Dark energy and curvature from a future baryonic acoustic oscillation survey using the Lyman-{alpha} forest
- Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, ON M5S 3H8 (Canada)
We explore the requirements for a Lyman-{alpha} forest survey designed to measure the angular diameter distance and Hubble parameter at 2 < or approx. z < or approx. 4 using the standard ruler provided by baryonic acoustic oscillations (BAO). The goal would be to obtain a high enough density of sources to probe the three-dimensional density field on the scale of the BAO feature. A percent-level measurement in this redshift range can almost double the Dark Energy Task Force figure of merit, relative to the case with only a similar precision measurement at z{approx}1, if the Universe is not assumed to be flat. This improvement is greater than the one obtained by doubling the size of the z{approx}1 survey, with Planck and a weak Sloan Digital Sky Survey-like z=0.3 BAO measurement assumed in each case. Galaxy BAO surveys at z{approx}1 may be able to make an effective Ly{alpha} forest measurement simultaneously at minimal added cost, because the required number density of quasars is relatively small. We discuss the constraining power as a function of area, magnitude limit (density of quasars), resolution, and signal-to-noise of the spectra. For example, a survey covering 2000 sq. deg. and achieving S/N=1.8 per A at g=23 ({approx}40 quasars per sq. deg.) with an R > or approx. 250 spectrograph is sufficient to measure both the radial and transverse oscillation scales to 1.4% from the Ly{alpha} forest (or better, if fainter magnitudes and possibly Lyman-break galaxies can be used). At fixed integration time and in the sky-noise-dominated limit, a wider, noisier survey is generally more efficient; the only fundamental upper limit on noise being the need to identify a quasar and find a redshift. Because the Ly{alpha} forest is much closer to linear and generally better understood than galaxies, systematic errors are even less likely to be a problem.
- OSTI ID:
- 21027750
- Journal Information:
- Physical Review. D, Particles Fields, Vol. 76, Issue 6; Other Information: DOI: 10.1103/PhysRevD.76.063009; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2821
- Country of Publication:
- United States
- Language:
- English
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