arXiv subjects

Hyunjin Shim

Publications and source records attributed to Hyunjin Shim.

At least 19 recordsLinked to original sources

arXiv2026

Comparing the Nebular and Stellar Dust Attenuation Curves in Nearby Star-Forming Galaxies

Differences in the spatial distributions of stars and ionized gas relative to dust in galaxies imply that stellar and nebular dust attenuation curves need not be identical. Although stellar attenuation curves have been extensively studied, nebular attenuation curves remain less explored. In this work, we investigate nebular attenuation curves using Balmer line ratios for a sample of 90,958 nearby star-forming galaxies from the Sloan Digital Sky Survey with well-constrained stellar attenuation curves. In the H$\alpha$/H$\beta$ versus H$\alpha$/H$\gamma$ diagram, the nebular attenuation curves are, on average, significantly shallower than typical stellar attenuation curves, which can be qualitatively reproduced by source-dust geometric effects. The nebular attenuation curve slopes show weak positive correlations with the stellar attenuation curve slopes and weak dependences on galaxy properties that broadly follow those of the stellar attenuation curve slopes. These results suggest that nebular attenuation curves are distinct from stellar attenuation curves, while remaining consistent with a connection between them.

astro-ph.GA↗

arXiv2026

Constructing a Hydrogen Line Library for Ly{\alpha} Emitters at Low Redshifts (z < 0.4): Estimating Dust Extinction and Assessing Paschen line Detectability with SPHEREx

Hydrogen recombination lines, one of the strongest emission lines from star-forming galaxies, are used to probe the early Universe as indicators of star formation rates and ionizing photon production rates. Ratios between different recombination lines provide clues to estimate dust attenuation, in addition to the H II region physical diagnostics. To prepare for future near-infrared spectral surveys and optical narrow-band imaging surveys aiming for hydrogen lines in different redshifts, we construct hydrogen recombination line libraries by compiling data from published literature. Our compilation includes 260 galaxies mostly at z < 0.4, of which at least one hydrogen recombination line is observed. The specific hydrogen emission lines under investigation encompass three Balmer lines (H{\alpha}, H\b{eta} and H{\gamma}) and Ly{\alpha} line. Of the compiled galaxies, we estimated dust extinction for 85 galaxies that have detections of at least two Balmer lines, by assuming the Case B recombination and Calzetti extinction curve, based on which Ly{\alpha} escape fraction is also inferred. For each of the 14 galaxies with detections of all three Balmer lines, we optimized the extinction curve so that it yields consistent E(B-V) values across the three possible Balmer line ratios, showing the variety in the slope of the dust attenuation curve. We further evaluated the feasibility of studying hydrogen emission line-selected galaxies with future spectral surveys such as SPHEREx by modeling the Paschen lines of our galaxy sample.

astro-ph.GA↗

arXiv2026

Black Hole Properties of Type-1 Active Galactic Nuclei in the North Ecliptic Pole Wide Field: I. Mid-infrared Sources with Optical Counterparts

We present measurements of black hole (BH) properties of 861 Type-1 active galactic nuclei (AGNs) in the North Ecliptic Pole (NEP)-Wide field. These AGNs are detected in both optical and mid-infrared (MIR) surveys and are identified as Type-1 AGNs in optical spectroscopic surveys. By performing spectral energy distribution (SED) and line fitting, we obtained their MIR continuum luminosities ($L_{\rm MIR}$) as well as full width at half maximum (FWHM) values for the \ion{C}{4}, \ion{Mg}{2}, H$\beta$, and H$\alpha$ lines. Using these measurements, we derived bolometric luminosities ($10^{43.20}$--$10^{47.27}~{\rm erg~s^{-1}}$), BH masses ($10^{7.29}$--$10^{9.67}$\,$M_{\odot}$), and Eddington ratios ($10^{-2.74}$--$10^{-0.08}$) for $\sim$450 objects over a wide redshift range ($z=0.09$--$4.71$). The use of $L_{\rm MIR}$ and FWHM values effectively alleviates the effects of dust extinction, enabling reliable estimates of BH properties even for dust-obscured AGNs. Moreover, we find that 34\,\% of the Type-1 AGNs in the NEP-Wide field are dust-obscured, and that their bolometric luminosities can be significantly underestimated without proper dust extinction correction. Our relatively extinction-free BH property estimates can (i) be combined with multi-wavelength data in the NEP-Wide field to facilitate diverse studies of AGN environments, number densities, host galaxies, and related topics, and (ii) serve as fiducial estimates for SPHEREx and other upcoming infrared (IR) spectroscopic missions covering the NEP-Wide field.

