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Linhua Jiang,
Eiichi Egami,
Matthew Mechtley,
Xiaohui Fan,
Seth H. Cohen,
Rogier A. Windhorst,
Romeel Dave,
Kristian Finlator,
Nobunari Kashikawa,
Masami Ouchi,
Kazuhiro Shimasaku
[show abstract]
[hide abstract]
ABSTRACT: We present deep HST near-IR and Spitzer mid-IR observations of a large sample
of spectroscopically-confirmed galaxies at z >= 6. The sample consists of 51
Lyman-alpha emitters (LAEs) at z ~ 5.7, 6.5, and 7.0, and 16 Lyman-break
galaxies (LBGs) at 5.9 < z < 6.5. The majority of them were discovered in the
Subaru Deep Field. They have extremely deep optical imaging data in a series of
broad and narrow bands taken with Subaru Suprime-Cam. The near-IR images were
mostly obtained from WFC3 with a typical depth of two HST orbits in the F125W
and F160W bands. The Spitzer mid-IR images have a depth of 3 ~ 6 hrs in IRAC
channels 1 and 2. We utilize the wealth of the multi-band data and the secure
redshifts to derive the properties of their rest-frame UV continuum and
Lyman-alpha emission. These galaxies have steep UV continuum slopes roughly
between beta ~ -1.5 and -3.5, with a median value of beta ~ -2.3, which is
slightly steeper than the slopes of photometrically-selected LBGs reported in
previous studies. The slope shows little dependence on UV continuum luminosity
except for a few of the brightest galaxies. We find a statistically significant
excess of galaxies with slopes around beta ~ -3, suggesting the existence of
very young stellar populations with extremely low metallicity and dust content.
Our galaxies have moderately strong rest-frame Lyman-alpha equivalent width
(EW) in a range of ~10 to ~300 \AA. The star-formation rates derived from the
Lyman-alpha and UV continuum luminosities are also moderate, from a few to a
few tens solar masses per year. The LAEs and LBGs in this sample share many
common properties, implying that LAEs represent a subset of LBGs with strong
Lyman-alpha emission. Finally, we derive the UV luminosity functions (LFs) of
LAEs with EW > 20 \AA\ at z ~ 5.7 and 6.5, and compare them with the UV LFs of
LBGs at similar redshifts. [abridged].
02/2013;
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Linhua Jiang,
Eiichi Egami,
Xiaohui Fan,
Rogier A. Windhorst,
Seth H. Cohen,
Romeel Dave,
Kristian Finlator,
Nobunari Kashikawa,
Matthew Mechtley,
Masami Ouchi,
Kazuhiro Shimasaku
[show abstract]
[hide abstract]
ABSTRACT: We present a detailed structural and morphological study of a large sample of
spectroscopically-confirmed galaxies at z>=6, using deep HST near-IR broad-band
images and Subaru optical narrow-band images. The galaxy sample consists of 51
Lyman-alpha emitters (LAEs) at z~5.7, 6.5, and 7.0, and 16 Lyman-break galaxies
(LBGs) at 5.9<z<6.5. These galaxies exhibit a wide range of rest-frame UV
continuum morphology in the HST images, from compact features to multiple
component systems. The fraction of merging/interacting galaxies reaches 40~50%
at M_UV<-20.5 mag, suggesting hierarchical build-up of the brightest galaxies
at high redshift. We use half-light radius to describe the galaxy sizes, and
find that the intrinsic radii r_{hl,in}, after correction for PSF broadening,
are roughly between 0.05" and 0.3", with a median value of 0.13" (~0.75 kpc).
This is consistent with the sizes of bright LAEs and LBGs at z>6 in previous
studies. In addition, more luminous galaxies tend to have larger physical
sizes, exhibiting a size-luminosity relation r_{hl,in} \propto L^0.2. The slope
0.2 is significantly flatter than those in previous fainter LBG samples. We for
the first time characterize the morphology of z>6 galaxies using nonparametric
methods, including the CAS system, the Gini and M_{20} parameters. Compared to
low-redshift galaxies, our galaxies appear in slightly different locations in
the parameter space, mainly due to their small sizes in the HST images.
However, we find strong correlations between the measured parameters, as
expected from their definitions. This implies that these nonparametric methods
could be still applicable for z>=6 galaxies, if used with caution. We search
for extended Lyman-alpha emission halos around LAEs at z~5.7 and 6.5, by
stacking a number of narrow-band images. We do not find evidence of extended
halos predicted. [abridged].
