PARTICLE MESH SIMULATIONS OF THE Lyα FOREST AND THE SIGNATURE OF BARYON ACOUSTIC OSCILLATIONS IN THE INTERGALACTIC MEDIUM

Abstract

We present a set of ultra-large particle-mesh simulations of the Lyman-α forest targeted at understanding the imprint of baryon acoustic oscillations (BAO) in the inter-galactic medium. We use 9 dark matter only simulations which can, for the first time, simultaneously resolve the Jeans scale of the intergalactic gas while covering the large volumes required to adequately sample the acoustic feature. Mock absorption spectra are generated using the fluctuating Gunn-Peterson approximation which have approximately correct flux probability density functions (PDFs) and small-scale power spectra. On larger scales there is clear evidence in the redshift space correlation function for an acoustic feature, which matches a linear theory template with constant bias. These spectra, which we make publicly available, can be used to test pipelines, plan future experiments and model various physical effects. As an illustration we discuss the basic properties of the acoustic signal in the forest, the scaling of errors with noise and source number density, modified statistics to treat mean flux evolution and mis-estimation, and non-gravitational sources such as fluctuations in the photo-ionizing background and temperature fluctuations due to HeII reionization. Subject headings: methods: N-body simulations -cosmology: large-scale structure of universe

Scale-dependent bias in the baryonic-acoustic-oscillation-scale intergalactic neutral hydrogen

“…Hints of the anti-correlation discussed at length in the present paper have been seen before in such efforts [28,30]. It would be helpful to include large scale temperature fluctuations arising from helium reionization [46].…”

“…By definition, regions separated by greater distances cannot efficiently exchange UV radiation. Ionization equilibrium will therefore depend on the density of sources in the local region; the bias of the forest on the largest scales will depend on the clustering of UV sources [28,[30][31][32].…”

“…Further fluctuations are imprinted by intrinsic variability in the IGM opacity [22]. This and related astrophysical effects have been widely investigated elsewhere [9,11,[23][24][25][26][27][28][29] with the conclusion that, if properly accounted for, the added noise * Electronic address: a.pontzen@ucl.ac.uk is not problematic for observational cosmology at z < 5. Measurements at higher redshift, during the epoch of reionization, will be affected more strongly [25,27] as the UV undulation amplitude increases.…”

“…the highest-column-density Lyman limit systems [36]); (iii) that non-linear corrections (including quasar duty cycles) can be ignored on sufficiently large scales [11,27,28], although I will include shot noise from the rarity of sources; (iv) that sources averaged on large scales radiate isotropically. These seem reasonable to obtain a good estimate of the effects but in future they should be checked against numerical simulations and more complicated analytic treatments that allow for departure from equilibrium [37].…”

SHADOW OF A COLOSSUS: A z = 2.44 GALAXY PROTOCLUSTER DETECTED IN 3D Lyα FOREST TOMOGRAPHIC MAPPING OF THE COSMOS FIELD

“…There is some disagreement in the distributions from the data and the simulations, but the Lyα forest absorption PDF is known to be a notoriously difficult quantity to model: our simulation used a DM-only N-body code that models only gravitational clustering, but not the hydrodynamics of the IGM (White et al 2010), nor have we attempted to accurately model systematics such as the continuum-errors, spectral noise, optically thick absorbers (e.g., Lee et al 2015), temperaturedensity relationship, or Jeans smoothing (Rorai et al 2013). For the present analysis, it is of some concern that our map PDF is somewhat larger at 3…”