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Dohyeong Kim

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astro-ph.GA math.NT astro-ph.CO astro-ph.HE Computation and Language hep-th Machine Learning math.AT math.QA Robotics

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preprint2026arXiv

Towards Efficient and Expressive Offline RL via Flow-Anchored Noise-conditioned Q-Learning

We propose Flow-Anchored Noise-conditioned Q-Learning (FAN), a highly efficient and high-performing offline reinforcement learning (RL) algorithm. Recent work has shown that expressive flow policies and distributional critics improve offline RL performance, but at a high computational cost. Specifically, flow policies require iterative sampling to produce a single action, and distributional critics require computation over multiple samples (e.g., quantiles) to estimate value. To address these inefficiencies while maintaining high performance, we introduce FAN. Our method employs a behavior regularization technique that utilizes only a single flow policy iteration and requires only a single Gaussian noise sample for distributional critics. Our theoretical analysis of convergence and performance bounds demonstrates that these simplifications not only improve efficiency but also lead to superior task performance. Experiments on robotic manipulation and locomotion tasks demonstrate that FAN achieves state-of-the-art performance while significantly reducing both training and inference runtimes. We release our code at https://github.com/brianlsy98/FAN.

preprint2022arXiv

KOBEST: Korean Balanced Evaluation of Significant Tasks

A well-formulated benchmark plays a critical role in spurring advancements in the natural language processing (NLP) field, as it allows objective and precise evaluation of diverse models. As modern language models (LMs) have become more elaborate and sophisticated, more difficult benchmarks that require linguistic knowledge and reasoning have been proposed. However, most of these benchmarks only support English, and great effort is necessary to construct benchmarks for other low resource languages. To this end, we propose a new benchmark named Korean balanced evaluation of significant tasks (KoBEST), which consists of five Korean-language downstream tasks. Professional Korean linguists designed the tasks that require advanced Korean linguistic knowledge. Moreover, our data is purely annotated by humans and thoroughly reviewed to guarantee high data quality. We also provide baseline models and human performance results. Our dataset is available on the Huggingface.

preprint2022arXiv

Metallicity-PAH Relation of MIR-selected Star-forming Galaxies in AKARI North Ecliptic Pole-wide Survey

We investigate the variation in the mid-infrared spectral energy distributions of 373 low-redshift ( $z<0.4$ ) star-forming galaxies, which reflects a variety of polycyclic aromatic hydrocarbon (PAH) emission features. The relative strength of PAH emission is parameterized as $q_\mathrm{PAH}$ , which is defined as the mass fraction of PAH particles in the total dust mass. With the aid of continuous mid-infrared photometric data points covering 7-24 $μ$ m and far-infrared flux densities, $q_\mathrm{PAH}$ values are derived through spectral energy distribution fitting. The correlation between $q_\mathrm{PAH}$ and other physical properties of galaxies, i.e., gas-phase metallicity ( $12+\mathrm{log(O/H)}$ ), stellar mass, and specific star-formation rate (sSFR) are explored. As in previous studies, $q_\mathrm{PAH}$ values of galaxies with high metallicity are found to be higher than those with low metallicity. The strength of PAH emission is also positively correlated with the stellar mass and negatively correlated with the sSFR. The correlation between $q_\mathrm{PAH}$ and each parameter still exists even after the other two parameters are fixed. In addition to the PAH strength, the application of metallicity-dependent gas-to-dust mass ratio appears to work well to estimate gas mass that matches the observed relationship between molecular gas and physical parameters. The result obtained will be used to calibrate the observed PAH luminosity-total infrared luminosity relation, based on the variation of MIR-FIR SED, which is used in the estimation of hidden star formation.

preprint2022arXiv

Path Integrals and p-adic L-functions

We prove an arithmetic path integral formula for the inverse p-adic absolute values of the Kubota-Leopoldt p-adic L-functions at roots of unity.

preprint2022arXiv

The Infrared Medium-deep Survey. IX. Discovery of Two New $z\sim6$ Quasars and Space Density down to $M_{1450}\sim-23.5$ mag