astro-ph.GA↗

arXiv2026

Galaxy-Galaxy Blending in SPHEREx Survey Data

The Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) will provide all-sky spectral survey data covering optical to mid-infrared wavelengths with a spatial resolution of 6\farcs2, which can be widely used to study galaxy formation and evolution. We investigate the galaxy-galaxy blending in SPHEREx datasets using the mock galaxy catalogs generated from cosmological simulations and observational data. Only $\sim0.7\%$ of the galaxies will be blended with other galaxies in all-sky survey data with a limiting magnitude of 19 AB mag. However, the fraction of blended galaxies dramatically increases to $\sim7$--$9\%$ in the deep survey area around the ecliptic poles, where the depth reaches $\sim22$ AB mag. We examine the impact of the blending in the number count and luminosity function analyses using the SPHEREx data. We find that the number count can be overestimated by up to $10$--$20\%$ in the deep regions due to the flux boosting, suggesting that the impact of galaxy-galaxy blending on the number count is moderate. However, galaxy-galaxy blending can marginally change the luminosity function by up to 50\%\ over a wide range of redshifts. As we only employ the magnitude limit at $K_s$-band for the source detection, the blending fractions determined in this study should be regarded as lower limits.

astro-ph.GA↗

arXiv2025

Possibility of using 3.3$\mu$m PAH luminosity as a molecular gas mass estimator

We present CO(1-0) observations of 50 star-forming galaxies at 0.01<z<0.35, for which 3.3$\,\mu$m PAH emission flux or its upper limit is available. A scaling relation between 3.3$\,\mu$m PAH luminosity and CO(1-0) luminosity is established covering ~2 orders of magnitude in total IR luminosity and CO luminosity, with a scatter of ~0.23 dex: $\mathrm{log}\,L_\mathrm{3.3}/\mathrm{L}_\odot=(1.00\pm0.07)\times\mathrm{log}\,L_\mathrm{CO(1-0)}^\prime/(\mathrm{K\,km\,s^{-1}\,pc^2})+(-1.10\pm0.70)$. The slope is near unity, allowing the use of a single value of $\langle\mathrm{log}\,(L_\mathrm{3.3}/L_\mathrm{CO(1-0)}^\prime)\rangle=-1.09\pm0.36~[\mathrm{L}_\odot/(\mathrm{K\,km\,s^{-1}\,pc^2})]$ in the conversion between 3.3$\,\mu$m PAH and CO luminosities. The variation in the $L_\mathrm{3.3}/L_\mathrm{CO}^\prime$ ratio is not dependent on the galaxy properties, including total IR luminosity, stellar mass, and SFR excess. The total gas mass, estimated using dust-to-gas ratio and dust mass, is correlated with 3.3$\,\mu$m PAH luminosity, in line with the prescription using $\alpha_\mathrm{CO}=0.8-4.5$ covering both normal star-forming galaxies and starburst galaxies. AGN-dominated galaxies tend to have a lower $L_\mathrm{3.3}/L_\mathrm{CO}^\prime$ than non-AGN galaxies, which needs to be investigated further with an increased sample size. The established $L_\mathrm{3.3}$-$L_\mathrm{CO}^\prime$ correlation is expected to be applicable to wide-field near-infrared spectrophotometric surveys that allow the detection of 3.3$\,\mu$m emission from numerous low-redshift galaxies.

astro-ph.GA↗

arXiv2025

Resolved Stellar Mass Estimation of Nearby Late-type Galaxies for the SPHEREx Era: Dependence on Stellar Population Synthesis Models

