Abstract
The presence of transitional dwarf galaxies in filaments and cluster outskirts may be closely related to preprocessing in the filament; however, the underlying mechanism is not yet ...comprehensively understood. We present the spatially resolved chemical and kinematical properties of three blue-cored dwarf early-type galaxies (dE(bc)s) in the Virgo cluster and Virgo-related filaments (Crater and Virgo III) using the Sydney-AAO Multi-object Integral-field spectrograph galaxy Survey. We map the spatial distribution of H
α
, oxygen abundance (O/H), nitrogen-to-oxygen abundance ratio (N/O), stellar population age, and gas-stellar internal kinematics. We find irregular shapes of enhanced star-forming regions from the centers to the outlying regions of blue cores in dE(bc)s. These regions are relatively metal poor compared with the surrounding regions, rendering the overall metallicity gradient of each galaxy positive. Furthermore, they exhibit higher N/O ratios at a given O/H relative to their surroundings, implying metal-poor gas infall by external processes. The equivalent width of the H
α
emission line in metal-poor regions indicates young age of star formation, 6–8 Myr. The disturbed ionized gas velocity field, one of the most prominent features of galaxy mergers is also discovered in two dE(bc)s. We propose that a moderately dense filament environment is favorable for the formation of blue cores in dEs, in which dE(bc)s in filaments may have already been transformed before they fall into the Virgo cluster. This process may contribute to the composition of galaxy population at the outskirts of the cluster.
Abstract
We investigate the stellar and ionized gas kinematics, and stellar populations of NGC 3182 galaxy using integral field spectrograph data from the Calar Alto Legacy Integral Field Area ...survey. We try to clarify the nature of the ring structure in NGC 3182. We find a negative stellar age gradient out to the ring, while
α
/Fe considerably enhanced in the ring. The stellar metallicity shows a smooth negative gradient. From the line-ratio diagnostic diagrams, we confirm that NGC 3182 is a Seyfert galaxy from emission-line flux ratio, while the gas in the inner ring is ionized mostly by young stars. However, any obvious feature of outflows is not found in its gas kinematics. In the ring, star formation seems to have recently occurred and the gas metallicity is slightly enhanced compared to the center. From our results, we conclude that star formation has occurred in the circumnuclear region within a short period and this may result from a positive feedback by active galactic nucleus radiation pressure.
Abstract
We present a BVI photometric study of four old open clusters (OCs) in the the Milky Way, Czernik 30, Berkeley 34, Berkeley 75, and Berkeley 76 using the observation data obtained with the ...Small and Moderate Aperture Research Telescope System 1.0 m telescope at the Cerro Tololo Inter-American Observatory, Chile. These four OCs are located at the anti-Galactocentric direction and in the Galactic plane. We determine the fundamental physical parameters for the four OCs, such as age, metallicity, distance modulus, and color excess, using red clump and PARSEC isochrone fitting methods after finding center and size of the four OCs. These four old OCs are 2–3 Gyr old and 6–8 kpc away from the Sun. The metallicity (Fe/H) values of the four OCs are between −0.6 and 0.0 dex. We combine data for these four OCs with those for old OCs from five literatures resulting in 236 objects to investigate Galactic radial-metallicity distribution. The gradient of a single linear fit for this Galactocentric Fe/H distribution is −0.052 ± 0.004 dex kpc
−1
. If we assume the existence of a discontinuity in this radial-metallicity distribution, the gradient at Galactocentric radius <12 kpc is −0.070 ± 0.006 dex kpc
−1
, while that at the outer part is −0.016 ± 0.010 which is flatter than that of the inner part. Although there are not many sample clusters at the outer part, the broken linear fit seems to better follow the observation data.
Abstract
We investigate the fraction of quenched satellite galaxies in host galaxy groups and clusters using TNG300 in the IllustrisTNG cosmological magnetohydrodynamical simulations. The simulations ...show that most satellites are quenched after they fall into their final hosts, and that post-processing is a more dominant mechanism of galaxy quenching than pre-processing. We find that the fraction of quenched satellites at
z
= 0 increases with host mass, which implies that more massive hosts have higher quenching efficiency because they have more massive groups infalling. Furthermore, we find that hosts that have many early-infall satellites show a higher fraction of quenched satellites at
z
= 0 than those that have many late-infall satellites, which results in a scatter of the quenched fraction of satellites in a given mass range of hosts at
z
= 0. Our results highlight the significance of the mass of hosts and the different infall times of satellites in understanding galaxy quenching.
