63 research outputs found
A Spectropolarimetric Study of Pictor A Radio Galaxy with MeerKAT
We present the results of a polarimetric study from our new high-sensitivity
L-band (0.8--1.7 GHz) observation of Pictor A with the MeerKAT radio telescope.
We confirm the presence of the radio jet extending from the nucleus to the
western hotspot of this source. Additionally, we show the radio emission
expected to be coincident with previously observed X-ray emission in the radio
lobes, confirming that the emission mechanism is of inverse Compton origin, as
suggested by a previous study. Our spectropolarimetric analysis using the
RM-Synthesis technique reveals a relatively uniform mean RM distribution across
the lobes of Pictor A, with most lines-of-sight exhibiting single-peaked
Faraday spectra. However, a number of the lines-of-sight exhibit single peaked
spectra with a wide base or multiple peaks, suggesting the presence of multiple
Faraday components or a Faraday thick structure along Pictor A's
lines-of-sight. We also confirm the asymmetry in RM variability and
depolarization between the two lobes of this source which were reported in a
previous study.Comment: 15 pages,15 figures. This is a pre-copyedited, author-produced PDF of
an article accepted for publication in MNRAS following peer review. The
version of record [Andati L.A.L. et al., 2024] is available online at:
https://doi.org/10.1093/mnras/stae59
GASP - XVII. H I imaging of the jellyfish galaxy JO206:Gas stripping and enhanced star formation
We present VLA HI observations of JO206, a prototypical ram-pressure stripped
galaxy in the GASP sample. This massive galaxy (M 8.5
10 M) is located at a redshift of 0.0513, near the
centre of the low-mass galaxy cluster, IIZw108 ( km/s). JO206
is characterised by a long tail (90 kpc) of ionised gas stripped away by
ram-pressure. We find a similarly long HI tail in the same direction as the
ionised gas tail and measure a total HI mass of
M. This is about half the expected HI mass given the stellar mass and
surface density of JO206. A total of M (60%) of
the detected HI is in the gas stripped tail. An analysis of the star formation
rate shows that the galaxy is forming more stars compared to galaxies with the
same stellar and HI mass. On average we find a HI gas depletion time of
0.5 Gyr which is about four times shorter than that of "normal" spiral
galaxies. We performed a spatially resolved analysis of the relation between
star formation rate density and gas density in the disc and tail of the galaxy
at the resolution of our HI data. The star formation efficiency of the disc is
about 10 times higher than that of the tail at fixed HI surface densities. Both
the inner and outer parts of JO206 show an enhanced star formation compared to
regions of similar HI surface density in field galaxies. The enhanced star
formation is due to ram-pressure stripping during the galaxy's first infall
into the cluster.Comment: 13 pages, 12 figures, Accepted for publication in MNRA
MeerKAT's discovery of a radio relic in the bimodal merging cluster A2384
We present the discovery of a single radio relic located at the edge of the
galaxy cluster A2384, using the MeerKAT radio telescope. A2384 is a nearby (
= 0.092), low mass, complex bimodal, merging galaxy cluster that displays a
dense X-ray filament ( 700 kpc in length) between A2384(N) (Northern
cluster) and A2384(S) (Southern cluster). The origin of the radio relic is
puzzling. By using the MeerKAT observation of A2384, we estimate that the
physical size of the radio relic is 824 264 kpc and that it is a
steep spectrum source. The radio power of the relic is
(3.87 0.40) 10 W Hz. This radio relic could
be the result of shock wave propagation during the passage of the low-mass
A2384(S) cluster through the massive A2384(N) cluster, creating a trail
appearing as a hot X-ray filament. In the previous GMRT 325 MHz observation we
