Linking dense gas from the milky way to external galaxies

Journal Article · Fri Jun 10 04:00:00 EDT 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/824/1/29· OSTI ID:22869000

Stephens, Ian W.; Jackson, James M.; Foster, Jonathan B. ^[1]; Whitaker, J. Scott; Sanhueza, Patricio ^[2]; Contreras, Yanett; Rathborne, Jill M. ^[3]

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1. Institute for Astrophysical Research, Boston University, Boston, MA 02215 (United States)
2. Physics Department, Boston University, Boston, MA 02215 (United States)
3. Australia Telescope National Facility, CSIRO Astronomy and Space Science, Epping, NSW (Australia)

In a survey of 65 galaxies, Gao and Solomon found a tight linear relation between the infrared luminosity (L {sub IR}, a proxy for the star formation rate) and the HCN(1–0) luminosity (L{sub HCN}). Wu et al. found that this relation extends from these galaxies to the much less luminous Galactic molecular high-mass star-forming clumps (∼1 pc scales), and posited that there exists a characteristic ratio L {sub IR}/L{sub HCN} for high-mass star-forming clumps. The Gao–Solomon relation for galaxies could then be explained as a summation of large numbers of high-mass star-forming clumps, resulting in the same L {sub IR}/L{sub HCN} ratio for galaxies. We test this explanation and other possible origins of the Gao–Solomon relation using high-density tracers (including HCN(1–0), N{sub 2}H{sup +}(1–0), HCO{sup +}(1–0), HNC(1–0), HC{sub 3}N(10–9), and C{sub 2}H(1–0)) for ∼300 Galactic clumps from the Millimetre Astronomy Legacy Team 90 GHz (MALT90) survey. The MALT90 data show that the Gao–Solomon relation in galaxies cannot be satisfactorily explained by the blending of large numbers of high-mass clumps in the telescope beam. Not only do the clumps have a large scatter in the L {sub IR}/L{sub HCN} ratio, but also far too many high-mass clumps are required to account for the Galactic IR and HCN luminosities. We suggest that the scatter in the L {sub IR}/L{sub HCN} ratio converges to the scatter of the Gao–Solomon relation at some size-scale ≳1 kpc. We suggest that the Gao–Solomon relation could instead result from of a universal large-scale star formation efficiency, initial mass function, core mass function, and clump mass function.

• OSTI ID: 22869000
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 824; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ASTRONOMY
COSMIC GASES
DENSITY
EFFICIENCY
HYDROCYANIC ACID
LUMINOSITY
MASS
MILKY WAY
MOLECULES
STARS
TELESCOPES