A Caltech Library Service

SDSS 0956+5128: A Broad-line Quasar with Extreme Velocity Offsets

Steinhardt, Charles L. and Schramm, Malte and Silverman, John D. and Alexandroff, Rachael and Capak, Peter and Civano, Francesca and Elvis, Martin and Masters, Dan and Mobasher, Bahram and Pattarakijwanich, Petchara and Strauss, Michael A. (2012) SDSS 0956+5128: A Broad-line Quasar with Extreme Velocity Offsets. Astrophysical Journal, 759 (1). Art. No. 24. ISSN 0004-637X. doi:10.1088/0004-637X/759/1/24.

PDF - Published Version
See Usage Policy.


Use this Persistent URL to link to this item:


We report on the discovery of a Type 1 quasar, SDSS 0956+5128, with a surprising combination of extreme velocity offsets. SDSS 0956+5128 is a broad-lined quasar exhibiting emission lines at three substantially different redshifts: a systemic redshift of z ~ 0.714 based on narrow emission lines, a broad Mg II emission line centered 1200 km s^(–1) bluer than the systemic velocity, at z ~ 0.707, and broad Hα and Hβ emission lines centered at z ~ 0.690. The Balmer line peaks are 4100 km s^(–1) bluer than the systemic redshift. There are no previously known objects with such an extreme difference between broad Mg II and broad Balmer emission. The two most promising explanations are either an extreme disk emitter or a high-velocity black hole recoil. However, neither explanation appears able to explain all of the observed features of SDSS 0956+5128, so the object may provide a challenge to our general understanding of quasar physics.

Item Type:Article
Related URLs:
URLURL TypeDescription
Steinhardt, Charles L.0000-0003-3780-6801
Silverman, John D.0000-0002-0000-6977
Capak, Peter0000-0003-3578-6843
Civano, Francesca0000-0002-2115-1137
Masters, Dan0000-0001-5382-6138
Strauss, Michael A.0000-0002-0106-7755
Additional Information:© 2012 American Astronomical Society. Received 2012 June 20; accepted 2012 September 4; published 2012 October 12. The authors thank Kevin Bundy, Masahiro Fukugita, Pat Hall, Daniel Proga, Robert Quimby, Allan Sadun, Masayuki Tanaka, and Alexander Tchekhovskoy for valuable comments. This work was supported by the World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan. M.A.S., P.P., and R.A. acknowledge the support of NSF grant AST-0707266. C.L.S. and M.E. thank the Aspen Center for Physics and the NSF Grant No. 1066293 for hospitality during the editing of this paper.
Group:COSMOS, Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Ministry of Education, Culture, Sports, Science and Technology (MEXT)UNSPECIFIED
Aspen Center for PhysicsUNSPECIFIED
Subject Keywords:accretion, accretion disks; black hole physics; galaxies: evolution; galaxies: nuclei; quasars: general
Issue or Number:1
Record Number:CaltechAUTHORS:20121217-092148266
Persistent URL:
Official Citation:SDSS 0956+5128: A Broad-line Quasar with Extreme Velocity Offsets Charles L. Steinhardt, Malte Schramm, John D. Silverman, Rachael Alexandroff, Peter Capak, Francesca Civano, Martin Elvis, Dan Masters, Bahram Mobasher, Petchara Pattarakijwanich, and Michael A. Strauss doi:10.1088/0004-637X/759/1/24
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:36004
Deposited On:17 Dec 2012 19:14
Last Modified:09 Nov 2021 23:19

Repository Staff Only: item control page