662 research outputs found
Antlia B: A faint dwarf galaxy member of the NGC 3109 association
We report the discovery of Antlia B, a faint dwarf galaxy at a projected
distance of 72 kpc from NGC 3109 (15 mag), the primary
galaxy of the NGC 3109 dwarf association at the edge of the Local Group. The
tip of the red giant branch distance to Antlia B is =1.290.10 Mpc,
which is consistent with the distance to NGC 3109. A qualitative analysis
indicates the new dwarf's stellar population has both an old, metal poor red
giant branch (10 Gyr, [Fe/H]2), and a younger blue population
with an age of 200-400 Myr, analogous to the original Antlia dwarf,
another likely satellite of NGC 3109. Antlia B has \ion{H}{1} gas at a velocity
of =376 km s, confirming the association with NGC 3109
(=403 km s). The HI gas mass
(M=2.80.210 M), stellar luminosity
(=9.70.6 mag) and half light radius (=27329 pc) are
all consistent with the properties of dwarf irregular and dwarf spheroidal
galaxies in the Local Volume, and is most similar to the Leo P dwarf galaxy.
The discovery of Antlia B is the initial result from a Dark Energy Camera
survey for halo substructure and faint dwarf companions to NGC 3109 with the
goal of comparing observed substructure with expectations from the
+Cold Dark Matter model in the sub-Milky Way regime.Comment: 7 pages, 3 figures. Submitted to ApJ
Simulating Diffuse Light in Galaxy Clusters
Using N-body simulations, we have modeled the production and evolution of low
surface brightness, diffuse intra-cluster light (ICL) in galaxy clusters. By
creating simulated observations of the clusters we have measured the evolution
of the ICL luminosity throughout the dynamical history of the clusters. We find
that ICL production tends to occur in short, discrete events, which correlate
very strongly with strong, small-scale interactions and accretions between
groups within the clusters.Comment: 5 pages, 2 figures; includes 1 color figure. To appear in ESO
Astrophysics Symposia: "Groups of Galaxies in the Nearby Universe
At the upper palaeolithic - mesolithic boundary: Revision of the human remains from riparo fredian (MOLAZZANA, LUCCA, ITALY)
Pleistocene and early Holocene human fossils in Tuscany are very few and poorly described. Any new information is thus an important contribution to our knowledge of the peopling of this region. Here we present a revision of the human fossil remains from the Riparo Fredian, a site located in Garfagnana and first published by Boschian et al., (1995). The authors described the human remains of the site pointing out the presence of 39 isolated human teeth (19 maxillary and 20 mandibular) and "fragments of one adult humerus, of a child's femur and of a youngster's ulna", considered as belonging to six individuals at least. A reanalysis of the human remains indicated that several specimens were incorrectly identified. It was thus deemed important to revise the identification of each fossil and their interpretation. The revision of human remains from Riparo Fredian has led to several changes in their anatomical identification with respect to the original publications. Of the 39 teeth previously described, the analysis revealed that two of them belonged to non-human animals, and 18 were mistakenly identified. A new, correct identification is provided for each of them. Also, two human teeth not described in the original papers have been identified. The anatomical identification of the post-cranial remains has been confirmed for two out of the three specimens. The minimum number of individuals, based on the dental remains, is confirmed as at least 5, but most probably 6, although with a different allocation of teeth to individual specimens. The age at death of the six individuals has also been reassessed, indicating the presence of two infants, two young adults and two mature adults
Hubble Space Telescope Imaging of the Ultra-Compact High Velocity Cloud AGC 226067: A stripped remnant in the Virgo Cluster
We analyze the optical counterpart to the ultra-compact high velocity cloud
AGC 226067, utilizing imaging taken with the Advanced Camera for Surveys (ACS)
on the Hubble Space Telescope. The color magnitude diagram of the main body of
AGC 226067 reveals an exclusively young stellar population, with an age of
7--50 Myr, and is consistent with a metallicity of [Fe/H]0.3 as
previous work has measured via HII region spectroscopy. Additionally, the color
magnitude diagram is consistent with a distance of 17 Mpc,
suggesting an association with the Virgo cluster. A secondary stellar system
located 1.6' (8 kpc) away in projection has a similar stellar
population. The lack of an old red giant branch (5 Gyr) is contrasted
with a serendipitously discovered Virgo dwarf in the ACS field of view (Dw
J122147+132853), and the total diffuse light from AGC~226067 is consistent with
the luminosity function of the resolved 7--50 Myr stellar population. The
main body of AGC~226067 has a =11.30.3, or
=5.41.310 given the stellar population.
