ST ScI Preprint #1378

A Nicmos Search for High Redshift Elliptical Galaxy Candidates

Based on observations collected at ESO, La Silla, at the CTIO, NOAO, which is operated by AURA, under cooperative agreement with the NSF, and with the NASA/ESA HST, obtained at the ST ScI, which is operated by AURA, under NASA contract NAS5-26555.

We have collected optical follow-up observations from the ground and the Hubble Space Telescope (HST) for 13.74 ' of archival images taken with HST Near Infrared Camera and Multi Object Spectrograph (NICMOS). We use two criteria to select E/S0 galaxy candidates at z 1 and z 1.5 (HizECs) based on colors and infrared morphology. The observed surface density of HizECs is significantly smaller than what is predicted assuming the local luminosity function (LF) of E/S0, constant comoving density, and pure passive evolution with a high redshift of formation of the stellar populations (z 5). On the other hand, assuming a low redshift (z 2) of formation, not enough HizECs are predicted. The data are very well matched assuming that a substantial fraction of present-day E/S0s (10-66%, depending on cosmology and on the local LF of E/S0s) formed at z = 3 or higher and then evolved passively. The rest of the current E/S0 population may have formed at lower redshift, or may have been rejected by the selection criteria because of interactions or more recent episodes of star-formation (disturbed morphology and/or bluer colors).

Status:

Appeared in: The Astrophysical Journal (Letters)

Affiliations:

¹⁾ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
²⁾ Scuola Normale Superiore, Piazza dei Cavalieri 7, I56126, Pisa, Italy
³⁾ On leave from Scuola Normale Superiore, Piazza dei Cavalieri 7, I56126, Pisa, Italy
⁴⁾ On assignment from the Space Science Department of the European Space Agency