376 research outputs found
Evidence for Ultra-Diffuse Galaxy `Formation' Through Galaxy Interactions
We report the discovery of two ultra-diffuse galaxies (UDGs) which show clear
evidence for association with tidal material and interaction with a larger
galaxy halo, found during a search of the Wide portion of the
Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The two new UDGs,
NGC2708-Dw1 and NGC5631-Dw1, are faint (=13.7 and 11.8 mag),
extended (=2.60 and 2.15 kpc) and have low central surface brightness
(=24.9 and 27.3 mag arcsec), while the stellar stream
associated with each has a surface brightness 28.2 mag
arcsec. These observations provide evidence that the origin of some UDGs
may connect to galaxy interactions, either by transforming normal dwarf
galaxies by expanding them, or because UDGs can collapse out of tidal material
(i.e. they are tidal dwarf galaxies). Further work is needed to understand the
fraction of the UDG population `formed' through galaxy interactions, and wide
field searches for diffuse dwarf galaxies will provide further clues to the
origin of these enigmatic stellar systems.Comment: 9 pages, 3 figures, accepted by ApJ
Systematically Measuring Ultra-Diffuse Galaxies (SMUDGes). V. The Complete SMUDGes Catalog and the Nature of Ultra-Diffuse Galaxies
We present the completed catalog of ultra-diffuse galaxy (UDG) candidates
(7070 objects) from our search of the DR9 Legacy Survey images, including
distance and total mass estimates for 1529 and 1436 galaxies, respectively,
that we provide and describe in detail. From the sample with estimated
distances, we obtain a sample of 585 UDGs ( mag arcsec
and kpc) over 20,000 sq. deg of sky in various environments. We
conclude that UDGs in our sample are limited to
M/M and are on average a factor of 1.5 to 7
deficient in stars relative to the general population of galaxies of the same
total mass. That factor increases with increasing galaxy size and mass up to a
factor of 10 when the total mass of the UDG increases beyond M M. We do not find evidence that this factor has a dependence
on the UDG's large-scale environment.Comment: 21 pages, accepted for publication in ApJS, full catalog available
upon reques
The Quenched Satellite Population Around Milky Way Analogs
We study the relative fractions of quenched and star-forming satellite
galaxies in the Satellites Around Galactic Analogs (SAGA) survey and
Exploration of Local VolumE Satellites (ELVES) program, two nearby and
complementary samples of Milky Way-like galaxies that take different approaches
to identify faint satellite galaxy populations. We cross-check and validate
sample cuts and selection criteria, as well as explore the effects of different
star-formation definitions when determining the quenched satellite fraction of
Milky Way analogs. We find the mean ELVES quenched fraction (), derived using a specific star formation rate (sSFR) threshold,
decreases from 50% to 27% after applying a cut in absolute
magnitude to match that of the SAGA survey (9%).
We show these results are consistent for alternative star-formation
definitions. Furthermore, these quenched fractions remain virtually unchanged
after applying an additional cut in surface brightness. Using a
consistently-derived sSFR and absolute magnitude limit for both samples, we
show that the quenched fraction and the cumulative number of satellites in the
ELVES and SAGA samples broadly agree. We briefly explore radial trends in the
ELVES and SAGA samples, finding general agreement in the number of star-forming
satellites per host as a function of radius. Despite the broad agreement
between the ELVES and SAGA samples, some tension remains with these quenched
fractions in comparison to the Local Group and simulations of Milky Way
analogs.Comment: 13 pages, 7 figures, 1 table, 1 appendix with 2 additional figures.
Main results in Figure 3-6. Submitted to MNRAS and comments welcome
Exploring the Structures and Substructures of the Andromeda Satellite Dwarf Galaxies Cassiopeia III, Perseus I, and Lacerta I
We present results from wide-field imaging of the resolved stellar
populations of the dwarf spheroidal galaxies Cassiopeia III (And XXXII) and
Perseus I (And XXXIII), two satellites in the outer stellar halo of the
Andromeda galaxy (M31). Our WIYN pODI photometry traces the red giant star
population in each galaxy to ~2.5-3 half-light radii from the galaxy center. We
use the Tip of the Red Giant Branch (TRGB) method to derive distances of
(m-M)_0 = 24.62+/-0.12 mag (839 (+48,-450) kpc, or 156 (+16,-13) kpc from M31)
for Cas III and 24.47+/-0.13 mag (738 (+48,-45) kpc, or 351 (+17,-16) kpc from
M31) for Per I. These values are consistent within the errors with TRGB
distances derived from a deeper Hubble Space Telescope study of the galaxies'
inner regions. For each galaxy, we derive structural parameters, total
magnitude, and central surface brightness. We also place upper limits on the
ratio of neutral hydrogen gas mass to optical luminosity, confirming the
gas-poor nature of both galaxies. We combine our data set with corresponding
data for the M31 satellite galaxy Lacerta I (And XXXI) from earlier work, and
search for substructure within the RGB star populations of Cas III, Per I, and
Lac I. We find an overdense region on the west side of Lac I at a significance
level of 2.5-3-sigma and a low-significance filament extending in the direction
of M31. In Cas III, we identify two modestly significant overdensities near the
center of the galaxy and another at two half-light radii. Per I shows no
evidence for substructure in its RGB star population, which may reflect this
galaxy's isolated nature.Comment: 26 pages, 15 figures, 5 tables. Accepted for publication in The
Astronomical Journa
Gas-rich, field ultra-diffuse galaxies host few globular clusters
We present Hubble Space Telescope imaging of 14 gas-rich, low surface
brightness and ultra-diffuse galaxies (UDGs) in the field at distances of 25-36
