Who am I?

I grew up in Davis, CA, a small-ish town in the valley of California. Unlike most small towns in the middle of farmland, there is a decent chance that you (likely an academic) know of my hometown as the location of UC Davis. I moved to the East Coast in 2013 to get my bachelor's at Tufts University, where I was advised by Danilo Marchesini. In 2017, I moved down to Princeton for graduate school; my advisor was Jenny Greene. I got my PhD in 2022, after which I moved slightly north to Connecticut where I became a YCAA Prize Fellow at the Yale Center for Astronomy and Astrophysics; in 2025, I'll head back to California as a Kavli fellow at the Kavli Center for Particle Astrophysics and Cosmology (KIPAC).

Where am I?

Office

Bluesky

Github

What do I do for fun (besides physics)?

Sport climbing in MA

More sport climbing in MA

Biking in CT

Bouldering in TN

Collaborations

I have the pleasure of participating in several great past and ongoing collaborative efforts.

See below for information and links to some of the surveys that I have been a part of over the years.

The Merian Survey

The Merian Survey will capture spatially-resolved emission properties for an estimated 100,000 dwarfs down to an Hα equivalent width of 10 Å and a stellar mass of 10⁸ solar masses. Merian has two main science goals: to characterize the star formation properties of bright dwarfs, and to measure the stellar-to-halo mass relation of low-mass galaxies via weak lensing. The survey utilizes two custom-built medium-band filters on the Dark Energy Camera (DECam) centered on [OIII] and Hα emission at 0.06<z<0.10 that will cover around 800 square degrees of the HSC-SSP footprint.

The Satellites Around Galactic Analogs Survey

The SAGA survey is a recently-completed spectroscopic census of the satellite galaxies around 101 nearby Milky Way analogs. The survey identified 300+ satellites with a mass-complete sample down to stellar masses of 10^7.5 solar masses, elucidating the nature of our own galaxy in a cosmological context.

The Prime Focus Spectrograph Subaru Strategic Program

PFS-SSP is the upcoming strategic program survey associated with the new flagship spectrograph on the Subaru Telescope. The NIR wavelength coverage, fast fiber positioner system, and high sensitivity of the Prime Focus Spectrograph make it an optimal workhorse instrument for a broad variety of science goals: PFS-SSP has three main science working groups: Cosmology, Galaxy Evolution, and Galactic Archaeology.

The Hyper Suprime-Cam Subaru Strategic Program

HSC-SSP is the 5-year flagship survey of the Hyper Suprime-Cam imager on the 8m Subaru Telescope. It surveyed more than 1000 square degrees of the sky in 5 optical broadbands (grizy) at high spatial resolution (average seeing of approximately 0.7 arcsec) and depth (five sigma point source depth of r~26).

CV

Welcome!

Galaxies are versatile, if immutable, laboratories. They are simultaneously tracers of larger scale cosmological processes and the laboratories in which smaller scale astrophysics proceeds. Given that we are not able to create either universes nor stars in the lab, my work focuses on how to best use the cosmic laboratories at our disposal to understand the physical processes that shape them.

My main interest is in the low-mass galaxy regime, where I think about how dwarf galaxies can inform our understanding of physics at both larger and smaller scales. I have a particular interest in the relationship between the star formation cycle and the dwarf population as a way to understand both the physics of star formation regulation and as a driver of the diversity of the dwarf population.

I am currently a YCAA prize fellow at the Yale Center for Astronomy and Astrophysics; I got my PhD from Princeton in 2022, and in 2025 I will become a Kavli fellow at the Kavli Institute for Particle Astrophysics and Cosmology at Stanford.

Out and About

Merian at DGSCS2024

Talk recording: GasPisa 2024

Group shot of Galactic Frontiers 2023

SOC photo of Galactic Frontiers 2023

Ceremony video: Jacobus Fellowship 2022

I study the interplay between baryonic processes and low-mass galaxy assembly.

I leverage statistical observations of low-mass galaxy samples to learn about the astrophysical processes that govern dwarf galaxy assembly via the application of purpose-built, physics-based inference frameworks on large-volume dwarf galaxy datasets. You can find short summaries of the works I've been involved in below; click through for NASA ADS links.

