English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We present the results of a blind search for intervening HI 21 cm absorptiontoward 260 radio sources in the redshift range 0<z<2.74 with the Green BankTelescope. The survey has the sensitivity to detect sub-damped Lyman-alpha(DLA) systems for HI spin temperatures $T_s/f$ = 100 K, and despite thesuccessful re-detection of ten known 21 cm absorbers in the sample, we detectno new absorption lines in the full survey. Sources detected in 21 cmabsorption were also searched for hydroxyl (OH) 18 cm absorption and were-detect 1667 MHz OH absorption toward PKS 1830-211. We searched forintervening HI 21 cm absorption along the line of sight in each sourceachieving a total redshift coverage of $\Delta z$ = 88.64 (comoving absorptionpath of $\Delta X$ = 159.5) after removing regions affected by radio frequencyinterference. We compute a 95% confidence upper limit on the column densityfrequency distribution $f(N_{\rm HI})$ and set a statistical constraint on thespin temperature $T_s$ in the range 100-1000 K, consistent with priorredshifted optical DLA surveys and HI 21 cm emission observations at the sameredshifts. We infer a value for the cosmological mass density of neutral gas,$\Omega_{\rm HI}$. Through comparison with prior $\Omega_{\rm HI}$measurements, we place a statistical constraint on the mean spin temperature of$T_s/f$ = 175 K. Our derived $\Omega_{\textrm {HI}}$ values support a relativemild evolution in $\Omega_{\textrm {HI}}$ over the last 11 Gyr and areconsistent with other methods that measure $\Omega_{\textrm {HI}}$.

The evolution of neutral hydrogen over the past 11 Gyr via HI 21 cm absorption