Near‐infrared spectroscopy of stellar populations in nearby spiral galaxies

We present high spatial resolution, medium spectral resolution near-infrared (NIR) H- and K-band long-slit spectroscopy for a sample of 29 nearby (z < 0.01) inactive spiral galaxies, to study the composition of their NIR stellar populations. These spectra contain a wealth of diagnostic stellar absorption lines, e.g., Mg i 1.575 μm, Si i 1.588 μm, CO (6–3) 1.619 μm, Mg i 1.711 μm, Na i 2.207 μm, Ca i 2.263 μm and the 12CO and 13CO bandheads longward of 2.29 μm. We use NIR absorption features to study the stellar population and star formation properties of the spiral galaxies along the Hubble sequence, and we produce the first high spatial resolution NIR HK-band template spectra for low-redshift spiral galaxies along the Hubble sequence. These templates will find applications in a variety of galaxy studies. The strength of the absorption lines depends on the luminosity and/or temperature of stars and, therefore, spectral indices can be used to trace the stellar population of galaxies. The entire sample indicates that the evolved red stars completely dominate the NIR spectra, and that the contribution from hot young stars is insignificant.