J. Sabater

The AMIGA sample of isolated galaxies VI. Radio continuum properties of isolated galaxies : a very radio-quiet sample

Context. This paper is part of a series that describes the results of the AMIGA (Analysis of the interstellar Medium of Isolated GAlaxies) project, studying the largest sample of very isolated galaxies in the local Universe. Aims. The study of the radio properties of the AMIGA sample is intended to characterize the radio continuum emission for a sample least affected by the local environment, thus providing a reference against which less isolated and interacting samples can be compared. Methods. Radio continuum data at 325, 1420, and 4850 MHz were extracted from the WENSS, NVSS/FIRST, and GB6 surveys, respectively. The source extractions have been obtained from reprocessing the data and new detections added to the cross-matched detections with the respective survey catalogs. We focus on the complete AMIGA subsample composed of 719 galaxies. Results. A catalog of radio fluxes was obtained from the above four surveys. Comparison between the NVSS and FIRST detections indicates that the radio continuum is coming from disk-dominated emission in spiral galaxies, in contrast to the results found in high-density environments where nuclear activity is more frequent. The comparison of the radio continuum power with a comparable sample, which is however not selected with respect to its environment, the Condon et al. UGC-SF sample of starforming field galaxies, shows a lower mean value for the AMIGA sample. We have obtained radio-to-optical flux ratios (R) using the NVSS radio continuum flux. The distribution of R for the AMIGA galaxies is consistent with a sample dominated by radio emission from star formation (SF) and a small number of active galactic nuclei (AGN), with less than 3% of the sample with R > 100. We derived the radio luminosity function (RLF) and total power density of the radio continuum emission for the AMIGA sample at 1.4 GHz, and compared them with results from other low-redshift studies. The Schechter fit of the RLF indicates a major weight of the low-luminosity galaxies. Conclusions. The results indicate the very low level of radio continuum emission in our sample of isolated galaxies, which is dominated by mild disk SF. It confirms thus the AMIGA sample as a suitable template to effectively quantify the role of interactions in samples extracted from denser environments.

Molecular gas properties of galaxies: The SMA CO(2-1) B0DEGA legacy project

In the last two decades high-resolution (<5″) CO observations for ~ 150 galaxies have provided a wealth of information about the molecular gas morphologies in the circumnuclear regions. While in samples of “normal” galaxies the molecular gas does not seem to peak toward the nuclear regions for about 50% of the galaxies, barred galaxies and mergers show larger concentrations. However, we do not exactly know from an observational point of view how the molecular gas properties of a galaxy evolve as a result of an interaction. Here we present the SMA CO(2–1) B0DEGA (Below 0 DEgree GAlaxies) legacy project (http://b0dega.iaa.es) in which we are imaging the CO(2–1) line of the circumnuclear regions (1´) of a large (~ 70) sample of nearby IR-bright spiral galaxies, likely interacting, and that still remained unexplored due to its location in the southern hemisphere. We find different molecular gas morphologies, such as rings, nuclear arms, nuclear bars, and asymmetries. We find a centrally peaked concentration in about 85% of the galaxies with typical size scales of about 0.5–1 kpc. This might be related to perturbations produced by recent interactions.

