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 ∼10″ 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.
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
μ
Jy beam
−1
), 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 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 around Fornax A 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.
We present MeerKAT observations of neutral hydrogen gas (H I) in the nearby merger remnant NGC 1316 (Fornax A), the brightest member of a galaxy group which is falling into the Fornax cluster. We ...find H I on a variety of scales, from the galaxy centre to its large-scale environment. For the first time we detect H I at large radii (70–150 kpc in projection), mostly distributed on two long tails associated with the galaxy. Gas in the tails dominates the H I mass of NGC 1316: 7 × 108 M⊙– 14 times more than in previous observations. The total H I mass is comparable to the amount of neutral gas found inside the stellar body, mostly in molecular form. The H I tails are associated with faint optical tidal features thought to be the remnant of a galaxy merger occurred a few billion years ago. They demonstrate that the merger was gas-rich. During the merger, tidal forces pulled some gas and stars out to large radii, where we now detect them in the form of optical tails and, thanks to our new data, H I tails; while torques caused the remaining gas to flow towards the centre of the remnant, where it was converted into molecular gas and fuelled the starburst revealed by the galaxy’s stellar populations. Several of the observed properties of NGC 1316 can be reproduced by a ∼10:1 merger between a dominant, gas-poor early-type galaxy and a smaller, gas-rich spiral occurred 1–3 Gyr ago, likely followed by subsequent accretion of satellite galaxies.
GASP Ramatsoku, M.; Serra, P.; Poggianti, B. M. ...
Astronomy and astrophysics (Berlin),
08/2020, Volume:
640
Journal Article
Peer reviewed
We present atomic hydrogen (H
I
) observations with the
Jansky
Very Large Array of one of the jellyfish galaxies in the GAs Stripping Phenomena sample, JO201. This massive galaxy (
M
*
= 3.5 × 10
...10
M
⊙
) is falling along the line-of-sight towards the centre of a rich cluster (
M
200
∼ 1.6 × 10
15
M
⊙
,
σ
cl
∼ 982 ± 55 km s
−1
) at a high velocity ≥3363 km s
−1
. Its H
α
emission shows a ∼40 kpc tail, which is closely confined to its stellar disc and a ∼100 kpc tail extending further out. We find that H
I
emission only coincides with the shorter clumpy H
α
tail, while no H
I
emission is detected along the ∼100 kpc H
α
tail. In total, we measured an H
I
mass of
M
HI
= 1.65 × 10
9
M
⊙
, which is about 60% lower than expected based on its stellar mass and stellar surface density. We compared JO201 to another jellyfish in the GASP sample, JO206 (of a similar mass but living in a ten times less massive cluster), and we find that they are similarly H
I
-deficient. Of the total H
I
mass in JO201, about 30% lies outside the galaxy disc in projection. This H
I
fraction is probably a lower limit since the velocity distribution shows that most of the H
I
is redshifted relative to the stellar disc and could be outside the disc. The global star formation rate (SFR) analysis of JO201 suggests an enhanced star formation for its observed H
I
content. The observed SFR would be expected if JO201 had ten times its current H
I
mass. The disc is the main contributor of the high star formation efficiency at a given H
I
gas density for both galaxies, but their tails also show higher star formation efficiencies compared to the outer regions of field galaxies. Generally, we find that JO201 and JO206 are similar based on their H
I
content, stellar mass, and star formation rate. This finding is unexpected considering their different environments. A toy model comparing the ram pressure of the intracluster medium (ICM) versus the restoring forces of these galaxies suggests that the ram pressure strength exerted on them could be comparable if we consider their 3D orbital velocities and radial distances relative to the clusters.
Abstract
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 10
10.0
M
⊙
, lies in proximity to a large galaxy group with
M
dyn
∼ 10
13.5
M
⊙
. We identify seven H ɪ peak concentrations, interconnected as a tenuous
chain
structure, extending ∼400 kpc from east to west, with the largest (central) concentration containing 10
9.7
M
⊙
in H ɪ 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 > 10
10.2
M
⊙
, while a lower limit to the dynamical mass in the case of full rotational support is 10
10.4
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.
