MOLECULAR GAS AND STAR FORMATION IN NEARBY DISK GALAXIES

By A. Leroy, F. Walter, K. Sandstrom, A. Schruba, J. Muńoz-Mateos, F. Bigiel, A. Bolatto, E. Brinks, W. D. de Blok, S. Meidt and 5 more. 2013

482 citations recorded by the source corpus.

We compare molecular gas traced by 12CO (2–1) maps from the HERACLES survey, with tracers of the recent star formation rate (SFR) across 30 nearby disk galaxies. We demonstrate a first-order linear correspondence between Σmol and ΣSFR but also find important second-order systematic variations in the apparent molecular gas depletion time, . At the 1 kpc common resolution of HERACLES, CO emission correlates closely with many tracers of the recent SFR. Weighting each line of sight equally, using a fixed αCO equivalent to the Milky Way value, our data yield a molecular gas depletion time, Gyr with 0.3 dex 1σ scatter, in very good agreement with recent literature data. We apply a forward-modeling approach to constrain the power-law index, N, that relates the SFR surface density and the molecular gas surface density, . We find N = 1 ± 0.15 for our full data set with some scatter from galaxy to galaxy. This also agrees with recent work, but we caution that a power-law treatment oversimplifies the topic given that we observe correlations between and other local and global quantities. The strongest of these are a decreased in low-mass, low-metallicity galaxies and a correlation of the kpc-scale with dust-to-gas ratio, D/G. These correlations can be explained by a CO-to-H2 conversion factor (αCO) that depends on dust shielding, and thus D/G, in the theoretically expected way. This is not a unique interpretation, but external evidence of conversion factor variations makes this the most conservative explanation of the strongest observed trends. After applying a D/G-dependent αCO, some weak correlations between and local conditions persist. In particular, we observe lower and enhanced CO excitation associated with nuclear gas concentrations in a subset of our targets. These appear to reflect real enhancements in the rate of star formation per unit gas, and although the distribution of τdep does not appear bimodal in galaxy centers, τdep does appear multivalued at fixed ΣH2, supporting the idea of “disk” and “starburst” modes driven by other environmental parameters.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/180647003a2e66c467d8dd3203249004c5e4ed09

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In Astronomy and Astrophysics

1. P. Hopkins
2. L. Hernquist
3. Mark R. Krumholz
4. M. Cappellari
5. R. Somerville
6. T. Naab
7. D. Narayanan
8. F. Walter

In Instrumentation

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2. P. Hopkins
3. L. Hernquist
4. T. Naab
5. R. Somerville
6. A. Dekel
7. R. Dav'e
8. P. V. van Dokkum

