The puzzling case of the radio-loud QSO 3C 186: a gravitational wave recoiling black hole in a young radio source?

Abstract

Context. Radio-loud active galactic nuclei with powerful relativistic jets are thought to be associated with rapidly spinning black holes (BHs). BH spin-up may result from a number of processes, including accretion of matter onto the BH itself, and catastrophic events such as BH-BH mergers. Aims. We study the intriguing properties of the powerful (L bol ∼ 10 47 erg s −1 ) radio-loud quasar 3C 186. This object shows peculiar features both in the images and in the spectra. Methods. We utilize near-IR Hubble Space Telescope (HST) images to study the properties of the host galaxy, and HST UV and Sloan Digital Sky Survey optical spectra to study the kinematics of the source. Chandra X-ray data are also used to better constrain the physical interpretation. Results. HST imaging shows that the active nucleus is offset by 1.3 ± 0.1 arcsec (i.e. ∼11 kpc) with respect to the center of the host galaxy. Spectroscopic data show that the broad emission lines are offset by −2140 ± 390 km s −1 with respect to the narrow lines. Velocity shifts are often seen in QSO spectra, in particular in high-ionization broad emission lines. The host galaxy of the quasar displays a distorted morphology with possible tidal features that are typical of the late stages of a galaxy merger. Conclusions. A number of scenarios can be envisaged to account for the observed features. While the presence of a peculiar outflow cannot be completely ruled out, all of the observed features are consistent with those expected if the QSO is associated with a gravitational wave (GW) recoiling BH. Future detailed studies of this object will allow us to confirm this type of scenario and will enable a better understanding of both the physics of BH-BH mergers and the phenomena associated with the emission of GW from astrophysical sources.

Kicking gravitational wave detectors with recoiling black holes

“…A systematic search was carried out and described in [19][20][21][22]. A particularly promising study of 3C186 [23][24][25] is currently underway. Early reviews on this field are given in Refs.…”

Prompt electromagnetic transients from binary black hole mergers

“…A number of mechanisms may provide signals associated with these sources across a broad range of time scales from ∼10 9 years before merger to ∼10 9 years after merger [13]. Considerable evidence for binary SMBH systems has already been observed, but is restricted to those either well before merger [14][15][16][17][18][19][20][21], or well after merger [22][23][24][25][26][27][28].…”

Modeling the Black Hole Merger of QSO 3C 186

“…We find that, independent of the merger model we adopt, the mass ratio has to be q 1 4 > and that the spin of the holes are likely above 50% of their maximum value. Note that according to Figure 1 (bottom right panel) of Chiaberge et al (2017) the presence of low signal-to-noise shells or tidal tails in the host galaxy are typical of major galaxy merger remnants, i.e., the two merging galaxies have masses that are equal to within a factor of 3.…”

“…Note that the estimates of the final black hole mass in Chiaberge et al (2017) set its value in the range M 3 6 10 9  -. Increasing the assumed total recoil velocity (see the bottom of Table 1) can dramatically narrow the possible region of the binary-parameter space and can even exclude some of the pre-merger scenarios, such as the cold accretion one.…”

“…A recent detailed study (Chiaberge et al 2017) of the radioloud quasar 3C 186, which has an active nucleus offset from the galactic center by 1.3±0.1 arcsec (i.e., ∼11 kpc) and broad-line emissions offset from the narrow line spectra by 2140±390 km s , has concluded that the most likely explanation is that the central supermassive black hole (BH) is recoiling away from the center of the galaxy at ∼2000 km s −1 . Studies of this sort have been carried out in the past (Bonning et al 2007;Komossa et al 2008;Bogdanović et al 2009;Heckman et al 2009;Shields et al 2009;Strateva & Komossa 2009;Decarli et al 2009Decarli et al , 2014Lauer & Boroson 2009;Vivek et al 2009;Robinson et al 2010;Shields & Bonning 2013), prompted by the numerical relativity simulations that predicted large recoil velocities from the merger of binary black holes (Campanelli et al 2007a(Campanelli et al , 2007bBrugmann et al 2008).…”