arXiv subjects

Tsutomu T. Takeuchi

Publications and source records attributed to Tsutomu T. Takeuchi.

At least 55 records · Page 3Linked to original sources

arXiv2023

EMPRESS. IX. Extremely Metal-Poor Galaxies are Very Gas-Rich Dispersion-Dominated Systems: Will JWST Witness Gaseous Turbulent High-z Primordial Galaxies?

We present kinematics of 6 local extremely metal-poor galaxies (EMPGs) with low metallicities ($0.016-0.098\ Z_{\odot}$) and low stellar masses ($10^{4.7}-10^{7.6} M_{\odot}$). Taking deep medium-high resolution ($R\sim7500$) integral-field spectra with 8.2-m Subaru, we resolve the small inner velocity gradients and dispersions of the EMPGs with H$α$ emission. Carefully masking out sub-structures originated by inflow and/or outflow, we fit 3-dimensional disk models to the observed H$α$ flux, velocity, and velocity-dispersion maps. All the EMPGs show rotational velocities ($v_{\rm rot}$) of 5--23 km s$^{-1}$ smaller than the velocity dispersions ($σ_{0}$) of 17--31 km s$^{-1}$, indicating dispersion-dominated ($v_{\rm rot}/σ_{0}=0.29-0.80<1$) systems affected by inflow and/or outflow. Except for two EMPGs with large uncertainties, we find that the EMPGs have very large gas-mass fractions of $f_{\rm gas}\simeq 0.9-1.0$. Comparing our results with other H$α$ kinematics studies, we find that $v_{\rm rot}/σ_{0}$ decreases and $f_{\rm gas}$ increases with decreasing metallicity, decreasing stellar mass, and increasing specific star-formation rate. We also find that simulated high-$z$ ($z\sim 7$) forming galaxies have gas fractions and dynamics similar to the observed EMPGs. Our EMPG observations and the simulations suggest that primordial galaxies are gas-rich dispersion-dominated systems, which would be identified by the forthcoming James Webb Space Telescope (JWST) observations at $z\sim 7$.

astro-ph.GA↗

arXiv2023

Photometric Observations and Period Analysis of an SU UMa-type Dwarf Nova, MASTER OT J004527.52+503213.8

MASTER OT J004527.52+503213.8 (hereafter MASTER J004527) is a dwarf nova discovered by the MASTER project in 2013. At 18:20 UTC on 24 October 2020, brightening of this object was reported to vsnet-alert (24843 by Denisenko). This was the second report of a superoutburst after its discovery. Photometric observations were made using the 23.5-cm Schmidt-Cassegrain telescope at Okayama University of Science observatory soon after the alert through 4 November 2020. In this work, we present the photometric data from our observation, and the analysis of the light curves of MASTER J004527 during the 2020 outburst. We propose a method to determine the period of superhumps by polynomial fitting, which can be applied to a light curve with many missing data. In addition to our own data, we incorporate other all sky survey data of the outburst to better understand the properties of the superhumps. Based on our observations, we conclude that MASTER J004527 is an SU UMa-type dwarf nova, since no early superhumps occurred.

astro-ph.SR↗

arXiv2022

EMPRESS. VIII. A New Determination of Primordial He Abundance with Extremely Metal-Poor Galaxies: A Suggestion of the Lepton Asymmetry and Implications for the Hubble Tension

