FUSE Survey of Interstellar Molecular Hydrogen Toward 45 High-Latitude AGN

Details FUSE Survey of Interstellar Molecular Hydrogen Toward 45 High-Latitude AGN FUSE Survey of Interstellar Molecular Hydrogen Toward 45 High-Latitude AGN

Jun 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aspc..348..439g&link_type=abstract

Astrophysics in the Far Ultraviolet: Five Years of Discovery with FUSE ASP Conference Series, Vol. 348, Proceedings of the Confe

Astronomy and Astrophysics

Astrophysics

Scientific paper

We report results from a Far Ultraviolet Spectroscopic Explorer (FUSE) survey of interstellar molecular hydrogen (H2) along 45 sightlines to background AGN at high Galactic latitudes (|b| > 20°). The high-latitude sightlines are effective at probing diffuse gas in the low Galactic halo, including large-scale gaseous structures. FUSE spectra of 87% (39 of 45) of the observed AGN show detectable Galactic H2 absorption from the Lyman and Werner bands between 920 and 1126 Å, with detected column densities ranging from N(H2)=1014.17-19.82 cm-2. Our survey is sensitive to N(H2)>1013.8-14.6 cm-2, depending on the S/N (2--11 per pixel) and spectral resolution (R=15,000-20,000). The broad range of column densities indicates large fluctuations in the spatial structure of high-latitude H2 clouds, particularly at b > 54°. In the northern hemisphere, we identify many regions of low N(H2) (≤ 1015 cm-2) between (l=60°-180° and b>54°). These ``H2 holes" may be related to the ``Northern Chimney" (region of low Na I absorption, Lallement et al. 2003) and the ``Lockman Hole" (region of low NHI, Lockman et al. 1986). A comparison of these high-latitude results with those from our FUSE survey of ˜130 OB-star sightlines in the Galactic disk suggests that that halo and disk clouds have different physical properties. The mean rotational temperature, < T01halo > = 125 ± 15 K, is higher than that found in the Galactic disk, < T01disk >= 86 ± 20 K. Because this H2 temperature is elevated compared to gas in the Milky Way disk (Savage et al. 1977; Shull et al. 2004) or in the LMC/SMC (Tumlinson et al. 2002), it may imply enhanced heating or reduced cooling rates in Galactic halo diffuse H2 clouds. The transition to appreciable molecular fractions, fH2 > 0.01, in our halo sample occurs at a lower total hydrogen column density (log NHhalo = 20.35) than in the Galactic disk (log NHdisk = 20.7), possibly indicating reduced H2 photodissociation rates offsetting a lower formation rate on dust grains in low-metallicity gas. By looking for correlations between high-latitude H2 detections and IRAS maps of infrared cirrus clouds, we hope to further characterize the halo clouds and explain why they differ from disk clouds.

Affiliated with

Also associated with

No associations

Rating

FUSE Survey of Interstellar Molecular Hydrogen Toward 45 High-Latitude AGN does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with FUSE Survey of Interstellar Molecular Hydrogen Toward 45 High-Latitude AGN, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and FUSE Survey of Interstellar Molecular Hydrogen Toward 45 High-Latitude AGN will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1860314