arXiv subjects

Junhyun Baek

Publications and source records attributed to Junhyun Baek.

12 recordsLinked to original sources

arXiv2026

BASS. LI. Cool gas supply of HI-massive local Seyfert galaxies

We present neutral atomic hydrogen (HI) imaging observations of 22 HI-rich ($M_{\rm HI} \gtrsim 10^{9.7} M_\odot$), hard X-ray-selected local Seyferts to explore how cool gas is supplied to active galactic nuclei (AGN) hosts. The sample predominantly resides in group-like, gas-rich environments. About 80% (18/22) of the galaxies have HI-detected neighbors, 61% (11/18) of which clearly exhibit strong lopsidedness, one-sided gas tails, and/or gas structures connecting to nearby companion galaxies, suggesting gas exchange histories. We examine the HI size-mass relation and star formation properties of these HI-rich AGN hosts, finding no systematic deviations from known scaling relations. In most cases, our samples are the most massive systems within their respective groups, implying that our sample is more likely to acquire gas rather than lose it. Interestingly, galaxies with more extended HI disks show stronger AGN activity. Considering that extended HI is often associated with external processes, this finding suggests that environmentally accreted gas - through galaxy interactions and gas exchange with neighboring systems - may have played a role in supplying additional fuel to the AGNs in our sample. Notably, the HI extent-AGN activity correlation becomes even tighter for those AGN hosts whose neighboring galaxies are gas poor or lack HI, further supporting externally supplied gas as a fuel source.

astro-ph.GA↗

arXiv2025

Possibility of using 3.3$μ$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$\,μ$m PAH emission flux or its upper limit is available. A scaling relation between 3.3$\,μ$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$\,μ$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$\,μ$m PAH luminosity, in line with the prescription using $α_\mathrm{CO}=0.8-4.5$ 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$\,μ$m emission from numerous low-redshift galaxies.

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arXiv2024

Detection of extragalactic anomalous microwave emission in NGC 2903 using KVN single-dish observations

We present the results of the single-dish observations using the Korean VLBI Network to search for anomalous microwave emission (AME) in nearby galaxies. The targets were selected from MApping the dense moLecular gAs in the sTrongest stAr-formiNg Galaxies (MALATANG), a legacy survey project of the James Clerk Maxwell Telescope. The MALATANG galaxies are good representatives of local galaxies with enhanced nuclear activity associated with star formation and/or AGN, providing IR-bright galaxy samples; thus, they are good candidates for AME hosts. Combining with the ancillary data, we investigated the radio-IR spectral energy distribution (SED), while searching for the AME signals in five galaxies. The AME in NGC 2903 was well detected at a significant confidence level, whereas that in NGC 2146 and M82 was marginal. NGC 1068 and Arp 299 indicated no significant hints, and we provided the upper limits for the AME. The best-fit SED exhibited local peaks of the AME components at higher frequencies and with stronger peak fluxes than those in the previous studies. This suggested the origin of AME being denser environments such as molecular clouds or photodissociation regions rather than warm neutral/ionized medium as commonly suggested by previous studies. Further, our AME-detected targets were observed to exhibit higher specific star-formation rates than the other extragalactic AME hosts. Furthermore, AME favored starburst galaxies among our sample rather than AGN hosts. Consequently, this might imply that AGNs are excessively harsh environments for tiny dust to survive.

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arXiv2023

Discovery of a large-scale H I plume in the NGC 7194 Group

We present the discovery of a new H I structure in the NGC 7194 group from the observations using the Karl G. Jansky Very Large Array. NGC 7194 group is a nearby (z ~ 0.027) small galaxy group with five quiescent members. The observations reveal a 200 kpc-long H I plume that spans the entire group with a total mass of M$_{HI}$ = 3.4 x 10$^{10}$ M$_{\odot}$. The line-of-sight velocity of the H I gas gradually increases from south (7200 km s$^{-1}$) to north (8200 km $^{-1}$), and the local velocity dispersion is up to 70 km s$^{-1}$. The structure is not spatially coincident with any member galaxies but it shows close associations with a number of blue star-forming knots. Intragroup H I gas is not rare, but this particular structure is still one of the unusual cases in the sense that it does not show any clear connection with sizable galaxies in the group. We discuss the potential origins of this large-scale H I gas in the NGC 7194 group and its relation with the intergalactic star-forming knots. We propose that this HI feature could have originated from tidal interactions among group members or the infall of a late-type galaxy into the group. Alternatively, it might be leftover gas from flyby intruders.

