SN 2014C: VLBI image shows a shell structure and decelerated expansion

We report on new Very Long Baseline Interferometry radio measurements of supernova 2014C in the spiral galaxy NGC 7331, made with the European VLBI Network ∼5 yr after the explosion, as well as on flux density measurements made with the Jansky Very Large Array (VLA). SN 2014C was an unusual supernova, initially of Type Ib, but over the course of ∼1 yr it developed strong Hα lines, implying the onset of strong interaction with some H-rich circumstellar medium (CSM). The expanding shock-front interacted with a dense shell of circumstellar material during the first year, but has now emerged from the dense shell and is expanding into the lower density CSM beyond. Our new VLBI observations show a relatively clear shell structure and continued expansion with some deceleration, with a suggestion that the deceleration is increasing at the latest times. Our multi-frequency VLA observations show a relatively flat powerlaw spectrum with Sν∝ν−0.56 ± 0.03, and show no decline in the radio luminosity since t ∼ 1 yr.

No missing photons for reionization: moderate ionizing photon escape fractions from the FIRE-2 simulations

ABSTRACT We present the escape fraction of hydrogen ionizing photons (fesc) from a sample of 34 high-resolution cosmological zoom-in simulations of galaxies at z ≥ 5 in the Feedback in Realistic Environments project, post-processed with a Monte Carlo radiative transfer code for ionizing radiation. Our sample consists of 8500 haloes in Mvir ∼ 108–$10^{12}\, M_{\odot }$ (M* ∼ 104–$10^{10}\, M_{\odot }$) at z = 5–12. We find the sample average 〈fesc〉increases with halo mass for Mvir ∼ 108–$10^{9.5}\, M_{\odot }$, becomes nearly constant for 109.5–$10^{11}\, M_{\odot }$, and decreases at ${\gtrsim}10^{11}\, M_{\odot }$. Equivalently, 〈fesc〉 increases with stellar mass up to $M_{\ast }\sim 10^8\, M_{\odot }$ and decreases at higher masses. Even applying single-star stellar population synthesis models, we find a moderate 〈fesc〉 ∼ 0.2 for galaxies at $M_{\ast }\sim 10^8\, M_{\odot }$. Nearly half of the escaped ionizing photons come from stars 1–3 Myr old and the rest from stars 3–10 Myr old. Binaries only have a modest effect, boosting 〈fesc〉 by ∼25–35 per cent and the number of escaped photons by 60–80 per cent. Most leaked ionizing photons are from vigorously star-forming regions that usually contain a feedback-driven kpc-scale superbubble surrounded by a dense shell. The shell is forming stars while accelerated, so new stars formed earlier in the shell are already inside the shell. Young stars in the bubble and near the edge of the shell can fully ionize some low-column-density paths pre-cleared by feedback, allowing a large fraction of their ionizing photons to escape. The decrease of 〈fesc〉 at the high-mass end is due to dust attenuation, while at the low-mass end, 〈fesc〉 decreases owing to inefficient star formation and hence feedback. At fixed mass, 〈fesc〉 tends to increase with redshift. Although the absolute 〈fesc〉does not fully converge with resolution in our simulations, the mass- and redshift-dependence of 〈fesc〉 is likely robust. Our simulations produce sufficient ionizing photons for cosmic reionization.

A novel design, analysis and 3D printing of Ti-6Al-4V alloy bio-inspired porous femoral stem

The current study is proposing a design envelope for porous Ti-6Al-4V alloy femoral stems to survive under fatigue loads. Numerical computational analysis of these stems with a body-centered-cube (BCC) structure is conducted in ABAQUS. Femoral stems without shell and with various outer dense shell thicknesses (0.5, 1.0, 1.5, and 2 mm) and inner cores (porosities of 90, 77, 63, 47, 30, and 18%) are analyzed. A design space (envelope) is derived by using stem stiffnesses close to that of the femur bone, maximum fatigue stresses of 0.3σys in the porous part, and endurance limits of the dense part of the stems. The Soderberg approach is successfully employed to compute the factor of safety Nf > 1.1. Fully porous stems without dense shells are concluded to fail under fatigue load. It is thus safe to use the porous stems with a shell thickness of 1.5 and 2 mm for all porosities (18–90%), 1 mm shell with 18 and 30% porosities, and 0.5 mm shell with 18% porosity. The reduction in stress shielding was achieved by 28%. Porous stems incorporated BCC structures with dense shells and beads were successfully printed.

