Ionised Gas in Early-type Galaxies with SAURON

In Sarzi et al. (2006, MNRAS, 366, 1151) the SAURON team have shown that extended ionised-gas emission is found in 75% of early-type galaxies, and comes with a variety of spatial distributions, kinematic behaviours, and line ratios. Dust absorption features were found to be always associated with nebular emission, and the stellar and gaseous kinematics were often found to be decoupled. The following picture vividly illustrates these results, which were achieved thanks to the high quality of the SAURON data and to a novel procedure to accurately separate the stellar and emission-line contribution to the observed spectra.

This procedure is available as an IDL code called GANDALF (Gas AND Absorption Line Fitting), and can be found here . Please send me a little e-mail so that I can keep you updated of upcoming versions of the code and warn you of any bug I come across.

The present version (v1.4) includes reddening by interstellar dust (the use of which is illustrated with SDSS data) and also returns formal errors on the position, width, amplitude and flux of the emission lines. In the present release you will find example wrappers that will make use of the pPXF code of Cappellari & Emsellem (2004) to derive the stellar kinematics. If you decide to use this code for this purpose, please acknowledge their work as well.

Figure 1: SAURON maps for four galaxies representative of the gas properties in the 48 E and S0 galaxies surveyed by the SAURON project (de Zeeuw et al. 2002, MNRAS, 329, 513). From top to bottom: (i) the reconstructed total intensity, (ii) the stellar velocity, (iii) the ionised-gas velocity, (iv) the equivalent width of the [OIII] emission line in Angstroms (in log units), (v) the value of the [OIII]/Hb ratio (also in log units), and (vi) unsharp-masked images obtained from HST observations. The cuts levels are indicated in the box at the right-hand side of each map. The grey boxes on the top figures indicate the field-of-view of the HST images in the last row. Notice how the gas distribution can vary from galaxy to galaxy, and how the kinematic major axis of the ionised gas deviates from that of the stars. The [OIII]/Hb ratio maps clearly reveal the presence of radial gradients and substructures in the ionisation properties of the gas. The low [OIII]/Hb values corresponding to the dust disk in NGC 4526 suggest ongoing star formation.

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Last modified: Tue Aug 28 10:26:33 GMT 2006