681 research outputs found
Post‐Impact Evolution of the Southern Hale Crater Ejecta; Mars
As one of the youngest large (> 100 km wide) impacts on Mars, Hale crater offers a unique opportunity to observe well‐preserved deposits of Mars’ former interior. We utilize visible imagery (CTX and HiRISE) and elevation data (MOLA, HRSC and HiRISE stereo pairs) to examine the region south of Hale crater, which contains the greatest density of landforms caused by with the impact. Linear depressions, mounds, and polygons indicate that the ejecta material contained volatiles and underwent substantial post–impact geomorphic evolution after it was emplaced. Ejecta landform formation was facilitated by volatiles, likely water ice displaced from the subsurface during the impact, contained within the material. We suggest that the ejecta flowed into valleys where it acted in a manner similar to terrestrial debris flows, leaving mounds, high‐standing deposits, lobate flow margins and fan structures. Continued flow and settling of the ejecta then caused deposit dewatering, producing networks of linear depressions, particularly in places where the flows of ejecta were constricted. However, these landforms are not present everywhere, and their formation was likely influenced by topography. This work highlights that, while volatiles were present over much of Hale crater’s ejecta blanket, the surface expression of them is spatially variable on local and regional scales
The SAMI Galaxy Survey: Satellite galaxies undergo little structural change during their quenching phase
At fixed stellar mass, satellite galaxies show higher passive fractions than
centrals, suggesting that environment is directly quenching their star
formation. Here, we investigate whether satellite quenching is accompanied by
changes in stellar spin (quantified by the ratio of the rotational to
dispersion velocity V/) for a sample of massive (10
M) satellite galaxies extracted from the SAMI Galaxy Survey. These
systems are carefully matched to a control sample of main sequence, high
central galaxies. As expected, at fixed stellar mass and
ellipticity, satellites have lower star formation rate (SFR) and spin than the
control centrals. However, most of the difference is in SFR, whereas the spin
decreases significantly only for satellites that have already reached the red
sequence. We perform a similar analysis for galaxies in the EAGLE
hydro-dynamical simulation and recover differences in both SFR and spin similar
to those observed in SAMI. However, when EAGLE satellites are matched to their
`true' central progenitors, the change in spin is further reduced and galaxies
mainly show a decrease in SFR during their satellite phase. The difference in
spin observed between satellites and centrals at 0 is primarily due to
the fact that satellites do not grow their angular momentum as fast as centrals
after accreting into bigger halos, not to a reduction of due to
environmental effects. Our findings highlight the effect of progenitor bias in
our understanding of galaxy transformation and they suggest that satellites
undergo little structural change before and during their quenching phase.Comment: 11 pages, 7 figures. Accepted for publication in MNRA
The SAMI Galaxy Survey: gas content and interaction as the drivers of kinematic asymmetry
In order to determine the causes of kinematic asymmetry in the H gas
in the SAMI Galaxy Survey sample, we investigate the comparative influences of
environment and intrinsic properties of galaxies on perturbation. We use
spatially resolved H velocity fields from the SAMI Galaxy Survey to
quantify kinematic asymmetry () in nearby galaxies and
environmental and stellar mass data from the GAMA survey.
