Day 1710

Wednesday, Thursday, Friday.

2005.13161
A census of baryons the universe from localized fast radio bursts
Macquart, Prochaska, et al

More than three quarters of the baryonic content of the Universe resides in a highly diffuse state that is difficult to observe, with only a small fraction directly observed in galaxies and galaxy clusters. Censuses of the nearby Universe have used absorption line spectroscopy to observe these invisible baryons, but these measurements rely on large and uncertain corrections and are insensitive to the majority of the volume, and likely mass. Specifically, quasar spectroscopy is sensitive either to only the very trace amounts of Hydrogen that exists in the atomic state, or highly ionized and enriched gas in denser regions near galaxies. Sunyaev-Zel'dovich analyses provide evidence of some of the gas in filamentary structures and studies of X-ray emission are most sensitive to gas near galaxy clusters. Here we report the direct measurement of the baryon content of the Universe using the dispersion of a sample of localized fast radio bursts (FRBs), thus utilizing an effect that measures the electron column density along each sight line and accounts for every ionised baryon. We augment the sample of published arcsecond-localized FRBs with a further four new localizations to host galaxies which have measured redshifts of 0.291, 0.118, 0.378 and 0.522, completing a sample sufficiently large to account for dispersion variations along the line of sight and in the host galaxy environment to derive a cosmic baryon density of $\Omega_{b} = 0.051_{-0.025}^{+0.021} \, h_{70}^{-1}$ (95% confidence). This independent measurement is consistent with Cosmic Microwave Background and Big Bang Nucleosynthesis values.

2005.13360

Say hello to Algol D and Algol E

Jetsu

Regular changes in the observed (O) and the computed (C) epochs of binary eclipses may reveal the presence of a third or a fourth body. One recent study showed that the probability for detecting a fourth body from the O-C data is only 0.00005. We apply the new Discrete Chi-square Method (DCM) to the O-C data of Algol, and detect three wide orbit stars having orbital periods 1.9 years (Algol C), 18.6 years (Algol D) and 52.5 years (Algol E). Since our estimate for the period of Algol C agrees perfectly with the previous estimates, the signals of Algol D and Algol E are certainly real. The orbits of all these three wide orbit stars are most probably co-planar, because no changes have been observed in eclipses of Algol.

2005.13990

Testing the cosmic curvature at high redshifts: the combination of lSST strong lensing systems and quasars as new standard candles

Liu, et al

The cosmic curvature, a fundamental parameter for cosmology could hold deep clues to inflation and cosmic origins. We propose an improved model-independent method to constrain the cosmic curvature by combining the constructed Hubble diagram of high-redshift quasars with galactic-scale strong lensing systems expected to be seen by the forthcoming LSST survey. More specifically, the most recent quasar data are used as a new type of standard candles in the range $0.036<z<5.100$, whose luminosity distances can be directly derived from the non-linear relation between X-ray and UV luminosities. Compared with other methods, the proposed one involving the quasar data achieves constraints with higher precision ($\Delta \Omega_k\sim 10^{-2}$) at high redshifts ($z\sim 5.0$). We also investigate the influence of lens mass distribution in the framework of three types of lens models extensively used in strong lensing studies (SIS model, power-law spherical model, and extended power-law lens model), finding the strong correlation between the cosmic curvature and the lens model parameters. When the power-law mass density profile is assumed, the most stringent constraint on the cosmic curvature $\Omega_k$ can be obtained. Therefore, the issue of mass density profile in the early-type galaxies is still a critical one that needs to be investigated further.

2005.14160

Restoring the night sky darkness at Observatorio delTeide: first application of he model Illumina version 2

Aubé, et al

The propagation of artificial light into real environments is complex. To perform its numerical modelling with accuracy one must consider hyperspectral properties of the lighting devices and their geographic positions, the hyperspectral properties of the ground reflectance, the size and distribution of small-scale obstacles, the blocking effect of topography, the lamps angular photometry and the atmospheric transfer function (aerosols and molecules). A detailed radiative transfer model can be used to evaluate how a particular change in the lighting infrastructure may affect the sky radiance. In this paper, we use the new version (v2) of the Illumina model to evaluate a night sky restoration plan for the Teide Observatory located on the island of Tenerife, Spain. In the past decades, the sky darkness was severely degraded by growing light pollution on the Tenerife Island. In this work, we use the contribution maps giving the effect of each pixel of the territory to the artificial sky radiance. We exploit the hyperspectral capabilities of Illumina v2 and show how the contribution maps can be integrated over regions or municipalities according to the Johnson-Cousins photometric bands spectral sensitivities. The sky brightness reductions per municipality after a complete shutdown and a conversion to Light-Emitting Diodes are calculated in the Johnson-Cousins B, V, R bands. We found that the conversion of the lighting infrastructure of Tenerife with LED (1800K and 2700K), according to the conversion strategy in force, would result in a zenith V band sky brightness reduction of about 0.3 mag arcsec-2.

Day 1709

Monday.

2005.11215
Galaxy and Mass Assembly (GAMA): assimilation of KiDS into the GAMA database
Bellstedt, Driver, et al

The Galaxy And Mass Assembly Survey (GAMA) covers five fields with highly complete spectroscopic coverage ($>95$ per cent) to intermediate depths ($r<19.8$ or $i < 19.0$ mag), and collectively spans 250 square degrees of Equatorial or Southern sky. Four of the GAMA fields (G09, G12, G15 and G23) reside in the ESO VST KiDS and ESO VISTA VIKING survey footprints, which combined with our GALEX, WISE and Herschel data provide deep uniform imaging in the $FUV\,NUV\,ugriZYJHK_s\,W1\,W2\,W3\,W4\,P100\,P160\,S250\,S350\,S500$ bands. Following the release of KiDS DR4, we describe the process by which we ingest the KiDS data into GAMA (replacing the SDSS data previously used for G09, G12 and G15), and redefine our core optical and near-IR catalogues to provide a complete and homogeneous dataset. The source extraction and analysis is based on the new ProFound image analysis package, providing matched-segment photometry across all bands. The data are classified into stars, galaxies, artefacts, and ambiguous objects, and objects are linked to the GAMA spectroscopic target catalogue. Additionally, a new technique is employed utilising ProFound to extract photometry in the unresolved MIR-FIR regime. The catalogues including the full FUV-FIR photometry are described and will be fully available as part of GAMA DR4. They are intended for both standalone science, selection for targeted follow-up with 4MOST, as well as an accompaniment to the upcoming and ongoing radio arrays now studying the GAMA $23^h$ field.


