Leo T
Project Goal
To characterize the Leo T dwarf galaxy, the only currently known dwarf to contain gas and to have undergone recent star formation, and analyze the object based on new and old data sets.
My Role(s):
Part-time undergraduate researcher, responsible for analyzing data, documenting procedures and results, and performing literature reviews, working under the mentorship of Professor Marla Geha.
Technical Skills: Non-technical Skills:
Python programming Time management
Literature review Communication
Data analysis
Critical thinking
Results
Completed a stellar membership for Leo T: I vetted a sample of 500+ stars based on radial velocity, color, proper motion, metallicity, and parallax to determine which stars are members of the dwarf galaxy and which are foreground interlopers. I performed a literature review for Leo T spaning 25+ papers and compiled my readings into a reference document.
Color image centered on Leo T (Irwin et al. 2007)
Key Takeaways
There is often more than meets the eye when it comes to research, particularly for a field like astrophysics. In a field where you can't directly perform experiments and events occur over timescales that span millions if not billions of years, you can infer much from manipulating data and understanding first principles.
Project Overview & Process
Leo T was discovered in 2007, and since then, there have been many papers exploring various properties of the dwarf galaxy, ranging from its stellar kinematics to spatial orientation and density of its gas. This object is especially interesting to astronomers because it is the only known dwarf galaxy to contain gas and star-forming material. It has displayed active star formation in the recent past, unlike most other dwarf galaxies, which had been quenched billions of years ago.
My major contribution to this project was performing a stellar membership. To study the kinematic and structural properties of Leo T, we needed to vet the 500+ stars from the DEep Image Multi-Object Spectrograph (DEIMOS) on the Keck telescope to obtain a set of Leo T candidate member stars. First, we perform a crude cut based on the expected color-magnitude distribution of Leo T members to weed out obvious foreground stars. We perform a second crude cut based on the expected system velocity of ~38 km/s (Simon & Geha, 2007). All stars with radial velocities that deviate largely from the systemic velocity were cut from the sample. Additionally, we cut out any stars with large radial velocity errors.
We then perform finer cuts based on metalicity, parallax, and proper motion. For the metalicity-based cuts, we follow R. P. Schiavon et al. 1997 and Battaglia et al. 2012 to discriminate between foreground dwarfs and red giant branch stars. Next, we perform sigma clippings on the radial velocity and stellar parallax. Finally, for the proper motion cut, the goal is to exclude targets with confidently measured proper motions far from the expected system proper motion ( obtained from McChonnachie & Venn, 2020). Due to the distance of Leo T (~420 kiloparsecs), it is difficult to obtain proper motion measurements for the stars. For the few stars that presented with a measured proper motion, there were large error bars that made it challenging to confidently exclude these targets. As a result, no stars were excluded based on this criterion. The remaining data set contained some velocity outliers that were excluded. The final data set consists of ~60 targets and contained within this sample are the original 19 Leo T member stars identified in Simon & Geha, 2007.