AGN populations in X-ray surveys Contents Advantage of X-ray - - PowerPoint PPT Presentation

AGN populations in X-ray surveys

Contents

• Advantage of X-ray surveys
• What they find
• How many AGN, over cosmic history
• X-ray spectra
• Winds and outflows
• Spectral energy distributions
• Star formation in their hosts

I’ve been asked to concentrate on Type 1 AGN

Why are X-ray surveys special for AGN?

• X-ray emission is ubiquitous in AGN

– no X-ray quiet AGN – though the X-rays can be absorbed

• For most objects, particularly stars and galaxies, far less

than 1% of the power emerges as X-rays.

– The contrast between AGN power and other forms of power highest in the X-rays.* In reality only a few % of an AGN’s power emerges in the X-ray. So why are X-rays so useful?

*Maybe that’s not true for radio galaxies, but powerful radio emission isn’t universal in AGN.

Brandt & Alexander 2015, A&ARv, 23, 1 Loaring et al. 2005, MNRAS, 362, 1371

Contrast

Large sky density. Most sources are AGN

AGN in X-ray surveys

• Quasars identified as

Uhuru sources.

• Seyferts confirmed as

X-ray sources with Ariel 5.

• Elvis et al. 1978 even

made an X-ray luminosity function!

Elvis et al. 1978, MNRAS 183, 129

Cosmological evolution

• X-ray imaging took

AGN luminosity functions to z>2

• Cosmic evolution of

AGN population similar in X-rays to

• ptical.
• 420 AGN in the

Einstein EMSS.

Maccacaro et al. 1991, ApJ, 374,117

Into the Rosat era

Boyle, Shanks & Peterson

1988, MNRAS 235, 935: – optical L.F. – peak at z~2

Page et al. 1997, MNRAS 291, 324:

– X-ray L.F. – peak at z~2

X-rays told us that this break is real

Chandra and XMM-Newton era

• Evolution models somewhat

more complex

• Basic shape and evolutionary

pattern close to those in Rosat era

• Studies try to constrain

luminosity function and absorption properties simultaneously

• 0.5-2 keV and 2-10 keV

bands have different sensitivity to absorption

Aird et al. 2015, MNRAS, 451, 1892

Clustering

• Clustering analyses

tell us (assuming LCDM) about the masses dark matter halos in which AGN reside.

• You need a lot of

pairs to get a good measurement.

• In the 90s X-rays won
• ut at low redshift
• But it’s hard to get

excited about 90s quality data.

Boyle & Mo 1993, MNRAS, 260, 925

Clustering

• Cosmos has good

geometry and size for AGN clustering study.

• AGN live in > 3x1010

solar mass galaxies

• Findings not radically

different to SDSS, or 2Qz though, and constraints much weaker.

Gilli et al. 2009, A&A 494, 33

Charting the AGN population: where do X-ray surveys win?

• Raw statistical power of optical surveys like SDSS is superior to

current X-ray surveys

• In clustering studies, I think optical surveys are currently way out in

front

– I’ll be delighted if you can convince me that this is honestly not the case

• Optical luminosity functions better constrained but limited by

systematics, particularly towards low luminosities, and in relation to

• bscuration.

– For low luminosity AGN, X-ray surveys win. – We need X-rays to understand how obscuration/absorption affects the luminosity function and its evolution.

AGN X-ray spectra

• X-rays come from some kind of corona around the

inner part of the accretion disc, very close to the black hole

• They carry information about the conditions and

geometry of the very innermost part

– Which is the most interesting part in physics terms

• X-ray spectra may also be related to (and so

diagnostic of) the Eddington ratios of AGN.

Soft spectrum AGN, Narrow line Seyfert 1s

• When you pick out X-ray

sources with very steep spectra, you find a lot of narrow-line Seyfert 1s.

• Same when you select in a

very soft band (Rosat WFC, PSPC)

• This really was a key

finding in working out that these are high Eddington ratio Seyferts.

Puchnarewicz et al. 1991, MNRAS 256, 589

Hard spectrum (X-ray absorbed) QSOs

Page, Mittaz & Carrera 2001, MNRAS 325, 575 Found using Rosat. Note the absorption lines in the restframe UV.

