BVRISURFACE PHOTOMETRY OF ISOLATED GALAXY TRIPLETS

Abstract

Optical broadband BVRI observations of 54 galaxies selected from the Catalog of Isolated Triplets of Galaxies in the Northern Hemisphere have been carried out at San Pedro Mártir National Observatory to evaluate their photometric and morphological properties. We complement our analysis with Two-Micron All Sky Survey (2MASS) and Sloan Digital Sky Survey (SDSS) images and look for signatures likely related to interactions/mergers. We report apparent/absolute BVRI magnitudes and colors for the 54 galaxies. The membership of these galaxies is re-evaluated by imposing a reasonable condition of concordant redshifts upon the original selection criteria, rendering a final sample of 34 galaxies in 13 triplets, 12 galaxies in close pairs, and 8 galaxy outliers. The triplets are spiral-dominated systems in different dynamical stages from loosely interacting to almost merged objects. The incidence fraction of features likely associated with interactions is ∼56%, similar to those found in northern and southern compact groups. The average fraction of bars is 35% with a mean value of maximum bar ellipticity max ≈ 0.4. Bars are hosted in the late-type triplet spirals, almost twice more than in early-type spirals. The global fraction of rings is 20%, all in the late-type components. The overdensity of triplets with respect to the background and their current dynamical status, as devised from our estimate of their dynamical parameters, namely the harmonic radius R H , velocity dispersion σ , dimensionless crossing time H 0 τ c , and virial mass M V , appear to be sufficient to favor galaxy transformations similar to those seen in dense groups and clusters. By contrast, the lower fraction of bonafide ellipticals and the relatively higher fraction of late-type spirals make these triplets essentially different from the Hickson Compact Groups and more representative of the field. A modest 1.6 enhancement factor in the optical luminosity of the late-type triplet components relative to an isolated galaxy control sample is also interpreted as consistent with interactions in physically bounded aggregates. Our results lead us to suggest that non-negligible populations of physical triplets might be found in complete and well-observed samples. We provide individual mosaics for the 54 galaxies containing (1) logarithmic-scaled R-band images, (2) R-band sharp/filtered images, (3) (B − I) color index maps, (4) RGB images from the SDSS database, (5) co-added J + H + K images generated from the 2MASS archives that were also sharp/filtered, and (6) , position angle radial profiles from a surface photometry analysis of (a) the R band and (b) the co-added near-infrared images, all used for the present analysis.

Fundamental parameters of isolated galaxy triplets in the local universe: statistical study

“…Parameters of primary (G1) and satellite galaxies (G2 and G3) show that G1 is always brighter and more luminous than G2 and G3. This confirm the hierarchical structure of isolated triplets (Hernández-Toledo et al 2011;Argudo-Fernández et al 2015;Duplancic et al 2015).…”

Galaxy triplets in Sloan Digital Sky Survey Data Release 7 - I. Catalogue

“…dynamically isolated systems. Nevertheless, Hernández‐Toledo et al (2011) have recently analysed a sample of galaxy triplets derived from the catalogue of isolated triplets of Karachentseva (1973), finding signatures of physical interactions (tidal bridges, excess of barred galaxies), which implies that most of these objects are indeed real physical structures.…”

Gravitational interaction signatures in isolated galaxy triplet systems: a photometric analysis

“…Systems of galaxy triplets are galaxy groups with the least number of galaxies and are natural laboratories that can provide insight into the formation of larger groups and perhaps even clusters (Hernández-Toledo et al, 2011). Based on the BVRI photometry of 54 triplet systems, Hernández-Toledo et al (2011) investigated the ellipticity, position angle and B − I colour maps of these systems and inferred that galaxy triplets are dominated by spirals, a population that is more representative of field galaxies.…”

“…Systems of galaxy triplets are galaxy groups with the least number of galaxies and are natural laboratories that can provide insight into the formation of larger groups and perhaps even clusters (Hernández-Toledo et al, 2011). Based on the BVRI photometry of 54 triplet systems, Hernández-Toledo et al (2011) investigated the ellipticity, position angle and B − I colour maps of these systems and inferred that galaxy triplets are dominated by spirals, a population that is more representative of field galaxies. Extending to a larger sample derived from a catalogue of 1092 triplets, O 'Mill et al (2011) and Duplancic et al (2013) compared physical properties such as star-formation rate (SFR), stellar population age, colour indices, compactness and concentration indices of galaxy triplets and compact groups.…”

“…The most popular optical ways used to identify the state of interaction between galaxies consists in investigating their morphologies, star forma-tion region properties and their colour distribution (Veilleux et al, 2002;Hernández-Toledo et al, 2011;Kilerci Eser et al, 2014). In addition, the analysis of hydrodynamical simulation and panchromatic spectral energy distribution play a key role in the identification of signs of interactions between galaxies (Steinmetz, 1999;Springel, 2000;Springel et al, 2005;Hopkins et al, 2006;Costa-Duarte et al, 2016).…”