The baryonic Tully-Fisher relation and galactic outflows

Most of the baryons in the Universe are not in the form of stars and cold gas in galaxies. Galactic outflows driven by supernovae/stellar winds are the leading mechanism for explaining this fact. The scaling relation between galaxy mass and outer rotation velocity (also known as the baryonic Tully-Fisher relation, BTF) has recently been used as evidence against this viewpoint. We use a LCDM based semi-analytic disk galaxy formation model to investigate these claims. In our model, galaxies with less efficient star formation and higher gas fractions are more efficient at ejecting gas from galaxies. This is due to the fact that galaxies with less efficient star formation and higher gas fractions tend to live in dark matter haloes with lower circular velocities, from which less energy is required to escape the potential well. In our model the intrinsic scatter in the BTF is 0.15 dex, and mostly reflects scatter in dark halo concentration. The observed scatter, equal to 0.24 dex, is dominated by measurement errors. The best estimate for the intrinsic scatter is that it is less than 0.15 dex, and thus our LCDM based model (which does not include all possible sources of scatter) is only just consistent with this. In our model, gas rich galaxies, at fixed virial velocity (V_vir), with lower stellar masses have lower baryonic masses. This is consistent with the expectation that galaxies with lower stellar masses have had less energy available to drive an outflow. However, when the outer rotation velocity (V_flat) is used the correlation has the opposite sign, with a slope in agreement with observations. This is due to scatter in the relation between V_flat and V_vir. In summary, contrary to some previous claims, we show that basic features of the BTF are consistent with a LCDM based model in which the low efficiency of galaxy formation is determined by galactic outflows.Comment: 7 pages, 4 figures, accepted to MNRA

Direct Spectrum of the Benchmark T Dwarf HD 19467 B

HD 19467 B is presently the only directly imaged T dwarf companion known to induce a measurable Doppler acceleration around a solar-type star. We present spectroscopy measurements of this important benchmark object taken with the Project 1640 integral field unit at Palomar Observatory. Our high-contrast R ≈ 30 observations obtained simultaneously across the JH bands confirm the cold nature of the companion as reported from the discovery article and determine its spectral type for the first time. Fitting the measured spectral energy distribution to SpeX/IRTF T dwarf standards and synthetic spectra from BT-Settl atmospheric models, we find that HD 19467 B is a T5.5 ± 1 dwarf with effective temperature T_eff=978^(+20)_(-43) K. Our observations reveal significant methane absorption affirming its substellar nature. HD 19467 B shows promise to become the first T dwarf that simultaneously reveals its mass, age, and metallicity independent from the spectrum of light that it emits

Unrest at the Nevados de Chillán volcanic complex: a failed or yet to unfold magmatic eruption?

Resuming erupting activity at volcanoes that have been long quiescent poses a significant challenge to hazard assessment, as it require assessment of whether the change in activity is an isolated event or the beginning of a new eruptive sequence. Such inception is often poorly characterised as quiescent volcanoes tend to be poorly equipped and not extensively monitored, especially with respect to gas geochemistry. Here, we report gas composition and flux measurements from a newly opened vent at the very onset of eruptive activity at the Nevados de Chillán volcanic complex (Chile) in January-February 2016. The molar proportions of H2O, CO2, SO2, H2S and H2 gases are found to be 98.4, 0.97, 0.11, 0.01 and 0.5 mol% respectively. The mean SO2 flux recorded in early February 2016 during periods of eruptive discharge amounts to 0.4-0.6 kg s-1. Our results indicate that the new vent opening was propelled by magmatic gases, triggering repeated eruptions. Ash particles ejected by the first blast of 8 January are dominated by lithic fragments of dacitic composition. By contrast the ash ejected in a subsequent eruption contains both lithic fragments of dense dacite, and a fresher, sparsely vesicular material of basaltic andesite composition. By October 2017 the ejected ash is back to being dominated by the dense dacitic lithic material. Together with the seismic and deformation record, these observations point to the explosive activity resulting from a small intrusion of basaltic to andesitic magma at shallow level. The fate of this magma, whether stalling or eventually triggering a magmatic eruption, remains to be seen, but current observations suggest the former is most likely

Rethinking Equality in the Global Society

The future of affirmative action, especially in the area of American higher education, has been called into question by the 1996 decision of the U.S. Court of Appeals for the Fifth Circuit in Hopwood v. State of Texas, requiring race-blind admission to state universities in Texas, and the passage of Proposition 209 in California. The seemingly endless American debate on this issue almost entirely has ignored the fact that other countries faced with comparable problems of remedying the effects of past discrimination have developed programs and acquired experience from which Americans might learn. Further, the legal debate has not been adequately informed by the social science disciplines. This conference was intended to expand discussion at a critical moment by introducing these missing perspectives

A CO2-gas precursor to the March 2015 Villarrica volcano eruption

We present here the first volcanic gas compositional time-series taken prior to a paroxysmal eruption of Villarrica volcano (Chile). Our gas plume observations were obtained using a fully autonomous Multi-component Gas Analyser System (Multi-GAS) in the 3 month-long phase of escalating volcanic activity that culminated into the 3 March 2015 paroxysm, the largest since 1985. Our results demonstrate a temporal evolution of volcanic plume composition, from low CO$_2$/SO$_2$ ratios (0.65-2.7) during November 2014-January 2015 to CO$_2$/SO$_2$ ratios up to ≈ 9 then after. The H$_2$O/CO$_2$ ratio simultaneously declined to <38 in the same temporal interval. We use results of volatile saturation models to demonstrate that this evolution toward CO$_2$-enriched gas was likely caused by unusual supply of deeply sourced gas bubbles. We propose that separate ascent of over-pressured gas bubbles, originating from at least 20-35 MPa pressures, was the driver for activity escalation toward the 3 March climax.This work was funded by the DECADE research initiative of the DCO observatory

Reference Array and Design Consideration for the next-generation Event Horizon Telescope

We describe the process to design, architect, and implement a transformative enhancement of the Event Horizon Telescope (ngEHT). This program - the next-generation Event Horizon Telescope (ngEHT) - will form a networked global array of radio dishes capable of making high-fidelity real-time movies of supermassive black holes (SMBH) and their emanating jets. This builds upon the EHT principally by deploying additional modest-diameter dishes to optimized geographic locations to enhance the current global mm/submm wavelength Very Long Baseline Interferometric (VLBI) array, which has, to date, utilized mostly pre-existing radio telescopes. The ngEHT program further focuses on observing at three frequencies simultaneously for increased sensitivity and Fourier spatial frequency coverage. Here, the concept, science goals, design considerations, station siting and instrument prototyping are discussed, and a preliminary reference array to be implemented in phases is described.Comment: Submitted to the journal Galaxie

Investigating variation in replicability

Although replication is a central tenet of science, direct replications are rare in psychology. This research tested variation in the replicability of 13 classic and contemporary effects across 36 independent samples totaling 6,344 participants. In the aggregate, 10 effects replicated consistently. One effect – imagined contact reducing prejudice – showed weak support for replicability. And two effects – flag priming influencing conservatism and currency priming influencing system justification – did not replicate. We compared whether the conditions such as lab versus online or US versus international sample predicted effect magnitudes. By and large they did not. The results of this small sample of effects suggest that replicability is more dependent on the effect itself than on the sample and setting used to investigate the effect