Signatures of Galaxy-Cluster Interactions: Spiral Galaxy Rotation Curve Asymmetry, Shape, and Extent

The environmental dependencies of the characteristics of spiral galaxy rotation curves are studied in this work. We use our large, homogeneously collected sample of 510 cluster spiral galaxy rotation curves to test the claim that the shape of a galaxy's rotation curve strongly depends on its location within the cluster, and thus presumably on the strength of the local intracluster medium and on the frequency and strength of tidal interactions with the cluster and cluster galaxies. Our data do not corroborate such a scenario, consistent with the fact that Tully-Fisher residuals are independent of galaxy location within the cluster; while the average late-type spiral galaxy shows more rise in the outer parts of its rotation curve than does the typical early-type spiral galaxy, there is no apparent trend for either subset with cluster environment. We also investigate as a function of cluster environment rotation curve asymmetry and the radial distribution of H II region tracers within galactic disks. Mild trends with projected cluster-centric distance are observed: (i) the (normalized) radial extent of optical line emission averaged over all spiral galaxy types shows a 4%+/-2% increase per Mpc of galaxy-cluster core separation, and (ii) rotation curve asymmetry falls by a factor of two between the inner and outer cluster for early-type spirals (a negligible decrease is found for late-type spirals). Such trends are consistent with spiral disk perturbations or even the stripping of the diffuse, outermost gaseous regions within the disks as galaxies pass through the dense cluster cores.Comment: 17 pages; to appear in the April 2001 Astronomical Journa

Galaxy Peculiar Velocities and Infall onto Groups

We perform statistical analyses to study the infall of galaxies onto groups and clusters in the nearby Universe. The study is based on the UZC and SSRS2 group catalogs and peculiar velocity samples. We find a clear signature of infall of galaxies onto groups over a wide range of scales 5 h^{-1} Mpc<r<30 h^{-1} Mpc, with an infall amplitude on the order of a few hundred kilometers per second. We obtain a significant increase in the infall amplitude with group virial mass (M_{V}) and luminosity of group member galaxies (L_{g}). Groups with M_{V}<10^{13} M_{\odot} show infall velocities V_{infall} \simeq 150 km s^{-1} whereas for M_{V}>10^{13} M_{\odot} a larger infall is observed, V_{infall} \simeq 200 km s^{-1}. Similarly, we find that galaxies surrounding groups with L_{g}<10^{15} L_{\odot} have V_{infall} \simeq 100 km s^{-1}, whereas for L_{g}>10^{15} L_{\odot} groups, the amplitude of the galaxy infall can be as large as V_{infall} \simeq 250 km s^{-1}. The observational results are compared with the results obtained from mock group and galaxy samples constructed from numerical simulations, which include galaxy formation through semianalytical models. We obtain a general agreement between the results from the mock catalogs and the observations. The infall of galaxies onto groups is suitably reproduced in the simulations and, as in the observations, larger virial mass and luminosity groups exhibit the largest galaxy infall amplitudes. We derive estimates of the integrated mass overdensities associated with groups by applying linear theory to the infall velocities after correcting for the effects of distance uncertainties obtained using the mock catalogs. The resulting overdensities are consistent with a power law with \delta \sim 1 at r \sim 10 h^{-1}Mpc.Comment: 25 pages, 10 figure

Signatures of Galaxy-Cluster Interactions: Tully-Fisher Observations at z~0.1

We have obtained new optical imaging and spectroscopic observations of 78 galaxies in the fields of the rich clusters Abell 1413 (z = 0.14), Abell 2218 (z = 0.18) and Abell 2670 (z = 0.08). We have detected line emission from 25 cluster galaxies plus an additional six galaxies in the foreground and background, a much lower success rate than what was found (65%) for a sample of 52 lower-richness Abell clusters in the range 0.02 < z < 0.08. We have combined these data with our previous observations of Abell 2029 and Abell 2295 (both at z = 0.08), which yields a sample of 156 galaxies. We evaluate several parameters as a function of cluster environment: Tully-Fisher residuals, H-alpha equivalent width, and rotation curve asymmetry, shape and extent. Although H-alpha is more easily detectable in galaxies that are located further from the cluster cores, we fail to detect a correlation between H-alpha extent and galaxy location in those where it is detected, again in contrast with what is found in the clusters of lesser richness. We fail to detect any statistically significant trends for the other parameters in this study. The zero-point in the z~0.1 Tully-Fisher relation is marginally fainter (by 1.5 sigma) than that found in nearby clusters, but the scatter is essentially unchanged.Comment: 27 pages including 5 figures; accepted for publication in the Astronomical Journa

