arXiv subjects

Yunpeng Jin

Publications and source records attributed to Yunpeng Jin.

12 recordsLinked to original sources

arXiv2026

The GECKOS survey: Assembly history of the lenticular galaxy NGC 3957

We analyse the assembly history of the edge-on lenticular galaxy NGC 3957 using deep integral-field spectroscopic MUSE data from the GECKOS survey. By applying a dust-corrected Multi-Gaussian Expansion and a population-orbit superposition model, we disentangle the galaxy's stellar kinematics, age, and metallicity. We dynamically decompose the galaxy and identify three distinct components: a dynamically-cold main disc, a compact Nuclear Stellar Disc (NSD), and a hot component. The NSD emerges as the youngest and most metal-rich component ($t = 6.9 \pm 0.4$ Gyr; $[Z/H] = 0.49 \pm 0.06$ dex), implying that the stellar bar is a long-lived structure that formed at least $\sim 7$ Gyr ago. The main stellar disc is dynamically cold ($σ_z \sim 20-30$ km/s), precluding any significant mergers over the last $\sim 8$ Gyr, and exhibits a strong positive age gradient (younger inside, older outside) beyond the bar radius. Synthesising these dynamical fossil records, NGC 3957 likely evolved as a `faded spiral' in a small-to-medium group environment. Its outer disc might passively fade due to mild gas starvation, while the bar fuelled prolonged central star formation. Comparison with S0s in the Fornax cluster reveals that this combination of internal secular evolution and mild starvation produces `outside-in' fading signatures that could mimic the environmental stripping typically seen in dense clusters.

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arXiv2026

Dissecting the 3D chemo-dynamical structures of NGC 1381: a galaxy hosting an ancient slow bar with an accreted bulge and thick disc

We applied the barred population-orbit superposition method developed in \citet{Jin2025a,Jin2025b} to construct 3D chemo-dynamical models for the barred S0 galaxy NGC~1381 in the Fornax cluster. Based on the stellar orbits in the models, we decomposed NGC~1381 into six components: (1) a dynamically warm nuclear disc with $f_{\rm nucl}\sim5\%$; (2) a rigidly rotating, BP/X-shaped bar with $f_{\rm bar}\sim30\%$; (3) a dynamically hot, spheroidal bulge with $f_{\rm bulge}\sim17\%$; (4) a dynamically cold thin disc with $f_{\rm thin}\sim28\%$; (5) a vertically extended thick disc with $f_{\rm thick}\sim16\%$; and (6) a dynamically hot, spatially diffuse stellar halo with $f_{\rm halo}\sim5\%$. The nuclear disc, bar, and thin disc are metal-rich ($[Z/\rm H]\gtrsim0$), $α$-poor ($\rm[Mg/Fe]\lesssim0.2$), and old ($\sim13\rm\,Gyr$), corresponding to in situ formation in the early Universe. The bulge, thick disc, and stellar halo are metal-poor ($[Z/\rm H]\lesssim0$), $α$-rich ($\rm[Mg/Fe]\gtrsim0.2$), and younger than or comparable in age to the in situ components, suggesting their relations with ex situ formation contributed by minor mergers. The flat metallicity and [Mg/Fe] gradients in the thick disc and stellar halo indicate they are dominated by a similar population of ex situ stars. In contrast, the bulge exhibits a negative metallicity gradient ($\nabla[Z/\rm H]_{bulge}<0$) pointing to a more complex formation history: the bulge could be either predominantly ex situ or contain a non-negligible mixture of in situ and ex situ stars. Our modelling also reveals the presence of a slow bar ($\mathcal{R}=2.40_{-0.27}^{+0.54}$), with a bar pattern speed of $\rmΩ_p=34_{-7}^{+4}\,km\,s^{-1}\,kpc^{-1}$, a bar length of $R_{\rm bar}=2.24_{-0.22}^{+0.43}\rm\,kpc$, and a corotation radius of $R_{\rm CR}=5.38_{-0.28}^{+1.59}\rm\,kpc$, which is consistent with its ancient formation time.

