arXiv subjects

Laura Blecha

Publications and source records attributed to Laura Blecha.

112 records · Page 7Linked to original sources

arXiv2011

Recoiling Black Holes in Merging Galaxies: Relationship to AGN Lifetimes and Merger Remnant Properties

Central supermassive black holes (SMBHs) are a ubiquitous feature of locally-observed galaxies, and ample evidence suggests that the growth of SMBHs and their host galaxies is closely linked. However, in the event of a merger, gravitational-wave (GW) recoil may displace a SMBH from its galactic center, or eject it entirely. To explore the consequences of this phenomenon, we use hydrodynamic simulations of gaseous galaxy mergers that include a range of BH recoil velocities. We have generated a suite of over 200 simulations with more than 60 merger models, enabling us to identify systematic trends in the behavior of recoiling BHs -- specifically (i) their dynamics, (ii) their observable signatures, and (iii) their effects on BH/galaxy co-evolution. (i) Recoiling BH trajectories depend heavily on the gas content of the host galaxy; maximal BH displacements from the center may vary by up to an order of magnitude between gas-rich and gas-poor mergers. In some cases, recoil trajectories also depend on the timing of the BH merger relative to the formation of the galaxy merger remnant. (ii) Recoiling BHs may be observable as offset active galactic nuclei (AGN) via either kinematic offsets (v > 800 km s^-1) or spatial offsets (R > 1 kpc) for lifetimes of about 1 - 100 Myr. In addition, recoil events affect the total AGN lifetime. GW recoil generally reduces the lifetimes of bright AGN, but may extend lower-luminosity AGN lifetimes. (iii) Rapidly-recoiling BHs may be up to about 5 times less massive than their stationary counterparts. These mass deficits lower the normalization of the M - sigma relation and contribute to both intrinsic and overall scatter. Furthermore, recoil events displace AGN feedback from the galactic center, which enhances central star formation rates. This results in longer starburst phases and higher central stellar densities in merger remnants.

astro-ph.CO↗

arXiv2011

Recoiling Black Holes in Merging Galaxies

Gravitational-wave (GW) recoil of merging supermassive black holes (SMBHs) may influence the co-evolution of SMBHs and their host galaxies. We examine this possibility using SPH/N-body simulations of gaseous galaxy mergers in which the merged BH receives a recoil kick. With our suite of over 200 merger simulations, we identify systematic trends in the behavior of recoiling BHs. Our main results are as follows. (1) While BHs kicked at nearly the central escape speed (vesc) are essentially "lost" to the galaxy, in gas rich mergers, BHs kicked with up to about 0.7 vesc may be confined to the central few kpc of the galaxy. (2) The inflow of cold gas during a gas-rich major merger may cause a rapid increase in central escape speed; in such cases recoil trajectories will depend on the timing of the BH merger relative to the change in vesc. (3) Recoil events generally reduce the lifetimes of bright active galactic nuclei (AGN) but may actually extend AGN lifetimes at lower luminosities. (4) Recoiling AGN may be observable via kinematic offsets (v > 500 km s^-1) or spatial offsets (R > 1 kpc) for lifetimes of up to about 10 - 100 Myr. (5) Rapidly-recoiling BHs may be up to about 5 times less massive than their stationary counterparts. These mass deficits lower the normalization of the M - sigma relation and contribute to both intrinsic and overall scatter. (6) Finally, the displacement of AGN feedback by a recoil event causes higher central star formation rates in the merger remnant, thereby extending the starburst phase of the merger and creating a denser, more massive stellar cusp.

astro-ph.CO↗

arXiv2010

Recoiling Black Holes in Merging Galaxies: Relationship to AGN Lifetimes, Starbursts, and the M-sigma Relation

Gravitational-wave (GW) recoil of merging supermassive black holes (SMBHs) may influence the co-evolution of SMBHs and their host galaxies. We examine this possibility using SPH/N-body simulations of gaseous galaxy mergers in which the merged BH receives a recoil kick. This enables us to follow recoiling BHs in self-consistent, evolving merger remnants. In contrast to recent studies on similar topics, we conduct a large parameter study, generating a suite of over 200 simulations with more than 60 merger models and a range of recoil velocities (vk). Our main results are as follows. (1) BHs kicked at nearly the central escape speed (vesc) may oscillate on large orbits for up to a Hubble time, but in gas-rich mergers, BHs kicked with up to ~ 0.7 vesc may be confined to the central few kpc of the galaxy, owing to gas drag and steep central potentials. (2) vesc in gas-rich mergers may increase rapidly during final coalescence, in which case trajectories may depend on the timing of the BH merger relative to the formation of the potential well. (3) Recoil events generally reduce the lifetimes of bright active galactic nuclei (AGN), but may actually extend AGN lifetimes at lower luminosities. (4) Kinematically-offset AGN (v > 800 km s^-1) may be observable for up to ~ 10 Myr either immediately after the recoil or during pericentric passages through a gas-rich remnant. (5) Spatially-offset AGN (R > 1 kpc) generally have low luminosities and lifetimes of ~ 1 - 100 Myr. (6) Rapidly-recoiling BHs may be up to ~ 5 times less massive than their stationary counterparts. This lowers the normalization of the M-sigma relation and contributes to both intrinsic and overall scatter. (7) Finally, the displacement of AGN feedback after a recoil event enhances central star formation rates, thereby extending the starburst phase of the merger and creating a denser stellar cusp. [Abridged.]

astro-ph.CO↗

arXiv2008

Effects of gravitational-wave recoil on the dynamics and growth of supermassive black holes

Simulations of binary black hole mergers indicate that asymmetrical gravitational wave (GW) emission can cause black holes to recoil at speeds up to thousands of km/s. These GW recoil events can dramatically affect the coevolution of recoiling supermassive black holes (SMBHs) and their host galaxies. However, theoretical studies of SMBH-galaxy evolution almost always assume a stationary central black hole. In light of the numerical results on GW recoil velocities, we relax that assumption here and consider the consequences of recoil for SMBH evolution. We follow the trajectories of SMBHs ejected in a smooth background potential that includes both a stellar bulge and a multi-component gaseous disk. In addition, we calculate the accretion rate onto the SMBH as a function of time using a hybrid prescription of viscous (alpha-disk) and Bondi accretion. We find that recoil kicks between 100 km/s and the escape speed cause SMBHs to wander through the galaxy and halo for about 1 Myr - 1 Gyr before settling back to the galactic center. However, the mass accreted during this time is roughly constant at about 10% of the initial mass, independent of the recoil velocity. This indicates that while large recoils may disrupt active galactic nuclei feedback processes, recoil itself is an effective means of regulating SMBH growth. Recoiling SMBHs may be observable as spatially or kinematically offset quasars, but finding such systems could be challenging, because the largest offsets correspond to the shortest quasar lifetimes.

astro-ph↗