Overview of the 2 Ms CDF-N survey

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The 2Ms Chandra Deep Field-North
Introduction to the X-ray background Chandra Deep
Field-North data Source Redshifts Diversity of
X-ray selected sources Constraints on AGN
evolution AGNs and binary AGNs in submm
galaxies Future Directions

• D. M. Alexander (IoA),
• F. E. Bauer, W. N. Brandt (PSU),
• A. E. Hornschemeier (JHU),
• J. Barger (Wisc/IfA),
• L. L. Cowie (IfA),
• and C. Vignali (Bologna)
• G. P. Garmire and D. P. Schneider (PSU)

2 Ms CDF-N (and 1 Ms CDF-S) catalogs are in
Alexander et al. (2003)
See http//www.astro.psu.edu/user/niel/hdf-chandra
.html
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Introduction to the X-ray background
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Cosmic Background Radiation
CXB first background discovered (e.g., Giacconi
et al. 1962)
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The Cosmic X-ray Background
(Comastri et al. 1995)
ROSAT 70 of 0.5-2.0 keV b/gd
resolved ASCA/SAX 30 of 2-10 keV b/gd
resolved Finding mostly unobscured AGNs (G2.0)
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The New Generation of X-ray Observatories
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The 2Ms Chandra Deep Field-North
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Deepest X-ray survey in 0.5-8.0 keV band
See also talks by Comastri, Georgantopoulos,
Green, and Mainieri
Deep enough to detect mod.lum starbursts at z1
and mod.lum AGNs at z6
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HDF-N
Alexander et al. (2003)
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Scores on the Doors
One count detected every 6 days!
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HDF-N
Deep optical-near-IR, and radio observations over
whole field 1000 spectroscopic redshifts
Alexander et al. (2003)
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(No Transcript)
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Source Redshifts
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Optical and Redshift Data
Spec-z are challenging even for 8-10m telescopes
Spec-z
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Redshift Distribution
Spec-z
Phot-z
Majority of the sources lie at low-z taking
account of incompleteness is unlikely to
significantly raise the z-peak
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Peaks in the Redshift Distribution
Optical cluster (Dawson et al. 2001) and infrared
redshift peak at z0.85
FRI radio galaxy (Richards et al. 1999), and
extended X-ray emission (Bauer et al. 2002) at
z1.01
Biasing due to large scale structure? See also
Gilli et al. (2003) Similar peaks seen in the
optical and infrared (e.g., Cohen et al. 2000)
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Diversity of X-ray selected sources
AGNs, starbursts, and galaxies
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X-ray-to-optical flux ratio diagram
Broad range of optical magnitudes at faint X-ray
fluxes could suggest a variety of different
source types
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AGN source diversity
AGN source density 5000 deg-2 10 times higher
than the deepest optical surveys
X-rays provide a very efficient route to
identifying AGNs and are relatively insensitive
to absorption
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AGN source diversity
Very few Compton-thick AGNs (30 Alexander et
al. 2003)
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AGN source diversity
Only a few obscured QSOs are identified they are
either rare or mostly exist at fainter fluxes
Very few Compton-thick AGNs (30 Alexander et
al. 2003)
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Starbursts and Normal galaxies
Evidence for X-ray detected galaxies infrared,
radio, optical, and X-ray (e.g., Alexander et al.
2002 Bauer et al. 2002 Hornschemeier et al.
2003)
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Starbursts and Normal galaxies
Normal galaxies may dominate the source counts at
very faint X-ray fluxes (Miyaji Griffiths 2002
Hornschemeier et al. 2003)
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Stacking sources below the detection limit
This technique has been successful in detecting
average X-ray emission from these other source
populations EROs (Alexander et al. 2002 Brusa
et al. 2002) Normal galaxies out to z1
(Hornschemeier et al. 2002 Nandra et al. 2002)
See Brusa talk for more details on ERO constraints
Stacking 24 individually undetected z2-4
Lyman-break galaxies, an overall X-ray detection
was achieved! Average X-ray luminosity is
comparable with that of a luminous starburst
galaxy (e.g., NGC 3256)
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Contributions to the cosmic background
15 micron (IR) background (70) 15 from AGNs
(Alexander et al. 2002 Fadda et al. 2002) 85
from starbursts/galaxies
0.5-8.0 keV background (70-95) Close to 100
from AGNs (many obscured) 2-5 from
starbursts/galaxies
850 micron (submm) background 15 from AGNs
(Barger et al. 2001) but many bright submm
galaxies host an AGN (Alexander et al. 2003) 85
from starbursts/galaxies
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Accretion Activity in the Universe
AGN evolution
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The cosmic evolution of AGNs
AGN evolution is a function of the luminosity of
the AGN gt moderate-luminosity activity peaks at
lower-z than high-luminosity activity (see also
Fiore et al. 2003 Hasinger et al. 2003)
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The cosmic evolution of AGNs
Less high-z AGNs than many models predicted too
few to re-ionise the Universe (see also Alexander
et al. 2001 and Cristiani et al. 2003)
See Brandt talk for properties of zgt4 AGNs
AGN evolution is a function of the luminosity of
the AGN gt moderate-luminosity activity peaks at
lower-z than high-luminosity activity (see also
Fiore et al. 2003 Hasinger et al. 2003)
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X-ray detected submm sources
AGNs in dusty starburst galaxies
Moderately deep Chandra surveys reported little
overlap with the submm source population (e.g.,
Fabian et al. 2000 Severgnini et al. 2000
Hornschemeier et al. 2000, 2001 Barger et al.
2001) What is the picture for a deep Chandra
survey?
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AGNs in submm galaxies
13 S/Ngt4 SCUBA galaxies detected with f(850um)gt5
mJy (Borys et al. 2003)
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AGNs in submm galaxies
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AGNs in submm galaxies
AGNs?
At least 5 are AGNs (38 of bright submm
galaxies) gt almost all appear to be
Compton-thin moderate-luminosity AGNs
Given that only 50 of local AGNs are
Compton-thin (i.e., Risaliti et al. 1999), most
(if not all) bright submm galaxies may contain an
accreting SMBH
AGNs are not luminous enough to power the submm
emission
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Binary AGNs?
2/7 (30) submm galaxies with close X-ray pairs
(lt3) vs 5/193 (3) over whole field (see also
Smail et al. in prep)
This phenomena seems to be more closely linked to
submm galaxies
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Future Directions
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Deeper vs Wider

