Imaging Arp 220 in CO 6-5 and dust at 100 pc resolution with ALMA

1. West Nucleus East Nucleus SiO absorption 5085 km/s 5135 km/s 5185 km/s 5235 km/s 5285 km/s 5335 km/s 5385 km/s 5435 km/s 5485 km/s 5535 km/s 5585 km/s 5635 km/s Imaging Arp 220 in CO 6-5 and dust at 100 pc resolution with ALMA C. Wilson, (McMaster); N. Rangwala, J. Glenn, P. Maloney, J. R. Kamenetzky (Colorado); M. P. Santaella, L. Spinoglio (INAF-IAPS); M. Schirm (McMaster) A toy model of Arp 220 Arp 220 is the closest example of an Ultraluminous Infrared Galaxy, with a star formation rate over 100 times that of our Galaxy. Its 1010 Mo of molecular gas is concentrated within 1 kpc of the center and has been observed extensively with high angular resolution (CO 6-5: Matsushita et al. 2009; CO 3-2: Sakamoto et al. 2008; CO 2-1: Konig et al. 2012; CO 1-0: Downes & Solomon 1998). A complete spectrum from 200 to 600 m with Herschel revealed 10% of this molecular gas is hot (1300 K) and the dust optical depth is 1 at 250 m (Rangwala et al. 2011). In December 2012, we mapped Arp 220 in CO J=6-5 and 430 m continuum with the Atacama Large Millimeter/submillimeter Array. Our data resolve the dust continuum emission from the two individual nuclei and reveal an unusual offset between the CO J=6-5 and the continuum emission. The kinematics in each nucleus are consistent with an inclined rotating ring (top right). We also detect CO absorption at extreme redshifted velocities as well as absorption by SiO J=16-15 towards the western nucleus. Figure 1: (left) CO J=6-5 integrated intensity (color) and 430 m continuum flux (contours) of Arp 220 obtained with ALMA. The resolution is 0.44”x0.22” (170x85 pc). Note the offset between the CO and dust peaks, which has not been observed before in Arp 220. (middle) CO J=6-5 velocity dispersion () with continuum contours. The peak dispersions are found at the two continuum peaks. (right) CO J=6-5 emission and absorption (contours) overlaid on the 430 m continuum image. Absorption (dashed contours) is seen in the extreme redshifted velocity channels. CO 6-5 line emission (color) and dust emission (contours) Figure 2: (center) velocity field of Arp 220 with 430 m continuum contours. Black lines show the location and orientation of the position velocity slices. (left) Velocity versus position through the eastern nucleus. The morphology is generally consistent with a rotating ring of CO emission. (right) Velocity versus position through the western nucleus. Again the dominant signature is of a rotating ring, but emission at forbidden velocities and extreme blue-shifts is also seen, as is absorption from SiO J=16-15. Arp 220: Distance = 77 Mpc (1” = 370 pc) L(FIR) = 2x1012 Lo Nuclei separation = 400 pc F(400m) = 7.6 Jy M(H2) = 1010 Mo (10% of H2 in warm gas) + + - - Figure 3: channel maps of CO J=6-5 emission around the eastern nucleus of Arp 220. White contours show the position of the continuum peak. Note the hole in the map at 5335 km/s, which suggests a lack of CO 6-5 emission in the nucleus itself. Emission associated with the western nucleus can be seen towards the west edge of the field of view in the first 8 channels. • r(FWHM): deconvolved from synthesized beam • Mgas: from continuum flux assuming Tdust=67 K, dust emissivity at 435 m of 5.2 cm2/g (Planck Collaboration 2011), and gas/dust=100 • gas: assumes source radius = 65 pc References: Downes & Solomon 1998, ApJ, 507, 615; Konig et al. 2012, ApJ, 754, 58; Matsushita et al. 2009, ApJ, 693, 56; Planck Collaboration 2011, A&A, 536, 25; Rangwala et al. 2011, ApJ, 743, 94; Sakamoto et al. 2008, ApJ, 684, 957