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arXiv2026

Gravitational lensing by a spiral galaxy I: the influence from bar's structure to the flux ratio anomaly

Gravitational lens flux ratio anomalies are a powerful probe of small-scale mass structures, often attributed to dark matter subhalos. However, baryonic components can also play a significant role. This study investigates, for the first time, the impact of bars on flux ratio anomalies. We conduct a systematic analysis using barred galaxies from the Auriga simulations. First, we model the projected mass distribution with the Multi-Gaussian Expansion formalism. This method yields smooth lens potentials that preserve the primary bar structure while mitigating numerical noise. We then perform strong lensing simulations and quantify flux ratio anomalies by measuring their deviation from the theoretical cusp-caustic relation, denoted as $R_{\text{cusp}}$. Our primary finding is a strong, statistically significant correlation between the flux ratio anomaly magnitude and the strength of higher-order even Fourier modes. Specifically, the strengths of the boxy/peanut and hexapole components show an exceptionally tight correlation with $R_{\text{cusp}}$, with Spearman correlation coefficients of $r = 0.85$ and $0.89$, and p-values on the order of $10^{-6}$ and $10^{-8}$, respectively. This demonstrates that flux ratio anomalies are highly sensitive to complex, non-axisymmetric bar features. We conclude that flux ratio anomalies can be powerful indicators of bar morphology. Failing to account for such morphology can lead to misinterpreting lensing signatures and potentially overestimating the dark matter subhalo population.

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arXiv2026

Orbit-based structural decomposition and stellar population recovery for edge-on barred galaxies

In our previous paper, we developed an orbit-superposition method for edge-on barred galaxies and constructed a set of dynamical models based on different mock observations of three galaxies from the Auriga simulations. In this study, we adopted 12 cases with side-on bars (three simulated galaxies, each with four different projections). We decomposed these galaxies into different structures combining the kinematic and morphological properties of stellar orbits. We then compared the model-predicted components to their true counterparts in the simulations. Our models can identify (BP/X-shaped) bars, spheroidal bulges, thin discs, and spatially diffuse stellar halos. The mass fractions of bars and discs are well constrained with absolute biases of $|f_{\rm model}-f_{\rm true}|\le0.15$. We recovered the mass fractions of halos with $|f_{\rm model}-f_{\rm true}|\le0.03$. For the bulge components, 10 out of 12 cases exhibit $|f_{\rm model}-f_{\rm true}|\le0.05$, while the other two cases exhibit $|f_{\rm model}-f_{\rm true}|\le0.10$. Then, by tagging the stellar orbits with ages and metallicities, we derived the chemical properties of each structure. For the stellar ages, our models recovered the negative gradients in the bars and discs, but exhibited relatively larger uncertainties for age gradients in the bulges and halos. The mean stellar ages of all components were constrained with absolute biases $|t_{\rm model}-t_{\rm true}|\rm\lesssim1\,Gyr$. For stellar metallicities, our models reproduced the steep negative gradients of the bars and bulges, as well as all different kinds of metallicity gradients in the discs and halos. Apart from the bulge in the simulated galaxy Au-18, the mean stellar metallicities of all other components were constrained with absolute biases of $|Z_{\rm model}-Z_{\rm true}|\rm\le0.5\,Z_{\odot}$.

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arXiv2026

Unifying the dynamical classification of early-type galaxies: kinematic deficits in IllustrisTNG versus observations

We conduct a comparative analysis of galaxy kinematics using IllustrisTNG simulations and integral-field spectroscopy (IFS) observations. We identify 2,342 early-type galaxies (ETGs) from the TNG100 simulation and 236 ETGs from the TNG50 simulation, comparing them with observations from MaNGA and ATLAS$^{3D}$. For these systems, we measure key kinematic parameters: the intrinsic spin parameter $λ_{R,\mathrm{intr}}$ (measured edge-on), the cylindrical rotational energy fraction $κ_{\mathrm{rot}}$, and structural mass ratios including the spheroid mass fraction $f_{\mathrm{spheroid}}$ and stellar halo mass fraction $f_{\mathrm{halo}}$. Our study reveals that standard classifiers--the $λ_{R}(R_e)=0.31\sqrt{\varepsilon}$ relation and $\overline{k_5}$ coefficient (higher-order Fourier term of velocity fields)--fail to align with observed kinematic bimodality. We propose revised thresholds: $λ_{R,\mathrm{intr}} \sim 0.4$, $κ_{\mathrm{rot}} \sim 0.5$, and $f_{\mathrm{spheroid}} \sim 0.6$, which classify galaxies into rotation-dominated (fast rotators) and random motion-dominated (slow rotators). Scaling relations from TNG enable observational estimates of $κ_{\mathrm{rot}}$ and $f_{\mathrm{spheroid}}$. The simulations exhibit a bimodality deficit, characterized by a lack of fast rotators and suppressed $λ_{R,\mathrm{intr}}$, attributed to excess galaxies with intermediate rotation and high spheroid/stellar halo mass. We introduce a novel method to estimate $f_{\mathrm{halo}}$ from IFS kinematics, though uncertainties remain.

