ATNF Science Symposium 2007
AbstractsSpeaker: Nadia Lo (UNSW)
Title: Detection of SiO emission from a massive dense cold core
With the new Mopra Spectrometers (MOPS) we have carried out multi-molecular line survey of the giant molecular cloud, G333. From this multi-line survey we have detected thermal SiO emission (a shocks and outflows tracer) from the massive cold dense core G333.125-0.56. The core is invisible at wavelengths shorter than 70 um and has compact 1.2 mm dust continuum. From ammonia inversion lines we obtained a temperature of 13 K. In addition we have also detected a 22 GHz water maser in the core, together with methanol maser emission, suggesting the core will host massive star formation.
Speaker: Ilana Feain (ATNF)
Title: A long overdue synthesis image of Centaurus A
Centaurus A is by far the closest active supermassive black hole in the Universe, and has radio jet/lobe structures that span about 4 x 9 degrees on the sky. To date, the large-scale structure of Centaurus A is known only from the Parkes single dish images. But with such low spatial resolution, it was simply not possible to study the lobe structure in much detail. Starting on 20 December 2006, we began an Australia Telescope Compact Array campaign to mosaic the entire radio source at 1.4GHz. The full polarisation images we are making will have a spatial resolution of about 600 parsecs, similar to the spatial resolution of the famous Virgo A (M87) and Cygnus A images made with the VLA. But the Centaurus A image will have at least 4 times the number of resolution elements, because the radio source is physically so much larger than both Virgo A (80kpc) and Cygnus A (140 kpc). This essentially means that Centaurus A's radio lobe structure can be studied in more detail than is possible for any other radio galaxy! Our scientific aims are (i) to explore elements of feedback (i.e. the interaction, influence and impact) between the radio plasma and physical processes in the intergalactic medium (IGM), like shocks, ionised filaments, star formation and hot gas bubbles, (ii) to probe the foreground magnetic fields (galaxies, high velocity clouds, our Galaxy) by exploiting Centuarus A as a background polarised screen and (iii) to investigate the Faraday rotation caused by the radio lobes and the IGM into which the lobes are expanding, using lines of sight to the hundreds of polarised background sources. We are now half way through and the results are indeed promising.
Speaker: Steve Longmore (UNSW)
Title: The molecular environment of massive star forming cores associated with Class II methanol maser emission
Class II methanol masers are exclusively observed towards high mass star formation regions and are generally either not associated or offset from UCHII regions. They are therefore thought to trace stages of massive star formation prior to UCHII region formation. To investigate their role as an evolutionary tracer, we have recently completed a large observing program with the ATCA to investigate the dynamical and physical properties of molecular gas towards a sample of massive star formation regions traced by Class II methanol maser emission. From LVG modelling of multiple ammonia inversion transitions, we have calculated reliable gas column densities and kinetic temperatures which have been used to separate the thermal and non-thermal contribution to the measured linewidth and hence investigate turbulent injection. With simultaneously observed 24GHz continuum emission and additional 95GHz observations we then investigated which of these regions was associated with free-free emission from gas ionised by an existing massive star and the location of thermal dust continuum emission within the region. We find that the molecular gas in many of these regions breaks up into multiple sub-clumps which we separate into groups based on their association with/without methanol maser and cm continuum emission. The temperature and dynamic state of the molecular gas is markedly different between the groups. We attempt to assess the evolutionary state of the cores in the groups and thus investigate the role of Class II methanol masers in massive star formation.
Speaker: Andrew Walsh (JCU)
Title: Mopra observations of southern massive star formation sites
With the recent upgrade of Mopra, including the new receivers and MOPS, the telescope has become a very efficient tool for surveying large parts of frequency space. I will report on some early observations made with this new system towards sites of massive star formation in our Galaxy at both 3mm and 12mm.
Speaker: Sarah Maddison (Swin)
Title: Millimetre and centimetre studies of protoplanetary disks
We have been conducting a 3mm continuum survey of disks around young stars (both T Tauri and Herbig Ae/B stars) in the Chamaeleons and Lupus clouds to investigate grain growth within protoplanetary disks. Using the fluxes to determine the millimetre spectral energy indices, we can obtain limits on the grain size in the disks. We present results from our successful 2005 millimetre season, in which we observed 15 sources. The opacity indices suggest the presence of mm-sized dust aggregates and hence substantial grain growth in the majority of these disks. We also present preliminary results from our follow-up 2006 observations of three sources (HD100546, WW Cha and RU Lup) are centimetre wavelengths (1.2, 3 and 6cm) and discuss the possibility of detecting pebble-sized "grains" in these disks.
