Bibcode
DOI
Cenarro, A. Javier; Beasley, Michael A.; Strader, Jay; Brodie, Jean P.; Forbes, Duncan A.
Referencia bibliográfica
The Astronomical Journal, Volume 134, Issue 1, pp. 391-410.
Fecha de publicación:
7
2007
Número de citas
50
Número de citas referidas
46
Descripción
We present high-quality Keck spectroscopic data for a sample of 20
globular clusters (GCs) in the massive E0 galaxy NGC 1407. A subset of
20 line-strength indices of the Lick/IDS system has been measured for
both the GC system and the central integrated starlight of the galaxy.
Ages, metallicities, and [α/Fe] ratios have been derived using
several different approaches. The majority of GCs in NGC 1407 studied
are old, follow a tight metallicity sequence reaching values slightly
above solar, and exhibit mean [α/Fe] ratios of ~0.3 dex. In
addition, three GCs are formally derived to be young (~4 Gyr), but we
argue that they are actually old GCs hosting blue horizontal branches.
We report, for the first time, evidence for the existence of two
chemically distinct subpopulations of metal-rich (MR) GCs. We find that
some MR GCs exhibit significantly larger [Mg/Fe] and [C/Fe] ratios.
Different star formation timescales are proposed to explain the
correlation between Mg and C abundances. We also find striking CN
overabundances over the entire GC metallicity range. It is interesting
to note that the behavior of C and N in metal-poor GCs clearly deviates
from that in MR GCs. In particular, for MR GCs, N increases dramatically
while C essentially saturates. This may be interpreted as a consequence
of the increasing importance of the CNO cycle with increasing
metallicity.