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GALEX Diffuse UV Background

2. Presentation of our Observing Program's "Target One" Results

 2.01
First, please take another look at the remarkable FUV/NUV images of Target One
 2.02
The conventional view has been that most of the diffuse background is simply starlight scattered from dust. So, let us see at how these observations correlate with the amount of dust: first:
a map of the dust distribution for this target,
then, the correlation we find in the FUV image
and then, the correlation we find in the NUV image
 2.03
That first correlation, the one with FUV, looks pretty ratty, doesn't it? Well, in due course we are going to look at 14 more such correlations, and we will see that that is NOT typical. (It would happen in OUR target, wouldn't it!) Anyway, the Correlation Coefficient that appears in each figure shows the amount of correlation, which is NOT large. We will see that this is often found in Deep Imaging Survey images, and this discovery represents our first important result: the conventional view is wrong, and a large amount of diffuse UV background is NOT starlight scattered from dust!
 2.04
When you looked at the FUV and NUV images alternating, you could see little or no correlation between the two images. However, there is indeed some correlation. Let's look at it, first with no attempt to remove dust-scattered starlight (using our observed correlations of intensity with E(B-V):
      NO dust-scattered light removed
      Now, the dust-scattered starlight has been removed!
Not much difference! Very little flux has been removed. This, our own target, shows MUCH MORE FUV/NUV correlation than do the DIS targets that are dust free. Once again, just our luck!
 2.05
Here is a map showing where this target is located in the sky. (We recommend saving the map, and opening it in Adobe Acrobat.) The name, 859-2(3) EG165, is from our Voyager work. Our Voyager observation was made at the center of our circular GALEX target, and the Voyager spectrometer slit is shown. It is 0.1 by 0.8 degrees. The target was chosen to have extremely low dust content. The background of the figure was constructed by us from the data of Schlegel, Finkbeiner, and Davis (1998). A few Yale Bright Star Catalog stars are in the area.
 2.06
So, what is the bottom line? We observed this target with GALEX specifically because we had already observed the location with Voyager and seen: virtually nothing. (Here is the same Voyager spectrum as a PDF file). Let us compare with what we have just seen in the FUV and NUV with GALEX!
 2.07
We see that although Voyager detected nothing, with GALEX we do see a significant, structured, background radiation. Now, you will have seen the word "contaminated" in the NUV brightness levels. What does that refer to? It refers to the fact that there is significant amounts of zodiacal light in the NUV images (there is none in the FUV images).

So, how shall we proceed? Of course we want to thoroughly test our GALEX data to try to understand its origin. Is is simply instrumental, for example? Well, we presented our Target One first, simply because it is OUR target, and we like it, warts and all. However, before critically examining the origin of the radiation, we will present the details of two more targets: not from our program, but from Data Release One - Deep Imaging Survey. We have analyzed all 14 of these targets (see later in this site), but what we want to do now is present two of the BEST targets (much better than our Target One). So in the Next Section we will present a target that has a very large contribution by dust-scattered starlight, and in the following section, we will present a target that, well, ... is like our Target One, only better! Next Section

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