The upcoming all-sky infrared spectrophotometric SPHEREx mission is set to provide spatially resolved stellar mass maps of nearby galaxies, offering more detailed insights than integrated light observations. In this study, we develop a strategy for estimating stellar mass using SPHEREx by examining the dependence on different stellar population synthesis (SPS) models and proposing new scaling relations based on simulated SPHEREx data. We estimate the resolved stellar masses of 19 nearby late-type galaxies from the PHANGS-MUSE survey, treating these as fiducial masses. By testing four SPS models covering infrared wavelengths, i.e., E-MILES, Bruzual \& Charlot 2003 (BC03), Charlot \& Bruzual 2019 (CB19), and FSPS, we find systematic differences in mass-to-light ratios at $3.6~{\rm \mu m}$ ($M_{\ast}/L_{\rm 3.6\mu m}$) among the SPS models. In particular, BC03 and CB19 yield mass-to-light ratios on average $\sim0.2-0.3~{\rm dex}$ lower than those from E-MILES and FSPS. These mass-to-light ratios strongly correlate with stellar age, indicating a significant impact of young stellar populations on stellar mass measurements. Our analysis, incorporating fiducial masses and simulated SPHEREx data, identifies the $1.6~{\rm \mu m}$ band as the optimal wavelength for stellar mass estimation, with the lowest scatter ($0.15-0.20~{\rm dex}$) of the stellar mass. This scatter can be further reduced to $0.10-0.12~{\rm dex}$ across all SPS models by incorporating optical and SPHEREx colors. These results can provide guidance for measuring the stellar masses of the numerous nearby galaxies that SPHEREx will survey.

astro-ph.GA↗

arXiv2025

Green peas in the southern sky: Broad-band color selection and spectroscopic follow up

We present a systematic search for 1696 Green Pea (GP) galaxy candidates in the southern hemisphere selected from the Dark Energy Survey Data Release 2 (DES DR2) and provide preliminary results from spectroscopic follow-up observations of 26 targets chosen among them. Our selection criteria include the colors in $gri$-bands and compact morphology in the color composite images. The multi-wavelength spectral energy distribution fitting shows that the selected GP candidates exhibit star formation rates up to several tens $\mathrm{M}_\odot\,\mathrm{yr}^{-1}$. With the mean stellar mass of $\mathrm{log}\,M_*/\mathrm{M}_\odot=8.6$, GP candidates are located at roughly 1 dex above the main sequence of star-forming galaxies at $z\sim0.3$. Spectroscopic follow-up observations of the GP candidates with Gemini/GMOS are underway. All 26 targets are spectroscopically confirmed to be at $z=0.3-0.41$ and have [OIII] equivalent width larger than 85$\r{A}$, classified to be starbursts with low to moderate dust attenuation. These confirmed GPs show a lower metallicity offset from the mass-metallicity relation of local star-forming galaxies, indicating that GPs are less chemically evolved systems at their early stage of evolution.

astro-ph.GA↗

arXiv2025

Machine learning based Photometric Redshifts for Galaxies in the North Ecliptic Pole Wide field: catalogs of spectroscopic and photometric redshifts

We perform an MMT/Hectospec redshift survey of the North Ecliptic Pole Wide (NEPW) field covering 5.4 square degrees, and use it to estimate the photometric redshifts for the sources without spectroscopic redshifts. By combining 2572 newly measured redshifts from our survey with existing data from the literature, we create a large sample of 4421 galaxies with spectroscopic redshifts in the NEPW field. Using this sample, we estimate photometric redshifts of 77755 sources in the band-merged catalog of the NEPW field with a random forest model. The estimated photometric redshifts are generally consistent with the spectroscopic redshifts, with a dispersion of 0.028, an outlier fraction of 7.3%, and a bias of -0.01. We find that the standard deviation of the prediction from each decision tree in the random forest model can be used to infer the fraction of catastrophic outliers and the measurement uncertainties. We test various combinations of input observables, including colors and magnitude uncertainties, and find that the details of these various combinations do not change the prediction accuracy much. As a result, we provide a catalog of 77755 sources in the NEPW field, which includes both spectroscopic and photometric redshifts up to z~2. This dataset has significant legacy value for studies in the NEPW region, especially with upcoming space missions such as JWST, Euclid, and SPHEREx.

