ASTRO-3D

Abstract We present Keck/MOSFIRE H -band spectroscopic measurements covering the [C iii ] λ 1907, C iii ] λ 1909 doublet for a sample of eight z ∼ 7 spectroscopically confirmed star-forming galaxies drawn from the Reionization Era Bright Emission Line Survey (REBELS). This REBELS–MOSFIRE sample is notable for its bright median UV luminosity ( M UV = −22.5 AB) and large median stellar mass ( log M * / M ⊙ = 9.2 ). Although three sources show tentative evidence of a C iii ] detection, we obtain no confident detections for any of the eight REBELS–MOSFIRE sources. The median [C iii ] λ 1907+C iii ] λ 1909 3 σ upper limit in equivalent width (EW) for the REBELS–MOSFIRE sample is 6.5 Å, and a stack of their H -band MOSFIRE spectra yields a nondetection with an associated 3 σ upper limit of 2.6 Å. These upper limits fall significantly below the C iii ] EW measured in a composite spectrum of representative z ∼ 7 star-forming galaxies, as well as those measured for notable early star-forming galaxies such as GN-z11, GHZ2, GS-z12, and RXCJ2248-ID. The lack of strong C iii ] emission can be understood within the context of the stellar populations of the REBELS galaxies, as well as the ionization conditions and gas-phase metallicity implied by rest-frame optical spectroscopic properties ([O iii ]+H β EWs, and [O iii ] λ 5007/[O ii ] λ 3727 and [Ne iii ] λ 3869/[O ii ] λ 3727 line ratios). The REBELS–MOSFIRE sample represents the higher-mass, higher-metallicity, lower-excitation tail of the z ∼ 7 galaxy population, whose ionizing properties must be fully characterized to constrain the role of star-forming galaxies during cosmic reionization.

Abstract Stellar feedback drives multiphase gas outflows from starburst galaxies, but the interpretation of dust emission in these winds remains uncertain. To investigate this, we analyze new JWST mid-infrared images tracing polycyclic aromatic hydrocarbon (PAH) emission at 7.7 and 11.3 μ m from the outflow of the prototypical starburst M82 out to 3.2 kpc. We find that PAH emission shows significant correlations with CO, H α , and X-ray emission within the outflow, though the strengths and behaviors of these correlations vary with gas phase and distance from the starburst. PAH emission correlates strongly with cold molecular gas, with PAH–CO scaling relations in the wind nearly identical to those in galaxy disks despite the very different conditions. The H α –PAH correlation indicates that H α traces the surfaces of PAH-bearing clouds, consistent with arising from ionized layers produced by shocks. Meanwhile, the PAH–X-ray correlation disappears once distance effects are controlled for past 2 kpc, suggesting that PAHs are decoupled from the hot gas and the global correlation merely reflects the large-scale structure of the outflow. The PAH-to-neutral gas ratio remains nearly flat to 2 kpc, with variations following changes in the radiation field. This implies that the product of PAH abundance and dust-to-gas ratio does not change significantly over the inner portion of the outflow. Together, these results demonstrate that PAHs robustly trace the cold phase of M82’s wind, surviving well beyond the starburst and providing a powerful, high-resolution proxy for mapping the life cycle of entrained cold material in galactic outflows.

Context. Understanding the most metal-poor objects is key to interpreting the nature of the first stars. HE 1327-2326 (HE 1327), with metallicity [Fe/H] = −5.2, is one of the most metal-poor stars detected and a candidate to be the offspring of the first stars. Numerous efforts have been made to reproduce its abundance pattern, especially with high-mass stars undergoing supernova (SN) explosions. However, no model satisfactorily explains its entire surface chemical composition. Aims. The characteristic high CNO pattern with [N/Fe] > [C/Fe] > [O/Fe], the light element ‘slide’ (between Na and Si), and the presence of Sr and Ba in HE 1327 is reminiscent of asymptotic giant branch (AGB) stars that undergo third dredge-up, hot-bottom burning, and s-processing – suggesting that these stars were the source of the chemistry of the star. We tested this hypothesis. Methods. We assumed that, where HE 1327 formed, the interstellar medium was well mixed, and adopted an initial stellar composition based on the observed chemical evolution of the early Universe. Zinc, which is enhanced in HE 1327, is well matched by this initial composition, as are the α -elements. We calculated models of hyper-metal-poor AGB stars and compared the predicted chemical yields to the observed chemical pattern of HE 1327. Resulst. We find our 3 M ⊙ models match 13 of the 14 measured elements in HE1327, more than any model thus far. They are also consistent with the seven elements with known upper limits. The only discrepancy is oxygen, which is underproduced by 0.5 − 1.0 dex. For elements up to Zn, the match is comparable to that of the best-fitting, finely tuned SN models. Unlike the SN models, the AGB models also match Sr and Ba. We stress that the AGB scenario requires only standard stellar evolution, without invoking exotic scenarios. Our model predicts high abundances of P and Pb; thus, observations of these elements would be useful in testing the AGB scenario. Conclusions. We propose that HE 1327 is the oldest known object that shows nucleosynthetic evidence of the first AGB stars. With lifetimes as short as 200 Myr, these stars may have formed and polluted the Universe very early on. Recent Pop III star formation simulations support this hypothesis, and their strong nitrogen production is qualitatively consistent with recent JWST observations showing high N/O ratios just 440 Myr after the Big Bang. Importantly, our results also suggest that the interstellar medium experienced some degree of homogeneity and mixing at these early epochs.

