Radio properties and optical identification of two samples of Millijansky radio sources at 1.4 GHz
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Abstract
- From the 1.4 GHz radio survey of Condon, Dickey, & Salpeter in a region much devoid of rich galaxy clusters at redshifts z less than or similar to 0.4, we selected a ''distant'' sample of 57 radio sources complete to a 1.4 GHz nux density of 35 mJy and a ''nearby'' sample of 36 mostly weaker radio sources which are optically brighter than B similar to 19 mag. Our ultimate goals are( 1) to study the radio, optical, and near-IR properties of those high-redshift(z similar to I), moderate-power radio sources in the distant sample and to compare them with that of more powerful radio sources, and (2) to make a comparison of primarily noncluster radio sources in the nearby sample with a companion survey of radio sources in a pair of rich superclusters at z similar to 0.1. In this first paper of a series, we report our new C-array VLA continuum snapshots at 4.86 GHz and optical R-band CCD imaging photometry for these two samples and tabulate the observational results on individual sources.
Some direct sample statistical properties are also discussed in the paper and summarized as follows: (1) The distant sample: (a) the sample median flux density at 1.4 GHz is about 65 mJy. (b) The majority (80%) of the sample sources have a steep spectrum between 1.4 and 4.86 GHz with a spectral index around 0.9. Nineteen (90%) of the 21 sources that are fully resolved at 4.86 GHz (i.e., angular sizes theta greater than or similar to 11 '') have a radio morphology of Fanaroff-Riley (FR) II type. (c) Thirty-seven ( 88%) of the 42 optically imaged sample sources were optically identified to a limiting R-band magnitude of R similar to 23.5 mag. About 15% of the identified radio sources appear to be point sources, and the others are extended galaxies with an appearance similar to nearby elliptical galaxies. (d) Twenty-eight (76%) of the optically identified sources have R > 20 mag, suggesting that these are probably distant (z greater than or similar to 0.8), with a redshift distribution peaking at z similar to 1, where their radio luminosities are about 10 times the break power between the FR I and II classes. (e) We found no strong evidence for the radio and optical axes of the resolved radio sources (i.e., a greater than or similar to 5 '') to be correlated or anticorrelated, nor any evidence for strong clustering around sample radio sources on average. (2) The nearby sample: except for R less than or similar to 15, the sample is dominated by elliptical galaxies with 16 less than or similar to R < 18.5 mag and a spectral index distribution similar to that of the distant sample. Based on the radial distribution of optical objects around each radio source, we found that the average radio source environment becomes richer from that characteristic of galaxy groups for R < 17 mag (z less than or similar to 0.2) to that of galaxy groups to clusters at R greater than or similar to 18 mag(z greater than or similar to 0.3).
Title | Radio properties and optical identification of two samples of Millijansky radio sources at 1.4 GHz |
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Creator | Salpeter, E. E. |
Houck, J. R. | |
Lu, N. Y. | |
Hoffman, G. Lyle | |
Publisher | Astrophysical Journal Supplement Series |
Academic Department | Physics |
Division | Natural Sciences |
Organization | Lafayette College |
Date Issued | April 1996 |
Date Available | 2015-04-06T15:14:08Z |
Type | Article |
Language | English |
Keyword | galaxies: photometry |
radio continuum: galaxies | |
galaxies: structure | |
galaxies: distances and redshifts | |
surveys | |
Bibliographic Citation | Lu, N. Y., et al. (1996 Apr.) "Radio properties and optical identification of two samples of Millijansky radio sources at 1.4 GHz." Astrophysical Journal Supplement Series 103 (2): 331-62. |
Standard Identifier | Handle 10385/1770 |
DOI 10.1086/192280 | |
Permalink | http://hdl.handle.net/10385/1770 |
Rights Statement | In Copyright |
Rights Holders | The American Astronomical Society |
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