2,364 research outputs found
A Progress Report on the Caltech Faint Galaxy Redshift Survey
I review recent progress on determining the spectral energy distributions and
luminosity functions for galaxies in the large magnitude limited sample in the
region of the HDF-North of the Caltech Faint Galaxy Redshift Survey.Comment: Invited contribution to Deep Fields meeting, Munich, Oct 2000, to be
published by Springer Verlag, ESO Astrophysics Symposia Series, reformatted
to use AASTex macros. 8 pages with 4 figure
[Rezension zu:] Ruth Katz, "The Lachmann problem" : an unsung chapter in comparative musicology. Jerusalem: The Hebrew University Magnes Press, 2003 (The Jewish Music Research Centre in collaboration with the Jewish Nationaland University Library)
Star Formation in the Hubble Deep Field North
I am currently analyzing the emission line spectra of the approximately 600
galaxies from the sample of Cohen et al. (2000) and Cohen (2001) in the region
of the HDF-North with z<1.5. A progress report on this effort of the Caltech
Faint Galaxy Redshift Survey is presented.Comment: For the proceedings of the meeting held in Cozumel, March 2002 on
Galaxy Evolution: Theory and Observations, to be edited by V. Avila-Reese, C.
Firmani, C. Frenk, & C. Allen, RevMexAA SC (2002
Magnesium Isotopes in Halo Stars
We have determined Mg isotope ratios in halo field dwarfs and giants in the
globular cluster M71 based on high S/N high spectral resolution (R = 10)
Keck HIRES spectra. Unlike previous claims of an important contribution from
intermediate-mass AGB stars to the Galactic halo, we find that our
Mg/Mg ratios can be explained by massive stars.Comment: Proceedings, First Stars III, July 16-20, 2007, Santa F
The Chemical Evolution of the Draco Dwarf Spheroidal Galaxy
We present an abundance analysis based on high resolution spectra of 8 stars
selected to span the full range in metallicity in the Draco dwarf spheroidal
galaxy. We find [Fe/H] for the sample stars ranges from -1.5 to -3.0 dex.
Combining our sample with previously published work for a total of 14 luminous
Draco giants, we show that the abundance ratios [Na/Fe], [Mg/Fe] and [Si/Fe]
for the Draco giants overlap those of Galactic halo giants at the lowest [Fe/H]
probed, but are significantly lower for the higher Fe-metallicity Draco stars.
For the explosive alpha-elements Ca and Ti, the abundance ratios for Draco
giants with [Fe/H] > -2.4 dex are approximately constant and slightly
sub-solar, well below values characteristic of Galactic halo stars. The
s-process contribution to the production of heavy elements begins at
significantly lower Fe-metallicity than in the Galactic halo.
Using a toy model we compare the behavior of the abundance ratios within the
sample of Draco giants with those from the literature of Galactic globular
clusters, and the Carina and Sgr dSph galaxies. The differences appear to be
related to the timescale for buildup of the heavy elements, with Draco having
the slowest rate.
We note the presence of a Draco giant with [Fe/H] < -3.0 dex in our sample,
and reaffirm that the inner Galactic halo could have been formed by early
accretion of Galactic satellite galaxies and dissolution of young globular
clusters, while the outer halo could have formed from those satellite galaxies
accreted later.Comment: Submitted to ApJ Dec 22, 2008; accepted June 4, 2009. 75 pages
including 22 figures and 9 table
Detailed Abundances of Two Very Metal-Poor Stars in Dwarf Galaxies
The most metal-poor stars in dwarf spheroidal galaxies (dSphs) can show the nucleosynthetic patterns of one or a few supernovae (SNe). These SNe could have zero metallicity, making metal-poor dSph stars the closest surviving links to Population III stars. Metal-poor dSph stars also help to reveal the formation mechanism of the Milky Way (MW) halo. We present the detailed abundances from Keck/HIRES spectroscopy for two very metal-poor stars in two MW dSphs. One star, in the Sculptor dSph, has [Fe I/H] = -2.40. The other star, in the Ursa Minor dSph, has [Fe I/H] = -3.16. Both stars fall in the previously discovered low-metallicity, high-[α/Fe] plateau. Most abundance ratios of very metal-poor stars in these two dSphs are largely consistent with very metal-poor halo stars. However, the abundances of Na and some r-process elements lie at the lower end of the envelope defined by inner halo stars of similar metallicity. We propose that the metallicity dependence of SN yields is the cause. The earliest SNe in low-mass dSphs have less gas to pollute than the earliest SNe in massive halo progenitors. As a result, dSph stars at –3 < [Fe/H] < –2 sample SNe with [Fe/H] Lt –3, whereas halo stars in the same metallicity range sample SNe with [Fe/H] ~ –3. Consequently, enhancements in [Na/Fe] and [r/Fe] were deferred to higher metallicity in dSphs than in the progenitors of the inner halo
Globular Cluster Abundances and What They Can Tell Us About Galaxy Formation
We review the properties of globular clusters which make them useful for
studying the Galactic halo, Galactic chemical evolution, and the early stages
of the formation of the Milky Way. We review the evidence that GCs have a
chemical inventory similar to those of halo field stars. We discuss the
abundance ratios for dSph galaxies and show that it is possible to have formed
at least part the Galactic halo field stellar population by dissolving globular
clusters and/or accreting dSph galaxies but only if this occurred at an early
stage in the formation of the Galaxy. We review the constraints on halo
formation timescales deduced from the low Mg isotopic ratios in metal-poor halo
field dwarfs which indicate that AGB stars did not have time to contribute
significantly, while M71 contains two populations, one without and also one
with a substantial AGB contribution. We review the limited evidence for GCs
with a second population showing additional contributions from SNII, currently
confined to Omega Cen, M54, and M22, all of which may have been the nuclei or
central regions of accreted galaxies. We check our own data for additional such
GCs, and find preliminary indications that NGC 2419, a massive GC far in the
outer Galactic halo, may also belong to this group.Comment: Invited Talk: IAU Symp. 266, Star Clusters - Basic Building Blocks
Throughout Time and Space, proceedings to be published by Cambridge
University Pres
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