Researchers reveal a galaxy sparkling with the universe's oldest star clusters AAS_Office
1. IntroductionDespite being the subject of very active research for decades , we do not know when, or understand how, globular clusters form. We do know that most globular clusters in the Milky Way , and those around nearby galaxies, are very old. The absolute ages of the oldest MW globular clusters, determined by main-sequence fitting and from the ages of the oldest white dwarfs, are about 12.5 Gyr, corresponding to formation redshifts of zform ∼ 5.
2. DataThe imaging and wide-field slitless spectroscopy data used for this work are from the JWST Early Release Observations program 2736 . The galaxy cluster was observed with all four instruments on JWST. Only Near-Infrared Camera imaging and Near-Infrared Imager and Slitless Spectrograph spectroscopy are used in this paper. NIRCam imaging is available in six broadband filters: F090W, F150W, F200W, F277W, F356W, and F444W.
3.1. Aperture PhotometryPhotometry is challenging in crowded fields, and in the case of the Sparkler the challenges are compounded by contamination from the host galaxy and from other nearby sources. This contamination can significantly alter the shape of the SED of the individual compact sources. In a future paper we will present a full catalog of compact sources around the Sparkler that attempts to account for these effects by subtracting contamination models and using PSF photometry.
3.3. Grism Extraction and FittingBefore extracting the individual NIRISS spectra, we constructed a contamination model of the entire field using Grizli. We modeled the sources at both grism orientations. This model was built using a segmentation map and photometric catalog created with SEP . We initially assumed a flat spectrum, normalized by the flux in the photometric catalog, in our models.
Notes. Reported uncertainties represent the 16th–84th percentiles of the posterior distribution for each quantity. We close this section with some preliminary discussion of the mass of the Sparkler. Fits to the integrated photometry of images 1 and 3 using Dense Basis recover log stellar masses of M⊙ and M⊙, respectively for the host galaxy , and SFHs that show a recent rise over the last ∼Gyr. We do not fit image 2 due to the strong differential magnification. Assuming a magnification of ∼5 for image 1 and Mahler et al.
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