27,453 research outputs found
Chemical Evolution of the Carina Dwarf Spheroidal
We explore a range of chemical evolution models for the Local Group dwarf
spheroidal (dSph) galaxy, Carina. A novel aspect of our work is the removal of
the star formation history (SFH) as a `free parameter' in the modeling, making
use, instead, of its colour-magnitude diagram (CMD)-constrained SFH. By varying
the relative roles of galactic winds, re-accretion, and ram-pressure stripping
within the modeling, we converge on a favoured scenario which emphasises the
respective roles of winds and re-accretion. While our model is successful in
recovering most elemental abundance patterns, comparable success is not found
for all the neutron capture elements. Neglecting the effects of stripping
results in predicted gas fractions approximately two orders of magnitude too
high, relative to that observed.Comment: Accepted for publication in PoS (Proceedings of Science): Nuclei in
the Cosmos XII (Cairns, Aug 2012); 6 pages; 4 figure
Simulating a White Dwarf-dominated Galactic Halo
Observational evidence has suggested the possibility of a Galactic halo which
is dominated by white dwarfs (WDs). While debate continues concerning the
interpretation of this evidence, it is clear that an initial mass function
(IMF) biased heavily toward WD precursors (1 < m/Msol < 8), at least in the
early Universe, would be necessary in generating such a halo. Within the
framework of homogeneous, closed-box models of Galaxy formation, such biased
IMFs lead to an unavoidable overproduction of carbon and nitrogen relative to
oxygen (as measured against the abundance patterns in the oldest stars of the
Milky Way). Using a three-dimensional Tree N-body smoothed particle
hydrodynamics code, we study the dynamics and chemical evolution of a galaxy
with different IMFs. Both invariant and metallicity-dependent IMFs are
considered. Our variable IMF model invokes a WD-precursor-dominated IMF for
metallicities less than 5% solar (primarily the Galactic halo), and the
canonical Salpeter IMF otherwise (primarily the disk). Halo WD density
distributions and C,N/O abundance patterns are presented. While Galactic haloes
comprised of ~5% (by mass) of WDs are not supported by our simulations, mass
fractions of ~1-2% cannot be ruled out. This conclusion is consistent with the
present-day observational constraints.Comment: accepted for publication in MNRA
Observationally-Motivated Analysis of Simulated Galaxies
The spatial and temporal relationships between stellar age, kinematics, and
chemistry are a fundamental tool for uncovering the physics driving galaxy
formation and evolution. Observationally, these trends are derived using
carefully selected samples isolated via the application of appropriate
magnitude, colour, and gravity selection functions of individual stars;
conversely, the analysis of chemodynamical simulations of galaxies has
traditionally been restricted to the age, metallicity, and kinematics of
`composite' stellar particles comprised of open cluster-mass simple stellar
populations. As we enter the Gaia era, it is crucial that this approach
changes, with simulations confronting data in a manner which better mimics the
methodology employed by observers. Here, we use the \textsc{SynCMD} synthetic
stellar populations tool to analyse the metallicity distribution function of a
Milky Way-like simulated galaxy, employing an apparent magnitude plus gravity
selection function similar to that employed by the RAdial Velocity Experiment
(RAVE); we compare such an observationally-motivated approach with that
traditionally adopted - i.e., spatial cuts alone - in order to illustrate the
point that how one analyses a simulation can be, in some cases, just as
important as the underlying sub-grid physics employed.Comment: Accepted for publication in PoS (Proceedings of Science): Nuclei in
the Cosmos XIII (Debrecen, Jul 2014); 6 pages; 3 figure
High-resolution N-body Simulations of Galactic Cannibalism: The Magellanic Stream
Hierarchical clustering represents the favoured paradigm for galaxy formation
throughout the Universe; due to its proximity, the Magellanic system offers one
of the few opportunities for astrophysicists to decompose the full
six-dimensional phase-space history of a satellite in the midst of being
cannibalised by its host galaxy. The availability of improved observational
data for the Magellanic Stream and parallel advances in computational power has
led us to revisit the canonical tidal model describing the disruption of the
Small Magellanic Cloud and the consequent formation of the Stream. We suggest
improvements to the tidal model in light of these recent advances.Comment: 6 pages, 4 figures, LaTeX (gcdv.sty). Refereed contribution to the
5th Galactic Chemodynamics conference held in Swinburne, July 2003. Accepted
for publication in PASA. Version with high resolution figures available at
http://astronomy.swin.edu.au/staff/tconnors/publications.htm
Galactic Archaeology and Minimum Spanning Trees
Chemical tagging of stellar debris from disrupted open clusters and
associations underpins the science cases for next-generation multi-object
spectroscopic surveys. As part of the Galactic Archaeology project TraCD
(Tracking Cluster Debris), a preliminary attempt at reconstructing the birth
clouds of now phase-mixed thin disk debris is undertaken using a parametric
minimum spanning tree (MST) approach. Empirically-motivated chemical abundance
pattern uncertainties (for a 10-dimensional chemistry-space) are applied to
NBODY6-realised stellar associations dissolved into a background sea of field
stars, all evolving in a Milky Way potential. We demonstrate that significant
population reconstruction degeneracies appear when the abundance uncertainties
approach 0.1 dex and the parameterised MST approach is employed; more
sophisticated methodologies will be required to ameliorate these degeneracies.Comment: To appear in "Multi-Object Spectroscopy in the Next Decade: Big
Questions, Large Surveys and Wide Fields"; Held: Santa Cruz de La Palma,
Canary Islands, Spain, 2-6 Mar 2015; ed. I Skillen & S. Trager; ASP
Conference Series (Figures now optimised for B&W printing
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