Research
Current research interests
I am currently interested in using cosmological probes of the post-reionization epoch (like the Lyman-alpha forest or HI line intensity mapping) to study the way our Universe transitioned from being mainly neutral to highly ionized, i.e. cosmic reionization. In particular, I am excited about quantifying how well we can constrain the astrophysics of reionization while simultaneously learning more about cosmology. Besides, I am interested in probes of the epoch of reionization itself like 21cm cosmology. Although my main focus lies on learning about reionization, my research interests are broader. For instance, I have a recurrent interest in shedding light on dark matter candidates and on the use of AI for astronomy.
Impact of the astrophysics of reionization on HI (21 cm) line intensity mapping
The baryonic content of the Universe is mainly hydrogen, perhaps then it is not surprising that hydrogen atoms offer great windows to peer at the evolution of the Universe, e.g. Lyman-alpha forest (see the next project) or with the 21 cm hyperfine transition of hydrogen. The 21 cm transition of hydrogen is actually a forbidden transition, it has a lifetime of 3 million years! Thus, waiting for a single hydrogen atom to emit a 21 cm photon is not a good strategy. Nevertheless, the Universe is a great laboratory! We have both abundant time gargantuan amounts of hydrogen.
Line intensity mapping using the 21 cm line is a promising probe of the post-reionization IGM; however, it can be affected by the astrophysics that govern cosmic hydrogen reionization. For instance, shallow potential wells could lose a significant fraction of baryons after the passage of an ionization front because of the additional injection of energy. Therefore, reionization modulates the amount of baryons that can sit in a given halo (with small enough potential wells). My collaborators and I recently estimated both the impact of this effect and the expected degree of biasing that could happen if one chooses to ignore this broadband systematic in radio telescopes like SKA1-LOW and PUMA.
Want to know more?
Extracting the astrophysics of reionization from the Lyman-alpha forest
The Lyman-alpha forest is sensitive to the thermal evolution of the intergalactic medium (IGM) in the post-reionization epoch. This sensitivity can be used to probe the thermal relics present in the IGM produced by the violent heating of the IGM done by ultraviolet photon in the reionization process. If one accounts for the way the small-scale structure reionizes, i.e. ultraviolet heating + shock heating, this thermal relics can even survive to redshift 2!
We recently forecasted – for the first time – the ability of DESI to extract the memory of reionization from the Lyman-alpha forest power spectrum. DESI’s ability to transform this broadband effect from a systematic to a window into the epoch of reionization is surprising since it may be able to constrain reionization only slightly worse than 21cm instrument like HERA.
Given the need of high-resolution simulations to account for the way the small-scale structure reionizes, we developed an analytical template to account for the memory of reionization in the Lyman-alpha forest without the use of expensive simulations. The template performs well, especially if the timeline of reionization is well-constrained.
We have also recently discovered that X-rays can affect the impact of inhomogeneous reionization in the post-reionization intergalactic medium. This novel mechanism could open a new avenue to constrain the sources of x-ray heating in the Cosmic Dawn (the stage of the Universe evolution before cosmic reionization). As seen in the following figure, X-rays tend to erase some structures in the small scales. Besides, X-ray heating set up the initial conditions for reionization.
Want to know more?
- First discovery of the impact of reionization in the low redshift IGM.
- Dependence with EoR astrophysics and CD preheating.
- Forecast.
- Template for the memory of reionization in the Lyman-alpha forest.
- The long-lasting effect of X-ray preheating in the post-reionization intergalactic medium.
Revisiting primordial black holes constraints in the asteroid-mass range
The nature of dark matter has eluded astrophysicists so far even though we have several dark matter candidates and substantial experimental/observational efforts are directed to answer this mystery. Among dark matter candidates, primordial black holes (PBHs) are conventional in the sense that they do not require any strong modification to the physics standard model. These black holes form in the early Universe from the collapse of order unity perturbations sourced by the inflationary potential.
I contributed to this field by opening the previously constrained sub-lunar mass window. The constraints that were previously limiting this mass range were microlensing and femtolensing of PBHs, neutrons star capture of PBHs, and white dwarf explosion due to the passage of PBHs.
Want to know more about tiny primordial black holes?
Possible conventional sources of circular polarization in the CMB
The standard model of cosmology does not offer any mechanism to produce circular polarization in cosmic microwave background (CMB) photons. Thus any deviation from zero may be a channel to learn something about the earlier Universe. In my work, I considered conventional sources of circular polarization in the CMB. In this context, conventional refers to not modifying the early Universe Lagrangian, instead, I focused on physical mechanisms that are part of the Standard Model of physics, e.g. 21 cm hyperfine transition of hydrogen, and non-linear polarizability.
We found that all sources of circular polarization studied in our work were to small to be concerned about possible leakage for linear polarization experiments.
Want to read a paper using order-of-magnitude calculations and learn about birefringence?
Detecting magnetic fields in exoplanets
A possible smoking gun for planets that may contain life or might be suitable for human life is the presence of a magnetic field to shield life from deadly radiation. We proposed a methodology to detect magnetic fields in exoplanets using spectropolarimetry of the helium 1083 nm hyperfine transition. We showed that in the conditions of escaping atmospheres, metastable helium atoms should align with the magnetic field. As a result, there should be linearly polarized absorption at 1083 nm that traces the magnetic field’s direction.
Want to learn more about magnetic fields in exoplanets or interested in using quantum mechanics to compute polarizations of metastable helium?
Dark Energy Spectroscopic Instrument
As part of the Dark Energy Spectroscopic Instrument (DESI), I have contributed to several observational efforts, primarily regarding the measurement of the Lyman-alpha forest, i.e. the background radiation from quasars that gets absorbed by neutral hydrogen clouds along the line of sight to the telescope.
Want to learn more about the DESI instrument and what can be achieved with it?
- Broad Absorption Line Quasars in the Dark Energy Spectroscopic Instrument Early Data Release!
- 3D Correlations in the Lyman-α Forest from Early DESI Data!
- The Lyman-α forest catalog from the Dark Energy Spectroscopic Instrument Early Data Release!
- The Early Data Release of the Dark Energy Spectroscopic Instrument!
- Validation of the Scientific Program for the Dark Energy Spectroscopic Instrument!
- The DESI Survey Validation: Results from Visual Inspection of the Quasar Survey Spectra!
- Overview of the Instrumentation for the Dark Energy Spectroscopic Instrument!
Towards a more realistic spacetime
Real astrophysical objects, say planet Earth, are not perfect spheres. Besides, they often have magnetic fields or other interesting physical phenomena. Nowadays we often use spacetimes that are good representations of static spherical bodies (Schwarzschild metric) or rotating bodies (Kerr metric). However, the Kerr metric cannot be matched to an interior physical solution. Motivated by this, I have occasionally gone through the mathematical exercise of finding new spacetimes that represent slightly more realistic scenarios.
Want to learn more about these Kerr-like metrics?
You can also find my articles on my Google Scholar profile. Or with my NASA ADS library.