Browsing by Author "Sheen, Yun-Kyeong"

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    Discovery of Ram-pressure stripped gas around an Elliptical Galaxy in Abell 2670.
    (2017) Sheen, Yun-Kyeong; Treister, Ezequiel; Smith, Rory; Jaffé, Yara; Kim, Minjin; Yi, Sukyoung K.; Duc, Pierre-Alain; Nantais, Julie; Candlish, Graeme; Demarco, R.
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    Distribution of Merging and Post-merger Galaxies in Nearby Galaxy Clusters
    (2024) Kim, Duho; Sheen, Yun-Kyeong; Jaffe, Yara L.; Kelkar, Kshitija; Ranjan, Adarsh; Piraino-Cerda, Franco; Crossett, Jacob P.; Lourenco, Ana Carolina Costa; Martin, Garreth; Nantais, Julie B.; Demarco, Ricardo; Treister, Ezequiel; Yi, Sukyoung K.
    We study the incidence and spatial distribution of galaxies that are currently undergoing gravitational merging (M) or that have signs of being post-merger (PM) in six galaxy clusters (A754, A2399, A2670, A3558, A3562, and A3716) within the redshift range of 0.05 less than or similar to z less than or similar to 0.08. To this aim, we obtained Dark Energy Camera mosaics in the u ' , g ' , and r ' bands covering up to 3 x R 200 of the clusters, reaching 28 mag arcsec-2 surface brightness limits. We visually inspect u ' g ' r ' color-composite images of volume-limited (M r < -20) cluster member galaxies to identify whether galaxies are of M or PM type. We find 4% M-type and 7% PM-type galaxies in the galaxy clusters studied. By adding spectroscopic data and studying the projected phase-space diagram (PPSD) of the projected clustocentric radius and the line-of-sight velocity, we find that PM-type galaxies are more virialized than M-type galaxies, having a 1%-5% higher fraction within the escape-velocity region, while the fraction of M-type was similar to 10% higher than the PM type in the intermediate environment. Similarly, on a substructure analysis, M types were found in groups in the outskirts, while PM-type populated groups were found in ubiquitous regions of the PPSD. Adopting literature-derived dynamical state indicator values, we observed a higher abundance of M types in dynamically relaxed clusters. This finding suggests that galaxies displaying post-merger features within clusters likely merged in low-velocity environments, including clusters outskirts and dynamically relaxed clusters.
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    Formation of S0s in extreme environments I: clues from kinematics and stellar populations
    (2020) Coccato, Lodovico; Jaffe, Yara L.; Cortesi, Arianna; Merrifield, Michael; Johnston, Evelyn; Rodriguez del Pino, Bruno; Haeussler, Boris; Chies-Santos, Ana L.; Mendes de Oliveira, Claudia L.; Sheen, Yun-Kyeong; Menendez-Delmestre, Karin
    Despite numerous efforts, it is still unclear whether lenticular galaxies (S0s) evolve from spirals whose star formation was suppressed, or formed trough mergers or disc instabilities. In this paper we present a pilot study of 21 S0 galaxies in extreme environments (field and cluster), and compare their spatially resolved kinematics and global stellar populations. Our aim is to identify whether there are different mechanisms that form S0s in different environments. Our results show that the kinematics of S0 galaxies in field and cluster are, indeed, different. Lenticulars in the cluster are more rotationally supported, suggesting that they are formed through processes that involve the rapid consumption or removal of gas (e.g. starvation, ram pressure stripping). In contrast, S0s in the field are more pressure supported, suggesting that minor mergers served mostly to shape their kinematic properties. These results are independent of total mass, luminosity, or disc-to-bulge ratio. On the other hand, the mass-weighted age, metallicity, and star formation time-scale of the galaxies correlate more with mass than with environment, in agreement with known relations from previous work, such as the one between mass and metallicity. Overall, our results re-enforce the idea that there are multiple mechanisms that produce S0s, and that both mass and environment play key roles. A larger sample is highly desirable to confirm or refute the results and the interpretation of this pilot study.
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    Formation of S0s in extreme environments II: The star-formation histories of bulges, discs, and lenses
    (2021) Johnston, Evelyn J.; Aragon-Salamanca, Alfonso; Fraser-McKelvie, Amelia; Merrifield, Michael; Haeussler, Boris; Coccato, Lodovico; Jaffe, Yara; Cortesi, Ariana; Chies-Santos, Ana; Rodriguez Del Pino, Bruno; Sheen, Yun-Kyeong
    Different processes have been proposed to explain the formation of S0s, including mergers, disc instabilities, and quenched spirals. These processes are expected to dominate in different environments, and thus leave characteristic footprints in the kinematics and stellar populations of the individual components within the galaxies. New techniques enable us to cleanly disentangle the kinematics and stellar populations of these components in IFU observations. In this paper, we use BUDDI to spectroscopically extract the light from the bulge, disc, and lens components within a sample of eight S0 galaxies in extreme environments observed with MUSE. While the spectra of bulges and discs in S0 galaxies have been separated before, this work is the first to isolate the spectra of lenses. Stellar populations analysis revealed that the bulges and lenses have generally similar or higher metallicities than the discs, and the alpha-enhancement of the bulges and discs are correlated, while those of the lenses are completely unconnected to either component. We conclude that the majority of the mass in these galaxies was built up early in the lifetime of the galaxy, with the bulges and discs forming from the same material through dissipational processes at high redshift. The lenses, on the other hand, formed over independent time-scales at more random times within the lifetime of the galaxy, possibly from evolved bars. The younger stellar populations and asymmetric features seen in the field S0s may indicate that these galaxies have been affected more by minor mergers than the cluster galaxies.
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    Recent Galaxy Mergers and Residual Star Formation of Red Sequence Galaxies in Galaxy Clusters
    (2016) Sheen, Yun-Kyeong; Treister, Ezequiel; Yi, Sukyoung K.; Ree, Chang H.; Jaffé, Yara; Demarco, R.