21 research outputs found
The Discovery of 63 Giant Radio Galaxies in the FIRST Survey
Giant Radio Galaxies (GRGs) are Active Galactic Nuclei (AGN) with radio
emission that extends over projected sizes Mpc. The large angular sizes
associated with GRGs complicate their identification in radio survey images
using traditional source finders. In this Note, we use DRAGNhunter, an
algorithm designed to find double-lobed radio galaxies, to search for GRGs in
the Faint Images of the Radio Sky at Twenty cm survey (FIRST). Radio and
optical images of identified candidates are visually inspected to confirm their
authenticity, resulting in the discovery of previously unreported GRGs.Comment: 5 pages, 1 Table. Catalog data available from
https://doi.org/10.5281/zenodo.1009417
Astronomical Data Management
We present a summary of the major contributions to the Special Session on
Data Management held at the IAU General Assembly in Prague in 2006. While
recent years have seen enormous improvements in access to astronomical data,
and the Virtual Observatory aims to provide astronomers with seamless access to
on-line resources, more attention needs to be paid to ensuring the quality and
completeness of those resources. For example, data produced by telescopes are
not always made available to the astronomical community, and new instruments
are sometimes designed and built with insufficient planning for data
management, while older but valuable legacy data often remain undigitised. Data
and results published in journals do not always appear in the data centres, and
astronomers in developing countries sometimes have inadequate access to on-line
resources. To address these issues, an 'Astronomers Data Manifesto' has been
formulated with the aim of initiating a discussion that will lead to the
development of a 'code of best practice' in astronomical data management.Comment: Proceedings of Special Session SPS6 (Astronomical Data Management) at
the IAU GA 2006. To appear in Highlights of Astronomy, Volume 14, ed. K.A.
van der Huch
A Chandra Observation of Abell 13: Investigating the Origin of the Radio Relic
We present results from the Chandra X-ray observation of Abell 13, a galaxy
cluster that contains an unusual noncentral radio source, also known as a radio
relic. This is the first pointed X-ray observation of Abell 13, providing a
more sensitive study of the properties of the X-ray gas. The X-ray emission
from Abell 13 is extended to the northwest of the X-ray peak and shows
substructure indicative of a recent merger event. The cluster X-ray emission is
centered on the bright galaxy H of Slee et al. 2001. We find no evidence for a
cooling flow in the cluster. A knot of excess X-ray emission is coincident with
the other bright elliptical galaxy F. This knot of emission has properties
similar to the enhanced emission associated with the large galaxies in the Coma
cluster.
With these Chandra data we are able to compare the properties of the hot
X-ray gas with those of the radio relic from VLA data, to study the interaction
of the X-ray gas with the radio emitting electrons. Our results suggest that
the radio relic is associated with cooler gas in the cluster. We suggest two
explanations for the coincidence of the cooler gas and radio source. First, the
gas may have been uplifted by the radio relic from the cluster core.
Alternatively, the relic and cool gas may have been displaced from the central
galaxy during the cluster merger event.Comment: 11 pages, 9 figures, Accepted for Publication in the Astrophysical
Journal, higher-resolution figures can be found at
http://www.astro.virginia.edu/~amj3r/Abell13
A New Sample of Gamma-Ray Emitting Jetted Active Galactic Nuclei
We considered the fourth catalog of gamma-ray point sources produced by the
Fermi Large Area Telescope (LAT) and selected only jetted active galactic
nuclei (AGN) or sources with no specific classification, but with a
low-frequency counterpart. Our final list is composed of 2980 gamma-ray point
sources. We then searched for optical spectra in all the available literature
and publicly available databases, to measure redshifts and to confirm or change
the original LAT classification. Our final list of gamma-ray emitting jetted
AGN is composed of BL Lac Objects (40%), flat-spectrum radio quasars (23%),
misaligned AGN (2.8%), narrow-line Seyfert 1, Seyfert, and low-ionization
nuclear emission-line region galaxies (1.9%). We also found a significant
number of objects changing from one type to another, and vice versa
(changing-look AGN, 1.1%). About 30% of gamma-ray sources still have an
ambiguous classification or lack one altogether.Comment: 18 pages, 5 figures, 1 Table. Accepted for publication on Universe,
Special Issue "Black Holes and Relativistic Jets", edited by I. Dutan and N.
R. MacDonald. This preprint contains only the main text. The full tables A1
and A2 are available on the journal web site
(https://www.mdpi.com/2218-1997/8/11/587
Tracing the assembly histories of galaxy clusters in the nearby universe
We have compiled a sample of 67 nearby ( < 0.15) clusters of galaxies, for
which on average more than 150 spectroscopic members are available, and, by
applying different methods to detect substructures in their galaxy
distribution, we have studied their assembly history. Our analysis confirms
that substructures are present in 70% of our sample, having a significant
dynamical impact in 57% of them. A classification of the assembly state of the
clusters based on the dynamical significance of their substructures is
proposed. In 19% of our clusters, the originally identified brightest cluster
galaxy is not the central gravitationally dominant galaxy (CDG), but turns out
to be either the second-rank, or the dominant galaxy of a substructure (a SDG,
in our classification), or even a possible "fossil" galaxy in the periphery of
the cluster. Moreover, no correlation was found in general between the
projected offset of the CDG from the X-ray peak and its peculiar velocity. The
comparison of the CDGs properties with the assembly states and dynamical state
of the intracluster media, especially the core cooling status, suggests a
complex assembly history, with clear evidence of co-evolution of the CDG and
its host cluster in the innermost regions.Comment: Contains 33 pages, 12 figures, 8 tables. On the accompanying webpage
( http://www.astro.ugto.mx/recursos/HP_SCls/Top70.html ), we offer the
complete set of figures describing all clusters presented in this articl
MeerKAT uncovers the physics of an odd radio circle
Odd radio circles (ORCs) are recently-discovered faint diffuse circles of radio emission, of unknown cause, surrounding galaxies at moderate redshift (z ∼0.2-0.6). Here, we present detailed new MeerKAT radio images at 1284 MHz of the first ORC, originally discovered with the Australian Square Kilometre Array Pathfinder, with higher resolution (6 arcsec) and sensitivity (∼2.4 μJy/beam). In addition to the new images, which reveal a complex internal structure consisting of multiple arcs, we also present polarization and spectral index maps. Based on these new data, we consider potential mechanisms that may generate the ORCs
The Evolutionary Map of the Universe Pilot Survey
We present the data and initial results from the first pilot survey of the Evolutionary Map of the Universe (EMU), observed at 944 MHz with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The survey covers 270 deg2 of an area covered by the Dark Energy Survey, reaching a depth of 25–30 μJy beam−1 rms at a spatial resolution of ∼11–18 arcsec, resulting in a catalogue of ∼220 000 sources, of which ∼180 000 are single-component sources. Here we present the catalogue of single-component sources, together with (where available) optical and infrared cross-identifications, classifications, and redshifts. This survey explores a new region of parameter space compared to
previous surveys. Specifically, the EMU Pilot Survey has a high density of sources, and also a high sensitivity to low surface brightness emission. These properties result in the detection of types of sources that were rarely seen in or absent from previous surveys. We present some of these new results here