Morphology of massive early-type galaxies at z>1.2: constraining galaxy formation models
Abstract
We ask for NICMOS-NIC2 H-band imaging of a sample of 10 massive early-type galaxies spectroscopically identified at 1.2<z<1.7. Our aim is to look for possible relics of merging events of their formation/evolution in their morphology. The requested observations, sampling their rest-frame at lambda>6500A, would map the mass distribution of the bulk of their stellar content. The targets have been revealed by our group on the basis of near-IR spectroscopy obtained in the framework of a spectroscopic survey of a complete sample of bright EROs {Ks<18.5}. Optical and near-IR photometry is available for all the targets, and low resolution near-IR spectra have allowed their identification and redshift measurement. Spectroscopic and photometric data in our hands show that they have already assembled stellar masses greater than 3 10^11 solar masses, and that the mean age of their stellar population is estimated older than 2-3 Gyr for 6 of them and about 1 Gyr for the other 4 galaxies. Thus, they are among the most luminous and massive evolved galaxies detected so far at z>1. Other data are needed to infer how they have assembled such high stellar masses, i.e. to trace back their evolution. The requested observations would allow us to reveal signs of past interaction/merger event. A smooth r^{1/m} profile, coupled with no other signs of interaction/merger {disturbed morphology}, would place the possible merger event of formation 1-2 Gyr before their redshift z Approx 1.5, i.e. at z > 2-3. On the other hand, if signs of recent merger events will be found, the last merger event forming the local massive spheroids will be constrained at 1.5 < z < 2. Thus, the requested HST observations will allow for the first time to see how massive early-type galaxies at z Approx 1.5 look like, constraining in any case the redshift of the possible merging event of their formation.
- Publication:
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HST Proposal
- Pub Date:
- July 2005
- Bibcode:
- 2005hst..prop10510L