Tuesday, 8/16/13

Two ALMA papers from yesterday – one on 30 Dor looking mostly in CO(2-1) and the other on the starburst galaxy NGC 1614 focusing on HCN/HNC/HCO+.

Title: ALMA Resolves 30 Doradus: Sub-parsec Molecular Cloud Structure Near the Closest Super-Star Cluster
Authors: Indebetouw, Remy; Brogan, Crystal; Chen, C.-H. Rosie; Leroy, Adam; Johnson, Kelsey; Muller, Erik; Madden, Suzanne; Cormier, Diane; Galliano, Frederic; Hughes, Annie;Hunter, Todd; Kawamura, Akiko; Kepley, Amanda; Lebouteiller, Vianney; Meixner, Margaret; Oliveira, Joana M.; Onishi, Toshikazu; Vasyunina, Tatiana
Publication: eprint arXiv:1307.3680
Publication Date: 07/2013
Origin: ARXIV
Keywords: Astrophysics – Galaxy Astrophysics
Comment: accepted to ApJ
Bibliographic Code: 2013arXiv1307.3680I


We present ALMA observations of 30 Doradus — the highest resolution view of molecular gas in an extragalactic star formation region to date (~0.4pc x 0.6pc). The 30Dor-10 cloud north of R136 was mapped in 12CO 2-1, 13CO 2-1, C18O 2-1, 1.3mm continuum, the H30alpha recombination line, and two H2CO 3-2 transitions. Most 12CO emission is associated with small filaments and clumps (<1pc, ~1000 Msun at the current resolution). Some clumps are associated with protostars, including "pillars of creation" photoablated by intense radiation from R136. Emission from molecular clouds is often analyzed by decomposition into approximately beam-sized clumps. Such clumps in 30 Doradus follow similar trends in size, linewidth, and surface density to Milky Way clumps. The 30 Doradus clumps have somewhat larger linewidths for a given size than predicted by Larson’s scaling relation, consistent with pressure confinement. They extend to higher surface density at a given size and linewidth compared to clouds studied at 10pc resolution. These trends are also true of clumps in Galactic infrared-dark clouds; higher resolution observations of both environments are required. Consistency of clump masses calculated from dust continuum, CO, and the virial theorem reveals that the CO abundance in 30 Doradus clumps is not significantly different from the LMC mean, but the dust abundance may be reduced by ~2. There are no strong trends in clump properties with distance from R136; dense clumps are not strongly affected by the external radiation field, but there is a modest trend towards lower dense clump filling fraction deeper in the cloud.

Title: High-density Molecular Gas Properties of the Starburst Galaxy NGC 1614 Revealed with ALMA
Authors: Imanishi, Masatoshi; Nakanishi, Kouichiro
Publication: eprint arXiv:1307.3694
Publication Date: 07/2013
Origin: ARXIV
Keywords: Astrophysics – Galaxy Astrophysics, Astrophysics – Cosmology and Extragalactic Astrophysics
Comment: 19 pages, 9 figures, accepted for publication in AJ
Bibliographic Code: 2013arXiv1307.3694I


We present the results of HCN/HCO+/HNC J=4-3 transition line observations of the nearby starburst galaxy NGC 1614, obtained with ALMA Cycle 0. We find that high density molecular gas, traced with these lines, shows a velocity structure such that the northern (southern) side of the nucleus is redshifted (blueshifted) with respect to the nuclear velocity of this galaxy. The redshifted and blueshifted emission peaks are offset by ~0.6" at the northern and southern sides of the nucleus, respectively. At these offset positions, observations at infrared >3 micron indicate the presence of active dusty starbursts, supporting the picture that high-density molecular gas is the site of active starbursts. The enclosed dynamical mass within the central ~2" in radius, derived from the dynamics of the high-density molecular gas, is ~10^9 Msun, which is similar to previous estimates. Finally, the HCN emission is weaker than HCO+ but stronger than HNC for J=4-3 for all starburst regions of NGC 1614, as seen for J=1-0 transition lines in starburst-dominated galaxies.

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