24 research outputs found
Recoiling Massive Black Holes in Gas-Rich Galaxy Mergers
The asymmetric emission of gravitational waves produced during the
coalescence of a massive black hole (MBH) binary imparts a velocity "kick" to
the system that can displace the hole from the center of its host. Here we
study the trajectories and observability of MBHs recoiling in three (one major,
two minor) gas-rich galaxy merger remnants that were previously simulated at
high resolution, and in which the pairing of the MBHs had been shown to be
successful. We run new simulations of MBHs recoiling in the major merger
remnant with Mach numbers in the range 1<M<6, and use simulation data to
construct a semi-analytical model for the orbital evolution of MBHs in gas-rich
systems. We show that: 1) in major merger remnants the energy deposited by the
moving hole into the rotationally supported, turbulent medium makes a
negligible contribution to the thermodynamics of the gas. This contribution
becomes significant in minor merger remnants, potentially allowing for an
electromagnetic signature of MBH recoil; 2) in major merger remnants, the
combination of both deeper central potential well and drag from high-density
gas confines even MBHs with kick velocities as high as 1200 km/s within 1 kpc
from the host's center; 3) kinematically offset nuclei may be observable for
timescales of a few Myr in major merger remnants in the case of recoil
velocities in the range 700-1,000 km/s; 4) in minor mergers remnants the effect
of gas drag is weaker, and MBHs with recoil speeds in the range 300-600 km/s
will wander through the host halo for longer timescales. When accounting for
the probability distribution of kick velocities, however, we find that the
likelihood of observing recoiling MBHs in gas-rich galaxy mergers is very low,
typically below 10^-5 - 10^-6.Comment: Revised version, accepted for publication in the Astrophysical
Journa
Massive Black Hole Recoil in High Resolution Hosts
The final inspiral and coalescence of a black hole binary can produce highly
beamed gravitational wave radiation. To conserve linear momentum, the black
hole remnant can recoil with "kick" velocity as high as 4000 km/s. We present
two sets of full N-body simulations of recoiling massive black holes (MBH) in
high-resolution, non-axisymmetric potentials. The host to the first set of
simulations is the main halo of the Via Lactea I simulation (Diemand et al.
2007). The nature of the resulting orbits is investigated through a numerical
model where orbits are integrated assuming an evolving, triaxial NFW potential,
and dynamical friction is calculated directly from the velocity dispersion
along the major axes of the main halo of Via Lactea I. By comparing the
triaxial case to a spherical model, we find that the wandering time spent by
the MBH is significantly increased due to the asphericity of the halo. For
kicks larger than 200 km/s, the remnant MBH does not return to the inner 200 pc
within 1 Gyr, a timescale an order of magnitude larger than the upper limit of
the estimated QSO lifetime. The second set of simulations is run using the
outcome of a high-resolution gas-rich merger (Mayer et al. 2007) as host
potential. In this case, a recoil velocity of 500 km/s cannot remove the MBH
from the nuclear region.Comment: 4 pages, 4 figures. Proceedings of the conference Galactic & Stellar
Dynamics In the Era of High Resolution Survey
Stellar and Gaseous Nuclear Disks Observed in Nearby (U)LIRGs
We present near-infrared integral field spectroscopy of the central
kiloparsec of 17 nearby luminous and ultra-luminous infrared galaxies
undergoing major mergers. These observations were taken with OSIRIS assisted by
the Keck I and II Adaptive Optics systems, providing spatial resolutions of a
few tens of parsecs. The resulting kinematic maps reveal gas disks in at least
16 out of 19 nuclei and stellar disks in 11 out of 11 nuclei observed in these
galaxy merger systems. In our late-stages mergers, these disks are young
(stellar ages Myr) and likely formed as gas disks which became unstable
to star formation during the merger. On average, these disks have effective
radii of a few hundred parsecs, masses between and ,
and between 1 and 5. These disks are similar to those created in
high-resolution hydrodynamical simulations of gas-rich galaxy mergers, and
favor short coalescence times for binary black holes. The few galaxies in our
sample in earlier stages of mergers have disks which are larger
( pc) and likely are remnants of the galactic disks that
have not yet been completely disrupted by the merger.Comment: accepted for publication in Ap
Simulations of Recoiling Massive Black Holes
The coalescence of black hole binaries is a significant source of gravitational wave radiation. The typically asymmetric nature of this emission, which carries linear momentum, can result in the recoil of the black hole remnant with velocities in the range 100 < Vrecoil < 3750 km s−1. The detectability of recoiling massive black holes (MBH) as off-nuclear QSOs is tightly connected with the properties of the host galaxy, which determine the MBH's orbit and fuel reservoir. We present the results of N-body simulations of recoiling MBHs in high-resolution, non-axisymmetric potentials. We find that if the recoil velocities are high enough to reach regions of the galaxy dominated by the generally triaxial dark matter distribution, the return time is significantly extended when compared to a spherical distribution. We also perform simulations of recoiling MBHs traveling in gas merger remnants, where large amounts of gas have been funneled to the central regions, In this case, the MBHs remain within R<1 kpc from the center of the host even for high recoil velocities (Vrecoil = 1200 km s−1) due to the compactness of the remnant galaxy's nuclear disk. We discuss the implications of both scenarios for detectabilit
The circumgalactic medium of massive galaxies at z~3: a test for stellar feedback, galactic outflows, and cold streams
We present new results on the kinematics, thermal and ionization state, and
spatial distribution of metal-enriched gas in the circumgalactic medium (CGM)
of massive galaxies at redshift 3, using the "Eris" suite of cosmological
"zoom-in" simulations. The reference run adopts a blastwave scheme for
supernova feedback that produces galactic outflows, a star formation recipe
based on a high gas density threshold, metal-dependent radiative cooling, and a
model for the diffusion of metals and thermal energy. Synthetic spectra through
the multiphase CGM produce interstellar absorption line strengths of Lya, CII,
CIV, SiII, and SiIV as a function of galactocentric impact parameter (scaled to
the virial radius) that are in broad agreement with those observed at
high-redshift by Steidel et al. (2010). Only about one third of all the gas
within R_vir is outflowing. The fraction of sightlines within one virial radius
that intercept optically thick material is 27%, in agreement with recent
observations by Rudie et al. (2012). Such optically thick absorption is shown
to trace inflowing "cold" streams that penetrate deep inside the virial radius.
