293 research outputs found
Environment, Ram Pressure, and Shell Formation in HoII
Neutral hydrogen VLA D-array observations of the dwarf irregular galaxy HoII,
a prototype galaxy for studies of shell formation, are presented. HI is
detected to radii over 16' or 4 R_25, and M_HI=6.44x10^8 M_sun. The total HI
map has a comet-like appearance suggesting that HoII is affected by ram
pressure from an intragroup medium (IGM). A rotation curve corrected for
asymmetric drift was derived and an analysis of the mass distribution yields a
total mass 6.3x10^9 M_sun, of which about 80% is dark. HoII lies northeast of
the M81 group's core, along with Kar52 (M81dwA) and UGC4483. No signs of
interaction are observed and it is argued that HoII is part of the NGC2403
subgroup, infalling towards M81. A case is made for ram pressure stripping and
an IGM in the M81 group. Stripping of the disk outer parts would require an IGM
density n_IGM>=4.0x10^-6 atoms/cm^3 at the location of HoII. This corresponds
to 1% of the virial mass of the group uniformly distributed over a volume just
enclosing HoII and is consistent with the X-ray properties of small groups. It
is argued that existing observations of HoII do not support self-propagating
star formation scenarios, whereby the HI holes and shells are created by
supernova explosions and stellar winds. Many HI holes are located in low
surface density regions of the disk, where no star formation is expected or
observed. Ram pressure has the capacity to enlarge preexisting holes and lower
their creation energies, helping to bridge the gap between the observed star
formation rate and that required to create the holes. (abridged)Comment: 43 pages, including 7 figures. 4 figures available as JPEG only.
Complete manuscript including full resolution figures available at
http://www.strw.leidenuniv.nl/~bureau/pub_list.html . Accepted for
publication in The Astronomical Journa
The Evolution of Supernovae in Circumstellar Wind Bubbles II: Case of a Wolf-Rayet star
(Abridged) Mass-loss from massive stars leads to the formation of
circumstellar wind-blown bubbles surrounding the star, bordered by a dense
shell. When the star ends its life in a supernova (SN) explosion, the resulting
shock wave will interact with this modified medium. In a previous paper we
discussed the basic parameters of this interaction. In this paper we go a step
further and study the evolution of SNe in the wind blown bubble formed by a 35
\msun star that starts off as an O star, goes through a red supergiant phase,
and ends its life as a Wolf-Rayet star. We model the evolution of the CSM and
then the expansion of the SN shock wave within this medium. Our simulations
clearly reveal fluctuations in density and pressure within the surrounding
medium. The SN shock interacting with these fluctuations, and then with the
dense shell surrounding the wind-blown cavity, gives rise to a variety of
transmitted and reflected shocks in the wind bubble. The interactions between
these various shocks and discontinuities is examined, and its effects on the
X-ray emission is noted. Our simulations reveal the presence of several
hydrodynamic instabilities. They show that the turbulent interior, coupled with
the large fluctuations in density and pressure, gives rise to an extremely
corrugated SN shock wave. The shock shows considerable wrinkles as it impacts
the dense shell, and the impact occurs in a piecemeal fashion, with some parts
of the shock wave interacting with the shell before the others. Therefore
different parts of the shell will `light-up' at different times. The
non-spherical nature of the interaction means that it will occur over a
prolonged period of time, and the spherical symmetry of the initial shock wave
is destroyed.Comment: 50 pages, 19 figures. Accepted to the Astrophysical Journal. For a
version with the original high-resolution color figures please download from
http://astro.uchicago.edu/~vikram/sncsm.htm
Demulsification of Pickering emulsions: advances in understanding mechanisms to applications
Pickering emulsions are ultra-stable dispersions of two immiscible fluids stabilized by solid or microgel particles rather than molecular surfactants. Although their ultra-stability is a signature performance indicator, often such high stability hinders their demulsification, i.e., prevents the droplet coalescence that is needed for phase separation on demand, or release of the active ingredients encapsulated within droplets and/or to recover the particles themselves, which may be catalysts, for example. This review aims to provide theoretical and experimental insights on demulsification of Pickering emulsions, in particular identifying the mechanisms of particle dislodgment from the interface in biological and non-biological applications. Even though the adhesion of particles to the interface can appear irreversible, it is possible to detach particles via (1) alteration of particle wettability, and/or (2) particle dissolution, affecting the particle radius by introducing a range of physical conditions: pH, temperature, heat, shear, or magnetic fields; or via treatment with chemical/biochemical additives, including surfactants, enzymes, salts, or bacteria. Many of these changes ultimately influence the interfacial rheology of the particle-laden interface, which is sometimes underestimated. There is increasing momentum to create responsive Pickering particles such that they offer switchable wettability (demulsification and re-emulsification) when these conditions are changed. Demulsification via wettability alteration seems like the modus operandi whilst particle dissolution remains only partially explored, largely dominated by food digestion-related studies where Pickering particles are digested using gastrointestinal enzymes. Overall, this review aims to stimulate new thinking about the control of demulsification of Pickering emulsions for release of active ingredients associated with these ultra-stable emulsions
