Searching for pairs of accreting supermassive black holes

K. É. Gabányi1, S. Frey1, Z. Paragi2, T. An3, S. Komossa4

1SGO, Hungary; 2JIVE, the Netherlands; 3SHAO, P.R.China; 4MPIfR, Germany

Why?• Galaxies grew via merging

events ⇒ the central BHs merge ⇒ dual/binary BH systems are expected to exist

• AGNs are “easy” to observe compared to non-active SMBHs

• Simultaneous activity is most likely at kpc-scale separation (e.g., van Wassenhove et al., 2012; Fu et al., 2015)

Simulated evolution of a 1:2 spiral–spiral merger

Van Wassenhove+ 2012, ApJ 748, L7

Strong dual AGN activity is expected at small separations (d<1...10 kpc)

Periods of accretion are not necessarily simultaneous in the two components

Small detectable fraction is expected (a few per cent)

van Wassenhove et al. 2012

Examples

Komossa et al., 2003 Beswick et al., 2001

NGC 6240

Examples

Komossa et al., 2003 Beswick et al., 2001

NGC 6240

3C75

Hudson et al., 2006

Mrk 739

Koss et al., 2011

LBQS 0103-2753

Junkkarinen et al. 2001

Mrk 463

Bianchi et al. 2008

0402+379

Rodriguez et al. 2006

How to find them?

• Double-peaked narrow optical emission lines - originating from the two distinct NLRs?

• >70% of the double-peaked AGN are isolated AGN (Fu et al., 2011) • Other reasons behind double-peaked: jet-cloud interaction, rotating

NLR, outflowing NLR, blobby NLR + extinction, single AGN illuminating the ISM of two merging galaxy,… (Xu & Komossa, 2009; Crenshaw et al., 2010; Heckman et al., 1984)

?

How to find them?

• Double-peaked narrow optical emission lines - originating from the two distinct NLRs?

• >70% of the double-peaked AGN are isolated AGN (Fu et al., 2011) • Other reasons behind double-peaked: jet-cloud interaction, rotating

NLR, outflowing NLR, blobby NLR + extinction, single AGN illuminating the ISM of two merging galaxy,… (Xu & Komossa, 2009; Crenshaw et al., 2010; Heckman et al., 1984)

?

• Double-peaked + Spatially compact emissions, along the host galaxy axes, an indication for a pair of AGN? (Comerford et al., 2012)

How to find them?

• Double-peaked narrow optical emission lines - originating from the two distinct NLRs?

• >70% of the double-peaked AGN are isolated AGN (Fu et al., 2011) • Other reasons behind double-peaked: jet-cloud interaction, rotating

NLR, outflowing NLR, blobby NLR + extinction, single AGN illuminating the ISM of two merging galaxy,… (Xu & Komossa, 2009; Crenshaw et al., 2010; Heckman et al., 1984)

?

• Double-peaked + Spatially compact emissions, along the host galaxy axes, an indication for a pair of AGN? (Comerford et al., 2012)

• Variability in continuum/emission lines? (e.g. Popovic, 2012, Bon et al., 2012, Charisi et al., 2016)

How to find them?

• Double-peaked narrow optical emission lines - originating from the two distinct NLRs?

• >70% of the double-peaked AGN are isolated AGN (Fu et al., 2011) • Other reasons behind double-peaked: jet-cloud interaction, rotating

NLR, outflowing NLR, blobby NLR + extinction, single AGN illuminating the ISM of two merging galaxy,… (Xu & Komossa, 2009; Crenshaw et al., 2010; Heckman et al., 1984)

?

• Double-peaked + Spatially compact emissions, along the host galaxy axes, an indication for a pair of AGN? (Comerford et al., 2012)

• Variability in continuum/emission lines? (e.g. Popovic, 2012, Bon et al., 2012, Charisi et al., 2016)

• Checking VLBI archival observations Burke-Spolaor (2011): 1/3114

Examples of double-peaked sources followed up by radio interferometric

observations

• Tingay & Wayth (2011): 0/11 (VLBA) • Müller-Sanchez et al. (2015): 3/18 (VLA) • Gabányi et al. 2016: 0/4 (VLBA)

Examples of double-peaked sources followed up by radio interferometric

observations

• Tingay & Wayth (2011): 0/11 (VLBA) • Müller-Sanchez et al. (2015): 3/18 (VLA) • Gabányi et al. 2016: 0/4 (VLBA)

Examples of double-peaked sources followed up by radio interferometric

observations

• Tingay & Wayth (2011): 0/11 (VLBA) • Müller-Sanchez et al. (2015): 3/18 (VLA) • Gabányi et al. 2016: 0/4 (VLBA)

• Bondi & Pérez-Torres (2010): a pair of sub-mJy AGN at 5 kpc separations (EVN)

• Fu et al. (2011): double in near-infrared, dual radio-emitters (sub-mJy, 7.4 kpc) (VLA) ➞ even triple? Deane et al. Nature 2014

