The link between submillimetre galaxies and luminous ellipticals: near-infrared IFU spectroscopy of submillimetre galaxies

We present two-dimensional spectroscopy covering the rest-frame wavelengths of strong optical emission lines in six luminous submillimetre galaxies (SMGs) at z= 1.3–2.5. Using this near-infrared integral field spectroscopy together with Hubble Space Telescope ACS and NICMOS imaging, we map the dynamics and morphologies of these systems on scales from 4–11 kpc. Four of the systems show multiple components in their spatially resolved spectra with average velocity offsets of ∼180 km s−1 across 8 kpc in projection. From the ensemble properties of eight galaxies, from our survey and the literature, we estimate the typical dynamical masses of bright SMGs as 5 ± 3 × 1011 M⊙. This is similar to recent estimates of their stellar masses – suggesting that the dynamics of the central regions of these galaxies are baryon dominated, with a substantial fraction of those baryons in stars by the epoch of observation. Combining our dynamical mass estimates with stellar luminosities for this population, we investigate whether SMGs can evolve on to the Faber–Jackson (FJ) relation for local ellipticals. Adopting a typical lifetime of τburst∼ 300 Myr for the submillimetre-luminous phase – using the latest estimates of gas masses, star formation rates and active galactic nucleus contribution to the bolometric luminosities – we find that the stellar populations of SMGs should fade to place them on the FJ relation, at MK∼−25.1. Furthermore, using the same starburst lifetime we correct the observed space density of SMGs for the duty cycle to derive a volume density of the progenitors of ∼1 × 10−4 Mpc−3. This is consistent with the space density of local luminous early-type galaxies with MK∼−25.1, indicating that SMGs can evolve on to the scaling relations observed for local early-type galaxies, and the observed population at z∼ 2 is then sufficient to account for the formation of the whole population of ≳3 L*K ellipticals seen at z∼ 0.