NEAR-INFRARED SPECTROSCOPY OF THE BLUE COMPACT DWARF GALAXY MARKARIAN 59

Abstract

We present near-infrared (NIR) spectroscopic observations of the blue compact dwarf (BCD) galaxy Markarian 59 (Mrk 59), obtained with the TripleSpec spectrograph mounted on the 3.5 m Apache Point Observatory telescope. The NIR spectrum of Mrk 59, which covers the 0.90 μm–2.40 μm wavelength range, shows atomic hydrogen, molecular hydrogen, helium, sulfur, and iron emission lines. The NIR data have been supplemented by a Sloan Digital Sky Survey optical spectrum. We found extinction in the BCD to be low (A(V) = 0.24 mag) and to be the same in both the optical and NIR ranges. The NIR light does not reveal hidden star formation. The H2 emission comes from dense clumps and the H2 vibrational emission-line intensities can be accounted for by photon excitation. No shock excitation is needed. A CLOUDY photoionization model of Mrk 59 reproduces well the observed optical and NIR emission-line fluxes. There is no need to invoke sources of ionization other than stellar radiation. The [Fe ii] 1.257 and 1.643 μm emission lines, often used as supernova shock indicators in low-excitation high-metallicity starburst galaxies, cannot play such a role in high-excitation low-metallicity H ii regions such as Mrk 59.