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J/ApJ/696/580    Properties of weak emission-line QSOs (WLQ)   (Shemmer+, 2009)

X-ray insights into the nature of weak emission-line quasars at high redshift. Shemmer O., Brandt W.N., Anderson S.F., Diamond-Stanic A.M., Fan X., Richards G.T., Schneider D.P., Strauss M.A. <Astrophys. J., 696, 580-590 (2009)> =2009ApJ...696..580S
ADC_Keywords: QSOs ; X-ray sources ; Active gal. nuclei ; Redshifts ; BL Lac objects Keywords: galaxies: active - galaxies: nuclei - quasars: emission lines - quasars: general - X-rays: galaxies Abstract: We present Chandra observations of nine high-redshift quasars (z=2.7-5.9) discovered by the Sloan Digital Sky Survey with weak or undetectable high-ionization emission lines in their UV spectra (WLQs). Adding archival X-ray observations of six additional sources of this class has enabled us to place the strongest constraints yet on the X-ray properties of this remarkable class of active galactic nuclei (AGNs). Although our data cannot rule out the possibility that the emission lines are overwhelmed by a relativistically boosted continuum, as manifested by BL Lac objects, we find that WLQs are considerably weaker in the X-ray and radio bands than the majority of BL Lacs found at much lower redshifts. If WLQs are high-redshift BL Lacs, then it is difficult to explain the lack of a large parent population of X-ray and radio bright weak-lined sources at high redshift. We also consider the possibility that WLQs are quasars with extreme properties, and in particular that the emission lines are suppressed by high accretion rates. Using joint spectral fitting of the X-ray spectra of 11 WLQs, we find that the mean photon index in the hard X-ray band is consistent with those observed in typical radio-quiet AGNs with no hint of an unusually steep hard-X-ray spectrum. This result poses a challenge to the hypothesis that WLQs have extremely high accretion rates, and we discuss additional observations required to test this idea. Description: We selected nine WLQs at z=2.7-5.9 for short (∼4-23ks) Chandra observations in Cycle 8 (2007-2008); see table 1. Two additional SDSS WLQs at z>2.2 were serendipitously observed by XMM-Newton on 2001 April 19 for 18.7ks (dataset ID 0111100201; PI M. Watson) and on 2006 October 25 for 20.7ks (dataset ID 0402250101; PI B. Maughan). For the purpose of comparing our WLQs to BL Lac objects, we have compiled a dataset of X-ray, optical, and radio luminosities for a sample of 279 BL Lacs from a variety of surveys. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 54 11 Chandra and XMM observation log of WLQs table3.dat 131 11 X-ray, optical, and radio properties of WLQs table5.dat 92 279 X-ray, optical, and radio properties of the BL Lac sample
See also: B/chandra : The Chandra Archive Log (CXC, 1999-) VII/260 : The SDSS-DR7 quasar catalog (Schneider+, 2010) J/AJ/135/2453 : Sample of BL Lac objects from SDSS and FIRST (Plotkin+, 2008) J/PASJ/60/161 : Multi-wave band emission from blazars (Yi+, 2008) J/AJ/129/2542 : BL Lac from SDSS (Collinge+, 2005) J/MNRAS/323/757 : Deep X-Ray Radio Blazar Survey (DXRBS). II. (Landt+, 2001) J/AJ/121/31 : High-redshift quasars in SDSS (Fan+, 2001) J/ApJ/525/127 : RGB sample of BL Lacertae objects (Laurent-Muehleisen+, 1999) J/AJ/115/1253 : Deep X-Ray Radio Blazar Survey (DXRBS). I. (Perlman+ 1998) J/A+AS/109/267 : Radio to X-Ray distribution of BL Lac Objects (Giommi+, 1995) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 18 A18 --- SDSS SDSS identification ( 20 A1 --- f_SDSS [hi] Note about the X-ray data (G1) 22- 24 F3.1 --- z Redshift 26- 28 F3.1 arcsec rOX ? Angular distance between the optical and X-ray position (2) 30 A1 --- f_ObsDate [d] Merged image (G1) 32- 41 A10 "YYYY/MM/DD" ObsDate Date of observation 43- 46 I4 --- ObsID ? Chandra observation identification number 48- 52 F5.2 ks ExpT Chandra exposure time (corrected for detector dead time) 54 I1 --- Ref ? Reference number in which the source were first identified as WLQ (Weak emission-Line quasar) or BL Lac candidate (5)
Note (2): The optical positions of the quasars have been obtained from the reference given in the seventh column, and the X-ray positions have been obtained with wavdetect. Note (5): Position reference as follows: 1 = Collinge et al. 2005, Cat. J/AJ/129/2542 2 = this work; 3 = Schneider et al. 2005, SDSS-DR3 quasar catalog, Cat. VII/243 (catalog superseded by VII/260); 4 = Fan et al. 2006AJ....131.1203F; 5 = Schneider et al. 2007, SDSS-DR5 quasar catalog, Cat. VII/252 (catalog superseded by VII/260).
