Galaxy Formation and Evolution

Dr. Pimol MothAstronomy Instructor

Hartnell College

Hubble Tuning Fork Diagram

Top Down Scenario of Galaxy FormationEggen, Lynden-Bell, & Sandage 1962

Bottom Up Scenario of Galaxy Formation(Searle and Zinn 1977)

Early Universe showed slight variations in density!

Are the density variations the seeds of galaxy formation??

View of the Early Universe with WMAP (2003)

The Hubble Deep Field North

• 1995• 10 days • WFPC2 (U300,

B450, V606) and NICMOS ( I814,

J110, H160) filters• 3000 galaxies

Young Galaxies in the Hubble Deep Field

• smaller• bluer• higher star

formation• more

irregular

Methodology

• Fit elliptical isophotes to the Hubble Deep Field North Wide Field Planetary Camera 2 (WFPC-2) and Near Infrared Camera and Multi-Object Spectrometer (NICMOS) imaging data

• Obtained the rest-frame (UV218 -U300 )0 color profiles of 33 low redshift galaxies (0.5 ≤ z ≤ 1.2) with I814 < 25, and 50 high-redshift galaxies (2.0 ≤ z ≤ 3.6) with H160 < 27

Redshift vs. Age

• (0.5 ≤ z ≤ 1.2): 8.6 Gyr to 5.1 Gyr• (2.0 ≤ z ≤ 3.6): 3.3 Gyr to 1.75 Byr

(Uv-U) Color Profiles of Low Redshift (0.5 ≤ z ≤ 1.2) Galaxies

(Uv-U) Color Profiles of High Redshift (2.0 ≤ z ≤ 3.5) Galaxies

Color Gradients of all Galaxies

Moth & Elston 2002 Results

• The mean of the color gradients for high redshift galaxies (2.0 ≤ z ≤ 3.5 ) was 0.272 ± 0.007 mag dex-1

• The mean of the color gradients for low redshift galaxies was (0.5 ≤ z ≤ 1.2) -0.091 ± 0.007 mag dex-1

• Change in color gradients demonstrate that star formation moved from the center of the galaxy to the outer parts over time

Moth & Elston 2002 Results

• Changes are caused by galaxy mergers • Major mergers in the past fueled gas towards the

center and triggered star formation in the centers of the galaxies.

• Over time, galaxies experience minor mergers that cause star formation to occur in the outer parts of the galaxies

• Similar results are seen in a sample of 22 galaxies inthe Hubble Deep Field South (Tam and Tenjes 2006)

Galaxy Mergers

Mergers cause the shapes of galaxies to change over time.

Recent Results

• Results of color profiles of 3248 galaxies in the Great Observatories Origins Deep Survey, (GOODs)-South field out to z=3 (Welikala &Kneib 2012) also showed positive color gradients (for galaxies with z > 2)

• Gargiulo, Saracco, & Longhetti 2011 demonstrated that 20 early-type galaxies (ETGs) at 1 < z < 2 selected from the GOODS-South field detect significant (UV-Urestframe) color gradients in 10 galaxies. They detect five ETGs with positive color gradients and five galaxies with negative color gradients.

• Mármol-Queraltó et al 2013 investigate the color profiles of satellite galaxies out to z = 2 and find that they have younger cores and postulate that if satellite galaxies create the envelopes of nearby massive galaxies, it would be compatible with the blueing in the envelope detected in nearby galaxies

Hubble Tuning Fork Diagram

Galaxy Mergers create Galaxy Clusters

The Local Group

The Local Super Cluster

Large Scale Structure of the Universe

Large-Scale Structure in the Universe

Superclusters, walls,and voids dominate thelarge scale structureof the Universe