We present the result of the Infrared Medium-deep Survey (IMS) $z\sim6$ quasar survey, using the combination of the IMS near-infrared images and the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) optical images. The traditional color-selection method results in 25 quasar candidates over $86$ deg $^{2}$ . We introduce the corrected Akaike Information Criterion (AICc) with the high-redshift quasar and late-type star models to prioritize the candidates efficiently. Among the color-selected candidates, seven plausible candidates finally passed the AICc selection of which three are known quasars at $z\sim6$ . The follow-up spectroscopic observations for the remaining four candidates were carried out, and we confirmed that two out of four are $z\sim6$ quasars. With this complete sample, we revisited the quasar space density at $z\sim6$ down to $M_{1450}\sim-23.5$ mag. Our result supports the low quasar space density at the luminosity where the quasar's ultraviolet ionizing emissivity peaks, favoring a minor contribution of quasars to the cosmic reionization.

preprint2021arXiv

Batalin-Vilkovisky formalism in the $p$ -adic Dwork theory

The goal of this article is to develop BV (Batalin-Vilkovisky) formalism in the $p$ -adic Dwork theory. Based on this formalism, we explicitly construct a $p$ -adic dGBV algebra (differential Gerstenhaber-Batalin-Vilkovisky algebra) for a smooth projective complete intersection variety $X$ over a finite field, whose cohomology gives the $p$ -adic Dwork cohomology of $X$ , and its cochain endomorphism (the $p$ -adic Dwork Frobenius operator) which encodes the information of the zeta function $X$ . As a consequence, we give a modern deformation theoretic interpretation of Dwork's theory of the zeta function of $X$ and derive a formula for the $p$ -adic Dwork Frobenius operator in terms of homotopy Lie morphisms and the Bell polynomials.

preprint2020arXiv

Gemini Multi-Object Spectrograph Integral Field Unit Spectroscopy of the Double-peaked Broad Emission Line of a Red Active Galactic Nucleus

Galaxy mergers are expected to produce multiple supermassive black holes (SMBHs) in close-separation, but the detection of such SMBHs has been difficult. 2MASS J165939.7 $+$ 183436 is a red active galactic nucleus (AGN) that is a prospective merging SMBH candidate owing to its merging features in Hubble Space Telescope imaging and double-peaked broad emission lines (BELs). Herein, we report a Gemini Multi-Object Spectrograph Integral Field Unit observation of a double-peaked broad H $α$ line of 2MASS J165939.7 $+$ 183436. Furthermore, we confirm the existence of two BEL peaks that are kinematically separated by 3000\, $\rm km\,s^{-1}$ , with the SMBH of each BEL component weighing at $10^{8.92\pm0.06}\,M_{\rm \odot}$ and $10^{7.13\pm0.06}\,M_{\rm \odot}$ , if they arise from independent BELs near the two SMBHs. The BEL components were not separated at $>0\farcs1$; however, under several plausible assumptions regarding the fitting of each spaxel, the two components are found to be spatially separated at $0\farcs085$ ( $\sim250$ \,pc). Different assumptions for the fitting can lead to a null ($< 0\farcs05$) or a larger spatial separation ($\sim0\farcs15$). Given the uncertainty regarding the spatial separation, various models, such as the disk emitter and multiple SMBH models, are viable solutions to explain the double BEL components. These results will promote future research for finding more multiple SMBH systems in red AGNs, and higher-resolution imaging validates these different models.

preprint2020arXiv

The Infrared Medium-deep Survey. \Romannum{7}. Faint Quasars at $z \sim 5$ in the ELAIS-N1 Field

