arXiv subjects

Bingxiao Xu

Publications and source records attributed to Bingxiao Xu.

10 recordsLinked to original sources

arXiv2026

Massive Galaxy Halos Contain Less Inner Dark Matter Than Predicted

The mass profiles of galaxy halos encode how baryons reshape dark matter distribution, yet direct observational constraints across the full radial range remain scarce. Here we combine stellar kinematics from MaNGA, H I dynamical measurements from ALFALFA, and independently calibrated halo masses of SDSS groups to statistically reconstruct the mass distribution of central galaxies over nearly two orders of magnitude in radius. We demonstrate that H I data alone do not provide reliable total halo mass estimates, necessitating an independent group-based halo-mass scale. Compared to the IllustrisTNG and EAGLE simulations, the observational profiles of low-mass halos are broadly consistent; in contrast, massive observed halos exhibit systematically lower dynamical masses at the H I radius, lower inner dark-matter masses, and lower central dark-matter fractions (about 4$σ$ difference in units of population scatter) at fixed total halo mass. After subtracting baryonic contributions, the inferred dark-matter profiles remain broadly consistent with an NFW form, but with lower effective concentrations than predicted for massive halos. These results suggest that the inner dark-matter content of massive halos has been reduced more significantly than predicted by current hydrodynamical simulations, plausibly due to long-term baryonic halo heating in massive systems.

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arXiv2026

Reconstructing the Projected Dark Matter Field across 0.1-100 Mpc Scales from the SDSS Survey

Dark matter sets the gravitational environment in which galaxies form and evolve, but cannot be observed directly. We present a conditional diffusion model that reconstructs the projected dark matter density field from the galaxy stellar-mass density field for direct application to galaxy surveys. The model is trained on CAMELS and validated on the independent IllustrisTNG300-1 simulation. Halo masses inferred from the reconstructed projected-aperture measurements agree well with the corresponding true values, with a scatter below 0.2 dex. On 100 kpc scales, reconstructed surface densities show a typical scatter of ~0.3 dex in the regime most relevant for observations. We apply the model to SDSS galaxies with $M_\star\ge10^9\,M_\odot$ in a contiguous low-redshift region. Averaging over 100 stochastic realizations, we reconstruct and publicly release a projected dark matter field covering $90\times90\,(h^{-1}\mathrm{Mpc})^2$ with a pixel size of $0.097\,h^{-1}\mathrm{Mpc}$. This pixel area corresponds to the characteristic projected area of halos with masses of ~$10^{10.6}\,h^{-1}\,M_\odot$. The map reveals the multiscale projected cosmic web, including cluster-scale overdensities, filaments and voids. Projected-aperture masses are statistically consistent with SDSS group-catalog masses, while the derived halo mass function broadly matches mock-catalog expectations. The reconstructed projected potential places Coma in one of the deepest wells and near a convergence region of the inferred projected acceleration field, suggesting that the reconstruction retains both local overdensities and coherent large-scale projected gravitational structure. This work shows that diffusion-based dark matter reconstruction can be applied to real galaxy surveys, enabling halo-mass- and spatially resolved dark-matter-environment-based studies of galaxy evolution in SDSS and future wide-area surveys.

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arXiv2026

No Detectable One-halo Galactic Conformity Signal with Halo-mass Estimates Consistent with Weak-lensing Constraints

