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Cosmic Murder Mystery: Investigating How Galaxies Die

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Cosmic Murder Mystery: Investigating How Galaxies Die Cosmic Murder Mystery: Investigating How Galaxies Die JENN COOPER Engineering Showcase 10 April 2021 Overview • Introduction to Galaxy Evolution • Cosmic murder mystery: what kills galaxies? ○ Method 1: Dead Galaxy Fraction by colors ○ Method 2: Star-formation Rates by Hydrogen • Conclusions NASA, HUDF BLUE: STAR FORMING NGC 1232 BLUE: STAR FORMING RED DEAD NGC 1232 VICTIM BLUE: STAR FORMING RED DEAD NGC 1232 THE ACCUSED Galaxy Cluster Galaxy Cluster Abell 370 credit: NASA Galaxy Cluster - Hot gases - Dense - Chaotic Galaxy Cluster Abell 370 credit: NASA Galaxy Cluster - Hot gases - Dense - Chaotic - Lots of dead galaxies! Galaxy Cluster Abell 370 credit: NASA Galaxy Cluster Field EVIDENCE METHOD 1: COLORS U: 364 nm V: 540 nm J: 1235 nm METHOD 1: COLORS Flux of galaxy at each 흺: U, V and J U: 364 nm V: 540 nm J: 1235 nm METHOD 1: COLORS Williams et al 2009: Found a relation of these 3 흺 for whether a galaxy is dead or alive METHOD 1: COLORS Dead Fraction = Number Dead Galaxies Number Total Galaxies METHOD 1: COLORS Dataset: 200 Galaxies in Clusters & 1000 Galaxies not in Clusters METHOD 1: RESULTS CLUSTERS FIELD FRACTION OF DEAD GALAXIES 4 5 6 7 8 BILLIONS OF YEARS AGO Cooper et al. 2021 METHOD 1: Conclusions > 6 billion years ago: Clusters & CLUSTERS FIELD the Field have FRACTION same % of dead OF DEAD GALAXIES galaxies 4 5 6 7 8 BILLIONS OF YEARS AGO Cooper et al. 2021 METHOD 1: Conclusions > 6 billion years ago: Clusters & CLUSTERS FIELD the Field have FRACTION same % of dead OF DEAD GALAXIES galaxies < 6 billion years ago: Clusters have higher % of 4 5 6 7 8 dead galaxies BILLIONS OF YEARS AGO Cooper et al. 2021 METHOD 1: VERDICT Clusters are the prime murder suspect 6 billion years ago METHOD 2: Hydrogen Hubble Space Telescope METHOD 2: Hydrogen We want to find how fast a galaxy makes stars: METHOD 2: Hydrogen We want to find how fast a galaxy makes stars: Hydrogen → fuel for stars Gas is heated & compressed → photon METHOD 2: Hydrogen We want to find how fast a galaxy makes H-alpha stars: Hydrogen-alpha emission flux → star formation rate (Kennicutt & Evans 2012) micrometers METHOD 2: Hydrogen We want to find how fast a galaxy makes H-alpha stars: Hydrogen-alpha emission flux → star formation rate (Kennicutt & Evans 2012) micrometers METHOD 2: Hydrogen Rate that the Galaxy Forms Stars Whitaker et al. 2012 Mass of the Galaxy METHOD 2: Hydrogen Rate that the Galaxy Forms Stars Whitaker et al. 2012 Mass of the Galaxy METHOD 2: Hydrogen Dataset (subset from Method 1): 76 Galaxies in Clusters & 80 Galaxies not in Clusters 5 - 6 billion years ago METHOD 2: Results Rate that the Galaxy Forms Stars CLUSTER GALAXY FIELD GALAXY Cooper et al. 2021 METHOD 2: VERDICT Rate that the Galaxy Forms Stars In agreement with Tiley et al. NO DIFFERENCE2020 CLUSTERS FIELD Cooper et al. 2021 METHOD 2: VERDICT Clusters are NOT murdering galaxies METHOD 2: VERDICT Clusters are NOT murdering galaxies However…. METHOD 2: Results We expect that all galaxies on the left plot are star-forming by COLOR on the main sequence Rate that the Galaxy Forms Stars CLUSTERS FIELD METHOD 2: VERDICT However…. If we compare galaxies with Method 1 (colors) and Method 2 (star-formation) Cooper et al. 2021 METHOD 2: RESULTS We find that there are dead galaxies with star-formation! METHOD 1 METHOD 2 Rate that the Galaxy U - V Forms STAR-FORMING Stars DEAD Cooper et al. 2021 V - J FINAL VERDICT ● By colors: galaxy clusters are the culprit ~6 billion years ago FINAL VERDICT ● By colors: galaxy clusters are the culprit ~6 billion years ago ● There are star-forming galaxies masquerading as being dead FINAL VERDICT ● By colors: galaxy clusters are the culprit ~6 billion years ago ● There are star-forming galaxies masquerading as being dead ○ We observe them as they are being killed or ○ They have black holes that are obscuring star-formation ○ Occurs in cluster & field ○ Clusters cannot be the culprit MORE EVIDENCE NEEDED ● We need more star-formation (Method 2) observations of galaxies 4 - 8 billion years ago to see how many dead galaxies are actually forming stars! ○ Change color classification? ● Visual inspection of the galaxies ○ How are they dying? ○ Where is the star-formation? ○ Measure how large they are FINAL VERDICT Clusters are free to go….for now Thank you! Acknowledgements References Cooper J. R., et al. 2021, MNRAS submitted. Kennicutt R. C., Evans N. J., 2012, ARA&A, 50, 531 Tiley A. L., et al., 2020, MNRAS, 496, 649. Williams R. J., Quadri R. F., Franx M., van Dokkum P., Labbé I., 2009, ApJ, 691, 1879. Whitaker K. E., van Dokkum P. G., Brammer G., Franx M., 2012, ApJ, 754, L29..
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