02/2013;
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Ran Wang,
Jeff Wagg,
Chris L. Carilli,
Fabian Walter,
Lindley Lentati,
Xiaohui Fan,
Dominik A. Riechers,
Frank Bertoldi,
Desika Narayanan,
Michael A. Strauss,
Pierre Cox,
Alain Omont,
Karl M. Menten,
Kirsten K. Knudsen,
Roberto Neri, Linhua Jiang
[show abstract]
[hide abstract]
ABSTRACT: We present ALMA observations of the [C II] 158 micron fine structure line and
dust continuum emission from the host galaxies of five redshift 6 quasars. We
also report complementary observations of 250 GHz dust continuum and CO (6-5)
line emission from the z=6.00 quasar SDSS J231038.88+185519.7. The ALMA
observations were carried out in the extended array at 0.7" resolution. We have
detected the line and dust continuum in all five objects. The derived [C II]
line luminosities are 1.6x10^{9} to 8.8x10^{9} Lsun and the [C II]-to-FIR
luminosity ratios are 3.0-5.6x10^{-4}, which is comparable to the values found
in other high-redshift quasar-starburst systems and local ultra-luminous
infrared galaxies. The sources are marginally resolved and the intrinsic source
sizes (major axis FWHM) are constrained to be 0.3" to 0.6" (i.e., 1.7 to 3.5
kpc) for the [C II] line emission and 0.2" to 0.4" (i.e., 1.2 to 2.3 kpc) for
the continuum. These measurements indicate that there is vigorous star
formation over the central few kpc in the quasar host galaxies. The ALMA
observations also constrain the dynamical properties of the atomic gas in the
starburst nuclei. The intensity-weighted velocity maps of three sources show
clear velocity gradients. Such velocity gradients are consistent with a
rotating, gravitationally bound gas component, although they are not uniquely
interpreted as such. Under the simplifying assumption of rotation, the implied
dynamical masses within the [C II]-emitting regions are of order 10^{10} to
10^{11} Msun. Given these estimates, the mass ratios between the SMBHs and the
spheroidal bulge are an order of magnitude higher than the mean value found in
local spheroidal galaxies, which is in agreement with results from previous CO
observations of high redshift quasars.
02/2013;
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Ian D. McGreer, Linhua Jiang,
Xiaohui Fan,
Gordon T. Richards,
Michael A. Strauss,
Nicholas P. Ross,
Martin White,
Yue Shen,
Donald P. Schneider,
Adam D. Myers,
W. Niel Brandt,
Colin DeGraf,
Eilat Glikman,
Jian Ge,
Alina Streblyanska
[show abstract]
[hide abstract]
ABSTRACT: We present a measurement of the Type I quasar luminosity function at z=5
using a large sample of spectroscopically confirmed quasars selected from
optical imaging data. We measure the bright end (M_1450<-26) with Sloan Digital
Sky Survey (SDSS) data covering ~6000 deg^2, then extend to lower luminosities
(M_1450<-24) with newly discovered, faint z~5 quasars selected from 235 deg^2
of deep, coadded imaging in the SDSS Stripe 82 region (the celestial equator in
the Southern Galactic Cap). The faint sample includes 14 quasars with spectra
obtained as ancillary science targets in the SDSS-III Baryon Oscillation
Spectroscopic Survey (BOSS), and 59 quasars observed at the MMT and Magellan
telescopes. We construct a well-defined sample of 4.7<z<5.1 quasars that is
highly complete, with 73 spectroscopic identifications out of 92 candidates.
Our color selection method is also highly efficient: of the 73 spectra
obtained, 71 are high redshift quasars. These observations reach below the
break in the luminosity function (M_1450* ~ -27). The bright end slope is steep
(beta <~ -4), with a constraint of beta < -3.1 at 95% confidence. The break
luminosity appears to evolve strongly at high redshift, providing an
explanation for the flattening of the bright end slope reported previously. We
find a factor of ~2 greater decrease in the number density of luminous quasars
(M_1450<-26) from z=5 to z=6 than from z=4 to z=5, suggesting a more rapid
decline in quasar activity at high redshift than found in previous surveys. Our
model for the quasar luminosity function predicts that quasars generate ~30% of
the ionizing photons required to keep the universe ionized at z=5.
12/2012;
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Nobunari Kashikawa,
Tohru Nagao,
Jun Toshikawa,
Yoshifumi Ishizaki,
Eiichi Egami,
Masao Hayashi,
Chun Ly,
Matthew A. Malkan,
Yuichi Matsuda,
Kazuhiro Shimasaku,
Masanori Iye,
Kazuaki Ota,
Takatoshi Shibuya, Linhua Jiang,
Yoshiaki Taniguchi,
Yasuhiro Shioya
[show abstract]
[hide abstract]
ABSTRACT: We have identified a very interesting Ly-alpha emitter, whose Ly-alpha
emission line has an extremely large observed equivalent width of
EW_0=436^{+422}_{-149}A, which corresponds to an extraordinarily large
intrinsic rest-frame equivalent width of EW_0^{int}=872^{+844}_{-298}A after
the average intergalactic absorption correction. The object was
spectroscopically confirmed to be a real Ly-alpha emitter by its apparent
asymmetric Ly-alpha line profile detected at z=6.538. The continuum emission of
the object was definitely detected in our deep z'-band image; thus, its EW_0
was reliably determined. Follow-up deep near-infrared spectroscopy revealed
emission lines of neither He II lambda1640 as an apparent signature of
Population III, nor C IV lambda1549 as a proof of active nucleus. No detection
of short-lived He II lambda1640 line is not necessarily inconsistent with the
interpretation that the underlying stellar population of the object is
dominated by Population III. We found that the observed extremely large EW_0 of
the Ly-alpha emission and the upper limit on the EW_0 of the He II lambda1640
emission can be explained by population synthesis models favoring a very young
age less than 2-4Myr and massive metal-poor (Z<10^{-5}) or even metal-free
stars. The observed large EW_0 of Ly-alpha is hardly explained by Population
I/II synthesis models with Z>10^{-3}. However, we cannot conclusively rule out
the possibility that this object is composed of a normal stellar population
with a clumpy dust distribution, which could enhance the Ly-alpha EW_0, though
its significance is still unclear.
