Photometric Redshift Techniques: Reliability and Applications

This article describes the various photometric techniques currently being used, including some preliminary results from the large CNOC2 redshift survey. It also presents a critical look at the reliability of the photometric redshift technique, in part using the HDF results from various groups as a case study.Comment: 11 pages, Latex, 3 postscript figures. A review article to appear in the proceedings of the Xth Recontres de Blois: Birth of Galaxies; Blois, France, July 199

Estimating Luminosities and Stellar Masses of Galaxies Photometrically without Determining Redshifts

Large direct-imaging surveys usually use a template-fitting technique to estimate photometric redshifts for galaxies, which are then applied to derive important galaxy properties such as luminosities and stellar masses. These estimates can be noisy and suffer from systematic biases because of the possible mis-selection of templates and the propagation of the photometric redshift uncertainty. We introduce an algorithm, the Direct Empirical Photometric method (DEmP), which can be used to directly estimate these quantities using training sets, bypassing photometric redshift determination. DEmP also applies two techniques to minimize the effects arising from the non-uniform distribution of training-set galaxy redshifts from a flux-limited sample. First, for each input galaxy, fitting is performed using a subset of the training-set galaxies with photometry and colors closest to those of the input galaxy. Second, the training set is artificially resampled to produce a flat distribution in redshift, or other properties, e.g., luminosity. To test the performance of DEmP, we use a 4-filter-band mock catalog to examine its ability to recover redshift, luminosity, stellar mass, and luminosity and stellar-mass functions. We also compare the results to those from two publicly available template-fitting methods, finding that the DEmP algorithm outperforms both. We find resampling the training set to have a uniform redshift distribution produces the best results not only in photometric redshift, but also in estimating luminosity and stellar mass. The DEmP method is especially powerful in estimating quantities such as near-IR luminosities and stellar mass using only data from a small number of optical bands.Comment: 17 Pages, 7 figures, accepted for publication in Ap

The Red-Sequence Cluster Survey

The Red-Sequence Cluster Survey (RCS) is a new galaxy cluster survey designed to provide a large sample of optically selected 0.1$<$z$<$1.4 clusters. The planned survey data are 100 square degrees of two color ($R$ and $z'$) imaging, with a 5$\sigma$ depth $\sim$2 mag past M$^{*}$ at $z=1$. The combined depth and area of the RCS make it the widest field, moderately deep survey ever undertaken using 4m class telescopes. This paper gives a brief outline of the RCS survey, with particular emphasis on the data reduction strategy. The remainder of the paper focuses on preliminary results from the first set of completely reduced data ($\sim$10 deg$^2$, of the $\sim$60 deg$^2$ in hand). We provide a new example of a rich $z>1$ cluster, illustrative of the dozens discovered in the data so far. Some of the possible science to come from the RCS is illustrated by a qualitative indication of $\Omega_{M}$ from the first 1/10th of the survey data. A high-precision measurement of the 2-point correlation function of luminous early-type galaxies at $0.4<z<1.2$ is also shown.Comment: 6 pages, 5 figures, to appear in the proceedings of "The New Era of Wide-Field Astronomy

The Red-Sequence Cluster Survey: The Value of Ωm\Omega_m and σ8\sigma_8

The Red-Sequence Cluster Survey (RCS) is a 100 deg$^2$ optical survey for high-redshift galaxy clusters. One of the goals of the survey is a measurement of $\Omega_m$ and $\sigma_8$ via the evolution of the mass spectrum of galaxy clusters. Herein we briefly describe how this will initially be done, and also demonstrate the eventual power of the RCS for this type of measurement by a qualitative analysis of the first 1/10th of the survey data.Comment: 2 pages, 1 figure, to appear in the proceedings of IAU S201: New Cosmological Data and the Values of the Fundemental Parameter

The Toronto Red-Sequence Cluster Survey: First Results

The Toronto Red-Sequence Cluster Survey (TRCS) is a new galaxy cluster survey designed to provide a large sample of optically selected 0.1 < z < 1.4 clusters. The planned survey data is 100 square degrees of two color (R and z') imaging, with a 5-sigma depth ~2 mag past M* at z=1. The primary scientific drivers of the survey are a derivation of Omega_m and sigma_8 (from N(M,z) for clusters) and a study of cluster galaxy evolution with a complete sample. This paper gives a brief outline of the TRCS survey parameters and sketches the methods by which we intend to pursue the main scientific goals, including an explicit calculation of the expected survey completeness limits. Some preliminary results from the first set of data (~6 deg^2) are also given. These preliminary results provide new examples of rich z~1 clusters, strong cluster lensing, and a possible filament at z~1.Comment: 4 pages, 5 figures, to be published in "Cosmic Evolution and Galaxy Formation: Structure, Interactions and Feedback", ASP Conference Serie

