(Candidate) massive black hole binaries in the realm of observations Massimo Dotti University of Milano Bicocca Collaborators R. Decarli P. Tsalmantza C. Montuori D. Hogg & many others...
Some Zoology Pre-merger phase D ~ few 10-100 kpc AGN PAIRS Known: 50-100
Some Zoology Pre-merger phase D ~ few 10-100 kpc AGN PAIRS Known: 50-100 125 kpc 11 kpc SDSS J0927+2943 A,B (Decarli et al. 2010) SDSS J1254+0846 (Green et al. 2010) IRAS J20210+1121 (Piconcelli et al. 2010)
Some Zoology Pre-merger phase D ~ few 10-100 kpc AGN PAIRS Known: 50-100 Merger phase D ~ 100 pc -10 kpc DUAL black holes Known: ~10
Some Zoology Pre-merger phase D ~ few 10-100 kpc AGN PAIRS Known: 50-100 Merger phase D ~ 100 pc -10 kpc DUAL black holes Known: ~10 Bound MBH binaries?
Scales: i.e., when (where) a binary forms assuming the M sigma relation (!)
Scales: i.e., when (where) a binary forms Begelman, Blandford & Rees (1980)
Scales: i.e., when (where) a binary forms assuming the M sigma relation (!) Note: 0.5 pc ~ 1 mas @ z~0.03 (d~130 Mpc)
THE BHB candidate: 0402+379 Maness et al. 2004 Rodriguez et al. 2006 7.3 pc the M BH L bulge relation implies M BH ~10 8 Msun
A different way to identify sub pc MBH binaries Begelman et al. 1980 BLR of (at least) one MBH
A different way to identify sub pc MBH binaries Begelman et al. 1980 BLR of (at least) one MBH The redshift of the BELs will be different from the galaxy redshift (NELs)
Spectroscopy Pro Huge amount of data (e.g. the SDSS database) Contra Huge amount of data! It requires an automatic search More effective at close (sub pc) separations, where we cannot spatially resolve MBHBs The binary model is not the only one predicting a frequency difference between BELs and NELs (more to come...) The model is falsifiable it predicts a frequency drift of the BELs over the binary orbit
No BHB candidate survived until 2008...then a new burst of (5) candidates appeared SDSS 0927+2943 Komossa et al. 2008, Bogdanovic et al. 2009, Dotti et al. 2009 SDSS J1050+3456 Shields et al. 2009
This burst called for a systematic search Tsalmantza et al. 2011 Search for multiple sets of emission lines at different redshifts Eracleous et al. 2012 Search for displaced/irregular broad H
This burst called for a systematic search Tsalmantza et al. 2011 Search for multiple sets of emission lines at different redshifts 32 peculiar objects, 9 considered good BHB candidates Eracleous et al. 2012 Search for displaced/irregular broad H 88 candidate selected 68 objects had follow ups 14 show accelerations 120 km/s/yr < a <120 km/s/yr (long periods, ~100 yr)
Caveats: alternative explanations to line shifts Recoiling black hole (Komossa et al. 2008) velocities up to 5000 km/s (Lousto et al. 2012) the bulk of the expected velocities is way smaller... Disk emission, e.g. double peak emitters (Eracleous et al. 1994) Cosmological superposition sub arcsec alignment of 2 AGN is unlikely Superposition in a cluster (e.g. Heckman et al. 2009) velocity differences are very high None of these models predict (periodic) frequency drifts on <100 yr timescale
Tsalmantza sample follow ups Optical spectroscopy to look for frequency drifts (Decarli et al. 2013) Optical/infrared imaging (Decarli et al. in prep) to probe the superposition scenario Broad SED to probe the recoiling scenario (presence of a torus / Lusso et al. submitted)
Tsalmantza sample follow ups Optical spectroscopy to look for frequency drifts (Decarli et al. 2013) Optical/infrared imaging (Decarli et al. in prep) to probe the superposition scenario Broad SED to probe the recoiling scenario (presence of a torus / Lusso et al. in prep) Every object (but possibly one?) has a torus
Tsalmantza sample follow ups Optical spectroscopy to look for frequency drifts (Decarli et al. 2013) Optical/infrared imaging (Decarli et al. in prep) to probe the superposition scenario Few (3) candidates are actually superpositions Broad SED to probe the recoiling scenario (presence of a torus / Lusso et al. in prep) Every object (but possibly one?) has a torus
Tsalmantza sample follow ups Optical spectroscopy to look for frequency drifts (Decarli et al. 2013) Few of the candidates show huge velocity changes Eg J1414+1658: v= 1800±350 km/s; a ~ 540 km/s/yr; P ~ 21 yr (!) Optical/infrared imaging (Decarli et al. in prep) to probe the superposition scenario Few (3) candidates are actually superpositions Broad SED to probe the recoiling scenario (presence of a torus / Lusso et al. in prep) Every object (but possibly one?) has a torus
Problem: Maximum redshift of a candidate ~0.7 The bright NELs move out of SDSS band We need a new approach to look for binaries at z>0.7 Peculiar broad line ratios
Peculiar broad line ratios C IV Mg II
35 Objects
35 Objects 5 selected for a IR followup 2 show BELs shifted with respect to the NELs
Roedig et al. 2012
M1=3e8 Msun M2=1e8 Msun Fedd=0.1 Montuori et al. 2012
Summary Samples of MBH binary candidates in large spectroscopic catalogues (both at low and high redshift) Follow up observations are needed to discriminate among different scenarios Few objects show significant frequency drifts Few superpositions have been found Only 1 object shows reduced IR emission (recoil candidate)