VLT L-band mapping of the Galactic center IRS 3-IRS 13 region - Evidence for new Wolf-Rayet type stars

This paper presents L -band ISAAC and NAOS/CONICA (VLT) spectroscopic observations of the IRS 3-IRS 13 Galactic Center region. The ISAAC data allowed us to build the first spectroscopic data cube of the region in the L -band domain. Using the L -band spectrum of the extinction along the line of sight towards the GC derived in a previous paper (Moultaka et al. 2004, A&A, 425, 529), it was also possible to correct the cube for the foreground extinction. Maps of the water ice and hydrocarbon absorption line strength were then derived. These maps are important diagnostics of the interstellar and circumstellar medium because water ices are observed in molecular clouds while hydrocarbons are usually good tracers of the diffuse ISM. These maps support our previous results that the absorption features most probably occur in the local Galactic center medium and can be associated with the individual sources. Moreover, turbulence seems to affect the studied region of the minispiral, which appears like a mixture of a dense and diffuse medium. Comparison of the concentrations of ice and hydrocarbon absorptions around IRS 13E, IRS 6E, and IRS 2, with similar concentrations at the location of the extended continuum emission around IRS 3, suggests that these sources might present outflows interacting with the surrounding ISM. It was also possible to derive Br α and Pf${\gamma}$ emission line maps. The results suggest that the physical conditions of the ISM are not uniform in the observed region of the minispiral especially at the edges of the minicavity. The emission line maps allowed us to find three sources with broad lines corresponding to an FWHM deconvolved line width of about 1100 km s -1 and moving towards us with a radial velocity of about -300 km s -1 . These sources are most probably new Wolf-Rayet type stars located in projection to the north and west of IRS 3. Their derived radial velocities and proper motions show that only two of them might belong to the two rotating disks of young stars reported by Genzel et al. (2003, ApJ, 594, 812) and Levin & Beloborodov (2003, ApJ, 590, L33). Previously, NAOS/CONICA (NACO) data allowed us to resolve the IRS13E3 region into two components E3N, and E3c (Eckart et al. 2004, ApJ, 602, 760). The new spectroscopic NACO data show that E3c is a good candidate for a Wolf-Rayet type star. In addition, three sources ( η , ζ , and γ ) out of the eight very red sources located in the IRS13N complex also presented in Eckart et al. (2004, ApJ, 602, 760) have been resolved spectroscopically with NACO. The spectra presented in this paper show that the red colors of the sources are probably due to extended dust emission.