Reflection off the wire bonds on the focal plane: No processing — Most of the reported shells are visible in the original FITS images without further processing, although many of them with difficulty. Elixir-LSB restores the true sky background to a flatness level lower than 0. It does not seem to be an extension of the hook Fig. It is caused by a strong local decrease in quantum efficiency. CCD characteristics per amplifier 2.

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Appendix A contains detailed images of all shells and other features found in the galaxy. We use the standard deviations of the Gaussian of After our observation, the galaxy becomes even more exceptional. The responses below are the average transmission.

Technical considerations to prepare MegaCam observations

We acknowledge support from the following sources: FITS extension Many keywords need to be updated as stated in the block added in the primary header; that same block of information is also added to each extension besides the update and addition of keywords. MegaCam filter set transmission and average CCD quantum efficiency. The median level of the overscan also changes slightly over long timescales say hours by as much as 10 ADUs for some amplifiers.


They can not be avoided and pretty much ruin any signal within the area of the halo, typically 7 arcminutes in diameter. The black dots indicate real photometry from various MegaCam fields.

Typical cosmic rays hits recorded on a long dark exposure. All of them are seen as very diffuse in the HST image. Note the wide gri filter in the 3rd generation. The red histograms show the megacxm distribution of the residuals in both directions. Press Release April 8, A summary of their properties are given in the Table below.

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Each CCD has a x pixels imaging area split into two x imaging areas as both chip’s amplifiers are used.

It is only a geometric change, the data remain unchanged in that process. A hook-like structure H in Figs. Their visibility benefits from some image processing for contrast improvement.

Current usage metrics About article metrics Return to article. Note megacqm extremely expanded scale for megcaam u-band. If the shell were to be discovered, it would be the first discovery of an object predicted by MOND, a test of MOND to exceptionally low gravitational acceleration for an elliptical galaxy, and the discovery of the biggest shell ever.

As a general note, notice that the upper half of the mosaic is flipped degrees in regard to the lower half.


We present a new table of shell radii and describe the other tidal features in the galaxy that can serve to constrain the gravitational potential e. However the sky brightness in these two bands depend greatly on the airmass. QE is in black, dot-dashed.

In a forthcoming paper, we will present a quantitative photometric analysis. This page follows the structure of the various sections found in the “General Summary” table and provides further details related to the impact they may have on an observing strategy.

The MegaPipe image stacking pipeline

The following characteristics were derived from transfer curves obtained with the LED internal calibration sources at the back of the MegaCam shutter. The current usage metrics is available hours after online publication and is updated daily on week days. This map was used subsequently for our tests. Prieur possibly confused the halves of the galaxy. Moreover, these methods implement a noise-smoothing step e.

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