Physics

Young stellar object

Galaxy

Star formation

Astronomy

Stars

Astrophysics

Star (game theory)

Redshift

Monthly Notices of the Royal Astronomical Society Letters

We present a first-look analysis of the JWST ERO data in the SMACS J0723.3-7327 cluster field. We begin by reporting 10 new spectroscopic redshifts from lambda(obs) = 1.8-5.2 mu m NIRSpec medium-resolution (R = lambda/Delta lambda = 1000) data. These are determined via multiple high-SNR emission line detections with five objects at 1 < z < 3 displaying multiple rest-frame near-infrared Hydrogen Paschen lines, and five objects at 5 < z < 9 displaying rest-frame optical Oxygen and Hydrogen Balmer lines. For the five higher-redshift galaxies we extract fluxes in six NIRCam bands spanning lambda(obs) = 0.8-5 mu m and perform spectral energy distribution fitting in combination with existing HST photometry. The 7 < z < 9 objects exhibit a U-shaped pattern across the F277W, F356 W, and F444 W bands, indicating a Balmer break seen in emission (Balmer jump) and high-equivalent-width [O III] emission. This indicates an extremely young stellar population with the bulk of the current mass having formed within the past 10 Myr. We report robust stellar masses and mean stellar ages from our spectral fitting with the four z > 6 galaxies exhibiting low-stellar masses from log (10) (M-*/M-circle dot) = 7.1-8.2, and correspondingly young mean stellar ages of only a few Myr. This work highlights the critical importance of combining large upcoming NIRCam surveys with NIRSpec follow-up to measure the spectroscopic redshifts necessary to robustly constrain physical parameters.

A first look at the SMACS0723 <i>JWST</i> ERO: spectroscopic redshifts, stellar masses, and star-formation histories

A first look at the SMACS0723 JWST ERO: spectroscopic redshifts, stellar masses, and star-formation histories