2020A&A...639A..26K

Query : 2020A&A...639A..26K

2020A&A...639A..26K - Astronomy and Astrophysics, volume 639A, 26-26 (2020/7-1)

H I filaments are cold and associated with dark molecular gas. HI4PI-based estimates of the local diffuse CO-dark H2 distribution.

KALBERLA P.M.W., KERP J. and HAUD U.

Abstract (from CDS):


Context. There are significant amounts of H2 in the Milky Way. Due to its symmetry H2 does not radiate at radio frequencies. CO is thought to be a tracer for H2; however, CO is formed at significantly higher opacities than H2. Thus, toward high Galactic latitudes significant amounts of H2 are hidden and are called CO-dark.
Aims. We demonstrate that the dust-to-gas ratio is a tool for identifying locations and column densities of CO-dark H2.
Methods. We adopt the hypothesis of a constant E(B-V)/NH ratio, independent of phase transitions from HI to H2. We investigate the Doppler temperatures TD, from a Gaussian decomposition of HI4PI data, to study temperature dependences of E(B-V)/NHI.
Results. The E(B-V)/NHI ratio in the cold HI gas phase is high in comparison to the warmer phase. We consider this as evidence that cold HI gas toward high Galactic latitudes is associated with H2. Beyond CO-bright regions, for TD≤1165K we find a correlation (NHI+2NH2)/NHI∝-logTD. In combination with a factor XCO=4.0x1020cm–2/(K.km/s) this yields NH/E(B-V)∼5.1 to 6.7x1021cm–2mag–1 for the full sky, which is compatible with X-ray scattering and UV absorption line observations.
Conclusions. Cold HI with TD≤1165K contains on average 46% CO-dark H2. Prominent filaments have TD≤220K and typical excitation temperatures Tex∼50K. With a molecular gas fraction of ≥61% they are dominated dynamically by H2.

Abstract Copyright: © ESO 2020

Journal keyword(s): ISM: clouds - ISM: structure - ISM: molecules - dust, extinction

VizieR on-line data: <Available at CDS (J/A+A/639/A26): list.dat fits/*>

Simbad objects: 1

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Number of rows : 1
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024 		#notes
1 NAME Magellanic Clouds GrG 03 00 -71.0           ~ 7065 0

Query : 2020A&A...639A..26K

Basic data :
NAME Magellanic Clouds -- Group of Galaxies
Origin of the objects types :

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  • [error ellipse] : measurement uncertainty, on (ra,dec) if the positional angle is 90 degrees, on (majaxis,minaxis) otherwise (in mas at defined epoch in the original catalogue),
    position angle (in degrees North celestial pole to East)
  • quality : flag of quality
    • E ≥ 10"
    • D : 1-10" (and some old data)
    • C : 0.1-1"
    • B : 0.01-0.1" + 2MASS, Tyc
    • A : VLBI, Hipparcos
  • bibcode : bibcode of the coordinates reference
ICRS coord. (ep=J2000) : 		03 00 00.0 -71 00 00 [ ] E ~
Syntax of coordinates is : "ra dec (wtype) [error ellipse] quality bibcode" :
  • ra dec : right ascension and declination (unit and frame defined according to your Output Options)
    Grey values are increasing the original precision due to the computation of frame transformations
  • (wtype) : wavelength class for the origin of the coordinates (Rad, mm, IR, Optical, UV, Xray, Gam)
  • [error ellipse] : measurement uncertainty, on (ra,dec) if the positional angle is 90 degrees, on (majaxis,minaxis) otherwise (in mas at defined epoch in the original catalogue),
    position angle (in degrees North celestial pole to East)
  • quality : flag of quality
    • E ≥ 10"
    • D : 1-10" (and some old data)
    • C : 0.1-1"
    • B : 0.01-0.1" + 2MASS, Tyc
    • A : VLBI, Hipparcos
  • bibcode : bibcode of the coordinates reference
FK4 coord. (ep=B1950 eq=1950) : 		02 59 44.2 -71 11 49 [ ]
Syntax of coordinates is : "ra dec (wtype) [error ellipse] quality bibcode" :
  • ra dec : right ascension and declination (unit and frame defined according to your Output Options)
    Grey values are increasing the original precision due to the computation of frame transformations
  • (wtype) : wavelength class for the origin of the coordinates (Rad, mm, IR, Optical, UV, Xray, Gam)
  • [error ellipse] : measurement uncertainty, on (ra,dec) if the positional angle is 90 degrees, on (majaxis,minaxis) otherwise (in mas at defined epoch in the original catalogue),
    position angle (in degrees North celestial pole to East)
  • quality : flag of quality
    • E ≥ 10"
    • D : 1-10" (and some old data)
    • C : 0.1-1"
    • B : 0.01-0.1" + 2MASS, Tyc
    • A : VLBI, Hipparcos
  • bibcode : bibcode of the coordinates reference
Gal coord. (ep=J2000) : 		289.3295 -42.5698 [ ]
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NAME Magellanic Clouds

References (7065 between 1850 and 2024) (Total 7065)
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