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, N (< θ), and the fractal correlation dimension, D 2 (θ), we find an angular scale of transition to homogeneity for this sample of θ H = 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 HI 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 asses 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 θ H agrees well with what is expected in the ΛCDM scenario. Although we can not prove spatial homogeneity within the approach followed, our results provide one more evidence of it, strengthening the validity of the Cosmological Principle.
We use the scaled counts in spherical caps N (< θ) and the fractal correlation dimension
Aims. We measure the transverse baryon acoustic oscillations (BAO) signal in the local Universe using a sample of blue galaxies from the Sloan Digital Sky Survey (SDSS) survey as a cosmological tracer. Methods. The method is weakly dependent on a cosmological model and is suitable for 2D analyses in thin redshift bins to investigate the SDSS data in the interval z ∈ [0.105, 0.115]. Results. We detect the transverse BAO signal θBAO = 19.8°±1.05° at zeff = 0.11, with a statistical significance of 2.2σ. Additionally, we perform tests that confirm the robustness of this angular BAO signature. Supported by a large set of log-normal simulations, our error analyses include statistical and systematic contributions. In addition, considering the sound horizon scale calculated by the Planck Collaboration, rsPlanck, and the θBAO value obtained here, we obtain a measurement of the angular diameter distance DA(0.11) =258.31 ± 13.71 h−1 Mpc. Moreover, combining this θBAO measurement at low redshift with other BAO angular scale data reported in the literature, we perform statistical analyses for the cosmological parameters of some Lambda cold dark matter type models.
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