STScI Preprint #1299

An Extremely Red R^1/4 Galaxy in the Test Image of the Hubble Deep Field South

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

We report the serendipitous discovery of an extremely red object in the Hubble Deep Field South (HDFS) Test NICMOS (Near Infrared Camera and Multi Object Spectrograph) field of view. The object is resolved in the NICMOS image and has a light profile very well described by an r^1/4 law with effective radius r_e=0." 20±0.05 and H_AB=21.7±0.1 magnitudes. In contrast, the galaxy is undetected in the R and I band ground based images taken at the CTIO 4 m Blanco Telescope, giving a lower limit to the color of (R-H)_AB>3.9 and (I-H)_AB>3.5 at the 95% confidence level. The colors of a range of synthetic galactic spectra are computed, showing that the object is likely to be an "old" elliptical galaxy at redshift z 1.7. Alternatively the colors can be reproduced by an "old" elliptical galaxy at somewhat lower redshift ( 1) with significant amount of dust, or by a younger galaxy at higher redshift. This object represents a very interesting target for future VLT observations.

Status:

Appeared in: Astronomy & Astrophysics, 340:L10-L14, 1998

Affiliations:

¹) Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218;
²) Scuola Normale Superiore, Piazza dei Cavalieri 7, I56126, Pisa, Italy;
³) On assignment from the Space Science Department of the European Space Agency.
⁴) Cerro Tololo Inter-American Observatory, NOAO, Casilla 603, La Serena, Chile;
⁵) University of Michigan, Dept. of Astronomy, 830 Dennison Building, Ann Arbor, MI 48109.
⁶) Johns Hopkins University, 3701 San Martin Drive, Baltimore, MD 21218.
⁷) Hubble Fellow.