1. The nature and density of Spitzer selected X-ray absorbed AGN:
Identification of sources with large MIR/Optical ratios in the XMM/SWIRE/ELAIS-S1
Fabio La Franca
and
N. Sacchi, S. Puccetti, F. Fiore, C. Gruppioni, C. Feruglio
et al.
Dipartimento di Fisica
Universita` degli Studi ROMA TRE

2. QUESTIONS
-What is the fraction of AGN among the sources with large MIR/O?
-What is the fraction of absorbed AGN?
-Is the density of absorbed AGN compatible to other estimates or
extrapolations (i.e. XLF)?

3. What do we know about the AGN evolution?
A Luminosity Dependent Density Evolution
(LDDE) for X-ray AGN is
observed
(e.g. Ueda+03; Fiore+03; La Franca+05;
Barger+05; Hasinger+05; Gilli+07; Silverman+07; Della Ceca+08)
Lower luminosity AGN
peak at lower redshifts:
DOWNSIZING
(see models of galaxy and
AGN formations)
La Franca+05

4. What do we know about the AGN evolution?
The fraction of absorbed AGN as function of LX and z
INCREASE WITH THE REDSHIFT
assumed *)
DECREASE WITH LUMINOSITY
Earlier evidences of a decrease of the fraction of absorbed AGN with luminosity from Lawrence & Elvis (1982), confirmed by Ueda et al. (2003).
expected
Fraction of Absorbed AGN
La Franca+05
*) Assuming no luminosity and redshift dependences

5. The LX-z plane
Many studies indicate that the majority
of the sources with extreme
F(24um)/F(R) (e.g. >1000) ratios are
obscured/absorbed AGNs
(see e.g. Martinez-Sansigre+05; Houck+05;
Weedman+06; Brown+06; Polletta+06; Yan+07; Daddi+07; Fiore+08; Georgantopoulos+08…) ?
X-ray stacking analysis of MIR selected AGNs
allows to probe more distand, more absorbed,
lower luminosity, regions of the LX-NH-z plane
However,
1) these sources are so faint, that direct optical spectroscopic classifications is available for very few of them;
2) the density estimates are based on assumptions on the NH distribution.

6. Looking for absorbed AGN in the XMM/SWIRE/ELAIS-S1 field
Method: data
AREA
0.6 deg2 (:0.5h, :-43.5o)
IMAGING
BVRIz (PI Franceschini; Berta+06+08)
JK (PI Cimatti/Maiolino; Dias+08)
SWIRE
(PI Lonsdale & Rowan-Robinson)
(3.6, 4.5, 5.8, 8.0 and 24 μm)
X-ray (PI: Fiore) by
XMM 4x100Ks (Puccetti+06)
Chandra x5 (Puccetti in prep)
SPECTROSCOPY
(PI La Franca; Sacchi in prep)
~100 hours with
VIMOS and
Total~1500 Zs (R<24.5)
(K, 3.6um and 24um sources)
Catalogue of ~ m sources with F24 > mJy
Redshift for 384 sources with R<24.2

7. Looking for absorbed AGN in the XMM/SWIRE/ELAIS-S1 field
Method: SED templates fitting
Red Power Law ~AGN1 (SED:1-6)
Adapted from Polletta et al. (2007)
ULIRG/Starburst (SED: 7-9)
Seyfert2/AGN2 (SED:10-13)
Spirals Star Forming (SED:14-20)
Ellipticals (SED:21)

8. Looking for absorbed AGN in the XMM/SWIRE/ELAIS-S1 field
Method: SED templates fitting
(see Polletta et al. 2007)
1st choice
2nd choice
3rd choice
AGN2
AGN1
χ2 best fit
analysis
Normal
Normal
SED