One-halo galactic conformity is the tendency for satellites in halos with quenched centrals to have lower star-formation activity than those in halos with star-forming centrals at fixed halo mass. It is an important probe of the galaxy--halo connection and halo-wide quenching processes that may couple central and satellite evolution. However, its existence remains controversial, because conformity must be measured at fixed halo mass, while halo masses are difficult to estimate accurately. In this Letter, we measure one-halo conformity in SDSS using five stellar-mass-complete samples and three halo-mass estimates: an ML estimate whose star-forming and quenched stellar mass--halo mass relations (SHMRs) agree with independent weak-lensing constraints, and two conventional abundance-matching (AM) estimates. We quantify conformity as the difference in median $\log({\rm sSFR})$ between satellites of star-forming and quenched centrals, using both satellite-level and halo-level statistics. The two AM estimates produce strong positive conformity signals, consistent with previous AM-based measurements, but these signals are not reproduced with the ML halo masses. For the halo-level statistic, the representative AM-based signals are $+0.38\pm0.04$ dex and $+0.23\pm0.04$ dex for the luminosity-ranking and mass-ranking AM halo masses, detected relative to no conformity at about $10σ$ and $6σ$, respectively. In contrast, the ML result is consistent with no conformity, $+0.00\pm0.03$ dex; the satellite-level statistic gives a similar result. Thus, with halo-mass estimates consistent with weak-lensing constraints, we find no detectable one-halo conformity signal in the present SDSS sample, suggesting that the strong AM-based signal is largely driven by halo-mass estimation biases.

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arXiv2025

From Halos to Galaxies. X: Decoding Galaxy SEDs with Physical Priors and Accurate Star Formation History Reconstruction

The spectral energy distribution (SED) of galaxies is essential for deriving fundamental properties like stellar mass and star formation history (SFH). However, conventional methods, including both parametric and non-parametric approaches, often fail to accurately recover the observed cosmic star formation rate (SFR) density due to oversimplified or unrealistic assumptions about SFH and their inability to account for the complex SFH variations across different galaxy populations. To address this issue, we introduce a novel approach that improves galaxy broadband SED analysis by incorporating physical priors derived from hydrodynamical simulations. Tests using IllustrisTNG simulations demonstrate that our method can reliably determine galaxy physical properties from broadband photometry, including stellar mass within 0.05 dex, current SFR within 0.3 dex, and fractional stellar formation time within 0.2 dex, with a negligible fraction of catastrophic failures. When applied to the Sloan Digital Sky Survey (SDSS) main photometric galaxy sample with spectroscopic redshift, our estimates of stellar mass and SFR are consistent with the widely used MPA-JHU and GSWLC catalogs. Notably, using the derived SFHs of individual SDSS galaxies, we estimate the cosmic SFR density and stellar mass density with remarkable consistency to direct observations up to $z \sim 6$. This demonstrates a significant advancement in deriving SFHs from SEDs that closely align with observational data. Consequently, our method can reliably recover observed spectral indices such as $\rm D_{\rm n}(4000)$ and $\rm Hδ_{\rm A}$ by synthesizing the full spectra of galaxies using the estimated SFHs and metal enrichment histories, relying solely on broadband photometry as input. Furthermore, this method is extremely computationally efficient compared to conventional approaches.

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arXiv2025

From Halos to Galaxies. VI. Improved halo mass estimation for SDSS groups and measurement of the halo mass function

In $Λ$CDM cosmology, galaxies form and evolve in their host dark matter (DM) halos. Halo mass is crucial for understanding the halo-galaxy connection. The abundance matching (AM) technique has been widely used to derive the halo masses of galaxy groups. However, quenching of the central galaxy can decouple the coevolution of its stellar mass and DM halo mass. Different halo assembly histories can also result in significantly different final stellar mass of the central galaxies. These processes can introduce substantial uncertainties in the halo masses derived from the AM method, particularly leading to a systematic bias between groups with star-forming centrals (blue groups) and passive centrals (red groups). To improve, we developed a new machine learning (ML) algorithm that accounts for these effects and is trained on simulations. Our results show that the ML method eliminates the systematic bias in the derived halo masses for blue and red groups and is, on average, $\sim1/3$ more accurate than the AM method. With careful calibration of observable quantities from simulations and observations from SDSS, we apply our ML model to the SDSS Yang et al. groups to derive their halo masses down to $10^{11.5}\mathrm{M_\odot}$ or even lower. The derived SDSS group halo mass function agrees well with the theoretical predictions, and the derived stellar-to-halo mass relations for both red and blue groups matches well with those obtained from direct weak lensing measurements. These new halo mass estimates enable more accurate investigation of the galaxy-halo connection and the role of the halos in galaxy evolution.

