19,437 research outputs found
Technology Teacher: Singing the Black and Blues
Gives simple, yet authoritative answers to the questions "Why is the sky blue?" and "Why is the sky black at night?" Combines technology with its application to Earth science, astronomy, and cosmology, and does so via language arts and music! This article was originally written for and published by the International Technology Education Association in its journal 'The Technology Teacher.' It is now archived on The Space Place Web site. Educational levels: Middle school, High school
The MUSIC of CLASH: predictions on the concentration-mass relation
We present the results of a numerical study based on the analysis of the
MUSIC-2 simulations, aimed at estimating the expected concentration-mass
relation for the CLASH cluster sample. We study nearly 1400 halos simulated at
high spatial and mass resolution, which were projected along many
lines-of-sight each. We study the shape of both their density and
surface-density profiles and fit them with a variety of radial functions,
including the Navarro-Frenk-White, the generalised Navarro-Frenk-White, and the
Einasto density profiles. We derive concentrations and masses from these fits
and investigate their distributions as a function of redshift and halo
relaxation. We use the X-ray image simulator X-MAS to produce simulated Chandra
observations of the halos and we use them to identify objects resembling the
X-ray morphologies and masses of the clusters in the CLASH X-ray selected
sample. We also derive a concentration-mass relation for strong-lensing
clusters. We find that the sample of simulated halos which resemble the X-ray
morphology of the CLASH clusters is composed mainly by relaxed halos, but it
also contains a significant fraction of un-relaxed systems. For such a sample
we measure an average 2D concentration which is ~11% higher than found for the
full sample of simulated halos. After accounting for projection and selection
effects, the average NFW concentrations of CLASH clusters are expected to be
intermediate between those predicted in 3D for relaxed and super-relaxed halos.
Matching the simulations to the individual CLASH clusters on the basis of the
X-ray morphology, we expect that the NFW concentrations recovered from the
lensing analysis of the CLASH clusters are in the range [3-6], with an average
value of 3.87 and a standard deviation of 0.61. Simulated halos with X-ray
morphologies similar to those of the CLASH clusters are affected by a modest
orientation bias.Comment: 21 pages, 16 figures, 3 tables, submitted to Ap
Halo Concentrations and the Fundamental Plane of Galaxy Clusters
According to the standard cold dark matter (CDM) cosmology, the structure of
dark halos including those of galaxy clusters reflects their mass accretion
history. Older clusters tend to be more concentrated than younger clusters.
Their structure, represented by the characteristic radius and mass
of the Navarro--Frenk--White (NFW) density profile, is related to their
formation time. In~this study, we showed that , , and the X-ray
temperature of the intracluster medium (ICM), , form a thin plane in the
space of . This tight correlation indicates
that the ICM temperature is also determined by the formation time of individual
clusters. Numerical simulations showed that clusters move along the fundamental
plane as they evolve. The plane and the cluster evolution within the plane
could be explained by a similarity solution of structure formation of the
universe. The angle of the plane shows that clusters have not achieved "virial
equilibrium" in the sense that mass/size growth and pressure at the boundaries
cannot be ignored. The distribution of clusters on the plane was related to the
intrinsic scatter in the halo concentration--mass relation, which originated
from the variety of cluster ages. The well-known mass--temperature relation of
clusters () can be explained by the fundamental
plane and the mass dependence of the halo concentration without the assumption
of virial equilibrium. The fundamental plane could also be used for calibration
of cluster masses.Comment: Invited review article, to be published in "From Dark Haloes to
Visible Galaxies", special issue of Galaxie
Cosmological thinking: cultural heritage and challenge
The limitations of current technology do not allow one to foresee the
expansion of the humankind beyond our planet for at least a few decades.
