Science.gov

Sample records for star formation galaxies

  1. 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.

  2. 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)

  3. 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.

  4. 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.

  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. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. Star Formation from Galaxies to Globules

    NASA Astrophysics Data System (ADS)

    Elmegreen, Bruce G.

    2002-09-01

    result from turbulence compression in a self-gravitating gas, in which case their mass fraction can be estimated from the density distribution function that results from turbulence. For Wada & Norman's lognormal function that arises in whole-galaxy simulations, the theoretically predicted mass fraction of star-forming material is the same as that observed directly from the galactic Schmidt law and is ~10-4. The unified view explains how independent star formation processes can combine into the empirical laws while preserving the fractal nature of interstellar gas and the pressurized, wind-swept appearance of most small-scale clouds. Likely variations in the relative roles of these processes from region to region should not affect the large-scale average star formation rate. Self-regulation by spiral instabilities and star formation ensures that most regions are in a marginally stable state in which turbulence limits the mass available for star formation and the overall rate is independent of the nature of the energy sources. In this sense, star formation is saturated to its largest possible value given the fractal nature of the interstellar medium. Invited paper, based on the Heineman Prize lecture presented at the 199th meeting of the American Astronomical Society in 2002 January.

  7. 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.

  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. 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. 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.

  12. 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.

  13. 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%.

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. Environmentally driven star formation during a super galaxy group merger

    NASA Astrophysics Data System (ADS)

    Monroe, Jonathan; Tran, Kim-Vy; Gonzalez, Anthony H.

    2016-01-01

    We find evidence for outside-in growth of galaxies within a merging super galaxy group at a redshift of z~0.37. We utilize Hubble Space Telescope imaging in rest-frame UV and visual to measure color gradients across the super group and internally within 138 individual galaxies that are spectroscopically confirmed members. The group members show enhanced star formation at intermediate environmental densities. The high resolution imaging shows that the group galaxies have bluer disks, i.e. most of the new stars are forming in the disk which supports outside-in growth. These disk-dominated galaxies will likely fade to become S0 members.

  20. 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.

  1. 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.

  2. 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.

  3. Recent Galaxy Mergers and Residual Star Formation of Red Sequence Galaxies in Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Sheen, Yun-Kyeong; Yi, Sukyoung K.; Ree, Chang H.; Jaffé, Yara; Demarco, Ricardo; Treister, Ezequiel

    2016-08-01

    This study explored the Galaxy Evolution Explorer ultraviolet (UV) properties of optical red sequence galaxies in four rich Abell clusters at z≤slant 0.1. In particular, we tried to find a hint of merger-induced recent star formation (RSF) in red sequence galaxies. Using the NUV - r\\prime colors of the galaxies, RSF fractions were derived based on various criteria for post-merger galaxies and normal galaxies. Following k-correction, about 36% of the post-merger galaxies were classified as RSF galaxies with a conservative criterion (NUV - r\\prime ≤slant 5), and that number was doubled (∼72%) when using a generous criterion (NUV - r\\prime ≤slant 5.4). The trend was the same when we restricted the sample to galaxies within 0.5 × R 200. Post-merger galaxies with strong UV emission showed more violent, asymmetric features in the deep optical images. The RSF fractions did not show any trend along the clustocentric distance within R 200. We performed a Dressler–Shectman test to check whether the RSF galaxies had any correlation with the substructures in the galaxy clusters. Within R 200 of each cluster, the RSF galaxies did not appear to be preferentially related to the clusters’ substructures. Our results suggested that only 30% of RSF red sequence galaxies show morphological hints of recent galaxy mergers. This implies that internal processes (e.g., stellar mass loss or hot gas cooling) for the supply of cold gas to early-type galaxies may play a significant role in the residual star formation of early-type galaxies at a recent epoch.

  4. Recent Galaxy Mergers and Residual Star Formation of Red Sequence Galaxies in Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Sheen, Yun-Kyeong; Yi, Sukyoung K.; Ree, Chang H.; Jaffé, Yara; Demarco, Ricardo; Treister, Ezequiel

    2016-08-01

    This study explored the Galaxy Evolution Explorer ultraviolet (UV) properties of optical red sequence galaxies in four rich Abell clusters at z≤slant 0.1. In particular, we tried to find a hint of merger-induced recent star formation (RSF) in red sequence galaxies. Using the NUV - r\\prime colors of the galaxies, RSF fractions were derived based on various criteria for post-merger galaxies and normal galaxies. Following k-correction, about 36% of the post-merger galaxies were classified as RSF galaxies with a conservative criterion (NUV - r\\prime ≤slant 5), and that number was doubled (˜72%) when using a generous criterion (NUV - r\\prime ≤slant 5.4). The trend was the same when we restricted the sample to galaxies within 0.5 × R 200. Post-merger galaxies with strong UV emission showed more violent, asymmetric features in the deep optical images. The RSF fractions did not show any trend along the clustocentric distance within R 200. We performed a Dressler–Shectman test to check whether the RSF galaxies had any correlation with the substructures in the galaxy clusters. Within R 200 of each cluster, the RSF galaxies did not appear to be preferentially related to the clusters’ substructures. Our results suggested that only 30% of RSF red sequence galaxies show morphological hints of recent galaxy mergers. This implies that internal processes (e.g., stellar mass loss or hot gas cooling) for the supply of cold gas to early-type galaxies may play a significant role in the residual star formation of early-type galaxies at a recent epoch.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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

  10. 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

  11. 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.

  12. Inhibition of star formation in Sa galaxies

    SciTech Connect

    Pompea, S.M.; Rieke, G.H. )

    1989-07-01

    Only 4 percent of Sas in the Revised Shapley-Ames Catalog with B(T) less than 12 have an infrared luminosity greater than 10 to the 10th solar. This proportion is about one-sixth of the corresponding one for Sbs and Scs. Although the infrared luminosities of most Sa galaxies are dominated by disk emission, the same trend appears in the incidence of nuclear starbursts. IRAS measurements indicate that no more than three Sas out of the entire RSA sample of 166 galaxies have nuclear starbursts that cannot be associated with interactions or active nuclei. Plots of H I fluxes do not strongly correlate with infrared fluxes. Similarly, for at least the infrared selected Sas, the trend of IR flux with CO flux is similar to that of later type spiral galaxies. This would imply that molecular cloud formation is inhibited in Sas, leading to the lack of infrared activity. 38 refs.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. Star Formation Bimodality in Early-type Galaxies

    NASA Astrophysics Data System (ADS)

    Amblard, A.; Riguccini, L.; Temi, P.; Im, S.; Fanelli, M.; Serra, P.

    2014-03-01

    We compute the properties of a sample of 221 local, early-type galaxies with a spectral energy distribution (SED) modeling software, CIGALEMC. Concentrating on the star-forming (SF) activity and dust contents, we derive parameters such as the specific star formation rate (sSFR), the dust luminosity, dust mass, and temperature. In our sample, 52% is composed of elliptical (E) galaxies and 48% of lenticular (S0) galaxies. We find a larger proportion of S0 galaxies among galaxies with a large sSFR and large specific dust emission. The stronger activity of S0 galaxies is confirmed by larger dust masses. We investigate the relative proportion of active galactic nuclei (AGNs) and SF galaxies in our sample using spectroscopic Sloan Digital Sky Survey data and near-infrared selection techniques, and find a larger proportion of AGN-dominated galaxies in the S0 sample than the E one. This could corroborate a scenario where blue galaxies evolve into red ellipticals by passing through an S0 AGN active period while quenching its star formation. Finally, we find a good agreement comparing our estimates with color indicators.

  18. Star formation bimodality in early-type galaxies

    SciTech Connect

    Amblard, A.; Riguccini, L.; Temi, P.; Im, S.; Fanelli, M.; Serra, P.

    2014-03-10

    We compute the properties of a sample of 221 local, early-type galaxies with a spectral energy distribution (SED) modeling software, CIGALEMC. Concentrating on the star-forming (SF) activity and dust contents, we derive parameters such as the specific star formation rate (sSFR), the dust luminosity, dust mass, and temperature. In our sample, 52% is composed of elliptical (E) galaxies and 48% of lenticular (S0) galaxies. We find a larger proportion of S0 galaxies among galaxies with a large sSFR and large specific dust emission. The stronger activity of S0 galaxies is confirmed by larger dust masses. We investigate the relative proportion of active galactic nuclei (AGNs) and SF galaxies in our sample using spectroscopic Sloan Digital Sky Survey data and near-infrared selection techniques, and find a larger proportion of AGN-dominated galaxies in the S0 sample than the E one. This could corroborate a scenario where blue galaxies evolve into red ellipticals by passing through an S0 AGN active period while quenching its star formation. Finally, we find a good agreement comparing our estimates with color indicators.

  19. Assessing and understanding diversity in galaxy star formation histories

    NASA Astrophysics Data System (ADS)

    Abramson, Louis Evan

    Galaxy star formation histories (SFHs) form a central thread of the cosmological narrative. Assessing and understanding them is therefore a central mission of the study of galaxy evolution. Although an ever-better picture is emerging of the build-up of the stellar mass of the average galaxy over time, the relevance of this track to the growth of individual galaxies is unclear. Largely, this ambiguity is due to the availability of only loose, ensemble-level constraints at any redshift appreciably greater than zero. In this thesis, I outline how these constraints --- principally the cosmic star formation rate density, stellar mass function, and the star formation rate/stellar mass relation --- shape empirically based SFH models, especially in terms of the diversity of paths leading to a given end-state. Along the way, I show that three models propose very different answers to this question, corresponding (largely) to three different interpretations of the scatter in instantaneous galaxy growth rates at fixed stellar mass. I describe how these interpretations affect one's stance on the fundamental importance of so-called galaxy "bimodality" and quenching mechanisms, the influence of environment, and the role starbursts play in galaxy evolution. Ultimately, I conclude that there is insufficient evidence at present to select one interpretation over all others, but suggest that the situation might soon be resolved by upcoming observations that could clearly identify which model (or hybrid) is the most accurate description of galaxy growth.

  20. PRIMUS: Enhanced Specific Star Formation Rates in Close Galaxy Pairs

    NASA Astrophysics Data System (ADS)

    Wong, Kenneth C.; Blanton, Michael R.; Burles, Scott M.; Coil, Alison L.; Cool, Richard J.; Eisenstein, Daniel J.; Moustakas, John; Zhu, Guangtun; Arnouts, Stéphane

    2011-02-01

    Tidal interactions between galaxies can trigger star formation, which contributes to the global star formation rate (SFR) density of the universe and could be a factor in the transformation of blue, star-forming galaxies to red, quiescent galaxies over cosmic time. We investigate tidally triggered star formation in isolated close galaxy pairs drawn from the Prism Multi-Object Survey (PRIMUS), a low-dispersion prism redshift survey that has measured ~120,000 robust galaxy redshifts over 9.1 deg2 out to z ~ 1. We select a sample of galaxies in isolated galaxy pairs at redshifts 0.25 <= z <= 0.75, with no other objects within a projected separation of 300 h -1 kpc and Δz/(1 + z) = 0.01, and compare them to a control sample of isolated galaxies to test for systematic differences in their rest-frame FUV - r and NUV - r colors as a proxy for relative specific star formation rates (SSFRs). We find that galaxies in rp <= 50 h -1 kpc pairs have bluer dust-corrected UV - r colors on average than the control galaxies by -0.134 ± 0.045 mag in FUV - r and -0.075 ± 0.038 mag in NUV - r, corresponding to an ~15%-20% increase in SSFR. This indicates an enhancement in SSFR due to tidal interactions. We also find that this relative enhancement is greater for a subset of rp <= 30 h -1 kpc pair galaxies, for which the average color offsets are -0.193 ± 0.065 mag in FUV - r and -0.159 ± 0.048 mag in NUV - r, corresponding to an ~25%-30% increase in SSFR. We test for evolution in the enhancement of tidally triggered star formation with redshift across our sample redshift range and find marginal evidence for a decrease in SSFR enhancement from 0.25 <= z <= 0.5 to 0.5 <= z <= 0.75. This indicates that a change in enhanced star formation triggered by tidal interactions in low-density environments is not a contributor to the decline in the global SFR density across this redshift range.

  1. 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

  2. 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

  3. Turbulence and Star Formation in a Sample of Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Maier, Erin R.; Hunter, Deidre Ann; Chien, Li-Hsin

    2016-01-01

    We investigate turbulent gas motions in spiral galaxies and their importance to star formation in far outer disks, where the column density is typically far below the critical value for spontaneous gravitational collapse. Following the methods of Burkhart et al. (2010) as applied to the Small Magellanic Cloud, we use the third and fourth statistical moments, skewness and kurtosis, which are indicators of structures caused by turbulence, to examine the integrated neutral hydrogen (Hι) column density of a sample of spiral galaxies selected from The Hι Nearby Galaxy Survey (THINGS, Walter et al. 2008). We examine the kurtosis and skewness values of each galaxy as a whole, as well as their variation as a function of radius and in discrete sub-regions defined by a square, moving 'kernel,' essentially splitting each galaxy into a grid. We then create individual grid maps of kurtosis and skewness for each galaxy. To investigate the relation between these moments and star formation, we compare these maps with maps of each galaxy's far-ultraviolet (FUV) image, taken by the Galaxy Evolution Explorer (GALEX) satellite. We find that the moments are largely uniform across the galaxies: the variation does not appear to trace any star forming regions. This may, however, be due to the spatial resolution of our analysis, which could potentially limit the scale of turbulent motions to at most ~700 pc. From our analysis of the comparison between the two moments themselves, we find that the gas motions in our sample galaxies are largely supersonic. This analysis shows that Burkhart et al. (2010)'s methods may be applied not just to dwarf galaxies but normal spiral galaxies as well.We acknowledge the NSF for their funding of this work through their Research Experience for Undergraduates (REU) program (Grant No. AST-1461200).

  4. 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

  5. Decreased specific star formation rates in AGN host galaxies

    NASA Astrophysics Data System (ADS)

    Shimizu, T. Taro; Mushotzky, Richard F.; Meléndez, Marcio; Koss, Michael; Rosario, David J.

    2015-09-01

    We investigate the location of an ultra-hard X-ray selected sample of active galactic nuclei (AGN) from the Swift Burst Alert Telescope (BAT) catalogue with respect to the main sequence (MS) of star-forming galaxies using Herschel-based measurements of the star formation rate (SFR) and M*'s from Sloan Digital Sky Survey photometry where the AGN contribution has been carefully removed. We construct the MS with galaxies from the Herschel Reference Survey and Herschel Stripe 82 Survey using the exact same methods to measure the SFR and M* as the Swift/BAT AGN. We find that a large fraction of the Swift/BAT AGN lie below the MS indicating decreased specific SFR (sSFR) compared to non-AGN galaxies. The Swift/BAT AGN are then compared to a high-mass galaxy sample (CO Legacy Database for GALEX Arecibo SDSS Survey, COLD GASS), where we find a similarity between the AGN in COLD GASS and the Swift/BAT AGN. Both samples of AGN lie firmly between star-forming galaxies on the MS and quiescent galaxies far below the MS. However, we find no relationship between the X-ray luminosity and distance from the MS. While the morphological distribution of the BAT AGN is more similar to star-forming galaxies, the sSFR of each morphology is more similar to the COLD GASS AGN. The merger fraction in the BAT AGN is much higher than the COLD GASS AGN and star-forming galaxies and is related to distance from the MS. These results support a model in which bright AGN tend to be in high-mass star-forming galaxies in the process of quenching which eventually starves the supermassive black hole itself.

  6. 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.

  7. 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.

  8. THE CURRENT STAR FORMATION RATE OF K+A GALAXIES

    SciTech Connect

    Nielsen, Danielle M.; Ridgway, Susan E.; De Propris, Roberto; Goto, Tomotsugu

    2012-12-20

    We derive the stacked 1.4 GHz flux from the FIRST survey for 811 K+A galaxies selected from the Sloan Digital Sky Survey Data Release 7. For these objects we find a mean flux density of 56 {+-} 9 {mu}Jy. A similar stack of radio-quiet white dwarfs yields an upper limit of 43 {mu}Jy at a 5{sigma} significance to the flux in blank regions of the sky. This implies an average star formation rate of 1.6 {+-} 0.3 M{sub Sun} yr{sup -1} for K+A galaxies. However, the majority of the signal comes from {approx}4% of K+A fields that have aperture fluxes above the 5{sigma} noise level of the FIRST survey. A stack of the remaining galaxies shows little residual flux consistent with an upper limit on star formation of 1.3 M{sub Sun} yr{sup -1}. Even for a subset of 456 'young' (spectral ages <250 Myr) K+A galaxies, we find that the stacked 1.4 GHz flux is consistent with no current star formation. Our data suggest that the original starburst has been terminated in the majority of K+A galaxies, but that this may represent part of a duty cycle where a fraction of these galaxies may be active at a given moment with dusty starbursts and active galactic nuclei being present.

  9. Star formation in globular clusters and dwarf galaxies and implications for the early evolution of galaxies

    NASA Technical Reports Server (NTRS)

    Lin, Douglas N. C.; Murray, Stephen D.

    1991-01-01

    Based upon the observed properties of globular clusters and dwarf galaxies in the Local Group, we present important theoretical constraints on star formation in these systems. These constraints indicate that protoglobular cluster clouds had long dormant periods and a brief epoch of violent star formation. Collisions between protocluster clouds triggered fragmentation into individual stars. Most protocluster clouds dispersed into the Galactic halo during the star formation epoch. In contrast, the large spread in stellar metallicity in dwarf galaxies suggests that star formation in their pregenitors was self-regulated: we propose the protocluster clouds formed from thermal instability in the protogalactic clouds and show that a population of massive stars is needed to provide sufficient UV flux to prevent the collapsing protogalactic clouds from fragmenting into individual stars. Based upon these constraints, we propose a unified scenario to describe the early epochs of star formation in the Galactic halo as well as the thick and thin components of the Galactic disk.

  10. 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

  11. 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.

  12. 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

  13. 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.

  14. Star Formation in the Central Regions of Galaxies

    NASA Astrophysics Data System (ADS)

    Tsai, Mengchun

    2015-08-01

    The galactic central region connects the galactic nucleus to the host galaxy. If the central black hole co-evolved with the host galaxies, there should be some evidence left in the central region. We use the environmental properties in the central regions such as star-forming activity, stellar population and molecular abundance to figure out a possible scenario of the evolution of galaxies. In this thesis at first we investigated the properties of the central regions in the host galaxies of active and normal galaxies. We used radio emission around the nuclei of the host galaxies to represent activity of active galactic nuclei (AGNs), and used infrared ray (IR) emission to represent the star-forming activity and stellar population of the host galaxies. We determined that active galaxies have higher stellar masses (SMs) within the central kiloparsec radius than normal galaxies do independent of the Hubble types of the host galaxies; but both active and normal galaxies exhibit similar specific star formation rates (SSFRs). We also discovered that certain AGNs exhibit substantial inner stellar structures in the IR images; most of the AGNs with inner structures are Seyferts, whereas only a few LINERs exhibit inner structures. We note that the AGNs with inner structures show a positive correlation between the radio activity of the AGNs and the SFRs of the host galaxies, but the sources without inner structures show a negative correlation between the radio power and the SFRs. These results might be explained with a scenario of starburst-AGN evolution. In this scenario, AGN activities are triggered following a nuclear starburst; during the evolution, AGN activities are accompanied by SF activity in the inner regions of the host galaxies; at the final stage of the evolution, the AGNs might transform into LINERs, exhibiting weak SF activity in the central regions of the host galaxies. For further investigation about the inner structure, we choose the most nearby and luminous

  15. Spatial Distribution of Star Formation in High Redshift Galaxies

    NASA Astrophysics Data System (ADS)

    Cunnyngham, Ian; Takamiya, M.; Willmer, C.; Chun, M.; Young, M.

    2011-01-01

    Integral field unit spectroscopy taken of galaxies with redshifts between 0.6 and 0.8 utilizing Gemini Observatory’s GMOS instrument were used to investigate the spatial distribution of star-forming regions by measuring the Hβ and [OII]λ3727 emission line fluxes. These galaxies were selected based on the strength of Hβ and [OII]λ3727 as measured from slit LRIS/Keck spectra. The process of calibrating and reducing data into cubes -- possessing two spatial dimensions, and one for wavelength -- was automated via a custom batch script using the Gemini IRAF routines. Among these galaxies only the bluest sources clearly show [OII] in the IFU regardless of total galaxy luminosity. The brightest galaxies lack [OII] emission and it is posited that two different modes of star formation exist among this seemingly homogeneous group of z=0.7 star-forming galaxies. In order to increase the galaxy sample to include redshifts from 0.3 to 0.9, public Gemini IFU data are being sought. Python scripts were written to mine the Gemini Science Archive for candidate observations, cross-reference the target of these observations with information from the NASA Extragalactic Database, and then present the resultant database in sortable, searchable, cross-linked web-interface using Django to facilitate navigation. By increasing the sample, we expect to characterize these two different modes of star formation which could be high-redshift counterparts of the U/LIRGs and dwarf starburst galaxies like NGC 1569/NGC 4449. The authors acknowledge funds provided by the National Science Foundation (AST 0909240).

  16. The evolution of galaxy star formation activity in massive haloes

    NASA Astrophysics Data System (ADS)

    Popesso, P.; Biviano, A.; Finoguenov, A.; Wilman, D.; Salvato, M.; Magnelli, B.; Gruppioni, C.; Pozzi, F.; Rodighiero, G.; Ziparo, F.; Berta, S.; Elbaz, D.; Dickinson, M.; Lutz, D.; Altieri, B.; Aussel, H.; Cimatti, A.; Fadda, D.; Ilbert, O.; Le Floch, E.; Nordon, R.; Poglitsch, A.; Xu, C. K.

    2015-02-01

    Context. There is now a large consensus that the current epoch of the cosmic star formation history (CSFH) is dominated by low mass galaxies while the most active phase, between redshifts 1 and 2, is dominated by more massive galaxies, which evolve more quickly. Aims: Massive galaxies tend to inhabit very massive haloes, such as galaxy groups and clusters. We aim to understand whether the observed "galaxy downsizing" could be interpreted as a "halo downsizing", whereas the most massive haloes, and their galaxy populations, evolve more rapidly than the haloes with lower mass. Methods: We studied the contribution to the CSFH of galaxies inhabiting group-sized haloes. This is done through the study of the evolution of the infra-red (IR) luminosity function of group galaxies from redshift 0 to redshift ~1.6. We used a sample of 39 X-ray-selected groups in the Extended Chandra Deep Field South (ECDFS), the Chandra Deep Field North (CDFN), and the COSMOS field, where the deepest available mid- and far-IR surveys have been conducted with Spitzer MIPS and with the Photodetector Array Camera and Spectrometer (PACS) on board the Herschel satellite. Results: Groups at low redshift lack the brightest, rarest, and most star forming IR-emitting galaxies observed in the field. Their IR-emitting galaxies contribute ≤10% of the comoving volume density of the whole IR galaxy population in the local Universe. At redshift ≳1, the most IR-luminous galaxies (LIRGs and ULIRGs) are mainly located in groups, and this is consistent with a reversal of the star formation rate (SFR) vs. density anti-correlation observed in the nearby Universe. At these redshifts, group galaxies contribute 60-80% of the CSFH, i.e. much more than at lower redshifts. Below z ~ 1, the comoving number and SFR densities of IR-emitting galaxies in groups decline significantly faster than those of all IR-emitting galaxies. Conclusions: Our results are consistent with a "halo downsizing" scenario and highlight the

  17. 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.

  18. Star formation in the Magellanic irregular galaxy NGC 4449

    NASA Technical Reports Server (NTRS)

    Thronson, Harley A., Jr.; Hunter, Deidre A.; Telesco, C. M.; Decher, R.; Harper, D. A.

    1987-01-01

    New NIR and FIR maps and J = 1-0 CO spectroscopy of the Magellanic irregular galaxy NGC 4449 are presented. The brighter 150-micron emission is concentrated along the central visual ridge of the galaxy, although there is lower intensity extended emission throughout the visible extent of the object. The maximum FIR emission is coincident, within the uncertainties, with the visual and NIR maxima, identified as the galactic nucleus. It is estimated that the IR luminosity of the 1-kpc-diameter central region in NGC 4449 is comparable to that for a similar-sized region at the center of the Galaxy. A large fraction of the 150-micron emission may arise from warm dust distributed throughout the galaxy and heated by the diffuse radiation field. Active star formation follows the NIR emission in part of the galaxy, but no coincidence is found in another region.

  19. 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.

  20. 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.

  1. Star Formation in Partially Gas-Depleted Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Rose, James A.; Robertson, Paul; Miner, Jesse; Levy, Lorenza

    2010-02-01

    Broadband B and R and Hα images have been obtained with the 4.1 m SOAR telescope atop Cerro Pachon, Chile, for 29 spiral galaxies in the Pegasus I galaxy cluster and for 18 spirals in non-cluster environments. Pegasus I is a spiral-rich cluster with a low-density intracluster medium and a low galaxy velocity dispersion. When combined with neutral hydrogen (H I) data obtained with the Arecibo 305 m radio telescope, acquired by Levy et al. (2007) and by Springob et al. (2005b), we study the star formation rates in disk galaxies as a function of their H I deficiency. To quantify H I deficiency, we use the usual logarithmic deficiency parameter, DEF. The specific star formation rate (SSFR) is quantified by the logarithmic flux ratio of Hα flux to R-band flux, and thus roughly characterizes the logarithmic SFR per unit stellar mass. We find a clear correlation between the global SFR per unit stellar mass and DEF, such that the SFR is lower in more H I-deficient galaxies. This correlation appears to extend from the most gas-rich to the most gas-poor galaxies. We also find a correlation between the central SFR per unit mass relative to the global values, in the sense that the more H I-deficient galaxies have a higher central SFR per unit mass relative to their global SFR values than do gas-rich galaxies. In fact, approximately half of the H I-depleted galaxies have highly elevated SSFRs in their central regions, indicative of a transient evolutionary state. In addition, we find a correlation between gas depletion and the size of the Hα disk (relative to the R-band disk); H I-poor galaxies have truncated disks. Moreover, aside from the elevated central SSFR in many gas-poor spirals, the SSFR is otherwise lower in the Hα disks of gas-poor galaxies than in gas-rich spirals. Thus, both disk truncation and lowered SSFR levels within the star-forming part of the disks (aside from the enhanced nuclear SSFR) correlate with H I deficiency, and both phenomena are found to

  2. STAR FORMATION IN PARTIALLY GAS-DEPLETED SPIRAL GALAXIES

    SciTech Connect

    Rose, James A.; Miner, Jesse; Levy, Lorenza; Robertson, Paul E-mail: paul@astr.as.utexas.edu E-mail: lorenza.levy@yahoo.com

    2010-02-15

    Broadband B and R and H{alpha} images have been obtained with the 4.1 m SOAR telescope atop Cerro Pachon, Chile, for 29 spiral galaxies in the Pegasus I galaxy cluster and for 18 spirals in non-cluster environments. Pegasus I is a spiral-rich cluster with a low-density intracluster medium and a low galaxy velocity dispersion. When combined with neutral hydrogen (H I) data obtained with the Arecibo 305 m radio telescope, acquired by Levy et al. (2007) and by Springob et al. (2005b), we study the star formation rates in disk galaxies as a function of their H I deficiency. To quantify H I deficiency, we use the usual logarithmic deficiency parameter, DEF. The specific star formation rate (SSFR) is quantified by the logarithmic flux ratio of H{alpha} flux to R-band flux, and thus roughly characterizes the logarithmic SFR per unit stellar mass. We find a clear correlation between the global SFR per unit stellar mass and DEF, such that the SFR is lower in more H I-deficient galaxies. This correlation appears to extend from the most gas-rich to the most gas-poor galaxies. We also find a correlation between the central SFR per unit mass relative to the global values, in the sense that the more H I-deficient galaxies have a higher central SFR per unit mass relative to their global SFR values than do gas-rich galaxies. In fact, approximately half of the H I-depleted galaxies have highly elevated SSFRs in their central regions, indicative of a transient evolutionary state. In addition, we find a correlation between gas depletion and the size of the H{alpha} disk (relative to the R-band disk); H I-poor galaxies have truncated disks. Moreover, aside from the elevated central SSFR in many gas-poor spirals, the SSFR is otherwise lower in the H{alpha} disks of gas-poor galaxies than in gas-rich spirals. Thus, both disk truncation and lowered SSFR levels within the star-forming part of the disks (aside from the enhanced nuclear SSFR) correlate with H I deficiency, and both

  3. Disc galaxies: Molecular hydrogen, star formation and radial migration

    NASA Astrophysics Data System (ADS)

    Halle, A.; Combes, F.; Di Matteo, P.; Haywood, M.

    2014-12-01

    We show the importance of molecular hydrogen to simulate the evolution of disc galaxies with improved realistic interstellar medium and stellar formation. The inclusion of H_2 cooling is especially important in the low-metallicity regions such as the outer parts of discs, in which it allows for some slow star formation. We study the evolution of the obtained stellar components of these galaxies and focus on the radial migration that occurs due to the resonances of the bar and transient spiral arms in the disc.

  4. Completing the Census of Isolated Dwarf Galaxy Star Formation Histories

    NASA Astrophysics Data System (ADS)

    Weisz, Daniel

    2014-10-01

    We propose to complete our census of the ancient star formation histories (SFHs) of isolated dwarf galaxies by obtaining deep ACS/WFC optical imaging of WLM and Pegasus Dwarf Irregular Galaxy (PegDIG). They are the only two systems without previous deep HST imaging that are isolated yet close enough to guarantee that their oldest main sequence turnoffs are accessible with HST. We will measure their lifetime SFHs with an age resolution of < 1 Gyr at all epochs to address questions about growth of stellar mass, the effects of reionization, radial population gradients, and variable star populations in WLM and PegDIG. This program is a concerted effort between theorists and observers to obtain the best possible observational constraints on the early epochs of star formation in isolated low-mass galaxies, which are essential to the next generation of galaxy simulations. With these new observations we will have completed our efforts to collect precise lifetime SFHs of all nearby isolated dwarfs that are accessible with HST. In combination with archival data, we will create a legacy sample isolated dwarfs with identically derived SFHs, that will be serve as the baseline for the community's understanding of how low-mass galaxies form and evolve over a Hubble time and in the absence of environmental effects of a massive host (e.g., tides, ram pressure).

  5. 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.

  6. Star Formation Quenching and Identifying AGN in Galaxies

    NASA Astrophysics Data System (ADS)

    Mendez, Alexander; Coil, A. L.; Lotz, J. M.; Aird, J.; Diamond-Stanic, A. M.; Moustakas, J.; Salim, S.; Simard, L.; Blanton, M. R.; Eisenstein, D.; Wong, K. C.; Cool, R. J.; Zhu, G.; PRIMUS; AEGIS

    2014-01-01

    I will discuss two observational projects related to galaxy and active galactic nuclei (AGN) evolution at z < 1. First I will present a statistical study of the morphologies of galaxies in which star formation is being shut down or quenched; this has implications for how red, elliptical galaxies are formed. I will discuss the physical processes behind star formation quenching from the morphological transformations that galaxies undergo during this process. Then I will focus on multi-wavelength AGN selection methods and tie together disparate results in the literature. Several IR-AGN selection methods have been developed using Spitzer/IRAC data in order to supplement traditional X-ray AGN selection; I will characterize the uniqueness and complementarity of these methods as a function of both IR and X-ray depth. I will use data from the PRIsm MUlti-object Survey (PRIMUS) to compare the efficiency of IR and X-ray AGN selection and discuss the properties of the AGN and host galaxy populations of each. Finally, I will briefly mention ongoing work to compare the clustering of observed IR and X-ray AGN samples relative to stellar mass-matched galaxy samples.

  7. 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.

  8. Fast outflows and star formation quenching in quasar host galaxies

    NASA Astrophysics Data System (ADS)

    Carniani, S.; Marconi, A.; Maiolino, R.; Balmaverde, B.; Brusa, M.; Cano-Díaz, M.; Cicone, C.; Comastri, A.; Cresci, G.; Fiore, F.; Feruglio, C.; La Franca, F.; Mainieri, V.; Mannucci, F.; Nagao, T.; Netzer, H.; Piconcelli, E.; Risaliti, G.; Schneider, R.; Shemmer, O.

    2016-06-01

    Negative feedback from active galactic nuclei (AGN) is considered a key mechanism in shaping galaxy evolution. Fast, extended outflows are frequently detected in the AGN host galaxies at all redshifts and luminosities, both in ionised and molecular gas. However, these outflows are only potentially able to quench star formation, and we are still lacking decisive evidence of negative feedback in action. Here we present observations obtained with the Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) H- and K-band integral-field of two quasars at z ~ 2.4 that are characterised by fast, extended outflows detected through the [Oiii]λ5007 line. The high signal-to-noise ratio of our observations allows us to identify faint narrow (FWHM< 500 km s-1) and spatially extended components in [Oiii]λ5007 and Hα emission associated with star formation in the host galaxy. This star formation powered emission is spatially anti-correlated with the fast outflows. The ionised outflows therefore appear to be able to suppress star formation in the region where the outflow is expanding. However, the detection of narrow spatially extended Hα emission indicates star formation rates of at least ~50-90 M⊙ yr-1, suggesting either that AGN feedback does not affect the whole galaxy or that many feedback episodes are required before star formation is completely quenched. On the other hand, the narrow Hα emission extending along the edges of the outflow cone may also lead also to a positive feedback interpretation. Our results highlight the possible double role of galaxy-wide outflows in host galaxy evolution. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, P.ID: 086.B-0579(A) and 091.A-0261(A).The reduced data cubes are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/591/A28

  9. 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.

  10. 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

  11. 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).

  12. Galaxy Star Formation as a function of Environment

    NASA Astrophysics Data System (ADS)

    Castander, F. J.; Balogh, M. L.; Bernardi, M.; Bower, R. G.; Connolly, A. J.; Gilbank, D. G.; Gómez, P. L.; Goto, T.; Hopkins, A. M.; Miller, C. J.; Nichol, R. C.; Schneider, D. P.; Seth, R.; Zabludoff, A. I.

    We study the galaxy star formation rate (SFR) as a function of environment using the SDSS EDR data. We find that the SFR is depressed in dense environments (clusters and groups) compared to the field. We find that the suppression of the SFR starts to be noticeable at around 4 virial radii. We find no evidence for SF triggering as galaxies fall into the clusters. We also present a project to study these effects in cluster pairs systems where the effects of filaments and large scale structure may be noticeable.

  13. Star Formation Rate in Holmberg IX Dwarf Galaxy

    NASA Astrophysics Data System (ADS)

    Andjelic, M. M.

    2011-12-01

    In this paper we use previously determined Hα fluxes for dwarf galaxy Holmberg IX (Arbutina et al. 2009) to calculate star formation rate (SFR) in this galaxy. We discuss possible contaminations of Hα flux and, for the first time, we take into account optical emission from supernova remnants (SNRs) as a possible source of contamination of Hα flux. Derived SFR for Holmberg IX is 3.4×10-4M_{⊙} yr-1. Our value is lower then in previous studies, due to luminous shock-heated source M&H 9-10, possible hypernova remnant, which we excluded from the total Hα flux in our calculation of SFR.

  14. Star formation and mass assembly in high redshift galaxies

    NASA Astrophysics Data System (ADS)

    Santini, P.; Fontana, A.; Grazian, A.; Salimbeni, S.; Fiore, F.; Fontanot, F.; Boutsia, K.; Castellano, M.; Cristiani, S.; de Santis, C.; Gallozzi, S.; Giallongo, E.; Menci, N.; Nonino, M.; Paris, D.; Pentericci, L.; Vanzella, E.

    2009-09-01

    Aims: The goal of this work is to infer the star formation properties and the mass assembly process of high redshift (0.3 ≤ z < 2.5) galaxies from their IR emission using the 24 μm band of MIPS-Spitzer. Methods: We used an updated version of the GOODS-MUSIC catalog, which has multiwavelength coverage from 0.3 to 24 μm and either spectroscopic or accurate photometric redshifts. We describe how the catalog has been extended by the addition of mid-IR fluxes derived from the MIPS 24 μm image. We compared two different estimators of the star formation rate (SFR hereafter). One is the total infrared emission derived from 24 μm, estimated using both synthetic and empirical IR templates. The other one is a multiwavelength fit to the full galaxy SED, which automatically accounts for dust reddening and age-star formation activity degeneracies. For both estimates, we computed the SFR density and the specific SFR. Results: We show that the two SFR indicators are roughly consistent, once the uncertainties involved are taken into account. However, they show a systematic trend, IR-based estimates exceeding the fit-based ones as the star formation rate increases. With this new catalog, we show that: a) at z>0.3, the star formation rate is correlated well with stellar mass, and this relationship seems to steepen with redshift if one relies on IR-based estimates of the SFR; b) the contribution to the global SFRD by massive galaxies increases with redshift up to ≃ 2.5, more rapidly than for galaxies of lower mass, but appears to flatten at higher z; c) despite this increase, the most important contributors to the SFRD at any z are galaxies of about, or immediately lower than, the characteristic stellar mass; d) at z≃ 2, massive galaxies are actively star-forming, with a median {SFR} ≃ 300 M_⊙ yr-1. During this epoch, our targeted galaxies assemble a substantial part of their final stellar mass; e) the specific SFR (SSFR) shows a clear bimodal distribution. Conclusions

  15. 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.

  16. 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.

  17. 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.

  18. Predicting galaxy star formation rates via the co-evolution of galaxies and haloes

    NASA Astrophysics Data System (ADS)

    Watson, Douglas F.; Hearin, Andrew P.; Berlind, Andreas A.; Becker, Matthew R.; Behroozi, Peter S.; Skibba, Ramin A.; Reyes, Reinabelle; Zentner, Andrew R.; van den Bosch, Frank C.

    2015-01-01

    In this paper, we test the age matching hypothesis that the star formation rate (SFR) of a galaxy of fixed stellar mass is determined by its dark matter halo formation history, e.g. more quiescent galaxies reside in older haloes. We present new Sloan Digital Sky Survey measurements of the galaxy two-point correlation function and galaxy-galaxy lensing as a function of stellar mass and SFR, separated into quenched and star-forming galaxy samples to test this simple model. We find that our age matching model is in excellent agreement with these new measurements. We also find that our model is able to predict: (1) the relative SFRs of central and satellite galaxies, (2) the SFR dependence of the radial distribution of satellite galaxy populations within galaxy groups, rich groups, and clusters and their surrounding larger scale environments, and (3) the interesting feature that the satellite quenched fraction as a function of projected radial distance from the central galaxy exhibits an ˜r-.15 slope, independent of environment. These accurate predictions are intriguing given that we do not explicitly model satellite-specific processes after infall, and that in our model the virial radius does not mark a special transition region in the evolution of a satellite. The success of the model suggests that present-day galaxy SFR is strongly correlated with halo mass assembly history.

  19. 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.

  20. Gravitational star formation thresholds and gas density in three galaxies

    NASA Technical Reports Server (NTRS)

    Oey, M. S.; Kennicutt, R. C., Jr.

    1990-01-01

    It has long been held that the star formation rate (SFR) may be described as a power law of the gas density, p(exp n), as given by Schmidt (1959). However, this relation has as yet remained poorly defined and is likewise poorly understood. In particular, most studies have been investigations of global gas and star formation properties of galaxies, due to lack of adequate high-resolution data for detailed studies of individual galaxies. The three spiral galaxies in this study have published maps of both H2 (as traced by CO), and HI, thereby enabling the authors to investigate the relationship between total gas surface density and SFR. The purpose of the present investigation is the comparison of spatially-resolved total surface gas density in three galaxies (NGC 6946, M51, and M83) to sigma sub c as given by the above model. CO, HI and H alpha data for NGC 6946 were taken from Tacconi-Garman (1988), and for M51 and M83 from Lord (1987). The authors used a CO-H2 conversion of N(H2)/I sub CO(exp cos i = 2.8 x 10(exp 20) atoms cm(-2)/(K kms(-1), and summed the H2 and HI data for each galaxy to obtain the total hydrogen gas density. This total was then multiplied by a factor of 1.36 to include the contribution of helium to the total surface gas density. The authors assumed distances to NGC 6946, M51, and M83 to be 6.0, 9.6, and 8.9 Mpc respectively, with inclination angles of 30, 20, and 26 degrees. H alpha flux was used as the measure of SFR for NGC 6946, and SFR for the remaining two galaxies was taken directly from Lord as computed from H alpha measurements. The results of these full-disk studies thus show a remarkable correlation between the total gas density and the threshold densities given by the gravitational stability criterion. In particular, the threshold density appears to mark a lower boundary to the range of gas densities in these galaxies, which may have consequence in determining appropriate models for star formation and gas dynamics. More evidence is

  1. The evolution of star formation activity in galaxy groups

    NASA Astrophysics Data System (ADS)

    Erfanianfar, G.; Popesso, P.; Finoguenov, A.; Wuyts, S.; Wilman, D.; Biviano, A.; Ziparo, F.; Salvato, M.; Nandra, K.; Lutz, D.; Elbaz, D.; Dickinson, M.; Tanaka, M.; Mirkazemi, M.; Balogh, M. L.; Altieri, M. B.; Aussel, H.; Bauer, F.; Berta, S.; Bielby, R. M.; Brandt, N.; Cappelluti, N.; Cimatti, A.; Cooper, M.; Fadda, D.; Ilbert, O.; Le Floch, E.; Magnelli, B.; Mulchaey, J. S.; Nordon, R.; Newman, J. A.; Poglitsch, A.; Pozzi, F.

    2014-12-01

    We study the evolution of the total star formation (SF) activity, total stellar mass (ΣM*) and halo occupation distribution (HOD) in massive haloes by using one of the largest X-ray selected sample of galaxy groups with secure spectroscopic identification in the major blank field surveys (ECDFS, CDFN, COSMOS, AEGIS). We provide an accurate measurement of star formation rate (SFR) for the bulk of the star-forming galaxies using very deep mid-infrared Spitzer MIPS and far-infrared Herschel PACS observations. For undetected IR sources, we provide a well-calibrated SFR from spectral energy distribution (SED) fitting. We observe a clear evolution in the level of SF activity in galaxy groups. The total SF activity in the high-redshift groups (0.5 < z < 1.1) is higher with respect to the low-redshift (0.15 < z < 0.5) sample at any mass by 0.8 ± 0.12 dex. A milder difference (0.35 ± 0.1 dex) is observed between the low-redshift bin and the groups at z ˜ 0. We show that the level of SF activity is declining more rapidly in the more massive haloes than in the more common lower mass haloes. We do not observe any evolution in the HOD and total stellar mass-halo mass relations in groups. The picture emerging from our findings suggests that the galaxy population in the most massive systems is evolving faster than galaxies in lower mass haloes, consistently with a `halo downsizing' scenario.

  2. Far-infrared emission and star formation in spiral galaxies

    NASA Technical Reports Server (NTRS)

    Trinchieri, G.; Fabbiano, G.; Bandiera, R.

    1989-01-01

    The correlations between the emission in the far-IR, H-alpha, and blue in a sample of normal spiral galaxies are investigated. It is found that the luminosities in these three bands are all tightly correlated, although both the strength of the correlations and their functional dependencies are a function of the galaxies' morphological types. The best-fit power laws to these correlations are different for the comparison of different quantities and deviate significantly from linearity in some cases, implying the presence of additional emission mechanisms not related to the general increase of luminosity with galactic mass. Clear evidence is found of two independent effects in the incidence of warm far-IR emission in late-type spirals. One is a luminosity effect shown by the presence of excess far-IR relative to H-alpha or optical emission in the more luminous galaxies. The other is a dependence on widespread star-formation activity.

  3. Galaxy Structure as a Driver of the Star Formation Sequence Slope and Scatter

    NASA Astrophysics Data System (ADS)

    Whitaker, Katherine E.; Franx, Marijn; Bezanson, Rachel; Brammer, Gabriel B.; van Dokkum, Pieter G.; Kriek, Mariska T.; Labbé, Ivo; Leja, Joel; Momcheva, Ivelina G.; Nelson, Erica J.; Rigby, Jane R.; Rix, Hans-Walter; Skelton, Rosalind E.; van der Wel, Arjen; Wuyts, Stijn

    2015-09-01

    It is well established that (1) star-forming galaxies follow a relation between their star formation rate (SFR) and stellar mass ({M}\\star ), the “star formation sequence,” and (2) the SFRs of galaxies correlate with their structure, where star-forming galaxies are less concentrated than quiescent galaxies at fixed mass. Here, we consider whether the scatter and slope of the star formation sequence is correlated with systematic variations in the Sérsic indices, n, of galaxies across the SFR-{M}\\star plane. We use a mass-complete sample of 23,848 galaxies at 0.5 < z < 2.5 selected from the 3D-HST photometric catalogs. Galaxy light profiles parameterized by n are based on Hubble Space Telescope Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey near-infrared imaging. We use a single SFR indicator empirically calibrated from stacks of Spitzer/MIPS 24 μm imaging, adding the unobscured and obscured star formation. We find that the scatter of the star formation sequence is related in part to galaxy structure; the scatter due to variations in n at fixed mass for star-forming galaxies ranges from 0.14 ± 0.02 dex at z ˜ 2 to 0.30 ± 0.04 dex at z < 1. While the slope of the {log} {SFR}-{log} {M}\\star relation is of order unity for disk-like galaxies, galaxies with n > 2 (implying more dominant bulges) have significantly lower {SFR}/{M}\\star than the main ridgeline of the star formation sequence. These results suggest that bulges in massive z ˜ 2 galaxies are actively building up, where the stars in the central concentration are relatively young. At z < 1, the presence of older bulges within star-forming galaxies lowers global {SFR}/{M}\\star , decreasing the slope and contributing significantly to the scatter of the star formation sequence.

  4. 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.

  5. 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

  6. The star formation rates of active galactic nuclei host galaxies

    NASA Astrophysics Data System (ADS)

    Ellison, Sara L.; Teimoorinia, Hossen; Rosario, David J.; Mendel, J. Trevor

    2016-05-01

    Using artificial neural network predictions of total infrared luminosities (LIR), we compare the host galaxy star formation rates (SFRs) of ˜21 000 optically selected active galactic nuclei (AGN), 466 low-excitation radio galaxies (LERGs) and 721 mid-IR-selected AGN. SFR offsets (ΔSFR) relative to a sample of star-forming `main-sequence' galaxies (matched in M⋆, z and local environment) are computed for the AGN hosts. Optically selected AGN exhibit a wide range of ΔSFR, with a distribution skewed to low SFRs and a median ΔSFR = -0.06 dex. The LERGs have SFRs that are shifted to even lower values with a median ΔSFR = -0.5 dex. In contrast, mid-IR-selected AGN have, on average, SFRs enhanced by a factor of ˜1.5. We interpret the different distributions of ΔSFR amongst the different AGN classes in the context of the relative contribution of triggering by galaxy mergers. Whereas the LERGs are predominantly fuelled through low accretion rate secular processes which are not accompanied by enhancements in SFR, mergers, which can simultaneously boost SFRs, most frequently lead to powerful, obscured AGN.

  7. Predicting Galaxy Star Formation Rates via the Co-evolution of Galaxies and Halos

    SciTech Connect

    Watson, Douglas F.; Hearin, Andrew P.; Berlind, Andreas A.; Becker, Matthew R.; Behroozi, Peter S.; Skibba, Ramin A.; Reyes, Reinabelle; Zentner, Andrew R.

    2014-03-06

    In this paper, we test the age matching hypothesis that the star formation rate (SFR) of a galaxy is determined by its dark matter halo formation history, and as such, that more quiescent galaxies reside in older halos. This simple model has been remarkably successful at predicting color-based galaxy statistics at low redshift as measured in the Sloan Digital Sky Survey (SDSS). To further test this method with observations, we present new SDSS measurements of the galaxy two-point correlation function and galaxy-galaxy lensing as a function of stellar mass and SFR, separated into quenched and star forming galaxy samples. We find that our age matching model is in excellent agreement with these new measurements. We also employ a galaxy group finder and show that our model is able to predict: (1) the relative SFRs of central and satellite galaxies, (2) the SFR-dependence of the radial distribution of satellite galaxy populations within galaxy groups, rich groups, and clusters and their surrounding larger scale environments, and (3) the interesting feature that the satellite quenched fraction as a function of projected radial distance from the central galaxy exhibits an approx r-.15 slope, independent of environment. The accurate prediction for the spatial distribution of satellites is intriguing given the fact that we do not explicitly model satellite-specific processes after infall, and that in our model the virial radius does not mark a special transition region in the evolution of a satellite, contrary to most galaxy evolution models. The success of the model suggests that present-day galaxy SFR is strongly correlated with halo mass assembly history.

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

    NASA Technical Reports Server (NTRS)

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

    1973-01-01

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

  9. Multiwavelength Study of Massive Galaxies at z~2. I. Star Formation and Galaxy Growth

    NASA Astrophysics Data System (ADS)

    Daddi, E.; Dickinson, M.; Morrison, G.; Chary, R.; Cimatti, A.; Elbaz, D.; Frayer, D.; Renzini, A.; Pope, A.; Alexander, D. M.; Bauer, F. E.; Giavalisco, M.; Huynh, M.; Kurk, J.; Mignoli, M.

    2007-11-01

    Examining a sample of massive galaxies at 1.4star formation rates (SFRs) and to explore the implications for galaxy assembly. For z~2 galaxies with moderate luminosities (L8μm<1011 Lsolar), we find that the SFR can be estimated consistently from the multiwavelength data based on local luminosity correlations. However, 20%-30% of massive galaxies, and nearly all those with L8μm>1011 Lsolar, show a mid-IR excess that is likely due to the presence of obscured active nuclei, as shown in a companion paper. There is a tight and roughly linear correlation between stellar mass and SFR for 24 μm-detected galaxies. For a given mass, the SFR at z=2 was larger by a factor of ~4 and ~30 relative to that in star-forming galaxies at z=1 and 0, respectively. Typical ultraluminous infrared galaxies (ULIRGs) at z=2 are relatively ``transparent'' to ultraviolet light, and their activity is long lived (>~400 Myr), unlike that in local ULIRGs and high-redshift submillimeter-selected galaxies. ULIRGs are the common mode of star formation in massive galaxies at z=2, and the high duty cycle suggests that major mergers are not the dominant trigger for this activity. Current galaxy formation models underpredict the normalization of the mass-SFR correlation by about a factor of 4 and the space density of ULIRGs by an order of magnitude but give better agreement for z>1.4 quiescent galaxies.

  10. BURST OF STAR FORMATION DRIVES BUBBLE IN GALAXY'S CORE

    NASA Technical Reports Server (NTRS)

    2002-01-01

    These NASA Hubble Space Telescope snapshots reveal dramatic activities within the core of the galaxy NGC 3079, where a lumpy bubble of hot gas is rising from a cauldron of glowing matter. The picture at left shows the bubble in the center of the galaxy's disk. The structure is more than 3,000 light-years wide and rises 3,500 light-years above the galaxy's disk. The smaller photo at right is a close-up view of the bubble. Astronomers suspect that the bubble is being blown by 'winds' (high-speed streams of particles) released during a burst of star formation. Gaseous filaments at the top of the bubble are whirling around in a vortex and are being expelled into space. Eventually, this gas will rain down upon the galaxy's disk where it may collide with gas clouds, compress them, and form a new generation of stars. The two white dots just above the bubble are probably stars in the galaxy. The close-up reveals that the bubble's surface is lumpy, consisting of four columns of gaseous filaments that tower above the galaxy's disk. The filaments disperse at a height of 2,000 light-years. Each filament is about 75 light-years wide. Velocity measurements taken by the Canada-France-Hawaii Telescope in Hawaii show that the gaseous filaments are ascending at more than 4 million miles an hour (6 million kilometers an hour). According to theoretical models, the bubble formed when ongoing winds from hot stars mixed with small bubbles of very hot gas from supernova explosions. Observations of the core's structure by radio telescopes indicate that those processes are still active. The models suggest that this outflow began about a million years ago. They occur about every 10 million years. Eventually, the hot stars will die, and the bubble's energy source will fade away. Astronomers have seen evidence of previous outbursts from radio and X-ray observations. Those studies show rings of dust and gas and long plumes of material, all of which are larger than the bubble. NGC 3079 is 50

  11. The history of star formation in nearby dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Weisz, Daniel Ray

    2010-11-01

    We present detailed analysis of color-magnitude diagrams (CMDs) of resolved stellar populations in nearby dwarf galaxies based on observations taken with the Hubble Space Telescope (HST). From the positions of individual stars on a CMD, we are able to derive the star formation histories (SFHs), i.e., the star formation rate (SFR) as a function of time and metallicity, of the observed stellar populations. Specifically, we apply this technique to a number of nearby dwarf galaxies to better understand the mechanisms driving their evolution. The ACS Nearby Galaxy Survey Treasury program (ANGST) provides multi-color photometry of resolved stars in ˜ 60 nearby dwarf galaxies from images taken with HST. This sample contains 12 dSph, 5 dwarf spiral, 28 dIrr, 12 dSph/dIrr (transition), and 3 tidal dwarf galaxies. The sample spans a range of ˜ 10 in MB and covers a wide range of environments, from highly interacting to truly isolated. From the best fit lifetime SFHs we find three significant results: (1) the average dwarf galaxy formed ˜ 60% of its stars by z ˜ 2 and 70% of its stars by z ˜ 1, regardless of morphological type, (2) the only statistically significant difference between the SFHs of different morphological types is within the most recent 1 Gyr (excluding tidal dwarf galaxies), and (3) the SFHs are complex and the mean values are inconsistent with simple SFH models, e.g., single epoch SF or constant SFH. We then present the recent ( ≲ 1 Gyr) SFHs of nine M81 Group Dwarf Galaxies. Comparing the SFHs, birthrate parameters, fraction of stars formed per time interval, and spatial distribution of stellar components as a function of luminosity, we find only minor differences in SF characteristics among the M81 Group dIs despite a wide range of physical properties. We extend our comparison to select dIs in the Local Group (LG), with similar quality photometry, and again find only minor differences in SF parameters. The lack of a clear trend in SF parameters over

  12. Are We Correctly Measuring the Star Formation in Galaxies?

    NASA Astrophysics Data System (ADS)

    McQuinn, K. B. W.; Skillman, E. D.; Dolphin, A. E.; Mitchell, N. P.

    2016-06-01

    Integrating our knowledge of star formation (SF) traced by observations at different wavelengths is essential for correctly interpreting and comparing SF activity in a variety of systems and environments. This study compares extinction corrected integrated ultraviolet (UV) emission from resolved galaxies with color-magnitude diagram (CMD) based star formation rates (SFRs) derived from resolved stellar populations and CMD fitting techniques in 19 nearby starburst and post-starburst dwarf galaxies. The data sets are from the panchromatic Starburst Irregular Dwarf Survey and include deep legacy GALEX UV imaging, Hubble Space Telescope optical imaging, and Spitzer MIPS imaging. For the majority of the sample, the integrated near-UV fluxes predicted from the CMD-based SFRs—using four different models—agree with the measured, extinction corrected, integrated near-UV fluxes from GALEX images, but the far-UV (FUV) predicted fluxes do not. Furthermore, we find a systematic deviation between the SFRs based on integrated FUV luminosities and existing scaling relations, and the SFRs based on the resolved stellar populations. This offset is not driven by different SF timescales, variations in SFRs, UV attenuation, nor stochastic effects. This first comparison between CMD-based SFRs and an integrated FUV emission SFR indicator suggests that the most likely cause of the discrepancy is the theoretical FUV-SFR calibration from stellar evolutionary libraries and/or stellar atmospheric models. We present an empirical calibration of the FUV-based SFR relation for dwarf galaxies, with uncertainties, which is 53% larger than previous relations.

