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The SAMI Galaxy Survey: a new method to estimate molecular gas surface densities from star formation rates

Federrath, Christoph and Salim, Diane M. and Medling, Anne M. and Davies, Rebecca L. and Yuan, Tiantian and Bian, Fuyan and Groves, Brent A. and Ho, I-Ting and Sharp, Robert and Kewley, Lisa J. and Sweet, Sarah M. and Richards, Samuel N. and Bryant, Julia J. and Brough, Sarah and Croom, Scott and Scott, Nicholas and Lawrence, Jon and Konstantopoulos, Iraklis and Goodwin, Michael (2017) The SAMI Galaxy Survey: a new method to estimate molecular gas surface densities from star formation rates. Monthly Notices of the Royal Astronomical Society, 468 (4). pp. 3965-3978. ISSN 0035-8711.

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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).

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Medling, Anne M.0000-0001-7421-2944
Davies, Rebecca L.0000-0002-3324-4824
Groves, Brent A.0000-0002-9768-0246
Ho, I-Ting0000-0002-0757-9559
Kewley, Lisa J.0000-0001-8152-3943
Sweet, Sarah M.0000-0002-1576-2505
Richards, Samuel N.0000-0002-5368-0068
Bryant, Julia J.0000-0003-1627-9301
Brough, Sarah0000-0002-9796-1363
Croom, Scott0000-0003-2880-9197
Scott, Nicholas0000-0001-8495-8547
Konstantopoulos, Iraklis0000-0003-2177-0146
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
Funding AgencyGrant Number
Australian Research CouncilDP150104329
Australian Research CouncilDP170100603
Australian GovernmentUNSPECIFIED
NASA Hubble FellowshipHST-HF2-51377
Australian Research CouncilFT140101202
Australian Research CouncilFT140101166
Australian Research CouncilFT100100457
University of SydneyUNSPECIFIED
Australian Research CouncilCE110001020
Subject Keywords:turbulence, techniques: spectroscopic, stars: formation, galaxies: ISM, galaxies: star formation, galaxies: structure
Issue or Number:4
Record Number:CaltechAUTHORS:20170629-124334903
Persistent URL:
Official Citation:Christoph Federrath, Diane M. Salim, Anne M. Medling, Rebecca L. Davies, Tiantian Yuan, Fuyan Bian, Brent A. Groves, I-Ting Ho, Robert Sharp, Lisa J. Kewley, Sarah M. Sweet, Samuel N. Richards, Julia J. Bryant, Sarah Brough, Scott Croom, Nicholas Scott, Jon Lawrence, Iraklis Konstantopoulos, Michael Goodwin; The SAMI Galaxy Survey: a new method to estimate molecular gas surface densities from star formation rates. Mon Not R Astron Soc 2017; 468 (4): 3965-3978. doi: 10.1093/mnras/stx727
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:78696
Deposited By: Tony Diaz
Deposited On:29 Jun 2017 23:47
Last Modified:03 Nov 2019 23:49

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