Furthermore, the laws of physics, as for as they are known, preclude any form
of traveling beyond the speed of light, as well as any viable and stable
space-time shortcuts (wormholes, warp-drives, etc) that would facilitate cosmic
traveling. Given the vastness of the Universe these are insurmountable
obstacles for any {\it in situ} exploration of the cosmos beyond our most
immediate cosmic neighbourhood. Nevertheless, the Universe is transparent and
contains countless sources of visible light. Actually, in the last decades,
technological developments have made possible to observe the cosmos throughout
most of the electromagnetic spectrum as well as to perform dynamical studies
that allow perceiving the presence of invisible components such as black holes,
dark matter and dark energy. In this respect, humankind has then been given the
opportunity to unravel the inner workings of the cosmos and through this
process be part of the cosmic habitat. In this contribution various forms of
cosmological thinking will be discussed, from some myths of creation till some
of the latest scientific discoveries.Comment: 18 pages, 2 figures. Talk delivered at the Third International
Symposium "Fronteiras da Ci\^encia: A Humanidade e o Cosmos", 13 - 14
November 2009, Universidade Fernando Pesssoa, Oporto, Portuga
Classical and Quantum Aspects of Gravitation and Cosmology
These are the proceedings of the XVIII Conference of the Indian Association
for General Relativity and Gravitation (IAGRG) held at the Institute of
Mathematical Sciences, Madras, INDIA during Feb. 15-17, 1996. The Conference
was dedicated the late Prof. S. Chandrasekhar.
The proceedings consists of 17 articles on:
- Chandrasekhar's work (N. Panchapkesan);
- Vaidya-Raychaudhuri Lecture (C.V. Vishveshwara)
- Gravitational waves (B.R. Iyer, R. Balasubramanian)
- Gravitational Collapse (T.P. Singh)
- Accretion on black hole (S. Chakrabarti)
- Cosmology (D. Munshi, S. Bharadwaj, G.S. Mohanty, P. Bhattacharjee);
- Classical GR (S. Kar, D.C. Srivatsava)
- Quantum aspects (J. Maharana, Saurya Das, P. Mitra, G. Date, N.D. Hari
Dass)
The body of THIS article contains ONLY the title, contents, foreword,
organizing committees, preface, list of contributed talks and list of
participants. The plenery talks are available at:
http://www.imsc.ernet.in/physweb/Conf/ both as post-script files of individual
articles and also as .uu source files. For further information please send
e-mail to [email protected]: 12 pages, latex, needs psfig.tex macros. Latex the file run.tex.
These Proceedings of the XVIII IAGRG Conference are available at
http://www.imsc.ernet.in/physweb/Conf/ MINOR TYPO's in the ABSTRACT correcte
Discovery of a new fundamental plane dictating galaxy cluster evolution from gravitational lensing
In cold dark matter (CDM) cosmology, objects in the Universe have grown under
the effect of gravity of dark matter. The intracluster gas in a galaxy cluster
was heated when the dark-matter halo formed through gravitational collapse. The
potential energy of the gas was converted to thermal energy through this
process. However, this process and the thermodynamic history of the gas have
not been clearly characterized in connection with with the formation and
evolution of the internal structure of dark-matter halos. Here, we show that
observational CLASH data of high-mass galaxy clusters lie on a plane in the
three-dimensional logarithmic space of their characteristic radius , mass
, and X-ray temperature with a very small orthogonal scatter. The
tight correlation indicates that the gas temperature was determined at a
specific cluster formation time, which is encoded in and . The plane
is tilted with respect to , which is the plane expected in
case of simplified virial equilibrium. We show that this tilt can be explained
by a similarity solution, which indicates that clusters are not isolated but
continuously growing through matter accretion from their outer environments.
