arXiv subjects

Shanquan Gui

Publications and source records attributed to Shanquan Gui.

6 recordsLinked to original sources

arXiv2026

Where Do Quasars Live? DESI DR1 Constraints from PAC Measurements

Quasar environments connect the growth of supermassive black holes, active galactic nucleus feedback, and galaxy evolution. Small-scale quasar clustering probes the one-halo regime and can test whether quasar activity depends on central--satellite status. We seek to obtain precise small-scale measurements of quasar environments at $0.8<z<1.0$ and use them to constrain the quasar--halo connection, particularly the relative probability for satellite subhalos and central halos of the same halo accretion mass to host a quasar. We apply the Photometric Objects Around Cosmic Webs (PAC) method to DESI Data Release~1 quasars and photometric galaxies from the DESI Legacy Imaging Surveys DR9, measuring the excess projected surface density of neighbouring galaxies around quasars, $\bar{n}_{2}w_{\rm p}$, down to a stellar mass of $M_{\ast}=10^{10.80}M_{\odot}$ over $0.1<r_{\rm p}/(h^{-1}\,\mathrm{Mpc})<15$. we jointly model the excess surface-density measurements, the quasar and luminous red galaxy (LRG) autocorrelation functions, and the quasar--LRG cross-correlation. We interpret these measurements using an N-body simulation together with a stellar-to-halo mass relation, an explicit stellar-mass-incompleteness model, and a Gaussian quasar occupation as a function of halo accretion mass. The Gaussian quasar occupation peaks at $\log_{10}(M_{\rm acc}/h^{-1}M_{\odot})=12.88^{+0.02}_{-0.02}$ with width $\sigma_{\rm q}=0.51^{+0.02}_{-0.01}$, and the relative satellite-hosting parameter, $B$, defined as the quasar-hosting probability of a satellite subhalo relative to that of a central halo at fixed halo accretion mass, is $B=1.01^{+0.03}_{-0.03}$. Within the adopted model framework, quasars are consistent with being equally likely to reside in central halos and satellite subhalos at fixed halo accretion mass. PAC has strong potential to deliver precise small-scale measurements of quasar environments.

astro-ph.GA↗

arXiv2026

Six-Class BPT Galaxy Classification for Survey-Scale AGN Candidate Prioritization: Deep Tabular Model and Informative Missingness Signals

The Baldwin--Phillips--Terlevich (BPT) diagram is widely used to classify galaxies into star-forming systems, composite galaxies, and active galactic nuclei (AGNs), but its survey-scale application is limited by the requirement for high signal-to-noise emission-line measurements. We test whether machine-learning models can reproduce six-class BPT labels while using measured quantities, derived line ratios, and potentially informative missing-data patterns as inputs. We analyze 1.47 million galaxies with a 27-dimensional feature set that combines raw survey measurements, derived quantities, and missingness indicators. Five deep tabular architectures are benchmarked against gradient-boosted trees and classical machine-learning baselines, and the resulting probabilities are evaluated through hard-classification metrics, precision--recall curves, top-$k$ retrieval, ablation tests, and feature-interpretation diagnostics. {CNN--Transformer gives the strongest overall classification performance (accuracy = 0.8266), while boosted trees remain highly competitive for this low-dimensional tabular problem. In the binary star-forming-versus-AGN comparison, CNN--Transformer achieves a Class~1 versus Class~4 ROC AUC of 0.9998. Missingness indicators provide substantial predictive information, especially the OH\_P50N\_missing feature. Feature interpretation further shows that $\log([\mathrm{Ne\,III}]/[\mathrm{O\,II}])$, combined with stellar mass or specific star-formation rate, separates star-forming galaxies from AGN hosts. The models are most useful as AGN candidate-ranking tools that complement, rather than replace, traditional BPT diagnostics. High-ranked samples can reach high purity, while broader candidate lists recover most AGNs, but transferability to other surveys requires further validation.

astro-ph.GA↗

arXiv2023

Photometric Objects Around Cosmic Webs (PAC). VI. High Satellite Fraction of Quasars

