Adaptive Optics AO Restframe Vband Imaging of Galaxies at z3 : High Surface Density Disklike Galaxie

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Adaptive Optics (AO) Rest-frame V-band Imaging
ofGalaxies at z3 High Surface Density
Disk-like Galaxies ?
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 Users Meeting 20080130

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Naive motivation

• The morphology of galaxies at z1 still follows
  Hubble sequence seen in the nearby universe. How
  about galaxies further away ?

3col images of z1 galaxies in GOODS
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Rest-frame optical morphology is important

• Rest-frame optical morphology of galaxies
  reflects the stellar mass distribution of
  galaxies, and provides important information on
  the dynamical structure of galaxies.

Two spiral galaxies at z1
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 _at_ z3 Adaptive Optics 0.1-0.2
0.8-1.5kpc
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Targets for Observations

• Our main targets are U-band dropout Lyman Break
  Galaxies (LBGs)
• Steidel et al. 2003 is the largest sample of
  spectroscopicaly-confirmed z3 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 z2.891)
• We also examined morphologies of serendipitously
  observed Distant Red Galaxies (DRGs) in our FoVs.
  DRG criterion of J-Kgt2.3 also selects red
  galaxies at similar redshifts to U-dropout LBGs.

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Observation Subaru Telescope Intensive Program

• Subaru 8.2m
• AO36 system
• Low-order correction with low-noise
  Shack-Hartmann wavefront sensor
• Good for extra-galactic studies !

• 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
  FWHM0.2 (1.5kpc_at_z3)

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Observation Subaru Telescope Intensive Program
An example of an FoV with 6.2h integration
PSF-reference(20) FWHM0.20
PSF-reference (15) FWHM0.18
LBG_at_z3.261
AO Guide Star
LBG_at_z3.088

• 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
  FWHM0.2 (1.5kpc_at_z3)

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Images of LBGs in order of K-band magnitudes
Kvegalt21.5
Kvegalt22.5
No detection

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

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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 Mv3.0)
• The LBG-selected galaxies cover not only the
  less-massive bluer galaxies (U-V-0.3) but also
  the massive redder galaxies (U-V0.5) 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
Kvegalt21.5
Kvegalt22.5
No detection

• 36 LBGs are observed, 31 are detected

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Examples of Sersic profile fittings for LBGs with
Kvegalt21.5

• LBGs are described better with n1 Sersic profile
  (similar to disk galaxies, less concentrated
  green) than n4 Sersic profiles (similar to
  spheroidal galaxies, more concetrated blue).

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Summary of Sersic fittings for Kvegalt21.5 LBGs
(DRGs)

• Most of the LBGs (an RadioG DRGs) are fitted
  well with Sersic profiles with nlt2.

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Summary of Sersic fittings for Kvegalt21.5 LBGs
(DRGs)

• Results of cloning simulations show if there
  are large number of elliptical or bulge-dominated
  galaxies at z3, they should be detected, and
  should be fitted well with large n-index.

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Concentration vs. Size distribution of
Kvegalt22.5 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 nlt2 disk-like profile than with ngt2
  spheroidal-like profiles.

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Surface brightness surface stellar mass density
z0-1 from Barden 2005

• 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 z0 and z1 disk galaxies,
  respectively.
• Surface stellar mass densities inferred from the
  size-stellar mass relation is 3-6 times larger
  than z0-1 disk galaxies shown with thick solid
  line.

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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
  z3 LBGs (DRGs) are brighter than z0-1 disk
  galaxies. Surface stellar mass densities of
  massive LBGs are also larger than z0-1 disk
  galaxies.

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Naive speculation placing the z3 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).
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New era of high-z morphology study with Laser
Guide stars

• Current sample is not sufficient statistically,
  especially for bright (ltMv) galaxies
• In order to confirm the disk-like morphology of
  z3 galaxies, the distribution of ellipticities
  is a next important observable.
• Most of the bright (Mv) z3 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.

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Why LBGs to understand formation and evolution of
galaxy bulges ?

• 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.

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Why Study Rest-frame Optical Morphologies of z3
Galaxies

• 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 z3. 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.

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
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Cloning z3 galaxies with GOODS Data

• Compare the K-band morphologies of z3 LBGs with
  z0.4-0.6 galaxies in the GOODSN region.
  K-band_at_z3 corresponds to I,z- band _at_ z0.4-0.6.
• Covered volume _at_z0.4-0.6 by GOODSN is comparable
  to that _at_z3 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.