Project Description

Radio-GOALS is a project co-funded by the ESP and the Greek state in support of postdoctoral research in Greece, and in collaboration with the Great Observatories All-sky LIRG Survey (GOALS; Armus et al.2009) team at the Infrared Processing and Analysis Center (IPAC), part of the California Institute of Technology (Caltech).

GOALS is a local (z < 0.088) infrared- selected unbiased sample of 181 LIRG and 21 ULIRG systems, made up from 293 individual galaxies. GOALS was selected from the IRAS Revised Bright Galaxy Sample (RBGS), a flux-limited sample of all extragalactic objects brighter than 5.24 Jy at 60 μm, covering the entire sky surveyed by IRAS at Galactic latitudes |b| > 5°. The GOALS sample is ideal not only in its completeness and sample size, but also in the proximity and brightness of the galaxies. The galaxies span the full range of nuclear spectral types (type-1 and type-2 AGN, LINERs and starbursts) and interaction stages (major mergers, minor mergers and isolated galaxies).

The multi-wavelength coverage of the GOALS sample includes Spitzer/IRAC imaging at 3.6, 4.5, 5.8 and 8.0 μm as well as Spitzer/MIPS at 24, 70 and 160 μm. Spitzer/IRS 5-37 μm spectra are available for the nuclei of all 293 galaxies. High resolution optical and near-IR Hubble Space Telescope imaging is available for 88 galaxies with LIR > 10^11.4 L_⊙ in addition to far-UV data for 25 objects, making GOALS one of the most complete local sample imaged by Hubble. In addition, 135 systems have been imaged in the near- and far-UV with the Galaxy Evolution Explorer (GALEX; Howell et al. 2010). Furthermore, a number of LIRGs and ULIRGs with L_IR > 10^11.67 L_⊙ have also been observed with Chandra in the X-rays. New observations with Herschel Space Telescope in the far-IR are in hand with high-resolution images with PACS, at 70, 100, and 160 μm, and SPIRE at 250, 360, and 520 μm, spectra of far-IR emission at [CII] 157.7 μm, [OI] 63.2 μm and [OIII] 88 μm, as well as the OH 79 μm absorption, and CO high-J transitions. A comprehensive multi-wavelength study of such a sample can contribute significantly in the understanding of co-evolution of black holes and stellar bulges in massive galaxies, and also to better constrain the infrared spectral energy distributions (SEDs) of the systems estimating accurately their total luminosity, as to better probe the physical conditions of the gas, and it’s density and excitation properties. Complete tables showing all available data can be found at http://goals.ipac.caltech.edu/. 

Here we present a new analysis of archival radio continuum maps available for the GOALS galaxies. For 151 LIRG systems, radio maps were obtained with the Very Large Array (VLA) at 1.4 GHz (Condon et al. 1990). In particular, 57 objects were observed in A configuration (1.5, 1.8, 2.1 and 2.4 resolution), 97 in B configuration (5′′, 6′′, 7′′ and 8′′ resolution), 103 in C configuration (15′′, 18′′, 21′′ and 24′′ resolution) and 6 in D configuration (48′′, 54′′ and 60′′ resolution). Objects that contain diffuse features, such as extended disks, require low-resolution configurations in order to recover that faint diffuse emission, while more luminous (L_IR > 10¹¹ L⊙) infrared sources are associated with smaller (∼ 1 kpc linear) radio sizes that are resolvable only at A configuration (Condon et al. 1990). Additionally, 40 objects with log(L_IR/L_⊙) ≥ 11.25 have been observed at 8.44 GHz in A configuration (0.25-0.50 arcsec resolution; Condon et al. 1991).

We create radio spectral index maps using the 1.49 and 8.44 GHz for 35 systems (46 individual galaxies) to identify the presence of an AGN using spectral index variations (Vardoulaki et al. 2014). We further compare this radio AGN diagnostic with known mid-IR (PAH emission and [NeV] emission-line detection) and optical (BPT diagram) diagnostics. We find that 3 out of the 46 galaxies in our sample are classified as radio AGN, while at mid-IR and optical are not classified as AGN. Finally, based on the correlation of compactness and flat radio spectral index, we calculate the size of the flat area in the maps and estimate a mean size of the compact SB of the order of 45 kpc². All radio spectral index maps can be found here.

The research project is implemented within the framework of the Action ''Supporting Postdoctoral Researchers'' of the Operational Program ''Education and Lifelong Learning'' (Action's Beneficiary: General Secretariat for Research and Technology), and is co-financed by the European Social Fund (ESF) and the Greek State.