The primordial He abundance $Y_\mathrm{P}$ is a powerful probe of cosmology. Currently, $Y_\mathrm{P}$ is best determined by observations of metal-poor galaxies, while there are only a few known local extremely metal-poor ($<0.1 Z_\odot$) galaxies (EMPGs) having reliable He/H measurements with HeI$λ$10830 near-infrared (NIR) emission. Here we present deep Subaru NIR spectroscopy for 10 EMPGs. Combining the existing optical data, He/H values of 5 out of the 10 EMPGs are reliably derived by the Markov chain Monte Carlo algorithm. Adding the existing 3 EMPGs and 51 moderately metal-poor ($0.1-0.4 Z_\odot$) galaxies with reliable He/H estimates, we obtain $Y_\mathrm{P}=0.2370^{+0.0034}_{-0.0033}$ by linear regression in the $\mathrm{(He/H)}-\mathrm{(O/H)}$ plane, where we increase the number of EMPGs from 3 to 8 anchoring He/H of the most metal-poor gas in galaxies. Although our $Y_\mathrm{P}$ measurement and previous measurements are consistent, our result is slightly ($\sim 1σ$) smaller due to our EMPGs. With our $Y_\mathrm{P}$ and the existing primordial deuterium $D_\mathrm{P}$ measurement, we constrain the effective number of neutrino species $N_\mathrm{eff}$ and the baryon-to-photon ratio $η$ showing $\gtrsim 1-2σ$ tensions with the Standard Model and Planck Collaboration et al. (2020). Motivated by the tensions, we allow the degeneracy parameter of electron-neutrino $ξ_e$ to vary as well as $N_\mathrm{eff}$ and $η$. We obtain $ξ_e = 0.05^{+0.03}_{-0.02}$, $N_\mathrm{eff}=3.11^{+0.34}_{-0.31}$, and $η\times10^{10}=6.08^{+0.06}_{-0.06}$ from the $Y_\mathrm{P}$ and $D_\mathrm{P}$ measurements with a prior of $η$ taken from Planck Collaboration et al. (2020). Our constraints suggest a lepton asymmetry and allow for a high value of $N_\mathrm{eff}$ within the $1σ$ level, which could mitigate the Hubble tension.

astro-ph.CO↗

arXiv2022

CO($J$=1-0) mapping survey of 64 galaxies in the Fornax cluster with the ALMA Morita array

We conduct a $^{12}$C$^{16}$O($J$=1-0) (hereafter CO) mapping survey of 64 galaxies in the Fornax cluster using the ALMA Morita array in cycle 5. CO emission is detected from 23 out of the 64 galaxies. Our sample includes dwarf, spiral and elliptical galaxies with stellar masses of $M_{\rm star}\sim10^{6.3-11.6}$~M$_\odot$. The achieved beam size and sensitivity are $15''\times8''$ and $\sim12$~mJy~beam$^{-1}$ at the velocity resolution of $\sim10$~km~s$^{-1}$, respectively. We study the cold-gas (molecular- and atomic-gas) properties of 38 subsamples with $M_{\rm star}>10^9$~M$_\odot$ combined with literature HI data. We find that: (1) the low star-formation (SF) activity in the Fornax galaxies is caused by the decrease in the cold-gas mass fraction with respect to stellar mass (hereafter, gas fraction) rather than the decrease of the SF efficiency from the cold gas; (2) the atomic-gas fraction is more heavily reduced than the molecular-gas fraction of such galaxies with low SF activity. A comparison between the cold-gas properties of the Fornax galaxies and their environmental properties suggests that the atomic gas is stripped tidally and by the ram pressure, which leads to the molecular gas depletion with an aid of the strangulation and consequently SF quenching. Pre-processes in the group environment would also play a role in reducing cold-gas reservoirs in some Fornax galaxies.

