GALEX measurements of the Big Blue Bump as a tool to study bolometric corrections
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GALEX measurements of the Big Blue Bump as a tool to study bolometric corrections
Elena MarcheseR. Della Ceca, A. Caccianiga, P. Severgnini, A. Corral
Active Galactic Nuclei 9 – Ferrara , 24-27 May 2010
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Study the spectral energy distribution (SED) of type 1 AGN in the optical, Near and Far-UV and X-ray energy bands .
Constrain the luminosity of the accretion disk emission component Derive the hard X-ray bolometric correction factors for a significant
sample of Type 1 AGN spanning a large range in z and Lx.
XXX
L
LBH LdLLK
cz
X
X
log)(1)(max,
2
Accretion rate density
dzdzdtzz
z
BHBH max
0
)()( Total accreted mass
Active Galactic Nuclei, powered by accretion onto a Super-massive Black Hole (SMBH), emit over the entire electromagnetic spectrum with the peak of the accretion disk emission in the far-UV, a wavelength range historically difficult to investigate.
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The XMM-Newton Bright Survey in pills XMM fields used: 237Covered Area (deg2): 28
Sources in the bright sample(BSS,0.5-4.5keV): 389 “ “ “hard” bright sample(HBSS,4.5-7-5 keV): 67
(56 sources are in common)
Total Sources: 400 (fx >~7x10-14 erg cm-2 s-1)
Della Ceca et al., 2004Caccianiga et al., 2008
The starting point of our study is a sample of 304 AGNs, counting 263 type 1 AGNs having intrinsic NH <4 ·1021 cm-2, belonging to the
XMM-Newton Bright Serendipitous Survey (XBS).
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GALEX (Galaxy Evolution Explorer) is a NASA Small Explorer mission that is performing surveys of different depths/sky coverage
in the far-UV and near-UV
The GALEX mission in pills
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CROSS CORRELATION WITH GALEX
160 matches 63 upper limits
263 X-ray selected AGN 1, with NH <4 ·1021 cm-2
CROSS CORRELATION WITH SDSS
82 sources having data from XBS-GALEX-SDSS
The sample
All these sources have an X-ray spectra from XMM-Newton which allows us to derive X-ray luminosities and spectral properties (e.g. Γ, Nh).
• Corral, Della Ceca, Caccianiga and Severgnini, 2010, in preparation
• A. Corral:this meeting
40 sources out GALEX field
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• The data points from the SDSS and from GALEX were described using a basic accretion disk model (DISKPN model in the XSPEC package). The maximum disc temperature was chosen in the range kT≈1-64 eV , and the normalization has been left has free parameter.
The model
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Corrections to measured fluxes
Observer
Our Galaxy
Amm oss ,
VB
VV E
AR
AGN
Galactic reddening:Allen law(1976) Rv =3.1 EB-V = AB – AV available from the GALEX database
Intrinsic AGN reddeningThe exact shape of the extinction curve in the Near-Far-UV is still a matter of debate
Gaskell e Benker, 2007 determined a parametrized average extinction law from
the study of 14 AGN, with FUSE and HST data.
1221108.4
magcmEN
VB
H
Bohlin et al. 1978
Host Galaxy
Hydrogen clouds (Lymanα forest)
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Corrections to measured fluxes- IVOptical emission from the host galaxy
About 20% of the sources have optical SEDs showing a hardening at the optical wavelengths. Optical spectra of these sourcescontamination by the stars in the host galaxy
Break at 4000 Å : indicator of the importance of the galaxy star-light in the total emission of the source.
Calcium- break
FFF
F+ e F- mean flux densities in the regions 4050-4250 Å and 3750-3950Å (in the source rest-frame) respectively.
