J/A+A/627/A95 Molecular DNM in Chamaeleon CO spectra (Liszt+, 2019)
Standing in the shadow of the dark gas:
ALMA observation of absorption from dark CO in the molecular dark neutral medium
of Chamaeleon.
Liszt H., Gerin M., Grenier I.
<Astron. Astrophys. 627, A95 (2019)>
=2019A&A...627A..95L 2019A&A...627A..95L (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Spectra, millimetric/submm ;
Interstellar medium
Keywords: ISM: molecules - dust, extinction - ISM: clouds
Abstract:
To determine carbon monoxide column densities along sightlines through
the Chamaeleon cloud complex where molecular absorption had been
observed but CO emission had not been detected.
We took 12CO J=1-0 absorption profiles toward 6 of 8 members of a
group of sightlines in Chamaeleon having abundant dark neutral matter
and molecular hydrogen but no detectable CO emission.
CO absorption was detected along five of the six sightlines at column
densities 4x10+13cm-2≲N(CO)≲1015cm-2 that are below typical
survey detection limits of 1-2K-km/s.
Dark gas absent in CO emission along sightlines in the outskirts of
the Chamaeleon complex where molecular gas is readily detected in
HCO+ absorption results from small CO column densities around the
onset of CO formation at the HI/H2 transition. Relative abundances
N(CO)/H2<3x10-6 in Chamaeleon are comparable to those
seen in UV absorption toward early-type stars and in a CO
absorption/emission line survey toward local quasar background targets
away from the Galactic plane.
Description:
12CO absorption line profiles in six directions in Chamaeleon in I*2
FITS format. The data are 1918-channel spectra with a velocity axis at
rest frequency 115271.202MHz and channel values are in units of
line/continuum - 1. In the header, the commented parameter TC is the
flux of the continuum background source in Jansky and the RMS, MIN and
MAX are accurate, but the other COMMENT parameters are dummy values.
The first FITS axis is the velocity, the 2nd gives the line rest
frequency, the 3rd and 4th give the J2000 Ra and Dec in decimal
degrees following the FITS convention.
A sample FITS header is shown below:
SIMPLE = T
BITPIX = 16
NAXIS = 4
NAXIS1 = 1918
NAXIS2 = 1
NAXIS3 = 1
NAXIS4 = 1
BLOCKED = T
BUNIT = 'L/C-1'
BSCALE = 0.0000017871958
BZERO = 0.0008269455283
DATAMAX = 0.0593879930675
DATAMIN = -0.057734102010
OBJECT = 'J1254-7138'
TELESCOP= 'DRAWSPEC'
OBSERVER= 'DRAWSPEC'
DATE-OBS= '17-12-20'
DATE = '20190605'
EQUINOX = 2000.0000000000
CTYPE1 = 'VELO-LSR'
CRVAL1 = -7609374.545169
CDELT1 = 7933.2316590184
CRPIX1 = 1.0000000000000
CTYPE2 = 'FREQ'
CRVAL2 = 1.1527120200E11
CDELT2 = -30503.54085557
CRPIX2 = 1.0000000000000
CTYPE3 = 'RA---GLS'
CRVAL3 = 193.74932666701
CDELT3 = 0.000000000000
CRPIX3 = 1.0000000000000
CTYPE4 = 'DEC--GLS'
CRVAL4 = -71.63846222217
CDELT4 = 0.000000000000
CRPIX4 = 1.0000000000000
COMMENT TC = 0.3229000000
COMMENT TSYS = 100.00000000
COMMENT DUR = 60.000000000
COMMENT NCH = 1918.0000000
COMMENT AZ = 0.000000000
COMMENT EL = 0.000000000
COMMENT RMS = 0.0182105759
COMMENT MIN = -0.057734102
COMMENT MAX = 0.0593879930
COMMENT MEAN = 0.0003391627
COMMENT Line = 12CO(1-0)
HISTORY Name Changed
HISTORY Chan edited
END
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 107 6 Sightline and velocity-integrated spectral
line properties
fits/* . 6 Individual fits spectra
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Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Source name
12- 20 F9.6 deg RAdeg Right ascension (J2000)
22- 31 F10.6 deg DEdeg Declination (J2000)
33- 39 F7.3 deg GLON Galactic longitude
41- 47 F7.3 deg GLAT Galactic latitude
49- 52 F4.2 mag E(B-V) Interstellar extinction (1)
54- 57 F4.1 10+20cm-2 NHI HI column density (2)
59- 63 F5.3 km/s GammaHCO+ HCO+ integrated J=1-0 optical depth
65- 69 F5.3 km/s e_GammaHCO+ rms uncertainty on GammaHCO+
71- 75 F5.3 Jy S115 Flux density at 115GHz
77- 81 F5.3 --- sigmal/c Line/continuum rms at zero optical depth in
the 2x oversampled spectrum
83 A1 --- l_GammaCO 3σ upper limit flag on GammaCO
84- 88 F5.3 km/s GammaCO CO integrated J=1-0 optical depth
90- 94 F5.3 km/s e_GammaCO ? rms uncertainty on GammaCO
96-107 A12 --- FileName Name of FITS 12CO J=1-0 spectrum,
in subdirectory fits
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Note (1): Schlegel et al. (1998ApJ...500..525S 1998ApJ...500..525S)
Note (2): NHI = int{TBdv}x1.823x1018cm-2 from the Gass III HI profile
(Kalberla & Haud, 2015A&A...578A..78K 2015A&A...578A..78K)
--------------------------------------------------------------------------------
Acknowledgements:
Harvey Liszt, hliszt(at)nrao.edu
Hotel Bel Esperance, Geneva
(End) Harvey Liszt [Geneva], Patricia Vannier [CDS] 05-Jun-2019