LABOCA observations of giant molecular clouds in the south west region of the Small Magellanic Cloud - Astrophysics > Cosmology and Nongalactic AstrophysicsReportar como inadecuado




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Abstract: The amount of molecular gas is a key for understanding the future starformation in a galaxy. Because H2 is difficult to observe directly in dense andcold clouds, tracers like CO are used. However, at low metallicitiesespecially, CO only traces the shielded interiors of the clouds. mm dustemission can be used as a tracer to unveil the total dense gas masses. Thecomparison of masses deduced from the continuum SIMBA 1.2 mm emission andvirial masses in a sample of giant molecular clouds GMCs, in the SW region ofthe Small Magellanic Cloud SMC, showed a discrepancy that is in need of anexplanation. This study aims at better assessing possible uncertainties on thedust emission observed in the sample of GMCs from the SMC and focuses on thedensest parts of the GMCs where CO is detected. New observations were obtainedwith the LABOCA camera on the APEX telescope. All GMCs previously observed inCO are detected and their emission at 870microns is compared to ancillary data.The different contributions to the sub-mmm emission are estimated, as well asdust properties, in order to deduce molecular cloud masses precisely. Thesub-mm emission observed in the GMCs in the SW region of the SMC is dominatedby dust emission and masses are deduced for the part of each cloud where CO isdetected and compared to the virial masses. The mass discrepancy between bothmethods is confirmed at 870microns with the LABOCA observations: the virialmasses are on average 4 times smaller than the masses of dense gas deduced fromdust emission, contrary to what is observed for equivalent clouds in ourGalaxy. The origin of this mass discrepancy in the SMC remains unkown. Thedirect interpretation of this effect is that the CO linewidth used to computevirial masses do not measure the full velocity distribution of the gas.Geometrical effects and uncertainties on the dust properties are alsodiscussed.



Autor: Caroline Bot, Monica Rubio, Francois Boulanger, Marcus Albrecht, Adam Leroy, Alberto D. Bolatto, Frank Bertoldi, Karl Gordon, Cha

Fuente: https://arxiv.org/







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