Effect of bars on the galaxy properties

Aims: With the aim of assessing the effects of bars on disc galaxy properties, we present an analysis of different characteristics of spiral galaxies with strong, weak and without bars. Method: We identified barred galaxies from the Sloan Digital Sky Survey. By visual inspection, we classified the face-on spiral galaxies brighter than g<16.5 mag into strong-bar, weak-bar and unbarred. In order to provide an appropiate quantification of the influence of bars on galaxy properties, we also constructed a suitable control sample of unbarred galaxies with similar redshift, magnitude, morphology, bulge sizes, and local density environment distributions to that of barred galaxies. Results: We found 522 strong-barred and 770 weak-barred galaxies, representing a 25.82% of the full sample of spiral galaxies, in good agreement with previous studies. We also found that strong-barred galaxies show less efficient star formation activity and older stellar populations compared to weak-barred and unbarred spirals from the control sample. In addition, there is a significant excess of strong barred galaxies with red colors. The color-color and color-magnitude diagrams show that unbarred and weak-barred galaxies are more extended towards the blue zone, while strong-barred objects are mostly grouped in the red region. Strong-barred galaxies present an important excess of high metallicity values, compared to the other types, showing similar 12+log(O/H) distributions. Regarding the mass-metallicity relation, we found that weak-barred and unbarred galaxies are fitted by similar curves, while strong-barred ones show a curve which falls abruptly, with more significance in the range of low stellar masses (log[Mstar/Msun] < 10.0). These results would indicate that prominent bars produced an accelerating effect on the gas processing, reflected in the significant changes in the physical properties of their host

AGN spiral galaxies in groups: effects of bars

We explore properties of barred active spiral galaxies in groups selected from the SDSS-DR7, with the aim of assessing the effects of bars on AGN and the role of the high density environment. We identified barred active galaxies that reside in groups from SDSS-DR7 group catalog. To provide a suitable quantification of the effects of bars, a reliable control sample of unbarred active galaxies in high density environments with similar redshift, magnitude, morphology, and bulge size distributions was constructed. We found that the fraction of barred AGN galaxies in groups (~ 38 %) is higher than those in the total barred AGN sample ( ~ 28 %), indicating that AGN spiral galaxies in groups are more likely to be barred than those in the field. We also found that barred AGN galaxies are more concentrated towards the group centers than the other unbarred AGN group members. In addition, barred AGN host galaxies show an excess of population dominated by red colors suggesting that bars produce an importanteffect on galaxy colors of AGN hosts. The host groups of the barred AGN exhibit a larger fraction of red colors than the host groups of the corresponding unbarred active galaxies. Color-magnitude relations of both host groups of AGN differ significantly: the host group colors of barred active galaxies display distributions spreading toward red populations, with respect to the host groups of the unbarred AGN objects. Barred active galaxies show an excess of nuclear activity compared to galaxies without bars. We found that barred active galaxies located farther from the group-center have stronger Lum[OIII]. Our findings suggest that the efficiency of bars to transport material towards the more central regions of the AGN galaxies in high density environments reveals an important dependence on the localization of objects within the group and on the host group colors.Comment: 10 pages, 10 figures. Accepted for Astronomy & Astrophysic

Galaxy triplets in Sloan Digital Sky Survey Data Release 7 - III. Analysis of Configuration and Dynamics

We analyse the spatial configuration and the dynamical properties of a sample of 92 galaxy triplets obtained from the SDSS-DR7 (SDSS-triplets) restricted to have members with spectroscopic redshifts in the range $0.01\le z \le 0.14$ and absolute r-band luminosities brighter than $M_r=-20.5$. The configuration analysis was performed through Agekyan & Anosova map (AA-map). We estimated dynamical parameters, namely the radius of the system, the velocity dispersion, a dimensionless crossing-time and the virial mass. We compared our results with those obtained for a sample of triplets from the catalogue "Isolated Triplets of Galaxies" (K-triplets) and a sample of Compact Groups. We have also studied a mock catalogue in order to compare real and projected configurations, and to estimate the three dimensional dynamical parameters of the triple systems. We found that the SDSS-triplets prefer alignment configurations while K-triplets present an uniform distribution in the AA-map. From the dynamical analysis we conclude that the SDSS-triplets, K-triplets and Compact Groups present a similar behaviour comprising compact systems with low crossing-time values, with velocity dispersions and virial masses similar to those of low mass loose groups. Moreover, we found that observed and simulated triplets present similar dynamical parameters. We also performed an analysis of the dark matter content of galaxy triplets finding that member galaxies of mock triplets belong to the same dark matter halo, showing a dynamical co-evolution of the system. These results suggest that the configuration and dynamics of triple systems favour galaxy interactions and mergers.Comment: Accepted for publication in MNRAS. 9 pages, 8 figure

Effects of galaxy interactions in different environments

We analyse star formation rates derived from photometric and spectroscopic data of galaxies in pairs in different environments using the 2dF Galaxy Redshift Survey (2dFGRS) and the Sloan Digital Sky Survey (SDSS). The two samples comprise several thousand pairs, suitable to explore into detail the dependence of star formation activity in pairs on orbital parameters and global environment. We use the projected galaxy density derived from the fifth nearest neighbour of each galaxy, with convenient luminosity thresholds to characterise environment in both surveys in a consistent way. Star formation activity is derived through the $\eta$ parameter in 2dFGRS and through the star formation rate normalised to the total mass in stars, $SFR/M^*$, given by Brinchmann et al. (2004) in the second data release SDSS-DR2. For both galaxy pair catalogs, the star formation birth rate parameter is a strong function of the global environment and orbital parameters. Our analysis on SDSS pairs confirms previous results found with the 2dFGRS where suitable thresholds for the star formation activity induced by interactions are estimated at a projected distance r_{\rm p} = 100 \kpc and a relative velocity $\Delta V = 350$ km $s^{-1}$. We observe that galaxy interactions are more effective at triggering important star formation activity in low and moderate density environments with respect to the control sample of galaxies without a close companion. Although close pairs have a larger fraction of actively star-forming galaxies, they also exhibit a greater fraction of red galaxies with respect to those systems without a close companion, an effect that may indicate that dust stirred up during encounters could be affecting colours and, partially, obscuring tidally-induced star formation.Comment: accepted MNRA

