Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userRevisiting the tension between fast bars and the $Lambda$CDM paradigm
87
0
0.0
(
0
)
Added by
Francesca Fragkoudi F
Publication date
2020
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
The pattern speed with which galactic bars rotate is intimately linked to the amount of dark matter in the inner regions of their host galaxies. In particular, dark matter haloes act to slow down bars via torques exerted through dynamical friction. Observational studies of barred galaxies tend to find that bars rotate fast, while hydrodynamical cosmological simulations of galaxy formation and evolution in the $Lambda$CDM framework have previously found that bars slow down excessively. This has led to a growing tension between fast bars and the $Lambda$CDM cosmological paradigm. In this study we revisit this issue, using the Auriga suite of high resolution, magneto-hydrodynamical cosmological zoom-in simulations of galaxy formation and evolution in the $Lambda$CDM framework, finding that bars remain fast down to $z=0$. In Auriga, bars form in galaxies that have higher stellar-to-dark matter ratios and are more baryon-dominated than in previous cosmological simulations; this suggests that in order for bars to remain fast, massive spiral galaxies must lie above the commonly used abundance matching relation. While this reduces the aforementioned tension between the rotation speed of bars and $Lambda$CDM, it accentuates the recently reported discrepancy between the dynamically inferred stellar-to-dark matter ratios of massive spirals and those inferred from abundance matching. Our results highlight the potential of using bar dynamics to constrain models of galaxy formation and evolution.
rate research
Read More
The dark energy plus cold dark matter ($Lambda$CDM) cosmological model has been a demonstrably successful framework for predicting and explaining the large-scale structure of Universe and its evolution with time. Yet on length scales smaller than $sim 1$ Mpc and mass scales smaller than $sim 10^{11} M_{odot}$, the theory faces a number of challenges. For example, the observed cores of many dark-matter dominated galaxies are both less dense and less cuspy than naively predicted in $Lambda$CDM. The number of small galaxies and dwarf satellites in the Local Group is also far below the predicted count of low-mass dark matter halos and subhalos within similar volumes. These issues underlie the most well-documented problems with $Lambda$CDM: Cusp/Core, Missing Satellites, and Too-Big-to-Fail. The key question is whether a better understanding of baryon physics, dark matter physics, or both will be required to meet these challenges. Other anomalies, including the observed planar and orbital configurations of Local Group satellites and the tight baryonic/dark matter scaling relations obeyed by the galaxy population, have been less thoroughly explored in the context of $Lambda$CDM theory. Future surveys to discover faint, distant dwarf galaxies and to precisely measure their masses and density structure hold promising avenues for testing possible solutions to the small-scale challenges going forward. Observational programs to constrain or discover and characterize the number of truly dark low-mass halos are among the most important, and achievable, goals in this field over then next decade. These efforts will either further verify the $Lambda$CDM paradigm or demand a substantial revision in our understanding of the nature of dark matter.
We investigate the $H_0$ tension in a range of extended model frameworks beyond the standard $Lambda$CDM without the data from cosmic microwave background (CMB). Specifically, we adopt the data from baryon acoustic oscillation, big bang nucleosynthesis and type Ia supernovae as indirect measurements of $H_0$ to study the tension. We show that the estimated value of $H_0$ from indirect measurements is overall lower than that from direct local ones regardless of the data sets and a range of extended models to be analyzed, which indicates that, although the significance of the tension varies depending on models, the $H_0$ tension persists in a broad framework beyond the standard $Lambda$CDM model even without CMB data.
