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Dr Cullan Howlett (The University of Queensland)03/02/2025, 08:30
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Edward Taylor (Swinburne University of Technology)03/02/2025, 08:50
I will give a brief overview of the 4MOST Hemisphere Survey (4HS), with particular emphasis on our cosmology science goals of mapping mass and motion on ~Gpc scales, and highlighting several key aspects of the 4HS experimental design relative to past and current surveys.
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Julian Ernesto BAUTISTA03/02/2025, 09:20
In this talk I will give an overview of the Dark Energy Spectroscopic Instrument (DESI) and their first cosmological results from the first-year dataset. I will briefly introduce the DESI peculiar velocity program, aiming the measurement of 180k distances with Tully-Fisher and Fundamental Plane relations. I will also briefly introduce the Zwicky Transient Facility (ZTF) and their supernovae...
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Prof. Elmo Tempel (University of Tartu)03/02/2025, 09:50
4MOST is a next-generation survey that will start operating in 2025 and will carry out a five-year survey program. 4MOST consists of 18 individual surveys that will be operationally carried out as a single survey. Among those 18 surveys, there are specific peculiar velocity subsurveys that will significantly extend currently available catalogues of peculiar velocities. To optimise the 4MOST...
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Dr Segev BenZvi (University of Rochester)03/02/2025, 10:10
The Tully-Fisher relation (TFR) is an empirical correlation between the instrinsic luminosity of a spiral galaxy and its asymptotic rotational velocity. Here we present measurements of the TFR from a secondary target program at the Dark Energy Spectroscopic Instrument, a robotic fiber-fed spectrograph located at Kitt Peak National Observatory. By positioning fibers on the galaxies' nuclei and...
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Khaled Said (Research Fellow)03/02/2025, 11:00
The Dark Energy Spectroscopic Instrument (DESI) Peculiar Velocity Survey aims to measure the peculiar velocities of early- and late-type galaxies within the DESI footprint using both the Fundamental Plane and Tully-Fisher relations. These direct measurements promise to tighten constraints on the growth rate by a factor of 2.5 at z=0.1 compared to redshift-space distortions alone. I'll present...
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Caitlin Ross (The University of Queensland)03/02/2025, 11:20
In this talk I will present the some of the peculiar velocity measurements from the first year of observations from the Dark Energy Spectroscopic Instrument (DESI) which will be used alongside redshift space distortion measurements to constrain the growth rate of structure. Over five years DESI is using a 5000 fibre spectrograph to map 3D positions of tens of millions of galaxies. At the same...
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Nora Sherman (Boston University)03/02/2025, 11:40
Type Ia supernova science holds steady as one of the leading probes to study the behavior of our universe, and yet, even the most complete and advanced datasets to date suffer from poor statistics and systematics at low redshift. To combat these pitfalls, the Dark Energy Bedrock All-Sky Supernovae (DEBASS) program will provide the largest consistently calibrated low-z SN Ia data in the...
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Bastien Carreres03/02/2025, 12:00
Various cosmological parameters such as $H_0$ and $f\sigma_8$ that can be measured using Type Ia Supernovae (SNe Ia) have been shown to be in tension with measurements from the early universe. We can improve cosmological parameter measurements and reduce scatter on the Hubble diagram by focusing on redshift scatter from leveraging galaxies in groups. Using the low-redshift sample from...
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Lister Staveley-Smith (ICRAR/UWA)03/02/2025, 12:20
We report on the successful completion and release of HI data for 2,400 galaxies from the ASKAP WALLABY pilot surveys covering 300 sq.deg of (mainly) southern sky. We also provide an update on the 5-yr full WALLABY survey which is mapping galaxies in HI over a further 15,000 sq.deg. It is anticipated that, by 2028, WALLABY will have 200,000 redshifts and velocity widths for the purposes of...
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Prof. Helene COURTOIS (University Lyon 1)03/02/2025, 15:30
We use direct galaxy distances to compute the 3D peculiar/gravitational velocity field, enabling us to reconstruct the mass distribution driving these motions. Filaments, walls, and voids are integrated into a broader view of large-scale gravitational structures defined by empty regions. The key benefit of mapping superclusters as watershed basins is their robust definition, making them...