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arXiv2025

Recovering the pattern speeds of edge-on barred galaxies via an orbit-superposition method

We developed an orbit-superposition method for edge-on barred galaxies and evaluated its capability to recover the bar pattern speed $\rmΩ_p$. We selected three simulated galaxies (Au-18, Au-23, and Au-28) with known pattern speeds from the Auriga simulations and created MUSE-like mock data sets with edge-on views (inclination angles $θ_{\rm T}\ge85^\circ$) and various bar azimuthal angles $φ_{\rm T}$. For mock data sets with side-on bars ($φ_{\rm T}\ge50^\circ$), the model-recovered pattern speeds $\rmΩ_p$ encompass the true pattern speeds $\rmΩ_T$ within the model uncertainties ($1σ$ confidence levels, $68\%$) for 10 of 12 cases. The average model uncertainty within the $1σ$ confidence levels is equal to $10\%$. For mock data sets with end-on bars ($φ_{\rm T}\le30^\circ$), the model uncertainties of $\rmΩ_p$ depend significantly on the bar azimuthal angles $φ_{\rm T}$, with the uncertainties of cases with $φ_{\rm T}=10^\circ$ approaching $\sim30\%$. However, by imposing a stricter constraint on the bar morphology ($p_{\rm bar}\le0.50$), the average uncertainties are reduced to $14\%$ , and $\rmΩ_p$ still encompass $\rmΩ_T$ within the model uncertainties for three of four cases. For all the models that we create in this paper, the $2σ$ ($95\%$) confidence levels of the model-recovered pattern speeds $\rmΩ_p$ always cover the true values $\rmΩ_T$.

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arXiv2024

Quantifying the stellar ages of dynamically separated bulges and disks of CALIFA spiral galaxies

We employ a recently developed population-orbit superposition technique to simultaneously fit the stellar kinematic and age maps of 82 CALIFA spiral galaxies and obtain the ages of stars in different dynamical structures. We first evaluated the capabilities of this method on CALIFA-like mock data created from the Auriga simulations. The recovered mean ages of dynamically cold, warm, and hot components match the true values well, with an observational error of up to $20\%$ in the mock age maps. For CALIFA spiral galaxies, we find that the stellar ages of the cold, warm, and hot components all increase with the stellar mass of the galaxies, from $\overline{t_{\rm cold}}\sim2.2$ Gyr, $\overline{t_{\rm warm}}\sim2.3$ Gyr, and $\overline{t_{\rm hot}}\sim2.6$ Gyr for galaxies with stellar mass $M_*<10^{10}\,\rm M_{\odot}$, to $\overline{t_{\rm cold}}\sim4.0$ Gyr, $\overline{t_{\rm warm}}\sim5.1$ Gyr, and $\overline{t_{\rm hot}}\sim5.9$ Gyr for galaxies with $M_*>10^{11}\,\rm M_{\odot}$. About $80\%$ of the galaxies in our sample have $t_{\rm hot}>t_{\rm cold}$, and the mean values of $t_{\rm hot}-t_{\rm cold}$ also increase with stellar mass, from $0.7_{-0.2}^{+0.6}$ Gyr in low-mass galaxies ($10^{8.9}\,\rm M_{\odot}<M_*\le10^{10.5}\,\rm M_{\odot}$) to $1.7_{-0.2}^{+0.7}$ Gyr in high-mass galaxies ($10^{10.5}\,\rm M_{\odot}<M_*<10^{11.3}\,\rm M_{\odot}$). The stellar age is younger in disks than in bulges, on average. This suggests that either the disks formed later and/or that they experienced a more prolonged and extensive period of star formation. Lower-mass spiral galaxies have younger bulges and younger disks, while higher-mass spiral galaxies generally have older bulges, and their disks span a wide range of ages. This is consistent with the scenario in which the bulges in more massive spirals formed earlier than those in less massive spirals.

