scholarly journals Magnetic Reconnection Triggered by the Parker Instability in the Galaxy: Two‐dimensional Numerical Magnetohydrodynamic Simulations and Application to the Origin of X‐Ray Gas in the Galactic Halo

2003 ◽  
Vol 582 (1) ◽  
pp. 215-229 ◽  
Author(s):  
Syuniti Tanuma ◽  
Takaaki Yokoyama ◽  
Takahiro Kudoh ◽  
Kazunari Shibata
Keyword(s):  
Magnetic Reconnection ◽  
Galactic Halo ◽  
Two Dimensional ◽  
X Ray ◽  
The Galaxy ◽  
Magnetohydrodynamic Simulations

scholarly journals Empirical estimates of the Galactic halo contribution to the dispersion measures of extragalactic fast radio bursts using X-ray absorption

2020 ◽  
Vol 500 (1) ◽  
pp. 655-662
Author(s):  
Sanskriti Das ◽  
Smita Mathur ◽  
Anjali Gupta ◽  
Fabrizio Nicastro ◽  
Yair Krongold
Keyword(s):  
Galactic Halo ◽  
Dispersion Measure ◽  
Radio Bursts ◽  
X Ray ◽  
Empirical Estimates ◽  
The Galaxy ◽  
Dispersion Measures ◽  
Baryonic Mass ◽  
X Ray Absorption ◽  
Galactic Longitude

ABSTRACT We provide an empirical list of the Galactic dispersion measure (DMGal) contribution to the extragalactic fast radio bursts (FRBs) along 72 sightlines. It is independent of any model of the Galaxy, i.e. we do not assume the density of the disc or the halo, spatial extent of the halo, baryonic mass content, or any such external constraints to measure DMGal. We use 21-cm, UV, EUV, and X-ray data to account for different phases, and find that DMGal is dominated by the hot phase probed by X-ray absorption. We improve upon the measurements of N($\rm{O}\,{\small VII}$) and f$_{\rm O\,{\small VII}}$ compared to previous studies, thus providing a better estimate of the hot phase contribution. The median DMGal = 64$^{+20}_{-23}$ cm−3 pc, with a 68 per cent (90 per cent) confidence interval of 33–172 (23–660) cm−3 pc. The DMGal does not appear to follow any trend with the Galactic longitude or latitude, and there is a large scatter around the values predicted by simple disc + spherical halo models. Our measurements provide more complete and accurate estimates of DMGal independent from the previous studies. We provide a table and a code to retrieve DMGal for any FRB localized in the sky.

scholarly journals MHD Numerical Simulations of Magnetic Reconnection Associated with Emerging Flux

1993 ◽  
Vol 141 ◽  
pp. 500-503
Author(s):  
K. Shibata ◽  
S. Nozawa ◽  
R. Matsumoto
Keyword(s):  
Magnetic Field ◽  
Numerical Simulations ◽  
Magnetic Reconnection ◽  
Coronal Magnetic Field ◽  
Two Dimensional ◽  
Magnetic Islands ◽  
X Ray ◽  
Hot Plasma ◽  
Mass Ejection ◽  
Coronal Field

AbstractTwo-dimensional (2D) magnetohydrodynamic (MHD) numerical simulations have been performed to study magnetic reconnection between emerging flux and the overlying coronal magnetic field, taking into account of gravity. It is found that (1) reconnection starts when most of chromospheric mass in the current sheet between the emerging flux and the coronal field has drained down along the loop because of gravity, (2) multiple magnetic islands, which confine cool, dense chromospheric plasma, are created in the sheet; the islands coalesce dynamically and are ejected along the sheet, together with the ambient hot plasma, at Alfven speed. The coexistence of hot and cool plasmas in the mass ejection (jet) associated with the reconnection seems to explain those X-ray jets observed by Yohkoh, which are identified with Hα surges.

scholarly journals Global axisymmetric simulations of photoevaporation and magnetically driven protoplanetary disk winds

2019 ◽  
Vol 633 ◽  
pp. A21 ◽  
Author(s):  
P. J. Rodenkirch ◽  
H. Klahr ◽  
C. Fendt ◽  
C. P. Dullemond
Keyword(s):  
Extreme Ultraviolet ◽  
Weak Field ◽  
Additional Treatment ◽  
Two Dimensional ◽  
X Ray ◽  
Accretion Flows ◽  
Initial Plasma ◽  
Magnetohydrodynamic Simulations ◽  
Axisymmetric Configuration ◽  
The Magnetic Field

