[en] Passive red galaxies frequently contain warm ionized gas and have spectra similar to low-ionization nuclear emission-line regions (LINERs). Here we investigate the nature of the ionizing sources powering this emission, by comparing nuclear spectroscopy from the Palomar survey with larger aperture data from the Sloan Digital Sky Survey. We find the line emission in the majority of passive red galaxies is spatially extended; the Hα surface brightness profile depends on radius r as r^–1.28. We detect strong line ratio gradients with radius in [N II]/Hα, [S II]/Hα, and [O III]/[S II], requiring the ionization parameter to increase outward. Combined with a realistic gas density profile, this outward increasing ionization parameter convincingly rules out active galactic nuclei (AGNs) as the dominant ionizing source and strongly favors distributed ionizing sources. Sources that follow the stellar density profile can additionally reproduce the observed luminosity dependence of the line ratio gradient. Post-asymptotic giant branch stars provide a natural ionization source candidate, though they have an ionization parameter deficit. Velocity width differences among different emission lines disfavor shocks as the dominant ionization mechanism, and suggest that the interstellar medium in these galaxies contains multiple components. We conclude that the line emission in most LINER-like galaxies found in large-aperture (>100 pc) spectroscopy is not primarily powered by AGN activity and thus does not trace the AGN bolometric luminosity. However, they can be used to trace warm gas in these red galaxies.

[en] We measure the mass growth rate by merging for a wide range of galaxy types. We present the small-scale (0.014 h ^–1₇₀ Mpc < r < 11 h ₇₀^–1 Mpc) projected cross-correlation functions w(r _p) of galaxy subsamples from the spectroscopic sample of the NYU Value-Added Galaxy Catalog (5 × 10⁵ galaxies of redshifts 0.03 < z < 0.15) with galaxy subsamples from the Sloan Digital Sky Survey imaging (4 × 10⁷ galaxies). We use smooth fits to de-project the two-dimensional functions w(r _p) to obtain smooth three-dimensional real-space cross-correlation functions ξ(r) for each of several spectroscopic subsamples with each of several imaging subsamples. Because close pairs are expected to merge, the three-space functions and dynamical evolution time estimates provide galaxy accretion rates. We find that the accretion onto massive blue galaxies and onto red galaxies is dominated by red companions, and that onto small-mass blue galaxies, red and blue galaxies make comparable contributions. We integrate over all types of companions and find that at fixed stellar mass, the total fractional accretion rates onto red galaxies (∼3 h ₇₀ percent per Gyr) are greater than that onto blue galaxies (∼1 h ₇₀ percent per Gyr). These rates are almost certainly overestimates because we have assumed that all close pairs merge as quickly as the merger time that we used. One conclusion of this work is that if the total growth of red galaxies from z = 1 to z = 0 is mainly due to merging, the merger rates must have been higher in the past.

[en] We infer stellar metallicity and abundance ratio gradients for a sample of red galaxies in the Sloan Digital Sky Survey (SDSS) Main galaxy sample. Because this sample does not have multiple spectra at various radii in a single galaxy, we measure these gradients statistically. We separate galaxies into stellar mass bins, stack their spectra in redshift bins, and calculate the measured absorption-line indices in projected annuli by differencing spectra in neighboring redshift bins. After determining the line indices, we use stellar population modeling from the EZ_Ages software to calculate ages, metallicities, and abundance ratios within each annulus. Our data cover the central regions of these galaxies, out to slightly higher than $1R_{\mathrm{e}}$. We find detectable gradients in metallicity and relatively shallow gradients in abundance ratios, similar to results found for direct measurements of individual galaxies. The gradients are only weakly dependent on stellar mass, and this dependence is well correlated with the change of R_e with mass. Based on these data, we report mean equivalent widths, metallicities, and abundance ratios as a function of mass and velocity dispersion for SDSS early-type galaxies, for fixed apertures of 2.5 kpc and of 0.5R_e.

[en] We describe a procedure for background subtracting Sloan Digital Sky Survey (SDSS) imaging that improves the resulting detection and photometry of large galaxies on the sky. Within each SDSS drift scan run, we mask out detected sources and then fit a smooth function to the variation of the sky background. This procedure has been applied to all SDSS-III Data Release 8 images, and the results are available as part of that data set. We have tested the effect of our background subtraction on the photometry of large galaxies by inserting fake galaxies into the raw pixels, reanalyzing the data, and measuring them after background subtraction. Our technique results in no size-dependent bias in galaxy fluxes up to half-light radii r₅₀ ∼ 100 arcsec; in contrast, for galaxies of that size the standard SDSS photometric catalog underestimates fluxes by about 1.5 mag. Our results represent a substantial improvement over the standard SDSS catalog results and should form the basis of any analysis of nearby galaxies using the SDSS imaging data.

