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MusE GAs FLOw and Wind (MEGAFLOW). VIII. Discovery of a Mgii emission halo probed by a quasar sightline

J. Zabl, N. Bouché, L. Wisotzki, J. Schaye, F. Leclercq, T. Garel, M. Wendt, I. Schroetter, S. Muzahid, S. Cantalupo, T. Contini, R. Bacon, J. Brinchmann, J. Richard

Abstract
Using deep (⁠11.2h⁠) VLT/MUSE data from the MEGAFLOW survey, we report the first detection of extended MgII emission from a galaxy's halo that is probed by a quasar sightline. The MgII λλ2796, 2803 emission around the z = 0.702 galaxy (⁠log(M/M) = 10.05+0.15−0.11⁠) is detected out to ≈25 kpc from the central galaxy and covers 1.0×103 kpc2 above a surface brightness of 14×10−19 ergs−1cm−2arcsec−2 (⁠2σ⁠; integrated over 1200 kms−1 = 19 Å and averaged over 1.5arcsec2⁠). The MgII emission around this highly inclined galaxy (i ≃ 75 deg) is strongest along the galaxy's projected minor axis, consistent with the MgII gas having been ejected from the galaxy into a bi-conical structure. The quasar sightline, which is aligned with the galaxy’s minor axis, shows strong MgII absorption (⁠EWλ27960 = 1.8A˚⁠) at an impact parameter of 39 kpc from the galaxy. Comparing the kinematics of both the emission and the absorption − probed with VLT/UVES − to the expectation from a simple toy model of a bi-conical outflow, we find good consistency when assuming a relatively slow outflow (⁠vout = 130 kms−1⁠). We investigate potential origins of the extended MgII emission using simple toy models. With continuum scattering models we encounter serious difficulties in explaining the luminosity of the MgII halo and in reconciling density estimates from emission and absorption. Instead, we find that shocks might be a more viable source to power the extended MgII (and non-resonant [OII]⁠) emission.

Keywords
galaxies: evolution, galaxies: haloes, intergalactic medium, quasars: absorption lines, quasars: individual: SDSSJ0937 + 0656

Monthly Notices of the Royal Astronomical Society
Volume 507, Issue 3, Page 4294
2021 November

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia