallicities, the low-redshift mass-metallicity relation is dominated by outflow properties because typical galaxies have relatively small gas fractions. Specifically, the mass-metallicity relation implies that the efficiency with which galaxies expel metals should scale steeply with galaxy mass. Combining this model with reasonable models for star formation feedback, I show that the outflow metallicity should likewise vary with galaxy mass; future measurements of wind metallicity can therefore inform models of the physics underlying galaxy winds. The high-redshift IGM is primarily observed through the Lyman-alpha absorption of neutral hydrogen along

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.

Using dust, gas and stellar mass-selected samples to probe dust sources and sinks in low-metallicity galaxies

NASA Astrophysics Data System (ADS)

De Vis, P.; Gomez, H. L.; Schofield, S. P.; Maddox, S.; Dunne, L.; Baes, M.; Cigan, P.; Clark, C. J. R.; Gomez, E. L.; Lara-López, M.; Owers, M.

2017-10-01

We combine samples of nearby galaxies with Herschel photometry selected on their dust, metal, H I and stellar mass content, and compare these to chemical evolution models in order to discriminate between different dust sources. In a companion paper, we used an H I-selected sample of nearby galaxies to reveal a subsample of very gas-rich (gas fraction >80 per cent) sources with dust masses significantly below predictions from simple chemical evolution models, and well below Md/M* and Md/Mgas scaling relations seen in dust and stellar-selected samples of local galaxies. We use a chemical evolution model to explain these dust-poor, but gas-rich, sources as well as the observed star formation rates (SFRs) and dust-to-gas ratios. We find that (I) a delayed star formation history is required to model the observed SFRs; (II) inflows and outflows are required to model the observed metallicities at low gas fractions; (III) a reduced contribution of dust from supernovae (SNe) is needed to explain the dust-poor sources with high gas fractions. These dust-poor, low stellar mass galaxies require a typical core-collapse SN to produce 0.01-0.16 M⊙ of dust. To match the observed dust masses at lower gas fractions, significant grain growth is required to counteract the reduced contribution from dust in SNe and dust destruction from SN shocks. These findings are statistically robust, though due to intrinsic scatter it is not always possible to find one single model that successfully describes all the data. We also show that the dust-to-metal ratio decreases towards lower metallicity.

Evolution of the Stellar Mass–Metallicity Relation. I. Galaxies in the z ∼ 0.4 Cluster Cl0024

NASA Astrophysics Data System (ADS)

Leethochawalit, Nicha; Kirby, Evan N.; Moran, Sean M.; Ellis, Richard S.; Treu, Tommaso

2018-03-01

We present the stellar mass–stellar metallicity relationship (MZR) in the galaxy cluster Cl0024+1654 at z ∼ 0.4 using full-spectrum stellar population synthesis modeling of individual quiescent galaxies. The lower limit of our stellar mass range is M * = 109.7 M ⊙, the lowest galaxy mass at which individual stellar metallicity has been measured beyond the local universe. We report a detection of an evolution of the stellar MZR with observed redshift at 0.037 ± 0.007 dex per Gyr, consistent with the predictions from hydrodynamical simulations. Additionally, we find that the evolution of the stellar MZR with observed redshift can be explained by an evolution of the stellar MZR with the formation time of galaxies, i.e., when the single stellar population (SSP)-equivalent ages of galaxies are taken into account. This behavior is consistent with stars forming out of gas that also has an MZR with a normalization that decreases with redshift. Lastly, we find that over the observed mass range, the MZR can be described by a linear function with a shallow slope ([{Fe}/{{H}}]\\propto (0.16+/- 0.03){log}{M}* ). The slope suggests that galaxy feedback, in terms of mass-loading factor, might be mass-independent over the observed mass and redshift range.

Revisiting The First Galaxies: The effects of Population III stars on their host galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muratov, Alexander L.; Gnedin, Oleg Y.; Gnedin, Nickolay Y.

2013-07-12

We revisit the formation and evolution of the first galaxies using new hydrodynamic cosmological simulations with the adaptive refinement tree code. Our simulations feature a recently developed model for H 2 formation and dissociation, and a star formation recipe that is based on molecular rather than atomic gas. Here, we develop and implement a recipe for the formation of metal-free Population III (Pop III) stars in galaxy-scale simulations that resolve primordial clouds with sufficiently high density. We base our recipe on the results of prior zoom-in simulations that resolved the protostellar collapse in pre-galactic objects. We find the epoch duringmore » which Pop III stars dominated the energy and metal budget of the first galaxies to be short-lived. Galaxies that host Pop III stars do not retain dynamical signatures of their thermal and radiative feedback for more than 10 8 years after the lives of the stars end in pair-instability supernovae, even when we consider the maximum reasonable efficiency of the feedback. Though metals ejected by the supernovae can travel well beyond the virial radius of the host galaxy, they typically begin to fall back quickly, and do not enrich a large fraction of the intergalactic medium. Galaxies with a total mass in excess of 3 × 10 6 M ⊙ re-accrete most of their baryons and transition to metal-enriched Pop II star formation.« less

REVISITING THE FIRST GALAXIES: THE EFFECTS OF POPULATION III STARS ON THEIR HOST GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muratov, Alexander L.; Gnedin, Oleg Y.; Zemp, Marcel

2013-08-01

We revisit the formation and evolution of the first galaxies using new hydrodynamic cosmological simulations with the adaptive refinement tree code. Our simulations feature a recently developed model for H{sub 2} formation and dissociation, and a star formation recipe that is based on molecular rather than atomic gas. Here, we develop and implement a recipe for the formation of metal-free Population III (Pop III) stars in galaxy-scale simulations that resolve primordial clouds with sufficiently high density. We base our recipe on the results of prior zoom-in simulations that resolved the protostellar collapse in pre-galactic objects. We find the epoch duringmore » which Pop III stars dominated the energy and metal budget of the first galaxies to be short-lived. Galaxies that host Pop III stars do not retain dynamical signatures of their thermal and radiative feedback for more than 10{sup 8} years after the lives of the stars end in pair-instability supernovae, even when we consider the maximum reasonable efficiency of the feedback. Though metals ejected by the supernovae can travel well beyond the virial radius of the host galaxy, they typically begin to fall back quickly, and do not enrich a large fraction of the intergalactic medium. Galaxies with a total mass in excess of 3 Multiplication-Sign 10{sup 6} M{sub Sun} re-accrete most of their baryons and transition to metal-enriched Pop II star formation.« less

High-resolution spectroscopy of the extended narrow-line region of IC 5063 and NGC 7212

NASA Astrophysics Data System (ADS)

Congiu, E.; Contini, M.; Ciroi, S.; Cracco, V.; Berton, M.; Di Mille, F.; Frezzato, M.; La Mura, G.; Rafanelli, P.

2017-10-01

We studied the properties of the gas of the extended narrow-line region (ENLR) of two Seyfert 2 galaxies: IC 5063 and NGC 7212. We analysed high-resolution spectra to investigate how the main properties of this region depend on the gas velocity. We divided the emission lines in velocity bins and we calculated several line ratios. Diagnostic diagrams and suma composite models (photoionization + shocks) show that in both galaxies there might be evidence of shocks significantly contributing in the gas ionization at high |V|, even though photoionization from the active nucleus remains the main ionization mechanism. In IC 5063, the ionization parameter depends on V and its trend might be explained assuming an hollow bi-conical shape for the ENLR, with one of the edges aligned with the galaxy disc. On the other hand, NGC 7212 does not show any kind of dependence. The models show that solar O/H relative abundances reproduce the observed spectra in all the analysed regions. They also revealed an high fragmentation of the gas clouds, suggesting that the complex kinematics observed in these two objects might be caused by interaction between the interstellar medium and high-velocity components, such as jets.

The young stellar population of IC 1613. III. New O-type stars unveiled by GTC-OSIRIS

NASA Astrophysics Data System (ADS)

Garcia, M.; Herrero, A.

2013-03-01

Context. Very low-metallicity massive stars are key to understanding the reionization epoch. Radiation-driven winds, chief agents in the evolution of massive stars, are consequently an important ingredient in our models of the early-Universe. Recent findings hint that the winds of massive stars with poorer metallicity than the SMC may be stronger than predicted by theory. Besides calling the paradigm of radiation-driven winds into question, this result would affect the calculated ionizing radiation and mechanical feedback of massive stars, as well as the role these objects play at different stages of the Universe. Aims: The field needs a systematic study of the winds of a large sample of very metal-poor massive stars. The sampling of spectral types is particularly poor in the very early types. This paper's goal is to increase the list of known O-type stars in the dwarf irregular galaxy IC 1613, whose metallicity is lower than the SMC's roughly by a factor 2. Methods: Using the reddening-free Q pseudo-colour, evolutionary masses, and GALEX photometry, we built a list of very likely O-type stars. We obtained low-resolution (R ~ 1000) GTC-OSIRIS spectra for a fraction of them and performed spectral classification, the only way to unequivocally confirm candidate OB-stars. Results: We have discovered 8 new O-type stars in IC 1613, increasing the list of 7 known O-type stars in this galaxy by a factor of 2. The best quality spectra were analysed with the model atmosphere code FASTWIND to derive stellar parameters. We present the first spectral type - effective temperature scale for O-stars beyond the SMC. Conclusions: The target selection method is successful. From the pre-selected list of 13 OB star candidates, we have found 8 new O-stars and 4 early-B stars and provided a similar type for a formerly known early-O star. Further tests are needed, but the presented procedure can eventually make preliminary low-resolution spectroscopy to confirm candidates unnecessary. The

ALMA Maps of Dust and Warm Dense Gas Emission in the Starburst Galaxy IC 5179

NASA Astrophysics Data System (ADS)

Zhao, Yinghe; Lu, Nanyao; Díaz-Santos, Tanio; Xu, C. Kevin; Gao, Yu; Charmandaris, Vassilis; van der Werf, Paul; Zhang, Zhi-Yu; Cao, Chen

2017-08-01

We present our high-resolution (0.″15 × 0.″13, ˜34 pc) observations of the CO (6-5) line emission, which probes the warm and dense molecular gas, and the 434 μm dust continuum emission in the nuclear region of the starburst galaxy IC 5179, conducted with the Atacama Large Millimeter Array (ALMA). The CO (6-5) emission is spatially distributed in filamentary structures with many dense cores and shows a velocity field that is characteristic of a circumnuclear rotating gas disk, with 90% of the rotation speed arising within a radius of ≲150 pc. At the scale of our spatial resolution, the CO (6-5) and dust emission peaks do not always coincide, with their surface brightness ratio varying by a factor of ˜10. This result suggests that their excitation mechanisms are likely different, as further evidenced by the southwest to northeast spatial gradient of both CO-to-dust continuum ratio and Pa-α equivalent width. Within the nuclear region (radius ˜ 300 pc) and with a resolution of ˜34 pc, the CO line flux (dust flux density) detected in our ALMA observations is 180 ± 18 Jy km s-1 (71 ± 7 mJy), which accounts for 22% (2.4%) of the total value measured by Herschel. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

The early phase of the SMBH-galaxy coevolution in low-z "young" galaxies

NASA Astrophysics Data System (ADS)

Nagao, Tohru

2014-01-01

It is now widely recognized that most galaxies have a supermassive black hole (SMBH) in their nucleus, and the evolution of SMBHs is closely related with that of their host galaxies (the SMBH-galaxy coevolution). This is suggested by the correlation in the mass of SMBHs and their host galaxies, that has been observed in low redshifts. However, the physics of the coevolution is totally unclear, that prevents us from complete understandings of the galaxy evolution. One possible strategy to tackle this issue is measuring the mass ratio between SMBHs and their host galaxies (M_BH/M_host) at high redshifs, since different scenarios predict different evolution of the ratio ofMBH/Mhost. However it is extremely challenging to measure the mass of the host of high-z quasars, given the faint surface brightness of the host at close to the glaring quasar nucleus. Here we propose a brand-new approach to assess the early phase of the SMBH-galaxy coevolution, by focusing on low-z AGN-hosting "young" galaxies. Specifically, we focus on some very metal-poor galaxies with broadline Balmer lines at z ~ 0.1 - 0.3. By examining the SMBH scaling relations in some low-z metal-poor AGNs through high-resolution IRCS imaging observations, we will discriminate various scenarios for the SMBH-galaxy coevolution.

30 CFR 57.22203 - Main fan operation (I-C mines).

Code of Federal Regulations, 2010 CFR

2010-07-01

... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Main fan operation (I-C mines). 57.22203... Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22203 Main fan operation (I-C mines). Main fans shall be operated continuously while ore production is in progress. ...

Metals and dust in the neutral ISM: the Galaxy, Magellanic Clouds, and damped Lyman-α absorbers

NASA Astrophysics Data System (ADS)

De Cia, Annalisa

2018-05-01

Context. The presence of dust in the neutral interstellar medium (ISM) dramatically changes the metal abundances that we measure. Understanding the metal content in the neutral ISM, and a direct comparison between different environments, has been hampered to date because of the degeneracy to the observed ISM abundances caused by the effects of metallicity, the presence of dust, and nucleosynthesis. Aims: We study the metal and dust content in the neutral ISM consistently in different environments, and assess the universality of recently discovered sequences of relative abundances. We also intend to assess the validity of [Zn/Fe] as a tracer of dust in the ISM. This has recently been cast into doubt based on observations of stellar abundances, and needs to be addressed before we can safely use it to study the ISM. Methods: In this letter we present a simple comparison of relative abundances observed in the neutral ISM in the Galaxy, the Magellanic Clouds, and damped Lyman-α absorbers (DLAs). The main novelty in this comparison is the inclusion of the Magellanic Clouds. Results: The same sequences of relative abundances are valid for the Galaxy, Magellanic Clouds, and DLAs. These sequences are driven by the presence of dust in the ISM and seem "universal". Conclusions: The metal and dust properties in the neutral ISM appear to follow a similar behaviour in different environments. This suggests that a dominant fraction of the dust budget is built up from grain growth in the ISM depending of the physical conditions and regardless of the star formation history of the system. In addition, the DLA gas behaves like the neutral ISM, at least from a chemical point of view. Finally, despite the deviations in [Zn/Fe] observed in stellar abundances, [Zn/Fe] is a robust dust tracer in the ISM of different environments, from the Galaxy to DLAs.

An Extreme Metallicity, Large-scale Outflow from a Star-forming Galaxy at z ~ 0.4

NASA Astrophysics Data System (ADS)

Muzahid, Sowgat; Kacprzak, Glenn G.; Churchill, Christopher W.; Charlton, Jane C.; Nielsen, Nikole M.; Mathes, Nigel L.; Trujillo-Gomez, Sebastian

2015-10-01

We present a detailed analysis of a large-scale galactic outflow in the circumgalactic medium of a massive ({M}{{h}}˜ {10}12.5 {M}⊙ ), star-forming (˜ 6.9 {M}⊙ yr-1), sub-L* (˜ 0.5{L}B*) galaxy at z = 0.39853 that exhibits a wealth of metal-line absorption in the spectra of the background quasar Q 0122-003 at an impact parameter of 163 kpc. The galaxy inclination angle (i=63^\\circ ) and the azimuthal angle ({{Φ }}=73^\\circ ) imply that the QSO sightline is passing through the projected minor-axis of the galaxy. The absorption system shows a multiphase, multicomponent structure with ultra-strong, wide velocity spread {{O}} {{VI}} ({log}N=15.16+/- 0.04, {{Δ }}{v}90 = 419 km s-1) and {{N}} {{V}} ({log}N=14.69+/- 0.07, {{Δ }}{v}90 = 285 km s-1) lines that are extremely rare in the literature. The highly ionized absorption components are well explained as arising in a low density (˜ {10}-4.2 cm-3), diffuse (˜10 kpc), cool (˜104 K) photoionized gas with a super-solar metallicity ([{{X}}/{{H}}]≳ 0.3). From the observed narrowness of the Lyβ profile, the non-detection of {{S}} {{IV}} absorption, and the presence of strong {{C}} {{IV}} absorption in the low-resolution FOS spectrum, we rule out equilibrium/non-equilibrium collisional ionization models. The low-ionization photoionized gas with a density of ˜ {10}-2.5 cm-3 and a metallicity of [{{X}}/{{H}}]≳ -1.4 is possibly tracing recycled halo gas. We estimate an outflow mass of ˜ 2× {10}10 {M}⊙ , a mass-flow rate of ˜ 54 {M}⊙ {{yr}}-1, a kinetic luminosity of ˜ 9× {10}41 erg s-1, and a mass loading factor of ˜8 for the outflowing high-ionization gas. These are consistent with the properties of “down-the-barrel” outflows from infrared-luminous starbursts as studied by Rupke et al. Such powerful, large-scale, metal-rich outflows are the primary means of sufficient mechanical and chemical feedback as invoked in theoretical models of galaxy formation and evolution.

VizieR Online Data Catalog: Galaxy stellar mass assembly (Cousin+, 2015)

NASA Astrophysics Data System (ADS)

Cousin, M.; Lagache, G.; Bethermin, M.; Blaizot, J.; Guiderdoni, B.

