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Research

Galaxy evolution and formation, and the co-evolution of E+A galaxies and AGN.

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Example of a prototypical E+A single-fiber spectrum from SDSS. 

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Refining the E+A Galaxy 

 E+A Galaxies are post-starburst galaxies whom rapidly quench all star formation after about 1 Gyr; the reason yet to be determined. By the time we are able to identify them, all O and B-type stars have died out, leaving behind an A-type population of stars to dominate the light of the galaxy, giving them their signature golden colour, and placing the system in the green valley range of evolution space. Throughout the last 6 years, I have developed a refined by-eye classification system for this galaxy type that focuses on:

  • A very specific continuum shape, noting a bluer-than-usual continuum.

  • Dn4000 ratio > 1.5 to indicate an older stellar population, not dominated by hot, young stars.

  • Strong Balmer absorption lines to indicate a recent and substantial starburst. 

  • A lack of Hα emission, and low to no [O II] emission to indicate that star formation has now ended.

Once a candidate sample is curated, we use the IFS capabilites of MaNGA to investiagte the spatially resolved entirety of the galaxy to prove E+Aness throughout the entirety of the system. to This carefully curated and confirmed set of E+A galaxies can serve as the basis of a series of investigations of

galaxy evolution-- in particular, studies of what may be

the last stage of transition between actively star-forming

and fully quenched galaxies.

 

See Greene et al., 2021 for information about this process.  

Plate-IFU: 8623-9102
MaNGA ID: 1-178823

Complete Catalog of E+A Galaxies from MaNGA MPL-11

The final data release (DR17) of SDSS-IV MaNGA MPL-11 is now complete and publicly available, containing a complete sample of 10,000+ spatially resolved, integral field spectroscopic galaxies. Using the Greene Method, we are in the process of finalizing a complete E+A catalog from this final release.

 

(in prep, estimated submission Sept, 2022). 

See the MaNGA DR17 Overview for more information about this data release. 

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The 2.5 meter telescope at Apache Point Observatory
Sunspot, New Mexico. Image credit APO Home Page

Exploring AGN activity in E+A Galaxies

One of the most efficient ways to quench a galaxy is by AGN feedback. While easily detectable AGN galaxies are usually associated alongside on-going intense starburst activity, and are most often found to be radio, x-ray and/or IR loud, many works have started looking into smaller, dimmer, and spectrally benign galaxies as a source of weak AGN emission, that could give insight into the early universe.

Even though E+A galaxies are small, the starburst died out 1 Gyr prior, and the system itself merged (theoretically) quite some time before that, it still tracks that these galaxies could contain a weak or turned-off AGN whose feedback was responsible for the galaxy’s gas starvation. While not necessarily extraordinary objects. E+A galaxies are unique intermediate systems, and exploring their particular evolution, and extended residence in the green valley, can hopefully provide insight into all galaxy dynamics.

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Plate-IFU: 8315-3703
MaNGA ID: 1-560826

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The BPT (Baldwin, Phillips and Terlevich) diagram diagnostic uses the intensity of the emission-line ratios shown above to classify extra-galactic objects into four categories, two of those being seyfert and LINER, and is one of the most widely used methods for the detection of centrally located AGN. The above diagrams show an E+A galaxy that is dominated by AGN activity leading us to believe that a dormant AGN exists in the system, even if evidence of that was no present in the single-fiber spectrum. 

Posters

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Refining the E+A Galaxy: A Spatially Resolved Spectral Analysis & Synthesis of Nearby Post-Starburst Systems in SDSS-IV MaNGA (MPL-5)

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Behind the Curtain: Revealing the effect of sub-grid models on supermassive black hole merger rates for LISA