J/A+A/580/A112 THOR. The HI, OH, Recombination Line Survey (Bihr+, 2015)
THOR - The HI, OH, Recombination Line Survey of the Milky Way.
The pilot study - HI observations of the giant molecular cloud W43.
Bihr S., Beuther H., Ott J., Johnston K.G., Brunthaler A., Anderson L.D.,
Bigiel F., Carlhoff P., Churchwell E., Glover S.C.O., Goldsmith P.F.,
Heitsch F., Henning T., Heyer M.H., Hill T., Hughes A., Klessen R.S.,
Linz H., Longmore S.N., McClure-Griffiths N.M., Menten K.M., Motte F.,
Nguyen-Lu'o'ng Q., Plume R., Ragan S.E., Roy N., Schilke P., Schneider N.,
Smith R.J., Stil J.M., Urquhart J.S., Walsh A.J., Walter F.
<Astron. Astrophys. 580, A112 (2015)>
=2015A&A...580A.112B 2015A&A...580A.112B
ADC_Keywords: Molecular clouds ; H I data
Keywords: ISM: clouds - ISM: structure - ISM: atoms - stars: formation -
radio lines: ISM - surveys
Abstract:
To study the atomic, molecular and ionized emission of Giant Molecular
Clouds (GMCs), we have initiated a Large Program with the VLA:
'THOR - The HI, OH, Recombination Line survey of the Milky Way'. We
map the 21cm HI line, 4 OH lines, 19 Hα recombination lines and
the continuum from 1 to 2GHz of a significant fraction of the Milky
Way (l=15-67°, |b|<1°) at ∼20" resolution. In this paper, we
focus on the HI emission from the W43 star-formation complex.
Classically, the HI 21cm line is treated as optically thin with column
densities calculated under this assumption. This might give reasonable
results for regions of low-mass star-formation, however, it is not
sufficient to describe GMCs. We analyzed strong continuum sources to
measure the optical depth, and thus correct the HI 21cm emission for
optical depth effects and weak diffuse continuum emission. Hence, we
are able to measure the HI mass of W43 more accurately and our
analysis reveals a lower limit of M=6.6x106M☉, which is a
factor of 2.4 larger than the mass estimated with the assumption of
optically thin emission. The HI column densities are as high as
N(HI)∼150M☉/pc2∼1.9x1022cm-2^, which is an order of
magnitude higher than for low mass star formation regions. This result
challenges theoretical models that predict a threshold for the HI
column density of ∼10M☉/pc2, at which the formation of
molecular hydrogen should set in. By assuming an elliptical layered
structure for W43, we estimate the particle density profiles. While at
the cloud edge atomic and molecular hydrogen are well mixed, the
center of the cloud is strongly dominated by molecular hydrogen. We do
not identify a sharp transition between hydrogen in atomic and
molecular form. Our results are an important characterization of the
atomic to molecular hydrogen transition in an extreme environment and
challenges current theoretical models.
Description:
We show HI 21cm data cubes of the W43 region including the continuum
emission. This data cube is made with the combination of VLA C and
D-array data. Units are given in Jy/beam.
Objects:
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RA (2000) DE Designation(s)
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18 47 32 -01 56.5 W43 = SNR G030.8-00.0
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 129 1 Datacube informations
datacube.fits 2880 1459164 Datacube FITS file
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See also:
J/A+A/538/A11 : 70um-1.2mm and N2H+ maps of IRDC18454 (W43) (Beuther+, 2012)
J/A+A/542/A76 : Herschel-HIFI water spectra of W43-MM1 (Herpin+, 2012)
J/A+A/560/A24 : IRAM 30m CO-observations in W43 (Carlhoff+, 2013)
Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1 A1 --- --- [G]
2- 10 F9.5 deg GLON Galactic longitude on image center
11- 19 F9.5 deg GLAT Galactic latitude on image center
21 I1 arcsec/pix Scale [4] Scale of the image
23- 26 I4 --- Nx [2534] Number of pixels along X-axis
28- 31 I4 --- Ny [2073] Number of pixels along Y-axis
33- 35 I3 --- Nz [200] Number of slices
37- 55 A19 "datime" Date Observation date (YYYY-MM-DDThh:mm:ss.s)
59- 66 F8.1 m/s V.min [-88606.9] Lower value of VRAD interval
68- 73 I6 m/s V.max [157457] Upper value of VRAD interval
75- 80 F6.1 m/s dV [1236.5]Radial velocity resolution
82- 88 I7 Kibyte size [4103902] Size of the FITS file
90-102 A13 --- FileName Name of the FITS datacube
104-129 A26 --- Title Title of the file
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Acknowledgements:
Simon Bihr, bihr(at)mpia.de
(End) S. Bihr [Max Planck Inst. for Astr.], P. Vannier [CDS] 21-Jul-2015