2009/12/31 by Sanchayeeta Borthakur, Min Su Yun, Lourdes Verdes-Montenegro
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #Brightness #Compact group #Content (measure theory) #Green Bank Telescope #Hydrogen #Mass fraction #RADIUS #Surface brightness #astro-ph.CO
paper · pdf · doi:10.1088/0004-637x/710/1/385
published as Astrophys.J.710:385-407,2010; Erratum-ibid.729:149,2011 · 57 pages including 13 figures and 7 tables
arxiv created 2010/01/16 · openalex publication_date 2010/01/19 · arxiv updated 2011/03/02 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
We present new Green Bank Telescope (GBT) 21 cm neutral hydrogen (H i ) observations of a complete distance-limited sample of 22 Hickson Compact Groups (HCGs) with at least four true members. We detected an average H i mass of 8 × 10 9 M ☉ (median = 6 × 10 9 M ☉ ), which is significantly larger than previous single-dish measurements. Consequently, the H i deficiencies for these HCGs have been reduced, although not completely eliminated. Spectral comparison of the GBT data with complementary Very Large Array data shows significant H i excess in the GBT spectra. The observed excess is primarily due to the high surface brightness (HSB) sensitivity of the GBT detecting diffuse, low column density H i in these groups. The excess gas forms a faint diffused neutral medium which is an intermediate stage in the evolution of HSB H i tidal debris in the intragroup medium (IGM) before it is fully ionized. The excess gas mass fraction, ( M (H i ) GBT − M (H i ) VLA )/ M (H i ) GBT , for our complete sample varies from 5% to 81% with an average of 36% (median = 30%). The excess gas mass fraction is highest in slightly H i deficient groups where the tidal debris has had enough time to evolve. We also find the excess gas content increases with the evolutionary phase of the group described in Verdes-Montenegro et al. Theoretical calculations indicate that an H i cloud of radius ⩾ 200 pc would survive in an IGM of 2 × 10 6 K for more than the typical dynamical lifetime of a group. However, smaller clouds get evaporated and assimilated into the hot IGM in a much shorter timescale.