Science.gov

Sample records for ii star formation

  1. H II REGIONS: WITNESSES TO MASSIVE STAR FORMATION

    SciTech Connect

    Peters, Thomas; Banerjee, Robi; Klessen, Ralf S.; Low, Mordecai-Mark Mac; Galvan-Madrid, Roberto; Keto, Eric R.

    2010-03-10

    We describe the first three-dimensional simulation of the gravitational collapse of a massive, rotating molecular cloud that includes heating by both non-ionizing and ionizing radiation. These models were performed with the FLASH code, incorporating a hybrid, long characteristic, ray-tracing technique. We find that as the first protostars gain sufficient mass to ionize the accretion flow, their H II regions are initially gravitationally trapped, but soon begin to rapidly fluctuate between trapped and extended states, in agreement with observations. Over time, the same ultracompact H II region can expand anisotropically, contract again, and take on any of the observed morphological classes. In their extended phases, expanding H II regions drive bipolar neutral outflows characteristic of high-mass star formation. The total lifetime of H II regions is given by the global accretion timescale, rather than their short internal sound-crossing time. This explains the observed number statistics. The pressure of the hot, ionized gas does not terminate accretion. Instead, the final stellar mass is set by fragmentation-induced starvation. Local gravitational instabilities in the accretion flow lead to the build-up of a small cluster of stars, all with relatively high masses due to heating from accretion radiation. These companions subsequently compete with the initial high-mass star for the same common gas reservoir and limit its mass growth. This is in contrast to the classical competitive accretion model, where the massive stars are never hindered in growth by the low-mass stars in the cluster. Our findings show that the most significant differences between the formation of low-mass and high-mass stars are all explained as the result of rapid accretion within a dense, gravitationally unstable, ionized flow.

  2. STELLAR POPULATIONS AND THE STAR FORMATION HISTORIES OF LOW SURFACE BRIGHTNESS GALAXIES. II. H II REGIONS

    SciTech Connect

    Schombert, James; McGaugh, Stacy; Maciel, Tamela E-mail: stacy.mcgaugh@case.edu

    2013-08-01

    The luminosities, colors, and H{alpha} emission for 429 H II regions in 54 low surface brightness (LSB) galaxies are presented. While the number of H II regions per galaxy is lower in LSB galaxies compared to star-forming irregulars and spirals, there is no indication that the size or luminosity function of H II regions differs from other galaxy types. The lower number of H II regions per galaxy is consistent with their lower total star formation rates. The fraction of the total L{sub H{alpha}} contributed by H II regions varies from 10% to 90% in LSB galaxies (the rest of the H{alpha} emission being associated with a diffuse component) with no correlation with galaxy stellar or gas mass. Bright H II regions have bluer colors, similar to the trend in spirals; their number and luminosities are consistent with the hypothesis that they are produced by the same H II luminosity function as spirals. Comparison with stellar population models indicates that the brightest H II regions in LSB galaxies range in cluster mass from a few 10{sup 3} M{sub Sun} (e.g., {rho} Oph) to globular-cluster-sized systems (e.g., 30 Dor) and that their ages are consistent with clusters from 2 to 15 Myr old. The faintest H II regions are comparable to those in the LMC powered by a single O or B star. Thus, star formation in LSB galaxies covers the full range of stellar cluster mass.

  3. STAR FORMATION IN RELIC H II REGIONS OF THE FIRST STARS: BINARITY AND OUTFLOW DRIVING

    SciTech Connect

    Machida, Masahiro N.; Omukai, Kazuyuki; Matsumoto, Tomoaki E-mail: machiam@scphys.kyoto-u.ac.j

    2009-11-01

    Star formation in relic H II regions of the first stars is investigated using magnetohydrodynamical simulations with a nested-grid method that covers approx10 orders of magnitude in spatial scale and approx20 orders of magnitude in density contrast. Due to larger fraction of H{sub 2} and HD molecules, its prestellar thermal evolution is considerably different from that in the first star formation. Reflecting the difference, two hydrostatic cores appear in a nested manner: a protostar is enclosed by a transient hydrostatic core, which appears during the prestellar collapse. If the initial natal core rotates fast at a rate with rotational to gravitational energy ratio beta{sub 0} approx> 0.01-0.1, the transient hydrostatic core fragments to approx10 M {sub sun} subcores at density approx10{sup 9} cm{sup -3}. With smaller rotation energy, fragmentation occurs at higher density while a single protostar forms without fragmentation if rotation is extremely slow with beta{sub 0} approx< 10{sup -6} to 10{sup -5}. If magnetic field is present, these threshold values of beta{sub 0} are boosted owing to angular momentum transport by the magnetic breaking. Magnetic field also drives the protostellar outflows. With strong magnetic field, two distinct outflows are observed: the slower one emanates from the transient hydrostatic core, while the faster one from the protostar. These flows may affect the final stellar mass by ejecting some of masses in the initial core, and also may play some role in driving and maintenance of interstellar turbulence in young galaxies.

  4. An investigation of the role of the H II region environment on star formation

    NASA Astrophysics Data System (ADS)

    Healy, Kevin Robert

    Data from the Very Large Array, Hubble Space Telescope, and Two Micron All Sky Survey are used to investigate low-mass star formation in the vicinity of HII regions. The gas in H II regions is strongly affected by massive stars through their intense ultraviolet radiation and winds. The H II region environment is expected to affect the process of star formation, from triggering the collapse of cloud cores within the molecular cloud to truncating circumstellar disks in the interior of the H II region. Massive stars end their lives as supernovae, injecting freshly synthesized radionuclides and large amounts of radiant and kinetic energy into their surroundings. Most stars in the Galaxy form in such environments and recent measurements of meteorites demonstrate that the Solar System formed in this setting. The first part of this work describes a Very Large Array survey of water masers in portions of six H II regions. Previous observational studies demonstrate the link between star formation and water maser activity. This study uses high-resolution observations of water masers to pinpoint the sites of star formation in crowded or confused regions. The water maser survey identifies several sites of star formation that are very close to the ionization fronts being driven into the surrounding molecular cloud. The locations and numbers of these water masers indicate that the H II region environment may trigger the formation of protostars, but that the passage of the ionization front may play a role in prematurely terminating infall. Later evolutionary stages of star formation are characterized by infrared emission from circumstellar disks. Near-infrared photometry from the Two Micron All Sky Survey is used to show that stars with circumstellar disks in the star-forming region NGC 6357 cluster near ionization fronts, strongly suggesting exposure to the H II region environment rapidly (~10 4 years) evaporates circumstellar gas and dust. Hubble Space Telescope images in the

  5. TIDAL TAILS OF MINOR MERGERS. II. COMPARING STAR FORMATION IN THE TIDAL TAILS OF NGC 2782

    SciTech Connect

    Knierman, Karen A.; Scowen, Paul; Veach, Todd; Groppi, Christopher; Mullan, Brendan; Charlton, Jane; Konstantopoulos, Iraklis; Knezek, Patricia M. E-mail: paul.scowen@asu.edu E-mail: cgroppi@asu.edu E-mail: iraklis@aao.gov.au

    2013-09-10

    The peculiar spiral NGC 2782 is the result of a minor merger with a mass ratio {approx}4: 1 occurring {approx}200 Myr ago. This merger produced a molecular and H I-rich, optically bright eastern tail and an H I-rich, optically faint western tail. Non-detection of CO in the western tail by Braine et al. suggested that star formation had not yet begun. However, deep UBVR and H{alpha} narrowband images show evidence of recent star formation in the western tail, though it lacks massive star clusters and cluster complexes. Using Herschel PACS spectroscopy, we discover 158 {mu}m [C II] emission at the location of the three most luminous H{alpha} sources in the eastern tail, but not at the location of the even brighter H{alpha} source in the western tail. The western tail is found to have a normal star formation efficiency (SFE), but the eastern tail has a low SFE. The lack of CO and [C II] emission suggests that the western tail H II region may have a low carbon abundance and be undergoing its first star formation. The western tail is more efficient at forming stars, but lacks massive clusters. We propose that the low SFE in the eastern tail may be due to its formation as a splash region where gas heating is important even though it has sufficient molecular and neutral gas to make massive star clusters. The western tail, which has lower gas surface density and does not form high-mass star clusters, is a tidally formed region where gravitational compression likely enhances star formation.

  6. Molecular Clouds and Star Formation in the Southern H II Regions

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Reiko; Saito, Hiro; Mizuno, Norikazu; Mine, Yoshihiro; Mizuno, Akira; Ogawa, Hideo; Fukui, Yasuo

    1999-12-01

    We have carried out extensive 13CO(J = 1-0) observations toward 23 southern H II regions associated with bright-rimmed clouds. In total, 95 molecular clouds have been identified to be associated with the H II regions. Among the 95, 57 clouds \\ are found to be associated with 204 IRAS point sources which are candidates for young stellar objects. There is a significant increase of star-formation efficiency on the side facing to the H II regions; the luminosity-to-mass ratio, defined as the ratio of the stellar luminosity to the molecular cloud mass, is higher by an order of magnitude on the near side of the H II \\ regions than that on the far side. This indicates that molecular gas facing to the H II regions is more actively forming massive s\\ tars whose luminosity is >~ 103 LO . In addition, the number density of the IRAS point sources increases by a factor of 2 on the near side of the H II regions compared with on the far side. These results strongly suggest that the active formation of massive stars on the near side of the H II regions is due to the effects of the H II regions, such as the compression of molecular material by the ionization/shock fronts. For the whole Galaxy, we estimate that the present star-formation rate under such effects is at least 0.2-0.4 MO yr-1, corresponding to a few 10% by mass.

  7. Multi-wavelength study of triggered star formation around 25 H II regions

    NASA Astrophysics Data System (ADS)

    Xu, Jin-Long; Wang, Jun-Jie; Ning, Chang-Chun; Zhang, Chuan-Peng

    2014-01-01

    We investigate 25 H II regions that show bubble morphology in 13CO(1-0) and infrared data, to search for quantitative evidence of triggered star formation by processes described by the collect and collapse (CC) and radiatively driven implosion (RDI) models. These H II regions display the morphology of a complete or partial bubble at 8 μm, and are all associated with the molecular clouds that surround them. We found that the electron temperature ranges from 5627 K to 6839 K in these H II regions, and the average electron temperature is 6083 K. The age of these H II regions is from 3.0 × 105 yr to 1.7 × 106 yr, and the mean age is 7.7 × 105 yr. Based on the morphology of the associated molecular clouds, we divide these H II regions into three groups, which may support CC and RDI models. We select 23 young IRAS sources which have an infrared luminosity of > 103Lsolar in 19 H II regions. In addition, we identify some young stellar objects (including Class I sources), which are only concentrated in H II regions G29.007+0.076, G44.339-0.827 and G47.028+0.232. The poly-cyclic aromatic hydrocarbon emissions of the three H II regions all show a cometary globule. Comparing the age of each H II region with the characteristic timescales for star formation, we suggest that the three H II regions can trigger clustered star formation by an RDI process. In addition, we detect seven molecular outflows in the five H II regions for the first time. These outflow sources may be triggered by the corresponding H II regions.

  8. H II regions and star formation in the Magellanic Clouds

    SciTech Connect

    Kennicutt, R.C.,JR.; Hodge, P.W.

    1986-07-01

    Photoelectrically calibrated maps of the H-alpha emission in the Magellanic Clouds have been used to measure integrated fluxes for several hundred H II regions and to study the properties of the H II region populations in the galaxies. The H II regions span a range of 10,000 in luminosity, from objects on the scale of the Orion Nebula to the 30 Doradus complex. The H-alpha luminosity function is well represented over this entire range by a power law function, indicating that there is no characteristic luminosity scale for the H II regions. The distributions of nebular diameters, on the other hand, are fitted well by exponential functions, with a scale length of 80 pc. Approximate fluxes for several of the extended filamentary networks in the galaxies have also been measured. This extended component probability contributes 15-25 percent of the total H-alpha luminosity of the galaxies. 42 references.

  9. H II regions and star formation in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    Kennicutt, R. C., Jr.; Hodge, P. W.

    1986-07-01

    Photoelectrically calibrated maps of the H-alpha emission in the Magellanic Clouds have been used to measure integrated fluxes for several hundred H II regions and to study the properties of the H II region populations in the galaxies. The H II regions span a range of 10,000 in luminosity, from objects on the scale of the Orion Nebula to the 30 Doradus complex. The H-alpha luminosity function is well represented over this entire range by a power law function, indicating that there is no characteristic luminosity scale for the H II regions. The distributions of nebular diameters, on the other hand, are fitted well by exponential functions, with a scale length of 80 pc. Approximate fluxes for several of the extended filamentary networks in the galaxies have also been measured. This extended component probability contributes 15-25 percent of the total H-alpha luminosity of the galaxies.

  10. Star Formation Activity in the Galactic H II Region Sh2-297

    NASA Astrophysics Data System (ADS)

    Mallick, K. K.; Ojha, D. K.; Samal, M. R.; Pandey, A. K.; Bhatt, B. C.; Ghosh, S. K.; Dewangan, L. K.; Tamura, M.

    2012-11-01

    We present a multiwavelength study of the Galactic H II region Sh2-297, located in the Canis Major OB1 complex. Optical spectroscopic observations are used to constrain the spectral type of ionizing star HD 53623 as B0V. The classical nature of this H II region is affirmed by the low values of electron density and emission measure, which are calculated to be 756 cm-3 and 9.15 × 105 cm-6 pc using the radio continuum observations at 610 and 1280 MHz, and Very Large Array archival data at 1420 MHz. To understand local star formation, we identified the young stellar object (YSO) candidates in a region of area ~7farcm5 × 7farcm5 centered on Sh2-297 using grism slitless spectroscopy (to identify the Hα emission line stars), and near infrared (NIR) observations. NIR YSO candidates are further classified into various evolutionary stages using color-color and color-magnitude (CM) diagrams, giving 50 red sources (H - K > 0.6) and 26 Class II-like sources. The mass and age range of the YSOs are estimated to be ~0.1-2 M ⊙ and 0.5-2 Myr using optical (V/V-I) and NIR (J/J-H) CM diagrams. The mean age of the YSOs is found to be ~1 Myr, which is of the order of dynamical age of 1.07 Myr of the H II region. Using the estimated range of visual extinction (1.1-25 mag) from literature and NIR data for the region, spectral energy distribution models have been implemented for selected YSOs which show masses and ages to be consistent with estimated values. The spatial distribution of YSOs shows an evolutionary sequence, suggesting triggered star formation in the region. The star formation seems to have propagated from the ionizing star toward the cold dark cloud LDN1657A located west of Sh2-297.

  11. A multiwavelength investigation of the H II region S311: young stellar population and star formation

    NASA Astrophysics Data System (ADS)

    Yadav, Ram Kesh; Pandey, A. K.; Sharma, Saurabh; Ojha, D. K.; Samal, M. R.; Mallick, K. K.; Jose, J.; Ogura, K.; Richichi, Andrea; Irawati, Puji; Kobayashi, N.; Eswaraiah, C.

    2016-09-01

    We present a multiwavelength investigation of the young stellar population and star formation activities around the H II region Sharpless 311. Using our deep near-infrared observations and archival Spitzer-IRAC observations, we have detected a total of 125 young stellar objects (YSOs) in an area of ˜86 arcmin2. The YSO sample includes eight Class I and 117 Class II candidate YSOs. The mass completeness of the identified YSO sample is estimated to be 1.0 M⊙. The ages and masses of the majority of the candidate YSOs are estimated to be in the range ˜0.1-5 Myr and ˜0.3-6 M⊙, respectively. The 8-μm image of S311 displays an approximately spherical cavity around the ionizing source, which was possibly created by the expansion of the H II region. The spatial distribution of the candidate YSOs reveals that a significant number of them are distributed systematically along the 8-μm emission with a majority clustered around the eastern border of the H II region. Four clumps/compact H II regions are detected in the radio continuum observations at 1280 MHz, which may have been formed during the expansion of the H II region. The estimated dynamical age of the region, main-sequence lifetime of the ionizing source, the spatial distribution and ages of the candidate YSOs indicate triggered star formation in the complex.

  12. Dynamical Expansion of Ionization and Dissociation Front around a Massive Star. II. On the Generality of Triggered Star Formation

    NASA Astrophysics Data System (ADS)

    Hosokawa, Takashi; Inutsuka, Shu-ichiro

    2006-07-01

    We analyze the dynamical expansion of the H II region, photodissociation region, and the swept-up shell, solving the UV and far-UV radiative transfer and the thermal and chemical processes in the time-dependent hydrodynamics code. Following our previous paper, we investigate the time evolutions with various ambient number densities and central stars. Our calculations show that basic evolution is qualitatively similar among our models with different parameters. The molecular gas is finally accumulated in the shell, and the gravitational fragmentation of the shell is generally expected. The quantitative differences among models are well understood with analytic scaling relations. The detailed physical and chemical structure of the shell is mainly determined by the incident far-UV flux and the column density of the shell, which also follow the scaling relations. The time of shell fragmentation and the mass of the gathered molecular gas are sensitive to the ambient number density. In the case of a low density, the shell fragmentation occurs over a longer timescale, and the accumulated molecular gas is more massive than in the case of a high density. The variations with different central stars are more moderate. The time of the shell fragmentation differs by a factor of several with the various stars of M*=12-101 Msolar. According to our numerical results, we conclude that the expanding H II region should be an efficient trigger for star formation in molecular clouds if the mass of the ambient molecular material is large enough.

  13. Is the First Epoch of Star Formation in Satellite Galaxies Universal? - Part II

    NASA Astrophysics Data System (ADS)

    Skillman, Evan

    2014-10-01

    We propose to derive detailed star formation and chemical enrichment histories of a representative sample of M31 dwarf spheroidal (dSph) companions in order to compare directly the timing, duration, and strength of their first episodes of star formation to those of the Milky Way (MW) satellites. Compared to the MW companion dSphs, the M31 companion dSphs have significantly different horizontal branch morphologies and a different range in structural parameters. We hypothesize that these differences are connected to the evolutionary histories of their host galaxies. The proposed deep HST imaging is the only means to accurately measure the early star formation histories of the Andromeda companions and thus to test our hypothesis. Fundamentally, we will be testing the assumption that the early evolution of the Milky Way satellites was typical and therefore representative of dSphs in general. The M31 dSphs are our only option.We have designed a representative sample of six galaxies which optimizes coverage in galaxy properties and observing efficiency. From cycle 20 observations of two of these galaxies (And II & XVI) we have discovered that - despite a factor of ~100 difference in mass - both galaxies show similar SFHs with star formation extending until intermediate ages and a synchronous termination in star formation ~5 Gyr ago. There are no MW satellite analogs to the lower luminosity M31 dSph And XVI. Here we propose observations of the rest of the sample, allowing direct inner/outer comparisons, comparison of SFHs as a function of luminosity and membership in substructures, and determination whether the synchronous truncation is observed in more of the M31 dSphs.

  14. Triggered massive-star formation on the borders of Galactic H II regions. III. Star formation at the periphery of Sh2-219

    NASA Astrophysics Data System (ADS)

    Deharveng, L.; Lefloch, B.; Massi, F.; Brand, J.; Kurtz, S.; Zavagno, A.; Caplan, J.

    2006-10-01

    Context: .Massive-star formation triggered by the expansion of H ii regions. Aims: .To understand if sequential star formation is taking place at the periphery of the H ii region Sh2-219. Methods: .We present 12CO J=2→ 1 line observations of this region, obtained at the IRAM 30-m telescope (Pico Veleta, Spain). Results: .In the optical, Sh2-219 is spherically symmetric around its exciting star; furthermore it is surrounded along three quarters of its periphery by a ring of atomic hydrogen. This spherical symmetry breaks down at infrared and millimetre wavelengths. A molecular cloud of about 2000 M_⊙ lies at the southwestern border of Sh2-219, in the H i gap. Two molecular condensations, elongated along the ionization front, probably result from the interaction between the expanding H ii region and the molecular cloud. In this region of interaction there lies a cluster containing many highly reddened stars, as well as a massive star exciting an ultracompact H ii region. More surprisingly, the brightest parts of the molecular cloud form a "chimney", perpendicular to the ionization front. This chimney is closed at its south-west extremity by Hα walls, thus forming a cavity. The whole structure is 7.5 pc long. A luminous Hα emission-line star, lying at one end of the chimney near the ionization front, may be responsible for this structure. Confrontation of the observations with models of H ii region evolution shows that Sh2-219 is probably 105 yr old. The age and origin of the near-IR cluster observed on the border of Sh2-219 remain unknown.

  15. [C II] 158 μm EMISSION AS A STAR FORMATION TRACER

    SciTech Connect

    Herrera-Camus, R.; Bolatto, A. D.; Wolfire, M. G.; Smith, J. D.; Croxall, K. V.; Kennicutt, R. C.; Boquien, M.; Calzetti, D.; Helou, G.; Walter, F.; Meidt, S. E.; Leroy, A. K.; Draine, B.; Brandl, B. R.; Armus, L.; Sandstrom, K. M.; Dale, D. A.; Aniano, G.; Hunt, L. K.; Galametz, M.; and others

    2015-02-10

    The [C II] 157.74 μm transition is the dominant coolant of the neutral interstellar gas, and has great potential as a star formation rate (SFR) tracer. Using the Herschel KINGFISH sample of 46 nearby galaxies, we investigate the relation of [C II] surface brightness and luminosity with SFR. We conclude that [C II] can be used for measurements of SFR on both global and kiloparsec scales in normal star-forming galaxies in the absence of strong active galactic nuclei (AGNs). The uncertainty of the Σ{sub [C} {sub II]} – Σ{sub SFR} calibration is ±0.21 dex. The main source of scatter in the correlation is associated with regions that exhibit warm IR colors, and we provide an adjustment based on IR color that reduces the scatter. We show that the color-adjusted Σ{sub [C} {sub II]} – Σ{sub SFR} correlation is valid over almost five orders of magnitude in Σ{sub SFR}, holding for both normal star-forming galaxies and non-AGN luminous infrared galaxies. Using [C II] luminosity instead of surface brightness to estimate SFR suffers from worse systematics, frequently underpredicting SFR in luminous infrared galaxies even after IR color adjustment (although this depends on the SFR measure employed). We suspect that surface brightness relations are better behaved than the luminosity relations because the former are more closely related to the local far-UV field strength, most likely the main parameter controlling the efficiency of the conversion of far-UV radiation into gas heating. A simple model based on Starburst99 population-synthesis code to connect SFR to [C II] finds that heating efficiencies are 1%-3% in normal galaxies.

  16. The massive star population in M101. II. Spatial variations in the recent star formation history

    SciTech Connect

    Grammer, Skyler; Humphreys, Roberta M. E-mail: roberta@umn.edu

    2014-09-01

    We investigate star formation history (SFH) as a function of radius in M101 using archival Hubble Space Telescope Advanced Camera for Surveys photometry. We derive the SFH from the resolved stellar populations in five 2' wide annuli. Binning the SFH into time frames corresponding to stellar populations traced by Hα, far-ultraviolet, and near-ultraviolet emission, we find that the fraction of stellar populations young enough to contribute in Hα is 15%-35% in the inner regions, compared to less than 5% in the outer regions. This provides a sufficient explanation for the lack of Hα emission at large radii. We also model the blue to red supergiant ratio in our five annuli, examine the effects that a metallicity gradient and variable SFH have on the predicted ratios, and compare to the observed values. We find that the radial behavior of our modeled blue to red supergiant ratios is highly sensitive to both spatial variations in the SFH and metallicity. Incorporating the derived SFH into modeled ratios, we find that we are able to reproduce the observed values at large radii (low metallicity), but at small radii (high metallicity) the modeled and observed ratios are discrepant.

  17. An Evolutionary Model for Collapsing Molecular Clouds and their Star Formation Activity. II. Mass Dependence of the Star Formation Rate

    NASA Astrophysics Data System (ADS)

    Zamora-Avilés, Manuel; Vázquez-Semadeni, Enrique

    2014-10-01

    We discuss the evolution and dependence on cloud mass of the star formation rate (SFR) and efficiency (SFE) of star-forming molecular clouds (MCs) within the scenario that clouds are undergoing global collapse and that the SFR is controlled by ionization feedback. We find that low-mass clouds (M max <~ 104 M ⊙) spend most of their evolution at low SFRs, but end their lives with a mini-burst, reaching a peak SFR ~104 M ⊙ Myr-1, although their time-averaged SFR is only langSFRrang ~ 102 M ⊙ Myr-1. The corresponding efficiencies are SFEfinal <~ 60% and langSFErang <~ 1%. For more massive clouds (M max >~ 105 M ⊙), the SFR first increases and then reaches a plateau because the clouds are influenced by stellar feedback since earlier in their evolution. As a function of cloud mass, langSFRrang and langSFErang are well represented by the fits langSFRrang ≈ 100(1 + M max/1.4 × 105 M ⊙)1.68 M ⊙ Myr-1 and langSFErang ≈ 0.03(M max/2.5 × 105 M ⊙)0.33, respectively. Moreover, the SFR of our model clouds follows closely the SFR-dense gas mass relation recently found by Lada et al. during the epoch when their instantaneous SFEs are comparable to those of the clouds considered by those authors. Collectively, a Monte Carlo integration of the model-predicted SFR(M) over a Galactic giant molecular cloud mass spectrum yields values for the total Galactic SFR that are within half an order of magnitude of the relation obtained by Gao & Solomon. Our results support the scenario that star-forming MCs may be in global gravitational collapse and that the low observed values of the SFR and SFE are a result of the interruption of each SF episode, caused primarily by the ionizing feedback from massive stars.

  18. Massive Star Formation of the SGR a East H (sub II) Regions Near the Galactic Center

    NASA Technical Reports Server (NTRS)

    Yusef-Zadeh, F.; Lacy, J. H.; Wardle, M.; Whitney, B.; Bushouse, H.; Roberts, D. A.; Arendt, R. G.

    2010-01-01

    A group of four compact H II regions associated with the well-known 50 km/s molecular cloud is the closest site of on-going star formation to the dynamical center of the Galaxy, at a projected distance of approximately 6 pc. We present a study of ionized gas based on the [Ne II] (12.8 micron) line, as well as multi-frequency radio continuum, Hubble Space Telescope Pa alpha, and Spitzer Infrared Array Camera observations of the most compact member of the H II group, Sgr A East H II D. The radio continuum image at 6 cm shows that this source breaks up into two equally bright ionized features, D1 and D2. The spectral energy distribution of the D source is consistent with it being due to a 25 =/- 3 solar mass star with a luminosity of 8 +/- 3 x 10(exp 4) Solar luminosity . The inferred mass, effective temperature of the UV source, and the ionization rate are compatible with a young O9-B0 star. The ionized features D1 and D2 are considered to be ionized by UV radiation collimated by an accretion disk. We consider that the central massive star photoevaporates its circumstellar disk on a timescale of 3x (exp 4) years giving a mass flux approximately 3 x 10(exp -5) Solar Mass / year and producing the ionized material in D1 and D2 expanding in an inhomogeneous medium. The ionized gas kinematics, as traced by the [Ne II] emission, is difficult to interpret, but it could be explained by the interaction of a bipolar jet with surrounding gas along with what appears to be a conical wall of lower velocity gas. The other H II regions, Sgr A East A-C, have morphologies and kinematics that more closely resemble cometary flows seen in other compact H II regions, where gas moves along a paraboloidal surface formed by the interaction of a stellar wind with a molecular cloud.

  19. MASSIVE STAR FORMATION OF THE SGR A EAST H II REGIONS NEAR THE GALACTIC CENTER

    SciTech Connect

    Yusef-Zadeh, F.; Lacy, J. H.; Wardle, M.; Whitney, B.; Bushouse, H.; Roberts, D. A.; Arendt, R. G.

    2010-12-20

    A group of four compact H II regions associated with the well-known 50 km s{sup -1} molecular cloud is the closest site of on-going star formation to the dynamical center of the Galaxy, at a projected distance of {approx}6 pc. We present a study of ionized gas based on the [Ne II] (12.8 {mu}m) line, as well as multi-frequency radio continuum, Hubble Space Telescope Pa{alpha}, and Spitzer Infrared Array Camera observations of the most compact member of the H II group, Sgr A East H II D. The radio continuum image at 6 cm shows that this source breaks up into two equally bright ionized features, D1 and D2. The spectral energy distribution of the D source is consistent with it being due to a 25 {+-} 3 M{sub sun} star with a luminosity of 8 {+-} 3 x 10{sup 4} L{sub sun}. The inferred mass, effective temperature of the UV source, and the ionization rate are compatible with a young O9-B0 star. The ionized features D1 and D2 are considered to be ionized by UV radiation collimated by an accretion disk. We consider that the central massive star photoevaporates its circumstellar disk on a timescale of 3 x 10{sup 4} years giving a mass flux {approx}3 x 10{sup -5} M{sub sun} yr{sup -1} and producing the ionized material in D1 and D2 expanding in an inhomogeneous medium. The ionized gas kinematics, as traced by the [Ne II] emission, is difficult to interpret, but it could be explained by the interaction of a bipolar jet with surrounding gas along with what appears to be a conical wall of lower velocity gas. The other H II regions, Sgr A East A-C, have morphologies and kinematics that more closely resemble cometary flows seen in other compact H II regions, where gas moves along a paraboloidal surface formed by the interaction of a stellar wind with a molecular cloud.

  20. X-ray sources in regions of star formation. II - The pre-main-sequence G star HDE 283572

    NASA Technical Reports Server (NTRS)

    Walter, F. M.; Brown, A.; Linsky, J. L.; Rydgren, A. E.; Vrba, F.

    1987-01-01

    This paper reports the detection of HDE 283572, a ninth-magnitude G star 8 arcmin south of RY Tau, as a bright X-ray source. The observations reveal this object to be a fairly massive (about 2 solar masses) pre-main-sequence star associated with the Taurus-Auriga star formation complex. It exhibits few of the characteristics of the classical T Tauri stars and is a good example of a 'naked' T Tauri star. The star is a mid-G subgiant, of about three solar radii and rotates with a period of 1.5 d. The coronal and chromospheric surface fluxes are similar to those of the most active late type stars (excluding T Tauri stars). The X-ray and UV lines most likely arise in different atmospheric structures. Radiative losses are some 1000 times the quiet solar value and compare favorably with those of T Tauri stars.

  1. X-ray sources in regions of star formation. II. The pre-main-sequence G star HDE 283572

    SciTech Connect

    Walter, F.M.; Brown, A.; Linsky, J.L.; Rydgren, A.E.; Vrba, F.

    1987-03-01

    This paper reports the detection of HDE 283572, a ninth-magnitude G star 8 arcmin south of RY Tau, as a bright X-ray source. The observations reveal this object to be a fairly massive (about 2 solar masses) pre-main-sequence star associated with the Taurus-Auriga star formation complex. It exhibits few of the characteristics of the classical T Tauri stars and is a good example of a naked T Tauri star. The star is a mid-G subgiant, of about three solar radii and rotates with a period of 1.5 d. The coronal and chromospheric surface fluxes are similar to those of the most active late type stars (excluding T Tauri stars). The X-ray and UV lines most likely arise in different atmospheric structures. Radiative losses are some 1000 times the quiet solar value and compare favorably with those of T Tauri stars. 49 references.

  2. An evolutionary model for collapsing molecular clouds and their star formation activity. II. Mass dependence of the star formation rate

    SciTech Connect

    Zamora-Avilés, Manuel; Vázquez-Semadeni, Enrique

    2014-10-01

    We discuss the evolution and dependence on cloud mass of the star formation rate (SFR) and efficiency (SFE) of star-forming molecular clouds (MCs) within the scenario that clouds are undergoing global collapse and that the SFR is controlled by ionization feedback. We find that low-mass clouds (M {sub max} ≲ 10{sup 4} M {sub ☉}) spend most of their evolution at low SFRs, but end their lives with a mini-burst, reaching a peak SFR ∼10{sup 4} M {sub ☉} Myr{sup –1}, although their time-averaged SFR is only (SFR) ∼ 10{sup 2} M {sub ☉} Myr{sup –1}. The corresponding efficiencies are SFE{sub final} ≲ 60% and (SFE) ≲ 1%. For more massive clouds (M {sub max} ≳ 10{sup 5} M {sub ☉}), the SFR first increases and then reaches a plateau because the clouds are influenced by stellar feedback since earlier in their evolution. As a function of cloud mass, (SFR) and (SFE) are well represented by the fits (SFR) ≈ 100(1 + M {sub max}/1.4 × 10{sup 5} M {sub ☉}){sup 1.68} M {sub ☉} Myr{sup –1} and (SFE) ≈ 0.03(M {sub max}/2.5 × 10{sup 5} M {sub ☉}){sup 0.33}, respectively. Moreover, the SFR of our model clouds follows closely the SFR-dense gas mass relation recently found by Lada et al. during the epoch when their instantaneous SFEs are comparable to those of the clouds considered by those authors. Collectively, a Monte Carlo integration of the model-predicted SFR(M) over a Galactic giant molecular cloud mass spectrum yields values for the total Galactic SFR that are within half an order of magnitude of the relation obtained by Gao and Solomon. Our results support the scenario that star-forming MCs may be in global gravitational collapse and that the low observed values of the SFR and SFE are a result of the interruption of each SF episode, caused primarily by the ionizing feedback from massive stars.

  3. Heavily reddened z ˜ 2 Type 1 quasars - II. H α star formation constraints from SINFONI IFU observations

    NASA Astrophysics Data System (ADS)

    Alaghband-Zadeh, S.; Banerji, Manda; Hewett, Paul C.; McMahon, Richard G.

    2016-06-01

    We use near-infrared integral field unit spectroscopy to search for H α emission associated with star formation in a sample of 28 heavily reddened (E(B - V) ≃ 0.5-1.9), hyperluminous (log({{L}}_{bol}/erg s^{-1})≃ 47-48) broad-line quasars at z ≃ 1.4-2.7. 16 of the 28 quasars show evidence for star formation with an average extinction-corrected star formation rate (SFR) of 320 ± 70 M⊙ yr-1. A stacked spectrum of the detections shows weak [N II], consistent with star formation as the origin of the narrow H α emission. The star-forming regions are spatially unresolved in 11 of the 16 detections and constrained to lie within ˜6 kpc of the quasar emission. In the five resolved detections we find the star-forming regions are extended on scales of ˜8 kpc around the quasar emission. The prevalence of high SFRs is consistent with the identification of the heavily reddened quasar population as representing a transitional phase from apparent `starburst galaxies' to optically luminous quasars. Upper limits are determined for 10 quasars in which star formation is undetected. In two of the quasars the SFR is constrained to be relatively modest, <50 M⊙ yr-1, but significantly higher levels of star formation could be present in the other eight quasars. The combination of the 16 strong star formation detections and the eight high SFR limits means that high levels of star formation may be present in the majority of the sample. Higher spatial resolution data, of multiple emission lines, will allow us to better understand the interplay between star formation and active galactic nucleus activity in these transitioning quasars.

  4. Star formation activity in the southern Galactic H II region G351.63-1.25

    NASA Astrophysics Data System (ADS)

    Vig, S.; Ghosh, S. K.; Ojha, D. K.; Verma, R. P.; Tamura, M.

    2014-06-01

    The southern Galactic high-mass star-forming region, G351.63-1.25, is an H II region-molecular cloud complex with a luminosity of ˜2.0 × 105 L⊙, located at a distance of 2.4 kpc from the Sun. In this paper, we focus on the investigation of the associated H II region, embedded cluster and the interstellar medium in the vicinity of G351.63-1.25. We address the identification of exciting source(s) as well as the census of the stellar populations, in an attempt to unfold star formation activity in this region. The ionized gas distribution has been mapped using the Giant Metrewave Radio Telescope, India, at three frequencies: 1280, 610 and 325 MHz. The H II region shows an elongated morphology and the 1280 MHz map comprises six resolved high-density regions encompassed by diffuse emission spanning 1.4 × 1.0 pc2. Based on the measurements of flux densities at multiple radio frequencies, the brightest ultracompact core has electron temperature Te˜7647 {±} 153 K and emission measure, EM˜2.0 {±} 0.8×107 cm-6 pc. The zero-age main-sequence spectral type of the brightest radio core is O7.5. We have carried out near-infrared observations in the JHKs bands using the SIRIUS camera on the 1.4 m Infrared Survey Facility telescope. The near-infrared images reveal the presence of a cluster embedded in nebulous fan-shaped emission. The log-normal slope of the K-band luminosity function of the embedded cluster is found to be ˜0.27 ± 0.03, and the fraction of the near-infrared excess stars is estimated to be 43 per cent. These indicate that the age of the cluster is consistent with ˜1 Myr. Other available data of this region show that the warm (mid-infrared) and cold (millimetre) dust emission peak at different locations indicating progressive stages of star formation process. The champagne flow model from a flat, thin molecular cloud is used to explain the morphology of radio emission with respect to the millimetre cloud and infrared brightness.

  5. Star formation - An overview

    NASA Technical Reports Server (NTRS)

    Evans, N. J., II

    1985-01-01

    Methods for studying star formation are reviewed. Stellar clusters and associations, as well as field stars, provide a fossil record of the star formation process. Regions of current star formation provide a series of snapshots of different epochs of star formation. A simplified picture of individual star formation as it was envisioned in the late 1970s is contrasted with the results of recent observations, in particular the outflow phenomenon.

  6. ON THE LINK BETWEEN ASSOCIATED Mg II ABSORBERS AND STAR FORMATION IN QUASAR HOSTS

    SciTech Connect

    Shen Yue; Menard, Brice E-mail: menard@pha.jhu.edu

    2012-04-01

    A few percent of quasars show strong associated Mg II absorption, with velocities (v{sub off}) lying within a few thousand km s{sup -1} from the quasar systemic redshift. These associated absorption line (AAL) systems are usually interpreted as absorbers that are either intrinsic to the quasar and its host, or arising from external galaxies clustering around the quasar. Using composite spectra of {approx}1800 Mg II AAL quasars selected from SDSS DR7 at 0.4 {approx}< z {approx}< 2, we show that quasars with AALs with v{sub off} < 1500 km s{sup -1} have a prominent excess in [O II] {lambda}3727 emission (detected at >7{sigma}) at rest relative to the quasar host, compared to unabsorbed quasars. We interpret this [O II] excess as due to enhanced star formation in the quasar host. Our results suggest that a significant fraction of AALs with v{sub off} < 1500 km s{sup -1} are physically associated with the quasar and its host. AAL quasars also have dust reddening lying between normal quasars and the so-called dust-reddened quasars. We suggest that the unique properties of AAL quasars can be explained if they are the transitional population from heavily dust-reddened quasars to normal quasars in the formation process of quasars and their hosts. This scenario predicts a larger fraction of young bulges, disturbed morphologies, and interactions of AAL quasar hosts compared to normal quasars. The intrinsic link between associated absorbers and quasar hosts opens a new window to probe massive galaxy formation and galactic-scale feedback processes, and provides a crucial test of the evolutionary picture of quasars.

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

    NASA Astrophysics Data System (ADS)

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

    2003-10-01

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

  8. Mass Transport and Turbulence in Gravitationally Unstable Disk Galaxies. II: The Effects of Star Formation Feedback

    NASA Astrophysics Data System (ADS)

    Goldbaum, Nathan J.; Krumholz, Mark R.; Forbes, John C.

    2016-08-01

    Self-gravity and stellar feedback are capable of driving turbulence and transporting mass and angular momentum in disk galaxies, but the balance between them is not well understood. In the previous paper in this series, we showed that gravity alone can drive turbulence in galactic disks, regulate their Toomre Q parameters to ∼1, and transport mass inwards at a rate sufficient to fuel star formation in the centers of present-day galaxies. In this paper we extend our models to include the effects of star formation feedback. We show that feedback suppresses galaxies’ star formation rates by a factor of ∼5 and leads to the formation of a multi-phase atomic and molecular interstellar medium. Both the star formation rate and the phase balance produced in our simulations agree well with observations of nearby spirals. After our galaxies reach steady state, we find that the inclusion of feedback actually lowers the gas velocity dispersion slightly compared to the case of pure self-gravity, and also slightly reduces the rate of inward mass transport. Nevertheless, we find that, even with feedback included, our galactic disks self-regulate to Q ∼ 1, and transport mass inwards at a rate sufficient to supply a substantial fraction of the inner disk star formation. We argue that gravitational instability is therefore likely to be the dominant source of turbulence and transport in galactic disks, and that it is responsible for fueling star formation in the inner parts of galactic disks over cosmological times.

  9. The double galaxy cluster Abell 2465 - II. Star formation in the cluster

    NASA Astrophysics Data System (ADS)

    Wegner, Gary A.; Chu, Devin S.; Hwang, Ho Seong

    2015-02-01

    We investigate the star formation rate and its location in the major merger cluster Abell 2465 at z = 0.245. Optical properties of the cluster are described in Paper I. Measurements of the Hα and infrared dust emission of galaxies in the cluster were made with an interference filter centred on the redshifted line at a wavelength of 817 nm and utilized data from the Wide-field Infrared Survey Explorer satellite 12 μm band. Imaging in the Johnson U and B bands was obtained, and along with Sloan Digital Sky Survey u and r was used to study the blue fraction, which appears enhanced, as a further signature of star formation in the cluster. Star formation rates were calculated using standard calibrations. The total star formation rate normalized by the cluster mass, ΣSFR/Mcl compared to compilations for other clusters indicate that the components of Abell 2465 lie above the mean z and Mcl relations, suggestive that interacting galaxy clusters have enhanced star formation. The projected radial distribution of the star-forming galaxies does not follow an NFW profile and is relatively flat indicating that fewer star-forming galaxies are in the cluster centre. The morphologies of the Hα sources within R200 for the cluster as a whole indicate that many are disturbed or merging, suggesting that a combination of merging or harassment is working.

  10. Star Formation in Galaxies

    NASA Technical Reports Server (NTRS)

    1987-01-01

    Topics addressed include: star formation; galactic infrared emission; molecular clouds; OB star luminosity; dust grains; IRAS observations; galactic disks; stellar formation in Magellanic clouds; irregular galaxies; spiral galaxies; starbursts; morphology of galactic centers; and far-infrared observations.

  11. Spitzer Follow-up of HST Observations of Star Formation in H II Regions

    NASA Astrophysics Data System (ADS)

    Hester, Jeff; Bally, John; Desch, Steve; Healy, Kevin; Snider, Keely

    2005-06-01

    Images of regions of star formation taken with HST have given us an extraordinary view of young stellar objects and their natal environments. These views differ tremendously between low-mass YSOs seen in regions of isolated low-mass star formation such as Taurus-Auriga, and the proplyds, EGGs, and other structures seen in regions of massive star formation. While YSOs in Taurus spend their adolescence buried in the dark interiors of molecular clouds, YSOs near massive stars quickly find themselves overrun by ionization fronts and exposed to the intense UV radiation from nearby massive stars. This difference in environment has a profound effect on the way in which the protoplanetary disk around a star evolves -- a fact that is of great importance to us, given the strength of the evidence suggesting that the Sun formed near a massive star. But HST while HST can inform us about the evolution of YSOs in HII region environments once they are overrun by ionization fronts, it cannot show us the birth of the stars themselves. These remain hidden in the dense molecular material beyond the ionized volumes of these regions. Only Spitzer can show us the properties of the YSOs that lie hidden in the dark shadows of HST images of HII regions, and only Spitzer can provide us with information about PDRs, warm dust, and other tracers of the interaction of massive stars with their surroundings. The combination of HST and Spitzer observations of star forming regions is far greater than the sum of its parts. If we are to build a complete picture of low-mass star formation and the evolution of disks near massive stars, we need to combine HST and Spitzer observations of the same regions. In this proposal we request time to obtain both IRAC and MIPS 24 micron images of each HII region that has been observed by HST, but has yet to be observed with Spitzer. Together with previous images obtained from the archives, this will comprise an indispensible data set for testing hypotheses about

  12. TRIGGERED STAR FORMATION AROUND MID-INFRARED BUBBLES IN THE G8.14+0.23 H II REGION

    SciTech Connect

    Dewangan, L. K.; Ojha, D. K.; Chakraborti, S.; Anandarao, B. G.; Ghosh, S. K.

    2012-09-10

    Mid-infrared shells or bubbles around expanding H II regions have received much attention due to their ability to initiate a new generation of star formation. We present multi-wavelength observations around two bubbles associated with a southern massive star-forming region G8.14+0.23, to investigate the triggered star formation signature on the edges of the bubbles by the expansion of the H II region. We have found observational signatures of the collected molecular and cold dust material along the bubbles and the {sup 12}CO(J = 3-2) velocity map reveals that the molecular gas in the bubbles is physically associated around the G8.14+0.23 region. We have detected 244 young stellar objects (YSOs) in the region and about 37% of these YSOs occur in clusters. Interestingly, these YSO clusters are associated with the collected material on the edges of the bubbles. We have found good agreement between the dynamical age of the H II region and the kinematical timescale of bubbles (from the {sup 12}CO(J = 3-2) line data) with the fragmentation time of the accumulated molecular materials to explain possible 'collect and collapse' process around the G8.14+0.23 region. However, one cannot entirely rule out the possibility of triggered star formation by compression of the pre-existing dense clumps by the shock wave. We have also found two massive embedded YSOs (about 10 and 22 M{sub Sun }) which are associated with the dense fragmented clump at the interface of the bubbles. We conclude that the expansion of the H II region is also leading to the formation of these two young massive embedded YSOs in the G8.14+0.23 region.

  13. SPITZER ANALYSIS OF H II REGION COMPLEXES IN THE MAGELLANIC CLOUDS: DETERMINING A SUITABLE MONOCHROMATIC OBSCURED STAR FORMATION INDICATOR

    SciTech Connect

    Lawton, B.; Gordon, K. D.; Meixner, M.; Sewilo, M.; Shiao, B.; Babler, B.; Bracker, S.; Meade, M.; Block, M.; Engelbracht, C. W.; Misselt, K.; Bolatto, A. D.; Carlson, L. R.; Hora, J. L.; Robitaille, T.; Indebetouw, R.; Madden, S. C.; Oliveira, J. M.; Vijh, U. P. E-mail: kgordon@stsci.ed

    2010-06-10

    H II regions are the birth places of stars, and as such they provide the best measure of current star formation rates (SFRs) in galaxies. The close proximity of the Magellanic Clouds allows us to probe the nature of these star forming regions at small spatial scales. To study the H II regions, we compute the bolometric infrared flux, or total infrared (TIR), by integrating the flux from 8 to 500 {mu}m. The TIR provides a measure of the obscured star formation because the UV photons from hot young stars are absorbed by dust and re-emitted across the mid-to-far-infrared (IR) spectrum. We aim to determine the monochromatic IR band that most accurately traces the TIR and produces an accurate obscured SFR over large spatial scales. We present the spatial analysis, via aperture/annulus photometry, of 16 Large Magellanic Cloud (LMC) and 16 Small Magellanic Cloud (SMC) H II region complexes using the Spitzer Space Telescope's IRAC (3.6, 4.5, 8 {mu}m) and MIPS (24, 70, 160 {mu}m) bands. Ultraviolet rocket data (1500 and 1900 A) and SHASSA H{alpha} data are also included. All data are convolved to the MIPS 160 {mu}m resolution (40 arcsec full width at half-maximum), and apertures have a minimum radius of 35''. The IRAC, MIPS, UV, and H{alpha} spatial analysis are compared with the spatial analysis of the TIR. We find that nearly all of the LMC and SMC H II region spectral energy distributions (SEDs) peak around 70 {mu}m at all radii, from {approx}10 to {approx}400 pc from the central ionizing sources. As a result, we find the following: the sizes of H II regions as probed by 70 {mu}m are approximately equal to the sizes as probed by TIR ({approx}70 pc in radius); the radial profile of the 70 {mu}m flux, normalized by TIR, is constant at all radii (70 {mu}m {approx} 0.45TIR); the 1{sigma} standard deviation of the 70 {mu}m fluxes, normalized by TIR, is a lower fraction of the mean (0.05-0.12 out to {approx}220 pc) than the normalized 8, 24, and 160 {mu}m normalized fluxes (0

  14. STAR FORMATION IN SELF-GRAVITATING DISKS IN ACTIVE GALACTIC NUCLEI. II. EPISODIC FORMATION OF BROAD-LINE REGIONS

    SciTech Connect

    WangJianmin; Du Pu; Ge Junqiang; Hu Chen; Baldwin, Jack A.; Ferland, Gary J.

    2012-02-20

    This is the second in a series of papers discussing the process and effects of star formation in the self-gravitating disk around the supermassive black holes in active galactic nuclei (AGNs). We have previously suggested that warm skins are formed above the star-forming (SF) disk through the diffusion of warm gas driven by supernova explosions. Here we study the evolution of the warm skins when they are exposed to the powerful radiation from the inner part of the accretion disk. The skins initially are heated to the Compton temperature, forming a Compton atmosphere (CAS) whose subsequent evolution is divided into four phases. Phase I is the duration of pure accumulation supplied by the SF disk. During phase II clouds begin to form due to line cooling and sink to the SF disk. Phase III is a period of preventing clouds from sinking to the SF disk through dynamic interaction between clouds and the CAS because of the CAS overdensity driven by continuous injection of warm gas from the SF disk. Finally, phase IV is an inevitable collapse of the entire CAS through line cooling. This CAS evolution drives the episodic appearance of broad-line regions (BLRs). We follow the formation of cold clouds through the thermal instability of the CAS during phases II and III, using linear analysis. Since the clouds are produced inside the CAS, the initial spatial distribution of newly formed clouds and angular momentum naturally follow the CAS dynamics, producing a flattened disk of clouds. The number of clouds in phases II and III can be estimated, as well as the filling factor of clouds in the BLR. Since the cooling function depends on the metallicity, the metallicity gradients that originate in the SF disk give rise to different properties of clouds in different radial regions. We find from the instability analysis that clouds have column density N{sub H} {approx}< 10{sup 22} cm{sup -2} in the metal-rich regions whereas they have N{sub H} {approx}> 10{sup 22} cm{sup -2} in the

  15. Galaxy formation in the Planck cosmology - II. Star-formation histories and post-processing magnitude reconstruction

    NASA Astrophysics Data System (ADS)

    Shamshiri, Sorour; Thomas, Peter A.; Henriques, Bruno M.; Tojeiro, Rita; Lemson, Gerard; Oliver, Seb J.; Wilkins, Stephen

    2015-08-01

    We adapt the L-GALAXIES semi-analytic model to follow the star formation histories (SFHs) of galaxies - by which we mean a record of the formation time and metallicities of the stars that are present in each galaxy at a given time. We use these to construct stellar spectra in post-processing, which offers large efficiency savings and allows user-defined spectral bands and dust models to be applied to data stored in the Millennium data repository. We contrast model SFHs from the Millennium Simulation with observed ones from the VESPA algorithm as applied to the Sloan Digital Sky Survey 7 (SDSS-7) catalogue. The overall agreement is good, with both simulated and SDSS galaxies showing a steeper SFH with increased stellar mass. The SFHs of blue and red galaxies, however, show poor agreement between data and simulations, which may indicate that the termination of star formation is too abrupt in the models. The mean star formation rate (SFR) of model galaxies is well defined and is accurately modelled by a double power law at all redshifts: SFR ∝ 1/(x-1.39 + x1.33), where x = (ta - t)/3.0 Gyr, t is the age of the stars and ta is the lookback time to the onset of galaxy formation; above a redshift of unity, this is well approximated by a gamma function: SFR ∝ x1.5e-x, where x = (ta - t)/2.0 Gyr. Individual galaxies, however, show a wide dispersion about this mean. When split by mass, the SFR peaks earlier for high-mass galaxies than for lower mass ones, and we interpret this downsizing as a mass-dependence in the evolution of the quenched fraction: the SFHs of star-forming galaxies show only a weak mass-dependence.

  16. THE X-FACTOR IN GALAXIES. II. THE MOLECULAR-HYDROGEN-STAR-FORMATION RELATION

    SciTech Connect

    Feldmann, Robert; Gnedin, Nickolay Y.; Kravtsov, Andrey V. E-mail: feldmann@fnal.gov

    2012-10-20

    There is ample observational evidence that the star formation rate (SFR) surface density, {Sigma}{sub SFR}, is closely correlated with the surface density of molecular hydrogen, {Sigma}{sub H{sub 2}}. This empirical relation holds both for galaxy-wide averages and for individual {approx}>kpc sized patches of the interstellar medium, but appears to degrade substantially at a sub-kpc scale. Identifying the physical mechanisms that determine the scale-dependent properties of the observed {Sigma}{sub H{sub 2}}-{Sigma}{sub SFR} relation using a set of cosmological, galaxy formation simulations with a peak resolution of {approx}100 pc. These simulations include a chemical network for molecular hydrogen, a model for the CO emission, and a simple, stochastic prescription for star formation that operates on {approx}100 pc scales. Specifically, star formation is modeled as a Poisson process in which the average SFR is directly proportional to the present mass of H{sub 2}. The predictions of our numerical model are in good agreement with the observed Kennicutt-Schmidt and {Sigma}{sub H{sub 2}}-{Sigma}{sub SFR} relations. We show that observations based on CO emission are ill suited to reliably measure the slope of the latter relation at low ({approx}< 20 M {sub Sun} pc{sup -2}) H{sub 2} surface densities on sub-kpc scales. Our models also predict that the inferred {Sigma}{sub H{sub 2}}-{Sigma}{sub SFR} relation steepens at high H{sub 2} surface densities as a result of the surface density dependence of the CO/H{sub 2} conversion factor. Finally, we show that on sub-kpc scales most of the scatter of the relation is a consequence of discreteness effects of the star formation process. In contrast, variations of the CO/H{sub 2} conversion factor are responsible for most of the scatter measured on super-kpc scales.

  17. The star formation histories of local group dwarf galaxies. II. Searching for signatures of reionization

    SciTech Connect

    Weisz, Daniel R.; Dolphin, Andrew E.; Skillman, Evan D.; Holtzman, Jon; Gilbert, Karoline M.; Dalcanton, Julianne J.; Williams, Benjamin F.

    2014-07-10

    We search for signatures of reionization in the star formation histories (SFHs) of 38 Local Group dwarf galaxies (10{sup 4} < M{sub *} < 10{sup 9} M{sub ☉}). The SFHs are derived from color-magnitude diagrams using archival Hubble Space Telescope/Wide Field Planetary Camera 2 imaging. Only five quenched galaxies (And V, And VI, And XIII, Leo IV, and Hercules) are consistent with forming the bulk of their stars before reionization, when full uncertainties are considered. Observations of 13 of the predicted 'true fossils' identified by Bovill and Ricotti show that only two (Hercules and Leo IV) indicate star formation quenched by reionization. However, both are within the virial radius of the Milky Way and evidence of tidal disturbance complicates this interpretation. We argue that the late-time gas capture scenario posited by Ricotti for the low mass, gas-rich, and star-forming fossil candidate Leo T is observationally indistinguishable from simple gas retention. Given the ambiguity between environmental effects and reionization, the best reionization fossil candidates are quenched low mass field galaxies (e.g., KKR 25).

  18. Panel Discussion II. Reconciling Observations and Modeling of Star Formation at High Redshifts

    NASA Astrophysics Data System (ADS)

    Knapen, J. H.

    2008-06-01

    This is the written account of the second of two panel discussions, on Reconciling observations and modeling of star formation at high redshifts. The chair of the panel was Pavel Kroupa, and panel members were Marc Balcells, John Beckman, Christopher Conselice, and Joseph Silk. After a short introduction by each of the panelists, panel and audience entered into a lively discussion, centered around the following six themes: the mass function of pre-stellar gas clouds; a possible top-heavy initial mass function at high redshifts versus mini-quasars as the first sources of ionization; the integrated galactic initial mass function; possible differences in specific star formation rates in disks and in massive galaxies; whether merging rates yield a wrong prediction for massive galaxies, and what is the physics behind the onset of the red sequence of galaxies; and the case of dark matter-dominated dwarf galaxies versus tidal dwarf galaxies.

  19. Massive Star Formation in a Gravitationally-Lensed H II Galaxy at z = 3.357

    SciTech Connect

    Villar-Martin, M; Stern, D; Hook, R N; Rosati, P; Lombardi, M; Humphrey, A; Fosbury, R; Stanford, S A; Holden, B P

    2004-03-02

    The Lynx arc, with a redshift of 3.357, was discovered during spectroscopic follow-up of the z = 0.570 cluster RX J0848+4456 from the ROSAT Deep Cluster Survey. The arc is characterized by a very red R - K color and strong, narrow emission lines. Analysis of HST WFPC 2 imaging and Keck optical and infrared spectroscopy shows that the arc is an H II galaxy magnified by a factor of {approx} 10 by a complex cluster environment. The high intrinsic luminosity, the emission line spectrum, the absorption components seen in Ly{alpha} and C IV, and the restframe ultraviolet continuum are all consistent with a simple H II region model containing {approx} 10{sup 6} hot O stars. The best fit parameters for this model imply a very hot ionizing continuum (T{sub BB} {approx} 80, 000 K), high ionization parameter (log U {approx} -1), and low nebular metallicity (Z/Z{sub {circle_dot}} {approx} 0.05). The narrowness of the emission lines requires a low mass-to-light ratio for the ionizing stars, suggestive of an extremely low metallicity stellar cluster. The apparent overabundance of silicon in the nebula could indicate enrichment by past pair instability supernovae, requiring stars more massive than {approx}140M{sub {circle_dot}}.

  20. GLOBAL STAR FORMATION REVISITED

    SciTech Connect

    Silk, Joseph; Norman, Colin E-mail: norman@stsci.edu

    2009-07-20

    A general treatment of disk star formation is developed from a dissipative multiphase model, with the dominant dissipation due to cloud collisions. The Schmidt-Kennicutt (SK) law emerges naturally for star-forming disks and starbursts. We predict that there should be an inverse correlation between Tully-Fisher law and SK law residuals. The model is extended to include a multiphase treatment of supernova feedback that leads to a turbulent pressure-regulated generalization of the star formation law and is applicable to gas-rich starbursts. Enhanced pressure, as expected in merger-induced star formation, enhances star formation efficiency. An upper limit is derived for the disk star formation rate in starbursts that depends on the ratio of global ISM to cloud pressures. We extend these considerations to the case where the interstellar gas pressure in the inner galaxy is dominated by outflows from a central active galactic nucleus (AGN). During massive spheroid formation, AGN-driven winds trigger star formation, resulting in enhanced supernova feedback and outflows. The outflows are comparable to the AGN-boosted star formation rate and saturate in the super-Eddington limit. Downsizing of both SMBH and spheroids is a consequence of AGN-driven positive feedback. Bondi accretion feeds the central black hole with a specific accretion rate that is proportional to the black hole mass. AGN-enhanced star formation is mediated by turbulent pressure and relates spheroid star formation rate to black hole accretion rate. The relation between black hole mass and spheroid velocity dispersion has a coefficient (Salpeter time to gas consumption time ratio) that provides an arrow of time. Highly efficient, AGN-boosted star formation can occur at high redshift.

  1. Comparative internal kinematics of the H II regions in interacting and isolated galaxies: implications for massive star formation modes

    NASA Astrophysics Data System (ADS)

    Zaragoza-Cardiel, Javier; Beckman, John E.; Font, Joan; García-Lorenzo, Begoña; Camps-Fariña, Artemi; Fathi, Kambiz; James, Philip A.; Erroz-Ferrer, Santiago; Barrera-Ballesteros, Jorge; Cisternas, Mauricio

    2015-08-01

    We have observed 12 interacting galaxy pairs using the Fabry-Perot interferometer GH αFaS (Galaxy H α Fabry-Perot system) on the 4.2-m William Herschel Telescope at the Observatorio del Roque de los Muchachos, La Palma. We present here the Hα surface brightness, velocity and velocity dispersion maps for the 10 systems we have not previously observed using this technique, as well as the physical properties (sizes, Hα luminosities and velocity dispersion) of 1259 H II regions from the full sample. We also derive the physical properties of 1054 H II regions in a sample of 28 isolated galaxies observed with the same instrument in order to compare the two populations of H II regions. We find a population of the brightest H II regions for which the scaling relations, for example the relation between the Hα luminosity and the radius, are clearly distinct from the relations for the regions of lower luminosity. The regions in this bright population are more frequent in the interacting galaxies. We find that the turbulence, and also the star formation rate (SFR), are enhanced in the H II regions in the interacting galaxies. We have also extracted the Hα equivalent widths for the H II regions of both samples, and we have found that the distribution of H II region ages coincides for the two samples of galaxies. We suggest that the SFR enhancement is brought about by gas flows induced by the interactions, which give rise to gravitationally bound gas clouds which grow further by accretion from the flowing gas, producing conditions favourable to star formation.

  2. Dark influences II. Gas and star formation in minor mergers of dwarf galaxies with dark satellites

    NASA Astrophysics Data System (ADS)

    Starkenburg, T. K.; Helmi, A.; Sales, L. V.

    2016-03-01

    Context. It has been proposed that mergers induce starbursts and lead to important morphological changes in galaxies. Most studies so far have focused on large galaxies, but dwarfs might also experience such events, since the halo mass function is scale-free in the concordance cosmological model. Notably, because of their low mass, most of their interactions will be with dark satellites. Aims: In this paper we follow the evolution of gas-rich disky dwarf galaxies as they experience a minor merger with a dark satellite. We aim to characterize the effects of such an interaction on the dwarf's star formation, morphology, and kinematical properties. Methods: We performed a suite of carefully set-up hydrodynamical simulations of dwarf galaxies that include dark matter, gas, and stars merging with a satellite consisting solely of dark matter. For the host system we vary the gas fraction, disk size and thickness, halo mass, and concentration, while we explore different masses, concentrations, and orbits for the satellite. Results: We find that the interactions cause strong starbursts of both short and long duration in the dwarfs. Their star formation rates increase by factors of a few to 10 or more. They are strongest for systems with extended gas disks and high gas fractions merging with a high-concentration satellite on a planar, radial orbit. In contrast to analogous simulations of Milky Way-mass galaxies, many of the systems experience strong morphological changes and become spheroidal even in the presence of significant amounts of gas. Conclusions: The simulated systems compare remarkably well with the observational properties of a large selection of irregular dwarf galaxies and blue compact dwarfs. This implies that mergers with dark satellites might well be happening but not be fully evident, and may thus play a role in the diversity of the dwarf galaxy population.

  3. Star formation towards the southern cometary H II region IRAS 17256-3631

    NASA Astrophysics Data System (ADS)

    Veena, V. S.; Vig, S.; Tej, A.; Varricatt, W. P.; Ghosh, S. K.; Chandrasekhar, T.; Ashok, N. M.

    2016-03-01

    IRAS 17256-3631 is a southern Galactic massive star-forming region located at a distance of 2 kpc. In this paper, we present a multiwavelength investigation of the embedded cluster, the H II region, as well as the parent cloud. Radio images at 325, 610 and 1372 MHz were obtained using Giant Metrewave Radio Telescope, India while the near-infrared imaging and spectroscopy were carried out using United Kingdom Infrared Telescope and Mt. Abu Infrared Telescope, India. The near-infrared K-band image reveals the presence of a partially embedded infrared cluster. The spectral features of the brightest star in the cluster, IRS-1, spectroscopically agree with a late O or early B star and could be the driving source of this region. Filamentary H2 emission detected towards the outer envelope indicates the presence of highly excited gas. The parent cloud is investigated at far-infrared to millimetre wavelengths and 18 dust clumps have been identified. The spectral energy distributions of these clumps have been fitted as modified blackbodies and the best-fitting peak temperatures are found to range from 14 to 33 K, while the column densities vary from 0.7 to 8.5 × 1022 cm-2. The radio maps show a cometary morphology for the distribution of ionized gas that is density bounded towards the north-west and ionization bounded towards the south-east. This morphology is better explained with the champagne flow model as compared to the bow-shock model. Using observations at near-, mid- and far-infrared, submillimetre and radio wavelengths, we examine the evolutionary stages of various clumps.

  4. Understanding star formation in molecular clouds. II. Signatures of gravitational collapse of IRDCs

    NASA Astrophysics Data System (ADS)

    Schneider, N.; Csengeri, T.; Klessen, R. S.; Tremblin, P.; Ossenkopf, V.; Peretto, N.; Simon, R.; Bontemps, S.; Federrath, C.

    2015-06-01

    We analyse column density and temperature maps derived from Herschel dust continuum observations of a sample of prominent, massive infrared dark clouds (IRDCs) i.e. G11.11-0.12, G18.82-0.28, G28.37+0.07, and G28.53-0.25. We disentangle the velocity structure of the clouds using 13CO 1→0 and 12CO 3→2 data, showing that these IRDCs are the densest regions in massive giant molecular clouds (GMCs) and not isolated features. The probability distribution function (PDF) of column densities for all clouds have a power-law distribution over all (high) column densities, regardless of the evolutionary stage of the cloud: G11.11-0.12, G18.82-0.28, and G28.37+0.07 contain (proto)-stars, while G28.53-0.25 shows no signs of star formation. This is in contrast to the purely log-normal PDFs reported for near and/or mid-IR extinction maps. We only find a log-normal distribution for lower column densities, if we perform PDFs of the column density maps of the whole GMC in which the IRDCs are embedded. By comparing the PDF slope and the radial column density profile of three of our clouds, we attribute the power law to the effect of large-scale gravitational collapse and to local free-fall collapse of pre- and protostellar cores for the highest column densities. A significant impact on the cloud properties from radiative feedback is unlikely because the clouds are mostly devoid of star formation. Independent from the PDF analysis, we find infall signatures in the spectral profiles of 12CO for G28.37+0.07 and G11.11-0.12, supporting the scenario of gravitational collapse. Our results are in line with earlier interpretations that see massive IRDCs as the densest regions within GMCs, which may be the progenitors of massive stars or clusters. At least some of the IRDCs are probably the same features as ridges (high column density regions with N> 1023 cm-2 over small areas), which were defined for nearby IR-bright GMCs. Because IRDCs are only confined to the densest (gravity dominated

  5. A study of four galactic small H II regions: Searching for spontaneous and sequential star formation scenarios

    NASA Astrophysics Data System (ADS)

    Kang, Sung-Ju

    This thesis describes observational studies of four small star-forming H II regions (KR 7, KR 81, KR 120 and KR 140) and star-formation scenario associated with the Young Stellar Objects (YSOs) in each region. In addition to that, we also present an analysis of HCO+ (J=3→2) and H13CO+ (J=3→2) observations of the Massive (M ˜ 20 M[special character omitted] ) submillimeter/infrared source IRAS 01202+6133 located on the periphery of the H II region. In this research, we improved existing 1-D radiative transfer model for a collapsing core that happens in the early phase -- Class I protostar -- of star formation. The molecular gas surrounding an H II region is thought to be a place where star formation can be induced. We selected four small H II region in order to minimize the feedbacks and dynamics from multiple exciting sources. These regions are very young and ionized by the single O or B spectral type stars. A space based telescope Wide-field Infrared Survey Explorer (WISE) used for identifying and classifying the YSOs population surrounding a sample of H II regions. First, we used WISE data from AllWISE catalog with some constrains such as spatial coordinates, signal-to-noise ratio and contaminations. After we retrieved sources from catalog in each region, we classified YSOs with two different methods; color-color diagram and spectral index (alpha). Based on the color-color diagram using WISE 3.4 mum, 4.6 mum and 12 mum bands, we classified the YSOs as Class I, Class II and using 3.4 mum, 4.6 mum and 22 mum, we were able to classify Transition Disks and Class III YSOs. 2MASS and WISE combined color-color diagram also used in order to compare the classification only use of WISE color-color diagram. Considering a reddening effect from 2MASS Ks band, the classification from both WISE only and 2MASS, WISE combined color-colordiagram. A spectral index (alpha) also can be used as classifying YSOs. Based on the WISE magnitude, spectral index (alpha) can be derived

  6. Near-infrared radiation background, gravitational wave background, and star formation rate of Pop III and Pop II during cosmic reionization

    NASA Astrophysics Data System (ADS)

    Yang, Y. P.; Wang, F. Y.; Dai, Z. G.

    2015-10-01

    Context. The transition from Population III (Pop III) to Population II (Pop II) stars plays an important role in the history of the Universe. The huge amount of ionizing photons generated by Pop III stars begin to ionize the intergalactic medium (IGM) at the early stage of reionization. Meanwhile, the feedback from reionization and metal enrichment changes the evolution of different populations. The near-infrared radiation background (NIRB) and the stochastic background of gravitational waves (SBGWs) from these early stars will provide important information about the transition form Pop III to Pop II stars. Aims: We obtain the NIRB and SBGWs from the early stars, which are constrained by the observation of reionization and star formation rate (SFR). Methods: We studied the transition from Pop III to Pop II stars via the star formation model of different populations, which takes into account the reionization and the metal enrichment evolution. We calculated the two main metal pollution channels arising from the supernova-driven protogalactic outflows and genetic channel. We obtained the SFRs of Pop III and Pop II and their NIRB and SBGWs radiation. Results: We predict that the upper limit of metallicity in metal-enriched IGM (the galaxies that are polluted via the genetic channel) reaches Zcrit = 10-3.5 Z⊙ at z ~ 13 (z ~ 11), which is consistent with our star formation model. We constrain the SFR of Pop III stars from reionization observations. The peak intensity of NIRB is about 0.03 - 0.2 nWm-2 sr-1 at ~1 μm for z> 6. The predicted NIRB signal is consistent with the metallicity evolution. We also obtain the gravitational wave background from the black holes formed by these early stars. The predicted gravitational wave background has a peak amplitude of ΩGW ≃ 8 × 10-9 at ν = 158 Hz for Pop II star remnants. However, the background generated by Pop III.2 stars is much lower than that of Pop II stars, with a peak amplitude of ΩGW ≃ 1.2 × 10-11 at ν = 28

  7. Chemical evolution in the early phases of massive star formation. II. Deuteration

    NASA Astrophysics Data System (ADS)

    Gerner, T.; Shirley, Y. L.; Beuther, H.; Semenov, D.; Linz, H.; Albertsson, T.; Henning, Th.

    2015-07-01

    The chemical evolution in high-mass star-forming regions is still poorly constrained. Studying the evolution of deuterated molecules allows distinguishing between subsequent stages of high-mass star formation regions based on the strong temperature dependence of deuterium isotopic fractionation. We observed a sample of 59 sources including 19 infrared dark clouds, 20 high-mass protostellar objects, 11 hot molecular cores and 9 ultra-compact Hii regions in the (3-2) transitions of the four deuterated molecules, DCN, DNC, DCO+, and N2D+ as well as their non-deuterated counterparts. The overall detection fraction of DCN, DNC, and DCO+ is high and exceeds 50% for most of the stages. N2D+ was only detected in a few infrared dark clouds and high-mass protostellar objects. This may be related to problems in the bandpass at the transition frequency and to low abundances in the more evolved, warmer stages. We find median D/H ratios of 0.02 for DCN, 0.005 for DNC, 0.0025 for DCO+, and 0.02 for N2D+. While the D/H ratios of DNC, DCO+, and N2D+ decrease with time, DCN/HCN peaks at the hot molecular core stage. We only found weak correlations of the D/H ratios for N2D+ with the luminosity of the central source and the FWHM of the line, and no correlation with the H2 column density. In combination with a previously observed set of 14 other molecules (Paper I), we fitted the calculated column densities with an elaborate 1D physico-chemical model with time-dependent D-chemistry including ortho- and para-H2 states. Good overall fits to the observed data were obtained with the model. This is one of the first times that observations and modeling were combined to derive chemically based best-fit models for the evolution of high-mass star formation including deuteration. Appendix A is available in electronic form at http://www.aanda.org

  8. NGC 147, NGC 185 and CassII: a genetic approach to orbital properties, star formation and tidal debris

    NASA Astrophysics Data System (ADS)

    Arias, Veronica; Guglielmo, Magda; Fernando, Nuwanthika; Lewis, Geraint F.; Bland-Hawthorn, Joss; Bate, Nicholas F.; Conn, Anthony; Irwin, Mike J.; Ferguson, Annette M. N.; Ibata, Rodrigo A.; McConnachie, Alan W.; Martin, Nicolas

    2016-02-01

    NGC 147, NGC 185 and Cassiopeia II (CassII) have similar positions in the sky, distances and measured line-of-sight velocities. This proximity in phase space suggests that these three satellites of M31 form a subgroup within the Local Group. Nevertheless, the differences in their star formation history and interstellar medium, and the recent discovery of a stellar stream in NGC 147, combined with the lack of tidal features in the other two satellites, are all indications of complex and diverse interactions between M31 and these three satellites. We use a genetic algorithm to explore the different orbits that these satellites can have and select six sets of orbits that could best explain the observational features of the NGC 147, NGC 185 and CassII satellites. The parameters of these orbits are then used as a starting point for N-body simulations. We present models for which NGC 147, NGC 185 and CassII are a bound group for a total time of at least 1 Gyr but still undergo different interactions with M31 and as a result NGC 147 has a clear stellar stream, whereas the other two satellites have no significant tidal features. This result shows that it is possible to find solutions that reproduce the contrasting properties of the satellites and for which NGC 147-NGC 185-CassII have been gravitationally bound.

  9. Rotating Stars and the Formation of Bipolar Planetary Nebulae. II. Tidal Spin-up

    NASA Astrophysics Data System (ADS)

    García-Segura, G.; Villaver, E.; Manchado, A.; Langer, N.; Yoon, S.-C.

    2016-06-01

    We present new binary stellar evolution models that include the effects of tidal forces, rotation, and magnetic torques with the goal of testing planetary nebulae (PNs) shaping via binary interaction. We explore whether tidal interaction with a companion can spin-up the asymptotic giant brach (AGB) envelope. To do so, we have selected binary systems with main-sequence masses of 2.5 M ⊙ and 0.8 M ⊙ and evolve them allowing initial separations of 5, 6, 7, and 8 au. The binary stellar evolution models have been computed all the way to the PNs formation phase or until Roche lobe overflow (RLOF) is reached, whatever happens first. We show that with initial separations of 7 and 8 au, the binary avoids entering into RLOF, and the AGB star reaches moderate rotational velocities at the surface (∼3.5 and ∼2 km s‑1, respectively) during the inter-pulse phases, but after the thermal pulses it drops to a final rotational velocity of only ∼0.03 km s‑1. For the closest binary separations explored, 5 and 6 au, the AGB star reaches rotational velocities of ∼6 and ∼4 km s‑1, respectively, when the RLOF is initiated. We conclude that the detached binary models that avoid entering the RLOF phase during the AGB will not shape bipolar PNs, since the acquired angular momentum is lost via the wind during the last two thermal pulses. This study rules out tidal spin-up in non-contact binaries as a sufficient condition to form bipolar PNs.

