back to [[TOP PAGE>Dusty Extreme Starburst Galaxies in the Early Universe]]
* global properties of ISM [#w795f84c]
** Rangwala et al. 2011, ApJ, submitted (arXiv:1106.5054) [#td493a70]
http://adsabs.harvard.edu/abs/2011arXiv1106.5054R
- We present Herschel SPIRE-FTS observations of Arp~220, a nearby ULIRG. The FTS continuously covers 190 -- 670 microns, providing a good measurement of the continuum and detection of several molecular and atomic species.
- We detect luminous CO (J = 4-3 to 13-12) and water ladders with comparable total luminosity; very high-J HCN absorption; OH+, H2O+, and HF in absorption; and CI and NII. Modeling of the continuum yields warm dust, with T = 66 K, and an unusually large optical depth of ~5 at 100 microns.
- Non-LTE modeling of the CO shows two temperature components: cold molecular gas at T ~ 50 K and warm molecular gas at T ~1350 K. The mass of the warm gas is 10% of the cold gas, but dominates the luminosity of the CO ladder. The temperature of the warm gas is in excellent agreement with H2 rotational lines. At 1350 K, H2 dominates the cooling (~20 L_sun/M_sun) in the ISM compared to CO (~0.4 L_sun/M_sun).
- We found that only a non-ionizing source such as the mechanical energy from supernovae and stellar winds can excite the warm gas and satisfy the energy budget of ~20 L_sun/M_sun.
- We detect a massive molecular outflow in Arp 220 from the analysis of strong P-Cygni line profiles observed in OH+, H2O+, and H2O. The outflow has a mass > 10^{7} M_sun and is bound to the nuclei with velocity < 250 km/s.
- The large column densities observed for these molecular ions strongly favor the existence of an X-ray luminous AGN (10^{44} ergs/s) in Arp 220.
** González-Alfonso et al. 2011, A&A, submitted. [#z1d88bca]
http://arxiv.org/abs/1109.1118
- 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 Mdot<~12 Msun 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.
* high angular resolution observations of gas and dust [#d66f1427]
** Engel et al. 2011, ApJ, 729, 58 [#k01538cb]
http://adsabs.harvard.edu/abs/2011ApJ...729...58E
- We analyze new spatially resolved integral field spectroscopic H- and K-band data at a resolution of 0farcs3 (100 pc) and reanalyze interferometric CO(2-1) line observations of the prototypical merging system Arp 220. We find that the majority of the K-band luminosity is due to a 10 Myr old starburst, with a significant contribution from an underlying gsim1 Gyr old stellar population and a small contribution from stars lsim8 Myr old. The Calzetti et al. reddening law provides the best fit to photometric data points spanning 0.45-2.12 μm. Furthermore, estimates of the bolometric luminosity from IRAS fluxes in conjunction with our stellar population analysis indicate that we observe less than 10% of the emitted K-band light. The stellar and CO(2-1) kinematic center of the western nucleus coincides with the compact hot dust emission, indicating that the latter marks the center of the gravitational potential. In the eastern nucleus, the CO(2-1) data are well matched by a model in which the gas orbits around the peak of the dust emission. This, and the similarity of the K-band tracer kinematics, shows that despite the irregular morphology, the eastern nucleus is also a kinematically coherent structure. Comparison of the extinction map with EWCO and EWBrγ maps indicates that the lower half of the eastern nucleus is significantly more extincted than the upper half, suggesting that the lower half is buried in the larger scale gas disk.
* radio observations: AGN or SNRs? [#s06e239a]
** Bateja et al. 2011, ApJ, 740, 95 [#kc9c498a]
http://adsabs.harvard.edu/abs/2011ApJ...740...95B
- We present 2 cm and 3.6 cm wavelength very long baseline interferometry images of the compact radio continuum sources in the nearby ultra-luminous infrared galaxy Arp220. Based on their radio spectra and variability properties, we confirm these sources to be a mixture of supernovae (SNe) and supernova remnants (SNRs). Of the 17 detected sources we resolve 7 at both wavelengths. The SNe generally only have upper size limits. In contrast all the SNRs are resolved with diameters >=0.27 pc. This size limit is consistent with them having just entered their Sedov phase while embedded in an interstellar medium (ISM) of density 104 cm-3. These objects lie on the diameter-luminosity correlation for SNRs (and so also on the diameter-surface brightness relation) and extend these correlations to very small sources. The data are consistent with the relation LvpropD -9/4. Revised equipartition arguments adjusted to a magnetic field to a relativistic particle energy density ratio of 1% combined with a reasonable synchrotron-emitting volume filling factor of 10% give estimated magnetic field strengths in the SNR shells of ~15-50 mG. The SNR shell magnetic fields are unlikely to come from compression of ambient ISM fields and must instead be internally generated. We set an upper limit of 7 mG for the ISM magnetic field. The estimated energy in relativistic particles, 2%-20% of the explosion kinetic energy, is consistent with estimates from models that fit the IR-radio correlation in compact starburst galaxies.
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