39 research outputs found
Galilean Field Theories and Conformal Structure
We perform a detailed analysis of Galilean field theories, starting with free
theories and then interacting theories. We consider non-relativistic versions
of massless scalar and Dirac field theories before we go on to review our
previous construction of Galilean Electrodynamics and Galilean Yang-Mills
theory. We show that in all these cases, the field theories exhibit
non-relativistic conformal structure (in appropriate dimensions). The
surprising aspect of the analysis is that the non-relativistic conformal
structure exhibited by these theories, unlike relativistic conformal
invariance, becomes infinite dimensional even in spacetime dimensions greater
than two. We then couple matter with Galilean gauge theories and show that
there is a myriad of different sectors that arise in the non-relativistic limit
from the parent relativistic theories. In every case, if the parent
relativistic theory exhibited conformal invariance, we find an infinitely
enhanced Galilean conformal invariance in the non-relativistic case. This leads
us to suggest that infinite enhancement of symmetries in the non-relativistic
limit is a generic feature of conformal field theories in any dimension.Comment: 47 pages, 4 figure
A VLA 20 and 90 centimetre radio survey of distant A-bell clusters with central cD galaxies
A radio survey, using the Very Large Array at 20 and 90 cm λ has been carried out in the direction of 46 distant Abell clusters (0.1 ≲ z ≲ 0.3) dominated by a cD galaxy (clusters classified to be Bautz-Morgan I type). A radio source coincident with the cD galaxy was detected in 16 clusters. We find that the radio luminosity function of the cD galaxies at 20cm λ, and below the luminosity P1.4GHz ≲ 1024.5 W Hz-1, is similar to that of brightest ellipticals in less clustered environments. Above this luminosity, the cDs seem to have a higher probability of becoming radio sources. The effect of optical brightness on radio emission is shown to be the same for the two classes. No significantly large population of very-steep-spectrum sources with spectral index α >1.2 (flux density ∝ frequency-α) was found to be associated with cD galaxies. A significant negative correlation is found between the radio luminosity of the cD galaxy and the cooling-time of the intra cluster medium near the galaxy. We also present evidence that the probability of radio emission from first-ranked galaxies is dependent upon their location relative to the geometrical centres of clusters and thus related to the morphological class and the evolutionary state of the clusters. We argue that both these effects are primarily caused by the dynamical evolution of these distant clusters of galaxies
Giant Ringlike Radio Structures Around Galaxy Cluster Abell 3376
In the current paradigm of cold dark matter cosmology, large-scale structures
are assembling through hierarchical clustering of matter. In this process, an
important role is played by megaparsec (Mpc)-scale cosmic shock waves, arising
in gravity-driven supersonic flows of intergalactic matter onto dark
matter-dominated collapsing structures such as pancakes, filaments, and
clusters of galaxies. Here, we report Very Large Array telescope observations
of giant (~2 Mpc by 1.6 Mpc), ring-shaped nonthermal radio-emitting structures,
found at the outskirts of the rich cluster of galaxies Abell 3376. These
structures may trace the elusive shock waves of cosmological large-scale matter
flows, which are energetic enough to power them. These radio sources may also
be the acceleration sites where magnetic shocks are possibly boosting
cosmic-ray particles with energies of up to 10^18 to 10^19 electron volts.Comment: Published on Science, 3 November 2006. Main paper and Supporting
Online Materia
The merging cluster of galaxies Abell 3376: an optical view
Abell 3376 is a merging cluster of galaxies at redshift z=0.046, famous
mostly for its giant radio arcs, and shows an elongated and highly
substructured X-ray emission, but has not been analysed in detail at optical
wavelengths. We have obtained wide field images of Abell 3376 in the B band and
derive the GLF applying a statistical subtraction of the background in three
regions: a circle of 0.29 deg radius (1.5 Mpc) encompassing the whole cluster,
and two circles centered on each of the two brightest galaxies (BCG2,
northeast, coinciding with the peak of X-ray emission, and BCG1, southwest) of
radii 0.15 deg (0.775 Mpc). We also compute the GLF in the zone around BCG1,
which is covered by the WINGS survey in the B and V bands, by selecting cluster
members in the red sequence in a (B-V) versus V diagram. Finally, we discuss
the dynamical characteristics of the cluster implied by a Serna & Gerbal
analysis. The GLFs are not well fit by a single Schechter function, but
satisfactory fits are obtained by summing a Gaussian and a Schechter function.