2014-11-01

There are five fits files corresponding to the different models: - m0 : model without any regulation process - m1 : reference model (Okamoto et al., 2008MNRAS.390..920O, photo-ionization prescription) - m2 : The Okamoto et al. (2008MNRAS.390..920O) photo-ionization prescription is replaced by Gnedin (2000ApJ...542..535G) prescription - m3 : SN ejecta processes are based on Somerville et al. (2008MNRAS.391..481S) model - m4 : Model with no-star-forming gas ad-hoc modification For each model: - galaxy properties are listed in eGalICS_m*.readme - data are saved in eGalICS_m*.fits All data "fits" files are compatible with the TOPCAT software available on: http://www.star.bris.ac.uk/~mbt/topcat/ If you used data associated to eGalICS semi-analytic model, please cite the following papers: * Cousin et al.: "Galaxy stellar mass assembly: the difficulty to match observations and semi-analytical predictions" (2015A&A...575A..32C) * Cousin et al.: "Toward a new modelling of gas flows in a semi-analytical model of galaxy formation and evolution" (2015A&A...575A..33C) (11 data files).

SBS 0335-052E+W: deep VLT/FORS+UVES spectroscopy of the pair of the lowest-metallicity blue compact dwarf galaxies

NASA Astrophysics Data System (ADS)

Izotov, Y. I.; Guseva, N. G.; Fricke, K. J.; Papaderos, P.

2009-08-01

Context: We present deep archival VLT/FORS1+UVES spectroscopic observations of the system of two blue compact dwarf (BCD) galaxies SBS 0335-052E and SBS 0335-052W. Aims: Our aim is to derive element abundances in different H ii regions of this unique system of galaxies and to study spatial abundance variations. Methods: The electron temperature Te (O iii) in all H ii regions, except for one, is derived from the [O iii] λ4363/(λ4959+λ5007) flux ratio. We determine ionic abundances of helium, nitrogen, oxygen, neon, sulfur, chlorine, argon and iron. The empirical relations for ionization correction factors are used to derive total abundances of these elements. Results: The oxygen abundance in the brighter eastern galaxy varies in the range 7.11 to 7.32 in different H ii regions supporting previous findings and suggesting the presence of oxygen abundance variations on spatial scales of ~1-2 kpc. Good seeing during FORS observations allowed us to extract spectra of four H ii regions in SBS 0335-052W. The oxygen abundance in the brightest region No. 1 of SBS 0335-052W is 7.22 ± 0.07, consistent with previous determinations. Three other H ii regions are much more metal-poor with an unprecedently low oxygen abundance of 12 + log O/H = 7.01 ± 0.07 (region No. 2), 6.98 ± 0.06 (region No. 3), and 6.86 ± 0.14 (region No. 4). These are the lowest oxygen abundances ever derived in emission-line galaxies, supporting earlier conclusions that SBS 0335-052W is the lowest-metallicity emission-line galaxy known. Helium abundances derived for the brightest H ii regions of both galaxies are mutually consistent. We derive weighted mean He mass fractions of 0.2485 ± 0.0012 and 0.2514 ± 0.0012 for two different sets of He i emissivities. The ratios of neon and sulfur to oxygen abundance are similar to the respective ratios obtained for other emission-line galaxies. On the other hand, the chlorine-to-oxygen abundance ratio in SBS 0335-052E is lower, while the argon

Mapping Gas Flows from the Disk to the Circumgalactic Medium

NASA Astrophysics Data System (ADS)

Zheng, Yong

2017-08-01

The feedback efficiency in galaxies remains a crucial component in simulations that is not well constrained by observations. To understand how effectively feedback drives metals into the circumgalactic medium (CGM), we propose to map the metal flows from the disk to the CGM of the nearby dwarf irregular galaxy IC 1613. This will be the first spatial and kinematic map of gas flows from the disk to the halo of a dwarf galaxy. In archival COS spectra of two IC 1613 stars we detect blue-shifted SiII, CII, and SiIV absorption lines, indicative of the existence of multiphase outflows from the disk. We propose to observe two more UV bright stars in IC 1613's disk to assess the covering fraction and strength of the outflow in relation to the galaxy's resolved star formation. We will also observe three QSO sightlines at 0.1, 0.3, and 0.5 Rvir to measure the ionization profile of the gas and the extent of the outflows. We will relate our measurements to the detailed observed star formation history of IC 1613 to directly determine the mass loading factor and feedback efficiency. The proposal will provide critical information on how galaxies evolve and how metals circulate between the disk and the CGM.

HUNTING FOR YOUNG DISPERSING STAR CLUSTERS IN IC 2574

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pellerin, Anne; Meyer, Martin M.; Calzetti, Daniella

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 Advancedmore » 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.« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moreno-Raya, Manuel E.; Mollá, Mercedes; López-Sánchez, Ángel R.

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 datamore » 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.« less

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)

ALMA Resolves the Molecular Gas in a Young Low-metallicity Starburst Galaxy at z = 1.7

NASA Astrophysics Data System (ADS)

González-López, Jorge; Barrientos, L. Felipe; Gladders, M. D.; Wuyts, Eva; Rigby, Jane; Sharon, Keren; Aravena, Manuel; Bayliss, Matthew B.; Ibar, Eduardo

2017-09-01

We present Atacama Large Millimeter/submillimeter Array observations of CO lines and dust continuum emission of the source RCSGA 032727-132609, a young z = 1.7 low-metallicity starburst galaxy. The CO(3-2) and CO(6-5) lines and continuum at rest-frame 450 μm are detected and show a resolved structure in the image plane. We use the corresponding lensing model to obtain a source plane reconstruction of the detected emissions revealing an intrinsic flux density of {S}450μ {{m}}={23.5}-8.1+26.8 μJy and intrinsic CO luminosities {L}{CO(3-2)}{\\prime }={2.90}-0.23+0.21 × {10}8 {{K}} {km} {{{s}}}-1 {{pc}}2 and {L}{CO(6-5)}{\\prime }={8.0}-1.3+1.4× {10}7 {{K}} {km} {{{s}}}-1 {{pc}}2. We used the resolved properties in the source plane to obtain molecular gas and star formation rate surface densities of {{{Σ }}}{{H}2}={16.2}-3.5+5.8 {M}⊙ {{pc}}-2 and {{{Σ }}}{SFR}={0.54}-0.27+0.89 {M}⊙ {{yr}}-1 {{kpc}}-2, respectively. The intrinsic properties of RCSGA 032727-132609 show an enhanced star formation activity compared to local spiral galaxies with similar molecular gas densities, supporting the ongoing merger-starburst phase scenario. RCSGA 032727-132609 also appears to be a low-density starburst galaxy similar to local blue compact dwarf galaxies, which have been suggested as local analogs to high-redshift low-metallicity starburst systems. Finally, the CO excitation level in the galaxy is consistent with having the peak at J˜ 5, with a higher excitation concentrated in the star-forming clumps.

SDSS-IV MaNGA: Spatially resolved star formation histories in galaxies as a function of galaxy mass and type

NASA Astrophysics Data System (ADS)

Goddard, D.; Thomas, D.; Maraston, C.; Westfall, K.; Etherington, J.; Riffel, R.; Mallmann, N. D.; Zheng, Z.; Argudo-Fernández, M.; Lian, J.; Bershady, M.; Bundy, K.; Drory, N.; Law, D.; Yan, R.; Wake, D.; Weijmans, A.; Bizyaev, D.; Brownstein, J.; Lane, R. R.; Maiolino, R.; Masters, K.; Merrifield, M.; Nitschelm, C.; Pan, K.; Roman-Lopes, A.; Storchi-Bergmann, T.; Schneider, D. P.

2017-04-01

We study the internal gradients of stellar population properties within 1.5 Re for a representative sample of 721 galaxies, with stellar masses ranging between 109 M⊙ and 1011.5 M⊙ from the SDSS-IV MaNGA Integral-Field-Unit survey. Through the use of our full spectral fitting code firefly, we derive light- and mass-weighted stellar population properties and their radial gradients, as well as full star formation and metal enrichment histories. We also quantify the impact that different stellar population models and full spectral fitting routines have on the derived stellar population properties and the radial gradient measurements. In our analysis, we find that age gradients tend to be shallow for both early-type and late-type galaxies. Mass-weighted age gradients of early-types arepositive (˜0.09 dex/Re) pointing to 'outside-in' progression of star formation, while late-type galaxies have negative light-weighted age gradients (˜-0.11 dex/Re), suggesting an 'inside-out' formation of discs. We detect negative metallicity gradients in both early- and late-type galaxies, but these are significantly steeper in late-types, suggesting that the radial dependence of chemical enrichment processes and the effect of gas inflow and metal transport are far more pronounced in discs. Metallicity gradients of both morphological classes correlate with galaxy mass, with negative metallicity gradients becoming steeper with increasing galaxy mass. The correlation with mass is stronger for late-type galaxies, with a slope of d(∇[Z/H])/d(log M) ˜ -0.2 ± 0.05 , compared to d(∇[Z/H])/d(log M) ˜ -0.05 ± 0.05 for early-types. This result suggests that the merger history plays a relatively small role in shaping metallicity gradients of galaxies.

Winds of metal-poor OB stars: Updates from HST-COS UV spectroscopy

NASA Astrophysics Data System (ADS)

García, M.; Herrero, A.; Najarro, F.; Lennon, D. J.; Urbaneja, M. A.

2015-01-01

In the race to break the SMC frontier and reach metallicity conditions closer to the First Stars the information from UV spectroscopy is usually overlooked. New HST-COS observations of OB stars in the metal-poor galaxy IC1613, with oxygen content ~1/10 solar, have proved the important role of UV spectroscopy to characterize blue massive stars and their winds. The terminal velocities (υ∞) and abundances derived from the dataset have shed new light on the problem of metal-poor massive stars with strong winds. Furthermore, our results question the υ∞-υ esc and υ∞-Z scaling relations whose use in optical-only studies may introduce large uncertainties in the derived mass loss rates and wind-momenta. Finally, our results indicate that the detailed abundance pattern of each star may have a non-negligible impact on its wind properties, and scaling these as a function of one single metallicity parameter is probably too coarse an approximation. Considering, for instance, that the [α/Fe] ratio evolves with the star formation history of each galaxy, we may be in need of updating all our wind recipes.

Detection of low-metallicity warm plasma in a galaxy overdensity environment at z ˜ 0.2

NASA Astrophysics Data System (ADS)

Narayanan, Anand; Savage, Blair D.; Mishra, Preetish K.; Wakker, Bart P.; Khaire, Vikram; Wadadekar, Yogesh

2018-04-01

We present results from the analysis of a multiphase O VI-broad Ly α (BLA) absorber at z = 0.19236 in the HubbleSpaceTelescope/Cosmic Origins Spectrograph spectrum of PG 1121 + 422. The low and intermediate ionization metal lines in this absorber have a single narrow component, whereas the Ly α has a possible broad component with b({H {I}}) ˜ 71 km s-1. Ionization models favour the low and intermediate ions coming from a T ˜ 8500 K, moderately dense (n H ˜ 10 - 3 cm-3) photoionized gas with near solar metallicities. The weak O VI requires a separate gas phase that is collisionally ionized. The O VI coupled with BLA suggests T ˜ 3.2 × 105 K, with significantly lower metal abundance and ˜1.8 orders of magnitude higher total hydrogen column density compared to the photoionized phase. Sloan Digitial Sky Survey (SDSS) shows 12 luminous (>L*) galaxies in the ρ ≤ 5 Mpc, |Δv| ≤ 800 km s-1 region surrounding the absorber, with the absorber outside the virial bounds of the nearest galaxy. The warm phase of this absorber is consistent with being transition temperature plasma either at the interface regions between the hot intragroup gas and cooler photoionized clouds within the group, or associated with high velocity gas in the halo of a ≲L* galaxy. The absorber highlights the advantage of O VI-BLA absorbers as ionization model independent probes of warm baryon reserves.

Constraining Both the Star-Formation History and Metal-Enrichment History of Galaxies

NASA Astrophysics Data System (ADS)

Heap, Sara

2005-07-01

Using 380 stellar spectra from Hubble's Next Generation Spectral Library {NGSL; PI=Michael Gregg; GO 9088, 9786} incorporated in our stellar population synthesis code {Bruzual & Charlot 2003}, we propose to constrain simultaneously the star-formation history and mean age, stellar metallicity and mass of galaxies over a wide redshift interval {z= 0 -2}. The main advantages of the NGSL are the high-quality spectrophotometry {S/N >50} and broad wavelength coverage {2000-10, 000 Ang} of the STIS spectra. The NGSL enables mid-UV as well as optical spectral indices to be used, thereby increasing the redshift interval of their application. It also guarantees consistency in treating low- and high-redshift galaxies, since the same stars are used as spectral templates. To realize the full potential of the NGSL, however, will require significant custom data-processing, calibration, and evaluation of the STIS data.

HI and Low Metal Ions at the Intersection of Galaxies and the CGM

NASA Astrophysics Data System (ADS)

Oppenheimer, Benjamin

2017-08-01

Over 1000 COS orbits have revealed a surprisingly complex picture of circumgalactic gas flows surrounding the diversity of galaxies in the evolved Universe. Cosmological hydrodynamic simulations have only begun to confront the vast amount of galaxy formation physics, chemistry, and dynamics revealed in the multi-ion CGM datasets. We propose the next generation of EAGLE zoom simulations, called EAGLE Cosmic Origins, to model HI and low metal ions (C II, Mg II, & Si II) throughout not just the CGM but also within the galaxies themselves. We will employ a novel, new chemistry solver, CHIMES, to follow time-dependent ionization, chemistry, and cooling of 157 ionic and molecular species, and include multiple ionization sources from the extra-galactic background, episodic AGN, and star formation. Our aim is to understand the complete baryon cycle of inflows, outflows, and gas recycling traced over 10 decades of HI column densities as well as the complex kinematic information encoded low ion absorption spectroscopy. This simulation project represents a pilot program for a larger suite of zoom simulations, which will be publicly released and lead to additional publications.

30 CFR 57.22210 - In-line filters (I-C mines).

Code of Federal Regulations, 2011 CFR

2011-07-01

... 30 Mineral Resources 1 2011-07-01 2011-07-01 false In-line filters (I-C mines). 57.22210 Section... Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22210 In-line filters (I-C mines). Filters or separators shall be installed on air-lift fan systems to prevent explosive concentrations of...

30 CFR 57.22210 - In-line filters (I-C mines).

Code of Federal Regulations, 2013 CFR

2013-07-01

... 30 Mineral Resources 1 2013-07-01 2013-07-01 false In-line filters (I-C mines). 57.22210 Section... Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22210 In-line filters (I-C mines). Filters or separators shall be installed on air-lift fan systems to prevent explosive concentrations of...

30 CFR 57.22210 - In-line filters (I-C mines).

Code of Federal Regulations, 2012 CFR

2012-07-01

... 30 Mineral Resources 1 2012-07-01 2012-07-01 false In-line filters (I-C mines). 57.22210 Section... Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22210 In-line filters (I-C mines). Filters or separators shall be installed on air-lift fan systems to prevent explosive concentrations of...

30 CFR 57.22210 - In-line filters (I-C mines).

Code of Federal Regulations, 2014 CFR

2014-07-01

... 30 Mineral Resources 1 2014-07-01 2014-07-01 false In-line filters (I-C mines). 57.22210 Section... Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22210 In-line filters (I-C mines). Filters or separators shall be installed on air-lift fan systems to prevent explosive concentrations of...

30 CFR 57.22210 - In-line filters (I-C mines).

Code of Federal Regulations, 2010 CFR

2010-07-01

... 30 Mineral Resources 1 2010-07-01 2010-07-01 false In-line filters (I-C mines). 57.22210 Section... Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22210 In-line filters (I-C mines). Filters or separators shall be installed on air-lift fan systems to prevent explosive concentrations of...

The Importance of Preventive Feedback: Inference from Observations of the Stellar Masses and Metallicities of Milky Way Dwarf Galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Yu; Benson, Andrew; Wetzel, Andrew

2017-09-01

Dwarf galaxies are known to have remarkably low star formation efficiency due to strong feedback. Adopting the dwarf galaxies of the Milky Way (MW) as a laboratory, we explore a flexible semi-analytic galaxy formation model to understand how the feedback processes shape the satellite galaxies of the MW. Using Markov Chain Monte Carlo, we exhaustively search a large parameter space of the model and rigorously show that the general wisdom of strong outflows as the primary feedback mechanism cannot simultaneously explain the stellar mass function and the mass–metallicity relation of the MW satellites. An extended model that assumes that amore » fraction of baryons is prevented from collapsing into low-mass halos in the first place can be accurately constrained to simultaneously reproduce those observations. The inference suggests that two different physical mechanisms are needed to explain the two different data sets. In particular, moderate outflows with weak halo mass dependence are needed to explain the mass–metallicity relation, and prevention of baryons falling into shallow gravitational potentials of low-mass halos (e.g., “pre-heating”) is needed to explain the low stellar mass fraction for a given subhalo mass.« less

The Importance of Preventive Feedback: Inference from Observations of the Stellar Masses and Metallicities of Milky Way Dwarf Galaxies

DOE PAGES

Lu, Yu; Benson, Andrew; Wetzel, Andrew; ...