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arXiv2024

Schwarzschild Modeling of Barred S0 Galaxy NGC 4371

We apply the barred Schwarzschild method developed by Tahmasebzadeh et al. (2022) to a barred S0 galaxy, NGC 4371, observed by IFU instruments from the TIMER and ATLAS3D projects. We construct the gravitational potential by combining a fixed black hole mass, a spherical dark matter halo, and stellar mass distribution deprojected from $3.6$ $μ$m S$^4$G image considering an axisymmetric disk and a triaxial bar. We independently modelled kinematic data from TIMER and ATLAS3D. Both models fit the data remarkably well. We find a consistent bar pattern speed from the two sets of models with $Ω_{\rm p} = 23.6 \pm 2.8 \hspace{.08cm} \mathrm{km \hspace{.04cm} s^{-1} \hspace{.04cm} kpc^{-1} }$ and $Ω_{\rm p} = 22.4 \pm 3.5 \hspace{.08cm} \mathrm{km \hspace{.04cm} s^{-1} \hspace{.04cm} kpc^{-1} }$, respectively. The dimensionless bar rotation parameter is determined to be $ 1.88 \pm 0.37$, indicating a likely slow bar in NGC 4371. Additionally, our model predicts a high amount of dark matter within the bar region ($M_{\rm DM}/ M_{\rm total}$ $\sim 0.51 \pm 0.06$), which, aligned with the predictions of cosmological simulations, indicates that fast bars are generally found in baryon-dominated disks. Based on the best-fitting model, we further decompose the galaxy into multiple 3D orbital structures, including a BP/X bar, a classical bulge, a nuclear disk, and a main disk. The BP/X bar is not perfectly included in the input 3D density model, but BP/X-supporting orbits are picked through the fitting to the kinematic data. This is the first time a real barred galaxy has been modelled utilizing the Schwarzschild method including a 3D bar.

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arXiv2020

A Universal fundamental plane and the $M_{dyn}-M_{\star}$ relation for galaxies with CALIFA and MaNGA

We use the stellar kinematics for $2458$ galaxies from the MaNGA survey to explore dynamical scaling relations between the stellar mass $M_{\star}$ and the total velocity parameter at the effective radius, $R_e$, defined as $S_{K}^{2}=KV_{R_e}^{2}+σ_{\star_e}^{2}$, which combines rotation velocity $V_{R_e}$, and velocity dispersion $σ_{\star_e}$. We confirm that spheroidal and spiral galaxies follow the same $M_{\star}-S_{0.5}$ scaling relation with lower scatter than the $M_{\star}-V_{R_e}$ and $M_{\star}-σ_{\star_e}$ ones. We also explore a more general Universal Fundamental Plane described by the equation $log(Υ_{e}) = log (S_{0.5}^{2}) - log (I_{e}) - log (R_{e}) + C$, which in addition to kinematics, $S_{0.5}$, and effective radius, $R_e$, it includes surface brightness, $I_e$, and dynamical mass-to-light ratio, $Υ_e$. We use sophisticated Schwarzschild dynamical models for a sub-sample of 300 galaxies from the CALIFA survey to calibrate the so called Universal Fundamental Plane. That calibration allows us to propose both: (i) a parametrization to estimate the difficult-to-measure dynamical mass-to-light ratio at the effective radius; and (ii) a new dynamical mass proxy consistent with dynamical models within $0.09\ dex$. We reproduce the relation between the dynamical mass and the stellar mass in the inner regions of galaxies. We use the estimated dynamical mass-to-light ratio from our analysis, $Υ_{e}^{fit}$, to explore the Universal Fundamental Plane with the MaNGA data set. We find that all classes of galaxies, from spheroids to disks, follow this Universal Fundamental Plane with a scatter significantly smaller $(0.05\ dex)$ than the one reported for the $M_{\star}-S_{0.5}$ relation $(0.1\ dex)$, the Fundamental Plane $(\sim 0.09\ dex)$ and comparable with Tully-Fisher studies $(\sim 0.05\ dex)$, but for a wider range of galaxy types.

