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| ULIRG Arp 220 | |
|---|---|
| Name | Arp 220 |
| Type | ULIRG; Merger remnant |
| Epoch | J2000 |
| Ra | 15h 34m 57.1s |
| Dec | +23° 30′ 11″ |
| Redshift | 0.018126 |
| Constellation | Serpens |
| Apparent magnitude | 13.2 |
ULIRG Arp 220 is an ultraluminous infrared galaxy noted for extreme luminosity, compact nuclei, and intense star formation triggered by a major merger. Located in the northern constellation Serpens and catalogued in the Atlas of Peculiar Galaxies by Halton Arp, it has been a cornerstone object in studies of galaxy interactions, starburst phenomena, and the coevolution of supermassive black holes and host galaxies. Observations across radio, infrared, submillimeter, optical, and X-ray bands by facilities such as the Hubble Space Telescope, Atacama Large Millimeter/submillimeter Array, and Chandra X-ray Observatory have revealed a complex system with dense molecular gas, compact nuclei, and energetic outflows.
Arp 220 was identified by Halton Arp in the Atlas of Peculiar Galaxies and later studied in the context of the IRAS survey that defined the class of ultraluminous infrared galaxys, alongside prototypes like NGC 6240 and Mrk 231. Its high infrared luminosity places it among the most luminous local universe mergers, comparable to luminous systems catalogued by Sanders et al. in studies linking infrared astronomy to galaxy evolution. Redshift measurements tie it to the nearby universe, studied using spectroscopy at observatories including Keck Observatory and the Very Large Telescope. The system’s integrated properties—far-infrared luminosity, molecular mass, and star-formation rate—are benchmarks in comparative analyses against high-redshift submillimeter galaxys and quasar hosts investigated with instruments like Spitzer Space Telescope and Herschel Space Observatory.
High-resolution imaging by Hubble Space Telescope and interferometric mapping by ALMA and the Very Large Array show a disturbed morphology with double nuclei, tidal tails, and luminous central concentrations, consistent with models of major mergers by groups such as Toomre and Barnes & Hernquist. Numerical simulations using codes developed by teams including Springel and Hopkins reproduce the observed nuclear separation and tidal features when initial conditions reflect interacting spirals similar to M51 and NGC 4038/4039. Kinematic studies employing CO, H I, and maser lines from facilities like IRAM and VLBI reveal complex rotation, streaming motions, and nuclear torques that drive gas inflows, as described in frameworks by Shlosman, Begelman & Frank and in treatments of angular momentum transport in mergers.
Arp 220 hosts an extreme central starburst with star-formation surface densities comparable to those inferred in the nuclei of M82 and NGC 253. Observations of molecular tracers—CO, HCN, HCO+, and OH—using ALMA, NOEMA, and single-dish telescopes such as IRAM 30m indicate molecular gas reservoirs exceeding 10^10 solar masses, with dense gas fractions and excitation conditions analyzed in the context of work by Gao & Solomon and Solomon & Vanden Bout. Infrared spectroscopy by Spitzer and millimeter studies uncover evidence for compact super star clusters and extreme initial mass function conditions discussed in literature by Kennicutt and Kroupa. Studies of isotopologues and radiative transfer models by groups including van der Tak constrain gas temperature, density, and column, supporting a picture of buried, optically thick star formation.
The possibility of one or more obscured active galactic nucleuse(s) in Arp 220 has been debated using X-ray, infrared, and radio diagnostics developed in comparisons with sources like NGC 1068 and Circinus Galaxy. Hard X-ray observations from Chandra and XMM-Newton and high-resolution radio imaging with VLBI probe compact, high-brightness features consistent with accretion onto supermassive black holes, while mid-infrared spectra obtained with Spitzer and ground-based instruments provide limits on buried Seyfert signatures. The nuclear structure includes two compact nuclei separated by a few hundred parsecs, each surrounded by dense molecular disks or tori resembling those modeled in studies by Kawakatu & Wada and Dopita & Sutherland. Maser emission, including OH megamasers, links to models of circumnuclear amplification explored by Baan and colleagues.
Arp 220’s defining trait is its extreme far-infrared output first highlighted by IRAS and subsequently resolved with ISO, Spitzer, and Herschel, situating it within the ULIRG population examined by Sanders & Mirabel. Submillimeter continuum and line imaging with SCUBA, ALMA, and SMA resolve compact dust cores with high optical depth; radio continuum and recombination line studies using VLA and ATCA trace supernova remnants and free-free emission akin to those catalogued in Arp 299. Ultraviolet/optical extinction, nebular emission lines observed with Hubble Space Telescope and ground-based facilities such as Keck inform extinction-corrected star-formation rates and metallicity estimates modeled in works by Osterbrock and Kewley.
Spectroscopic mapping in optical, infrared, and millimeter lines shows multiphase outflows, including ionized, neutral, and molecular components, paralleling phenomena studied in M82, NGC 253, and Mrk 231. Kinematic signatures in Na I D, Hα, CO, and OH indicate mass-loaded winds with velocities up to ~1000 km s^-1, studied in the context of feedback prescriptions by Veilleux, Rupke, and Heckman. Observations of supernova rates inferred from radio VLBI and synchrotron emission link to theoretical frameworks of starburst-driven winds by Chevalier and Clegg, and to models of chemical enrichment and dust entrainment discussed by Draine and Jones.
With a redshift z ≈ 0.018, Arp 220 lies at a luminosity distance of roughly 77 Mpc under concordance cosmology parameters used by Planck and earlier surveys; precise distance estimates draw on redshift-independent methods employed in studies by Tully and Faber-Jackson relations. It resides in a sparse group environment where tidal interactions with progenitor disk galaxies—likely similar to local spirals catalogued by Sloan Digital Sky Survey analogs—gave rise to the present merger remnant morphology. Companions and tidal debris have been catalogued via deep imaging campaigns associated with projects like Pan-STARRS and CFHT Legacy Survey, providing constraints on the merger history and mass assembly comparable to case studies of interacting systems in the Local Universe.
Category:Ultraluminous infrared galaxies Category:Atlas of Peculiar Galaxies