2017-08-31

Dwarf galaxies are known to have remarkably low star formation efficiency due to strong feedback. Adopting the dwarf galaxies of the Milky Way (MW) as a laboratory, we explore a flexible semi-analytic galaxy formation model to understand how the feedback processes shape the satellite galaxies of the MW. Using Markov Chain Monte Carlo, we exhaustively search a large parameter space of the model and rigorously show that the general wisdom of strong outflows as the primary feedback mechanism cannot simultaneously explain the stellar mass function and the mass–metallicity relation of the MW satellites. An extended model that assumes that amore » fraction of baryons is prevented from collapsing into low-mass halos in the first place can be accurately constrained to simultaneously reproduce those observations. Here, the inference suggests that two different physical mechanisms are needed to explain the two different data sets. In particular, moderate outflows with weak halo mass dependence are needed to explain the mass–metallicity relation, and prevention of baryons falling into shallow gravitational potentials of low-mass halos (e.g., "pre-heating") is needed to explain the low stellar mass fraction for a given subhalo mass.« less

30 CFR 57.22241 - Advance face boreholes (I-C mines).

Code of Federal Regulations, 2010 CFR

2010-07-01

...) Boreholes shall be drilled in such a manner to insure that the advancing face will not accidently break into... 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...

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 is...

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 is...

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 is...

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 is...

The Epoch of the First Star Formation in the Closest Metal-Poor Blue Compact Dwarf Galaxy UGC 4483

NASA Astrophysics Data System (ADS)

Aloisi, Alessandra

2017-08-01

Metal-poor Blue Compact Dwarf (BCD) galaxies have been interpreted as nearby galaxies in formation. This view has been challenged by HST detection of Red Giant Branch (RGB) stars in all metal-poor BCDs where an RGB tip (TRGB, brightest RGB phase) has been searched for, impling the presence of stars at least 1 Gyr old. Due to the age-metallicity degeneracy, the RGB color provides little insight into the exact star formation history (SFH) beyond 1 Gyr. So, the first SF epoch may have occurred anywhere between 13 and 1 Gyr ago. To resolve this, it is necessary to reach features in the color-magnitude diagram (CMD) that are much fainter than the TRGB. Here we propose new WFC3/UVIS observations (with ACS/WFC in parallel) of the closest metal-poor BCD, UGC 4483. These data will yield an I vs. V-I CMD that goes 4 mag deeper than the TRGB allowing to detect red clump (RC) and horizontal branch (HB) stars. Variable stars of RR Lyrae type will also be detected. With their mere presence, these variables will indisputably prove the existence of a population at least 10 Gyr old. Apparent mag and width of RC, HB and RGB will independently constrain age and metallicity of the old/evolved stars, the presence of multiple SF episodes, their duration and metallicity spread. This deep crowded-field photometric project is only possible with HST. Due to UGC 4483 location in CVZ, it can be done in half the number of orbits that it would otherwise take. Since UGC 4483 is so close, it may be the only BCD for which these questions can be answered in the near future. It provides our best chance for learning about the true cosmological age and evolutionary state of these enigmatic galaxies.

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.;

The dwarf galaxy UGC 5272 and its small companion galaxy

NASA Technical Reports Server (NTRS)

Hopp, U.; Schulte-Ladbeck, R. E.

1991-01-01

The present study of optical images and spectroscopy of the dwarf irregular galaxy UGC 5272 notes the presence, at 3.6 kpc, of a small neighboring galaxy which is also of irregular type and has a Holmberg diameter of 0.6 kpc. Attention is given to the possibility that the two galaxies, which are resolved into single stars, may form a physical pair. It is suggested that the blue-to-red supergiant ratio of UGC 5272 is high due to its low metallicity. While its extremely blue colors are suggestive of a recent starburst, the structural parameters of the galaxy are surprisingly normal. The gas contribution to total mass is high.

Hubble "Crane-s" in for a Closer Look at a Galaxy

NASA Image and Video Library

2017-12-08

In 1900, astronomer Joseph Lunt made a discovery: Peering through a telescope at Cape Town Observatory, the British–South African scientist spotted this beautiful sight in the southern constellation of Grus (The Crane): a barred spiral galaxy now named IC 5201. Over a century later, the galaxy is still of interest to astronomers. For this image, the NASA/ESA Hubble Space Telescope used its Advanced Camera for Surveys (ACS) to produce a beautiful and intricate image of the galaxy. Hubble’s ACS can resolve individual stars within other galaxies, making it an invaluable tool to explore how various populations of stars sprang to life, evolved, and died throughout the cosmos. IC 5201 sits over 40 million light-years away from us. As with two thirds of all the spirals we see in the Universe — including the Milky Way — the galaxy has a bar of stars slicing through its center. Credit: ESA/Hubble & NASA NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

The CO-12 and CO-13 J=2-1 and J=1-0 observations of hot and cold galaxies

NASA Technical Reports Server (NTRS)

Xie, Shuding; Schloerb, F. Peter; Young, Judith

1990-01-01

Researchers observed the nuclear regions of the galaxies NGC 2146 and IC 342 in CO-12 and CO-13 J=1-0 and J=2-1 lines using the Five College Radio Astronomy Observatory (FCRAO) 14m telescope. NGC 2146 is a peculiar Sab spiral galaxy. Its complex optical morphology and strong nuclear radio continuum emission suggest that it is experiencing a phase of violent activity and could have a polar ring which may have resulted from an interaction. IC 342 is a nearby luminous Scd spiral galaxy. Strong CO, infrared and radio continuum emission from the nuclear region of IC 342 indicate enhanced star-forming activity, and interferometric CO-12 J=1-0 observations reveal a bar-like structure centered on the nucleus, along the dark lane in the NS direction. These two galaxies are selected based on their different dust temperatures and star formation efficiencies (SFE) as derived from the Infrared Astronomy Satellite (IRAS) S sub 60 mu/S sub 100 mu flux density ratio and L sub IR/M(H2), respectively, with a relatively high SFE and dust temperature of 45 K in NGC 2146 and a relatively low SFE and dust temperature of 35 K in IC 342. The data from the different CO-12 and CO-13 lines are used to study the physical conditions in the molecular clouds in the galaxies. Researchers also consider the radiative transfer to determine whether a warm and optically thin gas component exists in these galaxies, as has been suggested in the case of M82 (Knapp et al. 1980), and whether the warm gas is related to the dust properties. Since optically thin CO-12 gas is rarely detected in our own Galaxy (except in outflow sources), to confirm its existence in external galaxies is very important in understanding the molecular content of external galaxies and its relationship to star formation activity. The present CO-12 J=2-1 and CO-13 J=2-1 and J=1-0 data for NGC 2146 are the first detections of this galaxy to our knowledge. The CO-12 J=1-0 distribution in NGC 2146 has been measured as part of the FCRAO

Blue diffuse dwarf galaxies: a clearer picture

NASA Astrophysics Data System (ADS)

James, Bethan L.; Koposov, Sergey E.; Stark, Daniel P.; Belokurov, Vasily; Pettini, Max; Olszewski, Edward W.; McQuinn, Kristen B. W.

2017-03-01

The search for chemically unevolved galaxies remains prevalent in the nearby Universe, mostly because these systems provide excellent proxies for exploring in detail the physics of high-z systems. The most promising candidates are extremely metal-poor galaxies (XMPs), I.e. galaxies with <1/10 solar metallicity. However, due to the bright emission-line-based search criteria traditionally used to find XMPs, we may not be sampling the full XMP population. In 2014, we reoriented this search using only morphological properties and uncovered a population of ˜150 'blue diffuse dwarf (BDD) galaxies', and published a sub-sample of 12 BDD spectra. Here, we present optical spectroscopic observations of a larger sample of 51 BDDs, along with their Sloan Digital Sky Survey (SDSS) photometric properties. With our improved statistics, we use direct-method abundances to confirm that BDDs are chemically unevolved (7.43 < 12 + log(O/H) < 8.01), with ˜20 per cent of our sample classified as being XMP galaxies, and find that they are actively forming stars at rates of ˜1-33 × 10-2 M⊙ yr-1 in H II regions randomly embedded in a blue, low-surface-brightness continuum. Stellar masses are calculated from population synthesis models and estimated to be in the range log (M*/M⊙) ≃ 5-9. Unlike other low-metallicity star-forming galaxies, BDDs are in agreement with the mass-metallicity relation at low masses, suggesting that they are not accreting large amounts of pristine gas relative to their stellar mass. BDD galaxies appear to be a population of actively star-forming dwarf irregular (dIrr) galaxies which fall within the class of low-surface-brightness dIrr galaxies. Their ongoing star formation and irregular morphology make them excellent analogues for galaxies in the early Universe.

30 CFR 57.22212 - Air flow (I-C, II-A, and V-A mines).

Code of Federal Regulations, 2011 CFR

2011-07-01

... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Air flow (I-C, II-A, and V-A mines). 57.22212 Section 57.22212 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND... Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22212 Air flow (I-C, II-A, and V-A mines...

CGM Evolution of a Simulated Dwarf Galaxy

NASA Astrophysics Data System (ADS)

Sheehan-Klenk, Patrick; Christensen, Charlotte

2018-06-01

The circumgalactic medium (CGM), which is fed by galactic outflows, is intrinsically connected to star formation and galactic evolution. We followed the evolution of the CGM of a simulated dwarf galaxy of mass 4.75 × 1010 solar masses., through five timesteps corresponding to z = 3, 2, 1, 0.5, 0.15. The simulation includes metal line cooling, metal diffusion, and supernova feedback, and the resulting galaxy has a realistic stellar mass and metallicity. We measured the surface densities of HI, CIV and OVI in the CGM gas composition and analyzed their trends in relation to the galaxy's evolution. Additionally, we created mock absorption line spectra, which we used to find the mean equivalent width for sight lines spaced 0.1R/Rvir apart. From this analysis, we saw there was high metallicity at large radii, and over time the CGM cooled and became more ordered. We note the impact of a merger with a smaller galaxy at z = 0.5. We compare these results to observations.

The CGM of Massive Galaxies: Where Cold Gas Goes to Die?

NASA Astrophysics Data System (ADS)

Howk, Jay

2017-08-01

We propose to survey the cold HI content and metallicity of the circumgalactic medium (CGM) around 50 (45 new, 5 archival) z 0.5 Luminous Red Galaxies (LRGs) to directly test a fundamental prediction of galaxy assembly models: that cold, metal-poor accretion does not survive to the inner halos of very massive galaxies. Accretion and feedback through the CGM play key roles in our models of the star formation dichotomy in galaxies. Low mass galaxies are thought to accrete gas in cold streams, while high mass galaxies host hot, dense halos that heat incoming gas and prevent its cooling, thereby quenching star formation. HST/COS has provided evidence for cold, metal-poor streams in the halos of star-forming galaxies (consistent with cold accretion). Observations have also demonstrated the presence of cool gas in the halos of passive galaxies, a potential challenge to the cold/hot accretion model. Our proposed observations will target the most massive galaxies and address the origin of the cool CGM gas by measuring the metallicity. This experiment is enabled by our novel approach to deriving metallicities, allowing the use of much fainter QSOs. It cannot be done with archival data, as these rare systems are not often probed along random sight lines. The H I column density (and metallicity) measurements require access to the UV. The large size of our survey is crucial to robustly assess whether the CGM in these galaxies is unique from that of star-forming systems, a comparison that provides the most stringent test of cold-mode accretion/quenching models to date. Conversely, widespread detections of metal-poor gas in these halos will seriously challenge the prevailing theory.

Metal flows of the circumgalactic medium, and the metal budget in galactic haloes

NASA Astrophysics Data System (ADS)

Muratov, Alexander L.; Kereš, Dušan; Faucher-Giguère, Claude-André; Hopkins, Philip F.; Ma, Xiangcheng; Anglés-Alcázar, Daniel; Chan, T. K.; Torrey, Paul; Hafen, Zachary H.; Quataert, Eliot; Murray, Norman

2017-07-01

We present an analysis of the flow of metals through the circumgalactic medium (CGM) in the Feedback in Realistic Environments (FIRE) simulations of galaxy formation, ranging from isolated dwarfs to L* galaxies. We find that nearly all metals produced in high-redshift galaxies are carried out in winds that reach 0.25Rvir. When measured at 0.25Rvir the metallicity of outflows is slightly higher than the interstellar medium (ISM) metallicity. Many metals thus reside in the CGM. Cooling and recycling from this reservoir determine the metal budget in the ISM. The outflowing metal flux decreases by a factor of ˜2-5 between 0.25Rvir and Rvir. Furthermore, outflow metallicity is typically lower at Rvir owing to dilution of the remaining outflow by metal-poor material swept up from the CGM. The inflow metallicity at Rvir is generally low, but outflow and inflow metallicities are similar in the inner halo. At low redshift, massive galaxies no longer generate outflows that reach the CGM, causing a divergence in CGM and ISM metallicity. Dwarf galaxies continue to generate outflows, although they preferentially retain metal ejecta. In all but the least massive galaxy considered, a majority of the metals are within the halo at z = 0. We measure the fraction of metals in CGM, ISM and stars, and quantify the thermal state of CGM metals in each halo. The total amount of metals in the low-redshift CGM of two simulated L* galaxies is consistent with estimates from the Cosmic Origin Spectrograph haloes survey, while for the other two it appears to be lower.

Tests of star formation metrics in the low-metallicity galaxy NGC 5253 using ALMA observations of H30α line emission

NASA Astrophysics Data System (ADS)

Bendo, G. J.; Miura, R. E.; Espada, D.; Nakanishi, K.; Beswick, R. J.; D'Cruze, M. J.; Dickinson, C.; Fuller, G. A.

2017-11-01

We use Atacama Large Millimeter/submillimeter Array (ALMA) observations of H30α (231.90 GHz) emission from the low-metallicity dwarf galaxy NGC 5253 to measure the star formation rate (SFR) within the galaxy and to test the reliability of SFRs derived from other commonly used metrics. The H30α emission, which originates mainly from the central starburst, yields a photoionizing photon production rate of (1.9 ± 0.3) × 1052 s-1 and an SFR of 0.087 ± 0.013 M⊙ yr-1 based on conversions that account for the low metallicity of the galaxy and for stellar rotation. Among the other star formation metrics we examined, the SFR calculated from the total infrared flux was statistically equivalent to the values from the H30α data. The SFR based on a previously published version of the H α flux that was extinction corrected using Paα and Paβ lines was lower than but also statistically similar to the H30α value. The mid-infrared (22 μm) flux density and the composite star formation tracer based on H α and mid-infrared emission give SFRs that were significantly higher because the dust emission appears unusually hot compared to typical spiral galaxies. Conversely, the 70 and 160 μm flux densities yielded SFRs lower than the H30α value, although the SFRs from the 70 μm and H30α data were within 1σ-2σ of each other. While further analysis on a broader range of galaxies is needed, these results are instructive of the best and worst methods to use when measuring SFR in low-metallicity dwarf galaxies like NGC 5253.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kepley, Amanda A.; Reines, Amy E.; Johnson, Kelsey E.

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 exceedsmore » 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.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ross, Teresa L.; Holtzman, Jon; Saha, Abhijit

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 individualmore » 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.« less

Evidence of a Bottom-heavy Initial Mass Function in Massive Early-type Galaxies from Near-infrared Metal Lines

NASA Astrophysics Data System (ADS)

Lagattuta, David J.; Mould, Jeremy R.; Forbes, Duncan A.; Monson, Andrew J.; Pastorello, Nicola; Persson, S. Eric

2017-09-01

We present new evidence for a variable stellar initial mass function (IMF) in massive early-type galaxies, using high-resolution, near-infrared spectroscopy from the Folded-port InfraRed Echellette spectrograph (FIRE) on the Magellan Baade Telescope at Las Campanas Observatory. In this pilot study, we observe several gravity-sensitive metal lines between 1.1 and 1.3 μm in eight highly luminous (L˜ 10{L}* ) nearby galaxies. Thanks to the broad wavelength coverage of FIRE, we are also able to observe the Ca II triplet feature, which helps with our analysis. After measuring the equivalent widths (EWs) of these lines, we notice mild to moderate trends between EW and central velocity dispersion (σ), with some species (K I, Na I, Mn I) showing a positive EW-σ correlation and others (Mg I, Ca II, Fe I) a negative one. To minimize the effects of metallicity, we measure the ratio R = [EW(K I)/EW(Mg I)], finding a significant systematic increase in this ratio with respect to σ. We then probe for variations in the IMF by comparing the measured line ratios to the values expected in several IMF models. Overall, we find that low-mass galaxies (σ ˜ 100 km s-1) favor a Chabrier IMF, while high-mass galaxies (σ ˜ 350 km s-1) are better described with a steeper (dwarf-rich) IMF slope. While we note that our galaxy sample is small and may suffer from selection effects, these initial results are still promising. A larger sample of galaxies will therefore provide an even clearer picture of IMF trends in this regime. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Spectroscopic decomposition of the galaxy and halo of the cD galaxy NGC 3311

NASA Astrophysics Data System (ADS)

Johnston, Evelyn J.; Merrifield, Michael; Aragón-Salamanca, Alfonso

2018-05-01

Information on the star-formation histories of cD galaxies and their extended stellar haloes lie in their spectra. Therefore, to determine whether these structures evolved together or through a two-phase formation, we need to spectroscopically separate the light from each component. We present a pilot study to use BUDDI to fit and extract the spectra of the cD galaxy NGC 3311 and its halo in an Integral Field Spectroscopy datacube, and carry out a simple stellar populations analysis to study their star-formation histories. Using MUSE data, we were able to isolate the light of the galaxy and its halo throughout the datacube, giving spectra representing purely the light from each of these structures. The stellar populations analysis of the two components indicates that, in this case, the bulk of the stars in both the halo and the central galaxy are very old, but the halo is more metal poor and less α-enriched than the galaxy. This result is consistent with the halo forming through the accretion of much smaller satellite galaxies with more extended star formation. It is noteworthy that the apparent gradients in age and metallicity indicators across the galaxy are entirely consistent with the radially-varying contributions of galaxy and halo components, which individually display no gradients. The success of this study is promising for its application to a larger sample of cD galaxies that are currently being observed by IFU surveys.

