On The Parent Population of Radio Galaxies and the FRI - FRII Dichotomy

Abstract

We test the hypothesis that radio galaxies are a random subset of otherwise normal elliptical galaxies. Starting with the observed optical luminosity functions for elliptical galaxies, we show that the probability of an elliptical forming a radio source is a continuous, increasing function of optical luminosity, proportional to L squared. With this probability function and the luminosity function of normal elliptical galaxies as input to Monte Carlo simulations, we reproduce the observed distribution of radio galaxies in the radio-optical luminosity plane. Our results show that radio galaxies are a luminosity-biased but otherwise random sample of elliptical galaxies. This unified view of radio-loud and radio-quiet ellipticals also explains the well known difference of ~0.5 mag in average optical luminosity between FRI and FRII radio galaxies as a simple selection effect. Specifically, FRII appear preferentially in smaller galaxies because both radio and optical luminosity functions are steep, so there is a negligible probability of observing a powerful radio source associated with a bright galaxy; no intrinsic physical differences between FRI and FRII host galaxies are required.

Accepted for publication on ApJ. Includes 7 figures, 16 pages in total

References in corpus (7)

• A Fundamental Relation Between Supermassive Black Holes and Their Host Galaxies
• A Relationship Between Nuclear Black Hole Mass and Galaxy Velocity Dispersion
• The FIRST Bright Quasar Survey. II. 60 Nights and 1200 Spectra Later
• The HST Survey of BL Lacertae Objects. II. Host Galaxies
• The HST Survey of BL Lacertae Objects. I. Surface Brightness Profiles, Magnitudes, and Radii of Host Galaxies
• The HST Survey of BL Lacertae Objects: Morphological Properties of Low redshift Host Galaxies
• Supermassive Black Holes and Galaxy Morphology

Cited by in corpus (11)

• X-ray Emission from the Hot ISM and SW Radio Lobe of the Nearby Radio Galaxy Centaurus A
• The nuclear properties and extended morphologies of powerful radio galaxies: the roles of host galaxy and environment
• The Fundamental Plane of Radio Galaxies
• Blazars spectral properties at 74 MHz
• X-Ray Absorption and an X-Ray Jet in the Radio-Loud Broad Absorption Line Quasar PG 1004+130
• Low-power Radio Galaxies in the Distant Universe: A search for FRI at 1<z<2 in the COSMOS field
• An Elusive Population of Massive Disk Galaxies Hosting Double-lobed Radio-loud AGNs
• Host Galaxy Evolution in Radio-Loud AGN
• J06587-5558 -- A Very Unusual Polarised Radio Source
• The X-ray properties of high-z FRI candidates in the COSMOS field
• Determination of cosmology and evolution from K-band magnitude-redshift and number count observations