@article{11446, abstract = {Suppose that n is not a prime power and not twice a prime power. We prove that for any Hausdorff compactum X with a free action of the symmetric group Sn, there exists an Sn-equivariant map X→Rn whose image avoids the diagonal {(x,x,…,x)∈Rn∣x∈R}. Previously, the special cases of this statement for certain X were usually proved using the equivartiant obstruction theory. Such calculations are difficult and may become infeasible past the first (primary) obstruction. We take a different approach which allows us to prove the vanishing of all obstructions simultaneously. The essential step in the proof is classifying the possible degrees of Sn-equivariant maps from the boundary ∂Δn−1 of (n−1)-simplex to itself. Existence of equivariant maps between spaces is important for many questions arising from discrete mathematics and geometry, such as Kneser’s conjecture, the Square Peg conjecture, the Splitting Necklace problem, and the Topological Tverberg conjecture, etc. We demonstrate the utility of our result applying it to one such question, a specific instance of envy-free division problem.}, author = {Avvakumov, Sergey and Kudrya, Sergey}, issn = {1432-0444}, journal = {Discrete & Computational Geometry}, keywords = {Computational Theory and Mathematics, Discrete Mathematics and Combinatorics, Geometry and Topology, Theoretical Computer Science}, number = {3}, pages = {1202--1216}, publisher = {Springer Nature}, title = {{Vanishing of all equivariant obstructions and the mapping degree}}, doi = {10.1007/s00454-021-00299-z}, volume = {66}, year = {2021}, } @inproceedings{11452, abstract = {We study efficient distributed algorithms for the fundamental problem of principal component analysis and leading eigenvector computation on the sphere, when the data are randomly distributed among a set of computational nodes. We propose a new quantized variant of Riemannian gradient descent to solve this problem, and prove that the algorithm converges with high probability under a set of necessary spherical-convexity properties. We give bounds on the number of bits transmitted by the algorithm under common initialization schemes, and investigate the dependency on the problem dimension in each case.}, author = {Alimisis, Foivos and Davies, Peter and Vandereycken, Bart and Alistarh, Dan-Adrian}, booktitle = {Advances in Neural Information Processing Systems - 35th Conference on Neural Information Processing Systems}, isbn = {9781713845393}, issn = {1049-5258}, location = {Virtual, Online}, pages = {2823--2834}, publisher = {Neural Information Processing Systems Foundation}, title = {{Distributed principal component analysis with limited communication}}, volume = {4}, year = {2021}, } @inproceedings{11453, abstract = {Neuronal computations depend on synaptic connectivity and intrinsic electrophysiological properties. Synaptic connectivity determines which inputs from presynaptic neurons are integrated, while cellular properties determine how inputs are filtered over time. Unlike their biological counterparts, most computational approaches to learning in simulated neural networks are limited to changes in synaptic connectivity. However, if intrinsic parameters change, neural computations are altered drastically. Here, we include the parameters that determine the intrinsic properties, e.g., time constants and reset potential, into the learning paradigm. Using sparse feedback signals that indicate target spike times, and gradient-based parameter updates, we show that the intrinsic parameters can be learned along with the synaptic weights to produce specific input-output functions. Specifically, we use a teacher-student paradigm in which a randomly initialised leaky integrate-and-fire or resonate-and-fire neuron must recover the parameters of a teacher neuron. We show that complex temporal functions can be learned online and without backpropagation through time, relying on event-based updates only. Our results are a step towards online learning of neural computations from ungraded and unsigned sparse feedback signals with a biologically inspired learning mechanism.}, author = {Braun, Lukas and Vogels, Tim P}, booktitle = {Advances in Neural Information Processing Systems - 35th Conference on Neural Information Processing Systems}, isbn = {9781713845393}, issn = {1049-5258}, location = {Virtual, Online}, pages = {16437--16450}, publisher = {Neural Information Processing Systems Foundation}, title = {{Online learning of neural computations from sparse temporal feedback}}, volume = {20}, year = {2021}, } @inproceedings{11463, abstract = {Efficiently approximating local curvature information of the loss function is a key tool for optimization and compression of deep neural networks. Yet, most existing methods to approximate second-order information have high computational or storage costs, which limits their practicality. In this work, we investigate matrix-free, linear-time approaches for estimating Inverse-Hessian Vector Products (IHVPs) for the case when the Hessian can be approximated as a sum of rank-one matrices, as in the classic approximation of the Hessian by the empirical Fisher matrix. We propose two new algorithms: the first is tailored towards network compression and can compute the IHVP for dimension d, if the Hessian is given as a sum of m rank-one matrices, using O(dm2) precomputation, O(dm) cost for computing the IHVP, and query cost O(m) for any single element of the inverse Hessian. The second algorithm targets an optimization setting, where we wish to compute the product between the inverse Hessian, estimated over a sliding window of optimization steps, and a given gradient direction, as required for preconditioned SGD. We give an algorithm with cost O(dm + m2) for computing the IHVP and O(dm + m3) for adding or removing any gradient from the sliding window. These two algorithms yield state-of-the-art results for network pruning and optimization with lower computational overhead relative to existing second-order methods. Implementations are available at [9] and [17].