Joon Hyeop Lee

AKARI NEAR-INFRARED SPECTROSCOPY OF LUMINOUS INFRARED GALAXIES

We present the AKARI near-infrared (NIR; 2.5-5 μm) spectroscopic study of 36 (ultra)luminous infrared galaxies ((U)LIRGs) at z = 0.01-0.4. We measure the NIR spectral features including the strengths of 3.3 μm polycyclic aromatic hydrocarbon emission and hydrogen recombination lines (Brα and Brβ), optical depths at 3.1 and 3.4 μm, and NIR continuum slope. These spectral features are used to identify optically elusive, buried active galactic nuclei (AGNs). We find that half of the (U)LIRGs optically classified as non-Seyferts show AGN signatures in their NIR spectra. Using a combined sample of (U)LIRGs with NIR spectra in the literature, we measure the contribution of buried AGNs to the infrared luminosity from the spectral energy distribution fitting to the IRAS photometry. The contribution of these buried AGNs to the infrared luminosity is 5%-10%, smaller than the typical AGN contribution of (U)LIRGs including Seyfert galaxies (10%-40%). We show that NIR continuum slopes correlate well with WISE [3.4]-[4.6] colors, which would be useful for identifying a large number of buried AGNs using the WISE data.

The nature of the Sloan Digital Sky Survey galaxies in various classes based on morphology, colour and spectral features - I. Optical properties: Optical properties of SDSS galaxy classes

We present a comprehensive study of the nature of the SDSS galaxies divided into various classes based on their morphology, colour, and spectral features. The SDSS galaxies are classified into early-type and late-type; red and blue; passive, HII, Seyfert, and LINER, returning a total of 16 fine classes of galaxies. We examine the luminosity dependence of seven physical parameters of galaxies in each class. We find that more than half of red early-type galaxies (REGs) have star formation or AGN activity, and that these active REGs have smaller axis ratio and bluer outside compared to the passive REGs. Blue early-type galaxies (BEGs) show structural features similar to those of REGs, but their centres are bluer than REGs. HII BEGs are found to have bluer centres than passive BEGs, but HII REGs have bluer outside than passive REGs. Bulge-dominated late-type galaxies have red colours. Passive red late-types are similar to REGs in several aspects. Most blue late-type galaxies (BLGs) have forming stars, but a small fraction of BLGs do not show evidence for current star formation activity. Differences of other physical parameters among different classes are inspected, and their implication on galaxy evolution is discussed.

The Nature of Blue Early-Type Galaxies in the GOODS Fields

We present a study of the nature of the blue early-type galaxies (BEGs) in the GOODS North and South fields using the GOODS archival HST ACS data. Using visual inspection, we have selected 58 BEGs and 113 normal red early-type galaxies (REGs) in the sample of 1949 galaxies with spectroscopic redshifts. We find that the BEGs are generally bluer, fainter, and less massive than the REGs, although a few BEGs are exceptionally bright and massive. The number fraction of BEGs to total early-type galaxies is almost constant (~0.3) at z ? 1.1. In addition, we find that the sizes of the BEGs in a given redshift bin decrease as redshift decreases. The BEGs look similar to the REGs in the images and surface brightness profiles. However, at least 27 BEGs show traces of tidal disturbances in their fine structure: elongated cores, off-center cores, asymmetric internal color distributions, tidally distorted outer structures, collisional rings, or very nearby companions. Twenty-one BEGs are detected in the X-ray bands, and 11 of them are as luminous as L0.5-10 keV ? 1043.5 ergs s-1, indicating the existence of AGNs at their centers. These results show that at least half of the BEGs may be the descendants of mergers or interacting galaxies and that at least a quarter of the BEGs may be AGN host galaxies. The BEGs may evolve into REGs, and the size evolution of the BEGs is consistent with the galactic downsizing scenario.

The connection between star-forming galaxies, AGN host galaxies, and early-type galaxies in the SDSS

We present a study of the connection between star-forming galaxies, AGN host galaxies, and normal early-type galaxies in the Sloan Digital Sky Survey (SDSS). Using the SDSS DR5 and DR4plus data, we select our early-type galaxy sample in the color versus color-gradient space, and we classify the spectral types of the selected early-type galaxies into normal, star-forming, Seyfert, and LINER classes, using several spectral line flux ratios. We investigate the slope in the fundamental space for each class of early-type galaxies and find that there are obvious differences in the slopes of the fundamental planes (FPs) among the different classes of early-type galaxies, in the sense that the slopes for Seyfert and star-forming galaxies are flatter than those for normal galaxies and LINERs. This may be the first identification of the systematic variation of the FP slope among the subclasses of early-type galaxies. The difference in the FP slope might be caused by the difference in the degree of nonhomology among different classes or by the difference of gas contents in their merging progenitors. One possible scenario is that the AGN host galaxies and star-forming galaxies are formed by gas-rich merging and that they may evolve into normal early-type galaxies after finishing their star formation or AGN activities.

