J/MNRAS/468/3965 SAMI Galaxy Survey. Gas surface densities (Federrath+, 2017)
The SAMI Galaxy Survey: a new method to estimate molecular gas surface
densities from star formation rates.
Federrath C., Salim D.M., Medling A.M., Davies R.L., Yuan T., Bian F.,
Groves B.A., Ho I.-T., Sharp R., Kewley L.J., Sweet S.M., Richards S.N.,
Bryant J.J., Brough S., Croom S., Scott N., Lawrence J.,
Konstantopoulos I., Goodwin M.
<Mon. Not. R. Astron. Soc., 468, 3965-3978 (2017)>
=2017MNRAS.468.3965F 2017MNRAS.468.3965F (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Star Forming Region ; Morphology
Keywords: turbulence - techniques: spectroscopic - stars: formation -
galaxies: ISM - galaxies: star formation - galaxies: structure
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 (Σgas) 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 Σgas by inverting the
multi-freefall star formation relation, which connects the star
formation rate surface density (ΣSFR) with Σgas and
the turbulent Mach number (M). Based on the measured range of
ΣSFR=0.005-1.5M☉/yr/kpc2 and M=18-130, we
predict Σgas=7-200M☉/pc2 in the star-forming
regions of our sample of 260 SAMI galaxies. These values are close to
previously measured Σgas 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
ΣSFR, M and Σgas are enhanced by factors of 2.0, 1.6
and 1.3, respectively, compared to star-forming galaxies. We compare
our predictions of Σgas with those obtained by inverting the
Kennicutt-Schmidt relation and find that our new method is a factor of
2 more accurate in predicting Σgas, with an average deviation
of 32 per cent from the actual Σgas.
Description:
We presented a new method to estimate the molecular gas column density
(Σgas) of a galaxy using only optical IFS data, by inverting
the star formation relation derived in Salim et al.,
2015ApJ...806L..36S 2015ApJ...806L..36S.
We apply our new method to estimate Σgas for star-forming and
composite/AGN/shock galaxies classified and observed in the SAMI
Galaxy Survey internal data release version 0.9. The SAMI (Croom et
al., 2012MNRAS.421..872C 2012MNRAS.421..872C).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1a.dat 101 219 Spaxel-averaged physical parameters required to
derive an estimate of the molecular gas surface
density Σgas,
star-forming classified galaxies
tablea1b.dat 100 41 Spaxel-averaged physical parameters required to
derive an estimate of the molecular gas surface
density Σgas,
composite/AGN/shock classified galaxies
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See also:
J/MNRAS/452/2087 : Galaxy And Mass Assembly (GAMA): DR2 (Liske+, 2015)
Byte-by-byte Description of file: tablea1a.dat tablea1b.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- GAMA GAMA identification number
8- 12 F5.3 --- z Redshift
14- 17 F4.2 --- eps Ellipticity
19- 21 I3 --- Nspax Number of valid spaxels for gas column
density estimate
23- 25 I3 pc Lspax Linear size of each spaxel
27- 32 F6.4 Msun/yr/kpc+2 SSFR Spaxel-averaged ΣSFR
34- 39 F6.4 Msun/yr/kpc+2 e_SSFR rms uncertainty on SSFR
41- 43 I3 --- M Spaxel-averaged turbulent Mach number
45- 46 I2 --- e_M rms uncertainty on M
48- 51 F4.1 10-24g/cm3 rho Spaxel-averaged gas volume density
53- 56 F4.1 10-24g/cm3 e_rho rms uncertainty on rho
58- 61 F4.1 Myr tff Spaxel-averaged local freefall time
63- 66 F4.1 Myr e_tff rms uncertainty on tff
68- 72 F5.1 Msun/yr/kpc+2 Sgas/tm Spaxel-averaged multi-freefall gas
consumption rate,
(Σgas/t)multi-ff
74- 77 F4.1 Msun/yr/kpc+2 e_Sgas/tm rms uncertainty on Sgas/tm
79- 83 F5.2 Msun/yr/kpc+2 Sgas/ts Spaxel-averaged single-freefall gas
consumption rate,
(Σgas/t)single-ff
85- 89 F5.2 Msun/yr/kpc+2 e_Sgas/ts rms uncertainty on Sgas/ts
91- 95 F5.1 Msun/pc2 Sgas Spaxel-averaged molecular gas surface
density, Σgas
97-101 F5.1 Msun/pc2 e_Sgas rms uncertainty on Sgas
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 16-Mar-2020