SHARKS II. Optimising a near−infrared imaging survey for low surface brightness science
Zohreh Ghaffari (Instituto de Astrofísica de Canarias)
15 March 2023
There has been extraordinary progress in the study of the low surface brightness Universe in the optical range, but much less so from near-infrared (NIR) imaging surveys. We present an observing and data analysis pipeline for the SHARKS survey using the 4 m VISTA telescope, designed to preserve the faint light in galaxy outskirts. We place particular emphasis on the sky subtraction. We use new Ks -band imaging of the Virgo grand-design spiral galaxy NGC 4030 to illustrate the results of our pipeline, which creates a sky flat-field, removes the true sky representation at the observation time, and then uses weighted co-adds to remove spurious detections. Using the images and radial profiles, we show how we recover most of the NIR emission from the outskirts of this large galaxy which was missing from the previous more standard reduction methods. We quantify the differences between the standard and new reduction procedures, and outline how the new method can be used across the SHARKS survey. The shell disclosed the NGC 4030 in our reduction increases significantly the total reported stellar mass by 50%. The new prominent structure that reveals better the morphology thus improves the stellar mass measurements which is one of the goals of the NIR observations.
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