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),D. M. Alexander (IoA),F. E. Bauer, W. N. Brandt (PSU),F. E. Bauer, W. N. Brandt (PSU),

A. E. Hornschemeier (JHU),A. E. Hornschemeier (JHU),A.A. J. Barger (Wisc/IfA),J. Barger (Wisc/IfA),

L. L. Cowie (IfA), L. L. Cowie (IfA), and C. Vignali (Bologna)and C. Vignali (Bologna)

G. P. Garmire and D. P. Schneider (PSU)G. P. Garmire and D. P. Schneider (PSU)

See http://www.astro.psu.edu/user/niel/hdf-chandra.html

The 2Ms Chandra Deep Field-NorthThe 2Ms Chandra Deep Field-North

2 Ms CDF-N (and 1 Ms CDF-S) catalogs are in Alexander et al. (2003)

Introduction to the X-ray backgroundIntroduction to the X-ray background

Cosmic Background Radiation

CXB: first background discovered (e.g., Giacconi et al. 1962)

The Cosmic X-ray Background

0.5-10.0 keV

ROSAT: ~70% of 0.5-2.0 keV b/gd resolvedASCA/SAX: ~30% of 2-10 keV b/gd resolvedFinding mostly unobscured AGNs

(Comastri et al. 1995)

~1.4

The New Generation of X-ray Observatories

Launched December 1999

~0.1-12.0 keV band sensitivity

5” spatial resolution

58 mirrors (4300 cm2)

~30’ field of view

Weisskopf et al. (2000) Jansen et al. (2001)

Launched July 1999

~0.1-10.0 keV band sensitivity

Unsurpassed 0.”5 spatial resolution

4 mirrors (1145 cm2)

16.’9x16.’9 field of view

Chandra XMM-Newton

The 2Ms Chandra Deep Field-NorthThe 2Ms Chandra Deep Field-North

Alexander et al. (2003)

Deepest X-ray survey in 0.5-8.0 keV band

~50 times deeper than deepest

ROSAT survey

~250 times deeper than deepest ASCA survey

Deep enough to detect mod.lum starbursts at z~1 and mod.lum AGNs at z~6

See also talks by Comastri, Georgantopoulos, Green,

and Mainieri

“True” color image0.5-2.0 keV 2.0-4.0 keV 4.0-8.0 keV

1.945 MsACIS-I

exposure

80-95% of 0.5-2 keV 70-90% of 2-8 keV

(447 arcmin2 )

20 observations spanning 27 months

HDF-N

Alexander et al. (2003)Still photon limited near the aim point

503 main independent sources

Alexander et al. (2003)+78 supplementary sources

+6 extended sources Bauer et al. (2002)

Scores on the Doors… One count detected every 6 days!

“True” color image0.5-2.0 keV 2.0-4.0 keV 4.0-8.0 keV

1.945 MsACIS-I

exposure

80-95% of 0.5-2 keV 70-90% of 2-8 keV

(447 arcmin2 )

20 observations spanning 27 months

HDF-N

SCUBA (sub-mm)

ISOCAM (mid-IR)

Deep optical-near-IR, and radio observations over whole field~1000 spectroscopic redshifts

GOODS survey (ACS+SIRTF)

Alexander et al. (2003)

P.I.: M. Giavalisco

Created by A. Koekemoer and Z. LevayAstrometry by S. Casertano and R. Hook

Verification by M. Giavalisco, H. Ferguson, A. Koekemoer, M. Dickinson, N. Grogin, S. Ravindranath, T. Dahlen, and GOODS/ACS team

HST ACS3/5 Epochs18000x24000

pixels

F850LP (z)

F775W (i)

F606W (V)

F435W (B)

GOODS survey (ACS+SIRTF)

3”

7.5”

6”

2.5”

Source RedshiftsSource Redshifts

Optical and Redshift Data

Redshifts mostly from the Keck telescope (Barger et al. 2003)

(56% with redshifts)503 Chandra sources

Optical data from the Subaru telescope (Capak et al. 2003)

Spec-z

Spec-z are challenging

even for 8-10m

telescopes

Barger et al. (2003)

Redshift Distribution

Majority of the sources lie at low-z; taking account of incompleteness is unlikely to significantly raise the z-peak

Spec-z

Phot-z

Peaks in the Redshift Distribution

Barger et al. (2003)

Optical cluster (Dawson et al. 2001)and infrared redshift peak at z~0.85

FRI radio galaxy (Richards et al. 1999), and extended X-ray emission

(Bauer et al. 2002) at z~1.01

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)

Diversity of X-ray selected sourcesDiversity of X-ray selected sources

AGNs, starbursts, and galaxies

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

AGN source diversity

Alexander et al. (2001)Barger et al. (2002)

Barger et al. (2002)Barger et al. (2002)

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

AGN source diversity

Many obscured AGNs are detected and the 183 fainter sources appear to

be heavily obscured

Column density distribution determined via X-ray

spectral analyses of 320/503 bright sources

Bauer et al., in prep.

