Effects of environment in galaxy evolution

Executive Summary: Isolated galaxies AMIGA to the Cube

The role played by the environment in the evolution of galaxies remains an open issue: the so called " nature versus nurture " debate. At present, it is known that the environment where galaxies are located appears to have a decisive influence on several processes that regulate the kinematics and activity of star formation in galaxies. To disentangle which effects can be attributed to gravitational interactions the full characterization of a well defined baseline of isolated galaxies is still incomplete.

The AMIGA (Analysis of the interstellar Medium of Isolated Galaxies) international project provides such a baseline by quantifying the properties of a well defined sample ~1000 isolated galaxies, for which a multifrequency database is made public through a VO-interface in the project Web page. The global properties of the sample have been studied and are being further exploited, choosing the best candidates for a better understanding of the processes involved in secular Star Formation (SF), tracing the ISM distribution and kinematics with the most competitive mm and submm instrumentation, with a special emphasis on the wealth of information provided by 3D datasets. From this study we will identify outstanding candidates requiring a higher resolution study with ALMA, that will be complemented in a next step with SKA. SKA will provide access to the 21cm line emission out to redshifts of z = 3, allowing as well high spatial and velocity resolution maps that will resolve the individual clouds of atomic hydrogen which will collapse to form stars in nearby galaxies. ALMA will be a key tool in the close future of AMIGA, since it will provide a powerful tracer of SF galaxies over a wide redshift range based on the measure of molecular line emission at short wavelengths. As it has been the case with the ALMA pathfinder SMA, eventually valuable collaborations are foreseen with the ATNF in the context of SKA pathfinder ASKAP, not only to expand the scientific goals of AMIGA but to exploit the expertise gained by the team in the radio-VO field, where limited efforts exist so far.

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Detailed Research

Isolated galaxies: AMIGA to the Cube is the next step on the road of the AMIGA (Analysis of the interstellar Medium of Isolated GAlaxies) project. So far the AMIGA multiwavelength catalog for 1000 isolated galaxies has been constructed, and the bulk of its exploitation started with a selection of the best isolated candidates for detailed studies of specific physical problems. Now our main goal is an in-depth study of these nature dominated galaxies with a special emphasis on the wealth of information provided by 3D datasets. An intensive effort is being invested to be prepared for the best use of the unique tools that ALMA in the close future, and SKA later, will be constitute for AMIGA. Our finished statistical analysis of the multiwavelength reference AMIGA sample allows us to start here also an evaluation of nurture (environment) driven effects. In particular the topics to be covered are the tests of galaxy formation models with isolated galaxies, the analysis of the conditions for secular star formation (SF) and nuclear activity in isolated galaxies and the determination of the minimum level of interaction producing measurable effects on galaxy evolution.

The study of the neutral component in individual galaxies is focussed on the distribution of molecular dense gas traced by different species and transitions (CO, HCN, etc) and of the atomic gas responsible of the HI emission. For this study we use first line different international radio facilities, like IRAM (30m and PdB), SMA, VLA, GBT or Arecibo among others. Since stars come from gas, it is useful to ask how SFR depends on local gas properties. A tight relation has been found in the bibliography between the surface density of the SF and the gas surface density, which can be well described by a Schmidt law, and a gas stability threshold. In this context it is of special the study if SF in the outer parts of the extended UV disks (XUV) recently detected at UV wavelengths. Given the low gas densities where the star formation in the XUV disks takes place, the XUV phenomenon is a challenge to our current ideas on the star formation threshold and law. Our main goal is then to identify the means to supply a rich reservoir of gas, whether through (tidal) removal of the ISM from the ordinary disk or infall/accretion.

With respect to the kinematical and dynamical properties of galaxies, again those for both isolated and members of interacting groups have to be characterized. The determination of the masses of galaxies can be calculated through the rotation curves in the spiral systems and/or through measures on the dynamics of satellites (globular clusters and dwarf galaxies). To do so multifrequency observations by using optical emission lines and HI velocities at the radiofrequencies regime are required. The study of the dynamics of galaxies in clusters, from both observational and theoretical approaches, provides information on the spatial distribution of matter and therefore on the nature of the main component of the cluster, giving a reasonable estimation on the importance of dark matter in large scale structures. The SDSS will make feasible a full 3D revision of the environment of ~ 200 isolated galaxies from AMIGA project, allowing an analysis of the dynamics of the satellite galaxies. This study will be complemented with a kinematical study of the globular clusters (GCs) around isolated galaxies with the VLT and GTC. In both studies the aim will be measuring the mass and extent of dark matter (DM) halos.

Scientific objectives

  1. To study the dynamics of isolated galaxies, selected from the AMIGA sample, which has minimized environmental effects. This analysis will be based on 1) data of the satellite galaxies obtained from the final release of SDSS and 2) globular clusters to be studied with 8-10-m telescopes (VLT and GTC). This will allow to characterize the populations of satellite galaxies and to set constraints on the dark matter content.
  2. To study the conditions of secular SF/AGN in the AMIGA sample, including a comparison between the mass, chemistry and excitation of the ISM, as well as SF rate and efficiency, making use of available and forthcoming facilities at mm/submm wavelengths.
  3. To investigate the link between kinematics and SF in the inner parts of isolated galaxies as well as in far outer regions of their disks, aiming also at identifying suitable candidates to be studied with ALMA, as well as with SKA in a next step. To investigate the minimum level of interaction needed to influence galaxy evolution, from the study of the most HI asymmetric isolated galaxies, and to test whether they originate from minor interactions.