http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
A WFC3 study of globular clusters in NGC 4150: an early‐type minor merger
Kaviraj, Sugata,Crockett, R. Mark,Whitmore, Bradley C.,Silk, Joseph,O’Connell, Robert W.,Windhorst, Rogier A.,Mutchler, Max,Rejkuba, Marina,Yi, Sukyoung,Frogel, Jay A.,Calzetti, Daniela Blackwell Publishing Ltd 2012 Monthly notices of the Royal Astronomical Society. Vol.422 No.1
<P><B>ABSTRACT</B></P><P>We combine near‐ultraviolet (NUV; 2250 Å) and optical (<I>U</I>, <I>B</I>, <I>V</I>, <I>I</I>) imaging from the Wide Field Camera 3 (WFC3), on‐board the <I>Hubble Space Telescope</I> (<I>HST</I>), to study the globular cluster (GC) population in NGC 4150, a sub‐L* (<I>M</I><SUB><I>B</I></SUB>∼−18.48 mag) early‐type minor‐merger remnant in the Coma I cloud. We use broad‐band NUV–optical photometry from the WFC3 to estimate individual ages, metallicities, masses and line‐of‐sight extinctions [<I>E</I>(<I>B</I>−<I>V</I>)] for 63 bright (<I>M</I><SUB><I>V</I></SUB> < −5 mag) GCs in this galaxy. In addition to a small GC population with ages greater than 10 Gyr, we find a dominant population of clusters with ages centred around 6 Gyr, consistent with the expected peak of stellar mass assembly in faint early types residing in low‐density environments. The old and intermediate‐age GCs in NGC 4150 are metal poor, with metallicities less than 0.1 Z<SUB>⊙</SUB>, and reside in regions of low extinction [<I>E</I>(<I>B</I>−<I>V</I>) < 0.05 mag]. We also find a population of young, metal‐rich (<I>Z</I> > 0.3 Z<SUB>⊙</SUB>) clusters that have formed within the last Gyr and reside in relatively dusty [<I>E</I>(<I>B</I>−<I>V</I>) > 0.3 mag] regions that are coincident with the part of the galaxy core that hosts significant recent star formation. Cluster disruption models (in which ∼80–90 per cent of objects younger than a few ×10<SUP>8</SUP> yr dissolve every dex in time) suggest that the bulk of these young clusters are a transient population.</P>
Suppression of star formation in early-type galaxies by feedback from supermassive black holes
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,Schimino Nature Publishing Group 2006 Nature Vol.442 No.7105
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.
DESTRUCTION OF MOLECULAR GAS RESERVOIRS IN EARLY-TYPE GALAXIES BY ACTIVE GALACTIC NUCLEUS FEEDBACK
Schawinski, Kevin,Lintott, Chris J.,Thomas, Daniel,Kaviraj, Sugata,Viti, Serena,Silk, Joseph,Maraston, Claudia,Sarzi, Marc,Yi, Sukyoung K.,Joo, Seok-Joo,Daddi, Emanuele,Bayet, Estelle,Bell, Tom,Zuntz, IOP Publishing 2009 The Astrophysical journal Vol.690 No.2
Decoding the spectra of SDSS early-type galaxies: new indicators of age and recent star formation
Rogers, Ben,Ferreras, Ignacio,Lahav, Ofer,Bernardi, Mariangela,Kaviraj, Sugata,Yi, Sukyoung K. Blackwell Publishing Ltd 2007 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.382 No.2
<P>ABSTRACT</P><P>We apply principal component analysis (PCA) to a sample of early-type galaxies from the Sloan Digital Sky Survey (SDSS) in order to infer differences in their star formation histories from their unresolved stellar populations. We select a <I>z</I> < 0.1 volume-limited sample comprising ∼7000 early-type galaxies from SDSS/Data Release 4. Out of the first few principal components (PC), we study four which give information about stellar populations and velocity dispersion. We construct two parameters (η and ζ) as linear combinations of PC1 and PC2. The four components can be presented as ‘optimal filters’ to explore in detail the properties of the underlying stellar populations. By comparing various photospectroscopic observables – including near-ultraviolet (NUV) photometry from Galaxy Evolution Explorer (GALEX) – we find ζ to be most sensitive to recent episodes of star formation, and η to be strongly dependent on the average age of the stellar populations. Both η and ζ also depend on metallicity. We apply these optimal filters to composite spectra assembled by Bernardi et al. The distribution of the η component of the composites appear to be indistinguishable between high- and low-density regions, whereas the distribution of ζ parameters have a significant skew towards lower values for galaxies in low-density regions. This result suggests that galaxies in lower density environments are less likely to present weak episodes of recent star formation. In contrast, a significant number of galaxies from our high-density subsample – which includes clusters (both outer regions and centres) and groups – underwent small but detectable recent star formation at high metallicity, in agreement with recent estimates targeting elliptical galaxies in Hickson Compact Groups and in the field.</P>
