Presentation on theme: "Subaru Adaptive Optics (AO) Rest-frame V-band Imaging of Galaxies at z~3 : High Surface Density Disk-like Galaxies ? Subaru Users Meeting 20080130 Masayuki."— Presentation transcript:
Subaru Adaptive Optics (AO) Rest-frame V-band Imaging of Galaxies at z~3 : High Surface Density Disk-like Galaxies ? Subaru Users Meeting Masayuki Akiyama (Subaru Telescope, NAOJ) Kouji Ohta (DoA, Kyoto Univ.) Yosuke Minowa (Mitaka, NAOJ) Naoto Kobayashi (IoA, Univ. of Tokyo) Ikuru Iwata (OAO, NAOJ) ApJS accepted, arXiv
Subaru n The morphology of galaxies at z~1 still follows Hubble sequence seen in the nearby universe. How about galaxies further away ? Naive motivation 3col images of z=1 galaxies in GOODS
Subaru n Rest-frame optical morphology of galaxies reflects the stellar mass distribution of galaxies, and provides important information on the dynamical structure of galaxies. Rest-frame optical morphology is important Longer than 4000A break: Distribution of red and long-lived stars = distribution of stellar mass Shorter than 4000A break: Distribution of young stars = distribution of star forming regions K-band = z=3 Adaptive Optics = kpc Two spiral galaxies at z~1
Subaru n Our main targets are U-band dropout Lyman Break Galaxies (LBGs) Steidel et al is the largest sample of spectroscopicaly- confirmed z~3 galaxies selected by U-dropout Lyman Break method. Select a sample not affected by the redshift uncertainty with LBG n An radio galaxy (4C28.58 at z=2.891) n We also examined morphologies of serendipitously observed Distant Red Galaxies (DRGs) in our FoVs. DRG criterion of J-K>2.3 also selects red galaxies at similar redshifts to U-dropout LBGs. Targets for Observations
Subaru Observation: Subaru Telescope Intensive Program n Natural guide star AO system on Subaru telescope with IRCS. n 154 hours of observation in total. n 13 FoVs with 36 LBGs, 1 RadioG., and 7 DRGs are observed. n Typical on-source effective integration is 5 hours. n Typical PSF size at the target position is FWHM=0.2 Subaru 8.2m + AO36 system: Low-order correction with low-noise Shack-Hartmann wavefront sensor = Good for extra- galactic studies !
Subaru Observation: Subaru Telescope Intensive Program AO Guide Star PSF-reference (15) FWHM=0.18 PSF-reference(20) FWHM=0.20 An example of an FoV with 6.2h integration n Natural guide star AO system on Subaru telescope with IRCS. n 154 hours of observation in total. n 13 FoVs with 36 LBGs, 1 RadioG., and 7 DRGs are observed. n Typical on-source effective integration is 5 hours. n Typical PSF size at the target position is FWHM=0.2
Subaru Images of LBGs in order of K-band magnitudes 36 LBGs are observed, 31 are detected n 3.5x3.5 ~ 30kpc x 30kpc K vega <21.5 K vega <22.5 No detection
Subaru Luminosity vs. J-K color of the LBGs n The observed sample covers a wide range of the rest-frame optical absolute magnitude (between Mv*-0.5 and Mv*+3.0) n The LBG-selected galaxies cover not only the less-massive bluer galaxies (U-V~-0.3) but also the massive redder galaxies (U-V~0.5) similar to DRGs.
Subaru Offset between optical and K-band Images n Bright LBGs show significant offsets between K-band (rest-frame optical) and seeing-limited optical (rest-frame UV) images. This indicates optical and UV morphologies are different.
Subaru One component Sersic profile fitting for bright (~Mv*) LBGs 36 LBGs are observed, 31 are detected K vega <21.5 K vega <22.5 No detection
Subaru Examples of Sersic profile fittings for LBGs with Kvega<21.5 n LBGs are described better with n=1 Sersic profile (similar to disk galaxies, less concentrated; green) than n=4 Sersic profiles (similar to spheroidal galaxies, more concetrated; blue).
