8,343 research outputs found
Abracadabra: Key Agents of Mediation that Define, Create, and Maintain TV Fandom
From a media industries, fan studies, and emerging socio-cultural public relations perspective, this project pulls back the Hollywood curtain to explore two questions: 1) How do TV public relations practitioners and key tastemaker/gatekeeper media define, create, build, and maintain fandom?; and 2) How do they make meaning of fandom and their agency/role in fan creation from their position of industrial producers, cultural intermediaries, members of the audience, and as fans themselves? This project brings five influential, working public relations and media professionals into a conversation about two case studies from the 2010-2011 television season – broadcast network CBS’ Hawaii Five-0 and basic cable network AMC’s The Walking Dead. Each of these shows speaks to fandom in particular ways and are representative of the industry’s current approaches in luring specific audiences to TV. This study shows that the relationship between entertainment publicists and media is dynamic, intertwined, complex, and historically hidden
The Nature of Lyman Break Galaxies in Cosmological Hydrodynamic Simulations
What type of objects are being detected as "Lyman break galaxies"?
Are they predominantly the most massive galaxies at that epoch, or are many of
them smaller galaxies undergoing a short-lived burst of merger-induced star
formation? We attempt to address this question using high-resolution
cosmological hydrodynamic simulations including star formation and feedback.
Our CDM simulation, together with Bruzual-Charlot population synthesis
models, reproduces the observed number density and luminosity function of Lyman
break galaxies when dust is incorporated. The inclusion of dust is crucial for
this agreement. In our simulation, these galaxies are predominantly the most
massive objects at this epoch, and have a significant population of older
stars. Nevertheless, it is possible that our simulations lack the resolution
and requisite physics to produce starbursts, despite having a physical
resolution of \la 700 pc at z=3. Thus we cannot rule out merger-induced
starburst galaxies also contributing to the observed population of
high-redshift objects.Comment: 5 pages, contribution to the Proceedings of Rencontres
Internationales de l'IGRAP, Clustering at High Redshift, Marseille 199
Theoretical Modeling of the High Redshift Galaxy Population
We review theoretical approaches to the study of galaxy formation, with
emphasis on the role of hydrodynamic simulations in modeling the high redshift
galaxy population. We present new predictions for the abundance of star-forming
galaxies in the Lambda + cold dark matter model (Omega_m=0.4, Omega_L=0.6),
combining results from several simulations to probe a wide range of redshift.
At a threshold density of one object per arcmin^2 per unit z, these simulations
predict galaxies with star formation rates of 2 msun/yr (z=10), 5 msun/yr
(z=8), 20 msun/yr (z=6), 70-100 msun/yr (z=4-2), and 30 msun/yr (z=0.5). For
galaxies selected at a fixed comoving space density n=0.003 h^3 Mpc^{-3], a (50
Mpc/h)^3 simulation predicts a galaxy correlation function (r/5 Mpc/h)^{-1.8}
in comoving coordinates, essentially independent of redshift from z=4 to z=0.5.
Different cosmological models predict global histories of star formation that
reflect their overall histories of mass clustering, but robust numerical
predictions of the comoving space density of star formation are difficult
because the simulations miss the contribution from galaxies below their
resolution limit. The LCDM model appears to predict a star formation history
with roughly the shape inferred from observations, but it produces too many
stars at low redshift, predicting Omega_* ~ 0.015 at z=0. We conclude with a
brief discussion of this discrepancy and three others that suggest gaps in our
current theory of galaxy formation: small disks, steep central halo profiles,
and an excess of low mass dark halos. While these problems could fade as the
simulations or observations improve, they could also guide us towards a new
understanding of galactic scale star formation, the spectrum of primordial
fluctuations, or the nature of dark matter.Comment: 12 pages, 3 figs. To be published in "Photometric Redshifts and High
Redshift Galaxies", eds. R. Weymann, L. Storrie-Lombardi, M. Sawicki & R.