10/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We present one of the most ultraviolet (UV) luminous Lyman Break Galaxies
(LBGs) (J1432+3358) at z=2.78, discovered in the NOAO Deep Wide-Field Survey
(NDWFS) Bootes field. The R-band magnitude of J1432+3358 is 22.29 AB, more than
two magnitudes brighter than typical L* LBGs at this redshift. The deep z-band
image reveals two components of J1432+3358 separated by 1.0" with flux ratio of
3:1. The high signal-to-noise ratio (S/N) rest-frame UV spectrum shows Lya
emission line and interstellar medium absorption lines. The absence of NV and
CIV emission lines, the non-detection in X-ray and radio wavelengths and
mid-infrared (MIR) colors indicate no or weak active galactic nuclei (AGN)
(<10%) in this galaxy. The galaxy shows broader line profile with the full
width half maximum (FWHM) of about 1000 km/s and larger outflow velocity (~500
km/s) than those of typical z~3 LBGs. The physical properties are derived by
fitting the spectral energy distribution (SED) with stellar synthesis models.
The dust extinction, E(B-V)=0.12, is similar to that in normal LBGs. The star
formation rates (SFRs) derived from the SED fitting and the dust-corrected UV
flux are consistent with each other, ~300 Msun/yr, and the stellar mass is
1.3e11 Msun. The SFR and stellar mass in J1432+3358 are about an order of
magnitude higher than those in normal LBGs. The SED-fitting results support
that J1432+3358 has a continuous star formation history with the star formation
episode of 630 Myr. The morphology of J1432+3358 and its physical properties
suggest that J1432+3358 is in an early phase of 3:1 merger process. The unique
properties and the low space number density (~1e-7 Mpc^{-3})are consistent with
the interpretation that such galaxies are either found in a short unobscured
phase of the star formation or that small fraction of intensive star-forming
galaxies are unobscured.
08/2012;
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SDSS-III Collaboration: Christopher P. Ahn,
Rachael Alexandroff,
Carlos Allende Prieto,
Scott F. Anderson,
Timothy Anderton,
Brett H. Andrews,
Éric Aubourg Stephen Bailey,
Rory Barnes,
Julian Bautista,
Timothy C. Beers, [......],
Brian Yanny,
Christophe Yèche,
Donald G. York,
O. Zamora,
Gail Zasowski,
Idit Zehavi,
Gong-Bo Zhao,
Zheng Zheng,
Guangtun Zhu,
Joel C. Zinn
[show abstract]
[hide abstract]
ABSTRACT: The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic
data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data
release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median
z=0.52), 102,100 new quasar spectra (median z=2.32), and 90,897 new stellar
spectra, along with the data presented in previous data releases. These spectra
were obtained with the new BOSS spectrograph and were taken between 2009
December and 2011 July. In addition, the stellar parameters pipeline, which
determines radial velocities, surface temperatures, surface gravities, and
metallicities of stars, has been updated and refined with improvements in
temperature estimates for stars with T_eff<5000 K and in metallicity estimates
for stars with [Fe/H]>-0.5. DR9 includes new stellar parameters for all stars
presented in DR8, including stars from SDSS-I and II, as well as those observed
as part of the SDSS-III Sloan Extension for Galactic Understanding and
Exploration-2 (SEGUE-2).
The astrometry error introduced in the DR8 imaging catalogs has been
corrected in the DR9 data products. The next data release for SDSS-III will be
in Summer 2013, which will present the first data from the Apache Point
Observatory Galactic Evolution Experiment (APOGEE) along with another year of
data from BOSS, followed by the final SDSS-III data release in December 2014.
