A High-Resolution, Dust-Selected Molecular Cloud Catalogue of M33, the Triangulum Galaxy. (arXiv:1812.06103v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Williams_T/0/1/0/all/0/1">Thomas G. Williams</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gear_W/0/1/0/all/0/1">Walter K. Gear</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Smith_M/0/1/0/all/0/1">Matthew W. L. Smith</a>
We present a catalogue of Giant Molecular Clouds (GMCs) in M33, extracted
from cold dust continuum emission. Our GMCs are identified by computing
dendrograms. We measure the spatial distribution of these clouds, and
characterise their dust properties. Combining these measured properties with
CO(J=2-1) and 21cm HI data, we calculate the gas-to-dust ratio (GDR) of these
clouds, and from this compute a total cloud mass. In total, we find 165 GMCs
with cloud masses in the range of 10$^4$-10$^7$ M$_odot$. We find that
radially, $log_{10}(mathrm{GDR}) = -0.043(pm0.038) ,mathrm{R [kpc]} +
1.88(pm0.15)$, a much lower GDR than found in the Milky Way, and a
correspondingly higher $alpha_{rm CO}$ factor. The mass function of these
clouds follows a slope proportional to M$^{-2.84}$, steeper than many previous
studies of GMCs in local galaxies, implying that M33 is poorer at forming
massive clouds than other nearby spirals. Whilst we can rule out interstellar
pressure as the major contributing factor, we are unable to disentangle the
relative effects of metallicity and HI velocity dispersion. We find a
reasonably featureless number density profile with galactocentric radius, and
weak correlations between galactocentric radius and dust temperature/mass.
These clouds are reasonably consistent with Larson’s scaling relationships, and
many of our sources are co-spatial with earlier CO studies. Massive clouds are
identified at large galactocentric radius, unlike in these earlier studies,
perhaps indicating a population of CO-dark gas dominated clouds at these larger
distances.
We present a catalogue of Giant Molecular Clouds (GMCs) in M33, extracted
from cold dust continuum emission. Our GMCs are identified by computing
dendrograms. We measure the spatial distribution of these clouds, and
characterise their dust properties. Combining these measured properties with
CO(J=2-1) and 21cm HI data, we calculate the gas-to-dust ratio (GDR) of these
clouds, and from this compute a total cloud mass. In total, we find 165 GMCs
with cloud masses in the range of 10$^4$-10$^7$ M$_odot$. We find that
radially, $log_{10}(mathrm{GDR}) = -0.043(pm0.038) ,mathrm{R [kpc]} +
1.88(pm0.15)$, a much lower GDR than found in the Milky Way, and a
correspondingly higher $alpha_{rm CO}$ factor. The mass function of these
clouds follows a slope proportional to M$^{-2.84}$, steeper than many previous
studies of GMCs in local galaxies, implying that M33 is poorer at forming
massive clouds than other nearby spirals. Whilst we can rule out interstellar
pressure as the major contributing factor, we are unable to disentangle the
relative effects of metallicity and HI velocity dispersion. We find a
reasonably featureless number density profile with galactocentric radius, and
weak correlations between galactocentric radius and dust temperature/mass.
These clouds are reasonably consistent with Larson’s scaling relationships, and
many of our sources are co-spatial with earlier CO studies. Massive clouds are
identified at large galactocentric radius, unlike in these earlier studies,
perhaps indicating a population of CO-dark gas dominated clouds at these larger
distances.
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