• 천문학회보
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• 제43권1호
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• pp.31.1-31.1
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• 2018

While astronomers are working hard to detect the earliest galaxies and to follow their evolution to redshift z~0, they remain baffled by the present-day dichotomy between disky, star forming (aka late-type) galaxies and quiescent, spheroidal (aka early-type) galaxies. The key is to find galaxies in transition from one class to the other, whose spectra indicate intense recent star formation that has now ended. We have identified thousands of such "post-starburst galaxies" and discovered that they are often the products of late-type galaxy-galaxy mergers. Their current kinematics, stellar populations, and morphologies are consistent with late- to early-type galaxy evolution. I will discuss recent work that suggests new connections between this violent history and the central supermassive black hole. In particular, the molecular gas reservoir of a post-starburst galaxy declines rapidly after the starburst ends and in a manner consistent with feedback from an active nucleus. Furthermore, a star is ~300x more likely to be tidally disrupted by the nucleus of a post-starburst galaxy than in other galaxies. Like the well-known black hole-bulge mass correlation, these surprising links between the properties of a galaxy on kpc scales and its supermassive black hole on pc scales require explanation.

• 천문학회지
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• 제29권2호
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• pp.255-268
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• 1996

We present VR CCD photometry and long-slit spectroscopy of a late type spiral galaxy NGC 7678. The grey scale images and isophotal maps illustrate the presence of a weak bar from which spiral arms emerge. There are many HII regions along the spiral arms, but bright giant HII regions are more concentrated in the massive southern arm. The bright compact nucleus of NGC 7678 is bluer than bulge and bar. The spectral features of the nucleus and HII regoins are very similar but the nuclear spectra shows higher $[NII]{\lambda}6583/H_\alpha$ than those of the HII regions. The nucleus of NGC 7678 seems to be intermediate type between HII region nulcei and LINERs by the ratio of $[NII]{\lambda}6583/H_\alpha$, but it is more likely to be HII region-like nucleus if we consider the $[NII]{\lambda}6716,6731/H_\alpha$ together. The star formation rate is estimated to be about $0.2 M_\bigodot\;yr^{-1}$ based on the $H_\alpha$ flux.

• 천문학회보
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• 제40권2호
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• pp.33.3-34
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• 2015

We present the spectroscopic study of the globular clusters (GCs) in the massive elliptical galaxy M86 in the Virgo galaxy cluster. Using the spectra obtained from the Multi-Object Spectroscopy (MOS) mode of Faint Object Camera and Spectrograph (FOCAS) on the Subaru Telescope, we measure the radial velocities for 56 GCs in M86. The mean velocity of the GCs is derived to be $<v_p>=-335{\pm}41km/s$, which is different from the velocity of the M86 nucleus ($<v_{gal}>=-224{\pm}5km/s$) within ${\sim}2.5{\sigma}$. The mean velocity ($<v_p>=-342{\pm}60km/s$) of 33 blue GCs in M86 is similar to that ($<v_p>=-314{\pm}71km/s$) of 23 red GCs. We also derive the mean velocities of the GC systems in other 16 nearby early-type galaxies (ETGs) from the radial velocity data in the literature. The mean value of the differences between the mean velocity of the GC systems in each galaxy and the nucleus velocity of their host galaxies, is almost zero except the M86 GC system. But the scatter of the differences in the blue GC system is larger than that in the red GC system. We will discuss these results in the context of GC formation in ETGs.

• 천문학회보
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• 제34권2호
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• pp.45.1-45.1
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• 2009

• 한국지구과학회지
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• 제27권5호
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• pp.569-578
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• 2006

CFHT 천문대 3.6 m 망원경에 부착된 OASIS 분광기를 사용하여 얻은 자료로부터 continuum, $H{\alpha},\;H{\beta}$, [O III], [N II] 등의 영상을 만들어 활동 은하핵 NGC 5728의 물리적 특성을 분석하였다. NGC 5728의 중심부에 NLR 영역으로 판단되는 약 $15"{\times}12"$ 범위 영역에 3개의 밝은 부분(NW knot, SE knot, nucleus)이 존재하고 있고, 이는 핵(nucleus)을 중심으로 북서방향이나 서쪽으로 물질의 흐름이 일어나고 있음을 암시한다. 우리는 직경 10"인 ring과 이의중심에 있는 NW knot의 구조가 은하중심과 일치하지 않음을 발견하였다. 우리는 이러한 구조의 생성 원인에 대해 알아보기 위하여 핵과 knot의 운동학적 특성을 비교하여 보았고, 방출선 영상에서 보이는 차이점을 비교함으로써 활동 은하 중심부의 구조를 살펴보았다.

