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 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 2013ApJ...765..119S). We used the Keck Low Resolution Imaging
Spectrometer (Keck/LRIS) to confirm its redshift.
File Summary:
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FileName Lrecl Records Explanations
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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
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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)
http://www.sdss3.org/ : SDSS-III home page
http://enigma.physics.ucsb.edu/ : ENIGMA home page
Byte-by-byte Description of file: table1.dat
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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)
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Note (1): References as follows:
1 = Reimers et al. (2005A&A...442...63R 2005A&A...442...63R);
2 = Shull et al. (2010ApJ...722.1312S 2010ApJ...722.1312S);
3 = Syphers et al. (2011ApJ...742...99S 2011ApJ...742...99S);
4 = Syphers et al. (2012AJ....143..100S 2012AJ....143..100S);
5 = Syphers et al. (2013ApJ...765..119S 2013ApJ...765..119S);
6 = Syphers et al. (2014ApJ...784...42S 2014ApJ...784...42S);
7 = Worseck et al., in prep
8 = Worseck et al. (2011ApJ...733L..24W 2011ApJ...733L..24W);
9 = Worseck et al. (2016ApJ...825..144W 2016ApJ...825..144W);
10 = Zheng et al. (2015ApJ...806..142Z 2015ApJ...806..142Z);
11 = this paper.
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Byte-by-byte Description of file: table2.dat
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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- 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- 48 I1 --- N-VLT [0/2]? Number of quasars detected with
VLT/VIMOS+LBT/LBC
50- 50 I1 --- N-NTT [0/2]? Number of quasars detected with NTT/EFOSC2
52- 52 I1 --- N-CAHA [0/5]? Number of quasars detected with CAHA/TWIN
54- 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)
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Note (1): From SDSS DR12, Alam+ (2015, V/147); Paris+ (2017, VII/279).
Note (2): Literature objects from Jakobsen+ (2003A&A...397..891J 2003A&A...397..891J);
Steidel+ (2003, J/ApJ/592/728); Hennawi+ (2006, J/ApJ/651/61);
Worseck & Wisotzki (2006A&A...450..495W 2006A&A...450..495W);
Worseck+ (2007A&A...473..805W 2007A&A...473..805W); Syphers & Shull (2013ApJ...765..119S 2013ApJ...765..119S).
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Byte-by-byte Description of file: table3.dat
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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)
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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.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 29-May-2018