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Dense gas is not enough : environmental variations in the star formation efficiency of dense molecular gas at 100 pc scales in M 51

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Abstract
It remains unclear what sets the efficiency with which molecular gas transforms into stars. Here we present a new VLA map of the spiral galaxy M 51 in 33 GHz radio continuum, an extinction-free tracer of star formation, at 3 '' scales (similar to 100 pc). We combined this map with interferometric PdBI/NOEMA observations of CO(1-0) and HCN(1-0) at matched resolution for three regions in M 51 (central molecular ring, northern and southern spiral arm segments). While our measurements roughly fall on the well-known correlation between total infrared and HCN luminosity, bridging the gap between Galactic and extragalactic observations, we find systematic offsets from that relation for different dynamical environments probed in M 51; for example, the southern arm segment is more quiescent due to low star formation efficiency (SFE) of the dense gas, despite its high dense gas fraction. Combining our results with measurements from the literature at 100 pc scales, we find that the SFE of the dense gas and the dense gas fraction anti-correlate and correlate, respectively, with the local stellar mass surface density. This is consistent with previous kpc-scale studies. In addition, we find a significant anti-correlation between the SFE and velocity dispersion of the dense gas. Finally, we confirm that a correlation also holds between star formation rate surface density and the dense gas fraction, but it is not stronger than the correlation with dense gas surface density. Our results are hard to reconcile with models relying on a universal gas density threshold for star formation and suggest that turbulence and galactic dynamics play a major role in setting how efficiently dense gas converts into stars.
Keywords
FORMATION RATES, UNCERTAINTY PRINCIPLE, MAGELLANIC CLOUDS, SYNTHESIS, MODELS, NEARBY GALAXIES, NGC-5194 M51A, FORMATION LAW, HII-REGIONS, DUST, HCN, galaxies: individual: NGC 5194, galaxies: ISM, galaxies: star formation, galaxies: structure

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MLA
Querejeta, M., et al. “Dense Gas Is Not Enough : Environmental Variations in the Star Formation Efficiency of Dense Molecular Gas at 100 Pc Scales in M 51.” ASTRONOMY & ASTROPHYSICS, vol. 625, 2019.
APA
Querejeta, M., Schinnerer, E., Schruba, A., Murphy, E., van der Wel, S. M., Usero, A., … Utomo, D. (2019). Dense gas is not enough : environmental variations in the star formation efficiency of dense molecular gas at 100 pc scales in M 51. ASTRONOMY & ASTROPHYSICS, 625.
Chicago author-date
Querejeta, M, E Schinnerer, A Schruba, E Murphy, Sharon Meidt van der Wel, A Usero, AK Leroy, et al. 2019. “Dense Gas Is Not Enough : Environmental Variations in the Star Formation Efficiency of Dense Molecular Gas at 100 Pc Scales in M 51.” ASTRONOMY & ASTROPHYSICS 625.
Chicago author-date (all authors)
Querejeta, M, E Schinnerer, A Schruba, E Murphy, Sharon Meidt van der Wel, A Usero, AK Leroy, J Pety, F Bigiel, M Chevance, CM Faesi, M Gallagher, S Garcia-Burillo, SCO Glover, APS Hygate, MJ Jimenez-Donaire, JMD Kruijssen, E Momjian, E Rosolowsky, and D Utomo. 2019. “Dense Gas Is Not Enough : Environmental Variations in the Star Formation Efficiency of Dense Molecular Gas at 100 Pc Scales in M 51.” ASTRONOMY & ASTROPHYSICS 625.
Vancouver
1.
Querejeta M, Schinnerer E, Schruba A, Murphy E, van der Wel SM, Usero A, et al. Dense gas is not enough : environmental variations in the star formation efficiency of dense molecular gas at 100 pc scales in M 51. ASTRONOMY & ASTROPHYSICS. 2019;625.
IEEE
[1]
M. Querejeta et al., “Dense gas is not enough : environmental variations in the star formation efficiency of dense molecular gas at 100 pc scales in M 51,” ASTRONOMY & ASTROPHYSICS, vol. 625, 2019.
@article{8622919,
  abstract     = {It remains unclear what sets the efficiency with which molecular gas transforms into stars. Here we present a new VLA map of the spiral galaxy M 51 in 33 GHz radio continuum, an extinction-free tracer of star formation, at 3 '' scales (similar to 100 pc). We combined this map with interferometric PdBI/NOEMA observations of CO(1-0) and HCN(1-0) at matched resolution for three regions in M 51 (central molecular ring, northern and southern spiral arm segments). While our measurements roughly fall on the well-known correlation between total infrared and HCN luminosity, bridging the gap between Galactic and extragalactic observations, we find systematic offsets from that relation for different dynamical environments probed in M 51; for example, the southern arm segment is more quiescent due to low star formation efficiency (SFE) of the dense gas, despite its high dense gas fraction. Combining our results with measurements from the literature at 100 pc scales, we find that the SFE of the dense gas and the dense gas fraction anti-correlate and correlate, respectively, with the local stellar mass surface density. This is consistent with previous kpc-scale studies. In addition, we find a significant anti-correlation between the SFE and velocity dispersion of the dense gas. Finally, we confirm that a correlation also holds between star formation rate surface density and the dense gas fraction, but it is not stronger than the correlation with dense gas surface density. Our results are hard to reconcile with models relying on a universal gas density threshold for star formation and suggest that turbulence and galactic dynamics play a major role in setting how efficiently dense gas converts into stars.},
  articleno    = {A19},
  author       = {Querejeta, M and Schinnerer, E and Schruba, A and Murphy, E and van der Wel, Sharon Meidt and Usero, A and Leroy, AK and Pety, J and Bigiel, F and Chevance, M and Faesi, CM and Gallagher, M and Garcia-Burillo, S and Glover, SCO and Hygate, APS and Jimenez-Donaire, MJ and Kruijssen, JMD and Momjian, E and Rosolowsky, E and Utomo, D},
  issn         = {1432-0746},
  journal      = {ASTRONOMY & ASTROPHYSICS},
  keywords     = {FORMATION RATES,UNCERTAINTY PRINCIPLE,MAGELLANIC CLOUDS,SYNTHESIS,MODELS,NEARBY GALAXIES,NGC-5194 M51A,FORMATION LAW,HII-REGIONS,DUST,HCN,galaxies: individual: NGC 5194,galaxies: ISM,galaxies: star formation,galaxies: structure},
  language     = {eng},
  pages        = {23},
  title        = {Dense gas is not enough : environmental variations in the star formation efficiency of dense molecular gas at 100 pc scales in M 51},
  url          = {http://dx.doi.org/10.1051/0004-6361/201834915},
  volume       = {625},
  year         = {2019},
}

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