• 천문학회지
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• 제53권6호
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• pp.117-123
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• 2020

We investigate the plausibility of mass return, from stellar mass loss processes within the central ~100 pc region of the Milky Way (the inner nuclear bulge), as a mass supply mechanism for the Circumnuclear Disk (CND). Gas in the Galactic disk migrates inward to the Galactic centre due to the asymmetric potential caused by the Galactic bar. The inward migration of gas stops and accumulates to form the central molecular zone (CMZ), at 100-200 pc from the Galactic center. It is commonly assumed that stars have formed in the CMZ throughout the lifetime of the Galaxy and have diffused inward to form a 'r-2 stellar cusp' within the inner nuclear bulge. We propose that the stars migrating inward from the CMZ supply gas to the inner nuclear bulge via stellar mass loss, resulting in the formation of a gas disk along the Galactic plane and subsequent inward migration down to the central 10 pc region (CND). We simulate the evolution of a gas distribution that initially follows the stellar distribution of the aforementioned stellar cusp, and illustrate the potential gas supply toward the CND.

• 천문학회보
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• 제42권1호
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• pp.28.2-28.2
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• 2017

Using numerical hydrodynamics code RAMSES, we perform idealized galaxy merger simulations and study the star formation of merging disk galaxies. In our simulations, we consider the active galactic nucleus (AGN) feedback effect. In order to investigate the star formation influenced by AGN, we run ~60 simulations with various initial conditions. We confirm that star formation is more efficiently suppressed in merging galaxies than in isolated galaxies. In the mergers, AGN effect is more significant when the masses of two galaxies are similar. Furthermore, we find that bulge fraction does not affect the star formation when the AGN effect is considered. We discuss the implications on semi-analytic galaxy formation models and the limitation of the current AGN prescriptions.

• 천문학회지
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• 제26권1호
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• pp.33-45
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• 1993

We have conducted surface photometry of a spiral galaxy NGC4419, by making use of photographic plates in U, B, V and R-bands taken by 105cm Schmidt Camera at Kiso Observatory. Two dimensional surface brightness distributions as well as luminosity profiles along the major axis are examined in detail to decipher the morphological properties of the galaxy. Analysis of the color distributions of NGC4419 shows that B-V and U-B colors remain constant throughout the galaxy with a weak trend of blue bulge in B-V color. The blue bulge might indicate an active star formation in the nucleus of NGC4419. For a quantitative analysis of the luminosity distribution of NGC4419, the observed luminosity profiles are decomposed into bulge and disk components, assuming the bulge component to follow de Vaucouleurs $\gamma^{1/4}-law$ while the disk component is assumed to be exponential. The fitting generally fails at the central part and at the shoulder near r = 15' where bulge and disk components overlap. The failure at the central part cannot be attributed wholly by the seeing disk since the core-radius of the central plateau is much larger than the width of point spread function. The failure at shoulder could be due to the luminosities from the spiral arms.

• 천문학회지
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• 제38권2호
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• pp.183-186
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• 2005

We present results of the VLBA observation toward the radio continuum and water maser emissions in a nearby LINER galaxy NGC 1052. The jet structure observed in 2000 is similar to that in 1998, and the two jet structures in 1998 and 2000 support the sub-luminal motion with apparent velocity of 0.26c. Distribution of water maser spots are located ${\~}$0.05 pc shifted to southwest from the component which is supported to be the nucleus, and no rapid positional change of the water maser gas with respect to the central engine is seen from 1995 to 2000. The maser gas is positionally coincident with a plasma torus, and the position of the maser gas relative to the nucleus is stable from 1995 to 2000. The maser gas in NGC 1052 could be explained to be associated with the nuclear circumnuclear torus or disk like the situation found in the nucleus of NGC 4258.

• 천문학회보
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• 제46권1호
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• pp.30.4-31
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• 2021

We will present a scenario of the presence of a second AGN in a nearby Seyfert galaxy, NGC 1068. Using VLT/MUSE IFU data, we investigated the complex kinematics of ionized gas in the central region of NGC 1068. Interestingly, at a distance of 180 pc to the northeast from the nucleus of NGC 1068, we detected a kinematical signature of the launching point of AGN gas outflows, which suggests that there would be a second AGN. We will also discuss another supporting evidence of the second AGN based on previous spectropolarimetric results.