Publications

Measurement of azimuthal anisotropy of muons from charm and bottom hadrons in pp collisions at sqrt[s]=13  TeV with the ATLAS Detector

Physical Review Letters American Physical Society 124 (2020) 82301

G Aad, B Abbott, D Abbott, A Abed Abud, D Abhayasinghe, O AbouZeid, N Abraham, H Abramowicz, Y Abulaiti, B Acharya, S Adachi, C Adam Bourdarios, L Adamczyk, A Affolder, X Ai, G Aielli, E Akilli, G Alberghi, M Aleksa, I Aleksandrov, C Alexa, D Alexandre, T Alexopoulos

The elliptic flow of muons from the decay of charm and bottom hadrons is measured in pp collisions at sqrt[s]=13  TeV using a data sample with an integrated luminosity of 150  pb^{-1} recorded by the ATLAS detector at the LHC. The muons from heavy-flavor decay are separated from light-hadron decay muons using momentum imbalance between the tracking and muon spectrometers. The heavy-flavor decay muons are further separated into those from charm decay and those from bottom decay using the distance-of-closest-approach to the collision vertex. The measurement is performed for muons in the transverse momentum range 4-7 GeV and pseudorapidity range |η|&lt;2.4. A significant nonzero elliptic anisotropy coefficient v_{2} is observed for muons from charm decays, while the v_{2} value for muons from bottom decays is consistent with zero within uncertainties.

The faint radio source population at 15.7 GHz – IV. The dominance of core emission in faint radio galaxies

Monthly Notices of the Royal Astronomical Society Oxford University Press 493 (2020) 2841-2853

I Whittam, DA Green, M Jarvis, JM Riley

We present 15-GHz Karl G. Jansky Very Large Array observations of a complete sample of radio galaxies selected at 15.7 GHz from the Tenth Cambridge (10C) survey. 67 out of the 95 sources (71 per cent) are unresolved in the new observations and lower frequency radio observations, placing an upper limit on their angular size of ∼2 arcsec. Thus, compact radio galaxies, or radio galaxies with very faint jets, are the dominant population in the 10C survey. This provides support for the suggestion in our previous work that low-luminosity (⁠L<1025W~Hz−1⁠) radio galaxies are core dominated, although higher resolution observations are required to confirm this directly. The 10C sample of compact, high-frequency selected radio galaxies is a mixture of high-excitation and low-excitation radio galaxies and displays a range of radio spectral shapes, demonstrating that they are a mixed population of objects.

Limits on absorption from a 332-MHz survey for fast radio bursts

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 493 (2020) 4418-4427

KM Rajwade, MB Mickaliger, BW Stappers, CG Bassa, RP Breton, A Karastergiou, EF Keane

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

&lt;jats:title&gt;Abstract&lt;/jats:title&gt; &lt;jats:p&gt;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 $10^{9.5} &amp;amp;lt; M_* ~(\rm M_{\odot }) &amp;amp;lt; 10^{11.75}$. 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.&lt;/jats:p&gt;

Search for chargino-neutralino production with mass splittings near the electroweak scale in three-lepton final states in root s=13 TeV pp collisions with the ATLAS detector

PHYSICAL REVIEW D 101 (2020) ARTN 072001

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.

Measurement of the relative response of small-electrode CMOS sensors at Diamond Light Source

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 956 (2020) ARTN 163381

M Mironova, K Metodiev, P Allport, I Berdalovic, D Bortoletto, C Buttar, R Cardella, V Dao, M Dyndal, P Freeman, LFS de Acedo, L Gonella, T Kugathasan, H Pernegger, F Piro, R Plackett, P Riedler, A Sharma, EJ Schioppa, I Shipsey, CS Sanchez, W Snoeys, H Wennlof, D Weatherill, D Wood, S Worm

A lack of evolution in the very bright-end of the galaxy luminosity function from z ≃ 8-10

Monthly Notices of the Royal Astronomical Society Oxford University Press 493 (2020) 2059-2084

