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

A M Swinbank,A W Blain,S C Chapman,G F Lewis,R J Ivison,Ian Smail,C Borys,C Lindner

doi:10.1111/j.1365-2966.2006.10673.x

Abstract

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.

Highlights

Deep optical and near-infrared imaging with the superlative resolution of the NICMOS and Advanced Camera for Surveys (ACS) cameras on-board Hubble Space Telescope (HST) has made it possible to study the morphologies and colours of high-redshift far-infrared luminous galaxies identified in the submillimetre waveband in unprecedented levels ofC 2006 The Authors
1 INTRODUCTION Deep optical and near-infrared imaging with the superlative resolution of the NICMOS and ACS cameras on-board Hubble Space Telescope (HST) has made it possible to study the morphologies and colours of high-redshift far-infrared luminous galaxies identified in the submillimetre waveband in unprecedented levels of
We have studied the rest-frame optical emission-line structures and dynamics of six high-redshift, luminous Submm galaxies (SMGs)

Summary

Introduction

Deep optical and near-infrared imaging with the superlative resolution of the NICMOS and ACS cameras on-board Hubble Space Telescope (HST) has made it possible to study the morphologies and colours of high-redshift far-infrared luminous galaxies identified in the submillimetre (submm) waveband in unprecedented levels ofC 2006 The Authors. Journal compilation C 2006 RAS detail (Smail et al 1998, 2002; Chapman et al 2003b; Smail et al 2004; Almaini et al 2005; Pope et al 2005) By combining this data with spectroscopically confirmed redshifts (Chapman et al 2003a, 2005), we are beginning to understand the processes which triggers the immense bolometric luminosity output in these galaxies, allowing us to address issues such as their true contribution to the star formation rate history of the Universe It is clearly important to establish firmly the masses for these galaxies in order to understanding the rapid evolution of the submm population Such diagnostics will allow us to determine how they relate to present-day galaxies and in particular to test whether they represent the formation phase of the most massive elliptical galaxies at the present day, as many suspect (Lilly et al 1999)

Results

Discussion

Conclusion