2005.11316

On the radial acceleration of disk galaxies

Wilhelm, Dwivedi

The physical processes defining the dynamics of disk galaxies are still poorly understood. Hundreds of articles have appeared in the literature over the last decades without arriving at an understanding within a consistent gravitational theory. Dark matter (DM) scenarios or a modification of Newtonian dynamics (MOND) are employed to model the non-Keplerian rotation curves in most of the studies, but the nature of DM and its interaction with baryonic matter remains an open question and MOND formulates a mathematical concept without a physical process. We have continued our attempts to use the impact theory of gravitation for a description of the peculiar acceleration and velocity curves and have considered five more galaxies. Using published data of the galaxies NGC 3198, NGC 2403, NGC 1090, UGC 3205 and NGC 1705, it has been possible to find good fits without DM for the observed disk velocities and, as example, also for the extraplanar matter of NGC 3198.

2005.11598

The cosmic web connection to the dark matter halo distribution through gravity

Kitaura, et al

In this letter we investigate the connection between the cosmic web and the halo distribution through the gravitational potential. We combine three fields of research, cosmic web classification, perturbation theory expansions of the halo bias, and halo (galaxy) mock catalog making methods. In particular, we use the invariants of the tidal field tensor as generating functions (dubbed I-web), to reproduce the halo number counts of a reference catalog from full gravity calculations, populating the dark matter field on a mesh well into the non-linear regime ($\sim5$ Mpc scales). Our results show an unprecedented agreement with the reference power spectrum within 0.5% up to $k=0.72\,h$ Mpc$^{-1}$. By analysing the three point statistics on large scales (configurations of up to $k=0.2\,h$ Mpc$^{-1}$), we find evidence for non-local bias at the 4.8 $\sigma$ confidence level (an information gain of $\sim$ 3.4 $\sigma$ over the commonly used T-web), being fully compatible with the reference catalog. In particular, we find that a detailed description of tidal anisotropic clustering on large scales is crucial to achieve this accuracy. We conclude that the I-web can potentially be useful to study the cosmic web, to improve the generation of mock galaxy catalogs, to improve on halo mass reconstructions, to study primordial non-Gaussianities, to develop new effective Eulerian galaxy bias models at the field level, and to investigate galaxy evolution improving on environmental studies.

2005.11798

The distribution of dark galaxies and spin bias

Jimenez, Heavens

In the light of the discovery of numerous (almost) dark galaxies from the ALFALAFA and LITTLE THINGS surveys, we revisit the predictions of Jimenez et al. 1997, based on the Toomre stability of rapidly-spinning gas disks. We have updated the predictions for $\Lambda$CDM with parameters given by Planck18, computing the expected number densities of dark objects, and their spin parameter and mass distributions. Comparing with the data is more challenging, but where the spins are more reliably determined, the spins are close to the threshold for disks to be stable according to the Toomre criterion, where the expected number density is highest, and reinforces the concept that there is a bias in the formation of luminous galaxies based on the spin of their parent halo.

Day 1708

Wednesday, Thursday, Friday.

2005.08940
A Starshot communication downlink
Parkin

Breakthrough Starshot is an initiative to propel a sailcraft to Alpha Centauri within the next generation. As the sailcraft transits Alpha Centauri at 0.2 c, it looks for signs of life by imaging planets and gathering other scientific data. After the transit, the 4.1-meter diameter sailcraft downlinks its data to an Earth-based receiver. The present work estimates the raw data rate of a 1.02 {\mu}m, 100 Watt laser that is received at 1.25 {\mu}m by a 30-meter telescope. The telescope receives 288 signal photons per second (-133 dBm) from the sailcraft after accounting for optical gains (+296 dBi), conventional losses (-476 dB), relativistic effects (-3.5 dB), and link margin (-3.0 dB). For this photon-starved Poisson channel with 0.1 nm equivalent noise bandwidth, 90% detector quantum efficiency, 1024-ary PPM modulation, and 10^-3 raw bit error rate, the raw data rate is 260 bit/s (hard-decision) to 1.5 kbit/s (ideal) raw data rate, which is 8-50 Gbit/year. This rate is slowed by noise, especially starlight from Alpha Centauri A scattered into the detector by the atmosphere and receiver optics as sailcraft nears the star. Because this is a flyby mission (the sailcraft does not stop in the Centauri system), the proper motion of Alpha Centauri relative to Earth carries it away from the sailcraft after transit, and the noise subsides over days to weeks. The downlink can resume as soon as a day after transit, starting at 7-22 bit/s and reaching nearly full speed after 4 months. By using a coronagraph on the receiving telescope, full-rate downlink speed could be reached much sooner.

2005.08983

Completeness of the Gaia-verse II: what are the odds that a star is missing from Gaia DR2?

