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Context. The location of the Solar System complicates the detection extragalactic sources beyond the Milky Way plane. The optical observations are hampered in the so-called zone of avoidance (ZOA), where stellar crowding and Galactic absorption are severe. Observations at longer wavelengths are needed in order to discover new background galaxies and complete the census in the ZOA. Aims. The goal of this work is to identify galaxies behind the Milky Way bulge using near-infrared (NIR) data from the VISTA Variables in Vía Láctea (VVV) survey. Methods. To this end, we made use of different VISTA Science Archive (VSA) tools in order to extract relevant information from more than 32 billion catalogued sources in the VVV bulge region. We find that initial photometric restriction on sources from the VSA vvvSource table combined with restrictions on star–galaxy separation parameters obtained from Source Extractor is a successful strategy for achieving acceptable levels of contamination (60%) and high completeness (75%) in the construction of a galaxy target sample. To remove contaminating Galactic sources from the initial target sample, our methodology also incorporates a visual inspection of false-colour RGB images, a crucial quality control carried out following a specifically defined procedure. Results. Under this methodology, we find 14 480 galaxy candidates in the VVV bulge region, making this sample the largest catalogue to date in the ZOA. Moreover, these new sources provide a fresh picture of the Universe hidden behind the curtain of stars, dust, and gas in the unexplored Milky Way bulge region. Conclusions. The results from this work further demonstrate the potential of the VVV/VVVX survey to find and study a large number of galaxies and extragalactic structures obscured by the Milky Way, expanding our knowledge of the Universe in this challenging and impressive region of the sky. [ABSTRACT FROM AUTHOR]

Aims. We present a statistical analysis of different characteristics of ringed spiral galaxies with the aim of assessing the effects of rings on disk galaxy properties. Methods. We built a catalog of ringed galaxies from the Sloan Digital Sky Survey Data Release 14 (SDSS-DR14). Via visual inspection of SDSS images, we classified the face-on spiral galaxies brighter than g < 16.0 mag into galaxies with: an inner ring, an outer ring, a nuclear ring, both an inner and an outer ring, and a pseudo-ring. In addition to rings, we recorded morphological types and the existence of bars, lenses, and galaxy pair companions with or without interaction. With the goal of providing an appropriate quantification of the influence of rings on galaxy properties, we also constructed a suitable control sample of non-ringed galaxies with similar redshift, magnitude, morphology, and local density environment distributions to those of ringed ones. Results. We found 1868 ringed galaxies, accounting for 22% of the full sample of spiral galaxies. In addition, within galaxies with ringed structures, 46% have an inner ring, 10% an outer ring, 20% both an inner and an outer ring, 6% a nuclear ring, and 18% a partial ring. Moreover, 64% of the ringed galaxies present bars. We also found that ringed galaxies have both a lower efficiency of star formation activity and older stellar populations (as derived with the Dn(4000) spectral index) with respect to non-ringed disk objects from the control sample. Moreover, there is a significant excess of ringed galaxies with red colors. These effects are more important for ringed galaxies that have inner rings and bars with respect to their counterparts that have some other types of rings and are non-barred. The color-magnitude and color-color diagrams show that ringed galaxies are mostly concentrated in the red region, while non-ringed spiral objects are more extended to the blue zone. Galaxies with ringed structures present an excess of high metallicity values compared to non-ringed ones, which show a 12 + Log(O/H) distribution toward lower values. These findings seem to indicate that rings are peculiar structures that produce an accelerating galactic evolution, strongly altering the physical properties of their host galaxies. [ABSTRACT FROM AUTHOR]