  13. 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.

  14. Galaxy Zoo and ALFALFA: atomic gas and the regulation of star formation in barred disc galaxies

    NASA Astrophysics Data System (ADS)

    Masters, Karen L.; Nichol, Robert C.; Haynes, Martha P.; Keel, William C.; Lintott, Chris; Simmons, Brooke; Skibba, Ramin; Bamford, Steven; Giovanelli, Riccardo; Schawinski, Kevin

    2012-08-01

    We study the observed correlation between atomic gas content and the likelihood of hosting a large-scale bar in a sample of 2090 disc galaxies. Such a test has never been done before on this scale. We use data on morphologies from the Galaxy Zoo project and information on the galaxies' H I content from the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) blind H I survey. Our main result is that the bar fraction is significantly lower among gas-rich disc galaxies than gas-poor ones. This is not explained by known trends for more massive (stellar) and redder disc galaxies to host more bars and have lower gas fractions: we still see at fixed stellar mass a residual correlation between gas content and bar fraction. We discuss three possible causal explanations: (1) bars in disc galaxies cause atomic gas to be used up more quickly, (2) increasing the atomic gas content in a disc galaxy inhibits bar formation and (3) bar fraction and gas content are both driven by correlation with environmental effects (e.g. tidal triggering of bars, combined with strangulation removing gas). All three explanations are consistent with the observed correlations. In addition our observations suggest bars may reduce or halt star formation in the outer parts of discs by holding back the infall of external gas beyond bar co-rotation, reddening the global colours of barred disc galaxies. This suggests that secular evolution driven by the exchange of angular momentum between stars in the bar, and gas in the disc, acts as a feedback mechanism to regulate star formation in intermediate-mass disc galaxies. This publication has been made possible by the participation of more than 200 000 volunteers in the Galaxy Zoo project. Their contributions are individually acknowledged at South East Physics Network, E-mail: karen.masters@port.ac.ukEinstein fellow.

  15. 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.

  16. 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.

  17. Gas and star formation in the Circinus galaxy

    NASA Astrophysics Data System (ADS)

    For, B.-Q.; Koribalski, B. S.; Jarrett, T. H.

    2012-09-01

    We present a detailed study of the Circinus galaxy, investigating its star formation, dust and gas properties, both in the inner and outer disc. To achieve this, we obtained high-resolution Spitzer mid-infrared images with the IRAC (3.6, 5.8, 4.5 and 8.0 μm) and MIPS (24 and 70 μm) instruments and sensitive H I data from the Australia Telescope Compact Array and the 64-m Parkes telescope. These were supplemented by CO maps from the Swedish-ESO Submillimetre Telescope. Because Circinus is hidden behind the Galactic plane, we demonstrate the careful removal of foreground stars as well as large- and small-scale Galactic emission from the Spitzer images. We derive a visual extinction of AV = 2.1 mag from the spectral energy distribution of the Circinus galaxy and total stellar and gas masses of 9.5 × 1010 and 9 × 109 M⊙, respectively. Using various wavelength calibrations, we find obscured global star formation rates between 3 and 8 M⊙ yr-1. Star-forming regions in the inner spiral arms of Circinus, which are rich in H I, are beautifully unveiled in the Spitzer 8 μm image. The latter is dominated by polycyclic aromatic hydrocarbon (PAH) emission from heated interstellar dust. We find a good correlation between the 8 μm emission in the arms and regions of dense H I gas. The (PAH 8 μm)/24 μm surface brightness ratio shows significant variations across the disc of Circinus.

  18. 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

  19. 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.

  20. 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

  1. Calibrating UV Star Formation Rates for Dwarf Galaxies from STARBIRDS

    NASA Astrophysics Data System (ADS)

    McQuinn, Kristen B. W.; Skillman, Evan D.; Dolphin, Andrew E.; Mitchell, Noah P.

    2015-08-01

    Integrating our knowledge of star formation (SF) traced by observations at different wavelengths is essential for correctly interpreting and comparing SF activity in a variety of systems and environments. This study compares extinction corrected integrated ultraviolet (UV) emission from resolved galaxies with color-magnitude diagram (CMD) based star formation rates (SFRs) derived from resolved stellar populations and CMD fitting techniques in 19 nearby starburst and post-starburst dwarf galaxies. The data sets are from the panchromatic Starburst Irregular Dwarf Survey and include deep legacy GALEX UV imaging, Hubble Space Telescope optical imaging, and Spitzer MIPS imaging. For the majority of the sample, the integrated near-UV fluxes predicted from the CMD-based SFRs—using four different models—agree with the measured, extinction corrected, integrated near-UV fluxes from GALEX images, but the far-UV (FUV) predicted fluxes do not. Furthermore, we find a systematic deviation between the SFRs based on integrated FUV luminosities and existing scaling relations, and the SFRs based on the resolved stellar populations. This offset is not driven by different SF timescales, variations in SFRs, UV attenuation, nor stochastic effects. This first comparison between CMD-based SFRs and an integrated FUV emission SFR indicator suggests that the most likely cause of the discrepancy is the theoretical FUV-SFR calibration from stellar evolutionary libraries and/or stellar atmospheric models. We present an empirical calibration of the FUV-based SFR relation for dwarf galaxies, with uncertainties, which is ˜53% larger than previous relations. Based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESA), and the Canadian Astronomy Data Centre (CADC/NRC/CSA).

  2. Star Formation in Galaxy Clusters Over the Past 10 Billion Years

    NASA Astrophysics Data System (ADS)

    Tran, Kim-Vy

    2012-01-01

    Galaxy clusters are the largest gravitationally bound systems in the universe and include the most massive galaxies in the universe; this makes galaxy clusters ideal laboratories for disentangling the nature versus nurture aspect of how galaxies evolve. Understanding how galaxies form and evolve in clusters continues to be a fundamental question in astronomy. The ages and assembly histories of galaxies in rich clusters test both stellar population models and hierarchical formation scenarios. Is star formation in cluster galaxies simply accelerated relative to their counterparts in the lower density field, or do cluster galaxies assemble their stars in a fundamentally different manner? To answer this question, I review multi-wavelength results on star formation in galaxy clusters from Coma to the most distant clusters yet discovered at look-back times of 10 billion years (z 2).

  3. The formation of cluster elliptical galaxies as revealed by extensive star formation.

    PubMed

    Stevens, J A; Ivison, R J; Dunlop, J S; Smail, Ian R; Percival, W J; Hughes, D H; Röttgering, H J A; Van Breugel, W J M; Reuland, M

    2003-09-18

    The most massive galaxies in the present-day Universe are found to lie in the centres of rich clusters. They have old, coeval stellar populations suggesting that the bulk of their stars must have formed at early epochs in spectacular starbursts, which should be luminous phenomena when observed at submillimetre wavelengths. The most popular model of galaxy formation predicts that these galaxies form in proto-clusters at high-density peaks in the early Universe. Such peaks are indicated by massive high-redshift radio galaxies. Here we report deep submillimetre mapping of seven high-redshift radio galaxies and their environments. These data confirm not only the presence of spatially extended regions of massive star-formation activity in the radio galaxies themselves, but also in companion objects previously undetected at any wavelength. The prevalence, orientation, and inferred masses of these submillimetre companion galaxies suggest that we are witnessing the synchronous formation of the most luminous elliptical galaxies found today at the centres of rich clusters of galaxies. PMID:13679908

  4. Star formation rates in isolated galaxies selected from the Two-Micron All-Sky Survey

    NASA Astrophysics Data System (ADS)

    Melnyk, O.; Karachentseva, V.; Karachentsev, I.

    2015-08-01

    We have considered the star formation properties of 1616 isolated galaxies from the 2MASS XSC (Extended Source Catalog) selected sample (2MIG) with the far-ultraviolet GALEX magnitudes. This sample was then compared with corresponding properties of isolated galaxies from the Local Orphan Galaxies (LOG) catalogue and paired galaxies. We found that different selection algorithms define different populations of isolated galaxies. The population of the LOG catalogue, selected from non-clustered galaxies in the Local Supercluster volume, mostly consists of low-mass spiral and late-type galaxies. The specific star formation rate (SSFR) upper limit in isolated and paired galaxies does not exceed the value of ˜dex(-9.4). This is probably common for galaxies of differing activity and environment (at least at z < 0.06). The fractions of quenched galaxies are nearly twice as high in the paired galaxy sample as in the 2MIG isolated galaxy sample. From the behaviour of (S)SFR versus M* relations we deduced that the characteristic value influencing evolutionary processes is the galaxy mass. However, the environmental influence is notable: paired massive galaxies with logM* > 11.5 have higher (S)SFR than isolated galaxies. Our results suggest that the environment helps to trigger the star formation in the highest mass galaxies. We found that the fraction of AGN in the paired sample is only a little higher than in our isolated galaxy sample. We assume that AGN phenomenon is probably defined by secular galaxy evolution.

  5. Star formation histories across the interacting galaxy NGC 6872, the largest-known spiral

    SciTech Connect

    Eufrasio, Rafael T.; De Mello, Duilia F.; Dwek, Eli; Arendt, Richard G.; Benford, Dominic J.; Gadotti, Dimitri A.; Urrutia-Viscarra, Fernanda; De Oliveira, Claudia Mendes

    2014-11-01

    NGC 6872, hereafter the Condor, is a large spiral galaxy that is interacting with its closest companion, the S0 galaxy IC 4970. The extent of the Condor provides an opportunity for detailed investigation of the impact of the interaction on the current star formation rate and its history across the galaxy, on the age and spatial distribution of its stellar population, and on the mechanism that drives the star formation activity. To address these issues we analyzed the far-ultraviolet (FUV) to near-infrared (near-IR) spectral energy distribution of seventeen 10 kpc diameter regions across the galaxy, and derived their star formation history, current star formation rate, and stellar population and mass. We find that most of the star formation takes place in the extended arms, with very little star formation in the central 5 kpc of the galaxy, in contrast to what was predicted from previous numerical simulations. There is a trend of increasing star formation activity with distance from the nucleus of the galaxy, and no evidence for a recent increase in the current star formation rate due to the interaction. The nucleus itself shows no significant current star formation activity. The extent of the Condor also provides an opportunity to test the applicability of a single standard prescription for conversion of the FUV + IR (22 μm) intensities to a star formation rate for all regions. We find that the conversion factor differs from region to region, arising from regional differences in the stellar populations.

  6. STAR Formation Histories Across the Interacting Galaxy NGC 6872, the Largest-Known Spiral

    NASA Technical Reports Server (NTRS)

    Eufrasio, Rafael T.; Dwek, E.; Arendt, RIchard G.; deMello, Duilia F.; Gadotti, DImitri A.; Urrutia-Viscarra, Fernanda; deOliveira, CLaudia Mendes; Benford, Dominic J.

    2014-01-01

    NGC6872, hereafter the Condor, is a large spiral galaxy that is interacting with its closest companion, the S0 galaxy IC 4970. The extent of the Condor provides an opportunity for detailed investigation of the impact of the interaction on the current star formation rate and its history across the galaxy, on the age and spatial distribution of its stellar population, and on the mechanism that drives the star formation activity. To address these issues we analyzed the far-ultraviolet (FUV) to near-infrared (near-IR) spectral energy distribution of seventeen 10 kpc diameter regions across the galaxy, and derived their star formation history, current star formation rate, and stellar population and mass. We find that most of the star formation takes place in the extended arms, with very little star formation in the central 5 kpc of the galaxy, in contrast to what was predicted from previous numerical simulations. There is a trend of increasing star formation activity with distance from the nucleus of the galaxy, and no evidence for a recent increase in the current star formation rate due to the interaction. The nucleus itself shows no significant current star formation activity. The extent of the Condor also provides an opportunity to test the applicability of a single standard prescription for conversion of the FUV + IR (22 micrometer) intensities to a star formation rate for all regions. We find that the conversion factor differs from region to region, arising from regional differences in the stellar populations.

  7. THE STAR FORMATION HISTORY AND CHEMICAL EVOLUTION OF STAR-FORMING GALAXIES IN THE NEARBY UNIVERSE

    SciTech Connect

    Torres-Papaqui, J. P.; Coziol, R.; Ortega-Minakata, R. A.; Neri-Larios, D. M. E-mail: rcoziol@astro.ugto.mx E-mail: daniel@astro.ugto.mx

    2012-08-01

    We have determined the metallicity (O/H) and nitrogen abundance (N/O) of a sample of 122,751 star-forming galaxies (SFGs) from the Data Release 7 of the Sloan Digital Sky Survey. For all these galaxies we have also determined their morphology and obtained a comprehensive picture of their star formation history (SFH) using the spectral synthesis code STARLIGHT. The comparison of the chemical abundance with the SFH allows us to describe the chemical evolution of the SFGs in the nearby universe (z {<=} 0.25) in a manner consistent with the formation of their stellar populations and morphologies. A high fraction (45%) of the SFGs in our sample show an excess abundance of nitrogen relative to their metallicity. We also find this excess to be accompanied by a deficiency of oxygen, which suggests that this could be the result of effective starburst winds. However, we find no difference in the mode of star formation of the nitrogen-rich and nitrogen-poor SFGs. Our analysis suggests that they all form their stars through a succession of bursts of star formation extended over a period of few Gyr. What produces the chemical differences between these galaxies seems therefore to be the intensity of the bursts: the galaxies with an excess of nitrogen are those that are presently experiencing more intense bursts or have experienced more intense bursts in their past. We also find evidence relating the chemical evolution process to the formation of the galaxies: the galaxies with an excess of nitrogen are more massive, and have more massive bulges and earlier morphologies than those showing no excess. Contrary to expectation, we find no evidence that the starburst wind efficiency decreases with the mass of the galaxies. As a possible explanation we propose that the loss of metals consistent with starburst winds took place during the formation of the galaxies, when their potential wells were still building up, and consequently were weaker than today, making starburst winds more

  8. Galaxy Structure as a Driver of the Star Formation Sequence Slope and Scatter

    NASA Astrophysics Data System (ADS)

    Whitaker, Katherine E.; 3D-HST Collaboration

    2016-01-01

    It is well established that (1) star-forming galaxies follow a relation between their star formation rate (SFR) and stellar mass (M*), the "star formation sequence," and (2) the SFRs of galaxies correlate with their structure, where star-forming galaxies are less concentrated than quiescent galaxies at fixed mass. In this talk, we consider whether the scatter and slope of the star formation sequence is correlated with systematic variations in the Sérsic indices, n, of galaxies across the SFR-M* plane. Using a mass-complete sample of 23,848 galaxies at 0.5 < z < 2.5 selected from the 3D-HST photometric catalogs, we find that the scatter of the star formation sequence is related in part to galaxy structure; the scatter due to variations in n at fixed mass for star-forming galaxies ranges from 0.14 ± 0.02 dex at z ˜ 2 to 0.30 ± 0.04 dex at z < 1. While the slope of the log(SFR)-log(M*) relation is of order unity for disk-like galaxies, galaxies with n > 2 (implying more dominant bulges) have significantly lower SFR/M* than the main ridgeline of the star formation sequence. These results suggest that bulges in massive z ˜ 2 galaxies are actively building up, where the stars in the central concentration are relatively young. At z < 1, the presence of older bulges within star-forming galaxies lowers global SFR/M*, decreasing the slope and contributing significantly to the scatter of the star formation sequence.

  9. Environmental effects on star formation in dwarf galaxies and star clusters

    NASA Astrophysics Data System (ADS)

    Pasetto, S.; Cropper, M.; Fujita, Y.; Chiosi, C.; Grebel, E. K.

    2015-01-01

    Context. The role of the environment in the formation of a stellar population is a difficult problem in astrophysics. The reason is that similar properties of a stellar population are found in star systems embedded in different environments or, vice versa, similar environments contain stellar systems with stellar populations having different properties. Aims: In this paper, we develop a simple analytical criterion to investigate the role of the environment on the onset of star formation. We will consider the main external agents that influence star formation (i.e. ram pressure, tidal interaction, Rayleigh-Taylor and Kelvin-Helmholtz instabilities) in a spherical galaxy moving through an external environment. The theoretical framework developed here has direct applications to the cases of dwarf galaxies in galaxy clusters and dwarf galaxies orbiting our Milky Way system, as well as any primordial gas-rich cluster of stars orbiting within its host galaxy. Methods: We develop an analytic formalism to solve the fluid dynamics equations in a non-inertial reference frame mapped with spherical coordinates. The two-fluids instability at the interface between a stellar system and its surrounding hotter and less dense environment is related to the star formation processes through a set of differential equations. The solution presented here is quite general, allowing us to investigate most kinds of orbits allowed in a gravitationally bound system of stars in interaction with a major massive companion. Results: We present an analytical criterion to elucidate the dependence of star formation in a spherical stellar system (as a dwarf galaxy or a globular cluster) on its surrounding environment useful in theoretical interpretations of numerical results as well as observational applications. We show how spherical coordinates naturally enlighten the interpretation of two-fluids instability in a geometry that directly applies to an astrophysical case. This criterion predicts the

  10. 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.

  11. Berkeley Prize: Mapping the Fuel for Star Formation in Early Universe Galaxies

    NASA Astrophysics Data System (ADS)

    Tacconi, Linda

    2012-01-01

    Stars form from cold molecular interstellar gas, which is relatively rare in galaxies like the Milky Way, which form only a few new stars per year. Massive galaxies in the distant universe formed stars much more rapidly. Was star formation more efficient in the past, and/or were early galaxies richer in molecular gas? The answer was elusive when our instruments could probe molecules only in the most luminous and rare objects such as mergers and quasars. But a new survey of molecular gas in typical massive star-forming galaxies at redshifts from about 1.2 to 2.3 (corresponding to when the universe was 24% to 40% of its current age) reveals that distant star-forming galaxies were indeed molecular-gas rich and that the star-formation efficiency is not strongly dependent on cosmic epoch.

  12. 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.

  13. 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.

  14. The star formation main sequence and stellar mass assembly of galaxies in the Illustris simulation

    NASA Astrophysics Data System (ADS)

    Sparre, Martin; Hayward, Christopher C.; Springel, Volker; Vogelsberger, Mark; Genel, Shy; Torrey, Paul; Nelson, Dylan; Sijacki, Debora; Hernquist, Lars

    2015-03-01

    Understanding the physical processes that drive star formation is a key challenge for galaxy formation models. In this paper, we study the tight correlation between the star formation rate (SFR) and stellar mass of galaxies at a given redshift, how halo growth influences star formation, and star formation histories of individual galaxies. We study these topics using Illustris, a state-of-the-art cosmological hydrodynamical simulation of galaxy formation. Illustris reproduces the observed relation (the star formation main sequence, SFMS) between SFR and stellar mass at redshifts z = 0 and 4, but at intermediate redshifts of z ≃ 1-2, the simulated SFMS has a significantly lower normalization than reported by observations. The scatter in the relation is consistent with the observed scatter. However, the fraction of outliers above the SFR-stellar mass relation in Illustris is less than that observed. Galaxies with halo masses of ˜1012 M⊙ dominate the SFR density of the Universe, in agreement with the results of abundance matching. Furthermore, more-massive galaxies tend to form the bulk of their stars at high redshift, which indicates that `downsizing' occurs in Illustris. We also studied the star formation histories of individual galaxies, including the use of a principal component analysis decomposition. We find that for fixed stellar mass, galaxies that form earlier have more-massive black holes at z = 0, indicating that star formation and black hole growth are tightly linked processes in Illustris. While many of the properties of normal star-forming galaxies are well reproduced in the Illustris simulation, forming a realistic population of starbursts will likely require higher resolution and probably a more sophisticated treatment of star formation and feedback from stars and black holes.

  15. Star formation in semi-analytic galaxy formation models with multiphase gas

    NASA Astrophysics Data System (ADS)

    Somerville, Rachel S.; Popping, Gergö; Trager, Scott C.

    2015-11-01

    We implement physically motivated recipes for partitioning cold gas into different phases (atomic, molecular, and ionized) in galaxies within semi-analytic models of galaxy formation based on cosmological merger trees. We then model the conversion of molecular gas into stars using empirical recipes motivated by recent observations. We explore the impact of these new recipes on the evolution of fundamental galaxy properties such as stellar mass, star formation rate (SFR), and gas and stellar phase metallicity. We present predictions for stellar mass functions, stellar mass versus SFR relations, and cold gas phase and stellar mass-metallicity relations for our fiducial models, from redshift z ˜ 6 to the present day. In addition we present predictions for the global SFR, mass assembly history, and cosmic enrichment history. We find that the predicted stellar properties of galaxies (stellar mass, SFR, metallicity) are remarkably insensitive to the details of the recipes used for partitioning gas into H I and H2. We see significant sensitivity to the recipes for H2 formation only in very low mass haloes (M_h ≲ 10^{10.5} M_{⊙}), which host galaxies with stellar masses m_* ≲ 10^8 M_{⊙}. The properties of low-mass galaxies are also quite insensitive to the details of the recipe used for converting H2 into stars, while the formation epoch of massive galaxies does depend on this significantly. We argue that this behaviour can be interpreted within the framework of a simple equilibrium model for galaxy evolution, in which the conversion of cold gas into stars is balanced on average by inflows and outflows.

  16. Linking the structural properties of galaxies and their star formation histories with STAGES

    NASA Astrophysics Data System (ADS)

    Hoyos, Carlos; Aragón-Salamanca, Alfonso; Gray, Meghan E.; Wolf, Christian; Maltby, David T.; Bell, Eric F.; Böhm, Asmus; Jogee, Shardha

    2016-01-01

    We study the links between star formation history and structure for a large mass-selected galaxy sample at 0.05 ≤ zphot ≤ 0.30. The galaxies inhabit a very broad range of environments, from cluster cores to the field. Using Hubble Space Telescope (HST) images, we quantify their structure following Hoyos et al., and divide them into disturbed and undisturbed. We also visually identify mergers. Additionally, we provide a quantitative measure of the degree of disturbance for each galaxy (`roughness'). The majority of elliptical and lenticular galaxies have relaxed structure, showing no signs of ongoing star formation. Structurally disturbed galaxies, which tend to avoid the lowest density regions, have higher star formation activity and younger stellar populations than undisturbed systems. Cluster spirals with reduced/quenched star formation have somewhat less disturbed morphologies than spirals with `normal' star formation activity, suggesting that these `passive' spirals have started their morphological transformation into S0s. Visually identified mergers and galaxies not identified as mergers but with similar roughness have similar specific star formation rates and stellar ages. The degree of enhanced star formation is thus linked to the degree of structural disturbance, regardless of whether it is caused by major mergers or not. This suggests that merging galaxies are not special in terms of their higher-than-normal star formation activity. Any physical process that produces `roughness', or regions of enhanced luminosity density, will increase the star formation activity in a galaxy with similar efficiency. An alternative explanation is that star formation episodes increase the galaxies' roughness similarly, regardless of whether they are merger induced or not.

  17. 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.

  18. Stellar velocity dispersion in dissipative galaxy mergers with star formation

    SciTech Connect

    Stickley, Nathaniel R.; Canalizo, Gabriela

    2014-05-01

    In order to better understand stellar dynamics in merging systems, such as NGC 6240, we examine the evolution of central stellar velocity dispersion (σ{sub *}) in dissipative galaxy mergers using a suite of binary disk merger simulations that include feedback from stellar formation and active galactic nuclei (AGNs). We find that σ{sub *} undergoes the same general stages of evolution that were observed in our previous dissipationless simulations: coherent oscillation, then phase mixing, followed by dynamical equilibrium. We also find that measurements of σ{sub *} that are based only upon the youngest stars in simulations consistently yield lower values than measurements based upon the total stellar population. This finding appears to be consistent with the so-called 'σ{sub *} discrepancy', observed in real galaxies. We note that quasar-level AGN activity is much more likely to occur when σ{sub *} is near its equilibrium value rather than during periods of extreme σ{sub *}. Finally, we provide estimates of the scatter inherent in measuring σ{sub *} in ongoing mergers.

  19. Feedback Regulated Star Formation in Cool Core Clusters of Galaxies

    NASA Astrophysics Data System (ADS)

    Tremblay, Grant Russell

    2011-07-01

    The classical "cooling flow" model historically associated with "cool core" clusters of galaxies fails in the absence of an external, non-gravitational heating mechanism needed to offset catastrophic radiative losses of the X-ray bright intracluster medium (ICM). Numerous proposed solutions exist, including feedback from active galactic nuclei (AGN), which may elegantly calibrate fundamental relationships such as the coupled co-evolution of black holes and the stellar component of their host galaxies. AGN feedback cannot completely offset cooling at all times, however, as the brightest cluster galaxies (BCGs) in cool core clusters harbor extensive warm (˜104 K) and cold (10 < T < 104 K) gas reservoirs whose physical properties are regulated by ongoing star formation and an unknown, non-stellar heating mechanism. We present a doctoral thesis broadly related to these issues, particularly as they pertain to cooling flows, the triggering of AGN activity, and the associated energetic feedback that may play a critical role in heating the ambient environment on tens to hundreds of kiloparsec scales. We begin with a summary of the relevant background material, and in Chapter 2 we present a multiwavelength study of effervescent AGN heating in the cool core cluster Abell 2597. Previously unpublished Chandra X-ray data show the central regions of the hot intracluster medium (ICM) to be highly anisotropic on the scale of the BCG, permeated by a network of kpc-scale X-ray cavities, the largest of which is cospatial in projection with extended 330 MHz radio emission. We present spectral maps of projected, modeled gas properties fit to the X-ray data. The X-ray temperature map reveals two discrete, "hard-edged'' structures, including a ˜15 kpc "cold filament'' and an arc of hot gas which in projection borders the inner edge of the large X-ray cavity. We interpret the latter in the context of the effervescent AGN heating model, in which cavity enthalpy is thermalized as the

  20. Gas infall and stochastic star formation in galaxies in the local universe

    NASA Astrophysics Data System (ADS)

    Kauffmann, Guinevere; Heckman, Timothy M.; De Lucia, Gabriella; Brinchmann, Jarle; Charlot, Stéphane; Tremonti, Christy; White, Simon D. M.; Brinkmann, Jon

    2006-04-01

    We study the recent star formation histories of local galaxies by analysing the scatter in their colours and spectral properties. We present evidence that the distribution of star formation histories changes qualitatively above a characteristic stellar surface mass density of 3 × 108Msolarkpc-2, corresponding to the transition between disc-dominated (late-type) galaxies and bulge-dominated (early-type) systems. When we average over subpopulations of galaxies with densities below this value, we find that subpopulations of all masses and densities form their stars at the same average rate per unit stellar mass. However, the scatter in galaxy colours, stellar absorption-line indices and emission-line strengths is larger for more compact galaxies of a given mass. This suggests that star formation occurs in shorter, higher amplitude events in galaxies with smaller sizes. Above the characteristic density, galaxy growth through star formation shuts down and the scatter in galaxy colours and spectral properties decreases. We propose that in low-density galaxies, star formation events are triggered when cold gas is accreted on to a galaxy. We have used a new high-resolution numerical simulation of structure formation in a `concordance' Lambda cold dark matter (ΛCDM) universe to quantify the incidence of these accretion events, and we show that the observational data are well fitted by a model in which the consumption time of accreted gas decreases with the surface density of the galaxy as tcons~μ-1*. The dark matter haloes that host massive galaxies with high stellar surface mass densities are also expected to grow through accretion, but the observations indicate that in bulge-dominated galaxies, star formation is no longer coupled to the hierarchical build-up of these systems.

  1. A CORRELATION BETWEEN STAR FORMATION RATE AND AVERAGE BLACK HOLE ACCRETION IN STAR-FORMING GALAXIES

    SciTech Connect

    Chen, Chien-Ting J.; Hickox, Ryan C.; Alberts, Stacey; Pope, Alexandra; Brodwin, Mark; Jones, Christine; Forman, William R.; Goulding, Andrew D.; Murray, Stephen S.; Alexander, David M.; Mullaney, James R.; Assef, Roberto J.; Gorjian, Varoujan; Brown, Michael J. I.; Dey, Arjun; Jannuzi, Buell T.; Le Floc'h, Emeric

    2013-08-10

    We present a measurement of the average supermassive black hole accretion rate (BHAR) as a function of the star formation rate (SFR) for galaxies in the redshift range 0.25 < z < 0.8. We study a sample of 1767 far-IR-selected star-forming galaxies in the 9 deg{sup 2} Booetes multi-wavelength survey field. The SFR is estimated using 250 {mu}m observations from the Herschel Space Observatory, for which the contribution from the active galactic nucleus (AGN) is minimal. In this sample, 121 AGNs are directly identified using X-ray or mid-IR selection criteria. We combined these detected AGNs and an X-ray stacking analysis for undetected sources to study the average BHAR for all of the star-forming galaxies in our sample. We find an almost linear relation between the average BHAR (in M{sub Sun} yr{sup -1}) and the SFR (in M{sub Sun} yr{sup -1}) for galaxies across a wide SFR range 0.85 < log SFR < 2.56: log BHAR = (- 3.72 {+-} 0.52) + (1.05 {+-} 0.33)log SFR. This global correlation between SFR and average BHAR is consistent with a simple picture in which SFR and AGN activity are tightly linked over galaxy evolution timescales.

  2. 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.

  3. The star formation rate intensity distribution function—. Comparison of observations with hierarchical galaxy formation

    NASA Astrophysics Data System (ADS)

    Barkana, Rennan

    2002-09-01

    Recently, Lanzetta et al. [ApJ (2002) in press] have measured the distribution of star formation rate intensity in galaxies at various redshifts. This data set has a number of advantages relative to galaxy luminosity functions; the effect of surface-brightness dimming on the selection function is simpler to understand, and this data set also probes the size distribution of galactic disks. We predict this function using semi-analytic models of hierarchical galaxy formation in a ΛCDM cosmology. We show that the basic trends found in the data follow naturally from the redshift evolution of dark matter halos. The data are consistent with a constant efficiency of turning gas into stars in galaxies, with a best-fit value of 2%, where dust obscuration is neglected; equivalently, the data are consistent with a cosmic star formation rate which is constant to within a factor of two at all redshifts above two. However, the practical ability to use this kind of distribution to measure the total cosmic star formation rate is limited by the predicted shape of an approximate power law with a smoothly varying power, without a sharp break.

  4. Towards Understanding the Star Formation-Feedback Loop in Galaxy Formation and Evolution

    NASA Astrophysics Data System (ADS)

    Kravtsov, Andrey

    We propose to carry out a comprehensive study of how star formation and feedback loop influences evolution of galaxies using a suite of ultra-high resolution cosmological simulations of galaxy formation using the Adaptive Mesh Refinement (AMR) approach implemented in the Adaptive Refinement Tree (ART) code. The simulations will result in the numerical models of galaxy evolution of unprecedented resolution and sophistication of the processes included. Our code includes treatment of a wide spectrum of processes critical for realistic modeling of galaxy formation from the primordial chemistry of hydrogen and helium species, radiative transfer of ionizing radiation, to the metallicity- dependent cooling, chemistry of molecular hydrogen on dust and treatment of radiative transfer of dissociating far ultraviolet radiation. The latter allows us to tie star formation with dense, molecular regions capable of self-shielding from heating radiation and avoid adopting arbitrary density and temperature thresholds for star formation. Simulations will also employ a new model for momentum injection due to radiation pressure exerted by young massive stars onto surrounding dust and gas. This early, pre-supernova feedback is critical to prompt dispersal of natal molecular clouds and regulating star formation efficiency and increasing efficiency of energy release by supernovae. The simulations proposed in this project will therefore treat the most important process to understanding the efficiency of baryon conversion to stars - the star formation - in the way most closely resembling the actual star formation observed in galaxies and stellar feedback model that is firmly rooted in observational evidence on how feedback operates in real molecular clouds. The simulations we propose will provide models of galaxy evolution during three important epochs in the history of the universe: (1) early evolution prior to and during the reionization of the universe (the first billion years of

  5. Mapping galaxy encounters in numerical simulations: the spatial extent of induced star formation

    NASA Astrophysics Data System (ADS)

    Moreno, Jorge; Torrey, Paul; Ellison, Sara L.; Patton, David R.; Bluck, Asa F. L.; Bansal, Gunjan; Hernquist, Lars

    2015-04-01

    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.

  6. Detection of Molecular Gas in Void Galaxies : Implications for Star Formation in Isolated Environments

    NASA Astrophysics Data System (ADS)

    Das, M.; Saito, T.; Iono, D.; Honey, M.; Ramya, S.

    2015-12-01

    We present the detection of molecular gas from galaxies located in nearby voids using the CO(1-0) line emission as a tracer. The observations were performed using the 45 m single dish radio telescope of the Nobeyama Radio Observatory. Void galaxies lie in the most underdense parts of our universe and a significant fraction of them are gas rich, late-type spiral galaxies. Although isolated, they have ongoing star formation but appear to be slowly evolving compared to galaxies in denser environments. Not much is known about their star formation properties or cold gas content. In this study, we searched for molecular gas in five void galaxies. The galaxies were selected based on their relatively high IRAS fluxes or Hα line luminosities, both of which signify ongoing star formation. All five galaxies appear to be isolated and two lie within the Bootes void. We detected CO(1-0) emission from four of the five galaxies in our sample and their molecular gas masses lie between 108 and 109 M⊙. We conducted follow-up Hα imaging observations of three detected galaxies using the Himalayan Chandra Telescope and determined their star formation rates (SFRs) from their Hα fluxes. The SFR varies from 0.2 to 1 M⊙ yr-1 which is similar to that observed in local galaxies. Our study indicates that although void galaxies reside in underdense regions, their disks contain molecular gas and have SFRs similar to galaxies in denser environments. We discuss the implications of our results.

  7. 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

  8. Properties of Outflows from Dwarf Galaxies: Insights into the Evolution of the Star Formation Rate

    NASA Astrophysics Data System (ADS)

    Martin, C. L.

    1997-12-01

    Stellar winds and supernovae from massive stars have a strong impact on the interstellar medium. In dwarf galaxies, for example, the supernova explosions following a burst of star formation are predicted to drive any remaining interstellar gas out of the galaxy (Larson 1974; Dekel & Silk 1986). Uncertainties about the role of this feedback process -- and related but less violent activity -- in regulating the star formation rate in a galaxy pose a critical problem for theories of galaxy formation and evolution. I will present measurements of disk mass-loss rates in 15 nearby dwarf galaxies, examine the efficiency of mass ejection relative to the star formation rate, and discuss the effect of the halo potential on the fate of the outflowing gas.

  9. MOLECULAR GAS AND STAR FORMATION IN NEARBY DISK GALAXIES

    SciTech Connect

    Leroy, Adam K.; Munoz-Mateos, Juan-Carlos; Walter, Fabian; Sandstrom, Karin; Meidt, Sharon; Rix, Hans-Walter; Schinnerer, Eva; Schruba, Andreas; Bigiel, Frank; Bolatto, Alberto; Brinks, Elias; De Blok, W. J. G.; Rosolowsky, Erik; Schuster, Karl-Friedrich; Usero, Antonio

    2013-08-01

    We compare molecular gas traced by {sup 12}CO (2-1) maps from the HERACLES survey, with tracers of the recent star formation rate (SFR) across 30 nearby disk galaxies. We demonstrate a first-order linear correspondence between {Sigma}{sub mol} and {Sigma}{sub SFR} but also find important second-order systematic variations in the apparent molecular gas depletion time, {tau}{sub dep}{sup mol}={Sigma}{sub mol}/{Sigma}{sub SFR}. At the 1 kpc common resolution of HERACLES, CO emission correlates closely with many tracers of the recent SFR. Weighting each line of sight equally, using a fixed {alpha}{sub CO} equivalent to the Milky Way value, our data yield a molecular gas depletion time, {tau}{sub dep}{sup mol}={Sigma}{sub mol}/{Sigma}{sub SFR}{approx}2.2 Gyr with 0.3 dex 1{sigma} scatter, in very good agreement with recent literature data. We apply a forward-modeling approach to constrain the power-law index, N, that relates the SFR surface density and the molecular gas surface density, {Sigma}{sub SFR}{proportional_to}{Sigma}{sub mol}{sup N}. We find N = 1 {+-} 0.15 for our full data set with some scatter from galaxy to galaxy. This also agrees with recent work, but we caution that a power-law treatment oversimplifies the topic given that we observe correlations between {tau}{sub dep}{sup mol} and other local and global quantities. The strongest of these are a decreased {tau}{sub dep}{sup mol} in low-mass, low-metallicity galaxies and a correlation of the kpc-scale {tau}{sub dep}{sup mol} with dust-to-gas ratio, D/G. These correlations can be explained by a CO-to-H{sub 2} conversion factor ({alpha}{sub CO}) that depends on dust shielding, and thus D/G, in the theoretically expected way. This is not a unique interpretation, but external evidence of conversion factor variations makes this the most conservative explanation of the strongest observed {tau}{sub dep}{sup mol} trends. After applying a D/G-dependent {alpha}{sub CO}, some weak correlations between {tau}{sub dep

  10. Star Formation and Gas Densities in the Dwarf Irregular Galaxy Sextans A

    NASA Astrophysics Data System (ADS)

    Plummer, Julia D.; Hunter, Deidre A.

    1995-12-01

    As a step in understanding the process of star formation in irregular galaxies, we have analysed the irregular galaxy Sextans A. Irregular galaxies provide star-forming systems that are unperturbed by spiral density waves. Sextans A is a tiny galaxy, 1.3 Mpc distant, just beyond the dynamic boundary of the Local Group. We studied the star formation properties of this galaxy using UBV and Hα images. Stars are not currently forming in the center of this galaxy, though they have in the past. The current star formation is in clumps in the outer parts of the galaxy and is not evenly distributed. The total Hα luminosity found for Sextans A is 9 x 10(38) erg/s, which corresponds to a star formation rate of 6 x 10(-3) Mmathordsun /yr for standard assumptions. The rate per unit area, within the Holmberg radius, is 6 x 10(-10) Mmathordsun /yr/pc(2) . Skillman et al. (1988) derived a total HI mass of 6 x 10(7) Mmathordsun . At its present rate, Sextans A will use up all of its gas in 12 x 10(9) yr, including the He contribution. We have also compared the star formation and gas density in Sextans A to critical gas surface density models (Toomre 1964, Quirk 1972, Kennicutt 1988). We used a published rotation curve to calculate the critical gas density necessary for the instabilities that produce star-forming clouds (Skillman et al. 1988). The ratio of observed to critical gas density is low in Sextans A, at the low end of values found by Kennicutt (1988) for spiral galaxies. The current star formation is located in the region of the galaxy with higher radially averaged observed gas densities relative to the critical density. This suggests that Sextans A has a difficult time forming gas clouds, resulting in an observed low star formation rate. This research was funded by the REU program at Northern Arizona University.

  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. Star formation and feedback from radio galaxies: Insights from large multiwavelength surveys

    NASA Astrophysics Data System (ADS)

    Pace, Cameron J.

    Active galactic nuclei (AGN) are believed to play an important role in the evolution of their host galaxies by influencing the galaxy's gas reservoirs. This may affect the growth of the galaxy's massive black hole and star formation in the host galaxy. I address two unanswered questions central to our understanding of AGN: what triggers AGN, and how and to what extent do they affect their host and neighboring galaxies? I study radio galaxies, which are a subset of AGN, because their radio jets may provide a natural feedback mechanism between the AGN and the host and neighboring galaxies. Previous studies, which were limited to small samples, produce conflicting results as to whether mergers or environmental effects lead to triggering. It is also uncertain whether radio galaxies have a net positive (via gas cloud collapse) or negative (via gas heating) effect on star formation. I use a large (˜7,200), statistically significant sample of radio galaxies, for which I extract photometric information from several large-scale, multiwavelength surveys. The radio galaxies are compared to a sample of control galaxies whose properties match those of the radio galaxies, except for their lack of radio activity. This approach allows me to determine the frequency of feedback events and whether radio galaxies are responsible. I derive and compare composite spectral energy distributions (SEDs) for the radio galaxies and control sample, and find a deficit of ultraviolet and infrared emission for slow accreting radio galaxies, suggesting that they may suppress star formation in their hosts. Fast accreting radio galaxies are found to have an infrared excess, which is characteristic of their high accretion rate and not a result of AGN feedback on star formation. I compare the populations of neighbor galaxies of the two samples and find that radio galaxies have an excess of neighbors within 100 kpc, which must play a role in triggering. My results also show that radio galaxies rarely

  13. SUSTAINING STAR FORMATION RATES IN SPIRAL GALAXIES: SUPERNOVA-DRIVEN TURBULENT ACCRETION DISK MODELS APPLIED TO THINGS GALAXIES

    SciTech Connect

    Vollmer, Bernd; Leroy, Adam K.

    2011-01-15

    Gas disks of spiral galaxies can be described as clumpy accretion disks without a coupling of viscosity to the actual thermal state of the gas. The model description of a turbulent disk consisting of emerging and spreading clumps contains free parameters, which can be constrained by observations of molecular gas, atomic gas, and the star formation rate for individual galaxies. Radial profiles of 18 nearby spiral galaxies from THINGS, HERACLES, SINGS, and GALEX data are used to compare the observed star formation efficiency, molecular fraction, and velocity dispersion to the model. The observed radially decreasing velocity dispersion can be reproduced by the model. In the framework of this model, the decrease in the inner disk is due to the stellar mass distribution which dominates the gravitational potential. Introducing a radial break in the star formation efficiency into the model improves the fits significantly. This change in the star formation regime is realized by replacing the free-fall time in the prescription of the star formation rate with the molecule formation timescale. Depending on the star formation prescription, the break radius is located near the transition region between the molecular-gas-dominated and atomic-gas-dominated parts of the galactic disk or closer to the optical radius. It is found that only less massive galaxies (log M(M{sub sun}) {approx}< 10) can balance gas loss via star formation by radial gas accretion within the disk. These galaxies can thus access their gas reservoirs with large angular momentum. On the other hand, the star formation of massive galaxies is determined by the external gas mass accretion rate from a putative spherical halo of ionized gas or from satellite accretion. In the absence of this external accretion, star formation slowly exhausts the gas within the optical disk within the star formation timescale.

  14. The evolution of the star-forming sequence in hierarchical galaxy formation models

    NASA Astrophysics Data System (ADS)

    Mitchell, Peter D.; Lacey, Cedric G.; Cole, Shaun; Baugh, Carlton M.

    2014-11-01

    It has been argued that the specific star formation rates of star-forming galaxies inferred from observational data decline more rapidly below z = 2 than is predicted by hierarchical galaxy formation models. We present a detailed analysis of this problem by comparing predictions from the GALFORM semi-analytic model with an extensive compilation of data on the average star formation rates of star-forming galaxies. We also use this data to infer the form of the stellar mass assembly histories of star-forming galaxies. Our analysis reveals that the currently available data favour a scenario where the stellar mass assembly histories of star-forming galaxies rise at early times and then fall towards the present day. In contrast, our model predicts stellar mass assembly histories that are almost flat below z = 2 for star-forming galaxies, such that the predicted star formation rates can be offset with respect to the observational data by factors of up to 2-3. This disagreement can be explained by the level of coevolution between stellar and halo mass assembly that exists in contemporary galaxy formation models. In turn, this arises because the standard implementations of star formation and supernova feedback used in the models result in the efficiencies of these process remaining approximately constant over the lifetime of a given star-forming galaxy. We demonstrate how a modification to the time-scale for gas ejected by feedback to be reincorporated into galaxy haloes can help to reconcile the model predictions with the data.

  15. The Mass Dependence of Star Formation Histories in Barred Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Carles, Christian; Martel, Hugo; Ellison, Sara L.; Kawata, Daisuke

    2016-08-01

    We performed a series of 29 gasdynamical simulations of disc galaxies, barred and unbarred, with various stellar masses, to study the impact of the bar on star formation history. Unbarred galaxies evolve very smoothly, with a star formation rate (SFR) that varies by at most a factor of three over a period of 2 Gyr. The evolution of barred galaxies is much more irregular, especially at high stellar masses. In these galaxies, the bar drives a substantial amount of gas toward the centre, resulting in a high SFR, and producing a starburst in the most massive galaxies. Most of the gas is converted into stars, and gas exhaustion leads to a rapid drop of star formation after the starburst. In massive barred galaxies (stellar mass M★ > 2 × 1010 M⊙) the large amount of gas funnelled toward the centre is completely consumed by the starburst, while in lower-mass barred galaxies it is only partially consumed. Gas concentration is thus higher in lower-mass barred galaxies than it is in higher-mass ones. Even though unbarred galaxies funnelled less gas toward their centre, the lower SFR allows this gas to accumulate. At late times, the star formation efficiency is higher in barred galaxies than unbarred ones, enabling these galaxies to maintain a higher SFR with a smaller gas supply. Several properties, such as the global SFR, central SFR, or central gas concentration, vary monotonically with time for unbarred galaxies, but not for barred galaxies. Therefore one must be careful when comparing barred and unbarred galaxies that share one observational property, since these galaxies might be at very different stages of their respective evolution.

  16. Ghostly Halos in Dwarf Galaxies: a probe of star formation in the Early Universe

    NASA Astrophysics Data System (ADS)

    Kang, Hoyoung; Ricotti, Massimo

    2016-01-01

    We carry out numerical simulations to characterize the size, stellar mass, and stellar mass surface density of extended stellar halos in dwarf galaxies as a function of dark matter halo mass. We expect that for galaxies smaller than a critical value, these ghostly halos will not exist because the smaller galactic subunits that build it up, do not form any stars. The detection of ghostly halos around isolated dwarf galaxies is a sensitive test of the efficiency of star formation in the first galaxies and of whether ultra-faint dwarf satellites of the Milky Way are fossils of the first galaxies.

  17. A Comparative Study of Knots of Star Formation in Interacting versus Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Smith, Beverly J.; Zaragoza-Cardiel, Javier; Struck, Curtis; Olmsted, Susan; Jones, Keith

    2016-03-01

    Interacting galaxies are known to have higher global rates of star formation on average than normal galaxies, relative to their stellar masses. Using UV and IR photometry combined with new and published Hα images, we have compared the star formation rates (SFRs) of ∼700 star forming complexes in 46 nearby interacting galaxy pairs with those of regions in 39 normal spiral galaxies. The interacting galaxies have proportionally more regions with high SFRs than the spirals. The most extreme regions in the interacting systems lie at the intersections of spiral/tidal structures, where gas is expected to pile up and trigger star formation. Published Hubble Space Telescope images show unusually large and luminous star clusters in the highest luminosity regions. The SFRs of the clumps correlate with measures of the dust attenuation, consistent with the idea that regions with more interstellar gas have more star formation. For the clumps with the highest SFRs, the apparent dust attenuation is consistent with the Calzetti starburst dust attenuation law. This suggests that the high luminosity regions are dominated by a central group of young stars surrounded by a shell of clumpy interstellar gas. In contrast, the lower luminosity clumps are bright in the UV relative to Hα, suggesting either a high differential attenuation between the ionized gas and the stars, or a post-starburst population bright in the UV but faded in Hα. The fraction of the global light of the galaxies in the clumps is higher on average for the interacting galaxies than for the spirals. Thus either star formation in interacting galaxies is “clumpier” on average, or the star forming regions in interacting galaxies are more luminous, dustier, or younger on average.

  18. DWARF GALAXY FORMATION WITH H{sub 2}-REGULATED STAR FORMATION

    SciTech Connect

    Kuhlen, Michael; Krumholz, Mark R.; Madau, Piero; Smith, Britton D.; Wise, John

    2012-04-10

    We describe cosmological galaxy formation simulations with the adaptive mesh refinement code Enzo that incorporate a star formation prescription regulated by the local abundance of molecular hydrogen. We show that this H{sub 2}-regulated prescription leads to a suppression of star formation in low-mass halos (M{sub h} {approx}< 10{sup 10} M{sub Sun }) at z > 4, alleviating some of the dwarf galaxy problems faced by theoretical galaxy formation models. H{sub 2} regulation modifies the efficiency of star formation of cold gas directly, rather than indirectly reducing the cold gas content with 'supernova feedback'. We determine the local H{sub 2} abundance in our most refined grid cells (76 proper parsec in size at z = 4) by applying the model of Krumholz, McKee, and Tumlinson, which is based on idealized one-dimensional radiative transfer calculations of H{sub 2} formation-dissociation balance in {approx}100 pc atomic-molecular complexes. Our H{sub 2}-regulated simulations are able to reproduce the empirical (albeit lower z) Kennicutt-Schmidt relation, including the low {Sigma}{sub gas} cutoff due to the transition from atomic to molecular phase and the metallicity dependence thereof, without the use of an explicit density threshold in our star formation prescription. We compare the evolution of the luminosity function, stellar mass density, and star formation rate density from our simulations to recent observational determinations of the same at z = 4-8 and find reasonable agreement between the two.

  19. Environmental Effects on the ISM and Star Formation Properties of Nearby Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Mok, Angus; Wilson, Christine

    2015-08-01

    We present the results from a sample of HI flux-selected spiral galaxies within 25 Mpc from the JCMT Nearby Galaxies Legacy Survey (NGLS), subdivided into isolated, group, and Virgo cluster samples. The CO J=3-2 line was observed with the James Clerk Maxwell Telescope (JCMT), a tracer for the dense molecular gas linked to star formation. We combine the CO data with integrated star formation rates using H-alpha measurements and stellar masses from the S4G Survey in order to study the link between the gas and stars inside these galaxies. We find that while the mean atomic gas mass is lower for the Virgo galaxies compared to the isolated galaxies, the distributions of molecular gas masses are not significantly different between the three samples. The specific star formation rate is also lower for the Virgo sample, followed by the group and isolated galaxies. Finally, the molecular gas depletion time is longer for the Virgo galaxies compared to the group and isolated galaxies, which suggests the possible effects of environment on the galaxy's star formation properties.

  20. A comparison of star formation characteristics in different types of irregular galaxies

    NASA Technical Reports Server (NTRS)

    Lamb, S. S.; Hunter, D. A.; Gallagher, J. S. I.

    1986-01-01

    Two regions of recent star formation in blue irregular galaxies were observed with the IUE in the short wavelength, low dispersion mode. The spectra indicates that the massive star content is similar in these regions and is best fit by massive stars formed in a burst and now are approximately 2.5 to 3.0 million years old.

  1. Tidally triggered star formation in gravitationally interacting galaxies and selected work in optical instrumentation

    NASA Astrophysics Data System (ADS)

    Woods, Deborah Freedman

    In the first part of this thesis I present studies of tidally triggered star formation in pairs of gravitationally interacting galaxies. I use spectroscopic and photometric observations of local systems to demonstrate that triggered star formation depends both on intrinsic galaxy properties and on relative properties of the system. Minor galaxy interactions, where the luminosity ratio of the galaxies exceeds about six, produce triggered star formation only in the lower luminosity companion. In interactions between galaxies of similar luminosity, the blue galaxies exhibit tidally triggered star formation, but the red galaxies do not. I measure the strength, frequency, and timescale of gravitational tidal interactions between galaxy pairs in a complete spectroscopic survey at redshifts 0.08 to 0.38. A third of the galaxies with young stellar populations interacting with a companion of similar luminosity experience enhanced star formation activity. However, the most extreme bursts of triggered star formation are rare and short lived. The typical duration for enhanced star formation in interacting galaxies is of order 300 Myr. In the second part of this thesis I describe the development of optical instrumentation in support of large spectroscopic surveys. I analyze the effects of flexure in the Binospec spectrograph, a multi-object spectrograph for the 6.5-meter MMT telescope at Mt. Hopkins, AZ. I design the active flexure control system and the calibration system, two physically distinct systems that together will enable accurate and stable spectro-photometric calibration. Improvements to telescope collimation and mirror support provide additional benefit to spectroscopic surveys through superior image quality and spectrograph efficiency. I design and build a Shack-Hartmann wavefront sensor for the 1.5-meter Tillinghast telescope at Mount Hopkins, AZ. The wavefront sensor and accompanying software serve as valuable tools for measuring and correcting for optical

  2. The rarity of star formation in brightest cluster galaxies as measured by WISE

    NASA Astrophysics Data System (ADS)

    Fraser-McKelvie, Amelia; Brown, Michael J. I.; Pimbblet, Kevin A.

    2014-10-01

    We present the mid-infrared star formation rates of 245 X-ray selected, nearby (z < 0.1) brightest cluster galaxies (BCGs). A homogeneous and volume limited sample of BCGs was created by X-ray selecting clusters with Lx > 1 × 1044 erg s- 1. The Wide-Field Infrared Survey Explorer (WISE) All WISE Data Release provides the first measurement of the 12 μm star formation indicator for all BCGs in the nearby Universe. Perseus A and Cygnus A are the only galaxies in our sample to have star formation rates of > 40 M⊙ yr- 1, indicating that these two galaxies are highly unusual at current times. Stellar populations of 99 ± 0.6 per cent of local BCGs are (approximately) passively evolving, with star formation rates of < 10 M⊙ yr- 1. We find that in general, star formation produces only modest BCG growth at the current epoch.

  3. Dynamical Properties of z ~ 2 Star-forming Galaxies and a Universal Star Formation Relation

    NASA Astrophysics Data System (ADS)

    Bouché, N.; Cresci, G.; Davies, R.; Eisenhauer, F.; Förster Schreiber, N. M.; Genzel, R.; Gillessen, S.; Lehnert, M.; Lutz, D.; Nesvadba, N.; Shapiro, K. L.; Sternberg, A.; Tacconi, L. J.; Verma, A.; Cimatti, A.; Daddi, E.; Renzini, A.; Erb, D. K.; Shapley, A.; Steidel, C. C.

    2007-12-01

    We present the first comparison of the dynamical properties of different samples of z~1.4-3.4 star-forming galaxies from spatially resolved imaging spectroscopy from SINFONI/VLT integral field spectroscopy and IRAM CO millimeter interferometry. Our samples include 16 rest-frame UV-selected, 16 rest-frame optically selected, and 13 submillimeter galaxies (SMGs). We find that rest-frame UV and optically bright (K<20) z~2 star forming galaxies are dynamically similar, and follow the same velocity-size relation as disk galaxies at z~0. In the theoretical framework of rotating disks forming from dissipative collapse in dark matter halos, the two samples require a spin parameter <λ> ranging from 0.06 to 0.2. In contrast, bright SMGs (S850μm>=5 mJy) have larger velocity widths and are much more compact. Hence, SMGs have lower angular momenta and higher matter densities than either the UV or optically selected populations. This indicates that dissipative major mergers may dominate the SMGs population, resulting in early spheroids, and that a significant fraction of the UV/optically bright galaxies have evolved less violently, either in a series of minor mergers, or in rapid dissipative collapse from the halo, given that either process may leads to the formation of early disks. These early disks may later evolve into spheroids via disk instabilities or mergers. Because of their small sizes and large densities, SMGs lie at the high surface density end of a universal (out to z=2.5) ``Schmidt-Kennicutt'' relation between gas surface density and star formation rate surface density. The best-fit relation suggests that the star formation rate per unit area scales as the surface gas density to a power of ~1.7, and that the star formation efficiency increases by a factor of 4 between non-starbursts and strong starbursts. Based on observations at the Very Large Telescope (VLT) of the European Southern Observatory (ESO), Paranal, Chile, under programs GTO 073.B-9018, 074.A-9011

  4. Galaxy pairs in the Sloan Digital Sky Survey - X. Does gas content alter star formation rate enhancement in galaxy interactions?

