A Stellar Mass Threshold for Quenching of Field Galaxies

We demonstrate that dwarf galaxies (10^7 < M_stellar < 10^9 Msun) with no active star formation are extremely rare (<0.06%) in the field. Our sample is based on the NASA-Sloan Atlas which is a re-analysis of the Sloan Digital Sky Survey Data Release 8. We examine the relative number of quenched versus star forming dwarf galaxies, defining quenched galaxies as having no Halpha emission (EW_Halpha < 2 AA) and a strong 4000AA-break. The fraction of quenched dwarf galaxies decreases rapidly with increasing distance from a massive host, leveling off for distances beyond 1.5 Mpc. We define galaxies beyond 1.5 Mpc of a massive host galaxy to be in the field. We demonstrate that there is a stellar mass threshold of M_stellar < 1.0x10^9 Msun below which quenched galaxies do not exist in the field. Below this threshold, we find that none of the 2951 field dwarf galaxies are quenched; all field dwarf galaxies show evidence for recent star formation. Correcting for volume effects, this corresponds to a 1-sigma upper limit on the quenched fraction of 0.06%. In more dense environments, quenched galaxies account for 23% of the dwarf population over the same stellar mass range. The majority of quenched dwarf galaxies (often classified as dwarf elliptical galaxies) are within 2 virial radii of a massive galaxy, and only a few percent of quenched dwarf galaxies exist beyond 4 virial radii. Thus, for galaxies with stellar mass less than 1.0x10^9 Msun, ending star-formation requires the presence of a more massive neighbor, providing a stringent constraint on models of star formation feedback.Comment: 9 pages, 6 figures, accepted to Ap

An investigation of rooftop STOL port aerodynamics

An investigation into aerodynamic problems associated with large building rooftop STOLports was performed. Initially, a qualitative flow visualization study indicated two essential problems: (1) the establishment of smooth, steady, attached flow over the rooftop, and (2) the generation of acceptable crosswind profile once (1) has been achieved. This study indicated that (1) could be achieved by attaching circular-arc rounded edge extensions to the upper edges of the building and that crosswind profiles could be modified by the addition of porous vertical fences to the lateral edges of the rooftop. Important fence parameters associated with crosswind alteration were found to be solidity, fence element number and spacing. Large scale building induced velocity fluctuations were discovered for most configurations tested and a possible explanation for their occurrence was postulated. Finally, a simple equation relating fence solidity to the resulting velocity profile was developed and tested for non-uniform single element fences with 30 percent maximum solidity

Who Gets A Dead Man\u27s Gold? The Dilemma of Lottery Winnings Payable to a Decedent\u27s Estate

This article addresses the federal estate tax and federal income tax consequences of lottery winnings which flow to the estate of a decedent or, alternatively, directly to the decedent\u27s beneficiaries. State income tax and state death tax considerations must also be taken into account. With respect to these secondary implications, this article draws largely upon the Code of Virginia and the relevant sections of Virginia\u27s income tax and estate tax statutes. Some references will be made to the possibility of contrary statutory treatment in other states, but primary reliance will be upon Virginia law

Cooperation, collective action, and the archeology of large-scale societies

Archeologists investigating the emergence of large-scale societies in the past have renewed interest in examining the dynamics of cooperation as a means of understanding societal change and organizational variability within human groups over time. Unlike earlier approaches to these issues, which used models designated voluntaristic or managerial, contemporary research articulates more explicitly with frameworks for cooperation and collective action used in other fields, thereby facilitating empirical testing through better definition of the costs, benefits, and social mechanisms associated with success or failure in coordinated group action. Current scholarship is nevertheless bifurcated along lines of epistemology and scale, which is understandable but problematic for forging a broader, more transdisciplinary field of cooperation studies. Here, we point to some areas of potential overlap by reviewing archeological research that places the dynamics of social cooperation and competition in the foreground of the emergence of large-scale societies, which we define as those having larger populations, greater concentrations of political power, and higher degrees of social inequality. We focus on key issues involving the communal-resource management of subsistence and other economic goods, as well as the revenue flows that undergird political institutions. Drawing on archeological cases from across the globe, with greater detail from our area of expertise in Mesoamerica, we offer suggestions for strengthening analytical methods and generating more transdisciplinary research programs that address human societies across scalar and temporal spectra

Bill of Sale of an Enslaved Person Named Malvina

Bill of sale of an enslaved woman named Malvina.https://egrove.olemiss.edu/lanternproject/1044/thumbnail.jp

Autocorrelations of stellar light and mass in the low-redshift Universe

The final data release of the Sloan Digital Sky Survey (SDSS) provides reliable photometry and spectroscopy for about half a million galaxies with median redshift 0.09. Here we use these data to estimate projected autocorrelation functions w_p(r_p) for the light of galaxies in the five SDSS photometric bands. Comparison with the analogous stellar mass autocorrelation, estimated in a previous paper, shows that stellar luminosity is less strongly clustered than stellar mass in all bands and on all scales. Over the full nonlinear range 10 kpc/h < r_p < 10 Mpc/h our autocorrelation estimates are extremely well represented by power laws. The parameters of the corresponding spatial functions \xi(r) = (r/r_0)^\gamma vary systematically from r_0=4.5 Mpc/h and \gamma=-1.74 for the bluest band (the u band) to r_0=5.8 Mpc/h and \gamma=-1.83 for the reddest one (the z band). These may be compared with r_0=6.1 Mpc/h and \gamma=-1.84 for the stellar mass. Ratios of w_p(r_p) between two given wavebands are proportional to the mean colour of correlated stars at projected distance r_p from a randomly chosen star. The ratio of the stellar mass and luminosity autocorrelations measures an analogous mean stellar mass-to-light ratio (M*/L). All colours get redder and all mass-to-light ratios get larger with decreasing r_p, with the amplitude of the effects decreasing strongly to redder passbands. Even for the u-band the effects are quite modest, with maximum shifts of about 0.1 in u-g and about 25% in M*/L_u. These trends provide a precise characterisation of the well-known dependence of stellar populations on environment.Comment: 6 pages, 4 figures, accepted to MNRAS; three new paragraphs added: two at the end of Sec. 2 concerning cross-correlations between different bands and possible biases due to photometry errors, and one at the end of the paper discussing marked correlation function

The Environments of Low and High Luminosity Radio Galaxies at Moderate Redshifts

In the local Universe, high-power radio galaxies live in lower density environments than low-luminosity radio galaxies. If this trend continues to higher redshifts, powerful radio galaxies would serve as efficient probes of moderate redshift groups and poor clusters. Photometric studies of radio galaxies at 0.3 < z < 0.5 suggest that the radio luminosity-environment correlation disappears at moderate redshifts, though this could be the result of foreground/background contamination affecting the photometric measures of environment. We have obtained multi-object spectroscopy of in the fields of 14 lower luminosity (L_1.4GHz 1.2x10^25 W/Hz) radio galaxies at z ~ 0.3 to spectroscopically investigate the link between the environment and the radio luminosity of radio galaxies at moderate redshifts. Our results support the photometric analyses; there does not appear to be a correlation between the luminosity of a radio galaxy and its environment at moderate redshifts. Hence, radio galaxies are not efficient signposts for group environments at moderate redshifts.Comment: 7 pages, 9 figures, Accepted for publication in A