J/MNRAS/432/2112 Estimating gas masses from HI and CO data (Brinchmann+ 2013)
Estimating gas masses and dust-to-gas ratios from optical spectroscopy.
Brinchmann J., Charlot S., Kauffmann G., Heckman T., White S.D.M.,
Tremonti C.
<Mon. Not. R. Astron. Soc., 432, 2112-2140 (2013)>
=2013MNRAS.432.2112B 2013MNRAS.432.2112B
ADC_Keywords: Galaxies, optical ; Equivalent widths
Keywords: galaxies: evolution - galaxies: fundamental parameters - galaxies: ISM
Abstract:
We present a method to estimate the total gas column density,
dust-to-gas and dust-to-metal ratios of distant galaxies from
rest-frame optical spectra. The technique exploits the sensitivity of
certain optical lines to changes in depletion of metals on to dust
grains and uses photoionization models to constrain these physical
ratios along with the metallicity and dust column density. We compare
our gas column density estimates with HI and CO gas mass estimates in
nearby galaxies to show that we recover their total gas mass surface
density to within a factor of 2 up to a total surface gas mass density
of ∼75M☉/pc2. Our technique is independent of the conversion
factor of CO to H2 and we show that a metallicity-dependent XCO
is required to achieve good agreement between our measurements and
that provided by CO and HI. However, we also show that our method
cannot be reliably aperture corrected to total integrated gas mass. We
calculate dust-to-gas ratios for all star-forming galaxies in the
Sloan Digital Sky Survey Data Release 7 and show that the resulting
dependence on metallicity agrees well with the trend inferred from
modelling of the dust emission of nearby galaxies using far-IR data.
We also present estimates of the variation of the dust-to-metal ratio
with metallicity and show that this is poorly constrained at
metallicities below 50% solar. We conclude with a study of the
inventory of gas in the central regions, defined both in terms of a
fixed physical radius and as a fixed fraction of the half-light
radius, of ∼70000 star-forming galaxies from the Sloan Digital Sky
Survey. We show that their central gas content and gas depletion time
are not accurately predicted by a single parameter, but in agreement
with recent studies we find that a combination of the stellar mass and
some measure of central concentration provides a good predictor of gas
content in galaxies. We also identify a population of galaxies with
low surface densities of stars and very long gas depletion times.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 57 104 An overview of regions with HI and CO
interferometric data, while at the same time
have spectroscopy from SDSS or from the NGC 628
IFU mosaic consistent with being ionised by stars
table4.dat 66 104 Measurements for the regions indicated in Table 3
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See also:
http://www.sdss.org : SDSS Home Page
http//www.mpa-garching.mpg.de/SDSS :
Data catalogues from SDSS studies at MPA/JHU
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Reg Region name (NGCnnnn-nn) (G1)
12- 15 I4 --- Plate ? SDSS Plate identification
16 A1 --- --- [-]
17- 21 I5 d MJD ? SDSS MJD observation date
22 A1 --- --- [-]
23- 25 I3 --- Fib ? SDSS Fiber identification
27- 28 I2 h RAh Right ascension (J2000) (2)
30- 31 I2 min RAm Right ascension (J2000) (2)
33- 37 F5.2 s RAs Right ascension (J2000) (2)
39 A1 --- DE- Declination sign (J2000) (2)
40- 41 I2 deg DEd Declination (J2000) (2)
43- 44 I2 arcmin DEm Declination (J2000) (2)
46- 50 F5.2 arcsec DEs Declination (J2000) (2)
52- 57 I6 --- IDR7 [311385/920120]? Zero-offset index of this
object in the MPA-JHU value-added catalogues
Brinchmann et al. (2004MNRAS.351.1151B 2004MNRAS.351.1151B) found
at http//www.mpa-garching.mpg.de/SDSS
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Note (2): Position of the fibre the spectrum of the SDSS spectroscopic
identification.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Reg Region name (NGCnnnn-nn) (G1)
12- 15 F4.2 [Msun/pc2] logSHI HI surface mass density (from HI)
17- 20 F4.2 [Msun/pc2] logSmol Molecular surface mass density (from CO)
22- 25 F4.2 [Msun/pc2] b_logSg Gas surface mass density at 16% of
confidence interval
27- 30 F4.2 [Msun/pc2] logSg Median gas surface mass density
32- 35 F4.2 [Msun/pc2] B_logSg Gas surface mass density at 84% of
confidence interval
37- 42 F6.1 0.1nm EWHa ?=- Hα equivalent width (Å)
44- 48 F5.1 0.1nm EWHb ?=- Hβ equivalent width (Å)
50- 53 F4.2 --- Ha/Hb ? Hα/Hβ Balmer decrement
54 A1 --- n_Ha/Hb [I] I for ∞
56- 60 F5.2 mag g-r g-r colour index
62- 66 F5.2 mag u-r u-r colour index
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Global Notes:
Note (G1): the region us named with the galaxy name, appended with a
running index for the region.
History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 08-Jul-2014