The Chandra Deep Field North Survey. XII. The Link between Faint X-Ray and Radio Source Populations

We investigate the relationship between faint X-ray and 1.4 GHz radio sourcepopulations detected within 3' of the Hubble Deep Field North using the 1 MsChandra and 40 uJy VLA surveys. Within this region, we find that ~42% of the 62X-ray sources have radio counterparts and ~71% of the 28 radio sources haveX-ray counterparts; thus a 40 uJy VLA survey at 1.4 GHz appears to bewell-matched to a 1 Ms Chandra observation. Among the different sourcepopulations sampled, we find that the majority of the 18 X-ray detectedemission-line galaxies (ELGs) have radio and mid-infrared ISOCAM counterpartsand appear to be luminous star-forming galaxies at z=0.3-1.3. Importantly, theradio-detected ELGs make up ~35% of the X-ray source population at 0.5-8.0 keVX-ray fluxes between ~(1-5)x10e-16 erg/cm2/s and signal the emergence of theluminous, high-z starburst galaxy population in the X-ray band. We find thatthe locally-determined correlation between X-ray luminosities and 1.4 GHz radioluminosity densities of the late-type galaxies can easily be extended toinclude the luminous intermediate-redshift ELGs, suggesting that the X-ray andradio emission processes are generally associated in star-forming galaxies.This result implies that the X-ray emission can be used as an indicator of starformation rate for star-forming galaxies. Finally, we show that there appear tobe two statistically distinct types of ISOCAM-detected star-forming galaxies:those with detectable radio and X-ray emission and those without. The lattertype may have stronger mid-infrared emission-line features that increase theirdetectability at mid-infrared wavelengths.Comment: 12 pages, 5 figures (1 color), LaTeX emulateapj5.sty, accepted for publication by the Astronomical Journa