اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدFractal analysis of the galaxy distribution in the redshift range 0.45 < z < 5.0
182
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Evidence is presented that the galaxy distribution can be described as a fractal system in the redshift range of the FDF galaxy survey. The fractal dimension $D$ was derived using the FDF galaxy volume number densities in the spatially homogeneous standard cosmological model with $Omega_{m_0}=0.3$, $Omega_{Lambda_0}=0.7$ and $H_0=70 ; mbox{km} ; {mbox{s}}^{-1} ; {mbox{Mpc}}^{-1}$. The ratio between the differential and integral number densities $gamma$ and $gamma^ast$ obtained from the red and blue FDF galaxies provides a direct method to estimate $D$, implying that $gamma$ and $gamma^ast$ vary as power-laws with the cosmological distances. The luminosity distance $d_{scriptscriptstyle L}$, galaxy area distance $d_{scriptscriptstyle G}$ and redshift distance $d_z$ were plotted against their respective number densities to calculate $D$ by linear fitting. It was found that the FDF galaxy distribution is characterized by two single fractal dimensions at successive distance ranges. Two straight lines were fitted to the data, whose slopes change at $z approx 1.3$ or $z approx 1.9$ depending on the chosen cosmological distance. The average fractal dimension calculated using $gamma^ast$ changes from $langle D rangle=1.4^{scriptscriptstyle +0.7}_{scriptscriptstyle -0.6}$ to $langle D rangle=0.5^{scriptscriptstyle +1.2}_{scriptscriptstyle -0.4}$ for all galaxies, and $D$ decreases as $z$ increases. Small values of $D$ at high $z$ mean that in the past galaxies were distributed much more sparsely and the large-scale galaxy structure was then possibly dominated by voids. Results of Iribarrem et al. (2014, arXiv:1401.6572) indicating similar fractal features with $langle D rangle =0.6 pm 0.1$ in the far-infrared sources of the Herschel/PACS evolutionary probe (PEP) at $1.5 lesssim z lesssim 3.2$ are also mentioned.
قيم البحث
اقرأ أيضاً
This paper seeks to test if the large-scale galaxy distribution can be characterized as a fractal system. Tools appropriate for describing galaxy fractal structures with a single fractal dimension $D$ in relativistic settings are developed and applie
d to the UltraVISTA galaxy survey. A graph of volume-limited samples corresponding to the redshift limits in each redshift bins for absolute magnitude is presented. Fractal analysis using the standard $Lambda$CDM cosmological model is applied to a reduced subsample in the range $0.1le z le 4$, and the entire sample within $0.1le zle 6$. Three relativistic distances are used, the luminosity distance $d_L$, redshift distance $d_z$ and galaxy area distance $d_G$, because for data at $zgtrsim 0.3$ relativistic effects are such that for the same $z$ these distance definitions yield different values. The results show two consecutive and distinct redshift ranges in both the reduced and complete samples where the data behave as a single fractal galaxy structure. For the reduced subsample we found that the fractal dimension is $D=left(1.58pm0.20right)$ for $z<1$, and $D=left(0.59pm0.28right)$ for $1le zle 4$. The complete sample yielded $D=left(1.63pm0.20right)$ for $z<1$ and $D=left(0.52pm0.29right)$ for $1le zle6$. These results are consistent with those found by Conde-Saavedra et al. (2015; arXiv:1409.5409v1), where a similar analysis was applied to a much more limited survey at equivalent redshift depths, and suggest that either there are yet unclear observational biases causing such decrease in the fractal dimension, or the galaxy clustering was possibly more sparse and the universe void dominated in a not too distant past.
We study the reduced skewness, $S_{3,g}equivbar{xi}_{3,g}/bar{xi}_{2,g}^2$ of galaxy distribution at $z=0.5$ in two families of modfied gravity models: the Hu-Sawicki $f(R)$-gravity and normal-branch of Dvali-Gabadadze-Porrati (nDGP) models. We use a
set of mock galaxy catalogues specifally designed to match CMASS spectroscopic galaxy sample. For the first time we investigate the third reduced moment of such galaxy distributions both in the redshift space. Our analysis confirms that the signal previously indicated only for dark matter halo catalogues persists also in realistic mock galaxy samples. This result offers a possibility to extract a potential modified gravity signal in $S_3$ from spectroscopic galaxy data without a need for a very precise and self-consistent RSD models constructed for each and every modified gravity scenario separately. We show that the relative deviations from $Lambda$CDM~ $S_{3,g}$ of various modified gravity models can vary from $7$ down to $sim 2-3%$ effects. Albeit, the effect looks small, we show that for considered models it can foster a $2-3sigma$ falsification. Finally we argue that galaxy sample of a significantly higher number density should provide even stronger constraints by limiting shot-noise effects affecting the $S_{3,g}$ estimates at small comoving separations.
