119 research outputs found
Cooling and Heating Functions of Photoionized Gas
Cooling and heating functions of cosmic gas are a crucial ingredient for any
study of gas dynamics and thermodynamics in the interstellar and intergalactic
medium. As such, they have been studied extensively in the past under the
assumption of collisional ionization equilibrium. However, for a wide range of
applications, the local radiation field introduces a non-negligible, often
dominant, modification to the cooling and heating functions. In the most
general case, these modifications cannot be described in simple terms, and
would require a detailed calculation with a large set of chemical species using
a radiative transfer code (the well-known code Cloudy, for example). We show,
however, that for a sufficiently general variation in the spectral shape and
intensity of the incident radiation field, the cooling and heating functions
can be approximated as depending only on several photoionization rates, which
can be thought of as representative samples of the overall radiation field.
This dependence is easy to tabulate and implement in cosmological or
galactic-scale simulations, thus economically accounting for an important but
rarely-included factor in the evolution of cosmic gas. We also show a few
examples where the radiation environment has a large effect, the most
spectacular of which is a quasar that suppresses gas cooling in its host halo
without any mechanical or non-radiative thermal feedback.Comment: replaced with the accepted version; note that the revised version
differs substantially from the original draf
CGM properties in VELA and NIHAO simulations; the OVI ionization mechanism: dependence on redshift, halo mass and radius
We study the components of cool and warm/hot gas in the circumgalactic medium
(CGM) of simulated galaxies and address the relative production of OVI by
photoionization versus collisional ionization, as a function of halo mass,
redshift, and distance from the galaxy halo center. This is done utilizing two
different suites of zoom-in hydro-cosmological simulations, VELA (6 halos;
) and NIHAO (18 halos; to ), which provide a broad theoretical basis
because they use different codes and physical recipes for star formation and
feedback. In all halos studied in this work, we find that collisional
ionization by thermal electrons dominates at high redshift, while
photoionization of cool or warm gas by the metagalactic radiation takes over
near . In halos of and above, collisions become
important again at , while photoionization remains significant down to
for less massive halos. In halos with , at most of the photoionized OVI is in a
warm, not cool, gas phase (~K). We also find that
collisions are dominant in the central regions of halos, while photoionization
is more significant at the outskirts, around , even in massive
halos. This too may be explained by the presence of warm gas or, in lower mass
halos, by cool gas inflows
High ions towards white dwarfs: circumstellar line shifts and stellar temperature
Based on a compilation of OVI, CIV, SiIV and NV data from IUE, FUSE, GHRS,
STIS, and COS, we derive an anti- correlation between the stellar temperature
and the high ion velocity shift w.r.t. to the photosphere, with positive (resp.
negative) velocity shifts for the cooler (resp. hotter) white dwarfs. This
trend probably reflects more than a single process, however such a dependence
on the WD's temperature again favors a CS origin for a very large fraction of
those ion absorptions, previously observed with IUE, HST-STIS, HST-GHRS, FUSE,
and now COS, selecting objects for which absorption line radial velocities,
stellar effective temperature and photospheric velocity can be found in the
literature. Interestingly, and gas in near-equilibrium in the star vicinity. It
is also probably significant that the temperature that corresponds to a null
radial velocity, i.e. \simeq 50,000K, also corresponds to the threshold below
which there is a dichotomy between pure or heavy elements atmospheres as well
as some temperature estimates for and a form of balance between radiation
pressure and gravitation. This is consistent with ubiquitous evaporation of
orbiting dusty material. Together with the fact that the fraction of stars with
(red-or blue-) shifted lines and the fraction of stars known to possess heavy
species in their atmosphere are of the same order, such a velocity-temperature
relationship is consistent with quasi-continuous evaporation of orbiting CS
dusty material, followed by accretion and settling down in the photosphere. In
view of these results, ion measurements close to the photospheric or the IS
velocity should be interpreted with caution, especially for stars at
intermediate temperatures. While tracing CS gas, they may be erroneously
attributed to photospheric material or to the ISM, explaining the difficulty of
finding a coherent pattern of the high ions in the local IS 3D distribution.Comment: Accepted by A&A. Body of paper identical to v1. This submission has a
more appropriate truncation of the original abstrac
UV to near-IR observations of the DART-Dimorphos collision
The impact of the Double Asteroid Redirection Test (DART) spacecraft with
Dimorphos allows us to study asteroid collision physics, including momentum
transfer, the ejecta properties, and the visibility of such events in the Solar
System. We report observations of the DART impact in the ultraviolet (UV),
visible light, and near-infrared (IR) wavelengths. The observations support the
existence of at least two separate components of the ejecta: a fast and a slow
component. The fast-ejecta component is composed of a gaseous phase, moving at
about 1.6 km/s with a mass of <10^4 kg. The fast ejecta is detected in the UV
and visible light, but not in the near-IR -band observations. Fitting a
simplified optical thickness model to these observations allows us to constrain
some of the properties of the fast ejecta, including its scattering efficiency
and the opacity of the gas. The slow ejecta component is moving at typical
velocities of up to about 10 m/s. It is composed of micrometer-size particles,
that have a scattering efficiency, at the direction of the observer, of the
order of 10^-3 and a total mass of about 10^6 kg. The larger particles in the
slow ejecta, whose size is bound to be in the range between ~1 mm to ~1 m,
