Ji Hoon Kim
A5100410796- Galaxies: Formation, Evolution, Phenomena
- Astronomy and Astrophysical Research
- Stellar, planetary, and galactic studies
- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- Astrophysics and Star Formation Studies
- Astrophysics and Cosmic Phenomena
- GaN-based semiconductor devices and materials
- Pulsars and Gravitational Waves Research
- Astronomical Observations and Instrumentation
- Ga2O3 and related materials
- Metal and Thin Film Mechanics
- Astro and Planetary Science
- Adaptive optics and wavefront sensing
- Advanced Measurement and Metrology Techniques
- Scientific Research and Discoveries
- Radio Astronomy Observations and Technology
- Magnetic Properties and Applications
- Infrared Target Detection Methodologies
- Neutrino Physics Research
- Silicon Carbide Semiconductor Technologies
- Advanced Optical Sensing Technologies
- Advanced Vision and Imaging
- Optical Systems and Laser Technology
- High-pressure geophysics and materials
Seoul National University
2012-2024
National Astronomical Observatory of Japan
2014-2022
Subaru (Japan)
2014-2022
National Institutes of Natural Sciences
2019-2022
Weatherford College
2022
Korea University
2013
National Research Foundation
2012
Korea Electronics Technology Institute
2011-2012
National Research Foundation of Korea
2012
University of Maryland, College Park
2007-2010
The first detected gravitational wave from a neutron star merger was GW170817. In this study, we present J-GEM follow-up observations of SSS17a, an electromagnetic counterpart SSS17a shows 2.5-mag decline in the $z$-band 1.7 days to 7.7 after merger. Such rapid is not comparable with supernovae light curves at any epoch. color also evolves rapidly and becomes redder for later epochs; $z-H$ changed by approximately 2.5 mag period 0.7 days. evolution both optical brightness are consistent...
Many results in modern astrophysics rest on the notion that Initial Mass Function (IMF) is universal. Our observations of HI selected galaxies light H-alpha and far-ultraviolet (FUV) challenge this notion. The flux ratio H-alpha/FUV from these two star formation tracers shows strong correlations with surface-brightness R band: Low Surface Brightness (LSB) have lower ratios compared to High expectations equilibrium models using commonly favored IMF parameters. Weaker but significant...
We present a catalog of extended low-surface-brightness galaxies (LSBGs) identified in the Wide layer Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Using first ${\sim}$200 deg$^2$ survey, we have uncovered 781 LSBGs, spanning red ($g-i\geq0.64$) and blue ($g-i<0.64$) colors wide range morphologies. Since focus on ($r_\mathrm{eff}=2.5$-$14^{\prime\prime}$), our sample is likely dominated by low-redshift objects. define LSBGs to mean surface brightnesses...
Abstract Recent detection of gravitational waves from a neutron star (NS) merger event GW170817 and identification an electromagnetic counterpart provide unique opportunity to study the physical processes in NS mergers. To derive properties ejected material merger, we perform radiative transfer simulations kilonova, optical near-infrared emissions powered by radioactive decays r-process nuclei synthesized merger. We find that observed emission lasting for &gt;10 d is explained 0.03 M⊙...
We present optical-line gas metallicity diagnostics established by the combination of local SDSS galaxies and largest compilation extremely metal-poor (EMPGs) including new EMPGs identified Subaru EMPRESS survey. A total 103 are included that cover a large parameter space magnitude (Mi=-19 to -7) H-beta equivalent width (10-600 Ang), i.e., wide ranges stellar mass star-formation rate. Using reliable measurements direct method for these galaxies, we derive relationships between strong ratios...
We present the rest-frame optical spectral properties of 155 luminous quasars at 3.3<z<6.4 taken with AKARI space telescope, including first detection H$\alpha$ emission line as far out z~6. extend scaling relation between continuum and luminosity active galactic nuclei (AGNs) to high luminosity, redshift regime that has rarely been probed before. Remarkably, we find a single log-linear can be applied 5100${\rm \AA}$ AGN luminosities over wide range (10$^{42}$<$L_{5100}$<10$^{47}$ergs/s) or...
