2021/10/14 by Yu-Heng Lin, Claudia Scarlata, Matthew Hayes +9
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Star Formation Studies #Doubly ionized oxygen #Emission spectrum #Galaxies: Formation, Evolution, Phenomena #Galaxy #Ionization #Line (geometry) #Luminosity #Photoionization #Physics #QSOS #Redshift #Spectral line #astro-ph.GA
paper · pdf · doi:10.1093/mnras/stab2978
13 pages, 8 figures
openalex publication_date 2021/10/14 · arxiv created 2021/11/05 · arxiv updated 2021/11/09 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
ABSTRACT We present S82-20, an unusual redshift ≈3 object identified in SDSS-Stripe 82 broad-band images. The rest-frame ultraviolet spectrum of S82-20 shows emission lines from highly ionized species, including He ii λ1640, and the C iv λλ1548, 1550 and O vi λλ1032, 1038 doublets. The high Ly α luminosity (3.5 × 1044 erg s−1), the high emission line equivalent widths (>200 Å for Ly α), the full width at half-maximum of the emission lines (<800 km s−1), and the high ionization O vi line strongly support the interpretation that S82-20 is a Type II Quasi-Stellar Objects (QSOs). However, photoionization models using Type II QSO do not fully explain the measured C iv/He ii line ratio, which requires either some contribution from star formation or high velocity shocks. Additionally, S82-20 is not detected at wavelengths longer than 2 μm, in tension with the expectation of isotropically infrared emission of a luminous QSO. We consider the possibility that S82-20 is a rare example of a changing-look QSO, observed in a temporarily low state, where the broad line region has faded, while the narrow line region still emits emission line. Otherwise, it may be a rare case of the short phase of the life of a massive galaxy, in which active star formation and accretion on to a supermassive black hole coexist.