TheSkySearchers

https://aasnova.org/2021/05/14/seeing-s ... 5Yrxf5JHCs

Looking at different element enrichments to assess inflow and outflow of gas in a star forming galaxy is interesting. It will be more interesting on a sample larger than one.

What's the thing about light from quasars? Predictabiity?

turboscrew wrote: ↑Sat May 15, 2021 11:34 pm What's the thing about light from quasars? Predictabiity?

Good question! The QSO provides background illumination. Without a QSO in the background to illuminate the foreground galaxy one can't do the absorption line spectroscopy.

But why quasars in particular? Are they the only kind of light sources strong enough? Or maybe white enough?

turboscrew wrote: ↑Sun May 16, 2021 5:55 am But why quasars in particular? Are they the only kind of light sources strong enough? Or maybe white enough?

The quasar is significantly more distant and much brighter than other sources. Since that difference is large there is a difference in redshift for lines of similar elements that might be in both the quasar and the foreground galaxy. QSOs are the only source bright enough in the background and at a different enough redshift to make the interpretation of the absorption spectrum straightforward.

Let's say that there was a nearer bright source, perhaps a supernova. If it were close enough to the galaxy being studied, the red shift wouldn't be that much different and it would be very difficult to interpret the absorption spectra unambiguously. What you need is a much more distant (different redshift) and therefore much brighter source to be able to do the analysis with some confidence.

OK, because of both brightness and distance (red shift).