The growth rate of cosmic structures in the local Universe with the ALFALFA survey

We investigate the growth rate of structures in the local Universe. For this, we use as a cosmological tracer the HI line extra-galactic sources from the Arecibo Legacy Fast ALFA (ALFALFA) survey to obtain a measurement of the normalized growth rate parameter, $f σ_{8}$, considered a powerful tool to constrain alternative models of gravity. For these analyses, we calculate the Local Group velocity due to the matter structures distribution in the ALFALFA catalogue and compare it with the Local Group velocity relative to the Cosmic Microwave Background frame to obtain the velocity scale parameter, $β$. Using Monte Carlo realizations and log-normal simulations, our methodology quantifies the errors introduced by shot-noise and partial sky coverage of the analysed data. The measurement of the velocity scale parameter $β$, and the calculation of the matter fluctuation of the cosmological tracer, $σ_{8}^{\text{tr}}$, lead us to $f σ_{8} = 0.46 \pm 0.06$ at $\bar{z} = 0.013$, in good agreement (at $1 σ$ level) with the value expected in the $Λ$CDM concordance model. In addition, our analyses of the ALFALFA sample also provide a measurement of the growth rate of structures $f \,=\, 0.56 \pm 0.07$, at $\bar{z} = 0.013$.