The changing-type SN 2014C may come from an 11-M⊙ star stripped by binary interaction and violent eruption

ABSTRACT SN 2014C was an unprecedented supernova (SN) that displayed a metamorphosis from Type Ib to Type IIn over ∼200 d. This transformation is consistent with a helium star having exploded in a cavity surrounded by a dense shell of the progenitor’s stripped hydrogen envelope. For at least 5 yr post-explosion, the ejecta continued to interact with an outer, extended component of circumstellar medium (CSM) that was ejected even before the dense shell. It is still unclear, however, what kind of progenitor could have undergone such a complicated mass-loss history before it produced this peculiar SN. In this paper, we report a new analysis of SN 2014C’s host star cluster based on data from the Hubble Space Telescope (HST). By carefully fitting its spectral energy distribution (SED), we derive a precise cluster age of 20.0$^{+3.5}_{-2.6}$ Myr, which corresponds to the progenitor’s lifetime assuming coevolution. Combined with binary stellar evolution models, we find that SN 2014C’s progenitor may have been an ∼11-M⊙ star in a relatively wide binary system. The progenitor’s envelope was partially stripped by Case C or Case BC mass transfer via binary interaction, followed by a violent eruption that ejected the last hydrogen layer before terminal explosion. Thus, SN 2014C, in common with SNe 2006jc and 2015G, may be a third example that violent eruptions, with mass-loss rates matching luminous blue variable (LBV) giant eruptions, can also occur in much lower mass massive stars if their envelopes are partially or completely stripped in interacting binaries.

The role of Galactic H II regions in the formation of filaments

Context. Massive stars and their associated ionized (H II) regions could play a key role in the formation and evolution of filaments that host star formation. However, the properties of filaments that interact with H II regions are still poorly known. Aims. To investigate the impact of H II regions on the formation of filaments, we imaged the Galactic H II region RCW 120 and its surroundings where active star formation takes place and where the role of ionization feedback on the star formation process has already been studied. Methods. We used the large-format bolometer camera ArTéMiS on the APEX telescope and combined the high-resolution ArTéMiS data at 350 and 450 μm with Herschel-SPIRE/HOBYS data at 350 and 500 μm to ensure good sensitivity to a broad range of spatial scales. This allowed us to study the dense gas distribution around RCW 120 with a resolution of 8′′ or 0.05 pc at a distance of 1.34 kpc. Results. Our study allows us to trace the median radial intensity profile of the dense shell of RCW 120. This profile is asymmetric, indicating a clear compression from the H II region on the inner part of the shell. The profile is observed to be similarly asymmetric on both lateral sides of the shell, indicating a homogeneous compression over the surface. On the contrary, the profile analysis of a radial filament associated with the shell, but located outside of it, reveals a symmetric profile, suggesting that the compression from the ionized region is limited to the dense shell. The mean intensity profile of the internal part of the shell is well fitted by a Plummer-like profile with a deconvolved Gaussian full width at half maximum of 0.09 pc, as observed for filaments in low-mass star-forming regions. Conclusions. Using ArTéMiS data combined with Herschel-SPIRE data, we found evidence for compression from the inner part of the RCW 120 ionized region on the surrounding dense shell. This compression is accompanied with a significant (factor 5) increase of the local column density. This study suggests that compression exerted by H II regions may play a key role in the formation of filaments and may further act on their hosted star formation. ArTéMiS data also suggest that RCW 120 might be a 3D ring, rather than a spherical structure.