    NASA Astrophysics Data System (ADS)

    Scudder, Jillian M.; Ellison, Sara L.; Momjian, Emmanuel; Rosenberg, Jessica L.; Torrey, Paul; Patton, David R.; Fertig, Derek; Mendel, J. Trevor

    2015-06-01

    New spectral line observations, obtained with the Jansky Very Large Array (VLA), of a sample of 34 galaxies in 17 close pairs are presented in this paper. The sample of galaxy pairs is selected to contain galaxies in close, major interactions (i.e. projected separations <30 h_{70}^{-1} kpc, and mass ratios less extreme than 4:1), while still having a sufficiently large angular separation that the VLA can spatially resolve both galaxies in the pair. Of the 34 galaxies, 17 are detected at >3σ. We compare the H I gas fraction of the galaxies with the triggered star formation present in that galaxy. When compared to the star formation rates (SFRs) of non-pair galaxies matched in mass, redshift, and local environment, we find that the star formation enhancement is weakly positively correlated (˜2.5σ) with H I gas fraction. In order to help understand the physical mechanisms driving this weak correlation, we also present results from a small suite of binary galaxy merger simulations with varying gas fractions. The simulated galaxies indicate that larger initial gas fractions are associated with lower levels of interaction-triggered star formation (relative to an identical galaxy in isolation), but also show that high gas fraction galaxies have higher absolute SFRs prior to an interaction. We show that when interaction-driven SFR enhancements are calculated relative to a galaxy with an average gas fraction for its stellar mass, the relationship between SFR and initial gas fraction dominates over the SFR enhancements driven by the interaction. Simulated galaxy interactions that are matched in stellar mass but not in gas fraction, like our VLA sample, yield the same general positive correlation between SFR enhancement and gas fraction that we observe.

  5. Galactic Scale Flows and the Triggering of Star Formation in Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Ramón-Fox, F. G.; Bonnell, I. A.

    2016-06-01

    Galactic scale gas flows feed the growth of molecular clouds where stars form in high-density cores. Large scale flows also play a role in injecting the energy that drives the internal dynamics of these clouds, which affects their overall stability and star formation activity. The triggering of star formation involves a connection between large and small-scale dynamical processes in galaxies, which can be explored using high-resolution hydrodynamical simulations. We present results of current work in high-resolution N-body and Smoothed Particle Hydrodynamics simulations of a model spiral galaxy with a realistic spiral arm morphology. These simulations allow to study gas flows in a self-consistent galaxy and their role on molecular cloud formation and growth. They also provide a ground for studying molecular cloud properties in different environments of a galaxy, the effects of spiral arms on large scale flows and for understanding global star formation relations.

  6. star formation rates of z > 1 galaxy clusters in the IRAC shallow cluster survey

    SciTech Connect

    Zeimann, Gregory R.; Stanford, S. A.; Brodwin, Mark; Gonzalez, Anthony H.; Mancone, Conor; Snyder, Gregory F.; Stern, Daniel; Eisenhardt, Peter; Dey, Arjun; Moustakas, John

    2013-12-20

    We present Hubble Space Telescope near-IR spectroscopy for 18 galaxy clusters at 1.0 galaxy clusters as well as in field galaxies. We find a large cluster-to-cluster scatter in the star formation rates within a projected radius of 500 kpc, and many of our clusters (∼60%) have significant levels of star formation within a projected radius of 200 kpc. A stacking analysis reveals that dust reddening in these star-forming galaxies is positively correlated with stellar mass and may be higher in the field than the cluster at a fixed stellar mass. This may indicate a lower amount of gas in star-forming cluster galaxies than in the field population. Also, Hα equivalent widths of star-forming galaxies in the cluster environment are still suppressed below the level of the field. This suppression is most significant for lower mass galaxies (log M {sub *} < 10.0 M {sub ☉}). We therefore conclude that environmental effects are still important at 1.0 star-forming galaxies in galaxy clusters with log M {sub *} ≲ 10.0 M {sub ☉}.

  7. ENVIRONMENTAL DEPENDENCE OF OTHER GALAXY PROPERTIES FOR THE SAME STAR FORMATION ACTIVITIES

    SciTech Connect

    Deng Xinfa; Bei Yang; He Jizhou; Tang Xiaoxun

    2010-01-01

    Using two volume-limited Main galaxy samples of the Sloan Digital Sky Survey Data Release 6 above and below the value of M*, we have investigated the environmental dependence of other galaxy properties for the same star formation activities. Only in the luminous passive class, a strong environmental dependence of the g - r color is observed, but the environmental dependence of other properties in this class is very weak. In other classes, we can conclude that the local density dependence of luminosity, g - r color, concentration index ci, and morphologies for star-forming galaxies and passive ones is much weaker than that obtained in the volume-limited Main galaxy samples. This suggests that star formation activity is a galaxy property very predictive of the local environment. In addition, we also note that passive galaxies are more luminous, redder, highly concentrated, and preferentially 'early type'.

  8. What do the star formation histories of galaxies tell us about the Starburst-AGN connection?

    NASA Astrophysics Data System (ADS)

    Torres-Papaqui, J. P.; Coziol, R.; Plauchu-Frayn, I.; Andernach, H.; Ortega-Minakata, R. A.

    2013-10-01

    We have determined the normal star formation histories (SFHs) for narrow emission line galaxies classified as star forming galaxies (SFGs), transition type objects (TOs), Seyfert 2s (Sy2s) and LINERs. The SFH varied with the activity type, following the mass of the galaxies and the importance of their bulge: LINERs reside in massive early-type galaxies, Sy2s and TOs in intermediate mass galaxies with intermediate morphological types, and SFGs are hosted in lower mass late-type spirals. Also, the maximum star formation rate in the past was found to increase with the virial mass within the aperture (VMA). This correlation suggests that the bulges and the supermassive black holes at the center of galaxies grow in parallel, in good agreement with the M_{BH}-σ_* relation.

  9. Star Formation in Galaxies vs Galaxy Environment from the Joint GALEX - CFHTLS - VVDS - SWIRE Data

    NASA Astrophysics Data System (ADS)

    Pollo, A.; Arnouts, S.; Heinis, S.; Milliard, B.

    2007-12-01

    We investigate the dependence of galaxy star-formation history on environment, using colors - in particular UV colors - as star-formation history indicators and the distance to the 3-rd projected neighbor as an environment indicator. Here we present the first attempt to analyze how this dependence changed with redshift from z ˜ 1 till the present epoch. To address this issue we use a multi-wavelength catalog, based on the joint GALEX, CFHLTLS, VVDS and SWIRE data. The photometric redshifts derived from this catalog, covering an area close to ˜ 1.0 square degree and containing more than 100 000 galaxies, are accurate enough for these studies and possibly allow for a homogeneous approach from the local Universe to z ˜ 1. We find that in the contemporary Universe the most luminous and reddest in UV (i.e. most recently star-forming) populate the densest regions, which is in agreement with other studies. At z closer to 1 this tendency seems to disappear. However, systematic effects, not easy to quantify, have to be taken into account when interpreting our results.

  10. Radio Constraints on Heavily Obscured Star Formation within Dark Gamma-Ray Burst Host Galaxies

    NASA Astrophysics Data System (ADS)

    Perley, D. A.; Perley, R. A.

    2013-12-01

    Highly dust-obscured starbursting galaxies (submillimeter galaxies and their ilk) represent the most extreme sites of star formation in the distant universe and contribute significantly to overall cosmic star formation beyond z > 1.5. Some stars formed in these environments may also explode as gamma-ray bursts (GRBs) and contribute to the population of "dark" bursts. Here we present Very Large Array wideband radio-continuum observations of 15 heavily dust-obscured Swift GRBs to search for radio synchrotron emission associated with intense star formation in their host galaxies. Most of these targets (11) are not detected. Of the remaining four objects, one detection is marginal, and for two others we cannot yet rule out the contribution of a long-lived radio afterglow. The final detection is secure, but indicates a star formation rate (SFR) roughly consistent with the dust-corrected UV-inferred value. Most galaxies hosting obscured GRBs are therefore not forming stars at extreme rates, and the amount of optical extinction seen along a GRB afterglow sightline does not clearly correlate with the likelihood that the host has a sufficiently high SFR to be radio-detectable. While some submillimeter galaxies do readily produce GRBs, these GRBs are often not heavily obscured—suggesting that the outer (modestly obscured) parts of these galaxies overproduce GRBs and the inner (heavily obscured) parts underproduce GRBs relative to their respective contributions to star formation, hinting at strong chemical or initial mass function gradients within these systems.

  11. Radio constraints on heavily obscured star formation within dark gamma-ray burst host galaxies

    SciTech Connect

    Perley, D. A.; Perley, R. A.

    2013-12-01

    Highly dust-obscured starbursting galaxies (submillimeter galaxies and their ilk) represent the most extreme sites of star formation in the distant universe and contribute significantly to overall cosmic star formation beyond z > 1.5. Some stars formed in these environments may also explode as gamma-ray bursts (GRBs) and contribute to the population of 'dark' bursts. Here we present Very Large Array wideband radio-continuum observations of 15 heavily dust-obscured Swift GRBs to search for radio synchrotron emission associated with intense star formation in their host galaxies. Most of these targets (11) are not detected. Of the remaining four objects, one detection is marginal, and for two others we cannot yet rule out the contribution of a long-lived radio afterglow. The final detection is secure, but indicates a star formation rate (SFR) roughly consistent with the dust-corrected UV-inferred value. Most galaxies hosting obscured GRBs are therefore not forming stars at extreme rates, and the amount of optical extinction seen along a GRB afterglow sightline does not clearly correlate with the likelihood that the host has a sufficiently high SFR to be radio-detectable. While some submillimeter galaxies do readily produce GRBs, these GRBs are often not heavily obscured—suggesting that the outer (modestly obscured) parts of these galaxies overproduce GRBs and the inner (heavily obscured) parts underproduce GRBs relative to their respective contributions to star formation, hinting at strong chemical or initial mass function gradients within these systems.

  12. Astronomers Discover Most Distant Galaxy Showing Key Evidence For Furious Star Formation

    NASA Astrophysics Data System (ADS)

    2003-12-01

    Astronomers have discovered a key signpost of rapid star formation in a galaxy 11 billion light-years from Earth, seen as it was when the Universe was only 20 percent of its current age. Using the National Science Foundation's Very Large Array (VLA) radio telescope, the scientists found a huge quantity of dense interstellar gas -- the environment required for active star formation -- at the greatest distance yet detected. A furious spawning of the equivalent of 1,000 Suns per year in a distant galaxy dubbed the Cloverleaf may be typical of galaxies in the early Universe, the scientists say. Cloverleaf galaxy VLA image (green) of radio emission from HCN gas, superimposed on Hubble Space Telescope image of the Cloverleaf galaxy. The four images of the Cloverleaf are the result of gravitational lensing. CREDIT: NRAO/AUI/NSF, STScI (Click on Image for Larger Version) "This is a rate of star formation more than 300 times greater than that in our own Milky Way and similar spiral galaxies, and our discovery may provide important information about the formation and evolution of galaxies throughout the Universe," said Philip Solomon, of Stony Brook University in New York. While the raw material for star formation has been found in galaxies at even greater distances, the Cloverleaf is by far the most distant galaxy showing this essential signature of star formation. That essential signature comes in the form of a specific frequency of radio waves emitted by molecules of the gas hydrogen cyanide (HCN). "If you see HCN, you are seeing gas with the high density required to form stars," said Paul Vanden Bout of the National Radio Astronomy Observatory (NRAO). Solomon and Vanden Bout worked with Chris Carilli of NRAO and Michel Guelin of the Institute for Millimeter Astronomy in France. They reported their results in the December 11 issue of the scientific journal Nature. In galaxies like the Milky Way, dense gas traced by HCN but composed mainly of hydrogen molecules is always

  13. Intense star formation within resolved compact regions in a galaxy at z = 2.3.

    PubMed

    Swinbank, A M; Smail, I; Longmore, S; Harris, A I; Baker, A J; De Breuck, C; Richard, J; Edge, A C; Ivison, R J; Blundell, R; Coppin, K E K; Cox, P; Gurwell, M; Hainline, L J; Krips, M; Lundgren, A; Neri, R; Siana, B; Siringo, G; Stark, D P; Wilner, D; Younger, J D

    2010-04-01

    Massive galaxies in the early Universe have been shown to be forming stars at surprisingly high rates. Prominent examples are dust-obscured galaxies which are luminous when observed at sub-millimetre wavelengths and which may be forming stars at a rate of 1,000 solar masses (M(middle dot in circle)) per year. These intense bursts of star formation are believed to be driven by mergers between gas-rich galaxies. Probing the properties of individual star-forming regions within these galaxies, however, is beyond the spatial resolution and sensitivity of even the largest telescopes at present. Here we report observations of the sub-millimetre galaxy SMMJ2135-0102 at redshift z = 2.3259, which has been gravitationally magnified by a factor of 32 by a massive foreground galaxy cluster lens. This magnification, when combined with high-resolution sub-millimetre imaging, resolves the star-forming regions at a linear scale of only 100 parsecs. We find that the luminosity densities of these star-forming regions are comparable to the dense cores of giant molecular clouds in the local Universe, but they are about a hundred times larger and 10(7) times more luminous. Although vigorously star-forming, the underlying physics of the star-formation processes at z approximately 2 appears to be similar to that seen in local galaxies, although the energetics are unlike anything found in the present-day Universe. PMID:20305639

  14. Unveiling the Effects of Environment on Star Formation in Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Rieke, George; Bai, Lei; Marcillac, Delphine; Momcheva, Ivelina; Mulchaey, John; Rieke, Marcia; Tyler, Krystal; Zabludoff, Ann

    2008-03-01

    As galaxies evolve, they are subject to a menagerie of violent events that can disrupt or entirely subdue ongoing star formation. Nowhere is this more apparent than in high-density environments. Clustering due to hierarchical formation results in interactions between galaxies and the intracluster medium, leading to the demise of star formation and the rise of red sequence galaxies. However, correlations between local density and galaxy properties like morphology, star formation rate, and color exist from the largest clusters down to the poorest groups. It is likely, since the majority of galaxies lie in groups, that global trends in fundamental properties are driven by this environment. That is, the strong observed decline in star formation rate from z ~ 1 is likely to be directly related to processes affecting group galaxies. Despite this, groups are rarely studied, especially compared to the massive amounts of data available for clusters. Indeed, if we wish to study the effect of density on galaxy evolution, we need to focus on all densities. We propose to observe 48 groups of galaxies at intermediate redshifts (0.12 < z < 0.82), the era where strong evolution and transformation are expected for groups, with MIPS at 24-microns. This waveband is ideal for studying obscured star formation in galaxies, which is especially useful for our intermediate redshift range, where other star formation indicators, such as H-alpha and [OII] emission lines, become difficult to acquire and/or correct for obscuration. We will combine our groups with additional data for nearby groups and those at z ~ 1, as well as data for clusters at similar redshifts, to study the effects of a wide variety of densities on galaxy evolution from z ~ 1 to the present.

  15. Star formation and dust extinction properties of local galaxies as seen from AKARI and GALEX

    NASA Astrophysics Data System (ADS)

    Sakurai, A.; Takeuchi, T. T.; Yuan, F.-T.; Buat, V.; Burgarella, D.

    2013-03-01

    An accurate estimation of the star formation-related properties of galaxies is crucial for understanding the evolution of galaxies. In galaxies, ultraviolet (UV) light emitted by recently formed massive stars is attenuated by dust, which is also produced by star formation (SF) activity, and is re-emitted at mid- and far- infrared (IR) wavelengths. In this study, we investigate the star formation rate (SFR) and dust extinction using UV and IR data. We selected local galaxies which are detected at AKARI FIS 90 μm and matched the IRAS IIFSC z 60 μm select catalog. We measured FUV and NUV flux densities from GALEX images. We examined the SF and extinction of Local galaxies using four bands of AKARI. Then, we calculated FUV and total IR luminosities, and obtained the SF luminosity, L SF, the total luminosity related to star formation activity, and the SFR. We find that in most galaxies, L SF is dominated by L dust. We also find that galaxies with higher SF activity have a higher fraction of their SF hidden by dust. In fact, the SF of galaxies with SFRs > 20 M⊙ yr-1 is almost completely hidden by dust. Our results boast a significantly higher precision with respect to previously published works, due to the use of much larger object samples from the AKARI and GALEX all sky surveys.

  16. Star formation in cooling flows in clusters of galaxies

    NASA Technical Reports Server (NTRS)

    Mcnamara, Brian R.; O'Connell, Robert W.

    1989-01-01

    Spectrophotometry (wavelength = 3400-5100 A) has been obtained for the nuclei of 13 cD galaxies in cooling flows. Spectral anomalies are found in 8 of the objects, consisting of abnormally strong forbidden O II emission or excess flux effects. Consideration is given to metallicity effects, the relationship between UV excesses and the presence of massive OB stars formed from the cooling flows, and low-level effects related to accretion.

  17. Molecular gas, the interstellar medium, and star formation in S0 and Sa galaxies

    NASA Technical Reports Server (NTRS)

    Thronson, Harley A., Jr.; Greenhouse, Matthew A.; Tacconi, Linda; Kenney, Jeffrey; Margulis, Michael

    1989-01-01

    The results are presented of a survey for CO J = 1 - 0 emission from S0 and S0/a galaxies. The results show that molecular gas is abundant within some early-type disk galaxies, and that the range in the ratio of molecular gas to atomic gas mass is similar to those in other disk galaxies. In the S0 and S0/a galaxies studied, estimated rates of star formation are substantially smaller than, but efficiencies of star formation are roughly the same as, those in Sb or Sc galaxies. Although the rate of cooling of the hot, X-ray emitting gas may be close to the estimated stellar mass return rate in the sample, the star formation rate probably exceeds both by a significant factor.

  18. The Hα Line Emission Contribution to Star Formation History Determination in Galaxies

    NASA Astrophysics Data System (ADS)

    Durán, E.; Magris, G.; Mateu, J.

    2009-05-01

    Recently, Mateu, Bruzual, & Magris (2006) developed a non parametric algorithm called GASPEX (GAlaxy Spectrum Parameter EXtraction) to recover a galaxy star formation history (SFH) and chemical evolution from its spectral energy distribution (SED). Nevertheless, in late type galaxies the youngest population contribution to the SED could be hidden in the optical continuum, which is mainly dominated by old and evolved stars; therefore the SFH obtained from an optical SED may not include an important fraction of the recent star formation events in the galaxy. In this work we show that imposing restrictions on the calculations, based on the H α line emission as a tracer of recent star formation events, we improve the determination of the SFR in the last 100 Myr.

  19. Galaxy Mergers with Adaptive Mesh Refinement: Star Formation and Hot Gas Outflow

    SciTech Connect

    Kim, Ji-hoon; Wise, John H.; Abel, Tom; /KIPAC, Menlo Park /Stanford U., Phys. Dept.

    2011-06-22

    In hierarchical structure formation, merging of galaxies is frequent and known to dramatically affect their properties. To comprehend these interactions high-resolution simulations are indispensable because of the nonlinear coupling between pc and Mpc scales. To this end, we present the first adaptive mesh refinement (AMR) simulation of two merging, low mass, initially gas-rich galaxies (1.8 x 10{sup 10} M{sub {circle_dot}} each), including star formation and feedback. With galaxies resolved by {approx} 2 x 10{sup 7} total computational elements, we achieve unprecedented resolution of the multiphase interstellar medium, finding a widespread starburst in the merging galaxies via shock-induced star formation. The high dynamic range of AMR also allows us to follow the interplay between the galaxies and their embedding medium depicting how galactic outflows and a hot metal-rich halo form. These results demonstrate that AMR provides a powerful tool in understanding interacting galaxies.

  20. Spatially resolved star-formation in nearby analogues of Lyman break galaxies

    NASA Astrophysics Data System (ADS)

    Appel, Sabrina; Baker, Andrew J.; Hall, Kirsten

    2016-01-01

    At redshifts of z > 1.5, UV-selected galaxy populations (such as z ~ 3 Lyman break galaxies = LBGs) have the largest number of spectroscopic redshifts. As a result, LBGs have an important role in our understanding of the history of galaxy formation. However, LBGs are rather poorly understood at longer wavelengths, and thus our understanding of the total star formation rates and (especially) gas masses in such galaxies is incomplete. A common strategy is to assume that the Kennicutt-Schmidt relation between star formation rate (SFR) surface density and gas mass surface density holds, even in these high redshift galaxies where testing the relation directly is not feasible. To help assess the validity of this assumption, we examine the Kennicutt-Schmidt relation in selected nearby (z ~ 0.2) starburst galaxies in the hope of better understanding key questions regarding star formation processes in UV-selected galaxies. Several nearby galaxies with high UV luminosities and surface brightnesses, reminiscent of those found in LBGs, were identified and used for this project. We have obtained new, spatially resolved observations of these nearby analogues in Paschen alpha emission and carbon monoxide emission, from the ESO Very Large Telescope and the IRAM Plateau de Bure Interferometer, respectively. We examine whether the galaxies follow the expected Kennicutt-Schmidt relation, and investigate any implied variation in gas depletion times between and within galaxies. This research has been supported by National Science Foundation grant AST-0955810.

  1. Surface Brightness Profiles and Star Formation Rates of Galaxies in NRGb054

    NASA Astrophysics Data System (ADS)

    Hansen, Ellen; Koopmann, Rebecca A.; Miller, Brendan; Durbala, Adriana; Fitzgerald, Garrett

    2016-01-01

    We present new optical R and H-alpha images of the galaxy group NRGb054, obtained with the WIYN 0.9m telescope at KPNO using the MOSAIC camera. This group was studied as part of the larger Undergraduate ALFALFA Team project investigating the effects of a group environment on star formation. The stacked H-alpha image was continuum subtracted by the removal of a scaled and stacked R image. Surface photometry was performed on R and continuum-subtracted H-alpha cutouts of 20 covered galaxies to determine the surface brightness as a function of radius. Integrating the continuum-subtracted H-alpha surface brightness profile provides the total star formation within that galaxy, while the shape of the profile illustrates how star formation is spread throughout the galaxy. We provide a catalog of surface brightness profiles and integrated star formation rates for NRGb054. We consider star formation as a function of galaxy-galaxy separation and galaxy location within the group, and discuss our findings in the context of the wider study. This work has been supported by NSF grant AST-1211005.

  2. Slow Quenching of Star Formation in OMEGAWINGS Clusters: Galaxies in Transition in the Local Universe

    NASA Astrophysics Data System (ADS)

    Paccagnella, A.; Vulcani, B.; Poggianti, B. M.; Moretti, A.; Fritz, J.; Gullieuszik, M.; Couch, W.; Bettoni, D.; Cava, A.; D'Onofrio, M.; Fasano, G.

    2016-01-01

    The star formation quenching depends on environment, but a full understanding of what mechanisms drive it is still missing. Exploiting a sample of galaxies with masses {M}*\\gt {10}9.8{M}⊙ , drawn from the WIde-field Nearby Galaxy-cluster Survey (WINGS) and its recent extension OMEGAWINGS, we investigate the star formation rate (SFR) as a function of stellar mass (M{}*) in galaxy clusters at 0.04\\lt z\\lt 0.07. We use non-member galaxies at 0.02 < z < 0.09 as a field control sample. Overall, we find agreement between the SFR-M{}* relation in the two environments, but detect a population of cluster galaxies with reduced SFRs, which is rare in the field. These transition galaxies are mainly found within the cluster virial radius (R200), but they impact on the SFR-M{}* relation only within 0.6R200. The ratio of transition to pure star-forming galaxies strongly depends on environment, being larger than 0.6 within 0.3R200 and rapidly decreasing with distance, while it is almost flat with M*. As galaxies move downward from the SFR-M{}* main sequence, they become redder and present older luminosity- and mass-weighted ages. These trends, together with the analysis of the star formation histories, suggest that transition galaxies have had a reduced SFR for the past 2-5 Gyr. Our results are consistent with the hypothesis that the interaction of galaxies with the intracluster medium via strangulation causes a gradual shut down of star formation, giving birth to an evolved population of galaxies in transition from being star forming to becoming passive.

  3. Hα imaging survey of Wolf-Rayet galaxies: morphologies and star formation rates

    NASA Astrophysics Data System (ADS)

    Jaiswal, S.; Omar, A.

    2016-06-01

    The Hα and optical broadband images of 25 nearby Wolf-Rayet (WR) galaxies are presented. The WR galaxies are known to have the presence of a recent (≤10 Myr) and massive star formation episode. The photometric Hα fluxes are estimated, and corrected for extinction and line contamination in the filter pass-bands. The star formation rates (SFRs) are estimated using Hα images and from the archival data in the far-ultraviolet (FUV), far-infrared (FIR) and 1.4 GHz radio continuum wave-bands. A comparison of SFRs estimated from different wavebands is made after including similar data available in literature for other WR galaxies. The Hα based SFRs are found to be tightly correlated with SFRs estimated from the FUV data. The correlations also exist with SFRs estimates based on the radio and FIR data. The WR galaxies also follow the radio-FIR correlation known for normal star forming galaxies, although it is seen here that majority of dwarf WR galaxies have radio deficiency. An analysis using ratio of non-thermal to thermal radio continuum and ratio of FUV to Hα SFR indicates that WR galaxies have lesser non-thermal radio emission compared to normal galaxies, most likely due to lack of supernova from the very young star formation episode in the WR galaxies. The morphologies of 16 galaxies in our sample are highly suggestive of an ongoing tidal interaction or a past merger in these galaxies. This survey strengthens the conclusions obtained from previous similar studies indicating the importance of tidal interactions in triggering star-formation in WR galaxies.

  4. Tracing recent star formation of red early-type galaxies out to z ∼ 1

    SciTech Connect

    Ko, Jongwan; Lee, Jong Chul; Hwang, Ho Seong; Im, Myungshin; Le Borgne, Damien; Elbaz, David

    2014-08-20

    We study the mid-infrared (IR) excess emission of early-type galaxies (ETGs) on the red sequence at z < 1 using a spectroscopic sample of galaxies in the fields of Great Observatories Origins Deep Survey (GOODS). In the mass-limited sample of 1025 galaxies with M {sub star} > 10{sup 10.5} M {sub ☉} and 0.4 < z < 1.05, we identify 696 Spitzer 24 μm detected (above the 5σ) galaxies and find them to have a wide range of NUV-r and r-[12 μm] colors despite their red optical u – r colors. Even in the sample of very massive ETGs on the red sequence with M {sub star} > 10{sup 11.2} M {sub ☉}, more than 18% show excess emission over the photospheric emission in the mid-IR. The combination with the results of red ETGs in the local universe suggests that the recent star formation is not rare among quiescent, red ETGs at least out to z ∼ 1 if the mid-IR excess emission results from intermediate-age stars or/and from low-level ongoing star formation. Our color-color diagram including near-UV and mid-IR emissions are efficient not only for identifying ETGs with recent star formation, but also for distinguishing quiescent galaxies from dusty star-forming galaxies.

  5. Star Formation as a Function of Neutral Hydrogen Gas Density in Local Group Galaxies

    NASA Astrophysics Data System (ADS)

    Carlson, Erika K.; Madore, Barry F.; Freedman, Wendy L.

    2016-06-01

    We present a study of the efficiency and timescales of star formation as a function of local neutral hydrogen gas density in four Local Group galaxies: M33, NGC 6822, the LMC, and the SMC. In this work, we conceptualize the process of star formation as a cycle of two major phases – (1) a gas dynamics phase in which neutral hydrogen gas coalesces into clouds, and (2) a stellar phase in which stars have formed and interrupt further gas coalescence during their active lifetimes. By examining the spatial distribution and number densities of stars on maps of neutral hydrogen, we estimate the timescale of the gas coalescence phase relative to the timescale of the stellar phase and infer an efficiency of star formation as a function of neutral hydrogen gas density. From these timescales and efficiencies, we will calculate star formation rates as a function of neutral hydrogen gas density in these galaxies.

  6. Star Formation and Tidal Encounters with the Low Surface Brightness Galaxy UGC 12695 and Companions

    NASA Astrophysics Data System (ADS)

    O'Neil, K.; Verheijen, M. A. W.; McGaugh, S. S.

    2000-05-01

    We present VLA H I observations of the low surface brightness (LSB) galaxy UGC 12695 and its two companions, UGC 12687 and a newly discovered dwarf galaxy 2333+1234. UGC 12695 shows solid-body rotation but has a very lopsided morphology of the H I disk, with the majority of the H I lying in the southern arm of the galaxy. The H I column density distribution of this very blue LSB galaxy coincides in detail with its light distribution. Comparing the H I column density of UGC 12695 with the empirical (but not well-understood) value of Σc=1021 atoms cm-2 found in, e.g., Skillman's 1987 paper shows the star formation to be a local affair, occurring only in those regions where the column density is above this star formation threshold. The low surface brightness nature of this galaxy could thus be attributed to an insufficient gas surface density, inhibiting star formation on a more global scale. Significantly, however, the Toomre criterion places a much lower critical density on the galaxy (~1020 atoms cm-2), which is shown by the galaxy's low star formation rate not to be applicable. Within a projected distance of 300 kpc/30 km s-1 of UGC 12695 lie two companion galaxies-UGC 12687, a high surface brightness barred spiral galaxy, and 2333+1234, a dwarf galaxy discovered during this investigation. The close proximity of the three galaxies, combined with UGC 12695's extremely blue color and regions of localized starburst and UGC 12687's UV, excess bring to mind mutually induced star formation through tidal activity.

  7. Global and radial variations in the efficiency of massive star formation among galaxies

    NASA Technical Reports Server (NTRS)

    Allen, Lori E.; Young, Judith S.

    1990-01-01

    In order to determine the regions within galaxies which give rise to the most efficient star formation and to test the hypothesis that galaxies with high infrared luminosities per unit molecular mass are efficiently producing high mass stars, researchers have undertaken an H alpha imaging survey in galaxies whose CO distributions have been measured as part of the Five College Radio Astronomy Observatory (FCRAO) Extragalactic CO Survey. From these images researchers have derived global H alpha fluxes and distributions for comparison with far infrared radiation (FIR) fluxes and CO fluxes and distributions. Here, researchers present results on the global massive star formation efficiency (SFE = L sub H sub alpha/M(H2)) as a function of morphological type and environment, and on the radial distribution of the SFE within both peculiar and isolated galaxies. On the basis of comparison of the global L sub H sub alpha/M(H2) and L sub FIR/M(H2) for 111 galaxies, researchers conclude that environment rather than morphological type has the strongest effect on the global efficiency of massive star formation. Based on their study of a small sample, they find that the largest radial gradients are observed in the interacting/peculiar galaxies, indicating that environment affects the star formation efficiency within galaxies as well.

  8. The influence of the cluster environment on the star formation efficiency of 12 Virgo spiral galaxies

    NASA Astrophysics Data System (ADS)

    Vollmer, B.; Wong, O. I.; Braine, J.; Chung, A.; Kenney, J. D. P.

    2012-07-01

    The influence of the environment on gas surface density and star formation efficiency of cluster spiral galaxies is investigated. We extend previous work on radial profiles by a pixel-to pixel analysis looking for asymmetries due to environmental interactions. The star formation rate is derived from GALEX UV and Spitzer total infrared data based on the 8, 24, 70, and 160 μm data. As in field galaxies, the star formation rate for most Virgo galaxies is approximately proportional to the molecular gas mass. Except for NGC 4438, the cluster environment does not affect the star formation efficiency with respect to the molecular gas. Gas truncation is not associated with major changes in the total gas surface density distribution of the inner disk of Virgo spiral galaxies. In three galaxies (NGC 4430, NGC 4501, and NGC 4522), possible increases in the molecular fraction and the star formation efficiency with respect to the total gas, of factors of 1.5 to 2, are observed on the windward side of the galactic disk. A significant increase of the star formation efficiency with respect to the molecular gas content on the windward side of ram pressure-stripped galaxies is not observed. The ram-pressure stripped extraplanar gas of 3 highly inclined spiral galaxies (NGC 4330, NGC 4438, and NGC 4522) shows a depressed star formation efficiency with respect to the total gas, and one of them (NGC 4438) shows a depressed rate even with respect to the molecular gas. The interpretation is that stripped gas loses the gravitational confinement and associated pressure of the galactic disk, and the gas flow is diverging, so the gas density decreases and the star formation rate drops. We found two such regions of low star formation efficiency in the more face-on galaxies NGC 4501 and NGC 4654 which are both undergoing ram pressure stripping. These regions show low radio continuum emission or unusually steep radio spectral index. However, the stripped extraplanar gas in one highly inclined

  9. The JCMT nearby galaxies legacy survey - X. Environmental effects on the molecular gas and star formation properties of spiral galaxies

    NASA Astrophysics Data System (ADS)

    Mok, Angus; Wilson, C. D.; Golding, J.; Warren, B. E.; Israel, F. P.; Serjeant, S.; Knapen, J. H.; Sánchez-Gallego, J. R.; Barmby, P.; Bendo, G. J.; Rosolowsky, E.; van der Werf, P.

    2016-03-01

    We present a study of the molecular gas properties in a sample of 98 H I - flux selected spiral galaxies within ˜25 Mpc, using the CO J = 3 - 2 line observed with the James Clerk Maxwell Telescope. We use the technique of survival analysis to incorporate galaxies with CO upper limits into our results. Comparing the group and Virgo samples, we find a larger mean H2 mass in the Virgo galaxies, despite their lower mean H I mass. This leads to a significantly higher H2 to H I ratio for Virgo galaxies. Combining our data with complementary Hα star formation rate measurements, Virgo galaxies have longer molecular gas depletion times compared to group galaxies, due to their higher H2 masses and lower star formation rates. We suggest that the longer depletion times may be a result of heating processes in the cluster environment or differences in the turbulent pressure. From the full sample, we find that the molecular gas depletion time has a positive correlation with the stellar mass, indicative of differences in the star formation process between low- and high-mass galaxies, and a negative correlation between the molecular gas depletion time and the specific star formation rate.

  10. Dwarf galaxies in the coma cluster: Star formation properties and evolution

    NASA Astrophysics Data System (ADS)

    Hammer, Derek M.

    The infall regions of galaxy clusters are unique laboratories for studying the impact of environment on galaxy evolution. This intermediate region links the low-density field environment and the dense core of the cluster, and is thought to host recently accreted galaxies whose star formation is being quenched by external processes associated with the cluster. In this dissertation, we measure the star formation properties of galaxies at the infall region of the nearby rich cluster of galaxies, Coma. We rely primarily on Ultraviolet (UV) data owing to its sensitivity to recent star formation and we place more emphasis on the properties of dwarf galaxies. Dwarf galaxies are good tracers of external processes in clusters but their evolution is poorly constrained as they are intrinsically faint and hence more challenging to detect. We make use of deep GALEX far-UV and near-UV observations at the infall region of the Coma cluster. This area of the cluster has supporting photometric coverage at optical and IR wavelengths in addition to optical spectroscopic data that includes deep redshift coverage of dwarf galaxies in Coma. Our GALEX observations were the deepest exposures taken for a local galaxy cluster. The depth of these images required alternative data analysis techniques to overcome systematic effects that limit the default GALEX pipeline analysis. Specifically, we used a deblending method that improved detection efficiency by a factor of ˜2 and allowed reliable photometry a few magnitudes deeper than the pipeline catalog. We performed deep measurements of the total UV galaxy counts in our field that were used to measure the source confusion limit for crowded GALEX fields. The star formation properties of Coma members were studied for galaxies that span from starbursts to passive galaxies. Star-forming galaxies in Coma tend to have lower specific star formation rates, on average, as compared to field galaxies. We show that the majority of these galaxies are likely

  11. The Star Formation History of the Leo I Dwarf Spheroidal Galaxy

    NASA Astrophysics Data System (ADS)

    Smecker-Hane, Tammy A.; Marsteller, B.; Cole, A.; Bullock, J.; Gallagher, J. S.

    2009-01-01

    We report on results of new deep imaging obtained with the Hubble Space Telescope (HST) Advance Camera for Surveys (ACS) that show the Leo I dwarf Spheroidal (dSph) galaxy has a much larger population of ancient (>10 Gyr old) stars than previously determined with shallower WFPC2 imaging (Gallart et al. 1999, Dolphin 2003), as well as the previously identified component of intermediate-aged stars. Our new imaging is much deeper, which allows us to unambiguously identify the main sequence turnoffs of the ancient population and constrain the star formation rate at the epoch of the formation of the "first stars” in this galaxy. We will determine the galaxy's star formation rate as a function of time from the observed density of stars in the color-magnitude diagram by comparing with Padova stellar evolutionary models (Girardi et al. 2000). We compare and contrast the star formation histories of the Leo I dSph, which is currently devoid of any gas, with that of the gas-rich Leo A dIrr galaxy. The two are very different in that the dSph formed most of its stars early and the dIrr formed most of its stars later, however both have been actively forming stars over most of the age of the universe.

  12. Galaxy formation

    SciTech Connect

    Silk, J.

    1984-11-01

    Implications of the isotropy of the cosmic microwave background on large and small angular scales for galaxy formation are reviewed. In primeval adiabatic fluctuations, a universe dominated by cold, weakly interacting nonbaryonic matter, e.g., the massive photino is postulated. A possible signature of photino annihilation in our galactic halo involves production of cosmic ray antiprotons. If the density is near its closure value, it is necessary to invoke a biasing mechanism for suppressing galaxy formation throughout most of the universe in order to reconcile the dark matter density with the lower astronomical determinations of the mean cosmological density. A mechanism utilizing the onset of primordial massive star formation to strip gaseous protogalaxies is described. Only the densest, early collapsing systems form luminous galaxies. (ESA)

  13. Star Formation Models for the Dwarf Galaxies NGC 2915 and NGC 1705

    NASA Astrophysics Data System (ADS)

    Elson, E. C.; de Blok, W. J. G.; Kraan-Korteweg, R. C.

    2012-01-01

    Crucial to a quantitative understanding of galaxy evolution are the properties of the interstellar medium that regulate galactic-scale star formation activity. We present here the results of a suite of star formation models applied to the nearby blue compact dwarf galaxies NGC 2915 and NGC 1705. Each of these galaxies has a stellar disk embedded in a much larger, essentially starless H I disk. These atypical stellar morphologies allow for rigorous tests of star formation models that examine the effects on star formation of the H I, stellar, and dark matter mass components, as well as the kinematics of the gaseous and stellar disks. We use far-ultraviolet and 24 μm images from the Galaxy Evolution Explorer and the Spitzer Infrared Nearby Galaxies Survey, respectively, to map the spatial distribution of the total star formation rate surface density within each galaxy. New high-resolution H I line observations obtained with the Australia Telescope Compact Array are used to study the distribution and dynamics of each galaxy's neutral interstellar medium. The standard Toomre Q parameter is unable to distinguish between active and non-active star-forming regions, predicting the H I disks of the dwarfs to be sub-critical. Two-fluid instability models incorporating the stellar and dark matter components of each galaxy, in addition to the gaseous component, yield unstable portions of the inner disk. Finally, a formalization in which the H I kinematics are characterized by the rotational shear of the gas produces models that very accurately match the observations. This suggests the time available for perturbations to collapse in the presence of rotational shear to be an important factor governing galactic-scale star formation.

  14. STAR FORMATION MODELS FOR THE DWARF GALAXIES NGC 2915 AND NGC 1705

    SciTech Connect

    Elson, E. C.; De Blok, W. J. G.; Kraan-Korteweg, R. C.

    2012-01-15

    Crucial to a quantitative understanding of galaxy evolution are the properties of the interstellar medium that regulate galactic-scale star formation activity. We present here the results of a suite of star formation models applied to the nearby blue compact dwarf galaxies NGC 2915 and NGC 1705. Each of these galaxies has a stellar disk embedded in a much larger, essentially starless H I disk. These atypical stellar morphologies allow for rigorous tests of star formation models that examine the effects on star formation of the H I, stellar, and dark matter mass components, as well as the kinematics of the gaseous and stellar disks. We use far-ultraviolet and 24 {mu}m images from the Galaxy Evolution Explorer and the Spitzer Infrared Nearby Galaxies Survey, respectively, to map the spatial distribution of the total star formation rate surface density within each galaxy. New high-resolution H I line observations obtained with the Australia Telescope Compact Array are used to study the distribution and dynamics of each galaxy's neutral interstellar medium. The standard Toomre Q parameter is unable to distinguish between active and non-active star-forming regions, predicting the H I disks of the dwarfs to be sub-critical. Two-fluid instability models incorporating the stellar and dark matter components of each galaxy, in addition to the gaseous component, yield unstable portions of the inner disk. Finally, a formalization in which the H I kinematics are characterized by the rotational shear of the gas produces models that very accurately match the observations. This suggests the time available for perturbations to collapse in the presence of rotational shear to be an important factor governing galactic-scale star formation.

  15. Panel Discussion I. Star Formation in Galaxies: How Do We Continue?

    NASA Astrophysics Data System (ADS)

    Knapen, J. H.

    2008-06-01

    This is the written account of the first of two panel discussions, on Star formation in galaxies: how do we continue? The chair of the panel was Phil James, and panel members were John Beckman, Torsten Böker, Daniela Calzetti, Angeles Díaz, and Rob Kennicutt. The panel and audience discussed the following four questions: 1) What are the most critically needed techniques to give accurate measurements of total rates and efficiencies of star formation? 2) Do we understand the form of the initial mass function and its variation as a function of redshift and environment? 3) Are there multiple modes of star formation in galaxies (bulge vs disk, burst vs continuous) or does the Schmidt law explain everything? 4) How do we bring together our understanding of star formation in our Galaxy and in external systems?

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

    SciTech Connect

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

    2012-09-20

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

  17. Feedback in the local Universe: Relation between star formation and AGN activity in early type galaxies

    NASA Astrophysics Data System (ADS)

    Vaddi, Sravani; O'Dea, Christopher; Baum, Stefi; Jones, Christine; Forman, William; Whitmore, Samantha; Ahmed, Rabeea; Pierce, Katherine; Leary, Sara

    2015-08-01

    Aim: We address the relation between star formation and AGN activity in a large sample of nearby early type (E and S0) galaxies. The redshift range of the galaxies is 0.0002star formation and thus the process of galaxy evolution and formation. Evidence of AGN feedback is found in massive galaxies in galaxy clusters. However, how common AGN feedback is in the local universe and in small scale systems is still not evident.Methods: To answer this question, we carried out a multiple wavelength study of a sample of 231 early type galaxies which were selected to have an apparent K-band magnitude brighter than 13.5 and whose positions correlate with Chandra ACIS-I and ACIS-S sources. The galaxies in the sample are unbiased regarding their star formation and radio source properties. Using the archival observations at radio, IR and UV from VLA, WISE and GALEX respectively, we obtained the radio power, estimate FUV star formation rate (SFR) and other galaxy properties to study AGN activity and ongoing star formation.Results: The relationship between radio power and stellar mass shows that there is an upper envelope of radio power that is a steep function of stellar luminosity. This suggests that less massive galaxies have low radio power while massive galaxies are capable of hosting powerful radio sources. The Radio-MIR relation shows that galaxies with P>=1022 WHz-1 are potential candidates for being AGN. About ~ 7% of the sample show evidence of ongoing star formation with SFR ranging from 10-3 to 1 M⊙yr-1. These are also less massive and radio faint suggesting the absence of active accretion. There is nearly equal fraction of star forming galaxies in radio faint (P<1022 WHz-1) and radio bright galaxies (P>=1022 WHz-1) . Only ~ 5% of the galaxies in our sample have P>=1022 WHz-1 and most of them do not show evidence of bright accretion disks. We see a weak correlation and a dispersion of

  18. The link between galaxy structure and star formation across cosmic time

    NASA Astrophysics Data System (ADS)

    Fang, Jerome Joseph

    The processes that fuel and quench star formation in galaxies are expected to leave imprints on their structure. Moreover, these imprints can serve as signposts to identify galaxies at various stages of their evolution. In this dissertation, we describe our efforts to characterize changes in galaxy structure (1) as star formation is going out, (2) after star formation has ostensibly quenched, and (3) during active star formation, with the goal of elucidating the relevant processes that regulate star formation in each case. In Chapter 2, we use a local (z ˜ 0) sample of galaxies drawn from the Sloan Digital Sky Survey (SDSS) to investigate the first two cases. We find that, as galaxies quench, their outer stellar mass density profiles remain essentially constant. However, their inner stellar mass density (within 1 kpc) increases, even while galaxies are still star-forming, until it reaches a mass-dependent threshold, at which point quenching can occur. The existence of this threshold indicates that quenching is connected with processes that grow bulges. In Chapter 3, we then study the morphologies and color profiles of 19 z ˜ 0 early-type galaxies located in the green valley. Combining high-resolution Hubble ultraviolet images with SDSS optical photometry, we find that these objects harbor low-level star formation that is clearly detectable in the ultraviolet. Moreover, the recently formed stars are distributed in symmetric rings that often span the entire optical extent of the galaxy. The presence of an old underlying population in their outer parts suggests that star formation in these galaxies is either gradually fading out or possibly rejuvenated by smooth accretion from the intergalactic medium. Such galaxies comprise ≈13% of green valley galaxies of similar mass and color, and they may linger in the green valley for several Gyr. Finally, in Chapter 4, we focus on the evolution of star-forming galaxies since z = 2.5, leveraging the rich multi

  19. Three-Dimensional Spectroscopy and Star Formation Histories of Field E+A Galaxies

    NASA Astrophysics Data System (ADS)

    Liu, Charles T.; Wolf, Marsha; Hooper, Eric J.; Bather, Joshua

    2015-02-01

    We present the initial results of an integral field spectroscopic survey of E+A galaxies in the field, which combined with radio continuum measurements and multi-wavelength photometry and imaging provides significant insight into the dynamical and star formation histories of these transitioning post-starburst systems. We focus on the E+A galaxy known as G515 (z = 0.088), a massive merger remnant that began its star formation quenching process ~ 1.0 Gyr ago. Its relatively young stellar population contrasts with its light profile and kinematics, which are more consistent with a slowly-rotating, early-type galaxy.

  20. CO observations of nearby galaxies and the efficiency of star formation

    NASA Technical Reports Server (NTRS)

    Young, Judith S.

    1987-01-01

    The CO distributions and total molecular content of 160 galaxies were observed using the 14 meter millimeter telescope of the FCRAO. For the luminous, relatively face-on Sc galaxies, the azimuthally averaged CO distributions are centrally peaked, while for the Sb and Sa galaxies the Co distributions often exhibit central CO holes up to 5 kpc across. None of the Sc galaxies have CO distributions which resemble the Milky Way. A general correlation was found between total CO and IR luminosities in galaxies. The scatter in this relation is highly correlated with dust temperature. No strong correlation of IR luminosities was found with HI masses, and it was thereby concluded that the infrared emission is more directly tied to the molecular content of galaxies. It is suggested that galaxies which have high Star Formation Effiencies (SFEs) produce more stars per unit molecular mass, thereby increasing the average temperature of the dust in the star forming regions. Irregular galaxies and galaxies previously identified as mergers have the highest observed star formation efficiencies. For the mergers, evidence was found that the IR/CO luminosity ratio increases with the merger age estimated by Joseph and Wright (1985).

  1. 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.

  2. Gas Content and Star Formation Efficiency of Massive Main Sequence Galaxies at z~3-4

    NASA Astrophysics Data System (ADS)

    Schinnerer, Eva; Groves, Brent; Karim, Alexander; Sargent, Mark T.; Oesch, Pascal; Le Fevre, Olivier; Tasca, Lidia; Magnelli, Benjamin; Cassata, Paolo; Smolcic, Vernesa

    2016-01-01

    Recent observations have shown that the neutral gas content and star formation efficiency of massive (with log(stellar masses) > 10), normal star forming galaxies, i.e. they reside on the main sequence of star forming galaxies, are steadily decreasing from the peak of star formation activity (at redshifts of z~2) till today. This decrease is coincident with the observed decline in the cosmic star formation rate density over this time range. However, only few observations have probed the evolution of the gas content and star formation efficiency beyond this peak epoch when the cosmic star formation rate density has been increasing, i.e. at redshifts of z~3-4.We will present new ALMA rest-frame 250um continuum detections of 45 massive, normal star forming galaxies in this critical redshift interval selected in the COSMOS deep field. Using the sub-mm continnum as proxy for the cold neutral gas content, we find gas mass fractions and depletions similar to those reported during the peak epoch of star formation. We will discuss our findings in the context of results from lower redshift observations and model expectations.

  3. Suppression of star formation in dwarf galaxies by photoelectric grain heating feedback

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    Photoelectric heating—heating of dust grains by far-ultraviolet photons—has long been recognized as the primary source of heating for the neutral interstellar medium. Simulations of spiral galaxies have shown some indication that photoelectric heating could suppress star formation; however, simulations that include photoelectric heating have typically shown that it has little effect on the rate of star formation in either spiral galaxies or dwarf galaxies, which suggests that supernovae are responsible for setting the gas depletion time in galaxies. This result is in contrast with recent work indicating that a star formation law that depends on galaxy metallicity—as is expected with photoelectric heating, but not with supernovae—reproduces the present-day galaxy population better than does a metallicity-independent one. Here we report a series of simulations of dwarf galaxies, the class of galaxy in which the effects of both photoelectric heating and supernovae are expected to be strongest. We simultaneously include space- and time-dependent photoelectric heating in our simulations, and we resolve the energy-conserving phase of every supernova blast wave, which allows us to directly measure the relative importance of feedback by supernovae and photoelectric heating in suppressing star formation. We find that supernovae are unable to account for the observed large gas depletion times in dwarf galaxies. Instead, photoelectric heating is the dominant means by which dwarf galaxies regulate their star formation rate at any given time, suppressing the rate by more than an order of magnitude relative to simulations with only supernovae.

  4. Suppression of star formation in dwarf galaxies by photoelectric grain heating feedback.

    PubMed

    Forbes, John C; Krumholz, Mark R; Goldbaum, Nathan J; Dekel, Avishai

    2016-07-28

    Photoelectric heating--heating of dust grains by far-ultraviolet photons--has long been recognized as the primary source of heating for the neutral interstellar medium. Simulations of spiral galaxies have shown some indication that photoelectric heating could suppress star formation; however, simulations that include photoelectric heating have typically shown that it has little effect on the rate of star formation in either spiral galaxies or dwarf galaxies, which suggests that supernovae are responsible for setting the gas depletion time in galaxies. This result is in contrast with recent work indicating that a star formation law that depends on galaxy metallicity--as is expected with photoelectric heating,but not with supernovae--reproduces the present-day galaxy population better than does a metallicity-independent one. Here we report a series of simulations of dwarf galaxies, the class of galaxy in which the effects of both photoelectric heating and supernovae are expected to be strongest. We simultaneously include space and time-dependent photoelectric heating in our simulations, and we resolve the energy-conserving phase of every supernova blast wave, which allows us to directly measure the relative importance of feedback by supernovae and photoelectric heating in suppressing star formation. We find that supernovae are unable to account for the observed large gas depletion times in dwarf galaxies. Instead, photoelectric heating is the dominant means by which dwarf galaxies regulate their star formation rate at any given time,suppressing the rate by more than an order of magnitude relative to simulations with only supernovae. PMID:27350244

  5. The Star Formation & Chemical Evolution Timescales of Two Nearby Dwarf Spheroidal Galaxies

    NASA Astrophysics Data System (ADS)

    de Boer, Thomas; Tolstoy, E.; Hill, V.; Saha, A.; Olsen, K.; Starkenburg, E.; Irwin, M.; Battaglia, G.

    2012-01-01

    We present wide-field photometry of resolved stars in the nearby Sculptor and Fornax dwarf spheroidal galaxies, going down to the oldest Main Sequence Turn-Off. The accurately flux calibrated wide-field Colour-Magnitude Diagrams are used directly in combination with spectroscopic metallicities of individual RGB stars to constrain the ages of different stellar populations, and derive the Star Formation History with particular accuracy. The Sculptor dSph contains a predominantly ancient stellar population (>10 Gyr old), which can easily be resolved into individual stars. A galaxy dominated by an old population provides a clear view of ancient processes of galaxy formation unimpeded by overlying younger populations. The Fornax dSph is dominated by stellar populations of intermediate and young ages, which can be used to study the processes of galaxy formation in a more complex mix of stellar populations We find that the known metallicity gradients are well matched to an age gradient. This is the first time that this link with age has been directly quantified. The detailed Star Formation History shows the distribution of age with regards to the metallicity for different radii out from the centre of the galaxy. By linking the obtained SFH to observed spectroscopic abundances (alpha-elements, r- and s-process elements) of RGB stars it is possible to put ages on the chemical evolution patterns observed in this galaxy. In this way we can study the timescale of chemical evolution in these two dwarf galaxies. By comparing both dwarfs we determine whether the chemical abundance patterns seen in galaxies with recent episodes of star formation are a direct continuation of those with only old populations.

  6. The formation of the first stars and galaxies.

    PubMed

    Bromm, Volker; Yoshida, Naoki; Hernquist, Lars; McKee, Christopher F

    2009-05-01

    Observations made using large ground-based and space-borne telescopes have probed cosmic history from the present day to a time when the Universe was less than one-tenth of its present age. Earlier still lies the remaining frontier, where the first stars, galaxies and massive black holes formed. They fundamentally transformed the early Universe by endowing it with the first sources of light and chemical elements beyond the primordial hydrogen and helium produced in the Big Bang. The interplay of theory and upcoming observations promises to answer the key open questions in this emerging field. PMID:19424148

  7. Are passive red spirals truly passive?. The current star formation activity of optically red disc galaxies

    NASA Astrophysics Data System (ADS)

    Cortese, L.

    2012-07-01

    We used GALEX ultraviolet and WISE 22 μm observations to investigate the current star formation activity of the optically red spirals recently identified as part of the Galaxy Zoo project. These galaxies were accurately selected from the Sloan Digital Sky Survey as pure discs with low or no current star formation activity, representing one of the best optically selected samples of candidate passive spirals. However, we show that these galaxies are not only still forming stars at a significant rate (≳1 M⊙ yr-1) but, more importantly, their star formation activity is not different from that of normal star-forming discs of the same stellar mass (M∗ ≳ 1010.2 M⊙). Indeed, these systems lie on the UV-optical blue sequence, even without any corrections for internal dust attenuation, and they follow the same specific star formation rate vs. stellar mass relation of star-forming galaxies. Our findings clearly show that at high stellar masses, optical colours do not allow to distinguish between actively star-forming and truly quiescent systems.

  8. Star formation and environmental quenching of GEEC2 group galaxies at z ˜ 1

    NASA Astrophysics Data System (ADS)

    Mok, Angus; Balogh, Michael L.; McGee, Sean L.; Wilman, David J.; Finoguenov, Alexis; Tanaka, Masayuki; Bower, Richard G.; Hou, Annie; Mulchaey, John S.; Parker, Laura C.

