Research and Codes

21-cm Cosmology

A big chunk of my work is on how to learn cosmology and astrophysics from 21-cm data. Here are some examples:

In two companion papers (1 and 2) I introduced 21cmvFAST, a version of 21cmFAST that included the effect of the dark matter-baryon relative velocities on the first galaxies. I showed that these produce velocity-induced acoustic oscillations (VAOs, or wiggles) in the 21-cm signal during cosmic dawn, which can be used as a standard ruler to cosmic dawn (z=10-20). In this paper I made the velocities part of the standard 21cmFAST software, and updated our reference 21-cm models of the first galaxies (see EOS21 for details and nice animations).

I have also developed the 21-cm line as a tool to learn about dark matter (DM). Here we argued that cosmic dawn is an ideal location to search for millicharged DM, and that only a sub-percent fraction of the DM is required to explain the EDGES anomaly at z=17. I have led the HERA theory analysis of DM, and found more stringent limits, though at z=8-10. Upcoming high-z HERA data will be able to test the origin of the EDGES depth, if real. The 21-cm line also has information about the timing of the first galaxies, which  in this paper I showed makes it is sensitive to the small-scale nature of dark matter, at much higher wavenumbers than currently accessible (k~50/Mpc). This can help identify self-interacting DM, like in the ETHOS models.

The future of 21-cm is to map the fluctuations across many redshifts and scales, which show a rich phenomenology of processes, ranging from heating of the IGM (likely due to high-mass X-ray binaries), to its reionization (due to galaxies of different masses). Key to understand all these processes are fast simulations across a range of scales. These are needed to explore the vast astrophysical---and cosmological---parameter space. Below I show a lightcone of the 21-cm signal across cosmic dawn and the EoR, along with the densities that seed the fluctuations.



Cosmology from UVLFs

Many of us are familiar with the beautiful Hubble ultra-deep field images. Not only do these teach us a lot about the formation of the first galaxies during the epoch of reionization, but also about cosmology and the nature of dark matter. In these two papers (1 and 2, led by grad student Nash Sabti) we developed a pipeline to measure the clustering of matter at z=4-10 marginalizing over the astrophysical uncertainties of this era (chiefly the unknown halo-galaxy connection). We obtained a measurement of the matter power spectrum up to k=10/Mpc, reaching smaller scales---and earlier times---than other cosmic probes.

Our measurement (black crosses) is shown along with other cosmic data (compiled in this paper, all linearly extrapolated to z=0, where the standard LCDM prediction is the black line) in this figure. The UVLFs allow us to access the unknown era of z=4-10 at smaller scales than we currently probe (albeit only at ~30% precision!) We used a similar technique to constrain primordial non-Gaussianity at small scales here.


Light but Massive Relics (LiMRs)

If you follow beyond-standard-model cosmology, you'll be familiar with Neff constraints on new physics. In a recent series of papers we studied how to use cosmological data to search for relics that are light but not massless. We call these LiMRs. In our first two papers we showed their effect on the matter power spectrum (here and here). LiMRs tend to suppress power for scales smaller than their free-streaming, like neutrinos, so measurements of galaxies and weak lensing are ideal to look for them.

In our most recent work, led by Linda Xu, we found the strongest constraints on light relics to date. Using SDSS+Planck+CFHTLens data we ruled out gravitinos with masses above ~2 eV (an order of magnitude tighter constraints than the Lyman-alpha forest!) 

Here are our constraints in the 2D space of relic temperature (directly related to Neff) and mass. The Neff constraint corresponds to the low-mass limit of this plot, and by using the power spectrum we can test heavier relics with even lower temperatures.


Press Releases

My recent work on VAOs as a standard ruler during cosmic dawn has been featured on the APS magazine Physics and on

My work on millicharged dark matter published in Nature has been featured in the Spanish newspaper El País, in Physics WorldCosmos Magazine, and Live Science, as well as in podcasts such as El Método and Señal y Ruido (in Spanish), amongst others.

Work done during my PhD on microlensing of Fast Radio Bursts, published in PRL, was also featured in Futurity and the JHU HUB.