We investigate the angular momentum evolution of four disk galaxies residing in Milky Way-sized halos formed in cosmological zoom-in simulations with various sub-grid physics and merging histories. We decompose these galaxies kinematically and photometrically, into their disk and bulge components. The simulated galaxies and their components lie on the observed sequences in the j * -M * diagram relating the specific angular momentum and mass of the stellar component. We find that galaxies in low-density environments follow the relation j * ∝ M α * past major mergers, with α ∼ 0.6 in the case of strong feedback, when bulge-to-disk ratios are relatively constant, and α ∼ 1.4 in the other cases, when secular processes operate on shorter timescales. We compute the retention factors (i.e. the ratio of the specific angular momenta of stars and dark matter) for both disks and bulges and show that they vary relatively slowly after averaging over numerous but brief fluctuations. For disks, the retention factors are usually close to unity, while for bulges, they are a few times smaller. Our simulations therefore indicate that galaxies and their halos grow in a quasi-homologous way.

We investigate the properties of halo gas using three cosmological 'zoom-in' simulations of realistic Milky Way-galaxy analogs with varying sub-grid physics. In all three cases, the mass of hot (T > 10 6 K) halo gas is ∼ 1% of the host's virial mass. The X-ray luminosity of two of the runs is consistent with observations of the Milky Way, while the third simulation is X-ray bright and resembles more closely a very massive, star-forming spiral. Hot halos extend to 140 kpc from the galactic center and are surrounded by a bubble of warm-hot (T = 10 5 −10 6 K) gas that extends to the virial radius. Simulated halos agree well outside 20-30 kpc with the β-model of Miller & Bregman (2013) based on OVII absorption and OVIII emission measurements. Warm-hot and hot gas contribute up to 80% of the total gas reservoir, and contain nearly the same amount of baryons as the stellar component. The mass of warm-hot and hot components falls into the range estimated for L * galaxies. With key observational constraints on the density of the Milky Way corona being satisfied, we show that concealing of the ubiquitous warm-hot baryons, along with the ejection of just 20 − 30% of the diffuse gas out of the potential wells by supernova-driven outflows, can solve the "missing baryon problem". The recovered baryon fraction within 3 virial radii is 90% of the universal value. With a characteristic density of ∼ 10 −4 cm −3 at 50 − 80 kpc, diffuse coronae meet the requirement for fast and complete ram-pressure stripping of the gas reservoirs in dwarf galaxy satellites.

We use high-resolution cosmological hydrodynamical simulations of Milky Way-sized galaxies with varying supernovae feedback strengths and merger histories to investigate the formation of their gaseous halos and especially their hot (> 10 6 K) X-ray luminous coronae. Our simulations predict the presence of significant hot gas in the halos as early as z = 3 − 4, well before the halos ought to be able to sustain hot mode accretion in the conventional picture. The nascent coronae grow inside-out and initially do so primarily as a result of outflows from the central galaxies powered by merger-induced shock heating and strong supernovae feedback, both of which are elemental features of today's successful galaxy formation models. Furthermore, the outflows and the forming coronae also accelerate the transition from cold to hot mode accretion by contributing to the conditions for sustaining stable accretion shocks. They also disrupt the filamentary streams funneling cold gas onto the central galaxies by causing their mouths to fray into a broad delta, detach from the galaxies, and be pushed away to larger radii. And even though at early times the filaments repeatedly re-form, the hot gas and the outflows act to weaken the filaments and accelerate their ultimate disruption. Although galactic outflows are generally thought of as ejective feedback, we find that their action on the filaments suggests a preventive role as well.

In yeast and mammals, prohibitins (PHBs) are considered as structural proteins that form a scaffold-like structure for interacting with a set of proteins involved in various processes occurring in the mitochondria. The role of PHB in plant mitochondria is poorly understood. In the study, the model organism Arabidopsis thaliana was used to identify the possible roles of type-II PHBs (homologs of yeast Phb2p) in plant mitochondria. The obtained results suggest that the plant PHB complex participates in the assembly of multisubunit complexes; namely, respiratory complex I and enzymatic complexes carrying lipoic acid as a cofactor (pyruvate dehydrogenase, 2-oxoglutarate dehydrogenase and glycine decarboxylase). PHBs physically interact with subunits of these complexes. Knockout of two Arabidopsis type-II prohibitins (AtPHB2 and AtPHB6) results in a decreased abundance of these complexes along with a reduction in mitochondrial acyl carrier proteins. Also, the absence of AtPHB2 and AtPHB6 influences the expression of the mitochondrial genome and leads to the activation of alternative respiratory pathways, namely alternative oxidase and external NADH-dependent alternative dehydrogenases.

