Research
Our group investigates the chemical evolution from the largest scales of molecular clouds to the smallest scales of protoplanetary disks, with particular emphasis on how different environments affect the chemistry. We address these fundamental questions:
- How do complex organic molecules (COMs) form during star and planet formation?
- How does the environment influence chemical processes?
- What is the origin of organic material in protoplanetary disks?
- To what extent are molecules inherited from parent molecular clouds?
Schematic illustration of chemical evolution across star and planet formation environments.
Understanding how different environments affect gas chemical composition is crucial because most stars form within dense stellar clusters where gas is exposed to intense radiation from nearby massive stars. Our research concentrates on two critical evolutionary stages where radiation interaction is particularly significant: (1) molecular clouds exposed to strong radiation fields, known as photo-dominated regions (PDRs), and (2) protoplanetary disks, which experience radiation both from their central star and neighboring stellar sources.
Protoplanetary Disks
Characterizing both the overall organic reservoir and the complexity level achieved before planet formation is essential for assessing the prebiotic potential of nascent planets. Ideally, we would map organic molecules across all complexity levels, but case studies reveal this is impractical since complex organic molecules (COMs) remain primarily locked in ice mantles, rendering them unobservable at millimeter wavelengths. Methanol (CH₃OH) would serve as an ideal COM tracer, but it has been detected in only one Class II disk (TW Hya) and in particular disk environments experiencing strong stellar outbursts or containing large dust cavities or traps. Consequently, we must rely on indirect tracers of COM chemistry. One effective approach is studying molecules that co-form with COMs, such as H₂CO. Formaldehyde (H₂CO) functions as an excellent tracer of the organic ice reservoir where COMs form, as it co-forms with methanol and readily converts into larger molecules in the ice phase. Our group leverages ALMA observations to better understand H₂CO's spatial distribution in disks, both radially and vertically.
Cartoon cross-section of a protoplanetary disk highlighting the chemistry of H₂CO.
ALMA observations revealing the spatial distribution of small organics in a protoplanetary disk. Figure from Guzmán et al. (2021), one of the MAPS papers.
We are also particularly focused on nitrogen fractionation in disks. Isotopic ratios in molecules (e.g., D/H, ¹⁴N/¹⁵N) frequently deviate from elemental values depending on formation pathways. These deviations provide valuable insights into the origins and chemical evolution of material in both the Solar System and star- and planet-forming regions. The nitrogen isotopic ratio is especially informative and has been measured in molecules such as NH₃, CN, and HCN across diverse environments—from prestellar cores to protoplanetary disks and Solar System bodies like comets.
Photodissociaton Regions (PDRs)
Photo-dissociation regions (PDRs) constitute the surface layers of molecular clouds directly exposed to stellar UV radiation. These layers form the critical interface between cold neutral and ionized gas. Our research examines the chemical complexity within these regions and how radiation affects COM formation and destruction processes.
The Horsehead nebula, a prototypical PDR and case study for COM formation under irradiation. Figure from Hernández-Vera et al. (2023)
The Horsehead nebula provides an exceptional laboratory for studying COM formation due to its proximity (400 pc), simple edge-on geometry, and well-constrained gas density profile. Located within the Orion-B giant molecular cloud, the Horsehead's edge is illuminated by the O9.5V star, σ Ori. The combination of moderate UV exposure and high density creates conditions where dust grains near the cloud edge remain cold and covered with ice mantles. Incident FUV photons can photodesorb these ices directly into the gas phase or fragment them into reactive radicals that diffuse and recombine on dust surfaces to produce more complex molecules. The continuous FUV photon flux ensures that a fraction of ices are released into the gas phase through non-thermal processes, creating distinctive chemical signatures and rich molecular content at the PDR edge.
Collaborations
We actively participate in several major collaborative projects:
The Disk-Exoplanet Connection (DECO and iDECO)
Millennium Nucleus on Young Exoplanets and their Moons (YEMS2)
Chemical Vertical Structures in Proto-planetary Disks (DiskStrat)
Center of Excellence in Astrophysics and Related Technologies (CATA)
Molecules with ALMA at Planet-forming Scales (MAPS)
Disk Substructures at High Angular Resolution Project (DSHARP)
Outstanding Radio-Imaging of OrioN-B (ORION-B)
© Viviana Guzmán Veloso