Planetary nebula luminosity function: Difference between revisions

Revision as of 19:35, 5 March 2019

Revision as of 12:02, 31 March 2019

Line 3:

== Procedure ==

The distance estimate to a galaxy using the PNLF requires discovery of such an object in the target galaxy that is visible at λ5007 but not when the entire spectrum is considered. These points are candidate PNe, however, there are three other types of objects that would also exhibit such an emission line that must be filtered out: [[HII region|HII&nbsp;regions]], [[supernova remnant]]s, and [[Lyα galaxy|Lyα galaxies]]. After the PNe are determined, to estimate a distance one must measure their monochromatic <nowiki>[O&nbsp;III]</nowiki> λ5007 lumonisity. What remains is a statistical sample of

PNe. The observed luminosity function is then fitted to some standard law.<ref name="Ciardullo2004">{{harvnb|Ciardullo|2004}}</ref>

Line 9:

== Physics behind process ==

The PNLF method is unbiased by [[metallicity]]. This is because [[oxygen]] is a primary nebular coolant; any drop in its concentration raises the plasma’splasma's electron temperature and raises the amount of [[collisional excitation]]s per ion. This compensates for having a smaller number of emitting ions in the PNe resulting in little change in the λ5007 emissions . Consequently, a reduction in oxygen density only lowers the emergent <nowiki>[O&nbsp;III]</nowiki> λ5007 emission line intensity by approximately the square root of the difference in abundance. At the same time, the PNe’sPNe's core responds to metallicity the opposite way. In the case where the metallicity of the progenitor star is smaller, the PNe’sPNe's [[central star]] will be a bit more massive and its illuminating ultraviolet flux will be a bit greater. This added energy almost precisely accounts for the decreased emissions of the PNe. Consequently, the total <nowiki>[O&nbsp;III]</nowiki> λ5007 lumonisity that is produced by a PNe is practically

uncorrelated to metallicity. This beneficial negation is in agreement with more precise models of PNe evolution. Only in extremely metal-poor PNe does the brightness of the PNLF cutoff dim by more than a small percentage.<ref name="Ciardullo2004" />