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Post Info TOPIC: Arp220
Blobrana


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Title: X-ray emission from the nuclear region of Arp 220
Author: Alessandro Paggi, Giuseppina Fabbiano, Guido Risaliti, Junfeng Wang, Margarita Karovska, Martin Elvis, W. Peter Maksym, Jonathan McDowell, Jay Gallagher

We present an imaging and spectral analysis of the nuclear region of the ULIRG merger Arp 220, using deep \textit{Chandra}-ACIS observations summing up to \(\sim 300\mbox{ ks}\). Narrow-band imaging with sub-pixel resolution of the innermost nuclear region reveals two distinct Fe-K emitting sources, coincident with the infrared and radio nuclear clusters. These sources are separated by 1' (\(\sim 380\) pc). The X-ray emission is extended and elongated in the eastern nucleus, like the disk emission observed in millimeter radio images, suggesting starburst dominance in this region. We estimate Fe-K equivalent width \(\gtrsim 1\) keV for both sources, and observed 2-10 keV luminosities \(\sim 2\times{10}^{40}\mbox{ erg}\mbox{ s}^{-1}\) (W) and \(\sim 3 \times {10}^{40}\mbox{ erg}\mbox{ s}^{-1}\) (E). In the 6-7 keV band the emission from these regions is dominated by the 6.7 keV Fe \textsc{xxv} line, suggesting contribution from collisionally ionized gas. The thermal energy content of this gas is consistent with kinetic energy injection in the interstellar medium by Type II SNe. However, nuclear winds from hidden AGN (\(\varv\sim 2000 \mbox{ km}\mbox{ s}^{-1}\)) cannot be excluded. The \(3\sigma\) upper limits on the neutral Fe-K\(\alpha\) flux of the nuclear regions correspond to intrinsic AGN 2-10 keV luminosities \(< 1\times {10}^{42}\mbox{ erg}\mbox{ s}^{-1}\) (W) and \(< 0.4\times {10}^{42}\mbox{ erg}\mbox{ s}^{-1}\) (E). For typical AGN SEDs the bolometric luminosities are \(< 3\times {10}^{43}\mbox{ erg}\mbox{ s}^{-1}\) (W) and \(< 8\times {10}^{43}\mbox{ erg}\mbox{ s}^{-1}\) (E), and black hole masses \(<1\times{10}^5 M_{\astrosun}\) (W) and \(< 5\times{10}^5 M_{\astrosun}\) (E) for Eddington limited AGNs with a standard 10\% efficiency.

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Blobrana


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Posts: 131433
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Arp 220
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Title: Excited OH+, H2O+, and H3O+ in NGC 4418 and Arp 220
Authors: E. González-Alfonso, J. Fischer, S. Bruderer, H. S. P. Müller, J. Graciá-Carpio, E. Sturm, D. Lutz, A. Poglitsch, H. Feuchtgruber, S. Veilleux, A. Contursi, A. Sternberg, S. Hailey-Dunsheath, A. Verma, N. Christopher, R. Davies, R. Genzel, L. Tacconi

We report on Herschel/PACS observations of absorption lines of OH+, H2O+ and H3O+ in NGC 4418 and Arp 220. Excited lines of OH+ and H2O+ with E_lower of at least 285 and ~200 K, respectively, are detected in both sources, indicating radiative pumping and location in the high radiation density environment of the nuclear regions. Abundance ratios OH+/H2O+ of 1-2.5 are estimated in the nuclei of both sources. The inferred OH+ column and abundance relative to H nuclei are (0.5-1)x10^{16} cm-2 and ~2x10^{-8}, respectively. Additionally, in Arp 220, an extended low excitation component around the nuclear region is found to have OH+/H2O+ ~5-10. H3O+ is detected in both sources with N(H3O+)~(0.5-2)x10^{16} cm-2, and in Arp 220 the pure inversion, metastable lines indicate a high rotational temperature of ~500 K, indicative of formation pumping and/or hot gas. Simple chemical models favour an ionisation sequence dominated by H+ - O+ - OH+ - H2O+ - H3O+, and we also argue that the H+ production is most likely dominated by X-ray/cosmic ray ionisation. The full set of observations and models leads us to propose that the molecular ions arise in a relatively low density (\gtrsim10^4 cm-3) interclump medium, in which case the ionisation rate per H nucleus (including secondary ionisations) is zeta>10^{-13} s-1, a lower limit that is several x10^2 times the highest rate estimates for Galactic regions. In Arp 220, our lower limit for zeta is compatible with estimates for the cosmic ray energy density inferred previously from the supernova rate and synchrotron radio emission, and also with the expected ionisation rate produced by X-rays. In NGC 4418, we argue that X-ray ionisation due to an AGN is responsible for the molecular ion production.

