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Emission line spectrum

Here we present only the results of the emission line spectrum that could be related to the starburst activity in these galaxies. However, we have to first to point out that the nuclear spectra show strong high-excitation emission lines such as [NeV] 1#13426 and HeII 1#14686, and line ratios that are typical of type 2 Seyfert nuclei. In particular, creating the NeV ion requires a copious supply of soft X-rays (E > 0.1 keV), and this rules out an ordinary population of hot (O) stars as the only photoionization source for the emission-line gas. After correcting by reddening, the ratio [NeV] 1#13426/H10#10 measured in our spectra is 0.6, 0.4, and 0.7 for NGC 7130, NGC 5135 and IC 3639, respectively.

NGC 7130 and NGC 5135 show evidence of their composite spectra in the profile of the H10#10 emisssion line. H10#10 is resolved into two components. In NGC 7130 the narrow and the broad components have FWHM's of 4.8 Å (70#70300 km s-1) and 15.8 Å(70#70960 km s-1) and fluxes of 1.3511#1110-14 erg s-1 cm-2 and 8.211#1110-14 erg s-1 cm-2, respectively. The broad component is blueshifted by 70#70200 km s-1with respect to the narrow one, which is at the systemic velocity. These results are in agreement with those reported by Shields & Filippenko (1991). We find a similar result in NGC 5135. The FWHM of the two components of H10#10 is 4.3 Å (260 km s-1) and 10.4 Å (640 km s-1), with the broad component blueshifted by 170 km s-1 with respect to the narrow one, which is also blueshifted by 65 km s-1 with respect to the systemic velocity (Figure 21a). In IC 3639, H10#10 is well fitted with only one component with FWHM of 5.2 Å (320 km s-1). Shields & Filippenko (1991) suggest that the narrow component of H10#10 in NGC 7130 is associated with the starburst component and the broad one with the AGN. This latter component would have to be associated with the so-called Narrow-Line Region of the AGN, since the widths of the broad components we observe is much lower than the width of Balmer lines formed in the Broad Line Region Thus, we don't believe that it could be associated with the hidden Seyfert 1 nucleus.

[OIII] 1#15007 is also resolved in two components in NGC 7130 and NGC 5135. IC 3639 is fitted with only one component of FWHM of 7.6 Å (450 km s-1). The two components in NGC 7130 have FWHM of 19.4 Å (1160 km s-1) and 6.9 Å (410 km s-1), with the narrow one blueshifted by 70 km s-1 with respect to the broad one which is at the systemic velocity. The fluxes are 4.111#1110-14 erg s-1 cm-2 and 9.211#1110-14 erg s-1 cm-2 for the narrow and broad component, respectively. In NGC 5135 the FWHM of the two components is 4.4 Å (260 km s-1) and 10.3 Å (610 km s-1), with the broad one blueshifted by 4.2 Å (250 km s-1) with respect to the systemic velocity (Figure 21b). The fluxes are 9.211#1110-14 erg cm-2 s-1 and 7.711#1110-14 erg cm-2 s-1 for the narrow and broad components, respectively.

HeII 1#14686 in NGC 7130 and NGC 5135 is also resolved into two components, but not in IC 3639. In NGC 7130, we can not fit the line properly due to the absorption features close to 4686 Å that make the position of the continuum very uncertain. Consequently, the fluxes and FWHM's can not be estimated to better than in a factor of two. However, it is clear that HeII shows a broad component. In NGC 5135, the broad component of FWHM 8.2 Å (525 km s-1) is blueshifted by 2.5 Å (150 km s-1) with respect to the narrow one (FWHM = 3.7 Å). The fluxes are 2.211#1110-15erg cm-2 s-1and 3.511#1110-15 erg cm-2 s-1 for the narrow and broad components respectively. Thus, the blueshifted component in H10#10, [OIII] and HeII 1#14686 could represent high velocity gas in the Narrow Line Region, as seen in other Seyfert nuclei (Wilson & Heckman 1985 and references therein), or an outflow of gas resulting from the star formation activity in the nuclei of these two galaxies. Outflowing gas is also a very common phenomenon in starburst galaxies (Heckman, Armus, & Miley, 1990).


next up previous
Next: Discussion and implications Up: Ground-based near-UV through near-IR Previous: Hydrogen recombination lines
Rosa Gonzalez
1998-06-20