Daniel Golombek

HST Snapshot Survey of 3CR Radio Source Counterparts. I. Intermediate Redshifts

We have obtained images of 267 3CR radio galaxies and quasars by conducting a snapshot survey with HSTs WFPC2 through a broadband red (F702W) filter. This is the first in a series of papers resulting from this survey, describing and presenting the basic data. Here we focus on the 77 radio galaxies within the redshift range 0.1 < z < 0.5 (91% of the total number of 3CR radio galaxies within this redshift range). The images show that on the 01 scale of the HST observations there is a wide variety of structure in radio galaxy morphology. At least 30% of the galaxies show dust, either well-defined dust lanes or chaotically distributed throughout the galaxy. We find disturbed morphologies, such as multiple nuclei and tails of emission, that could indicate merging systems. There is an obvious optical synchrotron jet in 3C 346, and another eight jet candidates are present.

THE DUST-RADIO CONNECTION IN 3CR RADIO GALAXIES

We investigate dust in the nuclear regions of radio galaxies on the basis of 120 images of 3CR radio galaxies in the redshift range 0 < z < 0.5, taken with the WFPC-2 on the Hubble Space Telescope. At least 40 of these radio galaxies show evidence for absorption due to clumpy dust features; a large range of morphologies is observed for these dust features, including disklike and filamentary structures. No difference in host galaxy properties was found between the radio galaxies with clumpy dust and those without. Where dust absorption is detected, the morphological properties of the dust depend strongly upon the Fanaroff & Riley (FR) classification of the source. The dust in FR I host galaxies is generally situated in sharply defined disks on small (<2.5 kpc) scales, and for eight out of the nine FR I galaxies with dust disks, the radio source lies nearly perpendicular to the dust disk. In contrast, FR II host galaxies have dust that varies both in morphology and in linear size, and the correlation between the dust and radio orientation only exists (and less strongly) for the sources that have a significant mass of dust in disks within a distance of 2.5 kpc of the center of the galaxy. The derived dust masses also correlate with the FR type of the host galaxy: high masses of clumpy dust are not seen in FR I radio galaxies, while they are present in FR II radio galaxies. Further, FR I galaxies have derived dust masses that are typically larger than the dust masses found in a matched sample of radio-quiet ellipticals. We suggest that the observed differences between FR I and FR II radio galaxies are produced due to differences in their formation.

Imaging observations of gas and dust in NGC 4696 and implications for cooling flow models

Continuum and emission-line direct CCD observations of the gas and dust in NGC 4696 are analyzed. The wavelength-dependence of extinction is normal. Line luminosities are derived and evidence that the gas and dust are well-mixed is presented. A total power output of the dust lane of roughly 2 x 10 to the 43rd ergs/s is deduced. Constraints on the physical conditions and geometry in the emission-line gas are inferred. An external origin for the dust-lane material is favored from the observations; infall from a gas-rich companion with a normal interstellar medium may have recently taken place. The energy input to the dust and gas of the dust lane by saturated heat conduction from the hot X-ray gas is sufficient to power the optical and infrared emission. If conduction operates, the cool gas and dust act as a heat sink for the hot X-ray atmosphere and this may mimic some of the peripheral properties of a cooling flow. 57 refs.

Hubble Space Telescope imaging of compact steep spectrum radio sources

We present Hubble Space Telescope WFPC2 images taken through a broad red filter (F702W) of 30 Third Cambridge Catalog compact steep spectrum (CSS) radio sources. We have overlaid radio maps taken from the literature on the optical images to determine the radio-optical alignment and to study detailed correspondence. All CSS sources for which the relative orientation between the optical and radio can be measured display good alignment between the optical and radio emission down to the lowest redshift in the sample, z similar to 0.1. The alignment effect does not occur at this relatively low redshift for the large-scale 3CR radio sources, which tend to show a significant alignment only at z > 0.6, as shown by McCarthy et al., Chambers et al., and de Koff et al. We find candidates for optical synchrotron hot spots in 3C 213.1 and 3C 380 and an optical jet in 3C 346.

