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19 April 2024 |
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Molecular Hydrogen in High-Velocity Clouds | | Philipp Richter
; Kenneth R. Sembach
; Bart P. Wakker & Blair D. Savage
; | | Date: |
11 Oct 2001 | | Subject: | astro-ph | | Abstract: | We present Far Ultraviolet Spectroscopic Explorer (FUSE) observations of interstellar molecular hydrogen (H_2) in two Galactic high-velocity clouds (HVCs). Molecular hydrogen absorption is detected in the Magellanic Stream (abundance ~0.3 solar) toward the Seyfert galaxy Fairall 9 in the lowest three rotational states (J=0-2) at v(LSR)=+190 km/s, yielding a total H_2 column density of log N(H_2)=16.40(+0.26)(-0.53). In contrast, no H_2 absorption is seen in the high-velocity cloud Complex C (abundance ~0.1 solar) toward the quasar PG 1259+593 (log N(H_2)<13.96 at v(LSR)=-130 km/s) although both HVCs have similar HI column densities on the order of log N(HI)~20. Weak H_2 absorption is detected in the Intermediate-Velocity Arch (IV Arch; abundance ~1.0 solar) toward PG 1259+593 (log N(H_2)=14.10(+0.21)(-0.44) at v(LSR)=-55 km/s and log N(HI)=19.5). It thus appears that metal- and dust-poor halo clouds like Complex C are not able to form and maintain widely distributed H_2, whereas metal and dust-rich halo clouds like the IV Arch can maintain H_2 even at low HI column densities. | | Source: | arXiv, astro-ph/0110279 | | Services: | Forum | Review | PDF | Favorites | |
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