High Redshift Simulations using the GALEXUltraviolet Images of Nearby Galaxies

Bum-Suk Yeom1, Young Kwang Kim1,2, Soo-Chang Rey1,Young Hoon Joe3, and Armando Gil de Paz4

1Department of Astronomy and Space Science, Chungnam National University, Daejeon 305-764, Korea, E-mail: bsyeom@gmail.com 2Korea Astronomy and Space Science Institute, Daejeon 305-348, Korea 3Center for Space Astrophysics, Yonsei University, Seoul 120-749, Korea 4Departamento de Astrofisica, Facultad de CC. Fisicas, Universidad Complutense de Madrid, E-28040 Madrid, Spain

SDSS-KSG Workshop, 18 – 20 February 2008

• Motivation• Data and Samples• Simulation Procedures• Results• Quantitative Morphological Analysis• Summary • Future Works

Outline

• Galaxy morphology plays an important role in the assessment of the evolutionary state of galaxies (Bohlin et al. 1991; Giavalisco et al. 1996)

• Prediction of optical-band morphologies at high redshift → Ultraviolet (UV) images of local galaxies with various morphologies

(Bohlin et al. 1991; Giavalisco et al. 1996; Kuchinski et al. 2001; Marcum et al. 2001;

Papovich et al. 2003, Lotz et al. 2006)

Motivation

• Previous works (Bohlin et al. 1991; Giavalisco et al. 1996; Burgarella et al. 2001;

Kuchinski et al. 2001; Marcum et al. 2001; Papovich et al. 2003; Lotz et al. 2006)

– UIT (Ultraviolet Imaging Telescope), FOCA, HST/FOC (Faint Object Camera)

– Used small size of the samples– Not representative of the overall population of galaxies in the Local

Universe

• To understand the morphology of galaxies at high-redshift→ Simulated optical images at high redshift using more diverse and

high-quality nearby galaxies obtained through the Galaxy Evolution Explorer (GALEX) UV observations

• Quantitative morphological analysis→ Concentration (C) parameter

Motivation

• GALEX : Mission and Instrument

– Performed the first space ultraviolet (UV) sky survey

– Satellite:• Launched by Pegasus-XL on April 28th 2003• Circular orbit, altitude: 700 km, inclination: 29°, period: 98

min

– Telescope: 50 cm modified Ritchey-Chrétien

– Instrument:• Simultaneous imaging in two UV bands (FUV & NUV; ~ 1516 & 2267 Å)

• Circular FOV of 1.2° in diameter• FWHM (FUV=4.5˝; NUV=6˝)• Pixel scale : 1.5˝/pixel

Data and Samples

M81 & M82

• Galaxy samples : 1034 galaxies

– Galaxies in the GALEX Nearby Galaxy Survey (NGS) plus galaxies obtained as part of other GALEX imaging surveys (Gil de Paz et al.

2007)

– Galaxies with the overall population of galaxies in the Local Universe

– Ellipticals/Spirals/Irregulars (23%/61%/8%)

Data and Samples

(Yeom et al. 2008 in preparation)

Simulation Procedures

• Artificially redshift our UV images into the HST ACS (Advanced

Camera for Surveys) observations (HUDF, Hubble Ultra Deep Field)

– General prescription outlined by Giavalisco et al. (1996)– Assumed zero evolutionary effects of stellar population

Results

• GALEX NUV and artificially redshifted images of M101 (z = 0.0, 0.9, 1.6, 2.4, 3.0 Wavelength = 2267, 4307, 5894, 7708,

9068 Å)

Results

• GALEX NUV and simulated images with various morphology

– Simulated galaxies are detected 30 percent of our sample at z~3

Quantitative Morphological Analysis

• To study the quantitative morphological analysis at high-z galaxies

→ Concentration (C) parameter → C index is very stable against a spatial resolution degradation

(Bershady et al. 2000)

• Concentration (C) parameter and results

– Total flux is the within 2.5 Kron radius (Kron 1980; Graham & Driver 2005) of the galaxy’s center

(Kent 1985; Bershady et al. 2000)

Quantitative Morphological Analysis

(Kent 1985; Bershady et al. 2000)

Quantitative Morphological Analysis

• Simulated the unprecedented nearby galaxies from the GALEX UV samples with various morphologies to investigate the optical-band morphologies seen in HST

• Many of the optical morphological features are still clearly observed at moderate redshift (z~1.6) • At high redshift (z~3)

– Most of the simulated galaxies are barely detected (30 percent of our sample)

– Simulated spiral galaxies can be mistaken for S0 or E types

• Measurement of the morphological parameters (Concentration index, C)

– E/S0

→ concentration index is decreasing as a function of redshift

– Spirals and Irregulars

→ little change globally as a function of redshift

Summary

Future Works

• Measurement of the various morphological parameters

– Asymmetry (A) index, Gini (G) coefficient, etc.

• Simulation of the nearby galaxies using the Swift UV data (Roming et al. 2005) with a higher resolution (0.5″/pixel)

Thank you !

• Galaxy samples : 1034 galaxies

– Galaxies in the GALEX Nearby Galaxy Survey (NGS) plus galaxies obtained as part of other GALEX imaging surveys (Gil de Paz et al.

2007)

– Galaxies with the overall population of galaxies in the Local Universe

– Ellipticals/Spirals/Irregulars (23%/61%/8%)