Shimajiri, Y., Andre, Ph., Braine, J., Konyves, V., Schneider, N., Bontemps, S., Ladjelate, B., Roy, A., Gao, Y. and Chen, H. (2017). Testing the universality of the star-formation efficiency in dense molecular gas. Astron. Astrophys., 604. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746
Full text not available from this repository.Abstract
Context.Recent studies with, for example,SpitzerandHerschelhave suggested that star formation in dense molecular gas may be governed by essentially the same law in Galactic clouds and external galaxies. This conclusion remains controversial, however, in large part because different tracers have been used to probe the mass of dense molecular gas in Galactic and extragalactic studies. Aims.We aimed to calibrate the HCN and HCO(+)lines commonly used as dense gas tracers in extragalactic studies and to test the possible universality of the star-formation efficiency in dense gas (greater than or similar to 10(4)cm(-3)), SFEdense. Methods.We conducted wide-field mapping of the Aquila, Ophiuchus, and Orion B clouds at similar to 0.04 pc resolution in theJ= 1 - 0 transition of HCN, HCO+, and their isotopomers. For each cloud, we derived a reference estimate of the dense gas mass M-Herschel(AV > 8), as well as the strength of the local far-ultraviolet (FUV) radiation field, usingHerschelGould Belt survey data products, and estimated the star-formation rate from direct counting of the number ofSpitzeryoung stellar objects. Results.The (HCO+)-C-13(1-0) and (HCN)-C-13(1-0) lines were observed to be good tracers of the dense star-forming filaments detected withHerschel. Comparing the luminositiesL(HCN)andL(HCO)(+)measured in the HCN and HCO(+)lines with the reference masses M-Herschel(AV > 8), the empirical conversion factors alpha(Herschel- HCN)(=M-Herschel(AV > 8)/L-HCN) an d alpha(+)(Herschel- HCO)(=M-Herschel(AV > 8)/L-HCO(+)) were found to be significantly anti-correlated with the local FUV strength. In agreement with a recent independent study of Orion B by Pety et al., the HCN and HCO(+)lines were found to trace gas down toA(V)greater than or similar to 2. As a result, published extragalactic HCN studies must be tracing all of the moderate density gas down ton(H2)less than or similar to 10(3)cm(-3). Estimating the contribution of this moderate density gas from the typical column density probability distribution functions in nearby clouds, we obtained the followingG (0)-dependent HCN conversion factor for external galaxies:alpha(fit ')(Herschel- HCN)=64 xG(0)(-0.34). Re-estimating the dense gas masses in external galaxies with alpha(fit ')(Herschel- HCN)(G(0)), we found that SFE(dense)is remarkably constant, with a scatter of less than 1.5 orders of magnitude around4.5 x 10(-8)yr(-1), over eight orders of magnitude in dense gas mass. Conclusions.Our results confirm that SFE(dense)of galaxies is quasi-universal on a wide range of scales from similar to 1-10 pc to> 10kpc. Based on the tight link between star formation and filamentary structure found inHerschelstudies of nearby clouds, we argue that SFE(dense)is primarily set by the microphysics of core and star formation along filaments.
| Item Type: | Journal Article | ||||||||||||||||||||||||||||||||||||||||||||
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| URN: | urn:nbn:de:hbz:38-221863 | ||||||||||||||||||||||||||||||||||||||||||||
| DOI: | 10.1051/0004-6361/201730633 | ||||||||||||||||||||||||||||||||||||||||||||
| Journal or Publication Title: | Astron. Astrophys. | ||||||||||||||||||||||||||||||||||||||||||||
| Volume: | 604 | ||||||||||||||||||||||||||||||||||||||||||||
| Date: | 2017 | ||||||||||||||||||||||||||||||||||||||||||||
| Publisher: | EDP SCIENCES S A | ||||||||||||||||||||||||||||||||||||||||||||
| Place of Publication: | LES ULIS CEDEX A | ||||||||||||||||||||||||||||||||||||||||||||
| ISSN: | 1432-0746 | ||||||||||||||||||||||||||||||||||||||||||||
| Language: | English | ||||||||||||||||||||||||||||||||||||||||||||
| Faculty: | Unspecified | ||||||||||||||||||||||||||||||||||||||||||||
| Divisions: | Unspecified | ||||||||||||||||||||||||||||||||||||||||||||
| Subjects: | no entry | ||||||||||||||||||||||||||||||||||||||||||||
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| Refereed: | Yes | ||||||||||||||||||||||||||||||||||||||||||||
| URI: | http://kups.ub.uni-koeln.de/id/eprint/22186 |
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