Based on sub-arcsecond Atacama Large Millimeter/submillimeter Array (ALMA) and Submillimeter Array (SMA) 1.3 mm continuum images of the massive protocluster NGC 6334I obtained in 2015 and 2008, we ...find that the dust emission from MM1 has increased by a factor of 4.0 0.3 during the intervening years, and undergone a significant change in morphology. The continuum emission from the other cluster members (MM2, MM4, and the UCH ii region MM3 = NGC 6334F) has remained constant. Long-term single-dish maser monitoring at HartRAO finds that multiple maser species toward NGC 6334I flared beginning in early 2015, a few months before our ALMA observation, and some persist in that state. New ALMA images obtained in 2016 July-August at 1.1 and 0.87 mm confirm the changes with respect to SMA 0.87 mm images from 2008, and indicate that the (sub)millimeter flaring has continued for at least a year. The excess continuum emission, centered on the hypercompact H ii region MM1B, is extended and elongated (1 6 × 1 0 2100 × 1300 au) with multiple peaks, suggestive of general heating of the surrounding subcomponents of MM1, some of which may trace clumps in a fragmented disk rather than separate protostars. In either case, these remarkable increases in maser and dust emission provide direct observational evidence of a sudden accretion event in the growth of a massive protostar yielding a sustained luminosity surge by a factor of 70 20, analogous to the largest events in simulations by Meyer et al. This target provides an excellent opportunity to assess the impact of such a rare event on a protocluster over many years.
We report the first sub-arcsecond VLA imaging of 6 GHz continuum, methanol maser, and excited-state hydroxyl maser emission toward the massive protostellar cluster NGC 6334I following the recent 2015 ...outburst in (sub)millimeter continuum toward MM1, the strongest (sub)millimeter source in the protocluster. In addition to detections toward the previously known 6.7 GHz Class II methanol maser sites in the hot core MM2 and the UCHII region MM3 (NGC 6334F), we find new maser features toward several components of MM1, along with weaker features ∼1″ north, west, and southwest of MM1, and toward the nonthermal radio continuum source CM2. None of these areas have heretofore exhibited Class II methanol maser emission in three decades of observations. The strongest MM1 masers trace a dust cavity, while no masers are seen toward the strongest dust sources MM1A, 1B, and 1D. The locations of the masers are consistent with a combination of increased radiative pumping due to elevated dust grain temperature following the outburst, the presence of infrared photon propagation cavities, and the presence of high methanol column densities as indicated by ALMA images of thermal transitions. The nonthermal radio emission source CM2 (2″ north of MM1) also exhibits new maser emission from the excited 6.035 and 6.030 GHz OH lines. Using the Zeeman effect, we measure a line-of-sight magnetic field of +0.5 to +3.7 mG toward CM2. In agreement with previous studies, we also detect numerous methanol and excited OH maser spots toward the UCHII region MM3, with predominantly negative line-of-sight magnetic field strengths of −2 to −5 mG and an intriguing south-north field reversal.
We compare multi-epoch sub-arcsecond Very Large Array imaging of the 22 GHz water masers toward the massive protocluster NGC 6334I observed before and after the recent outburst of MM1B in ...(sub)millimeter continuum. Since the outburst, the water maser emission toward MM1 has substantially weakened. Simultaneously, the strong water masers associated with the synchrotron continuum point source CM2 have flared by a mean factor of 6.5 (to 4.2 kJy) with highly blueshifted features (up to 70 km s−1 from the LSR) becoming more prominent. The strongest flaring water masers reside 3000 au north of MM1B and form a remarkable bow shock pattern whose vertex coincides with CM2 and tail points back to MM1B. Excited OH masers trace a secondary bow shock located ∼120 au downstream. Atacama Large Millimeter Array images of CS (6-5) reveal a highly collimated north-south structure encompassing the flaring masers to the north and the nonflaring masers to the south seen in projection toward the MM3-UCHII region. Proper motions of the southern water masers over 5.3 years indicate a bulk projected motion of 117 km s−1 southward from MM1B with a dynamical time of 170 years. We conclude that CM2, the water masers, and many of the excited OH masers trace the interaction of the high-velocity bipolar outflow from MM1B with ambient molecular gas. The previously excavated outflow cavity has apparently allowed the radiative energy of the current outburst to propagate freely until terminating at the northern bow shock where it strengthened the masers. Additionally, water masers have been detected toward MM7 for the first time, and a highly collimated CS (6-5) outflow has been detected toward MM4.
