Documentation

The WiFeS Atlas of Galactic Globular cluster Spectra (WAGGS) is a project to obtain integral field spectroscopy of globular clusters in the Milky Way and its satellite galaxies. Details of the survey are presented in Usher et al. (2017). We note that we adopt a definition of globular clusters as any massive, gravitationally bound stellar clusters and as such we include a number of star clusters in the Large and Small Magellanic Clouds that are significantly younger than classical globular clusters.

The Science

Measuring the metallicity, age, chemical abundance and initial mass function of integrated galaxy light requires the use of stellar population synthesis models. Before these models can be used, they need to be tested with integrated field spectra of stellar populations with known properties. Globular clusters in Milky Way and its satellites provide such a population as their stellar populations are relatively simple and well understood, with ages and present day mass functions available from HST photometry while metallicities and abundances are available from high resolution spectra of individual stars.

Due to their high surface brightness, globular clusters can be used to study how galaxies form and evolve at much greater distances than individual stars. With integrated spectra of globular clusters in Milky Way and its satellite galaxies, spectra of extragalactic globular clusters can be compared with globular clusters with known properties in a model independent manner.

Integral field spectroscopy of globular clusters also allows for the globular clusters to be studied themselves. Metallicities, ages and chemical abundances can all be measured from the integrated spectra. The spatial resolved kinematics can be used to model the dynamics of globular clusters and measure mass-to-light ratios.

Using the techniques of Kamann et al. (2013) we are able to extract the spectra of individual stars from our datacubes. This allows us to measure the kinematics and chemistries of individual stars and to compare the resolved star results with those from integrate light over the same field-of-view.

The Sample

The present WAGGS sample includes 93 globular clusters in the Milky Way, 20 in the Large Magellanic Cloud, 8 in the Small Magellanic Cloud and 3 in the Fornax dwarf spheroidal. Our sample is the largest yet of integrated light spectroscopy of Milky Way globular clusters.

The sample spans a wide range of metallicities - from [Fe/H] = −2.4 to [Fe/H] = −0.1 and a wide range of ages - from 20 Myr to 13 Gyr. We also cover a wide range of galactocentric distances and globular cluster masses.

The project prioritised star clusters which have both high quality HST photometry and high resolution spectroscopy of multiple member stars. However, a third of our sample lacks published abundances from high resolution spectroscopy.

The Observations

We used the Wide Field Spectrograph (WiFeS) on the ANU 2.3 m telescope on 33 nights from January 2015 to September 2018. WiFeS is a dual arm integral field spectrograph with a field-of-view of 38 by 25 arcsec. We used two grating set-ups to cover the wavelength range of 3300 to 9000 Å at a resolution of Δ R / R = 6800. Our wavelength coverage and spectral resolution greatly exceeds previous studies.