分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Subhalo abundance matching (SHAM) has played an important role in improving our understanding of how galaxies populate their host dark matter halos. In essence, the SHAM framework is to find a dark matter halo property that best correlates with an attribute of galaxies, such as stellar mass. The peak value of the maximum circular velocity ($V_{\rm max}$) a halo/subhalo has ever attained throughout its lifetime, $V_{\rm peak}$, has been a popular choice for SHAM. A recent study by Tonnesen & Ostriker (2021) suggested that quantity $\phi$, which combines the present-day $V_{\rm max}$ and the peak value of halo dark matter mass, performs better in predicting stellar mass than $V_{\rm peak}$. Inspired by their approach, in this work, we find that further improvement can be achieved by a quantity $\psi_5$ that combines the 90th percentile of $V_{\rm max}$ a halo/subhalo has ever achieved with the 60th percentile of the dark matter halo time variation rate. Tests based on the simulation IllustrisTNG300 show that our new SHAM scheme, with just three free parameters, can improve the stellar mass prediction and mass-dependent clustering by 15% and 16% from $\phi$, respectively, over the redshift range $z=0-2$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We propose a novel subhalo abundance matching (SHAM) model that uses the virial mass of the main progenitor of each (sub)halo $M_{\rm prog}$ as a proxy of the galaxy stellar mass $M_*$ at the time of observation. This $M_{\rm prog}$ model predicts the two-point correlation functions depending on the choice of the epoch $z_{\rm prog}$ at which $M_\mathrm{prog}$ is measured. With $z_{\rm prog}$ as a fitting parameter, we apply the $M_{\rm prog}$ model to the latest observed angular correlation functions of galaxy samples at $z\simeq0.4$ with varying stellar mass thresholds from $M_{*,~{\rm lim}}/(h^{-2}M_\odot)=10^{11}$ to $10^{8.6}$. The $M_{\rm prog}$ model can reproduce the observations very well over the entire scale range of $0.1\textrm{--}10~h^{-1}{\rm Mpc}$. We find that, for the samples of $10^9\leq M_{*,~{\rm lim}}/(h^{-2}M_\odot)\leq10^{10.2}$, the correlation functions predicted by the widely-used $V_{\rm peak}$ model lacks amplitudes at the scale of $\lesssim1~h^{-1}{\rm Mpc}$, demonstrating the high capability of our $M_\mathrm{prog}$ model to explain observed clustering measurements. The best-fit $z_{\rm prog}$ parameter is highest ($z_{\rm prog}\simeq5$) for intermediate mass galaxies at $M_*\simeq10^{9.7}~h^{-2}M_\odot$, and becomes smaller towards $z_\mathrm{prog}\simeq1$ for both lower- and higher-mass galaxies. We interpret these trends as reflecting the downsizing in the in-situ star formation in lower-mass galaxies and the larger contribution of ex-situ stellar mass growth in higher-mass galaxies.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Wei-Hao Wang
Sebastien Foucaud
Bau-Ching Hsieh
Hung-Yu Jian
Lihwai Lin
Yen-Ting Lin
Jean Coupon
Yasuhiro Hashimoto
Masami Ouchi
Kazuhiro Shimasaku
Youichi Ohyama
Keiichi Umetsu
Shiang-Yu Wang
Tzu-Ching Chang
摘要： The Subaru Hyper Suprime-Cam (HSC) Strategic Survey is the latest-generation
multi-band optical imaging survey for galaxy evolution and structure formation.
