High-Resolution Radio Continuum Measurements of the Nuclear Disks of Arp 220

Abstract

We present new Karl G. Jansky Very Large Array radio continuum images of the nuclei of Arp 220, the nearest ultra-luminous infrared galaxy. These images have both the angular resolution to study detailed morphologies of the two nuclei that power the system and sensitivity to a wide range of spatial scales. At 33 GHz, and with a resolution of 0".081 x 0".063 (29.9 x 23.3 pc), we resolve the emission surrounding both nuclei and conclude that is mostly synchrotron in nature. The spatial distributions of radio emission in both nuclei are well described by exponential profiles. These have deconvolved half-light radii of 51 and 35 pc for the eastern and western nuclei, and they match the number density profile of radio supernovae observed with very long baseline interferometry. This similarity might be due to the fast cooling of cosmic rays electrons caused by the presence of a strong (~ mG) magnetic field in this system. We estimate high luminosity surface densities of ${\mathrm{\Sigma }}_{\mathrm{IR}}\sim 4.2_{-0.7}^{+1.6}\times 10^{13}$ (east) and $\sim 9.7_{-2.4}^{+3.7}\times 10^{13}(\mathrm{west}){\mathrm{L}}_{\odot }\mathrm{kp}{\mathrm{c}}^{-2}$, and star formation rate surface densities of ${\mathrm{\Sigma }}_{\mathrm{SFR}}\sim 10^{3.7\pm 0.1}$ (east) and $\sim 10^{4.1\pm 0.1}(\mathrm{west}){\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}\mathrm{kp}{\mathrm{c}}^{-2}$. These values, especially for the western nucleus are, to our knowledge, the highest luminosity and star formation rate surface densities measured for any star-forming system. Despite these high values, the nuclei lie below the dusty Eddington limit in which radiation pressure is balanced only by self-gravity. The small measured sizes also imply that the nuclei of Arp 220 are only transparent in the frequency range ~ 5 to 350 GHz. Our results offer no clear evidence that an active galactic nucleus dominates the emission from either nucleus at 33 GHz.

15 pages, 3 Figures, 3 Tables and 2 appendices. Accepted for publication in ApJ

References in corpus (7)

• Mid-IR Galaxy Classification Based on Silicate Obscuration and PAH Equivalent Width
• VLBI Images of 49 Radio Supernovae in Arp 220
• SMA Imaging of CO(3-2) Line and 860 micron Continuum of Arp 220 : Tracing the Spatial Distribution of Luminosity
• Black hole in the West Nucleus of Arp 220
• Extragalactic Zeeman Detections in OH Megamasers
• Radiation Feedback in ULIRGS: Are Photons Movers and Shakers?
• Extreme dust disks in Arp 220 as revealed by ALMA

Cited by in corpus (19)

• Kiloparsec-scale dust disks in high-redshift luminous submillimeter galaxies
• ALMA Imaging of HCN, CS and dust in Arp 220 and NGC 6240
• Dense gas is not enough: environmental variations in the star formation efficiency of dense molecular gas at 100pc scales in M51
• CO emission in distant galaxies on and above the main sequence
• Subarcsecond international LOFAR radio images of Arp 220 at 150 MHz: A kpc-scale star forming disk surrounding nuclei with shocked outflows
• A 33 GHz Survey of Local Major Mergers: Estimating the Sizes of the Energetically Dominant Regions from High Resolution Measurements of the Radio Continuum
• Clumpy and Extended Starbursts in the Brightest Unlensed Submillimeter Galaxies
• Resolved Structure of Arp 220 Nuclei at λ~3 mm
• SPT0346-52: Negligible AGN Activity in a Compact, Hyper-starburst Galaxy at z = 5.7
• Hidden or missing outflows in highly obscured galaxy nuclei?
• Morphology and Kinematics of Warm Molecular Gas in the Nuclear Region of Arp 220 as Revealed by ALMA
• Detection of a methanol megamaser in a major-merger galaxy
• X-ray emission from the nuclear region of Arp 220
• A controlled study of cold dust content in galaxies from $z=0-2$
• Breaking the Radio - Gamma-Ray Connection in Arp 220
• Arp 220: New Observational Insights into the Structure and Kinematics of the Nuclear Molecular Disks and Surrounding Gas
• Dust masses, compositions, and luminosities in the nuclear disks and the diffuse circumnuclear medium of Arp220
• High Resolution Observations of Molecular Lines in Arp 220: Kinematics, Morphology, and Limits on the Applicability of the Ammonia Thermometer
• Probing the cold and warm molecular gas in the Whirlpool Galaxy: Herschel SPIRE-FTS Observations of the central region of M51 (NGC 5194)