  10. Molecules in star formation.

    NASA Astrophysics Data System (ADS)

    Shu, F. H.

    The author reviews current ideas and models in the problem of star formation from molecular cloud cores that are relatively isolated from the influences of other forming stars. He discusses the time scales, flow dynamics, and density and temperature structures applicable to each of the four stages of the entire process: (1) formation of a magnetized cloud core by ambipolar diffusion and evolution to a pivotal state of gravomagneto catastrophe; (2) self-similar collapse of the pivotal configuration and the formation of protostars, disks, and pseudo-disks; (3) onset of a magnetocentrifugally driven, lightly ionized wind from the interaction of an accretion disk and the magnetosphere of the central star, and the driving of bipolar molecular outflows; (4) evolution of pre-main-sequence stars surrounded by dusty accretion disks. For each of these stages and processes, he considers the characteristics of the molecular diagnostics needed to investigate the crucial aspects of the observational problem.

  11. A test of star formation laws in disk galaxies. II. Dependence on dynamical properties

    SciTech Connect

    Suwannajak, Chutipong; Tan, Jonathan C.; Leroy, Adam K.

    2014-05-20

    We use the observed radial profiles of the mass surface densities of total, Σ {sub g}, and molecular, Σ{sub H2}, gas, rotation velocity, and star formation rate (SFR) surface density, Σ{sub sfr}, of the molecular-rich (Σ{sub H2} ≥ Σ{sub HI}/2) regions of 16 nearby disk galaxies to test several star formation (SF) laws: a 'Kennicutt-Schmidt (K-S)' law, Σ{sub sfr}=A{sub g}Σ{sub g,2}{sup 1.5}; a 'Constant Molecular' law, Σ{sub sfr} = A {sub H2}Σ{sub H2,2}; the turbulence-regulated laws of Krumholz and McKee (KM05) and Krumholz, McKee, and Tumlinson (KMT09); a 'Gas-Ω' law, Σ{sub sfr}=B{sub Ω}Σ{sub g}Ω; and a shear-driven 'giant molecular cloud (GMC) Collision' law, Σ{sub sfr} = B {sub CC}Σ {sub g}Ω(1-0.7β), where β ≡ d ln v {sub circ}/d ln r. If allowed one free normalization parameter for each galaxy, these laws predict the SFR with rms errors of factors of 1.4-1.8. If a single normalization parameter is used by each law for the entire galaxy sample, then rms errors range from factors of 1.5-2.1. Although the Constant Molecular law gives the smallest rms errors, the improvement over the KMT, K-S, and GMC Collision laws is not especially significant, particularly given the different observational inputs that the laws utilize and the scope of included physics, which ranges from empirical relations to detailed treatment of interstellar medium processes. We next search for systematic variation of SF law parameters with local and global galactic dynamical properties of disk shear rate (related to β), rotation speed, and presence of a bar. We demonstrate with high significance that higher shear rates enhance SF efficiency per local orbital time. Such a trend is expected if GMC collisions play an important role in SF, while an opposite trend would be expected if the development of disk gravitational instabilities is the controlling physics.

  12. H II Region G46.5-0.2: The Interplay between Ionizing Radiation, Molecular Gas, and Star Formation

    NASA Astrophysics Data System (ADS)

    Paron, S.; Ortega, M. E.; Dubner, G.; Yuan, Jing-Hua; Petriella, A.; Giacani, E.; Li, Jin Zeng; Wu, Yuefang; Liu, Hongli; Huang, Ya Fang; Zhang, Si-Ju

    2015-06-01

    H ii regions are particularly interesting because they can generate dense layers of gas and dust, elongated columns or pillars of gas pointing toward the ionizing sources, and cometary globules of dense gas where triggered star formation can occur. Understanding the interplay between the ionizing radiation and the dense surrounding gas is very important to explain the origin of these peculiar structures, and hence to characterize triggered star formation. G46.5-0.2 (G46), a poorly studied galactic H ii region located at about 4 kpc, is an excellent target for performing this kind of study. Using public molecular data extracted from the Galactic Ring Survey (13CO J = 1-0) and from the James Clerk Maxwell Telescope data archive (12CO, 13CO, C18O J = 3-2, HCO+, and HCN J = 4-3), and infrared data from the GLIMPSE and MIPSGAL surveys, we perform a complete study of G46, its molecular environment, and the young stellar objects (YSOs) placed around it. We found that G46, probably excited by an O7V star, is located close to the edge of the GRSMC G046.34-00.21 molecular cloud. It presents a horse-shoe morphology opening in the direction of the cloud. We observed a filamentary structure in the molecular gas likely related to G46 and not considerable molecular emission toward its open border. We found that about 10‧ to the southwest of G46 there are some pillar-like features, shining at 8 μm and pointing toward the H ii region open border. We propose that the pillar-like features were carved and sculpted by the ionizing flux from G46. We found several YSOs likely embedded in the molecular cloud grouped in two main concentrations: one, closer to the G46 open border consisting of Class II type sources, and another mostly composed of Class I type YSOs located just ahead of the pillar-like features, strongly suggesting an age gradient in the YSO distribution.

  13. Star formation across galactic environments

    NASA Astrophysics Data System (ADS)

    Young, Jason

    . Complementing this study of normal star-forming galaxies, my study of quasar host galaxies utilizes narrow- and medium-band images of eight Palomar-Green (PG) quasars from the WFPC2 and NICMOS instruments aboard the Hubble Space Telescope. Using images of a point-spread function (PSF) star in the same filters, I subtract the PSF of the quasar from each of the target images. The residual light images clearly show the host galaxies of the respective quasars. The narrow-band images were chosen to be centered on the Hbeta, [O II ], [O III], and Paalpha emission lines, allowing the use of line ratios and luminosities to create extinction and star formation maps. Additionally, I utilize the line-ratio maps to distinguish AGN-powered line emission from star formation powered line emission with line-diagnostic diagrams. I find star formation in each of the eight quasar host galaxies in my study. The bulk star-formation rates are lower than expected, suggesting that quasar host galaxies may be dynamically more advanced than previously believed. Seven of the eight quasar host galaxies in this study have higher-than-typical mass-specific star-formation rates. Additionally, I see evidence of shocked gas, supporting the hypotheses presented in earlier works that suggest that AGN activity quenches star formation in its host galaxy by disrupting its gas reservoir.

  14. Enhancement of CO(3-2)/CO(1-0) ratios and star formation efficiencies in supergiant H II regions

    SciTech Connect

    Miura, Rie E.; Espada, Daniel; Komugi, Shinya; Nakanishi, Kouichiro; Sawada, Tsuyoshi; Fujii, Kosuke; Kawabe, Ryohei; Kohno, Kotaro; Tosaki, Tomoka; Hirota, Akihiko; Minamidani, Tetsuhiro; Okumura, Sachiko K.; Kuno, Nario; Muraoka, Kazuyuki; Onodera, Sachiko; Kaneko, Hiroyuki

    2014-06-20

    We present evidence that super giant H II regions (GHRs) and other disk regions of the nearby spiral galaxy, M33, occupy distinct locations in the correlation between molecular gas, Σ{sub H{sub 2}}, and the star formation rate surface density, Σ{sub SFR}. This result is based on wide-field and high-sensitivity CO(3-2) observations at 100 pc resolution. Star formation efficiencies (SFEs), defined as Σ{sub SFR}/Σ{sub H{sub 2}}, in GHRs are found to be ∼1 dex higher than in other disk regions. The CO(3-2)/CO(1-0) integrated intensity ratio, R {sub 3-2/1-0}, is also higher than the average over the disk. Such high SFEs and R {sub 3-2/1-0} can reach the values found in starburst galaxies, which suggests that GHRs may be the elements building up a larger-scale starburst region. Three possible contributions to high SFEs in GHRs are investigated: (1) the I {sub CO}-N(H{sub 2}) conversion factor, (2) the dense gas fraction traced by R {sub 3-2/1-0}, and (3) the initial mass function (IMF). We conclude that these starburst-like properties in GHRs can be interpreted by a combination of both a top-heavy IMF and a high dense gas fraction, but not by changes in the I {sub CO}-N(H{sub 2}) conversion factor.

  15. Isolating Triggered Star Formation

    SciTech Connect

    Barton, Elizabeth J.; Arnold, Jacob A.; Zentner, Andrew R.; Bullock, James S.; Wechsler, Risa H.; /KIPAC, Menlo Park /SLAC

    2007-09-12

    Galaxy pairs provide a potentially powerful means of studying triggered star formation from galaxy interactions. We use a large cosmological N-body simulation coupled with a well-tested semi-analytic substructure model to demonstrate that the majority of galaxies in close pairs reside within cluster or group-size halos and therefore represent a biased population, poorly suited for direct comparison to 'field' galaxies. Thus, the frequent observation that some types of galaxies in pairs have redder colors than 'field' galaxies is primarily a selection effect. We use our simulations to devise a means to select galaxy pairs that are isolated in their dark matter halos with respect to other massive subhalos (N= 2 halos) and to select a control sample of isolated galaxies (N= 1 halos) for comparison. We then apply these selection criteria to a volume-limited subset of the 2dF Galaxy Redshift Survey with M{sub B,j} {le} -19 and obtain the first clean measure of the typical fraction of galaxies affected by triggered star formation and the average elevation in the star formation rate. We find that 24% (30.5 %) of these L* and sub-L* galaxies in isolated 50 (30) h{sup -1} kpc pairs exhibit star formation that is boosted by a factor of {approx}> 5 above their average past value, while only 10% of isolated galaxies in the control sample show this level of enhancement. Thus, 14% (20 %) of the galaxies in these close pairs show clear triggered star formation. Our orbit models suggest that 12% (16%) of 50 (30) h{sup -1} kpc close pairs that are isolated according to our definition have had a close ({le} 30 h{sup -1} kpc) pass within the last Gyr. Thus, the data are broadly consistent with a scenario in which most or all close passes of isolated pairs result in triggered star formation. The isolation criteria we develop provide a means to constrain star formation and feedback prescriptions in hydrodynamic simulations and a very general method of understanding the importance of

  16. Comparing M31 and Milky Way satellites: The extended star formation histories of Andromeda II and Andromeda XVI

    SciTech Connect

    Weisz, Daniel R.; Skillman, Evan D.; McQuinn, Kristen B. W.; Hidalgo, Sebastian L.; Monelli, Matteo; Gallart, Carme; Aparicio, Antonio; McConnachie, Alan; Stetson, Peter B.; Bernard, Edouard J.; Boylan-Kolchin, Michael; Cassisi, Santi; Cole, Andrew A.; Ferguson, Henry C.; Irwin, Mike; Martin, Nicolas F.; Mayer, Lucio; Navarro, Julio F.

    2014-07-01

    We present the first comparison between the lifetime star formation histories (SFHs) of M31 and Milky Way (MW) satellites. Using the Advanced Camera for Surveys on board the Hubble Space Telescope, we obtained deep optical imaging of Andromeda II (And II; M{sub V} = –12.0; log(M {sub *}/M {sub ☉}) ∼ 6.7) and Andromeda XVI (And XVI; M{sub V} = –7.5; log(M {sub *}/M {sub ☉}) ∼ 4.9) yielding color-magnitude diagrams that extend at least 1 mag below the oldest main-sequence turnoff, and are similar in quality to those available for the MW companions. And II and And XVI show strikingly similar SFHs: both formed 50%-70% of their total stellar mass between 12.5 and 5 Gyr ago (z ∼ 5-0.5) and both were abruptly quenched ∼5 Gyr ago (z ∼ 0.5). The predominance of intermediate age populations in And XVI makes it qualitatively different from faint companions of the MW and clearly not a pre-reionization fossil. Neither And II nor And XVI appears to have a clear analog among MW companions, and the degree of similarity in the SFHs of And II and And XVI is not seen among comparably faint-luminous pairs of MW satellites. These findings provide hints that satellite galaxy evolution may vary substantially among hosts of similar stellar mass. Although comparably deep observations of more M31 satellites are needed to further explore this hypothesis, our results underline the need for caution when interpreting satellite galaxies of an individual system in a broader cosmological context.

  17. Jet-Induced Star Formation

    SciTech Connect

    van Breugel, W; Fragile, C; Anninos, P; Murray, S

    2003-12-16

    Jets from radio galaxies can have dramatic effects on the medium through which they propagate. We review observational evidence for jet-induced star formation in low ('FR-I') and high ('FR-II') luminosity radio galaxies, at low and high redshifts respectively. We then discuss numerical simulations which are aimed to explain a jet-induced starburst ('Minkowski's Object') in the nearby FR-I type radio galaxy NGC 541. We conclude that jets can induce star formation in moderately dense (10 cm{sup -3}), warm (10{sup 4} K) gas; that this may be more common in the dense environments of forming, active galaxies; and that this may provide a mechanism for 'positive' feedback from AGN in the galaxy formation process.

  18. Early phases of star formation

    NASA Astrophysics Data System (ADS)

    Bok, B. J.

    1981-04-01

    Five broad areas of potential star formation in our galaxy and the Magellanic Clouds are presented. The role of gravitational collapse in concentrating matter into eventual stars is examined briefly. The five areas of research are: (1) giant molecular clouds with dimensions of 50 to 100 parsecs and masses equivalent to 100,000 or more suns; (2) the proximity of an H II emission nebula with an embedded or attached cluster of association of O and B stars to a large molecular cloud; (3) the larger so-called globules, notably the roundish and often isolated dark nebulae called Barnard objects, of which 200 or so have been identified within 500 parsecs of the sun; (4) close passage or collisions between interstellar clouds; and (5) supernova explosions. The Large Magellanic Clouds are also examined as an example of an area of potential star formation without the protection of a cosmic dust cloud. Finally, the likelihood that many new stars might possess planets and perhaps even life is discussed.

  19. Embedded Protostellar Disks Around (Sub-)Solar Stars. II. Disk Masses, Sizes, Densities, Temperatures, and the Planet Formation Perspective

    NASA Astrophysics Data System (ADS)

    Vorobyov, Eduard I.

    2011-03-01

    We present basic properties of protostellar disks in the embedded phase of star formation (EPSF), which is difficult to probe observationally using available observational facilities. We use numerical hydrodynamics simulations of cloud core collapse and focus on disks formed around stars in the 0.03-1.0 M sun mass range. Our obtained disk masses scale near-linearly with the stellar mass. The mean and median disk masses in the Class 0 and I phases (M mean d,C0 = 0.12 M sun, M mdn d,C0 = 0.09 M sun and M mean d,CI = 0.18 M sun, M mdn d,CI = 0.15 M sun, respectively) are greater than those inferred from observations by (at least) a factor of 2-3. We demonstrate that this disagreement may (in part) be caused by the optically thick inner regions of protostellar disks, which do not contribute to millimeter dust flux. We find that disk masses and surface densities start to systematically exceed that of the minimum mass solar nebular for objects with stellar mass as low as M * = 0.05-0.1 M sun. Concurrently, disk radii start to grow beyond 100 AU, making gravitational fragmentation in the disk outer regions possible. Large disk masses, surface densities, and sizes suggest that giant planets may start forming as early as in the EPSF, either by means of core accretion (inner disk regions) or direct gravitational instability (outer disk regions), thus breaking a longstanding stereotype that the planet formation process begins in the Class II phase.

  20. Star Formation in Irregular Galaxies.

    ERIC Educational Resources Information Center

    Hunter, Deidre; Wolff, Sidney

    1985-01-01

    Examines mechanisms of how stars are formed in irregular galaxies. Formation in giant irregular galaxies, formation in dwarf irregular galaxies, and comparisons with larger star-forming regions found in spiral galaxies are considered separately. (JN)

  1. Multiple star formation

    NASA Astrophysics Data System (ADS)

    Kraus, Adam L.

    2010-11-01

    In this thesis, I present a study of the formation and evolution of stars, particularly multiple stellar systems. Binary stars provide a key constraint on star formation because any successful model should reproduce the mass-dependent frequency, distribution of separations, and distribution of mass ratios. I have pursued a number of surveys for different ranges of parameter space, all yielding one overarching conclusion: binary formation is fundamentally tied to mass. Solar-mass stars have a high primordial binary frequency (50%--75%) and a wide range of separations (extending to >10,000 AU), but as the system mass decreases, the frequency and separation distribution also decrease. For brown dwarfs, binaries are rare (~10%--15%) and have separations of <5 AU. Inside of this outer separation cutoff, the separation distribution appears to be log-flat for solar-mass stars, and perhaps for lower-mass systems. Solar-mass binary systems appear to have a flat mass ratio distribution, but for primary masses <0.3 Msun, the distribution becomes increasingly biased toward similar-mass companions. My results also constrain the binary formation timescale and the postformation evolutionary processes that sculpt binary populations. The dynamical interaction timescale in sparse associations like Taurus and Upper Sco is far longer than their ages, which suggests that those populations are dynamically pristine. However, binary systems in denser clusters undergo significant dynamical processing that strips outer binary companions; the difference in wide binary properties between my sample and the field is explained by the composite origin of the field population. I also have placed the individual components of young binary systems on the HR diagram in order to infer their coevality. In Taurus, binary systems are significantly more coeval (Δτ~0.5 Myr) than the association as a whole (Δτ~3--5 Myr). Finally, my survey of young very-low-mass stars and brown dwarfs found no planetary

  2. Processes and problems in secondary star formation

    SciTech Connect

    Klein, R.I.; Whitaker, R.W.; Sandford M.T. II

    1984-03-01

    Recent developments relating the conditions in molecular clouds to star formation triggered by a prior stellar generation are reviewed. Primary processes are those that lead to the formation of a first stellar generation. The secondary processes that produce stars in response to effects caused by existing stars are compared and evaluated in terms of the observational data presently available. We discuss the role of turbulence to produce clumpy cloud structures and introduce new work on colliding inter-cloud gas flows leading to non-linear inhomogeneous cloud structures in an intially smooth cloud. This clumpy morphology has important consequences for secondary formation. The triggering processes of supernovae, stellar winds, and H II regions are discussed with emphasis on the consequences for radiation driven implosion as a promising secondary star formation mechanism. Detailed two-dimensional, radiation-hydrodynamic calculations of radiation driven implosion are discussed. This mechanism is shown to be highly efficient in synchronizing the formation of new stars in congruent to 1-3 x 10/sup 4/ years and could account for the recent evidence for new massive star formation in several UCHII regions. It is concluded that, while no single theory adequately explains the variety of star formation observed, a uniform description of star formation is likely to involve several secondary processes. Advances in the theory of star formation will require multiple dimensional calculations of coupled processes. The important non-linear interactions include hydrodynamics, radiation transport, and magnetic fields.

  3. Star-formation in the Coalsack Loop

    NASA Astrophysics Data System (ADS)

    Golev, V.; Kaltcheva, N.

    The giant Galactic H II region known as the Coalsack Loop, which is associated with the H I supershell GSH 305+01-24, provides a unique opportunity to study the OB-star influence on the surrounding interstellar material. The bright OB-stars within this region contribute a sufficient wind injection energy consistent with the observed size and expansion velocity of the supershell. The derived age distribution of the OB-stars is suggestive for a continuous star-formation where the youngest stars are located at the supershell's periphery.

  4. Herschel Observations of the W3 GMC (II): Clues to the Formation of Clusters of High-mass Stars

    NASA Astrophysics Data System (ADS)

    Rivera-Ingraham, A.; Martin, P. G.; Polychroni, D.; Schneider, N.; Motte, F.; Bontemps, S.; Hennemann, M.; Men'shchikov, A.; Nguyen Luong, Q.; Zavagno, A.; André, Ph.; Bernard, J.-Ph.; Di Francesco, J.; Fallscheer, C.; Hill, T.; Könyves, V.; Marston, A.; Pezzuto, S.; Rygl, K. L. J.; Spinoglio, L.; White, G. J.

    2015-08-01

    The W3 giant molecular cloud is a prime target for investigating the formation of high-mass stars and clusters. This second study of W3 within the HOBYS Key Program provides a comparative analysis of subfields within W3 to further constrain the processes leading to the observed structures and stellar population. Probability density functions (PDFs) and cumulative mass distributions (CMDs) were created from dust column density maps, quantified as extinction {A}{{V}}. The shape of the PDF, typically represented with a lognormal function at low {A}{{V}} “breaking” to a power-law tail at high {A}{{V}}, is influenced by various processes including turbulence and self-gravity. The breaks can also be identified, often more readily, in the CMDs. The PDF break from lognormal ({A}{{V}}(SF) ≈ \\6-10 mag) appears to shift to higher {A}{{V}} by stellar feedback, so that high-mass star-forming regions tend to have higher PDF breaks. A second break at {A}{{V}}\\gt 50 mag traces structures formed or influenced by a dynamic process. Because such a process has been suggested to drive high-mass star formation in W3, this second break might then identify regions with potential for hosting high-mass stars/clusters. Stellar feedback appears to be a major mechanism driving the local evolution and state of regions within W3. A high initial star formation efficiency in a dense medium could result in a self-enhancing process, leading to more compression and favorable star formation conditions (e.g., colliding flows), a richer stellar content, and massive stars. This scenario would be compatible with the “convergent constructive feedback” model introduced in our previous Herschel study.

  5. Gaining Insight into Star Formation: Resolved Star Formation Laws

    NASA Astrophysics Data System (ADS)

    Liebst, Kelley; Scowen, Paul A.

    2014-06-01

    Until recently astronomers have used star formation laws to measure the star formation rate and star formation efficiency of galaxies only on global scales because of the poor resolution of available data. What I am now capable of producing is a spatially resolved star formation law that can provide direct insight into the physical processes that govern star formation and assess the short-term nature of bursts of star formation and the longer-term nature of larger-scale events that can dictate the global distribution of stars and the ultimate fate of a galaxy as a whole. I am using exquisite narrowband optical data from a variety of sources, including the Hubble Space Telescope, and Kitt Peak National Observatory, etc., in conjunction with infrared data from the Spitzer Infrared Nearby Galaxy Survey and the Spitzer Local Volume Legacy survey, neutral gas data from The HI Nearby Galaxy Survey, and molecular gas data from the Berkeley-Illinois-Maryland Association Survey of Nearby Galaxies, to provide star formation rates and star formation efficiencies on previously inaccessible small spatial scales across a suite of galaxies that represent a range of star formation environments and scales. My sample includes 18 spiral galaxies ranging from 2.1 to 15.1 Mpc in distance and offers a large range of morphological types (i.e. a large range of star formation environments). I am using these data to test different models of star formation modes under a variety of physical conditions and relate the variations I observe to the known local physical conditions and the associated star formation histories for each locale within each galaxy.This is the heart of the matter - that the nature and evolution of the local physical environment intimately influences how stars can form, how quickly and how massive those stars are allowed to form, and as a result how they shape the local conditions for subsequent star formation. It is this tracking of the stellar ecology that is vital for

  6. Multi-wavelength studies of spectacular ram-pressure stripping of a galaxy. II. Star formation in the tail

    SciTech Connect

    Yagi, Masafumi; Gu, Liyi; Nakazawa, Kazuhiro; Makishima, Kazuo; Fujita, Yutaka; Akahori, Takuya; Hattori, Takashi; Yoshida, Michitoshi

    2013-12-01

    With multiband photometric data in public archives, we detected four intracluster star-forming regions in the Virgo Cluster. Two of them were at a projected distance of 35 kpc from NGC 4388 and the other two were 66 kpc away. Our new spectroscopic observations revealed that their recessional velocities were comparable to the ram-pressure-stripped tail of NGC 4388 and confirmed the association. The stellar mass of the star-forming regions ranged from 10{sup 4} to 10{sup 4.5} M {sub ☉} except for that of the faintest one, which was <10{sup 3} M {sub ☉}. The metallicity was comparable to a solar abundance and the age of the stars was ∼10{sup 6.8} yr. Their young stellar age meant that the star formation should have started after the gas was stripped from NGC 4388. This implied in situ condensation of the stripped gas. We also found that two star-forming regions were located near the leading edge of a filamentary dark cloud. The extinction of the filament was smaller than that derived from the Balmer decrement of the star-forming regions, implying that the dust in the filament would be locally dense around the star-forming regions.

  7. THE COORDINATED RADIO AND INFRARED SURVEY FOR HIGH-MASS STAR FORMATION. II. SOURCE CATALOG

    SciTech Connect

    Purcell, C. R.; Hoare, M. G.; Lumsden, S. L.; Urquhart, J. S.; Cotton, W. D.; Chandler, C.; Churchwell, E. B.; Diamond, P.; Fuller, G.; Garrington, S. T.; Dougherty, S. M.; Fender, R. P.; Gledhill, T. M.; Goldsmith, P. F.; Hindson, L.; Jackson, J. M.; Kurtz, S. E.; Marti, J. [Departamento de Fisica, EPSJ, Universidad de Jaen, Campus Las Lagunillas s and others

    2013-03-01

    The CORNISH project is the highest resolution radio continuum survey of the Galactic plane to date. It is the 5 GHz radio continuum part of a series of multi-wavelength surveys that focus on the northern GLIMPSE region (10 Degree-Sign < l < 65 Degree-Sign ), observed by the Spitzer satellite in the mid-infrared. Observations with the Very Large Array in B and BnA configurations have yielded a 1.''5 resolution Stokes I map with a root mean square noise level better than 0.4 mJy beam{sup -1}. Here we describe the data-processing methods and data characteristics, and present a new, uniform catalog of compact radio emission. This includes an implementation of automatic deconvolution that provides much more reliable imaging than standard CLEANing. A rigorous investigation of the noise characteristics and reliability of source detection has been carried out. We show that the survey is optimized to detect emission on size scales up to 14'' and for unresolved sources the catalog is more than 90% complete at a flux density of 3.9 mJy. We have detected 3062 sources above a 7{sigma} detection limit and present their ensemble properties. The catalog is highly reliable away from regions containing poorly sampled extended emission, which comprise less than 2% of the survey area. Imaging problems have been mitigated by down-weighting the shortest spacings and potential artifacts flagged via a rigorous manual inspection with reference to the Spitzer infrared data. We present images of the most common source types found: H II regions, planetary nebulae, and radio galaxies. The CORNISH data and catalog are available online at http://cornish.leeds.ac.uk.

  8. He II emitters in the VIMOS VLT Deep Survey: Population III star formation or peculiar stellar populations in galaxies at 2 < z < 4.6?

    NASA Astrophysics Data System (ADS)

    Cassata, P.; Le Fèvre, O.; Charlot, S.; Contini, T.; Cucciati, O.; Garilli, B.; Zamorani, G.; Adami, C.; Bardelli, S.; Le Brun, V.; Lemaux, B.; Maccagni, D.; Pollo, A.; Pozzetti, L.; Tresse, L.; Vergani, D.; Zanichelli, A.; Zucca, E.

    2013-08-01

    Aims: The aim of this work is to identify He II emitters at 2 < z < 4.6 and to constrain the source of the hard ionizing continuum that powers the He II emission. Methods: We assembled a sample of 277 galaxies with a highly reliable spectroscopic redshift at 2 < z < 4.6 from the VIMOS-VLT Deep Survey (VVDS) Deep and Ultra-Deep data, and we identified 39 He II λ1640 emitters. We studied their spectral properties, measuring the fluxes, equivalent widths (EW), and full width at half maximum (FWHM) for most relevant lines, including He II λ1640, Lyα line, Si II λ1527, and C IV λ1549. Results: About 10% of galaxies at z ~ 3 and iAB ≤ 24.75 show He II in emission, with rest frame equivalent widths EW0 ~ 1-7 Å, equally distributed between galaxies with Lyα in emission or in absorption. We find 11 (3.9% of the global population) reliable He II emitters with unresolved He II lines (FWHM0 < 1200 km s-1), 13 (4.6% of the global population) reliable emitters with broad He II emission (FWHM0 > 1200 km s-1), 3 active galactic nuclei (AGN), and an additional 12 possible He II emitters. The properties of the individual broad emitters are in agreement with expectations from a Wolf-Rayet (W-R) model. Instead, the properties of the narrow emitters are not compatible with this model, nor with predictions of gravitational cooling radiation produced by gas accretion, unless this is severely underestimated by current models by more than two orders of magnitude. Rather, we find that the EW of the narrow He II line emitters are in agreement with expectations for a Population III (PopIII) star formation, if the episode of star formation is continuous, and we calculate that a PopIII star formation rate (SFR) of 0.1-10 M⊙ yr-1 alone is enough to sustain the observed He II flux. Conclusions: We conclude that narrow He II emitters are powered either by the ionizing flux from a stellar population rare at z ~ 0 but much more common at z ~ 3, or by PopIII star formation. As proposed by

  9. APERTURE SYNTHESIS OBSERVATIONS OF CO, HCN, AND 89 GHz CONTINUUM EMISSION TOWARD NGC 604 IN M33: SEQUENTIAL STAR FORMATION INDUCED BY A SUPERGIANT H II REGION

    SciTech Connect

    Miura, Rie; Okumura, Sachiko K.; Kurono, Yasutaka; Nakanishi, Kouichiro; Tosaki, Tomoka; Tamura, Yoichi; Kuno, Nario; Kawabe, Ryohei; Sakamoto, Seiichi; Hasegawa, Takashi

    2010-12-01

    We present the results from new Nobeyama Millimeter Array observations of CO(1-0), HCN(1-0), and 89 GHz continuum emission toward NGC 604, known as the supergiant H II region in the nearby galaxy M33. Our high spatial resolution images (4.''2 x 2.''6, corresponding to 17 pc x 11 pc physical size) of CO emission allowed us to uncover 10 individual molecular clouds that have masses of (0.8-7.4) x10{sup 5} M{sub sun} and sizes of 5-29 pc, comparable to those of typical Galactic giant molecular clouds. Moreover, we detected for the first time HCN emission in the two most massive clouds and 89 GHz continuum emission at the rims of the 'H{alpha} shells'. The HCN and 89 GHz continuum emission are offset from the CO peak and are distributed in the direction of the central cluster. Three out of ten CO clouds are well correlated with the H{alpha} shells both in spatial and velocity domains, implying an interaction between molecular gas and the expanding H II region. The CO clouds show varieties in star formation efficiencies (SFEs), which are estimated from the 89 GHz emission and combination of H{alpha} and Spitzer 24 {mu}m data. Furthermore, we found that the SFEs decrease with increasing projected distance measured from the heart of the central OB star cluster in NGC 604, suggesting radial changes in the evolutionary stages of the molecular clouds in the course of stellar cluster formation. Our results provide further support to the picture of sequential star formation in NGC 604 initially proposed by Tosaki et al. with the higher spatially resolved molecular clouds, in which an isotropic expansion of the H II region pushes gases outward, which accumulates to form dense molecular clouds, and then induces massive star formations.

  10. Ultraviolet studies of the Magellanic Clouds. II - Internal extinction, formation of massive stars, comparison with other galaxies

    NASA Astrophysics Data System (ADS)

    Vangioni-Flam, E.; Lequeux, J.; Maucherat-Joubert, M.; Rocca-Volmerange, B.

    1980-10-01

    The absolute integrated UV fluxes of the Magellanic Clouds measured by the D 2 B-Aura satellite (Maucherat-Joubert et al., 1980, Paper I) are corrected from interstellar extinction. For the purpose of this correction, we give a detailed discussion of the internal extinction in these galaxies. The corrected fluxes at 1690 Å are compared to the flux calculated for the solar neighbourhood, and used to compare the rate of massive star formation in the three regions. The rate per unit mass of gas is similar in the Large Magellanic Cloud and near the Sun, but 4 times smaller in the Small Magellanic Cloud. We also build quantitative upper HR diagrams and we find that the number of stars contained in similar portions of these diagrams and normalized to the far UV luminosity is roughly the same in all three objects. However, the Small Cloud appears to have relatively more of the brightest stars than the Large Cloud, and the latter than the Galaxy. We discuss the inference of these results on the rate of star formation and the Initial Mass Function. We discuss also for the sake of comparison the case of the irregular galaxies IC 1613, NGC 1569, 4449, 4490, 6822, and of the blue compact galaxy IZw 18.

  11. Star formation in the multiverse

    SciTech Connect

    Bousso, Raphael; Leichenauer, Stefan

    2009-03-15

    We develop a simple semianalytic model of the star formation rate as a function of time. We estimate the star formation rate for a wide range of values of the cosmological constant, spatial curvature, and primordial density contrast. Our model can predict such parameters in the multiverse, if the underlying theory landscape and the cosmological measure are known.

  12. Physics of primordial star formation

    NASA Astrophysics Data System (ADS)

    Yoshida, Naoki

    2012-09-01

    The study of primordial star formation has a history of nearly sixty years. It is generally thought that primordial stars are one of the key elements in a broad range of topics in astronomy and cosmology, from Galactic chemical evolution to the formation of super-massive blackholes. We review recent progress in the theory of primordial star formation. The standard theory of cosmic structure formation posits that the present-day rich structure of the Universe developed through gravitational amplification of tiny matter density fluctuations left over from the Big Bang. It has become possible to study primordial star formation rigorously within the framework of the standard cosmological model. We first lay out the key physical processes in a primordial gas. Then, we introduce recent developments in computer simulations. Finally, we discuss prospects for future observations of the first generation of stars.

  13. Star Formation for Predictive Primordial Galaxy Formation

    NASA Astrophysics Data System (ADS)

    Milosavljević, Miloš; Safranek-Shrader, Chalence

    The elegance of inflationary cosmology and cosmological perturbation theory ends with the formation of the first stars and galaxies, the initial sources of light that launched the phenomenologically rich process of cosmic reionization. Here we review the current understanding of early star formation, emphasizing unsolved problems and technical challenges. We begin with the first generation of stars to form after the Big Bang and trace how they influenced subsequent star formation. The onset of chemical enrichment coincided with a sharp increase in the overall physical complexity of star forming systems. Ab-initio computational treatments are just now entering the domain of the predictive and are establishing contact with local observations of the relics of this ancient epoch.

  14. Embedded star clusters and the formation of the Oort cloud. II. The effect of the primordial solar nebula

    NASA Astrophysics Data System (ADS)

    Brasser, R.; Duncan, M. J.; Levison, H. F.

    2007-11-01

    This paper deals with Oort cloud formation while the Sun was in an embedded cluster and surrounded by its primordial nebula. This work is a continuation of Brasser et al. [Brasser, R., Duncan, M., Levison, H., 2006. Icarus 184, 59-82], building on the model presented therein, and adding the aerodynamic drag and gravitational potential of the primordial solar nebula. Results are presented of numerical simulations of comets subject to the gravitational influence of the Sun, Jupiter, Saturn, star cluster and primordial solar nebula; some of the simulations included the gravitational influence of Uranus and Neptune as well. The primordial solar nebula was approximated by the minimum-mass Hayashi model [Hayashi, C., Nakozawa, K., Nakagawa, Y., 1985. In: Black, D.C., Matthews, M.S. (Eds.). Protostars and Planets II. Univ. of Arizona Press, Tucson, AZ] whose inner and outer radii have been truncated at various distances from the Sun. A comet size of 1.7 km was used for most of our simulations. In all of our simulations, the density of the primordial solar nebula decayed exponentially with an e-folding time of 2 Myr. It turns out that when the primordial solar nebula extends much beyond Saturn or Neptune, virtually no material will end up in the Oort cloud (OC) during this phase. Instead, the majority of the material will be on circular orbits inside of Jupiter if the inner edge of the disk is well inside Jupiter's orbit. If the disk's inner edge is beyond Jupiter's orbit, most comets end up on orbits in exterior mean-motion resonances with Saturn when Uranus and Neptune are not present. In those cases where the outer edge of the disk is close to Saturn or Neptune, the fraction of material that ends up in the subsequently formed OC is much less than that found in Brasser et al. [Brasser, R., Duncan, M., Levison, H., 2006. Icarus 184, 59-82] for the same cluster densities. This implies that for comets of roughly 2 km in size, the presence of the primordial solar nebula

  15. Star formation in Galactic flows

    NASA Astrophysics Data System (ADS)

    Smilgys, Romas; Bonnell, Ian A.

    2016-06-01

    We investigate the triggering of star formation in clouds that form in Galactic scale flows as the interstellar medium passes through spiral shocks. We use the Lagrangian nature of smoothed particle hydrodynamics simulations to trace how the star-forming gas is gathered into self-gravitating cores that collapse to form stars. Large-scale flows that arise due to Galactic dynamics create shocks of the order of 30 km s-1 that compress the gas and form dense clouds (n > several × 102 cm-3) in which self-gravity becomes relevant. These large-scale flows are necessary for creating the dense physical conditions for gravitational collapse and star formation. Local gravitational collapse requires densities in excess of n > 103 cm-3 which occur on size scales of ≈1 pc for low-mass star-forming regions (M < 100 M⊙), and up to sizes approaching 10 pc for higher mass regions (M > 103 M⊙). Star formation in the 250 pc region lasts throughout the 5 Myr time-scale of the simulation with a star formation rate of ≈10-1 M⊙ yr-1 kpc-2. In the absence of feedback, the efficiency of the star formation per free-fall time varies from our assumed 100 per cent at our sink accretion radius to values of <10-3 at low densities.

  16. Hubble Tarantula Treasury Project. II. The Star-formation History of the Starburst Region NGC 2070 in 30 Doradus

    NASA Astrophysics Data System (ADS)

    Cignoni, M.; Sabbi, E.; van der Marel, R. P.; Tosi, M.; Zaritsky, D.; Anderson, J.; Lennon, D. J.; Aloisi, A.; de Marchi, G.; Gouliermis, D. A.; Grebel, E. K.; Smith, L. J.; Zeidler, P.

    2015-10-01

    We present a study of the recent star formation (SF) of 30 Doradus in the Large Magellanic Cloud (LMC) using the panchromatic imaging survey Hubble Tarantula Treasury Project. In this paper we focus on the stars within 20 pc of the center of 30 Doradus, the starburst region NGC 2070. We recovered the SF history by comparing deep optical and near-infrared color-magnitude diagrams (CMDs) with state-of-the-art synthetic CMDs generated with the latest PAdova and TRieste Stellar Evolution Code (PARSEC) models, which include all stellar phases from pre-main-sequence to post-main-sequence. For the first time in this region we are able to measure the SF using intermediate- and low-mass stars simultaneously. Our results suggest that NGC 2070 experienced prolonged activity. In particular, we find that the SF in the region (1) exceeded the average LMC rate ≈ 20 Myr ago, (2) accelerated dramatically ≈ 7 Myr ago, and (3) reached a peak value 1-3 Myr ago. We did not find significant deviations from a Kroupa initial mass function down to 0.5 {M}⊙ . The average internal reddening E(B-V) is found to be between 0.3 and 0.4 mag. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA Inc., under NASA contract NAS 5-26555.

  17. The interstellar medium and star formation in edge-on galaxies. II. NGC 4157, 4565, and 5907

    SciTech Connect

    Yim, Kijeong; Wong, Tony; Xue, Rui; Rand, Richard J.; Rosolowsky, Erik; Hulst, J. M. van der; Benjamin, Robert; Murphy, Eric J.

    2014-12-01

    We present a study of the vertical structure of the gaseous and stellar disks in a sample of edge-on galaxies (NGC 4157, 4565, and 5907) using BIMA/CARMA {sup 12}COJ=1→0, VLA Hi, and Spitzer 3.6 μm data. In order to take into account projection effects when we measure the disk thickness as a function of radius, we first obtain the inclination by modeling the radio data. Using the measurement of the disk thicknesses and the derived radial profiles of gas and stars, we estimate the corresponding volume densities and vertical velocity dispersions. Both stellar and gas disks have smoothly varying scale heights and velocity dispersions, contrary to assumptions of previous studies. Using the velocity dispersions, we find that the gravitational instability parameter Q follows a fairly uniform profile with radius and is ⩾1 across the star-forming disk. The star formation law has a slope that is significantly different from those found in more face-on galaxy studies, both in deprojected and pixel-by-pixel plots. Midplane gas pressure based on the varying scale heights and velocity dispersions appears to roughly hold a power-law correlation with the midplane volume density ratio.

  18. Modes of clustered star formation

    NASA Astrophysics Data System (ADS)

    Pfalzner, S.; Kaczmarek, T.; Olczak, C.

    2012-09-01

    Context. The recent realization that most stars form in clusters, immediately raises the question of whether star and planet formation are influenced by the cluster environment. The stellar density in the most prevalent clusters is the key factor here. Whether dominant modes of clustered star formation exist is a fundamental question. Using near-neighbour searches in young clusters, Bressert and collaborators claim this not to be the case. They conclude that - at least in the solar neighbourhood - star formation is continuous from isolated to densely clustered environments and that the environment plays a minor role in star and planet formation. Aims: We investigate under which conditions near-neighbour searches in young clusters can distinguish between different modes of clustered star formation. Methods: Model star clusters with different memberships and density distributions are set up and near-neighbour searches are performed. We investigate the influence of the combination of different cluster modes, observational biases, and types of diagnostic on the results. Results: We find that the specific cluster density profile, the relative sample sizes, the limitations of the observation, and the choice of diagnostic method decide, whether modelled modes of clustered star formation are detected by near-neighbour searches. For density distributions that are centrally concentrated but span a wide density range (for example, King profiles), separate cluster modes are only detectable under ideal conditions (sample selection, completeness) if the mean density of the individual clusters differs by at least a factor of ~65. Introducing a central cut-off can lead to an underestimate of the mean density by more than a factor of ten especially in high density regions. The environmental effect on star and planet formation is similarly underestimated for half of the population in dense systems. Conclusions: Local surface-density distributions are a very useful tool for single

  19. Characterizing Spiral Arm and Interarm Star Formation

    NASA Astrophysics Data System (ADS)

    Kreckel, K.; Blanc, G. A.; Schinnerer, E.; Groves, B.; Adamo, A.; Hughes, A.; Meidt, S.

    2016-08-01

    Interarm star formation contributes significantly to a galaxy’s star formation budget and provides an opportunity to study stellar birthplaces unperturbed by spiral arm dynamics. Using optical integral field spectroscopy of the nearby galaxy NGC 628 with VLT/MUSE, we construct Hα maps including detailed corrections for dust extinction and stellar absorption to identify 391 H ii regions at 35 pc resolution over 12 kpc2. Using tracers sensitive to the underlying gravitational potential, we associate H ii regions with either arm (271) or interarm (120) environments. Using our full spectral coverage of each region, we find that most physical properties (luminosity, size, metallicity, ionization parameter) of H ii regions are independent of environment. We calculate the fraction of Hα luminosity due to the background of diffuse ionized gas (DIG) contaminating each H ii region, and find the DIG surface brightness to be higher within H ii regions than in the surroundings, and slightly higher within arm H ii regions. Use of the temperature-sensitive [S ii]/Hα line ratio instead of the Hα surface brightness to identify the boundaries of H ii regions does not change this result. Using the dust attenuation as a tracer of the gas, we find depletion times consistent with previous work (2 × 109 yr) with no differences between the arm and interarm, but this is very sensitive to the DIG correction. Unlike molecular clouds, which can be dynamically affected by the galactic environment, we see fairly consistent properties of H ii regions in both arm and interarm environments. This suggests either a difference in star formation and feedback in arms or a decoupling of dense star-forming clumps from the more extended surrounding molecular gas.

  20. Star Formation in the First Galaxies

    NASA Astrophysics Data System (ADS)

    Bromm, V.

    2016-05-01

    The formation of the first stars and galaxies mark the end of the cosmic dark ages, thus transforming the universe from its initial, pristine state into one of increasing complexity. We will review the current understanding, based on numerical simulations, of this crucial transition in early cosmic history. Specifically, the epoch of first light is predicted to be a two-stage process, where predominantly massive Population III stars form out of pure hydrogen-helium gas in small dark-matter minihalos, followed by Population II stars out of already metal-enriched material inside more massive host halos. Observations with upcoming next-generation telescopes promise to test our emerging theoretical picture of star formation in the first galaxies in ever inceasing detail.

  1. Star formation in the inner Galaxy - a far-infrared and radio study of two H II regions

    SciTech Connect

    Lester, D.F.; Dinerstein, H.L.; Harvey, P.M.; Evans, N.J. II; Werner, M.W.

    1985-09-01

    Far-infrared and radio continuum maps have been made of two inner-Galaxy H II region complexes, G30.8-0.0 and G25.4-0.2, along with radio and molecular line measurements at selected positions. The far-IR emission from each region is dominated by two sources. For both G25.4 and G30.8, the distribution of the emission is similar to that of the radio emission, indicating that OB stars provide most of the heating. There is evidence that extinction plays an important role in G30.8, even in the far-IR. A near-IR point source has been detected in G30.8 at the position of peak far-IR color temperature. This source may be the ionizing star for the core of G30.8. Measurement of forbidden S III 9532 A from G25.4SE indicates that the extinction toward this source is very low, which is difficult to reconcile with previously determined distance measurements to this source. 49 references.

  2. DWARF GALAXY FORMATION WITH H{sub 2}-REGULATED STAR FORMATION. II. GAS-RICH DARK GALAXIES AT REDSHIFT 2.5

    SciTech Connect

    Kuhlen, Michael; Madau, Piero; Krumholz, Mark R.

    2013-10-10

    We present a cosmological hydrodynamic simulation of the formation of dwarf galaxies at redshifts z ∼> 2.5 using a physically motivated model for H{sub 2}-regulated star formation. Our simulation, performed using the Enzo code and reaching a peak resolution of 109 proper parsecs at z = 2.5, extends the results of Kuhlen et al. to significantly lower redshifts. We show that a star formation prescription regulated by the local H{sub 2} abundance leads to the suppression of star formation in dwarf galaxy halos with M{sub h} ∼< 10{sup 10} M{sub ☉} and to a large population of gas-rich 'dark galaxies' at z = 2.5 with low star formation efficiencies and gas depletion timescales >20 Gyr. The fraction of dark galaxies is 60% at M{sub h} ≅ 10{sup 10} M{sub ☉} and increases rapidly with decreasing halo mass. Dark galaxies form late and their gaseous disks never reach the surface densities, ∼> 5700 M{sub ☉} pc{sup –2} (Z/10{sup –3} Z{sub ☉}){sup –0.88}, that are required to build a substantial molecular fraction. Despite this large population of dark galaxies, we show that our H{sub 2}-regulated simulation is consistent with both the observed luminosity function of galaxies and the cosmological mass density of neutral gas at z ∼> 2.5. Moreover, our results provide a theoretical explanation for the recent detection in fluorescent Lyα emission of gaseous systems at high redshift with little or no associated star formation. We further propose that H{sub 2}-regulation may offer a fresh solution to a number of outstanding 'dwarf galaxy problems' in ΛCDM. In particular, H{sub 2}-regulation leads galaxy formation to become effectively stochastic on mass scales of M{sub h} ∼ 10{sup 10} M{sub ☉}, and thus these massive dwarfs are not 'too big to fail'.

  3. High-Mass Star Formation

    NASA Astrophysics Data System (ADS)

    Schilke, P.

    2016-05-01

    A review on current theories and observations of high-mass star formation is given. Particularly the influence of magnetic fields and feedback mechanisms, and of varying initial conditions on theories are discussed. The, in my biased view, most important observations to put strong constraints on models of high-mass star formation are presented, in particular bearing on the existence and properties of high-mass starless cores, the role of filaments in the mass transport to high-mass cores, and the properties of disks around high-mass stars.

  4. PROBING THE LOW-REDSHIFT STAR FORMATION RATE AS A FUNCTION OF METALLICITY THROUGH THE LOCAL ENVIRONMENTS OF TYPE II SUPERNOVAE

    SciTech Connect

    Stoll, R.; Stanek, K. Z.; Pogge, R. W.; Prieto, J. L.

    2013-08-10

    Type II supernovae (SNe) can be used as a star formation tracer to probe the metallicity distribution of global low-redshift star formation. We present oxygen and iron abundance distributions of Type II SN progenitor regions that avoid many previous sources of bias. Because iron abundance, rather than oxygen abundance, is of key importance for the late stage evolution of the massive stars that are the progenitors of core-collapse supernovae, and because iron enrichment lags oxygen enrichment, we find a general conversion from oxygen abundance to iron abundance. The distributions we present here are the best yet observational standard of comparison for evaluating how different classes of supernovae depend on progenitor metallicity. We spectroscopically measure the gas-phase oxygen abundance near a representative subsample of the hosts of Type II SNe from the first-year Palomar Transient Factory (PTF) SN search, using a combination of Sloan Digital Sky Survey (SDSS) spectra near the SN location (9 hosts) and new longslit spectroscopy (25 hosts). The median metallicity of these 34 hosts at or near the SN location is 12+log(O/H) = 8.65, with a median error of 0.09. The median host galaxy stellar mass from fits to SDSS photometry is 10{sup 9.9} M{sub Sun }. They do not show a systematic offset in metallicity or mass from a redshift-matched sample of the MPA/JHU value-added catalog. In contrast to previous SN host metallicity studies, this sample is drawn from a single survey. It is also drawn from an areal rather than a targeted survey, so SNe in the lowest-mass galaxies are not systematically excluded. Indeed, the PTF SN search has a slight bias toward following up transients in low mass galaxies. The progenitor region metallicity distribution we find is statistically indistinguishable from the metallicity distribution of Type II SN hosts found by targeted surveys and by samples from multiple surveys with different selection functions. Using the relationship between

  5. Star formation in unperturbed LIRGs

    NASA Astrophysics Data System (ADS)

    Fuentes-Carrera, I.; Olguín, L.; Ambrocio-Cruz, P.; Verley, S.; Rosado, M.; Verdes-Montenegro, L.; Repetto, P.; Vázquez, C.; Aguilera, V.

    2011-10-01

    Luminous infrared galaxies (LIRGs) are galaxies with L_{FIR} > 10^11 L_{sun} (Sanders & Mirabel 1996). For a star-forming galaxy to emit at a LIRG level, it must have a very high star formation rate (SFR). In the local Universe, the star formation (SF) is primarily triggered by interactions. However, at intermediate redshift, a large fraction of LIRGs are disk galaxies with little sign of recent merger activity (Zheng et al. 2004). The question arises whether the intermediate redshift LIRGs are ``triggered'' or experiencing ``normal'', if elevated, SF. Understanding these SF processes is important since this type of systems may have contributed to 20% or more of the cosmic star-formation rate in the early Universe (Blain & Phillips 2002).

  6. THE M81 GROUP DWARF IRREGULAR GALAXY DDO 165. II. CONNECTING RECENT STAR FORMATION WITH INTERSTELLAR MEDIUM STRUCTURES AND KINEMATICS

    SciTech Connect

    Cannon, John M.; Most, Hans P.; Skillman, Evan D.; Weisz, Daniel R.; Warren, Steven R. E-mail: hmost@macalester.edu E-mail: dweisz@astro.umn.edu

    2011-07-01

    We compare the stellar populations and complex neutral gas dynamics of the M81 group dIrr galaxy DDO 165 using data from the Hubble Space Telescope and the Very Large Array. Cannon et al. in Paper I of this series identified two kinematically distinct H I components, multiple localized high velocity gas features, and eight H I holes and shells (the largest of which spans {approx}2.2 x 1.1 kpc). Using the spatial and temporal information from the stellar populations in DDO 165, we compare the patterns of star formation (SF) over the past 500 Myr with the H I dynamics. We extract localized star formation histories within 6 of the 8 H I holes identified in Paper I, as well as 23 other regions that sample a range of stellar densities and neutral gas properties. From population synthesis modeling, we derive the energy outputs (from stellar winds and supernovae) of the stellar populations within these regions over the last 100 Myr, and compare with refined estimates of the energies required to create the H I holes. In all cases, we find that 'feedback' is energetically capable of creating the observed structures in the interstellar medium (ISM). Numerous regions with significant energy inputs from feedback lack coherent H I structures but show prominent localized high velocity gas features; this feedback signature is a natural product of temporally and spatially distributed SF. In DDO 165, the extended period of heightened SF activity (lasting more than 1 Gyr) is energetically capable of creating the observed holes and high velocity gas features in the neutral ISM.

  7. Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars. II. Spectral line formation in the atmosphere of a giant located near the RGB tip

    NASA Astrophysics Data System (ADS)

    Kučinskas, A.; Steffen, M.; Ludwig, H.-G.; Dobrovolskas, V.; Ivanauskas, A.; Klevas, J.; Prakapavičius, D.; Caffau, E.; Bonifacio, P.

    2013-01-01

    Aims: We investigate the role of convection in the formation of atomic and molecular lines in the atmosphere of a red giant star. For this purpose we study the formation properties of spectral lines that belong to a number of astrophysically important tracer elements, including neutral and singly ionized atoms (Li I, N I, O I, Na I, Mg I, Al I, Si I, Si II, S I, K I, Ca I, Ca II, Ti I, Ti II, Cr I, Cr II, Mn I, Fe I, Fe II, Co I, Ni I, Zn I, Sr II, Ba II, and Eu II), and molecules (CH, CO, C2, NH, CN, and OH). Methods: We focus our investigation on a prototypical red giant located close to the red giant branch (RGB) tip (Teff = 3660 K, log g = 1.0, [M/H] = 0.0). We used two types of model atmospheres, 3D hydrodynamical and classical 1D, calculated with the CO5BOLD and LHD stellar atmosphere codes, respectively. Both codes share the same atmospheric parameters, chemical composition, equation of state, and opacities, which allowed us to make a strictly differential comparison between the line formation properties predicted in 3D and 1D. The influence of convection on the spectral line formation was assessed with the aid of 3D-1D abundance corrections, which measure the difference between the abundances of chemical species derived with the 3D hydrodynamical and 1D classical model atmospheres. Results: We find that convection plays a significant role in the spectral line formation in this particular red giant. The derived 3D-1D abundance corrections rarely exceed ± 0.1 dex when lines of neutral atoms and molecules are considered, which is in line with the previous findings for solar-metallicity red giants located on the lower RGB. The situation is different with lines that belong to ionized atoms, or to neutral atoms with high ionization potential. In both cases, the corrections for high-excitation lines (χ > 8 eV) may amount to Δ3D-1D ~ -0.4 dex. The 3D-1D abundance corrections generally show a significant wavelength dependence; in most cases they are smaller in

  8. Star formation in Taurus

    NASA Technical Reports Server (NTRS)

    Beichman, C. A.; Jarrett, Tom

    1994-01-01

    Data with the Two Micron All Sky Survey (2MASS) prototype camera were obtained in a 2.3 sq. deg region in Taurus containing Heiles Cloud 2, a region known from Infrared Astronomy Satellite (IRAS) observations to contain a number of very young solar type stars. Data at 1.25 (J), 1.65 (H), and 2.2 (K(sub s)) micrometers are presented. These data are representative of the type and quality of data expected from the planned near-IR surveys, 2MASS and Deep Near-Infrared Survey (DENIS). Near-IR surveys will be useful for determining the large scale variation of extinction with clouds, for determining the luminosity function in nearby clouds down to ranges of 0.1-1.0 solar luminosity, and for finding highly extincted T Tauri stars missed by IRAS because the bulk of their luminosity is emitted shortward of 12 micrometers.

  9. Triggered massive and clustered star formation by combined H II regions G38.91-0.44 and G39.30-1.04

    NASA Astrophysics Data System (ADS)

    Xu, Jin-Long; Wang, Jun-Jie; Liu, Xiao-Lan

    2013-11-01

    Aims: We investigate the triggered star formation occurring in the infrared dark clouds (IRDC) G38.95-0.47 between H II regions G38.91-0.44 and G39.30-1.04, and study the detailed morphology, distribution, and physical parameters of the molecular gas and dust in this region. Methods: We present the radio continuum, infrared, and CO molecular observations of IRDC G38.95-0.47 and its adjacent H II regions G38.91-0.44 (N74), G38.93-0.39 (N75), and G39.30-1.04. The Purple Mountain Observation (PMO) 13.7 m radio telescope was used to detect 12CO J = 1-0, 13CO J = 1-0 and C18O J = 1-0 lines. The carbon monoxide (CO) molecular observations can ensure the real association between the ionized gas and the neutral material observed nearby. To select young stellar objects (YSOs) associated this region, we used the GLIMPSE I catalog. Results: The 13CO J = 1-0 emission presents two large cloud clumps. The clump consistent with IRDC G38.95-0.47 shows a triangle-like shape, and has a steep integrated-intensity gradient toward H II regions G38.91-0.44 and G39.30-1.04, suggesting that the two H II regions have expanded into the IRDC. Four submillmeter continuum sources have been detected in the IRDC G38.95-0.47. Only the G038.95-00.47-M1 source with a mass of 117 M⊙ has outflow and infall motions, indicating a newly forming massive star. We detected a new collimated outflow in the clump compressed by G38.93-0.39. The derived ages of the three H II regions are 6.1 × 105 yr, 2.5 × 105 yr, and 9.0 × 105 yr, respectively. In the IRDC G38.95-0.47, the significant enhancement of several Class I YSOs indicates the presence of some recently formed stars. Comparing the ages of these H II regions with YSOs (Class I sources and massive G038.95-00.47-M1 source), we suggest that YSOs may be triggered by G38.91-0.44 and G39.30-1.04 together, which supports the radiatively driven implosion model. It may be the first time that the triggered star formation has occurred in the IRDC compressed by

  10. GAS SURFACE DENSITY, STAR FORMATION RATE SURFACE DENSITY, AND THE MAXIMUM MASS OF YOUNG STAR CLUSTERS IN A DISK GALAXY. II. THE GRAND-DESIGN GALAXY M51

    SciTech Connect

    Gonzalez-Lopezlira, Rosa A.; Pflamm-Altenburg, Jan; Kroupa, Pavel

    2013-06-20

    We analyze the relationship between maximum cluster mass and surface densities of total gas ({Sigma}{sub gas}), molecular gas ({Sigma}{sub H{sub 2}}), neutral gas ({Sigma}{sub H{sub I}}), and star formation rate ({Sigma}{sub SFR}) in the grand-design galaxy M51, using published gas data and a catalog of masses, ages, and reddenings of more than 1800 star clusters in its disk, of which 223 are above the cluster mass distribution function completeness limit. By comparing the two-dimensional distribution of cluster masses and gas surface densities, we find for clusters older than 25 Myr that M{sub 3rd}{proportional_to}{Sigma}{sub H{sub I}{sup 0.4{+-}0.2}}, whereM{sub 3rd} is the median of the five most massive clusters. There is no correlation with{Sigma}{sub gas},{Sigma}{sub H2}, or{Sigma}{sub SFR}. For clusters younger than 10 Myr, M{sub 3rd}{proportional_to}{Sigma}{sub H{sub I}{sup 0.6{+-}0.1}} and M{sub 3rd}{proportional_to}{Sigma}{sub gas}{sup 0.5{+-}0.2}; there is no correlation with either {Sigma}{sub H{sub 2}} or{Sigma}{sub SFR}. The results could hardly be more different from those found for clusters younger than 25 Myr in M33. For the flocculent galaxy M33, there is no correlation between maximum cluster mass and neutral gas, but we have determined M{sub 3rd}{proportional_to}{Sigma}{sub gas}{sup 3.8{+-}0.3}, M{sub 3rd}{proportional_to}{Sigma}{sub H{sub 2}{sup 1.2{+-}0.1}}, and M{sub 3rd}{proportional_to}{Sigma}{sub SFR}{sup 0.9{+-}0.1}. For the older sample in M51, the lack of tight correlations is probably due to the combination of strong azimuthal variations in the surface densities of gas and star formation rate, and the cluster ages. These two facts mean that neither the azimuthal average of the surface densities at a given radius nor the surface densities at the present-day location of a stellar cluster represent the true surface densities at the place and time of cluster formation. In the case of the younger sample, even if the clusters have not yet

  11. Supershells and propagating star formation

    NASA Technical Reports Server (NTRS)

    Maclow, M. M.; Mccray, R.; Kafatos, M.

    1986-01-01

    Correlated supernovae from an OB association can carve large cavities (greater than 100 pc) in the interstellar medium (ISM), and can punch holes completely through the disk of a spiral galaxy. Supernova remnant energy within such a cavity is thermalized before the shock reaches the supershell. Thus stellar wind theory may be used to model these superbubbles. We describe how the evolution of the superbubble depends on the density distribution of the galactic disk gas and the rate of supernovae in the OB association. At a radius of 100 to 300 pc, the supershell becomes gravitationally unstable, forming giant molecular clouds which are the sites for new star formation. This gravitational instability of the supershells provides a physical mechanism for propagating star formation and may account for the observation of bursts of star formation in galaxies.

  12. Angular momentum and star formation

    NASA Astrophysics Data System (ADS)

    Strittmatter, P. A.

    The present investigation is mainly concerned with the importance of high angular resolution observations in studies of star formation and, in particular, with elucidating the role which angular momentum plays in the process. A brief report is included on recent high angular resolution observations made with the Steward Observatory speckle camera system. A consideration of the angular momentum in interstellar clouds indicates that rotation precludes quasi-spherical contraction. A number of solutions to this angular momentum problem are examined, taking into account questions concerning the help provided by high angular resolution observations for an elucidation of the various possible scenarios of star formation. Technical aspects involved in obtaining suitable data are investigated. It is concluded that high angular resolution observations hold considerable promise for solving at least some of the problems associated with the role of angular momentum in star formation.

  13. Formation of the first stars.

    PubMed

    Bromm, Volker

    2013-11-01

    Understanding the formation of the first stars is one of the frontier topics in modern astrophysics and cosmology. Their emergence signalled the end of the cosmic dark ages, a few hundred million years after the Big Bang, leading to a fundamental transformation of the early Universe through the production of ionizing photons and the initial enrichment with heavy chemical elements. We here review the state of our knowledge, separating the well understood elements of our emerging picture from those where more work is required. Primordial star formation is unique in that its initial conditions can be directly inferred from the Λ cold dark matter (ΛCDM) model of cosmological structure formation. Combined with gas cooling that is mediated via molecular hydrogen, one can robustly identify the regions of primordial star formation, the so-called minihalos, having total masses of ~10(6) M⊙ and collapsing at redshifts z ≈ 20-30. Within this framework, a number of studies have defined a preliminary standard model, with the main result that the first stars were predominantly massive. This model has recently been modified to include a ubiquitous mode of fragmentation in the protostellar disks, such that the typical outcome of primordial star formation may be the formation of a binary or small multiple stellar system. We will also discuss extensions to this standard picture due to the presence of dynamically significant magnetic fields, of heating from self-annihalating WIMP dark matter, or cosmic rays. We conclude by discussing possible strategies to empirically test our theoretical models. Foremost among them are predictions for the upcoming James Webb space telescope (JWST), to be launched ~2018, and for 'stellar archaeology', which probes the abundance pattern in the oldest, most-metal poor stars in our cosmic neighborhood, thereby constraining the nucleosynthesis inside the first supernovae. PMID:24168986

  14. Star formation and its triggers

    NASA Astrophysics Data System (ADS)

    Combes, F.

    2016-06-01

    The relation between star formation and gas density appears linear for galaxies on the main sequence, and when the molecular gas is considered. However, the star formation efficiency (SFE) defined as the ratio of SFR to gas surface densities, can be much higher when SF is triggered by a dynamical process such as galaxy interaction or mergers, or even secular evolution and cold gas accretion. I review recent work showing how the SFE can vary as a function of morphological type, environment, or redshift. Physical processes able to explain positive and negative feedback from supernovae or AGN are discussed.

  15. Star formation and gas supply

    NASA Astrophysics Data System (ADS)

    Catinella, B.

    2016-06-01

    A detailed knowledge of how gas cycles in and around galaxies, and how it depends on galaxy properties such as stellar mass and star formation rate, is crucial to understand galaxy formation and evolution. We take advantage of the most sensitive surveys of cold gas in massive galaxies, GASS and COLD GASS, as well as of the state-of-the-art HI blind survey ALFALFA to investigate how molecular and atomic hydrogen reservoirs vary along and across the main sequence of star-forming galaxies.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    Recent work suggests that galaxy evolution, and the build-up of stellar mass (M★) over cosmic time, is characterized by changes with redshift of star formation rate (SFR) and oxygen abundance (O/H). In a companion paper, we have compiled a large dataset to study Metallicity Evolution and Galaxy Assembly (MEGA), consisting of ˜1000 galaxies to z ≃ 3.7 with a common O/H calibration. Here we interpret the MEGA scaling relations of M★, SFR, and O/H with an updated version of the model presented by Dayal et al. (2013). This model successfully reproduces the observed O/H ratio of ˜80 000 galaxies selected from the Sloan Digital Sky Survey to within 0.05-0.06 dex. By extending the model to the higher redshift MEGA sample, we find that although the specific mass loading of outflows does not change measurably during the evolution, the accretion rate and gas content of galaxies increase significantly with redshift. These two effects can explain, either separately or possibly in tandem, the observed lower metal abundance of high-z galaxies.

  17. Absorption of gamma-ray photons in a vacuum neutron star magnetosphere: II. The formation of 'lightnings'

    SciTech Connect

    Istomin, Ya. N. Sob'yanin, D. N.

    2011-10-15

    The absorption of a high-energy photon from the external cosmic gamma-ray background in the inner neutron star magnetosphere triggers the generation of a secondary electron-positron plasma and gives rise to a lightning-a lengthening and simultaneously expanding plasma tube. It propagates along magnetic fields lines with a velocity close to the speed of light. The high electron-positron plasma generation rate leads to dynamical screening of the longitudinal electric field that is provided not by charge separation but by electric current growth in the lightning. The lightning radius is comparable to the polar cap radius of a radio pulsar. The number of electron-positron pairs produced in the lightning in its lifetime reaches 10{sup 28}. The density of the forming plasma is comparable to or even higher than that in the polar cap regions of ordinary pulsars. This suggests that the radio emission from individual lightnings can be observed. Since the formation time of the radio emission is limited by the lightning lifetime, the possible single short radio bursts may be associated with rotating radio transients (RRATs).

  18. Star formation in distant galaxies.

    NASA Astrophysics Data System (ADS)

    Rocca-Volmerange, B.

    Scenarios of galactic evolution, essentially based on our knowledge of nearby galaxies have been proposed. Star formation laws, initial mass function, metallicity are the main parameters. The author shortly reviews the present status of these parameters in distant galaxies and gives some deductive conclusions from a comparison with the most distant (z ≥ 3) galaxies.

  19. BUDHIES II: a phase-space view of H I gas stripping and star formation quenching in cluster galaxies

    NASA Astrophysics Data System (ADS)

    Jaffé, Yara L.; Smith, Rory; Candlish, Graeme N.; Poggianti, Bianca M.; Sheen, Yun-Kyeong; Verheijen, Marc A. W.

    2015-04-01

    We investigate the effect of ram-pressure from the intracluster medium on the stripping of H I gas in galaxies in a massive, relaxed, X-ray bright, galaxy cluster at z = 0.2 from the Blind Ultra Deep H I Environmental Survey (BUDHIES). We use cosmological simulations, and velocity versus position phase-space diagrams to infer the orbital histories of the cluster galaxies. In particular, we embed a simple analytical description of ram-pressure stripping in the simulations to identify the regions in phase-space where galaxies are more likely to have been sufficiently stripped of their H I gas to fall below the detection limit of our survey. We find a striking agreement between the model predictions and the observed location of H I-detected and non-detected blue (late-type) galaxies in phase-space, strongly implying that ram-pressure plays a key role in the gas removal from galaxies, and that this can happen during their first infall into the cluster. However, we also find a significant number of gas-poor, red (early-type) galaxies in the infall region of the cluster that cannot easily be explained with our model of ram-pressure stripping alone. We discuss different possible additional mechanisms that could be at play, including the pre-processing of galaxies in their previous environment. Our results are strengthened by the distribution of galaxy colours (optical and UV) in phase-space, that suggests that after a (gas-rich) field galaxy falls into the cluster, it will lose its gas via ram-pressure stripping, and as it settles into the cluster, its star formation will decay until it is completely quenched. Finally, this work demonstrates the utility of phase-space diagrams to analyse the physical processes driving the evolution of cluster galaxies, in particular H I gas stripping.

  20. The Three-mm Ultimate Mopra Milky Way Survey. II.Cloud and Star Formation near the Filamentary Ministarburst RCW 106

    NASA Astrophysics Data System (ADS)

    Nguyen, Hans; Nguyen-Luong, Quang; Martin, Peter G.; Barnes, Peter J.; Muller, Erik; Lowe, Vicki; Lo, Nadia; Cunningham, Maria; Motte, Frédérique; Indermühle, B.; O'Dougherty, Stefan N.; Hernandez, Audra K.; Fuller, Gary A.

    2015-10-01

    We report here a study of gas, dust, and star formation rates (SFRs) in the molecular cloud complexes (MCCs) surrounding the giant H ii region RCW 106 using 12CO and 13CO(1-0) data from the Three-mm Ultimate Mopra Milky way Survey and archival data. We separate the emission in the Galactic Plane around l = 330°-335° and b = -1°-1° into two main MCCs: the RCW 106 (VLSR = -48 km s-1) complex and the MCC331-90 (VLSR = -90 km s-1) complex. While RCW 106 (M ˜ 5.9× {10}6 {M}⊙ ) is located in the Scutum-Centaurus arm at a distance of 3.6 kpc, MCC331-90 (M ˜ 2.8× {10}6 {M}⊙ ) is in the Norma arm at a distance of 5 kpc. Their molecular gas mass surface densities are ˜220 and ˜130 {M}⊙ pc-2, respectively. For the RCW 106 complex, using the 21 cm continuum fluxes and dense clumps counting, we obtain immediate past (˜-0.2 Myr) and immediate future (˜+0.2 Myr) SFRs of {0.25}-0.023+0.09 {M}⊙ {{yr}}-1 and 0.12+/- 0.1 {M}⊙ {{yr}}-1. This results in an immediate past SFR density of {9.5}-0.9+3.4 {M}⊙ {{yr}}-1 {{kpc}}-2 and an immediate future SFR density of {4.8}-3.8+3.8 {M}⊙ {{yr}}-1 {{kpc}}-2. As both SFRs are higher than the ministarburst threshold, they must be undergoing a ministarburst event although burst peak has already passed. This is one of the most active star forming complexes in the southern sky that is ideal for further investigations of massive star formation and potentially shedding light on the physics of high-redshift starbursts.

  1. Star formation at z=1.47 from HiZELS: an H>α+[O II] double-blind study

    NASA Astrophysics Data System (ADS)

    Sobral, David; Best, Philip N.; Matsuda, Yuichi; Smail, Ian; Geach, James E.; Cirasuolo, Michele

    2012-03-01

    This paper presents the results from the first wide and deep dual narrow-band survey to select Hα and [O II] line emitters at z= 1.47 ± 0.02, exploiting synergies between the United Kingdom Infrared Telescope and the Subaru telescope by using matched narrow-band filters in the H and z' bands. The Hα survey at z= 1.47 reaches a 3σ flux limit of FHα≈ 7 × 10-17 erg s-1 cm-2 (corresponding to a limiting star formation rate (SFR) in Hα of ≈7 M⊙ yr-1) and detects ≈200 Hα emitters over 0.7 deg2, while the much deeper [O II] survey reaches an effective flux of ≈7 × 10-18 erg s-1 cm-2 (SFR in [O II] of ˜1 M⊙ yr-1), detecting ≈1400 z= 1.47 [O II] emitters in a matched comoving volume of ˜2.5 × 105 Mpc3. The combined survey results in the identification of 190 simultaneous Hα and [O II] emitters at z= 1.47. Hα and [O II] luminosity functions are derived and both are shown to evolve significantly from z˜ 0 in a consistent way. The SFR density of the Universe at z= 1.47 is evaluated, with the Hα analysis yielding ρSFR= 0.16 ± 0.05 M⊙ yr-1 Mpc-3 and the [O II] analysis ρSFR= 0.17 ± 0.04 M⊙ yr-1 Mpc-3. The measurements are combined with other studies, providing a self-consistent measurement of the star formation history of the Universe over the last ˜11 Gyr. By using a large comparison sample at z˜ 0.1, derived from the Sloan Digital Sky Survey (SDSS), [O II]/Hα line ratios are calibrated as probes of dust extinction. Hα emitters at z˜ 1.47 show on average AHα≈ 1 mag, the same as found by SDSS in the local Universe. It is shown that although dust extinction correlates with SFR, the relation evolves by about ˜0.5 mag from z˜ 1.5 to ˜0, with local relations overpredicting the dust extinction corrections at high z by that amount. Stellar mass is found to be a much more fundamental extinction predictor, with the same relation between mass and dust extinction being valid at both z˜ 0 and ˜1.5, at least for low and moderate stellar

  2. Measuring Star Formation Rate and Far-infrared Color in High-redshift Galaxies Using the CO(7-6) and [N II] 205 μm Lines

    NASA Astrophysics Data System (ADS)

    Lu, Nanyao; Zhao, Yinghe; Xu, C. Kevin; Gao, Yu; Díaz-Santos, Tanio; Charmandaris, Vassilis; Inami, Hanae; Howell, Justin; Liu, Lijie; Armus, Lee; Mazzarella, Joseph M.; Privon, George C.; Lord, Steven D.; Sanders, David B.; Schulz, Bernhard; van der Werf, Paul P.

    2015-03-01

    To better characterize the global star formation activity in a galaxy, one needs to know not only the star formation rate (SFR) but also the rest-frame, far-infrared color (e.g., the 60-100 μm color, C(60/100)) of the dust emission. The latter probes the average intensity of the dust heating radiation field and scales statistically with the effective SFR surface density in star-forming galaxies including (ultra-)luminous infrared galaxies ((U)LIRGs). To this end, here we exploit a new spectroscopic approach involving only two emission lines: CO(7-6) at 372 μm and [N ii] at 205 μm([N ii]205μm). For local (U)LIRGs, the ratios of the CO(7-6) luminosity (LCO(7-6)) to the total infrared luminosity (LIR; 8-1000 μm) are fairly tightly distributed (to within ˜0.12 dex) and show little dependence on C(60/100). This makes LCO(7-6) a good SFR tracer, which is less contaminated by active galactic nuclei than LIR and may also be much less sensitive to metallicity than LCO(1-0). Furthermore, the logarithmic [N ii]205μm/CO(7-6) luminosity ratio depends fairly strongly (at a slope of ˜ -1.4) on C(60/100), with a modest scatter (˜0.23 dex). This makes it a useful estimator on C(60/100) with an implied uncertainty of ˜0.15 (or ≲4 K in the dust temperature (Tdust) in the case of a graybody emission with Tdust ≳ 30 K and a dust emissivity index β ≥ 1). Our locally calibrated SFR and C(60/100) estimators are shown to be consistent with the published data of (U)LIRGs of z up to ˜6.5. Based on Herschel observations. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

  3. Collective Properties of Neutron-star X-Ray Binary Populations of Galaxies. II. Pre-low-mass X-Ray Binary Properties, Formation Rates, and Constraints

    NASA Astrophysics Data System (ADS)

    Bhadkamkar, H.; Ghosh, P.

