arXiv subjects

Shun Nishida

Publications and source records attributed to Shun Nishida.

3 recordsLinked to original sources

arXiv2026

VENUS: Strong Lens Mass Models and Einstein Radii of 60 Galaxy Clusters

We present the strong lens mass modeling result of 60 galaxy clusters targeted by Vast Exploration for Nascent, Unexplored Sources (VENUS), the James Webb Space Telescope (JWST) multi-epoch Treasury program. We obtain refined mass models for the 60 clusters with the glafic software by fitting positions of $\sim 4500$ multiple images, $\sim 1150$ of which are newly identified multiple images with help of multi-band JWST images. Each cluster contains typically $\sim 50$ multiple images, thanks to the selection of target clusters based on their high lensing strengths. We validate our models with the Jackknife method. The median Einstein radius is $\sim 30''$ and the distribution of the Einstein radii extends out to $\sim 60''$ for the source redshift of 9, which confirms that their lensing strengths are indeed among the highest known to date. For the source redshift of 9, we identify MACS J0717.5+3745, MACS J0600.1$-$2008, and PLCK G287.0+32.9 as clusters with the largest Einstein radii as well as the largest areas of the high-magnification ($|μ|>10$) regions. We find that the observed Einstein radii of VENUS clusters are fully compatible with the standard cold dark matter model.

astro-ph.CO↗

arXiv2026

A stellar dynamical mass measurement of an inactive black hole at redshift 2

Supermassive black holes and their host galaxies grow together over time, producing correlations between the black hole mass and various galaxy properties. Determining the evolution of these correlations requires precise measurements of the masses of distant black holes. We observe the gravitationally lensed quiescent galaxy MRG-M0138, at redshift 1.95, using JWST integral field spectroscopy to spatially resolve the kinematics of stars within the black hole's sphere of influence. By using a foreground lens model and fitting stellar dynamical models, we determine the mass of its inactive black hole, $M_{\bullet}=6.0^{+2.1}_{-1.7}\times10^9$ solar masses. Comparing this measurement to local galaxies, we find that $M_{\bullet}$ is higher than expected given the galaxy's bulge mass, but consistent with the correlation with stellar velocity dispersion.

astro-ph.GA↗

arXiv2025

The Jackknife method as a new approach to validate strong lens mass models

The accuracy of a mass model in the strong lensing analysis is crucial for unbiased predictions of physical quantities such as magnifications and time delays. While the mass model is optimized by changing parameters of the mass model to match predicted positions of multiple images with observations, positional uncertainties of multiple images often need to be boosted to take account of the complex structure of dark matter in lens objects, making the interpretation of the chi-square value difficult. We introduce the Jackknife method as a new method to validate strong lens mass models, specifically focusing on cluster-scale mass modeling. In this approach, we remove multiple images of a source from the fitting and optimize the mass model using multiple images of the remaining sources. We then calculate the multiple images of the removed source and quantitatively evaluate how well they match the observed positions. We find that the Jackknife method performs effectively in simulations using a simple model. We also demonstrate our method with mass modeling of the galaxy cluster MACS J0647.7+7015. We discuss the potential of using the Jackknife method to validate the error estimation of the physical quantities by the Markov Chain Monte Carlo.

astro-ph.CO↗