اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدProbing the isotropy of cosmic acceleration using different supernova samples
35
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Recent studies have indicated that an anisotropic cosmic expansion may exist. In this paper, we use three datasets of type Ia supernovae (SNe Ia) to probe the isotropy of cosmic acceleration. For the Union2.1 dataset, the direction and magnitude of the dipole are $(l=309.3^{circ} {}^{+ 15.5^{circ}}_{-15.7^{circ}} , b = -8.9^{circ} {}^{ + 11.2^{circ}}_{-9.8^{circ}} ), A=(1.46 pm 0.56) times 10^{-3}$. For the Constitution dataset, the results are $(l=67.0^{circ}{}^{+ 66.5^{circ}}_{-66.2^{circ}}, b=-0.6^{circ}{}^{+ 25.2^{circ}}_{-26.3^{circ}}), A=(4.4 pm 5.0) times 10^{-4}$. For the JLA dataset, no significant dipolar deviation is found. We also explore the effects of anisotropic distributions of coordinates and redshifts on the results using Monte-Carlo simulations. We find that the anisotropic distribution of coordinates can cause dipole directions and make dipole magnitude larger. Anisotropic distribution of redshifts is found to have no significant effect on dipole fitting results.
قيم البحث
اقرأ أيضاً
Despite its fundamental importance in cosmology, there have been very few straight-forward tests of the cosmological principle. Such tests are especially timely because of the hemispherical asymmetry in the cosmic microwave background recently observ
ed by the Planck collaboration. Most tests to date looked at the redshift dependence of cosmological parameters. These are subject to large systematic effects that require modeling and bias corrections. Unlike previous tests, the tests described here compare galaxy distributions in equal volumes at the same redshift z. This allows a straight-forward test and z-dependent biases are not a problem. Using ~10^6 galaxies from the SDSS DR7 survey, I show that re- gions of space separated by ~2 Gpc have the same average galaxy correlation radii, amplitudes, and number density to within approx. 5%, which is consistent with standard model expectations.
Recently, some divergent conclusions about cosmic acceleration were obtained using type Ia supernovae (SNe Ia), with opposite assumptions on the intrinsic luminosity evolution. In this paper, we use strong gravitational lensing systems to probe the c
osmic acceleration. Since the theory of strong gravitational lensing is established certainly, and the Einstein radius is determined by stable cosmic geometry. We study two cosmological models, $Lambda$CDM and power-law models, through 152 strong gravitational lensing systems, incorporating with 30 Hubble parameters $H(z)$ and 11 baryon acoustic oscillation (BAO) measurements. Bayesian evidence are introduced to make a one-on-one comparison between cosmological models. Basing on Bayes factors $ln B$ of flat $Lambda$CDM versus power-law and $R_{h}=ct$ models are $ln B>5$, we find that the flat $Lambda$CDM is strongly supported by the combination of the datasets. Namely, an accelerating cosmology with non power-law expansion is preferred by our numeration.
We present a new signature by which to one could potentially discriminate between a spectrum of gravitational radiation generated by a self-ordering scalar field vs that of inflation, specifically a comparison of the magnitude of a flat spectrum at f
requencies probed by future direct detection experiments to the magnitude of a possible polarization signal in the Cosmic Microwave Background (CMB) radiation. In the process we clarify several issues related to the proper calculation of such modes, focusing on the effect of post-horizon-crossing evolution.
The isotropy of the late Universe is an assumption greatly used in astronomy. However, many studies have recently reported deviations from isotropy with a definitive conclusion yet to be made. New, independent methods to robustly test the cosmic isot
ropy are of crucial importance. In this work, we investigate the directional behavior of the X-ray luminosity-temperature ($L_X-T$) relation of galaxy clusters. A tight correlation exists between the luminosity and temperature of the X-ray-emitting intracluster medium. While the measured luminosity depends on the underlying cosmology, the temperature can be determined without any cosmological assumptions. By exploiting this property one can effectively test the isotropy of cosmological parameters over the full extragalactic sky. Here, we used 313 homogeneously selected X-ray galaxy clusters from the MCXC catalog and obtained core-excised temperatures for all of them. We find that the behavior of the $L_X-T$ relation heavily depends on the direction of the sky. Strong anisotropies are detected at a $sim 4sigma$ level toward $(l,b)sim (280^{circ}, -20^{circ})$. Several X-ray and cluster-related effects that could potentially explain these anisotropies were examined, but none did so. Interestingly, two other available cluster samples appear to have a similar behavior throughout the sky, while being fully independent of each other and our sample. Performing a joint analysis of the three samples, the final anisotropy is further intensified ($sim 5sigma$), toward $(l,b)sim (303^{circ}, -27^{circ})$, which is in good agreement with other cosmological probes. This result demonstrates that X-ray galaxy cluster studies that assume perfect isotropy can produce strongly biased results whether the underlying reason is cosmological or related to X-rays. The identification of the exact nature of these anisotropies is therefore crucial.
We analyse the distribution of position angles of 1 million galaxies from the Hyperleda catalogue, a sample that presents the galaxies coordinates in the celestial sphere, information that allows us to look for a possible privileged direction. Our an
alysis involves different tests and statistical methods, from which it is possible to infer with high probability ($p$-value extremely low) that the galactic planes are not randomly oriented in the sky. Whether this is an evidence of a cosmological anisotropy or an observational bias due to local effects is something deserving further studies.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
