173 research outputs found
21-cm signatures of residual HI inside cosmic HII regions during reionization
We investigate the impact of sinks of ionizing radiation on the
reionization-era 21-cm signal, focusing on 1-point statistics. We consider
sinks in both the intergalactic medium and inside galaxies. At a fixed filling
factor of HII regions, sinks will have two main effects on the 21-cm
morphology: (i) as inhomogeneous absorbers of ionizing photons they result in
smaller and more widespread cosmic HII patches; and (ii) as reservoirs of
neutral gas they contribute a non-zero 21-cm signal in otherwise ionized
regions. Both effects damp the contrast between neutral and ionized patches
during reionization, making detection of the epoch of reionization with 21-cm
interferometry more challenging. Here we systematically investigate these
effects using the latest semi-numerical simulations. We find that sinks
dramatically suppress the peak in the redshift evolution of the variance,
corresponding to the midpoint of reionization. As previously predicted,
skewness changes sign at midpoint, but the fluctuations in the residual HI
suppress a late-time rise. Furthermore, large levels of residual HI
dramatically alter the evolution of the variance, skewness and power spectrum
from that seen at lower levels. In general, the evolution of the large-scale
modes provides a better, cleaner, higher signal-to-noise probe of reionization.Comment: Minor edits to agree with MNRAS published versio
CO line emission from galaxies in the Epoch of Reionization
We study the CO line luminosity (), the shape of the CO Spectral
Line Energy Distribution (SLED), and the value of the CO-to-
conversion factor in galaxies in the Epoch of Reionization (EoR). To this aim,
we construct a model that simultaneously takes into account the radiative
transfer and the clumpy structure of giant molecular clouds (GMCs) where the CO
lines are excited. We then use it to post-process state-of-the-art zoomed, high
resolution (), cosmological simulation of a main-sequence
(, ) galaxy, "Alth{\ae}a", at . We find that the CO emission
traces the inner molecular disk () of Alth{\ae}a with
the peak of the CO surface brightness co-located with that of the [CII] 158 emission. Its is comparable
to that observed in local galaxies with similar stellar mass. The high
() gas surface density in
Alth{\ae}a, its large Mach number (\mach), and the warm kinetic
temperature () of GMCs yield a CO SLED peaked at the
CO(7-6) transition, i.e. at relatively high-, and a CO-to-
conversion factor lower than that of the Milky Way. The ALMA observing time
required to detect (resolve) at 5 the CO(7-6) line from galaxies
similar to Alth{\ae}a is h ( h).Comment: 16 pages, 14 figures, accepted for publication in MNRA
Models of rotating coronae
Fitting equilibrium dynamical models to observational data is an essential
step in understanding the structure of the gaseous hot haloes that surround our
own and other galaxies. However, the two main categories of models that are
used in the literature are poorly suited for this task: (i) simple barotropic
models are analytic and can therefore be adjusted to match the observations,
but are clearly unrealistic because the rotational velocity does
not depend on the distance from the galactic plane, while (ii) models
obtained as a result of cosmological galaxy formation simulations are more
realistic, but are impractical to fit to observations due to high computational
cost. Here we bridge this gap by presenting a general method to construct
axisymmetric baroclinic equilibrium models of rotating galactic coronae in
arbitrary external potentials. We consider in particular a family of models
whose equipressure surfaces in the plane are ellipses of varying axis
ratio. These models are defined by two one-dimensional functions, the axial
ratio of pressure and the value of the pressure along the galaxy's symmetry axis. These models can have a rotation
speed that realistically decreases as one moves away from the
galactic plane, and can reproduce the angular momentum distribution found in
cosmological simulations. The models are computationally cheap to construct and
can thus be used in fitting algorithms. We provide a python code that given
, and returns ,
, , . We show a few examples of these models using
the Milky Way as a case study.Comment: Accepted for publication in MNRA
Periodicity makes galactic shocks unstable - I. Linear analysis
We study the dynamical stability of stationary galactic spiral shocks. The
steady-state equilibrium flow contains a shock of the type derived by Roberts
in the tightly wound approximation. We find that boundary conditions are
critical in determining whether the solutions are stable or not. Shocks are
unstable if periodic boundary conditions are imposed. For intermediate
strengths of the spiral potential, the instability disappears if boundary
conditions are imposed such that the upstream flow is left unperturbed as in
the classic analysis of D'yakov and Kontorovich. This reconciles apparently
contradictory findings of previous authors regarding the stability of spiral
shocks. This also shows that the instability is distinct from the
Kelvin-Helmholtz instability, confirming the findings of Kim et al. We suggest
that instability is a general characteristics of periodic shocks, regardless of
the presence of shear, and provide a physical picture as to why this is the
case. For strong spiral potentials, high post-shock shear makes the system
unstable also to parasitic Kelvin-Helmholtz instability regardless of the
boundary conditions. Our analysis is performed in the context of a simplified
problem that, while preserving all the important characteristics of the
original problem, strips it from unnecessary complications, and assumes that
the gas is isothermal, non self-gravitating, non-magnetised.Comment: Accepted for publication in MNRA
Nuclear rings are the inner edge of a gap around the Lindblad Resonance
Gaseous nuclear rings are large-scale coherent structures commonly found at
the centres of barred galaxies. We propose that they are an accumulation of gas
at the inner edge of an extensive gap that forms around the Inner Lindblad
Resonance (ILR). The gap initially opens because the bar potential excites