07/2012;
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Jun Toshikawa,
Nobunari Kashikawa,
Kazuaki Ota,
Tomoki Morokuma,
Takatoshi Shibuya,
Masao Hayashi,
Tohru Nagao, Linhua Jiang,
Matthew A. Malkan,
Eiichi Egami,
Kazuhiro Shimasaku,
Kentaro Motohara,
Yoshifumi Ishizaki
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of a protocluster at z~6 containing at least eight
cluster member galaxies with spectroscopic confirmations in the wide-field
image of the Subaru Deep Field (SDF). The overdensity of the protocluster is
significant at the 6 sigma level, based on the surface number density of
i'-dropout galaxies. The overdense region covers ~36 sq. arcmin, and includes
30 i'-dropout galaxies. Follow-up spectroscopy revealed that 15 of these are
real z~6 galaxies (5.7 < z < 6.3). Eight of the 15 are clustering in a narrow
redshift range centered at z=6.01, corresponding to a seven-fold increase in
number density over the average in redshift space. We found no significant
difference in the observed properties, such as Ly-alpha luminosities and UV
continuum magnitudes, between the eight protocluster members and the seven
non-members. The velocity dispersion of the eight protocluster members is 647
km/s, which is about three times higher than that predicted by the standard
cold dark matter model. This discrepancy could be attributed to the
distinguishing three-dimensional distribution of the eight protocluster
members. We discuss two possible explanations for this discrepancy: either the
protocluster is already mature, with old galaxies at the center, or it is still
immature and composed of three subgroups merging to become a larger cluster. In
either case, this concentration of z=6.01 galaxies in the SDF may be one of the
first sites of formation of a galaxy cluster in the universe.
03/2012;
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James Annis,
Marcelle Soares-Santos,
Michael A. Strauss,
Andrew C. Becker,
Scott Dodelson,
Xiaohui Fan,
James E. Gunn,
Jiangang Hao,
Zeljko Ivezic,
Sebastian Jester, Linhua Jiang,
David E. Johnston,
Jeffrey M. Kubo,
Hubert Lampeitl,
Huan Lin,
Robert H. Lupton,
Gajus Miknaitis,
Hee-Jong Seo,
Melanie Simet,
Brian Yanny
[show abstract]
[hide abstract]
ABSTRACT: We present details of the construction and characterization of the coaddition
of the Sloan Digital Sky Survey Stripe 82 \ugriz\ imaging data. This survey
consists of 275 deg$^2$ of repeated scanning by the SDSS camera of $2.5\arcdeg$
of $\delta$ over $-50\arcdeg \le \alpha \le 60\arcdeg$ centered on the
Celestial Equator. Each piece of sky has $\sim 20$ runs contributing and thus
reaches $\sim2$ magnitudes fainter than the SDSS single pass data, i.e. to
$r\sim 23.5$ for galaxies. We discuss the image processing of the coaddition,
the modeling of the PSF, the calibration, and the production of standard SDSS
catalogs. The data have $r$-band median seeing of 1.1\arcsec, and are
calibrated to $\le 1%$. Star color-color, number counts, and psf size vs
modelled size plots show the modelling of the PSF is good enough for precision
5-band photometry. Structure in the psf-model vs magnitude plot show minor psf
mis-modelling that leads to a region where stars are being mis-classified as
galaxies, and this is verified using VVDS spectroscopy. As this is a wide area
deep survey there are a variety of uses for the data, including galactic
structure, photometric redshift computation, cluster finding and cross
wavelength measurements, weak lensing cluster mass calibrations, and cosmic
shear measurements.
11/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We present Keck spectroscopic observations of z>6 Lyman-break galaxy (LBG)
candidates in the Subaru Deep Field (SDF). The candidates were selected as
i'-dropout objects down to z'=27 AB magnitudes from an ultra-deep SDF z'-band
image. With the Keck spectroscopy we identified 19 LBGs with prominent Ly_alpha
emission lines at 6< z < 6.4. The median value of the Ly_alpha rest-frame
equivalent widths (EWs) is ~50 A, with four EWs >100 A. This well-defined
spectroscopic sample spans a UV-continuum luminosity range of -21.8<
M_{UV}<-19.5 (0.6~5 L*_{UV}) and a Ly_alpha luminosity range of (0.3~3) x
10^{43} erg s^{-1} (0.3~3 L*_ {Ly_alpha}). We derive the UV and Ly_alpha
luminosity functions (LFs) from our sample at ~6.2 after we correct for
sample incompleteness. We find that our measurement of the UV LF is consistent
with the results of previous studies based on photometric LBG samples at 5<z<7.
Our Ly_alpha LF is also generally in agreement with the results of
Ly_alpha-emitter surveys at z~5.7 and 6.6. This study shows that deep
spectroscopic observations of LBGs can provide unique constraints on both the
UV and Ly_alpha LFs at z>6.