astro-ph.GA↗

arXiv2022

Galaxy Manifold: Characterizing and understanding galaxies with two parameters

We report the discovery of a two-dimensional Galaxy Manifold within the multi-dimensional luminosity space of local galaxies. The multi-dimensional luminosity space is constructed using 11 bands that span from far ultraviolet to near-infrared for redshift < 0.1 galaxies observed with GALEX, SDSS, and UKIDSS. The two latent parameters are sufficient to express 93.2% of the variance in the galaxy sample, suggesting that this Galaxy Manifold is one of the most efficient representations of galaxies. The transformation between the observed luminosities and the manifold parameters as an analytic mapping is provided. The manifold representation provides accurate (85%) morphological classifications with a simple linear boundary, and galaxy properties can be estimated with minimal scatter (0.12 dex and 0.04 dex for star formation rate and stellar mass, respectively) by calibrating with the two-dimensional manifold location. Under the assumption that the manifold expresses the possible parameter space of galaxies, the evolution on the manifold is considered. We find that constant and exponentially decreasing star formation histories form almost orthogonal modes of evolution on the manifold. Through these simple models, we understand that the two modes are closely related to gas content, which suggests the close relationship of the manifold to gas accretion. Without assuming a star formation history, a gas-regulated model reproduces an exponentially declining star formation history with a timescale of $\sim$1.2 Gyrs on the manifold. Lastly, the found manifold suggests a paradigm where galaxies are characterized by their mass/scale and specific SFR, which agrees with previous studies of dimensionality reduction.

astro-ph.GA↗

arXiv2022

Deblurring galaxy images with Tikhonov regularization on magnitude domain

We propose a regularization-based deblurring method that works efficiently for galaxy images. The spatial resolution of a ground-based telescope is generally limited by seeing conditions and much worse than space-based telescopes. This circumstance has generated considerable research interest in restoration of spatial resolution. Since image deblurring is a typical inverse problem and often ill-posed, solutions tend to be unstable. To obtain a stable solution, much research has adopted regularization-based methods for image deblurring, but the regularization term is not necessarily appropriate for galaxy images. Although galaxies have an exponential or Sersic profile, the conventional regularization assumes the image profiles to behave linear in space. The significant deviation between the assumption and real situation leads to blurring the images and smoothing out the detailed structures. Clearly, regularization on logarithmic, i.e. magnitude domain, should provide a more appropriate assumption, which we explore in this study. We formulate a problem of deblurring galaxy images by an objective function with a Tikhonov regularization term on magnitude domain. We introduce an iterative algorithm minimizing the objective function with a primal-dual splitting method. We investigate the feasibility of the proposed method using simulation and observation images. In the simulation, we blur galaxy images with a realistic point spread function and add both Gaussian and Poisson noises. For the evaluation with the observed images, we use galaxy images taken by the Subaru HSC-SSP. Both of these evaluations show that our method successfully recovers the spatial resolution of the images and significantly outperforms the conventional methods. The code is publicly available from the Github ( https://github.com/kzmurata-astro/PSFdeconv_amag ).

astro-ph.IM↗

arXiv2022

Dissecting Nearby Galaxies with piXedfit: II. Spatially Resolved Scaling Relations Among Stars, Dust, and Gas

We study spatially resolved scaling relations among stars, dust, and gas in ten nearby spiral galaxies. In a preceding paper Abdurro'uf et al. (2022), we have derived spatially resolved properties of the stellar population and dust by panchromatic spectral energy distribution (SED) fitting using piXedfit. Now, we investigate resolved star formation ($Σ_{\rm H_{2}}$--$Σ_{\rm SFR}$--$Σ_{*}$) and dust scaling relations. While the relations with all sub-galactic regions of the galaxies are reasonably tight ($σ\lesssim 0.3$ dex), we find that most of the scaling relations exhibit galaxy-to-galaxy variations in normalization and shape. Only two relations of $Σ_{\rm dust}$--$Σ_{\rm gas}$ and $Σ_{\rm dust}$--$Σ_{\rm H_{2}}$ do not show noticeable galaxy-to-galaxy variations among our sample galaxies. We further investigate correlations among the scaling relations. We find significant correlations among the normalization of the $Σ_{\rm H_{2}}$--$Σ_{\rm SFR}$--$Σ_{*}$ relations, which suggest that galaxies with higher levels of resolved $\text{H}_{2}$ fraction ($f_{\rm H_{2}}$) tend to have higher levels of resolved star formation efficiency (SFE) and specific star formation rate (sSFR). We also observe that galaxies with higher levels of resolved dust-to-stellar mass ratios tend to have higher levels of resolved sSFR, SFE, and $f_{\rm H_{2}}$. Moreover, we find that galaxies with higher global sSFR and less compact morphology tend to have higher levels of the resolved sSFR, SFE, and $f_{\rm H_{2}}$, which can explain the variations in the normalization of the $Σ_{\rm H_{2}}$--$Σ_{\rm SFR}$--$Σ_{*}$ relationships. Overall, we observe indications of the contributions of both global and local factors in governing the star formation process in galaxies.

