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

Querejeta, Miguel; Schinnerer, E.; Schruba, Andreas; Murphy, E. J.; Meidt, Sharon E.; Usero, A.; Leroy, Adam K.; Pety, J.; Bigiel, Frank; Chevance, Mélanie; Faesi, Christopher M.; Gallagher, Molly; García‐Burillo, S.; Glover, Simon C. O.; Hygate, Alexander P. S.; Jiménez-Donaire, María J.; Kruijssen, J. M. Diederik; Momjian, Emmanuel; Rosolowsky, Erik; Utomo, Dyas

doi:10.1051/0004-6361/201834915

Cited by 72 publications

(144 citation statements)

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“…We adopt a thermal fraction of 70% for all apertures. This is simple, consistent with the free-free fraction found for 33 GHz peaks by Querejeta et al (2019). We show below that this leads to good agreement with the Paβ map.…”

Section: Archival 33 Ghz Datasupporting

confidence: 89%

“…We compare our recombination-line based results to the 33 GHz radio continuum map of NGC 5194 by Querejeta et al (2019). In normal star-forming galaxies, radio emission at 33 GHz contains a large contribution from free-free emission.…”

Section: Archival 33 Ghz Datamentioning

confidence: 95%

“…In combination with Hα, it offers an alternative way to estimate A(Hα). Querejeta et al (2019) describe the observations and processing of these data. This is one of the widest area 33 GHz maps of any nearby galaxy and covers a substantial fraction of our Paβ maps.…”

Section: Archival 33 Ghz Datamentioning

confidence: 99%

“…For NGC 5194 we repeat this exercise using 3 diameter apertures for comparison to the 33 GHz radio continuum data of Querejeta et al (2019) and the Hα spectroscopy of Blanc et al (2009). NGC 6946 lacks these comparison data, and we do not make 3 apertures for this galaxy.…”

Section: Aperture Placementmentioning

confidence: 99%

“…Given this, both galaxies have been targets of many previous studies focused on ionizing photons. For example, NGC 5194 has targeted by Kennicutt et al (2007), Calzetti et al (2007), Blanc et al (2009), and Querejeta et al (2019). NGC 6946 has been studied by Calzetti et al (2007), Murphy et al (2011), Li et al (2013), and Long et al (2019), among others.…”

Section: Introductionmentioning

confidence: 99%

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Paβ, Hα, and Attenuation in NGC 5194 and NGC 6946

Kessler

Leroy

Murphy

et al. 2020

ApJ

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We combine Hubble Space Telescope (HST) Paschen β (Paβ) imaging with ground-based, previously published Hα maps to estimate the attenuation affecting Hα, A(Hα), across the nearby, face-on galaxies NGC 5194 and NGC 6946. We estimate A(Hα) in ∼ 2,000 independent 2 ∼ 75 pc diameter apertures in each galaxy, spanning out to a galactocentric radius of almost 10 kpc. In both galaxies, A(Hα) drops with radius, with a bright, high attenuation inner region, though in detail the profiles differ between the two galaxies. Regions with the highest attenuation-corrected Hα luminosity show the highest attenuation, but the observed Hα luminosity of a region is not a good predictor of attenuation in our data. Consistent with much previous work, the IR-to-Hα color does a good job of predicting A(Hα). We calculate the best-fit empirical coefficients for use combining Hα with 8, 12, 24, 70, or 100µm to correct for attenuation. These agree well with previous work but we also measure significant scatter around each of these linear relations. The local atomic plus molecular gas column density, N (H), also predicts A(Hα) well. We show that a screen with magnitude ∼ 0.2 times that expected for a Milky Way gas-to-dust value does a reasonable job of explaining A(Hα) as a function of N (H). This could be expected if only ∼ 40% of gas and dust directly overlap regions of Hα emission.

