Simulations I: Stars, Gas, Temperature, Metals
The size of ae galaxy is on the order of 30-60 kpc in
diameter and it is embedded in a filamentary structure (out of which
the galaxy forms).
Stars form in the highest density regions. In the simulations,
individual stars cannot be modeled, instead massive star "particles"
represent a population
of stars, including their distribution of masses and lifetimes.
This still allows us to model the evolution of the stars, including how
they build up heavy chemical elements and how the supernovae explode
(including the outward force and heating of their energy into the
surrounding medium). The exploding stars pollute the surrounding gas
with heavy elements like carbon, nitrogen, carbon, and oxygen. So,
the complete star-gas cycles taking place in galaxies is modeled.
* A parsec is a unit
of distance equal to 3.26 light years, where a light year is the unit
of distance light travels in a year (~31,500,00 seconds at 300,00
km/s). A kiloparsec (kpc) is a thousand parsecs.A
Megaparsec (Mpc) is a million parsecs.
We need simulations to guide our understanding of the spatial and
dynamic properties of the gas relative to the galaxies. These
simulations provide our only window on such knowledge. How are the
gas structures spatially distributed? What are the motions of the gas
structures? What is the distribution of metals ions in these gas
structures? And, how did they form and how will they evolve with
time?
The three panels show an integrated (over depth) slice of a simulated
galaxy at three different cosmological redshifts (top: z=2.3, furthest
in the past; center: z=1.3; and bottom: z=0.2, closer to the present
epoch z=0). The bar across the top of each panel is 1000 kpc = 1
Megaparsec (Mpc). For comparison, The Milky Way and Andromeda galaxy
are presently separated by 700 kpc. Cosmic time is increasing
downward. From left to right, stars, gas density (cm^-3), gas
temperature (Kelvin), and metal enrichment in units of solar
metallicity. Though hard to read, legends for the color scale are
provided in the vertical bar in the right hand side of each panel. As
time passes, more stars form and the two galaxies merge (happens at
z=0.6, not shown), Note that the galaxies are connected via the gas
filament between them (z=2.3 and z=1.3), but then comprise single gas
structure by z=0.2. Note that the gas temperature increases with
time; the filaments at higher redshift are relatively cool. Also note
that the gas becomes very metal enriched over a 1 Mpc volume by z=0.2.
We run "mock" QSO sightlines through the simulations and generate
"mock" QSO spectra and study them. In tandem with the direct
knowledge from the simulations, we learn a great deal about observed
absorption line systems I the real word.
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