NGC 5907 and its stellar stream

Posted on 01/04/2022 

NGC 5907 (also known as the Splinter Galaxy or Knife Edge Galaxy) is a spiral galaxy located about 50 million light-years from Earth in the northern constellation Draco. It is a member of the NGC 5866 group.

NGC5907 was long considered a prototype example of a relatively isolated warped spiral.

In 2006, an international team of astronomers led by Dr. David Martínez Delgado, announced the presence of an extended tidal stream which surrounds the galaxy thus suggesting that gravitational perturbations induced by the progenitor of the stream may also be the cause of the deformation. 

My image is just a normal LRGB composition (with data collected last year) and processing focused on showing the details of the galaxy: the stream is not visible. However, this year I plan to accumulate more data to try to show the tidal stream.

Updated on 17/04/2022

The data gathered during 2021 from L filter was 31 x 900 s sub-exposures. In order to improve the captured signal, this year I decided to double both the exposure time and the number of exposures. 

Between January and April 2022, I managed to accumulate 60 x 1800 s sub-exposures. 

I have just finished processing them:

The colour image (top right) is a slightly improved version of the one presented two weeks ago, showing some more detail in the galaxy, but again...it does not show the stream: The reason is that the stream is actually very faint.

The second image gives an idea of how weak the signal is. It is the integration of the 60 x 1800 s sub-exposures, with only a histogram stretch (the stretch has been done with the default values of ScreenTransferFunction in PixInsight): The stream is only slightly visible.

The third image is the previous one, but heavily processed to make the stream stand out further against the background.

The last colour image is a combination of the 900 s and 1800 s data sets. In order to make it possible to display the stream, these images have been decomposed into their large-scale and small-scale components and processed separately.

The image has the background and other large-scale components mostly from the 1800 s image, and the stars and other small-scale components from the 900 s image. In order to highlight the stream against the background, a positive bias value has been applied to layers 8 and 9 of the large-scale component image (MultiscaleMedianTransform tool in Pixinsight).

Important clarification

I started my project on this image at the beginning of 2021.

Only very recently have I been informed that the publication of further scientific studies on this issue has stirred a controversy that has been hotly debated at conferences and in social media.

I was not aware of this controversy, and it is by no means my intention to participate in it.

As it should be obvious, I present the results obtained with "my" sky (Àger) and my equipment (a 150 mm aperture telescope and a STL11000M camera). Other observers with other equipment may have obtained different results.

Click on the images for a full size version, or go to the Gallery section for complete exposure details.