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We obtained dual-polarization VLBI observations at six frequencies of thecompact symmetric object J0029+3457 and the CSO candidate J1324+4048. Bycomparing the three lower-frequency maps with extrapolations of the highfrequency maps we produced maps of the optical depth as a function offrequency. The morphology of the optical-depth maps of J1324+4048 is strikinglysmooth, suggestive of a foreground screen of absorbing gas. The spectra at theintensity peaks fit a simple free-free absorption model, with a reduced chisquare ~ 2, better than a simple synchrotron self-absorption model, in whichthe reduced chi square ~ 3.5 - 5.5. We conclude that the case for free-freeabsorption in J1324+4048 is strong. The optical-depth maps of J0029+3457exhibit structure, but the morphology does not correlate with that in theintensity maps. The fit of the spectra at the peaks to a simple free-freeabsorption model yields a reduced chi square ~ 1, but since the turnover isgradual the fit is relatively insensitive to the input parameters. We find thatfree-free absorption by a thin amount of gas in J0029+3457 is likely, but notdefinitive. One compact feature in J0029+3457 has an inverted spectrum even atthe highest frequencies. We infer this to be the location of the core andestimate an upper limit to the magnetic field of order 3 Gauss at a radius oforder 1 pc. In comparison with maps from observations at earlier epochs, noapparent growth in either J1324+4048 or J0029+3457 is apparent, with upperlimits of 0.03 and 0.02 mas per yr, corresponding to maximum linear separationspeeds of 0.6c and 0.4c.

astrophysical journal/the astrophysical journal

Multi-Frequency Optical-Depth Maps and the Case for Free-Free Absorption  in Two Compact Symmetric Radio Sources: the CSO candidate J1324+4048 and the  CSO J0029+3457