Halos around edge-on disk galaxies in the SDSS

We present a statistical analysis of halo emission for a sample of 1047 edge-on disk galaxies imaged in five bands by the Sloan Digital Sky Survey (SDSS). Stacking the homogeneously rescaled images of the galaxies, we can measure surface brightnesses as deep as mu_r~31 mag/arcsec^2. The results strongly support the almost ubiquitous presence of stellar halos around disk galaxies, whose spatial distribution is well described by a power-law $\rho\propto r^{-3}$, in a moderately flattened spheroid (c/a~0.6). The colour estimates in g-r and r-i, although uncertain, give a clear indication for extremely red stellar populations, hinting at old ages and/or non-negligible metal enrichment. These results support the idea of halos being assembled via early merging of satellite galaxies.Comment: 15 pages, 9 figures. Accepted for publication on MNRAS. Version with full resolution images available at http://www.mpa-garching.mpg.de/~zibetti/papers/halos_edgeon.pd

Three-Dimensional Genus Statistics of Galaxies in the SDSS Early Data Release

We present the first analysis of three-dimensional genus statistics for the SDSS EDR galaxy sample. Due to the complicated survey volume and the selection function, analytic predictions of the genus statistics for this sample are not feasible, therefore we construct extensive mock catalogs from N-body simulations in order to compare the observed data with model predictions. This comparison allows us to evaluate the effects of a variety of observational systematics on the estimated genus for the SDSS sample, including the shape of the survey volume, the redshift distortion effect, and the radial selection function due to the magnitude limit. The observed genus for the SDSS EDR galaxy sample is consistent with that predicted by simulations of a $\Lambda$-dominated spatially-flat cold dark matter model. Standard ($\Omega_0=1$) cold dark matter model predictions do not match the observations. We discuss how future SDSS galaxy samples will yield improved estimates of the genus.Comment: 20 pages, 10 figures, accepted for publication in PASJ (Vol.54, No.5, 2002

Mass growth and mergers: direct observations of the luminosity function of LRG satellite galaxies out to z=0.7 from SDSS and BOSS images

We present a statistical study of the luminosity functions of galaxies surrounding luminous red galaxies (LRGs) at average redshifts =0.34 and =0.65. The luminosity functions are derived by extracting source photometry around more than 40,000 LRGs and subtracting foreground and background contamination using randomly selected control fields. We show that at both studied redshifts the average luminosity functions of the LRGs and their satellite galaxies are poorly fitted by a Schechter function due to a luminosity gap between the centrals and their most luminous satellites. We utilize a two-component fit of a Schechter function plus a log-normal distribution to demonstrate that LRGs are typically brighter than their most luminous satellite by roughly 1.3 magnitudes. This luminosity gap implies that interactions within LRG environments are typically restricted to minor mergers with mass ratios of 1:4 or lower. The luminosity functions further imply that roughly 35% of the mass in the environment is locked in the LRG itself, supporting the idea that mass growth through major mergers within the environment is unlikely. Lastly, we show that the luminosity gap may be at least partially explained by the selection of LRGs as the gap can be reproduced by sparsely sampling a Schechter function. In that case LRGs may represent only a small fraction of central galaxies in similar mass halos.Comment: ApJ accepted versio

Blue horizontal branch stars in the Sloan Digital Sky Survey: II. Kinematics of the Galactic halo

We carry out a maximum-likelihood kinematic analysis of a sample of 1170 blue horizontal branch (BHB) stars from the Sloan Digital Sky Survey presented in Sirko et al. (2003) (Paper I). Monte Carlo simulations and resampling show that the results are robust to distance and velocity errors at least as large as the estimated errors from Paper I. The best-fit velocities of the Sun (circular) and halo (rotational) are 245.9 +/- 13.5 km/s and 23.8 +/- 20.1 km/s but are strongly covariant, so that v_0 - v_halo = 222.1 +/- 7.7 km/s. If one adopts standard values for the local standard of rest and solar motion, then the halo scarcely rotates. The velocity ellipsoid inferred for our sample is much more isotropic [(sigma_r,sigma_theta,sigma_phi) = (101.4 +/- 2.8, 97.7 +/- 16.4, 107.4 +/- 16.6) km/s] than that of halo stars in the solar neighborhood, in agreement with a recent study of the distant halo by Sommer-Larsen et al. (1997). The line-of-sight velocity distribution of the entire sample, corrected for the Sun's motion, is accurately gaussian with a dispersion of 101.6 +/- 3.0 km/s.Comment: 23 pages including 4 figures, 1 color; submitted to A

