“MAPPING THE 2D MATTER DISTRIBUTION IN THE LOCAL UNIVERSE USING BLUE GALAXIES FROM SDSS DR12”

Abstract

Baryon Acoustic Oscillations (BAO), a preferred scale of approximately 150 Mpc im- printed on the large-scale matter distribution by acoustic waves in the primordial plasma, constitute one of the most robust standard rulers in cosmology. In contrast to the more common angular approach, based on the angular correlation function ω(θ), in this work the BAO are measured through the angular power spectrum Cℓ, in harmonic space, using a sample of star-forming blue galaxies at low redshift from the twelfth data release of the Sloan Digital Sky Survey (SDSS). The aim is to validate a pipeline for the angular analysis of BAO in harmonic space and to apply it to this unconventional sample. The methodology is only weakly dependent on the assumed cosmological model: by working in transverse harmonic space, it does not require the conversion of redshifts into radial dis- tances, so that the information on the acoustic scale follows exclusively from the position of the oscillatory feature in multipole space. For the analysis, the sample was divided into two redshift bins: 0.15 < z < 0.25 (the main measurement) and 0.05 < z < 0.15 (pipeline validation). The angular power spectrum of both samples is estimated with the pseudo-Cℓ formalism, and the covariance is built from 1000 lognormal catalogs generated with the GLASS code and iteratively recalibrated. The shift parameter α is determined by two independent methods: the profile likelihood and Markov Chain Monte Carlo (MCMC). For the main bin, we obtain α = 1.034+0.155-0.162 and α = 0.974+0.247-0.194, respectively, both consistent, within the uncertainties, with the value <α> = 1 expected in the ΛCDM model. The preference for the oscillatory model is marginal (∆χ2 = 1.38; 1.17σ), consistent with the accuracy allowed by the volume and sky coverage of the survey (f_sky ~ 0.18); in the low-redshift bin no significant preference is found (∆χ2 < 0.1), as expected in the absence of a detectable signal. The measured scale corresponds to a ratio between the transverse comoving distance and the sound horizon of D_M / r_d = 5.606 +/- 1.276 at z_eff = 0.20, without being able to discriminate between the predictions of Planck (2018) and DESI (2025), and to an acoustic angular scale θ_BAO = (10.21 +/- 2.326)deg. Combined with angular compilations from the literature, it yields Ωm,0 = 0.269+0.018-0.017 and h*r_d = 103.11+0.98-0.99 Mpc. Although the low significance reflects the intrinsic difficulty of the measurement in this regime, the results suggest the viability of blue galaxies as BAO tracers and validate the analysis framework for application to future surveys.