Witnessing galaxy assembly in an extended z≈3 structure

Abstract

We present new observations acquired with the Multi Unit Spectroscopic Explorer instrument on the Very Large Telescope in a quasar field that hosts a high columndensity damped Lyα absorber (DLA) at z ≈ 3.25. We detect Lyα emission from a nebula at the redshift of the DLA with line luminosity (27 ± 1) × 10 41 erg s −1 , which extends over 37±1 kpc above a surface brightness limit of 6×10 −19 erg s −1 cm −2 arcsec −2 at a projected distance of 30.5±0.5 kpc from the quasar sightline. Two clumps lie inside this nebula, both with Lyα rest-frame equivalent width > 50 Å and with relative lineof-sight velocities aligned with two main absorption components seen in the DLA spectrum. In addition, we identify a compact galaxy at a projected distance of 19.1 ± 0.5 kpc from the quasar sightline. The galaxy spectrum is noisy but consistent with that of a star-forming galaxy at the DLA redshift. We argue that the Lyα nebula is ionized by radiation from star formation inside the two clumps, or by radiation from the compact galaxy. In either case, these data imply the presence of a structure with size 50 kpc inside which galaxies are assembling, a picture consistent with galaxy formation in groups and filaments as predicted by cosmological simulations such as the eagle simulations.

Linking gas and galaxies at high redshift: MUSE surveys the environments of six damped Lyα systems at z ≈ 3

“…Table 1 indicates the ions used to estimate the metallicity of the DLAs in the sample. Fumagalli et al (2017b) showed that in the case of J0255+0048 the Si II column density estimated with Voigt profile decomposition of HIRES and X-Shooter data was consistent with the value obtained with ESI and the apparent optical depth method. We therefore conclude the ionic column densities to be robust and do not re-estimate them.…”

“…Notably, DLA J1220+0921 in our sample is very metal-poor, sitting at Z/Z = −2.33 although still somewhat above the metallicity floor at Z/Z −3 (Prochaska et al 2003;Rafelski et al 2012). One sightline in our sample was previously presented in Fumagalli et al 2017b, the DLA was revealed to be part of a 50 kpc structure which may be evidence of an ongoing merger.…”

The MUSE Ultra Deep Field (MUDF). II. Survey design and the gaseous properties of galaxy groups at 0.5 < z < 1.5

“…In particular, thanks to its large 1 arcmin 2 field of view, its extended wavelength coverage in the optical, and its exquisite sensitivity, MUSE has become the ideal instrument for studies of the CGM of galaxies in quasar fields (e.g. Schroetter et al 2016;Fumagalli et al 2016Fumagalli et al , 2017bPéroux et al 2017;Bielby et al 2017;Klitsch et al 2018;Chen et al 2019).…”

Into the Ly α jungle: exploring the circumgalactic medium of galaxies at z ∼ 4−5 with MUSE

“…As in previous analyses of MUSE data (e.g. Fumagalli et al 2017b;Mackenzie et al 2019;Lofthouse et al 2019;Fossati et al 2019), we conduct a redshift survey of galaxies detected in the continuum together with a search for line emitters in the cube. 18 19 20 21 22 23 24 25 26 27 28 29 30 31 33 34 36 37 38 39 41 42 43 44 45 46 47 48 49 50 52 53 54 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 80 81 82 84 86 87 89 90 91 92 93 95 96 97 98 99 100 101 103 104 105 106 107 108 110 111 112113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 129 130 131 132 133 ...…”

“…Observations have been reduced following the methodology described in previous work (Fumagalli et al 2016b(Fumagalli et al , 2017bLofthouse et al 2019). Briefly, we first use the standard ESO pipeline (v2.4.1; Weilbacher et al 2014) to perform basic reduction by applying calibrations.…”