Numerical simulations reproduce the observed plane and its angle. This result
holds independently of the gas physics implemented in the code, revealing the
fundamental origin of this plane.Comment: Replaced with a revised version to match the ApJ accepted versio
Locating sovereignty in the auto-ethnographic-political poetics of daily existence in two amazonian films
The theme of daily life is a common one in the Brazilian Video in the Villages (Vídeo nas aldeias) filmic archive. I analyze the diversity of cinematic treatments of and approaches to the theme of daily life in an Indigenous village by comparing, contrasting, and examining how two films construct, embody, and experience communal life through culturally specific methods of inquiry. In particular, I explore concepts of time, the senses, creativity, and the relations between the individual and the collectivity as all of the above are cinematically rendered in the intimacy, the performance, and the ritual of daily life. Specifically, I look at how these two VNA productions, Shomõtsi (2001) and Kiarãsã Tõ Sâty, The Agouti’s Peanut (2005), repoliticize the everyday through sovereign practices. I discuss these cinematic works as they relate to imperfect media (Salazar & Cordova, 2008), decolonial pedagogies, and the “cosmological embeddedness of the everyday” (Overing & Passes, 2000, p. 298).peer-reviewe
Kinetic Inductance Detectors for the OLIMPO experiment: design and pre-flight characterization
We designed, fabricated, and characterized four arrays of horn--coupled,
lumped element kinetic inductance detectors (LEKIDs), optimized to work in the
spectral bands of the balloon-borne OLIMPO experiment. OLIMPO is a 2.6 m
aperture telescope, aimed at spectroscopic measurements of the
Sunyaev-Zel'dovich (SZ) effect. OLIMPO will also validate the LEKID technology
in a representative space environment. The corrected focal plane is filled with
diffraction limited horn-coupled KID arrays, with 19, 37, 23, 41 active pixels
respectively at 150, 250, 350, and 460GHz. Here we report on the full
electrical and optical characterization performed on these detector arrays
before the flight. In a dark laboratory cryostat, we measured the resonator
electrical parameters, such as the quality factors and the electrical
responsivities, at a base temperature of 300mK. The measured average
resonator s are 1.7, 7.0, 1.0, and
1.0 for the 150, 250, 350, and 460GHz arrays, respectively.
The average electrical phase responsivities on resonance are 1.4rad/pW,
1.5rad/pW, 2.1rad/pW, and 2.1rad/pW; the electrical noise
equivalent powers are 45, 160,
80, and 140, at 12 Hz. In the OLIMPO
cryostat, we measured the optical properties, such as the noise equivalent
temperatures (NET) and the spectral responses. The measured NETs are
, , ,
and , at 12 Hz; under 78, 88, 92, and 90 mK
Rayleigh-Jeans blackbody load changes respectively for the 150, 250, 350, and
460 GHz arrays. The spectral responses were characterized with the OLIMPO
differential Fourier transform spectrometer (DFTS) up to THz frequencies, with
a resolution of 1.8 GHz.Comment: Published on JCA
Reconciling dwarf galaxies with LCDM cosmology: Simulating a realistic population of satellites around a Milky Way-mass galaxy
Low-mass "dwarf" galaxies represent the most significant challenges to the
cold dark matter (CDM) model of cosmological structure formation. Because these
faint galaxies are (best) observed within the Local Group (LG) of the Milky Way
(MW) and Andromeda (M31), understanding their formation in such an environment
is critical. We present first results from the Latte Project: the Milky Way on
FIRE (Feedback in Realistic Environments). This simulation models the formation
of a MW-mass galaxy to z = 0 within LCDM cosmology, including dark matter, gas,
and stars at unprecedented resolution: baryon particle mass of 7070 Msun with
gas kernel/softening that adapts down to 1 pc (with a median of 25 - 60 pc at z
= 0). Latte was simulated using the GIZMO code with a mesh-free method for
accurate hydrodynamics and the FIRE-2 model for star formation and explicit
feedback within a multi-phase interstellar medium. For the first time, Latte
self-consistently resolves the spatial scales corresponding to half-light radii
of dwarf galaxies that form around a MW-mass host down to Mstar > 10^5 Msun.
Latte's population of dwarf galaxies agrees with the LG across a broad range of
properties: (1) distributions of stellar masses and stellar velocity
dispersions (dynamical masses), including their joint relation; (2) the
mass-metallicity relation; and (3) a diverse range of star-formation histories,
including their mass dependence. Thus, Latte produces a realistic population of
dwarf galaxies at Mstar > 10^5 Msun that does not suffer from the "missing
satellites" or "too big to fail" problems of small-scale structure formation.
We conclude that baryonic physics can reconcile observed dwarf galaxies with
standard LCDM cosmology.Comment: 7 pages, 5 figures. Accepted for publication in ApJ Letters. Several
updates, including: (1) fixed a bug in halo finder, now identifies 13
satellite galaxies and more subhalos in the baryonic simulation; (2) fixed a
minor bug in the feedback coupling and reran the simulation, resulting in a
somewhat lower-mass host galaxy; (3) Fig 2 now shows stellar velocity
dispersion profiles of satellite
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