Witnessing Galaxy Assembly at the Edge of the Reionization Epoch

• Published in: Astrophysical journal. Letters 2018-08, Vol.863 (2), p.L29
• Main Authors: D’Odorico, V., Feruglio, C., Ferrara, A., Gallerani, S., Pallottini, A., Carniani, S., Maiolino, R., Cristiani, S., Marconi, A., Piconcelli, E., Fiore, F.
• Format: Article
• Language: English
• Subjects: Assembly; Astrochemistry; Galaxies; Ionization; Iron; Molecular gases; Organic chemistry; Quasars; Red shift; Star & galaxy formation; Star formation; Star formation rate
• ISSN: 2041-8205; 2041-8213
• DOI: 10.3847/2041-8213/aad7b7

We report the discovery of Serenity-18, a galaxy at z  ≃ 5.939 for which we could measure the content of molecular gas, M (H 2 ) ≃ 5 × 10 9 M ⊙ , traced by the CO(6–5) emission, together with the metal-poor ([Fe/H] =−3.08 ± 0.12, [Si/H] = −2.86 ± 0.14) gas clump/filament which is possibly feeding its growth. The galaxy has an estimated star formation rate of ≈100 M ⊙ yr −1 , implying that it is a typical main sequence galaxy at these redshifts. The metal-poor gas is detected through a damped Ly α absorber (DLA) observed at a spatial separation of 40 kpc and at the same redshift of Serenity-18, along the line of sight to the quasar SDSS J2310+1855 ( z em  ≃ 6.0025). The chemical abundances measured for the damped Ly α system are in very good agreement with those measured for other DLAs discovered at similar redshifts, indicating an enrichment due to massive PopII stars. The galaxy/damped system that we discovered is a direct observational evidence of the assembly of a galaxy at the edge of the reionization epoch.