Discovery of Hydrogen Radio Recombination Lines at z = 0.89 toward PKS 1830-211

We report the detection of stimulated hydrogen radio recombination line (RRL) emission from ionized gas in a z = 0.89 galaxy using 580-1670 MHz observations from the MeerKAT Absorption Line Survey. The RRL emission originates in a galaxy that intercepts and strongly lenses the radio blazar PKS 1830−211 (z = 2.5). This is the second detection of RRLs outside of the local Universe and the first clearly associated with hydrogen. We detect effective H144α (and H163α) transitions at observed frequencies of 1156 (798) MHz by stacking 17 (27) RRLs with 21σ (14σ) significance. The RRL emission contains two main velocity components and is coincident in velocity with H i 21 cm and OH 18 cm absorption. We use the RRL spectral line energy distribution and a Bayesian analysis to constrain the density (n e ) and the volume-averaged path length (ℓ) of the ionized gas. We determine log ( n e ) = 2.0 − 0.7 + 1.0 cm−3 and log ( ℓ ) = − 0.7 − 1.1 + 1.1 pc toward the northeast (NE) lensed image, likely tracing the diffuse thermal phase of the ionized ISM in a thin disk. Toward the southwest (SW) lensed image, we determine log ( n e ) = 3.2 − 1.0 + 0.4 cm−3 and log ( ℓ ) = − 2.7 − 0.2 + 1.8 pc, tracing gas that is more reminiscent of H scii regions. We estimate a star formation (surface density) rate of ΣSFR ∼ 0.6 M ⊙ yr−1 kpc−2 or SFR ∼ 50 M ⊙ yr−1, consistent with a star-forming main-sequence galaxy of M ⋆ ∼ 1011 M ⊙. The discovery presented here opens up the possibility of studying ionized gas at high redshifts using RRL observations from current and future (e.g., SKA and ngVLA) radio facilities

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 100 larger than during its dormant state. The X-ray flux one month after reactivation was at least 800 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

an overview of the MHONGOOSE survey: Observing nearby galaxies with MeerKAT

MHONGOOSE is a deep survey of the neutral hydrogen distribution in a representative sample of 30 nearby disk and dwarf galaxies with H I masses from ∼ 106 to ∼ 1011 M, and luminosities from MR ∼ 12 to MR ∼ −22. The sample is selected to uniformly cover the available range in log(MHI). Our extremely deep observations, down to H I column density limits of well below 1018 cm−2 — or a few hundred times fainter than the typical H I disks in galaxies — will directly detect the effects of cold accretion from the intergalactic medium and the links with the cosmic web. These observations will be the first ever to probe the very low-column density neutral gas in galaxies at these high resolutions. Combination with data at other wavelengths, most of it already available, will enable accurate modeling of the properties and evolution of the mass components in these galaxies and link these with the effects of environment, dark matter distribution, and other fundamental properties such as halo mass and angular momentum. MHONGOOSE can already start addressing some of the SKA-1 science goals and will provide a comprehensive inventory of the processes driving the transformation and evolution of galaxies in the nearby universe at high resolution and over 5 orders of magnitude in column density. It will be a Nearby Galaxies Legacy Survey that will be unsurpassed until the advent of the SKA, and can serve as a highly visible, lasting statement of MeerKAT’s capabilities

Inflation of 430-parsec bipolar radio bubbles in the Galactic Centre by an energetic event

The Galactic Centre contains a supermassive black hole with a mass of four million Suns1 within an environment that differs markedly from that of the Galactic disk. Although the black hole is essentially quiescent in the broader context of active galactic nuclei, X-ray observations have provided evidence for energetic outbursts from its surroundings2. Also, although the levels of star formation in the Galactic Centre have been approximately constant over the past few hundred million years, there is evidence of increased short-duration bursts3, strongly influenced by the interaction of the black hole with the enhanced gas density present within the ring-like central molecular zone4 at Galactic longitude |l|\ua0<\ua00.7\ua0degrees and latitude |b|\ua0<\ua00.2\ua0degrees. The inner 200-parsec region is characterized by large amounts of warm molecular gas5, a high cosmic-ray ionization rate6, unusual gas chemistry, enhanced synchrotron emission7,8, and a multitude of radio-emitting magnetized filaments9, the origin of which has not been established. Here we report radio imaging that reveals a bipolar bubble structure, with an overall span of 1\ua0degree by 3\ua0degrees (140\ua0parsecs\ua0 7\ua0430\ua0parsecs), extending above and below the Galactic plane and apparently associated with the Galactic Centre. The structure is edge-brightened and bounded, with symmetry implying creation by an energetic event in the Galactic Centre. We estimate the age of the bubbles to be a few million years, with a total energy of 7\ua0 7\ua01052\ua0ergs. We postulate that the progenitor event was a major contributor to the increased cosmic-ray density in the Galactic Centre, and is in turn the principal source of the relativistic particles required to power the synchrotron emission of the radio filaments within and in the vicinity of the bubble cavities