arXiv subjects

Jun-Sung Moon

Publications and source records attributed to Jun-Sung Moon.

At least 19 recordsLinked to original sources

arXiv2026

A Universal Relation Between Primordial Density-Potential Cross-correlation Coefficient and Spin Factor Distribution

Recent studies have revealed that the key properties of visible galaxies like their optical sizes, stellar ages, star formation rates and morphologies are closely linked with the angular momenta of their host dark matter halos. According to the linear tidal torque theory, the halo angular momentum, as a conserved quantity, is directly proportional to the primordial spin factor, $\tau$, defined as the degree of misalignment between the principal axes of the initial density and potential Hessian matrices, which were found by numerical experiments to follow a Gamma distribution, fully characterized by its mean and variance. In this study, we heuristically develop an analytic expression for the mean and variance of $\tau$ in terms of the initial density-potential cross-correlation coefficient, $q$. Analyzing a dataset from the Multiverse simulations performed for both of the flat $\Lambda$CDM and $w$CDM cosmologies, we prove that this analytic expression is universally valid in describing how the mean and variance of $\tau$ change with $q$, regardless of the smoothing scales for both of the cosmologies. Given the prior finding that the $\tau$-distribution can be reconstructed from the observable galaxy size distribution, this universal analytic expression may allow us to determine $q$ from the same observable via the mean and variance of $\tau$. We discuss a possibility of constraining the early universe physics from the reconstructed $q$ via our heuristic model, without suffering from cosmological degeneracies.

astro-ph.CO↗

arXiv2026

SN Ia Population Machine. I. A Unified Cosmological Simulation-Binary Synthesis Framework Establishing Non-universal Delay-time Distributions and Cosmic Progenitor-channel Dominance Crossover

We present a forward-modeling framework for synthesizing Type Ia supernova (SN Ia) populations by coupling cosmological hydrodynamic simulations to binary population synthesis (BPS). Using IllustrisTNG star particles as simple stellar populations, we generate binaries and evolve them with COMPAS to produce synthetic SNe Ia tagged with explosion times and progenitor channels (single- and double-degenerate; SD and DD). This cosmology-BPS pipeline enables self-consistent, end-to-end tracking of SN Ia populations from individual galaxies to cosmic scales. The model reproduces key SN-related observables, including host-galaxy demographics, delay-time distributions (DTDs), SN-rate trends with host properties and redshift, and a progenitor-age 'step' implicated by the mass step in Hubble residuals. Our main findings are as follows. (1) Contrary to the standard assumption, DTDs appear intrinsically non-universal: their form depends on progenitor channel and metallicity, and thus varies systematically across hosts and with redshift. The commonly adopted DTD is therefore best regarded as a population-averaged approximation rather than a fundamental kernel. (2) We predict that the dominant SN Ia progenitor population shifts from SD to DD with cosmic time, with a demographic crossover near z = 0.5 (~5.2 Gyr ago). This non-monolithic SN Ia population with a redshift-dependent SD/DD mixture weakens the universality implicit in a single globally calibrated standardization. Taken together, evolution in both the DTD and the channel mixture can imprint redshift-dependent systematics on SN Ia luminosities, strengthening the case for jointly inferring progenitor/host-driven effects alongside cosmic acceleration. The full catalogue and analysis scripts are available via Zenodo.

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arXiv2025

Galaxy Spin Alignment with Tidal Fields in the SDSS-IV MaNGA Survey

The tidal torque theory (TTT) predicts that galaxy spins are correlated with the surrounding tidal field, reflecting how angular momentum is acquired during structure formation. We present a new observational test of this prediction using the final data release of the Sloan Digital Sky Survey IV Mapping Nearby Galaxies at Apache Point Observatory integral field spectroscopy survey, which enables direct spin measurements from stellar and ionized gas kinematics for a sample of 6325 disk galaxies. We utilize the three-dimensional tidal field reconstructed from the galaxy distribution, providing a physically defined reference frame for the analysis. We find that massive galaxies tend to align their spins parallel to the intermediate axis of the tidal field, consistent with the prediction of the TTT, while also showing a tendency to align perpendicular to the major axis. In contrast, low-mass galaxies exhibit the opposite trend, with a transition mass of $M_* \sim 10^{10}-10^{10.5}M_\odot$. No significant alignment is detected with respect to the minor axis across all stellar masses. We further examine the dependence on morphology and environment, finding that S0 and early-type spiral galaxies exhibit stronger alignment signals than late-type spirals. The alignment trend becomes particularly pronounced in regions of high tidal anisotropy and high overdensity. A mutual information analysis identifies these environmental factors as the dominant drivers of the observed trends. Our results provide new empirical evidence for the connection between galaxy spins and the cosmic tidal field.

