GALEX measurements of the Big Blue Bump as

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

Active Galactic Nuclei, powered by accretion onto a Supermassive 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. Accretion rate density Total accreted mass

The XMM-Newton Bright Survey in pills XMM fields used: Covered Area (deg 2): 237 28 Della Ceca et al. , 2004 Caccianiga et al. , 2008 Sources in the bright sample(BSS, 0. 5 -4. 5 ke. V): 389 “ “ “hard” bright sample(HBSS, 4. 5 -7 -5 ke. V): 67 (56 sources are in common) Total Sources: 400 (fx >~7 x 10 -14 erg cm-2 s-1) 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).

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

The sample 263 X-ray selected AGN 1, with NH <4 · 1021 cm-2 CROSS CORRELATION WITH GALEX 63 upper limits 160 matches CROSS CORRELATION WITH SDSS 82 sources having data from XBS-GALEX-SDSS 40 sources out GALEX field All these sources have an X-ray spectra from XMM-Newton which allows us to derive Xray luminosities and spectral properties (e. g. Γ, Nh). • Corral, Della Ceca, Caccianiga and Severgnini, 2010, in preparation • A. Corral: this meeting

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 k. T≈1 -64 e. V , and the normalization has been left has free parameter.

Corrections to measured fluxes Host Galaxy Our Galaxy Hydrogen clouds (Lymanα forest) AGN Observer Intrinsic AGN reddening Galactic reddening: Allen law(1976) Rv =3. 1 EB-V = AB – AV available from the GALEX database The 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. Bohlin et al. 1978

Corrections to measured fluxes- IV Optical emission from the host galaxy SED OF ONE OF THE SOURCES About 20% of the sources have optical SEDs showing a hardening at the optical wavelengths. Optical spectra of these sources contamination by the stars in the host galaxy SDSS GALEX FLUX AGN + host galaxy Calcium break ENERGY (kev) Host galaxy AGN Calcium- break Break at 4000 Å : indicator of the importance of the galaxy star-light in the total emission of the source. F+ e F- mean flux densities in the regions 4050 -4250 Å and 3750 -3950Å (in the source rest-frame) respectively.

Corrections to measured fluxes- IV Optical emission from the host galaxy Model formulated to correct for the emission of the host galaxy Ca break≈40% ü Model of a normal galaxy: Heaviside function such that Δ=50% H. GALAXY+AGN ü AGN: αν =-0. 44 (αλ =-1. 56). HOST GALAXY FLUX (Vanden Berk et al. 2001) Δ from the combined emission of the AGN (with different normalizations) and host galaxy λ (Å) H. G FLUX ü We calculated the resulting FLUX RATIO AGN/GALAXY AGN ALA XY+ AGN HOST GALAXY Break at 4000 Å Ca break≈2% λ (Å)

BEFORE CORRECTION AFTER CORRECTION Δ=17. 3% SDSS L+A GALEX AGN GN SDSS 0. HOST GALAXY FLUX GA GALEX 0. ENERGIA (ke. V) ENERGY (ke. V) 0. SDSS GALEX FLUX Δ=33. 2% GAL+AGN SDSS GALEX HOST GALAXY AGN ENERGY (ke. V)

Corrections to measured fluxes Emission lines contribution 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… TIPICAL SPECTRA OF AN AGN FLUX Assuming R ~1 WAVELENGTH (Å) 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.

SPECTRAL ENERGY DISTRIBUTIONS OPTICAL-UV FLUSSI OTTICO-UV X-ray (XMM) FLUSSI OTTICO-UV X-ray FLUSSI XMM FLUSSIX X FLUSSI X ENERGIA (ke. V) Median maximum temperature : k. T ≈ 4 e. V

2 -10 ke. V luminosity 0. 1 -100 ke. Vluminosity Accretion disk luminosity Available for every object from the X-ray spectral analysis (Corral et al. 2010) Extrapolated from the 2 -10 ke. V luminosity, using the spectal index measured for every sorce Calculated as the integral of the SEDs in the optical-UV bands. L bol =L disc + L 0. 1 -100 ke. V

63 sources with XBSGALEX upper limits 78 sources with XBS-GALEX data 82 sources with XBS-GALEX-SDSS data discussed so far UV fluxes or their upper limits were fitted with the same model with a Tmax fixed to k. T ≈ 4 e. V

Results - I CORRELATION LDISK – L 2 -10 ke. V Strong dependence of the accretion disk luminosities to the X-ray luminosities the two emission mechanisms are highly correlated 78 sources XBS-GALEX 82 sources XBS-GALEXSDSS Best-fit bisector relation: 63 sources XBSGALEX upper limits In good agreement with previous results on X-ray selected sources: Lusso et al. 2010: β=1. 31± 0. 038

Results - II BOLOMETRIC CORRECTION AGAINST HARD X-RAY LUMINOSITY 78 sources XBS-GALEX 63 sources XBSGALEX upper limits üWe don’t find any significant correlation between bolometrc correction and X-ray luminosities 82 sources XBS-GALEXSDSS üThis 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

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