The AMIGA sample of isolated galaxies: VIII. The rate of asymmetric HI profiles in spiral galaxies

(abridged) Measures of the HI properties of a galaxy are among the most sensitive interaction diagnostic at our disposal. We report here on a study of HI profile asymmetries (e.g., lopsidedness) in a sample of some of the most isolated galaxies in the local Universe. This presents us with an excellent opportunity to quantify the range of intrinsic HI asymmetries and provides us with a zero-point calibration for evaluating these measurements in less isolated samples. We characterize the HI profile asymmetries and search for correlations between HI asymmetry and their environments, as well as their optical and far infrared (FIR) properties. We use high signal-to-noise global HI profiles for galaxies in the AMIGA project (http://amiga.iaa.csic.es). We restrict our study to N=166 galaxies with accurate measures of the HI shape properties. We quantify asymmetries using a flux ratio parameter. The asymmetry parameter distribution of our isolated sample is well described by a Gaussian model. The width of the distribution is sigma=0.13, and could be even smaller (sigma=0.11) if instrumental errors are reduced. Only 2% of our carefully vetted isolated galaxies sample show an asymmetry in excess of 3sigma. By using this sample we minimize environmental effects as confirmed by the lack of correlation between HI asymmetry and tidal force (one-on-one interactions) and neighbor galaxy number density. On the other hand, field galaxy samples show wider distributions and deviate from a Gaussian curve. As a result we find higher asymmetry rates (~10-20%) in such samples. We find evidence that the spiral arm strength is inversely correlated with the HI asymmetry. We also find an excess of FIR luminous galaxies with larger HI asymmetries that may be spirals associated with hidden accretion events. Our sample presents the smallest fraction of asymmetric HI profiles compared with any other yet studied.Comment: 18 pages, 17 figures, accepted for publication in A&

Chemistry in isolation: High CCH/HCO+ line ratio in the AMIGA galaxy CIG 638

Multi-molecule observations towards an increasing variety of galaxies have been showing that the relative molecular abundances are affected by the type of activity. However, these studies are biased towards bright active galaxies, which are typically in interaction. We study the molecular composition of one of the most isolated galaxies in the local Universe where the physical and chemical properties of their molecular clouds have been determined by intrinsic mechanisms. We present 3 mm broad band observations of the galaxy CIG 638, extracted from the AMIGA sample of isolated galaxies. The emission of the J=1-0 transitions of CCH, HCN, HCO+, and HNC are detected. Integrated intensity ratios between these line are compared with similar observations from the literature towards active galaxies including starburst galaxies (SB), active galactic nuclei (AGN), luminous infrared galaxies (LIRG), and GMCs in M33. A significantly high ratio of CCH with respect to HCN, HCO+, and HNC is found towards CIG 638 when compared with all other galaxies where these species have been detected. This points to either an overabundance of CCH or to a relative lack of dense molecular gas as supported by the low HCN/CO ratio, or both. The data suggest that the CIG 638 is naturally a less perturbed galaxy where a lower fraction of dense molecular gas, as well as a more even distribution could explain the measured ratios. In this scenario the dense gas tracers would be naturally dimmer, while the UV enhanced CCH, would be overproduced in a less shielded medium.Comment: Letter accepted for publication in A&

Gipsy 3D: Analysis, Visualization and Vo-Tools

The scientific goals of the AMIGA project are based on the analysis of a significant amount of spectroscopic 3D data. In order to perform this work we present an initiative to develop a new VO compliant package, including present core applications and tasks offered by the Groningen Image Processing System (GIPSY), and new ones based on use cases elaborated in collaboration with ad- vanced users. One of the main goals is to provide local interoperability between GIPSY (visualization and data analysis) and other VO software. The connectivity with the Virtual Observatory environment will provide general access to 3D data VO archives and services, maximizing the potential for scientific discovery.Comment: 2 pages, 1 figure, to appear in the proceedings of the "Multi-wavelength Astronomy and Virtual Observatory" Workshop held at ESAC 1-3 Dec 200

A ~ 12 kpc HI extension and other HI asymmetries in the isolated galaxy CIG 340 (IC 2487)

