New technique to select recent fast-quenching galaxies at z ~ 2 using the optical colours

• Published in: Monthly notices of the Royal Astronomical Society 2024-01, Vol.527 (1), p.403-413
• Main Authors: Kubo, Mariko, Nagao, Tohru, Uchiyama, Hisakazu, Yamashita, Takuji, Toba, Yoshiki, Kajisawa, Masaru, Yamamoto, Yuta
• Format: Article
• Language: English
• Subjects: A stars; Color; Galaxies; Infrared photometry; Infrared spectra; Infrared spectroscopy; Infrared stars; Near infrared radiation; Photometry; Quenching; Star & galaxy formation; Star formation; Stars & galaxies
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stad3210

ABSTRACT Many massive quiescent galaxies have been discovered at z > 2 thanks to multiwavelength deep and wide surveys; however, substantial deep near-infrared spectroscopic observations are needed to constrain their star formation histories statistically. Here, we present a new technique to select quiescent galaxies with a short quenching time-scale (≤0.1 Gyr) at z ∼ 2 photometrically. We focus on a spectral break at ∼1600 Å that appears for such fast-quenching galaxies ∼1 Gyr after quenching when early A-type stars go out, but late A-type stars still live. This spectral break at z ∼ 2 is similar to a Lyman break at z ∼ 4. We construct a set of colour criteria for z ∼ 2 fast-quenching galaxies on g − r versus r − i and i − J versus J − H or $\rm {\it i}-[3.6]$ versus $\rm [3.6]-[4.5]$ colour diagrams, which are available with the existing and/or future wide imaging surveys, by simulating various model galaxy spectra and test their robustnesses using the COSMOS2020 catalogue. Galaxies with photometric and/or spectroscopic redshifts z ∼ 2 and low specific star formation rates are successfully selected using these colours. The number density of these fast-quenching galaxy candidates at z ∼ 2 suggests that massive galaxies not so far above the star formation main sequence at z = 3–4 should be their progenitors.