arXiv subjects

Noam Libeskind

Publications and source records attributed to Noam Libeskind.

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

Tango of Titans: Centaurus A and M83 as a Local Group Analog

Centaurus A (CenA) and M83 form one of the most massive galaxy pairs in the nearby Universe. Although their observed heliocentric velocities suggest motion that is not obviously indicative of mutual attraction, this work presents evidence that CenA and M83 are in fact infalling toward each other, exhibiting a dynamical interaction analogous to the binary-like motion of the Milky Way and Andromeda in the Local Group (LG). Using the Timing Argument (TA), calibrated with analog galaxy pairs from the AbacusSummit simulation, we estimate the total mass of the CenA/M83 system under the assumption that the line-of-sight (LoS) velocity is dominated by motion toward the system's barycenter. This yields a total mass of $(6.36 \pm 1.30) \cdot 10^{12}\, M_\odot$. The inferred mass agrees well with independent estimates based on virial mass measurements and $K$-band luminosity--to-mass ratios. Together, the consistent bound signature and robust mass determination highlight the CenA/M83 system as a compelling nearby analog to the LG. Further discussion of NGC 4945 as a main perturber (as the Large Magellanic Could) for the CenA is also discussed.

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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

Ultra-Diffuse, Ultra-Different: Observed vs. Simulated Ultra-Diffuse Galaxies Live in Fundamentally Different Halos

In this work, we compare galaxies from the NIHAO and HESTIA simulation suites to ultra-diffuse galaxies (UDGs) with spectroscopically measured dynamical masses. For each observed UDG, we identify the simulated dark matter halo that best matches its dynamical mass. In general, observed UDGs are matched to simulated galaxies with lower stellar masses than they are observed to have. These simulated galaxies also have halo masses much less than would be expected given the observed UDG's stellar mass and the stellar mass -- halo mass relationship. We use the recently established relation between globular cluster (GC) number and halo mass, which has been shown to be applicable to UDGs, to better constrain their observed halo masses. This method indicates that observed UDGs reside in relatively massive dark matter halos. This creates a striking discrepancy: the simulated UDGs are matched to the dynamical masses of observed ones, but not their total halo masses. In other words, simulations can produce UDGs in halos with the correct inner dynamics, but not with the massive halos implied by GC counts. We explore several possible explanations for this tension, from both the observational and theoretical sides. We propose that the most likely resolution is that observed UDGs may have fundamentally different dark matter halo profiles than those produced in NIHAO and HESTIA. This highlights the need for a simulation that self-consistently produces galaxies of a stellar mass of $\sim 10^8 M_\odot$ in dark matter halos that exhibit the full range of large dark matter cores to cuspy NFW-like halos.

astro-ph.GA↗

arXiv2025

Reionization in HESTIA: Studying reionization in the LG through zoom simulations

While cosmic reionization has been broadly constrained by global observables, the interplay between internal sources [Milky Way (MW), M31, and their satellites] and external ionization fronts remains poorly understood in a realistic Local Group (LG) context. To address this issue, we perform radiative transfer post-processing on the original hestia LG constrained simulation. We calibrate our source models using a uniform $1024^3$ particle, dark matter-only, hestia simulation coupled with a subgrid collapse fraction model to match the global reionization observables. These source models are then applied to the hestia zoom-in simulations, which consist of a $4096^3$ particle effective resolution in the zoom region centred on the MW and M31 haloes, which resolves haloes down to $10^8$ M$_{\odot}$. We find that in all scenarios, reionization within the LG proceeds in an inside-out manner with the progenitors of the MW and M31 having 50 per cent of their material ionized by $z \sim 9-8.6$, significantly earlier than the global mid-point at $z \sim 7-7.7$, noting that external fronts from large-scale structure play a negligible role, even under the most permissive feedback model. We further show that present-day satellite galaxies exhibit only a weak correlation between their reionization redshift and their present-day radial distance from their host halo, with somewhat tighter trends around M31 than the MW. Finally, we find that presentday satellites whose assembly preceded the reionization of most of their $z = 0$ material are systematically more massive today, suggesting that the oldest stellar populations preferentially reside in the most massive $z = 0$ subhaloes.

