Leobersdorfer Flohmarkt

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The cosmological star formation history from the Local Volume of galaxies and constraints on the matter homogeneity

The Lilly-Madau plot is commonly interpreted as the history of the cosmic star formation of the Universe by showing the co-moving star formation rate density (SFRD) over cosmic time. Therefore, the Lilly-Madau plot is not only sensitive to the star formation history (SFH) but also to the number density of galaxies. Assessing the Catalogue of Neighbouring Galaxies, we reconstruct the SFHs of galaxies located in the Local Volume (LV) based on delayed-$\tau$ and power-law SFH models. Galaxies with stellar masses of $M_{*} \gtrsim 10^{10}\,\rm{M_{\odot}}$ typically evolve according to the delayed-$\tau$ model by having first increasing followed by exponentially declining SFRs, while the majority of less massive star-forming galaxies has an almost constant or increasing SFH. Deducing the cosmic SFRD evolution of the LV reveals that the SFHs of local galaxies are inconsistent with the Lilly-Madau plot. The SFRDs of the LV are significantly lower at redshifts of $z \lesssim 3$ underestimating the Lilly-Madau peak at $z = 1.86$ by a factor of $2.16\pm0.32$ (delayed-$\tau$) and $5.90\pm0.88$ (power-law model). Assuming the delayed-$\tau$ model for galaxies with $M_{*} \geq 10^{10}\,\rm{M_{\odot}}$ and a power-law model for less massive galaxies, the SFRD is $2.22\pm0.33$ lower than measured at $z = 1.86$. This inconsistency between the evolution of the local and global SFRD has cosmological implications. Since the Lilly-Madau plot also constrains the cosmological matter field, the near-constancy of SFHs of LV galaxies could imply that the peak of the Lilly-Madau plot at $z = 1.86$ is the imprint of a $\approx~5$ Gpc-scale inhomogeneity.Comment: Accepted for publication in the Monthly Notices of the Royal Astronomical Society (MNRAS), 12 pages, 5 figure

The KBC void and Hubble tension contradict ΛCDM on a Gpc scale - Milgromian dynamics as a possible solution

Funding Information: IB is supported by an Alexander von Humboldt Foundation postdoctoral research fellowship.The KBC void is a local underdensity with the observed relative density contrast δ 1 - ρ/ρ0 = 0.46 ± 0.06 between 40 and 300 Mpc around the Local Group. If mass is conserved in the Universe, such a void could explain the 5.3σ Hubble tension. However, the MXXL simulation shows that the KBC void causes 6.04σ tension with standard cosmology (ΛCDM). Combined with the Hubble tension, ΛCDM is ruled out at 7.09σ confidence. Consequently, the density and velocity distribution on Gpc scales suggest a long-range modification to gravity. In this context, we consider a cosmological MOND model supplemented with 11eV/c2 sterile neutrinos. We explain why this νHDM model has a nearly standard expansion history, primordial abundances of light elements, and cosmic microwave background (CMB) anisotropies. In MOND, structure growth is self-regulated by external fields from surrounding structures. We constrain our model parameters with the KBC void density profile, the local Hubble and deceleration parameters derived jointly from supernovae at redshifts 0.023-0.15, time delays in strong lensing systems, and the Local Group velocity relative to the CMB. Our best-fitting model simultaneously explains these observables at the 1.14 per cent confidence level (2.53σ tension) if the void is embedded in a time-independent external field of 0.055 a0. Thus, we show for the first time that the KBC void can naturally resolve the Hubble tension in Milgromian dynamics. Given the many successful a priori MOND predictions on galaxy scales that are difficult to reconcile with ΛCDM, Milgromian dynamics supplemented by 11eV/c2 sterile neutrinos may provide a more holistic explanation for astronomical observations across all scales.Publisher PDFPeer reviewe

