Catherine Braiding

The 22 m diameter Mopra telescope in Australia is being used to undertake an improved survey of the CO J = 1{0 line at 3mm along the 4th quadrant of the Galaxy, achieving an order of magnitude better spatial and spectral resolution (i.e. 0.6 and 0.1 km/s) than the Dame et al. (2001) survey that is publically available for the Southern Galactic plane. Furthermore, the Mopra CO survey includes the four principal isotopologues of the CO molecule (i.e. 12CO, 13CO, C18O and C17O). The survey makes use of an 8 GHz-wide spectrometer and a fast mode of on-the-y mapping developed for the Mopra telescope, where the cycle time has been reduced to just 1=4 of a second. 38 square degrees of the Galaxy, from l = 306{344, b = 0:5 have currently been surveyed, together with additional 9 sq. deg. regions around the Carina complex and the Central Molecular Zone. We present new results from the survey (see also Burton et al., 2013, 2014). The Mopra CO data are being made publically available as they are published; for the latest release see the project website at www.phys.unsw.edu.au/mopraco.

David Rebolledo, Michael Burton, Anne Green, Catherine Braiding, Sergio Molinari, Graeme Wong, Rebecca Blackwell, Davide Elia and Eugenio Schisano

We report high resolution observations of the 12CO(1 → 0) and 13CO(1 → 0) molecular lines in the Carina Nebula and the Gum 31 region obtained with the 22-m Mopra telescope as part of the The Mopra Southern Galactic Plane CO Survey. We cover 8 deg2 from l = 285◦ to 290◦ , and from b = −1.5 ◦ to +0.5◦ . The molecular gas column density distributions from both tracers have a similar range of values. By fitting a grey-body function to the observed infrared spectral energy distribution from Herschel maps, we derive gas column densities and dust temperatures. The gas column density has values in the range from 6.3× 1020 to 1.4×1023 cm−2 , while the dust temperature has values in the range from 17 to 43 K. The gas column density derived from the dust emission is approximately described by a log-normal function for a limited range of column densities. A high-column density tail is clearly evident for the gas column density distribution, which appears to be a common feature in regions with active star formation. There are regional variations in the fraction of the mass recovered by the CO emission lines with respect to the total mass traced by the dust emission. These variations may be related to changes in the radiation field strength, variation of the atomic to molecular gas fraction across the observed region, differences in the CO molecule abundance with respect to H2, and evolutionary stage differences of the molecular clouds that compose the Carina Nebula-Gum 31 complex.

Michael G. Burton, Michael C. B. Ashley, Catherine Braiding, Matthew Freeman, Craig Kulesa, Mark G. Wolfire, David J. Hollenbach, Gavin Rowell, and James Lau

We present spectral data cubes of the [CI] 809 GHz, 12CO 115 GHz, 13CO 110 GHz, and HI 1.4 GHz line emission from a ∼1 square degree region along the l = 328 (G328) sightline in the Galactic Plane. Emission arises principally from gas in three spiral arm crossings along the sightline. The distribution of emission in the CO and [CI] lines is found to be similar, with the [CI] slightly more extended, and both are enveloped in extensive HI. Spectral line ratios per voxel in the data cubes are found to be similar across the entire extent of the Galaxy. However, toward the edges of the molecular clouds the [CI]/13CO and 12CO/13CO line ratios rise by ∼50%, and the [CI]/HI ratio falls by ∼10%. We attribute this to these sightlines passing predominantly through the surfaces of photodissociation regions (PDRs), where the carbon is found mainly as C or C+, while the H2 is mostly molecular, and the proportion of atomic gas also increases. We undertake modeling of the PDR emission from low density molecular clouds excited by average interstellar radiation fields and cosmic-ray ionization to quantify this comparison, finding that depletion of sulfur and reduced PAH abundance is needed to match line fluxes and ratios. Roughly one-third of the molecular gas along the sightline is found to be associated with this surface region, where the carbon is largely not to be found in CO. Approximately 10% of the atomic hydrogen along the sightline is cold gas within PDRs.

S. Heinz , M. Burton, C. Braiding , W. N. Brandt , P. G. Jonker, P. Sell , R. P. Fender, M. A. Nowak, and N. S. Schulz

Circinus X-1 exhibited a bright X-ray flare in late 2013. Follow-up observations with Chandra and XMM-Newton from 40 to 80 days after the flare reveal a bright X-ray light echo in the form of four well-defined rings with radii from 5 to 13 arcmin, growing in radius with time. The large fluence of the flare and the large column density of interstellar dust toward Circinus X-1 make this the largest and brightest set of rings from an X-ray light echo observed to date. By deconvolving the radial intensity profile of the echo with the MAXI X-ray light curve of the flare we reconstruct the dust distribution toward Circinus X-1 into four distinct dust concentrations. By comparing the peak in scattering intensity with the peak intensity in CO maps of molecular clouds from the Mopra Southern Galactic Plane CO Survey we identify the two innermost rings with clouds at radial velocity ~ -74 and 81 km s ~ - -1 , respectively. We identify a prominent band of foreground photoelectric absorption with a lane of CO gas at 32 km s ~ - -1. From the association of the rings with individual CO clouds we determine the kinematic distance to Circinus X-1 to be DCirX 1 9.4 kpc 1.0 0.8 = - + ‐ . This distance rules out earlier claims of a distance around 4 kpc, implies that Circinus X-1 is a frequent super-Eddington source, and places a lower limit of G  22 on the Lorentz factor and an upper limit of q jet 3 on the jet viewing angle.