Ampliación de la distribución geográfica de <i>Liolaemus nazca</i> Aguilar, Ramírez, Castillo, Mendoza, Vargas & Sites Jr., 2019 (Iguania: Liolaemidae) para el extremo sur de Ica y norte de Arequipa, Perú : Hábitats y conservación
In the present investigation we broaden the geographical distribution of the endemic saurian of the Peruvian desert Liolaemus nazca. Its distribution is extended in approximately 45 km from its type locality (Lomas of the San Fernando National Reserve), reporting it for the first time for the department of Arequipa. Also, its distribution of occurrence is widened to other undocumented localities in San Juan de Marcona (Nasca, Ica) and Lomas (Caravelí, Arequipa) in Peru. These new records, added to those already known, allow us to characterize their habitats and analyze their state of conservation. These data highlight the importance and ecological value of the ‘lomas’ of Marcona, a site of interest in the conservation and protection of the biodiversity it refuge.Asociación Herpetológica Argentin
GEMINI 3D spectroscopy of BAL+IR+Fe II QSOs: II. IRAS 04505-2958 an explosive QSO with hypershell and a new scenario for galaxy formation and galaxy end
From a study of BAL + IR + Fe II QSOs (using deep Gemini GMOS-IFU
spectroscopy) new results are presented: for IRAS 04505-2958. Specifically, we
have studied in detail the out flow (OF) process and their associated
structures, mainly at two large galactic scales: (i) two blobs/shells (S1, S2)
at radius r = 1.1 and 2.2 kpc; and (ii) an external hypergiant shell (S3) at r
= 11 kpc. In addition, the presence of two very extended hypergiant shells (S4,
S5) at r = 80 kpc is discussed. From this GMOS study the following main results
were obtained: (i) For the external hypergiant shell S3 the kinematics GMOS
maps of the ionized gas show very similar features to those observed for the
prototype of exploding external supergiant shell: in NGC 5514. (ii) The main
knots K1, K2 and K3 -of this hypergiant shell S3- show a stellar population and
emission line ratios associated with the presence of a starburst + OF/shocks.
(iii) The internal shells S1 and S2 show structures, OF components and
properties very similar to those detected in the nuclear shells of Mrk 231.
(iv) The shells S1+S2 and S3 are aligned at PA = 131: i.e. suggesting that the
OF process is in the blow-out phase with bipolar structure. In addition, the
shells S4 and S5 (at 80-100 kpc scale) are aligned at PA = 40, i.e.: a bipolar
OF perpendicular to the internal OF. Finally, the generation of UHE cosmic rays
and neutrino/ dark-matter -associated with HyNe in BAL + IR + Fe II QSOs- is
discussed.Comment: Submitted MNRAS, 81 pages, 25 Figure
Photoevaporation Flows in Blister HII Regions: I. Smooth Ionization Fronts and Application to the Orion Nebula
We present hydrodynamical simulations of the photoevaporation of a cloud with
large-scale density gradients, giving rise to an ionized, photoevaporation
flow. The flow is found to be approximately steady during the large part of its
evolution, during which it can resemble a "champagne flow" or a "globule flow"
depending on the curvature of the ionization front. The distance from source to
ionization front and the front curvature uniquely determine the structure of
the flow, with the curvature depending on the steepness of the lateral density
gradient in the neutral cloud. We compare these simulations with both new and
existing observations of the Orion nebula and find that a model with a mildly
convex ionization front can reproduce the profiles of emission measure,
electron density, and mean line velocity for a variety of emitting ions on
scales of 10^{17} to 10^{18} cm. The principal failure of our model is that we
cannot explain the large observed widths of the [O I] 6300 Angstrom line that
forms at the ionization front.Comment: 21 pages, accepted for publication in The Astrophysical Journa
Photoionising feedback in star cluster formation
We present the first ever hydrodynamic calculations of star cluster formation
that incorporate the effect of feedback from ionising radiation. In our
simulations, the ionising source forms in the cluster core at the intersection
of several dense filaments of inflowing gas. We show that these filaments
collimate ionised outflows and suggest such an environmental origin for at
least some observed outflows in regions of massive star formation. Our
simulations show both positive feedback (i.e. promotion of star formation in
neutral gas compressed by expanding HII regions) and negative feedback (i.e.