ISM of Galaxies in Extremely Different Environments: Isolated vs Compact Groups

1 Instituto de Astrofisica de Andalucia, CSIC, Apdo. 3004, 18080 Granada, Spain lourdes@iaa.es,daniel@iaa.es,gilles@iaa.es,garcia@iaa.es,jsm@iaa.es, simon@iaa.es 2 Department of Astronomy, University of Massachussetts, Amherst, MA 01003, USA myun@bonito.astro.umass.edu,sanchayeeta-lg@yahoo.com 3 National Research Institute of Astronomy and Geophysics, Cairo Egypt ibrahimselim@hotmail.com 4 Observatoire de Marseille, 2 Place le Verrier, 13248 Marseille Cedez 4, France lia@oamp.fr,bosma@oamp.fr 5 LERMA, Observatoire de Paris, 61 Av. de l’Observatoire, 75014 Paris, France Simon.Verley@obspm.fr 6 Max-Planck-Institut fur Radiostronomie, Auf dem Hugel 69, 53121 Bonn, Germany p083huc@mpifr-bonn.mpg.de 7 Departamento de Fisica Teorica y del Cosmos, Facultad de Ciencias, Universidad de Granada, Spain ute@ugr.es 8 sco@astro.as.utexas.edu 9 tjp@xun0.sr.bham.ac.uk,jesper@star.sr.bham.ac.uk 10 Department of Astronomy, Univ. of Alabama, AL 35487, USA giacomo@merlot.astr.ua.edu

A GALAXY BASELINE: Multiwavelength Study of a Sample of the Most Isolated Galaxies in the Local Universe

We introduce and describe main results of the AMIGA project. AMIGA involves a panchromatic characterization for many of the most isolated galaxies in the local universe. Many of these galaxies have avoided major interaction events for all, or most, of their lives. Our studies show these galaxies to be the most IR/radio/optically “quiet” sample that is known. AMIGA data are publicly released under a VO interface at http://amiga.iaa.es/ and are also accessible by standard VO tools, as, e.g. TOPCAT.

AMIGA project: Active galaxies in a complete sample of isolated galaxies

The project AMIGA (Analysis of the interstellar Medium of Isolated GAlaxies) provides a statistically significant sample of the most isolated galaxies in the northern sky. Such a control sample is necessary to understand the role of the environment in evolution and galaxy properties like the interstellar medium (ISM), star formation and nuclear activity. The data is publicly released under a VO interface at this http URL. One of our main goals is the study of nuclear activity in non-interacting galaxies using different methods. We focus on the well known radiocontinuum-far infrared (FIR) correlation in order to findradio-excess galaxies which are candidates to host an active galactic nucleus (AGN) and FIR colours to find obscured AGN candidates. We looked for the existing information on nuclear activity in the Veron-Cetty catalogue and in the NASA Extragalactic Database (NED). We also used the nuclear spectra from the Sloan Digital Sky Survey which allow us to determine the possible presence of an AGN and to study the properties of the underlying stellar populations. We produced a final catalogue of AGN-candidate galaxies which will provide a baseline for the study of the nuclear activity depending on the environment. We find that the fraction of FIR selected AGN-candidates ranges between 7% and 20%. There are no radio-excess galaxies in our sample above a factor 5 of radio excess which is the lowest rate found in comparison with other samples in denser environments. Finally, we obtained a fraction of about 22% of AGN using the optical spectra, a significant fraction for a sample of isolated galaxies. We conclude that the environment plays a crucial and direct role in triggering radio nuclear activity and not only via the density-morphology or the density-luminosity relations.The aim of the AMIGA project (Analysis of the Interstellar Medium in Isolated GAlaxies) is building a reference sample of isolated galaxies to study the role of the environment in galactic evolution. AMIGA began in 2003 and nowadays involves more than 30 participants from 15 international institutions. Radio continuum emission in isolated spiral galaxies is coming from disk-dominated emission in spiral galaxies, in contrast to the results found in high-density environments where nuclear activity is more frequent. The radio continuum power is lower on average in our sample than in interacting galaxies or galaxies without an environment selection criterion. This confirms the relevance of our sample as a baseline to study the effects of the environment. Finally, we have studied the nuclear activity in isolated galaxies. We used different selection methods of isolated galaxies with active nucleus: (1) the far infrared colors give us a fraction of 7–20% of AGN candidates and (2) the rate of radio excess galaxies in the correlation of far infrared with radio continuum is less than 1%, which is the lowest rate found comparing with samples in other environments. This confirms the role of the environment as fundamental in the triggering of the radio nuclear activity.