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We present a sample of 723 optically selected BL Lac candidates from the SDSS DR7 spectroscopic database encompassing 8250 deg^2 of sky; our sample constitutes one of the largest uniform BL Lac samples yet derived. Each BL Lac candidate has a high-quality SDSS spectrum from which we determine spectroscopic redshifts for ~60% of the objects. Redshift lower limits are estimated for the remaining objects utilizing the lack of host galaxy flux contamination in their optical spectra; we find that objects lacking spectroscopic redshifts are likely at systematically higher redshifts. Approximately 80% of our BL Lac candidates match to a radio source in FIRST/NVSS, and ~40% match to a ROSAT X-ray source. The homogeneous multiwavelength coverage allows subdivision of the sample into 637 radio-loud BL Lac candidates and 86 weak-featured radio-quiet objects. The radio-loud objects broadly support the standard paradigm unifying BL Lac objects with beamed radio galaxies. We propose that the majority of the radio-quiet objects may be lower-redshift (z, 24 pages, 14 figures, 8 tables. Accepted for publication in AJ

We analyze the SDSS Ly-alpha forest P_F(k,z) measurement to determine the linear theory power spectrum. Our analysis is based on fully hydrodynamic simulations, extended using hydro-PM simulations. We account for the effect of absorbers with damping wings, which leads to an increase in the slope of the linear power spectrum. We break the degeneracy between the mean level of absorption and the linear power spectrum without significant use of external constraints. We infer linear theory power spectrum amplitude Delta^2_L(k_p=0.009s/km,z_p=3.0)=0.452_{-0.057-0.116}^{+0.069+0.141} and slope n_eff=-2.321_{-0.047-0.102}^{+0.055+0.131} (possible systematic errors are included through nuisance parameters in the fit - a factor >~5 smaller errors would be obtained on both parameters if we ignored modeling uncertainties). The errors are correlated and not perfectly Gaussian, so we provide a chi^2 table to accurately describe the results. The result corresponds to sigma_8=0.85, n=0.94, for a LCDM model with Omega_m=0.3, Omega_b=0.04, and h=0.7, but is most useful in a combined fit with the CMB. The inferred curvature of the linear power spectrum and the evolution of its amplitude and slope with redshift are consistent with expectations for LCDM models, with the evolution of the slope, in particular, being tightly constrained. We use this information to constrain systematic contamination, e.g., fluctuations in the UV background. This paper should serve as a starting point for more work to refine the analysis, including technical improvements such as increasing the size and number of the hydrodynamic simulations, and improvements in the treatment of the various forms of feedback from galaxies and quasars., Improved presentation, including fit results for (z). Simple code to produce LyaF chi^2 given linear power spectrum available at: http://www.cita.utoronto.ca/~pmcdonal/code.html

Using photometry and spectroscopy of 183,487 galaxies from the Sloan Digital Sky Survey, we present bivariate distributions of pairs of seven galaxy properties: four optical colors, surface brightness, radial profile shape as measured by the Sersic index, and absolute magnitude. In addition, we present the dependence of local galaxy density (smoothed on 8 h(-1) Mpc scales) on all of these properties. Several classic, well-known relations among galaxy properties are evident at extremely high signal-to-noise ratio: the color-color relations of galaxies, the color-magnitude relations, the magnitude-surface brightness relation, and the dependence of density on color and absolute magnitude. We show that most of the i-band luminosity density in the universe is in the absolute magnitude and surface brightness ranges used: - 23.5 < M-0,M-1i < - 17.0 mag and 17 < mu(0.1i) < 24 mag in 1 arcsec(2) [ the notation (z)b represents the b band shifted blueward by a factor (1 + z)]. Some of the relationships between parameters, in particular the color-magnitude relations, show stronger correlations for exponential galaxies and concentrated galaxies taken separately than for all galaxies taken together. We provide a simple set of fits of the dependence of galaxy properties on luminosity for these two sets of galaxies and other quantitative details of our results.

