Infrared Telescope Facility (IRTF) spectral library II: New indices in Y, J, H, and L atmospheric windows

Abstract

Stellar population studies in the infrared (IR) wavelength range have two main advantages with respect to the optical regime: they probe different populations, because most of the light in the IR comes from redder and generally older stars, and they allow us to see through dust because IR light is less affected by extinction. Unfortunately, IR modeling work was halted by the lack of adequate stellar libraries, but this has changed in the recent years. Our project investigates the sensitivity of various spectral features in the 1--5\,$\mu$m wavelength range to the physical properties of stars ($T_{eff}$, [Fe/H], log g and aims to objectively define spectral indices that can characterize the age and metallicity of unresolved stellar populations. We implemented a method that uses derivatives of the indices as functions of $T_{eff}$, [Fe/H] or log g across the entire available wavelength range to reveal the most sensitive indices to these parameters and the ranges in which these indices work. Here, we complement the previous work in the I and K bands, reporting a new system of 14, 12, 22, and 12 indices for Y, J, H, and L atmospheric windows, respectively, and describe their behavior. Our analysis indicates that features sensitive to the effective temperature are present and measurable in all the investigated atmospheric windows at the spectral resolution and in the metallicity range of the IRTF library for a signal-to-noise ratio greater than 20-30. The surface gravity is more challenging and only indices in the H and J windows are best suited for this. The metallicity range of the stars with available spectra is too narrow to search for suitable diagnostics. For the spectra of unresolved galaxies, the defined indices are valuable tools in tracing the properties of the stars in the IR-dominant stellar populations.

arXiv commentA&A in press. 69 pages, 47 figures, 8 Table

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Cited by in corpus (8)

• New infrared spectral indices of luminous cold stars: from early K to M-types
• Fingerprints of Stellar Populations in the Near-Infrared: An Optimised Set of Spectral Indices in the JHK-Bands
• Near-infrared spectroscopic indices for unresolved stellar populations. II. Index measurements
• TP-AGB stars and stellar population properties of a post-starburst galaxy at $z\sim 2$ through optical and NIR spectroscopy with JWST
• $H$-band Temperature and Metallicity Indicators for Cool Giants: Empirical Relations in Bayesian Framework
• Infrared Spectroscopy of Nearby Radio Active Early-Type Galaxies -- II: Spectral Atlas
• Supermassive black holes and nuclear star clusters in galaxies: constraining formation and co-evolution with SHARP and MICADO
• SPAN: A cross-platform Python GUI software for optical and near-infrared spectral analysis