The Dust Temperature of the “Dusty” Radio Galaxy MG 1019+0535: Evidence for an Outflow

Radio galaxies characteristically have strong Lya emission lines. However, afew have Lya equivalent widths that are substantially weaker in relation toother emission lines. One in particular was studied by Dey etal (1995), MG1019+0535 (z=2.765). We report on our reduction of Infrared Space Observatory(ISO}) data in the 160 micron-band for this galaxy. We also compile informationon two other high redshift active galaxies with weak Lya lines, the radiogalaxy TXS 0211-122, and the AGN-starburst galaxy F 10214+4724, to provide asmall weak-Lya line sample. IRAS plus ISO data show that F 10214+4724 has atemperature 89 +/- 12 K. TXS 0211-122 was not detected in either thesubmillimeter or microwave. Submillimeter measurements of MG 1019+0535 (Cimattietal 1998) were suggestive of a dust temperature in the range 35 K < T_d < 80K. However our 2-sigma upper limit on the flux at 160 microns shows that T_d <~32 K. An energy argument based on observations which constrain the totaloptical extinction strongly suggests that the dust temperature must be evenlower; T_d <~ 20 K. We find the contrast between the high-temperature dust inthe active starburst galaxy and the low-temperature dust in the evolved, albeitactive galaxy, is consistent with an expanding cloud of dust. We find that thetemperature range can be reconciled if we are seeing MG 1019+0535 at apost-starburst age of approx. 500-700 Myr, with the bulk of its dust cloud at agalactocentric distance R_d >~ 300 kpc.Comment: Insertion of figures inadvertantly left ou