}, author = {Frantar, Elias and Kurtic, Eldar and Alistarh, Dan-Adrian}, booktitle = {35th Conference on Neural Information Processing Systems}, isbn = {9781713845393}, issn = {1049-5258}, location = {Virtual, Online}, pages = {14873--14886}, publisher = {Neural Information Processing Systems Foundation}, title = {{M-FAC: Efficient matrix-free approximations of second-order information}}, volume = {34}, year = {2021}, } @inproceedings{11464, abstract = {We consider a standard distributed optimisation setting where N machines, each holding a d-dimensional function fi, aim to jointly minimise the sum of the functions ∑Ni=1fi(x). This problem arises naturally in large-scale distributed optimisation, where a standard solution is to apply variants of (stochastic) gradient descent. We focus on the communication complexity of this problem: our main result provides the first fully unconditional bounds on total number of bits which need to be sent and received by the N machines to solve this problem under point-to-point communication, within a given error-tolerance. Specifically, we show that Ω(Ndlogd/Nε) total bits need to be communicated between the machines to find an additive ϵ-approximation to the minimum of ∑Ni=1fi(x). The result holds for both deterministic and randomised algorithms, and, importantly, requires no assumptions on the algorithm structure. The lower bound is tight under certain restrictions on parameter values, and is matched within constant factors for quadratic objectives by a new variant of quantised gradient descent, which we describe and analyse. Our results bring over tools from communication complexity to distributed optimisation, which has potential for further applications.}, author = {Alistarh, Dan-Adrian and Korhonen, Janne}, booktitle = {35th Conference on Neural Information Processing Systems}, isbn = {9781713845393}, issn = {1049-5258}, location = {Virtual, Online}, pages = {7254--7266}, publisher = {Neural Information Processing Systems Foundation}, title = {{Towards tight communication lower bounds for distributed optimisation}}, volume = {34}, year = {2021}, } @article{11498, abstract = {Rest-frame ultraviolet (UV) emission lines probe electron densities, gas-phase abundances, metallicities, and ionization parameters of the emitting star-forming galaxies and their environments. The strongest main UV emission line, Lyα, has been instrumental in advancing the general knowledge of galaxy formation in the early universe. However, observing Lyα emission becomes increasingly challenging at z ≳ 6 when the neutral hydrogen fraction of the circumgalactic and intergalactic media increases. Secondary weaker UV emission lines provide important alternative methods for studying galaxy properties at high redshift. We present a large sample of rest-frame UV emission line sources at intermediate redshift for calibrating and exploring the connection between secondary UV lines and the emitting galaxies’ physical properties and their Lyα emission. The sample of 2052 emission line sources with 1.5 < z < 6.4 was collected from integral field data from the MUSE-Wide and MUSE-Deep surveys taken as part of Guaranteed Time Observations. The objects were selected through untargeted source detection (i.e., no preselection of sources as in dedicated spectroscopic campaigns) in the three-dimensional MUSE data cubes. We searched optimally extracted one-dimensional spectra of the full sample for UV emission features via emission line template matching, resulting in a sample of more than 100 rest-frame UV emission line detections. We show that the detection efficiency of (non-Lyα) UV emission lines increases with survey depth, and that the emission line strength of He IIλ1640 Å, [O III] λ1661 + O III] λ1666, and [Si III] λ1883 + Si III] λ1892 correlate with the strength of [C III] λ1907 + C III] λ1909. The rest-frame equivalent width (EW0) of [C III] λ1907 + C III] λ1909 is found to be roughly 0.22 ± 0.18 of EW0(Lyα). We measured the velocity offsets of resonant emission lines with respect to systemic tracers. For C IVλ1548 + C IVλ1551 we find that ΔvC IV ≲ 250 km s−1, whereas ΔvLyα falls in the range of 250−500 km s−1 which is in agreement with previous results from the literature. The electron density ne measured from [Si III] λ1883 + Si III] λ1892 and [C III] λ1907 + C III] λ1909 line flux ratios is generally < 105 cm−3 and the gas-phase abundance is below solar at 12 + log10(O/H)≈8. Lastly, we used “PhotoIonization Model Probability Density Functions” to infer physical parameters of the full sample and individual systems based on photoionization model parameter grids and observational constraints from our UV emission line searches. This reveals that the UV line emitters generally have ionization parameter log10(U) ≈ −2.5 and metal mass fractions that scatter around Z ≈ 10−2, that is Z ≈ 0.66 Z⊙. Value-added catalogs of the full sample of MUSE objects studied in this work and a collection of UV line emitters from the literature are provided with this paper.