MAUVE: Cold neutral gas in the outflow of NGC 4383 and evidence for a fountain flow

We present a multiphase study of the star-formation-driven outflow in the Virgo galaxy NGC 4383, combining ALMA CO(2-1) data with deep MeerKAT HI imaging and MUSE spectroscopy obtained as part of the Multiphase Astrophysics to Unveil the Virgo Environment (MAUVE) program. Our previous work revealed a spectacular ionised outflow, but the effect of the outflow on the cold phase remained unclear. Our analysis shows that potentially outflowing molecular gas is detected only within the inner 1 kpc above the disc, where CO clouds exhibit disturbed kinematics and spatial correspondence with the ionisation cone. At larger heights, the CO surface brightness rapidly drops, indicating that the molecular phase contributes little to the mass of outflowing gas. In contrast, the HI distribution shows plumes a few kiloparsecs above the disc that are aligned with the ionised cone, and complex kinematics suggestive of parts of the atomic phase being entrained in the outflow. However, the extended and warped HI disc associated with NGC 4383 complicates the unambiguous identification of outflowing atomic gas and, most importantly, the quantification of outflowing mass and loading factor. Independent support for a cold component in the outflow comes from dust extinction features associated with the outflow and coincident with HI plumes. Despite significant uncertainties in the estimate of the mass of cold gas associated with the outflow, these results suggest that the atomic phase likely dominates the cold outflow above 1 kpc. The observed cold gas velocities remain below the velocities of the ionised phase, suggesting that NGC 4383 does not host a large-scale escaping wind but more likely a galactic fountain, in which feedback redistributes material within the halo and regulates ongoing and future star formation.

💡 Research Summary

This paper presents a comprehensive, multi‑phase investigation of the star‑formation‑driven outflow in the Virgo cluster galaxy NGC 4383, as part of the MAUVE (Multiphase Astrophysics to Unveil the Virgo Environment) program. The authors combine high‑resolution ALMA CO(2‑1) observations (∼1″ ≈ 80 pc, 0.9 K km s⁻¹ sensitivity), deep MeerKAT H I imaging (12 × 7.3 arcsec beam, 0.2 mJy beam⁻¹ rms, 5.6 km s⁻¹ channels), and MUSE integral‑field spectroscopy (≈1.3″ seeing, 100 pc resolution) to trace the molecular, atomic, and ionised gas components of the outflow.

The ALMA data reveal that CO emission with disturbed kinematics is confined to the inner ∼1 kpc above the disc, where molecular clouds align spatially with the ionisation cone identified in the ionised gas. Beyond this region the CO surface brightness drops precipitously, indicating that the molecular phase contributes negligibly to the mass of gas at larger heights. The molecular gas mass inferred from CO is of order 10⁶–10⁷ M⊙, far smaller than typical outflow masses in more powerful starbursts.

In contrast, the MeerKAT H I cube shows prominent plumes extending a few kiloparsecs above the disc, roughly co‑linear with the ionisation cone. These atomic structures display complex, non‑rotational velocities that differ from the underlying warped H I disc previously reported for NGC 4383. The warped disc geometry makes it difficult to unambiguously separate outflowing H I from disc material, and consequently the atomic outflow mass and loading factor remain uncertain. Nevertheless, the detection of dust extinction features that coincide with the H I plumes provides independent evidence that cold material is present in the extraplanar region.

The MUSE data confirm a powerful ionised outflow traced by H α,