A GMOS-N IFU study of the central H II region in the blue compact dwarf galaxy NGC 4449: kinematics, nebular metallicity and star formation

NASA Astrophysics Data System (ADS)

Kumari, Nimisha; James, Bethan L.; Irwin, Mike J.

2017-10-01

We use integral field spectroscopic (IFS) observations from the Gemini Multi-Object Spectrograph North (GMOS-N) to study the central H II region in a nearby blue compact dwarf (BCD) galaxy NGC 4449. The IFS data enable us to explore the variation of physical and chemical conditions of the star-forming region and the surrounding gas on spatial scales as small as 5.5 pc. Our kinematical analysis shows possible signatures of shock ionization and shell structures in the surroundings of the star-forming region. The metallicity maps of the region, created using direct Te and indirect strong line methods (R23, O3N2 and N2), do not show any chemical variation. From the integrated spectrum of the central H II region, we find a metallicity of 12 + log(O/H) = 7.88 ± 0.14 ({˜ }0.15^{+0.06}_{-0.04} Z⊙) using the direct method. Comparing the central H II region metallicity derived here with those of H II regions throughout this galaxy from previous studies, we find evidence of increasing metallicity with distance from the central nucleus. Such chemical inhomogeneities can be due to several mechanisms, including gas loss via supernova blowout, galactic winds or metal-poor gas accretion. However, we find that the localized area of decreased metallicity aligns spatially with the peak of star-forming activity in the galaxy, suggesting that gas accretion may be at play here. Spatially resolved IFS data for the entire galaxy are required to confirm the metallicity inhomogeneity found in this study and determine its possible cause.

Color-magnitude Diagrams of the Star-forming Galaxies Ho IX, Cam B, NGC 2976, and UGC 1281

NASA Astrophysics Data System (ADS)

Georgiev, T. B.; Bomans, D. J.

We report results on a study of nearby late type galaxies performed with the 2m RC telescope of the Rozhen NAO with with 1×1 K CCD camera. The scale and the frame size are 0.32''/pix and 5.4'×5.4', respectively. At typical seeing of 1'' the data reach routinely a limiting magnitude of ˜4 mag. With these parameters many nearby galaxies, including the members of the IC 342 and M81 groups can be resolved into star-like and diffuse objects. This allows the determination of several fundamental properties of the galaxies, based on surface photometry and study of the brightest resolved objects. The most crucial parameter is the distance to the galaxy. It can be estimated to a standard error of 20 % using the brightest red and blue stars. Selection of these stars is greatly improved by analysis of the image shapes, which allows to detect diffuse objects, like cluster candidates and background galaxies. Further improvement gives the analysis of color-magnitude (CMD) and color-color diagrams. The CMDs also allow to estimate the age of the most recent star formation event and may hint at the metallicity. The CMDs of the low surface brightness irregular galaxies Ho IX and Cam B are very similar. Especially Cam B seems to be an extreme case of a low-mass star-forming dwarf galaxy. The CMD of NGC 2976 is very similar to this of the star burst galaxy M82 (Georgiev T., 2000, Compt. Rend. Acad. Bulg. Sci. 53/2, 5-8). The edge-on galaxy UGC 1281 is of intermediate star-forming activity, but the CMD is quite sparse.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zahid, H. J.; Sanders, D. B.; Chu, J.

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 ☉})more » 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.« less

How fast can an AGN shut down? XMM-Newton observation of IC 2497

NASA Astrophysics Data System (ADS)

Schawinski, Kevin

2008-10-01

We propose to observe IC 2497 with XMM-Newton to detect, or rule out, an obscured AGN that might account for the illumination of `Hanny's Voorwerp'. The Voorwerp is a highly ionised cloud of gas extended over 15-25 kpc next to the spiral galaxy IC 2497. There is no source of ionisation within the Voorwerp, implicating a luminous 1E44 erg/s AGN in IC 2497 as the source. Swift XRT observations do not yield a detection, allowing the presence of a highly obscured, sufficiently luminous AGN. With 34 ksec of XMM observations, we could detect an obscured AGN down to 1E42 erg/s. We can thus either locate an obscured AGN, or we can for the first time constrain the shutdown time scale for a powerful AGN, as it drops by a factor of 100 in luminosity in 1E5 years.

How Galaxies Acquire their Gas: A Map of Multiphase Accretion and Feedback in Gaseous Galaxy Halos

NASA Astrophysics Data System (ADS)

Tumlinson, Jason

2009-07-01

We propose to address two of the biggest open questions in galaxy formation - how galaxies acquire their gas and how they return it to the IGM - with a concentrated COS survey of diffuse multiphase gas in the halos of SDSS galaxies at z = 0.15 - 0.35. Our chief science goal is to establish a basic set of observational facts about the physical state, metallicity, and kinematics of halo gas, including the sky covering fraction of hot and cold material, the metallicity of infall and outflow, and correlations with galaxy stellar mass, type, and color - all as a function of impact parameter from 10 - 150 kpc. Theory suggests that the bimodality of galaxy colors, the shape of the luminosity function, and the mass-metallicity relation are all influenced at a fundamental level by accretion and feedback, yet these gas processes are poorly understood and cannot be predicted robustly from first principles. We lack even a basic observational assessment of the multiphase gaseous content of galaxy halos on 100 kpc scales, and we do not know how these processes vary with galaxy properties. This ignorance is presently one of the key impediments to understanding galaxy formation in general. We propose to use the high-resolution gratings G130M and G160M on the Cosmic Origins Spectrograph to obtain sensitive column density measurements of a comprehensive suite of multiphase ions in the spectra of 43 z < 1 QSOs lying behind 43 galaxies selected from the Sloan Digital Sky Survey. In aggregate, these sightlines will constitute a statistically sound map of the physical state and metallicity of gaseous halos, and subsets of the data with cuts on galaxy mass, color, and SFR will seek out predicted variations of gas properties with galaxy properties. Our interpretation of these data will be aided by state-of-the-art hydrodynamic simulations of accretion and feedback, in turn providing information to refine and test such models. We will also use Keck, MMT, and Magellan {as needed} to obtain

The edge of galaxy formation - II. Evolution of Milky Way satellite analogues after infall

NASA Astrophysics Data System (ADS)

Frings, Jonas; Macciò, Andrea; Buck, Tobias; Penzo, Camilla; Dutton, Aaron; Blank, Marvin; Obreja, Aura

2017-12-01

In the first paper, we presented 27 hydrodynamical cosmological simulations of galaxies with total masses between 5 × 108 and 1010 M⊙. In this second paper, we use a subset of these cosmological simulations as initial conditions (ICs) for more than 40 hydrodynamical simulations of satellite and host galaxy interaction. Our cosmological ICs seem to suggest that galaxies on these mass scales have very little rotational support and are velocity dispersion (σ) dominated. Accretion and environmental effects increase the scatter in the galaxy scaling relations (e.g. size-velocity dispersion) in very good agreement with observations. Star formation is substantially quenched after accretion. Mass removal due to tidal forces has several effects: it creates a very flat stellar velocity dispersion profile, and it reduces the dark matter content at all scales (even in the centre), which in turn lowers the stellar velocity on scales around 0.5 kpc even when the galaxy does not lose stellar mass. Satellites which start with a cored dark matter profile are more prone to either be destroyed or to end up in a very dark matter poor galaxy. Finally, we found that tidal effects always increase the 'cuspyness' of the dark matter profile, even for haloes that infall with a core.

Galaxy Surface Photometry

NASA Astrophysics Data System (ADS)

Milvang-Jensen, Bo; Jørgensen, Inger

We describe galaxy surface photometry based on fitting ellipses to the isophotes of the galaxies. Example galaxies with different isophotal shapes are used to illustrate the process, including how the deviations from elliptical isophotes are quantified using Fourier expansions. We show how the definitions of the Fourier coefficients employed by different authors are linked. As examples of applications of surface photometry we discuss the determination of the relative disk luminosities and the inclinations for E and S0 galaxies. We also describe the color-magnitude and color-color relations. When using both near-infrared and optical photometry, the age--metallicity degeneracy may be broken. Finally we discuss the Fundamental Plane where surface photometry is combined with spectroscopy. It is shown how the FP can be used as a sensitive tool to study galaxy evolution.

A molecular line survey toward the nearby galaxies NGC 1068, NGC 253, and IC 342 at 3 mm with the Nobeyama 45 m radio telescope: Impact of an AGN on 1 kpc scale molecular abundances

NASA Astrophysics Data System (ADS)

Nakajima, Taku; Takano, Shuro; Kohno, Kotaro; Harada, Nanase; Herbst, Eric

2018-01-01

It is important to investigate the relationships between the power sources and the chemical compositions of galaxies in order to understand the scenario of galaxy evolution. We carried out an unbiased molecular line survey towards active galactic nucleus (AGN) host galaxy NGC1068, and prototypical starburst galaxies, NGC 253 and IC 342, with the Nobeyama 45 m telescope in the 3 mm band. The advantage of this line survey is that the obtained spectra have the highest angular resolution ever obtained with single-dish telescopes. In particular, the beam size of this telescope is ˜15″-19″, which is able to separate spatially the nuclear molecular emission from that of the starburst ring (d ˜ 30″) in NGC 1068. We successfully detected approximately 23 molecular species in each galaxy, and calculated rotation temperatures and column densities. We estimate the molecular fractional abundances with respect to 13CO and CS molecules and compare them among three galaxies in order to investigate the chemical signatures of an AGN environment. As a result, we found clear trends in the abundances of molecules surrounding the AGN on a 1-kpc scale. HCN, H13CN, CN, 13CN, and HC3N are more abundant, and CH3CCH is deficient in NGC 1068 compared with the starburst galaxies. High abundances of HCN, H13CN, and HC3N suggest that the circumnuclear disk in NGC 1068 is in a high-temperature environment. The reason for the non-detection of CH3CCH is likely to be dissociation by high-energy radiation or less sublimation of a precursor of CH3CCH from grains.

Surface Brightness Profiles and Energetics of Intracluster Gas in Cool Galaxy Clusters and ROSAT Observations of Bright, Early-Type Galaxies

NASA Technical Reports Server (NTRS)

White, Raymond E., III

1994-01-01

Preliminary results on the elliptical galaxy NGC 1407 were published in the proceedings of the first ROSAT symposium. NGC 1407 is embedded in diffuse X-ray-emitting gas which is extensive enough that it is likely to be related to the surrounding group of galaxies, rather than just NGC 1407. Spectral data for NGC 1407 (AO2) and IC 1459 (AO3) are also included in a complete sample of elliptical galaxies I compiled in collaboration with David Davis. This allowed us to construct the first complete X-ray sample of optically-selected elliptical galaxies. The complete sample allows us to apply Malmquist bias corrections to the observed correlation between X-ray and optical luminosities. I continue to work on the implications of this first complete X-ray sample of elliptical galaxies. Paul Eskridge Dave Davis and I also analyzed three long ROSAT PSPC observations of the small (but not dwarf) elliptical galaxy M32. We found the X-ray spectra and variability to be consistent with either a Low Mass X-Ray Binary (LMXRB) or a putative 'micro"-AGN.

Type II supernovae in low luminosity host galaxies

NASA Astrophysics Data System (ADS)

Gutiérrez, C. P.; Anderson, J. P.; Sullivan, M.; Dessart, L.; González-Gaitan, S.; Galbany, L.; Dimitriadis, G.; Arcavi, I.; Bufano, F.; Chen, T.-W.; Dennefeld, M.; Gromadzki, M.; Haislip, J. B.; Hosseinzadeh, G.; Howell, D. A.; Inserra, C.; Kankare, E.; Leloudas, G.; Maguire, K.; McCully, C.; Morrell, N.; E, F. Olivares; Pignata, G.; Reichart, D. E.; Reynolds, T.; Smartt, S. J.; Sollerman, J.; Taddia, F.; Takáts, K.; Terreran, G.; Valenti, S.; Young, D. R.

2018-06-01

We present an analysis of a new sample of type II core-collapse supernovae (SNe II) occurring within low-luminosity galaxies, comparing these with a sample of events in brighter hosts. Our analysis is performed comparing SN II spectral and photometric parameters and estimating the influence of metallicity (inferred from host luminosity differences) on SN II transient properties. We measure the SN absolute magnitude at maximum, the light-curve plateau duration, the optically thick duration, and the plateau decline rate in the V -band, together with expansion velocities and pseudo-equivalent-widths (pEWs) of several absorption lines in the SN spectra. For the SN host galaxies, we estimate the absolute magnitude and the stellar mass, a proxy for the metallicity of the host galaxy. SNe II exploding in low luminosity galaxies display weaker pEWs of Fe II λ5018, confirming the theoretical prediction that metal lines in SN II spectra should correlate with metallicity. We also find that SNe II in low-luminosity hosts have generally slower declining light curves and display weaker absorption lines. We find no relationship between the plateau duration or the expansion velocities with SN environment, suggesting that the hydrogen envelope mass and the explosion energy are not correlated with the metallicity of the host galaxy. This result supports recent predictions that mass-loss for red supergiants is independent of metallicity.

Dust in High-Redshift Galaxies

NASA Astrophysics Data System (ADS)

Pettini, Max; King, David L.; Smith, Linda J.; Hunstead, Richard W.

1997-03-01

Measurements of Zn and Cr abundances in 18 damped Lyα systems (DLAs) at absorption redshifts zabs = 0.692-3.390 (but mostly between zabs ~= 2 and 3) show that metals and dust are much less abundant in high-redshift galaxies than in the Milky Way today. Typically, [Zn/H] ~= -1.2 as Zn tracks Fe closely in Galactic stars of all metallicities and is only lightly depleted onto interstellar grains, we conclude that the overall degree of metal enrichment of damped Lyα galaxies ~13.5 Gyr ago (H0 = 50 km s-1 Mpc-1, q0 = 0.05) was ~1/15 solar. Values of [Cr/Zn] span the range from ~=0 to <~ - 0.65 which we interpret as evidence for selective depletion of Cr onto dust in some DLAs. On average Cr and other refractory elements are depleted by only a factor of ~2, significantly less than in local interstellar clouds. We propose that this reflects an overall lower abundance of dust--which may be related to the lower metallicities, likely higher temperature of the ISM and higher supernova rates in these young galaxies--rather than an ``exotic'' composition of dust grains. Combining a metallicity ZDLA ~= 1/15 Z⊙ with a dust-to-metals ratio ~1/2 of that in local interstellar clouds, we deduce that the ``typical'' dust-to-gas ratio in damped Lyα galaxies is ~1/30 of the Milky Way value. This amount of dust will introduce an extinction at 1500 Å of only A1500 ~ 0.1 in the spectra of background QSOs. Similarly, we expect little reddening of the broad spectral energy distribution of the high-z field galaxies now being found routinely by deep imaging surveys. Even such trace amounts of dust, however, can explain the weakness of Lyα emission from star-forming regions. We stress the approximate nature of such general statements; in reality, the range of metallicities and dust depletions encountered indicates that some sight lines through high-redshift galaxies may be essentially dust-free, while others could suffer detectable extinction. Finally, we show that, despite claims to the

A blind HI search for galaxies in the northern Zone of Avoidance

NASA Astrophysics Data System (ADS)

Rivers, Andrew James

Searches for galaxies in the nearby and distant universe have long focused in the direction of the Galactic poles, or perpendicular to the plane of the Milky Way. Dust concentrated in the Milky Way's disk absorbs and scatters light and therefore precludes easy optical detection of extragalactic sources in this ``Zone of Avoidance'' (ZOA). The Dwingeloo Obscured Galaxies Survey (DOGS) was a 21-cm blind survey for galaxies hidden in the northern ZOA. Dust is transparent at radio wavelengths and therefore the survey is not biased against detection of galaxies near the Galactic plane. The DOGS project was designed to reveal hidden dynamically important nearby galaxies and to help ``fill in the blanks'' in the local large scale structure. During the survey and subsequent followup observations, 43 galaxies were detected; 28 of these were previously unknown. Obscuration by dust could effectively hide a massive member of the Local Group. This survey rules out the existence of a hidden gas-rich dynamically important source. The possibility of gas-poor elliptical galaxies and low-mass dwarfs remains; the low velocity of one detected dwarf irregular galaxy relative to the Milky Way indicates possible membership in the Local Group. Other nearby galaxies detected by DOGS were linked to the IC 342/Maffei group and to the nearby galaxy NGC 6946. Of the five galaxies in the IC 342/Maffei group, three were unknown at the time of the survey. Derived group properties indicate the group consists of two separate physical groups which appear close together in the sky. The five sources near NGC 6946 support the identification of a new nearby group associated with this large spiral galaxy. The distribution of massive spiral galaxies compared to low-mass dwarf galaxies may be used to test theories of structure formation. In a universe dominated by Cold Dark Matter (CDM) dwarf galaxies are more evenly distributed and are a more accurate tracer of the mass distribution. Open universe models

A remarkable oxygen-rich asymptotic giant branch variable in the Sagittarius Dwarf Irregular Galaxy

NASA Astrophysics Data System (ADS)

Whitelock, Patricia A.; Menzies, John W.; Feast, Michael W.; Marigo, Paola

2018-01-01

We report and discuss JHKS photometry for Sgr dIG, a very metal-deficient galaxy in the Local Group, obtained over 3.5 years with the Infrared Survey Facility in South Africa. Three large amplitude asymptotic giant branch variables are identified. One is an oxygen-rich star that has a pulsation period of 950 d, which was until recently undergoing hot bottom burning, with Mbol ∼ -6.7. It is surprising to find a variable of this sort in Sgr dIG, given their rarity in other dwarf irregulars. Despite its long period the star is relatively blue and is fainter, at all wavelengths shorter than 4.5 μm, than anticipated from period-luminosity relations that describe hot bottom burning stars. A comparison with models suggests it had a main-sequence mass Mi ∼ 5 M⊙ and that it is now near the end of its asymptotic giant branch evolution. The other two periodic variables are carbon stars with periods of 670 and 503 d (Mbol ∼ -5.7 and -5.3). They are very similar to other such stars found on the asymptotic giant branch of metal-deficient Local Group galaxies and a comparison with models suggests Mi ∼ 3 M⊙. We compare the number of asymptotic giant branch variables in Sgr dIG to those in NGC 6822 and IC 1613, and suggest that the differences may be due to the high specific star formation rate and low metallicity of Sgr dIG.