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arXiv2025

Living with Neighbors. V. Better-aligned Spiral+Spiral Galaxy Pairs Show Stronger Star Formation

Enhanced star formation (SF) with star-forming neighboring galaxies bolsters hydrodynamical contributions during paired interactions. Although the relative spin orientation between interacting galaxies can influence this effect, it has not been comprehensively explored. In this study, using a curated sample of nearby (0.02 < z < 0.06) spiral-spiral pairs and an isolated control sample from the Sloan Digital Sky Survey Data Release 7, coupled with Galaxy Zoo 2, and a method to estimate spin-spin alignment (SSA), we systematically compare the impact of the relative orientation, $\cos\xi$, on interaction-induced SF. We find that SSA is a key factor alongside the conventional parameters of projected separation and the SF of neighboring galaxies. The SF enhancement increases as configurations transition from perpendicular ($\cos\xi \sim 0$) to well aligned ($\cos\xi > 0.7$). The effect is strongest when neighboring galaxies have higher SF, indicating a hydrodynamical origin. The trend is consistent with increased hydrodynamical friction via stronger ram pressure and a higher likelihood of prograde orbits in well-aligned pairs.

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arXiv2025

An Observed Evidence for the Primordial Origin of Galaxy Sizes

We present an observational evidence supporting the scenario that the protogalactic angular momenta play an important role in molding the optical sizes of present galaxies. Analyzing the NASA-Sloan Atlas catalog in the redshift range of $0.02\le z<0.09$, we observationally determine the probability density distributions, $p(r_{50})$ and $p(r_{90})$, where $r_{50}$ and $r_{90}$ denote the galaxy sizes enclosing $50\%$ and $90\%$ of their $r$-band luminosities, respectively. Both of the distributions are found to be well described by a bimodal Gamma mixture model, which is consistent with the recent numerical results. Classifying the local galaxies by their ratios, $r_{50}/r_{90}$, we also show that for the case of late-type galaxies with $r_{50}/r_{90}\ge 0.45$ both of $p(r_{50})$ and $p(r_{90})$ exhibit no bimodal feature, following a unimodal Gamma model. Assuming the existence of a linear causal correlation between $\{r_{50},r_{90}\}$ of the late-type galaxies and the primordial spin factor, $\tau$, defined as the degree of misalignments between the initial tidal and protogalaxy inertia tensors, we reconstruct the probability density distributions, $p(\tau)$, directly from the observationally determined $p(r_{50})$ and $p(r_{90})$ of the late-type galaxies. It is shown that the reconstructed $p(\tau)$ is in an excellent agreement with the real distribution of $\tau$ that was determined at the protogalactic stages by numerical experiments. A critical implication of our result on reconstructing the initial conditions from observable galaxy sizes is discussed.

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arXiv2025

Dependence of Galaxy Stellar Properties on the Primordial Spin Factor

We present a numerical discovery that the observable stellar properties of present galaxies retain significant dependences on the primordial density and tidal fields. Analyzing the galaxy catalogs from the TNG300-1 simulations, we first compute the primordial spin factor, $τ$, defined as the mean degree of misalignments between the principal axes of the initial density and potential hessian tensors at the protogalactic sites. Then, we explore in the framework of Shannon's information theory if and how strongly each of six stellar properties of the present galaxies, namely two stellar sizes ($R_{90\star}$ and $R_{50\star}$), ages, specific star formation rates, optical colors and metallicities, share mutual information with $τ$, measured at $z=127$. Deliberately controlling the TNG galaxy samples to have no differences in the mass, environmental density and shear distributions, we single out net effects of $τ$ on each of the galaxy stellar properties. In the higher stellar mass range of $M_{\star}/(h^{-1}\,M_{\odot})\ge 10^{10}$, significant amounts of mutual information with $τ$ are exhibited by all of the six stellar properties, while in the lower range of $M_{\star}/(h^{-1}\,M_{\odot})< 10^{10}$ only four of the six properties except for the specific star formation rates and colors yield significant signals of $τ$-dependence. Examining how the mean values of the six stellar properties vary with $τ$, we also show that the galaxies originated from the protogalactic sites with higher $τ$ values tend to have larger sizes, later formation epochs, higher specific star formation rates, bluer colors and lower metallicities. It is also discovered that the galaxy stellar sizes, which turn out to be most robustly dependent on $τ$ regardless of $M_{\star}$, follow a bimodal Gamma distribution, the physical implication of which is discussed.

