BASS. XXI. The Data Release 2 Overview

The BAT AGN Spectroscopic Survey (BASS) is designed to provide a highly complete census of the key physical parameters of the supermassive black holes (SMBHs) that power local active galactic nuclei (AGNs) (z less than or similar to 0.3), including their bolometric luminosity (L (bol)), black hole (BH) mass (M (BH)), accretion rates (L (bol)/L (Edd)), line-of-sight gas obscuration (N (H)), and the distinctive properties of their host galaxies (e.g., star formation rates, masses, and gas fractions). We present an overview of the second data release of BASS (DR2), an unprecedented spectroscopic AGN survey in spectral range, resolution, and sensitivity, including 1449 optical (similar to 3200 angstrom-1 mu m) and 233 near-IR (1-2.5 mu m) spectra for the brightest 858 ultrahard X-ray (14-195 keV) selected AGNs across the entire sky and essentially all levels of obscuration. This release provides a highly complete set of key measurements (emission-line measurements and central velocity dispersions), with 99.9% measured redshifts and 98% BH masses estimated (for unbeamed AGNs outside the Galactic plane). The BASS DR2 AGN sample represents a unique census of nearby powerful AGNs, spanning over 5 orders of magnitude in AGN bolometric luminosity (L (bol) similar to 10(40)-10(47) erg s(-1)), BH mass (M (BH) similar to 10(5)-10(10) M (circle dot)), Eddington ratio (L (bol)/L (Edd) greater than or similar to 10(-5)), and obscuration (N (H) similar to 10(20)-10(25) cm(-2)). The public BASS DR2 sample and measurements can thus be used to answer fundamental questions about SMBH growth and its links to host galaxy evolution and feedback in the local universe, as well as open questions concerning SMBH physics. Here we provide a brief overview of the survey strategy, the key BASS DR2 measurements, data sets and catalogs, and scientific highlights from a series of DR2-based works pursued by the BASS team.