Boubert, Everall

The second data release of the Gaia mission contained astrometry and photometry for an incredible 1,692,919,135 sources, but how many sources did Gaia miss and where do they lie on the sky? The answer to this question will be crucial for any astronomer attempting to map the Milky Way with Gaia DR2. We infer the completeness of Gaia DR2 by exploiting the fact that it only contains sources with at least five astrometric detections. The odds that a source achieves those five detections depends on both the number of observations and the probability that an observation of that source results in a detection. We predict the number of times that each source was observed by Gaia and assume that the probability of detection is either a function of magnitude or a distribution as a function of magnitude. We fit both these models to the 1.7 billion stars of Gaia DR2, and thus are able to robustly predict the completeness of Gaia across the sky as a function of magnitude. We extend our selection function to account for crowding in dense regions of the sky, and show that this is vitally important, particularly in the Galactic bulge and the Large and Small Magellanic Clouds. We find that the magnitude limit at which Gaia is still 99% complete varies over the sky from $G=18.9$ to $21.3$. We have created a new Python package selectionfunctions (https://github.com/gaiaverse/selectionfunctions) which provides easy access to our selection functions.

2005.08987

SDSS-IV MaNGA: spatially resolved SF in barred galaxies

Fraser-McKelvie, et al

Bars inhabit the majority of local-Universe disk galaxies and may be important drivers of galaxy evolution through the redistribution of gas and angular momentum within disks. We investigate the star formation and gas properties of bars in galaxies spanning a wide range of masses, environments, and star formation rates using the MaNGA galaxy survey. Using a robustly-defined sample of 684 barred galaxies, we find that fractional (or scaled) bar length correlates with the host's offset from the star-formation main sequence. Considering the morphology of the H$\alpha$ emission we separate barred galaxies into different categories, including barred, ringed, and central configurations, together with H$\alpha$ detected at the ends of a bar. We find that only low-mass galaxies host star formation along their bars, and that this is located predominantly at the leading edge of the bar itself. Our results are supported by recent simulations of massive galaxies, which show that the position of star formation within a bar is regulated by a combination of shear forces, turbulence and gas flows. We conclude that the physical properties of a bar are mostly governed by the existing stellar mass of the host galaxy, but that they also play an important role in the galaxy's ongoing star formation.

2005.08995

Observing correlations between dark matter accretion and galaxy growth: I. Recent star formation activity in isolated Milky Way-mass galaxies

O'Donnell, Behroozi, More

The correlation between fresh gas accretion onto haloes and galaxy star formation is critical to understanding galaxy formation. Different theoretical models have predicted different correlation strengths between halo accretion rates and galaxy star formation rates, ranging from strong positive correlations to little or no correlation. Here, we present a technique to observationally measure this correlation strength for isolated Milky Way-mass galaxies with $z < 0.123$. This technique is based on correlations between dark matter accretion rates and the projected density profile of neighbouring galaxies; these correlations also underlie past work with splashback radii. We apply our technique to both observed galaxies in the Sloan Digital Sky Survey as well as simulated galaxies in the UniverseMachine where we can test any desired correlation strength. We find that positive correlations between dark matter accretion and recent star formation activity are ruled out with $\gtrsim 85\%$ confidence. Our results suggest that star formation activity may not be correlated with fresh accretion for isolated Milky Way-mass galaxies at $z=0$ and that other processes, such as gas recycling, dominate further galaxy growth.

2005.09122

Anchored in Shadows: Tying the celestial reference frame directly to Black Hole event horizons

Eubanks

Both the radio International Celestial Reference Frame (ICRF) and the optical Gaia Celestial Reference Frame (Gaia-CRF2) are derived from observations of jets produced by the Super Massive Black Holes (SMBH) powering active galactic nuclei and quasars. These jets are inherently subject to change and will appear different at different observing frequencies, leading to instabilities and systematic errors in the resulting Celestial Reference Frames (CRFs). Recently, the Event Horizon Telescope (EHT), a mm-wave Very Long Baseline Interferometry (VLBI) array, has observed the 40 micro-as diameter shadow of the SMBH in M87 at 1.3 mm, showing that the emitting region is smaller than the black-hole shadow. Use of these SMBH "emission rings" (and the associated photon rings) as astrometric references will enable the resulting CRF to be anchored directly in SMBH shadows; the ultimate reference points for any CRF for the forseeable future. A properly equipped space VLBI mission devoted to the observation of SMBH event horizons could lead to a two-orders-of-magnitude improvement in the accuracy and stabilty of the ICRF in the relatively near future.

2005.09642

COMPASS: VLBI beacons in support of Lunar Science and exploration

Eubanks

The large constellations of spacecraft planned for use in cislunar space (on the Lunar surface, in Lunar orbit, and in the vicinity of the Lunar Gateway) require new solutions for positioning, navigation and timing (PNT). Here, I describe COMPASS (Combined Observational Methods for Positional Awareness in the Solar System), a spacecraft navigation system to provide cost-effective techniques for the positioning of large numbers of spacecraft in cislunar space. COMPASS will use beacons that emit coherent ultra-wideband signals designed to be interoperable with existing and future Very Long Baseline Interferometry (VLBI) networks. Using differential VLBI, COMPASS will provide rapid determination of the interferometric phase delay with picosecond level accuracy during routine VLBI observing sessions. Multi-baseline phase-referenced COMPASS-VLBI observations with simultaneous calibrator observations should thus enable sub-meter accuracy transverse positioning and meter level lunar orbit determination using with small femtospacecraft beacons and a few seconds of observation per position determination.

2005.09661

A cold, massive, rotating disk galaxy 1.5 billion years after the Big Bang

Neeleman, Prochaska, Kenekar, Rafelski

Massive disk galaxies like the Milky Way are expected to form at late times in traditional models of galaxy formation, but recent numerical simulations suggest that such galaxies could form as early as a billion years after the Big Bang through the accretion of cold material and mergers. Observationally, it has been difficult to identify disk galaxies in emission at high redshift, in order to discern between competing models of galaxy formation. Here we report imaging, with a resolution of about 1.3 kiloparsecs, of the 158-micrometre emission line from singly ionized carbon, the far-infrared dust continuum and the near-ultraviolet continuum emission from a galaxy at a redshift of 4.2603, identified by detecting its absorption of quasar light. These observations show that the emission arises from gas inside a cold, dusty, rotating disk with a rotational velocity of 272 kilometres per second. The detection of emission from carbon monoxide in the galaxy yields a molecular mass that is consistent with the estimate from the ionized carbon emission of about 72 billion solar masses. The existence of such a massive, rotationally supported, cold disk galaxy when the Universe was only 1.5 billion years old favours formation through either cold-mode accretion or mergers, although its large rotational velocity and large content of cold gas remain challenging to reproduce with most numerical simulations.