    2014-04-01

    We continue our exploration of the collective properties of neutron-star X-ray binaries in the stellar fields (i.e., outside globular clusters) of normal galaxies. In Paper I of this series, we considered high-mass X-ray binaries (HMXBs). In this paper (Paper II), we consider low-mass X-ray binaries (LMXBs), whose evolutionary scenario is very different from that of HMXBs. We consider the evolution of primordial binaries up to the stage where the neutron star just formed in the supernova explosion of the primary is in a binary with its low-mass, unevolved companion, and this binary has circularized tidally, producing what we call a pre-low-mass X-ray binary (pre-LMXB). We study the constraints on the formation of such pre-LMXBs in detail (since these are low-probability events), and calculate their collective properties and formation rates. To this end, we first consider the changes in the binary parameters in the various steps involved, viz., the common-envelope phase, the supernova, and the tidal evolution. This naturally leads to a clarification of the constraints. We then describe our calculation of the evolution of the distributions of primordial binary parameters into those of pre-LMXB parameters, following the standard evolutionary scenario for individual binaries. We display the latter as both bivariate and monovariate distributions, discuss their essential properties, and indicate the influences of some essential factors on these. Finally, we calculate the formation rate of these pre-LMXBs. The results of this paper will be used in a subsequent one to compute the expected X-ray luminosity function of LMXBs.

  4. Are long gamma-ray bursts biased tracers of star formation? Clues from the host galaxies of the Swift/BAT6 complete sample of bright LGRBs. II. Star formation rates and metallicities at z < 1

    NASA Astrophysics Data System (ADS)

    Japelj, J.; Vergani, S. D.; Salvaterra, R.; D'Avanzo, P.; Mannucci, F.; Fernandez-Soto, A.; Boissier, S.; Hunt, L. K.; Atek, H.; Rodríguez-Muñoz, L.; Scodeggio, M.; Cristiani, S.; Le Floc'h, E.; Flores, H.; Gallego, J.; Ghirlanda, G.; Gomboc, A.; Hammer, F.; Perley, D. A.; Pescalli, A.; Petitjean, P.; Puech, M.; Rafelski, M.; Tagliaferri, G.

    2016-05-01

    Aims: Long gamma-ray bursts (LGRBs) are associated with the deaths of massive stars and might therefore be a potentially powerful tool for tracing cosmic star formation. However, especially at low redshifts (z< 1.5) LGRBs seem to prefer particular types of environment. Our aim is to study the host galaxies of a complete sample of bright LGRBs to investigate the effect of the environment on GRB formation. Methods: We studied host galaxy spectra of the Swift/BAT6 complete sample of 14 z< 1 bright LGRBs. We used the detected nebular emission lines to measure the dust extinction, star formation rate (SFR), and nebular metallicity (Z) of the hosts and supplemented the data set with previously measured stellar masses M⋆. The distributions of the obtained properties and their interrelations (e.g. mass-metallicity and SFR-M⋆ relations) are compared to samples of field star-forming galaxies. Results: We find that LGRB hosts at z< 1 have on average lower SFRs than if they were direct star formation tracers. By directly comparing metallicity distributions of LGRB hosts and star-forming galaxies, we find a good match between the two populations up to 12 +log ≤ft( frac{OHright)} 8.4-8.5, after which the paucity of metal-rich LGRB hosts becomes apparent. The LGRB host galaxies of our complete sample are consistent with the mass-metallicity relation at similar mean redshift and stellar masses. The cutoff against high metallicities (and high masses) can explain the low SFR values of LGRB hosts. We find a hint of an increased incidence of starburst galaxies in the Swift/BAT6 z< 1 sample with respect to that of a field star-forming population. Given that the SFRs are low on average, the latter is ascribed to low stellar masses. Nevertheless, the limits on the completeness and metallicity availability of current surveys, coupled with the limited number of LGRB host galaxies, prevents us from investigating more quantitatively whether the starburst incidence is such as expected

  5. Influence of Stellar Multiplicity on Planet Formation. II. Planets are Less Common in Multiple-star Systems with Separations Smaller than 1500 AU

    NASA Astrophysics Data System (ADS)

    Wang, Ji; Fischer, Debra A.; Xie, Ji-Wei; Ciardi, David R.

    2014-08-01

    Almost half of the stellar systems in the solar neighborhood are made up of multiple stars. In multiple-star systems, planet formation is under the dynamical influence of stellar companions, and the planet occurrence rate is expected to be different from that of single stars. There have been numerous studies on the planet occurrence rate of single star systems. However, to fully understand planet formation, the planet occurrence rate in multiple-star systems needs to be addressed. In this work, we infer the planet occurrence rate in multiple-star systems by measuring the stellar multiplicity rate for planet host stars. For a subsample of 56 Kepler planet host stars, we use adaptive optics (AO) imaging and the radial velocity (RV) technique to search for stellar companions. The combination of these two techniques results in high search completeness for stellar companions. We detect 59 visual stellar companions to 25 planet host stars with AO data. Three stellar companions are within 2'' and 27 within 6''. We also detect two possible stellar companions (KOI 5 and KOI 69) showing long-term RV acceleration. After correcting for a bias against planet detection in multiple-star systems due to flux contamination, we find that planet formation is suppressed in multiple-star systems with separations smaller than 1500 AU. Specifically, we find that compared to single star systems, planets in multiple-star systems occur 4.5 ± 3.2, 2.6 ± 1.0, and 1.7 ± 0.5 times less frequently when a stellar companion is present at a distance of 10, 100, and 1000 AU, respectively. This conclusion applies only to circumstellar planets; the planet occurrence rate for circumbinary planets requires further investigation.

  6. Influence of stellar multiplicity on planet formation. II. Planets are less common in multiple-star systems with separations smaller than 1500 AU

    SciTech Connect

    Wang, Ji; Fischer, Debra A.; Xie, Ji-Wei; Ciardi, David R.

    2014-08-20

    Almost half of the stellar systems in the solar neighborhood are made up of multiple stars. In multiple-star systems, planet formation is under the dynamical influence of stellar companions, and the planet occurrence rate is expected to be different from that of single stars. There have been numerous studies on the planet occurrence rate of single star systems. However, to fully understand planet formation, the planet occurrence rate in multiple-star systems needs to be addressed. In this work, we infer the planet occurrence rate in multiple-star systems by measuring the stellar multiplicity rate for planet host stars. For a subsample of 56 Kepler planet host stars, we use adaptive optics (AO) imaging and the radial velocity (RV) technique to search for stellar companions. The combination of these two techniques results in high search completeness for stellar companions. We detect 59 visual stellar companions to 25 planet host stars with AO data. Three stellar companions are within 2'' and 27 within 6''. We also detect two possible stellar companions (KOI 5 and KOI 69) showing long-term RV acceleration. After correcting for a bias against planet detection in multiple-star systems due to flux contamination, we find that planet formation is suppressed in multiple-star systems with separations smaller than 1500 AU. Specifically, we find that compared to single star systems, planets in multiple-star systems occur 4.5 ± 3.2, 2.6 ± 1.0, and 1.7 ± 0.5 times less frequently when a stellar companion is present at a distance of 10, 100, and 1000 AU, respectively. This conclusion applies only to circumstellar planets; the planet occurrence rate for circumbinary planets requires further investigation.

  7. Star formation in 30 Doradus

    NASA Astrophysics Data System (ADS)

    De Marchi, Guido; Paresce, F.; Sirianni, M.; Spezzi, L.; Andersen, M.; Panagia, N.; Mutchler, M.; SOC, WFC3

    2010-01-01

    We report on the preliminary results of our investigation of the properties of star formation in the 30 Doradus region, in the Large Magellanic Cloud. This study makes use of the panchromatic observations recently obtained with the Wide Field Camera 3 (WFC3) on board the HST in a number of broad- and narrow-band filters at visible and near infrared wavelengths (U, B, V, Halpha, I, J, H). The data clearly reveal the presence of considerable differential extinction across the field. We characterise and quantify this effect using both young main sequence stars and old red giants, showing that the two populations have different extinction properties, and use this information to derive a statistical reddening correction for each star in the field. We then search for pre-main sequence stars looking for objects with a strong (> 5 sigma) Halpha excess emission and find more than 1000 of them over the entire field. Comparison of their location in the H-R diagram with theoretical pre-main sequence evolutionary tracks reveals that about half of these objects have an age of 3 Myr, compatible with that of the massive stars in the field, whereas the rest have an age of 15 Myr, indicating that more than one episode of star formation has taken place in the recent past in this area. This paper is based on Early Release Science observations made by the WFC3 Scientific Oversight Committee. We are grateful to the Director of the Space Telescope Science Institute for awarding Director's Discretionary time for this programme.

  8. Star formation and extinct radioactivities

    NASA Technical Reports Server (NTRS)

    Cameron, A. G. W.

    1984-01-01

    An assessment is made of the evidence for the existence of now-extinct radioactivities in primitive solar system material, giving attention to implications for the early stages of sun and solar system formation. The characteristics of possible disturbances in dense molecular clouds which can initiate the formation of cloud cores is discussed, with emphasis on these disturbances able to generate fresh radioactivities. A one-solar mass red giant star on the asymptotic giant branch appears to have been the best candidate to account for the short-lived extinct radioactivities in the early solar system.

  9. Star Formation in Camelopardalis: Cam OB1

    NASA Astrophysics Data System (ADS)

    Lyder, David Anthony

    Star formation in the Cam OB1 region is investigated. Star formation, in general, is considered in terms of three elements: (a) the structural relationship between the parent molecular clouds and newly formed stars, (b) the temporal evolution of the parent molecular clouds, and (c) the probability of the occurrence of star formation. Star formation in Cam OB1, over the range in l and b considered in this work, is concentrated in the vicinity of Cam R1 and appears to have led to the formation of three distinct stellar groups: (a) Group I, formed ~1 - 50 × 10 6 yr ago, and located spatially and kinematically between two CO complexes, (b) Group II, formed ~1 - 3 × 106 yr ago, and coincident with one of the previously mentioned complexes, and (c) Group III, the youngest group, formed ~1 - 20 × 104 yr ago, and located at the current point of intersection between the two complexes in (a). The mass function (MF) for Groups I and II is similar to the cloud mass function of the parent molecular clouds, i.e., a power-law with exponent α ~ 2. A similar analysis for the Group III stars and associated molecular clouds cannot be performed due to the relatively small numbers in both samples. The star forming efficiency (SFE) in all cases is ~1%. It is proposed that cloud-cloud collisions between the CO complexes in the region triggered the formation of Groups I and III, while Group II was produced by a shock induced by the radiation pressure and stellar winds from the stars in Group I. An analysis of the molecular cloud structure in Cam OB1 and the background Perseus arm also shows that the clouds in both regions are turbulent, and typical of clouds seen elsewhere in the Galaxy. However, the clouds in Cam OB1 show a large dispersion in the degree with which they are self-gravitating, with the larger, warmer clouds being gravitationally bound. The principal data set for this work comprises fully sampled 12CO (J=1-0) observations of the western half of Cam OB1, which were

  10. Feedback During Massive Star Formation

    NASA Astrophysics Data System (ADS)

    Tanaka, Kei; Tan, Jonathan C.; Zhang, Yichen

    2016-01-01

    We present models of photoionization of massive protostellar cores, and show the impact of this ionization feedback on the efficiency of star formation and its observational features. Based on the Core Accretion scenario, we construct the collapse model of rotating massive-protostellar cloud cores together with a protostellar evolutional calculation, including feedback effects from a MHD disk wind, photoionization and radiation pressure. First, the MHD wind creates a bipolar outflow whose opening angle increases over the timescale of mass accretion. The ionizing luminosity dramatically increases after the protostar reaches ~ 5 Msun due to Kelvin-Helmholz contraction, and the MHD wind is photoionized when the protostellar mass reaches ~ 10 - 20 Msun. As the ionizing and bolometric luminosities increase, the outflow opening angle becomes wider due to radiation pressure feedback. By this combination of feedback processes, the envelope is eroded and the mass infall rate is significantly reduced to that arriving only from the disk-shielded equatorial region. At a protostellar mass of ~ 50 - 100 Msun, depending on the initial core properties, the mass accretion is halted by disk photoevaporation. In this way, feedback significantly reduces the star formation efficiency when forming massive stars from massive cloud cores, which could produce a cutoff at the high-mass end of the initial mass function. Along this evolutionary calculation, we also compute the detailed structure of the photoionized regions using a ray-tracing radiative transfer code and evaluate their emission signatures. Their free-free continuum and recombination line emissions are consistent with the variety of observed radio sources associated with massive protostars, i.e., jets and ultra/hyper-compact HII regions. The comparison between our models and such observations enables us to better define the evolutionary sequence of massive star formation.

  11. A HERSCHEL SURVEY OF THE [N II] 205 {mu}m LINE IN LOCAL LUMINOUS INFRARED GALAXIES: THE [N II] 205 {mu}m EMISSION AS A STAR FORMATION RATE INDICATOR

    SciTech Connect

    Zhao Yinghe; Gao Yu; Lu, Nanyao; Xu, C. Kevin; Lord, S.; Howell, J.; Appleton, P.; Mazzarella, J.; Schulz, B.; Isaak, K. G.; Charmandaris, V.; Diaz-Santos, T.; Surace, J.; Evans, A.; Iwasawa, K.; Leech, J.; Petric, A. O.; Sanders, D. B.; Van der Werf, P. P.

    2013-03-01

    We present, for the first time, a statistical study of [N II] 205 {mu}m line emission for a large sample of local luminous infrared galaxies using Herschel Spectral and Photometric Imaging Receiver Fourier Transform Spectrometer (SPIRE FTS) data. For our sample of galaxies, we investigate the correlation between the [N II] luminosity (L{sub [N{sub II]}}) and the total infrared luminosity (L{sub IR}), as well as the dependence of L{sub [N{sub II]}}/L{sub IR} ratio on L{sub IR}, far-infrared colors (IRAS f{sub 60}/f{sub 100}), and the [O III] 88 {mu}m to [N II] luminosity ratio. We find that L{sub [N{sub II]}} correlates almost linearly with L{sub IR} for non-active galactic nucleus galaxies (all having L{sub IR} < 10{sup 12} L{sub Sun }) in our sample, which implies that L{sub [N{sub II]}} can serve as a star formation rate tracer which is particularly useful for high-redshift galaxies that will be observed with forthcoming submillimeter spectroscopic facilities such as the Atacama Large Millimeter/submillimeter Array. Our analysis shows that the deviation from the mean L{sub [N{sub II]}}-L{sub IR} relation correlates with tracers of the ionization parameter, which suggests that the scatter in this relation is mainly due to the variations in the hardness, and/or ionization parameter, of the ambient galactic UV field among the sources in our sample.

  12. Fast H-alpha variations on a rapidly rotating, cool main-sequence star. II - Cloud formation and ejection

    NASA Astrophysics Data System (ADS)

    Collier Cameron, A.; Robinson, R. D.

    1989-05-01

    Time resolved H-alpha spectra of AB Doradus are presented that confirm a model in which large prominence-like condensations of neutral material are trapped in corotation with the stellar magnetic field. The results suggest that the entire confining field is deformed outward by the increasing centrifugal force acting on the corotating cloud materials as the cloud density increases. The angular momentum loss rate from the cloud ejections is shown to be sufficient to brake the rotation of the star's convective envelope on a time-scale of no more than 10 to the 8th yr.

  13. LINE PROFILES OF CORES WITHIN CLUSTERS. II. SIGNATURES OF DYNAMICAL COLLAPSE DURING HIGH-MASS STAR FORMATION

    SciTech Connect

    Smith, Rowan J.; Shetty, Rahul; Klessen, Ralf S.; Beuther, Henrik; Bonnell, Ian A.

    2013-07-01

    Observations of atomic or molecular lines can provide important information about the physical state of star-forming regions. In order to investigate the line profiles from dynamical collapsing massive star-forming regions (MSFRs), we model the emission from hydrodynamic simulations of a collapsing cloud in the absence of outflows. By performing radiative transfer calculations, we compute the optically thick HCO{sup +} and optically thin N{sub 2}H{sup +} line profiles from two collapsing regions at different epochs. Due to large-scale collapse, the MSFRs have large velocity gradients, reaching up to 20 km s{sup -1} pc{sup -1} across the central core. The optically thin lines typically contain multiple velocity components resulting from the superposition of numerous density peaks along the line of sight. The optically thick lines are only marginally shifted to the blue side of the optically thin line profiles, and frequently do not have a central depression in their profiles due to self-absorption. As the regions evolve, the lines become brighter and the optically thick lines become broader. The lower-order HCO{sup +} (1-0) transitions are better indicators of collapse than the higher-order (4-3) transitions. We also investigate how the beam sizes affect profile shapes. Smaller beams lead to brighter and narrower lines that are more skewed to the blue in HCO{sup +} relative to the true core velocity, but show multiple components in N{sub 2}H{sup +}. High-resolution observations (e.g., with Atacama Large Millimeter Array) can test these predictions and provide insights into the nature of MSFRs.

  14. Star Formation in Henize 206

    NASA Technical Reports Server (NTRS)

    2004-01-01

    explosion millions of years ago. The shock waves from that explosion impacted a cloud of nearby hydrogen gas, compressed it, and started a new generation of star formation. The death of one star led to the birth of many new stars. This is particularly evident in the MIPS inset, where the 24-micron emission peaks correspond to newly formed stars. The ultraviolet and visible-light photons from the new stars are absorbed by surrounding dust and re-radiated at longer infrared wavelengths, where it is detected by Spitzer.

    This emission nebula was cataloged by Karl Henize (HEN-eyes) while spending 1948-1951 in South Africa doing research for his Ph.D. dissertation at the University of Michigan. Henize later became a NASA astronaut and, at age 59, became the oldest rookie to fly on the Space Shuttle during an eight-day flight of the Challenger in 1985. He died just short of his 67th birthday in 1993 while attempting to climb the north face of Mount Everest, the world's highest peak.

  15. Relativistic jets and star formation

    NASA Astrophysics Data System (ADS)

    Bicknell, Geoffrey Vincent; Mukherjee, Dipanjan; Wagner, Alex; Slatyer Sutherland, Ralph

    2015-08-01

    We are conducting simulations of jets interacting with molecular and atomic gas on scales of a few kpc in forming galaxies. Competing processes, such as the dispersion of gas in the galaxy and star formation in the high-pressure environment determine whether positive or negative feedback predominates. We shall present our new simulations including an assessment of these different effects. Our simulations also predict the velocity and velocity dispersion of atomic and molecular gas in galaxies, which are undergoing interaction with relativistic jets. These results are of interest to radio and optical spectral imaging observations of galaxies undergoing feedback.

  16. Star formation: Sibling rivalry begins at birth

    NASA Astrophysics Data System (ADS)

    Kratter, Kaitlin M.

    2015-02-01

    High-resolution astronomical observations of a nearby molecular gas cloud have revealed a quadruplet of stars in the act of formation. The system is arguably the youngest multiple star system detected so far. See Letter p.213

  17. MASSIVE STAR FORMATION IN NGC 2074

    SciTech Connect

    Fleener, Christine E.; Chu, Y.-H.; Gruendl, Robert A.; Payne, James T.; Chen, C.-H. Rosie

    2010-01-15

    Spitzer observations of the Large Magellanic Cloud (LMC) have revealed a large population of young stellar objects (YSOs), but complementary high-resolution images in the optical or near-IR wavelengths are still needed to resolve the multiplicity and immediate environments of the YSOs. The Hubble Space Telescope imaged the star-forming region NGC 2074 in the LMC during its 100,000th orbit, providing an opportunity to more closely examine the YSOs and their environments in this region. We have studied the 10 YSO candidates identified from Spitzer observations, confirming their nature and determining their physical parameters by modeling their spectral energy distributions. The majority of the YSOs and central stars of ultracompact H II regions in NGC 2074 have masses consistent with spectral types of early B to late O. The co-existence of massive early-type O stars and the less massive YSOs indicates that their formation may have started at a similar time, a few 10{sup 5} yr ago. NGC 2074 provides an opportunity to study the evolution of massive stars at their infancy.

  18. STAR FORMATION IN 30 DORADUS

    SciTech Connect

    De Marchi, Guido; Spezzi, Loredana; Sirianni, Marco; Andersen, Morten; Paresce, Francesco; Panagia, Nino; Mutchler, Max; Whitmore, Bradley C.; Bond, Howard; Beccari, Giacomo; Balick, Bruce; Dopita, Michael A.; Frogel, Jay A.; Calzetti, Daniela; Marcella Carollo, C.; Disney, Michael J.; Hall, Donald N. B.; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.

    2011-09-20

    Using observations obtained with the Wide-Field Camera 3 on board the Hubble Space Telescope, we have studied the properties of the stellar populations in the central regions of 30 Dor in the Large Magellanic Cloud. The observations clearly reveal the presence of considerable differential extinction across the field. We characterize and quantify this effect using young massive main-sequence stars to derive a statistical reddening correction for most objects in the field. We then search for pre-main-sequence (PMS) stars by looking for objects with a strong (>4{sigma}) H{alpha} excess emission and find about 1150 of them over the entire field. Comparison of their location in the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for the appropriate metallicity reveals that about one-third of these objects are younger than {approx}4 Myr, compatible with the age of the massive stars in the central ionizing cluster R 136, whereas the rest have ages up to {approx}30 Myr, with a median age of {approx}12 Myr. This indicates that star formation has proceeded over an extended period of time, although we cannot discriminate between an extended episode and a series of short and frequent bursts that are not resolved in time. While the younger PMS population preferentially occupies the central regions of the cluster, older PMS objects are more uniformly distributed across the field and are remarkably few at the very center of the cluster. We attribute this latter effect to photo-evaporation of the older circumstellar disks caused by the massive ionizing members of R 136.

  19. Star Formation in 30 Doradus

    NASA Astrophysics Data System (ADS)

    De Marchi, Guido; Paresce, Francesco; Panagia, Nino; Beccari, Giacomo; Spezzi, Loredana; Sirianni, Marco; Andersen, Morten; Mutchler, Max; Balick, Bruce; Dopita, Michael A.; Frogel, Jay A.; Whitmore, Bradley C.; Bond, Howard; Calzetti, Daniela; Carollo, C. Marcella; Disney, Michael J.; Hall, Donald N. B.; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.; O'Connell, Robert W.; Saha, Abhijit; Silk, Joseph I.; Trauger, John T.; Walker, Alistair R.; Windhorst, Rogier A.; Young, Erick T.

    2011-09-01

    Using observations obtained with the Wide-Field Camera 3 on board the Hubble Space Telescope, we have studied the properties of the stellar populations in the central regions of 30 Dor in the Large Magellanic Cloud. The observations clearly reveal the presence of considerable differential extinction across the field. We characterize and quantify this effect using young massive main-sequence stars to derive a statistical reddening correction for most objects in the field. We then search for pre-main-sequence (PMS) stars by looking for objects with a strong (>4σ) Hα excess emission and find about 1150 of them over the entire field. Comparison of their location in the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for the appropriate metallicity reveals that about one-third of these objects are younger than ~4 Myr, compatible with the age of the massive stars in the central ionizing cluster R 136, whereas the rest have ages up to ~30 Myr, with a median age of ~12 Myr. This indicates that star formation has proceeded over an extended period of time, although we cannot discriminate between an extended episode and a series of short and frequent bursts that are not resolved in time. While the younger PMS population preferentially occupies the central regions of the cluster, older PMS objects are more uniformly distributed across the field and are remarkably few at the very center of the cluster. We attribute this latter effect to photo-evaporation of the older circumstellar disks caused by the massive ionizing members of R 136. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555.

  20. Orion and theories of star formation

    NASA Astrophysics Data System (ADS)

    Larson, R. B.

    1982-10-01

    Small-scale phenomena involved in the formation of stars and molecular clouds are discussed in connection with formation processes occurring in the Orion nebula. The Orion region is noted to display a large scale filamentary structure and complex velocity field, suggesting a turbulent formation process. The effects of gravity, shock compression, and tidal processes are considered, including the sequence of accelerated star formation within a molecular cloud once stars have formed the cloud. It is suggested that massive stars are forming in the centrally located IR source 0.1 pc from the Trapezium and will blow away the surrounding gas relatively soon. Mass spectra from T Tauri and Orion stars are compared, indicating the Orion young star cluster is more evolved, with the associated gas cloud having become denser as massive star formation accelerates accretion.

  1. A possible formation channel for blue hook stars in globular cluster II - Effects of metallicity, mass ratio, tidal enhancement efficiency and helium abundance

    NASA Astrophysics Data System (ADS)

    Lei, Zhenxin; Zhao, Gang; Zeng, Aihua; Shen, Lihua; Lan, Zhongjian; Jiang, Dengkai; Han, Zhanwen

    2016-09-01

    Employing tidally enhanced stellar wind, we studied in binaries the effects of metallicity, mass ratio of primary to secondary, tidal enhancement efficiency and helium abundance on the formation of blue hook (BHk) stars in globular clusters (GCs). Totally, 28 sets of binary models combined with different input parameters are studied. For each set of binary model, we presented the range of initial orbital periods which is needed to produce BHk stars in binaries. All the binary models could produce BHk stars within different range of initial orbital periods. We also compared our results with the observation in the Teff-logg diagram of GC NGC 2808 and ω Cen. Most of the BHk stars in these two GCs locate well in the region predicted by our theoretical models, especially when C/N enhanced model atmospheres is considered. We found that mass ratio of primary to secondary and tidal enhancement efficiency have little effects on the formation of BHk stars in binaries, while metallicity and helium abundance would play important roles, especially for helium abundance. Specifically, with helium abundance increasing in binary models, the space range of initial orbital periods needed to produce BHk stars becomes obviously wider, regardless of other input parameters adopted. Our results were discussed with recent observations and other theoretical models.

  2. Infrared observations of OB star formation in NGC 6334

    NASA Technical Reports Server (NTRS)

    Harvey, P. M.; Gatley, I.

    1983-01-01

    Infrared photometry and maps from 2 to 100 microns are presented for three of the principal far infrared sources in NGC 6334. Each region is powered by two or more very young stars. The distribution of dust and ionized gas is probably strongly affected by the presence of the embedded stars; one of the sources is a blister H II region, another has a bipolar structure, and the third exhibits asymmetric temperature structure. The presence of protostellar objects throughout the region suggests that star formation has occurred nearly simultaneously in the whole molecular cloud rather than having been triggered sequentially from within. Previously announced in STAR as N83-16263

  3. Star formation sustained by gas accretion

    NASA Astrophysics Data System (ADS)

    Sánchez Almeida, Jorge; Elmegreen, Bruce G.; Muñoz-Tuñón, Casiana; Elmegreen, Debra Meloy

    2014-07-01

    Numerical simulations predict that metal-poor gas accretion from the cosmic web fuels the formation of disk galaxies. This paper discusses how cosmic gas accretion controls star formation, and summarizes the physical properties expected for the cosmic gas accreted by galaxies. The paper also collects observational evidence for gas accretion sustaining star formation. It reviews evidence inferred from neutral and ionized hydrogen, as well as from stars. A number of properties characterizing large samples of star-forming galaxies can be explained by metal-poor gas accretion, in particular, the relationship among stellar mass, metallicity, and star-formation rate (the so-called fundamental metallicity relationship). They are put forward and analyzed. Theory predicts gas accretion to be particularly important at high redshift, so indications based on distant objects are reviewed, including the global star-formation history of the universe, and the gas around galaxies as inferred from absorption features in the spectra of background sources.

  4. Triggered star formation in the environment of young massive stars

    NASA Astrophysics Data System (ADS)

    Gritschneder, Matthias; Naab, T.; Heitsch, F.; Burkert, A.

    Recent observations with the Spitzer Space Telescope show clear evidence that star formation takes place in the surrounding of young massive O-type stars, which are shaping their environment due to their powerful radiation and stellar winds. In this work we investigate the effect of ionising radiation of massive stars on the ambient interstellar medium (ISM): In particular we want to examine whether the UV-radiation of O-type stars can lead to the observed pillar-like structures and can trigger star formation. We developed a new implementation, based on a parallel Smooth Particle Hydrodynamics code (VINE), that allows an efficient treatment of the effect of ionising radiation from massive stars on their turbulent gaseous environment. Here we present first results at very high resolution. We show that ionising radiation can trigger the collapse of an otherwise stable molecular cloud. The arising structures resemble observed structures (e.g. the pillars of creation in the Eagle Nebula (M16) or the Horsehead Nebula B33). Including the effect of gravitation we find small regions that can be identified as formation places of individual stars. We conclude that ionising radiation from massive stars alone can trigger substantial star formation in molecular clouds.

  5. Measuring star formation rates in blue galaxies

    NASA Technical Reports Server (NTRS)

    Gallagher, John S., III; Hunter, Deidre A.

    1987-01-01

    The problems associated with measurements of star formation rates in galaxies are briefly reviewed, and specific models are presented for determinations of current star formation rates from H alpha and Far Infrared (FIR) luminosities. The models are applied to a sample of optically blue irregular galaxies, and the results are discussed in terms of star forming histories. It appears likely that typical irregular galaxies are forming stars at nearly constant rates, although a few examples of systems with enhanced star forming activity are found among HII regions and luminous irregular galaxies.

  6. Star formation around isolated T Tauri stars?

    NASA Astrophysics Data System (ADS)

    Hoff, W.; Pfau, W.; Henning, T.

    1996-02-01

    The authors want to present their search for young stellar objects around the two isolated T Tau stars TW Hya (Rucinski and Krautter 1983) and CoD -29°8887 (de la Reza et al. 1989). From the known spectroscopic features of these objects, TW Hya is to be classified as a classical T Tau star (CTTS), but it is not associated with a dark cloud region like all other known CTTSs. The same situation turns out for the weak-line T Tau star (WTTS) CoD -29°8887. One possible explanation for their isolated position is that they have formed from small dark clouds or globules, which were later destroyed. The authors carried out two ROSAT PSPC observations pointing at TW Hya and CoD -29°8887 and used a source detection procedure considering all the standard ROSAT energy bands to test this hypothesis. Spectroscopic follow-up observations were made for 24 possible T Tauri candidates, but there are no further low-mass young stellar objects in the vicinity of the two targets. The study shows that the objects are definitely not formed in a cluster at the positions of the objects.

  7. ACTIVE GALACTIC NUCLEUS PAIRS FROM THE SLOAN DIGITAL SKY SURVEY. II. EVIDENCE FOR TIDALLY ENHANCED STAR FORMATION AND BLACK HOLE ACCRETION

    SciTech Connect

    Liu Xin; Shen Yue; Strauss, Michael A.

    2012-01-20

    Active galactic nuclei (AGNs) are occasionally seen in pairs, suggesting that tidal encounters are responsible for the accretion of material by both central supermassive black holes (BHs). In Paper I of this series, we selected a sample of AGN pairs with projected separations r{sub p} < 100 h{sup -1}{sub 70} kpc and velocity offsets <600 km s{sup -1} from the Seventh Data Release of the Sloan Digital Sky Survey and quantified their frequency. In this paper, we address the BH accretion and recent star formation properties in their host galaxies. AGN pairs experience stronger BH accretion, as measured by their [O III] {lambda}5007 luminosities (corrected for contribution from star formation) and Eddington ratios, than do control samples of single AGNs matched in redshift and host-galaxy stellar mass. Their host galaxies have stronger post-starburst activity and younger mean stellar ages, as indicated by stronger H{delta} absorption and smaller 4000 A break in their spectra. The BH accretion and recent star formation in the host galaxies both increase with decreasing projected separation in AGN pairs, for r{sub p} {approx}< 10-30 h{sup -1}{sub 70} kpc. The intensity of BH accretion, the post-starburst strength, and the mean stellar ages are correlated between the two AGNs in a pair. The luminosities and Eddington ratios of AGN pairs are correlated with recent star formation in their host galaxies, with a scaling relation consistent with that observed in single AGNs. Our results suggest that galaxy tidal interactions enhance both BH accretion and host-galaxy star formation in close AGN pairs, even though the majority of low-redshift AGNs are not coincident with on-going interactions.

  8. Studying the evolution of galaxies in compact groups over the past 3 Gyr - II. The importance of environment in the suppression of star formation

    NASA Astrophysics Data System (ADS)

    Bitsakis, T.; Dultzin, D.; Ciesla, L.; Díaz-Santos, T.; Appleton, P. N.; Charmandaris, V.; Krongold, Y.; Guillard, P.; Alatalo, K.; Zezas, A.; González, J.; Lanz, L.

    2016-06-01

    We present an in depth study on the evolution of galaxy properties in compact groups over the past 3 Gyr. We are using the largest multiwavelength sample to-date, comprised 1770 groups (containing 7417 galaxies), in the redshift range of 0.01 < z < 0.23. To derive the physical properties of the galaxies, we rely on ultraviolet (UV)-to-infrared spectral energy distribution modelling, using CIGALE. Our results suggest that during the 3 Gyr period covered by our sample, the star formation activity of galaxies in our groups has been substantially reduced (3 to 10 times). Moreover, their star formation histories as well as their UV-optical and mid-infrared colours are significantly different from those of field and cluster galaxies, indicating that compact group galaxies spend more time transitioning through the green valley. The morphological transformation from late-type spirals to early-type galaxies occurs in the mid-infrared transition zone rather than in the UV-optical green valley. We find evidence of shocks in the emission line ratios and gas velocity dispersions of the late-type galaxies located below the star forming main sequence. Our results suggest that in addition to gas stripping, turbulence and shocks might play an important role in suppressing the star formation in compact group galaxies.

  9. CARMA Survey Toward Infrared-bright Nearby Galaxies (STING). II. Molecular Gas Star Formation Law and Depletion Time across the Blue Sequence

    NASA Astrophysics Data System (ADS)

    Rahman, Nurur; Bolatto, Alberto D.; Xue, Rui; Wong, Tony; Leroy, Adam K.; Walter, Fabian; Bigiel, Frank; Rosolowsky, Erik; Fisher, David B.; Vogel, Stuart N.; Blitz, Leo; West, Andrew A.; Ott, Jürgen

    2012-02-01

    We present an analysis of the relationship between molecular gas and current star formation rate surface density at sub-kiloparsec and kiloparsec scales in a sample of 14 nearby star-forming galaxies. Measuring the relationship in the bright, high molecular gas surface density ({\\Sigma _H_2}\\gtrsim 20 M ⊙ pc-2) regions of the disks to minimize the contribution from diffuse extended emission, we find an approximately linear relation between molecular gas and star formation rate surface density, N mol ~ 0.96 ± 0.16, with a molecular gas depletion time, τmol dep ~ 2.30 ± 1.32 Gyr. We show that in the molecular regions of our galaxies there are no clear correlations between τmol dep and the free-fall and effective Jeans dynamical times throughout the sample. We do not find strong trends in the power-law index of the spatially resolved molecular gas star formation law or the molecular gas depletion time across the range of galactic stellar masses sampled (M * ~ 109.7-1011.5 M ⊙). There is a trend, however, in global measurements that is particularly marked for low-mass galaxies. We suggest that this trend is probably due to the low surface brightness CO J = 1-0, and it is likely associated with changes in CO-to-H2 conversion factor.

  10. A simple theory of bimodal star formation

    NASA Technical Reports Server (NTRS)

    Wyse, Rosemary F. G.; Silk, J.

    1987-01-01

    A model of bimodal star formation is presented, wherein massive stars form in giant molecular clouds (GNC), at a rate regulated by supernovae energy feedback through the interstellar medium, the heat input also ensuring that the initial mass function (IMF) remains skewed towards massive stars. The low mass stars form at a constant rate. The formation of the GMC is governed by the dynamics of the host galaxy through the rotation curve and potential perturbations such as a spiral density wave. The characteristic masses, relative normalizations, and rates of formation of the massive and low mass modes of star formation may be tightly constrained by the requirements of the chemical evolution in the Solar Neighborhood. Good fits were obtained for the age metallicity relation and the metallicity structure of thin disk and spheroid stars only for a narrow range of these parameters.

  11. STAR FORMATION IN THE OUTER DISK OF SPIRAL GALAXIES

    SciTech Connect

    Barnes, Kate L.; Van Zee, Liese; Cote, Stephanie; Schade, David E-mail: vanzee@astro.indiana.edu E-mail: David.Schade@nrc-cnrc.gc.ca

    2012-09-20

    We combine new deep and wide field of view H{alpha} imaging of a sample of eight nearby (d Almost-Equal-To 17 Mpc) spiral galaxies with new and archival H I and CO imaging to study the star formation and the star formation regulation in the outer disk. We find that, in agreement with previous studies, star formation in the outer disk has low covering fractions, and star formation is typically organized into spiral arms. The star formation in the outer disk is at extremely low levels, with typical star formation rate surface densities of {approx}10{sup -5} to 10{sup -6} M{sub Sun} yr{sup -1} kpc{sup -2}. We find that the ratio of the radial extent of detected H II regions to the radius of the H I disk is typically {approx}>85%. This implies that in order to further our understanding of the implications of extended star formation, we must further our understanding of the formation of extended H I disks. We measure the gravitational stability of the gas disk, and find that the outer gaseous disk is typically a factor of {approx}2 times more stable than the inner star-forming disk. We measure the surface density of outer disk H I arms, and find that the disk is closer to gravitational instability along these arms. Therefore, it seems that spiral arms are a necessary, but not sufficient, requirement for star formation in the outer disk. We use an estimation of the flaring of the outer gas disk to illustrate the effect of flaring on the Schmidt power-law index; we find that including flaring increases the agreement between the power-law indices of the inner and outer disks.

  12. TRIGGERED STAR FORMATION SURROUNDING WOLF-RAYET STAR HD 211853

    SciTech Connect

    Liu Tie; Wu Yuefang; Zhang Huawei; Qin Shengli

    2012-05-20

    The environment surrounding Wolf-Rayet (W-R) star HD 211853 is studied in molecular, infrared, as well as radio, and H I emission. The molecular ring consists of well-separated cores, which have a volume density of 10{sup 3} cm{sup -3} and kinematic temperature {approx}20 K. Most of the cores are under gravitational collapse due to external pressure from the surrounding ionized gas. From the spectral energy distribution modeling toward the young stellar objects, the sequential star formation is revealed on a large scale in space spreading from the W-R star to the molecular ring. A small-scale sequential star formation is revealed toward core 'A', which harbors a very young star cluster. Triggered star formations are thus suggested. The presence of the photodissociation region, the fragmentation of the molecular ring, the collapse of the cores, and the large-scale sequential star formation indicate that the 'collect and collapse' process functions in this region. The star-forming activities in core 'A' seem to be affected by the 'radiation-driven implosion' process.

  13. Star-forming galaxy models: Blending star formation into TREESPH

    NASA Technical Reports Server (NTRS)

    Mihos, J. Christopher; Hernquist, Lars

    1994-01-01

    We have incorporated star-formation algorithms into a hybrid N-body/smoothed particle hydrodynamics code (TREESPH) in order to describe the star forming properties of disk galaxies over timescales of a few billion years. The models employ a Schmidt law of index n approximately 1.5 to calculate star-formation rates, and explicitly include the energy and metallicity feedback into the Interstellar Medium (ISM). Modeling the newly formed stellar population is achieved through the use of hybrid SPH/young star particles which gradually convert from gaseous to collisionless particles, avoiding the computational difficulties involved in creating new particles. The models are shown to reproduce well the star-forming properties of disk galaxies, such as the morphology, rate of star formation, and evolution of the global star-formation rate and disk gas content. As an example of the technique, we model an encounter between a disk galaxy and a small companion which gives rise to a ring galaxy reminiscent of the Cartwheel (AM 0035-35). The primary galaxy in this encounter experiences two phases of star forming activity: an initial period during the expansion of the ring, and a delayed phase as shocked material in the ring falls back into the central regions.

  14. AN INFRARED CENSUS OF STAR FORMATION IN THE HORSEHEAD NEBULA

    SciTech Connect

    Bowler, Brendan P.; Waller, William H.; Megeath, S. Thomas; Patten, Brian M.; Tamura, Motohide E-mail: william.waller@tufts.edu E-mail: bpatten@nsf.gov

    2009-03-15

    At {approx} 400 pc, the Horsehead Nebula (B33) is the closest radiatively sculpted pillar to the Sun, but the state and extent of star formation in this structure is not well understood. We present deep near-infrared (IRSF/SIRIUS JHK {sub S}) and mid-infrared (Spitzer/IRAC) observations of the Horsehead Nebula to characterize the star-forming properties of this region and to assess the likelihood of triggered star formation. Infrared color-color and color-magnitude diagrams are used to identify young stars based on infrared excess emission and positions to the right of the zero-age main sequence, respectively. Of the 45 sources detected at both near- and mid-infrared wavelengths, three bona fide and five candidate young stars are identified in this 7' x 7' region. Two bona fide young stars have flat infrared spectral energy distributions and are located at the western irradiated tip of the pillar. The spatial coincidence of the protostars at the leading edge of this elephant trunk is consistent with the radiation-driven implosion model of triggered star formation. There is no evidence, however, for sequential star formation within the immediate {approx} 1.'5 (0.17 pc) region from the cloud/H II region interface.

  15. Properties and Formation of Star Clusters

    NASA Astrophysics Data System (ADS)

    Sharina, M. E.

    2016-03-01

    Many key problems in astrophysics involve research on the properties of star clusters, for example: stellar evolution and nucleosynthesis, the history of star formation in galaxies, formation dynamics of galaxies and their subsystems, the calibration of the fundamental distance scale in the universe, and the luminosity functions of stars and star clusters. This review is intended to familiarize the reader with modern observational and theoretical data on the formation and evolution of star clusters in our galaxy and others. Unsolved problems in this area are formulated and research on ways to solve them is discussed. In particular, some of the most important current observational and theoretical problems include: (1) a more complete explanation of the physical processes in molecular clouds leading to the formation and evolution of massive star clusters; (2) observation of these objects in different stages of evolution, including protoclusters, at wavelengths where interstellar absorption is minimal; and, (3) comparison of the properties of massive star clusters in different galaxies and of galaxies during the most active star formation phase at different red shifts. The main goal in solving these problems is to explain the variations in the abundance of chemical elements and in the multiple populations of stars in clusters discovered at the end of the twentieth century.

  16. The Embedded Phase of Massive Star Formation

    NASA Astrophysics Data System (ADS)

    van der Tak, Floris

    2000-11-01

    This thesis studies the physical and chemical structure of a set of massive young stars which are surrounded by a thick envelope of dust and gas, the earliest known phase of massive star formation. The primary scientific questions addressed are: (i) What is the evolutionary order of the phenomena associated with massive star formation? (ii) What is the physical and chemical structure of the envelopes of massive young stars? How do they compare to those of low-mass stars? Do specific molecules trace different stages? (iii) What are the masses of any circumstellar disks, and on what time scales are they dispersed? To answer these questions, a sample of infrared and submillimeter sources has been selected on high luminosity, close distance, isolated location and high mid-infrared flux. We present observations of these sources with single-dish submillimeter antennas, millimeter interferometers and near-infrared spectroscopy, and also discuss ISO spectra. For the interpretation, we have developed models with a detailed physical structure, combined with chemical differentiation, which is strongly coupled to the temperature. Some of the conclusions are: The envelopes of massive young stars are well described by centrally heated spherical models, with masses of ~ 100-1000 Modot within radii of ~0.1 pc. For a power-law density structure n(r) = n0 (r / r0)-α, we find α = 1.0-1.5 for the younger sources, significantly lower than α ≅ 2 found for the envelopes of low-mass stars at a comparable stage of evolution. This difference may indicate that the support against gravitational collapse in high-mass cores is by nonthermal (e.g., turbulent) pressure, and in low-mass cores by thermal pressure. For the more evolved sources, α = 1.5-2.0 fits the data best. Unlike in low-mass star formation, the near-infrared emission decreases as the envelope warms up, indicates that the hot dust close to the star is destroyed and/or pushed out by stellar radiation or mass loss. The

  17. RADIATION-HYDRODYNAMIC SIMULATIONS OF THE FORMATION OF ORION-LIKE STAR CLUSTERS. II. THE INITIAL MASS FUNCTION FROM WINDS, TURBULENCE, AND RADIATION

    SciTech Connect

    Krumholz, Mark R.; Klein, Richard I.; McKee, Christopher F.

    2012-07-20

    We report a series of simulations of the formation of a star cluster similar to the Orion Nebula Cluster (ONC), including both radiative transfer and protostellar outflows, and starting from both smooth and self-consistently turbulent initial conditions. Each simulation forms >150 stars and brown dwarfs, yielding a stellar mass distribution that ranges from <0.1 M{sub Sun} to >10 M{sub Sun }. We show that a simulation that begins with self-consistently turbulent density and velocity fields embedded in a larger turbulent volume, and that includes protostellar outflows, produces an initial mass function (IMF) that is consistent both with that of the ONC and the Galactic field, at least within the statistical power provided by the number of stars formed in our simulations. This is the first simulation published to date that reproduces the observed IMF in a cluster large enough to contain massive stars, and where the peak of the mass function is determined by a fully self-consistent calculation of gas thermodynamics rather than a hand-imposed equation of state. This simulation also produces a star formation rate that, while still somewhat too high, is much closer to observed values than if we omit either the larger turbulent volume or the outflows. Moreover, we show that the combination of outflows, self-consistently turbulent initial conditions, and turbulence continually fed by motions on scales larger than that of the protocluster yields an IMF that is in agreement with observations and invariant with time, resolving the 'overheating' problem in which simulations without these features have an IMF peak that shifts to progressively higher masses over time as more and more of the gas is heated, inconsistent with the observed invariance of the IMF. The simulation that matches the observed IMF also qualitatively reproduces the observed trend of stellar multiplicity strongly increasing with mass. We show that this simulation produces massive stars from distinct massive

  18. Star formation in the early universe

    NASA Astrophysics Data System (ADS)

    Bromm, Volker

    We investigate the formation of the first stars in the universe. In the context of hierarchical models of structure formation, these Population III stars are expected to form in high or peaks of mass ˜106 M⊙ , collapsing at redshifts ≃20-30. We present an exploratory survey, based on numerical simulations using the SPH method. The main results are: (1) Just before the onset of gravitational instability, the primordial gas attains a characteristic temperature of a few 100 K, and a density of 103-104cm-3, with corresponding Jeans mass MJ of ˜10 3 M⊙ . These characteristic values have robust explanation in the microphysics of H2 cooling, related to the minimum temperature that can be reached with the H2 coolant, and to the critical density at which the transition takes place between levels being populated according to NLTE, and according to LTE. The gas fragments into clumps with initial masses close to MJ. This result is remarkably insensitive to the initial conditions, and suggests that the first stars might have been quite massive. (2) The later evolutionary stages, during which the clumps grow in mass due to accretion and merging with other clumps, are quite sensitive to the initial conditions. The key process in building up very massive clumps, with masses up to a few times 104 M⊙ , is merging. (3) We follow the collapse of a clump up to central densities of ˜1014cm-3. Three-body reactions are very efficient in converting the hydrogen into fully molecular form. A central core of ˜102 M⊙ is in a state of free-fall, leaving behind an extended envelope with an isothermal profile. No further subfragmentation is seen. (4) We calculate the generic spectral signature of a population of massive stars at high redshifts. The production rate of ionizing radiation per stellar mass by stars more massive than ˜100 M⊙ is larger by ˜1 order of magnitude for hydrogen and He I, and by ˜2 orders of magnitude for He II, than the emission from a Salpeter IMF.

  19. The Star Formation Relation in Nearby Galaxies

    NASA Astrophysics Data System (ADS)

    Schruba, Andreas

    2013-03-01

    I review observational studies of the large-scale star formation process in nearby galaxies. A wealth of new multi-wavelength data provide an unprecedented view on the interplay of the interstellar medium and (young) stellar populations on a few hundred parsec scale in 100+ galaxies of all types. These observations enable us to relate detailed studies of star formation in the Milky Way to the zoo of galaxies in the distant universe. Within the disks of spiral galaxies, recent star formation strongly scales with the local amount of molecular gas (as traced by CO) with a molecular gas depletion time of ˜2 Gyr. This is consistent with the picture that stars form in giant molecular clouds that have about universal properties. Galaxy centers and star-bursting galaxies deviate from this normal trend as they show enhanced star formation per unit gas mass suggesting systematic changes in the molecular gas properties and especially the dense gas fraction. In the outer disks of spirals and in dwarf galaxies, the decreasing availability of atomic gas inevitably limits the amount of star formation, though with large local variations. The critical step for the gas-stars cycle seems therefore to be the formation of a molecular gas phase, a process that shows complex dependencies on various environmental properties and is being investigated by intensive simulational work.

  20. Star formation in the Magellanic clouds

    NASA Technical Reports Server (NTRS)

    Frogel, Jay A.

    1987-01-01

    Because of their proximity, the Magellanic Clouds provide the opportunity to conduct a detailed study of the history and current state of star formation in dwarf irregular galaxies. There is considerable evidence that star formation in the Clouds was and is proceeding in a manner different from that found in a typical well-ordered spiral galaxy. Star formation in both Clouds appears to have undergone a number of relatively intense bursts. There exist a number of similarities and differences in the current state of star formation in the Magellanic Clouds and the Milky Way. Examination of Infrared Astronomy Satellite (IRAS) sources with ground based telescopes allows identification of highly evolved massive stars with circumstellar shells as well as several types of compact emission line objects.

  1. Star formation rate in the solar neighborhood

    NASA Astrophysics Data System (ADS)

    Cignoni, Michele

    2006-08-01

    This thesis develops a method for obtaining the star formation histories of a mixed, resolved population through the use of color-magnitude diagrams (CMDs). The method is applied to the derivation of the local star formation rate, modeling observations of the Hipparcos satellite wigth synthetic CMDs computed for different star formation histories with an updated stellar evolution library. Parallax and photometric uncertainties are included explicitly and corrected using the Bayesian Richardson-Lucy algorithm. We find that the solar neighborhood star formation rate has a characteristic timescale for variation of about 6 Gyr, with a maximum activity close to 3 Gyr ago. This suggests a global, rather than local, star forming event. The summary and conclusions are included here, the full thesis is available at the URL listed above.

  2. The void galaxy survey: Star formation properties

    NASA Astrophysics Data System (ADS)

    Beygu, B.; Kreckel, K.; van der Hulst, J. M.; Jarrett, T. H.; Peletier, R.; van de Weygaert, R.; van Gorkom, J. H.; Aragon-Calvo, M. A.

    2016-05-01

    We study the star formation properties of 59 void galaxies as part of the Void Galaxy Survey (VGS). Current star formation rates are derived from H α and recent star formation rates from near-UV imaging. In addition, infrared 3.4, 4.6, 12 and 22 μm Wide-field Infrared Survey Explorer emission is used as star formation and mass indicator. Infrared and optical colours show that the VGS sample displays a wide range of dust and metallicity properties. We combine these measurements with stellar and H I masses to measure the specific SFRs (SFR/M*) and star formation efficiencies ({SFR/{M }_H I}). We compare the star formation properties of our sample with galaxies in the more moderate density regions of the cosmic web, `the field'. We find that specific SFRs of the VGS galaxies as a function of stellar and H I mass are similar to those of the galaxies in these field regions. Their SFR α is slightly elevated than the galaxies in the field for a given total H I mass. In the global star formation picture presented by Kennicutt-Schmidt, VGS galaxies fall into the regime of low average star formation and correspondingly low H I surface density. Their mean {SFR α /{M}_{H I} and SFR α/M* are of the order of 10- 9.9 yr- 1. We conclude that while the large-scale underdense environment must play some role in galaxy formation and growth through accretion, we find that even with respect to other galaxies in the more mildly underdense regions, the increase in star formation rate is only marginal.

  3. Nonuniversal Star Formation Efficiency in Turbulent ISM

    NASA Astrophysics Data System (ADS)

    Semenov, Vadim A.; Kravtsov, Andrey V.; Gnedin, Nickolay Y.

    2016-08-01

    We present a study of a star formation prescription in which star formation efficiency (SFE) depends on local gas density and turbulent velocity dispersion, as suggested by direct simulations of SF in turbulent giant molecular clouds (GMCs). We test the model using a simulation of an isolated Milky-Way-sized galaxy with a self-consistent treatment of turbulence on unresolved scales. We show that this prescription predicts a wide variation of local SFE per free-fall time, {ɛ }{ff} ˜ 0.1%–10%, and gas depletion time, {t}{dep} ˜ 0.1–10 Gyr. In addition, it predicts an effective density threshold for star formation due to suppression of {ɛ }{ff} in warm diffuse gas stabilized by thermal pressure. We show that the model predicts star formation rates (SFRs) in agreement with observations from the scales of individual star-forming regions to the kiloparsec scales. This agreement is nontrivial, as the model was not tuned in any way and the predicted SFRs on all scales are determined by the distribution of the GMC-scale densities and turbulent velocities σ in the cold gas within the galaxy, which is shaped by galactic dynamics. The broad agreement of the star formation prescription calibrated in the GMC-scale simulations with observations both gives credence to such simulations and promises to put star formation modeling in galaxy formation simulations on a much firmer theoretical footing.

  4. Nonuniversal Star Formation Efficiency in Turbulent ISM

    NASA Astrophysics Data System (ADS)

    Semenov, Vadim A.; Kravtsov, Andrey V.; Gnedin, Nickolay Y.

    2016-08-01

    We present a study of a star formation prescription in which star formation efficiency (SFE) depends on local gas density and turbulent velocity dispersion, as suggested by direct simulations of SF in turbulent giant molecular clouds (GMCs). We test the model using a simulation of an isolated Milky-Way-sized galaxy with a self-consistent treatment of turbulence on unresolved scales. We show that this prescription predicts a wide variation of local SFE per free-fall time, {ε }{ff} ∼ 0.1%–10%, and gas depletion time, {t}{dep} ∼ 0.1–10 Gyr. In addition, it predicts an effective density threshold for star formation due to suppression of {ε }{ff} in warm diffuse gas stabilized by thermal pressure. We show that the model predicts star formation rates (SFRs) in agreement with observations from the scales of individual star-forming regions to the kiloparsec scales. This agreement is nontrivial, as the model was not tuned in any way and the predicted SFRs on all scales are determined by the distribution of the GMC-scale densities and turbulent velocities σ in the cold gas within the galaxy, which is shaped by galactic dynamics. The broad agreement of the star formation prescription calibrated in the GMC-scale simulations with observations both gives credence to such simulations and promises to put star formation modeling in galaxy formation simulations on a much firmer theoretical footing.

  5. Infrared observations of OB star formation in NGC 6334

    NASA Technical Reports Server (NTRS)

    Harvey, P. M.; Gatley, I.

    1982-01-01

    Infrared photometry and maps from 2 to 100 microns are presented for three of the principal far infrared sources in NGC 6334. Each region is powered by two or more very young stars. The distribution of dust and ionized gas is probably strongly affected by the presence of the embedded stars; one of the sources is a blister H II region, another has a bipolar structure, and the third exhibits asymmetric temperature structure. The presence of protostellar objects throughout the region suggests that star formation has occurred nearly simultaneously in the whole molecular cloud rather than having been triggered sequentially from within.

  6. CARMA SURVEY TOWARD INFRARED-BRIGHT NEARBY GALAXIES (STING). II. MOLECULAR GAS STAR FORMATION LAW AND DEPLETION TIME ACROSS THE BLUE SEQUENCE

    SciTech Connect

    Rahman, Nurur; Bolatto, Alberto D.; Fisher, David B.; Vogel, Stuart N.; Xue Rui; Wong, Tony; Leroy, Adam K.; Walter, Fabian; Bigiel, Frank; Rosolowsky, Erik; Blitz, Leo; West, Andrew A.; Ott, Juergen

    2012-02-01

    We present an analysis of the relationship between molecular gas and current star formation rate surface density at sub-kiloparsec and kiloparsec scales in a sample of 14 nearby star-forming galaxies. Measuring the relationship in the bright, high molecular gas surface density ({Sigma}{sub H{sub 2}}{approx}>20 M{sub Sun} pc{sup -2}) regions of the disks to minimize the contribution from diffuse extended emission, we find an approximately linear relation between molecular gas and star formation rate surface density, N{sub mol} {approx} 0.96 {+-} 0.16, with a molecular gas depletion time, {tau}{sup mol}{sub dep} {approx} 2.30 {+-} 1.32 Gyr. We show that in the molecular regions of our galaxies there are no clear correlations between {tau}{sup mol}{sub dep} and the free-fall and effective Jeans dynamical times throughout the sample. We do not find strong trends in the power-law index of the spatially resolved molecular gas star formation law or the molecular gas depletion time across the range of galactic stellar masses sampled (M{sub *} {approx} 10{sup 9.7}-10{sup 11.5} M{sub Sun }). There is a trend, however, in global measurements that is particularly marked for low-mass galaxies. We suggest that this trend is probably due to the low surface brightness CO J = 1-0, and it is likely associated with changes in CO-to-H{sub 2} conversion factor.

  7. The Center for Star Formation Studies

    NASA Technical Reports Server (NTRS)

    Hollenbach, D.; Bell, K. R.; Laughlin, G.

    2002-01-01

    The Center for Star Formation Studies, a consortium of scientists from the Space Science Division at Ames and the Astronomy Departments of the University of California at Berkeley and Santa Cruz, conducts a coordinated program of theoretical research on star and planet formation. Under the directorship of D. Hollenbach (Ames), the Center supports postdoctoral fellows, senior visitors, and students; meets regularly at Ames to exchange ideas and to present informal seminars on current research; hosts visits of outside scientists; and conducts a week-long workshop on selected aspects of star and planet formation each summer.

  8. FINE-STRUCTURE Fe II* EMISSION AND RESONANT Mg II EMISSION IN z {approx} 1 STAR-FORMING GALAXIES

    SciTech Connect

    Kornei, Katherine A.; Shapley, Alice E.; Martin, Crystal L.; Coil, Alison L.; Lotz, Jennifer M.; Weiner, Benjamin J.

    2013-09-01

    We present a study of the prevalence, strength, and kinematics of ultraviolet Fe II and Mg II emission lines in 212 star-forming galaxies at z {approx} 1 selected from the DEEP2 survey. We find Fe II* emission in composite spectra assembled on the basis of different galaxy properties, indicating that Fe II* emission is common at z {approx} 1. In these composites, Fe II* emission is observed at roughly the systemic velocity. At z {approx} 1, we find that the strength of Fe II* emission is most strongly modulated by dust attenuation, and is additionally correlated with redshift, star formation rate, and [O II] equivalent width, such that systems at higher redshifts with lower dust levels, lower star formation rates, and larger [O II] equivalent widths show stronger Fe II* emission. We detect Mg II emission in at least 15% of the individual spectra and we find that objects showing stronger Mg II emission have higher specific star formation rates, smaller [O II] linewidths, larger [O II] equivalent widths, lower dust attenuations, and lower stellar masses than the sample as a whole. Mg II emission strength exhibits the strongest correlation with specific star formation rate, although we find evidence that dust attenuation and stellar mass also play roles in the regulation of Mg II emission. Future integral field unit observations of the spatial extent of Fe II* and Mg II emission in galaxies with high specific star formation rates, low dust attenuations, and low stellar masses will be important for probing the morphology of circumgalactic gas.

  9. Formation and Assembly of Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    McMillan, Stephen

    The formation of stars and star clusters is a major unresolved problem in astrophysics. It is central to modeling stellar populations and understanding galaxy luminosity distributions in cosmological models. Young massive clusters are major components of starburst galaxies, while globular clusters are cornerstones of the cosmic distance scale and represent vital laboratories for studies of stellar dynamics and stellar evolution. Yet how these clusters form and how rapidly and efficiently they expel their natal gas remain unclear, as do the consequences of this gas expulsion for cluster structure and survival. Also unclear is how the properties of low-mass clusters, which form from small-scale instabilities in galactic disks and inform much of our understanding of cluster formation and star-formation efficiency, differ from those of more massive clusters, which probably formed in starburst events driven by fast accretion at high redshift, or colliding gas flows in merging galaxies. Modeling cluster formation requires simulating many simultaneous physical processes, placing stringent demands on both software and hardware. Simulations of galaxies evolving in cosmological contexts usually lack the numerical resolution to simulate star formation in detail. They do not include detailed treatments of important physical effects such as magnetic fields, radiation pressure, ionization, and supernova feedback. Simulations of smaller clusters include these effects, but fall far short of the mass of even single young globular clusters. With major advances in computing power and software, we can now directly address this problem. We propose to model the formation of massive star clusters by integrating the FLASH adaptive mesh refinement magnetohydrodynamics (MHD) code into the Astrophysical Multi-purpose Software Environment (AMUSE) framework, to work with existing stellar-dynamical and stellar evolution modules in AMUSE. All software will be freely distributed on-line, allowing

  10. Educational Applications of Star Formation Research

    NASA Astrophysics Data System (ADS)

    Waller, William; Clemens, Cathy; Green, Paul

    2005-07-01

    Research into the formation of stars involves many exciting physical processes -- from vast magnetized clouds collapsing under their own weight, to thermonuclear reactions igniting inside dense stellar cores, to powerful jets being shot from proto-planetary disks. Star formation research also touches on many aspects of the educational enterprise that is ongoing in schools, museums, and other community venues. In this presentation, we will (1) show how the science of star formation relates to the various learning goals and standards that currently underlie formal K-14 science and technology education, (2) describe the various opportunities that exist for space scientists to get involved in educational outreach, and (3) provide some examples of available resources that support educational outreach involving star formation.

  11. THE JAMES CLERK MAXWELL TELESCOPE NEARBY GALAXIES LEGACY SURVEY. II. WARM MOLECULAR GAS AND STAR FORMATION IN THREE FIELD SPIRAL GALAXIES

    SciTech Connect

    Warren, B. E.; Wilson, C. D.; Sinukoff, E.; Israel, F. P.; Van der Werf, P. P.; Serjeant, S.; Bendo, G. J.; Clements, D. L.; Brinks, E.; Irwin, J. A.; Knapen, J. H.; Leech, J.; Tan, B. K.; Matthews, H. E.; Muehle, S.; Mortimer, A. M. J.; Petitpas, G.; Spekkens, K.; Tilanus, R. P. J.; Usero, A. E-mail: wilson@physics.mcmaster.c E-mail: israel@strw.leidenuniv.n

    2010-05-01

    We present the results of large-area {sup 12}CO J = 3-2 emission mapping of three nearby field galaxies, NGC 628, NGC 3521, and NGC 3627, completed at the James Clerk Maxwell Telescope as part of the Nearby Galaxies Legacy Survey. These galaxies all have moderate to strong {sup 12}CO J = 3-2 detections over large areas of the fields observed by the survey, showing resolved structure and dynamics in their warm/dense molecular gas disks. All three galaxies were part of the Spitzer Infrared Nearby Galaxies Survey sample, and as such have excellent published multiwavelength ancillary data. These data sets allow us to examine the star formation properties, gas content, and dynamics of these galaxies on sub-kiloparsec scales. We find that the global gas depletion time for dense/warm molecular gas in these galaxies is consistent with other results for nearby spiral galaxies, indicating this may be independent of galaxy properties such as structures, gas compositions, and environments. Similar to the results from The H I Nearby Galaxy Survey, we do not see a correlation of the star formation efficiency with the gas surface density consistent with the Schmidt-Kennicutt law. Finally, we find that the star formation efficiency of the dense molecular gas traced by {sup 12}CO J = 3-2 is potentially flat or slightly declining as a function of molecular gas density, the {sup 12}CO J = 3-2/J = 1-0 ratio (in contrast to the correlation found in a previous study into the starburst galaxy M83), and the fraction of total gas in molecular form.

  12. Star formation relations in nearby molecular clouds

    SciTech Connect

    Evans, Neal J. II; Heiderman, Amanda; Vutisalchavakul, Nalin

    2014-02-20

    We test some ideas for star formation relations against data on local molecular clouds. On a cloud by cloud basis, the relation between the surface density of star formation rate and surface density of gas divided by a free-fall time, calculated from the mean cloud density, shows no significant correlation. If a crossing time is substituted for the free-fall time, there is even less correlation. Within a cloud, the star formation rate volume and surface densities increase rapidly with the corresponding gas densities, faster than predicted by models using the free-fall time defined from the local density. A model in which the star formation rate depends linearly on the mass of gas above a visual extinction of 8 mag describes the data on these clouds, with very low dispersion. The data on regions of very massive star formation, with improved star formation rates based on free-free emission from ionized gas, also agree with this linear relation.

  13. How Galactic Environment Regulates Star Formation

    NASA Astrophysics Data System (ADS)

    Meidt, Sharon E.

    2016-02-01

    In a new simple model I reconcile two contradictory views on the factors that determine the rate at which molecular clouds form stars—internal structure versus external, environmental influences—providing a unified picture for the regulation of star formation in galaxies. In the presence of external pressure, the pressure gradient set up within a self-gravitating turbulent (isothermal) cloud leads to a non-uniform density distribution. Thus the local environment of a cloud influences its internal structure. In the simple equilibrium model, the fraction of gas at high density in the cloud interior is determined simply by the cloud surface density, which is itself inherited from the pressure in the immediate surroundings. This idea is tested using measurements of the properties of local clouds, which are found to show remarkable agreement with the simple equilibrium model. The model also naturally predicts the star formation relation observed on cloud scales and at the same time provides a mapping between this relation and the closer-to-linear molecular star formation relation measured on larger scales in galaxies. The key is that pressure regulates not only the molecular content of the ISM but also the cloud surface density. I provide a straightforward prescription for the pressure regulation of star formation that can be directly implemented in numerical models. Predictions for the dense gas fraction and star formation efficiency measured on large-scales within galaxies are also presented, establishing the basis for a new picture of star formation regulated by galactic environment.

  14. A Galaxy Blazes With Star Formation

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Scientists using NASA's Hubble Space Telescope (HST) are studying the colors of star clusters to determine the age and history of starburst galaxies, a technique somewhat similar to the process of learning the age of a tree by counting its rings. One such galaxy, Galaxy NGC 3310, a hotbed of star formation showcased in this HST photograph, is forming clusters of stars at a prodigious rate. The image shows several hundred star clusters, visible as the bright blue diffuse objects tracing the galaxy's spiral arms. Each of these star clusters represents the formation of up to about a million stars, a process that takes less than 100,000 years. In addition, hundreds of individual young stars can be seen throughout the galaxy. The star clusters become redder with age as the most massive and bluest stars exhaust their fuel and burn out. Measurements in this image of the wide range of cluster colors show their ages range between about one million and more that one hundred million years. This suggests the starburst 'turned on' more than 100 million years ago.

  15. Dissecting star formation in N159

    NASA Astrophysics Data System (ADS)

    Indebetouw, Remy

    2013-10-01

    We propose to investigate star formation as a function of time, space, and mass in the Large Magellanic Cloud star formation region N159. We will combine HST photometry in V, I, J, H, and Halpha equivalent filters with our already scheduled Atacama Large {sub} Millimeter Array {ALMA; PI Fukui} and our existing Australia Telescope Compact Array {ATCA; PI Seale and PI Chen} observations. These datasets will allow us for the first time to completely characterize protostars, HII regions, and molecular gas in this reduced-metallicity region. The region is a remarkable laboratory, containing at once a spontaneously cluster-forming giant molecular cloud {GMC}, an arguably triggered star-forming GMC, and a more quiescent GMC.We will use color-magnitude diagram {CMD} and spectral energy distribution {SED} modeling to separate redenning, circumstellar dust emission, and pre-main-sequence spectral type for each star, mapping not only current star formation activity but its history {over the last 50Myr using pre-main-sequence stars, and over a Hubble time using classical CMD fitting}. We will use Halpha excess to further characterize the HII regions and all currently accreting protostars with ages up to 50 Myr. We will resolve many limitations of previous Spitzer-based star formation studies, and search for variations in the stellar initial mass function. We will test whether there is a gas density threshold for star formation, and investigate the extent to which environment and feedback also play a role in how galaxies evolve by turning gas into stars.

  16. Induced star formation in interacting galaxies

    NASA Technical Reports Server (NTRS)

    Kennicutt, R. C.; Roettiger, K. A.; Keel, W. C.; Vanderhulst, J. M.; Hummel, E.

    1987-01-01

    Measurements of H alpha emission line fluxes and FIR fluxes in approx. 100 interacting spirals were used to investigate the effects of close tidal interactions on the disk and nuclear star formation rates in galaxies. Two samples of interacting spirals were studied, a complete sample of close pairs, and a set of strongly perturbed systems from the Arp atlas. Both the integrated H alpha luminosities and FIR luminosities are enhanced in the interacting galaxies, indicating that the encounters indeed trigger massive star formation in many cases. The response of individual galaxies is highly variable, however. A majority of the interacting spirals exhibit normal star formation rates, while a small fraction are undergoing bursts with luminosities which are rarely, if ever, observed in noninteracting systems. Virtually all of the latter are in the Arp sample, indicating that the Arp atlas is heavily biased to the most active star forming systems.

  17. Magnetic fields and galactic star formation rates

    SciTech Connect

    Loo, Sven Van; Tan, Jonathan C.; Falle, Sam A. E. G.

    2015-02-10

    The regulation of galactic-scale star formation rates (SFRs) is a basic problem for theories of galaxy formation and evolution: which processes are responsible for making observed star formation rates so inefficient compared to maximal rates of gas content divided by dynamical timescale? Here we study the effect of magnetic fields of different strengths on the evolution of giant molecular clouds (GMCs) within a kiloparsec patch of a disk galaxy and resolving scales down to ≃0.5 pc. Including an empirically motivated prescription for star formation from dense gas (n{sub H}>10{sup 5} cm{sup −3}) at an efficiency of 2% per local free-fall time, we derive the amount of suppression of star formation by magnetic fields compared to the nonmagnetized case. We find GMC fragmentation, dense clump formation, and SFR can be significantly affected by the inclusion of magnetic fields, especially in our strongest investigated B-field case of 80 μG. However, our chosen kiloparsec-scale region, extracted from a global galaxy simulation, happens to contain a starbursting cloud complex that is only modestly affected by these magnetic fields and likely requires internal star formation feedback to regulate its SFR.

  18. STAR FORMATION IN TWO LUMINOUS SPIRAL GALAXIES

    SciTech Connect

    Hunter, Deidre A.; Ashburn, Allison; Wright, Teresa; Elmegreen, Bruce G.; Rubin, Vera C.; Józsa, Gyula I. G.; Struve, Christian

    2013-10-01

    We examined star formation in two very luminous (M{sub V} = –22 to –23) Sc-type spiral galaxies, NGC 801 and UGC 2885, using ultra-deep Hα images. We combine these Hα images with UBV and Two-Micron All-Sky Survey JHK images and H I maps to explore the star formation characteristics of disk galaxies at high luminosity. Hα traces star formation in these galaxies to 4-6 disk scale lengths, but the lack of detection of Hα further out is likely due to the loss of Lyman continuum photons. Considering gravitational instabilities alone, we find that the gas and stars in the outer regions are marginally stable in an average sense, but considering dissipative gas and radial and azimuthal forcing, the outer regions are marginally unstable to forming spiral arms. Star formation is taking place in spiral arms, which are regions of locally higher gas densities. Furthermore, we have traced smooth exponential stellar disks over four magnitudes in V-band surface brightness and 4-6 disk scale lengths, in spite of a highly variable gravitational instability parameter. Thus, gravitational instability thresholds do not seem relevant to the stellar disk. One possibility for creating an exponential disk is that the molecular cloud densities and star formation rates have exponential profiles and this fact forces the stellar disk to build up such a profile. Another possibility is that the stellar disk is continuously adjusted to an exponential shape regardless of the star formation profile, for example, through global dynamical processes that scatter stars. However, such scattering processes are only known to operate in spiral systems, in which case they cannot explain the same dilemma of smooth exponential disks observed in dwarf irregular galaxies.

  19. Nearby regions of massive star formation

    NASA Astrophysics Data System (ADS)

    Bally, John; Cunningham, Nathaniel; Moeckel, Nickolas; Smith, Nathan

    Observations of the nearest regions of massive star formation such as Orion are reviewed. Early-type stars in the local OB associations, as well as their superbubbles and supershells provide a fossil record of massive star birth in the Solar vicinity over about the last 40 Myr. This record shows that most massive stars are born from dense, high-pressure, hot cores which spawn transient clusters that dissipate into the field soon after formation. A large fraction (15 to 30%) of massive stars are high-velocity runaways moving at more than 20 km s^{-1}. High-mass stars have a larger companion fraction than their lower-mass siblings. The Orion star forming complex contains the nearest site of on-going massive star formation. Studies of the Orion Nebula and the dense molecular cloud core located immediately behind the HII region provide our sharpest view of massive star birth. This region has formed a hierarchy of clusters within clusters. The Trapezium, OMC-1S, and OMC-1 regions represent three closely spaced sub-clusters within the more extended Orion Nebula Cluster. The oldest of these sub-clusters, which consists of the Trapezium stars, has completely emerged from its natal core. The OMC-1S and OMC-1 regions, are still highly embedded and forming clusters of additional moderate and high mass stars. Over a dozen YSOs embedded in OMC-1S are driving jets and outflows, many of which are injecting energy and momentum into the Orion Nebula. Recent proper motion measurements indicate that the Becklin-Neugebauer object is a high-velocity star moving away from the OMC1 core with a velocity of 30 km s^{-1}, making it the youngest high-velocity star known. Source I may be moving in the opposite direction with a velocity of about 12 km s^{-1}. The projected separation between source I and BN was less than few hundred AU about 500 years ago. The spectacular bipolar molecular outflow and system of shock-excited H_2 fingers emerging from OMC-1 has a dynamical age of about 1100

  20. High mass star formation in the galaxy

    NASA Technical Reports Server (NTRS)

    Scoville, N. Z.; Good, J. C.

