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J/ApJ/847/81       HeII photoionization rates of quasars       (Schmidt+, 2017)

Statistical detection of the HeII transverse proximity effect: evidence for sustained quasar activity for >25 million years. Schmidt T.M., Worseck G., Hennawi J.F., Prochaska J.X., Crighton N.H.M. <Astrophys. J., 847, 81 (2017)> =2017ApJ...847...81S
ADC_Keywords: QSOs ; Intergalactic medium ; Redshifts ; Spectra, optical ; Spectra, ultraviolet ; Surveys Keywords: dark ages, reionization, first stars; intergalactic medium; quasars: general Abstract: The HeII transverse proximity effect-enhanced HeII 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 HeII reionization. We conduct a comprehensive spectroscopic survey to find z∼3 quasars in the foreground of 22 background quasar sightlines with Hubble Space Telescope/COS HeII 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 HeII photoionization rates greater than the expected UV background at these redshifts (ΓQSOHeII>5x10-16s-1) we perform the first statistical analysis of the HeII transverse proximity effect. Our results show qualitative evidence for a large object-to-object variance: among the four foreground quasars with the highest ΓQSOHeII only one (previously known) quasar is associated with a significant HeII transmission spike. We perform a stacking analysis to average down these fluctuations, and detect an excess in the average HeII 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 ΓQSOHeII. Our detection places a purely geometrical lower limit on the quasar lifetime of tQ>25Myr. Improved modeling would additionally constrain quasar obscuration and the mean free path of HeII-ionizing photons. Description: Our foreground quasar survey targeted fields around 22 HeII-transparent quasars observed with HST/COS or HST/STIS (Table 1). Almost all spectra (20/22) have been taken with the HST/COS G140L grating (R∼2000 at 1150Å). For our deep imaging survey we used the Large Binocular Cameras at the Large Binocular Telescope (LBT/LBC) to obtain optical multiband photometry (USpec, g, r and i) over an area of 23'x25' approximately centered on the targeted HeII sightline. Imaging for 10 HeII sightlines was obtained over several runs in 2009, 2011, and 2013 (Table 2). For the field of HE 2347-4342 we obtained multiband imaging (U g r i) with the 36'x36' Mosaic II camera at the 4m Blanco Telescope at the Cerro Tololo Inter-American Observatory. The field of SDSS J1237+0126 was imaged in g r i with Mosaic 1.1 at the 4m Mayall Telescope at the Kitt Peak National Observatory, and in U with Magellan/Megacam. Spectroscopic verification of the quasar candidates was done with the VIsible MultiObject Spectrograph (VIMOS) at the Very Large Telescope (VLT); low-resolution spectra (LR blue grism, R∼180, wavelength range 3700-6700Å). For the field of Q 0302-003, additional quasar candidates outside our VIMOS pointing were observed with the DEep Imaging Multi-Object Spectrograph (DEIMOS) at Keck Observatory. Our deep multi-object spectroscopy was complemented by individual longslit observations of brighter quasar candidates at larger angular separations (10'≲Δθ≲90). For spectroscopic confirmation we used the ESO 3.5m New Technology Telescope Faint Object Spectrograph and Camera (NTT/EFOSC2) and the Calar Alto Observatory (CAHA) 3.5m telescope TWIN spectrograph. The CAHA/TWIN spectra (R=620-1000, wavelength range 3900-7000Å) were taken in 32 nights between 2014 November and 2015 August, while NTT/EFOSC2 observations (R=180-450, wavelength range 3700-9000Å) were performed over five nights in 2014 December. As part of the wide survey we also verified a quasar with an uncertain redshift in the vicinity of HS 1700+6416 (Syphers & Shull 2013ApJ...765..119S). We used the Keck Low Resolution Imaging Spectrometer (Keck/LRIS) to confirm its redshift. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 55 22 Overview of the FUV spectra used for this work table2.dat 57 22 Overview of the HeII sightlines and the number of foreground quasars table3.dat 86 131 Quasars discovered within our survey
