arXiv subjects

Guobao Tang

Publications and source records attributed to Guobao Tang.

3 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↗

arXiv2025

Dark Matter and the Early Formation of Supermassive Black Holes

We investigate the growth of supermassive black holes (SMBHs) at high redshift ($z \ge 10$) from a combination of dark matter capture, black-hole mergers, and gas accretion. It has previously been shown that SMBHs can form by $z \approx 10$ via black-hole mergers, Eddington-limited Bondi gas accretion and tidal disruption events with stars within dense nuclear clusters. Here, we examine the degree to which the capture of collisionless dark matter by a growing SMBH may also contribute. We first consider models deduced from cosmological simulations of galaxy formation and central BH formation. We show that in the case that the dense nuclear star cluster forms by cooling and collapse of gas, while the DM remains in a standard NFW profile, the contribution from cold dark matter accretion is insignificant. However, we suggest models for which dark matter clustering can occur (possibly by self interaction). We show that such clustering may affect SMBH growth. In such cases, a small seed stellar-remnant black hole can more easily reach $> 10^7$ M$_{\odot}$ by $z = 10$ in the core of dense nuclear star clusters. This remains true for either cold dark matter or ultralight dark matter with the observationally inferred mass of $\sim 10^{-22}$ eV. We highlight the unique possible evolution of ULDM capture by the growing SMBH due to the fact that the ULDM de Broglie wavelength exceeds the initial nuclear star cluster half-mass radius.

astro-ph.HE↗

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 $\Lambda CDM$ 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↗