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 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

Overview 1)Background - Summary of recent morphological studies of LAEs and other high-redshift SFGs 2)Methodology - Brief description of morphological diagnostics, including half-light radii and internal color dispersions 3)Results - Summarize UV-optical morphological properties of SFGs in our sample 4)Conclusions - Discuss implications for future work on SFGs and other high-z galaxies We analyze HST/ACS I 814 and HST/WFC3 H 160 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:

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) Venemans et al Ferguson et al. 2004

Morphological Properties of LAEs - LAEs are high-redshift (z > 2) emission-line galaxies that have low stellar masses (~10 9 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 ~ ), but span wide range (Gronwall et al. 2010) - Ly  emission is similarly compact in narrow-band HST images (see figure, Bond et al. 2010) - LAEs are high-redshift (z > 2) emission-line galaxies that have low stellar masses (~10 9 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 ~ ), 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

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 EW rest > spectroscopically-confirmed LBG/BX galaxies (blue triangles) at 2 < z < 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 EW rest > spectroscopically-confirmed LBG/BX galaxies (blue triangles) at 2 < z < 3.5

Methodology: Internal Color Dispersion -Internal color dispersion defined and demonstrated in Papovich et al Measures relative distribution of light for same object observed in two filters -Sum the squared difference of fluxes (I 1 and I 2 ) over all pixels, using the best-fit values of the relative sky background (  ) and ratio of total fluxes (  ) Papovich et al. 2005

Half-Light Radii of SFGs -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 SFGs

Results: Internal Color Dispersion - Internal color dispersion of a UV-selected population of galaxies at ) 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 Rest-optical selection (Papovich et al. 2005) Rest-UV selection (this work)

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

The majority of SFGs are compact ( 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

Spectral Energy Distribution of LAEs - Hubble Sequence seen locally disappears by z ~ 2, high-z galaxies typically compact and irregular: LBGs (2.5 < z < 7) - sizes range from < 1 kpc to ~5 kpc (smaller at high redshift), clumpy/irregular morphologies LAEs (3 < z < 6) - sizes typically < 1 kpc, well- resolved objects exhibit clumpy/irregular morphologies - Hubble Sequence seen locally disappears by z ~ 2, high-z galaxies typically compact and irregular: LBGs (2.5 < z < 7) - sizes range from < 1 kpc to ~5 kpc (smaller at high redshift), clumpy/irregular morphologies LAEs (3 < z < 6) - sizes typically < 1 kpc, well- resolved objects exhibit clumpy/irregular morphologies

Future Work Gronwall et al. have Ly  (narrow-band) HST images of several LAEs, check morphologies and look for diffuse emission due to resonant scattering Check ground-based narrow-band images for consistency with point source, is there an intermediate population between LAEs and Ly  blobs? Use pipeline to analyze morphologies of LBGs, BzK galaxies

Diagnostics: Depth Tests Want to see how morphological parameters depend upon the depth of the observations Plot shows change in measured fixed-aperture half- light radius between surveys Half-light radius measurements are consistent between surveys so long as S/N>30 in both

z=3.1 LAE Results: Sersic Index Distribution Sersic Index distribution in GEMS catalog Black: full sample Red: "Extended" Objects Most have disk-like Sersic indices, but may not be disks Very large n can be indicative of diffuse emission or "fluff"

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