Letter to the Editor

A Lyman-α blob in the GOODS South field: evidence for cold accretion onto a dark matter halo

¹ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany e-mail: knilsson@eso.org
² DARK Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
³ European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Vitacura, Santiago 19, Chile

Received: 14 December 2005
Accepted: 29 April 2006

Abstract

We report on the discovery of a Lyman-α emitting blob in the Great Observatories Origins Deep Survey (GOODS) South field. The discovery was made with the VLT, through narrow-band imaging. The blob has a total Lyα luminosity of  erg s^-1 and a diameter larger than 60 kpc. The available multi-wavelength data in the GOODS field consists of 13 bands from X-rays (Chandra) to infrared (Spitzer). Unlike other known Lyα blobs, this blob shows no obvious continuum counter-parts in any of the broad-bands. In particular, no optical counter-parts are found in deep HST/ACS imaging. For previously published blobs, AGN (Active Galactic Nuclei) or “superwind” models have been found to provide the best match to the data. We here argue that the most probable origin of the extended Lyα emission from this blob is cold accretion onto a dark matter halo.