[ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] NICMOS Observations of the Host Galaxies of Powerful Radio Sources: Does Size Matter?

Abstract

We present near-infrared J and K band imaging of a sample of powerful radio source host galaxies with the Hubble Space Telescope NICMOS2 camera. These sources have been selected on their double lobed radio structure, and include a wide range of projected radio source sizes. The largest projected linear sizes range from the compact Gigahertz Peaked Spectrum (GPS, < 1 kpc) and Compact Steep Spectrum (CSS, < 20 kpc) radio sources, up to the large-scale (> 20 kpc) classical doubles (FR II radio sources). We investigate the dependence of host galaxy properties (including near-IR surface brightness profiles) on radio source size, using both our own and published data. The absolute magnitudes and surface brightness profiles are consistent with the host galaxies being regular giant elliptical galaxies rather than Brightest Cluster Galaxies (BCGs). We find that the GPS, CSS, and FR II host galaxies are a uniform class of objects, consistent with a scenario in which a powerful radio source evolves along this size sequence.

Radio-ExcessIRASGalaxies. II. Host Galaxies

“…They use these to argue that their CSS/GPS sources are non-BCGs and therefore do not evolve into BCG FR I sources. Our derived slope agrees well with that for the CSS/GPS sources (de Vries et al 2000), but there is considerable scatter in our data points (Fig. 8).…”

“…Many of the hosts of powerful GPS sources also appear to be mergers, though not the high fraction that is seen in ULIRGs (O'Dea et al 1996). The hosts of CSS and GPS sources have been found to be similar to those of FR II radio galaxies, consistent with the hypothesis that CSS and GPS sources are young FR II galaxies (de Vries et al 2000). We expect the properties of the host galaxy to evolve much more slowly than the radio source and so the optical properties of the host galaxy should remain unchanged as the radio source evolves.…”

“…Radio sources may take time to develop and so occur in older merger remnants where evidence for the merger is now more difficult to detect. Consistent with this is evidence that CSS/GPS sources have predominantly old stellar populations (O'Dea et al 1996;de Vries et al 2000). Alternatively, radio sources may be associated with mergers between relatively gas-poor galaxies, such as a low-mass satellite galaxy falling into a large elliptical galaxy.…”

“…They note that the slope of the surface brightness versus radius relation does not vary significantly between optical and NIR wavelengths, so comparisons of slopes derived for different bands are useful. De Vries et al (2000) find slopes of 5.2 and 4.0 in the HST F110W and F205W bands, respectively. They use these to argue that their CSS/GPS sources are non-BCGs and therefore do not evolve into BCG FR I sources.…”

Nuclear Luminosities and Radio Loudness of Seyfert Nuclei

“…At low redshift, where high-resolution optical and nearinfrared images are now readily available, radio-loud quasars preferentially inhabit luminous, massive, early-type galaxies, whereas the hosts of radio-quiet quasars span a wider range of morphological types (e.g., McLure et al 1999 ;Hamilton, Casertano, & Turnshek 2001). Radio galaxies themselves have long been known to be predominantly giant ellipticals (e.g., Matthews, Morgan, & Schmidt 1964 ;Zirbel 1996 ;de Vries et al 2000). Within this backdrop, Seyfert galaxies, which are generally considered to be the low-luminosity extension of the quasar phenomenon, traditionally have been regarded as radio-quiet objects.…”