    2014-03-01

    We present new analysis from the Group Environment Evolution Collaboration 2 (GEEC2) spectroscopic survey of galaxy groups at 0.8 < z < 1. Our previous work revealed an intermediate population between the star-forming and quiescent sequences and a strong environmental dependence in the fraction of quiescent galaxies. Only ˜5 per cent of star-forming galaxies in both the group and field sample show a significant enhancement in star formation, which suggests that quenching is the primary process in the transition from the star-forming to the quiescent state. To model the environmental quenching scenario, we have tested the use of different exponential quenching time-scales and delays between satellite accretion and the onset of quenching. We find that with no delay, the quenching time-scale needs to be long in order to match the observed quiescent fraction, but then this model produces too many intermediate galaxies. Fixing a delay time of 3 Gyr, as suggested from the local Universe, produces too few quiescent galaxies. The observed fractions are best matched with a model that includes a delay that is proportional to the dynamical time and a rapid quenching time-scale (˜0.25 Gyr), but this model also predicts intermediate galaxies Hδ strength higher than that observed. Using stellar synthesis models, we have tested other scenarios, such as the rejuvenation of star formation in early-type galaxies and a portion of quenched galaxies possessing residual star formation. If environment quenching plays a role in the GEEC2 sample, then our work suggests that only a fraction of intermediate galaxies may be undergoing this transition and that quenching occurs quite rapidly in satellite galaxies (≲0.25 Gyr).

  9. Probing dust-obscured star formation in the most massive gamma-ray burst host galaxies

    NASA Astrophysics Data System (ADS)

    Greiner, Jochen; Michałowski, Michał J.; Klose, Sylvio; Hunt, Leslie K.; Gentile, Gianfranco; Kamphuis, Peter; Herrero-Illana, Rubén; Wieringa, Mark; Krühler, Thomas; Schady, Patricia; Elliott, Jonathan; Graham, John F.; Ibar, Eduardo; Knust, Fabian; Nicuesa Guelbenzu, Ana; Palazzi, Eliana; Rossi, Andrea; Savaglio, Sandra

    2016-08-01

    Context. As a result of their relation to massive stars, long-duration gamma-ray bursts (GRBs) allow the pinpointing of star formation in galaxies independent of redshift, dust obscuration, or galaxy mass/size, thus providing a unique tool to investigate star formation history over cosmic time. Aims: About half of the optical afterglows of long-duration GRBs are missed owing to dust extinction and are primarily located in the most massive GRB hosts. It is important to investigate the amount of obscured star formation in these GRB host galaxies to understand this bias. Methods: Radio emission of galaxies correlates with star formation, but does not suffer extinction as do the optical star formation estimators. We selected 11 GRB host galaxies with either large stellar mass or large UV-based and optical-based star formation rates (SFRs) and obtained radio observations of these with the Australia Telescope Compact Array and the Karl Jansky Very Large Array. Results: Despite intentionally selecting GRB hosts with expected high SFRs, we do not find any radio emission related to star formation in any of our targets. Our upper limit for GRB 100621A implies that the earlier reported radio detection was due to afterglow emission. We detect radio emission from the position of GRB 020819B, but argue that it is in large part, if not completely, due to afterglow contamination. Conclusions: Half of our sample has radio-derived SFR limits, which are only a factor 2-3 above the optically measured SFRs. This supports other recent studies that the majority of star formation in GRB hosts is not obscured by dust. Based on observations collected with ATCA under ID C2718, and at VLA under ID 13B-017.

  10. Star Formation Properties in the Local Volume Galaxies via Hα and Far-ultraviolet Fluxes

    NASA Astrophysics Data System (ADS)

    Karachentsev, Igor D.; Kaisina, Elena I.

    2013-09-01

    A distance-limited sample of 869 objects from the Updated Nearby Galaxy Catalog is used to characterize the star formation status of the Local Volume population. We present a compiled list of 1217 star formation rate (SFR) estimates for 802 galaxies within 11 Mpc, derived from the Hα imaging surveys and the GALEX far-ultraviolet survey. We briefly discuss some basic scaling relations between SFR and luminosity, morphology, H I mass, surface brightness, and the environment of the galaxies. About 3/4 of our sample consist of dwarf galaxies, for which we offer a more refined classification. We note that the specific SFR of nearly all luminous and dwarf galaxies does not exceed the maximum value: log (SFR/LK ) = -9.4 [yr-1]. Most spiral and blue dwarf galaxies have enough time to generate their stellar mass during the cosmological time, T 0, with the observed SFRs. They dispose of a sufficient amount of gas to support their present SFRs over the next T 0 term. We note that only a small fraction of BCD, Im, and Ir galaxies (about 1/20) proceed in a mode of vigorous starburst activity. In general, the star formation history of spiral and blue dwarf galaxies is mainly driven by their internal processes. The present SFRs of E, S0, and dSph galaxies typically have 1/30-1/300 of their former activity.

  11. The formation and assembly of a typical star-forming galaxy at redshift z approximately 3.

    PubMed

    Stark, Daniel P; Swinbank, A Mark; Ellis, Richard S; Dye, Simon; Smail, Ian R; Richard, Johan

    2008-10-01

    Recent studies of galaxies approximately 2-3 Gyr after the Big Bang have revealed large, rotating disks, similar to those of galaxies today. The existence of well-ordered rotation in galaxies during this peak epoch of cosmic star formation indicates that gas accretion is likely to be the dominant mode by which galaxies grow, because major mergers of galaxies would completely disrupt the observed velocity fields. But poor spatial resolution and sensitivity have hampered this interpretation; such studies have been limited to the largest and most luminous galaxies, which may have fundamentally different modes of assembly from those of more typical galaxies (which are thought to grow into the spheroidal components at the centres of galaxies similar to the Milky Way). Here we report observations of a typical star-forming galaxy at z = 3.07, with a linear resolution of approximately 100 parsecs. We find a well-ordered compact source in which molecular gas is being converted efficiently into stars, likely to be assembling a spheroidal bulge similar to those seen in spiral galaxies at the present day. The presence of undisrupted rotation may indicate that galaxies such as the Milky Way gain much of their mass by accretion rather than major mergers. PMID:18843363

  12. Star Formation in Dwarf Galaxies as a Function of Cluster-Centric Radii

    NASA Astrophysics Data System (ADS)

    Rude, Cody; Barkhouse, Wayne

    2015-01-01

    Galaxy clusters form the largest structures in the universe. The cluster galaxy population differs both by morphology and star formation histories relative to the field population. Several physical mechanisms have been proposed to account for these differences, including ram pressure stripping due to the intracluster medium, and harassment from close encounters with other galaxies. Dwarf galaxies could prove to be particularly important as their low mass makes them more susceptible to external influences. This study looks for evidence of enhanced/quenching of star formation in dwarf galaxies using photometric u- and r-band data of several Abell clusters taken with the CFHT. From the combined sample, scaled by r200, composite luminosity functions (LFs) and histograms of galaxy color at various cluster-centric radii are constructed. An increase in the faint-end slope of the u-band LF relative to the r-band is a possible indicator of enhanced star formation. Comparisons of the inner and outer regions of the cluster sample may yield insights into the physical mechanisms that affect star formation of infalling cluster dwarf galaxies.

  13. 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.

  14. Astrochemistry and star formation in nearby galaxies: from galaxy disks to hot nuclei

    NASA Astrophysics Data System (ADS)

    Aalto, S.

    2016-05-01

    Studying the molecular phase of the interstellar medium in galaxies is fundamental for the understanding of the onset and evolution of compact and extended star formation, and of the growth of supermassive black holes. Molecular line emission is an excellent tracer of chemical, physical and dynamical conditions in the cold neutral gas. Key molecules in extragalactic studies are e.g. HCN, HCO+, HC3N, SiO, CH3OH, H2O. Furthermore, we can use IR excited molecular emission to probe the very inner regions of luminous infrared galaxies allowing us to get past the optically thick dust barrier of the compact obscured nuclei where lines of CO, HCN and HCO+ in their vibrational ground state (ν=0) may be self-absorbed. Finally, molecular outflows and their chemistry are briefly discussed - including new ALMA results on for example the outflow of the lenticular galaxy NGC1377 and a study of the chemistry of the outflow of the quasar Mrk231.

  15. Consequences of bursty star formation on galaxy observables at high redshifts

    NASA Astrophysics Data System (ADS)

    Domínguez, Alberto; Siana, Brian; Brooks, Alyson M.; Christensen, Charlotte R.; Bruzual, Gustavo; Stark, Daniel P.; Alavi, Anahita

    2015-07-01

    The star formation histories (SFHs) of dwarf galaxies are thought to be bursty, with large - order of magnitude - changes in the star formation rate on time-scales similar to O-star lifetimes. As a result, the standard interpretations of many galaxy observables (which assume a slowly varying SFH) are often incorrect. Here, we use the SFHs from hydrodynamical simulations to investigate the effects of bursty SFHs on sample selection and interpretation of observables and make predictions to confirm such SFHs in future surveys. First, because dwarf galaxies' star formation rates change rapidly, the mass-to-light ratio is also changing rapidly in both the ionizing continuum and, to a lesser extent, the non-ionizing ultraviolet continuum. Therefore, flux limited surveys are highly biased towards selecting galaxies in the burst phase and very deep observations are required to detect all dwarf galaxies at a given stellar mass. Second, we show that a log10[νLν(1500 Å)/LHα] > 2.5 implies a very recent quenching of star formation and can be used as evidence of stellar feedback regulating star formation. Third, we show that the ionizing continuum can be significantly higher than when assuming a constant SFH, which can affect the interpretation of nebular emission line equivalent widths and direct ionizing continuum detections. Finally, we show that a star formation rate estimate based on continuum measurements only (and not on nebular tracers such as the hydrogen Balmer lines) will not trace the rapid changes in star formation and will give the false impression of a star-forming main sequence with low dispersion.

  16. Cosmic Evolution of Star Formation Enhancement in Close Major-merger Galaxy Pairs Since z = 1

    NASA Astrophysics Data System (ADS)

    Xu, C. K.; Shupe, D. L.; Béthermin, M.; Aussel, H.; Berta, S.; Bock, J.; Bridge, C.; Conley, A.; Cooray, A.; Elbaz, D.; Franceschini, A.; Le Floc'h, E.; Lu, N.; Lutz, D.; Magnelli, B.; Marsden, G.; Oliver, S. J.; Pozzi, F.; Riguccini, L.; Schulz, B.; Scoville, N.; Vaccari, M.; Vieira, J. D.; Wang, L.; Zemcov, M.

    2012-11-01

    The infrared (IR) emission of "M * galaxies" (1010.4 <= M star <= 1011.0 M ⊙) in galaxy pairs, derived using data obtained in Herschel (PEP/HerMES) and Spitzer (S-COSMOS) surveys, is compared to that of single-disk galaxies in well-matched control samples to study the cosmic evolution of the star formation enhancement induced by galaxy-galaxy interaction. Both the mean IR spectral energy distribution and mean IR luminosity of star-forming galaxies (SFGs) in SFG+SFG (S+S) pairs in the redshift bin of 0.6 < z < 1 are consistent with no star formation enhancement. SFGs in S+S pairs in a lower redshift bin of 0.2 < z < 0.6 show marginal evidence for a weak star formation enhancement. Together with the significant and strong sSFR enhancement shown by SFGs in a local sample of S+S pairs (obtained using previously published Spitzer observations), our results reveal a trend for the star formation enhancement in S+S pairs to decrease with increasing redshift. Between z = 0 and z = 1, this decline of interaction-induced star formation enhancement occurs in parallel with the dramatic increase (by a factor of ~10) of the sSFR of single SFGs, both of which can be explained by the higher gas fraction in higher-z disks. SFGs in mixed pairs (S+E pairs) do not show any significant star formation enhancement at any redshift. The difference between SFGs in S+S pairs and in S+E pairs suggests a modulation of the sSFR by the intergalactic medium (IGM) in the dark matter halos hosting these pairs. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

  17. COSMIC EVOLUTION OF STAR FORMATION ENHANCEMENT IN CLOSE MAJOR-MERGER GALAXY PAIRS SINCE z = 1

    SciTech Connect

    Xu, C. K.; Shupe, D. L.; Bock, J.; Bridge, C.; Cooray, A.; Lu, N.; Schulz, B.; Bethermin, M.; Aussel, H.; Elbaz, D.; Le Floc'h, E.; Riguccini, L.; Conley, A.; Franceschini, A.; Marsden, G.; Oliver, S. J.; Pozzi, F.; and others

    2012-11-20

    The infrared (IR) emission of 'M {sub *} galaxies' (10{sup 10.4} {<=} M {sub star} {<=} 10{sup 11.0} M {sub Sun }) in galaxy pairs, derived using data obtained in Herschel (PEP/HerMES) and Spitzer (S-COSMOS) surveys, is compared to that of single-disk galaxies in well-matched control samples to study the cosmic evolution of the star formation enhancement induced by galaxy-galaxy interaction. Both the mean IR spectral energy distribution and mean IR luminosity of star-forming galaxies (SFGs) in SFG+SFG (S+S) pairs in the redshift bin of 0.6 < z < 1 are consistent with no star formation enhancement. SFGs in S+S pairs in a lower redshift bin of 0.2 < z < 0.6 show marginal evidence for a weak star formation enhancement. Together with the significant and strong sSFR enhancement shown by SFGs in a local sample of S+S pairs (obtained using previously published Spitzer observations), our results reveal a trend for the star formation enhancement in S+S pairs to decrease with increasing redshift. Between z = 0 and z = 1, this decline of interaction-induced star formation enhancement occurs in parallel with the dramatic increase (by a factor of {approx}10) of the sSFR of single SFGs, both of which can be explained by the higher gas fraction in higher-z disks. SFGs in mixed pairs (S+E pairs) do not show any significant star formation enhancement at any redshift. The difference between SFGs in S+S pairs and in S+E pairs suggests a modulation of the sSFR by the intergalactic medium (IGM) in the dark matter halos hosting these pairs.

  18. The SAMI Galaxy Survey: extraplanar gas, galactic winds and their association with star formation history

    NASA Astrophysics Data System (ADS)

    Ho, I.-Ting; Medling, Anne M.; Bland-Hawthorn, Joss; Groves, Brent; Kewley, Lisa J.; Kobayashi, Chiaki; Dopita, Michael A.; Leslie, Sarah K.; Sharp, Rob; Allen, James T.; Bourne, Nathan; Bryant, Julia J.; Cortese, Luca; Croom, Scott M.; Dunne, Loretta; Fogarty, L. M. R.; Goodwin, Michael; Green, Andy W.; Konstantopoulos, Iraklis S.; Lawrence, Jon S.; Lorente, Nuria P. F.; Owers, Matt S.; Richards, Samuel; Sweet, Sarah M.; Tescari, Edoardo; Valiante, Elisabetta

    2016-04-01

    We investigate a sample of 40 local, main-sequence, edge-on disc galaxies using integral field spectroscopy with the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey to understand the link between properties of the extraplanar gas and their host galaxies. The kinematics properties of the extraplanar gas, including velocity asymmetries and increased dispersion, are used to differentiate galaxies hosting large-scale galactic winds from those dominated by the extended diffuse ionized gas. We find rather that a spectrum of diffuse gas-dominated to wind-dominated galaxies exist. The wind-dominated galaxies span a wide range of star formation rates (SFRs; -1 ≲ log (SFR/M⊙ yr-1) ≲ 0.5) across the whole stellar mass range of the sample (8.5 ≲ log (M*/M⊙) ≲ 11). The wind galaxies also span a wide range in SFR surface densities (10- 3-10- 1.5 M⊙ yr- 1 kpc- 2) that is much lower than the canonical threshold of 0.1 M⊙ yr- 1 kpc- 2. The wind galaxies on average have higher SFR surface densities and higher HδA values than those without strong wind signatures. The enhanced HδA indicates that bursts of star formation in the recent past are necessary for driving large-scale galactic winds. We demonstrate with Sloan Digital Sky Survey data that galaxies with high SFR surface density have experienced bursts of star formation in the recent past. Our results imply that the galactic winds revealed in our study are indeed driven by bursts of star formation, and thus probing star formation in the time domain is crucial for finding and understanding galactic winds.

  19. A WISE Survey of Star Formation in the Milky Way: New Insight into Galaxy Evolution

    NASA Astrophysics Data System (ADS)

    Koenig, Xavier

    We propose to measure the recent star formation rate (SFR) in the Perseus Arm of the Milky Way galaxy and its relation to the surface density of gas, whether molecular or atomic on a range of scales from star forming clusters through large star forming complexes to the full scale of the Galactic Arm. We will test the connection between the SFR-gas relationship in the Galaxy and comparable measurements made in external galaxies in order to probe its origin and better understand the role and contribution of star formation to cosmological galaxy evolution. We also propose to study star formation that has been triggered by the recent formation of massive star clusters in order to discern the mechanisms of triggering that may be operating on super bubble size scales of more than 100 parsecs. This study will allow us to understand one of the key factors that sets the efficiency with which gas becomes stars as galaxies evolve with time. In order to achieve these goals, we will carry out a census of young stellar objects in the outer Milky Way Perseus Arm, using data gathered by the WISE and 2MASS all-sky surveys, with additional use of archival data from the Spitzer Space Telescope. We will develop and refine a young star finding algorithm that uses WISE and 2MASS photometry to identify and classify young stars and filters out contaminating objects such as background galaxies. We will measure the gas content with extinction maps made with data from 2MASS. We will test the triggered star formation models by analyzing the spatial distributions of young stars in super-bubbles and massive star forming regions in the Perseus Arm. This study will produce a key, like-for-like comparison between the extragalactic star formation rate-molecular gas relation and the Galactic relation and will advance the progress in linking Galactic and extragalactic studies of star formation, studying massive star forming regions that are representative of the major mode of star formation. The

  20. The dynamical masses, densities, and star formation scaling relations of Lyα galaxies

    SciTech Connect

    Rhoads, James E.; Malhotra, Sangeeta; Richardson, Mark L. A.; McLinden, Emily M.; Finkelstein, Steven L.; Fynbo, Johan P. U.; Tilvi, Vithal S.

    2014-01-01

    We present the first dynamical mass measurements for Lyα galaxies at high redshift, based on velocity dispersion measurements from rest-frame optical emission lines and size measurements from Hubble Space Telescope imaging, for nine galaxies drawn from four surveys. We use these measurements to study Lyα galaxies in the context of galaxy scaling relations. The resulting dynamical masses range from 10{sup 9} to 10{sup 10} M {sub ☉}. We also fit stellar population models to our sample and use them to place the Lyα sample on a stellar mass versus line width relation. The Lyα galaxies generally follow the same scaling relation as star-forming galaxies at lower redshift, although, lower stellar mass fits are also acceptable in ∼1/3 of the Lyα galaxies. Using the dynamical masses as an upper limit on gas mass, we show that Lyα galaxies have unusually active star formation for their gas mass surface density. This behavior is consistent with what is observed in starburst galaxies, despite the typically smaller masses and sizes of the Lyα galaxy population. Finally, we examine the mass densities of these galaxies and show that their future evolution likely requires dissipational ('wet') merging. In short, we find that Lyα galaxies are low-mass cousins of larger starbursts.

  1. Star formation and black hole accretion activity in rich local clusters of galaxies

    NASA Astrophysics Data System (ADS)

    Bianconi, Matteo; Marleau, Francine R.; Fadda, Dario

    2016-04-01

    Context. We present a study of star formation and central black hole accretion activity of galaxies that are hosted in the two nearby (z ~ 0.2) rich galaxy clusters Abell 983 and 1731. Aims: We aim to quantify both the obscured and unobscured star formation rates, as well as the presence of active galactic nuclei (AGN) as a function of the environment in which the galaxy is located. Methods: We targeted the clusters with unprecedented deep infrared Spitzer observations (0.2 mJy at 24 micron), near-IR Palomar imaging and optical WIYN spectroscopy. The extent of our observations (~3 virial radii) covers the vast range of possible environments, from the very dense cluster centre to the very rarefied cluster outskirts and accretion regions. Results: The star-forming members of the two clusters present star formation rates that are comparable with those measured in coeval field galaxies. Analysis of the spatial arrangement of the spectroscopically confirmed members reveals an elongated distribution for A1731 with respect to the more uniform distribution of A983. The emerging picture is compatible with A983 being a fully evolved cluster, in contrast with the still actively accreting A1731. Conclusions: Analysis of the specific star formation rate reveals evidence of ongoing galaxy pre-processing along A1731's filament-like structure. Furthermore, the decrease in the number of star-forming galaxies and AGN towards the cluster cores suggests that the cluster environment is accelerating the ageing process of the galaxies and blocking further accretion of the cold gas that fuels both star formation and black hole accretion activity. The catalogue and the reduced images (FITS files) 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/588/A105

  2. Star formation and galaxy evolution since z˜2: Results from multiwavelength surveys

    NASA Astrophysics Data System (ADS)

    Brisbin, Drew

    Our recent studies in galaxy evolution have revealed a surprising new paradigm of star formation. Contrary to the notion that major mergers play an increasingly dominant role going backwards in cosmic history, we find that over the last ˜10 Gyr, much of star formation has been fueled by accreting cold gas from the cosmic web. Accretion rates were presumably larger in the past, so star forming systems may have very different properties in the early Universe and today. Large scale astronomical surveys, such as the Herschel Multi-Tiered Extragalactic Survey (HerMES), and the Sloan Digital Sky Survey (SDSS) have provided a wealth of extragalactic data covering a statistically large number of sources. Targeted, niche surveys, like our fine structure line survey of star forming galaxies in the early Universe observed with the redshift (z) Early Universe Spectrometer (ZEUS) have provided detailed observations of high interest sources. We have made use of this diverse set of data to study galaxy evolution from the epoch of peak star formation at z=1-2 up to the present. Data from HerMES is a reliable probe of infrared emission, particularly useful for characterizing the far infrared dust peak, and therefore determining star formation rates out to redshifts of a few. Deep integrations with the Herschel SPIRE photometer rapidly reach the confusion limit, tempering its utility in studying faint high redshift galaxies. With appropriate care taken to identify blended sources, however, HerMES data is useful in identifying bright, redshifted, star forming sources. We have compiled spectral energy distributions from HerMES and ancillary data and found that, even sources at high redshift are well fit by local star forming galaxy templates. In the local Universe, spectroscopic SDSS data has allowed us to estimate crucial galaxy properties on ˜105 sources, providing an opportunity to observe general statistical trends, and constrain theories of galaxy evolution. A toy model of cold

  3. Star formation rates and chemical abundances of emission-line galaxies in intermediate-redshift clusters

    NASA Astrophysics Data System (ADS)

    Mouhcine, M.; Bamford, S. P.; Aragón-Salamanca, A.; Nakamura, O.; Milvang-Jensen, B.

    2006-06-01

    We examine the evolutionary status of luminous, star-forming galaxies in intermediate-redshift clusters by considering their star formation rates (SFRs) and the chemical and ionization properties of their interstellar emitting gas. Our sample consists of 17 massive, star-forming, mostly disc galaxies with MB<~-20, in clusters with redshifts in the range 0.31 <~z<~ 0.59, with a median of = 0.42. We compare these galaxies with the identically selected and analysed intermediate-redshift field sample of Mouhcine et al., and with local galaxies from the Nearby Field Galaxy Survey of Jansen et al. From our optical spectra, we measure the equivalent widths of [OII]λ3727, Hβ and [OIII]λ5007 emission lines to determine diagnostic line ratios, oxygen abundances and extinction-corrected SFRs. The star-forming galaxies in intermediate-redshift clusters display emission-line equivalent widths which are, on average, significantly smaller than measured for field galaxies at comparable redshifts. However, a contrasting fraction of our cluster galaxies have equivalent widths similar to the highest observed in the field. This tentatively suggests a bimodality in the SFRs per unit luminosity for galaxies in distant clusters. We find no evidence for further bimodalities, or differences between our cluster and field samples, when examining additional diagnostics and the oxygen abundances of our galaxies. This maybe because no such differences exist, perhaps because the cluster galaxies which still display signs of star formation have recently arrived from the field. In order to examine this topic with more certainty, and to further investigate the way in which any disparity varies as a function of cluster properties, larger spectroscopic samples are needed.

  4. The Modes of Star Formation in Luminous and Ultraluminous Infrared Galaxies

    NASA Astrophysics Data System (ADS)

    Kartaltepe, Jeyhan S.; Candels Team

    2015-01-01

    In the local universe, Ultraluminous Infrared Galaxies (ULIRGs, LIR>1012 Lsun) are all interacting and merging systems. To date, studies of ULIRGs at high redshift have found a variety of results due to their varying selection effects and small sample sizes. Some studies have found that mergers still dominate the galaxy morphology while others have found a high fraction of morphologically normal or clumpy star forming disks. Near-infrared imaging is crucial for interpreting galaxy structure at high redshift since it probes the rest frame optical light of a galaxy and thus we can compare directly to studies in the local universe. We explore the evolution of the morphological properties of (U)LIRGs over cosmic time using a large sample of galaxies from Herschel observations of the CANDELS fields (including GOODS, COSMOS, and UDS). In particular, we investigate whether the role of galaxy mergers has changed between z~2 and now using the extensive visual classification catalogs produced by the CANDELS team. The combination of a selection from Herschel, near the peak of IR emission, and rest-frame optical morphologies from CANDELS, provides the ideal comparison to nearby (U)LIRGs. We then study the how role of galaxy mergers and the presence of AGN activity correspond to the galaxy's position in the star formation rate - stellar mass plane. Are galaxies that have specific star formation rates elevated above the main sequence more likely to be mergers?

  5. Cosmic web and star formation activity in galaxies at z ∼ 1

    SciTech Connect

    Darvish, B.; Mobasher, B.; Sales, L. V.; Sobral, D.; Scoville, N. Z.; Best, P.; Smail, I.

    2014-11-20

    We investigate the role of the delineated cosmic web/filaments on star formation activity by exploring a sample of 425 narrow-band selected Hα emitters, as well as 2846 color-color selected underlying star-forming galaxies for a large-scale structure at z = 0.84 in the COSMOS field from the HiZELS survey. Using the scale-independent Multi-scale Morphology Filter algorithm, we are able to quantitatively describe the density field and disentangle it into its major components: fields, filaments, and clusters. We show that the observed median star formation rate (SFR), stellar mass, specific SFR, the mean SFR-mass relation, and its scatter for both Hα emitters and underlying star-forming galaxies do not strongly depend on different classes of environment, in agreement with previous studies. However, the fraction of Hα emitters varies with environment and is enhanced in filamentary structures at z ∼ 1. We propose mild galaxy-galaxy interactions as the possible physical agent for the elevation of the fraction of Hα star-forming galaxies in filaments. Our results show that filaments are the likely physical environments that are often classed as the 'intermediate' densities and that the cosmic web likely plays a major role in galaxy formation and evolution which has so far been poorly investigated.

  6. 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.

  7. THE IMACS CLUSTER BUILDING SURVEY. IV. THE LOG-NORMAL STAR FORMATION HISTORY OF GALAXIES

    SciTech Connect

    Gladders, Michael D.; Abramson, Louis; Oemler, Augustus; Dressler, Alan; Poggianti, Bianca; Vulcani, Benedetta

    2013-06-10

    We present here a simple model for the star formation history (SFH) of galaxies that is successful in describing both the star formation rate density (SFRD) over cosmic time, as well as the distribution of specific star formation rates (sSFRs) of galaxies at the current epoch, and the evolution of this quantity in galaxy populations to a redshift of z = 1. We show first that the cosmic SFRD is remarkably well described by a simple log-normal in time. We next postulate that this functional form for the ensemble is also a reasonable description for the SFHs of individual galaxies. Using the measured sSFRs for galaxies at z {approx} 0 from Paper III in this series, we then construct a realization of a universe populated by such galaxies in which the parameters of the log-normal SFH of each galaxy are adjusted to match the sSFRs at z {approx} 0 as well as fitting, in ensemble, the cosmic SFRD from z = 0 to z = 8. This model predicts, with striking fidelity, the distribution of sSFRs in mass-limited galaxy samples to z = 1; this match is not achieved by other models with a different functional form for the SFHs of individual galaxies, but with the same number of degrees of freedom, suggesting that the log-normal form is well matched to the likely actual histories of individual galaxies. We also impose the sSFR versus mass distributions at higher redshifts from Paper III as constraints on the model, and show that, as previously suggested, some galaxies in the field, particularly low mass galaxies, are quite young at intermediate redshifts. As emphasized in Paper III, starbursts are insufficient to explain the enhanced sSFRs in intermediate redshift galaxies; we show here that a model using only smoothly varying log-normal SFHs for galaxies, which allows for some fraction of the population to have peak star formation at late times, does however fully explain the observations. Finally, we show that this model, constrained in detail only at redshifts z < 1, also produces

  8. Episodic Model For Star Formation History and Chemical Abundances in Giant and Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Debsarma, Suma; Chattopadhyay, Tanuka; Das, Sukanta; Pfenniger, Daniel

    2016-08-01

    In search for a synthetic understanding, a scenario for the evolution of the star formation rate and the chemical abundances in galaxies is proposed, combining gas infall from galactic halos, outflow of gas by supernova explosions, and an oscillatory star formation process. The oscillatory star formation model is a consequence of the modelling of the fractional masses changes of the hot, warm and cold components of the interstellar medium. The observed periods of oscillation vary in the range (0.1 - 3.0) × 107 yr depending on various parameters existing from giant to dwarf galaxies. The evolution of metallicity varies in giant and dwarf galaxies and depends on the outflow process. Observed abundances in dwarf galaxies can be reproduced under fast outflow together with slow evaporation of cold gases into hot gas whereas slow outflow and fast evaporation is preferred for giant galaxies. The variation of metallicities in dwarf galaxies supports the fact that low rate of SNII production in dwarf galaxies is responsible for variation in metallicity in dwarf galaxies of similar masses as suggested by various authors.

  9. THE RELATIONSHIP BETWEEN BLACK HOLE GROWTH AND STAR FORMATION IN SEYFERT GALAXIES

    SciTech Connect

    Diamond-Stanic, Aleksandar M.; Rieke, George H.

    2012-02-20

    We present estimates of black hole accretion rates (BHARs) and nuclear, extended, and total star formation rates for a complete sample of Seyfert galaxies. Using data from the Spitzer Space Telescope, we measure the active galactic nucleus (AGN) luminosity using the [O IV] {lambda}25.89 {mu}m emission line and the star-forming luminosity using the 11.3 {mu}m aromatic feature and extended 24 {mu}m continuum emission. We find that black hole growth is strongly correlated with nuclear (r < 1 kpc) star formation, but only weakly correlated with extended (r > 1 kpc) star formation in the host galaxy. In particular, the nuclear star formation rate (SFR) traced by the 11.3 {mu}m aromatic feature follows a relationship with the BHAR of the form SFR{proportional_to} M-dot{sub BH}{sup 0.8}, with an observed scatter of 0.5 dex. This SFR-BHAR relationship persists when additional star formation in physically matched r = 1 kpc apertures is included, taking the form SFR{proportional_to} M-dot{sub BH}{sup 0.6}. However, the relationship becomes almost indiscernible when total SFRs are considered. This suggests a physical connection between the gas on sub-kiloparsec and sub-parsec scales in local Seyfert galaxies that is not related to external processes in the host galaxy. It also suggests that the observed scaling between star formation and black hole growth for samples of AGNs will depend on whether the star formation is dominated by a nuclear or an extended component. We estimate the integrated black hole and bulge growth that occurs in these galaxies and find that an AGN duty cycle of 5%-10% would maintain the ratio between black hole and bulge masses seen in the local universe.

  10. Star Formation and Dense Gas in Galaxy Mergers from the VIXENS Survey

    NASA Astrophysics Data System (ADS)

    Heiderman, Amanda L.; VIXENS Team

    2016-01-01

    We present our λ= 3 mm IRAM and NRO single dish line survey for a sample of 15 interacting galaxies in the VIRUS-P Investigation of the eXtreme ENvironments of Starbursts (VIXENS) survey. Our sample of merging galaxies range from early to late interaction stages (close pairs to merger remnants, respectively). A variety of molecular lines are detected including dense gas tracers HCN, HCO+, HNC, CS, CN (and others) as well as 12CO and 13CO. We compare the dense gas fractions with 12CO and 13CO as well as star formation efficiencies defined by infrared-to-dense gas tracer luminosity ratio and discuss trends with interaction stage. We also investigate relations between star formation and dense gas content in our merger sample and compare them to non-interacting star forming galaxies and Galactic star forming regions in the Milky Way.

  11. Fireworks of Star Formation Light Up a Galaxy

    NASA Technical Reports Server (NTRS)

    2000-01-01

    Located some 13 million light-years from Earth, NGC 4214 is currently forming clusters of new stars from its interstellar gas and dust. In this Hubble image, we can see a sequence of steps in the formation and evolution of stars and star clusters. The picture was created from exposures taken in several color filters with Hubble's Wide Field Planetary Camera 2. NGC 4214 contains a multitude of faint stars covering most of the frame, but the picture is dominated by filigreed clouds of glowing gas surrounding bright stellar clusters. The youngest of these star clusters are located at the lower right of the picture, where they appear as about half a dozen bright clumps of glowing gas. Young, hot stars have a whitish to bluish color in the Hubble image, because of their high surface temperatures, ranging from 10,000 up to about 50,000 degrees Celsius. The radiation and wind forces from the young stars literally blow bubbles in the gas. Over millions of years, the bubbles increase in size as the stars inside them grow older. Moving to the lower left from the youngest clusters, we find an older star cluster, around which a gas bubble has inflated to the point that there is an obvious cavity around the central cluster. The most spectacular feature in the Hubble picture lies near the center of NGC 4214. This object is a cluster of hundreds of massive blue stars, each of them more than 10,000 times brighter than our own Sun. A vast heart-shaped bubble, inflated by the combined stellar winds and radiation pressure, surrounds the cluster. The expansion of the bubble is augmented as the most massive stars in the center reach the ends of their lives and explode as supernovae. The principal astronomers are: John MacKenty, Jesus Maiz-Apellaniz (Space Telescope Science Institute), Colin Norman (Johns Hopkins University), Nolan Walborn (Space Telescope Science Institute), Richard Burg (Johns Hopkins University), Richard Griffiths (Carnegie Mellon University), and Rosemary Wyse

  12. Constraints on the Star Formation Efficiency of Galaxies During Cosmic Reionization

    NASA Astrophysics Data System (ADS)

    Sun, Guochao; Furlanetto, Steven R.

    2016-01-01

    Cosmic reionization is thought to have occurred in the redshift range of 6 < z < 9, which is now being probed by both deep galaxy surveys and CMB observations. Using halo abundance matching over the redshift range 5 < z < 8 and an analytic prescription of gas accretion, we develop a model for the star formation efficiency f* of dark matter halos at z > 6 that matches the measured galaxy luminosity functions at these redshifts. We find that the star formation efficiency peaks near ˜ 10% at halo masses M ˜ 1011-1012 M⊙, in qualitative agreement with its behavior at lower redshifts. Recent lensing observations of z ˜ 7 galaxies suggest that the efficiency declines toward smaller masses, with f* proportional to M1/2 down to M ˜ 1010 M⊙ as expected by models of stellar feedback, albeit with large uncertainties. We then investigate the cosmic star formation histories and the corresponding models of cosmic reionization for a range of extrapolations to small halo masses. We compare these to a variety of observations, using them to further constrain the characteristics of the galaxy populations. Our approach provides an empirically-calibrated, physically-motivated model for the properties of star-forming galaxies sourcing the epoch of reionization. By modeling the redshift evolution of f*, we find a generally slower evolution of the cosmic star formation rate density compared to that predicted by f* fixed in time. In the case where star formation in low-mass halos is maximally efficient, an average escape fraction ˜ 0.1 can reproduce the CMB optical depth observed by Planck, whereas less efficient star formation in these halos requires about twice as many UV photons to escape, or an escape fraction that increases towards higher redshifts. Our models also predict how future observations with JWST can improve our understanding of these galaxy populations.

  13. 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.

  14. Star Formation and AGN Activity in Luminous and Ultraluminous Infrared Galaxies

    NASA Astrophysics Data System (ADS)

    Kartaltepe, Jeyhan

    2015-08-01

    In the local universe, Ultraluminous Infrared Galaxies (ULIRGs, L_IR > 10^12 L⊙) are all interacting and merging systems. We explore the evolution of the morphological and nuclear properties of (U)LIRGs over cosmic time using a large sample of galaxies from Her- schel observations of the CANDELS fields (including GOODS, COSMOS, and UDS). In particular, we investigate whether the role of galaxy mergers has changed between z ˜ 2 and now using the extensive visual classification catalogs produced by the CANDELS team. The combination of a selection from Herschel, near the peak of IR emission, and rest-frame optical morphologies from CANDELS, provides the ideal comparison to nearby (U)LIRGs. We also use rest-frame optical emission line diagnostics, X-ray luminosity, and MIR colors to separate AGN from star-formation dominated galaxies. We then study the how role of galaxy mergers and the presence of AGN activity correspond to the galaxy’s position in the star formation rate - stellar mass plane. Are galaxies that have specific star formation rates elevated above the main sequence more likely to be mergers? We investigate how AGN identified with different methods correspond to different morphologies and merger stages as well as position on the star formation rate - stellar mass plane.

  15. Multicolor Photometry of the Merging Galaxy Cluster A2319: Dynamics and Star Formation Properties

    NASA Astrophysics Data System (ADS)

    Yan, Peng-Fei; Yuan, Qi-Rong; Zhang, Li; Zhou, Xu

    2014-05-01

    Asymmetric X-ray emission and a powerful cluster-scale radio halo indicate that A2319 is a merging cluster of galaxies. This paper presents our multicolor photometry for A2319 with 15 optical intermediate filters in the Beijing-Arizona-Taiwan-Connecticut (BATC) system. There are 142 galaxies with known spectroscopic redshifts within the viewing field of 58' × 58' centered on this rich cluster, including 128 member galaxies (called sample I). A large velocity dispersion in the rest frame, 1622^{+91}_{-70} km s-1, suggests merger dynamics in A2319. The contour map of projected density and localized velocity structure confirm the so-called A2319B substructure, at ~10' northwest to the main concentration A2319A. The spectral energy distributions (SEDs) of more than 30,000 sources are obtained in our BATC photometry down to V ~ 20 mag. A u-band (~3551 Å) image with better seeing and spatial resolution, obtained with the Bok 2.3 m telescope at Kitt Peak, is taken to make star-galaxy separation and distinguish the overlapping contamination in the BATC aperture photometry. With color-color diagrams and photometric redshift technique, 233 galaxies brighter than h BATC = 19.0 are newly selected as member candidates after an exclusion of false candidates with contaminated BATC SEDs by eyeball-checking the u-band Bok image. The early-type galaxies are found to follow a tight color-magnitude correlation. Based on sample I and the enlarged sample of member galaxies (called sample II), subcluster A2319B is confirmed. The star formation properties of cluster galaxies are derived with the evolutionary synthesis model, PEGASE, assuming a Salpeter initial mass function and an exponentially decreasing star formation rate (SFR). A strong environmental effect on star formation histories is found in the manner that galaxies in the sparse regions have various star formation histories, while galaxies in the dense regions are found to have shorter SFR time scales, older stellar ages, and

  16. Multicolor photometry of the merging galaxy cluster A2319: Dynamics and star formation properties

    SciTech Connect

    Yan, Peng-Fei; Yuan, Qi-Rong; Zhang, Li; Zhou, Xu E-mail: yuanqirong@njnu.edu.cn

    2014-05-01

    Asymmetric X-ray emission and a powerful cluster-scale radio halo indicate that A2319 is a merging cluster of galaxies. This paper presents our multicolor photometry for A2319 with 15 optical intermediate filters in the Beijing-Arizona-Taiwan-Connecticut (BATC) system. There are 142 galaxies with known spectroscopic redshifts within the viewing field of 58' × 58' centered on this rich cluster, including 128 member galaxies (called sample I). A large velocity dispersion in the rest frame, 1622{sub −70}{sup +91} km s{sup –1}, suggests merger dynamics in A2319. The contour map of projected density and localized velocity structure confirm the so-called A2319B substructure, at ∼10' northwest to the main concentration A2319A. The spectral energy distributions (SEDs) of more than 30,000 sources are obtained in our BATC photometry down to V ∼ 20 mag. A u-band (∼3551 Å) image with better seeing and spatial resolution, obtained with the Bok 2.3 m telescope at Kitt Peak, is taken to make star-galaxy separation and distinguish the overlapping contamination in the BATC aperture photometry. With color-color diagrams and photometric redshift technique, 233 galaxies brighter than h {sub BATC} = 19.0 are newly selected as member candidates after an exclusion of false candidates with contaminated BATC SEDs by eyeball-checking the u-band Bok image. The early-type galaxies are found to follow a tight color-magnitude correlation. Based on sample I and the enlarged sample of member galaxies (called sample II), subcluster A2319B is confirmed. The star formation properties of cluster galaxies are derived with the evolutionary synthesis model, PEGASE, assuming a Salpeter initial mass function and an exponentially decreasing star formation rate (SFR). A strong environmental effect on star formation histories is found in the manner that galaxies in the sparse regions have various star formation histories, while galaxies in the dense regions are found to have shorter SFR time

  17. The bursting nature of star formation in compact star-forming galaxies from the Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    We study integrated characteristics of ˜ 14000 low-redshift (0 < z < 1) compact star-forming galaxies (SFGs) selected from the Data Release 12 of the Sloan Digital Sky Survey. It is found that emission of these galaxies is dominated by strong young bursts of star formation, implying that their luminosities experience rapid variations on a time scale of a few Myr. Reducing integrated characteristics of these galaxies to zero burst age would result in a considerably tighter and almost linear relation between stellar mass and star formation rate (SFR). The same correction implies that the specific star formation rate (the ratio of SFR and stellar mass) is not dependent on the galaxy stellar mass. We conclude that the correction for rapid luminosity evolution must be taken into account in a similar way when comparing different samples of low- and high-redshift SFGs. If the bursting nature of star formation and young burst ages are characteristics of the galaxies selected at high redshifts, the age correction of observed SFRs derived from the Hβ emission line or UV continua would modify the derived SFR densities in the early universe.

  18. Mechanisms for quenching star formation activities in green valley galaxies and its depends on morphologies

    NASA Astrophysics Data System (ADS)

    Kong, Xu; Pan, Zhizheng; Lian, Jianhui

    2015-08-01

    Galaxies are categorized into two main populations, red quiescent galaxies and blue star-forming galaxies. One of the key questions is which physical mechanisms are responsible for quenching star formation activities in blue galaxies and the resulting transformation? In this talk, we present research on the morphologies, spectra, and environments of "green valley" galaxies in the COSMOS field and low redshift "green valley" galaxies in SDSS. Our findings suggest that environmental conditions, most likely starvation and harassment, significantly affect the transformation of M* < 10^10.0 Msun blue galaxies into red galaxies, especially at z < 0.5. Using image from SDSS and GALEX, we analyze the radial ultraviolet-optical color distributions in a sample of low redshift green valley galaxies, and investigate how quenching is processing in a galaxy. The early-type "green valley" galaxies (ETGs) have dramatically different radial NUV-r color distributions compared to late-type "green valley" galaxies (LTGs), most of ETGs have blue cores, nearly all LTGs have uniform color profiles that can be well-interpreted as red bulges plus blue disk components. These results suggest that the LTGs follow a general model by which quenching first occurs in the core regions, and then finally extend to the rest of the galaxy; for ETGs, their star formations are centrally concentrated. Our results can be re-examined and have important implications for the IFU surveys, such as MaNGA and SAMI (2013ApJ...776...14P, 2014ApJ...792L...4P, 2015MNRAS.446.1449L).

  19. Multiwavelength Measures of Star Formation: Galaxies observed by GALEX, SDSS, and Spitzer

    NASA Astrophysics Data System (ADS)

    Johnson, B. D.; Schiminovich, D.; GALEX Science Team

    2006-06-01

    We combine data from SDSS and the GALEX and Spitzer observatories to create a sample of galaxies observed homogeneously from the UV to the Far-IR. This sample, consisting of ˜ 1000 galaxies observed spectroscopically by SDSS, provides a multiwavelength (presently 0.15-70 micron) view of star formation in nearby (z<0.3) galaxies with SFRs ranging from 0.01 to 100 M⊙/year. We present first results on the dust-age-color relation,showing that long wavelength-baseline colors (e.g. NUV-3.6 micron) can be cleanly decomposed into contributions from dust (measured with the infrared to UV ratio) and star formation history (measured with the relatively dust-insensitive D4000). We also show the relation of 8 micron PAH emission to other indicators of star formation and 8/24 micron vs. 24/70 micron color-color diagrams for the sample galaxies. Finally, we present initial empirical SEDs, split by relevant galaxy properties. The SEDs combined with many global measures of stellar, gas and dust properties will provide a useful local reference for models of galaxy formation and will also help guide interpretations of observations of higher redshift galaxies. We gratefully acknowledge NASA's support for construction, operation, and science analysis for the GALEX mission, developed in cooperation with the Centre National d'Etudes Spatiale of France and the Korean Ministry of Science and Technology. BDJ was supported by NASA GSRP Grant NNG05GO43H.

  20. ARM AND INTERARM STAR FORMATION IN SPIRAL GALAXIES

    SciTech Connect

    Foyle, K.; Rix, H.-W.; Walter, F.; Leroy, A. K.

    2010-12-10

    We investigate the relationship between spiral arms and star formation in the grand-design spirals NGC 5194 and NGC 628 and in the flocculent spiral NGC 6946. Filtered maps of near-IR (3.6 {mu}m) emission allow us to identify 'arm regions' that should correspond to regions of stellar mass density enhancements. The two grand-design spirals show a clear two-armed structure, while NGC 6946 is more complex. We examine these arm and interarm regions, looking at maps that trace recent star formation-far-ultraviolet (GALEX NGS) and 24 {mu}m emission (Spitzer SINGS)-and cold gas-CO (HERACLES) and H I (THINGS). We find the star formation tracers and CO more concentrated in the spiral arms than the stellar 3.6 {mu}m flux. If we define the spiral arms as the 25% highest pixels in the filtered 3.6 {mu}m images, we find that the majority (60%) of star formation tracers occur in the interarm regions; this result persists qualitatively even when considering the potential impact of finite data resolution and diffuse interarm 24 {mu}m emission. Even with a generous definition of the arms (45% highest pixels), interarm regions still contribute at least 30% to the integrated star formation rate (SFR) tracers. We look for evidence that spiral arms trigger star or cloud formation using the ratios of SFR (traced by a combination of FUV and 24 {mu}m emission) to H{sub 2} (traced by CO) and H{sub 2} to H I. Any enhancement of SFR/M(H{sub 2}) in the arm region is very small (less than 10%) and the grand-design spirals show no enhancement compared to the flocculent target. Arm regions do show a weak enhancement in H{sub 2}/H I compared to the interarm regions, but at a fixed gas surface density there is little clear enhancement in the H{sub 2}/H I ratio in the arm regions. Thus, it seems that spiral arms may only act to concentrate the gas to higher densities in the arms.

  1. Constraints on the Star Formation Efficiency of Galaxies During the Epoch of Reionization

    NASA Astrophysics Data System (ADS)

    Sun, G.; Furlanetto, S. R.

    2016-04-01

    Reionization is thought to have occurred in the redshift range of 6 < z < 9, which is now being probed by both deep galaxy surveys and CMB observations. Using halo abundance matching over the redshift range 5 < z < 8 and assuming smooth, continuous gas accretion, we develop a model for the star formation efficiency f⋆ of dark matter halos at z > 6 that matches the measured galaxy luminosity functions at these redshifts. We find that f⋆ peaks at ˜30% at halo masses M ˜ 1011-1012 M⊙, in qualitative agreement with its behavior at lower redshifts. We then investigate the cosmic star formation histories and the corresponding models of reionization for a range of extrapolations to small halo masses. We use a variety of observations to further constrain the characteristics of the galaxy populations, including the escape fraction of UV photons. Our approach provides an empirically-calibrated, physically-motivated model for the properties of star-forming galaxies sourcing the epoch of reionization. In the case where star formation in low-mass halos is maximally efficient, an average escape fraction ˜0.1 can reproduce the optical depth reported by Planck, whereas inefficient star formation in these halos requires either about twice as many UV photons to escape, or an escape fraction that increases towards higher redshifts. Our models also predict how future observations with JWST can improve our understanding of these galaxy populations.

  2. Molecular Gas and Star Formation in Tidal Dwarf Galaxies (Oral Contribution)

    NASA Astrophysics Data System (ADS)

    Lisenfeld, U.; Braine, J.; Duc, P.-A.; Charmandaris, V.; Vallejo, O.; Leon, S.; Brinks, E.

    Tidal Dwarf Galaxies (TDGs) are objects presently forming from gas which has been expelled from their parent galaxies during an interaction. We observed CO emission of a sample of 11 TDGs, of which 8 were detected. The CO is found at the peak of the HI observations and has and has the same line velocity and with, indicating that the molecular gas is forming in situ instead of being torn from the parent galaxies. The presence of Ha emission furthermore shows that stars are forming from this molecular gas. In order too investigate star formation in TDGs further, we compared their molecular gas content and star formation rate (SFR), traced by Ha, to those of spiral galaxies and classical dwarfs. The major difference between TDGs and classical dwarfs is the lower metallicity of the later. The star formation efficiency (SFR per molecular gas mass) of TDGs lies in the range typical of spiral galaxies indicating that star formation is proceeding in a normal fashion from molecular gas.

  3. Constraints on the star formation efficiency of galaxies during the epoch of reionization

    NASA Astrophysics Data System (ADS)

    Sun, G.; Furlanetto, S. R.

    2016-07-01

    Reionization is thought to have occurred in the redshift range of 6 < z < 9, which is now being probed by both deep galaxy surveys and CMB observations. Using halo abundance matching over the redshift range 5 < z < 8 and assuming smooth, continuous gas accretion, we develop a model for the star formation efficiency f⋆ of dark matter haloes at z > 6 that matches the measured galaxy luminosity functions at these redshifts. We find that f⋆ peaks at ˜30 per cent at halo masses M ˜ 1011-1012 M⊙, in qualitative agreement with its behaviour at lower redshifts. We then investigate the cosmic star formation histories and the corresponding models of reionization for a range of extrapolations to small halo masses. We use a variety of observations to further constrain the characteristics of the galaxy populations, including the escape fraction of UV photons. Our approach provides an empirically calibrated, physically motivated model for the properties of star-forming galaxies sourcing the epoch of reionization. In the case where star formation in low-mass haloes is maximally efficient, an average escape fraction ˜0.1 can reproduce the optical depth reported by Planck, whereas inefficient star formation in these haloes requires either about twice as many UV photons to escape, or an escape fraction that increases towards higher redshifts. Our models also predict how future observations with James Webb Space Telescope can improve our understanding of these galaxy populations.

  4. THE ACS NEARBY GALAXY SURVEY TREASURY. X. QUANTIFYING THE STAR CLUSTER FORMATION EFFICIENCY OF NEARBY DWARF GALAXIES

    SciTech Connect

    Cook, David O.; Dale, Daniel A.; Seth, Anil C.; Johnson, L. Clifton; Weisz, Daniel R.; Fouesneau, Morgan; Dalcanton, Julianne J.; Olsen, Knut A. G.; Engelbracht, Charles W.

    2012-06-01

    We study the relationship between the field star formation and cluster formation properties in a large sample of nearby dwarf galaxies. We use optical data from the Hubble Space Telescope and from ground-based telescopes to derive the ages and masses of the young (t{sub age} {approx}< 100 Myr) cluster sample. Our data provide the first constraints on two proposed relationships between the star formation rate (SFR) of galaxies and the properties of their cluster systems in the low SFR regime. The data show broad agreement with these relationships, but significant galaxy-to-galaxy scatter exists. In part, this scatter can be accounted for by simulating the small number of clusters detected from stochastically sampling the cluster mass function. However, this stochasticity does not fully account for the observed scatter in our data, suggesting that there may be true variations in the fraction of stars formed in clusters in dwarf galaxies. Comparison of the cluster formation and the brightest cluster in our sample galaxies also provide constraints on cluster destruction models.

  5. Suppressing star formation in quiescent galaxies with supermassive black hole winds

    NASA Astrophysics Data System (ADS)

    Cheung, Edmond; Bundy, Kevin; SDSS-IV/MaNGA

    2016-01-01

    In the last 10 billion years (i.e., since redshift z ~2) the number of quiescent galaxies with little to no ongoing star formation has grown by a factor ~25. This is challenging to understand since galaxy formation models predict that these galaxies will continue to accrete fresh gas over their lifetimes, relatively little of which is required to reignite measurable star formation. It is thought that feedback from fresh gas accreting onto a central active galactic nucleus (AGN) might help such galaxies maintain their quiescence, but observational evidence for such ``maintenance mode feedback'' remains sparse. Using novel imaging spectroscopy from the SDSS-IV MaNGA Survey (Sloan Digital Sky Survey IV: Mapping Nearby Galaxies at Apache Point Observatory), we present evidence for a new maintenance mode phenomenon we term ``red geysers,'' a potentially episodic but relatively low-power AGN driven wind present in typical quiescent field galaxies of moderate mass and spheroidal morphology. We examine an archetypal red geyser that appears to be accreting gas from a low-mass companion but has no corresponding star formation. Instead, we find evidence for a galaxy-scale ionized wind with outflow velocities reaching more than 300 km/s and high velocity dispersions. We also detect a narrow biconical pattern of strong emission line equivalent widths consistent with fast shocks. Given additional confirmation of a radio AGN present in the galaxy, we propose that red geysers such as this may be a common mode in which gas accretion activates an ionized wind feedback mechanism that prevents star formation and helps moderate luminosity quiescent galaxies maintain their quiescence.

  6. GMC evolution in a barred spiral galaxy with star formation and thermal feedback

    NASA Astrophysics Data System (ADS)

    Fujimoto, Yusuke; Bryan, Greg L.; Tasker, Elizabeth J.; Habe, Asao; Simpson, Christine M.

    2016-09-01

    We explore the impact of star formation and thermal stellar feedback on the giant molecular cloud population forming in a M83-type barred spiral galaxy. We compare three high-resolution simulations (1.5 pc cell size) with different star formation/feedback models: one with no star formation, one with star formation but no feedback, and one with star formation and thermal energy injection. We analyse the resulting population of clouds, finding that we can identify the same population of massive, virialized clouds and transient, low-surface density clouds found in our previous work (that did not include star formation or feedback). Star formation and feedback can affect the mix of clouds we identify. In particular, star formation alone simply converts dense cloud gas into stars with only a small change to the cloud populations, principally resulting in a slight decrease in the transient population. Feedback, however, has a stronger impact: while it is not generally sufficient to entirely destroy the clouds, it does eject gas out of them, increasing the gas density in the intercloud region. This decreases the number of massive clouds, but substantially increases the transient cloud population. We also find that feedback tends to drive a net radial inflow of massive clouds, leading to an increase in the star formation rate in the bar region. We examine a number of possible reasons for this and conclude that it is possible that the drag force from the enhanced intercloud density could be responsible.

  7. 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.

