A framework to measure the properties of intergalactic metal systems with two-point flux statistics

TL;DR

This paper introduces a novel two-point flux statistic method to measure intergalactic metal system properties unbiasedly, using large quasar spectral samples, revealing potential higher metal abundance and evolution over time.

Contribution

It presents a new framework employing two-point flux statistics to measure metal properties in the intergalactic medium from large quasar datasets, reducing bias from traditional methods.

Findings

Evidence of higher C IV abundance than previous estimates

Indications of metal abundance evolution over cosmic time

Initial results from DESI data support the method's effectiveness

Abstract

The abundance, temperature, and clustering of metals in the intergalactic medium are important parameters for understanding their cosmic evolution and quantifying their impact on cosmological analysis with the Ly $\alpha$ forest. The properties of these systems are typically measured from individual quasar spectra redward of the quasar's Ly $\alpha$ emission line, yet that approach may provide biased results due to selection effects. We present an alternative approach to measure these properties in an unbiased manner with the two-point statistics commonly employed to quantify large-scale structure. Our model treats the observed flux of a large sample of quasar spectra as a continuous field and describes the one-dimensional, two-point statistics of this field with three parameters per ion: the abundance (column density distribution), temperature (Doppler parameter) and clustering (cloud-cloud correlation function). We demonstrate this approach on multiple ions (e.g., C IV, Si IV, Mg II) with early data from the Dark Energy Spectroscopic Instrument (DESI) and high-resolution spectra from the literature. Our initial results show some evidence that the C IV abundance is higher than previous measurements and evidence for abundance evolution over time. The first full year of DESI observations will have over an order of magnitude more quasar spectra than this study. In a future paper we will use those data to measure the growth of clustering and its impact on the Ly $\alpha$ forest, as well as test other DESI analysis infrastructure such as the pipeline noise estimates and the resolution matrix.