The Low-Redshift Lyman Alpha Forest toward 3C 273

TL;DR

This study analyzes the low-redshift Lyman Alpha forest toward 3C 273 using high-resolution UV spectra, revealing absorber distributions, environmental associations, and clustering consistent with models, enhancing understanding of intergalactic medium structures.

Contribution

It provides detailed measurements of low-z Ly-alpha absorbers, their distribution, clustering, and environmental context, using high-resolution data and comparing with numerical simulations.

Findings

Absorber density is slightly below average but aligns with models.

Clustering detected at 3.4 sigma significance for certain column densities.

Evidence of overdense environments near broad Ly-alpha absorbers.

Abstract

We present an analysis of the Ly-a forest toward 3C 273 from the Space Telescope Imaging Spectrograph at ~7 km/s resolution, along with re-processed data from the Far Ultraviolet Spectroscopic Explorer. The high UV flux of 3C 273 allows us to probe the weak, low z absorbers. The main sample consists of 21 HI absorbers that we could discriminate to a sensitivity of log NHI~ 12.5. The redshift density for absorbers with 13.1<log NHI<14.0 is ~1.5 sigma below the mean for other lines of sight; for log NHI >= 12.5, it is consistent with numerical model predictions. The Doppler parameter distribution is consistent with other low z samples. We find no evidence for a break in the column density power-law distribution to log NHI=12.3. A broad Ly-a absorber (BLA) is within Delta v =< 50 km/s and 1.3 local frame Mpc of two ~0.5L* galaxies, with an OVI absorber ~700 km/s away, similarly close to three galaxies and indicating overdense environments. We detect clustering on the Delta v<1000 km/s scale at 3.4 sigma significance for log NHI >= 12.6, consistent with the level predicted from hydrodynamical simulations, and indication for a Ly-a forest void at 0.09<z<0.12. We find at least two components for the z=0.0053 Virgo absorber, but the total NHI column is not significantly changed.