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1. Structural and spectral properties of Galactic plane variable radio sources

   https://doi.org/10.1093/mnras/stab3804  

   Yang, Jun ; Chen, Yongjun ; Gurvits, Leonid I. ; Paragi, Zsolt ; Yang, Aiyuan ; Yang, Xiaolong ; Shen, Zhiqiang ( January 2022 , Monthly Notices of the Royal Astronomical Society)

   In the time domain, the radio sky in particular along the Galactic plane direction may vary significantly because of various energetic activities associated with stars, stellar, and supermassive black holes. Multi-epoch Very Large Array surveys of the Galactic plane at 5.0 GHz enabled the finding of a catalogue of 39 variable radio sources in the flux density range 1–70 mJy. To probe their radio structures and spectra, we observed 17 sources with the very-long-baseline interferometric (VLBI) imaging technique and collected additional multifrequency data from the literature. We detected all of the sources at 5 GHz with the Westerbork Synthesis Radio Telescope, but only G23.6644–0.0372 with the European VLBI Network (EVN). Together with its decadal variability and multifrequency radio spectrum, we interpret it as an extragalactic peaked-spectrum source with a size of ≲10 pc. The remaining sources were resolved out by the long baselines of the EVN because of either strong scatter broadening at the Galactic latitude < 1° or intrinsically very extended structures on centi-arcsec scales. According to their spectral and structural properties, we find that the sample has a diverse nature. We notice two young H ii regions and spot a radio star and a candidate planetary nebula. The rest of the sources are very likely associated with radio active galactic nuclei (AGNs). Two of them also display arcsec-scale faint jet activity. The sample study indicates that AGNs are common place even among variable radio sources in the Galactic plane.

    

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2. A global view on star formation: The GLOSTAR Galactic plane survey: IV. Radio continuum detections of young stellar objects in the Galactic Centre region

   https://doi.org/10.1051/0004-6361/202140802  

   Nguyen, H. ; Rugel, M. R. ; Menten, K. M. ; Brunthaler, A. ; Dzib, S. A. ; Yang, A. Y. ; Kauffmann, J. ; Pillai, T. G. ; Nandakumar, G. ; Schultheis, M. ; et al ( July 2021 , Astronomy & Astrophysics)

   Context. The Central Molecular Zone (CMZ), a ∼200 pc sized region around the Galactic Centre, is peculiar in that it shows a star formation rate (SFR) that is suppressed with respect to the available dense gas. To study the SFR in the CMZ, young stellar objects (YSOs) can be investigated. Here we present radio observations of 334 2.2 μm infrared sources that have been identified as YSO candidates. Aims: Our goal is to investigate the presence of centimetre wavelength radio continuum counterparts to this sample of YSO candidates which we use to constrain the current SFR in the CMZ. Methods: As part of the GLObal view on STAR formation (GLOSTAR) survey, D-configuration Very Large Array data were obtained for the Galactic Centre, covering −2° < l < 2° and −1° < b < 1° with a frequency coverage of 4-8 GHz. We matched YSOs with radio continuum sources based on selection criteria and classified these radio sources as potential H II regions and determined their physical properties. Results: Of the 334 YSO candidates, we found 35 with radio continuum counterparts. We find that 94 YSOs are associated with dense dust condensations identified in the 870 μm ATLASGAL survey, of which 14 have a GLOSTAR counterpart. Of the 35 YSOs with radio counterparts, 11 are confirmed as H II regions based on their spectral indices and the literature. We estimated their Lyman continuum photon flux in order to estimate the mass of the ionising star. Combining these with known sources, the present-day SFR in the CMZ is calculated to be ∼0.068 M⊙ yr−1, which is ∼6.8% of the Galactic SFR. Candidate YSOs that lack radio counterparts may not have yet evolved to the stage of exhibiting an H II region or, conversely, are older and have dispersed their natal clouds. Since many lack dust emission, the latter is more likely. Our SFR estimate in the CMZ is in agreement with previous estimates in the literature. 

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3. The SARAO MeerKAT 1.3 GHz Galactic Plane Survey

   https://doi.org/10.1093/mnras/stae1166  

   Goedhart, S. ; Cotton, W. D. ; Camilo, F. ; Thompson, M. A. ; Umana, G. ; Bietenholz, M. ; Woudt, P. A. ; Anderson, L. D. ; Bordiu, C. ; Buckley, D. A. H. ; et al ( May 2024 , Monthly Notices of the Royal Astronomical Society)

