arXiv subjects

Jounghun Lee

Publications and source records attributed to Jounghun Lee.

At least 37 records · Page 2Linked to original sources

arXiv2022

The Splashback Mass Function in the Presence of Massive Neutrinos

We present a complementary methodology to constrain the total neutrino mass, $\sum m_ν$, based on the diffusion coefficient of the splashback mass function of dark matter halos. Analyzing the snapshot data from the Massive Neutrino Simulations, we numerically obtain the number densities of distinct halos identified via the SPARTA code as a function of their splashback masses at various redshifts for two different cases of $\sum m_ν=0.0$ eV and $0.1$ eV. Then, we fit the numerical results to the recently developed analytic formula characterized by the diffusion coefficient that quantifies the degree of ambiguity in the identification of the splashback boundaries. Our analysis confirms that the analytic formula works excellently even in the presence of neutrinos and that the decrement of its diffusion coefficient with redshift is well described by a linear fit, $B(z-z_{c})$, in the redshift range of $0.2\le z\le 2$. It turns out that the massive neutrino case yields significantly lower value of $B$ and substantially higher value of $z_{c}$ than the massless neutrino case, which indicates that the higher masses the neutrinos have, the more severely the splashback boundaries become disturbed by the surroundings. Given our result, we conclude that the total neutrino mass can in principle be constrained by measuring how rapidly the diffusion coefficient of the splashback mass function diminishes with redshifts at $z\ge 0.2$. We also discuss the anomalous behavior of the diffusion coefficient found at lower redshifts for both of the $\sum m_ν$ cases, and ascribe it to the fundamental limitation of the SPARTA code at $z\le 0.13$.

astro-ph.CO↗

arXiv2022

How the Galaxy Stellar Spins Acquire a Peculiar Tidal Connection?

We explore how the galaxy stellar spins acquire a peculiar tendency of being aligned with the major principal axes of the local tidal fields, in contrast to their DM counterparts which tend to be perpendicular to them, regardless of their masses. Analyzing the halo and subhalo catalogs from the IllustrisTNG 300 hydrodynamic simulations at $z\le 1$, we determine the cosines of the alignment angles, $\cosα$, between the galaxy stellar and DM spins. Creating four $\cosα$-selected samples of the galaxies and then controlling them to share the same density and mass distributions, we determine the average strengths of the alignments between the galaxy stellar spins and the tidal tensor major axes over each sample. It is clearly shown that at $z\le 0.5$ the more severely the galaxy stellar spin directions deviate from the DM counterparts, the stronger the peculiar tidal alignments become. Taking the ensemble averages of such galaxy properties as central blackhole to stellar mass ratio, specific star formation rate, formation epoch, stellar-to-total mass ratio, velocity dispersions, average metallicity, and degree of the cosmic web anisotropy over each sample, we also find that all of these properties exhibit either strong correlations or anti-correlations with $\cosα$. Our results imply that the peculiar tidal alignments of the galaxy stellar spins may be caused by anisotropic occurrence of some baryonic process responsible for discharging stellar materials from the galaxies along the tidal major directions at $z<1$.

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arXiv2021

Detection of the Mass-Dependent Dual-Type Transition of Galaxy Spins in IllustrisTNG Simulations

A numerical detection of the mass-dependent spin transition of the galaxies is presented. Analyzing a sample of the galaxies with stellar masses in the range of $10^{9}< (M_{\star}/M_{\odot})\le 10^{11}$ from the IllustrisTNG300-1 simulations, we explore the alignment tendency between the galaxy baryon spins and the three eigenvectors of the linearly reconstructed tidal field as a function of $M_{\star}$ and its evolution in the redshift range of $0\le z \le 1.5$. Detecting a significant signal of the occurrence of the mass-dependent transition of the galaxy spins, we show that the centrals differ from the satellites in their spin transition type. As $M_{\star}$ increases beyond a certain threshold mass, the preferred directions of the central galaxy spins transit from the minor to the intermediate tidal eigenvectors (type two) at $z=0.5$ and $1$, while those of the satellites transit from the minor to the major tidal eigenvectors (type one) at $z=1$ and $1.5$. It is also shown that the mass range and type of the spin transition depend on the galaxy morphology, degree of the alignments between the baryon and total spin vectors as well as on the environmental density. Meanwhile, the stellar spins of the galaxies are found to yield a weak signal of the T1 transitions at $z=0$, whose strength and trend depend on the degree of the alignments between the stellar and baryon spins. The possible mechanisms responsible for the T1 and T2 spin transitions are discussed.

