REQUIEM-ALMA — REQUIEM

Images of six massive lensed galaxies where star formation has been quenched. The panels are rank-ordered from z=1.6 to z=3.2 (labeled a-f), showing a composite Hubble Space Telescope (HST) color image (F814W, F125W, F160W generally, substituting F110W for panel e) and contours of ALMA/Band 6 dust continuum observations. Each image is centered on the target galaxy, whose redshift is listed in the upper-left corner. The dashed ellipse indicates the ALMA beam size, with the 1σ noise level noted at the bottom of each panel in units of mJy per beam. From Whitaker et al. (2021). — **Images of six massive lensed galaxies where star formation has been quenched.** The panels are rank-ordered from z=1.6 to z=3.2 (labeled a-f), showing a composite *Hubble Space Telescope* (*HST)* color image (F814W, F125W, F160W generally, substituting F110W for panel e) and contours of ALMA/Band 6 dust continuum observations. Each image is centered on the target galaxy, whose redshift is listed in the upper-left corner. The dashed ellipse indicates the ALMA beam size, with the 1σ noise level noted at the bottom of each panel in units of mJy per beam. From Whitaker et al. (2021).

The cold gas reservoirs of the first massive quiescent galaxies remain poorly constrained. Using ALMA Band 6 continuum imaging, we are measuring the total dust mass of the REQUIEM sample to infer their molecular-gas fractions, star-formation efficiencies and depletion timescales. The REQUIEM-ALMA program is sensitive down to unprecedented gas fraction levels of 1%. Six out of the ten galaxies have deep Band 6 continuum imaging executed in ALMA’s Cycle 6 and 7, with first results recently published in Whitaker et al. (2021, Nature).

While current high-redshift studies are comprised of galaxies with high gas fractions, we expect the progenitors of massive quiescent galaxies to have lower gas fractions and high star-formation efficiencies. Gravitationally lensed quiescent galaxies offer a unique opportunity to push these studies into uncharted parameter space. Observing this key phase of galaxy formation is only possible due to the strong lensing magnification and ALMA's exquisite sensitivity. Constraining the gas fraction and star-formation efficiency allows us to distinguish between leading physical mechanisms driving the formation and quenching of star formation in massive galaxies.

Relevant Publications:

Quenching of star formation from a lack of inflowing gas to galaxies Whitaker, K., Williams, C., Mowla, L, Spilker, J., Toft, S., Narayanan, D., Pope, A., Magdis, G., van Dokkum, P., Akhshik, M., Bezanson, R., Brammer, G., Leja, J., Man, A., Nelson, E., Richard, J., Pacifici, C., Sharon, K., Valentino, F., 2021, Nature, 597, 7877.
- Link to open-access, read-only version of paper: https://rdcu.be/cyfgK
Early Science with the Large Millimeter Telescope: Constraining the Gas Fraction of a Compact Quiescent Galaxy at z = 1.883 Caliendo, J., Whitaker, K., Akhshik, M., Wilson, G., Williams, C., Spilker, J., Mahler, G., Pope, A., Sharon, K., Aguilar, E., Bezanson, R., Chavez Dagostino, M., Gòmez-Ruiz, A., Montaña, A., Toft, S., Velazquez de la Rosa, M., Zeballos, M., 2021, Astrophysical Journal Letters, 910, 7.