• Yang et al. (2016): in NGC 5252 an ULX turned out to be AGN (EVN), see also poster #5 by Minjin Kim

The case of J1425+3231

Hβ 4861Å O[III]

4959Å

O[III] 5007Å

Peng et al., 2011, RAA, 11, 141

SDSS spectrum

The case of J1425+3231

Hβ 4861Å O[III]

4959Å

O[III] 5007Å

Peng et al., 2011, RAA, 11, 141

SDSS spectrum

8.3 × 107 M⊙ 3.4 × 106 M⊙

European VLBI Network observations

1.7 GHz - 2011 Jan 265 GHz - 2011 Oct 18

EVN results at 1.7 GHz

443 mas 2.6 kpc

Frey et al., 2012, MNRAS, 425, 1185

EVN results at 1.7 GHz460 μJy

230 μJy

443 mas 2.6 kpc

C

S

Frey et al., 2012, MNRAS, 425, 1185

EVN results1.7 GHz

Frey et al., 2012, MNRAS, 425, 1185

EVN results

• Only the brighter (C) feature was detected

• flat spectrum, 𝛼=−0.23

• brightness temperature: 108K ⇒ suggests AGN

• S: <0.085 mJy at 5 GHz ⇒

• steep spectrum, 𝛼<−0.9

1.7 GHz

5 GHz

Frey et al., 2012, MNRAS, 425, 1185

e-MERLIN observations

1.6 GHz - 2015 Oct

5 GHz - 2014 Nov

Cm

De

Da

Kn

Pi

Mk2

Jb

e-MERLIN results at 1.6 GHz

e-MERLIN results at 1.6 GHzCONT: 1425+323 IPOL 1546.306 MHz 1425+3231 L.ICL001.1PLot file version 2 created 01-SEP-2016 11:23:33

Cont peak flux = 8.3638E-04 JY/BEAMLevs = 1.000E-04 * (-1, 1, 1.414, 2, 2.828, 4, 5.657,8, 11.31, 16, 22.63, 32, 45.25, 64, 90.51, 128, 181,256, 362, 512)

Decl

inat

ion

(J20

00)

Right Ascension (J2000)14 25 07.37 07.36 07.35 07.34 07.33 07.32 07.31 07.30 07.29 07.28

32 31 38.0

37.8

37.6

37.4

37.2

37.0

36.8

36.6

N

C

S

Peak: 840 μJy/beam 4σ: 100 μJy/beam

1.6 GHz

e-MERLIN resultsCONT: 1425+323 IPOL 1546.306 MHz 1425+3231 L.ICL001.1PLot file version 2 created 01-SEP-2016 11:23:33

Cont peak flux = 8.3638E-04 JY/BEAMLevs = 1.000E-04 * (-1, 1, 1.414, 2, 2.828, 4, 5.657,8, 11.31, 16, 22.63, 32, 45.25, 64, 90.51, 128, 181,256, 362, 512)

Decl

inat

ion

(J20

00)

Right Ascension (J2000)14 25 07.37 07.36 07.35 07.34 07.33 07.32 07.31 07.30 07.29 07.28

32 31 38.0

37.8

37.6

37.4

37.2

37.0

36.8

36.6

N

C

S

Peak: 840 μJy/beam 4σ: 100 μJy/beam

1.6 GHz

e-MERLIN resultsCONT: 1425+323 IPOL 1546.306 MHz 1425+3231 L.ICL001.1PLot file version 2 created 01-SEP-2016 11:23:33

Cont peak flux = 8.3638E-04 JY/BEAMLevs = 1.000E-04 * (-1, 1, 1.414, 2, 2.828, 4, 5.657,8, 11.31, 16, 22.63, 32, 45.25, 64, 90.51, 128, 181,256, 362, 512)

Decl

inat

ion

(J20

00)

Right Ascension (J2000)14 25 07.37 07.36 07.35 07.34 07.33 07.32 07.31 07.30 07.29 07.28

32 31 38.0

37.8

37.6

37.4

37.2

37.0

36.8

36.6

N

C

S

Peak: 840 μJy/beam 4σ: 100 μJy/beam

1.6 GHzCONT: 1425+323 IPOL 5072.518 MHz 1425+3231T-C.ICL001.10PLot file version 5 created 01-SEP-2016 14:12:53

Cont peak flux = 1.5363E-04 JY/BEAMLevs = 6.850E-05 * (-1, 1, 1.414, 2, 2.828, 4, 5.657,8, 11.31, 16, 22.63, 32, 45.25, 64, 90.51, 128, 181,256, 362, 512)

Decl

inat

ion

(J20

00)

Right Ascension (J2000)14 25 07.340 07.335 07.330 07.325 07.320 07.315 07.310

32 31 37.65

37.60

37.55

37.50

37.45

37.40

37.35

37.30

C

5 GHz

Peak: 150 μJy/beam 4σ: 70 μJy/beam

e-MERLIN resultsCONT: 1425+323 IPOL 1546.306 MHz 1425+3231 L.ICL001.1PLot file version 2 created 01-SEP-2016 11:23:33

