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Title: COLOR AND STELLAR POPULATION GRADIENTS IN PASSIVELY EVOLVING GALAXIES AT z {approx} 2 FROM HST/WFC3 DEEP IMAGING IN THE HUBBLE ULTRA DEEP FIELD

Abstract

We report the detection of color gradients in six massive (stellar mass (M{sub star}) > 10{sup 10} M{sub sun}) and passively evolving (specific star formation rate <10{sup -11} yr{sup -1}) galaxies at redshift 1.3 < z < 2.5 identified in the Hubble Ultra Deep Field using ultra-deep Hubble Space Telescope (HST) Advanced Camera for Surveys and WFC3/IR images. After carefully matching the different point-spread functions, we obtain color maps and multi-band optical/near-IR photometry (BVizYJH) in concentric annuli, from the smallest resolved radial distance ({approx}1.7 kpc) up to several times the H-band effective radius. We find that the inner regions of these galaxies have redder rest-frame UV-optical colors (U - V, U - B, and B - V) than the outer parts. The slopes of the color gradient have no obvious dependence on the redshift and on the stellar mass of the galaxies. They do mildly depend, however, on the overall dust obscuration (E(B - V)) and rest-frame (U - V) color, with more obscured or redder galaxies having steeper color gradients. The z {approx} 2 color gradients are also steeper than those of local early-type ones. The gradient of a single parameter (age, extinction, or metallicity) cannot fully explain themore » observed color gradients. Fitting the spatially resolved HST seven-band photometry to stellar population synthesis models, we find that, regardless of assumptions on the metallicity gradient, the redder inner regions of the galaxies have slightly higher dust obscuration than the bluer outer regions, implying that dust partly contributes to the observed color gradients, although the magnitude depends on the assumed extinction law. Due to the age-metallicity degeneracy, the derived age gradient depends on the assumptions for the metallicity gradient. We discuss the implications of a number of assumptions for metallicity gradients on the formation and evolution of these galaxies. We find that the evolution of the mass-size relationship from z {approx} 2 to the present cannot be driven by in situ extended star formation, which implies that accretion or merger is mostly responsible for the growth of their stellar mass and size. The lack of a correlation between the strength of the color gradient and the stellar mass argues against the metallicity gradient predicted by the monolithic-collapse scenario, which would require significant major mergers to evolve into the one observed at the present.« less

Authors:
; ; ;  [1]; ; ; ;  [2];  [3];  [4];  [5];  [6];  [7]
  1. Astronomy Department, University of Massachusetts, 710 N. Pleasant Street, Amherst, MA 01003 (United States)
  2. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
  3. NOAO-Tucson, 950 North Cherry Avenue, Tucson, AZ 85719 (United States)
  4. INAF-Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, I-35122 Padova (Italy)
  5. George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics, Texas A and M University, College Station, TX 77843-4242 (United States)
  6. INAF-Osservatorio Astronomico di Trieste, Via Tiepolo 11, I-34131 Trieste (Italy)
  7. INAF-Osservatorio Astronomico di Roma, via Frascati 33, Monteporzio-Catone (Roma) I-00040 (Italy)
Publication Date:
OSTI Identifier:
21576558
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 735; Journal Issue: 1; Other Information: DOI: 10.1088/0004-637X/735/1/18; Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COSMOLOGY; GALACTIC EVOLUTION; GALAXIES; MASS; SIZE; STARS; EVOLUTION