The GLF computed by selecting galaxies in the red sequence in the region
surrounding BCG1 can also be fit by a Gaussian plus a Schechter function. An
excess of galaxies in the brightest bins is detected in the BCG1 and BCG2
regions. The dynamical analysis based on the Serna & Gerbal method shows the
existence of a main structure of 82 galaxies which can be subdivided into two
main substructures of 25 and 6 galaxies. A smaller structure of 6 galaxies is
also detected. The B band GLFs of Abell 3376 are clearly perturbed, as already
found in other merging clusters. The dynamical properties are consistent with
the existence of several substructures, in agreement with a previously
published X-ray analysis.Comment: 11 pages, 12 figures, accepted for publication in A&
Spectral and polarization study of the double relics in Abell 3376 using the GMRT and the VLA
Double radio relics in galaxy clusters are rare phenomena that trace shocks
in the outskirts of merging galaxy clusters. We have carried out a spectral and
polarization study of the spectacular double relics in the galaxy cluster A3376
using the Giant Metrewave Radio Telescope at 150 and 325 MHz and the Very Large
Array at 1400 MHz. The polarization study at 1400 MHz reveals a high degree of
polarization (~30%) and aligned magnetic field vectors (not corrected for
Faraday rotation) in the eastern relic. A highly polarized (>60%) filamentary
radio source of size ~300 kpc near the eastern relic and north of the bent-jet
radio galaxy is detected for the first time. The western relic is less
polarized and does not show aligned magnetic field vectors. The distribution of
spectral indices between 325 and 1400 MHz over the radio relics show steepening
from the outer to the inner edges of the relics. The spectral indices of the
eastern and the western relics imply Mach numbers in the range 2.2 to 3.3.
Remarkable features such as the inward filament extending from the eastern
relic, the highly polarized filament, the complex polarization properties of
the western relic and the separation of the BCG from the ICM by a distance >900
kpc are noticed in the cluster. A comparison with simulated cluster mergers is
required to understand the complex properties of the double relics in the
context of the merger in A3376. An upper limit (log(P(1.4GHz) W/Hz < 23.0) on
the strength of a Mpc size radio halo in A3376 is estimated.Comment: 9 pages, 4 figures, accepted for publication in MNRA
SAGAN -- III: New insights into giant radio quasars
Giant radio quasars (GRQs) are radio-loud active galactic nuclei (AGNs),
propelling megaparsec-scale jets. In order to understand GRQs and their
properties, we have compiled all known GRQs ("the GRQ catalogue"), and a subset
of small (size <700 kpc) radio quasars (SRQs) from the literature. In this
process, we have found 10 new FR-II GRQs, in the redshift range of 0.66 < z <
1.72, which we include in the GRQ catalogue. Using the above samples, we have
carried out a systematic comparative study of GRQs and SRQs, using optical and
radio data. Our results show that the GRQs and SRQs statistically have similar
spectral index and black hole mass distributions. However, SRQs have higher
radio core power, core dominance factor, total radio power, jet kinetic power
and Eddington ratio compared to GRQs. On the other hand, when compared to giant
radio galaxies (GRGs), GRQs have higher black hole mass and Eddington ratio.
The high core dominance factor of SRQs is an indicator of them lying closer to
the line of sight than GRQs. We also find a correlation of the accretion disc
luminosity with the radio core and jet power of GRQs, which provides evidence
for disc-jet coupling. Lastly, we find the distributions of Eddington ratios of
GRGs and GRQs to be bi-modal, similar to that found in small radio galaxies
(SRGs) and SRQs, which indicate that size is not strongly dependent on the
accretion state. Using all of these, we provide a basic model for the growth of
SRQs to GRQs.Comment: Accepted for publication in Astronomy & Astrophysics. 9 figures, and
2 tables. This is the third paper in the series. Comments are welcome. "SAGAN
Project website this http https://sites.google.com/site/anantasakyatta/sagan