• 천문학회보
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• 제39권2호
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• pp.115-115
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• 2014

First, We will briefly introduce early science results of AGN observations with KVN and KaVA. KaVA is the combined array of the Korean VLBI network (KVN) and VLBI Exploration of Radio Astronomy (VERA). These include KaVA monitoring of M87, Sgr A* and a few bright blazars and KVN Search for circular polarized Blazars. Furthermore, we will present our future plan of monitoring observation of Sgr A* and M87 with KaVA and Low Radio Power AGN multi frequency polarization survey with KVN. Because of the largeness of their centralsuper-massive black holes, we select them as top-priority sources of our key science program (KSP). The main science goals of the KaVA KSP are (1) mapping the velocity field of the M87 jet and testing magnetically-driven-jet paradigm, and (2) obtaining tightest constraints on physical properties of radio emitting region in Sgr A. High sensitivity achieved through simultaneous multifrequency phase referencing technique of KVN will allow us to explore Low Radio Power AGN cores which build majority of AGNs and therefore are important for undestanding the evolution of AGNs and of their hosts.

• 천문학회보
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• 제39권2호
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• pp.59.1-59.1
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• 2014

AGN feedback has been believed as playing an important role in the galaxy-super massive black hole (SMBH) co-evolution. AGN gas outflow can lead to AGN feedback. We investigate gas outflow of low-redshift AGNs by using blue shift/asymmetric index (BAI), and velocity offset of CIV line. By comparing these gas outflow indicators (BAI and velocity offset) to AGN properties (i.e., SMBH mass, bolometric luminosity, and Eddington ratio) and BLR gas metallicity, we find positive correlations among outflow, Eddington ratio, and metallicity. These relations are consistent with those observed at high-redshift. We discuss the possibility of the connection between previous star formation with current AGN accretion and outflow.

• 천문학회보
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• 제43권1호
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• pp.37.2-37.2
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• 2018

The Wide-field Infrared Survey Explorer (WISE) mission has been efficient in selecting Active Galactic Nuclei (AGN) with high luminosities and large obscuration. According to the merger driven AGN powering scenarios, luminous and obscured AGN are in a stage where they go through feeding of gas accretion into the central black hole, and feedback to the host galaxy through outflows. We report the rest-frame UV-optical spectra of 11 Hot Dust Obscured Galaxies (Hot DOGs) at z~2, WISE color-selected to be extremely reddened AGN. A fraction of the targets show blueshifted and broadened [OIII] profiles indicative of ionized gas outflows. We present the occurrence and strength of the outflows, and discuss what impact these AGN activity could give on their hosts.

• 천문학회보
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• 제43권2호
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• pp.55.2-55.2
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• 2018

The Wide-field Infrared Survey Explorer (WISE) mission enabled efficient selection of Active Galactic Nuclei (AGN) with high luminosities and large obscuration. According to the merger driven AGN powering scenarios, luminous and obscured AGN are in a stage where they go through feeding of gas accretion into the central black hole, and feedback to the host galaxy through outflows. We report the rest-frame UV-optical spectra of Hot Dust Obscured Galaxies (Hot DOGs) at z~2, WISE color-selected to be extremely reddened AGN. Most of the targets show blueshifted and broadened [OIII] line profiles indicative of ionized gas outflows. We present the occurrence and strength of the outflows, and discuss the impact of luminous, obscured AGN activity on their hosts.

• 천문학회보
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• 제43권2호
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• pp.32.4-33
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• 2018

We present the BAT AGN Spectroscopic Survey (BASS) which is an optical/NIR spectroscopic survey of the least biased sample of hard X-ray selected local AGN. For more than a thousand AGN that identified through Swift-BAT hard X-ray all-sky survey, we are conducting dedicated spectroscopic observing runs using world-class telescopes such as ESO-VLT, Magellan, and Palomar. The goal of the project is measuring black hole mass, investigating supermassive blackhole growth and its structure, and providing a baseline for future X-ray missions that will perform deeper observations of more distant AGN. In this presentation, we briefly introduce the concept of the project, past and the current status, and future work.

• 천문학회보
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• 제46권1호
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• pp.32.2-32.2
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• 2021

Radio relics, Mpc-size elongated diffuse radio emissions found at galaxy cluster outskirts, are known as the result of shock acceleration during the cluster merger. Theories have claimed that low Mach number shocks are too inefficient to create the observed properties of radio relics. Alternative scenarios such as fossil cosmic ray electrons (CRes) from AGNs are required to explain the observations. However, how exactly the fossil CRes from AGNs can supply the Mpc-size radio relic is still an open question. In this study, we present our recent uGMRT radio observation results of the merging galaxy cluster Abell 514. We found three remarkable AGN jet tails that may have undergone multiple reorientations and extend nearly 800 kpc. Using multi-frequency data, we have performed spectral analysis along the AGN tails and track how the tails lose or gain energy as they propagate in the intracluster medium. We will discuss whether these AGN jets can provide sufficient seed CRes to radio relics.

