HST/WFC3 Near-Infrared spectroscopy of quenched galaxies at z~1.5 from the WISP Survey: Stellar population properties

We combine Hubble Space Telescope (HST) G102 and G141 near-IR (NIR) grism spectroscopy with HST/WFC3UVIS, HST/WFC3-IR, and Spitzer/IRAC [3.6 mu m] photometry to assemble a sample ofmassive (log(M-star/M-circle dot) similar to 11.0) and quenched (specific star formation rate < 0.01 Gyr-1) galaxies at z similar to 1.5. Our sample of 41 galaxies is the largest with G102+G141 NIR spectroscopy for quenched sources at these redshifts. In contrast to the local universe, z similar to 1.5 quenched galaxies in the high-mass range have a wide range of stellar population properties. We find that their spectral energy distributions (SEDs) are well fitted with exponentially decreasing star formation histories and short star formation timescales (tau