The cosmological constant $Lambda$ and cold dark matter (CDM) model ($Lambdatext{CDM}$) is one of the pillars of modern cosmology and is widely used as the de facto theoretical model by current and forthcoming surveys. As the nature of dark energy is very elusive, in order to avoid the problem of model bias, here we present a novel null test at the perturbation level that uses the growth of matter perturbation data in order to assess the concordance model. We analyze how accurate this null test can be reconstructed by using data from forthcoming surveys creating mock catalogs based on $Lambdatext{CDM}$ and three models that display a different evolution of the matter perturbations, namely a dark energy model with constant equation of state $w$ ($w$CDM), the Hu & Sawicki and designer $f(R)$ models, and we reconstruct them with a machine learning technique known as the Genetic Algorithms. We show that with future LSST-like mock data our consistency test will be able to rule out these viable cosmological models at more than 5$sigma$, help to check for tensions in the data and alleviate the existing tension of the amplitude of matter fluctuations $S_8=sigma_8left(Omega_m/0.3right)^{0.5}$.
The {Lambda} cold dark matter ({Lambda}CDM) paradigm of galaxy formation predicts that dense spheroidal stellar structures invariably grow at early cosmic time. These primordial spheroids evolve toward a virialized dynamical status as they finally become todays elliptical galaxies and large bulges at the center of disk galaxies. However, observations reveal that small bulges in spiral galaxies are common in the nearby universe. The prevailing belief that all small bulges form at later times from internal processes occurring in the disk represents a challenge for the {Lambda}CDM scenario. Notably, the coevolution of bulges and central supermassive black holes (SMBHs) at early phases of galaxy evolution is also at stake. However, observations have so far not provided conclusive evidence against their possible early origin. Here, we report new observations of small bulges showing that they follow the mass-velocity dispersion relation expected for virialized systems. Contrary to previous claims, small bulges bridge the gap between massive ellipticals and globular clusters. This dynamical picture supports a scenario where systems over seven orders of magnitude in stellar mass form at early cosmic time. These results alleviate the tension between {Lambda}CDM simulations and observations at galactic scales. We hypothesize that these small bulges are actually the low-mass descendants of compact objects observed at high redshift, also known as red nuggets, which are consistently produced in cosmological {Lambda}CDM simulations. Therefore, this also suggests that the established coevolution of SMBHs and large bulges naturally extends to spheroids in the low-mass regime.
Satellite galaxies are commonly used as tracers to measure the line-of-sight velocity dispersion ($sigma_{rm LOS}$) of the dark matter halo associated with their central galaxy, and thereby to estimate the halos mass. Recent observational dispersion estimates of the Local Group, including the Milky Way and M31, suggest $sigmasim$50 km/s, which is surprisingly low when compared to the theoretical expectation of $sigmasim$100s km/s for systems of their mass. Does this pose a problem for $Lambda$CDM? We explore this tension using the {small{SURFS}} suite of $N$-body simulations, containing over 10000 (sub)haloes with well tracked orbits. We test how well a central galaxys host halo velocity dispersion can be recovered by sampling $sigma_{rm LOS}$ of subhaloes and surrounding haloes. Our results demonstrate that $sigma_{rm LOS}$ is biased mass proxy. We define an optimal window in $v_{rm LOS}$ and projected distance ($D_p$) -- $0.5lesssim D_p/R_{rm vir}lesssim1.0$ and $v_{rm LOS} lesssim0.5V_{rm esc}$, where $R_{rm vir}$ is the virial radius and $V_{rm esc}$ is the escape velocity -- such that the scatter in LOS to halo dispersion is minimised - $sigma_{rm LOS}=(0.5pm0.1)sigma_{v,{rm H}}$. We argue that this window should be used to measure line-of-sight dispersions as a proxy for mass, as it minimises scatter in the $sigma_{rm LOS}-M_{rm vir}$ relation. This bias also naturally explains the results from cite{mcconnachie2012a}, who used similar cuts when estimating $sigma_{rm LOS,LG}$, producing a bias of $sigma_{rm LG}=(0.44pm0.14)sigma_{v,{rm H}}$. We conclude that the Local Groups velocity dispersion does not pose a problem for $Lambda$CDM and has a mass of $log M_{rm LG, vir}/M_odot=12.0^{+0.8}_{-2.0}$.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