The Magellanic Clouds are very rare in the IllustrisTNG simulations

Funding: IB is supported by Royal Society University Research Fellowship 211046 and was supported by Science and Technology Facilities Council grant ST/V000861/1, which also partially supports HZ. IB acknowledges support from a “Pathways to Research” fellowship from the University of Bonn. PK thanks the Deutscher Akademischer Austauschdienst-Eastern European Exchange Programme at the University of Bonn for support. EA acknowledges support through a teaching assistantship by the Helmholtz-Institut für Strahlen- und Kernphysik (HISKP).The Large and Small Magellanic Clouds (LMC and SMC) form the closest interacting galactic system to the Milky Way, therewith providing a laboratory to test cosmological models in the local Universe. We quantify the likelihood for the Magellanic Clouds (MCs) to be observed within the ΛCDM model using hydrodynamical simulations of the IllustrisTNG project. The orbits of the MCs are constrained by proper motion measurements taken by the Hubble Space Telescope and Gaia. The MCs have a mutual separation of dMCs = 24.5kpc and a relative velocity of vMCs =9 0.8kms−1, implying a specific phase-space density of fMCs,obs ≡ (dMCs·vMCs)−3 = 9.10 × 10−11 km−3 s3 kpc−3. We select analogues to the MCs based on their stellar masses and distances in MW-like halos. None of the selected LMC analogues have a higher total mass and lower Galactocentric distance than the LMC, resulting in >3.75σ tension. We also find that the fMCs distribution in the highest resolution TNG50 simulation is in 3.95σ tension with observations. Thus, a hierarchical clustering of two massive satellites like the MCs in a narrow phase-space volume is unlikely in ΛCDM, presumably because of short merger timescales due to dynamical friction between the overlapping dark matter halos. We show that group infall led by an LMC analogue cannot populate the Galactic disc of satellites (DoS), implying that the DoS and the MCs formed in physically unrelated ways in ΛCDM. Since the 20∘ alignment of the LMC and DoS orbital poles has a likelihood of P = 0.030 (2.17σ), adding this χ2 to that of fMCs gives a combined likelihood of P = 3.90 × 10−5 (4.11σ).Peer reviewe

The ultra-diffuse dwarf galaxies NGC 1052-DF2 and 1052-DF4 are in conflict with standard cosmology

Funding Information: IB is supported by an Alexander von Humboldt postdoctoral research fellowship. KG was supported by the German-Russian Interdisciplinary Science Center funded by the German Federal Foreign Office via the German Academic Exchange Service.Recently van Dokkum et al. reported that the galaxy NGC 1052-DF2 (DF2) lacks dark matter if located at 20 Mpc from Earth. In contrast,DF2 is a dark-matter-dominated dwarf galaxy with a normal globular cluster population if it has a much shorter distance near 10 Mpc. However, DF2 then has a high peculiar velocity wrt. the cosmic microwave background of 886 km s-1, which differs from that of the Local Group (LG) velocity vector by 1298 km s-1 with an angle of 117°.Taking into account the dynamical M/L ratio, the stellar mass, half-light radius, peculiar velocity, motion relative to the LG, and the luminosities of the globular clusters, we show that the probability of finding DF2-like galaxies in the lambda cold dark matter (CDM) TNG100-1 simulation is at most 1.0 × 10-4 at 11.5 Mpc and is 4.8 × 10-7 at 20.0 Mpc. At 11.5 Mpc, the peculiar velocity is in significant tension in the TNG100-1, TNG300-1, and Millennium simulations, but naturally in a Milgromian cosmology. At 20.0 Mpc, the unusual globular cluster population would challenge any cosmological model. Estimating that precise measurements of the internal velocity dispersion, stellar mass, and distance exist for 100 galaxies, DF2 is in 2.6σ (11.5 Mpc) and 4.1σ (20.0 Mpc) tension with standard cosmology. Adopting the former distance for DF2 and assuming that NGC 1052-DF4 is at 20.0 Mpc, the existence of both is in tension at ≥4.8σ with the ΛCDM model. If both galaxies are at 20.0 Mpc the ΛCDM cosmology has to be rejected by ≥5.8σ.Publisher PDFPeer reviewe

A simultaneous solution to the Hubble tension and observed bulk flow within 250 h−1 Mpc

