A bulge-disk decomposition is made for 737 spiral and lenticular galaxies drawn from a Sloan Digital Sky Survey galaxy sample for which morphological types are estimated. We carry out the bulge-disk decomposition using the growth curve fitting method. It is found that bulge properties, effective radius, effective surface brightness, and also absolute magnitude, change systematically with the morphological sequence; from early to late types, the size becomes somewhat larger, and surface brightness and luminosity fainter. In contrast, disks are nearly universal, their properties remaining similar among disk galaxies irrespective of detailed morphologies from S0 to Sc. While these tendencies were often discussed in previous studies, the present study confirms them based on a large homogeneous magnitude-limited field galaxy sample with morphological types estimated. The systematic change of bulge-to-total luminosity ratio, B/T, along the morphological sequence is therefore not caused by disks but mostly by bulges. It is also shown that elliptical galaxies and bulges of spiral galaxies are unlikely to be in a single sequence. We infer the stellar mass density (in units of the critical mass density) to be Ω = 0.0021 for spheroids, i.e., elliptical galaxies plus bulges of spiral galaxies, and Ω = 0.00081 for disks.

We present a catalog of morphologically classified bright galaxies in the north equatorial stripe (230 deg2) derived from the Third Data Release of the Sloan Digital Sky Survey (SDSS). Morphological classification is performed by visual inspection of images in the g band. The catalog contains 2253 galaxies complete to a magnitude limit of r = 16 after Galactic extinction correction, selected from 2658 objects that are judged to be extended in the photometric catalog in the same magnitude limit. A total of 1866 galaxies in our catalog have spectroscopic information. A brief statistical analysis is presented for the frequency of morphological types and mean colors in the catalog. A visual inspection of the images reveals that the rate of interacting galaxies in the local universe is approximately 1.5% in the r ≤ 16 sample. A verification is made for the photometric catalog generated by the SDSS, especially as to its brightend completeness. © 2007. The American Astronomical Society. All rights reserved.

We present elemental abundance measurements for nine damped Lyman α (Lyα) systems (DLAs) and one sub-DLA at 0.1 ≤ z ≤ 1.5 from recent observations with the Multiple Mirror Telescope (MMT). Most of these absorbers are found to be metal poor, while two are found to have ≈30-50 per cent solar metallicities. Combining our data with other data from the literature, we find that the systems with higher [Zn/H] also have stronger depletion as measured by [Cr/Zn] and [Fe/Zn]. The relationship between the metallicity and Hi column density is also investigated. Together with our previous MMT survey, we have discovered two of the four known absorbers at z < 1.5 that lie above (although near) the 'obscuration threshold'. This appears to be a result of selecting absorbers with strong metal lines in our sample. It would be interesting to find other similar systems by observing a larger sample and study how much such systems contribute to the cosmic budget of metals. Finally, an analysis of the NHI-weighted mean metallicity versus redshift for our sample combined with data from the literature supports previous conclusions that the NHI-weighted mean global DLA metallicity rises slowly at best and falls short of solar levels by a factor of >4 even at z = 0. © 2006 RAS.

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 , in clusters with redshifts in the range , with a median of . 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 and [O iii]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. © 2006 RAS.

We derive oxygen abundances for a sample of 40 luminous (MB ≲ -19), star-forming, mostly disc, field galaxies with redshifts in the range 0.2 ≲ z ≲ 0.8, with a median of 〈z〉 = 0.45. Oxygen abundances, relative to hydrogen, of the interstellar emitting gas are estimated by means of the empirically calibrated strong emission-line ratio technique. The derived 12 + log (O/H) values range from 8.4 to 9.0, with a median of 8.7. Twenty of these galaxies have securely measured rotation velocities, in the range 50-244 km s-1. The measured emission-line equivalent widths and diagnostic ratios for the intermediate redshift galaxies cover similar ranges to those observed across a large sample of local galaxies. The estimated oxygen abundances for our luminous star-forming intermediate redshift galaxies cover the same range as their local counterparts. However, at a given galaxy luminosity, many of our galaxies have significantly lower oxygen abundances, i.e. 12 + log (O/H) ∼8.6, than local galaxies with similar luminosities. Interestingly, these luminous, massive, intermediate redshift, star-forming galaxies with low oxygen abundances exhibit physical conditions, i.e. emission-line equivalent width and ionization state, very similar to those of local faint and metal-poor star-forming galaxies. The oxygen abundance of the interstellar gas does not seem to correlate with the maximum rotation velocity or the emission scalelength of the parent galaxy. This suggests that there is diversity in the intrinsic properties of the massive field galaxy population at intermediate redshifts. The distribution of the colour excess, derived from the ratio of extinction-uncorrected Hβ and [O II]λ3727 star formation rate indicators, covers a similar range to that observed locally, but exhibits a lower mean than is observed for local optically selected star-forming galaxies. Luminous field galaxies at intermediate redshifts show similar star formation rates to their local counterparts. However, metal-poor, massive, star-forming galaxies tend to be systematically less affected by internal reddening than metal-rich, massive galaxies, which cover similar range of colour excess to local metal-rich luminous galaxies. Finally, the correlation between oxygen abundance and colour excess for intermediate redshift galaxies is found to be similar to what is observed locally. This result indicates that the dust content of galaxies is more regulated by their chemical evolution rather than by galaxy luminosity. © 2006 RAS.