See also: B/hst : HST Archived Exposures Catalog (STScI, 2007) II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009) V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015) J/ApJ/592/728 : Lyman break galaxies at redshift z∼3 (Steidel+, 2003) J/ApJ/651/61 : Optically thick absorbers near luminous QSO (Hennawi+, 2006) J/ApJS/166/470 : SDSS-Spitzer type I QSOs IR photometry (Richards+, 2006) J/AJ/133/2222 : Clustering of high-redshift QSOs from SDSS (Shen+, 2007) J/MNRAS/391/1457 : Lymanα forest in QSO pairs (Kirkman+, 2008) J/ApJ/690/20 : Models of AGN and black hole populations (Shankar+, 2009) J/ApJ/716/348 : The XMM-Newton survey of the COSMOS field (Brusa+, 2010) J/ApJ/728/23 : GALEX UV-bright high-redshift quasars (Worseck+, 2011) J/ApJ/772/26 : AGN with WISE. II. The NDWFS Bootes field (Assef+, 2013) J/ApJ/794/75 : HST-COS UV spectra observations of AGNs (Stevans+, 2014) J/MNRAS/445/1745 : Giant Gemini GMOS survey. I. (Worseck+, 2014) J/MNRAS/449/4204 : WFC3/UVIS quasar-stacked spectrum at z≃2.4 (Lusso+, 2015) J/ApJS/219/39 : QSOs selection from SDSS and WISE (Richards+, 2015) J/ApJ/819/62 : The COSMOS-Legacy Survey (CLS) catalog (Civano+, 2016) J/ApJ/831/7 : SDSS-RM project: peak velocities of QSOs (Shen+, 2016) : SDSS-III home page : ENIGMA home page Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 16 A16 --- HE2QS He II-transparent quasar ID 18- 27 A10 --- Inst HST instrument +grating 29- 33 I5 --- R [1000/18000] Dispersion 35- 39 I5 --- HST [9350/13013] HST Program Id 41- 48 A8 --- PI HST Program PI 50- 55 A6 --- Ref Reference(s) (1)
Note (1): References as follows: 1 = Reimers et al. (2005A&A...442...63R); 2 = Shull et al. (2010ApJ...722.1312S); 3 = Syphers et al. (2011ApJ...742...99S); 4 = Syphers et al. (2012AJ....143..100S); 5 = Syphers et al. (2013ApJ...765..119S); 6 = Syphers et al. (2014ApJ...784...42S); 7 = Worseck et al., in prep 8 = Worseck et al. (2011ApJ...733L..24W); 9 = Worseck et al. (2016ApJ...825..144W); 10 = Zheng et al. (2015ApJ...806..142Z); 11 = this paper.
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 16 A16 --- HE2QS He II-transparent quasar ID 18- 19 I2 h RAh Hour of Right Ascension (J2000) 21- 22 I2 min RAm Minute of Right Ascension (J2000) 24- 28 F5.2 s RAs Second of Right Ascension (J2000) 30 A1 --- DE- Sign of the Declination (J2000) 31- 32 I2 deg DEd Degree of Declination (J2000) 34- 35 I2 arcmin DEm Arcminute of Declination (J2000) 37- 40 F4.1 arcsec DEs Arcsecond of Declination (J2000) 42- 46 F5.3 --- zBG [2.7/4] Spectroscopic redshift of HeII-transparent QSO 48 I1 --- N-VLT [0/2]? Number of quasars detected with VLT/VIMOS+LBT/LBC 50 I1 --- N-NTT [0/2]? Number of quasars detected with NTT/EFOSC2 52 I1 --- N-CAHA [0/5]? Number of quasars detected with CAHA/TWIN 54 I1 --- N-SDSS [0/7]? Number of quasars used from SDSS (1) 56- 57 I2 --- N-Lit [1/2]? Number of quasars used from the Literature (2)
Note (1): From SDSS DR12, Alam+ (2015, V/147); Paris+ (2017, VII/279). Note (2): Literature objects from Jakobsen+ (2003A&A...397..891J); Steidel+ (2003, J/ApJ/592/728); Hennawi+ (2006, J/ApJ/651/61); Worseck & Wisotzki (2006A&A...450..495W); Worseck+ (2007A&A...473..805W); Syphers & Shull (2013ApJ...765..119S).
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 16 A16 --- HE2QS He II-transparent quasar ID (1) 18- 26 F9.5 deg RAdeg Right Ascension, foreground QSOs (J2000) 28- 36 F9.5 deg DEdeg Declination, foreground QSOs (J2000) 38- 42 F5.3 --- zspec [0.6/4.2] Spectroscopic Redshift 44- 47 F4.1 mag rmag [17/24.5]? SDSS r band AB magnitude 49- 53 F5.1 mag M1450 [-27.8/-20.5]? Absolute M1450 magnitude 55- 58 F4.1 arcsec Sep [3.1/80.4] Angular separation 60- 63 F4.1 Mpc Dprop [1.5/39.8] Transverse separation in situation proper distances; in proper Mpc units 65- 72 E8.2 s-1 GamHeQSO [6.8e-17/1.1e-06] HeII photoionization rate 74- 86 A13 --- Inst Instrument used (CAHA 3.5/TWIN, VLT/VIMOS, NTT/EFOSC2 or Keck/LRIS; see the "Description" section above)
Note (1): For the sightlines of SDSS J0139-0847, LBQS 1216+1656, SDSS J2200+0008 and J2251-0857 no HeII spectra are available. Despite that, we still list discovered forground quasars.
History: From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 29-May-2018
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