2015ApJ...806L..20S

Gas and dust in star-forming galaxies at the peak epoch of galaxy assembly are presently the topic of intense study, but little is known about the interstellar medium (ISM) of distant, passively evolving galaxies. We report on a deep 3 mm band search with the IRAM/Plateau de Bure Interferometer for molecular (H₂) gas in a massive ( Å 6x10¹¹) elliptical galaxy at z = 1.4277, the first observation of this kind ever attempted. We place a 3σ upper limit of 0.32 Jy km/s on the flux of the CO(J = 2 1) line or < 8.8x10⁹ K km/s pc², assuming a disklike CO-morphology and a circular velocity scaling with the stellar velocity dispersion as in local early-type galaxies (ETGs). This translates to an H₂ mass of <3.9x10¹⁰ (/4.4) or a gas fraction of <Å6% assuming a Salpeter initial mass function and an ISM dominated by H₂, as observed in many local, high-mass ellipticals. This low value approaches that of local ETGs, suggesting that the low star formation activity in massive, high-z passive galaxies reflects a true dearth of gas and a lesser role for inhibitive mechanisms like morphological quenching.