arXiv subjects

Carter Meyerhoff

Publications and source records attributed to Carter Meyerhoff.

3 recordsLinked to original sources

arXiv2026

Physically Motivated Stellar Populations for Galaxies at Cosmic Dawn with a Temperature-Dependent IMF

The first few years of James Webb Space Telescope observations have identified previously undetected galaxies at $z>12$ and provided new constraints on galaxies at $z>8$. Many of these objects have stellar masses that are difficult to reconcile with $Λ$CDM, inferred from models not calibrated for the high-redshift Universe. This necessitates new, more astrophysically plausible stellar population models for estimating stellar masses of galaxies at cosmic dawn. We introduce a simple stellar population (SSP) library, Simple Stellar Populations with Temperature (SSPT), computed using a temperature-dependent stellar initial mass function and its implementation in the public code CIGALE. When used in a configuration designed for high-redshift galaxies that requires young stellar population ages, the new models predict stellar masses that are ~0.3-0.5 dex lower than estimates from similar CIGALE analyses using models calibrated to the local Universe, and nearly 2 dex lower than estimates from analyses using other codes and softer constraints on stellar ages. Application of these physically motivated stellar populations suggests that stellar masses of early star-forming galaxies are not in tension with $Λ$CDM, and that galaxy formation from virialized halos remains a reasonable hypothesis at the highest redshifts. The SSPT SSPs and their CIGALE implementation are released publicly.

astro-ph.GA↗

arXiv2026

Constraining the Light Curves of Magnified Stellar Events at z ~ 0.725

Extreme magnification by lensing galaxy clusters allows the detection of high-luminosity stars during cluster caustic transient events at cosmological distances. The Dragon Arc at z=0.725 is a frontier target for identifying transient events due to its high frequency of microlensing events, and so far >100 of these events have been detected. The high frequency of events and high cadence of observations allow for the measurement of minimal flux variation between epochs, and therefore the magnification evolution as a source approaches or recedes from a microcaustic can be measured from light curves. In this work, we model the light curves of 10 transient events in the Dragon Arc across eight epochs from two JWST/NIRCam medium-band filters taken over four days. Injected synthetic observations demonstrate that with additional observations, individual transient light curves allow the of apparent degeneracies between stellar characteristics and properties of motion.

astro-ph.GA↗

arXiv2026

Direct Evidence for Stellar Initial Mass Function Variation in the Milky Way

Because direct measurements require resolved stellar populations including low-mass stars, determining the stellar initial mass function (IMF) has been a historically difficult problem even within our own Galaxy and impossible everywhere else. As a result, even though it is predicted that the IMF should vary depending upon the properties of each individual star-forming molecular cloud, it is standard to assume a Universal IMF. Using recent observations from {\em Gaia}, it is now possible to test for IMF variation using resolved stellar populations in open clusters and a parameterization that separates properties of the IMF from subsequent dynamical evolution. Here, we show that the IMF is not Universal but instead varies across individual Galactic stellar populations, reflecting evolution in the average conditions of molecular clouds over cosmic time. This evolution is consistent with the predictions of a simple astrophysical model in which the IMF is environmentally-dependent and the Milky Way reflects typical galactic behavior in recent cosmic history. Thus, observational evidence now agrees with long-standing theoretical and numerical predictions.

astro-ph.GA↗