detected a peculiar FR I radio galaxy interacting with the hot X-ray filament
of A2384, but the extended radio relic was not detected; it was confused with
the southern lobe of the FR I galaxy. This newly detected radio relic is
elongated and perpendicular to the merger axis, as seen in other relic
clusters. In addition to the relic, we notice a candidate radio ridge in the
hot X-ray filament. The physical size of the radio ridge source is 182
129 kpc. Detection of the diffuse radio sources in the X-ray
filament is a rare phenomenon, and could be a new class of radio source found
between the two merging clusters of A2384(N) and A2384(S).Comment: 12 pages, 6 figures, accepted in MNRA
The Detection of a Massive Chain of Dark H i Clouds in the GAMA G23 Field
We report on the detection of a large, extended H i cloud complex in the Galaxy and Mass Survey G23 field, located at a redshift of z ∼0.03, observed as part of the MeerKAT Habitat of Galaxies Survey campaign (a pilot survey to explore the mosaicing capabilities of the MeerKAT telescope). The cloud complex, with a total mass of 1010.0 M, lies in proximity to a large galaxy group with M dyn ∼1013.5 M. We identify seven H peak concentrations, interconnected as a tenuous chain structure, extending ∼400 kpc from east to west, with the largest (central) concentration containing 109.7 M in H gas distributed across 50 kpc. The main source is not detected in ultraviolet, optical, or infrared imaging. The implied gas mass-to-light ratio (M H I/L r) is extreme (>1000) even in comparison to other dark clouds. The complex has very little kinematic structure (110 km s-1), making it difficult to identify cloud rotation. Assuming pressure support, the total mass of the central concentration is > 1010.2 M, while a lower limit to the dynamical mass in the case of full rotational support is 1010.4 M. If the central concentration is a stable structure, it has to contain some amount of unseen matter, but potentially less than is observed for a typical galaxy. It is, however, not clear whether the structure has any gravitationally stable concentrations. We report a faint UV-optical-infrared source in proximity to one of the smaller concentrations in the gas complex, leading to a possible stellar association. The system nature and origins is enigmatic, potentially being the result of an interaction with or within the galaxy group it appears to be associated with
MeerKAT-16 H I observation of the dIrr galaxy WLM
We present observations and models of the kinematics and the distribution of
the neutral hydrogen (HI) in the isolated dwarf irregular galaxy,
Wolf-Lundmark-Melotte (WLM). We observed WLM with the Green Bank Telescope
(GBT) and as part of the MeerKAT Early Science Programme, where 16 dishes were
available. The HI disc of WLM extends out to a major axis diameter of 30 arcmin
(8.5 kpc), and a minor axis diameter of 20 arcmin (5.6 kpc) as measured by the
GBT. We use the MeerKAT data to model WLM using the TiRiFiC software suite,
allowing us to fit different tilted-ring models and select the one that best
matches the observation. Our final best-fitting model is a flat disc with a
vertical thickness, a constant inclination and dispersion, and a
radially-varying surface brightness with harmonic distortions. To simulate
bar-like motions, we include second-order harmonic distortions in velocity in
the tangential and the vertical directions. We present a model with only
circular motions included and a model with non-circular motions. The latter
describes the data better. Overall, the models reproduce the global
distribution and the kinematics of the gas, except for some faint emission at
the 2-sigma level. We model the mass distribution of WLM with a
pseudo-isothermal (ISO) and a Navarro-Frenk-White (NFW) dark matter halo
models. The NFW and the ISO models fit the derived rotation curves within the
formal errors, but with the ISO model giving better reduced chi-square values.
