A Population of X-Ray Weak Quasars: PHL 1811 Analogs at High Redshift

Wu, Jianfeng; Brandt, W. N.; Hall, Patrick B.; Gibson, R. R.; Richards, Gordon T.; Schneider, Donald P.; Shemmer, Ohad; Just, Dennis W.; Schmidt, Sarah J.

doi:10.1088/0004-637x/736/1/28

Cited by 103 publications

(212 citation statements)

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“…In this scenario, such PHL 1811 analogs are a subset of WLQs, viewed through the shielding gas while "normal" WLQs are viewed at lines of sight that do not intersect this component. This may explain the observed X-ray weakness and apparently hard X-ray spectra of the PHL 1811 analogs (Wu et al 2011), although it is more difficult to explain the very steep (soft) X-ray spectrum of PHL 1811 itself using this model (Leighly et al 2007b).…”

Section: Discussionmentioning

confidence: 95%

“…Wu et al (2011) suggest that the weakness of the UV lines in their PHL 1811 analogs is due to a larger than usual high-ionization "shielding gas" component that covers most of the BELR, but little more than the BELR in such sources. In this scenario, such PHL 1811 analogs are a subset of WLQs, viewed through the shielding gas while "normal" WLQs are viewed at lines of sight that do not intersect this component.…”

Section: Discussionmentioning

confidence: 98%

“…Another possibility for obtaining a deficiency of high-energy photons, albeit with a typical underlying quasar SED, is based on a recent investigation of 10 SDSS quasars at z 2.2 selected to have UV line properties that are similar to those of PHL 1811 (hereafter "PHL 1811 analogs"; Wu et al 2011). Wu et al (2011) suggest that the weakness of the UV lines in their PHL 1811 analogs is due to a larger than usual high-ionization "shielding gas" component that covers most of the BELR, but little more than the BELR in such sources.…”

Section: Discussionmentioning

confidence: 99%

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The Ultraviolet-to-Mid-Infrared Spectral Energy Distribution of Weak Emission Line Quasars

Lane

Shemmer

Diamond‐Stanic

et al. 2011

ApJ

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We present Spitzer Space Telescope photometry of 18 Sloan Digital Sky Survey (SDSS) quasars at 2.7 z 5.9 which have weak or undetectable high-ionization emission lines in their rest-frame ultraviolet (UV) spectra (hereafter weak-lined quasars, or WLQs). The Spitzer data are combined with SDSS spectra and ground-based, near-infrared (IR) photometry of these sources to produce a large inventory of spectral energy distributions (SEDs) of WLQs across the rest-frame ∼0.1-5 μm spectral band. The SEDs of our sources are inconsistent with those of BL Lacertae objects which are dominated by synchrotron emission due to a jet aligned close to our line of sight, but are consistent with the SED of ordinary quasars with similar luminosities and redshifts that exhibit a near-to-mid-IR "bump," characteristic of hot dust emission. This indicates that broad emission lines in WLQs are intrinsically weak, rather than suffering continuum dilution from a jet, and that such sources cannot be selected efficiently from traditional photometric surveys.

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Section: Discussionmentioning

confidence: 95%

Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

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The Ultraviolet-to-Mid-Infrared Spectral Energy Distribution of Weak Emission Line Quasars

Lane

Shemmer

Diamond‐Stanic

et al. 2011

ApJ

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“…An unexpected population of ∼10 2 quasars were discovered within the spectra of the Sloan Digital Sky Survey (SDSS; York et al 2000) that display exceptionally weak or completely missing broad emission lines in the ultraviolet (UV) rest-frame (Fan et al 1999;Anderson et al 2001;Collinge et al 2005;Diamond-Stanic et al 2009, hereafter DS09;Plotkin et al 2010a, hereafter P10;Hryniewicz et al 2010;Wu et al 2011;Meusinger & Balafkan 2014). The first systematic search for such weak emission line quasars (WLQs) was performed by DS09, who examined the rest-frame equivalent width (W r ) distribution of the Lyα λ1216+N V λ1240 blend for SDSS quasars at z > 3.…”

Section: Introductionmentioning

confidence: 99%

Detection of Rest-Frame Optical Lines From X-Shooter Spectroscopy of Weak Emission-Line Quasars