strong trailing waves near the ILR, which remove angular momentum from the gas
disc and transport the gas inwards. The gap then widens because the bar
potential continuously excites trailing waves at the inner edge of the gap,
which remove further angular momentum, moving the edge further inwards until it
stops at a distance of several wavelengths from the ILR. The gas accumulating
at the inner edge of the gap forms the nuclear ring. The speed at which the gap
edge moves and its final distance from the ILR strongly depend on the sound
speed, explaining the puzzling dependence of the nuclear ring radius on the
sound speed in simulations.Comment: Submitted to MNRAS. Comments welcom
The Physical Origin and the Properties of Arm Spurs/Feathers in Local Simulations of the Wiggle Instability
Gaseous substructures such as feathers and spurs dot the landscape of spiral
arms in disc galaxies. One of the candidates to explain their formation is the
wiggle instability of galactic spiral shocks. We study the wiggle instability
using local 2D hydrodynamical isothermal non-self gravitating simulations. We
find that: (1) Simulations agree with analytic linear stability analysis only
under stringent conditions. They display surprisingly strong non-linear
coupling between the different modes, even for small mode amplitudes (). (2) We demonstrate that the wiggle instability originates from a
combination of two physically distinct mechanisms: the first is the
Kelvin-Helmholtz instability, and the second is the amplification of
infinitesimal perturbations from repeated shock passages. These two mechanisms
can operate simultaneously, and which mechanism dominates depends on the
underlying parameters. (3) We explore the parameter space and study the
properties of spurs/feathers generated by the wiggle instability. The wiggle
instability is highly sensitive to the underlying parameters. The feather
separation decreases, and the growth rate increases, with decreasing sound
speed, increasing potential strength and decreasing interarm distance. (4) We
compare our simulations with a sample of 20 galaxies in the HST Archival Survey
of Spiral Arm Substructure of La Vigne et al. and find that the wiggle
instability is able to reproduce the typical range of feather separations seen
in observations. It remains unclear how the wiggle instability relates to
competing mechanisms for spur/feather formation such as the magneto-jeans
instability and the stochastic accumulation of gas due to correlated supernova
feedback.Comment: Accepted for publication in MNRAS; Accepted 2022 April 26. Received
2022 April 26; in original form 2021 October 0
A homozygous contiguous gene deletion in chromosome 16p13.3 leads to autosomal recessive osteopetrosis in a Jordanian patient
Human malignant autosomal recessive osteopetrosis (ARO) is a genetically heterogeneous disorder caused by reduced bone resorption by osteoclasts. Mutations in the CLCN7 gene are responsible not only for a substantial portion of ARO patients, but also for other forms of osteopetrosis characterized by different severity and inheritance. The lack of a clear genotype/phenotype correlation makes genetic counselling a tricky issue for CLCN7-dependent osteopetrosis.
Here we characterize the first homozygous interstitial deletion in 16p13.3, detected by array Comparative Genomic Hybridization (a-CGH) in an ARO patient of Jordanian origin. The deletion involved other genes beside CLCN7, while the proband displayed a classic ARO phenotype; however her early death did not allow more extensive clinical investigations.
The identification of this novel genomic deletion involving a large part of the CLCN7 gene is of clinical relevance, especially in prenatal diagnosis, and suggests the possibility that this kind of mutation has been underestimated so far. This data highlights the need for alternative approaches to genetic analysis also in other ARO-causative genes
A high precision, compact electromechanical ground rotation sensor
We present a mechanical rotation sensor consisting of a balance pivoting on a tungsten carbide knife edge. These sensors are important for precision seismic isolation systems, as employed in land-based gravitational wave interferometers and for the new field of rotational seismology. The position sensor used is an air-core linear variable differential transformer with a demonstrated noise floor of 1×10^(−11)m/√Hz. We describe the instrument construction and demonstrate low noise operation with a noise floor upper bound of 5.7×10^(−9)rad/√Hz at 10 mHz and 6.4×10^(−10)rad/√Hz at 0.1 Hz. The performance of the knife edge hinge is compatible with a behaviorur free of noise from dislocation self-organized criticality
Metal Enrichment in the Reionization Epoch
The presence of elements heavier than helium ("metals") is of fundamental
importance for a large number of astrophysical processes occurring in planet,
star and galaxy formation; it also affects cosmic structure formation and
evolution in several ways. Even a small amount of heavy elements can
dramatically alter the chemistry of the gas, opening the path to complex
molecules. Metals might enhance the ability of the gas to radiate away its
thermal energy, thus favoring the formation of gravitationally bound objects;
they can also condensate in a solid phase (dust grains), partly or totally
blocking radiation from luminous sources. Finally, they represent useful
tracers of energy deposition by stars and probe the physical properties of the
environment by absorption or emission lines. Last, but certainly not least,
life -- as we know it on Earth -- is tightly related to the presence of at
least some of the heavy elements. In this pedagogical review I will concentrate
on the connection between early metal enrichment and cosmic reionization. As we
will see these two processes are intimately connected and their joint study
might turn out to be fundamental in understanding the overall evolution of the
Universe during the first billion years after the Big Bang, an epoch
corresponding to redshifts z>6.Comment: Book chapter in Understanding the Epoch of Cosmic Reionization:
Challenges and Progress, Springer International Publishing, Ed. Andrei
Mesinger, ISBN 978-3-319-21956-1. arXiv admin note: text overlap with
arXiv:astro-ph/0007248 by other author
- …