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Red quasars in the2XMMi/SDSS-DR7 cross-correlation
Angel Ruiz&R. della Ceca, A. Caccianiga, P. Severgnini, F. X. Pineau, V. Braito
Santander, 23rd November 2010
Summary
Introduction
Sample selection
X-ray analysis
Optical analysis
Conclusions
Introduction
Quasars typically selected as point-like objects bluer than stars (e.g. U-B < -0.44)
Blue colors related to the Big Blue Bump (BBB) accretion disk.
Red quasars Reddening by dust (Cutri et al. 2003)
New surveys discovered a population of intrinsic red quasars (no dust) Diminished BBB (Hall et al. 2006, Young et al. 2008)
Long term objectives:Build a large sample of intrinsic red quasars
Check the absence of the BBB (opt-UV SED)
Understand why the BBB has disappeared (e.g. low accretion rates)
Young et al. 2008: SDSS-dr3 / XMM Archive cross-correlation.Selection criteria: g-r>0.5
To avoid host galaxy (z>0.5) and Lya forest (z 0.35
D(g-i)
g-r
D(g - i)
g - r
Outline
Separate dust reddening QSO and intrinsic red QSO.
Study of the X-ray spectra:XMM-Newton/EPIC spectra automatically
extracted (V. Braito)
bright sources (>100 counts) only: 29 sources
Goal: estimate X-ray absorption.
Spectral model:Power law + intrinsic absorption
Power law + NH upper limit (90% confidence)
Study of the optical spectra:Goal: estimate E(B-V)
Spectral model:Dust:Composite QSO template (Vanden Berk et al. 2001)
SMC extinction law (Gordon et al. 2003)
No dust: Powerlaw: Fn na
X-ray results
1-2 keV flux / erg s-1 cm-2
c2 / d.o.f.
All sources well fitted
X-ray results
1-2 keV flux (erg s-1 cm-2)
NH (x1022 cm-2)
Absorption limit
X-ray results
1-2 keV flux (erg s-1 cm-2)
G
Young et al. 2008
Mateos et al. 2005
= 1.8 0.3
X-ray results
1-2 keV flux (erg s-1 cm-2)
G
= 1.8 0.3
Absorption limit
X-ray results
Xray absorbed sources:NH > 1022 @ 90% confidence: 4 sources
NH UL > 1022 and G 1022 @ 90% confidence: 4 sources
NH UL > 1022 and G0
Normal blue PL cont.: D(u-r) ~ D(g-i) ~ D(r-z)
Dust reddening cont.: D(u-r) > D(g-i) > D(r-z)
Redder PL continuum: D(u-r) < D(g-i) > D(r-z)
D(u-r) D(g-i) > 0 Dust red. continuumD(u-r) D(g-i) < 0 Intrinsic red continuum
Continuum shape
E(B-V)
D(u-r) - D(g-i)
PL
continuum
dust
continuum
Continuum shape
NH (x1022 cm-2)
D(u-r) - D(g-i)
X-ray absorption vs. optical extinction
NH (x1022 cm-2)
E(B-V)
High X-ray absorption Low X-ray absorption
GALEX UV colours
PL
continuum
dust
continuum
21 out of 29 sources with GALEX data
NUV - i
D(u-r) - D(g-i)
GALEX UV colours
PL
continuum
dust
continuum
21 out of 29 sources with GALEX data
FUV - i
D(u-r) - D(g-i)
Gas-to-dust ratio
NH / E(B-V)
Galactic ratio
high E(B-V) dust continuum int. red continuum
D(u-r) - D(g-i)
Conclusions
No clear link between X-ray absorption and optical obscuration (i.e. due to gas and dust) X-ray properties are not reliable to distinguish intrinsically red QSO.
7-9 intrinsically red QSO: ~25% of the X-ray bright red sample < 40% of Young et al. 2008
Conclusions
No clear link between X-ray absorption and optical obscuration (i.e. due to gas and dust) X-ray properties are not reliable to distinguish intrinsically red QSO.
7-9 intrinsically red QSO: ~25% of our X-ray bright red sample < 40% of Young et al. 2008
TODO:Correct optical photometry for strong emission lines.
Extend the analysis to the X-ray faint sources.
Build optical-to-X-ray SED of the continuum.