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  • Star Clusters in Early-Type Galaxies

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    Introduction

    Data

      F225W F300W F330W F435W F450W F475W F555W F814W Cluster Detection Method/ Source Detection Threshold(s) Distance Modulus Minimum Log Mass for observability
    NGC 524 WFC3   ACS       WFPC2 WFPC2 Cross-Compare/ F555W: 45\(\sigma\) F330W: 6\(\sigma\) 32.10 2.9926
    NGC 2685 WFC3       WFPC2   WFPC2 WFPC2 Cross-Compare/ F555W: 45\(\sigma\) F450W: 40\(\sigma\) 30.57 1.81605
    NGC 2768 WFC3     ACS     WFPC2 WFPC2 Cross-Compare/ F555W: 45\(\sigma\) F336W: 40\(\sigma\) 31.38 2.27633
    NGC 3032 WFC3         WFC3 WFC3 WFC3 White light/ 5\(\sigma\) 30.48 1.83302
    NGC 3156 WFC3         WFC3 WFC3 WFC3 White light/ 50\(\sigma\) 31.50 2.04135
    NGC 3489 WFC3         WFC3 WFC3 WFC3 White light/ 200\(\sigma\) 29.60 1.68015
    NGC 4459 WFC3 WFPC2       WFC3 WFC3 WFC3 White light/ 200\(\sigma\) 31.02 2.10882
    NGC 4477 WFC3         WFC3 WFC3 WFC3 White light/ 100\(\sigma\) 31.34 2.32347
    NGC 4550 WFC3 WFPC2       ACS WFPC2 WFPC2 Cross-Compare/ F555W: 45\(\sigma\) F300W: 6\(\sigma\) 31.06 2.13877

    Source detection

    All images examined were from the Hubble Space Telescope’s MAST archive, using different filters and cameras for each galaxy depending upon availability of data; Filter and camera choice for each galaxy is shown in Table 1. On these images, two point source detection methods were used: The primary method used was the “white light” detection method as in (Kaviraj 2012). The other method was to compile separate source catalogs for the F555W filter and the filter closest to F336W using the PYRAF command DAOFIND and take the overlapping sources as the output catalog. This Cross-comparison method was used whenever the galaxy had a combination of too many different cameras and low source counts leading to an unusable white light image.

    Table Caption: This table details the information relevant to each individual galaxy surveyed. The central wavelengths of all filters used as well as the camera with which the image was taken motivated the choice of cluster detection method, where the presence of more than two different cameras in the sample led to difficulties in white light image creation. The source detection threshold in sigma above the background is included, as well as the distance modulus of the galaxy and the calculated minimum detectable mass of a cluster in that galaxy.