I have served on many of the major telescope and instrument review panels of the past three decades, including the NSF Extragalactic Review Board, Hubble Space Telescope TAC, JWST TAC, ESO OPC, and served as an ESA representative on the JWST galactic ecosystems panel. I was the Project Scientist for KMOS, LUCI on the Large Binocular Telescope, and EAGLE — a direct precursor to the MOSAIC instrument for the ELT. I am currently serving on the steering committees and executive boards of HARMONI, 4MOST, BlueMUSE, and WST (see below).
My work spans the full lifecycle of baryons in the universe — from primordial accretion streams feeding the first massive galaxies, through the violent energetic processes of stellar and AGN feedback, to the chemical record etched into the stars of the Milky Way today.
I am currently serving on the steering committees and executive boards of four major next-generation astronomical facilities, committing approximately 20 days per year to this service. Clicking on any project opens its official website.
My current research is centered on the physics of gas in and around galaxies across cosmic time — from the very first massive galaxy clusters to the dense molecular nurseries where stars and planets are born. Below are the three main programs I am actively pursuing.
We have been awarded a substantial JWST MIRI imaging and IFU program (co-PI, Cycle 4) targeting the SpiderWeb radio galaxy at z = 2.16 — one of the most spectacular known protoclusters in the universe, where star formation is occurring across nearly 100 kpc of circum-galactic gas.
The central question is whether molecular hydrogen (H₂) is the dominant cooling channel in this turbulent, multi-phase CGM. As shocks and turbulent mixing cascade kinetic energy to small scales, they should radiate through H₂ rotational lines (pure-rotational 0–0 series; warm H₂ at ~10³ K) and ro-vibrational lines (hot H₂ at <5000 K). These lines carry the bulk of the emitting gas mass and are critical to modeling how the CGM cools from a hot tenuous phase to the cold, star-forming molecular clouds detected in CO.
The SpiderWeb is the most distant galaxy for which Spitzer detected H₂ 0–0 S(3) and S(5), making it likely the best system in which JWST MIRI can capture enough critical 0–0 lines before they redshift out of MIRI's bandpass. The data will provide the first spatially resolved energy budget for warm H₂ cooling across a protocluster CGM.
We have obtained MIRI imaging and IFU spectroscopy of 7 Brightest Cluster Galaxies (BCGs) as part of a JWST Cycle 3 program (co-I), a continuation of our MUSE survey that revealed ionized gas filaments extending up to 30 kpc in low-entropy BCGs.
The MIRI data are spectacular: they detect Ne II 12.8 µm, Ne III 15.5 µm, PAH features (7.7, 11.3, 17 µm), warm H₂ 0–0 S1–S9 lines, high-ionization metal lines, and hydrogen recombination lines — essentially a complete census of the mid-infrared ISM. Our goals are to measure the total molecular gas mass, map excitation and kinematic gradients, search for compact molecular disks near the central AGN, construct the full energy budget of the molecular gas phase, and determine why star formation does and does not occur within the filaments.
These observations will illuminate two key stages of the AGN feedback cycle: the formation of cold molecular filaments from the hot ICM (via chaotic cold accretion), and the subsequent formation of a central molecular disk that may then feed the AGN, closing the feedback loop.
Our understanding of star formation in the early universe is limited by our inability to trace gas cooling from diffuse warm phases all the way down to the cold, dense scales where stars and planets actually form. I am pursuing a high-risk, high-reward program to detect absorption from complex molecules — including potentially prebiotic species — against the bright radio and millimeter continuum of compact high-redshift radio galaxies.
Our target is B2 0902+34 at z = 3.4, where we have already detected CO(0–1), HCO⁺(0–1), and HCN(0–1) absorption in JVLA observations (Emonts et al. 2024). New sub-arcsecond JVLA data resolve the system spatially, revealing that the absorbing complex breaks into multiple distinct velocity components as we increase resolution — consistent with an unresolved hierarchy of dense molecular cloud structures of size ≲ a few hundred parsecs.
We are now conducting ~50 hours of JVLA observations targeting prebiotic molecules, with complementary ALMA data on methanimine (CH₂NH) and methylamine (CH₃NH₂) yet to be taken. If detected, these would be among the highest-redshift complex organic molecules ever found, opening a new window onto the chemistry of planet-forming environments in the early universe.
