scholarly journals The angular scale of homogeneity in the local Universe with the SDSS blue galaxies

2019 ◽  
Vol 488 (1) ◽  
pp. 1481-1487 ◽  
Author(s):  
F Avila ◽  
C P Novaes ◽  
A Bernui ◽  
E de Carvalho ◽  
J P Nogueira-Cavalcante

ABSTRACT We probe the angular scale of homogeneity in the local Universe using blue galaxies from the SDSS survey as a cosmological tracer. Through the scaled counts in spherical caps, $\mathcal {N}(\lt \theta)$, and the fractal correlation dimension, $\mathcal {D}_{2}(\theta)$, we find an angular scale of transition to homogeneity for this sample of θH = 22.19° ± 1.02°. A comparison of this measurement with another obtained using a different cosmic tracer at a similar redshift range (z < 0.06), namely, the H i extragalactic sources from the ALFALFA catalogue, confirms that both results are in excellent agreement (taking into account the corresponding bias correction). We also perform tests to assess the robustness of our results. For instance, we test if the size of the surveyed area is large enough to identify the transition scale we search for, and also we investigate a reduced sample of blue galaxies, obtaining in both cases a similar angular scale for the transition to homogeneity. Our results, besides confirming the existence of an angular scale of transition to homogeneity in different cosmic tracers present in the local Universe, show that the observed angular scale θH agrees well with what is expected in the ΛCDM scenario. Although we cannot prove spatial homogeneity within the approach followed, our results provide one more evidence of it, strengthening the validity of the Cosmological Principle.

2014 ◽  
Vol 578-579 ◽  
pp. 1228-1232
Author(s):  
Shou Jun Du ◽  
Li Bin Shi ◽  
Li Mei Zhang

Damage of steel truss structure can be determined by the sudden change of correlation dimension which was obtained from the structural vibration response through fractal theory. The streel truss structure was as exampled to verify this method. The results show that: this method can determine the damage location of the structure whether single damage or multi damage and can preliminarily judge the damage degree.


Author(s):  
E. de Carvalho ◽  
A. Bernui ◽  
F. Avila ◽  
C. P. Novaes ◽  
J. P. Nogueira-Cavalcante
Keyword(s):  

2019 ◽  
Vol 62 (Vol 62 (2019)) ◽  
Author(s):  
Saroj Mondal ◽  
Paresh SinghaRoy ◽  
Joshi Catherine ◽  
Auchitya Pandey

2019 ◽  
Vol 489 (2) ◽  
pp. 2014-2029 ◽  
Author(s):  
Tetsuya Hashimoto ◽  
Tomotsugu Goto ◽  
Rieko Momose ◽  
Chien-Chang Ho ◽  
Ryu Makiya ◽  
...  

ABSTRACT Galaxies evolve from a blue star-forming phase into a red quiescent one by quenching their star formation activity. In high-density environments, this galaxy evolution proceeds earlier and more efficiently. Therefore, local galaxy clusters are dominated by well-evolved red elliptical galaxies. The fraction of blue galaxies in clusters monotonically declines with decreasing redshift, i.e. the Butcher–Oemler effect. In the local Universe, observed blue fractions of massive clusters are as small as ≲0.2. Here we report a discovery of a ‘blue cluster’ that is a local galaxy cluster with an unprecedentedly high fraction of blue star-forming galaxies yet hosted by a massive dark matter halo. The blue fraction is 0.57, which is 4.0σ higher than those of the other comparison clusters under the same selection and identification criteria. The velocity dispersion of the member galaxies is 510 km s−1, which corresponds to a dark matter halo mass of 2.0$^{+1.9}_{-1.0}\times 10^{14}$ M⊙. The blue fraction of the cluster is more than 4.7σ beyond the standard theoretical predictions including semi-analytic models of galaxy formation. The probability to find such a high blue fraction in an individual cluster is only 0.003 per cent, which challenges the current standard frameworks of the galaxy formation and evolution in the ΛCDM universe. The spatial distribution of galaxies around the blue cluster suggests that filamentary cold gas streams can exist in massive haloes even in the local Universe. However these cold streams have already disappeared in the theoretically simulated local universes.


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