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Yehuda Hoffman

Publications and source records attributed to Yehuda Hoffman.

At least 19 recordsLinked to original sources
arXiv2026

Cosmography of the Sloan Basin of Attraction and Neighborhood

The Sloan Great Wall is a dominant structure that is relatively nearby. As well as evident in redshift survey maps, its presence is manifested in distortions to cosmic expansion. Here, Hamiltonian Monte Carlo forward reconstruction in a {\Lambda}CDM framework gives probabilistic density and velocity fields constrained by the Cosmicflows-4 compendium of galaxy distances and radial velocities. Streamlines of the reconstructed velocity field started from arbitrary points in space can be followed to sinks, i.e. the minima of the gravitational potential, due to the distribution of mass. A basin of attraction encompasses the volume of all streamlines ending at the same sink. The solution can be assigned probabilities, with uncertainties associated with the imperfect data and the random nature of the {\Lambda}CDM model. The Sloan basin of attraction is by far the largest basin in the study region, extending across a diameter of ~0.13c. It can be described by velocity streamlines that converge on the Sloan Great Wall, by the reconstructed density field, and by the network of filaments of the V-web, formulated by shear in the velocity field. The discussion of these elements is augmented by a video and interactive models. It is of interest to see the relationship of the Ho`oleilana baryon acoustic oscillation feature with the Sloan basin of attraction.

astro-ph.CO↗
arXiv2026

Constraining cosmological simulations with peculiar velocities: a forward-modeling approach

Numerical simulations are a key tool to decipher the dynamics of gravitation. Yet, they fail to spatially reproduce the Universe we observe, limiting comparison between observations and simulations to a statistical level. This is highly problematic for rare, faint or well studied nearby objects that are observed in a single environment. The computational cost of recovering this environment in random simulations is prohibitive. We present Hamlet-PM, a method that enables the constraining of initial conditions for cosmological simulations so as to produce evolved numerical universes that can be directly compared to observations of the Local Universe: constrained simulations. Our method implements the field-level forward modeling of the early-time density field from sparse and noisy measurements of late-time peculiar velocities. The dynamics are integrated with a particle-mesh gravity solver, thus probing the mildly non-linear regime. The code is applied to the Cosmicflows-4 compilation of peculiar velocities up to z < 0.05 (160 Mpc/h). The constrained ICs a re-simulated with a high precision N-body code. A series of one hundred dark-matter only cosmological constrained simulations with a resolution of 512^3 particles in a 500^3 [Mpc/h]3 box is presented. Special attention is given to twelve prominent nearby galaxy clusters, whose simulated counterparts are matched on criteria of mass and separation. We provide a mass estimate constrained by the dynamical environment for each cluster. Field-level forward modeling of the initial conditions produces highly constrained cosmological simulations. Currently, this method already overtakes in quality the pipeline in use in the peculiar-velocity community, although systematic biases still need to be addressed. Furthermore, improving the model is easy thanks to the inherent flexibility of the Bayesian approach.

astro-ph.CO↗
arXiv2025

Fermi-LAT Galactic Center Excess morphology of dark matter in simulations of the Milky Way galaxy

The strongest experimental evidence for dark matter is the Galactic Center gamma-ray excess observed by the Fermi telescope and even predicted prior to discovery as a potential dark matter signature via WIMP dark matter self-annihilations. However, an equally compelling explanation of the excess gamma-ray flux appeals to a population of old millisecond pulsars that also accounts for the observed boxy morphology inferred from the bulge old star population. We employ a set of Milky Way-like galaxies found in the Hestia constrained simulations of the local universe to explore the rich morphology of the central dark matter distribution, motivated by the GAIA discovery of a vigorous early merging history of the Milky Way galaxy. We predict a significantly non-spherical gamma-ray morphology from the WIMP interpretation. Future experiments, such as the Cherenkov Telescope Array, that extend to higher energies, should distinguish between the competing interpretations.

