53 research outputs found
On the Newtonian Anisotropic Configurations
In this paper we are concerned with the effects of anisotropic pressure on
the boundary conditions of anisotropic Lane-Emden equation and homology
theorem. Some new exact solutions of this equation are derived. Then some of
the theorems governing the Newtonian perfect fluid star are extended taking the
anisotropic pressure into account
Kinematics of galaxies from [CII] line emission
We study the kinematical properties of galaxies in the Epoch of Reionization
via the [CII] 158m line emission. The line profile provides information on
the kinematics as well as structural properties such as the presence of a disk
and satellites. To understand how these properties are encoded in the line
profile, first we develop analytical models from which we identify disk
inclination and gas turbulent motions as the key parameters affecting the line
profile. To gain further insights, we use "Althaea", a highly-resolved () simulated prototypical Lyman Break Galaxy, in the redshift range , when the galaxy is in a very active assembling phase. Based on
morphology, we select three main dynamical stages: I) Merger , II) Spiral Disk,
and III) Disturbed Disk. We identify spectral signatures of merger events,
spiral arms, and extra-planar flows in I), II), and III), respectively. We
derive a generalised dynamical mass vs. [CII]-line FWHM relation. If precise
information on the galaxy inclination is (not) available, the returned mass
estimate is accurate within a factor (). A Tully-Fisher relation is
found for the observed high- galaxies, i.e. for which we provide a simple, physically-based
interpretation. Finally, we perform mock ALMA simulations to check the
detectability of [CII]. When seen face-on, Althaea is always detected at ; in the edge-on case it remains undetected because the larger
intrinsic FWHM pushes the line peak flux below detection limit. This suggests
that some of the reported non-detections might be due to inclination effects.Comment: 14 pages, 12 figures, accepted for publication in MNRA
Deep into the structure of the first galaxies: SERRA views
We study the formation and evolution of a sample of Lyman Break Galaxies in
the Epoch of Reionization by using high-resolution (),
cosmological zoom-in simulations part of the SERRA suite. In SERRA, we follow
the interstellar medium (ISM) thermo-chemical non-equilibrium evolution, and
perform on-the-fly radiative transfer of the interstellar radiation field
(ISRF). The simulation outputs are post-processed to compute the emission of
far infrared lines ([CII], [NII], and [OIII]). At , the most massive
galaxy, `Freesia', has an age , stellar mass
, and a star formation rate
, due to a recent burst.
Freesia has two stellar components (A and B) separated by ; other 11 galaxies are found within . The
mean ISRF in the Habing band is and is spatially uniform; in
contrast, the ionisation parameter is , and
has a patchy distribution peaked at the location of star-forming sites. The
resulting ionising escape fraction from Freesia is .
While [CII] emission is extended (radius 1.54 kpc), [OIII] is concentrated in
Freesia-A (0.85 kpc), where the ratio . As many high- galaxies, Freesia lies below the local [CII]-SFR
relation. We show that this is the general consequence of a starburst phase
(pushing the galaxy above the Kennicutt-Schmidt relation) which
disrupts/photodissociates the emitting molecular clouds around star-forming
sites. Metallicity has a sub-dominant impact on the amplitude of [CII]-SFR
deviations.Comment: 22 pages, 14 figures, accepted by MNRA
Quantitative model for efficient temporal targeting of tumor cells and neovasculature
The combination of cytotoxic therapies and anti-angiogenic agents is emerging
as a most promising strategy in the treatment of malignant tumors. However, the
timing and sequencing of these treatments seem to play essential roles in
achieving a synergic outcome. Using a mathematical modeling approach that is
grounded on available experimental data, we investigate the spatial and
temporal targeting of tumor cells and neovasculature with a nanoscale delivery
system. Our model suggests that the experimental success of the nanoscale
delivery system depends crucially on the trapping of chemotherapeutic agents
within the tumor tissue. The numerical results also indicate that substantial
further improvements in the efficiency of the nanoscale delivery system can be
achieved through an adjustment of the temporal targeting mechanism.Comment: 17 pages, 5 figure
Dynamical characterization of galaxies up to
The characterization of the dynamical state of galaxies up to z~7 is crucial
for constraining the mechanisms driving the mass assembly in the early
Universe. However, it is unclear whether the data quality of current and future
observations is sufficient to perform a solid dynamical analysis. This paper
defines the angular resolution and S/N required for a robust characterization
of the dynamical state of galaxies up to the EoR. The final aim is to help
design spatially-resolved surveys targeting emission lines of primeval
galaxies. We investigate the [CII]-158um emission from z~6-7 LBGs from the
SERRA cosmological simulation, covering a range of dynamical states: from disks
to major mergers. We create ALMA mock observations with various data quality
and apply the kinematic classification methods used in the literature. These
tests allow us to quantify the performances of such methods as a function of
angular resolution and S/N. We find that barely-resolved observations do not
allow the correct dynamical characterization of a galaxy, resulting in the
misclassification of all disks in our sample. However, even when using
spatially-resolved observations with data quality typical of high-z galaxies,
the standard kinematic classification methods, based on the analysis of the
moment maps, fail to distinguish a merger from a disk. The high angular
resolution and S/N needed to apply these standard methods successfully can be
achieved with current data only for a handful of bright galaxies. We propose a
new classification method, called PVsplit, that quantifies the asymmetries and
morphological features in position-velocity diagrams using three empirical
parameters. We test PVsplit on our mock data concluding that it can predict
whether a galaxy is a disk or a merger provided that S/N , and the
major axis is covered by independent resolution elements.Comment: Submitted to Astronomy and Astrophysics (A&A) Journal. Comments are
welcom
Early galaxy growth: mergers or gravitational instability?