We have carried out spectroscopic observations in four cluster fields using Subaru's FOCAS multislit spectrograph and obtained spectra for 103 bright disc field and cluster galaxies at 0.06 &lt;= z &lt;= 1.20. 77 of these show emission lines, and 33 provide reasonably secure determinations of the galaxies' rotation velocity. The rotation velocities, luminosities, colours and emission-line properties of these galaxies are used to study the possible effects of the cluster environment on the star formation history of the galaxies. Comparing the Tully-Fisher relations of cluster and field galaxies at similar redshifts we find no measurable difference in rest-frame B-band luminosity at a given rotation velocity (the formal difference is 0.18 +/- 0.33). The colours of the cluster emission line galaxies are only marginally redder in rest-frame B-V(by 0.06 +/- 0.04 mag) than the field galaxies in our sample. Taken at face value, these results seem to indicate that bright star-forming cluster spirals are similar to their field counterparts in their star formation properties. However, we find that the fraction of disc galaxies with absorption-line spectra (i.e. with no current star formation) is larger in clusters than in the field by a factor of similar to 3-5. This suggests that the cluster environment has the overall effect of switching off star formation in (at least) some spiral galaxies. To interpret these observational results, we carry out simulations of the possible effects of the cluster environment on the star formation history of disc galaxies and thus their photometric and spectroscopic properties. This allows us to create mock samples of unperturbed 'field' galaxies [with approximately constant star formation rates (SFRs)] and perturbed 'cluster' galaxies with different star formation histories, including star formation truncation, with or without an associated starburst. We show that, if we select only bright galaxies with current star formation (i.e. with emission lines strong enough for rotation-curve measurements), the average colours and luminosities of the 'cluster' galaxies may not be very different from those of galaxies in the 'field' sample, even though their star formation histories may be significantly different. However, the fraction of emission and absorption-line galaxies would change significantly. We also use these simulations to estimate the size of field and cluster galaxy samples that would allow us to differentiate the different star formation scenarios considered. Finally, we find that the rest-frame absolute B-band magnitude of the field galaxies in our sample shows an evolution of -1.30 +/- 1.04 mag per unit redshift at fixed rotation velocity. This indicates that the average SFR of bright disc galaxies evolves more slowly than the universal SFR as determined from ultraviolet, H alpha, far-infrared and radio studies. This suggests the evolution of the universal SFR density is not dominated by bright star-forming disc galaxies, in agreement with previous studies.

We devise improved photometric parameters for the morphological classification of galaxies using a bright sample from the First Data Release of the Sloan Digital Sky Survey. In addition to using an elliptical aperture concentration index for classification, we introduce a new texture parameter, coarseness, which quantifies deviations from smooth galaxy isophotes. The elliptical aperture concentration index produces morphological classifications that are in appreciably better agreement with visual classifications than those based on circular apertures. With the addition of the coarseness parameter, the success rate of classifying galaxies into early and late types increases to ≃88% with respect to the reference visual classification. A reasonably high success rate (≃68%) is also attained in classifying galaxies into three types, early-type galaxies (E+S0) and early-type (Sa+Sb) and late-type (Sc+Sdm+Im) spiral galaxies. © 2005. The American Astronomical Society. All rights reserved.