08/2011;
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Daniel J. Eisenstein,
David H. Weinberg,
Eric Agol,
Hiroaki Aihara,
Carlos Allende Prieto,
Scott F. Anderson,
James A. Arns,
Éric Aubourg,
Stephen Bailey,
Eduardo Balbinot, [......],
John P. Wisniewski,
W. Michael Wood-Vasey,
Brian Yanny,
Naoki Yasuda,
Christophe Yèche,
Donald G. York,
Erick Young,
Gail Zasowski,
Idit Zehavi,
and Bo Zhao
[show abstract]
[hide abstract]
ABSTRACT: Building on the legacy of the Sloan Digital Sky Survey (SDSS-I and II), SDSS-III is a program of four spectroscopic surveys on three scientific themes: dark energy and cosmological parameters, the history and structure of the Milky Way, and the population of giant planets around other stars. In keeping with SDSS tradition, SDSS-III will provide regular public releases of all its data, beginning with SDSS Data Release 8 (DR8), which was made public in 2011 January and includes SDSS-I and SDSS-II images and spectra reprocessed with the latest pipelines and calibrations produced for the SDSS-III investigations. This paper presents an overview of the four surveys that comprise SDSS-III. The Baryon Oscillation Spectroscopic Survey will measure redshifts of 1.5 million massive galaxies and Lyα forest spectra of 150,000 quasars, using the baryon acoustic oscillation feature of large-scale structure to obtain percent-level determinations of the distance scale and Hubble expansion rate at z < 0.7 and at z 2.5. SEGUE-2, an already completed SDSS-III survey that is the continuation of the SDSS-II Sloan Extension for Galactic Understanding and Exploration (SEGUE), measured medium-resolution (R = λ/Δλ 1800) optical spectra of 118,000 stars in a variety of target categories, probing chemical evolution, stellar kinematics and substructure, and the mass profile of the dark matter halo from the solar neighborhood to distances of 100 kpc. APOGEE, the Apache Point Observatory Galactic Evolution Experiment, will obtain high-resolution (R 30,000), high signal-to-noise ratio (S/N ≥ 100 per resolution element), H-band (1.51 μm < λ < 1.70 μm) spectra of 105 evolved, late-type stars, measuring separate abundances for ~15 elements per star and creating the first high-precision spectroscopic survey of all Galactic stellar populations (bulge, bar, disks, halo) with a uniform set of stellar tracers and spectral diagnostics. The Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS) will monitor radial velocities of more than 8000 FGK stars with the sensitivity and cadence (10-40 m s–1, ~24 visits per star) needed to detect giant planets with periods up to two years, providing an unprecedented data set for understanding the formation and dynamical evolution of giant planet systems. As of 2011 January, SDSS-III has obtained spectra of more than 240,000 galaxies, 29,000 z ≥ 2.2 quasars, and 140,000 stars, including 74,000 velocity measurements of 2580 stars for MARVELS.
The Astronomical Journal 08/2011; 142(3):72. · 4.03 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The He II λ1640 emission line has been suggested as a direct probe of Population III (Pop III) stars at high redshift, since it can arise from highly energetic ionizing photons associated with hot, metal-free stars. We use the Hubble Space Telescope WFC3/F130N IR narrowband filter to probe He II λ1640 emission in galaxy IOK-1 at z = 6.96. The sensitivity of this measurement is 5× deeper than for previous measurements. From this deep narrowband imaging, combined with broadband observations in the F125W and F160W filters, we find the He II flux to be (1.2 ± 1.0) × 10–18 erg s–1 cm–2, corresponding to a 1σ upper limit on the Pop III star formation rate (SFR) of ~0.5 M ☉ yr–1 for the case of a Salpeter initial mass function (IMF) with 50 M/M ☉ 1000 and mass loss. Given that the broadband measurements can be fit with a UV-continuum spectral flux density of ~4.85 × 10–10 × λ–2.46 erg s–1 cm–2 Å–1, which corresponds to an overall SFR of ~16+2.6 – 2.6 M ☉ yr–1, massive Pop III stars represent 6% of the total star formation. This measurement places the strongest limit yet on metal-free star formation at high redshift, although the exact conversion from He II luminosity to Pop III SFR is highly uncertain due to the unknown IMF, stellar evolution, and photoionization effects. Although we have not detected He II λ1640 at more than the 1.2σ level, our work suggests that a 3σ level detection is possible with the James Webb Space Telescope.
The Astrophysical Journal Letters 07/2011; 736(2):L28. · 5.53 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The identifications of quasars in the redshift range 2.2<z<3 are known to be
very inefficient as their optical colors are indistinguishable from those of
stars. Recent studies have proposed to use optical variability or near-IR
colors to improve the identifications of the missing quasars in this redshift
range. Here we present a case study by combining both factors. We select a
sample of 70 quasar candidates from variables in SDSS Stripe 82, which are
non-UV excess sources and have UKIDSS near-IR public data. They are clearly
separated into two parts on the Y-K/g-z color-color diagram, and 59 of them
meet or lie close to a newly proposed Y-K/g-z selection criterion for z<4
quasars. 44 of these 59 sources have been previously identified as quasars in
SDSS DR7, and 35 among them are quasars at 2.2<z<3. We present spectroscopic
observations of 14 of 15 remaining quasar candidates using the Bok 2.3m
telescope and the MMT 6.5m telescope, and successfully identify all of them as
new quasars at z=2.36 to 2.88. We also apply this method to a sample of 643
variable quasar candidates with SDSS-UKIDSS nine-band photometric data selected
from 1875 new quasar candidates in SDSS Stripe 82 given by Butler & Bloom based
on the time-series selections, and find that 188 of them are probably new
quasars with photometric redshifts at 2.2<z<3. Our results indicate that the
combination of optical variability and optical/near-IR colors is probably the
most efficient way in finding 2.2<z<3 quasars and very helpful for constructing
a complete quasar sample. We discuss its implications to the ongoing and
upcoming large optical and near-IR sky surveys.
