THE STAR FORMATION RATE AND GAS SURFACE DENSITY RELATION IN THE MILKY WAY: IMPLICATIONS FOR EXTRAGALACTIC STUDIES

By A. Heiderman, N. Evans II, L. Allen, T. Huard, M. Heyer. 2010

346 citations recorded by the source corpus.

We investigate the relation between star formation rate (SFR) and gas surface densities in Galactic star-forming regions using a sample of young stellar objects (YSOs) and massive dense clumps. Our YSO sample consists of objects located in 20 large molecular clouds from the Spitzer cores to disks (c2d) and Gould's Belt (GB) surveys. These data allow us to probe the regime of low-mass star formation, essentially invisible to tracers of high-mass star formation used to establish extragalactic SFR–gas relations. We estimate the gas surface density (Σgas) from extinction (AV) maps and YSO SFR surface densities (ΣSFR) from the number of YSOs, assuming a mean mass and lifetime. We also divide the clouds into evenly spaced contour levels of AV, counting only Class I and Flat spectral energy distribution YSOs, which have not yet migrated from their birthplace. For a sample of massive star-forming clumps, we derive SFRs from the total infrared luminosity and use HCN gas maps to estimate gas surface densities. We find that c2d and GB clouds lie above the extragalactic SFR–gas relations (e.g., Kennicutt–Schmidt law) by factors of up to 17. Cloud regions with high Σgas lie above extragalactic relations up to a factor of 54 and overlap with high-mass star-forming regions. We use 12CO and 13CO gas maps of the Perseus and Ophiuchus clouds from the COMPLETE survey to estimate gas surface densities and compare to measurements from AV maps. We find that 13CO, with the standard conversions to total gas, underestimates the AV-based mass by factors of ∼4–5. 12CO may underestimate the total gas mass at Σgas ≳ 200 M☉ pc−2 by ≳30%; however, this small difference in mass estimates does not explain the large discrepancy between Galactic and extragalactic relations. We find evidence for a threshold of star formation (Σth) at 129 ± 14 M☉ pc−2. At Σgas>Σth, the Galactic SFR–gas relation is linear. A possible reason for the difference between Galactic and extragalactic relations is that much of Σgas is below Σth in extragalactic studies, which detect all the CO-emitting gas. If the Kennicutt–Schmidt relation (ΣSFR ∝ Σ1.4gas) and a linear relation between dense gas and star formation are assumed, the fraction of dense star-forming gas (fdense) increases as ∼Σ0.4gas. When Σgas reaches ∼300 Σth, the fraction of dense gas is ∼1, creating a maximal starburst.

