Galaxy formation and evolution

Abstract:

Combining observations of multiple CO lines with radiative transfer modelling is a verypowerful tool to investigate the physical properties of the molecular gas in galaxies. Usingnew observations and literature data, we provide the most complete CO ladders ever generatedfor eight star-forming regions in the spiral arms and inter-arms of the spiral galaxyNGC 6946, with observations of the CO(1-0), CO(2-1), CO(3-2), CO(4-3), CO(6-5),13CO(1-0) and 13CO(2-1) transitions. For each region, we use the large velocity gradientassumption to derive beam-averaged molecular gas physical properties, namely the gas kinetictemperature (TK), H2 number volume density (n(H2)) and CO number column density(N(CO)). Two complementary approaches are used to compare the observations with themodel predictions: x2 minimization and likelihood. The physical conditions derived varygreatly from one region to the next: TK = 10-250 K, n(H2) = 102.3-107.0 cm-3 and N(CO) =1015.0-1019.3 cm-2. The spectral line energy distribution (SLED) in some of these extranuclearregions indicate a star formation activity that is more intense than that at the centre of ourown Milky Way. The molecular gas in regions with a large SLED turnover transition (Jmax > 4) is hot but tenuous with a high CO column density, while that in regions with a low SLEDturnover transition (Jmax ≤ 4) is cold but dense with a low CO column density. We finallydiscuss and find some correlations between the physical properties of the molecular gas ineach region and the presence of young stellar population indicators (supernova remnants, HIIregions, HI holes, etc.). © 2013 The Authors.

Abstract:

With the first ELTs around the corner it is becoming ever more important to determine observational strategies and assess the prospective success of observing programs prior to making the observations. To this end, scientific simulations need to become more refined to understand the criteria required for a specific science case. We address the science simulations for HARMONI, an AO assisted first light integral field spectrograph (IFS) for the E-ELT. AO point spread functions (PSFs) vary markedly as a function of wavelength and type of AO system used, so there is need to create detailed PSFs across all IFS wavelength channels for accurate simulations. Detailed AO simulations have shown that for LTAO on the E-ELT, Strehl ratios can vary from 0.5% in V-band up to 75% in K-band. Using a single PSF for an entire datacube (especially with large instantaneous wavelength coverage) could introduce misleading features into simulated observations using HARMONI. We have developed a method to parameterise detailed PSFs using analytical models, which can then be interpolated as a function of wavelength. This allows us to create accurate, but computationally inexpensive, AO PSF datacubes for HARMONI simulations. This shall be developed to cover LTAO, SCAO and GLAO/no-AO PSFs.

Abstract:

In the lead-up to the Square Kilometre Array (SKA) project, several next-generation radio telescopes and upgrades are already being built around the world. These include APERTIF (The Netherlands), ASKAP (Australia), e-MERLIN (UK), VLA (USA), e-EVN (based in Europe), LOFAR (The Netherlands), MeerKAT (South Africa), and the Murchison Widefield Array. Each of these new instruments has different strengths, and coordination of surveys between them can help maximise the science from each of them. A radio continuum survey is being planned on each of them with the primary science objective of understanding the formation and evolution of galaxies over cosmic time, and the cosmological parameters and large-scale structures which drive it. In pursuit of this objective, the different teams are developing a variety of new techniques, and refining existing ones. To achieve these exciting scientific goals, many technical challenges must be addressed by the survey instruments. Given the limited resources of the global radio-astronomical community, it is essential that we pool our skills and knowledge. We do not have sufficient resources to enjoy the luxury of re-inventing wheels. We face significant challenges in calibration, imaging, source extraction and measurement, classification and cross-identification, redshift determination, stacking, and data-intensive research. As these instruments extend the observational parameters, we will face further unexpected challenges in calibration, imaging, and interpretation. If we are to realise the full scientific potential of these expensive instruments, it is essential that we devote enough resources and careful study to understanding the instrumental effects and how they will affect the data. We have established an SKA Radio Continuum Survey working group, whose prime role is to maximise science from these instruments by ensuring we share resources and expertise across the projects. Here we describe these projects, their science goals, and the technical challenges which are being addressed to maximise the science return. © 2013 Astronomical Society of Australia.

Abstract:

We present the Combined Array for Research in Millimeter Astronomy (CARMA) ATLAS3D molecular gas imaging survey, a systematic study of the distribution and kinematics of molecular gas in CO-rich early-type galaxies. Our full sample of 40 galaxies (30 newly mapped and 10 taken from the literature) is complete to a 12CO(1-0) integrated flux of 18.5 Jy km s-1,1 and it represents the largest, best studied sample of its type to date. A comparison of the CO distribution of each galaxy to the g - r colour image (representing dust) shows that the molecular gas and dust distributions are in good agreement and trace the same underlying interstellar medium. The galaxies exhibit a variety of CO morphologies, including discs (50 per cent), rings (15 per cent), bars+rings (10 per cent), spiral arms (5 per cent) and mildly (12.5 per cent) and strongly (7.5 per cent) disrupted morphologies. There appear to be weak trends between galaxy mass and CO morphology, whereby the most massive galaxies in the sample tend to have molecular gas in a disc morphology. We derive a lower limit to the total accreted molecular gas mass across the sample of 2.48 × 1010Mȯ, or approximately 8.3 × 108Mȯ per minor merger within the sample, consistent with minor merger stellar mass ratios. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.