Cosmic Murder Mystery: Investigating How Die

JENN COOPER Engineering Showcase 10 April 2021 Overview • Introduction to Evolution

• Cosmic murder mystery: what kills galaxies?

○ Method 1: Dead Galaxy Fraction by colors

○ Method 2: -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 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 : 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

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.