likely have a scattering efficiency larger than that of the pre-impact Didymos
system.Comment: Submitted to MNRA
PTF11kx: A Type-Ia Supernova with a Symbiotic Nova Progenitor
There is a consensus that Type-Ia supernovae (SNe Ia) arise from the
thermonuclear explosion of white dwarf stars that accrete matter from a binary
companion. However, direct observation of SN Ia progenitors is lacking, and the
precise nature of the binary companion remains uncertain. A temporal series of
high-resolution optical spectra of the SN Ia PTF 11kx reveals a complex
circumstellar environment that provides an unprecedentedly detailed view of the
progenitor system. Multiple shells of circumsteller are detected and the SN
ejecta are seen to interact with circumstellar material (CSM) starting 59 days
after the explosion. These features are best described by a symbiotic nova
progenitor, similar to RS Ophiuchi.Comment: 27 pages, 5 figures. In pres
NEBULAR EXCITATION IN z ∼ 2 STAR-FORMING GALAXIES FROM THE SINS AND LUCI SURVEYS: THE INFLUENCE OF SHOCKS AND AGN ∗
Based on high-resolution, spatially resolved data of 10 z ∼ 2 star-forming galaxies from th
Confined dense circumstellar material surrounding a regular type II supernova
With the advent of new wide-field, high-cadence optical transient surveys, our understanding of the diversity of core-collapse supernovae has grown tremendously in the last decade. However, the pre-supernova evolution of massive stars, which sets the physical backdrop to these violent events, is theoretically not well understood and difficult to probe observationally. Here we report the discovery of the supernova iPTF 13dqy = SN 2013fs a mere ∼3 h after explosion. Our rapid follow-up observations, which include multiwavelength photometry and extremely early (beginning at ∼6 h post-explosion) spectra, map the distribution of material in the immediate environment (≲1015 cm) of the exploding star and establish that it was surrounded by circumstellar material (CSM) that was ejected during the final ∼1 yr prior to explosion at a high rate, around 10-3 solar masses per year. The complete disappearance of flash-ionized emission lines within the first several days requires that the dense CSM be confined to within ≲1015 cm, consistent with radio non-detections at 70–100 days. The observations indicate that iPTF 13dqy was a regular type II supernova; thus, the finding that the probable red supergiant progenitor of this common explosion ejected material at a highly elevated rate just prior to its demise suggests that pre-supernova instabilities may be common among exploding massive stars. © 2017 Nature Publishing Grou
O VI Absorbers Tracing Hot Gas Associated with a Pair of Galaxies at z = 0.167
High signal-to-noise (S/N) observations of the QSO PKS 0405-123 (zem = 0.572)
with the Cosmic Origins Spectrograph from 1134 to 1796 A with a resolution of
17 km s-1 are used to study the multi-phase partial Lyman limit system (LLS) at
z = 0.16716 which has previously been studied using relatively low S/N spectra
from STIS and FUSE. The LLS and an associated H I-free broad O VI absorber
likely originate in the circumgalactic gas associated with a pair of galaxies
at z = 0.1688 and 0.1670 with impact parameters of 116 h70-1 and 99 h70-1. The
broad and symmetric O VI absorption is detected in the z = 0.16716 restframe
with v = -278 +/- 3 km s-1, log N(O VI) = 13.90 +/- 0.03 and b = 52 +/- 2 km
s-1. This absorber is not detected in H I or other species with the possible
exception of N V . The broad, symmetric O VI profile and absence of
corresponding H I absorption indicates that the circumgalactic gas in which the
collisionally ionized O VI arises is hot (log T ~ 5.8-6.2). The absorber may
represent a rare but important new class of low z IGM absorbers. The LLS has
strong asymmetrical O VI absorption with log N(O VI) = 14.72 +/- 0.02 spanning
a velocity range from -200 to +100 km s-1. The high and low ions in the LLS
have properties resembling those found for Galactic highly ionized HVCs where
the O VI is likely produced in the conductive and turbulent interfaces between
cool and hot gas.Comment: 68 pages including 13 figures. Accepted by ApJ (2010 Aug 20, vol 719
The Volatile Anesthetic Isoflurane Increases Endothelial Adenosine Generation via Microparticle Ecto-5′-Nucleotidase (CD73) Release
Endothelial dysfunction is common in acute and chronic organ injury. Isoflurane is a widely used halogenated volatile anesthetic during the perioperative period and protects against endothelial cell death and inflammation. In this study, we tested whether isoflurane induces endothelial ecto-5′-nucleotidase (CD73) and cytoprotective adenosine generation to protect against endothelial cell injury. Clinically relevant concentrations of isoflurane induced CD73 activity and increased adenosine generation in cultured human umbilical vein or mouse glomerular endothelial cells. Surprisingly, isoflurane-mediated induction of endothelial CD73 activity occurred within 1 hr and without synthesizing new CD73. We determined that isoflurane rapidly increased CD73 containing endothelial microparticles into the cell culture media. Indeed, microparticles isolated from isoflurane-treated endothelial cells had significantly higher CD73 activity as well as increased CD73 protein. In vivo, plasma from mice anesthetized with isoflurane had significantly higher endothelial cell-derived CD144+ CD73+ microparticles and had increased microparticle CD73 activity compared to plasma from pentobarbital-anesthetized mice. Supporting a critical role of CD73 in isoflurane-mediated endothelial protection, a selective CD73 inhibitor (APCP) prevented isoflurane-induced protection against human endothelial cell inflammation and apoptosis. In addition, isoflurane activated endothelial cells Rho kinase evidenced by myosin phosphatase target subunit-1 and myosin light chain phosphorylation. Furthermore, isoflurane-induced release of CD73 containing microparticles was significantly attenuated by a selective Rho kinase inhibitor (Y27632). Taken together, we conclude that the volatile anesthetic isoflurane causes Rho kinase-mediated release of endothelial microparticles containing preformed CD73 and increase adenosine generation to protect against endothelial apoptosis and inflammation
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