KODIAQ-Z: Metals and Baryons in the Cool Intergalactic and Circumgalactic Gas at 2.2 ≲ z ≲ 3.6
Abstract
We present the KODIAQ-Z survey aimed to characterize the cool, photoionized gas at 2.2 ≲ z ≲ 3.6 in 202 H I-selected absorbers with 14.6 ≤ $\mathrm{log}{N}_{{\rm{H}}\,{\rm\small{I}}}$ < 20 that probe the interface between galaxies and the intergalactic medium (IGM). We find that gas with $14.6\leqslant \mathrm{log}{N}_{{\rm{H}}\,{\rm\small{I}}}\lt 20$ at 2.2 ≲ z ≲ 3.6 can be metal-rich (-1.6 ≲ [X/H] ≲ - 0.2) as seen in damped Lyα absorbers (DLAs); it can also be very metal-poor ([X/H] < - 2.4) or even pristine ([X/H] < - 3.8), which is not observed in DLAs but is common in the IGM. For $16\lt \mathrm{log}{N}_{{\rm{H}}\,{\rm\small{I}}}\lt 20$ absorbers, the frequency of pristine absorbers is about 1%-10%, while for $14.6\leqslant \mathrm{log}{N}_{{\rm{H}}\,{\rm\small{I}}}\leqslant 16$ absorbers it is 10%-20%, similar to the diffuse IGM. Supersolar gas is extremely rare (<1%) at these redshifts. The factor of several thousand spread from the lowest to highest metallicities and large metallicity variations (a factor of a few to >100) between absorbers separated by less than Δv < 500 km s-1 imply that the metals are poorly mixed in $14.6\leqslant \mathrm{log}{N}_{{\rm{H}}\,{\rm\small{I}}}\lt 20$ gas. We show that these photoionized absorbers contribute to about 14% of the cosmic baryons and 45% of the cosmic metals at 2.2 ≲ z ≲ 3.6. We find that the mean metallicity increases with N H I , consistent with what is found in z < 1 gas. The metallicity of gas in this column density regime has increased by a factor ~8 from 2.2 ≲ z ≲ 3.6 to z < 1, but the contribution of the $14.6\leqslant \mathrm{log}{N}_{{\rm{H}}\,{\rm\small{I}}}\lt 19$ absorbers to the total metal budget of the universe at z < 1 is a quarter of that at 2.2 ≲ z ≲ 3.6. We show that FOGGIE cosmological zoom-in simulations have a similar evolution of [X/H] with N H I , which is not observed in lower-resolution simulations. In these simulations, very metal-poor absorbers with [X/H] < - 2.4 at z ~ 2-3 are tracers of inflows, while higher-metallicity absorbers are a mixture of inflows and outflows.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2022
- DOI:
- 10.3847/1538-4357/ac7400
- arXiv:
- arXiv:2112.03304
- Bibcode:
- 2022ApJ...936..156L
- Keywords:
-
- Circumgalactic medium;
- Damped Lyman-alpha systems;
- Cool intergalactic medium;
- Lyman limit systems;
- Quasar absorption line spectroscopy;
- Metallicity;
- 1879;
- 349;
- 303;
- 981;
- 1317;
- 1031;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- Submitted to the Astrophysical Journal. Comments welcome