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Interacting Galaxies NGC 3718 and NGC 3729, Hickson 56, Ursa Major, Annotated
Interacting Galaxies NGC 3718 and NGC 3729, Hickson 56, Ursa Major
NGC 3718 is an intermediate barred spiral galaxy whose spiral arms have been dramatically warped and stretched through gravitational interaction with a nearby neighbor to the ENE. The near-collision resulted in rapid displacement of galactic gas and dust triggering an outburst of new star formation. This is revealed in the form of several OB associations, or immense clusters of young, blue stars. The full extent of the spiral arms is about 13 arcmin, which corresponds to 173,000 light years. The luminous central portion is about 68,000 light years in diameter, and half as bright as the Milky Way. It consists of a large galactic bulge composed of ancient, yellow stars, surrounded by a light blue region of new star formation. The bulge is bisected by dark equatorial dust lanes, which also appear to be warped. NGC 3718 has a very bright active galactic nucleus of the Seyfert type powered by a central supermassive black hole.
The interacting galaxy, NGC 3729, which lies about 12 arcmin to the ENE, is also a barred spiral galaxy warped by gravitational interaction. Its spiral arms have beed dispersed into a featureless faint nebulosity. Its barred nucleus is surrounded by a prominent ring mottled with starburst activity. Based on the K_s band luminosity of the nucleus, the galaxy is thought to have a central intermediate-mass black hole. The oval cloud NE of the ncleus may be a tidal tail extending along the line of sight, or a disturbed satellite galaxy.
Measured and derived properties of the two galaxies are listed in the chart below. Although they appear to be very near to each other, their redshifts suggest the two galaxies are now about 1.1 million light years apart in 3 dimensions, NGC 3729 being the more distant. Eventually, the two galaxies are expected to merge into a giant elliptical galaxy.
On a larger scale, the pair belong to the Ursa Major Galaxy Cluster, which is itself a component of the Virgo Supercluster.
South of NGC 3718, around 370 million light years distant, lies Hickson Compact Group 56, a cluster of five tightly interacting galaxies, which is the subject for a separate post.
A number of remote galaxies and two quasars are identified in the annotated image, and listed in the chart below. The most remote is SDSS J113228.23+525328.8, located at light travel distance of 11.1 billion light years, or proper distance of 19.5 billion LY (in the present epoch). When the photons were emitted, the quasar was receding at 256,102 km/s, while at the present time it is estimated to be receding at superluminal 422,004 km/s. With absolute magnitude of -29.63, it is about 3,400 times brighter than the Milky Way galaxy. 99.38% of its light is extincted, or literally diluted by the expansion of the intervening space.
Image Details:
Meade 8'' ACF, AP 0.7x compressor, 200 x 1400 mm
iEQ30pro mount, Orion 60mm f/4 SSAGpro autoguider
Canon T3i modified camera, Astronomik L3 filter
29 x 300 sec subs (7 discarded), iso 1600, 30 darks, 30 bias, 2x drizzle, 40% linear crop
Software: PHD2, DSS, XnView, StarNet++, StarTools.
Interacting Galaxies NGC 3718 and NGC 3729, Hickson 56, Ursa Major, Annotated
Interacting Galaxies NGC 3718 and NGC 3729, Hickson 56, Ursa Major
NGC 3718 is an intermediate barred spiral galaxy whose spiral arms have been dramatically warped and stretched through gravitational interaction with a nearby neighbor to the ENE. The near-collision resulted in rapid displacement of galactic gas and dust triggering an outburst of new star formation. This is revealed in the form of several OB associations, or immense clusters of young, blue stars. The full extent of the spiral arms is about 13 arcmin, which corresponds to 173,000 light years. The luminous central portion is about 68,000 light years in diameter, and half as bright as the Milky Way. It consists of a large galactic bulge composed of ancient, yellow stars, surrounded by a light blue region of new star formation. The bulge is bisected by dark equatorial dust lanes, which also appear to be warped. NGC 3718 has a very bright active galactic nucleus of the Seyfert type powered by a central supermassive black hole.
The interacting galaxy, NGC 3729, which lies about 12 arcmin to the ENE, is also a barred spiral galaxy warped by gravitational interaction. Its spiral arms have beed dispersed into a featureless faint nebulosity. Its barred nucleus is surrounded by a prominent ring mottled with starburst activity. Based on the K_s band luminosity of the nucleus, the galaxy is thought to have a central intermediate-mass black hole. The oval cloud NE of the ncleus may be a tidal tail extending along the line of sight, or a disturbed satellite galaxy.
Measured and derived properties of the two galaxies are listed in the chart below. Although they appear to be very near to each other, their redshifts suggest the two galaxies are now about 1.1 million light years apart in 3 dimensions, NGC 3729 being the more distant. Eventually, the two galaxies are expected to merge into a giant elliptical galaxy.
On a larger scale, the pair belong to the Ursa Major Galaxy Cluster, which is itself a component of the Virgo Supercluster.
South of NGC 3718, around 370 million light years distant, lies Hickson Compact Group 56, a cluster of five tightly interacting galaxies, which is the subject for a separate post.
A number of remote galaxies and two quasars are identified in the annotated image, and listed in the chart below. The most remote is SDSS J113228.23+525328.8, located at light travel distance of 11.1 billion light years, or proper distance of 19.5 billion LY (in the present epoch). When the photons were emitted, the quasar was receding at 256,102 km/s, while at the present time it is estimated to be receding at superluminal 422,004 km/s. With absolute magnitude of -29.63, it is about 3,400 times brighter than the Milky Way galaxy. 99.38% of its light is extincted, or literally diluted by the expansion of the intervening space.
Image Details:
Meade 8'' ACF, AP 0.7x compressor, 200 x 1400 mm
iEQ30pro mount, Orion 60mm f/4 SSAGpro autoguider
Canon T3i modified camera, Astronomik L3 filter
29 x 300 sec subs (7 discarded), iso 1600, 30 darks, 30 bias, 2x drizzle, 40% linear crop
Software: PHD2, DSS, XnView, StarNet++, StarTools.