Active Galactic Nuclei Observing Program Coordinator:
112 Pebble Beach Drive
Royersford, PA 19468
Introduction and Overview
Galaxies with active nuclei were studied in the early 1940’s by Minkowski, Humason and Seyfert. Some ‘variable’ stars were later found to be categorized as Active Galactic Nuclei (AGN), including BL Lacertae objects. Radio galaxies were studied in the 1950’s followed in the 1960’s by quasi-stellar objects (QSO; quasars). Beginning in the 1980’s the numbers of known QSO, BLO and AGN objects have grown almost exponentially1, particularly due to those discovered by the Sloan Digital Sky Survey.
Active Galactic Nuclei are the highly energetic compact regions at the centers of some galaxies and are the most luminous sources of electromagnetic radiation in the universe. They are powered by a supermassive black hole and some have strong emission lines.
The following Table describes the differences of the various types of active galaxies as compared to normal galaxies:
Currently many investigators are using “orientation-based” unified models to explain some of the differences between active galaxy types. The types seen depend upon the angle from which we are observing the object, as depicted in Figure 1.
Seyfert I, Quasar
Figure 1. An orientation-based unified model of AGN
Types of Active Galactic Nuclei
Although radio galaxies are also included under the AGN umbrella, they are not part of this particular A. L. Program (though they are a part of the Radio Astronomy Observing Program of the Astronomical League). Here we are concentrating on those AGNs that emit much of their energy in the visible wavelengths.
Blazars (Blazing quasi-stellar objects) - These have relativistic jets pointing towards Earth and are of two types:
BL Lacertae Object (BLO) – This is a variable AGN hosted in a massive galaxy.
Optically Violent Variables (OVV) – These are highly variable AGNs, which are very few in number. These radio galaxies have light output that can change dramatically over a very short period of time. They differ from BLOs by having broader emission lines and higher red shifts.
Quasars – These are extremely bright AGNs, so bright that their light often overpowers that of the rest of the hosting galaxy. This is an important property of quasars. Subgroups of quasars will be discussed in the next section.
Seyferts - These are almost exclusively spiral galaxies. In contrast to quasars, Seyfert galaxies have AGNs that are less luminous making the rest of the galaxy visible to us.
Seyfert Type I - These have narrow and broad bands of spectral lines of ionized hydrogen, helium, nitrogen and oxygen.
Seyfert Type II – These only have a narrow band of spectral lines.
Both Seyfert Types I and II fluctuate rapidly, especially in the X-ray portion of the spectrum.2
Types in between I and II, e.g., Sy 1.2, Sy 1.5, denote differences in the appearance of the optical spectrum. Seyfert galaxies can also be categorized by Luminosity Classes I-V, with galaxies of a Luminosity Class I being the most massive, having the largest number of stars and having the most strength, greatest thickness and the most prominent arms.
All of these distant AGN display redshifts (z values) that correspond to a few hundred million light years to several billions of light years. These would be their proper distance and not the expanding distance.
This is one of two unusual subgroups of quasars. In this type, the light from the distant quasar is gravitationally-lensed by a massive foreground object, an effect predicted by Einstein’s General Theory of Relativity. In 1979 a twin quasar in Ursa Major was found. Each segment had identical spectra, leading to the conclusion that the light originated from a single source and was ‘split’ by a foreground object. This ‘optical illusion’ of multiple images of a single background object obviously requires the background object be more distant than the closer, foreground ‘lensing’ object. Since most quasars are very distant, they are very susceptible to being gravitationally lensed. Lists of gravitationally-lensed quasars can be found in an article by Wolfgang Steinicke3 and from the Gravitational Lens Database.4
True Double Quasars
The first pair in this second subgroup of quasars was discovered by Djorgovsky several years after the discovery of the first lensed quasar. In this subgroup the spectrum of each quasar in the pair is different. That is the clue that we have two quasars here, not two images of a single quasar. Lists are available from references 3 & 4.
Lists of Galactic Nuclei
Quasars, BL Lacertae Objects and Seyfert Galaxies
Since the total number of known quasars and BLO objects is truly ‘astronomical,’ we have, for the most part, limited the list to those described by Wolfgang Steinicke in 19985, where he tabulated objects brighter than 16.5 magnitude and north of -20 degrees declination. For this program we have chosen those Seyfert galaxies with a Luminosity Class of I and obtained the list from the NASA Extragalactic Database (NED)6 using that parameter. We also limited these Seyfert galaxies to those higher than -20 degrees declination.