astro-ph.GA↗

arXiv2022

A new galaxy spectral energy distribution model consistent with the evolution of dust

The spectral energy distribution (SED) of galaxies provides fundamental information on the related physical processes. However, the SED is significantly affected by dust in its interstellar medium. Dust is mainly produced by asymptotic giant branch stars and Type II supernovae. In addition, the dust mass increases through the metal accretion, and the grain size changes by the collisions between the grains. The contribution of each process and the extinction depend on the size distribution. Therefore, the SED model should treat the evolution of the dust mass and size distribution. In spite of the importance of dust evolution, many previous SED models have not considered the evolution of the total mass and size distribution in a physically consistent manner. In this work, we constructed a new radiative transfer SED model, based on our dust evolution model consistent with the chemical evolution. To reduce the computational cost, we adopted the mega-grain and the one-dimensional plane parallel galaxy approximation. As a fiducial case, we calculated Milky Way-like galaxy SEDs at various ages under the closed-box model. We found that a galaxy at the age of 100~Myr does not produce small grains such as polycyclic aromatic hydrocarbons. After 1~Gyr, we observed a drastic increase of infrared emission and attenuation caused by a rapid increase of dust mass. This phenomenon can be treated appropriately for the first time by our new model. This model can be used for the SED fitting to a galaxy at any stage of evolution.

astro-ph.GA↗

arXiv2022

Wavelets and sparsity for Faraday tomography

Faraday tomography through broadband polarimetry can provide crucial information on magnetized astronomical objects, such as quasars, galaxies, or galaxy clusters. However, the limited wavelength coverage of the instruments requires that we solve an ill-posed inverse problem when we want to obtain the Faraday dispersion function (FDF), a tomographic distribution of the magnetoionic media along the line of sight. This paper explores the use of wavelet transforms and the sparsity of the transformed FDFs in the form of wavelet shrinkage (WS) for finding better solutions to the inverse problem. We recently proposed the Constraining and Restoring iterative Algorithm for Faraday Tomography (CRAFT; Cooray et al. 2021), a new flexible algorithm that showed significant improvements over the popular methods such as Rotation Measure Synthesis. In this work, we introduce CRAFT+WS, a new version of CRAFT incorporating the ideas of wavelets and sparsity. CRAFT+WS exhibit significant improvements over the original CRAFT when tested for a complex FDF of realistic Galactic model. Reconstructions of FDFs demonstrate super-resolution in Faraday depth, uncovering previously unseen Faraday complexities in observations. The proposed approach will be necessary for effective cosmic magnetism studies using the Square Kilometre Array and its precursors.

astro-ph.IM↗

arXiv2022

The bimodality in the mass-metallicity relation in SDSS-MaNGA galaxy pairs

Aims: Interacting galaxies show a metallicity dilution compared to isolated galaxies of similar masses in the mass-metallicity space at the global scale. We investigate the spatially resolved mass-metallicity relation (MZR) of galaxy pairs in the SDSS-MaNGA survey to confirm that the local relation between the stellar mass surface density and the metallicity is consistent with the MZR at the global scale. Methods: We investigate the relationship between the stellar mass surface density and the metallicity abundance, 12+log (O/H), for star-forming spaxels belonging to 298 galaxy pairs identified using visual and kinematic indicators in the SDSS-MaNGA survey. We also investigate if a)the location of a spaxel relative to the galaxy centre and b)the galaxy pair separation have any effect on the local MZR. Results: We find that the correlation between mass and metallicity holds for interacting galaxies at the local level. However, we find two peaks in spaxel distribution, one peak with enriched metallicity and the other with diluted metallicity. We find that the spaxels belonging to the galaxy central regions (i.e. at lower R/Reff) are concentrated close to the two peaks. We also find that the metallicity-diluted spaxels belong to galaxy pairs with closer projected separations and that spaxels with enriched metallicity belong to galaxy pairs with greater projected separations. Conclusions: We find two discrete peaks in the spatially resolved MZR for star-forming spaxels that belong to galaxy pairs. The peaks are likely related to the galaxy projected separation or the stage of the interaction process of a galaxy pair.

