اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدMass Function of Low Mass Dark Halos
50
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The mass function of dark halos in a Lambda-dominated cold dark matter (LambdaCDM) universe is investigated. 529 output files from five runs of N-body simulations are analyzed using the friends-of-friends cluster finding algorithm. All the runs use 512^3 particles in the box size of 35 h^{-1}Mpc to 140 h^{-1}Mpc. Mass of particles for 35 h^{-1} Mpc runs is 2.67 times 10^7 h^{-1} M_{solar}. Because of the high mass resolution of our simulations, the multiplicity function in the low-mass range, where the mass is well below the characteristic mass and $ u = delta_c / sigma lesssim 1.0$, is evaluated in the present work, and is well fitted by the functional form proposed by Sheth & Tormen (ST). However, the maximum value of the multiplicity function from our simulations at $ u sim 1$ is smaller, and its low mass tail is shallower when compared with the ST multiplicity function.
قيم البحث
اقرأ أيضاً
Using numerical simulations and the Sheth-Tormen approximation we study the mass function of dark matter halos in voids. We find that the void mass function is significantly lower and its shape is different than that of the field halos. We predict th
at in the standard LCDM model a void with radius 10 h^-1 Mpc should have 50 halos with circular velocity v_c > 50 km/s and 600 halos with v_c > 20 km/s.
We compare the predicted conditional mass function (CMF) of dark matter halos from two theoretical prescriptions against numerical N-body simulations, both in overdense and underdense regions and at different Eulerian scales ranging from $5$ to $30,h
^{-1},$Mpc. In particular, we consider in detail a locally-implemented rescaling of the unconditional mass function (UMF) already discussed in the literature, and also a generalization of the standard rescaling method described in the extended Press-Schechter formalism. First, we test the consistency of these two rescalings by verifying the normalization of the CMF at different scales, and showing that none of the proposed cases provides a normalized CMF. In order to satisfy the normalization condition, we include a modification in the rescaling procedure. After this modification, the resulting CMF generally provides a better description of numerical results. We finally present an analytical fit to the ratio between the CMF and the UMF (also known as the matter-to-halo bias function) in underdense regions, which could be of special interest to speed-up the computation of the halo abundance when studying void statistics. In this case, the CMF prescription based on the locally-implemented rescaling provides a slightly better description of the numerical results when compared to the standard rescaling.
Dark matter halos of sub-solar mass are the first bound objects to form in cold dark matter theories. In this article, I discuss the present understanding of microhalos, their role in structure formation, and the implications of their potential prese
nce, in the interpretation of dark matter experiments.
Mass models of 15 nearby dwarf and spiral galaxies are presented. The galaxies are selected to be homogeneous in terms of the method used to determine their distances, the sampling of their rotation curves (RCs) and the mass-to-light ratio (M/L) of t
heir stellar contributions, which will minimize the uncertainties on the mass model results. Those RCs are modeled using the MOdified Newtonian Dynamics (MOND) prescription and the observationally motivated pseudo-isothermal (ISO) dark matter (DM) halo density distribution. For the MOND models with fixed (M/L), better fits are obtained when the constant a$_{0}$ is allowed to vary, giving a mean value of (1.13 $pm$ 0.50) $times$ 10$^{-8}$ cm s$^{-2}$, compared to the standard value of 1.21 $times$ 10$^{-8}$ cm s$^{-2}$. Even with a$_{0}$ as a free parameter, MOND provides acceptable fits (reduced $chi^{2}_{r}$ $<$ 2) for only 60% (9/15) of the sample. The data suggest that galaxies with higher central surface brightnesses tend to favor higher values of the constant a$_{0}$. This poses a serious challenge to MOND since a$_{0}$ should be a universal constant. For the DM models, our results confirm that the DM halo surface density of ISO models is nearly constant at $ rho_{0} R_{C} sim 120 M_{odot} pc^{-2}$. This means that if the (M/L) is determined by stellar population models, ISO DM models are left with only one free parameter, the DM halo central surface density.
We analyse the dark, gas, and stellar mass assembly histories of low-mass halos (Mvir ~ 10^10.3 - 10^12.3 M_sun) identified at redshift z = 0 in cosmological numerical simulations. Our results indicate that for halos in a given present-day mass bin,
the gas-to-baryon fraction inside the virial radius does not evolve significantly with time, ranging from ~0.8 for smaller halos to ~0.5 for the largest ones. Most of the baryons are located actually not in the galaxies but in the intrahalo gas; for the more massive halos, the intrahalo gas-to-galaxy mass ratio is approximately the same at all redshifts, z, but for the least massive halos, it strongly increases with z. The intrahalo gas in the former halos gets hotter with time, being dominant at z = 0, while in the latter halos, it is mostly cold at all epochs. The multiphase ISM and thermal feedback models in our simulations work in the direction of delaying the stellar mass growth of low-mass galaxies.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
