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1. Supernova neutrino signals based on long-term axisymmetric simulations

   https://doi.org/10.1093/mnras/stab1785  

   Nagakura, Hiroki; Burrows, Adam; Vartanyan, David (July 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We study theoretical neutrino signals from core-collapse supernova (CCSN) computed using axisymmetric CCSN simulations that cover the post-bounce phase up to ∼4 s. We provide basic quantities of the neutrino signals such as event rates, energy spectra, and cumulative number of events at some terrestrial neutrino detectors, and then discuss some new features in the late phase that emerge in our models. Contrary to popular belief, neutrino emissions in the late phase are not always steady, but rather have temporal fluctuations, the vigour of which hinges on the CCSN model and neutrino flavour. We find that such temporal variations are not primarily driven by proto-neutron star convection, but by fallback accretion in exploding models. We assess the detectability of these temporal variations, and find that IceCube is the most promising detector with which to resolve them. We also update fitting formulae first proposed in our previous paper for which the total neutrino energy emitted at the CCSN source is estimated from the cumulative number of events in each detector. This will be a powerful technique with which to analyse real observations, particularly for low-statistics data. 

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2. The 2D metallicity distribution and mixing scales of nearby galaxies

   https://doi.org/10.1093/mnras/stab3082  

   Williams, Thomas G; Kreckel, Kathryn; Belfiore, Francesco; Groves, Brent; Sandstrom, Karin; Santoro, Francesco; Blanc, Guillermo A; Bigiel, Frank; Boquien, Médéric; Chevance, Mélanie; et al (November 2021, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Understanding the spatial distribution of metals within galaxies allows us to study the processes of chemical enrichment and mixing in the interstellar medium. In this work, we map the 2D distribution of metals using a Gaussian Process Regression (GPR) for 19 star-forming galaxies observed with the Very Large Telescope/Multi Unit Spectroscopic Explorer (VLT–MUSE) as a part of the PHANGS–MUSE survey. We find that 12 of our 19 galaxies show significant 2D metallicity variation. Those without significant variations typically have fewer metallicity measurements, indicating this is due to the dearth of $${\rm H\, {\small II}}$$ regions in these galaxies, rather than a lack of higher-order variation. After subtracting a linear radial gradient, we see no enrichment in the spiral arms versus the disc. We measure the 50 per cent correlation scale from the two-point correlation function of these radially subtracted maps, finding it to typically be an order of magnitude smaller than the fitted GPR kernel scale length. We study the dependence of the two-point correlation scale length with a number of global galaxy properties. We find no relationship between the 50 per cent correlation scale and the overall gas turbulence, in tension with existing theoretical models. We also find more actively star-forming galaxies, and earlier type galaxies have a larger 50 per cent correlation scale. The size and stellar mass surface density do not appear to correlate with the 50 per cent correlation scale, indicating that perhaps the evolutionary state of the galaxy and its current star formation activity is the strongest indicator of the homogeneity of the metal distribution. 

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3. Retrieval of energy spectra for all flavours of neutrinos from core-collapse supernova with multiple detectors

   https://doi.org/10.1093/mnras/staa3287  

   Nagakura, Hiroki (November 2020, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We present a new method by which to retrieve energy spectrum for all falvours of neutrinos from core-collapse supernova (CCSN). In the retrieval process, we do not assume any analytic formulas to express the energy spectrum of neutrinos but rather take a direct way of spectrum reconstruction from the observed data; the singular value decomposition algorithm with a newly developed adaptive energy-gridding technique is adopted. We employ three independent reaction channels having different flavour sensitivity to neutrinos. Two reaction channels, inverse beta decay on proton and elastic scattering on electrons, from a water Cherenkov detector such as Super-Kamiokande (SK) and Hyper-Kamiokande (HK), and a charged current reaction channel with Argon from the Deep Underground Neutrino Experiment (DUNE) are adopted. Given neutrino oscillation models, we iteratively search the neutrino energy spectra at the CCSN source until they provide the consistent event counts in the three reaction channels. We test the capability of our method by demonstrating the spectrum retrieval to a theoretical neutrino data computed by our recent three-dimensional CCSN simulation. Although the energy spectrum with either electron-type or electron-type antineutrinos at the CCSN source has relatively large error compared to that of other species, the joint analysis with HK + DUNE or SK + DUNE will provide precise energy spectrum of all flavours of neutrinos at the source. Finally, we discuss perspectives for improvements of our method by using neutrino data of other detectors. 

