We examine the properties of the host galaxies of 22 623 narrow‐line active galactic nuclei (AGN) with 0.02 < z < 0.3 selected from a complete sample of 122 808 galaxies from the Sloan Digital Sky Survey. We focus on the luminosity of the [O iii]λ5007 emission line as a tracer of the strength of activity in the nucleus. We study how AGN host properties compare with those of normal galaxies and how they depend on L[O iii]. We find that AGN of all luminosities reside almost exclusively in massive galaxies and have distributions of sizes, stellar surface mass densities and concentrations that are similar to those of ordinary early‐type galaxies in our sample. The host galaxies of low‐luminosity AGN have stellar populations similar to normal early types. The hosts of high‐luminosity AGN have much younger mean stellar ages. The young stars are not preferentially located near the nucleus of the galaxy, but are spread out over scales of at least several kiloparsecs. A significant fraction of high‐luminosity AGN have strong Hδ absorption‐line equivalent widths, indicating that they experienced a burst of star formation in the recent past. We have also examined the stellar populations of the host galaxies of a sample of broad‐line AGN. We conclude that there is no significant difference in stellar content between type 2 Seyfert hosts and quasars (QSOs) with the same [O iii] luminosity and redshift. This establishes that a young stellar population is a general property of AGN with high [O iii] luminosities.

We utilize Sloan Digital Sky Survey imaging and spectroscopy of ∼53,000 star-forming galaxies at z ∼ 0.1 to study the relation between stellar mass and gas-phase metallicity. We derive gas-phase oxygen abundances and stellar masses using new techniques which make use of the latest stellar evolutionary synthesis and photoionization models. We find a tight (±0.1 dex) correlation between stellar mass and metallicity spanning over 3 orders of magnitude in stellar mass and a factor of 10 in metallicity. The relation is relatively steep from 10 8.5 -10 10.5 M ⊙ h −2 70 , in good accord with known trends between luminosity and metallicity, but flattens above 10 10.5 M ⊙ . We use indirect estimates of the gas mass based on the Hα luminosity to compare our data to predictions from simple closed box chemical evolution models. We show that metal loss is strongly anti-correlated with baryonic mass, with low mass dwarf galaxies being 5 times more metal-depleted than L * galaxies at z ∼ 0.1. Evidence for metal depletion is not confined to dwarf galaxies, but is found in galaxies with masses as high as 10 10 M ⊙ . We interpret this as strong evidence both of the ubiquity of galactic winds and of their effectiveness in removing metals from galaxy potential wells.

We present a comprehensive study of the physical properties of ∼ 105 galaxies with measurable star formation in the Sloan Digital Sky Survey (SDSS). By comparing physical information extracted from the emission lines with continuum properties, we build up a picture of the nature of star‐forming galaxies at z < 0.2. We develop a method for aperture correction using resolved imaging and show that our method takes out essentially all aperture bias in the star formation rate (SFR) estimates, allowing an accurate estimate of the total SFRs in galaxies. We determine the SFR density to be 1.915+0.02−0.01 (random)+0.14−0.42 (systematic) h7010−2 M⊙ yr−1 Mpc−3 at z= 0.1 (for a Kroupa initial mass function) and we study the distribution of star formation as a function of various physical parameters. The majority of the star formation in the low‐redshift Universe takes place in moderately massive galaxies (1010–1011 M⊙), typically in high surface brightness disc galaxies. Roughly 15 per cent of all star formation takes place in galaxies that show some sign of an active nucleus. About 20 per cent occurs in starburst galaxies. By focusing on the SFR per unit mass we show that the present to past average SFR, the Scalo b‐parameter, is almost constant over almost three orders of magnitude in mass, declining only at M* > 1010 M⊙. The volume averaged b parameter is 0.408+0.005−0.002 (random)+0.029−0.090 (systematic)h−170. We use this value to constrain the star formation history of the Universe. For the concordance cosmology the present‐day Universe is forming stars at at least 1/3 of its past average rate. For an exponentially declining cosmic star formation history this corresponds to a time‐scale of 7+0.7−1.5 Gyr. In agreement with other work we find a correlation between b and morphological type, as well as a tight correlation between the 4000‐Å break (D4000) and b. We discuss how D4000 can be used to estimate b parameters for high‐redshift galaxies.

The Sloan Digital Sky Survey (SDSS) will provide the data to support detailed investigations of the distribution of luminous and non- luminous matter in the Universe: a photometrically and astrometrically calibrated digital imaging survey of pi steradians above about Galactic latitude 30 degrees in five broad optical bands to a depth of g' about 23 magnitudes, and a spectroscopic survey of the approximately one million brightest galaxies and 10^5 brightest quasars found in the photometric object catalog produced by the imaging survey. This paper summarizes the observational parameters and data products of the SDSS, and serves as an introduction to extensive technical on-line documentation.Comment: 9 pages, 7 figures, AAS Latex. To appear in AJ, Sept 200

