Designing an inflation galaxy survey: How to measure σ(f_(NL))∼1 using scale-dependent galaxy bias

The most promising method for measuring primordial non-Gaussianity in the post-Planck era is to detect large-scale, scale-dependent galaxy bias. Considering the information in the galaxy power spectrum, we here derive the properties of a galaxy clustering survey that would optimize constraints on primordial non-Gaussianity using this technique. Specifically, we ask the question of what survey design is needed to reach a precision σ(f^(loc)_(NL))≈1. To answer this question, we calculate the sensitivity to f^(loc)_(NL) as a function of galaxy number density, redshift accuracy and sky coverage. We include the multitracer technique, which helps minimize cosmic variance noise, by considering the possibility of dividing the galaxy sample into stellar mass bins. We show that the ideal survey for f^(loc)_(NL) looks very different than most galaxy redshift surveys scheduled for the near future. Since those are more or less optimized for measuring the baryon acoustic oscillation scale, they typically require spectroscopic redshifts. On the contrary, to optimize the f^(loc)_(NL) measurement, a deep, wide, multiband imaging survey is preferred. An uncertainty σ(f^(loc)_(NL))=1 can be reached with a full-sky survey that is complete to an i-band AB magnitude i≈23 and has a number density ∼8  arcmin^(-2). Requirements on the multiband photometry are set by a modest photo-z accuracy σ(z)/(1+z)<0.1 and the ability to measure stellar mass with a precision ∼0.2 dex or better (or another proxy for halo mass with equivalent scatter). Finally, we estimate that for the idealized case of a survey measuring all halos down to a mass 10^(10)h^(-1)  M⊙ on the full sky out to high redshift, in principle a precision of order σ(f_(NL))∼0.1 can be achieved

Measuring the Radiative Histories of QSOs with the Transverse Proximity Effect

Since the photons that stream from QSOs alter the ionization state of the gas they traverse, any changes to a QSO's luminosity will produce outward-propagating ionization gradients in the surrounding intergalactic gas. This paper shows that at redshift z~3 the gradients will alter the gas's Lyman-alpha absorption opacity enough to produce a detectable signature in the spectra of faint background galaxies. By obtaining noisy (S:N~4) low-resolution (~7A) spectra of a several dozen background galaxies in an R~20' field surrounding an isotropically radiating 18th magnitude QSO at z=3, it should be possible to detect any order-of-magnitude changes to the QSO's luminosity over the previous 50--100 Myr and to measure the time t_Q since the onset of the QSO's current luminous outburst with an accuracy of ~5 Myr for t_Q<~50 Myr. Smaller fields-of-view are acceptable for shorter QSO lifetimes. The major uncertainty, aside from cosmic variance, will be the shape and orientation of the QSO's ionization cone. This can be determined from the data if the number of background sources is increased by a factor of a few. The method will then provide a direct test of unification models for AGN.Comment: Accepted for publication in the ApJ. 16 page

Review of the mathematical foundations of data fusion techniques in surface metrology

The recent proliferation of engineered surfaces, including freeform and structured surfaces, is challenging current metrology techniques. Measurement using multiple sensors has been proposed to achieve enhanced benefits, mainly in terms of spatial frequency bandwidth, which a single sensor cannot provide. When using data from different sensors, a process of data fusion is required and there is much active research in this area. In this paper, current data fusion methods and applications are reviewed, with a focus on the mathematical foundations of the subject. Common research questions in the fusion of surface metrology data are raised and potential fusion algorithms are discussed