Speaker: Ilana Feain (ATNF)
Title: First light at 7mm
Speaker: Naomi McClure-Griffiths (ATNF)
Title: Magnetically Dominated Strands of Cold Hydrogen in the Riegel-Crutcher Cloud
I present new high resolution (100") neutral hydrogen (HI) images of the Riegel-Crutcher cloud observed in self-absorption. The Riegel-Crutcher cloud lies in the direction of the Galactic center at a distance of 125+/-25 pc. Our observations resolve the very large, nearby sheet of cold hydrogen into a spectacular network of dozens of hairlike filaments. Individual filaments are remarkably elongated, being up to 17 pc long with widths of less than ~0.1 pc. The strands are reasonably cold, with spin temperatures of ~40 K and in many places appearing to have optical depths larger than 1. Comparing the H I images with observations of stellar polarization, we show that the filaments are very well aligned with the ambient magnetic field. We argue that the structure of the cloud has been determined by its magnetic field. In order for the cloud to be magnetically dominated the magnetic field strength must be >30 micro G.
Speaker: Alyson Ford (Swin)
Title: HI clouds in the lower Galactic halo
Faint, discrete HI clouds in the disk-halo interface of the Milky Way have been observed within the Galactic All Sky Survey (GASS). Because these clouds follow Galactic rotation, we can determine their distances. This provides a huge advantage over most HI clouds by allowing us to determine their physical properties such as size and mass. Results from a catalogue of HI clouds within the GASS pilot region will be presented, including a description of their physical properties, an analysis of their spatial distribution and implications for their origin.
Speaker: Paul Jones (UNSW)
Title: The Central Molecular Zone around Sagittarius B2
Using the new capabilities of the MOPS digital filter bank on the Mopra telescope, we have mapped a 5 x 5 arcmin area of the Sagittarius B2 molecular cloud complex. We have covered nearly all of the 83.5 to 113.5 GHz frequency range with 4 tunings of the 8 GHz wide-band mode to image over 50 spectral lines, and have also observed 24 of these lines with the zoom mode (3 tunings) at higher velocity resolution. This shows substantial differences in chemical and physical conditions within the complex. This is the first part of a larger study of the Central Molecular Zone (CMZ) in the inner few degrees around the Galactic Centre.
Speaker: Joris Verbiest (Swin)
Title: P140: A Decade of High Precision Pulsar Timing
The longest running project at the Parkes radio telescope has come to the end of its first decade. I present a selection of results that were recently obtained through combination of the data from this long campaign and demonstrate a new, robust and highly accurate method of distance determination to binary millisecond pulsars.
Speaker: Roberto Ricci (ATNF)
Title: The AT20G survey: an update
I will present an update on the status of the Australia Telescope 20 GHz (AT20G) survey. This survey has already covered the sky south of 15 deg declination at 20 GHz in the continuum down to a limiting flux density of 40 mJy. Its aim is to study the high-frequency properties (surface density, spectral shape, variability, and polarization) of source populations such as flat-spectrum radio quasars, BL Lac objects, and sources with highly inverted spectral components. The study of the Galactic source population (in particular Ultra Compact HII regions) is also part of the project. The survey will complete the coverage of the southern hemisphere next September.
Speaker: Kate Brooks (ATNF)
Title: A multiwavelength study of young massive star-forming regions: I. The ionized gas content
We present multi-frequency radio continuum observations made with the Australia Telescope Compact Array of a sample of 15 southern hemisphere luminous IRAS point sources, all with colours typical of compact HII regions and associated with CS(2-1) emission. We find that the HII regions in our sample, most of which lie at the centre of massive and dense molecular cores with molecular hydrogen densities of ~4x105 cm-3 and linewidths of ~3 km s-1, are excited by stars with an output of UV photons of typically less than 3x1048 s-1. Under these conditions the regions of ionised gas reach pressure equilibrium with the dense molecular surroundings in only ~5x103 yr. We conclude that the main mechanism of confinement of the compact HII regions in our sample is provided by the high density and large turbulent pressure of the surrounding molecular gas, and therefore their age can be much longer than their dynamical time scale. If the objects in our sample are representative of the Galactic IRAS sources with colours of compact HII regions, then the problem with the large rate of massive star formation in the Galaxy might be solved.
