A Lyα-only Active Galactic Nucleus from the Sloan Digital Sky Survey
Abstract
The Sloan Digital Sky Survey has discovered a z=2.4917 radio-loud active galactic nucleus (AGN) with a luminous, variable, low-polarization UV continuum, H I two-photon emission, and a moderately broad Lyα line (FWHM~=1430 km s-1) but without obvious metal-line emission. SDSS J113658.36+024220.1 does have associated metal-line absorption in three distinct, narrow systems spanning a velocity range of 2710 km s-1. Despite certain spectral similarities, SDSS J1136+0242 is not a Lyman break galaxy. Instead, the Lyα and two-photon emission can be attributed to an extended, low-metallicity narrow-line region. The unpolarized continuum argues that we see SDSS J1136+0242 very close to the axis of any ionization cone present. We can conceive of two plausible explanations for why we see a strong UV continuum but no broad-line emission in this ``face-on radio galaxy'' model for SDSS J1136+0242: the continuum could be relativistically beamed synchrotron emission that swamps the broad-line emission, or more likely, SDSS J1136+0242 could be similar to PG 1407+265, a quasar in which for some unknown reason the high-ionization emission lines are very broad, very weak, and highly blueshifted.
- Publication:
-
The Astronomical Journal
- Pub Date:
- June 2004
- DOI:
- 10.1086/420804
- arXiv:
- arXiv:astro-ph/0402648
- Bibcode:
- 2004AJ....127.3146H
- Keywords:
-
- Galaxies: Quasars: Emission Lines- Galaxies: Quasars: General;
- Galaxies: Quasars: Individual: Alphanumeric: PG 1407+265;
- Galaxies: Quasars: Individual: Alphanumeric: SDSS J113658.36+024220.1;
- Astrophysics
- E-Print:
- AJ, in press, 10 pages emulateapj format