astro-ph.HE↗
arXiv2025

Variable gravitational potential of Milky Way analogues in HESTIA suite

Investigations of trajectories of various objects orbiting the Milky Way (MW) halo with modern precision, achievable in observations by Gaia, requires sophisticated, non-stationary models of the Galactic potential. In this paper we analyze the evolution of the spherical harmonics expansion of MW analogues potential in constrained simulations of the Local Group (LG) from the HESTIA suite. We find that at distances $r\ge 100$~kpc the non-spherical part of the potential demonstrates a significant impact of the environment: ignoring the mass distribution outside the virial radius of the MW results in $>$20\% errors in the potential quadrupole at these distances. {Account of the environment results in a noticeable change of the angular momenta of objects orbiting MW analogues}. Spherical harmonics vary significantly during the last 6 Gyr. We attribute variations of the potential at $r\ge 30$~kpc to the motions of MW satellites and LG galaxies. We also predict that the non-sphericity of the real MW potential should grow with distance in the range $r_\mathrm{vir}<r<500$~kpc, since all realizations of simulated MW-like objects demonstrate such a trend.

astro-ph.GA↗
arXiv2023

The large scale velocity field from the Cosmicflows-4 data

The reconstruction of the large scale velocity field from the grouped Cosmicflows-4 (CF4) database is presented. The lognormal bias of the inferred distances and velocities data is corrected by the Bias Gaussianization correction (BGc) scheme, and the linear density and velocity fields are reconstructed by means of the Wiener filter (WF) and constrained realizations (CRs) algorithm. These tools are tested against a suite of random and constrained Cosmicflows-3-like mock data. The CF4 data consists of 3 main subsamples - the 6dFGS and the SDSS data - and the `others'. The individual contributions of the subsamples have been studied. The quantitative analysis of the velocity field is done mostly by the mean overdensity ($Δ_L(R)$) and the bulk velocity ($V_{\mathrm{bulk}}(R)$) profiles of the velocity field out to $300\, h^{-1}{\rm Mpc}$. The $V_{\mathrm{bulk}}(R)$ and $Δ_{\mathrm L}(R)$ profiles of the CF4 data without its 6dFGS component are consistent with the cosmic variance to within $1σ$. The 6dFGS sample dominates the $V_{\mathrm{bulk}}$ ($Δ_{\mathrm L}$) profile beyond $\sim120\, h^{-1}{\rm Mpc}$, and drives it to roughly a $3.4σ$ ($-1.9σ$) excess (deficiency) relative to the cosmic variance at $R\sim250\ (190)\ \, h^{-1}{\rm Mpc}$. The excess in the amplitude of $V_{\mathrm{bulk}}$ is dominated by its Supergalactic X component, roughly in the direction of the Shapley Concentration. The amplitude and alignment of the inferred velocity field from the CF4 data is at $\sim(2\,-\,3)\,σ$ discrepancy with respect to the $Λ$CDM model. Namely, it is somewhat atypical but yet there is no compelling tension with the model.

astro-ph.CO↗
arXiv2023

The stellar halo in Local Group Hestia simulations I. The in-situ component and the effect of mergers

Theory suggests that mergers play an important role in shaping galactic discs and stellar haloes, which was observationally confirmed in the MW thanks to Gaia data. In this work, aiming to probe the contribution of mergers to the in situ stellar halo formation, we analyse six M31/MW analogues from the HESTIA suite of cosmological hydrodynamical zoom-in simulations of the LG. We found that all the HESTIA galaxies experience between one to four mergers with stellar mass ratios between 0.2 and 1 relative to the host at the time of the merger. These significant mergers, with a single exception, happened 7-11Gyr ago. The overall impact of the most massive mergers in HESTIA is clearly seen as a sharp increase in the orbital eccentricity (and a corresponding decrease in the rotational velocity Vphi of pre-existing disc stars of the main progenitor, thus nicely reproducing the Splash-, Plume-like feature that was discovered in the MW. We do find a correlation between mergers and close pericentric passages of massive satellites and bursts of star formation in the in situ component. Massive mergers sharply increase the disc velocity dispersion of the in situ stars; however, the latest significant merger often heats up the disc up to the numbers when the contribution of the previous ones is less prominent in the age-velocity dispersion relation. In HESTIA galaxies, the in situ halo is an important component of the inner stellar halo where its fraction is about 30-40%, while in the outer parts it typically does not exceed ~5% beyond 15 kpc. The simulations suggest that this component of the stellar haloes continues to grow well after mergers conclude; however, the most significant contribution comes from stars that formed recently before the merger. The orbital analysis of the HESTIA galaxies suggests that wedges in Rmax-Zmax space are mainly populated by the stars born between significant mergers.