AGNHost galaxy
AGN + host galaxy
Calcium break FL
UX
ENERGY (kev)
SDSS GALEX
SED OF ONE OF THE SOURCES
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Model formulated to correct for the emission of the host galaxy
Model of a normal galaxy: Heaviside function such that Δ=50%
AGN: αν =-0.44 (αλ =-1.56).(Vanden Berk et al. 2001)
We calculated the resulting Δ from the combined emission of the AGN (with different normalizations) and host galaxy
FLU
X RA
TIO
AGN
/GAL
AXY
Break at 4000 Å
Ca break≈40%
HOST GALAXY
AGN
H.GALAXY+AGN
FLU
X
λ (Å)
HOST GALAXY
AGN
H. GALAXY+AGN
FLU
X λ (Å)Ca break≈2%
Corrections to measured fluxes- IVOptical emission from the host galaxy
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HOST GALAXY
AGN
GAL+AGN
AGN
HOST GALAXY
GAL+AGN
Δ=17.3%
Δ=33.2%
0.
0.
ENERGIA (keV)
FLU
X FL
UX
ENERGY (keV)
ENERGY(keV)
SDSS
SDSS
GALEX
GALEX FLU
X FL
UX 0.
ENERGY (keV)
ENERGY (keV)
SDSS
SDSSGALEX
GALEX
AFTER CORRECTIONBEFORE CORRECTION
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The presence of emission lines within the filter bandpass can contribute significantly to the observed magnitudes of an AGN. Since this effect is a strong function of redshift, we need to take it into account to derive the continuum…
Assuming R ~1
Average spectra and equivalent widths of the emission lines present in the energy bands we are studying, calculated by Telfer et al. 2002, from the spectra of 184 quasars with z>0.33 .
Corrections to measured fluxesEmission lines contribution
FLU
X
WAVELENGTH (Å)
TIPICAL SPECTRA OF AN AGN
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FLUSSI OTTICO-UV
FLUSSI X
ENERGIA (keV)
FLUSSI OTTICO-UV
FLUSSI X
ENERGIA (keV)
FLUSSI OTTICO-UV
FLUSSI X
ENERGIA (keV)
OPTICAL-UV
X-rayXMM
ENERGIA (keV)
SPECTRAL ENERGY DISTRIBUTIONS
OPTICAL-UV
X-ray (XMM)
ENERGIA (keV)
Median maximum temperature : kT ≈ 4 eV
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2-10 keV luminosityAvailable for every object from the X-ray spectral analysis (Corral et al. 2010)
0.1-100 keVluminosity Extrapolated from the 2-10 keV luminosity, using the spectal index measured for every sorce
Accretion disk luminosity
Calculated as the integral of the SEDs in the optical-UV bands.
L bol =L disc + L 0.1-100 keV
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82 sources with XBS-GALEX-SDSS data discussed so far
78 sources with XBS-GALEX data
63 sources with XBS-GALEX upper limits
UV fluxes or their upper limits were fitted with the same model with a Tmax
fixed to kT ≈ 4 eV
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Strong dependence of the accretion disk luminosities to the X-ray luminosities the
two emission mechanisms are highly correlated
Results - I CORRELATION LDISK – L2-10keV
Best-fit bisector relation:
913.8log)056.0232.1(log 102 keVdisc LL
In good agreement with previous results on X-ray selected sources: Lusso et al. 2010: β=1.31±0.038
78 sources XBS-GALEX
82 sources XBS-GALEX-SDSS
63 sources XBS-GALEX upper limits
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keV
bolbol L
Lk102
We don’t find any significant correlation between bolometrc
correction and X-ray luminosities
This is probably due to a very large spread in the distributions of
the hard X-ray bolometric corrections, going from ~5 up to few hundred, implying a large dispersion in the mean SED
Results - II BOLOMETRIC CORRECTION AGAINST HARD X-RAY LUMINOSITY
63 sources XBS-GALEX upper limits
78 sources XBS-GALEX
82 sources XBS-GALEX-SDSS
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We used a sample of 223 sources spanning a large range in X-ray luminosities (LX ≈1041 – 1046 erg/s) and redshift (z≈0-2.4) and we find :
• A high correlation between the accretion disk luminosity and the X-ray luminosity, in agreement with previous works on X-ray selected AGNs.
• A very large spread in the distributions of the hard X-ray bolometric corrections, going from ~5 up to few hundred -> a large intrinsic dispersion in the mean SED;
Conclusions
Thank you