Publications


Transport of high-energy charged particles through spatially-intermittent turbulent magnetic fields

Astrophysical Journal American Astronomical Society 892 (2020) 114

LE Chen, AFA Bott, P Tzeferacos, A Rigby, A Bell, R Bingham, C Graziani, J Katz, R Petrasso, G Gregori, F Miniati

Identifying the sources of the highest energy cosmic rays requires understanding how they are deflected by the stochastic, spatially intermittent intergalactic magnetic field. Here we report measurements of energetic charged-particle propagation through a laser-produced magnetized plasma with these properties. We characterize the diffusive transport of the particles experimentally. The results show that the transport is diffusive and that, for the regime of interest for the highest-energy cosmic rays, the diffusion coefficient is unaffected by the spatial intermittency of the magnetic field.


S2COSMOS: Evolution of Gas Mass with Redshift Using Dust Emission

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2020)

HS Hwang, M Michałowski, A Babul, L Ho, Y Ao, JS Millard, SA Eales, M Smith, J Simpson, H Gomez, K Małek, Y Peng, A Bunker, M Sawicki, R Beeston, Y Toba, N Scoville, H Shim

<jats:title>Abstract</jats:title> <jats:p>We investigate the evolution of the gas mass fraction for galaxies in the COSMOS field using submillimetre emission from dust at 850μm. We use stacking methodologies on the 850 μm S2COSMOS map to derive the gas mass fraction of galaxies out to high redshifts, 0 ≤ z ≤ 5, for galaxies with stellar masses of $10^{9.5} < M_* ~(\rm M_{\odot }) < 10^{11.75}$. In comparison to previous literature studies we extend to higher redshifts, include more normal star-forming galaxies (on the main sequence), and also investigate the evolution of the gas mass fraction split by star-forming and passive galaxy populations. We find our stacking results broadly agree with scaling relations in the literature. We find tentative evidence for a peak in the gas mass fraction of galaxies at around z ∼ 2.5 − 3, just before the peak of the star formation history of the Universe. We find that passive galaxies are particularly devoid of gas, compared to the star-forming population. We find that even at high redshifts, high stellar mass galaxies still contain significant amounts of gas.</jats:p>


Anomalous decay rate of quasinormal modes

PHYSICAL REVIEW D 101 (2020) ARTN 084018

M Lagos, PG Ferreira, OJ Tattersall


Quasi-normal modes of hairy scalar tensor black holes: odd parity

Classical and Quantum Gravity IOP Publishing 37 (2020) 115007

OJ Tattersall

The odd parity gravitational quasi-normal mode spectrum of black holes with non-trivial scalar hair in Horndeski gravity is investigated. We study 'almost' Schwarzschild black holes such that any modifications to the spacetime geometry (including the scalar field profile) are treated as small quantities. A modified Regge–Wheeler style equation for the odd parity gravitational degree of freedom is presented to quadratic order in the scalar hair and spacetime modifications, and a parameterisation of the modified quasi-normal mode spectrum is calculated. In addition, statistical error estimates for the new hairy parameters of the black hole and scalar field are given.


The rest-frame UV luminosity function at z≃4 : a significant contribution of AGN to the bright-end of the galaxy population

Monthly Notices of the Royal Astronomical Society Oxford University Press (2020) staa687

N Adams, R Bowler, M Jarvis, B Haussler, R McLure, A Bunker, J Dunlop, A Verma

We measure the rest-frame UV luminosity function (LF) at z ∼ 4 self-consistently over a wide range in absolute magnitude (−27 . MUV . −20). The LF is measured with 46,904 sources selected using a photometric redshift approach over ∼ 6 deg2 of the combined COSMOS and XMM-LSS fields. We simultaneously fit for both AGN and galaxy LFs using a combination of Schechter or Double Power Law (DPL) functions alongside a single power law for the faint-end slope of the AGN LF. We find a lack of evolution in the shape of the bright-end of the LBG component when compared to other studies at z ' 5 and evolutionary recipes for the UV LF. Regardless of whether the LBG LF is fit with a Schechter function or DPL, AGN are found to dominate at MUV < −23.5. We measure a steep faint-end slope of the AGN LF with αAGN = −2.09+0.35 −0.38 (−1.66+0.29 −0.58) when fit alongside a Schechter function (DPL) for the galaxies. Our results suggest that if AGN are morphologically selected it results in a bias to lower number densities. Only by considering the full galaxy population over the transition region from AGN to LBG domination can an accurate measurement of the total LF be attained.


