Warm, dense molecular gas in the ISM of starbursts, LIRGs, and ULIRGs

Desika Narayanan, Christopher E. Groppi, Craig A. Kulesa, Christopher K Walker

Research output: Contribution to journalArticle

50 Citations (Scopus)

Abstract

The role of star formation in luminous and ultraluminous infrared galaxies (LIRGs, LIR ≥ 1011 L; ULIRGs, L IR ≥ 1012 L) is a hotly debated issue: while it is clear that starbursts play a large role in powering the IR luminosity in these galaxies, the relative importance of possible enshrouded AGNs is unknown. It is therefore important to better understand the role of star-forming gas in contributing to the infrared luminosity in IR-bright galaxies. The J = 3 level of 12CO lies 33 K above ground and has a critical density of ∼ 1.5 × 104 cm-3. The 12CO J = 3-2 line serves as an effective tracer for warm, dense molecular gas heated by active star formation. Here we report on 12CO J = 3-2 observations of 17 starburst spiral galaxies, LIRGs, and ULIRGs, which we obtained with the Heinrich Hertz Submillimeter Telescope on Mount Graham, Arizona. Our main results are as follows. (1) We find a nearly linear relation between the infrared luminosity and warm, dense molecular gas such that the infrared luminosity increases as the warm, dense molecular gas to the power 0.92; we interpret this to be roughly consistent with the recent results of Gao & Solomon. (2) We find LIR/MH2 warm, dense ratios ranging from ∼38 to ∼482 L/M using a modified CO-H2 conversion factor of 8.3 × 1019 cm-2 (K km s-1)-1 derived in this paper.

Original languageEnglish (US)
Pages (from-to)269-279
Number of pages11
JournalAstrophysical Journal
Volume630
Issue number1 I
DOIs
StatePublished - Sep 1 2005

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molecular gases
luminosity
galaxies
gas
star formation
starburst galaxies
spiral galaxies
tracers
tracer
telescopes
stars
gases

Keywords

  • Galaxies: active
  • Galaxies: ISM
  • Galaxies: starburst
  • ISM: molecules
  • Submillimeter

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Warm, dense molecular gas in the ISM of starbursts, LIRGs, and ULIRGs. / Narayanan, Desika; Groppi, Christopher E.; Kulesa, Craig A.; Walker, Christopher K.

In: Astrophysical Journal, Vol. 630, No. 1 I, 01.09.2005, p. 269-279.

Research output: Contribution to journalArticle

Narayanan, Desika ; Groppi, Christopher E. ; Kulesa, Craig A. ; Walker, Christopher K. / Warm, dense molecular gas in the ISM of starbursts, LIRGs, and ULIRGs. In: Astrophysical Journal. 2005 ; Vol. 630, No. 1 I. pp. 269-279.
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AB - The role of star formation in luminous and ultraluminous infrared galaxies (LIRGs, LIR ≥ 1011 L⊙; ULIRGs, L IR ≥ 1012 L⊙) is a hotly debated issue: while it is clear that starbursts play a large role in powering the IR luminosity in these galaxies, the relative importance of possible enshrouded AGNs is unknown. It is therefore important to better understand the role of star-forming gas in contributing to the infrared luminosity in IR-bright galaxies. The J = 3 level of 12CO lies 33 K above ground and has a critical density of ∼ 1.5 × 104 cm-3. The 12CO J = 3-2 line serves as an effective tracer for warm, dense molecular gas heated by active star formation. Here we report on 12CO J = 3-2 observations of 17 starburst spiral galaxies, LIRGs, and ULIRGs, which we obtained with the Heinrich Hertz Submillimeter Telescope on Mount Graham, Arizona. Our main results are as follows. (1) We find a nearly linear relation between the infrared luminosity and warm, dense molecular gas such that the infrared luminosity increases as the warm, dense molecular gas to the power 0.92; we interpret this to be roughly consistent with the recent results of Gao & Solomon. (2) We find LIR/MH2 warm, dense ratios ranging from ∼38 to ∼482 L⊙/M⊙ using a modified CO-H2 conversion factor of 8.3 × 1019 cm-2 (K km s-1)-1 derived in this paper.

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