THE STATE OF THE GAS AND THE RELATION BETWEEN GAS AND STAR FORMATION AT LOW METALLICITY: THE SMALL MAGELLANIC CLOUD

By A. Bolatto, A. Leroy, K. Jameson, E. Ostriker, K. Gordon, B. Lawton, S. Stanimirović, F. Israel, S. Madden, S. Hony and 8 more. 2011

163 citations recorded by the source corpus.

We compare atomic gas, molecular gas, and the recent star formation rate (SFR) inferred from Hα in the Small Magellanic Cloud (SMC). By using infrared dust emission and local dust-to-gas ratios, we construct a map of molecular gas that is independent of CO emission. This allows us to disentangle conversion factor effects from the impact of metallicity on the formation and star formation efficiency of molecular gas. On scales of 200 pc to 1 kpc (where the distributions of H2 and star formation match well) we find a characteristic molecular gas depletion time of τmoldep ∼ 1.6 Gyr, similar to that observed in the molecule-rich parts of large spiral galaxies on similar spatial scales. This depletion time shortens on much larger scales to ∼0.6 Gyr because of the presence of a diffuse Hα component, and lengthens on much smaller scales to ∼7.5 Gyr because the Hα and H2 distributions differ in detail. We estimate the systematic uncertainties in our dust-based τmoldep measurement to be a factor of ∼2–3. We suggest that the impact of metallicity on the physics of star formation in molecular gas has at most this magnitude, rather than the factor of ∼40 suggested by the ratio of SFR to CO emission. The relation between SFR and neutral () gas surface density is steep, with a power-law index ≈2.2 ± 0.1, similar to that observed in the outer disks of large spiral galaxies. At a fixed total gas surface density the SMC has a 5–10 times lower molecular gas fraction (and star formation rate) than large spiral galaxies. We explore the ability of the recent models by Krumholz et al. and Ostriker et al. to reproduce our observations. We find that to explain our data at all spatial scales requires a low fraction of cold, gravitationally bound gas in the SMC. We explore a combined model that incorporates both large-scale thermal and dynamical equilibrium and cloud-scale photodissociation region structure and find that it reproduces our data well, as well as predicting a fraction of cold atomic gas very similar to that observed in the SMC.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/930545fb9369f21bd62ac29a86548d2f742c14d8

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In Astronomy and Astrophysics

