• 한국우주과학회:학술대회논문집(한국우주과학회보)
• /
• 한국우주과학회 2003년도 한국우주과학회보 제12권2호
• /
• pp.86-86
• /
• 2003

We present intermediate-band spectral energy distribution (SED) of QSO candidates in Leo Triplet field. Leo Triplet is composed of three galaxies, NGC3623, 3627, and 3628 which appear to interact with each other. Based on X -ray information, Arp et al. (2002) selected QSO candidates and suggested that the known QSOs and these candidates might belong to the triplet system in spite of their apparent high redshift. Our photometry is based on BATC survey data, which consist of hundreds of 15 intermediate-band images. In order to derive SED of high signal to noise ratio for every sources in the field, we have combined images of the same filter and matched the sources in the combined images. QSO candidates were identified based on the shape of derived SED curves. We compare our results with Arp et al. (2002)'s QSO candidates.

• 천문학회보
• /
• 제39권2호
• /
• pp.56.1-56.1
• /
• 2014

Although the growth of structure, as traced by galaxy clusters, has been extensively studied through cosmological simulations and large-scale surveys, the early formation and evolution of their galaxy content, and its relation to the transformation of the host environment, are still somewhat poorly understood. This is particularly true of the processes that give rise to the quiescent galaxy population between z=3 and z=2. Recent discoveries at z~2 are now bridging the gap between the well-established massive clusters of the last 9 Gyr and the high-redshift universe, and new datasets are now giving us access to statistical populations of intermediate-mass structures at this epoch. I will discuss the properties of quiescent galaxies in the most distant confirmed X-ray detected galaxy clusters, their implications for galaxy quenching at high-redshift as well as the regulation of star formation at group scales at z~2.

• 천문학논총
• /
• 제30권2호
• /
• pp.603-604
• /
• 2015

Standard thin disk theory predicts that an inner disk region dominated by radiation pressure is thermally unstable. However, this kind of instability isn't detected in the observations of X-ray binaries. In this work, we revisit this issue by investigating the stability of a thin disk with magnetically driven winds. It is found that the disk winds can help to make a thin disk stable by taking away most of the energy released in the disk, resulting in a much cooler disk. The disk can always be stable even for a very weak initial field strength ${\beta}_{p,0}{\leq}400$ when ${\alpha}=0.05$ and $B{\phi}=10B_p$ are adopted.

• 천문학회보
• /
• 제45권1호
• /
• pp.29.4-29.4
• /
• 2020

Structure in the universe forms hierarchically with the small scales forming first and merging into larger scales. Galaxy clusters are at the pinnacle of the formation process. Peering far into the universe, we can observe galaxy clusters early in their evolution. SpARCSJ1049+56 is a galaxy cluster located at a redshift of 1.71. It has been shown to be rich in cluster galaxies, to have intense star formation, and to have a significant amount of molecular gas. Through careful control of systematics, we detected the weak-lensing signal from this distant galaxy cluster. I will present our HST infrared weak-lensing detection of the cluster with a focus on the method. Our lensing analysis found that the cluster is massive and is rare in a LambdaCDM universe. I will also present the Chandra X-ray discovery of cold gas coincident with the intense star formation and discuss the implications of the detection.

• 천문학회보
• /
• 제40권1호
• /
• pp.43.1-43.1
• /
• 2015

We have discovered an unexplored population of galaxies featuring weak broad-line regions (BLRs) at z < 0.2 from detailed analysis of galaxy spectra in the Sloan Digital Sky Survey Data Release 7. These objects predominantly show a stellar continuum but also a broad $H{\alpha}$ emission line, indicating the presence of a low-luminosity active galactic nucleus (AGN) oriented so that we are viewing the central engine directly without significant obscuration. These accreting black holes have previously eluded detection due to their weak nature. The new BLR AGNs we found increased the number of known type 1 AGNs by 49%. Some of these new BLR AGNs were detected at the Chandra X-ray Observatory, and their X-ray properties confirm that they are indeed type 1 AGN. Based on our new and more complete catalogue of type 1 AGNs, we derived the type 1 fraction of AGNs as a function of [OIII] ${\lambda}5007$ emission luminosity and explored the possible dilution effect on the obscured AGN due to star-formation. The new type 1 AGN fraction shows much more complex behavior with respect to black hole mass and bolometric luminosity than suggested by the existing receding torus model. The type 1 AGN fraction is sensitive to both of these factors, and there seems to be a sweet spot (ridge) in the diagram of black hole mass and bolometric luminosity. Furthermore, we present a hint that the Eddington ratio plays a role in determining the opening angles. This work is submitted to ApJS.

