• 천문학논총
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• 제32권1호
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• pp.313-315
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• 2017

We present physical properties of $24{\mu}m$ galaxies detected by AKARI and Spitzer and their evolution between redshifts 0.4 < z < 2. Using multi-wavelength data from X-ray to radio observations in NEP Deep Field (for AKARI) and Subaru/XMM-Newton Deep Field (for Spitzer), we derive photometric redshift, stellar mass, star-formation rate (SFR), dust extinction magnitude and rest-frame luminosities/colors of the $24{\mu}m$ galaxies from photometric SED fitting. We infer the SFRs from rest-frame ultraviolet luminosity and total infrared luminosity calibrated against Herschel photometric data. For both survey fields, we obtain complete samples with stellar mass of > $10^{10}M_{\odot}$ and SFR of > $30M_{\odot}/yr$ up to z = 2. We find that specific SFRs evolves with redshift at all stellar masses in NON-power-law galaxies (non-PLGs) as star-formation dominant luminous infrared galaxies (LIRGs). The correlations between specific SFR and stellar mass in the Spitzer and AKARI galaxy samples are well consistent with trends of the main sequence galaxies. We also discuss nature of PLGs and their evolution.

• 천문학논총
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• 제32권1호
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• pp.235-237
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• 2017

The AKARI NEP Deep Field Survey is an international multiwavelength survey over $0.4deg^2$ of the sky. This is the deepest survey made by the InfraRed Camera (IRC) of the infrared astronomical satellite AKARI with 9 filters continuously covering the $2-25{\mu}m$ range, including three filters in the Spitzer gap between the IRAC and MIPS coverages. This enabled us to make sensitive MIR detection of AGN candidates at z~ 1, based on hot dust emission in the AGN torus. It is also efficient in detecting highly obscured Compton-thick AGN population. In this article, we report the first results of X-ray observations on this field. The field was covered by 15 overlapping Chandra ACIS-I observations with a total exposure of ~300 ks, detecting ${\approx}450$ X-ray sources. We utilize rest-frame stacking analysis of the MIR AGN candidates that are not detected individually. Our preliminary analysis shows a marginal detection of the rest-frame stacked Fe $k{\alpha}$ line from our strong Compton-thick candidates.

• 천문학회보
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• 제43권1호
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• pp.36.3-37
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• 2018

We present a new catalog of hard X-ray sources detected in the first 105 months of observations with the Burst Alert Telescope (BAT) on board the Neil Gehrels Swift observatory. The 105 month Swift-BAT survey is a uniform hard X-ray all-sky survey performed in the 14-195 keV band. The Swift-BAT 105 month catalog provides 1632 (422 new detections) hard X-ray sources in the 14 - 195 keV band above the 4.8 sigma significance level. Adding to the previously known hard X-ray sources, 34% (144/422) of the new detections are identified as Seyfert AGN in nearby galaxies (z < 0.2). The majority of the remaining identified sources are X-ray binaries (7%, 31) and blazars/BL Lac objects (10%, 43). As part of this new edition of the Swift-BAT catalog, we release eight-channel spectra and monthly sampled light curves for each object in the online journal and at the Swift-BAT 105 month Web site.

• 천문학회보
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• 제37권2호
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• pp.70.1-70.1
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• 2012

We investigate 53 late-type galaxies in Virgo to get better understanding galaxy evolution driven by environmental effects in the cluster. The goal is to study how galaxies are strongly affected gravitationally by their surroundings and/or how interstellar medium (ISM) of galaxies changes through the interaction with intracluster medium (ICM). To quantify these, a variety of diagnostic methods have been introduced. Our diagnostics have two different perspectives. First, we have carefully examined the morphological and kinematical properties of individual galaxies using high resolution HI images and compared with multi-wavelength data. Based on the visual inspection, we have identified signatures of the interactions with other galaxies or the ICM. Second, we have quantified influence of local environments of individual galaxies using X-ray data and optical catalog of the cluster. By combining all the diagnostics, we have identified the environmental effect(s) at work on individual galaxies. We also probe the environmental processes as a function of the cluster centric distance. Various gravitational interactions are found throughout the cluster, while the ICM-ISM interaction is mainly dominant near the cluster center. However, we find some evidence that galaxies start losing their gas already in the low density outskirts of the cluster.

