The Interstellar Medium Properties of Heavily Reddened Quasars & Companions at z~2.5 with ALMA & JVLA

TL;DR

This study investigates the interstellar medium properties of heavily reddened quasars and their companion galaxies at z~2.5 using ALMA and JVLA, revealing diverse, complex gas conditions influenced by mergers and challenging simplified interpretations.

Contribution

It provides new high-resolution observations of ISM conditions in high-redshift quasars and companions, highlighting the diversity and complexity of their gas properties and the limitations of low-resolution data.

Findings

High-density, high-temperature, metal-enriched gas in quasars.

Evidence of a close-separation major merger affecting ISM properties.

Range of CO excitation from starburst-like to quasar-like.

Abstract

We study the interstellar medium (ISM) properties of three heavily reddened quasars at $z\sim2.5$ as well as three millimetre-bright companion galaxies near these quasars. New JVLA and ALMA observations constrain the CO(1-0), CO(7-6) and [CI]$^3$P$_2-^3$P$_1$ line emission as well as the far infrared to radio continuum. The gas excitation and physical properties of the ISM are constrained by comparing our observations to photo-dissociation region (PDR) models. The ISM in our high-redshift quasars is composed of very high-density, high-temperature gas which is already highly enriched in elements like carbon. One of our quasar hosts is shown to be a close-separation ($<$2 arcsec) major merger with different line emission properties in the millimeter-bright galaxy and quasar components. Low angular resolution observations of high-redshift quasars used to assess quasar excitation properties should therefore be interpreted with caution as they could potentially be averaging over multiple components with different ISM conditions. Our quasars and their companion galaxies show a range of CO excitation properties spanning the full extent from starburst-like to quasar-like spectral line energy distributions. We compare gas masses based on CO, CI and dust emission, and find that these can disagree when standard assumptions are made regarding the values of $\alpha_{\rm{CO}}$, the gas-to-dust ratio and the atomic carbon abundances. We conclude that the ISM properties of our quasars and their companion galaxies are diverse and likely vary spatially across the full extent of these complex, merging systems.