CO Molecular Gas in Infrared-luminous Galaxies

By Lihong Yao, E. Seaquist, N. Kuno, L. Dunne. 2003

163 citations recorded by the source corpus.

We present the first statistical survey of the properties of the 12CO(1-0) and 12CO(3-2) line emission from the nuclei of a nearly complete subsample of 60 infrared (IR) luminous galaxies selected from SCUBA Local Universe Galaxy Survey (SLUGS). This subsample is flux limited at S60 μm ≥ 5.24 Jy with far-IR (FIR) luminosities mostly at LFIR > 1010 L☉. We compare the emission line strengths of 12CO(1-0) and (3-2) transitions at a common resolution of ~15''. The measured 12CO(3-2) to (1-0) line intensity ratios r31 vary from 0.22 to 1.72, with a mean value of 0.66 for the sources observed, indicating a large spread of the degree of excitation of CO in the sample. These CO data, together with a wide range of data at different wavelengths obtained from the literature, allow us to study the relationship between the CO excitation conditions and the physical properties of gas/dust and star formation in the central regions of galaxies. Our analysis shows that there is a nonlinear relation between CO and FIR luminosities, such that their ratio LCO/LFIR decreases linearly with increasing LFIR. This behavior was found to be consistent with the Schmidt law relating star formation rate to molecular gas content, with an index N = 1.4 ± 0.3. We also find a possible dependence of the degree of CO gas excitation on the efficiency of star-forming activity. Using the large velocity gradient (LVG) approximation to model the observed data, we investigate the CO-to-H2 conversion factor X for the SLUGS sample. The results show that the mean value of X for the SLUGS sample is lower by a factor of 10 compared to the conventional value derived for the Galaxy, if we assume the abundance of CO relative to H2, ZCO = 10-4. For a subset of 12 galaxies with H I maps, we derive a mean total face-on surface density of H2 + H of about 42 M☉ pc-2 within about 2 kpc of the nucleus. This value is intermediate between that in galaxies like our own and those with strong star formation.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/eee14d1a1037c698b82ac98e20f940d5455a5718

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In Astronomy and Astrophysics

1. P. Hopkins
2. L. Hernquist
3. D. Narayanan
4. Mark R. Krumholz
5. F. Walter
6. R. Somerville
7. A. Dekel
8. R. Dav'e

Citations in the corpus

• Dusty Star Forming Galaxies at High Redshift (2014, result): “This result was supported by observations of CO (J = 3–2) from nearby disks, LIRGs and ULIRGs that all found a roughly linear FIR-LCO J=3–2 relationship (Yao et al., 2003; Narayanan et al., 2005; Iono et al., 2009; Mao et al., 2010).”
• THE MULTIPHASE STRUCTURE AND POWER SOURCES OF GALACTIC WINDS IN MAJOR MERGERS (2013, background): “…with it hosting most of the molecular gas (∼1010 M ; Sanders et al. 1991; Chini et al. 1992), based on the narrow FWHM of CO (100 km s−1; Chini et al. 1992) and the measured CO velocity near that of the NW nucleus (cz = 12070−12090 km s−1; Chini et al. 1992; Yao et al. 2003; and this work).”
• Luminous Infrared Galaxies with the Submillimeter Array. I. Survey Overview and the Central Gas to Dust Ratio (2008, background): “For NGC 5257, there is a single spectrum published in Yao et al. (2003).”
• COLD GASS, an IRAM legacy survey of molecular gas in massive galaxies – I. Relations between H2, H i, stellar content and structural properties (2011, background): “They are taken from the compilations of Bettoni, Galletta & Garcı́aBurillo (2003), Yao et al. (2003), Casasola, Bettoni & Galletta (2004), Albrecht, Krügel & Chini (2007), Komugi et al. (2008) and Obreschkow & Rawlings (2009).”
• The Relationship between Molecular Gas Tracers and Kennicutt-Schmidt Laws (2007, background): “Similarly, starbursts, which preferentially occur at galactic centers, have systematically larger metallicities than galaxies like the Milky Way (e.g. Zaritsky et al. 1994; Yao et al. 2003; Netzer et al. 2005).”
• The molecular gas in Luminous Infrared Galaxies I: CO lines, extreme physical conditions, and their drivers (2011, methodology): “…will use a Large Velocity Gradient code (see Papadopoulos & Sequist 1998 and references therein) that has been shown adept at discerning the average thermal and kinematic states of the molecular gas when constrained by CO,13CO line ratios (e.g. Mao et al. 2000; Weiss et al. 2001; Yao et al. 2003).”
• VERY HIGH GAS FRACTIONS AND EXTENDED GAS RESERVOIRS IN z = 1.5 DISK GALAXIES (2009, methodology): “While the results and conclusions of this paper would remain the same if we were still using the Yao et al. (2003) sample, we here prefer the more recent samples as the Yao et al. sample was selected in the submm.”
• The CO-H2 Conversion Factor in Disc Galaxies and Mergers (2011, result): “Similarly, unresolved observations of starbursts have shown gas and dust temperatures in the range of 30-50 K, in agreement with the models presented here (Yao et al. 2003; Narayanan etl.”
• THE MOLECULAR GAS IN LUMINOUS INFRARED GALAXIES. II. EXTREME PHYSICAL CONDITIONS AND THEIR EFFECTS ON THE Xco FACTOR (2012, methodology): “The Xco range obtained using our one-phase models of global CO SLEDs is similar to that reported by DS98 and Yao et al. 2003.”
• The CO-to-H2 Conversion Factor (2013, background): “Yao et al. (2003) survey 60 local infraredluminous (starburst) galaxies spanning FIR luminosities LFIR ∼ 109 − 1012 L⊙, analyzing their 12CO J = 1 → 0 and J = 3 → 2 emission.”
• Vigorous Star Formation with Low Efficiency in Massive Disk Galaxies at z = 1.5 (2007, methodology): “We adapted published luminosities for local (Solomon et al. 1997; Yao et al 2003) and distant sources (Greve et al. 2005) to WMAP cosmological parameters (Spergel et al. 2007).”
• Star-formation laws in luminous infrared galaxies. New observational constraints on models (2011, background): “Yao et al. (2003) find an index n=1.40±0.30 in their CO survey of IR luminous galaxies.”
• The Resolved Properties of Extragalactic Giant Molecular Clouds (2008, background): “For example, mass estimates of molecular clouds subjected to extreme radiation fields, such as those in starburst environments, suggest that they have an XCO conversion factor 4 to 20 times smaller than in the Galaxy (e.g., Yao et al. 2003).”
• Tracing the molecular gas in distant submillimetre galaxies via CO(1-0) imaging with the EVLA (2010, background): “Secondly, we stress that there is a wide range in the apparent r3–2/1–0 values within the SMG sample but that formally these are consistent with our error-weighted mean value, given the quoted uncertainties, so we have yet to uncover the variation in r3–2/1–0 seen locally (Yao et al. 2003).”