Elaine M. Sadler

Galaxy destruction and diffuse light in clusters

ABSTRACT Deep images of the Centaurus and Coma clusters reveal two spectacular arcs ofdiffuse light that stretch for over 100 kpc, yet are just a few kpc wide. At a surfacebrightness of m b ∼ 27−28th arcsec −2 , the Centaurus arc is the most striking exampleknown of structure in the diffuse light component of a rich galaxy cluster. We usenumerical simulations to show that the Centaurus feature can be reproduced by thetidal debris of a spiral galaxy that has been tidally disrupted by the gravitational po-tential of NGC 4709. The surface brightness and narrow dimensions of the diffuse lightsuggest that the disk was co-rotating with its orbital path past pericenter. Featuresthis prominent in clusters will be relatively rare, although at fainter surface bright-ness levels the diffuse light will reveal a wealth of structure. Deeper imaging surveysmay be able to trace this feature for several times its presently observed extent andsomewhere along the tidal debris, a fraction of the original stellar component of thedisk will remain bound, but transformed into a faint spheroidal galaxy. It should bepossible to confirm the galactic origin of the Centaurus arc by observing planetarynebulae along its length with redshifts close to that of NGC 4709.Key words: galaxies: evolution – galaxies: clusters – galaxies: interactions – galaxies:formation.

Spectral Properties and the Effect on Redshift Cut-off of Compact AGNs from the AT20G Survey

We use high angular resolution data, measured from visibility of sources at the longest baseline of 4500 m of the Australia Telescope Compact Array (ATCA), for the Australia Telescope 20 GHz (AT20G) survey to obtain angular size information for > 94% of AT20G sources. We confirm the previous AT20G result that due to the high survey frequency of 20 GHz, the source population is strongly dominated by compact sources (79%). At 0.15 arcseconds angular resolution limit, we show a very strong correlation between the compact and extended sources with flat and steep-spectrum sources respectively. Thus, we provide a firm physical basis for the traditional spectral classification into flat and steep-spectrum sources to separate compact and extended sources. We find the cut-off of -0.46 to be optimum for spectral indices between 1 and 5 GHz and, hence, recommend the continued use of -0.5 for future studies. nWe study the effect of spectral curvature on redshift cut-off of compact AGNs using recently published redshift data. Using spectral indices at different frequencies, we correct for the redshift effect and produce restframe frequency spectra for compact sources for redshift up to ~5. We show that the flat spectra of most compact sources start to steepen at ~30 GHz. At higher frequencies, the spectra of both populations are steep so the use of spectral index does not separate the compact and extended source populations as well as in lower frequencies. We find that due to the spectral steepening, surveys of compact sources at higher frequencies (>5 GHz) will have redshift cut-off due to spectral curvature but at lower frequencies, the surveys are not significantly affected by spectral curvature, thus, the evidence for a strong redshift cut-off in AGNs found in lower frequency surveys is a real cut-off and not a result of K-correction.

A Radio-Optical Study of Resolved Star Formation in SAMI Galaxies

With integral field spectroscopic data from the the Sydney-AAO Multi-object Integralfield spectrograph (SAMI) survey and the VLA, we will study the relationship between star formation (as traced by Hα emission) and the radio continuum emission within galaxies with the aim of better understanding the intricacies of local scaling relations.

Spectral properties and the effect on redshift cut-off of compact active galactic nuclei from the AT20G survey: Spectral properties and z cut-off of AGNs

We use high angular resolution data, measured from visibility of sources at the longest baseline of 4500 m of the Australia Telescope Compact Array (ATCA), for the Australia Telescope 20 GHz (AT20G) survey to obtain angular size information for > 94% of AT20G sources. We confirm the previous AT20G result that due to the high survey frequency of 20 GHz, the source population is strongly dominated by compact sources (79%). At 0.15 arcseconds angular resolution limit, we show a very strong correlation between the compact and extended sources with flat and steep-spectrum sources respectively. Thus, we provide a firm physical basis for the traditional spectral classification into flat and steep-spectrum sources to separate compact and extended sources. We find the cut-off of -0.46 to be optimum for spectral indices between 1 and 5 GHz and, hence, recommend the continued use of -0.5 for future studies. nWe study the effect of spectral curvature on redshift cut-off of compact AGNs using recently published redshift data. Using spectral indices at different frequencies, we correct for the redshift effect and produce restframe frequency spectra for compact sources for redshift up to ~5. We show that the flat spectra of most compact sources start to steepen at ~30 GHz. At higher frequencies, the spectra of both populations are steep so the use of spectral index does not separate the compact and extended source populations as well as in lower frequencies. We find that due to the spectral steepening, surveys of compact sources at higher frequencies (>5 GHz) will have redshift cut-off due to spectral curvature but at lower frequencies, the surveys are not significantly affected by spectral curvature, thus, the evidence for a strong redshift cut-off in AGNs found in lower frequency surveys is a real cut-off and not a result of K-correction.

CO observations of high-z radio galaxies MRC 2104−242 and MRC 0943−242: spectral-line performance of the Compact Array Broadband Backend: CO observations of two high-z radio galaxies

We present the first 7-millimetre observations of two high-redshift, Lyα-bright radio galaxies (MRC 2104-242 and MRC 0943-242) performed with the 2×2 GHz instantaneous bandwidth of the Compact Array Broadband Backend (CABB) at the Australia Telescope Compact Array (ATCA). The aim was to search for 12 CO(1-0) emission in these systems and test the millimetre capabilities of CABB for performing spectral line observations at high redshifts. We show that the stable band and enhanced velocity coverage of CABB, combined with hybrid array configurations, provide the ATCA with excellent 7-mm capabilities that allow reliable searches for the ground transition of CO at high redshifts. In this paper we explicitly discuss the calibration procedures used to reach our results. We set a firm upper limit to the mass of molecular gas in MRC 2104-242 (z = 2.5) of MH2 < 2×10 10 (αx/0.8)M⊙. For MRC 0943-242 (z = 2.9) we derive an upper limit of MH2 < 6 × 10 10 (αx/0.8)M⊙. We also find a tentative 3σ CO detection in the outer part of the giant Lyα halo that surrounds MRC 0943242. The 30-33 GHz radio continuum of MRC 2104-242 and MRC 0943-242 is reliably detected. Both radio sources show a spectral index of α � 1.5 between 1.4 and 30 GHz, with no evidence for spectral curvature within this range of frequencies.

Radio-Mode Feedback in Massive Galaxies at Redshift 0 l z l 1

We have carried out a large observational study of the radio luminosities, stellar populations, and environments of massive galaxies over the redshift range 0 < z < 1. Radio jets powered by an accreting central black hole are common in massive galaxies, and there is a large class of “optically quiet AGN,” with radio emission but no optical/IR signature of blackhole accretion. The central black holes in these galaxies are probably accreting in a radiatively inefficient mode, and our results suggest that “radio-mode feedback” as described by Croton et al. is likely to occur in all masssive early-type galaxies at z < 0.8. While it appears that radioloud AGN occur episodically in all massive early-type galaxies, we also identify a sub-population of galaxies with powerful radio sources and a prominent younger (∼ 10 yr) stellar population that may have undergone recent mergers.