(obscured) supermassive black holes

(Obscured) Supermassive Black HolesEzequiel Treister (IfA)Meg Urry, Shanil Virani, Priya Natarajan (Yale)Credit: ESO/NASA, the AVO project and Paolo PadovaniThe Space Density of CT AGN and the XRB

Supermassive Black Holes Credit: ESO/NASA, the AVO project and Paolo PadovaniMany obscured by gas and dust How do we know that?

Local AGN Unification

Explain Extragalactic X-ray Background

Compton Thick AGN Defined as obscured sources with NH>1024 cm-2. Very hard to find (even in X-rays). Observed locally and needed to explain the X-ray background. Number density highly uncertain. High energy (E>10 keV) observations are required to find them.

SwiftINTEGRAL

ISDCSwift SourcesTueller et al. 2007

Significance Image, 20-50 keVDeep INTEGRAL Survey (3 Msec)

Log N-Log STreister et al. in prep.

Log N-Log STreister et al. in prep.

Fraction of CT AGNTreister et al. in prep.X-ray background does not constrain density of CT AGN

CT AGN and the XRBTreister et al. in prep.

X-Ray Background SynthesisTreister et al. in prep.

Contribution of CT AGN to the XRBTreister et al. in prep.

CT AGN at High RedshiftTreister et al. in prep.

CT AGN Space Density (Lx>1045)Treister et al. in prep.Polletta+06

Treister et al. in prep.Polletta+06CT AGN Space Density (Lx>1045)

Treister et al. in prep.Tozzi+06Alexander+08CT AGN Space Density (Lx>1044)

Treister et al. in prep.Tozzi+06Alexander+08CT AGN Space Density (Lx>1044)

Treister et al. in prep.Tozzi+06Fiore+08Risaliti+99INTEGRALCT AGN Space Density (Lx>1043)

Treister et al. in prep.INTEGRALTozzi+06Fiore+08Risaliti+99CT AGN Space Density (Lx>1043)

Treister et al. in prep.Daddi+07CT AGN Space Density (Lx>1042)

Treister et al. in prep.Daddi+07CT AGN Space Density (Lx>1042)

SMBHs Spatial DensityNatarajan & Treister, 2008

UMBHs Spatial DensityNatarajan & Treister, 2008

UMBHs Spatial DensityNatarajan & Treister, 2008Self-Regulation

Momentum-driven winds (Murray et al. 2004).Radiation pressure (Haehnelt et al. 98)Energy Driven Superwind (King 05)

SummaryThe number of CT AGN in the local Universe can be constrained, thanks to Swift and INTEGRAL.Number of CT AGN still roughly consistent with XRB, but can be increased by ~4x.Strong decrease in the number of UMBHs -> Self regulation process. (???)

Observed X-ray BackgroundFrontera et al. (2006)

AGN in X-raysIncreasing NH Photoelectric absorptionaffect mostly low energy emission making the observed spectrum look harder.

How to find high-z CT AGN NOW?X-rays?Trace rest-frame higher energies at higher redshifts Less affected by obscurationTozzi et al. claimed to have found 14 CT AGN (reflection dominated) candidates in the CDFS.Polletta et al. (2006) report 5 CT QSOs (transmission dominated) in the SWIRE survey.

Extremely Red X-ray Objects (ERXOs)ERXOs are new class of X-ray emitters about which little is known7 found in CDFS (Koekemoer et al, 2004)Defined by very red colors: R-K > 7 (Vega)Given X-ray detection and very red optical-IR spectrum, either:very high redshift AGN z > 6very obscured AGN with old or dusty host galaxies at z~2-3Probably a heterogeneous population?

ERXOs Examples in the ECDF-SUrry et al. in prep.

ECDF-S K band vs Hard X-ray FluxUrry et al. in prep.* ERXOs

Confirming the ERXOs NatureNo GALEX or GEMS counterpartsNIR spectroscopy crucial to determine the intrinsic nature no ERXO has a measured spectroscopic redshift4 ERXOs in ECDFS are bright enough to perform NIR spectroscopy. Targeted with VLT/SINFONI IFU. Three sources observed.

Sinfoni SpectroscopyUrry et al. in prep.Lx= 4.1x1044 erg/s = 1.20.4Lx= 2.6x1043 erg/s = 1.50.4Lx= 1.2x1043 erg/s = 1.31.0

How to find high-z CT AGN NOW?Mid-IR?

