S22A0061

It is well known that quiescent galaxies at z=3−4 are mostly compact with R_e<1 kpc. The compact stellar distribution and near-infrared spectroscopic studies suggest that they are formed by a short burst of star formation. In contrast to these results, we have recently discovered a promising candidate of an extended (R_e=3.2±0.2 kpc) quiescent galaxy at z_phot=4.4±0.1 by SWIMS observations with medium-band filters (K₁ and K₃). The SED is consistent with star formation histories involving a long-lived star formation, rather than an instantaneous starburst. However, the current SWIMS data is not sufficient to characterize the Balmer break, due to the low SNR in the K₁-band (2.8σ). Unfortunately, the faint (K_s=23−24 ABmag) and extended continuum emission make it difficult for us to detect the continuum emission by slit spectroscopy. We here propose deeper SWIMS observations of the extended quiescent galaxy candidate at z=4.4. A confirmation of an extended galaxy with the strong Balmer break would suggest that there is another evolutionary track to form galaxies at z>4. The SWIMS imaging observations are the only way to confirm the redshift of the quiescent galaxy candidate and constrain the star formation history using 8 m-class telescopes.

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