Tidal Effects in Clusters of Galaxies

High-redshift clusters of galaxies show an over-abundance of spirals by a factor of 2-3, and the corresponding under-abundance of S0 galaxies, relative to the nearby clusters. This morphological evolution can be explained by tidal interactions with neighboring galaxies and with the hierarchically growing cluster halo. The efficiency of tidal interactions depends on the size and structure of the cluster, as well as on the epoch of its formation. I simulate the formation and evolution of Virgo-type clusters in three cosmologies: a critical density model Omega_0=1, an open model Omega_0=0.4, and a flat model Omega_0=0.4 with a cosmological constant. The orbits of identified halos are traced with a high temporal resolution (~10^7 yr). Halos with low relative velocities merge only shortly after entering the cluster; after virialization mergers are suppressed. The dynamical evolution of galaxies is determined by the tidal field along their trajectories. The maxima of the tidal force do not always correspond to closest approach to the cluster center. They are produced to a large extent by the local density structures, such as the massive galaxies and the unvirialized remnants of infalling groups of galaxies. Collisions of galaxies are intensified by the substructure, with about 10 encounters within 10 kpc per galaxy in the Hubble time. These very close encounters add an important amount (10-50%) of the total heating rate. The integrated effect of tidal interactions is insufficient to transform a spiral galaxy into an elliptical, but can produce an S0 galaxy. Overall, tidal heating is stronger in the low Omega_0 clusters

Algorithmic aspects of disjunctive domination in graphs

For a graph $G=(V,E)$, a set $D\subseteq V$ is called a \emph{disjunctive dominating set} of $G$ if for every vertex $v\in V\setminus D$, $v$ is either adjacent to a vertex of $D$ or has at least two vertices in $D$ at distance $2$ from it. The cardinality of a minimum disjunctive dominating set of $G$ is called the \emph{disjunctive domination number} of graph $G$, and is denoted by $\gamma_{2}^{d}(G)$. The \textsc{Minimum Disjunctive Domination Problem} (MDDP) is to find a disjunctive dominating set of cardinality $\gamma_{2}^{d}(G)$. Given a positive integer $k$ and a graph $G$, the \textsc{Disjunctive Domination Decision Problem} (DDDP) is to decide whether $G$ has a disjunctive dominating set of cardinality at most $k$. In this article, we first propose a linear time algorithm for MDDP in proper interval graphs. Next we tighten the NP-completeness of DDDP by showing that it remains NP-complete even in chordal graphs. We also propose a $(\ln(\Delta^{2}+\Delta+2)+1)$-approximation algorithm for MDDP in general graphs and prove that MDDP can not be approximated within $(1-\epsilon) \ln(|V|)$ for any $\epsilon>0$ unless NP $\subseteq$ DTIME$(|V|^{O(\log \log |V|)})$. Finally, we show that MDDP is APX-complete for bipartite graphs with maximum degree $3$

A multi-site, double-blind, placebo-controlled pilot clinical trial to evaluate the efficacy of buspirone as a relapse-prevention treatment for cocaine dependence

Objective—To evaluate the potential efficacy of buspirone as a relapse-prevention treatment for cocaine dependence. Method—A randomized, double-blind, placebo-controlled, 16-week pilot trial conducted at six clinical sites between August 2012 and June 2013. Adult crack cocaine users meeting DSM-IVTR criteria for current cocaine dependence scheduled to be in inpatient/residential substance use disorder (SUD) treatment for 12–19 days when randomized, and planning to enroll in local outpatient treatment through the end of the active treatment phase were randomized to buspirone titrated to 60 mg/day (n=35) or to placebo (n=27). All participants received psychosocial treatment as usually provided by the SUD treatment programs in which they were enrolled. Outcome measures included maximum days of continuous cocaine abstinence (primary), proportion of cocaine use days, and days-to-first-cocaine-use during the outpatient treatment phase (study weeks 4–15) as assessed by self-report and urine drug screens. Results—There were no significant treatment effects on maximum continuous days of cocaine abstinence or days to first cocaine use. In the females (n=23), there was a significant treatment-bytime interaction effect (X2 (1)=6.06, p=.01), reflecting an increase in cocaine use by the buspirone, relative to placebo, participants early in the outpatient treatment phase. A similar effect was not detected in the male participants (n=39; X2 (1)=0.14, p=.70). Conclusions—The results suggest that buspirone is unlikely to have a beneficial effect on preventing relapse to cocaine use and that buspirone for cocaine-dependent women may worsen their cocaine-use outcomes. Trial Registration—Clinical Trials.gov http://www.clinicaltrials.gov; Identifier: NCT0164115

Structural relaxations in electronically excited poly(para-phenylene)

Structural relaxations in electronically excited poly(para-phenylene) are studied using many-body perturbation theory and density-functional-theory methods. A sophisticated description of the electron-hole interaction is required to describe the energies of the excitonic states, but we show that the structural relaxations associated with exciton formation can be obtained quite accurately within a constrained density-functional-theory approach. We find that the structural relaxations in the low-energy excitonic states extend over about 8 monomers, leading to an energy reduction of 0.22 eV and a Stokes shift of 0.40 eV.Comment: 4 pages, 3 figure