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Register a new userTowards a physical picture of star-formation quenching: the photometric properties of recently-quenched galaxies in the Sloan Digital Sky Survey
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J. Trevor Mendel
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We select a sample of young passive galaxies from the Sloan Digital Sky Survey Data Release 7 in order to study the processes that quench star formation in the local universe. Quenched galaxies are identified based on the contribution of A-type stars to their observed (central) spectra and relative lack of ongoing star formation; we find that such systems account for roughly 2.5 per cent of all galaxies with log M_sun >= 9.5, and have a space density of ~2.2x10^-4 Mpc^-3. We show that quenched galaxies span a range of morphologies, but that visual classifications suggest they are predominantly early-type systems. Their visual early-type classification is supported by quantitative structural measurements Sersic indices that show a notable lack of disk-dominated galaxies, suggesting that any morphological transformation associated with galaxies transition from star-forming to passive--e.g. the formation of a stellar bulge--occurs contemporaneously with the decline of their star-formation activity. We show that there is no clear excess of optical AGN in quenched galaxies, suggesting that: i) AGN feedback is not associated with the majority of quenched systems or ii) that the observability of quenched galaxies is such that the quenching phase in general outlives any associated nuclear activity. Comparison with classical post-starburst galaxies shows that both populations show similar signatures of bulge growth, and we suggest that the defining characteristic of post-starburst galaxies is the efficiency of their bulge growth rather than a particular formation mechanism.
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We study Red Misfits, a population of red, star-forming galaxies in the local Universe. We classify galaxies based on inclination-corrected optical colours and specific star formation rates derived from the Sloan Digital Sky Survey Data Release 7. Although the majority of blue galaxies are star-forming and most red galaxies exhibit little to no ongoing star formation, a small but significant population of galaxies ($sim$11 per cent at all stellar masses) are classified as red in colour yet actively star-forming. We explore a number of properties of these galaxies and demonstrate that Red Misfits are not simply dusty or highly-inclined blue cloud galaxies or quiescent red galaxies with poorly-constrained star formation. The proportion of Red Misfits is nearly independent of environment and this population exhibits both intermediate morphologies and an enhanced likelihood of hosting an AGN. We conclude that Red Misfits are a transition population, gradually quenching on their way to the red sequence and this quenching is dominated by internal processes rather than environmentally-driven processes. We discuss the connection between Red Misfits and other transition galaxy populations, namely S0s, red spirals and green valley galaxies.
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 Hbeta emission line or UV continua would modify the derived SFR densities in the early universe.
(abridged) We studied a large sample of ~14000 dwarf star-forming galaxies with strong emission lines selected from the Sloan Digital Sky Survey (SDSS) and distributed in the redshift range of z~0-0.6. We modelled spectral energy distributions (SED) of all galaxies which were based on the SDSS spectra in the visible range of 0.38-0.92 micron and included both the stellar and ionised gas emission. These SEDs were extrapolated to the UV and mid-infrared ranges to cover the wavelength range of 0.1-22 micron. The SDSS spectroscopic data were supplemented by photometric data from the GALEX, SDSS, 2MASS, WISE, IRAS, and NVSS all-sky surveys. We derived global characteristics of the galaxies, such as their element abundances, luminosities, and stellar masses. The luminosities and stellar masses range within the sample over ~5 orders of magnitude, thereby linking low-mass and low-luminosity blue compact dwarf (BCD) galaxies to luminous galaxies, which are similar to high-redshift Lyman-break galaxies (LBGs). The luminosity L(Hbeta) of the Hbeta emission line, a characteristic of the youngest stellar population with an age of a few Myr, is correlated with luminosities in other wavelength ranges. This implies that the most recent burst of star formation makes a significant contribution to the emission in the visible range and dominates in other wavelength ranges. We found 20 galaxies with very red WISE mid-infrared m(3.4micron)-m(4.6micron) colour (>2 mag), which suggests the important contribution of the hot (with a temperature of several hundred degree) dust emission in these galaxies. Our analysis of the balance between the luminosity in the WISE bands that covered a wavelength range of 3.4-22 micron and the luminosity of the emission absorbed at shorter wavelengths showed that the luminosity of the hot dust emission is increased with increasing L(Hbeta) and EW(Hbeta).
