2013/02/12 by Amy Furniss, A. Furniss, Michele Fumagalli +7 · 3 citations
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #BL Lac object #Blazar #Dark Matter and Cosmic Phenomena #Extragalactic background light #Intergalactic travel #Lyman limit #Neutrino Physics Research #Quasar #Redshift #Spectral line #astro-ph.CO
paper · pdf · doi:10.1088/0004-637x/766/1/35
arxiv created 2013/02/12 · openalex publication_date 2013/03/05 · arxiv updated 2015/06/15 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
As a bright gamma-ray source, 3C 66A is of great interest to the high-energy astrophysics community, having a potential for placing cosmological constraints on models for the extragalactic background light (EBL) and the processes which contribute to this photon field. No firm spectroscopic redshift measurement has been possible for this blazar due to a lack of intrinsic emission and absorption features in optical spectra. We present new far-ultraviolet spectra from the Hubble Space Telescope /Cosmic Origins Spectrograph ( HST /COS) of the BL Lac object 3C 66A covering the wavelength range 1132–1800 Å. The data show a smooth continuum with intergalactic medium absorption features which can be used to place a firm lower limit on the blazar redshift of z ⩾ 0.3347. An upper limit is set by statistically treating the non-detection of additional absorbers beyond z = 0.3347, indicating a redshift of less than 0.41 at 99% confidence and ruling out z ⩾ 0.444 at 99.9% confidence. We conclude by showing how the redshift limits derived from the COS spectra remove the potential for this gamma-ray emitting blazar to place an upper limit on the flux of the EBL using high energy data from a flare in 2009 October.