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arXiv · 1005.2191

HST/COS Observations of the Ly alpha Forest toward the BL Lac Object 1ES1553+113

Charles W. Danforth·Brian A. Keeney·John T. Stocke·J. Michael Shull·Yangsen Yao
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Abstract

We present new far-ultraviolet spectra from the Cosmic Origins Spectrograph (HST/COS) of the BL Lac object 1ES1553+113 covering the wavelength range 1135-1795 A. The data show a smooth continuum with a wealth of narrow absorption features arising in the ISM and IGM. These features include 41 Lya absorbers at 0 0.6 for the strongest component of the absorber complex. Galaxy redshift surveys show a number of massive galaxies at approximately the same redshift as this absorption complex, suggesting that it arises in a large-scale galaxy filament. As one of the brightest extragalactic X-ray and gamma-ray sources, 1ES1553+113 is of great interest to the high-energy astrophysics community. With no intrinsic emission or absorption features, 1ES1553+113 has no direct redshift determination. We use intervening Lya absorbers to place a direct limit on the redshift: z_em>0.395 based on a confirmed Lya+OVI absorber and z_em>0.433 based on a single-line detection of Lya. COS/FUV data are only sensitive to Lya absorbers at z<0.47, but we present statistical arguments that z_em<0.58 based on the non-detection of any Lyb absorbers at z>0.4.

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Charles W. Danforth, Brian A. Keeney, John T. Stocke, J. Michael Shull, Yangsen Yao. 2010-05-12. HST/COS Observations of the Ly alpha Forest toward the BL Lac Object 1ES1553+113. https://doi.org/10.1088/0004-637x%2F720%2F1%2F976

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