A spatially resolved study of ionized regions in galaxies at different ...

2.4. Discussion 31
1e−13
7
1
6
F(Hα)
J-V
0.2
0.0
Flux(Hα) (erg s−1
cm−2 )
5
4
3
2
1
34
2
10
2
34
7
7
E(B-V) = 0.1
8
11
5
−0.2
−0.4
−0.6
−0.8
J-V
1
0
10
−1.0
8 5
9
9 11
0.2 0.3 0.4 0.5 0.6
J-H
Figure 2.9: Hα and J-V versus J-H plot for the clusters identified in section 2.3.1. A clear correlation
of decreasing Hα with redder colors points to an aging effect within the ongoing starburst phase.
due to aging of the burst or to different clusters having different masses, less massive bursts
producing fewer ionizing photons 6 . However, if this latter were case there is no clear reason
why there should be a relationship with color, which is expected in the scenario of the clusters
aging. We conclude that most of the trend seen in this figure may be due to aging, with some
component due to different initial masses.
Knot 1 is the brightest in Hα and the results of the photometric analysis using CHORI-
ZOS give the youngest age, ∼ 3 Myr, with lowest extinction. Knots 2, 34, 7, 8, 9, 10 have
intermediate age, ∼ 4 − 7 Myr, with an intermediate extinction, except may be knot 9 which
has some indications for a somewhat higher extinction. Knots 5 and 11 are older, ∼ 10 Myr.
In summary, from the cluster analysis of individual bright knots and from the integrated
photometry of the whole complex there are clear indications that there is a complex history
of star formation in NGC 5471, with indications of an older population of B stars and the
6 Extinction may also play a small role, but it would require extinction values significantly larger than
reported in the literature, which are lower than E(B-V)=0.14.