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Section: Archival 33 Ghz Datasupporting

confidence: 89%

Section: Archival 33 Ghz Datamentioning

confidence: 95%

Section: Archival 33 Ghz Datamentioning

confidence: 99%

Section: Aperture Placementmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Paβ, Hα, and Attenuation in NGC 5194 and NGC 6946

Kessler

Leroy

Murphy

et al. 2020

ApJ

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DeGaS-MC: Dense Gas Survey in the Magellanic Clouds

Galametz

Schruba

Breuck

et al. 2020

A&A

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Context. Understanding the star-forming processes is key to understanding the evolution of galaxies. Investigating star formation requires precise knowledge of the properties of the dense molecular gas complexes where stars form and a quantification of how they are affected by the physical conditions to which they are exposed. The proximity, low metallicity, and wide range of star formation activity of the Large and Small Magellanic Clouds (LMC and SMC) make them prime laboratories to study how local physical conditions impact the dense gas reservoirs and their star formation efficiency. Aims. The aim of the Dense Gas Survey for the Magellanic Clouds (DeGaS-MC) project is to expand our knowledge of the relation between dense gas properties and star formation activity by targeting the LMC and SMC observed in the HCO+(2−1) and HCN(2−1) transitions. Methods. We carried out a pointing survey targeting two lines toward ∼30 LMC and SMC molecular clouds using the SEPIA180 instrument installed on the Atacama Pathfinder EXperiment (APEX) telescope. We performed a follow-up mapping campaign of the emission in the same transition in 13 star-forming regions. This first paper provides line characteristic catalogs and integrated line-intensity maps of the sources. Results. HCO+(2−1) is detected in 20 and HCN(2−1) in 8 of the 29 pointings observed. The dense gas velocity pattern follows the line-of-sight velocity field derived from the stellar population. The three SMC sources targeted during the mapping campaign were unfortunately not detected in our mapping campaign but both lines are detected toward the LMC 30Dor, N44, N105, N113, N159W, N159E, and N214 regions. The HCN emission is less extended than the HCO+ emission and is restricted to the densest regions. The HCO+(2−1)/HCN(2−1) brightness temperature ratios range from 1 to 7, which is consistent with the large ratios commonly observed in low-metallicity environments. A larger number of young stellar objects are found at high HCO+ intensities and lower HCO+/HCN flux ratios, and thus toward denser lines of sight. The dense gas luminosities correlate with the star formation rate traced by the total infrared luminosity over the two orders of magnitude covered by our observations, although substantial region-to-region variations are observed.

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ALMA resolves giant molecular clouds in a tidal dwarf galaxy

Lelli

Schinnerer

Colombo

et al. 2021

A&A

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Tidal dwarf galaxies (TDGs) are gravitationally bound condensations of gas and stars formed during galaxy interactions. Here we present multi-configuration ALMA observations of J1023+1952, a TDG in the interacting system Arp 94, where we resolve CO(2-1) emission down to giant molecular clouds (GMCs) at 0.64 ∼ 45 pc resolution. We find a remarkably high fraction of extended molecular emission (∼80−90%), which is filtered out by the interferometer and likely traces diffuse gas. We detect 111 GMCs that give a similar mass spectrum as those in the Milky Way and other nearby galaxies (a truncated power law with slope of −1.76 ± 0.13). We also study Larson's laws over the available dynamic range of GMC properties (∼2 dex in mass and ∼1 dex in size): GMCs follow the size-mass relation of the Milky Way, but their velocity dispersion is higher such that the size-linewidth and virial relations appear super-linear, deviating from the canonical values. The global molecular-to-atomic gas ratio is very high (∼1) while the CO(2-1)/CO(1-0) ratio is quite low (∼0.5), and both quantities vary from north to south. Star formation is predominantly taking place in the south of the TDG, where we observe projected offsets between GMCs and young stellar clusters ranging from ∼50 pc to ∼200 pc; the largest offsets correspond to the oldest knots, as seen in other galaxies. In the quiescent north, we find more molecular clouds and a higher molecular-to-atomic gas ratio (∼1.5); atomic and diffuse molecular gas also have a higher velocity dispersion there. Overall, the organisation of the molecular ISM in this TDG is quite different from other types of galaxies on large scales, but the properties of GMCs seem fairly similar, pointing to near universality of the star-formation process on small scales.

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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

Cited by 72 publications

References 147 publications

Paβ, Hα, and Attenuation in NGC 5194 and NGC 6946

Paβ, Hα, and Attenuation in NGC 5194 and NGC 6946

DeGaS-MC: Dense Gas Survey in the Magellanic Clouds

ALMA resolves giant molecular clouds in a tidal dwarf galaxy

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