Speaker: Jess Broderick (Sydney)
Title: High-redshift radio galaxies from the MRCR and SUMSS
High-redshift radio galaxies (HzRGs; z > 2) play a fundamental role in our understanding of the formation and evolution of the most massive galaxies in the early Universe. The most efficient way of finding these rare objects is through ultra-steep spectrum (USS) selection. We are conducting an extensive program to find HzRGs in the south by selecting USS sources from a deeper re-analysis of the 408 MHz Molonglo Reference Catalogue (MRCR), the 843 MHz Sydney University Molonglo Sky Survey (SUMSS) and the 1400 MHz NRAO VLA Sky Survey (NVSS). High-resolution 20 and 13 cm ATCA observations are used to secure each host galaxy identification for follow-up spectroscopy, and also to investigate the environments of the hosts through a combination of spectral energy distributions, fractional polarization and Faraday rotation measures. In this talk, I will discuss the radio properties of our sample, as well as a related 12 mm and 3 cm ATCA study that resulted in the discovery of an extreme rotation measure (-9600 rad/m^2) in the z=2.575 source PKS B0529-549, the largest seen thus far in the environment of a z > 2 radio galaxy.
Speaker: Ray Norris (ATNF)
Title: ATLAS: The Australia Telescope Large Area Survey
Understanding the formation and evolution of galaxies and AGN as a function of cosmic time is one of the most intensely investigated issues in contemporary astronomy, and is a key science driver for next-generation telescopes such as ELTs, SKA, and ALMA. Today's instruments can already give profound insights into the galaxy population at high redshifts, and a number of current surveys (e.g. ELAIS, GOODS, COSMOS) are asking questions like: When did most stars form? How do AGN influence star formation? What is the spatial distribution of evolved galaxies, starbursts, and AGN at 0:5 < z < 3? However, most of these surveys are primarily at optical and IR wavelengths, and can be significantly misled by dust extinction. Radio observations not only overcome dust extinction, but also provide data on AGNs that are unavailable at other wavelengths.
We are using the Australia Telescope Compact Array to image about seven square degrees surrounding the SWIRE Chandra Deep Field South and ELAIS-S1 regions, with the aim of producing the widest deep radio survey ever attempted, in fields with deep optical, infrared, and X-ray data. Our primary goal is to find out how galaxies formed and evolved through cosmic time, by penetrating the heavy dust extinction which is found in active galaxies at all redshifts, and studying the star formation activity and active galactic nuclei buried within.
Although we are only about half-way through the survey, our data are proving remarkably fruitful. For example, we have discovered a new and unexpected class of object (the Infrared-Faint Radio Sources), we have found that the radio-FIR correlation extends to low flux densities, and we have found powerful AGN-like radio objects in galaxies with star-forming SEDs. More information is on http://www.atnf.csiro.au/research/deep/
Speaker: Marcella Massardi (SISSA, Italy)
Title: The AT20G Survey and the CMB Missions
The knowledge of high frequency radio-sources population is poor at all the flux densities. However, the increasing interest in cosmic microwave background (CMB) maps provided by the on-going NASA WMAP mission and the forthcoming ESA Planck mission requires good measurements of high frequency properties of radio-sources to interpret the data both in flux density and polarization. Radio sources are in fact one of the major contaminants of the CMB observations in the radio band. The AT20G survey will give a decisive improvement to the knowledge of source population properties. Focusing mainly on the properties of the bright source sample of the AT20G survey (extragalactic sources with 20 GHz flux above 500 mJy), we'll show the main applications that our data may have in the Planck mission. AT20G results will give hints on positions, high frequency fluxes, spectral behaviour a nd polarization of sources that should be detected, improvements to the detection techniques and to the mothod of component separation and will suggest possible candidates as polarization calibrators.
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