Lineless Quasars at High-Redshift: BL Lacs or A New Class of Unbeamed Quasars?

Details Lineless Quasars at High-Redshift: BL Lacs or A New Class of Unbeamed Quasars? Lineless Quasars at High-Redshift: BL Lacs or A New Class of Unbeamed Quasars?

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006sptz.prop30476s&link_type=abstract

Spitzer Proposal ID #30476

Physics

Scientific paper

The Sloan Digital Sky Survey (SDSS) has recently discovered a class of high-redshift quasars with no or extremely weak optical emission lines. Their redshifts are determined by the presence of strong Lyman break and Lyman Limit Systems. Their nature remains unknown: they could be analogs of BL Lac objects at high redshift, a new type of unbeamed quasar whose broad emission-line region is very weak or absent, or a combination of both. Four members of this class were observed in the X-ray, radio, and recently in the IR by Spitzer, and the results are perplexing: two X-ray- and radio-weak sources exhibit BL Lac-like power-law SEDs, consistent with synchrotron emission, while two sources that are mildly X-ray and radio bright exhibit a hint of an IR `bump' consistent with thermal dust emission in typical quasars. We propose to continue our successful Spitzer A0-1 program and obtain IRAC and MIPS 24 micron photometry of 14 additional lineless quasars at z~3-5. The Spitzer photometry will probe the spectral region where there is a dramatic contrast between beamed synchrotron emission in BL Lac objects and thermal dust emission in unbeamed quasars: we expect a factor of ~3-10 difference in Spitzer fluxes between the two cases. It will reveal the nature of the IR emission mechanism, and unambiguously determine whether these lineless quasars are beamed sources similar to BL Lac objects, or a new type of unbeamed quasar.

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