astro-ph.CO↗

arXiv2021

The Diffusion Coefficient of the Splashback Mass Function as a Probe of Cosmology

We present an analytic model for the splashback mass function of dark matter halos, which is parameterized by a single coefficient and constructed in the framework of the generalized excursion set theory and the self-similar spherical infall model. The value of the single coefficient that quantifies the diffusive nature of the splashback boundary is determined at various redshifts by comparing the model with the numerical results from the Erebos N-body simulations for the Planck and the WMAP7 cosmologies. Showing that the analytic model with the best-fit coefficient provides excellent matches to the numerical results in the mass range of $5\le M/(10^{12}h^{-1}\,M_{\odot})< 10^{3}$, we employ the Bayesian and Akaike Information Criterion tests to confirm that our model is most preferred by the numerical results to the previous models at redshifts of $0.3\le z\le 3$ for both of the cosmologies. It is also found that the diffusion coefficient decreases almost linearly with redshifts, converging to zero at a certain threshold redshift, $z_{c}$, whose value significantly differs between the Planck and WMAP7 cosmologies. Our result implies that the splashback mass function of dark matter halos at $z\ge z_{c}$ is well described by a parameter-free analytic formula and that $z_{c}$ may have a potential to independently constrain the initial conditions of the universe.

astro-ph.CO↗

arXiv2020

Breaking the Dark Degeneracy with the Drifting Coefficient of the Field Cluster Mass Function

We present a numerical analysis supporting the evidence that the redshift evolution of the drifting coefficient of the field cluster mass function is capable of breaking several cosmic degeneracies. This evidence is based on the data from the CoDECS and DUSTGRAIN-pathfinder simulations performed separately for various non-standard cosmologies including coupled dark energy, $f(R)$ gravity and combinations of $f(R)$ gravity with massive neutrinos as well as for the standard $Λ$CDM cosmology. We first numerically determine the field cluster mass functions at various redshifts in the range of $0\le z\le 1$ for each cosmology. Then, we compare the analytic formula developed in previous works with the numerically obtained field cluster mass functions by adjusting its drifting coefficient, $β$, at each redshift. It is found that the analytic formula with the best-fit coefficient provides a good match to the numerical results at all redshifts for all of the cosmologies. The empirically determined redshift evolution of the drifting coefficient, $β(z)$, turns out to significantly differ among different cosmologies. It is also shown that even without using any prior information on the background cosmology the drifting coefficient, $β(z)$, can discriminate with high statistical significance the degenerate non-standard cosmologies not only from the $Λ$CDM but also from one another. It is concluded that the evolution of the departure from the Einstein-de Sitter state and spherically symmetric collapse processes quantified by $β(z)$ is a powerful probe of gravity and dark sector physics.