}, author = {Schmidt, K. B. and Kerutt, J. and Wisotzki, L. and Urrutia, T. and Feltre, A. and Maseda, M. V. and Nanayakkara, T. and Bacon, R. and Boogaard, L. A. and Conseil, S. and Contini, T. and Herenz, E. C. and Kollatschny, W. and Krumpe, M. and Leclercq, F. and Mahler, G. and Matthee, Jorryt J and Mauerhofer, V. and Richard, J. and Schaye, J.}, issn = {1432-0746}, journal = {Astronomy & Astrophysics}, keywords = {Space and Planetary Science, Astronomy and Astrophysics, ultraviolet: galaxies / galaxies: high-redshift / galaxies: ISM / ISM: lines and bands / methods: observational / techniques: imaging spectroscopy}, publisher = {EDP Sciences}, title = {{Recovery and analysis of rest-frame UV emission lines in 2052 galaxies observed with MUSE at 1.5 < z < 6.4}}, doi = {10.1051/0004-6361/202140876}, volume = {654}, year = {2021}, } @article{11500, abstract = {We report the discovery of diffuse extended Lyα emission from redshift 3.1 to 4.5, tracing cosmic web filaments on scales of 2.5−4 cMpc. These structures have been observed in overdensities of Lyα emitters in the MUSE Extremely Deep Field, a 140 h deep MUSE observation located in the Hubble Ultra-Deep Field. Among the 22 overdense regions identified, five are likely to harbor very extended Lyα emission at high significance with an average surface brightness of 5 × 10−20 erg s−1 cm−2 arcsec−2. Remarkably, 70% of the total Lyα luminosity from these filaments comes from beyond the circumgalactic medium of any identified Lyα emitter. Fluorescent Lyα emission powered by the cosmic UV background can only account for less than 34% of this emission at z ≈ 3 and for not more than 10% at higher redshift. We find that the bulk of this diffuse emission can be reproduced by the unresolved Lyα emission of a large population of ultra low-luminosity Lyα emitters (< 1040 erg s−1), provided that the faint end of the Lyα luminosity function is steep (α ⪅ −1.8), it extends down to luminosities lower than 1038 − 1037 erg s−1, and the clustering of these Lyα emitters is significant (filling factor < 1/6). If these Lyα emitters are powered by star formation, then this implies their luminosity function needs to extend down to star formation rates < 10−4 M⊙ yr−1. These observations provide the first detection of the cosmic web in Lyα emission in typical filamentary environments and the first observational clue indicating the existence of a large population of ultra low-luminosity Lyα emitters at high redshift.}, author = {Bacon, R. and Mary, D. and Garel, T. and Blaizot, J. and Maseda, M. and Schaye, J. and Wisotzki, L. and Conseil, S. and Brinchmann, J. and Leclercq, F. and Abril-Melgarejo, V. and Boogaard, L. and Bouché, N. F. and Contini, T. and Feltre, A. and Guiderdoni, B. and Herenz, C. and Kollatschny, W. and Kusakabe, H. and Matthee, Jorryt J and Michel-Dansac, L. and Nanayakkara, T. and Richard, J. and Roth, M. and Schmidt, K. B. and Steinmetz, M. and Tresse, L. and Urrutia, T. and Verhamme, A. and Weilbacher, P. M. and Zabl, J. and Zoutendijk, S. L.}, issn = {1432-0746}, journal = {Astronomy & Astrophysics}, keywords = {Space and Planetary Science, Astronomy and Astrophysics, galaxies: high-redshift / galaxies: groups: general / cosmology: observations}, publisher = {EDP Sciences}, title = {{The MUSE Extremely Deep Field: The cosmic web in emission at high redshift}}, doi = {10.1051/0004-6361/202039887}, volume = {647}, year = {2021}, } @article{11512, abstract = {We study the molecular gas content of 24 star-forming galaxies at z = 3–4, with a median stellar mass of 109.1 M⊙, from the MUSE Hubble Ultra Deep Field (HUDF) Survey. Selected by their Lyα λ1216 emission and HF160W-band magnitude, the galaxies show an average $\langle {\mathrm{EW}}_{\mathrm{Ly}\alpha }^{0}\rangle \approx 20$ Å, below the typical selection threshold for Lyα emitters (${\mathrm{EW}}_{\mathrm{Ly}\alpha }^{0}\gt 25$ Å), and a rest-frame UV spectrum similar to Lyman-break galaxies. We use rest-frame optical spectroscopy from KMOS and MOSFIRE, and the UV features observed with MUSE, to determine the systemic redshifts, which are offset from Lyα by 〈Δv(Lyα)〉 = 346 km s−1, with a 100 to 600 km s−1 range. Stacking 12CO J = 4 → 3 and [C i]3P1 → 3P0 (and higher-J CO lines) from the ALMA Spectroscopic Survey of the HUDF, we determine 3σ upper limits on the line luminosities of 4.0 × 108 K km s−1pc2 and 5.6 × 108 K km s−1pc2, respectively (for a 300 km s−1 line width). Stacking the 1.2 mm and 3 mm dust-continuum flux densities, we find a 3σ upper limits of 9 μJy and 1.2 μJy, respectively. The inferred gas fractions, under the assumption of a "Galactic" CO-to-H2 conversion factor and gas-to-dust ratio, are in tension with previously determined scaling relations. This implies a substantially higher αCO ≥ 10 and δGDR ≥ 1200, consistent with the subsolar metallicity estimated for these galaxies ($12+\mathrm{log}({\rm{O}}/{\rm{H}})\approx 7.8\pm 0.2$). The low metallicity of z ≥ 3 star-forming galaxies may thus make it very challenging to unveil their cold gas through CO or dust emission, warranting further exploration of alternative tracers, such as [C ii].