2005.09896

The Three Hundred project: shapes and radial alignment of satellite, inflating, and backsplash galaxies

Knebe, et al

Using 324 numerically modelled galaxy clusters we investigate the radial and galaxy-halo alignment of dark matter subhaloes and satellite galaxies orbiting within and around them. We find that radial alignment depends on distance to the centre of the galaxy cluster but appears independent of the dynamical state of the central host cluster. Furthermore, we cannot find a relation between radial alignment of the halo or galaxy shape with its own mass. We report that backsplash galaxies, i.e. objects that have already passed through the cluster radius but are now located in the outskirts, show a stronger radial alignment than infalling objects. We further find that there exists a population of well radially aligned objects passing very close to the central cluster's centre which were found to be on highly radial orbit.

2005.10656

H0 tension or T0 tension?

Ivanov, et al

We study whether the discrepancy between the local and cosmological measurements of the Hubble constant $H_0$ can be reformulated as a tension in the cosmic microwave background (CMB) monopole temperature $T_0$. The latter is customarily fixed to the COBE/FIRAS best-fit value in CMB anisotropy data analyses. We show that the primary CMB anisotropies and the shape of the matter power spectrum are not directly sensitive to $T_0$. They depend only on the dark matter and baryon densities per CMB photon. Once these ratios are fixed, $T_0$ only measures the time elapsed since recombination until today. This results is a nearly perfect geometric degeneracy between $T_0$ and $H_0$. Taken at face value, this implies that removing the FIRAS prior on $T_0$ is enough to make the Planck CMB and SH0ES measurements consistent within the base $\Lambda$CDM model without introducing new physics. One may break the degeneracy by combining Planck with SH0ES, yielding an independent measurement of $T_0$, which happens to be in a $4\sigma$ tension with FIRAS. Therefore, the Hubble tension can be fully recast into the $T_0$ tension. The agreement with FIRAS can be restored if we combine Planck with the baryon acoustic oscillation data instead of SH0ES. Thus, the tension between SH0ES and cosmological measurements of $H_0$ within $\Lambda$CDM persists even if we discard the FIRAS $T_0$ measurement.

Day 1707

Tuesday.

2005.07707
Effects of supernova redshift uncertainties on the determination of cosmological parameters
Steinhardt, Sneppen, Sen

Redshifts used in current cosmological supernova samples are measured using two primary techniques, one based on well-measured host galaxy spectral lines and the other based on supernova-dominated spectra. Here, we construct an updated Pantheon catalog with revised redshifts, redshift sources and estimated uncertainties for the entire sample to investigate whether these two techniques yield consistent results. The best-fit cosmological parameters using these two measurement techniques disagree, and we explore several possible sources of bias which could result from using the lower-precision supernova-dominated redshifts. In a pilot study, we show that using a host redshift-only subsample of the Pantheon catalog will result in lower $\Omega_m$ and matter density $\Omega_m h^2$ and slightly higher $H_0$ than previous analysis which, among other possibilities, could result in supernova and CMB measurements agreeing on $\Omega_m h^2$ despite tension in $H_0$. To obtain rigorous results, though, the Pantheon catalog should be improved by obtaining host spectra for supernova that have faded and future surveys should be designed to use host galaxy redshifts rather than lower-precision methods.

2005.07831

Science merit function for the KEPLER mission

Borucki

The Kepler Mission was a NASA Discovery-class mission designed to continuously monitor the brightness of at least 100,000 stars to determine the frequency of Earth-size and larger planets orbiting other stars. Once the Kepler proposal was chosen for a flight opportunity, it was necessary to optimize the design to accomplish the ambitious goals specified in the proposal and still stay within the available resources. To maximize the science return from the mission, a merit function (MF) was constructed that relates the science value (as determined by the PI and the Science Team) to the chosen mission characteristics and to models of the planetary and stellar systems. This MF served several purposes; prediction of the science results of the proposed mission, effects of varying the values of the mission parameters to increase the science product or to reduce the mission costs, and assessment of risks. The Merit Function was also valuable for the purposes of advocating the Mission by illustrating its expected capability. Later, it was used to keep management informed of the changing mission capability as trade-offs and mission down-sizing occurred. The MF consisted of models of the stellar environment, assumed exoplanet characteristics and distributions, parameter values for the mission point-design, and equations that related the science value to the predicted number and distributions of detected exoplanets. A description of the MF model and representative results are presented.

2005.08252

Gravitational focusing of low-velocity dark matter on the Earth's surface

Sofue

We show that the Earth acts as a high-efficiency gravitational collector of low-velocity flow of dark matter (DM). The focal point appears on the Earth's surface, when the DM flow speed is about 17 km s$^{-1}$ with respect to the geo-center. We discuss diurnal modulation of the local DM density influenced by the Earth's gravity. We also touch upon similar effects on galactic and solar system objects.

2005.08330

Formation of giant planet satellites

Batygin, Morbidelli

Recent analyses have shown that the concluding stages of giant planet formation are accompanied by the development of large-scale meridional flow of gas inside the planetary Hill sphere. This circulation feeds a circumplanetary disk that viscously expels gaseous material back into the parent nebula, maintaining the system in a quasi-steady state. Here we investigate the formation of natural satellites of Jupiter and Saturn within the framework of this newly outlined picture. We begin by considering the long-term evolution of solid material, and demonstrate that the circumplanetary disk can act as a global dust trap, where $s_{\bullet}\sim0.1-10\,$mm grains achieve a hydrodynamical equilibrium, facilitated by a balance between radial updraft and aerodynamic drag. This process leads to a gradual increase in the system's metallicity, and eventually culminates in the gravitational fragmentation of the outer regions of the solid sub-disk into $\mathcal{R}\sim100\,$km satellitesimals. Subsequently, satellite conglomeration ensues via pairwise collisions, but is terminated when disk-driven orbital migration removes the growing objects from the satellitesimal feeding zone. The resulting satellite formation cycle can repeat multiple times, until it is brought to an end by photo-evaporation of the parent nebula. Numerical simulations of the envisioned formation scenario yield satisfactory agreement between our model and the known properties of the Jovian and Saturnian moons.

