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Scott T.C.,Institute Astrofisica Of Andalucia Iaa Csic | Scott T.C.,University of Hertfordshire | Sengupta C.,Korea Astronomy and Space Science Institute | Verdes Montenegro L.,Institute Astrofisica Of Andalucia Iaa Csic | And 8 more authors.
Astronomy and Astrophysics | Year: 2014

Context. H i kinematic asymmetries are common in late-type galaxies irrespective of environment, although the amplitudes are strikingly low in isolated galaxies. As part of our studies of the H i morphology and kinematics in isolated late-type galaxies we have chosen several very isolated galaxies from the AMIGA sample for H i mapping. We present here the results of H i mapping of CIG 340 (IC 2487) which was selected because its integrated H i spectrum has a very symmetric profile (Aflux = 1.03 ± 0.02). Aims. Optical images of the galaxy hinted at a warped disk in contrast to the symmetric integrated H i spectrum profile. Our aim is to determine the extent to which the optical asymmetry is reflected in the resolved H i morphology and kinematics. Methods. Resolved 21-cm H i line mapping has been carried out using the Giant Metrewave Radio Telescope (GMRT). The H! i morphology and kinematics from this mapping together with other multi-wavelength data have been used to study the relationship between the H i and stellar components of CIG 340. Results. GMRT observations reveal significant H i morphological asymmetries in CIG 340 despite it's overall symmetric optical form and highly symmetric H i spectrum. The most notable H i features are: 1) a warp in the H i disk (with an optical counterpart), 2) the H i north/south flux ratio = 1.32 is much larger than expected from the integrated H i spectrum profile, and 3) a ~ 45′′ (12 kpc) H i extension containing ~6% of the detected H i mass on the northern side of the disk. Conclusions. Overall, we conclude that in isolated galaxies a highly symmetric H i spectrum can mask significant H i morphological asymmetries which can be revealed by H i interferometric mapping. The northern H i extension appears to be the result of a recent perturbation (108 yr), possibly by a satellite which is now disrupted or projected within the disk. But, we cannot rule out that the H i extension and the other observed asymmetries are the result of a long lived dark matter halo asymmetry. This study provides an important step in our ongoing programme to determine the predominant source of H i asymmetries in isolated galaxies. For CIG 340 the isolation from major companions, symmetric H i spectrum, optical morphology and interaction timescales have allowed us to narrow the possible causes the H i asymmetries and identify tests to further constrain the source of the asymmetries. © 2014 ESO.


Argudo-Fernandez M.,Institute Astrofisica Of Andalucia Csic | Argudo-Fernandez M.,University of Granada | Verley S.,University of Granada | Bergond G.,Centro Astronomico Hispano Aleman | And 10 more authors.
Astronomy and Astrophysics | Year: 2014

Context: We present a study of the 3D environment for a sample of 386 galaxies in the Catalogue of Isolated Galaxies (CIG, Karachentseva 1973) using the Ninth Data Release of the Sloan Digital Sky Survey (SDSS-DR9). Aims. We aim to identify and quantify the effects of the satellite distribution around a sample of galaxies in the CIG, as well as the effects of the large-scale structure (LSS). Methods: To recover the physically bound galaxies we first focused on the satellites that are within the escape speed of each CIG galaxy. We also propose a more conservative method using the stacked Gaussian distribution of the velocity difference of the neighbours. The tidal strengths affecting the primary galaxy were estimated to quantify the effects of the local and LSS environments. We also defined the projected number density parameter at the fifth nearest neighbour to characterise the LSS around the CIG galaxies. Results: Out of the 386 CIG galaxies considered in this study, at least 340 (88% of the sample) have no physically linked satellite. Following the more conservative Gaussian distribution of physical satellites around the CIG galaxies leads to upper limits. Out of the 386 CIG galaxies, 327 (85% of the sample) have no physical companion within a projected distance of 0.3 Mpc. The CIG galaxies are distributed following the LSS of the local Universe, although presenting a large heterogeneity in their degree of connection with it. When present around a CIG galaxy, the effect of physically bound galaxies largely dominates (typically by more than 90%) the tidal strengths generated by the LSS. Conclusions: The CIG samples a variety of environments, from galaxies with physical satellites to galaxies without neighbours within 3 Mpc. A clear segregation appears between early-type CIG galaxies with companions and isolated late-type CIG galaxies. Isolated galaxies are in general bluer, with probably younger stellar populations and very high star formation compared with older, redder CIG galaxies with companions. Reciprocally, the satellites are redder and with an older stellar populations around massive early-type CIG galaxies, while they have a younger stellar content around massive late-type CIG galaxies. This suggests that the CIG is composed of a heterogeneous population of galaxies, sampling from old to more recent, dynamical systems of galaxies. CIG galaxies with companions might have a mild tendency (0.3-0.4 dex) to be more massive, and may indicate a higher frequency of having suffered a merger in the past. © ESO 2014.


