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Session 104 - Radio Galaxies, Radio Observations of AGN Jets & Outflows.
Display session, Saturday, January 10
Exhibit Hall,
Mrk 348 is a type 2 Seyfert galaxy at a distance of approximately 61 Mpc, assuming a Hubble constant of 75 km/s/Mpc. It was imaged at 2, 6, and 18 cm as part of a VLBA survey of 8 Seyfert galaxies. The main focus of this survey is to investigate whether type 1 and type 2 Seyferts are distinguishable from one another by the kinds of absorption effects present at centimeter wavelengths. The 18 cm image shows bridges of emission to the north and south, with a total extent of nearly 60 pc; the size is consistent with a low-resolution EVN image from the early 1980s. Only the central part of Mrk 348 appears at all three wavelengths. At 2 cm it is resolved into two components, separated by \sim 0.3 pc and with brightness temperatures of about 10^8 K. The separation of these components is in a position angle \sim 90^\circ different from the larger-scale VLBI source.
Spectral indices calculated for the whole central source reveal a sharp change in spectral index between 2 and 6 cm, with a steep inverted spectrum between 6 and 18 cm, indicating absorption in both components. Possible spectra were derived for each component to find limits for their individual turn-over frequencies. Order of magnitude estimates were made of the electron densities needed for free-free absorption, and of the magnetic field strengths required for the presence of synchrotron self-absorption. The results indicate that electron densities of 1 to a few times 10^4cm^-3, which are similar to values expected for narrow-line clouds near the nucleus, are sufficient to account for the spectra by means of free-free absorption. Such absorption is consistent with results found in VLBA images of other galaxies in the survey.
