اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدFast galaxy bars continue to challenge standard cosmology
61
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Many observed disc galaxies harbour a central bar. In the standard cosmological paradigm, galactic bars should be slowed down by dynamical friction from the dark matter halo. This friction depends on the galaxys physical properties in a complex way, making it impossible to formulate analytically. Fortunately, cosmological hydrodynamical simulations provide an excellent statistical population of galaxies, letting us quantify how simulated galactic bars evolve within dark matter haloes. We measure bar lengths and pattern speeds in barred galaxies in state-of-the-art cosmological hydrodynamical simulations of the IllustrisTNG and EAGLE projects, using techniques similar to those used observationally. We then compare our results with the largest available observational sample at $z=0$. We show that the tension between these simulations and observations in the ratio of corotation radius to bar length is $12.62sigma$ (TNG50), $13.56sigma$ (TNG100), $2.94sigma$ (EAGLE50), and $9.69sigma$ (EAGLE100), revealing for the first time that the significant tension reported previously persists in the recently released TNG50. The lower statistical tension in EAGLE50 is actually caused by it only having 5 galaxies suitable for our analysis, but all four simulations give similar statistics for the bar pattern speed distribution. In addition, the fraction of disc galaxies with bars is similar between TNG50 and TNG100, though somewhat above EAGLE100. The simulated bar fraction and its trend with stellar mass both differ greatly from observations. These dramatic disagreements cast serious doubt on whether galaxies actually have massive cold dark matter haloes, with their associated dynamical friction acting on galactic bars.
قيم البحث
اقرأ أيضاً
The current description of fundamental interactions is based on two theories with the status of standard models. The electromagnetic and nuclear interactions are described at a quantum level by the Standard Model of particle physics, using tools like
gauge theories and spontaneous symmetry breaking by the Higgs mechanism. The gravitational interaction is described on the other hand by general relativity, based on a dynamical description of space-time at a classical level. Although these models are verified to high precision in the solar system experiments, they suffer from several theoretical weaknesses and a lack of predictive power at the Planck scale as well as at cosmological scales; they are thus not viewed anymore as fundamental theories. As its phenomenology involves both these extreme scales, cosmology is then a good laboratory to probe theories going beyond these standard models. The first part of this thesis focus on cosmic strings, topological defects forming during the spontaneous symmetry breaking of grand unified theories in the early universe. I show especially how to study these defects while taking into account the complete structure of the particles physics models leading to their formation, going beyond the standard descriptions in terms of simplified toy-models. The second part is devoted to the construction and the examination of different theories of modified gravity related to the Galileon model, a model which tries in particular to explain the dark energy phenomenology.
Gravitational waves (GWs) directly measure the luminosity distance to the merger, which, when combined with an independent measurement of the sources redshift, provides a novel probe of cosmology. The proposed next generation of ground-based GW detec
tors, Einstein Telescope and Cosmic Explorer, will detect tens of thousands of binary neutron stars (BNSs) out to cosmological distances ($z>2$), beyond the peak of the star formation rate (SFR), or cosmic noon. At these distances, it will be challenging to measure the sources redshifts by observing electromagnetic (EM) counterparts or statistically marginalizing over a galaxy catalog. In the absence of an EM counterpart or galaxy catalog, Ding et al. showed that theoretical priors on the merger redshift distribution can be used to infer parameters in a $w$CDM cosmology. We argue that in the BNS case, the redshift distribution will be measured by independent observations of short gamma ray bursts (GRBs), kilonovae, and known BNS host galaxies. We show that, in addition to measuring the background cosmology, this method can constrain the effects of dark energy on modified GW propagation. We consider the simple case in which the BNS rate is textit{a priori} known to follow the SFR. If the SFR is perfectly known, $mathcal{O}(10,000)$ events (to be expected within a year of observation with Cosmic Explorer) would yield a sub-tenth percent measurement of the combination $H_0^{2.8}Omega_M$. Fixing $H_0$ and $Omega_M$, this method may enable a 5% measurement of the dark energy equation of state parameter. Fixing the background cosmology and probing modified GW propagation, the running of the Planck mass parameter $c_M$ may be measured to $pm0.02$. Although realistically, the redshift evolution of the merger rate will be uncertain, prior knowledge of the peak redshift will provide valuable information for standard siren analyses.
We consider scenarios where the inflaton field decays dominantly to a hidden dark matter (DM) sector. By studying the typical behavior of the Standard Model (SM) Higgs field during inflation, we derive a relation between the primordial tensor-to-scal
ar ratio $r$ and amplitude of the residual DM isocurvature perturbations $beta$ which is typically generated if the DM is thermally decoupled from the SM sector. We consider different expansion histories and find that if the Universe was radiation- or matter-dominated after inflation, a future discovery of primordial DM isocurvature will rule out all simple scenarios of this type because generating observable $beta$ from the Higgs is not possible without violating the bounds on $r$. Seen another way, the Higgs field is generically not a threat to models where both the inflaton and DM reside in a decoupled sector. However, this is not necessarily the case for an early kination-dominated epoch, as then the Higgs can source sizeable $beta$. We also discuss why the Higgs cannot source the observed curvature perturbation at large scales in any of the above cases but how the field can still be the dominant source of curvature perturbations at small scales.
Galaxy bias, the unknown relationship between the clustering of galaxies and the underlying dark matter density field is a major hurdle for cosmological inference from large-scale structure. While traditional analyses focus on the absolute clustering
amplitude of high-density regions mapped out by galaxy surveys, we propose a relative measurement that compares those to the underdense regions, cosmic voids. On the basis of realistic mock catalogs we demonstrate that cross correlating galaxies and voids opens up the possibility to calibrate galaxy bias and to define a static ruler thanks to the observable geometric nature of voids. We illustrate how the clustering of voids is related to mass compensation and show that volume-exclusion significantly reduces the degree of stochasticity in their spatial distribution. Extracting the spherically averaged distribution of galaxies inside voids from their cross correlations reveals a remarkable concordance with the mass-density profile of voids.
In this paper we present four simple expressions for the relativistic first and second order fractional density perturbations for $Lambda$CDM cosmologies in different gauges: the Poisson, uniform curvature, total matter and synchronous gauges. A dist
inctive feature of our approach is the use of a canonical set of quadratic differential expressions involving an arbitrary spatial function, the so-called comoving curvature perturbation, to describe the spatial dependence, which enables us to unify, simplify and extend previous seemingly disparate results. The simple structure of the expressions makes the evolution of the density perturbations completely transparent and clearly displays the effect of the cosmological constant on the dynamics, namely that it stabilizes the perturbations. We expect that the results will be useful in applications, for example, studying the effects of primordial non-Gaussianity on the large scale structure of the universe.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
