284 research outputs found
Liquid London: Sporting spectacle, britishness and ban-optic surveillance
Under the rubrics of recent 'terror' attacks-especially 9/11 and 7/7-the discourses of security and surveillance, and the subsequent heightened awareness of risk and insecurity, have been framed within an increasingly global context. Through an appropriation of the ban-opticon dispositif (Bigo 2006, 2011), this article analyses the changing urban transformations of civic space and mediated messages perpetuated within, and through, the London 2012 Olympic Games. In so doing, we deconstruct the spatial and commercial (re)fashioning of London 2012 and key messages delivered throughout the opening ceremony via a postpanoptic lens, to identify how processes of both 'hard' and 'soft' social control are reiterated and (re)configured through the establishment of a clearly delineated 'other', that which is deemed 'unwelcome' and situated as posing a threat to the safety of the normalised and accepted majority. Thus, through a reading of the cultural politics of class, race and gender that are embedded within sporting spectacle, we argue that London 2012 capitalised on an institutionalised culture of fear to convey, and thus contain, an accepted vision of multiculturalism, while legitimising surveillance practices and security measures that became ingrained within the urban landscape and social fabric of the nation's capital. In so doing, we point towards a troubling yet all too tangible true London Olympic legacy, one that identifies and subjects specific yet significant 'others' to problematic forms of social control and corporeal governance. © The author(s), 2014
Maximum black-hole spin from quasi-circular binary mergers
Black holes of mass M must have a spin angular momentum S below the Kerr
limit chi = S/M^2 < 1, but whether astrophysical black holes can attain this
limiting spin depends on their accretion history. Gas accretion from a thin
disk limits the black-hole spin to chi_gas < 0.9980 +- 0.0002, as
electromagnetic radiation from this disk with retrograde angular momentum is
preferentially absorbed by the black hole. Extrapolation of
numerical-relativity simulations of equal-mass binary black-hole mergers to
maximum initial spins suggests these mergers yield a maximum spin chi_eq <
0.95. Here we show that for smaller mass ratios q = m/M << 1, the superradiant
extraction of angular momentum from the larger black hole imposes a fundamental
limit chi_lim < 0.9979 +- 0.0001 on the final black-hole spin even in the
test-particle limit q -> 0 of binary black-hole mergers. The nearly equal
values of chi_gas and chi_lim imply that measurement of supermassive black-hole
spins cannot distinguish a black hole built by gas accretion from one assembled
by the gravitational inspiral of a disk of compact stellar remnants. We also
show how superradiant scattering alters the mass and spin predicted by models
derived from extrapolating test-particle mergers to finite mass ratios.Comment: final version accepted in PRD, new Fig.4 and discussio
Active Galactic Nuclei in Void Regions
We present a comprehensive study of accretion activity in the most underdense
environments in the universe, the voids, based on the SDSS DR2 data. Based on
investigations of multiple void regions, we show that AGN's occurrence rate and
properties differ from those in walls. AGN are more common in voids than in
walls, but only among moderately luminous and massive galaxies (M_r < -20, log
M_*/M_sun < 10.5), and this enhancement is more pronounced for the weakly
accreting systems (i.e., L_[O III] < 10^39 erg/s). Void AGN hosted by
moderately massive and luminous galaxies are accreting at equal or lower rates
than their wall counterparts, show less obscuration than in walls, and
similarly aged stellar populations. The very few void AGN in massive bright
hosts accrete more strongly, are more obscured, and are associated with younger
stellar emission than wall AGN. Thus, accretion strength is probably connected
to the availability of fuel supply, and accretion and star-formation co-evolve
and rely on the same source of fuel. Nearest neighbor statistics indicate that
the weak accretion activity (LINER-like) is not influenced by the local
environment. However, H IIs, Seyferts, and Transition objects prefer more
grouped small scale structures, indicating that the rate at which galaxies
interact with each other affects their activity. These trends support a
potential H II -> Seyfert/Transition Object -> LINER evolutionary sequence that
we show is apparent in many properties of actively line-emitting galaxies, in