We searched 20 deg of imaging data adjacent to AGC~226067 in the Virgo
Cluster, and found two similar stellar systems dominated by a blue stellar
population, far from any massive galaxy counterpart -- if this population has
similar star formation properties as AGC~226067, it implies 0.1
yr in Virgo intracluster star formation. Given its unusual
stellar population, AGC~226067 is likely a stripped remnant and is plausibly
the result of compressed gas from the ram pressure stripped M86 subgroup
(350 kpc away in projection) as it falls into the Virgo Cluster.Comment: 9 pages, 4 figures, 1 table. Accepted by the Astrophysical Journa
The Mission Accessible Near-Earth Objects Survey: Four years of photometry
Over 4.5 years, the Mission Accessible Near-Earth Object Survey (MANOS)
assembled 228 Near-Earth Object (NEO) lightcurves. We report rotational
lightcurves for 82 NEOs, constraints on amplitudes and periods for 21 NEOs,
lightcurves with no detected variability within the image signal to noise and
length of our observing block for 30 NEOs, and 10 tumblers. We uncovered 2
ultra-rapid rotators with periods below 20s; 2016MA with a potential rotational
periodicity of 18.4s, and 2017QG rotating in 11.9s, and estimate the
fraction of fast/ultra-rapid rotators undetected in our project plus the
percentage of NEOs with a moderate/long periodicity undetectable during our
typical observing blocks. We summarize the findings of a simple model of
synthetic NEOs to infer the object morphologies distribution using the measured
distribution of lightcurve amplitudes. This model suggests a uniform
distribution of axis ratio can reproduce the observed sample. This suggests
that the quantity of spherical NEOs (e.g., Bennu) is almost equivalent to the
quantity of highly elongated objects (e.g., Itokawa), a result that can be
directly tested thanks to shape models from Doppler delay radar imaging
analysis. Finally, we fully characterized 2 NEOs as appropriate targets for a
potential robotic/human mission: 2013YS and 2014FA due to their
moderate spin periods and low .Comment: Accepted for Publication, The Astrophysical Journal Supplement Serie
Anterior tooth-use behaviors among early modern humans and Neandertals
Early modern humans (EMH) are often touted as behaviorally advanced to Neandertals, with more sophisticated technologies, expanded resource exploitation, and more complex clothing production. However, recent analyses have indicated that Neandertals were more nuanced in their behavioral adaptations, with the production of the Châtelperronian technocomplex, the processing and cooking of plant foods, and differences in behavioral adaptations according to habitat. This study adds to this debate by addressing the behavioral strategies of EMH (n = 30) within the context of non-dietary anterior tooth-use behaviors to glean possible differences between them and their Neandertal (n = 45) counterparts. High-resolution casts of permanent anterior teeth were used to collect microwear textures of fossil and comparative bioarchaeological samples using a Sensofar white-light confocal profiler with a 100x objective lens. Labial surfaces were scanned, totaling a work envelope of 204 x 276 μm for each individual. The microwear textures were examined for post-mortem damage and uploaded to SSFA software packages for surface characterization. Statistical analyses were performed to examine differences in central tendencies and distributions of anisotropy and textural fill volume variables among the EMH sample itself by habitat, location, and time interval, and between the EMH and Neandertal samples by habitat and location. Descriptive statistics for the EMH sample were compared to seven bioarchaeological samples (n = 156) that utilized different tooth-use behaviors to better elucidate specific activities that may have been performed by EMH. Results show no significant differences between the means within the EMH sample by habitat, location, or time interval. Furthermore, there are no significant differences found here between EMH and Neandertals. Comparisons to the bioarchaeological samples suggest both fossil groups participated in clamping and grasping activities. These results indicate that EMH and Neandertals were similar in their non-dietary anterior tooth-use behaviors and provide additional evidence for overlapping behavioral strategies employed by these two hominins
A Comprehensive Archival Search for Counterparts to Ultra-Compact High Velocity Clouds: Five Local Volume Dwarf Galaxies
We report five Local Volume dwarf galaxies (two of which are presented here
for the first time) uncovered during a comprehensive archival search for