{We find that local environment, measured as distance to nearest neighbour,
is inversely correlated with kinematic asymmetry for galaxies with
, but there is no significant correlation for
galaxies with . Moreover, low mass galaxies
() have greater kinematic asymmetry at all
separations, suggesting a different physical source of asymmetry is important
in low mass galaxies.}
We propose that secular effects derived from gas fraction and gas mass may be
the primary causes of asymmetry in low mass galaxies. High gas fraction is
linked to high (where is H velocity
dispersion and the rotation velocity), which is strongly correlated with
, and galaxies with have offset
from the rest of the sample. Further,
asymmetry as a fraction of dispersion decreases for galaxies with
. Gas mass and asymmetry are also inversely correlated
in our sample. We propose that low gas masses in dwarf galaxies may lead to
asymmetric distribution of gas clouds, leading to increased relative
turbulence.Comment: 15 pages, 20 figure
The SAMI Galaxy Survey: the intrinsic shape of kinematically selected galaxies
Using the stellar kinematic maps and ancillary imaging data from the Sydney
AAO Multi Integral field (SAMI) Galaxy Survey, the intrinsic shape of
kinematically-selected samples of galaxies is inferred. We implement an
efficient and optimised algorithm to fit the intrinsic shape of galaxies using
an established method to simultaneously invert the distributions of apparent
ellipticities and kinematic misalignments. The algorithm output compares
favourably with previous studies of the intrinsic shape of galaxies based on
imaging alone and our re-analysis of the ATLAS3D data. Our results indicate
that most galaxies are oblate axisymmetric. We show empirically that the
intrinsic shape of galaxies varies as a function of their rotational support as
measured by the "spin" parameter proxy Lambda_Re. In particular, low spin
systems have a higher occurrence of triaxiality, while high spin systems are
more intrinsically flattened and axisymmetric. The intrinsic shape of galaxies
is linked to their formation and merger histories. Galaxies with high spin
values have intrinsic shapes consistent with dissipational minor mergers, while
the intrinsic shape of low-spin systems is consistent with dissipationless
multi-merger assembly histories. This range in assembly histories inferred from
intrinsic shapes is broadly consistent with expectations from cosmological
simulations.Comment: 15 pages, 11 figures, MNRAS in prin
The SAMI Galaxy Survey: Stellar population radial gradients in early-type galaxies
We study the internal radial gradients of the stellar populations in a sample
comprising 522 early-type galaxies (ETGs) from the SAMI (Sydney- AAO
Multi-object Integral field spectrograph) Galaxy Survey. We stack the spectra
of individual spaxels in radial bins, and derive basic stellar population
properties: total metallicity ([Z/H]), [Mg/Fe], [C/Fe] and age. The radial
gradient () and central value of the fits (evaluated at R/4) are
compared against a set of six possible drivers of the trends. We find that
velocity dispersion () - or, equivalently gravitational potential - is
the dominant driver of the chemical composition gradients. Surface mass density
is also correlated with the trends, especially with stellar age. The decrease
of [Mg/Fe] with increasing is contrasted by a rather shallow
dependence of [Z/H] with (although this radial gradient is
overall rather steep). This result, along with a shallow age slope at the
massive end, imposes stringent constraints on the progenitors of the
populations that contribute to the formation of the outer envelopes of ETGs.
The SAMI sample is split between a 'field' sample and a cluster sample. Only
weak environment-related differences are found, most notably a stronger
dependence of central total metallicity ([Z/H]) with , along
with a marginal trend of [Z/H] to steepen in cluster galaxies, a result
that is not followed by [Mg/Fe]. The results presented here serve as
constraints on numerical models of the formation and evolution of ETGs.Comment: 14 pages, 9 figures, 3 tables. Submitted to MNRA
Seasonal dependence of peroxy radical concentrations at a northern hemisphere marine boundary layer site during summer and winter: evidence for photochemical activity in winter
International audiencePeroxy radicals (HO2+?RO2) were measured at the Weybourne Atmospheric Observatory (52° N, 1° E), Norfolk using a PEroxy Radical Chemical Amplifier (PERCA) during the winter and summer of 2002. The peroxy radical diurnal cycles showed a marked difference between the winter and summer campaigns with maximum concentrations of 12 pptv at midday in the summer and maximum concentrations as high as 30 pptv (10 min averages) in winter at night. The corresponding nighttime peroxy radical concentrations were not as high in summer (3 pptv). The peroxy radical concentration shows a distinct anti-correlation with increasing NOx during the daylight hours. At night, peroxy radicals increase with increasing NOx indicative of the role of NO3 chemistry. The average diurnal cycles for net ozone production, N(O3) show a large variability in ozone production, P(O3), and a large ozone loss, L(O3) in summer relative to winter. For a daylight average, net ozone production in summer than winter (1.51±0.5 ppbv h?1 and 1.11±0.47 ppbv h?1 respectively) but summer shows more variability of (meteorological) conditions than winter. The variability in NO concentration has a much larger effect on N(O3) than the peroxy radical concentrations. Photostationary state (PSS) calculations show an NO2 lifetime of 5 min in summer and 21 min in the winter, implying that steady-state NO-NO2 ratios are not always attained during the winter months. The results show an active peroxy radical chemistry at night and the ability of winter to make oxidant. The net effect of this with respect to production of ozone in winter is unclear owing to the breakdown in the photostationary state
Zinc depletion regulates the processing and secretion of IL-1β.
