arXiv subjects

David R. Patton

Publications and source records attributed to David R. Patton.

76 records · Page 5Linked to original sources

arXiv2004

The Deep2 Galaxy Redshift Survey: Evolution of Close Galaxy Pairs and Major-Merger Rates Up to z ~ 1.2

We derive the close, kinematic pair fraction and merger rate up to z ~ 1.2 from the initial data of the DEEP2 Redshift Survey. Assuming a mild luminosity evolution, the number of companions per luminous galaxy is found to evolve as (1+z)^{m}, with m = 0.51+-0.28; assuming no evolution, m = 1.60+-0.29. Our results imply that only 9% of present-day $L^{*}$ galaxies have undergone major mergers since z ~ 1.2 and that the average major merger rate is about 4* 10^{-4} h^{3} Mpc^{-3} Gyr^{-1} for z ~ 0.5 - 1.2. Most previous studies have yielded higher values.

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arXiv2000

Active Galactic Nuclei in the CNOC2 Field Galaxy Redshift Survey

We present a sample of 47 confirmed and 14 candidate Active Galactic Nuclei (AGN) discovered in the Canadian Network for Observational Cosmology field galaxy redshift survey (CNOC2). The sample consists of 38 objects identified from broad emission lines, 8 from narrow [NeV] emission, and 15 candidates from FeII or MgII absorption lines, one of which has been confirmed as a broad-line AGN via infrared spectroscopy. Redshifts of these AGN range from z=0.27 to z=4.67, and the average absolute magnitude is M_B=-22.25. No color selection criteria were involved in selecting this spectroscopically discovered sample. The sample is also unbiased against objects with luminous host galaxies since the spectroscopy preferentially targeted extended objects. Simple color-color diagram selection criteria can recover 81+-6% of the CNOC2 AGN, but several of the most unusual objects would be missing from such a color-selected sample. In the subsample with broad emission lines, the average equivalent widths for MgII and CIII] agree with the predictions of previous studies of the Baldwin effect. However, the average equivalent widths for CIV and Ly-alpha are smaller than predicted by previous studies of the Baldwin effect at lower redshift. This may imply that the slopes of the CIV and Ly-alpha Baldwin effects evolve with redshift, steepening with cosmic time. The broad emission line AGN also show a higher incidence of associated MgII and CIV absorption than in most previous surveys. This may arise from strong absorption being anti-correlated with optical luminosity or becoming less frequent with cosmic time, or possibly because our selection method is not biased against objects with resolved spatial structure or reddened by dust associated with the absorbing gas. (Abridged)

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arXiv2000

Spectroscopic Gravitational Lens Candidates in the CNOC2 Field Galaxy Redshift Survey

We present five candidate gravitational lenses discovered spectroscopically in the Canadian Network for Observational Cosmology Field Galaxy Redshift Survey (CNOC2), along with one found in followup observations. Each has a secure redshift based on several features, plus a discrepant emission line which does not match any known or plausible feature and is visible in multiple direct spectral images. We identify these lines as Lyman-alpha or [OII] emission from galaxies lensed by, or projected onto, the CNOC2 target galaxies. Einstein radii estimated from the candidate deflector galaxy luminosities indicate that for two candidates the lines are probably [OII] from projected z<1 galaxies (consistent with the detection of H-beta as well as [OII] in one of them), but that in the remaining four cases the lines could be Ly-alpha from lensed z>3 galaxies. We estimate that only 1.9+-0.7 [OII]-emitting galaxies are expected to project onto target galaxies in the original CNOC2 sample, consistent with three or four of the six candidates being true gravitational lenses.

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arXiv1999

Pre-Heated Isentropic Gas in Groups of Galaxies

We confirm that the standard assumption of isothermal, shock-heated gas in cluster potentials is unable to reproduce the observed X-ray luminosity- temperature relation of groups of galaxies. As an alternative, we construct a physically motivated model for the adiabatic collapse of pre-heated gas into an isothermal potential that improves upon the original work of Kaiser (1991). The luminosity and temperature of the gas is calculated, assuming an appropriate distribution of halo formation times and radiation due to both bremsstrahlung and recombination processes. This model successfully reproduces the slope and dispersion of the luminosity-temperature relation of galaxy groups. We also present calculations of the temperature and luminosity functions for galaxy groups under the prescription of this model. This model makes two strong predictions for haloes with total masses M<10^13 M_sun, which are not yet testable with current data: (1) the gas mass fraction will increase in direct proportion to the halo mass; (2) the gas temperature will be larger than the virial temperature of the mass. The second effect is strong enough that group masses determined from gas temperatures will be overestimated by about an order of magnitude if it is assumed that the gas temperature is the virial temperature. The entropy required to match observations can be obtained by heating the gas at the turnaround time, for example, to about 3 X 10^6 K at z=1, which is too high to be generated by a normal rate of supernova explosions. This model breaks down on the scale of low mass clusters, but this is an acceptable limitation, as we expect accretion shocks to contribute significantly to the entropy of the gas in such objects.

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