skip to main content

Title: CLUMPY GALAXIES IN CANDELS. I. THE DEFINITION OF UV CLUMPS AND THE FRACTION OF CLUMPY GALAXIES AT 0.5 < z < 3

Although giant clumps of stars are thought to be crucial to galaxy formation and evolution, the most basic demographics of clumps are still uncertain, mainly because the definition of clumps has not been thoroughly discussed. In this paper, we carry out a study of the basic demographics of clumps in star-forming galaxies at 0.5 < z < 3, using our proposed physical definition that UV-bright clumps are discrete star-forming regions that individually contribute more than 8% of the rest-frame UV light of their galaxies. Clumps defined this way are significantly brighter than the H II regions of nearby large spiral galaxies, either individually or blended, when physical spatial resolution and cosmological dimming are considered. Under this definition, we measure the fraction of star-forming galaxies that have at least one off-center clump (f {sub clumpy}) and the contributions of clumps to the rest-frame UV light and star formation rate (SFR) of star-forming galaxies in the CANDELS/GOODS-S and UDS fields, where our mass-complete sample consists of 3239 galaxies with axial ratio q > 0.5. The redshift evolution of f {sub clumpy} changes with the stellar mass (M {sub *}) of the galaxies. Low-mass (log (M {sub *}/M {sub ☉}) < 9.8) galaxies keepmore » an almost constant f {sub clumpy} of ∼60% from z ∼ 3 to z ∼ 0.5. Intermediate-mass and massive galaxies drop their f {sub clumpy} from 55% at z ∼ 3 to 40% and 15%, respectively, at z ∼ 0.5. We find that (1) the trend of disk stabilization predicted by violent disk instability matches the f {sub clumpy} trend of massive galaxies; (2) minor mergers are a viable explanation of the f {sub clumpy} trend of intermediate-mass galaxies at z < 1.5, given a realistic observability timescale; and (3) major mergers are unlikely responsible for the f {sub clumpy} trend in all masses at z < 1.5. The clump contribution to the rest-frame UV light of star-forming galaxies shows a broad peak around galaxies with log (M {sub *}/M {sub ☉}) ∼ 10.5 at all redshifts. The clump contribution in the intermediate-mass and massive galaxies is possibly linked to the molecular gas fraction of the galaxies. The clump contribution to the SFR of star-forming galaxies, generally around 4%-10%, also shows dependence on the galaxy M {sub *}, but for a given galaxy M {sub *}, its dependence on the redshift is mild.« less
Authors:
; ; ; ;  [1] ; ; ; ; ; ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ; ;  [7] ;  [8] ;  [9] ;  [10] more »; « less
  1. UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA (United States)
  2. Space Telescope Science Institute, Baltimore, MD (United States)
  3. Department of Astronomy, University of Michigan, Ann Arbor, MI (United States)
  4. School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom)
  5. Department of Astronomy, University of Massachusetts, Amherst, MA (United States)
  6. Kavli Institute for Particle Astrophysics and Cosmology, Stanford, CA (United States)
  7. Center for Astrophysics and Planetary Science, Racah Institute of Physics, The Hebrew University, Jerusalem 91904 Israel (Israel)
  8. Department of Physics and Astronomy, University of Missouri-Kansas City, Kansas City, MO (United States)
  9. Department of Physics, University of California, Santa Cruz, CA (United States)
  10. Departamento de Física Teórica, Universidad Autónoma de Madrid, E-28049 Madrid (Spain)
Publication Date:
OSTI Identifier:
22364226
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 800; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AXIAL RATIO; GALAXIES; MASS; RED SHIFT; SPATIAL RESOLUTION; STABILIZATION; STAR CLUSTERS; STAR EVOLUTION; STARS; ULTRAVIOLET RADIATION