144 research outputs found
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
Adaptive friends-of-friends algorithm for identifying gravitationally bound cosmological structures
The Universe at the present epoch is found to be a network of matter
over-dense and under-dense regions. To date, this picture of the Universe is
best revealed through cosmological large-volume simulations and large-scale
galaxy redshift surveys, in which, the most important step is the appropriate
identification of structures. So far, these structures are identified using
various group finding codes, mostly based on the friends-of-friends (FoF) or
spherical over-density (SO) algorithms. Although, the main purpose is to
identify gravitationally bound structures, surprisingly, the mass information
has hardly been used effectively by these codes. Moreover, the methods used so
far either constrain the over-density or use the real unstructured geometry
only. Even though these are key factors in the accurate determination of
structures-mass information, hardly any attempt has been made as yet to
consider these important parameters together while formulating the grouping
algorithms. In this paper, we present our proposed algorithm which takes care
of all the above-mentioned relevant features and ensures the bound structures
by means of physical quantities, mainly mass and the total energy information.
We introduced a novel concept of physically relevant arm-length for each
element depending on their individual gravity leading to a distinct linking
length for each unique pair of elements. This proposed algorithm is thus
fundamentally new that, not only able to catch the gravitationally bound, real
unstructured geometry, it does identify it roughly within a predefined
physically motivated density threshold. Such a thing could not be
simultaneously achieved before by any of the usual FoF or SO-based methods. We
also demonstrate the unique ability of the code in the appropriate
identification of structures, both from large volume cosmological simulations
as well as from galaxy redshift surveys.Comment: 28 pages, 13 figures, published in the Physical Review
The radio source in Abell 980: A Detached-Double-Double Radio Galaxy?
It is argued that the new morphological and spectral information gleaned from
the recently published LoFAR Two meter Sky Survey data release 2 (LoTSS-2 at
144 MHz) observations of the cluster Abell 980 (A980), in combination with its
existing GMRT and VLA observations at higher frequencies, provide the
much-needed evidence to strengthen the proposal that the cluster's radio
emission comes mainly from two double radio sources, both produced by the
brightest cluster galaxy (BCG) in two major episodes of jet activity. The two
radio lobes left from the previous activity have become diffuse and developed
an ultra-steep radio spectrum while rising buoyantly through the confining hot
intra-cluster medium (ICM) and, concomitantly, the host galaxy has drifted to
the cluster centre and entered a new active phase manifested by a coinciding
younger double radio source. The new observational results and arguments
presented here bolster the case that the old and young double radio sources in
A980 conjointly represent a `double-double' radio galaxy whose two lobe-pairs
have lost colinearity due to the (lateral) drift of their parent galaxy, making
this system by far the most plausible case of a `Detached-Double-Double Radio
Galaxy' (dDDRG).Comment: Accepted for publication by Publications of the Astronomical Society
of Australia (PASA); 10 pages, 6 figure
Low-frequency radio study of MACS clusters at 610 and 235 MHz using the GMRT
Studies have shown that mergers of massive galaxy clusters produce shocks and turbulence in the intra-cluster medium, the possible event that creates radio relics, as well as the radio halos. Here we present GMRT dual-band (235 and 610~MHz) radio observations of four such clusters from the MAssive Cluster Survey (MACS) catalogue. We report the discovery of a very faint, diffuse, elongated radio source with a projected size of about 0.5~Mpc in cluster MACSJ0152.5-2852. We also confirm the presence of a radio relic-like source (about 0.4~Mpc, previously reported at 325~MHz) in MACSJ0025.4-1222 cluster. Proposed relics in both these clusters are found apparently inside the virial radius instead of their usual peripheral location, while no radio halos are detected. These high-redshift clusters (z=0.584 and 0.413) are among the earliest merging systems detected with cluster radio emissions. In MACSJ1931-2635 cluster, we found a radio mini-halo and an interesting highly bent pair of radio jets. Further, we present here a maiden study of low frequency (GMRT 235&610~MHz) spectral and morphological signatures of a previously known radio cluster MACSJ0014.3-3022 (Abell~2744). This cluster hosts a relatively flat spectrum (α610235∼−1.15), giant (∼1.6~Mpc each) halo-relic structure and a close-by high-speed (1769±148359~km~s−1) merger-shock (M=2.02±0.170.41) originated from a possible second merger in the cluster
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