A Closed-Cycle Miniature Dilution Refrigerator for a Fast-Cooldown 100 mK Detector Wafer Test Cryostat

JOURNAL OF LOW TEMPERATURE PHYSICS 199 (2020) 771-779

S Azzoni, A May, S Chase, G Coppi, L Kenny, S Melhuish, L Piccirillo, A Suzuki, J Wenninger

&#xA9; 2020, The Author(s). The forthcoming generation of cosmic microwave background polarization observatories is developing large format detector arrays which will operate at 100&#xA0;mK. Given the volume of detector wafers that will be required, fast-cooldown 100&#xA0;mK test cryostats are increasingly needed. A miniature dilution refrigerator (MDR) has been developed for this purpose and is reported. The MDR is precooled by a double-stage 3He &#x2013;4He Chase Research Cryogenics sorption refrigerator. The test cryostat based on this MDR will enable fast cooldown to 100&#xA0;mK to support rapid feedback testing of detector wafers fabricated for the Simons Observatory. The MDR has been designed to provide a 100&#xA0;mK stage to be retrocompatible with existing CRC10 sorption coolers, reducing the base temperature from 250&#xA0;mK for the new generation of detectors. Other 250&#xA0;mK cryostats can be retrofitted in the same way. This configuration will meet the cryogenic requirements for single-wafer testing, providing 5&#x2013;10&#xA0;&#x3BC; W of cooling power at 100&#xA0;mk for over 8&#xA0;h. The system operates in a closed cycle, thereby avoiding external gas connections and cold o-rings. No moving parts are required, with the system operated entirely by heaters.


K-CLASH: Strangulation and ram pressure stripping in galaxy cluster members at 0.3 &lt; z &lt; 0.6

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 496 (2020) 3841-3861

SP Vaughan, AL Tiley, RL Davies, LJ Prichard, SM Croom, M Bureau, JP Stott, A Bunker, M Cappellari, B Ansarinejad, MJ Jarvis

<jats:title>ABSTRACT</jats:title> <jats:p>Galaxy clusters have long been theorized to quench the star formation of their members. This study uses integral-field unit observations from the K-band MultiObject Spectrograph (KMOS) – Cluster Lensing And Supernova survey with Hubble (CLASH) survey (K-CLASH) to search for evidence of quenching in massive galaxy clusters at redshifts 0.3 &amp;lt; z &amp;lt; 0.6. We first construct mass-matched samples of exclusively star-forming cluster and field galaxies, then investigate the spatial extent of their H α emission and study their interstellar medium conditions using emission line ratios. The average ratio of H α half-light radius to optical half-light radius ($r_{\mathrm{e}, {\rm {H}\,\alpha }}/r_{\mathrm{e}, R_{\mathrm{c} } }$) for all galaxies is 1.14 ± 0.06, showing that star formation is taking place throughout stellar discs at these redshifts. However, on average, cluster galaxies have a smaller $r_{\mathrm{e}, {\rm {H}\alpha }}/r_{\mathrm{e}, R_{\mathrm{c} } }$ ratio than field galaxies: 〈$r_{\mathrm{e}, {\rm {H}\alpha }}/r_{\mathrm{e}, R_{\mathrm{c} } }$〉 = 0.96 ± 0.09 compared to 1.22 ± 0.08 (smaller at a 98 per cent credibility level). These values are uncorrected for the wavelength difference between H α emission and Rc-band stellar light but implementing such a correction only reinforces our results. We also show that whilst the cluster and field samples follow indistinguishable mass–metallicity (MZ) relations, the residuals around the MZ relation of cluster members correlate with cluster-centric distance; galaxies residing closer to the cluster centre tend to have enhanced metallicities (significant at the 2.6σ level). Finally, in contrast to previous studies, we find no significant differences in electron number density between the cluster and field galaxies. We use simple chemical evolution models to conclude that the effects of disc strangulation and ram-pressure stripping can quantitatively explain our observations.</jats:p>


