Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

LAP1-B is the First Observed System Consistent with Theoretical Predictions for Population III Stars

Eli Visbal, Ryan Hazlett, Greg L. Bryan

TL;DR

This paper argues that LAP1-B, a highly magnified $z=6.6$ Pop III candidate behind MACS J0416, is the first object to align with three core Pop III predictions: formation in halos with $T_{\rm vir}\sim 10^3-10^4$ K, a top-heavy initial mass function, and formation in low-mass clusters of total stellar mass ${\sim}{\rm few}\times 10^3\,M_\odot$. By integrating JWST data with an updated semi-analytic Pop III model (Visbal et al. 2020), it links observed H$\alpha$ emission and gas properties to a cluster mass of ${\sim}10^3$–$5\times10^3\,M_\odot$ and a central gas reservoir of $\sim10^5\,M_\odot$, consistent with an atomic cooling halo. The abundance analysis predicts about one LAP1-B–like galaxy behind a MACS J0416–like lens at $z\sim6.5$, supporting the idea that the first Pop III detections occur near this redshift under current observational limits, while higher-redshift Pop III systems would require deeper surveys. The work also argues that several other JWST candidates imply unrealistically large Pop III stellar masses for classical Pop III star formation, highlighting the importance of IMF, metal enrichment, and halo temperature in interpreting early stellar populations.

Abstract

Recently, Nakajima et al. (2025) presented James Webb Space Telescope observations of the $z=6.6$ Population III (Pop III) candidate LAP1-B, which is gravitationally lensed by galaxy cluster MACS J0416. We argue that this is the first object to agree with three key theoretical predictions for Pop III stars: (1) formation in extremely low-metallicity halos with virial temperatures ranging from $T_{\rm vir}\sim 10^3-10^4~{\rm K}$, (2) a top-heavy initial mass function, and (3) formation of low-mass clusters with ${\sim}{\rm a ~few}\times 1000~M_\odot$ in massive Pop III stars. LAP1-B is consistent with recently formed Pop III stars hosted in a $\sim 5\times 10^7~M_\odot$ dark matter halo, some of which have enriched their surrounding gas either with supernovae or stellar winds. We use the semi-analytic model of Visbal et al. (2020) to predict the abundance of Pop III clusters observable at the high magnification provided by the foreground galaxy cluster MACS J0416. Using fiducial parameters unmodified from previous work, we expect about one observable Pop III galaxy similar to LAP1-B in the range $z=6-7$. At earlier times, the intrinsic abundance is higher, but Pop III systems would not have been detected because of their increased luminosity distance and lower mass dark matter halos, which would host fewer stars. Thus, we find that LAP1-B was found at the redshift theoretically expected, given current observable limits, despite the fact that most Pop III systems form much earlier.

LAP1-B is the First Observed System Consistent with Theoretical Predictions for Population III Stars

TL;DR

This paper argues that LAP1-B, a highly magnified Pop III candidate behind MACS J0416, is the first object to align with three core Pop III predictions: formation in halos with K, a top-heavy initial mass function, and formation in low-mass clusters of total stellar mass . By integrating JWST data with an updated semi-analytic Pop III model (Visbal et al. 2020), it links observed H emission and gas properties to a cluster mass of – and a central gas reservoir of , consistent with an atomic cooling halo. The abundance analysis predicts about one LAP1-B–like galaxy behind a MACS J0416–like lens at , supporting the idea that the first Pop III detections occur near this redshift under current observational limits, while higher-redshift Pop III systems would require deeper surveys. The work also argues that several other JWST candidates imply unrealistically large Pop III stellar masses for classical Pop III star formation, highlighting the importance of IMF, metal enrichment, and halo temperature in interpreting early stellar populations.

Abstract

Recently, Nakajima et al. (2025) presented James Webb Space Telescope observations of the Population III (Pop III) candidate LAP1-B, which is gravitationally lensed by galaxy cluster MACS J0416. We argue that this is the first object to agree with three key theoretical predictions for Pop III stars: (1) formation in extremely low-metallicity halos with virial temperatures ranging from , (2) a top-heavy initial mass function, and (3) formation of low-mass clusters with in massive Pop III stars. LAP1-B is consistent with recently formed Pop III stars hosted in a dark matter halo, some of which have enriched their surrounding gas either with supernovae or stellar winds. We use the semi-analytic model of Visbal et al. (2020) to predict the abundance of Pop III clusters observable at the high magnification provided by the foreground galaxy cluster MACS J0416. Using fiducial parameters unmodified from previous work, we expect about one observable Pop III galaxy similar to LAP1-B in the range . At earlier times, the intrinsic abundance is higher, but Pop III systems would not have been detected because of their increased luminosity distance and lower mass dark matter halos, which would host fewer stars. Thus, we find that LAP1-B was found at the redshift theoretically expected, given current observable limits, despite the fact that most Pop III systems form much earlier.

Paper Structure

This paper contains 7 sections, 1 equation, 2 figures.

Table of Contents

  1. Introduction
  2. Physical Properties of LAP1-B
  3. Mass of Pop III Stars
  4. Gas and Dark Matter Mass
  5. Metal Enrichment
  6. Predicted Abundance of LAP1-B like objects
  7. Discussion and Conclusions

Figures (2)

  • Figure 1: The total stellar mass of Pop III stars required to generate the H$\alpha$ emission observed in LAP1-B as a function of the mass of each individual star (computed from Eq. \ref{['eqn:mass']} assuming all stars are of the same mass). This value is calculated assuming fractional numbers of stars are allowed which is unphysical, but shows that the ionizing efficiency saturates at stellar masses of ${\sim}200~M_\odot$. Diagonal dashed lines indicate constant numbers of stars.
  • Figure 2: Top panel: Abundance of classical Pop III sources that have formed within the past 3 Myr. Middle Panel: The mean H$\alpha$ flux from these sources assuming a magnification of $\mu=100$. The horizontal dashed line corresponds to the 3$\sigma$ uncertainty in LAP1B. Bottom Panel: The predicted cumulative number of Pop III sources formed within 3 Myr at redshift from 5.9 to $z$ within the area where galaxy cluster MACS J0416 has magnification $\mu>30$. The dashed vertical line corresponds to the redshift of $z=8$ where the detection of the H$\alpha$ line is at ${\sim}3\sigma$. The dotted vertical line indicates the redshift of LAP1-B, $z=6.6$. The cumulative abundance at $z=6.6$ is 0.88, consistent with the detection of LAP1-B.