Ilana Klamer

Molecular gas at high redshift: Jet-induced star formation?

We present an alternative interpretation of the observations of BR 1202-0725 at z = 4.695 and show that its properties are consistent with a relativistic jet issuing from the quasar core, propagating into the intergalactic medium, and triggering star formation along its path. Prompted by this finding, we reviewed all the z > 3 objects detected in molecular line emission and found that the distribution of gas and dust in these sources is often spatially or kinematically offset from the host galaxy and preferentially aligned along the radio axis. These observations suggest to us a scenario in which CO emission observed in high-redshift galaxies is located where it forms: along the sites of star formation triggered initially by relativistic jets.

CO (1-0) and CO (5-4) observations of the most distant known radio galaxy at z=5.2

Using the Australia Telescope Compact Array, we have detected CO (1-0) and CO (5-4) from TN J0924-2201 at z = 5.2, the most distant radio galaxy known to date. This is the second highest redshift detection of CO published so far. The CO (1-0) line emission is 250-400 km s-1 wide with a peak flux density of 520 ± 115 μJy beam-1, while the CO (5-4) line emission is 200-300 km s-1 wide with a peak flux density of 7.8 ± 2.7 mJy beam-1. Both transitions are spatially unresolved, but there is marginal evidence for spatial offsets between the CO and the host galaxy; the CO (1-0) is located 28 ± 11 kpc (45 ± 17) north of the radio galaxy, while the CO (5-4) is located 18 ± 8 kpc (28 ± 12) south of the radio galaxy. Higher spatial resolution observations are required to determine the reality of these offsets. Our result is the second detection of CO in a high-redshift galaxy without preselection based on a massive dust content.

A search for distant radio galaxies from SUMSS and NVSS — I. Sample definition, radio and K-band imaging

We present the first results from a pilot study to search for distant radio galaxies in the southern hemisphere (δ 15 mJy. We observed 71 sources without bright optical or near-infrared counterparts at 1.385 GHz with the ATCA, providing ∼5 arcsec resolution images and subarcsec positional accuracy. To identify their host galaxies, we obtained near-infrared K-band images with IRIS2 at the AAT and Soft at the NTT. We identify 92 per cent of the USS sources down to K ∼ 20.5. The SUMSS-NVSS USS sources have a surface density more than 4 times higher than USS sources selected at lower frequencies. This is due to the higher effective selection frequency, and the well-matched resolutions of both surveys constructed using the same source fitting algorithm. The scattering of α > -1.3 sources into the USS sample due to spectral index uncertainties can account for only 35 per cent of the observed USS sources. Because our sample appears to contain a similar fraction of very distant (z > 3) galaxies, selecting USS sources from SUMSS-NVSS should allow us to identify large numbers of massive galaxies at high redshift.

RADIO SUPERNOVA 1987A AT 843 MHz

We report here the —ux densities of the evolving radio source SN 1987A at 843 MHz measured from observations made with the Molonglo Observatory Synthesis Telescope between 1994 September and 2000 May. The radio light curve shows that the rate of increase of the —ux density jumped markedly around days 2800¨3000 (i.e., in the —rst half of 1995) and that since then the radio evolution has been remarkably well —tted by a simple linear increase of 62.7 ^ 0.5 kJy day~1. We discuss in detail the relationship between the radio light curve and the recent brightening of the system at optical wavelengths.

A search for distant radio galaxies from SUMSS and NVSS – II. Optical spectroscopy

This is the second in a series of papers presenting observations and results for a sample of 76 ultra-steep-spectrum (USS) radio sources in the southern hemisphere designed to nd galaxies at high redshift. Here we focus on the optical spectroscopy program for 53 galaxies in the sample. We report 35 spectroscopic redshifts, based on observations with the Very Large Telescope (VLT), the New Technology Telescope (NTT) and the Australian National University’s 2.3m telescope; they include v e radio galaxies with z > 3. Spectroscopic redshifts for the remaining 18 galaxies could not be conrmed: three are occulted by Galactic stars, eight show continuum emission but no discernible spectral lines, whilst the remaining seven galaxies are undetected in medium-deep VLT integrations. The latter are either at very high redshift (z > 7) or heavily obscured by dust. A discussion of the eciency of the USS technique is presented. Based on the similar space density of z > 3 radio galaxies in our sample compared with other USS-selected samples, we argue that USS selection at 843{1400MHz is an ecien t and reliable technique for nding distant radio galaxies.

A binary system of tailed radio galaxies

We present a detailed study of a binary system of tailed radio galaxies which, along with 3C 75, is the only such binary known to exist. The binary is located in a region of low galaxy density at the periphery of a poor cluster Abell S345, but lies close to the massive Horologium‐ Reticulum supercluster. The radio sources have bent-tail morphologies and show considerable meandering and wiggling along the jets, which are collimated throughout their lengths. This work presents observations of the large-scale-structure environment of the binary tailed radio sources with a view to examining the influence of large-scale flows on the morphology and dynamics of the associated radio tails. We argue that the orbital motions of the host galaxies together with tidal accelerations toward the supercluster have resulted in the complex structure seen in these radio tails.