The intergalactic medium (IGM) at $z\sim$ 5 to 6 is largely ionized, and yet the main source for the IGM ionization in the early universe is uncertain. Of the possible contributors are faint quasars with $-26 \lesssim M_{\rm 1450} \lesssim -23$ , but their number density is poorly constrained at $z\sim5$ . In this paper, we present our survey of faint quasars at $z\sim5$ in the European Large-Area {\it ISO} Survey-North 1 (ELAIS-N1) field over a survey area of 6.51 deg $^2$ and examine if such quasars can be the dominant source of the IGM ionization. We use the deep optical/near-infrared data of the ELAIS-N1 field as well as the additional medium-band observations to find $z \sim 5$ quasars through a two-step approach using the broadband color selection, and SED fitting with the medium-band information included. Adopting Bayesian information criterion, we identify ten promising quasar candidates. Spectra of three of the candidates are obtained, confirming all of them to be quasars at $z\sim5$ and supporting the reliability of the quasar selection. Using the promising candidates, we derive the $z\sim5$ quasar luminosity function at $-26 \lesssim M_{\rm 1450} \lesssim -23$ . The number density of faint $z\sim5$ quasars in the ELAIS-N1 field is consistent with several previous results that quasars are not the main contributors to the IGM-ionizing photons at $z\sim5$

preprint2015arXiv

A modular approach to Thue-Mahler equations

Let $h(x,y)$ be a non-degenerate binary cubic form with integral coefficients, and let $S$ be an arbitrary finite set of prime numbers. By a classical theorem of Mahler, there are only finitely many pairs of relatively prime integers $x,y$ such that $h(x,y)$ is an $S$ -unit. In the present paper, we reverse a well known argument, which seems to go back to Shafarevich, and use the modularity of elliptic curves over $\mathbb{Q}$ to give upper bounds for the number of solutions of such a Thue-Mahler equation. In addition, our methods gives an effective method for determining all solutions, and we use Cremona's Elliptic Curve Database to give a wide range of numerical examples.

preprint2015arXiv

Accretion Rates of Red Quasars from the Hydrogen P $β$ line

Red quasars are thought to be an intermediate population between merger-driven star-forming galaxies in dust-enshrouded phase and normal quasars. If so, they are expected to have high accretion ratios, but their intrinsic dust extinction hampers reliable determination of Eddington ratios. Here, we compare the accretion rates of 16 red quasars at $z \sim 0.7$ to those of normal type 1 quasars at the same redshift range. The red quasars are selected by their red colors in optical through near-infrared (NIR) and radio detection. The accretion rates of the red quasars are derived from the P $β$ line in NIR spectra, which is obtained by the SpeX on the Infrared Telescope Facility (IRTF) in order to avoid the effects of dust extinction. We find that the measured Eddington ratios ( $L_{\rm bol}$ / $L_{\rm Edd} \simeq 0.69$ ) of red quasars are significantly higher than those of normal type 1 quasars, which is consistent with a scenario in which red quasars are the intermediate population and the black holes of red quasars grow very rapidly during such a stage.

preprint2015arXiv

Descent for the punctured universal elliptic curve, and the average number of integral points on elliptic curves

We show that the average number of integral points on elliptic curves, counted modulo the natural involution on a punctured elliptic curve, is bounded from above by $2.1 \times 10^8$ . To prove it, we design a descent map, whose prototype goes at least back to Mordell, which associates a pair of binary forms to an integral point on an elliptic curve. Other ingredients of the proof include the upper bounds for the number of solutions of a Thue equation by Evertse and Akhtari-Okazaki, and the estimation of the number of binary quartic forms by Bhargava-Shankar. Our method applies to $S$ -integral points to some extent, although our present knowledge is insufficient to deduce an upper bound for the average number of them. We work out the numerical example with $S=\{2\}$ .

