Uncovering the Weakest Absorbers in AGN Spectra

Type Conference Paper
Names Charles Danforth, J. T. Stocke, J. M. Shull, M. Pieri, B. Savage, K. France, S. Penton, B. Keeney
Proceedings Title Bulletin of the American Astronomical Society
Conference Name American Astronomical Society, AAS Meeting #217, #345.11
Volume 43
Pages 34511
Date January 1, 2011
URL http://adsabs.harvard.edu/abs/2011AAS...21734511D
Library Catalog NASA ADS
Abstract The exquisite far-UV sensitivity of the Cosmic Origins Spectrograph has yielded moderate-resolution AGN spectra of unprecedented quality with signal to noise ratios (S/N) of 50 per resolution element in some cases. This high data quality allows us to detect some of the weakest (W 10 mÅ) absorption features ever found in far-UV spectra including weak photoionized Lyα forest absorbers at column densities N > 1012 cm-2 that may trace significant numbers of baryons in the form of ionized hydrogen, weak broad HI absorbers with b > 40 km/s that potentially trace warm collisionally ionized gas, and weak metal-line counterparts to Lyα absorbers in the intergalactic medium. However, accurately identifying and measuring weak astrophysical absorbers requires detailed knowledge of the spectrograph detectors and the latest in flat-fielding techniques. We present the results of both interactive and automated line searches in several of the highest-quality (S/N=30-50) extragalactic COS datasets taken to date. We catalog weak narrow lines, broad absorption features, and comment on the applicability of these techniques to the larger catalog of COS observations with more modest S/N.
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