NEW NARROW-BAND IMAGING OF THE EXTENDED EMISSION-LINE REGION IN THE SEYFERT-GALAXY NGC3516

We present new flux-calibrated narrow-band images of the extended emission-fine region (EELR) in NGC 3516 in the light of [O III] lambda 4959, [Fe VII] + [Ca V] lambda 6087, [O I] lambda 6364 and H alpha + [N II] lambda lambda 6548, 6584 emission lines. Our [O III] and H alpha + [N II] images confirm the previously reported Z-shaped structure and other EELR features. In the extended zone (greater than or equal to 4-5 arcsec and less than or equal to 24 arcsec), we measure approximate to 1.3 x 10(-13) erg cm(-2) s(-1) in [O III] lambda 4959 and approximate to 1.7 x 10(-12) erg cm(-2) s(-1) in H alpha + [N II] lambda lambda 6548, 6584. The outlying feature 7, found by Miyaji et al., is most conspicuous in the [O III] lambda 4959 image. We measure the total emission flux of this feature to be similar to 2.7 x 10(-15) erg cm(-2) s(-1). Our image in the [Fe VII] + [Ca V] lambda 6087 line is spatially extended to about 7-8 arcsec and its axis is aligned with both the one-sided radio jet and the extended optical emission in the H alpha + [N II] and [O III] lambda lambda 4959, 5007 lines observed north-east of the nucleus. The measured flux in [Fe VII] lambda 6087 is similar to 10(-14) erg cm(-2) s(-1), which yields N(e)(2)f approximate to 0.35. It is clear that the photoionized coronal-line region (CLR) in NGC3516 is not so dense. We estimate the Q(rec)/Q(nuc) ratio from the observed [Fe VII] + [Ca V]lambda 6087 luminosity for the photons with energies higher than hv = 100 eV in the highly ionized structure, and we obtain (Q(rec)/Q(nuc))(hv) > 100 eV (approximate to 2.8.) This number, like the estimation made by Pogge using the Ha recombination line, does not present compelling evidence for a pronounced energy deficit like that observed in the EELR of the Seyfert 2 galaxies. These observations support the model of the coronal-line region proposed by Korista and Ferland. According to this model, the coronal emission in NGC 3516 may arise in a low-density (N-e similar to 1 cm(-3)) interstellar medium exposed to and photoionized by the bare active nucleus.