07/2011;
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[show abstract]
[hide abstract]
ABSTRACT: [abridged] Quasars (QSOs) at the highest known redshift (z~6) are unique
probes of the early growth of supermassive black holes (BHs). Until now, only
the most luminous QSOs have been studied, often one object at a time. Here we
present the most extensive consistent analysis to date of z>4 QSOs with
observed NIR spectra, combining three new z~6 objects from our ongoing
VLT-ISAAC program with nineteen 4<z<6.5 sources from the literature. The new
sources extend the existing SDSS sample towards the faint end of the QSO
luminosity function. Using a maximum likelihood fitting routine optimized for
our spectral decomposition, we estimate the black hole mass (MBH), the
Eddington ratio (defined as Lbol/LEdd) and the FeII/MgII line ratio, a proxy
for the chemical abundance, to characterize both the central object and the
broad line region gas. The QSOs in our sample host BHs with masses of ~10^9
M\odot that are accreting close to the Eddington luminosity, consistent with
earlier results. We find that the distribution of observed Eddington ratios is
significantly different than that of a luminosity-matched comparison sample of
SDSS QSOs at lower redshift (0.35<z<2.25): the average <log(Lbol/LEdd)>=-0.37
(Lbol/LEdd~0.43) with a scatter of 0.20 dex for the z>4 sample and the
<log(Lbol/LEdd)>=-0.80 (Lbol/LEdd~0.16) with a scatter of 0.24 dex for the
0.35<z<2.25 sample. This implies that, at a given luminosity, the MBH at high-z
is typically lower than the average MBH of the lower-redshift population, i.e.
the z>4 sources are accreting significantly faster than the lower-redshift
ones. We show that the derived FeII/MgII ratios depend sensitively on the
performed analysis: our self-consistent, homogeneous analysis significantly
reduces the FeII/MgII scatter found in previous studies. The measured FeII/MgII
line ratios show no sign of evolution with cosmic time in the redshift range
4<z<6.5 [...]
06/2011;
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Nobunari Kashikawa,
Kazuhiro Shimasaku,
Yuichi Matsuda,
Eiichi Egami, Linhua Jiang,
Tohru Nagao,
Masami Ouchi,
Matthew A. Malkan,
Takashi Hattori,
Kazuaki Ota,
Yoshiaki Taniguchi,
Sadanori Okamura,
Chun Ly,
Masanori Iye,
Hisanori Furusawa,
Yasuhiro Shioya,
Takatoshi Shibuya,
Yoshifumi Ishizaki,
and Jun Toshikawa
[show abstract]
[hide abstract]
ABSTRACT: We carried out extended spectroscopic confirmations of Lyα emitters (LAEs) at z = 6.5 and 5.7 in the Subaru Deep Field. Now, the total number of spectroscopically confirmed LAEs is 45 and 54 at z = 6.5 and 5.7, respectively, and at least 81% (70%) of our photometric candidates at z = 6.5 (5.7) have been spectroscopically identified as real LAEs. We made careful measurements of the Lyα luminosity, both photometrically and spectroscopically, to accurately determine the Lyα and rest-UV luminosity functions (LFs). The substantially improved evaluation of the Lyα LF at z = 6.5 shows an apparent deficit from z = 5.7 at least at the bright end, and a possible decline even at the faint end, though small uncertainties remain. The rest-UV LFs at z = 6.5 and 5.7 are in good agreement, at least at the bright end, in clear contrast to the differences seen in the Lyα LF. These results imply an increase in the neutral fraction of the intergalactic medium from z = 5.7 to 6.5. The rest-frame equivalent width (EW0) distribution at z = 6.5 seems to be systematically smaller than z = 5.7, and it shows an extended tail toward larger EW0. The bright end of the rest-UV LF can be reproduced from the observed Lyα LF and a reasonable EW0-UV luminosity relation. Integrating this rest-UV LF provides the first measurement of the contribution of LAEs to the photon budget required for reionization. The derived UV LF suggests that the fractional contribution of LAEs to the photon budget among Lyman break galaxies significantly increases toward faint magnitudes. Low-luminosity LAEs could dominate the ionizing photon budget, though this inference depends strongly on the uncertain faint-end slope of the Lyα LF.