Day 1706

Monday.

2005.07480
Zodiacal light observations and its link with cosmic dust: a review
Lasue, et al

The zodiacal light is a night-glow mostly visible along the plane of the ecliptic. It represents the background radiation associated with solar light scattered by the tenuous flattened interplanetary cloud of dust particles surrounding the Sun and the planets. It is an interesting subject of study, as the source of the micrometeoroids falling on Earth, as a link to the activity of the small bodies of the Solar System, but also as a foreground that veils the low brightness extrasolar astronomical light sources. In this review, we summarize the zodiacal light observations that have been done from the ground and from space in brightness and polarization at various wavelength ranges. Local properties of the interplanetary dust particles in some given locations can be retrieved from the inversion of the zodiacal light integrated along the light-of-sight. We show that the current community consensus favors that the majority of the interplanetary dust particles detected at 1 au originate from the activity of comets. Our current understanding of the interplanetary dust particles properties is then discussed in the context of the recent results from the Rosetta rendezvous space mission with comet 67P/Churyumov-Gerasimenko.

2005.07588

Formation of the large nearby galaxies

Peebles

Observations of the nearby large galaxies that can be examined in particularly close detail suggest that many have small stellar luminosity fractions in bulges and haloes. Simulations of galaxy formation tend to produce considerably larger fractions of the star particles in model bulges, stellar haloes, and more generally in orbits seriously different from circular. The situation might be improved by a prescription for non-Gaussian initial conditions on the scale of galaxies.

Day 1705

Friday.

2005.07122
Velocity dispersions of massive quiescent galaxies from weak lensing and spectroscopy
Utsumi, et al

We use MMT spectroscopy and deep Subaru Hyper Suprime-Cam (HSC) imaging to compare the spectroscopic central stellar velocity dispersion of quiescent galaxies with the effective dispersion of the dark matter halo derived from the stacked lensing signal. The spectroscopic survey (the Smithsonian Hectospec Lensing Survey) provides a sample of 4585 quiescent galaxy lenses with measured line-of-sight central stellar velocity dispersion ($\sigma_{\rm SHELS}$) that is more than 85% complete for $R < 20.6$, $D_{n}4000> 1.5$ and $M_* > 10^{9.5}{\rm M}_{\odot}$. The median redshift of the sample of lenses is 0.32. We measure the stacked lensing signal from the HSC deep imaging. The central stellar velocity dispersion is directly proportional to the velocity dispersion derived from the lensing $\sigma_{\rm Lens}$, $\sigma_{\rm Lens} = (0.98\pm 0.14)\sigma_{\rm SHELS}+(19.89\pm31.89)$. The independent spectroscopic and weak lensing velocity dispersions probe different scales, $\sim3$kpc and $\gtrsim$ 100 kpc, respectively, and strongly indicate that the observable central stellar velocity dispersion for quiescent galaxies is a good proxy for the velocity dispersion of the dark matter halo. We thus demonstrate the power of combining high-quality imaging and spectroscopy to shed light on the connection between galaxies and their dark matter halos.

Day 1704

Wednesday, Thursday.

2005.05331
The $n$-point streaming model: how velocities shape correlation functions in redshift space
Kuruvilla, Porciani

Starting from first principles, we derive the fundamental equations that relate the $n$-point correlation functions in real and redshift space. Our result generalises the so-called `streaming model' to higher-order statistics: the full $n$-point correlation in redshift-space is obtained as an integral of its real-space counterpart times the joint probability density of $n-1$ relative line-of-sight peculiar velocities. Equations for the connected $n$-point correlation functions are obtained by recursively applying the generalised streaming model for decreasing $n$. Our results are exact within the distant-observer approximation and completely independent of the nature of the tracers for which the correlations are evaluated. Focusing on 3-point statistics, we use an $N$-body simulation to study the joint probability density function of the relative line-of-sight velocities of pairs of particles in a triplet. On large scales, we find that this distribution is approximately Gaussian and that its moments can be accurately computed with standard perturbation theory. We use this information to formulate a phenomenological 3-point Gaussian streaming model. A practical implementation is obtained by using perturbation theory at leading order to approximate several statistics in real space. In spite of this simplification, the resulting predictions for the matter 3-point correlation function in redshift space are in rather good agreement with measurements performed in the simulation. We discuss the limitations of the simplified model and suggest a number of possible improvements. Our results find direct applications in the analysis of galaxy clustering but also set the basis for studying 3-point statistics with future peculiar-velocity surveys and experiments based on the kinetic Sunyaev-Zel'dovich effect.

Day 1703

Tuesday.

2005.04604
Intrinsic and extrinsic correlations of galaxy shapes and sizes in weak lensing data
Ghosh, et al

The subject of this paper are shape and size correlations of galaxies due to weak gravitational lensing and due to direct tidal interaction of elliptical galaxies with gravitational fields sourced by the cosmic large-scale structure. Setting up a linear intrinsic alignment model for elliptical galaxies which parameterises the reaction of the galaxy to an external tidal shear field through the velocity dispersion, we predict intrinsic correlations and cross-correlations with weak lensing for both shapes and sizes, juxtaposing both types of spectra with lensing. We quantify the observability of the intrinsic shape and size correlations and estimate with the Fisher-formalism how well the alignment parameter can be determined from the Euclid weak lensing survey. Specifically, we find a contamination of the weak lensing convergence spectra with an intrinsic size correlation amounting to up to 10% over a wide multipole range $\ell=100\ldots 300$, with a corresponding cross-correlation exhibiting a sign change, similar to the cross-correlation between weak lensing shear and intrinsic shapes. A determination of the alignment parameter yields a precision of a few percent forecasted for Euclid, and we show that all shape and many size correlations should be measurable with Euclid.

