arXiv subjects

Belinda Wu

Publications and source records attributed to Belinda Wu.

2 recordsLinked to original sources

arXiv2026

Taking a Break at Cosmic Noon: Continuum-selected Low-mass Galaxies Require Long Burst Cycles

While bursty star formation in low-mass galaxies has been observed in local populations and reproduced in simulations, the dormant phase of the burst cycle has not been well studied beyond the local Universe due to observational limitations. We present a unique sample of 43 JWST PRISM spectra of low-mass galaxies ($M_\star < 10^{9.5}\,M_\odot$) at cosmic noon ($1<z<3$), uniformly selected on F200W magnitude and precise photometric redshifts enabled by 20-band JWST photometry from the UNCOVER and MegaScience surveys. The spectra reveal numerous strong Balmer breaks, which are negatively correlated with the galaxies' H$α$ equivalent width. By comparing these observations to synthetic samples of spectra generated using a simple parametrization of bursty star formation histories, we show that star formation in low-mass galaxies at cosmic noon is likely dominated by burst cycles with long timescales ($\gtrsim 100$ Myr) and large deviations below the star-forming main sequence ($\gtrsim 0.8$ dex). Our results suggest that galaxies in this population--at least those within our detection limits--should not be classified solely by their current star formation rates, but instead viewed as a unified population undergoing dynamic movement above and below the star-forming main sequence. The derived constraints demonstrate that long-timescale fluctuations are important for this class of galaxies, indicating that galaxy-scale gas cycles--rather than molecular-cloud-scale stochasticity--are the primary regulators of star formation variability in low-mass galaxies at cosmic noon.

astro-ph.GA↗

arXiv2023

Density Profiles of Collapsed Rotating Massive Stars Favor Long Gamma-Ray Bursts

Long-duration gamma-ray bursts (lGRBs) originate in relativistic collimated outflows -- jets -- that drill their way out of collapsing massive stars. Accurately modeling this process requires realistic stellar profiles for the jets to propagate through and break out of. Most previous studies have used simple power laws or pre-collapse models for massive stars. However, the relevant stellar profile for lGRB models is in fact that of a star after its core has collapsed to form a compact object. To self-consistently compute such a stellar profile, we use the open-source code GR1D to simulate the core-collapse process for a suite of low-metallicity, rotating, massive stellar progenitors that have undergone chemically homogeneous evolution. Our models span a range of zero-age main sequence (ZAMS) masses: $M_\mathrm{ZAMS} = 13, 18, 21, 25, 35, 40$, and $45 M_\odot$. All of these models, at the onset of core-collapse, feature steep density profiles, $ρ\propto r^{-α}$ with $α\approx 2.5$, which would result in jets that are inconsistent with lGRB observables. We follow the collapse of four out of our seven models until they form BHs and the other three proto-neutron stars (PNSs). We find, across all models, that the density profile outside of the newly-formed BH or PNS is well-represented by a flatter power law with $α\approx 1.35{-}1.55$. Such flat density profiles are conducive to successful formation and breakout of BH-powered jets and, in fact, required to reproduce observable properties of lGRBs. Future models of lGRBs should be initialized with shallower \textit{post-collapse} stellar profiles like those presented here instead of the much steeper pre-collapse profiles that are typically used.

astro-ph.HE↗