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Matthew Colless (Australian National University)03/02/2025, 16:00
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Yuyu Wang04/02/2025, 08:30
In this paper, we introduce a U-Net model of deep learning algorithms for reconstructions of the 3D peculiar velocity field, which simplifies the reconstruction process with enhanced precision. We test the adaptability of the U-Net model with simulation data under more realistic conditions, including the redshift space distortion effect and halo mass threshold. Our results show that the U-Net...
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Aurélien Valade04/02/2025, 09:00
Scarce, anisotropic, extremely noisy and prone to various biases: peculiar velocity surveys are not trivial to interpret. In this talk, I'll present HAMLET, a powerful GPU-oriented code that implements a field-level forward modeling method, which enables the reconstruction of the matter distribution in the Local Universe and the large scale motion associated to it. An application to the 38,000...
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Prof. Jens Jasche (Stockholm University)04/02/2025, 09:30
The study of peculiar velocities provides a unique window into the dynamics of the nearby universe, allowing us to probe the non-linear regime of cosmic structure formation and test fundamental physics related to the Universe's expansion. As observational data quality and scale improve, modeling the nearby universe becomes more complex, requiring techniques that capture the non-linear dynamics...
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Daniel Pomarède04/02/2025, 10:00
The Cosmography inferred for the Cosmicflows-4 Catalog of 56000 peculiar velocities is presented, expanding on the HMC reconstruction recently published in Valade et al, Nature Astronomy (2024). Beside the 3D mapping of the overdensity and velocity fields, a map of the V-Web is constructed by analysis of the eigenvalues of the shear tensor. Earlier findings in the structure of the Cosmic...
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Rianna Bell (The University of Queensland)04/02/2025, 11:00
Over the last two decades, the rapid increase in both quantity and quality of cosmological observations has revealed growing evidence of discrepancies between values of key cosmological parameters within the standard model when measured using late vs early universe probes. Gravitational wave observations could provide new insight into these "cosmological tensions" by enabling independent...
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Richard Stiskalek (University of Oxford)04/02/2025, 11:20
The peculiar velocity field of the local Universe provides direct insights into its matter distribution and the underlying theory of gravity, and is essential in cosmological analyses for distinguishing systematic deviations from the Hubble flow. Numerous methods have been developed to reconstruct the local density and velocity fields (at $z \lesssim 0.05$), typically constrained by...
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Paula Boubel04/02/2025, 11:40
A density field mapped from a galaxy redshift survey can be used to predict the peculiar velocity field, up to normalisation and any external tidal field. Fitting such a model for the predicted peculiar velocities to those measured using a distance estimator such as the Tully-Fisher relation provides a test for theories of gravity via a measurement of the growth factor. We present a Bayesian...
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David Parkinson (Korea Astronomy and Space Science Institute)04/02/2025, 12:00
The standard model of cosmology, LambdaCDM, predicts a velocity field generated by, and coupled to, the distribution of matter density perturbations. This coupling, β, can be directly predicted from the theory of gravity, and when it is measured, can be used to test the cosmological model. However, correctly modelling the predicted velocity field, beyond linear theory, can be challenging. ...
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Dr Simon Goode (Monash University)04/02/2025, 12:20
As we discover increasing numbers of gravitational wave sources, our ability to use them for Cosmological studies advances. With next-generation gravitational-wave observatories, we expect constraints on H0 using gravitational waves to reach the sub-percent level. We must first understand the systematic uncertainties that affect current gravitational-wave cosmological methods to achieve this....
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Dr Alexandra Dupuy (Korea Institute for Advanced Study)04/02/2025, 15:30
The large-scale structures in our local Universe emerge from the rivalry between gravitation and the expansion of the Universe, akin to a cosmic tug-of-war. Peculiar velocities of galaxies reflect their motion primarily governed by gravitational interactions, making them unbiased dynamical tracers of the total matter in the Universe (including dark and luminous matter). These velocities serve...
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Mike Hudson (Waterloo Centre for Astrophysics)04/02/2025, 16:00
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Leonardo Giani05/02/2025, 08:30
Does the Universe look the same everywhere? Are we living in a special place?
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These questions have intrigued laypeople and philosophers alike for centuries, but for the first time, astronomers are in the position of addressing them quantitatively. Existing state-of-the-art maps of the Universe around us, combined with an upcoming wealth of observational data, compel us to seek a deeper... -
Francesco Sorrenti (University of Geneva)05/02/2025, 09:00
Peculiar velocities surveys are going to play a key role in testing our knowledge about the nearby universe and our cosmological assumptions. In this talk, I will review what peculiar velocities are and some recent fundings and analysis that I have been developed concerning these novel observables. In particular, I will focus on the information we can extrapolate about peculiar velocities from...
