Understanding an Extreme QSO: The Curious Case of SDSS 0956+5128
Abstract
SDSS 0956+5128 is an object unlike any other quasar in the SDSS catalog, and challenges our understanding of quasar broad-line regions. There is a wealth of ground-based observations on different instruments and at different wavelengths showing its narrow lines, Balmer lines, and MgII to all lie at substantially different velocities. The most promising of several possible explanations might be an analog of a tidal disruption event during the merger of two supermassive black holes, a stage of the merger process that has never been seen before. HST is uniquely able to shed substantial light on this puzzle in two ways. (1) Imaging with ACS will resolve emission from the host galaxy, determining whether the quasar emission is offset from the galactic bulge, as appears likely from ground-based Subaru IRCS AO observations, and whether the galaxy has undergone a recent merger. (2) STIS spectroscopy will be used to measure the velocity offset and profile of the CIV line, which cannot be seen from the ground. Because CIV is a higher ionization line than HB and MgII and its broad-line region is at 1/10 the radius, it provides an ideal test of whether SDSS 0956+5128 is undergoing a supermassive black hole merger and a good indicator of the dynamics of the inner broad-line region.
- Publication:
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HST Proposal
- Pub Date:
- June 2019
- Bibcode:
- 2019hst..prop15872S