Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...208.1503m&link_type=abstract
American Astronomical Society Meeting 208, #15.03; Bulletin of the American Astronomical Society, Vol. 38, p.96
Astronomy and Astrophysics
Astronomy
Scientific paper
The recently discovered low-z (z = 0.0063) ultraviolet absorption system toward the radio-faint quasar, PG 1216+069, has N(HI) 2 x 10(19) cm(-2). While technically classified as a sub-DLA (Damped Ly-alpha Absorption) system, its absorption profile does show clear damping wings. It is also one of very few Ly-alpha absorption systems known that are this nearby. Despite its low redshift, the system shows a very low metallicity, 1/40 solar, placing it among the lowest ever found for a low-z object, and similar to high-z DLA systems. No optical counterpart is seen with the HST. Previous attempts to detect radio HI emission from this sub-DLA have produced only a GMRT non-detection, and a tentative (3.1 σ) Westerbork detection. With the Arecibo 305-m telescope (HPBW = 3.4'), we have now made a solid detection (16 σ) of HI emission from this low-z absorber. A peak flux density of 2.8 mJy/beam is measured, with an HI velocity at the peak of 1917.6 ± 3.4 km/s (z=0.006396). It has an asymmetric line profile that is broader to the blue. The velocity width is 62 km/s at half power, and 150 ± 17 km/s at zero intensity. For a Hubble distance of 27 Mpc, an HI mass of 3 x 107 Msun results. From the GMRT non-detection and measurement of marginal beam broadening at Arecibo, a size of 40" < θ < 2' is derived, with the object being rather well centered on the sight-line to PG 1216+069. The measured parameters of this sub-DLA are discussed in the light of the wide range of galaxy types and luminosities found to represent low-z DLAs, but are not inconsistent with its being a small, low-surface-brightness galaxy.
Chengalur Jayaram
Ghosh Tamal
Kanekar Nissim
Keeney Brian A.
Momjian Emmanuel
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