Georgina V. Coldwell

Effect of bars in AGN host galaxies and black hole activity

Aims. With the aim of assessing the effects of bars on active galactic nuclei (AGN), we present an analysis of host characteristics and nuclear activity of active galaxies with and without bars. Methods. We selected AGN host galaxies from the Sloan Digital Sky Survey Data Release 7 (SDSS-DR7), using the available emission-line fluxes. By visual inspection of SDSS images we classified the face-on spiral hosts of AGNs brighter than g-mag < 16.5 into barred or unbarred. With the purpose of providing an appropriate quantification of the effects of bars, we also constructed a suitable control sample of unbarred active galaxies with similar redshift, magnitude, morphology, bulge sizes, and local environment distributions. Results. We find that the bar fraction, with respect to the full sample of spiral face-on AGN host galaxies, is 28.5%, in good agreement with previous works. barred AGN host galaxies show an excess of young stellar populations (as derived with the Dn(4000) spectral index), dominated by red u−r and g−r colors, with respect to the control sample, suggesting that bars produce an important effect on galaxy properties of AGN hosts. Regarding the nuclear activity distribution, we find that barred active galaxies show a shift toward higher Lum[OIII] values with respect to AGN without bars. In addition, we also find that this trend is more significant in less massive, younger stellar population and bluer AGN host galaxies. We found that the fraction of powerful AGN increases toward more massive hosts with bluer colors and younger stellar populations residing in denser environments. However, barred host AGN systematically show a higher fraction of powerful active nuclei galaxies with respect to the control sample. We also explored the accretion rate onto the central black holes, finding that barred AGN host show an excess of objects with high accretion rate values with respect to unbarred active galaxies.

Interacting galaxies: corotating and counter-rotating systems with tidal tails

We analyse interacting galaxy pairs with evidence of tidal features in the Sloan Digital Sky Survey Data Release 7. The pairs were selected within z< 0.1 by requiring a projected separa- tion rp < 50 h −1 kpc and relative radial velocityV < 500 km s −1 . We complete spectroscopic pairs using galaxies with photometric redshifts consideringV phot < 6800 km s −1 , taking into account the mean photometric redshift uncertainty. We classify by visual inspection pairs of spirals into corotating and counter-rotating systems. For a subsample of non-active galactic nucleus (non-AGN) galaxies, counter-rotating pairs have larger star formation rates and a higher fraction of young, star-forming galaxies. These effects are enhanced by restricting to rp < 12 h −1 kpc. The distributions of C, Dn(4000) and (Mu − Mr) for AGN galaxies show that counter-rotating hosts have bluer colours and younger stellar population than the corotating galaxies although the relative fractions of Seyfert, LINER, Composite and Ambiguous AGN are similar. Also, counter-rotating hosts have more powerful AGN as revealed by enhanced Lum(O III) values. The number of corotating systems is approximately twice the number of counter-rotating pairs which could be owed to a more rapid evolution of counter-rotating systems, besides possible different initial conditions of these interacting pairs.

Effect of bars on the galaxy properties

Aims. With the aim of assessing the effects of bars on disk galaxy properties, we present an analysis of different characteristics of spiral galaxies with strong bars, weak bars and without bars. Methods. We identified barred galaxies from the Sloan Digital Sky Survey (SDSS). By visual inspection of SDSS images we classified the face-on spiral galaxies brighter than g Results. We found 522 strong-barred and 770 weak-barred galaxies; this represents a bar fraction of 25.82% with respect to the full sample of spiral galaxies, in good agreement with several previous studies. We also found that strong-barred galaxies show lower efficiency in star formation activity and older stellar populations (as derived with the D n (4000) spectral index) with respect 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 disk objects are mostly grouped in the red region. Strong-barred galaxies present an important excess of high metallicity values compared to unbarred and weak-barred disk objects, which show 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 that falls abruptly with more significance in the range of low stellar masses (log ( M ∗ / M ⊙ ) < 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 the host galaxies.Fil: Vera Rueda, Gustavo Matias. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - San Juan. Instituto de Ciencias Astronomicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronomicas, de la Tierra y del Espacio; Argentina

Occurrence of LINER galaxies within the galaxy group environment

We study the properties of a sample of 3967 LINER galaxies selected from SDSS-DR7, respect to their proximity to galaxy groups. The host galaxies of LINER have been analysed and compared with a well defined control sample of 3841 non-LINER galaxies matched in redshift, luminosity, colour, morphology, age and stellar mass content. We find no difference between LINER and control galaxies in terms of colour and age of stellar population as function of the virial mass and distance to the geometric centre of the group. However, we find that LINER are more likely to populate low density environments in spite of their morphology, which is typical of high density regions such as rich galaxy clusters. For rich (poor) galaxy groups, the occurrence of LINER is

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

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Ultra Deep Catalogue of Galaxy Structures in the Cosmic Evolution Survey field

2 times lower (higher) than the occurrence of matched, non-LINER galaxies. Moreover, LINER hosts do not seem to follow the expected morphology-density relation in groups of high virial mass. The high frequency of LINERS in low density regions could be due to the combination of a sufficiently ample gas reservoir to power the low ionization emission and/or enhanced galaxy interaction rates benefiting the gas flow toward their central regions.

Triplets of quasars at high redshift – I. Photometric data

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

Triplets of quasars as lighthouses of rich galaxy clusters

Lum[OIII]

A POSSIBLE CORRELATION BETWEEN THE BLR AND STAR FORMATION RATE IN AGNS

) and accretion rate (

Evolución de la Estructura en el Universo. Evolution of structure in the universe.

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