[en] Many classes of active galactic nuclei (AGNs) have been observed and recorded since the discovery of Seyfert galaxies. In this paper, we examine the sample of luminous galaxies in the Baryon Oscillation Spectroscopic Survey. We find a potentially new observational class of AGNs, one with strong and broad Mg II λ2799 line emission, but very weak emission in other normal indicators of AGN activity, such as the broad-line Hα, Hβ, and the near-ultraviolet AGN continuum, leading to an extreme ratio of broad Hα/Mg II flux relative to normal quasars. Meanwhile, these objects' narrow-line flux ratios reveal AGN narrow-line regions with levels of activity consistent with the Mg II fluxes and in agreement with that of normal quasars. These AGN may represent an extreme case of the Baldwin effect, with very low continuum and high equivalent width relative to typical quasars, but their ratio of broad Mg II to broad Balmer emission remains very unusual. They may also be representative of a class of AGN where the central engine is observed indirectly with scattered light. These galaxies represent a small fraction of the total population of luminous galaxies (≅ 0.1%), but are more likely (about 3.5 times) to have AGN-like nuclear line emission properties than other luminous galaxies. Because Mg II is usually inaccessible for the population of nearby galaxies, there may exist a related population of broad-line Mg II emitters in the local universe which is currently classified as narrow-line emitters (Seyfert 2 galaxies) or low ionization nuclear emission-line regions.

[en] The attenuation of starlight by interstellar dust is investigated in a sample of low-redshift, disk-dominated star-forming galaxies using photometry from GALEX and SDSS. By considering broadband colors as a function of galaxy inclination, we are able to confidently separate trends arising from increasing dust opacity from possible differences in stellar populations, since stellar populations do not correlate with inclination. We are thus able to make firm statements regarding the wavelength-dependent attenuation of starlight for disk-dominated galaxies as a function of gas-phase metallicity and stellar mass. All commonly employed dust attenuation curves (such as the Calzetti curve for starbursts, or a power-law curve) provide poor fits to the ultraviolet colors for moderately and highly inclined galaxies. This conclusion rests on the fact that the average FUV-NUV color varies little from face-on to edge-on galaxies, while other colors such as NUV-u and u - r vary strongly with inclination. After considering a number of model variations, we are led to speculate that the presence of the strong dust extinction feature at 2175 A seen in the Milky Way extinction curve is responsible for the observed trends. If the 2175 A feature is responsible, these results would constitute the first detection of the feature in the attenuation curves of galaxies at low redshift. Independent of our interpretation, these results imply that the modeling of dust attenuation in the ultraviolet is significantly more complicated than traditionally assumed. These results also imply a very weak dependence of the FUV-NUV color on total FUV attenuation, and we conclude from this that it is extremely difficult to use only the observed UV spectral slope to infer the total UV dust attenuation, as is commonly done. We propose several simple tests that might finally identify the grain population responsible for the 2175 A feature.

[en] We measure the evolution of the [O II] λ3727 luminosity function (LF) at 0.75 < z < 1.45 using high-resolution spectroscopy of ∼14,000 galaxies observed by the Deep Extragalactic Evolutionary Probe 2 galaxy redshift survey. We find that brighter than L_[OII]=10⁴² erg s^-1 the LF is well represented by a power law dN/dL ∝ L ^α with slope α ∼ -3. The number density of [O II]-emitting galaxies above this luminosity declines by a factor of ∼>2.5 between z ∼ 1.35 and z ∼ 0.84. In the limit of no number-density evolution, the characteristic [O II] luminosity, L_[OII]*, defined as the luminosity where the space density equals 10^-3.5 dex^-1 Mpc^-3, declines by a factor of ∼1.8 over the same redshift interval. Assuming that L_[OII] is proportional to the star formation rate (SFR), and negligible change in the typical dust attenuation in galaxies at fixed [O II] luminosity, the measured decline in L_[OII]* implies a ∼25% per Gyr decrease in the amount of star formation in galaxies during this epoch. Adopting a faint-end power-law slope of -1.3 ± 0.2, we derive the comoving SFR density in four redshift bins centered around z ∼ 1 by integrating the observed [O II] LF using a local, empirical calibration between L_[OII] and SFR, which statistically accounts for variations in dust attenuation and metallicity among galaxies. We find that our estimate of the SFR density at z ∼ 1 is consistent with previous measurements based on a variety of independent SFR indicators.

