1. Astronomical Observatory of Rome Arcetri Astrophysical Observatory
X-ray absorption in AGNs
Roberto Maiolino
Astronomical Observatory of Rome
Guido Risaliti
Arcetri Astrophysical Observatory

2. Emission components
power law
FeK
cold reflection

3. Warm absorber NH~1022 cm-2 0.2 < D < 20 pc 2-3 components
Kaspi+ 02, Netzer+03, Krongold+ 03
0.2 < D < 20 pc
NH~1022 cm-2
2-3 components
in pressure eq.

4. Cold absorber

5. Evidence for cold absorption in X-ray spectra

6. Warnings: X-ray absorption due to metals
 assumption on metallicity to convert Nmet  NH
A reflection-dominated spectrum
may be associated
with a “fossil” AGN
(not Compton thick)
Gilli+ 00, Matt+04, Guainazzi+ 06 FX
EW(FeK)

7. NH distribution among AGNs
[OIII] selected
Risaliti+ 99
Salvati & Maiolino 01
Distance limited
10-100keV selected
Radio selected
Markwardt+ 05
Bassani+ 06
Cappi+ 06
Guainazzi+ 06
Sambruna+ 99, Grandi+ 06

8. Heavily obscured AGNs escaping the census
NGC 3690: HII optical spectrum, LX=2x1043 erg s-1, NH=3x1024 cm-2
FeK line
Della Ceca+ 02
Ballo+ 04
More cases in local galaxies:
optical  Sy2
X-ray  heavily absorbed Sy2
Maiolino+ 03, Imanishi+ 06,02, Vignati+ 99, Guainazzi+ 00
Also at high-z
Comastri+ 02, Severgnini+ 03, Barger+ 05, Cocchia+ 06, Szokoly+ 04

9. X-ray absorption on large scales torii / dust lanes / host disk
400 pc
520 pc
~100pc-scale
torii / dust lanes / host disk
Compton thin
Maiolino & Rieke 95
Malkan+ 98
Matt 00
Guainazzi+ 05

10. X-ray absorption on small scales
Dynamical mass constraints on
the size of the Compton thick absorber 
Circinus, NH= 4x1024 cm-2
torus mass
dynamical mass
log Mass (M)
allowed
Risaliti+ 99
R (pc)

11. X-ray absorption on small scales: NH variability
torus
BLR
torus
BLR
t ~ years
Risaliti+ 06
Elvis+ 05
Puccetti+ 06
t ~ weeks
Risaliti+ 02

12. optical and X-ray classification
X-ray absorption versus optical absorption
AV/NH generally lower than Galactic
Mismatch between
optical and X-ray classification
(type 1)
log NH (cm-2)
Wilkes+ 02, Hall+ 05
Most extreme cases
are BAL QSOs
Maiolino+ 01
Gallagher+ 06, Maiolino+ 01, Braito+ 04
Why?
Dust-free X-ray absorber
Dust properties
More cases at high-z
Szokoly+ 04, Barger+ 05
Fiore+ 03, Silverman+ 05

13. X-ray absorption versus IR absorption
Silicate 9.7m feature
Mid-IR continuum
NHSi
Shi+ 06
NHX
Silva+ 04
Why?
Dust-free X-ray absorber
Dust properties
Mid-IR emission much more
extended than X-ray absorber

14. X-ray absorption in high luminosity QSO (QSO2’s)
Extistence questioned until a few years ago.
Difficult to find because absorbed and rare.
Large numbers of QSO2’s have now been found
by systemic surveys over large sky area:
Optical Zakamska+ 03, Ptak+ 06
X-ray Norman+ 02, Fiore+ 03, Severgnini+ 03,
Barger+ 05, Silverman+ 05, Maccacaro+04
Infrared Martinez-Sansigre+ 05, Polletta+ 06,
Alonso-Herrero+ 06, Braito+04, Franceschini+ 05
Radio Hardcastle+ 06, Donley+ 05,
Grandi+ 06, Risaliti+ 03, Vink+ 06
IRAS z=0.44
LX = 2x1046 erg s-1
NH > 5x1024 cm-2
Franceschini+ 00

15. These AGN2’s are mostly Compton thin
Fraction of absorbed AGN versus luminosity
AGN2/AGN1 decreases with luminosity
Hasinger 06, Ueda+ 04,
La Franca+ 05, Barger+ 05, Akylas+ 06
X-ray surveys
(but see also Dwelly+06, Treister & Urry 05)
Tozzi+ 06
These AGN2’s are mostly
Compton thin
observed NH distr. in CDFS
sensitivity corrected
Theoretically explained
with “receiding turus” or
BH dynamical effects
Lamastra+ 06, Wada & Norman 04

16. Inferred from X-ray background
Fraction of Compton thick AGNs at high-z
Inferred from
X-ray background
Compton thick AGNs
from Spitzer surveys
Polletta+ 06
Alonso-Herrero+06
X-ray undetected
IR QSO
X-ray detected
AGN2 thin
AGN1
C-thick/C-thin ~ 2  local ratio
Gilli+ 06
required
by XRB

17. Open issues:
Geometry and dynamics
- Distance: is a compact (~BLR scale) absorber ubiquitous?
- Do every AGN have Compton-thick gas around it ?
Structure: two phase medium (cold, dense clouds inside
warm gas),
or more homogeneous, cold gas with density
gradients ?
Stability: how is the vertical structure supported ?
Dynamical stability (inflow, outflow) ?

18. AGNs with nuclear H2O maser disks are NOT preferentially Compton thick
Open issues
AGNs with nuclear H2O maser disks
are NOT preferentially Compton thick
Zhang+ 06
log NH (cm-2)
NH > cm-2
disk inclination < 10
required for maser amplification

19. X-ray obscuration (< pc) correlated
Open issues
X-ray obscuration (< pc) correlated
with bars in the host galaxy (> kpc)
STRONGLY-BARRED
WEAKLY-BARRED
NON-BARRED
adapted from
Cappi+ 06 & Guainazzi+ 05
Maiolino+ 99

20. THE END