astro-ph.CO↗

arXiv2020

The Halo Spin Transition as a Probe of Dark Energy

We present a numerical evidence supporting the claim that the mass-dependent transitions of the halo spin orientations from the intermediate to the minor principal directions of the local tidal fields can in principle be a useful discriminator of dark energy models. We first define a spin transition zone as the mass range of the halos, $Δm_{t}$, for which the intrinsic spin alignments with the minor tidal principal directions become as strong as that with the intermediate principal directions. Then, utilizing the halo samples from the DEUS simulations performed separately for the WMAP7 $Λ$CDM, phantom DE and quintessence models, we investigate if and how the three different dark energy models differ in $Δm_{t}$. It is shown that the differences in $Δm_{t}$ among the three dark energy models are significant enough to discriminate the models from one another and robust against the variations of the smoothing scale of the tidal field and redshift. Noting that a narrower spin transition zone is more powerful as a probe of dark energy, we also show that the spin transition zones become narrower at higher redshifts, in the filamentary environments and for the case that the tidal fields are smoothed on the smaller scales. Our result is consistent with the scenario that $Δm_{t}$ is mainly determined by how fast the nonlinear evolution of the tidal field proceeds, which in turn sensitively depends on the background cosmology.

astro-ph.CO↗

arXiv2020

The Effect of Massive Neutrinos on the Halo Spin Flip Phenomenon

The halo spin flip refers to the phenomenon that the spin axes of dark matter halos with masses above a certain threshold tend to be preferentially aligned perpendicular to the hosting large-scale filaments, while low-mass halos tend to have their spin axes aligned parallel to such structures. Extensive work has so far been conducted to understand this phenomenon under the assumption of cold dark matter and suggested that its origin should be closely related to the nonlinear evolution of the halo angular momentum in the anisotropic cosmic web. We present, for the first time, a numerical examination of this phenomenon assuming the presence of massive neutrinos, finding a clear and robust dependence of the threshold mass for the spin flip on the total neutrino mass. Our physical explanation is that the presence of more massive neutrinos retard the nonlinear evolution of the cosmic web, which in turn allows the halo spin vectors to better retain their memories of the initial tidal interactions in the nonlinear regime. Our finding implies that the statistical alignment of halo spins with the large-scale structures can be in principle used as a probe of the total neutrino mass.

astro-ph.CO↗

arXiv2020

Weighing the Neutrinos with the Galaxy Shape-Shape Correlations

The galaxies form and evolve in the early epochs through the anisotropic merging process along the primary narrow filaments, in the direction of which their shapes become elongated and intrinsically aligned. The nonlinear evolution of the cosmic web broadens the primary filaments, by entangling them with multiple secondary filaments, which has an effect of reducing the anisotropy of the merging process and in consequence weakens the galaxy shape-shape correlations in the later epochs. Assuming that the degree of the nonlinearity and complexity of the cosmic web depends on the nature of dark matter, we propose a hypothesis that the galaxy shape-shape correlation function, $η(r)$, may be a powerful complimentary probe of the total neutrino mass, $M_ν$. Testing this hypothesis against a high resolution N-body simulation, we show that the $M_ν$-dependence of $η(r)$ at $z=0$ is sensitive enough to distinguish between $M_ν=0.0$ eV and $M_ν=0.1$ eV. We also show that the differences in $η(r)$ at $r\le 5\,h^{-1}$Mpc between the models with massless and massive neutrinos cannot be explained by their differences in the small-scale density powers, $σ_{8}$, which implies that the galaxy shape-shape correlation function has a potential to break the notorious cosmic degeneracy between $M_ν$ and $σ_{8}$.

astro-ph.CO↗

arXiv2020

Constraining the Neutrino Mass with the Drifting Coefficient of the Field Cluster Mass Function

A new diagnostics to break the degeneracy between the total neutrino mass ($M_ν$) and the primordial power spectrum amplitude ($σ_{8}$) by using the drifting coefficient of the field cluster mass function is presented. Analyzing the data from the Cosmological Massive Neutrino Simulations, we first determine the numerical mass functions of the field clusters at various redshifts. Then, we compare the numerical results with the analytical model characterized by a single parameter called the drifting coefficient which measures the drifts of the collapse density threshold, $δ_{c}$, from the Einstein-de Sitter spherical value, $δ_{sc}$, at a given mass scale. It is found that the analytic model for the field cluster mass function is found to work excellently even in the presence of massive neutrinos and that its drifting coefficient evolves differently in the cosmologies with different values of $M_ν$. At low redshifts ($z\lesssim 0.3$) the more massive neutrinos drift $δ_{c}$ further from $δ_{sc}$, while the opposite trend is found at higher redshifts ($z\gtrsim0.3$). Speculating that this distinct redshift-dependent effect of massive neutrinos on the drifting coefficient of the field cluster mass function might help break the $σ_{8}$-$M_ν$ degeneracy, we also show that the sensitivity of this new diagnostics to $M_ν$ is high enough to discriminate the case of $M_ν=0.1\,{\rm eV}$ from that of massless neutrinos.