  8. Discrete X-Ray Source Populations and Star Formation History in Nearby Galaxies

    NASA Technical Reports Server (NTRS)

    Zezas, Andreas; Hasan, Hashima (Technical Monitor)

    2005-01-01

    This program aims in understanding the connection between the discrete X-ray source populations observed in nearby galaxies and the history of star-formation in these galaxies. The ultimate goal is to use this knowledge in order to constrain X-ray binary evolution channels. For this reason although the program is primarily observational it has a significant modeling component. During the second year of this study we focused on detailed studies of the Antennae galaxies and the Small Magellanic Cloud (SMC). We also performed the initial analysis of the 5 galaxies forming a starburst-age sequence.

  9. 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.

  10. THE DEEP2 GALAXY REDSHIFT SURVEY: CLUSTERING DEPENDENCE ON GALAXY STELLAR MASS AND STAR FORMATION RATE AT z {approx} 1

    SciTech Connect

    Mostek, Nick; Coil, Alison L.; Cooper, Michael; Davis, Marc; Newman, Jeffrey A.; Weiner, Benjamin J.

    2013-04-10

    We present DEEP2 galaxy clustering measurements at z {approx} 1 as a function of stellar mass, star formation rate (SFR), and specific SFR (sSFR). We find a strong positive correlation between stellar mass and clustering amplitude on 1-10 h {sup -1} Mpc scales for blue, star-forming galaxies with 9.5 < log(M{sub *}/M{sub Sun }) < 11 and no dependence for red, quiescent galaxies with 10.5 < log(M{sub *}/M{sub Sun }) < 11.5. Using recently re-calibrated DEEP2 SFRs from restframe B-band magnitude and optical colors, we find that within the blue galaxy population at z {approx} 1 the clustering amplitude increases strongly with increasing SFR and decreasing sSFR. For red galaxies there is no significant correlation between clustering amplitude and either SFR or sSFR. Blue galaxies with high SFR or low sSFR are as clustered on large scales as red galaxies. We find that the clustering trend observed with SFR can be explained mostly, but not entirely, by the correlation between stellar mass and clustering amplitude for blue galaxies. We also show that galaxies above the star-forming 'main sequence' are less clustered than galaxies below the main sequence, at a given stellar mass. These results are not consistent with the high-sSFR population being dominated by major mergers. We also measure the clustering amplitude on small scales ({<=}0.3 h {sup -1} Mpc) and find an enhanced clustering signal relative to the best-fit large-scale power law for red galaxies with high stellar mass, blue galaxies with high SFR, and both red and blue galaxies with high sSFR. The increased small-scale clustering for galaxies with high sSFRs is likely linked to triggered star formation in interacting galaxies. These measurements provide strong constraints on galaxy evolution and halo occupation distribution models at z {approx} 1.

  11. THE SUPPRESSION OF STAR FORMATION AND THE EFFECT OF THE GALAXY ENVIRONMENT IN LOW-REDSHIFT GALAXY GROUPS

    SciTech Connect

    Rasmussen, Jesper; Mulchaey, John S.; Bai, Lei; Ponman, Trevor J.; Raychaudhury, Somak; Dariush, Ali

    2012-10-01

    Understanding the interaction between galaxies and their surroundings is central to building a coherent picture of galaxy evolution. Here we use Galaxy Evolution Explorer imaging of a statistically representative sample of 23 galaxy groups at z Almost-Equal-To 0.06 to explore how local and global group environments affect the UV properties and dust-corrected star formation rates (SFRs) of their member galaxies. The data provide SFRs out to beyond 2R{sub 200} in all groups, down to a completeness limit and limiting galaxy stellar mass of 0.06 M{sub Sun} yr{sup -1} and 1 Multiplication-Sign 10{sup 8} M{sub Sun }, respectively. At fixed galaxy stellar mass, we find that the fraction of star-forming group members is suppressed relative to the field out to an average radius of R Almost-Equal-To 1.5 Mpc Almost-Equal-To 2R{sub 200}, mirroring results for massive clusters. For the first time, we also report a similar suppression of the specific SFR within such galaxies, on average by 40% relative to the field, thus directly revealing the impact of the group environment in quenching star formation within infalling galaxies. At fixed galaxy density and stellar mass, this suppression is stronger in more massive groups, implying that both local and global group environments play a role in quenching. The results favor an average quenching timescale of {approx}> 2 Gyr and strongly suggest that a combination of tidal interactions and starvation is responsible. Despite their past and ongoing quenching, galaxy groups with more than four members still account for at least {approx}25% of the total UV output in the nearby universe.

  12. ENVIRONMENTAL DEPENDENCE OF THE STAR FORMATION RATE, SPECIFIC STAR FORMATION RATE, AND THE PRESENCE OF ACTIVE GALACTIC NUCLEI FOR HIGH STELLAR MASS AND LOW STELLAR MASS GALAXIES

    SciTech Connect

    Deng Xinfa; Song Jun; Chen Yiqing; Jiang Peng; Ding Yingping

    2012-07-10

    Using two volume-limited main galaxy samples of the Sloan Digital Sky Survey Data Release 8 (SDSS DR8), we explore the environmental dependence of the star formation rate (SFR), specific star formation rate (SSFR), and the presence of active galactic nuclei (AGNs) for high stellar mass (HSM) and low stellar mass (LSM) galaxies. It is found that the environmental dependence of the SFR and SSFR for luminous HSM galaxies and faint LSM ones remains very strong: galaxies in the lowest density regime preferentially have higher SFR and SSFR than galaxies in the densest regime, while the environmental dependence of the SFR and SSFR for luminous LSM galaxies is substantially reduced. Our result also shows that the fraction of AGNs in HSM galaxies decreases as a function of density, while the one in LSM galaxies depends very little on local density. In the faint LSM galaxy sample, the SFR and SSFR of galaxies strongly decrease with increasing density, but the fraction of AGNs depends very little on local density. Such a result can rule out that AGNs are fueled by the cold gas in the disk component of galaxies that is also driving the star formation of those galaxies.

  13. The effect of ram pressure on the star formation, mass distribution and morphology of galaxies

    NASA Astrophysics Data System (ADS)

    Kapferer, Wolfgang; Schindler, Sabine; Ziegler, Bodo; Ferrari, Chiara

    We investigate the dependence of star formation and the distribution of the components of galaxies on the strength of ram pressure. Several mock observations in X-ray, H and HI wavelength for different ram-pressure scenarios are presented. By applying a combined N-body/hydrodynamic description (GADGET-2) with radiative cooling and a recipe for star formation and stellar feedback 12 different ram-pressure stripping scenarios for disc galaxies were calculated. Special emphasis was put on the gas within the disc and in the surroundings. The star formation of a galaxy is enhanced by more than a magnitude in the simulation with a high ram-pressure (5 x 10-11 dyn/cm2 ) in comparison to the same system evolving in isolation. The enhancement of the star formation depends more on the surrounding gas density than on the relative velocity. Up to 95% of all newly formed stars can be found in the wake of the galaxy out to distances of more than 350 kpc behind the stellar disc. Continuously stars fall back to the old stellar disc, building up a bulge-like structure. Young stars can be found throughout the stripped wake with surface densities locally comparable to values in the inner stellar disc. Ram-pressure stripping can shift the location of star formation from the disc into the wake on very short timescales. As the gas in a galaxy has a complex velocity pattern due to the rotation and spiral arms, the superposition of the internal velocity field and the ram pressure causes complex structures in the gaseous wake which survive dynamically up to several 100 Myr. Fi-nally we provide simulated X-ray, Hα and HI observations to be able to compare our results with observations in these wavebands. These simulated observations show many features which depend strongly both on the strength and the duration of the external ram pressure.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  15. Is main-sequence galaxy star formation controlled by halo mass accretion?

    NASA Astrophysics Data System (ADS)

    Rodríguez-Puebla, Aldo; Primack, Joel R.; Behroozi, Peter; Faber, S. M.

    2016-01-01

    The galaxy stellar-to-halo mass relation (SHMR) is nearly time-independent for z < 4. We therefore construct a time-independent SHMR model for central galaxies, wherein the in situ star formation rate (SFR) is determined by the halo mass accretion rate (MAR), which we call stellar halo accretion rate coevolution (SHARC). We show that the ˜0.3 dex dispersion of the halo MAR matches the observed dispersion of the SFR on the star formation main sequence (MS). In the context of `bathtub'-type models of galaxy formation, SHARC leads to mass-dependent constraints on the relation between SFR and MAR. Despite its simplicity and the simplified treatment of mass growth from mergers, the SHARC model is likely to be a good approximation for central galaxies with M* = 109-1010.5 M⊙ that are on the MS, representing most of the star formation in the Universe. SHARC predictions agree with observed SFRs for galaxies on the MS at low redshifts, agree fairly well at z ˜ 4, but exceed observations at z ≳ 4. Assuming that the interstellar gas mass is constant for each galaxy (the `equilibrium condition' in bathtub models), the SHARC model allows calculation of net mass loading factors for inflowing and outflowing gas. With assumptions about preventive feedback based on simulations, SHARC allows calculation of galaxy metallicity evolution. If galaxy SFRs indeed track halo MARs, especially at low redshifts, that may help explain the success of models linking galaxy properties to haloes (including age-matching) and the similarities between two-halo galaxy conformity and halo mass accretion conformity.

  16. CONSTRAINING THE STAR FORMATION HISTORIES IN DARK MATTER HALOS. I. CENTRAL GALAXIES

    SciTech Connect

    Yang Xiaohu; Mo, H. J.; Lu Zhankui; Van den Bosch, Frank C.; Bonaca, Ana; Li Shijie; Lu Yi; Lu Yu

    2013-06-20

    Using the self-consistent modeling of the conditional stellar mass functions across cosmic time by Yang et al., we make model predictions for the star formation histories (SFHs) of central galaxies in halos of different masses. The model requires the following two key ingredients: (1) mass assembly histories of central and satellite galaxies and (2) local observational constraints of the star formation rates (SFRs) of central galaxies as a function of halo mass. We obtain a universal fitting formula that describes the (median) SFH of central galaxies as a function of halo mass, galaxy stellar mass, and redshift. We use this model to make predictions for various aspects of the SFRs of central galaxies across cosmic time. Our main findings are the following. (1) The specific star formation rate at high z increases rapidly with increasing redshift [{proportional_to}(1 + z){sup 2.5}] for halos of a given mass and only slowly with halo mass ({proportional_to}M{sub h}{sup 0.12}) at a given z, in almost perfect agreement with the specific mass accretion rate of dark matter halos. (2) The ratio between the SFR in the main branch progenitor and the final stellar mass of a galaxy peaks roughly at a constant value, {approx}10{sup -9.3} h {sup 2} yr{sup -1}, independent of the halo mass or the final stellar mass of the galaxy. However, the redshift at which the SFR peaks increases rapidly with halo mass. (3) More than half of the stars in the present-day universe were formed in halos with 10{sup 11.1} h {sup -1} M{sub Sun} < M{sub h} < 10{sup 12.3} h {sup -1} M{sub Sun} in the redshift range 0.4 < z < 1.9. (4) The star formation efficiencies (SFEs) of central galaxies reveal a ''downsizing'' behavior, in that the halo ''quenching'' mass, at which the SFE peaks, shifts from {approx}10{sup 12.5} h {sup -1} M{sub Sun} at z {approx}> 3.5 to {approx}10{sup 11.3} h {sup -1} M{sub Sun} at z = 0. (5) At redshift z {approx}> 2.5 more than 99% of the stars in the progenitors of massive

  17. BUILDING LATE-TYPE SPIRAL GALAXIES BY IN-SITU AND EX-SITU STAR FORMATION

    SciTech Connect

    Pillepich, Annalisa; Madau, Piero; Mayer, Lucio

    2015-02-01

    We analyze the formation and evolution of the stellar components in ''Eris'', a 120 pc resolution cosmological hydrodynamic simulation of a late-type spiral galaxy. The simulation includes the effects of a uniform UV background, a delayed-radiative-cooling scheme for supernova feedback, and a star formation recipe based on a high gas density threshold. It allows a detailed study of the relative contributions of ''in-situ'' (within the main host) and ''ex-situ'' (within satellite galaxies) star formation to each major Galactic component in a close Milky Way analog. We investigate these two star-formation channels as a function of galactocentric distance, along different lines of sight above and along the disk plane, and as a function of cosmic time. We find that: (1) approximately 70% of today's stars formed in-situ; (2) more than two thirds of the ex-situ stars formed within satellites after infall; (3) the majority of ex-situ stars are found today in the disk and in the bulge; (4) the stellar halo is dominated by ex-situ stars, whereas in-situ stars dominate the mass profile at distances ≲ 5 kpc from the center at high latitudes; and (5) approximately 25% of the inner, r ≲ 20 kpc, halo is composed of in-situ stars that have been displaced from their original birth sites during Eris' early assembly history.

  18. Suppression of star formation in early-type galaxies by feedback from supermassive black holes.

    PubMed

    Schawinski, Kevin; Khochfar, Sadegh; Kaviraj, Sugata; Yi, Sukyoung K; Boselli, Alessandro; Barlow, Tom; Conrow, Tim; Forster, Karl; Friedman, Peter G; Martin, D Chris; Morrissey, Patrick; Neff, Susan; Schiminovich, David; Seibert, Mark; Small, Todd; Wyder, Ted K; Bianchi, Luciana; Donas, Jose; Heckman, Tim; Lee, Young-Wook; Madore, Barry; Milliard, Bruno; Rich, R Michael; Szalay, Alex

    2006-08-24

    Detailed high-resolution observations of the innermost regions of nearby galaxies have revealed the presence of supermassive black holes. These black holes may interact with their host galaxies by means of 'feedback' in the form of energy and material jets; this feedback affects the evolution of the host and gives rise to observed relations between the black hole and the host. Here we report observations of the ultraviolet emissions of massive early-type galaxies. We derive an empirical relation for a critical black-hole mass (as a function of velocity dispersion) above which the outflows from these black holes suppress star formation in their hosts by heating and expelling all available cold gas. Supermassive black holes are negligible in mass compared to their hosts but nevertheless seem to play a critical role in the star formation history of galaxies. PMID:16929291

  19. What controls star formation in the central 500 pc of the Galaxy?

    NASA Astrophysics Data System (ADS)

    Kruijssen, J. M. Diederik; Longmore, Steven N.; Elmegreen, Bruce G.; Murray, Norman; Bally, John; Testi, Leonardo; Kennicutt, Robert C.

    2014-06-01

    The star formation rate (SFR) in the Central Molecular Zone (CMZ, i.e. the central 500 pc) of the Milky Way is lower by a factor of ≥10 than expected for the substantial amount of dense gas it contains, which challenges current star formation theories. In this paper, we quantify which physical mechanisms could be responsible. On scales larger than the disc scaleheight, the low SFR is found to be consistent with episodic star formation due to secular instabilities or possibly variations of the gas inflow along the Galactic bar. The CMZ is marginally Toomre-stable when including gas and stars, but highly Toomre-stable when only accounting for the gas, indicating a low condensation rate of self-gravitating clouds. On small scales, we find that the SFR in the CMZ may be caused by an elevated critical density for star formation due to the high turbulent pressure. The existence of a universal density threshold for star formation is ruled out. The H I-H2 phase transition of hydrogen, the tidal field, a possible underproduction of massive stars due to a bottom-heavy initial mass function, magnetic fields, and cosmic ray or radiation pressure feedback also cannot individually explain the low SFR. We propose a self-consistent cycle of star formation in the CMZ, in which the effects of several different processes combine to inhibit star formation. The rate-limiting factor is the slow evolution of the gas towards collapse - once star formation is initiated it proceeds at a normal rate. The ubiquity of star formation inhibitors suggests that a lowered central SFR should be a common phenomenon in other galaxies. We discuss the implications for galactic-scale star formation and supermassive black hole growth, and relate our results to the star formation conditions in other extreme environments.

  20. Gas Dynamics in Dwarf-Spheroidal Galaxies: Explaining Carina's Star Formation History

    NASA Astrophysics Data System (ADS)

    Lariviere, P.; Noriega-Crespo, A.

    1993-12-01

    Computer models of gas dynamics are used to explain the complex star- formation history of the Carina dwarf-spheroidal galaxy, which comprises a small old ( ~ 15 Gyr) population and a much larger intermediate-age ( ~ 7 Gyr) population. The model indicates that the first generation of stars quickly photoionized the gas throughout the galaxy, preventing further star formation. Supernova explosions then set the gas in motion away from the center of the galaxy, with much of it accumulating in a dense shell behind the ensuing shock front. The presence of both significant amounts of dark matter in Carina and an inward-directed pressure from the material in the galactic halo prove to crucial in retaining the shell of gas, which oscillates near the boundary of the galaxy on the order of billions of years before cooling sufficiently to recollapse and set off a second wave of star formation. While only Carina's parameters have been explored with this model, the mechanism can be extended to the other dwarf spheroidals, which display similarly complex star-formation histories.

  1. THE OBSERVED RELATION BETWEEN STELLAR MASS, DUST EXTINCTION, AND STAR FORMATION RATE IN LOCAL GALAXIES

    SciTech Connect

    Zahid, H. J.; Kewley, L. J.; Kudritzki, R. P.; Yates, R. M.

    2013-02-15

    In this study, we investigate the relation between stellar mass, dust extinction, and star formation rate (SFR) using {approx}150,000 star-forming galaxies from SDSS DR7. We show that the relation between dust extinction and SFR changes with stellar mass. For galaxies at the same stellar mass, dust extinction is anti-correlated with the SFR at stellar masses <10{sup 10} M {sub Sun }. There is a sharp transition in the relation at a stellar mass of 10{sup 10} M {sub Sun }. At larger stellar masses, dust extinction is positively correlated with the SFR for galaxies at the same stellar mass. The observed relation between stellar mass, dust extinction, and SFR presented in this study helps to confirm similar trends observed in the relation between stellar mass, metallicity, and SFR. The relation reported in this study provides important new constraints on the physical processes governing the chemical evolution of galaxies. The correlation between SFR and dust extinction for galaxies with stellar masses >10{sup 10} M {sub Sun} is shown to extend to the population of quiescent galaxies suggesting that the physical processes responsible for the observed relation between stellar mass, dust extinction, and SFR may be related to the processes leading to the shutdown of star formation in galaxies.

  2. Star formation activity in Balmer break galaxies at z< 1.5

    NASA Astrophysics Data System (ADS)

    Díaz Tello, J.; Donzelli, C.; Padilla, N.; Akiyama, M.; Fujishiro, N.; Yoshikawa, T.; Hanami, H.

    2016-03-01

    Aims: We present a spectroscopic study of the properties of 64 Balmer break galaxies that show signs of star formation. The studied sample of star-forming galaxies spans a redshift range from 0.094 to 1.475 with stellar masses in the range 108-1012M⊙. The sample also includes eight broad emission line galaxies with redshifts between 1.5 star formation rates (SFRs) from emission line luminosities and investigated the dependence of the SFR and specific SFR (SSFR) on the stellar mass and color. Furthermore, we investigated the evolution of these relations with the redshift. Results: We found that the SFR correlates with the stellar mass; our data is consistent with previous results from other authors in that there is a break in the correlation, which reveals the presence of massive galaxies with lower SFR values (i.e., decreasing star formation). We also note an anticorrelation for the SSFR with the stellar mass. Again in this case, our data is also consistent with a break in the correlation, revealing the presence of massive star-forming galaxies with lower SSFR values, thereby increasing the anticorrelation. These results might suggest a characteristic mass (M0) at which the red sequence could mostly be assembled. In addition, at a given stellar mass, high-redshift galaxies have on average higher SFR and SSFR values than local galaxies. Finally, we explored whether a similar trend could be observed with redshift in the SSFR-(u - B) color diagram, and we hypothesize that a possible (u - B)0 break color may define a characteristic color for the formation of the red sequence.

  3. GAS RESERVOIRS AND STAR FORMATION IN A FORMING GALAXY CLUSTER AT zbsime0.2

    SciTech Connect

    Jaffe, Yara L.; Poggianti, Bianca M.; Verheijen, Marc A. W.; Deshev, Boris Z.; Van Gorkom, Jacqueline H.

    2012-09-10

    We present first results from the Blind Ultra-Deep H I Environmental Survey of the Westerbork Synthesis Radio Telescope. Our survey is the first direct imaging study of neutral atomic hydrogen gas in galaxies at a redshift where evolutionary processes begin to show. In this Letter we investigate star formation, H I content, and galaxy morphology, as a function of environment in Abell 2192 (at z = 0.1876). Using a three-dimensional visualization technique, we find that Abell 2192 is a cluster in the process of forming, with significant substructure in it. We distinguish four structures that are separated in redshift and/or space. The richest structure is the baby cluster itself, with a core of elliptical galaxies that coincides with (weak) X-ray emission, almost no H I detections, and suppressed star formation. Surrounding the cluster, we find a compact group where galaxies pre-process before falling into the cluster, and a scattered population of 'field-like' galaxies showing more star formation and H I detections. This cluster proves to be an excellent laboratory to understand the fate of the H I gas in the framework of galaxy evolution. We clearly see that the H I gas and the star formation correlate with morphology and environment at z {approx} 0.2. In particular, the fraction of H I detections is significantly affected by the environment. The effect starts to kick in in low-mass groups that pre-process the galaxies before they enter the cluster. Our results suggest that by the time the group galaxies fall into the cluster, they are already devoid of H I.

  4. How Environment Affects Star Formation: Tracing Activity in High Redshift Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Alberts, Stacey; Pope, A.; Brodwin, M.; Atlee, D. W.; Lin, Y.; Chary, R.; Dey, A.; Eisenhardt, P. R.; Gettings, D.; Gonzalez, A. H.; Jannuzi, B.; Mancone, C.; Moustakas, J.; Snyder, G. F.; Stanford, S. A.; Stern, D.; Weiner, B. J.; Zeimann, G.

    2014-01-01

    The emerging picture of the evolution of cluster galaxies indicates that the epoch of z>1 is a crucial period of active star formation and mass assembly in clusters. In this dissertation, I leverage a uniformly-selected cluster sample from the IRAC Shallow Cluster Survey (ISCS) with Herschel imaging to analyse the star formation (SF) activity in cluster galaxies over the past ten billion years. This analysis is two-fold: 1) using 274 clusters across the 9 square degree Bootes field, I perform a stacking analysis of mass-limited samples of cluster and field galaxies using wide-field Herschel observations over a long redshift baseline, z=0.3-1.5. I find that the average SF activity in cluster galaxies is evolving faster than in the field, with field-like SF in the cluster cores and enhanced SF activity in the cluster outskirts at z>1.2. By further breaking down my analysis by galaxy mass and type, I determine which mechanisms are capable of driving this evolution. 2) I use unique, deep Herschel imaging of 11 spectroscopically-confirmed clusters from z=1.1-1.8 to study the properties of individual infrared bright cluster galaxies as a function of redshift and cluster-centric radius. Combined with ancillary data, I determine the star formation, dust, and AGN properties of the most active cluster galaxies and tie the evolution of these properties back to the environment by comparing to field populations. By combining these two approaches, I constrain cluster galaxy properties during a pivotal epoch of dust-obscured star formation activity and mass assembly in some of the most extreme structures in the Universe.

  5. UNLEASHING POSITIVE FEEDBACK: LINKING THE RATES OF STAR FORMATION, SUPERMASSIVE BLACK HOLE ACCRETION, AND OUTFLOWS IN DISTANT GALAXIES

    SciTech Connect

    Silk, Joseph

    2013-08-01

    Pressure-regulated star formation is a simple variant on the usual supernova-regulated star formation efficiency that controls the global star formation rate as a function of cold gas content in star-forming galaxies, and accounts for the Schmidt-Kennicutt law in both nearby and distant galaxies. Inclusion of active galactic nucleus (AGN) induced pressure, by jets and/or winds that flow back onto a gas-rich disk, can lead, under some circumstances, to significantly enhanced star formation rates, especially at high redshift and most likely followed by the more widely accepted phase of star formation quenching. Simple expressions are derived that relate supermassive black hole growth, star formation, and outflow rates. The ratios of black hole to spheroid mass and of both black hole accretion and outflow rates to star formation rate are predicted as a function of time. I suggest various tests of the AGN-triggered star formation hypothesis.

  6. Resolved H I imaging of a population of massive H I-rich galaxies with suppressed star formation

    SciTech Connect

    Lemonias, Jenna J.; Schiminovich, David; Catinella, Barbara; Heckman, Timothy M.; Moran, Sean M.

    2014-07-20

    Despite the existence of well-defined relationships between cold gas and star formation, there is evidence that some galaxies contain large amounts of H I that do not form stars efficiently. By systematically assessing the link between H I and star formation within a sample of galaxies with extremely high H I masses (log M{sub H{sub I}}/M{sub ☉} > 10), we uncover a population of galaxies with an unexpected combination of high H I masses and low specific star formation rates that exists primarily at stellar masses greater than log M{sub *}/M{sub ☉} ∼ 10.5. We obtained H I maps of 20 galaxies in this population to understand the distribution of the H I and the physical conditions in the galaxies that could be suppressing star formation in the presence of large quantities of H I. We find that all of the galaxies we observed have low H I surface densities in the range in which inefficient star formation is common. The low H I surface densities are likely the main cause of the low specific star formation rates, but there is also some evidence that active galactic nuclei or bulges contribute to the suppression of star formation. The sample's agreement with the global star formation law highlights its usefulness as a tool for understanding galaxies that do not always follow expected relationships.

  7. Schmidt’s Conjecture and Star Formation in Galactic Molecular Clouds and External Galaxies

    NASA Astrophysics Data System (ADS)

    Alves, Joao; Lada, Charles; Lombardi, Marco; Forbrich, Jan

    2015-08-01

    The star formation rate and its variation in time are intimately connected to our understanding of the formation and evolution of the Milky Way and external galaxies. Ever since the pioneering work of Martin Schmidt a half-century ago there has been great interest in finding an appropriate empirical relation that would directly link some property of interstellar gas with the physical process of star formation within it. Schmidt conjectured that this might take the form of a relation between the rate of star formation and the surface density of the interstellar gas. In this talk I will describe how recent observations of nearby GMCs made with robust, high-dynamic range Planck-Herschel-2MASS maps, are providing new insights into the nature of this relationship. I will show that though a Schmidt relation is observed within individual molecular clouds, there is no Schmidt law that characterizes star formation between the clouds in the Milky Way. Instead, a linear scaling exists between the total SFR and the amount of dense gas within molecular clouds. This scaling may be the underlying physical relationship that most directly connects star formation activity with interstellar gas both between clouds in the Milky Way and within and between external galaxies. Finally I will discuss the implications of these results for the Kennicutt-Schmidt relation for galaxies.

  8. The Fundamental Plane of star formation in galaxies revealed by the EAGLE hydrodynamical simulations

    NASA Astrophysics Data System (ADS)

    Lagos, Claudia del P.; Theuns, Tom; Schaye, Joop; Furlong, Michelle; Bower, Richard G.; Schaller, Matthieu; Crain, Robert A.; Trayford, James W.; Matthee, Jorryt

    2016-07-01

    We investigate correlations between different physical properties of star-forming galaxies in the `Evolution and Assembly of GaLaxies and their Environments' (EAGLE) cosmological hydrodynamical simulation suite over the redshift range 0 ≤ z ≤ 4.5. A principal component analysis reveals that neutral gas fraction (fgas,neutral), stellar mass (Mstellar) and star formation rate (SFR) account for most of the variance seen in the population, with galaxies tracing a two-dimensional, nearly flat, surface in the three-dimensional space of fgas, neutral-Mstellar-SFR with little scatter. The location of this plane varies little with redshift, whereas galaxies themselves move along the plane as their fgas, neutral and SFR drop with redshift. The positions of galaxies along the plane are highly correlated with gas metallicity. The metallicity can therefore be robustly predicted from fgas, neutral, or from the Mstellar and SFR. We argue that the appearance of this `Fundamental Plane of star formation' is a consequence of self-regulation, with the plane's curvature set by the dependence of the SFR on gas density and metallicity. We analyse a large compilation of observations spanning the redshift range 0 ≲ z ≲ 3, and find that such a plane is also present in the data. The properties of the observed Fundamental Plane of star formation are in good agreement with EAGLE's predictions.

  9. Ultraviolet Morphology and Unobscured UV Star Formation Rates of CLASH Brightest Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Donahue, Megan; Connor, Thomas; Fogarty, Kevin; Li, Yuan; Voit, G. Mark; Postman, Marc; Koekemoer, Anton; Moustakas, John; Bradley, Larry; Ford, Holland

    2015-06-01

    Brightest cluster galaxies (BCGs) are usually quiescent, but many exhibit star formation. Here we exploit the opportunity provided by rest-frame UV imaging of galaxy clusters in the Cluster Lensing and Supernovae with Hubble (CLASH) Multi-Cycle Treasury Project to reveal the diversity of UV morphologies in BCGs and to compare them with recent simulations of the cool, star-forming gas structures produced by precipitation-driven feedback. All of the CLASH BCGs are detected in the rest-frame UV (280 nm), regardless of their star formation activity, because evolved stellar populations produce a modest amount of UV light that traces the relatively smooth, symmetric, and centrally peaked stellar distribution seen in the near infrared. Ultraviolet morphologies among the BCGs with strong UV excesses exhibit distinctive knots, multiple elongated clumps, and extended filaments of emission that distinctly differ from the smooth profiles of the UV-quiet BCGs. These structures, which are similar to those seen in the few star-forming BCGs observed in the UV at low redshift, are suggestive of bi-polar streams of clumpy star formation, but not of spiral arms or large, kiloparsec-scale disks. Based on the number of streams and lack of culprit companion galaxies, these streams are unlikely to have arisen from multiple collisions with gas-rich galaxies. These star-forming UV structures are morphologically similar to the cold-gas structures produced in simulations of precipitation-driven active galactic nucleus feedback in which jets uplift low-entropy gas to greater altitudes, causing it to condense. Unobscured star formation rates estimated from CLASH UV images using the Kennicutt relation range up to 80 {{M}⊙ } y{{r}-1} in the most extended and highly structured systems. The circumgalactic gas-entropy threshold for star formation in CLASH BCGs at z ˜ 0.2-0.5 is indistinguishable from that for clusters at z\\lt 0.2.

  10. The Magellanic irregular galaxy NGC 4214 - Star formation and the interstellar medium

    NASA Technical Reports Server (NTRS)

    Thronson, Harley A., Jr.; Greenhouse, Matthew; Hunter, Deidre A.; Telesco, C. M.; Harper, D. A.

    1988-01-01

    Near- and far-IR data and mm-wave CO observations are used to study the star-forming properties of the Magellanic irregular galaxy NGC 4214 and its interstellar medium. The galaxy is forming stars at present at about 0.5-1 solar mass/yr in its central few arcmin, if the new stars follow the Salpeter initial mass function from 0.1 to 100 solar masses. This has been maintained for around a Hubble time, although some regions of the galaxy may undergo periods of enhanced and depressed star formation. Based on the mass of dust in emission at 160 microns, a plausible star formation efficiency of about 1.5 percent is estimated, if the H I gas does not take part in forming stars. Molecular masses derived using the H + 1 - 0 line and a conversion to M(H2) appropriate to spiral galaxies produces a mass estimate that is too low by a factor of five to ten.

  11. Star formation and accretion in the circumnuclear disks of active galaxies

    NASA Astrophysics Data System (ADS)

    Wutschik, Stephanie; Schleicher, Dominik R. G.; Palmer, Thomas S.

    2013-12-01

    Aims: We explore the evolution of supermassive black holes (SMBH) centered in a circumnuclear disk (CND) as a function of the mass supply from the host galaxy and considering different star formation laws, which may give rise to a self-regulation via the injection of supernova-driven turbulence. Methods: A system of equations describing star formation, black hole accretion and angular momentum transport in the disk was solved self-consistently for an axisymmetric disk in which the gravitational potential includes contributions from the black hole, the disk and the hosting galaxy. Our model extends the framework provided by Kawakatu & Wada (2008, ApJ, 681, 73), by separately considering the inner and outer part of the disk, and by introducing a potentially non-linear dependence of the star formation rate on the gas surface density and the turbulent velocity. The star formation recipes are calibrated using observational data for NGC 1097, while the accretion model is based on turbulent viscosity as a source of angular momentum transport in a thin viscous accretion disk. Results: We find that current data provide no strong constraint on the star formation recipe, and can in particular not distinguish between models entirely regulated by the surface density, and models including a dependence on the turbulent velocity. The evolution of the black hole mass, on the other hand, strongly depends on the applied star formation law, as well as the mass supply from the host galaxy. We suggest to explore the star formation process in local AGN with high-resolution ALMA observations to break the degeneracy between different star formation models.

  12. Spitzer observations of red galaxies: Implication for high-redshift star formation

    NASA Astrophysics Data System (ADS)

    Papovich, Casey

    2006-03-01

    My colleagues and I identified distant red galaxies (DRGs) with J - Ks > 2.3 in the southern Great Observatories Origins Deep Surveys (GOODS-S) field. These galaxies reside at z ˜ 1-3.5, (< z> ≃ 2.2) and based on their ACS (0.4-1 μm), ISAAC (1-2.2 μm), and IRAC (3-8 μm) photometry, they typically have stellar masses M ⩾ 10 11 M⊙. Interestingly, more than 50% of these objects have 24 μm flux densities ⩾50 μJy. Attributing the IR emission to star-formation implies star-formation rates (SFRs) of ≃100-1000 M⊙ yr -1. As a result, galaxies with M ⩾ 10 11 M⊙ have specific SFRs equal to or exceeding the global value at z ˜ 1.5-3. In contrast, galaxies with M ⩾ 10 11 M⊙ at z ˜ 0.3-0.75 have specific SFRs less than the global average, and more than an order of magnitude lower than that for massive DRGs at z ˜ 1.5-3. Thus, the bulk of star formation in massive galaxies is largely complete by z ˜ 1.5. The red colors and large inferred stellar masses in the DRGs suggest that much of the star formation in these galaxies occurred at redshifts z ≳ 5-6. Using model star-formation histories that match the DRG colors and stellar masses at z ˜ 2-3, and measurements of the UV luminosity density at z ≳ 5-6, we consider what constraints exist on the stellar initial mass function in the progenitors of the massive DRGs at z ˜ 2-3.

  13. A Multi-Wavelength Investigation of the Star Formation Processes in the SHIELD Galaxies

    NASA Astrophysics Data System (ADS)

    Teich, Yaron G.; McNichols, Andrew Thomas; Cannon, John M.

    2015-08-01

    We analyze the relationships between HI mass surface density and star formation in the 12 galaxies that comprise the Survey of HI in Extremely Low-Mass Dwarfs (SHIELD). The SHIELD galaxies were selected from the first ~10% of data from the Arecibo Legacy Fast ALFA (ALFALFA) survey; they harbor low-mass HI reservoirs (6.6 < log(M(HI)) < 7.8) that make them critical testbeds for our understanding of the process of star formation in shallow potential wells. Using HI imaging from the VLA, Hα imaging from the WIYN 3.5m telescope, and archival GALEX imaging (available for most sample members), we compare the locations and intensities of star formation with the properties of the neutral ISM. Despite the low HI column densities observed in these systems, each SHIELD galaxy has a significant blue stellar population; there is ongoing star formation in all but one of the galaxies. We find that the regions of Hα emission are co-located with regions of high HI column densities. We compare the degree of overlap of HI dense knots with local UV maxima, with the goal of identifying whether Hα or UV emission more strongly correlates with regions of high HI column density. We calculate the specific SFR and SFR density for the galaxies in the sample, and examine the relationships of HI mass and SFR (from Hα, UV, and averaged from both) for selected sources. We also calculate the star formation efficiency (SFE) for each galaxy in the sample (total SFR / total gas mass) and note its dependence on HI column density.This work is a result of collaboration with the SHIELD Team and is supported by NSF grant 1211683.

  14. Star formation in infrared bright and infrared faint starburst interacting galaxies

    NASA Technical Reports Server (NTRS)

    Lamb, Susan A.; Bushouse, Howard A.; Towns, John W.

    1990-01-01

    Short wavelength IUE spectra of Arp 248b and UGC 8315N are combined with optical spectra and interpreted using a combination of spectrum synthesis and spectral diagnostics to place constraints on the massive star populations of the central regions of these galaxies and to deduce information about the star formation histories in the last 10(exp 8) years. The authors find that both galaxies have substantial fractions of their optical light coming from massive stars and that Arp 248b may be dominated in the UV by WR stars. The UV spectra are dominated by radiation from evolved massive stars and the authors place and age on the burst in Arp 248b of a few tens of millions of years.

  15. Neutral hydrogen gas, past and future star formation in galaxies in and around the `Sausage' merging galaxy cluster

    NASA Astrophysics Data System (ADS)

    Stroe, Andra; Oosterloo, Tom; Röttgering, Huub J. A.; Sobral, David; van Weeren, Reinout; Dawson, William

    2015-09-01

    CIZA J2242.8+5301 (z = 0.188, nicknamed `Sausage') is an extremely massive (M200 ˜ 2.0 × 1015 M⊙), merging cluster with shock waves towards its outskirts, which was found to host numerous emission line galaxies. We performed extremely deep Westerbork Synthesis Radio Telescope H I observations of the `Sausage' cluster to investigate the effect of the merger and the shocks on the gas reservoirs fuelling present and future star formation (SF) in cluster members. By using spectral stacking, we find that the emission line galaxies in the `Sausage' cluster have, on average, as much H I gas as field galaxies (when accounting for the fact cluster galaxies are more massive than the field galaxies), contrary to previous studies. Since the cluster galaxies are more massive than the field spirals, they may have been able to retain their gas during the cluster merger. The large H I reservoirs are expected to be consumed within ˜0.75-1.0 Gyr by the vigorous SF and active galactic nuclei activity and/or driven out by the outflows we observe. We find that the star formation rate (SFR) in a large fraction of H α emission line cluster galaxies correlates well with the radio broad-band emission, tracing supernova remnant emission. This suggests that the cluster galaxies, all located in post-shock regions, may have been undergoing sustained SFR for at least 100 Myr. This fully supports the interpretation proposed by Stroe et al. and Sobral et al. that gas-rich cluster galaxies have been triggered to form stars by the passage of the shock.

  16. The Evolution of Star Formation of Galaxies in the COSMOS Field1,2

    NASA Astrophysics Data System (ADS)

    Fang, Guan-Wen; Ma, Zhong-Yang; Chen, Yang; Kong, Xu

    2015-07-01

    Based on the multi-band photometric data of the COSMOS (Cosmic Evolution Survey)/Ultra VISTA (Ultra-deep Visible and Infrared Survey Telescope for Astronomy) field, we have selected a mass-limited sample of galaxies with the redshifts of 0 < z < 3.5. And according to the rest-frame UVJ twocolor (U-V vs. V-J) criteria, we classify the sample galaxies into the star-forming galaxies (SFGs) and the quiescent galaxies (QGs) in different redshift bins. In the redshift range of 0 < z < 1.5, the fraction of QGs with a mass of M* > 1011Mʘ is greater than 70%. In the range of 0 < z < 3.5, the star formation rates (SFRs) of SFGs exhibit a strong main sequence (MS) relation with the stellar mass M*. For a fixed stellar mass M*, the galaxy SFR and specific SFR (sSFR) increase with the redshift, indicating that the SFGs at high redshifts are more active in star formation. Relative to the low-mass galaxies, the large-mass SFGs have a lower sSFR, implying that the growth of a low-mass galaxy is more relying on the star formation activity of itself. In combination with the data given by the other literature, it is found that for the galaxies at higher redshifts (2 < z < 8), the evolution of sSFR with the redshift becomes weak, and the evolutionary relation is sSFR∝ (1 + z)0.94±0.17.

  17. VIPERS view of the star formation history of early-type galaxies

    NASA Astrophysics Data System (ADS)

    Siudek, M.; Malek, K.; Garilli, B.; Scodeggio, M.; Fritz, A.; Pollo, A.; Abbas, U.; Adami, C.; Arnouts, S.; Bel, J.; Bolzonella, M.; Bottini, D.; Branchini, E.; Cappi, A.; Coupon, J.; Cucciati, O.; Davidzon, I.; De Lucia, G.; de la Torre, S.; Franzetti, P.; Fumana, M.; Granett, B. R.; Guzzo, L.; Ilbert, O.; Iovino, A.; Krywult, J.; Le Brun, V.; Le Fèvre, O.; Maccagni, D.; Marulli, F.; McCracken, H. J.; Paioro, L.; Polletta, M.; Schlagenhaufer, H.; Tasca, L. A. M.; Tojeiro, R.; Vergani, D.; Zanichelli, A.; Burden, A.; Di Porto, C.; Marchetti, A.; Marinoni, C.; Mellier, Y.; Moscardini, L.; Nichol, R. C.; Peacock, J. A.; Percival, W. J.; Phleps, S.; Wolk, M.; Zamorani, G.

    2015-09-01

    We present studies over the relations between stellar mass, redshift and star formation history for a high quality sample of early-type galaxies (ETGs) observed by the by the VIMOS Public Extragalactic Redshift Survey (VIPERS). VIPERS is an ongoing Large Programme to map in detail the large-scale distribution of galaxies at 0:5 < z < 1:2 with a unique volume (24 deg2) and sampling rate (~= 45%). At this redshift, IPERS fills a unique niche in galaxy surveys, provides a exceptional opportunity to study galaxies and their evolution at an epoch when the Universe had approximately half its current age. VIPERS data set will become the z ~ 1 equivalent of current state-of-the-art local (z < 0:2) surveys, allowing us to compare measurements at these two different epochs on equal statistical footing. The final sample of this survey is going to reach nearly 100,000 galaxies. As the VIPERS sample contains ~ 15% of the early type galaxies with known spectroscopic redshift and a very good quality spectra, it is a perfect sample to study the star formation history based on their spectroscopic features. We show that there the age of stellar population is depending on the stellar mass and the redshift. Our results show that lower mass galaxies have young stellar populations, while higher mass ETGs are populated with old stars. This suggest that marginal star formation occurs in massive galaxies. This result is consistent with the observations of the local Universe. Moreover, this trend of evolution is preserved for the different redshift range between 0:4 < z < 1:2.

  18. Explaining the Three-decade Correlation between Star Formation Rate and Stellar Mass in Galaxies at z~1

    NASA Astrophysics Data System (ADS)

    Gawiser, Eric J.; Kurczynski, Peter; Acquaviva, Viviana; UVUDF Team, CANDELS Team

    2016-01-01

    In star-forming galaxies across cosmic time, a correlation has been found between the mass of stars already assembled and its time derivative, the star formation rate. This surprising correlation was not predicted by theory, but it can be reproduced within cosmological hydrodynamics simulations and semi-analytical models of galaxy formation. Here we use SpeedyMC, a Markov Chain Monte Carlo code for Spectral Energy Distribution fitting, to measure the star formation rates and stellar masses of 800 galaxies from the Ultraviolet Ultradeep Field (UVUDF) and CANDELS/GOODS-S field at redshift 1 < z < 1.5. This galaxy sample leverages the deepest images taken with the Hubble Space Telescope to extend the SFR-M* correlation a factor of 10-100X lower in M* than previous studies, down to values of 10^7 M_sun comparable to present-day dwarf galaxies. Accounting for each galaxy's parameter uncertainties, including their covariances, yields a power-law correlation across three decades with intrinsic scatter of 0.2 dex. Having assumed realistic star formation histories that can rise and fall with time, we are able to measure star formation rates on timescales varying from instantaneous to the "lifetime" average for each galaxy. As the timescale over which star formation rate is averaged increases, the power-law exponent of the correlation with stellar mass increases to unity, and the scatter decreases to 0.05 dex. We conclude that the observed correlation between star formation rate and stellar mass results from a tight correlation between recent and lifetime-average star formation rates and a narrow spread of galaxy ages at a given star formation rate. The resulting correlation provides crucial evidence that galaxy formation proceeds through self-regulated star formation. We gratefully acknowledge support from NSF grant AST-1055919 and grants from NASA via the Space Telescope Science Institute in support of programs 12060.57, 12445.56, and GO-12534.

  19. THE STELLAR POPULATION AND STAR FORMATION PROPERTIES OF BLUE COMPACT DWARF GALAXIES

    SciTech Connect

    Zhao Yinghe; Gao Yu; Gu Qiusheng E-mail: yugao@pmo.ac.cn

    2011-02-15

    We study stellar populations, star formation histories (SFHs), and star formation properties for a sample of blue compact dwarf galaxies (BCDs) selected by cross-correlating the Gil de Paz et al. sample with the Sloan Digital Sky Survey Data Release 6. The sample includes 31 BCDs, which span a large range of galactic parameters. Using a stellar population synthesis method, we derive stellar populations and reconstruct SFHs for these BCDs. Our studies confirm that BCDs are not young systems experiencing their first star formation, but old systems undergoing a starburst activity. The stellar mass-weighted ages can be up to 10 Gyr, while the luminosity-weighted ages might be up to approximately three orders of magnitude younger ({approx}10 Myr) for most galaxies. Based on multiwavelength data, we also study the integrated star formation properties. The star formation rate (SFR) for our sample galaxies spans nearly three orders of magnitude, from a few 10{sup -3} to {approx}1 M{sub sun} yr{sup -1}, with a median value of {approx}0.1 M{sub sun} yr{sup -1}. We find that about 90% of BCDs in our sample have their birthrate parameter (the ratio of the current SFR to the averaged past SFR) b>2-3. We further discuss correlations of the current SFR with the integrated galactic stellar mass and explore the connection between SFR and metallicity.

  20. Probing the Multiphase Interstellar Medium and Star Formation in Nearby Galaxies through Far Infrared Emission

    NASA Astrophysics Data System (ADS)

    Herrera-Camus, Rodrigo; Bolatto, Alberto D.; Wolfire, Mark G.; Smith, John-David T.; Kennicutt, Robert; Calzetti, Daniela; Croxall, Kevin V.; Fisher, David B.; Kingfish, Beyond The Peak

    2015-01-01

    We have studied the complex interplay between physical processes that play a crucial role in galaxy formation and evolution, in particular star formation and the thermal balance in the neutral and molecular interstellar medium. This work was based on far-infrared photometry and spectroscopy of nearby galaxies using Spitzer and Herschel space observatories. In our first project, we study the dust properties of one of the the most metal poor systems known in the local Universe, I Zw 18. We measured a dust-to-gas ratio in the range 3.2-13×10-6, which suggest that low metallicity galaxies, like I Zw 18, do not follow the same linear relationship between metallicity and dust-to-gas ratio as typical local spirals. In our second project, we studied the reliability of the [CII] 158 µm emission as a star formation tracer. The [CII] line is the major coolant for the neutral atomic gas and it can be observed by ALMA in normal, star forming galaxies at z > 2. Based on resolved observations of 46 nearby galaxies from the KINGFISH sample, we conclude that [CII] emission can be used for measurements of star formation rates (SFR) on both, global and kiloparsec scales, in normal star-forming galaxies in the absence of strong active galactic nuclei. 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 ∑[CII] - ∑SFR correlation is valid over almost 5 orders of magnitude in ∑SFR, holding for both normal star-forming galaxies and non-AGN luminous infrared galaxies. Using [CII] luminosity instead of surface brightness to estimate SFR suffers from worse systematics, frequently underpredicting SFR in luminous infrared galaxies. 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, most likely the main parameter

  1. Galaxy morphology and star formation in the Illustris Simulation at z = 0

    NASA Astrophysics Data System (ADS)

    Snyder, Gregory F.; Torrey, Paul; Lotz, Jennifer M.; Genel, Shy; McBride, Cameron K.; Vogelsberger, Mark; Pillepich, Annalisa; Nelson, Dylan; Sales, Laura V.; Sijacki, Debora; Hernquist, Lars; Springel, Volker

    2015-12-01

    We study how optical galaxy morphology depends on mass and star formation rate (SFR) in the Illustris Simulation. To do so, we measure automated galaxy structures in 10 808 simulated galaxies at z = 0 with stellar masses 109.7 < M*/M⊙ < 1012.3. We add observational realism to idealized synthetic images and measure non-parametric statistics in rest-frame optical and near-IR images from four directions. We find that Illustris creates a morphologically diverse galaxy population, occupying the observed bulge strength locus and reproducing median morphology trends versus stellar mass, SFR, and compactness. Morphology correlates realistically with rotation, following classification schemes put forth by kinematic surveys. Type fractions as a function of environment agree roughly with data. These results imply that connections among mass, star formation, and galaxy structure arise naturally from models matching global star formation and halo occupation functions when simulated with accurate methods. This raises a question of how to construct experiments on galaxy surveys to better distinguish between models. We predict that at fixed halo mass near 1012 M⊙, disc-dominated galaxies have higher stellar mass than bulge-dominated ones, a possible consequence of the Illustris feedback model. While Illustris galaxies at M* ˜ 1011 M⊙ have a reasonable size distribution, those at M* ˜ 1010 M⊙ have half-light radii larger than observed by a factor of 2. Furthermore, at M* ˜ 1010.5-1011 M⊙, a relevant fraction of Illustris galaxies have distinct `ring-like' features, such that the bright pixels have an unusually wide spatial extent.

  2. The Star Formation History of read and dead galaxies at z=[1.0--1.5

    NASA Astrophysics Data System (ADS)

    Domínguez Sánchez, H.; Pérez González, P.; Esquej, P.; Eliche Moral, C.; Alcalde Pampliega, B.; SHARDS Team

    2015-05-01

    We analyse the star formation histories (SFH) of M > 10^{10} M_⊙ read and dead galaxies at intermediate redshift (z=1.0-1.5). Current hierarchical models of galaxy formation predict many less massive high-z systems than observed. By combining SHARDS deep spectro-photometric optical data (25 contiguous OSIRIS/GTC medium band filters with R ˜ 50 at 4500-900 nm) with HST-WFC3 grism in the NIR (G141, 1.1-1.6 μm) and broad-band photometry (from FUV to FIR) we construct well-sampled optical SEDs with up to 150 photometric points and sufficient spectral resolution to obtain reliable stellar population parameters such as ages, star formation timescales, dust extinctions and metallicities. We define a complete and uncontaminated sample of red & dead galaxies by combining the color-color UVJ selection with a cut in sSFR (SFR/Mass). We check the robustness of the results depending on different stellar population models (Bruzual & Charlot 2003, Maraston 2005), SED fitting-codes (synthesizer, FAST) or star formation histories (exp{-t/τ}, t exp{-t/τ}). Finally, the dependence of the SFH with the galaxy stellar mass will be studied, to actually measure if more massive galaxies are formed earlier and more rapidly as downsizing suggests.

  3. The Turbulent ISM of Galaxies 10 Gyrs ago: Star Formation, Gas Accretion, and IMF

    NASA Astrophysics Data System (ADS)

    Le Tiran, Loïc; Lehnert, Matthew D.

    2011-12-01

    The utilization of integral-field spectroscopy has led us to a new understanding of the physical conditions in galaxies within the first few billion years after the Big Bang. In this proceedings, we analyze observations of ~50 massive galaxies as seen as they were 10 Gyrs ago using SINFONI from the ESO-VLT. We show that the large line width they exhibit can be explained by the intense mechanical energy output from the young stars. We also study the influence of cold gas accretion upon these galaxies: We show that an unrealistic amount of shocked gas would be needed in order to explain the Hα emission from these galaxies through shocks from gas accretion with velocity about the Hα line widths of these galaxies. We also use DEEP2 photometric measurements for a sub-sample of 10 of these galaxies to evaluate their ratio of Hα to FUV flux as a function of their Hα and R-band luminosity surface brightnesses. Our data suggests that perhaps their initial mass function (IMF) is flatter than Salpeter at the high mass end, as has been suggested recently for some local galaxies. It may be that high turbulence is responsible for skewing the IMF towards more massive stars as suggested by some theories of star-formation. Much work is however needed to accredit this hypothesis.

  4. Star formation in the outer Galaxy: the young cluster NGC 1893

    NASA Astrophysics Data System (ADS)

    Sanz-Forcada, J.; Prisinzano, L.; Micela, G.; Caramazza, M.; Sciortino, S.

    2013-05-01

    Stellar formation in the outer Galaxy is expected to be less conspicuous due to worse conditions. Several stellar forming regions in the outer Galaxy have shown similar characteristics to others in the inner Galaxy. The very recent episodes of stellar formation in NGC 1893 (age ˜1.5 Myr) demonstrates it. This cluster is an optimal laboratory to study stellar formation phenomena: it includes the presence of at least 6 O-type stars, two pennant nebulae, dark nebular clouds, and a high disc frequency among its members. We are conducting a series of papers on this cluster based on multiwavelength data, including Spitzer and Chandra observations. We study membership, morphology of the cluster, the spatial distribution of stellar ages and circumstellar discs, and the influence of the massive stars of the cluster in the evolution of circumstellar discs. NGC 1893 has shown similar characteristics to other stellar forming regions at closer distances to the Sun. The ionizing UV flux from massive stars plays an important role in the earlier dissipation of circumstellar discs in closer stars. There is a disc frequency of 52% in a sample complete in the mass range 0.35-2 M_{⊙}. This frequency is slightly lower than in clusters of similar age at closer distance. We attribute this to the faster disc evaporation by radiation of massive stars, the use of a different mass range in each case, and/or the method employed to select stars with and without discs.

  5. The Local Group Dwarf Irregular Galaxy NGC 6822: new insight on its star formation history .

    NASA Astrophysics Data System (ADS)

    Fusco, F.; Buonanno, R.; Bono, G.; Cassisi, S.; Monelli, M.; Pietrinferni, A.; Hidalgo, S. L.; Aparicio, A.

    We present a new photometric analysis of the Local Group Dwarf Irregular Galaxy NGC 6822 based on archival Hubble Space Telescope Advanced Camera for Surveys images. The data correspond to three fields covering the south-east region of the galaxy; for each field F475W and F814W HST bands are available. For each field an accurate color magnitude diagram (F814W, F475W-F814W) has been obtained. Preliminary hints on the galaxy star formation history are presented based on the comparison with isochrones from "A Bag of Stellar Tracks and Isochrones" (BaSTI) database.

  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. The Role of Star Formation in Radio-Loud Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Herbst, Hanna; Wilcots, E.; Hess, K.

    2010-01-01

    X-ray observations have shown that additional non-gravitational processes are required to explain the heating of the intergalactic medium in galaxy groups. The two most likely processes are galactic outflows from starbursts and feedback from AGN. Here, we look at star formation as a possible additional heating mechanism in X-ray luminous groups such as NGC 741, NGC 1052, NGC 524, and NGC 1587. We report on the results of optical imaging of these groups carried out using the WIYN 3.5m telescope with a specific emphasis on measuring the star formation rates of the resident galaxies in each group and estimating the impact of that star formation on the thermodynamics of the intragroup medium.

  8. Star-formation rates, molecular clouds, and the origin of the far-infrared luminosity of isolated and interacting galaxies

    NASA Technical Reports Server (NTRS)

    Solomon, P. M.; Sage, L. J.