    1987-01-01

    The Galactic distributions of HI, H2, and HII regions are reviewed in order to elucidate the high mass star formation occurring in galactic spiral arms and in active galactic nuclei. Comparison of the large scale distributions of H2 gas and radio HII regions reveals that the rate of formation of OB stars depends on (n sub H2) sup 1.9 where (n sub H2) is the local mean density of H2 averaged over 300 pc scale lengths. In addition the efficiency of high mass star formation is a decreasing function of cloud mass in the range 200,000 to 3,000,000 solar mass. These results suggest that high mass star formation in the galactic disk is initiated by cloud-cloud collisions which are more frequent in the spiral arms due to orbit crowding. Cloud-cloud collisions may also be responsible for high rates of OB star formation in interacting galaxies and galactic nuclei. Based on analysis of the Infrared Astronomy Satellite (IRAS) and CO data for selected GMCs in the Galaxy, the ratio L sub IR/M sub H2 can be as high as 30 solar luminosity/solar mass for GMCs associated with HII regions. The L sub IR/M sub H2 ratios and dust temperature obtained in many of the high luminosity IRAS galaxies are similar to those encountered in galactic GMCs with OB star formation. High mass star formation is therefore a viable explanation for the high infrared luminosity of these galaxies.

  1. Local-density-driven clustered star formation

    NASA Astrophysics Data System (ADS)

    Parmentier, G.; Pfalzner, S.

    2013-01-01

    Context. A positive power-law trend between the local surface densities of molecular gas, Σgas, and young stellar objects, Σ ⋆ , in molecular clouds of the solar neighbourhood has recently been identified. How it relates to the properties of embedded clusters, in particular to the recently established radius-density relation, has so far not been investigated. Aims: We model the development of the stellar component of molecular clumps as a function of time and initial local volume density. Our study provides a coherent framework able to explain both the molecular-cloud and embedded-cluster relations quoted above. Methods: We associate the observed volume density gradient of molecular clumps to a density-dependent free-fall time. The molecular clump star formation history is obtained by applying a constant star formation efficiency per free-fall time, ɛff. Results: For the volume density profiles typical of observed molecular clumps (i.e. power-law slope ≃ -1.7), our model gives a star-gas surface-density relation of the form Σ⋆ ∝ Σgas2, which agrees very well with the observations. Taking the case of a molecular clump of mass M0 ≃ 104 M⊙ and radius R ≃ 6 pc experiencing star formation during 2 Myr, we derive what star formation efficiency per free-fall time matches the normalizations of the observed and predicted (Σ ⋆ , Σgas) relations best. We find ɛff ≃ 0.1. We show that the observed growth of embedded clusters, embodied by their radius-density relation, corresponds to a surface density threshold being applied to developing star-forming regions. The consequences of our model in terms of cluster survivability after residual star-forming gas expulsion are that, owing to the locally high star formation efficiency in the inner part of star-forming regions, global star formation efficiency as low as 10% can lead to the formation of bound gas-free star clusters.

  2. Terrestrial Planet Formation in Binary Star Systems

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.; Quintana, Elisa V.; Chambers, John; Duncan, Martin J.; Adams, Fred

    2003-01-01

    Most stars reside in multiple star systems; however, virtually all models of planetary growth have assumed an isolated single star. Numerical simulations of the collapse of molecular cloud cores to form binary stars suggest that disks will form within such systems. Observations indirectly suggest disk material around one or both components within young binary star systems. If planets form at the right places within such circumstellar disks, they can remain in stable orbits within the binary star systems for eons. We are simulating the late stages of growth of terrestrial planets within binary star systems, using a new, ultrafast, symplectic integrator that we have developed for this purpose. We show that the late stages of terrestrial planet formation can indeed take place in a wide variety of binary systems and we have begun to delineate the range of parameter space for which this statement is true. Results of our initial simulations of planetary growth around each star in the alpha Centauri system and other 'wide' binary systems, as well as around both stars in very close binary systems, will be presented.

  3. Using young massive star clusters to understand star formation and feedback in high-redshift-like environments

    NASA Astrophysics Data System (ADS)

    Longmore, S.; Barnes, A.; Battersby, C.; Bally, J.; Kruijssen, J. M. Diederik; Dale, J.; Henshaw, J.; Walker, D.; Rathborne, J.; Testi, L.; Ott, J.; Ginsburg, A.

    2016-05-01

    The formation environment of stars in massive stellar clusters is similar to the environment of stars forming in galaxies at a redshift of 1 - 3, at the peak star formation rate density of the Universe. As massive clusters are still forming at the present day at a fraction of the distance to high-redshift galaxies they offer an opportunity to understand the processes controlling star formation and feedback in conditions similar to those in which most stars in the Universe formed. Here we describe a system of massive clusters and their progenitor gas clouds in the centre of the Milky Way, and outline how detailed observations of this system may be able to: (i) help answer some of the fundamental open questions in star formation and (ii) quantify how stellar feedback couples to the surrounding interstellar medium in this high-pressure, high-redshift analogue environment.

  4. Complex organic molecules and star formation

    NASA Astrophysics Data System (ADS)

    Bacmann, A.; Faure, A.

    2014-12-01

    Star forming regions are characterised by the presence of a wealth of chemical species. For the past two to three decades, ever more complex organic species have been detected in the hot cores of protostars. The evolution of these molecules in the course of the star forming process is still uncertain, but it is likely that they are partially incorporated into protoplanetary disks and then into planetesimals and the small bodies of planetary systems. The complex organic molecules seen in star forming regions are particularly interesting since they probably make up building blocks for prebiotic chemistry. Recently we showed that these species were also present in the cold gas in prestellar cores, which represent the very first stages of star formation. These detections question the models which were until now accepted to account for the presence of complex organic molecules in star forming regions. In this article, we shortly review our current understanding of complex organic molecule formation in the early stages of star formation, in hot and cold cores alike and present new results on the formation of their likely precursor radicals.

  5. TIME-VARYING DYNAMICAL STAR FORMATION RATE

    SciTech Connect

    Lee, Eve J.; Chang, Philip; Murray, Norman

    2015-02-10

    We present numerical evidence of dynamic star formation in which the accreted stellar mass grows superlinearly with time, roughly as t {sup 2}. We perform simulations of star formation in self-gravitating hydrodynamic and magnetohydrodynamic turbulence that is continuously driven. By turning the self-gravity of the gas in the simulations on or off, we demonstrate that self-gravity is the dominant physical effect setting the mass accretion rate at early times before feedback effects take over, contrary to theories of turbulence-regulated star formation. We find that gravitational collapse steepens the density profile around stars, generating the power-law tail on what is otherwise a lognormal density probability distribution function. Furthermore, we find turbulent velocity profiles to flatten inside collapsing regions, altering the size-line width relation. This local flattening reflects enhancements of turbulent velocity on small scales, as verified by changes to the velocity power spectra. Our results indicate that gas self-gravity dynamically alters both density and velocity structures in clouds, giving rise to a time-varying star formation rate. We find that a substantial fraction of the gas that forms stars arrives via low-density flows, as opposed to accreting through high-density filaments.

  6. ON STAR FORMATION RATES AND STAR FORMATION HISTORIES OF GALAXIES OUT TO z {approx} 3

    SciTech Connect

    Wuyts, Stijn; Foerster Schreiber, Natascha M.; Lutz, Dieter; Nordon, Raanan; Berta, Stefano; Genzel, Reinhard; Magnelli, Benjamin; Poglitsch, Albrecht; Altieri, Bruno; Andreani, Paola; Aussel, Herve; Daddi, Emanuele; Elbaz, David; Cimatti, Andrea; Koekemoer, Anton M.; Maiolino, Roberto; McGrath, Elizabeth J.

    2011-09-01

    We compare multi-wavelength star formation rate (SFR) indicators out to z {approx} 3 in the GOODS-South field. Our analysis uniquely combines U to 8 {mu}m photometry from FIREWORKS, MIPS 24 {mu}m and PACS 70, 100, and 160 {mu}m photometry from the PEP, and H{alpha} spectroscopy from the SINS survey. We describe a set of conversions that lead to a continuity across SFR indicators. A luminosity-independent conversion from 24 {mu}m to total infrared luminosity yields estimates of L{sub IR} that are in the median consistent with the L{sub IR} derived from PACS photometry, albeit with significant scatter. Dust correction methods perform well at low-to-intermediate levels of star formation. They fail to recover the total amount of star formation in systems with large SFR{sub IR}/SFR{sub UV} ratios, typically occuring at the highest SFRs (SFR{sub UV+IR} {approx}> 100 M{sub sun} yr{sup -1}) and redshifts (z {approx}> 2.5) probed. Finally, we confirm that H{alpha}-based SFRs at 1.5 < z < 2.6 are consistent with SFR{sub SED} and SFR{sub UV+IR} provided extra attenuation toward H II regions is taken into account (A{sub V,neb} = A{sub V,continuum}/0.44). With the cross-calibrated SFR indicators in hand, we perform a consistency check on the star formation histories inferred from spectral energy distribution (SED) modeling. We compare the observed SFR-M relations and mass functions at a range of redshifts to equivalents that are computed by evolving lower redshift galaxies backward in time. We find evidence for underestimated stellar ages when no stringent constraints on formation epoch are applied in SED modeling. We demonstrate how resolved SED modeling, or alternatively deep UV data, may help to overcome this bias. The age bias is most severe for galaxies with young stellar populations and reduces toward older systems. Finally, our analysis suggests that SFHs typically vary on timescales that are long (at least several 100 Myr) compared to the galaxies' dynamical time.

  7. Star Formation through the Chemical Lens

    NASA Astrophysics Data System (ADS)

    Tassis, K.

    2013-09-01

    Star formation is the process that connects the physical and the observable universe, that lights up the stars and creates planets. Yet to this day our understanding of it remains highly uncertain: the mechanism that is responsible for the fragmentation of star-forming clouds and that regulates the contraction of interstellar gas to form pre-stellar objects and protostars remains the subject of intense debate. At the heart of the problem lies the difficulty in observing star-forming sites and obtaining directly the initial conditions of star formation: molecular hydrogen, the raw material of star formation and the dominant constituent of interstellar clouds that act as stellar nurseries, does not have any transitions that are excitable and thus observable at the chillingly low temperatures of molecular clouds. For this reason, observations of star-forming sites rely heavily on the use of molecular tracers? chemical compounds present in molecular clouds. However, the abundance of these tracers is not constant: it is a result of a complex network of chemical reactions, and it depends on the age, density, and dynamical history of the star-forming site. In this talk, I will discuss how the coupling between chemistry and dynamics can help us probe the initial conditions of star formation and the origin of protostars. To this end, we have studied a variety of dynamical models describing the evolution of prestellar molecular cloud cores that cover the entire spectrum of proposed mechanisms, including pure hydrodynamical collapse and magnetically mediated collapse at various levels of importance of the magnetic field in the cloud dynamics. These models have been coupled to a network of chemical reactions that follow the relative abundances for ~100 molecular species, by solving the nonequilibrium chemical reactions for the first time simultaneously with the dynamical equations. I will present highlights from the results of this work, including newly proposed observables

  8. Star Formation from Galaxies to Globules

    NASA Astrophysics Data System (ADS)

    Elmegreen, Bruce G.

    2002-09-01

    The origin of the empirical laws of galactic scale star formation is considered in view of the self-similar nature of interstellar gas and the observation that most local clusters are triggered by specific high-pressure events. The empirical laws suggest that galactic scale gravity is involved in the first stages of star formation, but they do not identify the actual triggering mechanisms for clusters in the final stages. Many triggering processes satisfy the empirical laws, including turbulence compression and expanding shell collapse. The self-similar nature of the gas and associated young stars suggests that turbulence is more directly involved, but the energy source for this turbulence is not clear, and the small-scale morphology of gas around most embedded clusters does not look like a random turbulent flow. Most clusters appear to be triggered by other nearby stars. Such a prominent local influence makes it difficult to understand the universality of the Kennicutt and Schmidt laws on galactic scales. A unified view of multiscale star formation avoids most of these problems. The Toomre and Kennicutt surface density thresholds, along with the large-scale gas and star formation morphology, imply that ambient self-gravity produces spiral arms and giant cloud complexes and at the same time drives much of the turbulence that leads to self-similar structures. Localized energy input from existing clusters and field supernovae drives turbulence and cloud formation too, while triggering clusters directly in preexisting clouds. The hierarchical structure in the gas made by turbulence ensures that the triggering time scales with size, thereby giving the Schmidt law over a wide range of scales and the size-duration correlation for young star fields. Reanalysis of the Schmidt law from a local point of view suggests that the efficiency of star formation is determined by the fraction of the gas above a critical density of around 105 m(H2) cm-3. Such high densities probably

  9. Cepheid Associates: Star Formation and Distance Calibration

    NASA Astrophysics Data System (ADS)

    Remage Evans, Nancy

    2013-10-01

    XMM-Newton observations are powerful discriminants between young stars and the old field population because of the well known relation between the age of low mass stars and their X-ray strength. We use this property to identify young resolved physical companions of Cepheids and also low mass members of clusters containing Cepheids. This will probe the maximum separation in Cepheid binaries, a diagnostic of star formation. The target list contains the 5 brightest Cepheids in the recent analysis of Cepheids in clusters (Anderson, et al. 2013). This project will identify low mass cluster members which provide a calibration of the distances of clusters.

  10. WINGS-SPE II: A catalog of stellar ages and star formation histories, stellar masses and dust extinction values for local clusters galaxies

    NASA Astrophysics Data System (ADS)

    Fritz, J.; Poggianti, B. M.; Cava, A.; Valentinuzzi, T.; Moretti, A.; Bettoni, D.; Bressan, A.; Couch, W. J.; D'Onofrio, M.; Dressler, A.; Fasano, G.; Kjærgaard, P.; Moles, M.; Omizzolo, A.; Varela, J.

    2011-02-01

    Context. The WIde-field Nearby Galaxy clusters Survey (wings) is a project whose primary goal is to study the galaxy populations in clusters in the local universe (z < 0.07) and of the influence of environment on their stellar populations. This survey has provided the astronomical community with a high quality set of photometric and spectroscopic data for 77 and 48 nearby galaxy clusters, respectively. Aims: In this paper we present the catalog containing the properties of galaxies observed by the wings SPEctroscopic (wings-spe) survey, which were derived using stellar populations synthesis modelling approach. We also check the consistency of our results with other data in the literature. Methods: Using a spectrophotometric model that reproduces the main features of observed spectra by summing the theoretical spectra of simple stellar populations of different ages, we derive the stellar masses, star formation histories, average age and dust attenuation of galaxies in our sample. Results: ~ 5300 spectra were analyzed with spectrophotometric techniques, and this allowed us to derive the star formation history, stellar masses and ages, and extinction for the wings spectroscopic sample that we present in this paper. Conclusions: The comparison with the total mass values of the same galaxies derived by other authors based on sdss data, confirms the reliability of the adopted methods and data. Based on observations taken at the Anglo Australian Telescope (3.9 m- AAT), and at the William Herschel Telescope (4.2 m- WHT).Full Table 2 is available in electronic form both at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/526/A45, and by querying the wings database at http://web.oapd.inaf.it/wings/new/index.html

  11. STARS MDT-II targets mission

    SciTech Connect

    Sims, B.A.; White, J.E.

    1997-08-01

    The Strategic Target System (STARS) was launched successfully on August 31, 1996 from the Kauai Test Facility (KTF) at the Pacific Missile Range Facility (PMRF). The STARS II booster delivered a payload complement of 26 vehicles atop a post boost vehicle. These targets were designed and the mission planning was achieved to provide for a dedicated mission for view by the Midcourse Space Experiment (MSX) Satellite Sensor Suite. Along with the MSX Satellite, other corollary sensors were involved. Included in these were the Airborne Surveillance Test Bed (AST) aircraft, the Cobra Judy sea based radar platform, Kwajalein Missile Range (KMR), and the Kiernan Reentry Measurements Site (KREMS). The launch was a huge success from all aspects. The STARS Booster flew a perfect mission from hardware, software and mission planning respects. The payload complement achieved its desired goals. All sensors (space, air, ship, and ground) attained excellent coverage and data recording.

  12. Formation Channels for Blue Straggler Stars

    NASA Astrophysics Data System (ADS)

    Davies, Melvyn B.

    In this chapter we consider two formation channels for blue straggler stars: (1) the merger of two single stars via a collision, and (2) those produced via mass transfer within a binary. We review how computer simulations show that stellar collisions are likely to lead to relatively little mass loss and are thus effective in producing a young population of more-massive stars. The number of blue straggler stars produced by collisions will tend to increase with cluster mass. We review how the current population of blue straggler stars produced from primordial binaries decreases with increasing cluster mass. This is because exchange encounters with third, single stars in the most massive clusters tend to reduce the fraction of binaries containing a primary close to the current turn-off mass. Rather, their primaries tend to be somewhat more massive and have evolved off the main sequence, filling their Roche lobes in the past, often converting their secondaries into blue straggler stars (but more than 1 Gyr or so ago and thus they are no longer visible today as blue straggler stars).

  13. Low-metallicity Star Formation (IAU S255)

    NASA Astrophysics Data System (ADS)

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

    2009-01-01

    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

  14. THE FIRST GALAXIES: CHEMICAL ENRICHMENT, MIXING, AND STAR FORMATION

    SciTech Connect

    Greif, Thomas H.; Glover, Simon C. O.; Klessen, Ralf S.; Bromm, Volker

    2010-06-10

    Using three-dimensional cosmological simulations, we study the assembly process of one of the first galaxies, with a total mass of {approx}10{sup 8} M {sub sun}, collapsing at z {approx_equal} 10. Our main goal is to trace the transport of the heavy chemical elements produced and dispersed by a pair-instability supernova exploding in one of the minihalo progenitors. To this extent, we incorporate an efficient algorithm into our smoothed particle hydrodynamics code that approximately models turbulent mixing as a diffusion process. We study this mixing with and without the radiative feedback from Population III (Pop III) stars that subsequently form in neighboring minihalos. Our simulations allow us to constrain the initial conditions for second-generation star formation, within the first galaxy itself, and inside of minihalos that virialize after the supernova explosion. We find that most minihalos remain unscathed by ionizing radiation or the supernova remnant, while some are substantially photoheated and enriched to supercritical levels, likely resulting in the formation of low-mass Pop III or even Population II (Pop II) stars. At the center of the newly formed galaxy, {approx}10{sup 5} M {sub sun} of cold, dense gas uniformly enriched to {approx}10{sup -3} Z {sub sun} is in a state of collapse, suggesting that a cluster of Pop II stars will form. The first galaxies, as may be detected by the James Webb Space Telescope, would therefore already contain stellar populations familiar from lower redshifts.

  15. Resolved star formation on sub-galactic scales in a merger at z = 1.7

    SciTech Connect

    Whitaker, Katherine E.; Rigby, Jane R.; Teng, Stacy H.; Brammer, Gabriel B.; Gladders, Michael D.; Sharon, Keren; Wuyts, Eva

    2014-08-01

    We present a detailed analysis of Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) G141 grism spectroscopy for seven star-forming regions of the highly magnified lensed starburst galaxy RCSGA 032727-132609 at z = 1.704. We measure the spatial variations of the extinction in RCS0327 through the observed Hγ/Hβ emission line ratios, finding a constant average extinction of E(B – V){sub gas} = 0.40 ± 0.07. We infer that the star formation is enhanced as a result of an ongoing interaction, with measured star formation rates derived from demagnified, extinction-corrected Hβ line fluxes for the individual star-forming clumps falling >1-2 dex above the star formation sequence. When combining the HST/WFC3 [O III] λ5007/Hβ emission line ratio measurements with [N II]/Hα line ratios from Wuyts et al., we find that the majority of the individual star-forming regions fall along the local 'normal' abundance sequence. With the first detections of the He I λ5876 and He II λ4686 recombination lines in a distant galaxy, we probe the massive-star content of the star-forming regions in RCS0327. The majority of the star-forming regions have a He I λ5876 to Hβ ratio consistent with the saturated maximum value, which is only possible if they still contain hot O-stars. Two regions have lower ratios, implying that their last burst of new star formation ended ∼5 Myr ago. Together, the He I λ5876 and He II λ4686 to Hβ line ratios provide indirect evidence for the order in which star formation is stopping in individual star-forming knots of this high-redshift merger. We place the spatial variations of the extinction, star formation rate and ionization conditions in the context of the star formation history of RCS0327.

  16. Fragmentation of interstellar clouds and star formation

    NASA Technical Reports Server (NTRS)

    Silk, J.

    1982-01-01

    The principal issues are addressed: the fragmentation of molecular clouds into units of stellar mass and the impact of star formation on molecular clouds. The observational evidence for fragmentation is summarized, and the gravitational instability described of a uniform spherical cloud collapsing from rest. The implications are considered of a finite pressure for the minimum fragment mass that is attainable in opacity-limited fragmentation. The role of magnetic fields is discussed in resolving the angular momentum problem and in making the collapse anisotropic, with notable consequences for fragmentation theory. Interactions between fragments are described, with emphasis on the effect of protostellar winds on the ambient cloud matter and on inhibiting further star formation. Such interactions are likely to have profound consequences for regulating the rate of star formation and on the energetics and dynamics of molecular clouds.

  17. A LAW FOR STAR FORMATION IN GALAXIES

    SciTech Connect

    Escala, Andres

    2011-07-01

    We study the galactic-scale triggering of star formation. We find that the largest mass scale not stabilized by rotation, a well-defined quantity in a rotating system and with clear dynamical meaning, strongly correlates with the star formation rate in a wide range of galaxies. We find that this relation can be understood in terms of self-regulation toward marginal Toomre stability and the amount of turbulence allowed to sustain the system in this self-regulated quasi-stationary state. We test such an interpretation by computing the predicted star formation rates for a galactic interstellar medium characterized by a lognormal probability distribution function and find good agreement with the observed relation.

  18. Formation of star tracking reticles

    NASA Technical Reports Server (NTRS)

    Smith, W. O.; Toft, A. R. (Inventor)

    1974-01-01

    The present application is directed towards a process for producing high resolution, substantially non-reflective reticles or choppers suitable for use for transmitting in both the visible and near ultra-violet regions, able to withstand reasonable handling and extreme environmental conditions, and capable of operating at speeds of from 2800 to about 9000 revolutions per minute without distortion. In particular, the present invention is directed towards the production or reticles having a quartz base vacuum coated with chromium, chromium-silver alloy, and silver with electrodeposited copper and black chromium thereon, respectively, in the form of a reticle pattern. The quartz permits the transmission of light while the pattern is opaque to light. The reticles of the present invention are intended for use in optical trackers, such as star trackers used in outer space.

  19. The H II Region of a Primordial Star

    SciTech Connect

    Abel, Tom; Wise, John H.; Bryan, Greg L.; /Columbia U., Astron. Astrophys.

    2006-06-07

    The concordance model of cosmology and structure formation predicts the formation of isolated very massive stars at high redshifts in dark matter dominated halos of 10{sup 5} to 10{sup 6} Msun. These stars photo-ionize their host primordial molecular clouds, expelling all the baryons from their halos. When the stars die, a relic H II region is formed within which large amounts of molecular hydrogen form which will allow the gas to cool efficiently when gravity assembles it into larger dark matter halos. The filaments surrounding the first star hosting halo are largely shielded and provide the pathway for gas to stream into the halo when the star has died. We present the first fully three dimensional cosmological radiation hydrodynamical simulations that follow all these effects. A novel adaptive ray casting technique incorporates the time dependent radiative transfer around point sources. This approach is fast enough so that radiation transport, kinetic rate equations, and hydrodynamics are solved self-consistently. It retains the time derivative of the transfer equation and is explicitly photon conserving. This method is integrated with the cosmological adaptive mesh refinement code enzo, and runs on distributed and shared memory parallel architectures. Where applicable the three dimensional calculation not only confirm expectations from earlier one dimensional results but also illustrate the multi-fold hydrodynamic complexities of H II regions. In the absence of stellar winds the circumstellar environments of the first supernovae and putative early gamma-ray bursts will be of low density {approx}1 cm{sup -3}. Albeit marginally resolved, ionization front instabilities lead to cometary and elephant trunk like small scale structures reminiscent of nearby star forming regions.

  20. The H II Region of a Primordial Star

    NASA Astrophysics Data System (ADS)

    Abel, Tom; Wise, John H.; Bryan, Greg L.

    2007-04-01

    The concordance model of cosmology and structure formation predicts the formation of isolated, very massive stars at high redshifts in dark matter-dominated halos of 105-106 Msolar. These stars photoionize their host primordial molecular clouds, expelling all the baryons from their halos. When the stars die, a relic H II region is formed within which large amounts of molecular hydrogen form that will allow the gas to cool efficiently when gravity assembles it into larger dark matter halos. The filaments surrounding the first star-hosting halo are largely shielded and provide the pathway for gas to stream into the halo when the star has died. We present the first fully three-dimensional cosmological radiation hydrodynamical simulations that follow all these effects. A novel adaptive ray-casting technique incorporates the time-dependent radiative transfer around point sources. This approach is fast enough so that radiation transport, kinetic rate equations, and hydrodynamics are solved self-consistently. It retains the time derivative of the transfer equation and is explicitly photon-conserving. This method is integrated with the cosmological adaptive mesh refinement code Enzo and runs on distributed and shared memory parallel architectures. Where applicable, the three-dimensional calculation not only confirms expectations from earlier one-dimensional results but also illustrates the multifold hydrodynamic complexities of H II regions. In the absence of stellar winds, the circumstellar environments of the first supernovae and putative early gamma-ray bursts will be of low density, ~1 cm-3. Albeit marginally resolved, ionization front instabilities lead to cometary- and elephant trunk-like small-scale structures reminiscent of nearby star-forming regions.

  1. Star formation around supermassive black holes.

    PubMed

    Bonnell, I A; Rice, W K M

    2008-08-22

    The presence of young massive stars orbiting on eccentric rings within a few tenths of a parsec of the supermassive black hole in the galactic center is challenging for theories of star formation. The high tidal shear from the black hole should tear apart the molecular clouds that form stars elsewhere in the Galaxy, and transport of stars to the galactic center also appears unlikely during their lifetimes. We conducted numerical simulations of the infall of a giant molecular cloud that interacts with the black hole. The transfer of energy during closest approach allows part of the cloud to become bound to the black hole, forming an eccentric disk that quickly fragments to form stars. Compressional heating due to the black hole raises the temperature of the gas up to several hundred to several thousand kelvin, ensuring that the fragmentation produces relatively high stellar masses. These stars retain the eccentricity of the disk and, for a sufficiently massive initial cloud, produce an extremely top-heavy distribution of stellar masses. This potentially repetitive process may explain the presence of multiple eccentric rings of young stars in the presence of a supermassive black hole. PMID:18719276

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

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

  3. Far-IR selected star formation regions

    NASA Technical Reports Server (NTRS)

    Jaffe, D. T.; Hildebrand, R. H.; Keene, J.; Harper, D. A.; Loewenstein, R. F.; Moran, J. M.

    1984-01-01

    Detailed far-IR observations and complemenary submillimeter, 5 GHz continuum and c(18)0 observations of a sample of far-IR selected luminous regions of star formation. The clouds and that the exciting stars lie deep within these condensations. The far-IR sources have diversely shaped 40 micron to 180 micron spectra even through their 60 micron to 100 micron color temperatures are similar. The radio and far-IR results together show that the exciting stars are in clusters containing either zero-age main sequence and pre-main sequence stars or consisting entirely of premain sequence objects. C(18)0 and submillimeter observations imply gas densities approximately .00005 - high enough to make t(sub dust) approximately t(sub gas).

  4. Far-infrared selected star formation regions

    NASA Technical Reports Server (NTRS)

    Harper, D. A.; Loewenstein, R. F.; Moran, J. M.; Jaffe, D. T.; Hildebrand, R. H.; Keene, J.

    1984-01-01

    Detailed far-IR observations and complementary submillimeter, 5 GHz continuum and C(O-18) observations of a sample of eight far-IR selected luminous regions of star formation are presented. The observations show that the sources of luminosity coincide with density peaks in the molecular clouds and that the exciting stars lie deep within these condensations. The far-IR sources have diversely shaped 40-180 micron spectra even though their 60-100 micron color temperatures are similar. The radio and far-IR results together show that the exciting stars are in clusters containing either zero-age main-sequence and pre-main-sequence stars or consisting entirely of pre-main-sequence objects. C(O-18) and submillimeter observations imply gas densities approximately 100,000-high enough to make T(dust) approximately T(gas).

  5. Terrestrial Planet Formation in Binary Star Systems

    NASA Technical Reports Server (NTRS)

    Lissauer, J. J.; Quintana, E. V.; Adams, F. C.; Chambers, J. E.

    2006-01-01

    Most stars reside in binary/multiple star systems; however, previous models of planet formation have studied growth of bodies orbiting an isolated single star. Disk material has been observed around one or both components of various young close binary star systems. If planets form at the right places within such disks, they can remain dynamically stable for very long times. We have simulated the late stages of growth of terrestrial planets in both circumbinary disks around 'close' binary star systems with stellar separations ($a_B$) in the range 0.05 AU $\\le a_B \\le$ 0.4 AU and binary eccentricities in the range $0 \\le e \\le 0.8$ and circumstellar disks around individual stars with binary separations of tens of AU. The initial disk of planetary embryos is the same as that used for simulating the late stages of terrestrial planet growth within our Solar System and around individual stars in the Alpha Centauri system (Quintana et al. 2002, A.J., 576, 982); giant planets analogous to Jupiter and Saturn are included if their orbits are stable. The planetary systems formed around close binaries with stellar apastron distances less than or equal to 0.2 AU with small stellar eccentricities are very similar to those formed in the Sun-Jupiter-Saturn, whereas planetary systems formed around binaries with larger maximum separations tend to be sparser, with fewer planets, especially interior to 1 AU. Likewise, when the binary periastron exceeds 10 AU, terrestrial planets can form over essentially the entire range of orbits allowed for single stars with Jupiter-like planets, although fewer terrestrial planets tend to form within high eccentricity binary systems. As the binary periastron decreases, the radial extent of the terrestrial planet systems is reduced accordingly. When the periastron is 5 AU, the formation of Earth-like planets near 1 AU is compromised.

  6. Grain processes in massive star formation

    NASA Technical Reports Server (NTRS)

    Wolfire, M. G.; Cassinelli, J. P.

    1986-01-01

    Observational evidence suggests that stars greater than 100 M(solar) exist in the Galaxy and Large Magellanic Cloud (LMC), however classical star formation theory predicts stellar mass limits of only approx. 60 M(solar). A protostellar accretion flow consists of inflowing gas and dust. Grains are destroyed as they are near the central protostar creating a dust shell or cocoon. Radiation pressure acting on the grain can halt the inflow of material thereby limiting the amount of mass accumulated by the protostar. We first consider rather general constraints on the initial grain to gas ratio and mass accretion rates that permit inflow. We further constrain these results by constructing a numerical model. Radiative deceleration of grains and grain destruction processes are explicitly accounted for in an iterative solution of the radiation-hydrodynamic equations. Findings seem to suggest that star formation by spherical accretion requires rather extreme preconditioning of the grain and gas environment.

  7. Disentangling AGN and Star Formation in Soft X-Rays

    NASA Technical Reports Server (NTRS)

    LaMassa, Stephanie M.; Heckman, T. M.; Ptak, A.

    2012-01-01

    We have explored the interplay of star formation and active galactic nucleus (AGN) activity in soft X-rays (0.5-2 keV) in two samples of Seyfert 2 galaxies (Sy2s). Using a combination of low-resolution CCD spectra from Chandra and XMM-Newton, we modeled the soft emission of 34 Sy2s using power-law and thermal models. For the 11 sources with high signal-to-noise Chandra imaging of the diffuse host galaxy emission, we estimate the luminosity due to star formation by removing the AGN, fitting the residual emission. The AGN and star formation contributions to the soft X-ray luminosity (i.e., L(sub x,AGN) and L(sub x,SF)) for the remaining 24 Sy2s were estimated from the power-law and thermal luminosities derived from spectral fitting. These luminosities were scaled based on a template derived from XSINGS analysis of normal star-forming galaxies. To account for errors in the luminosities derived from spectral fitting and the spread in the scaling factor, we estimated L(sub x,AGN) and L(sub x,SF))from Monte Carlo simulations. These simulated luminosities agree with L(sub x,AGN) and L(sub x,SF) derived from Chandra imaging analysis within a 3sigma confidence level. Using the infrared [Ne ii]12.8 micron and [O iv]26 micron lines as a proxy of star formation and AGN activity, respectively, we independently disentangle the contributions of these two processes to the total soft X-ray emission. This decomposition generally agrees with L(sub x,SF) and L(sub x,AGN) at the 3 sigma level. In the absence of resolvable nuclear emission, our decomposition method provides a reasonable estimate of emission due to star formation in galaxies hosting type 2 AGNs.

  8. DISENTANGLING AGN AND STAR FORMATION IN SOFT X-RAYS

    SciTech Connect

    LaMassa, Stephanie M.; Heckman, T. M.; Ptak, A.

    2012-10-20

    We have explored the interplay of star formation and active galactic nucleus (AGN) activity in soft X-rays (0.5-2 keV) in two samples of Seyfert 2 galaxies (Sy2s). Using a combination of low-resolution CCD spectra from Chandra and XMM-Newton, we modeled the soft emission of 34 Sy2s using power-law and thermal models. For the 11 sources with high signal-to-noise Chandra imaging of the diffuse host galaxy emission, we estimate the luminosity due to star formation by removing the AGN, fitting the residual emission. The AGN and star formation contributions to the soft X-ray luminosity (i.e., L{sub x,AGN} and L{sub x,SF}) for the remaining 24 Sy2s were estimated from the power-law and thermal luminosities derived from spectral fitting. These luminosities were scaled based on a template derived from XSINGS analysis of normal star-forming galaxies. To account for errors in the luminosities derived from spectral fitting and the spread in the scaling factor, we estimated L{sub x,AGN} and L{sub x,SF} from Monte Carlo simulations. These simulated luminosities agree with L{sub x,AGN} and L{sub x,SF} derived from Chandra imaging analysis within a 3{sigma} confidence level. Using the infrared [Ne II]12.8 {mu}m and [O IV]26 {mu}m lines as a proxy of star formation and AGN activity, respectively, we independently disentangle the contributions of these two processes to the total soft X-ray emission. This decomposition generally agrees with L{sub x,SF} and L{sub x,AGN} at the 3{sigma} level. In the absence of resolvable nuclear emission, our decomposition method provides a reasonable estimate of emission due to star formation in galaxies hosting type 2 AGNs.

  9. A study of star formation in the disks of Sa galaxies

    SciTech Connect

    Caldwell, N.; Kennicutt, R.; Phillips, A.C.; Schommer, R.A. Steward Observatory, Tucson, AZ Washington Univ., Seattle Rutgers Univ., Piscataway, NJ )

    1991-04-01

    This paper compares the luminosity functions of the H II regions in several Sa galaxies with those of later-type galaxies. Broad UV measurements confirm expectations that the knots associated with the regions are very blue; the converse is also true. The H II region luminosity functions are very steep. The total H-alpha luminosities for the galaxies are computed and used to derive the current star-formation rates. It is found that, in contrast to the late-type galaxies, the current star-formation rates in Sa disks are less than one-tenth of the average rate over the last 15 Gyr. The formal depletion times of gas through star formation are longer than a Hubble time. If the star formation in late-type galaxies takes on the character of that currently seen in the Sas, star formation in such galaxies could continue for much longer than the usual estimate of 5 Gyr. 35 refs.

  10. Star Formation at the Galactic Center

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-08-01

    Could stars be forming in the inhospitable environment near Sagittarius A* in the heart of the Milky Way? A possible signature of low-mass star formation has recently been found just two light-years from the black hole at the center of our galaxy — a region that was previously thought to be too hostile for such activity. Searching for Signatures: Previous observations of the central few light-years of the Milky Way had focused on a population of about 200 massive, young and very bright stars in tight orbits around Sgr A*. These stars are only a few million years old and prompted scientists to wonder: have they somehow managed to form in situ, in spite of their close proximity to the black hole, or did they form further out and then migrate in? Motivated by this mystery, Farhad Yusef-Zadeh of Northwestern University and collaborators looked for evidence of even younger stars close to Sagittarius A*, which would demonstrate that star formation in the area is an ongoing process. Using the Very Large Array (VLA), the collaboration discovered several small sources in one arm of activity near Sgr A*. This 34-GHz image provides a close-up view of two protoplanetary disk candidates (labeled P26 and P8) located near Sgr A*. These objects are outlined on the right side by a bow shock caused by impacting stellar wind that streams from the young, hot stars closer to the Galactic center. The disks are thought to contain recently-formed, low-mass stars. (Credit: Yusef-Zadeh et al., 2015) Heated Disks: The team identified these sources as candidate photoevaporative protoplanetary disks, or “proplyds” — areas of dense, ionized gas and dust surrounding young, newly formed stars. The proplyd candidates are between 10,000 and 100,000 years old, and they lie along the edge of a large molecular cloud. It is likely that this cloud produced the disks by providing a reservoir of gas to feed the star-formation activity. The region surrounding these proplyds is blasted with harsh

  11. Star formation across cosmic time and its influence on galactic dynamics

    NASA Astrophysics Data System (ADS)

    Freundlich, Jonathan

    2015-12-01

    Observations show that ten billion years ago, galaxies formed their stars at rates up to twenty times higher than now. As stars are formed from cold molecular gas, a high star formation rate means a significant gas supply, and galaxies near the peak epoch of star formation are indeed much more gas-rich than nearby galaxies. Is the decline of the star formation rate mostly driven by the diminishing cold gas reservoir, or are the star formation processes also qualitatively different earlier in the history of the Universe? Ten billion years ago, young galaxies were clumpy and prone to violent gravitational instabilities, which may have contributed to their high star formation rate. Stars indeed form within giant, gravitationally-bound molecular clouds. But the earliest phases of star formation are still poorly understood. Some scenarii suggest the importance of interstellar filamentary structures as a first step towards core and star formation. How would their filamentary geometry affect pre-stellar cores? Feedback mechanisms related to stellar evolution also play an important role in regulating star formation, for example through powerful stellar winds and supernovae explosions which expel some of the gas and can even disturb the dark matter distribution in which each galaxy is assumed to be embedded. This PhD work focuses on three perspectives: (i) star formation near the peak epoch of star formation as seen from observations at sub-galactic scales; (ii) the formation of pre-stellar cores within the filamentary structures of the interstellar medium; and (iii) the effect of feedback processes resulting from star formation and evolution on the dark matter distribution.

  12. Galaxy Interactions with FIRE: Mapping Star Formation

    NASA Astrophysics Data System (ADS)

    Moreno, Jorge

    2016-01-01

    We utilize a suite of 75 simulations of galaxies in idealised major mergers (stellar mass ratio ~2.5:1), with a wide range of orbital parameters, to investigate the spatial extent of interaction-induced star formation. Two versions are used, one based on a Kennicult-like subgrid model (Gadget, Springel & Hernquist 2003); the other based on the new Feedback In Realistic Environments model (FIRE, Hopkins et al. 2014). Although the total star formation in galaxy encounters is generally elevated relative to isolated galaxies, we find that this elevation is a combination of intense enhancements within the central kpc and moderately suppressed activity at large galacto-centric radii. This effect appears to be stronger in the older Gadget model. Suppression is the disk is also found in the FIRE runs, but at larger scales. This is because tidal torques are weaker in the newer FIRE model, leading to a more extended nuclear starburt. Our predictions of the radial dependence of triggered star formation, and specifically the suppression of star formation beyond kpc-scales, will be testable with the next generation of integral-field spectroscopic surveys.

  13. Externally fed star formation: a numerical study

    NASA Astrophysics Data System (ADS)

    Mohammadpour, Motahareh; Stahler, Steven W.

    2013-08-01

    We investigate, through a series of numerical calculations, the evolution of dense cores that are accreting external gas up to and beyond the point of star formation. Our model clouds are spherical, unmagnetized configurations with fixed outer boundaries, across which gas enters subsonically. When we start with any near-equilibrium state, we find that the cloud's internal velocity also remains subsonic for an extended period, in agreement with observations. However, the velocity becomes supersonic shortly before the star forms. Consequently, the accretion rate building up the protostar is much greater than the benchmark value c_s^3/G, where cs is the sound speed in the dense core. This accretion spike would generate a higher luminosity than those seen in even the most embedded young stars. Moreover, we find that the region of supersonic infall surrounding the protostar races out to engulf much of the cloud, again in violation of the observations, which show infall to be spatially confined. Similar problematic results have been obtained by all other hydrodynamic simulations to date, regardless of the specific infall geometry or boundary conditions adopted. Low-mass star formation is evidently a quasi-static process, in which cloud gas moves inward subsonically until the birth of the star itself. We speculate that magnetic tension in the cloud's deep interior helps restrain the infall prior to this event.

  14. Neutral hydrogen and star formation in irregular galaxies

    NASA Technical Reports Server (NTRS)

    Skillman, Evan D.

    1987-01-01

    The Very Large Array and WSTR H I synthesis observations of seven irregular galaxies are presented. The total H I images of four Local Group dwarf irregular galaxies and three larger more distant irregular galaxies are constructed at the identical resolution of 500 pc. When compared to H II region distributions derived from H alpha images, all galaxies studied show an excellent correlation between the H I surface density and the presence of H II regions. This correlation is most easily interpreted in terms of a requisite threshold H I surface density for massive star formation. This threshold is 1 x 10 to the 21st power H I atoms/sq cm for a resolution of 500 pc. Giant extragalactic H II regions are only found near H I surface densities of a factor of 3 to 5 times this threshold level. The observed threshold implies a Jeans length of 150 pc, which is the same as the size scale at which the structure in the H I complexes correlates well with the H II region distribution. This, combined with the fact that in none of the galaxies observed is there H I above the threshold level with concomitant H II regions, implies an exclusively gravitational origin for the star formation events. That is, there is no need to involve a trigger as in the SSPSF theory (Seiden 1983) or feedback as in Dopita (1985).

  15. Predictions from star formation in the multiverse

    SciTech Connect

    Bousso, Raphael; Leichenauer, Stefan

    2010-03-15

    We compute trivariate probability distributions in the landscape, scanning simultaneously over the cosmological constant, the primordial density contrast, and spatial curvature. We consider two different measures for regulating the divergences of eternal inflation, and three different models for observers. In one model, observers are assumed to arise in proportion to the entropy produced by stars; in the others, they arise at a fixed time (5 or 10x10{sup 9} years) after star formation. The star formation rate, which underlies all our observer models, depends sensitively on the three scanning parameters. We employ a recently developed model of star formation in the multiverse, a considerable refinement over previous treatments of the astrophysical and cosmological properties of different pocket universes. For each combination of observer model and measure, we display all single and bivariate probability distributions, both with the remaining parameter(s) held fixed and marginalized. Our results depend only weakly on the observer model but more strongly on the measure. Using the causal diamond measure, the observed parameter values (or bounds) lie within the central 2{sigma} of nearly all probability distributions we compute, and always within 3{sigma}. This success is encouraging and rather nontrivial, considering the large size and dimension of the parameter space. The causal patch measure gives similar results as long as curvature is negligible. If curvature dominates, the causal patch leads to a novel runaway: it prefers a negative value of the cosmological constant, with the smallest magnitude available in the landscape.

  16. ANALYTICAL STAR FORMATION RATE FROM GRAVOTURBULENT FRAGMENTATION

    SciTech Connect

    Hennebelle, Patrick; Chabrier, Gilles

    2011-12-20

    We present an analytical determination of the star formation rate (SFR) in molecular clouds, based on a time-dependent extension of our analytical theory of the stellar initial mass function. The theory yields SFRs in good agreement with observations, suggesting that turbulence is the dominant, initial process responsible for star formation. In contrast to previous SFR theories, the present one does not invoke an ad hoc density threshold for star formation; instead, the SFR continuously increases with gas density, naturally yielding two different characteristic regimes, thus two different slopes in the SFR versus gas density relationship, in agreement with observational determinations. Besides the complete SFR derivation, we also provide a simplified expression, which reproduces the complete calculations reasonably well and can easily be used for quick determinations of SFRs in cloud environments. A key property at the heart of both our complete and simplified theory is that the SFR involves a density-dependent dynamical time, characteristic of each collapsing (prestellar) overdense region in the cloud, instead of one single mean or critical freefall timescale. Unfortunately, the SFR also depends on some ill-determined parameters, such as the core-to-star mass conversion efficiency and the crossing timescale. Although we provide estimates for these parameters, their uncertainty hampers a precise quantitative determination of the SFR, within less than a factor of a few.

  17. The cosmic history of star formation.

    PubMed

    Dunlop, James S

    2011-07-01

    Major advances in observational astronomy over the past 20 years have revolutionized our view of cosmic history, transforming our understanding of how the hot, smooth, early universe evolved into the complex and beautiful universe of stars and galaxies in which we now live. I describe how astronomers have used a range of complementary techniques to map out the rise and fall of star formation over 95% of cosmic time, back to the current observational frontier only ~500 million years after the Big Bang. PMID:21737733

  18. Sequential clustering of star formations in IC 1396

    NASA Astrophysics Data System (ADS)

    Huang, Ya-Fang; Li, Jin-Zeng

    2013-05-01

    We present a comprehensive study of the H II region IC 1396 and its star forming activity, in which multi-wavelength data ranging from the optical to the near- and far-infrared were employed. The surface density distribution of all the 2MASS sources with a certain detection toward IC 1396 indicates the existence of a compact cluster spatially consistent with the position of the exciting source of the H II region, HD 206267. The spatial distribution of the sources with excessive infrared emission, selected based on archived 2MASS data, reveals the existence of four sub-clusters in this region. One is associated with the open cluster Trumpler 37. The other three are found to be spatially coincident with the bright rims of the H II region. All the sources with excessive emission in the near infrared are cross-identified with AKARI IRC data. An analysis of the spectral energy distributions (SEDs) of the resultant sample leads to the identification of eight CLASS I, 15 CLASS II and 15 CLASS III sources in IC 1396. Optical identification of the sample sources with R magnitudes brighter than 17 mag corroborates the results from the SED analysis. Based on the spatial distribution of the infrared young stellar objects at different evolutionary stages, the surrounding sub-clusters located in the bright rims are believed to be younger than the central one. This is consistent with a scenario of sequential star formation in this region. Imaging data of a dark patch in IC 1396 by Herschel SPIRE, on the other hand, indicate the presence of two far-infrared cores in LDN 1111, which are likely to be a new generation of protostellar objects in formation. So we infer that the star formation process in this H II region was not continuous but rather episodic.

  19. Shocks, star formation and the JWST

    NASA Astrophysics Data System (ADS)

    Gusdorf, A.

    2015-12-01

    The interstellar medium (ISM) is constantly evolving due to unremitting injection of energy in various forms. Energetic radiation transfers energy to the ISM: from the UV photons, emitted by the massive stars, to X- and γ-ray ones. Cosmic rays are another source of energy. Finally, mechanical energy is injected through shocks or turbulence. Shocks are ubiquitous in the interstellar medium of galaxies. They are associated to star formation (through jets and bipolar outflows), life (via stellar winds), and death (in AGB stellar winds or supernovae explosion). The dynamical processes leading to the formation of molecular clouds also generate shocks where flows of interstellar matter collide. Because of their ubiquity, the study of interstellar shocks is also a useful probe to the other mechanisms of energy injection in the ISM. This study must be conducted in order to understand the evolution of the interstellar medium as a whole, and to address various questions: what is the peculiar chemistry associated to shocks, and what is their contribution to the cycle of matter in galaxies ? What is the energetic impact of shocks on their surroundings on various scales, and hence what is the feedback of stars on the galaxies ? What are the scenarios of star formation, whether this star formation leads to the propagation of shocks, or whether it is triggered by shock propagation ? What is the role of shocks in the acceleration of cosmic rays ? Can they shed light on their composition and diffusion processes ? In order to progress on these questions, it is paramount to interpret the most precise observations with the most precise models of shocks. From the observational point of view, the James Webb Space Telescope represents a powerful tool to better address the above questions, as it will allow to observe numerous shock tracers in the infrared range at an unprecedented spatial and spectral resolution.

  20. Triggered Star Formation From Shock to Disk

    NASA Astrophysics Data System (ADS)

    Blackman, Eric

    2014-10-01

    Triggered star formation {TSF} occurs when supersonic flows generated by distant supernova blast waves, stellar winds {wind blown bubbles} or ionization fronts {D-type fronts in HII regions} sweep over a stable cloud. TSF may play a role in massive regions of star formation where winds, HII regions and, eventually, blast-waves sweep through dense, heterogeneous molecular material. In addition TSF has played an important role in discussions of the formation of our own solar system because it offers a natural way of injecting short lived radioactive isotopes {SLRI's} like 26^Al into material which will then form planetary bodies.The purpose of this proposal is to use advanced numerical tools to explore the physics of TSF in greater detail than has been attempted before. Previous studies have not been able to follow triggering past the early stages before a star forms. Our 3-D Adaptive Mesh Refinement {AMR} MHD code contains well tested physics modules which will allow us to track the influence of self-gravity, radiation-transport, cooling by molecules/neutrals/atoms and, finally, the collapse of gas into stars {i.e.condensed gravitating point-like objects or "sink-particles"}. With this tool we will follow triggering well past the formation of the star to explore the creation of accretion disks and their properties. In addition the microphysics routines in the code allow us to make detailed contact with HST observations such as the pillars in the Carina nebula via synthetic observations of line profiles, proper motions, Position-Velocity diagrams and statistics.

  1. Constraints to the magnetospheric properties of T Tauri stars - II. The Mg II ultraviolet feature

    NASA Astrophysics Data System (ADS)

    López-Martínez, Fatima; Gómez de Castro, Ana Inés

    2015-03-01

    The atmospheric structure of T Tauri stars (TTSs) and its connection with the large-scale outflow is poorly known. Neither the effect of the magnetically mediated interaction between the star and the disc is well understood. The Mg II multiplet is a fundamental tracer of TTSs atmospheres and outflows, and is the strongest feature in the near-ultraviolet spectrum of TTSs. The International Ultraviolet Explorer and Hubble Space Telescope data archives provide a unique set to study the main physical compounds contributing to the line profile and to derive the properties of the line formation region. The Mg II profiles of 44 TTSs with resolution 13 000-30 000 are available in these archives. In this work, we use this data set to measure the main observables: flux, broadening, asymmetry, terminal velocity of the outflow, and the velocity of the discrete absorption components. For some few sources repeated observations are available and variability has been studied. There is a warm wind that at sub-au scales absorbs the blue wing of the Mg II profiles. The main result found in this work is the correlation between the line broadening, Mg II flux, terminal velocity of the flow and accretion rate. Both outflow and magnetospheric plasma contribute to the Mg II flux. The flux-flux correlation between Mg II and C IV or He II is confirmed; however, no correlation is found between the Mg II flux and the UV continuum or the H2 emission.

  2. Molecular cloud-scale star formation in NGC 300

    SciTech Connect

    Faesi, Christopher M.; Lada, Charles J.; Forbrich, Jan; Menten, Karl M.; Bouy, Hervé

    2014-07-01

    We present the results of a galaxy-wide study of molecular gas and star formation in a sample of 76 H II regions in the nearby spiral galaxy NGC 300. We have measured the molecular gas at 250 pc scales using pointed CO(J = 2-1) observations with the Atacama Pathfinder Experiment telescope. We detect CO in 42 of our targets, deriving molecular gas masses ranging from our sensitivity limit of ∼10{sup 5} M {sub ☉} to 7 × 10{sup 5} M {sub ☉}. We find a clear decline in the CO detection rate with galactocentric distance, which we attribute primarily to the decreasing radial metallicity gradient in NGC 300. We combine Galaxy Evolution Explorer far-ultraviolet, Spitzer 24 μm, and Hα narrowband imaging to measure the star formation activity in our sample. We have developed a new direct modeling approach for computing star formation rates (SFRs) that utilizes these data and population synthesis models to derive the masses and ages of the young stellar clusters associated with each of our H II region targets. We find a characteristic gas depletion time of 230 Myr at 250 pc scales in NGC 300, more similar to the results obtained for Milky Way giant molecular clouds than the longer (>2 Gyr) global depletion times derived for entire galaxies and kiloparsec-sized regions within them. This difference is partially due to the fact that our study accounts for only the gas and stars within the youngest star-forming regions. We also note a large scatter in the NGC 300 SFR-molecular gas mass scaling relation that is furthermore consistent with the Milky Way cloud results. This scatter likely represents real differences in giant molecular cloud physical properties such as the dense gas fraction.

  3. UV-TO-FIR ANALYSIS OF SPITZER/IRAC SOURCES IN THE EXTENDED GROTH STRIP. II. PHOTOMETRIC REDSHIFTS, STELLAR MASSES, AND STAR FORMATION RATES

    SciTech Connect

    Barro, G.; Perez-Gonzalez, P. G.; Gallego, J.; Villar, V.; Zamorano, J.; Ashby, M. L. N.; Kajisawa, M.; Yamada, T.; Miyazaki, S.

    2011-04-01

    Based on the ultraviolet to far-infrared photometry already compiled and presented in a companion paper (Paper I), we present a detailed spectral energy distribution (SED) analysis of nearly 80,000 IRAC 3.6 + 4.5 {mu}m selected galaxies in the Extended Groth Strip. We estimate photometric redshifts, stellar masses, and star formation rates (SFRs) separately for each galaxy in this large sample. The catalog includes 76,936 sources with [3.6] {<=} 23.75 (85% completeness level of the IRAC survey) over 0.48 deg{sup 2}. The typical photometric redshift accuracy is {Delta}z/(1 + z) = 0.034, with a catastrophic outlier fraction of just 2%. We quantify the systematics introduced by the use of different stellar population synthesis libraries and initial mass functions in the calculation of stellar masses. We find systematic offsets ranging from 0.1 to 0.4 dex, with a typical scatter of 0.3 dex. We also provide UV- and IR-based SFRs for all sample galaxies, based on several sets of dust emission templates and SFR indicators. We evaluate the systematic differences and goodness of the different SFR estimations using the deep FIDEL 70 {mu}m data available in the Extended Groth Strip. Typical random uncertainties of the IR-bases SFRs are a factor of two, with non-negligible systematic effects at z {approx}> 1.5 observed when only MIPS 24 {mu}m data are available. All data products (SEDs, postage stamps from imaging data, and different estimations of the photometric redshifts, stellar masses, and SFRs of each galaxy) described in this and the companion paper are publicly available, and they can be accessed through our the Web interface utility Rainbow-navigator.

  4. What the Spatial Distribution of Stars tells us about Star Formation and Massive Cluster Formation

    NASA Astrophysics Data System (ADS)

    Bressert, Eli; Bastian, N.; Testi, L.; Patience, J.; Longmore, S.

    2012-01-01

    We present a dissertation study on two recent results regarding the clustering properties of young stars. First, we discuss a global study of young stellar object (YSO) surface densities in star forming regions based on a comprehensive collection of Spitzer Space Telescope surveys, which encompasses nearly all star formation in the solar neighbourhood. It is shown that the distribution of YSO surface densities is a smooth distribution, being adequately described by a lognormal function from a few to 103 YSOs pc-2, with a peak at 22 YSOs pc-2 and a dispersion of 0.85. We find no evidence for multiple discrete modes of star-formation (e.g. clustered and distributed) and that not all stars form in clusters. A Herschel Space Observatory study confirms the YSO surface density results by observing and analyzing the prestellar core population in several star forming regions. Secondly, we propose that bound stellar clusters primarily form from dense clouds having escape speeds greater than the sound speed in photo-ionized gas. A list of giant molecular clumps with masses >103 M⊙ that have escape speeds greater than the sound speed in photo-ionized plasma is compiled from the Bolocam Galactic Plane Survey. In these clumps, radiative feedback in the form of gas ionization is bottled up, enabling star formation to proceed to sufficiently high efficiency so that the resulting star cluster remains bound even after gas removal. We present over ten candidates that will most likely form >103 M⊙ star clusters and two of them that are comparable to NGC 3603 (>104 M⊙). Thus, providing us with an outlook on the next generation of star clusters in the Milky Way and clues to the initial conditions of massive cluster formation.

  5. Turbulence and Star Formation in Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Hollyday, Gigja; Hunter, Deidre Ann; Little Things Team

    2015-01-01

    We are interested in understanding the nature and role of turbulence in the interstellar medium of dwarf irregular galaxies. Turbulence, resulting from a variety of processes, is a potential source for cloud formation, and thus star formation. We have undertaken an indirect analysis of turbulence via the third (skewness) and fourth (kurtosis) moments of the distribution of atomic hydrogen gas densities using the LITTLE THINGS data for a 40-count sample of nearby (<10.3 Mpc) dwarf galaxies. We followed the formulism used by Burkhart et al. (2010) in a study of the SMC. We found that there is evidence of turbulence in dwarf galaxies at a level comparable to that found in the SMC, but we have found no correlation between integrated star formation rates and integrated kurtosis values nor a clear correlation between kurtosis as a function of radius with gas surface density and star formation profiles. We are grateful for a summer internship provided by the Research Experiences for Undergraduates program at Northern Arizona University, run by Dr. Kathy Eastwood and Dr. David Trilling and funded by the National Science Foundation through grant AST-1004107.

  6. Killing Star Formation in Satellite Galaxies

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-08-01

    When a dwarf galaxy falls into the halo of a large galaxy like the Milky Way, how is star formation in the dwarf affected? A collaboration led by Andrew Wetzel (California Institute of Technology and Carnegie Observatories) recently set out to answer this question using observations of nearby galaxies and simulations of the infall process. Observed Quenching: Isolated dwarf galaxies tend to be gas-rich and very actively star-forming. In contrast, most dwarf galaxies within 300 kpc of us (the Milky Way's virial radius) contain little or no cold gas, and they're quiescent: there's not much star formation happening. And this isn't just true of the Milky Way; we observe the same difference in the satellite galaxies surrounding Andromeda galaxy. Once a dwarf galaxy has moved into the gravitational realm of a larger galaxy, the satellite's gas vanishes rapidly and its star formation is shut off — but how, and on what timescale? The known dwarf galaxies in the Local Group (out to 1.6 Mpc) are plotted by their distance from their host vs. their stellar mass. Blue stars indicate actively star-forming dwarfs and red circles indicate quiescent ones. Credit: Wetzel et al. 2015. Timescales for Quiescence: To answer these questions, the authors explored the process of galaxy infall using Exploring the Local Volume in Simulations (ELVIS), a suite of cosmological N-body simulations intended to explore the Local Group. They combined the infall times from the simulations with observational knowledge of the fraction of nearby galaxies that are currently quiescent, in order to determine what timescales are required for different processes to deplete the gas in the dwarf galaxies and quench star formation. Based on their results, two types of quenching culprits are at work: gas consumption (where a galaxy simply uses up its immediate gas supply and doesn't have access to more) and gas stripping (where external forces like ram pressure remove gas from the galaxy). These processes

  7. Did the Solar system form in a sequential triggered star formation event?

    NASA Astrophysics Data System (ADS)

    Parker, Richard J.; Dale, James E.

    2016-02-01

    The presence and abundance of the short-lived radioisotopes (SLRs) 26Al and 60Fe during the formation of the Solar system is difficult to explain unless the Sun formed in the vicinity of one or more massive star(s) that exploded as supernovae. Two different scenarios have been proposed to explain the delivery of SLRs to the protosolar nebula: (i) direct pollution of the protosolar disc by supernova ejecta, and (ii) the formation of the Sun in a sequential star formation event in which supernovae shockwaves trigger further star formation which is enriched in SLRs. The sequentially triggered model has been suggested as being more astrophysically likely than the direct pollution scenario. In this paper, we investigate this claim by analysing a combination of N-body and smoothed particle hydrodynamics simulations of star formation. We find that sequential star formation would result in large age spreads (or even bi-modal age distributions for spatially coincident events) due to the dynamical relaxation of the first star formation event(s). Secondly, we discuss the probability of triggering spatially and temporally discrete populations of stars and find this to be only possible in very contrived situations. Taken together, these results suggest that the formation of the Solar system in a triggered star formation event is as improbable, if not more so, than the direct pollution of the protosolar disc by a supernova.

  8. GAS, STARS, AND STAR FORMATION IN ALFALFA DWARF GALAXIES

    SciTech Connect

    Huang Shan; Haynes, Martha P.; Giovanelli, Riccardo; Brinchmann, Jarle; Stierwalt, Sabrina; Neff, Susan G. E-mail: haynes@astro.cornell.edu E-mail: jarle@strw.leidenuniv.nl E-mail: susan.g.neff@nasa.gov

    2012-06-15

    We examine the global properties of the stellar and H I components of 229 low H I mass dwarf galaxies extracted from the ALFALFA survey, including a complete sample of 176 galaxies with H I masses <10{sup 7.7} M{sub Sun} and H I line widths <80 km s{sup -1}. Sloan Digital Sky Survey (SDSS) data are combined with photometric properties derived from Galaxy Evolution Explorer to derive stellar masses (M{sub *}) and star formation rates (SFRs) by fitting their UV-optical spectral energy distributions (SEDs). In optical images, many of the ALFALFA dwarfs are faint and of low surface brightness; only 56% of those within the SDSS footprint have a counterpart in the SDSS spectroscopic survey. A large fraction of the dwarfs have high specific star formation rates (SSFRs), and estimates of their SFRs and M{sub *} obtained by SED fitting are systematically smaller than ones derived via standard formulae assuming a constant SFR. The increased dispersion of the SSFR distribution at M{sub *} {approx}< 10{sup 8} M{sub Sun} is driven by a set of dwarf galaxies that have low gas fractions and SSFRs; some of these are dE/dSphs in the Virgo Cluster. The imposition of an upper H I mass limit yields the selection of a sample with lower gas fractions for their M{sub *} than found for the overall ALFALFA population. Many of the ALFALFA dwarfs, particularly the Virgo members, have H I depletion timescales shorter than a Hubble time. An examination of the dwarf galaxies within the full ALFALFA population in the context of global star formation (SF) laws is consistent with the general assumptions that gas-rich galaxies have lower SF efficiencies than do optically selected populations and that H I disks are more extended than stellar ones.

  9. Gas, Stars, and Star Formation in Alfalfa Dwarf Galaxies

    NASA Technical Reports Server (NTRS)

    Huang, Shan; Haynes, Martha P.; Giovanelli, Riccardo; Brinchmann, Jarle; Stierwalt, Sabrina; Neff, Susan G.

    2012-01-01

    We examine the global properties of the stellar and Hi components of 229 low H i mass dwarf galaxies extracted from the ALFALFA survey, including a complete sample of 176 galaxies with H i masses <10(sup 7.7) solar mass and Hi line widths <80 kilometers per second. Sloan Digital Sky Survey (SDSS) data are combined with photometric properties derived from Galaxy Evolution Explorer to derive stellar masses (M*) and star formation rates (SFRs) by fitting their UV-optical spectral energy distributions (SEDs). In optical images, many of the ALFALFA dwarfs are faint and of low surface brightness; only 56% of those within the SDSS footprint have a counterpart in the SDSS spectroscopic survey. A large fraction of the dwarfs have high specific star formation rates (SSFRs), and estimates of their SFRs and M* obtained by SED fitting are systematically smaller than ones derived via standard formulae assuming a constant SFR. The increased dispersion of the SSFR distribution at M* approximately less than10(exp 8)M(sub 0) is driven by a set of dwarf galaxies that have low gas fractions and SSFRs; some of these are dE/dSphs in the Virgo Cluster. The imposition of an upper Hi mass limit yields the selection of a sample with lower gas fractions for their M* than found for the overall ALFALFA population. Many of the ALFALFA dwarfs, particularly the Virgo members, have H i depletion timescales shorter than a Hubble time. An examination of the dwarf galaxies within the full ALFALFA population in the context of global star formation (SF) laws is consistent with the general assumptions that gas-rich galaxies have lower SF efficiencies than do optically selected populations and that Hi disks are more extended than stellar ones.

  10. Dust in regions of massive star formation

    NASA Technical Reports Server (NTRS)

    Wolfire, Mark G.; Cassinelli, J. P.

    1989-01-01

    It is suggested that protostars increase mass by accreting the surrounding gas and dust. Grains are destroyed as they near the central protostar creating a dust shell or cocoon. Radiation pressure acting on the grains can halt the inflow of material thereby limiting the amount of mass accumulated by the protostar. General constraints were considered on the initial dust-to-gas ratio and mass accretion rates that permit inflow. These results were constrained further by constructing a numerical model, including radiative deceleration on grains and grain destruction processes. Also the constraints on dust properties were investigated which allow the formation of massive stars. The obtained results seem to suggest that massive star formation requires rather extreme preconditioning of the grain and gas environment.

  11. Star Formation and the Solar System

    NASA Technical Reports Server (NTRS)

    Bally, John; Boss, Alan; Papanastassiou, Dimitri; Sandford, Scott; Sargent, Anneila

    1988-01-01

    We have seen that studies of nearby star-forming regions are beginning to reveal the first signs of protoplanetary disks. Studies of interstellar and interplanetary grains are starting to provide clues about the processing and incorporation of matter into the Solar System. Studies of meteorites have yielded isotopic anomalies which indicate that some of the grains and inclusions in these bodies are very primitive. Although we have not yet detected a true interstellar grain, some of these materials have not been extensively modified since their removal from the ISM. We are indeed close to seeing our interstellar heritage. The overlap between astronomical and Solar System studies is in its infancy. What future experiments, observations, and missions can be performed in the near future that will greatly enhance our understanding of star formation and the formation of the Solar System?

  12. Reconstructing Star Formation Histories of Galaxies

    NASA Astrophysics Data System (ADS)

    Fritze-v. Alvensleben, U.; Lilly, T.

    2007-12-01

    We present a methodological study to find out how far back and to what precision star formation histories of galaxies can be reconstructed from CMDs, from integrated spectra and Lick indices, and from integrated multi-band photometry. Our evolutionary synthesis models GALEV allow to describe the evolution of galaxies in terms of all three approaches and we have assumed typical observational uncertainties for each of them and then investigated to what extent and accuracy different star formation histories can be discriminated. For a field in the LMC bar region with both a deep CMD from HST observations and a trailing slit spectrum across exactly the same field of view we could test our modelling results against real data.

  13. Astrochemical diagnostics of star and planet formation

    NASA Astrophysics Data System (ADS)

    Caselli, Paola

    2016-06-01

    Stars like our Sun and planets like our Earth form out of diffuse interstellar material, which first accumulates to form molecular clouds and then it fragments into cold (~10 K) and dense (~105 H2 molecules per cc) cloud cores, the cradle of future stellar systems. The physical structure and chemical composition of these dense cores set the stage for the next steps: gravitational contraction and the formation of protostars and protoplanetary disks. Molecules are unique tracers of the dynamical evolution of interstellar clouds and astrochemistry is needed to guide and interpret our observations. In this talk I will review work done on the early stages of star and planet formation, underlying how astrochemical diagnostics have helped us to shed light on chemical and physical processes important to constraints theories and to find connections with our Solar System. ALMA results will be highlighted.

  14. Quenching star formation in cluster galaxies

    NASA Astrophysics Data System (ADS)

    Taranu, Dan S.; Hudson, Michael J.; Balogh, Michael L.; Smith, Russell J.; Power, Chris; Oman, Kyle A.; Krane, Brad

    2014-05-01

    In order to understand the processes that quench star formation in cluster galaxies, we construct a library of subhalo orbits drawn from Λ cold dark matter cosmological N-body simulations of four rich clusters. We combine these orbits with models of star formation followed by environmental quenching, comparing model predictions with observed bulge and disc colours and stellar absorption line-strength indices of luminous cluster galaxies. Models in which the bulge stellar populations depend only on the galaxy subhalo mass while the disc is quenched upon infall are acceptable fits to the data. An exponential disc quenching time-scale of 3-3.5 Gyr is preferred. Quenching in lower mass groups prior to infall (`pre-processing') provides better fits, with similar quenching time-scales. Models with short (≲1 Gyr) quenching time-scales yield excessively steep cluster-centric gradients in disc colours and Balmer line indices, even if quenching is delayed for several Gyr. The data slightly prefer models where quenching occurs only for galaxies falling within ˜0.5r200. These results imply that the environments of rich clusters must impact star formation rates of infalling galaxies on relatively long time-scales, indicative of gentler quenching mechanisms such as slow `strangulation' over more rapid ram-pressure stripping.

  15. Star formation around active galactic nuclei

    NASA Technical Reports Server (NTRS)

    Keel, William C.

    1987-01-01

    Active galactic nuclei (Seyfert nuclei and their relatives) and intense star formation can both deliver substantial amounts of energy to the vicinity of a galactic nucleus. Many luminous nuclei have energetics dominated by one of these mechanisms, but detailed observations show that some have a mixture. Seeing both phenomena at once raises several interesting questions: (1) Is this a general property of some kinds of nuclei? How many AGNs have surround starbursts, and vice versa? (2) As in 1, how many undiscovered AGNs or starbursts are hidden by a more luminous instance of the other? (3) Does one cause the other, and by what means, or do both reflect common influences such as potential well shape or level of gas flow? (4) Can surrounding star formation tell us anything about the central active nuclei, such as lifetimes, kinetic energy output, or mechanical disturbance of the ISM? These are important points in the understanding of activity and star formation in galactic nuclei. Unfortunately, the observational ways of addressing them are as yet not well formulated. Some preliminary studies are reported, aimed at clarifying the issues involved in study of the relationships between stellar and nonstellar excitement in galactic nuclei.

  16. The star formation history of the Sagittarius stream

    NASA Astrophysics Data System (ADS)

    de Boer, T. J. L.; Belokurov, V.; Koposov, S.

    2015-08-01

    We present the first detailed quantitative study of the stellar populations of the Sagittarius (Sgr) streams within the Stripe 82 region, using photometric and spectroscopic observations from the Sloan Digital Sky Survey (SDSS). The star formation history (SFH) is determined separately for the bright and faint Sgr streams, to establish whether both components consist of a similar stellar population mix or have a distinct origin. Best-fitting SFH solutions are characterized by a well-defined, tight sequence in age-metallicity space, indicating that star formation occurred within a well-mixed, homogeneously enriched medium. Star formation rates dropped sharply at an age of ≈5-7 Gyr, possibly related to the accretion of Sgr by the MW. Finally, the Sgr sequence displays a change of slope in age-metallicity space at an age between 11 and 13 Gyr consistent with the Sgr α-element knee, indicating that supernovae Type Ia started contributing to the abundance pattern ≈1-3 Gyr after the start of star formation. Results for both streams are consistent with being drawn from the parent Sgr population mix, but at different epochs. The SFH of the bright stream starts from old, metal-poor populations and extends to a metallicity of [Fe/H] ≈ -0.7, with peaks at ≈7 and 11 Gyr. The faint SFH samples the older, more metal-poor part of the Sgr sequence, with a peak at ancient ages and stars mostly with [Fe/H] < -1.3 and age > 9 Gyr. Therefore, we argue in favour of a scenario where the faint stream consists of material stripped (i) earlier, and (ii) from the outskirts of the Sgr dwarf.

  17. A GALAXY BLAZES WITH STAR FORMATION

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Most galaxies form new stars at a fairly slow rate, but members of a rare class known as 'starburst' galaxies blaze with extremely active star formation. Scientists using NASA's Hubble Space Telescope are perfecting a technique to determine the history of starburst activity in galaxies by using the colors of star clusters. Measuring the clusters' colors yields information about stellar temperatures. Since young stars are blue, and older stars redder, the colors can be related to the ages, somewhat similar to counting the rings in a fallen tree trunk in order to determine the tree's age. The galaxy NGC 3310 is forming clusters of new stars at a prodigious rate. Astronomer Gerhardt Meurer of The Johns Hopkins University leads a team of collaborators who are studying several starburst galaxies, including NGC 3310, which is showcased in this month's Hubble Heritage image. There are several hundred star clusters in NGC 3310, visible in the Heritage image as the bright blue diffuse objects that trace the galaxy's spiral arms. Each of these star clusters represents the formation of up to about a million stars, a process that takes less than 100,000 years. In addition, hundreds of individual young, luminous stars can be seen throughout the galaxy. Once formed, the star clusters become redder with age as the most massive and bluest stars exhaust their fuel and burn out. Measurements in this image of the wide range of cluster colors show that they have ages ranging from about one million up to more than one hundred million years. This suggests that the starburst 'turned on' over 100 million years ago. It may have been triggered when a companion galaxy collided with NGC 3310. These observations may change astronomers' view of starbursts. Starbursts were once thought to be brief episodes, resulting from catastrophic events like a galactic collision. However, the wide range of cluster ages in NGC 3310 suggests that the starbursting can continue for an extended interval, once

  18. Early Star Formation and High-Redshift Quasars

    NASA Astrophysics Data System (ADS)

    Dietrich, Matthias; Peterson, B. M.

    2007-12-01

    We are investigating for a sample of about 30 high-redshift quasars, with redshifts up to z=6, the gas chemical metallicity based on emission line ratios and employing the FeII UV/MgII line ratio, we probe the differential metal enrichment timescale between iron and alpha-elements at these early epochs. The quasars show enhanced solar metallicities ( 5 times solar) in their broad emission-line region and no indication of a metallicity evolution up to redshifts z=6. The measured FeII UV/MgII ratios range from 3 to 5, typical for high redshift quasars, with a weighted mean of about 4. However, there is a weak tendency for a lower mean ratio at z>4.7. For the first time, we will compare the gas metallicity and the FeII UV/MgII ratio for high redshift quasars. In concert, the gas metallicity, the FeII UV/MgII ratio, and model-based estimated time scales for enriching the gas and building up the super-massive black holes suggest that a violent episode of star formation and the main growth of the black hole occur roughly contemporaneously beginning at redshifts z = 8 to 13. Support for this work was provided by NASA through grant HST-GO-10792 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

  19. The Extended Star-Forming Environments of Galactic H II Regions

    NASA Astrophysics Data System (ADS)

    Povich, Matthew S.

    2009-01-01

    H II regions are the bright beacons marking active sites of star formation throughout the Milky Way and other galaxies. The GLIMPSE and MIPSGAL Galactic plane surveys with the Spitzer Space Telescope have provided new views of the structure of H II regions and their relationship to extended star-forming environments in molecular cloud complexes. M17 is an excellent example of a well-studied H II region that is the most prominent part of a much larger star-formation event. We have found that the M17 H II region lies on the rim of a large shell structure, 0.5° in diameter ( 18 pc at 2.1 kpc), that is outlined both in diffuse IR emission from dust and in CO line emission near v=20 km/s. The molecular shell is best interpreted as an extended, expanding bubble outlining the photodissociation region of a faint, diffuse H II region several Myr old. We identify several candidate ionizing stars lying inside the bubble. We also find a concentration of candidate young stellar objects (YSOs) on the rim of the bubble. These location of these YSOs with respect to the diffuse IR and CO line emission indicates that star formation was triggered when the expanding bubble compressed one edge of an otherwise quiescent molecular cloud. The expansion of this precursor H II region may also have helped trigger the formation of the massive cluster ionizing the M17 H II region itself. The star formation history of the M17 extended molecular cloud environment has been punctuated by successive waves of massive star formation propagating through a giant molecular cloud complex.

