分类： 天文学 >> 天文学 提交时间： 2023-02-19
Seyoung Jeon
Sukyoung Yi
Yohan Dubois
Aeree Chung
Julien Devriendt
San Han
Ryan A. Jackson
Taysun Kimm
Christophe Pichon
Jinsu Rhee
摘要： Cluster galaxies exhibit substantially lower star formation rates than field galaxies today, but it is conceivable that clusters were sites of more active star formation in the early universe. Herein, we present an interpretation of the star formation history (SFH) of group/cluster galaxies based on the large-scale cosmological hydrodynamic simulation, Horizon-AGN. We find that massive galaxies in general have small values of e-folding timescales of star formation decay (i.e., ``mass quenching'') regardless of their environment, whilst low-mass galaxies exhibit prominent environmental dependence. In massive host halos (i.e., clusters), the e-folding timescales of low-mass galaxies are further decreased if they reside in such halos for a longer period of time. This ``environmental quenching'' trend is consistent with the theoretical expectation from ram pressure stripping. Furthermore, we define a ``transition epoch'' as where cluster galaxies become less star-forming than field galaxies. The transition epoch of group/cluster galaxies varies according to their stellar and host cluster halo masses. Low-mass galaxies in massive clusters show the earliest transition epoch of $\sim 7.6$ Gyr ago in lookback time. However, it decreases to $\sim 5.2$ Gyr for massive galaxies in low-mass clusters. Based on our findings, we can describe cluster galaxy's SFH with regard to the cluster halo-to-stellar mass ratio.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Harley Katz
Shenghua Liu
Taysun Kimm
Martin P. Rey
Eric P. Andersson
Alex J. Cameron
Francisco Rodriguez-Montero
Oscar Agertz
Julien Devriendt
Adrianne Slyz
摘要： We introduce the PRISM interstellar medium (ISM) model for thermochemistry and its implementation in the RAMSES-RTZ code. The model includes a non-equilibrium primordial, metal, and molecular chemistry network for 115 species coupled to on-the-fly multifrequency radiation transport. PRISM accurately accounts for the dominant ISM cooling and heating processes in the low-density regime (i.e. $\rho<10^5\ {\rm cm^{-3}}$), including photoheating, photoelectric heating, H$_2$ heating/cooling, cosmic-ray heating, H/He cooling, metal-line cooling, CO cooling, and dust cooling (recombination and gas-grain collisions). We validate the model by comparing 1D equilibrium simulations across six dex in metallicity to existing 1D ISM models in the literature. We apply PRISM to high-resolution (4.5 pc) isolated dwarf galaxy simulations that include state-of-the-art models for star formation and stellar feedback to take an inventory of which cooling and heating processes dominate each different gas phase of a galaxy and to understand the importance of non-equilibrium effects. We show that most of the ISM gas is either close to thermal equilibrium or exhibits a slight cooling instability, while from a chemical perspective, the non-equilibrium electron fraction is often more than three times higher or lower than the equilibrium value, which impacts cooling, heating, and observable emission lines. Electron enhancements are attributed to recombination lags while deficits are shown to be due to rapid cosmic-ray heating. The PRISM model and its coupling to RAMSES-RTZ is applicable to a wide variety of astrophysical scenarios, from cosmological simulations to isolated giant molecular clouds, and is particularly useful for understanding how changes to ISM physics impact observable quantities such as metallic emission lines.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
J. K. Jang
Sukyoug K. Yi
Yohan Dubois
Jinsu Rhee
Christophe Pichon
Taysun Kimm
Julien Devriendt
Marta Volonteri
Sugata Kaviraj
Sebastien Peirani
Sree Oh
Scott Croom
摘要： Based on the recent advancements in the numerical simulations of galaxy formation, we anticipate the achievement of realistic models of galaxies in the near future. Morphology is the most basic and fundamental property of galaxies, yet observations and simulations still use different methods to determine galaxy morphology, making it difficult to compare them. We hereby perform a test on the recent NewHorizon simulation which has spatial and mass resolutions that are remarkably high for a large-volume simulation, to resolve the situation. We generate mock images for the simulated galaxies using SKIRT that calculates complex radiative transfer processes in each galaxy. We measure morphological indicators using photometric and spectroscopic methods following observer's techniques. We also measure the kinematic disk-to-total ratios using the Gaussian mixture model and assume that they represent the true structural composition of galaxies. We found that spectroscopic indicators such as $V/{\sigma}$ and ${\lambda}_{R}$ closely trace the kinematic disk-to-total ratios. In contrast, photometric disk-to-total ratios based on the radial profile fitting method often fail to recover the true kinematic structure of galaxies, especially for small galaxies. We provide translating equations between various morphological indicators.
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