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ARP 294, Interacting Galaxies with Stellar Streams, NGC 3786 and NGC 3788, Ursa Major, NEGATIVE
ARP 294, Interacting Galaxies with Stellar Streams, NGC 3786 and NGC 3788, Ursa Major
NGC3786 and NGC3788 are a tight pair of apparently interacting spiral galaxies in the constellation of Ursa Major, first documented by W. Herschel around 1790. They are listed as ARP 294 in the Atlas of Peculiar Galaxies which includes examples of unusual structures found among galaxies. As the chart below indicates, the galaxies are very similar in angular size, around 2.2 arcmin, apparent magnitude of 13.3 (g), and morphological classification as peculiar intermediate spirals with a ring. Their redshift-based distances are 125.4 and 123.8 million light years respectively, suggesting a separation between them of 1.6 Mly. However, redshift-based distance estimates assume that redshift recession is due exclusively to the expansion of space, and do not correct for galaxies' "peculiar velocities" through space. For redshifts less than 0.01, or distances less than 138 Mly, it is generally accepted that redshift-independent distance measurements, such as the Cepheid period-luminosity relation, are more accurate. According to the NED extragalactic database, median redshift-independent distances for the pair are 158 and 183 Mly respectively, indicating a separation between them of 25 Mly. In either case, as their relatively undisturbed spiral arms confirm, the galaxies appear close due to similar lines of sight, and have not yet undergone major deformations due to close physical contact.
However, both galaxies are still interacting, although not with each other. Each one displays a faint stellar stream of a dwarf falaxy which appears to be in the process of merging. And, each displays a bright blue sector in its galactic disk where its intersecting stellar stream causes a blaze of starburst activity. On the annotated image the streams are marked as A and B, while the starburst regions are marked as S1, S2, and S3. Stream A appears to follow a straight line resulting from gravitational dispersal of a dwarf galaxy as it directly approached NGC3788, causing an explosion of starburst activity (S1) as it traversed the N perimeter of the spiral disk. Meanwhile, Stream B appears as a faint oval loop formed by stellar debris from a disrupted dwarf galaxy which has merged with NGC3786, and made at least one full orbit around it. Along the S and E perimeter of the main galaxy, two luminous blue regions (S2 and S3) indicate starburst activity at the intersections between the looping stellar stream and the main galactic disk.
Physical properties of the galaxies are listed in the chart on the annotated image. Values enclosed in parentheses are based on median redshift-independent distance measurements obtained from the NED database. Depending on the distance method used, the galaxies are between 25 and 50% smaller than the Milky Way, 30 to 70% less bright, and of approximately equal size to each other. Although both galaxies have faint emission lines in the spectrum of their nuclei, and the nucleus of NGC3786 appears bright in the X-ray band, NED extragalactic database does not register an active galactic nucleus in either galaxy.
Since galactic interactions and mergers significantly influence stellar dynamics, the rates of consumption, production, and the distribution of gas and dust, synthesis of new elements (metallicity), and the nature of the galactic nucleus, galactic encounters are of great interest in the study of galactic evolution.
The attached image includes a number of remote background galaxies and two quasars listed in the chart below. The most remote of these is LAMOST J114003.83+315503.5, lying at a light travel (lookback time) distance of 8.85 Bly. The object labeled G1 is identified by Simbad as a galaxy LAMOST J113941.45+315442.2, no angular size specified, which is not listed in the NED database. The object appears starlike on high resolution HST photographs, and is most likely mis-categorized.
HST image
Image details:
-Remote Takahashi TOA 150 x 1105mm, SBIG STF-8300C, Paramount GT GEM
-OSC 36 x 300 sec, 2x drizzle, 40% linear crop
-Software: DSS, XnView, StarNet++ v2, StarTools v1.3 and 1.8, Cosmological Calculator v3
ARP 294, Interacting Galaxies with Stellar Streams, NGC 3786 and NGC 3788, Ursa Major, NEGATIVE
ARP 294, Interacting Galaxies with Stellar Streams, NGC 3786 and NGC 3788, Ursa Major
NGC3786 and NGC3788 are a tight pair of apparently interacting spiral galaxies in the constellation of Ursa Major, first documented by W. Herschel around 1790. They are listed as ARP 294 in the Atlas of Peculiar Galaxies which includes examples of unusual structures found among galaxies. As the chart below indicates, the galaxies are very similar in angular size, around 2.2 arcmin, apparent magnitude of 13.3 (g), and morphological classification as peculiar intermediate spirals with a ring. Their redshift-based distances are 125.4 and 123.8 million light years respectively, suggesting a separation between them of 1.6 Mly. However, redshift-based distance estimates assume that redshift recession is due exclusively to the expansion of space, and do not correct for galaxies' "peculiar velocities" through space. For redshifts less than 0.01, or distances less than 138 Mly, it is generally accepted that redshift-independent distance measurements, such as the Cepheid period-luminosity relation, are more accurate. According to the NED extragalactic database, median redshift-independent distances for the pair are 158 and 183 Mly respectively, indicating a separation between them of 25 Mly. In either case, as their relatively undisturbed spiral arms confirm, the galaxies appear close due to similar lines of sight, and have not yet undergone major deformations due to close physical contact.
However, both galaxies are still interacting, although not with each other. Each one displays a faint stellar stream of a dwarf falaxy which appears to be in the process of merging. And, each displays a bright blue sector in its galactic disk where its intersecting stellar stream causes a blaze of starburst activity. On the annotated image the streams are marked as A and B, while the starburst regions are marked as S1, S2, and S3. Stream A appears to follow a straight line resulting from gravitational dispersal of a dwarf galaxy as it directly approached NGC3788, causing an explosion of starburst activity (S1) as it traversed the N perimeter of the spiral disk. Meanwhile, Stream B appears as a faint oval loop formed by stellar debris from a disrupted dwarf galaxy which has merged with NGC3786, and made at least one full orbit around it. Along the S and E perimeter of the main galaxy, two luminous blue regions (S2 and S3) indicate starburst activity at the intersections between the looping stellar stream and the main galactic disk.
Physical properties of the galaxies are listed in the chart on the annotated image. Values enclosed in parentheses are based on median redshift-independent distance measurements obtained from the NED database. Depending on the distance method used, the galaxies are between 25 and 50% smaller than the Milky Way, 30 to 70% less bright, and of approximately equal size to each other. Although both galaxies have faint emission lines in the spectrum of their nuclei, and the nucleus of NGC3786 appears bright in the X-ray band, NED extragalactic database does not register an active galactic nucleus in either galaxy.
Since galactic interactions and mergers significantly influence stellar dynamics, the rates of consumption, production, and the distribution of gas and dust, synthesis of new elements (metallicity), and the nature of the galactic nucleus, galactic encounters are of great interest in the study of galactic evolution.
The attached image includes a number of remote background galaxies and two quasars listed in the chart below. The most remote of these is LAMOST J114003.83+315503.5, lying at a light travel (lookback time) distance of 8.85 Bly. The object labeled G1 is identified by Simbad as a galaxy LAMOST J113941.45+315442.2, no angular size specified, which is not listed in the NED database. The object appears starlike on high resolution HST photographs, and is most likely mis-categorized.
HST image
Image details:
-Remote Takahashi TOA 150 x 1105mm, SBIG STF-8300C, Paramount GT GEM
-OSC 36 x 300 sec, 2x drizzle, 40% linear crop
-Software: DSS, XnView, StarNet++ v2, StarTools v1.3 and 1.8, Cosmological Calculator v3