Searching for Binary Super-Massive BHs in AGNs

Transcription

1 Searching for Binary Super-Massive BHs in AGNs Gulab Chand Dewangan IUCAA, Pune

2 Binary Super-massive BHs Galaxy mergers result in massive binary BHs Detection important to understand galaxy evolution, fueling of AGN, growth of SMBHs, triggering starburst activity, etc. Coalescing binary BHs strong sources of GW, detectable with LISA. Simulation of galaxy mergers (Mayer et al. 2007, Science)

3 Binary SMBHs - Examples (Komossa et al. 2006) Two hard X-ray nuclei with L X ~ (1.9, 0.7) x ergs/s. Separation ~ 1.4 arcsec (~1 kpc)

4 Binary AGNs in Mrk739 Koss et al SDSS composite gri image SDSS r image + Chandra X-ray contours 3.4 kpc Two point X-ray sources coincident with two bulges in the optical. L(2-10keV) = 1.1e43 ergs/s and 1.0e42 ergs/s The eastern source optical AGN, western source highly variable.

5 Candidate Binary AGN in SDSS Binary AGN with distinct Narrow-line regions Double-peaked [OIII] narrow emission lines 148 AGNs (86 type type 2) from DR7 (z<0.7) Only two Resolved double nuclei in SDSS images 148 Candidates of Binary SMBHs Separation > a few100pc (Smith et al. 2010)

6 A new technique to identify close binary SMBHs Distinct Broadband X-ray spectral shape (Dewangan & Misra 2011) Type 1 + Type 2 Nuclei Are there AGNs with such X-ray spectra? YES

7 Partial Covering X-ray Absorption (PCA) Patchy Absorber Correlated X-ray variability between soft & hard bands. 1H (Turner et al.2009) Difficult to find such AGN?

8 PCA model If the absorbed & Unabsorbed parts are both variable but not correlated?

9 PCA model for type 1 RQ AGNs (Dewangan & Misra 2011) Two close active nuclei Absorbed + Unabsorbed nuclei In a close binary Mrk739 (Koss et al. 2011) NGC6240 Chandra (Komossa et al 2003) Different amount of absorption along the individual nuclei. PCA+X-ray Variabilty Unresolved binary SMBHs Uncorrelated X-ray Variability between Soft & hard bands.

10 PDS456 Broadband X-ray Emission (Dewangan & Misra 2011) Most powerful quasar in the local universe High velocity outflows (v~0.25c) A combination of absorbed PL & relatively unabsorbed BB (kt~140ev) + PL (Г~2.7) Binary active nuclei?

11 PDS 456 X-ray Variability Complex X-ray Variability Correlations consistent with binary SMBH model

12 PDS456 - Cross-correlation Contribution of the first PL decreases with E Uncorrelated when the two nuclei dominate different bands. Physically Independent continua. Consistent with close binary SMBH.

13 PDS 456 as Binary SMBH Simpson et al Common BLR Separation < BLR size ~ 0.7 pc, M BH1 + M BH2 ~ 10 9 M M BH1 ~ M, M BH2 ~ M (Dewangan & Misra 2011)

14 Confirming Binary SMBHs X-ray Technique The technique can detect really close, sub-parsec scale binary SMBHs. Needs confirmation with other techniques. SDSS Candidates 148 SDSS Candidates based on double-peaked [OIII] emission lines Need confirmation with other techniques. Other Candidates : X-shaped radio galaxies, double-double radio galaxies, periodicities, etc. Direct imaging of double nuclei is the best way to confirm. Use adaptive-optics imaging.

15 Adaptive-optics imaging of double nuclei 0.2 arcsec resolution corresponds to sizes 365pc at z= pc at z= kpc at z=0.5 Adaptive-optics imaging can resolve sub-kpc to several kpc scale binary nuclei. X-ray technique: type 1+2 blue + red nuclei. B and R band images should reveal binary nuclei. SDSS images of AGNs with double-peaked [OIII] Images from 2.5m SDSS Telescope

16 Summary Number of candidate binary SMBHs from SDSS and X-ray observations. High resolution imaging with adaptive-optics well suited to confirm binary nuclei with sub-kpc to many kpc scale separation. Once confirmed, the X-ray technique has the potential to reveal really close, sub-parsec scale binary SMBHs which may be the sources of gravitational waves.

17 THANK YOU