arXiv subjects

Michael Harvanek

Publications and source records attributed to Michael Harvanek.

22 records · Page 2Linked to original sources

arXiv2003

Hdelta-Selected Galaxies in the Sloan Digital Sky Survey I: The Catalog

[Abridged] We present here a new and homogeneous sample of 3340 galaxies selected from the Sloan Digital Sky Survey (SDSS) based solely on the observed strength of their Hdelta absorption line. These galaxies are commonly known as ``post-starburst'' or ``E+A'' galaxies, and the study of these galaxies has been severely hampered by the lack of a large, statistical sample of such galaxies. In this paper, we rectify this problem by selecting a sample of galaxies which possess an absorption Hdelta equivalent width of EW(Hdelta_max) - Delta EW(Hdelta_max) > 4A from 106682 galaxies in the SDSS. We have performed extensive tests on our catalog including comparing different methodologies of measuring the Hdelta absorption and studying the effects of stellar absorption, dust extinction, emission-filling and measurement error. The measured abundance of our Hdelta-selected (HDS) galaxies is 2.6 +/- 0.1% of all galaxies within a volume-limited sample of 0.05<z<0.1 and M(r*)<-20.5, which is consistent with previous studies of such galaxies in the literature. We find that only 25 of our HDS galaxies in this volume-limited sample (3.5+/-0.7%) show no evidence for OII and Halpha emission, thus indicating that true E+A (or k+a) galaxies are extremely rare objects at low redshift, i.e., only 0.09+/-0.02% of all galaxies in this volume-limited sample are true E+A galaxies. In contrast, 89+/-5% of our HDS galaxies in the volume-limited sample have significant detections of the OII and Halpha emission lines. We find 27 galaxies in our volume-limited HDS sample that possess no detectable OII emission, but do however possess detectable Halpha emission. These galaxies may be dusty star-forming galaxies. We provide the community with this new catalog of Hdelta-selected galaxies to aid in the understanding of these galaxies.

astro-ph↗

arXiv2002

A Study of 3CR Radio Galaxies from z = 0.15 to 0.65. II. Evidence for an Evolving Radio Structure

Radio structure parameters were measured from the highest quality radio maps available for a sample of 3CR radio galaxies in the redshift range 0.15 < z < 0.65. Combined with similar data for quasars in the same redshift range, these morphology data are used in conjunction with a quantification of the richness of the cluster environment around these objects (the amplitude of the galaxy-galaxy spatial covariance function, Bgg) to search for indirect evidence of a dense intracluster medium (ICM). This is done by searching for confinement and distortions of the radio structure that are correlated with Bgg. Correlations between physical size and hot spot placement with Bgg show evidence for an ICM only at z < 0.4 and there are no correlations at z > 0.4, suggesting an epoch of z ~ 0.4 for the formation of an ICM in these Abell richness class 0-1, FR2-selected clusters. X-ray selected clusters at comparable redshifts, which contain FR1 type sources exclusively, are demonstrably richer than the FR2-selected clusters found in this study. The majority of the radio sources with high Bgg values at z < 0.4 can be described as ``fat doubles'' or intermediate FR2/FR1s. The lack of correlation between Bgg and bending angle or Bgg and lobe length asymmetry suggests that these types of radio source distortion are caused by something other than interaction with a dense ICM. Thus, a large bending angle cannot be used as an unambiguous indicator of a rich cluster around powerful radio sources. These results support the hypothesis made in Paper 1 that cluster quasars fade to become FR2s, then FR1s, on a timescale of 0.9 Gyrs (for H0 = 50 km s^-1 Mpc^-1).

astro-ph↗

arXiv2001

A Study of 3CR Radio Galaxies from z = 0.15 to 0.65. I. Evidence for an Evolutionary Relationship Between Quasars and Radio Galaxies

Deep optical images have been gathered for a nearly complete sample of radio galaxies from the Revised 3rd Cambridge (3CR) Catalog in the redshift range 0.15 < z < 0.65. Total and nuclear magnitudes and colors have been extracted. The richness of the galaxy clustering environment has also been quantified by calculating the amplitude of the galaxy-galaxy spatial covariance function (B_gg), showing overdensities ranging up to Abell class 0-1 clusters. These optical data are compared to similar data from an existing sample of radio-loud quasars in the same redshift range for the purpose of determining the relationship between radio galaxies and quasars. In the range 0.15 < z < 0.4, we find that quasars and radio galaxies have significantly different environments in that only radio galaxies are found in rich cluster environments. This comparison appears to rule out the hypothesis that all quasars are radio galaxies viewed from a particular angle at the 97% confidence level (99.6% confidence level if N-galaxies are considered quasars). The existence of quasars in clusters at z > 0.4 supports the hypothesis that some radio-loud quasars may dim with time and evolve into radio galaxies with an e-folding time of ~0.9 Gyr. A compatible scenario is presented for this evolution in which the quasar dims due to the absence of low velocity interactions between the quasar host and companion galaxies which trigger quasar activity and/or a diminishing fuel supply caused by the more effective gas ``sweeping'' of a growing intracluster medium.

astro-ph↗

arXiv1998

A VLA Study of 15 3CR Radio Galaxies

We present VLA radio maps in total intensity and polarization at 1.4, 4.9 and 8.4 GHz of fifteen 3CR radio galaxies for which good maps showing the large-scale radio structure have not previously been available. Previously unknown cores are detected in several sources and a bright one-sided jet in 3C 287.1 is mapped for the first time; several other jet-like features are also imaged. Total and core fluxes are tabulated and radio core positions are listed and compared to optical positions. The galaxy at the optical position listed for 3C 169.1 is found to lie farther from the radio core position than another dimmer, bluer galaxy. We discuss individual sources in some detail.

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