• 천문학회보
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• 제44권1호
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• pp.36.2-36.2
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• 2019

Using VLT/MUSE and ALMA data, we present a spatially-resolved analysis of the central part of NGC 5728. We find enhanced star formation (${\sim}1.8M{\odot}/yr/kpc2$) at a region where AGN gas outflows intersect the star formation ring. In contrast, significantly weaker CO emission (~3.5 times) is found at the same region compared to other regions in ring, suggesting positive AGN feedback on star formation. On the other hand, we detect gas outflows outside of the spiral arms, implying that the inflowing gas in the arms is removed (i.e., negative feedback). Even though the positive and negative feedback are expected at the central part of NGC 5728, the impact of the AGN feedback in galaxy scale may be insignificant.

• 천문학회보
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• 제45권1호
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• pp.60.1-60.1
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• 2020

We present optical variability of nearby luminous active galactic nucleus (AGN). We use the multi-epoch data of 46 AGNs obtained from 2015 to 2019 through SNU AGN Monitoring Project (SAMP), which was carried out for the reverberation mapping of luminous AGNs. We estimated variability amplitudes and time scales using the various types of analytic function, such as structure function and damped random work. We present the comparisons between physical properties of AGNs and optical variability in order to unveil the origin of the variability of AGNs.

• 천문학회보
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• 제46권1호
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• pp.54.1-54.1
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• 2021

Observing sub-mm continuum emission from cold dust can play an important role in measuring star formation rates of galaxies, especially in the case of AGN host ones, since AGNs contaminate FIR fluxes by dust heating. To measure star formation rates, we observed total 49 local AGN host galaxies(z<0.2) by SCUBA-2 camera at James Clerk Maxwell Telescope(JCMT) at 450㎛ and 850㎛. We performed several tests with the observed images to determine whether each source is detected, and adopted 3s as the flux upper limit in non-detection cases. Using these measurements and FIR archival data, we modeled spectral energy distributions of the galaxies to estimate star formation rates. The effect of AGN activity on host galaxy star formation will be discussed.

• 천문학회보
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• 제46권2호
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• pp.69.1-69.1
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• 2021

We present preliminary results of the VLA archival HI data of local AGN hosts. The sample consists of the galaxies selected from the Swift-BAT hard X-ray survey. The main goal is to probe the gas environment of the sample in order to verify the role of gas accretion as one of the major AGN triggering mechanisms. HI, as a mostly diffuse and extended gas component in many galaxies, is a sensitive tracer to explore the impact of the surroundings on galaxies. In this work, we therefore probe the HI imaging data of a subsample of BAT-BASS AGN hosts, starting with the cases for which relatively high HI fluxes have been reported from the past single-dish observations. Based on their resolved HI properties, we will discuss the possibility of gas accretion and its role in powering AGNs in these examples.

• 천문학회보
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• 제35권2호
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• pp.32.1-32.1
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• 2010

From my personal perspective, I will review the current status of observational studies on the fundamental properties of AGN and the role of supermassive black holes in galaxy evolution.

• 천문학논총
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• 제27권4호
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• pp.285-286
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• 2012

We combine data from two all-sky surveys, the Swift/Burst Alert Telescope 22 Month Source Catalog and the AKARI Point Source Catalogue, in order to study the connection between the hard X-ray (> 10 keV) and infrared (IR) properties of local active galactic nuclei (AGN). We find two photometric diagnostics are useful for source classification: one is the X-ray luminosity vs. IR color diagram, in which type 1 radio-loud AGN are well isolated from other AGN. The second one uses the X-ray vs. IR color-color diagram as a redshift-independent indicator for identifying Compton-thick (CT) AGN. Importantly, CT AGN and starburst galaxies in composite systems can also be separated in this plane based upon their hard X-ray fluxes and dust temperatures. This diagram may be useful as a new indicator to classify objects in new surveys such as with WISE and NuSTAR.

• 천문학회보
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• 제41권2호
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• pp.34.1-34.1
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• 2016

The ultra hard X-ray band (14-195 keV) provides an important and unbiased way to understand black hole growth and relationship to the host galaxy. The Burst Alert Telescope (BAT) instrument on the Swift satellite has surveyed sky to unprecedented sensitivity, improving the number of known hard X-ray sources by more than a factor of 20 to 836 nearby AGN. The BAT AGN Spectroscopic Survey (BASS) is a study for the first large (N>600) and complete sample of ultra hard X-ray selected AGN with optical spectroscopy. In this talk, I present the observed relationship between black hole mass, bolometric luminosity, and Eddington ratio with optical emission line ratios. We show that [NII]/Ha ratio exhibits a significant correlation with Eddington ratio. We propose that the [NII]/Ha ratio is a useful indicator of Eddington ratio with 0.6 dex of scatter, and that it can be used to measure Eddington ratio and thus black hole mass from the measured bolometric luminosity, even for high redshift obscured AGN.

