The SAMI Galaxy Survey: a new method to estimate molecular gas surface densities from star formation rates
- Creators
- Federrath, Christoph
- Salim, Diane M.
-
Medling, Anne M.
-
Davies, Rebecca L.
- Yuan, Tiantian
- Bian, Fuyan
-
Groves, Brent A.
-
Ho, I-Ting
- Sharp, Robert
-
Kewley, Lisa J.
-
Sweet, Sarah M.
-
Richards, Samuel N.
-
Bryant, Julia J.
-
Brough, Sarah
-
Croom, Scott
-
Scott, Nicholas
- Lawrence, Jon
-
Konstantopoulos, Iraklis
- Goodwin, Michael
Abstract
Stars form in cold molecular clouds. However, molecular gas is difficult to observe because the most abundant molecule (H_2) lacks a permanent dipole moment. Rotational transitions of CO are often used as a tracer of H_2, but CO is much less abundant and the conversion from CO intensity to H2 mass is often highly uncertain. Here we present a new method for estimating the column density of cold molecular gas (Σ_(gas)) using optical spectroscopy. We utilize the spatially resolved Hα maps of flux and velocity dispersion from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. We derive maps of Σ_(gas) by inverting the multi-freefall star formation relation, which connects the star formation rate surface density (Σ_(SFR)) with Σ_(gas) and the turbulent Mach number (M). Based on the measured range of Σ_(SFR) = 0.005-1.5M⊙ yr^(−1) kpc^(−2) and M=18–130, we predict Σ_(gas) = 7–200 M⊙ pc^(−2) in the star-forming regions of our sample of 260 SAMI galaxies. These values are close to previously measured Σ_(gas) obtained directly with unresolved CO observations of similar galaxies at low redshift. We classify each galaxy in our sample as 'star-forming' (219) or 'composite/AGN/shock' (41), and find that in 'composite/AGN/shock' galaxies the average Σ_(SFR), M and Σ_(gas) are enhanced by factors of 2.0, 1.6 and 1.3, respectively, compared to star-forming galaxies. We compare our predictions of Σ_(gas) with those obtained by inverting the Kennicutt–Schmidt relation and find that our new method is a factor of 2 more accurate in predicting Σ_(gas), with an average deviation of 32 per cent from the actual Σ_(gas).
Additional Information
© 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2017 March 22. Received 2017 March 19; in original form 2016 October 15. Published: 27 March 2017. We thank Mark Krumholz and the anonymous referee for their useful comments, which helped to improve this work. CF acknowledges funding provided by the Australian Research Council's (ARC) Discovery Projects (grants DP150104329 and DP170100603). DMS is supported by an Australian Government's New Colombo Plan scholarship. Support for AMM is provided by NASA through Hubble Fellowship grant #HST-HF2-51377 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. BAG gratefully acknowledges the support of the ARC as the recipient of a Future Fellowship (FT140101202). LJK gratefully acknowledges the support of an ARC Laureate Fellowship. The SAMI Galaxy Survey is based on observations made at the Anglo-Australian Telescope. SB acknowledges the funding support from the ARC through a Future Fellowship (FT140101166). SC acknowledges the support of an ARC Future Fellowship (FT100100457). NS acknowledges support of a University of Sydney Post-doctoral Research Fellowship. The Sydney-AAO Multi-object Integral field spectrograph (SAMI) was developed jointly by the University of Sydney and the Australian Astronomical Observatory. The SAMI input catalogue is based on data taken from the Sloan Digital Sky Survey, the GAMA Survey and the VST ATLAS Survey. The SAMI Galaxy Survey is funded by the ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020, and other participating institutions. The SAMI Galaxy Survey website is http://sami-survey.org/.Attached Files
Published - stx727.pdf
Submitted - 1703.09224.pdf
Supplemental Material - stx727_Supp.zip
Files
Additional details
- Eprint ID
- 78696
- Resolver ID
- CaltechAUTHORS:20170629-124334903
- DP150104329
- Australian Research Council
- DP170100603
- Australian Research Council
- Australian Government
- HST-HF2-51377
- NASA Hubble Fellowship
- NAS5-26555
- NASA
- FT140101202
- Australian Research Council
- FT140101166
- Australian Research Council
- FT100100457
- Australian Research Council
- University of Sydney
- CE110001020
- Australian Research Council
- Created
-
2017-06-29Created from EPrint's datestamp field
- Updated
-
2021-11-15Created from EPrint's last_modified field