60 research outputs found
Quasars as Probes of Late Reionization and Early Structure Formation
Observations of QSOs at z ~ 5.7 - 6.4 show the appearance of Gunn-Peterson
troughs around z ~ 6, and a change in the slope of the IGM optical depth tau(z)
near z ~ 5.5. These results are interpreted as a signature of the end of the
reionization era, which probably started at considerably higher redshifts.
However, there also appears to be a substantial cosmic variance in the
transmission of the IGM, both along some lines of sight, and among different
lines of sight, in this intriguing redshift regime. We suggest that this is
indicative of a spatially uneven reionization, possibly caused by the
bias-driven primordial clustering of the reionization sources. There is also
some independent evidence for a strong clustering of QSOs at z ~ 4 - 5 and
galaxies around them, supporting the idea of the strong biasing of the first
luminous sources at these redshifts. Larger samples of high-z QSOs are needed
in order to provide improved, statistically significant constraints for the
models of these phenomena. We expect that the Palomar-Quest (PQ) survey will
soon provide a new set of QSOs to be used as cosmological probes in this
redshift regime.Comment: To appear in proceedings of UC Irvine May 2005 workshop on "First
Light & Reionization", eds. E. Barton & A. Cooray, New Astronomy Reviews, in
pres
Data challenges of time domain astronomy
Astronomy has been at the forefront of the development of the techniques and
methodologies of data intensive science for over a decade with large sky
surveys and distributed efforts such as the Virtual Observatory. However, it
faces a new data deluge with the next generation of synoptic sky surveys which
are opening up the time domain for discovery and exploration. This brings both
new scientific opportunities and fresh challenges, in terms of data rates from
robotic telescopes and exponential complexity in linked data, but also for data
mining algorithms used in classification and decision making. In this paper, we
describe how an informatics-based approach-part of the so-called "fourth
paradigm" of scientific discovery-is emerging to deal with these. We review our
experiences with the Palomar-Quest and Catalina Real-Time Transient Sky
Surveys; in particular, addressing the issue of the heterogeneity of data
associated with transient astronomical events (and other sensor networks) and
how to manage and analyze it.Comment: 15 pages, 3 figures, to appear in special issue of Distributed and
Parallel Databases on Data Intensive eScienc
Exploring the Use of Virtual Worlds as a Scientific Research Platform: The Meta-Institute for Computational Astrophysics (MICA)
We describe the Meta-Institute for Computational Astrophysics (MICA), the
first professional scientific organization based exclusively in virtual worlds
(VWs). The goals of MICA are to explore the utility of the emerging VR and VWs
technologies for scientific and scholarly work in general, and to facilitate
and accelerate their adoption by the scientific research community. MICA itself
is an experiment in academic and scientific practices enabled by the immersive
VR technologies. We describe the current and planned activities and research
directions of MICA, and offer some thoughts as to what the future developments
in this arena may be.Comment: 15 pages, to appear in the refereed proceedings of "Facets of Virtual
Environments" (FaVE 2009), eds. F. Lehmann-Grube, J. Sablating, et al., ICST
Lecture Notes Ser., Berlin: Springer Verlag (2009); version with full
resolution color figures is available at
http://www.mica-vw.org/wiki/index.php/Publication
A Nearly Model-Independent Characterization of Dark Energy Properties as a Function of Redshift
Understanding the acceleration of the universe and its cause is one of the
key problems in physics and cosmology today, and is best studied using a
variety of mutually complementary approaches. Daly and Djorgovski (2003, 2004)
proposed a model independent approach to determine the expansion and
acceleration history of the universe and a number of important physical
parameters of the dark energy as functions of redshift directly from the data.