It has been recently recognized that the observational relativistic effects, mainly arising from the light propagation in an inhomogeneous universe, induce the dipole asymmetry in the cross-correlation function of galaxies. In particular, the dipole
asymmetry at small scales is shown to be dominated by the gravitational redshift effects. In this paper, we exploit a simple analytical description for the dipole asymmetry in the cross-correlation function valid at quasi-linear regime. In contrast to the previous model, a new prescription involves only one dimensional integrals, providing a faster way to reproduce the results obtained by Saga et al. (2020). Using the analytical model, we discuss the detectability of the dipole signal induced by the gravitational redshift effect from upcoming galaxy surveys. The gravitational redshift effect at small scales enhances the signal-to-noise ratio (S/N) of the dipole, and in most of the cases considered, the S/N is found to reach a maximum at $zapprox0.5$. We show that current and future surveys such as DESI and SKA provide an idealistic data set, giving a large S/N of $10sim 20$. Two potential systematics arising from off-centered galaxies are also discussed (transverse Doppler effect and diminution of the gravitational redshift effect), and their impacts are found to be mitigated by a partial cancellation between two competitive effects. Thus, the detection of the dipole signal at small scales is directly linked to the gravitational redshift effect, and should provide an alternative route to test gravity.
We analyse the structures of all the clusters in the DAFT/FADA survey for which XMM-Newton and/or a sufficient number of galaxy redshifts in the cluster range is available, with the aim of detecting substructures and evidence for merging events. Thes
e properties are discussed in the framework of standard cold dark matter cosmology.XMM-Newton data were available for 32 clusters, for which we derive the X-ray luminosity and a global X-ray temperature for 25 of them. For 23 clusters we were able to fit the X-ray emissivity with a beta-model and subtract it to detect substructures in the X-ray gas. A dynamical analysis based on the SG method was applied to the clusters having at least 15 spectroscopic galaxy redshifts in the cluster range: 18 X-ray clusters and 11 clusters with no X-ray data. Only major substructures will be detected. Ten substructures were detected both in X-rays and by the SG method. Most of the substructures detected both in X-rays and with the SG method are probably at their first cluster pericentre approach and are relatively recent infalls. We also find hints of a decreasing X-ray gas density profile core radius with redshift. The percentage of mass included in substructures was found to be roughly constant with redshift with values of 5-15%, in agreement both with the general CDM framework and with the results of numerical simulations. Galaxies in substructures show the same general behaviour as regular cluster galaxies; however, in substructures, there is a deficiency of both late type and old stellar population galaxies. Late type galaxies with recent bursts of star formation seem to be missing in the substructures close to the bottom of the host cluster potential well. However, our sample would need to be increased to allow a more robust analysis.
BINGO (BAO from Integrated Neutral Gas Observations) is a unique radio telescope designed to map the intensity of neutral hydrogen distribution at cosmological distances, making the first detection of Baryon Acoustic Oscillations (BAO) in the frequen
cy band 980 MHz - 1260 MHz, corresponding to a redshift range $0.127 < z < 0.449$. BAO is one of the most powerful probes of cosmological parameters and BINGO was designed to detect the BAO signal to a level that makes it possible to put new constraints on the equation of state of dark energy. The telescope will be built in Paraiba, Brazil and consists of two $thicksim$ 40m mirrors, a feedhorn array of 28 horns, and no moving parts, working as a drift-scan instrument. It will cover a $15^{circ}$ declination strip centered at $sim delta=-15^{circ}$, mapping $sim 5400$ square degrees in the sky. The BINGO consortium is led by University of S~ao Paulo with co-leadership at National Institute for Space Research and Campina Grande Federal University (Brazil). Telescope subsystems have already been fabricated and tested, and the dish and structure fabrication are expected to start in late 2020, as well as the road and terrain preparation.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
