arXiv subjects

Xinghai Zhao

Publications and source records attributed to Xinghai Zhao.

7 recordsLinked to original sources

arXiv2025

Analysis of the plane of satellites around Milky Way- mass galaxies in the IllustrisTNG simulation

It has been suggested that the Plane of Satellites (PoS) phenomenon may imply a tension with current $\Lambda$CDM cosmology since a Milky Way (MW)-like PoS is very rare in simulations. In this study, we analyze a large sample of satellite systems of MW-{ mass} galaxies identified within the IllustrisTNG simulations. We analyze their spatial aspect ratio, orbital pole dispersion, Gini coefficient, radial distribution, and bulk satellite velocity relative to the host galaxy. These are compared to properties of the observed Milky~Way PoS. We identified galaxy samples in two virial mass ranges ($0.1 - 0.8 \times 10^{12} $ M$_\odot$ and $0.8 - 3.0 \times 10^{12}$ M$_\odot$). { We find for both mass ranges that only $\sim$ 1 percent of MW-like galaxies contain a PoS similar to that of the MW. Nevertheless, these outliers occur naturally in $\Lambda$CDM cosmology. We analyze the formation, environment, and evolution of the PoS for nine systems that are most MW-like in the TNG50 simulation. By using a new analysis of the local large scale structure surrounding the satellite systems, we suggest that a PoS can form from one or more of at least five different processes. Moreover, consistent with the SAGA DR3 results, we find that about 1/3 of the identified systems contain a recent infall of a LMC and/or a SMC like system. We find a tendency for about half of the satellites to have recently arrived at $z < 0.2$, indicating that a MW-like PoS is a recent and transient phenomenon.

astro-ph.GA↗

arXiv2023

A Study of the Properties and Dynamics of the Disk of Satellites in a Milky-Way-like Galaxy System

The dynamics of the satellite systems of Milky-Way-like galaxies offer a useful means by which to study the galaxy formation process in the cosmological context. It has been suggested that the currently observed anisotropic distribution of the satellites in such galaxy systems is inconsistent with the concordance $ΛCDM$ cosmology model on the galactic scale if the observed satellites are random samples of the dark matter (DM) sub-halos that are nearly isotropically distributed around the central galaxy. In this study, we present original high-resolution zoom-in studies of central galaxies and satellite systems based upon initial conditions for the DM distribution from the Aquarius simulations but with substantial high-resolution baryon physics added. We find that the galaxy most like the Milky Way in this study does indeed contain a disk of satellites (DOS). Although one galaxy DOS system does not answer the question of how common such disks are, it does allow the opportunity to explore the properties and dynamics of the DOS system. Our investigation centers on the spatial arrangement (distances, angles, etc.) of satellites in this Milky-Way-like galaxy system with a specific emphasis on identifying and analyzing the disk-like structure along with its dynamical and morphological properties. Among the conclusions from this study, we find that the satellites and DM sub-halos in the galaxy simulations are anisotropically distributed. The dynamical properties of the satellites, however, indicate that the direction of the angular momentum vector of the whole satellite system is different from the normal direction of the fitted DOS and from the normal direction of the velocity dispersion of the system. Hence, the fitted DOS appears to be comprised of infalling sub-halos and is not a rotationally supported system.

astro-ph.GA↗

arXiv2013

The Effects of Local Primordial Non-Gaussianity on the Formation and Evolution of Galaxies

Thanks to the rapid progress in precision cosmology in the last few years, we now have access to physical observables that may constrain the theory of inflation through the non-Gaussianity (NG) signatures in the cosmic microwave background radiation and the distribution of large-scale structure. Numerical modeling of the NG signals from different inflation models is essential to correctly interpret current and near future data from large-scale structure surveys. In this study, we use high-resolution cosmological hydrodynamical simulations to investigate the effects of primordial NG on the formation and evolution of galaxies from the cosmic dawn to the present day. Focusing on the local type primordial NG, we find that it may affect the formation history of stars and black holes in galaxies, and their distribution. Compared to the Gaussian case, large non-Gaussian potential with $f_{NL} \gtrsim 10^3$ leads to earlier collapse of the first structures, more massive galaxies especially at high redshifts, stronger clustering of galaxies, and higher halo bias. However, for smaller NG with $f_{NL} \lesssim 10^2$, the effect is significantly weaker. Observations of the distribution and properties of high-redshift, rare objects such as the first galaxies and quasars may provide further constraints on the primordial NG.