astro-ph.CO↗

arXiv2024

Self-assembling T7 phage syringes with modular genomes for targeted delivery of penicillin against beta-lactam-resistant Escherichia coli

Bacteriophages are promising alternative antimicrobial agents due to their high specificity for host bacteria and minimal immunogenicity in humans. However, their therapeutic application is limited by their nature as biological entities, which can lead to unintended evolutionary consequences such as horizontal gene transfer. In this study, we address these challenges by repurposing only the structural components of bacteriophages as vesicles to deliver antibiotics directly into the cytoplasm of bacterial hosts. This approach is based on two key hypotheses: first, antibiotics such as beta-lactams remain effective against resistant bacteria if injected directly into the cytoplasm, bypassing resistance mechanisms; second, phage structures can be synthesized and self-assembled in vitro using modular genomes and cell-free protein expression systems to carry small molecules such as antibiotics as cargo. To test these hypotheses, we utilized T7 phages and penicillin-resistant Escherichia coli as a model system. First, we designed the T7 phage genome into a modular format containing only the genes encoding structural components and synthesized the gene fragments via de novo gene synthesis. These phage structures were then rebooted in vitro using a cell-free protein expression system in the presence of penicillin G, allowing the antibiotics to be incorporated as cargo during the self-assembly process. Finally, we tested the antimicrobial activity of these antibiotic-loaded phage syringes against penicillin-resistant E. coli. The results demonstrate that phage syringes effectively reduce the population of penicillin-resistant E. coli compared to negative controls, including free penicillin and water. This study highlights the potential of using phage structures as antibiotic delivery vehicles, offering a novel strategy to overcome both antibiotic resistance and the limitations of phage therapy.

q-bio.QM↗

arXiv2024

Accuracy of Stellar Mass-to-light Ratios of Nearby Galaxies in the Near-Infrared

Future satellite missions are expected to perform all-sky surveys, thus providing the entire sky near-infrared spectral data and consequently opening a new window to investigate the evolution of galaxies. Specifically, the infrared spectral data facilitate the precise estimation of stellar masses of numerous low-redshift galaxies. We utilize the synthetic spectral energy distribution (SED) of 2853 nearby galaxies drawn from the DustPedia (435) and Stripe 82 regions (2418). The stellar mass-to-light ratio ($M_*/L$) estimation accuracy over a wavelength range of $0.75-5.0$ $μ$m is computed through the SED fitting of the multi-wavelength photometric dataset, which has not yet been intensively explored in previous studies. We find that the scatter in $M_*/L$ is significantly larger in the shorter and longer wavelength regimes due to the effect of the young stellar population and the dust contribution, respectively. While the scatter in $M_*/L$ approaches its minimum ($\sim0.10$ dex) at $\sim1.6$ $μ$m, it remains sensitive to the adopted star formation history model. Furthermore, $M_*/L$ demonstrates weak and strong correlations with the stellar mass and the specific star formation rate (SFR), respectively. Upon adequately correcting the dependence of $M_*/L$ on the specific SFR, the scatter in the $M_*/L$ further reduces to $0.02$ dex at $\sim1.6$ $μ$m. This indicates that the stellar mass can be estimated with an accuracy of $\sim0.02$ dex with a prior knowledge of SFR, which can be estimated using the infrared spectra obtained with future survey missions.

astro-ph.GA↗

arXiv2024

Exploring Unobscured QSOs in the Southern Hemisphere with KS4

We present a catalog of unobscured QSO candidates in the southern hemisphere from the early interim data of the KMTNet Synoptic Survey of Southern Sky (KS4). The KS4 data covers $\sim2500\,{\rm deg}^{2}$ sky area, reaching 5$σ$ detection limits of $\sim$22.1-22.7 AB mag in the $BVRI$ bands. Combining this with available infrared photometric data from the surveys covering the southern sky, we select the unobscured QSO candidates based on their colors and spectral energy distributions (SEDs) fitting results. The final catalog contains 72,964 unobscured QSO candidates, of which only 0.4% are previously identified as QSOs based on spectroscopic observations. Our selection method achieves an 87% recovery rate for spectroscopically confirmed bright QSOs at $z<2$ within the KS4 survey area. In addition, the number count of our candidates is comparable to that of spectroscopically confirmed QSOs from the Sloan Digital Sky Survey in the northern sky. These demonstrate that our approach is effective in searching for unobscured QSOs in the southern sky. Future spectro-photometric surveys covering the southern sky will enable us to discern their true nature and enhance our understanding of QSO populations in the southern hemisphere.

