146 research outputs found
Formation pathways and dynamics of supermassive black holes in hierarchical galaxy formation
Cold Dark Matter Substructures in Early-Type Galaxy Halos
We present initial results from the "Ponos" zoom-in numerical simulations of
dark matter substructures in massive ellipticals. Two very highly resolved dark
matter halos with and and different ("violent" vs. "quiescent")
assembly histories have been simulated down to in a CDM
cosmology with a total of 921,651,914 and 408,377,544 particles, respectively.
Within the virial radius, the total mass fraction in self-bound subhalos at the present epoch is 15% for the violent
host and 16.5% for the quiescent one. At , these fractions increase to
19 and 33%, respectively, as more recently accreted satellites are less prone
to tidal destruction. In projection, the average fraction of surface mass
density in substructure at a distance of ( kpc)
from the two halo centers ranges from 0.6% to %, significantly
higher than measured in simulations of Milky Way-sized halos. The contribution
of subhalos with to the projected mass
fraction is between one fifth and one third of the total, with the smallest
share found in the quiescent host. We assess the impact of baryonic effects via
twin, lower-resolution hydrodynamical simulations that include
metallicity-dependent gas cooling, star formation, and a
delayed-radiative-cooling scheme for supernova feedback. Baryonic contraction
produces a super-isothermal total density profile and increases the number of
massive subhalos in the inner regions of the main host. The host density
profiles and projected subhalo mass fractions appear to be broadly consistent
with observations of gravitational lenses.Comment: 14 pages, 15 figures, accepted for publication in ApJ after minor
revisions, note the new Fig.
Pollen taphonomy at Shanidar Cave (Kurdish Iraq): An initial evaluation
Caves provide important locations for the study of ancient human activity and environment. One important strand of this ancient environmental work is palynology, yet the taphonomy of pollen in caves is locally contingent and often complex. Shanidar Cave in Kurdish Iraq was the site of important Neanderthal finds and early palynological research, but pollen taphonomy in the cave has not been previously studied, so it is difficult to judge what these ancient pollen assemblages might represent. In this paper we present pollen from a transect of surface samples within the cave and from comparative surface samples from outside the cave. These show that at present there is a reasonably close correspondence between assemblages accumulating within and in the external environs of the cave, and with the local vegetation. This may suggest that stratigraphic samples may also reflect past local vegetation
Growing massive black holes through super-critical accretion of stellar-mass seeds
The rapid assembly of the massive black holes that power the luminous quasars
observed at remains a puzzle. Various direct collapse models have
been proposed to head-start black hole growth from initial seeds with masses
, which can then reach a billion solar mass while
accreting at the Eddington limit. Here we propose an alternative scenario based
on radiatively inefficient super-critical accretion of stellar-mass holes
embedded in the gaseous circum-nuclear discs (CNDs) expected to exist in the
cores of high redshift galaxies. Our sub-pc resolution hydrodynamical
simulations show that stellar-mass holes orbiting within the central 100 pc of
the CND bind to very high density gas clumps that arise from the fragmentation
of the surrounding gas. Owing to the large reservoir of dense cold gas
available, a stellar-mass black hole allowed to grow at super-Eddington rates
according to the "slim disc" solution can increase its mass by 3 orders of
magnitudes within a few million years. These findings are supported by
simulations run with two different hydro codes, RAMSES based on the Adaptive
Mesh Refinement technique and GIZMO based on a new Lagrangian Godunov-type
method, and with similar, but not identical, sub-grid recipes for star
formation, supernova feedback, black hole accretion and feedback. The low
radiative efficiency of super-critical accretion flows are instrumental to the
rapid mass growth of our black holes, as they imply modest radiative heating of
the surrounding nuclear environment.Comment: 12 pages, 8 figures, 2 tables. Accepted for publication in MNRA
Palynology of surface sediments from caves in the Zagros Mountains (Kurdish Iraq): patterns and processes
Cave palynology has been widely used to reconstruct past vegetation in areas where other conventional sources of pollen are scarce. However, the mechanisms involved in pollen transport, deposition and accumulation in caves are still poorly understood, mostly because of the number of interplaying factors that affect these processes. In this paper we explore some of these factors further by assessing differences in pollen assemblages in transects of surface samples from six caves in the Zagros Mountains of Kurdish Iraq. Simple sac-like caves show a clear pattern in pollen distribution with anemophilous taxa declining from the highest percentages near the front of the cave to lower percentages at the rear of the cave and entomophilous taxa showing the opposite trend. There is a tendency for this pattern to be most marked in caves which are narrow in relation to their length. It is less clear at Shanidar Cave, most probably because of the geometry of the cave but also because of the disturbance and mixing of the superficial sediments caused by the large numbers of people visiting the cave. Only one of the sampled caves shows a different pattern, which is likely to reflect its geomorphological complexity and, consequently, its air circulation. Other factors, such as the presence of a cave entrance flora, are considered but here they seem to have little influence on the pollen assemblages, contrary to that found in temperate-zone caves
Orbital Decay of Supermassive Black Hole Binaries in Clumpy Multiphase Merger Remnants
We simulate an equal-mass merger of two Milky Way-size galaxy discs with
moderate gas fractions at parsec-scale resolution including a new model for
radiative cooling and heating in a multi-phase medium, as well as star
formation and feedback from supernovae. The two discs initially have a
supermassive black hole (SMBH) embedded in
their centers. As the merger completes and the two galactic cores merge, the
SMBHs form a a pair with a separation of a few hundred pc that gradually
decays. Due to the stochastic nature of the system immediately following the
merger, the orbital plane of the binary is significantly perturbed.
