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Abstract: We have examined in detail the morphologies of seven z~1.5 passively evolvingluminous red galaxies using high resolution HST NICMOS and ACS imaging data.Almost all of these galaxies appear to be relaxed systems, with smoothmorphologies at both rest-frame UV and visible wavelengths. Previous resultsfrom spectral synthesis modeling favor a single burst of star formation morethan 1 Gyr before the observed epoch. The prevalence of old stellarpopulations, however, does not correlate exclusively with early-typemorphologies as it does in the local universe; the light profiles for some ofthese galaxies appear to be dominated by massive exponential disks. Thisevidence for massive old disks, along with the apparent uniformity of stellarage across the disk, suggests formation by a mechanism better described as aform of monolithic collapse than as a hierarchical merger. These galaxies couldnot have undergone a single major merging event since the bulk of their starswere formed, more than 1 Gyr earlier. There is at least one case, however, thatappears to be undergoing a -dry merger-, which may be an example of the processthat converts these unusual galaxies into the familiar spheroids that dominategalaxies comprising old stellar populations at the present epoch.



Author: Elizabeth J. McGrath, Alan Stockton, Gabriela Canalizo, Masanori Iye, Toshinori Maihara

Source: https://arxiv.org/







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