GeminiFocus December 2012 | Page 19

The SAURON IFU data for this object were taken as part of the wider ATLAS3D which attempts to understand the formation and evolution of red-sequence galaxies (Cappellari et al., 2011). The SAURON data only provide H-beta, [O III] and faint [N I] lines — insufficient to securely characterize the ionized gas properties. We therefore used the GMOS IFU (2-slit mode) to obtain complementary data around the H-alpha line, making a mosaic of four pointings. The coverage of the two IFU data sets can been seen in Figure 1. A Surprise Finding While analyzing the data, we encountered our first surprise: the ionized gas lines had strange profile shapes, implying that at least two ionized gas components exist along each line of sight. After carefully separating these lines to ensure a robust determination of the ionized gas kinematics of each component, we found that one of them traced the outflow, which emerges in the galaxy’s polar plane. The ionized gas in this outflow pushes outwards at speeds of up to 800 kilometers per second (kms), ensuring it will leave its host galaxy entirely, enriching the intergalactic medium with metals. The second ionized gas component extends to larger radii, and appears bound to the galaxy, but its origin is unclear. It may simply reflect unrelated gas components at different locations along the line of sight, or it may be a coherent rotating structure that has been disturbed by the outflow. Figure 2 shows the GMOS view of these components. December2012 In addition to the ionized gas, the GMOS data also shed light on the kinematics of the neutral atomic gas in this system — thanks to the detection of absorption lines caused by sodium atoms in the gas phase, visible after careful subtraction of the stellar absorption spectrum. Alatalo et al. (2011) detected atomic hydrogen in absorption in NGC 1266, and our GMOS observations confirmed that the outflow is indeed expelling neutral gas from the galaxy at speeds up to 500 kms. As we view the gas projected against the galaxy’s starlight, we were able to use the observed sodium (Na D) absorption profiles to set constraints on the size and orientation of the outflow. The results show well-correlated neutral and molecular outflows along a slightly different axis to the ionized gas. The cause of this effect is unclear. High-resolution radio observations of NGC 1266 reveal it to have a small asymmetric double radio jet. Alatalo et al. (2011) hypothesized that the AGN is driving this nascent structure into the extremely dense molecular ISM surrounding it, causing the outflow. GeminiFocus Figure 3. An example BPT-type diagram — which demonstrates how LINERs can be distinguished from normal H II regions and normal AGNs — for the inner part of NGC 1266. The Y-axis shows the [O III]/H-beta ratio derived from SAURON data, and it is plotted versus the [S II]/H-alpha line ratio from GMOS observations. In the bottom right of the plot is the typical error bar associated with each point. Overplotted are diagnostic lines, which indicate the dominant line excitation mechanism. 19