optical counterparts to ultra-compact high velocity clouds (UCHVCs). The UCHVC
population of HI clouds are thought to be candidate gas-rich, low mass halos at
the edge of the Local Group and beyond, but no comprehensive search for stellar
counterparts to these systems has been presented. Careful visual inspection of
all publicly available optical and ultraviolet imaging at the position of the
UCHVCs revealed six blue, diffuse counterparts with a morphology consistent
with a faint dwarf galaxy beyond the Local Group. Optical spectroscopy of all
six candidate dwarf counterparts show that five have an H-derived
velocity consistent with the coincident HI cloud, confirming their association,
the sixth diffuse counterpart is likely a background object. The size and
luminosity of the UCHVC dwarfs is consistent with other known Local Volume
dwarf irregular galaxies. The gas fraction () of the five
dwarfs are generally consistent with that of dwarf irregular galaxies in the
Local Volume, although ALFALFA-Dw1 (associated with ALFALFA UCHVC
HVC274.68+74.70123) has a very high 40. Despite the
heterogenous nature of our search, we demonstrate that the current dwarf
companions to UCHVCs are at the edge of detectability due to their low surface
brightness, and that deeper searches are likely to find more stellar systems.
If more sensitive searches do not reveal further stellar counterparts to
UCHVCs, then the dearth of such systems around the Local Group may be in
conflict with CDM simulations.Comment: 18 pages, 4 tables, 4 figures, ApJ Accepte
Bootes II ReBooted: An MMT/MegaCam Study of An Ultra-Faint Milky Way Satellite
[abridged] We present MMT/Megacam imaging in Sloan and of the
extremely low luminosity Bo\"otes II Milky Way companion. We use a bootstrap
approach to perform robust measurements of, and uncertainties on, Bo\"otes II's
distance, luminosity, size, and morphology. We show that Bo\"otes II's stellar
population is old and metal-poor ([Fe/H] \lta -2). Assuming a stellar
population like that of M92, Bo\"otes II is at a distance of 42 2 kpc,
closer than the initial published estimate of 60 10 kpc. This distance
revision, combined with a more robust measurement of Bo\"otes II's structure
with a Plummer model (exponential model) results in a more compact half-light
size of pc and lower luminosity of
mag. This revised size and luminosity move
Bo\"otes II into a region of size-luminosity space not previously known to be
occupied by old stellar populations, but also occupied by the recently
discovered Milky Way satellites Willman 1 and SEGUE 1. We show that the
apparently distorted morphology of Bo\"otes II is not statistically significant
given the present data. We use a tidal argument to support a scenario where
Bo\"otes II is a dwarf galaxy (dark matter dominated) rather than a globular
cluster (not dark matter dominated). However, we can not rule out that Bo\"otes
II is a star cluster on the verge of disruption, such as Palomar 5.Comment: 10 pages, 8 figures. ApJ accepted. Conclusions are unchanged, but
content and figures have changed substantively in this accepted versio
Genetic and demographic vulnerability of adder populations: Results of a genetic study in mainland Britain
Genetic factors are often overlooked in conservation planning, despite their importance in small isolated populations. We used mitochondrial and microsatellite markers to investigate population genetics of the adder (Vipera berus) in southern Britain, where numbers are declining. We found no evidence for loss of heterozygosity in any of the populations studied. Genetic diversity was comparable across sites, in line with published levels for mainland Europe. However, further analysis revealed a striking level of relatedness. Genetic networks constructed from inferred first degree relationships suggested a high proportion of individuals to be related at a level equivalent to that of half-siblings, with rare inferred full-sib dyads. These patterns of relatedness can be attributed to the high philopatry and low vagility of adders, which creates high local relatedness, in combination with the polyandrous breeding system in the adder, which may offset the risk of inbreeding in closed populations. We suggest that reliance on standard genetic indicators of inbreeding and diversity may underestimate demographic and genetic factors that make adder populations vulnerable to extirpation. We stress the importance of an integrated genetic and demographic approach in the conservation of adders, and other taxa of similar ecology
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