astro-ph.GA↗

arXiv2024

The Future of Decoding Non-Standard Nucleotides: Leveraging Nanopore Sequencing for Expanded Genetic Codes

Expanding genetic codes from natural standard nucleotides to artificial non-standard nucleotides marks a significant advancement in synthetic biology, with profound implications for biotechnology and medicine. Decoding the biological information encoded in these non-standard nucleotides presents new challenges, as traditional sequencing technologies are unable to recognize or interpret novel base pairings. In this perspective, we explore the potential of nanopore sequencing, which is uniquely suited to decipher both standard and non-standard nucleotides by directly measuring the biophysical properties of nucleic acids. Nanopore technology offers real-time, long-read sequencing without the need for amplification or synthesis, making it particularly advantageous for expanded genetic systems like Artificially Expanded Genetic Information Systems (AEGIS). We discuss how the adaptability of nanopore sequencing and advancements in data processing can unlock the potential of these synthetic genomes and open new frontiers in understanding and utilizing expanded genetic codes.

q-bio.GN↗

arXiv2024

The Radio Galaxy Environment Reference Survey (RAGERS): a submillimetre study of the environments of massive radio-quiet galaxies at $z = 1{\rm -}3$

Measuring the environments of massive galaxies at high redshift is crucial to understanding galaxy evolution and the conditions that gave rise to the distribution of matter we see in the Universe today. While high-$z$ radio galaxies (H$z$RGs) and quasars tend to reside in protocluster-like systems, the environments of their radio-quiet counterparts are relatively unexplored, particularly in the submillimetre, which traces dust-obscured star formation. In this study we search for 850 $μ$m-selected submillimetre galaxies in the environments of massive ($M_{\star} > 10^{11} M_{\odot}$), radio-quiet ($L_{500 {\rm MHz}} \lesssim 10^{25}$ W Hz$^{-1}$) galaxies at $z \sim 1\text{--}3$ using S2COSMOS data. By constructing number counts in circular regions of radius 1--6 arcmin and comparing with blank-field measurements, we find no significant overdensities of SMGs around massive radio-quiet galaxies at any of these scales, despite being sensitive down to overdensities of $δ\sim 0.4$. To probe deeper than the catalogue we also examine the distribution of peaks in the SCUBA-2 SNR map, which reveals only tentative signs of any difference in the SMG densities of the radio-quiet galaxy environments compared to the blank field, and only on smaller scales (1$^{\prime}$ radii, corresponding to $\sim0.5$ Mpc) and higher SNR thresholds. We conclude that massive, radio-quiet galaxies at cosmic noon are typically in environments with $δ\lesssim0.4$, which are either consistent with the blank field or contain only weak overdensities spanning sub-Mpc scales. The contrast between our results and studies of H$z$RGs with similar stellar masses and redshifts implies an intrinsic link between the wide-field environment and radio AGN luminosity at high redshift.

astro-ph.GA↗

arXiv2024

The Calibration of Polycyclic Aromatic Hydrocarbon Dust Emission as a Star Formation Rate Indicator in the AKARI NEP Survey

