The Morphology of Passively Evolving Galaxies at z ~ 2 from HST/WFC3 Deep Imaging in the Hubble Ultradeep Field

TL;DR

This study uses deep HST/WFC3 imaging to analyze the morphology of six passive, massive galaxies at z~2, revealing compact sizes, regular profiles, and minimal wavelength-dependent morphological differences, advancing understanding of early galaxy evolution.

Contribution

First detailed near-IR morphological analysis of passive galaxies at z~2 showing their compactness and structural similarity across wavelengths.

Findings

Galaxies have small effective radii (~1 kpc), much smaller than local counterparts.

Light profiles are well described by Sersic models with indices typical of spheroids.

Minimal morphological change between UV and optical wavelengths.

Abstract

We present near-IR images, obtained with the Hubble Space Telescope (HST) and the WFC3/IR camera, of six passive and massive galaxies at redshift 1.3<z<2.4 (SSFR<10^{-2} Gyr^{-1}; stellar mass M~10^{11} M_{sun}), selected from the Great Observatories Origins Deep Survey (GOODS). These images, which have a spatial resolution of ~1.5 kpc, provide the deepest view of the optical rest-frame morphology of such systems to date. We find that the light profile of these galaxies is regular and well described by a Sersic model with index typical of today's spheroids. Their size, however, is generally much smaller than today's early types of similar stellar mass, with four out of six galaxies having r_e ~ 1 kpc or less, in quantitative agreement with previous similar measures made at rest-frame UV wavelengths. The images reach limiting surface brightness mu~26.5 mag arcsec^{-2} in the F160W bandpass; yet, there is no evidence of a faint halo in the galaxies of our sample, even in their stacked image. We also find that these galaxies have very weak "morphological k-correction" between the rest-frame UV (from the ACS z-band), and the rest--frame optical (WFC3 H-band): the Sersic index, physical size and overall morphology are independent or only mildly dependent on the wavelength, within the errors.