• 천문학회보
• /
• 제36권2호
• /
• pp.67.2-67.2
• /
• 2011

은하단에 속한 은하들의 광도함수에 의하면, 어두운 은하들(MB>-18,확인요망)의 수가 이 론적 예측에 비해 현저하게 적게 관측된다. 우리는 이와 같은 "어두운 은하들의 결핍 현상"을 설명하기위해 은하단 간의 충돌/병합과 같은 역학적 기원론을 제시하고자 한다. 본 연구는 은하단 간의 충돌/병합 과정에서 비교적 작은 질량의 은하들이 은하단의 중력적 구속에서 벗어날 가능성이 높다는 점에 착안하였다. 이러한 가능성을 검증하기 위해 (ㄱ) 우주론적 다. 체수치모사의 방법을 활용하고, (ㄴ) 유체수치모사에서 도입하여 발전시킨 "어떤 주어진 입자로부터 N번째 떨어진 입자의 거리 분석(N-th Particle)"이라는 새로운 방법으로 다체입자들의 공간분포 해석을 시도하였다. 이러한 방대한 자료를 효과적으로 분석하기 위해, GPU(Graphic Processing Unit)를 기반으로 설계된 분석 알고리즘을 독자 개발하였다.

• 천문학회보
• /
• 제36권2호
• /
• pp.62.2-62.2
• /
• 2011

The correlation between black hole mass and stellar velocity dispersion provides an important clue on the black hole growth and galaxy evolution. In the case of AGN, however, it is extremely difficult to measure stellar velocity dispersions in the optical since AGN continuum dilutes stellar absorption features. In contrast, stellar velocity dispersions of active galaxies can be measured in the near-IR, where AGN-to-star flux ratio is much smaller. Expecting that more stellar velocity dispersion measurements will be available using future near-IR facilities, it is crucial to test whether the stellar velocity dispersions measured from the near-IR spectra are consistent with those measured from the optical spectra. For a sample of 35 nearby galaxies, for which optical stellar velocity dispersion measurements and dynamical black hole masses are available, we obtained high quality H-band spectra, using the TripleSpec at the Palomar 5-m Telescope, in order to calibrate the stellar velocity dispersions and define the $M_{BH}-sigma_*$ relation in the near-IR. Based on the spatially resolved kinematics, we correct for the rotation component and determine the luminosity-weighted stellar velocity dispersion of the spheroid component in each galaxy. In this presentation, we will show the comparison between optical and near-IR stellar velocity dispersion measurements and define the $M_{BH}-sigma_*$ relation based on uniformly measured stellar velocity dispersion in the near-IR.

• 천문학회보
• /
• 제39권1호
• /
• pp.41.2-41.2
• /
• 2014

Hierarchical merging scenario indicates that galaxies go through major and minor merger events during their formation and evolution. As a result of the merging, substructural features of remnants such as stellar stream are shown around a current galaxy system. To find evidence of stellar substructures on M31 system, we used the near-infrared images of JHK filters obtained from the Wide Field Camera (WFCAM) at UKIRT 3.8m. A total sky coverage is an area of about$ 4.5^{\circ}{\times}6^{\circ}$ around M31. Indeed, M31 system which consists of several satellite systems contains stellar substructures such as giant stellar stream, loops, and spurs. By analysing stellar populations on the near-infrared color-magnitude diagrams, we selected member star candidates of each stellar substructure, from which we map out spatial distribution of stars in the vicinity of M31 system. Here, we present spatial density distribution maps of stars on each substructure over the entire field of M31 system. Also, we discuss the possible origin of the substructures and the implications on the galaxy assembly process.

• 천문학회보
• /
• 제38권1호
• /
• pp.42.1-42.1
• /
• 2013

In the LCDM paradigm, hierarchical merging is thought to play a key role in the formation and evolution of massive galaxies. Theoretical and observational studies suggest that massive galaxies started forming at high redshifts and were assembled via numerous mergers. Galaxy clusters are the sites where the most massive galaxies are found and the most dramatic merger histories are embedded. The previous work of Sheen et al. (2012) identified via visual inspection many massive galaxies with merger features in clusters, which surprised the community. In this study we aim to quantify peculiarity of galaxies to pin down the merger frequency in cluster environments more objectively. We have performed optical deep imaging of 4 Abell clusters by using IMACS f/2 on a Magellan Badde 6.5-m telescope. For the galaxies in our data, we applied GALFIT algorithm, which fits analytic models to galaxy data, and we analyzed their residuals. We present the preliminary results of our sample galaxies.

• 천문학회보
• /
• 제41권1호
• /
• pp.70.4-71
• /
• 2016

The links between super-massive black hole masses and their host galaxy properties are observed, indicating that black hole growth and host galaxy evolution are closely related. Reverberation mapping, which uses the time delay from the central black hole to broad line regions, is one of the best methods to estimate masses of black holes of active galactic nuclei (AGNs). However, only masses of about 50 black holes have been determined in reverberation mapping studies so far, and most of them are limited to optical luminosities below 10^45 erg/s due to the challenges of long-term time domain observations in both photometry and spectroscopy. In this project, we expand reverberation mapping samples to higher luminosities of > 10^44.5 erg/s at 0.1 < z < 0.35, that have expected time lags of 40 - 250 light days. Photometric (using LOAO 1-m and MDM 1.3-m) and spectroscopic (using MDM 2.4-m and Lick 3-m) monitoring campaigns are being conducted for a 3 year duration and 20 day cadence. Precedent photometric observations in 2015B show some targets with variability and follow-up spectroscopic observations are on-going. In this presentation, we introduce our project, present reverberation mapping simulation results, and preliminary results on photometry. These reverberation mapping masses of relatively high luminous AGNs will provide a strong constraint on black hole mass calibration, e.g., the single-epoch mass estimation.

