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Revisiting the Integrated Star Formation Law. II. Starbursts and the Combined Global Schmidt Law

Kennicutt, Robert C., Jr. and de los Reyes, Mithi A. C. (2021) Revisiting the Integrated Star Formation Law. II. Starbursts and the Combined Global Schmidt Law. Astrophysical Journal, 908 (1). Art. No. 61. ISSN 1538-4357. https://resolver.caltech.edu/CaltechAUTHORS:20210217-084138607

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Abstract

We compile observations of molecular gas contents and infrared-based star formation rates (SFRs) for 112 circumnuclear star-forming regions, in order to reinvestigate the form of the disk-averaged Schmidt surface density star-formation law in starbursts. We then combine these results with total gas and SFR surface densities for 153 nearby nonstarbursting disk galaxies from de los Reyes & Kennicutt (2019), to investigate the properties of the combined star formation law, following Kennicutt (1998). We confirm that the combined Schmidt law can be fitted with a single power law with slope n = 1.5 ± 0.05 (including fitting method uncertainties), somewhat steeper than the value n = 1.4 ± 0.15 found by Kennicutt. Fitting separate power laws to the nonstarbursting and starburst galaxies, however, produces very different slopes (n = 1.34 ± 0.07 and 0.98 ± 0.07, respectively), with a pronounced offset in the zero-point (~0.6 dex) of the starburst relation to higher SFR surface densities. This offset is seen even when a common conversion factor between CO intensity and molecular hydrogen surface density is applied, and it is confirmed when disk surface densities of interstellar dust are used as proxies for gas measurements. Tests for possible systematic biases in the starburst data fail to uncover any spurious sources for such a large offset. We tentatively conclude that the global Schmidt law in galaxies, at least as it is conventionally measured, is bimodal or possibly multimodal. Possible causes may include changes in the small-scale structure of the molecular interstellar medium or the stellar initial mass function. A single n ~ 1.5 power law still remains as a credible approximation or "recipe" for analytical or numerical models of galaxy formation and evolution.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-4357/abd3a2DOIArticle
https://arxiv.org/abs/2012.05363arXivDiscussion Paper
ORCID:
AuthorORCID
Kennicutt, Robert C., Jr.0000-0001-5448-1821
de los Reyes, Mithi A. C.0000-0002-4739-046X
Additional Information:© 2021 The American Astronomical Society. Received 2020 July 22; revised 2020 November 11; accepted 2020 December 4; published 2021 February 15. The authors wish to thank an anonymous referee for a report that led to significant improvements in this paper. Early phases of this research were supported in part by the Science and Technology Facilities Council (STFC) through a consolidated grant to the Institute of Astronomy, University of Cambridge. M.A.C. de los R. also acknowledges the financial support of the NSF Graduate Research Fellowship Program. Finally, we would like to express our deep gratitude to the staff at the academic and telescope facilities, particularly those whose communities are excluded from the academic system, but whose labor maintains spaces for scientific inquiry. Software: Matplotlib (Hunter 2007), Linmix (Kelly 2007), Astropy (Robitaille et al. 2013).
Funders:
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)UNSPECIFIED
NSF Graduate Research FellowshipUNSPECIFIED
Subject Keywords:Disk galaxies; Galaxy evolution; Spiral galaxies; Interacting galaxies; Luminous infrared galaxies; Starburst galaxies; Blue compact dwarf galaxies; Star formation; Interstellar dust
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Disk galaxies (391); Galaxy evolution (594); Spiral galaxies (1560); Interacting galaxies (802); Luminous infrared galaxies (946); Starburst galaxies (1570); Blue compact dwarf galaxies (165); Star formation (1569);
Record Number:CaltechAUTHORS:20210217-084138607
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20210217-084138607
Official Citation:Robert C. Kennicutt Jr. and Mithi A. C. De Los Reyes 2021 ApJ 908 61
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108085
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:18 Feb 2021 19:34
Last Modified:18 Feb 2021 19:34

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