Subaru Summary of Sersic fittings for Kvega<21.5 LBGs (+DRGs) n Most of the LBGs (+an RadioG +DRGs) are fitted well with Sersic profiles with n<2.
Subaru Summary of Sersic fittings for Kvega<21.5 LBGs (+DRGs) n Results of cloning simulations show if there are large number of elliptical or bulge-dominated galaxies at z~3, they should be detected, and should be fitted well with large n-index.
Subaru Concentration vs. Size distribution of Kvega<22.5 LBGs / DRGs n For fainter LBGs/DRGs, profile fittings with free n is not reliable, thus we compared their concentration with those of nearby galaxies. The distribution of LBGs/DRGs are more consistent with n 2 spheroidal-like profiles.
Subaru Surface brightness & surface stellar mass density n If we assume that the LBGs/DRGs have disk-like morphology, V-band surface brightnesses inferred from the size-luminosity relation is 2.9mag, and 1.7mag brighter than z=0 and z=1 disk galaxies, respectively. n Surface stellar mass densities inferred from the size-stellar mass relation is 3- 6 times larger than z=0-1 disk galaxies shown with thick solid line. z=0-1 from Barden 2005
Subaru Summary of the results n K-band peaks of bright red LBGs show offsets from the optical positions. Their inside stellar mass distributions are different from the distributions of star forming regions. n Radial profiles of LBGs (+RadioG. +DRGs) are relatively flat, and similar to disk-galaxies in the local universe. n Rest-frame optical surface brightnesses of the z=3 LBGs (DRGs) are brighter than z=0-1 disk galaxies. Surface stellar mass densities of massive LBGs are also larger than z=0-1 disk galaxies.
Subaru Naive speculation: placing the z~3 galaxies in the growth paths of galaxies Basically, gas-poor dissipation-less merging produce concentrated structure similar to elliptical galaxies. So in order to maintain the disk-like structure of the galaxies, gas- rich merging process can be a key (e.g., Springel & Hernquist 2005).
Subaru New era of high-z morphology study with Laser Guide stars Current sample is not sufficient statistically, especially for bright (
Subaru n Strong spatial clustering of LBGs indicates that they reside in massive halos and are progenitors of massive galaxies (=elliptical or bulge- dominated galaxies) in the local universe (e.g. Giavalisco & Dickinson 2001). n The apparent sizes of the LBGs in the rest-frame UV-band are similar to the sizes of the spheroids in the local universe (e.g. Steidel et al. 1996). n Therefore, LBGs are thought to be closely related to the formation of the spheroidal (elliptical or bulge) component of galaxies. Why LBGs to understand formation and evolution of galaxy bulges ?
Subaru Why Study Rest-frame Optical Morphologies of z~3 Galaxies Longer than 4000A break : Distribution of red and long- lived stars = distribution of stellar mass Shorter than 4000A break: Distribution of young stars = distribution of star forming regions K-band Adaptive Optics = kpc n HST/NICMOS H-band Observations are not sufficient ! H-band observation only covers up to 4000A in the rest-frame, and star-forming regions can dominate the morphology. n HST/NICMOS sample is limited to a small number of objects in Hubble Deep Field and does not have bright (~Mv*) galaxies at z~3. The physical properties of LBGs clearly depends on the luminosity (more luminous LBGs have redder color, have stronger clustering, have weaker Lya emission, and so on), thus it is still important to observe a sample covering wide luminosity range.
Subaru Cloning z=3 galaxies with GOODS Data n Compare the K-band morphologies of z=3 LBGs with z= galaxies in the GOODSN region. corresponds to I,z- z= n Covered by GOODSN is comparable to by IRCS/AO LBGs. 2PLE case
Subaru Estimated the PSFs at the target positions n Estimate the PSF shape at the positions of the targets, using a few stars in the FoV. n During the Sersic profile fitting, the parameters are changed within the range shown with yellow hatch.