  20. SUPPRESSION OF STAR FORMATION IN NGC 1266

    SciTech Connect

    Alatalo, Katherine; Lanz, Lauranne; Bitsakis, Theodoros; Appleton, Philip N.; Ogle, Patrick M.; Lacy, Mark; Lonsdale, Carol J.; Nyland, Kristina; Meier, David S.; Cales, Sabrina L.; Chang, Philip; Davis, Timothy A.; De Zeeuw, P. T.; Martín, Sergio

    2015-01-01

    NGC 1266 is a nearby lenticular galaxy that harbors a massive outflow of molecular gas powered by the mechanical energy of an active galactic nucleus (AGN). It has been speculated that such outflows hinder star formation (SF) in their host galaxies, providing a form of feedback to the process of galaxy formation. Previous studies, however, indicated that only jets from extremely rare, high-power quasars or radio galaxies could impart significant feedback on their hosts. Here we present detailed observations of the gas and dust continuum of NGC 1266 at millimeter wavelengths. Our observations show that molecular gas is being driven out of the nuclear region at M-dot {sub out}≈110 M{sub ⊙} yr{sup –1}, of which the vast majority cannot escape the nucleus. Only 2 M {sub ☉} yr{sup –1} is actually capable of escaping the galaxy. Most of the molecular gas that remains is very inefficient at forming stars. The far-infrared emission is dominated by an ultra-compact (≲ 50 pc) source that could either be powered by an AGN or by an ultra-compact starburst. The ratio of the SF surface density (Σ{sub SFR}) to the gas surface density (Σ{sub H{sub 2}}) indicates that SF is suppressed by a factor of ≈50 compared to normal star-forming galaxies if all gas is forming stars, and ≈150 for the outskirt (98%) dense molecular gas if the central region is powered by an ultra-compact starburst. The AGN-driven bulk outflow could account for this extreme suppression by hindering the fragmentation and gravitational collapse necessary to form stars through a process of turbulent injection. This result suggests that even relatively common, low-power AGNs are able to alter the evolution of their host galaxies as their black holes grow onto the M-σ relation.

  1. Recent star formation in 30 Doradus

    NASA Astrophysics Data System (ADS)

    De Marchi, Guido; Paresce, F.; Panagia, N.; Beccari, G.; Spezzi, L.; Sirianni, M.; Andersen, M.; SOC, WFC3

    2011-01-01

    Using observations obtained with the WFC3 camera on board the Hubble Space Telescope, we have studied the star formation properties of the central regions of 30 Dor, in the Large Magellanic Cloud. The observations clearly reveal the presence of considerable differential extinction across the field. We characterise and quantify this effect using young massive main sequence stars to derive a statistical reddening correction for each object in the field. We then search for pre-main sequence (PMS) stars by looking for objects with a strong (>5 sigma) Halpha excess emission and find about 1200 of them over the entire field. Comparison of their location in the Hertzprung--Russell diagram with theoretical PMS evolutionary tracks for the appropriate metallicity reveals that about one third of these objects have an age of < 3 Myr, compatible with that of the massive stars in the central ionising cluster R136, whereas the rest have ages up to 30 Myr, with a median of 10 Myr. This indicates that star formation has proceeded over an extended period of time, although we cannot discriminate between an extended episode and a series of short and frequent bursts that are not resolved in time. While the younger PMS population preferentially occupies the central regions of the cluster, older PMS objects are more uniformly distributed across the field and are remarkably few at the very centre of the cluster. We attribute this latter effect to photoevaporation of the older circumstellar discs caused by the massive ionising members of R136. This paper is based on Early Release Science observations made by the WFC3 Scientific Oversight Committee. We are grateful to the Director of the Space Telescope Science Institute for awarding Director's Discretionary time for this program.

  2. The FMOS-COSMOS survey of star-forming galaxies at z ∼ 1.6. II. The mass-metallicity relation and the dependence on star formation rate and dust extinction

    SciTech Connect

    Zahid, H. J.; Sanders, D. B.; Chu, J.; Hasinger, G.; Kashino, D.; Silverman, J. D.; Kewley, L. J.; Daddi, E.; Renzini, A.; Rodighiero, G.; Nagao, T.; Arimoto, N.; Kartaltepe, J.; Lilly, S. J.; Carollo, C. M.; Maier, C.; Geller, M. J.; Capak, P.; Ilbert, O.; Kajisawa, M.; Collaboration: COSMOS Team; and others

    2014-09-01

    We investigate the relationships between stellar mass, gas-phase oxygen abundance (metallicity), star formation rate (SFR), and dust content of star-forming galaxies at z ∼ 1.6 using Subaru/FMOS spectroscopy in the COSMOS field. The mass-metallicity (MZ) relation at z ∼ 1.6 is steeper than the relation observed in the local universe. The steeper MZ relation at z ∼ 1.6 is mainly due to evolution in the stellar mass where the MZ relation begins to turnover and flatten. This turnover mass is 1.2 dex larger at z ∼ 1.6. The most massive galaxies at z ∼ 1.6 (∼10{sup 11} M {sub ☉}) are enriched to the level observed in massive galaxies in the local universe. The MZ relation we measure at z ∼ 1.6 supports the suggestion of an empirical upper metallicity limit that does not significantly evolve with redshift. We find an anti-correlation between metallicity and SFR for galaxies at a fixed stellar mass at z ∼ 1.6, which is similar to trends observed in the local universe. We do not find a relation between stellar mass, metallicity, and SFR that is independent of redshift; rather, our data suggest that there is redshift evolution in this relation. We examine the relation between stellar mass, metallicity, and dust extinction, and find that at a fixed stellar mass, dustier galaxies tend to be more metal rich. From examination of the stellar masses, metallicities, SFRs, and dust extinctions, we conclude that stellar mass is most closely related to dust extinction.

  3. HIERARCHICAL STAR FORMATION IN NEARBY LEGUS GALAXIES

    SciTech Connect

    Elmegreen, Debra Meloy; Elmegreen, Bruce G.; Adamo, Angela; Gouliermis, Dimitrios A.; Aloisi, Alessandra; Bright, Stacey N.; Cignoni, Michele; Lee, Janice; Sabbi, Elena; Andrews, Jennifer; Calzetti, Daniela; Annibali, Francesca; Evans, Aaron S.; Johnson, Kelsey; Gallagher III, John S.; Grebel, Eva K.; Hunter, Deidre A.; Kim, Hwihyun; Smith, Linda J.; Thilker, David; and others

    2014-05-20

    Hierarchical structure in ultraviolet images of 12 late-type LEGUS galaxies is studied by determining the numbers and fluxes of nested regions as a function of size from ∼1 to ∼200 pc, and the number as a function of flux. Two starburst dwarfs, NGC 1705 and NGC 5253, have steeper number-size and flux-size distributions than the others, indicating high fractions of the projected areas filled with star formation. Nine subregions in seven galaxies have similarly steep number-size slopes, even when the whole galaxies have shallower slopes. The results suggest that hierarchically structured star-forming regions several hundred parsecs or larger represent common unit structures. Small galaxies dominated by only a few of these units tend to be starbursts. The self-similarity of young stellar structures down to parsec scales suggests that star clusters form in the densest parts of a turbulent medium that also forms loose stellar groupings on larger scales. The presence of super star clusters in two of our starburst dwarfs would follow from the observed structure if cloud and stellar subregions more readily coalesce when self-gravity in the unit cell contributes more to the total gravitational potential.

  4. Hierarchical Star Formation in Nearby LEGUS Galaxies

    NASA Astrophysics Data System (ADS)

    Elmegreen, Debra Meloy; Elmegreen, Bruce G.; Adamo, Angela; Aloisi, Alessandra; Andrews, Jennifer; Annibali, Francesca; Bright, Stacey N.; Calzetti, Daniela; Cignoni, Michele; Evans, Aaron S.; Gallagher, John S., III; Gouliermis, Dimitrios A.; Grebel, Eva K.; Hunter, Deidre A.; Johnson, Kelsey; Kim, Hwihyun; Lee, Janice; Sabbi, Elena; Smith, Linda J.; Thilker, David; Tosi, Monica; Ubeda, Leonardo

    2014-05-01

    Hierarchical structure in ultraviolet images of 12 late-type LEGUS galaxies is studied by determining the numbers and fluxes of nested regions as a function of size from ~1 to ~200 pc, and the number as a function of flux. Two starburst dwarfs, NGC 1705 and NGC 5253, have steeper number-size and flux-size distributions than the others, indicating high fractions of the projected areas filled with star formation. Nine subregions in seven galaxies have similarly steep number-size slopes, even when the whole galaxies have shallower slopes. The results suggest that hierarchically structured star-forming regions several hundred parsecs or larger represent common unit structures. Small galaxies dominated by only a few of these units tend to be starbursts. The self-similarity of young stellar structures down to parsec scales suggests that star clusters form in the densest parts of a turbulent medium that also forms loose stellar groupings on larger scales. The presence of super star clusters in two of our starburst dwarfs would follow from the observed structure if cloud and stellar subregions more readily coalesce when self-gravity in the unit cell contributes more to the total gravitational potential.

  5. Coeval Intermediate-mass Star Formation in N4W

    NASA Astrophysics Data System (ADS)

    Chen, Zhiwei; Zhang, Shaobo; Zhang, Miaomiao; Jiang, Zhibo; Tamura, Motohide; Kwon, Jungmi

    2016-05-01

    Protostars are mostly found in star-forming regions, where the natal molecular gas still remains. At about 5\\prime west of the molecular bubble N4, N4W is identified as a star-forming clump hosting three Class II (IRS 1–3), and one Class I (IRS 4) young stellar objects (YSOs), as well as a submillimeter source SMM1. The near-IR polarization imaging data of N4W reveal two infrared reflection nebulae close to each other, which are in favor of the outflows of IRS 1 and IRS 2. The bipolar mid-IR emission centered on IRS 4 and the arc-like molecular gas shell are lying on the same axis, indicating a bipolar molecular outflow from IRS 4. There are two dust temperature distributions in N4W. The warmer one is widely distributed and has a temperature of {T}{{d}}≳ 28 {{K}}, with the colder one being from the embedded compact submillimeter source SMM1. N4W’s mass is estimated to be ˜ 2.5× {10}3 {M}ȯ , and the mass of SMM1 is ˜ 5.5× {10}2 {M}ȯ at {T}{{d}}=15 {{K}}, calculated from the CO 1 ‑ 0 emission and 870 μm dust continuum emission, respectively. Based on the estimates of the bolometric luminosity of IRS 1–4, these four sources are intermediate-mass YSOs at least. SMM1 is gravitationally bound, and is capable of forming intermediate-mass stars or even possibly massive stars. The co-existence of the IR bright YSOs and the submillimeter source represents potential sequential star formation processes separated by ˜0.5 Myr in N4W. This small age spread implies that the intermediate-mass star formation processes happening in N4W are almost coeval.

  6. Star Formation in the Taurus-Auriga Dark Clouds

    NASA Astrophysics Data System (ADS)

    Imhoff, Catherine L.

    The era of space astronomy has given researchers new insight into pre-main sequence evolution. IUE, Einstein, and IRAS have already revolutionized this topic by identification of new classes of PMS stars and by yielding detailed information on chromospheres, coronae, winds, and disks. One approach to understanding PMS evolution involves the detailed study of individual objects; this is the basis of nearly all IUE programs to date. Another approach is to perform a statistical study of a number of stars. This avenue is essential to establish the generality of individual studies, and to find trends and correlations among the stars involving differences in age, angular momentum, mass, and so forth. The ultraviolet provides essential diagnostics of the chromosphere and transition region and of the accretion disk boundary layer. However, of the various data sets, the IUE data on pre-main sequence stars is the most incomplete (a natural limitation of a pointed instrument). The limitations of the data set, especially the bias toward the brighter, more massive, less typical PMS stars, make the statistical analysis of the IUE data difficult. We propose to survey a prototypical low-mass star-formation region, the Taurus-Auriga dark clouds, with IUE. We find that it is feasible to obtain IUE data down to specific limiting magnitudes for the various classes of objects (T Tauri stars, "weak" T Tauri stars, SU Aurigae stars, Herbig Ae/Be stars). Doing so would result in a substantial improvement in the data set for this region. The data would include Mg II fluxes, long-wavelength UV "continuum" spectra, and far-ultraviolet emission-line fluxes in order to study chromospheric emission, winds, and disks, either active or passive. New and archival IUE data will be combined with satellite and ground-based data at all wavelength regimes for statistical analysis. We will examine the indicators of various phenomena (chromospheres winds, disks), study their occurence in the various

  7. Featured Image: A Bubble Triggering Star Formation

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-05-01

    This remarkable false-color, mid-infrared image (click for the full view!) was produced by the Wide-field Infrared Survey Explorer (WISE). It captures a tantalizing view of Sh 2-207 and Sh 2-208, the latter of which is one of the lowest-metallicity star-forming regions in the Galaxy. In a recent study led by Chikako Yasui (University of Tokyo and the Koyama Astronomical Observatory), a team of scientists has examined this region to better understand how star formation in low-metallicity environments differs from that in the solar neighborhood. The authors analysis suggests that sequential star formation is taking place in these low-metallicity regions, triggered by an expanding bubble (the large dashed oval indicated in the image) with a ~30 pc radius. You can find out more about their study by checking out the paper below!CitationChikako Yasui et al 2016 AJ 151 115. doi:10.3847/0004-6256/151/5/115

  8. Investigation of Star Formation: Instrumentation and Methodology

    NASA Astrophysics Data System (ADS)

    Veach, Todd Justin

    A thorough exploration of star formation necessitates observation across the electromagnetic spectrum. In particular, observations in the submillimeter and ultra-violet allow one to observe very early stage star formation and to trace the evolution from molecular cloud collapse to stellar ignition. Submillimeter observations are essential for piercing the heart of heavily obscured stellar nurseries to observe star formation in its infancy. Ultra-violet observations allow one to observe stars just after they emerge from their surrounding environment, allowing higher energy radiation to escape. To make detailed observations of early stage star formation in both spectral regimes requires state-of-the-art detector technology and instrumentation. In this dissertation, I discuss the calibration and feasibility of detectors developed by Lawrence Berkeley National Laboratory and specially processed at the Jet Propulsion Laboratory to increase their quantum efficiency at far-ultraviolet wavelengths. A cursory treatment of the delta-doping process is presented, followed by a thorough discussion of calibration procedures developed at JPL and in the Laboratory for Astronomical and Space Instrumentation at ASU. Subsequent discussion turns to a novel design for a Modular Imager Cell forming one possible basis for construction of future large focal plane arrays. I then discuss the design, fabrication, and calibration of a sounding rocket imaging system developed using the MIC and these specially processed detectors. Finally, I discuss one scientific application of sub-mm observations. I used data from the Heinrich Hertz Sub-millimeter Telescope and the Sub-Millimeter Array (SMA) to observe sub-millimeter transitions and continuum emission towards AFGL 2591. I tested the use of vibrationally excited HCN emission to probe the protostellar accretion disk structure. I measured vibrationally excited HCN line ratios in order to elucidate the appropriate excitation mechanism. I find

  9. A search for technetium (Tc II) in barium stars

    NASA Technical Reports Server (NTRS)

    Little-Marenin, Irene R.; Little, Stephen J.

    1987-01-01

    The authors searched without success for the lines of Tc II at 2647.02, 2610.00 and 2543.24 A in IUE spectra of the barium stars HR 5058, Omicron Vir, and Zeta Cap. The lack of Tc II implies that the observed s-process enhancements were produced more than half a million years ago and supports the suggestion that the spectral peculiarities of barium stars are probably related to the binary nature of the stars.

  10. On the Formation of Massive Stars

    NASA Astrophysics Data System (ADS)

    Yorke, Harold W.; Sonnhalter, Cordula

    2002-04-01

    We calculate numerically the collapse of slowly rotating, nonmagnetic, massive molecular clumps of masses 30, 60, and 120 Msolar, which conceivably could lead to the formation of massive stars. Because radiative acceleration on dust grains plays a critical role in the clump's dynamical evolution, we have improved the module for continuum radiation transfer in an existing two-dimensional (axial symmetry assumed) radiation hydrodynamic code. In particular, rather than using ``gray'' dust opacities and ``gray'' radiation transfer, we calculate the dust's wavelength-dependent absorption and emission simultaneously with the radiation density at each wavelength and the equilibrium temperatures of three grain components: amorphous carbon particles, silicates, and ``dirty ice''-coated silicates. Because our simulations cannot spatially resolve the innermost regions of the molecular clump, however, we cannot distinguish between the formation of a dense central cluster or a single massive object. Furthermore, we cannot exclude significant mass loss from the central object(s) that may interact with the inflow into the central grid cell. Thus, with our basic assumption that all material in the innermost grid cell accretes onto a single object, we are able to provide only an upper limit to the mass of stars that could possibly be formed. We introduce a semianalytical scheme for augmenting existing evolutionary tracks of pre-main-sequence protostars by including the effects of accretion. By considering an open outermost boundary, an arbitrary amount of material could, in principal, be accreted onto this central star. However, for the three cases considered (30, 60, and 120 Msolar originally within the computation grid), radiation acceleration limited the final masses to 31.6, 33.6, and 42.9 Msolar, respectively, for wavelength-dependent radiation transfer and to 19.1, 20.1, and 22.9 Msolar for the corresponding simulations with gray radiation transfer. Our calculations

  11. Star formation triggering and its influence on ISM: multiwavelength view on the nearby galaxies.

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    We report the results of our study of the ionized and neutral gas morphology and kinematics in the regions of triggered star formation in nearby galaxies. The main goal of our study was to answer the questions: which processes are responsible for the triggering of star formation at global scale and how the feedback from new regions of star formation influences on ISM for each individual galaxy studied. In this poster we mostly focus on our recent findings about two galaxies: IC 2574 and Holmberg II.

  12. Interstellar MHD Turbulence and Star Formation

    NASA Astrophysics Data System (ADS)

    Vázquez-Semadeni, Enrique

    This chapter reviews the nature of turbulence in the Galactic interstellar medium (ISM) and its connections to the star formation (SF) process. The ISM is turbulent, magnetized, self-gravitating, and is subject to heating and cooling processes that control its thermodynamic behavior, causing it to behave approximately isobarically, in spite of spanning several orders of magnitude in density and temperature. The turbulence in the warm and hot ionized components of the ISM appears to be trans- or subsonic, and thus to behave nearly incompressibly. However, the neutral warm and cold components are highly compressible, as a consequence of both thermal instability (TI) in the atomic gas and of moderately-to-strongly supersonic motions in the roughly isothermal cold atomic and molecular components. Within this context, we discuss: (1) the production and statistical distribution of turbulent density fluctuations in both isothermal and polytropic media; (2) the nature of the clumps produced by TI, noting that, contrary to classical ideas, they in general accrete mass from their environment in spite of exhibiting sharp discontinuities at their boundaries; (3) the density-magnetic field correlation (and, at low densities, lack thereof) in turbulent density fluctuations, as a consequence of the superposition of the different wave modes in the turbulent flow; (4) the evolution of the mass-to-magnetic flux ratio (MFR) in density fluctuations as they are built up by dynamic compressions; (5) the formation of cold, dense clouds aided by TI, in both the hydrodynamic (HD) and the magnetohydrodynamic (MHD) cases; (6) the expectation that star-forming molecular clouds are likely to be undergoing global gravitational contraction, rather than being near equilibrium, as generally believed, and (7) the regulation of the star formation rate (SFR) in such gravitationally contracting clouds by stellar feedback which, rather than keeping the clouds from collapsing, evaporates and disperses

  13. A SIMPLE LAW OF STAR FORMATION

    SciTech Connect

    Padoan, Paolo; Haugbolle, Troels; Nordlund, Ake E-mail: haugboel@nbi.dk

    2012-11-10

    We show that supersonic MHD turbulence yields a star formation rate (SFR) as low as observed in molecular clouds, for characteristic values of the free-fall time divided by the dynamical time, t{sub ff}/t{sub dyn}, the Alfvenic Mach number, M{sub a}, and the sonic Mach number, M{sub s}. Using a very large set of deep adaptive-mesh-refinement simulations, we quantify the dependence of the SFR per free-fall time, {epsilon}{sub ff}, on the above parameters. Our main results are (1) that {epsilon}{sub ff} decreases exponentially with increasing t{sub ff}/t{sub dyn}, but is insensitive to changes in M{sub s}, for constant values of t{sub ff}/t{sub dyn} and M{sub a}. (2) Decreasing values of M{sub a} (stronger magnetic fields) reduce {epsilon}{sub ff}, but only to a point, beyond which {epsilon}{sub ff} increases with a further decrease of M{sub a}. (3) For values of M{sub a} characteristic of star-forming regions, {epsilon}{sub ff} varies with M{sub a} by less than a factor of two. We propose a simple star formation law, based on the empirical fit to the minimum {epsilon}{sub ff}, and depending only on t{sub ff}/t{sub dyn}: {epsilon}{sub ff} Almost-Equal-To {epsilon}{sub wind}exp (- 1.6 t{sub ff}/t{sub dyn}). Because it only depends on the mean gas density and rms velocity, this law is straightforward to implement in simulations and analytical models of galaxy formation and evolution.

  14. Magnetic fields and massive star formation

    SciTech Connect

    Zhang, Qizhou; Keto, Eric; Ho, Paul T. P.; Ching, Tao-Chung; Chen, How-Huan; Qiu, Keping; Girart, Josep M.; Juárez, Carmen; Liu, Hauyu; Tang, Ya-Wen; Koch, Patrick M.; Rao, Ramprasad; Lai, Shih-Ping; Li, Zhi-Yun; Frau, Pau; Li, Hua-Bai; Padovani, Marco; Bontemps, Sylvain

    2014-09-10

    Massive stars (M > 8 M {sub ☉}) typically form in parsec-scale molecular clumps that collapse and fragment, leading to the birth of a cluster of stellar objects. We investigate the role of magnetic fields in this process through dust polarization at 870 μm obtained with the Submillimeter Array (SMA). The SMA observations reveal polarization at scales of ≲0.1 pc. The polarization pattern in these objects ranges from ordered hour-glass configurations to more chaotic distributions. By comparing the SMA data with the single dish data at parsec scales, we found that magnetic fields at dense core scales are either aligned within 40° of or perpendicular to the parsec-scale magnetic fields. This finding indicates that magnetic fields play an important role during the collapse and fragmentation of massive molecular clumps and the formation of dense cores. We further compare magnetic fields in dense cores with the major axis of molecular outflows. Despite a limited number of outflows, we found that the outflow axis appears to be randomly oriented with respect to the magnetic field in the core. This result suggests that at the scale of accretion disks (≲ 10{sup 3} AU), angular momentum and dynamic interactions possibly due to close binary or multiple systems dominate over magnetic fields. With this unprecedentedly large sample of massive clumps, we argue on a statistical basis that magnetic fields play an important role during the formation of dense cores at spatial scales of 0.01-0.1 pc in the context of massive star and cluster star formation.

  15. Star formation along the Hubble sequence. Radial structure of the star formation of CALIFA galaxies

    NASA Astrophysics Data System (ADS)

    González Delgado, R. M.; Cid Fernandes, R.; Pérez, E.; García-Benito, R.; López Fernández, R.; Lacerda, E. A. D.; Cortijo-Ferrero, C.; de Amorim, A. L.; Vale Asari, N.; Sánchez, S. F.; Walcher, C. J.; Wisotzki, L.; Mast, D.; Alves, J.; Ascasibar, Y.; Bland-Hawthorn, J.; Galbany, L.; Kennicutt, R. C.; Márquez, I.; Masegosa, J.; Mollá, M.; Sánchez-Blázquez, P.; Vílchez, J. M.

    2016-05-01

    The spatially resolved stellar population content of today's galaxies holds important information for understanding the different processes that contribute to the star formation and mass assembly histories of galaxies. The aim of this paper is to characterize the radial structure of the star formation rate (SFR) in galaxies in the nearby Universe as represented by a uniquely rich and diverse data set drawn from the CALIFA survey. The sample under study contains 416 galaxies observed with integral field spectroscopy, covering a wide range of Hubble types and stellar masses ranging from M⋆ ~ 109 to 7 × 1011 M⊙. Spectral synthesis techniques are applied to the datacubes to derive 2D maps and radial profiles of the intensity of the star formation rate in the recent past (ΣSFR), as well as related properties, such as the local specific star formation rate (sSFR), defined as the ratio between ΣSFR and the stellar mass surface density (μ⋆). To emphasize the behavior of these properties for galaxies that are on and off the main sequence of star formation (MSSF), we stack the individual radial profiles in seven bins of galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd), and several stellar masses. Our main results are: (a) the intensity of the star formation rate shows declining profiles that exhibit very small differences between spirals with values at R = 1 half light radius (HLR) within a factor two of ΣSFR ~ 20 M⊙Gyr-1pc-2. The dispersion in the ΣSFR(R) profiles is significantly smaller in late type spirals (Sbc, Sc, Sd). This confirms that the MSSF is a sequence of galaxies with nearly constant ΣSFR. (b) sSFR values scale with Hubble type and increase radially outward with a steeper slope in the inner 1 HLR. This behavior suggests that galaxies are quenched inside-out and that this process is faster in the central, bulge-dominated part than in the disks. (c) As a whole and at all radii, E and S0 are off the MSSF with SFR much smaller than spirals of the

  16. The Ionizing Star Clusters of Giant H II Regions in NGC 2403

    NASA Astrophysics Data System (ADS)

    Drissen, Laurent; Roy, Jean-René; Moffat, Anthony F. J.; Shara, Michael M.

    1999-03-01

    We present the results of a study on the massive star population down to about M_V~-3.1, or 12-15 M_solar, of the most luminous giant H II regions in the nearby spiral galaxy NGC 2403, based on Hubble Space Telescope images and ground-based spectrograms. Particular emphasis is placed on the distribution of the Wolf-Rayet and red supergiant stars and the information they provide about the recent star-forming history of these large complexes. We find direct evidence for the presence of Wolf-Rayet (WR) stars in five of the six giant H II regions investigated; 25-40 WR stars are inferred for the sole NGC 2403-I giant H II region. Red supergiant (RSG) stars are mainly distributed over a more extended halo, while the young blue stars and most WR stars are in or close to a compact core. One appears to be seeing young cores of O and WR stars surrounded by older halos containing red supergiants. We propose a scenario in which RSG stars belonging to an early phase of star formation were followed by a more recent burst corresponding to a very blue mean sequence. Delayed trigger with preheating over several 100 pc by the first generation of massive stars allowed the build-up of the required confinement for the production of parsec-scale cluster cores with luminosity up to a few times 10^6 L_solar. Finally, we present some interesting objects found in the field of NGC 2403 outside the giant H II regions, such as field WR stars, globular clusters and background galaxies.

  17. Hierarchical Star Formation in LEGUS Galaxies

    NASA Astrophysics Data System (ADS)

    Elmegreen, Debra M.; Elmegreen, Bruce

    2014-06-01

    Star formation generally follows a hierarchical distribution in galaxies from kpc scales in giant star complexes down to sub-pc scales in embedded clusters. This hierarchy corresponds to a power law distribution function for the number of star forming regions as a function of size or luminosity. Using the Legacy ExtraGalactic Ultraviolet Survey (LEGUS), we examine six galaxies, NGC 1566, NGC 1705, NGC 2500, NGC 5253, NGC 5477, and IC 4247, which span types from grand design and flocculent spirals to irregulars and starburst irregulars. Power law size and luminosity distributions were measured from Gaussian-blurred images in the NUV and UV using SExtractor. Slopes ranged from -1 to -1.8, with the steepest slopes corresponding to the starburst galaxies. The slopes did not vary from the NUV to the UV. The fraction of light contained within the largest scales ranged from 85 to 95 percent, independent of galaxy type. We acknowledge support from grant HST-GO-13364.

  18. Calibration of Evolutionary Diagnostics in High-mass Star Formation

    NASA Astrophysics Data System (ADS)

    Molinari, S.; Merello, M.; Elia, D.; Cesaroni, R.; Testi, L.; Robitaille, T.

    2016-07-01

    The evolutionary classification of massive clumps that are candidate progenitors of high-mass young stars and clusters relies on a variety of independent diagnostics based on observables from the near-infrared to the radio. A promising evolutionary indicator for massive and dense cluster-progenitor clumps is the L/M ratio between the bolometric luminosity and the mass of the clumps. With the aim of providing a quantitative calibration for this indicator, we used SEPIA/APEX to obtain CH3C2H(J = 12–11) observations, which is an excellent thermometer molecule probing densities ≥slant {10}5 cm‑3, toward 51 dense clumps with M≥slant 1000 M {}ȯ and uniformly spanning ‑2 ≲ Log(L/M) [L {}ȯ /M {}ȯ ] ≲ 2.3. We identify three distinct ranges of L/M that can be associated to three distinct phases of star formation in massive clumps. For L/M ≤slant 1 no clump is detected in CH3C2H, suggesting an inner envelope temperature below ∼30K. For 1 ≲ L/M ≲ 10 we detect 58% of the clumps with a temperature between ∼30 and ∼35 K independently from the exact value of L/M; such clumps are building up luminosity due to the formation of stars, but no star is yet able to significantly heat the inner clump regions. For L/M ≳ 10 we detect all the clumps with a gas temperature rising with Log(L/M), marking the appearance of a qualitatively different heating source within the clumps; such values are found toward clumps with UCH ii counterparts, suggesting that the quantitative difference in T versus L/M behavior above L/M ∼ 10 is due to the first appearance of ZAMS stars in the clumps.

  19. Calibration of Evolutionary Diagnostics in High-mass Star Formation

    NASA Astrophysics Data System (ADS)

    Molinari, S.; Merello, M.; Elia, D.; Cesaroni, R.; Testi, L.; Robitaille, T.

    2016-07-01

    The evolutionary classification of massive clumps that are candidate progenitors of high-mass young stars and clusters relies on a variety of independent diagnostics based on observables from the near-infrared to the radio. A promising evolutionary indicator for massive and dense cluster-progenitor clumps is the L/M ratio between the bolometric luminosity and the mass of the clumps. With the aim of providing a quantitative calibration for this indicator, we used SEPIA/APEX to obtain CH3C2H(J = 12–11) observations, which is an excellent thermometer molecule probing densities ≥slant {10}5 cm‑3, toward 51 dense clumps with M≥slant 1000 M {}ȯ and uniformly spanning ‑2 ≲ Log(L/M) [L {}ȯ /M {}ȯ ] ≲ 2.3. We identify three distinct ranges of L/M that can be associated to three distinct phases of star formation in massive clumps. For L/M ≤slant 1 no clump is detected in CH3C2H, suggesting an inner envelope temperature below ˜30K. For 1 ≲ L/M ≲ 10 we detect 58% of the clumps with a temperature between ˜30 and ˜35 K independently from the exact value of L/M; such clumps are building up luminosity due to the formation of stars, but no star is yet able to significantly heat the inner clump regions. For L/M ≳ 10 we detect all the clumps with a gas temperature rising with Log(L/M), marking the appearance of a qualitatively different heating source within the clumps; such values are found toward clumps with UCH ii counterparts, suggesting that the quantitative difference in T versus L/M behavior above L/M ˜ 10 is due to the first appearance of ZAMS stars in the clumps.

  20. Late Pop III Star Formation During the Epoch of Reionization: Results from the Renaissance Simulations

    NASA Astrophysics Data System (ADS)

    Xu, Hao; Norman, Michael L.; O’Shea, Brian W.; Wise, John H.

    2016-06-01

    We present results on the formation of Population III (Pop III) stars at redshift 7.6 from the Renaissance Simulations, a suite of extremely high-resolution and physics-rich radiation transport hydrodynamics cosmological adaptive-mesh refinement simulations of high-redshift galaxy formation performed on the Blue Waters supercomputer. In a survey volume of about 220 comoving Mpc3, we found 14 Pop III galaxies with recent star formation. The surprisingly late formation of Pop III stars is possible due to two factors: (i) the metal enrichment process is local and slow, leaving plenty of pristine gas to exist in the vast volume; and (ii) strong Lyman–Werner radiation from vigorous metal-enriched star formation in early galaxies suppresses Pop III formation in (“not so”) small primordial halos with mass less than ˜3 × 107 M ⊙. We quantify the properties of these Pop III galaxies and their Pop III star formation environments. We look for analogs to the recently discovered luminous Ly α emitter CR7, which has been interpreted as a Pop III star cluster within or near a metal-enriched star-forming galaxy. We find and discuss a system similar to this in some respects, however, the Pop III star cluster is far less massive and luminous than CR7 is inferred to be.

  1. Effects of Ionization Feedback in Massive Star Formation

    NASA Astrophysics Data System (ADS)

    Peters, Thomas; Banerjee, R.; Klessen, R. S.; Mac Low, M.

    2009-01-01

    We present 3D high-resolution radiation-hydrodynamical simulations of massive star formation. We model the collapse of a massive molecular cloud core forming a high-mass star in its center. We use a version of the FLASH code that has been extended by including sink particles which are a source of both ionizing and non-ionizing radiation. The sink particles evolve according to a prestellar model which determines the stellar and accretion luminosities. Radiation transfer is done using the hybrid characteristics raytracing approach on the adaptive mesh developed by Rijkhorst et al. (2006). The radiative transfer module has been augmented to allow simulations with arbitrarily high resolution. Our highest resolution models resolve the disk scale height by at least 16 zones. Opacities for non-ionizing radiation have been added to account for the accretion heating, which is expected to be strong at the initial stage of star formation and believed to prevent fragmentation. Studies of collapsing massive cores show the formation of a gravitationally highly unstable disk. The accretion heating is not strong enough to suppress this instability. The ionizing radiation builds up an H II region around the protostar, which destroys the accretion disk close to it. We describe preliminary results, with a focus on how long the H II region remains confined by the accretion flow, and whether it can ever cut off accretion entirely. Thomas Peters acknowledges support from a Kade Fellowship for his visit to the American Museum of Natural History. He is a fellow of the International Max Planck Research School for Astronomy and Cosmic Physics at the University of Heidelberg and the Heidelberg Graduate School of Fundamental Physics. We also thank the DFG for support via the Emmy Noether Grant BA 3607/1 and the individual grant KL1358/5.

  2. The case against bimodal star formation in elliptical galaxies

    NASA Astrophysics Data System (ADS)

    Gibson, B. K.

    1996-02-01

    We consider the present-day photometric and chemical properties of elliptical galaxies, adopting the bimodal star formation scenario of Elbaz, Arnaud & Vangioni-Flam. These models utilize an initial mass function (IMF) biased heavily toward massive stars during the early phases of galactic evolution, leading to early Type II supernovae-driven galactic winds. A subsequent lengthy, milder star formation phase with a normal IMF ensues, supposedly responsible for the stellar population observed today. Based upon chemical evolution arguments alone, this scenario has been invoked to explain the observed metal mass, and their abundance ratios, in the intracluster medium of galaxy clusters. Building upon the recent compilations of metallicity-dependent isochrones for simple stellar populations, we have constructed a coupled photometric and chemical evolution package for composite stellar populations in order to quantify the effects of such a model upon the photochemical properties of the resultant elliptical galaxies. We demonstrate that these predicted properties are incompatible with those observed at the current epoch.

  3. STAR FORMATION AND YOUNG STELLAR CONTENT IN THE W3 GIANT MOLECULAR CLOUD

    SciTech Connect

    Rivera-Ingraham, Alana; Martin, Peter G.; Polychroni, Danae; Moore, Toby J. T.

    2011-12-10

    In this work, we have carried out an in-depth analysis of the young stellar content in the W3 giant molecular cloud (GMC). The young stellar object (YSO) population was identified and classified in the Infrared Array Camera/Multiband Imaging Photometer color-magnitude space according to the 'Class' scheme and compared to other classifications based on intrinsic properties. Class 0/I and II candidates were also compared to low-/intermediate-mass pre-main-sequence (PMS) stars selected through their colors and magnitudes in the Two Micron All Sky Survey. We find that a reliable color/magnitude selection of low-mass PMS stars in the infrared requires prior knowledge of the protostar population, while intermediate-mass objects can be more reliably identified. By means of the minimum spanning tree algorithm and our YSO spatial distribution and age maps, we investigated the YSO groups and the star formation history in W3. We find signatures of clustered and distributed star formation in both triggered and quiescent environments. The central/western parts of the GMC are dominated by large-scale turbulence likely powered by isolated bursts of star formation that triggered secondary star formation events. Star formation in the eastern high-density layer (HDL) also shows signs of quiescent and triggered stellar activity, as well as extended periods of star formation. While our findings support triggering as a key factor for inducing and enhancing some of the major star-forming activity in the HDL (e.g., W3 Main/W3(OH)), we argue that some degree of quiescent or spontaneous star formation is required to explain the observed YSO population. Our results also support previous studies claiming a spontaneous origin for the isolated massive star(s) powering KR 140.

  4. Star Formation and Young Stellar Content in the W3 Giant Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Rivera-Ingraham, Alana; Martin, Peter G.; Polychroni, Danae; Moore, Toby J. T.

    2011-12-01

    In this work, we have carried out an in-depth analysis of the young stellar content in the W3 giant molecular cloud (GMC). The young stellar object (YSO) population was identified and classified in the Infrared Array Camera/Multiband Imaging Photometer color-magnitude space according to the "Class" scheme and compared to other classifications based on intrinsic properties. Class 0/I and II candidates were also compared to low-/intermediate-mass pre-main-sequence (PMS) stars selected through their colors and magnitudes in the Two Micron All Sky Survey. We find that a reliable color/magnitude selection of low-mass PMS stars in the infrared requires prior knowledge of the protostar population, while intermediate-mass objects can be more reliably identified. By means of the minimum spanning tree algorithm and our YSO spatial distribution and age maps, we investigated the YSO groups and the star formation history in W3. We find signatures of clustered and distributed star formation in both triggered and quiescent environments. The central/western parts of the GMC are dominated by large-scale turbulence likely powered by isolated bursts of star formation that triggered secondary star formation events. Star formation in the eastern high-density layer (HDL) also shows signs of quiescent and triggered stellar activity, as well as extended periods of star formation. While our findings support triggering as a key factor for inducing and enhancing some of the major star-forming activity in the HDL (e.g., W3 Main/W3(OH)), we argue that some degree of quiescent or spontaneous star formation is required to explain the observed YSO population. Our results also support previous studies claiming a spontaneous origin for the isolated massive star(s) powering KR 140.

  5. Star formation and chemical abundances in clumpy irregular galaxies

    SciTech Connect

    Boesgaard, A.M.; Edwards, S.; Heidmann, J.

    1982-01-15

    Clumpy irregular galaxies consist of several bright clumps which are huge H II complexes (about 100 times brighter and more massive than 30 Doradus) and contain about 10/sup 5/ O and B stars. Image-tube spectrograms with 1--3 A resolution have been obtained of the brightest emission regions of three clumpy galaxies and one candidate clumpy galaxy with the Mauna Kea 2.24 m telescope. The electron temperatures were found to be in the range 7000--9000 K and electron densities a few hundred cm/sup 3/: quite typical for normal H II regions. The abundances of O, N. S in Mrk 432 are comparable to those in Orion, while the three clumpy galaxies are slightly deficient in O and S (by factors of 2 to 4) and N (by factors of 3 to 6). The galaxies appear to be normal (like Sc galaxies) in mass and composition. Supernovae remnants are indicated by the high (S II)/H..cap alpha.. ratio. Possible triggering mechanisms for the exceptional star formation activity are discussed.

  6. Metallicity and star formation history of globular clusters

    NASA Astrophysics Data System (ADS)

    Zhang, Mei; Ma, Er

    1993-01-01

    Using population synthesis method, the star formation history in globular clusters has been studied. No single star formation mode with a constant star formation rate (SER) and an invariable initial mass function (IMF) can fit the observations of globular clusters. There are at least two stages of star formation: a pollution stage and a starburst stage. In the pollution stage, either the IMF is very peculiar (only form massive stars), or its SFR is so small that the low-mass stars form only a little. A starburst then follows to form most stars in the globular cluster. Within the framework of Fall and Rees'model, the collisions between warm clouds in the two phase medium may provide a suitable external cause to stimulate the starburst.

  7. Metallicity and star formation history of globular clusters

    NASA Astrophysics Data System (ADS)

    Zhang, Mei; Ma, Er

    1993-03-01

    Using population synthesis method, the star formation history in globular clusters has been studied. No single star formation mode with a constant star formation rate (SER) and an invariable initial mass function (IMF) can fit the observations of globular clusters. There are at least two stages of star formation: a pollution stage and a starburst stage. In the pollution stage, either the IMF is very peculiar (only form massive stars), or its SFR is so small that the low-mass stars form only a little. A starburst then follows to form most stars in the globular cluster. Within the framework of Fall and Rees' model, the collisions between warm clouds in the two phase medium may provide a suitable external cause to stimulate the starburst.

  8. The Origin of MN II Emission in the Spectra of Chemically Peculiar Stars

    NASA Astrophysics Data System (ADS)

    Sigut, T. A. A.

    2001-01-01

    Emission from Mn II multiplet 13 (λλ6122-6132) in the spectrum of the 3He star 3 Centauri A and the hot, mild, HgMn star 46 Aquilae can be naturally explained by interlocked non-LTE effects. However, reproduction of the strength of the Mn II emission in both stars requires vertical stratification of the manganese abundance, with manganese concentrated high in the photosphere (column mass <~10-2 g cm-2). If this formation picture is correct, several additional transitions of Mn II with λ>8000 Å should also be present in emission in the spectrum of 3 Cen A. The wide range in the strength of Mn II multiplet 13 among upper main-sequence stars (ranging from absorption to emission) is made possible by the interplay in the non-LTE radiative transfer solution of the stellar Teff, manganese abundance, and manganese stratification profile. In particular, emission is strongly suppressed by a large manganese overabundance in the photosphere. This explains why the hot, mild, HgMn star 46 Aql, which has only a modest manganese enhancement, is detected in emission in Mn II multiplet 13 while other HgMn stars of similar Teff but with large photospheric manganese overabundances, such as κ Cancri, present Mn II multiplet 13 in absorption.

  9. Recovering the Star Formation Rate in the Solar Neighborhood

    NASA Astrophysics Data System (ADS)

    Cignoni, M.; Degl'Innocenti, S.; Moroni, P. G. P.; Shore, S. N.

    2007-11-01

    This paper develops a method for obtaining the star formation histories of a mixed, resolved population through the use of color-magnitude diagrams (CMDs). The method is applied to the derivation of the local star formation rate, analyzing the observations of the Hipparcos satellite through a comparison with synthetic CMDs computed for different star formation histories with an updated stellar evolution library. Parallax and photometric uncertainties are included explicitly and corrected using the Bayesian Richardson-Lucy algorithm. We find that the solar neighborhood star formation rate has a characteristic timescale for variation of about 6 Gyr, with a maximum activity close to 3 Gyr ago.

  10. Star Formation in Dwarf Galaxies: Life in a Rough Neighborhood

    SciTech Connect

    Murray, S

    2003-10-16

    Star formation within dwarf galaxies is governed by several factors. Many of these factors are external, including ram-pressure stripping, tidal stripping, and heating by external UV radiation. The latter, in particular, may prevent star formation in the smallest systems. Internal factors include negative feedback in the form of UV radiation, winds and supernovae from massive stars. These act to reduce the star formation efficiency within dwarf systems, which may, in turn, solve several theoretical and observational problems associated with galaxy formation. In this contribution, we discuss our recent work being done to examine the importance of the many factors in the evolution of dwarf galaxies.

  11. Sequential Star Formation in RCW 34: A Spectroscopic Census of the Stellar Content of High-Mass Star-Forming Regions

    NASA Astrophysics Data System (ADS)

    Bik, A.; Puga, E.; Waters, L. B. F. M.; Horrobin, M.; Henning, Th.; Vasyunina, T.; Beuther, H.; Linz, H.; Kaper, L.; van den Ancker, M.; Lenorzer, A.; Churchwell, E.; Kurtz, S.; Kouwenhoven, M. B. N.; Stolte, A.; de Koter, A.; Thi, W. F.; Comerón, F.; Waelkens, Ch.

    2010-04-01

    In this paper, we present VLT/SINFONI integral field spectroscopy of RCW 34 along with Spitzer/IRAC photometry of the surroundings. RCW 34 consists of three different regions. A large bubble has been detected in the IRAC images in which a cluster of intermediate- and low-mass class II objects is found. At the northern edge of this bubble, an H II region is located, ionized by 3 OB stars, of which the most massive star has spectral type O8.5V. Intermediate-mass stars (2-3 M sun) are detected of G- and K-spectral type. These stars are still in the pre-main-sequence (PMS) phase. North of the H II region, a photon-dominated region is present, marking the edge of a dense molecular cloud traced by H2 emission. Several class 0/I objects are associated with this cloud, indicating that star formation is still taking place. The distance to RCW 34 is revised to 2.5 ± 0.2 kpc and an age estimate of 2 ± 1 Myr is derived from the properties of the PMS stars inside the H II region. Between the class II sources in the bubble and the PMS stars in the H II region, no age difference could be detected with the present data. The presence of the class 0/I sources in the molecular cloud, however, suggests that the objects inside the molecular cloud are significantly younger. The most likely scenario for the formation of the three regions is that star formation propagated from south to north. First the bubble is formed, produced by intermediate- and low-mass stars only, after that, the H II region is formed from a dense core at the edge of the molecular cloud, resulting in the expansion similar to a champagne flow. More recently, star formation occurred in the rest of the molecular cloud. Two different formation scenarios are possible. (1) The bubble with the cluster of low- and intermediate-mass stars triggered the formation of the O star at the edge of the molecular cloud, which in its turn induces the current star formation in the molecular cloud. (2) An external triggering is

  12. A WISE VIEW OF STAR FORMATION IN LOCAL GALAXY CLUSTERS

    SciTech Connect

    Chung, Sun Mi; Gonzalez, Anthony H.; Eisenhardt, Peter R.; Stern, Daniel; Stanford, Spencer A.; Brodwin, Mark; Jarrett, Thomas

    2011-12-10

    We present results from a systematic study of star formation in local galaxy clusters using 22 {mu}m data from the Wide-field Infrared Survey Explorer (WISE). The 69 systems in our sample are drawn from the Cluster Infall Regions Survey, and all have robust mass determinations. The all-sky WISE data enable us to quantify the amount of star formation, as traced by 22 {mu}m, as a function of radius well beyond R{sub 200}, and investigate the dependence of total star formation rate upon cluster mass. We find that the fraction of star-forming galaxies increases with cluster radius but remains below the field value even at 3R{sub 200}. We also find that there is no strong correlation between the mass-normalized total specific star formation rate and cluster mass, indicating that the mass of the host cluster does not strongly influence the total star formation rate of cluster members.

  13. Star Formation Activity in CLASH Brightest Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Fogarty, Kevin; Postman, Marc; Connor, Thomas; Donahue, Megan; Moustakas, John

    2015-11-01

    The CLASH X-ray selected sample of 20 galaxy clusters contains 10 brightest cluster galaxies (BCGs) that exhibit significant (>5σ) extinction-corrected star formation rates (SFRs). Star formation activity is inferred from photometric estimates of UV and Hα+[N ii] emission in knots and filaments detected in CLASH Hubble Space Telescope ACS and WFC3 observations. UV-derived SFRs in these BCGs span two orders of magnitude, including two with a SFR ≳ 100 M⊙ yr-1. These measurements are supplemented with [O ii], [O iii], and Hβ fluxes measured from spectra obtained with the SOAR telescope. We confirm that photoionization from ongoing star formation powers the line emission nebulae in these BCGs, although in many BCGs there is also evidence of a LINER-like contribution to the line emission. Coupling these data with Chandra X-ray measurements, we infer that the star formation occurs exclusively in low-entropy cluster cores and exhibits a correlation with gas properties related to cooling. We also perform an in-depth study of the starburst history of the BCG in the cluster RXJ1532.9+3021, and create 2D maps of stellar properties on scales down to ˜350 pc. These maps reveal evidence for an ongoing burst occurring in elongated filaments, generally on ˜0.5-1.0 Gyr timescales, although some filaments are consistent with much younger (≲100 Myr) burst timescales and may be correlated with recent activity from the active galactic nucleus. The relationship between BCG SFRs and the surrounding intracluster medium gas properties provide new support for the process of feedback-regulated cooling in galaxy clusters and is consistent with recent theoretical predictions. Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel

  14. Solving the problem of magnetic flux transport during star formation

    NASA Astrophysics Data System (ADS)

    Santos de Lima, Reinaldo; de Gouveia Dal Pino, Elisabete; Guerrero, Gustavo; Leao, Marcia; Lazarian, Alex

    2015-08-01

    Fast magnetic reconnection is an omnipresent process in turbulent astrophysical flows. It allows the magnetic flux to diffuse through the gas even when the electrical conductivity is very high. Recently we have tested this diffusive mechanism (termed Reconnection Diffusion, RD) for solving two intriguing problems related to star formation: (i) the removal of magnetic flux from collapsing molecular clouds in order to explain the observed magnetic field intensities in protostars, and (ii) the formation of rotationally sustained protostellar disks in the presence of the magnetic fields, which tend to remove all the angular momentum. Using 3D MHD simulations we have demonstrated successfully the efficiency of the RD in both problems. More recently, we have also identified the conditions under which RD is able to produce supercritical cores from self-gravitating subcritical molecular cloud clumps. In this presentation we review the RD theory and the results of our numerical studies in different phases of star formation. We also derive the RD coefficient from the numerical simulations and compare with the theoretical predictions

  15. The role of Reconnection Diffusion in star formation

    NASA Astrophysics Data System (ADS)

    Santos-Lima, Reinaldo; Lazarian, Alex; De Gouveia Dal Pino, Elisabete; Guerrero, Gustavo; Leao, Marcia

    Fast magnetic reconnection is an omnipresent process in turbulent astrophysical flows. It allows the magnetic flux to diffuse through the gas even when the ideal MHD approximation is applicable. Recently we have tested this diffusive mechanism (termed ``Reconnection Diffusion'', RD) for solving two intriguing problems related to star formation: (i) the removal of magnetic flux from collapsing molecular clouds in order to explain the observed magnetic field intensities in protostars (the ``magnetic flux problem''), and (ii) the formation of rotationally sustained protostellar disks in the presence of the magnetic fields, which tend to remove all the angular momentum (the ``magnetic braking catastrophe''). Using 3D MHD simulations we have demonstrated successfully the efficiency of the RD in both problems. More recently, we have also identified the conditions under which RD is able to produce supercritical cores from self-gravitating subcritical molecular cloud clumps. In this presentation we review the RD theory and the results of our numerical studies in different phases of star formation. We also derive the RD coefficient profile from the numerical simulations and compare with the theoretical predictions.

  16. Star formation and substructure in galaxy clusters

    SciTech Connect

    Cohen, Seth A.; Hickox, Ryan C.; Wegner, Gary A.; Einasto, Maret; Vennik, Jaan

    2014-03-10

    We investigate the relationship between star formation (SF) and substructure in a sample of 107 nearby galaxy clusters using data from the Sloan Digital Sky Survey. Several past studies of individual galaxy clusters have suggested that cluster mergers enhance cluster SF, while others find no such relationship. The SF fraction in multi-component clusters (0.228 ± 0.007) is higher than that in single-component clusters (0.175 ± 0.016) for galaxies with M{sub r}{sup 0.1}<−20.5. In both single- and multi-component clusters, the fraction of star-forming galaxies increases with clustercentric distance and decreases with local galaxy number density, and multi-component clusters show a higher SF fraction than single-component clusters at almost all clustercentric distances and local densities. Comparing the SF fraction in individual clusters to several statistical measures of substructure, we find weak, but in most cases significant at greater than 2σ, correlations between substructure and SF fraction. These results could indicate that cluster mergers may cause weak but significant SF enhancement in clusters, or unrelaxed clusters exhibit slightly stronger SF due to their less evolved states relative to relaxed clusters.

  17. Molecular cloud cores and bimodal star formation

    NASA Technical Reports Server (NTRS)

    Lizano, Susana; Shu, Frank H.

    1989-01-01

    The phenomenon of bimodal star formation is reviewed in the context of supercritical and subcritical states for molecular clouds that are supported against their self-gravitation by magnetic fields. The governing set of equations is derived subject to the quasi-static and axisymmetric approximations. The method of numerical solution and tests of the resultant computer code are outlined. The results of the evolutionary calculations are discussed, emphasizing time scales, masses, and typical sizes of modeled cores that can be compared with observations. For a fixed mass, it is found that the level or turbulent support determines whether a dense core forms or not. This is used to generalize the concept of a critical mass to account for the contributions of turbulence and thermal pressures to the support of a cloud.

  18. Dynamics of H II regions around exiled O stars

    NASA Astrophysics Data System (ADS)

    Mackey, Jonathan; Langer, Norbert; Gvaramadze, Vasilii V.

    2013-11-01

    At least 25 per cent of massive stars are ejected from their parent cluster, becoming runaways or exiles, travelling with often-supersonic space velocities through the interstellar medium (ISM). Their overpressurized H II regions impart kinetic energy and momentum to the ISM, compress and/or evaporate dense clouds, and can constrain properties of both the star and the ISM. Here, we present one-, two- and (the first) three-dimensional simulations of the H II region around a massive star moving supersonically through a uniform, magnetized ISM, with properties appropriate for the nearby O star ζ Oph. The H II region leaves an expanding overdense shell behind the star and, inside this, an underdense wake that should be filled with hot gas from the shocked stellar wind. The gas column density in the shell is strongly influenced by the ISM magnetic field strength and orientation. Hα emission maps show that H II region remains roughly circular, although the star is displaced somewhat from the centre of emission. For our model parameters, the kinetic energy feedback from the H II region is comparable to the mechanical luminosity of the stellar wind, and the momentum feedback rate is >100 times larger than that from the wind and ≈10 times larger than the total momentum input rate available from radiation pressure. Compared to the star's eventual supernova explosion, the kinetic energy feedback from the H II region over the star's main-sequence lifetime is >100 times less, but the momentum feedback is up to 4 times larger. H II region dynamics are found to have only a small effect on the ISM conditions that a bow shock close to the star would encounter.

  19. Tracking star formation in dwarf cluster galaxies

    NASA Astrophysics Data System (ADS)

    Rude, Cody Millard

    The evolution of galaxies in dense environments can be affected by close encounters with neighboring galaxies and interactions with the intracluster medium (ICM). Dwarf galaxies may be especially susceptible to these effects due to their low mass. The goal of my dissertation research is to look for signs of star formation in cluster dwarf galaxies by measuring and comparing the r- and u-band luminosity functions of 15 low redshift Abell galaxy clusters using archival data from the Canada-France-Hawaii Telescope (CFHT). Luminosity functions, dwarf-to-giant ratios, and blue fractions are measured in four cluster-centric annuli from stacked cluster data. To account for differences in cluster optical richness, each cluster is scaled according to r200, where r200 is the radius of a sphere, centered on the cluster, whose average density is 200 times the critical density of the universe. The outer region of the cluster sample shows an increase in the faint-end slope of the u-band luminosity function relative to the r-band, indicating star formation in dwarf galaxies. The blue fraction for dwarf galaxies steadily rises with increasing cluster-centric radii. The change in the blue fraction of giant galaxies also increases, but at a lower rate. Additionally, the inner regions of clusters ranging from 0.185 < z < 0.7 from the "Cluster Lensing and Supernova survey with Hubble (CLASH)" are used to generate blue- and red-band luminosity functions, dwarf-to-giant ratios, and blue fractions. Comparisons of the inner region of the CLASH and CFHT clusters show an increase in the blue fraction of dwarf galaxies with redshift that is not present in giant galaxies.

  20. The Object CLN 138 - a Double Star-Formation Region

    NASA Astrophysics Data System (ADS)

    Gyulbudaghian, A. L.

    2016-09-01

    A double star formation region associated with the biconical cometary nebula CLN 138 is studied. 12CO(1-0) observations of a molecular cloud associated with this object reveal the existence of several molecular clouds in this region, as well as the existence of red and blue molecular outflows. Several new Herbig-Haro objects are found, two of which have undergone a luminosity increase of at least 8m. The first star formation region is basically embedded in the molecular cloud; most of the stars in it are infrared stars and many have dust envelopes. The second star formation region has already left the molecular cloud; it has no IR stars and few of its stars have dust clouds.

  1. Star Formation in the Cometary Globule Ori I-2

    NASA Astrophysics Data System (ADS)

    Mookerjea, Bhaswati; Sandell, Göran

    2009-11-01

    We investigate the young stellar population in and near the cometary globule Ori I-2. The analysis is based on deep Nordic Optical Telescope R-band and Hα images, JCMT SCUBA 450 and 850 μm images combined with near-infrared Two Micron All Sky Survey (2MASS) photometry and mid-infrared archival Spitzer images obtained with the Infrared Array Camera (IRAC; 3.6, 4.5, 5.8, and 8 μm), and MIPS (24 and 70 μm) instruments. We identify a total of 125 sources within the 5'×5' region imaged by the IRAC. Of these sources, 87 are detected in the R-band image and 51 are detected in the 2MASS. The detailed physical properties of the sources are explored using a combination of near/mid-infrared color-color diagrams, graybody fitting of spectral energy distributions (SEDs) and an online SED fitting tool that uses a library of two-dimensional radiation transfer based accretion models of young stellar objects with disks. Ori I-2 shows clear evidence of triggered star formation with four young low-luminosity pre-main-sequence (PMS) stars embedded in the globule. At least two, possibly as many as four, additional low-mass PMS objects were discovered in the field which are probably part of the young σ Orionis cluster. Among the PMS stars which have formed in the globule, MIR-54 is a young, deeply embedded Class 0/I object; MIR-51 and 52 are young Class II sources, while MIR-89 is a more evolved, heavily extincted Class II object with its apparent colors mimicking a Class 0/I object. The Class 0/I object MIR-54 coincides with a previously known IRAS source and is a strong submillimeter source. It is most likely the source for the molecular outflow and the large parsec-scale Herbig-Haro (HH) flow. However, the nearby Class II source, MIR-52, which is strong a Hα emission line star, also appears to drive an outflow approximately aligned with the outflow from MIR-54, and because of the proximity of the two outflows, either star could contribute. MIR-89 appears to excite a low

  2. ON THE LACK OF EVOLUTION IN GALAXY STAR FORMATION EFFICIENCY

    SciTech Connect

    Behroozi, Peter S.; Wechsler, Risa H.; Conroy, Charlie

    2013-01-10

    Using reconstructed galaxy star formation histories, we calculate the instantaneous efficiency of galaxy star formation (i.e., the star formation rate divided by the baryon accretion rate) from z = 8 to the present day. This efficiency exhibits a clear peak near a characteristic halo mass of 10{sup 11.7} M{sub Sun }, which coincides with longstanding theoretical predictions for the mass scale relevant to virial shock heating of accreted gas. Above the characteristic halo mass, the efficiency falls off as the mass to the minus four-thirds power; below the characteristic mass, the efficiency falls off at an average scaling of mass to the two-thirds power. By comparison, the shape and normalization of the efficiency change very little since z = 4. We show that a time-independent star formation efficiency simply explains the shape of the cosmic star formation rate since z = 4 in terms of dark matter accretion rates. The rise in the cosmic star formation from early times until z = 2 is especially sensitive to galaxy formation efficiency. The mass dependence of the efficiency strongly limits where most star formation occurs, with the result that two-thirds of all star formation has occurred inside halos within a factor of three of the characteristic mass, a range that includes the mass of the Milky Way.

  3. Low Mass Star Formation in the Norma Cloud

    NASA Astrophysics Data System (ADS)

    Reipurth, B.; Nielbock, M.

    2008-12-01

    A small filamentary cloud in Norma hosts a number of young low-mass stars in various stages of evolution, from visible Hα emission stars to embedded sources detected only in the sub-millimeter regime. The best known source is V346 Nor, an FU Orionis star that brightened in the early 1980s. The morphology of the cloud complex and an apparent age gradient along the cloud suggests that star formation in this region was triggered by an external event.

  4. Magnetic Stars After the Hayashi Phase. II.

    NASA Astrophysics Data System (ADS)

    Glagolevskij, Yu. V.

    2016-09-01

    The properties of magnetic stars derived from observational data are analyzed. The degree of "magnetic" braking of parent protostars, which depends the magnetic field and mass, is studied. The conditions under which magnetic and "normal" nonmagnetic stars are separated, which appear to depend only on the rotational velocity of the protostars, are examined. The reasons for differences in the average magnitudes of the magnetic field in massive and low-mass magnetic stars are analyzed. The magnetic field structures of magnetic stars and their stability over time (rigidity of rotation) are examined.

  5. On the formation of Be stars through binary interaction

    SciTech Connect

    Shao, Yong; Li, Xiang-Dong

    2014-11-20

    Be stars are rapidly rotating B-type stars. The origin of their rapid rotation is not certain, but binary interaction remains as a possibility. In this work, we investigate the formation of Be stars resulting from mass transfer in binaries in the Galaxy. We calculate binary evolution with both stars evolving simultaneously and consider different possible mass accretion histories for the accretor. From the calculated results, we obtain the critical mass ratios q {sub cr} that determine the stability of the mass transfer. We also numerically calculate the parameter λ in common envelope evolution and then incorporate both q {sub cr} and λ into the population synthesis calculations. We present the predicted numbers and characteristics of Be stars in binary systems with different types of companions, including helium stars, white dwarfs, neutron stars, and black holes. We find that in Be/neutron star binaries, the Be stars can have a lower mass limit ∼8 M {sub ☉} if they are formed by stable (i.e., without the occurrence of common envelope evolution) and nonconservative mass transfer. We demonstrate that isolated Be stars may originate from both mergers of two main-sequence stars and disrupted Be binaries during the supernova explosions of the primary stars, but mergers seem to play a much more important role. Finally, the fraction of Be stars that have involved binary interactions in all B-type stars can be as high as ∼13%-30%, implying that most Be stars may result from binary interaction.

  6. A Cautionary Note about Composite Galactic Star Formation Relations

    NASA Astrophysics Data System (ADS)

    Parmentier, G.

    2016-07-01

    We explore the pitfalls that affect the comparison of the star formation relation for nearby molecular clouds with that for distant compact molecular clumps. We show that both relations behave differently in the ({{{Σ }}}{{gas}}, {{{Σ }}}{{SFR}}) space, where {{{Σ }}}{{gas}} and {{{Σ }}}{{SFR}} are, respectively, the gas and star formation rate surface densities, even when the physics of star formation is the same. This is because the star formation relation of nearby clouds relates the gas and star surface densities measured locally, that is, within a given interval of gas surface density, or at a given protostar location. We refer to such measurements as local measurements, and the corresponding star formation relation as the local relation. In contrast, the stellar content of a distant molecular clump remains unresolved. Only the mean star formation rate can be obtained, e.g., from the clump infrared luminosity. One clump therefore provides one single point to the ({{{Σ }}}{{gas}}, {{{Σ }}}{{SFR}}) space, that is, its mean gas surface density and star formation rate surface density. We refer to this star formation relation as a global relation since it builds on the global properties of molecular clumps. Its definition therefore requires an ensemble of cluster-forming clumps. We show that although the local and global relations have different slopes, this cannot per se be taken as evidence for a change in the physics of star formation with gas surface density. It therefore appears that great caution should be taken when physically interpreting a composite star formation relation, that is, a relation combining local and global relations.

  7. KEY ISSUES REVIEW: Insights from simulations of star formation

    NASA Astrophysics Data System (ADS)

    Larson, Richard B.

    2007-03-01

    Although the basic physics of star formation is classical, numerical simulations have yielded essential insights into how stars form. They show that star formation is a highly nonuniform runaway process characterized by the emergence of nearly singular peaks in density, followed by the accretional growth of embryo stars that form at these density peaks. Circumstellar discs often form from the gas being accreted by the forming stars, and accretion from these discs may be episodic, driven by gravitational instabilities or by protostellar interactions. Star-forming clouds typically develop filamentary structures, which may, along with the thermal physics, play an important role in the origin of stellar masses because of the sensitivity of filament fragmentation to temperature variations. Simulations of the formation of star clusters show that the most massive stars form by continuing accretion in the dense cluster cores, and this again is a runaway process that couples star formation and cluster formation. Star-forming clouds also tend to develop hierarchical structures, and smaller groups of forming objects tend to merge into progressively larger ones, a generic feature of self-gravitating systems that is common to star formation and galaxy formation. Because of the large range of scales and the complex dynamics involved, analytic models cannot adequately describe many aspects of star formation, and detailed numerical simulations are needed to advance our understanding of the subject. 'The purpose of computing is insight, not numbers.' Richard W Hamming, in Numerical Methods for Scientists and Engineers (1962) 'There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.' William Shakespeare, in Hamlet, Prince of Denmark (1604)

  8. Magnetic Fields in Population III Star Formation

    SciTech Connect

    Turk, Matthew J.; Oishi, Jeffrey S.; Abel, Tom; Bryan, Greg

    2012-02-22

    We study the buildup of magnetic fields during the formation of Population III star-forming regions, by conducting cosmological simulations from realistic initial conditions and varying the Jeans resolution. To investigate this in detail, we start simulations from identical initial conditions, mandating 16, 32 and 64 zones per Jeans length, and studied the variation in their magnetic field amplification. We find that, while compression results in some amplification, turbulent velocity fluctuations driven by the collapse can further amplify an initially weak seed field via dynamo action, provided there is sufficient numerical resolution to capture vortical motions (we find this requirement to be 64 zones per Jeans length, slightly larger than, but consistent with previous work run with more idealized collapse scenarios). We explore saturation of amplification of the magnetic field, which could potentially become dynamically important in subsequent, fully-resolved calculations. We have also identified a relatively surprising phenomena that is purely hydrodynamic: the higher-resolved simulations possess substantially different characteristics, including higher infall-velocity, increased temperatures inside 1000 AU, and decreased molecular hydrogen content in the innermost region. Furthermore, we find that disk formation is suppressed in higher-resolution calculations, at least at the times that we can follow the calculation. We discuss the effect this may have on the buildup of disks over the accretion history of the first clump to form as well as the potential for gravitational instabilities to develop and induce fragmentation.

  9. Star formation and the nature of bipolar outflows

    NASA Technical Reports Server (NTRS)

    Shu, Frank H.; Ruden, Steven P.; Lada, Charles J.; Lizano, Susana

    1991-01-01

    This paper presents a simple physical model for the bipolar molecular outflows that frequently accompany star formation. The model forges an intrinsic link between the bipolar flow phenomenon and the process of star formation, and it helps to explain many of the systematics known for existing sources.

  10. Formative Assessment Probes: Where Are the Stars?

    ERIC Educational Resources Information Center

    Keeley, Page

    2011-01-01

    Gazing at the night sky is a familiar experience for many elementary students. Depending on where children live, they can often look out a window and see the Moon and stars. Children may have seen the Moon and stars in television shows, movies, posters, or children's picture books. Regardless of whether they see the Moon and stars firsthand or…

  11. Molecular emission in regions of star formation

    NASA Astrophysics Data System (ADS)

    Gusdorf, Antoine

    2008-11-01

    Recent observations show that young stars being formed eject matter at several tens of kilometers per second, in the form of 'jets' that impact the matter whose collapse is at the origin of the formation of the star. The supersonic impact between this jet and the parent interstellar cloud of the star generates a shock front, in the form of a bow-shock, which propagates in the collapsing interstellar gas, and also an inverse shock that propagates along the jet itself. The structure of these shocks depends on their velocity as well as on the physical properties of the gas in which they propagate, and specially on the value of the local magnetic field. Numerical MagnetoHydroDynamical simulations of the propagation of such shocks are a way to constrain the physical and chemical properties of the gas in which molecular lines are emitted. Interstellar shocks are modelled, both in stationary and non stationary ways, and grids of models are built for various ranges of input, preshock parameters (shock velocity, preshock density, magnetic field, and shock age for non stationary models). The case of molecular hydrogen is investigated first. Because of its particular importance (due to its large density and crucial role as a gas coolant or as a collision partner for molecular species), its level populations are solved within the shock code, as well as its population transfer. The shock wave modifies the chemical composition of the gas, partially or totally dissociating the molecular hydrogen, which is the main coolant of the gas. In the regions where molecular hydrogen still remains, H2 is collisionally excited, generating rovibrational and purely rotational transitions emission. These emissions are actually observed, from the ground in Infrared region, by ISO (Infrared Space Observatory) and Spitzer satellites. Excitation diagrams are used to compare the models with existing observations in the L1157 outflow around a young, Class 0 proto-star, confirming that non

  12. MMT HYPERVELOCITY STAR SURVEY. II. FIVE NEW UNBOUND STARS

    SciTech Connect

    Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J. E-mail: mgeller@cfa.harvard.edu

    2012-05-20

    We present the discovery of five new unbound hypervelocity stars (HVSs) in the outer Milky Way halo. Using a conservative estimate of Galactic escape velocity, our targeted spectroscopic survey has now identified 16 unbound HVSs as well as a comparable number of HVSs ejected on bound trajectories. A Galactic center origin for the HVSs is supported by their unbound velocities, the observed number of unbound stars, their stellar nature, their ejection time distribution, and their Galactic latitude and longitude distribution. Other proposed origins for the unbound HVSs, such as runaway ejections from the disk or dwarf galaxy tidal debris, cannot be reconciled with the observations. An intriguing result is the spatial anisotropy of HVSs on the sky, which possibly reflects an anisotropic potential in the central 10-100 pc region of the Galaxy. Further progress requires measurement of the spatial distribution of HVSs over the southern sky. Our survey also identifies seven B supergiants associated with known star-forming galaxies; the absence of B supergiants elsewhere in the survey implies there are no new star-forming galaxies in our survey footprint to a depth of 1-2 Mpc.

  13. Inner Milky Way Raging with Star Formation

    NASA Technical Reports Server (NTRS)

    2008-01-01

    More than 444,580 frames from NASA's Spitzer Space Telescope were stitched together to create this portrait of the raging star-formation occurring in the inner Milky Way.

    As inhabitants of a flat galactic disk, Earth and its solar system have an edge-on view of their host galaxy, like looking a glass dish from its edge. From our perspective, most of the galaxy is condensed into a blurry narrow band of light that stretches completely around the sky, also known as the galactic plane.

    In this mosaic the galactic plane is broken up into five components: the far-left side of the plane (top image); the area just left of the galactic center (second to top); galactic center (middle); the area to the right of galactic center (second to bottom); and the far-right side of the plane (bottom). Together, these panels represent more than 50 percent of our entire Milky Way galaxy.

    The red haze that permeates the picture comes from organic molecules called polycyclic aromatic hydrocarbons, which are illuminated by light from massive baby stars. On Earth, these molecules are found in automobile exhaust, or charred barbeque grills anywhere carbon molecules are burned incompletely.

    The patches of black are dense, obscuring dust clouds impenetrable by even Spitzer's super-sensitive infrared eyes. Bright arcs of white throughout the image are massive stellar incubators. The bluish-white haze that hovers heavily in the middle panel is starlight from the older stellar population towards the center of the galaxy.

    This picture was taken with Spitzer's infrared array camera, as part of the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) project. This is a four-color composite where blue is 3.6-micron light, green is 4.5 microns, orange is 5.8 microns and red is 8.0 microns.

  14. SPECTRA OF TYPE II CEPHEID CANDIDATES AND RELATED STARS

    SciTech Connect

    Schmidt, E. G.; Rogalla, Danielle; Thacker-Lynn, Lauren E-mail: drogall1@bigred.unl.edu

    2011-02-15

    We present low-resolution spectra for variable stars in the Cepheid period range from the ROTSE-I Demonstration Project and the All Sky Automated Survey, some of which were previously identified as type II Cepheid candidates. We have derived effective temperatures, gravities, and metallicities from the spectra. Based on this, three types of variables were identified: Cepheid strip stars, cool stars that lie along the red subgiant and giant branch, and cool main-sequence stars. Many fewer type II Cepheids were found than expected and most have amplitudes less than 0.4 mag. The cool variables include many likely binaries as well as intrinsic variables. Variation among the main-sequence stars is likely to be mostly due to binarity or stellar activity.

  15. Star Formation and Gas Accretion in Nearby Galaxies

    NASA Astrophysics Data System (ADS)

    Yim, Kijeong; van der Hulst, J. M.

    2016-08-01

    In order to quantify the relationship between gas accretion and star formation, we analyse a sample of 29 nearby galaxies from the WHISP survey which contains galaxies with and without evidence for recent gas accretion. We compare combined radial profiles of FUV (GALEX) and IR 24 μm (Spitzer) characterizing distributions of recent star formation with radial profiles of CO (IRAM, BIMA, or CARMA) and H I (WSRT) tracing molecular and atomic gas contents to examine star formation efficiencies in symmetric (quiescent), asymmetric (accreting), and interacting (tidally disturbed) galaxies. In addition, we investigate the relationship between star formation rate and H I in the outer discs for the three groups of galaxies. We confirm the general relationship between gas surface density and star formation surface density, but do not find a significant difference between the three groups of galaxies.

  16. Inclination Dependence of Estimated Galaxy Masses and Star Formation Rates

    NASA Astrophysics Data System (ADS)

    Hernandez, Betsy; Maller, Ariyeh; McKernan, Barry; Ford, Saavik

    2016-01-01

    We examine the inclination dependence of inferred star formation rates and galaxy mass estimates in the Sloan Digital Sky Survey by combining the disk/bulge de-convolved catalog of Simard et al 2011 with stellar mass estimates catalog of Mendel et al 2014 and star formation rates measured from spectra by Brinchmann et al 2004. We know that optical star formation indicators are reddened by dust, but calculated star formation rates and stellar mass estimates should account for this. However, we find that face-on galaxies have a higher calculated average star formation rates than edge-on galaxies. We also find edge-on galaxies have ,on average, slightly smaller but similar estimated masses to face-on galaxies, suggesting that there are issues with the applied dust corrections for both models.

  17. Multiplicity among chemically peculiar stars. II. Cool magnetic Ap stars

    NASA Astrophysics Data System (ADS)

    Carrier, F.; North, P.; Udry, S.; Babel, J.

