1,522 research outputs found
The Dwarfs Beyond: The Stellar-to-Halo Mass Relation for a New Sample of Intermediate Redshift Low Mass Galaxies
A number of recent challenges to the standard Lambda-CDM paradigm relate to
discrepancies that arise in comparing the abundance and kinematics of local
dwarf galaxies with the predictions of numerical simulations. Such arguments
rely heavily on the assumption that the local dwarf and satellite galaxies form
a representative distribution in terms of their stellar-to-halo mass ratios. To
address this question, we present new, deep spectroscopy using DEIMOS on Keck
for 82 low mass (10^7-10^9 solar masses) star-forming galaxies at intermediate
redshift (z=0.2-1). For 50 percent of these we are able to determine resolved
rotation curves using nebular emission lines and thereby construct the stellar
mass Tully-Fisher relation to masses as low as 10^7 solar masses. Using scaling
relations determined from weak lensing data, we convert this to a
stellar-to-halo mass (SHM) relation for comparison with abundance matching
predictions. We find a discrepancy between the propagated predictions from
simulations compared to our observations, and suggest possible reasons for this
as well as future tests that will be more effective.Comment: 11 pages, 7 figures, submitted to ApJ, comments welcom
Fluorescent C II* 1335A emission spectroscopically resolved in a galaxy at z = 5.754
We report the discovery of the first spectroscopically resolved C II /C II*
1334, 1335A doublet in the Lyman-break galaxy J0215-0555 at z = 5.754. The
separation of the resonant and fluorescent emission channels was possible
thanks to the large redshift of the source and long integration time, as well
as the small velocity width of the feature, 0.6 +- 0.2A. We model this emission
and find that at least two components are required to reproduce the combination
of morphologies of C II* emission, C II absorption and emission, and
Lyman-alpha emission from the object. We suggest that the close alignment
between the fluorescence and Lyman-alpha emission could indicate an ionisation
escape channel within the object. While the faintness of such a C II /C II*
doublet makes it prohibitively difficult to pursue for similar systems with
current facilities, we suggest it can become a valuable porosity diagnostic in
the era of JWST and the upcoming generations of ELTs.Comment: 5 pages, 3 figures; accepted for publication in MNRAS Letter
The alternate GNB3 splice variant, Gβ3s, exhibits an altered signalling response to EGF stimulation, which leads to enhanced cell migration
It has recently been reported that the duplication of the GNB3 gene has been shown to be directly linked to an obesity phenotype, both in humans and also in a humanised mouse model. Moreover, the common human GNB3 c.825C>T polymorphism (rs5443) causes this ubiquitously expressed gene to be aberrantly spliced approximately 50% of the time leading to the production of both a normal Gβ3 protein and a truncated, possibly less stable subunit, known as Gβ3s. The presence of the GNB3 825T allele has previously been shown to be associated with predisposition to hypertension, obesity, various cancers, Alzheimers, age related cognitive function, erectile dysfunction as well as a marker for pharmacogenetic drug action. Great controversy, however, currently exists as to whether these phenotypes associated with the 825T allele are a) mainly due to the presence of the smaller, possibly more active, Gβ3s subunit or b) merely down to the haploinsufficiency of the normal GNB3 transcript, due to its frequent aberrant splicing. In order to try and address these two conflicting hypothesis, we report on the identification and characterisation of signalling alterations unique to the presence of Gβ3s protein subunit. Moreover we also show the physiological consequences associated with altered signalling, directly induced by the Gβ3s subunit. For this, we used both an EBV transformed lymphoblast cell line homozygote for GNB3 825T/825T (TT) and a stable Gβ3s expressing recombinant COS-7 clone. In both of these cell lines that express the Gβ3s subunit, we found enhanced cytosolic calcium influx upon stimulation with EGF, TGFα and VEGF ligands, as compared to “normal” GNB3 controls with the 825C/825C (CC) genotype. This aberrant calcium influx also led to an increase in ERK, but not AKT1, phosphorylation. Despite the lack of AKT1 activation, we paradoxically observed a significant increase in phosphorylation of its downstream substrates, namely mTOR and p70S6k (KS6B2). Moreover we observed a decrease in phospho FoxO3a only in Gβ3s expressing cells, but not in the “normal” GNB3 (CC) control cell line. The presence of the Gβ3s subunit also appeared to alter the distinct localisation patterns of both Foxo3a and AKT1, while also increasing the colocalisation of mTOR and p70S6K. Subsequent growth factor stimulation studies revealed that EGF treatment, of Gβ3s expressing cells, appeared to cause a significant decrease in cAMP levels, which, in turn resulted in both enhanced caveolin-1a phosphorylation, and an increase in actin stress fibre formation. The identification of these distinct Gβ3s specific signalling alterations were indicative of a more aggressive migratory phenotype. This led us to further investigate and confirm that the presence of the Gβ3s subunit also appears to cause significantly enhanced migration and robust scratch wound healing kinetics, as compared to cells harbouring only the normal copy of the gene. These data therefore present convincing evidence that the Gβ3s subunit is stable, functional and its presence can significantly alter signalling pathways, in different cell types
Constraints on Omega_Lambda and Omega_m from Distant Type 1a Supernovae and Cosmic Microwave Background Anisotropies
We perform a combined likelihood analysis of the latest cosmic microwave
background anisotropy data and distant Type 1a Supernova data of Perlmutter
etal (1998a). Our analysis is restricted to cosmological models where structure
forms from adiabatic initial fluctuations characterised by a power-law spectrum
with negligible tensor component. Marginalizing over other parameters, our best
fit solution gives Omega_m = 0.25 (+0.18, -0.12) and Omega_Lambda = 0.63
(+0.17, -0.23) (95 % confidence errors) for the cosmic densities contributed by
matter and a cosmological constant respectively. The results therefore strongly
favour a nearly spatially flat Universe with a non-zero cosmological constant.Comment: 6 pages, 6 Postscript figures, uses mn.sty. submitted to MNRA
The Young Lady\u27s Guide
Contents
Papers for thoughtful girls, by Sarah Tytler.
