Cosmological Evolution of
Blazars:
new findings from the Swift/BAT and
Fermi/LAT surveys
M. Ajello [KIPAC/SLAC]
L. Costamante, R. Sambruna, N. Gehrels, J. Greiner, J. Tueller,
J. Chiang, A. Escala, R. Mushotzky, A. Rau, J. Wall
+
On behalf of Fermi/LAT collaboration
Instruments
Fermi-LAT
Band: 0.1-300 GeV
FoV: 2.4 sr
Monitor: 100% sky/3hr
Pos. res.: 3’-21’
Swift-BAT
Band: 15-200 keV
FoV: 1.4 sr
Monitor: 70% sky/day
Pos. res.: 1’-5’
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Why to study blazars at high-E ?
Ajello+, 2008, ApJ, 689, 666
@ -rays
@ hard -rays
-Blazars are >85% of extraG.
-Blazars are ~15% of extraG.
sources
-Evolution of blazars studied
with EGRET: low numbers
-GeV background ?
sources
-Evolution of blazars unknown
-MeV background unexplained
(see Inoue+08 and ref. therein)
M. Ajello
(see Chiang+98,Dermer+05,Narumoto+06)
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PKS 0528+134
Ghisellini+99
Tagliaferri+00
IBL
HBL
Pian+98
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FSRQ
FSRQs and
IBL/LBL ‘peak’
in the MeV band
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The BAT 3yr Sample
Ajello+09,ApJ 699, 603
Seyferts
blazars
• 38 blazars (26 FSRQs, 12 BL Lacs) detected up to z~4
• 9 FSRQs and 3 BL Lacs in common with EGRET/LAT
• No blazars at low LX and low redshift
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Test of Evolution
• Luminosity function needed to assess the
contribution of a source class to the diffuse
background
Seyferts
Blazars
1. Blazars evolve positively
at ~3
2. No significant
difference between the
2 sub-classes
3. Seyferts ‘do not’ evolve
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Parametric XLF
Luminosity Evolution
i.e. objects were more
luminous in the past
Lx(z)=(1+z)k Lx
Density Evolution
i.e. objects were more
numerous in the past
(L,z)= (L,0) (1+z)k
Method
(Marshall+83, Borgani+01, Wall+05)
Maximize Likelihood function based on the product of
Poisson prob. of observing 0 or 1 blazars in a dLxdz
element:
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Best-fit XLF for entire population
Best Fit Model:
PLE with a redshift
cutoff coupled to a local
double power law XLF
Parameters:
1=-0.871.31 <--beaming?
2= 2.730.38 (Urry&Schafer84)
k= 3.45 0.44
=-0.25 0.07 <--3
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Separating the populations
FSRQs (26)
BL Lacs (12)
Best fit model:
PLE: k=3.67, =-0.30
Best fit model:
Local XLF slope: 2.49 ±0.37
Local XLF slope: 2.61 ±0.36
PLE: k=-0.8±2.4 !!
Claim of negative (Rector+00,
Beckmann+03) or no (Caccianiga+02,
Padovani+07) evolution not
confirmed/denied
BL Lacs ‘produce’ <1% CXB
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The MeV Background
•Blazars produce:
–10% of CXB @ 2-10 keV
–20% of CXB @ 15-55 keV
–~100% CXB @ 1 MeV
RQ AGN, from Gilli+07
•FSRQs detected by BAT
AGN,at
from
Gilli+07
mustRQpeak
‘MeV’
energy
not to violate CXB constraint
FSRQs
•EGRET did not detect highz BAT blazars. According to
Zhang+05, Sambruna+07, FSRQs
Tavecchio+07, Watanabe+09 they
are MeV blazars
Watanabe+09
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The LAT view of blazars
(Abdo et al. 2009, ApJ 700, 597)
• Aug/Sep/Oct high confidence list: 205 sources with >10 detection
• 132 with |b| > 10 (7 pulsars, 14 unid)
– 111/125 are bright, flat spectrum radio sources
– 98/111 have optical classifications, 89/111 have redshifts
FSRQ
BL Lac
Radio Galaxy
Uncertain
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Some Key Properties
LAT
BLLacs
FSRQs
nFn
nFn
BAT
n
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n
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Blazar Evolution in LAT
FSRQs (59)
Strong Positive Evolution
V/Vm=0.6450.043
Power-law slopes: ~2.5
BL Lacs (29)
No significant Evolution
V/Vm=0.4220.055
But: 13/42 BL have no z
Power-law slopes: ~2.2
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Anti-hierarchical growth
• Larger structures comes
first: tracing the
merging history of
spheroids (eg. Franceschini+99)
• The bulk of supermassive BHs is formed
at z~1 : tracing the SFR
of galaxies (eg. Madau+99)
• Beaming allows to study
AGNs at large z
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Hasinger+05
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Galaxy-AGN co-evolution
•SMBHs and galaxies coevolve through the history of
the Universe
–MBH-relation (e.g.Merrit&Ferrarese01)
–Co-evolution of SFR and AGN
(e.g. Madau99, Hasinger+05)
Hasinger+05
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AGN-Cluster Interaction
AGNs inflates cavities in the ICM
Total non-thermal pressure in the
atmospheres of giant E gal is ~10%
(Churazov+09)
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Abdo+, ApJ 699, 31
Turbulent pressure <5%(Werner+09)
CR pressure <15%
(Keith’s talk)
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Conclusions
• Blazars in BAT are 15% of total AGN population
– Strong evolution (PLE) with evidence for a redshift
peak
– They account for ~100% of the MeV background
• Blazars in LAT are the main population:
– FSRQs evolve strongly, evolution is complex
– BL Lacs seem not to evolve….but wait for a larger
sample
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Paucity of blazars at low LX: beaming effect ?
Beaming alters the intrinsic
luminosity function
->(L)dL = P(L|L) (L)dL
where L=p L
Urry & Shafer+84
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Previous attempts
Required to produce
~10% of CXB at 1
keV and not exceed
the CXB at ~MeV
RQ AGN, from Gilli+07
Derived from
logN-logS of
blazar in radio
FSRQs
Giommi+07
Comastri+06
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In deep surveys
• Deep X-ray surveys
‘must’ contain a
fraction of blazars
• Selection of C-thick
AGN using hardness
ratios becomes
dangerous
• Unless the evolution
of RQ and RL AGN is
different…..
logN- logS [0.5-2.4 keV]
Courtesy P. Giommi
blazars
RQ AGN, Hasinger+05
Looking forward to AstroH/NuSTAR
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The BAT survey: Deep, all-sky and Unbiased
• All-sky observed down to ~0.5
mCrab (~6e-12 erg/cm2/s)
• No bias against NH up to
Compton-thick regime
15-55 keV @ z=0, z=1
2-10 keV
@ z=0
2-10 keV
@ z=1
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• Chandra/XMM much
better sensitivity but
smaller FOV and biased
• BAT more sensitive
than Suzaku/HXD on
long exposures
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