The mass distribution in WLM is dominated by dark matter at all radii.Comment: Accepted for publication in MNRAS, 25 pages, 21 figures, 5 table
MeerKAT-64 discovers wide-spread tidal debris in the nearby NGC 7232 galaxy group
We report the discovery of large amounts of previously undetected cold neutral atomic hydrogen (H I) around the core triplet galaxies in the nearby NGC 7232 galaxy group with MeerKAT. With a physical resolution of ∼1 kpc, we detect a complex web of low-surface-brightness HI emission down to a 4σ column density level of ∼1 × 1019 cm-2 (over 44 km s-1). The newly discovered HI streams extend over ∼20 arcmin corresponding to 140 kpc in projection. This is approximately three times the HI extent of the galaxy triplet (52 kpc). The HI debris has an HI mass of ∼6.6 × 109 M⊙, more than 50 per cent of the total HI mass of the triplet. Within the galaxy triplet, NGC 7233 and NGC 7232 have lost a significant amount of HI while NGC 7232B appears to have an excess of HI. TheHI deficiency in NGC 7232 and NGC 7233 indicates that galaxÿCgalaxy interaction in the group concentrates on this galaxy pair while the other disc galaxies have visited them over time. In comparison to the AMIGA sample of isolated galaxies, we find that with regards to its total HI mass the NGC 7232/3 galaxy triplet is not HI-deficient. Despite the many interactions associated to the triplet galaxies, no HI seems to have been lost from the group (yet)
Revival of the magnetar PSR J1622-4950: observations with MeerKAT, Parkes, XMM-Newton, Swift, Chandra, and NuSTAR
New radio (MeerKAT and Parkes) and X-ray (XMM-Newton, Swift, Chandra, and
NuSTAR) observations of PSR J1622-4950 indicate that the magnetar, in a
quiescent state since at least early 2015, reactivated between 2017 March 19
and April 5. The radio flux density, while variable, is approximately 100x
larger than during its dormant state. The X-ray flux one month after
reactivation was at least 800x larger than during quiescence, and has been
decaying exponentially on a 111+/-19 day timescale. This high-flux state,
together with a radio-derived rotational ephemeris, enabled for the first time
the detection of X-ray pulsations for this magnetar. At 5%, the 0.3-6 keV
pulsed fraction is comparable to the smallest observed for magnetars. The
overall pulsar geometry inferred from polarized radio emission appears to be
broadly consistent with that determined 6-8 years earlier. However, rotating
vector model fits suggest that we are now seeing radio emission from a
different location in the magnetosphere than previously. This indicates a novel
way in which radio emission from magnetars can differ from that of ordinary
pulsars. The torque on the neutron star is varying rapidly and unsteadily, as
is common for magnetars following outburst, having changed by a factor of 7
within six months of reactivation.Comment: Published in ApJ (2018 April 5); 13 pages, 4 figure
The flickering nuclear activity of Fornax A
We present new observations of Fornax A taken at 1 GHz with the MeerKAT
telescope and at 6 GHz with the Sardinia Radio Telescope (SRT). The sensitive
(noise ~16 micro-Jy beam), high resolution ( < 10'') MeerKAT images show
that the lobes of Fornax A have a double-shell morphology, where dense
filaments are embedded in a diffuse and extended cocoon. We study the spectral
properties of these components by combining the MeerKAT and SRT observations
with archival data between 84 MHz and 217 GHz. For the first time, we show that
multiple episodes of nuclear activity must have formed the extended radio
lobes. The modelling of the radio spectrum suggests that the last episode of
injection of relativistic particles into the lobes started ~ 24 Myr ago and
stopped approximately 12 Myr ago. More recently (~ 3 Myr ago), a less powerful
and short ( < 1 Myr) phase of nuclear activity generated the central jets.
Currently, the core may be in a new active phase. It appears that Fornax A is
rapidly flickering. The dense environment in which Fornax A lives has lead to a
complex recent merger history for this galaxy, including mergers spanning a
range of gas contents and mass ratios, as shown by the analysis of the galaxy's
stellar- and cold-gas phases. This complex recent history may be the cause of
the rapid, recurrent nuclear activity of Fornax A.Comment: Accepted for publication in Astronomy & Astrophysic
Collimated synchrotron threads linking the radio lobes of ESO 137-006
We present MeerKAT 1000 MHz and 1400 MHz observations of a bright radio galaxy in the southern hemisphere, ESO 137-006. The
galaxy lies at the centre of the massive and merging Norma galaxy cluster. The MeerKAT continuum images (rms ∼0.02 mJy beam−1
at ∼1000 resolution) reveal new features that have never been seen in a radio galaxy before: collimated synchrotron threads of yet
unknown origin, which link the extended and bent radio lobes of ESO 137-006. The most prominent of these threads stretches in
projection for about 80 kpc and is about 1 kpc in width. The radio spectrum of the threads is steep, with a spectral index of up to α ' 2
between 1000 and 1400 MHz.http://www.aanda.orgpm2021Physic
- …