}, author = {Boogaard, Leindert A. and Bouwens, Rychard J. and Riechers, Dominik and van der Werf, Paul and Bacon, Roland and Matthee, Jorryt J and Stefanon, Mauro and Feltre, Anna and Maseda, Michael and Inami, Hanae and Aravena, Manuel and Brinchmann, Jarle and Carilli, Chris and Contini, Thierry and Decarli, Roberto and González-López, Jorge and Nanayakkara, Themiya and Walter, Fabian}, issn = {1538-4357}, journal = {The Astrophysical Journal}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, number = {1}, publisher = {IOP Publishing}, title = {{Measuring the average molecular gas content of star-forming galaxies at z = 3–4}}, doi = {10.3847/1538-4357/ac01d7}, volume = {916}, year = {2021}, } @article{11522, abstract = {The decline in abundance of Lyman-α (Lyα) emitting galaxies at z ≳ 6 is a powerful and commonly used probe to constrain the progress of cosmic reionization. We use the CODAII simulation, which is a radiation hydrodynamic simulation featuring a box of ∼94 comoving Mpc side length, to compute the Lyα transmission properties of the intergalactic medium (IGM) at z ∼ 5.8 to 7. Our results mainly confirm previous studies, i.e. we find a declining Lyα transmission with redshift and a large sightline-to-sightline variation. However, motivated by the recent discovery of blue Lyα peaks at high redshift, we also analyse the IGM transmission on the blue side, which shows a rapid decline at z ≳ 6 of the blue transmission. This low transmission can be attributed not only to the presence of neutral regions but also to the residual neutral hydrogen within ionized regions, for which a density even as low as nHI∼10−9cm−3 (sometimes combined with kinematic effects) leads to a significantly reduced visibility. Still, we find that ∼1 per cent of sightlines towards M1600AB ∼ −21 galaxies at z ∼ 7 are transparent enough to allow a transmission of a blue Lyα peak. We discuss our results in the context of the interpretation of observations.}, author = {Gronke, Max and Ocvirk, Pierre and Mason, Charlotte and Matthee, Jorryt J and Bosman, Sarah E I and Sorce, Jenny G and Lewis, Joseph and Ahn, Kyungjin and Aubert, Dominique and Dawoodbhoy, Taha and Iliev, Ilian T and Shapiro, Paul R and Yepes, Gustavo}, issn = {1365-2966}, journal = {Monthly Notices of the Royal Astronomical Society}, keywords = {dark ages, reionization, first stars, intergalactic medium, galaxies: formation}, number = {3}, pages = {3697--3709}, publisher = {Oxford University Press}, title = {{Lyman-α transmission properties of the intergalactic medium in the CoDaII simulation}}, doi = {10.1093/mnras/stab2762}, volume = {508}, year = {2021}, } @article{11523, abstract = {We present the first results from the X-SHOOTER Lyman α survey at z = 2 (XLS-z2). XLS-z2 is a deep spectroscopic survey of 35 Lyman α emitters (LAEs) utilizing ≈90 h of exposure time with Very Large Telescope/X-SHOOTER and covers rest-frame Ly α to H α emission with R ≈ 4000. We present the sample selection, the observations, and the data reduction. Systemic redshifts are measured from rest-frame optical lines for 33/35 sources. In the stacked spectrum, our LAEs are characterized by an interstellar medium with little dust, a low metallicity, and a high ionization state. The ionizing sources are young hot stars that power strong emission lines in the optical and high-ionization lines in the ultraviolet (UV). The LAEs exhibit clumpy UV morphologies and have outflowing kinematics with blueshifted Si II absorption, a broad [O III] component, and a red-skewed Ly α line. Typically, 30 per cent of the Ly α photons escape, of which one quarter on the blue side of the systemic velocity. A fraction of Ly α photons escape directly at the systemic suggesting clear channels enabling an ≈10 per cent escape of ionizing photons, consistent with an inference based on Mg II. A combination of a low effective H I column density, a low dust content, and young starburst determines whether a star-forming galaxy is observed as an LAE. The first is possibly related to outflows and/or a fortunate viewing angle, while we find that the latter two in LAEs are typical for their stellar mass of 109 M⊙.}, author = {Matthee, Jorryt J and Sobral, David and Hayes, Matthew and Pezzulli, Gabriele and Gronke, Max and Schaerer, Daniel and Naidu, Rohan P and Röttgering, Huub and Calhau, João and Paulino-Afonso, Ana and Santos, Sérgio and Amorín, Ricardo}, issn = {1365-2966}, journal = {Monthly Notices of the Royal Astronomical Society}, keywords = {Space and Planetary Science, Astronomy and Astrophysics, galaxies: formation, galaxies: ISM, galaxies: starburst, dark ages, reionization, first stars}, number = {1}, pages = {1382--1412}, publisher = {Oxford University Press}, title = {{The X-SHOOTER Lyman α survey at z = 2 (XLS-z2) I: What makes a galaxy a Lyman α emitter?}}, doi = {10.1093/mnras/stab1304}, volume = {505}, year = {2021}, } @article{11524, abstract = {We measure the evolution of the rest-frame UV luminosity function (LF) and the stellar mass function (SMF) of Lyman-α (Ly α) emitters (LAEs) from z ∼ 2 to z ∼ 6 by exploring ∼4000 LAEs from the SC4K sample. We find a correlation between Ly α luminosity (LLy α) and rest-frame UV (MUV), with best fit MUV=−1.6+0.2−0.3log10(LLyα/ergs−1)+47+12−11 and a shallower relation between LLy α and stellar mass (M⋆), with best fit log10(M⋆/M⊙)=0.9+0.1−0.1log10(LLyα/ergs−1)−28+4.0−3.8⁠. An increasing LLy α cut predominantly lowers the number density of faint MUV and low M⋆ LAEs. We estimate a proxy for the full UV LFs and SMFs of LAEs with simple assumptions of the faint end slope. For the UV LF, we find a brightening of the characteristic UV luminosity (M∗UV⁠) with increasing redshift and a decrease of the characteristic number density (Φ*). For the SMF, we measure a characteristic stellar mass (⁠M∗⋆/M⊙⁠) increase with increasing redshift, and a Φ* decline. However, if we apply a uniform luminosity cut of log10(LLyα/ergs−1)≥43.0⁠, we find much milder to no evolution in the UV and SMF of LAEs. The UV luminosity density (ρUV) of the full sample of LAEs shows moderate evolution and the stellar mass density (ρM) decreases, with both being always lower than the total ρUV and ρM of more typical galaxies but slowly approaching them with increasing redshift. Overall, our results indicate that both ρUV and ρM of LAEs slowly approach the measurements of continuum-selected galaxies at z > 6, which suggests a key role of LAEs in the epoch of reionization.