γ-ray Emission in Radio Galaxies Under the VLBI Scope

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aut.relation.articlenumberA152
aut.relation.endpageA152
aut.relation.journalAstronomy & Astrophysics
aut.relation.startpageA152
aut.relation.volume641
dc.contributor.authorAngioni, R
dc.contributor.authorRos, E
dc.contributor.authorKadler, M
dc.contributor.authorOjha, R
dc.contributor.authorMüller, C
dc.contributor.authorEdwards, PG
dc.contributor.authorBurd, PR
dc.contributor.authorCarpenter, B
dc.contributor.authorDutka, MS
dc.contributor.authorGulyaev, S
dc.contributor.authorHase, H
dc.contributor.authorHoriuchi, S
dc.contributor.authorKrauß, F
dc.contributor.authorLovell, JEJ
dc.contributor.authorNatusch, T
dc.contributor.authorPhillips, C
dc.contributor.authorPlötz, C
dc.contributor.authorQuick, JFH
dc.contributor.authorRösch, F
dc.contributor.authorSchulz, R
dc.contributor.authorStevens, J
dc.contributor.authorTzioumis, AK
dc.contributor.authorWeston, S
dc.contributor.authorWilms, J
dc.contributor.authorZensus, JA
dc.date.accessioned2023-10-24T21:27:30Z
dc.date.available2023-10-24T21:27:30Z
dc.date.issued2020-09-23
dc.description.abstractAims. This is the second paper in our series studying the evolution of parsec-scale radio emission in radio galaxies in the Southern Hemisphere. Following our study of the radio and high-energy properties of <jats:italic>γ</jats:italic>-ray-emitting sources, here we investigate the kinematic and spectral properties of the parsec-scale jets of radio galaxies that have not yet been detected by the <jats:italic>Fermi</jats:italic> Large Area Telescope (<jats:italic>Fermi</jats:italic>-LAT) instrument on board NASA’s <jats:italic>Fermi</jats:italic> Gamma-ray Space Telescope. For many sources, these results represent the first milliarcsecond resolution information in the literature. These studies were conducted within the framework of the Tracking Active Nuclei with Austral Milliarcsecond Interferometry (TANAMI) monitoring program and in the context of high-energy <jats:italic>γ</jats:italic>-ray observations from <jats:italic>Fermi</jats:italic>-LAT.</jats:p> Methods. We took advantage of the regular 8.4 GHz and 22.3 GHz Very Long Baseline Interferometry (VLBI) observations provided by the TANAMI monitoring program, and explored the kinematic properties of six <jats:italic>γ</jats:italic>-ray-faint radio galaxies. We complemented this with ∼8.5 years of <jats:italic>Fermi</jats:italic>-LAT data, deriving updated upper limits on the <jats:italic>γ</jats:italic>-ray emission from this subsample of TANAMI radio galaxies. We included publicly available VLBI kinematics of <jats:italic>γ</jats:italic>-ray-quiet radio galaxies monitored by the MOJAVE program and performed a consistent <jats:italic>Fermi</jats:italic>-LAT analysis. We combined these results with those from our previous paper to construct the largest sample of radio galaxies with combined VLBI and <jats:italic>γ</jats:italic>-ray measurements to date. The connection between parsec-scale jet emission and high-energy properties in the misaligned jets of radio galaxies was explored.</jats:p> Results. For the first time, we report evidence of superluminal motion up to <jats:italic>β</jats:italic><jats:sub>app</jats:sub> = 3.6 in the jet of the <jats:italic>γ</jats:italic>-ray-faint radio galaxy PKS 2153−69. We find a clear trend of higher apparent speed as a function of distance from the jet core, which indicates that the jet is still being accelerated on scales of tens of parsecs, or ∼10<jats:sup>5</jats:sup> <jats:italic>R</jats:italic><jats:sub>s</jats:sub>, corresponding to the end of the collimation and acceleration zone in nearby radio galaxies. We find evidence of subluminal apparent motion in the jets of PKS 1258−321 and IC 4296, and no measurable apparent motion for PKS 1549−79, PKS 1733−565, and PKS 2027−308. For all these sources, TANAMI provides the first multi-epoch kinematic analysis on parsec scales. We then compare the VLBI properties of <jats:italic>γ</jats:italic>-ray-detected and undetected radio galaxies, and find that the two populations show a significantly different distribution of median core flux density, and, possibly, of median core brightness temperature. In terms of correlation between VLBI and <jats:italic>γ</jats:italic>-ray properties, we find a significant correlation between median core flux density and <jats:italic>γ</jats:italic>-ray flux, but no correlation with typical Doppler boosting indicators such as median core brightness temperature and core dominance.</jats:p> Conclusions. Our study suggests that high-energy emission from radio galaxies is related to parsec-scale radio emission from the inner jet, but is not driven by Doppler boosting effects, in contrast to the situation in their blazar counterparts. This implies that <jats:italic>γ</jats:italic>-ray loudness does not necessarily reflect a higher prevalence of boosting effects.
dc.identifier.citationAstronomy & Astrophysics, ISSN: 0004-6361 (Print); 1432-0746 (Online), EDP Sciences, 641, A152-A152. doi: 10.1051/0004-6361/202038236
dc.identifier.doi10.1051/0004-6361/202038236
dc.identifier.issn0004-6361
dc.identifier.issn1432-0746
dc.identifier.urihttp://hdl.handle.net/10292/16817
dc.publisherEDP Sciences
dc.relation.urihttps://www.aanda.org/articles/aa/full_html/2020/09/aa38236-20/aa38236-20.html
dc.rights© ESO 2020. Free access.
dc.rights.accessrightsOpenAccess
dc.subject0201 Astronomical and Space Sciences
dc.subjectAstronomy & Astrophysics
dc.subject5101 Astronomical sciences
dc.subject5107 Particle and high energy physics
dc.subject5109 Space sciences
dc.titleγ-ray Emission in Radio Galaxies Under the VLBI Scope
dc.typeJournal Article
pubs.elements-id392416
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