2015/07/31 by A. B. Pushkarev, Y. Y. Kovalev
Physics and Astronomy · #Active galactic nucleus #Angular diameter #Astronomy #Astrophysics #Astrophysics and Cosmic Phenomena #Galactic Center #Galactic plane #Galaxies: Formation, Evolution, Phenomena #Galaxy #Interstellar medium #Opacity #Optics #Physics #Quasar #Radio Astronomy Observations and Technology #Redshift #Scattering #Sky #Stars #Supermassive black hole #Very Long Baseline Array #Very-long-baseline interferometry #astro-ph.HE
paper · pdf · doi:10.1093/mnras/stv1539
published as MNRAS 452 (2015) 4274 · 9 pages, 7 figures, 5 tables, published by MNRAS; full electronic table 2 (redshifts updated) is available from ftp://cdsarc.u-strasbg.fr/pub/cats/J/MNRAS/452/4274/
openalex publication_date 2015/08/12 · arxiv created 2017/05/30 · arxiv updated 2017/05/31 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We have measured the angular sizes of radio cores of active galactic nuclei (AGNs) and analysed their sky distributions and frequency dependences to study synchrotron opacity in AGN jets and the strength of angular broadening in the interstellar medium. We have used archival very long baseline interferometry (VLBI) data of more than 3000 compact extragalactic radio sources observed at frequencies, ν, from 2 to 43 GHz to measure the observed angular size of VLBI cores. We have found a significant increase in the angular sizes of the extragalactic sources seen through the Galactic plane (|b| ≲ 10°) at 2, 5 and 8 GHz, about one-third of which show significant scattering. These sources are mainly detected in directions to the Galactic bar, the Cygnus region and a region with galactic longitudes 220° ≲ l ≲ 260° (the Fitzgerald window). The strength of interstellar scattering of the AGNs is found to correlate with the Galactic Hα intensity, free-electron density and Galactic rotation measure. The dependence of scattering strengths on source redshift is insignificant, suggesting that the dominant scattering screens are located in our Galaxy. The observed angular size of Sgr A* is found to be the largest among thousands of AGNs observed over the sky; we discuss possible reasons for this strange result. Excluding extragalactic radio sources with significant scattering, we find that the angular size of opaque cores in AGNs scales typically as ν−1, confirming predictions of a conical synchrotron jet model with equipartition.