9. Looking for absorbed AGN in the XMM/SWIRE/ELAIS-S1 field
SED classification of high MIR/O sources

10. Looking for absorbed AGN in the XMM/SWIRE/ELAIS-S1 field
SED classification of high MIR/O sources

11. Looking for absorbed AGN in the XMM/SWIRE/ELAIS-S1 field
SED classification of high MIR/O sources

12. Looking for absorbed AGN in the XMM/SWIRE/ELAIS-S1 field
SED classification of high MIR/O sources
20%
43%
34% 3%
Local relationship
un-absorbed AGN
What is the fraction/density
of (possibly absorbed) AGN
among these high MIR/O
sources?
First look at the OPT spectra…

13. Looking for absorbed AGN in the XMM/SWIRE/ELAIS-S1 field
OPTICAL VLT SPECTROSCOPY of faint (R>22) high MIR/O sources
TOTAL: 384 spectra

14. Looking for absorbed AGN in the XMM/SWIRE/ELAIS-S1 field
OPTICAL VLT SPECTROSCOPY of faint (R>22) high MIR/O sources
composite spectra
TOTAL: 384 spectra

15. Looking for absorbed AGN in the XMM/SWIRE/ELAIS-S1 field
OPTICAL VLT SPECTROSCOPY of faint (R>22) high MIR/O sources
composite spectra
TOTAL: 384 spectra
40% AGN2 (& AGN1)
60% ELG
56 spectra
What about their SED?
82% of SED-PWL are optical AGN
93% of SED-ULIRG are optical ELG
SED-Seyfert2: no preferences

16. Looking for absorbed AGN in the XMM/SWIRE/ELAIS-S1 field
X-ray stacking analysys of faint (R>22) high MIR/O sources
X-ray detections and stacking (filled symbols)
STACKED DATA
82% of OPT-AGN
are X-ray absorbed AGN
85% of OPT-ELG
are mildly X-ray absorbed with
L2-10~
MID TERM SUMMARY:
SED-PWL --> optical AGN(2) --> X-ray absorbed AGN
SED-ULIRG --> optical ELG --> mildly absorbed low LX

17. Looking for absorbed AGN in the XMM/SWIRE/ELAIS-S1 field
SED classification of high MIR/O sources
Spec. and phot. redshifts
Spec. and phot. redshifts
Analysis for
∆z= *
i.e.
∆LogL24=
*) At z>1.3 the sample is incomplete becouse
of fainter R>25 unindentified sources
The sources with F24/FR>120 have
z>0.6 and LogL24>44

18. Looking for absorbed AGN in the XMM/SWIRE/ELAIS-S1 field
X-ray properties of low MIR/O sources
X-ray detections and stacking (filled symbols)
Low MIR/O sources show low LX and mild absorption,
compatible with absorbed X-ray spectra of strong
star-forming galaxies

19. 73% of large MIR/O (F24/R>120) sources
Looking for absorbed AGN in the XMM/SWIRE/ELAIS-S1 field
SOFT
keV
HARD
1.5-6 keV
R>25
SED-SEY2
SED-Red PWL
X-ray properties of high MIR/O sources
X-ray detections and stacking (filled symbols)
73% of large MIR/O (F24/R>120) sources
are absorbed AGN
What are their densities?…

20. Looking for absorbed AGN in the XMM/SWIRE/ELAIS-S1 field
Density of X-ray absorbed large MIR/O sources
LogNH~22.3
LogNH~23.1
The density is compatible with the extrapolations
coming from previous estimates at z~1
of the XLF of Compton thin AGN

21. ? Looking for absorbed AGN in the XMM/SWIRE/ELAIS-S1 field
Density of X-ray absorbed large MIR/O sources ?
We have probed a one decade less luminous region at z~1
or a 0.7 larger redshift at LogL2-10~42.5

22. SUMMARY
We have carried out optical spectroscopic identification of 56 sources
with F24/R>120 and R<24.2.
- The fraction of optically classified (or X-ray luminous) AGN is 40(45)%.
SED-PWL --> optical AGN(2) --> X-ray absorbed AGN
SED-ULIRG --> optical ELG --> mildly absorbed, low LX
-According to the X-ray stacking analysis, 73% of the sources are absorbed
(22<LogNH<23.5) AGN with Log(L2-10)>42 cgs.
-Their density is compatible with the extrapolations at z~1 of the XLF
of Compton thin AGN.