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The CO-to-H2 Conversion Factor and Dust-to-Gas Ratio on Kiloparsec Scales in Nearby Galaxies | | K. M. Sandstrom
; A. K. Leroy
; F. Walter
; A. D. Bolatto
; K. V. Croxall
; B. T. Draine
; C. D. Wilson
; M. Wolfire
; D. Calzetti
; R. C. Kennicutt
; G. Aniano
; J. Donovan Meyer
; A. Usero
; F. Bigiel
; E. Brinks
; W. J. G de Blok
; A. Crocker
; D. Dale
; C. W. Engelbracht
; M. Galametz
; B. Groves
; L. K. Hunt
; J. Koda
; K. Kreckel
; H. Linz
; S. Meidt
; E. Pellegrini
; H.-W. Rix
; H. Roussel
; E. Schinnerer
; A. Schruba
; K.-F. Schuster
; R. Skibba
; T. van der Laan
; P. Appleton
; L. Armus
; B. Brandl
; K. Gordon
; J. Hinz
; O. Krause
; E. Montiel
; M. Sauvage
; A. Schmiedeke
; J. D. T. Smith
; L. Vigroux
; | | Date: |
6 Dec 2012 | | Abstract: | We present maps of the CO-to-H2 conversion factor (alpha_co) and dust-to-gas
ratio (DGR) in 26 nearby, star-forming galaxies with ~kiloparsec spatial
resolution. We have simultaneously solved for alpha_co and DGR by assuming that
the DGR is approximately constant on kpc scales. With this assumption, we can
combine maps of dust mass surface density, CO integrated intensity and HI
column density to solve for both alpha_co and DGR with no assumptions about
their value or dependence on metallicity or other parameters. Such a study has
just become possible with the availability of high resolution far-IR maps from
the Herschel key program KINGFISH, 12CO J=(2-1) maps from the IRAM 30m large
program HERACLES and HI 21-cm line maps from THINGS. We use a fixed ratio
between the (2-1) and (1-0) lines to present our alpha_co results on the more
typically used 12CO J=(1-0) scale and show using literature measurements that
variations in the line ratio do not effect our results. In total, we derive 782
individual solutions for alpha_co and DGR. On average, alpha_co = 3.1 Msun
pc^-2 (K km s^-1)^-1 for our sample with a standard deviation of 0.3 dex.
Within galaxies we observe a generally flat profile of alpha_co as a function
of galactocentric radius. However, most galaxies exhibit a lower alpha_co in
the central kiloparsec---a factor of ~2 below the galaxy mean, on average. In
some cases, the central alpha_co value can be factors of 5 to 10 below the
standard MW value of alpha_co,MW = 4.4 Msun pc^-2 (K km s^-1)^-1. While for
alpha_co we find only weak correlations with metallicity, DGR is
well-correlated with metallicity, with an approximately linear slope. Finally,
we present several recommendations for choosing an appropriate alpha_co for
studies of nearby galaxies. | | Source: | arXiv, 1212.1208 | | Services: | Forum | Review | PDF | Favorites | |
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