614 research outputs found
Infrared Emission from the Nearby Cool Core Cluster Abell 2597
We observed the brightest central galaxy (BCG) in the nearby (z=0.0821) cool
core galaxy cluster Abell 2597 with the IRAC and MIPS instruments on board the
Spitzer Space Telescope. The BCG was clearly detected in all Spitzer
bandpasses, including the 70 and 160 micron wavebands. We report aperture
photometry of the BCG. The spectral energy distribution exhibits a clear excess
in the FIR over a Rayleigh-Jeans stellar tail, indicating a star formation rate
of ~4-5 solar masses per year, consistent with the estimates from the UV and
its H-alpha luminosity. This large FIR luminosity is consistent with that of a
starburst or a Luminous Infrared Galaxy (LIRG), but together with a very
massive and old population of stars that dominate the energy output of the
galaxy. If the dust is at one temperature, the ratio of 70 to 160 micron fluxes
indicate that the dust emitting mid-IR in this source is somewhat hotter than
the dust emitting mid-IR in two BCGs at higher-redshift (z~0.2-0.3) and higher
FIR luminosities observed earlier by Spitzer, in clusters Abell 1835 and Zwicky
3146.Comment: Accepted at Ap
Compact radio cores: from the first black holes to the last
One of the clearest signs of black hole activity is the presence of a compact
radio core in the nuclei of galaxies. With the Square Kilometer Array (SKA)
these cores can be used to study the evolution of black holes throughout the
universe and even to detect the very first generation of supermassive black
holes. We start by introducing some of the basic properties of compact radio
cores and how they scale with accretion power. The relative contribution of
jets and radio cores to the Spectral Energy Distribution (SED) is strongest in
sub-Eddington black holes but also present in the most luminous objects. Radio
and X-rays are correlated as a function of black hole mass such that the most
massive black holes are most suited for radio detections. We present a radio
core luminosity function for the present universe down to the least luminous
AGN. The SKA will essentially detect all dormant black holes in the local
universe, such as that in our Milky Way, out to several tens of Megaparsecs. It
will also be able to see black holes in the making at redshifts z>10 for black
hole masses larger than 10^7 M_sun. Finally, we suggest that the first
generation of black holes may have jets that are frustrated in their dense
environment and thus appear as Gigahertz-Peaked-Spectrum (GPS) sources. Since
their intrinsic size and peak frequency are related and angular size and
frequency scale differently with redshift, there is a unique region in
parameter space that should be occupied by emerging black holes in the epoch of
reionization. This can be well probed by radio-only methods with the SKA.
(abridged)Comment: latex, 16 pages, 11 figures, to appear in: "Science with the Square
Kilometer Array," eds. C. Carilli and S. Rawlings, New Astronomy Reviews,
(Elsevier: Amsterdam
Optically Faint Radio Sources: Reborn AGN?
We have discovered a number of relatively strong radio sources in the
field-of-view of SDSS galaxy clusters which present no optical counterparts
down to the magnitude limits of the SDSS. The optically faint radio sources
appear as double-lobed or core-jet objects on the FIRST radio images and have
projected angular sizes ranging from 0.5 to 1.0 arcmin. We have followed-up
these sources with near-infrared imaging using the wide-field imager HAWK-I on
the VLT. K_s-band emitting regions, about 1.5 arcsec in size and coincident
with the centers of the radio structures, were detected in all the sources,
with magnitudes in the range 17-20 mag. We have used spectral modelling to
characterize the sample sources. In general, the radio properties are similar
to those observed in 3CRR sources but the optical-radio slopes are consistent
with moderate to high redshift (z<4) gigahertz-peaked spectrum sources. Our
results suggest that these unusual objects are galaxies whose black hole has
been recently re-ignited but retain large-scale radio structures, signatures of
previous AGN activity.Comment: Accepted for publication in A&
Research Weaving: Visualizing the Future of Research Synthesis
We propose a new framework for research synthesis of both evidence and influence, named research weaving. It summarizes and visualizes information content, history, and networks among a collection of documents on any given topic. Research weaving achieves this feat by combining the power of two methods: systematic mapping and bibliometrics. Systematic mapping provides a snapshot of the current state of knowledge, identifying areas needing more research attention and those ready for full synthesis. Bibliometrics enables researchers to see how pieces of evidence are connected, revealing the structure and development of a field. We explain how researchers can use some or all of these tools to gain a deeper, more nuanced understanding of the scientific literature
Chandra Discovery of a 300 kpc X-ray Jet in the GPS Quasar PKS1127-145
We have discovered an X-ray jet with Chandra imaging of the z=1.187
radio-loud quasar PKS1127-145. In this paper we present the Chandra X-ray data,
follow-up VLA observations, and optical imaging using the HST WFPC2. The X-ray
jet contains 273+/-5 net counts in 27ksec and extends ~30 arcsec, from the
quasar core, corresponding to a minimum projected linear size of ~330/h_50 kpc.