We investigate the spatially-resolved morphology of galaxies in the early
Universe. We consider a typical redshift z = 6 Lyman Break galaxy, "Althaea"
from the SERRA hydrodynamical simulations. We create mock rest-frame
ultraviolet, optical, and far-infrared observations, and perform a
two-dimensional morphological analysis to de-blend the galaxy disk from
substructures (merging satellites or star-forming regions). We find that the
[CII]158um emitting region has an effective radius 1.5 - 2.5 times larger than
the optical one, consistent with recent observations. This [CII] halo in our
simulated galaxy arises as the joint effect of stellar outflows and carbon
photoionization by the galaxy UV field, rather than from the emission of
unresolved nearby satellites. At the typical angular resolution of current
observations (> 0.15") only merging satellites can be detected; detection of
star-forming regions requires resolutions of < 0.05". The [CII]-detected
satellite has a 2.5 kpc projected distance from the galaxy disk, whereas the
star-forming regions are embedded in the disk itself (distance < 1 kpc). This
suggests that multi-component systems reported in the literature, which have
separations > 2 kpc, are merging satellites, rather than galactic
substructures. Finally, the star-forming regions found in our mock maps follow
the local L[CII] - SFR_UV relation of galaxy disks, although sampling the
low-luminosity, low-SFR tail of the distribution. We show that future JWST
observations, bridging UV and [CII] datasets, will be exceptionally suited to
characterize galaxy substructures thanks to their exquisite spatial resolution
and sensitivity to both low-metallicity and dust-obscured regions that are
bright at infrared wavelengths.Comment: Accepted for publication in MNRAS; 17 pages (plus appendix), 7
figures, 4 table
ALMA hints at the presence of turbulent disk galaxies at z > 5
High-redshift galaxies are expected to be more turbulent than local galaxies
because of their smaller size and higher star formation and thus stronger
feedback from star formation, frequent mergers events, and gravitational
instabilities. However, this scenario has recently been questioned by the
observational evidence of a few galaxies at z~4-5 with a gas velocity
dispersion similar to what is observed in the local population. Our goal is to
determine whether galaxies in the first Gyrs of the Universe have already
formed a dynamically cold rotating disk similar to the local counterparts. We
studied the gas kinematic of 22 main-sequence star-forming galaxies at z > 5
and determined their dynamical state by estimating the ratio of the rotational
velocity and of the gas velocity dispersion. We mined the ALMA archive and
exploited the [CII] and [OIII] observations to perform a kinematic analysis of
the cold and warm gas of z>5 main-sequence galaxies. The gas kinematics of the
high-z galaxies is consistent within the errors with rotating but turbulent
disks. We infer a velocity dispersion that is systematically higher by 4 times
than the local galaxy population and the z~5 dust-obscured galaxies reported in
the literature. The difference between our results and those reported at
similar redshift can be ascribed to the systematic difference in the galaxy
properties in the two samples: the disks of massive dusty galaxies are
dynamically colder than the disks of dust-poor galaxies. The comparison with
the theoretical predictions suggests that the main driver of the velocity
dispersion in high-z galaxies is the gravitational energy that is released by
the transport of mass within the disk. Finally, we stress that future deeper
ALMA high-angular resolution observations are crucial to constrain the
kinematic properties of high-z galaxies and to distinguish rotating disks from
kpc-scale mergers.Comment: 14 pages, 11 figures, 1 tables, accepted for publication in A&
A survey of high-z galaxies: serra simulations
We introduce SERRA, a suite of zoom-in high-resolution (1.2 ×104 M⊙, ≃ 25 pc at z = 7.7) cosmological simulations including non-equilibrium chemistry and on-the-fly radiative transfer. The outputs are post-processed to derive galaxy ultraviolet (UV) + far-infrared (FIR) continuum and emission line properties. Results are compared with available multiwavelength data to constrain the physical properties [e.g. star formation rates (SFRs), stellar/gas/dust mass, metallicity] of high-redshift 6 ≲ z ≲ 15 galaxies. This flagship paper focuses on the z = 7.7 sub-sample, including 202 galaxies with stellar mass 107 M⊙ ≲ M⊙ ≲ 5 ×1010 M⊙, and specific star formation rate ranging from sSFR ∼100 Gyr-1 in young, low-mass galaxies to ∼10 Gyr-1 for older, massive ones. At this redshift, SERRA galaxies are typically bursty, i.e. they are located abo v e the Schmidt-Kennicutt relation by a factor κs = 3.03+4.9-1.8, consistent with recent findings for [O III ] and [C II ] emitters at high z. They also show relatively large InfraRed eXcess (IRX = LFIR/LUV) values as a result of their compact/clumpy morphology effectively blocking the stellar UV luminosity. Note that this conclusion might be affected by insufficient spatial resolution at the molecular cloud level. We confirm that early galaxies lie on the standard [C II ] -SFR relation; their observed L[OIII]/L [CII] ≃ 1-10 ratios can be reproduced by a part of the SERRA galaxies without the need of a top-heavy initial mass function and/or anomalous C/O abundances. [O I] line intensities are similar to local ones, making ALMA high-z detections challenging but feasible ( ∼6 h for an SFR of 50 M⊙yr-1)
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