The GECKOS Survey: resolved, multiphase observations of mass loading and gas density in the galactic wind of NGC4666

Mazzilli Ciraulo, B ORCID: 0000-0002-5808-1961, Fisher, DB ORCID: 0000-0003-0645-5260, Elliott, R, Fraser-McKelvie, A ORCID: 0000-0001-9557-5648, Hayden, MR, Martig, M ORCID: 0000-0001-5454-1492, Van de Sande, J, Battisti, AJ, Bland-Hawthorn, J, Bolatto, AD, Brown, TH, Catinella, B ORCID: 0000-0002-7625-562X, Combes, F, Cortese, L ORCID: 0000-0002-7422-9823, Davis, TA ORCID: 0000-0003-4932-9379, Emsellem, E, Gadotti, DA ORCID: 0000-0003-1775-2367, Lagos, CDP, Lin, X ORCID: 0000-0002-4250-2709, Marasco, A ORCID: 0000-0002-5655-6054 et al (2025) The GECKOS Survey: resolved, multiphase observations of mass loading and gas density in the galactic wind of NGC4666. Monthly Notices of the Royal Astronomical Society, 544 (4). pp. 3290-3311. ISSN 0035-8711

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Abstract

We present a multiphase, resolved study of the galactic wind extending from the nearby starburst galaxy NGC 4666. For this, we use VLT/MUSE observations from the GECKOS program and H I data from the WALLABY survey. We identify both ionized and H I gas in a biconical structure extending to at least z ∼ 8 kpc from the galaxy disc, with increasing velocity offsets above the mid-plane in both phases, consistent with a multiphase wind. The measured electron density, using [S II], differs significantly from standard expectations of galactic winds. We find electron density declines from the galaxy centre to ∼ 2 kpc, then rises again, remaining high (∼ 100 − 300 cm−3) out to ∼5 kpc. We find that H I dominates the mass loading. The total H I mass outflow rate (above z > 2 kpc) is between 5 − 13 M⊙ −1, accounting for uncertainties from disc-blurring and group interactions. The total ionized mass outflow rate (traced by Hα) is between 0.5 and 5 M⊙yr−1, depending on ne(z) assumptions. From ALMA/ACA observations, we place an upper limit on CO flux in the outflow which correlates to 2.9 M⊙ yr−1. We also show that the entire outflow is not limited to the bicone, but a secondary starburst at the edge generates a more widespread outflow, which should be included in simulations. The cool gas in NGC 4666 wind has insufficient velocity to escape the halo of a galaxy of its mass, especially because most of the mass is present in the slower atomic phase. This strong biconical wind contributes to gas cycling around the galaxy.

Item Type:	Article
Uncontrolled Keywords:	5109 Space Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press (OUP)
Date of acceptance:	24 October 2025
Date of first compliant Open Access:	22 January 2026
Date Deposited:	22 Jan 2026 11:56
Last Modified:	22 Jan 2026 11:56
DOI or ID number:	10.1093/mnras/staf1875
URI:	https://researchonline.ljmu.ac.uk/id/eprint/27953

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