Recovering the systemic redshift of galaxies from their Lyman alpha line profile

A. Verhamme (1) , T. Garel (1) , E. Ventou (2) , T. Contini (2) , N. Bouché (3) , Ec C Herenz , J. Richard , R Bacon , Kb B Schmidt , M Maseda , Ra A Marino , J Brinchmann , S Cantalupo , J Caruana , B Clément , C Diener , Ab B Drake , T Hashimoto , H Inami , J Kerutt , W Kollatschny , F Leclercq , V Patrício , J Schaye , L Wisotzki , J Zabl

1 CRAL - Centre de Recherche Astrophysique de Lyon
2 IRAP - Institut de recherche en astrophysique et planétologie
3 MPE - Max Planck Institute for Extraterrestrial Physics

The Lyman alpha (Ly α) line of Hydrogen is a prominent feature in the spectra of star-forming galaxies, usually redshifted by a few hundreds of km s −1 compared to the systemic redshift. This large offset hampers follow-up surveys, galaxy pair statistics, and correlations with quasar absorption lines when only Ly α is available. We propose diagnostics that can be used to recover the systemic redshift directly from the properties of the Ly α line profile. We use spectroscopic observations of Ly α emitters for which a precise measurement of the systemic redshift is available. Our sample contains 13 sources detected between z ≈ 3 and z ≈ 6 as part of various multi-unit spectroscopic explorer guaranteed time observations. We also include a compilation of spectroscopic Ly α data from the literature spanning a wide redshift range (z ≈ 0-8). First, restricting our analysis to double-peaked Ly α spectra, we find a tight correlation between the velocity offset of the red peak with respect to the systemic redshift, V red peak , and the separation of the peaks. Secondly, we find a correlation between V red peak and the full width at half-maximum of the Ly α line. Fitting formulas to estimate systemic redshifts of galaxies with an accuracy of ≤100 km s −1 , when only the Ly α emission line is available, are given for the two methods.

Domaines: Astrophysique [astro-ph]

A. Verhamme, T. Garel, E. Ventou, T. Contini, N. Bouché, et al.. Recovering the systemic redshift of galaxies from their Lyman alpha line profile. Monthly Notices of the Royal Astronomical Society: Letters, 2018, 478 (1), pp.L60-L65. ⟨10.1093/mnrasl/sly058⟩. ⟨hal-02325325⟩