Space Density of Heavily-Space Density of Heavily-Obscured AGN, Star Formation Obscured AGN, Star Formation

and Mergersand Mergers

Ezequiel Treister (IfA, Ezequiel Treister (IfA, HawaiiHawaii)

Meg Urry, Priya Natarajan, Carie Cardamone, Kevin Schawinski (Yale), Eric Gawiser (Rutgers), Dave Sanders

(IfA)

Credit: ESO/NASA, the AVO project and Paolo Padovani

How to find high-z Obscured How to find high-z Obscured AGN?AGN?X-raysX-rays

Tozzi et al. 2006

Trace rest-frame higher energies at higher redshifts Less affected by obscurationTozzi et al. claimed

to have found 14 Compton-Thick AGN (reflection dominated) candidates in the CDFS.Polletta et al. (2006) report 5 CT QSOs (transmission dominated) in the SWIRE survey.

Fiore et al. 2008

Mid-IRMid-IR X-ray StackingX-ray Stacking

FF2424/F/FRR>1000>1000

FF2424/F/FRR<200<200

• 4 detection in X-ray stack. Hard spectral shape, harder than X-ray detected sources.Good CT AGN candidates.• Similar results found by Daddi et al. (2007)

How to find high-z Obscured How to find high-z Obscured AGN?AGN?

Extended Chandra Deep Field-Extended Chandra Deep Field-SouthSouth

Area:Area: 0.3 deg2

X-rays:X-rays: Chandra 250ks/pointing

Optical:Optical: Broad band UBVRIz (V=26.5)+ 18 Medium band filters (to R=26)

Near-IR:Near-IR: JHK to K=20 (Vega)

Mid-IR:Mid-IR: IRAC 3.6-8 microns + MIPS 24 microns to 35 µJy

Spectroscopy:Spectroscopy: VLT/VIMOS, Magellan/IMACS (optical) VLT/SINFONI, Subaru/MOIRCS (near-IR)

Mid-IR SelectionMid-IR Selection

R-K (Vega)

- 211 sources with f24m/fR>1000 and R-K>4.5- f24m>35Jy- 18 X-ray detected

Treister et al. ApJ in press

Redshift DistributionRedshift Distribution

All Sources

X-ray Detected

X-ray Undetected- Photo-z for ~50% of the sources- X-ray sources brighter at all wavelengths- Spec-z for 3 X-ray sources and photo-z for 12 (83% complete).

Treister et al. ApJ in press

Hardness Ratio Hardness Ratio N NHH

X-ray sources with redshift onlyX-ray sources with redshift only

- 2 unobscured- 11 obscured Compton-thin- 2 Compton Thick

Assumed fixed =1.9

Treister et al. ApJ in press

Stacking of non-Xrays SourcesStacking of non-Xrays Sources

Soft (0.5-2 keV) Hard (2-8 keV)

- ~4 detection in each band.- fsoft=2.1x10-17erg cm-2s-1. Fhard= 8x10-17erg cm-2s-1

- Sources can be detected individually in ~10 Msec.- Hardness ratio 0.13, NH=1.8x1023cm-2.- Alternatively, ~90% CT AGN and 10% star-forming galaxies.- Some evidence for a flux dependence. >95% CT AGN at the brightest bin, 80% at the lowest. Large error bars.

Treister et al. ApJ in press

Rest-Frame StackingRest-Frame Stacking

Good fit with either NH1023cm-2 or combination of CT AGN with star-forming galaxies.

Consistent results with observed-frame stacking.

Treister et al. ApJ in press

X-Ray to Mid-IR RatioX-Ray to Mid-IR Ratio

Both X-rays and 12µm good tracers of AGN activity.Observed ratios for X-ray sources consistent with local AGN (dashed line).

Treister et al. ApJ in press

X-Ray to Mid-IR RatioX-Ray to Mid-IR Ratio

Effects of obscuration in X-ray band luminosity.

Only important for Compton Thick sources.

Treister et al. ApJ in press

X-Ray to Mid-IR RatioX-Ray to Mid-IR Ratio

~100x lower ratio for X-ray undetected sources.