Citations in the corpus

• Physical Models of Galaxy Formation in a Cosmological Framework (2014, background): “…to form in the dense, cold, molecular phase of the ISM, and current observations support a (nearly) universal star formation efficiency in molecular gas, where about 1% of the gas is converted into stars per free fall time (Bigiel et al. 2008, 2011, Krumholz et al. 2012, Leroy et al. 2013).”
• Dense gas in the Galactic central molecular zone is warm and heated by turbulence (2015, background): “…this region therefore appears to be suppressed relative to the expectations from nearby starforming regions and nearby galaxy disks, where the star formation timescale decreases with increasing gas surface density (Kennicutt 1998; Kennicutt & Evans 2012; Leroy et al. 2013; Heiderman et al. 2010).”
• THE PdBI ARCSECOND WHIRLPOOL SURVEY (PAWS). I. A CLOUD-SCALE/MULTI-WAVELENGTH VIEW OF THE INTERSTELLAR MEDIUM IN A GRAND-DESIGN SPIRAL GALAXY (2013, background): “For more details on the latest observational findings on the conversion factor in external galaxies we refer the reader to Sandstrom et al. (2012) and Leroy et al. (2013).”
• The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function (2014, background): “There is some uncertainty as to whether this value is in fact constant (Bigiel et al. 2008; Blanc et al. 2009; Rahman et al. 2011, 2012; Leroy et al. 2013), or varies slightly with the gas surface density or other large-scale properties of a galaxy (Ken- nicutt et al. 2007; Liu et al. 2011;…”
• Dusty Star Forming Galaxies at High Redshift (2014, background): “Similarly, Leroy et al. (2013) employ a dust to gas ratio-dependent XCO when studying 1 kpc regions in nearby galaxies, and find that the star formation efficiency towards nearby galaxy centers may increase from the typical field GMC.”
• PHIBSS: Unified Scaling Relations of Gas Depletion Time and Molecular Gas Fractions (2017, background): “…in the literature that the depletion time scale is about one Gyr, and dropping by a factor of 2 to 4 between z=0 and 2.5 (Bigiel et al. 2008, Leroy et al. 2013, Saintonge et al. 2011b, 2013, 2016, Tacconi et al. 2010, 2013, Daddi et al. 2010b, Santini et al. 2014, Sargent et al. 2014,…”
• How Stellar Feedback Simultaneously Regulates Star Formation and Drives Outflows (2015, background): “In contrast,the actual efficiency is only a few per cent (e.g.Bigiel et al. 2008, 2011; Krumholz et al. 2012; Leroy et al. 2013), although the efficiency per free-fall time can be as high as unity for individual giant molecular clouds (GMCs;Murray 2011).”
• An uncertainty principle for star formation - I. Why galactic star formation relations break down below a certain spatial scale (2014, background): “…comparison with observations is deferred to K14,Figure 3 does show which part of parameter space is covered by the observed nearby galaxies of Leroy et al. (2013), as well as M33 (Schruba et al. 2010) and M51 (Blanc et al. 2009), indicatinghat our model agrees very well with the trend of…”
• Modeling UV Radiation Feedback from Massive Stars. II. Dispersal of Star-forming Giant Molecular Clouds by Photoionization and Radiation Pressure (2018, background): “While the typical GMC freefall time is only of order ∼ 1– 10 Myr, the gas depletion timescale tdep estimated from the ratio between gas mass and star formation rate is ∼ 1 Gyr for molecular gas averaged over ∼ kpc scales in normal disk galaxies (e.g., Bigiel et al. 2008; Leroy et al. 2013) and somew”
• A unified model for galactic discs: star formation, turbulence driving, and mass transport (2017, methodology): “…that it continues to hold even at high redshift (e.g. Bouché et al. 2007; Daddi et al. 2008, 2010a,b; Genzel et al. 2010; Tacconi et al. 2013), and on ∼1 kpc scales in the local Universe (Kennicutt et al. 2007; Bigiel et al. 2008; Leroy et al. 2008, 2013; Liu et al. 2011; Momose et al. 2013).”
• Star formation in semi-analytic galaxy formation models with multiphase gas (2015, background): “Bigiel et al. (2008) found, based on observations of spiral galaxies from the THINGS survey, that the starformation rate surface density can be directly related to the surface density of molecular gas, i.e. ΣSFR = ( ASF 10M⊙pc−2 ) ΣH2 NSF (6) with NSF ≃ 1 (see also Bigiel et al. 2011; Leroy et al. 2”
• ISM MASSES AND THE STAR FORMATION LAW AT Z = 1 TO 6: ALMA OBSERVATIONS OF DUST CONTINUUM IN 145 GALAXIES IN THE COSMOS SURVEY FIELD (2015, background): “For the nearby galaxies, the gas depletion times are ∼ 1.5 Gyr (Young & Scoville 1991; Young et al. 1995; Leroy et al. 2013).”
• The ATLAS3D Project – XXVIII. Dynamically driven star formation suppression in early-type galaxies (2014, background): “By construction our systems are even more bulge-dominated than the objects studied by Leroy et al. (2013), and thus the effects of a changingXCO could be stronger.”
• Star formation rates and efficiencies in the Galactic Centre (2017, background): “Leroy et al. (2013) selected a sample of 30 nearby galaxies from the HERACLES survey to study the distribution of gas and stars on scales of ∼1 kpc.”
• Cold gas properties of the Herschel Reference Survey - II. Molecular and total gas scaling relations (2014, methodology): “These values can be compared to the mean value d termined from the HERACLES sample of resolved galaxies by Leroy et al. (2008, 2013),τH2 ≃ 1.3-2.2 Gyr, measured on a typical 800 pc scale, or to those determined for different samples of galaxies as listed in Table 5 of Leroy et al. (2013).”
• THE CO-TO-H2 CONVERSION FACTOR AND DUST-TO-GAS RATIO ON KILOPARSEC SCALES IN NEARBY GALAXIES (2012, methodology): “The model predictions are discussed in detail in Leroy et al. (2013).”
• Physical Processes in the Interstellar Medium (2014, background): “This correlation is close to linear, although arguments continue as to whether it is truly linear (Leroy et al., 2013), or is actually slightly sub-linear (Shetty et al.”
• xCOLD GASS: The Complete IRAM 30 m Legacy Survey of Molecular Gas for Galaxy Evolution Studies (2017, background): “The xCOLD GASS value of r21 ∼ 0.8 corresponds to an excitation temperature of 10K, assuming that the gas is optically thick (Leroy et al. 2013).”