astro-ph.GA↗
arXiv2023

The stellar halo in Local Group Hestia simulations II. The accreted component

In the Milky Way, recent progress in the exploration of its assembly history is driven by the tremendous amount of high-quality data delivered by Gaia, which has revealed a number of substructures potentially linked to several ancient accretion events. In this work, aiming to explore the phase-space structure of accreted stars, we analyze six M31/MW analogues from the HESTIA suite of cosmological hydrodynamics zoom-in simulations of the Local Group. We found that all the HESTIA galaxies experience a few dozen mergers but only 1-4 mergers have the stellar mass ratio >0.2 where, depending on the halo definition, the most massive merger contributes from 20% to 70% of the total stellar halo. Individual merger remnants show diverse density distributions at z=0, significantly overlapping with each other and with the in-situ stars in the ELz, UV and RVphi coordinates. The mergers debris often change their position in the ELz with time due to the galactic mass growth and the non-axisymmetry of the potential. In agreement with previous works, we show that even individual merger debris exhibit a number of distinct ELz features. In the UV plane, all HESTIA galaxies reveal radially hot, non-rotating or weakly counter-rotating, Gaia-Sausage-like features. We found an age gradient in Elz space for the individual debris, where the youngest stars, formed in the inner regions of accreting systems, deposit to the innermost regions of the host. The bulk of these stars is being formed during the last stages of accretion, making it possible to date the merger. In actions space (Jr, Jz, Jϕ), the mergers debris do not appear as isolated substructures but are instead scattered over a large parameters area and overlapping with the in-situ stars. We also introduce a purely kinematic space (Jz/Jr-eccentricity), where different merger debris can be disentangled better from each other and from the in-situ stars.

astro-ph.GA↗
arXiv2023

The stellar halo in Local Group Hestia simulations III. Chemical abundance relations for accreted and in-situ stars

Since the chemical abundances of stars are the fossil records of the physical conditions in galaxies, they provide the key information for recovering the assembly history of galaxies. In this work, we explore the chemo-chrono-kinematics of accreted and in-situ stars, by analyzing six M31/MW analogues from the HESTIA suite of cosmological hydrodynamics zoom-in simulations of the Local Group. We found that the merger debris are chemically distinct from the survived dwarf galaxies. The mergers debris have abundances expected for stars originating from dwarfs that had their star formation activity quenched at early times. Accreted stellar haloes, including individual debris, reveal abundance gradients in the ELz, where the most metal-rich stars have formed in the inner parts of the disrupted systems before the merger and mainly contribute to the central regions of the hosts. Therefore, we suggest that abundance measurements in the inner MW will allow constraining better the parameters of building blocks of the MW stellar halo. The MDFs of the individual debris show several peaks and the majority of debris have lower metallicity than the in-situ stars for Lz>0, while non-rotating and retrograde accreted stars are similar to the in-situ. Prograde accreted stars show a prominent knee in the [Fe/H]-[Mg/Fe] plane while the retrograde stars typically deposit to a high-[Mg/Fe] sequence. We found that the metal-poor stars ([Fe/H]<-1) of the HESTIA galaxies exhibit between zero to 80 km/s net rotation which is consistent with the Aurora population. At higher metallicities, we detect a sharp transition (spin-up) from the turbulent phase to a disk-like rotation. Mergers debris are similar in the [Fe/H]-[Mg/Fe] plane. However, combining a set of abundances allows to capture chemical patterns corresponding to different debris, which are the most prominent as a function of stellar age.

