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1. Deep uGMRT observations of the ELAIS-North 1 field: statistical properties of radio–infrared relations up to z ∼ 2

   https://doi.org/10.1093/mnras/stac1504  

   Sinha, Akriti ; Basu, Aritra ; Datta, Abhirup ; Chakraborty, Arnab ( June 2022 , Monthly Notices of the Royal Astronomical Society)

   Comprehending the radio–infrared (IR) relations of the faint extragalactic radio sources is important for using radio emission as a tracer of star formation in high redshift (z) star-forming galaxies (SFGs). Using deep uGMRT observations of the ELAIS-N1 field in the 0.3–0.5 GHz range, we study the statistical properties of the radio–IR relations and the variation of the ‘q-parameter’ up to z = 2 after broadly classifying the faint sources as SFGs and AGN. We find the dust temperature (Tdust) to increase with z. This gives rise to $q_{\rm 24\,\mu m}$, measured at $24\, \mu$m, to increase with z as the peak of IR emission shifts towards shorter wavelengths, resulting in the largest scatter among different measures of q-parameters. $q_{\rm 70\,\mu m}$ measured at $70\, \mu$m, and qTIR using total-IR (TIR) emission are largely unaffected by Tdust. We observe strong, non-linear correlations between the radio luminosities at 0.4 and 1.4 GHz with $70\, \mu$m luminosity and TIR luminosity(LTIR). To assess the possible role of the radio-continuum spectrum in making the relations non-linear, for the first time we study them at high z using integrated radio luminosity (LRC) in the range 0.1–2 GHz. In SFGs, the LRC–LTIR relation remains non-linear with a slope of 1.07 ± 0.02,more »has a factor of 2 lower scatter compared to monochromatic radio luminosities, and $q^{\rm RC}_{\rm TIR}$ decreases with z as $q^{\rm RC}_{\rm TIR}= (2.27 \pm 0.03)\, (1+z)^{-0.12 \pm 0.03}$. A redshift variation of q is a natural consequence of non-linearity. We suggest that a redshift evolution of magnetic field strengths and/or cosmic ray acceleration efficiency in high-z SFGs could give rise to non-linear radio–IR relations.

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2. SuperCLASS – II. Photometric redshifts and characteristics of spatially resolved μJy radio sources

   https://doi.org/10.1093/mnras/staa657  

   Manning, Sinclaire M ; Casey, Caitlin M ; Hung, Chao-Ling ; Battye, Richard ; Brown, Michael L ; Jackson, Neal ; Abdalla, Filipe ; Chapman, Scott ; Demetroullas, Constantinos ; Drew, Patrick ; et al ( June 2020 , Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We present optical and near-infrared imaging covering a ∼1.53 deg2 region in the Super-Cluster Assisted Shear Survey (SuperCLASS) field, which aims to make the first robust weak lensing measurement at radio wavelengths. We derive photometric redshifts for ≈176 000 sources down to $i^\prime _{\rm AB}\sim 24$ and present photometric redshifts for 1.4 GHz expanded Multi-Element Radio Linked Interferometer Network (e-MERLIN) and Karl G. Jansky Very Large Array (VLA) detected radio sources found in the central 0.26 deg2. We compile an initial catalogue of 149 radio sources brighter than S1.4 > 75 μJy and find their photometric redshifts span 0 < zphot < 4 with radio luminosities between 1021 and 1025 W Hz−1, with medians of $\langle z \rangle \, =0.55$ and $\langle L_{1.4}\rangle \, =1.9\times 10^{23}$ W Hz−1, respectively. We find 95 per cent of the μJy radio source sample (141/149) have spectral energy distributions (SEDs) best fit by star-forming templates while 5 per cent (8/149) are better fit by active galactic nuclei (AGN). Spectral indices are calculated for sources with radio observations from the VLA and Giant Metrewave Radio Telescope (GMRT) at 325 MHz, with an average spectral slope of α = 0.59 ± 0.04. Using the full photometric redshift catalogue, we construct a density map at the redshift of the known galaxy clusters,more »z = 0.20 ± 0.08. Four of the five clusters are prominently detected at $\gt 7\, \sigma$ in the density map and we confirm the photometric redshifts are consistent with previously measured spectra from a few galaxies at the cluster centres.« less
3. 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 sourcesmore »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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4. Radio Scattering Horizons for Galactic and Extragalactic Transients

   https://doi.org/10.3847/1538-4357/ac75ba  

   Ocker, Stella Koch ; Cordes, James M. ; Chatterjee, Shami ; Gorsuch, Miranda R. ( July 2022 , The Astrophysical Journal)