The impact of bars and interactions on optically selected AGNs in spiral galaxies

Aims. With the aim of performing a suitable comparison of the internal process of galactic bars with respect to the external effect of interactions on driving gas toward the inner most region of the galaxies, we explored the efficiency of both mechanisms on central nuclear activity in active galactic nuclei (AGN) in spiral galaxies. Methods. We selected samples of barred AGN and active objects residing in pair systems, derived from the Sloan Digital Sky Survey (SDSS). In order to carry out a reliable comparison of both samples (AGNs in barred hosts in isolation and in galaxy pairs), we selected spiral AGN galaxies with similar distributions of redshift, magnitude, stellar mass, color and stellar age population from both catalogs. With the goal of providing an appropriate quantification of the influence of bars and interactions on nuclear activity, we also constructed a suitable control sample of unbarred spiral AGNs with similar host properties than the other two samples. Results. We found that barred AGNs show an excess of nuclear activity (as derived from the $Lum[OIII]$) and accretion rate ($\cal R$) with respect to AGN in pairs. In addition, both samples show an excess of high values of $Lum[OIII]$ and $\cal R$ with respect to unbarred AGNs in the control sample. We also found that the fractions of AGNs with powerful nuclear activity and high accretion rates increase toward more massive hosts with bluer colors and younger stellar populations. Moreover, AGNs with bars exhibit a higher fraction of galaxies with powerful $Lum[OIII]$ and efficient $\cal R$ with respect to AGNs inhabiting pair systems. Regarding to AGN belonging to pair systems, we found that the central nuclear activity is remarkably dependent on the galaxy pair companion features.Comment: 13 pages, 9 figures. Accepted for publication in A&

AGN spiral galaxies in groups: effects of bars

AIMS: We explore properties of barred active spiral galaxies in groups and clusters selected from the Sloan Digital Sky Survey data release 7 (SDSS-DR7), with the aim of assessing the effects of bars on active galactic nuclei (AGN) and the role of the high density environment. METHODS: We identified barred active galaxies that reside in groups and clusters by cross-correlating the total barred AGN sample with the SDSS-DR7 group catalog. With the goal of providing a suitable quantification of the effects of bars, a reliable control sample of unbarred active galaxies in high density environments with similar redshift, magnitude, morphology, and bulge size distributions was also constructed. RESULTS: We found that the fraction of barred AGN galaxies in groups and clusters (≈38%) is higher than those in the total barred AGN sample (≈28%), indicating that AGN spiral galaxies in groups are more likely to be barred than those in the field. We also found that barred AGN galaxies are more concentrated towards the group centers than the other unbarred AGN group members. In addition, barred AGN host galaxies show an excess of population dominated by red colors, with respect to the control sample, suggesting that bars produce an important effect on galaxy colors of AGN hosts. The groups of AGN galaxies with and without bars show similar virial masses; however, the host groups of the barred AGN exhibit a larger fraction of red colors than the host groups of the corresponding unbarred active galaxies in the control sample. Color-magnitude relations of both host groups of AGN differ significantly: the host group colors of barred active galaxies display distributions spreading toward red populations, at the same (Mr)Group, with respect to the host groups of the unbarred AGN objects. This trend is more significant in less massive groups than in groups with MVirial> 1013.5M⊙. Barred active galaxies show an excess of nuclear activity compared to galaxies without bars in the control sample. We found that barred active galaxies located farther from the group-center have stronger Lum[OIII], while the nuclear activity in AGN galaxies without bars remain approximately constant with the group-centric distance. In addition, for both AGN samples, nuclear activity increases in bluer host groups however, barred active objects systematically show higher Lum[OIII] values, irrespective of the global group colors. Our findings suggest that the efficiency of bars to transport material towards the more central regions of the AGN galaxies in high density environments reveals an important dependence on the localization of objects within the group/cluster and on the host group colors.Fil: Alonso Giraldes, Maria Sol. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Coldwell Lloveras, Georgina Vanesa. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Garcia Lambas, Diego Rodolfo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentin

Confirmation of a cluster of galaxies hidden behind the Galactic bulge using the VVV Survey

Suzaku and Chandra X-ray observations detected a new cluster of galaxies, Suzaku J1759-3450, at a redshift z=0.13. It is located behind the Milky Way, and the high Galactic dust extinction renders it nearly invisible at optical wavelengths. We attempt here to confirm the galaxy cluster with near-infrared imaging observations, and to characterize its central member galaxies. Images from the VVV survey were used to detect candidate member galaxies of Suzaku J1759-3450 within the central region of the cluster, up to 350 kpc from the X-ray peak emission. Color-magnitude and color-color diagrams and morphology criteria allowed us to select the galaxies among the numerous foreground sources. Fifteen candidate cluster members were found very close to a modeled red-sequence at the redshift of the cluster. Five members are extremely bright, and one is possibly a cD galaxy. The asymmetry in the spatial distribution of the galaxies respect to the X-ray peak emission is an indicator of that this cluster is still suffering a virialization process. Our investigation of Suzaku J1759-3450 demonstrates the potential of the VVV Survey to study the hidden population of galaxies in the Zone of Avoidance.Comment: 7 pages, 5 figures. Accepted for Publication in Astronomy & Astrophysic