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arXiv2023

Unraveling the Complex Structure of AGN-driven Outflows. VI. Strong Ionized Outflows in Type 1 AGNs and the Outflow Size-Luminosity Relation

We present spatially resolved gas kinematics, ionization, and energetics of 11 type 1 and 5 type 2 active galactic nuclei (AGNs) with strong ionized gas outflows at z $<0.3$ using Gemini Multi-Object Spectrograph Integral Field Unit (GMOS-IFU) data. We find a strongly blueshifted region in [OIII] velocity maps, representing an approaching cone in biconical outflows, and blueshifted and redshifted regions in H$α$ velocity maps, which show gravitationally rotating kinematics. AGN photoionization is dominant in the central region of most targets, and some of them also show ring-like structures of LINER or composite that surround the AGN-dominated center. Following our previous studies, we kinematically determine outflow sizes by the ratio between [OIII] and stellar velocity dispersion. Outflow sizes of type 1 AGNs follow the same kinematic outflow size-[OIII] luminosity relation obtained from the type 2 IFU sample in Kang & Woo and Luo (updated slope $0.29\pm0.04$), while they are limited to the central kpc scales, indicating the lack of global impact of outflows on the interstellar medium. Small mass outflow rates and large star formation rates of the combined sample support that there is no evidence of rapid star formation quenching by outflows, which is consistent with the delayed AGN feedback.

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arXiv2023

AMUSE-antlia I: Nuclear X-ray properties of early-type galaxies in a dynamically young galaxy cluster

To understand the formation and growth of supermassive black holes (SMBHs) and their co-evolution with host galaxies, it is essential to know the impact of environment on the activity of active galactic nuclei (AGN). We present new Chandra X-ray observations of nuclear emission from member galaxies in the Antlia cluster, the nearest non-cool core and the nearest merging galaxy cluster, residing at D = 35.2 Mpc. Its inner region, centered on two dominant galaxies NGC 3268 and NGC 3258, has been mapped with three deep Chandra ACIS-I pointings. Nuclear X-ray sources are detected in 7/84 (8.3%) early-type galaxies (ETG) and 2/8 (25%) late-type galaxies with a median detection limit of 8x10^38 erg/s. All nuclear X-ray sources but one have a corresponding radio continuum source detected by MeerKAT at the L-band. Nuclear X-ray sources detected in early-type galaxies are considered as the genuine X-ray counterpart of low-luminosity AGN. When restricted to a detection limit of logLx(erg/s) > 38.9 and a stellar mass of 10 < log Ms(Msun) <11.6, 6/11 (54.5%) ETG are found to contain an X-ray AGN in Antlia, exceeding the AGN occupation fraction of 7/39 (18.0%) and 2/12 (16.7%) in the more relaxed, cool core clusters, Virgo and Fornax, respectively, and rivaling that of the AMUSE-Field ETG of 27/49 (55.1%). Furthermore, more than half of the X-ray AGN in Antlia are hosted by its younger subcluster, centered on NGC 3258. We believe that this is because SMBH activity is enhanced in a dynamically young cluster compared to relatively relaxed clusters.

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arXiv2022

Circumnuclear Medium around the Central AGN in a Cool-Core Cluster, Abell 1644-South

We present the circumnuclear multi-phase gas properties of the brightest cluster galaxy (BCG) in the center of Abell 1644-South. A1644-S is the main cluster in a merging system, which is well known for X-ray hot gas sloshing in its core. The sharply peaked X-ray profile of A1644-S implies the presence of a strongly cooling gas core. In this study, we analyze ALMA CO (1-0) data, JVLA HI data, and KaVA 22 GHz data for the central region of A1644-S to probe the potential origin of the cool gas and its role in (re)powering the central active galactic nucleus (AGN). We find CO clumps distributed in an arc shape along the X-ray gas sloshing, which is suggestive of a connection between the cold gas and the hot intracluster medium (ICM). HI and CN are detected in absorption against the AGN continuum emission. The absorption dip is observed at the systemic velocity of the BCG with an extended, redshifted tail. Based on the spatial and spectral configurations of the HI, CN and CO gases, it is inferred that cool gas spirals into the core of the BCG, which is then fed to the central AGN. Indeed, our KaVA observation reveals a parsec-scale bipolar jet, implying that this AGN could have been (re)powered quite recently. Combining this, we suggest that some cold gas in A1644-S could have been formed from the cooling of the ICM, triggering the activity of the central AGN in the early development of a cool-core cluster.

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arXiv2022

Determining star formation rates of active galactic nuclei host galaxies based on SED fitting with sub-mm data

We present the star formation rate (SFR) measurements based on the spectral energy distribution (SED) analysis with new sub-mm fluxes combined with archival multi-wavelength data for a sample of 52 AGN host galaxies at z $<0.2$. We carried out sub-mm observations using the SCUBA-2 camera at the James Clerk Maxwell Telescope, and obtained flux or an upper limit at 450 and 850 $μ$m for each target. By experimenting the effect of the AGN dust component in the SED fit, we find that dust luminosity can be overestimated if AGN contribution is ignored. While the SFR based on 4000Å break shows a significant offset compared to dust luminosity based SFR, the SFR obtained by the artificial neural network (Ellison et al. 2016) generally shows consistency albeit with a large scatter. We find that SFR correlates with AGN outflow strength manifested by the [OIII] $λ5007$ emission line, and that AGNs with higher Eddington ratios and stronger outflows are in general hosted by galaxies with higher SFR, which is consistent with the correlation reported by Woo et al. (2020). This suggests no instantaneous quenching of star formation due to AGN feedback.

