7 research outputs found
J021659-044920: a relic giant radio galaxy at z ~ 1.3
We report the discovery of a relic Giant Radio Galaxy (GRG) J021659-044920 at
redshift that exhibits large-scale extended, nearly co-spatial,
radio and X-ray emission from radio lobes, but no detection of Active Galactic
Nuclei core, jets and hotspots. The total angular extent of the GRG at the
observed frame 0.325 GHz, using Giant Metrewave Radio Telescope observations is
found to be 2.4 arcmin, that corresponds to a total projected linear
size of 1.2 Mpc. The integrated radio spectrum between 0.240 and 1.4 GHz
shows high spectral curvature ( 1.19) with sharp steepening above
0.325 GHz, consistent with relic radio emission that is 8
10 yr old. The radio spectral index map between observed frame 0.325 and
1.4~GHz for the two lobes varies from 1.4 to 2.5 with the steepening trend from
outer-end to inner-end, indicating backflow of plasma in the lobes. The
extended X-ray emission characterized by an absorbed power-law with photon
index 1.86 favours inverse-Compton scattering of the Cosmic Microwave
Background (ICCMB) photons as the plausible origin. Using both X-ray and radio
fluxes under the assumption of ICCMB we estimate the magnetic field in the
lobes to be 3.3 G. The magnetic field estimate based on energy
equipartition is 3.5 G. Our work presents a case study of a rare
example of a GRG caught in dying phase in the distant Universe.Comment: 10 pages, 5 figures, 3 tables. Published in MNRAS. Corrected typos
and added a referenc
A search for radio emission from exoplanets around evolved stars
The majority of searches for radio emission from exoplanets have to date
focused on short period planets, i.e., the so-called hot Jupiter type planets.
However, these planets are likely to be tidally locked to their host stars and
may not generate sufficiently strong magnetic fields to emit electron cyclotron
maser emission at the low frequencies used in observations (typically >150
MHz). In comparison, the large mass-loss rates of evolved stars could enable
exoplanets at larger orbital distances to emit detectable radio emission. Here,
we first show that the large ionized mass-loss rates of certain evolved stars
relative to the solar value could make them detectable with the Low Frequency
Array (LOFAR) at 150 MHz ( = 2 m), provided they have surface magnetic
field strengths >50 G. We then report radio observations of three long period
(>1 au) planets that orbit the evolved stars Gem, Dra, and
UMi using LOFAR at 150 MHz. We do not detect radio emission from any
system but place tight 3 upper limits of 0.98, 0.87, and 0.57 mJy on
the flux density at 150 MHz for Gem, Dra, and UMi,
respectively. Despite our non-detections these stringent upper limits highlight
the potential of LOFAR as a tool to search for exoplanetary radio emission at
meter wavelengths.Comment: 9 pages, 3 figure
On the nature of infrared-faint radio sources in the SXDF and VLA-VVDS fields
Infrared-Faint Radio Sources (IFRSs) are an unusual class of objects that are
relatively bright at radio wavelengths but have faint or undetected infrared
counterparts even in deep surveys. We identify and investigate the nature of
IFRSs using deep radio (S 100 Jy beam at
5), optical (m 26 - 27.7 at 5), and near-IR
(S 1.3 - 2.0 Jy beam at 5) data
available in two deep fields namely the Subaru X-ray Deep Field (SXDF) and the
Very Large Array - VIMOS VLT Deep Survey (VLA-VVDS) field. In 1.8 deg of
the two fields we identify a total of nine confirmed and ten candidate IFRSs.
We find that our IFRSs are high-redshift radio-loud AGN, with 12/19 sources
having redshift estimates in the range of 1.7 - 4.3, while a limit
of 2.0 is placed for the remaining seven sources. Notably, our study
finds, for the first time, IFRSs with measured redshift 3.0, and also, the
redshift estimates for IFRSs in the faintest 3.6 m flux regime i.e.,
S 1.3 Jy. Radio observations show that our IFRSs
exhibit both compact unresolved as well as extended double-lobe morphologies,
and have predominantly steep radio spectra between 1.4 GHz and 325 MHz. The
non-detection of all but one IFRSs in the X-ray band and the optical-to-MIR
colour (m - m) suggest that a significant fraction
of IFRSs are likely to be hosted in dusty obscured galaxies.Comment: 20 pages, 8 figures, 4 tables, accepted for publication in MNRA