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

56 3 • IFS of a GEHR in NGC 6946
4.0
1e−13
◦A−1
)
s−2
Flux (erg cm−2
3.5
3.0
2.5
2.0
Counts103
7500 8000 8500 9000 9500 10000
Wavelength (◦A)
Figure 3.10: Upper panel: Spectrophotometric standard star BD+17 ◦ 4708. Bottom panel: Solid
(blue) line represents a extrated 1D spectrum of the star BD+17 ◦ 4708 and dashed (green) line a
smooth fit to the continuum. The atmospheric absorption features in the spectrum of the standard
star are clearly seen along all the wavelength coverage. Notice the strong absorptions in the 8900 -
9700 Å range. The scale is logarithmic in order to enhance the mean features.
absolute flux calibration in IFUs with filling factors less than 1. Assuming that the pointspread
function (PSF) of the star can be represented as a 2-dimensional Gaussian, it can be
divided in increasing rings apertures. The maximum is in the center, while the external ring
would have a minimum flux. Therefore, most of the flux would be concentrated in the first
rings. In the case of the one-pointing frame, the gap between the first ring (the first fiber),
and the second one (a ring of 6 fibers, as it can be seen in left upper panel of Figure 3.8),
can hold a important fraction of the flux of the star. This effect is clearly seen in the jump
of the flux ratio curve derived for a one fiber extraction to the 7 fibers one. Next rings would
have less weight in the total flux, as seen in the convergence of curves from 7 up to 37 fibers,
taking into account each case independently.
It is important to have a smooth final flux ratio curve. In general, this is accomplished
by convolving the spectra with a Gaussian kernel to match solutions between the measured
spectrum of the spectrophotometric standard star and its absolute value as obtained from
tables, so that the final flux ratio (i.e. sensitivity function) is a continuous, smooth curve.
Sometimes a smooth spline function of gaussian kernel is not enough, so another approach