Brunner, (San Francisco: ASP Conference Series
The Population of Damped Lyman-alpha and Lyman Limit Systems in the Cold Dark Matter Model
Lyman limit and damped Lyman-alpha absorption systems probe the distribution
of collapsed, cold gas at high redshift. Numerical simulations that incorporate
gravity and gas dynamics can predict the abundance of such absorbers in
cosmological models. We develop a semi-analytical method to correct the
numerical predictions for the contribution of unresolved low mass halos, and we
apply this method to the Katz et al. (1996) simulation of the standard cold
dark matter model (, , , ). Using
this simulation and higher resolution simulations of individual low mass
systems, we determine the relation between a halo's circular velocity and
its cross section for producing Lyman limit or damped absorption. We combine
this relation with the Press-Schechter formula for the abundance of halos to
compute the number of absorbers per unit redshift. The resolution correction
increases the predicted abundances by about a factor of two at z=2, 3, and 4,
bringing the predicted number of damped absorbers into quite good agreement
with observations. Roughly half of the systems reside in halos with circular
velocities v_c>100\kms and half in halos with 35\kms. Halos
with v_c>150\kms typically harbor two or more systems capable of producing
damped absorption. Even with the resolution correction, the predicted abundance
of Lyman limit systems is a factor of three below observational estimates,
signifying either a failure of standard CDM or a failure of these simulations
to resolve the systems responsible for most Lyman limit absorption. By
comparing simulations with and without star formation, we find that depletion
of the gas supply by star formation affects absorption line statistics at
only for column densities exceeding .Comment: AASlatex, 17 pages w/ 3 embedded ps figures. Submitted to Ap
The Neuroscience Information Framework: A Data and Knowledge Environment for Neuroscience
With support from the Institutes and Centers forming the NIH Blueprint for Neuroscience Research, we have designed and implemented a new initiative for integrating access to and use of Web-based neuroscience resources: the Neuroscience Information Framework. The Framework arises from the expressed need of the neuroscience community for neuroinformatic tools and resources to aid scientific inquiry, builds upon prior development of neuroinformatics by the Human Brain Project and others, and directly derives from the Society for Neuroscience’s Neuroscience Database Gateway. Partnered with the Society, its Neuroinformatics Committee, and volunteer consultant-collaborators, our multi-site consortium has developed: (1) a comprehensive, dynamic, inventory of Web-accessible neuroscience resources, (2) an extended and integrated terminology describing resources and contents, and (3) a framework accepting and aiding concept-based queries. Evolving instantiations of the Framework may be viewed at http://nif.nih.gov, http://neurogateway.org, and other sites as they come on line
Cooling Radiation and the Lyman-alpha Luminosity of Forming Galaxies
We examine the cooling radiation from forming galaxies in hydrodynamic
simulations of the LCDM model (cold dark matter with a cosmological constant),
focusing on the Ly-alpha line luminosities of high-redshift systems. Primordial
composition gas condenses within dark matter potential wells, forming objects
with masses and sizes comparable to the luminous regions of observed galaxies.
As expected, the energy radiated in this process is comparable to the
gravitational binding energy of the baryons, and the total cooling luminosity
of the galaxy population peaks at z ~= 2. However, in contrast to the classical
picture of gas cooling from the \sim 10^6 K virial temperature of a typical
dark matter halo, we find that most of the cooling radiation is emitted by gas
with T < 20,000 K. As a consequence, roughly 50% of this cooling radiation
emerges in the Ly-alpha line. While a galaxy's cooling luminosity is usually
smaller than the ionizing continuum luminosity of its young stars, the two are
comparable in the most massive systems, and the cooling radiation is produced
at larger radii, where the Ly-alpha photons are less likely to be extinguished
by dust. We suggest, in particular, that cooling radiation could explain the
two large (\sim 100 kpc), luminous (L_{Ly-alpha} \sim 10^{44} erg s^{-1})
``blobs'' of Ly-alpha emission found in Steidel et al.'s (1999) narrow band
survey of a z = 3 proto-cluster. Our simulations predict objects of the
observed luminosity at about the right space density, and radiative transfer
effects can account for the observed sizes and line widths. We discuss
observable tests of this hypothesis for the nature of the Ly-alpha blobs, and
we present predictions for the contribution of cooling radiation to the
Ly-alpha luminosity function of galaxies as a function of redshift.Comment: Submitted to ApJ. 28 pages including 9 PS figures. Version with color
figures available at
http://donald.astro.umass.edu/~fardal/papers/cooling/cooling.htm
Spectroscopic Confirmation of Two Massive Red-Sequence-Selected Galaxy Clusters at z ~ 1.2 in the SpARCS-North Cluster Survey
The Spitzer Adaptation of the Red-sequence Cluster Survey (SpARCS) is a deep z'-band imaging survey covering the Spitzer Wide-Area Infrared Extragalactic Survey (SWIRE) Legacy fields designed to create the first large homogeneously selected sample of massive clusters at z > 1 using an infrared adaptation of the cluster red-sequence method. We present an overview of the northern component of the survey which has been observed with Canada-France-Hawaii Telescope (CFHT)/MegaCam and covers 28.3 deg^2. The southern component of the survey was observed with Cerro Tololo Inter-American Observatory (CTIO)/MOSAICII, covers 13.6 deg^2, and is summarized in a companion paper by Wilson et al. We also present spectroscopic confirmation of two rich cluster candidates at z ~ 1.2. Based on Nod-and-Shuffle spectroscopy from GMOS-N on Gemini, there are 17 and 28 confirmed cluster members in SpARCS J163435+402151 and SpARCS J163852+403843 which have spectroscopic redshifts of 1.1798 and 1.1963, respectively. The clusters have velocity dispersions of 490 ± 140 km s^(–1) and 650 ± 160 km s^(–1), respectively, which imply masses (M_(200)) of (1.0 ± 0.9) × 10^(14) M_⊙ and (2.4 ± 1.8) × 10^(14) M_⊙. Confirmation of these candidates as bonafide massive clusters demonstrates that two-filter imaging is an effective, yet observationally efficient, method for selecting clusters at z > 1
Spectroscopic Confirmation of a Massive Red-Sequence-Selected Galaxy Cluster at z = 1.34 in the SpARCS-South Cluster Survey
The Spitzer Adaptation of the Red-sequence Cluster Survey (SpARCS) is a
z'-passband imaging survey, consisting of deep (z' ~ 24 AB) observations made
from both hemispheres using the CFHT 3.6m and CTIO 4m telescopes. The survey
was designed with the primary aim of detecting galaxy clusters at z >~ 1. In
tandem with pre-existing 3.6um observations from the Spitzer Space Telescope
SWIRE Legacy Survey, SpARCS detects clusters using an infrared adaptation of
the two-filter red-sequence cluster technique. The total effective area of the
SpARCS cluster survey is 41.9 deg^2. In this paper, we provide an overview of
the 13.6 deg^2 Southern CTIO/MOSAICII observations. The 28.3 deg^2 Northern
CFHT/MegaCam observations are summarized in a companion paper by Muzzin et al.
