A Kpc-scale radio polarization study of PG BL Lacs with the uGMRT




Baghel Janhavi, Kharb P., Hovatta T., Gulati S., Lindfors E., Silpa S.

PublisherOXFORD UNIV PRESS

OXFORD

2024

Monthly Notices of the Royal Astronomical Society

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

MON NOT R ASTRON SOC

527

1

672

688

17

0035-8711

1365-2966

DOIhttps://doi.org/10.1093/mnras/stad3173

https://doi.org/10.1093/mnras/stad3173

https://research.utu.fi/converis/portal/detail/Publication/387432276



We present here uGMRT band 4 (~650 MHz) polarization images of 8 BL Lac objects belonging to the Palomar -Green (PG) 'blazar' sample. A large fraction of the sources (~63 per cent ) reveal core-halo radio structures with most of the polarization detected in the inner core-jet regions. PG1101 + 385 and PG2254 + 075 exhibit a 'spine -sheath structure' in polarization. The core-halo and 'spine -sheath' structures are consistent with the Unified Scheme suggestion that BL Lacs are the pole-on beamed counterparts of Fanaroff-Riley (FR) type I radio galaxies. PG1418 + 546 and PG0851 + 203 (OJ287) show the presence of terminal hotspots similar to FR type II radio galaxies. They were also found to be low-spectrally peaked BL Lacs, supportive of the 'blazar envelope' scenario for BL Lacs and quasars. Fractional polarization ranges from 1 to 13 per cent in the cores and 2 to 26 per cent in the inner jets/lobes of the sample BL Lacs. Compared to the varied radio morphology of quasars from the PG 'blazar' sample, the BL Lacs appear to be less diverse. A comparison of the inferred core magnetic (B-) field structures on arcsec(kpc-) scales w.r.t. the Very Long Baseline Interferometry jet direction does not reveal any preferred orientation, suggesting that if large-scale ordered B-fields exist, they do so on scales smaller than probed by the current observations. However, the presence of polarized emission on arcsec-scales suggests that any mixing of thermal plasma with the synchrotron emitting plasma is insufficient to fully depolarize the emission via the internal depolarization process.


Last updated on 2024-26-11 at 23:12