astro-ph.CO↗

arXiv2019

Evolution of the Deterministic Collapse Barrier of the Field Clusters as a Probe of Cosmology

The collapse barrier, $δ_{c}$, of the field clusters located in the low-density environment is deterministic rather than diffusive, unlike that of the wall counterparts located in the superclusters. Analyzing the data from the Mira-Titan simulations for eleven different cosmologies including the standard $Λ$CDM cosmology at various redshifts, we investigate the evolution of the deterministic collapse barrier of the field clusters and explore its dependence on the background cosmology. Regardless of the background cosmology, the deterministic $δ_{c}$ exhibits a universal behavior of having a higher value than the Einstein-de Sitter spherical collapse barrier height of $δ_{sc}=1.686$, at $z=0$ but gradually converging down to $δ_{sc}$ as the dominance of dark energy diminishes with the increment of $z$. A significant difference among different cosmologies, however, is found in its convergence rate as well as in the critical redshift $z_{c}$ at which $δ_{c}=δ_{sc}$. Showing that the convergence rate and critical redshifts can distinguish even between the degenerate cosmologies which yield almost identical linear growth factor and cluster mass functions, we suggest that the evolution of the deterministic collapse barrier of the field clusters should be a powerful complementary probe of cosmology.

astro-ph.CO↗

arXiv2019

Modeling the Anisotropic Tidal Effect on the Spin-Spin Correlations of Low-Mass Galactic Halos

The halo spin-spin correlation function, $η(r)$, measures how rapidly the strength of the alignments of the spin directions between the neighbor halos change with the separation distance, $r$. The previous model based on the tidal torque theory expresses the halo spin-spin correlation function as a power of the linear density two-point correlation function, $η(r)\propto ξ^{n}(r)$, predicting $n=2$ in the linear regime and $n=1$ in the non-linear regime. Using a high-resolution N-body simulation, we show that the halo spin-spin correlation function in fact drops much less rapidly with $r$ than the prediction of the previous model, finding $η(r)$ to be statistically significant even at $r\ge 10\,h^{-1}$Mpc on the dwarf galaxy scale. Claiming that the anisotropic tidal effect is responsible for the failure of the previous model, we propose a new formula for the halo spin-spin correlation function expressed in terms of the integrals of $ξ(r)$. The new formula with the best-fit parameters turns out to agree excellently with the numerical results in a broad mass range, $0.05\le M/(10^{11}\,h^{-1}\,M_{\odot})\le 50$, describing well the large-scale tail of $η(r)$. We discuss a possibility of using the large-scale spin-spin correlations of the dwarf galactic halos as a complementary probe of dark matter.

astro-ph.CO↗

arXiv2019

A Multidimensional Dependence of the Substructure Evolution on the Tidal Coherence

