The CGM$^2$ Survey: Circumgalactic O VI from dwarf to massive star-forming galaxies

Abstract

We combine 126 new galaxy-O VI absorber pairs from the CGM 2 survey with 123 pairs drawn from the literature to examine the simultaneous dependence of the column density of O VI absorbers (N O VI ) on galaxy stellar mass, star formation rate, and impact parameter. The combined sample consists of 249 galaxy-O VI absorber pairs covering z = 0-0.6, with host galaxy stellar masses M * = 10 7.8 -10 11.2 M and galaxy-absorber impact parameters R ⊥ = 0-400 proper kiloparsecs. In this work, we focus on the variation of N O VI with galaxy mass and impact parameter among the star-forming galaxies in the sample. We find that the average N O VI within one virial radius of a star-forming galaxy is greatest for star-forming galaxies with M * = 10 9.2 -10 10 M . Star-forming galaxies with M * between 10 8 and 10 11.2 M can explain most O VI systems with column densities greater than 10 13.5 cm −2 . 60% of the O VI mass associated with a star-forming galaxy is found within one virial radius and 35% is found between one and two virial radii. In general, we find that some departure from hydrostatic equilibrium in the CGM is necessary to reproduce the observed O VI amount, galaxy mass dependence, and extent. Our measurements serve as a test set for CGM models over a broad range of host galaxy masses.

Absorption-based Circumgalactic Medium Line Emission Estimates

“…11 This N OVI is a factor of a few lower than the median column for L * galaxies (Tumlinson et al 2011;Werk et al 2014), and as shown in equation ( 11), the emission scales linearly with the O vi and total gas density column. In fact our estimates may have wider applicability as columns of N OVI = 10 14−15 cm −2 are observed for star forming galaxies over a broad range in stellar mass (Tchernyshyov et al 2021). With this normalization, we have checked that the columns associated with other ions in all of our P (T ) models are likely below measured values; the columns that are observed from absorption studies in other ions would be associated with a pile-up of gas at the equilibrium temperature of ∼ 10 4 K, gas which does not emit substantially in the UV.…”

Cool circumgalactic gas in galaxy clusters: connecting the DESI legacy imaging survey and SDSS DR16 MgII absorbers

“…The 𝑥 o characterizes the scale where the slope (defined by 𝛼) changes and both functions are comparable and contribute significantly to the observed distributions. Note that similar functional form (including redshift dependence, with 5-6 parameters) has been used to characterize Mg and O absorber properties around passive and star-forming galaxies from the DESI legacy imaging survey (Lan 2020) and COS-Halos and COS-Dwarfs surveys (Tchernyshyov et al 2021).…”

“…A value of log(sSFR) = −11 often defines the boundary (at 𝑧 = 0) below which galaxies are classified as passive, while galaxies above this limit are considered star-forming. A similar cut was applied by Werk et al (2012) in COS-Halos survey, though other studies may use slightly different cuts for this purpose (Donnari et al 2019), e.g, a higher cut, log(sSFR) = −10 was applied by Tchernyshyov et al (2021) in CGM 2 survey galaxies.…”

“…The complex interplay between gas inflows and outflows powered by supernova explosions or accreting black holes is known as the cosmic baryon cycle, and is a key ingredient to understanding galaxy formation and evolution (see Tumlinson et al 2017;Péroux & Howk 2020, for reviews). Both observations (Stocke et al 2013;Zhu et al 2014;Lan & Mo 2018;Zahedy et al 2019;Tchernyshyov et al 2021) and simulations (Oppenheimer et al 2018;Peeples et al 2019;Fielding et al 2020;Nelson et al 2020;Byrohl et al 2021) have revealed that the CGM is multi-phase and hosts gas with a wide range of temperatures and densities.…”

“…Tchernyshyov et al (2021) recently reported an association of OFigure 11. Mean 𝐸𝑊 2796 (left) and Mg surface density (right) as a function of projected distance from the central galaxy.…”