The nine papers below represent highlights from my recent work, spanning cosmological cold accretion, AGN feedback, JWST observations, and the chemical evolution of the Milky Way. Click any paper to expand the full summary.
ALMA observations of the [CI](1–0) fine-structure line tracing cold atomic carbon gas in and around the powerful high-redshift radio galaxy 4C 41.17 at z = 3.792. The study aimed to detect and characterize cold gas in the CGM of this massive, star-forming protogalaxy embedded in a large Lyα halo.
A cold gas stream extending ~120 kpc from the host galaxy was detected in [CI] emission. The stream contains ~6.7 × 10¹⁰ M☉ of cold gas — comparable to the stellar mass of the galaxy itself — with velocities up to ~650 km s⁻¹ at its outermost point, decreasing steadily toward the galaxy. The stream kinematics are consistent with gravitational infall along a large-scale cosmic filament.
Direct observational evidence for cosmological cold accretion — the dominant mode by which galaxies are predicted to acquire their star-forming fuel at high redshift. The stream can sustain the extreme star formation rates observed in 4C 41.17 (~1000 M☉ yr⁻¹), confirming that cold cosmic filaments reach deep into the halos of the most massive protogalaxies.
MUSE integral-field spectroscopy combined with ALMA continuum and molecular line data to characterize the multi-phase CGM of radio galaxy 4C 19.71 at z ≈ 3.6. The joint dataset probed ionized gas structure (Lyα, CIV, HeII, [CIII]) alongside cold molecular gas and dust continuum.
A kinematically narrow [CI] emission component (σ ≈ 40 km s⁻¹) is detected at ~75 kpc from the host galaxy, indicating quiescent cold gas at large radii. Photoionization modeling constrains the outer CGM metallicity to 0.03–0.1 Z☉ — near-pristine, recently accreted gas.
AGN-driven feedback (radio jets + ionizing radiation) coexists with cold gas accretion in this system, revealing a complex multi-phase CGM in which the AGN both ejects gas on small scales and draws in cold material at large scales — a compelling case study for how radio-loud AGN regulate their own gas supply.
SED fitting analysis of 10 gravitationally lensed galaxy candidates at z ~ 9–16 identified in JWST NIRCam imaging of galaxy cluster SMACS 0723. The BEAGLE SED-fitting code simultaneously constrained photometric redshifts and physical properties while accounting for gravitational lensing magnification (μ ~ 2–10).
All 10 candidates are genuine high-redshift sources at z > 9. Stellar masses are uniformly low (10⁷–10⁸ M☉) with young stellar ages (10–100 Myr) and blue UV slopes (β ≈ −2 to −3), indicating little to no dust. No candidate is a low-redshift interloper when lensing is properly modeled.
Validates that JWST is detecting genuine examples of the universe's earliest, least-massive galaxies — intense, dust-free star-forming systems caught in the first few hundred million years of cosmic time. Places useful constraints on the UV luminosity function at z > 9 and supports early, rapid galaxy assembly.
ALMA Band 5 observations of hydrogen fluoride HF(J=1–0) and water H₂O(2₂₀–2₁₁) emission in the QSO–submillimeter galaxy pair BR 1202-0725 at z = 4.7. HF traces warm, dense molecular gas excited by far-infrared photons, making it a diagnostic of AGN-heated environments.
The QSO in BR 1202-0725 is the most luminous HF J=1–0 emitter known (L_HF ≈ 3.1 × 10⁹ L☉). The HF/H₂O luminosity ratio is consistent with AGN-heated dust and gas. No evidence for high-velocity molecular outflows is found in either component, despite the enormous AGN power.
Establishes BR 1202-0725 as a benchmark for extreme molecular environments at high z. The HF detection links gas heating to AGN activity rather than star formation. The absence of fast molecular outflows suggests AGN feedback in this system does not currently manifest as large-scale molecular gas ejection, challenging simple feedback models.
Results from the COALAS survey — a deep ATCA CO(1–0) mosaic of the SpiderWeb Galaxy protocluster field at z = 2.16. CO(1–0) is the most robust tracer of total molecular gas mass. The survey covered a 6.5′ × 6.5′ field and searched for both known member galaxies and serendipitous CO emitters.
