35 research outputs found
Merger relics of cluster galaxies
Context. Sheen and collaborators recently found that a surprisingly large
portion (38%) of massive early-type galaxies in heavy clusters show strong
merger-related disturbed features. This contradicts the general understanding
that massive clusters are hostile environments for galaxy mergers. Considering
the significance of mergers in galaxy evolution, it is important to understand
this. Aims. We aim to present a theoretical foundation that explains galaxy
mergers in massive clusters. Methods. We used the N-body simulation technique
to perform a cosmological-volume simulation and derive dark-halo merger trees.
Then, we used the semi-analytic modeling technique to populate each halo with
galaxies. We ran hydrodynamic simulations of galaxy mergers to estimate the
lifetime of merger features for the imaging condition used by Sheen and
collaborators. We applied this merger feature lifetime to our semi-analytic
models. Finally, we counted the massive early-type galaxies in heavy model
clusters that would show strong merger features. Results. While there still are
substantial uncertainties, our preliminary results are remarkably close to the
observed fraction of galaxies with merger features. Key ingredients for the
success are twofold: firstly, the subhalo motion in dark haloes has been
accurately traced, and, second, the lifetime of merger features has been
properly estimated. As a result, merger features are expected to last very long
in cluster environments. Many massive early-type galaxies in heavy clusters
therefore show merger features not because they experience mergers in the
current clusters in situ, but because they still carry their merger features
from their previous halo environments. Conclusions. Investigating the merger
relics of cluster galaxies is potentially important, because it uniquely allows
us to backtrack the halo merger history.Comment: 4 pages, 3 figures, accepted for publication in A&A Research Not
Discovery of ram-pressure stripped gas around an elliptical galaxy in Abell 2670
Studies of cluster galaxies are increasingly finding galaxies with
spectacular one-sided tails of gas and young stars, suggestive of intense
ram-pressure stripping. These so-called "jellyfish" galaxies typically have
late-type morphology. In this paper, we present MUSE observations of an
elliptical galaxy in Abell 2670 with long tails of material visible in the
optical spectra, as well as blobs with tadpole-like morphology. The spectra in
the central part of the galaxy reveals a stellar component as well as ionized
gas. The stellar component does not have significant rotation, while the
ionized gas defines a clear star-forming gas disk. We argue, based on deep
optical images of the galaxy, that the gas was most likely acquired during a
past wet merger. It is possible that the star-forming blobs are also remnants
of the merger. In addition, the direction and kinematics of the one-sided
ionized tails, combined with the tadpole morphology of the star-forming blobs,
strongly suggests that the system is undergoing ram pressure from the
intracluster medium. In summary, this paper presents the discovery of a
post-merger elliptical galaxy undergoing ram pressure stripping.Comment: 6 pages, 5 figures, accepted for publication in ApJ
The influence of the Drygalski Ice Tongue on the local ocean
ABSTRACT
The Drygalski Ice Tongue presents an ~80 km long floating obstacle to alongshore flows in the Victoria Land coastal ocean region of the Western Ross Sea. Here we use oceanographic data from near to the tongue to explore the interplay between the floating glacier and the local currents and stratification. A vessel-based circuit of the glacier, recording ocean temperature and salinity profiles, reveals the southwest corner to be the coldest and most complex in terms of vertical structure. The southwest corner structure beneath the surface warm, salty layer sustains a block of very cold water extending to 200 m depth. In this same location there was a distinct layer at 370 m not seen anywhere else of water at ~â1.93°C. The new observations broadly, but not directly, support the presence of a coherent Victoria Land Coastal Current. The data suggest the northward moving coastal current turns against the Coriolis force and works its way anticlockwise around the glacier, but with leakage beneath the glacier through the highly 'rippled' underside, resulting in a spatially heterogeneous supply to the Terra Nova Bay Polynya region â an important location for the formation of high-salinity shelf water
Post-merger Signatures of Red-sequence Galaxies in Rich Abell Clusters at
We have investigated the post-merger signatures of red-sequence galaxies in
rich Abell clusters at 0.1: A119, A2670, A3330 and A389. Deep
images in u', g', r' and medium-resolution galaxy spectra were taken using
MOSAIC 2 CCD and Hydra MOS mounted on a Blanco 4-m telescope at CTIO.
