Field Galaxy NGC 2903, Satellite Galaxy UGC 5086, and Three Quasars, Leo

NGC 2903 is a barred spiral galaxy in the constellation of Leo, first documented by William Herschel in 1784. Although it is bright and fairly large, easily seen in binoculars, it escaped the attention of Charles Messier and his associate Pierre Mechain. On a large scale, NGC 2903 lies within the Virgo Supercluster which includes the Milky Way and Andromeda galaxies. Except for dwarf elliptical galaxy UGC 5086, at a distance of 2 million ly, it has no near neighbors, and does not belong to any local galaxy cluster. Such isolated galaxies, undisturbed by gravitational fields of large neighbors, are called "field galaxies", constitute 10-20% of the total galaxy population, and follow different evolutionary pathways than "cluster galaxies". Unaffected by major tidal forces and mergers, large field galaxies are most commonly low-surface-brightness (LSB) spirals with delicate and symmetrical spiral arm structure, and usually with low star formation rates (SFR). However, NGC 2903 is far from quiescent. Although its energy output is insufficient to qualify it as an active galactic nucleus (AGN), the nucleus is still bright in all bands, from radio waves to X-rays, suggesting the presence of a central supermassive black hole (SMBH) with polar jets and an accretion disk. Photometric and spectroscopic analysis of the central region reveals increased star formation rates generated by interstellar medium turbulence initiated by radiation pressure and feedback outflows from the central SMBH. The turbulence then extends outward, augmented by stellar winds and supernovae, enhancing new star formation further afield. The distinct blue floccules in the spiral arms represent "OB associations", huge clusters of very hot young stars. <a href="https://www.cloudynights.com/articles/cat/articles/basic-extragalactic-astronomy-part-9-supermassive-black-hole-and-host-galaxy-coevolution-r3312" rel="noreferrer nofollow">www.cloudynights.com/articles/cat/articles/basic-extragal...</a>

From its measurable properties it can be calculated that NGC 2903 is about 26 million ly distant, and 100,000 light years in diameter, roughly 30% smaller than the Milky Way, and proportionally less luminous. Several interesting features within the galaxy are marked on the annotated image. Some sources define object NGC 2905 as a bright region near the nucleus, at the S end of the bulge. Opinions differ whether the object is a large collection of stars or a very hot ionized hydrogen (Hii) region. Meanwhile, both NED and SIMBAD extragalactic databases list NGC 2905 simply as a duplicate identifier for the main galaxy, NGC 2903. At the NE extremity of the galaxy there is evidence of a curved luminous region which does not seem to be a part of the spiral arm. I speculate it may be a small satellite galaxy in the process of merging, stretched into a "stellar stream" by the tidal forces of the main galaxy. Computer models show that stellar streams can persist through multiple galactic orbits, for billions of years, before they are ultimately dispersed into anonymity. Gaps in stellar streams are thought to be caused by encounters with dark matter overdensities (subhalos) within the galactic halo. At the W perimeter of the galaxy, ULX marks the location of an ultra-luminous X-ray source. Such objects can be associated with intermediate-mass black holes (IMBH), and may emit optical transients during the periods of more active accretion. <a href="https://www.cloudynights.com/articles/cat/articles/basic-extragalactic-astronomy-part-5-black-holes-and-quasars-r3233" rel="noreferrer nofollow">www.cloudynights.com/articles/cat/articles/basic-extragal...</a>

Numerous distant galaxies are visible on close inspection of the background, many of which have no identifier. Of the more prominent ones, the most formidable is SDSS J093239.53+214555.7, a hyperluminous giant galaxy, at least 160,000 ly in diameter, lying at a distance around 3.2 billion ly. Near the threshold of the limiting magnitude are seen three quasars (QSOs) listed in the chart below. The most remote is QSO B0929+2128, nearly 3,000 times brighter than the Miky Way, whose light travelled 10.9 billion years before reching us. When its photons were emitted, the quasar was receding at 251,428 km/s (relativistic or redshift recession velocity). In the present epoch, it lies at a "comoving = proper distance" of 18.7 billion ly, receding at a superluminal "proper recession velocity" of 405,052 km/s. The quasar is now located well beyond the "cosmic event horizon". Since the space between us is expanding faster than its light is moving toward us, the photons it is presently emitting can never reach us.

Image details: -Remote Takahashi TOA 150 x 1105mm, Paramount GT GEM -27 x 300 sec subs, OSC, 2x drizzle, 50% linear crop