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GALEX measurements of the Big Blue Bump as a tool to study bolometric corrections. Elena Marchese R. Della Ceca, A. Caccianiga, P. Severgnini, A. Corral. Active Galactic Nuclei 9 – Ferrara , 24-27 May 2010. Accretion rate density. Total accreted mass.

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galex measurements of the big blue bump as a tool to study bolometric corrections

GALEX measurementsof the Big BlueBumpas a tooltostudybolometriccorrections

Elena Marchese

R. Della Ceca, A. Caccianiga, P. Severgnini, A. Corral

Active Galactic Nuclei 9 – Ferrara , 24-27 May 2010

slide2

Accretion rate density

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.

  • 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.
slide3

The XMM-Newton Bright Survey in pills

XMM fields used: 237

Covered Area (deg2): 28

Sources in the bright sample(BSS,0.5-4.5keV): 389

“ “ “hard” bright sample(HBSS,4.5-7-5 keV): 67

(56sources are in common)

Total Sources: 400(fx>~7x10-14 erg cm-2 s-1)

Della Ceca et al., 2004

Caccianiga 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).

slide4

The GALEX mission in pills

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

slide5

The sample

263 X-ray selected AGN 1, with NH <4 ·1021 cm-2

CROSS CORRELATION WITH GALEX

40 sources out GALEX field

63 upper limits

160 matches

  • 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

CROSS CORRELATION WITH SDSS

82 sources having data from XBS-GALEX-SDSS

the model
The model
  • 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.
slide7

Correctionstomeasuredfluxes

Host Galaxy

Our Galaxy

AGN

Hydrogenclouds (Lymanαforest)

Intrinsic AGN reddening

The exact shape of the extinction curve in the Near-Far-UV is still a matter of debate

Observer

Galacticreddening:

Allen law(1976)

Rv =3.1

EB-V = AB – AV available from the GALEX database

Gaskell e Benker, 2007

determined a parametrized average extinction law from the study of 14 AGN, with FUSE and HST data.

Bohlin et al. 1978

slide8

Corrections to measured fluxes- IVOptical emission from the host galaxy

SED OF ONE OF THE SOURCES

About 20% of the sourceshaveopticalSEDsshowing a hardening at the opticalwavelengths.

Opticalspectraofthesesourcescontaminationby the stars in the hostgalaxy

SDSS

GALEX

AGN + hostgalaxy

FLUX

Calcium break

ENERGY (kev)

Break at 4000 Å : indicatorofthe importanceof the galaxy star-light in the total emissionof the source.

Hostgalaxy

AGN

F+ e F-meanfluxdensities in the regions4050-4250 Å and 3750-3950Å (in the source rest-frame) respectively.

Calcium- break

slide9

Corrections to measured fluxes- IVOptical emission from the host galaxy

Modelformulatedtocorrectfor the emissionof the hostgalaxy

  • Modelof a normalgalaxy: HeavisidefunctionsuchthatΔ=50%

Ca break≈40%

  • Wecalculated the resultingΔfrom the combined emission of the AGN (with different normalizations) and host galaxy

H.GALAXY+AGN

  • AGN: αν =-0.44 (αλ =-1.56).
  • (Vanden Berk et al. 2001)

HOST GALAXY

FLUX

AGN

λ (Å)

H. GALAXY+AGN

FLUX RATIO AGN/GALAXY

FLUX

AGN

HOST GALAXY

Break at 4000 Å

λ (Å)

Ca break≈2%

slide10

BEFORE CORRECTION

AFTER CORRECTION

Δ=17.3%

GAL+AGN

AGN

SDSS

GALEX

FLUX

SDSS

GALEX

HOST GALAXY

0.

0.

FLUX

ENERGY(keV)

ENERGIA (keV)

ENERGY (keV)

Δ=33.2%

SDSS

GAL+AGN

FLUX

SDSS

FLUX

GALEX

GALEX

0.

HOST GALAXY

AGN

ENERGY (keV)

ENERGY (keV)

slide11

Corrections to measured fluxesEmission lines contribution

The presenceofemissionlineswithin the filterbandpass can contributesignificantlyto the observedmagnitudesofan AGN. Sincethiseffectis a strong functionofredshift, weneedto take itinto account to derive the continuum…

TIPICAL SPECTRA OF AN AGN

Assuming R ~1

FLUX

WAVELENGTH (Å)

Averagespectra and equivalentwidthsof the emissionlinespresent in the energybandswe are studying, calculatedbyTelferet al. 2002, from the spectraof 184 quasarswith z>0.33 .

spectral energy distributions
SPECTRAL ENERGY DISTRIBUTIONS

OPTICAL-UV

FLUSSI OTTICO-UV

FLUSSI OTTICO-UV

FLUSSI OTTICO-UV

OPTICAL-UV

X-ray (XMM)

X-ray

XMM

FLUSSI X

FLUSSI X

FLUSSI X

ENERGIA (keV)

ENERGIA (keV)

ENERGIA (keV)

ENERGIA (keV)

ENERGIA (keV)

Medianmaximum temperature : kT ≈ 4 eV

slide13

Availableforeveryobjectfrom the X-rayspectralanalysis (Corralet al. 2010)

2-10 keVluminosity

Extrapolatedfrom the 2-10 keVluminosity, using the spectalindexmeasuredforeverysorce

0.1-100 keVluminosity

Accretion disk luminosity

Calculatedas the integralof the SEDs in the optical-UVbands.

L bol=Ldisc + L 0.1-100 keV

slide14

UV fluxes or their upper limits were fitted with the same model with a Tmax fixed to kT ≈ 4 eV

63 sources with XBS-GALEX upper limits

78 sources with XBS-GALEX data

82 sources with XBS-GALEX-SDSS data discussed so far

results i
Results - I

CORRELATION LDISK – L2-10keV

Strong dependenceof the accretion disk luminositiesto the X-rayluminosities the twoemissionmechanisms are highlycorrelated

78 sources XBS-GALEX

82 sources XBS-GALEX-SDSS

Best-fit bisector relation:

In good agreement withpreviousresults on X-rayselectedsources:

Lusso et al. 2010: β=1.31±0.038

63 sources XBS-GALEX upper limits

slide16

Results - II

BOLOMETRIC CORRECTION AGAINST HARD X-RAY LUMINOSITY

63 sources XBS-GALEX upper limits

78 sources XBS-GALEX

  • 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

82 sources XBS-GALEX-SDSS

conclusions
Conclusions

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;

Thank you