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arXiv2024

A New Rarity Assessment of the `Disk of Satellites': the Milky Way System Is the Exception Rather than the Rule in the $Λ$CDM Cosmology

The majority of satellite galaxies around the Milky Way (MW) show disk-like distributions (the disk of satellites; DoS), which is a small-scale problem of the $Λ$CDM cosmology. The conventional definition of the MW-like DoS is a satellite system with a minor-to-major axis ratio ($c$/$a$) lower than the MW's $c$/$a$ value of 0.181. Here we question the validity of the $c$/$a$-based DoS rarity assessment and propose an alternative approach. How satellites are placed around a galaxy is dictated mainly by two factors: the distributions of satellites' orbital poles and distances from the host. Based on this premise, we construct the `satellite distribution generator' code and generate 10$^5$ `spatially and kinematically analogous systems (SKASs)' sharing these two factors. The SKAS can disclose the intrinsic, underlying $c$/$a$ probability distribution function (PDF), from which a present-day $c$/$a$ value is fortuitously determined. We find that the $c$/$a$ PDF of the MW DoS defined by 11 classical satellites is quite broad ($σ_{c/a}$$\sim$0.105), implying that a simple present-day $c$/$a$ value, combined with its highly time-variable nature, cannot fully represent the degree of flatness. Moreover, based on the intrinsic $c$/$a$ PDF, we re-evaluate the rarity of the MW DoS by comparing it with IllustrisTNG50-1 host-satellite systems and find that even with the new measure, the MW DoS remains rare (0.00$\sim$3.40%). We show that the reason behind the rareness is that both orbital poles and distances of the 11 MW satellites are far more plane-friendly than those of simulated host-satellite systems, challenging the current structure and galaxy formation model.

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arXiv2024

The dependence of halo bias on the protohalo shape alignment with the initial tidal field

We present a numerical evidence supporting the primordial origin of secondary halo bias even on the galactic mass scale. Analyzing the data from the IllustrisTNG 300-1 simulations, we investigate the dependence of halo bias on the degree of misalignment between the protohalo inertia and initial tidal tensors, $τ$, measured at redshift, $z_{i}=127$. From the TNG 300-1 galactic halos in logarithmic mass range of $10.5< m\equiv \log[M/(h^{-1}M_{\odot})]\le 13$ identified at $z=0,\ 0.5$ and $1$, a clear signal of $τ$ bias is detected. For the case that $τ$ is measured from the initial tidal field smoothed on the scale of $R_{f}/(h^{-1}\,{\rm Mpc})\lesssim 1$, the halo $τ$ bias is found to be very similar in its tendency and amplitude to the spin bias at all of the three redshifts, if the effects of backsplash halos are properly eliminated. For the case of $R_{f}/(h^{-1}\,{\rm Mpc})=2$, the $τ$ bias at $z=1$ turns out to behave like the age bias, diminishing rapidly in the range of $m> 12$. At $z=0$ and $0.5$, however, the $τ$ and age bias factors show large differences in their overall strengths, which is attributed to the dominant nonlinear effects that undermine the former but enhance the latter. Given these numerical results along with the previous finding that $τ$ shares a large amount of mutual information with the formation epochs and spin parameters of galactic halos, it is concluded that the origins of halo age and spin bias must be closely linked with the primordial factor, $τ$, and that the difference in the tendency between the two bias factors on the galactic mass scale reflects the multi-scale influence of $τ$ on the halo secondary properties.