Citation Formats

Yicheng, Guo, Giavalisco, Mauro, Cassata, Paolo, Salimbeni, Sara, Ferguson, Henry C, Koekemoer, Anton, Grogin, Norman A, Lotz, Jennifer M, Dickinson, Mark, Renzini, Alvio, Papovich, Casey, Tundo, Elena, and Fontana, Adriano. COLOR AND STELLAR POPULATION GRADIENTS IN PASSIVELY EVOLVING GALAXIES AT z {approx} 2 FROM HST/WFC3 DEEP IMAGING IN THE HUBBLE ULTRA DEEP FIELD. United States: N. p., 2011. Web. doi:10.1088/0004-637X/735/1/18.
Yicheng, Guo, Giavalisco, Mauro, Cassata, Paolo, Salimbeni, Sara, Ferguson, Henry C, Koekemoer, Anton, Grogin, Norman A, Lotz, Jennifer M, Dickinson, Mark, Renzini, Alvio, Papovich, Casey, Tundo, Elena, & Fontana, Adriano. COLOR AND STELLAR POPULATION GRADIENTS IN PASSIVELY EVOLVING GALAXIES AT z {approx} 2 FROM HST/WFC3 DEEP IMAGING IN THE HUBBLE ULTRA DEEP FIELD. United States. https://doi.org/10.1088/0004-637X/735/1/18
Yicheng, Guo, Giavalisco, Mauro, Cassata, Paolo, Salimbeni, Sara, Ferguson, Henry C, Koekemoer, Anton, Grogin, Norman A, Lotz, Jennifer M, Dickinson, Mark, Renzini, Alvio, Papovich, Casey, Tundo, Elena, and Fontana, Adriano. 2011. "COLOR AND STELLAR POPULATION GRADIENTS IN PASSIVELY EVOLVING GALAXIES AT z {approx} 2 FROM HST/WFC3 DEEP IMAGING IN THE HUBBLE ULTRA DEEP FIELD". United States. https://doi.org/10.1088/0004-637X/735/1/18.
@article{osti_21576558,
title = {COLOR AND STELLAR POPULATION GRADIENTS IN PASSIVELY EVOLVING GALAXIES AT z {approx} 2 FROM HST/WFC3 DEEP IMAGING IN THE HUBBLE ULTRA DEEP FIELD},
author = {Yicheng, Guo and Giavalisco, Mauro and Cassata, Paolo and Salimbeni, Sara and Ferguson, Henry C and Koekemoer, Anton and Grogin, Norman A and Lotz, Jennifer M and Dickinson, Mark and Renzini, Alvio and Papovich, Casey and Tundo, Elena and Fontana, Adriano},
abstractNote = {We report the detection of color gradients in six massive (stellar mass (M{sub star}) > 10{sup 10} M{sub sun}) and passively evolving (specific star formation rate <10{sup -11} yr{sup -1}) galaxies at redshift 1.3 < z < 2.5 identified in the Hubble Ultra Deep Field using ultra-deep Hubble Space Telescope (HST) Advanced Camera for Surveys and WFC3/IR images. After carefully matching the different point-spread functions, we obtain color maps and multi-band optical/near-IR photometry (BVizYJH) in concentric annuli, from the smallest resolved radial distance ({approx}1.7 kpc) up to several times the H-band effective radius. We find that the inner regions of these galaxies have redder rest-frame UV-optical colors (U - V, U - B, and B - V) than the outer parts. The slopes of the color gradient have no obvious dependence on the redshift and on the stellar mass of the galaxies. They do mildly depend, however, on the overall dust obscuration (E(B - V)) and rest-frame (U - V) color, with more obscured or redder galaxies having steeper color gradients. The z {approx} 2 color gradients are also steeper than those of local early-type ones. The gradient of a single parameter (age, extinction, or metallicity) cannot fully explain the observed color gradients. Fitting the spatially resolved HST seven-band photometry to stellar population synthesis models, we find that, regardless of assumptions on the metallicity gradient, the redder inner regions of the galaxies have slightly higher dust obscuration than the bluer outer regions, implying that dust partly contributes to the observed color gradients, although the magnitude depends on the assumed extinction law. Due to the age-metallicity degeneracy, the derived age gradient depends on the assumptions for the metallicity gradient. We discuss the implications of a number of assumptions for metallicity gradients on the formation and evolution of these galaxies. We find that the evolution of the mass-size relationship from z {approx} 2 to the present cannot be driven by in situ extended star formation, which implies that accretion or merger is mostly responsible for the growth of their stellar mass and size. The lack of a correlation between the strength of the color gradient and the stellar mass argues against the metallicity gradient predicted by the monolithic-collapse scenario, which would require significant major mergers to evolve into the one observed at the present.},
doi = {10.1088/0004-637X/735/1/18},
url = {https://www.osti.gov/biblio/21576558}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 735,
place = {United States},
year = {Fri Jul 01 00:00:00 EDT 2011},
month = {Fri Jul 01 00:00:00 EDT 2011}
}