Up: Star formation history of environments
We present the first of a series of papers (Longhetti et al. 1997a,b,c)
that will study the star formation history in early-type galaxies.
In the present paper, we present a sample of 20 shell galaxies and 32 pair members
in low density environments that is studied for this purpose.
Most of the objects show present/past interaction
signatures.
The paper describes the observations and the reduction of the
spectrophotometric data obtained from spectra
in the wavelength range of 3700 Å
5700 Å at
2.1 Å FWHM resolution.
A set of 16 red (
4200 Å) nuclear (5
)line-strength indices defined by the Lick Group has been obtained and
converted into the Lick-IDS "standard'' system. 5 reference galaxies,
selected from the G93 sample, are also included to test the
results of the procedure.
Three blue (
4200) nuclear line-strength indices, namely
(4000 Å), H+K(CaII) and H
/FeI, have been also
determined with the purpose of tracing recent starbursts in the galaxies
history.
The kinematics of the gas and of the stellar components are the subject
of the Paper II. Stellar kinematical data (organized and discussed in the Paper II)
have been used to correct present line-strength indices for velocity dispersion.
![\begin{figure}
\centering
\includegraphics [width=8cm,clip=]{ds1429f5.eps}\end{figure}](/articles/aas/full/1998/11/ds1429/Timg81.gif) |
Figure 5:
Atlas of the spectra of the observed galaxies:
galaxies from the G93 sample used as spectrophotometric templates.
Plots are in the rest frame, and the fluxes are in
arbitrary units. The most remarkable features
are labelled on top |
![\begin{figure*}
\centering
\includegraphics [width=7.5cm]{1429f6a.eps}
\includegraphics [width=7.5cm]{1429f6b.eps}
a)\hspace{8cm} b)\end{figure*}](/articles/aas/full/1998/11/ds1429/Timg82.gif) |
Figure 6:
Same as Fig. 5 for shell galaxies |
![\begin{figure*}
\includegraphics [width=6.8cm]{1429f7a.eps}
\includegraphics [width=6.8cm]{1429f7b.eps}
\includegraphics [width=6.8cm]{1429f7c.eps}\end{figure*}](/articles/aas/full/1998/11/ds1429/Timg83.gif) |
Figure 7:
Same as Fig. 5 for pair members |
A fraction of the galaxies of the present study shows detectable
emission lines, as can be deduced from the Atlas of the spectra (Figs. 5
to 7). A discussion about the physical conditions of the (e.g. LINER
properties of the nucleus, ect.) is also given in the Paper II.
Line-strength indices suffer the contamination caused by
emission lines. G93 corrected the H
absorption line-strength for the
filling due to the H
emission by means of a relation between the
H
line emission strength and that of the [OIII] line at
5007 Å. Namely
H
=0.7[OIII]. The validity of this
correction has been questioned by Carrasco et al. (1995).
We discuss
the correction of the line-strength indices for the emission line
filling in a forthcoming papera forthcoming paper.
Up: Star formation history of environments
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