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Object Of The Week March 10, 2018: NGC 3147
NGC 3147, MCG+12-10-025, UGC 5532
SBc, Seyfert 2 galaxy
Constellation: Draco
RA: 10 16 53.632
DE: +73 24 02.34
Mag: 10.61
Size: 2.847' x 2.334'
Most of the text of this OOTW article is shamelessly copied from wikipedia.org. I only copied some sentences for otherwise this text would become too large.
Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei (very luminous, distant and bright sources of electromagnetic radiation) with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable. They were first detected in 1908 by Edward A. Fath and Vesto Slipher, who were using the Lick Observatory to look at the spectra of astronomical objects that were thought to be "spiral nebulae". They noticed that NGC 1068 showed six bright emission lines, which was considered unusual as most objects observed showed an absorption spectrum corresponding to stars. In 1926, Edwin Hubble looked at the emission lines of NGC 1068 and two other such "nebulae" and classified them as extragalactic objects. In 1943, Carl Keenan Seyfert discovered more galaxies similar to NGC 1068 and reported that these galaxies have very bright stellar-like nuclei that produce broad emission lines. By the end of the 1950s, more important characteristics of Seyfert galaxies were discovered, including the fact that their nuclei are extremely compact (< 100 pc, i.e. "unresolved"), have high mass (≈109±1 solar masses), and the duration of peak nuclear emissions is relatively short (>108 years).
Seyferts were first classified as Type I or II, depending on the emission lines shown by their spectra. Type I Seyferts are very bright sources of ultraviolet light and X-rays in addition to the visible light coming from their cores. They have two sets of emission lines on their spectra: narrow lines with widths (measured in velocity units) of several hundred km/s, and broad lines with widths up to 104 km/s.[41] The broad lines originate above the accretion disc of the supermassive black hole thought to power the galaxy, while the narrow lines occur beyond the broad line region of the accretion disc. In 1981, Donald Osterbrock introduced the notations Seyfert 1.5, 1.8 and 1.9, where the subclasses are based on the optical appearance of the spectrum, with the numerically larger subclasses having weaker broad-line components relative to the narrow lines.
Type II Seyfert galaxies have the characteristic bright core, as well as appearing bright when viewed at infrared wavelengths. Their spectra contain narrow lines associated with forbidden transitions, and broad lines associated with allowed strong dipole or intercombination transitions. In some Type II Seyfert galaxies, analysis with a technique called spectro-polarimetry (spectroscopy of polarised light component) revealed obscured type I regions. In the case of NGC 1068, nuclear light reflected off a dust cloud was measured, which led scientists to believe in the presence of an obscuring dust torus around a bright continuum and broad emission line nucleus. When the galaxy is viewed from the side, the nucleus is indirectly observed through reflection by gas and dust above and below the torus. This reflection causes the polarisation.
Visually, Seyfert galaxies are commonly known as galaxies with a very bright core and much fainter outer regions. However, the galaxies Messier 51 and 88 are Seyfert galaxies as well of which the outer regions are very well visible as well. Most images of NGC 3147 clearly show the bright core and the fainter halo, as this one taken from jwinman.com
Attachment 2932
I observed NGC 3147 once on March 13, 2015 using my 20" telescope. My notes read
"This galaxies is visible at 320x as a large, round spot with a brighter centrum. Close inspection reveals hints of spiral structure but it is only visible faintly."
The online database of amateur observations at DeepSkyLog.org has observations of the galaxy in telescopes as small as 8 cm. Almost all observations note the much brighter core and a faint halo. Details in the halo varying from a dust lane to actual mention of spiral arms were seen in instruments as small as an 11" telescope.
As always,
"Give it a go and let us know!
Good luck and great viewing!"
