Stellar Populations of High- Redshift Star-Forming Galaxies Using Rest-Frame Optical and UV Imaging Nicholas Bond (Rutgers University) Collaborators: Eric.

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

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 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:

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)

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Venemans et al. 2005

Ferguson et al. 2004

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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 PSFBlue 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 EWrest > 20

- 107 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. 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 ()

Papovich et al. 2005

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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 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

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

= 0.15

4.8"

Rest-UV Rest-optical

• 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