    1988-01-01

    The CO luminosities of 93 galaxies have been determined and are compared with their IRAS FIR luminosities. Strongly interacting/merging galaxies have L(FIR)/L(CO) substantially higher than that of isolated galaxies or galactic giant molecular clouds (GMCs). Galaxies with tidal tails/bridges are the most extreme type with L(FIR)/L(CO) nine times as high as isolated galaxies. Interactions between close pairs of galaxies do not have much effect on the molecular content and global star-formation rate. If the high ratio L(FIR)/L(CO) in strongly interacting galaxies is due to star formation then the efficiency of this process is higher than that of any galactic GMC. Isolated galaxies, distant pairs, and close pairs have an FIR/CO luminosity ratio which is within a factor of two of galactic GMCs with H II regions. The CO luminosities of FIR-luminous galaxies are among the highest observed for any spiral galaxies.

  9. Modeling The GRB Host Galaxy Mass Distribution: Are GRBs Unbiased Tracers of Star Formation?

    SciTech Connect

    Kocevski, Daniel; West, Andrew A.; Modjaz, Maryam; /UC, Berkeley, Astron. Dept.

    2009-08-03

    We model the mass distribution of long gamma-ray burst (GRB) host galaxies given recent results suggesting that GRBs occur in low metallicity environments. By utilizing measurements of the redshift evolution of the mass-metallicity (M-Z) relationship for galaxies, along with a sharp host metallicity cut-off suggested by Modjaz and collaborators, we estimate an upper limit on the stellar mass of a galaxy that can efficiently produce a GRB as a function of redshift. By employing consistent abundance indicators, we find that sub-solar metallicity cut-offs effectively limit GRBs to low stellar mass spirals and dwarf galaxies at low redshift. At higher redshifts, as the average metallicity of galaxies in the Universe falls, the mass range of galaxies capable of hosting a GRB broadens, with an upper bound approaching the mass of even the largest spiral galaxies. We compare these predicted limits to the growing number of published GRB host masses and find that extremely low metallicity cut-offs of 0.1 to 0.5 Z{sub {circle_dot}} are effectively ruled out by a large number of intermediate mass galaxies at low redshift. A mass function that includes a smooth decrease in the efficiency of producing GRBs in galaxies of metallicity above 12+log(O/H){sub KK04} = 8.7 can, however, accommodate a majority of the measured host galaxy masses. We find that at z {approx} 1, the peak in the observed GRB host mass distribution is inconsistent with the expected peak in the mass of galaxies harboring most of the star formation. This suggests that GRBs are metallicity biased tracers of star formation at low and intermediate redshifts, although our model predicts that this bias should disappear at higher redshifts due to the evolving metallicity content of the universe.

  10. Star Formation Activity in a Young Galaxy Cluster at Z = 0.866

    NASA Astrophysics Data System (ADS)

    Laganá, T. F.; Ulmer, M. P.; Martins, L. P.; da Cunha, E.

    2016-07-01

    The galaxy cluster RX J1257+4738 at z = 0.866 is one of the highest redshift clusters with a richness of multi-wavelength data, and is thus a good target to study the star formation–density relation at early epochs. Using a sample of spectroscopically confirmed cluster members, we derive the star-formation rates (SFRs) of our galaxies using two methods: (1) the relation between SFR and total infrared luminosity extrapolated from the observed Spitzer Multiband Imaging Photometer for Spitzer 24 μm imaging data; and (2) spectral energy distribution fitting using the MAGPHYS code, including eight different bands. We show that, for this cluster, the SFR–density relation is very weak and seems to be dominated by the two central galaxies and the SFR presents a mild dependence on stellar mass, with more massive galaxies having higher SFR. However, the specific SFR (SSFR) decreases with stellar mass, meaning that more massive galaxies are forming fewer stars per unit of mass, and thus suggesting that the increase in star-forming members is driven by cluster assembly and infall. If the environment is somehow driving the star formation, one would expect a relation between the SSFR and the cluster centric distance, but that is not the case. A possible scenario to explain this lack of correlation is the contamination by infalling galaxies in the inner part of the cluster, which may be on their initial pass through the cluster center. As these galaxies have higher SFRs for their stellar mass, they enhance the mean SSFR in the center of the cluster.

  11. Extraordinary views of ordinary galaxies: Multiwavelength measures of star formation and attenuation

    NASA Astrophysics Data System (ADS)

    Johnson, Benjamin D.

    2008-01-01

    The meaningful comparison of models of galaxy evolution to observations is critically dependent on the accurate treatment of dust attenuation. To investigate dust absorption and emission in galaxies we have assembled a sample of ~1000 galaxies from the ultrviolet (UV) through the Infrared (IR) by the GALEX, SDSS, and Spitzer observatories. The ratio of IR to UV emission (IRX) is used to constrain the dust attenuation in galaxies. We consider this measure in optically red galaxies making several simplfying assumptions we estimate the fraction of IR emission due to the heating of by old stars to be as much as 99%. We use the 4000Å break as a robust and useful, though coarse, indicator of star formation history (SFH). Dust attenuation and star formation history (SFH) are the dominant factors affecting the color of galaxies. We explore the empirical relation between SFH, attenuation, and color (especially the UV color) for a wide range of galaxies, including early types. This relation is compared to models that separately predict the effects of dust and SFH on color. We perform fits to the relation between SFH, attenuation, and color, which links the production of starlight and its absorption by dust to the subsequent reemmision of the absorbed light in the IR. Galaxy models that self-consistently treat dust absorption and emission as well as stellar populations will need to reproduce these fitted relations in the low-redshift universe. We construct estimates of dust attenuation and star formation rate (SFR) from the UV and IR photmetry and compare them to optical indicators, including the SFR b of Brinchmann et al. (2004). We find that there is a significant trend of the ratio of SFR b to the IR+UV luminosity with D n (4000) that cannot be explained as due to the additional IR emission from dust heatred by old stars. We find that the dust attenuation inferred from the ratio of optical emission lines is ~ 2-3 times higher than that inferred from IRX for a wide range

  12. A tale of two feedbacks: Star formation in the host galaxies of radio AGNs

    SciTech Connect

    Karouzos, Marios; Im, Myungshin; Jeon, Yiseul; Kim, Ji Hoon; Trichas, Markos; Goto, Tomo; Malkan, Matt; Ruiz, Angel; Lee, Hyung Mok; Kim, Seong Jin; Oi, Nagisa; Matsuhara, Hideo; Takagi, Toshinobu; Murata, K.; Wada, Takehiko; Wada, Kensuke; Shim, Hyunjin; Hanami, Hitoshi; Serjeant, Stephen; White, Glenn J.; and others

    2014-04-01

    Several lines of argument support the existence of a link between activity at the nuclei of galaxies, in the form of an accreting supermassive black hole, and star formation activity in these galaxies. Radio jets have long been argued to be an ideal mechanism that allows active galactic nuclei (AGNs) to interact with their host galaxies and affect star formation. We use a sample of radio sources in the North Ecliptic Pole (NEP) field to study the nature of this putative link, by means of spectral energy distribution (SED) fitting. We employ the excellent spectral coverage of the AKARI infrared space telescope and the rich ancillary data available in the NEP to build SEDs extending from UV to far-IR wavelengths. We find a significant AGN component in our sample of relatively faint radio sources (star formation in the host galaxy, independent of the radio luminosity. In contrast, for narrow redshift and AGN luminosity ranges, we find that increasing radio luminosity leads to a decrease in the specific star formation rate. The most radio-loud AGNs are found to lie on the main sequence of star formation for their respective redshifts. For the first time, we potentially see such a two-sided feedback process in the same sample. We discuss the possible suppression of star formation, but not total quenching, in systems with strong radio jets, that supports the maintenance nature of feedback from radio AGN jets.

  13. 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.

  14. The Mass Assembly and Star Formation Characteristics of Field Galaxies of Known Morphology.

    PubMed

    Brinchmann; Ellis

    2000-06-20

    We discuss a new method for inferring the stellar mass of a distant galaxy of known redshift based on the combination of a near-IR luminosity and multiband optical photometry. The typical uncertainty for field galaxies with I<22 in the redshift range 0galaxies with redshifts and Hubble Space Telescope morphologies enabling us to construct the stellar mass density associated with various morphologies as a function of redshift. We find a marked decline with time in the stellar mass associated with peculiar galaxies accompanied by a modest rise in that observed for elliptical galaxies. The result suggests that peculiar galaxies decline in abundance because they transform and merge into regular systems. The star formation rate per unit stellar mass indicates that massive systems completed the bulk of their star formation before redshift 1, whereas dwarf galaxies continue to undergo major episodes of activity until the present epoch. PMID:10859122

  15. The Average Star Formation Histories of Galaxies in Dark Matter Halos from z = 0-8

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

    We present a robust method to constrain average galaxy star formation rates (SFRs), star formation histories (SFHs), and the intracluster light (ICL) as a function of halo mass. Our results are consistent with observed galaxy stellar mass functions, specific star formation rates (SSFRs), and cosmic star formation rates (CSFRs) from z = 0 to z = 8. We consider the effects of a wide range of uncertainties on our results, including those affecting stellar masses, SFRs, and the halo mass function at the heart of our analysis. As they are relevant to our method, we also present new calibrations of the dark matter halo mass function, halo mass accretion histories, and halo-subhalo merger rates out to z = 8. We also provide new compilations of CSFRs and SSFRs; more recent measurements are now consistent with the buildup of the cosmic stellar mass density at all redshifts. Implications of our work include: halos near 1012 M ⊙ are the most efficient at forming stars at all redshifts, the baryon conversion efficiency of massive halos drops markedly after z ~ 2.5 (consistent with theories of cold-mode accretion), the ICL for massive galaxies is expected to be significant out to at least z ~ 1-1.5, and dwarf galaxies at low redshifts have higher stellar mass to halo mass ratios than previous expectations and form later than in most theoretical models. Finally, we provide new fitting formulae for SFHs that are more accurate than the standard declining tau model. Our approach places a wide variety of observations relating to the SFH of galaxies into a self-consistent framework based on the modern understanding of structure formation in ΛCDM. Constraints on the stellar mass-halo mass relationship and SFRs are available for download online.

  16. THE AVERAGE STAR FORMATION HISTORIES OF GALAXIES IN DARK MATTER HALOS FROM z = 0-8

    SciTech Connect

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

    2013-06-10

    We present a robust method to constrain average galaxy star formation rates (SFRs), star formation histories (SFHs), and the intracluster light (ICL) as a function of halo mass. Our results are consistent with observed galaxy stellar mass functions, specific star formation rates (SSFRs), and cosmic star formation rates (CSFRs) from z = 0 to z = 8. We consider the effects of a wide range of uncertainties on our results, including those affecting stellar masses, SFRs, and the halo mass function at the heart of our analysis. As they are relevant to our method, we also present new calibrations of the dark matter halo mass function, halo mass accretion histories, and halo-subhalo merger rates out to z = 8. We also provide new compilations of CSFRs and SSFRs; more recent measurements are now consistent with the buildup of the cosmic stellar mass density at all redshifts. Implications of our work include: halos near 10{sup 12} M{sub Sun} are the most efficient at forming stars at all redshifts, the baryon conversion efficiency of massive halos drops markedly after z {approx} 2.5 (consistent with theories of cold-mode accretion), the ICL for massive galaxies is expected to be significant out to at least z {approx} 1-1.5, and dwarf galaxies at low redshifts have higher stellar mass to halo mass ratios than previous expectations and form later than in most theoretical models. Finally, we provide new fitting formulae for SFHs that are more accurate than the standard declining tau model. Our approach places a wide variety of observations relating to the SFH of galaxies into a self-consistent framework based on the modern understanding of structure formation in {Lambda}CDM. Constraints on the stellar mass-halo mass relationship and SFRs are available for download online.

  17. 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.

  18. Covariance between Star Formation Rates and Dust Mass of KINGFISH Galaxies

    NASA Astrophysics Data System (ADS)

    Rojas Bolivar, Randall; Calzetti, Daniela; Dale, Daniel A.; Cook, David

    2016-01-01

    We present the initial results for a study of the potential covariance between galaxy physical parameters (e.g., the star formation rate and dust mass) derived from the infrared spectral energy distributions (SEDs) of galaxies. With the emergence of powerful facilities and instruments in the millimeter and sub-millimeter wavelengths, which complement data from infrared space telescopes like Herschel, scientists have been able to observe the infrared SEDs of faraway galaxies (with redshifts between 2 and 5). These SEDs are being used to derive both star formation rates (SFR) and dust masses, the latter related to gas masses. The relationship between SFRs and gas masses determine the fundamental scaling laws of star formation (the Schmidt Kennicutt Law). Thus, it is fundamental to ascertain whether derivation of these quantities from IR SEDs may be affected by covariance. We will use the Spitzer and Herschel data from the nearby survey: Key Insights on Nearby Galaxies: A Far-IR Survey with Herschel (KINGFISH), which includes 61 nearby galaxies observed between 3.6 and 500 micron.

  19. Suppressing star formation in quiescent galaxies with supermassive black hole winds.

    PubMed

    Cheung, Edmond; Bundy, Kevin; Cappellari, Michele; Peirani, Sébastien; Rujopakarn, Wiphu; Westfall, Kyle; Yan, Renbin; Bershady, Matthew; Greene, Jenny E; Heckman, Timothy M; Drory, Niv; Law, David R; Masters, Karen L; Thomas, Daniel; Wake, David A; Weijmans, Anne-Marie; Rubin, Kate; Belfiore, Francesco; Vulcani, Benedetta; Chen, Yan-mei; Zhang, Kai; Gelfand, Joseph D; Bizyaev, Dmitry; Roman-Lopes, A; Schneider, Donald P

    2016-05-26

    Quiescent galaxies with little or no ongoing star formation dominate the population of galaxies with masses above 2 × 10(10) times that of the Sun; the number of quiescent galaxies has increased by a factor of about 25 over the past ten billion years (refs 1-4). Once star formation has been shut down, perhaps during the quasar phase of rapid accretion onto a supermassive black hole, an unknown mechanism must remove or heat the gas that is subsequently accreted from either stellar mass loss or mergers and that would otherwise cool to form stars. Energy output from a black hole accreting at a low rate has been proposed, but observational evidence for this in the form of expanding hot gas shells is indirect and limited to radio galaxies at the centres of clusters, which are too rare to explain the vast majority of the quiescent population. Here we report bisymmetric emission features co-aligned with strong ionized-gas velocity gradients from which we infer the presence of centrally driven winds in typical quiescent galaxies that host low-luminosity active nuclei. These galaxies are surprisingly common, accounting for as much as ten per cent of the quiescent population with masses around 2 × 10(10) times that of the Sun. In a prototypical example, we calculate that the energy input from the galaxy's low-level active supermassive black hole is capable of driving the observed wind, which contains sufficient mechanical energy to heat ambient, cooler gas (also detected) and thereby suppress star formation. PMID:27225122

  20. KBSS-MOSFIRE: Abundances, star-formation, and physical conditions in star-forming galaxies at z~2-3

    NASA Astrophysics Data System (ADS)

    Strom, Allison; Steidel, Charles; Rudie, Gwen; Trainor, Ryan

    2015-08-01

    I will present new results from the MOSFIRE component of the Keck Baryonic Structure Survey (KBSS), the largest-ever rest-optical spectroscopic survey of star-forming galaxies at z~2-3, conducted using the recently-commissioned multi-object near-infrared spectrograph on Keck I. Currently, the KBSS comprises ~800 galaxies with rest-optical spectroscopy from MOSFIRE, with stellar masses ranging from 109 to 1011.5 M⊙ and star-formation rates down to a few M⊙/yr. The first results from KBSS-MOSFIRE have already confirmed that HII regions in high-redshift galaxies are physically distinct from those at z~0 our data suggest that both harder ionizing radiation and larger ionization parameters are needed to produce the observed nebular line emission in z~2 galaxies. In addition, our observations show that gas-phase abundances and abundance ratios in these galaxies likely differ greatly from local samples. Understanding the origin of these differences has important implications for galaxy evolution and requires observations of the entire suite of strong rest-optical diagnostic emission lines for a statistical sample of individual galaxies. A substantial fraction of the galaxies in our survey have robust measurements of the strongest rest-optical diagnostic lines (including H-alpha, H-beta, [OIII], [NII], and [OII]), which together facilitate a detailed analysis of the physical conditions in high-z galaxies. Nearly 2/3 of the KBSS-MOSFIRE sample also have complementary rest-UV spectra taken with Keck-LRIS that help constrain the properties of the massive stellar populations driving the rest-optical nebular emission. I will also report on measurements from deep co-averaged spectral stacks, which reveal weak emission and absorption features undetected in individual objects and offer another powerful tool for studying populations of high-redshift star-forming galaxies.

  1. The ultraviolet and infrared star formation rates of compact group galaxies: an expanded sample

    NASA Astrophysics Data System (ADS)

    Lenkić, Laura; Tzanavaris, Panayiotis; Gallagher, Sarah C.; Desjardins, Tyler D.; Walker, Lisa May; Johnson, Kelsey E.; Fedotov, Konstantin; Charlton, Jane; Hornschemeier, Ann E.; Durrell, Pat R.; Gronwall, Caryl

    2016-07-01

    Compact groups of galaxies provide insight into the role of low-mass, dense environments in galaxy evolution because the low velocity dispersions and close proximity of galaxy members result in frequent interactions that take place over extended time-scales. We expand the census of star formation in compact group galaxies by Tzanavaris et al. (2010) and collaborators with Swift UVOT, Spitzer IRAC and MIPS 24 μm photometry of a sample of 183 galaxies in 46 compact groups. After correcting luminosities for the contribution from old stellar populations, we estimate the dust-unobscured star formation rate (SFRUV) using the UVOT uvw2 photometry. Similarly, we use the MIPS 24 μm photometry to estimate the component of the SFR that is obscured by dust (SFRIR). We find that galaxies which are MIR-active (MIR-`red'), also have bluer UV colours, higher specific SFRs, and tend to lie in H I-rich groups, while galaxies that are MIR-inactive (MIR-`blue') have redder UV colours, lower specific SFRs, and tend to lie in H I-poor groups. We find the SFRs to be continuously distributed with a peak at about 1 M⊙ yr-1, indicating this might be the most common value in compact groups. In contrast, the specific SFR distribution is bimodal, and there is a clear distinction between star-forming and quiescent galaxies. Overall, our results suggest that the specific SFR is the best tracer of gas depletion and galaxy evolution in compact groups.

  2. Nature or nurture? Clues from the distribution of specific star formation rates in SDSS galaxies

    NASA Astrophysics Data System (ADS)

    Casado, J.; Ascasibar, Y.; Gavilán, M.; Terlevich, R.; Terlevich, E.; Hoyos, C.; Díaz, A. I.

    2015-07-01

    This work investigates the main mechanism(s) that regulate the specific star formation rate (SSFR) in nearby galaxies, cross-correlating two proxies of this quantity - the equivalent width of the Hα line and the (u - r) colour - with other physical properties (mass, metallicity, environment, morphology, and the presence of close companions) in a sample of ˜82 500 galaxies extracted from the Sloan Digital Sky Survey. The existence of a relatively tight `ageing sequence' in the colour-equivalent width plane favours a scenario where the secular conversion of gas into stars (i.e. nature) is the main physical driver of the instantaneous SSFR and the gradual transition from a `chemically primitive' (metal-poor and intensely star-forming) state to a `chemically evolved' (metal-rich and passively evolving) system. Nevertheless, environmental factors (i.e. nurture) are also important. In the field, galaxies may be temporarily affected by discrete `quenching' and `rejuvenation' episodes, but such events show little statistical significance in a probabilistic sense, and we find no evidence that galaxy interactions are, on average, a dominant driver of star formation. Although visually classified mergers tend to display systematically higher EW(Hα) and bluer (u - r) colours for a given luminosity, most galaxies with high SSFR have uncertain morphologies, which could be due to either internal or external processes. Field galaxies of early and late morphological types are consistent with the gradual `ageing' scenario, with no obvious signatures of a sudden decrease in their SSFR. In contrast, star formation is significantly reduced and sometimes completely quenched on a short time-scale in dense environments, where many objects are found on a `quenched sequence' in the colour-equivalent width plane.

  3. ULTRA-FAINT DWARF GALAXIES AS A TEST OF EARLY ENRICHMENT AND METALLICITY-DEPENDENT STAR FORMATION

    SciTech Connect

    Tassis, Konstantinos; Gnedin, Nickolay Y.; Kravtsov, Andrey V.

    2012-01-20

    The close relation of star formation with molecular gas indicated by observations and assumed in recent models implies that the efficiency with which galaxies convert their gas into stars depends on gas metallicity. This is because abundance of molecular hydrogen is sensitive to abundance of dust, which catalyzes formation of H{sub 2} and helps to shield it from dissociating radiation. In this study, we point out that in the absence of significant pre-enrichment by Population III stars forming out of zero metallicity gas, such H{sub 2}-based star formation is expected to leave an imprint in the form of bi-modality in the metallicity distribution among dwarf galaxies and in the metallicity distribution of stars within individual galaxies. The bi-modality arises because when gas metallicity (and dust abundance) is low, formation of molecular gas is inefficient, the gas consumption timescale is long, and star formation and metal enrichment proceed slowly. When metallicity reaches a critical threshold value star formation and enrichment accelerate, which leads to rapid increase in both stellar mass and metallicity of galaxies. We demonstrate this process both using a simple analytical model and full cosmological simulations. In contrast, the observed metallicity distributions of dwarf galaxies or stars within them are not bi-modal. We argue that this discrepancy points to substantial early stochastic pre-enrichment by Population III stars to levels Z {approx} 10{sup -2} Z{sub Sun} in dense, star-forming regions of early galaxies.

  4. Galaxy Zoo: the dependence of the star formation-stellar mass relation on spiral disc morphology

    NASA Astrophysics Data System (ADS)

    Willett, Kyle W.; Schawinski, Kevin; Simmons, Brooke D.; Masters, Karen L.; Skibba, Ramin A.; Kaviraj, Sugata; Melvin, Thomas; Wong, O. Ivy; Nichol, Robert C.; Cheung, Edmond; Lintott, Chris J.; Fortson, Lucy

    2015-05-01

    We measure the stellar mass-star formation rate (SFR) relation in star-forming disc galaxies at z ≤ 0.085, using Galaxy Zoo morphologies to examine different populations of spirals as classified by their kiloparsec-scale structure. We examine the number of spiral arms, their relative pitch angle, and the presence of a galactic bar in the disc, and show that both the slope and dispersion of the M⋆-SFR relation is constant when varying all the above parameters. We also show that mergers (both major and minor), which represent the strongest conditions for increases in star formation at a constant mass, only boost the SFR above the main relation by ˜0.3 dex; this is significantly smaller than the increase seen in merging systems at z > 1. Of the galaxies lying significantly above the M⋆-SFR relation in the local Universe, more than 50 per cent are mergers. We interpret this as evidence that the spiral arms, which are imperfect reflections of the galaxy's current gravitational potential, are either fully independent of the various quenching mechanisms or are completely overwhelmed by the combination of outflows and feedback. The arrangement of the star formation can be changed, but the system as a whole regulates itself even in the presence of strong dynamical forcing.

  5. Physical origin of the large-scale conformity in the specific star formation rates of galaxies

    NASA Astrophysics Data System (ADS)

    Kauffmann, Guinevere

    2015-12-01

    Two explanations have been put forward to explain the observed conformity between the colours and specific star formation rates (SFR/M*) of galaxies on large scales: (1) the formation times of their surrounding dark matter haloes are correlated (commonly referred to as `assembly bias'), (2) gas is heated over large scales at early times, leading to coherent modulation of cooling and star formation between well-separated galaxies (commonly referred to as `pre-heating'). To distinguish between the pre-heating and assembly bias scenarios, we search for relics of energetic feedback events in the neighbourhood of central galaxies with different specific SFRs. We find a significant excess of very high mass (log M* > 11.3) galaxies out to a distance of 2.5 Mpc around low SFR/M* central galaxies compared to control samples of higher SFR/M* central galaxies with the same stellar mass and redshift. We also find that very massive galaxies in the neighbourhood of low-SFR/M* galaxies have much higher probability of hosting radio-loud active galactic nuclei (AGN). The radio-loud AGN fraction in neighbours with log M* > 11.3 is four times higher around passive, non star-forming centrals at projected distances of 1 Mpc and two times higher at projected distances of 4 Mpc. Finally, we carry out an investigation of conformity effects in the recently publicly released Illustris cosmological hydrodynamical simulation, which includes energetic input both from quasars and from radio mode accretion on to black holes. We do not find conformity effects of comparable amplitude on large scales in the simulations and we propose that gas needs to be pushed out of dark matter haloes more efficiently at high redshifts.

  6. STAR FORMATION IN THE OUTER DISKS OF SPIRAL GALAXIES: ULTRAVIOLET AND H{alpha} PHOTOMETRY

    SciTech Connect

    Barnes, Kate L.; Van Zee, Liese; Skillman, Evan D. E-mail: vanzee@astro.indiana.edu

    2011-12-20

    We present an analysis of ultradeep UV and H{alpha} imaging of five nearby spiral galaxies to study the recent star formation in the outer disk. Using azimuthally averaged ellipse photometry as well as aperture photometry of individual young stellar complexes, we measure how star formation rates (SFRs) and UV and H{alpha} colors vary with radius. We detect azimuthally averaged UV flux to {approx}1.2-1.4 R{sub 25} in most galaxies; at the edge of the detected UV disk, the surface brightnesses are 28-29 mag arcsec{sup -2}, corresponding to SFR surface densities of {approx}3 Multiplication-Sign 10{sup -4} M{sub Sun} yr{sup -1} kpc{sup -2}. Additionally, we detect between 120 and 410 young stellar complexes per galaxy, with a significant number of detections out to {approx}1.5 R{sub 25}. We measure radial FUV-NUV profiles, and find that the dispersion in the UV colors of individual young stellar complexes increases with radius. We investigate how radial variations in the frequency of star formation episodes can create color gradients and increasing dispersion in the UV colors of star-forming regions, like those observed in our study. Specifically, we use recently published, high spatial and temporal resolution measurements of {Sigma}{sub SFR} throughout the disk of M33 to estimate the frequency of star formation episodes throughout the disk of a typical spiral galaxy. We use stellar synthesis models of these star formation histories (SFHs) to measure the variations in UV colors and find that we can replicate large dispersions in UV colors based on episodic SFHs.

  7. THE NATURE OF STARBURSTS. I. THE STAR FORMATION HISTORIES OF EIGHTEEN NEARBY STARBURST DWARF GALAXIES

    SciTech Connect

    McQuinn, Kristen B. W.; Skillman, Evan D.; Stark, David; Weisz, Daniel; Cannon, John M.; Dalcanton, Julianne; Williams, Benjamin; Dolphin, Andrew; Hidalgo-RodrIguez, Sebastian

    2010-09-20

    We use archival Hubble Space Telescope observations of resolved stellar populations to derive the star formation histories (SFHs) of 18 nearby starburst dwarf galaxies. In this first paper, we present the observations, color-magnitude diagrams (CMDs), and the SFHs of the 18 starburst galaxies, based on a homogeneous approach to the data reduction, differential extinction, and treatment of photometric completeness. We adopt a star formation rate (SFR) threshold normalized to the average SFR of the individual system as a metric for classifying starbursts in SFHs derived from resolved stellar populations. This choice facilitates finding not only the currently bursting galaxies but also 'fossil' bursts increasing the sample size of starburst galaxies in the nearby (D < 8 Mpc) universe. Thirteen of the eighteen galaxies are experiencing ongoing bursts and five galaxies show fossil bursts. From our reconstructed SFHs, it is evident that the elevated SFRs of a burst are sustained for hundreds of Myr with variations on small timescales. A long >100 Myr temporal baseline is thus fundamental to any starburst definition or identification method. The longer lived bursts rule out rapid 'self-quenching' of starbursts on global scales. The bursting galaxies' gas consumption timescales are shorter than the Hubble time for all but one galaxy confirming the short-lived nature of starbursts based on fuel limitations. Additionally, we find that the strength of the H{alpha} emission usually correlates with the CMD-based SFR during the last 4-10 Myr. However, in four cases, the H{alpha} emission is significantly less than what is expected for models of starbursts; the discrepancy is due to the SFR changing on timescales of a few Myr. The inherently short timescale of the H{alpha} emission limits identifying galaxies as starbursts based on the current characteristics which may or may not be representative of the recent SFH of a galaxy.

  8. The Spitzer Interacting Galaxies Survey: A Mid-infrared Atlas of Star Formation

    NASA Astrophysics Data System (ADS)

    Brassington, N. J.; Zezas, A.; Ashby, M. L. N.; Lanz, L.; Smith, Howard. A.; Willner, S. P.; Klein, C.

    2015-05-01

    The Spitzer Interacting Galaxies Survey is a sample of 103 nearby galaxies in 48 systems, selected using association likelihoods and therefore free from disturbed morphology biases. All galaxies have been observed with Infrared Array Camera and MIPS 24 μm bands from the Spitzer Space Telescope. This catalog presents the global flux densities and colors of all systems and correlations between the interacting systems and their specific star formation rate (sSFR). This sample contains a wide variety of galaxy interactions with systems ranging in mass, mass ratios, and gas-content as well as interaction strength. This study seeks to identify the process of triggering star formation in galaxy interactions, therefore, we focus on the non-active galactic nucleus spiral galaxies only. From this subset of 70 spiral galaxies we have determined that this sample has enhanced sSFR compared to a sample of non-interacting field galaxies. Through optical data we have classified each system by “interaction strength” the strongly interacting (Stage 4) galaxies have higher sSFR values than the weakly (Stage 2) and moderately (Stage 3) interacting systems. However, the Stage 2 and 3 systems have statistically identical sSFR properties, despite the lack of optical interaction signatures exhibited by the Stage 2 galaxies. We suggest that the similarity of sSFR in these stages could be a consequence of some of these Stage 2 systems actually being post-perigalactic and having had sufficient time for their tidal features to fade to undetectable levels. This interpretation is consistent with the correlation of sSFR with separation, which we have determined to have little variation up to 100 kpc.

  9. 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.

  10. 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.

  11. Ultrafaint dwarfs—star formation and chemical evolution in the smallest galaxies

    SciTech Connect

    Webster, David; Bland-Hawthorn, Joss; Sutherland, Ralph

    2014-11-20

    In earlier work, we showed that a dark matter halo with a virial mass of 10{sup 7} M {sub ☉} can retain a major part of its baryons in the face of the pre-ionization phase and supernova (SN) explosion from a 25 M {sub ☉} star. Here, we expand on the results of that work, investigating the star formation and chemical evolution of the system beyond the first SN. In a galaxy with a mass M {sub vir} = 10{sup 7} M {sub ☉}, sufficient gas is retained by the potential for a second period of star formation to occur. The impact of a central explosion is found to be much stronger than that of an off-center explosion both in blowing out the gas and in enriching it, as in the off-center case most of the SN energy and metals escape into the intergalactic medium. We model the star formation and metallicity, given the assumption that stars form for 100, 200, 400, and 600 Myr, and discuss the results in the context of recent observations of very low-mass galaxies. We show that we can account for most features of the observed relationship between [α/Fe] and [Fe/H] in ultra-faint dwarf galaxies with the assumption that the systems formed at a low mass, rather than being remnants of much larger systems.

  12. A connection between star formation activity and cosmic rays in the starburst galaxy M82

    NASA Astrophysics Data System (ADS)

    VERITAS Collaboration; Acciari, V. A.; Aliu, E.; Arlen, T.; Aune, T.; Bautista, M.; Beilicke, M.; Benbow, W.; Boltuch, D.; Bradbury, S. M.; Buckley, J. H.; Bugaev, V.; Byrum, K.; Cannon, A.; Celik, O.; Cesarini, A.; Chow, Y. C.; Ciupik, L.; Cogan, P.; Colin, P.; Cui, W.; Dickherber, R.; Duke, C.; Fegan, S. J.; Finley, J. P.; Finnegan, G.; Fortin, P.; Fortson, L.; Furniss, A.; Galante, N.; Gall, D.; Gibbs, K.; Gillanders, G. H.; Godambe, S.; Grube, J.; Guenette, R.; Gyuk, G.; Hanna, D.; Holder, J.; Horan, D.; Hui, C. M.; Humensky, T. B.; Imran, A.; Kaaret, P.; Karlsson, N.; Kertzman, M.; Kieda, D.; Kildea, J.; Konopelko, A.; Krawczynski, H.; Krennrich, F.; Lang, M. J.; Lebohec, S.; Maier, G.; McArthur, S.; McCann, A.; McCutcheon, M.; Millis, J.; Moriarty, P.; Mukherjee, R.; Nagai, T.; Ong, R. A.; Otte, A. N.; Pandel, D.; Perkins, J. S.; Pizlo, F.; Pohl, M.; Quinn, J.; Ragan, K.; Reyes, L. C.; Reynolds, P. T.; Roache, E.; Rose, H. J.; Schroedter, M.; Sembroski, G. H.; Smith, A. W.; Steele, D.; Swordy, S. P.; Theiling, M.; Thibadeau, S.; Varlotta, A.; Vassiliev, V. V.; Vincent, S.; Wagner, R. G.; Wakely, S. P.; Ward, J. E.; Weekes, T. C.; Weinstein, A.; Weisgarber, T.; Williams, D. A.; Wissel, S.; Wood, M.; Zitzer, B.

    2009-12-01

    Although Galactic cosmic rays (protons and nuclei) are widely believed to be mainly accelerated by the winds and supernovae of massive stars, definitive evidence of this origin remains elusive nearly a century after their discovery. The active regions of starburst galaxies have exceptionally high rates of star formation, and their large size-more than 50 times the diameter of similar Galactic regions-uniquely enables reliable calorimetric measurements of their potentially high cosmic-ray density. The cosmic rays produced in the formation, life and death of massive stars in these regions are expected to produce diffuse γ-ray emission through interactions with interstellar gas and radiation. M82, the prototype small starburst galaxy, is predicted to be the brightest starburst galaxy in terms of γ-ray emission. Here we report the detection of >700-GeV γ-rays from M82. From these data we determine a cosmic-ray density of 250eVcm-3 in the starburst core, which is about 500 times the average Galactic density. This links cosmic-ray acceleration to star formation activity, and suggests that supernovae and massive-star winds are the dominant accelerators.

  13. Cooling, AGN Feedback and Star Formation in Cool-Core Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Li, Yuan; Bryan, Greg; Ruszkowski, Mateusz

    2015-01-01

    The feedback from active galactic nuclei (AGNs) is widely considered to be the major heating source in cool-core galaxy clusters to prevent a classical cooling flow. Numerical simulations with AGN feedback have successfully suppressed radiative cooling, but generally fail to reproduce the right amount of cold gas and the expected cyclical AGN activities. We perform adaptive mesh simulations including both momentum-driven AGN feedback and star formation to study the interplay between cooling, AGN heating and star formation over ~ 6.5 Gyr time in an isolated cool-core cluster. Cold clumps first cool out of the ICM due to the non-liner perturbation driven by the AGN jets. These cold clumps feed both star formation and the supermassive black hole (SMBH), triggering an AGN outburst which increases the entropy of the ICM and reduces its cooling rate. Within 1-2 Gyr, star formation completely consumes the cold gas, which leads to a brief shutoff of the AGN. The ICM quickly cools and develops multiphase gas again, followed by another cycle of star formation/AGN outburst. Within 6.5 Gyr, we observe three such cycles. The average star formation rate is ~40 solar mass/yr. The black hole accretion rate shows a large scatter, but the average correlates well with the star formation rate and is roughly one order of magnitude lower.

  14. Galaxy Zoo: evidence for diverse star formation histories through the green valley

    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.

    2015-06-01

    Does galaxy evolution proceed through the green valley via multiple pathways or as a single population? Motivated by recent results highlighting radically different evolutionary pathways between early- and late-type galaxies, we present results from a simple Bayesian approach to this problem wherein we model the star formation history (SFH) of a galaxy with two parameters, [t, τ] and compare the predicted and observed optical and near-ultraviolet colours. We use a novel method to investigate the morphological differences between the most probable SFHs for both disc-like and smooth-like populations of galaxies, by using a sample of 126 316 galaxies (0.01 < z < 0.25) with probabilistic estimates of morphology from Galaxy Zoo. We find a clear difference between the quenching time-scales preferred by smooth- and disc-like galaxies, with three possible routes through the green valley dominated by smooth- (rapid time-scales, attributed to major mergers), intermediate- (intermediate time-scales, attributed to minor mergers and galaxy interactions) and disc-like (slow time-scales, attributed to secular evolution) galaxies. We hypothesize that morphological changes occur in systems which have undergone quenching with an exponential time-scale τ < 1.5 Gyr, in order for the evolution of galaxies in the green valley to match the ratio of smooth to disc galaxies observed in the red sequence. These rapid time-scales are instrumental in the formation of the red sequence at earlier times; however, we find that galaxies currently passing through the green valley typically do so at intermediate time-scales.†

  15. Star Formation in Damped Lyman-alpha systems and the Outskirts of Lyman Break Galaxies

    NASA Astrophysics Data System (ADS)

    Rafelski, Marc Alexander

    In this thesis we begin to unify two pictures of the high redshift universe: absorption line systems such as damped Lyman alpha systems (DLAs) that provide the fuel for star formation, and compact star forming regions such as Lyman break galaxies (LBGs) which form the majority of stars. Wolfe & Chen (2006) find that the in situ star formation in DLAs is less than 5% of what is expected from the Kennicutt-Schmidt (KS) relation, but they do not constrain DLAs associated with bright star-forming regions such as LBGs. In this work we search for spatially-extended star formation in the outskirts of LBGs at z ∼3. To this end, we create a sample of z ∼3 LBGs in the Hubble Ultra Deep Field (UDF) by using photometric redshifts enabled by the introduction of an extremely deep u -band image. By stacking these galaxies, we find spatially extended low surface brightness emission around LBGs in the V -band image of the UDF, corresponding to the z ∼3 rest-frame far-ultraviolet light, which is a sensitive measure of star formation rates (SFRs). We connect this emission around LBGs to the expected emission from DLAs, and the results suggest that the SFR efficiency in such gas at z ∼3 is between factors of 10 and 50 lower than predictions based on the KS relation. This decreased efficiency is likely due to the lower metallicity of DLA gas. In addition, we measure the metallicity evolution of DLAs out to z ∼5, and find a continued decrease of metallicity with increasing redshift and a metallicity "floor"' around one thousandth of the solar value. We also compare the metallicity distribution and chemistry of DLAs and halo stars, and find that they are not inconsistent. Lastly, we study the photometric variability of stars in the Galactic center in order to further our understanding of the massive young stars forming in the presence of a super massive black hole. All together, these results improve our understanding of star formation and provide constraints for models and

  16. A parsec-resolution simulation of the Antennae galaxies: formation of star clusters during the merger

    NASA Astrophysics Data System (ADS)

    Renaud, Florent; Bournaud, Frédéric; Duc, Pierre-Alain

    2015-01-01

    We present a hydrodynamical simulation of an Antennae-like galaxy merger at parsec resolution, including a multicomponent model for stellar feedback and reaching numerical convergence in the global star formation rate for the first time. We analyse the properties of the dense stellar objects formed during the different stages of the interaction. Each galactic encounter triggers a starburst activity, but the varying physical conditions change the triggering mechanism of each starburst. During the first two pericentre passages, the starburst is spatially extended and forms many star clusters. However, the starburst associated with the third, final passage is more centrally concentrated: stars form almost exclusively in the galactic nucleus and no new star cluster is formed. The maximum mass of stars clusters in this merger is more than 30 times higher than those in a simulation of an isolated Milky Way-like galaxy. Antennae-like mergers are therefore a formation channel of young massive clusters possibly leading to globular clusters. Monitoring the evolution of a few clusters reveals the diversity of formation scenarios including the gathering and merger of gas clumps, the monolithic formation and the hierarchical formation in sub-structures inside a single cloud. Two stellar objects formed in the simulation yield the same properties as ultracompact dwarf galaxies. They share the same formation scenario than the most massive clusters, but have a larger radius either since birth, or get it after a violent interaction with the galactic centre. The diversity of environments across space and time in a galaxy merger can account for the diversity of the stellar objects formed, both in terms of mass and size.

  17. The star formation and chemical evolution history of the sculptor dwarf spheroidal galaxyâ

    NASA Astrophysics Data System (ADS)

    de Boer, T. J. L.; Tolstoy, E.; Hill, V.; Saha, A.; Olsen, K.; Starkenburg, E.; Lemasle, B.; Irwin, M. J.; Battaglia, G.

    2012-03-01

    We have combined deep photometry in the B, V and I bands from CTIO/MOSAIC of the Sculptor dwarf spheroidal galaxy, going down to the oldest main sequence turn-offs, with spectroscopic metallicity distributions of red giant branch stars. This allows us to obtain the most detailed and complete star formation history to date, as well as an accurate timescale for chemical enrichment. The star formation history shows that Sculptor is dominated by old (>10 Gyr), metal-poor stars, but that younger, more metal-rich populations are also present. Using star formation histories determined at different radii from the centre we show that Sculptor formed stars with an increasing central concentration with time. The old, metal-poor populations are present at all radii, while more metal-rich, younger stars are more centrally concentrated. We find that within an elliptical radius of 1 degree, or 1.5 kpc from the centre, a total mass in stars of 7.8 × 10^6 Mstar formation history to determine age estimates for individual red giant branch stars with high resolution spectroscopic abundances. Thus, for the first time, we can directly determine detailed timescales for the evolution of individual chemical elements. We find that the trends in alpha-elements match what is expected from an extended, relatively uninterrupted period of star formation continuing for 6-7 Gyr. The knee in the alpha-element distribution occurs at an age of 10.9 ± 1Gyr, suggesting that SNe Ia enrichment began ≈2 ± 1 Gyr after the start of star formation in Sculptor.

  18. Variations in the Star Formation Efficiency of the Dense Molecular Gas across the Disks of Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Usero, Antonio; Leroy, Adam K.; Walter, Fabian; Schruba, Andreas; García-Burillo, Santiago; Sandstrom, Karin; Bigiel, Frank; Brinks, Elias; Kramer, Carsten; Rosolowsky, Erik; Schuster, Karl-Friedrich; de Blok, W. J. G.

    2015-10-01

    We present a new survey of HCN(1-0) emission, a tracer of dense molecular gas, focused on the little-explored regime of normal star-forming galaxy disks. Combining HCN, CO, and infrared (IR) emission, we investigate the role of dense gas in star formation, finding systematic variations in both the apparent dense gas fraction (traced by the HCN-to-CO ratio) and the apparent star formation efficiency of dense gas (traced by the IR-to-HCN ratio). The latter may be unexpected, given the recent popularity of gas density threshold models to explain star formation scaling relations. Our survey used the IRAM 30 m telescope to observe HCN(1-0), CO(1-0), and several other emission lines across 29 nearby disk galaxies whose CO(2-1) emission has previously been mapped by the HERACLES survey. We detected HCN in 48 out of 62 observed positions. Because our observations achieve a typical resolution of ˜1.5 kpc and span a range of galaxies and galactocentric radii (56% lie at {r}{gal}\\gt 1 kpc), we are able to investigate the properties of the dense gas as a function of local conditions in a galaxy disk. We focus on how the ratios IR-to-CO, HCN-to-CO, and IR-to-HCN (observational cognates of the star formation efficiency, dense gas fraction, and dense gas star formation efficiency) depend on the stellar surface density, {{{Σ }}}{star}, and the molecular-to-atomic gas ratio, {{{Σ }}}{mol}/{{{Σ }}}{atom}. The HCN-to-CO ratio is low, often ˜1/30, and correlates tightly with both the molecular-to-atomic ratio and the stellar mass surface density across a range of 2.1 dex (factor of ≈125) in both parameters. Thus for the assumption of fixed CO-to-H2 and HCN-to-dense gas conversion factors, the dense gas fraction depends strongly on location in the disk, being higher in the high surface density, highly molecular parts of galaxies. At the same time, the IR-to-HCN ratio (closely related to the star formation efficiency of dense molecular gas) decreases systematically with these

  19. Cosmological Evolution of Dwarf Galaxies: The Influence of Star Formation and the Multiphase Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Spaans, Marco; Norman, Colin A.

    1997-07-01

    A model is developed to explain the cosmological evolution of dwarf galaxies. The population of small galaxies is found to evolve rapidly for z < 1, which provides a natural explanation for the evolution observed in the galaxy luminosity function. A tail is found in the redshift distribution of the faint blue excess that can extend to a redshift of 2. The star formation history is followed in detail for these objects. Constraints on the metallicity are identified for which stars are formed with much higher efficiency in a multiphase interstellar medium than in massive galaxies. Blue dwarf galaxies at the current epoch are identified with this starburst mode. The collapse of 1 and 2 σ perturbations of the initial density fluctuation spectrum is followed using the extended standard hierarchical clustering formalism. The collapse of these perturbations is normally associated with the formation of dwarf galaxies. These objects have shallow gravitational potential wells, and their evolution strongly depends upon the cooling time of the gas. The latter is determined by the ionization and chemical equilibrium of the gas in the presence of the intergalactic and local stellar radiation fields. The latter generally dominates and creates a feedback mechanism that regulates the evolutionary timescale. To improve upon previous models, essential new astrophysical ingredients are incorporated, such as a more detailed description of the physical processes regulating the multiphase structure of the interstellar medium in dwarf galaxies and the effects of evolution in the galaxy's metallicity on the formation of stars in molecular clouds. It is found that for a low star formation rate of 0.1 M⊙ yr-1, the cooling time of interstellar gas is longer than the local Hubble time until z ~ 1. At this epoch, a two-phase medium makes the dwarf interstellar medium less fragile against supernova explosions, and the volume filling factor of the hot phase (107 K) becomes of order unity. The

  20. Formation of an embryonic supermassive star in the first galaxy

    NASA Astrophysics Data System (ADS)

    Inayoshi, Kohei; Omukai, Kazuyuki; Tasker, Elizabeth

    2014-11-01

    We studied the gravitational collapse of a warm (˜8000 K) primordial-gas cloud as a candidate progenitor for a supermassive star (SMS; ≳ 105 M⊙) using a three-dimensional hydrodynamical simulation including all the relevant cooling processes of both H2 and H, which can potentially induce cloud fragmentation. This is the first simulation of this kind to resolve protostar formation. We find that from a weakly turbulent initial condition, the cloud undergoes runaway collapse without a major episode of fragmentation. Although the H2 fraction jumps by a large factor via the three-body reaction at ˜10-13 g cm-3, its cooling remains inefficient due to the optical thickness, and the temperature remains ≳ 3000 K. When the central core of the cloud becomes opaque to continuum radiation at ˜10-8 g cm-3, a hydrostatic protostar with ≃0.2 M⊙ is formed. The protostar grows to the mass ≃1 M⊙ and the radius ≃2 au within ˜1 yr via rapid accretion of dense filamentary flows. With high accretion rate, ˜2 M⊙ yr-1, the protostar is expected to turn into an SMS within its lifetime, eventually collapsing to a seed for the supermassive black hole observed in the early Universe at z ˜ 7.

  1. Star Formation Suppression Due to Jet Feedback in Radio Galaxies with Shocked Warm Molecular Gas

    NASA Astrophysics Data System (ADS)

    Lanz, Lauranne; Ogle, Patrick M.; Alatalo, Katherine; Appleton, Philip N.

    2016-07-01

    We present Herschel observations of 22 radio galaxies, selected for the presence of shocked, warm molecular hydrogen emission. We measured and modeled spectral energy distributions in 33 bands from the ultraviolet to the far-infrared to investigate the impact of jet feedback on star formation activity. These galaxies are massive, early-type galaxies with normal gas-to-dust ratios, covering a range of optical and infrared colors. We find that the star formation rate (SFR) is suppressed by a factor of ˜3–6, depending on how molecular gas mass is estimated. We suggest that this suppression is due to the shocks driven by the radio jets injecting turbulence into the interstellar medium (ISM), which also powers the luminous warm H2 line emission. Approximately 25% of the sample shows suppression by more than a factor of 10. However, the degree of SFR suppression does not correlate with indicators of jet feedback including jet power, diffuse X-ray emission, or intensity of warm molecular H2 emission, suggesting that while injected turbulence likely impacts star formation, the process is not purely parameterized by the amount of mechanical energy dissipated into the ISM. Radio galaxies with shocked warm molecular gas cover a wide range in SFR–stellar mass space, indicating that these galaxies are in a variety of evolutionary states, from actively star-forming and gas-rich to quiescent and gas-poor. SFR suppression appears to have the largest impact on the evolution of galaxies that are moderately gas-rich.

  2. Suppressing star formation in quiescent galaxies with supermassive black hole winds

    NASA Astrophysics Data System (ADS)

    Cheung, Edmond; Bundy, Kevin; Cappellari, Michele; Peirani, Sébastien; Rujopakarn, Wiphu; Westfall, Kyle; Yan, Renbin; Bershady, Matthew; Greene, Jenny E.; Heckman, Timothy M.; Drory, Niv; Law, David R.; Masters, Karen L.; Thomas, Daniel; Wake, David A.; Weijmans, Anne-Marie; Rubin, Kate; Belfiore, Francesco; Vulcani, Benedetta; Chen, Yan-Mei; Zhang, Kai; Gelfand, Joseph D.; Bizyaev, Dmitry; Roman-Lopes, A.; Schneider, Donald P.

    2016-05-01

    Quiescent galaxies with little or no ongoing star formation dominate the population of galaxies with masses above 2 × 1010 times that of the Sun; the number of quiescent galaxies has increased by a factor of about 25 over the past ten billion years (refs 1, 2, 3, 4). Once star formation has been shut down, perhaps during the quasar phase of rapid accretion onto a supermassive black hole, an unknown mechanism must remove or heat the gas that is subsequently accreted from either stellar mass loss or mergers and that would otherwise cool to form stars. Energy output from a black hole accreting at a low rate has been proposed, but observational evidence for this in the form of expanding hot gas shells is indirect and limited to radio galaxies at the centres of clusters, which are too rare to explain the vast majority of the quiescent population. Here we report bisymmetric emission features co-aligned with strong ionized-gas velocity gradients from which we infer the presence of centrally driven winds in typical quiescent galaxies that host low-luminosity active nuclei. These galaxies are surprisingly common, accounting for as much as ten per cent of the quiescent population with masses around 2 × 1010 times that of the Sun. In a prototypical example, we calculate that the energy input from the galaxy’s low-level active supermassive black hole is capable of driving the observed wind, which contains sufficient mechanical energy to heat ambient, cooler gas (also detected) and thereby suppress star formation.

  3. THE STAR FORMATION AND NUCLEAR ACCRETION HISTORIES OF NORMAL GALAXIES IN THE AGES SURVEY

    SciTech Connect

    Watson, Casey R.; Kochanek, Christopher S.; Forman, William R.; Hickox, Ryan C.; Jones, Christine J.; Kenter, Almus T.; Murray, Steve S.; Vikhlinin, Alexey; Fazio, Giovani G.; Green, Paul J.; Brown, Michael J. I.; Brand, Kate; Dey, Arjun; Jannuzi, Buell T.; Rieke, Marcia; Eisenstein, Daniel J.; McNamara, Brian R.; Shields, Joseph C.

    2009-05-10

    We combine IR, optical, and X-ray data from the overlapping, 9.3 deg{sup 2} NOAO Deep Wide-Field Survey, AGN and Galaxy Evolution Survey (AGES), and XBooetes Survey to measure the X-ray evolution of 6146 normal galaxies as a function of absolute optical luminosity, redshift, and spectral type over the largely unexplored redshift range 0.1 {approx}< z {approx}< 0.5. Because only the closest or brightest of the galaxies are individually detected in X-rays, we use a stacking analysis to determine the mean properties of the sample. Our results suggest that X-ray emission from spectroscopically late-type galaxies is dominated by star formation, while that from early-type galaxies is dominated by a combination of hot gas and active galactic nucleus (AGN) emission. We find that the mean star formation and supermassive black hole accretion rate densities evolve like {approx}(1 + z){sup 3{+-}}{sup 1}, in agreement with the trends found for samples of bright, individually detectable starburst galaxies and AGN. Our work also corroborates the results of many previous stacking analyses of faint source populations, with improved statistics.

  4. Extended far-infrared emission and star formation in Seyfert galaxies

    NASA Technical Reports Server (NTRS)

    Marston, A. P.

    1994-01-01

    An investigation into the extended distribution of far-infrared (FIR) emission associated with nearby Seyfert galaxies is made using a set of MEM reconstructions of IRAS Chopped Photometric Channel (CPC) data (Marston 1993). The data is compared to a set of HII/starburst galaxy images similarly processed in order to compare distributions and FIR color properties. It is shown that the central 1 kpc or so of Seyfert galaxies show extended FIR emission. FIR colors suggest that the bulk of this emission is not directly associated with an active nucleus. They further suggest that the origins of the majority of the emission is from heated dust associated with star formation surrounding the nucleus rather than dust heated by the active nucleus. Nearby Seyfert galaxies are shown to have a higher concentration of far-infrared emission from their centers than the HII/starburst galaxies and a number appear to reside in disk galaxies with relatively low ongoing star formation in their disks. An example of this is NGC 7582 which has a smooth disk but an active nucleus/starbust center.

  5. What is the Dominant Mode of Star-Formation as a Function of Galaxy Mass and Redshift?

    NASA Astrophysics Data System (ADS)

    Kassin, Susan

    We propose to determine star formation histories of galaxies since a redshift of 5. In particular, we will measure the fraction of galaxies which experience significantly elevated and depressed star-formation activity with respect to the cosmic average, and quantify the amount of time galaxies spend in such states. We will do this using our new galaxy spectral models which are based on a combination of star-formation and chemical enrichment histories from hierarchical simulations of galaxy formation. We propose to use these models to fit an extremely large data set of 105,000 galaxies over 0.2 < z < 5 with photometry spanning the UV through the infrared and with spectroscopic (80%, mostly from low resolution spectra) and photometric (20%) redshifts. There is no other data set larger or more complete in terms of redshift or wavelength, and there will likely not be one until JWST or 30-meter class telescopes are online.

  6. Intrinsically polarized stars and implication for star formation in the central parsec of our galaxy

    SciTech Connect

    Yoshikawa, Tatsuhito; Nagata, Tetsuya; Nishiyama, Shogo; Tamura, Motohide; Ishii, Miki

    2013-12-01

    We have carried out adaptive-optics assisted observations at the Subaru Telescope and have found 11 intrinsically polarized sources in the central parsec of our Galaxy. They are selected from 318 point sources with K{sub S} < 15.5, and their interstellar polarizations are corrected using a Stokes Q/I-U/I diagram. Considering brightness, near-infrared color excess, and the amount of intrinsic polarization, two of them are good young stellar object (YSO) candidates with an age of ∼10{sup 5} yr. If they are genuine YSOs, their existence provides strong constraints on star formation mechanisms in this region. In the remaining sources, two are known as bow-shock sources in the Northern Arm. One other is also located in the Northern Arm and shows very similar properties, and thus it is likely to be a so far unknown bow-shock source. The origin of the intrinsic polarization of the other sources is as yet uncertain.