Day 1702

Monday.

2005.03664
Cosmic variance of the 21-cm global signal
Muñoz, Cyr-Racine

Cosmological measurements of the 21-cm line of neutral hydrogen are poised to dramatically enhance our understanding of the early universe. In particular, both the epochs of reionization and cosmic dawn remain largely uncharted, and the 21-cm signal is one of the few probes to reach them. The simplest 21-cm measurement is the global signal (GS), which corresponds to the averaged absorption or emission of 21-cm photons across the entire sky. While bright radio foregrounds swamp the cosmic signal over the entire frequency range observable, presenting a formidable hurdle, they can in principle be subtracted, given enough sensitivity. Here, however, we point out an additional---and irreducible---source of uncertainty for the 21-cm GS: cosmic variance. The cosmic-variance noise arises from the finite volume of the universe accessible to 21-cm experiments. Due to the cosmological redshifting of 21-cm photons, each observed frequency probes our universe during a particular cosmic age, corresponding to a narrow redshift slice. The presence of large 21-cm fluctuations makes the GS within each slice different than the GS averaged over the entire universe. We estimate the size of this cosmic-variance noise, and find that for a standard scenario it has a size of $\sim 0.1$ mK, which is $\sim 10\%$ of the size of the expected instrumental noise of a year-long experiment. Interestingly, cosmic variance can overtake instrumental noise for scenarios with extreme 21-cm fluctuations, such as those suggested to explain the sharpness of the claimed EDGES detection. Moreover, as large-scale 21-cm fluctuations are coherent over long distances, cosmic variance correlates the measurements of the GS at nearby redshifts, leading to off-diagonal uncertainties that have so far been neglected.

2005.03733

Cataclysmic variables as possible counterparts of ancient Far Eastern guest stars

Hoffmann, Vogt

Continuing our efforts to select possible classical nova candidates among Far Eastern guest stars and to identify them with modern cataclysmic variables (CVs), we present a search for counterparts in 24 promising areas of the sky corresponding to ancient observations between 204 BCE and 1690 CE. These areas have been derived by us in a previous paper. Based on physical entities of the CVs in our areas and reasonable magnitude limits compatible with the distribution of known eruption amplitudes of telescopic classical novae, we present a catalogue of a total of 80 CVs and related targets which could possibly have caused the historical sightings. This list could potentially be reduced by additionally discussing further information more vaguely given in the text. In some cases, we present a detailed discussion of the interpretation of ancient sources confronting them with properties of the brightest CVs in the field. In order to estimate whether this list is representative, we discuss the distribution of CV types in our catalogue of counterparts for the historical events. Compared to the entire sky, the surface density of most CV subtypes in our search fields reveals similar values, except for polars and intermediate polars, i. e. strongly magnetic CVs, for which a significant excess in our search fields was detected. Finally, we give an outlook towards future research in this topic, and add in an Appendix a complete atlas of the celestial maps of all 24 guest star events, displaying the search areas and locations of CVs within them.

2005.04109

Reconstructing the gravitational lensing potential from the Lyman-$\alpha$ Forest

Metcalf, et al

We demonstrate a method for reconstructing the weak lensing potential from the Lyman-$\alpha$ forest data. We derive an optimal estimator for the lensing potential on the sky based on the correlation between pixels in real space. This method effectively deals with irregularly spaced data, holes in the survey, missing data and inhomogeneous noise. We demonstrate an implementation of the method with simulated spectra and weak lensing. It is shown that with a source density of $>\sim 0.5$ per square arcminutes and $\sim 200$ pixels in each spectrum ($\lambda / \Delta\lambda = 1300$) the lensing potential can be reconstructed with high fidelity if the relative absorption in the spectral pixels is signal dominated. When noise dominates the measurement of the absorption in each pixel the noise in the lensing potential is higher, but for reasonable numbers of sources and noise levels and a high fidelity map the lensing potential is obtainable. The lensing estimator could also be applied to lensing of the Cosmic Microwave Background (CMB), 21 cm intensity mapping (IM) or any case in which the correlation function of the source can be accurately estimated.

2005.04207

KiDS+VIKING-450: improved cosmological parameter constraints from redshift calibration with self-orgainising maps

Wright, et al

We present updated cosmological constraints for the KiDS+VIKING-450 cosmic shear dataset (KV450), estimated using redshift distributions and photometric samples defined using self organising maps (SOMs). Our fiducial analysis finds marginal posterior constraints of $S_8\equiv\sigma_8\sqrt{\Omega_{\rm m}/0.3}=0.716^{+0.043}_{-0.038}$; smaller than, but fully consistent with, previous work using this dataset ($|\Delta S_8| = 0.023$). We analyse additional samples and redshift distributions constructed in three ways: excluding certain spectroscopic surveys during redshift calibration, excluding lower-confidence spectroscopic redshifts in redshift calibration, and considering only photometric sources which are jointly calibrated by at least three spectroscopic surveys. In all cases, the method utilised here proves robust: we find a maximal deviation from our fiducial analysis of $|\Delta S_8| \leq 0.009$ for all samples defined and analysed using our SOM. Our largest shift in $S_8$ is found when calibrating redshift distributions without the DEEP2 spectroscopic subset, where we find $S_8=0.707_{-0.042}^{+0.046}$. This difference with respect to the fiducial is both significantly smaller than, and in the opposite direction to, the equivalent shift from previous work. No sample analysed in this work results in a meaningful positive shift in $S_8$ with respect to our fiducial constraints. These results suggest that our improved cosmological parameter estimates are insensitive to pathological misrepresentation of photometric sources by the spectroscopy used for direct redshift calibration, and therefore that this systematic effect cannot be responsible for the observed difference between $S_8$ estimates made with KV450 and Planck CMB probes.

