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Mayer, L.

Publications and source records attributed to Mayer, L..

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Diffuse coronae in cosmological simulations of Milky Way-sized galaxies

We investigate the properties of halo gas using three cosmological “zoom-in” simulations of realistic Milky Way-galaxy analogs with varying sub-grid physics. In all three cases, the mass of hot (T > 10{sup 6} K) halo gas is ∼1% of the host's virial mass. The X-ray luminosity of two of the runs is consistent with observations of the Milky Way, while the third simulation is X-ray bright and resembles more closely a very massive, star-forming spiral. Hot halos extend to 140 kpc from the galactic center and are surrounded by a bubble of warm-hot (T=10{sup 5}−10{sup 6} K) gas that extends to the virial radius. Simulated halos agree well outside 20–30 kpc with the β-model of Miller and Bregman based on O vii absorption and O viii emission measurements. Warm-hot and hot gas contribute up to 80% of the total gas reservoir, and contain nearly the same amount of baryons as the stellar component. The mass of warm-hot and hot components falls into the range estimated for L{sup ∗} galaxies. With key observational constraints on the density of the Milky Way corona being satisfied, we show that concealing of the ubiquitous warm-hot baryons, along with the ejection of just 20%–30% of the diffuse gas out of the potential wells by supernova-driven outflows, can solve the “missing baryon problem.” The recovered baryon fraction within 3 virial radii is 90% of the universal value. With a characteristic density of ∼10{sup −4} cm{sup −3} at 50–80 kpc, diffuse coronae meet the requirement for fast and complete ram-pressure stripping of the gas reservoirs in dwarf galaxy satellites.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

On the gap-opening criterion of migrating planets in protoplanetary disks

We perform two-dimensional hydrodynamical simulations to quantitatively explore the torque balance criterion for gap-opening (as formulated by Crida et al.) in a variety of disks when considering a migrating planet. We find that even when the criterion is satisfied, there are instances when planets still do not open gaps. We stress that gap-opening is not only dependent on whether a planet has the ability to open a gap, but whether it can do so quickly enough. This can be expressed as an additional condition on the gap-opening timescale, t{sub gap}, versus the crossing time, t{sub cross}, i.e., the time it takes the planet to cross the region which it is carving out. While this point has been briefly made in the previous literature, our results quantify it for a range of protoplanetary disk properties and planetary masses, demonstrating how crucial it is for gap-opening. This additional condition has important implications for the survival of planets formed by core accretion in low mass disks as well as giant planets or brown dwarfs formed by gravitational instability in massive disks. It is particularly important for planets with intermediate masses susceptible to Type III-like migration. For some observed transition disks or disks with gaps, we expect that estimates on the potential planet masses based on the torque balance gap-opening criterion alone may not be sufficient. With consideration of this additional timescale criterion theoretical studies may find a reduced planet survivability or that planets may migrate further inwards before opening a gap.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

TRENDS IN DWARF EARLY-TYPE KINEMATICS WITH CLUSTER-CENTRIC RADIUS DRIVEN BY TIDAL STIRRING

We model the dynamics of dwarf early-type galaxies in the Virgo cluster when subject to a variety of environmental processes. We focus on how these processes imprint trends in the dynamical state (rotational versus pressure support as measured by the λ{sub Re/2}{sup ∗} statistic) with projected distance from the cluster center, and compare these results to observational estimates. We find a large scatter in the gradient of λ{sub Re/2}{sup ∗} with projected radius. A statistical analysis shows that models with no environmental effects produce gradients as steep as those observed in none of the 100 cluster realizations we consider, while in a model incorporating tidal stirring by the cluster potential 34% of realizations produce gradients as steep as that observed. Our results suggest that tidal stirring may be the cause of the observed radial dependence of dwarf early-type dynamics in galaxy clusters.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1985

Quantitative analysis in megageomorphology

Megageomorphology is the study of regional topographic features and their relations to independent geomorphic variables that operate at the regional scale. These independent variables can be classified as either tectonic or climatic in nature. Quantitative megageomorphology stresses the causal relations between plate tectonic factors and landscape features or correlations between climatic factors and geomorphic processes. In addition, the cumulative effects of tectonics and climate on landscape evolution that simultaneously operate in a complex system of energy transfer is of interst. Regional topographic differentiation, say between continents and ocean floors, is largely the result of the different densities and density contrasts within the oceanic and continental lithosphere and their isostatic consequences. Regional tectonic processes that alter these lithospheric characteristics include rifting, collision, subduction, transpression and transtension.

Mayer, L.↗
NASA NTRS1979

Modified polymers for gas chromatography

Polymeric materials are modified to serve as stationary phase in chromatographic columns used for separation of atmospheric gases. Materials simplify and improve separation of atmospheric gases in terms of time, quantity of material needed, and sharpness of separation.

Woeller, F. H.↗