169 research outputs found
Substructure within the SSA22 protocluster at
We present the results of a densely sampled spectroscopic survey of the SSA22
protocluster at . Our sample with Keck/LRIS spectroscopy
includes 106 Ly Emitters (LAEs) and 40 Lyman Break Galaxies (LBGs) at
. These galaxies are contained within the region in
which the protocluster was discovered, which also hosts the maximum galaxy
overdensity in the SSA22 region. The redshift histogram of our spectroscopic
sample reveals two distinct peaks, at (blue, 43 galaxies) and
(red, 103 galaxies). Furthermore, objects in the blue and red peaks
are segregated on the sky, with galaxies in the blue peak concentrating towards
the western half of the field. These results suggest that the blue and red
redshift peaks represent two distinct structures in physical space. Although
the double-peaked redshift histogram is traced in the same manner by LBGs and
LAEs, and brighter and fainter galaxies, we find that nine out of 10 X-ray AGNs
in SSA22, and all seven spectroscopically-confirmed giant Ly "blobs,"
reside in the red peak. We combine our dataset with sparsely sampled
spectroscopy from the literature over a significantly wider area, finding
preliminary evidence that the double-peaked structure in redshift space extends
beyond the region of our dense spectroscopic sampling. In order to fully
characterize the three-dimensional structure, dynamics, and evolution of
large-scale structure in the SSA22 overdensity, we require the measurement of
large samples of LAE and LBG redshifts over a significantly wider area, as well
as detailed comparisons with cosmological simulations of massive cluster
formation.Comment: 6 pages, 4 figures, Accepted to ApJ Letter
The clustering of Luminous Red Galaxies around MgII absorbers
We study the cross-correlation between 212 MgII quasar absorption systems and
\~20,000 Luminous Red Galaxies (LRGs) selected from the Sloan Digital Sky
Survey Data Release 1 in the redshift range 0.4<z<0.8. The MgII systems were
selected to have 2796 & 2803 rest-frame equivalent widths >=1.0 Angstrom and
identifications confirmed by the FeII 2600 or MgI 2852 lines. Over comoving
scales 0.05--13 h^-1 Mpc, the MgII--LRG cross-correlation has an amplitude
0.69+/-0.09 times that of the LRG--LRG auto-correlation. Since LRGs have
halo-masses greater than 3.5 x 10^12 solar masses for M_R<-21, this relative
amplitude implies that the absorber host-galaxies have halo-masses greater than
2--8 x 10^11 Msun. For 10^13 Msun LRGs, the absorber host-galaxies have
halo-masses 0.5--2.5 x 10^12 Msun. Our results appear consistent with those of
Steidel et al. (1994) who found that MgII absorbers with W_r>=0.3 Angstrom are
associated with ~0.7 L^*_B galaxies.Comment: 7 pages, 3 figs; Accepted for publication in MNRAS Letters; Extended
version with Appendix; Text version of MgII absorber catalogue (Table 1) can
be found at http://www.ast.cam.ac.uk/~mim/pub.html. Minor changes to match
the published tex
Halo gas cross sections and covering fractions of MgII absorption selected galaxies
We examine halo gas cross sections and covering fractions, fc, of intermediate-redshift Mg II absorption selected galaxies. We computed statistical absorber halo radii, Rx, using current values of dN/dz and Schechter luminosity function parameters, and have compared these values to the distribution of impact parameters and luminosities from a sample of 37 galaxies. For equivalent widths Wr(2796) â„ 0.3 Ă
, we find 43 †Rx †88 kpc, depending on the lower luminosity cutoff and the slope, ÎČ, of the Holmberg-like luminosity scaling, R â α L^ÎČ . The observed distribution of impact parameters, D, are such that several absorbing galaxies lie at D > Rx and several non-absorbing galaxies lie at D ~ 0.5 for our sample. Moreover, the data suggest that halo radii of Mg II absorbing galaxies do not follow a luminosity scaling with ÎČ in the range of 0.2â0.28, if fc = 1 as previously reported. However, provided fc ~ 0.5, we find that halo radii can remain consistent with a Holmberg-like luminosity relation with ÎČ â 0.2 and Râ = Rx/â(fc) ~ 110 kpc. No luminosity scaling (ÎČ = 0) is also consistent with the observed distribution of impact parameters if fc †0.37. The data support a scenario in which gaseous halos are patchy and likely have non-symmetric geometric distributions about the galaxies. We suggest that halo gas distributions may not be governed primarily by galaxy mass/luminosity but also by stochastic processes local to the galaxy
The myth of speeding up business processes through parallel job processing
Strukturierung , Koordination , Theorie, Mustervergleich , Prozesssimulatio
Deuterium Abundance in the Most Metal-Poor Damped Lyman alpha System: Converging on Omega_baryons
The most metal-poor DLA known to date, at z = 2.61843 in the spectrum of the
QSO Q0913+072, with an oxygen abundance only about 1/250 of the solar value,
shows six well resolved D I Lyman series transitions in high quality echelle
spectra recently obtained with the ESO VLT. We deduce a value of the deuterium
abundance log (D/H) = -4.56+/-0.04 which is in good agreement with four out of
the six most reliable previous determinations of this ratio in QSO absorbers.
We find plausible reasons why in the other two cases the 1 sigma errors may
have been underestimated by about a factor of two. The addition of this latest
data point does not change significantly the mean value of the primordial
abundance of deuterium, suggesting that we are now converging to a reliable
measure of this quantity. We conclude that = -4.55+/-0.03 and
Omega_b h^2 (BBN) = 0.0213+/-0.0010 (68% confidence limits). Including the
latter as a prior in the analysis of the five year data of WMAP leads to a
revised best-fitting value of the power-law index of primordial fluctuations
n_s = 0.956+/-0.013 (1 sigma) and n_s < 0.990 with 99% confidence. Considering
together the constraints provided by WMAP 5, (D/H)_p, baryon oscillations in
the galaxy distribution, and distances to Type Ia supernovae, we arrive at the
current best estimates Omega_b h^2 = 0.0224+/-0.0005 and n_s = 0.959+/-0.013.Comment: 13 pages, 8 Figures. Revised version following referee's comments.
