- The method of using overlapping distance indicators to get
farther and farther distances-- known as the cosmological
distance ladder-- relies heavily on the local Cepheid calibration
(zero-point and slope). Most distance indicators are tied to a
distance (modulus) to the Small and Large Magellanic Clouds (or
dependent on an indicator that is tied to the S/LMC
modulus).
- Relatively precise, secondary indicators for cosmological
distances that are tied to the Cepheid scale (this is just a
list):
- Supernovae type Ia:
Before HST, there was a severe lack of measured Cepheids in
galaxies that were hosts to SNe Ia. In order to refine the
correlation between maximum luminosity of SNe Ia and their
apparent maximum luminosity, we have to measure the distance to
the host galaxy with cepheids.
- Tully-Fisher relation:
A rather interesting and widely applicable distance measure is
the Tully-Fisher relation. This relies on the fact that the
total luminosity from a face-on spiral galaxy is strongly
correlated with the maximum rotationaly velocity of the galaxy.
Under the assumption of a constant mass-to-light ratio, you can
apply the virial relation in framework of the galaxy being
rotationally supported and get a distance. In a similar vein as
SNe Ia, it is a good check to calibrate the closer Tully-Fisher
callibrator galaxies to the Cepheid scale.
- Fundamental Plane for elliptical galaxies:
For ellipticals, there is a Tully-Fisher analog called the
fundamental plane technique. This technique notes that there is
a strong correlation between surface brightness of an elliptical
and its velocity dispersion. Namely they occupy a
"fundamental plane" where re is proportional to
vdisp * <I>e where a defined
effective radius of the elliptical (re) is correlated
with the surface brightness (<I>e) within that
radius and the velocity dispersion (vdisp). We have
to calibrate this with Cepheids.
- Surface Brightness Fluctuations (SBF):
This relies on the fact that the resolution of stars within a
galaxy (spiral or elliptical) is distance dependent. By
normalizing the average total flux and correcting for a color
dependence, we can measure the relative distances of galaxies.
Once again, calibrating the near SBF calibrators with Cepheids
is needed and ongoing.
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- Supernovae type Ia:
Before HST, there was a severe lack of measured Cepheids in galaxies that were hosts to SNe Ia. In order to refine the correlation between maximum luminosity of SNe Ia and their apparent maximum luminosity, we have to measure the distance to the host galaxy with cepheids.
- Tully-Fisher relation:
A rather interesting and widely applicable distance measure is the Tully-Fisher relation. This relies on the fact that the total luminosity from a face-on spiral galaxy is strongly correlated with the maximum rotationaly velocity of the galaxy. Under the assumption of a constant mass-to-light ratio, you can apply the virial relation in framework of the galaxy being rotationally supported and get a distance. In a similar vein as SNe Ia, it is a good check to calibrate the closer Tully-Fisher callibrator galaxies to the Cepheid scale.
- Fundamental Plane for elliptical galaxies:
For ellipticals, there is a Tully-Fisher analog called the fundamental plane technique. This technique notes that there is a strong correlation between surface brightness of an elliptical and its velocity dispersion. Namely they occupy a "fundamental plane" where re is proportional to vdisp * <I>e where a defined effective radius of the elliptical (re) is correlated with the surface brightness (<I>e) within that radius and the velocity dispersion (vdisp). We have to calibrate this with Cepheids.
- Surface Brightness Fluctuations (SBF):
This relies on the fact that the resolution of stars within a galaxy (spiral or elliptical) is distance dependent. By normalizing the average total flux and correcting for a color dependence, we can measure the relative distances of galaxies. Once again, calibrating the near SBF calibrators with Cepheids is needed and ongoing.