    2002-10-01

    We present new orbits for sixteen Ap spectroscopic binaries, four of which might in fact be Am stars, and give their orbital elements. Four of them are SB2 systems: HD 5550, HD 22128, HD 56495 and HD 98088. The twelve other stars are: HD 9996, HD 12288, HD 40711, HD 54908, HD 65339, HD 73709, HD 105680, HD 138426, HD 184471, HD 188854, HD 200405 and HD 216533. Rough estimates of the individual masses of the components of HD 65339 (53 Cam) are given, combining our radial velocities with the results of speckle interferometry and with Hipparcos parallaxes. Considering the mass functions of 74 spectroscopic binaries from this work and from the literature, we conclude that the distribution of the mass ratio is the same for cool Ap stars and for normal G dwarfs. Therefore, the only differences between binaries with normal stars and those hosting an Ap star lie in the period distribution: except for the case of HD 200405, all orbital periods are longer than (or equal to) 3 days. A consequence of this peculiar distribution is a deficit of null eccentricities. There is no indication that the secondary has a special nature, like e.g. a white dwarf. Based on observations collected at the Observatoire de Haute-Provence (CNRS), France. Tables 1 to 3 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/394/151 Appendix B is only available in electronic form at http://www.edpsciences.org

  18. Star formation associated with a large-scale infrared bubble

    NASA Astrophysics Data System (ADS)

    Xu, Jin-Long; Ju, Bing-Gang

    2014-09-01

    Aims: To investigate how a large-scale infrared bubble centered at l = 53.9° and b = 0.2° forms, and to study if star formation is taking place at the periphery of the bubble, we performed a multiwavelength study. Methods: Using the data from the Galactic Ring Survey (GRS) and Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), we performed a study of a large-scale infrared bubble with a size of about 16 pc at a distance of 2.0 kpc. We present the 12CO J = 1-0, 13CO J = 1-0, and C18O J = 1-0 observations of HII region G53.54-0.01 (Sh2-82) obtained at the Purple Mountain Observation (PMO) 13.7 m radio telescope to investigate the detailed distribution of associated molecular material. In addition, we also used radiorecombination line and VLA data. To select young stellar objects (YSOs) consistent with this region, we used the GLIMPSE I catalog. Results: The large-scale infrared bubble shows a half-shell morphology at 8 μm. The H II regions of G53.54-0.01, G53.64+0.24, and G54.09-0.06 are situated on the bubble. Comparing the radio recombination line velocities and associated 13CO J = 1-0 components of the three H II regions, we found that the 8 μm emission associated with H II region G53.54-0.01 should belong to the foreground emission, and only overlap with the large-scale infrared bubble in the line of sight. Three extended green objects (EGOs, the candidate massive young stellar objects), as well as three H II regions and two small-scale bubbles are found located in the G54.09-0.06 complex, indicating an active massive star-forming region. Emission from C18O at J = 1-0 presents four cloud clumps on the northeastern border of H II region G53.54-0.01. By comparing the spectral profiles of 12CO J = 1-0, 13CO J = 1-0, and C18O J = 1-0 at the peak position of each clump, we found the collected gas in the three clumps, except for the clump coinciding with a massive YSO (IRAS 19282+1814). Using the evolutive model of the H II region, we derived that

  19. Bimodal star formation - Constraints from the solar neighborhood

    NASA Technical Reports Server (NTRS)

    Wyse, Rosemary F. G.; Silk, J.

    1987-01-01

    The chemical evolution resulting from a simple model of bimodal star formulation is investigated, using constraints from the solar neighborhood to set the parameters of the initial mass function and star formation rate. The two modes are an exclusively massive star mode, which forms stars at an exponentially declining rate, and a mode which contains stars of all masses and has a constant star formation rate. Satisfactory agreement with the age-metallicity relation for the thin disk and with the metallicity structure of the thin-disk and spheroid stars is possible only for a small range of parameter values. The preferred model offers a resolution to several of the long-standing problems of galactic chemical evolution, including explanations of the age-metallicity relation, the gas consumption time scale, and the stellar cumulative metallicity distributions.

  20. THE STAR FORMATION LAW AT LOW SURFACE DENSITY

    SciTech Connect

    Wyder, Ted K.; Martin, D. Christopher; Barlow, Tom A.; Foster, Karl; Friedman, Peter G.; Morrissey, Patrick; Neill, James D.; Neff, Susan G.; Schiminovich, David; Seibert, Mark; Madore, Barry F.; Bianchi, Luciana; Donas, Jose; Milliard, Bruno; Heckman, Timothy M.; Szalay, Alex S.; Lee, Young-Wook; Yi, Sukyoung K.; Rich, R. Michael

    2009-05-10

    We investigate the nature of the star formation law at low gas surface densities using a sample of 19 low surface brightness (LSB) galaxies with existing H I maps in the literature, UV imaging from the Galaxy Evolution Explorer satellite, and optical images from the Sloan Digital Sky Survey. All of the LSB galaxies have (NUV - r) colors similar to those for higher surface brightness star-forming galaxies of similar luminosity indicating that their average star formation histories are not very different. Based upon four LSB galaxies with both UV and far-infrared (FIR) data, we find FIR/UV ratios significantly less than 1, implying low amounts of internal UV extinction in LSB galaxies. We use the UV images and H I maps to measure the star formation rate (SFR) and hydrogen gas surface density within the same region for all the galaxies. The LSB galaxy star formation rate surface densities lie below the extrapolation of the power law fit to the SFR surface density as a function of the total gas density for higher surface brightness galaxies. Although there is more scatter, the LSB galaxies also lie below a second version of the star formation law in which the SFR surface density is correlated with the gas density divided by the orbital time in the disk. The downturn seen in both star formation laws is consistent with theoretical models that predict lower star formation efficiencies in LSB galaxies due to the declining molecular fraction with decreasing density.

  1. The Recent Star Formation History of the M31 Disk

    NASA Astrophysics Data System (ADS)

    Williams, Benjamin F.

    2003-09-01

    The star formation history of the northern and southern M31 disk is measured using samples of BV photometry for 4'×4' regions taken from the KPNO/CTIO Local Group Survey. The distances, mean reddening values, and age distributions of the stars in these regions were measured using the routines of Dolphin. Independent measurements of overlapping fields show that the results are stable for most samples. A slight distance gradient is seen across the major axis of the southern disk, and a mean distance of 24.47+/-0.03 is found by combining the results. Higher mean reddening values are seen to follow the spiral structure. The stellar age distributions are consistent with episodic star formation confined mainly to the gas-rich arm regions. If these episodes were caused by propagating density waves, the waves did not cause significant star formation episodes in the gas-poor interarm regions. A combination of all of the results provides the total star formation rate for 1.4 deg2 of the M31 disk for six epochs. These results suggest that star formation in the disk declined by ~50% from ~250 to ~50 Myr ago. The lowest star formation rate occurred ~25 Myr ago, followed by a ~20% increase to the present. The mean star formation rate for this large portion of M31 over the past 60 Myr is 0.63+/-0.07 Msolar yr-1, suggesting a total mean rate for the disk of ~1 Msolar yr-1.

  2. Terrestrial Planet Formation Around Close Binary Stars

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.; Quintana, Elisa V.

    2003-01-01

    Most stars reside in multiple star systems; however, virtually all models of planetary growth have assumed an isolated single star. Numerical simulations of the collapse of molecular cloud cores to form binary stars suggest that disks will form within such systems. Observations indirectly suggest disk material around one or both components within young binary star systems. If planets form at the right places within such circumstellar disks, they can remain in stable orbits within the binary star systems for eons. We are simulating the late stages of growth of terrestrial planets around close binary stars, using a new, ultrafast, symplectic integrator that we have developed for this purpose. The sum of the masses of the two stars is one solar mass, and the initial disk of planetary embryos is the same as that used for simulating the late stages of terrestrial planet growth within our Solar System and in the Alpha Centauri wide binary star system. Giant planets &are included in the simulations, as they are in most simulations of the late stages of terrestrial planet accumulation in our Solar System. When the stars travel on a circular orbit with semimajor axis of up to 0.1 AU about their mutual center of mass, the planetary embryos grow into a system of terrestrial planets that is statistically identical to those formed about single stars, but a larger semimajor axis and/or a significantly eccentric binary orbit can lead to significantly more dynamically hot terrestrial planet systems.

  3. The Star Formation History of Trumpler 14 and Trumpler 16

    NASA Astrophysics Data System (ADS)

    DeGioia-Eastwood, K.; Throop, H.; Walker, G.; Cudworth, K. M.

    2001-03-01

    H-R diagrams are presented for the very young galactic clusters Trumpler 14 and Trumpler 16, which are the two most populous clusters in the region of vigorous star formation surrounding η Carinae. Point spread function photometry of UBV CCD images is presented down to V~19 for over 560 stars in Tr 16 and 290 stars in Tr 14. We have also obtained similar data for a local background field. After determining cluster membership through proper motions from a previous work, we find that the reddening of cluster members is significantly lower than that of the local background stars. Thus, we are able to use individual reddenings to identify likely members at far deeper levels than possible with proper motions. This work has revealed a significant population of pre-main-sequence (PMS) stars in both clusters. The location of the PMS stars in the H-R diagram indicates that the theoretical ``stellar birthline'' of Palla & Stahler follows the locus of stars far better than that of Beech & Mitalas. Comparison with both pre- and post-main-sequence isochrones also reveals that although intermediate-mass stars have been forming continuously over the last 10 Myr, the high-mass stars formed within the last 3 Myr. There is no evidence that the formation of the intermediate-mass stars was truncated by the formation of the high-mass stars.

  4. X-ray sources in regions of star formation. I - The naked T Tauri stars

    NASA Technical Reports Server (NTRS)

    Walter, F. M.

    1986-01-01

    Einstein X-ray observations of regions of active star formation in Taurus, Ophiuchus, and Corona Australis show a greatly enhanced surface density of stellar X-ray sources over that seen in other parts of the sky. Many of the X-ray sources are identified with low-mass, pre-main-sequence stars which are not classical T Tauri stars. The X-ray, photometric, and spectroscopic data for these stars are discussed. Seven early K stars in Oph and CrA are likely to be 1-solar-mass post-T Tauri stars with ages of 10-million yr. The late K stars in Taurus are not post-T Tauri, but 'naked' T Tauri stars, which are coeval with the T Tauri stars, differing mainly in the lack of a circumstellar envelope.

  5. STAR FORMATION IN NUCLEAR RINGS OF BARRED GALAXIES

    SciTech Connect

    Seo, Woo-Young; Kim, Woong-Tae E-mail: wkim@astro.snu.ac.kr

    2013-06-01

    Nuclear rings in barred galaxies are sites of active star formation. We use hydrodynamic simulations to study the temporal and spatial behavior of star formation occurring in nuclear rings of barred galaxies where radial gas inflows are triggered solely by a bar potential. The star formation recipes include a density threshold, an efficiency, conversion of gas to star particles, and delayed momentum feedback via supernova explosions. We find that the star formation rate (SFR) in a nuclear ring is roughly equal to the mass inflow rate to the ring, while it has a weak dependence on the total gas mass in the ring. The SFR typically exhibits a strong primary burst followed by weak secondary bursts before declining to very small values. The primary burst is associated with the rapid gas infall to the ring due to the bar growth, while the secondary bursts are caused by re-infall of the ejected gas from the primary burst. While star formation in observed rings persists episodically over a few Gyr, the duration of active star formation in our models lasts for only about half of the bar growth time, suggesting that the bar potential alone is unlikely to be responsible for gas supply to the rings. When the SFR is low, most star formation occurs at the contact points between the ring and the dust lanes, leading to an azimuthal age gradient of young star clusters. When the SFR is large, on the other hand, star formation is randomly distributed over the whole circumference of the ring, resulting in no apparent azimuthal age gradient. Since the ring shrinks in size with time, star clusters also exhibit a radial age gradient, with younger clusters found closer to the ring. The cluster mass function is well described by a power law, with a slope depending on the SFR. Giant gas clouds in the rings have supersonic internal velocity dispersions and are gravitationally bound.

  6. Non-parametric star formation histories for four dwarf spheroidal galaxies of the Local Group

    NASA Astrophysics Data System (ADS)

    Hernandez, X.; Gilmore, Gerard; Valls-Gabaud, David

    2000-10-01

    We use recent Hubble Space Telescope colour-magnitude diagrams of the resolved stellar populations of a sample of local dSph galaxies (Carina, Leo I, Leo II and Ursa Minor) to infer the star formation histories of these systems, SFR(t). Applying a new variational calculus maximum likelihood method, which includes a full Bayesian analysis and allows a non-parametric estimate of the function one is solving for, we infer the star formation histories of the systems studied. This method has the advantage of yielding an objective answer, as one need not assume a priori the form of the function one is trying to recover. The results are checked independently using Saha's W statistic. The total luminosities of the systems are used to normalize the results into physical units and derive SN type II rates. We derive the luminosity-weighted mean star formation history of this sample of galaxies.

  7. Quenching star formation: insights from the local main sequence

    NASA Astrophysics Data System (ADS)

    Leslie, S. K.; Kewley, L. J.; Sanders, D. B.; Lee, N.

    2016-01-01

    The so-called star-forming main sequence of galaxies is the apparent tight relationship between the star formation rate and stellar mass of a galaxy. Many studies exclude galaxies which are not strictly `star forming' from the main sequence, because they do not lie on the same tight relation. Using local galaxies in the Sloan Digital Sky Survey, we have classified galaxies according to their emission line ratios, and studied their location on the star formation rate-stellar mass plane. We find that galaxies form a sequence from the `blue cloud' galaxies which are actively forming stars, through a combination of composite, Seyfert, and low-ionization nuclear emission-line region galaxies, ending as `red-and-dead' galaxies. The sequence supports an evolutionary pathway for galaxies in which star formation quenching by active galactic nuclei plays a key role.

  8. Morphology, star formation, and kinematics of nuclear rings

    NASA Astrophysics Data System (ADS)

    Mazzuca, Lisa M.

    This thesis presents a detailed optical study with the goal of better understanding the elusive physical nature of nuclear rings. We first image the central kilo-parsec region of a large sample of spiral galaxies known for intense star formation via the Hal6563 line and the optical broad bands B and I . The distribution of massive young stars in the nuclear and circumnuclear environments verifies that nuclear rings occur primarily in spiral types Sa- Sbc. Late-type galaxies have a patchy and more diffuse circumnuclear appearance in Ha. We identify three previously unknown nuclear rings, and confirm that nuclear rings are preferentially found in barred galaxies. From the parent sample, we identify 22 nuclear rings and analyze the H II regions that comprise them. Comparing the Ha equivalent widths of these regions with population synthesis models, we derive the ages throughout each nuclear ring, and find that the stellar content within the rings is consistently very young, with ages ranging from 1 Myr to 10 Myrs. Approximately half of the rings contain azimuthal age gradients that encompass at least 25% of the ring, although there is no apparent relationship between the presence or absence of age gradients and the morphology of the rings or their host galaxies. Two-thirds of the galaxies containing a nuclear ring and a bar show a link between the youngest H II region(s) and the location along the ring where the bar dust lanes merge. We show that regions of enhanced star formation, as seen in nuclear rings, correspond to regions with (1) the strongest Ha emission, (2) high luminosities of order 10 40 erg s -1 - 10 42 erg s -1 , (3) low residual velocities of order 10 km s -1 , and (4) low velocity dispersions ranging from 20 km s -1 - 50 km s -1 . Thus, within the rings, the relatively cool and calm gas allows star formation to trigger. The lack of strong non-circular motions in the rings, coupled with a direct relationship between the position angles and

  9. Terrestrial Planet Formation around Low-Mass Stars: Effect of the Mass of Central Stars

    NASA Astrophysics Data System (ADS)

    Oshino, Shoichi; Matsumoto, Yuji; Kokubo, Eiichiro

    2015-12-01

    The Kepler space telescope has detected several thousand planets and candidates.Their central stars are mainly FGK-type stars.It is difficult to observe M-stars by using visible light since M-stars have their peak radiation in the infrared region.However, recently there are several survey projects for planets around M-stars such as the InfraRed Doppler (IRD) survey of the Subaru telescope.Therefore it is expected that the number of planets around M-stars will increase in the near future.The habitable zone of M-stars is closer to the stars than that of G-stars.For this reason, the possibility of finding habitable planets is expected to be higher.Here we study the formation of close-in terrestrial planets by giant impacts of protoplanets around low-mass stars by using N-body simulations.An important parameter that controls formation processes is the ratio between the physical radius of a planet and its Hill radius, which decreases with the stellar mass.We systematically change the mass of the central stars and investigate its effects on terrestrial planet formation.We find that the mass of the maximum planet decreases with the mass of central stars, while the number of planets in the system increases.We also find that the orbital separation of adjacent planets normalized by their Hill radius increases with the stellar mass.

  10. Star Formation near Berkeley 59: Embedded Protostars

    NASA Astrophysics Data System (ADS)

    Rosvick, J. M.; Majaess, D.

    2013-12-01

    A group of suspected protostars in a dark cloud northwest of the young (~2 Myr) cluster Berkeley 59 and two sources in a pillar south of the cluster have been studied in order to determine their evolutionary stages and ascertain whether their formation was triggered by Berkeley 59. Narrowband near-infrared observations from the Observatoire du Mont Mégantic, 12CO (J = 3-2) and SCUBA-2 (450 and 850 μm) observations from the JCMT, 2MASS, and WISE images, and data extracted from the IPHAS survey catalog were used. Of 12 sources studied, two are Class I objects, while three others are flat/Class II, one of which is a T Tauri candidate. A weak CO outflow and two potential starless cores are present in the cloud, while the pillar possesses substructure at different velocities, with no outflows present. The CO spectra of both regions show peaks in the range v LSR = -15 to -17 km s-1, which agrees with the velocity adopted for Berkeley 59 (-15.7 km s-1), while spectral energy distribution models yield an average interstellar extinction AV and distance of 15 ± 2 mag and 830 ± 120 pc, respectively, for the cloud, and 6.9 mag and 912 pc for the pillar, indicating that the regions are in the same vicinity as Berkeley 59. The formation of the pillar source appears to have been triggered by Berkeley 59. It is unclear whether Berkeley 59 triggered the association's formation.

  11. Mg II 2800 A emission in late type stars

    NASA Technical Reports Server (NTRS)

    Doherty, L. R.

    1972-01-01

    The largest body of data on ultraviolet spectra of late-type stars now available is the series of scans made with the long wavelength spectrometer onboard OAO-2. Some features of selected scans from this series and estimates of Mg II emission fluxes were reported earlier. Since that time, the effects of sky background, scattered light and variable instrumental sensitivity have become better understood. Additional stars are used to define more clearly the transition from Mg II 2800 A absorption to emission with advancing spectral type, and additional scans of alpha Sco provide a better estimate of Mg II emission strength for this supergiant in OAO observations.

  12. The star formation history inferred from long gamma-ray bursts with high pseudo-redshifts

    NASA Astrophysics Data System (ADS)

    Tan, Wei-Wei; Cao, Xiao-Feng; Yu, Yun-Wei

    2015-07-01

    By employing a simple semi-analytical star formation model where the formation rates of Population (Pop) I/II and III stars can be calculated, respectively, we account for the number distribution of gamma-ray bursts (GRBs) with high pseudo-redshifts that was derived from an empirical luminosity-indictor relationship. It is suggested that a considerable number of Pop III GRBs could exist in the present sample of Swift GRBs. By further combining the implication for the star formation history from the optical depth of the CMB photons, it is also suggested that only a very small fraction (∼ 0.6 %) of Pop III GRBs could have triggered the Swift BAT. These results could provide an useful basis for estimating future detectability of Pop III stars and their produced transient phenomena.

  13. Shocks and star formation in Stephan's Quintet. I. Gemini spectroscopy of Hα-bright knots

    SciTech Connect

    Konstantopoulos, I. S.; Cluver, M. E.; Appleton, P. N.; Guillard, P.; Trancho, G.; Bastian, N.; Charlton, J. C.; Fedotov, K.; Gallagher, S. C.; Smith, L. J.; Struck, C. J.

    2014-03-20

    We present a Gemini-GMOS spectroscopic study of Hubble Space Telescope (HST)-selected Hα-emitting regions in Stephan's Quintet (HCG 92), a nearby compact galaxy group, with the aim of disentangling the processes of shock-induced heating and star formation in its intra-group medium. The ≈40 sources are distributed across the system, but most densely concentrated in the ∼kiloparsec-long shock region. Their spectra neatly divide them into narrow- and broad-line emitters, and we decompose the latter into three or more emission peaks corresponding to spatial elements discernible in HST imaging. The emission-line ratios of the two populations of Hα-emitters confirm their nature as H II regions (90% of the sample) or molecular gas heated by a shock front propagating at ≲300 km s{sup –1}. Their redshift distribution reveals interesting three-dimensional structure with respect to gas-phase baryons, with no H II regions associated with shocked gas, no shocked regions in the intruder galaxy NGC 7318B, and a sharp boundary between shocks and star formation. We conclude that star formation is inhibited substantially, if not entirely, in the shock region. Attributing those H II regions projected against the shock to the intruder, we find a lopsided distribution of star formation in this galaxy, reminiscent of pileup regions in models of interacting galaxies. The Hα luminosities imply mass outputs, star formation rates, and efficiencies similar to nearby star-forming regions. Two large knots are an exception to this, being comparable in stellar output to the prolific 30 Doradus region. We also examine Stephan's Quintet in the context of compact galaxy group evolution, as a paradigm for intermittent star formation histories in the presence of a rich, X-ray-emitting intra-group medium. All spectra are provided as supplemental materials.

  14. Shocks and Star Formation in Stephan's Quintet. I. Gemini Spectroscopy of Hα-bright Knots

    NASA Astrophysics Data System (ADS)

    Konstantopoulos, I. S.; Appleton, P. N.; Guillard, P.; Trancho, G.; Cluver, M. E.; Bastian, N.; Charlton, J. C.; Fedotov, K.; Gallagher, S. C.; Smith, L. J.; Struck, C. J.

    2014-03-01

    We present a Gemini-GMOS spectroscopic study of Hubble Space Telescope (HST)-selected Hα-emitting regions in Stephan's Quintet (HCG 92), a nearby compact galaxy group, with the aim of disentangling the processes of shock-induced heating and star formation in its intra-group medium. The ≈40 sources are distributed across the system, but most densely concentrated in the ~kiloparsec-long shock region. Their spectra neatly divide them into narrow- and broad-line emitters, and we decompose the latter into three or more emission peaks corresponding to spatial elements discernible in HST imaging. The emission-line ratios of the two populations of Hα-emitters confirm their nature as H II regions (90% of the sample) or molecular gas heated by a shock front propagating at lsim300 km s-1. Their redshift distribution reveals interesting three-dimensional structure with respect to gas-phase baryons, with no H II regions associated with shocked gas, no shocked regions in the intruder galaxy NGC 7318B, and a sharp boundary between shocks and star formation. We conclude that star formation is inhibited substantially, if not entirely, in the shock region. Attributing those H II regions projected against the shock to the intruder, we find a lopsided distribution of star formation in this galaxy, reminiscent of pileup regions in models of interacting galaxies. The Hα luminosities imply mass outputs, star formation rates, and efficiencies similar to nearby star-forming regions. Two large knots are an exception to this, being comparable in stellar output to the prolific 30 Doradus region. We also examine Stephan's Quintet in the context of compact galaxy group evolution, as a paradigm for intermittent star formation histories in the presence of a rich, X-ray-emitting intra-group medium. All spectra are provided as supplemental materials.

  15. Derivation of the Star Formation Intensity Distribution from Empirical Laws

    NASA Astrophysics Data System (ADS)

    Thompson, R. I.

    2002-12-01

    The star formation intensity distribution function, first presented by Lanzetta and his colleagues, has received significant attention both as a constraint on models of galaxy formation and as a correction for star formation missed by surface brightness dimming at high redshift. This talk demonstrates that the distribution at a redshift of 1, where it is well measured, can be matched with well known empirical laws. In particular the Schmidt law with a roll off of star formation at a critical density, a Schechter distribution of galaxy masses, and the assumption that star formation occurs in exponential disks suffices to derive the distribution with reasonable values for the adjustable parameters. Using values of the parameters at high z that are consistent with the hierarchical models of galaxy formation shows the possible evolution of the distribution with redshift.

  16. Bursts of star formation in computer simulations of dwarf galaxies

    SciTech Connect

    Comins, N.F.

    1984-09-01

    A three-dimensional Stochastic Self-Propagating Star Formation (SSPSF) model of compact galacies is presented. Two phases of gas, active and inactive, are present, and permanent depletion of gas in the form of long lived, low mass stars and remnants occurs. Similarly, global infall of gas from a galactic halo or through galactic cannibalism is permitted. We base our parameters on the observed properties of the compact blue galaxy I Zw 36. Our results are that bursts of star formation occur much more frequently in these runs than continuous nonbursting star formation, suggesting that the blue compact galaxies are probably undergoing bursts rather than continuous, nonbursting low-level star formation activity.

  17. TESTING HOMOGENEITY WITH GALAXY STAR FORMATION HISTORIES

    SciTech Connect

    Hoyle, Ben; Jimenez, Raul; Tojeiro, Rita; Maartens, Roy; Heavens, Alan; Clarkson, Chris

    2013-01-01

    Observationally confirming spatial homogeneity on sufficiently large cosmological scales is of importance to test one of the underpinning assumptions of cosmology, and is also imperative for correctly interpreting dark energy. A challenging aspect of this is that homogeneity must be probed inside our past light cone, while observations take place on the light cone. The star formation history (SFH) in the galaxy fossil record provides a novel way to do this. We calculate the SFH of stacked luminous red galaxy (LRG) spectra obtained from the Sloan Digital Sky Survey. We divide the LRG sample into 12 equal-area contiguous sky patches and 10 redshift slices (0.2 < z < 0.5), which correspond to 120 blocks of volume {approx}0.04 Gpc{sup 3}. Using the SFH in a time period that samples the history of the universe between look-back times 11.5 and 13.4 Gyr as a proxy for homogeneity, we calculate the posterior distribution for the excess large-scale variance due to inhomogeneity, and find that the most likely solution is no extra variance at all. At 95% credibility, there is no evidence of deviations larger than 5.8%.

  18. Star Formation in Lynds Dark Nebulae

    NASA Astrophysics Data System (ADS)

    Johnson, Chelen H.; Bemis, G. E.; Paulsen, K. M.; Yueh, N. J.; Rebull, L. M.; DeWolf, C.; DeWolf, T.; Brock, S.; Boerna, J.; Schaefers, J.; McDonald, D. W.; McDonald, J.; Troudt, B.; Wilkinson, B.; Guastella, P.; Peter, A.; Wassmer, W.; Haber, R.; Scaramucci, A.; Spuck, T. S.; Butchart, J.; Holcomb, A.; Karns, B.; Kennedy, S.; Siegel, R.; Weiser, S.; Connelley, M.

    2009-01-01

    Our team observed two Lynds clouds (LDN 425 and LDN 981) using the Spitzer Space Telescope IRAC (3.6, 4.5, 5.8, and 8 microns), and MIPS (24 microns). A preliminary literature search provided IRAS data indicating star formation may be taking place in LDN 425 and LDN 981. The goals of this project were to further explore the known young stellar objects (YSOs) in the two clouds and to search for additional embedded YSOs. In this poster we present our observational methods and the results of our observations including SEDs, color-color diagrams, and color composite images. This research was made possible through the Spitzer Space Telescope Research Program for Teachers and Students and was funded by the Spitzer Science Center (SSC) and the National Optical Astronomy Observatory (NOAO). Please see our companion education posters by McDonald et al. titled "Spitzer - Hot and Colorful Student Activities" and Guastella et al. entitled "Research Based Astronomy in The Secondary Classroom: Lessons Developed for Investigating YSOs Using APT, Excel, and MOPEX".

  19. Star Formation in The HI Nearby Galaxy Survey

    NASA Astrophysics Data System (ADS)

    Leroy, A.; Bigiel, F.; Walter, F.; Brinks, E.; de Blok, W. J. G.; Madore, B.

    2008-05-01

    We combine The HI Nearby Galaxy Survey (THINGS) with our new survey of CO at the IRAM~30m, the Spitzer Infrared Nearby Galaxies Survey, and the GALEX Nearby Galaxies Survey to assemble an atlas of "star formation in context" for 24 nearby galaxies. This includes kinematics and estimates of the surface densities of atomic gas, molecular gas, stellar mass, and star formation rate. We use these data to test theories and recipes of star formation on galactic scales. Here we present two basic results for spiral galaxies. First, molecular gas and star formation rate surface density (SFRSD) are well related by a linear relation across most of our sample while atomic gas and SFRSD are essentially uncorrelated. We interpret this as evidence that star formation is proceeding in a more or less universal population of giant molecular clouds (GMCs) across most of the area we survey. Second, while the star formation efficiency (SFE), i.e., the star formation per unit neutral gas, is nearly constant where the ISM is mostly molecular, it drops steadily with increasing galactocentric radius where the ISM is mostly atomic. This drop is well-defined and common to most galaxies. We interpret this as a decreasing efficiency of GMC formation with changing local conditions. At intermediate galactocentric radii, the observed SFE is roughly consistent with several expectations for GMC formation: either formation occuring over the free fall time in the disk or the equilibrium molecular fraction being set by the gas pressure. If GMC formation occurs over a dynamical timescale, a star formation threshold must come into play in the outer disk to match the observed SFE.

  20. STAR FORMATION IN THE BULLET CLUSTER. I. THE INFRARED LUMINOSITY FUNCTION AND STAR FORMATION RATE ,

    SciTech Connect

    Sun Mi Chung; Gonzalez, Anthony H.; Clowe, Douglas; Markevitch, Maxim; Zaritsky, Dennis

    2010-12-20

    The Bullet Cluster is a massive galaxy cluster at z = 0.297 undergoing a major supersonic (Mach 3) merger event. Using data from Spitzer MIPS and the Infrared Array Camera, optical imaging, and optical spectroscopy, we present the global star formation rate (SFR) of this unique cluster. Using a 90% spectroscopically complete sample of 37 star-forming MIPS confirmed cluster members out to R < 1.7 Mpc, and the Rieke et al. relation to convert from 24 {mu}m flux to SFR, we calculate an integrated obscured SFR of 267 M{sub sun} yr{sup -1} and a specific SFR of 28 M{sub sun} yr{sup -1} per 10{sup 14} M{sub sun}. The cluster mass normalized integrated SFR of the Bullet Cluster is among the highest in a sample of eight other clusters and cluster mergers from the literature. Five LIRGs and one ULIRG contribute 30% and 40% of the total SFR of the cluster, respectively. To investigate the origin of the elevated specific SFR, we compare the infrared luminosity function (IR LF) of the Bullet Cluster to those of Coma (evolved to z = 0.297) and CL1358+62. The Bullet Cluster IR LF exhibits an excess of sources compared to the IR LFs of the other massive clusters. A Schechter function fit of the Bullet Cluster IR LF yields L* = 44.68 {+-} 0.11 erg s{sup -1}, which is {approx}0.25 and 0.35 dex brighter than L* of evolved Coma and CL1358+62, respectively. The elevated IR LF of the Bullet Cluster relative to other clusters can be explained if we attribute the 'excess' star-forming IR galaxies to a population associated with the infalling group that has not yet been transformed into quiescent galaxies. In this case, the timescale required for quenching star formation in the cluster environment must be longer than the timescale since the group's accretion-a few hundred million years. We suggest that 'strangulation' is likely to be an important process in the evolution of star formation in clusters.

  1. X-ray insights into star and planet formation

    PubMed Central

    Feigelson, Eric D.

    2010-01-01

    Although stars and planets form in cold environments, X-rays are produced in abundance by young stars. This review examines the implications of stellar X-rays for star and planet formation studies, highlighting the contributions of NASA’s (National Aeronautics and Space Administration) Chandra X-ray Observatory. Seven topics are covered: X-rays from protostellar outflow shocks, X-rays from the youngest protostars, the stellar initial mass function, the structure of young stellar clusters, the fate of massive stellar winds, X-ray irradiation of protoplanetary disks, and X-ray flare effects on ancient meteorites. Chandra observations of star-forming regions often show dramatic star clusters, powerful magnetic reconnection flares, and parsec-scale diffuse plasma. X-ray selected samples of premain sequence stars significantly advance studies of star cluster formation, the stellar initial mass function, triggered star-formation processes, and protoplanetary disk evolution. Although X-rays themselves may not play a critical role in the physics of star formation, they likely have important effects on protoplanetary disks by heating and ionizing disk gases. PMID:20404197

  2. Towards universal hybrid star formation rate estimators

    NASA Astrophysics Data System (ADS)

    Boquien, M.; Kennicutt, R.; Calzetti, D.; Dale, D.; Galametz, M.; Sauvage, M.; Croxall, K.; Draine, B.; Kirkpatrick, A.; Kumari, N.; Hunt, L.; De Looze, I.; Pellegrini, E.; Relaño, M.; Smith, J.-D.; Tabatabaei, F.

    2016-06-01

    Context. To compute the star formation rate (SFR) of galaxies from the rest-frame ultraviolet (UV), it is essential to take the obscuration by dust into account. To do so, one of the most popular methods consists in combining the UV with the emission from the dust itself in the infrared (IR). Yet, different studies have derived different estimators, showing that no such hybrid estimator is truly universal. Aims: In this paper we aim at understanding and quantifying what physical processes fundamentally drive the variations between different hybrid estimators. In so doing, we aim at deriving new universal UV+IR hybrid estimators to correct the UV for dust attenuation at local and global scales, taking the intrinsic physical properties of galaxies into account. Methods: We use the CIGALE code to model the spatially resolved far-UV to far-IR spectral energy distributions of eight nearby star-forming galaxies drawn from the KINGFISH sample. This allows us to determine their local physical properties, and in particular their UV attenuation, average SFR, average specific SFR (sSFR), and their stellar mass. We then examine how hybrid estimators depend on said properties. Results: We find that hybrid UV+IR estimators strongly depend on the stellar mass surface density (in particular at 70 μm and 100 μm) and on the sSFR (in particular at 24 μm and the total infrared). Consequently, the IR scaling coefficients for UV obscuration can vary by almost an order of magnitude: from 1.55 to 13.45 at 24 μm for instance. This result contrasts with other groups who found relatively constant coefficients with small deviations. We exploit these variations to construct a new class of adaptative hybrid estimators based on observed UV to near-IR colours and near-IR luminosity densities per unit area. We find that they can reliably be extended to entire galaxies. Conclusions: The new estimators provide better estimates of attenuation-corrected UV emission than classical hybrid estimators

  3. The Formation of Massive Stars and Star Clusters in the Milky Way

    NASA Astrophysics Data System (ADS)

    Battersby, C. D.

    2013-10-01

    The life cycle of stars and gas in the Milky Way illuminates and shapes our view of the universe. This cycle is driven largely by massive stars through their immense ionizing radiation, powerful winds and outflows, and explosive supernovae, yet the processes leading to their formation remain elusive. I review the status of our understanding of massive star and cluster formation, beginning with a theoretical framework outlining the varying modes proposed for the accumulation of material onto forming stars: core accretion and competitive accretion. The observable consequences of each theory and their current statuses are discussed. I then delve into the growing body of observations toward massive star and cluster forming regions, focusing on recent observations of the structure and evolution of cluster- forming regions at early stages. I conclude with an outlook for the next stages in the field of massive star formation.

  4. College Students' Preinstructional Ideas about Stars and Star Formation

    ERIC Educational Resources Information Center

    Bailey, Janelle M.; Prather, Edward E.; Johnson, Bruce; Slater, Timothy F.

    2009-01-01

    This study (Note 1) investigated the beliefs about stars that students hold when they enter an undergraduate introductory astronomy course for nonscience majors. Students' preinstructional ideas were investigated through the use of several student-supplied-response (SSR) surveys, which asked students to describe their ideas about topics such as…

  5. Cygnus OB2: Star Formation Ugly Duckling Causes a Flap

    NASA Astrophysics Data System (ADS)

    Drake, Jeremy J.; Wright, Nicholas; Guarcello, Mario

    2015-08-01

    Cygnus OB2 is one of the largest known OB associations in our Galaxy, with a total stellar mass of 30,000 Msun and boasting an estimated 65 O-type stars and hundreds of OB stars. At a distance of only 1.4kpc, it is also the closest truly massive star forming region and provides a valuable testbed for star and planet formation theory. We have performed a deep stellar census using observations from X-ray to infrared, which has enabled studies of sub-structuring, mass segregation and dynamics, while infrared data reveal a story of protoplanetary disk attrition in an extremely harsh radiation environment. I will discuss how Cygnus OB2 challenges the idea that stars must form in dense, compact clusters, and demonstrates that stars as massive as 100 Msun can form in relatively low-density environments. Convincing evidence of disk photoevaporation poses a potential problem for planet formation and growth in starburst environments.

  6. Advanced Spectral Library II: Hot Stars

    NASA Astrophysics Data System (ADS)

    Ayres, Thomas

    2013-10-01

    Stars are the bright matter of the Universe. Without them, it would be a dull and dreary place indeed: no light, no heavy elements, no planets, no life. It also is safe to say that stellar spectroscopy is a cornerstone of astrophysics, providing much of what we know concerning temperatures and masses of stars, their compositions, planets, and the dynamics and evolution of the galaxies they inhabit. This is especially true for the satellite ultraviolet, owing to the rich collection of atomic and ionic transitions found there. Unfortunately, the archive of Space Telescope Imaging Spectrograph rarely achieves the high S/N of the best ground-based spectra, and relatively few objects have the full wavelength coverage for which the powerful, highly multiplexed, second generation Hubble instrument was designed. Our aim is to collect STIS UV echelle spectra - comparable in S/N and resolution to the best ground-based material - for a diverse sample of representative stars, to build an Advanced Spectral Library; a foundation for astrophysical exploration: stellar, interstellar, and beyond. Our first effort, in Cycle 18, involved cool stars. Now we turn attention to the hot side of the H-R diagram.Our Treasury program will provide detailed stellar "atlases," based on advanced processing of the STIS echellegrams. Members of our broad collaboration will analyze these data for specific purposes, such as dynamics of O-star mass-loss; detection of rare species in sharp-lined B stars; and properties and kinematics of local interstellar clouds; but public release {based on the "ASTRAL-I" model} will enable many other investigations by a much wider community, for decades to come.

  7. Multiplicity among F-type Stars. II.

    NASA Astrophysics Data System (ADS)

    Fuhrmann, K.; Chini, R.

    2015-08-01

    In continuation of our previous study we present an updated census of new companions and model atmosphere analyses for some 50 southern dwarfs, mostly in the mass range 0.90≤slant M≤slant 1.10 {M}⊙ . For the common-proper-motion companions μ Vir B, HR 2225 B, HD 67199 B, and HD 114853 B, we confirm their physical association from their radial velocities. We report the discovery of the F-type visual binary α For as a field blue straggler and confirm (ζ Ret, HR 5864) or identify (HD 67199, HR 4013, HR 8843) another five mass transfer systems or candidates. For the F stars {τ }1 Eri and 111 Tau, we present 10σ and 7σ cases for astrometric binaries by virtue of the very accurate van Leeuwen Hipparcos parallaxes. Following the work of Shaya & Olling, we suggest the F-type star ι Vir to be a wide (0.37 pc) hierarchical quadruple system. We confirm the visual binary NLTT 23781/2 as a common-proper-motion object to the very wide (0.54 pc) F star 40 Leo, but discard the G star HD 128987 as an ultra-wide (1.01 pc) physical companion to the α Lib quadruple system on account of a diverse metallicity. The improved statistics of our sample establishes the previously discovered positive correlation of stellar multiplicities with primary mass. For the F star multiplicity census in the mass range 1.10≤slant M≤slant 1.70 {M}⊙ , we find that at least a quarter consists of triple or higher level systems and at least two out of three F stars are non-single.

  8. Star formation in bulgeless late type spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Das, M.; Ramya, S.; Sengupta, C.; Mishra, K.

    We present radio and follow-up optical observations of a sample of bulgeless late type spiral galaxies. We searched for signs of nuclear activity and disk star formation in the sample galaxies. Interaction induced star formation can often trigger bulge formation. We found significant radio emission associated with star formation in two sample galaxies, NGC3445 and NGC4027, both of which are tidally interacting with nearby companions. For the others, the star formation was either absent or limited to only localized regions in the disk. Both galaxies also have oval bars that are possibly pseudobulges that may later evolve into bulges. We did follow up optical Hα imaging and nuclear spectroscopy of NGC3445 and NGC4027 using the Himalayan Chandra Telescope (HCT). The Hα emission is mainly associated with strong spiral arms that have been triggered by the tidal interact1ions. The nuclear spectra of both galaxies indicate ongoing nuclear star formation but do not show signs of AGN activity. We thus conclude that star formation in bulgeless galaxies is generally low but is enhanced when the galaxies interact with nearby companions; this activity may ultimately lead to the formation of bulges in these galaxies.

  9. Galaxies on FIRE: Stellar Feedback Explains Inefficient Star Formation

    NASA Astrophysics Data System (ADS)

    Hopkins, Philip F.

    2014-06-01

    Many of the most fundamental unsolved questions in star and galaxy formation revolve around star formation and "feedback" from both massive stars and accretion onto super-massive black holes. I'll present new simulations which attempt to realistically model the diverse physics of the interstellar medium, star formation, and feedback from stellar radiation pressure, supernovae, stellar winds, and photo-ionization. These mechanisms lead to 'self-regulated' galaxy and star formation, in which global correlations such as the Schmidt-Kennicutt law and the global inefficiency of star formation -- the stellar mass function -- emerge naturally. Within galaxies, feedback regulates the structure of the interstellar medium, and many observed properties of the ISM, star formation, and galaxies can be understood as a fundamental consequence of super-sonic turbulence in a rapidly cooling, self-gravitating medium. But feedback also produces galactic super-winds that can dramatically alter the cosmological evolution of galaxies, their behavior in galaxy mergers, and structure of the inter-galactic medium: these winds depend non-linearly on multiple feedback mechanisms in a way that explains why they have been so difficult to model in previous "sub-grid" approaches.

  10. Star-formation in a Transitioning Radio Source

    NASA Astrophysics Data System (ADS)

    Mao, Minnie; Norris, Ray; Sharp, Rob

    2012-10-01

    With this proposal we will obtain high resolution (1 arcsec) radio maps of IRAS F00183-711 to resolve the star-forming component of this ULIRG. Recent VLBI observations have demonstrated the presence of an AGN at the heart of the source, but the relative contribution from star-formation is unknown and likely significant. IRAS F00183-711 has been caught in the fleeting act of transitioning from ``cold-mode'' accretion to ``hot-mode'' accretion. It represents the missing link between young (e.g. CSS/GPS sources) and evolved radio galaxies (e.g. FRI/FRII sources) whose AGN activity have suppressed their own star-formation. Direct measurement of the star-forming of this source will provide key insight into the star-formation history of the radio galaxies of today.

  11. Star formation in the outer disks of spiral galaxies

    NASA Astrophysics Data System (ADS)

    Barnes, Kate Lynn

    I present results from a multi-wavelength study of star formation and the gaseous content in the outer disks of a sample of eight nearby spiral galaxies. In particular, the study focuses on galaxies with typical HI-to-optical sizes of ˜1--2, to provide a comparison to studies of galaxies with star formation occurring in extended gas disks. The study features new, ultra-deep ground-based H-alpha imaging and deep ultraviolet (UV) imaging from the GALEX space telescope to trace the recent star formation. I find that star formation typically extends through most (>85%) of the gas disk, with an outermost star forming regime characterized by low covering fractions and low star formation rate surface densities. The result that star formation extends through most of the gas disk regardless of the HI-to-optical size implies that it is important to further our understanding of the formation of extended gas disks to fully understand the implications of extended star forming disks. I find that the outer gaseous disks are gravitationally stable, which is in agreement with the lower level of star formation. I use ultraviolet and H-alpha colors to probe the recent star formation in the outer disks and find significant variations between colors of young stellar clusters. I run stellar population synthesis models to show how episodic star formation histories (SFHs) with periods of 100--250 Myr could cause similar color variations as are seen in outer disks. An episodic SFH would have implications for the gas depletion time and chemical evolution of spiral galaxies. In addition to an episodic SFH, the observed ultraviolet and H-alpha colors of young stellar clusters in the outer disks of galaxies in our sample are also in agreement with recently published models of a stochastically sampled initial mass function (IMF). Therefore, there remains some uncertainty for the possible cause of this observational result. Finally, we present a pilot study of deep, near infrared (NIR) imaging

  12. The history of star formation in nearby dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Weisz, Daniel Ray

    2010-11-01

    a wide range of diverse environments suggests that SF in low mass systems may be dominated by stochastic processes. The fraction of stars formed per time interval for an average M81 Group and LG dI is consistent with a constant SFH. However, individual galaxies can show significant departures from a constant SFH. Thus, we find this result underlines the importance of stochastic SF in dIs. Comparing the recent SFHs and spatial locations of young stars with observations of the neutral interstellar medium (HI), we are able to gain new insight into the physics of stellar 'feedback'. We first make this type of comparison in IC 2754, a luminous dwarf irregular galaxy in the M81 Group with a ˜ 1 kpc supergiant HI shell. We find two significant episodes of SF inside the SGS from 200--300 Myr and ˜ 25 Myr ago. Comparing the timing of the SF events to the dynamic age of the SGS and the energetics from the HI and SF, we find compelling evidence that stellar feedback is responsible for creating the SGS and triggering secondary SF around its rim. We then conduct an extensive analysis of HI holes in M81 Group dwarf irregular galaxy, Holmberg II. From the deep photometry, we construct the CMDs and measure the SFHs for stars contained in HI holes from two independent holes catalogs, as well as select control fields, i.e., similar sized regions that span a range of HI column densities. The CMDs reveal young (< 200 Myr) stellar populations inside all HI holes, which contain very few bright OB stars with ages less than 10 Myr, indicating they are not reliable tracers of HI hole locations while the recent SFHs confirm multiple episodes of star formation within most holes. Converting the recent SFHs into stellar feedback energies, we find that enough energy has been generated to have created all holes. However, the required energy is not always produced over a time scale that is less than the estimated kinematic age of the hole. A similar analysis of stars in the control fields finds

  13. FAKE STAR FORMATION BURSTS: BLUE HORIZONTAL BRANCH STARS MASQUERADE AS YOUNG MASSIVE STARS IN OPTICAL INTEGRATED LIGHT SPECTROSCOPY

    SciTech Connect

    Ocvirk, P.

    2010-01-20

    Model color-magnitude diagrams of low-metallicity globular clusters (GCs) usually show a deficit of hot evolved stars with respect to observations. We investigate quantitatively the impact of such modeling inaccuracies on the significance of star formation history reconstructions obtained from optical integrated spectra. To do so, we analyze the sample of spectra of galactic globular clusters of Schiavon et al. with STECKMAP (Ocvirk et al.), and the stellar population models of Vazdekis et al. and Bruzual and Charlot, and focus on the reconstructed stellar age distributions. First, we show that background/foreground contamination correlates with E(B - V), which allows us to define a clean subsample of uncontaminated GCs, on the basis of an E(B - V) filtering. We then identify a 'confusion zone' where fake young bursts of star formation pop up in the star formation history although the observed population is genuinely old. These artifacts appear for 70%-100% of cases depending on the population model used, and contribute up to 12% of the light in the optical. Their correlation with the horizontal branch (HB) ratio indicates that the confusion is driven by HB morphology: red HB clusters are well fitted by old stellar population models while those with a blue HB require an additional hot component. The confusion zone extends over [Fe/H] = [ - 2, - 1.2], although we lack the data to probe extreme high and low metallicity regimes. As a consequence, any young starburst superimposed on an old stellar population in this metallicity range could be regarded as a modeling artifact, if it weighs less than 12% of the optical light, and if no emission lines typical of an H II region are present. This work also provides a practical method for constraining HB morphology from high signal to noise integrated light spectroscopy in the optical. This will allow post-asymptotic giant branch evolution studies in a range of environments and at distances where resolving stellar populations

  14. Dynamical models of a sample of Population II stars

    NASA Astrophysics Data System (ADS)

    Levison, H. F.; Richstone, D. O.

    1986-09-01

    Dynamical models are constructed in order to investigate the implications of recent kinematic data of distant Population II stars on the emissivity distribution of those stars. Models are constructed using a modified Schwarzschild method in two extreme scale-free potentials, spherical and E6 elliptical. Both potentials produce flat rotation curves and velocity dispersion profiles. In all models, the distribution of stars in this sample is flat. Moreover, it is not possible to construct a model with a strictly spheroidal emissivity distribution. Most models have dimples at the poles. The dynamics of the models indicate that the system is supported by both the third integral and z angular momentum.

  15. Probing Massive Star Cluster Formation with ALMA

    NASA Astrophysics Data System (ADS)

    Johnson, Kelsey

    2015-08-01

    Observationally constraining the physical conditions that give rise to massive star clusters has been a long-standing challenge. Now with the ALMA Observatory coming on-line, we can finally begin to probe the birth environments of massive clusters in a variety of galaxies with sufficient angular resolution. In this talk I will give an overview of ALMA observations of galaxies in which candidate proto-super star cluster molecular clouds have been identified. These new data probe the physical conditions that give rise to super star clusters, providing information on their densities, pressures, and temperatures. In particular, the observations indicate that these clouds may be subject to external pressures of P/k > 108 K cm-3, which is consistent with the prevalence of optically observed adolescent super star clusters in interacting galaxy systems and other high pressure environments. ALMA observations also enable an assessement of the molecular cloud chemical abundances in the regions surrounding super star clusters. Molecular clouds associated with existing super star clusters are strongly correlated with HCO+ emission, but appear to have relatively low ratio of CO/HCO+ emission compared to other clouds, indicating that the super star clusters are impacting the molecular abundances in their vicinity.

  16. 25 GHz methanol masers in regions of massive star formation

    NASA Astrophysics Data System (ADS)

    Britton, Tui R.; Voronkov, Maxim A.

    2012-07-01

    The bright 25 GHz series of methanol masers is formed in highly energetic regions of massive star formation and provides a natural signpost of shocked gas surrounding newly forming stars. A systematic survey for the 25 GHz masers has only recently been carried out. We present the preliminary results from the interferometric follow up of 51 masers at 25 GHz in the southern sky.

  17. HOBYS insights on high-mass star formation

    NASA Astrophysics Data System (ADS)

    Motte, F.

    2016-05-01

    The Herschel/HOBYS key program allows to statistically study the formation of 10 - 20 M⊙ stars. It reveals high-density cloud filaments of several pc3, which are forming clusters of OB-type stars. It also strongly suggests and higher-angular resolution images tend to confirm that high-mass prestellar cores do not exist.

  18. Studying the star formation process with adaptive optics

    NASA Astrophysics Data System (ADS)

    Menard, Francois; Dougados, Catherine; Duchene, Gaspard; Bouvier, Jerome; Duvert, Gilles; Lavalley, Claudia; Monin, Jean-Louis; Beuzit, Jean-Luc

    2000-07-01

    Young Stellar Objects (YSOs) are the builders of worlds. During its infancy, a star transforms ordinary interstellar dust particles into astronomical gold: planets to say the process is complex, and largely unknown to data. Yet, violent and spectacular events of mass ejection are witnessed, disks in keplerian rotation are detected, multiple stars dancing around each other are found. These are as many traces of the stellar and planet formation process. The high angular resolution provided by adaptive optics, and the related gain in sensitivity, have allowed major breakthrough discoveries to be made in each of these specific fields and our understanding of the various physical processes involved in the formation of a star has leaped forward tremendously over the last few years. In the following, meant as a report of the progress made recently in star formation due to adaptive optics, we will describe new results obtained at optical and near- infrared wavelengths, in imaging and spectroscopic modes. Our images of accretion disks and ionized stellar jets permit direct measurements of many physical parameters and shed light into the physics of the accretion and ejection processes. Although the accretion/ejection process so fundamental to star formation is usually studied around single objects, most of young stars form as part of multiple systems. We also present our findings on how the fraction of stars in binary systems evolves with age. The implications of these results on the conditions under which these stars must have formed are discussed.

  19. Formation and Evolution of Binary Systems Containing Collapsed Stars

    NASA Technical Reports Server (NTRS)

    Rappaport, Saul; West, Donald (Technical Monitor)

    2003-01-01

    This research includes theoretical studies of the formation and evolution of five types of interacting binary systems. Our main focus has been on developing a number of comprehensive population synthesis codes to study the following types of binary systems: (i) cataclysmic variables (#3, #8, #12, #15), (ii) low- and intermediate-mass X-ray binaries (#13, #20, #21), (iii) high-mass X-ray binaries (#14, #17, #22), (iv) recycled binary millisecond pulsars in globular clusters (#5, #10, #ll), and (v) planetary nebulae which form in interacting binaries (#6, #9). The numbers in parentheses refer to papers published or in preparation that are listed in this paper. These codes take a new unified approach to population synthesis studies. The first step involves a Monte Carlo selection of the primordial binaries, including the constituent masses, and orbital separations and eccentricities. Next, a variety of analytic methods are used to evolve the primary star to the point where either a dynamical episode of mass transfer to the secondary occurs (the common envelope phase), or the system evolves down an alternate path. If the residual core of the primary is greater than 2.5 solar mass, it will evolve to Fe core collapse and the production of a neutron star and a supernova explosion. In the case of systems involving neutron stars, a kick velocity is chosen randomly from an appropriate distribution and added to the orbital dynamics which determine the state of the binary system after the supernova explosion. In the third step, all binaries which commence stable mass transfer from the donor star (the original secondary in the binary system) to the compact object, are followed with a detailed binary evolution code. Finally, we include all the relevant dynamics of the binary system. For example, in the case of LMXBs, the binary system, with its recoil velocity from the supernova explosion, is followed in time through its path in the Galactic potential. For our globular cluster

  20. The era of star formation in galaxy clusters

    SciTech Connect

    Brodwin, M.; Stanford, S. A.; Gonzalez, Anthony H.; Mancone, C. L.; Gettings, D. P.; Zeimann, G. R.; Snyder, G. F.; Ashby, M. L. N.; Pope, A.; Alberts, S.; Eisenhardt, P. R.; Stern, D.; Moustakas, L. A.; Brown, M. J. I.; Chary, R.-R.; Dey, Arjun; Galametz, A.; Jannuzi, B. T.; Miller, E. D.; Moustakas, J.

    2013-12-20

    We analyze the star formation properties of 16 infrared-selected, spectroscopically confirmed galaxy clusters at 1 < z < 1.5 from the Spitzer/IRAC Shallow Cluster Survey (ISCS). We present new spectroscopic confirmation for six of these high-redshift clusters, five of which are at z > 1.35. Using infrared luminosities measured with deep Spitzer/Multiband Imaging Photometer for Spitzer observations at 24 μm, along with robust optical + IRAC photometric redshifts and spectral-energy-distribution-fitted stellar masses, we present the dust-obscured star-forming fractions, star formation rates, and specific star formation rates in these clusters as functions of redshift and projected clustercentric radius. We find that z ∼ 1.4 represents a transition redshift for the ISCS sample, with clear evidence of an unquenched era of cluster star formation at earlier times. Beyond this redshift, the fraction of star-forming cluster members increases monotonically toward the cluster centers. Indeed, the specific star formation rate in the cores of these distant clusters is consistent with field values at similar redshifts, indicating that at z > 1.4 environment-dependent quenching had not yet been established in ISCS clusters. By combining these observations with complementary studies showing a rapid increase in the active galactic nucleus (AGN) fraction, a stochastic star formation history, and a major merging episode at the same epoch in this cluster sample, we suggest that the starburst activity is likely merger-driven and that the subsequent quenching is due to feedback from merger-fueled AGNs. The totality of the evidence suggests we are witnessing the final quenching period that brings an end to the era of star formation in galaxy clusters and initiates the era of passive evolution.

  1. The simultaneous formation of massive stars and stellar clusters

    NASA Astrophysics Data System (ADS)

    Smith, Rowan J.; Longmore, Steven; Bonnell, Ian

    2009-12-01

    We show that massive stars and stellar clusters are formed simultaneously, the global evolution of the forming cluster is what allows the central stars to become massive. We predict that massive star-forming clumps, such as those observed in Motte et al., contract and grow in mass leading to the formation of massive stars. This occurs as mass is continually channelled from large radii on to the central protostars, which can become massive through accretion. Using smoothed particle hydrodynamic simulations of massive star-forming clumps in a giant molecular cloud, we show that clumps are initially diffuse and filamentary, and become more concentrated as they collapse. Simulated interferometry observations of our data provide an explanation as to why young massive star-forming regions show more substructure than older ones. The most massive stars in our model are found within the most bound cluster. Most of the mass accreted by the massive stars was originally distributed throughout the clump at low densities and was later funnelled to the star due to global infall. Even with radiative feedback no massive pre-stellar cores are formed. The original cores are of intermediate mass and gain their additional mass in the protostellar stage. We also find that cores which form low-mass stars exist within the volume from which the high-mass stars accrete, but are largely unaffected by this process.

  2. Hubble Space Telescope Observations of Accretion-Induced Star Formation in the Tadpole Galaxy Kiso 5639

    NASA Astrophysics Data System (ADS)

    Elmegreen, Debra Meloy; Elmegreen, Bruce G.; Sánchez Almeida, Jorge; Muñoz-Tuñón, Casiana; Mendez-Abreu, Jairo; Gallagher, John S.; Rafelski, Marc; Filho, Mercedes; Ceverino, Daniel

    2016-07-01

    The tadpole galaxy Kiso 5639 has a slowly rotating disk with a drop in metallicity at its star-forming head, suggesting that star formation was triggered by the accretion of metal-poor gas. We present multi-wavelength Hubble Space Telescope Wide Field Camera 3 images of UV through I band plus Hα to search for peripheral emission and determine the properties of various regions. The head has a mass in young stars of ∼ {10}6 {M}ȯ and an ionization rate of 6.4× {10}51 s‑1, equivalent to ∼2100 O9-type stars. There are four older star-forming regions in the tail, and an underlying disk with a photometric age of ∼1 Gyr. The mass distribution function of 61 star clusters is a power law with a slope of ‑1.73 ± 0.51. Fourteen young clusters in the head are more massive than {10}4 {M}ȯ , suggesting a clustering fraction of 30%–45%. Wispy filaments of Hα emission and young stars extend away from the galaxy. Shells and holes in the head H ii region could be from winds and supernovae. Gravity from the disk should limit the expansion of the H ii region, although hot gas might escape through the holes. The star formation surface density determined from Hα in the head is compared to that expected from likely pre-existing and accreted gas. Unless the surface density of the accreted gas is a factor of ∼3 or more larger than what was in the galaxy before, the star formation rate has to exceed the usual Kennicutt–Schmidt rate by a factor of ≥slant 5.

  3. Hubble Space Telescope Observations of Accretion-Induced Star Formation in the Tadpole Galaxy Kiso 5639

    NASA Astrophysics Data System (ADS)

    Elmegreen, Debra Meloy; Elmegreen, Bruce G.; Sánchez Almeida, Jorge; Muñoz-Tuñón, Casiana; Mendez-Abreu, Jairo; Gallagher, John S.; Rafelski, Marc; Filho, Mercedes; Ceverino, Daniel

    2016-07-01

    The tadpole galaxy Kiso 5639 has a slowly rotating disk with a drop in metallicity at its star-forming head, suggesting that star formation was triggered by the accretion of metal-poor gas. We present multi-wavelength Hubble Space Telescope Wide Field Camera 3 images of UV through I band plus Hα to search for peripheral emission and determine the properties of various regions. The head has a mass in young stars of ˜ {10}6 {M}ȯ and an ionization rate of 6.4× {10}51 s‑1, equivalent to ˜2100 O9-type stars. There are four older star-forming regions in the tail, and an underlying disk with a photometric age of ˜1 Gyr. The mass distribution function of 61 star clusters is a power law with a slope of ‑1.73 ± 0.51. Fourteen young clusters in the head are more massive than {10}4 {M}ȯ , suggesting a clustering fraction of 30%–45%. Wispy filaments of Hα emission and young stars extend away from the galaxy. Shells and holes in the head H ii region could be from winds and supernovae. Gravity from the disk should limit the expansion of the H ii region, although hot gas might escape through the holes. The star formation surface density determined from Hα in the head is compared to that expected from likely pre-existing and accreted gas. Unless the surface density of the accreted gas is a factor of ˜3 or more larger than what was in the galaxy before, the star formation rate has to exceed the usual Kennicutt–Schmidt rate by a factor of ≥slant 5.

  4. IC 3418: STAR FORMATION IN A TURBULENT WAKE

    SciTech Connect

    Hester, Janice A.; Neill, James D.; Wyder, Ted K.; Martin, D. Christopher; Seibert, Mark; Madore, Barry F.; Gil de Paz, Armando; Schiminovich, David; Rich, R. Michael

    2010-06-10

    Galaxy Evolution Explorer observations of IC 3418, a low surface brightness galaxy in the Virgo Cluster, revealed a striking 17 kpc UV tail of bright knots and diffuse emission. H{alpha} imaging confirms that star formation is ongoing in the tail. IC 3418 was likely recently ram pressure stripped on its first pass through Virgo. We suggest that star formation is occurring in molecular clouds that formed in IC 3418's turbulent stripped wake. Tides and ram pressure stripping (RPS) of molecular clouds are both disfavored as tail formation mechanisms. The tail is similar to the few other observed star-forming tails, all of which likely formed during RPS. The tails' morphologies reflect the forces present during their formation and can be used to test for dynamical coupling between molecular and diffuse gas, thereby probing the origin of the star-forming molecular gas.

  5. Local Magnetic Field Role in Star Formation

    NASA Astrophysics Data System (ADS)

    Koch, P. M.; Tang, Y. W.; Ho, P. T. P.; Zhang, Q.; Girart, J. M.; Chen, H. R. V.; Lai, S. P.; Li, H. B.; Li, Z. Y.; Liu, H. B.; Padovani, M.; Qiu, K.; Rao, R.; Yen, H. W.; Frau, P.; Chen, H. H.; Ching, T. C.

    2016-05-01

    We highlight distinct and systematic observational features of magnetic field morphologies in polarized submm dust continuum. We illustrate this with specific examples and show statistical trends from a sample of 50 star-forming regions.

  6. EARLY-STAGE MASSIVE STAR FORMATION NEAR THE GALACTIC CENTER: Sgr C

    SciTech Connect

    Kendrew, S.; Johnston, K.; Beuther, H.; Ginsburg, A.; Bally, J.; Battersby, C.; Cyganowski, C. J.

    2013-10-01

    We present near-infrared spectroscopy and 1 mm line and continuum observations of a recently identified site of high mass star formation likely to be located in the Central Molecular Zone (CMZ) near Sgr C. Located on the outskirts of the massive evolved H II region associated with Sgr C, the area is characterized by an Extended Green Object (EGO) measuring ∼10'' in size (0.4 pc), whose observational characteristics suggest the presence of an embedded massive protostar driving an outflow. Our data confirm that early-stage star formation is taking place on the periphery of the Sgr C H II region, with detections of two protostellar cores and several knots of H{sub 2} and Brackett γ emission alongside a previously detected compact radio source. We calculate the cores' joint mass to be ∼10{sup 3} M {sub ☉}, with column densities of 1-2 × 10{sup 24} cm{sup –2}. We show the host molecular cloud to hold ∼10{sup 5} M {sub ☉} of gas and dust with temperatures and column densities favorable for massive star formation to occur, however, there is no evidence of star formation outside of the EGO, indicating that the cloud is predominantly quiescent. Given its mass, density, and temperature, the cloud is comparable to other remarkable non-star-forming clouds such as G0.253 in the eastern CMZ.

  7. The formation of Stars and Planets

    NASA Technical Reports Server (NTRS)

    Terebey, S.

    1995-01-01

    This oral presentation relates to the concept that new stars are constantly forming in our Galaxy. While much of the visible activity is hidden from view by the dust and gas from which they form, our infrared and millimeter wavelength telescopes let us see through the veil. An emerging paradigm that defines much of the process by which stars and planets form is explained. Hubble Space Telescope images.

  8. Star formation laws in the Andromeda galaxy: gas, stars, metals and the surface density of star formation

    NASA Astrophysics Data System (ADS)

    Rahmani, S.; Lianou, S.; Barmby, P.

    2016-03-01

    We use hierarchical Bayesian regression analysis to investigate star formation laws in the Andromeda galaxy (M31) in both local (30, 155 and 750 pc) and global cases. We study and compare the well-known Kennicutt-Schmidt law, the extended Schmidt law and the metallicity/star formation correlation. Using a combination of Hα and 24 μm emission, a combination of far-ultraviolet and 24 μm, and the total infrared emission, we estimate the total star formation rate (SFR) in M31 to be between 0.35 ± 0.04 and 0.4 ± 0.04 M⊙ yr-1. We produce a stellar mass surface density map using IRAC 3.6 μm emission and measured the total stellar mass to be 6.9 × 1010 M⊙. For the Kennicutt-Schmidt law in M31, we find the power-law index N to be between 0.49 and 1.18; for all the laws, the power-law index varies more with changing gas tracer than with SFR tracer. The power-law index also changes with distance from the centre of the galaxy. We also applied the commonly used ordinary least-squares fitting method and showed that using different fitting methods leads to different power-law indices. There is a correlation between the surface density of SFR and the stellar mass surface density, which confirms that the Kennicutt-Schmidt law needs to be extended to consider the other physical properties of galaxies. We found a weak correlation between metallicity, the SFR and the stellar mass surface density.

  9. The interstellar medium and star formation in nearby galaxies. Ludwig Biermann Award Lecture 2013

    NASA Astrophysics Data System (ADS)

    Bigiel, F.; Cormier, D.; Schmidt, T.

    In this overview article we present some of the key projects we pursue in our Emmy Noether group. Our work is focused on nearby galaxies, where we use multi-wavelength, state-of-the-art survey data to probe distribution, abundance and properties of gas and dust in the interstellar medium (ISM) on [Si II] kpc scales. We study the average, radial distributions of atomic (H I) and molecular hydrogen (H2) across the disks of spiral galaxies and assess local (on 1 kpc scales) correlations between H I, H2 and star formation rate (SFR) surface densities across the inner, optical disks of our sample of [Si II] 30 spiral galaxies. The short H2 depletion times ([Si II] 2 Gyr) we find raises the question of if and how star formation is refueled in galactic disks. We look for such signatures of radial gas flows in our H I data and find compelling evidence at least in one case. We extend and compare our gas-SFR studies to the outer disks of galaxies, where conditions change significantly in the ISM, e.g., low metallicity and dust abundance. We focus on star formation at low-metallicity further with detailed ISM studies in dwarf galaxies, where we combine spectroscopic observations in the infrared with detailed modelling to learn about composition and detailed physical properties of the ISM. Of particular interest is the question of what drives large scale star formation in galaxies at low metallicity.

  10. Exploring the Connection Between Star Formation and AGN Activity in the Local Universe

    NASA Technical Reports Server (NTRS)

    LaMassa, Stephanie M.; Heckman. T. M.; Ptak, Andrew; Schiminovich, D.; O'Dowd, M.; Bertincourt, B.

    2012-01-01

    We study a combined sample of 264 star-forming, 51 composite, and 73 active galaxies using optical spectra from SDSS and mid-infrared (mid-IR) spectra from the Spitzer Infrared Spectrograph. We examine optical and mid-IR spectroscopic diagnostics that probe the amount of star formation and relative energetic con- tributions from star formation and an active galactic nucleus (AGN). Overall we find good agreement between optical and mid-IR diagnostics. Misclassifications of galaxies based on the SDSS spectra are rare despite the presence of dust obscuration. The luminosity of the [NeII] 12.8 micron emission-line is well correlated with the star formation rate (SFR) measured from the SDSS spectra, and this holds for the star forming, composite, and AGN-dominated systems. AGN show a clear excess of [NeIII] 15.6 micron emission relative to star forming and composite systems. We find good qualitative agreement between various parameters that probe the relative contributions of the AGN and star formation, including: the mid-IR spectral slope, the ratio of the [NeV] 14.3 micron to [NeII] micron 12.8 fluxes, the equivalent widths of the 7.7, 11.3, and 17 micron PAH features, and the optical "D" parameter which measures the distance a source lies from the locus of star forming galaxies in the optical BPT emission-line diagnostic diagram. We also consider the behavior of the three individual PAH features by examining how their flux ratios depend upon the degree of AGN-dominance. We find that the PAH 11.3 micron feature is significantly suppressed in the most AGN-dominated systems.

  11. Direct measurements of dust attenuation in z ∼ 1.5 star-forming galaxies from 3D-HST: Implications for dust geometry and star formation rates

    SciTech Connect

    Price, Sedona H.; Kriek, Mariska; Brammer, Gabriel B.; Conroy, Charlie; Schreiber, Natascha M. Förster; Wuyts, Stijn; Franx, Marijn; Fumagalli, Mattia; Lundgren, Britt; Momcheva, Ivelina; Nelson, Erica J.; Van Dokkum, Pieter G.; Skelton, Rosalind E.; Whitaker, Katherine E.

    2014-06-10

    The nature of dust in distant galaxies is not well understood, and until recently few direct dust measurements have been possible. We investigate dust in distant star-forming galaxies using near-infrared grism spectra of the 3D-HST survey combined with archival multi-wavelength photometry. These data allow us to make a direct comparison between dust around star-forming regions (A {sub V,} {sub H} {sub II}) and the integrated dust content (A {sub V,} {sub star}). We select a sample of 163 galaxies between 1.36 ≤ z ≤ 1.5 with Hα signal-to-noise ratio ≥5 and measure Balmer decrements from stacked spectra to calculate A {sub V,} {sub H} {sub II}. First, we stack spectra in bins of A {sub V,} {sub star}, and find that A {sub V,} {sub H} {sub II} = 1.86 A {sub V,} {sub star}, with a significance of σ = 1.7. Our result is consistent with the two-component dust model, in which galaxies contain both diffuse and stellar birth cloud dust. Next, we stack spectra in bins of specific star formation rate (log SSFR), star formation rate (log SFR), and stellar mass (log M {sub *}). We find that on average A {sub V,} {sub H} {sub II} increases with SFR and mass, but decreases with increasing SSFR. Interestingly, the data hint that the amount of extra attenuation decreases with increasing SSFR. This trend is expected from the two-component model, as the extra attenuation will increase once older stars outside the star-forming regions become more dominant in the galaxy spectrum. Finally, using Balmer decrements we derive dust-corrected Hα SFRs, and find that stellar population modeling produces incorrect SFRs if rapidly declining star formation histories are included in the explored parameter space.

  12. HEAD II: Exotic Neutron Stars Introduction

    NASA Astrophysics Data System (ADS)

    Harding, A. K.

    1998-12-01

    There has recently been growing evidence for a new class of astronomical object: isolated neutron stars with extremely high magnetic fields. Such objects were predicted to exist and would be the first known source to be powered by magnetic energy. The talks in this sessions will review evidence from observations of two types of sources: Soft Gamma-ray Repeaters, a class of galactic gamma-ray burst source, and Anomalous X-ray Pulsars, as well as current models.

  13. GAMMA RAYS FROM STAR FORMATION IN CLUSTERS OF GALAXIES

    SciTech Connect

    Storm, Emma M.; Jeltema, Tesla E.; Profumo, Stefano

    2012-08-20

    Star formation in galaxies is observed to be associated with gamma-ray emission, presumably from non-thermal processes connected to the acceleration of cosmic-ray nuclei and electrons. The detection of gamma rays from starburst galaxies by the Fermi Large Area Telescope (LAT) has allowed the determination of a functional relationship between star formation rate and gamma-ray luminosity. Since star formation is known to scale with total infrared (8-1000 {mu}m) and radio (1.4 GHz) luminosity, the observed infrared and radio emission from a star-forming galaxy can be used to quantitatively infer the galaxy's gamma-ray luminosity. Similarly, star-forming galaxies within galaxy clusters allow us to derive lower limits on the gamma-ray emission from clusters, which have not yet been conclusively detected in gamma rays. In this study, we apply the functional relationships between gamma-ray luminosity and radio and IR luminosities of galaxies derived by the Fermi Collaboration to a sample of the best candidate galaxy clusters for detection in gamma rays in order to place lower limits on the gamma-ray emission associated with star formation in galaxy clusters. We find that several clusters have predicted gamma-ray emission from star formation that are within an order of magnitude of the upper limits derived in Ackermann et al. based on non-detection by Fermi-LAT. Given the current gamma-ray limits, star formation likely plays a significant role in the gamma-ray emission in some clusters, especially those with cool cores. We predict that both Fermi-LAT over the course of its lifetime and the future Cerenkov Telescope Array will be able to detect gamma-ray emission from star-forming galaxies in clusters.

  14. Star-formation histories of local luminous infrared galaxies

    NASA Astrophysics Data System (ADS)

    Pereira-Santaella, Miguel; Alonso-Herrero, Almudena; Colina, Luis; Miralles-Caballero, Daniel; Pérez-González, Pablo G.; Arribas, Santiago; Bellocchi, Enrica; Cazzoli, Sara; Díaz-Santos, Tanio; Piqueras López, Javier

    2015-05-01

    We present analysis of the integrated spectral energy distribution (SED) from the ultraviolet (UV) to the far-infrared and Hα of a sample of 29 local systems and individual galaxies with infrared (IR) luminosities between 1011L⊙ and 1011.8L⊙. We combined new narrow-band Hα + [N ii] and broad-band g, r optical imaging taken with the Nordic Optical Telescope (NOT), with archival GALEX, 2MASS, Spitzer, and Herschel data. Their SEDs(photometry and integrated Hα flux) were fitted simultaneously with a modified version of the magphys code using stellar population synthesis models for the UV-near-IR range and thermal emission models for the IR emission taking the energy balance between the absorbed and re-emitted radiation into account. From the SED fits, we derive the star-formation histories (SFH) of these galaxies. For nearly half of them, the star-formation rate appears to be approximately constant during the last few Gyr. In the other half, the current star-formation rate seems to be enhanced by a factor of 3-20 with respect to what occurred ~1 Gyr ago. Objects with constant SFH tend to be more massive than starbursts, and they are compatible with the expected properties of a main-sequence (M-S) galaxy. Likewise, the derived SFHs show that all our objects were M-S galaxies ~1 Gyr ago with stellar masses between 1010.1 and 1011.5 M⊙. We also derived the average extinction (Av = 0.6-3 mag) and the polycyclic aromatic hydrocarbon luminosity to LIR ratio (0.03-0.16) from our fits. We combined the Av with the total IR and Hα luminosities into a diagramthat can be used to identify objects with rapidly changing (increasing or decreasing) SFR during the past 100 Myr. Appendices are available in electronic form at http://www.aanda.orgFITS files for all the reduced images are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/577/A78

  15. Star formation rates of spiral galaxies in the Cosmic Web

    NASA Astrophysics Data System (ADS)

    Alpaslan, Mehmet; Marcum, Pamela M.; Galaxy And Mass Assembly (GAMA)

    2016-01-01

    We look for shifts in stellar mass and star formation rate along filaments in the cosmic web by examining the stellar masses and UV-derived star formation rates of 1,799 ungrouped and unpaired spiral galaxies from the Galaxy And Mass Assembly (GAMA) survey that reside in filaments. We devise multiple distance metrics to characterise the complex geometry of filaments, and find that galaxies closer to the orthogonal core of a filament have higher stellar masses than their counterparts near the periphery of filaments, on the edges of voids. We also find that these peripheral galaxies have higher specific star formations at a given mass. Our results suggest a model in which gas accretion from voids onto filaments is primarily in an orthogonal direction. While the star formation rates of spiral galaxies in filaments are susceptible to their locations, we find that the global star formation rates of galaxies in different large scale environments are similar to each other. The primary discriminant in star formation rates is therefore the stellar mass of each spiral galaxy, as opposed to its large scale environment.

