Flavor asymmetry of polarized antiquark distributions and semi-inclusive DIS

The $1/N_c$-expansion of QCD suggests large flavor asymmetries of the polarized antiquark distributions in the nucleon. This is confirmed by model calculations in the large-$N_c$ limit (chiral quark-soliton model), which give sizable results for $\Delta\bar u (x) - \Delta\bar d (x)$ and $\Delta\bar u (x) + \Delta\bar d (x) - 2 \Delta \bar s (x)$. We compute the contributions of these flavor asymmetries to the spin asymmetries in hadron production in semi-inclusive deep-inelastic scattering. We show that the large flavor asymmetries predicted by the chiral quark-soliton model are consistent with the recent HERMES data for spin asymmetries in charged hadron production.Comment: 21 pages, LaTeX2e, 9 eps figures include

A wide-field spectroscopic survey of the cluster of galaxies Cl0024+1654: I. The catalogue

We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final catalogue contains data for 687 objects with redshifts identified for 650 of them. 295 galaxies have redshifts in the range 0.37<z<0.41, i. e. are cluster members or lie in the immediate neighbourhood of the cluster. The area covered by the survey is 21x25 arcmin2 in size, corresponding to 4x4.8 h^-2 Mpc2 at the cluster redshift. The survey is 45% complete down to V=22 over the whole field covered; within 3 arcmin of the cluster centre the completeness exceeds 80% at the same magnitude. A detailed completeness analysis is presented. The catalogue gives astrometric position, redshift, V magnitude and V-I colour, as well as the equivalent widths for a number of lines. Apart from the cluster Cl0024+1654 itself, three other structures are identified in redshift space: a group of galaxies at z=0.38, just in front of Cl0024+1654 and probably interacting with it, a close pair of groups of galaxies at z~0.495 and an overdensity of galaxies at z~0.18 with no obvious centre. The spectroscopic catalogue will be used to trace the three-dimensional structure of the cluster Cl0024+1654 as well as study the physical properties of the galaxies in the cluster and in its environment.Comment: 14 pages - figures included - A&A (re)submitted versio

Red-sequence galaxies with young stars and dust: The cluster Abell 901/902 seen with COMBO-17

We report the discovery of a rich component of dusty star-forming galaxies contaminating the red-sequence in the supercluster system comprising Abell 901a, 901b and A902 at redshift ~0.17. These galaxies do not fit into the colour-density relation, because their preferred habitat is different from that of regular red-sequence galaxies, which are typically dust-poor, old and passively evolving. The dusty red galaxies prefer the medium-density outskirts of clusters while being rare in both the low-density field and the high-density cluster cores. This new result is based on the information content in the medium-band photometry of the COMBO-17 survey. The photo-z accuracy of the ~800 brightest cluster galaxies is <0.01 and of the order of the velocity dispersion of the cluster. This enables us to select a rich and clean cluster sample, in which we can trace age-sensitive and dust-sensitive spectral features independently with the detailed medium-band SED data. We find the red colour of the dusty galaxies to be a result of dust extinction combined with relatively old stellar ages. We speculate that the dusty red galaxies could either be a product of minor mergers between established old red cluster galaxies with infalling blue field galaxies, or mark a period in the internal transformation of blue field galaxies into red cluster galaxies, which is triggered by the environmental influences experienced during cluster infall.Comment: accepted version, only minor changes and typos corrected, 17 pages in A&A print forma

The Origin of [OII] in Post-Starburst and Red-Sequence Galaxies in High-Redshift Clusters