astro-ph.GA↗
arXiv2023

Exploring the centre of mass properties of LG-like galaxies

From high resolution cosmological simulations of the Local Group in realistic environment, namely HESTIA simulations, we study the position and kinematic deviations that may arise between the disc of a Milky Way (or Andromeda)-like galaxy and its halo. We focus on the 3-dimensional analysis of the centres of mass (COM). The study presents two parts. We first consider individual particles to track down the very nature and amplitude of the physical deviations of the COM with respect to the distance from the disc centre. Dark matter dominates the behaviour of the COM of all particles at all distances. But the total COM is also very close to the COM of stars. In the absence of a significant merger, the velocity offsets are marginal (10 km/s) but the positional shifts can be important compared to the disc characteristics (>10 kpc). In the event of a massive accretion, discrepancies are of the same order as the recent finding for the MW under the Magellanic Clouds influence. In a second part, the accent is put on the study of various populations of subhaloes and satellites. We show that satellites properly represent the entire subhalo population. There exists strong mismatch in phase space between the satellites' COM and the host disc. Moreover, the results are highly inhomogeneous between the simulations, and thus between the accretion histories. Finally, we point out that these shifts are mainly due to a few of the most massive objects.

astro-ph.GA↗
arXiv2023

A Local Universe model for constrained simulations

The aim of cosmological simulations is to reproduce the properties of the observed Universe, serving as tools to test structure and galaxy formation models. Constrained simulations of our local cosmological region up to a few hundred Mpc/h , the local Universe, are designed to reproduce the actual cosmic web of structures as observed. A question that often arises is how to judge the quality of constrained simulations against the observations of the Local Universe. Here we introduce the Local Universe model (LUM), a new methodology, whereby many constrained simulations can be judged and the ''best'' initial conditions can be identified. By characterising the Local Universe as a set of rich clusters, the model identifies haloes that serve as simulated counterparts to the observed clusters. Their merit is determined against a null hypothesis, the probability that such a counterpart could be identified in a random, unconstrained simulation. This model is applied to 100 constrained simulations using the Cosmicflows-3 data. Cluster counterparts are found for all constrained simulations, their distribution of separation from the true observed cluster position and their mass distribution are investigated. Lastly, the ''best'' constrained simulation is selected using the LUM and discussed in more detail.

astro-ph.CO↗
arXiv2023

The undiscovered ultra-diffuse galaxies of the Local Group

Ultra-diffuse galaxies (UDGs) are attractive candidates to probe cosmological models and test theories of galaxy formation at low masses; however, they are difficult to detect because of their low surface brightness. In the Local Group a handful of UDGs have been found to date, most of which are satellites of the Milky Way and M31, and only two are isolated galaxies. It is unclear whether so few UDGs are expected. We address this by studying the population of UDGs formed in hydrodynamic constrained simulations of the Local Group from the HESTIA suite. For a Local Group with a total enclosed mass $M_{\rm LG}\!\left(< 2.5\, {\rm Mpc}\right)=8\times10^{12}\, {\rm M_\odot}$, we predict that there are $12\pm3$ isolated UDGs (68% confidence) with stellar masses $10^6 \leq M_\ast\, /\, {\rm M_\odot} < 10^9,$ and effective radii $R_{\rm e} \geq 1.5\, {\rm kpc}$, within 2.5 Mpc of the Local Group, of which $2^{+2}_{-1}$ (68% confidence) are detectable in the footprint of the Sloan Digital Sky Survey (SDSS). Accounting for survey incompleteness, we find that almost the entire population of UDGs in the Local Group field would be observable in a future all-sky survey with a depth similar to the SDSS, the Dark Energy Survey, or the Legacy Survey of Space and Time. Our results suggest that there is a population of UDGs in the Local Group awaiting discovery.

astro-ph.GA↗
arXiv2023

Constrained simulations of the local Universe with Modified Gravity

We present a methodology for constructing modified gravity (MG) constrained simulations of the local Universe using positions and peculiar velocities from the CosmicFlows data set. Our analysis focuses on the following MG models: the normal branch of the Dvali-Gabadadze-Porrati (nDGP) model and Hu-Sawicki $f(R)$ model. We develop a model independent methodology for constructing constrained simulations with any given power spectra and numerically calculated linear growth functions. Initial conditions (ICs) for a set of constrained simulations are constructed for the standard cosmological model $Λ$CDM and the MG models. Differences between the model's reconstructed Wiener filtered density and the resultant simulation density are presented showing the importance for the generation of MG constrained ICs to study the subtle effects of MG in the local Universe. These are the first MG constrained simulations ever produced. The current work paves the way to improved approximate methods for models with scale-dependent growth functions, such as $f(R)$, and for high-resolution hydrodynamical MG zoom-in simulations of the local Universe.