K-CLASH: spatially-resolving star-forming galaxies in field and cluster environments at z ≈ 0.2-0.6

Monthly Notices of the Royal Astronomical Society Oxford University Press (2020)

AL Tiley, JP Stott, R Davies, LJ Prichard, A Bunker, M Bureau, M Cappellari, M Jarvis, A Robotham, L Cortese, S Bellstedt, B Ansarinejad

We present the KMOS-CLASH (K-CLASH) survey, a K-band Multi-Object Spectrograph (KMOS) survey of the spatially-resolved gas properties and kinematics of 191 (predominantly blue) Hα-detected galaxies at 0.2 ≲ z ≲ 0.6 in field and cluster environments. K-CLASH targets galaxies in four Cluster Lensing And Supernova survey with Hubble (CLASH) fields in the KMOS IZ-band, over 7′ radius (≈2–3 Mpc) fields-of-view. K-CLASH aims to study the transition of star-forming galaxies from turbulent, highly star-forming disc-like and peculiar systems at z ≈ 1–3, to the comparatively quiescent, ordered late-type galaxies at z ≈ 0, and to examine the role of clusters in the build-up of the red sequence since z ≈ 1. In this paper, we describe the K-CLASH survey, present the sample, and provide an overview of the K-CLASH galaxy properties. We demonstrate that our sample comprises star-forming galaxies typical of their stellar masses and epochs, residing both in field and cluster environments. We conclude K-CLASH provides an ideal sample to bridge the gap between existing large integral-field spectroscopy surveys at higher and lower redshifts. We find that star-forming K-CLASH cluster galaxies at intermediate redshifts have systematically lower stellar masses than their star-forming counterparts in the field, hinting at possible “downsizing” scenarios of galaxy growth in clusters at these epochs. We measure no difference between the star-formation rates of Hα-detected, star-forming galaxies in either environment after accounting for stellar mass, suggesting that cluster quenching occurs very rapidly during the epochs probed by K-CLASH, or that star-forming K-CLASH galaxies in clusters have only recently arrived there, with insufficient time elapsed for quenching to have occured.


The C-Band All-Sky Survey (C-BASS): total intensity point source detection over the northern sky

Monthly Notices of the Royal Astronomical Society Oxford University Press (2020) staa1572

R Grumitt, A Taylor, L Jew, ME Jones, C Dickinson, A Barr, R Cepeda-Arroita, H Chiang, S Harper, H Heilgendorff, JL Jonas, JP Leahy, J Leech, TJ Pearson, MW Peel, ACS Readhead, J Sievers

We present a point source detection algorithm that employs the second order Spherical Mexican Hat Wavelet filter (SMHW2), and use it on C-BASS northern intensity data to produce a catalogue of point sources. The SMHW2 allows us to filter the entire sky at once, avoiding complications from edge effects arising when filtering small sky patches. The algorithm is validated against a set of Monte Carlo simulations, consisting of diffuse emission, instrumental noise, and various point source populations. The simulated source populations are successfully recovered. The SMHW2 detection algorithm is used to produce a $4.76\,\mathrm{GHz}$ northern sky source catalogue in total intensity, containing 1729 sources and covering declinations $\delta\geq-10^{\circ}$. The C-BASS catalogue is matched with the GB6 and PMN catalogues over their common declinations. From this we estimate the $90\%$ completeness level to be approximately $630\,\mathrm{mJy}$, with a corresponding reliability of $95\%$, when applying a Galactic mask covering $20\%$ of the sky. We find the C-BASS and GB6/PMN flux density scales to be consistent with one another to within $3\%$. The absolute positional offsets of C-BASS sources from matched GB6/PMN sources peak at approximately $3.5\,\mathrm{arcmin}$.


