http://arxiv.org/abs/2012.05926
The Ly$\alpha$ forest decomposed into Voigt profile components (or “clouds”) allow us to study clustering properties of the intergalactic medium and its dependence on various physical quantities. Here, we report the first detections of longitudinal three-point ($\zeta$) and reduced three-point (Q) correlations of low-$z$ (i.e $z<0.48$) Ly$\alpha$ clouds over a scale of $r_\parallel\leq 4$ pMpc. We measure $\zeta = 6.9\pm 1.3$ and Q = 1.7$\pm$0.4 at a transverse separation of 1-2 pMpc. We show the amplitude of $\zeta$ increases with increasing HI column density ($N_{\rm HI}$) while Q does not show any $N_{\rm HI}$ dependence. We find the radial profile of $\zeta$ to be different for high-$b$ (i.e $b>$40 km/s) and low-$b$ absorbers. About 84% of the triplets contributing to $\zeta$ have nearby galaxies within a velocity separation of 500 km/s and a median impact parameter of 405 pkpc. The measured impact parameters are consistent with appreciable number of triplets not originating from individual galaxies but tracing the underlying galaxy distribution. Frequency of occurrence of high-$b$ absorbers in triplets ($\sim$88%) is a factor $\sim3$ higher than that found among the full sample ($\sim$32%). Using four different cosmological simulations, we quantify the effect of peculiar velocities, feedback effects and show that most of the observed trends can be broadly reproduced. However, $\zeta$ at small scales ($r_\parallel<1$ pMpc) and $b$-dependence of $\zeta$ in simulations are found inconsistent with the observations. This could either be related to the fact that none of these simulations reproduce the observed $b$-distribution and $N_{\rm HI}$ distribution for $N_{\rm HI}>10^{14}$ cm$^{-2}$ self-consistently or to the widespread of signal-to-noise ratio in the observed data.
S. Maitra, R. Srianand, P. Gaikwad, et. al.
Mon, 14 Dec 20
47/74
Comments: 21 pages, 17 figures. Submitted to MNRAS