astro-ph.CO↗
arXiv2022

Testing Bayesian reconstruction methods from peculiar velocities

Reconstructing the large scale density and velocity fields from surveys of galaxy distances, is a major challenge for cosmography. The data is very noisy and sparse. Estimated distances, and thereby peculiar velocities, are strongly affected by the Malmquist-like lognormal bias. Two algorithms have been recently introduced to perform reconstructions from such data: the Bias Gaussian correction coupled with the Wiener filter (BGc/WF) and the HAMLET implementation of the Hamiltonian Monte Carlo forward modelling. The two methods are tested here against mock catalogs that mimic the Cosmicflows-3 data. Specifically the reconstructed cosmography and moments of the velocity field (monopole, dipole) are examined. A comparison is made to the ``exact'' wiener filter as well - namely the Wiener Filter in the unrealistic case of zero observational errors. This is to understand the limits of the WF method. The following is found. In the nearby regime ($d \lesssim 40 {\rm Mpc}/h$) the two methods perform roughly equally well. HAMLET does slightly better in the intermediate regime ($ 40 \lesssim d \lesssim 120 {\rm Mpc}/h$). The main differences between the two appear in the most distant regime ($d \gtrsim 120 {\rm Mpc}/h$), close to the edge of the data. The HAMLET outperforms the BGc/WF in terms of better and tighter correlations, yet in the distant regime the HAMLET yields a somewhat biased reconstruction. Such biases are missing from the BGc/WF reconstruction. In sum, both methods perform well and create reliable reconstructions with significant differences apparent when details are examined.

astro-ph.CO↗
arXiv2022

Anisotropic satellite accretion onto the Local Group with HESTIA

How the cosmic web feeds halos, and fuels galaxy formation is an open question with wide implications. This study explores the mass assembly in the Local Group within the context of the local cosmography by employing simulations whose initial conditions have been constrained to reproduce the local environment. The goal of this study is to inspect whether the direction of accretion of satellites on to the Milky Way and Andromeda galaxies, is related to the cosmic web. The analysis considers the three high-resolution simulations available in the HESTIA simulation suite, as well as the derived velocity shear and tidal tensors. We notice two eras in the Local Group accretion history, delimited by an epoch around $z \approx 0.7$. We also find that satellites can travel up to $\sim 4$ Mpc, relative to their parent halo before crossing its viral radius $R_{200}$. Finally, we observe a strong alignment of the infall direction with the axis of slowest collapse $\vec{e_3}$ of both tidal and shear tensors, implying satellites of the Local Group originated from one particular region of the cosmic web and were channeled towards us via the process of accretion.This alignment is dominated by the satellites that enter during the early infall era, i.e $z>0.7$.

astro-ph.GA↗
arXiv2022

Hermeian haloes: Field haloes that interacted with both the Milky Way and M31

The Local Group is a unique environment in which to study the astrophysics of galaxy formation. The proximity of the Milky Way and M31 enhances the frequency of interactions of the low-mass halo population with more massive dark matter haloes, which increases their concentrations and strips them of gas and other material. Some low-mass haloes pass through the haloes of the Milky Way or M31 and are either ejected into the field or exchanged between the two primary hosts. We use high resolution gas-dynamical simulations to describe a new class of field haloes that passed through the haloes of both the Milky Way and M31 at early times and are almost twice as concentrated as field haloes that do not interact with the primary pair. These 'Hermeian' haloes are distributed anisotropically at larger distances from the Local Group barycentre than the primary haloes and appear to cluster along the line connecting the Milky Way and M31. Hermeian haloes facilitate the exchange of dark matter, gas, and stars between the Milky Way and M31 and can enhance the star formation rate of the gas in the primary haloes during their interactions with them. We also show that some Hermeian haloes can host galaxies that, because they are embedded in haloes that are more concentrated than regular field haloes, are promising targets for indirect dark matter searches beyond the Milky Way virial radius and can produce signals that are competitive with those of some dwarf galaxies. Hermeian galaxies in the Local Group should be detectable by forthcoming wide-field imaging surveys.

