2019A&A...621A.127P


Query : 2019A&A...621A.127P

2019A&A...621A.127P - Astronomy and Astrophysics, volume 621A, 127-127 (2019/1-1)

Low-frequency measurements of synchrotron absorbing HII regions and modeling of observed synchrotron emissivity.

POLDERMAN I.M., HAVERKORN M., JAFFE T.R. and ALVES M.I.R.

Abstract (from CDS):


Context. Cosmic rays (CRs) and magnetic fields are dynamically important components in the Galaxy, and their energy densities are comparable to that of the turbulent interstellar gas. The interaction of CRs and Galactic magnetic fields (GMF) produces synchrotron radiation clearly visible in the radio regime. Detailed measurements of synchrotron radiation averaged over the line-of-sight (LOS), so-called synchrotron emissivities, can be used as a tracer of the CR density and GMF strength.
Aims. Our aim is to model the synchrotron emissivity in the Milky Way using a three-dimensional dataset instead of LOS-integrated intensity maps on the sky.
Methods. Using absorbed HII regions, we measured the synchrotron emissivity over a part of the LOS through the Galaxy, changing from a two-dimensional to a three-dimensional view. Performing these measurements on a large scale is one of the new applications of the window opened by current low-frequency arrays. Using various simple axisymmetric emissivity models and a number of GMF-based emissivity models, we were able to simulate the synchrotron emissivities and compare them to the observed values in the catalog.
Results. We present a catalog of low-frequency absorption measurements of HII regions, their distances and electron temperatures, compiled from literature. These data show that the axisymmetric emissivity models are not complex enough, but the GMF-based emissivity models deliver a reasonable fit. These models suggest that the fit can be improved by either an enhanced synchrotron emissivity in the outer reaches of the Milky Way or an emissivity drop near the Galactic center.
Conclusions. Current GMF models plus a constant CR density model cannot explain low-frequency absorption measurements, but the fits improved with slight (ad hoc) adaptations. It is clear that more detailed models are needed, but the current results are very promising.

Abstract Copyright: © ESO 2019

Journal keyword(s): cosmic rays - ISM: magnetic fields - HII regions - Galaxy: structure - radio continuum: ISM - catalogs

VizieR on-line data: <Available at CDS (J/A+A/621/A127): tablea1.dat>

Status at CDS : All or part of tables of objects could be ingested in SIMBAD with priority 2.

CDS comments: Paragraph. 3.1 G6.3+26.5 not identified.

Simbad objects: 12

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Number of rows : 12
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 NAME Per Arm PoG 03 30 +45.0           ~ 1380 0
2 IC 342 SBG 03 46 48.514 +68 05 45.98   10.5       ~ 1451 1
3 NAME Hya A LIN 09 18 05.6783347248 -12 05 43.634531472   14.38 14.8     ~ 957 1
4 NAME North Polar Spur ISM 12 00 +00.0           ~ 331 1
5 NAME Nor Arm PoG 16 00 -50.0           ~ 380 0
6 NAME Fermi Bubbles bub 17 45 -29.0           ~ 344 0
7 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 12913 0
8 NAME Sgr Arm PoG 19 00 -30.0           ~ 585 1
9 NAME Cyg A Sy2 19 59 28.35645829 +40 44 02.0966496   16.22 15.10     ~ 2237 2
10 NAME Sct-Cen PoG ~ ~           ~ 177 0
11 NAME Local Arm reg ~ ~           ~ 443 0
12 NAME Galactic Bar reg ~ ~           ~ 1041 0

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2022.05.26-01:47:34

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