• 천문학회보
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• 제45권1호
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• pp.32.3-33
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• 2020

Jellyfish galaxies show spectacular features such as star-forming knots and tails due to strong ram-pressure stripping in galaxy clusters. Thus, jellyfish galaxies are very useful targets to investigate the effects of ram-pressure stripping on the star formation activity in galaxies. Integral field spectroscopy (IFS) studies are the best way to study star formation in jellyfish galaxies, but they have been limited to those in low-mass galaxy clusters until now. In this study, we present a Gemini GMOS/IFU study of three jellyfish galaxies in very massive clusters (M_200 > 10^15 Mo). The host clusters (Abell 2744, MACSJ0916.1-0023, and MACSJ1752.0+4440) are X-ray luminous and dynamically unstable, suggesting that ram-pressure stripping in these clusters is much stronger than in low-mass clusters. We present preliminary results of star formation rates, kinematics, dynamical states, and ionization mechanisms of our sample galaxies and discuss how ram-pressure stripping relates with the star formation activity of jellyfish galaxies in massive clusters.

• Journal of Astronomy and Space Sciences
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• 제10권2호
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• pp.163-188
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• 1993

적색편이 공간에서 보이는 국부 요동지역 주변의 초면은 프리이드만 배경 우주에 포함된 툴만 시공간 모형 관점에서 보면 국부 중력장에 유도된 국부 팽창율이 원인이 됨을 알고 있다. 초면은 국부적인 것으로서 요동지역에 포함된 질량에 크게 지배되고 물질들의 동력학적 상태와 밀접한 관계가 았다. 은하단의 밀도 분포 모형으로 광학 관측과 X-선 관측을 잘 맞추는 아벨 윤곽과 폴리트로프적 밀도 분포 윤곽을 택하여 틀만 시공간 모형으로 계산한 적색편이 공간에 나타나는 초면과 코마 은하단과 페르세우스 은하단 성분은하들에서 관측되는 적색편이-중심거리 형태와 비교하였을 때, 초면은 은하단의 크기와 질량에 한계값을 설정할 수 있었고, 뜨거운 기체의 물질 상태를 짐작할 수 있는 단서를 제공한다.

• 천문학회보
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• 제40권2호
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• pp.30.2-30.2
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• 2015

Abell 2744 is a giant merging cluster, called the Pandora's Cluster, at the redshift of z=0.308 (corresponding to a distance of 1270 Mpc). Taking the advantage of the deep high resolution images in the Hubble Frontier Field program, we study the properties of compact stellar systems including globular clusters and ultracompact dwarfs (UCDs) as well as dwarf galaxies in this cluster. We find a rich population of globular clusters and UCDs in Abell 2744. The spatial distribution of these objects is consistent with the mass map derived from lensing analysis, while showing a significant offset from the X-ray map of hot gas. The faint end of the luminosity function of the galaxies in the red sequence is fit by a flat slope, showing no faint upturn. We discuss these finding in relation with the origin of UCDs, formation of red sequence dwarf galaxies, and formation of the Pandora's cluster.

• 천문학논총
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• 제30권2호
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• pp.499-502
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• 2015

Starburst galaxies have strong star formation activity and generate large scale outflows which eject a huge amount of gas mass. This process affects galaxy activity, and therefore, the detailed study of nearby starburst galaxies could provide valuable information for the study of distant ones. So far there have been only a few studies of galactic-scale molecular outflows due to the sensitivity limitation of telescopes. Our study provides two nearby examples, NGC 2146 and NGC 3628. We used Nobeyama Millimeter Array (NMA) CO(1-0) data, Chandra soft X-ray data, and NMA 3 mm data to study the kinematics of molecular outflows, their interaction with ionized outflows, and the star forming activity in the starburst region. We found that the gas ejected through molecular outflows is much more significant than that used to form stars.

• 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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• 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.