preprint2015arXiv

Discovery of A Faint Quasar at z~6 and Implications for Cosmic Reionization

Recent studies suggest that faint active galactic nuclei may be responsible for the reionization of the universe. Confirmation of this scenario requires spectroscopic identification of faint quasars ( $M_{1450}>-24$ mag) at $z \gtrsim6$ , but only a very small number of such quasars have been spectroscopically identified so far. Here, we report the discovery of a faint quasar IMS J220417.92+011144.8 at z~6 in a 12.5 deg $^{2}$ region of the SA22 field of the Infrared Medium-deep Survey (IMS). The spectrum of the quasar shows a sharp break at $\sim8443~\rmÅ$ , with emission lines redshifted to $z=5.944 \pm 0.002$ and rest-frame ultraviolet continuum magnitude $M_{1450}=-23.59\pm0.10$ AB mag. The discovery of IMS J220417.92+011144.8 is consistent with the expected number of quasars at z~6 estimated from quasar luminosity functions based on previous observations of spectroscopically identified low-luminosity quasars . This suggests that the number of $M_{1450}\sim-23$ mag quasars at z~6 may not be high enough to fully account for the reionization of the universe. In addition, our study demonstrates that faint quasars in the early universe can be identified effectively with a moderately wide and deep near-infrared survey such as the IMS.

preprint2015arXiv

Rest-frame Optical Spectra and Black Hole Masses of 3<z<6 Quasars

We present the rest-frame optical spectral properties of 155 luminous quasars at 3.3<z<6.4 taken with the AKARI space telescope, including the first detection of H $α$ emission line as far out as z~6. We extend the scaling relation between the rest-frame optical continuum and line luminosity of active galactic nuclei (AGNs) to the high luminosity, high redshift regime that has rarely been probed before. Remarkably, we find that a single log-linear relation can be applied to the 5100 ${\rm Å}$ and H $α$ AGN luminosities over a wide range of luminosity (10 $^{42}$ < $L_{5100}$ <10 $^{47}$ ergs/s) or redshift (0<z<6), suggesting that the physical mechanism governing this relation is unchanged from z=0 to 6, over five decades in luminosity. Similar scaling relations are found between the optical and the UV continuum luminosities or line widths. Applying the scaling relations to the H $β$ black hole mass ( $M_{\rm BH}$ ) estimator of local AGNs, we derive the $M_{\rm BH}$ estimators based on H $α$ , MgII, and CIV lines, finding that the UV-line based masses are overall consistent with the Balmer-line based, but with a large intrinsic scatter of 0.40dex for the CIV estimates. Our 43 $M_{\rm BH}$ estimates from H $α$ confirm the existence of BHs as massive as ~10 $^{10}M_{\odot}$ out to z~5, and provide a secure footing for previous MgII-line based studies that a rapid $M_{\rm BH}$ growth has occurred in the early universe.

preprint2015arXiv

The AKARI 2.5-5.0 Micron Spectral Atlas of Type-1 Active Galactic Nuclei: Black Hole Mass Estimator, Line Ratio, and Hot Dust Temperature

We present 2.5-5.0 $μ$ 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 2.5-5.0 $μ$ m spectral region contains emission lines such as Br $β$ (2.63 $μ$ m), Br $α$ (4.05 $μ$ m), and polycyclic aromatic hydrocarbons (PAH; 3.3 $μ$ m), which can be used for studying the black hole (BH) masses and star formation activities in the host galaxies of AGNs. The spectral region also suffers less dust extinction than in the ultra violet (UV) or optical wavelengths, which may provide an unobscured view of dusty AGNs. Our sample is selected from bright quasar surveys of Palomar-Green (PG) and SNUQSO, and AGNs with reverberation-mapped BH masses from Peterson et al. (2004). Using 11 AGNs with reliable detection of Brackett lines, we derive the Brackett-line-based BH mass estimators. We also find that the observed Brackett line ratios can be explained with the commonly adopted physical conditions of the broad line region (BLR). Moreover, we fit the hot and warm dust components of the dust torus by adding photometric data of SDSS, 2MASS, $\it{WISE}$ , and $\it{ISO}$ to the $\it{AKARI}$ spectra, finding hot and warm dust temperatures of $\sim1100\,\rm{K}$ and $\sim220\,\rm{K}$ , respectively, rather than the commonly cited hot dust temperature of 1500 K.