Post-merger features are identified by visual inspection based on asymmetric
disturbed features, faint structures, discontinuous halo structures, rings and
dust lanes. We found that ~ 25% of bright (M_r < -20) cluster red-sequence
galaxies show post-merger signatures in four clusters consistently. Most (~
71%) of the featured galaxies were found to be bulge-dominated, and for the
subsample of bulge-dominated red-sequence galaxies, the post-merger fraction
rises to ~ 38%. We also found that roughly 4% of bulge-dominated red-sequence
galaxies interact (on-going merger). A total of 42% (38% post-merger, 4%
on-going merger) of galaxies show merger-related features. Compared to a field
galaxy study with a similar limiting magnitude (van Dokkum 2005), our cluster
study presents a similar post-merger fraction but a markedly lower on-going
merger fraction. The merger fraction derived is surprisingly high for the high
density of our clusters, where the fast internal motions of galaxies are
thought to play a negative role in galaxy mergers. The fraction of post-merger
and on-going merger galaxies can be explained as follows. Most of the
post-merger galaxies may have carried over their merger features from their
previous halo environment, whereas interacting galaxies interact in the current
cluster in situ. According to our semi-analytic calculation, massive cluster
haloes may very well have experienced tens of halo mergers over the last 4-5
Gyr; post-merger features last that long, allowing these features to be
detected in our clusters today. (Abridged)Comment: 16 pages, 15 figures, 7 tables, accepted for publication in ApJ
Ross ice shelf icequakes associated with ocean gravity wave activity
Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 46(15), (2019): 8893-8902, doi:10.1029/2019GL084123.Gravity waves impacting ice shelves illicit a suite of responses that can affect ice shelf integrity. Broadband seismometers deployed on the Ross Ice Shelf, complemented by a nearâicefront seafloor hydrophone, establish the association of strong icequake activity with ocean gravity wave amplitudes (AG) below 0.04 Hz. The Ross Ice Shelfâfront seismic vertical displacement amplitudes (ASV) are well correlated with AG, allowing estimating the frequencyâdependent transfer function from gravity wave amplitude to icefront vertical displacement amplitude (TGSV(f)). TGSV(f) is 0.6â0.7 at 0.001â0.01 Hz but decreases rapidly at higher frequencies. Seismicity of strong icequakes exhibits spatial and seasonal associations with different gravity wave frequency bands, with the strongest icequakes observed at the icefront primarily during the austral summer when sea ice is minimal and swell impacts are strongest.Bromirski, Gerstoft, and Chen were supported by NSF grant PLRâ1246151. Bromirski also received support from NSF grant OPPâ1744856 and CALâDPRâC1670002. Stephen, Wiens, Aster, and Nyblade were supported under NSF grants PLRâ1246416, 1142518, 1141916, and 1142126, respectively. Lee and Yun were support by a research grant from the Korean Ministry of Oceans and Fisheries (KIMST20190361; PM19020). Seismic instruments and onâice support were provided by the Incorporated Research Institutions for Seismology (IRIS) through the PASSCAL Instrument Center at New Mexico Tech. The RIS and KPDR seismic data are archived at the IRIS Data Management Center, http://ds.iris.edu/ds/nodes/dmc/, with network codes XH and KP, respectively. The facilities of the IRIS Consortium are supported by the National Science Foundation under Cooperative Agreement EARâ1261681 and the DOE National Nuclear Security Administration. We thank Patrick Shore, Michael Baker, Cai Chen, Robert Anthony, Reinhard Flick, Jerry Wanetick, Weisen Shen, Tsitsi Madziwa Nussinov, and Laura Stevens for their help with field operations. Logistical support from the U.S. Antarctica Program and staff at McMurdo Station was critical and is much appreciated.2020-02-0
A Spectro-photometric Search for Galaxy Clusters in SDSS
Recent large-scale galaxy spectroscopic surveys, such as the Sloan Digital
Sky Survey (SDSS), enable us to execute a systematic, relatively-unbiased
search for galaxy clusters. Such surveys make it possible to measure the 3-d
distribution of galaxies but are hampered by the incompleteness problem due to
fiber collisions. In this study we aim to develop a density measuring technique
that alleviates the problem and derives densities more accurately by adding
additional cluster member galaxies that follow optical color-magnitude
relations for the given redshift. The new density measured with both
spectroscopic and photometric data shows a good agreement with apparent
information on cluster images and is supported by follow-up observations. By
adopting this new method, a total of 924 galaxy clusters are found
from the SDSS DR5 database in the redshift range , of which 212 are
new. Local maximum-density galaxies successfully represent cluster centers. We
provide the cluster catalogue including a number of cluster parameters.Comment: Web-page address has been revised and minor corrections are don