分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Using two sets of large $N$-body simulations, we study the origin of the correlations of halo assembly time ($z_{\rm f}$), concentration ($v_{\rm max}/v_{\rm 200}$) and spin ($\lambda$) with the large-scale evolved density field at given halo mass, i.e. the secondary bias. We find that the secondary bias is the secondary effect of the correlations of halo properties with the linear density estimated at the same comoving scale. Using the linear density on different scales, we find two types of correlations. The internal correlation, which reflects the correlation of halo properties with the mean linear over-density $\delta_{\rm L}$ within the halo Lagrangian radius $R_{\rm L}$, is positive for both $z_{\rm f}$ and $v_{\rm max}/v_{\rm 200}$, and negative for $\lambda$. The external correlation, which describes the correlation of halo properties with linear overdensity at $R>R_{\rm L}$ for given $\delta_{\rm L}$, shows trends opposite to the internal correlation. Both of the external and internal correlations depend only weakly on halo mass, indicating a similar origin for halos of different masses. Our findings offer a transparent perspective on the origin of the secondary bias. The secondary bias can be largely explained by the competition of the external and internal correlations together with the correlation of the linear density field on different scales. These two types of correlations combined can establish the complex halo-mass dependence of the secondary bias observed in the simulations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ziwen Zhang
Huiyuan Wang
Wentao Luo
H. J. Mo
Zhixiong Liang
Ran Li
Xiaohu Yang
Tinggui Wang
Hongxin Zhang
Hui Hong
Xiaoyu Wang
Enci Wang
Pengfei Li
JingJing Shi
摘要： Based on the spectroscopic and shear catalogs for SDSS galaxies in the local Universe, we compare optically-selected active galactic nuclei (AGNs) with control star-forming and quiescent galaxies on galactic, inter-halo and larger scales. We find that AGNs are preferentially found in two specific stages of galaxy evolution: star-burst and `green valley' phases, and that the stellar population of their host galaxies is quite independent of stellar mass, different from normal galaxies. Combining galaxy-galaxy lensing and galaxy clustering on large scales, we measure the mass of AGN host halos. The typical halo mass is about $10^{12}h^{-1}\rm M_{\odot}$, similar to the characteristic mass in the stellar mass-halo mass relation (SHMR). For given stellar mass, AGN host galaxies and star-forming galaxies share the same SHMR, while quiescent galaxies have more massive halos. Clustering analysis on halo scales reveals that AGNs are surrounded by a larger number of satellites (with stellar mass down to 1/1000 of the mass of the central galaxy) than star-forming galaxies, and that galaxies with larger stellar velocity dispersion have more satellites. The number of satellites also increase with halo mass, reaching unity around $10^{12}h^{-1}\rm M_{\odot}$. Our results suggest a scenario, in which the interaction of the central galaxy with the satellites triggers an early episode of star burst and AGN activities, followed by multiple AGN cycles driven by the non-axisymmetric structure produced by the interaction. The feedback from the starburst and AGN reduces the amount of cold gas for fueling the central black hole, producing a characteristic halo mass scale, $\sim 10^{12}h^{-1}\rm M_{\odot}$, where the AGN fraction peaks.
分类： 物理学 >> 核物理学 提交时间： 2024-01-21
Chong ZOU
Qi SUN
Xiaoyu WANG
Mengxiao KANG
Jincheng WANG
Yingyi LIU
Haolan YANG
Xuanbo CHEN
Qiwei ZHANG
Jie REN
Guangyuan LUAN
Haotian LUO
Hongyi WU
Xichao RUAN
Hanxiong HUANG
Zhaohui WANG
Guozhu HE
Jie BAO
摘要： To fulfill the needs of neutron capture reaction cross-section measurement in keV energy scale in the field of nuclear astrophysics and advanced nuclear energy system development, the 4 BaF2 Gamma-ray Total Absorption Facility (GTAF) developed by the Key Laboratory of Nuclear Data of the China Institute of Atomic Energy (CIAE) has been transplanted and installed at the Back-streaming White Neutron Source (Back-n) of the China Spallation Neutron Source (CSNS) in 2019. A series of results has been achieved and published based on the GTAF since then, and due to which the needs of reducing backgrounds are becoming increasingly urgent. In order to understand the origins of backgrounds and to optimize the facilities, a detailed simulation program using GEANT4 toolkits was established and presented in this paper. To demonstrate the availability of the proved codes, several practical examples of assisting the process of experimental data and helping verify the optimization proposition are also shown in this paper.
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