We present the 3D real space clustering power spectrum of a sample of \~600,000 luminous red galaxies (LRGs) measured by the Sloan Digital Sky Survey (SDSS), using photometric redshifts. This sample of galaxies ranges from redshift z=0.2 to 0.6 over 3,528 deg^2 of the sky, probing a volume of 1.5 (Gpc/h)^3, making it the largest volume ever used for galaxy clustering measurements. We measure the angular clustering power spectrum in eight redshift slices and combine these into a high precision 3D real space power spectrum from k=0.005 (h/Mpc) to k=1 (h/Mpc). We detect power on gigaparsec scales, beyond the turnover in the matter power spectrum, on scales significantly larger than those accessible to current spectroscopic redshift surveys. We also find evidence for baryonic oscillations, both in the power spectrum, as well as in fits to the baryon density, at a 2.5 sigma confidence level. The statistical power of these data to constrain cosmology is ~1.7 times better than previous clustering analyses. Varying the matter density and baryon fraction, we find \Omega_M = 0.30 \pm 0.03, and \Omega_b/\Omega_M = 0.18 \pm 0.04, The detection of baryonic oscillations also allows us to measure the comoving distance to z=0.5; we find a best fit distance of 1.73 \pm 0.12 Gpc, corresponding to a 6.5% error on the distance. These results demonstrate the ability to make precise clustering measurements with photometric surveys (abridged)., Comment: 23 pages, 27 figures, submitted to MNRAS

We construct and analyse a u-band selected galaxy sample from the Sloan Digital Sky Survey (SDSS) Southern Survey, which covers 275 deg2. The sample includes 43223 galaxies with spectroscopic redshifts in the range 0.005 < z < 0.3 and with 14.5 < u < 20.5. The signal-to-noise (S/N) ratio in the u-band Petrosian aperture is improved by co-adding multiple epochs of imaging data and by including sky-subtraction corrections. Luminosity functions for the near-UV 0.1u band (λ≈ 322 ± 26 nm) are determined in redshift slices of width 0.02, which show a highly significant evolution in M* of −0.8 ± 0.1 mag between z= 0 and 0.3; with M*−5 log h70=−18.84 ± 0.05 (AB mag), log φ*=−2.06 ± 0.03 (h370 Mpc−3) and log ρL= 19.11 ± 0.02 (h70 WHz−1 Mpc−3) at z= 0.1. The faint-end slope determined for z < 0.06 is given by =−1.05 ± 0.08. This is in agreement with recent determinations from the Galaxy Evolution Explorer at shorter wavelengths. Comparing our z < 0.3 luminosity density measurements with 0.2 < z < 1.2 from Classifying Objects by Medium Band Observations in 17 Filters (COMBO-17), we find that the 280-nm density evolves as ρL∝ (1 +z)β with β= 2.1 ± 0.2; and find no evidence for any change in slope over this redshift range. By comparing with other measurements of cosmic star formation history, we estimate that the effective dust attenuation at 280 nm has increased by 0.8 ± 0.3 mag between z= 0 and 1.

The distribution of early-type galaxy velocity dispersions, phi(sigma), is measured using a sample drawn from the SDSS database. Its shape differs significantly from that which one obtains by simply using the mean correlation between luminosity, L, and velocity dispersion, sigma, to transform the luminosity function into a velocity function: ignoring the scatter around the mean sigma-L relation is a bad approximation. An estimate of the contribution from late-type galaxies is also made, which suggests that phi(sigma) is dominated by early-type galaxies at velocities larger than ~ 200 km/s., Minor changes, matches version to appear in ApJ, 1 September 2003

We present 13 Broad Absorption Line (BAL) quasars, including 12 new objects, which were identified in the Sloan Digital Sky Survey (SDSS) and matched within 2'' to sources in the FIRST radio survey catalog. The surface density of this sample of radio-detected BAL quasars is 4.5 +- 1.2 per 100 deg^2, i.e. approximately 4 times larger than previously found by the shallower FIRST Bright Quasar Survey (FBQS). A majority of these radio-detected BAL quasars are moderately radio-loud objects. The fraction of BAL quasars in the entire radio quasar sample, 4.8 +- 1.3 %, is comparable to the fraction of BAL quasars among the SDSS optical quasar sample (ignoring selection effects). We estimate that the true fraction of BAL quasars (mostly HiBALs) in the radio sample is 9.2 +- 2.6 % once selection effects are accounted for. We caution that the absorption troughs of 4 of the 13 radio-detected quasars considered do not strictly satisfy the standard BALnicity criterion. One or possibly two of the new radio-detected BAL quasars are of the rare ``iron LoBAL'' type. BAL quasars are generally redder than the median SDSS quasar at the same redshift., Comment: 10 pages, 3 figures, accepted for publication in ApJ