preprint2014arXiv

On the transfer congruence between $p$ -adic Hecke $L$ -functions

We prove the transfer congruence between $p$ -adic Hecke $L$ -functions for CM fields over cyclotomic extensions, which is a non-abelian generalization of the Kummer's congruence. The ingredients of the proof include the comparison between Hilbert modular varieties, the $q$ -expansion principle, and some modification of Hsieh's Whittaker model for Katz' Eisenstein series. As a first application, we prove explicit congruence between special values of Hasse-Weil $L$ -function of a CM elliptic curve twisted by Artin representations. As a second application, we prove the existence of a non-commutative $p$ -adic $L$ -function in the algebraic $K_1$ -group of the completed localized Iwasawa algebra.

preprint2014arXiv

The Infrared Medium-Deep Survey II: How to Trigger Radio-AGN? Hints from Their Environments

Activity at the centers of galaxies, during which the central supermassive black hole is accreting material, is nowadays accepted to be rather ubiquitous and most probably a phase of every galaxy's evolution. It has been suggested that galactic mergers and interactions may be the culprits behind the triggering of nuclear activity. We use near-infrared data from the new Infrared Medium-Deep Survey (IMS) and the Deep eXtragalactic Survey (DXS) of the VIMOS-SA22 field and radio data at 1.4 GHz from the FIRST survey and a deep VLA survey to study the environments of radio-AGN over an area of ~25 sq. degrees and down to a radio flux limit of 0.1 mJy and a J-band magnitude of 23 mag AB. Radio-AGN are predominantly found in environments similar to those of control galaxies at similar redshift, J-band magnitude, and U-R rest-frame absolute color. However, a sub-population of radio-AGN is found in environments up to 100 times denser than their control sources. We thus preclude merging as the dominant triggering mechanism of radio-AGN. Through the fitting of the broadband spectral energy distribution of radio-AGN in the least and most dense environments, we find that those in the least dense environments show higher radio-loudness, higher star formation efficiencies, and higher accretion rates, typical of the so-called high-excitation radio-AGN. These differences tend to disappear at z>1. We interpret our results in terms of a different triggering mechanism for these sources that is driven by mass-loss through winds of young stars created during the observed ongoing star formation.

preprint2010arXiv

New Estimators of Black Hole Mass in Active Galactic Nuclei with Hydrogen Paschen Lines

More than 50% of Active Galactic Nuclei (AGNs) are suspected to be red and affected by dust-obscuration. Meanwhile, popular spectral diagnostics of AGNs are based on optical or ultraviolet light, making the dust obscuration as a primary concern for understanding the general nature of AGNs and supermassive black holes residing in them. To provide with a method of investigating properties of the dusty AGNs, we derive new black hole (BH) mass estimators based on velocity widths and luminosities of Near Infrared (NIR) hydrogen emission lines such as P $α$ and P $β$ , and also investigate the line ratios of these Hydrogen lines. To derive the BH mass ( $M_{\rm BH}$ ) estimators, we used a sample of 37 unobscured Type-1 AGNs with a $M_{\rm BH}$ range of $10^{6.8}$ - $10^{9.4} M_{\odot}$ , where $M_{\rm BH}$ come from either reverberation mapping method or single-epoch measurement method using Balmer lines. Our work shows that $M_{\rm BH}$ can be estimated from the Paschen line luminosities and the velocity widths to the accuracy of 0.18 - 0.24 dex (rms scatter). We also show that the mean line ratios of the Paschen lines and the Balmer lines are $\mathrm{\frac{Hα}{Pα}} \simeq 9.00$ , $\mathrm{\frac{Hβ}{Pα}} \simeq 2.70$ , which are consistent with a Case B recombination under a typical AGN broad line region environment. These ratios can be used as reference points when estimating the amount of dust extinction over the broad line region (BLR) for red AGNs. We expect the future application of the new BH mass estimators on red, dusty AGNs to provide a fresh view of obscured AGNs.

