MeerKAT

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JWST detection of heavy neutron capture elements in a compact object merger

Authors:

Andrew Levan, Benjamin Gompertz, Om Sharan Salafia, Mattia Bulla, Eric Burns, Kenta Hotokezaka, Luca Izzo, Gavin Lamb, Daniele Malesani, Samantha Oates, Maria Ravasio, Alicia Rouco Escorial, Benjamin Schneider, Nikhil Sarin, Steve Schulze, Nial Tanvir, Kendall Ackley, Gemma Anderson, Gabriel Brammer, Lise Christensen, Vikram Dhillon, Phil Evans, Michael Fausnaugh, Wen-fai Fong, Andrew Fruchter, Chris Fryer, Johan Fynbo, Nicola Gaspari, Kasper Heintz, Jens Hjorth, Jamie Kennea, Mark Kennedy, Tanmoy Laskar, Giorgos Leloudas, Ilya Mandel, Antonio Martín-Carrillo, Brian Metzger, Matt Nicholl, Anya Nugent, Jesse Palmerio, Giovanna Pugilese, Jillian Rastinejad, Lauren Rhodes, Andrea Rossi, Stephen Smartt, Heloise Stevance, Aaron Tohuvavohu, Alexander van der Horst, Susanna Vergani, Darach Watson, Thomas Barclay, Kornpob Bhirombhakdi, Elme Breedt, Alice Breeveld, Alex Brown, Sergio Campana, Paolo D'Avanzo, Valerio D'Elia, Massimiliano De Pasquale, Martin Dyer, Duncan Galloway, James Garbutt, Matthew Green, Dieter Hartmann, Pall Jakobsson, Paul Kerry, Danial Langeroodi, James Leung, Stuart Littlefair, James Munday, Paul O'Brien, Steven Parsons, Ingrid Pelisoli, Dave Sahman, Ruben Salvaterra, Gianpiero Tagliaferri, Christina Thöne, Antonio de Ugarte Postigo, Boris Sbarufatti, Ashley Chrimes, Danny Steeghs, David Kann
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Large Synoptic Survey Telescope White Paper; The Case for Matching U-band on Deep Drilling Fields

Authors:

BW Holwerda, A Baker, S Blyth, S Kannappan, D Obreschkow, S Ravindranath, E Elson, M Vaccari, S Crawford, M Bershady, N Hathi, N Maddox, R Taylor, MATTHEW Jarvis, J Bridge

Abstract:

U-band observations with the LSST have yet to be fully optimized in cadence. The straw man survey design is a simple coverage of the medium-deep-fast survey. Here we argue that deep coverage of the four deep drilling fields (XMM-LSS, ECDFS, ELAIS-S1 and COSMOS) has a much higher scientific return, given that these are also the target of the Southern Hemisphere's Square Kilometer Array Pathfinder, the MeerKAT specifically, deep radio observations.
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MIGHTEE - HI: The relation between the HI gas in galaxies and the cosmic web

Monthly Notices of the Royal Astronomical Society, Volume 513, Issue 2, pp.2168-2177

Authors:

Tudorache, Madalina N. ; Jarvis, M. J. ; Heywood, I. ; Ponomareva, A. A. ; Maddox, N. ; Frank, B. S. ; Adams, N. J. ; Bowler, R. A. A. ; Whittam, I. H. ; Baes, M. ; Pan, H. ; Rajohnson, S. H. A. ; Sinigaglia, F. ; Spekkens, K.

Abstract:

We study the 3D axis of rotation (3D spin) of 77 H I galaxies from the MIGHTEE-H I Early Science observations, and its relation to the filaments of the cosmic web. For this HI-selected sample, the alignment between the spin axis and the closest filament (|cos ψ|) is higher for galaxies closer to the filaments, with ⟨|cos ψ|⟩ = 0.66 ± 0.04 for galaxies <5 Mpc from their closest filament compared to ⟨|cos ψ|⟩ = 0.37 ± 0.08 for galaxies at 5 < d < 10 Mpc. We find that galaxies with a low HI-to-stellar mass ratio (log10(MHI/M⋆) < 0.11) are more aligned with their closest filaments, with ⟨|cos ψ|⟩ = 0.58 ± 0.04; whilst galaxies with (log10(MHI/M⋆) > 0.11) tend to be mis-aligned, with ⟨|cos ψ|⟩ = 0.44 ± 0.04. We find tentative evidence that the spin axis of HI-selected galaxies tend to be aligned with associated filaments (d < 10 Mpc), but this depends on the gas fractions. Galaxies that have accumulated more stellar mass compared to their gas mass tend towards stronger alignment. Our results suggest that those galaxies that have accrued high gas fraction with respect to their stellar mass may have had their spin axis alignment with the filament disrupted by a recent gas-rich merger, whereas the spin vector for those galaxies in which the neutral gas has not been strongly replenished through a recent merger tend to orientate towards alignment with the filament. We also investigate the spin transition between galaxies with a high HI content and a low HI content at a threshold of MHI≈10^9.5M⊙ found in simulations; however, we find no evidence for such a transition with the current data.
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Radio studies of relativistic outflows from black hole transients

Abstract:

In this thesis I will present observational studies of transient systems that produce mildly to extremely relativistic outflows through a coupling to an accretion flow. I will focus on the analysis of data taken from three source classes: black hole X-ray binaries (BHXRBs; particularly the system MAXI J1820+070), gamma-ray bursts (GRBs; particularly the system GRB 171010A), and tidal disruption events (TDEs; particularly the systems ASASSN-14li and Swift J1644+57).