A woman’s thoughts about women, by the author of John Halifax, gentleman .
Fashion, from Mrs. Sydney Cox’s Friendly counsel for girls .
Novel-reading, from the Greyson letters, by Henry Rogers.
From Daughters and Women of England, by Sarah S. Ellis.
From Hannah More.--From The young ladies’ mentor , by a lady.
The social position and culture due to woman, by W. R. Williams.--Education of the heart, woman’s best, by Sarah S. Ellis.
From The young woman’s friend , by J. A. James
Vegetation Controls on Weathering Intensity During the Last Deglacial Transition in Southeast Africa
Tropical climate is rapidly changing, but the effects of these changes on the geosphere are unknown, despite a likelihood of climatically-induced changes on weathering and erosion. The lack of long, continuous paleo-records prevents an examination of terrestrial responses to climate change with sufficient detail to answer questions about how systems behaved in the past and may alter in the future. We use high-resolution records of pollen, clay mineralogy, and particle size from a drill core from Lake Malawi, southeast Africa, to examine atmosphere-biosphere-geosphere interactions during the last deglaciation (~ 18-9 ka), a period of dramatic temperature and hydrologic changes. The results demonstrate that climatic controls on Lake Malawi vegetation are critically important to weathering processes and erosion patterns during the deglaciation. At 18 ka, afromontane forests dominated but were progressively replaced by tropical seasonal forest, as summer rainfall increased. Despite indication of decreased rainfall, drought-intolerant forest persisted through the Younger Dryas (YD) resulting from a shorter dry season. Following the YD, an intensified summer monsoon and increased rainfall seasonality were coeval with forest decline and expansion of drought-tolerant miombo woodland. Clay minerals closely track the vegetation record, with high ratios of kaolinite to smectite (K/S) indicating heavy leaching when forest predominates, despite variable rainfall. In the early Holocene, when rainfall and temperature increased (effective moisture remained low), open woodlands expansion resulted in decreased K/S, suggesting a reduction in chemical weathering intensity. Terrigenous sediment mass accumulation rates also increased, suggesting critical linkages among open vegetation and erosion during intervals of enhanced summer rainfall. This study shows a strong, direct influence of vegetation composition on weathering intensity in the tropics. As climate change will likely impact this interplay between the biosphere and geosphere, tropical landscape change could lead to deleterious effects on soil and water quality in regions with little infrastructure for mitigation
The Assembly History of Disk Galaxies: II. Probing the Emerging Tully-Fisher Relation During 1<z<1.7
Through extended integrations using the recently-installed deep depletion CCD
on the red arm of the Keck I Low Resolution Imaging Spectrograph, we present
new measurements of the resolved spectra of 70 morphologically-selected
star-forming galaxies with i_AB<24.1 in the redshift range 1<z<1.7. Using the
formalism introduced in Paper I of this series and available HST ACS images, we
successfully recover rotation curves using the extended emission line
distribution of [O II] 3727 A to 2.2 times the disk scale radius for a sample
of 42 galaxies. Combining these measures with stellar masses derived from HST
and ground-based near-infrared photometry enables us to construct the stellar
mass Tully-Fisher relation in the time interval between the well-constructed
relation defined at z~1 in Paper I and the growing body of resolved dynamics
probed with integral field unit spectrographs at z>2. Remarkably, we find a
well-defined Tully-Fisher relation with up to 60% increase in scatter and
stellar mass zero-point shift constraint of 0.02+/-0.02 dex since z~1.7,
compared to the local relation. Although our sample is incomplete in terms of
either a fixed stellar mass or star formation rate limit, we discuss the
implications that typical star-forming disk galaxies evolve to arrive on a
well-defined Tully-Fisher relation within a surprisingly short period of cosmic
history.Comment: 13 pages, 8 figures, accepted for publication at Ap
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