}, author = {Santos, S and Sobral, D and Butterworth, J and Paulino-Afonso, A and Ribeiro, B and da Cunha, E and Calhau, J and Khostovan, A A and Matthee, Jorryt J and Arrabal Haro, P}, issn = {1365-2966}, journal = {Monthly Notices of the Royal Astronomical Society}, keywords = {Space and Planetary Science, Astronomy and Astrophysics, galaxies: evolution, galaxies: high-redshift, galaxies: luminosity function, mass function}, number = {1}, pages = {1117--1134}, publisher = {Oxford University Press}, title = {{The evolution of the UV luminosity and stellar mass functions of Lyman-α emitters from z ∼ 2 to z ∼ 6}}, doi = {10.1093/mnras/stab1218}, volume = {505}, year = {2021}, } @article{11525, abstract = {The intensity of the Cosmic UV background (UVB), coming from all sources of ionizing photons such as star-forming galaxies and quasars, determines the thermal evolution and ionization state of the intergalactic medium (IGM) and is, therefore, a critical ingredient for models of cosmic structure formation. Most of the previous estimates are based on the comparison between observed and simulated Lyman-α forest. We present the results of an independent method to constrain the product of the UVB photoionization rate and the covering fraction of Lyman limit systems (LLSs) by searching for the fluorescent Lyman-α emission produced by self-shielded clouds. Because the expected surface brightness is well below current sensitivity limits for direct imaging, we developed a new method based on 3D stacking of the IGM around Lyman-α emitting galaxies (LAEs) between 2.9 < z < 6.6 using deep MUSE observations. Combining our results with covering fractions of LLSs obtained from mock cubes extracted from the EAGLE simulation, we obtain new and independent constraints on the UVB at z > 3 that are consistent with previous measurements, with a preference for relatively low UVB intensities at z = 3, and which suggest a non-monotonic decrease of ΓH I with increasing redshift between 3 < z < 5. This could suggest a possible tension between some UVB models and current observations which however require deeper and wider observations in Lyman-α emission and absorption to be confirmed. Assuming instead a value of UVB from current models, our results constrain the covering fraction of LLSs at 3 < z < 4.5 to be less than 25 per cent within 150 kpc from LAEs.}, author = {Gallego, Sofia G and Cantalupo, Sebastiano and Sarpas, Saeed and Duboeuf, Bastien and Lilly, Simon and Pezzulli, Gabriele and Marino, Raffaella Anna and Matthee, Jorryt J and Wisotzki, Lutz and Schaye, Joop and Richard, Johan and Kusakabe, Haruka and Mauerhofer, Valentin}, issn = {1365-2966}, journal = {Monthly Notices of the Royal Astronomical Society}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, number = {1}, pages = {16--32}, publisher = {Oxford University Press}, title = {{Constraining the cosmic UV background at z > 3 with MUSE Lyman-α emission observations}}, doi = {10.1093/mnras/stab796}, volume = {504}, year = {2021}, } @article{11526, abstract = {We present the results from a MUSE survey of twelve z ≃ 3.15 quasars, which were selected to be much fainter (20 < iSDSS < 23) than in previous studies of giant Ly α nebulae around the brightest quasars (16.6 < iAB < 18.7). We detect H I Ly α nebulae around 100 per cent of our target quasars, with emission extending to scales of at least 60 physical kpc, and up to 190 pkpc. We explore correlations between properties of the nebulae and their host quasars, with the goal of connecting variations in the properties of the illuminating QSO to the response in nebular emission. We show that the surface brightness profiles of the nebulae are similar to those of nebulae around bright quasars, but with a lower normalization. Our targeted quasars are on average 3.7 mag (≃30 times) fainter in UV continuum than our bright reference sample, and yet the nebulae around them are only 4.3 times fainter in mean Ly α surface brightness, measured between 20 and 50 pkpc. We find significant correlations between the surface brightness of the nebula and the luminosity of the quasar in both UV continuum and Ly α. The latter can be interpreted as evidence for a substantial contribution from unresolved inner parts of the nebulae to the narrow components seen in the Ly α lines of some of our faint quasars, possibly from the inner circumgalactic medium or from the host galaxy’s interstellar medium.