3,426 research outputs found
VLT Spectroscopy of the z=4.11 Radio Galaxy TN J1338-1942
We present optical, infrared and radio data of the z=4.11 radio galaxy TN
J1338-1942, including an intermediate resolution spectrum obtained with FORS1on
the VLT Antu telescope. TN J1338-1942 was the first z>4 radio galaxy to be
discovered in the southern hemisphere and is one of the most luminous Ly-alpha
objects in its class. The Ly-alpha and rest-frame optical emission appear
co-spatial with the brightest radio hotspot of this very asymmetric radio
source, suggesting extremely strong interaction with dense ambient clouds. The
VLT observations are sufficiently sensitive to detect the continuum flux both
blue-ward and red-ward of the Ly-alpha emission, allowing us to measure the
Ly-alpha forest continuum break (Ly-alpha 'discontinuity', D_A) and the Lyman
limit. We measure a D_A=0.37+-0.1, which is ~0.2 lower than the values found
for quasars at this redshift. We interpret this difference as possibly due to a
bias towards large D_A introduced in high--redshift quasar samples that are
selected on the basis of specific optical colors. If such a bias would exist in
optically selected quasars, - and even in samples of Lyman break galaxies -,
then the space density of both classes of object will be underestimated.
Furthermore, the average HI column density along cosmological lines of sight as
determined using quasar absorption lines would be overestimated. Because of
their radio-based selection, we argue that z>4 radio galaxies are excellent
objects for investigating D_A statistics. [abridged]Comment: 6 Pages, including 4 PostScript figures. Accepted for publication in
the Astronomy & Astrophysics Letter
Spectroscopic confirmation of a galaxy cluster associated with 7C1756+6520 at z=1.416
We present spectroscopic follow-up of an overdensity of galaxies
photometrically selected to be at 1.4<z<2.5 found in the vicinity of the radio
galaxy 7C1756+6520 at z=1.4156. Using the DEIMOS optical multi-object
spectrograph on the Keck 2 telescope, we observed a total of 129 BzK-selected
sources, comprising 82 blue, star-forming galaxy candidates (sBzK) and 47 red,
passively-evolving galaxy candidates (pBzK*), as well as 11 mid-infrared
selected AGN candidates. We obtain robust spectroscopic redshifts for 36 blue
galaxies, 7 red galaxies and 9 AGN candidates. Assuming all foreground
interlopers were identified, we find that only 16% (9%) of the sBzK (pBzK*)
galaxies are at z<1.4. Therefore, the BzK criteria are shown to be relatively
robust at identifying galaxies at moderate redshifts. Twenty-one galaxies,
including the radio galaxy, four additional AGN candidates and three red galaxy
candidates are found with 1.4156 +/- 0.025, forming a large scale structure at
the redshift of the radio galaxy. Of these, eight have projected offsets <2Mpc
relative to the radio galaxy position and have velocity offsets <1000km/s
relative to the radio galaxy redshift. This confirms that 7C1756+6520 is
associated with a high-redshift galaxy cluster. A second compact group of four
galaxies is found at z~1.437, forming a sub-group offset by Dv~3000km/s and
approximately 1.5' east of the radio galaxy.Comment: 9 pages, 6 figures, 2 tables, accepted for publication in A&A
Galaxy Cluster Correlation Function to z ~ 1.5 in the IRAC Shallow Cluster Survey
We present the galaxy cluster autocorrelation function of 277 galaxy cluster
candidates with 0.25 \le z \le 1.5 in a 7 deg^2 area of the IRAC Shallow
Cluster Survey. We find strong clustering throughout our galaxy cluster sample,
as expected for these massive structures. Specifically, at = 0.5 we find a
correlation length of r_0 = 17.40^{+3.98}_{-3.10} h^-1 Mpc, in excellent
agreement with the Las Campanas Distant Cluster Survey, the only other
non-local measurement. At higher redshift, = 1, we find that strong
clustering persists, with a correlation length of r_0=19.14^{+5.65}_{-4.56}
h^-1 Mpc. A comparison with high resolution cosmological simulations indicates
these are clusters with halo masses of \sim 10^{14} Msun, a result supported by
estimates of dynamical mass for a subset of the sample. In a stable clustering
picture, these clusters will evolve into massive (10^{15} Msun) clusters by the
present day.Comment: 4 pages, 4 figures, 1 table. ApJ Letters, in pres
The Intracluster Medium in z > 1 Galaxy Clusters
The Chandra X-ray Observatory was used to obtain a 190 ks image of three high
redshift galaxy clusters in one observation. The results of our analysis of
these data are reported for the two z > 1 clusters in this Lynx field,
including the most distant known X-ray selected cluster. Spatially-extended
X-ray emission was detected from both these clusters, indicating the presence
of hot gas in their intracluster media. A fit to the X-ray spectrum of RX
J0849+4452, at z=1.26, yields a temperature of kT = 5.8^{+2.8}_{-1.7} keV.
Using this temperature and the assumption of an isothermal sphere, the total
mass of RX J0849+4452 is found to be 4.0^{+2.4}_{-1.9} X 10^{14} h_{65}^{-1}
M_{\sun} within r = 1 h_{65}^{-1} Mpc. The T_x for RX J0849+4452 approximately
agrees with the expectation based on its L_{bol} = 3.3^{+0.9}_{-0.5} X 10^{44}^{-1} according to the low redshift L_x - T_x relation. The very
different distributions of X-ray emitting gas and of the red member galaxies in
the two z > 1 clusters, in contrast to the similarity of the optical/IR colors
of those galaxies, suggests that the early-type galaxies mostly formed before
their host clusters.Comment: 4 pages in emulateapj style plus 2 color jpegs for Figure 3. Accepted
by The Astrophysical Journa
Optical Spectroscopic Survey of High-latitude WISE-selected Sources
We report on the results of an optical spectroscopic survey at high Galactic latitude (|b| ≥ 30°) of a sample of WISE-selected targets, grouped by WISE W1 (λ_eff = 3.4 μm) flux, which we use to characterize the sources WISE detected. We observed 762 targets in 10 disjoint fields centered on ultraluminous infrared galaxy candidates using DEIMOS on Keck II. We find 0.30 ± 0.02 galaxies arcmin–2 with a median redshift of z = 0.33 ± 0.01 for the sample with W1 ≥ 120 μJy. The foreground stellar densities in our survey range from 0.23 ± 0.07 arcmin–2 to 1.1 ± 0.1 arcmin–2 for the same sample. We obtained spectra that produced science grade redshifts for ≥90% of our targets for sources with W1 flux ≥120 μJy that also had an i-band flux gsim 18 μJy. We used this for targeting very preliminary data reductions available to the team in 2010 August. Our results therefore present a conservative estimate of what is possible to achieve using WISE's Preliminary Data Release for the study of field galaxies
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