Measuring the slopes of mass profiles for dwarf spheroidals in triaxial CDM potentials

We generate stellar distribution functions (DFs) in triaxial haloes in order to examine the reliability of slopes $\Gamma\equiv \Delta {\rm log} M / \Delta {\rm log} r$ inferred by applying mass estimators of the form $M\propto R_e\sigma^2$ (i.e. assuming spherical symmetry, where $R_e$ and $\sigma$ are luminous effective radius and global velocity dispersion, respectively) to two stellar sub-populations independently tracing the same gravitational potential. The DFs take the form $f(E)$, are dynamically stable, and are generated within triaxial potentials corresponding directly to subhaloes formed in cosmological dark-matter-only simulations of Milky Way and galaxy cluster haloes. Additionally, we consider the effect of different tracer number density profiles (cuspy and cored) on the inferred slopes of mass profiles. For the isotropic DFs considered here, we find that halo triaxiality tends to introduce an anti-correlation between $R_e$ and $\sigma$ when estimated for a variety of viewing angles. The net effect is a negligible contribution to the systematic error associated with the slope of the mass profile, which continues to be dominated by a bias toward greater overestimation of masses for more-concentrated tracer populations. We demonstrate that simple mass estimates for two distinct tracer populations can give reliable (and cosmologically meaningful) lower limits for $\Gamma$, irrespective of the degree of triaxiality or shape of the tracer number density profile.Comment: 5 pages, 4 figures, submitted to MNRA

Carbonate Facies of the Helderberg Group (Lower Devonian) of New York

Guidebook for field trips in New York, Massachusetts and Vermont: 61st annual meeting at the State University of New York at Albany, Albany, New York October 10, 11, 12, 1969: Trip

Carbon and nitrogen isotope records of the Hirnantian glaciation

The Hirnantian mass extinction was the second largest of the Phanerozoic. A global sea level fall resulting from a glaciation on Gondwanaland caused significant changes in ocean circulation patterns and nutrient cycling that is recorded as a worldwide positive δ¹³C excursion. In chapter 2, carbon and nitrogen isotope profiles were reconstructed from two North American carbonate platforms in Nevada and one in the Yukon with the purpose of gaining a better understanding of proximal to proximal gradients in δ¹³C values from Hirnantian epeiric seaway sediment. Positive δ¹³C excursions are recorded in bulk inorganic and organic carbon fractions from all three sections, and in graptolite periderms from one section. A larger positive excursion is recorded in the proximal sediment (7‰) compared to proximal sediment (3-4‰). This gradient appears to reflect differences in surface water dissolved inorganic carbon δ¹³C values across epeiric seas. These findings are consistent with the carbonate weathering hypothesis, that predicts larger positive δ¹³C shifts in proximal settings of tropical epeiric seas resulting from changes in the local carbon weathering flux caused by the exposure of vast areas of carbonate sediment during glacioeustatic sea level fall and restricted shelf circulation. A 2‰ positive excursion in δ¹⁵N is interpreted to result from increased ocean ventilation, greater partitioning of atmospheric oxygen into downwelling surface waters, oxygen minimum zone shrinkage, and declining denitrification rates. This allowed for upwelling of recycled nitrogen with high δ¹⁵N values into the photic zone that forced exported organic matter from the photic zone to higher δ¹⁵N values, consistent with the observed positive shift in δ¹⁵N during the Hirnantian glaciation. This study presents a conceptual model to explain secular changes in δ¹³C and δ¹⁵N during the transition from a greenhouse to icehouse climate. The second focus of this research, presented in chapter 3, was on improving the chemical and analytical methods for δ¹⁸O analysis of biogenic apatites. The technique applies cation exchange chromatography that allows for small sample sizes of apatite (200 µg) to be used for chemical conversion to Ag3PO4. The precision (0.15‰, 1σ) of δ¹⁸O analysis obtained using a Thermal Conversion Elemental Analyser Continuous Flow – Isotope Ratio Mass Spectrometer (TC/EA CF-IRMS), and the ability to collect multipe isotopes (O, Ca, Sr, REE) using a cation exchange column, makes this technique valuable for high-resolution, multi-isotope studies of biogenic apatites

Epistemological Matters Matter for Theological Understanding

This article leads the reader to appreciate some of the importance of philosophical epistemology, to the field of theology, by way of two fascinating philosophical topics. As it does so, it provides some development and clarification of two notions important in epistemology: first, rationality, and second, the distinction sometimes called the “propositional–experiential” distinction. The first is the more central to mainstream philosophy today. Since at least Plato, philosophers have asked: what is it to know something, or to be rational or right-headed, as opposed to kooky or gullible, in believing something? Christian philosophers have applied this study to the question: can faith be known/rational/right-headed? This topic is especially germane today, with the “New Atheism” claiming that faith on the basis of Revelation is gullible or worse. The other big epistemological topic I’ll address has a history just as old. It’s discussed here and there, piecemeal, rather than systematically, today and throughout the philosophical tradition. Augustine, for one, reflects powerfully upon it. That topic is, broadly, the difference between experiential knowledge and propositional knowledge. Sometimes we seem to know something, as thoroughly as you please—you’d pass an exam on it with flying colors—without really knowing it--in a more felt, experienced, deeper way. The importance of this issue comes out in a variety of contexts. Here’s one important connection: What sort of knowledge does it take to trust God? What sort of knowledge are we missing, if we know in our minds that we should trust God, but we don’t “feel it in our nerves” (as C.S. Lewis would put it)? Experiential knowledge seems to be saliently responsible in a way that propositional knowledge isn’t, for moving us to action, affection, value judgment, and prioritizing in life (= wisdom, a gift of the HS), as well. There are further applications to judging moral responsibility, and to effective preaching and teaching

The Growth in Size and Mass of Cluster Galaxies since z=2

We study the formation and evolution of Brightest Cluster Galaxies starting from a $z=2$ population of quiescent ellipticals and following them to $z=0$. To this end, we use a suite of nine high-resolution dark matter-only simulations of galaxy clusters in a $\Lambda$CDM universe. We develop a scheme in which simulation particles are weighted to generate realistic and dynamically stable stellar density profiles at $z=2$. Our initial conditions assign a stellar mass to every identified dark halo as expected from abundance matching; assuming there exists a one-to-one relation between the visible properties of galaxies and their host haloes. We set the sizes of the luminous components according to the observed relations for $z\sim2$ massive quiescent galaxies. We study the evolution of the mass-size relation, the fate of satellite galaxies and the mass aggregation of the cluster central. From $z=2$, these galaxies grow on average in size by a factor 5 to 10 of and in mass by 2 to 3. The stellar mass growth rate of the simulated BCGs in our sample is of 1.9 in the range $0.3<z<1.0$ consistent with observations, and of 1.5 in the range $0.0<z<0.3$. Furthermore the satellite galaxies evolve to the present day mass-size relation by $z=0$. Assuming passively evolving stellar populations, we present surface brightness profiles for our cluster centrals which resemble those observed for the cDs in similar mass clusters both at $z=0$ and at $z=1$. This demonstrates that the $\Lambda$CDM cosmology does indeed predict minor and major mergers to occur in galaxy clusters with the frequency and mass ratio distribution required to explain the observed growth in size of passive galaxies since $z=2$. Our experiment shows that Brightest Cluster Galaxies can form through dissipationless mergers of quiescent massive $z=2$ galaxies, without substantial additional star formation.Comment: submitted to MNRAS, 10 pages, 8 figures, 2 table