3,272 research outputs found
Number Density of Bright Lyman-Break Galaxies at z~6 in the Subaru Deep Field
We report on the bright Lyman-break galaxies (LBGs) selected in a 767
arcmin^2 area of the Subaru Deep Field. The selection is made in the i-zR vs
zB-zR plane, where zB and zR are new bandpasses with a central wavelength of
8842A and 9841A, respectively. This set of bandpasses enables us to separate
well z~6 LBGs from foreground galaxies and Galactic cool stars. We detect 12
LBG candidates down to zR=25.4, and calculate the normalization of the
rest-frame far-ultraviolet (FUV: 1400A) luminosity function at MFUV = -21.6 to
be \phi(-21.6) = (2.6+/-0.7) x 10^{-5} mag^{-1} Mpc^{-3}. This must be the most
reliable measurement ever obtained of the number density of bright z~6 LBGs,
because it is more robust against both contamination and cosmic variance than
previous values. The FUV luminosity density contributed from LBGs brighter than
MFUV = -21.3 is (2.8+/-0.8) x 10^{24} ergs/s/Hz/Mpc^3, which is equivalent to a
star formation rate density of (3.5+/-1.0) x 10^{-4} Msun/yr/Mpc^3. Combining
our measurement with those at z<6 in the literature, we find that the FUV
luminosity density of bright galaxies increases by an order of magnitude from
z~6 to z~3 and then drops by 10^3 from z~3 to the present epoch, while the
evolution of the total luminosity density is much milder. The evolutionary
behavior of bright LBGs resembles that of luminous dusty star-forming galaxies
and bright QSOs. The redshift of z~3 appears to be a remarkable era in the
cosmic history when massive galaxies were being intensively formed.Comment: 12 pages, accepted for PASJ, a high resolution version is available
at http://hikari.astron.s.u-tokyo.ac.jp/~shima/z6LBGs
Chaotic diffusion of particles with finite mass in oscillating convection flows
Deterministic diffusion in temporally oscillating convection is studied for
particles with finite mass. The particles are assumed to obey a simple
dissipative dynamical system and the particle diffusion is induced by the
strange attractor. The diffusion constants are numerically calculated for
convection models with free and rigid boundary conditions.Comment: 5 figure
Large Cosmic Variance in the Clustering Properties of Lyman Alpha Emitters at z~5
We reported in a previous paper the discovery of large-scale structure of
Lyman Alpha emitters (LAEs) at z=4.86+-0.03 with a projected size of 20 Mpc x
50 Mpc in narrow-band data of a 25' x 45' area of the Subaru Deep Field
(Omega_0=0.3, lambda_0=0.7, H0=70 km/s/Mpc). However, the surveyed area, which
corresponds to 55 Mpc x 100 Mpc, was not large enough that we can conclude that
we are seeing a typical distribution of z~5 LAEs. In this Letter, we report the
results of follow-up imaging of the same sky area using a new narrow-band
filter (NB704, lambda_c=7046 A and FWHM=100 A) to detect LAEs at z=4.79, i.e.,
LAEs lying closer to us by 39 Mpc on average than the z=4.86 objects. We detect
51 LAEs at z=4.79+-0.04 down to NB704=25.7, and find that their sky
distribution is quite different from the z=4.86 LAEs'. The clustering of z=4.79
LAEs is very weak on any scales and there is no large-scale high- contrast
structure. The shape and the amplitude of the angular correlation function are
thus largely different between the two samples. These results demonstrate a
large cosmic variance in the clustering properties of LAEs on scales of ~ 50
Mpc.Comment: 4 pages (uses emulateapj5.sty), accepted for ApJ
Evidence for Low Extinction in Actively Star Forming Galaxies at z6.5
We present a search for the [CII] 158micron fine structure line (a main
cooling line of the interstellar medium) and the underlying far-infrared (FIR)
continuum in three high-redshift (6.6<z<8.2) star-forming galaxies using the
IRAM Plateau de Bure interferometer. We targeted two Lyman-Alpha-selected
galaxies (Lyman-Alpha-Emitters, LAEs) with moderate UV-based star formation
rates (SFR~20 M_sun/yr; Himiko at z=6.6 and IOK-1 at z=7.0) and a Gamma Ray
Burst (GRB) host galaxy (GRB 090423 at z~8.2). Based on our 3 sigma rest-frame
FIR continuum limits, previous (rest-frame) UV continuum measurements and
spectral energy distribution (SED) fitting, we rule out SED shapes similar to
highly obscured galaxies (e.g. Arp220, M82) and less extreme dust-rich nearby
spiral galaxies (e.g. M51) for the LAEs. Conservatively assuming a SED shape
typical of local spiral galaxies we derive upper limits for the FIR-based star
formation rates (SFRs) of ~70 M_sun/yr, ~50 M_sun/yr and ~40 M_sun/yr for
Himiko, IOK-1 and GRB 090423, respectively. For the LAEs these limits are only
a factor ~3 higher than the published UV-based SFRs (uncorrected for
extinction). This indicates that the dust obscuration in the z>6 LAEs studied
here is lower by a factor of a few than what has recently been found in some
LAEs at lower redshift (2<z<3.5) with similar UV-based SFRs. A low obscuration
in our z>6 LAE sample is consistent with recent rest-frame UV studies of z~7
Lyman-Break-Galaxies (LBGs).Comment: Accepted for publication in the Astrophysical Journa
Cosmic Galaxy-IGM HI Relation at Probed in the COSMOS/UltraVISTA deg Field
We present spatial correlations of galaxies and IGM HI in the
COSMOS/UltraVISTA 1.62 deg field. Our data consist of 13,415 photo-
galaxies at with and the Ly forest absorptions in
the background quasar spectra selected from SDSS data with no signature of
damped Ly system contamination. We estimate a galaxy overdensity
in an impact parameter of 2.5 pMpc, and calculate the Ly
forest fluctuations whose negative values
correspond to the strong Ly forest absorptions. We identify weak
evidence of an anti-correlation between and with a Spearman's rank correlation coefficient of suggesting
that the galaxy overdensities and the Ly forest absorptions positively
correlate in space at the confidence level. This positive
correlation indicates that high- galaxies exist around an excess of HI gas
in the Ly forest. We find four cosmic volumes, dubbed
-, that have extremely large (small) values of () and (), three
out of which, -, significantly depart from the correlation,
and weaken the correlation signal. We perform cosmological hydrodynamical
simulations, and compare with our observational results. Our simulations
reproduce the correlation, agreeing with the observational results. Moreover,
our simulations have model counterparts of -, and suggest
that the observations pinpoint, by chance, a galaxy overdensity like a
proto-cluster, gas filaments lying on the sightline, a large void, and
orthogonal low-density filaments. Our simulations indicate that the significant
departures of - are produced by the filamentary large-scale
structures and the observation sightline effects.Comment: 14 pages, 12 figures. Accepted for publication in Ap
Why and How did the Middle Pleistocene Transition occurred? ~Modelling challenge of the ice sheet change in both hemispheres
第3回極域科学シンポジウム 横断セッション「海・陸・氷床から探る後期新生代の南極寒冷圏環境変動」11月26日(月) 国立国語研究所 2階講
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