Candidate type II quasars at 2 &lt; z &lt; 4.3  in the Sloan Digital Sky Survey III

Alexandroff, Rachael; Strauss, Michael A.; Greene, Jenny E.; Zakamska, Nadia L.; Ross, Nicholas P.; Brandt, W. N.; Liu, Guilin; Smith, Paul S.; Ge, Jian; Hamann, Fred; Myers, Adam D.; Petitjean, P.; Schneider, Donald P.; Yesuf, Hassen M.; York, Donald G.

doi:10.1093/mnras/stt1500

Cited by 102 publications

(152 citation statements)

References 136 publications

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“…We obtain an upper limit on the C IV emission from the companion galaxy by using the redshift obtained from the quasar O I line to set the wavelength and a fiducial linewidth of σ v = 200 km s −1 . This limit is EW 0 < 6Å (1σ), whereas nearly all of the Type II quasar candidates in Alexandroff et al (2013) have EW 0 (C IV) > 10Å. Additionally, no N V emission is detected from the galaxy, to a limit of EW 0 (N V) < 0.2Å.…”

Section: Discussionmentioning

confidence: 94%

Close Companions to Two High-Redshift Quasars

McGreer

Fan

Strauss

et al. 2014

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We report the serendipitous discoveries of companion galaxies to two high-redshift quasars. SDSS J025617.7+001904 is a z = 4.79 quasar included in our recent survey of faint quasars in the SDSS Stripe 82 region. The initial MMT slit spectroscopy shows excess Lyα emission extending well beyond the quasar's light profile. Further imaging and spectroscopy with LBT/MODS1 confirms the presence of a bright galaxy (i AB = 23.6) located 2 ′′ (12 kpc projected) from the quasar with strong Lyα emission (EW 0 ≈ 100Å) at the redshift of the quasar, as well as faint continuum. The second quasar, CFHQS J005006.6+344522 (z = 6.25), is included in our recent HST SNAP survey of z ∼ 6 quasars searching for evidence of gravitational lensing. Deep imaging with ACS and WFC3 confirms an optical dropout ∼ 4.5 mag fainter than the quasar (Y AB = 25) at a separation of 0.9 ′′ . The red i 775 − Y 105 color of the galaxy and its proximity to the quasar (5 kpc projected if at the quasar redshift) strongly favor an association with the quasar. Although it is much fainter than the quasar it is remarkably bright when compared to field galaxies at this redshift, while showing no evidence for lensing. Both systems may represent late-stage mergers of two massive galaxies, with the observed light for one dominated by powerful ongoing star formation and for the other by rapid black hole growth. Observations of close companions are rare; if major mergers are primarily responsible for high-redshift quasar fueling then the phase when progenitor galaxies can be observed as bright companions is relatively short.

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Section: Discussionmentioning

confidence: 94%

Close Companions to Two High-Redshift Quasars

McGreer

Fan

Strauss

et al. 2014

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“…The left panel of Figure 4 demonstrates this empirically. RXC J2248-ID3 and other metal-poor C IV emitters (Stark et al 2014(Stark et al , 2015bBerg et al 2016;Vanzella et al 2016) have larger O III]/C IV flux ratios than both  z 2 3 -UV-selected AGNs (Hainline et al 2011) and the majority of type II  z 2 4 -quasars from Alexandroff et al (2013). This follows naturally if the metal-poor galaxies have spectra that are deficient in the 4 Ryd photons that power He II and triply ionize oxygen.…”