Recent Publications

(site in progress, complete 2022/10-present)

SAGAbg. II. The Low-mass Star-forming Sequence Evolves Significantly between 0.05 < z < 0.21

Kado-Fong, Geha, Mao, de los Reyes, Wechsler, Weiner, Asali, Kallivayalil, Nadler, Tollerud, & Wang

Precision in language. The relationship between galaxy stellar mass and star formation rate is one of the most well-known and oft-measured galaxy scaling relations. Low-redshift galaxy samples are often used as cosmological context for Nearby galaxies, but the evolving nature of Universe means that care must be taken to deconvolve effects imposed by the peculiarities of our cosmic neighborhood and bulk redshift evolution -- especially in the era of high precision extragalactic astrophysics that will be afforded by upcoming surveys. With the SAGAbg-A sample, we show that the z~0 approximation holds only to z=0.05, above which there is statistically significant evolution in the Star-forming Sequence. We show that some contemporary cosmological simulations do not reproduce this evolution, despite arriving at the observed z=0 SFS, and that neglecting this evolution can convolve redshift evolution with environmental astrophysical effects even at community consensus definitions for "low redshift".

Merian: A Wide-Field Imaging Survey of Dwarf Galaxies at z~0.06-0.10

Danieli, Kado-Fong, Huang, Luo et al.

Snow White and the 100,000 dwarfs. We present the first data reduction of the Merian medium-band imaging survey, which is set to cover around 750 square degrees of the HSC-SSP wide fields in two purpose-built medium-band filters covering Hα and [OIII] at 0.06<z<0.1. Here we provide an overview of the first few hundred square degrees of the survey, and look forward to incoming science results related to dwarf weak lensing and baryonic structure.

A Nonparametric Morphological Analysis of Hα Emission in Bright Dwarfs Using the Merian Survey

Mintz, Greene, Kado-Fong, Danieli et al.

The mass-dependent shape of starbursts. In the first science paper from the Merian medium-band imaging survey, we study the morphology of Hα emission as a function of galaxy stellar mass and specific star formation rate. We find that galaxies with low stellar masses and high specific star formation rates tend to have more compact and spatially homogeneous star formation relative to more massive star-bursting galaxies, implying that different dynamical mechanisms may be at play in driving starbursts on different galaxy mass scales.

Stellar Mass Calibrations for Local Low-Mass Galaxies

de los Reyes, Asali, Wechsler et al. incl. Kado-Fong

The systematic uncertainties of calling a rose by any other name. Measuring stellar masses is commonplace, but the uncertainties and biases related to these estimates have not been well-characterized in the dwarf mass regime. Here, we demonstrate that broadband photometry are able to recover model galaxy stellar masses to a precision of around 0.1 dex, but that a new calibration is needed to eliminate mass-dependent biases. We also show that while non-parametric SED fitting can recover unbiased estimates of the stellar mass, parametric SED fitting may underestimate stellar mass by up to around 0.4 dex.

SAGAbg. I. A Near-unity Mass-loading Factor in Low-mass Galaxies via Their Low-redshift Evolution in Stellar Mass, Oxygen Abundance, and Star Formation Rate

Kado-Fong, Geha, Mao, de los Reyes, Wechsler, Asali, Kallivayalil, Nadler, Tollerud, & Weiner

Star formation drives moderate winds of change. The efficiency at which star formation feedback drives galactic winds in dwarf galaxies underpins the physical processes of dwarf assembly and informs physical models of star formation regulation. We model both observational and physical effects to infer a moderate wind-driving efficiency that is consistent with modern ISM-scale simulations, but over an order of magnitude lower than what some cosmological simulations use to produce dwarf galaxies that are realistic in other aspects.

The Merian survey: design, construction, and characterization of a filter set optimized to find dwarf galaxies and measure their dark matter halo properties with weak lensing

Luo, Leauthaud, Greene, Huang, Song, Kado-Fong, Danieli, et al.

Filtering for dwarfs. As the size of our imaging datasets increase, finding dwarf galaxies at scale is becoming an increasingly difficult proposition: standard photometric distance determinations are not sufficiently precise, and spectroscopic surveys are prohibitively resource-intensive. We designed and manufactured a set of two medium-band filters purpose-built to find 100,000 dwarfs via their [OII] and Hα line emission at 0.06<z<0.10 for the Merian Survey.

The SAGA Survey. III. A Census of 101 Satellite Systems around Milky Way-mass Galaxies

Mao, Geha, Wechsler, Asali, Wang, Kado-Fong, et al.

Counting satellites around cosmic sisters. We present the third data release of the Satellites Around Galactic Analog (SAGA) Survey, a spectroscopic census of the satellite systems around 101 Milky Way-like hosts down to 10⁷ solar masses. The SAGA Survey places the Milky Way and its satellites in cosmological context by quantifying both the average and variance of satellite properties across a statistical sample of MW-like hosts.

The SAGA Survey. IV. The Star Formation Properties of 101 Satellite Systems around Milky Way-mass Galaxies

Geha, Mao, Wechsler, Asali, Kado-Fong, Kallivayalil, et al.