• How come these QSOs are absorbed in X-ray but not in

the optical/UV?

• XMM-Newton EPIC spectra show that they have ionised
• winds. (Page et al. 2011, MNRAS 416, 2792)

Similar story for X-ray weak AGN

• Searching for AGN

which are unusually weak in X-rays shows up an overlapping but related population of absorbed QSOs with ionised winds.

• BALQSOs are the

extreme end of the distribution.

Brandt, Laor & Wills 2000, ApJ 528, 637

AGN X-ray spectra

• AGN spectra are

roughly power law shaped

• Small dispersion in

slopes

Mateos et al. 2010, A&A 510, A35

AGN X-ray spectra

• Stacking (i.e.

averaging) AGN spectra has a long heritage.

• The Ginga 12 here

show that AGN typically have Fe lines and reflection features

Pounds et al. 1991, Nature

X-ray spectra

*though there are some pitfalls to watch out for in doing this.

• XMM-Newton’s large

throughput and lare serendipitous surveys let us do this at cosmological distances.*

• Typical AGN at z=1

look rather similar to present day AGN.

Corral et al. 2008, A&A 492, 71

AGN spectral energy distributions

• Pioneering

work by Martin Elvis et al.

Elvis et al. 1994, ApJS 95, 1

• The black hole/bulge mass relation tells us that

the formation of spheroids and black holes are intimately linked.

• QSOs had their heyday at z~2.

– Most vigorous period of black hole growth. – If black holes and stars grow together, QSOs should also be forming stars rapidly.

• Peak of star formation rate also at 1< z < 3.

Star formation in z=1-3 AGN

Energy release from black holes and stars

Black holes growing by accretion are best found by X-ray emission The most rapidly star- forming galaxies are

• ften highly obscured,

emitting the bulk of their energy in the far infrared

Arp 220

Star formation and AGN in the Chandra deep field North

Page et al. 2012 Nature 485, 213 Significant 250 micron detection fraction at z>1, at moderate AGN luminosities. Many moderate luminosity AGN (~25%) lived in ULIRGs between redshifts of 1 and 3. No 250 micron detections: prolific star formation is rare in powerful AGN.

Rather different picture from stacking analyses

• AGN luminosity

and star formation appear unrelated at low L.

• Star formation

evolves with redshift

• Star formation and

AGN luminosity correlated at high redshift

Rosario et al. 2012, A&A 545, A45

The SED is really rather key for disentangling star formation and dust heated by the AGN.

• PAHs in mid-IR can be

used to give an independent estimate

• n the star formation

rate

• Otherwise population

properties e.g. covariance between different parts of AGN SEDs the only tool.

Symeonidis et al., submitted to MNRAS

So where is the frontier today?

Position errors

Association of X-ray sources with optical/ Multiwavelength counterparts is so easy now compared to the

• ld days.

Elvis et al. 1978, MNRAS 183, 129 Puchnarewicz et al. 1991, MNRAS 256, 589 Mason et al. 1995, MNRAS 274, 1194

Today’s key questions that X-ray surveys might address

• How does the AGN luminosity function behave at

low luminosity and high redshift?

• What really are the star formation properties of

AGN?

Progress with the luminosity function

• Low L, high z, i.e. where X-ray sources are faint.
• Detecting the X-ray sources is not the (only) limiting

problem.

• Need high completeness
• Must distinguish X-rays from star formation and AGN

Aird et al. 2015, MNRAS, 451, 1892

Star formation in AGN hosts

• Opposite end of the spectrum, opposite problem.
• Distinguish AGN emission from star formation in

the infrared.

• Current AGN template + SF template approach
• nly gives you what you put in.
• One route to a solution

might be through statistical analysis of the SEDs.

Page et al. 2012, Nature 485, 213

• We know an awful lot about AGN through X-ray

surveys

• The limiting factor right now in understanding AGN

through X-ray surveys is how well we can understand the combination of X-ray and multiwavelength data.

Conclusions