• Why Go Deeper?
• Discovery space (still approx. photon limited)
• Detect more Compton-thick AGNs
• Improve X-ray spectral analysis
• Detect more galaxies

• Why Go Wider?
• Detect rarer source types (e.g., obscured QSOs,
  high-z AGNs)
• Improve statistics on AGN evolution/luminosity
  function
• Trace both obscured and unobscured AGN evolution
• Uncover extent of large-scale structure (i.e.,
  redshift peaks)

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Summary

• Resolved close to 100 of the 0.5-8.0 keV
  background
• most sources lie at at zlt1
• peaks in z-distribution suggest large-scale
  structure effects
• Broad variety of source types are detected
• optically (and X-ray) obscured and unobscured
  AGNs
• starburst and normal galaxies
• stars, galaxy groups and clusters
• stacking analyses provides constraints on
  sources below detection limit
• Efficient (and mostly absorption independent)
  AGN selection
• AGN source density gt10 times larger than in
  optical (5000 deg-2)
• but few Compton thick AGNs are detected (further
  AGNs to be found?)
• Mod-lum AGNs dominant at low-z, contrary to
  high-lum AGNs
• Many (all?) bright submm galaxies contain an
  AGN/binary AGN

For all papers and data products (CDF-N and
CDF-S) http//www.astro.psu.edu/user/niel/hdf-cha
ndra.html