James Webb Reveals Galaxy Evolution at Cosmic Dawn with NIRCam.

Observations of high-redshift galaxies at z≈7 reveal that dense multi-filter imaging with the NIRCam instrument can effectively determine stellar population properties and rest-frame colours, even without coverage of specific rest-frame optical wavelengths provided by MIRI. Delayed-tau star formation history assumptions yield the most consistent results.

Understanding the earliest epochs of star formation remains a significant challenge in cosmology. Disentangling the contributions of young stars, surrounding gas, and obscuring dust within distant galaxies requires detailed observations across multiple wavelengths. A recent investigation, detailed in ‘The Stellar Populations and Rest-Frame Colors of Star-Forming Galaxies at : Exploring the Impact of Filter Choice and Star Formation History Assumption with JADES’, addresses these complexities using data from the James Webb Space Telescope’s Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI). The research, conducted by Jakob M. Helton, Stacey Alberts, Benjamin D. Johnson, Brant Robertson, Sandro Tacchella, Lily Whitler, George H. Rieke, Kevin N. Hainline, Zhiyuan Ji, Marcia J. Rieke, William M. Baker, Rachana Bhatawdekar, Phillip A. Cargile, Stefano Carniani, Kristan Boyett, Stephane Charlot, Andrew J. Bunker, Jacopo Chevallard, Emma Curtis-Lake, Eiichi Egami, Daniel J. Eisenstein, Ryan Hausen, Jianwei Lyu, Roberto Maiolino, Erica Nelson, Pablo G. P´erez-Gonz´alez, Meredith Stone, Fengwu Sun, Christina C. Williams, Pierluigi Rinaldi, and Christopher N. A. Willmer, demonstrates that dense spectral coverage with NIRCam can, for many galaxies, mitigate the need for observations in specific rest-frame optical wavelengths typically provided by MIRI, when determining stellar population characteristics. The team’s analysis of galaxies at a redshift of approximately 7, utilising the JADES survey, highlights the importance of modelling star formation histories to accurately characterise these early stellar populations.

Characterising Distant Galaxies with the James Webb Space Telescope

Recent research utilising data from the James Webb Space Telescope (JWST) indicates that comprehensive characterisation of high-redshift galaxies – those observed at a substantial distance, and therefore from an earlier epoch in the universe’s history – is frequently achievable using observations from the Near-Infrared Camera (NIRCam) instrument alone. However, the inclusion of data from the Mid-Infrared Instrument (MIRI) proves critical for a specific subset of these distant objects.

The study focuses on galaxies at a redshift of approximately 8 (denoted as z≈8). Redshift is a measure of how much the light from an object has been stretched due to the expansion of the universe; higher redshift values correspond to greater distances and earlier times. Analysing the spectral energy distributions (SEDs) – the amount of energy emitted by a galaxy across different wavelengths – allows astronomers to infer properties such as stellar mass, age, and star formation rate.

Results demonstrate that for the majority of galaxies examined, estimations of these key properties remain consistent whether data from MIRI is incorporated into the analysis or not. This underscores the capability of multi-filter NIRCam observations to provide robust characterisations. Multi-filter observations involve capturing images through a series of filters, each allowing only a specific range of wavelengths to pass through, thereby providing a more detailed spectral analysis.

However, a discernible subset of galaxies exhibits significant sensitivity to the inclusion of MIRI data. For these objects, incorporating mid-infrared observations substantially alters estimations of stellar population properties and star formation histories. This suggests that MIRI observations are essential for accurately characterising these specific galaxies, likely due to its ability to detect emission from dust which is often obscured from view at shorter wavelengths.

The research team employed a delayed-tau model – a mathematical function describing the rate of star formation over time – and found it consistently yielded the most reliable estimations of galaxy properties. This model assumes that star formation begins at a certain time and then gradually slows down.

Ongoing research concentrates on identifying the specific characteristics that determine whether MIRI data is essential for accurate characterisation. Factors under investigation include stellar mass, dust content, and the intensity of star formation.

The overarching goal of this work is to refine our understanding of galaxy evolution during the Epoch of Reionization – a period in the early universe when the first stars and galaxies began to ionise the surrounding gas. By leveraging the complementary capabilities of JWST’s NIRCam and MIRI instruments, astronomers aim to build a more complete picture of this crucial phase in cosmic history.