J/A+A/628/A56 Extragalactic MHz Peaked Sources at mas scales (Keim+, 2019)
Extragalactic megahertz-peaked spectrum radio sources at milliarcsecond scales.
Keim M.A., Callingham J.R., Roettgering H.J.A.
<Astron. Astrophys. 628, A56 (2019)>
=2019A&A...628A..56K 2019A&A...628A..56K (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Galaxies, radio ; Radio continuum
Keywords: galaxies: active - galaxies: evolution - radio continuum: galaxies
Abstract:
Extragalactic peaked-spectrum radio sources are thought to be the
progenitors of larger, radio-loud active galactic nuclei (AGN).
Synchrotron self-absorption (SSA) has often been identified as the
cause of their spectral peak. The identification of new
megahertz-peaked spectrum sources from the GaLactic and Extragalactic
All-sky Murchison Widefield Array (GLEAM) survey provides an
opportunity to test how radio sources with spectral peaks below 1GHz
fit within this evolutionary picture. We observed six peaked-spectrum
sources selected from the GLEAM survey, three that have spectral
characteristics which violate SSA and three that have spectral peaks
below 230MHz, with the Very Long Baseline Array at 1.55 and 4.96 GHz.
We present milliarcsecond resolution images of each source and
constrain their morphology, linear size, luminosity, and magnetic
field strength. Of the sources that are resolved by our study, the
sources that violate SSA appear to be compact doubles, while the
sources with peak frequencies below 230MHz have core-jet features. We
find that all of our sources are smaller than expected from SSA by
factors of ≳20. We also find that component magnetic field strengths
calculated from SSA are likely inaccurate, differing by factors of ≳5
from equipartition estimates. The calculated equipartition magnetic
field strengths more closely resemble estimates from previously
studied gigahertz-peaked spectrum sources. Exploring a model of the
interaction between jets and the interstellar medium, we demonstrate
that free-free absorption (FFA) can accurately describe the linear
sizes and peak frequencies of our sources. Our findings support the
theory that there is a fraction of peaked-spectrum sources whose
spectral peaks are best modelled by FFA, implying our understanding of
the early stages of radio AGN is incomplete.
Description:
Reduced VLBA images of J0231-0433, J0235-0100, J0330-0740, J1509+1406,
J1525+0308, and J1548+1320 at 1.55 and 4.96 GHz (L and C-Band).
Objects:
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RA (2000) DE Designation(s)
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02 31 59.286 -04 33 57.12 J0231-0433 = GLEAM J023159-043352
02 35 16.809 -01 00 51.66 J0235-0100 = GLEAM J023516-010051
03 30 23.115 -07 40 52.56 J0330-0740 = GLEAM J033023-074052
15 09 15.626 +14 06 14.55 J1509+1406 = GLEAM J150915+140615 = 4C +14.58
15 25 48.957 +03 08 25.95 J1525+0308 = GLEAM J152548+030825 = 4C +03.33
15 48 52.740 +13 20 56.07 J1548+1320 = GLEAM J154852+132058
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 112 12 List of fits images
fits/* . 12 Individual fits images
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 39 A10 "date" Obs.date Observation date
41- 47 F7.5 GHz Freq Observed frequency
49- 53 I5 Kibyte size Size of FITS file
55- 70 A16 --- FileName Name of FITS file, in subdirectory fits
72-112 A41 --- Title Title of the FITS file
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Acknowledgements:
Michael Alan Keim, keim(a)strw.leidenuniv.nl
(End) Michael Keim [Leiden, The Netherlands] Patricia Vannier [CDS] 31-Jul-2019