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

The Host Galaxies of Type Ia Supernovae Discovered by the Palomar Transient Factory

NASA Technical Reports Server (NTRS)

Pan, Y.-C.; Sullivan, M.; McGuire, K.; Hook, I. M.; Nugent, P. E.; Howell, D. A.; Arcavi, I.; Botyanszki, J.; Cenko, Stephen Bradley; DeRose, J.

2013-01-01

We present spectroscopic observations of the host galaxies of 82 low-redshift type Ia supernovae (SNe Ia) discovered by the Palomar Transient Factory (PTF). We determine star-formation rates, gas-phase stellar metallicities, and stellar masses and ages of these objects. As expected, strong correlations between the SN Ia light-curve width (stretch) and the host age mass metallicity are found: fainter, faster-declining events tend to be hosted by older massive metal-rich galaxies. There is some evidence that redder SNe Ia explode in higher metallicity galaxies, but we found no relation between the SN colour and host galaxy extinction based on the Balmer decrement, suggesting that the colour variation of these SNe does not primarily arise from this source. SNe Ia in higher-mass metallicity galaxies also appear brighter after stretch colour corrections than their counterparts in lower mass hosts, and the stronger correlation is with gas-phase metallicity suggesting this may be the more important variable. We also compared the host stellar mass distribution to that in galaxy targeted SN surveys and the high-redshift untargeted Supernova Legacy Survey (SNLS). SNLS has many more low mass galaxies, while the targeted searches have fewer. This can be explained by an evolution in the galaxy stellar mass function, coupled with a SN delay-time distribution proportional to t1. Finally, we found no significant difference in the mass--metallicity relation of our SN Ia hosts compared to field galaxies, suggesting any metallicity effect on the SN Ia rate is small.

Investigating early-type galaxy evolution with a multiwavelength approach. II. The UV structure of 11 galaxies with Swift-UVOT

NASA Astrophysics Data System (ADS)

Rampazzo, R.; Mazzei, P.; Marino, A.; Uslenghi, M.; Trinchieri, G.; Wolter, A.

2017-06-01

Context. GALEX detected a significant fraction of early-type galaxies, in particular S0s, showing far-UV bright structures, sometimes involving an entire galaxy out to its outskirts. These features suggest the presence of either recent ongoing and/or prolonged star formation episodes, shedding new light on the evolution of these systems. Aims: We aim at understanding the evolutionary path[s] of these early-type galaxies and the mechanisms at the origin of their UV-bright structures. We investigate with a multiwavelength approach the link between the inner and outer galaxy regions of a set of 11 early-type galaxies that were selected because of their nearly passive stage of evolution in the nuclear region. Methods: This paper, second of a series, focuses on the information coming from the comparison between UV features detected by Swift-UVOT, which trace recent star formation, and the galaxy optical structure, which maps older stellar populations. We performed a surface photometric study of these early-type galaxies, observed with the Swift-UVOT UV filters W2 2030 Å λ0, M2 2231 Å λ0, W1 2634 Å λ0 and the UBV bands. BVRI photometry from other sources in the literature was also used. Our integrated magnitude measurements were analyzed and compared with corresponding values in the literature. We characterize the overall galaxy structure that best fits the UV and optical luminosity profiles using a single Sérsic law. Results: The galaxies NGC 1366, NGC 1426, NGC 3818, NGC 3962, and NGC 7192 show featureless luminosity profiles. Excluding NGC 1366, which has a clear edge-on disk (n ≈ 1-2), and NGC 3818, the remaining three galaxies have Sérsic's indices n ≈ 3-4 in the optical and a lower index in the UV. Bright ring- or arm-like structures are revealed by UV images and luminosity profiles of NGC 1415, NGC 1533, NGC 1543, NGC 2685, NGC 2974, and IC 2006. The ring- or arm-like structures differ from galaxy to galaxy. Sérsic indices of UV profiles for these

Spectroscopic classification of AT 2018adg as a Type Ic supernova

NASA Astrophysics Data System (ADS)

Williams, S. C.; Nordin, J.; Hook, I. M.

2018-03-01

We obtained a spectrum of the transient AT 2018adg (see TNS) with the SPRAT spectrograph (resolution R 350; Piascik et al. 2014) on the 2-m Liverpool Telescope (LT; Steele et al. 2004) on 2018 Mar 11.13 UT. The spectrum is consistent with AT 2018adg being a Type Ic supernova around peak brightness, at a redshift of z 0.02 to 0.03, in agreement with the host galaxy redshift of z = 0.022 (da Costa et al. 1998).

Formation of massive clouds and dwarf galaxies during tidal encounters

NASA Technical Reports Server (NTRS)

Kaufman, Michele; Elmegreen, Bruce G.; Thomasson, Magnus; Elmegreen, Debra M.

1993-01-01

Gerola et al. (1983) propose that isolated dwarf galaxies can form during galaxy interactions. As evidence of this process, Mirabel et al. (1991) find 10(exp 9) solar mass clouds and star formation complexes at the outer ends of the tidal arms in the Antennae and Superantennae galaxies. We describe observations of HI clouds with mass greater than 10(exp 8) solar mass in the interacting galaxy pair IC 2163/NGC 2207. This pair is important because we believe it represents an early stage in the formation of giant clouds during an encounter. We use a gravitational instability model to explain why the observed clouds are so massive and discuss a two-dimensional N-body simulation of an encounter that produces giant clouds.

How Do Inflows and Outflows from Galaxies Create Their Inner Circumgalactic Medium?

NASA Astrophysics Data System (ADS)

Bowen, David

2017-08-01

We propose using COS to observe 7 QSO sightlines within half a virial radius each of two galaxies in order to probe their circumgalactic mediums (CGMs) along multiple sightlines. Results from higher redshift QSO absorption line surveys suggest that this is the region where most metal line absorbing gas clouds reside, but their origin remains controversial. The two spiral galaxies studied in this proposal are NGC 4565 (the Needle Galaxy) which is highly inclined (i=86 degrees), and NGC 3184, which has a very low inclination (i=9 degrees). Their orientation makes them ideal targets for looking for kinematic and metallicity signatures from outflows along the minor axis, or inflows into the disk along the major axis. For both galaxies, we will measure how HI and metal line column densities change globally with radius, and how the ionzation structure of the absorbers varies with position. We predict that the HI column densities we detect will be similar to the Lyman Limit, or partial-Lyman Limit systems, and that we will be able to measure the gas metallicity in these clouds. These measurements can be used to infer whether the absorbing gas is flowing into the galaxy from the IGM (where the metallicity is lower than in the galaxy) or out of the galaxy (which should be metal enriched). Given that LLS and pLLS have been shown to have a bimodal distribution in their metallicity, we will see which of the two regimes the gas in our galaxies belong to, and even whether the bimodality can be seen in a single galaxy towards different sightlines.

Mapping Nearby Galaxies at APO: The MaNGA IFU Galaxy Survey

NASA Astrophysics Data System (ADS)

Law, David R.; MaNGA Team

2014-01-01

MaNGA is a new survey that will begin in August 2014 as part of SDSS-IV with the aim of obtaining integral-field spectroscopy for an unprecedented sample of 10,000 nearby galaxies. MaNGA's key goals are to understand the "life cycle" of present day galaxies from imprinted clues of their birth and assembly, through their ongoing growth via star formation and merging, to their death from quenching at late times. To achieve these goals, MaNGA will channel the impressive capabilities of the SDSS-III BOSS spectrographs in a fundamentally new direction by marshaling the unique power of 2D spectroscopy. MaNGA will deploy 17 pluggable Integral Field Units (IFUs) made by grouping fibers into hexagonal bundles ranging from 19 to 127 fibers each. The spectra obtained by MaNGA will cover the wavelength range 3600-10,000 Angstroms (with a velocity resolution of ~ 60 km/s) and will characterize the internal composition and the dynamical state of a sample of 10,000 galaxies with stellar masses greater than 10^9 Msun and an average redshift of z ~ 0.03. Such IFU observations enable a leap forward because they provide an added dimension to the information available for each galaxy. MaNGA will provide two-dimensional maps of stellar velocity and velocity dispersion, mean stellar age and star formation history, stellar metallicity, element abundance ratio, stellar mass surface density, ionized gas velocity, ionized gas metallicity, star formation rate, and dust extinction for a statistically powerful sample. This legacy dataset will address urgent questions in our understanding of galaxy formation, including 1) The formation history of galaxy subcomponents, including the disk, bulge, and dark matter halo, 2) The nature of present-day galaxy growth via merging and gas accretion, and 3) The processes responsible for terminating star formation in galaxies. Finally, MaNGA will also play a vital role in the coming era of advanced IFU instrumentation, serving as the low-z anchor for

What Happened to Leo P's Metals?

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-12-01

Measurements of metal abundances in galaxies present a conundrum: compared to expectations, there are not nearly enough metals observed within galaxies. New observations of a nearby dwarf galaxy may help us understand where this enriched material went.Removal ProcessesStar formation is responsible for the build-up of metals (elements heavier than helium) in a galaxy. But when we use a galaxys star-formation history to estimate the amount of enriched material it should contain, our predictions are inconsistent with measured abundances: large galaxies contain only about 2025% of the expected metals, and small dwarf galaxies contain as little as 1%!So what happens to galaxies metals after they have been formed? The favored explanation is that metals are removed from galaxies via stellar feedback: stars that explode in violent supernovae can drive high-speed winds, expelling the enriched material from a galaxy. This process should be more efficient in low-mass galaxies due to their smaller gravitational wells, which would explain why low-mass galaxies have especially low metallicities.But external processes may also contribute to the removal of metals, such as tidal stripping during interactions between galaxies. To determine the role of stellar feedback alone, an ideal test would be to observe an isolated low-mass, star-forming galaxy i.e., one that is not affected by external processes.Luckily, such an isolated, low-mass galaxy has recently been discovered just outside of the Local Group: Leo P, a gas-rich dwarf galaxy with a total stellar mass of 5.6 x 105 solar masses.Isolated ResultsPercentage of oxygen lost in Leo P compared to the percentage of metals lost in three other, similar-size dwarfs that are not isolated. If the gas-phase oxygen in Leo P were removed, Leo Ps measurements would be consistent with those of the other dwarfs. [McQuinn et al. 2015]Led by Kristen McQuinn (University of Minnesota, University of Texas at Austin), a team of researchers has used

Extended Schmidt law holds for faint dwarf irregular galaxies

NASA Astrophysics Data System (ADS)

Roychowdhury, Sambit; Chengalur, Jayaram N.; Shi, Yong

2017-12-01

Context. The extended Schmidt law (ESL) is a variant of the Schmidt which relates the surface densities of gas and star formation, with the surface density of stellar mass added as an extra parameter. Although ESL has been shown to be valid for a wide range of galaxy properties, its validity in low-metallicity galaxies has not been comprehensively tested. This is important because metallicity affects the crucial atomic-to-molecular transition step in the process of conversion of gas to stars. Aims: We empirically investigate for the first time whether low metallicity faint dwarf irregular galaxies (dIrrs) from the local universe follow the ESL. Here we consider the "global" law where surface densities are averaged over the galactic discs. dIrrs are unique not only because they are at the lowest end of mass and star formation scales for galaxies, but also because they are metal-poor compared to the general population of galaxies. Methods: Our sample is drawn from the Faint Irregular Galaxy GMRT Survey (FIGGS) which is the largest survey of atomic hydrogen in such galaxies. The gas surface densities are determined using their atomic hydrogen content. The star formation rates are calculated using GALEX far ultraviolet fluxes after correcting for dust extinction, whereas the stellar surface densities are calculated using Spitzer 3.6 μm fluxes. The surface densities are calculated over the stellar discs defined by the 3.6 μm images. Results: We find dIrrs indeed follow the ESL. The mean deviation of the FIGGS galaxies from the relation is 0.01 dex, with a scatter around the relation of less than half that seen in the original relation. In comparison, we also show that the FIGGS galaxies are much more deviant when compared to the "canonical" Kennicutt-Schmidt relation. Conclusions: Our results help strengthen the universality of the ESL, especially for galaxies with low metallicities. We suggest that models of star formation in which feedback from previous generations

Galaxy evolution. Isolated compact elliptical galaxies: stellar systems that ran away.

PubMed

Chilingarian, Igor; Zolotukhin, Ivan

2015-04-24

Compact elliptical galaxies form a rare class of stellar system (~30 presently known) characterized by high stellar densities and small sizes and often harboring metal-rich stars. They were thought to form through tidal stripping of massive progenitors, until two isolated objects were discovered where massive galaxies performing the stripping could not be identified. By mining astronomical survey data, we have now found 195 compact elliptical galaxies in all types of environment. They all share similar dynamical and stellar population properties. Dynamical analysis for nonisolated galaxies demonstrates the feasibility of their ejection from host clusters and groups by three-body encounters, which is in agreement with numerical simulations. Hence, isolated compact elliptical and isolated quiescent dwarf galaxies are tidally stripped systems that ran away from their hosts. Copyright © 2015, American Association for the Advancement of Science.

Role of Massive Stars in the Evolution of Primitive Galaxies

NASA Technical Reports Server (NTRS)

Heap, Sara

2012-01-01

An important factor controlling galaxy evolution is feedback from massive stars. It is believed that the nature and intensity of stellar feedback changes as a function of galaxy mass and metallicity. At low mass and metallicity, feedback from massive stars is mainly in the form of photoionizing radiation. At higher mass and metallicity, it is in stellar winds. IZw 18 is a local blue, compact dwarf galaxy that meets the requirements for a primitive galaxy: low halo mass greater than 10(exp 9)Msun, strong photoionizing radiation, no galactic outflow, and very low metallicity,log(O/H)+12=7.2. We will describe the properties of massive stars and their role in the evolution of IZw 18, based on analysis of ultraviolet images and spectra obtained with HST.

The gas-phase metallicities of star-forming galaxies in aperture-matched SDSS samples follow potential rather than mass or average surface density

NASA Astrophysics Data System (ADS)

D'Eugenio, Francesco; Colless, Matthew; Groves, Brent; Bian, Fuyan; Barone, Tania M.

2018-05-01

We present a comparative study of the relation between the aperture-based gas-phase metallicity and three structural parameters of star-forming galaxies: mass (M ≡ M*), average potential (Φ ≡ M*/Re) and average surface mass density (Σ ≡ M_*/R_e^2; where Re is the effective radius). We use a volume-limited sample drawn from the publicly available SDSS DR7, and base our analysis on aperture-matched sampling by selecting sets of galaxies where the SDSS fibre probes a fixed fraction of Re. We find that between 0.5 and 1.5 Re, the gas-phase metallicity correlates more tightly with Φ than with either {M} or Σ, in that for all aperture-matched samples, the potential-metallicity relation has (i) less scatter, (ii) higher Spearman rank correlation coefficient and (iii) less residual trend with Re than either the mass-metallicity relation and the average surface density-metallicity relation. Our result is broadly consistent with the current models of gas enrichment and metal loss. However, a more natural explanation for our findings is a local relation between the gas-phase metallicity and escape velocity.

GRAVITATIONAL WAVE BACKGROUND FROM BINARY MERGERS AND METALLICITY EVOLUTION OF GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakazato, Ken’ichiro; Sago, Norichika; Niino, Yuu, E-mail: nakazato@artsci.kyushu-u.ac.jp

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 metallicitymore » 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.« less

Separate Ways: The Mass-Metallicity Relation Does Not Strongly Correlate with Star Formation Rate in SDSS-IV MaNGA Galaxies

NASA Astrophysics Data System (ADS)

Barrera-Ballesteros, J. K.; Sánchez, S. F.; Heckman, T.; Blanc, G. A.; The MaNGA Team

2017-07-01

We present the integrated stellar mass-metallicity relation (MZR) for more than 1700 galaxies included in the integral field area SDSS-IV MaNGA survey. The spatially resolved data allow us to determine the metallicity at the same physical scale (effective radius, R eff) using a heterogeneous set of 10 abundance calibrators. In addition to scale factors, the shape of the MZR is similar for all calibrators, consistent with those reported previously using single-fiber and integral field spectroscopy. We compare the residuals of this relation against the star formation rate (SFR) and specific SFR (sSFR). We do not find a strong secondary relation of the MZR with either SFR or sSFR for any of the calibrators, in contrast with previous single-fiber spectroscopic studies. Our results agree with a scenario in which metal enrichment happens at local scales, with global outflows playing a secondary role in shaping the chemistry of galaxies and cold-gas inflows regulating the stellar formation.

