Free Access
Volume 572, December 2014
Article Number A40
Number of page(s) 13
Section Extragalactic astronomy
Published online 26 November 2014

Online material

Appendix A: Properties H2 transitions

In this Appendix we provide the spectra and line fluxes derived from fitting two Gaussian components to the emission-line spectra of the various H2 transitions in regions A, B and C.

Appendix A.1: Method

For each of the seven H2 transitions in our SINFONI data we extracted an emission-line spectrum from a circular aperture of 13 spaxels centered around the peak flux in regions A, B and C (similar to what is shown in Fig. 1 for H2 10 S(1)).

As mentioned in Sect. 2, we used an IDL routine based on the MPFIT package to perform the line-fitting. We used a three-component model to simultaneously fit the continuum and both the narrow and broad component of the emission lines. The continuum was fitted using a linear term, whereas a Gaussian profile was used for each emission-line component.

As can be seen in Fig. A.1, the signal-to-noise of some of the lines is too low to derive accurate results when using this multi-component analysis without placing any constraints on the line-fitting procedure. To reduce the uncertainties of the fitting and obtain more robust measurements of the line fluxes, we assume that all transitions share the same kinematics. We first performed

the fitting routine on the strong 10 S(1) 2.1218 μm line without placing constraints on the line-fitting parameters. Subsequently, we used these results to fix the position and line width (both in km s-1) of the narrow and broad component of the other emission lines.

The uncertainties of the flux measurements were calculated using a Monte Carlo technique. This method consists of measuring the noise in the spectra as the root-mean-square of the residuals after the subtraction of our multi-component model. Taking this estimation of the noise into account, we construct a total of 500 independent simulations/realizations of the spectra, where the lines are again fitted. These simulations yield distributions of each free parameter of our model. The uncertainty of each parameter is then defined as the standard deviation of its corresponding distribution.

Appendix A.2: Results

In Fig. A.1 we show the results of the line-fitting procedure. In Table A.1 we summarize the line ratios for the broad and narrow component with respect to the flux of the 10 S(1) 2.1218 μm line. The upper limits are defined as 1-sigma detections, using the noise estimation from the Monte Carlo method described in Sect. A.1.

Table A.1

Flux ratios of the broad and narrow components of all seven H2 lines in our SINFONI data with respect to 10 S(1) in regions A, B and C.

thumbnail Fig. A.1

Emission-line spectra and 2-component Gaussian fit of the various H2 transitions in regions A, B and C. The spectra were extracted from a circular aperture of 13 spaxels, centered on the broad-component H2 feature in each region. The line width and shift between the peak of the narrow and broad component were constrained in velocity to those of the strong 10 S(1) line. A straight line was fitted to the continuum across a wide velocity range of −1800 to +1800 km s-1 in order to handle potential features in the continuum (see, e.g., the H2 10S(3) transition in region B). However, a smaller velocity range is plotted in the figures to high-light the details of the fits to the emission lines. After extracting flux measurements, for visualisation purposes the spectra in the plots were normalized to the fitted continuum.

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