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A Lyman-alpha-only AGN from the Sloan Digital Sky Survey

Patrick B. Hall·Erik A. Hoversten·Christy A. Tremonti·Daniel E. Vanden Berk·Donald P. Schneider·Michael A. Strauss·Gillian R. Knapp·Donald G. York·Damien Hutsemekers·P. R. Newman
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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 Lyman-alpha line (FWHM = 1430 km/s) 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. Despite certain spectral similarities, SDSS J1136+0242 is not a Lyman-break galaxy. Instead, the Ly-alpha 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 which 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.

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Patrick B. Hall, Erik A. Hoversten, Christy A. Tremonti, Daniel E. Vanden Berk, Donald P. Schneider, Michael A. Strauss, Gillian R. Knapp, Donald G. York, Damien Hutsemekers, P. R. Newman. 2004-02-26. A Lyman-alpha-only AGN from the Sloan Digital Sky Survey. https://doi.org/10.1086/420804

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