ABSTRACT
We investigated the nature of protostellar objects in G358.46−0.39 and their gas kinematics using ALMA data, with the aim of understanding the ongoing star formation activities in the ...region. The dust continuum map reveals multiple cores (MM1a, MM1b, MM1c, and MM2) dominated by MM1a, with no detectable free–free emission. We calculated the masses and the column densities of the various objects (MM1a, MM1b, MM1c, and MM2). A total of 33, 10, 10, and 9 molecular transitions are detected towards MM1a, MM1b, MM1c, and MM2, respectively. The differences in the number of molecular lines detected towards each of the cores support different excitation conditions at different positions. We derived the kinetic temperature ranges of MM1a, MM1b, MM1c, and MM2 to be ∼96–118, 96–114, 72–74, and 80–84 K, respectively. A highly collimated bipolar outflow traced by 12CO emission is observed to be associated with MM1a, with knots along the outflow lobes, which could be an indication of episodic ejection. The C17O emission is observed to be likely tracing a slowly rotating envelope of gas around MM1a. The velocity field map of CH3OH (22, 1 − 31, 2) emission suggests the presence of a rotating structure, possibly a disc. The physical and kinematic properties of MM1a are strong indication of a massive young stellar object, with ongoing outflow activity and accretion in its early stage of formation.
Context.
During their lifetimes, galaxy clusters grow through the accretion of matter from the filaments of the large-scale structure and from mergers with other clusters. These mergers release a ...large amount of energy into the intracluster medium (ICM) through merger shocks and turbulence. These phenomena are associated with the formation of radio sources known as radio relics and radio halos, respectively. Radio relics and halos are unique proxies for studying the complex properties of these dynamically active regions of clusters and the microphysics of the ICM more generally.
Aims.
Abell 3667 is a spectacular example of a merging system that hosts a large pair of radio relics. Due to its proximity (
z
= 0.0553) and large mass, the system enables the study of these sources to a uniquely high level of detail. However, being located at Dec = −56.8°, the cluster could only be observed with a limited number of radio facilities.
Methods.
We observed Abell 3667 with MeerKAT as part of the MeerKAT Galaxy Cluster Legacy Survey. We used these data to study the large-scale emission of the cluster, including its polarisation and spectral properties. The results were then compared with simulations.
Results.
We present the most detailed view of the radio relic system in Abell 3667 to date, with a resolution reaching 3 kpc. The relics are filled with a network of filaments with different spectral and polarisation properties that are likely associated with multiple regions of particle acceleration and local enhancements of the magnetic field. Conversely, the magnetic field in the space between filaments has strengths close to what would be expected in unperturbed regions at the same cluster-centric distance. Comparisons with magnetohydrodynamic cosmological and Lagrangian simulations support the idea of filaments as multiple acceleration sites. Our observations also confirm the presence of an elongated radio halo, developed in the wake of the bullet-like sub-cluster that merged from the south-east. Finally, we associate the process of magnetic draping with a thin polarised radio source surrounding the remnant of the bullet’s cool core.
Conclusions.
Our observations have unveiled the complexity of the interplay between the thermal and non-thermal components in the most active regions of a merging cluster. Both the intricate internal structure of radio relics and the direct detection of magnetic draping around the merging bullet are powerful examples of the non-trivial magnetic properties of the ICM. Thanks to its sensitivity to polarised radiation, MeerKAT will be transformational in the study of these complex phenomena.
ABSTRACT This study presents a detailed analysis of the GAL045.804 − 0.356 massive star-forming clump. A high-angular resolution and sensitivity observations were conducted using MeerKAT at 1.28 GHz ...and ALMA interferometer at 1.3 mm. Two distinct centimetre radio continuum emissions (source A and source B) were identified within the clump. A comprehensive investigation was carried out on source A, the G45.804 − 0.355 star-forming region (SFR) due to its association with Extended Green Object (EGO), 6.7 GHz methanol maser and the spatial coincidence with the peak of the dust continuum emission at 870 µm. The ALMA observations revealed seven dense dust condensations (MM1–MM7) in source A. The brightest (Sν ∼ 87 mJy) and massive main dense core, MM1, was co-located with the 6.7 GHz methanol maser. Explorations into the kinematics revealed gas motions characterized by a velocity gradient across the MM1 core. Furthermore, molecular line emission showed the presence of an extended arm-like structure, with a physical size of 0.25 pc × 0.18 pc (∼ 50 000 au × 30 000 au) at a distance of 7.3 kpc. Amongst these arms, two arms were prominently identified in both the dust continuum and some of the molecular lines. A blue-shifted absorption P-Cygni profile was seen in the H2CO line spectrum. The findings of this study are both intriguing and new, utilizing data from MeerKAT and ALMA to investigate the characteristics of the AGAL45 clump. The evidence of spiral arms, the compact nature of the EGO and < 2 km s−1 velocity gradient are all indicative of G45.804 − 0.355 being oriented face-on.
