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T. Wong
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A new astronomical window into the southern skies has been opened with the high-frequency upgrade to the Australia Telescope Compact Array (ATCA), which allows radio-interferometric mapping of sources at wavelengths as short as 3mm. In anticipation of the upgrades completion, a two-day workshop was held at the University of Melbourne in November 2001. The workshop covered a diverse range of fields, tied together by a common theme of identifying key areas where ATCA observations can have an impact. More than half of the talks were concerned with molecular clouds and star formation, with the remainder covering topics such as molecular gas in the Galactic Centre, Seyfert nuclei, and high-redshift objects. Some early results from the 3mm and 12mm prototype systems were also presented. In consultation with the speakers, we are presenting in this article a summary of the talks. The original slides are available at http://www.atnf.csiro.au/whats_on/workshops/mm_science2001/ .
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Sensitive, imaging observations of the 1.1 mm dust continuum emission from a 1 deg^2 area collected with the AzTEC bolometer camera on the Large Millimeter Telescope are presented. A catalog of 1545 compact sources is constructed based on a Wiener-optimization filter. These sources are linked to larger clump structures identified in the Bolocam Galactic Plane Survey. Hydrogen column densities are calculated for all sources and mass and mean volume densities are derived for the subset of sources for which kinematic distances can be assigned. The AzTEC sources are localized, high density peaks within the massive clumps of molecular clouds and comprise 5-15% of the clump mass. We examine the role of the gravitational instability in generating these fragments by comparing the mass of embedded AzTEC sources to the Jeans mass of the parent BGPS object. For sources with distances less than 6 kpc the fragment masses are comparable to the clump Jeans mass, despite having isothermal Mach numbers between 1.6 and 7.2. AzTEC sources linked to ultra-compact HII regions have mass surface densities greater than the critical value implied by the mass-size relationship of infrared dark clouds with high mass star formation while AzTEC sources associated with Class II methanol masers have mass surface densities greater than 0.7 g cm^{-2} that approaches the proposed threshold required to form massive stars.
The supermassive black hole, Sagittarius A* (Sgr A*), at the centre of the Milky Way undergoes regular flaring activity which is thought to arise from the innermost region of the accretion flow. We performed the monitoring observations of the Galactic Centre to study the flux-density variations at 3mm using the Australia Telescope Compact Array (ATCA) between 2010 and 2014. We obtain the light curves of Sgr A* by subtracting the contributions from the extended emission around it, and the elevation and time dependent gains of the telescope. We perform structure function analysis and the Bayesian blocks representation to detect flare events. The observations detect six instances of significant variability in the flux density of Sgr A* in three observations, with variations between 0.5 to 1.0 Jy, which last for 1.5 $-$ 3 hours. We use the adiabatically expanding plasmon model to explain the short time-scale variations in the flux density. We derive the physical quantities of the modelled flare emission, such as the source expansion speed $v_{mathrm{exp}}$, source sizes, spectral indices, and the turnover frequency. These parameters imply that the expanding source components are either confined to the immediate vicinity of Sgr A* by contributing to the corona or the disc, or have a bulk motion greater than $v_{mathrm{exp}}$. No exceptional flux density variation on short flare time-scales was observed during the approach and the flyby of the dusty S-cluster object (DSO/G2). This is consistent with its compactness and the absence of a large bow shock.
Extremely high velocity emission likely related to jets is known to occur in some proto-Planetary Nebulae. However, the molecular complexity of this kinematic component is largely unknown. We observed the known extreme outflow from the proto-Planetary Nebula IRAS 16342-3814, a prototype water fountain, in the full frequency range from 73 to 111 GHz with the RSR receiver on the Large Millimetre Telescope. We detected the molecules SiO, HCN, SO, and $^{13}$CO. All molecular transitions, with the exception of the latter are detected for the first time in this source, and all present emission with velocities up to a few hundred km s$^{-1}$. IRAS 16342-3814 is therefore the only source of this kind presenting extreme outflow activity simultaneously in all these molecules, with SO and SiO emission showing the highest velocities found of these species in proto-Planetary Nebulae. To be confirmed is a tentative weak SO component with a FWHM $sim$ 700 km s$^{-1}$. The extreme outflow gas consists of dense gas (n$_{rm H_2} >$ 10$^{4.8}$--10$^{5.7}$ cm$^{-3}$), with a mass larger than $sim$ 0.02--0.15 M$_{odot}$. The relatively high abundances of SiO and SO may be an indication of an oxygen-rich extreme high velocity gas.
The Cherenkov Telescope Array, CTA, will be the major global observatory for very high energy gamma-ray astronomy over the next decade and beyond. The scientific potential of CTA is extremely broad: from understanding the role of relativistic cosmic particles to the search for dark matter. CTA is an explorer of the extreme universe, probing environments from the immediate neighbourhood of black holes to cosmic voids on the largest scales. Covering a huge range in photon energy from 20 GeV to 300 TeV, CTA will improve on all aspects of performance with respect to current instruments. The observatory will operate arrays on sites in both hemispheres to provide full sky coverage and will hence maximize the potential for the rarest phenomena such as very nearby supernovae, gamma-ray bursts or gravitational wave transients. With 99 telescopes on the southern site and 19 telescopes on the northern site, flexible operation will be possible, with sub-arrays available for specific tasks. CTA will have important synergies with many of the new generation of major astronomical and astroparticle observatories. Multi-wavelength and multi-messenger approaches combining CTA data with those from other instruments will lead to a deeper understanding of the broad-band non-thermal properties of target sources. The CTA Observatory will be operated as an open, proposal-driven observatory, with all data available on a public archive after a pre-defined proprietary period. Scientists from institutions worldwide have combined together to form the CTA Consortium. This Consortium has prepared a proposal for a Core Programme of highly motivated observations. The programme, encompassing approximately 40% of the available observing time over the first ten years of CTA operation, is made up of individual Key Science Projects (KSPs), which are presented in this document.
Here we describe the Compact Array Broadband Backend (CABB) and present first results obtained with the upgraded Australia Telescope Compact Array (ATCA). The 16-fold increase in observing bandwidth, from 2 x 128 MHz to 2 x 2048 MHz, high bit sampling, and addition of 16 zoom windows (each divided into a further 2048 channels) provide major improvements for all ATCA observations. The benefits of the new system are: (1) hugely increased radio continuum and polarization sensitivity as well as image fidelity, (2) substantially improved capability to search for and map emission and absorption lines over large velocity ranges, (3) simultaneous multi-line and continuum observations, (4) increased sensitivity, survey speed and dynamic range due to high-bit sampling, and (5) high velocity resolution, while maintaining full polarization output. The new CABB system encourages all observers to make use of both spectral line and continuum data to achieve their full potential. Given the dramatic increase of the ATCA capabilities in all bands (ranging from 1.1 to 105 GHz) CABB enables scientific projects that were not feasible before the upgrade, such as simultaneous observations of multiple spectral lines, on-the-fly mapping, fast follow-up of radio transients (e.g., the radio afterglow of new supernovae) and maser observations at high velocity resolution and full polarization. The first science results presented here include wide-band spectra, high dynamic-range images, and polarization measurements, highlighting the increased capability and discovery potential of the ATCA.
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