3,663 research outputs found
Keck Spectroscopy of Faint 3<z<7 Lyman Break Galaxies:- II. A High Fraction of Line Emitters at Redshift Six
As Lyman-alpha photons are scattered by neutral hydrogen, a change with
redshift in the Lyman-alpha equivalent width distribution of distant galaxies
offers a promising probe of the degree of ionization in the intergalactic
medium and hence when cosmic reionization ended. This simple test is
complicated by the fact that Lyman-alpha emission can also be affected by the
evolving astrophysical details of the host galaxies. In the first paper in this
series, we demonstrated both a luminosity and redshift dependent trend in the
fraction of Lyman-alpha emitters seen within color-selected Lyman-break
galaxies (LBGs) over the range 3<z<6; lower luminosity galaxies and those at
higher redshift show an increased likelihood of strong emission. Here we
present the results from much deeper 12.5 hour exposures with the Keck DEIMOS
spectrograph focused primarily on LBGs at z~6 which enable us to confirm the
redshift dependence of line emission more robustly and to higher redshift than
was hitherto possible. We find 54+/-11% of faint z~6 LBGs show strong (W_0>25
A) emission, an increase of 1.6x from a similar sample observed at z~4. With a
total sample of 74 z~6 LBGs, we determine the luminosity-dependent Lyman-alpha
equivalent width distribution. Assuming continuity in these trends to the new
population of z~7 sources located with the Hubble WFC3/IR camera, we predict
that unless the neutral fraction rises in the intervening 200 Myr, the success
rate for spectroscopic confirmation using Lyman-alpha emission should be high.Comment: 6 pages, 3 figures, submitted to ApJ
The infrared-dark dust content of high redshift galaxies
We present a theoretical model aimed at explaining the IRX- relation
for high redshift (z >5) galaxies. Recent observations (Capak+2015;
Bouwens+2016) have shown that early Lyman Break Galaxies, although
characterized by a large UV attenuation (e.g. flat UV beta slopes), show a
striking FIR deficit, i.e. they are "infrared-dark". This marked deviation from
the local IRX-beta relation can be explained by the larger molecular gas
content of these systems. While dust in the diffuse ISM attains relatively high
temperatures (Td = 45 K for typical size a=0.1 um; smaller grains can reach Td
= 60 K), a sizable fraction of the dust mass is embedded in dense gas, and
therefore remains cold. If confirmed, the FIR deficit might represent a novel,
powerful indicator of the molecular content of high-z galaxies which can be
used to pre-select candidates for follow-up deep CO observations. Thus, high-z
CO line searches with ALMA might be much more promising than currently thought.Comment: 8 pages, 4 Figures, MNRAS Submitte
The Effects of Elevated Shoe Heights on Static and Dynamic Balance in Healthy Younger Women
The purpose of this study was to determine the effects of elevated shoe heights on static and dynamic balance in healthy young women. The balance of 30 female volunteer subjects with ages ranging from 20 to 26 years (mean age = 22.3 years) was tested. Dynamic balance was tested using the limits of stability (LOS) test on the NeuroCom® Balance Master (NBM®), version 6.1 as well as the Functional Reach Test (FRT). Each subject\u27s static balance was tested using the bilateral stance test on the NBM®. Subjects participated in a one time testing session which consisted of the performance of the three balance tests in a random order with elevated-soled shoes on (minimum heel height of 4.0 cm) and barefoot.
Significant differences in dynamic stability were noted in the LOS test and in the FRT. The results of the two dynamic tests suggest that balance may be impaired with the wearing of shoes with elevated soles. The bilateral stance test for static stability found that subjects exhibited increased postural sway when barefoot as compared to with elevated-soled shoes on. The results of this static test suggest that stationary balance may be somewhat more stable with elevated shoe wear.
The findings of the LOS test and FR T are in agreement with much of the previous high-heeled shoe literature, however, the bilateral stance test for postural sway is not in agreement with some of the previous research. Nonetheless, it is apparent that elevated shoe heights can produce dynamic balance deficits and therefore clinicians should always carefully inspect and assess a clients footwear as part of the evaluation procedure
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
Fluorescent C II* 1335A emission spectroscopically resolved in a galaxy at z = 5.754
We report the discovery of the first spectroscopically resolved C II /C II*
1334, 1335A doublet in the Lyman-break galaxy J0215-0555 at z = 5.754. The
separation of the resonant and fluorescent emission channels was possible
thanks to the large redshift of the source and long integration time, as well
as the small velocity width of the feature, 0.6 +- 0.2A. We model this emission
and find that at least two components are required to reproduce the combination
of morphologies of C II* emission, C II absorption and emission, and
Lyman-alpha emission from the object. We suggest that the close alignment
between the fluorescence and Lyman-alpha emission could indicate an ionisation
escape channel within the object. While the faintness of such a C II /C II*
doublet makes it prohibitively difficult to pursue for similar systems with
current facilities, we suggest it can become a valuable porosity diagnostic in
the era of JWST and the upcoming generations of ELTs.Comment: 5 pages, 3 figures; accepted for publication in MNRAS Letter
Spectroscopic Confirmation of Three z-Dropout Galaxies at z = 6.844 - 7.213: Demographics of Lyman-Alpha Emission in z ~ 7 Galaxies
We present the results of our ultra-deep Keck/DEIMOS spectroscopy of
z-dropout galaxies in the SDF and GOODS-N. For 3 out of 11 objects, we detect
an emission line at ~ 1um with a signal-to-noise ratio of ~ 10. The lines show
asymmetric profiles with high weighted skewness values, consistent with being
Lya, yielding redshifts of z=7.213, 6.965, and 6.844. Specifically, we confirm
the z=7.213 object in two independent DEIMOS runs with different spectroscopic
configurations. The z=6.965 object is a known Lya emitter, IOK-1, for which our
improved spectrum at a higher resolution yields a robust skewness measurement.
The three z-dropouts have Lya fluxes of 3 x 10^-17 erg s^-1 cm^-2 and
rest-frame equivalent widths EW_0^Lya = 33-43A. Based on the largest
spectroscopic sample of 43 z-dropouts that is the combination of our and
previous data, we find that the fraction of Lya-emitting galaxies (EW_0^Lya >
25A) is low at z ~ 7; 17 +- 10% and 24 +- 12% for bright (Muv ~= -21) and faint
(Muv ~= -19.5) galaxies, respectively. The fractions of Lya-emitting galaxies
drop from z ~ 6 to 7 and the amplitude of the drop is larger for faint galaxies
than for bright galaxies. These two pieces of evidence would indicate that the
neutral hydrogen fraction of the IGM increases from z ~ 6 to 7, and that the
reionization proceeds from high- to low-density environments, as suggested by
an inside-out reionization model.Comment: 15 pages, 9 figures, accepted for publication in Ap
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
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