astro-ph.CO↗

arXiv2024

Mutual information between galaxy properties and the initial predisposition

The immense diversity of the galaxy population in the universe is believed to stem from their disparate merging and star formation histories, and multi-scale influences of diverse environments. No single causal factor of the initial state is known to explain how the galaxies formed and evolved to end up possessing such various traits as they have at the present epoch. However, several observational studies have revealed that the key physical properties of the observed galaxies in the local universe appeared to have a much simpler, lower-dimensional correlation structure than expected, the origin of which remains unexplained. Speculating that the emergence of such a simple correlation structure of the galaxy properties must be triggered by nature rather than by nurture, we explore if the present galaxy properties may be correlated with the initial precondition for protogalaxy angular momentum, $τ$, and test it against the data from the IllustrisTNG300-1 hydrodynamic simulation. Employing Shannon's information theory, we discover that $τ$ shares a significantly large amount of mutual information with each of the four basic traits of the TNG galaxies at $z=0$: the spin parameters, formation epochs, stellar-to-total mass ratios, and fraction of kinetic energy in ordered rotation. These basic traits except for the stellar-to-total mass ratios are found to contain even a larger amount of MI about $τ$ than about the total masses and environments for the case of giant galaxies with $11.5\le \log[M_{\rm t}/(h^{-1}\,M_{\odot})]<13$. Our results imply that the initial condition of the universe must be more impactful on the galaxy evolution than conventionally thought.

astro-ph.CO↗

arXiv2024

Galaxy Spin Transition Driven by the Misalignments between the Protogalaxy Inertia and Initial Tidal Tensors

A numerical detection of the $τ$-driven transition of galaxy spins is presented, where $τ$ is the degree of misalignment between the initial tidal field and protogalaxy inertia tensors. Analyzing the data from the IllustrisTNG 300-1 simulations, we first measure the values of $τ$ at the protogalactic sites found by tracing the constituents of the galactic halos in the mass range of $10.5\le \log \left[M_{h}/(h^{-1}M_{\odot})\right] \le 13$ back to the initial stage, $z_{i}=127$. The probability density functions of $τ$ are shown to be well modeled by the $Γ$-distributions, whose shape and scale parameters turn out to have universal values on a certain critical scale. Then, we investigate how the strength and tendency of the galaxy spin alignments with the principal axes of the local tidal fields depend on the initial condition, $τ$. It is found that on the scale lower than the critical one, the galaxy spin transition occurs at two different thresholds from the major to intermediate and from the intermediate to minor principal axes of the local tidal fields, respectively. Noting that the $τ$-dependent spin transition supersedes in strength the previously found mass-dependent, morphology-dependent, and radius-dependent counterparts, we suggest that $τ$ should be the key driver of all types of the galaxy spin transition and that the present galaxy spins are indeed excellent fossil records of the initial condition.

astro-ph.CO↗

arXiv2023

An Observed Transition of Galaxy Spins on the Void Surfaces

In the linear theory, the galaxy angular momentum vectors which originate from the initial tidal interactions with surrounding matter distribution intrinsically develop perpendicular alignments with the directions of maximum matter compression, regardless of galaxy mass. In simulations, however, the galaxy spins exhibit parallel alignments in the mass-range lower than a certain threshold, which depends on redshift, web type, and background cosmology. We show that the observed three dimensional spins of the spiral galaxies located on the void surfaces from the Sloan Digital Sky Survey indeed transit from the perpendicular to the parallel alignments with the directions toward the nearest void centers at the threshold zone, $9.51\le\log [M_{th,\star}/(h^{-1}\,M_{\odot})]\le10.03$. This study presents a first direct observational evidence for the occurrence of the mass-dependent spin transition of the real galaxies with respect to the non-filamentary structures of the cosmic web, opening a way to constrain the initial conditions of the early universe by measuring the spin transition threshold.

astro-ph.CO↗

arXiv2023

Reoriented Memory of Galaxy Spins for the Early Universe

Galaxy spins are believed to retain the initially acquired tendency of being aligned with the intermediate principal axes of the linear tidal field, which disseminates a prospect of using them as a probe of early universe physics. This roseate prospect, however, is contingent upon the key assumption that the observable stellar spins of the present galaxies measured at inner radii have the same alignment tendency toward the initial tidal field as their dark matter counterparts measured at virial limits. We test this assumption directly against a high-resolution hydrodynamical simulation by tracing back the galaxy component particles back to the protogalactic stage. It is discovered that the galaxy stellar spins at $z=0$ have strong but {\it reoriented} memory for the early universe, exhibiting a significant signal of cross-correlation with the {\it major} principal axes of the initial tidal field at $z=127$. An analytic single-parameter model for this reorientation of the present galaxy stellar spins relative to the initial tidal field is devised and shown to be in good accord with the numerical results.