  16. Star Formation and Dynamics in the Galactic Centre

    NASA Astrophysics Data System (ADS)

    Mapelli, Michela; Gualandris, Alessia

    The centre of our Galaxy is one of the most studied and yet enigmatic places in the Universe. At a distance of about 8 kpc from our Sun, the Galactic centre (GC) is the ideal environment to study the extreme processes that take place in the vicinity of a supermassive black hole (SMBH). Despite the hostile environment, several tens of early-type stars populate the central parsec of our Galaxy. A fraction of them lie in a thin ring with mild eccentricity and inner radius ˜ 0.04 pc, while the S-stars, i.e. the ˜ 30 stars closest to the SMBH ( lesssim 0.04 pc), have randomly oriented and highly eccentric orbits. The formation of such early-type stars has been a puzzle for a long time: molecular clouds should be tidally disrupted by the SMBH before they can fragment into stars. We review the main scenarios proposed to explain the formation and the dynamical evolution of the early-type stars in the GC. In particular, we discuss the most popular in situ scenarios (accretion disc fragmentation and molecular cloud disruption) and migration scenarios (star cluster inspiral and Hills mechanism). We focus on the most pressing challenges that must be faced to shed light on the process of star formation in the vicinity of a SMBH.

  17. TIDAL TAILS OF MINOR MERGERS: STAR FORMATION EFFICIENCY IN THE WESTERN TAIL OF NGC 2782

    SciTech Connect

    Knierman, Karen; Scowen, Paul; Jansen, Rolf A.; Knezek, Patricia M.; Wehner, Elizabeth E-mail: paul.scowen@asu.edu E-mail: pknezek@noao.edu

    2012-04-10

    While major mergers and their tidal debris are well studied, they are less common than minor mergers (mass ratios {approx}< 0.3). The peculiar spiral NGC 2782 is the result of a merger between two disk galaxies with a mass ratio of {approx}4: 1 occurring {approx}200 Myr ago. This merger produced a molecular and H I-rich, optically bright eastern tail and an H I-rich, optically faint western tail. Non-detection of CO in the western tail by Braine et al. suggested that star formation had not yet begun to occur in that tidal tail. However, deep H{alpha} narrowband images show evidence of recent star formation in the western tail. Across the entire western tail, we find the global star formation rate per unit area ({Sigma}{sub SFR}) to be several orders of magnitude less than expected from the total gas density. Together with extended FUV+NUV emission from Galaxy Evolution Explorer along the tail, this indicates a low global star formation efficiency in the tidal tail producing lower mass star clusters. The H II region that we observed has a local (few-kiloparsec scale) {Sigma}{sub SFR} from H{alpha} that is less than that expected from the total gas density, which is consistent with other observations of tidal debris. The star formation efficiency of this H II region inferred from the total gas density is low, but normal when inferred from the molecular gas density. These results suggest the presence of a very small, locally dense region in the western tail of NGC 2782 or of a low-metallicity and/or low-pressure star-forming region.

  18. The Suppression of Star Formation by Powerful Active Galactic Nuclei

    NASA Technical Reports Server (NTRS)

    Dwek, E.

    2012-01-01

    The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight corre1ation between the mass of the black hole and the mas. of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming ga1axies are usually dust-obscured and are brightest at infrared and submillimeter wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10(exp 44) ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expe11ing the interstellar medium of its host and transforming the galaxy's properties in a brief period of cosmic time.

  19. The suppression of star formation by powerful active galactic nuclei.

    PubMed

    Page, M J; Symeonidis, M; Vieira, J D; Altieri, B; Amblard, A; Arumugam, V; Aussel, H; Babbedge, T; Blain, A; Bock, J; Boselli, A; Buat, V; Castro-Rodríguez, N; Cava, A; Chanial, P; Clements, D L; Conley, A; Conversi, L; Cooray, A; Dowell, C D; Dubois, E N; Dunlop, J S; Dwek, E; Dye, S; Eales, S; Elbaz, D; Farrah, D; Fox, M; Franceschini, A; Gear, W; Glenn, J; Griffin, M; Halpern, M; Hatziminaoglou, E; Ibar, E; Isaak, K; Ivison, R J; Lagache, G; Levenson, L; Lu, N; Madden, S; Maffei, B; Mainetti, G; Marchetti, L; Nguyen, H T; O'Halloran, B; Oliver, S J; Omont, A; Panuzzo, P; Papageorgiou, A; Pearson, C P; Pérez-Fournon, I; Pohlen, M; Rawlings, J I; Rigopoulou, D; Riguccini, L; Rizzo, D; Rodighiero, G; Roseboom, I G; Rowan-Robinson, M; Sánchez Portal, M; Schulz, B; Scott, D; Seymour, N; Shupe, D L; Smith, A J; Stevens, J A; Trichas, M; Tugwell, K E; Vaccari, M; Valtchanov, I; Viero, M; Vigroux, L; Wang, L; Ward, R; Wright, G; Xu, C K; Zemcov, M

    2012-05-10

    The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight correlation between the mass of the black hole and the mass of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming galaxies are usually dust-obscured and are brightest at infrared and submillimetre wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10(44) ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expelling the interstellar medium of its host and transforming the galaxy's properties in a brief period of cosmic time. PMID:22575961

  20. Star Formation in the Seemingly Quiet GMC N159-S

    NASA Astrophysics Data System (ADS)

    Chen, Chang-Hui; Wong, Tony; Ott, Juergen; Looney, Leslie; Chu, You-Hua; Gruendl, Robert; Indebetouw, Remy; Seale, Jonathan; Heitsch, Fabian; Madden, Suzanne

    2009-07-01

    Despite significant progress in understanding the physics involved with the formation of single stars, we still only have crude ides about why a giant molecular cloud (GMC) form clusters, distributed associations, or no stars at all. The key properties of GMCs displaying various intensities of star formation must be explored observationally in more detail. Two GMCs associated with the LMC HII region N159, N159-S and N159-W, have similar size and mass, but exhibit very different star formation activity as N159-S is paucity in stars and young stellar objects (YSOs) unlike its active neighbor N159-W. To examine whether N159-S may just start to form massive stars, or doesn't have that potential at all, we request 30 hours of 3mm HCO+ and HCN to map the CO core and 870um clumps. The observations will be used to study morphologies and spatial and mass distributions of dense gas clumps, to search for sites of massive YSOs at earliest evolutionary stage, and compare to the previous N159-W observations to assess whether N159-S can form YSOs as massive as O-type. This program will help us better understand the relation between GMCs and their star formation properties.

  1. Theoretical Developments in Understanding Massive Star Formation

    NASA Astrophysics Data System (ADS)

    Yorke, H. W.; Bodenheimer, P.

    2008-05-01

    Except under special circumstances massive stars in galactic disks will form through accretion. The gravitational collapse of a molecular cloud core will initially produce one or more low-mass quasi-hydrostatic objects of a few Jupiter masses. Through subsequent accretion the masses of these cores grow as they simultaneously evolve toward hydrogen-burning central densities and temperatures. We review the evolution of accreting (proto-)stars, including new results calculated with a publicly available stellar evolution code written by the authors. The evolution of accreting stars depends strongly on the accretion history. We find that for the high accretion rates considered, ˜10^{-3} M_⊙yr^{-1}, stars of ˜5-10 M_⊙ tend to bloat up to radii which may exceed 100 R_⊙. Because of the high rate of binarity among massive stars, we expect that these large radii during short phases of evolution will result in mass transfer, common envelope evolution, and a higher number of tight binaries with periods of a few days.

  2. Star formation and the distribution of HI and infrared emission in M51

    NASA Technical Reports Server (NTRS)

    Rand, Richard J.; Kulkarni, Shrinivas R.; Rice, W.

    1990-01-01

    H I, infrared, CO, H alpha and beta band observations of M51, the prototypical grand-design spiral galaxy, are used to study the consequences of star formation for the distribution of H I and dust. Using the H I and CO data sets new tests of the idea that the H I is largely a dissociation product in star-forming regions were performed. It was confirmed that the H I spiral arms are generally coincident with the H II region arms, and offset downstream from the CO arms. The radial distributions of total gas, H alpha and H I surface density have a simple explanation in the dissociation picture. The distributions also demonstrate how the surface density of H I might be related to the star formation efficiency in molecule-rich galaxies. The large width of the H I regions along the arms compared to that of the H II regions can be understood in terms of a simple Stroemgren sphere calculation. The longer lifetime of the stars producing dissociating radiation vs. those producing ionizing radiation will also contribute to the greater width of the H I arms if stars are continuously forming on the arms. The lack of detailed coincidence of the H I and H II regions along the inner arms has a variety of possible explanations within the dissociation scenario. Two simple tests to probe the origin of the IRAS emission in M51 were performed.

  3. Infrared atomic hydrogen line formation in luminous stars

    NASA Technical Reports Server (NTRS)

    Krolik, J. H.; Smith, H. A.

    1981-01-01

    Infrared atomic hydrogen lines observed in luminous stars, generally attributed to compact circumstellar H II regions, can also be formed in the winds likely to emanate from these stars. Implications are discussed for the class of obscured infrared point sources showing these lines, and an illustrative model is derived for the BN object in Orion. Such stellar winds should also produce weak, but detectable, radio emission.

  4. Segue 1 -- A Compressed Star Formation History before Reionization

    NASA Astrophysics Data System (ADS)

    Webster, David; Frebel, Anna; Bland-Hawthorn, Joss

    2016-02-01

    Segue 1 is the current best candidate for a “first galaxy,” a system that experienced only a single, short burst of star formation and has since remained unchanged. Here we present possible star formation scenarios that can explain Segue 1’s unique metallicity distribution. While the majority of stars in all other ultra-faint dwarfs are within 0.5 dex of the mean [Fe/H] for the galaxy, five of the seven stars in Segue 1 have a spread of Δ[Fe/H] > 0.8 dex. We show that this distribution of metallicities cannot be explained by a gradual buildup of stars, but instead requires clustered star formation. Chemical tagging allows the separate unresolved delta functions in abundance space to be associated with discrete events in space and time. This provides an opportunity to put the enrichment events into a time sequence and unravel the history of the system. We investigate two possible scenarios for the star formation history of Segue 1 using Fyris Alpha simulations of gas in a 107 M⊙ dark matter halo. The lack of stars with intermediate metallicities -3 < [Fe/H] < -2 can be explained either by a pause in star formation caused by supernova feedback or by the spread of metallicities resulting from one or two supernovae in a low-mass dark matter halo. Either possibility can reproduce the metallicity distribution function (MDF) as well as the other observed elemental abundances. The unusual MDF and the low luminosity of Segue 1 can be explained by it being a first galaxy that originated with Mvir ˜ 107M⊙ at z ˜ 10.

  5. Star Formation Research - Now And With Alma

    NASA Astrophysics Data System (ADS)

    Shepherd, Debra S.

    2006-06-01

    Optical, infrared, X-ray, and radio (single dish and interferometric) observations of star forming regions have made great strides toward improving our understanding of the characteristics and evolution of molecular clouds and embedded forming stars and their circumstellar disks. Once the Atacama Large Millimeter Array (ALMA) is completed, it will provide a significant increase in sensitivity and resolution at millimeter and sub-millimeter wavelengths that will allow all astronomers to address critical issues that cannot be explored with established observatories. I will review our current observational limitations and provide examples about how ALMA will contribute to the study of star forming regions and compliment other new or expanded observatories at optical, infrared, and radio wavelengths.The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

  6. Infrared Spectroscopy of Star Formation in Galactic and Extragalactic Regions

    NASA Technical Reports Server (NTRS)

    Smith, Howard A.; Hasan, Hashima (Technical Monitor)

    2002-01-01

    This report details work done in a project involving spectroscopic studies, including data analysis and modeling, of star-formation regions using an ensemble of archival space-based data including some from the Infrared Space Observatory's Long Wavelength Spectrometer and Short Wavelength Spectrometer, and other spectroscopic databases. We will include four kinds of regions: (1) disks around more evolved objects; (2) young, low or high mass pre-main sequence stars in star-formation regions; (3) star formation in external, bright IR (infrared) galaxies; and (4) the galactic center. During this period, work proceeded fully on track and on time. Details on workshops and conferences attended and research results are presented. A preprint article entitled 'The Far Infrared Lines of OH as Molecular Cloud Diagnostics' is included as an appendix.

  7. Star Formation in the Zw1400 + 09 Poor Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    McElroy, Alyssa

    2015-04-01

    Galaxies in dense clusters are known to have less gas and star formation, likely due to environmental interactions within the clusters. Less is known about the properties of galaxies in lower density poor clusters and group environments. In this project, star formation properties of galaxies in the Zwicky 1400 + 09 (NRGb282, NGC 5416) poor cluster were found by reducing and analyzing narrowband H-alpha and broadband R images taken with the WIYN 0.9m MOSAIC camera at Kitt Peak National Observatory. Surface photometry and total star formation rates and extents are presented for a sample of galaxies within the cluster. This work is supported by NSF AST-0725267 and AST-1211005 and is a part of an Undergraduate ALFALFA (Arecibo Legacy Fast ALFA) Team study of the star forming and gas properties of 16 nearby groups of galaxies. ALFALFA Consortium.

  8. ONE MOMENT IN TIME-MODELING STAR FORMATION IN THE ANTENNAE

    SciTech Connect

    Karl, Simon J.; Naab, Thorsten; Johansson, Peter H.; Kotarba, Hanna; Boily, Christian M.; Renaud, Florent; Theis, Christian E-mail: naab@mpa-garching.mpg.d

    2010-06-01

    We present a new high-resolution N-body/smoothed particle hydrodynamics simulation of an encounter of two gas-rich disk galaxies that closely matches the morphology and kinematics of the interacting Antennae galaxies (NGC 4038/39). The simulation includes radiative cooling, star formation, and feedback from Type II supernovae. The large-scale morphology and kinematics are determined by the internal structure and the orbit of the progenitor disks. The properties of the central region, in particular the starburst in the overlap region, only match the observations for a very short time interval ({Delta}t {approx} 20 Myr) after the second encounter. This indicates that the Antennae galaxies are in a special phase only about 40 Myr after the second encounter and 50 Myr before their final collision. This is the only phase in the simulation when a gas-rich overlap region between the nuclei is forming accompanied by enhanced star formation. The star formation rate as well as the recent star formation history in the central region agree well with observational estimates. For the first time, this new model explains the distributed extra-nuclear star formation in the Antennae galaxies as a consequence of the recent second encounter. The proposed model predicts that the Antennae are in a later merger stage than the Mice (NGC 4676) and would therefore lose their first place in the classical Toomre sequence.

  9. THE MILKY WAY PROJECT: A STATISTICAL STUDY OF MASSIVE STAR FORMATION ASSOCIATED WITH INFRARED BUBBLES

    SciTech Connect

    Kendrew, S.; Robitaille, T. P.; Simpson, R.; Lintott, C. J.; Bressert, E.; Povich, M. S.; Sherman, R.; Schawinski, K.; Wolf-Chase, G.

    2012-08-10

    The Milky Way Project citizen science initiative recently increased the number of known infrared bubbles in the inner Galactic plane by an order of magnitude compared to previous studies. We present a detailed statistical analysis of this data set with the Red MSX Source (RMS) catalog of massive young stellar sources to investigate the association of these bubbles with massive star formation. We particularly address the question of massive triggered star formation near infrared bubbles. We find a strong positional correlation of massive young stellar objects (MYSOs) and H II regions with Milky Way Project bubbles at separations of <2 bubble radii. As bubble sizes increase, a statistically significant overdensity of massive young sources emerges in the region of the bubble rims, possibly indicating the occurrence of triggered star formation. Based on numbers of bubble-associated RMS sources, we find that 67% {+-} 3% of MYSOs and (ultra-)compact H II regions appear to be associated with a bubble. We estimate that approximately 22% {+-} 2% of massive young stars may have formed as a result of feedback from expanding H II regions. Using MYSO-bubble correlations, we serendipitously recovered the location of the recently discovered massive cluster Mercer 81, suggesting the potential of such analyses for discovery of heavily extincted distant clusters.

  10. Molecular Clouds, Star Formation and Galactic Structure.

    ERIC Educational Resources Information Center

    Scoville, Nick; Young, Judith S.

    1984-01-01

    Radio observations show that the gigantic clouds of molecules where stars are born are distributed in various ways in spiral galaxies, perhaps accounting for the variation in their optical appearance. Research studies and findings in this area are reported and discussed. (JN)

  11. Delayed star formation in isolated dwarf galaxies: Hubble space telescope star formation history of the Aquarius dwarf irregular

    SciTech Connect

    Cole, Andrew A.; Weisz, Daniel R.; Dolphin, Andrew E.; Skillman, Evan D.; McConnachie, Alan W.; Brooks, Alyson M.; Leaman, Ryan E-mail: drw@ucsc.edu E-mail: skillman@astro.umn.edu E-mail: abrooks@physics.rutgers.edu

    2014-11-01

    We have obtained deep images of the highly isolated (d = 1 Mpc) Aquarius dwarf irregular galaxy (DDO 210) with the Hubble Space Telescope Advanced Camera for Surveys. The resulting color-magnitude diagram (CMD) reaches more than a magnitude below the oldest main-sequence turnoff, allowing us to derive the star formation history (SFH) over the entire lifetime of the galaxy with a timing precision of ≈10% of the lookback time. Using a maximum likelihood fit to the CMD we find that only ≈10% of all star formation in Aquarius took place more than 10 Gyr ago (lookback time equivalent to redshift z ≈ 2). The star formation rate increased dramatically ≈6-8 Gyr ago (z ≈ 0.7-1.1) and then declined until the present time. The only known galaxy with a more extreme confirmed delay in star formation is Leo A, a galaxy of similar M {sub H} {sub I}/M {sub *}, dynamical mass, mean metallicity, and degree of isolation. The delayed stellar mass growth in these galaxies does not track the mean dark matter accretion rate from CDM simulations. The similarities between Leo A and Aquarius suggest that if gas is not removed from dwarf galaxies by interactions or feedback, it can linger for several gigayears without cooling in sufficient quantity to form stars efficiently. We discuss possible causes for the delay in star formation including suppression by reionization and late-time mergers. We find reasonable agreement between our measured SFHs and select cosmological simulations of isolated dwarfs. Because star formation and merger processes are both stochastic in nature, delayed star formation in various degrees is predicted to be a characteristic (but not a universal) feature of isolated small galaxies.

  12. Bimodal star formation - Constraints from galaxy colors at high redshift

    NASA Technical Reports Server (NTRS)

    Wyse, Rosemary F. G.; Silk, Joseph

    1987-01-01

    The possibility that at early epochs the light from elliptical galaxies is dominated by stars with an initial mass function (IMF) which is deficient in low-mass stars, relative to the solar neighborhood is investigated. V-R colors for the optical counterparts of 3CR radio sources offer the most severe constraints on the models. Reasonable fits are obtained to both the blue, high-redshift colors and the redder, low-redshift colors with a model galaxy which forms with initially equal star formation rates in each of two IMF modes: one lacking low-mass stars, and one with stars of all masses. The net effect is that the time-integrated IMF has twice as many high-mass stars as the solar neighborhood IMF, relative to low mass stars. A conventional solar neighborhood IMF does not simultaneously account for both the range in colors at high redshift and the redness of nearby ellipticals, with any single star formation epoch. Models with a standard IMF require half the stellar population to be formed in a burst at low redshift z of about 1.

  13. Panchromatic Hubble Andromeda Treasury. XVI. Star Cluster Formation Efficiency and the Clustered Fraction of Young Stars

    NASA Astrophysics Data System (ADS)

    Johnson, L. Clifton; Seth, Anil C.; Dalcanton, Julianne J.; Beerman, Lori C.; Fouesneau, Morgan; Lewis, Alexia R.; Weisz, Daniel R.; Williams, Benjamin F.; Bell, Eric F.; Dolphin, Andrew E.; Larsen, Søren S.; Sandstrom, Karin; Skillman, Evan D.

    2016-08-01

    We use the Panchromatic Hubble Andromeda Treasury survey data set to perform spatially resolved measurements of star cluster formation efficiency (Γ), the fraction of stellar mass formed in long-lived star clusters. We use robust star formation history and cluster parameter constraints, obtained through color–magnitude diagram analysis of resolved stellar populations, to study Andromeda’s cluster and field populations over the last ∼300 Myr. We measure Γ of 4%–8% for young, 10–100 Myr-old populations in M31. We find that cluster formation efficiency varies systematically across the M31 disk, consistent with variations in mid-plane pressure. These Γ measurements expand the range of well-studied galactic environments, providing precise constraints in an H i-dominated, low-intensity star formation environment. Spatially resolved results from M31 are broadly consistent with previous trends observed on galaxy-integrated scales, where Γ increases with increasing star formation rate surface density (ΣSFR). However, we can explain observed scatter in the relation and attain better agreement between observations and theoretical models if we account for environmental variations in gas depletion time (τ dep) when modeling Γ, accounting for the qualitative shift in star formation behavior when transitioning from a H2-dominated to a H i-dominated interstellar medium. We also demonstrate that Γ measurements in high ΣSFR starburst systems are well-explained by τ dep-dependent fiducial Γ models.

  14. Panchromatic Hubble Andromeda Treasury. XVI. Star Cluster Formation Efficiency and the Clustered Fraction of Young Stars

    NASA Astrophysics Data System (ADS)

    Johnson, L. Clifton; Seth, Anil C.; Dalcanton, Julianne J.; Beerman, Lori C.; Fouesneau, Morgan; Lewis, Alexia R.; Weisz, Daniel R.; Williams, Benjamin F.; Bell, Eric F.; Dolphin, Andrew E.; Larsen, Søren S.; Sandstrom, Karin; Skillman, Evan D.

    2016-08-01

    We use the Panchromatic Hubble Andromeda Treasury survey data set to perform spatially resolved measurements of star cluster formation efficiency (Γ), the fraction of stellar mass formed in long-lived star clusters. We use robust star formation history and cluster parameter constraints, obtained through color–magnitude diagram analysis of resolved stellar populations, to study Andromeda’s cluster and field populations over the last ˜300 Myr. We measure Γ of 4%–8% for young, 10–100 Myr-old populations in M31. We find that cluster formation efficiency varies systematically across the M31 disk, consistent with variations in mid-plane pressure. These Γ measurements expand the range of well-studied galactic environments, providing precise constraints in an H i-dominated, low-intensity star formation environment. Spatially resolved results from M31 are broadly consistent with previous trends observed on galaxy-integrated scales, where Γ increases with increasing star formation rate surface density (ΣSFR). However, we can explain observed scatter in the relation and attain better agreement between observations and theoretical models if we account for environmental variations in gas depletion time (τ dep) when modeling Γ, accounting for the qualitative shift in star formation behavior when transitioning from a H2-dominated to a H i-dominated interstellar medium. We also demonstrate that Γ measurements in high ΣSFR starburst systems are well-explained by τ dep-dependent fiducial Γ models.

  15. Star formation in blue compact dwarf (BCD) galaxies

    NASA Astrophysics Data System (ADS)

    Sethuram, Ramya

    I present the optical photometry, spectroscopy using HCT of Blue compact dwarf (BCD) galaxies. The BCDs are observed through UBVRI filters. The colour-colour diagram (CCD) of U-B vs V-I and U-B vs B-V are created from integrated magnitudes. We have for the first time employed the mixed population technique using CCDs to find out ages of the underlying population intermixed with the starburst regions. A combination of few Gyr population, few hundred million years population and an young burst of age 5-15 Myr is detected for most of these galaxies. The structure of BCDs is a smooth background of low surface brightness (LSB) old stellar population and intermixed with the clumps of H II regions. The spectra of BCDs are typical H II region kind of spectra. The electron densities are < 100 cm^{-3} and temperatures are in the range 6000-15000 K. The oxygen abundance is calculated using the standard bright line methods. The oxygen abundance (log[O/H] + 12) of the sample of BCDs varies from as low as 7.9 to as high as 8.5. So these galaxies are (1/5 - 1/2.5) times metal poor when compared to solar. The BCDs are observed through H_α filters installed in the HFOSC system. The H_α fluxes and luminosities are used to calculate star formation rates (SFR) that are in the range 0.01 to 0.1 M_⊙/yr for individual H II regions and ranges between 0.1 to 1.0 M_⊙/yr for the whole galaxy. The archival data from 2MASS is used to obtain the integrated colour-colour diagrams of (J-H) vs (V-K). NIR colours are less affected by reddening and are better signatures of old stellar population. The results are compared with optical CCD, the interesting dichotomy are presented.

  16. VARIABILITY AND STAR FORMATION IN LEO T, THE LOWEST LUMINOSITY STAR-FORMING GALAXY KNOWN TODAY

    SciTech Connect

    Clementini, Gisella; Cignoni, Michele; Ramos, Rodrigo Contreras; Federici, Luciana; Tosi, Monica; Ripepi, Vincenzo; Marconi, Marcella; Musella, Ilaria E-mail: rodrigo.contreras@oabo.inaf.it E-mail: monica.tosi@oabo.inaf.it E-mail: ripepi@na.astro.it E-mail: ilaria@na.astro.it

    2012-09-10

    We present results from the first combined study of variable stars and star formation history (SFH) of the Milky Way 'ultra-faint' dwarf (UFD) galaxy Leo T, based on F606W and F814W multi-epoch archive observations obtained with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. We have detected 14 variable stars in the galaxy. They include one fundamental-mode RR Lyrae star and 11 Anomalous Cepheids with periods shorter than 1 day, thus suggesting the occurrence of multiple star formation episodes in this UFD, of which one about 10 Gyr ago produced the RR Lyrae star. A new estimate of the distance to Leo T of 409{sup +29}{sub -27} kpc (distance modulus of 23.06 {+-} 0.15 mag) was derived from the galaxy's RR Lyrae star. Our V, V - I color-magnitude diagram (CMD) of Leo T reaches V {approx} 29 mag and shows features typical of a galaxy in transition between dwarf irregular and dwarf spheroidal types. A quantitative analysis of the SFH, based on the comparison of the observed V, V - I CMD with the expected distribution of stars for different evolutionary scenarios, confirms that Leo T has a complex SFH dominated by two enhanced periods about 1.5 and 9 Gyr ago, respectively. The distribution of stars and gas shows that the galaxy has a fairly asymmetric structure.

  17. PROGRESSIVE STAR FORMATION IN THE YOUNG GALACTIC SUPER STAR CLUSTER NGC 3603

    SciTech Connect

    Beccari, Giacomo; Spezzi, Loredana; De Marchi, Guido; Andersen, Morten; Paresce, Francesco; Young, Erick; Panagia, Nino; Bond, Howard; Balick, Bruce; Calzetti, Daniela; Carollo, C. Marcella; Disney, Michael J.; Dopita, Michael A.; Frogel, Jay A.; Hall, Donald N. B.; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.; O'Connell, Robert W.; Saha, Abhijit

    2010-09-10

    Early Release Science observations of the cluster NGC 3603 with the WFC3 on the refurbished Hubble Space Telescope allow us to study its recent star formation history. Our analysis focuses on stars with H{alpha} excess emission, a robust indicator of their pre-main sequence (PMS) accreting status. The comparison with theoretical PMS isochrones shows that 2/3 of the objects with H{alpha} excess emission have ages from 1 to 10 Myr, with a median value of 3 Myr, while a surprising 1/3 of them are older than 10 Myr. The study of the spatial distribution of these PMS stars allows us to confirm their cluster membership and to statistically separate them from field stars. This result establishes unambiguously for the first time that star formation in and around the cluster has been ongoing for at least 10-20 Myr, at an apparently increasing rate.

  18. Progressive Star Formation in the Young Galactic Super Star Cluster NGC 3603

    NASA Astrophysics Data System (ADS)

    Beccari, Giacomo; Spezzi, Loredana; De Marchi, Guido; Paresce, Francesco; Young, Erick; Andersen, Morten; Panagia, Nino; Balick, Bruce; Bond, Howard; Calzetti, Daniela; Carollo, C. Marcella; Disney, Michael J.; Dopita, Michael A.; Frogel, Jay A.; Hall, Donald N. B.; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.; O'Connell, Robert W.; Saha, Abhijit; Silk, Joseph I.; Trauger, John T.; Walker, Alistair R.; Whitmore, Bradley C.; Windhorst, Rogier A.

    2010-09-01

    Early Release Science observations of the cluster NGC 3603 with the WFC3 on the refurbished Hubble Space Telescope allow us to study its recent star formation history. Our analysis focuses on stars with Hα excess emission, a robust indicator of their pre-main sequence (PMS) accreting status. The comparison with theoretical PMS isochrones shows that 2/3 of the objects with Hα excess emission have ages from 1 to 10 Myr, with a median value of 3 Myr, while a surprising 1/3 of them are older than 10 Myr. The study of the spatial distribution of these PMS stars allows us to confirm their cluster membership and to statistically separate them from field stars. This result establishes unambiguously for the first time that star formation in and around the cluster has been ongoing for at least 10-20 Myr, at an apparently increasing rate.

  19. Hubble studies generations of star formation in neighbouring galaxy

    NASA Astrophysics Data System (ADS)

    2004-07-01

    N11B Credits: NASA/ESA and the Hubble Heritage Team (AURA/STScI)/HEIC The iridescent tapestry of star birth The NASA/ESA Hubble Space Telescope captures the iridescent tapestry of star birth in a neighbouring galaxy in this panoramic view of glowing gas, dark dust clouds, and young, hot stars. The star-forming region, catalogued as N11B lies in the Large Magellanic Cloud (LMC), located only 160 000 light-years from Earth. With its high resolution, the Hubble Space Telescope is able to view details of star formation in the LMC as easily as ground-based telescopes are able to observe stellar formation within our own Milky Way galaxy. One neighbouring galaxy, the Large Magellanic Cloud (LMC), lies in the constellation of Dorado and contains a number of regions harbouring recent and ongoing star formation. One of these star-forming region, N11B, is shown in this Hubble image. It is a subregion within a larger area of star formation called N11. N11 is the second largest star-forming region in LMC. It is only surpassed in the size and activity by ‘the king of stellar nurseries’, 30 Doradus, located at the opposite side of LMC. N11B Credits: NASA/ESA and the Hubble Heritage Team (AURA/STScI)/HEIC A view of star formation The NASA/ESA Hubble Space Telescope captures the iridescent tapestry of star birth in a neighbouring galaxy in this panoramic view of glowing gas, dark dust clouds, and young, hot stars. The star-forming region, catalogued as N11B lies in the Large Magellanic Cloud (LMC), located only 160 000 light-years from Earth. With its high resolution, the Hubble Space Telescope is able to view details of star formation in the LMC as easily as ground-based telescopes are able to observe stellar formation within our own Milky Way galaxy. One neighbouring galaxy, the Large Magellanic Cloud (LMC), lies in the constellation of Dorado and contains a number of regions harbouring recent and ongoing star formation. One of these star-forming regions, N11B, is shown in

  20. Star Formation Histories in CLASH Brightest Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Fogarty, Kevin; Postman, Marc; Donahue, Megan; Moustakas, John; Connor, Thomas; Clash Science Team

    2015-01-01

    The CLASH sample of 25 lensing galaxy clusters contains 11 Brightest Cluster Galaxies (BCG) that exhibit significant unobscured (>5 Msol yr-1) star formation activity. The star formation is inferred from UV emission and from evidence for H-alpha filaments as detected in the ACS and WFC3 observations. We use photometry from the 16-band CLASH imaging along with spectra from the SOAR and SDSS telescopes to examine the star formation histories of these galaxies. Using SED fits to synthetic stellar population and nebular emission models, we constrain the burst histories of the two most UV and H-alpha luminous BCGs in our sample, RXJ1532.9+3021 and MACS1931.8-2635. The BCG in both of these clusters have reddening-corrected UV estimates of star formation rates in excess of 100 solar masses per year. We model the timescales and sizes of the starbursts that can account for the photometric and spectroscopic properties in these BCGs and create maps of their stellar properties on scales of ~350 pc. These maps reveal recent bursts occurring in elongated filaments on relatively long (~0.5-1.0 Gyr) timescales. In addition, we constrain the star formation properties of all of the remaining BCGs in the CLASH sample. These results and their implications for BCG formation and evolution will be presented.

  1. EXTENDED SCHMIDT LAW: ROLE OF EXISTING STARS IN CURRENT STAR FORMATION

    SciTech Connect

    Shi Yong; Helou, George; Yan Lin; Armus, Lee; Wu Yanling; Stierwalt, Sabrina; Papovich, Casey

    2011-06-01

    We propose an 'extended Schmidt law' with explicit dependence of the star formation efficiency (SFE = SFR/M{sub gas}) on the stellar mass surface density ({Sigma}{sub star}). This relation has a power-law index of 0.48 {+-} 0.04 and a 1{sigma} observed scatter on the SFE of 0.4 dex, which holds over five orders of magnitude in the stellar density for individual global galaxies, including various types and especially the low-surface-brightness (LSB) galaxies that deviate significantly from the Kennicutt-Schmidt (KS) law. When applying it to regions of a sample of 12 spiral galaxies at sub-kiloparsec resolution, the extended Schmidt law not only holds for LSB regions but also shows significantly smaller scatters both within and across galaxies compared with the KS law. We argue that this new relation points to the role of existing stars in regulating the SFE, thus better encoding the star formation physics. Comparison with physical models of star formation recipes shows that the extended Schmidt law can be reproduced by some models including gas free fall in a stellar-gravitational potential and pressure-supported star formation. By implementing this new law into the analytic model of gas accretion in {Lambda}CDM, we show that it can reproduce the observed main sequence of star-forming galaxies (a relation between the SFR and stellar mass) from z = 0 up to z = 2.

  2. Extended Schmidt Law: Role of Existing Stars in Current Star Formation

    NASA Astrophysics Data System (ADS)

    Shi, Yong; Helou, George; Yan, Lin; Armus, Lee; Wu, Yanling; Papovich, Casey; Stierwalt, Sabrina

    2011-06-01

    We propose an "extended Schmidt law" with explicit dependence of the star formation efficiency (SFE = SFR/M gas) on the stellar mass surface density (Σstar). This relation has a power-law index of 0.48 ± 0.04 and a 1σ observed scatter on the SFE of 0.4 dex, which holds over five orders of magnitude in the stellar density for individual global galaxies, including various types and especially the low-surface-brightness (LSB) galaxies that deviate significantly from the Kennicutt-Schmidt (KS) law. When applying it to regions of a sample of 12 spiral galaxies at sub-kiloparsec resolution, the extended Schmidt law not only holds for LSB regions but also shows significantly smaller scatters both within and across galaxies compared with the KS law. We argue that this new relation points to the role of existing stars in regulating the SFE, thus better encoding the star formation physics. Comparison with physical models of star formation recipes shows that the extended Schmidt law can be reproduced by some models including gas free fall in a stellar-gravitational potential and pressure-supported star formation. By implementing this new law into the analytic model of gas accretion in ΛCDM, we show that it can reproduce the observed main sequence of star-forming galaxies (a relation between the SFR and stellar mass) from z = 0 up to z = 2.

  3. Small-scale star formation at low metallicity

    NASA Technical Reports Server (NTRS)

    Mccall, Marshall L.; Hill, Robert; English, Jayanne

    1990-01-01

    Massive star formation in a low metallicity environment is investigated by studying the morphology of small HII regions in the Small Magellanic Cloud. A classification scheme based upon the symmetry of form in the light of H-alpha is proposed to make possible an examination of the properties of blister candidates with respect to nebulas embedded in a more uniform medium. A new diagnostic of size is developed to derive quantitative information about the ionized gas and ionizing stars. The asymmetrical surface-brightness distribution of many HII regions demonstrates that massive stars often form at the edge of dense neutral clouds. However, the existence of many symmetrical nebulas with similar sizes, luminosities, and surface brightnesses shows that massive star formation often occurs within these clouds. Nevertheless, the statistics of the two different forms indicate that the rate of massive star formation declines less steeply with radius across host clouds than in the Milky Way, suggesting that external triggering may play a larger role in initiating star formation.

  4. Star Formation Laws, Rates, and Thresholds in Galaxies

    NASA Astrophysics Data System (ADS)

    Di Francesco, James

    2015-08-01

    It has been long recognized that stars form out of gas within the interstellar mediums of galaxies. Though earlier treatments focused on the relationship between star formation and the surface densities of available molecular gas in disks (e.g., the Kennicutt-Schmidt law), more recently the relevance of dense molecular gas within galaxies has become better appreciated. In this short review talk, I will provide an overview of how this shift in thinking in the last few years has occurred through observations. For example, strong correlations have been seen between the luminosities of HCN 1-0 (tracing dense gas) and infrared emission (tracing young stars) over nearly ten orders of magnitude. Also, the number of young stellar objects in nearby clouds seems to be related to the amount of mass in a cloud above a column density 'threshold' of Av ≈ 6 (surface density ≈ 120 Msun/pc2). Indeed, recent far-infrared/submillimetre continuum data of nearby molecular clouds from Herschel have shown strong links between star formation and filamentary structures in clouds above a critical mass per unit length of ~16 Msun/pc (Av ≈ 8), providing a possible origin of the observed 'threshold.' Also, the current star formation rate in a dense molecular cloud clump, as traced by the local number of Class 0 objects, appears to be highly correlated with the relative fraction of high column density material in the clump. Prospects for future exploration of star-formation thresholds will also be discussed.

  5. PHAT Star Clusters in M31: Insight on Environmental Dependence of Star & Cluster Formation

    NASA Astrophysics Data System (ADS)

    Johnson, Lent C.; Dalcanton, Julianne; Seth, Anil; Beerman, Lori; Lewis, Alexia; Fouesneau, Morgan; Weisz, Daniel R.; Andromeda Project Team, PHAT Team

    2015-01-01

    Theoretical studies of star cluster formation suggest that the star formation efficiency (SFE) of a cluster's progenitor cloud dictates whether or not a gravitationally bound grouping will emerge from an embedded region after gas expulsion. I measure the fraction of stars formed in long-lived clusters relative to unbound field stars on a spatial resolved basis in the Andromeda galaxy. These observations test theoretical predictions that star clusters are formed within a hierarchical interstellar medium at peaks in the gas density where local SFEs are enhanced and regions become stellar dominated. Using data from the Panchromatic Hubble Andromeda Treasury (PHAT) survey and ancillary observations of M31's gas phase, I investigate how cluster formation correlates with galactic environment and galaxy-scale properties of the star formation. We construct a sample of >2700 star clusters through a crowd-sourced visual search of the high spatial resolution HST imaging data. Our catalog uses ~2 million image classifications collected by the Andromeda Project citizen science website to provide an unparalleled census of clusters that spans ~4 orders of magnitude in mass (50% completeness at ~500 M⊙ at <100 Myr) and increases the number of known clusters within the PHAT survey footprint by a factor of ~6. Cluster ages and masses are obtained by fitting to color-magnitude diagrams (CMDs) of individually resolved stars within each cluster. Furthermore, we insure our ability to accurately interpret cluster age and mass distributions through careful catalog completeness characterization, made possible by thousands of synthetic cluster tests included during catalog construction work. We combine our high quality cluster sample with spatially resolved star formation histories, derived from CMD fitting of PHAT's photometry of ~117 million resolved field stars. We derived the fraction of stars formed in long-lived clusters and show that only a few percent of coeval stars are found in

  6. Star formation and evolution in spiral galaxies.

    NASA Technical Reports Server (NTRS)

    Quirk, W. J.; Tinsley, B. M.

    1973-01-01

    Evolutionary models for regions of M31 and M33 and the solar neighborhood are based on a stellar birthrate suggested by the dynamics of spiral structure: we assume that stars are formed very efficiently until the gas content reaches equilibrium at its present value, which takes about 1 b.y.; thereafter, the birthrate just equals the rate at which gas enters the system from stellar mass-loss or infall of intergalactic matter. Each model represents an average around a cylindrical-shell-shaped region, which is homogeneous and closed except for possible infall. The disk and spiral-arm populations only are considered. Each star is followed in the H-R diagram from the main sequence to death as an invisible remnant. Integrated magnitudes, colors, mass-to-light ratio (M/L), gas content, helium and metal abundance (Z), are computed in steps of 1 b.y.

  7. Star formation and dynamics in starburst nuclei

    NASA Technical Reports Server (NTRS)

    Norman, Colin A.

    1987-01-01

    A simple model is presented for gas inflow through a disk galaxy driven by interacting galaxies through the action of a non-axisymmetric disturbance acting on the disk whose gas is modelled as an ensemble of gas clouds. Cloud collisions, as well as being a vital process in forcing gas inflow to the center of the disk, are also assumed to generate massive stars. This ever increasing rate of gas flow toward the center of the galaxy and the associated rapid increase in cloud collisions lead to a centrally concentrated starburst. Starbursts have important consequences for the immediate environment of galaxies. Mildly collimated outflows can be driven by a combination of multiple supernovae and OB star winds. Jets associated with activity in the galactic nucleus can interact strongly with a starburst environment.

  8. THE STAR FORMATION HISTORY OF THE MILKY WAY'S NUCLEAR STAR CLUSTER

    SciTech Connect

    Pfuhl, O.; Fritz, T. K.; Eisenhauer, F.; Genzel, R.; Gillessen, S.; Ott, T.; Dodds-Eden, K.; Zilka, M.; Sternberg, A.; Maness, H.

    2011-11-10

    We present spatially resolved imaging and integral field spectroscopy data for 450 cool giant stars within 1 pc from Sgr A*. We use the prominent CO bandheads to derive effective temperatures of individual giants. Additionally we present the deepest spectroscopic observation of the Galactic center (GC) so far, probing the number of B9/A0 main-sequence stars (2.2-2.8 M{sub sun}) in two deep fields. From spectrophotometry we construct a Hertzsprung-Russell diagram of the red giant population and fit the observed diagram with model populations to derive the star formation history of the nuclear cluster. We find (1) that the average nuclear star formation rate dropped from an initial maximum {approx}10 Gyr ago to a deep minimum 1-2 Gyr ago and increased again during the last few hundred Myrs, (2) that roughly 80% of the stellar mass formed more than 5 Gyr ago, and (3) that mass estimates within R {approx} 1 pc from Sgr A* favor a dominant star formation mode with a 'normal' Chabrier/Kroupa initial mass function for the majority of the past star formation in the GC. The bulk stellar mass seems to have formed under conditions significantly different from the young stellar disks, perhaps because at the time of the formation of the nuclear cluster the massive black hole and its sphere of influence were much smaller than today.

  9. Star formation seen with high resolution spectroscopy.

    NASA Astrophysics Data System (ADS)

    Winnewisser, G.

    1990-03-01

    More than 90 anorganic and organic molecules have been detected by high resolution spectroscopy in interstellar molecular clouds or in the envelopes of stars. The detected wavelengths of the lines - predominantly located in the millimeter- and submillimeter wavelength region - unequivocally identify the molecules and give precise knowledge of the physical and chemical conditions of molecular clouds from which the radiation emanates. The line intensities and line profiles contain information about the densities, temperatures and dynamics prevailing in molecular clouds.

  10. Cu(II) promotes amyloid pore formation

    SciTech Connect

    Zhang, Hangyu; Rochet, Jean-Christophe; Stanciu, Lia A.

    2015-08-14

    The aggregation of α-synuclein is associated with dopamine neuron death in Parkinson's disease. There is controversy in the field over the question of which species of the aggregates, fibrils or protofibrils, are toxic. Moreover, compelling evidence suggested the exposure to heavy metals to be a risk of PD. Nevertheless, the mechanism of metal ions in promoting PD remains unclear. In this research, we investigated the structural basis of Cu(II) induced aggregation of α-synuclein. Using transmission electron microscopy experiments, Cu(II) was found to promote in vitro aggregation of α-synuclein by facilitating annular protofibril formation rather than fibril formation. Furthermore, neuroprotective baicalein disaggregated annular protofibrils accompanied by considerable decrease of β-sheet content. These results strongly support the hypothesis that annular protofibrils are the toxic species, rather than fibrils, thereby inspiring us to search novel therapeutic strategies for the suppression of the toxic annular protofibril formation. - Highlights: • Cu(II) promoted the annular protofibril formation of α-synuclein in vitro. • Cu(II) postponed the in vitro fibrillization of α-synuclein. • Neuroprotective baicalein disaggregated annular protofibrils.

  11. Anatomy of a Spiral Arm: Gas, Dust and Star Formation

    NASA Astrophysics Data System (ADS)

    Schinnerer, Eva; Meidt, Sharon; Pety, Jerome; Leroy, Adam; Hughes, Annie; Colombo, Dario

    2015-08-01

    Spiral arms can be easily depicted in disk galaxies from the numerous young stars associated with them. However, it is on a fundamental level not clear where, how and when star formation starts relative to the spiral arm. We address these questions by utilizing high 1-3'' resolution observation of the total and dense molecular gas in a spiral arm segment of the nearby grand-design spiral galaxy M51 from PAWS (PdBI Arcsecond Whirlpool Survey) in combination with observations of young stars, HII regions and dust emission. We build a complete picture of the onset, progression and impact of star formation for this segment and discuss this picture in light of theoretical expectations.

  12. Probing Isolated Massive Star Formation in the LMC

    NASA Astrophysics Data System (ADS)

    Stephens, Ian

    2012-10-01

    Whether massive stars can form in isolation is one of the most debated questions in star formation. Observations of main sequence O-stars indicate that 5-10% of them form in isolation, but models of massive star formation suggest that massive stars should form in cluster environments. Isolated massive young stellar objects {YSOs} are better suited to address whether or not massive stars truly form in isolation since YSOs have had less time to disrupt their natal environment or move away from their stellar siblings. We have developed a unique sample of 7 candidates for isolated massive YSOs in the LMC. Within 80 pc, these objects are not associated with 1} other massive and intermediate-mass YSOs, 2} OB associations, and 3} giant molecular clouds {GMCs}. In all cases ground-based H-alpha observations show that they are affiliated with non-elongated, small HII regions and therefore are unlikely to be part of a runaway population. We request WFC3/UVIS and IR observations in the F656N, F555W, F814W, F110W, and F160W bands to examine the interstellar environment and determine the main sequence and pre-main sequence {PMS} populations down to 0.7 solar masses. In addition, coordinated parallel ACS/WFC F555W, F814W, and F658N observations will be used to assess the nearby control-field populations. From these observations we can search for lower-mass PMS stars, infer the local star formation history, and determine whether evidence exists for remnants of a disrupted GMC. With this statistically significant sample, we will have the ability to assess the possibility of massive stars forming in isolation.

  13. FUEL EFFICIENT GALAXIES: SUSTAINING STAR FORMATION WITH STELLAR MASS LOSS

    SciTech Connect

    Leitner, Samuel N.; Kravtsov, Andrey V.

    2011-06-10

    We examine the importance of secular stellar mass loss for fueling ongoing star formation in disk galaxies during the late stages of their evolution. For a galaxy of a given stellar mass, we calculate the total mass loss rate of its entire stellar population using star formation histories derived from the observed evolution of the M{sub *}-star formation rate (SFR) relation, along with the predictions of standard stellar evolution models for stellar mass loss for a variety of initial stellar mass functions. Our model shows that recycled gas from stellar mass loss can provide most or all of the fuel required to sustain the current level of star formation in late-type galaxies. Stellar mass loss can therefore remove the tension between the low gas infall rates that are derived from observations and the relatively rapid star formation occurring in disk galaxies. For galaxies where cold gas infall rates have been estimated, we demonstrate explicitly that stellar mass loss can account for most of the deficit between their SFR and infall rate.

  14. The spatial extent of star formation in interacting galaxies

    NASA Astrophysics Data System (ADS)

    Moreno, Jorge

    2015-08-01

    We employ a suite of 75 simulations of galaxies in idealized major mergers (stellar mass ratio ˜2.5:1), with a wide range of orbital parameters, to investigate the spatial extent of interaction-induced star formation. Although the total star formation in galaxy encounters is generally elevated relative to isolated galaxies, we find that this elevation is a combination of intense enhancements within the central kpc and moderately suppressed activity at larger galactocentric radii. The radial dependence of the star formation enhancement is stronger in the less massive galaxy than in the primary, and is also more pronounced in mergers of more closely aligned disc spin orientations. Conversely, these trends are almost entirely independent of the encounter’s impact parameter and orbital eccentricity. Our predictions of the radial dependence of triggered star formation, and specifically the suppression of star formation beyond kpc-scales, will be testable with the next generation of integral-field spectroscopic surveys.Co-authors: Paul Torrey, Sara Ellison, David Patton, Asa Bluck, Gunjan Bansal & Lars Hernquist

  15. Recovering the star formation rate in the solar neighborhood

    NASA Astrophysics Data System (ADS)

    Cignoni, M.; Degl'Innocenti, S.; Prada Moroni, P. G.; Shore, S. N.

    2006-12-01

    Aims.This paper develops a method for obtaining the star formation histories of a mixed, resolved population through the use of color-magnitude diagrams (CMDs). The method provides insight into the local star formation rate, analyzing the observations of the Hipparcos satellite through a comparison with synthetic CMDs computed for different histories with an updated stellar evolution library. Methods: .Parallax and photometric uncertainties are included explicitly and corrected using the Bayesian Richardson-Lucy algorithm. We first describe our verification studies using artificial data sets. From this sensitivity study, the critical factors determining the success of a recovery for a known star formation rate are a partial knowledge of the IMF and the age-metallicity relation, and sample contamination by clusters and moving groups (special populations whose histories are different than that of the whole sample). Unresolved binaries are less important impediments. We highlight how these limit the method. Results: .For the real field sample, complete to MV < 3.5, we find that the solar neighborhood star formation rate has a characteristic timescale for variation of about 6 Gyr, with a maximum activity close to 3 Gyr ago. The similarity of this finding with column integrated star formation rates may indicate a global origin, possibly a collision with a satellite galaxy. We also discuss applications of this technique to general photometric surveys of other complex systems (e.g. Local Group dwarf galaxies) where the distances are well known.

  16. The role of turbulence in star formation laws and thresholds

    SciTech Connect

    Kraljic, Katarina; Renaud, Florent; Bournaud, Frédéric; Combes, Françoise; Elmegreen, Bruce; Emsellem, Eric; Teyssier, Romain

    2014-04-01

    The Schmidt-Kennicutt relation links the surface densities of gas to the star formation rate in galaxies. The physical origin of this relation, and in particular its break, i.e., the transition between an inefficient regime at low gas surface densities and a main regime at higher densities, remains debated. Here, we study the physical origin of the star formation relations and breaks in several low-redshift galaxies, from dwarf irregulars to massive spirals. We use numerical simulations representative of the Milky Way and the Large and Small Magellanic Clouds with parsec up to subparsec resolution, and which reproduce the observed star formation relations and the relative variations of the star formation thresholds. We analyze the role of interstellar turbulence, gas cooling, and geometry in drawing these relations at 100 pc scale. We suggest in particular that the existence of a break in the Schmidt-Kennicutt relation could be linked to the transition from subsonic to supersonic turbulence and is independent of self-shielding effects. With this transition being connected to the gas thermal properties and thus to the metallicity, the break is shifted toward high surface densities in metal-poor galaxies, as observed in dwarf galaxies. Our results suggest that together with the collapse of clouds under self-gravity, turbulence (injected at galactic scale) can induce the compression of gas and regulate star formation.

  17. The Star Formation Properties of Void Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Moorman, Crystal; Vogeley, Michael S.

    2016-01-01

    We measure the star formation properties of two large samples of galaxies from the SDSS in large-scale cosmic voids on time scales of 10 Myr and 100 Myr, using Ha emission line strengths and GALEX FUV fluxes, respectively. The first sample consists of 109,818 optically selected galaxies. We find that void galaxies in this sample have higher specific star formation rates (SSFRs; star formation rates per unit stellar mass) than similar stellar mass galaxies in denser regions. The second sample is a subset of the optically selected sample containing 8070 galaxies with reliable S/N HI detections from ALFALFA. For the HI detected sample, SSFRs are similar regardless of large-scale environment. Investigating only the HI detected dwarf galaxies reveals a trend towards higher SSFRs in voids. Furthermore, we estimate the star formation rate per unit HI mass, known as the star formation efficiency (SFE) of a galaxy, as a function of environment. For the overall HI detected population, we notice no environmental dependence. Limiting the sample to dwarf galaxies again reveals a trend towards higher SFEs in voids. These results suggest that void environments provide a nurturing environment for dwarf galaxy evolution.

  18. Nothing to Hide -- An X-ray Survey of Star Formation Activity in the Pipe Nebula

    NASA Astrophysics Data System (ADS)

    Forbrich, Jan; Posselt, Bettina; Lada, Charles J.; Covey, Kevin

    2009-09-01

    The Pipe Nebula, a large nearby molecular cloud, lacks obvious signposts of star formation in all but one of more than 130 dust extinction cores that have been identified within it. In a recent mid-infrared survey using Spitzer-MIPS to cover 13 square degrees, we have established that the star formation efficiency for the entire cloud is only ˜0.06%. The mid-infrared data are most sensitive for the earliest evolutionary stages of Young Stellar Objects (YSOs), covering class I protostars and typical class II sources (classical T Tauri stars). X-ray observations allow us to extend our survey to constrain any population of classical and weak-line T Tauri stars. In a first step, we use the ROSAT All-Sky Survey to constrain any overall T Tauri star population of the Pipe Nebula. Due to the fact that the Pipe Nebula is at a distance of only 130 pc, the ROSAT survey is already quite sensitive. Assuming a typical level of extinction, the completeness for G- and K-type stars is estimated to be about 50%. Subsequently, we use XMM-Newton observations pointed at three high-extinction regions within the Pipe Nebula to analyze these areas at higher sensitivity. These three regions are Barnard 59, the only core with ongoing star formation, the ``ring'' (i.e., the highest extinction region in the ``bowl'' of the Pipe), and Barnard 68. We additionally analyze the YSOs of Barnard 59 in the radio continuum to constrain high-energy processes. Overall, our results corroborate our previous Spitzer result that the star formation efficiency of the Pipe Nebula is very low.

  19. FORMATION AND EVOLUTION OF NUCLEAR STAR CLUSTERS WITH IN SITU STAR FORMATION: NUCLEAR CORES AND AGE SEGREGATION

    SciTech Connect

    Aharon, Danor; Perets, Hagai B.

    2015-02-01

    Nuclear stellar cluster (NSCs) are known to exist around massive black holes (MBHs) in galactic nuclei. Two formation scenarios were suggested for their origin: (1) buildup of NSCs from consecutive infall of stellar clusters and (2) continuous in situ star formation. Though the cluster infall scenario has been extensively studied, the in situ formation scenario has been hardly explored. Here we use Fokker-Planck (FP) calculations to study the effects of star formation on the buildup of NSCs and its implications for their long-term evolution and their resulting structure. We use the FP equation to describe the evolution of stellar populations and add appropriate source terms to account for the effects of newly formed stars. We show that continuous star formation even 1-2 pc away from the MBH can lead to the buildup of an NSC with properties similar to those of the Milky Way NSC. We find that the structure of the old stellar population in the NSC with in situ star formation could be very similar to the steady-state Bahcall-Wolf cuspy structure. However, its younger populations do not yet achieve a steady state. In particular, formed/evolved NSCs with in situ star formation contain differential age-segregated stellar populations that are not yet fully mixed. Younger stellar populations formed in the outer regions of the NSC have a cuspy structure toward the NSC outskirts, while showing a core-like distribution inward, with younger populations having larger core sizes. In principal, such a structure can give rise to an apparent core-like radial distribution of younger stars, as observed in the Galactic center.

  20. Star Formation in Massive Clusters via Bondi Accretion

    NASA Astrophysics Data System (ADS)

    Murray, Norman; Chang, Philip

    2012-02-01

    Essentially all stars form in giant molecular clouds (GMCs). However, inside GMCs, most of the gas does not participate in star formation; rather, denser gas accumulates in clumps in the GMC, with the bulk of the stars in a given GMC forming in a few of the most massive clumps. In the Milky Way, these clumps have masses M cl <~ 5 × 10-2 of the GMC, radii r cl ~ 1 pc, and free-fall times τcl ~ 2 × 105 yr. We show that clumps inside GMCs should accrete at a modified Bondi accretion rate, which depends on clump mass as \\dot{M}_{cl}\\sim M_{cl}^{5/4}. This rate is initially rather slow, usually slower than the initial star formation rate inside the clump (we adopt the common assumption that inside the clump, \\dot{M}_*=\\epsilon _ffM_{cl}/\\tau _{cl}, with epsilonff ≈ 0.017). However, after ~2 GMC free-fall times τGMC, the clump accretion rate accelerates rapidly; formally, the clump can accrete the entire GMC in ~3τGMC. At the same time, the star formation rate accelerates, tracking the Bondi accretion rate. If the GMC is disrupted by feedback from the largest clump, half the stars in that clump form in the final τGMC before the GMC is disrupted. The theory predicts that the distribution of effective star formation rates, measured per GMC free-fall time, is broad, ranging from ~0.001 up to 0.1 or larger and that the mass spectrum of star clusters is flatter than that of clumps, consistent with observations.

  1. Star Formation and ISM studies with the SKA

    NASA Astrophysics Data System (ADS)

    Bourke, T. L.

    2016-05-01

    The Square Kilometre Array (SKA) will be the largest radio telescope when completed early next decade, providing a significant improvement in sensitivity, survey speed and angular resolution over existing facilities. A wide variety of star-formation and ISM studies will be possible with the SKA, from proto-planetary disks to massive star-forming regions. A few examples are highlighted in this article.

  2. PRIMUS: The Relationship between Star Formation and AGN Accretion

    NASA Astrophysics Data System (ADS)

    Azadi, Mojegan; Aird, James; Coil, Alison L.; Moustakas, John; Mendez, Alexander J.; Blanton, Michael R.; Cool, Richard J.; Eisenstein, Daniel J.; Wong, Kenneth C.; Zhu, Guangtun

    2015-06-01

    We study the evidence for a connection between active galactic nuclei (AGNs) fueling and star formation by investigating the relationship between the X-ray luminosities of AGNs and the star formation rates (SFRs) of their host galaxies. We identify a sample of 309 AGNs with {10}41\\lt {L}X\\lt {10}44 erg s-1 at 0.2\\lt z\\lt 1.2 in the PRIMUS redshift survey. We find AGNs in galaxies with a wide range of SFR at a given LX. We do not find a significant correlation between SFR and the observed instantaneous LX for star-forming AGN host galaxies. However, there is a weak but significant correlation between the mean LX and SFR of detected AGNs in star-forming galaxies, which likely reflects that LX varies on shorter timescales than SFR. We find no correlation between stellar mass and LX within the AGN population. Within both populations of star-forming and quiescent galaxies, we find a similar power-law distribution in the probability of hosting an AGN as a function of specific accretion rate. Furthermore, at a given stellar mass, we find a star-forming galaxy ˜2-3 more likely than a quiescent galaxy to host an AGN of a given specific accretion rate. The probability of a galaxy hosting an AGN is constant across the main sequence of star formation. These results indicate that there is an underlying connection between star formation and the presence of AGNs, but AGNs are often hosted by quiescent galaxies.

  3. Questions on star formation and observations to answer them

    NASA Astrophysics Data System (ADS)

    Harwit, Martin

    1987-05-01

    The nature of processes triggering protostellar collapse; cooling mechanisms necessary for subsequent continued contraction; means for shedding angular momentum from rotating clouds; ways in which contracting gas clouds divest themselves of embedded magnetic fields; and fragmentation of massive clouds to form rich stellar aggregates are discussed. Infrared and submillimeter observations from space should answer questions on contemporary star formation and on the appearance of the earliest stars in primordial galaxies.

  4. Physical parameters of galaxies with star formation through mid-infrared SED models

    NASA Astrophysics Data System (ADS)

    Ramos P., A. F.; Martínez-Galarza, J. R.; Higuera-G., M. A.; Quintero, S.

    2014-10-01

    We present a mid-infrared study of a sample of 19 Starburst galaxies in the local (z<0.2) universe. We derive physical parameters such as Metallicity, Interstellar Medium Pressure, Compactness Parameter C (related to the dust heating flux), PDR Fraction f_{PDR} and Extinction A_{V} by fitting the Spitzer-IRS spectra of these systems using state-of-the-art radiative transfer models and Bayesian techniques. Our results are fundamental in the understanding of massive star formation in the local counterparts of intermediate and high redshift Ultra Luminous Infrared Galaxies (ULIRGs). We reconstruct the star forming histories of these systems by obtaining posterior probability distribution functions (PDFs) for the star formation rates in different epochs an estimate the contribution to the bolometric luminosity from very recent (< 1 Myr) star formation events, and the contribution of Polycyclic Aromatic Hydrocarbons, which is significant in some cases. By comparing the derived PDFs with particular spectral signatures, such as the nebular emission of atomic species like [NeII] and [NeIII], and the H_{2} temperatures we also relate the global pattern of star formation in Starburst galaxies with the internal physics of the ISM.

  5. FORMATION CRITERIA AND THE MASS OF SECONDARY POPULATION III STARS

    SciTech Connect

    Susa, Hajime; Umemura, Masayuki; Hasegawa, Kenji E-mail: umemura@ccs.tsukuba.ac.jp

    2009-09-01

    We explore the formation of secondary Population III (Pop III) stars under radiation hydrodynamic (RHD) feedback by a preformed massive star. To properly treat RHD feedback, we perform three-dimensional RHD simulations incorporating the radiative transfer of ionizing photons as well as H{sub 2} dissociating photons from a preformed star. A collapsing gas cloud is settled at a given distance from a 120 M{sub sun} Pop III star, and the evolution of the cloud is pursued including RHD feedback. We derive the threshold density depending on the distance, above which the cloud can keep collapsing owing to the shielding of H{sub 2} dissociating radiation. We find that an H{sub 2} shell formed ahead of an ionizing front works effectively to shield the H{sub 2} dissociating radiation, leading to the positive feedback for the secondary Pop III star formation. Also, near the threshold density, the envelope of gas cloud is stripped significantly by a shock associated with an ionizing front. By comparing the mass accretion timescale with the Kelvin-Helmholtz timescale, we estimate the mass of secondary Pop III stars. It turns out that the stripping by a shock can reduce the mass of secondary Pop III stars down to {approx}20 M{sub sun}.

  6. Cu(II) Promotes Amyloid Pore Formation

    PubMed Central

    Zhang, Hangyu; Rochet, Jean-Christophe; Stanciu, Lia A

    2015-01-01

    The aggregation of α-synuclein is associated with dopamine neuron death in Parkinson's disease. There is controversy in the field over the question of which species of the aggregates, fibrils or protofibrils, are toxic. Moreover, compelling evidence suggested the exposure to heavy metals to be a risk of PD. Nevertheless, the mechanism of metal ions in promoting PD remains unclear. In this research, we investigated the structural basis of Cu(II) induced aggregation of α-synuclein. Using transmission electron microscopy experiments, Cu(II) was found to promote in vitro aggregation of α-synuclein by facilitating annular protofibril formation rather than fibril formation. Furthermore, neuroprotective baicalein disaggregated annular protofibrils accompanied by considerable decrease of β-sheet content. These results strongly support the hypothesis that annular protofibrils are the toxic species, rather than fibrils, thereby inspiring us to search novel therapeutic strategies for the suppression of the toxic annular protofibril formation. PMID:26129772

  7. New View of Distant Galaxy Reveals Furious Star Formation

    NASA Astrophysics Data System (ADS)

    2007-12-01

    A furious rate of star formation discovered in a distant galaxy shows that galaxies in the early Universe developed either much faster or in a different way from what astronomers have thought. "This galaxy is forming stars at an incredible rate," said Wei-Hao Wang, an astronomer at the National Radio Astronomy Observatory (NRAO) in Socorro, New Mexico. The galaxy, Wang said, is forming the equivalent of 4,000 Suns a year. This is a thousand times more violent than our own Milky Way Galaxy. Location of Distant Galaxy Visible-light, left (from HST) and Infrared, right, (from Spitzer) Images: Circles indicate location of GOODS 850-5. CREDIT: Wang et al., STScI, Spitzer, NASA, NRAO/AUI/NSF Click on image for high-resolution file (1 MB) The galaxy, called GOODS 850-5, is 12 billion light-years from Earth, and thus is seen as it was only about 1.5 billion years after the Big Bang. Wang and his colleagues observed it using the Smithsonian Astrophysical Observatory's Submillimeter Array (SMA) on Mauna Kea in Hawaii. Young stars in the galaxy were enshrouded in dust that was heated by the stars and radiated infrared light strongly. Because of the galaxy's great distance from Earth, the infrared light waves have been stretched out to submillimeter-length radio waves, which are seen by the SMA. The waves were stretched or "redshifted," as astronomers say, by the ongoing expansion of the Universe. "This evidence for prolific star formation is hidden by the dust from visible-light telescopes," Wang explained. The dust, in turn, was formed from heavy elements that had to be built up in the cores of earlier stars. This indicates, Wang said, that significant numbers of stars already had formed, then spewed those heavy elements into interstellar space through supernova explosions and stellar winds. "Seeing the radiation from this heated dust revealed star formation we could have found in no other way," Wang said. Similar dusty galaxies in the early Universe may contain most of the

  8. Modeling jet and outflow feedback during star cluster formation

    SciTech Connect

    Federrath, Christoph; Schrön, Martin; Banerjee, Robi; Klessen, Ralf S.

    2014-08-01

    Powerful jets and outflows are launched from the protostellar disks around newborn stars. These outflows carry enough mass and momentum to transform the structure of their parent molecular cloud and to potentially control star formation itself. Despite their importance, we have not been able to fully quantify the impact of jets and outflows during the formation of a star cluster. The main problem lies in limited computing power. We would have to resolve the magnetic jet-launching mechanism close to the protostar and at the same time follow the evolution of a parsec-size cloud for a million years. Current computer power and codes fall orders of magnitude short of achieving this. In order to overcome this problem, we implement a subgrid-scale (SGS) model for launching jets and outflows, which demonstrably converges and reproduces the mass, linear and angular momentum transfer, and the speed of real jets, with ∼1000 times lower resolution than would be required without the SGS model. We apply the new SGS model to turbulent, magnetized star cluster formation and show that jets and outflows (1) eject about one-fourth of their parent molecular clump in high-speed jets, quickly reaching distances of more than a parsec, (2) reduce the star formation rate by about a factor of two, and (3) lead to the formation of ∼1.5 times as many stars compared to the no-outflow case. Most importantly, we find that jets and outflows reduce the average star mass by a factor of ∼ three and may thus be essential for understanding the characteristic mass of the stellar initial mass function.

  9. Theoretical considerations for star formation at low and high redshifts

    NASA Astrophysics Data System (ADS)

    Elmegreen, Bruce G.

    2015-08-01

    Star formation processes in strongly self-gravitating cloud cores should be similar at all redshifts, forming single or multiple stars with a range of masses determined by local magneto-hydrodynamics. The formation processes for these cores, however, as well as their structures, temperatures, Mach numbers, etc., and the boundedness and mass distribution functions of the resulting stars, should depend on environment, as should the characteristic mass, density, and column density at which cloud self-gravity dominates other forces. Because the environments for high and low redshift star formation differ significantly, we expect the resulting gas to stellar conversion details to differ also. At high redshift, the universe is denser and more gas-rich, so the active parts of galaxies are denser and more gas rich too, leading to shorter gas consumption timescales, higher cloud pressures, and denser, more massive, bound stellar clusters at the high mass end. With shorter consumption times corresponding to higher relative cosmic accretion rates, and with the resulting higher star formation rates and their higher feedback powers, the ISM has greater turbulent speeds relative to the rotation speeds, thicker gas disks, and larger cloud and star complex sizes at the characteristic Jeans length. The result is a more chaotic appearance at high redshift, bridging the morphology gap between today’s quiescent spirals and today’s major-mergers, with neither spiral nor major-merger processes actually in play at that time. The result is also a thick disk at early times, and after in-plane accretion from relatively large clump torques, a classical bulge. Today’s disks are much thinner and torque-driven accretion is much slower outside of the inner barred regions. This talk will review the basic theoretical processes involved with star formation in order to illustrate its evolution over time and environment.

  10. THE DEPENDENCE OF STAR FORMATION EFFICIENCY ON GAS SURFACE DENSITY

    SciTech Connect

    Burkert, Andreas; Hartmann, Lee E-mail: lhartm@umich.edu

    2013-08-10

    Studies by Lada et al. and Heiderman et al. have suggested that star formation mostly occurs above a threshold in gas surface density {Sigma} of {Sigma}{sub c} {approx} 120 M{sub Sun} pc{sup -2} (A{sub K} {approx} 0.8). Heiderman et al. infer a threshold by combining low-mass star-forming regions, which show a steep increase in the star formation rate per unit area {Sigma}{sub SFR} with increasing {Sigma}, and massive cores forming luminous stars which show a linear relation. We argue that these observations do not require a particular density threshold. The steep dependence of {Sigma}{sub SFR}, approaching unity at protostellar core densities, is a natural result of the increasing importance of self-gravity at high densities along with the corresponding decrease in evolutionary timescales. The linear behavior of {Sigma}{sub SFR} versus {Sigma} in massive cores is consistent with probing dense gas in gravitational collapse, forming stars at a characteristic free-fall timescale given by the use of a particular molecular tracer. The low-mass and high-mass regions show different correlations between gas surface density and the area A spanned at that density, with A {approx} {Sigma}{sup -3} for low-mass regions and A {approx} {Sigma}{sup -1} for the massive cores; this difference, along with the use of differing techniques to measure gas surface density and star formation, suggests that connecting the low-mass regions with massive cores is problematic. We show that the approximately linear relationship between dense gas mass and stellar mass used by Lada et al. similarly does not demand a particular threshold for star formation and requires continuing formation of dense gas. Our results are consistent with molecular clouds forming by galactic hydrodynamic flows with subsequent gravitational collapse.

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  12. Implications for Interstellar Chemistry and Star Formation

    NASA Astrophysics Data System (ADS)

    Bergin, E. A.; Melnick, G. J.; Stauffer, J. R.; Ashby, M. L. N.; Kleiner, S. C.; Patten, B. M.; Plume, R.; Tolls, V.; Wang, Z.; Zhang, Y. F.; Goldsmith, P. F.; Harwit, M.; Erickson, N. R.; Howe, J. E.; Snell, R. L.; Neufeld, D. A.; Koch, D. G.; Schieder, R.; Winnewisser, G.; Chin, G.

    1999-12-01

    A long standing prediction of current theory has been that water and molecular oxygen are important reservoirs of elemental oxygen in the interstellar medium and, as a consequence, major coolants of the molecular gas as it collapses to form stars and planets. The analysis of SWAS observations has set sensitive upper limits on the abundance of O2 and has provided H2O abundances toward a variety of star forming regions. Based on these results, we show that H2O and O2 are not primary carriers of elemental oxygen in extended molecular clouds. Instead the available oxygen -- which may or may not be the solar oxygen abundance -- is presumably frozen on dust grains in the form of molecular ices, with a significant portion potentially remaining in atomic form, along with CO, in the gas phase. Given the low abundances for H2O and O2 in extended quiescent molecular gas, they are not significant coolants. In the case of H2O, a number of known chemical processes can locally elevate its abundance in regions with enhanced temperatures, such as warm regions surrounding young stars or in hot shocked gas. Thus, locally water can be an important, if not dominant, coolant. The new information provided by SWAS, when combined with recent results from the Infrared Space Observatory, also provide several hard observational constraints for theoretical models of the chemistry in molecular clouds and we will discuss the various models that satisfy these conditions. The SWAS Team gratefully acknowledges NASA contract NAS5-30702

  13. Extended Schmidt Law: Role of Existing Stars in Current Star Formation

    NASA Astrophysics Data System (ADS)

    Shi, Yong; Helou, G.; Armus, L.; Stierwalt, S.; Yan, L.

    2012-01-01

    We propose an ``extended Schmidt law'' with explicit dependence of the star formation efficiency (SFE=SFR/Mgas) on the stellar mass surface density. This relation has a power-law index of 0.48+-0.04 and an 1-sigma observed scatter on the SFE of 0.4 dex, which holds over 5 orders of magnitude in the stellar density for individual global galaxies including various types especially the low-surface-brightness (LSB) galaxies that deviate significantly from the Kennicutt-Schmidt law. When applying it to regions at sub-kpc resolution of a sample of 12 spiral galaxies, the extended Schmidt law not only holds for LSB regions but also shows significantly smaller scatters both within and across galaxies compared to the Kennicutt-Schmidt law. We argue that this new relation points to the role of existing stars in regulating the SFE, thus encoding better the star formation physics. Comparison with physical models of star formation recipes shows that the extended Schmidt law can be reproduced by some models including gas free-fall in a stellar-gravitational potential and pressure-supported star formation. By implementing this new law into the analytic model of gas accretion in Lambda CDM, we show that it can re-produce the observed main sequence of star-forming galaxies (a relation between the SFR and stellar mass) from z=0 up to z=2.

  14. Star formation enhancement characteristics in interacting galaxies

    NASA Astrophysics Data System (ADS)

    Zaragoza-Cardiel, J.; Beckman, J. E.; Font, J.; Camps-Fariña, A.; García-Lorenzo, B.; Erroz-Ferrer, S.

    2015-02-01

    We have observed 12 interacting galaxies using the Fabry-Perot interferometer GHαFaS (Galaxy Hα Fabry-Perot system) on the 4.2m William Herschel Telescope (La Palma). We have extracted the physical properties (sizes, Hα luminosity and velocity dispersion) of 236 HII regions for the full sample of interacting galaxies. We have derived the physical properties of 664 HII regions for a sample of 28 isolated galaxies observed with the same instrument in order to compare both populations of HII regions, finding that there are brighter and denser star forming regions in the interacting galaxies compared with the isolated galaxies sample.

