Next: Conclusions Up: Discussion and implications Previous: Constraints on the starburst

## Starburst vs AGN Energetics

From the UV luminosity of the GHRS spectra and the reddening derived from the UV continuum we have estimated the mass of the burst and the bolometric luminosity (see Table 5). The latter are typically in the range of 1010 L16#16 for the three nuclei studied here, while the bolometric luminosity of the starburst nucleus of Mrk 477 is a factor 3-10 larger.

How large is the starburst contribution to the total intrinsic UV luminosity of these galaxies? Assuming that the infrared luminosity computed with the four IRAS bands (see Table 1) is due entirely to reprocessing of the total intrinsic UV luminosity of the galaxy, and comparing with the bolometric luminosity of the central starburst as deduced from their UV luminosity via the models, we estimate that the central starburst contributes about 25% in Mrk 477, 6% in NGC 7130, 7% in NGC 5135, and 6% in IC 3639 to the total intrinsic UV galactic luminosity (see Table 5). It is also possible (see the next paragraph) that much of the infrared luminosity is due to reprocessing of light generated by the AGN. In contrast, the intrinsic UV luminosities implied by the de-extincted IUE spectra (which pertain to much larger regions in each galaxy) are quite comparable to the total IR luminosities.

We can also compare the luminosity of the nuclear starburst to that of a hidden AGN. We will do so using two techniques. First, we will follow the procedure used by Heckman et al (1997) for Mrk 477 in which the low-ionization UV resonance emission-lines are attributed to resonance-scattering of the UV continuum light from the hidden Seyfert 1 nucleus off circum-nuclear gas clouds that cover a fraction fof the sky as seen by the type 1 Seyfert nucleus. The CII 1#11335 emission-line in NGC 7130 and IC 3639 has a flux (and FWHM) of 71#71 erg s-1 cm-2 (2.1 Å) and 72#72 erg s-1 cm-2 (2.7 Å) for NGC 7130 and IC 3639, respectively. Following Heckman et al (1997), we derive values for the monochromatic UV continuum luminosity at 1335 Å of the hidden Seyfert 1 nucleus of 2 73#73 f-1 L16#16 and 74#74 f-1 L16#16 for NGC 7130 and IC 3639, respectively, where f is the covering factor. The ratio of the relative numbers of type 1 and type 2 Seyfert nuclei (in the context of the standard unified model) implies that f < 0.25. We further adopt a bolometric correction factor of 5 (Elvis et al 1994), and therefore estimate that the lower limit to the bolometric luminosity of the hidden Seyfert 1 nucleus is 75#75L16#16 and 76#76 L16#16 for NGC 7130 and IC 3639, respectively. Using this procedure, Heckman et al estimated a lower limit to the luminosity of the hidden Seyfert 1 nucleus in Mrk 477 of 77#77 L16#16. These values represent a lower limit to the luminosities not only becuase of the upper limit to f, but because we have not applied any correction for intrinsic extinction (we have applied only a correction for Galactic extinction).

We can also use the case of NGC 1068, in which the bolometric luminosity of the hidden Seyfert 1 nucleus is about 1011 L16#16, based on its reflected spectrum (Pier et al 1994). We will refer these other four type 2 Seyfert galaxies to the fiducial value for NGC 1068 using three tracers of the intrinsic AGN luminosity: the [OIII]1#15007 emission-line, the nuclear radio power at 1.4 GHz, and the nuclear mid-IR monochromatic power at 1078#78 (Whittle 1992b; Heckman 1995). Taking the log-average ratio of these three measures, we find that the hidden Seyfert 1 nucleus in NGC 7130, NGC 5135, IC 3639, and Mrk 477 has a bolometric luminosity that is 30%, 20%, 13%, and 150% as luminous as NGC 1068 respectively. That is, we estimate corresponding bolometric luminosities of 79#79 L16#16, 80#80 L16#16, 81#81 L16#16, and 82#82 L16#16. These are consistent with (several times larger than) the lower limits to the luminosities from the CII 1#11335 line above.

Comparing these luminosities to those of the nuclear starburst (Table 5), we see that in these cases it appears that the bolometric luminosity of the hidden type 1 Seyfert nucleus is comparable to that of the nuclear starburst It will be important to see if this result of a rough scaling in the luminosity of the type 1 Seyfert nucleus and nuclear starburst is generally true in Seyferts.

Next: Conclusions Up: Discussion and implications Previous: Constraints on the starburst
Rosa Gonzalez
1998-06-20