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 Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

We present the results of a systematic search for molecular hydrogen (H2) inlow redshift ($ 0.05 \lesssim z \lesssim 0.7$) DLAs and sub-DLAs with $N(HI)\gtrsim 10^{19.0}$ cm$^{-2}$, in the archival HST/COS spectra. Our core sampleis comprised of 27 systems with a median $\log N(HI) = 19.6$. On the average,our survey is sensitive down to $\log N(H2) = 14.4$ corresponding to amolecular fraction of $\log f_{H2} = -4.9$ at the median $N(HI)$. H2 isdetected in 10 cases (3/5 DLAs and 7/22 sub-DLAs) down to this $f_{H2}$ limit.The H2 detection rate of $50^{+25}_{-12}$ percent seen in our sample, is afactor of $\gtrsim 2$ higher than that of the high-$z$ sample of Noterdaeme etal. (2008), for systems with $N(H2) > 10^{14.4}$ cm$^{-2}$. In spite of having$N(HI)$ values typically lower by a factor of 10, low-$z$ H2 systems showmolecular fractions ($\log f_{H2}=-1.93\pm0.63$) that are comparable to thehigh-$z$ sample. The rotational excitation temperatures ($T_{01} = 133\pm55$K), as measured in our low-$z$ sample, are typically consistent with high-$z$measurements. Simple photoionization models favour a radiation field muchweaker than the mean Galactic ISM field for a particle density in the range 10- 100 cm$^{-3}$. The impact parameters of the identified host-galaxy candidatesare in the range $10 \lesssim \rho$ (kpc) $\lesssim 80$. We, therefore,conjecture that the low-$z$ H2 bearing gas is not related to star-forming disksbut stems from self-shielded, tidally stripped or ejected disk-material in theextended halo.

An HST/COS survey of molecular hydrogen in DLAs & sub-DLAs at z < 1: Molecular fraction and excitation temperature