Which Galaxies Are the Most Habitable?

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-09-01

Habitable zones are a hot topic in exoplanet studies: where, around a given star, could a planet exist that supports life? But if you scale this up, you get a much less common question: which type of galaxy is most likely to host complex life in the universe? A team of researchers from the UK believes it has the answer.Criteria for HabitabilityLed by Pratika Dayal of the University of Durham, the authors of this study set out to estimate the habitability of a large population of galaxies. The first step in this process is to determine what elements contribute to a galaxys habitability. The authors note three primary factors:Total number of starsMore stars means more planets!Metallicity of the starsPlanets are more likely to form in stellar vicinities with higher metallicities, since planet formation requires elements heavier than iron.Likelihood of Type II supernovae nearbyPlanets that are located out of range of supernovae have a higher probability of being habitable, since a major dose of cosmic radiation is likely to cause mass extinctions or delay evolution of complex life. Galaxies supernova rates can be estimated from their star formation rates (the two are connected via the initial mass function).Hospitable Cosmic GiantsLower panel: the number of Earth-like habitable planets (given by the color bar, which shows the log ratio relative to the Milky Way) increases in galaxies with larger stellar mass and lower star formation rates. Upper panel: the larger stellar-mass galaxies tend to be elliptical (blue line) rather than spiral (red line). Click for larger view. [Dayal et al. 2015]Interestingly, these three conditions have previously been shown to be linked via something termed the fundamental metallicity relation, which relates the total stellar masses, metallicities, and star formation rates of galaxies. By using this relation, the authors were able to create predictions for the number of habitable planets in more than 100,000 galaxies in the local universe

X-Ray Binaries in Local Analogs to the First Galaxies

NASA Astrophysics Data System (ADS)

Brorby, Matthew G.

2017-02-01

The focus of this dissertation is to investigate the effect of metallicity on high-mass X-ray binary (HMXB) formation and evolution as a means to understand the evolution of the early Universe (z > 6). Understanding the population and X-ray output of HMXBs are vital to modelling the heating and ionization morphology of the intergalactic medium during the epoch of reionization. Current X-ray instruments are unable to directly detect very high redshift HMXBs, making it impossible to constrain population sizes in this way. Instead certain local galaxies may be used as analogs to infer the properties of galaxies in the early Universe. These local analogs should have properties consistent with those expected for the first galaxies, such as low-metallicity, compact morphology, and intense recent star formation. I present an X-ray population study of 25 blue compact dwarf galaxies (BCD), using multiwavelength data and Bayesian analysis techniques. We find a significant enhancement of the HMXB population in low-metallicity environments and suggest the same may be true in the early Universe. I continue the investigation of HMXB populations in a sample of 10 moderate metallicity (Z ≥ 0.3, Z solar masses), local star-forming galaxies known as Lyman Break Analogs (LBAs). I find evidence of a LX-SFR-metallicity plane in the combined sample of BCDs, LBAs, and regular star-forming galaxies. Then I study a third type of local analog to early Universe galaxies, the Green Pea galaxies. These are a subclass of luminous compact galaxies (LCGs) which show strong [OIII]lambda5007A emission indicative of extreme, recent star-formation. This pilot study was carried out to look, for the first time in X-rays, at this recently established class of galaxies and use them to test the LX-SFR-metallicity plane. Determining the spectral properties of bright HMXBs in low-metallicity environments also has important implications for models of X-ray heating leading up to the Epoch of Reionization. I

CEMP Stars in Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Thidemann Hansen, Terese

2018-06-01

Exploration of the metal-poor stellar halo population of the Milky Way over the past decades has revealed a large number of stars strongly enhanced in carbon (CEMP stars). However, these stars are not as commonly detected in the dwarf galaxy satellites of the Milky Way (MW). The present-day satellites are thought to be similar to systems from which the MW and in particular its halo was formed via hierarchical mergers. I will present the results of abundance analysis for new samples of extremely metal-poor stars in Sculptor and Carina exploring the fraction of CEMP stars at low metallicity in these systems. I will also present the detailed abundance analyses of six CEMP stars detected in the Carina dwarf spheroidal galaxy. Five of these stars also show enhancement in slow neutron-capture elements and can thus be classified as CEMP-s stars, while the most metal-poor star with [Fe/H]=-2.5 shows no such enhancement and belongs to the CEMP-no class. The detection of CEMP stars in dwarf galaxies supports the hierarchical assembly of the MW halo and by providing a birth environment, can help to further constrain the formation of these stars.

The evolution of early-type galaxies in nearby clusters: breaking the age-metallicity degeneracy with Spitzer IRS Blue Peak-Up Imaging

NASA Astrophysics Data System (ADS)

Bressan, Alessandro; Buson, Lucio; Clemens, Marcel; Danese, Luigi; Granato, Gian Luigi; Panuzzo, Pasquale; Rampazzo, Roberto; Silva, Laura; Valdes, Jose Ramon

2005-06-01

We have shown with Cycle 1 observations that Spitzer has the capability of disentangling age and metallicity in old stellar populations. By looking to the broad emission feature left by dust enshrouded asymptotic giant branch stars above 9.7 microns, Spitzer IRS can provide direct evidence that the colour- magnitude relation of Virgo ellipticals is mainly driven by metallicity. However, with the IRS spectrograph we can only probe the bright tail of the colour-magnitude relation, and only in the nearest cluster. We propose to use IRS Blue Peak-Up, the only Spitzer band that looks directly in the core of that spectral feature, to reach fainter galaxies. We will perform a thorough investigation of early type galaxies along the colour-magnitude relation in Virgo and in Coma clusters. These observations, when coupled with already existing IRAC and Optical-NIR observations, will allow a) an unbiased census of the stellar populations in cluster early type galaxies; b) an estimate of the AGB material recycled into the ISM in these systems; c) a direct check of the universality of the colour- magnitude relation on a wide range of magnitudes; d) a spatial study of the stellar populations within the galaxies, e.g. investigating differences between bulge and disk populations within S0; e) the most secure reference frame with which to compare the evolution of early type galaxies in other environments (groups and field).

New CO and H alpha observations of Magellanic-type irregular galaxies

NASA Astrophysics Data System (ADS)

Dettmar, Ralf-Jurgen; Becker, Renate; Shaw, Martin

In order to study the star-forming regions in Magellanic-type irregular galaxies and their relation to molecular cloud complexes, we obtained hydrogen alpha images of several southern objects. In addition, we detected and mapped some of these objects in the J = 1-0 CO line. The weak CO emission of most irregulars made it necessary to integrate for 2-8 hours per position. We describe some preliminary results for IC 4662, DDO 70 (Sex B), and IC 5052.

Star-Formation Histories of MUSCEL Galaxies

NASA Astrophysics Data System (ADS)

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

2018-01-01

The MUSCEL program (MUltiwavelength observations of the Structure, Chemistry and Evolution of LSB galaxies) uses combined ground-based/space-based data to determine the spatially resolved star-formation histories of low surface brightness (LSB) galaxies. LSB galaxies are paradoxical in that they are gas rich but have low star-formation rates. Here we present our observations and fitting technique, and the derived histories for select MUSCEL galaxies. It is our aim to use these histories in tandem with velocity fields and metallicity profiles to determine the physical mechanism(s) that give these faint galaxies low star-formation rates despite ample gas supplies.

Similar star formation rate and metallicity variability time-scales drive the fundamental metallicity relation

NASA Astrophysics Data System (ADS)

Torrey, Paul; Vogelsberger, Mark; Hernquist, Lars; McKinnon, Ryan; Marinacci, Federico; Simcoe, Robert A.; Springel, Volker; Pillepich, Annalisa; Naiman, Jill; Pakmor, Rüdiger; Weinberger, Rainer; Nelson, Dylan; Genel, Shy

2018-06-01

The fundamental metallicity relation (FMR) is a postulated correlation between galaxy stellar mass, star formation rate (SFR), and gas-phase metallicity. At its core, this relation posits that offsets from the mass-metallicity relation (MZR) at a fixed stellar mass are correlated with galactic SFR. In this Letter, we use hydrodynamical simulations to quantify the time-scales over which populations of galaxies oscillate about the average SFR and metallicity values at fixed stellar mass. We find that Illustris and IllustrisTNG predict that galaxy offsets from the star formation main sequence and MZR oscillate over similar time-scales, are often anticorrelated in their evolution, evolve with the halo dynamical time, and produce a pronounced FMR. Our models indicate that galaxies oscillate about equilibrium SFR and metallicity values - set by the galaxy's stellar mass - and that SFR and metallicity offsets evolve in an anticorrelated fashion. This anticorrelated variability of the metallicity and SFR offsets drives the existence of the FMR in our models. In contrast to Illustris and IllustrisTNG, we speculate that the SFR and metallicity evolution tracks may become decoupled in galaxy formation models dominated by feedback-driven globally bursty SFR histories, which could weaken the FMR residual correlation strength. This opens the possibility of discriminating between bursty and non-bursty feedback models based on the strength and persistence of the FMR - especially at high redshift.

Circumgalactic Matter Matters in Galaxy Evolution

NASA Astrophysics Data System (ADS)

Werk, Jessica

2018-01-01

The circumgalactic medium (CGM; non-ISM gas within a galaxy virial radius) regulates the gas flows that shape the assembly and evolution of galaxies. Owing to the vastly improved capabilities in space-based UV spectroscopy with the installation of HST/COS, observations and simulations of the CGM have emerged as the new frontier of galaxy evolution studies. In the last decade, we have learned that the CGM of Milky Way mass galaxies likely contains enough material to harbor most of the metals lost in galaxy winds and to sustain star-formation for billions of years. Remarkably, this implies that most of the heavy elements on earth cycled back and forth multiple times through the Milky Way’s own CGM before the formation of the solar system. In this talk, I will describe constraints we have placed on the origin and fate of this material by studying the gas kinematics, metallicity and ionization state. I will conclude by posing several unanswered questions about the CGM that will be addressed with future survey data and hydrodynamic simulations in a cosmological context.

Feedback Driven Chemical Evolution in Simulations of Low Mass Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Emerick, Andrew; Bryan, Greg; Mac Low, Mordecai-Mark

2018-06-01

Galaxy chemical properties place some of the best constraints on models of galaxy evolution. Both gas and stellar metal abundances in galaxies depend upon the integrated star formation history of the galaxy, gas accretion, outflows, and the effectiveness of metal mixing within the interstellar medium (ISM). Capturing the physics that governs these processes in detail, however, is challenging, in part due to the difficulty in self-consistently modelling stellar feedback physics that impacts each of these processes. Using high resolution hydrodynamics simulations of isolated dwarf galaxies where we follow stars as individual star particles, we examine the role of feedback in driving dwarf galaxy chemical evolution. This star-by-star method allows us to directly follow feedback from stellar winds from massive and AGB stars, stellar ionizing radiation and photoelectric heating, and supernovae. Additionally, we track 15 individual metal species yields from these stars as they pollute the ISM and enrich new stellar populations. I will present initial results from these simulations in the context of observational constraints on the retention/ejection of metals from Local Group dwarf galaxies. In addition, I will discuss the variations with which individual elements evolve in the various phases of the ISM, as they progress from hot, ionized gas down to cold, star forming regions. I will conclude by outlining the implications of these results on interpretations of observed chemical abundances in dwarf galaxies and on standard assumptions made in semi-analytic chemical evolution models of these galaxies.

Peering Into an Early Galaxy

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2018-04-01

Thirteen billion years ago, early galaxies ionized the gas around them, producing some of the first light that brought our universe out of its dark ages. Now the Atacama Large Millimeter/submillimeter Array (ALMA) has provided one of the first detailed looks into the interior of one of these early, distant galaxies.Sources of LightArtists illustration of the reionization of the universe (time progresses left to right), in which ionized bubbles that form around the first sources of light eventually overlap to form the fully ionized universe we observe today. [Avi Loeb/Scientific American]For the first roughly hundred million years of its existence, our universe expanded in relative darkness there were no sources of light at that time besides the cosmic microwave background. But as mass started to condense to form the first objects, these objects eventually shone as the earliest luminous sources, contributing to the reionization of the universe.To learn about the early production of light in the universe, our best bet is to study in detail the earliest luminous sources stars, galaxies, or quasars that we can hunt down. One ideal target is the galaxy COSMOS Redshift 7, known as CR7 for short.Targeting CR7CR7 is one of the oldest, most distant galaxies known, lying at a redshift of z 6.6. Its discovery in 2015 and subsequent observations of bright, ultraviolet-emitting clumps within it have led to broad speculation about the source of its emission. Does this galaxy host an active nucleus? Or could it perhaps contain the long-theorized first generation of stars, metal-free Population III stars?To determine the nature of CR7 and the other early galaxies that contributed to reionization, we need to explore their gas and dust in detail a daunting task for such distant sources! Conveniently, this is a challenge that is now made possible by ALMAs incredible capabilities. In a new publication led by Jorryt Matthee (Leiden University, the Netherlands), a team of scientists now

On the Scatter of the Present-day Stellar Metallicity–Mass Relation of Cluster Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Engler, Christoph; Lisker, Thorsten; Pillepich, Annalisa

2018-04-01

We examine the scatter of the relation between stellar mass and stellar metallicity for cluster dwarf galaxies in the cosmological simulation Illustris. The mass-metallicity relation exhibits the smallest intrinsic scatter at the galaxies' times of peak stellar mass, suggesting stellar mass stripping to be the primary effect responsible for the rather broad relation at present. However, for about 40% of galaxies in the high-metallicity tail of the relation, we find mass stripping to coincide with an increased enrichment of stellar metallicity, possibly caused by the stripping of low-metallicity stars in the galaxy outskirts.

New analytical solutions for chemical evolution models: characterizing the population of star-forming and passive galaxies

NASA Astrophysics Data System (ADS)

Spitoni, E.; Vincenzo, F.; Matteucci, F.

2017-03-01

Context. Analytical models of chemical evolution, including inflow and outflow of gas, are important tools for studying how the metal content in galaxies evolves as a function of time. Aims: We present new analytical solutions for the evolution of the gas mass, total mass, and metallicity of a galactic system when a decaying exponential infall rate of gas and galactic winds are assumed. We apply our model to characterize a sample of local star-forming and passive galaxies from the Sloan Digital Sky Survey data, with the aim of reproducing their observed mass-metallicity relation. Methods: We derived how the two populations of star-forming and passive galaxies differ in their particular distribution of ages, formation timescales, infall masses, and mass loading factors. Results: We find that the local passive galaxies are, on average, older and assembled on shorter typical timescales than the local star-forming galaxies; on the other hand, the star-forming galaxies with higher masses generally show older ages and longer typical formation timescales compared than star-forming galaxies with lower masses. The local star-forming galaxies experience stronger galactic winds than the passive galaxy population. Exploring the effect of assuming different initial mass functions in our model, we show that to reproduce the observed mass-metallicity relation, stronger winds are requested if the initial mass function is top-heavy. Finally, our analytical models predict the assumed sample of local galaxies to lie on a tight surface in the 3D space defined by stellar metallicity, star formation rate, and stellar mass, in agreement with the well-known fundamental relation from adopting gas-phase metallicity. Conclusions: By using a new analytical model of chemical evolution, we characterize an ensemble of SDSS galaxies in terms of their infall timescales, infall masses, and mass loading factors. Local passive galaxies are, on average, older and assembled on shorter typical

Radio Non-Detections of SN 2010cu and PSN J13203538+3408222 in IC 883

NASA Astrophysics Data System (ADS)

Romero-Canizales, Cristina; Perez-Torres, Miguel A.; Alberdi, Antxon; Kankare, Erkki; Ryder, Stuart D.; Mattila, Seppo

2011-04-01

We report 5 GHz eEVN observations of the luminous infrared galaxy IC 883 intended as a radio follow-up of SN 2010cu (CBET # 2213 and 2286) and PSN J13203538+3408222 (ATel # 3245) that were recently discovered within the nuclear regions of IC 883 by near-IR adaptive-optics observations. The observations were carried out on 23rd March 2011 between 0200UT and 0400UT (total time on source ~1.3 hours) and included the following antennae (diameter, location): Effelsberg (100m, Germany), Jodrell Bank (25m, UK), Medicina (32 m, Italy), Onsala (25 m, Sweden), Torun (32 m, Poland), Westerbork array (14x25 m, NL) and Yebes (40 m, Spain).

