Universität zu Köln

Kim, W. -J., Urquhart, J. S., Wyrowski, F., Menten, K. M. and Csengeri, T. (2018). New detections of (sub)millimeter hydrogen radio recombination lines towards high-mass star-forming clumps. Astron. Astrophys., 616. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Aims. Previous radio recombination line (RRL) observations of dust clumps identified in the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) have led to the detection of a large number of RRLs in the 3 mm range. Here, we aim to study their excitation with shorter wavelength (sub) millimeter radio recombination line (submm-RRL) observations. Methods. We made observations of submm-RRLs with low principal quantum numbers (n <= 30) using the APEX 12 m telescope, toward 104 HII regions associated with massive dust clumps from ATLASGAL. The observations covered the H25 alpha, H28 alpha, and H35 beta transitions. Toward a small subsample the H26 alpha, H27 alpha, H29 alpha, and H30 alpha lines were observed to avoid contamination by molecular lines at adjacent frequencies. Results. We have detected submm-RRLs (signal-to-noise (S/N) >= 3 sigma) from compact HII regions embedded within 93 clumps. The submm-RRLs are approximately a factor of two brighter than the mm-RRLs and consistent with optically thin emission in local thermodynamic equilibrium (LTE). The average ratio (0.31) of the measured H35 beta/H28 alpha fluxes is close to the LTE value of 0.28. No indication of RRL maser emission has been found. The Lyman photon flux, bolometric, and submm-RRL luminosities toward the submm-RRL detected sources present significant correlations. The trends of dust temperature and the ratio of bolometric luminosity to clump mass, L-bol/M-clump, indicate that the HII regions are related to the most massive and luminous clumps. By estimating the production rate of ionizing photons, Q, from the submm-RRL flux, we find that the Q(H28 alpha) measurements provide estimates of the Lyman continuum photon flux consistent with those determined from 5 GHz radio continuum emission. Six RRL sources show line profiles that are a combination of a narrow and a broad Gaussian feature. The broad features are likely associated with high-velocity ionized flows. Conclusions. We have detected submm-RRLs toward 93 ATLASGAL clumps. Six RRL sources have high-velocity RRL components likely driven by high-velocity ionized flows. Their observed properties are consistent with thermal emission that correlates well with the Lyman continuum flux of the HII regions. The sample of HII regions with mm/submm-RRL detections probes, in our Galaxy, luminous clumps (L-bol > 10(4) L-circle dot) with high L-bol/M-clump. We also provide suitable candidates for further studies of the morphology and kinematics of embedded, compact HII regions with the Atacama Large Millimeter/submillimeter Array (ALMA).

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Kim, W. -J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Urquhart, J. S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Wyrowski, F. UNSPECIFIED UNSPECIFIED UNSPECIFIED Menten, K. M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Csengeri, T. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-176003
DOI:	10.1051/0004-6361/201732330
Journal or Publication Title:	Astron. Astrophys.
Volume:	616
Date:	2018
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:	Keywords Language H-II REGIONS; RMS SURVEY; GALACTIC PLANE; COMPACT; ATLASGAL; APEX; G29.96-0.02; HEMISPHERE; FACILITY; MODELS Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/17600