}, author = {Mackenzie, Ruari and Pezzulli, Gabriele and Cantalupo, Sebastiano and Marino, Raffaella A and Lilly, Simon and Muzahid, Sowgat and Matthee, Jorryt J and Schaye, Joop and Wisotzki, Lutz}, issn = {1365-2966}, journal = {Monthly Notices of the Royal Astronomical Society}, keywords = {Space and Planetary Science, Astronomy and Astrophysics, techniques: imaging spectroscopy, intergalactic medium, quasars: emission lines, quasars: general}, number = {1}, pages = {494--509}, publisher = {Oxford University Press}, title = {{Revealing the impact of quasar luminosity on giant Lyα nebulae}}, doi = {10.1093/mnras/staa3277}, volume = {502}, year = {2021}, } @article{11585, abstract = {Observations show that star-forming galaxies reside on a tight three-dimensional plane between mass, gas-phase metallicity and star formation rate (SFR), which can be explained by the interplay between metal-poor gas inflows, SFR and outflows. However, different metals are released on different time-scales, which may affect the slope of this relation. Here, we use central, star-forming galaxies with Mstar = 109.0−10.5 M from the EAGLE hydrodynamical simulation to examine three-dimensional relations between mass, SFR and chemical enrichment using absolute and relative C, N, O and Fe abundances. We show that the scatter is smaller when gas-phase α-enhancement is used rather than metallicity. A similar plane also exists for stellar α-enhancement, implying that present-day specific SFRs are correlated with long time-scale star formation histories. Between z = 0 and 1, the α-enhancement plane is even more insensitive to redshift than the plane using metallicity. However, it evolves at z > 1 due to lagging iron yields. At fixed mass, galaxies with higher SFRs have star formation histories shifted toward late times, are more α-enhanced and this α-enhancement increases with redshift as observed. These findings suggest that relations between physical properties inferred from observations may be affected by systematic variations in α-enhancements.}, author = {Matthee, Jorryt J}, issn = {2397-3366}, journal = {Nature Astronomy}, keywords = {Astronomy and Astrophysics, galaxies, formation - galaxies, evolution - galaxies, star formation - galaxies, abundances}, pages = {984--985}, publisher = {Springer Nature}, title = {{Differences in galaxy colours are not just about the mass}}, doi = {10.1038/s41550-021-01415-y}, volume = {5}, year = {2021}, } @article{11604, abstract = {The NASA Transiting Exoplanet Survey Satellite (TESS) is observing tens of millions of stars with time spans ranging from ∼27 days to about 1 yr of continuous observations. This vast amount of data contains a wealth of information for variability, exoplanet, and stellar astrophysics studies but requires a number of processing steps before it can be fully utilized. In order to efficiently process all the TESS data and make it available to the wider scientific community, the TESS Data for Asteroseismology working group, as part of the TESS Asteroseismic Science Consortium, has created an automated open-source processing pipeline to produce light curves corrected for systematics from the short- and long-cadence raw photometry data and to classify these according to stellar variability type. We will process all stars down to a TESS magnitude of 15. This paper is the next in a series detailing how the pipeline works. Here, we present our methodology for the automatic variability classification of TESS photometry using an ensemble of supervised learners that are combined into a metaclassifier. We successfully validate our method using a carefully constructed labeled sample of Kepler Q9 light curves with a 27.4 days time span mimicking single-sector TESS observations, on which we obtain an overall accuracy of 94.9%. We demonstrate that our methodology can successfully classify stars outside of our labeled sample by applying it to all ∼167,000 stars observed in Q9 of the Kepler space mission.}, author = {Audenaert, J. and Kuszlewicz, J. S. and Handberg, R. and Tkachenko, A. and Armstrong, D. J. and Hon, M. and Kgoadi, R. and Lund, M. N. and Bell, K. J. and Bugnet, Lisa Annabelle and Bowman, D. M. and Johnston, C. and García, R. A. and Stello, D. and Molnár, L. and Plachy, E. and Buzasi, D. and Aerts, C.}, issn = {1538-3881}, journal = {The Astronomical Journal}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, number = {5}, publisher = {IOP Publishing}, title = {{TESS Data for Asteroseismology (T’DA) stellar variability classification pipeline: Setup and application to the Kepler Q9 data}}, doi = {10.3847/1538-3881/ac166a}, volume = {162}, year = {2021}, } @article{11605, abstract = {Context. The discovery of moderate differential rotation between the core and the envelope of evolved solar-like stars could be the signature of a strong magnetic field trapped inside the radiative interior. The population of intermediate-mass red giants presenting surprisingly low-amplitude mixed modes (i.e. oscillation modes that behave as acoustic modes in their external envelope and as gravity modes in their core) could also arise from the effect of an internal magnetic field. Indeed, stars more massive than about 1.1 solar masses are known to develop a convective core during their main sequence. The field generated by the dynamo triggered by this convection could be the progenitor of a strong fossil magnetic field trapped inside the core of the star for the remainder of its evolution. Aims. Observations of mixed modes can constitute an excellent probe of the deepest layers of evolved solar-like stars, and magnetic fields in those regions can impact their propagation. The magnetic perturbation on mixed modes may therefore be visible in asteroseismic data. To unravel which constraints can be obtained from observations, we theoretically investigate the effects of a plausible mixed axisymmetric magnetic field with various amplitudes on the mixed-mode frequencies of evolved solar-like stars. Methods. First-order frequency perturbations due to an axisymmetric magnetic field were computed for dipolar