astro-ph.CO↗

arXiv2013

Critical components in 0.14 THz communication systems

In the super-heterodyne terahertz communication system, the proper design of the critical components like mixers and filters are of great importance for enhancing its performance. In this work, some issues on our newly developed system setup design for 0.14 THz wireless communications and the key components subharmonic mixer (SHM) based on Schottky diode, as well as silicon micromachined bandpass rectangular waveguide filters are presented. According to ADS simulation, the optimum conversion loss of the 140 GHz SHM is around 8.2 dB. And the silicon-micromachined rectangular waveguide filters have been fabricated and the measured lowset insertion losses are lower than 0.5 dB.

physics.ins-det↗

arXiv2012

The Co-evolution of Cosmic Entropy and Structures in the Universe

According to the second law of thermodynamics, the arrow of time points to an ever increasing entropy of the Universe. However, exactly how the entropy evolves with time and what drives the growth remain largely unknown. Here, for the first time, we quantify the evolving entropy of cosmic structures using a large-scale cosmological hydrodynamical simulation. Our simulation starts from initial conditions predicted by the leading LambdaCDM cosmology, self-consistently evolves the dynamics of both dark and baryonic matter, star formation, black hole growth and feedback processes, from the cosmic dawn to the present day. Tracing the entropy contributions of these distinct components in the simulation, we find a strong link between entropy growth and structure formation. The entropy is dominated by that of the black holes in all epochs, and its evolution follows the same path as that of galaxies: it increases rapidly from a low-entropy state at high redshift until z~2, then transits to a slower growth. Our results suggest that cosmic entropy may co-evolve with cosmic structure, and that its growth may be driven mainly by the formation of black holes in galaxies. We predict that the entropy will continue to increase in the near future, but likely at a constant rate.

astro-ph.CO↗

arXiv2012

Vertical-external-cavity surface-emitting lasers and quantum dot lasers

The use of cavity to manipulate photon emission of quantum dots (QDs) has been opening unprecedented opportunities for realizing quantum functional nanophotonic devices and also quantum information devices. In particular, in the field of semiconductor lasers, QDs were introduced as a superior alternative to quantum wells to suppress the temperature dependence of the threshold current in vertical-external-cavity surface-emitting lasers (VECSELs). In this work, a review of properties and development of semiconductor VECSEL devices and QD laser devices is given. Based on the features of VECSEL devices, the main emphasis is put on the recent development of technological approach on semiconductor QD VECSELs. Then, from the viewpoint of both single QD nanolaser and cavity quantum electrodynamics (QED), a single-QD-cavity system resulting from the strong coupling of QD cavity is presented. A difference of this review from the other existing works on semiconductor VECSEL devices is that we will cover both the fundamental aspects and technological approaches of QD VECSEL devices. And lastly, the presented review here has provided a deep insight into useful guideline for the development of QD VECSEL technology and future quantum functional nanophotonic devices and monolithic photonic integrated circuits (MPhICs).

cond-mat.mes-hall↗

arXiv2011

Effects of structure formation on the expansion rate of the Universe: An estimate from numerical simulations

General relativistic corrections to the expansion rate of the Universe arise when the Einstein equations are averaged over a spatial volume in a locally inhomogeneous cosmology. It has been suggested that they may contribute to the observed cosmic acceleration. In this paper, we propose a new scheme that utilizes numerical simulations to make a realistic estimate of the magnitude of these corrections for general inhomogeneities in (3+1) spacetime. We then quantitatively calculate the volume averaged expansion rate using N-body large-scale structure simulations and compare it with the expansion rate in a standard FRW cosmology. We find that in the weak gravitational field limit, the converged corrections are slightly larger than the previous claimed 10^{-5} level, but not large enough nor even of the correct sign to drive the current cosmic acceleration. Nevertheless, the question of whether the cumulative effect can significantly change the expansion history of the Universe needs to be further investigated with strong-field relativity.

astro-ph.CO↗