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Blobrana


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Posts: 131433
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Title: The merger Seyfert galaxy Arp 220. Line and continuum absorption and emission
Authors: M. Contini

The line and continuum spectra of the merger galaxy Arp 220 are analysed with the aim of investigating the ionising and heating sources. We refer to radio, optical, infrared and X-ray spectra. The results show that in agreement with other merger galaxies, the optical lines are emitted from gas photoionised by the AGN and heated by the shocks in the extended NLR. The infrared lines are better explained by the emission from gas close to the starburst. The starburst dominates the infrared emission. [OI] and [CI] lines in the far-infrared are formed in the internal region of extended clouds and are therefore absorbed, while [CII] lines are emitted from the external edges of outflowing clouds. The O/H relative abundances are about solar and N/H are higher than solar by a factor of 1.5, throughout the starburst region, while in the AGN extended NLR the O/H ratio is half solar. A relatively high dust-to-gas ratio is indicated by modelling the dust reprocessed radiation peak consistently with bremsstrahlung emitted from the clouds. The observed radio emission is thermal bremsstrahlung, while synchrotron radiation created by the Fermi mechanism at the shock front is absorbed.

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Blobrana


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Posts: 131433
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Arp 220
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Title: The Arp 220 merger on kpc scales
Authors: S. König, M. García-Marín, A. Eckart, D. Downes, J. Scharwächter

For the first time we study the Eastern nucleus in greater detail and search for the more extended emission in the molecular gas in different CO line transitions of the famous ULIRG Arp 220. Furthermore we present a model of the merger in Arp 220 on large scales with the help of the CO data and an optical and near-infrared composite HST image of the prototypical ULIRG. Using the Plateau de Bure Interferometer (PdBI) we obtained CO(2-1) and (1-0) data at wavelengths of 1 and 3 mm in 1994, 1996, 1997 and 2006 at different beam sizes and spatial resolutions. The simulations of the merger in Arp 220 were performed with the Identikit modelling tool. The model parameters that describe the galaxy merger best give a mass ratio of 1:2 and result in a merger of ~6x10^8 yrs. The low resolution CO(1-0) PdBI observations suggest that there are indications for emission ~10" towards the south, as well as to the north and to the west of the two nuclei.

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Blobrana


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Title: Rapid variability of the compact radio sources in Arp220. Evidence for a population of microblazars?
Authors: F. Batejat, J. E. Conway, A. Rushton, R. Parra, P. J. Diamond, C. J. Lonsdale, C. J. Lonsdale

Context. The two nuclei of the starburst galaxy Arp220 contain multiple compact radio sources previously identified as radio supernovae or supernova remnants.
Aims. In order to search for an embedded radio AGN, or other possible exotic objects, we have carried out a program of VLBI monitoring at 6 cm over three epochs each separated by four months.
Methods. Combining the new data with existing data at 6 cm and 18 cm (spanning 4 and 12 years respectively) we are able to characterise source flux density variability on a range of time-scales. Additionally we analyse the variability of sources in shape and position.
Results. We detect rapid (< 4 months) variability in three sources (W7, W26 and W29). These sources show possible superluminal motion (> 4c) of jet-like features near rapidly varying almost stationary components. These enigmatic sources might be associated with an AGN or a highly beamed microquasar (i.e. microblazar). Other hypotheses include that the apparent variability is intrinsic and is produced by neutron star powered central components within a supernova remnant, by a sequence of several supernovae within super star clusters, or is extrinsic and is produced by Galactic interstellar scintillation of very compact non-varying objects.
Conclusions. A microquasar/microblazar origin seems to be the best explanation for the nature of the variable sources in Arp220.

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Blobrana


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Arp 220
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Astronomers reveal supernova factory

A team led by astronomers at Chalmers and Onsala Space Observatory has detected seven previously unknown supernovae in a galaxy 250 million light years away. Never before have so many supernovae been discovered at the same time in the same galaxy. The results are accepted for publication in the Astrophysical Journal.
The discovery proves what astronomers have long believed: that the galaxies which are the universe's most efficient star-factories are also supernova factories.
The astronomers used a worldwide network of radio telescopes in five countries, including Sweden, to be able to create extremely sharp images of the galaxy Arp 220. The scientists observed around 40 radio sources in the center of the galaxy Arp 220. These radio sources are hidden behind thick layers of dust and gas and invisible in ordinary telescopes. To discover the nature of these radio sources, they made measurements at different radio wavelengths and watched how they changed over several years.
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Blobrana


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Posts: 131433
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RE: Arp220
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Title: Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H2O, H2^{18}O, OH, ^{18}OH, O^0, HCN and NH3
Authors: E. González-Alfonso, J. Fischer, J. Graciá-Carpio, E. Sturm, S. Hailey-Dunsheath, D. Lutz, A. Poglitsch, A. Contursi, H. Feuchtgruber, S. Veilleux, H. W. W. Spoon, A. Verma, N. Christopher, R. Davies, A. Sternberg, R. Genzel, L. Tacconi