Abstract The metallicity of galaxies, and its variation with galactocentric radius, provides key insights into the formation histories of galaxies and the physical processes driving their evolution. In this work, we analyze the radial metallicity gradients of star-forming galaxies in the EAGLE, Illustris, IllustrisTNG, and SIMBA cosmological simulations across broad mass (108.0 M ⊙ ≤ M ⋆ ≲ 1012.0 M ⊙) and redshift (0 ≤ z ≤ 8) ranges. We find that all simulations predict strong negative (i.e., radially decreasing) metallicity gradients at early cosmic times, likely due to their similar treatments of relatively smooth stellar feedback not providing sufficient mixing to quickly flatten gradients. The strongest redshift evolution occurs in galaxies with stellar masses of 1010.0–1011.0 M ⊙, while galaxies with stellar mass < 1010 M ⊙ and >1011 M ⊙ exhibit weaker redshift evolution. Our result of negative gradients at high redshift contrast with the many positive and flat gradients in the 1 < z < 4 observational literature. At z > 6, the negative gradients observed with JWST and the Atacama Large Millimeter/submillimeter Array are flatter than those in simulations, albeit with closer agreement than at lower redshift. Overall, we suggest that these smooth stellar feedback galaxy simulations may not sufficiently mix their metal content radially, and that either stronger stellar feedback or additional subgrid turbulent metal diffusion models may be required to better reproduce observed metallicity gradients.

ABSTRACT Giant pulses (GPs) occur in high magnetic field millisecond pulsars and young Crab-like pulsars. Motivated by the fast radio bursts (FRBs) discovered in a globular cluster (GC) in the M81, we undertook baseband observations of PSR J1823–3021A, the most active GP emitter in a GC with the Meer Karoo Array Telescope (MeerKAT) ultra high frequency (UHF) band receiver (544–1088 MHz). The steep spectral index of the pulsar yields a GP rate of over 37 000 GPs h−1 with $\mathrm{ S/N}>7$, significantly higher than the 3000 GPs h−1 rate detected by previous work with the L-band (856–1712 MHz) receiver. Similarly to the previous work, we find that the GPs are (1) strongly clustered in two particular phases of its rotation, (2) well described by a power-law in terms of energies, (3) typically broad-band, and have steep spectral indices of ${\approx} {-}3$. Although the integrated pulse profile is not significantly polarized (${<} 1~{{\ \rm per\ cent}}$ linear and ${<} 3~{{\ \rm per\ cent}}$ circular), one of the brightest GPs displays notable polarization of 7 per cent (linear) and 8 per cent (circular). The high-time resolution data reveals the GPs have a range of single-peak and multipeak morphologies, including GPs with three distinct peaks. For the first time, we measured the temporal scattering of the pulsar using 49 bright, narrow, single-pulse GPs, obtaining a mean value of $5.5\pm 0.6$ $\mu$s at 1 GHz. The distinct periodicity and low polarization of GPs differentiate them from typical FRBs, although potential quasi-periodicity substructures in some GPs may suggest a connection to magnetars/FRBs.

Abstract There is a broad consensus from theory that stellar feedback in galaxies at high redshifts is essential to their evolution, alongside conflicting evidence in the observational literature about its prevalence and efficacy. To this end, we utilize deep, high-resolution [C II] emission-line data taken as part of the [C II] resolved interstellar medium (ISM) in star-forming galaxies with the Atacama Large Millimeter/submillimeter Array (CRISTAL) survey. Excluding sources with kinematic evidence for gravitational interactions, we perform a rigorous stacking analysis of the remaining 15 galaxies to search for broad emission features that are too weak to detect in the individual spectra, finding only weak evidence that a broad component is needed to explain the composite spectrum. Additionally, such evidence is mostly driven by CRISTAL-02, which is already known to exhibit strong outflows in multiple ISM phases. Interpreting modest residuals in the stack at v ∼ 300 km s−1 as an outflow, we derive a mass outflow rate of M ̇ out = 26 ± 11 M ⊙ yr−1 and a cold outflow mass-loading factor of η m = 0.49 ± 0.20. This result holds for the subsample with the highest star formation rate surface density (ΣSFR > 1.93 M ⊙ yr−1 kpc−2), but no such broad component is present in the composite of the lower-star-formation-rate density subsample. Our results imply that the process of star-formation-driven feedback may already be in place in typical galaxies at z = 5, but on average are not strong enough to completely quench ongoing star formation.

Erratum: “Evidence of Ultrafaint Radio Frequency Interference in Deep 21 cm Epoch of Reionization Power Spectra with the Murchison Wide-field Array” (2023, ApJ, 957, 78), Wilensky, Michael J., Morales, Miguel F., Hazelton, Bryna J., Star, Pyxie L., Barry, Nichole, Byrne, Ruby, Jordan, C. H., Jacobs, Daniel C., Pober, Jonathan C., Trott, C. M.

Abstract We examine the energy distribution of the fast radio burst (FRB) population using a well-defined sample of 63 FRBs from the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope, 28 of which are localised to a host galaxy. We apply the luminosity-volume ( $V/V_{\mathrm{max}}$ ) test to examine the distribution of these transient sources, accounting for cosmological and instrumental effects, and determine the energy distribution for the sampled population over the redshift range $0.01 \lesssim z \lesssim 1.02$ . We find the distribution between $10^{23}$ and $10^{26}$ J Hz $^{-1}$ to be consistent with both a pure power-law with differential slope $\gamma=-1.96 \pm 0.15$ , and a Schechter function with $\gamma = -1.82 \pm 0.12$ and downturn energy $E_\mathrm{max} \sim 6.3 \, \times 10^{25}$ J Hz $^{-1}$ . We identify systematic effects which currently limit our ability to probe the luminosity function outside this range and give a prescription for their treatment. Finally, we find that with the current dataset, we are unable to distinguish between the evolutionary and spectral models considered in this work.