THE AZIMUTHAL DEPENDENCE OF OUTFLOWS AND ACCRETION DETECTED USING O vi ABSORPTION

Abstract

We report a bimodality in the azimuthal angle (Φ) distribution of gas around galaxies traced by O VI absorption. We present the mean Φ probability distribution function of 29 HST-imaged O VI absorbing (EW>0.1 Å) and 24 non-absorbing (EW<0.1 Å) isolated galaxies (0.08<z<0.67) within ∼ 200 kpc of background quasars. We show that EW is anti-correlated with impact parameter and O VI covering fraction decreases from 80% within 50 kpc to 33% at 200 kpc. The presence of O VI absorption is azimuthally dependent and occurs between ±10-20 • of the galaxy projected major axis and within ±30 • of the projected minor axis. We find higher EWs along the projected minor axis with weaker EWs along the project major axis. Highly inclined galaxies have the lowest covering fractions due to minimized outflow/inflow cross-section geometry. Absorbing galaxies also have bluer colors while non-absorbers have redder colors, suggesting that star-formation is a key driver in the O VI detection rate. O VI surrounding blue galaxies exists primarily along the projected minor axis with wide opening angles while O VI surrounding red galaxies exists primarily along the projected major axis with smaller opening angles, which may explain why absorption around red galaxies is less frequently detected. Our results are consistent with CGM originating from major axis-fed inflows/recycled gas and from minor axis-driven outflows. Non-detected O VI occurs between Φ=20-60 • , suggesting that O VI is not mixed throughout the CGM and remains confined within the outflows and the disk-plane. We find low O VI covering fractions within ±10 • of the projected major axis, suggesting that cool dense gas resides in a narrow planer geometry surrounded by diffuse O VI gas.

Flickering AGN can explain the strong circumgalactic O viobserved by COS-Halos

“…If the dust obscuration is aligned with the stellar disk, then this could help explain why Kacprzak et al (2015) observes that the azimuthal dependence of O vi around bluer galaxies peaks along the semi-minor axis. This study partially motivated our consideration of the bicone model, since Kacprzak et al (2015) suggest a wide opening angle of stronger O vi at b 100 kpc.…”

“…If the dust obscuration is aligned with the stellar disk, then this could help explain why Kacprzak et al (2015) observes that the azimuthal dependence of O vi around bluer galaxies peaks along the semi-minor axis. This study partially motivated our consideration of the bicone model, since Kacprzak et al (2015) suggest a wide opening angle of stronger O vi at b 100 kpc. Our model provides an alternative to the model of star formation-driven winds being responsible for strong O vi along the semi-minor axis, and represents an addendum to the Opp16 model of O vi "haloes" tracing the virialized 3 × 10 5 K gas of L * galaxies with little relation to recent star formation.…”

The Impact of the Group Environment on the O vi Circumgalactic Medium

“…We compare the CGM for a total of six group galaxy environments to the CGM of 29 isolated galaxies from Kacprzak et al (2015) associated with O VI absorption. We also have another 12 groups and 38 isolated galaxies with only an upper limit on O VI absorption.…”

“…RESULTS Here we present an analysis of the equivalent width, covering fractions and kinematics of both group and isolated galaxies to determine whether environment plays a role in shaping the properties of the CGM. Kacprzak et al (2015) found that the equivalent width decreases as the distance of the absorber from the galaxy increases for the isolated sample. Similarly, Tumlinson et al (2011) and Johnson et al (2015) found that the column density decreases as the ratio of the impact parameter and the virial radius increases.…”

“…Similarly, we show in Figure 2 the locations of galaxies which were not associated with O VI absorption (red points) relative to the location of the quasar sightline (central black cross). We compare this group environment sample to the isolated galaxy sample presented in Kacprzak et al (2015), who identified 53 isolated galaxies associated with 29 absorbers and 24 non-absorbers. However, the Kacprzak et al (2015) sample only extends out to 200 kpc.…”