A groundbreaking observation from astronomers at the University of Tokyo has revealed the absence of fluorine in a galaxy that existed just 0.9 billion years after the Big Bang. Led by graduate student Akiyoshi Tsujita from the Institute of Astronomy, Graduate School of Science, the team used the Atacama Large Millimeter/submillimeter Array (ALMA) to search for hydrogen fluoride (HF), the primary molecular reservoir of fluorine in interstellar gas. Their non-detection sets stringent upper limits on fluorine abundance, challenging models of early cosmic chemical evolution.

This discovery, published in The Astrophysical Journal Letters on February 27, 2026, highlights the prowess of Japanese higher education in forefront astrophysics research. The University of Tokyo's Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) played a pivotal role, underscoring Japan's leadership in international collaborations probing the universe's infancy.

🌌 The Mystery of Fluorine in the Cosmos

Fluorine, the 13th most abundant element in Earth's crust and key to fluoride in teeth and bones, is rare in the universe compared to neighbors like oxygen or carbon. Its production puzzles astronomers: primary channels include the neutrino-process (ν-process) in core-collapse supernovae during helium burning, asymptotic giant branch (AGB) stars ejecting via winds, and Wolf-Rayet (WR) stars, massive evolved stars (M > 25 M⊙) rich in helium and carbon-oxygen cores that rapidly forge fluorine through proton captures on neon-20.

In the early universe, AGB stars were absent due to insufficient time for low-mass progenitors to evolve, leaving supernovae and potential WR stars as candidates. Prior detections of HF in galaxies at z~0.5-4.5 suggested WR contributions ramp up post-reionization. The UTokyo team's non-detection at z=6 tests this timeline.

Understanding fluorine traces metal enrichment, star formation history (SFH), and feedback processes shaping the first galaxies.

The Target: G09.83808 at Cosmic Dawn

The observed galaxy, dubbed G09.83808 (or SPT0311-58 at z=6.024), is a dusty star-forming galaxy (DSFG) magnified by gravitational lensing (μ~8-9), enabling sub-kpc resolution. Located 12.9 billion light-years away, it formed ~0.9 Gyr post-Big Bang during cosmic reionization.

Properties include: star formation rate (SFR) ~1000 M⊙/yr, molecular gas mass 2×10^{10} M⊙ (N_H2 ~2.7×10^{23} cm^{-2}), metallicity Z~0.5-0.7 Z⊙ from [N II]/[O III] ratios, dust temperature T_dust=51 K. It lies on the main sequence, with compact size (~1 kpc half-light radius).

This 'normal' high-z galaxy, unlike extreme quasar hosts, provides a benchmark for average early enrichment.

ALMA's Precision: Hunting HF(1–0)

ALMA Band 5 (161.7-175.8 GHz) targeted HF(1–0) at rest-frame 2703 GHz, redshifted to 175.47 GHz. Cycle 10-11 observations (2023.1.01281.S) used C43-3/4/5 arrays for high resolution (beam 1.2''×0.96'').

Data reduction: CASA pipeline calibration, continuum subtraction, natural weighting cleaning to 2σ rms=0.08 mJy/beam/50 km/s. Spectra at peak continuum; integrated flux -43±20 mJy km/s (2.2σ non-detection). Upper limit from optical depth τ ∫dv =4.16×10^{-13} N_HF, yielding N_HF <6×10^{14} cm^{-2}, N_HF/N_H2 <2.2×10^{-9} (5σ).

Assumptions: LTE ground state dominance (T=50K, n_crit~10^{10} cm^{-3}); H2 from CO(2-1) with α_CO=1 M⊙/(K km/s pc²), r21=0.83.

Findings: Fluorine Scarce in the Infant Universe

No HF absorption constrains fluorine to levels an order below Galactic ISM (10^{-8}). This implies [F/H] << solar at z=6, despite Z~0.5 Z⊙.

AGB negligible (progenitors need >1 Gyr); ν-process in SNe II insufficient alone. WR stars, proposed for rapid enrichment, appear absent or yields overestimated early on. Intermittent SFH or delayed WR phase possible.

• Challenges WR dominance pre-z=4.
• Supports stochastic models with rotating massive stars later.
• HF depletion to dust unlikely (high T_dust).

Implications for Cosmic Chemical Evolution

This pushes fluorine constraints to highest z, breaking degeneracies in models. Early galaxies rely on SNe II; WR/AGB kick in later, aligning with metal-poor halo stars low in F.

Resolves 'fluorine conundrum': observed Galactic F requires multiple channels, timed precisely. Future JWST/ALMA spectra of more z>6 DSFGs will map WR onset, refining nucleosynthesis yields.Read the full paper

Broader: Informs galaxy formation simulations, IMF at high z, feedback roles.

University of Tokyo: Powerhouse in Astronomy

UTokyo's Institute of Astronomy leads Japan in observational cosmology. Home to Subaru Telescope collaborations, ALMA key projects, Kavli IPMU (Nobel-linked), it trains top talent. Recent feats: JWST early galaxies, gravitational waves.

This study exemplifies grad-led innovation, fostering PhD/postdocs via JSPS grants. Links to research jobs in Japan highlight opportunities.

Spotlight: Akiyoshi Tsujita and Team

Lead author Tsujita, PhD candidate, specializes in molecular line observations. Co-authors: Prof. Chiaki Kobayashi (Kavli IPMU/UTokyo-Hertfordshire) models nucleosynthesis; Prof. Kotaro Kohno (UTokyo) extragalactic mm-wave expert; Yuki Yoshimura et al. from NAOJ, Nagoya U.

"Our non-detection redefines early fluorine timelines," Tsujita notes. Kobayashi adds: "Consistent with no WR yet—AGB later." International team boosts Japan's astro profile.

Japan's Astronomy Renaissance

Japan invests heavily: ALMA (Chile), Subaru (Hawaii), upcoming Thirty Meter Telescope. UTokyo grads staff JAXA, NAOJ. This fuels higher ed jobs in Japan, postdocs via Humboldt/JSPS.

Impacts: Enhances NIRF rankings, attracts global talent to Tokyo.

Future Horizons: Probing Cosmic Chemistry

Next: ALMA Cycle 12 for more z=6-8 DSFGs, JWST MIRI for mid-IR F lines. Simulations refine WR yields. UTokyo plans HF surveys, linking to academic careers.

Actionable: Aspiring astronomers, explore UTokyo's MSc/PhD programs.

Photo by Tsuyoshi Kozu on Unsplash

This UTokyo breakthrough illuminates the universe's chemical dawn, showcasing Japan's higher ed excellence. For faculty roles, visit higher ed jobs; rate profs at Rate My Professor; career tips at higher ed career advice. Explore university jobs and Japan opportunities.