The SDSS-GALEX viewpoint of the truncated red sequence in field environments at z~0

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 07/2007; 385(3). DOI: 10.1111/j.1365-2966.2008.12954.x
Source: arXiv


We combine Galaxy Evolution ExplorerGALEX near-ultraviolet (NUV) photometry with a volume-limited sample of local (0.005 < z < 0.037) Sloan Digital Sky Survey (SDSS) DR4 galaxies to examine the composition and the environmental dependencies of the
optical and ultraviolet (UV)-optical colour–magnitude (CM) diagrams. We find that ∼30 per cent of red-sequence galaxies in
the optical CM diagram show signs of ongoing star formation from their spectra having EW(Hα) > 2 Å. This contamination is
greatest at faint magnitudes (Mr > −19) and in field regions where as many as three-quarters of red-sequence galaxies are star forming, and as such has important
consequences for following the build-up of the red sequence. The NUV −r colour instead allows a much more robust separation of passively evolving and star-forming galaxies, which allows the build-up
of the UV-selected red sequence with redshift and environment to be directly interpreted in terms of the assembly of stellar
mass in passively evolving galaxies. In isolated field regions, the number density of UV-optical red-sequence galaxies declines
rapidly at magnitudes fainter than Mr∼−19 and appears completely truncated at Mr∼−18. These results support the downsizing paradigm whereby the red sequence is assembled from the top down, being already
largely in place at the bright end by z∼ 1, and the faint end filled in at later epochs in clusters and groups through environment-related processes such as ram-pressure
stripping or galaxy harassment.

Download full-text


Available from: Christopher Paul Haines, Oct 16, 2012
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present an analysis of star-formation and nuclear activity in galaxies as a function of both luminosity and environment in the SDSS DR4 dataset. Using a sample of 27753 galaxies at 0.005<z<0.037 that is >90% complete to Mr=-18.0 we find that the EW(Ha) distribution is strongly bimodal, allowing galaxies to be robustly separated into passive and star-forming populations about a value EW(Ha)=2A. In high-density regions ~70% of galaxies are passive independent of luminosity. In the rarefied field however, the fraction of passively-evolving galaxies is a strong function of luminosity, dropping from ~50% for Mr<-21 to zero by Mr~-18. Indeed for the lowest luminosity range covered (-18<Mr<-16) none of the ~600 galaxies in the lowest density quartile are passive. The few passively-evolving dwarf galaxies in field regions appear as satellites to bright (~L*) galaxies. The fraction of galaxies with optical AGN signatures decreases steadily from ~50% at Mr~-21 to ~0% by Mr~-18 closely mirroring the luminosity-dependence of the passive galaxy fraction in low-density environments. This result reflects the increasing importance of AGN feedback with galaxy mass for their evolution, such that the star-formation histories of massive galaxies are primarily determined by their past merger history. In contrast, the complete absence of passively-evolving dwarf galaxies more than ~2 virial radii from the nearest massive halo (i.e. cluster, group or massive galaxy) indicates that internal processes, such as merging, AGN feedback or gas consumption through star-formation, are not responsible for terminating star-formation in dwarf galaxies. Instead the evolution of dwarf galaxies is primarily driven by the mass of their host halo, probably through the combined effects of tidal forces and ram-pressure stripping. Comment: 29 pages, 11 figures. Accepted for publication in MNRAS
    Full-text · Article · Jul 2007 · Monthly Notices of the Royal Astronomical Society
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The most massive galaxies in the Universe are also the oldest. To overturn this apparent contradiction with hierarchical growth models, we focus on the group scale haloes which host most of these galaxies. A stellar mass selected M_* >~ 2x10^10M_sol sample at z~0.4 is constructed within the CNOC2 redshift survey. A sensitive Mid InfraRed (MIR) IRAC colour is used to isolate passive galaxies. It produces a bimodal distribution, in which passive galaxies (highlighted by morphological early-types) define a tight MIR colour sequence (Infrared Passive Sequence, IPS). This is due to stellar atmospheric emission from old stellar populations. Significantly offset from the IPS are galaxies where reemission by dust boosts emission at 8microns (InfraRed-Excess or IRE galaxies). They include all known morphological late-types. Comparison with EW[OII] shows that MIR colour is highly sensitive to low levels of activity, and allows us to separate dusty-active from passive galaxies. The fraction of IRE galaxies, f(IRE) drops with M_*, such that f(IRE)=0.5 at a ``crossover mass'' of ~1.3x10^11M_sol. Within our optically-defined group sample there is a strong and consistent deficit in f(IRE) at all masses, and most clearly at M_* >~10^11M_sol. Using a mock galaxy catalogue derived from the Millenium Simulation we show that the observed trend of f(IRE) with M_* can be explained if suppression of star formation occurs primarily in the group environment, and particularly for M_*>~10^11M_sol galaxies. In this way, downsizing can be driven solely by structure growth in the Universe. Comment: 15 pages, 6 figures. Accepted for publication in ApJ
    Full-text · Article · Feb 2008 · The Astrophysical Journal
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present GALEX near-ultraviolet (NUV) and Two-Micron All-Sky Survey J-band photometry for red-sequence galaxies in local clusters. We define quiescent samples according to a strict emission threshold, removing galaxies with very recent star formation. We analyse the NUV–J colour–magnitude relation (CMR) and find that the intrinsic scatter is an order of magnitude larger than for the analogous optical CMR (∼0.35 rather than 0.05 mag), in agreement with previous studies. Comparing the NUV–J colours with spectroscopically derived stellar population parameters, we find a strong (>5.5σ) correlation with metallicity, only a marginal trend with age, and no correlation with the α/Fe ratio. We explore the origin of the large scatter and conclude that neither aperture effects nor the UV upturn phenomenon contribute significantly. We show that the scatter could be attributed to simple ‘frosting’ by either a young or a low-metallicity subpopulation.
    Preview · Article · Feb 2008 · Monthly Notices of the Royal Astronomical Society
Show more