Here, we apply the method to explicitly determine the first and second
derivatives of the coordinate distance with respect to redshift and combine
them to solve for the acceleration of the universe and the kinetic and
potential energy density of the dark energy as functions of redshift. A data
set of 228 supernova and 20 radio galaxy measurements with redshifts from zero
to 1.79 is used for this study. The values we obtain are shown to be consistent
with the values expected in a standard Lambda Cold Dark Matter model.Comment: 5 pages, 8 figure
Dark Energy From Vacuum Fluctuations
We describe briefly a novel interpretation of the physical nature of dark
energy (DE), based on the vacuum fluctuations model by Gurzadyan & Xue, and
describe an internally consistent solution for the behavor of DE as a function
of redshift. A key choice is the nature of the upper bound used for the
computation of energy density contributions by vacuum modes. We show that use
of the comoving horizon radius produces a viable model, whereas use of the
proper horizon radius is inconsistent with the observations. After introduction
of a single phenomenological parameter, the model is consistent with all of the
curently available data, and fits them as well as the standard cosmological
constant model, while making testable predictions. While some substantial
interpretative uncertainties remain, future developments of this model may lead
to significant new insights into the physical nature of DE.Comment: To appear in Proc. UCLA Conference "Dark Matter 2006", eds. D. Cline
et al., Nuclear Pysics B, in press (2006); 5 page
`Zwicky's Nonet': a compact merging ensemble of nine galaxies and 4C 35.06, a peculiar radio galaxy with dancing radio jets
We report the results of our radio, optical and infra-red studies of a
peculiar radio source 4C~35.06, an extended radio-loud AGN at the center of
galaxy cluster Abell 407 (). The central region of this cluster hosts
a remarkably tight ensemble of nine galaxies, the spectra of which resemble
those of passive red ellipticals, embedded within a diffuse stellar halo of
1~arcmin size. This system (named the `Zwicky's Nonet') provides unique
and compelling evidence for a multiple-nucleus cD galaxy precursor.
Multifrequency radio observations of 4C~35.06 with the Giant Meterwave Radio
Telescope (GMRT) at 610, 235 and 150 MHz reveal a system of 400~kpc scale
helically twisted and kinked radio jets and outer diffuse lobes. The outer
extremities of jets contain extremely steep spectrum (spectral index -1.7 to
-2.5) relic/fossil radio plasma with a spectral age of a few yr. Such ultra-steep spectrum relic radio lobes without definitive
hot-spots are rare, and they provide an opportunity to understand the
life-cycle of relativistic jets and physics of black hole mergers in dense
environments. We interpret our observations of this radio source in the context
of the growth of its central black hole, triggering of its AGN activity and jet
precession, all possibly caused by galaxy mergers in this dense galactic
system. A slow conical precession of the jet axis due to gravitational
perturbation between interacting black holes is invoked to explain the unusual
jet morphology.Comment: Published in MNRAS | No. of pages 12, 10 figures and 4 tables.
Comments are welcom
Gravitational Mesoscopic Constraints in Cosmological Dark Matter Halos
We present an analysis of the behaviour of the `coarse-grained'
(`mesoscopic') rank partitioning of the mean energy of collections of particles
composing virialized dark matter halos in a Lambda-CDM cosmological simulation.
We find evidence that rank preservation depends on halo mass, in the sense that
more massive halos show more rank preservation than less massive ones. We find
that the most massive halos obey Arnold's theorem (on the ordering of the
characteristic frequencies of the system) more frequently than less massive
halos. This method may be useful to evaluate the coarse-graining level (minimum
number of particles per energy cell) necessary to reasonably measure signatures
of `mesoscopic' rank orderings in a gravitational system.Comment: LaTeX, 15 pages, 3 figures. Accepted for publication in Celestial
Mechanics and Dynamical Astronomy Journa
A serendipitous all sky survey for bright objects in the outer solar system
We use seven yearʼs worth of observations from the Catalina Sky Survey and the Siding Spring Survey covering most of the northern and southern hemisphere at galactic latitudes higher than 20° to search for serendipitously imaged moving objects in the outer solar system. These slowly moving objects would appear as stationary transients in these fast cadence asteroids surveys, so we develop methods to discover objects in the outer solar system using individual observations spaced by months, rather than spaced by hours, as is typically done. While we independently discover eight known bright objects in the outer solar system, the faintest having no new objects are discovered. We find that the survey is nearly 100% efficient at detecting objects beyond 25 AU for ( in the southern hemisphere) and that the probability that there is one or more remaining outer solar system object of this brightness left to be discovered in the unsurveyed regions of the galactic plane is approximately 32%
Primordial magnetic fields and the HI signal from the epoch of reionization
The implication of primordial magnetic-field-induced structure formation for
the HI signal from the epoch of reionization is studied. Using semi-analytic
models, we compute both the density and ionization inhomogeneities in this