Funding: IB was supported by Science and Technology Facilities Council grant ST/V000861/1. PK thanks the Deutscher Akademischer Austauschdienst-Eastern European exchange programme for support.The Λ cold dark matter (ΛCDM) standard cosmological model is in severe tension with several cosmological observations. Foremost is the Hubble tension, which exceeds 5σ confidence. Galaxy number counts show the Keenan–Barger–Cowie (KBC) supervoid, a significant underdensity out to 300 Mpc that cannot be reconciled with ΛCDM cosmology. Haslbauer et al. previously showed that a high local Hubble constant arises naturally due to gravitationally driven outflows from the observed KBC supervoid. The main prediction of this model is that peculiar velocities are typically much larger than expected in the ΛCDM framework. This agrees with the recent discovery by Watkins et al. that galaxies in the CosmicFlows-4 catalogue have significantly faster bulk flows than expected in the ΛCDM model on scales of 100-250 h-1 Mpc. The rising bulk flow curve is unexpected in standard cosmology, causing 4.8σ tension at 200 h-1 Mpc. In this work, we determine what the semi-analytic void model of Haslbauer et al. predicts for the bulk flows on these scales. We find qualitative agreement with the observations, especially if our vantage point is chosen to match the observed bulk flow on a scale of 50 h-1 Mpc. This represents a highly non-trivial success of a previously published model that was not constrained by bulk flow measurements, but which was shown to solve the Hubble tension and explain the KBC void consistently with the peculiar velocity of the Local Group. Our results suggest that several cosmological tensions can be simultaneously resolved if structure grows more efficiently than in the ΛCDM paradigm on scales of tens to hundreds of Mpc.Publisher PDFPeer reviewe

Galaxies lacking dark matter in the Illustris simulation

IB is supported by an Alexander von Humboldt research fellowship. We thank the DAAD-Ostpartnerschaftsprogramm für 2018 at the University of Bonn for funding exchange visits between Charles University in Prague and Bonn University.Context. Any viable cosmological model in which galaxies interact predicts the existence of primordial and tidal dwarf galaxies (TDGs). In particular, in the standard model of cosmology (ΛCDM), according to the dual dwarf galaxy theorem, there must exist both primordial dark matter-dominated and dark matter-free TDGs with different radii.  Aims. We study the frequency, evolution, and properties of TDGs in a ΛCDM cosmology.  Methods. We use the hydrodynamical cosmological Illustris-1 simulation to identify TDG candidates (TDGCs) and study their present-day physical properties. The positions of galaxies in the radius-mass plane, depending on their nonbaryonic content, are compared with observational data and other simulations. We also present movies on the formation of a few galaxies lacking dark matter, confirming their tidal dwarf nature. Tidal dwarf galaxy candidates can however also be formed via other mechanisms, such as from ram-pressure-stripped material or, speculatively, from cold-accreted gas.  Results. We find 97 TDGCs with Mstellar > 5 × 107M⊙ at redshift z = 0, corresponding to a co-moving number density of 2.3 × 10-4 h3 cMpc-3. The most massive TDGC has Mtotal = 3.1 × 109 M⊙, comparable to that of the Large Magellanic Cloud. Tidal dwarf galaxy candidates are phase-space-correlated, reach high metallicities, and are typically younger than dark matter-rich dwarf galaxies.  Conclusions. We report for the first time the verification of the dual dwarf theorem in a self-consistent ΛCDM cosmological simulation. Simulated TDGCs and dark matter-dominated galaxies populate different regions in the radius-mass diagram in disagreement with observations of early-type galaxies. The dark matter-poor galaxies formed in Illustris-1 have comparable radii to observed dwarf galaxies and to TDGs formed in other galaxy-encounter simulations. In Illustris-1, only 0.17 percent of all selected galaxies with Mstellar = 5 × 107-109 M⊙ are TDGCs or dark matter-poor dwarf galaxies. The occurrence of NGC 1052-DF2-type objects is discussed.Publisher PDFPeer reviewe

The high fraction of thin disk galaxies continues to challenge ΛCDM cosmology

Funding: I.B. is supported by Science and Technology Facilities Council grant ST/V000861/1. He acknowledges support from an Alexander von Humboldt Foundation postdoctoral research fellowship (2018–2020) and the University of Bonn "Pathways to Research" program.Any viable cosmological framework has to match the observed proportion of early- and late-type galaxies. In this contribution, we focus on the distribution of galaxy morphological types in the standard model of cosmology (Lambda cold dark matter, ΛCDM). Using the latest state-of-the-art cosmological ΛCDM simulations known as Illustris, IllustrisTNG, and EAGLE, we calculate the intrinsic and sky-projected aspect ratio distribution of the stars in subhalos with stellar mass M* > 1010 M⊙ at redshift z = 0. There is a significant deficit of intrinsically thin disk galaxies, which however comprise most of the locally observed galaxy population. Consequently, the sky-projected aspect ratio distribution produced by these ΛCDM simulations disagrees with the Galaxy And Mass Assembly (GAMA) survey and Sloan Digital Sky Survey at ≥12.52σ (TNG50-1) and ≥14.82σ (EAGLE50) confidence. The deficit of intrinsically thin galaxies could be due to a much less hierarchical merger-driven build-up of observed galaxies than is given by the ΛCDM framework. It might also arise from the implemented sub-grid models, or from the limited resolution of the above-mentioned hydrodynamical simulations. We estimate that an 85 times better mass resolution realization than TNG50-1 would reduce the tension with GAMA to the 5.58σ level. Finally, we show that galaxies with fewer major mergers have a somewhat thinner aspect ratio distribution. Given also the high expected frequency of minor mergers in ΛCDM, the problem may be due to minor mergers. In this case, the angular momentum problem could be alleviated in Milgromian dynamics because of a reduced merger frequency arising from the absence of dynamical friction between extended dark matter halos.Publisher PDFPeer reviewe

