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. and Walter, F. (2015). THOR: The HI, OH, Recombination line survey of the Milky Way The pilot study: HI observations of the giant molecular cloud W43. Astron. Astrophys., 580. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

Full text not available from this repository.

Abstract

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 21 cm HI line, 4 OH lines, up to 19 H alpha recombination lines and the continuum from 1 to 2 GHz of a significant fraction of the Milky Way (l = 15 degrees-67 degrees, vertical bar b vertical bar <= 1 degrees) at an angular resolution of similar to 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 21 cm 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 21 cm 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(-1.8) x 10(6) M-circle dot (nu(LSR) = 60-120 km s(-1)), 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 similar to 150 M-circle dot pc(-2) approximate to 1.9 x 10(22) cm(-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 similar to 10 M-circle dot pc(-2), 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 n(HI) = 20 cm(-3) near the cloud edge to almost 0 cm(-3) 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 n(H2) > 200 cm(-3), averaged over a region of similar to 10 pc. While atomic and molecular hydrogen are well mixed at the cloud edge, the center of the cloud is strongly dominated by H-2 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.

Item Type: Journal Article
Creators:
CreatorsEmailORCIDORCID Put Code
Bihr, S.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Beuther, H.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Ott, J.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Johnston, K. G.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Brunthaler, A.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Anderson, L. D.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Bigiel, F.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Carlhoff, P.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Churchwell, E.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Glover, S. C. O.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Goldsmith, P. F.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Heitsch, F.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Henning, T.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Heyer, M. H.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Hill, T.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Hughes, A.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Klessen, R. S.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Linz, H.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Longmore, S. N.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
McClure-Griffiths, N. M.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Menten, K. M.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Motte, F.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Nguyen-Lu'o'ng, Q.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Plume, R.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Ragan, S. E.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Roy, N.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Schilke, P.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Schneider, N.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Smith, R. J.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Stil, J. M.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Urquhart, J. S.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Walsh, A. J.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Walter, F.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
URN: urn:nbn:de:hbz:38-397962
DOI: 10.1051/0004-6361/201425370
Journal or Publication Title: Astron. Astrophys.
Volume: 580
Date: 2015
Publisher: EDP SCIENCES S A
Place of Publication: LES ULIS CEDEX A
ISSN: 1432-0746
Language: English
Faculty: Unspecified
Divisions: Unspecified
Subjects: no entry
Uncontrolled Keywords:
KeywordsLanguage
GALACTIC PLANE SURVEY; NARROW SELF-ABSORPTION; NEUTRAL ATOMIC PHASES; INFRARED DARK CLOUDS; MASS STAR-FORMATION; I-21 CM ABSORPTION; HIGH-RESOLUTION; MINI-STARBURST; EXTRAGALACTIC SOURCES; INTERSTELLAR-MEDIUMMultiple languages
Astronomy & AstrophysicsMultiple languages
URI: http://kups.ub.uni-koeln.de/id/eprint/39796

Downloads

Downloads per month over past year

Altmetric

Export

Actions (login required)

View Item View Item