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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: [email protected] 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%)