Section: Discussion and Summarymentioning

confidence: 96%

Evidence for a Hard Ionizing Spectrum from a z = 6.11 Stellar Population

Mainali¹,

Kollmeier

Stark³

et al. 2017

ApJL

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We present the Magellan/FIRE detection of highly ionized C IVλ1550 and O III]λ1666 in a deep infrared spectrum of the z=6.11 gravitationally lensed low-mass galaxy RXC J2248.7-4431-ID3, which has previously known Lyα. No corresponding emission is detected at the expected location of He IIλ1640. The upper limit on He II, paired with detection of O III] and C IV, constrains possible ionization scenarios. Production of C IV and O III] requires ionizing photons of 2.5-3.5 Ryd, but once in that state their multiplet emission is powered by collisional excitation at lower energies (∼0.5 Ryd). As a pure recombination line, He II emission is powered by 4 Ryd ionizing photons. The data therefore require a spectrum with significant power at 3.5 Ryd but a rapid drop toward 4.0 Ryd. This hard spectrum with a steep drop is characteristic of low-metallicity stellar populations, and less consistent with soft AGN excitation, which features more 4 Ryd photons and hence higher He II flux. The conclusions based on ratios of metal line detections to helium non-detection are strengthened if the gas metallicity is low. RXJ2248-ID3 adds to the growing handful of reionization-era galaxies with UV emission line ratios distinct from the general = z 2 3 -population in a way that suggests hard ionizing spectra that do not necessarily originate in AGNs.

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“…As Hα is redshifted out of the optical bandpass at z 0.5 > , alternative obscured AGN selection methods using observed optical spectra have been developed to capitalize on the existing rich data sets from wide-area optical surveys, including: Gilli et al 2010;Mignoli et al 2013) 20 ; 5. a combination of narrow emission lines withFWHMva-lues <2000 km s −1 , ratios of narrow emission lines suggesting AGNs rather than star formation ionization, and a high [O III] luminosity, which is applicable between z 0.3 0.83 < < (Zakamska et al 2003;Reyes et al 2008); 6. strong C IV and Lyα emission with FWHM <2000 km s −1 and weak rest-frame ultraviolet continuum values, which identifies AGNs between z 2 4.3 < < (Alexandroff et al 2013; see also Steidel et al 2002;Hainline et al 2011).…”

Section: Identifying Type 2 Agnsmentioning

confidence: 93%

On R − W1 as a Diagnostic to Discover Obscured Active Galactic Nuclei in Wide-Area X-Ray Surveys

LaMassa

Civano

Brusa

et al. 2016

ApJ

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Capitalizing on the all-sky coverage of WISEand the 35% and 50% sky coverage from Sloan Digital Sky Survey and Pan-STARRS, respectively, we explore the efficacy of-, as a color diagnostic to identify obscured supermassive black hole accretion in wide-area X-ray surveys. We use the ∼16.5 deg 2 Stripe 82 X-ray survey data as a testbed to compare R W1 -with R−K, an oft-used obscured active galactic nucleus (AGN) selection criterion, and examine where different classes of objects lie in this parameter space. Most stars follow a well-defined path in R−K versus R W1space. We demonstrate that optically normal galaxies hosting X-ray AGNs at redshifts z 0.5 1 < < can be recovered with an R W1 4 -> colorcut, while they typically are not selected as AGNs based on their W W 1 2 -colors. Additionally, different observed X-ray luminosity bins favor different regions in R W1 -parameter space: moderate-luminosity AGNs > -erg s −1 ) have bluer colors; higher spectroscopic completeness of the Stripe 82X sample is needed to determine whether this is a selection effect or an intrinsic property. Finally, we parameterize X-ray obscuration of Stripe 82X AGNs by calculating their hardness ratios (HRs) and find no clear trends between HR and optical reddening. Our results will help inform best-effort practices in followingup obscured AGN candidates in current and future wide-area, shallow X-ray surveys, including the all-sky eROSITA mission.

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Candidate type II quasars at 2 < z < 4.3 in the Sloan Digital Sky Survey III

Cited by 102 publications

References 136 publications

Close Companions to Two High-Redshift Quasars

Close Companions to Two High-Redshift Quasars

Evidence for a Hard Ionizing Spectrum from a z = 6.11 Stellar Population

On R − W1 as a Diagnostic to Discover Obscured Active Galactic Nuclei in Wide-Area X-Ray Surveys

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