  15. Star Formation Studies with SOFIA and its Synergy with TMT

    NASA Astrophysics Data System (ADS)

    De Buizer, James

    2014-07-01

    The Stratospheric Observatory For Infrared Astronomy (SOFIA) is a modified Boeing 747 aircraft equipped with a 2.5m telescope that performs observations at high altitude from the optical to the sub-mm. The observatory just reached full operational capability in April of this year. Given that it is slated for a 20-year mission lifetime, SOFIA will overlap TMT by more than a decade. I will discuss the contrasting and complementary features of SOFIA and TMT in the context of star formation, discuss some of the early results from SOFIA in this field, and finish with a discussion of how TMT data can enhance and extended our understanding of star formation processes.[This talk could also be generalized to discuss more about synergies between SOFIA and TMT in a broader context (not just star formation), should the organizers prefer that.

  16. Star formation in the M17 SW giant molecular cloud

    NASA Technical Reports Server (NTRS)

    Jaffe, D. T.; Fazio, G. G.

    1982-01-01

    The first high-sensitivity, high-resolution far-IR survey of an entire molecular cloud complex is presented. The 20 km/s M17 SW complex, in addition to the three luminous M17 sources, contains 10 sources spread over 110 pc. The 10 lower luminosity sources divide into two groups: small blister sources powered by late O stars and compact sources powered by clusters of early B stars. No compact far-IR sources with luminosities between the detection limit and 10,000 solar luminosities were detected. Three possible formation mechanisms for the stars that power the far-IR sources in the M17 SW complex are examined. Sequential formation cannot explain the sources seen throughout the complex. Some type of stochastic formation mechanism or collapse induced by a spiral density wave could explain the observations.

  17. Spatially Resolved Star Formation Main Sequence of Galaxies

    NASA Astrophysics Data System (ADS)

    Cano-Díaz, M.; Sánchez, S. F.; Zibetti, S.; Ascaribar, Y.; Bland-Hawthorn, J.; Ziegler, B.; González-Delgado, R. M.; Walcher, C. J.; García-Benito, R.; Mast, D.; Mendoza-Pérez, M. A.; Falcón-Barroso, J.; Galbany, L.; Husemann, B.; Kehring, C.; Marino, R. A.; Sánchez-Blázquez, P.; López-Cobá, C.; López-Sánchez, A. R.; Vilchez, J. M.

    2016-06-01

    The relation known as Star Formation Main Sequence (SFMS) of galaxies is defined in terms of stellar mass and star formation rate. This approximately linear relation has been proven to be tight and holds for several star formation indicators at local and at high redshifts. In this talk I will show recent results about our first attempts to study the Spatially Resolved SFMS, using integral field spectroscopic data, coming primarily from the CALIFA survey. I will present as a main result that a local SFMS is found with a slope and zero point of 0.72 +/ 0.04, and -7.95 +/ 0.29 respectively. I will also discuss the influence of characteristics such as environment and morphology in the relation. Finally I will present some extensions of these results for data com in from the MaNGA survey.

  18. Connecting Galaxies, Halos, and Star Formation Rates Across Cosmic Time

    SciTech Connect

    Conroy, Charlie; Wechsler, Risa H.

    2008-06-02

    A simple, observationally-motivated model is presented for understanding how halo masses, galaxy stellar masses, and star formation rates are related, and how these relations evolve with time. The relation between halo mass and galaxy stellar mass is determined by matching the observed spatial abundance of galaxies to the expected spatial abundance of halos at multiple epochs--i.e. more massive galaxies are assigned to more massive halos at each epoch. This 'abundance matching' technique has been shown previously to reproduce the observed luminosity- and scale-dependence of galaxy clustering over a range of epochs. Halos at different epochs are connected by halo mass accretion histories estimated from N-body simulations. The halo-galaxy connection at fixed epochs in conjunction with the connection between halos across time provides a connection between observed galaxies across time. With approximations for the impact of merging and accretion on the growth of galaxies, one can then directly infer the star formation histories of galaxies as a function of stellar and halo mass. This model is tuned to match both the observed evolution of the stellar mass function and the normalization of the observed star formation rate--stellar mass relation to z {approx} 1. The data demands, for example, that the star formation rate density is dominated by galaxies with M{sub star} {approx} 10{sup 10.0-10.5} M{sub {circle_dot}} from 0 < z < 1, and that such galaxies over these epochs reside in halos with M{sub vir} {approx} 10{sup 11.5-12.5} M{sub {circle_dot}}. The star formation rate--halo mass relation is approximately Gaussian over the range 0 < z < 1 with a mildly evolving mean and normalization. This model is then used to shed light on a number of issues, including (1) a clarification of 'downsizing', (2) the lack of a sharp characteristic halo mass at which star formation is truncated, and (3) the dominance of star formation over merging to the stellar build-up of galaxies

  19. Feedback and the Physics of Star Formation Quenching

    NASA Astrophysics Data System (ADS)

    Martin, Crystal; G3 Science Development Team

    2014-07-01

    Over the last decade, observations have revealed a number of surprising discoveries about how the baryonic content of galaxies is assembled. Roughly half the mass in present-day galaxies was assembled since redshift z~1 over an era when the cosmic star formation rate steadily declined. While the stellar mass in passive, red-sequence galaxies continued to grow, the mass in star-forming galaxies remained essentially constant. Over this period, some process, yet to be securely identified, quenched star formation in massive galaxies. This quenching was not predicted by theoretical models of the underlying cosmology and the hierarchical growth of gravitationally bound structures. Understanding the growth of the baryonic component of galaxies requires following the accretion and ejection of gas from galaxies. This gas physics depends on the highly non-linear gas cooling rate and the feedback of energy, momentum, and heavy elements produced by star formation and active galactic nuclei (AGN). I will discuss the ways in which detailed studies of galaxies over the era of strongly evolving star formation activity (roughly redshift 1.5 to the present) with TMT will provide answers to some of the questions which the above discoveries have raised.

  20. Signatures of Star Cluster Formation by Cold Collapse

    NASA Astrophysics Data System (ADS)

    Kuznetsova, Aleksandra; Hartmann, Lee; Ballesteros-Paredes, Javier

    2015-12-01

    Subvirial gravitational collapse is one mechanism by which star clusters may form. Here we investigate whether this mechanism can be inferred from observations of young clusters. To address this question, we have computed smoothed particle hydrodynamics simulations of the initial formation and evolution of a dynamically young star cluster through cold (subvirial) collapse, starting with an ellipsoidal, turbulently seeded distribution of gas, and forming sink particles representing (proto)stars. While the initial density distributions of the clouds do not have large initial mass concentrations, gravitational focusing due to the global morphology leads to cluster formation. We use the resulting structures to extract observable morphological and kinematic signatures for the case of subvirial collapse. We find that the signatures of the initial conditions can be erased rapidly as the gas and stars collapse, suggesting that kinematic observations need to be made early in cluster formation and/or at larger scales, away from the growing cluster core. Our results emphasize that a dynamically young system is inherently evolving on short timescales, so that it can be highly misleading to use current-epoch conditions to study aspects such as star formation rates as a function of local density. Our simulations serve as a starting point for further studies of collapse including other factors such as magnetic fields and stellar feedback.

  1. The Star Formation Activity in the Shapley Supercluster

    NASA Astrophysics Data System (ADS)

    Ho, P.-L.; Chen, L.-W.

    2013-10-01

    The Shapley supercluster (SSC) is the densest region in the local universe (z < 0.1)(Zucca et al. 1993), it hosts a wide variety of environments from massive clusters to filamentary structure. A total of 81 clusters and groups are identified in this region. In this study, a sample of 208 star-forming galaxies (SFGs) are used to study the effects of local galaxy density and cluster dynamic state on galaxy star formation activity. Our results show that the SFG fraction is highly suppressed in denser regions, for early type SFGs, they especially prefer the low density regions. As for the star formation activity in clusters/groups environment, higher SFG fractions are only detected in clusters/groups with velocity dispersion lower than ˜400 km sec-1, no matter the clusters/groups show merging evidence or not. These results may imply that the gas supply for star formation activity in denser and richer cluster/group regions has been removed by some cluster-specific processes, such as strangulation, ram pressure stripping and harassment, and thus the star formation activity is reduced.

  2. DUST-OBSCURED STAR FORMATION IN INTERMEDIATE REDSHIFT GALAXY CLUSTERS

    SciTech Connect

    Finn, Rose A.; Desai, Vandana; Rudnick, Gregory; Poggianti, Bianca; Bell, Eric F.; Hinz, Joannah; Zaritsky, Dennis; Jablonka, Pascale; Milvang-Jensen, Bo; Moustakas, John; Rines, Kenneth E-mail: jmoustakas@ucsd.ed

    2010-09-01

    We present Spitzer MIPS 24 {mu}m observations of sixteen 0.4 < z < 0.8 galaxy clusters drawn from the ESO Distant Cluster Survey. This is the first large 24 {mu}m survey of clusters at intermediate redshift. The depth of our imaging corresponds to a total IR luminosity of 8 x 10{sup 10} L{sub sun}, just below the luminosity of luminous infrared galaxies (LIRGs), and 6{sup +1}{sub -1}% of M{sub V} < -19 cluster members show 24 {mu}m emission at or above this level. We compare with a large sample of coeval field galaxies and find that while the fraction of cluster LIRGs lies significantly below that of the field, the IR luminosities of the field and cluster galaxies are consistent. However, the stellar masses of the EDisCS LIRGs are systematically higher than those of the field LIRGs. A comparison with optical data reveals that {approx}80% of cluster LIRGs are blue and the remaining 20% lie on the red sequence. Of LIRGs with optical spectra, 88{sup +4} {sub -5}% show [O II] emission with EW([O II]) > 5 A, and {approx}75% exhibit optical signatures of dusty starbursts. On average, the fraction of cluster LIRGs increases with projected clustercentric radius but remains systematically lower than the field fraction over the area probed (<1.5x R {sub 200}). The amount of obscured star formation declines significantly over the 2.4 Gyr interval spanned by the EDisCS sample, and the rate of decline is the same for the cluster and field populations. Our results are consistent with an exponentially declining LIRG fraction, with the decline in the field delayed by {approx}1 Gyr relative to the clusters.

  3. The star formation rate density from z = 1 to 6

    NASA Astrophysics Data System (ADS)

    Rowan-Robinson, Michael; Oliver, Seb; Wang, Lingyu; Farrah, Duncan; Clements, David L.; Gruppioni, Carlotta; Marchetti, Lucia; Rigopoulou, Dimitra; Vaccari, Mattia

    2016-09-01

    We use 3035 Herschel-SPIRE 500 μm sources from 20.3 deg2 of sky in the HerMES Lockman, ES1 and XMM-LSS areas to estimate the star formation rate density at z = 0-6. 500 μm sources are associated first with 350 and 250 μm sources, and then with Spitzer 24 μm sources from the SWIRE photometric redshift catalogue. The infrared and submillimetre data are fitted with a set of radiative-transfer templates corresponding to cirrus (quiescent) and starburst galaxies. Lensing candidates are removed via a set of colour-colour and colour-redshift constraints. Star formation rates are found to extend from <1 to 20 000 M⊙ yr-1. Such high values were also seen in the all-sky IRAS Faint Source Survey. Star formation rate functions are derived in a series of redshift bins from 0 to 6, combined with earlier far-infrared estimates, where available, and fitted with a Saunders et al (1990) functional form. The star formation rate density as a function of redshift is derived and compared with other estimates. There is reasonable agreement with both infrared and ultraviolet estimates for z < 3, but we find higher star formation rate densities than ultraviolet estimates at z = 3-6. Given the considerable uncertainties in the submillimetre estimates, we cannot rule out the possibility that the ultraviolet estimates are correct. But the possibility that the ultraviolet estimates have seriously underestimated the contribution of dust-shrouded star formation can also not be excluded.

  4. CEPHEID VARIABLE STARS IN THE PEGASUS DWARF IRREGULAR GALAXY: CONSTRAINTS ON THE STAR FORMATION HISTORY

    SciTech Connect

    Meschin, I.; Gallart, C.; Aparicio, A.; Rosenberg, A.; Cassisi, S. E-mail: carme@iac.es E-mail: alf@iac.es

    2009-03-15

    Observations of the resolved stars obtained over a period of 11 years in the Local Group dwarf irregular galaxy Pegasus have been used to search for Cepheid variable stars. Images were obtained in 55 epochs in the V band and in 24 epochs in the I band. We have identified 26 Cepheids and have obtained their light curves and periods. On the basis of their position in the period-luminosity (PL) diagram, we have classified them as 18 fundamental modes and eight first overtone Cepheids. Two PL relations for Cepheids have been used to derive the distance, resulting in 1.07 {+-} 0.05 Mpc. We present the VARFINDER code which finds the variable stars and their predicted periods in a given synthetic color-magnitude diagram computed with IAC-star and we propose the use of the Cepheid population as a constraint of the star formation history of Pegasus.

  5. Star Formation in Isolated LIRGs: Clues to Star-forming Processes at Higher z

    NASA Astrophysics Data System (ADS)

    Fuentes-Carrera, Isaura; Olguín, Lorenzo; Ambrocio-Cruz, Patricia; Verley, Simon; Rosado, Margarita; Verdes-Montenegro, Lourdes; Repetto, Paolo; Vázquez, Celia; Aguilera, Verónica

    2011-12-01

    Luminous infrared galaxies (LIRGs) are galaxies with LIR > 1011 L⊙. For a star-forming galaxy to emit at a LIRG level, it must have a very high star formation rate (SFR). In the local Universe, the star formation (SF) is primarily triggered by interactions. However, at intermediate redshift, a large fraction of LIRGs are disk galaxies with little sign of recent merger activity. The question arises whether the intermediate redshift LIRGs are ``triggered'' or experiencing ``normal'', if elevated, SF. Understanding these SF processes is important since this type of systems may have contributed to 20% or more of the cosmic SFR in the early Universe. In order to address this issue we study similar systems in the Local Universe, that is isolated late-type galaxies displaying LIRG activity. We use different observational techniques in order to trace the star-forming history of these systems. Here we present preliminary results.

  6. Star formation rates and abundance gradients in disk galaxies

    NASA Technical Reports Server (NTRS)

    Wyse, Rosemary F. G.; Silk, Joseph

    1989-01-01

    Analytic models for the evolution of disk galaxies are presented, placing special emphasis on the radial properties. These models are straightforward extensions of the original Schmidt (1959, 1963) models, with a dependence of star formation rate on gas density. The models provide successful descriptions of several measures of galactic disk evolution, including solar neighborhood chemical evolution, the presence and amplitude of metallicity and color gradients in disk galaxies, and the global rates of star formation in disk galaxies, and aid in the understanding of the apparent connection between young and old stellar populations in spiral galaxies.

  7. Star Formation: Chemistry as a Probe of Embedded Protostars

    NASA Astrophysics Data System (ADS)

    Visser, R.

    2013-10-01

    The embedded phase of star formation is the crucial phase where most of the stellar mass is assembled. Velocity-resolved spectra reveal an infalling envelope, bipolar outflows, and perhaps an infant circumstellar disk - all locked together in a cosmic dance of gravitational collapse and magnetic winds. Densities and temperatures change by orders of magnitude as the protostar evolves, driving a chemistry as exotic as it is fascinating. I will review two examples of how to exploit chemistry and molecular spectroscopy to study the physics of low-mass star formation: energetic feedback and episodic accretion.

  8. Nuclear Star Formation in the Hot-Spot Galaxy NGC 2903

    NASA Technical Reports Server (NTRS)

    Alonso-Herrero, A.; Ryder, S. D.; Knapen, J. H.

    1994-01-01

    We present high-resolution near-infrared imaging obtained using adaptive optics and HST/NICMOS and ground-based spectroscopy of the hot-spot galaxy NGC 2903. Our near-infrared resolution imaging enables us to resolve the infrared hot spots into individual young stellar clusters or groups of these. The spatial distribution of the stellar clusters is not coincident with that of the bright H II regions, as revealed by the HST/NICMOS Pace image. Overall, the circumnuclear star formation in NGC 2903 shows a ring-like morphology with an approximate diameter of 625 pc. The SF properties of the stellar clusters and H II regions have been studied using the photometric and spectroscopic information in conjunction with evolutionary synthesis models. The population of bright stellar clusters shows a very narrow range of ages, 4 to 7 x 10(exp 6) yr after the peak of star formation, or absolute ages 6.5 to 9.5 x 10(exp 6) yr (for the assumed short-duration Gaussian bursts), and luminosities similar to the clusters found in the Antennae interacting galaxy. This population of young stellar clusters accounts for some 7 - 12% of the total stellar mass in the central 625 pc of NGC 2903. The H II regions in the ring of star formation have luminosities close to that of the super-giant H II region 30 Doradus, they are younger than the stellar clusters, and will probably evolve into bright infrared stellar clusters similar to those observed today. We find that the star formation efficiency in the central regions of NGC 2903 is higher than in normal galaxies, approaching the lower end of infrared luminous galaxies.

  9. Star Formation in Ultrafaint Dwarfs: Continuous or Single-Age Bursts?

    NASA Astrophysics Data System (ADS)

    Webster, David; Bland-Hawthorn, Joss; Sutherland, Ralph

    2015-02-01

    We model the chemical evolution of six ultra-faint dwarfs (UFDs): Bootes I, Canes Venatici II, Coma Berenices, Hercules, Leo IV, and Ursa Major I based on their recently determined star formation histories. We show that two single-age bursts cannot explain the observed [α/Fe] versus [Fe/H] distribution in these galaxies and that some self-enrichment is required within the first burst. An alternative scenario is modeled, in which star formation is continuous except for short interruptions when one or more supernovae temporarily blow the dense gas out from the center of the system. This model allows for self-enrichment and can reproduce the chemical abundances of the UFDs in which the second burst is only a trace population. We conclude that the most likely star formation history is one or two extended periods of star formation, with the first burst lasting for at least 100 Myr. As found in earlier work, the observed properties of UFDs can be explained by formation at a low mass ({{M}vir}∼ {{10}7} M⊙), rather than being stripped remnants of much larger systems.

  10. STAR FORMATION IN ULTRA-FAINT DWARFS: CONTINUOUS OR SINGLE-AGE BURSTS?

    SciTech Connect

    Webster, David; Bland-Hawthorn, Joss; Sutherland, Ralph

    2015-01-30

    We model the chemical evolution of six ultra-faint dwarfs (UFDs): Bootes I, Canes Venatici II, Coma Berenices, Hercules, Leo IV, and Ursa Major I based on their recently determined star formation histories. We show that two single-age bursts cannot explain the observed [α/Fe] versus [Fe/H] distribution in these galaxies and that some self-enrichment is required within the first burst. An alternative scenario is modeled, in which star formation is continuous except for short interruptions when one or more supernovae temporarily blow the dense gas out from the center of the system. This model allows for self-enrichment and can reproduce the chemical abundances of the UFDs in which the second burst is only a trace population. We conclude that the most likely star formation history is one or two extended periods of star formation, with the first burst lasting for at least 100 Myr. As found in earlier work, the observed properties of UFDs can be explained by formation at a low mass (M{sub vir}∼10{sup 7} M{sub ⊙}), rather than being stripped remnants of much larger systems.

  11. Deep Imaging of Eridanus II and Its Lone Star Cluster

    NASA Astrophysics Data System (ADS)

    Crnojević, D.; Sand, D. J.; Zaritsky, D.; Spekkens, K.; Willman, B.; Hargis, J. R.

    2016-06-01

    We present deep imaging of the most distant dwarf discovered by the Dark Energy Survey, Eridanus II (Eri II). Our Magellan/Megacam stellar photometry reaches ∼3 mag deeper than previous work and allows us to confirm the presence of a stellar cluster whose position is consistent with Eri II’s center. This makes Eri II, at {M}V=-7.1, the least luminous galaxy known to host a (possibly central) cluster. The cluster is partially resolved, and at {M}V=-3.5 it accounts for ∼4% of Eri II’s luminosity. We derive updated structural parameters for Eri II, which has a half-light radius of ∼280 pc and is elongated (ɛ ∼ 0.48) at a measured distance of D ∼ 370 kpc. The color–magnitude diagram displays a blue, extended horizontal branch, as well as a less populated red horizontal branch. A central concentration of stars brighter than the old main-sequence turnoff hints at a possible intermediate-age (∼3 Gyr) population; alternatively, these sources could be blue straggler stars. A deep Green Bank Telescope observation of Eri II reveals no associated atomic gas. This paper includes data gathered with the 6.5 m Magellan Telescopes at Las Campanas Observatory, Chile.

  12. StarPy: Quenched star formation history parameters of a galaxy using MCMC

    NASA Astrophysics Data System (ADS)

    Smethurst, R. J.; Lintott, C. J.; Simmons, B. D.; Schawinski, K.; Marshall, P. J.; Bamford, S.; Fortson, L.; Kaviraj, S.; Masters, K. L.; Melvin, T.; Nichol, R. C.; Skibba, R. A.; Willett, K. W.

    2016-09-01

    StarPy derives the quenching star formation history (SFH) of a single galaxy through the Bayesian Markov Chain Monte Carlo method code emcee (ascl:1303.002). The sample function implements the emcee EnsembleSampler function for the galaxy colors input. Burn-in is run and calculated for the length specified before the sampler is reset and then run for the length of steps specified. StarPy provides the ability to use the look-up tables provided or creating your own.

  13. Effect of Population III Multiplicity on Dark Star Formation

    NASA Technical Reports Server (NTRS)

    Stacy, Athena; Pawlik, Andreas H.; Bromm, Volker; Loeb, Abraham

    2012-01-01

    We numerically study the mutual interaction between dark matter (DM) and Population III (Pop III) stellar systems in order to explore the possibility of Pop III dark stars within this physical scenario. We perform a cosmological simulation, initialized at z approx. 100, which follows the evolution of gas and DM. We analyze the formation of the first mini halo at z approx. 20 and the subsequent collapse of the gas to densities of 10(exp 12)/cu cm. We then use this simulation to initialize a set of smaller-scale 'cut-out' simulations in which we further refine the DM to have spatial resolution similar to that of the gas. We test multiple DM density profiles, and we employ the sink particle method to represent the accreting star-forming region. We find that, for a range of DM configurations, the motion of the Pop III star-disk system serves to separate the positions of the protostars with respect to the DM density peak, such that there is insufficient DM to influence the formation and evolution of the protostars for more than approx. 5000 years. In addition, the star-disk system causes gravitational scattering of the central DM to lower densities, further decreasing the influence of DM over time. Any DM-powered phase of Pop III stars will thus be very short-lived for the typical multiple system, and DM will not serve to significantly prolong the life of Pop III stars.

  14. Spontaneous and Induced Star Formation in the LMC

    NASA Astrophysics Data System (ADS)

    Efremov, Y. N.; Elmegreen, B. G.

    The Large Magellanic Cloud is the best site in the Universe to investigate star formation processes not connected with the spiral arms. This is because the galaxy is close, nearly pole-on, and has only a small depth on the line of sight (unlike the SMC). This give the best possible opportunity to learn about large-scale properties of star formation. Spontaneous star formation in turbulent gas implies hierarchical structure in the distribution of young stars. This is indeed observed as sequences of embedded young star groups, from mini-clusters to clusters to associations, aggregates, and complexes. Quantitative evidence for such a sequence is also present in the stellar ages, as follows from the data for the LMC clusters. The average age differences between clusters increases with their separation, from about 100 pc to 1000 pc throughout the LMC. From this we infer that the duration of star formation increases with the size of the region. The time - size relation also implies that the size of a young stellar group is determined by its age. This explains the characteristic size of an OB-association, which is always about ~80 pc because the age is about 10-15 Myrs. OB associations are only one level in a continuous hierarchy of structures. The Cepheids data with new period - age relation based on the same age scale as for the LMC clusters (with mild overshooting) display the similar separation - age difference relation, which is worse based statistically than this for clusters, however. There is at least one region in the LMC where triggered star formation has been suggested by many investigators: the Constellation III/LMC4 region. There has not been any agreement, though, on the mechanism of triggering and no age gradient has been found. We find that the 600 pc-long arc of young stars and clusters commonly called Constellation III was probably swept up by a central source of pressure that was associated with a visible cluster of six A-type supergiant stars having an

  15. Hierarchical Star Formation in the Milky Way Disk

    NASA Astrophysics Data System (ADS)

    de la Fuente Marcos, R.; de la Fuente Marcos, C.

    2009-07-01

    Hierarchical star formation leads to a progressive decrease in the clustering of star clusters both in terms of spatial scale and age. Consistently, statistical analysis of the positions and ages of clusters in the Milky Way disk strongly suggests that a correlation between the duration of star formation in a region and its size does exist. The average age difference between pairs of open clusters increases with their separation as the ~0.16 power. In contrast, for the Large Magellanic Cloud, Efremov & Elmegreen found that the age difference scales with the ~0.35 power of the region size. This discrepancy may be tentatively interpreted as an argument in support of intrinsically shorter (faster) star formation timescales in smaller galaxies. However, if both the effects of cluster dissolution and incompleteness are taken into consideration, the average age difference between cluster pairs in the Galaxy increases with their separation as the ~0.4 power. This result implies that the characteristic timescale for coherent, clustered-mode star formation is nearly 1 Myr. Therefore, the overall consequence of ignoring the effect of cluster dissolution is to overestimate the star formation timescale. On the other hand, in the Galactic disk and for young clusters separated by less than three times the characteristic cluster tidal radius (10 pc), the average age difference is 16 Myr, which suggests common origin. A close pair classification scheme is introduced and a list of 11 binary cluster candidates with physical separation less than 30 pc is compiled. Two of these pairs are likely primordial: ASCC 18/ASCC 21 and NGC 3293/NGC 3324. A triple cluster candidate in a highly hierarchical configuration is also identified: NGC 1981/NGC 1976/Collinder 70 in Orion. We find that binary cluster candidates seem to show a tendency to have components of different size—evidence for dynamical interaction.

  16. HIERARCHICAL STAR FORMATION IN THE MILKY WAY DISK

    SciTech Connect

    De la Fuente Marcos, R.; De la Fuente Marcos, C.

    2009-07-20

    Hierarchical star formation leads to a progressive decrease in the clustering of star clusters both in terms of spatial scale and age. Consistently, statistical analysis of the positions and ages of clusters in the Milky Way disk strongly suggests that a correlation between the duration of star formation in a region and its size does exist. The average age difference between pairs of open clusters increases with their separation as the {approx}0.16 power. In contrast, for the Large Magellanic Cloud, Efremov and Elmegreen found that the age difference scales with the {approx}0.35 power of the region size. This discrepancy may be tentatively interpreted as an argument in support of intrinsically shorter (faster) star formation timescales in smaller galaxies. However, if both the effects of cluster dissolution and incompleteness are taken into consideration, the average age difference between cluster pairs in the Galaxy increases with their separation as the {approx}0.4 power. This result implies that the characteristic timescale for coherent, clustered-mode star formation is nearly 1 Myr. Therefore, the overall consequence of ignoring the effect of cluster dissolution is to overestimate the star formation timescale. On the other hand, in the Galactic disk and for young clusters separated by less than three times the characteristic cluster tidal radius (10 pc), the average age difference is 16 Myr, which suggests common origin. A close pair classification scheme is introduced and a list of 11 binary cluster candidates with physical separation less than 30 pc is compiled. Two of these pairs are likely primordial: ASCC 18/ASCC 21 and NGC 3293/NGC 3324. A triple cluster candidate in a highly hierarchical configuration is also identified: NGC 1981/NGC 1976/Collinder 70 in Orion. We find that binary cluster candidates seem to show a tendency to have components of different size-evidence for dynamical interaction.

  17. Spectroscopic Observations of the Star Formation Regions in Nearby Galaxies

    NASA Astrophysics Data System (ADS)

    Kong, X.; Lin, L.; Li, J. R.; Zhou, X.; Zou, H.; Li, H. Y.; Chen, F. Z.; Du, W.; Fan, Z.; Mao, Y. W.; Wang, J.; Zhu, Y. N.; Zhou, Z. M.

    2014-01-01

    During the late 1990s and the first decade of the 21st century, the 8˜10 m scale ground-based telescopes are helping astronomers learn much more about how galaxies develop. The existing 2˜4 m scale telescopes become less important for astrophysical researches. To use the existing 2˜4 m scale telescopes to address important issues in cosmology and extragalactic and galactic astronomy, we have to consider very carefully which kind of things we can do, and which we can not. For this reason, the Time Allocation Committee (TAC) of the National Astronomical Observatories of China (NAOC) 2.16 m telescope decides to support some key projects since 2013. Nearby galaxies supply us with the opportunity to study galaxy dynamics and star formation on large scales, yet are close enough to reveal the details. Star formation regions in nearby galaxies provide an excellent laboratory to study the star formation processes, the evolution of massive stars, and the properties of the surrounding interstellar medium. A wealth of information can be obtained from the spectral analysis of the bright emission lines and the stellar continuum. Considering these, we proposed a long-term project ``Spectroscopic Observations of the Star Formation Regions in Nearby Galaxies'', and it becomes the key project of the NAOC 2.16 m telescope since 2013, supported with 30 dark/grey nights per year. The primary goal of this project is to observe the spectroscopy of star formation regions in 20 nearby galaxies, with the NAOC 2.16 m telescope and the Hectospec/MMT (Multiple Mirror Telescope) multifiber spectrograph by Telescope Access Program (TAP). With the spectra of a large sample of star formation regions, combining multi-wavelength data from UV to IR, we can investigate, understand, and quantify the nature of the deviation from the starbursts' IRX-β (the IR/UV ratio ``IRX'' versus the UV color ``β'') correlation. It will be important for a better understanding of the interaction of dust and

  18. On the cosmic evolution of the specific star formation rate

    NASA Astrophysics Data System (ADS)

    Lehnert, M. D.; van Driel, W.; Le Tiran, L.; Di Matteo, P.; Haywood, M.

    2015-05-01

    The apparent correlation between the specific star formation rate (sSFR) and total stellar mass (M⋆) of galaxies is a fundamental relationship indicating how they formed their stellar populations. To attempt to understand this relation, we hypothesize that the relation and its evolution is regulated by the increase in the stellar and gas mass surface density in galaxies with redshift, which is itself governed by the angular momentum of the accreted gas, the amount of available gas, and by self-regulation of star formation. With our model, we can reproduce the specific SFR - M⋆ relations at z ~ 1-2 by assuming gas fractions and gas mass surface densities similar to those observed for z = 1-2 galaxies. We further argue that it is the increasing angular momentum with cosmic time that causes a decrease in the surface density of accreted gas. The gas mass surface densities in galaxies are controlled by the centrifugal support (i.e., angular momentum), and the sSFR is predicted to increase as, sSFR(z) = (1 + z)3/tH0, as observed (where tH0 is the Hubble time and no free parameters are necessary). In addition, the simple evolution for the star-formation intensity we propose is in agreement with observations of Milky Way-like galaxies selected through abundance matching. At z ≳ 2, we argue that star formation is self-regulated by high pressures generated by the intense star formation itself. The star formation intensity must be high enough to either balance the hydrostatic pressure (a rather extreme assumption) or to generate high turbulent pressure in the molecular medium which maintains galaxies near the line of instability (i.e. Toomre Q ~ 1). We provide simple prescriptions for understanding these self-regulation mechanisms based on solid relationships verified through extensive study. In all cases, the most important factor is the increase in stellar and gas mass surface density with redshift, which allows distant galaxies to maintain high levels of s

  19. Angular momentum evolution during star and planetary system formation

    NASA Astrophysics Data System (ADS)

    Davies, Claire L.; Greaves, Jane S.

    2014-01-01

    We focused on analysing the role played by protoplanetary disks in the evolution of angular momentum during star formation. If all the angular momentum contained within collapsing pre-stellar cores was conserved during their formation, proto-stars would reach rotation rates exceeding their break-up velocities before they reached the main sequence (Bodenheimer 1995). In order to avoid this occuring, methods by which proto-stars can lose angular momentum must exist. Angular momentum can be transferred from star to disk via stellar magnetic field lines through a process called magnetic braking (Camenzind 1990; Königl 1991). Alternatively, the stellar angular momentum can be lost from the star-disk system entirely via stellar- or disk-winds (e.g. Pelletier & Pudritz 1992; Matt & Pudritz 2005). The proportion of lost stellar angular momentum retained within the protoplanetary disk is important to studies of planetary system formation. If the bulk motion within the disk remains Keplerian, any increase of angular momentum in the disk causes an outward migration of disk material and an expansion of the disk. Therefore, an increase in disk angular momentum may cause a reduction in the disk surface density, often used to indicate the disk's ability to form planets. We made use of multi-wavelength data available in the literature to directly calculate the stellar and disk angular momenta for two nearby regions of star formation. Namely, these were the densely populated and highly irradiated Orion Nebula Cluster (ONC) and the comparitively sparse Taurus-Auriga region. Due to the limited size of the ONC dataset, we produced an average surface density profile for the region. We modelled the stars as solid body rotators due to their fully convective nature (Krishnamurthi et al. 1997) and assumed the disks are flat and undergo Keplerian rotation about the same rotation axis as the star. We observed the older disks within each of the two star forming regions to be preferentially

  20. The ABC of Population III. [star formation and cosmological consequences

    NASA Technical Reports Server (NTRS)

    Carr, B. J.

    1986-01-01

    The author discusses the circumstances in which Population III stars are expected to form and examines their cosmological consequences. Consideration of their production of light, metals, and remnants places a strong constraint on their formation epoch and mass spectrum. However, these constraints would still allow Population III stars to provide the dark matter in galactic halos, a helium abundance of around 25 percent, a detectable background of gravitational waves, a possible infrared background, and the generation of large-scale cosmological structure through explosions. All of these features could be achieved by VMOs in the range 100 to 100,000 solar masses. On the other hand, the Population III scenario would be most compatible with the standard Big Bang picture if the stars were SMOs with mass around a million solar masses. Such stars could still provide the dark matter and detectable gravitational waves.

  1. Stellar signatures of AGN-jet-triggered star formation

    SciTech Connect

    Dugan, Zachary; Silk, Joseph; Bryan, Sarah; Gaibler, Volker; Haas, Marcel

    2014-12-01

    To investigate feedback between relativistic jets emanating from active galactic nuclei and the stellar population of the host galaxy, we analyze the long-term evolution of the orbits of the stars formed in the galaxy-scale simulations by Gaibler et al. of jets in massive, gas-rich galaxies at z ∼ 2-3. We find strong, jet-induced differences in the resulting stellar populations of galaxies that host relativistic jets and galaxies that do not, including correlations in stellar locations, velocities, and ages. Jets are found to generate distributions of increased radial and vertical velocities that persist long enough to effectively augment the stellar structure of the host. The jets cause the formation of bow shocks that move out through the disk, generating rings of star formation within the disk. The bow shock often accelerates pockets of gas in which stars form, yielding populations of stars with significant radial and vertical velocities, some of which have large enough velocities to escape the galaxy. These stellar population signatures can serve to identify past jet activity as well as jet-induced star formation.

  2. Connecting the Dense Gas and Young Stars in the CARMA Large Area Star Formation Survey

    NASA Astrophysics Data System (ADS)

    Mundy, Lee G.; Storm, Shaye; Looney, Leslie; Lee, Katherine I.; Fernandez Lopez, Manuel; Ostriker, Eve C.; Chen, Che-Yu; CLASSy Team

    2016-01-01

    The CARMA Large Area Star Formation Survey (CLASSy) imaged the dense gas structure and kinematics in five, roughly 1 pc scale regions in the Serpens and Perseus clouds with 7" angular resolution. The spatial distribution and Class of the young stellar population (YSOs) is available for these regions from the Spitzer c2d and Gould Belt surveys, with added sources from the Herschel 70 micron images. Together, these datasets allow us to compare, for the first time at similar spatial resolutions, the distributions of the dense gas and YSOs over regions containing up to 90 identified YSOs. This enables a detailed look at the separation between YSOs and the nearest dense gas peak and a measure of overall relationship between the YSO and dense gas distributions. We find that most Class 0 YSOs are forming in the highest column density regions: leaves in the dendrogram analysis utilized by CLASSy. In Serpens and Perseus, we find that 29% and 38%, respectively, of the leaves have identified embedded YSOs. Class 1 sources are less confined to leaf locations; Class II sources are distributed throughout regions, mostly away from hierarchical peaks. This trend could be due to a modest (0.1 km/sec) velocity difference between YSOs and their natal cores, or due to the YSOs consuming or dispersing their natal cores.

  3. STAR FORMATION EFFICIENCY IN THE COOL CORES OF GALAXY CLUSTERS

    SciTech Connect

    McDonald, Michael; Veilleux, Sylvain; Mushotzky, Richard; Reynolds, Christopher; Rupke, David S. N. E-mail: veilleux@astro.umd.edu

    2011-06-20

    We have assembled a sample of high spatial resolution far-UV (Hubble Space Telescope Advanced Camera for Surveys/Solar Blind Channel) and H{alpha} (Maryland-Magellan Tunable Filter) imaging for 15 cool core galaxy clusters. These data provide a detailed view of the thin, extended filaments in the cores of these clusters. Based on the ratio of the far-UV to H{alpha} luminosity, the UV spectral energy distribution, and the far-UV and H{alpha} morphology, we conclude that the warm, ionized gas in the cluster cores is photoionized by massive, young stars in all but a few (A1991, A2052, A2580) systems. We show that the extended filaments, when considered separately, appear to be star forming in the majority of cases, while the nuclei tend to have slightly lower far-UV luminosity for a given H{alpha} luminosity, suggesting a harder ionization source or higher extinction. We observe a slight offset in the UV/H{alpha} ratio from the expected value for continuous star formation which can be modeled by assuming intrinsic extinction by modest amounts of dust (E(B - V) {approx} 0.2) or a top-heavy initial mass function in the extended filaments. The measured star formation rates vary from {approx}0.05 M{sub sun} yr{sup -1} in the nuclei of non-cooling systems, consistent with passive, red ellipticals, to {approx}5 M{sub sun} yr{sup -1} in systems with complex, extended, optical filaments. Comparing the estimates of the star formation rate based on UV, H{alpha}, and infrared luminosities to the spectroscopically determined X-ray cooling rate suggests a star formation efficiency of 14{sup +18}{sub -8}%. This value represents the time-averaged fraction, by mass, of gas cooling out of the intracluster medium, which turns into stars and agrees well with the global fraction of baryons in stars required by simulations to reproduce the stellar mass function for galaxies. This result provides a new constraint on the efficiency of star formation in accreting systems.

  4. Formaldehyde Masers: Exclusive Tracers of High-mass Star Formation

    NASA Astrophysics Data System (ADS)

    Araya, E. D.; Olmi, L.; Morales Ortiz, J.; Brown, J. E.; Hofner, P.; Kurtz, S.; Linz, H.; Creech-Eakman, M. J.

    2015-11-01

    The detection of four formaldehyde (H2CO) maser regions toward young high-mass stellar objects in the last decade, in addition to the three previously known regions, calls for an investigation of whether H2CO masers are an exclusive tracer of young high-mass stellar objects. We report the first survey specifically focused on the search for 6 cm H2CO masers toward non high-mass star-forming regions (non HMSFRs). The observations were conducted with the 305 m Arecibo Telescope toward 25 low-mass star-forming regions, 15 planetary nebulae and post-AGB stars, and 31 late-type stars. We detected no H2CO emission in our sample of non HMSFRs. To check for the association between high-mass star formation and H2CO masers, we also conducted a survey toward 22 high-mass star-forming regions from a Hi-GAL (Herschel infrared Galactic Plane Survey) sample known to harbor 6.7 GHz CH3OH masers. We detected a new 6 cm H2CO emission line in G32.74-0.07. This work provides further evidence that supports an exclusive association between H2CO masers and young regions of high-mass star formation. Furthermore, we detected H2CO absorption toward all Hi-GAL sources, and toward 24 low-mass star-forming regions. We also conducted a simultaneous survey for OH (4660, 4750, 4765 MHz), H110α (4874 MHz), HCOOH (4916 MHz), CH3OH (5005 MHz), and CH2NH (5289 MHz) toward 68 of the sources in our sample of non HMSFRs. With the exception of the detection of a 4765 MHz OH line toward a pre-planetary nebula (IRAS 04395+3601), we detected no other spectral line to an upper limit of 15 mJy for most sources.

  5. STAR CLUSTER COMPLEXES AND THE HOST GALAXY IN THREE H II GALAXIES: Mrk 36, UM 408, AND UM 461

    SciTech Connect

    Lagos, P.; Telles, E.; Nigoche-Netro, A.

    2011-11-15

    We present a stellar population study of three H II galaxies (Mrk 36, UM 408, and UM 461) based on the analysis of new ground-based high-resolution near-infrared J, H, and K{sub p} broadband and Br{gamma} narrowband images obtained with Gemini/NIRI. We identify and determine the relative ages and masses of the elementary star clusters and/or star cluster complexes of the starburst regions in each of these galaxies by comparing the colors with evolutionary synthesis models that include the contribution of stellar continuum, nebular continuum, and emission lines. We found that the current star cluster formation efficiency in our sample of low-luminosity H II galaxies is {approx}10%. Therefore, most of the recent star formation is not in massive clusters. Our findings seem to indicate that the star formation mode in our sample of galaxies is clumpy, and that these complexes are formed by a few massive star clusters with masses {approx}>10{sup 4} M{sub Sun }. The age distribution of these star cluster complexes shows that the current burst started recently and likely simultaneously over short timescales in their host galaxies, triggered by some internal mechanism. Finally, the fraction of the total cluster mass with respect to the low surface brightness (or host galaxy) mass, considering our complete range in ages, is less than 1%.

  6. Formation, Evolution, and Survival of Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Fall, Michael

    2015-08-01

    This talk presents a synoptic theory for the formation, evolution, and survival of massive star clusters. These objects are important in the ecology of galaxies, as the sites of star formation and stellar feedback, as the building blocks of stellar populations. The talk is organized around the mass function of star clusters (i.e., the spectrum of cluster masses) and how it evolves with time (age). Observations show some remarkable similarities in the mass functions of clusters in different galaxies, analogous to the similarities in stellar initial mass functions (IMFs). Explaining the similarity of the mass functions of star clusters is one of the goals and successes of the theory presented here. A byproduct of this theory is a unified concept of star clusters of all types: associations, open clusters, populous clusters, globular clusters, etc. The physical processes that affect the mass functions of star clusters include the following: star formation and stellar feedback in the gas-dominated protoclusters, and the subsequent gravitational effects in the gas-free clusters, primarily stellar mass loss, tidal interactions with passing molecular clouds, and internal two-body relaxation. These processes all reduce the masses of clusters, thus lowering the amplitude of their mass function, but in such a way that the shape of the mass function is nearly preserved. The talk presents a quantitative, albeit approximate, analysis of all these effects. As a result of recent developments, there is now a growing connection between theory and observation in this field. The work presented here points to some future observations that would strengthen this connection.

  7. The interstellar medium and star formation in local galaxies: Variations of the star formation law in simulations

    SciTech Connect

    Becerra, Fernando; Escala, Andrés

    2014-05-01

    We use the adaptive mesh refinement code Enzo to model the interstellar medium (ISM) in isolated local disk galaxies. The simulation includes a treatment for star formation and stellar feedback. We get a highly supersonic turbulent disk, which is fragmented at multiple scales and characterized by a multi-phase ISM. We show that a Kennicutt-Schmidt relation only holds when averaging over large scales. However, values of star formation rates and gas surface densities lie close in the plot for any averaging size. This suggests an intrinsic relation between stars and gas at cell-size scales, which dominates over the global dynamical evolution. To investigate this effect, we develop a method to simulate the creation of stars based on the density field from the snapshots, without running the code again. We also investigate how the star formation law is affected by the characteristic star formation timescale, the density threshold, and the efficiency considered in the recipe. We find that the slope of the law varies from ∼1.4 for a free-fall timescale, to ∼1.0 for a constant depletion timescale. We further demonstrate that a power law is recovered just by assuming that the mass of the new stars is a fraction of the mass of the cell m {sub *} = ερ{sub gas}Δx {sup 3}, with no other physical criteria required. We show that both efficiency and density threshold do not affect the slope, but the right combination of them can adjust the normalization of the relation, which in turn could explain a possible bi-modality in the law.

  8. Observations of Protostellar Outflow Feedback in Clustered Star Formation

    NASA Astrophysics Data System (ADS)

    Nakamura, F.

    2016-05-01

    We discuss the role of protostellar outflow feedback in clustered star formation using the observational data of recent molecular outflow surveys toward nearby cluster-forming clumps. We found that for almost all clumps, the outflow momentum injection rate is significantly larger than the turbulence dissipation rate. Therefore, the outflow feedback is likely to maintain supersonic turbulence in the clumps. For less massive clumps such as B59, L1551, and L1641N, the outflow kinetic energy is comparable to the clump gravitational energy. In such clumps, the outflow feedback probably affects significantly the clump dynamics. On the other hand, for clumps with masses larger than about 200 M⊙, the outflow kinetic energy is significantly smaller than the clump gravitational energy. Since the majority of stars form in such clumps, we conclude that outflow feedback cannot destroy the whole parent clump. These characteristics of the outflow feedback support the scenario of slow star formation.

  9. CONNECTING GALAXIES, HALOS, AND STAR FORMATION RATES ACROSS COSMIC TIME

    SciTech Connect

    Conroy, Charlie; Wechsler, Risa H.

    2009-05-01

    A simple, observationally motivated model is presented for understanding how halo masses, galaxy stellar masses, and star formation rates are related, and how these relations evolve with time. The relation between halo mass and galaxy stellar mass is determined by matching the observed spatial abundance of galaxies to the expected spatial abundance of halos at multiple epochs, i.e., more massive galaxies are assigned to more massive halos at each epoch. This 'abundance matching' technique has been shown previously to reproduce the observed luminosity and scale dependence of galaxy clustering over a range of epochs. Halos at different epochs are connected by halo mass accretion histories estimated from N-body simulations. The halo-galaxy connection at fixed epochs in conjunction with the connection between halos across time provides a connection between observed galaxies across time. With approximations for the impact of merging and accretion on the growth of galaxies, one can then directly infer the star formation histories of galaxies as a function of stellar and halo mass. This model is tuned to match both the observed evolution of the stellar mass function and the normalization of the observed star formation rate (SFR)-stellar mass relation to z {approx} 1. The data demands, for example, that the star formation rate density is dominated by galaxies with M {sub star} {approx} 10{sup 10.0-10.5} M {sub sun} from 0 < z < 1, and that such galaxies over these epochs reside in halos with M {sub vir} {approx} 10{sup 11.5-12.5} M {sub sun}. The SFR-halo mass relation is approximately Gaussian over the range 0 < z < 1 with a mildly evolving mean and normalization. This model is then used to shed light on a number of issues, including (1) a clarification of {sup d}ownsizing{sup ,} (2) the lack of a sharp characteristic halo mass at which star formation is truncated, and (3) the dominance of star formation over merging to the stellar buildup of galaxies with M {sub star

  10. STAR FORMATION HISTORY OF A YOUNG SUPER-STAR CLUSTER IN NGC 4038/39: DIRECT DETECTION OF LOW-MASS PRE-MAIN SEQUENCE STARS

    SciTech Connect

    Greissl, Julia; Meyer, Michael R.; Christopher, Micol H.; Scoville, Nick Z.

    2010-02-20

    We present an analysis of the near-infrared spectrum of a young massive star cluster in the overlap region of the interacting galaxies NGC 4038/39 using population synthesis models. Our goal is to model the cluster population as well as provide rough constraints on its initial mass function (IMF). The cluster shows signs of youth, such as thermal radio emission and strong hydrogen emission lines in the near-infrared. Late-type absorption lines are also present which are indicative of late-type stars in the cluster. The strength and ratio of these absorption lines cannot be reproduced through either late-type pre-main sequence (PMS) stars or red supergiants alone. Thus, we interpret the spectrum as a superposition of two star clusters of different ages, which is feasible since the 1'' spectrum encompasses a physical region of {approx}90 pc and radii of super-star clusters (SSCs) are generally measured to be a few parsecs. One cluster is young (<= 3 Myr) and is responsible for part of the late-type absorption features, which are due to PMS stars in the cluster, and the hydrogen emission lines. The second cluster is older (6 Myr-18 Myr) and is needed to reproduce the overall depth of the late-type absorption features in the spectrum. Both are required to accurately reproduce the near-infrared spectrum of the object. Thus, we have directly detected PMS objects in an unresolved SSC for the first time using a combination of population synthesis models and PMS tracks. This analysis serves as a testbed of our technique to constrain the low-mass IMF in young SSCs as well as an exploration of the star formation history of young UC H II regions.

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

    SciTech Connect

    Harwit, Martin; Brisbin, Drew

    2015-02-20

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

  12. Time Dependent Models of Grain Formation Around Carbon Stars

    NASA Technical Reports Server (NTRS)

    Egan, M. P.; Shipman, R. F.

    1996-01-01

    Carbon-rich Asymptotic Giant Branch stars are sites of dust formation and undergo mass loss at rates ranging from 10(exp -7) to 10(exp -4) solar mass/yr. The state-of-the-art in modeling these processes is time-dependent models which simultaneously solve the grain formation and gas dynamics problem. We present results from such a model, which also includes an exact solution of the radiative transfer within the system.

  13. The optical flares of active star II Pegasi in 2005

    NASA Astrophysics Data System (ADS)

    Gu, Shenghong; Kim, Kang Min; Lee, Byeong-Cheol

    2015-08-01

    We observed the active star II Peg using high-resolution spectrographs of 2.16m telescope at Xinglong station of NAOC and 1.8m telescope at BOAO of KASI from November to December, 2005. By means of spectral subtraction technique, the chromospheric activities of II Peg are analyzed at several activity indicators, including CaII IRT, Hα, NaI D1D2 and HeI D3 lines. The results demonstrate that the magnetic activity of II Peg is very strong, and its chromospheric activities show rotational modulations which imply there are active regions in its chromosphere. Two flare events were hunted during the observations, which were identified by HeI D3 line emission above the continuum. The first flare was happened in November 2005, the second one in December 2005, and they were located in different hemisphere of the star. This may indicate the evolution of active regions. Considering the photospheric spot activities, the possible origin of the detected flares is discussed.

  14. ACCESS - IV. The quenching of star formation in a cluster population of dusty S0s

    NASA Astrophysics Data System (ADS)

    Haines, C. P.; Merluzzi, P.; Busarello, G.; Dopita, M. A.; Smith, G. P.; La Barbera, F.; Gargiulo, A.; Raychaudhury, S.; Smith, R. J.

    2011-11-01

    We present an analysis of the mid-infrared (MIR) colours of 165 70-μm-detected galaxies in the Shapley supercluster core (SSC) at z= 0.048 using panoramic Spitzer/MIPS 24- and 70-μm imaging. While the bulk of galaxies show f70/f24 colours typical of local star-forming galaxies, we identify a significant subpopulation of 23 70-μm-excess galaxies, whose MIR colours (f70/f24 > 25) are much redder and cannot be reproduced by any of the standard model IR spectral energy distributions (SEDs). These galaxies are found to be strongly concentrated towards the cores of the five clusters that make up the SSC, and also appear rare among local field galaxies, confirming them as a cluster-specific phenomenon. Their optical spectra and lack of significant ultraviolet emission imply little or no ongoing star formation, while fits to their panchromatic SEDs require the far-IR emission to come mostly from a diffuse dust component heated by the general interstellar radiation field rather than ongoing star formation. Most of these 70-μm-excess galaxies are identified as ˜L* S0s with smooth profiles. We find that almost every cluster galaxy in the process of star formation quenching is already either an S0 or Sa, while we find no passive galaxies of class Sb or later. Hence the formation of passive early-type galaxies in cluster cores must involve the prior morphological transformation of late-type spirals into Sa/S0s, perhaps via pre-processing or the impact of cluster tidal fields, before a subsequent quenching of star formation once the lenticular encounters the dense environment of the cluster core. In the cases of many cluster S0s, this phase of star formation quenching is characterized by an excess of 70-μm emission, indicating that the cold dust content is declining at a slower rate than star formation. We suggest that the excess 70-μm emission during quenching is due to either (i) a reduction of the star formation efficiency as proposed within the morphological quenching

  15. Connecting the density structure of molecular clouds and star formation.

    NASA Astrophysics Data System (ADS)

    Kainulainen, Jouni

    2015-08-01

    In the current paradigm of turbulence-regulated interstellar medium (ISM), star formation rates of entire galaxies are intricately linked to the density structure of the individual molecular clouds in the ISM. This density structure is essentially encapsulated in the probability distribution function of volume densities (rho-PDF), which directly affects the star formation rates predicted by analytic models. Contrasting its fundamental role, the rho-PDF function and its evolution have remained virtually unconstrained by observations. I describe in this contribution our recent progress in attaining observational constraints for the rho-PDFs of molecular clouds. Specifically, I review our first systematic determination of the rho-PDFs in Solar neighborhood molecular clouds. I will also present new evidence of the time evolution of the projected rho-PDFs, i.e., column density PDFs. These results together enable us to build the first observationally constrained link between the evolving density structure of molecular clouds and the star formation within. Finally, I discuss our work to expand the analysis into a Galactic context and to observationally connect the physical processes acting at the scale of molecular clouds with star formation at the scale of galaxies.

  16. SUPERNOVA REMNANTS AND STAR FORMATION IN THE LARGE MAGELLANIC CLOUD

    SciTech Connect

    Desai, Karna M.; Chu, You-Hua; Gruendl, Robert A.; Dluger, William; Katz, Marshall; Wong, Tony; Looney, Leslie W.; Chen, C.-H. Rosie; Hughes, Annie; Muller, Erik; Ott, Juergen; Pineda, Jorge L.

    2010-08-15

    It has often been suggested that supernova remnants (SNRs) can trigger star formation. To investigate the relationship between SNRs and star formation, we have examined the known sample of 45 SNRs in the Large Magellanic Cloud (LMC) to search for associated young stellar objects (YSOs) and molecular clouds. We find seven SNRs associated with both YSOs and molecular clouds, three SNRs associated with YSOs but not molecular clouds, and eight SNRs near molecular clouds but not associated with YSOs. Among the 10 SNRs associated with YSOs, the association between the YSOs and SNRs either can be rejected or cannot be convincingly established for eight cases. Only two SNRs have YSOs closely aligned along their rims; however, the time elapsed since the SNR began to interact with the YSOs' natal clouds is much shorter than the contraction timescales of the YSOs, and thus we do not see any evidence of SNR-triggered star formation in the LMC. The 15 SNRs that are near molecular clouds may trigger star formation in the future when the SNR shocks have slowed down to <45 km s{sup -1}. We discuss how SNRs can alter the physical properties and abundances of YSOs.

  17. Resolved Star Formation Law In Nearby Infrared-bright Galaxies

    NASA Astrophysics Data System (ADS)

    Rahman, Nurur; Bolatto, A.; Wong, T.; Leroy, A.; Ott, J.; Calzetti, D.; Blitz, L.; Walter, F.; Rosolowsky, E.; West, A.; Vogel, S.; Bigiel, F.; Xue, R.

    2009-05-01

    An accurate knowledge of star formation law is crucial to make progress in understanding galaxy formation and evolution. We are studying this topic using CARMA STING (Survey Toward Infrared-bright Nearby Galaxies), an interferometric CO survey of a sample of 27 star-forming nearby galaxies with a wealth of multi-wavelength data designed to study star formation in environments throughout the blue sequence at sub-kpc scales. We present results for NGC 4254 (M99), one of our sample galaxies. We construct star formation rate surface density (SFRSD) and gas (atomic and molecular) surface density indicators using a combination of high resolution data from CARMA, KPNO, Spitzer, IRAM and VLA. We find a tight correlation between SFRSD and molecular gas surface density (MGSD), whereas the relation between atomic gas surface density and SFRSD shows very large scatter. Within the central 6 kpc (radius) where CARMA is the most sensitive the MGSD derived from CO(1-0) and CO(2-1) shows similar trend, however, in the extended disk the slope, derived from CO(2-1) data alone, gets steeper.

  18. Star and cluster formation in NGC 1275

    NASA Technical Reports Server (NTRS)

    Richer, Harvey B.; Crabtree, Dennis R.; Fabian, A. C.; Lin, D. N. C.

    1993-01-01

    Luminous, blue, and unresolved objects have been found by imaging the nuclear region of the central galaxy in the Perseus Cluster, NGC 1275. Stellar formation in a cooling flow in which gas clouds confined by weak magnetic fields are allowed to remain at low densities is favored. Cloud-cloud collisions and coagulation in the high cloud density environment at the center of the galaxy then causes some clouds to become gravitationally unstable and to form globular clusters.

  19. Delayed Star Formation in Isolated Dwarf galaxies: Hubble Space Telescope Star Formation History of the Aquarius Dwarf Irregular

    NASA Astrophysics Data System (ADS)

    Cole, Andrew A.; Weisz, Daniel R.; Dolphin, Andrew E.; Skillman, Evan D.; McConnachie, Alan W.; Brooks, Alyson M.; Leaman, Ryan

    2014-11-01

    We have obtained deep images of the highly isolated (d = 1 Mpc) Aquarius dwarf irregular galaxy (DDO 210) with the Hubble Space Telescope Advanced Camera for Surveys. The resulting color-magnitude diagram (CMD) reaches more than a magnitude below the oldest main-sequence turnoff, allowing us to derive the star formation history (SFH) over the entire lifetime of the galaxy with a timing precision of ≈10% of the lookback time. Using a maximum likelihood fit to the CMD we find that only ≈10% of all star formation in Aquarius took place more than 10 Gyr ago (lookback time equivalent to redshift z ≈ 2). The star formation rate increased dramatically ≈6-8 Gyr ago (z ≈ 0.7-1.1) and then declined until the present time. The only known galaxy with a more extreme confirmed delay in star formation is Leo A, a galaxy of similar M H I /M sstarf, dynamical mass, mean metallicity, and degree of isolation. The delayed stellar mass growth in these galaxies does not track the mean dark matter accretion rate from CDM simulations. The similarities between Leo A and Aquarius suggest that if gas is not removed from dwarf galaxies by interactions or feedback, it can linger for several gigayears without cooling in sufficient quantity to form stars efficiently. We discuss possible causes for the delay in star formation including suppression by reionization and late-time mergers. We find reasonable agreement between our measured SFHs and select cosmological simulations of isolated dwarfs. Because star formation and merger processes are both stochastic in nature, delayed star formation in various degrees is predicted to be a characteristic (but not a universal) feature of isolated small galaxies. Based on observations made with the NASA/ESA Hubble Space Telescope, 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. These observations were obtained under program GO

  20. Morphology, star formation, and nuclear activity in void galaxies

    NASA Astrophysics Data System (ADS)

    Wiedmann, Sophia; Miller, Brendan; Gallo, Elena; Pazar, Beni; Alfvin, Erik

    2015-01-01

    We report on new Chandra observations of six early-type galaxies located within cosmic voids, from a program examining the influence of Mpc-scale environment upon star formation and low-level supermassive black hole activity. Simple feedback prescriptions are predicted to operate independently of the surrounding density once outside the dark matter halo, and further link star formation quenching to black hole activity. Alternatively, mediation of the cold gas supply by the large-scale environment, for example through increased cold-stream accretion and reduced harassment or stripping within more isolated regions, could mutually enhance star formation and (perhaps indirectly) low-level supermassive black hole activity. The six targeted early-type galaxies have comparable stellar masses of 6-9e10 solar, chosen to be near the predicted "critical value" for efficient feedback, but span a wide range of star-formation rates. Specifically, they have SFRs of 6.5, 1.4, 0.45, 0.10, 0.04, and 0.03 solar masses per year. All galaxies are detected in the Chandra ACIS-S observations with 0.3-8 keV X-ray luminosities ranging from 2e39 to 1e41 erg/s. Specifically, they have log Lx values of 40.4, 41.1, 41.1, 39.3, 39.2, and 39.2, again ordered by decreasing SFR. The three galaxies with moderate-to-high star formation rates have nuclear X-ray luminosities that are significantly greater than those of the three galaxies with low star formation rates. This result is more consistent with a symbiotic relationship between current low-level star formation and supermassive black hole activity than with simple feedback quenching models. We additionally situate these galaxies in the context of void and cluster galaxies in the local universe, model their optical surface brightness profiles and color gradients, discuss caveats including the possibility of X-ray binary contamination, and consider other supermassive black hole activity indicators.

  1. Coronagraphic imaging of pre-main-sequence stars: Remnant evvelopes of star formation seen in reflection

    NASA Technical Reports Server (NTRS)

    Nakajima, Tadashi; Golimowski, David A.

    1995-01-01

    We have obtained R- and I-band coronagraphic images of the vicinities of 11 pre-main sequence (PMS) stars to search for faint, small-scale reflection nebulae. The inner radius of the search and the field of view are 1.9 arcsec and 1x1 arcmin, respectively. Reflection nebulae were imaged around RY Tau, T Tau,DG Tau, SU Aur, AB Aur, FU Ori, and Z CMa. No nebulae were detected around HBC 347, GG Tau, V773 Tau, and V830 Tau. Categorically speaking, most of the classical T Tauri program stars and all the FU Orionis-type program stars are associated with the reflection nebulae, while none of the weak-line T Tauri program stars are associated with nebulae. The detected nebulae range in size from 250 to 37 000 AU. From the brightness ratios of the stars and nebulae, we obtain a lower limit to the visual extinction of PMS star light through the nebulae of (A(sub V))(sub neb) = 0.1. The lower limits of masses and volume densities of the nebulae associated with the classical T Tauri stars are 10(exp-6) Solar mass and N(sub H) = 10(exp 5)/cu cm, respectively. Lower limits for the nebulae around FU Orionis stars are 10(exp -5) Solar mass and n(sub H) = 10 (exp 5)/cu cm, respectively. Some reflection nebulae may trace the illuminated surfaces of the optically thick dust nebulae, so these mass estimates are not stringent. All the PMS stars with associated nebulae are strong far-infrared emitters. Both the far-infrared emission and the reflection nebulae appear to originate from the remnant envelopes of star formation. The 100 micrometers emitting regions of SU Aur and FU Ori are likely to be cospatial with the reflection nebulae. A spatial discontinuity between FU Ori and its reflection nebula may explain the dip in the far-infrared spectral energy distribution at 60 micrometers. The warped, disk-like nebulae around T Tau and Z CMa are aligned with and embrace the inner star/circumstellar disk systems. The arc-shaped nebula around DG Tau may be in contact with the coaligned inner

  2. On the Interplay between Star Formation and Feedback in Galaxy Formation Simulations

    NASA Astrophysics Data System (ADS)

    Agertz, Oscar; Kravtsov, Andrey V.

    2015-05-01

    We investigate the star formation-feedback cycle in cosmological galaxy formation simulations, focusing on the progenitors of Milky Way (MW)-sized galaxies. We find that in order to reproduce key properties of the MW progenitors, such as semi-empirically derived star formation histories (SFHs) and the shape of rotation curves, our implementation of star formation and stellar feedback requires (1) a combination of local early momentum feedback via radiation pressure and stellar winds, and subsequent efficient supernovae feedback, and (2) an efficacy of feedback that results in the self-regulation of the global star formation rate on kiloparsec scales. We show that such feedback-driven self-regulation is achieved globally for a local star formation efficiency per free fall time of {{ɛ }ff}≈ 10%. Although this value is larger that the {{ɛ }ff}˜ 1% value usually inferred from the Kennicutt-Schmidt (KS) relation, we show that it is consistent with direct observational estimates of {{ɛ }ff} in molecular clouds. Moreover, we show that simulations with local efficiency of {{ɛ }ff}≈ 10% reproduce the global observed KS relation. Such simulations also reproduce the cosmic SFH of the MW-sized galaxies and satisfy a number of other observational constraints. Conversely, we find that simulations that a priori assume an inefficient mode of star formation, instead of achieving it via stellar feedback regulation, fail to produce sufficiently vigorous outflows and do not reproduce observations. This illustrates the importance of understanding the complex interplay between star formation and feedback, and the detailed processes that contribute to the feedback-regulated formation of galaxies.

  3. Star formation rates in luminous quasars at 2 < z < 3

    NASA Astrophysics Data System (ADS)

    Harris, Kathryn; Farrah, Duncan; Schulz, Bernhard; Hatziminaoglou, Evanthia; Viero, Marco; Anderson, Nick; Béthermin, Matthieu; Chapman, Scott; Clements, David L.; Cooray, Asantha; Efstathiou, Andreas; Feltre, Anne; Hurley, Peter; Ibar, Eduardo; Lacy, Mark; Oliver, Sebastian; Page, Mathew J.; Pérez-Fournon, Ismael; Petty, Sara M.; Pitchford, Lura K.; Rigopoulou, Dimitra; Scott, Douglas; Symeonidis, Myrto; Vieira, Joaquin; Wang, Lingyu

    2016-04-01

    We investigate the relation between star formation rates (dot{{M}}_s) and AGN properties in optically selected type 1 quasars at 2 < z < 3 using data from Herschel and the SDSS. We find that dot{{M}}_s remains approximately constant with redshift, at 300 ± 100 M⊙ yr-1. Conversely, dot{{M}}_s increases with AGN luminosity, up to a maximum of ˜ 600 M⊙ yr-1, and with C IV FWHM. In context with previous results, this is consistent with a relation between dot{{M}}_s and black hole accretion rate (dot{{M}}_{bh}) existing in only parts of the z-dot{{M}}s-dot{{M}}_{bh} plane, dependent on the free gas fraction, the trigger for activity, and the processes that may quench star formation. The relations between dot{{M}}_s and both AGN luminosity and C IV FWHM are consistent with star formation rates in quasars scaling with black hole mass, though we cannot rule out a separate relation with black hole accretion rate. Star formation rates are observed to decline with increasing C IV equivalent width. This decline can be partially explained via the Baldwin effect, but may have an additional contribution from one or more of three factors; Mi is not a linear tracer of L2500, the Baldwin effect changes form at high AGN luminosities, and high C IV EW values signpost a change in the relation between dot{{M}}_s and dot{{M}}_{bh}. Finally, there is no strong relation between dot{{M}}_s and Eddington ratio, or the asymmetry of the C IV line. The former suggests that star formation rates do not scale with how efficiently the black hole is accreting, while the latter is consistent with C IV asymmetries arising from orientation effects.

  4. Inefficient star formation in extremely metal poor galaxies.

    PubMed

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

    2014-10-16

    The first galaxies contain stars born out of gas with few or no 'metals' (that is, elements heavier than helium). The lack of metals is expected to inhibit efficient gas cooling and star formation, but this effect has yet to be observed in galaxies with an oxygen abundance (relative to hydrogen) below a tenth of that of the Sun. Extremely metal poor nearby galaxies may be our best local laboratories for studying in detail the conditions that prevailed in low metallicity galaxies at early epochs. Carbon monoxide emission is unreliable as a tracer of gas at low metallicities, and while dust has been used to trace gas in low-metallicity galaxies, low spatial resolution in the far-infrared has typically led to large uncertainties. Here we report spatially resolved infrared observations of two galaxies with oxygen abundances below ten per cent of the solar value, and show that stars formed very inefficiently in seven star-forming clumps in these galaxies. The efficiencies are less than a tenth of those found in normal, metal rich galaxies today, suggesting that star formation may have been very inefficient in the early Universe. PMID:25318522

  5. Inefficient star formation in extremely metal poor galaxies

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  6. Characterizing star cluster formation with WISE: 652 newly found star clusters and candidates

    NASA Astrophysics Data System (ADS)

    Camargo, D.; Bica, E.; Bonatto, C.

    2016-01-01

    We report the discovery of 652 star clusters, stellar groups and candidates in the Milky Way with Wide-field Infrared Survey Explorer (WISE). Most of the objects are projected close to Galactic plane and are embedded clusters. The present sample complements a similar study (Paper I) which provided 437 star clusters and alike. We find evidence that star formation processes span a wide range of sizes, from populous dense clusters to small compact embedded ones, sparse stellar groups or in relative isolation. The present list indicates multiple stellar generations during the embedded phase, with giant molecular clouds collapsing into several clumps composing an embedded cluster aggregate. We investigate the field star decontaminated colour-magnitude diagrams and radial density profiles of nine cluster candidates in the list, and derive their parameters, confirming them as embedded clusters.

  7. EXTENDED STAR FORMATION IN THE INTERMEDIATE-AGE LARGE MAGELLANIC CLOUD STAR CLUSTER NGC 2209

    SciTech Connect

    Keller, Stefan C.; Mackey, A. Dougal; Da Costa, Gary S.

    2012-12-10

    We present observations of the 1 Gyr old star cluster NGC 2209 in the Large Magellanic Cloud made with the GMOS imager on the Gemini South Telescope. These observations show that the cluster exhibits a main-sequence turnoff that spans a broader range in luminosity than can be explained by a single-aged stellar population. This places NGC 2209 amongst a growing list of intermediate-age (1-3 Gyr) clusters that show evidence for extended or multiple epochs of star formation of between 50 and 460 Myr in extent. The extended main-sequence turnoff observed in NGC 2209 is a confirmation of the prediction in Keller et al. made on the basis of the cluster's large core radius. We propose that secondary star formation is a defining feature of the evolution of massive star clusters. Dissolution of lower mass clusters through evaporation results in only clusters that have experienced secondary star formation surviving for a Hubble time, thus providing a natural connection between the extended main-sequence turnoff phenomenon and the ubiquitous light-element abundance ranges seen in the ancient Galactic globular clusters.

  8. Massive Star Formation: Characterising Infall and Outflow in dense cores.

    NASA Astrophysics Data System (ADS)

    Akhter, Shaila; Cunningham, Maria; Harvey-Smith, Lisa; Jones, Paul Andrew; Purcell, Cormac; Walsh, Andrew John

    2015-08-01

    Massive stars are some of the most important objects in the Universe, shaping the evolution of galaxies, creating chemical elements, and hence shaping the evolution of the Universe. However, the processes by which they form, and how they shape their environment during their birth processes, are not well understood. We are using NH3 data from the "The H2O Southern Galactic Plane Survey" (HOPS) to define the positions of dense cores/clumps of gas in the southern Galactic plane that are likely to form stars. Due to its effective critical density, NH3 can detect massive star forming regions effectively compared to other tracers. We did a comparative study with different methods for finding clumps and found Fellwalker as the best. We found ~ 10% of the star forming clumps with multiple components and ~ 90% clumps with single component along the line of sight. Then, using data from the "The Millimetre Astronomy Legacy Team 90 GHz" (MALT90) survey, we search for the presence of infall and outflow associated with these cores. We will subsequently use the "3D Molecular Line Radiative Transfer Code" (MOLLIE) to constrain properties of the infall and outflow, such as velocity and mass flow. The aim of the project is to determine how common infall and outflow are in star forming cores, hence providing valuable constraints on the timescales and physical process involved in massive star formation.

  9. IR Emission Models from High-Mass Star Formation Cores

    NASA Astrophysics Data System (ADS)

    Campbell, M. F.; Deutsch, L. K.

    2001-12-01

    Recognition that high-mass stars form only in clusters has motivated us to make new radiative transfer models for infrared emission from compact, dense cloud cores surrounding very young high-mass stars. We assume outer cloud radii are limited by the formation of stars in clusters to 0.1 pc. Since there is a high efficiency of conversion of gas into stars within clusters, we assumed the mass of gas and dust in the cloud models is equal or less than the mass of the central star. We assumed Draine and Lee (1984) dust properties with 100:1 gas to dust mass ratio, and used the Egan, Leung, and Spagna (1988) radiative transfer code. The central star in all models is an O8 ZAMS type at 1700 pc distance (the distance to NGC6334). The dust emitting clouds were assumed to have inner cavities of radius 0.006 pc, just outside an ultracompact HII region. Density distributions were taken as uniform or proportional to r-3/2. Except for the highest mass clouds, the models showed the 10 micron silicate feature in emission rather than self absorption. All models' spectral energy distributions peak shortward of 50 microns. The lack of silicate self absorption and the SEDs peaking shortward of 50 microns are apparently due to the small size of these models. In order to match observed silicate absorption in UCHIIs, an external cold absorbing component must be added to the models. The results suggest that individual high mass star-formation cores should be searched for in mid-infrared rather than far-infrared wavelengths, and that SEDs which peak in the far- infrared are at least partly produced by separate, larger outer cloud envelopes. Draine, B. T. & Lee, H. M. 1984 ApJ, 285, 89; Egan, M.P., Leung, C.M., & Spagna, G.F, Jr. 1988 Comput. Phys. Comm., 48, 271

  10. The star formation histories of Hickson compact group galaxies

    NASA Astrophysics Data System (ADS)

    Plauchu-Frayn, I.; Del Olmo, A.; Coziol, R.; Torres-Papaqui, J. P.

    2012-10-01

    Aims: We study the star formation fistory (SFH) of 210 galaxy members of 55 Hickson compact groups (HCG) and 309 galaxies from the Catalog of Isolated Galaxies (CIG). The SFH traces the variation of star formation over the lifetime of a galaxy, and consequently yields a snapshot picture of its formation. Comparing the SFHs in these extremes in galaxy density allows us to determine the main effects of compact groups (CG) on the formation of galaxies. Methods: We fit our spectra using the spectral synthesis code STARLIGHT and obtained the stellar population contents and mean stellar ages of HCG and CIG galaxies in three different morphological classes: early-type galaxies (EtG), early-type spirals (EtS), and late-type spirals (LtS). Results: We find that EtG and EtS galaxies in HCG show higher contents of old and intermediate stellar populations as well as an important deficit of the young stellar population, which clearly implies an older average stellar age in early galaxies in HCG. For LtS galaxies we find similar mean values for the stellar content and age in the two samples. However, we note that LtS can be split into two subclasses, namely old and young LtS. In HCG we find a higher fraction of young LtS than in the CIG sample, in addition, most of these galaxies belong to groups in which most of the galaxies are also young and actively forming stars. The specific star formation rate (SSFR) of spiral galaxies in the two samples differ. The EtS in HCG show lower SSFR values, while LtS peak at higher values compared with their counterparts in isolation. We also measured the shorter star formation time scale (SFTS) in HCG galaxies, which indicates that they have a shorter star formation activity than CIG galaxies. We take these observations as evidence that galaxies in CG have evolved more rapidly than galaxies in isolation, regardless of their morphology. Our observations are consistent with the hierarchical galaxy formation model, which states that CGs are

  11. PRIMUS: Enhanced Specific Star Formation Rates in Close Galaxy Pairs