• 대한한의학회지
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• 제25권4호
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• pp.209-219
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• 2004

The author investigated whether ACE/DD, AGN/TT, and ApoE/ε4 genotypes are associated with CI and whether genetic risk is enhanced by Sasang constitutional classification. The author ascertained these genotypes in patients with CI (n=211), diagnosed by brain computed tomography. Control subjects for the infarction group were randomly selected from 319 subjects matched for age, gender, and history of hypertension with patients. The ACE/DD genotype was not associated with CI. However. there was significant association between ApoE polymorphism and CI (x²=15.089, p<.05). Furthermore, frequency of AGN/TT genotype was higher in the patients with CI than in the controls (x²=20.072, p<.05). The frequency of T allele Was 0.91 in patients and 0.82 in controls (x²=17.237, p<.05). However, the Sasang constitutional classification did not increase the relative risk for CI in the subjects with ApoE/ε4 or AGN/T allele. These results suggest that ApoE and AGN polymorphism predict CI. but Sasang constitutional classification does not enhance the risk for CI associated with ApoE/ε4 or AGN/TT in a Korean population.

• 천문학회보
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• 제40권2호
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• pp.37.1-37.1
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• 2015

It is suggested that relativistic jets associated with active galactic nuclei (AGNs) can have great impacts on the evolution of the host galaxy. However, the physical properties of AGN jets including the formation mechanism are not well known to date, and hence the AGN feedback on the host galaxy is yet poorly understood. OVV 1633+382 as a highly variable AGN source (a.k.a. blazer) with a compact core and very well developed jet components is an excellent laboratory to study the jet formation mechanism of radio-loud AGN. Near 2002, a major flare was reported at mm wavelength with a dramatic increase of the flux, which is likely to be followed by a dense and bright outflow. In order to probe the evolution of the innermost region of this radio-loud AGN, we have monitored using the Very Large Baseline Array (VLBA) and the Effelsberg 100m single-dish radio telescope in 12 epochs from 2002 and 2005. The observations were conducted at 22, 43 and 86 GHz in full polarization mode. In this work, we present the intensity and spectral index maps at 22 and 43 GHz from our monitoring observations. We probe the kinematics and geometry of individual jet components to discuss the evolution of the jet.

• 천문학회보
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• 제38권2호
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• pp.43.2-43.2
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• 2013

AGN are known for irregular variability on all time scales, down to intra-day variability with relative variations of a few percent within minutes to hours. In the shortest time scale of AGN activity, unexplored territory still exists: first, the existence of a shortest time scale of AGN activity and secondly the shape of high frequency end of AGN power spectrum. Also the spectral variations at the shortest timescale. Here, we present the preliminary results of AGN fast photometry performed with Korean VLBI Network(KVN). Observations were done in a 'anti-correlated' mode using two antennas, with always either one antenna pointing at the target. This results in an effective time resolution of 3 minutes. We used all four KVN frequencies, 22, 43, 86, and 129 GHz, in order to trace spectral variability. We have been able to derive high-quality light curves for 3C111 and 3C279 at 22 and 86 GHz observed on 31st of May and 30th of Nov. in 2012. We are currently performing detailed statistical analysis in order to assess the levels of variability or the corresponding upper limits.

• 천문학회보
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• 제39권1호
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• pp.37.1-37.1
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• 2014

There exists strong evidence supporting the co-evolution of central supermassive black holes and their host galaxies; however it is still under debate how such a relation comes about and whether it is relevant for all or only a subset of galaxies. An important mechanism connecting AGN to their host galaxies is AGN feedback, potentially heating up or even expelling gas from galaxies. AGN feedback may hence be responsible for the eventual quenching of star formation and halting of galaxy growth. A rich multi-wavelength dataset ranging from the X-ray regime (Chandra), to far-IR (Herschel), and radio (WSRT) is available for the North Ecliptic Pole field, most notably surveyed by the AKARI infrared space telescope, covering a total area on the sky of 5.4 sq. degrees. We investigate the star-formation properties and possible signatures of radio feedback mechanisms in the host galaxies of 237 radio-AGN below redshift z=2 and at a radio 1.4 GHz flux density limit of 0.1 mJy. Using broadband SED modeling, the nuclear and host galaxy components of these sources are studied simultaneously as a function of their radio luminosity. Here we present results concerning the AGN content of the radio sources in this field, while offering evidence supporting a "maintenance" type of feedback from powerful radio-jets.