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Dohyeong Kim

Research overview

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17 publications

Towards Efficient and Expressive Offline RL via Flow-Anchored Noise-conditioned Q-Learning

KOBEST: Korean Balanced Evaluation of Significant Tasks

Metallicity-PAH Relation of MIR-selected Star-forming Galaxies in AKARI North Ecliptic Pole-wide Survey

Path Integrals and p-adic L-functions

The Infrared Medium-deep Survey. IX. Discovery of Two New $z\sim6$ Quasars and Space Density down to $M_{1450}\sim-23.5$ mag

Batalin-Vilkovisky formalism in the $p$ -adic Dwork theory

Gemini Multi-Object Spectrograph Integral Field Unit Spectroscopy of the Double-peaked Broad Emission Line of a Red Active Galactic Nucleus

The Infrared Medium-deep Survey. \Romannum{7}. Faint Quasars at $z \sim 5$ in the ELAIS-N1 Field

A modular approach to Thue-Mahler equations

Accretion Rates of Red Quasars from the Hydrogen P $β$ line

Descent for the punctured universal elliptic curve, and the average number of integral points on elliptic curves

Discovery of A Faint Quasar at z~6 and Implications for Cosmic Reionization

Rest-frame Optical Spectra and Black Hole Masses of 3<z<6 Quasars

The AKARI 2.5-5.0 Micron Spectral Atlas of Type-1 Active Galactic Nuclei: Black Hole Mass Estimator, Line Ratio, and Hot Dust Temperature

On the transfer congruence between $p$ -adic Hecke $L$ -functions

The Infrared Medium-Deep Survey II: How to Trigger Radio-AGN? Hints from Their Environments

New Estimators of Black Hole Mass in Active Galactic Nuclei with Hydrogen Paschen Lines

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Dohyeong Kim

Research overview

Is this your work?

17 publications

Towards Efficient and Expressive Offline RL via Flow-Anchored Noise-conditioned Q-Learning

KOBEST: Korean Balanced Evaluation of Significant Tasks

Metallicity-PAH Relation of MIR-selected Star-forming Galaxies in AKARI North Ecliptic Pole-wide Survey

Path Integrals and p-adic L-functions

The Infrared Medium-deep Survey. IX. Discovery of Two New z∼6z\sim6z∼6 Quasars and Space Density down to M1450∼−23.5M_{1450}\sim-23.5M1450​∼−23.5 mag

Batalin-Vilkovisky formalism in the ppp-adic Dwork theory

Gemini Multi-Object Spectrograph Integral Field Unit Spectroscopy of the Double-peaked Broad Emission Line of a Red Active Galactic Nucleus

The Infrared Medium-deep Survey. \Romannum{7}. Faint Quasars at z∼5z \sim 5z∼5 in the ELAIS-N1 Field

A modular approach to Thue-Mahler equations

Accretion Rates of Red Quasars from the Hydrogen Pβββ line

Descent for the punctured universal elliptic curve, and the average number of integral points on elliptic curves

Discovery of A Faint Quasar at z~6 and Implications for Cosmic Reionization

Rest-frame Optical Spectra and Black Hole Masses of 3<z<6 Quasars

The AKARI 2.5-5.0 Micron Spectral Atlas of Type-1 Active Galactic Nuclei: Black Hole Mass Estimator, Line Ratio, and Hot Dust Temperature

On the transfer congruence between ppp-adic Hecke LLL-functions

The Infrared Medium-Deep Survey II: How to Trigger Radio-AGN? Hints from Their Environments

New Estimators of Black Hole Mass in Active Galactic Nuclei with Hydrogen Paschen Lines

See the researcher in context

Building this map preview

The Infrared Medium-deep Survey. IX. Discovery of Two New $z\sim6$ Quasars and Space Density down to $M_{1450}\sim-23.5$ mag

Batalin-Vilkovisky formalism in the $p$ -adic Dwork theory

The Infrared Medium-deep Survey. \Romannum{7}. Faint Quasars at $z \sim 5$ in the ELAIS-N1 Field

Accretion Rates of Red Quasars from the Hydrogen P $β$ line

On the transfer congruence between $p$ -adic Hecke $L$ -functions