Abstract
We report the discovery of two ultra-faint satellites in the vicinity of the Large Magellanic Cloud (LMC) in data from the Magellanic Satellites Survey (MagLiteS ). Situated 18 deg (∼20 kpc) ...from the LMC and separated from each other by only 18 arcmin, Carina II and III form an intriguing pair. By simultaneously modelling the spatial and the colour–magnitude stellar distributions, we find that both Carina II and Carina III are likely dwarf galaxies, although this is less clear for Carina III. There are in fact several obvious differences between the two satellites. While both are well described by an old and metal poor population, Carina II is located at ∼36 kpc from the Sun, with MV ∼ −4.5 and rh ∼ 90 pc, and it is further confirmed by the discovery of 3 RR Lyrae at the right distance. In contrast, Carina III is much more elongated, measured to be fainter (MV ∼ −2.4), significantly more compact (rh ∼ 30 pc), and closer to the Sun, at ∼28 kpc, placing it only 8 kpc away from Car II. Together with several other systems detected by the Dark Energy Camera, Carina II and III form a strongly anisotropic cloud of satellites in the vicinity of the Magellanic Clouds.
ABSTRACT We report a new ultra-faint stellar system found in Dark Energy Camera data from the first observing run of the Magellanic Satellites Survey (MagLiteS). MagLiteS J0644−5953 (Pictor II or Pic ...II) is a low surface brightness ( within its half-light radius) resolved overdensity of old and metal-poor stars located at a heliocentric distance of . The physical size ( ) and low luminosity ( ) of this satellite are consistent with the locus of spectroscopically confirmed ultra-faint galaxies. MagLiteS J0644−5953 (Pic II) is located from the Large Magellanic Cloud (LMC), and comparisons with simulation results in the literature suggest that this satellite was likely accreted with the LMC. The close proximity of MagLiteS J0644−5953 (Pic II) to the LMC also makes it the most likely ultra-faint galaxy candidate to still be gravitationally bound to the LMC.
The European, multicentre, quarterly point-prevalence study of community-acquired diarrhoea (EUCODI) analysed stool samples received at ten participating clinical microbiology laboratories (Austria, ...Finland, France, Germany, Greece, Ireland, Italy, Portugal, Romania, and the UK) in 2014. On four specified days, each local laboratory submitted samples from ≤20 consecutive patients to the Austrian Study Centre for further testing with the FilmArray GI Panel (BioFire Diagnostics, Salt Lake City, UT, USA). Of the 709 samples from as many patients received, 325 (45.8%) tested negative, 268 (37.8%) yielded only one organism, and 116 (16.4%) yielded multiple organisms. Positivity rates ranged from 41% (30 of 73 samples) in France to 74% (59 of 80 samples) in Romania. With the exception of Entamoeba histolytica and Vibrio cholerae, all of the 22 targeted pathogens were detected at least once. Enteropathogenic Escherichia coli, Campylobacter species, toxigenic Clostridium difficile, enteroaggregative E. coli, norovirus and enterotoxigenic E. coli were the six most commonly detected pathogens. When tested according to local protocols, seven of 128 positive samples (5.5%) yielded multiple organisms. Overall, the FilmArray GI Panel detected at least one organism in 54.2% (384/709) of the samples, as compared with 18.1% (128/709) when testing was performed with conventional techniques locally. This underlines the considerable potential of multiplex PCR to improve routine stool diagnostics in community-acquired diarrhoea. Classic culture methods directed at the isolation of specific pathogens are increasingly becoming second-line tools, being deployed when rapid molecular tests give positive results. This optimizes the yield from stool examinations and dramatically improves the timeliness of diagnosis.
Abstract
We report the discovery of a new ultra-faint stellar system found near the Magellanic Clouds in the DECam Local Volume Exploration Survey. This new system, DELVE J0155−6815 (DELVE 2), is ...located at a heliocentric distance of
D
⊙
= 71 ± 4 kpc, which places it at a 3D physical separation of 12 ± 3 kpc from the center of the Small Magellanic Cloud and
from the center of the Large Magellanic Cloud (LMC). DELVE 2 is identified as a resolved overdensity of old (
τ
> 13.3 Gyr) and metal-poor (
dex) stars with a projected half-light radius of
and an absolute magnitude of
. The size and luminosity of DELVE 2 are consistent with both the population of recently discovered ultra-faint globular clusters and the smallest ultra-faint dwarf galaxies. However, its photometrically derived age and metallicity would place it among the oldest and most metal-poor globular clusters in the Magellanic system. In the absence of spectroscopic measurements of the system’s metallicity dispersion and internal kinematics, we are unable to conclusively classify this system at this time. DELVE 2 is detected in
Gaia
DR2 with a clear proper-motion signal, with multiple blue horizontal-branch stars near the centroid of the system with proper motions consistent with the systemic mean. We measure the system proper motion to be
=
mas yr
−1
. We compare the spatial position and proper motion of DELVE 2 with simulations of the accreted satellite population of the LMC and find that it is very likely to be associated with the LMC.