A part of the radio structure of the galaxy 0932+075 emerged as a possible compact symmetric object (CSO) after the observation with the Very Long Baseline Array (VLBA) at 5 GHz in 1997. More than a decade later, we carried out observations at 5, 15.4, and 22.2 GHz using the VLBA to test this possibility. We report here that we have found a component whose spectrum is inverted in the whole range from 5 GHz to 22 GHz and we label it a high-frequency peaker (HFP). Using a set of 5 GHz images from two epochs separated by 11.8 years and a set of 15.4 GHz images separated by 8.2 years, we were able to examine the proper motions of the three components of the CSO candidate with respect to the HFP. We found that their displacements cannot be reconciled with the CSO paradigm. This has led to the rejection of the hypothesis that the western part of the arcsecond-scale radio structure of 0932+075 is a CSO anchored at the HFP. Consequently, the HFP cannot be labelled a core and its role in this system is unclear.

<p><strong>Introduction</strong></p> <p>Mars is a cold dry planet, yet there is ample evidence for fluvial activity on its surface, which paints a different picture for its past climate [1]. If Mars has ever been covered by an ancient ocean or ubiquitous paleolakes, the signatures of the presence of water would have been preserved in the ejecta blankets of some impact sites because the thermodynamics of the excavation flow depends on the target material properties such as its composition and mechanical properties [2]. The main objective of this work is to test whether the difference between impact sites of water-covered, ice-rich, and dry target subsurfaces on Mars is significant enough to be observable.</p> <p><strong>Method<span class="Apple-converted-space"> </span></strong></p> <p>To simulate hypervelocity impact processes in solid materials, we use the iSALE-2D shock physics code [3,4,5]. Our simulations make use of its following models: the elasto-plastic constitutive model for multiple materials, the fragmentation and modified strength model, the porosity compaction model, and the acoustic fluidisation block model. Target materials are described by the ANEOS equations of state for basalt, water ice, and water.</p> <p>We consider different impact scenarios with varied target composition: i) 200-400m of liquid water covering basalt, ii) 100-200m basalt surface covering 200-400m of subsurface water ice, iii) dry basaltic surface with no ice or water. The impact parameters are fixed across these scenarios: impacts are vertical and triggered by a single impactor with the impact velocity of 10km/s and the radius of 100m. The projectile is made of intact basalt described by the Lundborg strength model, while the the strength of the target basalt is described by the ROCK model, in which the yield strength is a function of both pressure and damage, with the latter computed by the iSALE damage model.</p> <p>The full trajectories and final distribution of the impact ejecta have to be quantified in post-processing due to the fact that high above the crater, ejecta becomes underresolved in the Eulerian grid. We thus analyse the characteristics (i.e. velocity, launch time, launch position) of tracer particles when they reach an altitude of one projectile radius above the surface [2]. We then calculate their final landing positions, assuming ballistic trajectories, and analyse the ejecta mass distributions.</p> <p><strong>Results</strong></p> <p> </p> <table border="1"> <tbody> <tr> <td> <p><strong><img src="" alt="" width="911" height="732" /><br /></strong></p> </td> </tr> <tr> <td> <p><strong>Figure 1. </strong>Pressure and density maps of different impact scenarios shown at the resolution of 10CPPR (cells per projectile radius). The naming of the scenarios is as follows: ThD1: dry case of pure basalt, ThI200200: 200m of basalt covering 200m of water ice over basalt; ThW200: 200m of water over basalt.<span class="Apple-converted-space"> </span></p> </td> </tr> </tbody> </table> <p> </p> <p>In Figure 1 we present different impact scenarios at 3 distinct periods of the excavation stage: 2s, 6s and 20s after the impact. The presence of water or water ice modifies the volume of the cavity during the entire excavation phase. The shapes and angles of the ejecta curtains are also different for varied target scenarios.</p> <p> </p> <table border="1"> <tbody> <tr> <td> <p><strong><img src="" alt="" /><br /></strong></p> </td> </tr> <tr> <td> <p><strong>Figure 2. </strong>The evolution of crater volumes and radii over time.