Massive frenemies halt star formation. It is well-established that dwarf galaxies that are satellites of more massive galaxies are more likely to be non-star-forming, but the physical processes that lead to satellite quenching are poorly understood. We catalog the star-forming properties of the satellite systems of 101 nearby Milky Way-like hosts in the SAGA survey to examine the imprint of host environment on the present and past star formation of low-mass galaxies.

The SAGA Survey. V. Modeling Satellite Systems around Milky Way-mass Galaxies with Updated UniverseMachine

Wang, Nadler, Mao, Wechsler, Abel, Behroozi, et al. incl. Kado-Fong

Reframing our cosmic environment. Massive galaxies exert a marked effect on the evolutionary trajectory of the dwarf galaxies that fall into their potentials. Here we extend the UniverseMachine semi-empirical model of galaxy formation by using a satellite census of 101 Milky Way-like hosts from the SAGA survey to constrain the relation between the cessation of star formation in dwarf galaxies and the presence of MW-like galaxy.

Dwarf–Dwarf Interactions Can Both Trigger and Quench Star Formation

Kado-Fong, Robinson, Nyland, Greene, Suess, Stierwalt, & Beaton

Pulling a fast one in Little League. Almost all dwarf galaxies with less than around 10⁹ solar masses of stars are found to be star-forming when not interacting with a massive host galaxy. Interactions with another low-mass galaxy have been demonstrated to trigger periods of intense star formation; here we show that these dwarf-dwarf interactions can also temporarily halt star formation by displacing the gas needed for star formation via gravitational encounters.

Beyond Ultra-diffuse Galaxies. II. Environmental Quenching of Mass-Size Outliers among the Satellites of Milky Way Analogs

Li, Greene, Greco, Beaton, Danieli, et al. incl. Kado-Fong

Bigger but not better (or worse). The future of a small galaxy is irreparably altered if it falls into the gravitational potential of a more massive host. Indeed, the gravitational and hydrodynamical effects exerted by massive galaxies on their satellites contribute strongly to the observed diversity in the structures of low-mass galaxies. However, here we show that the lowest density dwarfs are quenched at a rate similar to their denser analogs. This result runs contrary to the naive expectation in which the processes that allow for very low stellar densities also lead low-density dwarfs to be more susceptible to environmental disruption.

Beyond Ultra-diffuse Galaxies. I. Mass-Size Outliers among the Satellites of Milky Way Analogs

Li, Greene, Greco, Huang, Melchior, et al. incl. Kado-Fong

When you say jump, I say "how high is high, really?" Ultra-diffuse galaxies are called as such due to their large sizes and low surface brightnesses. Canonically, however, these galaxies have been defined with a flat cut in surface brightness and physical size. We argue that defining galaxies based on their deviation from the mass-size relation is a more physically-motivated way of describing these outliers in the galaxy population.

Identification of tidal features in deep optical galaxy images with convolutional neural networks

Domínguez Sánchez, Martin, Damjanov, Buitrago, Huertas-Company, Bottrell, et al. incl. Kado-Fong

Train Against the Machine. Stellar tidal features are formed from the remnants of satellite galaxies as they are ripped apart under the gravitational influence of a massive host galaxy. These structures provide insight into a galaxy's recent merger history, the stellar population of its satellite galaxies, and the gravitational potential of the host halo -- however, their diffuse and triaxial structure makes their identification a complex natural imaging problem. Here, we train a convolutional neural net using mock observations of hydrodynamical simulations; we find that the classifier performs significantly worse on real data, possibly due to insufficient realism in current cosmological simulations.

Ultra-diffuse Galaxies as Extreme Star-forming Environments. I. Mapping Star Formation in H I-rich UDGs

Kado-Fong, Greene, Huang, & Goulding

Cloudy with a lowered chance of star formation. Ultra-Diffuse Galaxies, or UDGs, are dwarf galaxies with remarkably low stellar densities; this diffuse nature makes UDGs an extreme environment for star formation. Here, we map out the stellar mass and star formation rate surface densities of a sample of nearby gas-rich UDGs. We find that the UDGs are systematically less efficient at forming stars given the size of their gas reservoirs, and that although these puffy galaxies are large for their stellar mass, their sizes are actually normal for their HI masses.

Ultra-diffuse Galaxies as Extreme Star-forming Environments. II. Star Formation and Pressure Balance in H I-rich UDGs

Kado-Fong, Kim, Greene, & Lancaster

Cloudy with a lowered chance of star formation. In the second paper of our series on UDG star formation, we investigate the implications of UDG structure and star formation efficiency on the strength of their star formation feedback. We find that descriptions of star formation that incorporate information about galaxy structure, rather than just gas availability, accurately account for low star formation efficiency in UDGs without the need to artificially change the strength of star formation feedback in these diffuse galaxies.

