HST-COS OBSERVATIONS OF AGNs. III. SPECTRAL CONSTRAINTS IN THE  LYMAN CONTINUUM FROM COMPOSITE COS/G140L DATA*

Tilton, Evan M.; Stevans, Matthew L.; Shull, Michael; Danforth, Charles W.

doi:10.3847/0004-637x/817/1/56

Cited by 34 publications

(50 citation statements)

References 70 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The quasar spectral slope α beyond 912Å is not very well constrained since the frequencies between the extreme UV and soft X-rays are basically unobservable. We adopt a value of α = −1.7 as determined by Lusso et al (2015) (however with a large uncertainty of ±0.6), which is consistent with the independent measurement of Stevans et al (2014), as well as the slope between UV and X-ray regime (Lusso et al 2015), but differs from the value of α = −0.73 ± 0.26 reported by Tilton et al (2016). The uncertainty in α and the long range of extrapolation from 912Å beyond 228Å causes substantial uncertainty in the inferred photoionization rate, e.g.…”

Section: Systemic Quasar Redshiftsmentioning

confidence: 48%

Statistical Detection of the He ii Transverse Proximity Effect: Evidence for Sustained Quasar Activity for >25 Million Years

Schmidt

Worseck

Prochaska

et al. 2017

ApJ

View full text Add to dashboard Cite

The He ii transverse proximity effect -enhanced He ii Lyα transmission in a background sightline caused by the ionizing radiation of a foreground quasar -offers a unique opportunity to probe the morphology of quasar-driven He ii reionization. We conduct a comprehensive spectroscopic survey to find z ∼ 3 quasars in the foreground of 22 background quasar sightlines with HST /COS He ii Lyα transmission spectra. With our two-tiered survey strategy, consisting of a deep pencil-beam survey and a shallow wide-field survey, we discover 131 new quasars, which we complement with known SDSS/BOSS quasars in our fields. Using a restricted sample of 66 foreground quasars with inferred He ii photoionization rates greater than the expected UV background at these redshifts (Γ HeII QSO > 5 × 10 −16 s −1 ) we perform the first statistical analysis of the He ii transverse proximity effect. Our results show qualitative evidence for a large object-to-object variance: among the four foreground quasars with the highest Γ HeII QSO only one (previously known) quasar is associated with a significant He ii transmission spike. We perform a stacking analysis to average down these fluctuations, and detect an excess in the average He ii transmission near the foreground quasars at 3σ significance. This statistical evidence for the transverse proximity effect is corroborated by a clear dependence of the signal strength on Γ HeII QSO . Our detection places a purely geometrical lower limit on the quasar lifetime of t Q > 25 Myr. Improved modeling would additionally constrain quasar obscuration and the mean free path of He ii-ionizing photons.

show abstract

Section: Systemic Quasar Redshiftsmentioning

confidence: 48%

Statistical Detection of the He ii Transverse Proximity Effect: Evidence for Sustained Quasar Activity for >25 Million Years

Schmidt

Worseck

Prochaska

et al. 2017

ApJ

View full text Add to dashboard Cite

show abstract

“…Weaker emission lines, unidentifiable in single objects, are detectable in composite spectra. This method has been employed over a wide range of quasar samples such as the Large Bright Quasar Survey (Francis et al 1991;Hewett et al 1995), FIRST Bright Quasar Survey (White et al 2000;Brotherton et al 2001), Sloan Digital Sky Survey (SDSS; York et al 2000;Vanden Berk et al 2001), Hubble Space Telescope (HST; Zheng et al 1997;Telfer et al 2002), HST-Far Ultraviolet Spectroscopic Explorer (Scott et al 2004), HST-Cosmic Origin Spectrograph (Shull et al 2012;Stevans et al 2014;Tilton et al 2016), Baryon Acoustic Oscillation Spectroscopic Survey (BOSS; Dawson et al 2013;Harris et al 2016), and VLT-XSHOOTER (Selsing et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Spectral Evolution in High Redshift Quasars From the Final Baryon Oscillation Spectroscopic Survey Sample