On the absence of backsplash analogues to NGC 3109 in the ΛCDM framework

Funding: IB is supported by an Alexander von Humboldt Foundation postdoctoral research fellowship. MSP and BF thank the Deutscher Akademischer Austauschdienst for PPP grant 57512596 funded by the Bundesministerium für Bildung und Forschung, and the Partenariat Hubert Curien (PHC) for PROCOPE project 44677UE. MSP thanks the Klaus Tschira Stiftung and German Scholars Organization e.V. for support via a Klaus Tschira Boost Fund. BF acknowledges funding from the Agence Nationale de la Recherche (projects ANR-18-CE31-0006 and ANR-19-CE31-0017) and from the European Research Council (ERC) under the European Union’s Horizon 2020 Framework Programme (grant agreement number 834148).The dwarf galaxy NGC 3109 is receding 105 km s−1 faster than expected in a Lambda cold dark matter (ΛCDM) timing argument analysis of the Local Group and external galaxy groups within 8 Mpc. If this few-body model accurately represents long-range interactions in ΛCDM, this high velocity suggests that NGC 3109 is a backsplash galaxy that was once within the virial radius of the Milky Way and was slingshot out of it. Here, we use the Illustris TNG300 cosmological hydrodynamical simulation and its merger tree to identify backsplash galaxies. We find that backsplashers as massive (≥4.0 × 1010 M⊙) and distant (≥1.2 Mpc) as NGC 3109 are extremely rare, with none having also gained energy during the interaction with their previous host. This is likely due to dynamical friction. Since we identified 13 225 host galaxies similar to the Milky Way or M31, we conclude that postulating NGC 3109 to be a backsplash galaxy causes >3.96σ tension with the expected distribution of backsplashers in ΛCDM. We show that the dark matter only version of TNG300 yields much the same result, demonstrating its robustness to how the baryonic physics is modelled. If instead NGC 3109 is not a backsplasher, consistency with ΛCDM would require the 3D timing argument analysis to be off by 105 km s−1 for this rather isolated dwarf, which we argue is unlikely. We discuss a possible alternative scenario for NGC 3109 and the Local Group satellite planes in the context of MOND, where the Milky Way and M31 had a past close flyby 7–10 Gyr ago.Publisher PDFPeer reviewe

Constraints on the star formation histories of galaxies in the Local Cosmological Volume

IB is supported by an Alexander von Humboldt postdoctoral research fellowship. PK acknowledges support from the Grant Agency of the Czech Republic under grant number 20-21855S. This work benefited from the International Space Science Institute (ISSI/ISSI-BJ) in Bern and Beijing, thanks to the funding of the team ‘Chemical abundances in the ISM: the litmus test of stellar IMF variations in galaxies across cosmic time’ (Donatella Romano and Zhi-Yu Zhang).The majority of galaxies with current star formation rates (SFRs), SFRo≥10−3M⊙yr−1⁠, in the Local Cosmological Volume, where observations should be reliable, have the property that their observed SFRo is larger than their average SFR. This is in tension with the evolution of galaxies described by delayed-τ models, according to which the opposite would be expected. The tension is apparent in that local galaxies imply the star formation time-scale τ ≈ 6.7 Gyr, much longer than the 3.5–4.5 Gyr obtained using an empirically determined main sequence at several redshifts. Using models where the SFR is a power law in time of the form ∝(t − t1)η for t1 = 1.8 Gyr (with no stars forming prior to t1) implies that η = 0.18 ± 0.03. This suggested near-constancy of a galaxy’s SFR over time raises non-trivial problems for the evolution and formation time of galaxies, but is broadly consistent with the observed decreasing main sequence with increasing age of the Universe.Publisher PDFPeer reviewe