We numerically explore how the subhalo mass-loss evolution is affected by the tidal coherences measured along different eigenvector directions. The mean virial-to-accretion mass ratios of the subhalos are used to quantify the severity of their mass-loss evolutions within the hosts, and the tidal coherence is expressed as an array of three numbers each of which quantifies the alignment between the tidal fields smoothed on the scales of $2$ and $30\,h^{-1}$Mpc in each direction of three principal axes. Using a Rockstar halo catalog retrieved from a N-body simulation, we investigate if and how the mass-loss evolutions of the subhalos hosted by distinct halos at fixed mass scale of [$1$-$3$]$10^{14}\,h^{-1}\,M_{\odot}$ are correlated with three components of the tidal coherence. The tides coherent along different eigenvector directions are found to have different effects on the subhalo mass-loss evolution, which cannot be ascribed to the differences in the densities and ellipticities of the local environments. It is shown that the substructures surrounded by the tides highly coherent along the first eigenvector direction and highly {\it incoherent} along the third eigenvector direction experience the least severe mass-loss evolution, while the tides highly {\it incoherent} only along the first eigenvector direction is responsible for the most severe mass-loss evolution of the subhalos. Explaining that the coherent tides have an obstructing effect on the satellite infalls onto their hosts and that the strength of the obstruction effect depends on which directions the tides are coherent or {\it incoherent} along, we suggest that the multidimensional dependence of the substructure evolution on the tidal coherence should be deeply related to the complex nature of the large-scale assembly bias.

astro-ph.CO↗

arXiv2019

How the Coherent Tides Obstruct the Radial Infalls of Satellite Galaxies onto Clusters

A direct numerical evidence for the obstructing effect of the coherent tides on the infall-zone satellites around the cluster halos is presented. Analyzing the numerical data from a high-resolution N-body simulation, we calculate the mean fractions of the radial and tangential velocities of the infall-zone satellites around the cluster halos and investigate if and how they depend on the tidal coherence defined as the alignments between the major principal axes of the local tidal fields smoothed on the linear and nonlinear scales. It is found that the infall-zone satellites located in the regions with higher tidal coherence have significantly smaller and larger mean fractions of the radial and tangential velocities, respectively, which indicates that the radial infall of satellites onto host clusters are obstructed by the coherent tides. We also show that those satellites separated by shorter distances from the host clusters, having lower-masses, and embedded in the anisotropic large-scale environments like filaments and sheets, are more vulnerable to the obstructing effect of the coherent tides.

astro-ph.CO↗

arXiv2019

Revisiting the Galaxy Shape and Spin Alignments with the Large-Scale Tidal Field: An Effective Practical Model

An effective practical model with two characteristic parameters is presented to describe both of the tidally induced shape and spin alignments of the galactic halos with the large-scale tidal fields. We test this model against the numerical results obtained from the Small MultiDark Planck simulation on the galactic mass scale of $0.5\le M/(10^{11}\,h^{-1}\,M_{\odot})\le 50$ at redshift $z=0$. Determining empirically the parameters from the numerical data, we demonstrate how successfully our model describes simultaneously and consistently the amplitudes and behaviors of the probability density functions of three coordinates of the shape and spin vectors in the principal frame of the large scale tidal field. Dividing the samples of the galactic halos into multiple subsamples in four different mass ranges and four different types of the cosmic web, and also varying the smoothing scale of the tidal field from $5\,h^{-1}$Mpc to $10,\ 20,\ 30\,h^{-1}$Mpc, we perform repeatedly the numerical tests with each subsample at each scale. Our model is found to match well the numerical results for all of the cases of the mass range, smoothing scale and web type and to properly capture the scale and web dependence of the spin flip phenomenon.

astro-ph.CO↗

arXiv2018

A New Perspective on the Large-Scale Tidal Effect on the Galaxy Luminosity and Morphology

We study the mean tidal coherence of galaxy environments as a function of intrinsic luminosity determined by the absolute $r$-band magnitude. The tidal coherence of a galaxy environment is estimated as the cosine of the angle between two minor eigenvectors of the tidal field smoothed at the scales of $2$ and $30\,h^{-1}$Mpc centered on each of the local galaxies from the Sloan Digital Sky Data Release 10. Creating four luminosity-selected samples of the Sloan galaxies, we control them to have identical density distributions, in order to nullify the dominant effect of the local density. It is found that the samples containing more luminous wall and field galaxies yield lower mean values of the tidal coherence, which trend turns out to be robust against the variation of the smoothing scales. At fixed morphology, the same trend is found for the late-type spiral and lenticular galaxies in both of the field and wall environments. The early-type spiral field galaxies show no significant dependence on the tidal coherence, while both of the least and most luminous elliptical wall galaxies are found to dwell in the regions with highest tidal coherence.

