Shocked Molecular Hydrogen in the 3C 326 Radio Galaxy System

• Published in: The Astrophysical journal 2007-10, Vol.668 (2), p.699-707
• Main Authors: Ogle, Patrick, Antonucci, Robert, Appleton, P. N, Whysong, David
• Format: Article
• Language: English
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/521334

The Spitzer spectrum of the giant FR II radio galaxy 3C 326 is dominated by very strong molecular hydrogen emission lines on a faint IR continuum. The H sub(2) emission originates in the northern component of a double-galaxy system associated with 3C 326. The integrated luminosity in H sub(2) pure rotational lines is 8.0 x 10 super(41) erg s super(-1), which corresponds to 17% of the 8-70 mu m luminosity of the galaxy. A wide range of temperatures (125-1000 K) is measured from the H sub(2) 0-0 S(0)-S(7) transitions, leading to a warm H sub(2) mass of 1.1 x 10 sub(9) M [unk]. Low-excitation ionic forbidden emission lines are consistent with an optical LINER classification for the active nucleus, which is not luminous enough to power the observed H sub(2) emission. The H sub(2) could be shock heated by the radio jets, but there is no direct indication of this. More likely, the H sub(2) is shock heated in a tidal accretion flow induced by interaction with the southern companion galaxy. The latter scenario is supported by an irregular morphology, a tidal bridge, and a possible tidal tail imaged with IRAC at 3-9 mu m. Unlike ultraluminous infrared galaxies, which in some cases exhibit H sub(2) line luminosities of comparable strength, 3C 326 shows little star formation activity ( similar to 0.1 M [unk] yr super(-1)). This may represent an Important stage in galaxy evolution. Starburst activity and efficient accretion onto the central supermassive black hole may be delayed until the shock-heated H sub(2) can kinematically settle and cool.