The puzzling case of the radio-loud QSO 3C 186: a gravitational wave recoiling black hole in a young radio source? (1611.05501v3)

Abstract: Context. Radio-loud AGNs 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 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.

• The paper demonstrates that 3C 186 shows an 11 kpc spatial offset and a −2140 km/s blue-shift in broad emission lines, supporting a gravitational wave recoil scenario.
• It utilizes HST imaging, SDSS spectroscopy, and Chandra X-ray data with 2-D modeling to pinpoint the quasar's displacement from its host galaxy.
• The findings imply that a merger-induced gravitational wave recoil is the most consistent explanation for the observed anomalies in this radio-loud quasar.

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

This paper investigates the radio-loud quasar 3C~186, which exhibits peculiar spatial and spectral properties suggestive of a gravitational wave (GW) recoiling black hole. The authors explore various scenarios to explain these phenomena, ultimately favoring the GW recoiling black hole hypothesis as the most consistent explanation.

Context and Objectives

Rapidly spinning black holes (BHs) are associated with the presence of powerful relativistic jets in radio-loud active galactic nuclei (AGNs). These BHs might result from matter accretion or BH mergers. The object 3C~186, presenting both image and spectral anomalies, is investigated to determine if it signifies a GW recoiling BH in a young radio source. This paper aims to elucidate whether the observed features can be attributed to a gravitational wave recoil induced by a BH merger or if alternative explanations are more plausible.

Methodology

The paper utilizes a comprehensive set of data:

1. Imaging: Near-infrared images from the Hubble Space Telescope (HST) are analyzed to assess the host galaxy's properties.
2. Spectroscopy: HST UV and Sloan Digital Sky Survey (SDSS) optical spectra investigate the object's kinematics.
3. X-ray Data: Chandra observations provide additional constraints.

The team used a 2-D modeling technique on the HST images to determine the spatial offset between the quasar and the host galaxy's nucleus. For spectral analysis, line offsets between broad and narrow emission components were scrutinized, and their significance evaluated.

Key Findings

• Spatial Offset: The quasar is offset by approximately 1.3 arcsec (about 11 kpc) from the center of the host galaxy, evidenced through detailed imaging analysis.
• Velocity Offset: Broad emission lines are blue-shifted by approximately -2140 km/s relative to narrow line emissions, indicating kinematic discrepancy.
• Absence of Additional Host Galaxy Influence: Spectral data analysis and simulations confirm the host galaxy as the QSO's true residence, with no evidence supporting additional galaxy effects.

Interpretations and Implications

After considering several scenarios, including dual AGN presence, an extreme disk emitter, or peculiar winds, the authors conclude the most coherent explanation is the GW recoiling BH scenario. Given the peculiar velocity and spatial anomalies observed, the BH merger likely induced a gravitational wave recoil effect, explaining both the positional and spectral offsets.

Theoretical and Practical Impact

This interpretation is consistent with expected behaviors postulated for GW recoiling BHs, suggesting that 3C~186 could serve as a key observational target to understand the impacts of BH mergers and associated anisotropic GW emissions. The insights gained have implications for the paper of long-term AGN evolution, galaxy mergers, and the nature of relativistic jets in the presence of recoiling BHs.

Future Prospects

The paper calls for further detailed observational efforts to strengthen the GW recoiling BH hypothesis for 3C~186, including deeper imaging and higher-resolution spectroscopy. Future studies on this quasar will enhance comprehension of post-merger dynamics and enrich understanding of SMBH formations and their evasive mergers. The eventual detection of such GW events by observatories like LISA would further athenticate the predictions outlined in this work, reinforcing multimedia strategies in astrophysics for unveiling cosmic phenomena.