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

Citations in the corpus

• ON THE INTERPLAY BETWEEN STAR FORMATION AND FEEDBACK IN GALAXY FORMATION SIMULATIONS (2014, methodology): “This is corroborated by measurements of the molecular gas consumption time scale distribution of molecular gas in patches of 12 pc radius in the SMC by Bolatto et al. (2011).”
• An analytic model for the evolution of the stellar, gas and metal content of galaxies (2011, background): “Another avenue is to raise tdep by appealing to the observed lower gas consumption rate in lowmetallicity systems (Bolatto et al. 2011).”
• VALIDATION OF THE EQUILIBRIUM MODEL FOR GALAXY EVOLUTION TO z ∼ 3 THROUGH MOLECULAR GAS AND DUST OBSERVATIONS OF LENSED STAR-FORMING GALAXIES (2013, methodology): “…produce consistent results, which in the mean and within their errors reproduce the metallicity-dependence of αCO recently calibrated at z > 1 by Genzel et al. (2012), and previously also observed locally (e.g. Wilson 1995; Israel 1997; Boselli et al. 2002; Bolatto et al. 2011; Leroy et al. 2011).”
• The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function (2014, methodology): “…2010; Glover & Mac Low 2011; Krumholz et al. 2011b; Narayanan et al. 2011, 2012; Shetty et al. 2011a,b; Feldmann et al. 2012a,b) and observations (Bolatto et al. 2011; Leroy et al. 2011; Genzel et al. 2012; Leroy et al. 2013; Bolatto et al. 2013) suggest that, at low metallicity dark, CO-free…”
• LOW CO LUMINOSITIES IN DWARF GALAXIES (2012, methodology): “Dust Modeling This method uses IR observations and dust modeling to estimate the gas mass and distribution which has the advantage that it is independent of CO emission (Thronson et al. 1988; Israel 1997; Dame et al. 2001; Leroy et al. 2007, 2009, 2011; Gratier et al. 2010b; Bolatto et al. 2011).”
• THE IMPACT OF INTERACTIONS, BARS, BULGES, AND ACTIVE GALACTIC NUCLEI ON STAR FORMATION EFFICIENCY IN LOCAL MASSIVE GALAXIES (2012, background): “…µ∗ local galaxies where high resolution measurements of both gas and star formation are possible, for example M33 (Gardan et al. 2007; Gratier et al. 2010), IC10 (Leroy et al. 2006), and NGC6822 (Gratier et al. 2010) (see however the counter argument in the case of the SMC in Bolatto et al. 2011).”
• METALLICITY-DEPENDENT QUENCHING OF STAR FORMATION AT HIGH REDSHIFT IN SMALL GALAXIES (2011, background): “…sensitive to the metallicity of the gas, occurring at a very different column density in the Milky Way, at Solar metallicity, than in the Small Magellanic Cloud, at ∼ 20% Solar metallicity (Tumlinson et al. 2002; Bolatto et al. 2007; Leroy et al. 2007; Krumholz et al. 2009b; Bolatto et al. 2011).”
• MOLECULAR GAS AND STAR FORMATION IN NEARBY DISK GALAXIES (2013, background): “This scenario of a rapidly varying conversion factor and a weakly varying τmoldep has been discussed in the context of the Small Magellanic Cloud by Bolatto et al. (2011) and in a theoretical context by Krumholz et al. (2011).”
• SUBMILLIMETER GALAXIES AS PROGENITORS OF COMPACT QUIESCENT GALAXIES (2014, methodology): “This method has been used successfully in the local Universe (e.g. Leroy et al. 2011; Bolatto et al. 2011) as well as at high redshift (Magdis et al. 2011, 2012; Magnelli et al. 2012).”
• The CO-to-H2 Conversion Factor (2013, background): “We show an ensemble of dust and FIR determinations (Israel 1997; Madden et al. 1997; Leroy et al. 2007; Gratier et al. 2010; Leroy et al. 2011; Bolatto et al. 2011; Smith et al. 2012) targeting local galaxies along with XCO estimates determined Sandstrom et al. (2012) for a sample of 22 nearby disk…”
• A unified model for galactic discs: star formation, turbulence driving, and mass transport (2017, background): “By restricting our attention to haloes with present-day masses above this limit, we stay in the part of parameter space where the ISM is at least marginally molecule-dominated, and thus we can adopt fsf ≈ 1 and σ th ≈ 0.2 km s−1 without making too large an error.”
• A survey of molecular gas in luminous sub-millimetre galaxies (2012, background): “D ow nloaded from https://academ ic.oup.com /m nras/article-abstract/429/4/3047/1011515 by guest on 16 January 2020 R E F E R E N C E S Alaghband-Zadeh S. et al., 2012, MNRAS, 424, 2232 Alexander D. M. et al., 2003, AJ, 125, 383 Alexander D. M., Smail I., Bauer F. E., Chapman S. C., Blain A. W., Bra”
• Cold gas properties of the Herschel Reference Survey - II. Molecular and total gas scaling relations (2014, background): “The same THINGS team has recently made several efforts to extend their analysis to different physical conditions, such as those encountered in the outskirt of extended discs (Bigiel et al. 2010), in Hi-dominated regions (Schruba et al. 2012), or in metal-poor regions (Bolatto et al. 2011).”
• Star Formation in the Milky Way and Nearby Galaxies (2012, background): “A recent study of the SMC (∼ 1/5Z⊙) by Bolatto et al. (2011) offers clues to how these results may change in low-metallicity environments.”