The Impact of Police Killings on Proximal Voter Turnout

This paper studies how spatial proximity to pre-election police killings affects voter turnout. I argue that incidents of police violence have neighborhood-level effects. Nearby voters are more likely to learn about proximal killings than those further away. If perceived as unjust, police killings teach political lessons that reduce voters’ trust in government and political efficacy. In turn, this impacts voter turnout. Observing the 2016 presidential election, I test this theory using geolocated voter data and a difference-in-differences design with matched groups. I find that pre-election police killings reduce voter turnout by 3 percentage points in the killings’ one-mile radius. Space and race matter. Police killings reduce Black voter turnout by 5.9 percentage points in the killings’ one-mile radius, but Black voters one to two miles away from the killings are unaffected. However, police killings do not affect White and Latino voter turnout regardless of the distance

Bifurcations of periodic and chaotic attractors in pinball billiards with focusing boundaries

We study the dynamics of billiard models with a modified collision rule: the outgoing angle from a collision is a uniform contraction, by a factor lambda, of the incident angle. These pinball billiards interpolate between a one-dimensional map when lambda=0 and the classical Hamiltonian case of elastic collisions when lambda=1. For all lambda<1, the dynamics is dissipative, and thus gives rise to attractors, which may be periodic or chaotic. Motivated by recent rigorous results of Markarian, Pujals and Sambarino, we numerically investigate and characterise the bifurcations of the resulting attractors as the contraction parameter is varied. Some billiards exhibit only periodic attractors, some only chaotic attractors, and others have coexistence of the two types.Comment: 30 pages, 17 figures. v2: Minor changes after referee comments. Version with some higher-quality figures available at http://sistemas.fciencias.unam.mx/~dsanders/publications.htm

The Diverse Infrared Properties of a Complete Sample of Star-Forming Dwarf Galaxies

We present mid-infrared Spitzer Space Telescope observations of a complete sample of star-forming dwarf galaxies selected from the KPNO International Spectroscopic Survey. The galaxies span a wide range in mid-infrared properties. Contrary to expectations, some of the galaxies emit strongly at 8 micron indicating the presence of hot dust and/or PAHs. The ratio of this mid-infrared dust emission to the stellar emission is compared with the galaxies' luminosity, star-formation rate, metallicity, and optical reddening. We find that the strength of the 8.0 micron dust emission to the stellar emission ratio is more strongly correlated with the star-formation rate than it is with the metallicity or the optical reddening in these systems. Nonetheless, there is a correlation between the 8.0 micron luminosity and metallicity. The slope of this luminosity-metallicity correlation is shallower than corresponding ones in the B-band and 3.6 micron. The precise nature of the 8.0 micron emission seen in these galaxies (i.e., PAH versus hot dust or some combination of the two) will require future study, including deep mid-IR spectroscopy.Comment: 14 pages, accepted Ap

Exponential speed of mixing for skew-products with singularities

Let $f: [0,1]\times [0,1] \setminus {1/2} \to [0,1]\times [0,1]$ be the $C^\infty$ endomorphism given by $$f(x,y)=(2x- [2x], y+ c/|x-1/2|- [y+ c/|x-1/2|]),$$ where $c$ is a positive real number. We prove that $f$ is topologically mixing and if $c>1/4$ then $f$ is mixing with respect to Lebesgue measure. Furthermore we prove that the speed of mixing is exponential.Comment: 23 pages, 3 figure

The Second Byurakan Survey Galaxies. I. The Optical Database

A database for the entire catalog of the Second Byurakan Survey (SBS) galaxies is presented. It contains new measurements of their optical parameters and additional information taken from the literature and other databases. The measurements were made using Ipg(near-infrared), Fpg(red) and Jpg(blue) band images from photographic sky survey plates obtained by the Palomar Schmidt telescope and extracted from the STScI Digital Sky Survey (DSS). The database provides accurate coordinates, morphological type, spectral and activity classes, apparent magnitudes and diameters, axial ratios, and position angles, as well as number counts of neighboring objects in a circle of radius 50 kpc. The total number of individual SBS objects in the database is now 1676. The 188 Markarian galaxies which were re-discovered by SBS are not included in this database. We also include redshifts that are now available for 1576 SBS objects, as well as 2MASS infrared magnitudes for 1117 SBS galaxies.Comment: 13 pages, 1 figure, 1 tabl

IC 225: a dwarf elliptical galaxy with a peculiar blue core

We present the discovery of a peculiar blue core in the elliptical galaxy IC 225 by using images and spectrum from the Sloan Digital Sky Survey (SDSS). The outer parts of the surface brightness profiles of u-, g-, r-, i- and z-band SDSS images for IC 225 are well fitted with an exponential function. The fitting results show that IC 225 follows the same relations between the magnitude, scale length and central surface brightness for dwarf elliptical galaxies. Its absolute blue magnitude (M_B) is -17.14 mag, all of which suggest that IC 225 is a typical dwarf elliptical galaxy. The g-r color profile indicates a very blue core with a radius of 2 arcseconds, which is also clearly seen in the RGB image made of g-, r- and i-band SDSS images. The SDSS optical spectrum exhibits strong and very narrow nebular emission lines. The metal abundances derived by the standard methods, which are 12+log(O/H) = 8.98, log(N/O) = -0.77 and 12+log(S+/H+) = 6.76, turn out to be significantly higher than that predicted by the well-known luminosity-metallicity relation. After carefully inspecting the central region of IC 225, we find that there are two distinct nuclei, separated by 1.4 arcseconds, the off-nucleated one is even bluer than the nucleus of IC 225. The asymmetric line profiles of higher-order Balmer lines indicate that the emission lines are bluer shifted relative to the absorption lines, suggesting that the line emission arises from the off-center core, whose nature is a metal-rich Hii region. To the best of our knowledge, it is the first high-metallicity Hii region detected in a dwarf elliptical galaxy.Comment: 7 figures, accepted for publication in A

