1,003 research outputs found
The Rhaeto-Romance Languages
The Rhaeto-Romance languages have been known as such to the linguistic community since the pioneering studies of Ascoli and Gartner over a century ago. There has never been a community of RR speakers based on a common history or polity and the various dialects are mutually unintelligible, but a unity, based on a number of common features, has been advanced. This book is the first general description of the Rhaeto-Romance languages to be written in Eng. It provides a critical examination of the phonology, morphology, lexicon, and syntax of the modern Rhaeto-Romance dialects within the broader perspective of Romance comparative linguistics
How long do high-redshift massive black hole seeds remain outliers in black hole vs. host galaxy relations?
The existence of supermassive black holes (SMBHs)
within the first billion years of the universe remains a puzzle in our
conventional understanding of black hole formation and growth. Several
suggested formation pathways for these SMBHs lead to a heavy seed, with an
initial black hole mass of . This can lead to an
overly massive BH galaxy (OMBG), whose nuclear black hole's mass is comparable
to or even greater than the surrounding stellar mass: the black hole to stellar
mass ratio is , well in excess of the typical
values at lower redshift. We investigate how long these newborn BHs remain
outliers in the relation, by exploring the subsequent
evolution of two OMBGs previously identified in the \texttt{Renaissance}
simulations. We find that both OMBGs have during their
entire life, from their birth at until they merge with much more
massive haloes at . We find that the OMBGs are spatially resolvable
from their more massive, , neighboring haloes until
their mergers are complete at . This affords a window for future
observations with {\it JWST} and sensitive X-ray telescopes to diagnose the
heavy-seed scenario, by detecting similar OMBGs and establishing their uniquely
high black hole-to-stellar mass ratio.Comment: 15 pages, 10 figures. Accepted in MNRA
"Subordination" in Universal Grammar
Proceedings of the Tenth Annual Meeting of the Berkeley Linguistics Society (1984), pp. 510-52
Self-lensing flares from black hole binaries III: general-relativistic ray tracing of circumbinary accretion simulations
Self-lensing flares (SLFs) are expected to be produced once or twice per
orbit by an accreting massive black hole binary (MBHB), if the eclipsing MBHBs
are observed close to edge-on. SLFs can provide valuable electromagnetic (EM)
signatures to accompany the gravitational waves (GWs) detectable by the
upcoming Laser Interferometer Space Antenna (LISA). EM follow-ups are crucial
for, e.g., sky-localization, and constraining the Hubble constant and the
graviton mass. We use high-resolution two-dimensional viscous hydrodynamical
simulations of a circumbinary disk (CBD) embedding a MBHB. We then use very
high-cadence output of these hydrodynamical simulation inputs for a
general-relativistic ray-tracing code to produce synthetic spectra and
phase-folded light curves. Our main results show a significant periodic
amplification of the flux with the characteristic shape of a sharp flare with a
central dip, as the foreground black hole (BH) transits across the minidisk and
shadow of the background BH, respectively. These corroborate previous
conclusions based on the microlensing approximation and analytical toy models
of the emission geometry. We also find that at lower inclinations, without some
occlusion of the minidisk emission by the CBD, shocks from quasi-periodic
mass-trading between the minidisks can produce bright flares which can mimic
SLFs and could hinder their identification.Comment: 14 pages, 11 figures, submitted to journal, split Fig. 1 by
frequency, fixed some typo
Disappearing thermal X-ray emission as a tell-tale signature of merging massive black hole binaries
The upcoming Laser Interferometer Space Antenna (LISA) is expected to detect
gravitational waves (GWs) from massive black hole binaries (MBHB). Finding the
electromagnetic (EM) counterparts for these GW events will be crucial for
understanding how and where MBHBs merge, measuring their redshifts,
constraining the Hubble constant and the graviton mass, and for other novel
science applications. However, due to poor GW sky localisation,
multi-wavelength, time-dependent electromagnetic (EM) models are needed to
identify the right host galaxy among many candidates. We studied merging MBHBs
embedded in a circumbinary disc using high-resolution two-dimensional
simulations, with a -law equation of state, incorporating viscous
heating, shock heating, and radiative cooling. We simulate the binary from
large separation until after merger, allowing us to model the decoupling of the
binary from the circumbinary disc (CBD). We compute the EM signatures and
identify distinct features before, during, and after the merger. Our main
result is a multi-band EM signature: we find that the MBHB produces strong
thermal X-ray emission until 1-2 days prior to the merger. However, as the
binary decouples from the CBD, the X-ray-bright minidiscs rapidly shrink in
size, become disrupted, and the accretion rate drops precipitously. As a
result, the thermal X-ray luminosity drops by orders of magnitude, and the
source remains X-ray dark for several days after the merger, regardless of any
post-merger effects such as GW recoil or mass loss. Looking for the abrupt
spectral change where the thermal X-ray disappears is a tell-tale EM signature
of LISA mergers that does not require extensive pre-merger monitoring.Comment: 14 pages, 16 figures, 1 table, submitted to journa
