NGC7013 and Galactic Cold Clumps

This image exhibits a fascinating juxtaposition.  The dominant feature in the upper right quadrant is a molecular cloud complex that is within the bounds of our Milky Way Galaxy.  Through an open area beneath the cloud, a distant galaxy, NGC7013, shines through.  These are the two major subjects of the image, but there are interesting nuances.

In the Milky Way the vast regions in between stars, known as the interstellar medium, is seemingly empty space but actually contains atoms in very low density, mostly hydrogen and helium.  In some areas these atoms are compressed into interstellar clouds.  When such clouds are dense enough that molecules form, they are known as molecular clouds.  The most common component of these clouds is molecular hydrogen (H2), but other organic compounds (dust) can also be found.  Molecular clouds are regions in which new stars are formed, and are fundamental to the life cycle of galaxies.

Molecular clouds are typically very cold.  In 2015 a catalog of so-called galactic cold clumps was published based on observations from the Planck satellite mission (https://www.aanda.org/articles/aa/full_html/2016/10/aa25819-15/aa25819-15.html).  Two clumps from this catalog comprise sections of the large interconnected cloud seen in this image.  These are designated as PGCC G075.46-11.06 and PGCC G075.24-10.99.  The former has an estimated temperature of 13.464K and the latter 14.419K, so barely above absolute zero.  The study of these extremely cold regions provides insight into the very earliest stage of new star formation.

I have spent hours trying to learn basic information about the molecular cloud seen in this image.  How far away is it?  How large is it?  What is its mass?  I have not found the answers!  If anyone reading this can point to a source, I would appreciate it.  Even more troubling is the fact that I do not know what is illuminating this molecular cloud to the extent that I was able to capture it in this image.  Many molecular clouds are dark blobs that are seen only as they obscure light from other sources.  So, I suspect this cloud may be illuminated by the combined light of our Milky Way galaxy, similar to nebulae known as Integrated Flux Nebulae, but it is also possible that the illumination is provided by several nearby stars.

You will note that the color of the molecular cloud in my image is largely pale blue.  I did not alter the color, but only increased color saturation in processing, so this is what the sensor in my camera detected.  Whether this sheds “light” on the illumination question is unclear.

The primary galaxy in the image, NGC7013, is classified as either a spiral galaxy or a lenticular galaxy (a galaxy somewhere between spiral and elliptical).  My image shows weak spiral structure, so perhaps it is slowly evolving into an elliptical.  The nucleus of NGC7013 is active and so NGC7013 is also classified as a low-ionization nuclear emission-line region galaxy (LINER).  Some sources mention a perceived ring structure for NGC7013, with the inner core region disconnected from the ill-defined spiral structure, but my image seems to show more connecting material, so I am not sure this is truly a ring galaxy.  The stars seen in the image - in particular those which overlap the galaxy - are foreground stars within our Milky Way Galaxy and are far closer to Earth than NGC7013, which lies at an estimated distance of 37 to 41.4 million light years.  At this distance the galaxy would be an estimated 42,000 light years in diameter.  The bright yellow star overlapping the upper portion of the halo is HD 335465, a magnitude 9.88 star located 48 light years from Earth.  Also, note the bright knot located at the bottom of the halo (opposite side from HD 335465).  This is galaxy PGC1881063 and it is estimated to be some 929 million light years distant; so it lies far beyond NGC7013 and its light struggles to pierce through the edge of NGC7013’s outer halo.  There are several other distant galaxies scattered throughout the image.

The data for this image were obtained over four nights in late July, 2022 at my private observatory in eastern Washington.  It was a taxing experience, as daytime temperatures reached 113 degrees F during my entire stay, and I had only a fan to stir the air in my living quarters.  But, the nights were clear and atmospheric seeing was pretty good.  This is the last set of image data that I acquired with the venerable SBIG 11000M CCD camera before I replaced it.  The sensor had numerous age-related problems that required extra work to manage during image processing.  I hope you will enjoy the result of my labors.