Myoungwon Jeon

Abstract We investigate the star formation history (SFH) and chemical evolution of isolated analogs of Local Group (LG) ultrafaint dwarf galaxies (UFDs; stellar mass range of ) and gas-rich, low-mass dwarfs (Leo P analogs; stellar mass range of ). We perform a suite of cosmological hydrodynamic zoom-in simulations to follow their evolution from the era of the first generation of stars down to z = 0. We confirm that reionization, combined with supernova (SN) feedback, is primarily responsible for

Recent work suggests that the first generation of stars, the so-called Population III (Pop III), could have formed primarily in binaries or as members of small multiple systems. Here we investigate the impact of X-ray feedback from high-mass X-ray binaries (HMXBs) left behind in stellar binary systems after the primary forms a black hole (BH), accreting gas at a high rate from the companion, a process that is thought to be favoured at the low metallicities characteristic of high-redshift gas. Th

We use cosmological simulations to assess how the explosion of the first stars in supernovae (SNe) influences early cosmic history. Specifically, we investigate the impact by SNe on the host systems for Population III (Pop III) star formation and explore its dependence on halo environment and Pop III progenitor mass. We then trace the evolution of the enriched gas un-til conditions are met to trigger second-generation star formation. To this extent, we quantify the recovery timescale, which meas

We introduce a new suite of radiation-hydrodynamical simulations of galaxy formation and reionization called Aurora. The Aurora simulations make use of a spatially adaptive radiative transfer technique that lets us accurately capture the small-scale structure in the gas at the resolution of the hydrodynamics, in cosmological volumes. In addition to ionizing radiation, Aurora includes galactic winds driven by star formation and the enrichment of the universe with metals synthesized in the stars.

Abstract We measure homogeneous distances to M31 and 38 associated stellar systems (−16.8 ≤ M V ≤ −6.0), using time-series observations of RR Lyrae stars taken as part of the Hubble Space Telescope Treasury Survey of M31 Satellites. From >700 orbits of new/archival Advanced Camera for Surveys imaging, we identify >4700 RR Lyrae stars and determine their periods and mean magnitudes to a typical precision of 0.01 day and 0.04 mag. Based on period–Wesenheit–metallicity relationships consisten

We investigate the formation of a galaxy reaching a virial mass of ≈108 M⊙ at z ≈ 10 by carrying out a zoomed radiation-hydrodynamical cosmological simulation. This simulation traces Population III (Pop III) star formation, characterized by a modestly top-heavy initial mass function, and considers stellar feedback such as photoionization heating from Pop III and Population II (Pop II) stars, mechanical and chemical feedback from supernovae (SNe), and X-ray feedback from accreting black holes and

ABSTRACT Carbon enhanced metal poor (CEMP)-no stars, a subset of CEMP stars ($\rm [C/Fe]\ge 0.7$ and $\rm [Fe/H]\lesssim -1$) have been discovered in ultra-faint dwarf (UFD) galaxies, with $M_{\rm vir}\approx 10^8{\, \mathrm{ M}_\odot }$ and $M_{\ast }\approx 10^3-10^4{\, \mathrm{ M}_\odot }$ at z = 0, as well as in the halo of the Milky Way (MW). These CEMP-no stars are local fossils that may reflect the properties of the first (Pop III) and second (Pop II) generation of stars. However, cosmolo

We investigate the impact of a cosmic X-ray background (CXB) on Population III stars forming in a minihalo at z ≃ 25. Using the smoothed particle hydrodynamics code gadget-2, we attain sufficient numerical resolution to follow gas collapsing into the centre of the minihalo from cosmological initial conditions up to densities of 1012 cm−3, at which point we form sink particles. This allows us to study how the presence of a CXB affects the formation of H2 and HD in the gas prior to becoming fully

ABSTRACT Highly r-process enhanced metal-poor stars (MP r-II; $\rm [Eu/Fe]\gt 1$ and $\rm [Fe/H]\lesssim -1.5$) have been observed in ultra-faint dwarf (UFD) galaxy, specifically in Reticulum II (Ret II). The fact that only a few UFDs contain such stars implies that the r-process site may reflect very rare but individually prolific events, such as neutron star mergers (NSMs). Considering the relatively short star formation history of UFDs, it is puzzling how they could experience such a rare phe

Abstract We examine the assembly process and the observability of a first galaxy ($M_{\rm vir}\approx 10^9{\, \rm M_\odot }$ at z ≈ 8) with cosmological zoom-in, hydrodynamic simulations, including the radiative, mechanical, and chemical feedback exerted by the first generations of stars. To assess the detectability of such dwarf systems with the upcoming James Webb Space Telescope (jwst), we construct the spectral energy distribution for the simulated galaxy in a post-processing fashion. We fin

We study the behaviors of galactic disks in triaxial halos both numerically and analytically to see if warps can be excited and sustained in triaxial potentials. We consider the following two scenarios: 1) galactic disks that are initially tilted relative to the equatorial plane of the halo (for a pedagogical purpose), and 2) tilted infall of dark matter relative to the equatorial plane of the disk and the halo. With numerical simulations of 100,000 disk particles in a fixed halo potential, we f

ABSTRACT Observing the first generation of stars, Population III (Pop III), is still a challenge even with the JWST due to their faintness. Instead, searching for fossil records of Pop III stars in nearby dwarf galaxies provides an alternative method for studying their physical properties. It is intriguing that a star recently discovered in the Sculptor dwarf galaxy, named AS0039, is considered to show the unique signature of a Pop III star. The detailed abundance patterns of AS0039 are well mat

Abstract We investigate how patchy reionization affects the star formation history (SFH) and stellar metallicity of ultrafaint dwarf galaxies (UFDs). Patchy reionization refers to varying ultraviolet background strengths depending on a galaxy’s environment. Recent observations highlight the significance of this effect on UFDs, as UFDs can have different SFHs depending on their relative position with respect to their host halo during the period of reionization. However, most cosmological hydrodyn

We study how the first galaxies were assembled under feedback from the accretion onto a central black hole (BH) that is left behind by the first generation of metal-free stars through selfconsistent, cosmological simulations. X-ray radiation from the accretion of gas onto BH remnants of Population III (Pop III) stars, or from high-mass X-ray binaries (HMXBs), again involving Pop III stars, influences the mode of second generation star formation. We track the evolution of the black hole accretion

ABSTRACT We examine the impact of various Initial Mass Function (IMF) sampling and supernova (SN) feedback injection methods on the star formation and metal enrichment histories of Ultra-Faint Dwarf (UFD) galaxy analogs. These analogs, characterized by $M_{\rm vir}\approx 10^8{\, \mathrm{ M}_\odot }$ and $M_{\ast }\lesssim 10^{4.5}\,{\, \mathrm{ M}_\odot }$ at $z=0$, are simulated using high-resolution cosmological hydrodynamic zoom-in simulations with a gas particle mass resolution of $\sim 63\