Search for cold gas in z > 2 damped Lyα systems: 21-cm and H2 absorption

摘要: We present the results of a systematic Green Bank Telescope (GBT) and Giant Metrewave Radio (GMRT) survey for 21-cm absorption in sample 10 damped Lyman-α (DLA) systems at 2 � zabs� 3.4. Analysis L-band Very Long Baseline Array (VLBA) images background QSOs are also presented. detect only one DLA (at zabs = 3.1745 towards J1337+3152). Thus detection rate is 10% when no limit on integrated optical depth ( R τ(v)dv) imposed 13% 3σ 0.4 km s 1 . Combining our data with from literature (a 28 DLAs) assuming measured core fraction milliarcsecond scale to represent gas covering factor, we find that H i DLAs z predominantly constituted by warm neutral medium. The seems be higher N(H i) or metallicity. However, clear correlation found between (or spin-temperature, TS) either i), metallicity velocity spread low ionization species. There 13 which high resolution spectra expected wavelength range H2 available. report molecules 3.3871 absorber J0203+1134 (PKS 0201+113). In 8 cases, neither (with molecular f(H2)� 6 ) nor TS/fc 700 K) detected. lack these can explained if most originate density temperature gas. case have not showing absorption. two both species detected but do same component. remaining cases despite presence evidence cold All this consistent idea components seen compact sizes 15 pc) contain small (i.e typically 10%) total DLAs. This implies fractions f(H2) reported surveys should considered as conservative lower limits components.