Formation channels of slowly rotating early-type galaxies

Astronomy and Astrophysics EDP Sciences 635 (2020) A129

D Krajnovic, U Ural, H Kuntschner, P Goudfrooij, M Wolfe, M Cappellari, R Davies, TP de Zeeuw, P-A Duc, E Emsellem, A Karick, RM McDermid, S Mei, T Naab

We study the evidence for a diversity of formation processes in early-type galaxies by presenting the first complete volume-limited sample of slow rotators with both integral-field kinematics from the ATLAS3D Project and high spatial resolution photometry from the Hubble Space Telescope. Analysing the nuclear surface brightness profiles of 12 newly imaged slow rotators, we classify their light profiles as core-less, and place an upper limit to the core size of about 10 pc. Considering the full magnitude and volume-limited ATLAS3D sample, we correlate the presence or lack of cores with stellar kinematics, including the proxy for the stellar angular momentum (λRe) and the velocity dispersion within one half-light radius (σe), stellar mass, stellar age, α-element abundance, and age and metallicity gradients. More than half of the slow rotators have core-less light profiles, and they are all less massive than 1011 M⊙. Core-less slow rotators show evidence for counter-rotating flattened structures, have steeper metallicity gradients, and a larger dispersion of gradient values (Δ[Z/H]¯ = −0.42 ± 0.18) than core slow rotators (Δ[Z/H]¯ = −0.23 ± 0.07). Our results suggest that core and core-less slow rotators have different assembly processes, where the former, as previously discussed, are the relics of massive dissipation-less merging in the presence of central supermassive black holes. Formation processes of core-less slow rotators are consistent with accretion of counter-rotating gas or gas-rich mergers of special orbital configurations, which lower the final net angular momentum of stars, but support star formation. We also highlight core fast rotators as galaxies that share properties of core slow rotators (i.e. cores, ages, σe, and population gradients) and core-less slow rotators (i.e. kinematics, λRe, mass, and larger spread in population gradients). Formation processes similar to those for core-less slow rotators can be invoked to explain the assembly of core fast rotators, with the distinction that these processes form or preserve cores.


Search for PeV Gamma-Ray Emission from the Southern Hemisphere with 5 Years of Data from the IceCube Observatory

The Astrophysical Journal: an international review of astronomy and astronomical physics American Astronomical Society (2020)

H Bagherpour, C Argüelles, J Auffenberg, T Anderson, I Ansseau, P Backes, G Anton, S Axani, X Bai, E Bernardini, DZ Besson, E Blaufuss, D Bindig, S BenZvi, D Berley, JB Tjus, G Binder, S Blot, J Brostean-Kaiser, RS Busse, D Chirkin, A Burgman, J Buscher, T Carver, E Cheung

The measurement of diffuse PeV gamma-ray emission from the Galactic plane would provide information about the energy spectrum and propagation of Galactic cosmic rays, and the detection of a point-like source of PeV gamma rays would be strong evidence for a Galactic source capable of accelerating cosmic rays up to at least a few PeV. This paper presents several un-binned maximum likelihood searches for PeV gamma rays in the Southern Hemisphere using 5 years of data from the IceTop air shower surface detector and the in-ice array of the IceCube Observatory. The combination of both detectors takes advantage of the low muon content and deep shower maximum of gamma-ray air showers, and provides excellent sensitivity to gamma rays between $\sim$0.6 PeV and 100 PeV. Our measurements of point-like and diffuse Galactic emission of PeV gamma rays are consistent with background, so we constrain the angle-integrated diffuse gamma-ray flux from the Galactic Plane at 2 PeV to $2.61 \times 10^{-19}$ cm$^{-2}$ s$^{-1}$ TeV$^{-1}$ at 90% confidence, assuming an E$^{-3}$ spectrum, and we estimate 90% upper limits on point-like emission at 2 PeV between 10$^{-21}$ - 10$^{-20}$ cm$^{-2}$ s$^{-1}$ TeV$^{-1}$ for an E$^{-2}$ spectrum, depending on declination. Furthermore, we exclude unbroken power-law emission up to 2 PeV for several TeV gamma-ray sources observed by H.E.S.S., and calculate upper limits on the energy cutoffs of these sources at 90% confidence. We also find no PeV gamma rays correlated with neutrinos from IceCube's high-energy starting event sample. These are currently the strongest constraints on PeV gamma-ray emission.