astro-ph.GA↗
arXiv2022

NIHAO-LG: The uniqueness of Local Group dwarf galaxies

Recent observational and theoretical studies of the Local Group (LG) dwarf galaxies have highlighted their unique star-formation history, stellar metallicity, gas content, and kinematics. We investigate the commonality of these features by comparing constrained LG and field central dwarf halo simulations in the Numerical Investigation of a Hundred Astrophysical Objects (NIHAO) project. Our simulations, performed with NIHAO-like hydrodynamics which track the evolution of the Milky Way (MW) and M31 along with ~100 dwarfs in the LG, reveal the total gas mass and stellar properties (velocity dispersion, evolution history, etc.) of present-day LG dwarfs to be similar to field systems. However, relative to field galaxies, LG dwarfs have more cold gas in their central parts and more metal-rich gas in the halo stemming from interactions with other dwarfs living in a high-density environment like the LG. Interestingly, the direct impact of massive MW/M31 analogues on the metallicity evolution of LG dwarfs is minimal; LG dwarfs accrete high-metallicity gas mostly from other dwarfs at late times. We have also tested for the impact of metal diffusion on the chemical evolution of LG dwarfs, and found that it does not affect the stellar or gaseous content of LG dwarfs. Our simulations suggest that the stellar components of LG dwarfs offer a unique and unbiased local laboratory for galaxy-formation tests and comparisons, especially against the overall dwarf population in the Universe.

astro-ph.GA↗
arXiv2022

Estimation of the masses in the Local Group by Gradient Boosted Decision Trees

Our goal is to estimate the mass of the Local Group (LG) and the individual masses of its primary galaxies, the M31 and the Milky Way (MW). We do this by means of a supervised machine learning algorithm, the gradient boosted decision trees (GBDT) and using the observed distance and relative velocity of the two as input parameters. The GBDT is applied to a sample of 2148 mock LGs drawn from a set of 5 dark matter (DM)-only simulations, ran within the standard $Λ$CDM\ cosmological model. The selection of the mock LGs is guided by a LG model, which defines such objects. The role of the observational uncertainties of the input parameters is gauged by applying the model to an ensemble of mock LGs pairs whose observables are these input parameters perturbed by their corresponding observational errors. Finally the observational data of the actual LG is used to infer its relevant masses. Our main results are the sum and the individual masses of the MW and M31: $M_{tot} = 3.31 ^{+0.79}_{-0.67} $, $M_{MW}=1.15^{+0.25}_{-0.22}$ and $M_{M31}=2.01^{+0.65}_{-0.39} \ \ \times 10^{12}M_{\odot}$ (corresponding to the median and the 1st and 3rd quartiles). The ratio of the masses is $M_{M31}/M_{MW}=1.75^{+0.54}_{-0.28}$, where by convention the M31 is defined here to be the more massive of the two halos.

astro-ph.CO↗
arXiv2022

Cold and Hot gas distribution around the Milky-Way-M31 system in the HESTIA simulations

Recent observations have revealed remarkable insights into the gas reservoir in the circumgalactic medium (CGM) of galaxy haloes. In this paper, we characterise the gas in the vicinity of Milky Way and Andromeda analogues in the HESTIA (High resolution Environmental Simulations of The Immediate Area) suite of constrained Local Group (LG) simulations. The HESTIA suite comprise of a set of three high-resolution {\sc arepo}-based simulations of the LG, run using the Auriga galaxy formation model. For this paper, we focus only on the $z = 0$ simulation datasets and generate mock skymaps along with a power spectrum analysis to show that the distributions of ions tracing low-temperature gas (HI and SiIII) are more clumpy in comparison to warmer gas tracers (OVI, OVII and OVIII). We compare to the spectroscopic CGM observations of M31 and low-redshift galaxies. HESTIA under-produces the column densities of the M31 observations, but the simulations are consistent with the observations of low-redshift galaxies. A possible explanation for these findings is that the spectroscopic observations of M31 are contaminated by gas residing in the CGM of the Milky Way.

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