SMALL-SCALE CONFORMITY OF THE VIRGO CLUSTER GALAXIES

We investigate the small-scale conformity in color between bright galaxies and their faint companions in the Virgo cluster. Cluster member galaxies are spectroscopically determined using the Extended Virgo Cluster Catalog (EVCC) and the Sloan Digital Sky Survey Data Release 12 (SDSS DR12). We find that the luminosity-weighted mean color of faint galaxies depends on the color of adjacent bright galaxy as well as on the cluster-scale environment (gravitational potential index). From this result for the entire area of the Virgo cluster, it is not distinguishable whether the small-scale conformity is genuine or is artificially produced due to cluster-scale variation of galaxy color. To disentangle this degeneracy, we divide the Virgo cluster area into three sub-areas so that the cluster-scale environmental dependence is minimized: A1 (central), A2 (intermediate) and A3 (outermost). We find conformity in color between bright galaxies and their faint companions (color-color slope significance S ~ 2.73 sigma and correlation coefficient cc ~ 0.50) in A2, where the cluster-scale environmental dependence is almost negligible. On the other hand, the conformity is not significant or very marginal (S ~ 1.75 sigma and cc ~ 0.27) in A1. The conformity is not significant either in A3 (S ~ 1.59 sigma and cc ~ 0.44), but the sample size is too small in this area. These results are consistent with a scenario in which the small-scale conformity in a cluster is a vestige of infallen groups and these groups lose conformity as they come closer to the cluster center.

MEASURABLE RELATIONSHIP BETWEEN BRIGHT GALAXIES AND THEIR FAINT COMPANIONS IN WHL J085910.0+294957, A GALAXY CLUSTER AT z = 0.30: VESTIGES OF INFALLEN GROUPS?

The properties of satellite galaxies are closely related to their host galaxies in galaxy groups. In cluster environments, on the other hand, the interaction between close neighbors is known to be limited. Our goal is to examine the relationships between host and satellite galaxies in the harsh environment of a galaxy cluster. To achieve this goal, we study a galaxy cluster WHL J085910.0+294957 at z = 0.30 using deep images obtained with CQUEAN CCD camera mounted on the 2.1-m Otto Struve telescope. After member selection based on the scaling relations of photometric and structural parameters, we investigate the relationship between bright (M_i < -18) galaxies and their faint (-18 < M_i < -15) companions. The weighted mean color of faint companion galaxies shows no significant dependence (< 1 sigma to Bootstrap uncertainties) on cluster-centric distance and local luminosity density as well as the luminosity and concentration of an adjacent bright galaxy. However, the weighted mean color shows marginal dependence (~ 2.2 sigma) on the color of an adjacent bright galaxy, when the sample is limited to bright galaxies with at least 2 faint companions. By using a permutation test, we confirm that the correlation in color between bright galaxies and their faint companions in this cluster is statistically significant with a confidence level of 98.7%. The statistical significance increases if we additionally remove non-members using the SDSS photometric redshift information (~ 2.6 sigma and 99.3%). Our results suggest three possible scenarios: (1) vestiges of infallen groups, (2) dwarf capturing, and (3) tidal tearing of bright galaxies.

Distance and Reddening of the Isolated Dwarf Irregular Galaxy NGC 1156

We present a photometric estimation of the distance and reddening values to the dwarf irregular galaxy NGC 1156, that is one of the best targets for the study of isolated dwarf galaxies in the nearby universe. We used imaging data sets of the Hubble Space Telescope (HST) Advanced Camera for Surveys, High Resolution Channel of the central region of NGC 1156 (26 00 � 29 00 ) available in the HST archive for this study. From the (UB, BV ) color-color diagram, we first estimated the total (foreground + internal) reddening toward NGC 1156 of E(BV ) = 0.35 ˙ 0.05 mag, whereas only the foreground reddening was previously known to be E(BV ) = 0.16 mag (1984, ApJS, 54, 33) or 0.24 mag (1998, ApJ, 500, 525). Based on the brightest-star method, selecting the three brightest blue supergiant (BSG) stars with a mean B magnitude of hB(3B)i = 21.94 and the three brightest red supergiant (RSG) stars with a mean V magnitude of hV (3R)i = 22.76, we derived the distance modulus to NGC 1156 to be (mM )0;BSG = 29.16 mag and .mM/ 0;RSG = 29.55 mag. By using weights of 1 for BSGs and 1.5 for RSGs, we finally obtained a weighted mean distance modulus to NGC 1156, .mM/ 0 = 29.39 ˙ 0.20 mag (distance = 7.6 ˙ 0.7 Mpc), which is in agreement with previous estimates. Combining the photometry data of this study with those of Karachentsev, Musella, and Grimardi (1996, A&A, 310, 722) gives a smaller distance to NGC 1156, which is discussed together with the limits of the data.

Intra-night optical variability of AGN in the COSMOS field with the KMTNet

Active Galactic Nucleus (AGN) variability can be used to study the physics of the region in the vicinity of the central black hole. In this paper, we investigated intra-night optical variability of AGN in the COSMOS field in order to understand the AGN instability at the smallest scale. Observations were performed using the KMTNet on three separate nights for 2.5-5 hour at a cadence of 20-30 min. We find that the observation enables the detection of the short-term variability as small as

Color Dispersion as an Indicator of Stellar Population Complexity: Insights from the Pixel Color–Magnitude Diagrams of 32 Bright Galaxies in Abell 1139 and Abell 2589

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JINGLE, a JCMT legacy survey of dust and gas for galaxy evolution studies : I. Survey overview and first results

0.02 and 0.1 mag for