A Database of 2MASS Near-Infrared Colors of Magellanic Cloud Star Clusters

Abstract

The (rest-frame) near-IR domain contains important stellar population diagnostics and is often used to estimate masses of galaxies at low as well as high redshifts. However, many stellar population models are still relatively poorly calibrated in this part of the spectrum. To allow an improvement of this calibration we present a new database of integrated near-infrared JHK s magnitudes for 75 star clusters in the Magellanic Clouds, using the 2-Micron All-Sky Survey (2MASS). The majority of the clusters in our sample have robust age and metallicity estimates from color-magnitude diagrams available in the literature, and populate a range of ages from 10 Myr to 15 Gyr and a range in [Fe/H] from −2.17 to +0.01 dex. A comparison with matched star clusters in the 2MASS Extended Source Catalog (XSC) reveals that the XSC only provides a good fit to the unresolved component of the cluster stellar population. We also compare our results with the often-cited single-channel JHK photometry of Persson et al. (1983), and find significant differences, especially for their 30 ′′ -diameter apertures up to ∼ 2.5 mag in the K-band, more than 1 mag in J −K, and up to 0.5 mag in H −K. Using simulations to center apertures based on maximum light throughput (as performed by Persson et al.), we show that these differences can be attributed to near-IR-bright cluster stars (e.g., Carbon stars) located away from the true center of the star clusters. The wide age and metallicity coverage of our integrated JHK s photometry sample constitutes a fundamental dataset for testing population synthesis model predictions, and for direct comparison with near-IR observations of distant stellar populations.

IntegratedK-band spectra of old and intermediate-age globular clusters in the Large Magellanic Cloud

“…25 spatial sampling) centred on each cluster. We estimated the total light sampled by the central mosaic (24 × 24 ) for all clusters using the following equation and the 20 radius aperture K-band photometry: Pessev et al (2006) with aperture radius 20 , which matches reasonably well our central SINFONI mosaics; (6) sampled bolometric luminosity within the clusters central mosaics in L , computed following Eq. (1); (7) integration radius, to which we have added stars from the additional bright AGB star sample; (8), (9) and (10) photometry with the fixed aperture radius of 90 of Mucciarelli et al (2006).…”

“…The selected of addition bright stars outside the central mosaics are denoted with diamond symbols. Their photometry comes from the 2MASS Point Source Catalogue and magnitudes were dereddened following the same method as Pessev et al (2006) -extinction values were obtained from the Magellanic Clouds Photometric Survey (Zaritsky et al 1997) and adopting the extinction law of Bessell & Brett (1988). The slanted line in this figure represents the separation between oxygen-and carbon-rich giant stars of Cioni et al (2006).…”

“…We used the K-band grating, which covers the wavelength range from 1.95 to 2.45 μm at a dispersion of 2.45 Å/pix. The spectral resolution around the centre of the wavelength range is R 3500 (6.2 Å FWHM), as measured from arc The green circles and crosses represent the 20 radius aperture and the centre used in the photometry by Pessev et al (2006). The large yellow circles on the images of the intermediate age clusters (bottom row) illustrate the 90 radius aperture of Mucciarelli et al (2006).…”

“…Colour-magnitude diagram including all the objects in our observational sample. The photometry of the six GCs (coloured square symbols) comes from the catalogue by Pessev et al (2006). Data for the additional bright stars (diamond symbols) come from the 2MASS Point Source Catalogue (Skrutskie et al 2006).…”

“…8 with open circles. The large open symbols represent the colours, derived from 100 radius aperture photometry, the small open symbols from 20 radius aperture photometry from Pessev et al (2006). With blue lines we have overplotted SSP model predictions from Maraston (2005) for a Kroupa IMF and blue horizontal branch morphology.…”