The Seyfert Galaxy

The spectrum of this object is shown in Figure 6, which is the average of four separate CCD exposures. The radial velocity of 8730 km s^-1 and clearly defined emission lines from a small area $\le$ 1.5 arcseconds in diameter are typical of an Active Galactic Nucleus (AGN). The emission line source is at the centre of a larger optical source of size $\sim 20^{\prime\prime} \times 30^{\prime\prime}$ , and a still larger radio source of size $\sim 1.5^{\prime}$ in diameter. A radio image of the object is shown in Figure 7, taken from the VLA NVSS at 1.4 GHz. This image is approximately $15^\prime \times 15^\prime$ in size.

**Figure** 6: Spectrum of IRAS 07245-3548.
$\textstyle \parbox[c]{0.5cm}{\rotatebox{90}{\footnotesize \axsize Flux $(\times 10^{-15}$erg cm$^{-2}$\ s$^{-1}$\ Hz$^{-1})$}}$ $\textstyle \parbox{10cm}{\scalebox{0.8}{\includegraphics*{spec25.eps}}}$ Wavelength (Å)

Distance is estimated at 120 Mpc using a Hubble constant of 75 km s^-1 Mpc^-1. Linewidths are $\sim 500$ km s^-1, and the 5 GHz power output, calculated from the PMN flux and a distance of 120 Mpc, is 2 x 10²³ W Hz^-1. Classification of this object as a Seyfert 2 galaxy is based on its known properties and the properties of the various AGN classes discussed by Woltjer (1990).

The presence of the 3727 [OII] line is typical of PN and of many AGN types, including Seyfert galaxies. However in PN, the excitation is produced by a central star, with an approximately black-body continuum, in a relatively narrow range of wavelengths. The power-law spectra of AGN is broader, and allows a wider range of excitation states to be seen. In this object, the 3727 [OII] and the [OIII] lines are all much stronger than H $_\beta$ , a feature not typically seen in nebulae excited by starlight. Woltjer (1990) quotes typical values for the flux ratios 5007 [OIII]/H $_\beta$ and 3727 [OII]/H $\beta$ for Seyfert 2 galaxies as 13 and 2 respectively. For IRAS 07245-3548 these ratios are 16 and 5 respectively, which may suggest a broader than average range of ionisation states.

**Figure** 7: 1.4 GHz radio image of IRAS 07245-3548.
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