Detection of an orthogonal alignment between parsec-scale AGN jets and their host galaxies

Abstract

The relationship between galaxies and their supermassive black holes (SMBHs) is an area of active research. One way to investigate this relationship is to compare parsec-scale jets formed by SMBHs to the projected shape of their kiloparsec-scale host galaxies. Here we analyse very-long-baseline interferometry (VLBI) images of active galactic nuclei (AGNs) and optical images of their host galaxies by comparing the inner-jet position angle in VLBI-detected radio sources with the optical shapes of galaxies as measured by several large optical surveys. In total, 6,273 galaxy–AGN pairs were found. We carefully account for the systematics of the cross-matched sources and find that Dark Energy Spectroscopic Instrument Legacy Imaging Surveys (DESI LS) data are significantly less affected by them. Using DESI LS data, with which 5,853 galaxy–AGN pairs were cross-matched, we find a weak but significant alignment signal (with P ≲ 0.01) between the parsec-scale AGN jet and the kiloparsec-scale projected minor axis of the optical host galaxy in sources with measured spectroscopic redshifts. Our results show that the observed source properties are connected over three orders of magnitude in scale. This finding points towards an intimate connection between a SMBH, its host galaxy and its subsequent evolution.