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Prof. Tamara Davis (The University of Queensland)05/02/2025, 09:30
In this talk I will look at some theoretical details of peculiar velocities. We’ll explore different ways that peculiar velocities can be measured and corrected for. We’ll discuss what it means to say “space is expanding” and answer the question of whether it is possible to have a galaxy “at rest” with respect to us if it is beyond the Hubble sphere (which is similar to asking whether a...
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Dr Mark Neyrinck (Blue Marble Space Institute of Science; University of Denver)05/02/2025, 09:50
There is an analogy between terrestrial and cosmic watersheds, and river networks. A terrestrial (usual) watershed is a patch of land where water all flows into the same river. Cosmic watersheds gather matter into the cosmic web of walls and filaments, all flowing inward toward galaxies. How good is that analogy? One quantitative way to investigate this question is through a "cosmic...
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David Wiltshire05/02/2025, 10:10
The timescape model revisits the foundations of general relativity — the issues of quasilocal energy and angular momentum in a universe with large complex structures. Quantitative predictions had to wait til the 2020s for observations to reach a precision to distinguish the timescape model from the 100-year old Friedmann-Lemaître models, on which standard cosmology is based. With a huge...
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Prof. Renee Kraan-Korteweg (University of Cape Town)05/02/2025, 11:00
The deep SARAO MeerKAT Galactic Plane Survey (SMGPS) covers the whole southern Milky Way along a narrow strip of Δ𝑏 ∼ 3◦. While primarily aimed at exploring the inner Galaxy, the SMGPS provides a unique opportunity to trace the large-scale distribution of galaxies from their redshifted HI-line emission. Thanks to the excellent resolution and sensitivity of the SMGPS (rms = 0.30-0.60 mJy/beam),...
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Sambatriniaina Rajohnson (Department of Astronomy, University of Cape Town; INAF - Osservatorio Astronomico di Cagliari.)05/02/2025, 11:20
The Vela supercluster (VSCL) is an extended and massive supercluster located at l ~ 275°±15°; |b| < 10°, and cz ~ 18000 km s-1. Its location is of particular interest in view of its proximity to the apex, where residual bulk flows suggest a considerable surplus of mass. However, a major fraction of its extent has little data below Galactic latitudes of |b| < 7–8° because of the obscuration by...
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Dmitry Makarov (Special Astrophysical Observatory of the Russian Academy of Sciences)05/02/2025, 11:40
A representative sample of nearby galaxies is the basis for solving various problems of extragalactic astronomy, a source of important information about galaxies, their formation and evolution, distribution in space and the formation of the large-scale structure of the Universe. The Local Volume, a sphere of about 10 Mpc radius, gives us a unique opportunity to observe a large number of dwarf...
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Danila Makarov05/02/2025, 12:00
We analyzed the velocity field near the Local Group outside the virial zones of Milky Way and Andromeda galaxies on scales from 400 to 1400 kpc. The Hubble flow model allows us to estimate the total mass of the Local Group of $M_\mathrm{LG} = (2.42 \pm 0.12) \times 10^{12}$ $M_\odot$, which is in excellent agreement with the sum of the individual masses of Our Galaxy and Andromeda inside their...
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Jenny Sorce06/02/2025, 08:30
To understand dark matter and dark energy, which make up 95% of the Universe, cosmological surveys must achieve percent-level precision. However, this precision uncovers tensions between observations and the standard cosmological model, potentially arising from systematic biases. CLONES (Constrained LOcal & Nesting Environment Simulations) are digital twins of the local Universe, derived from...
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Dr Francisco Villaescusa-Navarro06/02/2025, 09:00
I will present a new framework to infer the value of cosmological parameters from peculiar velocity surveys. Our approach, which has been tested on thousands of state-of-the-art cosmological hydrodynamic simulations from the CAMELS project, takes a set of galaxies, together with their peculiar velocities, and performs field-level simulation-based inference while marginalizing over baryonic...
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Bastien Carreres06/02/2025, 09:30
Type Ia supernovae have been widely used to constrain the dark energy density and its equation of state parameter. The statistics and homogeneity expected from new generations of photometric surveys such as ZTF and Rubin-LSST will allow us to use SNe Ia to probe large-scale structures and make new constraints on parameters including the growth rate of structure, $f\sigma_8$. To prepare for...
