Subaru

　Adaptive Optics (AO) Rest-frame V-band Imaging of

Galaxies at z~3 :High Surface Density Disk-like Galaxies ?

Subaru User’s Meeting 20080130

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.0709.2714

Subaru

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

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 = 5600A @ z=3 Adaptive Optics

0.1-0.2” = 0.8-1.5kpc

Two spiral galaxies at z~1

Subaru

Our main targets are U-band dropout Lyman Break Galaxies (LBGs)• Steidel et al. 2003 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

An radio galaxy (4C28.58 at z=2.891)

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

Natural guide star AO system on Subaru telescope with IRCS. 154 hours of observation in total. 13 FoVs with 36 LBGs , 1 RadioG., and 7 DRGs are observed. Typical on-source effective integration is 5 hours. Typical PSF size at the target position is FWHM=0.2” (~1.5kpc@z=3)

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”

LBG@z=3.088

LBG@z=3.261

An example of an FoV with 6.2h integration

Natural guide star AO system on Subaru telescope with IRCS. 154 hours of observation in total. 13 FoVs with 36 LBGs, 1 RadioG., and 7 DRGs are observed. Typical on-source effective integration is 5 hours. Typical PSF size at the target position is FWHM=0.2” (~1.5kpc@z=3)

Subaru

Images of LBGs in order of K-band magnitudes

36 LBGs are observed, 31 are detected 3.5”x3.5” ~ 30kpc x 30kpc

Kvega<21.5

Kvega<22.5

No detection

Subaru

Luminosity vs. J-K color of the LBGs

The observed sample covers a wide range of the rest-frame optical absolute magnitude (between Mv*-0.5 and Mv*+3.0)

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.

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Offset between optical and K-band Images

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.

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One component Sersic profile fitting for bright (~Mv*) LBGs

36 LBGs are observed, 31 are detected

Kvega<21.5

Kvega<22.5

No detection

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Examples of Sersic profile fittings for LBGs with Kvega<21.5

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).

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Summary of Sersic fittings for Kvega<21.5 LBGs (+DRGs)

Most of the LBGs (+an RadioG +DRGs) are fitted well with Sersic profiles with n<2.

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Summary of Sersic fittings for Kvega<21.5 LBGs (+DRGs)

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.

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Concentration vs. Size distribution of Kvega<22.5 LBGs / DRGs

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 disk-like profile than with n>2 spheroidal-like profiles.

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Surface brightness & surface stellar mass density

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.

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

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Summary of the results

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.

Radial profiles of LBGs (+RadioG. +DRGs) are relatively flat, and similar to disk-galaxies in the local universe.

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.

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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 (<Mv*) galaxies …

In order to confirm the disk-like morphology of z~3 galaxies, the distribution of ellipticities is a next important observable.

Most of the bright (Mv*) z~3 LBGs in Steidel et al. (2003) with Natural Guide stars are observed in this program, thus in order to extend the sample of bright LBGs, we need AO observation with Laser Guide star. • Gemini / Altair / NIRI observation is in the S07B ques of the

current semester, BUT ONLY 7 hours out of 16 hours (A)+8 hours(B), NOT SO CONVINCING EVEN FOR Rank A !! 　

Stellar dynamics is also important, but difficult.

Subaru

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).

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).

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

0.1-0.2”　=　0.8-1.5kpc

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.

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.

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“Cloning” z=3 galaxies with GOODS Data

Compare the K-band morphologies of z=3 LBGs with z=0.4-0.6 galaxies in the GOODSN region. K-band@z=3 corresponds to I,z- band @ z=0.4-0.6.

Covered volume @z=0.4-0.6 by GOODSN is comparable to that @z=3 by IRCS/AO LBGs. 　　　　

2PLE　case

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Estimated the PSFs at the target positions

Estimate the PSF shape at the positions of the targets, using a few stars in the FoV.

During the Sersic profile fitting, the parameters are changed within the range shown with yellow hatch.