# Presentation: 679072

## X-ray (and multiwavelength) surveys

- Fabrizio Fiore

## Table of content

- A historical perspective
- Tools for the interpretation of survey data
- Number counts
- Luminosity functions
- Main current X-ray surveys
- What next

## A historical perspective

- First survey of cosmological objects: radio galaxies and radio loud AGN
- The discovery of the Cosmic X-ray Background
- The first imaging of the sources making the CXB
- The resolution of the CXB
- What next?

## Radio sources number counts

**Radio sources number counts**

**First results from Cambridge surveys during the 50’: Ryle**
**Number counts steeper than expected from Euclidean universe**

##                          Number counts

**                         ****Number counts**
- Flux limited sample: all sources in a given region of the sky with flux > than
- some detection limit Flim.
-  Consider a population of objects with the same L
-  Assume Euclidean space

##                                       Number counts

-                                       **Number counts**
- Test of evolution of a source population (e.g. radio sources). Distances of
- individual sources are not required, just fluxes or magnitudes:
- the number of objects increases by a factor of 100.6=4 with each magnitude.
- So, for a constant space density, 80% of the sample will be within 1 mag
- from the survey detection limit.

- If the sources have some distribution in L:

##       Problems with the derivation of the number counts

-  Completeness of the samples.
-  Eddington bias: random error on mag measurements can alter the number
-   counts. Since the logN-logFlim are steep, there are more sources at faint
-   fluxes, so random errors tend to increase the differential number counts.
-   If the tipical error is of 0.3 mag near the flux limit, than the correction
-   is 15%.
-  Variability.
-  Internal absorption affects “color” selection.
-  SED, *‘K-correction’*, redshift dependence of the flux (magnitude).

## Galaxy number counts

## Optically selected AGN number counts

- z<2.2
- B=22.5
- 100 deg-2
- B=19.5
- 10 deg-2
- z>2.2
- B=22.5
- 50 deg-2
- B=19.5
- 1 deg-2
- B-R=0.5

## X-ray AGN number counts

**X-ray AGN number counts**

- <X/O> OUV sel. AGN=0.3
- R=22 ==> 310-15 1000deg-2
- R=19 ==> 510-14 25deg-2

- The surface density of X-ray selected AGN
- is 2-10 times higher than OUV selected AGN

## The cosmic backgrounds energy densities

**The cosmic backgrounds energy densities**

## The Cosmic X-ray Background

- Giacconi (and collaborators) program:
- 1962 sounding rocket
- 1970 Uhuru
- 1978 HEAO1
- 1978 Einstein
- 1999 Chandra!

## The Cosmic X-ray Background

- The CXB energy density:
- Collimated instruments:
- 1978 HEAO1
- 2006 BeppoSAX PDS
- 2006 Integral
- 2008 Swift BAT
- Focusing instruments:
- 1980 Einstein 0.3-3.5 keV
- 1990 Rosat 0.5-2 keV
- 1996 ASCA 2-10 keV
- 1998 BeppoSAX 2-10 keV
- 2000 RXTE 3-20 keV
- 2002 XMM 0.5-10 keV
- 2002 Chandra 0.5-10 keV
- 2012 NuSTAR 6-100 keV
- 2014 Simbol-X 1-100 keV
- 2014 NeXT 1-100 keV
- 2012 eROSITA 0.5-10 keV
- 2020 IXO 0.5-40 keV

##                           The V/Vmax test

**                          ****The V/V****max**** test**
- Marteen Schmidt (1968) developed a test** **for evolution not sensitive to
- the completeness of the sample.
- Suppose we detect a source of luminosity L and flux *F >F**lim* at a distance
*r*** **in Euclidean space:

- If we consider a sample of sources distributed uniformly, we expect that
- half will be found in the inner half of the volume Vmax and half in the outer
- half. So, on average, we expect V/Vmax=0.5

## The V/Vmax test

**The V/V****max**** test**

- In an expanding Universe the luminosity distance must be used in place
- of r and rmax and the constant density assumption becomes one of
- constant density per unit *comuving volume* .

##                        Luminosity function

**                       ****Luminosity function**
- In most samples of AGN <V/Vmax> > 0.5. This means that the luminosity
- function cannot be computed from a sample of AGN regardless of their z.
- Rather we need to consider restricted z bins.

- More often sources are drawn from flux-limited samples, and the volume
- surveyed is a function of the Luminosity L.  Therefore, we need to account
- for the fact that more luminous objects can be detected at larger
- distances and are thus over-represented in flux limited samples. This is
- done by weighting each source by the reciprocal of the volume over which
- it could have been found:

## Luminosity function

## Assume that the intrinsic

- spectrum of the sources
- making the CXB has E=1
- I0=9.810-8 erg/cm2/s/sr
- ’=4I0/c

- Optical (and soft X-ray) surveys gives values 2-3 times lower
- than those obtained from the  CXB
- (and of the F.&M. and G. et al. estimates)

## A survey of X-ray surveys

**A survey of X-ray surveys**

## A survey of X-ray surveys

- Point sources                             Clusters of galaxies

## A survey of surveys

- Main areas with large multiwavelength coverage:
- CDFS-GOODS 0.05 deg2: HST, Chandra, XMM, Spitzer, ESO, Herschel, ALMA
- CDFN-GOODS 0.05 deg2: HST, Chandra, VLA, Spitzer, Hawaii, Herschel
- AEGIS(GS) 0.5 deg2: HST, Chandra, Spitzer, VLA, Hawaii, Herschel
- COSMOS 2 deg2: HST, Chandra, XMM, Spitzer, VLA, ESO, Hawaii, LBT, Herschel, ALMA
- NOAO DWFS 9 deg2 : Chandra, Spitzer, MMT, Hawaii, LBT
- SWIRE 50 deg2 (Lockman hole, ELAIS, XMMLSS,ECDFS): Spitzer, some Chandra/XMM, some HST, Herschel
- eROSITA! 20.000 deg2 10-14 cgs 200 deg2 310-15 cgs

## Chandra deep and wide fields

**Chandra deep and wide fields**

- CDFS 2Msec 0.05deg2           CCOSMOS 200ksec 0.5deg2 100ksec 0.4deg2
- ~400 sources                                         1.8 Msec         ~1800 sources
-                                                                       Elvis et al. 2008
-                      20 arcmin                                                     1 deg

## XMM surveys

- COSMOS 1.4Msec 2deg2
-                                                               Lockman Hole 0.7Msec 0.3deg2

## Chandra surveys

- AEGIS: Extended Groth Strip                        Bootes field

## Spitzer large area surveys: SWIRE

## eROSITA

- ~30ks on poles, ~1.7ksec equatorial

## What next? The X-ray survey discovery space

- Einstein  ROSAT

- ROSAT                   eROSITA

- ASCA/BSAX      XMM         Chandra     IXO

- IXO

- NS NeXT  SX

- BSAX/ASCA   XMM

- Swift