J/MNRAS/428/3355 Hydrogen volume densities in nearby galaxies (Heiner+, 2013)
Hydrogen volume densities in nearby galaxies. I. An automated approach.
Heiner J.S., Sanchez-Gallego J.R., Rousseau-Nepton L., Knapen J.H.
<Mon. Not. R. Astron. Soc., 428, 3355-3365 (2013)>
=2013MNRAS.428.3355H 2013MNRAS.428.3355H
ADC_Keywords: Galaxies, nearby ; H I data ; Ultraviolet
Keywords: ISM: atoms - ISM: clouds - ISM: molecules -
galaxies: individual: M74 - galaxies: ISM - ultraviolet: galaxies
Abstract:
Using a simple model of photodissociated atomic hydrogen on a galactic
scale, it is possible to derive total hydrogen volume densities. These
densities, obtained through a combination of atomic hydrogen,
far-ultraviolet and metallicity data, provide an independent probe of
the combined atomic and molecular hydrogen gas in galactic discs. We
present a new, flexible and fully automated procedure using this
simple model. This automated method will allow us to take full
advantage of a host of available data on galaxies in order to
calculate the total hydrogen volume densities of the giant molecular
clouds surrounding sites of recent star formation. Until now this was
only possible on a galaxy-by-galaxy basis using by-eye analysis of
candidate photodissociation regions.
We test the automated method by adopting various models for the
dust-to-gas ratio and comparing the resulting densities for M74,
including a new metallicity map of M74 produced by integral field
spectroscopy. We test the procedure against previously published M83
volume densities based on the same method and find no significant
differences. The range of total hydrogen volume densities obtained for
M74 is approximately 5-700cm-3. Different dust-to-gas ratio models do
not result in measurably different densities.
The cloud densities presented here mean that M74 is added to the list
of galaxies analysed using the assumption of photodissociated atomic
hydrogen occurring near sites of recent star formation, and
consolidate the method.
For the first time, full metallicity maps are included in the analysis
as opposed to metallicity gradients. The results will need to be
compared with other tracers of the interstellar medium and
photodissociation regions, such as CO and CII, in order to test our
basic assumptions, specifically our assumption that the HI we detect
originates in photodissociation regions.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
ngc5236.dat 201 142 NGC 5236 locations and properties of candidate PDRs
(PhotoDissociation Regions)
ngc628pi.dat 201 81 NGC 628 locations and properties of candidate PDRs
with densities derived from PINGS metallicities
ngc628po.dat 201 121 NGC 628 locations and properties of candidate PDRs
with densities derived from metallicity slope
ngc628sl.dat 201 176 NGC 628 locations and properties of candidate PDRs
with densities derived from SpIOMM metallicities
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See also:
J/MNRAS/416/2 : Photodissociation regions in M33 (Heiner+, 2011)
Byte-by-byte Description of file: ngc*
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Bytes Format Units Label Explanations
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1- 3 I3 --- PDRID [1/172] Photo-Dissociation Region (PDR)
identification number
5- 13 F9.6 kpc Rgal Galactocentric distance
15- 22 F8.6 --- Rnorm Normalized radius in R25 units (1)
24- 36 E13.7 cm-2 NHI HI column density
38- 49 E12.7 cm-2 e_NHI rms uncertainty on NHI
50- 57 F8.6 [-] d/d0 Dust-to-gas ratio log(δ/δ0),
scaled to solar neighborhood (2)
59- 66 F8.6 [-] e_d/d0 ? rms uncertainty on d/d0
68- 75 F8.4 pc rhoHI Source-patch separation
77- 83 F7.4 pc e_rhoHI rms uncertainty on rhoHI
85- 96 E12.7 cW/m2/nm Flux Flux of PDR (erg/cm2/s/Å)
98-109 E12.7 cW/m2/nm e_Flux ?=0 rms uncertainty on Flux
111-120 F10.6 --- G0 Incident flux (scaled to solar neighborhood)
122-132 F11.6 ---- G/Gbg Source contrast
133-144 F12.6 cm-3 nH Total HI volume density
146-157 F12.6 cm-3 e_nH ? rms uncertainty on nH
159-168 F10.6 deg RAdeg Right ascension (J2000)
170-179 F10.6 deg DEdeg Declinaton (J2000)
181-190 F10.6 deg RApdeg Patch right ascension (J2000)
192-201 F10.6 deg DEpdeg Patch declination (J2000)
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Note (1): R25 is 11.0kpc for NGC 628 and 7.63kpc for ngc5236.
Note (2): the Dust-to-gas ratio is estimated from the oxygen abundance
(12+log(O/H)=8.69 in the solar neighborhood), and the value taken is
log(δ/δ0)=(12+log(O/H)-8.69
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 07-Mar-2014