scenario. We show that: (a) The global HI signal can only be seen in emission,
unlike in the standard CDM models, (b) the density perturbations
induced by primordial fields, leave distinctive signatures of the magnetic
field Jeans' length on the HI two-point correlation function, (c) the length
scale of ionization inhomogeneities is \la 1 \rm Mpc. We find that the peak
expected signal (two-point correlation function) is in
the range of scales for magnetic field strength in the
range . We also discuss the
detectability of the HI signal. The angular resolution of the on-going and
planned radio interferometers allows one to probe only the largest magnetic
field strengths that we consider. They have the sensitivity to detect the
magnetic field-induced features. We show that thefuture SKA has both the
angular resolution and the sensitivity to detect the magnetic field-induced
signal in the entire range of magnetic field values we consider, in an
integration time of one week.Comment: 19 pages, 5 figures, to appear in JCA
SNhunt151: An explosive event inside a dense cocoon
Indexación: Scopus.We thank S. Spiro, R. Rekola, A. Harutyunyan, and M. L. Graham for their help with the observations. We are grateful to the collaboration of Massimo Conti, Giacomo Guerrini, Paolo Rosi, and Luz Marina Tinjaca Ramirez from the Osservatorio Astronomico Provinciale di Montarrenti. The staffs at the different observatories provided excellent assistance with the observations.The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement No. 267251, ‘Astronomy Fellowships in Italy’ (AstroFIt)’. NE-R acknowledges financial support from MIUR PRIN 2010-2011, ‘The Dark Universe and the Cosmic Evolution of Baryons: From Current Surveys to Euclid’. NE-R, AP, SB, LT, MT, and GP are partially supported by the PRIN-INAF 2014 (project ‘Transient Universe: Unveiling New Types of Stellar Explosions with PESSTO’). GP acknowledges support provided by the Millennium Institute of Astrophysics (MAS) through grant IC120009 of the Programa Iniciativa CientÃifica Milenio del Ministerio de EconomÃa, Fomento y Turismo de Chile. TK acknowledges financial support from the Emil Aaltonen Foundation. CRTS was supported by the NSF grants AST-0909182, AST-1313422, and AST-1413600. AVF is grateful for generous financial assistance from the Christopher R. Redlich Fund, the TABASGO Foundation, the Miller Institute for Basic Research in Science (UC Berkeley), and NASA/HST grant GO-14668 from the Space Telescope Science Institute, which is operated by AURA, Inc. under NASA contract NAS5-26555. The work of AVF was conducted in part at the Aspen Center for Physics, which is supported by NSF grantPHY-1607611; he thanks the Center for its hospitality during the neutron stars workshop in June and July 2017. NE-R acknowledges the hospitality of the ‘Institut de Ciències de l'Espai (CSIC), where this work was completed.This research is based on observations made with the Nordic Optical Telescope, operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de AstrofÃsica de Canarias; the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de AstrofÃsica de Canarias, on the island of La Palma; the Italian Telescopio Nazionale Galileo (TNG), operated on the island of La Palma by the Fundaci Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de AstrofÃsica de Canarias; the Liverpool Telescope, operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de AstrofÃsica de Canarias with financial support from the UK Science and Technology Facilities Council; the 1.82-m Copernico Telescope and the Schmidt 67/92 cm of INAF-Asiago Observatory; the Catalina Real Time Survey (CRTS) Catalina Sky Survey (CSS) 0.7-m Schmidt Telescope; and the Las Cumbres Observatory (LCO) network. This work is also based in part on archival data obtained with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555; the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA (support was provided by NASA through an award issued by JPL/Caltech); and the Swift telescope.This work has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.SNhunt151 was initially classified as a supernova (SN) impostor (nonterminal outburst of a massive star). It exhibited a slow increase in luminosity, lasting about 450 d, followed by a major brightening that reaches M V ≈ -18 mag. No source is detected to M V ≳ -13 mag in archival images at the position of SNhunt151 before the slow rise. Low-to-mid-resolution optical spectra obtained during the pronounced brightening show very little evolution, being dominated at all times by multicomponent Balmer emission lines, a signature of interaction between the material ejected in the new outburst and the pre-existing circumstellar medium. We also analysed mid-infrared images from the Spitzer Space Telescope, detecting a source at the transient position in 2014 and 2015. Overall, SNhunt151 is spectroscopically a Type IIn SN, somewhat similar to SN 2009ip. However, there are also some differences, such as a slow pre-discovery rise, a relatively broad light-curve peak showing a longer rise time (~50 d), and a slower decline, along with a negligible change in the temperature around the peak (T ≤ 10 4 K). We suggest that SNhunt151 is the result of an outburst, or an SN explosion, within a dense circumstellar nebula, similar to those embedding some luminous blue variables like η Carinae and originating from past mass-loss events. © 2017 The Author(s).https://academic.oup.com/mnras/article/475/2/2614/479530
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