arXiv subjects

Patrick B. Hall

Publications and source records attributed to Patrick B. Hall.

172 records · Page 10Linked to original sources

arXiv1998

A Deep Multicolor Survey. IV. The Electronic Stellar Catalog

We make available in electronic form the stellar catalog of 19,494 objects from the Deep Multicolor Survey (DMS). The DMS is based on CCD imaging with the Mayall 4-m telescope in U,B,V,R',I75,I86 and covers 0.83 sq. deg. in six fields at high galactic latitude. The survey reached 5 sigma limiting magnitudes of 22.1 in I86 to 23.8 in B. The catalog gives positions, magnitudes and error estimates, and classification codes in the six filter bands for all the objects. We present tables that summarize the spectroscopic results for the 55 quasars, 44 compact narrow emission-line galaxies, and 135 stars in the DMS that we have confirmed to date. We also make available illustrations of all the spectra. The catalog and spectra can be obtained from the World Wide Web at http://www.astronomy.ohio-state.edu/~posmer/DMS/.

astro-ph↗

arXiv1998

An Optical/Near-Infrared Study of Radio-Loud Quasar Environments II. Imaging Results

We use optical and near-IR imaging to examine the properties of the significant excess population of K>=19 galaxies found in the fields of 31 z=1-2 radio-loud quasars by Hall, Green & Cohen (1998). The excess occurs on two spatial scales: a component at <40'' from the quasars significant compared to the galaxy surface density at >40'' in the same fields, and a component roughly uniform to ~100'' significant compared to the galaxy surface density seen in random-field surveys in the literature. The r-K color distributions of the excess galaxy populations are indistinguishable and are significantly redder than the color distribution of the field population. The excess galaxies are consistent with being predominantly early-type galaxies at the quasar redshifts, and there is no evidence that they are associated with intervening MgII absorption systems. The average excess within 0.5 Mpc (~65'') of the quasars corresponds to Abell richness class ~0 compared to the galaxy surface density at >0.5 Mpc from the quasars, and to Abell richness class ~1.5 compared to that from the literature. We discuss the spectral energy distributions (SEDs) of galaxies in fields with data in several passbands. Most candidate quasar-associated galaxies are consistent with being 2-3 Gyr old early-types at the quasar redshifts of z~1.5. However, some objects have SEDs consistent with being 4-5 Gyr old at z~1.5, and a number of others are consistent with ~2 Gyr old but dust-reddened galaxies at the quasar redshifts. These potentially different galaxy types suggest there may be considerable dispersion in the properties of early-type cluster galaxies at z~1.5. There is also a population of galaxies whose SEDs are best modelled by background galaxies at z>2.5.

astro-ph↗

arXiv1998

An Optical/Near-Infrared Study of Radio-Loud Quasar Environments I. Methods and z=1-2 Observations

We have conducted an optical/near-infrared study of the environments of radio-loud quasars (RLQs) at redshifts z=0.6-2. In this paper we discuss the sample selection and observations for the z=1-2 subsample and the reduction and cataloguing techniques used. We discuss technical issues at some length, since few detailed descriptions of near-IR data reduction and multicolor object cataloguing are currently available in single literature references. Our sample of 33 RLQs contains comparable numbers of flat- and steep- radio spectrum sources and sources of various radio morphologies, and spans a similar range of absolute magnitude and radio power, allowing us to disentangle dependence of environment on such properties from redshift evolution. We use the standard ``shift-and-stare'' method of creating deep mosaiced images where the exposure time (and thus the RMS noise) at each pixel is not constant across the mosaic. An unusual feature of our reduction procedure is the creation of images with constant RMS noise from such mosaics. We adopted this procedure to enable use of the FOCAS detection package over almost the entire mosaic instead of only in the area of deepest observation where the RMS noise is constant, thereby roughly doubling our areal coverage. We correct the object counts in our fields for stellar contamination using the SKY model of Cohen (1995) and compare the galaxy counts to those in random fields. Even after accounting for possible systematic magnitude offsets we find a significant excess of K>=19 galaxies. Analysis and discussion of this excess population is presented by Hall & Green (1998).

astro-ph↗

arXiv1998

Luminosity Functions And Evolution Of Blue Galaxies In A Deep Multicolor CCD Field Survey