We report the late-time evolution of Type IIb supernova (SN IIb) 2013df. SN 2013df showed a dramatic change in its spectral features at ∼1 yr after explosion. Early on it typical characteristics shared by SNe IIb/Ib/Ic dominated metal emission lines, while later was broad and flat-topped Hα He i emissions. The spectra are strikingly similar to 1993J, which is only previous example clearly showing same transition. This fully explained energy input from 56Co decay interaction between ejecta...
We have initiated a new survey for local extremely metal-poor galaxies (EMPGs) with Subaru/Hyper Suprime-Cam (HSC) large-area (~500 deg^2) optical images reaching 5 sigma limit of ~26 magnitude, about 100 times deeper than the Sloan Digital Sky Survey (SDSS). To select Z/Z_sun<0.1 EMPGs from ~40 million sources detected in Subaru images, we first develop machine-learning (ML) classifier based on deep neural network algorithm training data set consisting photometry galaxy, star, and QSO...
Abstract We present Keck/LRIS follow-up spectroscopy for 13 photometric candidates of extremely metal-poor galaxies (EMPGs) selected by a machine-learning technique applied to the deep (∼26 AB mag) optical and wide-area (∼500 deg 2 ) Subaru imaging data in EMPRESS survey. Nine out are EMPGs with an oxygen abundance (O/H) less than ∼10% solar value ⊙ , four sources contaminants moderately metal-rich or no emission-line objects. Notably, two nine have low stellar masses abundances 5 × 10 4 –7...
Abstract We present the demography of dynamics and gas mass fraction 33 extremely metal-poor galaxies (EMPGs) with metallicities 0.015–0.195 Z ⊙ low stellar masses 10 4 –10 8 M in local universe. conduct deep optical integral field spectroscopy (IFS) for low-mass EMPGs medium-high resolution ( R = 7500) grism m Subaru FOCAS IFU instrument by EMPRESS 3D survey, investigate H α emission EMPGs. Exploiting high enough galaxies, we derive lines fitting three-dimensional disk models. obtain an...
Abstract The circumstellar envelope of the carbon star CW Leo exhibited various unexpected changes in recent optical imaging observations. We have performed a follow-up observation using Near-infrared Integral-Field Spectrograph (NIFS) equipped on Gemini-North telescope. report near-infrared counterparts local brightness peak at stellar position Leo. On other hand, second detected short wavelengths J band coincides with brightest, bluest images. absorption features K are minimized radius 0...
We examine the amplitude of rotation velocity that can be attributed to dark matter halos disk galaxies, focusing on well measured intermediate radii. The data for 60 galaxies spanning a large range mass and Hubble types, taken together, are consistent with halo log(Vh) = C + B log(r) 1.47 (+0.15, -0.19) 1/2 over 1 < r 74 kpc. in stems from different choices stellar estimator, minimum maximum disk. For all plausible mass, implied densities lower than expected structure formation simulations...
We present results from the first systematic search for outlying H ii regions, as part of a sample 96 emission-line point sources (referred to ELdots–emission-line dots) derived NOAO Survey Ionization in Neutral Gas Galaxies (SINGG). Our automated ELdot finder searches SINGG narrowband and continuum images high equivalent width outside optical radius target galaxy (>2 × r25 R band). Follow-up long-slit spectroscopy deep Galaxy Evolution Explorer (GALEX) (exposure time >1000 s) distinguish...
We present optical long-slit spectroscopy and far-ultraviolet to near-infrared spectral energy distribution fitting of two diffuse dwarf galaxies, LSBG-285 LSBG-750, which were recently discovered by the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). measure redshifts using H$\alpha$ line emission, find that these galaxies are at comoving distances ${\approx}25$ ${\approx}41$ Mpc, respectively, after correcting for local velocity field. They have effective radii $r_\mathrm{eff}=1.2$...
Recent studies suggest that faint active galactic nuclei may be responsible for the reionization of universe. Confirmation this scenario requires spectroscopic identification quasars (M1450 > −24 mag) at z ≳ 6, but only a very small number such have been spectroscopically identified so far. Here, we report discovery quasar IMS J220417.92+011144.8 ∼ 6 in 12.5 deg2 region SA22 field Infrared Medium-deep Survey (IMS). The spectrum shows sharp break ∼8443 Å, with emission lines redshifted to =...