Context. Photoevaporation and magnetically driven winds are two independent mechanisms that remove mass from protoplanetary disks. In addition to accretion, the effect of these two principles acting concurrently could be significant, and the transition between them has not yet been extensively studied and quantified. Aims. In order to contribute to the understanding of disk winds, we present the phenomena emerging in the framework of two-dimensional axisymmetric, nonideal magnetohydrodynamic simulations including extreme-ultraviolet (EUV) and X-ray driven photoevaporation. Of particular interest are the examination of the transition region between photoevaporation and magnetically driven wind, the possibility of emerging magnetocentrifugal wind effects, and the morphology of the wind itself, which depends on the strength of the magnetic field. Methods. We used the PLUTO code in a two-dimensional axisymmetric configuration with additional treatment of EUV and X-ray heating and dynamic ohmic diffusion based on a semi-analytical chemical model. Results. We determine that the transition between the two outflow types occurs for values of the initial plasma beta β ≥ 107, while magnetically driven winds generally outperform photoevaporation for stronger fields. In our simulations we observe irregular and asymmetric outflows for stronger magnetic fields. In the weak-field regime, the photoevaporation rates are slightly lowered by perturbations of the gas density in the inner regions of the disk. Overall, our results predict a wind with a lever arm smaller than 1.5, consistent with a hot magnetothermal wind. Stronger accretion flows are present for values of β < 107.

Tubulin structure at intermediate resolution

1995 ◽  
Vol 53 ◽  
pp. 852-853
Author(s):  
K. H. Downing ◽  
S. G. Wolf ◽  
E. Nogales
Keyword(s):  
High Resolution ◽  
Structural Data ◽  
Therapeutic Drug ◽  
Zinc Ions ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
X Ray ◽  
Negative Stain ◽  
Functional Mechanisms ◽  
Tubulin Structure

Microtubules are involved in a host of critical cell activities, many of which involve transport of organelles through the cell. Different sets of microtubules appear to form during the cell cycle for different functions. Knowledge of the structure of tubulin will be necessary in order to understand the various functional mechanisms of microtubule assemble, disassembly, and interaction with other molecules, but tubulin has so far resisted crystallization for x-ray diffraction studies. Fortuitously, in the presence of zinc ions, tubulin also forms two-dimensional, crystalline sheets that are ideally suited for study by electron microscopy. We have refined procedures for forming the sheets and preparing them for EM, and have been able to obtain high-resolution structural data that sheds light on the formation and stabilization of microtubules, and even the interaction with a therapeutic drug.Tubulin sheets had been extensively studied in negative stain, demonstrating that the same protofilament structure was formed in the sheets and microtubules. For high resolution studies, we have found that the sheets embedded in either glucose or tannin diffract to around 3 Å.

Two dimensional Sr silicate grown on Si(001) studied using X-ray Photoelectron Spectroscopy

2006 ◽  
Vol 132 ◽  
pp. 87-90
Author(s):  
M. El Kazzi ◽  
G. Delhaye ◽  
S. Gaillard ◽  
E. Bergignat ◽  
G. Hollinger
Keyword(s):  
Photoelectron Spectroscopy ◽  
Two Dimensional ◽  
X Ray

Synthesis and Structure of a Clathrated Two-Dimensional Metal-Organic Framework: [Cd(4,4'-bpy)2(H2O)2](ClO4)2·(L)2·H2O (L = Bis(1-pyrazinylethylidene)hydrazine)

2008 ◽  
Vol 73 (1) ◽  
pp. 24-31
Author(s):  
Dayu Wu ◽  
Genhua Wu ◽  
Wei Huang ◽  
Zhuqing Wang
Keyword(s):  
Metal Organic Framework ◽  
Channel Structure ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
Guest Molecules ◽  
X Ray ◽  
Square Planar ◽  
Metal Organic ◽  
Aqueous Meoh ◽  
Organic Framework

