Sok-Jin Yoon

The colors of globular clusters in most large elliptical galaxies are bimodal. This is generally taken as evidence for the presence of two cluster subpopulations that have different geneses. However, here we find that, because of the nonlinear nature of the metallicity-to-color transformation, a coeval group of old clusters with a unimodal metallicity spread can exhibit color bimodality. The models of cluster colors indicate that horizontal-branch stars are the main drivers behind the empirical

The industrial clusters literature has shaped contemporary thinking on the potential of small firms to become globally competitive through agglomeration gains and collective action. However, clusters often generate negative environmental externalities. The industrial ecology framework suggests that producer agglomerations can spawn closed loop production arrangements that reduce environmental diseconomies. To date there has been little engagement between the industrial cluster and industrial eco

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One of the long-standing problems in modern astronomy is the curious division of Galactic globular clusters, the "Oosterhoff dichotomy," according to the properties of their RR Lyrae stars. Here, we find that most of the lowest metallicity ([Fe/H] < -2.0) clusters, which are essential to an understanding of this phenomenon, display a planar alignment in the outer halo. This alignment, combined with evidence from kinematics and stellar population, indicates a captured origin from a satellite gala

One of the conundrums in extragalactic astronomy is the discrepancy in observed metallicity distribution functions (MDFs) between the two prime stellar components of early-type galaxies-globular clusters (GCs) and halo field stars. This is generally taken as evidence of highly decoupled evolutionary histories between GC systems and their parent galaxies. Here we show, however, that new developments in linking the observed GC colors to their intrinsic metallicities suggest nonlinear color-to-meta

ABSTRACT The dynamical formation of black hole binaries in globular clusters that merge due to gravitational waves occurs more frequently in higher stellar density. Meanwhile, the probability to form intermediate mass black holes (IMBHs) also increases with the density. To explore the impact of the formation and growth of IMBHs on the population of stellar mass black hole binaries from globular clusters, we analyse the existing large survey of Monte Carlo globular cluster simulation data (mocca-

Strong Balmer absorption lines and the lack of Hα and [O ii] emission lines signify that E+A galaxies are post-starburst systems. Recent studies suggest that E+As may undergo the transition from the ‘blue cloud’ to the ‘red sequence’ and eventually migrate to red-sequence early-type galaxies. An observational validation of this scenario is to identify the intervening galaxy population between E+As and the red sequence. Motivated by recent findings with Galaxy Evolution Explorer (GALEX) that an u

Abstract Galaxies in pairs show enhanced star formation (SF) compared to their counterparts in isolation, which is often explained by the tidal effect of neighboring galaxies. Recent observations, however, reported that galaxies paired with early-type neighbors do not undergo the SF enhancement. Here we revisit the influence of neighbors using a large sample of paired galaxies from the Sloan Digital Sky Survey and a carefully constructed control sample of isolated counterparts. We find that star

Abstract We present a statistical analysis of the flybys of dark matter halos compared to mergers, using cosmological N -body simulations. We mainly focus on gravitationally interacting target halos with mass of 10 10.8 –10 13.0 h −1 M ⊙ , and their neighbors are counted only when the mass ratio is 1:3–3:1 and the distance is less than the sum of the virial radii of target and neighbor. The neighbors are divided into the flyby or merger samples if the pair’s total energy is greater or smaller, r

Abstract We present an extensive catalog of 5405 early-type dwarf (dE) galaxies located in the various environments, i.e., clusters, groups, and fields, of the local universe ( z &lt; 0.01). The dEs are selected through visual inspection of the Legacy survey’s g – r – z combined tricolor images. The inspected area, covering a total sky area of 7643 deg 2 , encompasses two local clusters (Virgo and Fornax), 265 groups, and the regions around 586 field galaxies of M K &lt; −21 mag. The catalog aim

Abstract We study a low-mass spiral galaxy NGC 2750 (∼5 times less massive than the Milky Way), located ∼40 Mpc away in a sparse region that hosts seven satellite galaxies within a projected distance of 150 Kpc. Among them six are star-forming dwarfs with stellar masses of &gt;≈10 7 M ⊙ and one is an early-type dwarf with a stellar mass of 2.6 × 10 6 M ⊙ . The star-forming dwarfs are gas rich, with gas mass fractions as high as Log( M H i / M * ) = 1.2 and their star formation rates vary between

Abstract The color distributions of globular clusters (GCs) in individual early-type galaxies show great diversity in their morphology. Based on the conventional “linear” relationship between the colors and metallicities of GCs, the GC metallicity distributions inferred from colors and in turn their formation histories, should be as diverse as they appear. In contrast, here we show that an alternative scenario rooted in the “nonlinear” nature of the metallicity-to-color transformation points to

ABSTRACT The metallicity distribution function of globular clusters (GCs) in galaxies is a key to understanding galactic formation and evolution. The calcium II triplet (CaT) index has recently become a popular metal abundance indicator thanks to its sensitivity to GC metallicity. Here we revisit and assess the reliability of CaT as a metallicity indicator using our new stellar population synthesis simulations based on empirical high-resolution fluxes. The model shows that the CaT strength of ol