We present moderate-resolution spectrophotometry of 36 red supergiants (RSGs) in the LMC and 37 RSGs in the SMC. Using the MARCS atmosphere models to fit this spectrophotometry, we determine the ...stars' physical properties and compare the results to evolutionary models. The (V - R) sub(0) broadband colors agree with those from fitting the optical spectrophotometry, but (V - K) sub(0) results show metallicity-dependent systematic differences in the physical properties. We conclude that this is likely due to the limitations of static 1D models, and accept that there is still some uncertainty in the effective temperature scale. We find that the temperature scales for Milky Way, LMC, and SMC K-type supergiants agree with each other, while for M-type supergiants the LMC and SMC scales are cooler than the Galactic scale by 50 and 150 K, respectively. Since spectral classification of RSGs is based on TiO line strengths, it follows that stars with lower abundances of these elements must be cooler in order to have the line strengths associated with a given spectral type. However, this effect is not sufficient to explain the shift in average spectral type between the three galaxies. Instead, metallicity's effect on the coolest extent of stellar evolution is primarily responsible. Our results bring RSGs into much better agreement with stellar evolutionary theory, although the SMC RSGs show a considerably larger spread in effective temperatures at a given luminosity than the LMC stars. This is expected due to the larger effects of rotational mixing in lower metallicity stars. We also find that the reddening distribution of RSGs in the Clouds is skewed significantly toward higher values, consistent with our recent finding that Galactic RSGs show extra extinction due to circumstellar dust.
We present UBVRI photometry obtained from Mosaic images of M31 and M33 using the Kitt Peak National Observatory 4 m telescope. We describe our data reduction and automated photometry techniques in ...some detail, as we will shortly perform a similar analysis of other Local Group galaxies. The present study covered 2.2 deg2 along the major axis of M31 and 0.8 deg2 on M33, chosen so as to include all of the regions currently active in forming massive stars. We calibrated our data using photometry from the Lowell 1.1 m telescope, and this external method resulted in millimagnitude differences in the photometry of overlapping fields, providing some assurance that our photometry is reliable. The final catalog contains 371,781 and 146,622 stars in M31 and M33, respectively, where every star has a counterpart in (at least) the B, V, and R passbands. Our survey goes deep enough to achieve 1%-2% photometry at 21 mag (corresponding to stars more massive than 20 M) and achieves <10% errors at U ~ B ~ V ~ R ~ I ~ 23 mag. Although our typical seeing was only modest (08-14, with median 10) by some standards, we find excellent correspondence between our catalog sources and those we see in our Hubble Space Telescope ACS data for OB48, a crowded region in M31. We compare our final photometry with that of others and find good agreement with the CCD catalog of M31 stars by Magnier et al., although our study covers twice the area and goes about 2 mag deeper. There is also excellent agreement with the CCD 'DIRECT' surveys of M31 and M33. The photographic studies of others fare less well, particularly at the faint end in V, where accurate background subtraction is needed for good photometry. We provide cross-references to the stars confirmed as members by spectroscopy and compare the locations of these to the complete set in color-magnitude diagrams. While follow-up spectroscopy is needed for many projects, we demonstrate the success of our photometry in being able to distinguish M31/M33 members from foreground Galactic stars. Finally, we present the results of a single night of spectroscopy on the WIYN 3.5 m telescope, examining the brightest likely members of M31. The spectra identify 34 newly confirmed members, including B-A supergiants, the earliest O star known in M31, and two new luminous blue variable candidates whose spectra are similar to that of P Cygni.