• 천문학논총
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• 제30권2호
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• pp.447-449
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• 2015

Although the link between activity in the nuclei of galaxy and galactic mergers has been under scrutiny for several years, it is still unclear to what extent and for which populations of active galaxies merger-triggered activity is relevant. The environments of AGN allow an indirect probe of the past merger history and future merger probability of these systems, suffering less from sensitivity issues when extended to higher redshifts than traditional morphological studies of AGN host galaxies. Here we present results from our investigation of the environment of radio selected sources out to a redshift z=2. We employ the first data release J-band catalog of the new near-IR Infrared Medium-Deep Survey (IMS), 1.4 GHz radio data from the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey and a deep dedicated VLA survey of the VIMOS field, covering a combined total of 20 sq. degrees. At a flux limit of the combined radio catalog of 0.1 mJy, we probe over 8 orders of magnitude of radio luminosity. Using the second closest neighbor density parameters, we test whether active galaxies inhabit denser environments. We find evidence for a sub-population of radio-selected AGN that reside in significantly overdense environments at small scales, although we do not find significant overdensities for the bulk of our sample. We show that radio-AGN in the most underdense environments have vigorous ongoing star formation. We interpret these results in terms of the triggering and fuelling mechanism of radio-AGN.

• 천문학회보
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• 제44권1호
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• pp.36.3-36.3
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• 2019

Feedback process is one of the most important topics in the study of AGNs since it plays a key role in linking the SMBHs and their host galaxies. In order to further understand the co-evolution of SMBHs and their host galaxies, we probe the feedback process in local type-2 AGNs with a series of integral-field-spectroscopy observations. In the first part of my talk, I will introduce our GMOS observations of luminous type-2 AGNs at z < 0.1, which are selected using the integrated [O III] kinematics. Based on the dedicated emission-line diagnostics and kinematic studies, we identify the signatures of AGN-driven outflows and quantify the outflow size in the targets with extreme [O III] kinematics. For the targets without extreme [O III] kinematics, we find the presence of weak AGN-driven outflows, which are indicated by the significant differences between the kinematics of gas and stars. Then, I will present our recent study of 40 type-2 AGNs based on the SNIFS IFU. By comparing the radial profile of velocity dispersion of gas and stars, we measure the size of AGN-driven outflows in these targets and extend the outflow size-AGN luminosity relation in our previous GMOS studies. We also discuss the feedback effect of AGN-driven outflows by connecting the outflow velocity and host galaxy properties. These results highlight the importance of spatially-resolved observation in investigating gas kinematics and identifying the signatures of AGN-driven outflows.

• 천문학회보
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• 제46권1호
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• pp.54.4-55
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• 2021

The Seoul National University AGN Monitoring Project (SAMP) is a welldesigned long-term AGN reverberation mapping project. SAMP focuses on the luminous AGNs out to z~0.5 with relative long time lags between AGN continuum and broad emission lines and aims to probe the high-end of the AGN broad line region (BLR) size-luminosity (R-L) relation. The pilot observations started in October 2015 for 100 AGNs to confirm the variability and the H and [O III] emission line strengths. Based on the initial variability test, 48 quasars has been continued spectroscopic monitoring since Feb. 2016 with Lick 3m and MDM 2.4m telescopes with a cadence of ~20 days. Supporting photometric monitoring in B and V band was conducted at multiple facilities including the MDM 1.3m, LOAO, and DOAO telescopes with a cadence of ~10 days. By the time of Feb. 2021, we have obtained five years spectroscopic and photometric data. More than 30 AGNs shows significant variability in five-year baseline and 16 of them show well detected lags between B-band and H. Here, we report some examples of SAMP light curves and lag detections using the first five-year data as well as the location of our 16 targets in the AGN BLR R-L relation. These measurements are consistent with the existing R-L relation and located at the high-end. With the coming data, SAMP are hopefully to report more AGNs with well detected lags. Our results demonstrate the general feasibility and potential of long-term reverberation project with medium cadence for luminous AGNs.