astro-ph.CO↗

arXiv2023

The Density Parity Model for the Evolution of the Subhalo Inner Spin Alignments with the Cosmic Web

We develop a new model within which the radius-dependent transition of the subhalo inner spins with respect to the cosmic web and the variation of the transition threshold radius ($r_{\rm th}$) with subhalo mass ($M_{\rm vir}$), smoothing scale ($r_{f}$), and redshift ($z$) can be coherently explained. The key tenet of this model is that the competition between the pressure effect of the inner mass and the compression effect of the local tidal field determines which principal direction of the tidal field the inner spins are aligned with. If the former predominates, then only the tidal torques turn on, resulting in the alignments of the inner spins with the intermediate principal axes of the tidal field. Otherwise, the subhalo spins acquire a tendency to be aligned with the shortest axes of the subhalo shapes, which is in the major principal directions of the tidal field. Quantifying the two effects in terms of the densities, we make a purely analytical prediction for $r_{\rm th}(M_{\rm vir}, z, r_{f})$. Testing this model against the numerical results from a high-resolution dark matter only N-body simulation in the redshift range of $0\le z\le 3$ on the galactic mass scale of $11.8\le \log[M_{\rm vir}/(h^{-1}M_{\odot})]\le 12.6$ for two different cases of $r_{f}/(h^{-1}{\rm Mpc})=0.5$ and $1$, we find excellent agreements of the model predictions with the numerical results. It is also shown that this model naturally predicts the alignments between the inner spins of the present subhalos with the principal axes of the high-$z$ tidal field at the progenitors' locations.

astro-ph.CO↗

arXiv2023

Unraveling Joint Evolution of Bars, Star Formation, and Active Galactic Nuclei of Disk Galaxies

We aim to unravel the interplay between bars, star formation (SF), and active galactic nuclei (AGNs) in barred galaxies. To this end, we utilize the SDSS DR12 to select a sample of nearby (0.02 < z < 0.06) disk galaxies that are suitable for bar examination ($M_r < -20.12$ and inclination $\lesssim$ 53$^{\circ}$). We identify 3662 barred galaxies and measure the length and axis ratio of each bar. We invent new bar parameters that mitigate the stellar and bulge mass biases and show, for the first time, that the evolution of non-AGN and AGN-hosting barred galaxies should be tracked using different bar parameters; the bar length for non-AGN galaxies and the bar axis ratio for AGN-hosting galaxies. Our analysis confirms that barred galaxies have a higher specific SF rate than unbarred control galaxies. Moreover, we find a positive correlation of bar length with both the SF enhancement and the centrally star-forming galaxy fraction, indicating the interconnectivity of bars and SF through the bar-driven gas inflow. We also find that while the AGN fraction of barred galaxies is the same as that of the unbarred control sample, galaxies hosting more massive black holes (BHs) have rounder (i.e., higher axis ratio) bars, implying that the bar is not a cause of AGN activity; rather, AGNs appear to regulate bars. Our findings corroborate theoretical predictions that bars in non-AGN galaxies grow in length, and bars in AGN-hosting galaxies become rounder as BHs grow and eventually get destroyed.

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arXiv2022

Radius-Dependent Spin Transition of Dark Matter Halos

A numerical detection of the radius-dependent spin transition of dark matter halos is reported. Analyzing the data from the IllustrisTNG simulations, we measure the halo spin vectors at several inner radii within the virial boundaries and investigate their orientations in the principal frames of the tidal and velocity shear fields, called the Tweb and Vweb, respectively. The halo spin vectors in the high-mass section exhibit a transition from the Tweb intermediate to major principal axes as they are measured at more inner radii, which holds for both of the dark matter and baryonic components. The radius threshold at which the transition occurs depends on the smoothing scale, $R_{f}$, becoming larger as $R_{f}$ decreases. For the case of the Vweb, the occurrence of the radius-dependent spin transition is witnessed only when $R_{f}\ge 1\, h^{-1}$Mpc. Repeating the same analysis but with the vorticity vectors, we reveal a critical difference from the spins. The vorticity vectors are always perpendicular to the Tweb (Vweb) major principal axes, regardless of $R_{f}$, which indicates that the halo inner spins are not strongly affected by the generation of vorticity. It is also shown that the halo spins, as well as the Tweb (Vweb) principal axes, have more directional coherence over a wide range of radial distances in the regions where the vorticity vectors have higher magnitudes. The physical interpretations and implications of our results are discussed.