Reaching for the Edge I: probing the outskirts of massive galaxies with HSC, DECaLS, SDSS, and Dragonfly

Li, Huang, Leauthaud et al. incl. Kado-Fong

Subtracting the haystack from the needle. The stellar outskirts of massive galaxies are thought to be dominated by stars deposited by accreted satellite galaxies; they thus encode substantial information about galaxies' unique assembly histories. Because these outskirts are low density and therefore low surface-brightness, it is especially important to disentangle systematic effects of data reduction and processing that may impact inferred outskirt properties. Here, we compare the limits of wide-field survey instruments and propose new methods to subtract the sky background in order to accurately delve into the stellar outskirts of massive galaxies.

Walter: A Tool for Predicting Resolved Stellar Population Observations with Applications to the Roman Space Telescope

Lancaster, Pearson, Williams et al. incl. Kado-Fong

How to count a Sky Full of Stars. The incoming generation of space-based missions will greatly expand the distance at which we are able to resolve galaxy light into individual stars. These resolved star studies are able to leverage our knowledge of stellar physics and evolution to infer galaxy distances, stellar population ages, and enrichment histories. Here we develop a new tool that predicts the necessary exposure time to reach specific branches of stellar evolution, as well as the potential crowding limit of a stellar population given its surface brightness and stellar population.

The Nature of Low-surface-brightness Galaxies in the Hyper Suprime-Cam Survey

Greene, Greco, Goulding et al. incl. Kado-Fong

Finding faint fuzzies. Characterizing the low surface-brightness tail of the galaxy population is crucial for quantifying the full diversity of the galaxy population. In this work, we use a cross-correlation approach to infer the redshift distribution of the low surface brightness galaxy catalog of Greco et al. 2018; we find that the galaxies selected via low-surface brightness detection methods from HSC-SSP typically have stellar masses of around 10⁷ solar masses and, unlike Ultra-Diffuse Galaxies, lie on the mass-size relation at a distance of approximately 100 Mpc.

The In Situ Origins of Dwarf Stellar Outskirts in FIRE-2

Kado-Fong, Sanderson, Greene, et al.

A Burst Too Far. Our previous work demonstrated that bright dwarfs generically host three-dimensionally round stellar outskirts; here, we consider whether the strong star formation feedback prescriptions of the Feedback in Realistic Environments (FIRE-2) simulations are able to reproduce these structures. We find that although the FIRE-2 galaxies do redistribute stars to large radii, many of the simulated dwarfs fail to form the thick disks that appear in the observed population. The simulated galaxies that do not form disks are also characterized by burstier star formation histories and lower cold gas fractions than the dwarfs that form disks, suggesting that the three-dimensional structure of galaxies is a key benchmark linked to star formation feedback and galaxy assembly.

The Intrinsic Shapes of Low Surface Brightness Galaxies (LSBGs): A Discriminant of LSBG Galaxy Formation Mechanisms

Kado-Fong, Petrescu, Mohammad, et al.

How Our Pasts Shape Our Present. Using an array of samples from the literature, we infer the three-dimensional shapes of low surface brightness and Ultra-diffuse galaxies from the distribution of their two-dimensional, on-sky projected ellipticities. Because these galaxies are selected to be low surface-brightness observationally, a galaxy may be considered to be low surface brightness only from certain viewing angles, which we explicilty model. We find that contemporary simulations produce low surface brightness galaxies with distinct three-dimensional shape distributions according to formation path, suggesting that 3D shape measurements are a considerable benchmark for realism in simulated galaxy populations.

Tracing the Intrinsic Shapes of Dwarf Galaxies Out to Four Effective Radii: Clues to Low-mass Stellar Halo Formation

Kado-Fong, Sanderson, Greene, et al.

How Our Pasts Shape Our Present. Although we view external galaxies in projection on the sky, they are of course intrinsically three-dimensional structures. In this work, we use a sample of more than 6500 dwarf galaxies with deep imaging from the Hyper Suprime Cam Subaru Strategic Program to infer their three-dimensional shapes as a function of radius using statistical deprojection at the sample level. We find that the bright dwarfs in our sample host relatively well-ordered but thick stellar disks that become increasingly more spheroidal at increasing radius -- these observations indicate that, unlike those of more massive galaxies, the stellar outskirts of low-mass galaxies may be dominated by in-situ stellar migration through dynamical heating or feedback processes.