The Chandra survey of the COSMOS field

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The Chandra survey of the COSMOS field
Fabrizio Fiore the C-COSMOS team Particular
thanks to T. Aldcroft, M. Brusa, N. Cappelluti,
F. Civano, A. Comastri, M. Elvis, S. Puccetti, C.
Vignali, G. Zamorani M. Salvato S-COSMOS team
many others
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Table of content

• Presentation of the survey
• C-COSMOS in a context
• Selected scientific results
• Close pairs
• High-z QSOs
• Fraction of obscured AGN
• Summary (what you should bring home after all..)
• Multiwavelength coverage is mandatory
• X-ray is the leading band for all AGN studies
  (provided that X-ray coverage is deep enough)

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Co-evolution of galaxies and SMBH

• Two seminal results
• The discovery of SMBH in the most local bulges
  tight correlation between MBH and bulge
  properties.
• The BH mass density obtained integrating the AGN
  L.-F. and the CXB that obtained from local
  bulges

• ? most BH mass accreted during luminous AGN
  phases!
• Most bulges passed a phase of activity
• Complete SMBH census,
• 2) full understanding of AGN feedback
• are key ingredients to understand galaxy evolution

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The C-COSMOS survey which science

• Black hole growth and census
• XMM has 20 of ambiguous identifications.
  Chandra survey secures the discovery and
  identifications of rare objects (elusive AGN,
  high-z AGN).
• The combination of Chandra data and Spitzers
  24?m and 3-8 ?m data allows us to unveil highly
  obscured accretion, thus providing a complete
  census of accreting SMBH
• The influence of the environment on galaxy
  activity
• excesses of X-ray point sources (AGN) within a
  few Mpc of clusters at 0.2ltzlt1.
• spikes in the redshift distribution of the X-ray
  sources
• The AGN and galaxy ACF and CCF down to a few
  arcsec how the AGNs trace the cosmic web.
• AGN pairs with separationlt10-20 galaxy activity
  vs. galaxy interaction

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The C-COSMOS survey how

• The Chandra high resolution permits to resolve
  sources 2 apart over 0.9 sq. deg., corresponding
  to 8-16 kpc separations for z 0.3-0.9, and
  locates point sources to lt 4 kpc at any z. Thus
  close mergers can be resolved, and AGNs can be
  distinguished from ULXs and off-nuclear starbust.
• Thanks to the good PFS, ACIS-I is not background
  limited, then C-COSMOS reaches 3 times deeper
  than XMM-COSMOS in both hard and soft bands and
  cross the threshold where starburst galaxies
  become common in X-rays.
• The low ACIS background enables stacking
  analysis, in which counts at the positions of
  known classes of objects are co-added to
  increase the effective exposure time

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C-COSMOS in a context
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C-COSMOS numbers

• 1.8 Ms total exposure time
• 36 ACIS-I pointings
• 200 ksec average exposure 0.5deg2
• 100 ksec average exposure 0.4deg2
• Flim2x10-16 cgs
• (0.5-2 keV)
• 1759 X-ray sources (probability
• threshold 2x10-5)

Elvis et al. 2008
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The C-COSMOS multiwavelenth catalog

• Identification in the 3.6micron K, and I bands
  using a statistical method to match the X-ray
  error box to the most likely cp (likelihood
  ratio technique)
• identification in 3 bands sample 94 !!
• IR identified sample 5
• most interesting sources
• high-z QSOs, obscured QSOs
• ambiguous/unidentified sample 1
• 870 sources in common with XMM 895 NEW sources!!
• 450 spectroscopic redshift already in
  hand(SDSS,VIMOS,IMACS)
• Photometric redshift already available for 60
  of the sample

Civano et al 2008
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Close pairs

• Thanks to the good Chandra PSF it is possible to
  study close pairs to search for X-rays from
  galaxy interactions.
• Wavelet detection algorithm (PWDETECT, Damiani et
  al.) optimized to resolve nearby sources
  (Puccetti et al. 2008).
• A total of 106 sources closer than 12 are
  present in the X-ray catalog. gt than expected
  from simulation.
• Next step is to obtain the spectroscopic
  identification to verify the fraction of physical
  pairs (Vignali et al. 2008)

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Chandra/XMM comparison
BLUE circles 0.5-7 keV chandra detections.
Green XMM contours

• 50 of the chandra pairs have associated only
  one XMM source. In several cases the brightness
  of the sources of the pair is similar.

