J/A+A/639/A26 Cold HI, H2 and total H column density FITS maps (Kalberla+, 2020)
HI 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., Haud U.
<Astron. Astrophys. 639, A26 (2020)>
=2020A&A...639A..26K 2020A&A...639A..26K (SIMBAD/NED BibCode)
+2024A&A...684C...1K 2024A&A...684C...1K
ADC_Keywords: Surveys ; H I data ; Milky Way ; Interstellar medium ;
Spectroscopy
Keywords: ISM: clouds - ISM: structure - ISM: molecules - dust, extinction
Abstract:
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 called CO-dark.
We demonstrate that the dust-to-gas ratio is a tool to identify
locations and column densities of CO-dark H2.
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 dependencies of E(B-V)/NHI.
The E(B-V)/NHI ratio in the cold HI gas phase is high in comparison to
the warmer one. We consider this as evidence that cold HI gas toward
high Galactic latitudes is associated with H2. Beyond CO-bright
regions we find for TD<1165K a correlation
(NHI+2NH2)/NHI∝-log TD. In combination with a factor
XCO=4.0x1020cm-2(K.km/s)-1 this yields for the full-sky
NH/E(B-V)∼5.1 to 6.7 1021cm-2mag-1, compatible with X-ray
scattering and UV absorption line observations.
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.
Description:
We use a Gaussian decomposition of HI4PI data (Haud,
2000A&A...364...83H 2000A&A...364...83H, HI4PI Collaboration et al. 2016, Cat.
J/A+A/594/A116) to derive all-sky HI column densities and Doppler
temperatures TD. Assuming a constant gas-to-dust ratio we derive TD
dependent CO-dark H2 column densities, further from a constant XCO
factor CO-bright H2 column densities.
For column densities in the velocity range -90<vlsr<90km/s we present
FITS maps for CO-dark H2, total H2 (CO-dark and CO-bright) and
total hydrogen (HI + CO-dark and CO-bright H2).
In addition we give CO-dark H2 column densities for the velocity
range -8<vlsr<8km/s, characteristic for filaments in the local
vicinity.
HEALPix FITS data for other velocity ranges can be downloaded from
https://www.astro.uni-bonn.de/hisurvey/ also HI profiles and column
densities at individual positions are given there.
The FITS binary tables contain column densities sampled on a HEALPix
grid (nside=1024, Galactic coordinates, Ring indexing scheme, Gorski
et al., 2005ApJ...622..759G 2005ApJ...622..759G).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 93 4 List of fits files (corrected files, 05/02/2024)
fits/* . 4 Individual fits files
(corrected files, 05/02/2024)
--------------------------------------------------------------------------------
See also:
J/A+A/594/A116 : HI4PI spectra and column density maps (HI4PI team+, 2016)
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- Nx Number of pixels along X-axis
6- 10 I5 --- Ny Number of pixels along Y-axis
12- 16 I5 Kibyte size Size of FITS file
18- 33 A16 --- FileName Name of FITS file, in subdirectory fits
35- 93 A59 --- Title Title of the FITS file
--------------------------------------------------------------------------------
Acknowledgements:
Peter Kalberla, pkalberla(at)astro.uni-bonn.de
History:
06-Jul-2020: on-line version
05-Feb-2024: corrected fits files
(End) Patricia Vannier [CDS] 06-May-2020