# Presentation: 116035

## X-ray Surveys	

- Ann Hornschemeier
- NASA GSFC
- _[Ann.Hornschemeier.Cardiff@nasa.gov](mailto:Ann.Hornschemeier.Cardiff@nasa.gov)_
- Material liberally borrowed from Richard Mushotzky, Niel Brandt, and others

## Missing from talk

- The Galaxy (focus is extragalactic)
- Wider-field/shallower surveys at 0.2-10 keV (see P. Green talk from 2005 that focused more on wider-field surveys)
- Extended sources:  note that clusters and groups of galaxies are significant populations particularly in the 0.5-2 keV bandpass, see Rosati, Borgani & Norman (2002) for galaxy cluster review and Keith Arnaud’s talk this AM
- Surveys of objects (focus here is on ‘blank-field’ serendipitous surveys of the Universe)

## Good news!

- REVIEW article on X-ray Surveys:
- Brandt & Hasinger (2005; ARA&A, 43, pp.827-859)
- Presentations from November 2006     X-ray Surveys meeting at SAO:
- http://cxc.harvard.edu/xsurveys06/agenda/presentations/

## The spectrum of the Universe

- Extragalactic Background Studies

**Notes:**
May broadly divide astronomy in two: 
focused study of individual objects and phenomena (e.g. comets, stars, the hot gas within the Milky Way)
 statistical studies of large numbers of objects
When individual objects can’t be resolved, the latter becomes the study of ‘’background radiation”
In general, when we are careful to exclude the Galaxy, this latter type of study is that of “extragalactic background radiation”
The X-ray background (NEED TO ADD FIGURE) was the first extragalactic background radiation reported
(in 1962) It peaks at very high energies, near 40 keV and covers four decades of frequency (0.1 keV to gamma rays above 1 MeV) 
Progress over the last 40 years has been impeded by the difficulty of building arcsecond quality optics in the 
X-ray band
The largest amount of progress in characterizing the sources of the X-ray background 
before Chandra occurred with the ROSAT satellite in the softer 0.5-2 keV band and with
ASCA and BeppoSAX in the harder 2-10 keV band.  About 80% of the background was resolved in the soft band and about 30% of the background was resolved in the hard band.  The vast majority of sources were found to be AGN.  

## The Extragalactic X-ray Background (XRB)

- Chandra/XMM: higher-quality X-ray imaging in the 2-10 keV bandpass resolving 50-80% of this part of the XRB, closer to the energy peak.
- Note that ~50% of the CXRB is resolved at E>8 keV (Worsley et al. 2005)

- Note: CXRB peaks
- at E~40 keV!

**Notes:**
May broadly divide astronomy in two: 
focused study of individual objects and phenomena (e.g. comets, stars, the hot gas within the Milky Way)
 statistical studies of large numbers of objects
When individual objects can’t be resolved, the latter becomes the study of ‘’background radiation”
In general, when we are careful to exclude the Galaxy, this latter type of study is that of “extragalactic background radiation”
The X-ray background was the first extragalactic background radiation reported
(in 1962) It peaks at very high energies, near 40 keV and covers four decades of frequency (0.1 keV to gamma rays above 1 MeV) 
Progress over the last 40 years has been impeded by the difficulty of building arcsecond quality optics in the 
X-ray band
The largest amount of progress in characterizing the sources of the X-ray background 
before Chandra occurred with the ROSAT satellite in the softer 0.5-2 keV band and with
ASCA and BeppoSAX in the harder 2-10 keV band.  About 80% of the background was resolved in the soft band and about 30% of the background was resolved in the hard band.  The vast majority of sources were found to be AGN.  

## Existing X-ray Surveys:Most sensitive surveys in the soft X-ray bandpass (0.5-2 keV)

- NOTE:
- Very few
- all-sky X-ray
- surveys!

