Recombination Lines and Molecular Gas from Hypercompact HII regions in W51 A
Por:
Rivera-Soto, Rudy, Galvan-Madrid, Roberto, Ginsburg, Adam, Kurtz, Stan
Publicada:
1 ago 2020
Resumen:
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) H77 alpha and H30
alpha, and the lines of H2CO(3(0.3) - 2(0.2)), H2CO(3(2,1) - 2(2,0)).,
and SO(6(5) - 5(4)). We derive diameters for 10/20 sources in the range
D similar to 10(-3)to similar to 10(-2)pc, thus placing them in the
regime of hypercompact Hiiregions (HC Hii's). Their continuum-derived
electron densities are in the range n(e) similar to 10(4)-10(5)cm(-3),
lower than typically considered for HC HII's. We combined the RL
measurements and independently derivedn(e), 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 n(e) versus D shows that they
follow the inverse relation previously derived for ultracompact (UC) and
compact HII's. When determined, the ionized-gas kinematics is always
(7/7) indicative of outflow. Similarly, 5 and 3 out of the 8 HC HII'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) HII regions:
those that essentially are smaller, expanding UC Hii's; and those that
are also hyper dense (n(e) > 10(6)cm(-3)), probably associated with
O-type stars in a specific stage of their formation or early life.
Filiaciones:
Rivera-Soto, Rudy:
UNAM, Inst Radioastron & Astrofis IRyA, Apdo Postal 72-3 Xangari, Morelia 58089, Michoacan, Mexico
Galvan-Madrid, Roberto:
UNAM, Inst Radioastron & Astrofis IRyA, Apdo Postal 72-3 Xangari, Morelia 58089, Michoacan, Mexico
Ginsburg, Adam:
Univ Florida, Dept Astron, POB 112055, Gainesville, FL 32611 USA
Natl Radio Astron Observ, 1003 Lopezville Rd, Socorro, NM 87801 USA
Kurtz, Stan:
UNAM, Inst Radioastron & Astrofis IRyA, Apdo Postal 72-3 Xangari, Morelia 58089, Michoacan, Mexico
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