Ly α forest decomposed into Voigt profile components allows us to study clustering properties of the intergalactic-medium and its dependence on various physical quantities. Here, we report the first detections of probability excess of low-z (i.e z < 0.48) Ly α absorber triplets over redshift-space scale of r∥ ≤ 8 pMpc (Mpc in physical units) with maximum amplitude of $8.76^{+1.96}_{-1.65}$ at a longitudinal separation of 1–2 pMpc. We measure non-zero three-point correlation ($\zeta = 4.76^{+1.98}_{-1.67}$) only at this scale with reduced three-point correlation Q = $0.95^{+0.39}_{-0.38}$. The measured ζ shows an increasing trend with increasing minimum H i column density (NH i) threshold while Q does not show any NH i dependence. About 88 per cent of the triplets contributing to ζ (at z ≤ 0.2) have nearby galaxies (whose distribution is known to be complete for ∼0.1L* at z < 0.1 and for ∼L* at z ∼ 0.25 within 20 arcsec to the quasar sightlines) within velocity separation of 500 km s−1 and median impact parameter of 405 pkpc. The measured impact parameters are consistent with majority of the identified triplets not originating from individual galaxies but tracing the underlying galaxy distribution. Frequency of occurrence of Broad-Ly α absorbers (b > 40 km s−1) in triplets (∼85 per cent) is factor ∼3 higher than that found among the full sample (∼32 per cent). Using four different cosmological simulations, we quantify the effect of peculiar velocities and feedback and show that most of the observed trends are broadly reproduced. However, ζ at small scales (r∥ < 1 pMpc) and its b-dependence found in simulations are inconsistent with observations. This could either be related to the failure of these simulations to reproduce the observed b and NH i distributions for NH i > 1014 cm−2 self-consistently or to the wide spread of signal-to-noise ratio in the observed data.
We study the statistical properties of O vi, C iv, and Ne viii absorbers at low-z (i.e. z < 0.5) using Sherwood simulations with ‘WIND’ only and ‘WIND + AGN’ feedback and massive black-II simulation that incorporates both ‘WIND’ i.e. outflows driven by stellar feedback and active galactic nucleus (AGN) feedbacks. For each simulation, by considering a wide range of metagalactic ionizing ultraviolet background (UVB), we show the statistical properties such as distribution functions of column density (N), b-parameter and velocity spread (ΔV90), the relationship between N and b-parameter, and the fraction of Ly α absorbers showing detectable metal lines as a function of N(H i) are influenced by the UVB used. This is because UVB changes the range in density, temperature, and metallicity of gas contributing to a given absorption line. For simulations considered here, we show the difference in some of the predicted distributions between different simulations is similar to the one obtained by varying the UVB for a given simulation. Most of the observed properties of O vi absorbers are roughly matched by Sherwood simulation with ‘WIND + AGN’ feedback when using the UVB with a lower O vi ionization rate. However, this simulation fails to produce observed distributions of C iv and fraction of H i absorbers with detectable metals. Therefore, in order to constrain different feedback processes and/or UVBs, using observed properties of H i and metal ions, it is important to perform simultaneous analysis of various observable parameters.
more » « less- NSF-PAR ID:
- 10418435
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 523
- Issue:
- 2
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- p. 2296-2316
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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