Accepted for publication in Monthly Notices of the Royal Astronomical
Society. A few typos correcte
Understanding large-scale structure in the SSA22 protocluster region using cosmological simulations
We investigate the nature and evolution of large-scale structure within the
SSA22 protocluster region at using cosmological simulations. A
redshift histogram constructed from current spectroscopic observations of the
SSA22 protocluster reveals two separate peaks at (blue) and (red). Based on these data, we report updated overdensity and mass
calculations for the SSA22 protocluster. We find ,
for the blue and red peaks, respectively, and
for the entire region. These overdensities
correspond to masses of , , and
for the red, blue, and
total peaks, respectively. We use the Small MultiDark Planck (SMDPL) simulation
to identify comparably massive protoclusters, and uncover the
underlying structure and ultimate fate of the SSA22 protocluster. For this
analysis, we construct mock redshift histograms for each simulated
protocluster, quantitatively comparing them with the observed SSA22 data. We
find that the observed double-peaked structure in the SSA22 redshift histogram
corresponds not to a single coalescing cluster, but rather the proximity of a
protocluster and at least one cluster progenitor. Such associations in the SMDPL simulation are
easily understood within the framework of hierarchical clustering of dark
matter halos. We finally find that the opportunity to observe such a phenomenon
is incredibly rare, with an occurrence rate of 7.4h^3 \mbox{ Gpc}^{-3}.Comment: 13 pages, 8 figures, Accepted to Ap
Possible High-Redshift, Low-Luminosity AGN Activity in the Hubble Deep Field
In the Hubble Deep Field (HDF), twelve candidate sources of high-redshift (z
> 3.5) AGN activity have been identified. The color selection criteria were
established by passing spectra of selected quasars and Seyfert galaxies
(appropriately redshifted and modified for "Lyman forest" absorption), as well
as stars, observed normal and starburst galaxies, and galaxy models for various
redshifts through the filters used for the HDF observations. The actual
identification of AGN candidates also involved convolving a
Laplacian-of-Gaussian filter with the HDF images, thereby removing relatively
flat galactic backgrounds and leaving only the point-like components in the
centers. Along with positions and colors, estimated redshifts and absolute
magnitudes are reported, with the candidates falling toward the faint end of
the AGN luminosity function. One candidate has been previously observed
spectroscopically, with a measured redshift of 4.02. The number of sources
reported here is consistent with a simple extrapolation of the observed quasar
luminosity function to magnitude 30 in B_Johnson. Implications for ionization
of the intergalactic medium and for gravitational lensing are discussed.Comment: 10 pages LaTex plus 2 separate files (Table 1 which is a two-page
landscape LaTex file; and Figure 6 which is a large (0.7 MB) non-encapsulated
postscript file). Accepted for publication in the Astronomical Journa
Parameter identification for soil simulation based on the discrete element method and application to small scale shallow penetration tests
The Discrete Element Method (DEM) is well-established and widely used in soil-tool interaction related applications. As for all simulation tools, a proper calibration of the model parameters is crucial. In this contribution, we present the parametrization procedure of the DEM software GRAnular Physics Engine (GRAPE), developed and implemented at Fraunhofer ITWM, and attempt to use two parametrized soil samples for the simulation of small scale shallow penetration tests. The results are compared to laboratory measurements
New perspectives on strong z=0.5 MgII absorbers: are halo-mass and equivalent width anti-correlated?
We measure the mean halo-mass of z=0.5 MgII absorbers using the
cross-correlation (over co-moving scales 0.05-13h^{-1}Mpc) between 1806 MgII
quasar absorption systems and ~250,000 Luminous Red Galaxies (LRGs), both
selected from the SDSS DR3. The MgII systems have rest-frame equivalent widths
W_r(2796)>=0.3A. From the ratio of the MgII-LRG cross-correlation to the
LRG-LRG auto-correlation, we find that the bias ratio between MgII absorbers
and LRGs is 0.65+/-0.08, which implies that the absorber host-galaxies have a
mean halo-mass 20-40 times smaller than that of the LRGs; the MgII absorbers
have halos of mean mass =11.94+/-0.31(stat)+/-0.25(sys). We
demonstrate that this statistical technique, which does not require any
spectroscopic follow-up, does not suffer from contaminants such as stars or
foreground and background galaxies. Finally, we find that the absorber
halo-mass is anti-correlated with the equivalent width. If MgII absorbers were
virialized in galaxy halos a positive M_h-W_r correlation would have been
observed since W_r(2796) is a direct measure of the velocity spread of the MgII
sub-components. Thus, our results demonstrate that the individual clouds of a
MgII system are not virialized in the gaseous halos of the host-galaxies. We
review past results in the literature on the statistics of MgII absorbers and
find that they too require an M_h-W_r anti-correlation. When combined with
measurements of the equivalent width distribution, the M_h-W_r anti-correlation
naturally explains why absorbers with W_r(2796)>=2A are not seen at large
impact parameters. We interpret the M_h-W_r anti-correlation within the
starburst scenario where strong MgII absorbers are produced by
supernovae-driven winds.Comment: 18 pages, 12 EPS figures, Accepted by MNRAS. Full table of MgII
absorbers available at http://www.ast.cam.ac.uk/~mim/pub.html, minor changes
to match the published tex
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