A high-resolution study of intergalactic O vi absorbers at z∼ 2.3

Abstract

We present a detailed study of the largest sample of intervening O vi systems in the redshift range 1.9 ≤z≤ 3.1 detected in high‐resolution (R∼ 45 000) spectra of 18 bright quasi‐stellar objects observed with Very Large Telescope/Ultraviolet and Visible Echelle Spectrograph. Based on Voigt profile and apparent optical depth analysis we find that (i) the Doppler parameters of the O vi absorption are usually broader than those of C iv, (ii) the column density distribution of O vi is steeper than that of C iv, (iii) line spread (δv) of the O vi and C iv is strongly correlated (at 5.3σ level) with δv(O vi) being systematically larger than δv(C iv) and (iv) δv(O vi) and δv(C iv) are also correlated (at >5σ level) with their respective column densities and with N(H i) (3 and 4.5σ, respectively). The median column densities of H i, O vi and C iv are found to be higher when low ions are present. N(C iv) and N(H i) are strongly correlated (at 4.3σ level). However, no significant correlation is found between N(O vi) and N(H i). These findings favour the idea that C iv and O vi absorption originate from different phases of a correlated structure and systems with large velocity spread is probably associated with overdense regions. The velocity offset between optical depth weighted redshifts of C iv and O vi absorption is found to be in the range 0 ≤|Δv(O vi–C iv)|≤ 48 km s−1 with a median value of 8 km s−1. We do not find any evidence for the ratios N(O vi)/N(H i), N(O vi)/N(C iv) and N(C iv)/N(H i) to evolve with z over the redshift range considered here. However, a lack of systems with high N(O vi)/N(H i) ratio (i.e. ≥−0.5 dex) for z > 2.5 is noticeable. Similar trend is also seen for the N(C iv)/N(H i) ratio. We compare the properties of O vi systems in our sample with that of low‐redshift (z < 0.5) samples from the literature and find that (i) the O vi components at low z are systematically wider than at high z with an enhanced non‐thermal contribution to their b parameter, (ii) the slope of the column density distribution functions for high and low z is consistent, (iii) the range in gas temperature estimated from a subsample of well‐aligned absorbers is similar at both high and low z and (iv) for N(O vi) > 1013.7 cm−2, estimated in our high‐z sample, is very similar to low‐z estimations.

The Cosmic Evolution of the Metallicity Distribution of Ionized Gas Traced by Lyman Limit Systems

“…The breadth and strength of the O VI absorption in strong H I absorbers atz 2-3.5 are quite similar to those observed in starburst galaxies at low redshift (see, e.g., Grimes et al 2009;Tripp et al 2011;Muzahid et al 2015) Simcoe et al 2002;Muzahid et al 2012). This strongly suggests that the bulk of the strong and broad O VI associated with pLLSs and LLSs traces large-scale outflows from high-redshift starforming galaxies.…”

Column Density, Kinematics, and Thermal State of Metal-bearing Gas within the Virial Radius of z ∼ 2 Star-forming Galaxies in the Keck Baryonic Structure Survey

“…They also found both narrow and broad C IV components and broad O VI absorbers they suggest were collisionally ionized. Muzahid et al (2012) considered the full population of O VI absorbers in QSO spectra and found that the Doppler parameters of O VI absorbers were typically larger than those of C IV. Simcoe et al (2002) measured the widths of O VI absorbers in high-z QSO spectra, finding a median b d, OVI = 16 km s −1 , similar to the value we find here.…”

Probing the thermal state of the intergalactic medium at z &gt; 5 with the transmission spikes in high-resolution Ly α forest spectra

“…Statistics of the flux distribution in transmission spikes5.2.1 Spike width (b-parameter) distribution functionFor absorption features the line width distribution is frequently used as a diagnostic for the gas temperature, turbulence, and the impact of stellar and AGN feedback on the IGM at z < 5(Rauch et al 1996;Tripp et al 2008; Op- penheimer & Davé 2009;Muzahid et al 2012;Viel et al 2017;Gaikwad et al 2017a;Nasir et al 2017…”