Explained by NH~5x1024 to 1025cm-2

Treister et al. ApJ in press

X-Ray to Mid-IR RatioX-Ray to Mid-IR Ratio

Ratio for sources with L12µm>1043erg/s (~80% of the sources) ~2-3x higher than star-forming galaxies

Treister et al. ApJ in press

X-Ray to Mid-IR RatioX-Ray to Mid-IR RatioUsing Lx/L12µm=0.007 to separate AGN and star-forming galaxies ~80% AGN, consistent with HR value.

In sources with L12µm>1044erg/s outside selection region fraction of AGN ~10%.

Treister et al. ApJ in press

MorphologiesMorphologies

Ground based: K,H,R

HST/WFC3J,H,Y

GOODS-SUDF

Optical/Near-IR SED FittingOptical/Near-IR SED Fitting

X-ray Detected

X-ray Undetected

X-ray Detected

X-ray Undetected

- Median stellar mass for X-ray detected sources ~4.6x1011 Msun.- For X-ray undetected source ~1011 Msun.

- Mild extinction values found in general.- Maximum Av~4 mags.- Median E(B-V)=0.6 for X-ray detected sources and 0.4 for undetected ones.

Treister et al. ApJ in press

Evidence for significant recent star formation in most sources

Heavily-Obscured AGN Space Heavily-Obscured AGN Space DensityDensity

Systematic excess for Lx>1044erg/s sources relative to extrapolation of Compton-thin LF

Strong evolution in number of sources from z=1.5 to 2.5.

Consistent with heavily-obscured phase after merger?

Treister et al. ApJ in press

Obscured to Unobscured Quasar Obscured to Unobscured Quasar RatioRatio

Treister et al. in prep.

The Merger-Quasar ConnectionThe Merger-Quasar Connection

Treister et al. in prep.

Obscured quasars are the product of the gas-rich merger of two massive galaxies. After a time t the quasar becomes unobscured.

€

NobscNUnobsc

(z) =Δtd2merger

dtdNNgal (> Mmin (z)) fgas(z)

NUnobsc (z)

The Merger-Quasar ConnectionThe Merger-Quasar Connection

Treister et al. in prep.

t=9623 Myrs

SummarySummary

• Mid-IR selection finds large number of heavily obscured AGN at z>1.5.

• Morphologies indicates interactions/mergers.

• Host galaxy masses ~1011 Msun with young and obscured stellar populations.

• Strong evolution in numbers up to z~3.• This could be evidence for a heavily obscured phase after quasar triggering.

• Mid-IR selection finds large number of heavily obscured AGN at z>1.5.

• Morphologies indicates interactions/mergers.

• Host galaxy masses ~1011 Msun with young and obscured stellar populations.

• Strong evolution in numbers up to z~3.• This could be evidence for a heavily obscured phase after quasar triggering.

IRAC ColorsIRAC Colors

[5.8]-[8] (Vega)

z=0-1

z>1

AGNFaint 8 µm

Treister et al. ApJ submitted

Log N-Log SLog N-Log S

Treister et al. 2009

CT AGN Space DensityCT AGN Space Density

z=0 LFNumber of sources roughly consistent with extrapolation of Compton-thin LF

Steeper evolution suggested by Della Ceca et al. (2008) and Yencho et al. (2009) work better

Treister et al. ApJ submitted

IRAC ColorsIRAC Colors

log (f5.8/f3.6)F

ain

t 8µ

m

Treister et al. ApJ submitted

Near to Mid-IR ColorsNear to Mid-IR Colors- Distributions significantly different- X-ray detected sources much bluer- Average f8/f24=0.2 for X-ray sources and 0.04 for X-ray undetected sample

BluerRedder

Well explained by different viewing angle (30o vs 90o) in the same torus model Can it be star-formation versus AGN?

Treister et al. ApJ in press

Near to Mid-IR ColorsNear to Mid-IR Colors

Armus et al. 2007

ULIRG, LINER

ULIRG, Sey2