Characterizing circumgalactic gas around massive ellipticals atz∼ 0.4 – II. Physical properties and elemental abundances

Abstract

We present a systematic investigation of the circumgalactic medium (CGM) within projected distances d < 160 kpc of luminous red galaxies (LRGs). The sample comprises 16 intermediate-redshift (z = 0.21−0.55) LRGs of stellar mass M star > 10 11 M . Combining far-ultraviolet Cosmic Origin Spectrograph spectra from the Hubble Space Telescope and optical echelle spectra from the ground enables a detailed ionization analysis based on resolved component structures of a suite of absorption transitions, including the full H i Lyman series and various ionic metal transitions. By comparing the relative abundances of different ions in individually-matched components, we show that cool gas (T ∼ 10 4 K) density and metallicity can vary by more than a factor of ten in an LRG halo. Specifically, metal-poor absorbing components with < 1/10 solar metallicity are seen in 50% of the LRG halos, while gas with solar and super-solar metallicity is also common. These results indicate a complex multiphase structure and poor chemical mixing in these quiescent halos. We calculate the total surface mass density of cool gas, Σ cool , by applying the estimated ionization fraction corrections to the observed H i column densities. The radial profile of Σ cool is best-described by a projected Einasto profile of slope α = 1 and scale radius r s = 48 kpc. We find that typical LRGs at z ∼ 0.4 contain cool gas mass of M cool = (1 − 2) × 10 10 M at d < 160 kpc (or as much as M cool ≈ 4 × 10 10 M at d < 500 kpc), comparable to the cool CGM mass of star-forming galaxies. Furthermore, we show that high-ionization O vi and low-ionization absorption species exhibit distinct velocity profiles, highlighting their different physical origins. We discuss the implications of our findings for the origin and fate of cool gas in LRG halos.

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

“…The measured O VI column densities (N OVI > 10 13.9 cm −2 ) are similar to the typical O VI columns found surrounding low-redshift galaxies Johnson et al 2015Johnson et al , 2017Zahedy et al 2018) and also the typical column den- Figure 6. The velocities and impact parameters of metal-enriched absorbers within 100 pkpc of a galaxy in the KBSS sample.…”

“…Given the generally high inferred temperatures of the O VI absorbers, we do not compare directly to the models proposed by Stern et al (2018) where the gas is photoionized; however, we note that the absorbers with lower inferred temperatures may be better described by such a model (see e.g. Zahedy et al 2018). Alternatively, absorbers with low inferred temperatures could be over-ionized gas that has rapidly cooled.…”

“…7.3. Comparison of the derived temperature and gas turbulence to low-redshift CGM measurements Zahedy et al (2018) compared the Doppler parameters of Mg II and H I absorbers within the inner CGM of massive elliptical galaxies at z ∼ 0.4. These authors report that the low ionization CGM has a mean temperature of 2 × 10 4 K, similar to typical IGM temperatures and cooler than we have found here.…”

Quasar Sightline and Galaxy Evolution (QSAGE) survey – I. The galaxy environment of O vi absorbers up to z = 1.4 around PKS 0232−04

“…Moreover, Johnson et al (2017) showed that star-forming field dwarfs of <0.1 L * without massive neighbours account for ≈20 per cent of O VI absorption systems with rest equivalent widths stronger than ≈0.1Å, and that this phase of their CGM likely dominates the baryon budget of these low-mass systems. More recently, Chen et al (2018) and Zahedy et al (2019) showed that O VI absorption systems with logN(O VI) > 13.5 are common in the CGM of luminous, quiescent galaxies.…”

Modeling Photoionized Turbulent Material in the Circumgalactic Medium

“…In all cases the material was assumed to be irradiated with a redshift zero Haardt & Madau (2012) (HM2012) EUVB whose specific intensity was normalized to 8.23 × 10 −24 erg cm −2 s −1 Hz −1 sr −1 at the Lyman limit following the radio-quiet AGN spectral index (α = 0.157). Note that our simulations assume chemical homogeneity, while observations indicate that the composition of the CGM is likely to be significantly inhomogeneous (Zahedy et al 2019). However, the impact of this additional factor is left for future investigation.…”