Plotkin

Shemmer

Trakhtenbrot

et al. 2015

ApJ

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104

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Over the past 15 years, examples of exotic radio-quiet quasars with intrinsically weak or absent broad emission line regions (BELRs) have emerged from large-scale spectroscopic sky surveys. Here, we present spectroscopy of seven such weak emission line quasars (WLQs) at moderate redshifts (z = 1.4 − 1.7) using the X-shooter spectrograph, which provides simultaneous optical and nearinfrared spectroscopy covering the rest-frame ultraviolet through optical. These new observations effectively double the number of WLQs with spectroscopy in the optical rest-frame, and they allow us to compare the strengths of (weak) high-ionization emission lines (e.g., C IV) to low-ionization lines (e.g., Mg II, Hβ, Hα) in individual objects. We detect broad Hβ and Hα emission in all objects, and these lines are generally toward the weaker end of the distribution expected for typical quasars (e.g., Hβ has rest-frame equivalent widths ranging from 15-40Å.). However, these low-ionization lines are not exceptionally weak, as is the case for high-ionization lines in WLQs. The X-shooter spectra also display relatively strong optical Fe II emission, Hβ FWHM 4000 km s −1 , and significant C IV blueshifts (≈1000-5500 km s −1 ) relative to the systemic redshift; two spectra also show elevated ultraviolet Fe II emission, and an outflowing component to their (weak) Mg II emission lines. These properties suggest that WLQs are exotic versions of "wind-dominated" quasars. Their BELRs either have unusual high-ionization components, or their BELRs are in an atypical photoionization state because of an unusually soft continuum.

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“…Various suggestions have been made to explain the absence of broad lines in unobscured quasars (e.g., Shemmer et al 2010;Laor & Davis 2011, and references therein) but this AGN type remains puzzling. A subset of quasars with weak UV emission lines have been identified that are known as PHL 1811 analogs (Leighly et al 2001;Leighly et al 2007;Wu et al 2011Wu et al , 2012. Leighly et al (2007) suggested that the weak UV emission lines of these objects are due to an unusual soft SED deficient in ionising photons, perhaps due to exceptionally high Eddington ratios (see e.g., Shemmer et al 2009, and references therein).…”

Section: Introductionmentioning

confidence: 99%

Unusual quasars from the Sloan Digital Sky Survey selected by means of Kohonen self-organising maps

Meusinger¹,

Schalldach²,

Scholz³

et al. 2012

A&A

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Context. Large spectroscopic surveys have discovered very peculiar and hitherto unknown types of active galactic nuclei (AGN). Such rare objects may hold clues to the accretion history of the supermassive black holes at the centres of galaxies. Aims. We aim to create a sizeable sample of unusual quasars from the unprecedented spectroscopic database of the Sloan Digital Sky Survey (SDSS). Methods. We exploit the spectral archive of the SDSS Data Release 7 to select unusual quasar spectra. The selection method is based on a combination of the power of self-organising maps and the visual inspection of a huge number of spectra. Self-organising maps were applied to nearly 10 5 spectra classified as quasars at redshifts from z = 0.6 to 4.3 by the SDSS pipeline. Particular attention was paid to minimise possible contamination by rare peculiar stellar spectral types. All selected quasar spectra were individually studied to determine the object type and the redshift.Results. We present a catalogue of 1005 quasars with unusual spectra. These spectra are dominated by either broad absorption lines (BALs; 42%), unusual red continua (27%), weak emission lines (18%), or conspicuously strong optical and/or UV iron emission (11%). This large sample provides a useful resource for both studying properties and relations of/between different types of unusual quasars and selecting particularly interesting objects, even though the compilation is not aimed at completeness in a quantifiable sense. The spectra are grouped into six types for which composite spectra are constructed and mean properties are computed. Remarkably, all these types turn out to be on average more luminous than comparison samples of normal quasars after a statistical correction is made for intrinsic reddening (E(B − V) ≈ 0 to 0.4 for SMC-like extinction). Both the unusual BAL quasars and the strong iron emitters have significantly lower radio luminosities than normal quasars. We also confirm that strong BALs avoid the most radioluminous quasars. For 32 particularly interesting objects, individual spectra are presented. Among these objects are quasars with many narrow BAL troughs and one quasar where the continuum is strongly suppressed by overlapping BAL troughs across nearly the whole SDSS spectrum. Finally, we create a sample of quasars similar to the two "mysterious" objects discovered by Hall et al. (2002, ApJS, 141, 267) and briefly discuss the quasar properties and possible explanations of their highly peculiar spectra.

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A Population of X-Ray Weak Quasars: PHL 1811 Analogs at High Redshift

Cited by 103 publications

References 113 publications

The Ultraviolet-to-Mid-Infrared Spectral Energy Distribution of Weak Emission Line Quasars

The Ultraviolet-to-Mid-Infrared Spectral Energy Distribution of Weak Emission Line Quasars

Detection of Rest-Frame Optical Lines From X-Shooter Spectroscopy of Weak Emission-Line Quasars

Unusual quasars from the Sloan Digital Sky Survey selected by means of Kohonen self-organising maps

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