Star counts on short-exposure plates are presented for eight globular clusters. The data are given to several limiting magnitudes for each cluster. Projected radial distributions are determined from the star counts; no significant segregation is observed among the distributions to various limiting magnitudes. The structural parameters of the clusters (core radii and concentration factors) are determined from best-fitting King curves to the observed distributions. The central densities, total masses, central escape velocities, and relaxation times are also calculated. NGC 6093 (M80) and NGC 7099 (M30) have dense compact stellar cores, similar to the established globular X-ray sources. Upper limits are given for the masses of possible central black holes in the eight clusters.

The redshifts of the cluster Abell 2241 have been determined from spectra of five galaxies. The area is found to contain two clusters (or groups) with different redshifts (z = 0.063 and z = 0.101). The X-ray luminosity of the cluster, if the identification with the X-ray source 3U1706 + 32 is correct, is 1 or 2.9 x 1041 ergs -1, depending on which of the two redshifts is assumed. Key words: galaxy clusters - redshifts

Radio observations at 610 MHz with the Westerbork Synthesis Radio Telescope (WSRT) are combined with optical data from the 48 inch Palomar telescope to search for radio-optical candidates for five high-latitude Uhuru X-ray sources (3U 0042+32, 0917+63, 1443+43, 1555+27, and 1809+50). From the data for two of these fields we suggest the following: (1) The rich cluster of galaxies A2142 (zapprox. =0.1), which is found to contain several extended radio sources in its central region, is a likely candidate for 3U 1555+27, as first suggested from purely optical observations. (2) The ''near'' Zwicky cluster, Zw 1810.2+4949, which contains a complex radio source associated with a 15 mag galaxy, is a candidate identification for 3U 1809+50. The unusual radio galaxy OU 516, as well as the double galaxy NGC 6582, both located in the cluster, are also candidates for 3U 1809+50, especially if the X-rays indicate variability. (AIP)

The entire sample of 37 X-ray clusters of galaxies detected by the Ariel 5 satellite at high latitudes is analyzed optically. Morphological types (for all clusters) and central galaxy densities (for all clusters with measured redshifts) are determined, and the positions, redshifts, and richness groups of the set of Southern Hemisphere X-ray clusters are estimated. The X-ray luminosity is found to be correlated with both cluster morphology and central galaxy density. The observed correlations are consistent with a thermal-bremsstrahlung model in which the hot intracluster gas density is proportional to the galaxy density, and the temperature is proportional to the galaxy velocity dispersion.

The central region of the x-ray globular cluster NGC 6624 is studied optically on short exposure photographic plates. A bright unresolved region, about 4'' in size and approx.12.5 mag in apparent visual brightness is observed near the center of the cluster on the shortest-exposure plates. The projected density distribution of the stars is determined from star counts that extend to within about 5'' (= 0.25 pc x d/sub 10/, where d/sub 10/ is the distance in units of 10 kpc) of the center of the cluster. The structural parameters of the cluster are derived to be: core radius = 0''

Observational results are reported concerning the optical properties of the X-ray cluster of galaxies A478. A cluster redshift of 0.09 is determined, which implies a cluster X-ray luminosity of 10 to the 45th power erg/s over the energy range from 2 to 6 keV. The cluster is classified as type cD, the center of the cluster is found to be consistent with the position of the cD galaxy, and it is shown that the surface distribution of the galaxies in the cluster is well described by a bounded isothermal gas-sphere model. The core radius of the galaxy distribution is estimated to be about 1.5 arcmin, corresponding to approximately 0.20 Mpc for a Hubble constant of 50 km/s per Mpc. It is noted that the observed galaxy distribution is somewhat asymmetric, being elongated along the NE-SW direction.