Near-Infrared Imaging of Steep Spectrum Radio Quasars

Abstract

We present the results of a high resolution (0.27 ′′ px −1 ) near-infrared H band (1.65 µm) imaging survey of a complete sample of 20 flat radio spectrum quasars (FSRQ) extracted from the 2Jy catalogue of radio sources (Wall & Peacock 1985). The observed objects are intrinsically luminous with median M(B) = -25.5. The median redshift of the objects in the sample is z = 0.65. At this redshift, the H band observations probe the old stellar population of the hosts at rest frame wavelength of ∼1 µm.We are able to detect the host galaxy clearly for six (30 %) FSRQs and marginally for six (30 %) other FS-RQs, while the object remains unresolved for eight (40 %) cases. We find the galaxies hosting FSRQs to be very luminous (M(H)∼-27). Compared with the typical galaxy luminosity L* (M*(H)∼-25) they appear ∼2 mag brighter, although the undetected hosts may reduce this difference. They are also at least as bright as, and probably by ∼1 mag brighter than, the brightest cluster galaxies (M(H)∼-26). The luminosities of the FSRQ hosts are intermediate between host galaxies of low redshift radio-loud quasars and BL Lac objects (M(H)∼-26), and the hosts of high redshift radio-loud quasars (M(H)∼-29), in good agreement with current unified models for radio-loud AGN, taking into account stellar evolution in the elliptical host galaxies. Finally, we find an indicative trend between the host and nuclear luminosity for the most luminous FS-RQs, supporting the suggestion based on studies of lower redshift AGN, that there is a minimum host galaxy luminosity which increases linearly with the quasar luminosity.

An optical imaging study of 0.4≤z≤0.8 quasar host galaxies

“…Compared to a present-day field galaxy with a Schechter magnitude of M * R = −20.9 (Lin et al 1996), the mean values found for the hosts correspond to ∼10 L * , similar to the values found in other intermediate redshift studies (5−12 L * , Hooper et al 1997;Kotilainen et al 1998;Kotilainen & Falomo 2000). The difference in mean magnitude between radio-loud and radio-quiet hosts is quite small and less than 1σ (but in the case of I band 2σ).…”

“…When turning to redshifts >0.5 but lower than unity, very few observations of radio-quiet host galaxies exist. The mean magnitudes of radio-loud hosts have grown brighter by < ∼ 0.5 mag; Márquez et al (1999) find a mean of −23.0 ± 0.4, while Kotilainen et al (1998) derive a mean of −23.1 ± 0.5 for FS host galaxies and −23.6 ± 0.3 for SS hosts (Kotilainen & Falomo 2000), where quoted magnitudes have been recomputed to the R band and the cosmology of this paper.…”

“…Later investigations have been performed mainly in the nearinfrared, where the contrast between host and nuclear light is greater (Carballo et al 1998;Kotilainen et al 1998;Kotilainen & Falomo 2000;Márquez et al 1999Márquez et al , 2001, resulting in host luminosities a few factors of L * brighter than those obtained at lower redshifts. Since RLQ:s have been targetted almost exclusively, the difference in mean magnitude between RLQ and RQQ host galaxies is not very well studied at these redshifts.…”

Host Galaxies of Low‐zRadio‐loud Quasars: A Search ofHubble Space TelescopeArchives

“…Extended nebulosities around quasars were investigated by several groups using various facilities from the ground (e.g., Hutchings, Janson, & Neff 1989;Veron-Cetty & Woltjer 1990;McLeod & Rieke 1995;Taylor et al 1996;Kotilainen & Falomo 2000). Altogether, these works have confirmed the presence of the host galaxies.…”

QSO Hosts and Companions at Higher Redshifts

“…As well as the redshifts above 1, I have selected host galaxy measurements over the redshift range below 1 to cover the redshift range down to the well-studied low redshift QSOs (Kotilainen et al 1998, Kotilainen andFalomo 2000) . The diagrams show the result, attempting to be comprehensive at higher redshifts, while selecting quantities derived with reliable methods and good data.…”