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Measuring Stellar Popula1on Gradients in Illustris Stellar Halos
Ben Cook 05/04/15 Astro 193 Final Presenta1on


What is a "Stellar Halo"?
· Huge, diffuse region around galaxies
­ 100-
200 kpc around MW type galaxies ­ Only few % of stellar mass

· Retain memory of galac1c accre1on
­ Large gal-
gal variance

· Believed to be a key to understanding build-
up and evolu1on of galaxies
Mar1nez-
Delgado+2010


Stellar Popula1on Gradients in Illustris
· High resolu1on, cosmological simula1on with gas physics/star forma1on · Recover all stellar par1cles in a given galaxy (and its stellar halo)


Stellar Popula1on Gradients in Illustris
· High resolu1on, cosmological simula1on with gas physics/star forma1on · Recover all stellar par1cles in a given galaxy (and its stellar halo) · Stellar popula1on gradients · Age, Metallicity · Clues to what contributed to halo in that region


Stellar Popula1on Gradients in Illustris
· High resolu1on, cosmological simula1on with gas physics/star forma1on · Recover all stellar par1cles in a given galaxy (and its stellar halo) · Stellar popula1on gradients · Age, Metallicity · Clues to what contributed to halo in that region · Replicate observa1ons by: · Average over radial bins (weight by luminosity in some band)


Stellar Popula1on Gradients in Illustris
· High resolu1on, cosmological simula1on with gas physics/star forma1on · Recover all stellar par1cles in a given galaxy (and its stellar halo) · Stellar popula1on gradients · Age, Metallicity · Clues to what contributed to halo in that region · Replicate observa1ons by: · Average over radial bins (weight by luminosity in some band) · Fit to power-
law gradient · Research ques1on: how does this gradient correlate with (eg.) insitu frac1on?


Sta1s1cal Uncertainty ...
· Measured using Bootstrap resampling
­ Intrinsic uncertainty on gradient, from simula1on alone


vs. Systema1c Uncertainty
· Calculate gradients for 100 random projec1ons
­ Es1mate observa1onal uncertain1es


Results
· Variance due to projec1on effects dominates over sta1s1cal uncertainty


Thanks!