  7. Star formation histories of z~2 galaxies and their intrinsic characteristics on the SFR-M* plane

    NASA Astrophysics Data System (ADS)

    Lee, Bomee; Giavalisco, Mauro; CANDELS

    2016-01-01

    Using CANDELS in the GOODS-North and South field, we investigate how galaxies quench their star formations and evolve on the SFR-M* plane at 1star formation histories (SFH) for each galaxy, not just commonly used tau model. We show that galaxies are apparently separated in four different populations: starbursts which lie above the main sequence of star formation (MS), normal star-forming galaxies on the tight MS, galaxies below the MS with a little star-forming activity, and quiescent galaxies with different time evolutions of SFR. We constrain the slope and the scatter on the MS better at 110.5, indicating that star formation efficiency decreases at high masses. We study morphologies of galaxies using non-parametric (Sersic Index) and parametric measures as well as a projected mass surface density. We find that the average morphologies of SB galaxies are disky and generally have much more diffuse optical light profile than massive compact early-type galaxies (ETGs). The sizes of the SB galaxies are clearly larger than those of the MS galaxies on average. Using a projected mass surface density, more distinct morphological differences are shown among different galaxy populations. As star formation activities decrease, galaxies become more compact at all explored redshifts. The morphologies of galaxies below the MS are similar to those of quiescent galaxies, which are compact and mostly have steep optical light profiles. The existence of compact star-forming galaxies (SFGs) supports the idea that galaxies quench their star formations as they increase the core-growth in SFGs. Very compact SB galaxies are rather rare. Our morphological analysis is not consistent with the dissipative mechanism that gas-rich merging is the key driver to assemble very compact

  8. The accuracy of the UV continuum as an indicator of the star formation rate in galaxies

    NASA Astrophysics Data System (ADS)

    Wilkins, Stephen M.; Gonzalez-Perez, Violeta; Lacey, Cedric G.; Baugh, Carlton M.

    2012-12-01

    The rest-frame intrinsic UV luminosity is often used as an indicator of the instantaneous star formation rate (SFR) in a galaxy. While it is in general a robust indicator of the ongoing star formation activity, the precise value of the calibration relating the UV luminosity to the SFR (Bν) is sensitive to various physical properties, such as the recent star formation and metal enrichment histories, along with the choice of stellar initial mass function (IMF). The distribution of these properties for the star-forming galaxy population then suggests that the adoption of a single calibration is not appropriate unless properly qualified with the uncertainties on the calibration. We investigate, with the aid of the GALFORM semi-analytic model of galaxy formation, the distribution of UV-SFR calibrations obtained using realistic star formation and metal enrichment histories. At z = 0, we find that when the IMF is fixed (to the Kennicutt IMF), the median calibration is Bfuv = 0.9 where SFR/[M⊙ yr-1] = Bν × 10-28 × Lν/[erg s-1 Hz-1]. However, the width of the distribution Bfuv suggests that for a single object there is around a 20 per cent intrinsic uncertainty (at z = 0, rising to ≃30 per cent at z = 6) on the SFR inferred from the FUV luminosity without additional constraints on the star formation history or metallicity. We also find that the median value of the calibration Bfuv is correlated with the SFR and redshift (at z > 3) raising implications for the correct determination of the SFR from the UV.

  9. On Iron Enrichment, Star Formation, and Type Ia Supernovae in Galaxy Clusters

    NASA Technical Reports Server (NTRS)

    Loewenstein, Michael

    2006-01-01

    The nature of star formation and Type Ia supernovae (SNIa) in galaxies in the field and in rich galaxy clusters are contrasted by juxtaposing the buildup of heavy metals in the universe inferred from observed star formation and supernovae rate histories with data on the evolution of Fe abundances in the intracluster medium (ICM). Models for the chemical evolution of Fe in these environments are constructed, subject to observational constraints, for this purpose. While models with a mean delay for SNIa of 3 Gyr and standard initial mass function (IMF) are fully consistent with observations in the field, cluster Fe enrichment immediately tracked a rapid, top-heavy phase of star formation - although transport of Fe into the ICM may have been more prolonged and star formation likely continued beyond redshift 1. The means of this prompt enrichment consisted of SNII yielding greater than or equal to 0.1 solar mass per explosion (if the SNIa rate normalization is scaled down from its value in the field according to the relative number of candidate progenitor stars in the 3 - 8 solar mass range) and/or SNIa with short delay times originating during the rapid star formation epoch. Star formation is greater than 3 times more efficient in rich clusters than in the field, mitigating the overcooling problem in numerical cluster simulations. Both the fraction of baryons cycled through stars, and the fraction of the total present-day stellar mass in the form of stellar remnants, are substantially greater in clusters than in the field.

  10. The imprint of reionization on the star formation histories of dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Benítez-Llambay, A.; Navarro, J. F.; Abadi, M. G.; Gottlöber, S.; Yepes, G.; Hoffman, Y.; Steinmetz, M.

    2015-07-01

    We use a compilation of star formation histories (SFHs) and cosmological simulations to explore the impact of cosmic reionization on nearby isolated dwarf galaxies. Nearby dwarfs show a wide diversity of SFHs; from ancient systems that completed their star formation (SF) ˜10 Gyr ago to young dwarfs that formed the majority of their stars in the past ˜5 Gyr to `two-component' systems characterized by the overlap of old and young stars. As an ensemble, SF in nearby dwarfs dips to lower-than-average rates at intermediate times (4 < t/Gyr < 8), a feature caused in the simulation by cosmic reionization. Reionization heats the gas and drives it out of low-mass haloes, affecting especially systems with virial temperatures of ˜2 × 104 K at zreion. SF begins before zreion in systems above this threshold; its associated feedback compounds the effects of reionization, emptying the haloes of gas and leaving behind old stellar systems. In haloes below the threshold at zreion, reionization leads to a delay in the onset of SF that lasts until the halo grows massive enough to allow gas to cool and form stars, leading to a system with a prominent young stellar component. `Two-component' systems may be traced to late accretion events that allow young stars to form in systems slightly above the threshold at zreion. The dearth of intermediate-age stars in nearby dwarfs might be the clearest signature of the imprint of cosmic reionization on the SFHs of dwarf galaxies.

  11. GLOBAL STAR FORMATION RATES AND DUST EMISSION OVER THE GALAXY INTERACTION SEQUENCE

    SciTech Connect

    Lanz, Lauranne; Zezas, Andreas; Smith, Howard A.; Ashby, Matthew L. N.; Fazio, Giovanni G.; Hernquist, Lars; Brassington, Nicola; Da Cunha, Elisabete; Hayward, Christopher C.; Jonsson, Patrik

    2013-05-01

    We measured and modeled spectral energy distributions (SEDs) in 28 bands from the ultraviolet to the far-infrared (FIR) for 31 interacting galaxies in 14 systems. The sample is drawn from the Spitzer Interacting Galaxy Survey, which probes a range of galaxy interaction parameters at multiple wavelengths with an emphasis on the infrared bands. The subset presented in this paper consists of all galaxies for which FIR Herschel SPIRE observations are publicly available. Our SEDs combine the Herschel photometry with multi-wavelength data from Spitzer, GALEX, Swift UVOT, and 2MASS. While the shapes of the SEDs are broadly similar across our sample, strongly interacting galaxies typically have more mid-infrared emission relative to their near-infrared and FIR emission than weakly or moderately interacting galaxies. We modeled the full SEDs to derive host galaxy star formation rates (SFRs), specific star formation rates (sSFRs), stellar masses, dust temperatures, dust luminosities, and dust masses. We find increases in the dust luminosity and mass, SFR, and cold (15-25 K) dust temperature as the interaction progresses from moderately to strongly interacting and between non-interacting and strongly interacting galaxies. We also find increases in the SFR between weakly and strongly interacting galaxies. In contrast, the sSFR remains unchanged across all the interaction stages. The ultraviolet photometry is crucial for constraining the age of the stellar population and the SFR, while dust mass is primarily determined by SPIRE photometry. The SFR derived from the SED modeling agrees well with rates estimated by proportionality relations that depend on infrared emission.

  12. Constraints on Feedback in the Local Universe: The Relation between Star Formation and AGN Activity in Early-type Galaxies

    NASA Astrophysics Data System (ADS)

    Vaddi, Sravani; O'Dea, Christopher P.; Baum, Stefi A.; Whitmore, Samantha; Ahmed, Rabeea; Pierce, Katherine; Leary, Sara

    2016-02-01

    We address the relation between star formation and active galactic nucleus (AGN) activity in a sample of 231 nearby (0.0002 < z < 0.0358) early-type galaxies by carrying out a multi-wavelength study using archival observations in the UV, IR, and radio. Our results indicate that early-type galaxies in the current epoch are rarely powerful AGNs, with P\\lt {10}22 {{WHz}}-1 for a majority of the galaxies. Only massive galaxies are capable of hosting powerful radio sources while less massive galaxies are hosts to lower radio power sources. Evidence of ongoing star formation is seen in approximately 7% of the sample. The star formation rate (SFR) of these galaxies is less than 0.1 M⊙ yr-1. They also tend to be radio faint (P\\lt {10}22 {{WHz}}-1). There is a nearly equal fraction of star-forming galaxies in radio faint (P\\lt {10}22 {{WHz}}-1) and radio bright galaxies (P≥slant {10}22 {{WHz}}-1) suggesting that both star formation and radio mode feedback are constrained to be very low in our sample. We notice that our galaxy sample and the Brightest Cluster Galaxies follow similar trends in radio power versus SFR. This may be produced if both radio power and SFR are related to stellar mass.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  14. The star formation-AGN interplay in merging galaxies: insights from hydrodynamical simulations and observations.

    NASA Astrophysics Data System (ADS)

    Martinez Galarza, Juan R.; Smith, Howard Alan; Weiner, Aaron; Hayward, Christopher C.; Lanz, Lauranne; Zezas, Andreas; Rosenthal, Lee; Ashby, Matthew

    2016-01-01

    Thermal emission from an Active Galactic Nucleus (AGN) can provide a significant contribution to the bolometric luminosity of galaxies, and its effect at infrared wavelengths can mimic the process of star-formation, jeopardizing star formation rate (SFR) diagnostics. It is therefore important to model the AGN emission and to quantify its effect on the estimated SFRs when SED fitting tools are applied. We tackle this problem by studying the dust radiative transfer calculations of hydrodynamically simulated binary galaxy mergers covering a broad range of parameters, including stellar mas ratios, gas contents, AGN luminosity and viewing angles. We apply the energy balance SED fitting codes CHIBURST and CIGALE to the mock SEDs of our simulated merger, and then compare with the results of applying the same codes to the SEDs of observed merging galaxies in the Local Universe. At different stages of the interaction, we compare their derived SFRs and AGN fractions with those predicted by the hydrodynamical simulations, for a broad range of the interaction parameters, but focus on the stages near coalescence, when the AGN contribution exceed 10% of the total luminosity. We show that the contribution to IR luminosity is greatest during and immediately after coalescence, when the two supermassive black holes of the interacting pair merge and undergo and enhanced period of accretion. Under certain conditions, CIGALE succeeds at recovering the SFRs and AGN fractions with higher accuracy than other available codes, such as MAGPHYS, even during these extreme stages. Our results show that using the IR luminosity as a simple surrogate for star formation can significantly overestimate the true SFR by underestimating the contribution from the AGN. Finally, we study the effect of using different parametric star formation histories (SFHs) when fitting the SEDs of galaxies, and show that a delayed SFH is usually a reasonable choice for merging galaxies.

  15. Probing Bursty Star Formation in Faint Galaxies with the Hubble Frontier Fields

    NASA Astrophysics Data System (ADS)

    Finkelstein, Steven; Livermore, Rachael; Song, Mimi

    2015-08-01

    The Hubble Frontier Fields have magnified our view into the formation and evolution of galaxies in the first billion years after the Big Bang. One key issue these data can probe is how galaxies grow their stellar masses. Do they grow smoothly with time, dominated by steady gas inflow? Or is their growth more stochastic, dominated by starburst triggering events such as mergers or clumpy gas inflows? A bevy of observational studies have shown that the star formation rates (SFRs) of distant galaxies increase with time, while theoretical studies, which broadly agree on long timescales, show that the SFRs may vary significantly on shorter timescales. We have compiled a sample of galaxies over a wide dynamic range in SFR by combining the HFF imaging with the CANDELS and HUDF datasets. By comparing the scatter in SFRs to SPH and semi-analytic models with known star formation histories, we directly measure the fraction of galaxies at a given epoch undergoing starbursts. This has a variety of implications on the distant universe, including reionization, as a significant burst fraction could both increase the number of ionizing photons being produced, as well as disturb the interstellar medium enough to allow these photons to escape.

  16. On the formation redshift of Low-Mass Star-Forming Galaxies at intermediate redshifts

    NASA Astrophysics Data System (ADS)

    Gallego, Jesus; Rodriguez-Muñoz, Lucía; Pacifici, Camilla; Tresse, Laurence; Charlot, Stéphane; Gil de Paz, Armando; Barro, Guillermo; Gomez-Guijarro, Carlos; Villar, Víctor

    2015-08-01

    Dwarf galaxies play a key role in galaxy formation and evolution: (1) hierarchical models predict that low-mass systems merged to form massive galaxies (building block paradigm; Dekel & Silk 1986); (2) dwarf systems might have been responsible for the reionization of the Universe (Wyithe & Loeb 2006); (3) theoretical models are particularly sensitive to the density of low-mass systems at diferent redshifts (Mamon et al. 2011), being one of the key science cases for the future E-ELT (Evans et al. 2013). While the history of low-mass dark matter halos is relatively well understood, the formation history of dwarf galaxies is still poorly reproduced by the models due to the distinct evolution of baryonic and dark matter.We present constraints on the star formation histories (SFHs) of a sample of low-mass Star-Forming Galaxies (LMSFGs; 7.3 < log M∗/Mo < 8.0, at 0.3 < zspec < 0.9) selected by photometric stellar mass and apparent magnitude. The SFHs were obtained through the analysis of their spectral energy distributions using a novel approach (Pacifici et al. 2012) that (1) consistently combines photometric (HST and ground-based multi-broadband) and spectroscopic (equivalent widths of emission lines from VLT and GTC spectroscopy) data, and (2) uses physically motivated SFHs with non-uniform variations of the star formation rate (SFR) as a function of time.The median SFH of our LMSFGs appears to form 90% of the median stellar mass inferred for the sample in the ˜0.5-1.8 Gyr immediately preceding the observation. These results suggest a recent stellar mass assembly for dwarf SFGs, consistent with the cosmological downsizing trends. We find similar median SFH timescales for a slightly more massive secondary sample 8.0 < log M∗/Mo < 9.1).This is a pilot study for future surveys on dwarf galaxies at high redshift.

  17. A UNIVERSAL, LOCAL STAR FORMATION LAW IN GALACTIC CLOUDS, NEARBY GALAXIES, HIGH-REDSHIFT DISKS, AND STARBURSTS

    SciTech Connect

    Krumholz, Mark R.; Dekel, Avishai; McKee, Christopher F. E-mail: dekel@phys.huji.ac.il

    2012-01-20

    Star formation laws are rules that relate the rate of star formation in a particular region, either an entire galaxy or some portion of it, to the properties of the gas, or other galactic properties, in that region. While observations of Local Group galaxies show a very simple, local star formation law in which the star formation rate per unit area in each patch of a galaxy scales linearly with the molecular gas surface density in that patch, recent observations of both Milky Way molecular clouds and high-redshift galaxies apparently show a more complicated relationship in which regions of equal molecular gas surface density can form stars at quite different rates. These data have been interpreted as implying either that different star formation laws may apply in different circumstances, that the star formation law is sensitive to large-scale galaxy properties rather than local properties, or that there are high-density thresholds for star formation. Here we collate observations of the relationship between gas and star formation rate from resolved observations of Milky Way molecular clouds, from kpc-scale observations of Local Group galaxies, and from unresolved observations of both disk and starburst galaxies in the local universe and at high redshift. We show that all of these data are in fact consistent with a simple, local, volumetric star formation law. The apparent variations stem from the fact that the observed objects have a wide variety of three-dimensional size scales and degrees of internal clumping, so even at fixed gas column density the regions being observed can have wildly varying volume densities. We provide a simple theoretical framework to remove this projection effect, and we use it to show that all the data, from small solar neighborhood clouds with masses {approx}10{sup 3} M{sub Sun} to submillimeter galaxies with masses {approx}10{sup 11} M{sub Sun }, fall on a single star formation law in which the star formation rate is simply {approx}1% of

  18. The effect of ram pressure on the star formation, mass distribution and morphology of galaxies

    NASA Astrophysics Data System (ADS)

    Kapferer, W.; Sluka, C.; Schindler, S.; Ferrari, C.; Ziegler, B.

    2009-05-01

    Aims: We investigate the dependence of star formation and the distribution of the components of galaxies on the strength of ram pressure. Several mock observations in X-ray, Hα and HI wavelength for different ram-pressure scenarios are presented. Methods: By applying a combined N-body/hydrodynamic description (GADGET-2) with radiative cooling and a recipe for star formation and stellar feedback 12 different ram-pressure stripping scenarios for disc galaxies were calculated. Special emphasis was put on the gas within the disc and in the surroundings. All gas particles within the computational domain having the same mass resolution. The relative velocity was varied from 100 km s-1 to 1000 km s-1 in different surrounding gas densities in the range from 1 × 10-28 to 5 × 10-27 g/cm^3. The temperature of the surrounding gas was initially 1 × 107 K. Results: The star formation of a galaxy is enhanced by more than a magnitude in the simulation with a high ram-pressure (5 × 10-11 dyn/cm^2) in comparison to the same system evolving in isolation. The enhancement of the star formation depends more on the surrounding gas density than on the relative velocity. Up to 95% of all newly formed stars can be found in the wake of the galaxy out to distances of more than 350 kpc behind the stellar disc. Continuously stars fall back to the old stellar disc, building up a bulge-like structure. Young stars can be found throughout the stripped wake with surface densities locally comparable to values in the inner stellar disc. Ram-pressure stripping can shift the location of star formation from the disc into the wake on very short timescales. As the gas in a galaxy has a complex velocity pattern due to the rotation and spiral arms, the superposition of the internal velocity field and the ram pressure causes complex structures in the gaseous wake which survive dynamically up to several 100 Myr. Finally we provide simulated X-ray, Hα and HI observations to be able to compare our results

  19. Star formation and molecular hydrogen in dwarf galaxies: a non-equilibrium view

    NASA Astrophysics Data System (ADS)

    Hu, Chia-Yu; Naab, Thorsten; Walch, Stefanie; Glover, Simon C. O.; Clark, Paul C.

    2016-06-01

    We study the connection of star formation to atomic (H I) and molecular hydrogen (H2) in isolated, low-metallicity dwarf galaxies with high-resolution (mgas = 4 M⊙, Nngb = 100) smoothed particle hydrodynamics simulations. The model includes self-gravity, non-equilibrium cooling, shielding from a uniform and constant interstellar radiation field, the chemistry of H2 formation, H2-independent star formation, supernova feedback and metal enrichment. We find that the H2 mass fraction is sensitive to the adopted dust-to-gas ratio and the strength of the interstellar radiation field, while the star formation rate is not. Star formation is regulated by stellar feedback, keeping the gas out of thermal equilibrium for densities n < 1 cm-3. Because of the long chemical time-scales, the H2 mass remains out of chemical equilibrium throughout the simulation. Star formation is well correlated with cold (T ≤ 100 K) gas, but this dense and cold gas - the reservoir for star formation - is dominated by H I, not H2. In addition, a significant fraction of H2 resides in a diffuse, warm phase, which is not star-forming. The interstellar medium is dominated by warm gas (100 K < T ≤ 3 × 104 K) both in mass and in volume. The scaleheight of the gaseous disc increases with radius while the cold gas is always confined to a thin layer in the mid-plane. The cold gas fraction is regulated by feedback at small radii and by the assumed radiation field at large radii. The decreasing cold gas fractions result in a rapid increase in depletion time (up to 100 Gyr) for total gas surface densities Σ _{H I+H_2} ≲ 10 M⊙ pc-2, in agreement with observations of dwarf galaxies in the Kennicutt-Schmidt plane.

  20. Dulling Occam's Razor: ICM Enrichment, the Elliptical Galaxy IMF, and the Diversity of Star Formation

    NASA Astrophysics Data System (ADS)

    Loewenstein, Michael

    2013-04-01

    Stars born in galaxy cluster potential wells must be responsible for the high level of enrichment measured in the intracluster medium (ICM); however, there is increasing tension between this truism and the parsimonious assumption that the stars in the generally old population studied optically in cluster galaxies emerged from the same formation sites at the same epochs. We construct a phenomenological cluster model to demonstrate that ICM enrichment is underestimated by a factor >2 for standard assumptions, and quantify the adjustments to the star formation efficiency and initial mass function (IMF), and SNIa production efficiency, required to rectify this while being consistent with the observed ICM abundance pattern. Given recent evidence of a steep IMF in elliptical galaxies that conflicts with the nucleosynthetic requirements of the ICM, we are led to conclude that the stellar population responsible for enriching the ICM is currently hidden and offer some suggestions as to where. This study proves that the star formation cannot be invariant in space and time.

  1. REVERSAL OF FORTUNE: INCREASED STAR FORMATION EFFICIENCIES IN THE EARLY HISTORIES OF DWARF GALAXIES?

    SciTech Connect

    Madau, Piero; Weisz, Daniel R.; Conroy, Charlie

    2014-08-01

    On dwarf galaxy scales, the different shapes of the galaxy stellar mass function and the dark halo mass function require a star-formation efficiency (SFE) in these systems that is currently more than 1 dex lower than that of Milky Way-size halos. Here, we argue that this trend may actually be reversed at high redshift. Specifically, by combining the resolved star-formation histories of nearby isolated dwarfs with the simulated mass-growth rates of dark matter halos, we show that the assembly of these systems occurs in two phases: (1) an early, fast halo accretion phase with a rapidly deepening potential well, characterized by a high SFE; and (2) a late, slow halo accretion phase where, perhaps as a consequence of reionization, the SFE is low. Nearby dwarfs have more old stars than predicted by assuming a constant or decreasing SFE with redshift, a behavior that appears to deviate qualitatively from the trends seen among more massive systems. Taken at face value, the data suggest that at sufficiently early epochs, dwarf galaxy halos above the atomic cooling mass limit can be among the most efficient sites of star formation in the universe.

  2. MORPHOLOGICAL QUENCHING OF STAR FORMATION: MAKING EARLY-TYPE GALAXIES RED

    SciTech Connect

    Martig, Marie; Bournaud, Frederic; Teyssier, Romain; Dekel, Avishai

    2009-12-10

    We point out a natural mechanism for quenching of star formation in early-type galaxies (ETGs). It automatically links the color of a galaxy with its morphology and does not require gas consumption, removal or termination of gas supply. Given that star formation takes place in gravitationally unstable gas disks, it can be quenched when a disk becomes stable against fragmentation to bound clumps. This can result from the growth of a stellar spheroid, for instance by mergers. We present the concept of morphological quenching (MQ) using standard disk instability analysis, and demonstrate its natural occurrence in a cosmological simulation using an efficient zoom-in technique. We show that the transition from a stellar disk to a spheroid can be sufficient to stabilize the gas disk, quench star formation, and turn an ETG red and dead while gas accretion continues. The turbulence necessary for disk stability can be stirred up by sheared perturbations within the disk in the absence of bound star-forming clumps. While other quenching mechanisms, such as gas stripping, active galactic nucleus feedback, virial shock heating, and gravitational heating are limited to massive halos, MQ can explain the appearance of red ETGs also in halos less massive than approx10{sup 12} M {sub sun}. The dense gas disks observed in some of today's red ellipticals may be the relics of this mechanism, whereas red galaxies with quenched gas disks could be more frequent at high redshift.

  3. SHIELD: The Star Formation Law in Extremely Low-mass Galaxies

    NASA Astrophysics Data System (ADS)

    Teich, Yaron; McNichols, Andrew; Cannon, John M.; SHIELD Team

    2016-01-01

    The "Survey of HI in Extremely Low-mass Dwarfs" (SHIELD) is a multiwavelength, legacy-class observational study of 12 low-mass dwarf galaxies discovered in Arecibo Legacy Fast ALFA (ALFALFA) survey data products. Here we analyze the relationships between HI and star formation in these systems using multi-configuration, high spatial (~300 pc) and spectral (0.82 - 2.46 km s-1 ch-1) resolution HI observations from the Karl G. Jansky Very Large Array, Hα imaging from the WIYN 3.5m telescope, and archival GALEX far-ultraviolet imaging. We compare the locations and intensities of star formation with the properties of the neutral ISM. We quantify the degree of local co-spatiality between star forming regions and regions of high HI column densities using the Kennicutt-Schmidt (K-S) relation. The values of the K-S index N vary considerably from system to system; because no single galaxy is representative of the sample, we instead focus on the narratives of the individual galaxies and their complex distribution of gaseous and stellar components. At the extremely faint end of the HI mass function, these systems are dominated by stochastic fluctuations in their interstellar media, which governs whether or not they show signs of recent star formation.Support for this work was provided by NSF grant AST-1211683 to JMC at Macalester College.

  4. Differences in the Structural Properties and Star-formation Rates of Field and Cluster Galaxies at z~1

    NASA Astrophysics Data System (ADS)

    Allen, Rebecca J.; Kacprzak, Glenn G.; Glazebrook, Karl; Tran, Kim-Vy H.; Spitler, Lee R.; Straatman, Caroline M. S.; Cowley, Michael; Nanayakkara, Themiya

    2016-07-01

    We investigate the dependence of galaxy sizes and star formation rates (SFRs) on their environment using a mass-limited sample of quiescent and star-forming galaxies with log(M */{M}ȯ ) ≥ 9.5 at \\bar{z}=0.92 selected from the NEWFIRM medium-band Survey (NMBS). Using the Galaxy Environment Evolution Collaboration 2 spectroscopic cluster catalog and the accurate photometric redshifts from the NMBS, we select quiescent and star-forming cluster (\\bar{σ }=490 km s‑1) galaxies within two virial radius, R vir, intervals of 2 > R vir > 0.5 and R vir < 0.5. Galaxies residing outside of the 2 R vir of both the cluster centers and the additional candidate over-densities are defined as our field sample. Galaxy structural parameters are measured from the COSMOS legacy Hubble Space Telescope/ACS F814W image. The sizes and Sérsic indices of quiescent field and cluster galaxies have the same distribution regardless of R vir. However, cluster star-forming galaxies within 0.5 R vir have lower mass-normalized average sizes by 16+/- 7 % , and a higher fraction of Sérsic indices with n\\gt 1, than field star-forming galaxies. The average SFRs of star-forming cluster galaxies show a trend of decreasing SFR with clustocentric radius. The mass-normalized average SFR of cluster star-forming galaxies is a factor of 2{--}2.5 (7{--}9σ ) lower than that of star-forming galaxies in the field. While we find no significant dependence on environment for quiescent galaxies, the properties of star-forming galaxies are affected, which could be the result of environment acting on their gas content.

  5. 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.

  6. The most distant galaxies: star formation rates, stellar populations and contribution to reionization

    NASA Astrophysics Data System (ADS)

    Bunker, Andrew; Stanway, Elizabeth R.; Wilkins, Stephen M.

    2015-08-01

    Over the last decade we have identified the first galaxies at redshift 6 and beyond, within the first billion years when the Gunn-Peterson absorption produces significant Lyman breaks in the spectra. Since the original Hubble Ultra Deep Field (HUDF) was imaged with HST/ACS, the advent of sensitive near-infrared imaging on HST with WFC3 has enabled us to push the use of the Lyman break technique to redshifts between 7 and 12, within the epoch of reionization. Rest-frame UV luminosity functions derived from various deep HST fields such as the HUDF and Frontier Fields, wider field imaging such as CANDELS, and ground-based imaging such as UltraVISTA, can be used to constrain the contribution of ionizing photons from star-forming galaxies. I will review what we have learned about the role of galaxies in the reionization of the IGM, and discuss the implications of the observed blue spectral slopes at these epochs and the redshift evolution of the fraction of strong Lyman-alpha emitters. Coupled with observations from Spitzer/IRAC, we can estimate the stellar masses as well as star formation rates for this population of proto-galaxies. I will look ahead to the prospects with JWST, in particular our NIRSpec GTO programme to obtain spectra of star-forming galaxies within the epoch of reionization.

  7. Using Herschel Far-Infrared Photometry to Constrain Star Formation Rates in CLASH Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Larson, Rebecca L.; Postman, Marc; Fogarty, Kevin

    2016-01-01

    The Cluster Lensing And Supernova survey with Hubble (CLASH) program obtained broadband images of 25 massive galaxy clusters in 16 passbands from the UV to the near-IR. The data was taken with the Wide-field Camera 3 (WFC3), and the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). These 25 clusters have also been observed in the mid-IR by Spitzer IRAC, the far-IR by the Herschel Space Observatory PACS and SPIRE, and in the x-ray by the Chandra and XMM observatories. We focused on the two brightest cluster galaxies (BCGs) in the survey (MACS1931.8-2653 and RXJ1532.9+3021) that have reddening-corrected UV-derived star formation rates (SFRs) > 100 M⊙ yr-1 as measured by Fogarty et al (2015). The inclusion of Herschel data provides unique constraints on dust content and independent estimates of the star formation rates in these interesting galaxies. We performed photometry on the five Herschel bands (100-500μm), and removed any contamination from other cluster members. We fit a UV-FIR SED to each galaxy to measure the bolometric dust luminosity (Lbol), which we use to derive the FIR obscured SFR. We calculate the sum of the measured UV unobscured SFR from the HST photometry and the FIR obscured SFR from the Herschel photometry to get a total SFR for these two BCGs. We compared this to the reddening-corrected SFRs and found they were in agreement within error. This confirms that the Kennicutt and Calzetti methods for calculating star formation rates are both applicable for these highly star-forming massive cluster galaxies.

  8. Star Formation Driven Outflows In Edge-On Spiral Galaxies Based on HST/ACS Observations

    NASA Astrophysics Data System (ADS)

    Rossa, Joern; Dahlem, M.; Dettmar, R.; van der Marel, R. P.

    2007-12-01

    We present new results on extraplanar diffuse ionized gas (eDIG) in four late-type, actively star-forming edge-on spirals. The high spatial resolution narrowband imaging observations were obtained with ACS on-board HST. Our H-alpha observations reveal a multitude of structures on both small and large scales. Whereas all four galaxies have been studied with ground-based telescopes before, here the small scale structure of the extended emission line gas is presented for the very first time at a spatial resolution of 0.05", corresponding to 5 pc at the mean distance to our galaxies. The eDIG morphology is very different for all four targets, as a result of their different star formation activity and galaxy mass. There is a very smooth DIG morphology observed in two of the galaxies (NGC4634 and NGC5775), whereas the other two (NGC4700 and NGC7090) show a much more complex morphology with intricate filaments, bubbles and supershells. We discuss how the morphology of the eDIG, in particular the break-up of diffuse emission into filaments in galaxy halos, depends on physical parameters such as galaxy mass and SF activity and other tracers as well as the galactic environment. Support for proposal 10416 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  9. Regulation of star formation in giant galaxies by precipitation, feedback and conduction.

    PubMed

    Voit, G M; Donahue, M; Bryan, G L; McDonald, M

    2015-03-12

    The Universe's largest galaxies reside at the centres of galaxy clusters and are embedded in hot gas that, if left undisturbed, would cool quickly and create many more new stars than are actually observed. Cooling can be regulated by feedback from accretion of cooling gas onto the central black hole, but requires an accretion rate finely tuned to the thermodynamic state of the hot gas. Theoretical models in which cold clouds precipitate out of the hot gas via thermal instability and accrete onto the black hole exhibit the necessary tuning. Recent observational evidence shows that the abundance of cold gas in the centres of clusters increases rapidly near the predicted threshold for instability. Here we report observations showing that this precipitation threshold extends over a large range in cluster radius, cluster mass and cosmic time. We incorporate the precipitation threshold into a framework of theoretical models for the thermodynamic state of hot gas in galaxy clusters. According to that framework, precipitation regulates star formation in some giant galaxies, while thermal conduction prevents star formation in others if it can compensate for radiative cooling and shut off precipitation. PMID:25739501

  10. Regulation of star formation in giant galaxies by precipitation, feedback and conduction

    NASA Astrophysics Data System (ADS)

    Voit, G. M.; Donahue, M.; Bryan, G. L.; McDonald, M.

    2015-03-01

    The Universe's largest galaxies reside at the centres of galaxy clusters and are embedded in hot gas that, if left undisturbed, would cool quickly and create many more new stars than are actually observed. Cooling can be regulated by feedback from accretion of cooling gas onto the central black hole, but requires an accretion rate finely tuned to the thermodynamic state of the hot gas. Theoretical models in which cold clouds precipitate out of the hot gas via thermal instability and accrete onto the black hole exhibit the necessary tuning. Recent observational evidence shows that the abundance of cold gas in the centres of clusters increases rapidly near the predicted threshold for instability. Here we report observations showing that this precipitation threshold extends over a large range in cluster radius, cluster mass and cosmic time. We incorporate the precipitation threshold into a framework of theoretical models for the thermodynamic state of hot gas in galaxy clusters. According to that framework, precipitation regulates star formation in some giant galaxies, while thermal conduction prevents star formation in others if it can compensate for radiative cooling and shut off precipitation.

  11. Inclusion of horizontal branch stars in the derivation of star formation histories of dwarf galaxies: The Carina dSph

    NASA Astrophysics Data System (ADS)

    Savino, Alessandro; Salaris, Maurizio; Tolstoy, Eline

    2015-11-01

    We present a detailed analysis of the horizontal branch of the Carina dwarf spheroidal galaxy by means of synthetic modelling techniques, taking consistently into account the star formation history and metallicity evolution as determined from main sequence and red giant branch spectroscopic observations. We found that a range of integrated red giant branch mass loss values of 0.1-0.14 M⊙ increasing with metallicity is able to reproduce the colour extension of the old horizontal branch. Nonetheless, leaving the mass loss as the only free parameter is not enough to match the detailed morphology of Carina horizontal branch. We then investigated the role played by the star formation history on the discrepancies between synthetic and observed horizontal branches. We derived a "toy" bursty star formation history that reproduces well the observed horizontal branch star counts, and also matches qualitatively the red giant and the turn-off regions. This bursty star formation history is made of a subset of age and [M/H] components of the star formation history based on turn off and red giants only, and entails four separate bursts of star formation of different strengths, centred at 2, 5, 8.6, and 11.5 Gyr, respectively, with mean [M/H] decreasing from ~-1.7 to ~-2.2 when the age of the burst increases, and with a Gaussian spread of σ 0.1 dex around these mean values. The comparison between the metallicity distribution function of our bursty star formation history and the one measured from the infrared CaT feature using a CaT-[Fe/H] calibration shows a qualitative agreement, once the range of [Ca/Fe] abundances measured in a sample of Carina stars have been taken into account, that causes a bias of the derived [Fe/H] distribution toward values that are too low. In conclusion, we show how the information contained within the horizontal branch of Carina (and dwarf galaxies in general) can be extracted and interpreted to refine the star formation history derived exclusively

  12. Going out with a bang or a whimper? Star formation and quenching in the Local Group's satellite galaxies

    NASA Astrophysics Data System (ADS)

    Benson, Andrew

    2014-10-01

    HST observations of the Milky Way and M31's satellite galaxies show that those galaxies have an incredible diversity of star-formation histories, yet with the exception of the Magellanic Clouds, NGC205, and NGC185, none have active star formation or cold gas at the present. What accounts for the variation in star-formation histories, and what turns off star formation? We propose to use the publicly available Galacticus semi-analytic modeling code to explore the mechanisms for star formation and quenching of Local Group dwarf galaxies, comparing the satellite galaxies of the Milky Way and M31 with the star-forming "field" galaxies of the Local Group. We will create new modules for Galacticus to incorporate physical processes necessary to follow star formation and quenching {e.g., ram- pressure and tidal stripping and compression of gas}, and perform a Markov Chain Monte Carlo analysis of the HST-derived star-formation histories to determine the best-fit physical model and degeneracies of parameters for star formation in the Local Group. These new modules and the Markov chains will be publicly released via the Galacticus web server. With this study, we can determine to what extent the star-formation histories and quenching of Local Group dwarfs are governed by physical processes that depend on properties of the Milky Way and M31's dark and gas halos versus other "external" {e.g., reionization-induced photoionization} or "internal" {e.g., supernova feedback} processes. This study will be a window into the broader question of star formation in dwarf galaxies.

  13. Evolution of Galaxies and the Star Formation Rate in the Infrared

    NASA Technical Reports Server (NTRS)

    Pahre, Michael A.; Oliversen, Ronald J. (Technical Monitor)

    2005-01-01

    A central goal of extragalactic observational astronomy is to understand how normal galaxies evolve with redshift, and particularly when galaxies formed their stars. While optical and rest-frame UV observations have begun to address these issues, the interpretation of such data is particularly challenging because of the sensitivity to dust obscuration (at optical and UV wavelengths). The absorbed light is re-radiated at IR wavelengths, hence the optimal indicators of the star formation rate (SFR) is at a rest-frame wavelength of approx. 60 microns. The Spitzer Space Telescope mission is revolutionizing the study of the global properties and evolution of galaxies. Spitzer reaches nearly two orders of magnitude more sensitivity than previous IR space missions. This research program is to study the SFR using statistical samples of galaxies in the local universe, at intermediate redshifts, and set the stage for continuing studies up to z=5. The overall research program is divided into three main investigations: A Mid-IR Hubble Atlas and SFR estimators in the local universe, Evolution of the SFR at 0 < z < 1 using pencil beam redshift surveys, and Galaxy formation and evolution at 1 < z < 5. The first papers from Spitzer were published during the last year, including ten refereed journal papers where the PI was first or co-author.

  14. Understanding the In-Situ Star Formation in a z=1.7 Cluster Core Galaxy

    NASA Astrophysics Data System (ADS)

    Webb, Tracy

    2014-10-01

    We have discovered a rare beast of a central galaxy within a z=1.7 rich galaxy cluster (estimated ~4x10^14 Msun), forming stars at a prodigious rate of 1200 Msun/yr. This system is infrared bright and its SED and the detection of PAHs at the cluster redshift, implies the IR luminosity is dominated by star formation. Such an extreme system has to date, only been confirmed in the z=0.6 Phoenix cluster (McDonald et al. 2012, 2013, 2014), whereas this object is observed at a much earlier and more active epoch of galaxy and cluster evolution. Here we propose deep HST imaging with WFC3 F160W/F105W to investigate the morphology of the BCG galaxy and its nearest neighbours. Our main goal is to understand the physical processes fuelling the intense starburst, be it a major merger or infalling gas from a cooling flow. We will also characterize the morphological properties (with color information) of the central BCG. These data will be the first of their kind at this redshift and will relate overall formation and evolution of the central galaxy massive parent halo at a cosmological epoch where these processes may begin to dominate.

  15. A magnified view of star formation at z = 0.9 from two lensed galaxies

    SciTech Connect

    Olmstead, Alice; Veilleux, Sylvain; Rigby, Jane R.; Swinbank, Mark

    2014-10-01

    We present new narrowband Hα imaging from the Hubble Space Telescope of two z = 0.91 galaxies that have been lensed by the foreground galaxy cluster A2390. These data probe spatial scales as small as ∼0.3 kpc, providing a magnified look at the morphology of star formation at an epoch when the global star formation rate (SFR) was high. However, dust attenuates our spatially resolved SFR indicators, the Hα and rest-UV emission, and we lack a direct measurement of extinction. Other studies have found that ionized gas in galaxies tends to be roughly 50% more obscured than stars; however, given an unextincted measurement of the SFR we can quantify the relative stellar to nebular extinction and the extinction in Hα. We infer SFRs from Spitzer and Herschel mid- to far-infrared observations and compare these to integrated Hα and rest-UV SFRs; this yields stellar to nebular extinction ratios consistent with previous studies. We take advantage of high spatial resolution and contextualize these results in terms of the source-plane morphologies, comparing the distribution of Hα to that of the rest-frame UV and optical light. In one galaxy, we measure separate SFRs in visually distinct clumps, but can set only a lower limit on the extinction and thus the star formation. Consequently, the data are also consistent with there being an equal amount of extinction along the lines of sight to the ionized gas as to the stars. Future observations in the far-infrared could settle this by mapping out the dust directly.

  16. SDSS IV MaNGA: Gradients in Recent Star Formation Histories as Diagnostics for Galaxy Growth and Death

    NASA Astrophysics Data System (ADS)

    Li, Cheng; MaNGA Team

    2016-01-01

    The spatially resolved spectroscopy from MaNGA allows the radial gradients of recent star formation histories (SFH), as indicated by the 4000Å break (D4000) and the equivalent width of both Hδ absorption line and Hα emission line, to be obtained with high accuracy for a large sample of galaxies in the nearby universe. Analyses of both a dozen galaxies observed by the MaNGA prototype run (P-MaNGA) and ~700 galaxies in the current MaNGA sample have shown that the SFH gradients are useful for understanding disk growth and star formation cessation in local galaxies. We find the SFH gradient of a galaxy to strongly depend on the evolution stage of its central region. Centrally star-forming galaxies generally show very weak or no radial variations. In contrast, centrally quiescent galaxies present significant radial gradients in the sense that Dn(4000) decreases, while both EW(HδA) and EW(Hα) increase from the galactic center outward. This effect is seen mainly for high-mass galaxies with stellar mass above a few ×1010 M⊙, and depends weakly on galaxy morphology type. These results are consistent with a picture in which the cessation of star formation propagates from the center of a galaxy outward as it moves to the red sequence. In this talk I will present these analyses and discuss their implications on galaxy evolution.

  17. Low-mass spiral galaxies with little molecular gas and prodigious star formation

    NASA Technical Reports Server (NTRS)

    Kenney, Jeffrey D.; Young, Judith S.

    1988-01-01

    A comparison of CO and H I properties is used here to demonstrate that many CO-poor low-mass Virgo spiral galaxies are rich in atomic gas, which implies that the lack of CO emission from them is due, at least partly, to a lack of molecular gas. Despite the paucity of molecular gas, these H I-rich, CO-poor, low-mass spiral galaxies are undergoing extensive massive star formation. A column density of 10 to the 21st nuclei/sq cm is a necessary but insufficient condition for the creation of an H2-dominated interstellar medium.

  18. Star Formation in Distant Red Galaxies: Spitzer Observations in the Hubble Deep Field-South

    NASA Astrophysics Data System (ADS)

    Webb, Tracy M. A.; van Dokkum, Pieter; Egami, Eiichi; Fazio, Giovanni; Franx, Marijn; Gawiser, Eric; Herrera, David; Huang, Jiasheng; Labbé, Ivo; Lira, Paulina; Marchesini, Danilo; Maza, José; Quadri, Ryan; Rudnick, Gregory; van der Werf, Paul

    2006-01-01

    We present Spitzer 24 μm imaging of 1.5galaxies (DRGs) in the 10'×10' extended Hubble Deep Field-South of the Multiwavelength Survey by Yale-Chile. We detect 65% of the DRGs with KAB<23.2 mag at S24μm>~40 μJy and conclude that the bulk of the DRG population is dusty active galaxies. A mid-infrared (MIR) color analysis with IRAC data suggests that the MIR fluxes are not dominated by buried AGNs, and we interpret the high detection rate as evidence for a high average star formation rate of =130+/-30 Msolar yr-1. From this, we infer that DRGs are important contributors to the cosmic star formation rate density at z~2, at a level of ~0.02 Msolar yr-1 Mpc-3 to our completeness limit of KAB=22.9 mag.

  19. 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).

  20. The Star Formation Histories of Local Group Dwarf Galaxies. III. Characterizing Quenching in Low-mass Galaxies

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    We explore the quenching of low-mass galaxies (104 ≲ {{M}\\star } ≲ 108 {{M}⊙ }) as a function of lookback time using the star formation histories (SFHs) of 38 Local Group dwarf galaxies. The SFHs were derived by analyzing color-magnitude diagrams of resolved stellar populations in archival Hubble Space Telescope/Wide Field Planetary Camera 2 imaging. We find: (1) lower-mass galaxies quench earlier than higher-mass galaxies; (2) inside of Rvirial there is no correlation between a satellite’s current proximity to a massive host and its quenching epoch; and (3) there are hints of systematic differences in the quenching times of M31 and Milky Way (MW) satellites, although the sample size and uncertainties in the SFHs of M31 dwarfs prohibit definitive conclusions. Combined with results from the literature, we qualitatively consider the redshift evolution (z = 0-1) of the quenched galaxy fraction over ˜7 dex in stellar mass (104 ≲ {{M}\\star } ≲ 1011.5 {{M}⊙ }). The quenched fraction of all galaxies generally increases toward the present, with both the lowest and highest-mass systems exhibiting the largest quenched fractions at all redshifts. In contrast, galaxies between {{M}\\star } ˜ 108-1010 {{M}⊙ } have the lowest quenched fractions. We suggest that such intermediate-mass galaxies are the least efficient at quenching. Finally, we compare our quenching times with predictions for infall times for low-mass galaxies associated with the MW. We find that some of the lowest-mass satellites (e.g., CVn II, Leo IV) may have been quenched before infall, while higher-mass satellites (e.g., Leo I, Fornax) typically quench ˜1-4 Gyr after infall. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA constract NAS 5-26555.

  1. The evolution of galaxies at constant number density: a less biased view of star formation, quenching, and structural formation

    NASA Astrophysics Data System (ADS)

    Ownsworth, Jamie R.; Conselice, Christopher J.; Mundy, Carl J.; Mortlock, Alice; Hartley, William G.; Duncan, Kenneth; Almaini, Omar

    2016-09-01

    Due to significant galaxy contamination and impurity in stellar mass selected samples (up to 95 per cent from z = 0-3), we examine the star formation history, quenching time-scales, and structural evolution of galaxies using a constant number density selection with data from the United Kingdom Infra-Red Deep Sky Survey Ultra-Deep Survey field. Using this methodology, we investigate the evolution of galaxies at a variety of number densities from z = 0-3. We find that samples chosen at number densities ranging from 3 × 10-4 to 10-5 galaxies Mpc-3 (corresponding to z ˜ 0.5 stellar masses of M* = 1010.95-11.6 M0) have a star-forming blue fraction of ˜50 per cent at z ˜ 2.5, which evolves to a nearly 100 per cent quenched red and dead population by z ˜ 1. We also see evidence for number density downsizing, such that the galaxies selected at the lowest densities (highest masses) become a homogeneous red population before those at higher number densities. Examining the evolution of the colours for these systems furthermore shows that the formation redshift of galaxies selected at these number densities is zform > 3. The structural evolution through size and Sérsic index fits reveal that while there remains evolution in terms of galaxies becoming larger and more concentrated in stellar mass at lower redshifts, the magnitude of the change is significantly smaller than for a mass-selected sample. We also find that changes in size and structure continues at z < 1, and is coupled strongly to passivity evolution. We conclude that galaxy structure is driving the quenching of galaxies, such that galaxies become concentrated before they become passive.

  2. Self-consistent photometric and spectroscopic Star Formation Histories in Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    García-Benito, R.; Pérez, E.; Pérez-Montero, E.; González Delgado, R.; Vílchez, J. M.

    2016-06-01

    This project aims to unify the spectroscopic and stellar photometric views by performing a comprehensive study of a sample of the nearest Blue Compact Dwarf Galaxies (BCDs). We plan to derive Star Formation Histories (SFH) both by means of Color-Magnitude Diagrams (CMDs) from extant Hubble Space Telescope (HST) optical imaging and with spectral fitting methods techniques using MUSE, allowing us to obtain state-of-the-art 2D stellar properties and abundances of the gas in BCDs.

  3. 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.

  4. Panoramic spectroscopy of galaxies with star-formation regions. a study of SBS 1202 + 583

    NASA Astrophysics Data System (ADS)

    Hakopian, S. A.; Balayan, S. K.; Dodonov, S. N.; Moiseev, A. V.; Smirnova, A. A.

    2012-03-01

    The methods of panoramic (3D) spectroscopy are used by us in a detailed study of galaxies with ongoing star formation chosen from among objects in seven selected fields of the Second Byurakan Survey (SBS). This article deals with the irregular galaxy SBS 1202 + 583, which our classification scheme identifies as being in a continuous phase of star formation. Observations were made with the panoramic spectrographs MPFS at the 6-m telescope of the Special Astrophysical Observatory (SAO) of the Russian Academy of Sciences and VAGR at the 2.6-m telescope of the Byurakan Astrophysical Observatory (BAO) in Armenia. The data are used to construct maps of the radiative fluxes in the continuum and various emission lines. Special attention is devoted to analyzing the emission in the H α hydrogen recombination line and in the forbidden low-ionization doublets of nitrogen [NII] λλ6548, 6583 and sulfur [SII] λλ6716, 6731, and the ratios of the intensities of the forbidden lines to H α. The observable characteristics (size, H α fluxes, etc.) of nine HII regions are studied. The estimated current rates of star formation in the individual HII regions based on the H α fluxes lie within the range of 0.3-1.2⨀ M /year. The dependence of the ratio of the intensities of the emission in these above mentioned forbidden doublets on the rate of star formation in the HII regions is found.

  5. Connecting AGN Feedback, the Star-Forming Interstellar Medium, and Galaxy Formation

    NASA Astrophysics Data System (ADS)

    Hopkins, Philip

    The biggest shortcoming in our models of star, supermassive black hole, and galaxy formation is our poor and incomplete understanding of 'feedback' processes. In nearly all models, strong feedback from stars and black holes plays a critical role in regulating the nature of the interstellar medium (ISM) and subsequent generations of star formation and black hole growth. But our theoretical understanding of these processes has largely been restricted to either idealized cases, or simple phenomenological 'sub-grid' prescriptions. These have limited predictive power, and invoke highly uncertain assumptions for the unresolved ISM physics. As such, developing more realistic, explicit treatment of these processes is critical, and one of the primary challenges facing models of both galaxy and star formation. In this proposal, we focus on improving our understanding of AGN feedback by combining novel, high-resolution studies of both black hole growth and galaxy evolution. Critically, these will simultaneously resolve the ISM and both fueling and feedback from black holes, and include fundamentally new physics on galactic scales. Our goal is to anchor these calculations as much as possible in first principles, eliminating large uncertainties in the current models, and enable new predictions on galactic scales. Recently, we developed new numerical models to resolve star formation and feedback on scales from molecular cloud star-forming regions through galaxies. These simulations explicitly follow the energy, momentum, mass, and metal fluxes from stellar radiation pressure, photo-heating, supernovae, and stellar winds; in all cases feedback is tied directly to stellar evolution models. Unlike those previous, the models naturally produce an ISM in which molecular clouds form and disperse rapidly, with realistic phase structure and turbulence. These mechanisms simultaneously drive large galactic outflows; the galactic environment is radically different from the smooth medium of

  6. Sharing Gravity's Microscope: Star Formation and Galaxy Evolution for Underserved Arizonans

    NASA Astrophysics Data System (ADS)

    Knierman, Karen A.; Monkiewicz, Jacqueline A.; Bowman, Catherine DD; Taylor, Wendy

    2016-01-01

    Learning science in a community is important for children of all levels and especially for many underserved populations. This project combines HST research of galaxy evolution using gravitationally lensed galaxies with hands-on activities and the Starlab portable planetarium to link astronomy with families, teachers, and students. To explore galaxy evolution, new activities were developed and evaluated using novel evaluation techniques. A new set of galaxy classification cards enable inquiry-based learning about galaxy ages, evolution, and gravitational lensing. Activities using new cylinder overlays for the Starlab transparent cylinder will enable the detailed examination of star formation and galaxy evolution as seen from the viewpoint inside of different types of galaxies. These activities were presented in several Arizona venues that enable family and student participation including ASU Earth and Space Open House, Arizona Museum of Natural History Homeschooling Events, on the Salt River Pima-Maricopa Indian Community, and inner city Phoenix schools serving mainly Hispanic populations. Additional events targeted underserved families at the Phoenix Zoo, in Navajo County, and for the Pascua Yaqui Tribe. After evaluation, the activities and materials will also be shared with local teachers and nationally.

  7. Connecting CO Intensity Mapping to Molecular Gas and Star Formation in the Epoch of Galaxy Assembly

    NASA Astrophysics Data System (ADS)

    Li, Tony Y.; Wechsler, Risa H.; Devaraj, Kiruthika; Church, Sarah E.

    2016-02-01

    Intensity mapping, which images a single spectral line from unresolved galaxies across cosmological volumes, is a promising technique for probing the early universe. Here we present predictions for the intensity map and power spectrum of the CO(1-0) line from galaxies at z˜ 2.4-2.8, based on a parameterized model for the galaxy-halo connection, and demonstrate the extent to which properties of high-redshift galaxies can be directly inferred from such observations. We find that our fiducial prediction should be detectable by a realistic experiment. Motivated by significant modeling uncertainties, we demonstrate the effect on the power spectrum of varying each parameter in our model. Using simulated observations, we infer constraints on our model parameter space with an MCMC procedure, and show corresponding constraints on the {L}{IR}-{L}{CO} relation and the CO luminosity function. These constraints would be complementary to current high-redshift galaxy observations, which can detect the brightest galaxies but not complete samples from the faint end of the luminosity function. By probing these populations in aggregate, CO intensity mapping could be a valuable tool for probing molecular gas and its relation to star formation in high-redshift galaxies.

  8. Star Formation, Structure and Evolution of Galaxies in Loose Groups: The Environmental Connection

    NASA Astrophysics Data System (ADS)

    Marcum, Pamela Marie

    1994-01-01

    Galaxies seldom live in isolation. Rather, they reside in multi-galaxy systems (clusters, loose groups, compact groups) spanning a large range in kinematical properties. This thesis investigates the relationship between environment and properties of galaxies belonging to loose groups. The galactic properties which we consider are morphology, near infrared colors, Ha surface brightness (proportional to star formation rate), Ha emission equivalent width (sensitive to the star formation history), color gradients light distribution profiles, and luminosity functions. Recent N-body simulations predict that transitory compact configurations, each typically consisting of approx. 2 to 5 galaxies, are created continuously during collapse of a loose group. Given this model, a loose group is expected to acquire an increasing number of merger remnants and peculiar galaxies as that group evolves dynamically. This thesis investigates the possible observational consequences of group evolution by comparing two samples of galaxy groups: (1) groups that contain galaxies listed in the 'Atlas of Peculiar Galaxies', which either have obvious disturbed morphologies and/or are likely to be involved in an interaction with a close neighboring group member(s), and (2) a control sample containing members having 'normal' galaxy properties. The thesis consists of 3 papers: the first paper describes observations and data analysis for the near infrared (JHK) imaging, taken with the Kitt Peak SQIID detector at the 1.3 meter telescope. Near infrared contours, aperture photometry, and results based on the near infrared colors are presented. The second paper provides a description of the data analysis for the R and H(alpha) CCD images, taken with the Case Western Reserve University Burrell Schmidt telescope at Kitt Peak. The morphology of the star forming regions are shown by displaying H(alpha) maps overlaid with R band contours. Near infrared H(alpha) band and optical R band surface brightness

  9. Analyzing Star Formation Properties in Dusty Early Universe Galaxies Using Gravitational Lensing

    NASA Astrophysics Data System (ADS)

    Bradli, Jaclyn C.; Bussmann, R. Shane; Riechers, Dominik A.; Clements, David; Perez-Fournon, Ismael

    2015-01-01

    Strong gravitational lensing has recently become one of the most important tools for studying star formation properties in extremely high redshift galaxies. Dust-obscured star-forming galaxies found at far-infrared/sub-millimeter wavelengths are important in the assembly of stellar mass and the evolution of massive galaxies. We present Submillimeter Array (SMA) imaging of Lockman 102, a strongly lensed submillimeter galaxy at z=5.29, discovered by the Herschel Space Observatory. The system was observed at 250, 350, 500 and 1000 microns, corresponding to rest frame wavelengths of 40, 56, 80, and 159 microns respectively. The observations were targeted at the thermal dust emission and the [CII] interstellar medium cooling line. We report an estimated photometric redshift of ~1.9 for the lensing galaxy, making it possibly the most distant lens currently known. We use uvmcmcfit, a publicly available Markov Chain Monte Carlo software tool we have developed for interferometric data, to fit lens models to Lockman 102. The results obtained from uvmcmcfit suggest the lensed system is composed of a single lensing galaxy and two extended sources. We have strong constraints on an intrinsic flux density of Lockman 102 of 4.55 + 0.45 mJy magnified by a factor of 12.5 + 1.2. From a modified blackbody fit we compute an intrinsic far infrared luminosity of 5.5e12 L⊙.This implies a star formation rate of ~950 M⊙ yr-1, making Lockman 102 an extremely active dusty galaxy. We also compare Lockman 102 to other dusty luminous starburst galaxies at similar redshift, HLS0918 (Rawle et al. 2014) and AzTEC-3 (Riechers et al. 2014a) and determine it is among the most luminous and active galaxies ~1 Gyr after the Big Bang. It is only with strong lensing that the SMA is able to undertake such a detailed study of a galaxy at this distance; the continued improvements from new facilities such as ALMA offer a promising future in observing even more distant lensed systems.