NuSTAR

We know that there should be many obscured SMBHs, why?Locally the obscured/unobscured ratio is ~3:1. In fact, 2 of the 3 nearest AGN are Compton Thick. More importantly, this is the case at all redshifts because of the X-ray background*There is a population that was completely missed in soft energies surveys.Those are the most obscured sources. So obscured that are not detectedeven in X-rays. Those are the CT AGN.

Even though we dont know the exact density of these sources, they arerequired in large numbers by XRB synthesis models and are observed locally.*Right now we are starting to construct a better view of the local (z LargeDiscrepancy of factors of ~2-3.Why? XRB does not constrain number of CT AGN.**However, now we can constrain the density of CT AGN directly from theINTEGRAL observations, finding that the most likely solution has aCT AGN fraction ~4x lower than previously expected.We can see that adding ~4 times more CT AGN doesnt change the XRBsignificantly.*The situation is even worse at high-z. This is because ~50% of the XRB comesFrom AGN with z2 only change total contribution ofCT AGN by ~10%.*How to count CT at moderate redshifts, z~0.5-1?Not now, but with new planned missions like EXIST and NuSTAR it will be possible inless than 10 years.*So, how many CT AGN there are?We need high energy observations at intermediate redshifts. We will have to wait for EXIST, NuSTAR and Simbol-X.*- Very luminous sources: 5 CT candidate AGN (transmission dominated) in the Chandra/SWIRE field*Density higher than expected from XRB models*At Lx=10^44, Tozzi et al. found ~7 CT AGN candidates. Alexander et al. used mid-IR Excess to find a sample of ~6 CT AGN candidates confirmed by IRS spectroscopy.*Risaliti and INTEGRAL measurements in the local Universe. Tozzi et al in the CDFSAnd Fiore et al from mid-IR excess. Corrections to Tozzi et al. comes from fraction ofCT AGN expected to be missed based on flat NH distribution.*Obvious mismatch in the local Universe, but works well at high-z.*Daddi et al. number still under heavy discussion. From excess of mid-IR SFR comparedto UV SFR.*However matches expectations from XRB models.*In general good match between observed space density of SMBHs.Efficiencies of ~10%, consistent with common assumptions.However, only works well up to 10^9*At higher masses, extrapolation of LF just doesnt work.

Tell us something about BH growth Harder to keep increasingBH mass after ~10^9

*Tried playing with Efficiency or Eddington ratio, as a function of massOr redshift Nothing really worked!

Only way to fix it: change luminosity function.

Self regulation processes?

**We know now that the X-ray background is just collective emission from previously unresolved sources,90% of them AGN.The X-ray background spectrum is very steep, with a peak at ~30 keV.This is good indication that obscured AGN should outnumber the unobscured ones.*The reason is that obscuration makes the X-ray spectrum appear harder. In these units, an unobscured AGNis roughly flat, while as we add more and more obscuration (parameterized as a neutral hydrogen column density)the observed spectrum appears harder and harder, thus closer to the observed X-ray background.Can we start now?

K correction help us! We can start looking now in Chandra and XMM data.Examples from Tozzi et al. and Polletta et al.*How do the CT AGN at high-z look like? Probably like ERXOs.i.e., no optical counterpart, but strong near and mid-IR sourcesSo we started studying ERXOS.*This is how they look line: no BVR detection to mag~27K detection and strong in Spitzer IRAC bands*In a K-band versus hard X-ray they are separated from the rest of the population.They are in a location dominated by hard spectrum sources.*Only way to confirm their real nature -> near-IR spectroscopy*We got SINFONI spectra for these three sources.

In all cases we detect continuum and at least two emission linesLx~43-44.Not possible to measure NH (only 50 counts maximum), but they have very hard spectra!*Another way to find CT AGN: mid-IR excess sources

Somewhat more indirect than X-rays, but seems to workConfirmed by X-ray stacking. *EXIST will be a all-sky mission covering from 5-600 keV. Like ROSAT but at higher energies. Many (~1000) AGN includingCT ones up to z~0.5.*NuSTAR is a complementary approach.

Pointed observations, covering relatively small areas (maximum ~1 sq. degree)But ~20x deeper than NuSTAR. Good for sources up to z~2.*