astro-ph.GA↗

arXiv2021

Dissecting Nearby Galaxies with piXedfit: I. Spatially Resolved Properties of Stars, Dust, and Gas as Revealed by Panchromatic SED Fitting

We study spatially resolved properties (on spatial scales of $\sim 1-2$ kpc out to at least $3$ effective radii) of the stars, dust, and gas in ten nearby spiral galaxies. The properties of the stellar population and dust are derived by fitting the spatially resolved spectral energy distribution (SED) with more than 20 photometric bands ranging from far-ultraviolet to far-infrared. Our newly developed software piXedfit performs point spread function matching of images, pixel binning, and models the stellar light, dust attenuation, dust emission, and emission from a dusty torus heated by an active galactic nucleus simultaneously through the energy balance approach. With this self-consistent analysis, we present the spatially resolved version of the IRX--$β$ relation, finding that it is consistent with the relationship from the integrated photometry. We show that the old stellar populations contribute to the dust heating, which causes an overestimation of star formation rate (SFR) derived from the total ultraviolet and infrared luminosities on kpc scales. With archival high-resolution maps of atomic and molecular gas, we study the radial variation of the properties of the stellar populations (including stellar mass, age, metallicity, and SFR), dust (including dust mass, dust temperature, and abundance of polycyclic aromatic hydrocarbon), gas, as well as dust-to-stellar mass and dust-to-gas mass ratios. We observe a depletion of molecular gas mass fraction in the central region of the majority of the galaxies, suggesting that the lack of available fuel is an important factor in suppressing the specific SFR at the center.

astro-ph.GA↗

arXiv2021

Jets from MRC 0600-399 bent by magnetic fields in the cluster Abell 3376

Galaxy clusters are known to harbour magnetic fields. The nature of the intra-cluster magnetic fields remains an unresolved question. Intra-cluster magnetic field can be observed at the density contact discontinuity formed by cool and dense plasma running into hot ambient plasma, and the discontinuity exists near the 2nd BCG MRC 0600-399 of a merging galaxy cluster Abell 3376 (z=0.0461, hereafter as A3376). Elongated X-ray image in the east-west direction with a comet-like structure reaches a Mpc-scale (Fig1.(a)). Previous radio observations detected the bent jets from MRC 0600-399, moving in same direction as the sub-cluster's motion against ram pressure.Here we report a new radio observation of a radio galaxy MRC 0600-399 which is 3.4 times and 11 times higher resolution and sensitivity than the previous results. Contrary to typical jets, the MRC 0600-399 shows a 90deg bend at the contact discontinuity and the collimated jets further extend over 100 kpc from the bend point. Diffuse, elongated emission named "double-scythe" structures were detected for the first time. The spectral index flattens downstream of the bend point, indicating cosmic-ray re-acceleration. High-resolution numerical simulations reveal that the ordered magnetic field along the discontinuity plays a significant role in the change in the jet direction. The morphology of the "double-scythe" bear remarkable similarities with the simulations, which strengthens our understanding of the interaction between relativistic electrons and intra-cluster magnetic field.

astro-ph.GA↗

arXiv2021

Constraining the luminosity function of active galactic nuclei through the reionization observations in the SKA era

