A search for HI 21cm absorption toward the highest redshift radio loud objects
Abstract
We have searched for HI 21cm absorption toward the two brightest radio AGN at high redshift, J0924--2201 at z = 5.20, and J0913+5919 at z=5.11, using the Giant Meter Wave Radio Telescope (GMRT). These data set a 3σ upper limit to absorption of < 30% at 40 km s-1 resolution for the 30 mJy source J0913+5919, and < 3% for the 0.55 Jy source J0924--2201 at 20 km s-1 resolution. For J0924--2201, limits to broader lines at the few percent level are set by residual spectral baseline structure. For J0924--2201 the column density limit per 20 km s -1 channel is: N(HI) < 2.2× 1018 Ts cm-2 over a velocity range of -700 km s-1 to +1180 km s-1 centered on the galaxy redshift determined through CO emission, assuming a covering factor of one. For J0913+5919 the column density limit per 40 km s-1 channel is: N(HI) < 2.2× 1019 Ts cm-2 within 2400 km s-1 of the optical redshift. These data rule out any cool, high column density HI clouds within roughly 1000 km s-1 of the galaxies, as are often seen in Compact Steep Spectrum radio AGN, or clouds that might correspond to residual gas left over from cosmic reionization.
Turn this paper into a full lesson
ArcXiv compiles a staged curriculum from this paper: 8-12 lessons across beginner → advanced, synthesised section guides, visuals, flashcards, a quiz, exercises, and on-demand deep dives per section. Grounded in the abstract, never invented.