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Title: 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

We obtained dual-polarization very long baseline interferometry observations at six frequencies of the compact symmetric object J0029 + 3457 and the compact symmetric object candidate J1324 + 4048. By comparing the three lower-frequency maps with extrapolations of the high-frequency maps, we produced maps of the optical depth as a function of frequency. The morphology of the optical-depth maps of J1324 + 4048 is strikingly smooth, suggestive of a foreground screen of absorbing gas. The spectra at the intensity peaks fit a simple free-free absorption (FFA) model, with χ{sub ν}{sup 2}≈2, better than a simple synchrotron self-absorption model, in which χ{sub ν}{sup 2}≈3.5--5.5. We conclude that the case for FFA in J1324 + 4048 is strong. The optical-depth maps of J0029 + 3457 exhibit structure, but the morphology does not correlate with that in the intensity maps. The fit of the spectra at the peaks to a simple FFA model yields χ{sub ν}{sup 2}≈1, but because the turnover is gradual, the fit is relatively insensitive to the input parameters. We find that FFA by a thin amount of gas in J0029 + 3457 is likely but not definitive. One compact feature in J0029 + 3457 has an inverted spectrum even atmore » the highest frequencies. We infer this to be the location of the core and estimate an upper limit to the magnetic field of order 3 Gauss at a radius of order 1 pc. In comparison with maps from observations at earlier epochs, no apparent growth in either J1324 + 4048 or J0029 + 3457 is apparent, with upper limits of 0.03 and 0.02 mas yr{sup –1}, corresponding to maximum linear separation speeds of 0.6c and 0.4c.« less
Authors:
; ;  [1] ;  [2] ;  [3]
  1. Union College, Schenectady, NY 12308 (United States)
  2. University of Wisconsin, Madison, WI 53706 (United States)
  3. University of New Mexico, Albuquerque, NM 87131 (United States)
Publication Date:
OSTI Identifier:
22348208
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 780; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; EXTRAPOLATION; FREQUENCY DEPENDENCE; GALAXIES; GALAXY NUCLEI; INTERFEROMETRY; MAGNETIC FIELDS; POLARIZATION; SCREENS; SELF-ABSORPTION; SPECTRA; SYNCHROTRONS