and quadrupolar mixed modes. These computations were carried out for a range of stellar ages, masses, and metallicities. Conclusions. We show that typical fossil-field strengths of 0.1 − 1 MG, consistent with the presence of a dynamo in the convective core during the main sequence, provoke significant asymmetries on mixed-mode frequency multiplets during the red giant branch. We provide constraints and methods for the detectability of such magnetic signatures. We show that these signatures may be detectable in asteroseismic data for field amplitudes small enough for the amplitude of the modes not to be affected by the conversion of gravity into Alfvén waves inside the magnetised interior. Finally, we infer an upper limit for the strength of the field and the associated lower limit for the timescale of its action in order to redistribute angular momentum in stellar interiors.}, author = {Bugnet, Lisa Annabelle and Prat, V. and Mathis, S. and Astoul, A. and Augustson, K. and García, R. A. and Mathur, S. and Amard, L. and Neiner, C.}, issn = {1432-0746}, journal = {Astronomy & Astrophysics}, keywords = {Space and Planetary Science, Astronomy and Astrophysics, stars, oscillations / stars, magnetic field / stars, interiors / stars, evolution / stars, rotation}, publisher = {EDP Sciences}, title = {{Magnetic signatures on mixed-mode frequencies: I. An axisymmetric fossil field inside the core of red giants}}, doi = {10.1051/0004-6361/202039159}, volume = {650}, year = {2021}, } @article{11606, abstract = {Context. Our knowledge of the dynamics of stars has undergone a revolution through the simultaneous large amount of high-quality photometric observations collected by space-based asteroseismology and ground-based high-precision spectropolarimetry. They allowed us to probe the internal rotation of stars and their surface magnetism in the whole Hertzsprung-Russell diagram. However, new methods should still be developed to probe the deep magnetic fields in these stars. Aims. Our goal is to provide seismic diagnoses that allow us to probe the internal magnetism of stars. Methods. We focused on asymptotic low-frequency gravity modes and high-frequency acoustic modes. Using a first-order perturbative theory, we derived magnetic splittings of their frequencies as explicit functions of stellar parameters. Results. As in the case of rotation, we show that asymptotic gravity and acoustic modes can allow us to probe the different components of the magnetic field in the cavities in which they propagate. This again demonstrates the high potential of using mixed-modes when this is possible.}, author = {Mathis, S. and Bugnet, Lisa Annabelle and Prat, V. and Augustson, K. and Mathur, S. and Garcia, R. A.}, issn = {1432-0746}, journal = {Astronomy & Astrophysics}, keywords = {Space and Planetary Science, Astronomy and Astrophysics, asteroseismology / waves / stars, magnetic field / stars, oscillations / methods, analytical}, publisher = {EDP Sciences}, title = {{Probing the internal magnetism of stars using asymptotic magneto-asteroseismology}}, doi = {10.1051/0004-6361/202039180}, volume = {647}, year = {2021}, } @article{11608, abstract = {In order to understand stellar evolution, it is crucial to efficiently determine stellar surface rotation periods. Indeed, while they are of great importance in stellar models, angular momentum transport processes inside stars are still poorly understood today. Surface rotation, which is linked to the age of the star, is one of the constraints needed to improve the way those processes are modelled. Statistics of the surface rotation periods for a large sample of stars of different spectral types are thus necessary. An efficient tool to automatically determine reliable rotation periods is needed when dealing with large samples of stellar photometric datasets. The objective of this work is to develop such a tool. For this purpose, machine learning classifiers constitute relevant bases to build our new methodology. Random forest learning abilities are exploited to automate the extraction of rotation periods in Kepler light curves. Rotation periods and complementary parameters are obtained via three different methods: a wavelet analysis, the autocorrelation function of the light curve, and the composite spectrum. We trained three different classifiers: one to detect if rotational modulations are present in the light curve, one to flag close binary or classical pulsators candidates that can bias our rotation period determination, and finally one classifier to provide the final rotation period. We tested our machine learning pipeline on 23 431 stars of the Kepler K and M dwarf reference rotation catalogue for which 60% of the stars have been visually inspected. For the sample of 21 707 stars where all the input parameters are provided to the algorithm, 94.2% of them are correctly classified (as rotating or not). Among the stars that have a rotation period in the reference catalogue, the machine learning provides a period that agrees within 10% of the reference value for 95.3% of the stars. Moreover, the yield of correct rotation periods is raised to 99.5% after visually inspecting 25.2% of the stars. Over the two main analysis steps, rotation classification and period selection, the pipeline yields a global agreement with the reference values of 92.1% and 96.9% before and after visual inspection. Random forest classifiers are efficient tools to determine reliable rotation periods in large samples of stars. The methodology presented here could be easily adapted to extract surface rotation periods for stars with different spectral types or observed by other instruments such as K2, TESS or by PLATO in the near future.