GEMS Home

GEMS:
Galaxy Evolution From Morphology And SEDs

GEMS in a Nutshell:

largest contiguous field ever imaged with HST (900 arcmin²)
mosaic of 9x9 Advanced Camera for Surveys (ACS) pointings
Field: Extended Chandra Deep Field South (E-CDFS)
Filters: V (F606W) and z (F850LP)
10000 redshifts from COMBO-17 (galaxies down to R<24) in the range: 0.2<z<1.2
SEDs from COMBO-17 in the range 3500 to 9250 Ångstroms

GEMS tile #58

(clicking on the red boxes displays the full-resolution version of that region; a larger (334kb) version of the total frame is available by clicking here)

Simulation of a galaxy merger

(animations are available by clicking on the image)

Science Questions:

Why has star formation activity declined so dramatically sinze z~1:

changes in interaction and merger rate?
waning fuel supply?
shift of star-formation to progressively less massive systems?

How did galactic discs and bulges form and evolve with time?

simple dimming of bulges?
radial growth of discs?
evolution of bars

How did AGN host galaxies evolve over the last 10Gyrs?

Comparison of COMBO-17 and GEMS data

(for a larger version (330kb) click on the image)

GEMS has imaged an area of 900 square minutes of arc on the sky with the Advanced Camera for Surveys (ACS) on-board Hubble Space telescope. This contiguous field centred on the Chandra Deep Field South contains roughly 10000 galaxies down to a depth of 24th magnitude in the R-band. The central part was observed by the GOODS-project to an even fainter flux-limit, while GEMS mainly concentrates on the outer regions, the extended Chandra Deep Field South. For those 10000 objects redshifts in the range 0.2<z<1.2 were determined in the COMBO-17 project, by means of low-resolution spectra using 17 medium band filters. Those spectra not only provide redshifts but also spectral energy distributions (SEDs) from 3500 to 9250 Ångstroms. The mosaic of 9 by 9 ACS pointings in the F606W and F850LP filters will allow us in combination with the known redshifts to construct a rest-frame B-band image of all target galaxies with resolutions < 0.1 arcseconds, corresponding to < 500 parsec in the object's rest-frame. This unique data set including SED and high resolution morphological information will let us determine the evolution of galaxy structure over the last half of cosmic history.