EDP Sciences
Free access
Volume 370, Number 3, May II 2001
Page(s) 923 - 930
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20010304

A&A 370, 923-930 (2001)
DOI: 10.1051/0004-6361:20010304

Radial density and density evolution of radio galaxies in the Las Campanas redshift survey

J. Machalski and W. Godlowski

Astronomical Observatory, Jagellonian University, ul. Orla 171, 30244 Cracow, Poland

(Received 23 November 2000 / Accepted 27 February 2001)

The sample of 1157 radio-identified galaxies from the Las Campanas Redshift Survey (LCRS) (Machalski & Condon 1999) is used to determine the radial density of both star-forming (starburst) and AGN-type galaxies with the mean redshift of 0.07 and 0.18, respectively. It is shown that the radial density distribution of these radio galaxies is essentially different from the respective distribution of optical galaxies in the parent LCRS sample. While the optical galaxies reveal a systematic decrease of their spatial density with redshift (which likely is due to some incompleteness of the optical sample increasing with the apparent isophotal magnitude of galaxies), the radio-emitting galaxies exhibit evident positive evolution of their radial density with redshift. Moreover, most of this density evolution is connected to starburst-type galaxies whose evolution can be parametrized by $g(z)\propto (1+z)^{2.5\pm 0.5}$. No evident density evolution is detected in LCRS AGN galaxies. Correcting the 1.4 GHz luminosity function (RLF) (Machalski & Godlowski 2000) for the above density evolution in starbursts and assuming its lack in AGN, a pure luminosity evolution $f(z)\propto (1+z)^{2.4\pm 0.9}$ is found for AGN galaxies after the comparison of the corrected RLF with the local luminosity function based on nearby UGC galaxies (cf. Condon 1989). Oppositely, no significant luminosity evolution in starbursts is found.

Key words: galaxies: active -- galaxies: evolution -- radio continuum: galaxies

Offprint request: J. Machalski, machalsk@oa.uj.edu.pl

© ESO 2001