Ultraviolet (UV) and X-ray photons from active galactic nuclei (AGNs) can ionize hydrogen in the intergalactic medium (IGM). We solve radiative transfer around AGNs in high redshift to evaluate the 21-cm line emission from the neutral hydrogen in the IGM and obtain the radial profile of the brightness temperature in the epoch of reionization. The ionization profile extends over 10 [Mpc] comoving distance which can be observed in the order of 10 [arcmin]. From estimation of the radio galaxy number counts with high sensitivity observation through the Square Kilometre Array (SKA), we investigate the capability of parameter constrains for AGN luminosity function with Fisher analysis for three evolution model through cosmic time. We find that the errors for each parameter are restricted to a few percent when AGNs are sufficiently bright at high redshifts. We also investigate the possibility of further parameter constraints with future observation beyond the era of SKA.

astro-ph.GA↗

arXiv2021

Dynamical Evolution of Voids with Surrounding Gravitational Tidal Field

The void ellipticity distribution today can be well explained by the tidal field. Going a step further from the overall distribution, we investigate individuality on the tidal response of void shape in non-linear dynamical evolution. We perform an N-body simulation and trace individual voids using particle ID. The voids are defined based on Voronoi tessellation and watershed algorithm, using public code VIDE. A positive correlation is found between the time variation of void ellipticity and tidal field around a void if the void maintains its constituent particles. Such voids tend to have smaller mass densities. Conversely, not a few voids significantly deform by particle exchange, rather than the tidal field. Those voids may prevent us from correctly proving a quadrupole field of gravity out of a void shape.

astro-ph.CO↗

arXiv2020

CO Multi-line Imaging of Nearby Galaxies (COMING). IX. $^{12}$CO($J$=2-1)/$^{12}$CO($J$=1-0) line ratio on kiloparsec scales

While molecular gas mass is usually derived from $^{12}$CO($J$=1-0) - the most fundamental line to explore molecular gas - it is often derived from $^{12}$CO($J$=2-1) assuming a constant $^{12}$CO($J$=2-1)/$^{12}$CO($J$=1-0) line ratio ($R_{2/1}$). We present variations of $R_{2/1}$ and effects of the assumption that $R_{2/1}$ is a constant in 24 nearby galaxies using $^{12}$CO data obtained with the Nobeyama 45-m radio telescope and IRAM 30-m telescope. The median of $R_{2/1}$ for all galaxies is 0.61, and the weighted mean of $R_{2/1}$ by $^{12}$CO($J$=1-0) integrated-intensity is 0.66 with a standard deviation of 0.19. The radial variation of $R_{2/1}$ shows that it is high (~0.8) in the inner ~1 kpc while its median in disks is nearly constant at 0.60 when all galaxies are compiled. In the case that the constant $R_{2/1}$ of 0.7 is adopted, we found that the total molecular gas mass derived from $^{12}$CO($J$=2-1) is underestimated/overestimated by ~20%, and at most by 35%. The scatter of a molecular gas surface density within each galaxy becomes larger by ~30%, and at most by 120%. Indices of the spatially resolved Kennicutt-Schmidt relation by $^{12}$CO($J$=2-1) are underestimated by 10-20%, at most 39% in 17 out of 24 galaxies. $R_{2/1}$ has good positive correlations with star-formation rate and infrared color, and a negative correlation with molecular gas depletion time. There is a clear tendency of increasing $R_{2/1}$ with increasing kinetic temperature ($T_{\rm kin}$). Further, we found that not only $T_{\rm kin}$ but also pressure of molecular gas is important to understand variations of $R_{2/1}$. Special considerations should be made when discussing molecular gas mass and molecular gas properties inferred from $^{12}$CO($J$=2-1) instead of $^{12}$CO($J$=1-0).