Rutkowski, Michael J.,Jeong, Hyunjin,Cohen, Seth H.,Kaviraj, Sugata,Windhorst, Rogier A.,Ryan Jr., Russell E.,Koekemoer, Anton,Yi, Sukyoung K.,Hathi, Nimish P.,Dopita, Michael A. IOP Publishing 2014 The Astrophysical journal Vol.796 No.2
<P>We present an analysis of the stellar populations of 102 visually selected early-type galaxies (ETGs) with spectroscopic redshifts (0.35 less than or similar to z less than or similar to 1.5) from observations in the Early Release Science program with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). We fit one-and two-component synthetic stellar models to the ETGs UV-optical-near-IR spectral energy distributions and find that a large fraction (similar to 40%) are likely to have experienced a minor (f(YC) less than or similar to 10% of stellar mass) burst of recent (t(YC) less than or similar to 1 Gyr) star formation. The measured age and mass fraction of the young stellar populations do not strongly trend with measurements of galaxy morphology. We note that massive (M > 10(10.5) M-circle dot) recent star-forming ETGs appear to have larger sizes. Furthermore, high-mass, quiescent ETGs identified with likely companions populate a distinct region in the size-mass parameter space, in comparison with the distribution of massive ETGs with evidence of recent star formation (RSF). We conclude that both mechanisms of quenching star formation in disk-like ETGs and (gas-rich, minor) merger activity contribute to the formation of young stars and the size-mass evolution of intermediate redshift ETGs. The number of ETGs for which we have both HST WFC3 panchromatic (especially UV) imaging and spectroscopically confirmed redshifts is relatively small, therefore, a conclusion about the relative roles of both of these mechanisms remains an open question.</P>
Galaxy Zoo: a sample of blue early-type galaxies at low redshift<sup>★</sup>
Schawinski, Kevin,Lintott, Chris,Thomas, Daniel,Sarzi, Marc,Andreescu, Dan,Bamford, Steven P.,Kaviraj, Sugata,Khochfar, Sadegh,Land, Kate,Murray, Phil,Nichol, Robert C.,Raddick, M. Jordan,Slosar, An Blackwell Publishing Ltd 2009 Monthly notices of the Royal Astronomical Society Vol.396 No.2
<P>ABSTRACT</P><P>We report the discovery of a population of nearby, blue early-type galaxies with high star formation rates (0.5 < SFR < 50 M<SUB>⊙</SUB> yr<SUP>−1</SUP>). They are identified by their visual morphology as provided by Galaxy Zoo for Sloan Digital Sky Survey Data Release 6 and their <I>u</I>−<I>r</I> colour. We select a volume-limited sample in the redshift range 0.02 < <I>z</I> < 0.05, corresponding to luminosities of approximately <I>L</I>* and above and with <I>u</I>−<I>r</I> colours significantly bluer than the red sequence. We confirm the early-type morphology of the objects in this sample and investigate their environmental dependence and star formation properties. Blue early-type galaxies tend to live in lower density environments than ‘normal’ red sequence early-types and make up 5.7 ± 0.4 per cent of the low-redshift early-type galaxy population. We find that such blue early-type galaxies are virtually absent at high velocity dispersions above 200 km s<SUP>−1</SUP>. Our analysis uses emission line diagnostic diagrams and we find that ∼25 per cent of them are actively star forming, while another ∼25 per cent host both star formation and an active galactic nucleus (AGN). Another ∼12 per cent are AGN. The remaining 38 per cent show no strong emission lines. When present and uncontaminated by an AGN contribution, the star formation is generally intense. We consider star formation rates derived from Hα, <I>u</I> band and infrared luminosities, and radial colour profiles, and conclude that the star formation is spatially extended. Of those objects that are not currently undergoing star formation must have ceased doing so recently in order to account for their blue optical colours. The gas-phase metallicity of the actively star-forming blue early-types galaxies is supersolar in all cases. We discuss the place of these objects in the context of galaxy formation. A catalogue of all 204 blue early-type galaxies in our sample, including star formation rates, emission line classification is provided.</P>