A search for HI 21cm absorption toward the highest redshift radio loud objects

Details A search for HI 21cm absorption toward the highest redshift radio loud objects A search for HI 21cm absorption toward the highest redshift radio loud objects

2007-03-30

arxiv.org/abs/astro-ph/0703797v1

Astron.J.133:2841-2845,2007

Astronomy and Astrophysics

Astrophysics

accepted to the Astronomical Journal; 7 figures; 9 pages aastex format

Scientific paper

10.1086/518436

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 3$\sigma$ 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) $< 2.2\times 10^{18} \rm T_s$ 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) $< 2.2\times 10^{19} \rm T_s$ cm$^{-2}$ within $\pm 2400$ km s$^{-1}$ of the optical redshift. These data rule out any cool, high column density HI clouds within roughly $\pm 1000$ 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.

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