The compound [Cd(4,4'-bpy)2(H2O)2](ClO4)2·(L)2 was obtained by the reaction of Cd(ClO4)2, bis(1-pyrazinylethylidene)hydrazine (L) and 4,4'-bipyridine in aqueous MeOH. Single-crystal X-ray diffraction has revealed its two-dimensional metal-organic framework. The 2-D layers superpose on each other, giving a channel structure. The square planar grids consist of two pairs of shared edges with Cd(II) ion and a 4,4'-bipyridine molecule each vertex and side, respectively. The square cavity has a dimension of 11.817 × 11.781 Å. Two guest molecules of bis(1-pyrazinylethylidene)hydrazine are clathrated in every hydrophobic host cavity, being further stabilized by π-π stacking and hydrogen bonding. The results suggest that the hydrazine molecules present in the network serve as structure-directing templates in the formation of crystal structures.

scholarly journals The role of AGN activity in the building up of the BCG at z ∼ 1.6

2019 ◽  
Vol 15 (S356) ◽  
pp. 280-284
Author(s):  
Angela Bongiorno ◽  
Andrea Travascio
Keyword(s):  
Galaxy Cluster ◽  
Cluster Galaxy ◽  
X Ray ◽  
Groups Of Galaxies ◽  
Star Forming ◽  
The Core ◽  
The Galaxy ◽  
Multi Wavelength

AbstractXDCPJ0044.0-2033 is one of the most massive galaxy cluster at z ∼1.6, for which a wealth of multi-wavelength photometric and spectroscopic data have been collected during the last years. I have reported on the properties of the galaxy members in the very central region (∼ 70kpc × 70kpc) of the cluster, derived through deep HST photometry, SINFONI and KMOS IFU spectroscopy, together with Chandra X-ray, ALMA and JVLA radio data.In the core of the cluster, we have identified two groups of galaxies (Complex A and Complex B), seven of them confirmed to be cluster members, with signatures of ongoing merging. These galaxies show perturbed morphologies and, three of them show signs of AGN activity. In particular, two of them, located at the center of each complex, have been found to host luminous, obscured and highly accreting AGN (λ = 0.4−0.6) exhibiting broad Hα line. Moreover, a third optically obscured type-2 AGN, has been discovered through BPT diagram in Complex A. The AGN at the center of Complex B is detected in X-ray while the other two, and their companions, are spatially related to radio emission. The three AGN provide one of the closest AGN triple at z > 1 revealed so far with a minimum (maximum) projected distance of 10 kpc (40 kpc). The discovery of multiple AGN activity in a highly star-forming region associated to the crowded core of a galaxy cluster at z ∼ 1.6, suggests that these processes have a key role in shaping the nascent Brightest Cluster Galaxy, observed at the center of local clusters. According to our data, all galaxies in the core of XDCPJ0044.0-2033 could form a BCG of M* ∼ 1012Mȯ hosting a BH of 2 × 108−109Mȯ, in a time scale of the order of 2.5 Gyrs.

scholarly journals Quantiles as Robust Probes of Non-Gaussianity in 21-cm Images

2021 ◽  
Author(s):  
Alon Banet ◽  
Rennan Barkana ◽  
Anastasia Fialkov ◽  
Or Guttman
Keyword(s):  
Galactic Halo ◽  
Angular Resolution ◽  
Research Effort ◽  
First Stars ◽  
X Ray ◽  
Global Signal ◽  
Radio Background ◽  
Halo Masses ◽  
The Universe ◽  
Cosmic History

Abstract The epoch in which the first stars and galaxies formed is among the most exciting unexplored eras of the Universe. A major research effort is focused on probing this era with the 21-cm spectral line of hydrogen. While most research focuses on statistics like the 21-cm power spectrum or the sky-averaged global signal, there are other ways to analyze tomographic 21-cm maps, which may lead to novel insights. We suggest statistics based on quantiles as a method to probe non-Gaussianities of the 21-cm signal. We show that they can be used in particular to probe the variance, skewness, and kurtosis of the temperature distribution, but are more flexible and robust than these standard statistics. We test these statistics on a range of possible astrophysical models, including different galactic halo masses, star-formation efficiencies, and spectra of the X-ray heating sources, plus an exotic model with an excess early radio background. Simulating data with angular resolution and thermal noise as expected for the Square Kilometre Array (SKA), we conclude that these statistics can be measured out to redshifts above 20 and offer a promising statistical method for probing early cosmic history.

Sign in / Sign up

Export Citation Format

Share Document