Hubble/COS Observations of AGN Ionizing Continua

Details Hubble/COS Observations of AGN Ionizing Continua Hubble/COS Observations of AGN Ionizing Continua

Jan 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21714236s&link_type=abstract

American Astronomical Society, AAS Meeting #217, #142.36; Bulletin of the American Astronomical Society, Vol. 43, 2011

Astronomy and Astrophysics

Astronomy

Scientific paper

The high-throughput Cosmic Origins Spectrograph (COS) installed on the Hubble Space Telescope (HST) allows us to obtain high-quality UV spectra of active galactic nuclei (AGN), many of which served as background targets for studies of the low-redshift intergalactic medium (IGM). We present power-law continuum fits for a sample of 13 AGN with redshifts 0.0296 < z < 0.852, sufficient to explore their far ultraviolet (FUV) and extreme ultraviolet (EUV) continua. New spectra from HST/COS provide spectral coverage in the rest-frame Lyman continuum of AGN at z > 0.24, with high sensitivity and moderate resolution (20 km/s) in the G130M grating. This allows broad emission lines (Ne VIII, O IV) to be resolved. In cases when Far Ultraviolet Spectroscopic Explorer (FUSE) and International Ultraviolet Explorer (IUE) data are available, we create and fit composite spectra covering between 900 - 3300 Å in the observed frame. We compare COS-based power-law spectra to these data. Describing the EUV continuum fluxes by a power-law spectrum, Fν = A να with index α, gives insight into the formation of emission lines, defines the "big blue bump" in the spectral energy distribution of AGNs, and constrains the ionization state of the IGM. We examine our results for correlations of spectral slope with redshift and compare our results to previous spectral fits from HST/FOS (Telfer et al. 2002, ApJ, 565, 773) and FUSE (Scott et al. 2004, ApJ, 615, 135). This work is supported by the COS-support grant from the STScI (NNX08-AC14G).

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