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The nature of X-ray selected Broad Absorption Line Quasars
Alex Blustin
With Tom Dwelly (Southampton), Mat Page (UCL-MSSL)
UCL-MSSL and IoA, Cambridge
X-ray Universe 2008, Granada, Spain
What are Broad Absorption Line Quasars (BALQSOs)?
Quasars with very broad restframe UV absorption features from the wind:
z ~ 0.1 – 6
wind outflow speed up to60,000 km/s
NH ~ 1024 cm-2
Rarely detectable in X-rays due (probably) to high absorption from the ionised wind
Why have we started to find BALQSOs in X-ray surveys?
Optically-selected (OBALQSOs): discovered in optical surveys
X-ray selected (XBALQSOs): discovered in X-ray surveys
Why have we started to find BALQSOs in X-ray surveys?
Optically-selected (OBALQSOs): discovered in optical surveys
X-ray selected (XBALQSOs): discovered in X-ray surveys
Are they easier to detect in the X-rays due to low absorption from the wind?
Are they exceptionally luminous BALQSOs with high dust extinction (hence faint in optical but bright in X-rays)?
Do they have intrinsically higher X-ray to optical flux ratios?
XBALQSOs in two deep XMM-Newton X-ray survey fields
1H field
CDFS
~400 ksXMMEPIC
z = 2.63
z = 1.793
z = 1.40
z = 2.64
z = 2.82
~100 ksXMMEPIC
Keck-LRIS
Keck-LRIS
Keck-LRIS
WHT-AF2 WYFFOS
VLT-FORSSzokoly et al. 2004
XBALQSOs in two deep XMM-Newton X-ray survey fields
1H field
CDFS
~400 ksXMMEPIC
C IV 1549 Å absorption from wind
z = 2.63
z = 1.793
z = 1.40
z = 2.64
z = 2.82
~100 ksXMMEPIC
Keck-LRIS
Keck-LRIS
Keck-LRIS
WHT-AF2 WYFFOS
VLT-FORSSzokoly et al. 2004
Fitting the X-ray absorption due to the wind
Same velocity structure as in UV
Standard Spectral Energy Distribution (SED)/continuum for absorber model generation and spectral fitting
Same ionisation parameter and column NH
for all velocity components
Few X-ray counts in spectra
We need to make some assumptions:
Velocity structure of the (rest-frame) UV-absorbing wind
Vout
= 670, 2170 km/s FWHM = 1140, 2610 km/s
Vout
= 1680 km/s FWHM = 2430 km/s
Vout
= 4100, 1330 km/s FWHM = 2390, 1460 km/s
Vout
= 12740, 18750 km/s FWHM = 3790, 5210 km/s
Vout
= 1900, 4220 km/s FWHM = 1940, 3220 km/s
Spectral Energy Distributions
Based on Marconi et al. 2004 Read-out from refl reflection model in SPEX 2.00.11
X-ray to optical slope set using
ox calculated from 2500 Å flux
(Vignali, Brandt & Schneider 2003)
X-ray fits
Three free parameters:
continuum normalisation
absorbing column NH
ionisation parameter
Spectra from XMM-Newton EPIC (combined)
Is there less X-ray absorption from the wind in XBALQSOs?
PG1115+080 (Chartas et al. 2007)Q1246-057 (Grupe et al. 2003)SBS1542+541 (Grupe et al 2003)PG2112+059 (Gallagher et al. 2004)
OBALQSOs
Is there less X-ray absorption from the wind in XBALQSOs?
If so, XBALQSOs here
OBALQSOs
PG1115+080 (Chartas et al. 2007)Q1246-057 (Grupe et al. 2003)SBS1542+541 (Grupe et al 2003)PG2112+059 (Gallagher et al. 2004)
Is there less X-ray absorption from the wind in XBALQSOs?
If so, XBALQSOs here
OBALQSOsXBALQSOs
Is there less X-ray absorption from the wind in XBALQSOs?
Probably not
OBALQSOsXBALQSOsNearby AGN (Blustin et al. 2005)
How does the UV absorption by the wind compare?
Consistent with amount of UV line absorption in SDSS OBALQSOs
SDSS OBALQSOs from Trump et al. 2006
Are XBALQSOs just highly luminous BALQSOs with extra dust extinction?
OBALQSOs (Gallagher et al. 2006)XBALQSOs
No, consistent with OBALQSOs
Expected B-Ks for SDSS QSOs
Vanden Berk et al. 2001
X-ray flux, optical flux and ox
Log
2 ke
V f
lux
Log
2500
Å f
lux
ox
OBALQSOs: medianox
= -2.20 (stdev 0.21)
XBALQSOs: medianox
= -1.90 (stdev 0.13)
Given the median UV fluxes of the samples, the Vignali, Brandt & Schneider (2003) relation
predicts a 0.13 difference in ox
; we observe a difference of 0.30.
OBALQSOs (Gallagher et al. 2006)XBALQSOs
X-ray flux, optical flux and ox
Log
2 ke
V f
lux
Log
2500
Å f
lux
ox
OBALQSOs: medianox
= -2.20 (stdev 0.21)
XBALQSOs: medianox
= -1.90 (stdev 0.13)
Given the median UV fluxes of the samples, the Vignali, Brandt & Schneider (2003) relation
predicts a 0.13 difference in ox
; we observe a difference of 0.30.
The XBALQSOs may have an intrinsically higher X-ray to optical flux ratio than the OBALQSOs
OBALQSOs (Gallagher et al. 2006)XBALQSOs
Conclusion:
These XBALQSOs are probably not fundamentally different from the broader BALQSO population.
However - they are relatively X-ray rich.
Deep (hard) X-ray surveys are now sensitive to this part of the AGN population...
As (hard) X-ray surveys get deeper, we can expect to detect a lot more BALQSOs like these in X-rays.