The Astrophysical Journal 06/2011; 734(2):119. · 6.02 Impact Factor
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Nobunari Kashikawa,
Kazuhiro Shimasaku,
Yuichi Matsuda,
Eiichi Egami, Linhua Jiang,
Tohru Nagao,
Masami Ouchi,
Matthew A. Malkan,
Takashi Hattori,
Kazuaki Ota,
Yoshiaki Taniguchi,
Sadanori Okamura,
Chun Ly,
Masanori Iye,
Hisanori Furusawa,
Yasuhiro Shioya,
Takatoshi Shibuya,
Yoshifumi Ishizaki,
Jun Toshikawa
[show abstract]
[hide abstract]
ABSTRACT: We carried out extended spectroscopic confirmations of Ly-alpha emitters
(LAEs) at z=6.5 and 5.7 in the Subaru Deep Field. Now, the total number of
spectroscopically confirmed LAEs is 45 and 54 at z=6.5 and 5.7, respectively,
and at least 81% (70%) of our photometric candidates at z=6.5 (5.7) have been
spectroscopically identified as real LAEs. We made careful measurements of the
Ly-alpha luminosity, both photometrically and spectroscopically, to accurately
determine the Ly-alpha and rest-UV luminosity functions (LFs). The
substantially improved evaluation of the Ly-alpha LF at z=6.5 shows an apparent
deficit from z=5.7 at least at the bright end, and a possible decline even at
the faint end, though small uncertainties remain. The rest-UV LFs at z=6.5 and
5.7 are in good agreement, at least at the bright end, in clear contrast to the
differences seen in the Ly-alpha LF. These results imply an increase in the
neutral fraction of the intergalactic medium from z=5.7 to 6.5. The rest-frame
equivalent width (EW_0) distribution at z=6.5 seems to be systematically
smaller than z=5.7, and it shows an extended tail toward larger EW_0. The
bright end of the rest-UV LF can be reproduced from the observed Ly-alpha LF
and a reasonable EW_0-UV luminosity relation. Integrating this rest-UV LF
provides the first measurement of the contribution of LAEs to the photon budget
required for reionization. The derived UV LF suggests that the fractional
contribution of LAEs to the photon budget among Lyman break galaxies
significantly increases towards faint magnitudes. Low-luminosity LAEs could
dominate the ionizing photon budget, though this inference depends strongly on
the uncertain faint-end slope of the Ly-alpha LF.
04/2011;
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SDSS-III collaboration: Hiroaki Aihara,
Carlos Allende Prieto,
Deokkeun An,
Scott F. Anderson,
Éric Aubourg,
Eduardo Balbinot,
Timothy C. Beers,
Andreas A. Berlind,
Steven J. Bickerton,
Dmitry Bizyaev, [......],
David A. Wake,
Ji Wang,
Benjamin A. Weaver,
David H. Weinberg,
Martin White,
Simon D. M. White,
Brian Yanny,
Naoki Yasuda,
Christophe Yeche,
Idit Zehavi
[show abstract]
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ABSTRACT: The Sloan Digital Sky Survey (SDSS) started a new phase in August 2008, with
new instrumentation and new surveys focused on Galactic structure and chemical
evolution, measurements of the baryon oscillation feature in the clustering of
galaxies and the quasar Ly alpha forest, and a radial velocity search for
planets around ~8000 stars. This paper describes the first data release of
SDSS-III (and the eighth counting from the beginning of the SDSS). The release
includes five-band imaging of roughly 5200 deg^2 in the Southern Galactic Cap,
bringing the total footprint of the SDSS imaging to 14,555 deg^2, or over a
third of the Celestial Sphere. All the imaging data have been reprocessed with
an improved sky-subtraction algorithm and a final, self-consistent photometric
recalibration and flat-field determination. This release also includes all data
from the second phase of the Sloan Extension for Galactic Understanding and
Evolution (SEGUE-2), consisting of spectroscopy of approximately 118,000 stars
at both high and low Galactic latitudes. All the more than half a million
stellar spectra obtained with the SDSS spectrograph have been reprocessed
through an improved stellar parameters pipeline, which has better determination
of metallicity for high metallicity stars.
