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Abstract
We compare the structure of molecular gas at 40 pc resolution to the ability of gas to form stars across the disk of the spiral galaxy M51. We break the PAWS survey into 370 pc and 1.1 kpc resolution elements, and within each we estimate the molecular gas depletion time (tau(mol)(Dep)), the star-formation efficiency per free-fall time (epsilon(ff)), and the mass-weighted cloud-scale (40 pc) properties of the molecular gas: surface density, Sigma, line width, sigma, and b equivalent to Sigma/sigma(2) proportional to alpha(-1)(vir), a parameter that traces the boundedness of the gas. We show that the cloud-scale surface density appears to be a reasonable proxy for mean volume density. Applying this, we find a typical star-formation efficiency per free-fall time, epsilon(ff)(<Sigma(40) (pc)>) similar to 0.3%-0.36%, lower than adopted in many models and found for local clouds. Furthermore, the efficiency per free-fall time anti-correlates with both Sigma and sigma, in some tension with turbulent star-formation models. The best predictor of the rate of star formation per unit gas mass in our analysis is b equivalent to Sigma/sigma(2), tracing the strength of self-gravity, with tau(mol)(Dep) proportional to b(-0.9). The sense of the correlation is that gas with stronger self-gravity (higher b) forms stars at a higher rate (low tau(mol)(Dep)). The different regions of the galaxy mostly overlap in tau(mol)(Dep) as a function of b, so that low b explains the surprisingly high tau(mol)(Dep) found toward the inner spiral arms found by Meidt et al. (2013).
Keywords
CO-TO-H-2 CONVERSION FACTOR, WHIRLPOOL SURVEY PAWS, GIANT MOLECULAR, CLOUDS, GAS DEPLETION TIME, NEARBY GALAXIES, FORMATION LAW, FORMATION, EFFICIENCY, INTERSTELLAR-MEDIUM, FORMATION RATES, COLD GAS, galaxies: individual (M51), galaxies: ISM, galaxies: spiral, galaxies: star formation, ISM: general, ISM: structure

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MLA
Leroy, Adam K., et al. “Cloud-Scale ISM Structure and Star Formation in M51.” ASTROPHYSICAL JOURNAL, vol. 846, no. 1, 2017.
APA
Leroy, A. K., Schinnerer, E., Hughes, A., Kruijssen, J. D., van der Wel, S. M., Schruba, A., … Usero, A. (2017). Cloud-scale ISM structure and star formation in M51. ASTROPHYSICAL JOURNAL, 846(1).
Chicago author-date
Leroy, Adam K, Eva Schinnerer, Annie Hughes, JM Diederik Kruijssen, Sharon Meidt van der Wel, Andreas Schruba, Jiayi Sun, et al. 2017. “Cloud-Scale ISM Structure and Star Formation in M51.” ASTROPHYSICAL JOURNAL 846 (1).
Chicago author-date (all authors)
Leroy, Adam K, Eva Schinnerer, Annie Hughes, JM Diederik Kruijssen, Sharon Meidt van der Wel, Andreas Schruba, Jiayi Sun, Frank Bigiel, Gonzalo Aniano, Guillermo A Blanc, Alberto Bolatto, Melanie Chevance, Dario Colombo, Molly Gallagher, Santiago Garcia-Burillo, Carsten Kramer, Miguel Querejeta, Jerome Pety, Todd A Thompson, and Antonio Usero. 2017. “Cloud-Scale ISM Structure and Star Formation in M51.” ASTROPHYSICAL JOURNAL 846 (1).
Vancouver
1.
Leroy AK, Schinnerer E, Hughes A, Kruijssen JD, van der Wel SM, Schruba A, et al. Cloud-scale ISM structure and star formation in M51. ASTROPHYSICAL JOURNAL. 2017;846(1).
IEEE
[1]
A. K. Leroy et al., “Cloud-scale ISM structure and star formation in M51,” ASTROPHYSICAL JOURNAL, vol. 846, no. 1, 2017.
@article{8622217,
  abstract     = {We compare the structure of molecular gas at 40 pc resolution to the ability of gas to form stars across the disk of the spiral galaxy M51. We break the PAWS survey into 370 pc and 1.1 kpc resolution elements, and within each we estimate the molecular gas depletion time (tau(mol)(Dep)), the star-formation efficiency per free-fall time (epsilon(ff)), and the mass-weighted cloud-scale (40 pc) properties of the molecular gas: surface density, Sigma, line width, sigma, and b equivalent to Sigma/sigma(2) proportional to alpha(-1)(vir), a parameter that traces the boundedness of the gas. We show that the cloud-scale surface density appears to be a reasonable proxy for mean volume density. Applying this, we find a typical star-formation efficiency per free-fall time, epsilon(ff)(<Sigma(40) (pc)>) similar to 0.3%-0.36%, lower than adopted in many models and found for local clouds. Furthermore, the efficiency per free-fall time anti-correlates with both Sigma and sigma, in some tension with turbulent star-formation models. The best predictor of the rate of star formation per unit gas mass in our analysis is b equivalent to Sigma/sigma(2), tracing the strength of self-gravity, with tau(mol)(Dep) proportional to b(-0.9). The sense of the correlation is that gas with stronger self-gravity (higher b) forms stars at a higher rate (low tau(mol)(Dep)). The different regions of the galaxy mostly overlap in tau(mol)(Dep) as a function of b, so that low b explains the surprisingly high tau(mol)(Dep) found toward the inner spiral arms found by Meidt et al. (2013).},
  articleno    = {71},
  author       = {Leroy, Adam K and Schinnerer, Eva and Hughes, Annie and Kruijssen, JM Diederik and van der Wel, Sharon Meidt and Schruba, Andreas and Sun, Jiayi and Bigiel, Frank and Aniano, Gonzalo and Blanc, Guillermo A and Bolatto, Alberto and Chevance, Melanie and Colombo, Dario and Gallagher, Molly and Garcia-Burillo, Santiago and Kramer, Carsten and Querejeta, Miguel and Pety, Jerome and Thompson, Todd A and Usero, Antonio},
  issn         = {0004-637X},
  journal      = {ASTROPHYSICAL JOURNAL},
  keywords     = {CO-TO-H-2 CONVERSION FACTOR,WHIRLPOOL SURVEY PAWS,GIANT MOLECULAR,CLOUDS,GAS DEPLETION TIME,NEARBY GALAXIES,FORMATION LAW,FORMATION,EFFICIENCY,INTERSTELLAR-MEDIUM,FORMATION RATES,COLD GAS,galaxies: individual (M51),galaxies: ISM,galaxies: spiral,galaxies: star formation,ISM: general,ISM: structure},
  language     = {eng},
  number       = {1},
  pages        = {20},
  title        = {Cloud-scale ISM structure and star formation in M51},
  url          = {http://dx.doi.org/10.3847/1538-4357/aa7fef},
  volume       = {846},
  year         = {2017},
}

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