The "Ultra-Deep" component of the HSC survey provides $grizy$ broad-band images
over $\sim3.4$ deg$^2$ to detection limits of $\sim26$-28 AB, along with
narrow-band images, in the COSMOS and the SXDS fields. These images provide an
unprecedented combination of depths and area coverage, for the studies galaxies
up to $z\sim7$. However, the lack of coverage at $<4000$ Ang implies incomplete
sampling of the rest-frame UV at $z\lesssim 3$, which is critically needed for
understanding the buildup of stellar mass in the later cosmic time. We
conducted a multi-year CFHT $u^\ast$-band imaging campaign in the two HSC
Ultra-Deep fields with CFHT MegaCam. By including shallower archival data, we
reach 5-$\sigma$ depths of $u^\ast=28.1$ and 28.4 (AB) at the centers of the
COSMOS and SXDS fields, respectively, and $u^\ast=27.7$ and 27.8 in the central
1 deg$^2$ fields. The image quality is $\gtrsim0.90$ arcsec, fairly good for
the $u^\ast$ band. Both the photometric and astrometric quality of our data are
excellent. We show that the combination of our $u^\ast$-band and HSC data can
lead to high-quality photometric redshifts at $z=0$-3, and robust measurements
of rest-frame UV on galaxies at $0.4
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： If the formation of central galaxies in dark matter haloes traces the assembly history of their host haloes, in haloes of fixed mass, central galaxy clustering may show dependence on properties indicating their formation history. Such a galaxy assembly bias effect has been investigated by Lin et al. 2016, with samples of central galaxies constructed in haloes of similar mass and with mean halo mass verified by galaxy lensing measurements, and no significant evidence of assembly bias is found from the analysis of the projected two-point correlation functions of early- and late-forming central galaxies. In this work, we extend the the investigation of assembly bias effect from real space to redshift (velocity) space, with an extended construction of early- and late-forming galaxies. We carry out halo occupation distribution modelling to constrain the galaxy-halo connection to see whether there is any sign of the effect of assembly bias. We find largely consistent host halo mass for early- and late-forming central galaxies, corroborated by lensing measurements. The central velocity bias parameters, which are supposed to characterise the mutual relaxation between central galaxies and their host haloes, are inferred to overlap between early- and late-forming central galaxies. However, we find a large amplitude of velocity bias for early-forming central galaxies (e.g. with central galaxies moving at more than 50% that of dark matter velocity dispersion inside host haloes), which may signal an assembly bias effect. A large sample with two-point correlation functions and other clustering measurements and improved modelling will help reach a conclusive result.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yu-Yen Chang
Bau-Ching Hsieh
Wei-Hao Wang
Yen-Ting Lin
Chen-Fatt Lim
Yoshiki Toba
Yuxing Zhong
Siou-Yu Chang
摘要： We use machine learning techniques to investigate their performance in classifying active galactic nuclei (AGNs), including X-ray selected AGNs (XAGNs), infrared selected AGNs (IRAGNs), and radio selected AGNs (RAGNs). Using known physical parameters in the Cosmic Evolution Survey (COSMOS) field, we are able to well-established training samples in the region of Hyper Suprime-Cam (HSC) survey. We compare several Python packages (e.g., scikit-learn, Keras, and XGBoost), and use XGBoost to identify AGNs and show the performance (e.g., accuracy, precision, recall, F1 score, and AUROC). Our results indicate that the performance is high for bright XAGN and IRAGN host galaxies. The combination of the HSC (optical) information with the Wide-field Infrared Survey Explorer (WISE) band-1 and WISE band-2 (near-infrared) information perform well to identify AGN hosts. For both type-1 (broad-line) XAGNs and type-1 (unobscured) IRAGNs, the performance is very good by using optical to infrared information. These results can apply to the five-band data from the wide regions of the HSC survey, and future all-sky surveys.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The halo assembly bias, a phenomenon referring to dependencies of the large-scale bias of a dark matter halo other than its mass, is a fundamental property of the standard cosmological model. First discovered in 2005 from the Millennium Run simulation, it has been proven very difficult to be detected observationally, with only a few convincing claims of detection so far. The main obstacle lies in finding an accurate proxy of the halo formation time. In this study, by utilizing a constrained simulation that can faithfully reproduce the observed structures larger than $2\,$Mpc in the local universe, for a sample of 634 massive clusters at $z\le 0.12$, we find their counterpart halos in the simulation and use the mass growth history of the matched halos to estimate the formation time of the observed clusters. This allows us to construct a pair of early- and late-forming clusters, with similar mass as measured via weak gravitational lensing, and large-scale bias differing at $\approx 3\sigma$ level, suggestive of the signature of assembly bias, which is further corroborated by the properties of cluster galaxies, including the brightest cluster galaxy, and the spatial distribution and number of member galaxies. Our study paves a way to further detect assembly bias based on cluster samples constructed purely on observed quantities.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Subhalo abundance matching (SHAM) has played an important role in improving our understanding of how galaxies populate their host dark matter halos. In essence, the SHAM framework is to find a dark matter halo property that best correlates with an attribute of galaxies, such as stellar mass. The peak value of the maximum circular velocity ($V_{\rm max}$) a halo/subhalo has ever attained throughout its lifetime, $V_{\rm peak}$, has been a popular choice for SHAM. A recent study by Tonnesen & Ostriker (2021) suggested that quantity $\phi$, which combines the present-day $V_{\rm max}$ and the peak value of halo dark matter mass, performs better in predicting stellar mass than $V_{\rm peak}$. Inspired by their approach, in this work, we find that further improvement can be achieved by a quantity $\psi_5$ that combines the 90th percentile of $V_{\rm max}$ a halo/subhalo has ever achieved with the 60th percentile of the dark matter halo time variation rate. Tests based on the simulation IllustrisTNG300 show that our new SHAM scheme, with just three free parameters, can improve the stellar mass prediction and mass-dependent clustering by 15% and 16% from $\phi$, respectively, over the redshift range $z=0-2$.
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