astro-ph.CO↗

arXiv2022

Early-type Dwarf Galaxies in the Local Universe. Evidence of Ex-situ Growth

We report the discovery of a rare early-type dwarf galaxy (dE), SDSS J125651.47+163024.2 (hereafter dE1256), possessing a tidal feature that was likely built up by accretion of an even smaller dwarf galaxy. dE1256 is located in a nearly isolated environment, at the outskirt of the Virgo cluster. A detailed morphological examination reveals that the accreted stellar population is mainly deposited in the outer part of dE1256, where the tidal tail is most prominent. The inner part of dE1256 is perfectly modeled with a simple Sérsic function of index n = 0.63 and half-light radius R$_{h}$ = 0.6 kpc, but in contrast, the entire galaxy has a size of R$_{h}$ = 1.2 kpc. The mass ratio between the host and the putative accreted dwarf galaxy is calculated to be 5:1, assuming that the observed two components, inner Sérsic, and outer tidal tail residual, represent the host's and accreted galaxy's stellar populations, respectively. We suggest that while the accretion contributes only 20% of the overall stellar population, the size of dE1256 grew by a factor of two via the accretion event. Our results provide, for the first time, strong observational evidence that a dE is undergoing a two-phase growth, a common phenomenon for massive galaxies.

astro-ph.GA↗

arXiv2022

Warped Disk Galaxies. I. Linking U type Warps in Groups/Clusters to Jellyfish Galaxies

arped disk galaxies are classified into two morphologies: S- and U-types. Conventional theories routinely attribute both types to galactic tidal interaction and/or gas accretion, but reproducing of U-types in simulations is extremely challenging. Here we investigate whether both types are governed by the same mechanisms using the most extensive sample of $\sim$8000 nearby (0.02\,$<$\,z\,$<$\,0.06) massive ($M_{*}/M_{\odot}$\,$>$\,$10^9$) edge-on disks from SDSS. We find that U-types show on average bluer optical colors and higher specific star formation rate (sSFR) than S-types, with more strongly warped U-types having higher sSFR. We also find that while the S-type warp properties correlate with the tidal force by the nearest neighbor regardless of the environment, there is no such correlation for U-types in groups/clusters, suggesting a non-tidal environmental could be at play for U-types, such as ram pressure stripping (RPS). Indeed, U-types are more common in groups/clusters than in fields and they have stellar mass, gas fraction, sSFR enhancement and phase-space distribution closely analogous to RPS-induced jellyfish galaxies in clusters. We furthermore show that the stellar disks of most RPS galaxies in the IllustirsTNG simulation are warped in U-shape and bent in opposite direction of stripped gas tails, satisfying theoretical expectations for stellar warps embeded in jellyfishes. We therefore suggest that despite the majority of U-types that live in fields being still less explained, RPS can be an alternative origin for those in groups/clusters.

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arXiv2022

Merger Effects on the Spin and Shape Alignments of Galaxy Stellar, Cold and Hot Gas, and Dark Matter Components

We present a numerical evidence supporting the scenario that the peculiar alignments of the galaxy stellar spins with the major principal axes of the local tidal tensors are produced during the quiescent evolution period when the galaxies experience no recent merger events. Analyzing the merger tree from the TNG300-1 simulation of the IllustrisTNG project, we find the latest merger epochs, $a(z_{m})$, of the galaxies, and create four $a(z_{m})$-selected samples that are controlled to share the identical mass and density distributions. For each sample, we determine the spin and shape vectors of the galaxy stellar, cold and hot gas, and dark matter components separately, and compute the average strengths of their alignments with the principal directions of the local tidal fields as well as their mutual alignment tendencies. It is found that the stellar (cold gas) spin axes of the galaxies whose latest merger events occur at earlier epochs are more strongly aligned (weakly anti-aligned) with the major principal axes of the tidal fields. It is also shown that although the mass-dependent transition of the galaxy DM spins have little connection with the merger events, the morphologies, spin-shape and shape-shear alignment strengths of the galaxy four components sensitively depend on $a(z_{m})$. Noting that the stellar components of the galaxies which undergo long quiescent evolution have distinctively oblate shapes and very strong spin-shape alignments, we suggest that the local tidal field might be traced by using the stellar shapes of galaxies without signatures of mergers as a proxy of their stellar spins.

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