Jensen

Vivek

Dawson

et al. 2016

ApJ

View full text Add to dashboard Cite

We report on the diversity in quasar spectra from the Baryon Oscillation Spectroscopic Survey. After filtering the spectra to mitigate selection effects and Malmquist bias associated with a nearly flux-limited sample, we create high signal-to-noise ratio composite spectra from 58,656 quasars (   z 2.1 3.5), binned by luminosity, spectral index, and redshift. With these composite spectra, we confirm the traditional Baldwin effect (BE, i.e., the anticorrelation of C IV equivalent width (EW) and luminosity) that follows the relation µ , and −0.41±0.005 for z=2.25, 2.46, and 2.84, respectively. In addition to the redshift evolution in the slope of the BE, we find redshift evolution in average quasar spectral features at fixed luminosity. The spectroscopic signature of the redshift evolution is correlated at 98% with the signature of varying luminosity, indicating that they arise from the same physical mechanism. At a fixed luminosity, the average C IV FWHM decreases with increasing redshift and is anti-correlated with C IV EW. The spectroscopic signature associated with C IV FWHM suggests that the trends in luminosity and redshift are likely caused by a superposition of effects that are related to black hole mass and Eddington ratio. The redshift evolution is the consequence of a changing balance between these two quantities as quasars evolve toward a population with lower typical accretion rates at a given black hole mass.

show abstract

“…Therefore, we should consider this effect while modeling AGN SEDs. To correct for the intervening Lyα forest and continuum absorption, one possibility is to employ a set of IGM transmission functions (T λ ) calibrated from multiple quasar absorption-line observables (Lusso et al 2015, see also Stevans et al 2014;Tilton et al 2016 for a different approach) over a wide range of redshifts. Such functions can be estimated statistically given the stochasticity of Lyman limit systems (e.g., Worseck & Prochaska 2011;Prochaska et al 2014) and critically depends on the parametrization of the H 1 column density distribution (Madau 1995;Meiksin 2006;Inoue et al 2014;Prochaska et al 2014).…”

Section: Igm Absorptionmentioning

confidence: 99%

“…To estimate the intrinsic shape of the BBB,one must take into account the intergalactic medium (IGM) absorption by neutral hydrogen along the line of sight (Stevans et al 2014;Lusso et al 2015;Tilton et al 2016). Absorption from intergalactic H I, blueward of Lyα emission in the AGN rest frame, attenuates the source flux both in the Lyman series (creating the so-called H I forest), and in the Lyman continuum at rest l < 912 Å r (e.g., Moller & Jakobsen 1990).…”

Section: Igm Absorptionmentioning

confidence: 99%

AGNfitter: A BAYESIAN MCMC APPROACH TO FITTING SPECTRAL ENERGY DISTRIBUTIONS OF AGNs

Rivera

Lusso

Hennawi

et al. 2016

ApJ

117

View full text Add to dashboard Cite

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACTWe present AGNfitter, a publicly available open-source algorithm implementing a fully Bayesian Markov Chain Monte Carlo method to fit the spectral energy distributions (SEDs) of active galactic nuclei (AGNs) from the submillimeter to the UV, allowing one to robustly disentangle the physical processes responsible for their emission. AGNfitter makes use of a large library of theoretical, empirical, and semi-empirical models to characterize both the nuclear and host galaxy emission simultaneously. The model consists of four physical emission components: an accretion disk, a torus of AGN heated dust, stellar populations, and cold dust in star-forming regions. AGNfitter determines the posterior distributions of numerous parameters that govern the physics of AGNs with a fully Bayesian treatment of errors and parameter degeneracies, allowing one to infer integrated luminosities, dust attenuation parameters, stellar masses, and star-formation rates. We tested AGNfitter's performance on real data by fitting the SEDs of a sample of 714 X-ray selected AGNs from the XMM-COSMOS survey, spectroscopically classified as Type1 (unobscured) and Type2 (obscured) AGNs by their optical-UV emission lines. We find that two independent model parameters, namely the reddening of the accretion disk and the column density of the dusty torus, are good proxies for AGN obscuration, allowing us to develop a strategy for classifying AGNs as Type1 or Type2, based solely on an SED-fitting analysis. Our classification scheme is in excellent agreement with the spectroscopic classification, giving a completeness fraction of~86% and~70%, and an efficiency of~80% and 77%, for Type1 and Type2 AGNs, respectively.

show abstract

HST-COS OBSERVATIONS OF AGNs. III. SPECTRAL CONSTRAINTS IN THE LYMAN CONTINUUM FROM COMPOSITE COS/G140L DATA*

Cited by 34 publications

References 70 publications

Statistical Detection of the He ii Transverse Proximity Effect: Evidence for Sustained Quasar Activity for >25 Million Years

Statistical Detection of the He ii Transverse Proximity Effect: Evidence for Sustained Quasar Activity for >25 Million Years

Spectral Evolution in High Redshift Quasars From the Final Baryon Oscillation Spectroscopic Survey Sample

AGNfitter: A BAYESIAN MCMC APPROACH TO FITTING SPECTRAL ENERGY DISTRIBUTIONS OF AGNs

Contact Info

Product

Resources

About