Edge-On Spiral Galaxy in Draco

Click here for higher-resolution versions:  full resolution (3956x3966)  65% (2571x2577)  40% (1582x1586)
Click on image to toggle between the image and a negative showing the star trail described below


NGC5907: This is a somewhat dim (magnitude 11.28) spiral galaxy in Draco, presenting to us edge on. It is generally estimated to be about 50 million light years from Earth, and about 150,000 light years in diameter (somewhat larger than our Milky Way galaxy).

A few years ago, a highly-skilled amateur named R. Jay GaBany discovered very faint trails looping around this galaxy, now thought to be evidence of a death dance between a dwarf galaxy and this galaxy; this took place over a period of about 4 billion years, and resulted in the dwarf galaxy being absorbed into NGC5907. I was curious whether I could capture those trails, called "tidal tails," and, indeed, I was able to get one loop (which, probably not coincidentally, is very elliptical in shape, with the center of NGC5907 very close to one focus of that ellipse). If you click on the image, it will toggle to a negative image of the field; the loop to the right of the galaxy is that tidal tail.

Astronomers long had known that this galaxy was warped (not perfectly flat, as would be expected), but they did not know why; NGC5907 was thought to be an example of a warped galaxy in isolation (meaning that there was no other significant galaxy close by to warp it with gravitational pull). Jay GaBany's discovery changed all that.

As an aside, I think it's really cool that astronomy is a science in which true amateurs still regularly make significant discoveries! As I have noted on other images, I am always charmed by the huge number of small background galaxies in my images. This one has that even more than most; in particular, there is a whole group of galaxies at the top of the image just to the right of center (it's easier to tell they're not stars in the larger images).

This is the second time I have imaged this target. I had imaged it nineteen years earlier from my yard. If you want to compare that image to this one (to see what much darker skies, better equipment, and (hopefully) more skill can do, click here.


Technical Information:

LRGB: 1170:180:180:240 (that's almost 30 hours of exposure time; I also took ten hours of hydrogen-alpha exposures, but they added nothing, so I did not use them in the final image). The luminance layer is the combination of thirty 15-minute images and twenty-four 30-minute images (done to maximize the chances of capturing the star trail, and to be able to use HDR processing to avoid blowing out the bright areas with the long exposures); the red channel and green channel both consiste of the combination of twelfe 15-minute images, and the blue channel is the combination of twelve 20-minute exposures. All subexposures were unbinned.

Equipment: RC Optical Systems 14.5 inch Ritchey-Chretien carbon fiber truss telescope, with ion-milled optics and RCOS field flattener, at about f/9, and an SBIG STX-16803 monochrome camera with internal filter wheel (SBIG filter set), guided by an SBIG AO-X, all riding on a Bisque Paramount ME German Equatorial Mount.

Image Acquisition/Camera Control: Maxim DL, controlled with ACP Expert/Scheduler, working in concert with TheSky X Professional Edition.

Processing: All images calibrated (darks, bias and sky flats), aligned, combined and cropped in Pixinsight. RGB Color combine in Pixinsight. Some finish work (background neutralization, color calibration, HDR Mulitscale Transform and Multiscale Linear Transform of luminance data for both noise reduction and sharpening)) done in Pixinsight; LRGB combination and some further finish work was done in Photoshop CC.

Location: Data acquired remotely with my equipment hosted by Sierra Remote Observatories, Auberry, California, USA.

Date: Images taken on many nights in June, July and August of 2021. Image posted August 20, 2021.

Date: Image scale of full-resolution image: 0.56 arcseconds per pixel.

Seeing: Generally excellent, with individual calibrated luminance frames varying from 1.4 to 1.8 arcsecond FWHM.

CCD Chip temperature: -25C

Copyright 2021 Mark de Regt

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