Evidence for a warm interstellar medium in the Fornax dwarf ellipticals FCC046 and FCC207

We present Hα+[N ii] narrow-band imaging of FCC046 and FCC207, two dwarf ellipticals (dES) in the Fornax cluster. B—R and B—I colour maps clearly show signs of dust absorption in FCC207. FCC046 has a very bright blue nucleus, offset by about 1.1 arcsec with respect to the outer isophotes. FCC046 was classified as a non-nucleated dE4 so the presence of its nucleus came as a surprise. Moreover, FCC046 shows a pronounced lopsided shape. Given that FCC046 is an isolated galaxy, it is unlikely that an encounter caused this asymmetry. The emitting regions differ considerably between the two galaxies. Whereas FCC207 has only one central emission region, FCC046 also contains fainter emission regions. Based on broad-band colours, its disturbed shape and its very bright nucleus, FCC046 is akin to the class of amorphous dwarfs. The central emission regions of both galaxies are barely resolved under seeing conditions of FWHM ≈0.8 arcsec and we estimate their diameters at about 60 pc. Their Hα luminosities can be explained as photoionization by post asymptotic giant branch stars in an old population. Some of the fainter extended emission regions in FCC046 are resolved and have diameters of the order of 50–150 pc and Hα luminosities of the order of 1030 W, comparable to supernova remnants or nebulae around Wolf—Rayet stars. Hence, FCC046 is clearly undergoing star formation while for FCC207 the case is not as clear-cut. We estimate the mass of the H ii gas in FCC046 at MHii= 40–150 M⊙ (for T= 104 K, Ne= 1000 cm−3). The ionized-gas content of FCC207 is somewhat higher: MHii= 60–190 M⊙.