Polycyclic aromatic hydrocarbon (PAH) dust emission has been proposed as an effective extinction-independent star formation rate (SFR) indicator in the mid-infrared (MIR), but this may depend on conditions in the interstellar medium. The coverage of the AKARI/Infrared Camera (IRC) allows us to study the effects of metallicity, starburst intensity, and active galactic nuclei on PAH emission in galaxies with $f_ν(L18W)\lesssim 19$ AB mag. Observations include follow-up, rest-frame optical spectra of 443 galaxies within the AKARI North Ecliptic Pole survey that have IRC detections from 7-24 $μ$m. We use optical emission line diagnostics to infer SFR based on H$α$ and [O II]$λλ3726,3729$ emission line luminosities. The PAH 6.2 $μ$m and PAH 7.7 $μ$m luminosities ($L(PAH\ 6.2\ μm)$ and $L(PAH\ 7.7\ μm)$, respectively) derived using multi-wavelength model fits are consistent with those derived from slitless spectroscopy within 0.2 dex. $L(PAH\ 6.2\ μm)$ and $L(PAH\ 7.7\ μm)$ correlate linearly with the 24 $μ$m-dust corrected H$α$ luminosity only for normal, star-forming ``main-sequence" galaxies. Assuming multi-linear correlations, we quantify the additional dependencies on metallicity and starburst intensity, which we use to correct our PAH SFR calibrations at $0<z<1.2$ for the first time. We derive the cosmic star formation rate density (SFRD) per comoving volume from $0.15 \lesssim z \lesssim 1$. The PAH SFRD is consistent with that of the far-infrared and reaches an order of magnitude higher than that of uncorrected UV observations at $z\sim1$. Starburst galaxies contribute $\gtrsim 0.7$ of the total SFRD at $z\sim1$ compared to main-sequence galaxies.

astro-ph.GA↗

arXiv2024

SCUBA-2 Ultra Deep Imaging EAO Survey (STUDIES). V. Confusion-limited Submillimeter Galaxy Number Counts at 450 $μ$m and Data Release for the COSMOS Field

We present confusion-limited SCUBA-2 450-$μ$m observations in the COSMOS-CANDELS region as part of the JCMT Large Program, SCUBA-2 Ultra Deep Imaging EAO Survey (STUDIES). Our maps at 450 and 850 $μ$m cover an area of 450 arcmin$^2$. We achieved instrumental noise levels of $σ_{\mathrm{450}}=$ 0.59 mJy beam$^{-1}$ and $σ_{\mathrm{850}}=$ 0.09 mJy beam$^{-1}$ in the deepest area of each map. The corresponding confusion noise levels are estimated to be 0.65 and 0.36 mJy beam$^{-1}$. Above the 4 (3.5) $σ$ threshold, we detected 360 (479) sources at 450 $μ$m and 237 (314) sources at 850 $μ$m. We derive the deepest blank-field number counts at 450 $μ$m, covering the flux-density range of 2 to 43 mJy. These are in agreement with other SCUBA-2 blank-field and lensing-cluster observations, but are lower than various model counts. We compare the counts with those in other fields and find that the field-to-field variance observed at 450 $μ$m at the $R=6^\prime$ scale is consistent with Poisson noise, so there is no evidence of strong 2-D clustering at this scale. Additionally, we derive the integrated surface brightness at 450 $μ$m down to 2.1 mJy to be $57.3^{+1.0}_{-6.2}$~Jy deg$^{-2}$, contributing to (41$\pm$4)\% of the 450-$μ$m extragalactic background light (EBL) measured by COBE and Planck. Our results suggest that the 450-$μ$m EBL may be fully resolved at $0.08^{+0.09}_{-0.08}$~mJy, which extremely deep lensing-cluster observations and next-generation submillimeter instruments with large aperture sizes may be able to achieve.

astro-ph.GA↗

arXiv2024

A large population of strongly lensed faint submillimetre galaxies in future dark energy surveys inferred from JWST imaging

Bright galaxies at sub-millimetre wavelengths from Herschel are now well known to be predominantly strongly gravitationally lensed. The same models that successfully predicted this strongly lensed population also predict about one percent of faint $450μ$m-selected galaxies from deep James Clerk Maxwell Telescope (JCMT) surveys will also be strongly lensed. Follow-up ALMA campaigns have so far found one potential lens candidate, but without clear compelling evidence e.g. from lensing arcs. Here we report the discovery of a compelling gravitational lens system confirming the lensing population predictions, with a $z_{s} = 3.4 {\pm} 0.4$ submm source lensed by a $z_{spec} = 0.360$ foreground galaxy within the COSMOS field, identified through public JWST imaging of a $450μ$m source in the SCUBA-2 Ultra Deep Imaging EAO Survey (STUDIES) catalogue. These systems will typically be well within the detectable range of future wide-field surveys such as Euclid and Roman, and since sub-millimetre galaxies are predominantly very red at optical/near-infrared wavelengths, they will tend to appear in near-infrared channels only. Extrapolating to the Euclid-Wide survey, we predict tens of thousands of strongly lensed near-infrared galaxies. This will be transformative for the study of dusty star-forming galaxies at cosmic noon, but will be a contaminant population in searches for strongly lensed ultra-high-redshift galaxies in Euclid and Roman.