We study the luminosity and color dependence of the galaxy two-point correlation function in the Sloan Digital Sky Survey, starting from a sample of ∼200,000 galaxies over 2500 deg2. We concentrate our analysis on volume-limited subsamples of specified luminosity ranges, for which we measure the projected correlation function wp(rp), which is directly related to the real-space correlation function ξ(r). The amplitude of wp(rp) rises continuously with luminosity from M r ≈ -17.5 to Mr ≈ -22.5, with the most rapid increase occurring above the characteristic luminosity L* (Mr ≈ -20.5). Over the scales 0.1 h-1 Mpc < rp < 10 h-1 Mpc, the measurements for samples with Mr > -22 can be approximated, imperfectly, by power-law three-dimensional correlation functions ξ(r) = (r/r0)-γ with γ ≈ 1.8 and r0(L*) ≈ 5.0 h-1 Mpc. The brightest subsample, -23 < Mr < -22, has a significantly steeper ξ(r). When we divide samples by color, redder galaxies exhibit a higher amplitude and steeper correlation function at all luminosities. The correlation amplitude of blue galaxies increases continuously with luminosity, but the luminosity dependence for red galaxies is less regular, with bright red galaxies exhibiting the strongest clustering at large scales and faint red galaxies exhibiting the strongest clustering at small scales. We interpret these results using halo occupation distribution (HOD) models assuming concordance cosmological parameters. For most samples, an HOD model with two adjustable parameters fits the wp(rp) data better than a power law, explaining inflections at rp ∼ 1-3 h-1 Mpc as the transition between the one-halo and two-halo regimes of ξ(r). The implied minimum mass for a halo hosting a central galaxy more luminous than L grows steadily, with Mmin ∝ L at low luminosities and a steeper dependence above L*. The mass at which a halo has, on average, one satellite galaxy brighter than L is M1 ≈ 23Mmin(L), at all luminosities. These results imply a conditional luminosity function (at fixed halo mass) in which central galaxies lie far above a Schechter function extrapolation of the satellite population. The HOD model fits nicely explain the color dependence of wp(rp) and the cross correlation between red and blue galaxies. For galaxies with Mr < -21, halos slightly above M min have blue central galaxies, while more massive halos have red central galaxies and predominantly red satellite populations. The fraction of blue central galaxies increases steadily with decreasing luminosity and host halo mass. The strong clustering of faint red galaxies follows from the fact that nearly all of them are satellite systems in high-mass halos. The HOD fitting results are in good qualitative agreement with the predictions of numerical and semianalytic models of galaxy formation. © 2005. The American Astronomical Society. All rights reserved.

We report on spectroscopic observations with the Multiple Mirror Telescope for 11 damped Lyα absorbers (DLAs) or strong DLA candidates at 0.1 < z < 1.5, including several absorbers discovered in the Sloan Digital Sky Survey. In particular, we have measured absorption lines of Zn II, Cr II, Ni II, Fe II, Mn II, Ti II, Ca II, and Si II. These measurements have doubled the sample of Zn and Cr measurements at z < 1. The average relative abundance patterns in these objects are very similar to those found for high-redshift DLAs reported in the literature. Our observations suggest that the dust content, as determined by [Cr/Zn], does not show much change with redshift. We also examine the sample for correlation of [Cr/Zn] with estimates of the quasar reddening. Our data suggest that the global mean metallicity of DLAs, as measured by the gas-phase abundance of Zn, at best shows a weak evolution with redshift over the range 0.4 < z < 3.9.

We present a study of the Halpha line emission from a sample of 1482 optically selected, morphologically classified bright galaxies (median redshift of 0.05) derived from the Sloan Digital Sky Survey. The luminosity function is calculated for each morphological class and for the total sample. The luminosity function fitted with the Schechter form gives a slope alpha = -1.43 +/- 0.10 for the total sample, and the Halpha luminosity density is 10(-0.07)(39.31 +/- 0.04)(+0.10) h ergs s(-1) Mpc(-3), where the first error is statistical and the second is systematic. This value is consistent with that derived by Gallego et al. in 1995, but this agreement is caused by a fortuitous cancellation of their neglect of stellar absorption that affects the estimate of extinction corrections and a significant sample incompleteness of emission-line galaxies. The fraction of Halpha emitters monotonically increases from early ( a few percent for elliptical galaxies) to late types (100% for irregular galaxies), whereas strong emitters exist in all classes of morphological types. We find that 83% of the luminosity density comes from spiral galaxies, 5% from irregular galaxies, and 9% from early-type galaxies; a small number of morphologically disturbed galaxies contribute by 3%.

We present an investigation of the environment (≈600 kpc radius) of a pair of luminous z = 4.25 quasars, SDSS J1439-0034A and B, separated by 33″. An analysis of high-quality Subaru spectra of the quasars suggests that this configuration is indeed a physical pair and not a gravitational lens; the redshifts are slightly different (although marginally consistent with being the same), and the two spectra have strikingly different features. We search for bright galaxies (L ≳ 0.4L*) having similar redshifts using the V dropout technique and semi-narrowband imaging looking for strong Lyα emission. We find no enhancement in the galaxy density around the quasar pair; its environment differs very little from a general field, with the upper limit of the density enhancement being about 3.5 at a 90% confidence. We infer that bright quasars happened to appear in two normal galaxies in a general field.