01/2011;
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Daniel J. Eisenstein,
David H. Weinberg,
Eric Agol,
Hiroaki Aihara,
Carlos Allende Prieto,
Scott F. Anderson,
James A. Arns,
Eric Aubourg,
Stephen Bailey,
Eduardo Balbinot, [......],
John P. Wisniewski,
W. Michael Wood-Vasey,
Brian Yanny,
Naoki Yasuda,
Christophe Yeche,
Donald G. York,
Erick Young,
Gail Zasowski,
Idit Zehavi,
Bo Zhao
[show abstract]
[hide abstract]
ABSTRACT: Building on the legacy of the Sloan Digital Sky Survey (SDSS-I and II),
SDSS-III is a program of four spectroscopic surveys on three scientific themes:
dark energy and cosmological parameters, the history and structure of the Milky
Way, and the population of giant planets around other stars. In keeping with
SDSS tradition, SDSS-III will provide regular public releases of all its data,
beginning with SDSS DR8 (which occurred in Jan 2011). This paper presents an
overview of the four SDSS-III surveys. BOSS will measure redshifts of 1.5
million massive galaxies and Lya forest spectra of 150,000 quasars, using the
BAO feature of large scale structure to obtain percent-level determinations of
the distance scale and Hubble expansion rate at z<0.7 and at z~2.5. SEGUE-2,
which is now completed, measured medium-resolution (R=1800) optical spectra of
118,000 stars in a variety of target categories, probing chemical evolution,
stellar kinematics and substructure, and the mass profile of the dark matter
halo from the solar neighborhood to distances of 100 kpc. APOGEE will obtain
high-resolution (R~30,000), high signal-to-noise (S/N>100 per resolution
element), H-band (1.51-1.70 micron) spectra of 10^5 evolved, late-type stars,
measuring separate abundances for ~15 elements per star and creating the first
high-precision spectroscopic survey of all Galactic stellar populations (bulge,
bar, disks, halo) with a uniform set of stellar tracers and spectral
diagnostics. MARVELS will monitor radial velocities of more than 8000 FGK stars
with the sensitivity and cadence (10-40 m/s, ~24 visits per star) needed to
detect giant planets with periods up to two years, providing an unprecedented
data set for understanding the formation and dynamical evolution of giant
planet systems. (Abridged)
01/2011;
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Linhua Jiang,
Xiaohui Fan,
W N Brandt,
Chris L Carilli,
Eiichi Egami,
Dean C Hines,
Jaron D Kurk,
Gordon T Richards,
Yue Shen,
Michael A Strauss,
Marianne Vestergaard,
Fabian Walter
[show abstract]
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ABSTRACT: The most distant quasars known, at redshifts z approximately 6, generally have properties indistinguishable from those of lower-redshift quasars in the rest-frame ultraviolet/optical and X-ray bands. This puzzling result suggests that these distant quasars are evolved objects even though the Universe was only seven per cent of its current age at these redshifts. Recently one z approximately 6 quasar was shown not to have any detectable emission from hot dust, but it was unclear whether that indicated different hot-dust properties at high redshift or if it is simply an outlier. Here we report the discovery of a second quasar without hot-dust emission in a sample of 21 z approximately 6 quasars. Such apparently hot-dust-free quasars have no counterparts at low redshift. Moreover, we demonstrate that the hot-dust abundance in the 21 quasars builds up in tandem with the growth of the central black hole, whereas at low redshift it is almost independent of the black hole mass. Thus z approximately 6 quasars are indeed at an early evolutionary stage, with rapid mass accretion and dust formation. The two hot-dust-free quasars are likely to be first-generation quasars born in dust-free environments and are too young to have formed a detectable amount of hot dust around them.
Nature 03/2010; 464(7287):380-3. · 36.28 Impact Factor
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Branimir Sesar,
Željko Ivezić,
Skyler H. Grammer,
Dylan P. Morgan,
Andrew C. Becker,
Mario Jurić,
Nathan De Lee,
James Annis,
Timothy C. Beers,
Xiaohui Fan,
Robert H. Lupton,
James E. Gunn,
Gillian R. Knapp, Linhua Jiang,
Sebastian Jester,
David E. Johnston,
and Hubert Lampeitl
[show abstract]
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ABSTRACT: We present an improved analysis of halo substructure traced by RR Lyrae stars in the Sloan Digital Sky Survey (SDSS) stripe 82 region. With the addition of SDSS-II data, a revised selection method based on new ugriz light curve templates results in a sample of 483 RR Lyrae stars that is essentially free of contamination. The main result from our first study persists: the spatial distribution of halo stars at galactocentric distances 5-100 kpc is highly inhomogeneous. At least 20% of halo stars within 30 kpc from the Galactic center can be statistically associated with substructure. We present strong direct evidence, based on both RR Lyrae stars and main-sequence stars, that the halo stellar number density profile significantly steepens beyond a Galactocentric distance of ~30 kpc, and a larger fraction of the stars are associated with substructure. By using a novel method that simultaneously combines data for RR Lyrae and main-sequence stars, and using photometric metallicity estimates for main-sequence stars derived from deep co-added u-band data, we measure the metallicity of the Sagittarius dSph tidal stream (trailing arm) toward R.A. ~2h-3h and decl. ~ 0° to be 0.3 dex higher ([Fe/H] = –1.2) than that of surrounding halo field stars. Together with a similar result for another major halo substructure, the Monoceros stream, these results support theoretical predictions that an early forming, smooth inner halo, is metal-poor compared to high surface brightness material that have been accreted onto a later-forming outer halo. The mean metallicity of stars in the outer halo that are not associated with detectable clumps may still be more metal-poor than the bulk of inner-halo stars, as has been argued from other data sets.
The Astrophysical Journal 12/2009; 708(1):717. · 6.02 Impact Factor
