The final data release of ALLSMOG: a survey of CO in typical local low-M* star-forming galaxies

We present the final data release of the APEX low-redshift legacy survey for molecular gas (ALLSMOG), comprising CO(2-1) emission line observations of 88 nearby, low-mass (10^8.5<M* [M_Sun]<10^10) star-forming galaxies carried out with the 230 GHz APEX-1 receiver on the APEX telescope. The main goal of ALLSMOG is to probe the molecular gas content of more typical and lower stellar mass galaxies than have been studied by previous CO surveys. We also present IRAM 30m observations of the CO(1-0) and CO(2-1) emission lines in nine galaxies aimed at increasing the M*<10^9 M_Sun sample size. In this paper we describe the observations, data reduction and analysis methods and we present the final CO spectra together with archival HI 21cm line observations for the entire sample of 97 galaxies. At the sensitivity limit of ALLSMOG, we register a total CO detection rate of 47%. Galaxies with higher M*, SFR, nebular extinction (A_V), gas-phase metallicity (O/H), and HI gas mass have systematically higher CO detection rates. In particular, the parameter according to which CO detections and non-detections show the strongest statistical differences is the gas-phase metallicity, for any of the five metallicity calibrations examined in this work. We investigate scaling relations between the CO(1-0) line luminosity and galaxy-averaged properties using ALLSMOG and a sub-sample of COLD GASS for a total of 185 sources that probe the local main sequence (MS) of star-forming galaxies and its +-0.3 dex intrinsic scatter from M* = 10^8.5 M_Sun to M* = 10^11 M_Sun. L'_{CO(1-0)} is most strongly correlated with the SFR, but the correlation with M* is closer to linear and almost comparably tight. The relation between L'_{CO(1-0)} and metallicity is the steepest one, although deeper CO observations of galaxies with A_V<0.5 mag may reveal an as much steep correlation with A_V. [abridged

A dust-enshrouded tidal disruption event with a resolved radio jet in a galaxy merger

Tidal disruption events (TDEs) are transient flares produced when a star is ripped apart by the gravitational field of a supermassive black hole (SMBH). We have observed a transient source in the western nucleus of the merging galaxy pair Arp 299 that radiated >1.5 × 1052 erg in the infrared and radio but was not luminous at optical or x-ray wavelengths. We interpret this as a TDE with much of its emission reradiated at infrared wavelengths by dust. Efficient reprocessing by dense gas and dust may explain the difference between theoretical predictions and observed luminosities of TDEs. The radio observations resolve an expanding and decelerating jet, probing the jet formation and evolution around a SMBH

A dust-enshrouded tidal disruption event with a resolved radio jet in a galaxy merger

Tidal disruption events (TDEs) are transient flares produced when a star is ripped apart by the gravitational field of a supermassive black hole (SMBH). We have observed a transient source in the western nucleus of the merging galaxy pair Arp 299 that radiated > 1.5 x 10(52) erg at infrared and radio wavelengths but was not luminous at optical or x-ray wavelengths. We interpret this as a TDE with much of its emission reradiated at infrared wavelengths by dust. Efficient reprocessing by dense gas and dust may explain the difference between theoretical predictions and observed luminosities of TDEs. The radio observations resolve an expanding and decelerating jet, probing the jet formation and evolution around a SMBH

Subarcsecond international LOFAR radio images of Arp 220 at 150 MHz

Context. Arp 220 is the prototypical ultra luminous infrared galaxy (ULIRG). Despite extensive studies, the structure at MHz-frequencies has remained unknown because of limits in spatial resolution. Aims. This work aims to constrain the flux and shape of radio emission from Arp 220 at MHz frequencies. Methods. We analyse new observations with the International Low Frequency Array (LOFAR) telescope, and archival data from the Multi-Element Radio Linked Interferometer Network (MERLIN) and the Karl G. Jansky Very Large Array (VLA). We model the spatially resolved radio spectrum of Arp 220 from 150 MHz to 33 GHz. Results. We present an image of Arp 220 at 150 MHz with resolution 0.̋65 × 0.̋35, sensitivity 0.15 mJy beam-1, and integrated flux density 394 ± 59 mJy. More than 80% of the detected flux comes from extended (6′′≈ 2.2 kpc) steep spectrum (α = −0.7) emission, likely from star formation in the molecular disk surrounding the two nuclei. We find elongated features extending 0.3′′ (110 pc) and 0.9′′ (330 pc) from the eastern and western nucleus respectively, which we interpret as evidence for outflows. The extent of radio emission requires acceleration of cosmic rays far outside the nuclei. We find that a simple three component model can explain most of the observed radio spectrum of the galaxy. When accounting for absorption at 1.4 GHz, Arp 220 follows the FIR/radio correlation with q = 2.36, and we estimate a star formation rate of 220 M⊙ yr-1. We derive thermal fractions at 1 GHz of less than 1% for the nuclei, which indicates that a major part of the UV-photons are absorbed by dust. Conclusions. International LOFAR observations shows great promise to detect steep spectrum outflows and probe regions of thermal absorption. However, in LIRGs the emission detected at 150 MHz does not necessarily come from the main regions of star formation. This implies that high spatial resolution is crucial for accurate estimates of star formation rates for such galaxies at 150 MHz