Abstract We present element abundance ratios and ionizing radiation of local young low-mass (∼10 6 M ⊙ ) extremely metal-poor galaxies (EMPGs) with a 2% solar oxygen (O/H) high specific star formation rate (sSFR ∼ 300 Gyr −1 other (extremely) galaxies, which are compiled from Extremely Metal-Poor Representatives Explored by the Subaru Survey (EMPRESS) literature. Weak emission lines such as [Fe iii ] λ 4658 He ii 4686 detected in very deep optical spectra EMPGs taken 8 m class telescopes,...
JINGLE is a new JCMT legacy survey designed to systematically study the cold interstellar medium of galaxies in local Universe. As part we perform 850 µm continuum measurements with SCUBA-2 for representative sample 193 Herschel-selected M* > 109 M⊙, as well integrated CO(2–1) line fluxes RxA3m subset 90 these galaxies. The selected from fields covered by Herschel-ATLAS that are also targeted MaNGA optical integral-field spectroscopic survey. observations combined multiwavelength ancillary...
Faint $z\sim5$ quasars with $M_{1450}\sim-23$ mag are known to be the potentially important contributors ultraviolet ionizing background in post-reionization era. However, their number density has not been well determined, making it difficult assess role early ionization of intergalactic medium (IGM). In this work, we present updated results our quasar survey using Infrared Medium-deep Survey (IMS), a near-infrared imaging covering an area 85 deg$^{2}$. From spectroscopic observations Gemini...
Abstract We study emission line profiles of 21 nearby low-mass ( M * = 10 4 –10 7 ⊙ ) galaxies in deep medium-high resolution spectra taken with Magellan/MagE. These are actively star-forming systems high specific star formation rates ∼100–1000 Gyr −1 that well above the main sequence and its extrapolation. identify broad-line components H α [O iii ] λ 5007 14 out cannot be explained by MagE instrumental profile or natural broadening emission. conduct double-Gaussian fitting to galaxies,...
Several lines of argument support the existence a link between activity at nuclei galaxies, in form an accreting supermassive black hole, and star formation these galaxies. Radio jets have long been argued to be ideal mechanism that allows active galactic (AGNs) interact with their host galaxies affect formation. We use sample radio sources North Ecliptic Pole (NEP) field study nature this putative link, by means spectral energy distribution (SED) fitting. employ excellent coverage AKARI...
Abstract Large diffuse galaxies are hard to find, but understanding the environments where they live, their numbers, and ultimately origins, is of intense interest importance for galaxy formation evolution. Using Subaru’s Hyper Suprime-Cam Strategic Survey Program, we perform a systematic search low surface brightness present novel effective methods detecting modeling them. As case study, surveyed 922 Milky Way analogs in nearby Universe (0.01 < z 0.04) built large sample satellite that...
We investigate the connection between starburst and AGN activity by comparing 3.3 {\mu}m PAH eimission with properties. Utilizing slit-less spectroscopic capability of AKARI space telescope, we observe moderate-luminosity Type I at z~0.4 to measure global activity. The emissions are detected for 7 out 26 target galaxies. find no strong correlation emission luminosity in limted range observed luminosity, suggesting that star formation may not be tightly related Combining our measurements...
We perform a $z$-band survey for an optical counterpart of binary neutron star coalescence GW170817 with Subaru/Hyper Suprime-Cam. Our untargeted transient search covers $23.6$ deg$^2$ corresponding to the $56.6\%$ credible region and reaches $50\%$ completeness magnitude $20.6$ mag on average. As result, we find 60 candidates extragalactic transients, including J-GEM17btc (a.k.a. SSS17a/DLT17ck). While is associated NGC 4993 that firmly located inside 3D skymap GW170817, other 59 do not...
We present 2.5-5.0 $\mu$m spectra of 83 nearby ($0.002\,<\,z\,<\,0.48$) and bright ($K<14$mag) type-1 active galactic nuclei (AGNs) taken with the Infrared Camera (IRC) on board $\it{AKARI}$. The spectral region contains emission lines such as Br$\beta$ (2.63 $\mu$m), Br$\alpha$ (4.05 polycyclic aromatic hydrocarbons (PAH; 3.3 which can be used for studying black hole (BH) masses star formation activities in host galaxies AGNs. also suffers less dust extinction than ultra violet (UV) or...