The streams, enriched to metallicities above 0.01 solar, give origin to strong
(log N > 13) CII absorption with a covering factor of 22% within R_vir and 10%
within 2 R_vir. Galactic outflows do not cause any substantial suppression of
the cold accretion mode. The central galaxy is surrounded by a large OVI halo,
with a typical column density log N>14 and a near unity covering factor
maintained all the way out to 150 kpc. This matches the trends recently
observed in star-forming galaxies at low redshift by Tumlinson et al. (2011).
Our zoom-in simulations of this single system appear to reproduce
quantitatively the complex baryonic processes that determine the exchange of
matter, energy, and metals between galaxies and their surroundings. (Abridged)Comment: 16 pages, 13 figures, accepted for publication in The Astrophysical
Journa
Formation and Detectability of Terrestrial Planets Around Alpha Centauri B
We simulate the formation of planetary systems around Alpha Centauri B. The
N-body accretionary evolution of a 1/r disk populated with 400-900 lunar-mass
protoplanets is followed for 200 Myr. All simulations lead to the formation of
multiple-planet systems with at least one planet in the 1-2 MEarth mass range
at 0.5-1.5 AU. We examine the detectability of our simulated planetary systems
by generating synthetic radial velocity observations including noise based on
the radial velocity residuals to the recently published three planet fit to the
nearby K0V star HD 69830. Using these synthetic observations, we find that we
can reliably detect a 1.8 MEarth planet in the habitable zone of Alpha Centauri
B after only three years of high cadence observations. We also find that the
planet is detectable even if the radial velocity precision is 3 m/s, as long as
the noise spectrum is white. Our results show that the greatest uncertainty in
our ability to detect rocky planets in the Alpha Centauri system is the unknown
magnitude of ultra-low frequency stellar noise.Comment: 17 pages, 5 figures; accepted for publication in the Astrophysical
Journa
An Off-center Density Peak in the Milky Way's Dark Matter Halo?
We show that the position of the central dark matter density peak may be
expected to differ from the dynamical center of the Galaxy by several hundred
parsec. In Eris, a high resolution cosmological hydrodynamics simulation of a
realistic Milky-Way-analog disk galaxy, this offset is 300 - 400 pc (~3
gravitational softening lengths) after z=1. In its dissipationless
dark-matter-only twin simulation ErisDark, as well as in the Via Lactea II and
GHalo simulations, the offset remains below one softening length for most of
its evolution. The growth of the DM offset coincides with a flattening of the
central DM density profile in Eris inwards of ~1 kpc, and the direction from
the dynamical center to the point of maximum DM density is correlated with the
orientation of the stellar bar, suggesting a bar-halo interaction as a possible
explanation. A dark matter density offset of several hundred parsec greatly
affects expectations of the dark matter annihilation signals from the Galactic
Center. It may also support a dark matter annihilation interpretation of recent
reports by Weniger (2012) and Su & Finkbeiner (2012) of highly significant 130
GeV gamma-ray line emission from a region 1.5 degrees (~200 parsec projected)
away from Sgr A* in the Galactic plane.Comment: 12 pages, 11 figures, replaced with version accepted for publication
in Ap
Forming Realistic Late-Type Spirals in a LCDM Universe: The Eris Simulation
Simulations of the formation of late-type spiral galaxies in a cold dark
matter LCDM universe have traditionally failed to yield realistic candidates.
Here we report a new cosmological N-body/SPH simulation of extreme dynamic
range in which a close analog of a Milky Way disk galaxy arises naturally.
Termed Eris, the simulation follows the assembly of a galaxy halo of mass
Mvir=7.9x10^11 Msun with a total of N=18.6 million particles (gas + dark matter
+ stars) within the final virial radius, and a force resolution of 120 pc. It
includes radiative cooling, heating from a cosmic UV field and supernova
explosions, a star formation recipe based on a high gas density threshold
(nSF=5 atoms cm^-3 rather than the canonical nSF=0.1 atoms cm^-3), and neglects
AGN feedback. At the present epoch, the simulated galaxy has an extended
rotationally-supported disk with a radial scale length Rd=2.5 kpc, a gently
falling rotation curve with circular velocity at 2.2 disk scale lenghts of
V2.2=214 km/s, a bulge-to-disk ratio B/D=0.35, and a baryonic mass fraction
that is 30% below the cosmic value. The disk is thin, is forming stars in the
region of the Sigma_SFR - Sigma_HI plane occupied by spiral galaxies, and falls
on the photometric Tully-Fisher and the stellar mass-halo virial mass
relations. Hot (T>3x10^5 K), X-ray luminous halo gas makes only 26% of the
universal baryon fraction and follows a flattened density profile proportional
to r^-1.13 out to r=100 kpc. Eris appears then to be the first cosmological
hydrodynamic simulation in which the galaxy structural properties, the mass
budget in the various components, and the scaling relations between mass and
luminosity are all consistent with a host of observational constraints.
(Abridged)Comment: 12 pages, 7 figures, accepted for publication on the Astrophysical
Journa