THE ASTRONOMICAL JOURNAL    VOLUME 109, NUMBER 6, PAGE 2318           JUNE 1995

              RADIO IDENTIFICATIONS OF EXTRAGALACTIC IRAS SOURCES

                         J. J. CONDON AND E. ANDERSON

           National Radio Astronomy Observatory, 520 Edgemont Road,
                        Charlottesville, Virginia 22903
             Electronic mail: jcondon@nrao.edu, eanderso@nrao.edu

                                J. J. BRODERICK

  Department of Physics, Virginia Polytechnic Institute and State University,
                          Blacksburg, Virginia 24061
                    Electronic mail: jjb@vtpcn.phys.vt.edu


                                   ABSTRACT

    Extragalactic sources detected at lambda = 60 um were selected from the
    IRAS Faint Source Catalog, Version 2 by the criterion S(60 um) >= 
    S(12 um).  They were identified by position coincidence with radio
    sources stronger than 25 mJy at 4.85 GHz in the 6.0 sr declination band
    0 deg < Dec. < +75 deg (excluding the 0.05 sr region 12h 40m < R.A. <
    14h 40m, 0 deg < Dec. < +5 deg) and with radio sources stronger than 80
    mJy in the 3.4 sr area 0h < R.A. < 20h, -40 deg < Dec. < 0 deg (plus the
    region 12h 40m < R.A. < 14h 40m, 0 deg < Dec. < +5 deg).  Fields
    containing new candidate identifications were mapped by the VLA at 4.86
    GHz with about 15" FWHM resolution.  Difficult cases were confirmed or
    rejected with the aid of accurate (sigma ~ 1") radio and optical
    positions.  The final sample of 354 identifications in Omega = 9.4 sr
    is reliable and large enough to contain statistically useful numbers of
    radio-loud FIR galaxies and quasars.  The logarithmic FIR/radio flux
    ratio parameter q can be used to distinguish radio sources powered by
    "starbursts" from those powered by "monsters."  Starbursts and normal
    spiral galaxies in a lambda = 60 um flux-limited sample have a narrow
    (sigma_q = 0.14 +/- 0.01) q distribution with mean <q> = 2.74 +/-
    0.01, and none have "warm" FIR spectra [alpha(25 um, 60 um) < 1.5].  The
    absence of radio-quiet (but not completely silent) blazars indicates
    that nearly all blazars become optically thin at frequencies nu <~ 100
    GHz.  Nonthermal sources with steep FIR/optical spectra and
    dust-embedded sources visible only at FIR and radio wavelengths must be
    very rare.