Insights on the Formation, Evolution, and Activity of Massive Galaxies from Ultracompact and Disky Galaxies at z = 2--3

The Astrophysical Journal (Impact Factor: 6.73). 01/2011; 743. DOI: 10.1088/0004-637X/743/1/87

ABSTRACT We present our results on the structure and activity of massive galaxies at z = 1-3 using one of the largest (166 with M sstarf >= 5 × 1010 M ☉) and most diverse samples of massive galaxies derived from the GOODS-NICMOS survey: (1) Sérsic fits to deep NIC3 F160W images indicate that the rest-frame optical structures of massive galaxies are very different at z = 2-3 compared to z ~ 0. Approximately 40% of massive galaxies are ultracompact (re

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    ABSTRACT: We examine in this paper a stellar-mass-selected sample of galaxies at 1 < z 1. By using a locally defined definition of disc and elliptical galaxies based on structure and spectral type, we find no true ellipticals at z > 2, and a fraction of 3.2 ± 2.3 per cent at 1.5 < z < 2. Local counterparts of disc galaxies are at a similar level of 7-10 per cent, much lower than the 75 per cent fraction at lower redshifts. We further compare WFC3 images with the rest-frame ultraviolet view of galaxies from ACS imaging, showing that galaxies imaged with the ACS, which appear peculiar, often contain an `elliptical'-like morphology in the WFC3. We show through several simulations that this larger fraction of elliptical-like galaxies is partially due to the courser point spread function of the WFC3, and that the `elliptical' morphological class very likely includes early-type discs. We also measure the merger history for our sample using concentration, asymmetry and clumpiness parameters, finding a redshift evolution increasing with redshift, and a peak merger fraction of ˜30 per cent at z˜ 2 for the most massive galaxies with M* > 1010 M&sun;, consistent with previous results from the ACS and NICMOS. We also compare our results to semi-analytical model results and find a relatively good agreement between our morphological breakdown and the predictions. We finally argue that galaxies classified visually as peculiar, elliptical or peculiar ellipticals, all have similar structural and stellar population properties, suggesting that these galaxies are in a similar formation mode, likely driven by major mergers.
    Monthly Notices of the Royal Astronomical Society 01/2011; 417:2770-2788. · 5.52 Impact Factor
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    ABSTRACT: There is cumulative evidence showing that, for the most massive galaxies, the fraction of disk-like objects compared to those with spheroidal properties increases with redshift. However, this evidence is thus far based on detailed morphological analyses of these objects which ultimately rests on the shape of their surface brightness profiles. To explore the consistency of this scenario, it is necessary to measure the dynamical status of these galaxies. With this aim we have obtained near-infrared integral field spectra in the H-band for 10 massive galaxies (M_{stellar} >10^{11} h_{70}^-2 M_{Sun}) at z~1.4 with SINFONI at the VLT. Our sample is selected by their stellar mass and EW[OII] > 15\AA, to secure their kinematic measurements, but without accounting for any morphological or flux criteria a priori. Through this 3D kinematic spectroscopy analysis we find that half (i.e. 50+/-7%) of our galaxies are compatible with being rotationally supported disks, in agreement with previous morphological expectations. This is a factor of approximately two higher than what is observed in the present Universe for objects of the same stellar mass. Strikingly, the majority of our sample of massive galaxies show clear and fairly large rotational velocity maps, implying that massive galaxies acquire rapidly rotational support and hence gravitational equilibrium. Our sample also show evidence for ongoing interactions and mergers. This demonstrates that massive galaxies at this epoch are not a homogenous sample, but show significant diversity and must have continued evolution beyond the fading of stellar populations, to become the massive galaxies we find in today's Universe.
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    ABSTRACT: We present a study on spectral energy distributions, morphologies, and star formation for an IRAC-selected extremely red object sample in the GOODS Chandra Deep Field-South. This work was enabled by new HST/WFC3 near-IR imaging from the CANDELS survey as well as the deepest available X-ray data from Chandra 4 Ms observations. This sample consists of 133 objects with the 3.6 {mu}m limiting magnitude of [3.6] = 21.5 and is approximately complete for galaxies with M{sub *} > 10{sup 11} M{sub Sun} at 1.5 {<=} z {<=} 2.5. We classify this sample into two types, quiescent and star-forming galaxies (SFGs), in the observed infrared color-color ([3.6]-[24] versus K - [3.6]) diagram. The further morphological study of this sample shows a consistent result with the observed color classification. The classified quiescent galaxies are bulge dominated and SFGs in the sample have disk or irregular morphologies. Our observed infrared color classification is also consistent with the rest-frame color (U - V versus V - J) classification. We also found that quiescent and SFGs are well separated in the nonparametric morphology parameter (Gini versus M{sub 20}) diagram measuring their concentration and clumpiness: quiescent galaxies have a Gini coefficient higher than 0.58 and SFGs have a Gini coefficient lower than 0.58. We argue that the star formation quenching process must lead to or be accompanied by the increasing galaxy concentration. One prominent morphological feature of this sample is that disks are commonly seen in this massive galaxy sample at 1.5 {<=} z {<=} 2.5: 30% of quiescent galaxies and 70% of SFGs with M{sub *} > 10{sup 11} M{sub Sun} have disks in their rest-frame optical morphologies. The prevalence of these extended, relatively undisturbed disks challenges the merging scenario as the main mode of massive galaxy formation.
    The Astrophysical Journal 06/2012; 752(2). · 6.73 Impact Factor

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