3. Additional optical data
An intermediate resolution spectrum (1.8 Å per pixel) of the region of NGC 4619 was obtained in January 1996 at OHP. The calibrated one dimensional spectrum has been extracted in two ways, shown in Fig. 5.
The first one (upper spectrum in Fig. 5) integrates over all the length were is detected (about 40"): the emission lines are clearly detected, with a [NII ]/ ratio stronger than in standard HII regions. This ratio was the basis for the LINER claim in M96. Unfortunately, the [SII ] lines, which could provide an additional diagnostic, fall into an atmospheric absorption line. As any clear broad component, revealing an AGN, could be hidden in a much larger star forming region, a second extraction was performed over a smaller extension (about 10"), corresponding to the strong continuum. This is the lower spectrum of Fig. 5, where only weak [NII ] emission lines are seen, and almost no . As the latter may however be hidden in the corresponding stellar absorption, it is difficult to use the [NII ]/ line ratio alone to claim for a diagnostic of Seyfert or LINER. In both spectra a broad component may be marginally seen but, if present, is certainly not as strong as seen in the high dispersion spectrum of M96 (and even less so than in their low dispersion one).
We finally obtained a new, low dispersion spectrum, in June 1999 at OHP, and the result is shown in Fig. 6. This spectrum, extracted over a similar 10" width as the lower one in Fig. 5, shows a clear, broad, asymmetric wing to , with a strong component on the blue side (where nothing was suspected in our 1992 spectrum) very similar to the one seen in the low dispersion spectra of M96 and Moran et al. (1994). While a quantitative comparison between the various spectra is difficult, as slit orientations and extraction lengths are different (and not always well documented), we have here reasonable evidence for variations of a broad-line component in a spectrum otherwise dominated by intermediate-type stars. The broad component is absent or weak in the first available spectra (ours in March 1992, the high-resolution one of April 1992 in M96), is strong in the low dispersion spectra of Moran et al. (1994) and of M96 (July 1994), dimmed again in our data of January 1996 and strong again in our last spectrum in June 1999. The variations seen are between a Seyfert 1.9 spectrum and a spectrum dominated by stellar features. Some indications exist for a LINER identification: we see a strong [NII ]/H ratio, as M96 did, and our 1999 spectrum shows also an [OII ]/[OIII ] ratio much greater than one. We have however no detection of the [OI ] line with a strength which could confirm the LINER diagnostic (Heckman, 1980). We note that up to now, only one case is known where broad lines developed in a LINER (NGC 1097; Storchi-Bergmann et al. 1993). The substantial reddening derived in our last spectrum [, consistent between the Balmer decrement in the narrow component and the NaD absorption], is certainly an element of importance in the following discussion.
© European Southern Observatory (ESO) 2000
Online publication: March 17, 2000