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Citations in the corpus

COMBINED CO AND DUST SCALING RELATIONS OF DEPLETION TIME AND MOLECULAR GAS FRACTIONS WITH COSMIC TIME, SPECIFIC STAR-FORMATION RATE, AND STELLAR MASS (2014, background): “…(AV>7, Σgas>100 M pc -2 ) to decouple the dense cores from the external radiation field and allow it to cool and initiate collapse; these conditions may then also be conducive to molecule formation (Glover & Clark 2012, Krumholz, Leroy & McKee 2011, Heiderman et al.2010, Lada et al. 2012).”
STAR FORMATION RATES IN MOLECULAR CLOUDS AND THE NATURE OF THE EXTRAGALACTIC SCALING RELATIONS (2011, background): “This interpretation is also favored by Heiderman et al. (2010) who suggested that the maximal starburst activity occurs when fDG = 1 which they posit to happen when the mass surface density exceeds values ∼ 104 M⊙ pc −2.”
MOLECULAR GAS AND STAR FORMATION IN NEARBY DISK GALAXIES (2013, background): “Galactic studies also highlight the impact of density on the SFR on cloud scales (Wu et al. 2005; Heiderman et al. 2010; Lada et al. 2010).”
Cluster-formation in the Rosette molecular cloud at the junctions of filaments (2012, neutral): “Other studies (e.g., Lada et al. 2010; Heiderman et al. 2010; André et al., 2010) have arrived at the same value of around 8m.”
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): “…measures of AV from individual stars with NIR colors typically find that the 12CO(1-0) emission has an almost linear relation to AV for 2mag ≤ AV ≤ (4−6) mag while for large extinction values the 12CO emission appears to saturate (Lombardi et al. 2006; Pineda et al. 2008; Heiderman et al. 2010).”
A CONSTANT MOLECULAR GAS DEPLETION TIME IN NEARBY DISK GALAXIES (2011, background): “Departures are also expected on scales of individual molecular clouds, where only a small fraction of the molecular gas actively forms stars (e.g., Heiderman et al. 2010).”
THE STAR FORMATION RATE OF TURBULENT MAGNETIZED CLOUDS: COMPARING THEORY, SIMULATIONS, AND OBSERVATIONS (2012, methodology): “This procedure yields best-fit values of the local efficiency parameter = 0.7, 0.5, and 0.3 for SFE = 1%, 3%, and 10%, respectively, in our comparison of simulation data with the Heiderman et al. (2010) Galactic cloud sample.”
The CO-to-H2 Conversion Factor (2013, background): “Along similar lines, Heiderman et al. (2010) find that in Ophiuchus and Perseus CO can underpredict H2 with respect to AV for Σmol > 200 M⊙ pc −2 by as much as ∼ 30%.”
ON THE STAR FORMATION EFFICIENCY OF TURBULENT MAGNETIZED CLOUDS (2012, methodology): “From their Table 2, we can compute SFE ∼ SFR × tSF/Mc with an assumed star formation timescale tSF = 2 Myr (Evans et al. 2009; Heiderman et al. 2010; Lada et al. 2010).”
ATLASGAL - properties of a complete sample of Galactic clumps (2017, background): “We also show the minimum threshold of ∼116-129 M pc−2 (thick magenta band) proposed by Lada et al. (2010) and Heiderman et al. (2010) (hereafter referred to as the “LH threshold”) for “efficient” star formation in nearby molecular clouds (d ≤ 500 pc).”
ANALYTICAL STAR FORMATION RATE FROM GRAVOTURBULENT FRAGMENTATION (2011, background): “Evans et al. (2009) and Heiderman et al. (2010) find SFR’s in the range ≈ 0.02-0.12 for nearby molecular clouds and ≈ 0.03-0.5 for massive star-forming dense clumps, yielding a mean value ≈ 0.1, about an order of magnitude larger than the values predicted by KM. Krumholz & Tan (2007, Fig.”
RESOLVING THE LUMINOSITY PROBLEM IN LOW-MASS STAR FORMATION (2011, background): “…rather than true line-of-sight extinctions, and thus may underestimate the true extinction since current, active star formation (and thus the position of the youngest, embedded sources) is associated with the densest parts of molecu- 16 lar clouds (e.g., Heiderman et al. 2010; Lada et al. 2010).”
Inefficient star formation through turbulence, magnetic fields and feedback (2015, background): “The observational data are a collection of star-forming Milky Way clouds, molecular clumps and young stellar objects (YSOs) from Heiderman et al. (2010), Lada et al. (2010) and Gutermuth et al. (2011), as well as the Central Molecular Zone (CMZ) from Yusef-Zadeh et al. (2009).”
A census of dense cores in the Aquila cloud complex: SPIRE/PACS observations from the Herschel Gould Belt survey (2015, background): “12) connect very well with recent near-/midinfrared studies of the star formation rate (SFR) as a function of gas surface density in nearby molecular clouds (e.g., Heiderman et al. 2010; Lada et al. 2010, 2012; Evans et al. 2014).”
A UNIVERSAL, LOCAL STAR FORMATION LAW IN GALACTIC CLOUDS, NEARBY GALAXIES, HIGH-REDSHIFT DISKS, AND STARBURSTS (2011, positive): “…fact that the regions observed by Wu et al. are too young for the infrared luminosity to serve as a reasonable proxy for the star formation rate, as Wu et al. assume; indeed, Heiderman et al. (2010) note that the Wu et al.’s assumption likely introduces an order of magnitude-level systematic error.”
Dusty Star Forming Galaxies at High Redshift (2014, result): “Lada et al. (2010) find roughly linear relationships between SFR and gas above an extinction threshold of AK ≈ 0.8 mag in Galactic clumps, a result consistent with the work of Heiderman et al. (2010).”
Turbulent molecular clouds (2012, methodology): “Direct comparisons with SFR inferred from observations (e.g. Heiderman et al. 2010, Kennicutt and Evans, 2012) have been performed but given the relatively large scatter of the data, it seems hard to draw firm conclusions.”
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).”
Physical Processes in the Interstellar Medium (2014, background): “…et al., 1998; Johnstone et al., 2004; Lada et al., 2010) or simply a steep dependence of the star formation rate on the column density (Hatchell et al., 2005; Enoch et al., 2008; Heiderman et al., 2010; Gutermuth et al., 2011; Burkert & Hartmann, 2013; Lada et al., 2013; Evans et al., 2014).”
Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions (2019, background): “S = - -M1000 yr kpcSFR,max 1 2 is close to the value for the maximum SSFR that can be sustained without radiation pressure instabilities (Thompson et al. 2005; Heiderman et al. 2010; Hopkins et al. 2010).”