Day 1701

Wednesday, Thursday, Friday.

2005.?????

A naked-eye triple system with a non accreting black hole in the inner binary
Triviniu, et al


Several dozen optical echelle spectra demonstrate that HR 6819 is a hierarchical triple. A classical Be star is in a wide orbit with an unconstrained period around an inner 40 d binary consisting of a B3 III star and an unseen companion in a circular orbit. The radial-velocity semi-amplitude of 61.3 km s−1 of the inner star and its minimum (probable) mass of 5.0 M⊙ (6.3 ± 0.7 M⊙ ) imply a mass of the unseen object of ≥4.2 M⊙ (≥5.0 ± 0.4 M⊙), that is, a black hole (BH). The spectroscopic time series is stunningly similar to observations of LB-1. A similar triple-star architecture of LB-1 would reduce the mass of the BH in LB-1 from ∼70 M⊙ to a level more typical of Galactic stellar remnant BHs. The BH in HR 6819 probably is the closest known BH to the Sun, and together with LB-1, suggests a population of quiet BHs. Its embedment in a hierarchical triple structure may be of interest for models of merging double BHs or BH + neutron star binaries. Other triple stars with an outer Be star but without BH are identified; through stripping, such systems may become a source of single Be stars.

2005.02419
KiDS+VIKING+GAMA: testing semi-analytic models of galaxy evolution with galaxy-galaxy-galaxy-lensing
Like, et al

Several semi-analytic models (SAMs) try to explain how galaxies form, evolve and interact inside the dark matter large-scale structure. These SAMs can be tested by comparing their predictions for galaxy-galaxy-galaxy-lensing (G3L), which is weak gravitational lensing around galaxy pairs, with observations. We evaluate the SAMs by Henriques et al. (2015; H15) and by Lagos et al. (2012; L12), implemented in the Millennium Run, by comparing their predictions for G3L to observations at smaller scales than previous studies and also for pairs of lens galaxies from different populations. We compare the G3L signal predicted by the SAMs to measurements in the overlap of the Galaxy And Mass Assembly survey (GAMA), the Kilo-Degree Survey (KiDS), and the VISTA Kilo-degree Infrared Galaxy survey (VIKING), splitting lens galaxies into two colour and five stellar-mass samples. Using an improved G3L estimator, we measure the three-point correlation of the matter distribution for mixed lens pairs with galaxies from different samples, and unmixed lens pairs with galaxies from the same sample. Predictions by the H15 SAM agree with the observations for all colour-selected and all but one stellar-mass-selected sample with 95% confidence. Deviations occur for lenses with stellar masses below $9.5h^{-2}\mathrm{M}_\odot$ at scales below $0.2h^{-1}\mathrm{Mpc}$. Predictions by the L12 SAM for stellar-mass selected samples and red galaxies are significantly higher than observed, while the predicted signal for blue galaxy pairs is too low. The L12 SAM predicts more pairs of small stellar-mass and red galaxies than the H15 SAM and the observations, as well as fewer pairs of blue galaxies. Likely explanations are different treatments of environmental effects by the SAMs and different models of the initial mass function. We conclude that G3L provides a stringent test for models of galaxy formation and evolution.

2005.02465

Fisher matrix for multiple tracers: all you can learn from large-scale structure without assuming a model

Boschetti, et al

The galaxy power spectrum is one of the central quantities in cosmology. It contains information about the primordial inflationary process, the matter clustering, the baryon-photon interaction, the effects of gravity, the galaxy-matter bias, the cosmic expansion, the peculiar velocity field, etc.. Most of this information is however difficult to extract without assuming a specific cosmological model, for instance $\Lambda$CDM and standard gravity. In this paper we explore instead how much information can be obtained that is independent of the cosmological model, both at background and linear perturbation level. We determine the full set of model-independent statistics that can be constructed by combining two redshift bins and two distinct tracers. We focus in particular on the statistics $r(k,z_1,z_2)$, defined as the ratio of $f\sigma_8(z)$ at two redshift shells, and we show how to estimate it with a Fisher matrix approach. Finally, we forecast the constraints on $r$ that can be achieved by future galaxy surveys, and compare it with the standard single-tracer result. We find that $r$ can be measured with a precision from 3 to 11%, depending on the survey. Using two tracers, we find improvements in the constraints up to a factor of two.

2005.03030

Observability of dark matter substructure with pulsar timing correlations

Ramani, et al

Dark matter substructure on small scales is currently weakly constrained, and its study may shed light on the nature of the dark matter. In this work we study the gravitational effects of dark matter substructure on measured pulsar phases in pulsar timing arrays (PTAs). Due to the stability of pulse phases observed over several years, dark matter substructure around the Earth-pulsar system can imprint discernible signatures in gravitational Doppler and Shapiro delays. We compute pulsar phase correlations induced by general dark matter substructure, and project constraints for a few models such as monochromatic primordial black holes (PBHs), and Cold Dark Matter (CDM)-like NFW subhalos. This work extends our previous analysis, which focused on static or single transiting events, to a stochastic analysis of multiple transiting events. We find that stochastic correlations, in a PTA similar to the Square Kilometer Array (SKA), are uniquely powerful to constrain subhalos as light as $\sim 10^{-13}~M_\odot$, with concentrations as low as that predicted by standard CDM.

Day 1700

Tuesday.