ABSTRACT
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 H i emission down to a 4σ column density level of ∼1 × 1019 cm−2 (over 44 km s−1). The newly discovered H i streams extend over ∼20 arcmin corresponding to 140 kpc in projection. This is approximately three times the H i extent of the galaxy triplet (52 kpc). The H i debris has an H i mass of ∼6.6 × 109 M⊙, more than 50 per cent of the total H i mass of the triplet. Within the galaxy triplet, NGC 7233 and NGC 7232 have lost a significant amount of H i while NGC 7232B appears to have an excess of H i. The H i deficiency in NGC 7232 and NGC 7233 indicates that galaxy–galaxy 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 H i mass the NGC 7232/3 galaxy triplet is not H i-deficient. Despite the many interactions associated to the triplet galaxies, no H i seems to have been lost from the group (yet).
ABSTRACT
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 (z = 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. Using the MeerKAT observation of A2384, we estimate that the physical size of the radio relic is 824 × 264 kpc2 and that it is a steep spectrum source. The radio power of the relic is $P_{1.4\mathrm{GHz}}\, \sim$ (3.87 ± 0.40) × 1023 W Hz−1. 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 kpc2. 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).
GASP Ramatsoku, M; Serra, P; Poggianti, B M ...
Astronomy & astrophysics,
08/2020, Volume:
640
Journal Article
Peer reviewed
Open access
We present atomic hydrogen (H I) observations with the Jansky Very Large Array of one of the jellyfish galaxies in the GAs Stripping Phenomena sample, JO201. This massive galaxy (M* = 3.5 × 1010 M⊙) ...is falling along the line-of-sight towards the centre of a rich cluster (M200 ∼ 1.6 × 1015 M⊙, σcl ∼ 982 ± 55 km s−1) at a high velocity ≥3363 km s−1. Its Hα emission shows a ∼40 kpc tail, which is closely confined to its stellar disc and a ∼100 kpc tail extending further out. We find that H I emission only coincides with the shorter clumpy Hα tail, while no H I emission is detected along the ∼100 kpc Hα tail. In total, we measured an H I mass of MHI = 1.65 × 109 M⊙, which is about 60% lower than expected based on its stellar mass and stellar surface density. We compared JO201 to another jellyfish in the GASP sample, JO206 (of a similar mass but living in a ten times less massive cluster), and we find that they are similarly H I-deficient. Of the total H I mass in JO201, about 30% lies outside the galaxy disc in projection. This H I fraction is probably a lower limit since the velocity distribution shows that most of the H I is redshifted relative to the stellar disc and could be outside the disc. The global star formation rate (SFR) analysis of JO201 suggests an enhanced star formation for its observed H I content. The observed SFR would be expected if JO201 had ten times its current H I mass. The disc is the main contributor of the high star formation efficiency at a given H I gas density for both galaxies, but their tails also show higher star formation efficiencies compared to the outer regions of field galaxies. Generally, we find that JO201 and JO206 are similar based on their H I content, stellar mass, and star formation rate. This finding is unexpected considering their different environments. A toy model comparing the ram pressure of the intracluster medium (ICM) versus the restoring forces of these galaxies suggests that the ram pressure strength exerted on them could be comparable if we consider their 3D orbital velocities and radial distances relative to the clusters.
The 1.28 GHz MeerKAT Galactic Center Mosaic Heywood, I.; Rammala, I.; Camilo, F. ...
Astrophysical journal/The Astrophysical journal,
02/2022, Volume:
925, Issue:
2
Journal Article
Peer reviewed
Open access
Abstract
The inner ∼200 pc region of the Galaxy contains a 4 million M
⊙
supermassive black hole (SMBH), significant quantities of molecular gas, and star formation and cosmic-ray energy densities ...that are roughly two orders of magnitude higher than the corresponding levels in the Galactic disk. At a distance of only 8.2 kpc, the region presents astronomers with a unique opportunity to study a diverse range of energetic astrophysical phenomena, from stellar objects in extreme environments, to the SMBH and star-formation-driven feedback processes that are known to influence the evolution of galaxies as a whole. We present a new survey of the Galactic center conducted with the South African MeerKAT radio telescope. Radio imaging offers a view that is unaffected by the large quantities of dust that obscure the region at other wavelengths, and a scene of striking complexity is revealed. We produce total-intensity and spectral-index mosaics of the region from 20 pointings (144 hr on-target in total), covering 6.5 square degrees with an angular resolution of 4″ at a central frequency of 1.28 GHz. Many new features are revealed for the first time due to a combination of MeerKAT’s high sensitivity, exceptional
u
,
v
-plane coverage, and geographical vantage point. We highlight some initial survey results, including new supernova remnant candidates, many new nonthermal filament complexes, and enhanced views of the Radio Arc bubble, Sagittarius A, and Sagittarius B regions. This project is a South African Radio Astronomy Observatory public legacy survey, and the image products are made available with this article.
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