Gaps in Globular Cluster Stellar Streams as Probes for Dark Matter in M31 and Other Galaxies

Cosmological simulations that include dark matter predict the existence of low-mass subhalos. These subhalos can perturb thin stellar streams formed by tidal disruption of globular clusters, creating a gap-like feature like those detected in Gaia data (e.g. GD-1). In Aganze et al. 2023, we predict that the Nancy Grace Roman Telescope should be able to detect these gaps in galaxies within 3 Mpc with resolved stars. This research is done in collaboration primarily with Dr. Sarah Pearson and Dr. Tjitske Starkenburg.

drawing A simulation of a mock image of a metal-poor GC stream in an external galaxy for 1-hour exposure with Roman with resolved stars. The gap from a dark matter subhalo of $\approx 5 \times 10^6$ solar masses is show at the center.

Galactic Archeology with Brown Dwarfs at Large Distances

Finding Brown Dwarfs and Low-mass Stars in Deep HST Parallel Fields with Machine Learning

In Aganze et al. 2022a, we used traditional index-selection methods, and machine learning techniques (random forests and neural networks) to isolate a sample of 164 M7-T9 ultracool dwarfs up to distances of ~2~kpc in the Galaxy. Similar surveys with JWST (such as the PASSAGES survey) will uncover a comparable number of objects in the galactic thick disk and halo.

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Top Left: Cutout from a processed image of an L dwarf in the WISP survey with the F140W filter (1.4 µm). Top Right: a 2D G141 (1.1-1.7 µm) spectrum of the same pointing. Bottom: 1D- Spectrum fitted to best-match spectral templates of dwarfs and metal-poor subdwarfs.

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Scaleheights and Ages Brown Dwarfs and Low-Mass Stars in Deep HST Parallel Fields

In Aganze et al. 2022b, we used the sample from Aganze et al. 2022a to constrain the scaleheight and ages using a simulation that takes into account the stellar mass function, multiplicity, UCD evolutionary models, galactic structure and survey selection function. We found that late-M dwarfs are generally older than L and T dwarfs as expected from cooling models, with median ages ranging from 3.6-2.4 Gyr.

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Figure from the paper showing the simulated age (blue) vs inferred age (green) of UCD sub-populations. Dots show the median age of a population.

Local M Dwarfs

Metal Poor GJ 660.1AB System

I’m also interested in the study of nearby UCDs. GJ 660.1AB is a binary system (M1 and M7 secondary) previously overlooked; in Aganze et al. 2016, we showed that the peculiarities in the spectrum of the secondary can be explained by its low metallicity.

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Moderate resolution SpeX SXD spectrum of the primary showing prominent atomic and molecular features in its atmosphere

Machine Learning Projects

I have mentored UCSD undergraduate students on summer projects that involve using supervised learning techniques (random forests and neural networks) to classify brown dwarfs and to identify rare populations (binaries, subdwarfs).

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