New narrow-band imaging of the extended emission-line region in the Seyfert galaxy NGC 3516

• Published in: Monthly notices of the Royal Astronomical Society 1995-03, Vol.273 (1), p.129-138
• Main Authors: Golev, V., Yankulova, I., Bonev, T., Jockers, K.
• Format: Article
• Language: English
• Subjects: galaxies: active; galaxies: individual: NGC 3516; galaxies: ISM; galaxies: Seyfert
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/273.1.129

We present new flux-calibrated narrow-band images of the extended emission-line region (EELR) in NGC 3516 in in the light of [O III] λ4959, [Fe VII]+[Ca V] λ6087, [O I] λ6364 and Hα+[N II]λλ6548, 6584 emission lines. Our [O III] and Hα+[N II] images confirm the previously reported Z-shaped structure and other EELR features. In the extended zone (≥4-5 arcsec and ≤24 arcsec), we measure $\approx 1.3\times10^{-13} \text {erg}\enspace\text {cm}^{-2} s^{-1}$ in [O III] λ4959 and $\approx 1.7\times10^{-12} \text {erg}\enspace\text {cm}^{-2} s^{-1}$ in Hα+[N II] λλ6548, 6584. The outlying feature 7, found by Miyaji et al. is most conspicuous in the [OIII] λ4959 image. We measure the total emission flux of this feature to be ∼2.7×10-15 erg cm-2 s-1. Our image in the [Fe VII]+[Ca V] λ6087 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 Hα+[N II] and [O III] λλ4959, 5007 lines observed north-east of the nucleus. The measured flux in [Fe VII] λ6087 is ∼10-14 erg cm-2 s-1, which yields $N^2_e\ f\approx0.35$. It is clear that the photoionized coronal-line region (CLR) in NGC 3516 is not so dense. We estimate the Qrec/Qnuc ratio from the observed [Fe VII]+[Ca V] λ6087 luminosity for the photons with energies higher than hv=100 eV in the highly ionized structure, and we obtain $(Q_{\text{rec}}/Q_{\text{nuc}})_{hv}\gt100\enspace\text {eV}\approx 2.8$ This number, like the estimation made by Pogge using the Hα 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 & Ferland. According to this model, the coronal emission in NGC 3516 may arise in a low-density (Ne∼1 cm-3) interstellar medium exposed to and photoionized by the bare active nucleus.