I will present an extensive radio monitoring campaign on MAXI J1820+070 utilising five different interferometers, along with extensive X-ray observations, during the system's 2018 outburst. Together these data allowed me to probe the coupling between accretion and jet production throughout an entire outburst cycle, as well as during multiple hard accretion state only re-brightenings, tracked over a two year time frame. As MAXI J1820+070 transitioned from the hard to soft accretion state, contemporaneous time-series indicators of the launch of bipolar relativistic ejections were observed at both radio and X-ray frequencies (manifesting as a radio flare and an evolving quasi-period oscillation, respectively). I then confirmed the presence of these ejecta utilising multiple interferometers, and was able to track the evolution of both the approaching and receding ejecta for over ~150 d. Through utilising interferometers sensitive to very different angular scales, I was able to infer the internal energy of the ejection, and found it to be much larger than the value implied from the state transition radio flare. This is strong evidence for ongoing particle acceleration as ejections interact with the surrounding interstellar medium. In addition to the study of MAXI J1820+070, I will also present a broader population study of state transition radio flares from black hole X-ray binaries, and demonstrate that commonly employed models (which attribute flares to an optical depth evolution from an expanding region) are not appropriate for the majority of flares in the sample studied. I describe the ability of extended periods of particle acceleration to explain the flare profiles.

GRB 171010A was a luminous and nearby long GRB detected at early times by the Arcminute Microkelvin Imager Large Array interferometer, as well as with the Swift X-ray telescope. Long GRBs produce highly relativistic outflows that are best studied through their interaction with the circumburst material. This interaction produced a broadband synchrotron afterglow. I present a study of the radio through X-ray afterglow of GRB 171010A in the context of the fireball model (which details the interaction of the jet and interstellar medium). By fitting the time evolving spectra, the values and evolution of the characteristic synchrotron frequencies can be inferred. GRB 171010A is one of the most energetic GRBs detected below z~0.5, allowing for our theoretical understanding of afterglows to be investigated. While I find general agreement with the canonical models (particularly the spectral indices either side of the minimum energy frequency) a number of deviations are seen. I discuss possible solutions to these deviations, which likely include the addition of a second spectral component resulting from a reverse shock.

Finally, I will present late time radio and X-ray observations of the thermal TDE ASASSN-14li, and late time radio only observations of the relativistic TDE Swift J1644+57. Tidal disruption events occur when a star passes too close to a supermassive black hole and is torn apart by tidal forces. Approximately half of the stellar material is accreted and the rest is unbound. ASASSN-14li is a radio bright thermal TDE, and the origin of this radio emission is disputed. I will show that the late time radio properties are now consistent with background AGN activity, but that while the TDE was the dominant radio component, the radio emission was correlated with the X-ray emission. This provides evidence that thermal TDEs produce jets. It is not disputed that the relativistic TDE Swift J1644+57 produced a jet, and said jet's radio emission has now been monitored for ~10 yrs. I will present the most recent monitoring of Swift J1644+57 in the context of previously proposed jet models for the source. I will additionally discuss the up-to-date population of radio loud TDEs.

My conclusions contain a comparison of the outflows produced by these sources, and how they are analysed in different frameworks.

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Revealing new high-redshift quasar populations through Gaussian mixture model selection

Astronomy & Astrophysics, Volume 660, id.A22, 15 pp.

Authors:

J. D. Wagenveld, A. Saxena, K. J. Duncan, H. J. A. Röttgering, M. Zhang

Abstract:

We present a novel method for identifying candidate high-redshift quasars (HzQs; z ≳ 5.5) -which are unique probes of supermassive black hole growth in the early Universe- from large-area optical and infrared photometric surveys. Using Gaussian mixture models to construct likelihoods and incorporating informed priors based on population statistics, our method uses a Bayesian framework to assign posterior probabilities that differentiate between HzQs and contaminating sources. We additionally include deep radio data to obtain informed priors. Using existing HzQ data in the literature, we set a posterior threshold that accepts ∼90% of known HzQs while rejecting > 99% of contaminants such as dwarf stars or lower redshift galaxies. Running the probability selection on test samples of simulated HzQs and contaminants, we find that the efficacy of the probability method is higher than traditional colour cuts, decreasing the fraction of accepted contaminants by 86% while retaining a similar fraction of HzQs. As a test, we apply our method to the Pan-STARRS Data Release 1 (PS1) source catalogue within the HETDEX Spring field area on the sky, covering 400 sq. deg. and coinciding with deep radio data from the LOFAR Two-metre Sky Survey Data Release 1. From an initial sample of ∼5 × 105 sources in PS1, our selection shortlists 251 candidate HzQs, which are further reduced to 63 after visual inspection. Shallow spectroscopic follow-up of 13 high-probability HzQs resulted in the confirmation of a previously undiscovered quasar at z = 5.66 with photometric colours i ‒ z = 1.4, lying outside the typically probed regions when selecting HzQs based on colours. This discovery demonstrates the efficacy of our probabilistic HzQ selection method in selecting more complete HzQ samples, which holds promise when employed on large existing and upcoming photometric data sets.
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