2005.00543
Predicting cosmological observables with PyCosmo
Tarsitano, et al

Current and upcoming cosmological experiments open a new era of precision cosmology, thus demanding accurate theoretical predictions for cosmological observables. Because of the complexity of the codes delivering such predictions, reaching a high level of numerical accuracy is challenging. Among the codes already fulfilling this task, $\textsf{PyCosmo}$ is a Python based framework providing solutions to the Einstein-Boltzmann equations and accurate predictions for cosmological observables. In this work, we first describe how the observables are implemented. Then, we check the accuracy of the theoretical predictions for background quantities, power spectra and Limber and beyond-Limber angular power spectra by comparison with other codes: the Core Cosmology Library ($\texttt{CCL}$), $\texttt{CLASS}$, $\texttt{HMCode}$ and $\texttt{iCosmo}$. In our analysis we quantify the agreement of $\textsf{PyCosmo}$ with the other codes, for a range of cosmological models, monitored through a series of $\textit{unit tests}$. $\textsf{PyCosmo}$, conceived as a multi purpose cosmology calculation tool in $\texttt{Python}$, is designed to be interactive and user friendly. A current version of the code (without the Boltzmann Solver) is publicly available and can be used interactively on the platform $\textsf{PyCosmo Hub}$, all accessible from this link: https://cosmology.ethz.ch/research/software-lab/PyCosmo.html . On the hub the users can perform their own computations using $\texttt{Jupyter Notebooks}$ without the need of installing any software, access to the results presented in this work and benefit from tutorial notebooks illustrating the usage of the code. The link above also redirects to the code release and documentation.

Day 1699

Monday.

2005.00009
A hydrodynamical halo model for weak-lensing cross correlations
Mead, et al

On the scale of galactic haloes, the distribution of matter in the cosmos is affected by energetic, non-gravitational processes; so-called baryonic feedback. A lack of knowledge about the details of how feedback processes redistribute matter is a source of uncertainty for weak-lensing surveys, which accurately probe the clustering of matter in the Universe over a wide range of scales. We develop a cosmology-dependent model for the matter distribution that simultaneously accounts for the clustering of dark matter, gas and stars. We inform our model by comparing it to power spectra measured from the BAHAMAS suite of hydrodynamical simulations. As well as considering matter power spectra, we also consider spectra involving the electron-pressure field, which directly relates to the thermal Sunyaev-Zel'dovich (tSZ) effect. We fit parameters in our model so that it can simultaneously model both matter and pressure data and such that the distribution of gas as inferred from tSZ has influence on the matter spectrum predicted by our model. We present two variants; one that matches the feedback-induced suppression seen in the matter-matter power spectrum at the per-cent level and a second that matches the matter-matter data slightly less well (~2 per cent), but that is able to simultaneously model the matter-electron pressure spectrum at the ~15 per-cent level. We envisage our models being used to simultaneously learn about cosmological parameters and the strength of baryonic feedback using a combination of tSZ and lensing auto- and cross-correlation data.

2005.00055

The importance of galaxy clustering and weak lensing cross-correlations within the photometric Euclid survey

Tutusaus, et al

The data from the Euclid mission will enable the measurement of the photometric redshifts, angular positions, and weak lensing shapes for over a billion galaxies. This large dataset will allow for cosmological analyses using the angular clustering of galaxies and cosmic shear. The cross-correlation (XC) between these probes can tighten constraints and it is therefore important to quantify their impact for Euclid. In this study we carefully quantify the impact of XC not only on the final parameter constraints for different cosmological models, but also on the nuisance parameters. In particular, we aim at understanding the amount of additional information that XC can provide for parameters encoding systematic effects, such as galaxy bias or intrinsic alignments (IA). We follow the formalism presented in Euclid Collaboration: Blanchard et al. (2019) and make use of the codes validated therein. We show that XC improves the dark energy Figure of Merit (FoM) by a factor $\sim 5$, whilst it also reduces the uncertainties on galaxy bias by $\sim 17\%$ and the uncertainties on IA by a factor $\sim 4$. We observe that the role of XC on the final parameter constraints is qualitatively the same irrespective of the galaxy bias model used. We also show that XC can help in distinguishing between different IA models, and that if IA terms are neglected then this can lead to significant biases on the cosmological parameters. We find that the XC terms are necessary to extract the full information content from the data in future analyses. They help in better constraining the cosmological model, and lead to a better understanding of the systematic effects that contaminate these probes. Furthermore, we find that XC helps in constraining the mean of the photometric-redshift distributions, but it requires a more precise knowledge of this mean in order not to degrade the final FoM. [Abridged]

Day 1698

Friday.

2004.14630
HI filaments are cold and associated with dark molecular gas.  HI4PI based estimates of the local diffuse CO-dark H2 distribution
Kalberia, Kerp, Haud

Context. There are significant amounts of H2 in the Milky Way. Due to its symmetry H2 does not radiate at radio frequencies. CO is thought to be a tracer for H2, however CO is formed at significantly higher opacities than H2. Thus, toward high Galactic latitudes significant amounts of H2 are hidden and called CO-dark. Aims. We demonstrate that the dust-to-gas ratio is a tool to identify locations and column densities of CO-dark H2. Methods. We adopt the hypothesis of a constant E(B-V)/NH ratio, independent of phase transitions from HI to H2 . We investigate the Doppler temperatures TD , from a Gaussian decomposition of HI4PI data, to study temperature dependencies of E(B-V)/NHI. Results. The E(B-V)/NHI ratio in the cold HI gas phase is high in comparison to the warmer one. We consider this as evidence that cold HI gas toward high Galactic latitudes is associated with H2. Beyond CO-bright regions we find for TD < 1165 K a correlation (NHI + 2NH2 )/NHI prop -log T_D. In combination with a factor XCO = 4.0 10 20 cm^-2 (K km s^-1 )-1 this yields for the full-sky NH /E(B-V) sim 5.1 to 6.7 10^21 cm^-2 mag^-1, compatible with X-ray scattering and UV absorption line observations. Conclusions. Cold HI with T_D < 1165 K contains on average 46% CO-dark H2. Prominent filaments have TD < 220 K and typical exitation temperatures Tex sim 50 K. With a molecular gas fraction of > 61% they are dominated dynamically by H2.