QUBIC: The Q & U Bolometric Interferometer for Cosmology

Journal of Low Temperature Physics Springer Science and Business Media LLC 199 (2020) 482-490

E Battistelli, P Ade, J Alberro, A Almela, G Amico, L Arnaldi, D Auguste, J Aumont, S Azzoni, S Banfi, P Battaglia, A Baù, B Bélier, D Bennett, L Bergé, J-P Bernard, M Bersanelli, M-A Bigot-Sazy, N Bleurvacq, J Bonaparte, J Bonis, A Bottani, E Bunn, D Burke, F Cavaliere


Parametric Amplification at Ka Band via Nonlinear Dynamics in Superconducting 3D Cavities

Journal of Low Temperature Physics Springer Science and Business Media LLC (2020)

D Banys, M McCulloch, S Azzoni, B Cooper, A May, S Melhuish, L Piccirillo, J Wenninger


QUBIC: Using NbSi TESs with a Bolometric Interferometer to Characterize the Polarization of the CMB

Journal of Low Temperature Physics Springer Science and Business Media LLC (2020)

M Piat, B Bélier, L Bergé, N Bleurvacq, C Chapron, S Dheilly, L Dumoulin, M González, L Grandsire, J-C Hamilton, S Henrot-Versillé, D Hoang, S Marnieros, W Marty, J Aumont, S Azzoni, S Banfi, J Bonaparte, J Bonis, A Bottani, E Bunn, D Burke, A Buzzelli, F Cavaliere, P Chanial


Updated Design of the CMB Polarization Experiment Satellite LiteBIRD

JOURNAL OF LOW TEMPERATURE PHYSICS 199 (2020) 1107-1117

H Sugai, PAR Ade, Y Akiba, D Alonso, K Arnold, J Aumont, J Austermann, C Baccigalupi, AJ Banday, R Banerji, RB Barreiro, S Basak, J Beall, S Beckman, M Bersanelli, J Borrill, F Boulanger, ML Brown, M Bucher, A Buzzelli, E Calabrese, FJ Casas, A Challinor, V Chan, Y Chinone, J-F Cliche, F Columbro, A Cukierman, D Curtis, P Danto, P de Bernardis, T de Haan, M De Petris, C Dickinson, M Dobbs, T Dotani, L Duband, A Ducout, S Duff, A Duivenvoorden, J-M Duval, K Ebisawa, T Elleflot, H Enokida, HK Eriksen, J Errard, T Essinger-Hileman, F Finelli, R Flauger, C Franceschet, U Fuskeland, K Ganga, J-R Gao, R Genova-Santos, T Ghigna, A Gomez, ML Gradziel, J Grain, F Grupp, A Gruppuso, JE Gudmundsson, NW Halverson, P Hargrave, T Hasebe, M Hasegawa, M Hattori, M Hazumi, S Henrot-Versille, D Herranz, C Hill, G Hilton, Y Hirota, E Hivon, R Hlozek, D-T Hoang, J Hubmayr, K Ichiki, T Iida, H Imada, K Ishimura, H Ishino, GC Jaehnig, M Jones, T Kaga, S Kashima, Y Kataoka, N Katayama, T Kawasaki, R Keskitalo, A Kibayashi, T Kikuchi, K Kimura, T Kisner, Y Kobayashi, N Kogiso, A Kogut, K Kohri, E Komatsu, K Komatsu, K Konishi, N Krachmalnicoff, CL Kuo, N Kurinsky, A Kushino, M Kuwata-Gonokami, L Lamagna, M Lattanzi, AT Lee, E Linder, B Maffei, D Maino, M Maki, A Mangilli, E Martinez-Gonzalez, S Masi, R Mathon, T Matsumura, A Mennella, M Migliaccio, Y Minami, K Mistuda, D Molinari, L Montier, G Morgante, B Mot, Y Murata, JA Murphy, M Nagai, R Nagata, S Nakamura, T Namikawa, P Natoli, S Nerval, T Nishibori, H Nishino, Y Nomura, F Noviello, C O'Sullivan, H Ochi, H Ogawa, H Ogawa, H Ohsaki, I Ohta, N Okada, N Okada, L Pagano, A Paiella, D Paoletti, G Patanchon, F Piacentini, G Pisano, G Polenta, D Poletti, T Prouve, G Puglisi, D Rambaud, C Raum, S Realini, M Remazeilles, G Roudil, JA Rubino-Martin, M Russell, H Sakurai, Y Sakurai, M Sandri, G Savini, D Scott, Y Sekimoto, BD Sherwin, K Shinozaki, M Shiraishi, P Shirron, G Signorelli, G Smecher, P Spizzi, SL Stever, R Stompor, S Sugiyama, A Suzuki, J Suzuki, E Switzer, R Takaku, H Takakura, S Takakura, Y Takeda, A Taylor, E Taylor, Y Terao, KL Thompson, B Thorne, M Tomasi, H Tomida, N Trappe, M Tristram, M Tsuji, M Tsujimoto, C Tucker, J Ullom, S Uozumi, S Utsunomiya, J Van Lanen, G Vermeulen, P Vielva, F Villa, M Vissers, N Vittorio, F Voisin, I Walker, N Watanabe, I Wehus, J Weller, B Westbrook, B Winter, E Wollack, R Yamamoto, NY Yamasaki, M Yanagisawa, T Yoshida, J Yumoto, M Zannoni, A Zonca