both voids and walls. The subtle differences between void and wall AGN might be
explained by a longer, less disturbed duty cycle of these systems in voids.Comment: 19 pages, 7 figures (1 color); to appear in ApJ, submitted on May 11,
200
Ribbons on the CBR Sky: A Powerful Test of a Baryon Symmetric Universe
If the Universe consists of domains of matter and antimatter, annihilations
at domain interfaces leave a distinctive imprint on the Cosmic Background
Radiation (CBR) sky. The signature is anisotropies in the form of long, thin
ribbons of width , separated by angle where L is the characteristic domain size, and
y-distortion parameter . Such a pattern could potentially be
detected by the high-resolution CBR anisotropy experiments planned for the next
decade, and such experiments may finally settle the question of whether or not
our Hubble volume is baryon symmetric.Comment: LaTeX, 10 pages, 4 figures in epsf. Revised version corrects a couple
of relevant mistake
Biases in Virial Black Hole Masses: An SDSS Perspective
We compile black hole (BH) masses for quasars in the redshift
range included in the Fifth Data Release of the
Sloan Digital Sky Survey (SDSS), using virial BH mass estimators based on the
\hbeta, \MgII, and \CIV emission lines. We find that: (1) within our sample,
the widths of the three lines follow log-normal distributions, with means and
dispersions that do not depend strongly on luminosity or redshift;(2) the
\MgII- and \hbeta-estimated BH masses are consistent with one another; and (3)
the \CIV BH mass estimator may be more severely affected by a disk wind
component than the \MgII and \hbeta estimators, giving a positive bias in mass
correlated with the \CIV-\MgII blueshift. Most SDSS quasars have virial BH
masses in the range . There is a clear upper mass limit of
for active BHs at , decreasing at lower
redshifts. Making the reasonable assumptions that the underlying BH mass
distribution decreases with mass and that the Eddington ratio distribution at
fixed BH mass has non-zero width, we show that the measured virial BH mass
distribution and Eddington ratio distribution are subject to Malmquist bias. A
radio quasar subsample (with ) has mean virial BH
mass larger by dex than the whole sample. A broad absorption line
(BAL) quasar subsample (with ) has identical virial
mass distribution as the nonBAL sample, with no mean offset. (Abridged)Comment: Updated virial mass measurements; improved presentation of the MC
simulation; added new discussion sections; conclusions unchanged. The full
table1 is available at
http://www.astro.princeton.edu/~yshen/BH_mass/datafile1.txt.tar.g
Star formation in 30 Doradus
Using observations obtained with the Wide Field Camera 3 (WFC3) on board the
Hubble Space Telescope (HST), we have studied the properties of the stellar
populations in the central regions of 30 Dor, in the Large Magellanic Cloud.
The observations clearly reveal the presence of considerable differential
extinction across the field. We characterise and quantify this effect using
young massive main sequence stars to derive a statistical reddening correction
for most objects in the field. We then search for pre-main sequence (PMS) stars
by looking for objects with a strong (> 4 sigma) Halpha excess emission and
find about 1150 of them over the entire field. Comparison of their location in
the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for
the appropriate metallicity reveals that about one third of these objects are
younger than ~4Myr, compatible with the age of the massive stars in the central
ionising cluster R136, whereas the rest have ages up to ~30Myr, with a median
age of ~12Myr. This indicates that star formation has proceeded over an
extended period of time, although we cannot discriminate between an extended
episode and a series of short and frequent bursts that are not resolved in
time. While the younger PMS population preferentially occupies the central
regions of the cluster, older PMS objects are more uniformly distributed across
the field and are remarkably few at the very centre of the cluster. We
attribute this latter effect to photoevaporation of the older circumstellar
discs caused by the massive ionising members of R136.Comment: 15 pages, 12 figures. Accepted for publication in The Astrophysical
Journa
The Luminosity, Mass, and Age Distributions of Compact Star Clusters in M83 Based on HST/WFC3 Observations
The newly installed Wide Field Camera 3 (WFC3) on the Hubble Space Telescope
has been used to obtain multi-band images of the nearby spiral galaxy M83.