R Bowler, M Jarvis, JS Dunlop, HJ McCracken

We utilize deep near-infrared survey data from the UltraVISTA fourth data release (DR4) and the VIDEO survey, in combination with overlapping optical and Spitzer data, to search for bright star-forming galaxies at z ≳ 7.5. Using a full photometric redshift fitting analysis applied to the ∼6 deg2 of imaging searched, we find 27 Lyman break galaxies (LBGs), including 20 new sources, with best-fitting photometric redshifts in the range 7.4 < z < 9.1. From this sample, we derive the rest-frame UV luminosity function at z = 8 and z = 9 out to extremely bright UV magnitudes (MUV ≃ −23) for the first time. We find an excess in the number density of bright galaxies in comparison to the typically assumed Schechter functional form derived from fainter samples. Combined with previous studies at lower redshift, our results show that there is little evolution in the number density of very bright (MUV ∼ −23) LBGs between z ≃ 5 and z ≃ 9. The tentative detection of an LBG with best-fitting photometric redshift of z = 10.9 ± 1.0 in our data is consistent with the derived evolution. We show that a double power-law fit with a brightening characteristic magnitude (ΔM*/Δz ≃ −0.5) and a steadily steepening bright-end slope (Δβ/Δz ≃ −0.5) provides a good description of the z > 5 data over a wide range in absolute UV magnitude (−23 < MUV < −17). We postulate that the observed evolution can be explained by a lack of mass quenching at very high redshifts in combination with increasing dust obscuration within the first ∼1Gyr of galaxy evolution.

Search for direct stau production in events with two hadronic tau-leptons in root s=13 TeV pp collisions with the ATLAS detector

Physical Review D American Physical Society 101 (2020) 32009

D Abbott, AA Abud, D Abhayasinghe, O AbouZeid, N Abraham, H Abramowicz, CA Bourdarios, M Adersberger, T Adye, Y Afik, X Ai, G Aielli, S Akatsuka, T Akesson, E Akilli, A Akimov, K Al Khoury, G Alberghi, J Albert, S Alderweireldt, M Aleksa, I Aleksandrov, C Alexa, D Alexandre, T Alexopoulos

A search for the direct production of the supersymmetric partners of τ-leptons (staus) in final states with two hadronically decaying τ-leptons is presented. The analysis uses a dataset of pp collisions corresponding to an integrated luminosity of 139 fb-1, recorded with the ATLAS detector at the Large Hadron Collider at a center-of-mass energy of 13 TeV. No significant deviation from the expected Standard Model background is observed. Limits are derived in scenarios of direct production of stau pairs with each stau decaying into the stable lightest neutralino and one τ-lepton in simplified models where the two stau mass eigenstates are degenerate. Stau masses from 120 GeV to 390 GeV are excluded at 95% confidence level for a massless lightest neutralino.

Evidence for electroweak production of two jets in association with a Z gamma pair in pp collisions at root S=13 TeV with the ATLAS detector

Physics Letters B Elsevier 803 (2020) 135341

G Aad, B Abbott, D Abbott, AA Abud, K Abeling, D Abhayasinghe, S Abidi, O AbouZeid, N Abraham, H Abramowicz, B Acharya, CA Bourdarios, L Adamczyk, M Adersberger, A Adiguzel, A Affolder, C Agapopoulou, C Agheorghiesei, J Aguilar-Saavedra, X Ai, G Aielli, A Akimov, T Alexopoulos

Evidence for electroweak production of two jets in association with a Zγ pair in s=13 TeV proton–proton collisions at the Large Hadron Collider is presented. The analysis uses data collected by the ATLAS detector in 2015 and 2016 that corresponds to an integrated luminosity of 36.1fb−1. Events that contain a Z boson candidate decaying leptonically into either e+e− or μ+μ−, a photon, and two jets are selected. The electroweak component is measured with observed and expected significances of 4.1 standard deviations. The fiducial cross-section for electroweak production is measured to be σZγjj−EW=7.8±2.0fb, in good agreement with the Standard Model prediction.

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.