astro-ph.GA↗

arXiv2020

Spatially Resolved Properties of Galaxies with a Kinematically Distinct Core

Aims. Interacting galaxies show unique irregularities in their kinematic structure. By investigating the spatially resolved kinematics and stellar population properties of galaxies that show irregularities, we can paint a detailed picture of the formation and evolutionary processes that took place during its lifetimes. Methods. In this work, we focus on galaxies with a specific kinematic irregularity, a kinematically distinct stellar core (KDC), in particular, counter-rotating galaxies where the core and main body of the galaxy are rotating in opposite directions. We visually identify eleven MaNGA galaxies with a KDC from their stellar kinematics, and investigate their spatially resolved stellar and gaseous kinematic properties, namely the two-dimensional stellar and gaseous velocity and velocity dispersion (σ) maps. Additionally, we examine the stellar population properties, as well as spatially resolved recent star formation histories using the Dn4000 and Hδ gradients. Results. The galaxies display multiple off-centred, symmetrical peaks in the stellar σ maps. The gaseous velocity and σ maps display regular properties. The stellar population properties and their respective gradients show differing properties depending on the results of the spatially resolved emission line diagnostics of the galaxies, with some galaxies showing inside-out quenching but others not. The star formation histories also largely differ based on the spatially resolved emission line diagnostics, but most galaxies show indications of recent star formation either in their outskirts or core. Conclusions. We find a distinct difference in kinematic and stellar population properties in galaxies with a counter-rotating stellar core, depending on its classification using spatially resolved emission line diagnostics.

astro-ph.GA↗

arXiv2020

An Iterative Reconstruction Algorithm for Faraday Tomography

Faraday tomography offers crucial information on the magnetized astronomical objects, such as quasars, galaxies, or galaxy clusters, by observing its magnetoionic media. The observed linear polarization spectrum is inverse Fourier transformed to obtain the Faraday dispersion function (FDF), providing us a tomographic distribution of the magnetoionic media along the line of sight. However, this transform gives a poor reconstruction of the FDF because of the instrument's limited wavelength coverage. The current Faraday tomography techniques' inability to reliably solve the above inverse problem has noticeably plagued cosmic magnetism studies. We propose a new algorithm inspired by the well-studied area of signal restoration, called the Constraining and Restoring iterative Algorithm for Faraday Tomography (CRAFT). This iterative model-independent algorithm is computationally inexpensive and only requires weak physically-motivated assumptions to produce high fidelity FDF reconstructions. We demonstrate an application for a realistic synthetic model FDF of the Milky Way, where CRAFT shows greater potential over other popular model-independent techniques. The dependence of observational frequency coverage on the various techniques' reconstruction performance is also demonstrated for a simpler FDF. CRAFT exhibits improvements even over model-dependent techniques (i.e., QU-fitting) by capturing complex multi-scale features of the FDF amplitude and polarization angle variations within a source. The proposed approach will be of utmost importance for future cosmic magnetism studies, especially with broadband polarization data from the Square Kilometre Array and its precursors. We make the CRAFT code publicly available.

astro-ph.IM↗

arXiv2020

Constructing a multivariate distribution function with a vine copula: toward multivariate luminosity and mass functions

The need for a method to construct multidimensional distribution function is increasing recently, in the era of huge multiwavelength surveys. We have proposed a systematic method to build a bivariate luminosity or mass function of galaxies by using a copula. It allows us to construct a distribution function when only its marginal distributions are known, and we have to estimate the dependence structure from data. A typical example is the situation that we have univariate luminosity functions at some wavelengths for a survey, but the joint distribution is unknown. Main limitation of the copula method is that it is not easy to extend a joint function to higher dimensions ($d > 2$), except some special cases like multidimensional Gaussian. Even if we find such a multivariate analytic function in some fortunate case, it would often be inflexible and impractical. In this work, we show a systematic method to extend the copula method to unlimitedly higher dimensions by a vine copula. This is based on the pair-copula decomposition of a general multivariate distribution. We show how the vine copula construction is flexible and extendable. We also present an example of the construction of an stellar mass--atomic gas--molecular gas 3-dimensional mass function. We demonstrate the maximum likelihood estimation of the best functional form for this function, as well as a proper model selection via vine copula.

astro-ph.GA↗