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 18 A18 --- SDSS SDSS identification ( 20 A1 --- f_SDSS [hi] Note about the X-ray data (G1) 22- 25 F4.2 10+20cm-2 NH Neutral galactic absorption column density from Dickey & Lockman (1990ARA&A..28..215D) 27- 30 F4.1 mag AB1450 Monochromatic AB magnitude at a rest-frame wavelength of 1450Å 32 A1 --- f_AB1450 [j] Spectrum from Keck (G1) 34- 38 F5.1 mag BMAG Absolute B-band magnitude 40- 43 F4.1 10uJy F2500 Flux density at rest-frame 2500Å in units of 10-28erg/cm2/s/Hz (10-5Jy) 45- 48 F4.1 [10-7W] L2500 Log monochromatic luminosity at a rest-frame wavelength of 2500Å 50 A1 --- l_CRate Limit flag on CRate 51- 55 F5.2 ct/ks CRate Observed count rate in the 0.5-2keV band 57- 60 F4.2 ct/ks E_CRate ? Positive error on CRate 62- 65 F4.2 ct/ks e_CRate ? Negative error on CRate 67 A1 --- f_CRate [k] corrected for exposure map (G1) 69 A1 --- l_Fx Limit flag on Fx 70- 73 F4.1 aW/m2 Fx Galactic absorption-corrected flux in the 0.5-2keV band (in 10-15erg/cm2/s) 75- 78 F4.1 aW/m2 E_Fx ? Positive error on Fx 80- 83 F4.1 aW/m2 e_Fx ? Negative error on Fx 85 A1 --- l_F2keV Limit flag on F2keV 86- 90 F5.2 nJy F2keV Flux density at rest-frame 2keV in units of 10-32erg/cm2/s/Hz (10-9Jy) 92 A1 --- l_L2keV Limit flag on log2keV 93- 96 F4.1 [10-7W] L2keV Log monochromatic luminosity at rest-frame 2keV (log(νLν)) 98 A1 --- l_logL Limit flag on logL 99-102 F4.1 [10-7W] logL Log luminosity in the rest-frame 2-10keV band 104 A1 --- l_aox Limit flag on aox 105-109 F5.2 --- aox Optical-to-X-ray power-law slope (4) 111 A1 --- l_Daox Limit flag on Daox 112-116 F5.2 --- Daox Difference between measured and predicted αox (5) 118 A1 --- l_Sigox Limit flag on Sigox 119-121 F3.1 --- Sigox Significance of the difference between measured and predicted αox (6) 124 A1 --- l_aro Limit flag on aro 125-129 F5.2 --- aro Radio-to-optical power-law slope (7) 131 A1 --- f_aro [l] Radio flux density from NVSS (G1)
Note (4): αox, defined as: αox=log(f2keV/f2500Å)/log(ν2keV2500Å) where f2keV and f2500Å are the flux densities at rest-frame 2keV and 2500Å, respectively. Note (5): Δαox is the difference between measured (aOX) and predicted αox, given the UV luminosity of log2500, based on the observed αox-Lν(2500Å) relation in AGNs (given as Equation (3) of Just et al. 2007ApJ...665.1004J) Note (6): The statistical significance of the difference (DaOX) is also given in units of σ, where σ=0.146 for 31<logLν(2500Å)<32, and σ=0.131 for 32<logLν(2500Å)<33 (see Table 5 of Steffen et al. 2006AJ....131.2826S; these differences do not account for flux-density measurement errors). Note (7): Unless otherwise noted, radio-to-optical flux ratios (αro; see Section 3.1 for the conversion of these values to the radio-loudness parameter R) involve radio flux densities at an observed-frame frequency of 1.4GHz taken from the FIRST survey (Becker et al. 1995ApJ...450..559B); upper limits on αro are calculated from the 3σ FIRST detection threshold at the source position.
