7 research outputs found
Individual Elemental Abundances in Elliptical Galaxies
Using synthetic spectra to gauge the observational consequences of altering
the abundance of individual elements, I determine the observability of new Lick
IDS style indices designed to target individual elements. Then using these new
indices and single stellar population models, I investigate a new method to
determine Balmer series emission in a Sloan Digital Sky Surveys grand average
of quiescent galaxies. I also investigate the effects of an old metal-poor
stellar population on the near ultra violet spectrum through the use of these
new indices and find that the presence of a small old metal-poor population
accounts for discrepancies observed between index trends in the near UV and
optical spectral regimes. Index trends for 74 indices and three data sets are
presented and discussed. Finally, I determine the near nuclear line-strength
gradients of 18 red sequence elliptical Virgo cluster galaxies for 74 indices
Emission Corrections for Hydrogen Features of the Graves et. al 2007 Sloan Digital Sky Survey Averages of Early Type, Non-liner Galaxies
For purposes of stellar population analysis, emission corrections for Balmer
series indices on the Lick index system in Sloan Digital Sky Survey (SDSS)
stacked quiescent galaxy spectra are derived, along with corrections for
continuum shape and gross stellar content, as a function of the Mg Lick
index strength. These corrections are obtained by comparing the observed Lick
index measurements of the SDSS with new observed measurements of 13 Virgo
Cluster galaxies, and checked with model grids. From the H Mg
diagram a linear correction for the observed measurement is constructed using
best fit trend lines. Corrections for H, H and H are
constructed using stellar population models to predict continuum shape changes
as a function of Mg and Balmer series emission intensities typical of H{\sc
II} regions. The corrections themselves are fairly secure, but the
interpretation for H and H indices is complicated by the fact
that the H and H indices are sensitive to elemental abundances
other than hydrogen
NH and Mg Index Trends in Elliptical Galaxies
We examine the spectrum in the vicinity of the NH3360 index of Davidge &
Clark (1994), which was defined to measure the NH absorption around 3360 \AA
and which shows almost no trend with velocity dispersion (Toloba et al. 2009),
unlike other N- sensitive indices, which show a strong trend (Graves et al.
2007). Computing the effect of individual elements on the integrated spectrum
with synthetic stellar population integrated spectra, we find that, while being
well correlated with nitrogen abundance, NH3360 is almost equally well
anti-correlated with Mg abundance. This prompts the definition of two new
indices, Mg3334, which is mostly sensitive to magnesium, and NH3375, which is
mostly sensitive to nitrogen. Rather surprisingly, we find that the new NH3375
index shows a trend versus optical absorption feature indices that is as
shallow as the NH3360 index. We hypothesize that the lack of a strong index
trend in these near-UV indices is due to the presence of an old metal-poor
component of the galactic population. Comparison of observed index trends and
those predicted by models shows that a modest fraction of an old, metal-poor
stellar population could easily account for the observed flat trend in these
near-UV indices, while still allowing substantial N abundance increase in the
larger galaxies.Comment: 19 pages, 6 figures, 6 table
On the Anomalous Balmer Line Strengths in Globular Clusters
Spectral feature index diagrams with integrated globular clusters and simple
stellar population models often show that some clusters have weak H beta, so
weak that even the oldest models cannot match the observed feature depths. In
this work, we rule out the possibility that abundance mixture effects are
responsible for the weak indices unless such changes operate to cool the entire
isochrone. We discuss this result in the context of other explanations,
including horizontal branch morphology, blue straggler populations, and nebular
or stellar emission fill-in, finding a preference for flaring in M giants as an
explanation for the H beta anomaly.Comment: Submitted to the A