arXiv subjects

Patrick S. Osmer

Publications and source records attributed to Patrick S. Osmer.

22 records · Page 2Linked to original sources

arXiv1997

A Deep Multicolor Survey. III. Additional Spectroscopy and Implications for the Number Counts of Faint Quasars

We have made spectroscopic identifications of 39 additional quasar candidates from the Deep Multicolor Survey (DMS) of Hall et al. (1996, ApJ, 462, 614, astro-ph/9512052). We have identified 9 new quasars with 0.3 < z < 2.8 and 16.8 < B < 21.6, all from the group of candidates with ultraviolet excess (UVX). No new quasars with z > 3 were found among the observed candidates selected due to their red (B-R) and (V-R) colors. As a result, there are now 55 confirmed quasars in the survey: 42 with 0.3 < z < 2, nine with 2 < z < 3, three with 3 < z < 4, and 1 at z = 4.3. One new quasar, DMS 0059-0055, is very bright with B=16.8 and z=0.3, making its detection by our survey very unexpected. Including this new spectroscopy, the results of the DMS are converging with the predicted space densities of other surveys. In particular, we no longer find an excess of quasars with z < 2.3 and B < 21 in the survey over predictions based on models by Koo & Kron. Also, the excess in the number of quasars seen at z > 3 over predictions based on models by Warren, Hewett, & Osmer is less than previously suggested. We also demonstrate the success of our quasar color modeling which is important in assessing the completeness of our survey.

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arXiv1997

Quasar Clustering and Spacetime Geometry

The non-Euclidean geometry of spacetime induces an anisotropy in the apparent correlation function of high-redshift quasars. This effect can constrain the cosmological constant Λindependent of any assumptions about evolution of luminosities, sizes, or clustering. We examine the prospects for distinguishing between low-density (Ω_0=0.1-0.4) cosmological models with flat and open space geometry using the quasar samples anticipated from the 2dF and Sloan redshift surveys. We show that even these large quasar surveys are likely to reside in the "sparse sampling" regime, so that measurement errors in the correlation function obey Poisson statistics. As a result: (a) one can devise a simple maximum-likelihood scheme for estimating clustering parameters, (b) one can generate Monte Carlo realizations of correlation function measurements without creating artificial quasar distributions, and (c) for fixed quasar number, a deeper survey over a smaller area has greater statistical power than a shallow, large-area survey. Adopting recent (quite uncertain) estimates of the quasar correlation length, we find that the 2dF and Sloan samples can provide clear discrimination between flat and open geometries for Ω<= 0.2 but only marginal discrimination for Ω= 0.4. Clear discrimination is possible for Ω= 0.4 if the true quasar correlation length is a factor of two larger, and a high-density survey of 30,000 quasars in 200 square degrees would provide clear discrimination even for the lower correlation length.

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arXiv1995

A Deep Multicolor Survey II. Initial Spectroscopy and Comparison With Expected Quasar Number Counts

We have used the KPNO 4-meter Mayall telescope to image 0.83 square degrees of sky in six fields at high galactic latitude in six filters spanning 3000-10000Å to magnitude limits ranging from 22.1 to 23.8. As a first use of this database, we have conducted a multicolor survey for quasars. We discuss various methods of selecting outliers in different color-color diagrams and multicolor space that have been used to identify quasars at all redshifts from their colors alone. We discuss the initial results of our program of spectroscopic identification which has so far resulted in the identification of over forty faint quasars, including one at z$>$4, a similar number of compact narrow-emission-line galaxies, and a number of unusual and potentially interesting stars. We use these spectroscopic results, along with extensive simulations of quasar spectra, to study the efficiency of our candidate selection procedures. Finally, we compare the number counts of our quasars and quasar candidates to the expected numbers based on previous studies of the quasar luminosity function. The agreement of our observations with these expectations is good in most cases. However, we do estimate that our survey contains more quasars with B$<$21 and z$<$2.3 than expected from the results of Koo \& Kron (1988) and more z$>$3 quasars than expected from the results of Warren, Hewett, \& Osmer (1994), both at the 3$σ$\ level. Additional spectroscopic observations will be required to confirm or refute these excesses.

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arXiv1995

A Deep Multicolor Survey I. Imaging Observations and Catalog of Stellar Objects

We have used the KPNO 4-meter Mayall telescope to image 0.83 square degrees of sky in six fields at high galactic latitude in six filters spanning 3000-10000Å to magnitude limits ranging from 22.1 to 23.8. We have assembled a catalog of 21,375 stellar objects detected in the fields for use primarily in conducting a multicolor search for quasars. This paper describes the data reduction techniques used on the CCD data, the methods used to construct the stellar object catalog, and the simulations performed to understand its completeness and contamination.

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