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arXiv2019

SDSS-IV MaNGA: Internal mass distributions and orbital structures of early-type galaxies and their dependence on environment

In our earlier 2019 paper, we evaluated the reliability of Schwarzschild's orbit-superposition dynamical modelling method in estimating the internal mass distribution, intrinsic stellar shapes and orbit distributions of early-type galaxies (ETGs) taken from the Illustris cosmological simulation. We now apply the same techniques to galaxies taken from the integral-field survey Mapping Nearby Galaxies with APO (MaNGA), using a sample of 149 ETGs in the mass range of $10^{9.90}\sim10^{11.80} M_{\odot}$ and made up of 105 central and 44 satellite galaxies. We find that low-mass ETGs with $\log(M_*/M_{\odot})<11.1$ have an average dark matter fraction of $\sim0.2$ within one effective radius $R_{\rm e}$, tend to be oblate-like, and are dominated by rotation about their minor axis. High-mass ETGs with $\log(M_*/M_{\odot})>11.1$ have an average dark matter fraction of $\sim0.4$ within one effective radius $R_{\rm e}$, tend to be prolate-like, and are dominated by rotation about their major axis and by centrophilic orbits. The changes of internal structures within one $R_{\rm e}$ are dominated by the total stellar mass of the individual galaxies. We find no differences of internal structures between central and satellite ETGs for the same stellar masses. However, for similar stellar mass and colour distributions, we find that ETGs more prolate-like, or with more hot orbits, tend to have higher close neighbour counts at $r_p\sim40$ kpc.

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arXiv2019

Evaluating the ability of triaxial Schwarzschild modelling to estimate properties of galaxies from the Illustris simulation

We evaluate the capabilities of Schwarzschild's orbit-superposition method by applying it to galaxies from the large scale, high resolution Illustris simulation. Nine early-type galaxies with a range of triaxiality are selected, and we create mock integral field unit data for five line-of-sight projections of each galaxy. Each of the 45 mock data sets is taken as an independent observed galaxy. Using van den Bosch's 2008 triaxial Schwarzschild implementation, we assess model estimates of various galaxy properties, covering mass profiles, intrinsic shapes, stellar orbit distributions and velocity anisotropies. Total mass within $\overline{R_{\rm e}}$ is recovered well with average deviations within $\pm15$ percent. Stellar mass is underestimated by $\sim24$ percent and dark matter overestimated by $\sim38$ percent (assuming an NFW dark matter profile and allowing for degeneracy between stellar mass and dark matter mass). Using a gNFW profile, these values improve to $\sim13$ percent for stellar mass and $\sim18$ percent for dark matter. Axis ratio estimates show a moderate bias of $Δ(b/a)=0.07$ and $Δ(c/a)=0.14$ ($a\ge b\ge c$). Distributions of the orbit circularities $λ_z$ and $λ_x$, representing rotation about the minor and major axes, are well reconstructed. Separating orbits into thermal categories, our models match the average fractions of these categories to within $10$ percent. Velocity anisotropy is well estimated with values matching in the inner regions but becoming slightly radially biased in the outer regions. Overall, the galaxy property estimates we obtained using Schwarzschild modelling are not implausible and are representative of the simulated galaxies we modelled.

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arXiv2018

The stellar orbit distribution in present-day galaxies inferred from the CALIFA survey

Galaxy formation entails the hierarchical assembly of mass, along with the condensation of baryons and the ensuing, self-regulating star formation. The stars form a collisionless system whose orbit distribution retains dynamical memory that can constrain a galaxy's formation history. The ordered-rotation dominated orbits with near maximum circularity $λ_z \simeq1$ and the random-motion dominated orbits with low circularity $λ_z \simeq0$ are called kinematically cold and kinematically hot, respectively. The fraction of stars on `cold' orbits, compared to the fraction of stars on `hot' orbits, speaks directly to the quiescence or violence of the galaxies' formation histories. Here we present such orbit distributions, derived from stellar kinematic maps via orbit-based modelling for a well defined, large sample of 300 nearby galaxies. The sample, drawn from the CALIFA survey, includes the main morphological galaxy types and spans the total stellar mass range from $10^{8.7}$ to $10^{11.9}$ solar masses. Our analysis derives the orbit-circularity distribution as a function of galaxy mass, $p(λ_z~|~M_\star)$, and its volume-averaged total distribution, $p(λ_z)$. We find that across most of the considered mass range and across morphological types, there are more stars on `warm' orbits defined as $0.25\le λ_z \le 0.8$ than on either `cold' or `hot' orbits. This orbit-based "Hubble diagram" provides a benchmark for galaxy formation simulations in a cosmological context.

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