Characterising the Extended Morphologies of BL Lacertae Objects at 144 MHz with LOFAR
Artikel i vetenskaplig tidskrift, 2021
We present a morphological and spectral study of a sample of 99 BL Lac objects using the LOFAR Two-Metre Sky Survey Second Data Release (LDR2). Extended emission has been identified at gigahertz frequencies around BL Lac objects, but with LDR2 it is now possible to systematically study their morphologies at 144 MHz, where more diffuse emission is expected. LDR2 reveals the presence of extended radio structures around 66/99 of the BL Lac nuclei, with angular extents ranging up to 115 '', corresponding to spatial extents of 410 kpc. The extended emission is likely to be both unbeamed diffuse emission and beamed emission associated with relativistic bulk motion in jets. The spatial extents and luminosities of the extended emission are consistent with the unification scheme for active galactic nuclei, where BL Lac objects correspond to low-excitation radio galaxies with the jet axis aligned along the line of sight. While extended emission is detected around the majority of BL Lac objects, the median 144-1400 MHz spectral index and core dominance at 144 MHz indicate that the core component contributes similar to 42% on average to the total low-frequency flux density. A stronger correlation was found between the 144 MHz core flux density and the gamma-ray photon flux (r = 0.69) than between the 144 MHz extended flux density and the gamma-ray photon flux (r = 0.42). This suggests that the radio-to-gamma-ray connection weakens at low radio frequencies because the population of particles that give rise to the gamma-ray flux are distinct from the electrons producing the diffuse synchrotron emission associated with spatially extended features.
Författare
Sean Mooney
University College Dublin
Francesco Massaro
Universita degli Studi di Torino
John Quinn
University College Dublin
Alessandro Capetti
Istituto nazionale di astrofisica (INAF)
Ranieri D. Baldi
University of Southampton
Istituto nazionale di astrofisica (INAF)
Guelay Guerkan
Thüringer Landessternwarte Tautenburg
Martin J. Hardcastle
University of Hertfordshire
Cathy Horellou
Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik
Beatriz Mingo
Open University
Raffaella Morganti
Rijksuniversiteit Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
Shane O'Sullivan
Dublin City University
Urszula Pajdosz-Smierciak
Uniwersytet Jagiellonski w Krakowie
Mamta Pandey-Pommier
Université de Lyon
Observatoire de Paris
Huub Roettgering
Universiteit Leiden
Astrophysical Journal, Supplement Series
0067-0049 (ISSN) 1538-4365 (eISSN)
Vol. 257 2 30Ämneskategorier
Subatomär fysik
Astronomi, astrofysik och kosmologi
Atom- och molekylfysik och optik
DOI
10.3847/1538-4365/ac1c0b