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

Christoph Federrath; Diane M. Salim; Diane M. Salim; Anne M. Medling; Anne M. Medling; Rebecca L. Davies; Tiantian Yuan; Fuyan Bian; Brent A. Groves; I. Ting Ho; I. Ting Ho; Robert Sharp; Lisa J. Kewley; Sarah M. Sweet; Samuel N. Richards; Samuel N. Richards; Samuel N. Richards; Julia J. Bryant; Sarah Brough; Scott Croom; Scott Croom; Nicholas Scott; Nicholas Scott; Iraklis Konstantopoulos; Michael Goodwin

doi:10.1093/mnras/stx727

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

Christoph Federrath^*, Diane M. Salim, Diane M. Salim, Anne M. Medling, Anne M. Medling, Rebecca L. Davies, Tiantian Yuan, Fuyan Bian, Brent A. Groves, I. Ting Ho, I. Ting Ho, Robert Sharp, Lisa J. Kewley, Sarah M. Sweet, Samuel N. Richards, Samuel N. Richards, Samuel N. Richards, Julia J. Bryant, Sarah Brough, Scott CroomScott Croom, Nicholas Scott, Nicholas Scott, Iraklis Konstantopoulos, Michael Goodwin

^*Corresponding author for this work

Research output: Contribution to journal › Review article › peer-review

26 Citations (Scopus)

Abstract

Stars form in cold molecular clouds. However, molecular gas is difficult to observe because the most abundant molecule (H2) lacks a permanent dipole moment. Rotational transitions of CO are often used as a tracer of H2, 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 (gas) using optical spectroscopy. We utilize the spatially resolved Ha maps of flux and velocity dispersion from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. We derive maps of gas by inverting the multi-freefall star formation relation, which connects the star formation rate surface density (SFR) with gas and the turbulent Mach number (M). Based on the measured range of SFR = 0.005 1.5 M yr-1 kpc-2 and M = 18 130, we predict 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 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 SFR, M and gas are enhanced by factors of 2.0, 1.6 and 1.3, respectively, compared to star-forming galaxies. We compare our predictions of 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 gas, with an average deviation of 32 per cent from the actual gas.

Original language	English
Pages (from-to)	3965-3978
Number of pages	14
Journal	Monthly Notices of the Royal Astronomical Society
Volume	468
Issue number	4
DOIs	https://doi.org/10.1093/mnras/stx727
Publication status	Published - 1 Jul 2017

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10.1093/mnras/stx727

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Federrath, C., Salim, D. M., Salim, D. M., Medling, A. M., Medling, A. M., Davies, R. L., Yuan, T., Bian, F., Groves, B. A., Ho, I. T., Ho, I. T., Sharp, R., Kewley, L. J., Sweet, S. M., Richards, S. N., Richards, S. N., Richards, S. N., Bryant, J. J., Brough, S., ... Goodwin, M. (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), 3965-3978. https://doi.org/10.1093/mnras/stx727

@article{65685837722f425096e3a960a74b9ad5,

title = "The SAMI Galaxy Survey: A new method to estimate molecular gas surface densities from star formation rates",

abstract = "Stars form in cold molecular clouds. However, molecular gas is difficult to observe because the most abundant molecule (H2) lacks a permanent dipole moment. Rotational transitions of CO are often used as a tracer of H2, 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 (gas) using optical spectroscopy. We utilize the spatially resolved Ha maps of flux and velocity dispersion from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. We derive maps of gas by inverting the multi-freefall star formation relation, which connects the star formation rate surface density (SFR) with gas and the turbulent Mach number (M). Based on the measured range of SFR = 0.005 1.5 M yr-1 kpc-2 and M = 18 130, we predict 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 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 SFR, M and gas are enhanced by factors of 2.0, 1.6 and 1.3, respectively, compared to star-forming galaxies. We compare our predictions of 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 gas, with an average deviation of 32 per cent from the actual gas.",

keywords = "Galaxies: ISM, Galaxies: structure, Stars: formation, Techniques: spectroscopic, Turbulence, galaxies: star formation",

