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NGC3718: A Qualitative Analysis

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The first step in the analysis of the NGC3718 NIR data is to align the J , H , and K S images.
Due to the absence of secondary sources in the FoV, I choose an alignment method based on fitting ellipses on the isophote contours of NGC3718. For this, the Image Reduction and
Analysis Facility’s (IRAF)19 ellipse task was used, which fits ellipses on the iso-intensity contours of the light distribution of a galaxy. In figure 2.4, I plot the X cent er and Ycent er coordinates, as indicated by each fitted ellipse versus its semi-major axis (SMA).
With the exception of the J band X cent er coordinate and the K S band Ycent er coordi- nate, the rest of the curves are close to what would be normally expected20 . The behavior of the J band is, likely, the result of its lower total flux (i.e. F J ) compared to the fluxes of the …show more content…

This is mainly because the dom- inant stellar population is comprised of old K/M type stars21 and, partly, also due to the lower total integration time of the J band (t J = 300 sec, t H = 660 sec and tK S = 720 sec). In turn, the lower flux leads to noisier isophote contours and, therefore, to higher uncertain- ties. The dust lane of NGC3718 is not expected to affect the central NIR light distribution to a large extent, mainly because its projection lies relatively far from the center (see section
2.4 and appendix B). Moreover, both in terms of structural size and illumination, the dom- inant component seen in the NIR images should be the stellar bulge of the galaxy, which appears to be largely relaxed, as the absence of large-scale contour deformations and the nearly round contour shape22

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