Kinematic unrest of low mass galaxy groups

Astronomy and Astrophysics EDP Sciences 635 (2020) A36

J Devriendt, G Gozaliasl, A Finoguenov, HG Khosroshahi, C Laigle, CC Kirkpatrick, K Kiiveri, Y Dubois, J Ahoranta

In an effort to better understand the formation of galaxy groups, we examine the kinematics of a large sample of spectroscopically confirmed X-ray galaxy groups in the Cosmic Evolution Survey (COSMOS) with a high sampling of galaxy group members up to $z=1$. We compare our results with predictions from the cosmological hydrodynamical simulation of {\sc Horizon-AGN}. Using a phase-space analysis of dynamics of groups with halo masses of $M_{\mathrm{200c}}\sim 10^{12.6}-10^{14.50}M_\odot$, we show that the brightest group galaxies (BGG) in low mass galaxy groups ($M_{\mathrm{200c}}&lt;2 \times 10^{13} M_\odot$) have larger proper motions relative to the group velocity dispersion than high mass groups. The dispersion in the ratio of the BGG proper velocity to the velocity dispersion of the group, $\sigma_{\mathrm{BGG}}/\sigma_{group}$, is on average $1.48 \pm 0.13$ for low mass groups and $1.01 \pm 0.09$ for high mass groups. A comparative analysis of the {\sc Horizon-AGN} simulation reveals a similar increase in the spread of peculiar velocities of BGGs with decreasing group mass, though consistency in the amplitude, shape, and mode of the BGG peculiar velocity distribution is only achieved for high mass groups. The groups hosting a BGG with a large peculiar velocity are more likely to be offset from the $L_x-\sigma_{v}$ relation; this is probably because the peculiar motion of the BGG is influenced by the accretion of new members.


Resolved observations at 31 GHz of spinning dust emissivity variations in rho Oph

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 495 (2020) 3482-3493

C Arce-Tord, M Vidal, S Casassus, M Carcamo, C Dickinson, BS Hensley, R Genova-Santos, JR Bond, ME Jones, ACS Readhead, AC Taylor, JA Zensus


A flexible method for estimating luminosity functions via kernel density estimation

Astrophysical Journal Supplement American Astronomical Society 248 (2020)

