211 research outputs found
New Supporting Evidence for the Overdensity of Galaxies around the Radio-Loud Quasar SDSS J0836+0054 at z =5.8
Recently, Zheng et al. (2005) found evidence for an overdensity of galaxies
around a radio-loud quasar, SDSS J0836+0054, at z=5.8 (a five arcmin
region). We have examined our deep optical imaging data (B, V, r', i', z', and
NB816) taken with the Suprime-Cam on the Subaru Telescope. The NB816
narrow-band filter (lambda_c = 815 nm and nm) is suitable
for searching for Ly emitters at . We have found a new
strong Ly emitter at close to object B identified by
Zheng et al. Further, the non detection of the nine objects selected by Zheng
et al. (2005) in our B, V, and r' images provides supporting evidence that they
are high-z objects.Comment: 5 pages, 1 figure, accepted for PAS
Strong Emission-Line Galaxies at Low Redshift in the Field around the Quasar SDSSp J104433.04-012502.2
We discuss observational properties of strong emission-line galaxies at low
redshift found by our deep imaging survey for high-redshift Ly alpha emitters.
In our surveys, we used the narrowband filter, NB816 (lambda_center=8150A with
FWHM = 120A), and the intermediate-band filter, IA827 (lambda_center = 8270A
with FWHM = 340A). In this survey, 62 NB816-excess (> 0.9 mag) and 21
IA827-excess (> 0.8 mag) objects were found. Among them, we found 20
NB816-excess and 4 IA827-excess Ly alpha emitter candidates. Therefore, it
turns out that 42 NB816-excess and 17 IA827-excess objects are strong
emission-line objects at lower redshift. Since 4 objects in the two low-z
samples are common, the total number of strong low-z emitters is 55. Applying
our photometric redshift technique, we identify 7 H alpha emitters at z~0.24,
20 H beta-[OIII] ones at z~0.65, and 11 [OII] ones at z~1.19. However, we
cannot determine reliable photometric redshifts of the remaining 17 emitters.
The distributions of their rest frame equivalent widths are consistently
understood with recent studies of galaxy evolution from z~1 to z~0.Comment: 28 pages, 8 figures, PASJ, Vol. 58, No. 1, in pres
Sensitive observations at 1.4 and 250 GHz of z > 5 QSOs
We present 1.4 and 5 GHz observations taken with the Very Large Array (VLA),
and observations at 250 GHz obtained with the Max-Planck millimeter bolometer
(MAMBO) at the IRAM 30~m telescope, of ten optically selected Quasi-stellar
Objects (QSOs) at 5.0 < z < 6.28. Four sources are detected at 1.4 GHz two of
which are radio loud and are also detected at 5 GHz. These results are roughly
consistent with there being no evolution of the radio-loud QSO fraction out to
z~6.
Three sources have been detected at 250 GHz or 350 GHz at much higher levels
than their 1.4 GHz flux densities suggesting that the observed mm emission is
likely thermal emission from warm dust, although more exotic possibilities
cannot be precluded.
The highest redshift source in our sample (J1030+0524 at z=6.28) is not
detected at 1.4 or 250 GHz, but four fairly bright radio sources (flux density
at 1.4GHz > 0.2 mJy) are detected in a 2' field centered on the QSO, including
an edge-brightened ('FRII') double radio source with an extent of about 1'.
A similar over-density of radio sources is seen in the field of the highest
redshift QSO J1148+5251. We speculate that these over-densities of radio
sources may indicate clusters along the lines-of-sight, in which case
gravitational lensing by the cluster could magnify the QSO emission by a factor
2 or so without giving rise to arcsecond-scale distortions in the optical
images of the QSOs.Comment: 25 pages, 12 figures. accepted by A
A Subaru Search for Lyman Emitters at Redshift 5.7
We present the results of a survey for Ly emitters at
based on optical narrow-band ( \AA ~ and \AA), and broad-band (, , , and )
observations of the field surrounding the high redshift quasar, SDSSp
J104433.04012522.2, on the 8.2 m Subaru Telescope with the Subaru Prime
Focus Camera, Suprime-Cam. This survey covers a sky area of
arcmin and a co-moving volume of
Mpc. We have found 20 candidates of Ly emitters at 5.7
with . Two of them have been confirmed star-forming
galaxies at and from our follow-up optical spectroscopy. We
discuss star-formation properties of the 20 objects from a statistical point of
view. Our survey leads to a new estimate of the star formation rate density at
, yr
Mpc.Comment: 18 pages, 19 figures, accepted for A
The Isophotal Structure of Early-Type Galaxies in the SDSS: Dependence on AGN Activity and Environment
We study the dependence of the isophotal shape of early-type galaxies on
their absolute B-band magnitude, their dynamical mass, and their nuclear
activity and environment, using an unprecedented large sample of 847 early-type
galaxies identified in the SDSS by Hao et al (2006). We find that the fraction
of disky galaxies smoothly decreases with increasing luminosity. The large
sample allows us to describe these trends accurately with tight linear
relations that are statistically robust against the uncertainty in the
isophotal shape measurements. There is also a host of significant correlations
between the disky fraction and indicators of nuclear activity (both in the
optical and in the radio) and environment (soft X-rays, group mass, group
hierarchy). Our analysis shows however that these correlations can be
accurately matched by assuming that the disky fraction depends only on galaxy
luminosity or mass. We therefore conclude that neither the level of activity,
nor group mass or group hierarchy help in better predicting the isophotal shape
of early-type galaxies.Comment: 31 pages, 10 figures, accepted for publication in Ap
Stellar populations in gas-rich galaxy mergers II. Feedback effects of Type Ia and II supernovae
We numerically investigate chemodynamical evolution of major disk-disk galaxy
mergers in order to explore the origin of mass-dependent chemical, photometric,
and spectroscopic properties observed in elliptical galaxies. We particularly
investigate the dependence of the fundamental properties on merger progenitor
disk mass (M_d). Main results obtained in this study are the following three.
