2015A&A...580A.112B


C.D.S. - SIMBAD4 rel 1.7 - 2019.10.20CEST04:07:44

2015A&A...580A.112B - Astronomy and Astrophysics, volume 580A, 112-112 (2015/8-1)

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-LUONG Q., PLUME R., RAGAN S.E., ROY N., SCHILKE P., SCHNEIDER N., SMITH R.J., STIL J.M., URQUHART J.S., WALSH A.J. and WALTER F.

Abstract (from CDS):

To study the atomic, molecular, and ionized emission of giant molecular clouds (GMCs) in the Milky Way, we initiated a large program with the Karl G. Jansky Very Large Array (VLA): ``THOR: The HI, OH, Recombination line survey of the Milky Way''. We map the 21cm HI line, 4 OH lines, up to 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 an angular resolution of ∼20". Starting in 2012, as a pilot study we mapped 4 square degrees of the GMC associated with the W43 star formation complex. The rest of the THOR survey area was observed during 2013 and 2014. In this paper, we focus on the HI emission from the W43 GMC complex. Classically, the HI 21cm line is treated as optically thin with properties such as the column density calculated under this assumption. This approach might yield 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 along the line of sight, 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 this region more accurately and our analysis reveals a lower limit for the HI mass of M=6.6–1.8x106M (vLSR=60-120km/s), 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 NHI∼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 profile. For the atomic gas particle density, we find a linear decrease toward the center of W43 with values decreasing from nHI=20cm–3 near the cloud edge to almost 0/cm3 at its center. On the other hand, the molecular hydrogen, traced via dust observations with the Herschel Space Observatory, shows an exponential increase toward the center with densities increasing to nH2>200cm–3, averaged over a region of ∼10pc. While atomic and molecular hydrogen are well mixed at the cloud edge, the center of the cloud is strongly dominated by H2 emission. We do not identify a sharp transition between hydrogen in atomic and molecular form. Our results, which challenge current theoretical models, are an important characterization of the atomic to molecular hydrogen transition in an extreme environment.

Abstract Copyright:

Journal keyword(s): ISM: clouds - ISM: structure - ISM: atoms - stars: formation - radio lines: ISM - surveys

VizieR on-line data: <Available at CDS (J/A+A/580/A112): list.dat HIcont–includedC-D1.2kmgal.fits>

Simbad objects: 20

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Number of rows : 20

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2019
#notes
1 NAME Per Arm PoG 03 30 +45.0           ~ 1193 0
2 NAME Perseus Cloud SFR 03 35.0 +31 13           ~ 1007 0
3 3C 286 Sy1 13 31 08.2885060664 +30 30 32.960825108   17.51 17.25     ~ 3615 1
4 PMN J1822-0939 Rad 18 22 28.70 -09 38 57.0           ~ 28 1
5 GPSR 029.089+0.511 Rad 18 42 35.95 -03 11 07.6           ~ 3 0
6 4C -01.46 Rad 18 43 51.33 -01 29 15.5           ~ 40 2
7 GAL 029.96-00.02 Y*O 18 46 03.7 -02 39 21           ~ 325 1
8 SNR G029.7-00.3 SNR 18 46 25.5 -02 59 14           ~ 280 2
9 GPSR 030.535+0.021 Rad 18 46 59.37 -02 07 25.6           ~ 5 0
10 IRAS 18443-0231 PN? 18 47 00.418 -02 27 52.27   13.62 13.41 12.27   ~ 22 0
11 SNR G030.8-00.0 SNR 18 47 32 -01 56.5           ~ 423 0
12 IRAS 18449-0115 cor 18 47 34.4947 -01 12 40.269           ~ 291 0
13 [MSL2003] W43-MM1 cor 18 47 47.0 -01 54 28           ~ 83 0
14 CORNISH G031.2420-00.1106 HII 18 48 44.690 -01 33 14.49           ~ 3 0
15 [LPH96] 030.693-0.630 HII 18 49 35.6 -02 16 44           ~ 3 0
16 NVSS J184959-013256 Rad 18 49 59.2 -01 32 57           ~ 8 1
17 NAME Sgr Arm PoG 19 00 -30.0           ~ 496 1
18 NAME Galactic Bar reg ~ ~           ~ 815 0
19 NAME Sct-Cen PoG ~ ~           ~ 120 0
20 NAME Scutum Spiral Arm PoG ~ ~           ~ 256 0

    Equat.    Gal    SGal    Ecl

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2019.10.20-04:07:44

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