Constraints on precipitation-limited hot haloes from massive galaxies to galaxy clusters

ABSTRACT We present constraints on a simple analytical model for hot diffuse halo gas, derived from a fit spanning two orders of magnitude in halo mass ($M_{500} \sim 10^{12.5}\!-\!10^{14.5} \, \mathrm{M}_{\odot }$). The model is motivated by the observed prevalence of a precipitation limit, and its main free parameter is the central ratio of gas cooling time-scale to free-fall time-scale (tcool/tff). We use integrated X-ray and thermal Sunyaev–Zel’dovich observations of the environments around massive galaxies, galaxy groups, and clusters, averaged in halo mass bins, and obtain the best-fitting model parameters. We find tcool/tff ∼ 50–110, depending on the model extrapolation beyond the halo virial radius and possibly on biases present in the data sets used in the fitting analysis. The model adequately describes the entire mass range, except for intermediate mass haloes ($M_{500} \sim 10^{13.5} \, \mathrm{M}_{\odot }$) that systematically fall below the model predictions. However, the best fits for tcool/tff substantially exceed the values typically derived from X-ray observations of individual systems (tcool/tff ∼ 10–30). We consider several explanations for those discrepancies, including X-ray selection biases and a potential anticorrelation between X-ray luminosity and the central galaxy’s stellar mass.

MECHANOCHEMICAL METHOD OF PROCESSING SILICA-CONTAINING PLANT MATTER

The possibility of complex processing of silica-containing plant biomass with the selection of a line of target products is investigated. The method includes the mechanochemical treatment of biomass in a solution of sodium hydroxide in a rotary pulsation apparatus at a temperature of self-heating not lower than 80 °C. The resulting suspension is separated on a solid residue and an extract. The solid residue is washed and dried to obtain pulp powder. The bio-filled silica gel with an SiO2 content of 49.4 wt.% to 62.6 wt.% is isolated from the extract after separation of the solid residue. By ashing the silicon-containing product at a temperature of 600 °C, amorphous silica is obtained. The content of SiO2 (as the target component) in the ash is 85.5–92.0%. The SiO2 diffraction pattern is characterized by the presence of a diffuse halo with a maximum at 2q=22.75 ° and the absence of diffraction peaks. Preliminary acid leaching can increase the purity of the resulting silica to 99.0%. The specific surface area of the obtained silica was determined by the BET method for nitrogen sorption at 260 m2/g. The effect of the concentration of the extractant on the yield of alkali-soluble substances and the degree of leaching of silicon was studied. It was shown that even at a 1% concentration of the extractant (NaOH), almost complete leaching of silicon from the plant matrix occurs. Depending on the increase in the concentration of NaOH, the degree of delignification of the biomass increases to 13–18–22%, respectively, with an increase in the concentration of NaOH 1–5–10%. Powdered cellulose was obtained with a content (%): silicon – 1.12, lignin – 34.8, alpha cellulose – 86.0, with a yield of 33.0% and a particle distribution of 80–300 μm. The amount of biomass loss is 17.6 wt.%.

All-sky angular power spectrum – I. Estimating brightness temperature fluctuations using the 150-MHz TGSS survey

ABSTRACT Measurements of the Galactic synchrotron emission are important for the 21-cm studies of the epoch of reionization. The study of synchrotron emission is also useful for quantifying the fluctuations in the magnetic field and the cosmic-ray electron density of the turbulent interstellar medium (ISM) of our Galaxy. Here, we present the all-sky angular power spectrum (Cℓ) measurements of the diffuse synchrotron emission obtained using the TIFR GMRT Sky Survey (TGSS) at 150 MHz. We estimate Cℓ using visibility data both before and after subtracting the modelled point sources. The amplitude of the measured Cℓ decreases significantly after subtracting the point sources, and it is slightly higher in the Galactic plane for the residual data. The residual Cℓ is most likely to be dominated by the Galactic synchrotron emission. The amplitude of the residual Cℓ decreases significantly away from the Galactic plane. We find that the measurements are quite symmetric in the Northern and Southern hemispheres except in the latitude range 15°−30°, which is the transition region from the disc-dominated to the diffuse halo-dominated region. A comparison between this interferometric measurement and the scaled version of the Haslam rms map at 150 MHz shows that the correlation coefficient (r) is greater than 0.5 for most of the latitude ranges considered here. This indicates that the TGSS is quite sensitive to the diffuse Galactic synchrotron radiation.

