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.
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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. ...
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....
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...
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...
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...
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...
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),...
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...
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...
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...
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...
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...
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...
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 flip (Ravoux et al. in prep.(a),...
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...
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...
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...
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.
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...
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...
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...
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...
