Repository logo
 

ALMA suggests outflows in z ~ 5.5 galaxies

Published version
Peer-reviewed

Change log

Authors

Gallerani, S 
Feruglio, C 
Ferrara, A 

Abstract

We present the first attempt to detect outflows from galaxies approaching the Epoch of Reionization (EoR) using a sample of 9 star-forming (SFR=31±20 M yr−1) z∼5.5 galaxies for which the [CII]158μm line has been previously obtained with ALMA. We first fit each line with a Gaussian function and compute the residuals by subtracting the best fitting model from the data. We combine the residuals of all sample galaxies and find that the total signal is characterised by a flux excess of ∼0.5 mJy extended over ∼1000 km~s−1. Although we cannot exclude that part of this signal is due to emission from faint satellite galaxies, we show that the most probable explanation for the detected flux excess is the presence of broad wings in the [CII] lines, signatures of starburst-driven outflows. We infer an average outflow rate of M˙=54±23 M yr−1, providing a loading factor η=M˙/SFR=1.7±1.3 in agreement with observed local starbursts. Our interpretation is consistent with outcomes from zoomed hydro-simulations of {\it Dahlia}, a z∼6 galaxy (SFR∼100 M yr−1) whose feedback-regulated star formation results into an outflow rate M˙∼30 M yr−1. The quality of the ALMA data is not sufficient for a detailed analysis of the [CII] line profile in individual galaxies. Nevertheless, our results suggest that starburst-driven outflows are in place in the EoR and provide useful indications for future ALMA campaigns. Deeper observations of the [CII] line in this sample are required to better characterise feedback at high-z and to understand the role of outflows in shaping early galaxy formation.

Description

Keywords

galaxies: evolution, galaxies: high-redshift, galaxies: ISM

Journal Title

Monthly Notices of the Royal Astronomical Society

Conference Name

Journal ISSN

0035-8711
1365-2966

Volume Title

473

Publisher

Oxford University Press (OUP)
Sponsorship
Science and Technology Facilities Council (ST/K003119/1)
Science and Technology Facilities Council (ST/M001172/1)
European Research Council (695671)