A young star-forming galaxy at z = 3.5 with an extended Lyman α halo seen with MUSE

Abstract

Spatially resolved studies of high-redshift galaxies, an essential insight into galaxy formation processes, have been mostly limited to stacking or unusually bright objects. We present here the study of a typical (L * , M = 6 × 10 9 M ) young lensed galaxy at z = 3.5, observed with Multi Unit Spectroscopic Explorer (MUSE), for which we obtain 2D resolved spatial information of Lyα and, for the first time, of C III] emission. The exceptional signal-to-noise ratio of the data reveals UV emission and absorption lines rarely seen at these redshifts, allowing us to derive important physical properties (T e ∼ 15600 K, n e ∼ 300 cm −3 , covering fraction f c ∼ 0.4) using multiple diagnostics. Inferred stellar and gas-phase metallicities point towards a low-metallicity object (Z stellar = ∼0.07 Z and Z ISM < 0.16 Z ). The Lyα emission extends over ∼10 kpc across the galaxy and presents a very uniform spectral profile, showing only a small velocity shift which is unrelated to the intrinsic kinematics of the nebular emission. The Lyα extension is approximately four times larger than the continuum emission, and makes this object comparable to low-mass LAEs at low redshift, and more compact than the Lyman-break galaxies and Lyα emitters usually studied at high redshift. We model the Lyα line and surface brightness profile using a radiative transfer code in an expanding gas shell, finding that this model provides a good description of both observables.Key words: techniques: imaging spectroscopy -galaxies: abundances -galaxies: highredshift -galaxies: individual: SMACSJ2031.8-4036. I N T RO D U C T I O NDuring the past few decades, our understanding of galaxy formation and evolution has made significant progress thanks to the hundreds of high-redshift (z > 3) galaxies which have been detected in dedicated observing campaigns (e.g. Shapley et al. 2003;Vanzella et al. 2009;Stark et al. 2013). The main spectral feature used to confirm the distances of these galaxies is the Lyα emission, since it E-mail: vera.patricio@univ-lyon1.fr (VP); johan.richard@univ-lyon1.fr (JR) is the brightest emission line we can observe in distant sources. Unfortunately, many of these objects are too faint to show any other emission line at rest-frame UV wavelengths or, even less likely, continuum and absorption lines, offering a limited picture of the characteristics of high-redshift galaxies. The complexity of the Lyα resonant process, which depends not only on the gas dynamics but also on gas density and dust content, also requires the observation of non-resonant lines in order to robustly probe the physical properties of such galaxies.Stacking techniques, which combine spectra or images of dozens or even hundreds of objects in order to increase signal-to-noise ratio (e.g.

Lyman-Alpha Spectra From Multiphase Outflows, and Their Connection to Shell Models

“…The shell model has been used to fit observed Lyα spectra (e.g., recently by Verhamme et al 2015;Yang et al 2015;Patrício et al 2015) with surprising successgiven the simplicity of the model compared to the complexity of galactic structures. In the following, we use the improved pipeline described by Gronke et al (2015) to fit shell model spectra to Lyα spectra obtained from the clumpy model.…”

“…On the other hand, the spectra presented in Yang et al (2015) which cannot be reproduced by the shell-model might hint towards the need for an extension of the modelling parameter space. Also, the shell model has difficulties in reproducing surface-brightness profiles of spatially extended Lyα sources (Barnes & Haehnelt 2010, but see Patrício et al 2015).…”