The Radio Quiescence of Active Galaxies with High Accretion Rates

We present 6 cm Very Large Array observations of the Greene & Ho (2004) sample of 19 low-mass active galaxies with high accretion rates. This is one of the only studies of a uniform sample of narrow-line Seyfert 1 (NLS1) galaxies with such high sensitivity and resolution. Although we detect only one source, the entire sample is very radio-quiet down to strong limits. GH10 was found to have a radio power of 8.5 x 10^21 W/Hz, and a ratio R = f(6 cm)/f(4400 A) of 2.8. The 3 sigma upper limits for the remaining nondetections correspond to radio powers from 3 x 10^20 to 8 x 10^21 W/Hz and 0.47 < R <9.9. Stacking all nondetections yields an even stronger upper limit of R < 0.27. An assessment of existing observations in the literature confirms our finding that NLS1s are consistently radio-quiet, with a radio-loud fraction of 0%-6%, which is significantly lower than the 10%-20% observed in the general quasar population. By analogy with stellar-mass black holes, we argue that AGNs undergo a state transition at L_bol/L_Edd~0.01. Below this value a radiatively inefficient accretion flow effectively drives an outflow, which disappears when the flow turns into an optically thick, geometrically thin disk, or a radiation pressure-dominated slim disk at still higher L_bol/L_Edd.Comment: To appear in ApJ; 8 pages, 3 figures; uses emulateapj5.st

Radio Continuum Emission at 1.4 GHz from KISS Emission-Line Galaxies

We have searched the Faint Images of the Radio Sky at Twenty centimeters (FIRST) and the NRAO VLA Sky Survey (NVSS) 1.4 GHz radio surveys for sources that are coincident with emission-line galaxy (ELG) candidates from the KPNO International Spectroscopic Survey (KISS). A total of 207 of the 2157 KISS ELGs (~10%) in the first two H-alpha-selected survey lists were found to possess radio detections in FIRST and/or NVSS. Follow-up spectra exist for all of the radio detections, allowing us to determine the activity type (star-forming vs. AGN) for the entire sample. We explore the properties of the radio-detected KISS galaxies in order to gain a better insight into the nature of radio-emitting galaxies in the local universe (z < 0.1). No dwarf galaxies were detected, despite the large numbers of low-luminosity galaxies present in KISS, suggesting that lower mass, lower luminosity objects do not possess strong galaxian-scale magnetic fields. Due to the selection technique used for KISS, our radio ELGs represent a quasi-volume-limited sample, which allows us to develop a clearer picture of the radio galaxy population at low redshift. Nearly 2/3rds of the KISS radio galaxies are starburst/star-forming galaxies, which is in stark contrast to the results of flux-limited radio surveys that are dominated by AGNs and elliptical galaxies (i.e., classic radio galaxies). While there are many AGNs among the KISS radio galaxies, there are no objects with large radio powers in our local volume. We derive a radio luminosity function (RLF) for the KISS ELGs that agrees very well with previous RLFs that adequately sample the lower-luminosity radio population.Comment: Accepted for publication in the Astronomical Journal (April 2004); 23 pages, 16 figure

The Massive Stellar Content in the Starburst NGC3049: A Test for Hot-Star Mode

We have obtained high-spatial resolution ultraviolet and optical STIS spectroscopy and imaging of the metal-rich nuclear starburst in NGC3049. The stellar continuum and the absorption line spectrum in the ultraviolet are used to constrain the massive stellar population. The strong, blueshifted stellar lines of CIV and SiIV detected in the UV spectra indicate a metal-rich, compact, massive (1E6 Msol) cluster of age 3--4 Myr emitting the UV-optical continuum. We find strong evidence against a depletion of massive stars in this metal-rich cluster. The derived age and the upper mass-limit cut-off of the initial mass function are also consistent with the detection of Wolf-Rayet (WR) features at optical wavelengths. As a second independentconstraint on the massive stellar content, the nebular emission-line spectrum is modeled with photoionization codes using stellar spectra from evolutionary synthesis models. However, the nebular lines are badly reproduced by 3--4 Myr instantaneous bursts, as required by the UV line spectrum, when unblanketed WR and/or Kurucz stellar atmospheres are used. The corresponding number of photons above 24 and 54 eV in the synthetic models is too high in comparison with values suggested by the observed line ratios. Since the ionizing spectrum in this regime is dominated by emission from WR stars, this discrepancy between observations and models is most likely the result of incorrect assumptions about the WR stars. Thus we conclude that the nebular spectrum of high-metallicity starbursts is poorly reproduced by models for WR dominated populations. However, the new model set of Smith et al. (2002) with blanketed WR and O atmospheres and adjusted WR temperatures predicts a softer far-UV radiation field, providing a better match to the data.Comment: To be published in ApJ, Dec. issue 17 figures, 3 in gif forma