New constraints on direct collapse black hole formation in the early Universe
Direct collapse black holes (DCBH) have been proposed as a solution to the
challenge of assembling supermassive black holes by to explain the bright
quasars observed at this epoch. The formation of a DCBH seed with requires a pristine atomic-cooling halo to
be illuminated by an external radiation field that is sufficiently strong to
entirely suppress H cooling in the halo. Many previous studies have
attempted to constrain the critical specific intensity that is likely required
to suppress H cooling, denoted as . However, these studies
have typically assumed that the incident external radiation field can be
modeled with a black-body spectrum. Under this assumption, it is possible to
derive a {unique} value for that depends only on the temperature
of the black-body. In this study we consider a more realistic spectral energy
distribution (SED) for the external source of radiation that depends entirely
on its star formation history and age. The rate of destruction of the species
responsible for suppressing molecular hydrogen cooling depends on the detailed
shape of the SED. Therefore the value of is tied to the shape of
the incident SED of the neighbouring galaxy. We fit a parametric form to the
rates of destruction of H and H that permit direct collapse. Owing to
this, we find that is not a fixed threshold but can lie anywhere
in the range --, depending on the details of the
source stellar population.Comment: 10 pages, 6 figures. Accepted for publication in MNRA
Pathways to massive black holes and compact star clusters in pre-galactic dark matter haloes with virial temperatures > 10000K
Large dynamic range numerical simulations of atomic cooling driven collapse
of gas in pre-galactic DM haloes with T_vir ~ 10000 K show that the gas loses
90% and more of its angular momentum before rotational support sets in. In a
fraction of these haloes where the metallicity is low and UV radiation
suppresses H_2 cooling, conditions are thus very favourable for the rapid
build-up of massive black holes. Depending on the progression of metal
enrichment, the continued suppression of H_2 cooling by external and internal
UV radiation and the ability to trap the entropy produced by the release of
gravitational energy, the gas at the centre of the halo is expected to form a
supermassive star, a stellar-mass black hole accreting at super-Eddington
accretion rates or a compact star-cluster undergoing collisional run-away of
massive stars at its centre. In all three cases a massive black hole of
initially modest mass finds itself at the center of a rapid inflow of gas with
inflow rates of ~ 1 M_solar\yr. The massive black hole will thus grow quickly
to a mass of 10^5 to 10^6 M_solar until further inflow is halted either by
consumption of gas by star formation or by the increasing energy and momentum
feedback from the growing massive black hole. Conditions for the formation of
massive seed black holes in this way are most favourable in haloes with T_vir ~
15000 K and V_vir ~ 20 km\s with less massive haloes not allowing collapse of
gas by atomic cooling and more massive haloes being more prone to
fragmentation. This should imprint a characteristic mass on the mass spectrum
of an early population of massive black hole seeds in pre-galactic haloes which
will later grow into the observed population of supermassive black holes in
galactic bulges.Comment: 13 pages, 8 figures. Submitted to MNRA
Effect of cosmic ray/X-ray ionization on supermassive black hole formation
We study effects of external ionization by cosmic rays (CRs) and X-rays on
the thermal evolution of primordial clouds under strong far-ultraviolet (FUV)
radiation. A strong FUV radiation dissociates H2 and quenches its cooling. Even
in such an environment, a massive cloud with Tvir>10^4 K can contract
isothermally at 8000 K by Lyman alpha cooling. This cloud collapses
monolithically without fragmentation, and a supermassive star (>10^5 Msun) is
believed to form at the center, which eventually evolves to a supermassive
black hole (SMBH). However, candidates of FUV sources, including star-forming
galaxies, are probably sources of strong CRs and X-rays, as well. We find that
the external ionization promotes H2 production and elevates the threshold FUV
intensity Jcr needed for the SMBH formation for CR energy density U_CR>10^-14
erg/cm^3 or X-ray intensity J_X>10^-24 erg/s/cm^2/sr/Hz at 1 keV. The critical
FUV flux increases in proportion to U_CR^{1/2} (J_X^{1/2}) in the high CR
(X-ray, respectively) limit. With the same value of FUV intensity at the Lyman
limit (13.6 eV), the H^- photodissociation rate, with threshold of 0.755 eV,
increases and the H2 molecules decrease with decreasing effective temperature
of the FUV sources T*. The lower value of T* thus results in the lower critical
FUV flux at 13.6 eV. Using an empirical relation between intensities of FUV and
CR/X-ray from nearby star-forming galaxies, we find that external ionization
effect remarkably enhances the critical FUV flux for sources with T* as high as
10^5 K and composed of stars with <100 Msun to a level that is not realized in
any halo. This indicates that, to induce SMBH formation, the FUV sources must
be either Pop II/I galaxies with low brightness temperature, Pop III galaxies
with a very top-heavy IMF, or Pop III galaxies too young to harbor sources of
CR/X-ray, e.g., supernova remnants or high-mass X-ray binaries.Comment: 14 pages, 8 figures, 2 tables, accepted for publication in MNRA
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