598 research outputs found
Speciesistic Veganism: An Anthropocentric Argument
The paper proposes an anthropocentric argument for veganism based on a speciesistic premise that most carnists likely affirm: human flourishing should be promoted. I highlight four areas of human suffering promoted by a carnistic diet: (1) health dangers to workers (both physical and psychological), (2) economic dangers to workers, (3) physical dangers to communities around slaughterhouses, and (4) environmental dangers to communities-at-large. Consequently, one could ignore the well-being of non-human animals and nevertheless recognize significant moral failings in the current standard system of meat production
Application of a Self-Similar Pressure Profile to Sunyaev-Zel'dovich Effect Data from Galaxy Clusters
We investigate the utility of a new, self-similar pressure profile for
fitting Sunyaev-Zel'dovich (SZ) effect observations of galaxy clusters. Current
SZ imaging instruments - such as the Sunyaev-Zel'dovich Array (SZA) - are
capable of probing clusters over a large range in physical scale. A model is
therefore required that can accurately describe a cluster's pressure profile
over a broad range of radii, from the core of the cluster out to a significant
fraction of the virial radius. In the analysis presented here, we fit a radial
pressure profile derived from simulations and detailed X-ray analysis of
relaxed clusters to SZA observations of three clusters with exceptionally high
quality X-ray data: A1835, A1914, and CL J1226.9+3332. From the joint analysis
of the SZ and X-ray data, we derive physical properties such as gas mass, total
mass, gas fraction and the intrinsic, integrated Compton y-parameter. We find
that parameters derived from the joint fit to the SZ and X-ray data agree well
with a detailed, independent X-ray-only analysis of the same clusters. In
particular, we find that, when combined with X-ray imaging data, this new
pressure profile yields an independent electron radial temperature profile that
is in good agreement with spectroscopic X-ray measurements.Comment: 28 pages, 6 figures, accepted by ApJ for publication (probably April
2009
"The Book of Negroes’ illustrated edition: circulating African-Canadian history through the Middlebrow"
This article examines the 2009 deluxe illustrated edition of Lawrence Hill’s Commonwealth Writers’ Prize– and Canada Reads–winning novel The Book of Negroes, originally published in 2007. It relates the story of Aminata, a West African girl kidnapped and sold into slavery, and her experiences on an indigo plantation in the American south, followed by further displacements to Charleston, Nova Scotia, Sierra Leone, and London. In New York, as the Revolutionary War comes to a close, Aminata becomes the scribe for the Book of Negroes, documenting the Black Loyalists, as well as the slaves and indentured servants of white Loyalists, granted passage by the British to Canada. Hill has commented that the Book of Negroes is an important document about which Canadians are largely ignorant. This desire to circulate knowledge about African-Canadian history through the novel is particularly manifest in the illustrated edition of 2009, where a photograph of the Book of Negroes features prominently, along with countless other images and captions which supplement and interrupt Hill’s narrative. This article considers the significance and implications of this “keepsake” or “souvenir” edition, particularly its circulation of knowledge about African-Canadian history through visual pleasure
The Growth of Cool Cores and Evolution of Cooling Properties in a Sample of 83 Galaxy Clusters at 0.3 < z < 1.2 Selected from the SPT-SZ Survey
We present first results on the cooling properties derived from Chandra X-ray
observations of 83 high-redshift (0.3 < z < 1.2) massive galaxy clusters
selected by their Sunyaev-Zel'dovich signature in the South Pole Telescope
data. We measure each cluster's central cooling time, central entropy, and mass
deposition rate, and compare to local cluster samples. We find no significant
evolution from z~0 to z~1 in the distribution of these properties, suggesting
that cooling in cluster cores is stable over long periods of time. We also find
that the average cool core entropy profile in the inner ~100 kpc has not
changed dramatically since z ~ 1, implying that feedback must be providing
nearly constant energy injection to maintain the observed "entropy floor" at
~10 keV cm^2. While the cooling properties appear roughly constant over long
periods of time, we observe strong evolution in the gas density profile, with
the normalized central density (rho_0/rho_crit) increasing by an order of
magnitude from z ~ 1 to z ~ 0. When using metrics defined by the inner surface
brightness profile of clusters, we find an apparent lack of classical, cuspy,
cool-core clusters at z > 0.75, consistent with earlier reports for clusters at
z > 0.5 using similar definitions. Our measurements indicate that cool cores
have been steadily growing over the 8 Gyr spanned by our sample, consistent
with a constant, ~150 Msun/yr cooling flow that is unable to cool below
entropies of 10 keV cm^2 and, instead, accumulates in the cluster center. We
estimate that cool cores began to assemble in these massive systems at z ~ 1,
which represents the first constraints on the onset of cooling in galaxy
cluster cores. We investigate several potential biases which could conspire to
mimic this cool core evolution and are unable to find a bias that has a similar
redshift dependence and a substantial amplitude.Comment: 17 pages with 15 figures, plus appendix. Published in Ap
SPT-CLJ2040-4451: An SZ-Selected Galaxy Cluster at z = 1.478 With Significant Ongoing Star Formation
SPT-CLJ2040-4451 -- spectroscopically confirmed at z = 1.478 -- is the
highest redshift galaxy cluster yet discovered via the Sunyaev-Zel'dovich
effect. SPT-CLJ2040-4451 was a candidate galaxy cluster identified in the first
720 deg^2 of the South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey, and
confirmed in follow-up imaging and spectroscopy. From multi-object spectroscopy
with Magellan-I/Baade+IMACS we measure spectroscopic redshifts for 15 cluster
member galaxies, all of which have strong [O II] 3727 emission.