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4. New constraints on the 12CO(2–1)/(1–0) line ratio across nearby disc galaxies

   https://doi.org/10.1093/mnras/stab859  

   den Brok, J S; Chatzigiannakis, D; Bigiel, F; Puschnig, J; Barnes, A T; Leroy, A K; Jiménez-Donaire, M J; Usero, A; Schinnerer, E; Rosolowsky, E; et al (May 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT Both the CO(2–1) and CO(1–0) lines are used to trace the mass of molecular gas in galaxies. Translating the molecular gas mass estimates between studies using different lines requires a good understanding of the behaviour of the CO(2–1)-to-CO(1–0) ratio, R21. We compare new, high-quality CO(1–0) data from the IRAM 30-m EMIR MultiLine Probe of the ISM Regulating Galaxy Evolution survey to the latest available CO(2–1) maps from HERA CO-Line Extragalactic Survey, Physics at High Angular resolution in Nearby Galaxies-ALMA, and a new IRAM 30-m M51 Large Program. This allows us to measure R21 across the full star-forming disc of nine nearby, massive, star-forming spiral galaxies at 27 arcsec (∼1–2 kpc) resolution. We find an average R21 = 0.64 ± 0.09 when we take the luminosity-weighted mean of all individual galaxies. This result is consistent with the mean ratio for disc galaxies that we derive from single-pointing measurements in the literature, $$R_{\rm 21, lit}~=~0.59^{+0.18}_{-0.09}$$. The ratio shows weak radial variations compared to the point-to-point scatter in the data. In six out of nine targets, the central enhancement in R21 with respect to the galaxy-wide mean is of order of $${\sim}10{-}20{{\ \rm per\ cent}}$$. We estimate an azimuthal scatter of ∼20 per cent in R21 at fixed galactocentric radius but this measurement is limited by our comparatively coarse resolution of 1.5 kpc. We find mild correlations between R21 and carbon monoxide (CO) brightness temperature, infrared (IR) intensity, 70–160 µm ratio, and IR-to-CO ratio. All correlations indicate that R21 increases with gas surface density, star formation rate surface density, and the interstellar radiation field. 

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5. The progenitor of the Vela pulsar

   https://doi.org/10.1093/mnras/stac098  

   Kochanek, C. S. (February 2022, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT With Gaia parallaxes, it is possible to study the stellar populations associated with individual Galactic supernova remnants (SNRs) to estimate the mass of the exploding star. Here, we analyse the luminous stars near the Vela pulsar and SNR to find that its progenitor was probably ($$\mathrel {\raise.3ex\rm{\gt }\lower0.6ex\rm{\sim }}90\rm \,per\,cent$$) low mass (8.1–$$10.3\, {\rm M}_\odot$$). The presence of the O star γ2 Vel a little over 100 pc from Vela is the primary ambiguity, as including it in the analysis volume significantly increases the probability (to 5 per cent) of higher mass ($$\gt 20\, {\rm M}_\odot$$) progenitors. However, to be a high-mass star associated with γ2 Vel’s star cluster at birth, the progenitor would have to be a runaway star from an unbound binary with an unusually high velocity. The primary impediment to analysing large numbers of Galactic SNRs in this manner is the lack of accurate distances. This can likely be solved by searching for absorption lines from the SNR in stars as a function of distance, a method which yielded a distance to Vela in agreement with the direct pulsar parallax. If Vela was a $$10\, {\rm M}_\odot$$ supernova in an external galaxy, the 50-pc search region used in extragalactic studies would contain only $$\simeq 10\rm \,per\,cent$$ of the stars formed in a 50-pc region around the progenitor at birth and $$\simeq 90\rm \,per\,cent$$ of the stars in the search region would have been born elsewhere. 

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