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Abstract:

Future cosmological measurements should enable the sum of neutrino masses to be determined indirectly through their effects on the expansion rate of the Universe and the clustering of matter. We consider prospects for the gravitationally lensed cosmic microwave background (CMB) anisotropies and baryon acoustic oscillations (BAOs) in the galaxy distribution, examining how the projected uncertainty of ≈15 meV on the neutrino mass sum (a 4σ detection of the minimal mass) might be reached over the next decade. The current 1σ uncertainty of ≈103 meV (Planck-2015 þ BAO-15) will be improved by upcoming “Stage-3” (S3) CMB experiments (S3 þ BAO-15∶ 44 meV), then upcoming BAO measurements (S3 þ DESI∶ 22 meV), and planned next-generation “Stage 4” (S4) CMB experiments (S4 þ DESI∶ 15–19 meV, depending on angular range). An improved optical depth measurement is important: the projected neutrino mass uncertainty increases to 26 meV if S4 is limited to l > 20 and combined with current large-scale polarization data. Looking beyond ΛCDM, including curvature uncertainty increases the forecast mass error by ≈50% for S4 þ DESI, and more than doubles the error with a two-parameter dark-energy equation of state. Complementary low-redshift probes including galaxy lensing will play a role in distinguishing between massive neutrinos and a departure from a w ¼ −1, flat geometry.

Abstract:

© 2015 The Authors Published by 91̽�� University Press on behalf of the Royal Astronomical Society. We correlate the positions of radio galaxies in the FIRST survey with the cosmic microwave background lensing convergence estimated from the Atacama Cosmology Telescope over 470 deg < sup > 2 < /sup > to determine the bias of these galaxies. We remove optically cross-matched sources below redshift z = 0.2 to preferentially select active galactic nuclei (AGN). We measure the angular cross-power spectrum C < inf > l < /inf > < sup > kg < /sup > at 4.4σ significance in the multipole range 100 < l < 3000, corresponding to physical scales within ≈2-60 Mpc at an effective redshift z < inf > eff < /inf > = 1.5. Modelling the AGN population with a redshift-dependent bias, the cross-spectrum is well fitted by the Planck best-fitting Λ cold dark matter cosmological model. Fixing the cosmology and assumed redshift distribution of sources, we fit for the overall bias model normalization, finding b(z < inf > eff < /inf > ) = 3.5 ± 0.8 for the full galaxy sample and b(z < inf > eff < /inf > ) = 4.0 ± 1.1(3.0 ± 1.1) for sources brighter (fainter) than 2.5 mJy. This measurement characterizes the typical halo mass of radio-loud AGN: we find log(M < inf > halo < /inf > /M < inf > ⊙ < /inf > ) = 13.6 < inf > -0.4 < /inf > < sup > +0.3 < /sup > .