The Photometric objects Around Cosmic webs (PAC) approach developed in Xu et al. (2022b) has the advantage of making full use of spectroscopic and deeper photometric surveys. With the merits of PAC, the excess surface density $\bar{n}_2w_{{\rm{p}}}$ of neighboring galaxies can be measured down to stellar mass $10^{10.80}\,M_{\odot}$ around quasars at redshift $0.8<z_{\rm{s}}<1.0$, with the data from the Sloan Digital Sky Survey IV (SDSS-IV) extended Baryon Oscillation Spectroscopic Survey (eBOSS) and the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys. We find that $\bar{n}_2w_{{\rm{p}}}$ generally increases quite steeply with the decrease of the separation. Using subhalo abundance matching method, we can accurately model the $\bar{n}_2w_{{\rm{p}}}$ both on small and large scales. We show that the steep increase of the $\bar{n}_2w_{{\rm{p}}}$ towards the quasars requires that a large fraction $f_{\mathrm{sate}}=0.29_{-0.06}^{+0.05}$ of quasars should be satellites in massive halos, and find that this fraction measurement is insensitive to the assumptions of our modeling. This high satellite fraction indicates that the subhalos have nearly the same probability to host quasars as the halos for the same (infall) halo mass, and the large scale environment has negligible effect on the quasar activity. We show that even with this high satellite fraction, each massive halo on average does not host more than one satellite quasar due to the sparsity of quasars.

astro-ph.GA↗

arXiv2023

The DESI One-Percent Survey: A concise model for galactic conformity of ELGs

Galactic conformity is the phenomenon in which a galaxy of a certain physical property is correlated with its neighbors of the same property, implying a possible causal relationship. The observed auto correlations of emission line galaxies (ELGs) from the highly complete DESI One-Percent survey exhibit a strong clustering signal on small scales, providing clear evidence for the conformity effect of ELGs. Building upon the original subhalo abundance matching (SHAM) method developed by Gao et al. (2022, 2023), we propose a concise conformity model to improve the ELG-halo connection. In this model, the number of satellite ELGs is boosted by a factor of $\sim 5$ in the halos whose central galaxies are ELGs. We show that the mean ELG satellite number in such central halos is still smaller than 1, and the model does not significantly increase the overall satellite fraction. With this model, we can well recover the ELG auto correlations to the smallest scales explored with the current data (i.e. $r_{\mathrm{p}} > 0.03$ $\mathrm{Mpc}\,h^{-1}$ in real space and at $s > 0.3$ $\mathrm{Mpc}\,h^{-1}$ in redshift space), while the cross correlations between luminous red galaxies (LRGs) and ELGs are nearly unchanged. Although our SHAM model has only 8 parameters, we further verify that it can accurately describe the ELG clustering in the entire redshift range from $z = 0.8$ to $1.6$. We therefore expect that this method can be used to generate high-quality ELG lightcone mocks for DESI.

astro-ph.GA↗

arXiv2023

The DESI One-Percent survey: constructing galaxy-halo connections for ELGs and LRGs using auto and cross correlations

In the current Dark Energy Spectroscopic Instrument (DESI) survey, emission line galaxies (ELGs) and luminous red galaxies (LRGs) are essential for mapping the dark matter distribution at $z \sim 1$. We measure the auto and cross correlation functions of ELGs and LRGs at $0.8 0.1$ $\mathrm{Mpc}\,h^{-1}$. We can also reproduce the auto correlations of ELGs at $r_{\mathrm{p}}>0.3$ $\mathrm{Mpc}\,h^{-1}$ ($s>1$ $\mathrm{Mpc}\,h^{-1}$) in real (redshift) space. Although our model has only seven parameters, we show that it can be extended to higher redshifts and reproduces the observed auto correlations of ELGs in the whole range of $0.8<z<1.6$, which enables us to generate a lightcone ELG mock for DESI. With the above model, we further derive halo occupation distributions (HODs) for ELGs which can be used to produce ELG mocks in coarse simulations without resolving subhalos.

astro-ph.GA↗

arXiv2021

Mission Design for the TAIJI misson and Structure Formation in Early Universe

Gravitational wave detection in space promises to open a new window in astronomy to study the strong field dynamics of gravitational physics in astrophysics and cosmology. The present article is an extract of a report on a feasibility study of gravitational wave detection in space, commissioned by the National Space Science Center, Chinese Academy of Sciences almost a decade ago. The objective of the study was to explore various possible mission options to detect gravitational waves in space alternative to that of the (e)LISA mission concept and look into the requirements on the technological fronts. On the basis of relative merits and balance between science and technological feasibility, a set of representative mission options were studied and in the end a mission design was recommended as the starting point for research and development in the Chinese Academy of Sciences. The mission design was eventually adopted by the current TAIJI mission as the baseline parameters for the project. Subject to technological constraints, the baseline parameters of the TAIJI mission were designed in such a way to optimise the capability of a spaceborne gravitational wave detector to probe high redshift light seed, intermediate mass black holes and thereby shed important light on the structure formation in early Universe.

gr-qc↗