- Deepest X-ray
- surveys are truly “pencil-beam”

- Chandra
- XMM
- ROSAT

## Importance of sampling hard X-ray energies (which gets easier at higher redshift)

- 1020 cm-2

- unabsorbed

- 1021 cm-2

- 1022 cm-2

**10****23**** cm****-2**

- 2-8 keV bandpass:
- Pierces through high
- obscuring column densities

## 2-10 keV X-ray Surveys(stolen from A. Comastri)

- Census of the hard X-ray Universe
- requires a range of survey depths & sizes

- Pencil-beam surveys

- All-sky surveys

**Notes:**
We put together a full picture using multiple X-ray surveys of varying depths and sizes

## The Swift BAT Hard X-ray Survey

## X-ray surveys at E>10 keV

- We simply have not accounted for the vast majority of the accretion energy budget of the Universe (the CXRB is <5% resolved at hard energies)
- There is some chance of wide-field moderately sensitive hard X-ray survey missions going up in ~5 years from now (big breakthrough portion of EM spectrum)

## Great leap forward in hard X-ray surveys: the Swift BAT Survey

- 10X more sensitive than HEAO-1 A4; Levine et al. 1984
**Piggy-backed on Swift GRB observing plan)**
**Energy Range****	****   ****14  -  195 keV**
**Spatial Resolution ****21’ sky pixel,  centroided to <1-3’**
**FIRST 9 MOS:**
- survey of whole sky complete at ~4x10-11 ergs cm-2 s-1
- 155 galactic sources
- 147 AGN
- 20 other sources

- Exposure time after 9 months of operations

- Markwardt et al. (2005)

**Notes:**
Spectral Resolution	
      6 keV FWHM @ 60 keV,  average
(1.6 milliCrab for the whole sky and 1.2 milliCrab for 1/2 sky)

PREDICTED STATE AT 3 YEARS- assume
sqrt time for sensitivity
 logN/logS slope for AGN 3/2
 logN/logS for slope galactic 1
bright transients are linear with time

## Selecting AGN via hard X-ray emission

- no correlation between BAT and ROSAT count rates
- 44 BAT sources not detected by ROSAT

- no correlation with total 2MASS J band
- soft x-ray and IR do not measure true AGN  luminosity or complete populations

## Swift BAT AGN Survey

- Redshifts of BAT Selected
-  Non-Blazar AGN

## Deep X-ray Surveys

## Deep X-ray Surveys

- Science focus: formation and evolution of cosmic building blocks, including galaxies and supermassive black holes
- Probe intrinsically less luminous and more typical objects than wide-field, shallower surveys.

## The deepest X-ray survey (CDF-N)Alexander et al. 2003Chandra allows for:More sensitive X-ray surveys due to sub-arcsecond imaging capability (deepest and highest-redshift objects)XMM allows for deep harder X-ray (5-10 keV) surveys (higher collecting area than Chandra in 8-12 keV bandpass)

- The deepest X-ray survey (CDF-N)Alexander et al. 2003Chandra allows for:More sensitive X-ray surveys due to sub-arcsecond imaging capability (deepest and highest-redshift objects)XMM allows for deep harder X-ray (5-10 keV) surveys (higher collecting area than Chandra in 8-12 keV bandpass)

**“****True” color images**
**0.5-2.0 keV **
** ****2.0-4.0 keV**** **
** ****4.0-8.0 keV**

- 1.945 Ms
- ACIS-I
- exposure

- (447 arcmin2 )

- HDF-N

**Notes:**
Look-back time at these redshifts:
z=0.1  , 1.4 billion years
z=0.3  , 3.7 billion years
z=0.5  , 5.4 billion years

## What are these X-ray sources?

- Classification using:
- spectroscopic ID
- X-ray spectra (NH > 1022  cm2 OR <1)
- LX,AGN >  3 1042
- Problems
- Optical faintness of sources prevent collecting spectra
- X-ray ‘spectra’ are really just single-band detections! (or maybe a hardness/band ratio)
- Some X-ray luminous galaxies may be expected at earlier times when the average SFR was higher