46 CO(1–0) line detections were found, including 21 previously unknown sources. The CO luminosity function in the protocluster field is elevated by 1.6 ± 0.5 dex above the field CO LF at the same redshift. The molecular gas mass density is 0.6–1.3 × 10⁹ M☉ cMpc⁻³ — among the highest values measured at any epoch.
The first statistical characterization of molecular gas on protocluster scales at cosmic noon. The dramatically enhanced CO luminosity function confirms that protoclusters are extraordinarily gas-rich environments — reservoirs of star-forming fuel that will eventually build the massive cluster ellipticals we see today.
Chemo-dynamical simulations of four Milky Way-type disc galaxies evolved for 10 Gyr from cosmologically motivated initial conditions, investigating the origin of the observed bimodality in the [α/Fe] vs. [Fe/H] chemical abundance plane — the chemical fingerprint that separates the Galactic thin and thick discs.
The [α/Fe]–[Fe/H] bimodality emerges naturally in all four simulations without mergers or radial migration. The thick disc (high-α sequence) forms rapidly in the first 3–4 Gyr during intense, turbulent star formation. The thin disc grows subsequently through slower, secular star formation as the gas cools and settles.
The Milky Way's chemical bimodality is an imprint of its star formation history, not of dynamical processes. This inside-out, two-phase growth scenario is consistent with all observational constraints and predicts that chemical bimodality should be common among Milky Way-mass spirals — making our Galaxy a template for understanding the general formation history of disc galaxies.
A 154-pointing NOEMA CO(1–0) mosaic of the nearby starburst galaxy M82 — the first complete, spatially resolved map of its molecular gas at ~30 pc resolution — covering both the star-forming disc and the molecular outflow/streamer regions driven by its famous superwind.
1891 molecular clouds were catalogued. In the outflow region, clouds systematically decrease in size, mass, and surface density with increasing distance from the disc, consistent with cloud destruction during outward transport. The total molecular gas mass in the outflow is ~5 × 10⁷ M☉.
The first complete molecular map of M82 reveals a well-structured outflow. The streamers' kinematic stability supports entrainment by the hot superwind rather than direct acceleration by radiation or shocks. These results directly inform our understanding of molecular feedback in distant starburst galaxies observed with ALMA.
MUSE integral-field spectroscopy of 18 nearby brightest group galaxies (BGGs) — the massive ellipticals at galaxy group centers — searching for filamentary ionized gas structures as signatures of cold gas condensation from the intragroup medium.
10 of 18 BGGs display extended ionized gas: 7 show filamentary nebulae (5–30 kpc extent), 3 host compact rotating ionized gas discs. Filament presence correlates strongly with low central entropy (K₀ < 30 keV cm²) and short cooling times (t_cool < 1 Gyr) — consistent with the threshold for chaotic cold accretion (CCA).
Demonstrates that chaotic cold accretion from the hot intragroup medium is operating in galaxy groups, not just massive clusters. The strong entropy–filament correlation supports the CCA theoretical framework and motivates ALMA follow-up to test whether the ionized filaments are the warm outer envelopes of underlying cold molecular structures.
ALMA observations of [CII] 158-µm emission in the fields of four powerful radio AGN at z ≈ 3.5, targeting companion galaxies within 10–100 kpc of the radio AGN hosts. [CII] is one of the brightest far-infrared lines and an excellent tracer of cold gas and star formation activity.
Eight [CII]-emitting companions are detected across the four AGN fields. The cold gas is predominantly associated with the companion galaxies rather than the AGN hosts themselves, suggesting that AGN feedback has already cleared cold gas from the host galaxy environments.
Radio AGN at z ≈ 3.5 reside in cold gas-poor hosts while their companions retain substantial reservoirs — a striking asymmetry that directly implicates radio-mode AGN feedback as the mechanism responsible for removing cold gas from massive host galaxies. This has important implications for understanding the role of AGN feedback in the "downsizing" of massive galaxies across cosmic time.
A searchable, up-to-date list of all my publications on the arXiv astrophysics server.
Browse my papers on arXiv ↗