Cont peak flux = 8.3638E-04 JY/BEAMLevs = 1.000E-04 * (-1, 1, 1.414, 2, 2.828, 4, 5.657,8, 11.31, 16, 22.63, 32, 45.25, 64, 90.51, 128, 181,256, 362, 512)

Decl

inat

ion

(J20

00)

Right Ascension (J2000)14 25 07.37 07.36 07.35 07.34 07.33 07.32 07.31 07.30 07.29 07.28

32 31 38.0

37.8

37.6

37.4

37.2

37.0

36.8

36.6

N

C

S

712 μJy

1.6 GHzCONT: 1425+323 IPOL 5072.518 MHz 1425+3231T-C.ICL001.10PLot file version 5 created 01-SEP-2016 14:12:53

Cont peak flux = 1.5363E-04 JY/BEAMLevs = 6.850E-05 * (-1, 1, 1.414, 2, 2.828, 4, 5.657,8, 11.31, 16, 22.63, 32, 45.25, 64, 90.51, 128, 181,256, 362, 512)

Decl

inat

ion

(J20

00)

Right Ascension (J2000)14 25 07.340 07.335 07.330 07.325 07.320 07.315 07.310

32 31 37.65

37.60

37.55

37.50

37.45

37.40

37.35

37.30

C

5 GHz1835 μJy

1122 μJy

319 μJy

Explaining the radio data of J1425+3231

(I) single AGN:

• core - C

• N - jet

• S - lobe with a compact hotspot

(II) pair of AGN:

• C and S are cores

• N: one-sided jet of C

CONT: 1425+323 IPOL 1546.306 MHz 1425+3231 L.ICL001.1PLot file version 2 created 01-SEP-2016 11:23:33

Cont peak flux = 8.3638E-04 JY/BEAMLevs = 1.000E-04 * (-1, 1, 1.414, 2, 2.828, 4, 5.657,8, 11.31, 16, 22.63, 32, 45.25, 64, 90.51, 128, 181,256, 362, 512)

Decl

inat

ion

(J20

00)

Right Ascension (J2000)14 25 07.37 07.36 07.35 07.34 07.33 07.32 07.31 07.30 07.29 07.28

32 31 38.0

37.8

37.6

37.4

37.2

37.0

36.8

36.6

N

C

S

712 μJy

1.6 GHz

1835 μJy

1122 μJy

Explaining the radio data of J1425+3231

(I) single AGN:

• core - C

• N - jet

• S - lobe with a compact hotspot

(II) pair of AGN:

• C and S are cores

• N: one-sided jet of C

CONT: 1425+323 IPOL 1546.306 MHz 1425+3231 L.ICL001.1PLot file version 2 created 01-SEP-2016 11:23:33

Cont peak flux = 8.3638E-04 JY/BEAMLevs = 1.000E-04 * (-1, 1, 1.414, 2, 2.828, 4, 5.657,8, 11.31, 16, 22.63, 32, 45.25, 64, 90.51, 128, 181,256, 362, 512)

Decl

inat

ion

(J20

00)

Right Ascension (J2000)14 25 07.37 07.36 07.35 07.34 07.33 07.32 07.31 07.30 07.29 07.28

32 31 38.0

37.8

37.6

37.4

37.2

37.0

36.8

36.6

N

C

S

712 μJy

1.6 GHz

1835 μJy

1122 μJy S is undetected at 5 GHz

Explaining the radio data of J1425+3231

(I) single AGN:

• core - C

• N - jet

• S - lobe with a compact hotspot

(II) pair of AGN:

• C and S are cores

• N: one-sided jet of C

CONT: 1425+323 IPOL 1546.306 MHz 1425+3231 L.ICL001.1PLot file version 2 created 01-SEP-2016 11:23:33

Cont peak flux = 8.3638E-04 JY/BEAMLevs = 1.000E-04 * (-1, 1, 1.414, 2, 2.828, 4, 5.657,8, 11.31, 16, 22.63, 32, 45.25, 64, 90.51, 128, 181,256, 362, 512)

Decl

inat

ion

(J20

00)

Right Ascension (J2000)14 25 07.37 07.36 07.35 07.34 07.33 07.32 07.31 07.30 07.29 07.28

32 31 38.0

37.8

37.6

37.4

37.2

37.0

36.8

36.6

N

C

S

712 μJy

1.6 GHz

1835 μJy

1122 μJy S is undetected at 5 GHz

double-peaked lines are likely

related to outflows

Conclusion

• Not everything is dual AGN which looks like a dual AGN

• We still need reliable indicators to assemble large sample of dual AGN candidates

Conclusion

• Not everything is dual AGN which looks like a dual AGN

• We still need reliable indicators to assemble large sample of dual AGN candidates

If you see too many doubles: