88 research outputs found
A search for ultra-compact dwarf galaxies in the NGC 1023 group of galaxies
We present a photometric search for UCD candidates in the nearby galaxy group
NGC 1023 (d=11 Mpc) -- the poorest environment searched for UCDs yet --, based
on wide field imaging with CFHT. After photometric and morphological selection,
we obtain a sample of 21 UCD candidates with -12<M_V<-11 mag, if located at NGC
1023's distance. From spectroscopy taken at Calar Alto observatory, we identify
the UCD candidate in closest projection to NGC 1023 as an emission line
background galaxy. Our photometric data show that in the NGC 1023 group, the
mass spectrum of analogs to Fornax/Virgo UCD is restricted to about 1/4 of the
maximum Fornax/Virgo UCD mass. More spectroscopy is needed to further constrain
the mass range of UCDs in this galaxy group.Comment: 5 pages, 4 figures, to appear in the proceedings of ESO Astrophysics
Symposia: "Groups of Galaxies in the Nearby Universe", eds. I. Saviane, V.
Ivanov, J. Borissov
Time variation of fundamental couplings and dynamical dark energy
Scalar field dynamics may give rise to a nonzero cosmological variation of
fundamental constants. Within different scenarios based on the unification of
gauge couplings, the various claimed observations and bounds may be combined in
order to trace or restrict the time history of the couplings and masses. If the
scalar field is responsible for a dynamical dark energy or quintessence,
cosmological information becomes available for its time evolution. Combining
this information with the time variation of couplings, one can determine the
interaction strength between the scalar and atoms, which may be observed by
tests of the Weak Equivalence Principle. We compute bounds on the present rate
of coupling variation from experiments testing the differential accelerations
for bodies with equal mass and different composition and compare the
sensitivity of various methods. In particular, we discuss two specific models
of scalar evolution: crossover quintessence and growing neutrino models.Comment: 26 pages, 2 figures; minor typos & added references, to be published
in JCA
Constraints on the Variation of the Fine Structure Constant from Big Bang Nucleosynthesis
We put bounds on the variation of the value of the fine structure constant
, at the time of Big Bang nucleosynthesis. We study carefully all light
elements up to Li. We correct a previous upper limit on estimated from He primordial abundance and we find interesting new
potential limits (depending on the value of the baryon-to-photon ratio) from
Li, whose production is governed to a large extent by Coulomb barriers. The
presently unclear observational situation concerning the primordial abundances
preclude a better limit than |\Delta \alpha/\alpha| \lsim 2\cdot 10^{-2}, two
orders of magnitude less restrictive than previous bounds. In fact, each of the
(mutually exclusive) scenarios of standard Big Bang nucleosynthesis proposed,
one based on a high value of the measured deuterium primordial abundance and
one based on a low value, may describe some aspects of data better if a change
in of this magnitude is assumed.Comment: 21 pages, eps figures embedded using epsfig macr
Dark mammoth trunks in the merging galaxy NGC 1316 and a mechanism of cosmic double helices
NGC 1316 is a giant, elliptical galaxy containing a complex network of dark,
dust features. The morphology of these features has been examined in some
detail using a Hubble Space Telescope, Advanced Camera for Surveys image. It is
found that most of the features are constituted of long filaments. There also
exist a great number of dark structures protruding inwards from the filaments.