Herschel/PACS spectroscopy of the (ultra)luminous infrared galaxies NGC 4418 and Arp 220 reveals high excitation in H2O, OH, HCN, and NH3. In NGC 4418, absorption lines were detected with E_lower>800 K (H2O), 600 K (OH), 1075 K (HCN), and 600 K (NH3), while in Arp 220 the excitation is somewhat lower. While clear outflow signatures are seen in Arp 220 as has been seen in previous studies, in NGC 4418 the lines tracing its outer regions are redshifted relative to the nucleus, suggesting an inflow with solar masses<~12 solar masses yr^{-1}. Both galaxies have compact and warm (T_dust >~100 K) nuclear continuum components, together with a more extended and colder component that is much more prominent and massive in Arp 220. A chemical dichotomy is found in both sources: on the one hand, the nuclear regions have high H2O abundances, ~0.5x10^{-5}, and high HCN/H2O and HCN/NH3 column density ratios of 0.2-0.7 and 6-9, respectively, indicating a chemistry typical of evolved hot cores where grain mantle evaporation has occurred. On the other hand, the high OH abundance, with OH/H2O ratios of ~0.5, indicates the effects of X-rays and/or cosmic rays. Very thick (N_H>~10^{25} cm^{-2}) nuclear media are responsible for the frequency degradation of the intrinsic luminosities, with surface brightnesses of >~10^{13} Lsun/kpc^2. While NGC 4418 shows weak absorption in H2^{18}O and ^{18}OH, the absorption of the rare isotopologues in Arp 220 indicates ^{18}O enhancement, with ^{16}O-to-^{18}O of 70-100. Further away from the nuclear regions, the H2O abundance decreases to <~10^{-7} and the OH/H2O ratio is reversed relative to the nuclear region to 2.5-10. Preliminary evidence is found for an evolutionary sequence from infall, hot-core like chemistry, and solar oxygen isotope ratio to high velocity outflow, disruption of the hot core chemistry and cumulative high mass stellar processing of ^{18}O.

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Blobrana


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Title: Optical spectroscopy of Arp220: the star formation history of the closest ULIRG
Authors: J.Rodriguez Zaurin, C.N. Tadhunter, R.M. Gonzalez Delgado

We present optical spectra of the merging system Arp 220,taken with the William Herschel Telescope(WHT) on La Palma. These data were taken with the aim of investigating the evolution and star formation history of this object. Spectral synthesis modelling has been used to estimate the ages of the stellar populations found in the diffuse light sampled by the spectra. The data show a remarkable uniformity in the stellar populations across the full 65 arcsec covered by our slit positions, sampling the measurable extent of the galaxy. The results are consistent with a dominant intermediate-age stellar population (ISP) with age 0.5 < t_{ISP} >= 0.9 Gyr that is present at all locations, with varying contributions from a young (>= 0.1 Gyr) stellar population (YSP) component. However, it is notable that while the flux contribution of the YSP component in the extended regions is relatively small (>= 40%), adequate fits in the nuclear region are only found for combinations with a significant contribution of a YSP component (22 - 63%). Moreover, while a low intrinsic reddening (E(B - V) ~ 0.3) is found for the ISPs in the extended regions, intrinsic reddening values as high as E(B - V) ~ 1.0 are required in the galactic centre. This clearly reflects the presence of a reddening gradient, with higher concentrations of gas and dust towards the nuclear regions, coinciding with dust lanes in the HST images. Overall, our results are consistent with models that predict an epoch of enhanced star formation coinciding with the first pass of the merging nuclei (represented by the ISP), with a further episode of star formation occurring as the nuclei finally merge together (represented by the YSP and ULIRG).

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Title: Arp 220 - IC 4553/4: understanding the system and diagnosing the ISM
Authors: W. A. Baan

Arp220 is a nearby system in final stages of galaxy merger with powerful ongoing star-formation at and surrounding the two nuclei. Arp 220 was detected in HI absorption and OH Megamaser emission and later recognized as the nearest ultra-luminous infrared galaxy also showing powerful molecular and X-ray emissions. In this paper we review the available radio and mm-wave observational data of Arp 220 in order to obtain an integrated picture of the dense interstellar medium that forms the location of the powerful star-formation at the two nuclei.

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Blobrana


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Arp 220
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Staring into the crowded, dusty core of two merging galaxies, NASA's Hubble Space Telescope has uncovered a region where star formation has gone wild.


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Credit NASA
Position (2000): R.A. 15h 34m 57s.21 Dec. +23° 30' 9".5

The interacting galaxies appear as a single, odd-looking galaxy called Arp 220. The galaxy is a nearby example of the aftermath of two colliding galaxies. In fact, Arp 220 is the brightest of the three galactic mergers closest to Earth. This latest view of the galaxy is yielding new insights into the early universe, when galactic wrecks were more common. The sharp eye of Hubble's Advanced Camera for Surveys has unveiled more than 200 mammoth star clusters. The clusters are the bluish-white dots scattered throughout the image.

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