Substructure within the SSA22 protocluster at z≈3.09z\approx3.09

We present the results of a densely sampled spectroscopic survey of the SSA22 protocluster at $z\approx 3.09$. Our sample with Keck/LRIS spectroscopy includes 106 Ly$\alpha$ Emitters (LAEs) and 40 Lyman Break Galaxies (LBGs) at $z=3.05-3.12$. These galaxies are contained within the $9'\times9'$ 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 $z=3.069$ (blue, 43 galaxies) and $z=3.095$ (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$\alpha$ "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) ≥ 0.3 Å, we find 43 ≤ Rx ≤ 88 kpc, depending on the lower luminosity cutoff and the slope, β, of the Holmberg-like luminosity scaling, R ∝ α L^β . 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 β in the range of 0.2–0.28, 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 β ≃ 0.2 and R∗ = Rx/√(fc) ~ 110 kpc. No luminosity scaling (β = 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 $z=3.09$ using cosmological simulations. A redshift histogram constructed from current spectroscopic observations of the SSA22 protocluster reveals two separate peaks at $z = 3.065$ (blue) and $z = 3.095$ (red). Based on these data, we report updated overdensity and mass calculations for the SSA22 protocluster. We find $\delta_{b,gal}=4.8 \pm 1.8$, $\delta_{r,gal}=9.5 \pm 2.0$ for the blue and red peaks, respectively, and $\delta_{t,gal}=7.6\pm 1.4$ for the entire region. These overdensities correspond to masses of $M_b = (0.76 \pm 0.17) \times 10^{15} h^{-1} M_{\odot}$, $M_r = (2.15 \pm 0.32) \times 10^{15} h^{-1} M_{\odot}$, and $M_t=(3.19 \pm 0.40) \times 10^{15} h^{-1} M_{\odot}$ for the red, blue, and total peaks, respectively. We use the Small MultiDark Planck (SMDPL) simulation to identify comparably massive $z\sim 3$ protoclusters, and uncover the underlying structure and ultimate fate of the SSA22 protocluster. For this analysis, we construct mock redshift histograms for each simulated $z\sim 3$ 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 $\sim 10^{15}h^{-1} M_{\odot}$ protocluster and at least one $>10^{14} h^{-1} M_{\odot}$ 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