Abstract
We investigate the formation of jellyfish galaxies using radiation-hydrodynamic simulations of gas-rich dwarf galaxies with a multiphase interstellar medium (ISM). We find that the ...ram-pressure-stripped (RPS) ISM is the dominant source of molecular clumps in the near wake within 10 kpc from the galactic plane, while in situ formation is the major channel for dense gas in the distant tail of the gas-rich galaxy. Only 20% of the molecular clumps in the near wake originate from the intracluster medium (ICM); however, the fraction reaches 50% in the clumps located at 80 kpc from the galactic center since the cooling time of the RPS gas tends to be short owing to the ISM–ICM mixing (≲10 Myr). The tail region exhibits a star formation rate of 0.001–0.01
M
⊙
yr
−1
, and most of the tail stars are born in the stripped wake within 10 kpc from the galactic plane. These stars induce bright H
α
blobs in the tail, while H
α
tails fainter than 6 × 10
38
erg s
−1
kpc
−2
are mostly formed via collisional radiation and heating due to mixing. We also find that the stripped tails have intermediate X-ray-to-H
α
surface brightness ratios (1.5 ≲
F
X
/
F
H
α
≲ 20), compared to the ISM (≲1.5) or pure ICM (≫20). Our results suggest that jellyfish features emerge when the ISM from gas-rich galaxies is stripped by strong ram pressure, mixes with the ICM, and enhances the cooling in the tail.
We present the KASI-Yonsei Deep Imaging Survey of Clusters targeting 14 clusters at 0.015 z 0.144 using the Inamori Magellan Areal Camera and Spectrograph on the 6.5 m Magellan Baade telescope and ...the MegaCam on the 3.6 m Canada-France-Hawaii Telescope. We provide a catalog of cluster galaxies that lists magnitudes, redshifts, morphologies, bulge-to-total ratios, and local density. Based on the 1409 spectroscopically confirmed cluster galaxies brighter than −19.8 in the r band, we study galaxy morphology, color, and visual features generated by galaxy mergers. We see a clear trend between morphological content and cluster velocity dispersion, which was not presented by previous studies using local clusters. Passive spirals are preferentially found in a highly dense region (i.e., cluster center), indicating that they have gone through environmental quenching. In deep images ( r′ ∼ 27 ), 20% of our sample shows signatures of recent mergers, which is not expected from theoretical predictions and a low frequency of ongoing mergers in our sample (∼4%). Such a high fraction of recent mergers in the cluster environment supports a scenario that the merger events that made the features have preceded the galaxy accretion into the cluster environment. We conclude that mergers affect a cluster population mainly through the preprocessing of recently accreted galaxies.
ABSTRACT
Ram pressure stripping (RPS) is known to be a key environmental effect that can remove interstellar gas from galaxies in a cluster. The RPS process is commonly described as a competition ...between the ram pressure by the intracluster medium and the anchoring pressure on the interstellar medium by the gravitational potential of a galaxy. However, the actual gas stripping process can be more complicated due to the complexity of gas physics such as compression and geometrical self-shielding as well as cooling and heating. In order to verify how well the observed signatures of the RPS process can be understood as simple momentum transfer, we compare the stripping radii of Virgo cluster galaxies in different stages of RPS measured from the H i observation with the predicted gas truncation radii for the given conditions. For the sample undergoing active RPS, we generally find good agreements between predictions and observations within a measurement uncertainty. On the other hand, galaxies likely in the early or later RPS stage and/or the ones with signs of environmental impacts other than RPS such as tidal interaction or starvation show some discrepancies. Our results imply that the conventional RPS relation works reasonably well in a broad sense when RPS is the most dominant process and the galaxy is located where the surrounding environment can be well defined. Otherwise, more careful inspections on the second mechanism and local environment are required to assess the impact of RPS on the target.
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 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 ≲
z
≲0.08. To this aim, we obtained Dark Energy Camera mosaics in the
u
′
,
g
′
, and
r
′
bands covering up to 3 ×
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 ∼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.
Abstract
We perform a deep, wide-field imaging survey of nearby galaxies using H
α
and broadband filters to investigate the characteristics of star formation in galaxies. Motivated by the finding ...that star formation rates (SFRs) derived from H
α
fluxes in dwarf galaxies are systematically lower than those inferred from far-ultraviolet (FUV) fluxes, we attempt to determine whether the same trend exists in the extended disks of two star-forming galaxies. We perform spatially resolved photometry using grid-shaped apertures to measure the FUV and H
α
fluxes of star-forming regions. We also perform spectral energy distribution (SED) fittings using 11 photometric data points (FUV-to-MIR), including data from the literature, to estimate the local properties such as internal attenuation of individual star-forming clumps. Comparing SFR
FUV
and SFR
H
α
, which are converted from the H
α
and FUV fluxes corrected for the local properties, we find that SFR
H
α
/SFR
FUV
tend to decrease as the SFR decreases. We evaluate possible causes of this discrepancy between the two SFRs by restricting parameters in the SED fitting and conclude that deficient H
α
fluxes in the extended disks of galaxies are tightly correlated with recent starbursts. The strong and short starburst, which has been rapidly suppressed over the last 10 Myr, seems to induce a significant discrepancy between the SFR
H
α
and SFR
FUV
. In addition, the recent bursts in the extended disks of galaxies appear to have occurred azimuth-symmetrically, implying that these were likely triggered by gas accretion or internal processes rather than external perturbation.
ABSTRACT
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.
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.
ABSTRACT
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 α-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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