astro-ph.CO↗

arXiv2025

The frozen outskirts: a cold Hubble flow and the mass of the Local Group

We analyze the velocity field of peripheral members of the Local Group. The Hubble flow at distances from 400 to 1400~kpc, formed by 7 of 11 nearby galaxies, is characterized by an extremely small line-of-sight velocity dispersion of 15 km/s, which differs significantly from the predictions of cosmological simulations of about 70 km/s. This fact allows us to determine the total mass of the Local Group as $M_{LG} = (2.47 \pm 0.15) \times 10^{12}$ $M_\odot$ using an analytical model of the Hubble flow around a spherical overdensity in the standard flat \LCDM{} universe. The practical equality of this mass to the sum of the masses of our Galaxy and the Andromeda Galaxy, as well as the absence of mass growth in the range of distances under consideration, gives grounds to conclude that the entire mass of the Local Group is confined within the virial radii around its two main galaxies. The barycenter, found from the minimal scatter of mass estimates, corresponds to the mass ratio of the Milky Way and the Andromeda Galaxy equal to $M_{MW}/M_{M31} = 0.74\pm0.10$. The velocity of our Galaxy to the barycenter turns out to be $62.6\pm2.6$ km/s. This allows us to determine the apex of the Sun relative to the barycenter of the Local Group to be $(l,b,V) = ( +94.0^\circ \pm 0.7^\circ, -2.7^\circ \pm 0.3^\circ, 301 \pm 3$ km/s in the Galactic coordinates.

astro-ph.GA↗

arXiv2025

MUSE observations of dwarf galaxies and a stellar stream in the M83 group

Spectroscopy for faint dwarf galaxies outside of our own Local Group is challenging. Here, we present MUSE spectroscopy to study the properties of four known dwarf satellites and one stellar stream (KK208) surrounding the nearby grand spiral M83, which resides together with the lenticular galaxy Cen A in the Centaurus group. This data complete the phase-space information for all known dwarf galaxies around M83 down to a completeness of $-$10 mag in the $V$ band. All studied objects have an intermediate to old and metal-poor stellar population and follow the stellar luminosity-metallicity relation as defined by the Local Group dwarfs. For the stellar stream we serendipitously identify a previously unknown globular cluster, which is old and metal-poor. Two dwarf galaxies (NGC5264 and dw1341-29) may be a bound satellite of a satellite system due to their proximity and shared velocities. Having access to the positions and velocities of 13 dwarfs around M83, we estimate the mass of the group with different estimators. Ranging between 1.3 and $3.0 \times 10^{12}$ M$_\odot$ for the halo mass we find it to be larger than previously assumed. This may impact the previously reported tension for cold dark matter cosmology with the count of dwarf galaxies. In contrast to Cen A, we do not find a co-rotating plane-of-satellites around M83.

astro-ph.GA↗

arXiv2025

A Pre-Infall Magellanic Analog-Corona and Stream formation in the \textsc{HESTIA} cosmological simulations

We identify and investigate a pre-infall analog of the Large and Small Magellanic Clouds (LMC, SMC) in the HESTIA suite of constrained cosmological simulations. The system, dynamically isolated from the Local Group, evolves over ~6 Gyr and forms a multiphase warm coronal halo and a neutral gas stream via repeated tidal interactions, ~150 kpc in length. The LMC-analog's corona forms self-consistently through virial accretion and inhibits the survival of clumpy neutral structures beyond ~600 Myr. The SMC analog remains bound through to z=0, and the pair also exhibits bridge-like and leading-arm features. These results suggest that while most of the ionized Stream is formed by the LMC coronal gas, the neutral gas stream, bridge, and leading arm components of the Magellanic System can arise from dwarf-dwarf interactions prior to infall, while the survival and ionization of these features likely require additional environmental processing. Furthermore, we identify a stellar component out of phase to the neutral component of the stream, implying that if the Magellanic stellar stream exists, it may not be spatially coexistent to the dominant H I stream. This system offers a valuable pre-infall reference point for interpreting the Magellanic System and identifying analogs beyond the Local Group.