The evaluation of the X-ray emission processes is complicated by the observed
offsets between X-ray and radio brightness peaks. We discuss the problems posed
by these observations to jet models. In addition, PKS1127-145 is a Giga-Hertz
Peaked Spectrum radio source, a member of the class of radio sources suspected
to be young or ``frustrated'' versions of FRI radio galaxies. However the
discovery of an X-ray and radio jet extending well outside the host galaxy of
PKS1127-145 suggests that activity in this and other GPS sources may be
long-lived and complex.Comment: 22 pages, 11 ps figures, 1 figure in a JPG file, 3 tables. AASTEX.
Accepted by The Astrophysical Journa
An optical-IR jet in 3C133
We report the discovery of a new optical-IR synchrotron jet in the radio
galaxy 3C133 from our HST/NICMOS snapshot survey. The jet and eastern hotspot
are well resolved, and visible at both optical and IR wavelengths. The IR jet
follows the morphology of the inner part of the radio jet, with three distinct
knots identified with features in the radio. The radio-IR SED's of the knots
are examined, along with those of two more distant hotspots at the eastern
extreme of the radio feature. The detected emission appears to be synchrotron,
with peaks in the NIR for all except one case, which exhibits a power-law
spectrum throughout.Comment: ApJ accepted. 14 pages, 6 figure
Radio spectra and polarisation properties of a bright sample of Radio-Loud Broad Absorption Line Quasars
The origin of broad-absorption-line quasars (BAL QSOs) is still an open
issue. Accounting for ~20% of the QSO population, these objects present broad
absorption lines in their optical spectra generated from outflows with
velocities up to 0.2c. In this work we present the results of a multi-frequency
study of a well-defined radio-loud BAL QSO sample, and a comparison sample of
radio-loud non-BAL QSOs, both selected from the Sloan Digital Sky Survey
(SDSS).
We aim to test which of the currently-popular models for the BAL phenomenon -
`orientation' or 'evolutionary' - best accounts for the radio properties of BAL
quasars. Observations from 1.4 to 43 GHz have been obtained with the VLA and
Effelsberg telescopes, and data from 74 to 408 MHz have been compiled from the
literature.
The fractions of candidate GHz-peaked sources are similar in the two samples
(36\pm12% vs 23\pm8%), suggesting that BAL QSOs are not generally younger than
non-BAL QSOs. BAL and non-BAL QSOs show a large range of spectral indices,
consistent with a broad range of orientations. There is weak evidence (91%
confidence) that the spectral indices of the BAL QSOs are steeper than those of
non-BAL QSOs, mildly favouring edge-on orientations. At a higher level of
significance (\geq97%), the spectra of BAL QSOs are not flatter than those of
non-BAL QSOs, which suggests that a polar orientation is not preferred.Comment: Accepted by A&
A multiphase multiscale model for nutrient limited tissue growth
In this work, an effective macroscale description is derived for the growth of tissue on a porous scaffold. A multiphase model is employed to describe the tissue dynamics; linearisation to facilitate a multiple-scale homogenisation provides an effective macroscale description, which incorporates dependence on the microscale structure and dynamics. In particular, the resulting description admits both interstitial growth and active cell motion. This model comprises Darcy flow, and differential equations for the volume fraction of cells within the scaffold and the concentration of nutrient, required for growth. These are coupled to underlying Stokes-type cell problems that provide permeability tensors, with multiscale dependence incorporating active cell motion, with which to parameterise the macroscale flow. A subset of solutions are illustrated by numerical simulations
Radio-Excess IRAS Galaxies: PMN/FSC Sample Selection
A sample of 178 extragalactic objects is defined by correlating the 60 micron
IRAS FSC with the 5 GHz PMN catalog. Of these, 98 objects lie above the
radio/far-infrared relation for radio-quiet objects. These radio-excess
galaxies and quasars have a uniform distribution of radio excesses and appear
to be a new population of active galaxies not present in previous
radio/far-infrared samples. The radio-excess objects extend over the full range
of far-infrared luminosities seen in extragalactic objects. Objects with small
radio excesses are more likely to have far-infrared colors similar to
starbursts, while objects with large radio excesses have far-infrared colors
typical of pure AGN. Some of the most far-infrared luminous radio-excess
objects have the highest far-infrared optical depths. These are good candidates
to search for hidden broad line regions in polarized light or via near-infrared
spectroscopy. Some low far-infrared luminosity radio-excess objects appear to
derive a dominant fraction of their far-infrared emission from star formation,
despite the dominance of the AGN at radio wavelengths. Many of the radio-excess
objects have sizes likely to be smaller than the optical host, but show
optically thin radio emission. We draw parallels between these objects and high
radio luminosity Compact Steep-Spectrum (CSS) and GigaHertz Peaked-Spectrum
(GPS) objects. Radio sources with these characteristics may be young AGN in
which the radio activity has begun only recently. Alternatively, high central
densities in the host galaxies may be confining the radio sources to compact
sizes. We discuss future observations required to distinguish between these
possibilities and determine the nature of radio-excess objects.Comment: Submitted to AJ. 44 pages, 11 figures. A version of the paper with
higher quality figures is available from
http://www.mso.anu.edu.au/~cdrake/PMNFSC/paperI
- …