Z Yuan, MJ Jarvis, J Wang

We propose a flexible method for estimating luminosity functions (LFs) based on kernel density estimation (KDE), the most popular nonparametric density estimation approach developed in modern statistics, to overcome issues surrounding the binning of LFs. One challenge in applying KDE to LFs is how to treat the boundary bias problem, as astronomical surveys usually obtain truncated samples predominantly due to the flux-density limits of surveys. We use two solutions, the transformation KDE method ( ) and the transformation–reflection KDE method ( ) to reduce the boundary bias. We develop a new likelihood cross-validation criterion for selecting optimal bandwidths, based on which the posterior probability distribution of the bandwidth and transformation parameters for and are derived within a Markov Chain Monte Carlo sampling procedure. The simulation result shows that and perform better than the traditional binning method, especially in the sparse data regime around the flux limit of a survey or at the bright end of the LF. To further improve the performance of our KDE methods, we develop the transformation–reflection adaptive KDE approach ( ). Monte Carlo simulations suggest that it has good stability and reliability in performance, and is around an order of magnitude more accurate than using the binning method. By applying our adaptive KDE method to a quasar sample, we find that it achieves estimates comparable to the rigorous determination in a previous work, while making far fewer assumptions about the LF. The KDE method we develop has the advantages of both parametric and nonparametric methods.


The Karl G. Jansky very large array sky survey (VLASS). Science case and survey design

Publications of the Astronomical Society of the Pacific 132 (2020)

M Lacy, SA Baum, CJ Chandler, S Chatterjee, TE Clarke, S Deustua, J English, J Farnes, BM Gaensler, N Gugliucci, G Hallinan, BR Kent, A Kimball, CJ Law, TJW Lazio, J Marvil, SA Mao, D Medlin, K Mooley, EJ Murphy, S Myers, R Osten, GT Richards, E Rosolowsky, L Rudnick

© 2020. The Astronomical Society of the Pacific. The Very Large Array Sky Survey (VLASS) is a synoptic, all-sky radio sky survey with a unique combination of high angular resolution (≈2.″5), sensitivity (a 1σ goal of 70 μJy/beam in the coadded data), full linear Stokes polarimetry, time domain coverage, and wide bandwidth (2–4 GHz). The first observations began in 2017 September, and observing for the survey will finish in 2024. VLASS will use approximately 5500 hr of time on the Karl G. Jansky Very Large Array (VLA) to cover the whole sky visible to the VLA (decl. &gt; −40°), a total of 33 885 deg2. The data will be taken in three epochs to allow the discovery of variable and transient radio sources. The survey is designed to engage radio astronomy experts, multi-wavelength astronomers, and citizen scientists alike. By utilizing an “on the fly” interferometry mode, the observing overheads are much reduced compared to a conventional pointed survey. In this paper, we present the science case and observational strategy for the survey, and also results from early survey observations.


Reionization history constraints from neural network based predictions of high-redshift quasar continua

Monthly Notices of the Royal Astronomical Society Oxford University Press 493 (2020) 4256–4275-

D Ďurovčíková, H Katz, SEI Bosman, FB Davies, J Devriendt, A Slyz

Observations of the early Universe suggest that reionization was complete by z ∼ 6, however, the exact history of this process is still unknown. One method for measuring the evolution of the neutral fraction throughout this epoch is via observing the Lyα damping wings of high-redshift quasars. In order to constrain the neutral fraction from quasar observations, one needs an accurate model of the quasar spectrum around Lyα, after the spectrum has been processed by its host galaxy but before it is altered by absorption and damping in the intervening IGM. In this paper, we present a novel machine learning approach, using artificial neural networks, to reconstruct quasar continua around Lyα. Our QSANNDRA algorithm improves the error in this reconstruction compared to the state-of-the-art PCA-based model in the literature by 14.2% on average, and provides an improvement of 6.1% on average when compared to an extension thereof. In comparison with the extended PCA model, QSANNDRA further achieves an improvement of 22.1% and 16.8% when evaluated on low-redshift quasars most similar to the two high-redshift quasars under consideration, ULAS J1120+0641 at z = 7.0851 and ULAS J1342+0928 at z = 7.5413, respectively. Using our more accurate reconstructions of these two z > 7 quasars, we estimate the neutral fraction of the IGM using a homogeneous reionization model and find x¯H1=0.25+0.05−0.05 at z = 7.0851 and x¯H1=0.60+0.11−0.11 at z = 7.5413. Our results are consistent with the literature and favour a rapid end to reionization.

Pages