Many of these structures are strikingly similar to elephant trunks in H II
regions in the Milky Way Galaxy, although much larger. The structures, termed
mammoth trunks, generally are filamentary and often have shapes resembling the
letters V or Y. In some of the mammoth trunks the stem of the Y can be resolved
into two or more filaments, many of which showing signs of being intertwined. A
model of the mammoth trunks, related to a recent theory of elephant trunks, is
proposed. Based on magnetized filaments, the model is capable of giving an
account of the various shapes of the mammoth trunks observed, including the
twined structures.Comment: Accepted for publication in Astrophysics & Space Scienc
Constraints on Decaying Dark Matter from Fermi Observations of Nearby Galaxies and Clusters
We analyze the impact of Fermi gamma-ray observations (primarily
non-detections) of selected nearby galaxies, including dwarf spheroidals, and
of clusters of galaxies on decaying dark matter models. We show that the fact
that galaxy clusters do not shine in gamma rays puts the most stringent limits
available to-date on the lifetime of dark matter particles for a wide range of
particle masses and decay final states. In particular, our results put strong
constraints on the possibility of ascribing to decaying dark matter both the
increasing positron fraction reported by PAMELA and the high-energy feature in
the electron-positron spectrum measured by Fermi. Observations of nearby dwarf
galaxies and of the Andromeda Galaxy (M31) do not provide as strong limits as
those from galaxy clusters, while still improving on previous constraints in
some cases.Comment: 27 pages, 5 figures, submitted to JCAP, revised version with some
additions and correction
Leech blood-meal invertebrate-derived DNA reveals differences in Bornean mammal diversity across habitats
The application of metabarcoding to environmental and invertebrate-derived DNA (eDNA and iDNA) is a new and increasingly applied method for monitoring biodiversity across a diverse range of habitats. This approach is particularly promising for sampling in the biodiverse humid tropics, where rapid land-use change for agriculture means there is a growing need to understand the conservation value of the remaining mosaic and degraded landscapes. Here we use iDNA from blood-feeding leeches (Haemadipsa picta) to assess differences in mammalian diversity across a gradient of forest degradation in Sabah, Malaysian Borneo. We screened 557 individual leeches for mammal DNA by targeting fragments of the 16S rRNA gene and detected 14 mammalian genera. We recorded lower mammal diversity in the most heavily degraded forest compared to higher quality twice logged forest. Although the accumulation curves of diversity estimates were comparable across these habitat types, diversity was higher in twice logged forest, with more taxa of conservation concern. In addition, our analysis revealed differences between the community recorded in the heavily logged forest and that of the twice logged forest. By revealing differences in mammal diversity across a human-modified tropical landscape, our study demonstrates the value of iDNA as a noninvasive biomonitoring approach in conservation assessments. © 2020 The Authors. Molecular Ecology published by John Wiley & Sons Lt
Cosmological distance indicators
We review three distance measurement techniques beyond the local universe:
(1) gravitational lens time delays, (2) baryon acoustic oscillation (BAO), and
(3) HI intensity mapping. We describe the principles and theory behind each
method, the ingredients needed for measuring such distances, the current
observational results, and future prospects. Time delays from strongly lensed
quasars currently provide constraints on with < 4% uncertainty, and with
1% within reach from ongoing surveys and efforts. Recent exciting discoveries
of strongly lensed supernovae hold great promise for time-delay cosmography.
BAO features have been detected in redshift surveys up to z <~ 0.8 with
galaxies and z ~ 2 with Ly- forest, providing precise distance
measurements and with < 2% uncertainty in flat CDM. Future BAO
surveys will probe the distance scale with percent-level precision. HI
intensity mapping has great potential to map BAO distances at z ~ 0.8 and
beyond with precisions of a few percent. The next years ahead will be exciting
as various cosmological probes reach 1% uncertainty in determining , to
assess the current tension in measurements that could indicate new
physics.Comment: Review article accepted for publication in Space Science Reviews
(Springer), 45 pages, 10 figures. Chapter of a special collection resulting
from the May 2016 ISSI-BJ workshop on Astronomical Distance Determination in
the Space Ag
Bounds on the possible evolution of the Gravitational Constant from Cosmological Type-Ia Supernovae
Recent high-redshift Type Ia supernovae results can be used to set new bounds
on a possible variation of the gravitational constant . If the local value
of at the space-time location of distant supernovae is different, it would
change both the kinetic energy release and the amount of Ni synthesized
in the supernova outburst. Both effects are related to a change in the
Chandrasekhar mass . In addition, the integrated
variation of with time would also affect the cosmic evolution and therefore
the luminosity distance relation. We show that the later effect in the
magnitudes of Type Ia supernovae is typically several times smaller than the
change produced by the corresponding variation of the Chandrasekhar mass. We
investigate in a consistent way how a varying could modify the Hubble
diagram of Type Ia supernovae and how these results can be used to set upper
bounds to a hypothetical variation of . We find G/G_0 \la 1.1 and G'/G
\la 10^{-11} yr^{-1} at redshifts . These new bounds extend the
currently available constrains on the evolution of all the way from solar
and stellar distances to typical scales of Gpc/Gyr, i.e. by more than 15 orders
of magnitudes in time and distance.Comment: 9 pages, 4 figures, Phys. Rev. D. in pres
The SAMI Galaxy Survey: Data Release Two with absorption-line physics value-added products
Instrumentatio
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