Measurement of the azimuthal anisotropy of charged-particle production in Xe plus Xe collisions at root S-NN=5.44 TeV with the ATLAS detector

Physical Review C American Physical Society 101 (2020) 24906

B Abbott, D Abbott, AA Abud, K Abeling, D Abhayasinghe, S Abidi, O AbouZeid, N Abraham, H Abramowicz, H Abreu, Y Abulaiti, B Acharya, B Achkar, S Adachi, L Adam, CA Bourdarios, L Adamczyk, L Adamek, J Adelman, M Adersberger, A Adiguzel, C Agheorghiesei, J Aguilar-Saavedra

This paper describes the measurements of flow harmonics v2-v6 in 3μb-1 of Xe+Xe collisions at sNN=5.44 TeV performed using the ATLAS detector at the Large Hadron Collider (LHC). Measurements of the centrality, multiplicity, and pT dependence of the vn obtained using two-particle correlations and the scalar product technique are presented. The measurements are also performed using a template-fit procedure, which was developed to remove nonflow correlations in small collision systems. This nonflow removal is shown to have a significant influence on the measured vn at high pT, especially in peripheral events. Comparisons of the measured vn with measurements in Pb+Pb collisions and p+Pb collisions at sNN=5.02 TeV are also presented. The vn values in Xe+Xe collisions are observed to be larger than those in Pb+Pb collisions for n=2, 3, and 4 in the most central events. However, with decreasing centrality or increasing harmonic order n, the vn values in Xe+Xe collisions become smaller than those in Pb+Pb collisions. The vn in Xe+Xe and Pb+Pb collisions are also compared as a function of the mean number of participating nucleons, (Npart), and the measured charged-particle multiplicity in the detector. The v3 values in Xe+Xe and Pb+Pb collisions are observed to be similar at the same (Npart) or multiplicity, but the other harmonics are significantly different. The ratios of the measured vn in Xe+Xe and Pb+Pb collisions, as a function of centrality, are also compared to theoretical calculations.

Measurement of differential cross sections for single diffractive dissociation in root s=8 TeV pp collisions using the ATLAS ALFA spectrometer

Journal of High Energy Physics Springer 2020 (2020) 42

G Aad, B Abbott, DC Abbott, O Abdinov, A Abed Abud, K Abeling, DK Abhayasinghe, SH Abidi, OS AbouZeid, N Abraham, H Abramowicz, H Abreu, Y Abulaiti, BS Acharya, B Achkar, S Adachi, C Adam Bourdarios, L Adamczyk, M Adersberger, A Adiguzel, C Agapopoulou, C Agheorghiesei, JA Aguilar-Saavedra, Et al.

A dedicated sample of Large Hadron Collider proton-proton collision data at centre-of-mass energy s√ = 8 TeV is used to study inclusive single diffractive dissociation, pp → X p. The intact final-state proton is reconstructed in the ATLAS ALFA forward spectrometer, while charged particles from the dissociated system X are measured in the central detector components. The fiducial range of the measurement is −4.0 < log10ξ < −1.6 and 0.016 < |t| < 0.43 GeV2, where ξ is the proton fractional energy loss and t is the squared four-momentum transfer. The total cross section integrated across the fiducial range is 1.59 ± 0.13 mb. Cross sections are also measured differentially as functions of ξ, t, and ∆η, a variable that characterises the rapidity gap separating the proton and the system X . The data are consistent with an exponential t dependence, dσ/dt ∝ eBt with slope parameter B = 7.65 ± 0.34 GeV−2. Interpreted in the framework of triple Regge phenomenology, the ξ dependence leads to a pomeron intercept of α(0) = 1.07 ± 0.09.

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.

The Thousand-Pulsar-Array programme on MeerKAT - I. Science objectives and first results

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 493 (2020) 3608-3615

S Johnston, A Karastergiou, MJ Keith, X Song, P Weltevrede, F Abbate, M Bailes, S Buchner, F Camilo, M Geyer, B Hugo, A Jameson, M Kramer, A Parthasarathy, DJ Reardon, A Ridolfi, M Serylak, RM Shannon, R Spiewak, W van Straten, VV Krishnan, F Jankowski, BW Meyers, L Oswald, B Posselt, C Sobey, A Szary, J van Leeuwen

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.

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.