The structure and ionization of the extended emission-line filaments surrounding the QSO MR 2251-178

This paper presents new VLA radio maps, at 6 cm and 20 cm, of the QSO MR 2251-178, together with deep high-spatial-resolution images in the O II forbidden 3727-A line in the O III forbidden 5007-A line, and H-alpha emission lines, showing the presence of extended emission-line filaments surrounding the MR 2251-178. The morphology of the circumnuclear emission-line regions and an extended system of filaments in different ionization states are shown. The physical characteristics, such as luminosities, densities, mass, and ionization parameters of different filaments are derived. 48 refs.

Hubble Space Telescope Observations of Obscuration Rings in Hercules A: Implications for Energy Transport in Powerful Radio Galaxies

We have used the Hubble Space Telescope to obtain snapshot images of Hercules A, the host galaxy to the powerful radio source 3C 348, through a broadband red filter. We report the discovery of interlocking, kiloparsec-scale rings of obscuration aligned near the radio axis and slightly offset from the galaxys nucleus. We discuss possible models for these rings and their implications for models of energy transport in extragalactic radio jets.

An optical study of 3C 31, 3C 66B, 3C 120, and their jets

The paper presents the results of BVRI CCD photometry of the radio galaxies 3C 31, 3C 66B, and 3C 120, and V polarimetry of 3C 120. The photometry of the jet of 3C 66B definitively establishes the synchrotron nature of the optical emission. No optical counterpart of the radio counterjet in 3C 66B and of the radio jets in 3C 31 and 3C 120 is found. A rotating ring and an ionized region are present, respectively, in 3C 31 (NGC 383) and its companion galaxy NGC 382, but no isophotal distortions are found which could have revealed a gravitational interaction between the two galaxies as is the case in 3C 66B. The elliptical isophotes of 3C 120 show a slight off-centering, roughly in the direction of the radio jet, very much like 3C 66B. An upper limit of 20 percent is found for the polarization level of the condensations in 3C 120. 50 refs.

Southern IRAS quasar with extreme Fe II emission

A new extreme Fe II emission IRAS quasar was found during a search of new southern warm IRAS AGNs. The optical spectrum of this object is dominated by extremely strong Fe II emission and also by the H I, He I, and O III forbidden lines, swamped by the Fe II multiplets. A careful and detailed analysis of the spectrum was carried out to determine the Fe II 4570 A/H-beta ratio. The value obtained, as well as other observed properties, are described and compared with those obtained for the three other known objects with similar extreme Fe II emission. 22 refs.

New Optical Fields and Candidates of 10 3C Radio Sources. I. The R-Band Images*

Using new R-band images acquired as part of the 3CR Snapshot Survey with the Wide Field Planetary Camera 2 on the Hubble Space Telescope, we present positive optical identifications of three previously unidentified 3C radio sources (3C 91, 134, and 141). The fields of five others (3C 131, 152, 399.1, 415.2, and 468.1) are also presented with tentative identifications for some. The fields of two other sources (3C 249 and 3C 250) are empty. Eight sources lie along the Galactic plane (|b| < 10°) and are consequently heavily obscured, while the two empty fields are located at higher Galactic latitudes. Observed and corrected R magnitudes of each candidate are calculated. Confirmation of the true optical counterpart will require deep near-IR imaging and long-slit spectroscopy to determine the nature and redshift of the counterparts and candidates.

The Elusive Optical Jets

Imaging observations in the U band of eight radio galaxies are presented. We find no optical counterpart to the radio jets. For the three radio galaxies 3C 147, 3C 279 and 3C 433, we show that the radio to optical spectral index of the jet is significantly higher than the typical values found in the three best known optical jets (M87, 3C 273 and 3C 66B). We conclude that the cut-off frequencies are lower than