Supervised artificial neural networks are used to predict useful properties of galaxies in the Sloan Digital Sky Survey, in this instance morphological classifications, spectral types and redshifts. By giving the trained networks unseen data, it is found that correlations between predicted and actual properties are around 0.9 with rms errors of order ten per cent. Thus, given a representative training set, these properties may be reliably estimated for galaxies in the survey for which there are no spectra and without human intervention.

We report the discovery of actively star-forming elliptical galaxies in a morphologically classified sample of bright galaxies at a low redshift obtained from the Sloan Digital Sky Survey. The emission lines of these galaxies do not show the characteristics of active galactic nuclei, and thus their strong Hα emission is ascribed to star formation with a rate nearly as high as that seen in typical late spiral galaxies. This is taken as evidence against the traditional view that all elliptical galaxies formed early and now evolve only passively. The frequency of such star-forming elliptical galaxies is a few tenths of a percent in the sample but increases to 3% if we include active S0 galaxies. We can identify these galaxies as probable progenitors of so-called E+A galaxies that show the strong Balmer absorption feature of A stars superimposed on an old star population. The approximate match of the abundance of active elliptical plus S0 galaxies to that of E+A galaxies indicates that the duration of such late star formation episodes is of the order of ≲1 Gyr. If we interpret these galaxies as new additions to the early-type galaxy population, and if we assume a power law for their number evolution, the abundance of early-type galaxies at z = 1 is about 30% less than that at z = 0.

The morphological dependence of the luminosity function is studied, using a sample containing approximately 1500 bright galaxies classified into Hubble types by visual inspection, for a homogeneous sample obtained from the Sloan Digital Sky Survey northern equatorial stripes. Early-type galaxies are shown to have a characteristic magnitude 0.45 mag brighter than that of spiral galaxies in the r* band, consistent with the "universal characteristic luminosity'' in the B band. The shape of the luminosity function differs rather little among different morphological types: we do not see any symptoms of the sharp decline in the faint end of the luminosity function for early-type galaxies at least 2 mag fainter than the characteristic magnitude, although the faint-end behavior shows a slight decline (alpha less than or similar to -1) compared with the total sample. We also show that the rather. at faint-end slope for early-type galaxies is not due to an increasing mixture of dwarf galaxies, which have softer cores. This means that there are numerous faint early-type galaxies with highly concentrated cores.

We combine Sloan Digital Sky Survey spectra of 22,000 luminous, red, bulge-dominated galaxies to get high signal-to-noise ratio average spectra in the rest-frame optical and ultraviolet (2600-7000 A). The average spectra of these massive, quiescent galaxies are early type with weak emission lines and with absorption lines indicating an apparent excess of α-elements over solar abundance ratios. We make average spectra of subsamples selected by luminosity, environment, and redshift. The average spectra are remarkable in their similarity. What variations do exist in the average spectra as a function of luminosity and environment are found to form a nearly one-parameter family in spectrum space. We present a high signal-to-noise ratio spectrum of the variation. We measure the properties of the variation with a modified version of the Lick index system and compare to model spectra from stellar population syntheses. The variation may be a combination of age and chemical abundance differences, but the conservative conclusion is that the quality of the data considerably exceeds the current state of the models.

We explore the origin of the color-magnitude relation (CMR) of early-type galaxies in the Virgo Cluster using spectra of very high signal-to-noise ratio for six elliptical galaxies selected along the CMR. The data are analyzed using a new evolutionary stellar population synthesis model to generate galaxy spectra at the resolution given by their velocity dispersions. In particular, we use a new age indicator that is virtually free of the effects of metallicity. We find that the luminosity-weighted mean ages of Virgo ellipticals are greater than ∼8 Gyr and show no clear trend with galaxy luminosity. We also find a positive correlation of metallicity with luminosity, color, and velocity dispersion. We conclude that the CMR is driven primarily by a luminosity-metallicity correlation. However, not all elements increase equally with the total metallicity, and we speculate that the CMR may be driven by both a total metallicity increase and a systematic departure from solar abundance ratios of some elements along the CMR. A full understanding of the role played by the total metallicity, abundance ratios, and age in generating the CMR requires the analysis of spectra of very high quality, such as those reported here, for a larger number of galaxies in Virgo and other clusters.