These new observations are the deepest and highest resolution images ever taken
of a grand-design spiral, particularly in the near ultraviolet, and allow us to
better differentiate compact star clusters from individual stars and to measure
the luminosities of even faint clusters in the U band. We find that the
luminosity function for clusters outside of the very crowded starburst nucleus
can be approximated by a power law, dN/dL \propto L^{alpha}, with alpha = -2.04
+/- 0.08, down to M_V ~ -5.5. We test the sensitivity of the luminosity
function to different selection techniques, filters, binning, and aperture
correction determinations, and find that none of these contribute significantly
to uncertainties in alpha. We estimate ages and masses for the clusters by
comparing their measured UBVI,Halpha colors with predictions from single
stellar population models. The age distribution of the clusters can be
approximated by a power-law, dN/dt propto t^{gamma}, with gamma=-0.9 +/- 0.2,
for M > few x 10^3 Msun and t < 4x10^8 yr. This indicates that clusters are
disrupted quickly, with ~80-90% disrupted each decade in age over this time.
The mass function of clusters over the same M-t range is a power law, dN/dM
propto M^{beta}, with beta=-1.94 +/- 0.16, and does not have bends or show
curvature at either high or low masses. Therefore, we do not find evidence for
a physical upper mass limit, M_C, or for the earlier disruption of lower mass
clusters when compared with higher mass clusters, i.e. mass-dependent
disruption. We briefly discuss these implications for the formation and
disruption of the clusters.Comment: 36 pages, 13 figures, 1 table; accepted for publication in the
Astrophysical Journa
Red Galaxy Growth and the Halo Occupation Distribution
We have traced the past 7 Gyr of red galaxy stellar mass growth within dark
matter halos. We have determined the halo occupation distribution, which
describes how galaxies reside within dark matter halos, using the observed
luminosity function and clustering of 40,696 0.2<z<1.0 red galaxies in Bootes.
Half of 10^{11.9} Msun/h halos host a red central galaxy, and this fraction
increases with increasing halo mass. We do not observe any evolution of the
relationship between red galaxy stellar mass and host halo mass, although we
expect both galaxy stellar masses and halo masses to evolve over cosmic time.
We find that the stellar mass contained within the red population has doubled
since z=1, with the stellar mass within red satellite galaxies tripling over
this redshift range. In cluster mass halos most of the stellar mass resides
within satellite galaxies and the intra-cluster light, with a minority of the
stellar mass residing within central galaxies. The stellar masses of the most
luminous red central galaxies are proportional to halo mass to the power of a
third. We thus conclude that halo mergers do not always lead to rapid growth of
central galaxies. While very massive halos often double in mass over the past 7
Gyr, the stellar masses of their central galaxies typically grow by only 30%.Comment: Accepted for publication in the ApJ. 34 pages, 22 Figures, 5 Table
AEGIS: New Evidence Linking Active Galactic Nuclei to the Quenching of Star Formation
Utilizing Chandra X-ray observations in the All-wavelength Extended Groth
Strip International Survey (AEGIS) we identify 241 X-ray selected Active
Galactic Nuclei (AGNs, L > 10^{42} ergs/s) and study the properties of their
host galaxies in the range 0.4 < z < 1.4. By making use of infrared photometry
from Palomar Observatory and BRI imaging from the Canada-France-Hawaii
Telescope, we estimate AGN host galaxy stellar masses and show that both
stellar mass and photometric redshift estimates (where necessary) are robust to
the possible contamination from AGNs in our X-ray selected sample. Accounting
for the photometric and X-ray sensitivity limits of the survey, we construct
the stellar mass function of X-ray selected AGN host galaxies and find that
their abundance decreases by a factor of ~2 since z~1, but remains roughly flat
as a function of stellar mass. We compare the abundance of AGN hosts to the
rate of star formation quenching observed in the total galaxy population. If
the timescale for X-ray detectable AGN activity is roughly 0.5-1 Gyr--as
suggested by black hole demographics and recent simulations--then we deduce
that the inferred AGN "trigger" rate matches the star formation quenching rate,
suggesting a link between these phenomena. However, given the large range of
nuclear accretion rates we infer for the most massive and red hosts, X-ray
selected AGNs may not be directly responsible for quenching star formation.Comment: 12 pages. Submitted to ApJ. Comments welcom
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