MALT-45: A 7 mm survey of the southern Galaxy - I. Techniques and spectral line data

We present the first results from the MALT-45 (Millimetre Astronomers Legacy Team - 45 GHz) Galactic Plane survey. We have observed 5 square-degrees ($l = 330 - 335$, $b = pm0.5$) for spectral lines in the 7 mm band (42-44 and 48-49 GHz), including $text{CS}$ $(1-0)$, class I $text{CH}_3text{OH}$ masers in the $7(0,7)-6(1,6)$ $text{A}^{+}$ transition and $text{SiO}$ $(1-0)$ $v=0,1,2,3$. MALT-45 is the first unbiased, large-scale, sensitive spectral line survey in this frequency range. In this paper, we present data from the survey as well as a few intriguing results; rigorous analyses of these science cases are reserved for future publications. Across the survey region, we detected 77 class I $text{CH}_3text{OH}$ masers, of which 58 are new detections, along with many sites of thermal and maser $text{SiO}$ emission and thermal $text{CS}$. We found that 35 class I $text{CH}_3text{OH}$ masers were associated with the published locations of class II $text{CH}_3text{OH}$, $text{H}_2text{O}$ and $text{OH}$ masers but 42 have no known masers within 60 arcsec. We compared the MALT-45 $text{CS}$ with $text{NH}_3$ (1,1) to reveal regions of $text{CS}$ depletion and high opacity, as well as evolved star-forming regions with a high ratio of $text{CS}$ to $text{NH}_3$. All $text{SiO}$ masers are new detections, and appear to be associated with evolved stars from the $it{Spitzer}$ Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE). Generally, within $text{SiO}$ regions of multiple vibrational modes, the intensity decreases as $v=1,2,3$, but there are a few exceptions where $v=2$ is stronger than $v=1$.

Molecular line mapping of the giant molecular cloud associated with RCW 106 - IV. Ammonia towards dust emission

Here we report observations of the two lowest inversion transitions of ammonia with the 70-m Tidbinbilla radio telescope. They were conducted to determine the kinetic temperatures in the dense clumps of the G333 giant molecular cloud associated with RCW 106 and to examine the effect that accurate temperatures have on the calculation of derived quantities such as mass. This project is part of a larger investigation to understand the timescales and evolutionary sequence associated with high-mass star formation, particularly its earliest stages. Assuming that the initial chemical composition of a giant molecular cloud is uniform, any abundance variations within will be due to evolutionary state. We have identified 63 clumps using SIMBA 1.2-mm dust continuum maps and have calculated gas temperatures for most (78 per cent) of these dense clumps. After using Spitzer GLIMPSE 8.0 $mu$m emission to separate the sample into IR-bright and IR-faint clumps, we use statistical tests to examine whether our classification shows different populations in terms of mass and temperature. We find that clump mass and column density show no significant population difference, and that kinetic temperature is the best parameter to distinguish between the gravitationally bound state of each clump. The kinetic temperature was the only parameter found to have a significantly low probability of being drawn from the same population. This suggests that clump radii does not have a large effect on the temperature of a clump, so clumps of similar radii may have different internal heating mechanisms. We also find that while the IR-bright clumps have a higher median virial mass, both samples have a similar range for both virial mass and FWHM. There are 87 per cent (40 of 46) of the clumps with masses larger than the virial mass, suggesting that they will form stars or are already undergoing star formation.

Pilot Observations for MALT-45: A Galactic Plane Survey at 7mm

We introduce the MALT-45 (Millimetre Astronomers Legacy Team - 45 GHz) Galactic plane survey and describe pilot survey results with the Australia Telescope Compact Array (ATCA). The pilot survey was conducted to test the instrumentation and observational technique of MALT-45, before commencing the full survey. We mapped two half-square degree regions within the southern Galactic plane around the G333 giant molecular cloud, using fast mosaic mapping. Using the new Compact Array Broadband Backend (CABB) on the ATCA, we were able to observe two 2048 MHz spectral windows, centred on frequencies 43.2 and 48.2 GHz. Although only a coarse spectral resolution of around 7 km/s was available to us, we detect widespread, extended emission in the CS (1-0) ground state transition. We also detect eight Class I CH3OH masers at 44 GHz and three SiO masers in vibrationally excited (1-0) transitions. We also detect the H53a radio recombination line, non-vibrationally excited SiO (1-0) and emission in the CH3OH 1_1-0_0 A+ line.