BULGELESS GIANT GALAXIES CHALLENGE OUR PICTURE OF GALAXY FORMATION BY HIERARCHICAL CLUSTERING ,

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kormendy, John; Cornell, Mark E.; Drory, Niv

2010-11-01

To better understand the prevalence of bulgeless galaxies in the nearby field, we dissect giant Sc-Scd galaxies with Hubble Space Telescope (HST) photometry and Hobby-Eberly Telescope (HET) spectroscopy. We use the HET High Resolution Spectrograph (resolution R {identical_to} {lambda}/FWHM {approx_equal} 15, 000) to measure stellar velocity dispersions in the nuclear star clusters and (pseudo)bulges of the pure-disk galaxies M 33, M 101, NGC 3338, NGC 3810, NGC 6503, and NGC 6946. The dispersions range from 20 {+-} 1 km s{sup -1} in the nucleus of M 33 to 78 {+-} 2 km s{sup -1} in the pseudobulge of NGC 3338.more » We use HST archive images to measure the brightness profiles of the nuclei and (pseudo)bulges in M 101, NGC 6503, and NGC 6946 and hence to estimate their masses. The results imply small mass-to-light ratios consistent with young stellar populations. These observations lead to two conclusions. (1) Upper limits on the masses of any supermassive black holes are M{sub .} {approx}< (2.6 {+-} 0.5) x 10{sup 6} M{sub sun} in M 101 and M{sub .} {approx}< (2.0 {+-} 0.6) x 10{sup 6} M{sub sun} in NGC 6503. (2) We show that the above galaxies contain only tiny pseudobulges that make up {approx}<3% of the stellar mass. This provides the strongest constraints to date on the lack of classical bulges in the biggest pure-disk galaxies. We inventory the galaxies in a sphere of radius 8 Mpc centered on our Galaxy to see whether giant, pure-disk galaxies are common or rare. We find that at least 11 of 19 galaxies with V{sub circ} > 150 km s{sup -1}, including M 101, NGC 6946, IC 342, and our Galaxy, show no evidence for a classical bulge. Four may contain small classical bulges that contribute 5%-12% of the light of the galaxy. Only four of the 19 giant galaxies are ellipticals or have classical bulges that contribute {approx}1/3 of the galaxy light. We conclude that pure-disk galaxies are far from rare. It is hard to understand how bulgeless galaxies could form as the

A Spatially Resolved Study of the GRB 020903 Host Galaxy

NASA Astrophysics Data System (ADS)

Thorp, Mallory D.; Levesque, Emily M.

2018-03-01

GRB 020903 is a long-duration gamma-ray burst with a host galaxy close enough and extended enough for spatially resolved observations, making it one of less than a dozen GRBs where such host studies are possible. GRB 020903 lies in a galaxy host complex that appears to consist of four interacting components. Here we present the results of spatially resolved spectroscopic observations of the GRB 020903 host. By taking observations at two different position angles, we were able to obtain optical spectra (3600–9000 Å) of multiple regions in the galaxy. We confirm redshifts for three regions of the host galaxy that match that of GRB 020903. We measure the metallicity of these regions, and find that the explosion site and the nearby star-forming regions both have comparable subsolar metallicities. We conclude that, in agreement with past spatially resolved studies of GRBs, the GRB explosion site is representative of the host galaxy as a whole rather than localized in a metal-poor region of the galaxy.

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 changes...

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 changes...

DISCOVERY OF AN ULTRA-FAINT DWARF GALAXY IN THE INTRACLUSTER FIELD OF THE VIRGO CENTER: A FOSSIL OF THE FIRST GALAXIES?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jang, In Sung; Lee, Myung Gyoon, E-mail: isjang@astro.snu.ac.kr, E-mail: mglee@astro.snu.ac.kr

2014-11-01

Ultra-faint dwarf galaxies (UFDs) are newcomers among galaxies, and are the faintest galaxies in the observed universe. To date, they have only been found around the Milky Way Galaxy and M31 in the Local Group. We present the discovery of a UFD in the intracluster field in the core of the Virgo cluster (Virgo UFD1), which is far from any massive galaxies. The color-magnitude diagram of the resolved stars in this galaxy shows a narrow red giant branch, similar to those of metal-poor globular clusters in the Milky Way. We estimate its distance by comparing the red giant branch withmore » isochrones, and we obtain a value 16.4 ± 0.4 Mpc. This shows that it is indeed a member of the Virgo cluster. From the color of the red giants we estimate its mean metallicity to be very low, [Fe/H] =–2.4 ± 0.4. Its absolute V-band magnitude and effective radius are derived to be M{sub V} = –6.5 ± 0.2 and r {sub eff} = 81 ± 7 pc, much fainter and smaller than the classical dwarf spheroidal galaxies. Its central surface brightness is estimated to be as low as μ {sub V,} {sub 0} = 26.37 ± 0.05 mag arcsec{sup –2}. Its properties are similar to those of the Local Group analogs. No evidence of tidal features are found in this galaxy. Considering its narrow red giant branch with no asymptotic giant branch stars, low metallicity, and location, it may be a fossil remnant of the first galaxies.« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maseda, Michael V.; Van der Wel, Arjen; Rix, Hans-Walter

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 aremore » 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.« less

Extinction Mapping and Dust-to-Gas Ratios of Nearby Galaxies using LEGUS

NASA Astrophysics Data System (ADS)

Kahre, Lauren; Walterbos, Rene; Kim, Hwihyun; Thilker, David; Lee, Janice; LEGUS Team

2018-01-01

Dust is commonly used as a tracer for cold dense gas, either through IR and NIR emission maps or through extinction mapping, and dust abundance and gas metallicity are critical constraints for chemical and galaxy evolution models. Extinction mapping has been used to trace dust column densities in the Milky Way, the Magellanic Clouds, and M31. The maps for M31 use IR and NIR photometry of red giant branch stars, which is more difficult to obtain for more distant galaxies. Work by Kahre et al. (in prep) uses the extinctions derived for individual massive stars using the isochrone-matching method described by Kim et al. (2012) to generate extinction maps for these more distant galaxies.Isochrones of massive stars lie in the same location on a color-color diagram with little dependence on metallicity and luminosity class, so the extinction can be directly derived from the observed photometry. We generate extinction maps using photometry of massive stars from the Hubble Space Telescope for several of the nearly 50 galaxies observed by the Legacy Extragalactic Ultraviolet Survey (LEGUS). The derived extinction maps will allow us to correct ground-based and HST Halpha maps for extinction, and will be used to constrain changes in the dust-to-gas ratio across the galaxy sample and in different star formation, metallicity and morphological environments. Previous studies have found links between galaxy metallicity and the dust-to-gas mass ratio. We present a study of LEGUS galaxies spanning a range of distances, metallicities, and galaxy morphologies, expanding on our previous study of metal-poor dwarfs Holmberg I and II and giant spirals NGC 6503 and NGC 628. We see clear evidence for changes in the dust-to-gas mass ratio with changing metallicity. We also examine changes in the dust-to-gas mass ratio with galactocentric radius. Ultimately, we will provide constraints on the dust-to-gas mass ratio across a wide range of galaxy environments.

Chemical evolution of Local Group dwarf galaxies in a cosmological context - I. A new modelling approach and its application to the Sculptor dwarf spheroidal galaxy

NASA Astrophysics Data System (ADS)

Romano, Donatella; Starkenburg, Else

2013-09-01

We present a new approach for chemical evolution modelling, specifically designed to investigate the chemical properties of dwarf galaxies in a full cosmological framework. In particular, we focus on the Sculptor dwarf spheroidal galaxy, for which a wealth of observational data exists, as a test bed for our model. We select four candidate Sculptor-like galaxies from the satellite galaxy catalogue generated by implementation of a version of the Munich semi-analytic model for galaxy formation on the level 2 Aquarius dark matter simulations and use the mass assembly and star formation histories predicted for these four systems as an input for the chemical evolution code. We follow explicitly the evolution of several chemical elements, both in the cold gas out of which the stars form and in the hot medium residing in the halo. We take into account in detail the lifetimes of stars of different initial masses, the distribution of the delay times for Type Ia supernova explosions and the dependence of the stellar yields from the initial metallicity of the stars. We allow large fractions of metals to be deposited into the hot phase, either directly as stars die or through reheated gas flows powered by supernova explosions. We find that, in order to reproduce both the observed metallicity distribution function and the observed abundance ratios of long-lived stars of Sculptor, large fractions of the reheated metals must never re-enter regions of active star formation. With this prescription, all the four analogues to the Sculptor dwarf spheroidal galaxy extracted from the simulated satellites catalogue on the basis of luminosity and stellar population ages are found to reasonably match the detailed chemical properties of real Sculptor stars. However, all model galaxies do severely underestimate the fraction of very metal poor stars observed in Sculptor. Our analysis thus sets further constraints on the semi-analytical models and, at large, on possible metal enrichment

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.

2017-05-01

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 by 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 the 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 colour excess E(B - V) with the metallicity in this kind of objects, we do not find correlations between them.

A Missing Link in Galaxy Evolution: The Mysteries of Dissolving Star Clusters

NASA Astrophysics Data System (ADS)

Pellerin, Anne; Meyer, Martin; Harris, Jason; Calzetti, Daniela

2007-05-01

Star-forming events in starbursts and normal galaxies have a direct impact on the global stellar content of galaxies. These events create numerous compact clusters where stars are produced in great number. These stars eventually end up in the star field background where they are smoothly distributed. However, due to instrumental limitations such as spatial resolution and sensitivity, the processes involved during the transition phase from the compact clusters to the star field background as well as the impact of the environment (spiral waves, bars, starburst) on the lifetime of clusters are still poorly constrained observationally. I will present our latest results on the physical properties of dissolving clusters directly detected in HST/ACS archival images of the three nearby galaxies IC 2574, NGC 1313, and IC 10 (D < 5 Mpc). The ACS has the capability to detect and spatially resolve individual stars in nearby galaxies within a large field-of-view. For all ACS images obtained in three filters (F435W, F555W or F606W, and F814W), we performed PSF stellar photometry in crowded field. Color-magnitude diagrams (CMD) allow us to identify the most massive stars more likely to be part of dissolving clusters (A-type and earlier), and to isolate them from the star field background. We then adapt and use a clustering algorithm on the selected stars to find groups of stars to reveal and quantify the properties of all star clusters (compactness, size, age, mass). With this algorithm, even the less compact clusters are revealed while they are being destroyed. Our sample of three galaxies covers an interesting range in gravitational potential well and explores a variety of galaxy morphological types, which allows us to discuss the dissolving cluster properties as a function of the host galaxy characteristics. The properties of the star field background will also be discussed.

Extraplanar H II Regions in Spiral Galaxies. I. Low-metallicity Gas Accreting through the Disk-halo Interface of NGC 4013

NASA Astrophysics Data System (ADS)

Howk, J. Christopher; Rueff, Katherine M.; Lehner, Nicolas; Wotta, Christopher B.; Croxall, Kevin; Savage, Blair D.

2018-04-01

The interstellar thick disks of galaxies serve as the interface between the thin star-forming disk, where feedback-driven outflows originate, and the distant halo, the repository for accreted gas. We present optical emission line spectroscopy of a luminous, thick disk H II region located at z = 860 pc above the plane of the spiral galaxy NGC 4013 taken with the Multi-Object Double Spectrograph on the Large Binocular Telescope. This nebula, with an Hα luminosity ∼4–7 times that of the Orion nebula, surrounds a luminous cluster of young, hot stars that ionize the surrounding interstellar gas of the thick disk, providing a measure of the properties of that gas. We demonstrate that strong emission line methods can provide accurate measures of relative abundances between pairs of H II regions. From our emission line spectroscopy, we show that the metal content of the thick disk H II region is a factor of ≈2 lower than gas in H II regions at the midplane of this galaxy (with the relative abundance of O in the thick disk lower by ‑0.32 ± 0.09 dex). This implies incomplete mixing of material in the thick disk on small scales (hundreds of parsecs) and that there is accretion of low-metallicity gas through the thick disks of spirals. The inclusion of low-metallicity gas this close to the plane of NGC 4013 is reminiscent of the recently proposed “fountain-driven” accretion models.

Spectroscopy of dwarf elliptical galaxies in the Fornax cluster

NASA Technical Reports Server (NTRS)

Held, Enrico V.; Mould, Jeremy R.

1994-01-01

We present the results of spectroscopic observations of 10 nucleated dwarf elliptical galaxies (dE's) in the Fornax cluster. The blue spectra of Fornax dE galaxies indicate a wide range of metallicities at a given luminosity, similar to those of intermediate to metal-rich globular clusters. Metal abundances derived in this paper are well correlated with optical colors and agree with previous spectroscopic results. A discrepancy with metallicities inferred from infrared colors is evident; possible causes include an intermediate age population and dilution of spectral features by a blue light excess. Dwarf ellipticals exhibit a wide variation of hydrogen line strength which points to a complex star formation history. Prominent Balmer absorption lines are the signature of a young stellar population in the nuclei of some (but not all) dE's, while moderately strong Balmer lines in relatively metal-rich dE's are more consistent with an extended main sequence. In a few metal-poor dE galaxies, the hydrogen lines are consisent with, or perhaps weaker than, those found in Galactic globulars of similar metallicity. In the limited magnitude range of this sample, there is no apparent correlation of metallicity either with effective and central surface brightness, or with total and nuclear magnitudes. The velocity distribution of the Fornax dwarfs is flatter than that of brighter galaxies at the 75% confidence level, possibly indicating a difference in the kinematics of the two samples.

Dissolved Massive Metal-rich Globular Clusters Can Cause the Range of UV Upturn Strengths Found among Early-type Galaxies

NASA Astrophysics Data System (ADS)

Goudfrooij, Paul

2018-04-01

I discuss a scenario in which the ultraviolet (UV) upturn of giant early-type galaxies (ETGs) is primarily due to helium-rich stellar populations that formed in massive metal-rich globular clusters (GCs), which subsequently dissolved in the strong tidal field in the central regions of the massive host galaxy. These massive GCs are assumed to show UV upturns similar to those observed recently in M87, the central giant elliptical galaxy in the Virgo cluster of galaxies. Data taken from the literature reveal a strong correlation between the strength of the UV upturn and the specific frequency of metal-rich GCs in ETGs. Adopting a Schechter function parameterization of GC mass functions, simulations of long-term dynamical evolution of GC systems show that the observed correlation between UV upturn strength and GC specific frequency can be explained by variations in the characteristic truncation mass {{ \\mathcal M }}{{c}} such that {{ \\mathcal M }}{{c}} increases with ETG luminosity in a way that is consistent with observed GC luminosity functions in ETGs. These findings suggest that the nature of the UV upturn in ETGs and the variation of its strength among ETGs are causally related to that of helium-rich populations in massive GCs, rather than intrinsic properties of field stars in massive galactic spheroids. With this in mind, I predict that future studies will find that [N/Fe] decreases with increasing galactocentric radius in massive ETGs, and that such gradients have the largest amplitudes in ETGs with the strongest UV upturns.

Separate Ways: The Mass–Metallicity Relation Does Not Strongly Correlate with Star Formation Rate in SDSS-IV MaNGA Galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barrera-Ballesteros, J. K.; Heckman, T.; Sánchez, S. F.

We present the integrated stellar mass–metallicity relation (MZR) for more than 1700 galaxies included in the integral field area SDSS-IV MaNGA survey. The spatially resolved data allow us to determine the metallicity at the same physical scale (effective radius, R {sub eff}) using a heterogeneous set of 10 abundance calibrators. In addition to scale factors, the shape of the MZR is similar for all calibrators, consistent with those reported previously using single-fiber and integral field spectroscopy. We compare the residuals of this relation against the star formation rate (SFR) and specific SFR (sSFR). We do not find a strong secondarymore » relation of the MZR with either SFR or sSFR for any of the calibrators, in contrast with previous single-fiber spectroscopic studies. Our results agree with a scenario in which metal enrichment happens at local scales, with global outflows playing a secondary role in shaping the chemistry of galaxies and cold-gas inflows regulating the stellar formation.« less

Long-slit Spectroscopy of Edge-on Low Surface Brightness Galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Du, Wei; Wu, Hong; Zhu, Yinan

2017-03-10

We present long-slit optical spectra of 12 edge-on low surface brightness galaxies (LSBGs) positioned along their major axes. After performing reddening corrections for the emission-line fluxes measured from the extracted integrated spectra, we measured the gas-phase metallicities of our LSBG sample using both the [N ii]/H α and the R {sub 23} diagnostics. Both sets of oxygen abundances show good agreement with each other, giving a median value of 12 + log(O/H) = 8.26 dex. In the luminosity–metallicity plot, our LSBG sample is consistent with the behavior of normal galaxies. In the mass–metallicity diagram, our LSBG sample has lower metallicitiesmore » for lower stellar mass, similar to normal galaxies. The stellar masses estimated from z -band luminosities are comparable to those of prominent spirals. In a plot of the gas mass fraction versus metallicity, our LSBG sample generally agrees with other samples in the high gas mass fraction space. Additionally, we have studied stellar populations of three LSBGs, which have relatively reliable spectral continua and high signal-to-noise ratios, and qualitatively conclude that they have a potential dearth of stars with ages <1 Gyr instead of being dominated by stellar populations with ages >1 Gyr. Regarding the chemical evolution of our sample, the LSBG data appear to allow for up to 30% metal loss, but we cannot completely rule out the closed-box model. Additionally, we find evidence that our galaxies retain up to about three times as much of their metals compared with dwarfs, consistent with metal retention being related to galaxy mass. In conclusion, our data support the view that LSBGs are probably just normal disk galaxies continuously extending to the low end of surface brightness.« less

The Nature of LSB galaxies revealed by their Globular Clusters

NASA Astrophysics Data System (ADS)

Kissler-Patig, Markus

2005-07-01

Low Surface Brightness {LSB} galaxies encompass many of the extremes in galaxy properties. Their understanding is essential to complete our picture of galaxy formation and evolution. Due to their historical under-representation on galaxy surveys, their importance to many areas of astronomy has only recently began to be realized. Globular clusters are superb tracers of the formation histories of galaxies and have been extensively used as such in high surface brightness galaxies. We propose to investigate the nature of massive LSB galaxies by studying their globular cluster systems. No globular cluster study has been reported for LSB galaxies to date. Yet, both the presence or absence of globular clusters set very strong constraints on the conditions prevailing during LSB galaxy formation and evolution. Both in dwarf and giant high surface brightness {HSB} galaxies, globular clusters are known to form as a constant fraction of baryonic mass. Their presence/absence immediately indicates similarities or discrepancies in the formation and evolution conditions of LSB and HSB galaxies. In particular, the presence/absence of metal-poor halo globular clusters infers similarities/differences in the halo formation and assembly processes of LSB vs. HSB galaxies, while the presence/absence of metal-rich globular clusters can be used to derive the occurrence and frequency of violent events {such as mergers} in the LSB galaxy assembly history. Two band imaging with ACS will allow us to identify the globular clusters {just resolved at the selected distance} and to determine their metallicity {potentially their rough age}. The composition of the systems will be compared to the extensive census built up on HSB galaxies. Our representative sample of six LSB galaxies {cz < 2700 km/s} are selected such, that a large system of globular clusters is expected. Globular clusters will constrain phases of LSB galaxy formation and evolution that can currently not be probed by other means. HST

Galaxy And Mass Assembly (GAMA): blue spheroids within 87 Mpc

NASA Astrophysics Data System (ADS)

Mahajan, Smriti; Drinkwater, Michael J.; Driver, S.; Hopkins, A. M.; Graham, Alister W.; Brough, S.; Brown, Michael J. I.; Holwerda, B. W.; Owers, Matt S.; Pimbblet, Kevin A.