Argudo-Fernandez M.,University of Granada | Argudo-Fernandez M.,Institute Astrofisica Of Andalucia Csic Apdo 3004 | Argudo-Fernandez M.,Chinese Academy of Sciences | Verley S.,University of Granada | And 12 more authors.
Astronomy and Astrophysics | Year: 2015

Context. The construction of catalogues of galaxies and the a posteriori study of galaxy properties in relation to their environment have been hampered by scarce redshift information. The new 3-dimensional (3D) surveys permit small, faint, physically bound satellites to be distinguished from a background-projected galaxy population, giving a more comprehensive 3D picture of the surroundings. Aims. We aim to provide representative samples of isolated galaxies, isolated pairs, and isolated triplets for testing galaxy evolution and secular processes in low density regions of the local Universe, as well as to characterise their local and large-scale environments. Methods. We used spectroscopic data from the tenth data release of the Sloan Digital Sky Survey (SDSS-DR10) to automatically and homogeneously compile catalogues of 3702 isolated galaxies, 1240 isolated pairs, and 315 isolated triplets in the local Universe (z ≤ 0:080). To quantify the effects of their local and large-scale environments, we computed the projected density and the tidal strength for the brightest galaxy in each sample. Results. We find evidence of isolated pairs and isolated triplets that are physically bound at projected separations up to d ≤ 450 kpc with radial velocity difference Δv ≤ 160 km s-1, where the effect of the companion typically accounts for more than 98% of the total tidal strength a ecting the central galaxy. For galaxies in the catalogues, we provide their positions, redshifts, and degrees of relation with their physical and large-scale environments. The catalogues are publicly available to the scientific community. Conclusions. For isolated galaxies, isolated pairs, and isolated triplets, there is no difference in their degree of interaction with the large-scale structure (up to 5 Mpc), which may suggest that they have a common origin in their formation and evolution. We find that most of them belong to the outer parts of filaments, walls, and clusters, and generally differ from the void population of galaxies. © ESO 2015.


Argudo-Fernandez M.,Institute Astrofisica Of Andalucia Csic | Argudo-Fernandez M.,University of Granada | Verley S.,University of Granada | Bergond G.,Centro Astronomico Hispano Aleman | And 11 more authors.
Astronomy and Astrophysics | Year: 2013

Context. To understand the evolution of galaxies, it is necessary to have a reference sample where the effect of the environment is minimized and quantified. In the framework of the AMIGA project (Analysis of the interstellar Medium of Isolated GAlaxies), we present a revision of the environment for galaxies in the Catalogue of Isolated Galaxies (CIG, Karachentseva 1973, Astrof. Issledovaniia Byu. Spec. Ast. Obs., 8, 3) using the ninth data release of the Sloan Digital Sky Survey (SDSS-DR9). Aims. The aims of this study are to refine the photometric-based AMIGA sample of isolated galaxies and to provide an improvement of the quantification of the isolation degree with respect to previous works, using both photometry and spectroscopy. Methods. We developed an automatic method to search for neighbours within a projected area of 1 Mpc radius centred on each primary galaxy to revise the CIG isolation criteria introduced by Karachentseva (1973). The local number density at the fifth nearest neighbour and the tidal strength affecting the CIG galaxy were estimated to quantify the isolation degree. Results. Of the 636 CIG galaxies considered in the photometric study, 426 galaxies fulfil the CIG isolation criteria within 1 Mpc, taking into account projected neighbours. Of the 411 CIG galaxies considered in the spectroscopic study, 347 galaxies fulfil the CIG isolation criteria when a criterion about redshift difference is added. The available redshifts allow us to reject background neighbours and thus improve the photometric assessment. On average, galaxies in the AMIGA sample show lower values in the local number density and the tidal strength parameters than galaxies in denser environments such as pairs, triplets, compact groups, and clusters. Conclusions. For the first time, the environment and the isolation degree of AMIGA galaxies are quantified using digital data. The use of the SDSS database permits one to identify fainter and smaller-size satellites than in previous AMIGA works. The AMIGA sample is improved by this study, because we reduced the sample of isolated galaxies used in previous AMIGA works by about 20%. The availability of the spectroscopic data allows us to check the validity of the CIG isolation criteria, which is not fully efficient. About 50% of the neighbours considered as potential companions in the photometric study are in fact background objects. We also find that about 92% of the neighbour galaxies that show recession velocities similar to the corresponding CIG galaxy are not considered by the CIG isolation criteria as potential companions, which may have a considerable influence on the evolution of the central CIG galaxy. © 2013 ESO.

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