**Peterson et al. **
**(2005)**

## Optical spectra for dividing  AGN from SB

- Possible reasons for missing AGN features
- X-ray emission dominated by non-AGN emission (e.g., Hornschemeier et al. 2005)
- Optical or X-ray dilution (e.g., Moran et al. 2002; Peterson et al. 2005)
- Evolution of NLR at low-luminosities (e.g., HST work of Barger et al. 2003)

- Hornschemeier et al. (2005)

- Many X-ray background sources lack clear signatures of AGN in their optical spectra (i.e., XBONGS; Comastri et al. 2002)

**“****Passive” SDSS Optical Spectrum**
**for a Chandra-detected galaxy**

## Number Counts  & the CXRB          (see P. Green’s 2005 talk for general Log N - Log S equations)

- Number Counts  & the CXRB          *(see P. Green’s 2005 talk for** general Log N - Log S equations)*

- Number counts well-measured over 4 orders of magnitude in 0.5-2.0 keV flux (down to ~2.5 10-17 erg cm2 s-1(0.5 –2keV) **(Hornschemeier et al. 2003; Bauer et al. 2004; Georgakakis et al. 2004)**
- In the current deepest X-ray surveys, galaxies comprise a MINORITY of X-ray sources and make <5% of the diffuse XRB **(e.g., Hornschemeier et al. 2002;  Persic & Raphaeli 2003) **

**Bauer et al. (2004)**

- AGN

- Normal Galaxies

- “Blank” field log*N*-log*S* from
- 1-2 Ms Chandra Deep Fields

**Notes:**
Look-back time at these redshifts:
z=0.1  , 1.4 billion years
z=0.3  , 3.7 billion years
z=0.5  , 5.4 billion years

## Snapshot of Science Results from Deep X-ray Surveys

## “When” was the CXRB made?

- It appears that the bulk of the CXRB was produced at relatively modest redshift (z<1; e.g., Barger et al. 2005)
- The CXRB is dominated by Seyfert-luminosity AGN (rather than the extremely luminous QSOs)

- Barger et al. 2005

## Cosmic Downsizing

- X-ray surveys result (discovered in X-rays first!)
- Massive black holes actively accreting at early times in Universe

- Hasinger, Miyaji & Schmidt (2005).
-                         Ueda et al. (2003).

**Notes:**
he comoving space density of AGN selected in the 0.5–2 keV band as a function of redshift. Results are shown for five luminosity ranges; these are labeled with logarithmic luminosity values. Adapted from Hasinger, Miyaji & Schmidt (2005). (b) The same for AGN selected in the 2–10 keV band using three luminosity ranges. Adapted from Ueda et al. (2003).

## X-ray emission detected from many “normal” galaxies

- “Normal” galaxy = ... galaxy whose X-ray emission is dominated by binaries, hot gas, etc. rather than a luminous AGN
- Can use X-ray emission as tracer of global star formation history of the Universe

- The Milky Way
- (RXTE data, Grimm et al. 2003)
- LX (0.5-8 keV) ~ 6 x 1039 erg s-1

**HMXBs**

**LMXBs**

**Log Lx > 38.3**

**Notes:**
So the title of this talk has to do with normal galaxies, and OF COURSE there is no such thing as normal!
ACTUALLY TALKING ABOUT GALAXIES LIKE OUR OWN  MILKY WAY (not dominated by SMBH)
Indeed our own Milky Way has a pathetic excuse for a supermassive black hole... it is hardly accreting any material at all and is easily outshone by many of the accreting binary systems
Just to remind everyone what the Milky Way looks like in the X-ray band, I show a chart, X and Y here are distance in kpc, showing the distribution of accreting binaries more luminous than ~10^38 erg/s
If we compare with this distant galaxy... 