2018-03-01

In this paper, we test if nearby blue spheroid (BSph) galaxies may become the progenitors of star-forming spiral galaxies or passively evolving elliptical galaxies. Our sample comprises 428 galaxies of various morphologies in the redshift range 0.002 < z < 0.02 (8-87 Mpc) with panchromatic data from the Galaxy and Mass Assembly survey. We find that BSph galaxies are structurally (mean effective surface brightness, effective radius) very similar to their passively evolving red counterparts. However, their star formation and other properties such as colour, age, and metallicity are more like star-forming spirals than spheroids (ellipticals and lenticulars). We show that BSph galaxies are statistically distinguishable from other spheroids as well as spirals in the multidimensional space mapped by luminosity-weighted age, metallicity, dust mass, and specific star formation rate. We use H I data to reveal that some of the BSphs are (further) developing their discs, hence their blue colours. They may eventually become spiral galaxies - if sufficient gas accretion occurs - or more likely fade into low-mass red galaxies.

The evolution of high-metallicity horizontal-branch stars and the origin of the ultraviolet light in elliptical galaxies

NASA Technical Reports Server (NTRS)

Horch, E.; Demarque, P.; Pinsonneault, M.

1992-01-01

Evolutionary calculations of high-metallicity horizontal-branch stars show that for the relevant masses and helium abundances, post-HB evolution in the HR diagram does not proceed toward and along the AGB, but rather toward a 'slow blue phase' in the vicinity of the helium-burning main sequence, following the extinction of the hydrogen shell energy source. For solar and twice solar metallicity, the blue phase begins during the helium shell-burning phase (in agreement with the work of Brocato and Castellani and Tornambe); for 3 times solar metallicity, it begins earlier, during the helium core-burning phase. This behavior differs from what takes place at lower metallicities. The implications for high-metallicity old stellar populations in the Galactic bulge and for the integrated colors of elliptical galaxies are discussed.

The metal-poor knee in the Fornax dwarf spheroidal galaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hendricks, Benjamin; Koch, Andreas; Lanfranchi, Gustavo A.

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 tomore » 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.« less

The Physical Conditions, Metallicity and Metal Abundance Ratios in a Highly Magnified Galaxy at z = 3.6252

NASA Astrophysics Data System (ADS)

Bayliss, Matthew B.; Rigby, Jane R.; Sharon, Keren; Wuyts, Eva; Florian, Michael; Gladders, Michael D.; Johnson, Traci; 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 */M ⊙) = 9.5 ± 0.35, star formation rates from [O II] λλ3727 and Hβ of 55 ± 25 and 84 ± 24 M ⊙ yr-1, respectively, an electron density of ne <= 103 cm-2, an electron temperature of Te <= 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. Based on observations from the Magellan Telescopes at Las Campanas Observatory, from 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 United States, Canada, Chile, Australia, Brazil and Argentina, with additional supporting data obtained at the Subaru telescope

Dust and ionized gas in active radio elliptical galaxies

NASA Technical Reports Server (NTRS)

Forbes, D. A.; Sparks, W. B.; Macchetto, F. D.

1990-01-01

The authors present broad and narrow bandwidth imaging of three southern elliptical galaxies which have flat-spectrum active radio cores (NGC 1052, IC 1459 and NGC 6958). All three contain dust and extended low excitation optical line emission, particularly extensive in the case of NGC 1052 which has a large H alpha + (NII) luminosity. Both NGC 1052 and IC 1459 have a spiral morphology in emission-line images. All three display independent strong evidence that a merger or infall event has recently occurred, i.e., extensive and infalling HI gas in NGC 1052, a counter-rotating core in IC 1459 and Malin-Carter shells in NGC 6958. This infall event is the most likely origin for the emission-line gas and dust, and the authors are currently investigating possible excitation mechanisms (Sparks et al. 1990).

Unveiling the AGN in IC 883: discovery of a parsec-scale radio jet

NASA Astrophysics Data System (ADS)

Romero-Cañizales, C.; Alberdi, A.; Ricci, C.; Arévalo, P.; Pérez-Torres, M. Á.; Conway, J. E.; Beswick, R. J.; Bondi, M.; Muxlow, T. W. B.; Argo, M. K.; Bauer, F. E.; Efstathiou, A.; Herrero-Illana, R.; Mattila, S.; Ryder, S. D.

2017-05-01

IC 883 is a luminous infrared galaxy (LIRG) classified as a starburst-active galactic nucleus (AGN) composite. In a previous study, we detected a low-luminosity AGN (LLAGN) radio candidate. Here, we report on our radio follow-up at three frequencies that provides direct and unequivocal evidence of the AGN activity in IC 883. Our analysis of archival X-ray data, together with the detection of a transient radio source with luminosity typical of bright supernovae, gives further evidence of the ongoing star formation activity, which dominates the energetics of the system. At sub-parsec scales, the radio nucleus has a core-jet morphology with the jet being a newly ejected component showing a subluminal proper motion of 0.6-1 c. The AGN contributes less than 2 per cent of the total IR luminosity of the system. The corresponding Eddington factor is ˜10-3, suggesting this is a low-accretion rate engine, as often found in LLAGNs. However, its high bolometric luminosity (˜1044 erg s-1) agrees better with a normal AGN. This apparent discrepancy may just be an indication of the transition nature of the nucleus from a system dominated by star formation, to an AGN-dominated system. The nucleus has a strongly inverted spectrum and a turnover at ˜4.4 GHz, thus qualifying as a candidate for the least luminous (L5.0 GHz ˜ 6.3 × 1028 erg s-1 Hz-1) and one of the youngest (˜3 × 103 yr) gigahertz-peaked spectrum (GPS) sources. If the GPS origin for the IC 883 nucleus is confirmed, then advanced mergers in the LIRG category are potentially key environments to unveil the evolution of GPS sources into more powerful radio galaxies.

Long-Duration Gamma-Ray Burst Host Galaxies in Emission and Absorption

NASA Astrophysics Data System (ADS)

Perley, Daniel A.; Niino, Yuu; Tanvir, Nial R.; Vergani, Susanna D.; Fynbo, Johan P. U.

2016-12-01

The galaxy population hosting long-duration GRBs provides a means to constrain the progenitor and an opportunity to use these violent explosions to characterize the nature of the high-redshift universe. Studies of GRB host galaxies in emission reveal a population of star-forming galaxies with great diversity, spanning a wide range of masses, metallicities, and redshifts. However, as a population GRB hosts are significantly less massive and poorer in metals than the hosts of other core-collapse transients, suggesting that GRB production is only efficient at metallicities significantly below Solar. GRBs may also prefer compact galaxies, and dense and/or central regions of galaxies, more than other types of core-collapse explosion. Meanwhile, studies of hosts in absorption against the luminous GRB optical afterglow provide a unique means of unveiling properties of the ISM in even the faintest and most distant galaxies; these observations are helping to constrain the chemical evolution of galaxies and the properties of interstellar dust out to very high redshifts. New ground- and space-based instrumentation, and the accumulation of larger and more carefully-selected samples, are continually enhancing our view of the GRB host population.

The uniformity and time-invariance of the intra-cluster metal distribution in galaxy clusters from the IllustrisTNG simulations

NASA Astrophysics Data System (ADS)

Vogelsberger, Mark; Marinacci, Federico; Torrey, Paul; Genel, Shy; Springel, Volker; Weinberger, Rainer; Pakmor, Rüdiger; Hernquist, Lars; Naiman, Jill; Pillepich, Annalisa; Nelson, Dylan

2018-02-01

The distribution of metals in the intra-cluster medium (ICM) encodes important information about the enrichment history and formation of galaxy clusters. Here, we explore the metal content of clusters in IllustrisTNG - a new suite of galaxy formation simulations building on the Illustris project. Our cluster sample contains 20 objects in TNG100 - a ˜(100 Mpc)3 volume simulation with 2 × 18203 resolution elements, and 370 objects in TNG300 - a ˜(300 Mpc)3 volume simulation with 2 × 25003 resolution elements. The z = 0 metallicity profiles agree with observations, and the enrichment history is consistent with observational data going beyond z ˜ 1, showing nearly no metallicity evolution. The abundance profiles vary only minimally within the cluster samples, especially in the outskirts with a relative scatter of ˜ 15 per cent. The average metallicity profile flattens towards the centre, where we find a logarithmic slope of -0.1 compared to -0.5 in the outskirts. Cool core clusters have more centrally peaked metallicity profiles (˜0.8 solar) compared to non-cool core systems (˜0.5 solar), similar to observational trends. Si/Fe and O/Fe radial profiles follow positive gradients. The outer abundance profiles do not evolve below z ˜ 2, whereas the inner profiles flatten towards z = 0. More than ˜ 80 per cent of the metals in the ICM have been accreted from the proto-cluster environment, which has been enriched to ˜0.1 solar already at z ˜ 2. We conclude that the intra-cluster metal distribution is uniform among our cluster sample, nearly time-invariant in the outskirts for more than 10 Gyr, and forms through a universal enrichment history.

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.

Surface Photometric Properties of HII Galaxies

NASA Astrophysics Data System (ADS)

Vajgel, B.; Telles, E.

2009-05-01

HII galaxies are dwarf galaxies undergoing violent star formation. They were firstly selected by objective-prism spectroscopy and were object of extensive studies to characterize their physical conditions of the interstellar medium. Their SFR together with their low Z raised the question whether some of them can be truly ``young'' galaxies. To infer the SFH, one needs information in a large spectral range. We obtained images in the optical region of the spectrum with the 0.6 m B&C and the 1.6 m telescopes at the Laboratório Nacional de Astrofísica, for a sample of 50 objects in B, V, R and I, which combined with recent evolutionary models, enable us to deduce the stellar population content and its spatial distribution. These seem to be the nearest youngest galaxies that can be studied in detail, and their structural properties offer important indications about the evolutionary relation and the origin of dwarf galaxies in the universe. With this sample we built a morphological catalogue with broad-band photometry, including the structural analysis through the brightness profiles. The initial analysis suggests that the galaxies can be segregated in two broad classes, in agreement with what had already been proposed in the literature; Type I have irregular envelopes with signs of perturbation and turn out to the more luminous sub-sample; while Type II have regular external isophotes and are less luminous. The brightness profiles are well represented by exponential fits, as in irregular and elliptical dwarf galaxies. However, HII galaxies are more compact in comparison with their more diffuse counterparts. We study the behavior of the HII galaxies in the metallicity-luminosity plane. This relation, interpreted as a relation between the mass and the metallicity of dwarf galaxies of low surface brightness (dE and dIrr), has direct implications for their formation and evolution, and over the possible evolutionary links between HII galaxies and other types of dwarf

Heavy-Element Abundances in Blue Compact Galaxies

NASA Astrophysics Data System (ADS)

Izotov, Yuri I.; Thuan, Trinh X.

1999-02-01

We present high-quality ground-based spectroscopic observations of 54 supergiant H II regions in 50 low-metallicity blue compact galaxies with oxygen abundances 12+logO/H between 7.1 and 8.3. We use the data to determine abundances for the elements N, O, Ne, S, Ar, and Fe. We also analyze Hubble Space Telescope (HST) Faint Object Spectrograph archival spectra of 10 supergiant H II regions to derive C and Si abundances in a subsample of seven BCGs. The main result of the present study is that none of the heavy element-to-oxygen abundance ratios studied here (C/O, N/O, Ne/O, Si/O, S/O, Ar/O, Fe/O) depend on oxygen abundance for BCGs with 12+logO/H<=7.6 (Z<=Zsolar/20). This constancy implies that all of these heavy elements have a primary origin and are produced by the same massive (M>=10 Msolar) stars responsible for O production. The dispersion of the ratios C/O and N/O in these galaxies is found to be remarkably small, being only +/-0.03 and +/-0.02 dex, respectively. This very small dispersion is strong evidence against any time-delayed production of C and primary N in the lowest metallicity BCGs (secondary N production is negligible at these low metallicities). The absence of a time-delayed production of C and N is consistent with the scenario that galaxies with 12+logO/H<=7.6 are now undergoing their first burst of star formation, and that they are therefore young, with ages not exceeding 40 Myr. If very low metallicity BCGs are indeed young, this would argue against the commonly held belief that C and N are produced by intermediate-mass (3 Msolar<=M<=9 Msolar) stars at very low metallicities, as these stars would not have yet completed their evolution in these lowest metallicity galaxies. In higher metallicity BCGs (7.6<12+logO/H<8.2), the abundance ratios Ne/O, Si/O, S/O, Ar/O, and Fe/O retain the same constant value they had at lower metallicities. By contrast, there is an increase of C/O and N/O along with their dispersions at a given O. We interpret this

Mod 1 ICS TI Report: ICS Conversion of a 140% HPGe Detector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bounds, John Alan

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.

30 CFR 57.22209 - Auxiliary fans (I-C mines).

Code of Federal Regulations, 2010 CFR

2010-07-01

... Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22209 Auxiliary fans (I-C mines.... Tests for methane shall be made at electric auxiliary fans before they are started. Such fans shall not be operated when air passing over or through them contains 0.5 percent or more methane. ...

30 CFR 57.22310 - Electrical cables (I-C mines).

Code of Federal Regulations, 2013 CFR

2013-07-01

... Standards for Methane in Metal and Nonmetal Mines Equipment § 57.22310 Electrical cables (I-C mines). Electrical cables used to power submersible sump pumps shall be accepted or approved by MSHA as flame... be sealed to prevent entry of explosive gas or dust. [57 FR 61223, Dec. 23, 1992] ...

30 CFR 57.22310 - Electrical cables (I-C mines).

Code of Federal Regulations, 2014 CFR

2014-07-01

... Standards for Methane in Metal and Nonmetal Mines Equipment § 57.22310 Electrical cables (I-C mines). Electrical cables used to power submersible sump pumps shall be accepted or approved by MSHA as flame... be sealed to prevent entry of explosive gas or dust. [57 FR 61223, Dec. 23, 1992] ...

30 CFR 57.22310 - Electrical cables (I-C mines).

Code of Federal Regulations, 2012 CFR

2012-07-01

... Standards for Methane in Metal and Nonmetal Mines Equipment § 57.22310 Electrical cables (I-C mines). Electrical cables used to power submersible sump pumps shall be accepted or approved by MSHA as flame... be sealed to prevent entry of explosive gas or dust. [57 FR 61223, Dec. 23, 1992] ...

30 CFR 57.22310 - Electrical cables (I-C mines).

Code of Federal Regulations, 2011 CFR

2011-07-01

... Standards for Methane in Metal and Nonmetal Mines Equipment § 57.22310 Electrical cables (I-C mines). Electrical cables used to power submersible sump pumps shall be accepted or approved by MSHA as flame... be sealed to prevent entry of explosive gas or dust. [57 FR 61223, Dec. 23, 1992] ...

30 CFR 57.22310 - Electrical cables (I-C mines).

Code of Federal Regulations, 2010 CFR

2010-07-01

... Standards for Methane in Metal and Nonmetal Mines Equipment § 57.22310 Electrical cables (I-C mines). Electrical cables used to power submersible sump pumps shall be accepted or approved by MSHA as flame... be sealed to prevent entry of explosive gas or dust. [57 FR 61223, Dec. 23, 1992] ...

30 CFR 57.22209 - Auxiliary fans (I-C mines).

Code of Federal Regulations, 2011 CFR

2011-07-01