Photometric Redshifts in the Hubble Deep Field

Photometric redshifts for galaxies in the Hubble Deep Field are measured. Luminosity functions show steepening of the faint-end slope and mild brightening of M* out to z~3, followed by a decline at higher z; an excess of faint, star-forming galaxies is seen at low z. Our results are consistent with the formation of large galaxies at z=2-3, followed by that of dwarfs at z<1.Comment: 2 pages. To appear in the proceedings of the 37th Herstmonceux conference, "HST and the High Redshift Universe

Star Formation and Galaxy Environment

The dependence of star formation rate on galaxian environment is a key issue in the understanding of galaxy formation and evolution. However, the study of this subject is complex and observationally challenging. This paper reviews some of the current results, drawing mostly from recent large redshift surveys such the LCRS, the MORPH collaboration, and the CNOC1 and CNOC2 redshift surveys

Mergers in Galaxy Groups - I. Structure and Properties of Elliptical Remnants

We present collisionless simulations of dry mergers in groups of three to twenty-five galaxies to test the hypothesis that elliptical galaxies form at the centers of such groups. Mock observations of the central remnants confirm their similarity to ellipticals, despite having no dissipational component. We vary the profile of the original spiral's bulge and find that ellipticals formed from spirals with exponential bulges have too low Sersic indices. Mergers of spirals with de Vaucouleurs (classical) bulges produce remnants with larger Sersic indices correlated with luminosity, as with SDSS ellipticals. Exponential bulge mergers are better fits to faint ellipticals, whereas classical bulge mergers better match luminous ellipticals. Similarly, luminous ellipticals are better reproduced by remnants undergoing many (>5) mergers, and fainter ellipticals by those with fewer mergers. The remnants follow tight size-luminosity and velocity dispersion-luminosity (Faber-Jackson) relations (<0.12 dex scatter), demonstrating that stochastic merging can produce tight scaling relations if the merging galaxies also follow tight scaling relations. The slopes of the size-luminosity and Faber-Jackson relations are close to observations but slightly shallower in the former case. Both relations' intercepts are offset - remnants are too large but have too low dispersions at fixed luminosity. Some remnants show substantial (v/\sigma > 0.1) rotational support, although most are slow rotators and few are very fast rotators (v/\sigma > 0.5). These findings contrast with previous studies concluding that dissipation necessary to produce ellipticals from binary mergers of spirals. Multiple, mostly minor and dry mergers can produce bright ellipticals, whereas significant dissipation could be required to produce faint, rapidly-rotating ellipticals.Comment: ApJ accepte

Population Gradients in Galaxy Clusters at 0.2 < Z < 0.6

We present a principal component analysis of galaxy spectra from the CNOC sample of rich X-ray luminous clusters at 0.18 < z < 0.55. Composite radial distributions of different stellar populations show strong gradients as a function of cluster-centric redshift. The composite population is dominated by evolved populations in the core, and gradually changes to one which is similar to coeval field galaxies at radii greater than the virial radius. We do not see evidence in the clusters for an excess of star formation over that seen in the coeval field. Within this redshift range, significant evolution in the gradient shape is seen, with higher redshift clusters showing steeper gradients. This results in larger numbers of younger galaxies seen towards the inner regions of the clusters-- in effect, a restatement of the Butcher-Oemler effect. Luminosity density profiles are consistent with a scenario where this phenomenon is due to a decline over time in the infall rate of field galaxies into clusters. Depending on how long galaxies reside in clusters before their star formation rates are diminished, this suggests an epoch for maximal infall into clusters at z > 0.7. We also discuss alternative scenarios for the evolution of cluster populations.Comment: to appear in the PASP proceedings of the conference "The Hy-Redshift Universe: Galaxy Formation and Evolution at High Redshift," eds. Andrew J. Bunker & Wil J. M. van Breuge

Optical-IR Spectral Energy Distribution of the Proto-Galaxy Candidate MS1512-cB58

The spectral energy distribution of the proto-galaxy candidate MS1512-cB58 at $z =2.72$ discovered by Yee et al. (1996) is presented. Photometry in seven bands ranging from $g$ to $K$$'$ (1300--6000 \AA~rest wavelength) are fitted with population synthesis models from Bruzual \& Charlot (1993). The data confirm a very young age for this galaxy, in agreement with ages estimated from preliminary \CIV~P-Cygni profile modeling. Single-burst models with ages greater than about 20 Myr can be discarded at the 99\% confidence level, and continuous star formation models with ages greater than about 35 Myr can be discarded at the 95\% confidence level. The spectral energy distribution is most consistent with a continuous star formation model of about 10--20 Myr, with reddening of $E(B-V)\sim 0.3$. No evidence for an older population of stars is seen, but the possibility of an older population with as much as 90\% of the galaxy mass cannot be ruled out. We discuss the possible ramifications of a non-standard IMF and gravitational lensing on the galaxy's age and mass.Comment: LaTeX and 3 .ps figures, accepted by ApJ