Gaseous dynamical friction under radiative feedback: do intermediate-mass black holes speed up or down?

ABSTRACT Coalescence of intermediate-mass black holes (IMBHs) as a result of the migration toward galactic centres via dynamical friction may contribute to the formation of supermassive BHs. Here we reinvestigate the gaseous dynamical friction, which was claimed to be inefficient with radiative feedback from BHs in literature, by performing 3D radiation-hydrodynamics simulations that solve the flow structure in the vicinity of BHs. We consider a 104-M⊙ BH moving at the velocity vflow through the homogeneous medium with metallicity Z in the range of 0–0.1 Z⊙ and density n∞. We show that, if n∞ ≲ 106 cm−3 and vflow ≲ 60 km s−1, the BH is accelerated forward because of the gravitational pull from a dense shell ahead of an ionized bubble around the BH, regardless of the value of Z. If n∞ ≳ 106 cm−3, however, our simulation shows the opposite result. The ionized bubble and associating shell temporarily appear, but immediately go downstream with significant ram pressure of the flow. They eventually converge into a massive downstream wake, which gravitationally drags the BH backward. The BH decelerates over the time-scale of ∼0.01 Myr, much shorter than the dynamical time-scale in galactic discs. Our results suggest that IMBHs that encounter the dense clouds rapidly migrate toward galactic centres, where they possibly coalescence with others.

Supramolecular attack particles are autonomous killing entities released from cytotoxic T cells

Cytotoxic T lymphocytes (CTLs) kill infected and cancerous cells. We detected transfer of cytotoxic multiprotein complexes, called supramolecular attack particles (SMAPs), from CTLs to target cells. SMAPs were rapidly released from CTLs and were autonomously cytotoxic. Mass spectrometry, immunochemical analysis, and CRISPR editing identified a carboxyl-terminal fragment of thrombospondin-1 as an unexpected SMAP component that contributed to target killing. Direct stochastic optical reconstruction microscopy resolved a cytotoxic core surrounded by a thrombospondin-1 shell of ~120 nanometer diameter. Cryo-soft x-ray tomography analysis revealed that SMAPs had a carbon-dense shell and were stored in multicore granules. We propose that SMAPs are autonomous extracellular killing entities that deliver cytotoxic cargo targeted by the specificity of shell components.

The explosion energy of the type IIP supernova SN 2013fs with a confined dense circumstellar shell

ABSTRACT The recent study of the SN 2013fs flash spectrum suggests an enormous explosion energy for SNe IIP, far beyond the possibilities of the neutrino mechanism. The issue of the explosion energy of SN 2013fs is revisited, making use of the effects of the early supernova interaction with the dense circumstellar shell. The velocity of the cold dense shell between reverse and forward shocks is inferred from the analysis of the broad He ii 4686 Å on day 2.4. This velocity, alongside other observables, provides us with an alternative energy estimate of ∼1.8 × 1051 erg for the preferred mass of ∼10 M⊙. The inferred value is within the range of neutrino-driven explosions.

Preparation of zirconia granules with a low molecular weight dispersant

In the present work, different conditions, such as PVA content as a high molecular weight polymer, Dolapix CE64 level with a lower molecular weight and pH adjusted by HCl, were investigated for the preparation of the yttria-stabilized zirconia (YSZ) granules from nanosized YSZ particles. It was found that the suspension prepared at pH = 4 and with 0.1 wt.% Dolapix CE64 has a reasonable value of viscosity for spray drying. The morphology of granules and their cross-sections were characterized through microstructural observation. The flowability of the prepared granules and the Hausner ratio were also evaluated. The results indicated that the addition of only 0.1 wt.% of PVA binder and the use of Dolapix can produce the YSZ granules with good flowability. Replacement of PAA by Dolapix has the benefits of achieving uniform granules with a dense shell layer, decreasing the amount of binder and accelerating the feeding rate of suspensions. The mechanism of the solid and hollow granule formation by a low molecular weight dispersant was suggested.