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The census of Galactic H Ⅱ regions is vastly incomplete in the southern sky. We use the Australia Telescope Compact Array to observe 4-10 radio continuum and hydrogen radio recombination line (RRL) emission from candidate H Ⅱ regions in the Galactic zone 250° < 𝓁 < 344°,|b|4°. In this first data release, we target the brightest H Ⅱ region candidates and observe 282 fields in the direction of at least one previously known or candidate H Ⅱ region. We detect radio continuum emission and RRL emission in 275 (97.5%) and 258 (91.5%) of these fields, respectively. We catalog the ∼7 GHz radio continuum peak flux densities and positions of 80 previously known and 298 candidate H Ⅱ regions. After averaging ∼18 RRL transitions, we detect 77 RRL velocity components toward 76 previously known H Ⅱ regions and 267 RRL velocity components toward 256 H Ⅱ region candidates. The discovery of RRL emission from these nebulae increases the number of known Galactic H Ⅱ regions in the surveyed zone by 82% to 568 nebulae. In the fourth quadrant, we discover 50 RRLs with positive velocities, placing those sources outside the solar circle. Including the pilot survey, the Southern H Ⅱ Region Discovery Survey has now discovered 295 Galactic H Ⅱ regions. In the next data release, we expect to add ∼200 fainter and more distant nebulae.

Item Type:	Refereed Article
Keywords:	galaxy: kinematics and dynamics - galaxy: structure - (ISM:) Hii regions - ISM: kinematics and dynamics - radio lines: ISM - surveys, radio astronomy
Research Division:	Physical Sciences
Research Group:	Astronomical sciences
Research Field:	Galactic astronomy
Objective Division:	Expanding Knowledge
Objective Group:	Expanding knowledge
Objective Field:	Expanding knowledge in the physical sciences
UTAS Author:	Dickey, JM (Professor John Dickey)
ID Code:	133222
Year Published:	2019
Web of Science® Times Cited:	5
Deposited By:	Mathematics and Physics
Deposited On:	2019-06-19
Last Modified:	2020-05-20
Downloads:	4 View Download Statistics