Obscured AGNs in Advanced Mergers

Shobita SatyapalLaura Blecha, Sara Ellison, Nathan Secrest, Ryan

Hickox,Claudio Ricci, Barry Rothberg, Mario Gliozzi, William McAlpine, Anca Constantin, Jason Ferguson

§ LCDM predicts that interactions are ubiquitous§ Theory predicts gas is funneled towards center § AGNs can be missed at various stages on merger sequence§ Peak of SMBH growth occurs near coalescence§ Key phase in galaxy evolution and BH growth may be

obscured

(Di Matteo, Springel, & Hernquist 2005)

Motivation and Overview

Key unanswered questions:

• How much do SMBHs grow in mergers?

• How are the SMBH and galaxy scaling relations

established?

• How efficient are feedback processes?

• How often do galaxies coalesce? -> G-waves

Goal of this Work

• Study the AGNs and SF properties in the most advanced mergers to study a key phase in galaxy evolution

Wide Field Infrared Survey Explorer (WISE)+ Chandra + NIR Ground-based Spectroscopy

• Conduct a large systematic MIR study of AGNs in galaxy pairs and mergers to quantify the incidence of obscured AGNs triggered by interactions

DR7 pairs sample: Projected separation <80 kpcDV <300 km/sMass ratio 025 - 4

Yields: ~14,000 galaxies in pairs.

Construct control samples that are matched in mass, redshift and environment: typically 100 control galaxies per pair.

Matched to WISE

Yields: ~5,000 galaxies in pairs.

Galaxy pairs in the SDSS

Post-merger sample

97 visually selected post-mergers from Galaxy Zoo.

Control matching and analysis done exactly same as for pairs.

AGN frequency: from optical emission lines

See also Ellison et al. (2011), Khabiboulline et al. (2014)

Although AGN may be triggered by first pass, fraction increases most strongly after coalescence

Ellison et al. (2013)

Mer

ger A

GN

frac

tion/

cont

rol

AGN

frac

tion

AGN frequency: from mid-IR colours

Satyapal et al. (2014)

W1-W2>0.8

W1-W2>0.5

Optical BPT

Significant fraction of merger triggered AGN are dust obscured and not seen as AGN in optical.

Increase in AGN luminosity at smaller separations.

Measured in the mid-IR with WISE: Satyapal et al. (2014)

Measured in the optical with [OIII]:Ellison et al. (2013)

Obscured Phase Occurs at Peak BH growthand small pair separations

D<10kpc

(van Wassenhove et al. 2012)

Dual AGNs

• Duals (sep<10kpc) predicted in late stage mergers

• Identifies most efficient environments for rapid SMBH growth

• Unique signature of merger driven BH growth in both nuclei

• Enables determination of BH mass and accretion rate in both hosts

• Observationally more accessible precursor to true binary stage

Importance of Dual AGNs

GOAL: Obtain Large Sample of Dual AGNs

Previous Searches: Optical Studies

Dual AGNs are exremely rare

• < 0.1 % of quasars are binaries (Hennawi et al. 2010) peak at ~ 30 kpc separations (Foreman et al. 2008)

• Double-peaked SDSS spectra (~ 1% of all low-z AGN; e.g., Liu et al. 2010, Smith et al. 2010, Wang et al. 2009)

• Only ~2% confirmed dual in follow-up spatially resolved studies (Fu et al. 2011,2012, Shen et al. 2011, Smith et al. 2012, Comerford et al. 2012,2015)

Limitations with Optical Searches

• Double-peaked emission lines can arise from rotating disks or bi-conical outflows from singleAGN

• Theory predicts double-peaks for only small fraction of time (Blecha et al. 2013)

• Dual AGNs may be optically obscured the majority of the time when they are active

3C 75 SDSS J1107+6505 0402+37 SDSS J2206+0003 SDSS J1126+2944 SDSS J2300-0005

SDSS J17154+6008 SDSS J1023+3243 SDSS J1158+3231 SDSS J0051+0020 Mrk 266 SDSS J1146+5110

SDSS J0038+4128 SDSS J1108+0659 NGC 6240 SDSS J223+00122 Mrk 739 SDSS J1623+0808

SDSS J0952+2552 SDSS J1502+1115 SDSS J1425+3231 Mrk 463 SDSS J1323-0159

Only a few (<10 kpc) Duals Known

Most early discoveries serendiptious in X-ray

> W1-W2

MIR Properties of Confirmed Duals

• Most duals are red in MIR

•Highest luminosity duals in AGN wedge

Dual Candidates Pre-selected by WISE

Sample Selection• Drawn from Galaxy zoo (667,000 galaxies)• Required high probability of merger

(40%;~12,000)• Required W1-W2>0.8 (178 candidates)• Obtained follow-up Chandra (cycles 15 and 17)

observations of 15 brightest candidates• XMM follow-up + NuSTAR

WISE-Selected Chandra Sample

J0122+0100 J1036+0221 J1045+3519

J1126+1913 J1221+1137J1306+0735

WISE-Selected Chandra Sample

ACIS-S 0.3-8.0 keV

WISE-Selected Chandra Sample

4/6 dual X-ray sources; all have at least one!

WISE-Selected Chandra Sample

Not enough counts for spectral fitting, intrinsic NH unknown

L2-10 keV > 1041 erg s-1

(Satyapal et al. in prep)

LBT Near-IR Spectra show AGN Signatures

• Can estimate SFR from H-recombination linesNot sufficient to account for observed LX

High Incidence of MIR duals consistent with simulations

SEE POSTER BY LAURA BLECHA

Near-IR spectra consistent with young starbursts

• Stellar population consistent with < 10 Myr

1 2 5

10−6

10−5

2×10

−65×

10−6

2×10

−5

Phot

ons

cm−2

s−1

keV

−1

Energy (keV)

Unfolded Spectrum

WISE Selected mergers have high NH

(Ricci et al. 2015,2016)

Duals reside near CT sources in the Swift/BAT survey

a b

c d

a b c d

Very high NH consistent with simulations

Blecha et al., in prepSEE POSTER BY LAURA BLECHA

Conclusions• FractionofMIRAGNincreaseswithdecreasingpairseparation;mostdramaticinmostadvancedmergers

• WISEpre-selectionpromisingavenueofinvestigationinfindingdualAGNsinlatestagemergers

• CandoubleknowndualAGNsat<10kpcseparations

• ChandraobservationssuggestthattheseAGNsarehighlyabsorbed(NH>1023 cm2)

• Thissamplerepresentsakeystageinco-evalevolutionofgalaxiesandBHsinvisibletoopticalstudies

• Ourresultsareconsistentwiththeoreticalpredictions