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

Short-range force detection using optically-cooled levitated microspheres

We propose an experiment using optically trapped and cooled dielectric microspheres for the detection of short-range forces. The center-of-mass motion of a microsphere trapped in vacuum can experience extremely low dissipation and quality factors of $10^{12}$, leading to yoctonewton force sensitivity. Trapping the sphere in an optical field enables positioning at less than 1 $\mu$m from a surface, a regime where exotic new forces may exist. We expect that the proposed system could advance the search for non-Newtonian gravity forces via an enhanced sensitivity of $10^5-10^7$ over current experiments at the 1 $\mu$m length scale. Moreover, our system may be useful for characterizing other short-range physics such as Casimir forces.Comment: 4 pages, 3 figures, minor changes, Figs. 1 and 2 replace

Centered Partition Process: Informative Priors for Clustering

There is a very rich literature proposing Bayesian approaches for clustering starting with a prior probability distribution on partitions. Most approaches assume exchangeability, leading to simple representations in terms of Exchangeable Partition Probability Functions (EPPF). Gibbs-type priors encompass a broad class of such cases, including Dirichlet and Pitman-Yor processes. Even though there have been some proposals to relax the exchangeability assumption, allowing covariate-dependence and partial exchangeability, limited consideration has been given on how to include concrete prior knowledge on the partition. For example, we are motivated by an epidemiological application, in which we wish to cluster birth defects into groups and we have prior knowledge of an initial clustering provided by experts. As a general approach for including such prior knowledge, we propose a Centered Partition (CP) process that modifies the EPPF to favor partitions close to an initial one. Some properties of the CP prior are described, a general algorithm for posterior computation is developed, and we illustrate the methodology through simulation examples and an application to the motivating epidemiology study of birth defects

A short note on the presence of spurious states in finite basis approximations

The genesis of spurious solutions in finite basis approximations to operators which possess a continuum and a point spectrum is discussed and a simple solution for identifying these solutions is suggested

Latitudinal Shear Instabilities during Type I X-ray Bursts

Coherent oscillations have been observed during Type I X-ray bursts from 14 accreting neutron stars in low mass X-ray binaries, providing important information about their spin frequencies. However, the origin of the brightness asymmetry on the neutron star surface producing these oscillations is still not understood. We study the stability of a zonal shearing flow on the neutron star surface using a shallow water model. We show that differential rotation of >2% between pole and equator, with the equator spinning faster than the poles, is unstable to hydrodynamic shear instabilities. The unstable eigenmodes have properties well-matched to burst oscillations: low azimuthal wavenumber m, wave speeds 1 or 2% below the equatorial spin rate, and e-folding times close to a second. Instability is related to low frequency buoyantly driven r-modes that have a mode frequency within the range of rotation frequencies in the differentially rotating shell. We discuss the implications for burst oscillations. Growth of shear instabilities may explain the brightness asymmetry in the tail of X-ray bursts, although some fine tuning of the level of differential rotation and a spin frequency near 300 Hz are required in order for the fastest growing mode to have m=1. If shear instabilities are to operate during a burst, temperature contrasts of 30% across the star must be created during ignition and spreading of the flash.Comment: To appear in ApJ (12 pages, 11 figures

First record of an Odontaspidid shark in Ascension Island waters

The occurrence of the poorly understood shark species Odontapsis ferox is reported at an oceanic seamount in the central south Atlantic, within the Exclusive Economic Zone of Ascension Island. The presence of the species at this location is confirmed by the discovery of a tooth embedded in scientific equipment, and footage of at least one animal on autonomous underwater video. The new record of this shark species at this location demonstrates the knowledge gaps which still exist at many remote, oceanic structures and their candidacy for status as important conservation areas.info:eu-repo/semantics/publishedVersio

Glutathione-Mediated Neuroprotection Against Methylmercury Neurotoxicity in Cortical Culture is Dependent on MRP1

Methylmercury (MeHg) exposure at high concentrations poses significant neurotoxic threat to humans worldwide. The present study investigated the mechanisms of glutathione-mediated attenuation of MeHg neurotoxicity in primary cortical culture. MeHg (5 μM) caused depletion of mono- and disulfide glutathione in neuronal, glial and mixed cultures. Supplementation with exogenous glutathione, specifically glutathione monoethyl ester (GSHME) protected against the MeHg induced neuronal death. MeHg caused increased reactive oxygen species (ROS) formation measured by dichlorodihydrofluorescein (DCF) fluorescence with an early increase at 30 min and a late increase at 6 h. This oxidative stress was prevented by the presence of either GSHME or the free radical scavenger, trolox. While trolox was capable of quenching the ROS, it showed no neuroprotection. Exposure to MeHg at subtoxic concentrations (3 μM) caused an increase in system xc− mediated 14C-cystine uptake that was blocked by the protein synthesis inhibitor, cycloheximide (CHX). Interestingly, blockade of the early ROS burst prevented the functional upregulation of system xc−. Inhibition of multidrug resistance protein-1 (MRP1) potentiated MeHg neurotoxicity and increased cellular MeHg. Taken together, these data suggest glutathione offers neuroprotection against MeHg toxicity in a manner dependent on MRP1-mediated efflux

Detection Rates for Close Binaries Via Microlensing

Microlensing is one of the most promising methods of reconstructing the stellar mass function down to masses even below the hydrogen-burning limit. The fundamental limit to this technique is the presence of unresolved binaries, which can in principle significantly alter the inferred mass function. Here we quantify the fraction of binaries that can be detected using microlensing, considering specifically the mass ratio and separation of the binary. We find that almost all binary systems with separations greater than $b \sim 0.4$ of their combined Einstein ring radius are detectable assuming a detection threshold of $3\%$. For two M dwarfs, this corresponds to a limiting separation of \gsim 1 \au. Since very few observed M dwarfs have companions at separations \lsim 1 \au, we conclude that close binaries will probably not corrupt the measurements of the mass function. We find that the detectability depends only weakly on the mass ratio. For those events for which individual masses can be determined, we find that binaries can be detected down to $b \sim 0.2$.Comment: 19 pages including 6 figures. Uses phyyzx format. Send requests for higher quality figures to [email protected]