author = "Christoph Federrath and Salim, {Diane M.} and Salim, {Diane M.} and Medling, {Anne M.} and Medling, {Anne M.} and Davies, {Rebecca L.} and Tiantian Yuan and Fuyan Bian and Groves, {Brent A.} and Ho, {I. Ting} and Ho, {I. Ting} and Robert Sharp and Kewley, {Lisa J.} and Sweet, {Sarah M.} and Richards, {Samuel N.} and Richards, {Samuel N.} and Richards, {Samuel N.} and Bryant, {Julia J.} and Sarah Brough and Scott Croom and Scott Croom and Nicholas Scott and Nicholas Scott and Iraklis Konstantopoulos and Michael Goodwin",

note = "Publisher Copyright: {\textcopyright} 2017 The Authors.",

year = "2017",

month = jul,

day = "1",

doi = "10.1093/mnras/stx727",

language = "English",

volume = "468",

pages = "3965--3978",

journal = "Monthly Notices of the Royal Astronomical Society",

issn = "0035-8711",

publisher = "Oxford University Press ",

number = "4",

}

Federrath, C, Salim, DM, Salim, DM, Medling, AM, Medling, AM, Davies, RL, Yuan, T, Bian, F, Groves, BA, Ho, IT, Ho, IT, Sharp, R , Kewley, LJ, Sweet, SM, Richards, SN, Richards, SN, Richards, SN, Bryant, JJ, Brough, S, Croom, S, Croom, S, Scott, N, Scott, N, Konstantopoulos, I & Goodwin, M 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, vol. 468, no. 4, pp. 3965-3978. https://doi.org/10.1093/mnras/stx727

TY - JOUR

T1 - The SAMI Galaxy Survey

T2 - A new method to estimate molecular gas surface densities from star formation rates

AU - Federrath, Christoph

AU - Salim, Diane M.

AU - Medling, Anne M.

AU - Davies, Rebecca L.

AU - Yuan, Tiantian

AU - Bian, Fuyan

AU - Groves, Brent A.

AU - Ho, I. Ting

AU - Sharp, Robert

AU - Kewley, Lisa J.

AU - Sweet, Sarah M.

AU - Richards, Samuel N.

AU - Bryant, Julia J.

AU - Brough, Sarah

AU - Croom, Scott

AU - Scott, Nicholas

AU - Konstantopoulos, Iraklis

AU - Goodwin, Michael

PY - 2017/7/1

Y1 - 2017/7/1

N2 - Stars form in cold molecular clouds. However, molecular gas is difficult to observe because the most abundant molecule (H2) lacks a permanent dipole moment. Rotational transitions of CO are often used as a tracer of H2, 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 (gas) using optical spectroscopy. We utilize the spatially resolved Ha maps of flux and velocity dispersion from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. We derive maps of gas by inverting the multi-freefall star formation relation, which connects the star formation rate surface density (SFR) with gas and the turbulent Mach number (M). Based on the measured range of SFR = 0.005 1.5 M yr-1 kpc-2 and M = 18 130, we predict 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 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 SFR, M and gas are enhanced by factors of 2.0, 1.6 and 1.3, respectively, compared to star-forming galaxies. We compare our predictions of 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 gas, with an average deviation of 32 per cent from the actual gas.

AB - Stars form in cold molecular clouds. However, molecular gas is difficult to observe because the most abundant molecule (H2) lacks a permanent dipole moment. Rotational transitions of CO are often used as a tracer of H2, 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 (gas) using optical spectroscopy. We utilize the spatially resolved Ha maps of flux and velocity dispersion from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. We derive maps of gas by inverting the multi-freefall star formation relation, which connects the star formation rate surface density (SFR) with gas and the turbulent Mach number (M). Based on the measured range of SFR = 0.005 1.5 M yr-1 kpc-2 and M = 18 130, we predict 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 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 SFR, M and gas are enhanced by factors of 2.0, 1.6 and 1.3, respectively, compared to star-forming galaxies. We compare our predictions of 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 gas, with an average deviation of 32 per cent from the actual gas.

KW - Galaxies: ISM

KW - Galaxies: structure

KW - Stars: formation

KW - Techniques: spectroscopic

KW - Turbulence

KW - galaxies: star formation

UR - http://www.scopus.com/inward/record.url?scp=85037692720&partnerID=8YFLogxK

U2 - 10.1093/mnras/stx727

DO - 10.1093/mnras/stx727

M3 - Review article

SN - 0035-8711

VL - 468

SP - 3965

EP - 3978

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

IS - 4

ER -

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

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