Fig. 2: The Hot DOG W0410-0913 evolves in an very dense environment.

We quantify the significance of the overdensity of companion galaxies discovered around W0410-0913, both in the whole volume defined by the offset velocity range [−6.000; +10.000] km s⁻¹ (green triangle) and in the denser volume defined by the offset velocity range [−2.500; +1.500] km s⁻¹ (blue triangle). We compare their Lyman-α luminosity-weighted number densities with the expected values for field galaxies at comparable redshift according to the Lyman-α luminosity functions measured with MUSE in wide²⁷ (gray line and yellow shaded region, representing the ±1σ uncertainty on the fitting parameters) and deep²⁶ surveys (red points and black lines, representing the ±1σ errors). The number density of Lyman-α-emitting galaxies, n_LyE, associated with W0410-0913 is a factor of about 14 higher than the value (<n_LyE>) expected for field galaxies with comparable Lyman-α luminosity. The green and blue error bars represent the range of Lyman-α luminosities covered by companion galaxies in the whole and denser volume, respectively.