OBSERVING H_2 EMISSION IN FORMING GALAXIES

摘要

We study the H_2 cooling emission of forming galaxies and discuss their observability using the future infrared facility Single Aperture Far-Infrared Observatory (SAFIR). Forming galaxies with mass approx< 10~(11) solar mass emit most of their gravitational energy liberated by contraction in molecular hydrogen line radiation, although a large part of thermal energy at virialization is radiated away by the hydrogen Lyα emission. For more massive objects, the degree of heating due to dissipation of kinetic energy is so great that the temperature does not drop below 10~4 K, and the gravitational energy is emitted mainly by the Lyα emission. Therefore, the total H_2 luminosity attains the peak value of L_(H_2) ～ 10~(42) ergs s~(-1) for forming galaxies whose total mass M_(tot) ～ 10~(11) solar mass. If these sources are situated at redshift z ～ 8, they can be detected by rotational lines of 0-0 S(3) at 9.7 μm and 0-0 S(1) at 17 μm by SAFIR. An efficient way to find such H_2 emitters is to look at the Lyα emitters, since the brightest H_2 emitters are also luminous in Lyα emission.