Intergalactic stars in z~0.25 galaxy clusters: systematic properties from stacking of Sloan Digital Sky Survey imaging data

We analyse the spatial distribution and colour of the intracluster light (ICL) in 683 clusters of galaxies between z=0.2 and 0.3, selected from approx 1500 deg^2 of the SDSS-DR1. Surface photometry in the g, r and i bands is conducted on stacked images of the clusters, after rescaling them to the same metric size and masking out resolved sources. We are able to trace the average surface brightness profile of the ICL out to 700 kpc, where it is less than 1/10,000 of the mean surface brightness of the dark night sky. The ICL appears as a clear surface brightness excess with respect to an inner R^1/4 profile which characterises the mean profile of the BCG. The surface brightness (SB) of the ICL ranges from 27.5 mag/arcsec^2 at 100 kpc to roughly 32 at 700 kpc in the observed r-band (26.5 to 31 in the rest-frame g-band). We find that, on average, the ICL contributes only a small fraction of the total optical emission in a cluster (10.9+-5.0% within 500 kpc). The radial distribution of the ICL is more centrally concentrated than that of the cluster galaxies, but the colours of the two components are identical within the statistical uncertainties. In the mean the ICL is aligned with and more flattened than the BCG itself. This alignment is substantially stronger than that of the cluster light as a whole. The SB of the ICL correlates both with BCG luminosity and with cluster richness, while the fraction of the total light in the ICL is almost independent of these quantities. These results support the idea that the ICL is produced by stripping and disruption of galaxies as they pass through the central regions of clusters. Our measurements of the diffuse light also constrain the faint-end slope of the cluster LF. Slopes alpha<-1.35 would imply more light from undetected galaxies than is observed in the diffuse component.Comment: 21 pages, 12 figures. Accepted for publication in MNRAS. Figures 3 and 4 degraded. Full resolution paper available at http://www.mpa-garching.mpg.de/~zibetti/ICL_paper.ps.g

Large Scale Clustering of Sloan Digital Sky Survey Quasars: Impact of the Baryon Density and the Cosmological Constant

We report the first result of the clustering analysis of Sloan Digital Sky Survey (SDSS) quasars. We compute the two-point correlation function (2PCF) of SDSS quasars in redshift space at $8h^{-1}{\rm Mpc} < s < 500h^{-1}{\rm Mpc}$, with particular attention to its baryonic signature. Our sample consists of 19986 quasars extracted from the SDSS Data Release 4 (DR4). The redshift range of the sample is $0.72 \le z \le 2.24$ (the mean redshift is $\bar z = 1.46$) and the reddening-corrected $i$-band apparent magnitude range is $15.0 \le m_{i,{\rm rc}} \le 19.1$. Due to the relatively low number density of the quasar sample, the bump in the power spectrum due to the baryon density, $\Omega_{\rm b}$, is not clearly visible. The effect of the baryon density is, however, to distort the overall shape of the 2PCF.The degree of distortion makes it an interesting alternate measure of the baryonic signature. Assuming a scale-independent linear bias and the spatially flat universe, i.e., $\Omega_{\rm b} + \Omega_{\rm d} + \Omega_\Lambda =1$, where $\Omega_{\rm d}$ and $\Omega_\Lambda$ denote the density parameters of dark matter and the cosmological constant, we combine the observed quasar 2PCF and the predicted matter 2PCF to put constraints on $\Omega_{\rm b}$ and $\Omega_\Lambda$. Our result is fitted as $0.80- 2.8\Omega_{\rm b} < \Omega_\Lambda < 0.90 - 1.4\Omega_{\rm b}$ at the 2$\sigma$ confidence level, which is consistent with results from other cosmological observations such as WMAP. (abridged)Comment: 26 pages, 12 figures, Accepted for publication in the PAS