DETECTION OF DIFFUSE NEUTRAL INTRAGROUP MEDIUM IN HICKSON COMPACT GROUPS

Journal Article · Wed Feb 10 04:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/710/1/385· OSTI ID:21394503

Borthakur, Sanchayeeta; Yun, Min Su ^[1]; Verdes-Montenegro, Lourdes ^[2]

---

1. Astronomy Department, University of Massachusetts, Amherst, MA 01003 (United States)
2. Instituto de Astrofisica de AndalucIa, CSIC, Apdo. Correos 3004, E-18080 Granada (Spain)

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 x 10{sup 9} M{sub sun} (median = 6 x 10{sup 9} M{sub sun}), 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){sub GBT} - M(H I){sub VLA})/M(H I){sub 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 x 10{sup 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.

• OSTI ID: 21394503
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 710; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BRIGHTNESS
DISTANCE
ELEMENTS
EVOLUTION
GALACTIC EVOLUTION
GALAXIES
HYDROGEN
LIFETIME
MASS
NONMETALS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
SPECTRA
TELESCOPES