HI 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 HI morphology and kinematics in isolated late-type galaxies we have chosen several very isolated galaxies from the AMIGA sample for HI mapping. Here we present GMRT 21-cm HI line mapping of CIG 340 which was selected because its integrated HI spectrum has a very symmetric profile, Aflux = 1.03. Optical images of the galaxy hinted at a warped disk in contrast to the symmetric integrated HI spectrum profile. Our aim is to determine the extent to which the optical asymmetry is reflected in the resolved HI morphology and kinematics. GMRT observations reveal significant HI morphological asymmetries in CIG 340 despite it's overall symmetric optical form and highly symmetric HI spectrum. The most notable HI features are: 1) a warp in the HI disk (with an optical counterpart), 2) the HI north/south flux ratio = 1.32 is much larger than expected from the integrated HI spectrum profile and 3) a ~ 45" (12 kpc) HI extension, containing ~ 6% of the detected HI mass on the northern side of the disk. We conclude that in isolated galaxies a highly symmetric HI spectrum can mask significant HI morphological asymmetries. The northern HI extension appears to be the result of a recent perturbation (10^8 yr), possibly by a satellite which is now disrupted or projected within the disk. This study provides an important step in our ongoing program to determine the predominant source of HI asymmetries in isolated galaxies. For CIG 340 the isolation from major companions, symmetric HI spectrum, optical morphology and interaction timescales have allowed us to narrow the possible causes the HI asymmetries and identify tests to further constrain the source of the asymmetries.Comment: 10 page

The AMIGA sample of isolated galaxies. IV. A catalogue of neighbours around isolated galaxies

Studies of the effects of environment on galaxy properties and evolution require well defined control samples. Such isolated galaxy samples have up to now been small or poorly defined. The AMIGA project (Analysis of the interstellar Medium of Isolated GAlaxies) represents an attempt to define a statistically useful sample of the most isolated galaxies in the local (z < 0.05) Universe. A suitable large sample for the AMIGA project already exists, the Catalogue of Isolated Galaxies (CIG, Karachentseva 1973; 1050 galaxies), and we use this sample as a starting point to refine and perform a better quantification of its isolation properties. Digitised POSS-I E images were analysed out to a minimum projected radius R > 0.5 Mpc around 950 CIG galaxies (those within Vr = 1500 km s-1 were excluded). We identified all galaxy candidates in each field brighter than B = 17.5 with a high degree of confidence using the LMORPHO software. We generated a catalogue of approximately 54 000 potential neighbours (redshifts exist for 30% of this sample). Six hundred sixty-six galaxies pass and two hundred eighty-four fail the original CIG isolation criterion. The available redshift data confirm that our catalogue involves a largely background population rather than physically associated neighbours. We find that the exclusion of neighbours within a factor of four in size around each CIG galaxy, employed in the original isolation criterion, corresponds to Delta Vr ~ 18000 km s-1 indicating that it was a conservative limit. Galaxies in the CIG have been found to show different degrees of isolation. We conclude that a quantitative measure of this is mandatory. It will be the subject of future work based on the catalogue of neighbours obtained here.Comment: Accepted by A&A, 10 pages, 8 figures, 4 table

Effects of the environment on galaxies in the Catalogue of Isolated Galaxies: physical satellites and large scale structure

We aim to identify and quantify the effects of the satellite distribution around a sample of galaxies in the Catalogue of Isolated Galaxies (CIG), as well as the effects of the Large Scale Structure (LSS) using the SDSS-DR9. To recover the physically bound galaxies we focus on the satellites which 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 are estimated to quantify the effects of the local and LSS environments. We also define the projected number density parameter at the 5$^{\rm th}$ nearest neighbour to characterise the LSS around the CIG galaxies. Out of the 386 CIG galaxies considered in this study, at least 340 (88\% of the sample) have no physically linked satellite. 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. A clear segregation appears between early-type CIG galaxies with companions and isolated late-type CIG galaxies. Isolated galaxies are in general bluer, with likely younger stellar populations and rather high star formation with respect to 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.Comment: 19 pages, 10 figures, 1 table, accepted for publication in Astronomy & Astrophysic

Setting the normalcy level of HI properties in isolated galaxies

Studying the atomic gas (HI) properties of the most isolated galaxies is essential to quantify the effect that the environment exerts on this sensitive component of the interstellar medium. We observed and compiled HI data for a well defined sample of ~ 800 galaxies in the Catalog of Isolated Galaxies, as part of the AMIGA project (Analysis of the ISM in Isolated GAlaxies, http://amiga.iaa.es), which enlarges considerably previous samples used to quantify the HI deficiency in galaxies located in denser environments. By studying the shape of 182 HI profiles, we revisited the usually accepted result that, independently of the environment, more than half of the galaxies present a perturbed HI disk. In isolated galaxies this would certainly be a striking result if these are supposed to be the most relaxed systems, and has implications in the relaxation time scales of HI disks and the nature of the most frequent perturbing mechanisms in galaxies. Our sample likely exhibits the lowest HI asymmetry level in the local Universe. We found that other field samples present an excess of ~ 20% more asymmetric HI profiles than that in CIG. Still a small percentage of galaxies in our sample present large asymmetries. Follow-up high resolution VLA maps give insight into the origin of such asymmetries.Comment: 4 pages, 2 figures, Conference 'Galaxies in Isolation: Exploring Nature vs. Nurture', Granada, 12-15 May 2009. To be published in the ASP Conference Serie