Welcome
I explore the formation and evolution of galaxies through cosmic time.
I am an associate research scientist (equivalent to research faculty) at Caltech.
I study the formation and evolution of galaxies through cosmic time using multi-wavelength spatially-resolved observations from world-class ground- and space-based telescopes, as well as theoretical models and simulations.
My aim is to understand how galaxies form and evolve in their structural and chemical properties, and how they connect to the environment they live in. To study this, I lead several observational programs using ALMA, JWST, and Euclid.
I am also very passionate about public outreach and education, and I am involved in several initiatives to bring the wonders of the Universe to the public.
Research Highlights
ALPINE-CRISTAL-JWST Survey: First Papers Out!
Hurray! The first papers from the ALPINE-CRISTAL-JWST collaboration have been published, showcasing groundbreaking research with the unique synergy between JWST and ALMA on the chemical enrichment, structure, super-massive black holes, and star formation or early galaxies. Check out the survey paper Faisst et al. (2025a). For all paper, see here.
Dust and SPHEREx
No, SPHEREx does not have dust... but check out my student's paper on the capabilities of SPHEREx to observe dust in far-away galaxies! The paper showcases the use of SPHEREx to observe Polycyclic Aromatic Hydrocarbons (PAHs) in the distant universe.
SPHEREx Launched!
SPHEREx (led by Caltech) is a NASA mission that will conduct a comprehensive survey of the entire sky in near-infrared light. This brand-new space telescope will be used to answer big questions about the early universe, the history of galaxies, and the prevalence of life-sustaining molecules in planet-forming regions of space. I am core part of SPHEREx, leading parts of the data reduction pipeline.
Starburst Galaxies and Disk Instability
Galaxies that form stars excessively (so called starbursts) are usually connected to galaxy-galaxy collisions and interactions, which can drive gas inflows and gas-compression that enhance star formation efficiency. Here, we find a signifcant number of isolated disk galaxies (similar to our Milky Way in shape) to be starbursts. Thanks to the high spatial resolution of JWST observations from COSMOS-Web, we show for the first time a high fraction of these disk galaxies are undergoing disk instabilities causing high star formation efficiencies.
The ALPINE-CRISTAL-JWST Survey Approved!
I am happy to share that our 60h program with JWST has been approved to follow up 18 ALPINE galaxies with JWST/NIRSpec Integral Field Spectroscopy! The ALPINE-CRISTAL-JWST survey will study jointly the hot ionized gas, stars, and warm gas of galaxies during the first billion years of cosmic evolution.
Dead or Alive??
JWST has observed some galaxies that seem to be "dead" (i.e., not forming stars) at the earliest times. However, it is unclear whether these galaxies are truly inactive or if they are simply in a dormant phase. In this paper we quantify using computer simulations how likely such phases are. Short answer: at least every second galaxy in the early Universe went through a dormant phase, which typically only lasts only 10-20 million years.
CHAMPS: Uncovering the Dark Early Universe
Happy to announce that the 144h CHAMPS ALMA large proposal has been accepted! CHAMPS will be the largest ALMA blind-survey to-date to search for dust-obscured galaxies in the early Universe to decipher the early formation of dust, which constitutes the matter we are built of.
Why do Galaxies Stop Star Formation?
Quiescent galaxies are ubiquitous in the local universe, but when do they emerge? Here, we published an atlas of quiescent galaxies uniquely detected by JWST at the earliest times - the first step for understanding the last stretch in the lives of galaxies.
Globular Clusters in Far-Away Galaxies
In this study, we investigate the properties of globular clusters in a distant galaxy cluster using the first-ever data from the JWST. These star clusters seem to have a mix of ages and metallicities, suggesting different formation mechanisms in this high-density environment.
COSMOS-Web JWST cycle 1 proposal accepted!
COSMOS-Web starts a new era of research on the COSMOS field. This 250h JWST cycle 1 program will provide the largest ever contiguously images are on sky in four NIRCam filters and one MIRI filter. Excited to be core part of this new survey!
Early Galaxies are Hot!
The dust temperature of early galaxies is a key factor in understanding their formation and evolution, especially their dust masses. Dust is what ultimately determines the physical conditions in these galaxies and influences their star formation activity - hence ultimately the formation of stars and planets. Through the first comprehensive study of dust temperatures in galaxies 10 billion years ago, we found that dust temperatures were higher in early galaxies compared to galaxies today, which is linked to their more vigorous star formation activity in the past.
First Results from the ALPINE Survey
The ALPINE-ALMA large program aims at studying the gas and dust properties of 118 typical galaxies 1 billion years after the Big Bang (z = 4-6). The first exciting results from this survey include: the finding of significantly dust-obscured sources, the first statistical study of dust-obscured star formation, the first statistical measurement of kinematics suggesting early formation of disk galaxies, and better constraints on the merger rates. Read more in the review paper by Faisst et al. (2022) or visit our webpage.
How Bursty is the Star Formation of Early Galaxies?
The star formation of low-mass galaxies is highly variable due to their shallow gravitational potential wells, which makes it easier for feedback processes to disrupt star formation. But what about high-mass galaxies? Are they also subject to such variability, or do they maintain a more steady star formation rate? In this work, we answer this question: their star formation is very bursty, which has a large effect on the properties we measure.
The Lyman Escape Crisis Solved?
Whether galaxies can reionize the early universe is still an open question. The fraction of escaping UV emission is a key factor in this process. In this study, we select local analogs of high-redshift galaxies and measure their UV escape fractions and show that the escape fractions are consistent with the values needed for reionization.