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Matthew Colless (Australian National University), Melissa Campbell (Australian National University)06/02/2025, 09:50
Galaxy distances measured using the Fundamental Plane have relative errors of 20-30%. Beyond a few tens of Mpc, this means that the errors in galaxy peculiar velocities are generally larger than the peculiar velocities themselves. It is therefore highly desirable to find ways to reduce the uncertainties in Fundamental Plane distance estimates. The intrinsic scatter about the Fundamental Plane...
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Dr Trystan Scott Lambert (ICRAR-UWA)06/02/2025, 10:10
The Wide Area Vista Extragalactic Survey (WAVES) is part of a suite of ambitious surveys utilizing the dedicated 4-meter Multi-Object Spectrograph (4MOST) in Chile. WAVES aims to measure the redshifts of 1.7 million galaxies and is scheduled to launch in December 2025. These next-generation redshift surveys are essential for probing the large-scale structure of the universe, offering...
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Andrew Nguyen (Swinburne University of Technology)06/02/2025, 11:00
Correlations between new large-scale structure and transient surveys allow us to perform novel tests of gravitational physics. Peculiar velocities create magnitude fluctuations in transient sources. In this talk I will present correlation measurements using data from the Dark Energy Spectroscopic Instrument and Pantheon+ supernovae magnitudes along with matched simulations. By fitting...
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Corentin RAVOUX (LPCA, Clermont-Ferrand, France)06/02/2025, 11:20
Using supernovae of type Ia for inferring the growth rate of structure (fσ8) has seen a significant gain in interest in recent years. In particular, maximizing the potential of fσ8 constraints can be achieved by coupling peculiar velocity estimators with the underlying density field. I will present a recent software called
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Mr Michael Williams06/02/2025, 11:40
We apply fully general relativistic (GR) ray-tracing to large cosmological simulations. The simulations of Macpherson et al. integrate the full Einstein equations from initial conditions at the cosmic microwave background (CMB) to the present epoch. These simulations reproduce a realistic cosmic web from the initial matter power spectrum, which is already well studied.
For the first time,...
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Joël Mayor (ETH Zürich)06/02/2025, 12:00
With the advent of next-generation radio observations with the upcoming SKA Observatory, HI Galaxy surveys will be able to probe the late-time Universe with unprecedented sensitivity, offering the possibility to constraint cosmology in a complementary manner to standard spectroscopic surveys. In preparation for this scientific case, realistic simulations of large-sky volumes with good...
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Yan Lai (The University of Queensland)06/02/2025, 12:20
The latest Dark Energy Spectroscopic Instrument (DESI) survey results show that dark energy could evolve with time. This is achieved by constraining one of the standard rulers: the sound horizon at the drag epoch, with DESI Baryon Acoustic Oscillation, Cosmic Microwave Background, and supernovae. However, we could also constrain cosmological parameters with the other standard ruler: the...
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Amber Hollinger (Université Claude Bernard Lyon 1)06/02/2025, 15:30
A promising method for measuring fσ8 involves comparing observed peculiar velocities with those predicted from a galaxy density field using linear perturbation theory. While previous studies have evaluated the effectiveness of this method using N-body simulations these typically focus on idealized mock galaxy surveys which ignore systematic biases that can arise solely due to survey selection...
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Cullan Howlett06/02/2025, 16:00
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Dr Brent Tully (University of Hawaii)07/02/2025, 08:30
The path from Cepheid variables to type Ia supernovae gives a value of the Hubble constant which significantly disagrees with the value determined from observations of conditions in the early universe and a cosmological model. A totally independent measurement of H0 from observed redshifts and distances is needed to evaluate the possibilities of systematic errors. A path is being explored...
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Rick Watkins07/02/2025, 09:00
We present estimates of the Bulk Flow in volumes of increasing radii using the minimum variance method with data from the CosmicFlows4 catalog. Contrary to expectations, we find that the Bulk Flow amplitude increases with increasing radius, with the Bulk Flow amplitude in a volume of radius $200h^{-1}$Mpc being large enough to have only a 0.003% chance of occurring in the Standard Model. We...
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Abbe Whitford07/02/2025, 09:30
For over a decade there have been contradictory claims in the literature regarding measurements of local bulk flow motions of galaxies, as to whether measurements are consistent or in tension with the currently accepted model of cosmology, Lambda-CDM. A bulk flow measurement can be thought of as an average of galaxy motions sourced by gravity in a volume of space. The robustness of various...