Mpc. An inspection of point-like sources brighter than the turnover magnitude
of the globular cluster luminosity function and within twice the half-light
radii of each galaxy reveals that, unlike those in denser environments,
gas-rich, field UDGs host very few old globular clusters (GCs). Most of the
targets (nine) have zero candidate GCs, with the remainder having one or two
candidates each. These findings are broadly consistent with expectations for
normal dwarf galaxies of similar stellar mass. This rules out gas-rich, field
UDGs as potential progenitors of the GC-rich UDGs that are typically found in
galaxy clusters. However, some in galaxy groups may be directly accreted from
the field. In line with other recent results, this strongly suggests that there
must be at least two distinct formation pathways for UDGs, and that this
sub-population is simply an extreme low surface brightness extension of the
underlying dwarf galaxy population. The root cause of their diffuse stellar
distributions remains unclear, but the formation mechanism appears to only
impact the distribution of stars (and potentially dark matter), without
strongly impacting the distribution of neutral gas, the overall stellar mass,
or the number of GCs.Comment: Submitted to AAS journal
Total knee arthroplasty: good agreement of clinical severity scores between patients and consultants
BACKGROUND: Nearly 20,000 patients per year in the UK receive total knee arthroplasty (TKA). One of the problems faced by the health services of many developed countries is the length of time patients spend waiting for elective treatment. We therefore report the results of a study in which the Salisbury Priority Scoring System (SPSS) was used by both the surgeon and their patients to ascertain whether there were differences between the surgeon generated and patient generated Salisbury Priority Scores. METHODS: The Salisbury Priority Scoring System (SPSS) was used to assign relative priority to patients with knee osteoarthritis as part of a randomised controlled trial comparing the standard medial parapatellar approach versus the sub-vastus approach in TKA. The operating surgeons and each patient completed the SPSS at the same pre-assessment clinic. The SPSS assesses four criteria, namely progression of disease, pain or distress, disability or dependence on others, and loss of usual occupation. Crosstabs and agreement measures (Cohen's kappa) were performed. RESULTS: Overall, the four SPSS criteria showed a kappa value of 0.526, 0.796, 0.813, and 0.820, respectively, showing moderate to very good agreement between the patient and the operating consultant. Male patients showed better agreement than female patients. CONCLUSION: The Salisbury Priority Scoring System is a good means of assessing patients' needs in relation to elective surgery, with high agreement between the patient and the operating surgeon
An Enigmatic 380 kpc Long Linear Collimated Galactic Tail
We present an intriguing, serendipitously-detected system consisting of an
S0/a galaxy, which we refer to as the "Kite", and a highly-collimated tail of
gas and stars that extends over 380 kpc and contains pockets of star formation.
In its length, narrowness, and linearity the Kite's tail is an extreme example
relative to known tails. The Kite (PGC 1000273) has a companion galaxy, Mrk
0926 (PGC 070409), which together comprise a binary galaxy system in which both
galaxies host active galactic nuclei. Despite this systems being previously
searched for signs of tidal interactions, the tail had not been discovered
prior to our identification as part of the validation process of the SMUDGes
survey for low surface brightness galaxies. We confirm the kinematic
association between various H knots along the tail, a small galaxy, and
the Kite galaxy using optical spectroscopy obtained with the Magellan telescope
and measure a velocity gradient along the tail. The Kite shares characteristics
common to those formed via ram pressure stripping ("jellyfish" galaxies) and
formed via tidal interactions. However, both scenarios face significant
challenges that we discuss, leaving open the question of how such an extreme
tail formed. We propose that the tail resulted from a three-body interaction
from which the lowest-mass galaxy was ejected at high velocity.Comment: Submitted to publication in MNRAS (comments welcome
Gas and Star Formation in Satellites of Milky Way Analogs
We have imaged the entirety of eight (plus one partial) Milky Way (MW)–like satellite systems, a total of 42 (45) satellites, from the Satellites Around Galactic Analogs II catalog in both Hα and H i with the Canada–France–Hawaii Telescope and the Jansky Very Large Array. In these eight systems we have identified four cases where a satellite appears to be currently undergoing ram pressure stripping (RPS) as its H i gas collides with the circumgalactic medium (CGM) of its host. We also see a clear suppression of gas fraction (M HI/M *) with decreasing (projected) satellite–host separation—to our knowledge, the first time this has been observed in a sample of MW-like systems. Comparisons to the Auriga, A Project Of Simulating The Local Environment, and TNG50 cosmological zoom-in simulations show consistent global behavior, but they systematically underpredict gas fractions across all satellites by roughly 0.5 dex. Using a simplistic RPS model, we estimate the average peak CGM density that satellites in these systems have encountered to be logρcgm/gcm−3≈−27.3 . Furthermore, we see tentative evidence that these satellites are following a specific star formation rate to gas fraction relation that is distinct from field galaxies. Finally, we detect one new gas-rich satellite in the UGC 903 system with an optical size and surface brightness meeting the standard criteria to be considered an ultra-diffuse galaxy
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