Empirical constraints on the turbulence in QSO host nebulae from velocity structure function measurements

Abstract

We present the first empirical constraints on the turbulent velocity field of the diffuse circumgalactic medium around four luminous QSOs at z ≈ 0.5–1.1. Spatially extended nebulae of ≈50–100 physical kpc in diameter centered on the QSOs are revealed in [O ii] λλ 3727, 3729 and/or [O iii] λ 5008 emission lines in integral field spectroscopic observations obtained using MUSE on the VLT. We measure the second- and third-order velocity structure functions (VSFs) over a range of scales, from ≲ 5 kpc to ≈20–50 kpc, to quantify the turbulent energy transfer between different scales in these nebulae. While no constraints on the energy injection and dissipation scales can be obtained from the current data, we show that robust constraints on the power-law slope of the VSFs can be determined after accounting for the effects of atmospheric seeing, spatial smoothing, and large-scale bulk flows. Out of the four QSO nebulae studied, one exhibits VSFs in spectacular agreement with the Kolmogorov law, expected for isotropic, homogeneous, and incompressible turbulent flows. The other three fields exhibit a shallower decline in the VSFs from large to small scales. However, with a limited dynamic range in the spatial scales in seeing-limited data, no constraints can be obtained for the VSF slopes of these three nebulae. For the QSO nebula consistent with the Kolmogorov law, we determine a turbulence energy cascade rate of ≈0.2 cm2 s−3. We discuss the implication of the observed VSFs in the context of QSO feeding and feedback in the circumgalactic medium.

The Cosmic Ultraviolet Baryon Survey: Empirical Characterization of Turbulence in the Cool Circumgalactic Medium

“…IFS observations of nearby massive galaxy clusters have revealed spatially extended lineemitting gaseous streams in the intercluster medium enabling VSF measurements on scales from 30 pc to 10 kpc (Li et al 2020). Similarly, VSF measurements have also been reported for QSO host halos on scales from 10 kpc to ≈60 kpc based on lineemitting nebulae discovered around luminous QSOs (Chen et al 2023). However, detections of line-emitting nebulae around typical galaxies or galaxy groups remain extremely rare beyond the nearby Universe (e.g., Chen et al 2019;Dutta et al 2023) and even for extreme systems like QSO nebulae and intracluster medium the ground-based seeing imposes a limit on the smallest scale one can probe with IFS observations.…”

“…Recently, Chen et al (2023) analyzed IFS observations of spatially extended line-emitting nebulae around four QSOs at z ≈ 0.5-1. While three of the four cases did not have a sufficiently large dynamic range in spatial scales to provide meaningful constraints on the VSFs, the largest QSO nebula in their sample exhibits a VSF that was in remarkable agreement with the Kolmogorov energy cascade from ≈40 to <10 kpc at an extremely high energy transfer rate per unit mass of ò ≈ 0.2 cm 2 s −3 .…”

“…Despite the vital scientific implications, robust empirical constraints of turbulence on large scales in diffuse halo gas remain scarce (see, e.g., Rauch et al 2001;Rudie et al 2019;Li et al 2020;Chen et al 2023). Here we report the first measurement of the turbulent velocity-size relation in the diffuse CGM around typical L * and sub-L * galaxy halos at intermediate redshifts, z ≈ 0.4-1, based on observations that utilize high-resolution absorption spectroscopy.…”

Discovery of Optically Emitting Circumgalactic Nebulae around the Majority of UV-luminous Quasars at Intermediate Redshift

“…Both the CUBS and MUSEQuBES surveys were designed to study the CGM and IGM around galaxies at z ≈ 0.1-1.4 using deep and highly complete galaxy redshift surveys with MUSE in the fields of UV-bright background quasars with highquality UV absorption spectra from the Cosmic Origins Spectrograph (Green et al 2012) aboard the Hubble Space Telescope (HST). The broad spectral coverage (4700-9350 Å), wide field of view (1 1 ¢ ´¢), and high throughput (peaking at 35% at 7000 Å) of MUSE (Bacon et al 2010) collectively enable searches for low-surface-brightness nebulae in the environments of the CUBS and MUSEQuBES background quasars at z = 0.4-1.4 (Johnson et al 2018(Johnson et al , 2022M. C. Chen et al 2023;Liu et al 2024) at the same time.…”

An Ensemble Study of Turbulence in Extended QSO Nebulae at z ≈ 0.5–1

“…Recently, Chen et al (2023b; hereafter Paper I) obtained two-dimensional line-of-sight velocity maps of line-emitting gas around four QSOs up to scales of ∼100 kpc using IFS data. Taking advantage of the spatially resolved velocity maps from IFS observations, these authors constructed velocity structure functions (VSFs), S p , defined as…”