- Visual observations, (13-15” as a minimum) log sheets (Appendix F) should contain:
- Latitude and Longitude of observation.
- Sky conditions: transparency and seeing.
- Telescope aperture and focal length.
- Whether the object was found manually, with digital setting circles or a go-to telescope.
- The reference number of the quasar, BLO or Seyfert galaxy observed.
- Constellation the object is within
- A small sketch indicating the position of the object in reference to the foreground stars.
- Indicate direction of North and West
- Indicate size of field
- The distance of the object using the redshift z value provided.
- Photographic or digital imaging observations, (at least a 4” telescope is suggested) the image:
- All of the requirements for visual observers.
- The object must be indicated on the image with an arrow or line.
- Type of camera used.
- Total exposure time
- Size of field
Submitting for Certification
The log sheets and electronic files containing digital images (which can be submitted on a CD or through an internet-based delivery system - e.g., web site, Drop Box, Google Drive, etc.) can either be sent to the Program Coordinator or to one of your astronomy club officers for verification.
The certificate will have an indication after the certificate number: a V for Visual observations or an I for electronically-imaged observations.
Appendix A, Quasar list
Appendix B, Seyfert list
Appendix C, BLO list
Appendix D, Gravitationally-lensed quasar list
Appendix E, Double Quasar list
Appendix F, Log Sheet
Hints on Observing Quasars, BLOs, and AGNs
The Wolfgang Steinicke reference5 is a very valuable tool in compiling a strategy for attacking these objects. To make things that much easier we also added the pages of the Uranometria (1st and 2nd editions) and Millennium star atlases. One may use other software programs such as MegaStar© for such purposes.
Preliminary ‘homework’ beforehand includes making an observing list for the upcoming session(s). The observing list will have the object name, constellation, magnitude, distance and page of Uranometria or page of Millennium. In the observing field one would then star hop using the Uranometria atlas under low magnification and, if need be, star hop using the fainter stars plotted in the Millennium atlas. The image provided from the aforementioned web site will prove helpful in determining which star-like object is the quasar. To view the dimmest objects, higher magnification is highly recommended. Once the object is located, then a verbal description can be dictated in a micro cassette recorder and/or a rough sketch of the eyepiece field can be made. The appendices also provide the observer with the redshift (z)7. Having the distance of the object available to the observer at the eyepiece adds an additional sense of wonder, awe and satisfaction.
Time Delay Distances of Lensed Quasars
Light from lensed quasars has been used to further confirm Einstein's General Theory of Relativity. Calculations show that the light being lensed takes more time to travel around a massive foreground object to reach the observer, perhaps up to 0.3 years in one cited example.8
Active Galactic Nuclei Observing Program Coordinator:
112 Pebble Beach Drive
Royersford, PA 19468
1 Veron-Cetty, M.-P. and Veron, P. A Catalogue of quasars and active galactic nuclei: 13th edition, Astronomy & Astrophysics 518: 1-8, 2010.
3 “Faint Objects and How to Observe Them”, Brian Cudnik, Chapter 5, “The Nature of Quasars and Other Exotics” Springer, 2013
4 “On False and True Double Quasars” Wolfgang Steinicke,
6 “Catalogue of Bright Quasars and BL Lacertae Objects”, Wolfgang Steinicke http://www.klima-luft.de/steinicke/KHQ/khq_e.htm
8www.ifa.hawaii.edu/users/kud/teaching_15/16_time_delay.pdf (p. 9), Rolf Kudritzki, 2015
“Active Galactic Nuclei and the Amateur” Hewitt, N. and Poyner, G. Deep Sky Observer 116: 3-13, 1999.
“Observing Variable Galaxies” Alvin Huey, 2013 (http://faintfuzzies.com/DownloadableObservingGuides2.html)
For the truly adventurous, “The million quasars (Milliquas) catalogue, version 3.4 (2013)” at http://quasars.org/milliquas.htm
John Bajtelsmit, Mark Huss, Vince Scheetz, Frank Colosimo and Joe Lamb of the Delaware Valley Amateur Astronomers contributed their expertise in the development of this Program. Dick Steinberg provided the images used on the certificate. Aurore Simonnet of Sonoma University kindly gave permission to use her drawing of the quasar depicted on the pin.