astro-ph.GA↗

arXiv2025

Andromeda's asymmetric satellite system as a challenge to cold dark matter cosmology

The Andromeda galaxy is surrounded by a strikingly asymmetrical distribution of satellite dwarf galaxies aligned towards the Milky Way. The standard model of cosmology predicts that most satellite galaxy systems are near-isotropic, and dwarf associations observed in the local Universe are only weakly asymmetric. Here, we characterise the Andromeda system's asymmetry, and test its agreement with expectations from concordance cosmology. All but one of Andromeda's 37 satellite galaxies are contained within 107 degrees of our Galaxy. In standard cosmological simulations, less than 0.3% (0.5% when accounting for possible observational incompleteness) of Andromeda-like systems demonstrate a comparably significant asymmetry. None are as collectively lopsided as the observed satellite configuration. In conjunction with its satellite plane, our results paint the Andromeda system as an extreme outlier in the prevailing cosmological paradigm, further challenging our understanding of structure formation at small scales.

astro-ph.GA↗

arXiv2025

Line-of-sight mass estimator and the masses of the Milky Way and Andromeda Galaxy

The total mass of a galaxy group, such as the Milky Way (MW) and the Andromeda Galaxy (M 31), is typically determined from the kinematics of satellites within their virial zones. Bahcall and Tremaine (1981) proposed the $v^2r$ estimator as an alternative to the virial theorem. In this work, we extend their approach by incorporating the three-dimensional spatial distribution of satellites within the system to improve the reliability and accuracy of galaxy mass estimates. Applying this method to a comprehensive dataset of Local Group satellites based on recent, high-precision distance measurements, we estimate the total mass of the MW to be $(7.9 \pm 2.3) \times 10^{11}$ $M_\odot$ and that of M~31 to be $(15.5 \pm 3.4) \times 10^{11}$ $M_\odot$. The effectiveness of the method is constrained by the precision of distance measurements, making it particularly well suited for the Local Group, but challenging to apply to more distant systems.

astro-ph.GA↗

arXiv2025

A physically motivated galaxy size definition across different state-of-the-art hydrodynamical simulations

Galaxy sizes are a key parameter to distinguishing between different galaxy types and morphologies, reflecting their formation and assembly histories. Several methods define galaxy boundaries, often relying on light concentration or isophotal densities. However, these approaches were often constrained by observational limitations and did not necessarily provide a clear physical boundary for galaxy outskirts. With modern deep imaging surveys, a new physically motivated definition has emerged using the radial position of the star formation threshold as the galaxy size, approximated by the stellar mass density contour at 1 Msun pc^-2 (R_1). We test this definition using three state-of-the-art hydrodynamical simulation suites, analyzing stellar surface density profiles across a wide range of stellar masses and redshifts. We measure the galaxy sizes according to this new definition and compare them with the most traditional size metric, the stellar half-mass radius. Our analysis demonstrates that the R_1-M_star relation exhibits consistent behaviour across both low and high-stellar mass galaxies, with remarkably low scatter. This relation is independent of redshift and holds across the three different cosmological hydrodynamical simulation suites, highlighting its robustness to variations in galaxy formation models. Furthermore, we explore the connection between a galaxy's total mass within R1 and its stellar mass, finding very little scatter in this relation. This suggests that R1 could serve as a reliable observational tracer for the galaxy's dynamical mass. The size-stellar mass relation proposed provides a reliable and physically motivated method for defining the outskirts of galaxies. This method remains consistent not only at z=0 but also throughout the evolutionary history of galaxies, offering a robust and meaningful framework for galaxy evolution studies.

