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Nicholas Bond (Rutgers University)

Stellar Populations of High-Redshift Star-Forming Galaxies Using Rest-Frame Optical and UV Imaging. Nicholas Bond (Rutgers University) Collaborators: Eric Gawiser (Rutgers), Caryl Gronwall (PSU), Robin Ciardullo (PSU), John Feldmeier (YSU), Ana Matkovic (PSU)

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Nicholas Bond (Rutgers University)

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  1. Stellar Populations of High-Redshift Star-Forming Galaxies Using Rest-Frame Optical and UV Imaging Nicholas Bond (Rutgers University) Collaborators: Eric Gawiser (Rutgers), Caryl Gronwall (PSU), Robin Ciardullo (PSU), John Feldmeier (YSU), Ana Matkovic (PSU) See also: Related posters by Peter Kurczynski and Viviana Acquaviva

  2. Overview We analyze HST/ACS I814 and HST/WFC3 H160 images taken as part of the WFC3 Early Release Science Program. Our sample consists of 134 star-forming galaxies (SFGs) at 2 < z < 3.5, including 27 Ly Emitters (LAEs). The talk is arranged as follows: Background - Summary of recent morphological studies of LAEs and other high-redshift SFGs Methodology - Brief description of morphological diagnostics, including half-light radii and internal color dispersions Results - Summarize UV-optical morphological properties of SFGs in our sample Conclusions - Discuss implications for future work on SFGs and other high-z galaxies

  3. Sizes and Morphologies of SFGs in the Rest-Frame UV • Hubble Sequence seen locally disappears by z ~ 2, high-z galaxies typically compact and irregular (e.g. Giavalisco et al. 1996, van den Bergh et al. 2001) • LBG sizes range from < 1 kpc to ~5 kpc (smaller at high redshift), largest have clumpy/irregular morphologies (e.g. Bouwens et al. 2004, Ferguson et al. 2004, Oesch et al. 2009) • Morphology very difficult on these faint objects, even half-light radius requires S/N > 30 (Bond et al. 2009) Ferguson et al. 2004 Venemans et al. 2005

  4. Morphological Properties of LAEs LAEs are high-redshift (z > 2) emission-line galaxies that have low stellar masses (~109 solar), are low in dust, and are the progenitors of modern L* galaxies(e.g. Venemans et al. 2005, Gawiser et al. 2007) LAEs typically < 2 kpc in size, well-resolved objects also exhibit clumpy/irregular morphologies (.e.g. Venemans et al. 2005, Pirzkal et al. 2007, Bond et al. 2009) Resolved LAEs tend to have disk-like best-fit Sersic index (n ~ 0.5 - 2), but span wide range(Gronwall et al. 2010) Ly emission is similarly compact in narrow-band HST images(see figure, Bond et al. 2010) Red dotted: WFPC2 PSF Blue and Green dashed: Individual detected LAEs Black solid: Stacked undetected LAEs

  5. Sample of Star-Forming Galaxies Objects identified as part of MUSYC survey (Gawiser et al. 2006) in E-CDFS 18 z = 3.1 LAEs (red squares), and 9 z = 2.1 LAEs (magenta stars), all with EWrest > 20 107 spectroscopically-confirmed LBG/BX galaxies (blue triangles) at 2 < z < 3.5

  6. Internal color dispersion defined and demonstrated in Papovich et al. 2003 • Measures relative distribution of light for same object observed in two filters • Sum the squared difference of fluxes (I1 and I2) over all pixels, using the best-fit values of the relative sky background () and ratio of total fluxes () Methodology: Internal Color Dispersion Papovich et al. 2005

  7. Fluxes measured using 1.2"-radius fixed apertures (uniform sky subtraction in 5" x 5" cutouts) • Simple definition of half-light radius -- aperture that encloses half of this light • Half-light radii similar between rest-UV and rest-optical, with some outliers • Color-coding indicates rest-UV to rest-optical internal color dispersion (red is high) • Large objects (R ~ 4 kpc) often show strong morphological variation between bandpasses not revealed by half-light radius differences Half-Light Radii of SFGs SFGs

  8. - Internal color dispersion of a UV-selected population of galaxies at 2 < z < 3 generally higher (31% with  > 0.08) than a rest-frame B-band selected population in same redshift range (8% with  > 0.08) - Implies presence of spatially distinct stellar populations of different ages or non-uniform dust distribution Results: Internal Color Dispersion Rest-optical selection (Papovich et al. 2005) Rest-UV selection (this work)

  9. Rest-UV Rest-optical • SFGs with  > 0.1 shown on right, morphologies consistent with mergers and/or clumpy star formation • High- objects have redder UV-optical colors Internal Color Dispersion (cont.)  = 0.17  = 0.32  = 0.21  = 0.18  = 0.15 4.8"

  10. The majority of SFGs are compact (< 3 kpc) at z > 2 in all observed bandpasses, but there exists a subset of larger objects that are typically clumpy and irregular • Half-light radii alone are a poor tracer of the morphological differences between rest-UV and rest-optical images: It is better to measure the morphological properties of the difference image than the difference in morphological properties between bandpasses. • SFGs at 2 < z < 3 have higher average internal color dispersions than galaxies selected by stellar mass at the same redshift, with the largest SFGs exhibiting the most variation between bandpasses • Morphologies of SFGs with very high (>0.1) internal color dispersion are suggestive of mergers and/or clumpy star formation • SFGs with high internal color dispersions tend to have redder rest-frame UV-to-optical colors, suggesting the presence of an underlying population of older stars or non-uniform dust distribution Conclusions

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