448 research outputs found
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
and absolute r-band luminosities brighter than . 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 parameter in 2dFGRS and through the star formation
rate normalised to the total mass in stars, , 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 km
. 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
) and accretion rate () with respect to AGN in pairs. In
addition, both samples show an excess of high values of and 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 and efficient 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
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