On the model of the circumgalactic mist: the implications of cloud sizes in galactic winds and haloes

ABSTRACT Ubiquitous detections of cold/warm gas around galaxies indicate that the circumgalactic medium (CGM) is multiphase and dynamic. Recent state-of-the-art cosmological galaxy simulations have generally underproduced the column density of cold halo gas. We argue that this may be due to a mismatch of spatial resolution in the circumgalactic space and the relevant physical scales at which the cold gas operates. Using semi-analytic calculations and a set of magnetohydrodynamic simulations, we present a multiphase model of the gaseous haloes around galaxies, the circumgalactic mist (CGmist). The CGmist model is based on the idea that the observed cold halo gas may be a composite of cold, dense, and small cloudlets embedded in a hot diffuse halo, resembling terrestrial clouds and mist. We show that the resulting cold gas from thermal instabilities conforms to a characteristic column density of $N_{\rm H}\approx 10^{17}\, \rm {cm^{-2}}$ as predicted by the cstcool ansatz. The model implies a large number of cold clumps in the inner galactic halo with a small volume filling factor but a large covering fraction. The model also naturally gives rise to spatial extents and differential covering fractions of cold, warm, and hot gas. To self-consistently model the co-evolution of the CGM and star formation within galaxies, future simulations must address the mismatch of the spatial resolution and characteristic scale of cold gas.

FEATURES OF X-RAY ANALYSIS OF CRYSTALLINITY DEGREE OF POLYPROPYLENE FIBRES

The need to take into account the anisotropy of compact samples pressed from grinded polypropylene (PP) fibres at a determination of the degree of polymer crystallinity by X-ray method was shown. It was proved that the breach of the spherical scattering symmetry of X-rays by PP fiber samples is not connected with an amorphous phase of polymer. The method for calculating the degree of crystallinity of fibres from the normalized intensity of the diffuse halo of preparations under study and standard powder PP samples was proposed.

The Circumgalactic Medium of Andromeda

Our view of galaxies has been transformed in recent years with diffuse halo gas surrounding galaxies that contains at least as many metals and baryons as their disks. While single sight lines through galaxy halos seen in absorption have provided key new constraints, they provide only average properties. Our massive neighbor, the Andromeda (M31) galaxy, provides an unique way to study its circumgalactic medium whereby we can study it using not one or two, but ~36 sightlines thanks to its proximity. With our Large HST program — Project AMIGA (Absorption Maps In the Gas of Andromeda), our goals are to determine the spatial distribution of the halo properties of a L* galaxy using 36 background targets at different radii and azimuths. In this brief paper, I discuss briefly the scientific rationale of Project AMIGA and some early science results. In particular, for the first time we have demonstrated that M31 has a gaseous halo that extends to Rvir with as much as metal and baryonic masses than in its disk and has substantial change in its ionization properties with more highly ionized gas found at R ~ Rvir than cooler gas found near the disk.