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arXiv2023

Dead man tells tales: metallicity distribution of the Milky Way stellar halo reveals the past of the GSE progenitor galaxy

The Gaia-Sausage-Enceladus~(GSE) stands out as the largest known ancient accretion event in the Milky Way~(MW) history. Despite this significance, the parameters of its progenitor galaxy are still poorly constrained. We identify GSE stars from the APOGEE DR17 using Gaussian mixture models and recover a negative radial metallicity gradient for the GSE debris within the MW stellar halo, with a magnitude of $\approx -0.014^{-0.002}_{-0.022}$ dex/kpc. We argue that this gradient reflects the radial metallicity gradient of the GSE galaxy progenitor before it was disrupted by the MW. By investigating the cosmological HESTIA simulations and $N$-body models of galaxy mergers, we constrain the radial metallicity gradient of the GSE-progenitor to be $\approx -0.1^{-0.06}_{-0.15}$ dex/kpc. We, therefore, propose that a chemical tagging of accreted stars using their integrals of motion, although they are not conserved during mergers, provide essential information about the structure and the past of systems accreted onto the MW.

astro-ph.GA↗

arXiv2023

Why does the Milky Way have a bar?

There is no doubt that the Milky Way is a barred galaxy; however, factors that establish its prominent morphology remain largely elusive and poorly comprehended. In this work, we attempt to constrain the history of the MW by tracing the present-day parameters and evolution of a set of MW and M31 analogues from the TNG50 cosmological simulations. We find that the strength of bars at $z=0$ correlates well not only with the total mass build-up of galaxies but, more crucially, with the time of rapid onset of stellar discs. Discs of strongly barred galaxies form early ($ z \gtrsim 2-3$), compared to weakly barred and non-barred galaxies ($z \approx 1-1.5$). Although we are cautious to draw ultimate conclusions about the governing factor of discs formation due to the complexity and correlations between different physical phenomena~(dark matter mass growth, gas accretion rate, mergers and others) affecting galaxy growth, the observed morphological diversity of galaxies can be tentatively explained by a substantial variation in the gas angular momentum around proto-galaxies already at $z\approx 3-5$; in such a way, early discs with the strongest bars at $z=0$ formed from gas with the largest angular momentum. By comparing the formation time scales of discs of barred galaxies in the TNG50 sample, we suggest that the MW has a strong bar ($0.35<A_2<0.6$) and that its stellar disc started to dominate over the spheroidal component already at $z \approx 2$, with a mass of $\approx 1 \pm 0.5 \times 10^{10} M_\odot$. We, therefore, conclude that the presence of a strong bar in the MW is a natural manifestation of the early formation of the stellar disc, which made possible bursty but highly efficient star formation at high redshift.

astro-ph.GA↗

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

The LMC impact on the kinematics of the Milky Way satellites: clues from the running solar apex

Dwarf galaxies provide a unique opportunity for studying the evolution of the Milky Way (MW) and the Local Group as a whole. Analysing the running solar apex based on the kinematics of the MW satellites, we discovered an unexpected behaviour of the dipole term of the radial velocity distribution as a function of the galactocentric distance. The nearby satellites (<100 kpc) have a bulk motion with an amplitude of 140-230 km/s while the more distant ones show an isotropic distribution of the radial velocities. Such strong solar apex variations can not be explained by the net rotation of the satellites, as it would require an enormously high rotation rate (~970 km/s). If we exclude the LMC and its most closely related members from our sample, this does not suppress the bulk motion of the nearby satellites strongly enough. Nevertheless, we have demonstrated that the observed peculiar kinematics of the MW satellites can be explained by a perturbation caused by the first infall of the LMC. First, we `undone' the effect of the perturbation by integrating the orbits of the MW satellites backwards (forwards) with (without) massive LMC. It appears that the present-day peculiar enhancement of the solar apex in the inner halo is diminished the most in the case of 2x10^{11} Msun LMC. Next, in self-consistent high-resolution N-body simulations of the MW-LMC interaction, we found that the solar apex shows the observed behaviour only for the halo particles with substantial angular momentum, comparable to that of the MW satellites.

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