J/MNRAS/498/4906 Pressure components in the central HII regions (Barnes+, 2020)
Which feedback mechanisms dominate in the high-pressure environment of the
central molecular zone?
Barnes A.T., Longmore S.N., Dale J.E., Krumholz M.R., Kruijssen J.M.D.,
Bigiel F.
<Mon. Not. R. Astron. Soc., 498, 4906-4923 (2020)>
=2020MNRAS.498.4906B 2020MNRAS.498.4906B (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Interstellar medium ; H II regions ;
Star Forming Region ; Galactic center ; Milky Way ;
Radio sources ; Infrared
Keywords: stars: formation - ISM: clouds - Galaxy: centre
Abstract:
Supernovae (SNe) dominate the energy and momentum budget of stellar
feedback, but the efficiency with which they couple to the
interstellar medium (ISM) depends strongly on how effectively early,
pre-SN feedback clears dense gas from star-forming regions. There are
observational constraints on the magnitudes and time-scales of early
stellar feedback in low ISM pressure environments, yet no such
constraints exist for more cosmologically typical high ISM pressure
environments. In this paper, we determine the mechanisms dominating
the expansion of HII regions as a function of size-scale and
evolutionary time within the high-pressure (P/kB∼107-8K.cm-3)
environment in the inner 100pc of the Milky Way. We calculate the
thermal pressure from the warm ionized (PHII; 104K) gas, direct
radiation pressure (Pdir), and dust processed radiation pressure
(PIR). We find that (1) Pdir dominates the expansion on small
scales and at early times (0.01-0.1pc; <0.1Myr); (2) the expansion is
driven by PHII on large scales at later evolutionary stages (>0.1pc;
>1Myr); (3) during the first ~<1Myr of growth, but not thereafter,
either PIR or stellar wind pressure likely make a comparable
contribution. Despite the high confining pressure of the environment,
natal star-forming gas is efficiently cleared to radii of several pc
within ∼2Myr, i.e. before the first SNe explode. This 'pre-processing'
means that subsequent SNe will explode into low density gas, so their
energy and momentum will efficiently couple to the ISM. We find the
HII regions expand to a radius of ∼3pc, at which point they have
internal pressures equal with the surrounding external pressure. A
comparison with HII regions in lower pressure environments shows that
the maximum size of all HII regions is set by pressure equilibrium
with the ambient ISM.
Description:
We investigate the dominant pressures within H II regions using the
methods outlined by Lopez et al. (2011ApJ...731...91L 2011ApJ...731...91L,
2014ApJ...795..121L 2014ApJ...795..121L), and McLeod et al. (2019MNRAS.486.5263M 2019MNRAS.486.5263M). These
authors calculate the four sources of pressure responsible for the
expansion of H II regions as: thermal pressure from the warm (104K)
ionized gas (PHII), direct radiation pressure from the luminous
stellar population (Pdir), pressure from the photons released by
heated dust (PIR), and thermal pressure from the shock heated (106K)
X-ray emitting gas (PX). Here we calculate three of these, PHII,
Pdir, and PIR within four large, Galactic Centre HII region
complexes (Sgr B2, G0.6, Sgr B1 and G0.3); PX is unfortunately
inaccessible due to the very large extinction and strong foreground
towards the Galactic Centre at soft X-ray wavelengths.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 172 165 Discrete pressure component measurements
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Region Galactic Centre HII regions
(SgrB2, G0.6, SgrB1, or G0.3)
7- 8 I2 --- ID Source internal identifier
10- 31 F22.19 pc Reff Effective radius
33- 56 F24.10 K/cm3 Pdir/kB ? Direct radiation pressure Pdir/kB
58- 80 F23.11 K/cm3 PHII/kB ? Warm ionised gas pressure PHII/kB
82- 99 F18.10 10+7K/J PIR/kB ? Dust reprocessed emission pressure using
the extinction determined along each line
of sight PIR/kB
101- 119 F19.11 10+7K/J PIR20/kB ? Dust reprocessed emission pressure using
a constant visual extinction of AV=20mag
PIR,Av=20/kB
121- 172 A52 --- Ref Reference
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 09-Aug-2023