BASIC EXTRAGALACTIC ASTRONOMY - Part 3: Luminosity Corrections, Cosmological Extinction, and Mass to Luminosity Conversion
Posted 16 January 2020 - 09:55 AM
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- Dave Mitsky likes this
Posted 10 February 2020 - 12:57 PM
Wow... Sorry I can't add anything of substance to this topic, not before taking a crash course in cosmology first. Still, I really appreciate that knowledgeable people are sharing their expertise of such advanced topics here in CN.
- Gerry Smith likes this
Posted 28 February 2020 - 12:42 AM
Extragalactic Cosmological Calculator, CosmiCalc.exe, is finally finished. It derives a number of physical properties of remote galaxies and quasars based on objective data, such as redshift, apparent magnitude, and apparent diameter. Such data is readily available for all named objects at:
the SIMBAD Astronomical Database, [ http://simbad.u-strasbg.fr/simbad/ ]
and at the NASA/IPAC Extragalactic Database (NED), [ http://ned.ipac.caltech.edu/ ]
The program is based on equations in the CloudyNights.com series of articles titled Basic Extragalactic Astronomy. These equations are accurate within several percent of professional results for extragalactic objects which recede primarily by Hubble flow, or by the expansion of the universe. They will not be accurate for very nearby galaxies, like M31, whose motion relative to us is mostly due to the "peculiar velocity" through space.
The program is free and compatible with all Windows versions. It is self-contained, with no need for INI files or registry entries. It is "portable", which means it can be run from any location in the file system, including the Desktop, or from an external USB drive.
The program can be downloaded from Google Drive at
The source code BAS file can be opened with Notepad, and is available at
The first screenshot is for quasar 3c 273.
The second screenshot is for the distant quasar APM 8279 which is used as an example in the articles.
Suggestions on improving the program will be appreciated.
Edited by rekokich, 29 February 2020 - 12:05 AM.
- donstar likes this
Posted 04 November 2020 - 05:54 PM
How were non-Lya absorption lines nulled out of these spectra?
Why is there such a pronounced luminosity drop just leftward of 500.0 nm in the case of APM 8279?
- rekokich likes this
Posted 12 November 2020 - 08:34 AM
Nightfall S Africa,
When we observe high redshift objects, we see light which had been emitted billions of years ago. On the way to the observer, that light underwent selective absorption while passing from the early universe (distant, early space) to the recent universe (nearby, local space). In very general terms, the early universe was filled with neutral and ionized hydrogen (~75%), helium (~25%), and trace amounts of "metals", or lithium and heavier elements (~10E-10%). As the light approaches the observer, it passes through clouds of matter of ever higher metallicity, containing heavy elements produced in more recent epochs by "stellar nucleosynthesis". All these species of intervening matter, early and recent, elements and even simple molecules, each at its own redshift, contribute to the absorption lines observed in distant quasars.
You made a good observation regarding the drop in brightness in the quasar's spectrum below ~5,000 A. The answer becomes self-evident when you compare the spectrum of the Lyman series to the quasar's spectrum at the same scale. The wavelength of the Ly-beta line is Le = 1026 A. With quasar's redshift of z = 3.911, this corresponds to the observed wavelength, Lo
Lo = Le (z + 1) = 1026 x 4.911 = 5039 A
Since all the lines of the Lyman series, except Ly-a, are densely packed to the left of the Ly-b line, you would expect to see more absorption below 5039 A.
Posted 18 November 2020 - 09:52 PM
Light which had been emitted billions of years ago! Wow.
This is awesome science. Just bought my first grownup telescope today and eagerly awaiting its arrival, and thought I'd do a little LIGHT READING.
Today I learned what WHIM is. (Mind is blown.)
This is just amazing.