Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995mnras.273..129g&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 273, Issue 1, pp. 129-138.
Astronomy and Astrophysics
Astronomy
10
Galaxies: Active, Galaxies: Individual: Ngc 3516, Galaxies: Ism, Galaxies: Seyfert
Scientific paper
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] lambda4959, [Fe VII]+[Ca V] lambda6087, [O I] lambda6364 and H alpha+[N II]lambdalambda6548, 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 (>=4-5 arcsec and <=24 arcsec), we measure ~=1.3x10^-13 erg cm^-2 s^-1 in [O III] lambda4959 and ~=1.7x10^-12 erg cm^-2 s^-1 in H alpha+[N II] lambdalambda6548, 6584. The outlying feature 7, found by Miyaji et al. is most conspicuous in the [OIII] lambda4959 image. We measure the total emission flux of this feature to be ~2.7x10^-15 erg cm^-2 s^-1. Our image in the [Fe VII]+[Ca V] lambda6087 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] lambdalambda4959, 5007 lines observed north-east of the nucleus. The measured flux in [Fe VII] lambda6087 is ~10^-14 erg cm^-2 s^-1, which yields N^2_ef~=0.35. It is clear that the photoionized coronal-line region (CLR) in NGC 3516 is not so dense. We estimate the Q_rec/Q_nuc ratio from the observed [Fe VII]+[Ca V] lambda6087 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~=2.8. This number, like the estimation made by Pogge using the H alpha 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 (N_e~1 cm^-3) interstellar medium exposed to and photoionized by the bare active nucleus.
Bonev Tanyu
Golev Valeri
Jockers Klaus
Yankulova I.
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