• 천문학회지
• /
• 제37권5호
• /
• pp.543-546
• /
• 2004

The inverse Compton scattering of the cosmic microwave background (CMB) radiation with electrons in the intracluster medium which has a temperature gradient, was examined by the third-order perturbation theory of the Compton scattering. A new type of the spectrum distortion of the CMB was found and named as gradient T Sunyaev-Zel'dovich effect (gradT SZE). The spectrum has an universal shape. There is a zero distortion point, the cross over frequency, at 326GHz. When the hotter region locates closer to an observer, the intensity becomes brighter than the CMB in the frequency region lower than the cross over frequency and fainter than the CMB in the frequency region higher than the cross over frequency. When the cooler region locates closer to an observer, the distorted part of the spectrum has an opposite sign to the above case. The amplitude of the spectrum distortion does not de-pend on the electron density and depends on the heat conductivity and the total temperature variation along a line of sight. Therefore, the gradT SZE provides an unique opportunity to measure thermally nonequilibrium electron momentum distribution function in the ICM and combined with the X-ray measurements of the electron temperature distribution provides an opportunity of direct measurement of the heat conductivity in the ICM.

• 천문학회지
• /
• 제37권5호
• /
• pp.605-609
• /
• 2004

We present a set of high-resolution 3D MHD simulations exploring the evolution of light, supersonic jets in cluster environments. We model sets of high- and low-Mach jets entering both uniform surroundings and King-type atmospheres and propagating distances more than 100 times the initial jet radius. Through complimentary analyses of synthetic observations and energy flow, we explore the detailed interactions between these jets and their environments. We find that jet cocoon morphology is strongly influenced by the structure of the ambient medium. Jets moving into uniform atmospheres have more pronounced backflow than their non-uniform counterparts, and this difference is clearly reflected by morphological differences in the synthetic observations. Additionally, synthetic observations illustrate differences in the appearances of terminal hotspots and the x-ray and radio correlations between the high- and low-Mach runs. Exploration of energy flow in these systems illustrates the general conversion of kinetic to thermal and magnetic energy in all of our simulations. Specifically, we examine conversion of energy type and the spatial transport of energy to the ambient medium. Determination of the evolution of the energy distribution in these objects will enhance our understanding of the role of AGN feedback in cluster environments.

• 천문학논총
• /
• 제32권1호
• /
• pp.271-273
• /
• 2017

The AKARI North Ecliptic Pole Deep Field is a natural location to accomplish deep extragalactic surveys. It is supported by comprehensive ancillary data extending from radio to X-ray wavelengths, which have been used to classify radio sources as radio-loud and radio-quiet objects and to create a catalogue of Active Galactic Nuclei (AGN). This has been achieved by using a radio-optical classification and colour-colour diagrams rather than the more usual way based on spectroscopy Furthermore, we explore whether this technique can be extended by using a far-Infrared (FIR) colour-colour diagram which has been used to identify 268 high redshift candidates.

• 천문학회보
• /
• 제42권1호
• /
• pp.54.3-55
• /
• 2017

The nature and physical environments of SNRs are diverse, and for this reason, the understanding of the properties of nearby SNRs is useful in interpreting the emission from SNRs in remote galaxies where we cannot resolve them. In this regard, the LMC is a unique place to study SNRs due to its proximity, location, and composition compared with our galaxy. We carried out a multi-wavelength study of SNR N63A in the LMC, a young remnant of the SN explosion of one of the most massive (> 40 Msun) stars in a cluster. It is currently expanding within a large H II region formed by OB stars in the cluster and engulfing a molecular cloud (MC). As such, N63A is a prototypical SNR showing the impact of SN explosion on the cluster and its environment. Its morphology varies strongly across the wave bands, e.g. the size in X-ray is three times larger than in optical. However, the bright optical nebula would correspond to a MC swept up by the SNR, and consequently the interaction SNR-MC is limited to the central portion of the SNR. We aimed to study the overall structure of N63A, using near-IR imaging and spectroscopic observations to obtain the physical parameters of the atomic shocks, and also to understand how the SNR- MC interaction works and reveal the structure of the shocked cloud as well as the consequences of the impact of the SNR shock on the MC, comparing information obtained in different wavelengths.

• 천문학회보
• /
• 제43권1호
• /
• pp.35.1-35.1
• /
• 2018

Shock waves have been observed in the outskirts of galaxy clusters. They are commonly interpreted as being driven by mergers of sub-clumps, so are called "merger shocks". We here report a study of the properties of merger shocks in merging galaxy clusters with cosmological hydrodynamic simulations. As a representative case, we describe the case where sub-clusters with mass ratio ~ 2 go through an almost head-on, binary-like merger. Because of the turbulent nature of hierarchical clustering, shock surfaces are not uniform, but composed of parts with different Mach numbers. As merger shocks expand from the core to the outskirts, the average Mach number, < $M_s$ >, increases. The shocks propagating along the merger axis could be observed as X-ray shocks and/or radio relics. The kinetic energy through the shocks peaks at ~ 1 Gyr after shock launching, or at ~ 1 - 2 Mpc from the core. The most energetic shocks are found to have the kinetic-energy weighted Mach number, < $M_s$ > $_{\phi}{\simeq}2-3$, and the CR-energy weighted Mach number, < $M_s$ > $_{CR}{\simeq}3-4$. We then discuss the observational implications of our results.