ABSTRACT
We report the results of our pilot millimeter observations of periodic maser sources. Using SMA, we carried out 1.3-mm observations of G22.357+0.066 and G25.411+0.105, while ALMA 1.3-mm ...archival data were used in the case of G9.62+0.19E. Two continuum cores (MM1 and MM2) were detected in G22.357+0.066, while three cores (MM1 – MM3) detected in G25.411 + 0.105. Assuming dust-to-gas ratio of 100, we derived the masses of the detected cores. Using the 12CO (2–1) and 13CO (2–1) line emission, we observed gas kinematics tracing the presence of bipolar outflows in all three star-forming regions. In the cases of G22.357+0.066 and G9.62+0.19E, both with similar periodic maser light-curve profiles, the outflowing gas is seen in the north-west south-east direction. This suggest edge-on view of the two sources. G25.411+0.105, with a contrasting light-curve profile, show a spatially collocated blue and red outflow lobes, suggesting a face-on view. Our results suggest that orientation effects may play a role in determining the characteristics of the light curves of periodic methanol masers.
We present results from the most comprehensive radio monitoring campaign towards the closest star to our Sun, Proxima Centauri. We report 1.1–3.1 GHz observations with the Australia Telescope Compact ...Array over 18 consecutive days in April 2017. We detected radio emission from Proxima Centauri for most of the observing sessions, which spanned ~1.6 orbital periods of the planet Proxima b. The radio emission is stronger at the low-frequency band, centered around 1.6 GHz, and is consistent with the expected electron-cyclotron frequency for the known star’s magnetic field intensity of ~600 gauss. The 1.6 GHz light curve shows an emission pattern that is consistent with the orbital period of the planet Proxima b around the star Proxima, with its maxima of emission happening near the quadratures. We also observed two short-duration flares (a few minutes) and a long-duration burst (about three days) whose peaks happened close to the quadratures. We find that the frequency, large degree of circular polarization, change in the sign of circular polarization, and intensity of the observed radio emission are all consistent with expectations from electron cyclotron-maser emission arising from sub-Alfvénic star–planet interaction. We interpret our radio observations as signatures of interaction between the planet Proxima b and its host star Proxima. We advocate for monitoring other dwarf stars with planets to eventually reveal periodic radio emission due to star–planet interaction, thus opening a new avenue for exoplanet hunting and the study of a new field of exoplanet–star plasma interaction.
ABSTRACT
We aim to carry out a radio study of the SoUthern Cluster sCale Extended Source Survey (SUCCESS) sample consisting of 20 massive (M500 > 5 × 1014 M⊙), nearby (redshift <0.3) and southern ...(−50° < δ < −30°) galaxy clusters detected by the Planck satellite and the South Pole Telescope. Here, we report targeted GMRT observations (325/610 MHz) for a subsample of nine clusters. We also use the first data release of MeerKAT Galaxy Cluster Legacy Survey (1283 MHz) for five of these nine clusters. The properties of the mini-halo in RXC J0528.9-3927, a candidate mini-halo in A3322, the radio halo and candidate double relics in A3399, and the radio halo in RXC J0232.2-4420 are presented. We also report a detection of candidate radio relics at distances 1 and 1.9 Mpc from the centre of RXC J0232.2-4420. The southeast relic of A3399 is consistent with the radio power–mass scaling relation for radio relics, while the candidate relics around RXC J0232.2-4420 are outliers. This indicates an origin of the candidate relics near RXC J0232.2-4420 to be independent of this cluster and a cluster merger-shock origin for the relic in A3399. In this subsample of clusters, 1/9 hosts a radio halo and double relics, 1/9 hosts a radio halo and 2/9 host mini-haloes. The dynamical states based on X-ray morphology show that A3399 is a disturbed cluster; however, the radio halo cluster RXC J0232.2-4420 is relaxed, and the mini-halo clusters have intermediate morphologies, adding to the cases of the less commonly found associations.
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