astro-ph.GA↗

arXiv2021

The variability of brightest cluster galaxies at high radio frequencies

Variability of a galaxy's core radio source can be a significant consequence of AGN accretion. However, this variability has not been well studied, particularly at high radio frequencies. As such, we report on a campaign monitoring the high radio frequency variability of 20 nearby, cool-core brightest cluster galaxies. From our representative sample, we show that most vary significantly over timescales of approximately one year and longer. Our highest cadence observations are at 15 GHz and are from the Owens Valley Radio Observatory (OVRO). They have a median time interval of 7 days and mostly span between 8 and 13 years. We apply a range of variability detection techniques to the sources' lightcurves to analyse changes on week to decade long timescales. Most notably, at least half of the sources show 20 per cent peak to trough variability on 3 year timescales, while at least a third vary by 60 per cent on 6 year timescales. Significant variability, which is important to studies of the Sunyaev-Zel'dovich Effect in the radio/sub-mm, is therefore a common feature of these sources. We also show how the variability relates to spectral properties at frequencies of up to 353 GHz using data from the Korean VLBI network (KVN), the NIKA2 instrument of the IRAM 30m telescope, and the SCUBA-2 instrument of the James Clerk Maxwell Telescope.

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arXiv2020

BAT AGN Spectroscopic Survey -- XV: The High Frequency Radio Cores of Ultra-hard X-ray Selected AGN

We have conducted 22 GHz radio imaging at 1" resolution of 100 low-redshift AGN selected at 14-195 keV by the Swift-BAT. We find a radio core detection fraction of 96%, much higher than lower-frequency radio surveys. Of the 96 radio-detected AGN, 55 have compact morphologies, 30 have morphologies consistent with nuclear star formation, and 11 have sub-kpc to kpc-scale jets. We find that the total radio power does not distinguish between nuclear star formation and jets as the origin of the radio emission. For 87 objects, we use optical spectroscopy to test whether AGN physical parameters are distinct between radio morphological types. We find that X-ray luminosities tend to be higher if the 22 GHz morphology is jet-like, but find no significant difference in other physical parameters. We find that the relationship between the X-ray and core radio luminosities is consistent with the $L_R/L_X \sim 10^{-5}$ of coronally active stars. We further find that the canonical fundamental planes of black hole activity systematically over-predict our radio luminosities, particularly for objects with star formation morphologies.

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arXiv2019

BAT AGN Spectroscopic Survey -- XVII: The Parsec-scale Jet Properties of the Ultra Hard X-ray Selected Local AGN

We have performed a very long baseline interferometry (VLBI) survey of local (z < 0.05) ultra hard X-ray (14-195 keV) selected active galactic nuclei (AGN) from the Swift Burst Alert Telescope (BAT) using KVN, KaVA, and VLBA. We first executed fringe surveys of 142 BAT-detected AGN at 15 or 22 GHz. Based on the fringe surveys and archival data, we find 10/279 nearby AGN (~4%) VLBI have 22 GHz flux above 30 mJy. This implies that the X-ray AGN with a bright nuclear jet are not common. Among these 10 radio-bright AGN, we obtained 22 GHz VLBI imaging data of our own for four targets and reprocessed archival data for six targets. We find that, although our 10 AGN observed with VLBI span a wide range of pc-scale morphological types, they lie on a tight linear relation between accretion luminosity and nuclear jet luminosity. Our result suggests that a powerful nuclear radio jet correlates with the accretion disc luminosity. We also probed the fundamental plane of black hole activity at VLBI scales (e.g., few milli-arcsecond). The jet luminosity and size distribution among our sample roughly fit into the proposed AGN evolutionary scenario, finding powerful jets after the blow-out phase based on the Eddington ratio (λ_{Edd})-hydrogen column density (N_{H}) relation. In addition, we find some hints of gas inflow or galaxy-galaxy merger in the majority of our sample. This implies that gas supply via tidal interactions in galactic scale may help the central AGN to launch a powerful parsec-scale jet.

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arXiv2019

Positive and negative feedback of AGN outflows in NGC 5728

We present a spatially-resolved analysis of ionized and molecular gas in a nearby Seyfert 2 galaxy NGC 5728, using the VLT/MUSE and ALMA data. We find ionized gas outflows out to ~kpc scales, which encounter the star formation ring at 1 kpc radius. The star formation rate of the encountering region is significantly high (~1.8 M$_{\rm sol}/yr/kpc^2$) compared to other regions in the ring. In contrast, the CO (2-1) emission is significantly weaker by a factor of ~3.5, indicating very high star formation efficiency. These results support the positive feedback scenario that the AGN-driven outflows compress the ISM in the ring, enhancing the star formation activity. In addition, we detect outflow regions outside of spiral arms, in which gas is likely to be removed from the spiral arms and no clear sign of star formation is detected. The overall impact of AGN outflows on the global star formation in NGC 5728 is limited, suggesting the feedback of the low-luminosity AGN is insignificant.

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