We use SDSS-DR14 to construct a sample of galaxy systems consisting of a central object and two satellites. We adopt projected distance and radial velocity difference criteria and impose an isolation criterion to avoid membership in larger structures. We also classify the interaction between the members of each system through a visual inspection of galaxy images, finding |${\sim}80{{\ \rm per\ cent}}$| of the systems lack evidence of interactions whilst the remaining |${\sim}20{{\ \rm per\ cent}}$| involve some kind of interaction, as inferred from their observed distorted morphology. We have considered separately, samples of satellites and central galaxies, and each of these samples were tested against suitable control sets to analyse the results. We find that central galaxies showing signs of interactions present evidence of enhanced star formation activity and younger stellar populations. As a counterpart, satellite samples show these galaxies presenting older stellar populations with a lower star formation rate than the control sample. The observed trends correlate with the stellar mass content of the galaxies and with the projected distance between the members involved in the interaction. The most massive systems are less affected since they show no star formation excess, possibly due to their more evolved stage and less gas available to form new stars. Our results suggest that it is arguably a transfer of material during interactions, with satellites acting as donors to the central galaxy. As a consequence of the interactions, satellite stellar population ages rapidly and new bursts of star formation may frequently occur in the central galaxy. [ABSTRACT FROM AUTHOR]

Aims. With the aim of performing an analysis of the orientations of galaxy pair systems with respect to the underlying large-scale structure, we study the alignment between the axis connecting the pair galaxies and the host cosmic filament where the pair resides. In addition, we analyze the dependence of the amplitude of the alignment on the morphology of pair members as well as filament properties. Methods. We build a galaxy pair catalog requiring rp < 100 h−1 kpc and ΔV < 500 km s−1 within redshift z < 0.1 from the Sloan Digital Sky Survey (SDSS). We divided the galaxy pair catalog taking into account the morphological classification by defining three pair categories composed by elliptical–elliptical (E–E), elliptical–spiral (E–S) and spiral–spiral (S–S) galaxies. We use a previously defined catalog of filaments obtained from SDSS and we select pairs located closer than 1 h−1 Mpc to the filament spine, which are considered as members of filaments. For these pairs, we calculate the relative angle between the axis connecting each galaxy, and the direction defined by the spine of the parent filament. Results. We find a statistically significant alignment signal between the pair axes and the spine of the host filaments consistent with a relative excess of ∼15% aligned pairs. We obtain that pairs composed by elliptical galaxies exhibit a stronger alignment, showing a higher alignment signal for pairs closer than 200 h−1 kpc to the filament spine. In addition, we find that the aligned pairs are associated with luminous host filaments populated with a high fraction of elliptical galaxies. The findings of this work show that large-scale structures play a fundamental role in driving galactic anisotropic accretion as induced by galaxy pairs exhibiting a preferred alignment along the filament direction. [ABSTRACT FROM AUTHOR]

We analyse the properties of a sample of 5560 low-ionization nuclear emission-line region (LINER) galaxies selected from SDSS-DR12 at low red shift, for a complete range of local density environments. The host LINER galaxies were studied and compared with a well-defined control sample of 5553 non-LINER galaxies matched in red shift, luminosity, morphology and local density. By studying the distributions of galaxy colours and the stellar age population, we find that LINERs are redder and older than the control sample over a wide range of densities. In addition, LINERs are older than the control sample, at a given galaxy colour, indicating that some external process could have accelerated the evolution of the stellar population. The analysis of the host properties shows that the control sample exhibits a strong relation between colours, ages and the local density, while more than 90 per cent of the LINERs are redder and older than the mean values, independently of the neighbourhood density. Furthermore, a detailed study in three local density ranges shows that, while control sample galaxies are redder and older as a function of stellar mass and density, LINER galaxies mismatch the known morphology-density relation of galaxies without low-ionization features. The results support the contribution of hot and old stars to the low-ionization emission although the contribution of nuclear activity is not discarded. [ABSTRACT FROM AUTHOR]

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 separation rp < 50 h− 1 kpc and relative radial velocity ΔV < 500 km s−1. We complete spectroscopic pairs using galaxies with photometric redshifts considering ΔVphot < 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. [ABSTRACT FROM AUTHOR]