Sterile inflammation contributes to many common and serious human diseases. The pro-inflammatory cytokine interleukin-1β (IL-1β) drives sterile inflammatory responses and is thus a very attractive therapeutic target. Activation of IL-1β in sterile diseases commonly requires an intracellular multi-protein complex called the NLRP3 (NACHT, LRR, and PYD domains-containing protein 3) inflammasome. A number of disease-associated danger molecules are known to activate the NLRP3 inflammasome. We show here that depletion of zinc from macrophages, a paradigm for zinc deficiency, also activates the NLRP3 inflammasome and induces IL-1β secretion. Our data suggest that zinc depletion damages the integrity of lysosomes and that this event is important for NLRP3 activation. These data provide new mechanistic insight to how zinc deficiency contributes to inflammation and further unravel the mechanisms of NLRP3 inflammasome activation
GAMA/H-ATLAS: Common star-formation rate indicators and their dependence on galaxy physical parameter
We compare common star-formation rate (SFR) indicators in the local Universe in the GAMA equatorial fields (∼ 160 deg2), using ultraviolet (UV) photometry from
GALEX, far-infrared (FIR) and sub-millimetre (sub-mm) photometry from H-ATLAS,
and Hα spectroscopy from the GAMA survey. With a high-quality sample of 745 galaxies (median redshift (z) = 0.08), we consider three SFR tracers: UV luminosity
corrected for dust attenuation using the UV spectral slope β (SFRUV,corr), Hα line luminosity corrected for dust using the Balmer decrement (BD) (SFRHα,corr), and the combination of UV and IR emission (SFRUV+IR). We demonstrate that SFRUV,corr can be reconciled with the other two tracers after applying attenuation corrections by calibrating IRX (i.e. the IR to UV luminosity ratio) and attenuation in the Hα (derived from BD) against β. However, β on its own is very unlikely to be a reliable attenuation indicator. We find that attenuation correction factors depend on parameters such as stellar mass (M∗), z and dust temperature (Tdust), but not on Hα equivalent width (EW) or Sersic index. Due to the large scatter in the IRX vs β correlation, when compared to SFRUV+IR, the β-corrected SFRUV,corr exhibits systematic deviations as a function of IRX, BD and Tdust
Intercomparison of aircraft instruments on board the <i>C-130</i> and <i>Falcon 20</i> over southern Germany during EXPORT 2000
International audienceIn the summer 2000 Export aircraft campaign (European eXport of Precursors and Ozone by long-Range Transport), two comprehensively instrumented research aircraft measuring a variety of chemical species flew wing tip to wing tip for a period of one and a quarter hours. During this interval a comparison was undertaken of the measurements of nitrogen oxide (NO), odd nitrogen species (NOy), carbon monoxide (CO) and ozone (O3). The comparison was performed at two different flight levels, which provided a 10-fold variation in the concentrations of both NO (10 to 1000 parts per trillion by volume (pptv)) and NOy (200 to over 2500 pptv). Large peaks of NO and NOy observed from the Falcon 20, which were at first thought to be from the exhaust of the C-130, were also detected on the 4 channel NOx,y instrument aboard the C-130. These peaks were a good indication that both aircraft were in the same air mass and that the Falcon 20 was not in the exhaust plume of the C-130. Correlations and statistical analysis are presented between the instruments used on the two separate aircraft platforms. These were found to be in good agreement giving a high degree of correlation for the ambient air studied. Any deviations from the correlations are accounted for in the estimated inaccuracies of the instruments. These results help to establish that the instruments aboard the separate aircraft are reliably able to measure the corresponding chemical species in the range of conditions sampled and that data collected by both aircraft can be co-ordinated for purposes of interpretation
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