Study of the Milky Way's hot coronal gas with its dwarf galaxies

A large amount (5 × 1010 M⊙) of hot gas is thought to exist in an extended (≈ 200 kpc) hot diffuse halo around the Milky Way. We investigate the competitive role of the different dissipative phenomena acting on the onset of star formation of this gravitationally bound systems in this external environment. Ram pressure, Kelvin-Helmholtz and Rayleigh- Taylor instabilities, and tidal forces are accounted for separately in an analytical framework and compared in their role in influencing the star forming regions. We present an analytical criterion to elucidate the dependence of star formation in a spherical stellar system on its surrounding environment, useful in observational applications as well as theoretical interpretations of numerical results. We consider the different signatures of these phenomena in synthetically realized colour-magnitude diagrams (CMDs) of the orbiting system, thus investigating the detectability limits and relevance of these different effects for future observational projects. The theoretical framework developed has direct applications to the cases of our MW system as well as dwarf galaxies in galaxy clusters or any primordial gas-rich star cluster of stars orbiting within its host galaxy.

A 3D view of the Hydra I galaxy cluster core - I. Kinematic substructures

We used FORS2 in MXU mode to mimic a coarse ‘IFU’ in order to measure the 3D large-scale kinematics around the central Hydra I cluster galaxy NGC 3311. Our data show that the velocity dispersion field varies as a function of radius and azimuthal angle and violates point symmetry. Also, the velocity field shows similar dependence, hence the stellar halo of NGC 3311 is a dynamically young structure. The kinematic irregularities coincide in position with a displaced diffuse halo North-East of NGC 3311 and with tidal features of a group of disrupting dwarf galaxies. This suggests that the superposition of different velocity components is responsible for the kinematic substructure in the Hydra I cluster core.

Dynamical Influences of the Last Magellanic Interaction on the Magellanic Clouds

We investigate the present distributions of gas and young stars in the Large and Small Magellanic Clouds (LMC and SMC) based on fully self-consistent numerical simulations of the Clouds for the last ∼0.8 Gyr. Our principal results, which can be tested against observations, are as follows. The last dynamical and hydrodynamical interaction between the Clouds about ∼0.2 Gyr ago can form the apparently off-center bar and peculiar Hı spirals of the LMC. The present spatial distributions of young stars with ages less than ∼20 Myr in the LMC can be significantly asymmetric and clumpy owing to the interaction. A small but non-negligible fraction of stellar and gaseous components can be transferred from the SMC into the LMC during the interaction to form diffuse halo components around the LMC. The burst of star formation in the SMC can be synchronized with that of the LMC about 0.2 Gyr ago in some models. New stars can form from gas in the SMC's tidal tails, one of which can be observed as the Magellanic Bridge (MB). The metallicity distribution function of new stars in the MB has a peak of [Fe/H] ∼ −0.8, which is significantly smaller than the stellar metallicity of the SMC. Based on these results, we discuss the origin of 30 Doradus, the southern molecular ridge of the LMC, the globular cluster ESO 121-SC03, metal-poor inter-Cloud stars within the MB, and giant Hı holes of the LMC.

THOR—Cloud Thickness from Offbeam Lidar Returns

Conventional wisdom is that lidar pulses do not significantly penetrate clouds having an optical thickness exceeding about τ = 2, and that no returns are detectible from more than a shallow skin depth. Yet optically thicker clouds of τ ≫ 2 reflect a larger fraction of visible photons and account for much of the earth’s global average albedo. As cloud-layer thickness grows, an increasing fraction of reflected photons are scattered multiple times within the cloud and return from a diffuse concentric halo that grows around the incident pulse, increasing in horizontal area with layer physical thickness. The reflected halo is largely undetected by narrow field-of-view (FOV) receivers commonly used in lidar applications. Cloud Thickness from Offbeam Returns (THOR) is an airborne wide-angle detection system with multiple FOVs, capable of observing the diffuse halo as a wide-angle signal, from which the physical thickness of optically thick clouds can be retrieved. This paper describes the THOR system, demonstrates that the halo signal is stronger for thicker clouds, and presents a validation of physical thickness retrievals for clouds having τ > 20, from NASA’s P-3B flights over the Department of Energy’s Atmospheric Radiation Measurement Southern Great Plains site, using the lidar, radar, and other ancillary ground-based data.