We present the first results from a near-IR spectroscopic campaign of the Cl1604 supercluster at z~0.9 and the cluster RX J1821.6+6827 at z~0.82 to investigate the nature of [OII] 3727A emission in cluster galaxies at high redshift. Of the 401 members in the two systems, 131 galaxies have detectable [OII] emission with no other signs of current star-formation, as well as strong absorption features indicative of a well-established older stellar population. The combination of these features suggests that the primary source of [OII] emission in these galaxies is not the result of star-formation, but rather due to the presence of a LINER or Seyfert component. Using the NIRSPEC spectrograph on the Keck II 10-m telescope, 19 such galaxies were targeted, as well as six additional [OII]-emitting cluster members that exhibited other signs of ongoing star-formation. Nearly half (~47%) of the 19 [OII]-emitting, absorption-line dominated galaxies exhibit [OII] to Ha equivalent width ratios higher than unity, the typical value for star-forming galaxies. A majority (~68%) of these 19 galaxies are classified as LINER/Seyfert based on the emission-line ratio of [NII] and Ha, increasing to ~85% for red [OII]-emitting, absorption-line dominated galaxies. The LINER/Seyfert galaxies exhibit L([OII])/L(Ha) ratios significantly higher than that observed in populations of star-forming galaxies, suggesting that [OII] is a poor indicator of star-formation in a large fraction of high-redshift cluster members. We estimate that at least ~20% of galaxies in high-redshift clusters contain a LINER/Seyfert component that can be revealed with line ratios. We also investigate the effect this population has on the star formation rate of cluster galaxies and the post-starburst fraction, concluding that LINER/Seyferts must be accounted for if these quantities are to be meaningful.Comment: 33 pages, 17 figures, to appear in Ap

Galaxies at z=4 and the Formation of Population II

We report the discovery of four high-redshift objects (3.3 < z < 4) observed behind the rich cluster CL0939+4713 (Abell 851). One object (DG 433) has a redshift of z=3.3453; the other three objects have redshifts of z\approx 4: A0 at z=3.9819, DG 353 and P1/P2 at z=3.9822. It is possible that all four objects are being lensed in some way by the cluster, DG 433 being weakly sheared, A0 being strongly sheared, and DG 353 and P1/P2 being an image pair of a common source object; detailed modelling of the cluster potential will be necessary to confirm this hypothesis. The weakness of common stellar wind features like N V and especially C IV in the spectra of these objects argues for sub-solar metallicities, at least as low as the SMC. DG 353 and DG 433, which have ground-based colors, are moderately dusty [E_{int}(B-V) < 0.15], similar to other z>3 galaxies. Star formation rates range from 2.5 (7.8) h^{-2} to 22. (78.) h^{-2} M_{\odot}/yr, for q_0=0.5 (0.05), depending on assumptions about gravitational lensing and extinction, also typical of other z>3 galaxies. These objects are tenatively identified as the low-metallicity proto-spheroid clumps that will merge to form the Population II components of today's spheroids.Comment: 16 pages, including 2 PostScript figures. Needs aaspp4.sty (included). Accepted for publication in the Astrophysical Journa

The Role of Parked Cars in Content Downloading for Vehicular Networks

When it comes to content access using Inter-Vehicle Communication (IVC), data will mostly flow through Road Side Units (RSUs), deployed in our cities. Unfortunately, the RSU coverage is expected to be rather scattered. Instead of relying on RSUs only, the paper investigate the possibility of exploiting parked vehicles to extend the RSU service coverage. Our approach leverages optimization models aiming at maximizing the freshness of content that downloaders retrieve, the efficiency in the utilization of radio resources, and the fairness in exploiting the energy resources of parked vehicles. The latter is constrained so as not to excessively drain parked vehicle batteries. Our approach provides an estimate of the system performance, even in those cases where users may only be willing to lease a limited amount of their battery capacity to extend RSU coverage. Our optimization-based results are validated by comparing them against ns-3 simulations. Performance evaluation highlights that the use of parked vehicles enhances the efficiency of the content downloading process by 25%-35% and can offload more than half the data traffic from RSUs, with respect to the case where only moving cars are used as relays. Such gains in performance come at a small cost in terms of battery utilization for the parked vehicles, and they are magnified when a backbone of parked vehicles can be formed