Host Galaxies, Obscuration, and Nuclear Structure of Three Nearby Compact Symmetric Objects

Abstract

We present three-band Hubble Space T elescope imaging of three nearby (z ¹ 0.1) compact symmetric objects : 4C 31. 04, 1946]708, and 1146]596. These objects were chosen on the basis of proximity to Earth as well as H I 21 cm line absorption. The inner H-band isophotes of these galaxies are well Ðtted by Nuker models, typical of nearby elliptical galaxies. Each shows a signiÐcant Ñattening in the isophotal proÐle at radii as well as signiÐcant variations in ellipticity and P.A. However, as previous D0A .5, authors have noted, neither is uncommon for elliptical galaxies. All three objects show modest departures from Nuker law models at radii of 1È5 kpc. Each galaxy shows large well-distributed dust h 60 1 features, which are somewhat concentrated in the nuclear regions in features that resemble disks or tori. We Ðnd that the amount of dust in these galaxies is about 10 times higher than normal for elliptical galaxies and radio galaxy hosts. The major axes of the nuclear dust disks tend to be oriented roughly perpendicular to the radio axis. One galaxy, 4C 31.04, exhibits bright nuclear regions well aligned with the radio axis, while another, 1146]596, shows a signiÐcant near-IR excess resembling a stellar bar along its dust disk. The combination of outwardly normal isophotal proÐles with signiÐcant variations in P.A. and ellipticity is consistent with the host galaxies being relatively recent merger remnants and the mergers having occurred yr ago. Such a merger could have "" triggered ÏÏ the onset of the current Z108 active phase seen in these objects, but our data require a signiÐcant time delay between the merger event and the onset of nuclear activity. However, these data are also consistent with the hypothesis that the onset of nuclear activity in radio galaxies is due to relatively minor "" feeding ÏÏ events and/or the formation of "" bars within bars,ÏÏ events which would disturb the internal kinematics only slightly.

Lobe advance velocities in the extragalactic compact symmetric object 4C 31.04

“…The presence of a circumnuclear disk is also supported by HST observations (Perlman et al 2001), which reveal a disk-like dusty feature of somewhat larger scale but similar orientation to the one suggested by Conway. The optical nucleus is also found to have cone-like features well aligned with the radio axis.…”

The Centaurus A Northern Middle Lobe as a Buoyant Bubble

“…For example Perlman et al (2001) have found evidence for old (D108 yr) merging activity in three young compact symmetric object (CSO) radio galaxies and have suggested that the mergers may be related to a delayed onset of radio activity. The parallels with Cen A are obvious.…”

Compact sources in the Bologna Complete Sample: high-resolution VLA observations and optical data

“…VLBA (Very Long Baseline Array) images at 5 GHz show a compact core component with hot spots and lobes on either side (Giroletti et al 2003). Spectral line VLBI (Very Long Baseline Interferometer) observations reveal the presence of an edge-on circumnstellar H I disk (Perlman et al 2001). The optical nucleus is also found to have cone-like features well aligned with the radio axis.…”