[en] We study the baryon content of low-mass galaxies selected from the Sloan Digital Sky Survey (SDSS DR8), focusing on galaxies in isolated environments where the complicating physics of galaxy–galaxy interactions are minimized. We measure neutral hydrogen (HI) gas masses and line widths for 148 isolated galaxies with stellar mass between 10⁷ and ${10}^{9.5}{M}_{\odot <!--\; ???\; -->}$. We compare isolated low-mass galaxies to more massive galaxies and galaxies in denser environments by remeasuring HI emission lines from the Arecibo Legacy Fast ALFA survey 40% data release. All isolated low-mass galaxies either have large atomic gas fractions or large atomic gas fractions cannot be ruled out via their upper limits. We measure a median atomic gas fraction of $f_{\mathrm{g}\mathrm{a}\mathrm{s}}=0.81\pm <!--\; ??\; -->0.13$ for our isolated low-mass sample with no systems below 0.30. At all stellar masses, the correlations between galaxy radius, baryonic mass, and velocity width are not significantly affected by environment. Finally, we estimate a median baryon to total dynamical mass fraction of $f_{\mathrm{b}\mathrm{a}\mathrm{r}\mathrm{y}\mathrm{o}\mathrm{n},\mathrm{d}\mathrm{i}\mathrm{s}\mathrm{k}}=0.15\pm <!--\; ??\; -->0.17$. We also estimate two different median baryon to halo mass fractions using the results of semi-analytic models $(f_{\mathrm{b}\mathrm{a}\mathrm{r}\mathrm{y}\mathrm{o}\mathrm{n},\mathrm{h}\mathrm{a}\mathrm{l}\mathrm{o}}=0.04\pm <!--\; ??\; -->0.06)$ and abundance matching $(f_{\mathrm{b}\mathrm{a}\mathrm{r}\mathrm{y}\mathrm{o}\mathrm{n},\mathrm{h}\mathrm{a}\mathrm{l}\mathrm{o}}=0.04\pm <!--\; ??\; -->0.02)$. Baryon fractions estimated directly using HI observations appear independent of environment and maximum circular velocity, while baryon fractions estimated using abundance matching show a significant depletion of baryons at low maximum circular velocities.

[en] We study the optical properties of the host galaxies of nuclear 22 GHz (λ = 1.35 cm) water masers. To do so, we cross-match the galaxy sample surveyed for water maser emission (123 detections and 3806 non-detections) with the Sloan Digital Sky Survey (SDSS) low-redshift galaxy sample (z < 0.05). Out of 1636 galaxies with SDSS photometry, we identify 48 detections; out of the 1063 galaxies that also have SDSS spectroscopy, we identify 33 detections. We find that maser detection rate is higher at higher optical luminosity (M_B ), larger velocity dispersion (σ), and higher [O III] λ5007 luminosity, with [O III] λ5007 being the dominant factor. These detection rates are essentially the result of the correlations of isotropic maser luminosity with all three of these variables. These correlations are natural if maser strength increases with central black hole mass and the level of active galactic nucleus (AGN) activity. We also find that the detection rate is higher in galaxies with higher extinction. Based on these results, we propose that maser surveys seeking to efficiently find masers should rank AGN targets by extinction-corrected [O III] λ5007 flux when available. This prioritization would improve maser detection efficiency, from an overall ∼3% without pre-selection to ∼16% for the strongest intrinsic [O III] λ5007 emitters, by a factor of ∼5.

[en] We present the large-scale correlation function measured from a spectroscopic sample of 46,748 luminous red galaxies from the Sloan Digital Sky Survey. The survey region covers 0.72h^-3 Gpc³ over 3816 square degrees and 0.16 < z < 0.47, making it the best sample yet for the study of large-scale structure. We find a well-detected peak in the correlation function at 100h^-1 Mpc separation that is an excellent match to the predicted shape and location of the imprint of the recombination-epoch acoustic oscillations on the low-redshift clustering of matter. This detection demonstrates the linear growth of structure by gravitational instability between z ∼ 1000 and the present and confirms a firm prediction of the standard cosmological theory. The acoustic peak provides a standard ruler by which we can measure the ratio of the distances to z = 0.35 and z = 1089 to 4% fractional accuracy and the absolute distance to z = 0.35 to 5% accuracy. From the overall shape of the correlation function, we measure the matter density (Omega)_mh² to 8% and find agreement with the value from cosmic microwave background (CMB) anisotropies. Independent of the constraints provided by the CMB acoustic scale, we find (Omega)_m = 0.273 ± 0.025 + 0.123(1 + w₀) + 0.137(Omega)_K. Including the CMB acoustic scale, we find that the spatial curvature is (Omega)_K = -0.010 ± 0.009 if the dark energy is a cosmological constant. More generally, our results provide a measurement of cosmological distance, and hence an argument for dark energy, based on a geometric method with the same simple physics as the microwave background anisotropies. The standard cosmological model convincingly passes these new and robust tests of its fundamental properties