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High redshift AGN

• XMM-COSMOS
• QSO zgt3 30 deg2
• QSO zgt4 3 deg2
• Chandra 3 times deeper than XMM
• 100-200 QSO zgt3 deg2
• 10-20 QSO zgt4 deg2

• C-COSMOS XMM-COSMOS
• Elvis et al. 2008 Brusa et al. 2008
• Civano et al. 2008

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Obscured AGN
High X/O, high MIR/O
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Evidences for missing SMBH
While the CXB energy density provides a
statistical estimate of SMBH growth, the lack, so
far, of focusing instrument above 10 keV (where
the CXB energy density peaks), frustrates our
effort to obtain a comprehensive picture of the
SMBH evolutionary properties.
Gilli et al. 2007
43-44
44-44.5
Marconi 2004-2007
Menci , Fiore et al. 2004, 2006, 2008
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AGN density
La Franca, Fiore et al. 2005 Menci, Fiore et al.
2008
Paucity of Seyfert like sources _at_ zgt1 is real?
Or, is it, at least partly, a selection effect?
Are we missing in Chandra and XMM surveys highly
obscured (NH?1024 cm-2) AGN? Which are common in
the local Universe
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Why multiwavelength surveys

• IR surveys
• AGNs highly obscured at optical and X-ray
  wavelengths shine in the MIR thanks to the
  reprocessing of the nuclear radiation by dust

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IR surveys

• Difficult to isolate AGN from star-forming
  galaxies (Lacy 2004, Barnby 2005, Stern 2005,
  Polletta 2006 and many others)

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Why multiwavelength surveys

• Use both X-ray and MIR surveys
• Select unobscured and moderately obscured AGN in
  X-rays
• Add highly obscured AGNs selected in the MIR
• Simple approach Differences are emphasized in a
  wide-band SED analysis

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MIR selection of CT AGN
Fiore et al. 2003
ELAIS-S1 obs. AGN
ELAIS-S1 24mm galaxies
HELLAS2XMM CDFS obs. AGN
Unobscured obscured
MIR/O
Open symbols unobscured AGN
Filled symbols optically obscured AGN
photo-z
X/0
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MIR selection of CT AGN
Fiore et al. 2008a
Fiore et al. 2008b
COSMOS X-ray COSMOS 24um galaxies
CDFS X-ray HELLAS2XMM
GOODS 24um galaxies
R-K
Open symbols unobscured AGN Filled symbols
optically obscured AGN photo-z
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Template highly obscured QSOs

• IRAS091044109
• High L(IR)/Lx ratio
• No PAH emission features in IRS spectrum
• IR SED dominated by the AGN

Abel269075 (Pozzi et al 2007)
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COSMOS MIR AGN
Stack of Chandra images of MIR sources not
directly detected in X-rays
Fiore et al. 2008b
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AGN fraction
Chandra survey of the Bootes field (5ks effective
exposure) Brand et al. 2006 assume that AGN
populate the peak at F24um/F8um0 only. They miss
a large population of obscured AGN, not detected
at the bright limits of their survey.
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AGN fraction
Caputi et al. 2007
La Franca et al. 2005 2-10 keV
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CT AGN volume density
A B C
GCH 2007 logNHgt24
z1.2-2.2 density IR-CT AGN 45 density X-ray
selected AGN, 90 of unobscured or moderately
obscured AGN z0.7-1.2 density IR-CT AGN 100
density X-ray selected AGN, 200 of unobscured
or moderately obscured AGN The correlation
between the fraction of obscured AGN and their
luminosity holds including CT AGN, and it is in
place by z2
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AGN obscuration, AGN feedback and star-formation

• CT absorbers can be naturally included in the
  Menci et al. feedback scenario as an extension
  toward smaller distances to the nucleus where gas
  density can be high.
• If this is the case and if the fundamental
  correlation between the fraction of obscured AGN
  and L is due to different timescales over which
  nuclear feedback is at work
• Evolutionary star-formation sequence
• CT moderately obscured
  unobscured
• Strong moderate
  small

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AGN obscuration, AGN feedback and star-formation

• COSMOS
• Log(L5.8/L1.4GHz)4.74 (0.12) 38 CT QSOs
  z1.2-2.2
• Log(L5.8/L1.4GHz)5.07 (0.13) 25 QSOs z1.2-2.2
• X-ray selected, type-2 QSO have higher submm
  detection rate than unobscured QSO

Page et al. 2004
Stevens et al. 2005 unobscured
obscured
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Density of Obscured AGNs
? ?
Dashed lines Menci model, no AGN feeback Solid
lines Menci model, AGN feedback 2-10 keV data
La Franca, FF et al. 2005 Spectroscopic
confirmation very difficult for the CDFS-GOODS
sources (R27, F(24um)100uJy Possible for the
COSMOS sources!! F24um1mJy gt Spitzer IRS AO5
program (Pri. C, Salvato et al.)
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Summary

• Chandra sensitive survey of the COSMOS field
  1758 sources, half new, I.e. not detected by XMM
• 100 sources with optical counterpart fainter
  than I26.5 gt highly obscured QSOs, high-z
  QSOs
• Large sample of bright pairs
• gt galaxy interaction vs. galaxy activity
• Combined use of Chandra and Spitzer over a large
  field gt discovery of CT type 2 QSOs at z1-2
• gt fraction of X-ray detected and X-ray
  emitting AGN in 24um samples is large (50)
• All this will allow a precise determination of
  the evolution of the accretion in the Universe, a
  precise census of accreting SMBH
• While multiwavelength coverage is mandatory,
  X-ray is the leading band for AGN studies
  (provided that X-ray coverage is deep enough)