Very few Compton-thick AGNs (~30: Alexander et al. 2003)

AGN source diversity

Many obscured AGNs are detected and the 183 fainter sources appear to

be heavily obscured

Column density distribution determined via X-ray

spectral analyses of 320/503 bright sources

Very few Compton-thick AGNs (~30: Alexander et al. 2003)

Only a few obscured QSOs are identified: they are either rare or

mostly exist at fainter fluxes

Starbursts and Normal galaxiesHornschemeier et al. (2003)

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)

Bauer et al. (2002)

Starburst Galaxies

Normal Galaxies

Starbursts and Normal galaxies

Normal galaxies may dominate the source counts at very faint X-ray fluxes (Miyaji & Griffiths 2002; Hornschemeier et al. 2003)

Hornschemeier et al. (2003)

Brandt et al. (2001) Brandt et al. (2001)

Stacking sources below the detection limit

Stacking 24 individually undetected z=2-4 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)

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 z~1 (Hornschemeier et al. 2002; Nandra

et al. 2002)

See Brusa talk for moredetails on ERO constraints

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

Contributions to the cosmic background

0.5-8.0 keV background (~70-95%):Close to 100% from AGNs

(many obscured)2-5% from starbursts/galaxies

15 micron (IR) background (~70%):~15% from AGNs (Alexander et al. 2002;

Fadda et al. 2002)~85% from starbursts/galaxies

Accretion Activity in the UniverseAccretion Activity in the Universe

AGN evolution

The cosmic evolution of AGNs

Cowie et al. (2003)

AGN evolution is a function of the luminosity of the AGN

=> moderate-luminosity activity peaks at lower-z than high-luminosity

activity (see also Fiore et al. 2003; Hasinger et al. 2003)

CDF-N

SDSSBarger et al. (2003)

The cosmic evolution of AGNs

Cowie et al. (2003)

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 z>4 AGNs

AGN evolution is a function of the luminosity of the AGN

=> moderate-luminosity activity peaks at lower-z than high-luminosity

activity (see also Fiore et al. 2003; Hasinger et al. 2003)

X-ray detected submm sourcesX-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?

850 micron SCUBA image

Borys et al. (2003)

AGNs in submm galaxies

13 S/N>4 SCUBA galaxies detected with f(850um)>5 mJy (Borys et al. 2003)

850 micron SCUBA image

Borys et al. (2003)

AGNs in submm galaxies

7 (54%) of the sources are X-ray detected (Alexander et al. 2003)

850 micron SCUBA image

Borys et al. (2003)

AGNs in submm galaxies

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

7 (54%) of the sources are X-ray detected (Alexander et al. 2003)

At least 5 are AGNs (38% of bright submm galaxies)

=> almost all appear to be Compton-thin moderate-

luminosity AGNs

AGNs are not luminous enough to power the submm

emission

Binary AGNs?

~20kpc

Alexander et al. (2003)

~20kpc

Alexander et al. (2003)

2/7 (30%) submm galaxies with close X-ray pairs (<3”) 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

~1kpc

Komossa et al. (2003)

NGC6240

Future DirectionsFuture Directions

Why Go Deeper?Why Go Deeper?1. Discovery space

(still approx. photon limited)

2. Detect more Compton-thick AGNs

3. Improve X-ray spectral analysis

4. Detect more galaxies

Why Go Wider?Why Go Wider?1. Detect rarer source types (e.g.,

obscured QSOs, high-z AGNs)2. Improve statistics on AGN

evolution/luminosity function3. Trace both obscured and

unobscured AGN evolution4. Uncover extent of large-scale

structure (i.e., redshift peaks)

Deeper vs Wider

SummarySummary

• Resolved close to 100% of the 0.5-8.0 keV background:• most sources lie at at z<1

• 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 >10 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-chandra.html