   We present the SARAO MeerKAT Galactic Plane Survey (SMGPS), a 1.3 GHz continuum survey of almost half of the Galactic Plane (251° ≤l ≤ 358° and 2° ≤l ≤ 61° at |b| ≤ $1{_{.}^{\circ}}5$). SMGPS is the largest, most sensitive, and highest angular resolution 1 GHz survey of the plane yet carried out, with an angular resolution of 8 arcsec and a broad-band root-mean-square sensitivity of ∼10–20 μJy beam−1. Here, we describe the first publicly available data release from SMGPS which comprises data cubes of frequency-resolved images over 908–1656 MHz, power-law fits to the images, and broad-band zeroth moment integrated intensity images. A thorough assessment of the data quality and guidance for future usage of the data products are given. Finally, we discuss the tremendous potential of SMGPS by showcasing highlights of the Galactic and extragalactic science that it permits. These highlights include the discovery of a new population of non-thermal radio filaments; identification of new candidate supernova remnants, pulsar wind nebulae and planetary nebulae; improved radio/mid-infrared classification of rare luminous blue variables and discovery of associated extended radio nebulae; new radio stars identified by Bayesian cross-matching techniques; the realization that many of the largest radio-quiet Wide-field Infrared Survey Explorer (WISE) H ii region candidates are not true H ii regions; and a large sample of previously undiscovered background H i galaxies in the Zone of Avoidance.

    

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4. The MPIfR–MeerKAT Galactic Plane Survey – I. System set-up and early results

   https://doi.org/10.1093/mnras/stad1900  

   Padmanabh, P. V. ; Barr, E. D. ; Sridhar, S. S. ; Rugel, M. R. ; Damas-Segovia, A. ; Jacob, A. M. ; Balakrishnan, V. ; Berezina, M. ; Bernadich, M. C. ; Brunthaler, A. ; et al ( June 2023 , Monthly Notices of the Royal Astronomical Society)

   Galactic plane radio surveys play a key role in improving our understanding of a wide range of astrophysical phenomena. Performing such a survey using the latest interferometric telescopes produces large data rates necessitating a shift towards fully or quasi-real-time data analysis with data being stored for only the time required to process them. We present here the overview and set-up for the 3000-h Max-Planck-Institut für Radioastronomie (MPIfR)–MeerKAT Galactic Plane Survey (MMGPS). The survey is unique by operating in a commensal mode, addressing key science objectives of the survey including the discovery of new pulsars and transients and studies of Galactic magnetism, the interstellar medium and star formation rates. We explain the strategy coupled with the necessary hardware and software infrastructure needed for data reduction in the imaging, spectral, and time domains. We have so far discovered 78 new pulsars including 17 confirmed binary systems of which two are potential double neutron star systems. We have also developed an imaging pipeline sensitive to the order of a few tens of micro-Jansky ($\mu{\rm Jy}$) with a spatial resolution of a few arcseconds. Further science operations with an in-house built S-band receiver operating between 1.7 and 3.5 GHz are about to commence. Early spectral line commissioning observations conducted at S-band, targeting transitions of the key molecular gas tracer CH at 3.3 GHz already illustrate the spectroscopic capabilities of this instrument. These results lay a strong foundation for future surveys with telescopes like the Square Kilometre Array (SKA).

    

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5. Intermediate-mass black holes and the Fundamental Plane of black hole accretion

   https://doi.org/10.1093/mnras/stac2608  

   Gültekin, Kayhan ; Nyland, Kristina ; Gray, Nichole ; Fehmer, Greg ; Huang, Tianchi ; Sparkman, Matthew ; Reines, Amy E. ; Greene, Jenny E. ; Cackett, Edward M. ; Baldassare, Vivienne ( September 2022 , Monthly Notices of the Royal Astronomical Society)

   We present new 5 GHz Very Large Array observations of a sample of eight active intermediate-mass black holes with masses 104.9 M⊙ < M < 106.1 M⊙ found in galaxies with stellar masses M* < 3 × 109 M⊙. We detected five of the eight sources at high significance. Of the detections, four were consistent with a point source, and one (SDSS J095418.15+471725.1, with black hole mass M < 105 M⊙) clearly shows extended emission that has a jet morphology. Combining our new radio data with the black hole masses and literature X-ray measurements, we put the sources on the Fundamental Plane of black hole accretion. We find that the extent to which the sources agree with the Fundamental Plane depends on their star-forming/composite/active galactic nucleus (AGN) classification based on optical narrow emission-line ratios. The single star-forming source is inconsistent with the Fundamental Plane. The three composite sources are consistent, and three of the four AGN sources are inconsistent with the Fundamental Plane. We argue that this inconsistency is genuine and not a result of misattributing star formation to black hole activity. Instead, we identify the sources in our sample that have AGN-like optical emission-line ratios as not following the Fundamental Plane and thus caution the use of the Fundamental Plane to estimate masses without additional constraints, such as radio spectral index, radiative efficiency, or the Eddington fraction.

    

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