(2008). In this paper, we also report spectroscopic confirmation of SpARCS
J003550-431224, a very rich galaxy cluster at z = 1.335, discovered in the
ELAIS-S1 field. To date, this is the highest spectroscopically confirmed
redshift for a galaxy cluster discovered using the red-sequence technique.
Based on nine confirmed members, SpARCS J003550-431224 has a preliminary
velocity dispersion of 1050 +/- 230 km/s. With its proven capability for
efficient cluster detection, SpARCS is a demonstration that we have entered an
era of large, homogeneously-selected z > 1 cluster surveys.Comment: 10 pages, 6 Figures, Submitted to the Ap
The Infuence of Omega_baryon on High-Redshift Structure
We analyze high-redshift structure in three hydrodynamic simulations that
have identical initial conditions and cosmological parameters and differ only
in the value of the baryon density parameter, Omega_b=0.02, 0.05, 0.125.
Increasing Omega_b does not change the fraction of baryons in the diffuse
(unshocked) phase of the intergalactic medium, but it increases cooling rates
and therefore transfers some baryons from the shocked intergalactic phase to
the condensed phase associated with galaxies. Predictions of Lyman-alpha forest
absorption are almost unaffected by changes of Omega_b provided that the UV
background intensity is adjusted so that the mean opacity of the forest matches
the observed value. The required UV background intensity scales as Omega_b^1.7,
and the higher photoionization rate increases the gas temperature in low
density regions. Damped Lyman-alpha absorption and Lyman limit absorption both
increase with increasing Omega_b, though the impact is stronger for damped
absorption and is weaker at z=4 than at z=2-3. The mass of cold gas and stars
in high-redshift galaxies increases faster than Omega_b but slower than
Omega_b^2, and the global star formation rate scales approximately as
Omega_b^1.5. In the higher Omega_b models, the fraction of baryonic material
within the virial radius of dark matter halos is usually higher than the
universal fraction, indicating that gas dynamics and cooling can lead to
over-representation of baryons in virialized systems. On the whole, our results
imply a fairly intuitive picture of the influence of Omega_b on high-redshift
structure, and we provide scalings that can be used to estimate the impact of
Omega_b uncertainties on the predictions of hydrodynamic simulations.Comment: 22 pages, 9 figures, submitted to ApJ, high-resolution version
availible at http://lahmu.phyast.pitt.edu/~gardner/publications/omegab.ps.g
Testing Cosmological Models Against the Abundance of Damped Lyman-Alpha Absorbers
We calculate the number of damped Lyman-alpha absorbers expected in various
popular cosmological models as a function of redshift and compare our
predictions with observed abundances. The Press-Schechter formalism is used to
obtain the distribution of halos with circular velocity in different
cosmologies, and we calibrate the relation between circular velocity and
absorption cross-section using detailed gas dynamical simulations of a
``standard'' cold dark matter (CDM) model. Because of this calibration, our
approach makes more realistic assumptions about the absorption properties of
collapsed objects than previous, analytic calculations of the damped
Lyman-alpha abundance. CDM models with Omega_0=1, H_0=50, baryon density
Omega_b=0.05, and scale-invariant primeval fluctuations reproduce the observed
incidence and redshift evolution of damped Lyman-alpha absorption to within
observational uncertainty, for both COBE normalization (sigma_8=1.2) and a
lower normalization (sigma_8=0.7) that better matches the observed cluster
abundance at z=0. A tilted (n=0.8, sigma_8=0.7) CDM model tends to underproduce
absorption, especially at z=4. With COBE normalization, a CDM model with
Omega_0=0.4, Omega_{Lambda}=0.6 gives an acceptable fit to the observed
absorption; an open CDM model is marginally acceptable if Omega_0 is at least
0.4 and strongly inconsistent with the z=4 data if Omega_0=0.3. Mixed dark
matter models tend not to produce sufficient absorption, being roughly
comparable to tilted CDM models if Omega_{nu} = 0.2 and failing drastically if
Omega_{nu} = 0.3.Comment: AASlatex, 13 pages w/ 2 embedded ps figures. To be published in ApJ,
Sept. 1, 199
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