• 천문학회보
• /
• 제39권1호
• /
• pp.37.1-37.1
• /
• 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.

• 천문학회보
• /
• 제37권2호
• /
• pp.75.1-75.1
• /
• 2012

Narrow-Line Seyfert 1 galaxies are arguably the most important AGN subclass in investigating the origin of the black hole mass-galaxy stellar velocity dispersion (MBH-${\sigma}$) relation because of their high accretion rates close to the Eddington limit. Currently, it is still under discussion whether NLS1s are off from the local MBH-${\sigma}$ relation. We select a sample of 325 NLS1 at relatively low redshift (z<0.1) from the SDSS DR7 by constraining FWHM of $H{\beta}$ in the range of 800-2,200 km/s. Among them, we measured stellar velocity dispersion of 40 objects which show strong stellar absorption lines, e.g. Mg b triplet(${\sim}5175{\AA}$), Fe($5270{\AA}$). In contrast, the other 285 objects show too weak stellar absorption lines to measure velocity dispersion. Using the sample of 40 objects with stellar velocity dispersion measurements, we investigate whether NLS1s follow the same MBH-${\sigma}$ relation as normal galaxies and broad line AGNs. We also test the reliability of the width of narrow lines as a surrogate of stellar velocity dispersion by comparing directly measured stellar velocity dispersion with ${\sigma}$ inferred from [O III], [N II], [S II] line widths, respectively. We will discuss the connection between AGN activity in NLS1s and galaxy evolution based on these results.

• 천문학회보
• /
• 제37권2호
• /
• pp.69.2-69.2
• /
• 2012

NGC 6861 is the brightest S0 galaxy in the Telescopium group. It has unusually high central stellar velocity dispersion (~400 km/s) and clear rotation (~250 km/s). Considering the well-known M-sigma relation, this large central dispersion implies that the central supermassive black hole (SMBH) has mass comparable to the most massive black holes in the Universe. However, the mass implied by the bulge luminosity-SMBH mass relation is an order of magnitude lower than that predicted by the M-sigma relation. In order to determine the origin of this inconsistency, we obtain integral field spectroscopy using the Wide Field Spectrograph (WiFeS) on the ANU 2.3m telescope. The data are used to map the velocity and velocity dispersion fields which show that our measurements are consistent with those from the other literature. The large field of view the WiFeS observations have allows us to map the kinematics of a much greater portion of NGC 6861 and reveals that the eastern part of the galaxy has higher velocity and dispersion than the rest of halo. We discuss the origin of the unusual fast rotation and the discrepancy of two SMBH mass estimations from three plausible perspectives: 1) the interaction between subgroups of NGC 6861 and its counterpart, NGC 6868; 2) the inhibited growth of the stellar bulge by the AGN activity which leads to an underestimate the SMBH mass when using the bulge luminosity-SMBH mass relation; and 3) gas rich minor mergers that could be crucial for increasing both rotation velocity and velocity dispersion during the evolution of NGC 6861.

• 천문학회보
• /
• 제43권2호
• /
• pp.35.3-36
• /
• 2018

One of the most prevalent knowledge about disk galaxies, which dominate the population of the local Universe, is that they consist of stellar structures with different kinematics, such as thin disk, bulge, and halo. Therefore, investigating when and how these components develop in a galaxy is the key to understanding the evolution of galaxies. Using the NewHorizon simulation, we can resolve the detailed structures of galaxies, in the field environment, from the early Universe where star formation and mergers were most active. We first decompose stellar particles in a galaxy into a disk and a dispersion-dominated, spheroidal, component based on their orbits and then see how these components evolve in terms of mass and structure. At high redshift z~3, galaxies are mostly dispersion-dominated as stars are formed misaligned with the galactic rotational axis. At z=1~2, massive galaxies start to dominantly form disk stars, while less massive galaxies do much later. Furthermore, massive galaxies are forming thinner and larger disks with time, and the preexistent disks are heated or even disrupted to become a part of dispersion-dominated component. Thus, the mass growth of spheroidal components at later epochs is dominated by disrupted stars with disk origins and accreted stars at large radii.

• 천문학회보
• /
• 제43권2호
• /
• pp.33.1-33.1
• /
• 2018

Ram pressure stripping by intracluster medium (ICM) can play a crucial role in galaxy evolution in the high-density environment as seen by many examples of cluster galaxies. Although much progress has been made by direct numerical simulations of galaxies (or a galaxy) as a whole in a cluster environment, the interstellar medium (ISM) in galactic disks is not well resolved to understand responses of the ISM in details. In order to overcome this, we utilize the TIGRESS simulation suite that focuses on a local region of galactic disks and resolves key physical processes in the ISM with uniformly high resolution. In this talk, we present the results from the solar neighborhood TIGRESS model facing the ICM winds with a range of ram pressures. When ram pressure is weaker than and comparable to the ISM weight, the ICM winds simply reshape the ISM to the one-sided disk, but star formation rates remain unchanged. Although there exist low-density channels in the multiphase ISM that allow the ICM winds to penetrate through, the ISM turbulence quickly closes the channels and prevents efficient stripping. When ram pressure is stronger than the ISM weight, a significant amount of the ISM can be stripped away rapidly, and star formation is quickly quenched. While the low-density gas is stripped rapidly, star formation still occurs in the extraplanar dense ISM (1-2kpc away from the stellar disk). Finally, we quantify the momentum transfer from the ICM to the ISM using the mass-and momentum-weighted velocity distribution functions of each gas phase.