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Mike Hudson (Waterloo Centre for Astrophysics)07/02/2025, 09:50
Cosmic flows are currently undergoing a renaissance with major new peculiar velocity and redshift surveys such as 4HS, DESI and ZTF, as well as new methods like kinetic Sunyaev-Zeldovich effect at high redshifts. I will review the challenges of current data sets that must be overcome to turn Cosmic Flows into competitive cosmological probe, and prospects for the future.
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Y Ma07/02/2025, 10:10
The kinetic Sunyaev-Zeldovich (kSZ) effect represents a secondary anisotropy in the cosmic microwave background (CMB) radiation, caused by the inverse Compton scattering of free electrons in galaxy clusters. Observations from the Planck satellite, as well as the ACT and SPT experiments, have enabled the measurement of this effect, providing insights into the dynamics of large-scale structures....
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Ryan Camilleri (The University of Queensland)07/02/2025, 11:00
Type Ia Supernovae act as standard candles which provide a fundamental way to probe the expansion history of the Universe. While the standard cosmological model fits current data well, uncertainty remains. This uncertainty has led to a wealth of exotic cosmological models being proposed. In my work, I constrain a variety non-standard models using the DES 5-year sample - the largest single...
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Giulia Degni07/02/2025, 11:20
Cosmic voids, large under-dense regions in the Universe, serve as promising laboratories for extracting cosmological information. They offer opportunities to explore deviations from $\Lambda$CDM and provide insights into dark energy and modification of gravity. Upcoming surveys will enable detailed void analyses, allowing access to a huge number of voids. Voids' significance lies in their...
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Geraint Lewis07/02/2025, 11:40
I will present our recent results exploring the integrity of the cosmological principle, the idea that, on sufficient scales, the universe is homogeneous and isotropic. Recent tensions have arisen between the dipole of cosmological sources and its interpretation from the CMB as a kinematic departure from the local Hubble Flow, bringing the cosmological principle into doubt. With a...
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Dr Fei Qin (CPPM)07/02/2025, 12:00
The large-scale structure of the Universe and its evolution over time contains an abundance of cosmological information.One way to unlock this is by measuring the density and momentum power spectrum from the positions and peculiar velocities of galaxies, and fitting the cosmological parameters from these power spectrum.In this work, we will explore the cross power spectrum between the ...
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Anthony Carr (Korea Astronomy and Space Science Institute)07/02/2025, 12:20
At low redshift, peculiar velocities are particularly well-suited to studying the nature of dark energy through the growth rate of structure. Supernovae Ia are precise distance indicators, and we can estimate peculiar velocities from their Hubble residuals at low-redshift, i.e., roughly their departure from motion caused purely by expansion. The Pantheon+ supernova sample is currently the most...
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Ryan Turner (Swinburne University of Technology)07/02/2025, 15:30
Peculiar velocities are velocities imparted onto galaxies by the gravitational influence of their local environment, and so are uniquely suited to be optimal probes of cosmic growth in the local universe. Current and future surveys will cover the entire sky out to redshift z ~ 0.15 and will measure peculiar velocities for hundreds of thousands of galaxies in that volume. Using such an...
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Tamara Davis (The University of Queensland)07/02/2025, 16:00
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Mrs Natalí Soler Matubaro de Santi
A powerful approach to constraining cosmological parameters from galaxy peculiar velocities is to train graph neural networks (GNNs) for field-level likelihood-free inference without scale restrictions. We developed models that robustly infer the value of $\Omega_{\rm m}$ using only the positions and radial velocities of galaxies, achieving resilience to various astrophysical complexities,...
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Minh Nguyen (Kavli IPMU, University of Tokyo)
Field-level inference (FLI) of 3D galaxy data such as those from galaxy surveys or peculiar velocity surveys guarantee optimal constraints since there is no data compression (hence information loss). FLI is further tied to a forward model; such forward model also allows for flexible, modular treatment of differen astrophysical and observational effects, including but not limited to galaxy bias...
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Dr Sushma Kurapati (ASTRON)
Voids are extended low density regions. Recent studies have shown that they have substructure consisting of sub-voids, walls, tendrils, filaments and nodes. Moreover, the structure formation in voids appears to be similar to structure formation of a low density universe. Numerical simulations suggest that the galaxies in voids may preferentially lie within these filamentary void...
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