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Using the photometric parallax method we estimate the distances to ∼48 million stars detected by the Sloan Digital Sky Survey (SDSS) and map their three-dimensional number density distribution in the Galaxy. The currently available data sample the distance range from 100 pc to 20 kpc and cover 6,500 deg 2 of sky, mostly at high galactic latitudes (|b| > 25). These stellar number density maps allow an investigation of the Galactic structure with no a priori assumptions about the functional form of its components. The data show strong evidence for a Galaxy consisting of an oblate halo, a disk component, and a number of localized overdensities. The number density distribution of stars as traced by M dwarfs in the Solar neighborhood (D < 2 kpc) is well fit by two exponential disks (the thin and thick disk) with scale heights and lengths, bias-corrected for an assumed 35% binary fraction, of H 1 = 300 pc and L 1 = 2600 pc, and H 2 = 900 pc and L 2 = 3600 pc, and local thick-tothin disk density normalization ρ thick (R ⊙ )/ρ thin (R ⊙ ) = 12%. We use the stars near main-sequence turnoff to measure the shape of the Galactic halo. We find a strong preference for oblate halo models, with best-fit axis ratio c/a = 0.64, ρ H ∝ r −2.8 power-law profile, and the local halo-to-thin disk normalization of 0.5%. Based on a series of Monte-Carlo simulations, we estimate the errors of derived model parameters not to be larger than ∼ 20% for the disk scales and ∼ 10% for the density normalization, with largest contributions to error coming from the uncertainty in calibration of the photometric parallax relation and poorly constrained binary fraction. While generally consistent with the above model, the measured density distribution shows a number of statistically significant localized deviations. In addition to known features, such as the Monoceros stream, we detect two overdensities in the thick disk region at cylindrical galactocentric radii and heights (R, Z) ∼ (6.5, 1.5) kpc and (R, Z) ∼ (9.5, 0.8) kpc, and a remarkable density enhancement in the halo covering over a thousand square degrees of sky towards the constellation of Virgo, at distances of ∼6-20 kpc. Compared to counts in a region symmetric with respect to the l = 0 • line and with the same Galactic latitude, the Virgo overdensity is responsible for a factor of 2 number density excess, and may be a nearby tidal stream or a low-surface brightness dwarf galaxy merging with the Milky Way. The u − g color distribution of stars associated with it implies metallicity lower than that of thick disk stars, and consistent with the halo metallicity distribution. After removal of the resolved overdensities, the remaining data are consistent with a smooth density distribution; we detect no evidence of further unresolved clumpy substructure at scales ranging from ∼ 50 pc in the disk, to ∼ 1 − 2 kpc in the halo.

We measure cosmological parameters using the three-dimensional power spectrum P (k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in combination with WMAP and other data. Our results are consistent with a "vanilla" flat adiabatic ΛCDM model without tilt (ns = 1), running tilt, tensor modes or massive neutrinos. Adding SDSS information more than halves the WMAP-only error bars on some parameters, tightening 1σ constraints on the Hubble parameter from h ≈ 0.74−0.03 , on the matter density from Ωm ≈ 0.25 ± 0.10 to Ωm ≈ 0.30 ± 0.04 (1σ) and on neutrino masses from < 11 eV to < 0.6 eV (95%). SDSS helps even more when dropping prior assumptions about curvature, neutrinos, tensor modes and the equation of state. Our results are in substantial agreement with the joint analysis of WMAP and the 2dF Galaxy Redshift Survey, which is an impressive consistency check with independent redshift survey data and analysis techniques. In this paper, we place particular emphasis on clarifying the physical origin of the constraints, i.e., what we do and do not know when using different data sets and prior assumptions. For instance, dropping the assumption that space is perfectly flat, the WMAP-only constraint on the measured age of the Universe tightens from t0 ≈ 16.3 +2.3 −1.8 Gyr to t0 ≈ 14.1Gyr by adding SDSS and SN Ia data. Including tensors, running tilt, neutrino mass and equation of state in the list of free parameters, many constraints are still quite weak, but future cosmological measurements from SDSS and other sources should allow these to be substantially tightened.

We analyze the bivariate distribution, in color versus absolute magnitude (uÀr vs. M r ), of a low-redshift sample of galaxies from the Sloan Digital Sky Survey (2400 deg 2 , 0:004 < z < 0:08, À23:5 < M r < À15:5). We trace the bimodality of the distribution from luminous to faint galaxies by fitting double Gaussians to the color functions separated in absolute magnitude bins. Color-magnitude (CM) relations are obtained for red and blue distributions (early-and late-type, predominantly field, galaxies) without using any cut in morphology. Instead, the analysis is based on the assumption of normal Gaussian distributions in color. We find that the CM relations are well fitted by a straight line plus a tanh function. Both relations can be described by a shallow CM trend (slopes of about À0.04, À0.05) plus a steeper transition in the average galaxy properties over about 2 mag. The midpoints of the transitions (M r ¼ À19:8 and À20.8 for the red and blue distributions, respectively) occur around 2 Â 10 10 M after converting luminosities to stellar mass. Separate luminosity functions are obtained for the two distributions. The red distribution has a more luminous characteristic magnitude and a shallower faint-end slope (M Ã ¼ À21:5, ¼ À0:8) compared to the blue distribution ( % À1:3, depending on the parameterization). These are approximately converted to galaxy stellar mass functions. The red distribution galaxies have a higher number density per magnitude for masses greater than about 3 Â 10 10 M . Using a simple merger model, we show that the differences between the two functions are consistent with the red distribution being formed from major galaxy mergers.