New Neutrino Mass Bounds from Sloan Digital Sky Survey III Data Release 8 Photometric Luminous Galaxies

TL;DR

This paper derives cosmological bounds on the sum of neutrino masses using the angular power spectra of photometric CMASS galaxies from SDSS-III DR8. By modeling galaxy clustering with four bias parameters, incorporating redshift-space distortions, non-linear corrections via HaloFit, and combining with CMB and H₀ priors, the authors obtain a 95% CL bound of $\sum m_ν < 0.26$ eV when including the HST prior, with a more conservative bound of $0.36$ eV when allowing additional nuisance parameters. The analysis emphasizes the dominant role of small-scale growth suppression due to neutrinos over purely geometric effects and validates the modeling with mock catalogs, finding mild biases that can be mitigated by marginalizing nuisance terms. The results demonstrate the power of large-volume photometric surveys for neutrino cosmology and foreshadow stronger constraints from upcoming BOSS spectroscopic data and three-dimensional clustering measurements.

Abstract

We present neutrino mass bounds using 900,000 luminous galaxies with photometric redshifts measured from Sloan Digital Sky Survey III Data Release Eight (SDSS DR8). The galaxies have photometric redshifts between $z = 0.45$ and $z = 0.65$, and cover 10,000 square degrees and thus probe a volume of 3$h^{-3}$Gpc$^3$, enabling tight constraints to be derived on the amount of dark matter in the form of massive neutrinos. A new bound on the sum of neutrino masses $\sum m_ν< 0.26$ eV, at 95% confidence level (CL), is obtained after combining our sample of galaxies, which we call "CMASS", with WMAP 7 year Cosmic Microwave Background (CMB) data and the most recent measurement of the Hubble parameter from the Hubble Space Telescope (HST). This constraint is obtained with a conservative multipole range choice of $30 < \ell < 200$ in order to minimize non-linearities, and a free bias parameter in each of the four redshift bins. We study the impact of assuming this linear galaxy bias model using mock catalogs, and find that this model causes a small ($\sim 1-1.5 σ$) bias in $Ω_{\rm DM} h^2$. For this reason, we also quote neutrino bounds based on a conservative galaxy bias model containing additional, shot noise-like free parameters. In this conservative case, the bounds are significantly weakened, e.g. $\sum m_ν< 0.36$ eV (95% confidence level) for WMAP+HST+CMASS ($\ell_{\rm max}=200$). We also study the dependence of the neutrino bound on multipole range ($\ell_{\rm max}=150$ vs $\ell_{\rm max}=200$) and on which combination of data sets is included as a prior. The addition of supernova and/or Baryon Acoustic Oscillation data does not significantly improve the neutrino mass bound once the HST prior is included. [abridged]

Figures (8)

• Figure 1: Normalized true redshift distribution of CMASS galaxies in four photometric redshift bins. The number of galaxies in each bin is $214971$, $258736$, $248895$ and $150319$ (from low to high redshift).
• Figure 2: Observed power spectra (black points) with error bars and theoretical power spectra (solid curves). We show the theoretical power spectra for different models: the default, HaloFit (HF) based model used in our analysis (black; see text for details), the same model, but using the linear matter power spectrum as input (red), the default model, but using the Limber approximation (blue) and the default model without redshift space distortions (green). We restrict ourselves to the range $\ell = 30 - 200$ in our analysis. For the theoretical spectra, we assume the WMAP7+HST best-fit cosmology and use the bias $b_i$ that best fits the data. We do not here include the shot noise parameters $a_i$.
• Figure 3: Left panel: Minimum multipole at which 3-D power spectrum contribution to the angular power spectrum receives important non-linear corrections, as a function of redshift, $\ell_{\rm NL} \equiv k_{\rm NL} \, d(z)$. We consider several choices of the non-linear scale $k_{\rm NL}$. The dashed curves are for $k = 0.15 h$Mpc$^{-1}$ (top) and $0.1 h$Mpc$^{-1}$ (bottom). The solid curve is for a simple model of a redshift dependent $k_{\rm NL}(z) = R_{\rm NL}(z=0)/R_{\rm NL}(z) \times 0.1 h$Mpc$^{-1}$, where $R_{\rm NL}(z)$ is such that the matter overdensity variance averaged over spheres with this radius equals one (using the linear power spectrum). Right panel: The $\chi^2$ difference as a function of $\ell_{\rm max}$ between our default template, which uses Halofit, and a template using the linear matter power spectrum, given the covariance matrix for the CMASS spectra. We assume the WMAP7 plus HST best fit cosmology and fix the bias parameters $b_i = 2$ ($a_i=0$). Both plots suggest that non-linear effects start to become (mildly) relevant at $\ell_{\rm max}$ between 150 and 200.
• Figure 4: Effect of neutrinos on the angular power spectra. The solid and dashed curves depict the massless and $\Sigma m_{\nu} = 0.3$ eV cases, respectively.
• Figure 5: Example of an averaged mock spectrum (green points with error bars) and theoretical spectra (solid lines). Fixing the cosmology to the mock input cosmology (see text), we fit the averaged mock spectrum in the range $\ell = 30-200$ to our model described in the text. The black curve is the resulting best-fit spectrum if we only fit a (scale-independent) galaxy bias $b_0$ (best-fit value $b_0 = 2.02$), while the red curve is the best fit in a model that also includes the nuisance parameter $a_0$ (best fit values $b_0=2.00, \, a_0=1.05 \cdot 10^{-6}$). To provide a hint of the importance of non-linear effects in this multipole range, we plot the spectrum based on a linear three dimensional matter power spectrum in blue ($b_0 = 2.02, a_0=0$)