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arXiv2018

Linear Tidal Vestige found in the WM Sheet

We present a vestige of the linear tidal influence on the spin orientations of the constituent galaxies of the WM sheet discovered in the vicinity of the Virgo cluster and the Local Void. The WM sheet is chosen as an optimal target since it has a rectangular parallelepiped-like shape whose three sides are in parallel with the supergalactic Cartesian axes. Determining three probability density functions of the absolute values of the supergalactic Cartesian components of the spin vectors of the WM sheet galaxies, we investigate their alignments with the principal directions of the surrounding large-scale tidal field. When the WM sheet galaxies located in the central region within the distance of $2\,h^{-1}$Mpc are excluded, the spin vectors of the remaining WM sheet galaxies are found to be weakly aligned, strongly aligned, and strongly anti-aligned with the minor, intermediate and major principal directions of the surrounding large-scale tidal field, respectively. To examine whether or not the origin of the observed alignment tendency from the WM sheet is the linear tidal effect, we infer the eigenvalues of the linear tidal tensor from the axial ratios of the WM sheet with the help of the Zel'dovich approximation and conduct a full analytic evaluation of the prediction of the linear tidal torque model for the three probability density functions. A detailed comparison between the analytical and the observational results reveals a good quantitative agreement not only in the behaviors but also in the amplitudes of the three probability density functions.

astro-ph.CO↗

arXiv2018

Detection of the Intrinsic Spin Alignments in Isolated Spiral Pairs

An observational evidence for the intrinsic galaxy alignments in isolated spiral pairs is presented. From the catalog of the galaxy groups identified by Tempel et al. in the flux limited galaxy sample of the Sloan Digital Sky Survey Data Release 10, we select those groups consisting only of two spiral galaxies as isolated spiral pairs and investigate if and how strongly the spin axes of their two spiral members are aligned with each other. We detect a clear signal of intrinsic spin alignment in the isolated spiral pairs, which leads to the rejection of the null hypothesis at the $99.9999\%$ confidence level via the Rayleigh test. It is also found that those isolated pairs comprising two early-type spiral galaxies exhibit the strongest signal of intrinsic spin alignment and that the strength of the alignment signal depends on the angular separation distance as well as on the luminosity ratio of the member galaxies. Using the dark matter halos consisting of only two subhalos resolved in the EAGLE hydrodynamic simulations, we repeat the same analysis but fail to find any alignment tendency between the spin angular momentum vectors of the stellar components of the subhalos, which is in tension with the observational result. A couple of possible sources of this apparent inconsistency between the observational and the numerical results are discussed.

astro-ph.CO↗

arXiv2018

Estimating the Turn-Around Radii of Six Isolated Galaxy Groups in the Local Universe

The estimates of the turn-around radii of six isolated galaxy groups in the nearby universe are presented. From the Tenth Data Release of the Sloan Digital Sky Survey, we first select those isolated galaxy groups at redshifts $z\le 0.05$ in the mass range of [0.3-1]$\times10^{14}\,h^{-1}M_{\odot}$ whose nearest neighbor groups are located at distances larger than fiften times their virial radii. Then, we search for a gravitationally interacting web-like structure around each isolated group, which appears as an inclined streak pattern in the anisotropic spatial distribution of the neighbor field galaxies . Out of 59 isolated groups, only seven are found to possess such web-like structures in their neighbor zones, but one of them turns out to be NGC 5353/4, whose turn-around radius was already measured in the previous work and thus excluded from our analysis. Applying the Turn-around Radius Estimator algorithm devised by Lee et al. to the identified web-like structures of the remaining six target groups, we determine their turn-around radii and show that three out of the six targets have larger turn-around radii than the spherical bound limit predicted by the Planck cosmology. We discuss possible sources of the apparent violations of the three groups, including the underestimated spherical bound-limit due to the approximation of the turn-around mass by the virial mass.

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