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arXiv2024

From Halos to Galaxies. IX. Estimate of Halo Assembly History for SDSS Galaxy Groups

The properties of the galaxies are tightly connected to their host halo mass and halo assembly history. Accurate measurement of the halo assembly history in observation is challenging but crucial to the understanding of galaxy formation and evolution. The stellar-to-halo mass ratio ($M_*/M_{\mathrm{h}}$) for the centrals has often been used to indicate the halo assembly time $t_{\mathrm{h,50}}$ of the group, where $t_{\mathrm{h,50}}$ is the lookback time at which a halo has assembled half of its present-day virial mass. Using mock data from the semi-analytic models, we find that $M_*/M_{\mathrm{h}}$ shows a significant scatter with $t_{\mathrm{h,50}}$, with a strong systematic difference between the group with a star-forming central (blue group) and passive central (red group). To improve the accuracy, we develop machine-learning models to estimate $t_{\mathrm{h,50}}$ for galaxy groups using only observable quantities in the mocks. Since star-formation quenching will decouple the co-growth of the dark matter and baryon, we train our models separately for blue and red groups. Our models have successfully recovered $t_{\mathrm{h,50}}$, within an accuracy of $\sim$ 1.09 Gyr. With careful calibrations of individual observable quantities in the mocks with SDSS observations, we apply the trained models to the SDSS Yang et al. groups and derive the $t_{\mathrm{h,50}}$ for each group for the first time. The derived SDSS $t_{\mathrm{h,50}}$ distributions are in good agreement with that in the mocks, in particular for blue groups. The derived halo assembly history, together with the halo mass, make an important step forward in studying the halo-galaxy connections in observation.

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arXiv2023

Revealing Impact of Critical Stellar Central Density on Galaxy Quenching through Cosmic Time

In the previous work of Xu & Peng (2021), we investigated the structural and environmental dependence on quenching in the nearby universe. In this work we extend our investigations to higher redshifts by combining galaxies from SDSS and ZFOURGE surveys. In low density, we find a characteristic $Σ_{1\ kpc}$ above which the quenching is initiated as indicated by their population-averaged color. $Σ^{crit}_{1\ kpc}$ shows only weakly mass-dependency at all redshifts, which suggests that the internal quenching process is more related to the physics that acts in the central region of galaxies. In high density, $Σ^{crit}_{1\ kpc}$ for galaxies at $z > 1$ is almost indistinguishable with their low-density counterparts. At $z < 1$, $Σ^{crit}_{1\ kpc}$ for low-mass galaxies becomes progressively strongly mass-dependent, which is due to the increasingly stronger environmental effects at lower redshifts. $Σ^{crit}_{1\ kpc}$ in low density shows strong redshift evolution with $\sim 1$ dex decrement from $z = 2.5$ to $z = 0$. It is likely due to that at a given stellar mass, the host halo is on average more massive and gas-rich at higher redshifts, hence a higher level of integrated energy from more massive black hole is required to quench. As the halo evolves from cold to hot accretion phase at lower redshifts, the gas is shock-heated and becomes more vulnerable to AGN feedback processes, as predicted by theory. Meanwhile, angular momentum quenching also becomes more effective at low redshifts, which complements a lower level of integrated energy from black hole to quench.