The Sloan Digital Sky Survey (SDSS) first data release provides a database of 106000 unique galaxies in the main galaxy sample with measured spectra. A sample of star-forming (SF) galaxies are identified from among the 3079 of these having 1.4 GHz luminosities from FIRST, by using optical spectral diagnostics. Using 1.4 GHz luminosities as a reference star formation rate (SFR) estimator insensitive to obscuration effects, the SFRs derived from the measured SDSS Halpha, [OII] and u-band luminosities, as well as far-infrared luminosities from IRAS, are compared. It is established that straightforward corrections for obscuration and aperture effects reliably bring the SDSS emission line and photometric SFR estimates into agreement with those at 1.4 GHz, although considerable scatter (~60%) remains in the relations. It thus appears feasible to perform detailed investigations of star formation for large and varied samples of SF galaxies through the available spectroscopic and photometric measurements from the SDSS. We provide herein exact prescriptions for determining the SFR for SDSS galaxies. The expected strong correlation between [OII] and Halpha line fluxes for SF galaxies is seen, but with a median line flux ratio F_[OII]/F_Halpha=0.23, about a factor of two smaller than that found in the sample of Kennicutt (1992). This correlation, used in deriving the [OII] SFRs, is consistent with the luminosity-dependent relation found by Jansen et al. (2001). The median obscuration for the SDSS SF systems is found to be A_Halpha=1.2 mag, while for the radio detected sample the median obscuration is notably higher, 1.6 mag, and with a broader distribution.
The Sloan Digital Sky Survey (SDSS) surveyed 14,555 square degrees, and delivered over a trillion pixels of imaging data. We present a study of galaxy clustering using 900,000 luminous galaxies with photometric redshifts, spanning between $z=0.45$ and $z=0.65$, constructed from the SDSS using methods described in Ross et al. (2011). This data-set spans 11,000 square degrees and probes a volume of $3h^{-3} rm{Gpc}^3$, making it the largest volume ever used for galaxy clustering measurements. We present a novel treatment of the observational systematics and its applications to the clustering signals from the data set. In this paper, we measure the angular clustering using an optimal quadratic estimator at 4 redshift slices with an accuracy of ~15% with bin size of delta_l = 10 on scales of the Baryon Acoustic Oscillations (BAO) (at l~40-400). We derive cosmological constraints using the full-shape of the power-spectra. For a flat Lambda CDM model, when combined with Cosmic Microwave Background Wilkinson Microwave Anisotropy Probe 7 (WMAP7) and H_0 constraints from 600 Cepheids observed by HST, we find Omega_Lambda = 0.73 +/- 0.019 and H_0 to be 70.5 +/- 1.6 km/s/Mpc. For an open Lambda CDM model, when combined with WMAP7 + HST, we find $Omega_K = 0.0035 +/- 0.0054, improved over WMAP7+HST alone by 40%. For a wCDM model, when combined with WMAP7+HST+SN, we find w = -1.071 +/- 0.078, and H_0 to be 71.3 +/- 1.7 km/s/Mpc, which is competitive with the latest large scale structure constraints from large spectroscopic surveys such as SDSS Data Release 7 (DR7) (Reid et al. 2010, Percival et al. 2010, Montesano et al. 2011) and WiggleZ (Blake et al. 2011). The SDSS-III Data Release 8 (SDSS-III DR8) Angular Clustering Data allows a wide range of investigations into the cosmological model, cosmic expansion (via BAO), Gaussianity of initial conditions and neutrino masses. (abridged)
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