Metal line emission around z < 1 galaxies

¹ IUCAA, Postbag 4 Ganeshkind, Pune 411007, India
² Dipartimento di Fisica G. Occhialini, Università degli Studi di Milano Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
³ INAF – Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, I-34143 Trieste, Italy
⁴ INAF – Osservatorio Astronomico di Brera, Via Bianchi 46, 23087 Merate, (LC), Italy
⁵ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁶ Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
⁷ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, D-85748 Garching bei München, Germany
⁸ Scuola Normale Superiore, P.zza dei Cavalieri, I-56126 Pisa, Italy
⁹ IFPU-Institute for Fundamental Physics of the Universe, via Beirut 2, I-34151 Trieste, Italy
¹⁰ European Southern Observatory, Karl-Schwarzschildstrasse 2, D-85748 Garching bei München, Germany
¹¹ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille), UMR 7326, F-13388 Marseille, France
¹² Centre for Extragalactic Astronomy, Department of Physics Durham University, South Road, Durham DH1 3LE, UK

^⋆ Corresponding author; rajeshwari.dutta@iucaa.in

Received: 15 May 2024
Accepted: 4 August 2024

Abstract

We characterize, for the first time, the average extended emission in multiple lines ([O II], [O III], and Hβ) around a statistical sample of 560 galaxies at z ≈ 0.25 − 0.85. By stacking the Multi Unit Spectroscopic Explorer (MUSE) 3D data from two large surveys, the MUSE Analysis of Gas around Galaxies (MAGG) and the MUSE Ultra Deep Field (MUDF), we detect significant [O II] emission out to ≈40 kpc, while [O III] and Hβ emission is detected out to ≈30 kpc. Via comparisons with the nearby average stellar continuum emission, we find that the line emission at 20–30 kpc likely arises from the disk-halo interface. Combining our results with that of our previous study at z ≈ 1, we find that the average [O II] surface brightness increases independently with redshift over z ≈ 0.4 − 1.3 and with stellar mass over M_* ≈10^6 − 12 M_⊙, which is likely driven by the star formation rate as well as the physical conditions of the gas. By comparing the observed line fluxes with photoionization models, we find that the ionization parameter declines with distance, going from log q (cm s⁻¹) ≈ 7.7 at ≤5 kpc to ≈7.3 at 20–30 kpc, which reflects a weaker radiation field in the outer regions of galaxies. The gas-phase metallicity shows no significant variation over 30 kpc, with a metallicity gradient of ≈0.003 dex kpc⁻¹, which indicates an efficient mixing of metals on these scales. Alternatively, there could be a significant contribution from shocks and diffuse ionized gas to the line emission in the outer regions.