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

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

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

  11. An empirical model for the galaxy luminosity and star formation rate function at high redshift

    NASA Astrophysics Data System (ADS)

    Mashian, Natalie; Oesch, Pascal A.; Loeb, Abraham

    2016-01-01

    Using the most recent measurements of the ultraviolet (UV) luminosity functions (LFs) and dust estimates of early galaxies, we derive updated dust-corrected star formation rate functions (SFRFs) at z ˜ 4-8, which we model to predict the evolution to higher redshifts, z > 8. We employ abundance matching techniques to calibrate a relation between galaxy star formation rate (SFR) and host halo mass Mh by mapping the shape of the observed SFRFs at z ˜ 4-8 to that of the halo mass function. The resulting scaling law remains roughly constant over this redshift range. We apply the average SFR-Mh relation to reproduce the observed SFR functions at 4 ≲ z ≲ 8 and also derive the expected UV LFs at higher redshifts. At z ˜ 9 and z ˜ 10 these model LFs are in excellent agreement with current observed estimates. Our predicted number densities and UV LFs at z > 10 indicate that James Webb Space Telescope will be able to detect galaxies out to z ˜ 15 with an extensive treasury sized program. We also derive the redshift evolution of the star formation rate density (SFRD) and associated reionization history by galaxies. Models which integrate down to the current HUDF12/XDF detection limit (MUV ˜ -17.7 mag) result in a SFRD that declines as (1 + z)-10.4 ± 0.3 at high redshift and fail to reproduce the observed cosmic microwave background electron scattering optical depth, τ ≃ 0.066, to within 1σ. On the other hand, we find that the inclusion of galaxies with SFRs well below the current detection limit (MUV < -5.7 mag) leads to a fully reionized universe by z ˜ 6.5 and an optical depth of τ ≃ 0.054, consistent with the recently derived Planck value at the 1σ level.

  12. The impact of thermally pulsing asymptotic giant branch stars on hierarchical galaxy formation models

    NASA Astrophysics Data System (ADS)

    Tonini, Chiara; Maraston, Claudia; Devriendt, Julien; Thomas, Daniel; Silk, Joseph

    2009-06-01

    The spectro-photometric properties of galaxies in galaxy formation models are obtained by combining the predicted history of star formation and mass accretion with the physics of stellar evolution through stellar population models. In the recent literature, significant differences have emerged regarding the implementation of the thermally pulsing asymptotic giant branch phase of stellar evolution. The emission in the TP-AGB phase dominates the bolometric and near-IR spectrum of intermediate-age (~1Gyr) stellar populations, hence it is crucial for the correct modelling of the galaxy luminosities and colours. In this paper, for the first time, we incorporate a full prescription of the TP-AGB phase in a semi-analytic model of galaxy formation. We find that the inclusion of the TP-AGB in the model spectra dramatically alters the predicted colour-magnitude relation and its evolution with redshift. When the TP-AGB phase is active, the rest-frame V - K galaxy colours are redder by almost 2 mag in the redshift range z ~ 2-3 and by 1 mag at z ~ 1. Very red colours are produced in disc galaxies, so that the V - K colour distributions of disc and spheroids are virtually undistinguishable at low redshifts. We also find that the galaxy K-band emission is more than 1 mag higher in the range z ~ 1-3. This may alleviate the difficulties met by the hierarchical clustering scenario in predicting the red galaxy population at high redshifts. The comparison between simulations and observations has to be revisited in the light of our results.

  13. Constraints on Feedback in the Local Universe: The Relation Between Star Formation and AGN Activity in Early Type Galaxies

    NASA Astrophysics Data System (ADS)

    Vaddi, Sravani; O'Dea, Christopher P.; Baum, Stefi Alison

    2016-01-01

    We address the relation between star formation and AGN activity in a sample of 231 nearby (0.0002 < z < 0.0358) early type galaxies by carrying out a multi-wavelength study using archival observations in the UV, IR and radio. Our results indicate that early type galaxies in the current epoch are rarely powerful AGNs, with P < 1022 WHz-1 for a majority of the galaxies. Only massive galaxies are capable of hosting powerful radio sources while less massive galaxies are hosts to lower radio power sources. Evidence of ongoing star formation is seen in approximately 7% of the sample. The SFR of these galaxies is less than 0.1 M⊙yr-1. They also tend to be radio faint (P < 1022 WHz-1). There is a nearly equal fraction of star forming galaxies in radio faint (P < 1022 WHz-1) and radio bright galaxies (P ≥ 1022 WHz-1) suggesting that both star formation and radio mode feedback are constrained to be very low in our sample. We notice that our galaxy sample and the Brightest Cluster Galaxies (BCGs) follow similar trends in radio power versus SFR. This may be produced if both radio power and SFR are related to stellar mass.

  14. Star formation history in early-type galaxies - I. The line absorption indices diagnostics

    NASA Astrophysics Data System (ADS)

    Tantalo, Rosaria; Chiosi, Cesare

    2004-09-01

    To unravel the formation mechanism and the evolutionary history of elliptical galaxies (EGs) is one of the goals of modern astrophysics. In a simplified picture of the issue, the question to be answered is whether they have formed by hierarchical merging of pre-existing substructures (maybe disc galaxies) made of stars and gas, with each merging event probably accompanied by strong star formation, or conversely, whether they originated from the early aggregation of lumps of gas turned into stars in the remote past via a burst-like episode ever since followed by quiescence so as to mimic a sort of monolithic process. Even if the two alternatives seem to oppose each other, actually they may both contribute to shaping the final properties of EGs as seen today. Are there distinct signatures of the underlying dominant process in the observational data? To this aim we have examined the line absorption indices on the Lick system of the normal, field EGs of Trager and the interacting EGs (pair- and shell-objects) of Longhetti et al. The data show that both normal, field and interacting galaxies have the same scattered but smooth distribution in the Hβ versus [MgFe] plane even if the interacting ones show a more pronounced tail toward high Hβ values. This may suggest that a common physical cause is at the origin of their distribution. There are two straightforward interpretations of increasing complexity. (i) EGs span true large ranges of ages and metallicities. A young age is the signature of the aggregation mechanism, each event accompanied by metal enrichment. This simple scheme cannot, however, explain other spectro-photometric properties of EGs and has to be discarded. (ii) The bulk population of stars is old but subsequent episodes of star formation scatter the EGs in the diagnostic planes. However, this scheme would predict an outstanding clump at low Hβ values, contrary to what is observed. The model can be cured by supposing that the primary star formation

  15. Star formation in massive Milky Way molecular clouds: Building a bridge to distant galaxies

    NASA Astrophysics Data System (ADS)

    Willis, Sarah Elizabeth

    The Kennicutt-Schmidt relation is an empirical power-law linking the surface density of the star formation rate (SigmaSFR) to the surface density of gas (Sigmagas ) averaged over the observed face of a starforming galaxy Kennicutt (1998). The original presentation used observations of CO to measure gas density and H alpha emission to measure the population of hot, massive young stars (and infer the star formation rate). Observations of Sigma SFR from a census of young stellar objects in nearby molecular clouds in our Galaxy are up to 17 times higher than the extragalactic relation would predict given their Sigmagas. These clouds primarily form low-mass stars that are essentially invisible to star formation rate tracers. A sample of six giant molecular cloud (GMC) complexes with signposts of massive star formation was identified in our galaxy. The regions selected have a range of total luminosity and morphology. Deep ground-based observations in the near-infrared with NEWFIRM and IRAC observations with the Spitzer Space Telescope were used to conduct a census of the young stellar content associated with each of these clouds. The star formation rates from the stellar census in each of these regions was compared with the star formation rates measured by extragalactic star formation rate tracers based on monochromatic mid-infrared luminosities. Far-infrared Herschel observations from 160 through 500 mum were used to determine the column density and temperature in each region. The region NGC 6334 served as a test case to compare the Herschel column density measurements with the measurements for near-infrared extinction. The combination of the column density maps and the stellar census lets us examine SigmaSFR vs. Sigma gas for the massive GMCs. These regions are consistent with the results for the low-mass molecular clouds, indicating Sigma SFR levels that are higher than predicted based on Sigma gas. The overall Sigmagas levels are higher for the massive star forming

  16. Enhanced Star Formation of Less Massive Galaxies in a Protocluster at z = 2.5

    NASA Astrophysics Data System (ADS)

    Hayashi, Masao; Kodama, Tadayuki; Tanaka, Ichi; Shimakawa, Rhythm; Koyama, Yusei; Tadaki, Ken-ichi; Suzuki, Tomoko L.; Yamamoto, Moegi

    2016-08-01

    We investigate a correlation between star formation rate (SFR) and stellar mass for Hα emission-line galaxies (HAEs) in one of the richest protoclusters ever known at z ˜ 2.5, the USS 1558-003 protocluster. This study is based on a 9.7 hr narrowband imaging data with MOIRCS on the Subaru telescope. We are able to construct a sample in combination with additional H-band data taken with WFC3 on the Hubble Space Telescope, of 100 HAEs reaching the dust-corrected SFRs down to 3 M ⊙ yr‑1 and the stellar masses down to 108.0 M ⊙. We find that while the star-forming galaxies with ≳109.3 M ⊙ are located on the universal SFR-mass main sequence (MS) irrespective of the environment, less massive star-forming galaxies with ≲109.3 M ⊙ show a significant upward scatter from the MS in this protocluster. This suggests that some less massive galaxies are in a starburst phase, although we do not know yet if this is due to environmental effects.

  17. Cold-gas outflows in typical low-redshift galaxies are driven by star formation, not AGN

    NASA Astrophysics Data System (ADS)

    Sarzi, Marc; Kaviraj, Sugata; Nedelchev, Borislav; Tiffany, Joshua; Shabala, Stanislav S.; Deller, Adam T.; Middelberg, Enno

    2016-02-01

    Energetic feedback from active galactic nuclei (AGN) is an important ingredient for regulating the star formation history of galaxies in models of galaxy formation, which makes it important to study how AGN feedback actually occurs in practice. In order to catch AGNs in the act of quenching star formation, we have used the interstellar Na I λλ5890, 5895(NaD) absorption lines to look for cold-gas outflows in a sample of 456 nearby galaxies for which we could unambiguously ascertain the presence of radio-AGN activity, thanks to radio imaging at milli-arcsecond scales. While compact radio emission indicating a radio AGN was found in 103 galaxies (23 per cent of the sample), and 23 objects (5 per cent) exhibited NaD absorption-line kinematics suggestive of cold-gas outflows, not one object showed evidence of a radio AGN and of a cold-gas outflow simultaneously. Radio-AGN activity was found predominantly in early-type galaxies, while cold-gas outflows were mainly seen in spiral galaxies with central star formation or composite star formation/AGN activity. Optical AGNs also do not seem capable of driving galactic winds in our sample. Our work adds to a picture of the low-redshift Universe, where cold-gas outflows in massive galaxies are generally driven by star formation and where radio-AGN activity occurs most often in systems in which the gas reservoir has already been significantly depleted.

  18. Formaldehyde Densitometry of Starburst Galaxies: Density-independent Global Star Formation

    NASA Astrophysics Data System (ADS)

    Mangum, Jeffrey G.; Darling, Jeremy; Henkel, Christian; Menten, Karl M.

    2013-04-01

    Accurate techniques that allow for the derivation of the spatial density in star formation regions are rare. A technique that has found application for the derivation of spatial densities in Galactic star formation regions utilizes the density-sensitive properties of the K-doublet transitions of formaldehyde (H2CO). In this paper, we present an extension of our survey of the formaldehyde 110-111 (λ = 6.2 cm) and 211-212 (λ = 2.1 cm) K-doublet transitions of H2CO in a sample of 56 starburst systems. We have extended the number of galaxies in which both transitions have been detected from 5 to 13. We have improved our spatial density measurements by incorporating kinetic temperatures based upon NH3 measurements of 11 of the galaxies with a total of 14 velocity components in our sample. Our spatial density measurements lie in a relatively narrow range from 104.5 to 105.5 cm-3. This implies that the Schmidt-Kennicutt relation between L IR and M dense (1) is an indication of the dense gas mass reservoir available to form stars and (2) is not directly dependent upon a higher average density driving the star formation process in the most luminous starburst galaxies. We have also used our H2CO measurements to derive two separate measures of the dense gas mass which are generally smaller, in many cases by a factor of 102-103, than those derived using HCN. This disparity suggests that H2CO traces a denser, more compact component of the giant molecular clouds in our starburst galaxy sample. We also report measurements of the rotationally excited λ = 6.3 cm 2Π1/2 J = 1/2 state of OH and the H111α radio recombination line taken concurrently with our H2CO 110-111 measurements.

  19. 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'.

  20. Star Formation in 3CR Radio Galaxies and Quasars at z < 1

    NASA Astrophysics Data System (ADS)

    Westhues, Christian; Haas, Martin; Barthel, Peter; Wilkes, Belinda J.; Willner, S. P.; Kuraszkiewicz, Joanna; Podigachoski, Pece; Leipski, Christian; Meisenheimer, Klaus; Siebenmorgen, Ralf; Chini, Rolf

    2016-05-01

    Using the Herschel Space Observatory we have observed a representative sample of 87 powerful 3CR sources at redshift z\\lt 1. The far-infrared (FIR, 70-500 μm) photometry is combined with mid-infrared (MIR) photometry from the Wide-Field Infrared Survey Explorer and cataloged data to analyze the complete spectral energy distributions (SEDs) of each object from optical to radio wavelength. To disentangle the contributions of different components, the SEDs are fitted with a set of templates to derive the luminosities of host galaxy starlight, dust torus emission powered by active galactic nuclei (AGNs), and cool dust heated by stars. The level of emission from relativistic jets is also estimated to isolate the thermal host galaxy contribution. The new data are in line with the orientation-based unification of high-excitation radio-loud AGN, in that the dust torus becomes optically thin longwards of 30 μ {{m}}. The low-excitation radio galaxies and the MIR-weak sources represent an MIR- and FIR-faint AGN population that is different from the high-excitation MIR-bright objects; it remains an open question whether they are at a later evolutionary state or an intrinsically different population. The derived luminosities for host starlight and dust heated by star formation are converted to stellar masses and star-formation rates (SFR). The host-normalized SFR of the bulk of the 3CR sources is low when compared to other galaxy populations at the same epoch. Estimates of the dust mass yield a 1–100 times lower dust/stellar mass ratio than for the Milky Way, which indicates that these 3CR hosts have very low levels of interstellar matter and explains the low level of star formation. Less than 10% of the 3CR sources show levels of star formation above those of the main sequence of star-forming galaxies. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

  1. GAS REGULATION OF GALAXIES: THE EVOLUTION OF THE COSMIC SPECIFIC STAR FORMATION RATE, THE METALLICITY-MASS-STAR-FORMATION RATE RELATION, AND THE STELLAR CONTENT OF HALOS

    SciTech Connect

    Lilly, Simon J.; Carollo, C. Marcella; Pipino, Antonio; Peng Yingjie; Renzini, Alvio

    2013-08-01

    A very simple physical model of galaxies is one in which the formation of stars is instantaneously regulated by the mass of gas in a reservoir with mass loss scaling with the star-formation rate (SFR). This model links together three different aspects of the evolving galaxy population: (1) the cosmic time evolution of the specific star-formation rate (sSFR) relative to the growth of halos, (2) the gas-phase metallicities across the galaxy population and over cosmic time, and (3) the ratio of the stellar to dark matter mass of halos. The gas regulator is defined by the gas consumption timescale ({epsilon}{sup -1}) and the mass loading {lambda} of the wind outflow {lambda}{center_dot}SFR. The simplest regulator, in which {epsilon} and {lambda} are constant, sets the sSFR equal to exactly the specific accretion rate of the galaxy; more realistic situations lead to an sSFR that is perturbed from this precise relation. Because the gas consumption timescale is shorter than the timescale on which the system evolves, the metallicity Z is set primarily by the instantaneous operation of the regulator system rather than by the past history of the system. The metallicity of the gas reservoir depends on {epsilon}, {lambda}, and sSFR, and the regulator system therefore naturally produces a Z(m{sub star}, SFR) relation if {epsilon} and {lambda} depend on the stellar mass m{sub star}. Furthermore, this relation will be the same at all epochs unless the parameters {epsilon} and {lambda} themselves change with time. A so-called fundamental metallicity relation is naturally produced by these conditions. The overall mass-metallicity relation Z(m{sub star}) directly provides the fraction f{sub star}(m{sub star}) of incoming baryons that are being transformed into stars. The observed Z(m{sub star}) relation of Sloan Digital Sky Survey (SDSS) galaxies implies a strong dependence of stellar mass on halo mass that reconciles the different faint-end slopes of the stellar and halo mass

  2. Star Formation in the Galaxy and the Fluctuating UV Radiation Field

    NASA Technical Reports Server (NTRS)

    Hollenbach, David; Parravano, Antonio; McKee, Christopher H.; Fonda, Mark (Technical Monitor)

    2001-01-01

    We examine the formation of massive stars in the Galaxy, the resultant fluctuating UV radiation field, and the effect of this field on the star-forming interstellar medium (ISM). There are substantial fluctuations of the UV radiation field in space (scales of 100's of parsecs) and time (time-scales of order 100 million years) at the solar circle. The Far Ultraviolet (FUV) (6 eV< hv < 13.6 eV) field and the pressure determines whether the thermal balance of the neutral gas results in cold clouds or warm (T - 10(exp 4) neutral medium. We show how to calculate the average fractions of the gas in the cold and warm phases when the interstellar gas is subject to this fluctuating FUV field. The knowledge of how these fractions depend on the gas properties and on the FUV sources is a basic step in building a model of the large scale behavior of the ISM and the mutual relation between the ISM and the star formation rate. Application is made to observations of spiral galaxies which correlate the star formation rate per unit area with the surface density of the gas. We acknowledge support from the NASA Astrophysical Theory program.

  3. ALMA resolves extended star formation in high-z AGN host galaxies

    NASA Astrophysics Data System (ADS)

    Harrison, C. M.; Simpson, J. M.; Stanley, F.; Alexander, D. M.; Daddi, E.; Mullaney, J. R.; Pannella, M.; Rosario, D. J.; Smail, Ian

    2016-03-01

    We present high-resolution (0.3 arcsec) Atacama Large Millimeter Array (ALMA) 870 μm imaging of five z ≈ 1.5-4.5 X-ray detected AGN (with luminosities of L2-8keV > 1042 erg s-1). These data provide a ≳20 times improvement in spatial resolution over single-dish rest-frame far-infrared (FIR) measurements. The sub-millimetre emission is extended on scales of FWHM ≈ 0.2 arcsec-0.5 arcsec, corresponding to physical sizes of 1-3 kpc (median value of 1.8 kpc). These sizes are comparable to the majority of z=1-5 sub-millimetre galaxies (SMGs) with equivalent ALMA measurements. In combination with spectral energy distribution analyses, we attribute this rest-frame FIR emission to dust heated by star formation. The implied star-formation rate surface densities are ≈20-200 M⊙ yr-1 kpc-2, which are consistent with SMGs of comparable FIR luminosities (i.e. LIR ≈ [1-5] × 1012 L⊙). Although limited by a small sample of AGN, which all have high-FIR luminosities, our study suggests that the kpc-scale spatial distribution and surface density of star formation in high-redshift star-forming galaxies is the same irrespective of the presence of X-ray detected AGN.

  4. Dynamical state and star formation properties of the merging galaxy cluster Abell 3921

    NASA Astrophysics Data System (ADS)

    Ferrari, C.; Benoist, C.; Maurogordato, S.; Cappi, A.; Slezak, E.

    2005-01-01

    We present the analysis and results of a new VRI photometric and spectroscopic survey of the central ˜1.8×1.2 Mpc2 region of the galaxy cluster A3921 (z=0.094). We detect the presence of two dominant clumps of galaxies with a mass ratio of ˜5: a main cluster centred on the Brightest Cluster Galaxy (BCG) (A3921-A), and an NW sub-cluster (A3921-B) hosting the second brightest cluster galaxy. The distorted morphology of the two sub-clusters suggests that they are interacting, while the velocity distribution of 104 confirmed cluster members does not reveal strong signatures of merging. By applying a two-body dynamical formalism to the two sub-clusters of A3921, and by comparing our optical results to the X-ray analysis of A3921 based on XMM observations (Belsole et al. \\cite{Belsole04}), we conclude that A3921-B is probably tangentially traversing the main cluster along the SW/NE direction. The two sub-clusters are observed in the central phase of their merging process (±0.3 Gyr), with a collision axis nearly perpendicular to the line of sight. Based on the spectral features of the galaxies belonging to A3921 we estimate the star formation properties of the confirmed cluster members. Substantial fractions of both emission-line (˜13%) and post-star-forming objects (so called k+a's, ˜16%) are detected, comparable to those measured at intermediate redshifts. Our analysis reveals a lack of bright post-star-forming objects in A3921 with respect to higher redshift clusters, while the fraction of k+a's increases towards fainter magnitudes (MR_AB>-20). Similar results were obtained in the Coma cluster by Poggianti et al. (\\cite{Poggianti04}), but at still fainter magnitudes, suggesting that the maximum mass of actively star-forming galaxies increases with redshift (``downsizing effect''). The spatial and velocity distributions of k+a galaxies do not show significant differences to those of the passive population, and to the whole cluster. Most of these objects show

  5. Star Formation in Disk Galaxies. III. Does Stellar Feedback Result in Cloud Death?

    NASA Astrophysics Data System (ADS)

    Tasker, Elizabeth J.; Wadsley, James; Pudritz, Ralph

    2015-03-01

    Stellar feedback, star formation, and gravitational interactions are major controlling forces in the evolution of giant molecular clouds (GMCs). To explore their relative roles, we examine the properties and evolution of GMCs forming in an isolated galactic disk simulation that includes both localized thermal feedback and photoelectric heating. The results are compared with the three previous simulations in this series, which consists of a model with no star formation, star formation but no form of feedback, and star formation with photoelectric heating in a set with steadily increasing physical effects. We find that the addition of localized thermal feedback greatly suppresses star formation but does not destroy the surrounding GMC, giving cloud properties closely resembling the run in which no stellar physics is included. The outflows from the feedback reduce the mass of the cloud but do not destroy it, allowing the cloud to survive its stellar children. This suggests that weak thermal feedback such as the lower bound expected for a supernova may play a relatively minor role in the galactic structure of quiescent Milky-Way-type galaxies, compared to gravitational interactions and disk shear.

  6. Another short-burst host galaxy with an optically obscured high star formation rate: The case of GRB 071227

    SciTech Connect

    Nicuesa Guelbenzu, A.; Klose, S.; Kann, D. A.; Rossi, A.; Schmidl, S.; Michałowski, M. J.; McKenzie, M. R. G.; Savaglio, S.; Greiner, J.; Hunt, L. K.; Gorosabel, J.

    2014-07-01

    We report on radio continuum observations of the host galaxy of the short gamma-ray burst 071227 (z = 0.381) with the Australia Telescope Compact Array. We detect the galaxy in the 5.5 GHz band with an integrated flux density of F {sub ν} = 43 ± 11 μJy, corresponding to an unobscured star-formation rate of about 24 M {sub ☉} yr{sup –1}, 40 times higher than what was found from optical emission lines. Among the ∼30 well-identified and studied host galaxies of short bursts this is the third case where the host is found to undergo an episode of intense star formation. This suggests that a fraction of all short-burst progenitors hosted in star-forming galaxies could be physically related to recent star formation activity, implying a relatively short merger timescale.

  7. Star formation in z > 1 3CR host galaxies as seen by Herschel

    NASA Astrophysics Data System (ADS)

    Podigachoski, P.; Barthel, P. D.; Haas, M.; Leipski, C.; Wilkes, B.; Kuraszkiewicz, J.; Westhues, C.; Willner, S. P.; Ashby, M. L. N.; Chini, R.; Clements, D. L.; Fazio, G. G.; Labiano, A.; Lawrence, C.; Meisenheimer, K.; Peletier, R. F.; Siebenmorgen, R.; Verdoes Kleijn, G.

    2015-03-01

    We present Herschel (PACS and SPIRE) far-infrared (FIR) photometry of a complete sample of z> 1 3CR sources, from the Herschel guaranteed time project The Herschel Legacy of distant radio-loud AGN. Combining these with existing Spitzer photometric data, we perform an infrared (IR) spectral energy distribution (SED) analysis of these landmark objects in extragalactic research to study the star formation in the hosts of some of the brightest active galactic nuclei (AGN) known at any epoch. Accounting for the contribution from an AGN-powered warm dust component to the IR SED, about 40% of our objects undergo episodes of prodigious, ULIRG-strength star formation, with rates of hundreds of solar masses per year, coeval with the growth of the central supermassive black hole. Median SEDs imply that the quasar and radio galaxy hosts have similar FIR properties, in agreement with the orientation-based unification for radio-loud AGN. The star-forming properties of the AGN hosts are similar to those of the general population of equally massive non-AGN galaxies at comparable redshifts, thus there is no strong evidence of universal quenching of star formation (negative feedback) within this sample. Massive galaxies at high redshift may be forming stars prodigiously, regardless of whether their supermassive black holes are accreting or not. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Tables 1, 2, 4 and Appendices are available in electronic form at http://www.aanda.org

  8. CONSTRAINTS ON OBSCURED STAR FORMATION IN HOST GALAXIES OF GAMMA-RAY BURSTS

    SciTech Connect

    Hatsukade, Bunyo; Ohta, Kouji; Hashimoto, Tetsuya; Nakanishi, Kouichiro; Tamura, Yoichi; Kohno, Kotaro

    2012-04-01

    We present the results of the 16 cm wave band continuum observations of four host galaxies of gamma-ray bursts (GRBs) 990705, 021211, 041006, and 051022 using the Australia Telescope Compact Array. Radio emission was not detected in any of the host galaxies. The 2{sigma} upper limits on star formation rates derived from the radio observations of the host galaxies are 23, 45, 27, and 26 M{sub Sun} yr{sup -1}, respectively, which are less than about 10 times those derived from UV/optical observations, suggesting that they have no significant dust-obscured star formation. GRBs 021211 and 051022 are known as the so-called dark GRBs and our results imply that dark GRBs do not always occur in galaxies enshrouded by dust. Because large dust extinction was not observed in the afterglow of GRB 021211, our result suggests the possibility that the cause of the dark GRB is the intrinsic faintness of the optical afterglow. On the other hand, by considering the high column density observed in the afterglow of GRB 051022, the likely cause of the dark GRB is the dust extinction in the line of sight of the GRB.

  9. The ACS Nearby Galaxies Survey Treasury: Recovering Spatially Resolved Recent Star Formation Histories

    NASA Astrophysics Data System (ADS)

    Skillman, Evan D.; ANGST Team

    2006-12-01

    Because the supergiant phase of stellar evolution is short relative to the main sequence phase, it is possible to use them as chronometers to reconstruct the spatially resolved recent star formation histories of galaxies (cf., Dohm-Palmer et al. 1997, AJ, 114, 2514). Under the aegis of a cycle 14 HST program to observe a sample of M81 group dwarf galaxies (GO-HST-10605), we have used the star formation history codes of Dolphin (2002, MNRAS, 332, 91) to re-engineer the programs used in Dohm-Palmer et al. and produced automated codes with a wide range of applicability. The ANGST database will allow us our first opportunity to make the transition from analyzing prototypes to analyzing a statistically meaningful sample of galaxies. This promises real progress in quantifying the role of feedback in the evolution of galaxies. This work is supported by NASA grants HST-GO-10605.01-A and HST-GO-10915.06-A

  10. Star Cluster Formation and Destruction in the Merging Galaxy NGC 3256

    NASA Astrophysics Data System (ADS)

    Mulia, A. J.; Chandar, R.; Whitmore, B. C.

    2016-07-01

    We use the Advanced Camera for Surveys on the Hubble Space Telescope to study the rich population of young massive star clusters in the main body of NGC 3256, a merging pair of galaxies with a high star formation rate (SFR) and SFR per unit area (ΣSFR). These clusters have luminosity and mass functions that follow power laws, dN/dL ∝ L α with α = ‑2.23 ± 0.07, and dN/dM ∝ M β with β = ‑1.86 ± 0.34 for τ < 10 Myr clusters, similar to those found in more quiescent galaxies. The age distribution can be described by dN/dτ ∝ τ γ , with γ ≈ ‑0.67 ± 0.08 for clusters younger than about a few hundred million years, with no obvious dependence on cluster mass. This is consistent with a picture where ˜80% of the clusters are disrupted each decade in time. We investigate the claim that galaxies with high ΣSFR form clusters more efficiently than quiescent systems by determining the fraction of stars in bound clusters (Γ) and the CMF/SFR statistic (CMF is the cluster mass function) for NGC 3256 and comparing the results with those for other galaxies. We find that the CMF/SFR statistic for NGC 3256 agrees well with that found for galaxies with ΣSFR and SFRs that are lower by 1–3 orders of magnitude, but that estimates for Γ are only robust when the same sets of assumptions are applied. Currently, Γ values available in the literature have used different sets of assumptions, making it more difficult to compare the results between galaxies.

  11. Star Cluster Formation and Destruction in the Merging Galaxy NGC 3256

    NASA Astrophysics Data System (ADS)

    Mulia, A. J.; Chandar, R.; Whitmore, B. C.

    2016-07-01

    We use the Advanced Camera for Surveys on the Hubble Space Telescope to study the rich population of young massive star clusters in the main body of NGC 3256, a merging pair of galaxies with a high star formation rate (SFR) and SFR per unit area (ΣSFR). These clusters have luminosity and mass functions that follow power laws, dN/dL ∝ L α with α = ‑2.23 ± 0.07, and dN/dM ∝ M β with β = ‑1.86 ± 0.34 for τ < 10 Myr clusters, similar to those found in more quiescent galaxies. The age distribution can be described by dN/dτ ∝ τ γ , with γ ≈ ‑0.67 ± 0.08 for clusters younger than about a few hundred million years, with no obvious dependence on cluster mass. This is consistent with a picture where ∼80% of the clusters are disrupted each decade in time. We investigate the claim that galaxies with high ΣSFR form clusters more efficiently than quiescent systems by determining the fraction of stars in bound clusters (Γ) and the CMF/SFR statistic (CMF is the cluster mass function) for NGC 3256 and comparing the results with those for other galaxies. We find that the CMF/SFR statistic for NGC 3256 agrees well with that found for galaxies with ΣSFR and SFRs that are lower by 1–3 orders of magnitude, but that estimates for Γ are only robust when the same sets of assumptions are applied. Currently, Γ values available in the literature have used different sets of assumptions, making it more difficult to compare the results between galaxies.

  12. Investigating star formation properties of galaxies in massive clusters with Herschel and ALMA

    NASA Astrophysics Data System (ADS)

    Wu, John F.; Baker, Andrew J.; Aguirre, Paula; Barkats, D.; Halpern, Mark; Hilton, Matt; Hughes, John Patrick; Infante, Leopoldo; Lindner, Robert; Marriage, Tobias; Menanteau, Felipe; Sifon, Cristobal; Weiss, Axel; ACT Collaboration

    2016-01-01

    I will present results from an investigation of star formation properties of galaxies residing in two massive z ~ 1 clusters (including the 'El Gordo' merger) that were initially selected via their Sunyaev-Zeldovich decrements by the Atacama Cosmology Telescope (ACT) southern survey. This study uses new Herschel Space Observatory and Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 2 observations, which provide information about the dust and cold gas content of galaxies in our targeted clusters. We have detected CO (4-3) and [CI] in individual star-forming cluster galaxies, and also measured stacked continuum and spectral line fluxes at long (e.g., far-infrared, submillimeter, and radio) wavelengths. We use these results to explore the relations between star formation and local environment and cluster dynamical state.This work has been supported by (i) an award issued by JPL/Caltech in association with Herschel, which is a European Space Agency Cornerstone Mission with significant participation by NASA, and (ii) the National Science Foundation through award GSSP SOSPA2-018 from the National Radio Astronomy Observatory, which is operated under cooperative agreement by Associated Universities, Inc.

  13. Smoothed particle hydrodynamics for galaxy-formation simulations: improved treatments of multiphase gas, of star formation and of supernovae feedback

    NASA Astrophysics Data System (ADS)

    Marri, S.; White, S. D. M.

    2003-10-01

    We investigate a new implementation of the smoothed particle hydrodynamics technique designed to improve the realism with which galaxy formation can be simulated. In situations where cooling leads to the coexistence of phases of very different density and temperature, our method substantially reduces artificial overcooling near phase boundaries, prevents the exclusion of hot gas from the vicinity of cold `clouds' and allows relative motion of the two phases at each point. We demonstrate the numerical stability of our scheme in the presence of extremely steep density and temperature gradients, as well as in strong accretion shocks and cooling flows. In addition, we present new implementations of star formation and feedback which simulate the effect of energy injection into multiphase gas more successfully than previous schemes. Our feedback recipes deposit thermal energy separately in cold dense gas and hot diffuse gas, and can explicitly re-inject cold gas into the hot phase. They make it possible to dampen star formation effectively, to reheat cold gas, and to drive outflows into the galaxy halo and beyond. We show feedback effects to be strongest in small-mass objects where much of the gas can be expelled. After idealized tests, we carry out a first low-resolution study of galaxy formation in a Λ-cold dark matter universe. Feedback results in substantial and mass-dependent reductions in the total baryonic mass gathered on to the final object as well as in significant modulation of the star formation history.

  14. SED Fitting of Virgo Cluster Galaxies and Evidence for Enhanced Star Formation due to Accretion

    NASA Astrophysics Data System (ADS)

    Fulmer, Leah; Kenney, Jeffrey D.; Edwards, Louise O. V.

    2016-01-01

    Using UV through FIR data in matched apertures, we modeled the spectral energy distributions (SED) of 49 Virgo cluster spiral galaxies with the modeling program Magphys (daCunha+ 2008). We used the results from these models to explore the relationships between the stellar masses (M*), specific star formation rates (sSFR), and HI properties in our sample. The poster highlights one initial result from these comparisons: supportive evidence for gas accretion in the outskirts of the Virgo cluster. The galaxies with the highest sSFRs in the mass range 10^9-10^10 M_sun are all HI-rich, have extended irregular HI envelopes, and lie in the outskirts of the cluster. We propose that these galaxies are accreting gas onto their disks, a process which enhances their SFRs.

  15. 2D spectroscopy of galaxies with star formation regions. Study of SBS 1533+574

    NASA Astrophysics Data System (ADS)

    Hakopian, S. A.; Balayan, S. K.; Dodonov, S. N.; Movsessian, T. A.

    2006-10-01

    A preliminary analysis is given of 2D spectroscopic data on the galaxy SBS 1533+574(AB) obtained using the multipupil spectrographs on the 2.6-m telescope at the BAO (VAGR) and the 6-m telescope at the SAO (MPFS). The two components of the galaxy are star formation regions in different stages. The component SBS 1533+574B is known to be a BCDG. The plots of the intensity distribution of the radiation in the recombination lines of hydrogen and the forbidden lines of gases with a low degree of ionization obtained here make it possible to compare the basic characteristics of the HII-zones and the surrounding shell. The velocity distribution over the field of the galaxy is indicative of a common rotation of the system and of an intrinsic rotation of the components which is more distinct for component B.

  16. The Rise and Fall of Star Formation Histories of Blue Galaxies at Redshifts 0.2 < z < 1.4

    NASA Technical Reports Server (NTRS)

    Pacifici, Camilla; Kassin, Susan A.; Weiner, Benjamin; Charlot, Stephane; Gardner, Jonathan P.

    2012-01-01

    Popular cosmological scenarios predict that galaxies form hierarchically from the merger of many progenitor, each with their own unique star formation history (SFH). We use the approach recently developed by Pacifici et al. to constrain the SFHs of 4517 blue (presumably star-forming) galaxies with spectroscopic redshifts in the range O.2 < z < 1:4 from the All-Wavelength Extended Groth Strip International Survey (AEGIS). This consists in the Bayesian analysis of the observed galaxy spectral ' energy distributions with a comprehensive library of synthetic spectra assembled using state-of-the-art models of star formation and chemical enrichment histories, stellar population synthesis, nebular emission and attenuation by dust. We constrain the SFH of each galaxy in our sample by comparing the observed fluxes in the B, R,l and K(sub s) bands and rest-frame optical emission-line luminosities with those of one million model spectral energy distributions. We explore the dependence of the resulting SFH on galaxy stellar mass and redshift. We find that the average SFHs of high-mass galaxies rise and fall in a roughly symmetric bell-shaped manner, while those of low-mass galaxies rise progressively in time, consistent with the typically stronger activity of star formation in low-mass compared to high-mass galaxies. For galaxies of all masses, the star formation activity rises more rapidly at high than at low redshift. These findings imply that the standard approximation of exponentially declining SFHs wIdely used to interpret observed galaxy spectral energy distributions is not appropriate to constrain the physical parameters of star-forming galaxies at intermediate redshifts.

  17. Star Formation in High Redshift Galaxies with Cluster Lenses as Cosmic Telescopes

    NASA Astrophysics Data System (ADS)

    Bradac, Marusa

    2014-07-01

    In the recent years HST enabled us to detect galaxies as far as z~11. They are likely beacons of the epoch of reionization, which marked the end of the so-called ``Dark Ages'' and signified the transformation of the universe from opaque to transparent. However very little is known about those galaxies, and a confirmation of their redshift is still out of our hands. TMT will be a major powerhorse in this endeavor in the future. In addition, clusters of galaxies, when used as cosmic telescopes, can greatly simplify the task of studying and finding highest-z galaxies. With a massive cluster one can gain several magnitudes of magnification over a typical observing field, enabling imaging and spectroscopic studies of intrinsically lower-luminosity galaxies than would otherwise be observable, even with the largest telescopes. We are involved and leading several large surveys (SURFS UP for Spitzer imaging, GLASS for HST spectrscopy, and Frontier Field initiative for ultra deep HST imaging) with the main goal of identifying and studying star formation of galaxies at z=1-11. I will present first results from these surveys, show successful measurements of SFR at z~7 and beyond, and discuss the role TMT will be playing in exploring epoch of reionization.

  18. Connecting CO intensity mapping to molecular gas and star formation in the epoch of galaxy assembly

    DOE PAGESBeta

    Li, Tony Y.; Wechsler, Risa H.; Devaraj, Kiruthika; Church, Sarah E.

    2016-01-29

    Intensity mapping, which images a single spectral line from unresolved galaxies across cosmological volumes, is a promising technique for probing the early universe. Here we present predictions for the intensity map and power spectrum of the CO(1–0) line from galaxies atmore » $$z\\sim 2.4$$–2.8, based on a parameterized model for the galaxy–halo connection, and demonstrate the extent to which properties of high-redshift galaxies can be directly inferred from such observations. We find that our fiducial prediction should be detectable by a realistic experiment. Motivated by significant modeling uncertainties, we demonstrate the effect on the power spectrum of varying each parameter in our model. Using simulated observations, we infer constraints on our model parameter space with an MCMC procedure, and show corresponding constraints on the $${L}_{\\mathrm{IR}}$$–$${L}_{\\mathrm{CO}}$$ relation and the CO luminosity function. These constraints would be complementary to current high-redshift galaxy observations, which can detect the brightest galaxies but not complete samples from the faint end of the luminosity function. Furthermore, by probing these populations in aggregate, CO intensity mapping could be a valuable tool for probing molecular gas and its relation to star formation in high-redshift galaxies.« less

  19. The Nature of Starbursts. I. The Star Formation Histories of Eighteen Nearby Starburst Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    McQuinn, Kristen B. W.; Skillman, Evan D.; Cannon, John M.; Dalcanton, Julianne; Dolphin, Andrew; Hidalgo-Rodríguez, Sebastian; Holtzman, Jon; Stark, David; Weisz, Daniel; Williams, Benjamin

    2010-09-01

    We use archival Hubble Space Telescope observations of resolved stellar populations to derive the star formation histories (SFHs) of 18 nearby starburst dwarf galaxies. In this first paper, we present the observations, color-magnitude diagrams (CMDs), and the SFHs of the 18 starburst galaxies, based on a homogeneous approach to the data reduction, differential extinction, and treatment of photometric completeness. We adopt a star formation rate (SFR) threshold normalized to the average SFR of the individual system as a metric for classifying starbursts in SFHs derived from resolved stellar populations. This choice facilitates finding not only the currently bursting galaxies but also "fossil" bursts increasing the sample size of starburst galaxies in the nearby (D < 8 Mpc) universe. Thirteen of the eighteen galaxies are experiencing ongoing bursts and five galaxies show fossil bursts. From our reconstructed SFHs, it is evident that the elevated SFRs of a burst are sustained for hundreds of Myr with variations on small timescales. A long >100 Myr temporal baseline is thus fundamental to any starburst definition or identification method. The longer lived bursts rule out rapid "self-quenching" of starbursts on global scales. The bursting galaxies' gas consumption timescales are shorter than the Hubble time for all but one galaxy confirming the short-lived nature of starbursts based on fuel limitations. Additionally, we find that the strength of the Hα emission usually correlates with the CMD-based SFR during the last 4-10 Myr. However, in four cases, the Hα emission is significantly less than what is expected for models of starbursts; the discrepancy is due to the SFR changing on timescales of a few Myr. The inherently short timescale of the Hα emission limits identifying galaxies as starbursts based on the current characteristics which may or may not be representative of the recent SFH of a galaxy. Based on observations made with the NASA/ESA Hubble Space Telescope

  20. Cooling, AGN Feedback, and Star Formation in Simulated Cool-core Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Li, Yuan; Bryan, Greg L.; Ruszkowski, Mateusz; Voit, G. Mark; O'Shea, Brian W.; Donahue, Megan

    2015-10-01

    Numerical simulations of active galactic nuclei (AGNs) feedback in cool-core galaxy clusters have successfully avoided classical cooling flows, but often produce too much cold gas. We perform adaptive mesh simulations that include momentum-driven AGN feedback, self-gravity, star formation, and stellar feedback, focusing on the interplay between cooling, AGN heating, and star formation in an isolated cool-core cluster. Cold clumps triggered by AGN jets and turbulence form filamentary structures tens of kpc long. This cold gas feeds both star formation and the supermassive black hole (SMBH), triggering an AGN outburst that increases the entropy of the intracluster medium (ICM) and reduces its cooling rate. Within 1-2 Gyr, star formation completely consumes the cold gas, leading to a brief shutoff of the AGN. The ICM quickly cools and redevelops multiphase gas, followed by another cycle of star formation/AGN outburst. Within 6.5 Gyr, we observe three such cycles. There is good agreement between our simulated cluster and the observations of cool-core clusters. ICM cooling is dynamically balanced by AGN heating, and a cool-core appearance is preserved. The minimum cooling time to free-fall time ratio typically varies between a few and ≳ 20. The star formation rate (SFR) covers a wide range, from 0 to a few hundred {M}⊙ {{yr}}-1, with an average of ˜ 40 {M}⊙ {{yr}}-1. The instantaneous SMBH accretion rate shows large variations on short timescales, but the average value correlates well with the SFR. Simulations without stellar feedback or self-gravity produce qualitatively similar results, but a lower SMBH feedback efficiency (0.1% compared to 1%) results in too many stars.

  1. Effects of spiral arms on star formation in nuclear rings of barred-spiral galaxies

    SciTech Connect

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

    2014-09-01

    We use hydrodynamic simulations to study the effect of spiral arms on the star formation rate (SFR) in nuclear rings of barred-spiral galaxies. We find that spiral arms can be an efficient means of gas transport from the outskirts to the central parts, provided that the arms are rotating slower than the bar. While the ring star formation in models with no arms or corotating arms is active only during around the bar growth phase, arm-driven gas accretion both significantly enhances and prolongs the ring star formation in models with slow-rotating arms. The arm-enhanced SFR is larger by a factor of ∼3-20 than in the no-arm model, with larger values corresponding to stronger and slower arms. Arm-induced mass inflows also make dust lanes stronger. Nuclear rings in slow-arm models are ∼45% larger than in the no-arm counterparts. Star clusters that form in a nuclear ring exhibit an age gradient in the azimuthal direction only when the SFR is small, whereas no notable age gradient is found in the radial direction for models with arm-induced star formation.

  2. MEASURING GALAXY STAR FORMATION RATES FROM INTEGRATED PHOTOMETRY: INSIGHTS FROM COLOR-MAGNITUDE DIAGRAMS OF RESOLVED STARS

    SciTech Connect

    Johnson, Benjamin D.; Weisz, Daniel R.; Dalcanton, Julianne J.; Johnson, L. C.; Williams, Benjamin F.; Dale, Daniel A.; Dolphin, Andrew E.; Gil de Paz, Armando; Lee, Janice C.; Skillman, Evan D.; Boquien, Mederic

    2013-07-20

    We use empirical star formation histories (SFHs), measured from Hubble-Space-Telescope-based resolved star color-magnitude diagrams, as input into population synthesis codes to model the broadband spectral energy distributions (SEDs) of 50 nearby dwarf galaxies (6.5 < log M{sub *}/M{sub Sun} < 8.5, with metallicities {approx}10% solar). In the presence of realistic SFHs, we compare the modeled and observed SEDs from the ultraviolet (UV) through near-infrared and assess the reliability of widely used UV-based star formation rate (SFR) indicators. In the FUV through i bands, we find that the observed and modeled SEDs are in excellent agreement. In the Spitzer 3.6 {mu}m and 4.5 {mu}m bands, we find that modeled SEDs systematically overpredict observed luminosities by up to {approx}0.2 dex, depending on treatment of the TP-AGB stars in the synthesis models. We assess the reliability of UV luminosity as a SFR indicator, in light of independently constrained SFHs. We find that fluctuations in the SFHs alone can cause factor of {approx}2 variations in the UV luminosities relative to the assumption of a constant SFH over the past 100 Myr. These variations are not strongly correlated with UV-optical colors, implying that correcting UV-based SFRs for the effects of realistic SFHs is difficult using only the broadband SED. Additionally, for this diverse sample of galaxies, we find that stars older than 100 Myr can contribute from <5%-100% of the present day UV luminosity, highlighting the challenges in defining a characteristic star formation timescale associated with UV emission. We do find a relationship between UV emission timescale and broadband UV-optical color, though it is different than predictions based on exponentially declining SFH models. Our findings have significant implications for the comparison of UV-based SFRs across low-metallicity populations with diverse SFHs.

  3. The rise and fall of star formation in z ˜ 0.2 merging galaxy clusters

    NASA Astrophysics Data System (ADS)

    Stroe, Andra; Sobral, David; Dawson, William; Jee, M. James; Hoekstra, Henk; Wittman, David; van Weeren, Reinout J.; Brüggen, Marcus; Röttgering, Huub J. A.

    2015-06-01

    CIZA J2242.8+5301 (`Sausage') and 1RXS J0603.3+4213 (`Toothbrush') are two low-redshift (z ˜ 0.2), massive (˜2 × 1015 M⊙), post-core passage merging clusters, which host-shock waves traced by diffuse radio emission. To study their star formation properties, we uniformly survey the `Sausage' and `Toothbrush' clusters in broad- and narrow-band filters and select a sample of 201 and 463 line emitters, down to a rest-frame equivalent width (13 Å). We robustly separate between Hα and higher redshift emitters using a combination of optical multiband (B, g, V, r, i, z) and spectroscopic data. We build Hα luminosity functions for the entire cluster region, near the shock fronts, and away from the shock fronts and find striking differences between the two clusters. In the dynamically younger, 1 Gyr old `Sausage' cluster we find numerous (59) Hα emitters above a star formation rate (SFR) of 0.17 M⊙ yr-1 surprisingly located in close proximity to the shock fronts, embedded in very hot intracluster medium plasma. The SFR density for the cluster population is at least at the level of typical galaxies at z ˜ 2. Down to the same SFR, the possibly dynamically more evolved `Toothbrush' cluster has only nine Hα galaxies. The cluster Hα galaxies fall on the SFR-stellar mass relation z ˜ 0.2 for the field. However, the `Sausage' cluster has an Hα emitter density >20 times that of blank fields. If the shock passes through gas-rich cluster galaxies, the compressed gas could collapse into dense clouds and excite star formation for a few 100 Myr. This process ultimately leads to a rapid consumption of the molecular gas, accelerating the transformation of gas-rich field spirals into cluster S0s or ellipticals.

  4. The Sensitive Side of Galaxy Formation: How sub-L* Galaxies Accrete, Form Stars, and Enrich the IGM

    NASA Astrophysics Data System (ADS)

    Oppenheimer, Benjamin

    2012-10-01

    We propose a series of cosmological zoom simulations specifically targeting the formation and evolution of dwarf and sub-L* galaxies living in halos of 10^11- 10^12 solar masses. The shallow potential wells and low-density environments of these halos provide uniquely sensitive laboratories to understand the physics of galactic feedback, as well as the thermal history of the intergalactic medium, from which these galaxies accrete. Given that 129 orbits of Cycle 18 COS data probing such halos is now being completed, combined with the insufficiency of current cosmological simulations to resolve these halos, the theory is lagging the data. We will remedy this by running zoom simulations of individual halos with 1000-10,000 times greater mass resolution than current cosmological simulations used for similar studies. We aim to resolve the sub-kpc scale of high-velocity cloud-like structures and <100 pc scales of the interstellar medium. We will simulate circumgalactic quasar absorption metal-line and H I statistics using our novel non-equilibrium ionization solver that follows individual ionic states. We will also investigate the delicate balance of accretion, star formation, and feedback required to reproduce the observed stellar properties of these small galaxies. In the spirit of transparency, we will make our simulation results available on a public website to encourage new projects and collaborations with observers and theorists understanding the physics regulating galaxy growth.

  5. THE MASS-DEPENDENT STAR FORMATION HISTORIES OF DISK GALAXIES: INFALL MODEL VERSUS OBSERVATIONS

    SciTech Connect

    Chang, R. X.; Hou, J. L.; Shen, S. Y.; Shu, C. G.

    2010-10-10

    We introduce a simple model to explore the star formation histories of disk galaxies. We assume that the disk originate and grows by continuous gas infall. The gas infall rate is parameterized by the Gaussian formula with one free parameter: the infall-peak time t{sub p} . The Kennicutt star formation law is adopted to describe how much cold gas turns into stars. The gas outflow process is also considered in our model. We find that, at a given galactic stellar mass M{sub *}, the model adopting a late infall-peak time t{sub p} results in blue colors, low-metallicity, high specific star formation rate (SFR), and high gas fraction, while the gas outflow rate mainly influences the gas-phase metallicity and star formation efficiency mainly influences the gas fraction. Motivated by the local observed scaling relations, we 'construct' a mass-dependent model by assuming that the low-mass galaxy has a later infall-peak time t{sub p} and a larger gas outflow rate than massive systems. It is shown that this model can be in agreement with not only the local observations, but also with the observed correlations between specific SFR and galactic stellar mass SFR/M{sub *} {approx} M{sub *} at intermediate redshifts z < 1. Comparison between the Gaussian-infall model and the exponential-infall model is also presented. It shows that the exponential-infall model predicts a higher SFR at early stage and a lower SFR later than that of Gaussian infall. Our results suggest that the Gaussian infall rate may be more reasonable in describing the gas cooling process than the exponential infall rate, especially for low-mass systems.

  6. The star formation history of mass-selected galaxies from the VIDEO survey

    NASA Astrophysics Data System (ADS)

    Zwart, Jonathan T. L.; Jarvis, Matt J.; Deane, Roger P.; Bonfield, David G.; Knowles, Kenda; Madhanpall, Nikhita; Rahmani, Hadi; Smith, Daniel J. B.

    2014-04-01

    We measure star formation rates (SFRs) and specific SFRs (SSFRs) of Ks -selected galaxies from the VISTA Deep Extragalactic Observations survey by stacking 1.4 GHz Very Large Array data. We split the sample, which spans 0 < z < 3 and stellar masses 108.0 < M*/M⊙ < 1011.5, into elliptical, irregular or starburst galaxies based on their spectral energy distributions. We find that SSFR falls with stellar mass, in agreement with the `downsizing' paradigm. We consider the dependence of the SSFR-mass slope on redshift: for our full and elliptical samples the slope flattens, but for the irregular and starburst samples the slope is independent of redshift. The rate of SSFR evolution reduces slightly with stellar mass for ellipticals, but irregulars and starbursts co-evolve across stellar masses. Our results for SSFR as a function of stellar mass and redshift are in agreement with those derived from other radio-stacking measurements of mass-selected passive and star-forming galaxies, but inconsistent with those generated from semi-analytic models, which tend to underestimate SFRs and SSFRs. There is a need for deeper high-resolution radio surveys such as those from telescopes like the next-generation MeerKAT in order to probe lower masses at earlier times and to permit direct detections, i.e. to study individual galaxies in detail.

  7. Cloud fluid models of gas dynamics and star formation in galaxies

    NASA Technical Reports Server (NTRS)

    Struck-Marcell, Curtis; Scalo, John M.; Appleton, P. N.

    1987-01-01

    The large dynamic range of star formation in galaxies, and the apparently complex environmental influences involved in triggering or suppressing star formation, challenges the understanding. The key to this understanding may be the detailed study of simple physical models for the dominant nonlinear interactions in interstellar cloud systems. One such model is described, a generalized Oort model cloud fluid, and two simple applications of it are explored. The first of these is the relaxation of an isolated volume of cloud fluid following a disturbance. Though very idealized, this closed box study suggests a physical mechanism for starbursts, which is based on the approximate commensurability of massive cloud lifetimes and cloud collisional growth times. The second application is to the modeling of colliding ring galaxies. In this case, the driving processes operating on a dynamical timescale interact with the local cloud processes operating on the above timescale. The results is a variety of interesting nonequilibrium behaviors, including spatial variations of star formation tha