suppression of the accretion flow in to the central regions). We show that the
volume filling factor of ionised gas is very different in our simulations than
would result from the case where the central source interacted with an
azimuthally smoothed gas density distribution. As expected, gas density is the
key parameter in determining whether clusters are unbound by photoionising
radiation. Nevertheless, we find - on account of the acceleration of a small
fraction of the gas to high velocities in the outflows - that the deposition in
the gas of an energy that exceeds the binding energy of the cluster is not a
sufficient criterion for unbinding the bulk of the cluster mass.Comment: 16 pages, 21 figures, LaTeX. Accepted for publication in MNRA
Bright Stars and Recent Star Formation in the Irregular Magellanic Galaxy NGC2366
The stellar content of the Im galaxy NGC 2366 is discussed on the basis of
CCD BVR photometry. The three brightest blue and red stars have been used to
estimate its distance, obtaining a balue of 2.9 Mpc. The spatial distribution
of the young stellar population is discussed in the light of the integrated
color indices and the color-magnitude diagrams of different zones of the
galaxy. A generalized star formation burst seems to have taken place about 50
Myr ago. The youngest stars are preferentially formed in the South-West part of
the bar, where the giant HII complex NGC 2363 is located, being younger and
bluer. The bar seems to play a role favouring star formation in one of its
extremes. Self-propagation however, does not seem to be triggering star
formation at large scale. A small region, populated by very young stars has
also been found at the East of the galaxy.Comment: Astronomical Journal, accepted. This is a uuencoded, compressed, tar
file (102 Kbytes) of 1 text, 1 table postscript files. Figures are retrieved
as a separate file. One single file with all figures and tables (552Kb) also
available from http://www.ast.cam.ac.uk/~etelles/astronomy.htm
Mutations in SCNM1 cause orofaciodigital syndrome due to minor intron splicing defects affecting primary cilia
Orofaciodigital syndrome (OFD) is a genetically heterogeneous ciliopathy characterized by anomalies of the oral cavity, face, and digits. We describe individuals with OFD from three unrelated families having bi-allelic loss-of-function variants in SCNM1 as the cause of their condition. SCNM1 encodes a protein recently shown to be a component of the human minor spliceosome. However, so far the effect of loss of SCNM1 function on human cells had not been assessed. Using a comparative transcriptome analysis between fibroblasts derived from an OFD-affected individual harboring SCNM1 mutations and control fibroblasts, we identified a set of genes with defective minor intron (U12) processing in the fibroblasts of the affected subject. These results were reproduced in SCNM1 knockout hTERT RPE-1 (RPE-1) cells engineered by CRISPR-Cas9-mediated editing and in SCNM1 siRNA-treated RPE-1 cultures. Notably, expression of TMEM107 and FAM92A encoding primary cilia and basal body proteins, respectively, and that of DERL2, ZC3H8, and C17orf75, were severely reduced in SCNM1-deficient cells. Primary fibroblasts containing SCNM1 mutations, as well as SCNM1 knockout and SCNM1 knockdown RPE-1 cells, were also found with abnormally elongated cilia. Conversely, cilia length and expression of SCNM1-regulated genes were restored in SCNM1-deficient fibroblasts following reintroduction of SCNM1 via retroviral delivery. Additionally, functional analysis in SCNM1-retrotransduced fibroblasts showed that SCNM1 is a positive mediator of Hedgehog (Hh) signaling. Our findings demonstrate that defective U12 intron splicing can lead to a typical ciliopathy such as OFD and reveal that primary cilia length and Hh signaling are regulated by the minor spliceosome through SCNM1 activity.This work was supported by a grant from the Spanish Ministry of Science and Innovation (PID2019-105620RB-I00/AEI/10.13039/501100011033)
Hydrodynamics of Cometary Compact HII Regions
We present numerical radiation-hydrodynamic simulations of cometary HII
regions for a number of champagne flow and bowshock models. For the champagne
flow models we study smooth density distributions with both steep and shallow
gradients. We also consider cases where the ionizing star has a strong stellar
wind, and cases in which the star additionally has a proper motion within the
ambient density gradient. We present simulated emission-measure maps and
long-slit spectra of our results. Our numerical models are not tailored to any
particular object but comparison with observations from the literature shows
that, in particular, the models combining density gradients and stellar winds
are able to account for both the morphology and radial velocity behavior of
several observed cometary HII regions, such as the well-studied object
G29.96-0.02.Comment: Astrophysical Journal Supplement Series in press. 25 pages in emulate
ApJ style. Revised to correspond to accepted pape
- …