## Beyond the faintest limits: X-ray Emission from starbursts at z~3  

- Take individually UNDETECTED Chandra sources, owing to good Chandra PSF and low background, stack the X-ray data to search for an average signal
- Stacking analysis:                        <LX>  1-3 1041 erg s-1 (2-8 keV;                                        Brandt, Hornschemeier et al. 2001; Nandra et al. 2002; Lehmer et al. 2005)
- Independent verification of UV methodology for measuring extinction at high z                 (Seibert, Meurer & Heckman 2001)
- Recently has been extended to even higher redshift (z~4) by Lehmer et al. (2005)

**Brandt, Hornschemeieret al. (2001)**

- X-rays provide one of few
- direct cross-checks to
-  UV-derived SFRs at z≥3

**Notes:**
Much of what we have learned about star formation at redshifts greater than 3 has hinged upon galaxies selected in the ultraviolet bandpass via the Lyman Break technique. 
These galaxies, although individually undetected in the X-ray band, have X-ray lumionsities consistent with the X-ray/star formation rate correlations in the local Universe, indicating star formation rates that are typically 10 to 30 solar masses per year
Notably these X-ray studies have provided an important cross-check to the UV methodology is the IRX-Beta Meurer et al. extinction-correction

## Some handy resources & a few notes

## REALLY X-ray faint sources:Did I detect anything??

- For faint sources (<10 counts on-axis), multiwavelength counterparts provide extra assurance of reality.  Advanced tools like ACIS_EXTRACT should be used to evaluate PSF at large Chandra off-axis angles
- For ratios of low numbers of counts: recommend Lyons’ method (see scanned pages from Niel Brandt’s webpage at end of this talk)
- Useful reference : Kraft, Burrows & Nousek (1991) - upper limits given LOW numbers of counts, including look-up tables

## X-ray Survey Tools/Resources

- HEASARC (_[http://heasarc.gsfc.nasa.gov](http://heasarc.gsfc.nasa.gov/)_)
- Includes many fully-reduced all-sky (or wide-field) survey X-ray catalogs (RASS, ASCA)
- Can easily search multiple catalogs
- XASSIST webpage (_[http://xassist.pha.jhu.edu](http://xassist.pha.jhu.edu/)_)
- Automatic reduction of many individual Chandra fields --> includes images & X-ray source catalogs as well as multiwavelength identifications
- ACIS_EXTRACT (_[http://www.astro.psu.edu/xray/docs/TARA/](http://www.astro.psu.edu/xray/docs/TARA/)_ )
- Top-notch IDL program that allows one to deal with large numbers of point and diffuse sources observed with the ACIS instrument
- Wrapper for CIAO tools like mkpsf, etc.

## BONUS:

- X-ray K corrections
- for Power Law Spectra
- (see also Ptak et al. 2007 appendix on X-ray k-corrections for thermal plasmas)

## X-ray bandpass at high z

- Most AGN are power-law sources in the X-ray: a few handy equations result for converting bandpasses & flux at high-z
- Take a power-law spectrum:
-          	              		 	 rest-frame photon flux
- 				 	 (photons/s*Hz)
- 					erg/s
- 					observed photon flux
- 					(photons/s*Hz)

## X-ray Bandpass at High-z

- Handy relations for X-ray bandpasses at high-z

- :  rest-frame luminosity in bandpass [E3,E4]
- :  observed-frame energy flux in bandpass [E1,E2]

## X-ray Bandpass at High-z

- Example:  for =2 power-law, if we “match” the observed and rest-frame bandpasses, no k-correction is needed:

- L(2-8 keV) = f(0.5-2 keV) * 4.0DL2
- E1 = 0.5 (keV), E2 = 2 (keV)   :OBSERVED
- E3 = 2  (keV), E4 = 8 (keV)     :REST-FRAME

- Lyons’ Method for Calculating Errors on Ratios

## Finale:

- Glimpse of the future
-  of X-ray surveys

## Going deeper in the X-ray band

**Bauer et al. (2004)**

- Ultra-deep X-ray survey
- (≤10-18 erg cm-2 s-1)

- Chandra background is less than           *1 count per pixel every ten days*
- Chandra can reach depths of (>5 Ms)

**Notes:**
And normal galaxies outnumber luminous AGN by a factor of ~100