The Rest‐Frame Extreme‐Ultraviolet Spectral Properties of Quasi‐stellar Objects

Abstract

We use a sample of 332 Hubble Space Telescope spectra of 184 QSOs with z > 0.33 to study the typical ultraviolet spectral properties of QSOs, with emphasis on the ionizing continuum. Our sample is nearly twice as large as that of Zheng et al. (1997) and provides much better spectral coverage in the extreme ultraviolet (EUV). The overall composite continuum can be described by a power law with index α EUV = −1.76 ± 0.12 ( f ν ∝ ν α ) between 500 and 1200 Å. The corresponding results for subsamples of radio-quiet and radio-loud QSOs are α EUV = −1.57 ± 0.17 and α EUV = −1.96 ± 0.12, respectively. We also derive α EUV for as many individual objects in our sample as possible, totaling 39 radio-quiet and 40 radio-loud QSOs. The typical individually measured values of α EUV are in good agreement with the composites. We find no evidence for evolution of α EUV with redshift for either radio-loud or radio-quiet QSOs. However, we do find marginal evidence for a trend towards harder EUV spectra with increasing luminosity for radio-loud objects. An extrapolation of our radio-quiet QSO spectrum is consistent with existing X-ray data, suggesting that the ionizing continuum may be represented by a single power law. The resulting spectrum is roughly in agreement with models of the intergalactic medium photoionized by the integrated radiation from QSOs.

Lyα emission-line reconstruction for high-zQSOs

“…Vanden Berk et al 2001;Shang et al 2007), however, this is beyond our QSO sample wavelength coverage. Typically, a broken power-law continuum is also adopted blueward of Lyα, visible in low-z HST spectra (e.g Telfer et al 2002;Shull et al 2012). In this work, we do not consider a different slope near Lyα as we only fit down redshift) and the corresponding low number of sources potentially affected by this systematic shift, we deem the exclusion of Si III] a valid simplification.…”

On the location and composition of the dust in the MCG–6-30-15 warm absorber

“…where we have assumed L ν ∝ ν −β for the ionizing luminosity (β ≈ 1.6 for radio-quiet quasars; Telfer et al 2002), and used a H = 6 × 10 −18 cm 2 and α H (20 000 K) = 2.5 × 10 −13 cm 3 s −1 (Osterbrock 1989). With a typical Seyfert 1 Lyman luminosity of L > = 10 44 erg s −1 , and assuming hν = 45 eV, the ionization parameter of a n H = 10 cm −3 cloud at 1 kpc is 0.04.…”

Covering factors of the dusty obscurers in radio-loud and radio-quiet quasars

“…therein), explanation for the rarity of FRII quasars in terms of the intermittent jet production scenario would require RQ quasar phase lifetimes to be longer than the Salpeter timescale (Salpeter 1964). Furthermore, spectral properties of RQ and RL quasars are strikingly similar in all bands but radio (Sanders et al 1989;Francis et al 1993;Elvis et al 1994;Zheng et al 1997;Telfer et al 2002;de Vries et al 2006;Richards et. al 2006;Shang et al 2011;Shankar et al 2016).…”