The Lick-Index Calibration of the Gemini Multi-Object Spectrographs

Abstract

We present the calibration of the spectroscopic Lick/IDS standard line-index system for measurements obtained with the Gemini Multi-Object Spectrographs known as GMOS-North and GMOS-South. We provide linear correction functions for each of the 25 standard Lick line indices for the B600 grism and two instrumental setups, one with 0.5 ′′ slit width and 1×1 CCD pixel binning (corresponding to ∼ 2.5Å spectral resolution) and the other with 0.75 ′′ slit width and 2×2 binning (∼ 4Å). We find small and well-defined correction terms for the set of Balmer indices Hβ, Hγ A , and Hδ A along with the metallicity sensitive indices Fe5015, Fe5270, Fe5335, Fe5406, Mg 2 and Mgb that are widely used for stellar population diagnostics of distant stellar systems. We find other indices that sample molecular absorption bands, such as TiO 1 and TiO 2 , with very wide wavelength coverage or indices that sample very weak molecular and atomic absorption features, such as Mg 1 , as well as indices with particularly narrow passband definitions, such as Fe4384, Ca4455, Fe4531, Ca4227, and Fe5782, less robustly calibrated. These indices should be used with caution.

The Stellar Contents of Intermediate-mass Disk Galaxies in the Virgo Cluster. I. GMOS Spectra* † ‡

“…Indices in the same instrumental system are measured from model spectra, and compared with the observations in Section 6. Puzia et al (2013) examine the transformation of indices measured from GMOS spectra using the B600 grating into the Lick system. The B600 grating was used for the GMOS-N spectra of NGC 4305 and NGC 4620, thereby allowing a body of internally consistent indices to be selected from those examined by Puzia et al (2013) that enable reliable galaxy-to-galaxy and intergalaxy (i.e.…”

“…The transformation coefficients listed in Tables 4 (2 × 2 pixel binning; 0.75 arcsec slit) and 5 (1 × 1 binning; 0.5 arcsec slit) of Puzia et al (2013) can be used to identify indices that have a low sensitivity to spectral resolution. The GMOS-N spectra of NGC 4305 and NGC 4620 were recorded with a 1 arcsec slit, and thus have a lower resolution than those used to construct Table 4 of Puzia et al (2013). This difference notwithstanding, The different wavelength resolutions of the GS and GN spectra are obvious, and the shorter wavelength coverage of the GN spectra allows Hγ and Hδ to be detected.…”

“…These provide an independent measure of age, and so can be used to assess the influence of line emission on ages estimated from lower order Balmer lines. The entries in Tables 4 and 5 of Puzia et al (2013) indicate that Hγ A is a relatively robust index in terms of spectral resolution, and so it is measured in the GMOS-N spectra of NGC 4305 and NGC 4620.…”

THE STAR-FORMING HISTORIES OF THE NUCLEUS, BULGE, AND INNER DISK OF NGC 5102: CLUES TO THE EVOLUTION OF A NEARBY LENTICULAR GALAXY,,

“…The indices measured in NGC 5102 probe age (Hβ) and chemical composition (Mg 2 , Mgb, Fe5270, Fe5335). These indices sample some of the strongest absorption features in the visible part of the spectra of composite stellar systems, and have comparatively robust transformation properties (Puzia et al 2013). The Fe5270 and Fe5335 indices are averaged together for this study to boost the S/N ratio of the Fe features, and the mean index is referred to as < F e >.…”

A Gemini/Gmos Study of Intermediate Luminosity Early-Type Virgo Cluster Galaxies. I. Globular Cluster and Stellar Kinematics

“…Both grisms give a spectral resolution of R = 1688. (Puzia et al 2013) 2.3. Data Reduction The data reduction was performed by using the Gemini/GMOS IRAF package (Version 1.11).…”