Abstract
We present the discovery of a new H
i
structure in the NGC 7194 group from the observations using the Karl G. Jansky Very Large Array. NGC 7194 group is a nearby (
z
∼ 0.027) small galaxy ...group with five quiescent members. The observations reveal a 200 kpc long H
i
plume that spans the entire group with a total mass of
M
H I
= 3.4 × 10
10
M
⊙
. The line-of-sight velocity of the H
i
gas gradually increases from south (7200 km s
−1
) to north (8200 km s
−1
), and the local velocity dispersion is up to 70 km s
−1
. The structure is not spatially coincident with any member galaxies but it shows close associations with a number of blue star-forming knots. Intragroup H
i
gas is not rare, but this particular structure is still one of the unusual cases in the sense that it does not show any clear connection with sizable galaxies in the group. We discuss the potential origins of this large-scale H
i
gas in the NGC 7194 group and its relation with the intergalactic star-forming knots. We propose that this H
i
feature could have originated from tidal interactions among group members or the infall of a late-type galaxy into the group. Alternatively, it might be leftover gas from flyby intruders.
Abstract We search for quasi-stellar objects (QSOs) in a wide area of the south ecliptic pole (SEP) field, which has been and will continue to be intensively explored through various space missions. ...For this purpose, we obtain deep broadband optical images of the SEP field covering an area of ∼14.5 × 14.5 deg 2 with the Korea Microlensing Telescope Network (KMTNet). The 5 σ detection limits for point sources in the BVRI bands are estimated to be ∼22.59, 22.60, 22.98, and 21.85 mag, respectively. Utilizing data from the Wide-field Infrared Survey Explorer, unobscured QSO candidates are selected among the optically pointlike sources using mid-infrared (MIR) and optical–MIR colors. To refine our selection further and eliminate any contamination not adequately removed by the color-based selection, we perform spectral energy distribution fitting with archival photometric data ranging from optical to MIR. As a result, we identify a total of 2383 unobscured QSO candidates in the SEP field. We also apply a similar method to the north ecliptic pole field using Pan-STARRS data and obtain a similar result of identifying 2427 candidates. The differential number count per area of our QSO candidates is in good agreement with those measured from spectroscopically confirmed ones in other fields. Finally, we compare the results with the literature and discuss how this work will impact future studies, especially upcoming space missions.
We present a study on the environments of the Sloan Digital Sky Survey (SDSS) galaxies divided into fine classes based on their morphology, colour and spectral features. The SDSS galaxies are ...classified into early-type and late-type; red and blue; passive, H ii, Seyfert and low-ionization nuclear emission-line region (LINER), which returns a total of 16 fine classes of galaxies. We estimate the local number density, target-excluded local luminosity density, local colour, close pair fraction and the luminosity and colour of the brightest neighbour, which are compared between the fine classes comprehensively. The morphology–colour class of galaxies strongly depends on the local density, with the approximate order of high-density preference: red early-type galaxies (REGs); red late-type galaxies (RLGs); blue early-type galaxies (BEGs) and blue late-type galaxies (BLGs). We find that high-density environments (like cluster environments) seem to suppress active galactic nucleus activity. The pair fraction of H ii REGs does not show a statistically significant difference from that of passive REGs, while the pair fraction of H ii BLGs is smaller than that of non-H ii BLGs. H ii BLGs show obvious double (red + blue) peaks in the distribution of the brightest neighbour colour, while red galaxies show a single red peak. The brightest neighbours of Seyfert BLGs tend to be blue, while those of LINER BLGs tend to be red, which implies that the difference between Seyfert and LINER may be related to the pair interaction. Other various environments of the fine classes are investigated, and their implications for galaxy evolution are discussed.
In hierarchical galaxy formation models, galaxies evolve through mergers and accretions. Tidally disrupted debris from these processes can remain as diffuse, faint structures, which can provide ...useful insight into the assembly history of galaxies. To investigate the properties of the faint structures in outskirts of nearby galaxies, we conduct deep and wide-field imaging survey with Korea Microlensing Telescope Network (KMTNet). We present our observing strategy and optimal data reduction process to recover the faint extended features in the imaging data of NGC 1291 taken with KMTNet. Through the dark sky flat-fielding and optimal sky subtraction, we can effectively remove inhomogeneous patterns. In the combined images, the peak-to-peak global sky gradients were reduced to less than ∼0.5% and ∼0.3% of the original B- and R-band sky levels, respectively. However, we find local spatial fluctuations in the background sky that can affect the precise measurement of the sky value. Consequently, we can reach the surface brightness of and mag arcsec−2 in azimuthally averaged one-dimensional surface brightness profiles, which is mainly limited by the uncertainty in the sky determination. These results suggest that the deep imaging data produced by KMTNet are suitable to study the faint features of nearby galaxies such as outer disks and dwarf companions, but unideal (not impossible) to detect stellar halos. The one-dimensional profile revealed that NGC 1291 appeared to have a Type I disk out to R ∼30 kpc with no obvious color gradient, and excess light due to a stellar halo was undetected.
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