ABSTRACT
We use the SMASH survey to obtain unprecedented deep photometry reaching down to the oldest main-sequence turn-offs in the colour–magnitude diagrams (CMDs) of the Small Magellanic Cloud ...(SMC) and quantitatively derive its star formation history (SFH) using CMD fitting techniques. We identify five distinctive peaks of star formation in the last 3.5 Gyr, at ∼3, ∼2, ∼1.1, ∼0.45 Gyr ago, and one presently. We compare these to the SFH of the Large Magellanic Cloud (LMC), finding unequivocal synchronicity, with both galaxies displaying similar periods of enhanced star formation over the past ∼3.5 Gyr. The parallelism between their SFHs indicates that tidal interactions between the MCs have recurrently played an important role in their evolution for at least the last ∼3.5 Gyr, tidally truncating the SMC and shaping the LMC’s spiral arm. We show, for the first time, an SMC–LMC correlated SFH at recent times in which enhancements of star formation are localized in the northern spiral arm of the LMC, and globally across the SMC. These novel findings should be used to constrain not only the orbital history of the MCs but also how star formation should be treated in simulations.
We analyze resolved stellar near-infrared photometry of 21 Hubble Space Telescope (HST) fields in M31 to constrain the impact of metallicity on the formation of carbon stars. Observations of nearby ...galaxies show that carbon stars are increasingly rare at higher metallicity. Models indicate that carbon star formation efficiency drops due to the decrease in dredge-up efficiency in metal-rich thermally pulsing Asymptotic Giant Branch (TP-AGB) stars, coupled to a higher initial abundance of oxygen. However, while models predict a metallicity ceiling above which carbon stars cannot form, previous observations have not yet pinpointed this limit. Our new observations reliably separate carbon stars from M-type TP-AGB stars across 2.6-13.7 kpc of M31's metal-rich disk using HST WFC3/IR medium-band filters. We find that the ratio of C to M stars (C/M) decreases more rapidly than extrapolations of observations in more metal-poor galaxies, resulting in a C/M that is too low by more than a factor of 10 in the innermost fields and indicating a dramatic decline in C star formation efficiency at metallicities higher than M/H −0.1 dex. The metallicity ceiling remains undetected, but must occur at metallicities higher than what is measured in M31's inner disk (M/H +0.06 dex).
Abstract
We perform a detailed photometric and astrometric analysis of stars in the Jet stream using data from the first data release of the DECam Local Volume Exploration Survey DR1 and Gaia EDR3. ...We discover that the stream extends over ∼ 29° on the sky (increasing the known length by 18°), which is comparable to the kinematically cold Phoenix, ATLAS, and GD-1 streams. Using blue horizontal branch stars, we resolve a distance gradient along the Jet stream of 0.2 kpc deg
−1
, with distances ranging from
D
⊙
∼ 27–34 kpc. We use natural splines to simultaneously fit the stream track, width, and intensity to quantitatively characterize density variations in the Jet stream, including a large gap, and identify substructure off the main track of the stream. Furthermore, we report the first measurement of the proper motion of the Jet stream and find that it is well aligned with the stream track, suggesting the stream has likely not been significantly perturbed perpendicular to the line of sight. Finally, we fit the stream with a dynamical model and find that it is on a retrograde orbit, and is well fit by a gravitational potential including the Milky Way and Large Magellanic Cloud. These results indicate the Jet stream is an excellent candidate for future studies with deeper photometry, astrometry, and spectroscopy to study the potential of the Milky Way and probe perturbations from baryonic and dark matter substructure.
Abstract
We present the discovery of a candidate ultra-faint Milky-Way satellite, Eridanus IV (DELVE J0505−0931), detected in photometric data from the DECam Local Volume Exploration survey (DELVE). ...Eridanus IV is a faint (
M
V
= − 4.7 ± 0.2), extended (
r
1
/
2
=
75
−
13
+
16
pc
), and elliptical (
ϵ
= 0.54 ± 0.1) system at a heliocentric distance of
76.7
−
6.1
+
4.0
kpc
, with a stellar population that is well described by an old, metal-poor isochrone (age of
τ
∼ 13.0 Gyr and metallicity of Fe/H ≲ − 2.1 dex). These properties are consistent with the known population of ultra-faint Milky-Way satellite galaxies. Eridanus IV is also prominently detected using proper-motion measurements from Gaia Early Data Release 3, with a systemic proper motion of
(
μ
α
cos
δ
,
μ
δ
)
=
(
+
0.25
±
0.06
,
−
0.10
±
0.05
)
mas yr
−1
measured from its horizontal branch and red-giant-branch member stars. We find that the spatial distribution of likely member stars hints at the possibility that the system is undergoing tidal disruption.
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