EPoS Contribution

Almost like home: deep CO isotopologue, dust continuum and HCN observations of resolved Giant Molecular Clouds in the Andromeda Galaxy Jan Forbrich Herts, Hatfield, UK
Recent improvements in capabilities of millimeter-wavelength interferometers have enabled not only the detection of thermal dust continuum emission but also of critical molecular tracers on scales of just 15-pc in the Andromeda Galaxy. As a result, it is possible to directly measure the physical properties of resolved GMCs in the most nearby large spiral galaxy with a fidelity approaching that obtained for GMCs in the Milky Way. Deep 230 GHz SMA wideband observations designed to detect the faint thermal continuum emission also yield molecular line detections at high S/N, resulting in possibly the deepest CO isotopologue observations (12CO, 13CO, C18O) of resolved GMCs in an external disk galaxy. Combining the molecular data with the dust continuum, we obtain first direct dust-mass to light ratios for CO isotopologues and HCN in particular. Furthermore, we examine the Larson scaling relations in both 12CO and 13CO, leading to new insights into their physical foundations and the boundedness of clouds, with implications also for Milky Way GMCs. Finally, we elucidate the role of dense gas in these clouds, where our analysis reveals that, given our observational parameters, HCN is indeed tracing the densest gas. Our main overall conclusion is that the M31 GMCs are found to be very similar in nearly every aspect to local Milky Way clouds. In closing, we present first results from our complementary surveys of HII regions in M31, using the VLA to detect the free-free continuum and MMT/Hectospec for optical spectroscopy to constrain the role of metallicity.

Caption: 230 GHz (SMA) dust continuum image of K026, K136, K176, K191, and K213 (top to bottom) with contour lines indicating the 3, 6, 12, ... sigma extent of the 230 GHz (SMA) continuum (blue dashed), 13CO(1-0) (green), and (left) HCN(1-0) (red), (centre) HNC(1-0) (red), and (right) HCO+(1-0) (red). The synthesized beam sizes are indicated in the lower left corner in blue (230 GHz dust continuum), red dashed contours (HCN, HNC, and HCO+), and white dashed contours (13CO(1-0)).
Collaborators: C. J. Lada, CfA, US	Key publication Relevant topic(s): Extra-Galactic SF Molecular Clouds
Relevant Big Question: Which properties of the interstellar medium govern the physical onset of star formation and thus the star formation rate in clouds?