SPT-CLJ2040-4451 has an SZ-measured mass of M_500,SZ = 3.2 +/- 0.8 X 10^14
M_Sun/h_70, corresponding to M_200,SZ = 5.8 +/- 1.4 X 10^14 M_Sun/h_70. The
velocity dispersion measured entirely from blue star forming members is sigma_v
= 1500 +/- 520 km/s. The prevalence of star forming cluster members (galaxies
with > 1.5 M_Sun/yr) implies that this massive, high-redshift cluster is
experiencing a phase of active star formation, and supports recent results
showing a marked increase in star formation occurring in galaxy clusters at z
>1.4. We also compute the probability of finding a cluster as rare as this in
the SPT-SZ survey to be >99%, indicating that its discovery is not in tension
with the concordance Lambda-CDM cosmological model.Comment: 14 pages, 8 figures, 4 tables, Accepted to Ap
A Massive, Cooling-Flow-Induced Starburst in the Core of a Highly Luminous Galaxy Cluster
In the cores of some galaxy clusters the hot intracluster plasma is dense
enough that it should cool radiatively in the cluster's lifetime, leading to
continuous "cooling flows" of gas sinking towards the cluster center, yet no
such cooling flow has been observed. The low observed star formation rates and
cool gas masses for these "cool core" clusters suggest that much of the cooling
must be offset by astrophysical feedback to prevent the formation of a runaway
cooling flow. Here we report X-ray, optical, and infrared observations of the
galaxy cluster SPT-CLJ2344-4243 at z = 0.596. These observations reveal an
exceptionally luminous (L_2-10 keV = 8.2 x 10^45 erg/s) galaxy cluster which
hosts an extremely strong cooling flow (dM/dt = 3820 +/- 530 Msun/yr). Further,
the central galaxy in this cluster appears to be experiencing a massive
starburst (740 +/- 160 Msun/yr), which suggests that the feedback source
responsible for preventing runaway cooling in nearby cool core clusters may not
yet be fully established in SPT-CLJ2344-4243. This large star formation rate
implies that a significant fraction of the stars in the central galaxy of this
cluster may form via accretion of the intracluster medium, rather than the
current picture of central galaxies assembling entirely via mergers.Comment: 11 pages, 3 figures, 1 table. Supplemental material contains 15
additional pages. Published in Natur
The Chandra Source Catalog
The Chandra Source Catalog (CSC) is a general purpose virtual X-ray
astrophysics facility that provides access to a carefully selected set of
generally useful quantities for individual X-ray sources, and is designed to
satisfy the needs of a broad-based group of scientists, including those who may
be less familiar with astronomical data analysis in the X-ray regime. The first
release of the CSC includes information about 94,676 distinct X-ray sources
detected in a subset of public ACIS imaging observations from roughly the first
eight years of the Chandra mission. This release of the catalog includes point
and compact sources with observed spatial extents <~ 30''. The catalog (1)
provides access to the best estimates of the X-ray source properties for
detected sources, with good scientific fidelity, and directly supports
scientific analysis using the individual source data; (2) facilitates analysis
of a wide range of statistical properties for classes of X-ray sources; and (3)
provides efficient access to calibrated observational data and ancillary data
products for individual X-ray sources, so that users can perform detailed
further analysis using existing tools. The catalog includes real X-ray sources
detected with flux estimates that are at least 3 times their estimated 1 sigma
uncertainties in at least one energy band, while maintaining the number of
spurious sources at a level of <~ 1 false source per field for a 100 ks
observation. For each detected source, the CSC provides commonly tabulated
quantities, including source position, extent, multi-band fluxes, hardness
ratios, and variability statistics, derived from the observations in which the
source is detected. In addition to these traditional catalog elements, for each
X-ray source the CSC includes an extensive set of file-based data products that
can be manipulated interactively.Comment: To appear in The Astrophysical Journal Supplement Series, 53 pages,
27 figure
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