2020ApJ...899...94R

Query : 2020ApJ...899...94R

2020ApJ...899...94R - Astrophys. J., 899, 94-94 (2020/August-3)

Recombination lines and molecular gas from hypercompact HII regions in W51 A.

RIVERA-SOTO R., GALVAN-MADRID R., GINSBURG A. and KURTZ S.

Abstract (from CDS):

We present a detailed characterization of the population of compact radio-continuum sources in W51 A using subarcsecond Very Large Array and Atacama Large Millimeter/submillimeter Array observations. We analyze their 2 cm continuum, the recombination lines (RLs) H77α and H30α, and the lines of H2CO(30,3-20,2), H2CO(32,1-22,0) , and SO(65-54). We derive diameters for 10/20 sources in the range D ∼ 10–3 to ∼10–2 pc, thus placing them in the regime of hypercompact H II regions (HC H II's). Their continuum-derived electron densities are in the range ne ∼ 104 -105 cm–3, lower than typically considered for HC H II's. We combined the RL measurements and independently derived ne, finding the same range of values but significant offsets for individual measurements between the two methods. We find that most of the sources in our sample are ionized by early B-type stars, and a comparison of ne versus D shows that they follow the inverse relation previously derived for ultracompact (UC) and compact H II's. When determined, the ionized-gas kinematics is always (7/7) indicative of outflow. Similarly, 5 and 3 out of the 8 HC H II's still embedded in a compact core show evidence for expansion and infall motions in the molecular gas, respectively. We hypothesize that there could be two different types of hypercompact (D < 0.05 pc) H II regions: those that essentially are smaller, expanding UC H II's; and those that are also hyperdense (ne > 106 cm–3), probably associated with O-type stars in a specific stage of their formation or early life.

Abstract Copyright: © 2020. The American Astronomical Society. All rights reserved.

Journal keyword(s): H II regions - Star formation - Radio astronomy - Giant molecular clouds

Simbad objects: 25

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Number of rows : 25
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2026 		#notes
1 W 51a HII 19 23 29.3 +14 31 38           ~ 186 0
2 [GGK2017] d2 HII 19 23 39.821 +14 31 05.03           ~ 1 0
3 [WBN74] W 51 IRS 2 SFR 19 23 39.93 +14 31 09.4           ~ 321 0
4 NAME W 51 North Rad 19 23 40.0 +14 30 51           ~ 169 0
5 W 51d7 HII 19 23 40.919 +14 31 06.58           ~ 1 0
6 W 51d6 Y*O 19 23 41.238 +14 31 11.58           ~ 2 0
7 W 51e6 HII 19 23 41.785 +14 31 02.56           ~ 5 0
8 W 51e5 HII 19 23 41.863 +14 30 56.73           ~ 4 0
9 NAME W 51 IRS 1 HII 19 23 41.9 +14 30 36           ~ 124 0
10 W 51e14 HII 19 23 42.605 +14 30 42.11           ~ 1 0
11 W 51e22 HII 19 23 42.781 +14 30 27.67           ~ 1 0
12 W 51e13 HII 19 23 42.819 +14 30 37.11           ~ 1 0
13 W 51e21 HII 19 23 42.848 +14 30 27.69           ~ 1 0
14 W 51e20 HII 19 23 42.857 +14 30 27.72           ~ 1 0
15 W 51e12 HII 19 23 42.861 +14 30 30.41           ~ 1 0
16 W 51e23 HII 19 23 43.058 +14 30 34.92           ~ 1 0
17 W 51e9 HII 19 23 43.654 +14 30 26.81           ~ 2 0
18 W 51e1 HII 19 23 43.785 +14 30 26.11           ~ 141 0
19 W 51e3 HII 19 23 43.842 +14 30 24.72           B0.5 14 0
20 [GGG2016] W51e8n HII 19 23 43.906 +14 30 28.17           ~ 1 0
21 W 51e2 Ma* 19 23 43.906 +14 30 34.48           ~ 222 0
22 [GGG2016] W51e8s HII 19 23 43.907 +14 30 27.91           ~ 1 0
23 W 51e4 HII 19 23 43.913 +14 30 29.49           B0.5 17 0
24 W 51e10 HII 19 23 43.958 +14 30 26.98           ~ 1 0
25 [SZH2010] W51e2-E Rad 19 23 43.960 +14 30 34.56           ~ 18 0

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