STAR FORMATION RATES IN MOLECULAR CLOUDS AND THE NATURE OF THE EXTRAGALACTIC SCALING RELATIONS

By C. Lada, J. Forbrich, Marco Lombardi, Joao F. Alves. 2011

223 citations recorded by the source corpus.

In this paper, we investigate scaling relations between star formation rates and molecular gas masses for both local Galactic clouds and a sample of external galaxies. We specifically consider relations between the star formation rates and measurements of dense, as well as total, molecular gas masses. We argue that there is a fundamental empirical scaling relation that directly connects the local star formation process with that operating globally within galaxies. Specifically, the total star formation rate in a molecular cloud or galaxy is linearly proportional to the mass of dense gas within the cloud or galaxy. This simple relation, first documented in previous studies, holds over a span of mass covering nearly nine orders of magnitude and indicates that the rate of star formation is directly controlled by the amount of dense molecular gas that can be assembled within a star formation complex. We further show that the star formation rates and total molecular masses, characterizing both local clouds and galaxies, are correlated over similarly large scales of mass and can be described by a family of linear star formation scaling laws, parameterized by fDG, the fraction of dense gas contained within the clouds or galaxies. That is, the underlying star formation scaling law is always linear for clouds and galaxies with the same dense gas fraction. These considerations provide a single unified framework for understanding the relation between the standard (nonlinear) extragalactic Schmidt–Kennicutt scaling law, that is typically derived from CO observations of the gas, and the linear star formation scaling law derived from HCN observations of the dense gas.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/f38f572232717056a519ad76f5a20071d5d119f4

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Citations in the corpus

Molecular Clouds in the Milky Way (2015, background): “These simple, single-point statistics are effective tools to distinguish different dynamical components within molecular clouds (Kainulainen et al. 2009; Lada et al. 2010, 2012; Schneider et al. 2011, 2015; Kainulainen & Tan 2013).”
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).”
MOLECULAR GAS AND STAR FORMATION IN NEARBY DISK GALAXIES (2013, background): “…molecular ISM, meaning unbound material and the low density outskirts of bound clouds, may represent a reservoir of nonstar-forming molecular gas (though note that even the bulk of bound, molecular material does not directly participate in star-formation; see references in Lada et al. 2012).”
The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function (2014, background): “The star formation rate per unit mass within a given cloud also appears to be strongly correlated with the amount of gas it possesses above some threshold volume or column density (Heiderman et al. 2010; Lada et al. 2010, 2012; Evans et al. 2014).”
Star Formation in the Milky Way and Nearby Galaxies (2012, methodology): “The surface and volume density criteria roughly agree in nearby clouds (Lada et al. 2012) but may not in other environments.”
The confinement of star-forming galaxies into a main sequence through episodes of gas compaction, depletion and replenishment (2015, background): “Already Elbaz et al. (2011), Wuyts et al. (2011), Lada et al. (2012), and Sargent et al. (2014) put forward the idea that the decrease in tdep above the MS may be associated with internal parameters such as the central gas density.”
Star formation rates and efficiencies in the Galactic Centre (2017, methodology): “We find that the constraints on the SFR within the dust-ridge clouds ‘d’, ‘e’ and ‘f’ are too poor to test the Lada et al. (2010, 2012) predictions with any significance.”
PHIBSS: Unified Scaling Relations of Gas Depletion Time and Molecular Gas Fractions (2017, background): “For fixed conversion factors, these results are incompatible with a simple model in which star formation depends only on the amount of gas mass above some density threshold (Lada et al. 2012).”
A census of dense cores in the Aquila cloud complex: SPIRE/PACS observations from the Herschel Gould Belt survey (2015, background): “As pointed out by Lada et al. (2010, 2012), the nearby cloud value of the “efficiency” of the star formation process in dense gas is also very similar to the efficiency value SFR/Mdense ∼ 2 × 10−8 yr−1 found by Gao & Solomon (2004) for external galaxies, using HCN observations of dense gas and…”
What controls star formation in the central 500 pc of the Galaxy (2013, background): “This provides a theoretical justification for the conclusion made in§2 that the observed SFR is inconsistent with the universal threshold density from Lada et al. (2012).”
STAR FORMATION RELATIONS IN NEARBY MOLECULAR CLOUDS (2014, background): “Lada et al. (2012) have argued that their scaling law can be compatible with a volumetric law only if x = 1 and ρgas > ρth, where ρth is a threshold volume density that corresponds on average to the surface density threshold.”
Variations in the Galactic star formation rate and density thresholds for star formation (2012, background): “The Lada et al. (2012) column-density threshold relation proposes the SFR in a molecular cloud is set by the amount of gas above a column density threshold corresponding to an extinction of AV = 8mag.”