</p> </td> </tr> </tbody> </table> <p> </p> <p>In Figure 2 we show the time evolution of the crater volumes and radii quantitatively. The most striking difference is between the volume of the excavated material in dry vs. ice-rich or water-rich targets, which translates into the difference in volumes of the ejecta blanket. Crater radii are also a discriminator between those cases, with water-covered and ice-rich targets being deeper than the “dry” one. However, over time their depth would also be decreased by the sublimation of subsurface ice and evaporation of the surface water.</p> <p> </p> <table border="1"> <tbody> <tr> <td><strong><img src="" alt="" /><br /></strong></td> </tr> <tr> <td><strong>Figure 3. </strong>Ejecta properties for the cases with varied ice depth. a) Mass distribution of ejected material. b) Dependency of the median ejection angle of the target material on where it landed. c) Evolution of the crater volume over time. d) Dependency of the ejection velocity of target material on where it landed. Rcrater were computed at t=20s.</td> </tr> </tbody> </table> <p> </p> <p>In Figure 3 we compare the ejection properties for targets with 200m ice at different depths: 0m (ThI0200); 100m (ThI100200) and 200m (ThI200200) depths. The final mass distributions and ejection angles are substantially different between these cases, and those differences would be reflected in the morphologies of the ejecta blankets. The final crater volumes (c) alone are insufficient to discriminate between these cases.</p> <p><strong>Conclusion</strong></p> <p>We conducted numerical experiments of impact cratering into varied targets: ice-rich, water-rich and dry (pure basalt). Our preliminary results show that for the constant projectile and velocity, one can discriminate between those cases based on the crater size and ejecta volume. We also show that the depth of buried ice would leave a characteristic signature in the blanket.</p> <p><strong>Future work</strong></p> <p>We plan to address the effects of the atmosphere and vapour plumes on the trajectories of ejecta. The interaction of ejected material with an atmosphere, accounting for drag forces and momentum exchange, was recently implemented in iSALE [6].</p> <p><strong>References</strong></p> <p>[1] Zachary I Dickeson, Joel M Davis, Martian oceans, <em>Astronomy & Geophysics</em>, Volume 61, Issue 3, June 2020, Pages 3.11–3.17, https://doi.org/10.1093/astrogeo/ataa038</p> <p>[2] Luther, R., Zhu, M.-H., Collins, G. and Wünnemann, K. (2018), Effect of target properties and impact velocity on ejection dynamics and ejecta deposition. Meteorit Planet Sci, 53: 1705-1732. https://doi.org/10.1111/maps.13143</p> <p>[3] Amsden, A., Ruppel, H., and Hirt, C. (1980). SALE: A simplified ALE computer program for fluid flow at all speeds. Los Alamos National Laboratories Report, LA-8095:101p. Los Alamos, New Mexico: LANL.</p> <p>[4] Collins, G. S., Melosh, H. J., and Ivanov, B. A. (2004). Modeling damage and deformation in impact simulations. Meteoritics and Planetary Science, 39:217--231.</p> <p>[5] Wünnemann, K., Collins, G., and Melosh, H. (2006). A strain-based porosity model for use in hydrocode simulations of impacts and implications for transient crater growth in porous targets. Icarus, 180:514--527.</p> <p>[6] Robert Luther, Natalia Artemieva, Kai Wünnemann, The effect of atmospheric interaction on impact ejecta dynamics and deposition, Icarus, Volume 333, 2019, Pages 71-86, https://doi.org/10.1016/j.icarus.2019.05.007.</p>

<div> <div>Mars is a cold dry planet, yet there is ample evidence for fluvial activity on its past surface, including sediments suggestive of shallow lakes, which paints a different picture for the Martian past climate. Mars is also heavily cratered, and some of those craters may have resulted from impact cratering into water-covered targets. Distinguishing between water-overed and dry surface at the time of the impact is the topic of this project. We approach this problem from the theoretical point of view and use a shock physics code iSALE capable of simulating different materials with various strength and damage models. This hydrocode is widely used in impact physics and has been extensively tested against laboratory experiments. We realise several impact scenarios with varied rheology, as well as sizes of projectiles and impact angles, in particular water-covered (simulated paleolake), water ice-rich and dry targets. We discuss the theoretical effects of the presence of surface water on the morphology and dynamics of impact sites (both craters and ejecta). Distinguishing between these scenarios can aid the interpretation of remote sensing observations, and open a possibility of using a new independent observable to study the past climate of Mars.</div> </div>

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