Furthermore, owing to the strong starburst the gas from the central region is
completely evacuated, requiring ~Myr for a nuclear disc to rebuild.
Most importantly, the clumpy nature of the interstellar medium has a major
impact on the the dynamical evolution of the SMBH pair, which undergo
gravitational encounters with massive gas clouds and stochastic torquing by
both clouds and spiral modes in the disk. These effects combine to greatly
delay the decay of the two SMBHs to separations of a few parsecs by nearly two
orders of magnitude, yr, compared to previous work. In mergers of
more gas-rich, clumpier galaxies at high redshift stochastic torques will be
even more pronounced and potentially lead to stronger modulation of the orbital
decay. This suggests that SMBH pairs at separations of several tens of parsecs
should be relatively common at any redshift.Comment: submitted to MNRAS; Comments very welcom
The Argo Simulation: II. The Early Build-up of the Hubble Sequence
The Hubble sequence is a common classification scheme for the structure of
galaxies. Despite the tremendous usefulness of this diagnostic, we still do not
fully understand when, where, and how this morphological ordering was put in
place. Here, we investigate the morphological evolution of a sample of 22 high
redshift () galaxies extracted from the Argo simulation. Argo is a
cosmological zoom-in simulation of a group-sized halo and its environment. It
adopts the same high resolution ( M, pc) and
sub-grid physical model that was used in the Eris simulation but probes a
sub-volume almost ten times bigger with as many as 45 million gas and star
particles in the zoom-in region. Argo follows the early assembly of galaxies
with a broad range of stellar masses (
at ), while resolving properly their structural properties. We
recover a diversity of morphologies, including late-type/irregular disc
galaxies with flat rotation curves, spheroid dominated early-type discs, and a
massive elliptical galaxy, already established at . We identify major
mergers as the main trigger for the formation of bulges and the steepening of
the circular velocity curves. Minor mergers and non-axisymmetric perturbations
(stellar bars) drive the bulge growth in some cases. The specific angular
momenta of the simulated disc components fairly match the values inferred from
nearby galaxies of similar once the expected redshift evolution of
disc sizes is accounted for. We conclude that morphological transformations of
high redshift galaxies of intermediate mass are likely triggered by processes
similar to those at low redshift and result in an early build-up of the Hubble
sequence.Comment: 17 pages, 13 figures, accepted for publication in MNRA
Using facial electromyography to detect preserved emotional processing in disorders of consciousness: A proof-of-principle study
Objective To examine whether emotional functioning can be observed in patients who are behaviourally non-responsive using peripheral markers of emotional functioning. Method We tested two patients, both diagnosed as being in a vegetative state (VS) following hypoxia secondary to cardiac arrest. Thirty-seven healthy participants with no history of neurological illness served as a control group. The activity of two facial muscles (zygomaticus major, corrugator supercilii) was measured using facial electromyography (EMG) to probe for patterned responses that differentiate between auditorily presented joke and non-joke stimuli in VS patients. Results One of the two VS patients we tested demonstrated greater zygomatic and reduced corrugator activity in response to jokes compared with non-jokes. Critically, these responses followed the pattern and temporal profile of muscle activity observed in our healthy control sample. Conclusions Despite their behaviorally non-responsive profile, some patients diagnosed as VS appear to retain some aspects of emotional experience. Significance Our findings represent, to our knowledge, the first demonstration that a patient diagnosed as VS can exhibit intact emotional responses to humor as assessed by facial EMG. Therefore, our approach may constitute a feasible bedside tool capable of providing novel insight into the mental and emotional lives of patients who are behaviourally non-responsive
Validation of a method for the determination of the sensible-heat flux with Sodar data in free convection cases
A simple method to determine the value of the ground sensible-heat flux using Sodar data is presented and validated. The measurement of the variance of
the wind velocity components gives us an estimate of the intensity of the atmospheric turbulence; the local value of variance of the vertical wind velocity s2w depends on the
efficiency of thermal and mechanical turbulence production. The portion of the atmospheric boundary layer, where turbulent kinetic energy is prevalently produced by buoyancy forces, is characterised by profiles of s3w Oz and of (sensible-) heat flux which decrease linearly with height. The extrapolation to the ground of the former
profile gives an estimate of the value of sensible-heat flux at the surface. The validation of the results is performed by comparison of the energy involved in the
development of convective episodes calculated, over the same time interval, from sensible-heat flux at the surface with that derived from potential temperature profiles relative to two successive radio soundings. When perturbative processes like, for example, rise up of breezes, are absent, the estimates of energies are in
excellent agreement, being the angular coefficient of regression line 1.01 and the linear correlation coefficient 0.93
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