   Radio wave scattering can cause severe reductions in detection sensitivity for surveys of Galactic and extragalactic fast (∼ms duration) transients. While Galactic sources like pulsars undergo scattering in the Milky Way interstellar medium (ISM), extragalactic fast radio bursts (FRBs) can also experience scattering in their host galaxies and other galaxies intervening in their lines of sight. We assess Galactic and extragalactic scattering horizons for fast radio transients using a combination of NE2001 to model the dispersion measure and scattering time (τ) contributed by the Galactic disk, and independently constructed electron density models for the Galactic halo and other galaxies’ ISMs and halos that account for different galaxy morphologies, masses, densities, and strengths of turbulence. For source redshifts 0.5 ≤z_s≤ 1, an all-sky, isotropic FRB population has simulated values ofτ(1 GHz) ranging from ∼1μs to ∼2 ms (90% confidence, observer frame) that are dominated by host galaxies, althoughτcan be ≫2 ms at low Galactic latitudes. A population atz_s= 5 has 0.01 ≲τ≲ 300 ms at 1 GHz (90% confidence), dominated by intervening galaxies. About 20% of these high-redshift FRBs are predicted to haveτ> 5 ms at 1 GHz (observer frame), and ≳40% of FRBs betweenz_s∼ 0.5–5 haveτ≳ 1 ms forν≤more »800 MHz. Our scattering predictions may be conservative if scattering from circumsource environments is significant, which is possible under specific conditions. The percentage of FRBs selected against from scattering could also be substantially larger than we predict if circumgalactic turbulence causes more small-scale (≪1 au) density fluctuations than observed from nearby halos.

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5. The ALPINE-ALMA [CII] survey: The nature, luminosity function, and star formation history of dusty galaxies up to z  ≃ 6

   https://doi.org/10.1051/0004-6361/202038487  

   Gruppioni, C. ; Béthermin, M. ; Loiacono, F. ; Le Fèvre, O. ; Capak, P. ; Cassata, P. ; Faisst, A. L. ; Schaerer, D. ; Silverman, J. ; Yan, L. ; et al ( November 2020 , Astronomy & Astrophysics)

   Aims. We present the detailed characterisation of a sample of 56 sources serendipitously detected in ALMA band 7 as part of the ALMA Large Program to INvestigate CII at Early Times (ALPINE). These sources, detected in COSMOS and ECDFS, have been used to derive the total infrared luminosity function (LF) and to estimate the cosmic star formation rate density (SFRD) up to z  ≃ 6. Methods. We looked for counterparts of the ALMA sources in all the available multi-wavelength (from HST to VLA) and photometric redshift catalogues. We also made use of deeper UltraVISTA and Spitzer source lists and maps to identify optically dark sources with no matches in the public catalogues. We used the sources with estimated redshifts to derive the 250 μ m rest-frame and total infrared (8–1000 μ m) LFs from z  ≃ 0.5 to 6. Results. Our ALMA blind survey (860 μ m flux density range: ∼0.3–12.5 mJy) allows us to further push the study of the nature and evolution of dusty galaxies at high- z , identifying luminous and massive sources to redshifts and faint luminosities never probed before by any far-infrared surveys. The ALPINE data are the first ones to sample the faint end of themore »infrared LF, showing little evolution from z  ≃ 2.5 to z ≃ 6, and a “flat” slope up to the highest redshifts (i.e. 4.5 <   z  <  6). The SFRD obtained by integrating the luminosity function remains almost constant between z  ≃ 2 and z  ≃ 6, and significantly higher than the optical or ultra-violet derivations, showing a significant contribution of dusty galaxies and obscured star formation at high- z . About 14% of all the ALPINE serendipitous continuum sources are found to be optically and near-infrared (near-IR) dark (to a depth K s  ∼ 24.9 mag). Six show a counterpart only in the mid-IR and no HST or near-IR identification, while two are detected as [C II] emitters at z  ≃ 5. The six HST+near-IR dark galaxies with mid-IR counterparts are found to contribute about 17% of the total SFRD at z  ≃ 5 and to dominate the high-mass end of the stellar mass function at z  >  3.« less