and Cosmology

9. The Universe at High Redshift
388
Applied to individual galaxies, each of these estimates
is quite uncertain, which can be seen by
comparing the resulting estimates from the various
methods (see Fig. 9.32). For instance, Hα and UV photons
are readily absorbed by dust in the interstellar
medium of the galaxy or in the star-formation regions
themselves. Therefore, the relations above should be
corrected for this self-absorption, which is possible
when the redding can be obtained from multicolor data.
It is also expected that the larger the dust absorption,
the stronger the FIR luminosity will be, causing deviations
from the linear relation SFR FIR ∝ SFR UV .After
the appropriate corrections, the values for the SFR de-
rived from the various indicators are quite similar, but
still have a relatively large scatter.
There are also a number of other indicators of star
formation. The fine-structure line of singly ionized carbon
at λ = 157.7 μm is of particular importance as it is
one of the brightest emission lines in galaxies, which
can account for a fraction of a percent of their total luminosity.
The emission is produced in regions which are
subject to UV radiation from hot stars, and thus associated
with star-formation activity. Due to its wavelength,
this line is difficult to observe and has, until recently,
been detected only in star-forming regions in our Galaxy
and in other local galaxies. However, recently this
Fig. 9.32. Correlations of the star-formation rates in a sample
of galaxies, as derived from observation in different wavebands.
In all four diagrams, the dashed line marks the identity
relation SFR i = SFR 2 ; as is clearly seen, using the Hα luminosity
and UV radiation as star-formation indicators seems
to underestimate the SFR. Since radiation may be absorbed
by dust at these wavelengths, and also since the amount of
warm dust probably depends on the SFR itself, this effect
can be corrected for, as shown by the solid curves in the four
panels