A complete sample of 659 field galaxies with 17.0$<$U$\leq$21.1, each with U-B-V-R-I7500-I8600 photometry, has been selected from a deep field survey which covers 0.83 deg$^2$ along six lines of sight (Hall et al. 1996a). Each galaxy's spectral type and redshift has been estimated using a multicolor photometric technique (Liu & Green 1998). Total number counts of the galaxies in the U-band give a count slope d(logN)/dM = 0.55 $\pm$ 0.05, consistent with previous studies. The 545 galaxies in the sample classified as spectral type Sbc or bluer are analyzed for signs of evolution with redshift, and for unusual star formation histories. The U-band luminosity function of these blue galaxies at 0.02$<$z$<$0.15 has a steep $α$ $\simeq$ -1.85 down to M(B)$\simeq$-14. The luminosity functions at 0.15$\leq$z$<$0.3 and 0.3$\leq$z$\leq$0.5 show significant evolution in M* and $ϕ*$, at levels consistent with those found in the Canada-France and Autofib Redshift Surveys. A significant population of very blue (rest frame U-B$<$-0.35) galaxies, with spectral energy distributions indicating strong starburst activity, is observed at z$\gtrsim$0.3 but not at z$<$0.3. This population is confirmed via spectroscopy of part of the sample. These may be galaxies temporarily brightened by global starbursts, which subsequently fade and redden at lower redshifts.

astro-ph↗

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.

astro-ph↗

arXiv1997

The Optical/Near-IR Colors of Broad Absorption Line Quasars, Including the Candidate Radio-Loud BAL Quasar 1556+3517

A candidate radio-loud broad absorption line quasar (RLBAL) has been reported by Becker et al. (1997). We present JHK observations of this object and three other radio-detected BALs taken with the new Michigan-Dartmouth-MIT/Ohio State/Aladdin IR Camera (MOSAIC) on the KPNO 4-meter. The candidate RLBAL 1556+3517 has B-K=6.63, redder than all but one or two known z>1 quasars. This strongly suggests the observed continuum of this quasar is reddened by dust. Even when this extreme reddening is taken into account 1556+3517 is still probably radio-loud, although near-IR spectroscopy to measure its Balmer decrement will be needed to verify this. In addition, since it is a flat-spectrum object, VLBI observations to determine the extent (if any) to which beaming affects our estimate of its radio luminosity will be needed before 1556+3517 can be unequivocally declared a radio-loud BAL. We also use our data and data from the literature to show that optically selected BALs as a class have B-K colors consistent with the observed distribution for optically selected quasars as a whole. Thus there is currently no evidence that the tendency of optically selected BALs to be preferentially radio-intermediate (Hooper, Francis, & Impey 1993) is due to extinction artificially lowering estimated BAL optical luminosities. However, as most quasar surveys, both radio and optical, would be insensitive to a population of reddened radio-quiet BALs, the existence of a large population of reddened BALs similar to 1556+3517 cannot yet be ruled out.

astro-ph↗

arXiv1996

X-ray Emission from the Host Clusters of Powerful AGN

(Abridged) We report the detection of X-ray emission from the host cluster of the radio-quiet quasar H1821+643 with the ROSAT HRI, and the non-detection of the host cluster of the radio-loud quasar 3C206 using the EINSTEIN HRI. CL1821+643 has a rest-frame 0.1-2.4 keV luminosity of 3.74$\pm$0.57 h$_{50}^{-2}$ 10^45 ergs/sec, 38% from a barely resolved cooling flow component, which places it among the most X-ray luminous clusters known. The cluster emission complicates interpretation of previous X-ray spectra of this field; in particular, the observed FeK$α$ emission can probably be attributed entirely to the cluster, and either the quasar is relatively X-ray quiet for its optical luminosity or the cluster has a relatively low temperature for its luminosity. We combine these data with the recent detection of X-ray emission from the host cluster of the `buried' radio-quiet quasar IRAS 09104+4109, our previous upper limits for the host clusters of two z$\sim$0.7 RLQs, and literature data on FR II radio galaxies and compare to the predictions of three models for the presence and evolution of powerful AGN in clusters: the low-velocity-dispersion model, the low-ICM-density model, and the cooling flow model. Neither of the latter two models can explain all the observations. We suggest that strong interactions with gas-containing galaxies may be the only mechanism needed to explain the presence and evolution of powerful AGN in clusters, consistent with the far-IR and optical properties of the host galaxies studied here. However, the cooling flow model cannot be ruled out for at least some objects, and it is likely that both processes are at work. Each scenario makes predictions for future X-ray and optical observations which can test their relative importance.

astro-ph↗

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.

astro-ph↗

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.

astro-ph↗

arXiv1995

A ROSAT Search for X-ray Emission from Quasar Host Clusters

We report the results of a search for X-ray emission from quasar host clusters at moderate redshift using the {\sl ROSAT} HRI. We detect no emission from the host clusters of 3C~263 (z=0.646) and PKS~2352-34 (z=0.706) to 3$σ$\ limits of 3.26 and 2.86 $\times$10$^{44}$\ ergs~s$^{-1}$ respectively (H$_o$=50, q$_o$=1/2) for clusters with r$_{core}$=125~kpc and T=5~keV. These limits show that these quasar host clusters are not substantially more X-ray luminous than optically or X-ray selected clusters of similar richnesses at z$\gtrsim$0.5. We also report the possible detection of a clump of X-ray emitting gas coincident with the brightest radio lobe of 3C~263. This may be evidence for the existence of a clumpy ICM in the host cluster of 3C~263.

astro-ph↗