astro-ph.GA↗

arXiv2023

Estimators of Bolometric Luminosity and Black Hole Mass with Mid-infrared Continuum Luminosities for Dust-obscured Quasars: Prevalence of Dust-obscured SDSS Quasars

We present bolometric luminosity ($L_{\rm bol}$) and black hole (BH) mass ($M_{\rm BH}$) estimators based on mid-infrared (MIR) continuum luminosity (hereafter, $L_{\rm MIR}$) that are measured from infrared (IR) photometric data. The $L_{\rm MIR}$-based estimators are relatively immune from dust extinction effects, hence they can be used for dust-obscured quasars. To derive the $L_{\rm bol}$ and $M_{\rm BH}$ estimators, we use unobscured quasars selected from the Sloan Digital Sky Survey (SDSS) quasar catalog, which have wide ranges of $L_{\rm bol}$ ($10^{44.62}$--$10^{46.16}$\,$\rm erg\,s^{-1}$) and $M_{\rm BH}$ ($10^{7.14}$--$10^{9.69}$\,$M_{\odot}$). We find empirical relations between (i) continuum luminosity at 5100\,$\rm{Å}$ (hereafter, L5100) and $L_{\rm MIR}$; (ii) $L_{\rm bol}$ and $L_{\rm MIR}$. Using these relations, we derive the $L_{\rm MIR}$-based $L_{\rm bol}$ and $M_{\rm BH}$ estimators. We find that our estimators allow the determination of $L_{\rm bol}$ and $M_{\rm BH}$ at an accuracy of $\sim$0.2\,dex against the fiducial estimates based on the optical properties of the unobscured quasars. We apply the $L_{\rm MIR}$-based estimators to SDSS quasars at $z \lesssim 0.5$ including obscured ones. The ratios of $L_{\rm bol}$ from the $L_{\rm MIR}$-based estimators to those from the optical luminosity-based estimators become larger with the amount of the dust extinction, and a non-negligible fraction ($\sim$15\,\%) of the SDSS quasars exhibits ratios greater than 1.5. This result suggests that dust extinction can significantly affect physical parameter derivations even for SDSS quasars, and that dust extinction needs to be carefully taken into account when deriving quasar properties.

astro-ph.GA↗

arXiv2023

Photometric Selection of Unobscured QSOs in the Ecliptic Poles: KMTNet in the South Field and Pan-STARRS in the North Field

We search for quasi-stellar objects (QSOs) in a wide area of the south ecliptic pole (SEP) field, which has been and will continue to be intensively explored through various space missions. For this purpose, we obtain deep broadband optical images of the SEP field covering an area of $\sim$$14.5\times14.5$ deg$^2$ with the Korea Microlensing Telescope Network. The 5$σ$ detection limits for point sources in the $BVRI$ bands are estimated to be $\sim$22.59, 22.60, 22.98, and 21.85 mag, respectively. Utilizing data from Wide-field Infrared Survey Explorer, unobscured QSO candidates are selected among the optically point-like sources using the mid-infrared (MIR) and optical-MIR colors. To further refine our selection and eliminate any contamination not adequately removed by the color-based selection, we perform the spectral energy distribution fitting with archival photometric data ranging from optical to MIR. As a result, we identify a total of 2,383 unobscured QSO candidates in the SEP field. We also apply a similar method to the north ecliptic pole field using the Pan-STARRS data and obtain a similar result of identifying 2,427 candidates. The differential number count per area of our QSO candidates is in good agreement with those measured from spectroscopically confirmed ones in other fields. Finally, we compare the results with the literature and discuss how this work will be implicated in future studies, especially with the upcoming space missions.

astro-ph.GA↗