The new multi-epoch near-infrared VISTA Variables in the Vía Láctea (VVV) survey is sampling 562 deg 2 of the Galactic bulge and adjacent regions of the disk. Accurate astrometry established for the region surveyed allows the VVV data to be merged with overlapping surveys (e.g., GLIMPSE, WISE, 2MASS, etc.), thereby enabling the construction of longer baseline spectral energy distributions for astronomical targets. However, in order to maximize use of the VVV data, a set of transformation equations are required to place the VVV JHK s photometry onto the 2MASS system. The impetus for this work is to develop those transformations via a comparison of 2MASS targets in 152 VVV fields sampling the Galactic disk. The transformation coefficients derived exhibit a reliance on variables such as extinction. The transformed data were subsequently employed to establish a mean reddening law of E J−H /E H−Ks = 2.13 ± 0.04, which is the most precise determination to date and merely emphasizes the pertinence of the VVV data for determining such important parameters.

We present the deepest near-infrared (ZJK s ) photometry yet obtained of the Sagittarius dwarf spheroidal (Sgr dSph), using VISTA to survey 11 square degrees centred on its core. We list locations and ZJK s -band magnitudes for over 2.9 million sources in the field. We discuss the isolation of the Sgr dSph from the foreground and Galactic Bulge populations, identify the Sgr dSph's horizontal branch in the near-infrared for the first time, and map the density of the galaxy's stars. We present isochrones for the Sgr dSph and Bulge populations. These are consistent with the previously-reported properties of the Sgr dSph core: namely that it is dominated by a population between [Fe/H] ≈ -1 dex and solar, with a significant [α/Fe] versus [Fe/H] gradient. While strong contamination from the Galactic Bulge prevents accurate measurement of the (Galactic) north side of the Sgr dSph, the dwarf galaxy can be well-approximated by a roughly ovaloid projection of characteristic size 4 • × 2 • , beyond which the projected stellar density is less than half that of the region surrounding the core. The galaxy's major axis is perpendicular to the Galactic Plane, as in previous studies. We find slight evidence to confirm a metallicity gradient in the Sgr dSph and use isochrones to fit a distance of 24.3 ± 2.3 kpc. We were unable to fully constrain the metallicity distribution of the Sgr dSph due to the Bulge contamination and strong correlation of [α/Fe] with metallicity, however we find that metal-poor stars ([Fe/H] < ∼ -1) make up < ∼ 29 per cent of the Sgr dSph's upper-RGB population. The Bulge population is best fit by a younger population with [Fe/H] ≈ 0 and [α/Fe] ≈ 0 or slightly higher. We find no evidence for a split, peanut-or X-shaped Bulge population in this line of sight (l = 5.6 • ± ∼ 1 • , b = −14.1 • ± ∼ 3 • ).

Context. The growth of the structure within the Universe manifests in the form of accretion flows of galaxies onto groups and clusters. Thus, the present-day properties of groups and their member galaxies are influenced by the characteristics of this continuous infall pattern. Several works both theoretical (in numerical simulations) and observational, have studied this process and provided useful steps for a better understanding of galaxy systems and their evolution. Aims. We aim to explore the streaming flow of galaxies onto groups using observational peculiar velocity data. The effects of distance uncertainties are also analyzed, as well as the relation between the infall pattern and the group and environment properties. Methods. This work deals with the analysis of peculiar velocity data and their projection in the direction of group centers, in order to determine the mean galaxy infall flow. We applied this analysis to the galaxies and groups extracted from the Cosmicflows–3 catalog. We also used mock catalogs derived from numerical simulations to explore the effects of distance uncertainties on the derivation of the galaxy velocity flow onto groups. Results. We determine the infalling velocity field onto galaxy groups with cz < 0.033 using peculiar velocity data. We measured the mean infall velocity onto group samples of different mass ranges, and also explored the impact of the environment where the group resides. Far beyond the group virial radius, the surrounding large-scale galaxy overdensity may impose additional infalling streaming amplitudes in the range of 200−400 km s−1. Also, we find that groups in samples with a well-controlled galaxy density environment show an infalling velocity amplitude that increases with group mass, consistent with the predictions of the linear model. These results from observational data are in excellent agreement with those derived from the mock catalogs.