Byte-by-byte Description of file: table5.dat
Bytes Format Units Label Explanations
1- 24 A24 --- Name Source name 26- 34 F9.5 deg RAdeg Right Ascension in decimal degrees (J2000) 36- 44 F9.5 deg DEdeg Declination in decimal degrees (J2000) 46- 50 F5.3 --- z Redshift 52- 56 F5.2 [10-7W] log2keV Log monochromatic luminosity at 2keV in erg/s 58 I1 --- f_log2keV [0/1] 0 = upper limit in log2keV (1) 60- 64 F5.2 [10-7W] log5500 Log monochromatic luminosity at 5500Å 66 I1 --- f_log5500 [0/1] 0 = upper limit on log5500 (1) 68- 72 F5.2 [10-7W] log5GHz Log monochromatic luminosity at 5GHz in erg/s 74 I1 --- f_log5GHz [0/1] 0 = upper limit on log5GHz (1) 76- 80 F5.2 --- aox Optical/X-ray spectral index 82 I1 --- f_aox [0/1] 0 = upper limit on aox (1) 84- 88 F5.2 --- aro Radio/Optical spectral index 90 I1 --- f_aro [0/1] 0 = upper limit on aro (1) 92 I1 --- Ref Reference for multiwavelength data (2)
Note (1): 0 = upper limit, 1 = measured value. Note (2): Reference as follows: 1 = Plotkin et al. (2008, Cat. J/AJ/135/2453); 2 = Laurent-Muehleisen et al. (1999, Cat. J/ApJ/525/127); 3 = Collinge et al. (2005, Cat. J/AJ/129/2542); 4 = Perlman et al. (1998, Cat. J/AJ/115/1253); 5 = Rector et al. (2000AJ....120.1626R); 6 = Perlman et al. (1996ApJS..104..251P); 7 = Landt et al. (2001, Cat. J/MNRAS/323/757).
Global Notes: Note (G1): Flag as follows: d = Based on a merged image composed of Chandra Cycle 4 and Cycle 8 exposures. h = X-ray data obtained from serendipitous XMM-Newton observations. i = A 10.81ks Chandra Cycle 4 exposure of the source (Obs. ID 3958) is not reflected in this Table. The Cycle 8 observation raises the total exposure time on the source to 21.31ks, and the merged event file is used in subsequent analyses throughout the paper (see Shemmer et al., 2006ApJ...644...86S and Section 2 for details). The X-ray count rate, fluxes, luminosities, and αox were obtained from the merged event file of two Chandra exposures in table 3. j = Obtained from the Keck spectrum of Fan et al. (2006AJ....131.1203F). k = Count rate corrected for the exposure map. l = Flux density at an observed-frame frequency of 1.4GHz taken from the NVSS survey (Condon et al. 1998, Cat. VIII/65); upper limits are calculated from the NVSS detection threshold of 2.5mJy.
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 02-May-2011
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