10,051 research outputs found
From the Big Bang to the Multiverse: Translations in Space and Time
Since 2004, I have been collaborating with artist Josiah McElheny on the
design of cosmological sculptures, inspired originally by the chandeliers of
the Metropolitan Opera House in New York. This article describes the science
behind the four works that have emerged from this collaboration to date: An End
to Modernity (2005), The Last Scattering Surface (2006), The End of the Dark
Ages (2008), and Island Universe (2008). These works incorporate idealized
representations of many fundamental aspects of contemporary cosmology,
including expansion of the universe, the last scattering surface, cosmic
microwave background anisotropies, the growth and morphological transformation
of galaxies, the rise and fall of the quasar population, the development of
large scale structure, and the possibility that our universe is one of many
cosmic islands in an eternally inflating multiverse. A companion article
describes the history of the collaboration.Comment: From "Josiah McElheny: A Prism," edited by L. Neri and J. McElheny,
published by Skira/Rizzoli, New York, 2010. More information and higher
resolution images available at
http://www.astronomy.ohio-state.edu/~dhw/McElhen
First Spectroscopic Confirmations of z ~ 7.0 Lya Emitting Galaxies in the LAGER Survey
Narrowband imaging is a highly successful approach for finding large numbers
of high redshift Lya emitting galaxies (LAEs) up to z~6.6. However, at z>~7
there are as yet only 3 narrowband selected LAEs with spectroscopic
confirmations (two at z~6.9-7.0, one at z~7.3), which hinders extensive studies
on cosmic reionization and galaxy evolution at this key epoch. We have selected
23 candidate z~6.9 LAEs in COSMOS field with the large area narrowband survey
LAGER (Lyman-Alpha Galaxies at the End of Reionization). In this work we
present spectroscopic followup observations of 12 candidates using IMACS on
Magellan. For 9 of these, the observations are sufficiently deep to detect the
expected lines. Lya emission lines are identified in six sources (yielding a
success rate of 2/3), including 3 luminous LAEs with Lya luminosities of L(Lya)
~ 10^{43.5} erg/s, the highest among known spectroscopically confirmed galaxies
at >~7.0. This triples the sample size of spectroscopically confirmed
narrowband selected LAEs at z>~7, and confirms the bright end bump in the Lya
luminosity function we previously derived based on the photometric sample,
supporting a patchy reionization scenario. Two luminous LAEs appear physically
linked with projected distance of 1.1 pMpc and velocity difference of ~ 170
km/s. They likely sit in a common ionized bubble produced by themselves or with
close neighbors, which reduces the IGM attenuation of Lya. A tentative narrow
NV1240 line is seen in one source, hinting at activity of a central
massive black hole with metal rich line emitting gas.Comment: 6 pages, 3 figures, 2 tables, accepted by ApJ
Radio galaxy feedback in X-ray selected groups from COSMOS: the effect on the ICM
We quantify the importance of the mechanical energy released by
radio-galaxies inside galaxy groups. We use scaling relations to estimate the
mechanical energy released by 16 radio-AGN located inside X-ray detected galaxy
groups in the COSMOS field. By comparing this energy output to the host groups'
gravitational binding energy, we find that radio galaxies produce sufficient
energy to unbind a significant fraction of the intra-group medium. This
unbinding effect is negligible in massive galaxy clusters with deeper potential
wells. Our results correctly reproduce the breaking of self-similarity observed
in the scaling relation between entropy and temperature for galaxy groups.Comment: Accepted for publication in the Astrophysical Journal. 12 Page
WISE morphological study of Wolf-Rayet nebulae
We present a morphological study of nebulae around Wolf-Rayet (WR) stars
using archival narrow-band optical and Wide-field Infrared Survey Explorer
(WISE) infrared images. The comparison among WISE images in different bands and
optical images proves to be a very efficient procedure to identify the nebular
emission from WR nebulae, and to disentangle it from that of the ISM material
along the line of sight. In particular, WR nebulae are clearly detected in the
WISE W4 band at 22 m. Analysis of available mid-IR Spitzer spectra shows
that the emission in this band is dominated by thermal emission from dust
spatially coincident with the thin nebular shell or most likely with the
leading edge of the nebula. The WR nebulae in our sample present different
morphologies that we classified into well defined WR bubbles (bubble -type nebulae), clumpy and/or disrupted shells (clumpy/disrupted -type nebulae), and material mixed with the diffuse medium (mixed -type nebulae). The variety of morphologies presented by WR nebulae shows a
loose correlation with the central star spectral type, implying that the
nebular and stellar evolutions are not simple and may proceed according to
different sequences and time-lapses. We report the discovery of an obscured
shell around WR35 only detected in the infrared.Comment: 11 pages, 6 figures, plus 23 appendix figures; to appear in Astronomy
and Astrophysic
Phase Transitions in the Universe
During the past two decades, cosmologists turned to particle physics in order
to explore the physics of the very early Universe. The main link between the
physics of the smallest and largest structures in the Universe is the idea of
spontaneous symmetry breaking, familiar from condensed matter physics.
Implementing this mechanism into cosmology leads to the interesting possibility
that phase transitions related to the breaking of symmetries in high energy
particle physics took place during the early history of the Universe. These
cosmological phase transitions may help us understand many of the challenges
faced by the standard hot Big Bang model of cosmology, while offering a unique
window into the very early Universe and the physics of high energy particle
interactions.Comment: 31 pages, LaTeX, 10 figures, 8 provided (7 EPS + 1 PS). Uses
psfig.tex. Invited article for ``Contemporary Physics'
Nuclear Astrophysics
Nuclear astrophysics is that branch of astrophysics which helps understanding
some of the many facets of the Universe through the knowledge of the microcosm
of the atomic nucleus. In the last decades much advance has been made in
nuclear astrophysics thanks to the sometimes spectacular progress in the
modelling of the structure and evolution of the stars, in the quality and
diversity of the astronomical observations, as well as in the experimental and
theoretical understanding of the atomic nucleus and of its spontaneous or
induced transformations. Developments in other sub-fields of physics and
chemistry have also contributed to that advance. Many long-standing problems
remain to be solved, however, and the theoretical understanding of a large
variety of observational facts needs to be put on safer grounds. In addition,
new questions are continuously emerging, and new facts endanger old ideas. This
review shows that astrophysics has been, and still is, highly demanding to
nuclear physics in both its experimental and theoretical components. On top of
the fact that large varieties of nuclei have to be dealt with, these nuclei are
immersed in highly unusual environments which may have a significant impact on
their static properties, the diversity of their transmutation modes, and on the
probabilities of these modes. In order to have a chance of solving some of the
problems nuclear astrophysics is facing, the astrophysicists and nuclear
physicists are obviously bound to put their competence in common, and have
sometimes to benefit from the help of other fields of physics, like particle
physics, plasma physics or solid-state physics.Comment: LaTeX2e with iopart.cls, 84 pages, 19 figures (graphicx package), 374
updated references. Published in Reports on Progress in Physics, vol.62, pp.
395-464 (1999
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