}, author = {Breton, S. N. and Santos, A. R. G. and Bugnet, Lisa Annabelle and Mathur, S. and García, R. A. and Pallé, P. L.}, issn = {1432-0746}, journal = {Astronomy & Astrophysics}, keywords = {Space and Planetary Science, Astronomy and Astrophysics, methods: data analysis / stars: solar-type / stars: activity / stars: rotation / starspots}, publisher = {EDP Sciences}, title = {{ROOSTER: A machine-learning analysis tool for Kepler stellar rotation periods}}, doi = {10.1051/0004-6361/202039947}, volume = {647}, year = {2021}, } @article{11609, abstract = {Context. Stellar interiors are the seat of efficient transport of angular momentum all along their evolution. In this context, understanding the dependence of the turbulent transport triggered by the instabilities of the vertical and horizontal shears of the differential rotation in stellar radiation zones as a function of their rotation, stratification, and thermal diffusivity is mandatory. Indeed, it constitutes one of the cornerstones of the rotational transport and mixing theory, which is implemented in stellar evolution codes to predict the rotational and chemical evolutions of stars. Aims. We investigate horizontal shear instabilities in rotating stellar radiation zones by considering the full Coriolis acceleration with both the dimensionless horizontal Coriolis component f̃ and the vertical component f. Methods. We performed a linear stability analysis using linearized equations derived from the Navier-Stokes and heat transport equations in the rotating nontraditional f-plane. We considered a horizontal shear flow with a hyperbolic tangent profile as the base flow. The linear stability was analyzed numerically in wide ranges of parameters, and we performed an asymptotic analysis for large vertical wavenumbers using the Wentzel-Kramers-Brillouin-Jeffreys (WKBJ) approximation for nondiffusive and highly-diffusive fluids. Results. As in the traditional f-plane approximation, we identify two types of instabilities: the inflectional and inertial instabilities. The inflectional instability is destabilized as f̃ increases and its maximum growth rate increases significantly, while the thermal diffusivity stabilizes the inflectional instability similarly to the traditional case. The inertial instability is also strongly affected; for instance, the inertially unstable regime is also extended in the nondiffusive limit as 0 < f < 1 + f̃ 2/N2, where N is the dimensionless Brunt-Väisälä frequency. More strikingly, in the high thermal diffusivity limit, it is always inertially unstable at any colatitude θ except at the poles (i.e., 0° < θ <  180°). We also derived the critical Reynolds numbers for the inertial instability using the asymptotic dispersion relations obtained from the WKBJ analysis. Using the asymptotic and numerical results, we propose a prescription for the effective turbulent viscosities induced by the inertial and inflectional instabilities that can be possibly used in stellar evolution models. The characteristic time of this turbulence is short enough so that it is efficient to redistribute angular momentum and to mix chemicals in stellar radiation zones.}, author = {Park, J. and Prat, V. and Mathis, S. and Bugnet, Lisa Annabelle}, issn = {1432-0746}, journal = {Astronomy & Astrophysics}, keywords = {Space and Planetary Science, Astronomy and Astrophysics, hydrodynamics / turbulence / stars, rotation / stars, evolution}, publisher = {EDP Sciences}, title = {{Horizontal shear instabilities in rotating stellar radiation zones: II. Effects of the full Coriolis acceleration}}, doi = {10.1051/0004-6361/202038654}, volume = {646}, year = {2021}, } @inproceedings{11649, abstract = {While operating communication networks adaptively may improve utilization and performance, frequent adjustments also introduce an algorithmic challenge: the re-optimization of traffic engineering solutions is time-consuming and may limit the granularity at which a network can be adjusted. This paper is motivated by question whether the reactivity of a network can be improved by re-optimizing solutions dynamically rather than from scratch, especially if inputs such as link weights do not change significantly. This paper explores to what extent dynamic algorithms can be used to speed up fundamental tasks in network operations. We specifically investigate optimizations related to traffic engineering (namely shortest paths and maximum flow computations), but also consider spanning tree and matching applications. While prior work on dynamic graph algorithms focusses on link insertions and deletions, we are interested in the practical problem of link weight changes. We revisit existing upper bounds in the weight-dynamic model, and present several novel lower bounds on the amortized runtime for recomputing solutions. In general, we find that the potential performance gains depend on the application, and there are also strict limitations on what can be achieved, even if link weights change only slightly.}, author = {Henzinger, Monika H and Paz, Ami and Schmid, Stefan}, booktitle = {IFIP Networking Conference}, issn = {1861-2288}, location = { Espoo and Helsinki, Finland}, publisher = {Institute of Electrical and Electronics Engineers}, title = {{On the complexity of weight-dynamic network algorithms}}, doi = {10.23919/ifipnetworking52078.2021.9472803}, year = {2021}, }