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arXiv2023

From Halos to Galaxies. VII. The Connections Between Stellar Mass Growth History, Quenching History and Halo Assembly History for Central Galaxies

The assembly of galaxies over cosmic time is tightly connected to the assembly of their host dark matter halos. We investigate the stellar mass growth history and the chemical enrichment history of central galaxies in SDSS-MaNGA. We find that the derived stellar metallicity of passive central galaxies is always higher than that of the star-forming ones. This stellar metallicity enhancement becomes progressively larger towards low-mass galaxies (at a given epoch) and earlier epochs (at a given stellar mass), which suggests strangulation as the primary mechanism for star formation quenching in central galaxies not only in the local universe, but also very likely at higher redshifts up to $z\sim3$. We show that at the same present-day stellar mass, passive central galaxies assembled half of their final stellar mass $\sim 2$ Gyr earlier than star-forming central galaxies, which agrees well with semi-analytic model. Exploring semi-analytic model, we find that this is because passive central galaxies reside in, on average, more massive halos with a higher halo mass increase rate across cosmic time. As a consequence, passive central galaxies are assembled faster and also quenched earlier than their star-forming counterparts. While at the same present-day halo mass, different halo assembly history also produces very different final stellar mass of the central galaxy within, and halos assembled earlier host more massive centrals with a higher quenched fraction, in particular around the "golden halo mass" at $10^{12}\mathrm{M_\odot}$. Our results call attention back to the dark matter halo as a key driver of galaxy evolution.

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arXiv2021

Critical Stellar Central Densities Drive Galaxy Quenching in the Nearby Universe

We study the structural and environmental dependence of the star formation on the plane of stellar mass versus central core density ($Σ_{\rm 1\ kpc}$) in the nearby universe. We study the central galaxies in the sparse environment and find a characteristic population-averaged $\rm Σ_{1\ kpc} \sim 10^9-10^{9.2}\ M_{\odot}\ kpc^{-2}$, above which quenching is operating. This $\rm Σ^{crit}_{1\ kpc}$ only weakly depends on the stellar mass, suggesting that the mass-quenching of the central galaxies is more closely related to the processes that operate in the central regions than over the entire galaxies. For satellites, at a given stellar mass, environment-quenching appears to operate in a similar fashion as mass-quenching in centrals, also starting from galaxies with high $\rm Σ_{1\ kpc}$ to low $\rm Σ_{1\ kpc}$, and $\rm Σ^{crit}_{1\ kpc}$ becomes strongly mass-dependent, in particular in dense regions. This is because (1) more low-mass satellites are quenched by the environmental effects in denser regions and (2) at fixed stellar mass and environment, the environment-quenched satellites have, on average, larger $Σ_{\rm 1\ kpc}$, $\rm M_{1\ kpc}/M_{\star}$ and Sersic index $n$, and as well as smaller size. These results imply that either some dynamical processes change the structure of the satellites during quenching or the satellites with higher $Σ_{\rm 1\ kpc}$ are more susceptible to the environmental effects.

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arXiv2015

The Detection and Statistics of Giant Arcs Behind CLASH Clusters

We developed an algorithm to find and characterize gravitationally lensed galaxies (arcs) to perform a comparison of the observed and simulated arc abundance. Observations are from the Cluster Lensing And Supernova survey with Hubble (CLASH). Simulated CLASH images are created using the MOKA package and also clusters selected from the high resolution, hydrodynamical simulations, MUSIC, over the same mass and redshift range as the CLASH sample. The algorithm' s arc elongation accuracy, completeness and false positive rate are determined and used to compute an estimate of the true arc abundance. We derive a lensing efficiency of $4 \pm 1$ arcs (with length $\ge 6"$ and length-to-width ratio $\ge 7$) per cluster for the X-ray selected CLASH sample, $4 \pm 1$ arcs per cluster for the MOKA simulated sample and $3 \pm 1$ arcs per cluster for the MUSIC simulated sample. The observed and simulated arc statistics are in full agreement. We measure the photometric redshifts of all detected arcs and find a median redshift $z_s = 1.9$ with 33% of the detected arcs having $z_s > 3$. We find that the arc abundance does not depend strongly on the source redshift distribution but is sensitive to the mass distribution of the dark matter halos (e.g. the $c-M$ relation). Our results show that consistency between the observed and simulated distributions of lensed arc sizes and axial ratios can be achieved by using cluster-lensing simulations that are carefully matched to the selection criteria used in the observations.

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