(1) More massive (luminous) ellipticals formed by galaxy mergers between more
massive spirals have larger metallicity (Z) and thus show redder colors: The
typical metallicity ranges from ~ 1.0 solar abundance (Z~ 0.02) for ellipticals
formed by mergers with M_d = 10^10 M_solar to ~ 2.0 solar (Z ~ 0.04) for those
with M_d = 10^12 M_solar. (2) The absolute magnitude of negative metallicity
gradients developed in galaxy mergers is more likely to be larger for massive
ellipticals.
Absolute magnitude of metallicity gradient correlates with that of age
gradient in ellipticals in the sense that an elliptical with steeper negative
metallicity gradient is more likely to show steeper age gradient. (3) Both
M/L_B and M/L_K, where M, L_B, and L_K are total stellar mass of galaxy
mergers, B-band luminosity, and K-band one, respectively, depend on galactic
mass in such a way that more massive ellipticals have larger M/L_B and smaller
M/L_K.Comment: 58 pages 16 figures, ApJ in press (March 1999 issue
Gravitational lensing magnification without multiple imaging
Gravitational lensing can amplify the apparent brightness of distant sources.
Images that are highly magnified are often part of multiply-imaged systems, but
we consider the possibility of having large magnifications without additional
detectable images. In rare but non-negligible situations, lensing can produce a
singly highly magnified image; this phenomenon is mainly associated with
massive cluster-scale halos (>~1e13.5 Msun). Alternatively, lensing can produce
multiply-imaged systems in which the extra images are either unresolved or too
faint to be detectable. This phenomenon is dominated by galaxies and lower-mass
halos (<~1e12 Msun), and is very sensitive to the inner density profile of the
halos. Although we study the general problem, we customize our calculations to
four quasars at redshift z~6 in the Sloan Digital Sky Survey (SDSS), for which
Richards et al. (2004) have ruled out the presence of extra images down to an
image splitting of 0.3" and a flux ratio of f=0.01. We predict that 9-29% of
all z~6 quasars that are magnified by a factor of mu>10 would lack detectable
extra images, with 5-10% being true singly-imaged systems. The maximum of 29%
is reached only in the unlikely event that all low-mass (<~1e10 Msun) halos
have highly concentrated (isothermal) profiles. In more realistic models where
dwarf halos have flatter (NFW) inner profiles, the maximum probability is ~10%.
We conclude that the probability that all four SDSS quasars are magnified by a
factor of 10 is <~1e-4. The only escape from this conclusion is if there are
many (>10) multiply-imaged z~6 quasars in the SDSS database that have not yet
been identified, which seems unlikely. In other words, lensing cannot explain
the brightnesses of the z~6 quasars, and models that invoke lensing to avoid
having billion-Msun black holes in the young universe are not viable.Comment: accepted in ApJ; 15 emulateapj pages; small revisions to clarify the
tex
A survey of NB921 dropouts in the Subaru Deep Field
In order to search for high-redshift galaxies beyond in the Subaru
Deep Field, we have investigated NB921-dropout galaxies where NB921 is the
narrowband filter centered at 919.6 nm with FWHM of 13.2 nm for the Suprime-Cam
on the Subaru Telescope. There are no secure NB921-dropout candidates brighter
than . Based on this result, we discuss the UV luminosity
function of star-forming galaxies at .Comment: 10 pages, 5 figures, PASJ, Vol.57, No.5, in pres
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