7.3. Future Observations
And what will the future bring? Will new and better data resolve most of the problems addressed in this book or will they open up a whole new set of cosmological challenges that indicate a more complex Universe than we would care to deal with? This is what makes the study of cosmology invigorating. The influx of good data can't be ignored and often times good data illuminates things that we don't understand rather than verifying that we, in fact, do understand something. Such is the balance between observations and theory and the following set of planned observations will most certainly upset that balance in an unpredictable manner:
The Sloan Digital Sky
Survey: This five color survey for
galaxies and followup spectroscopy to reach a goal of 106 redshifts
should produce a uniform set of data that can be corrected for
surface brightness selection effects to finally produce a real
catalog of galaxies. This will be the acid test of the preponderance
of LSB systems in the Universe and should provide a definitive measure
of the local luminosity function of galaxies and hence a proper
census of baryonic material. A million redshifts should also provide
us with a "fair" sample from which the large scale peculiar velocity
field can be determined to greater accuracy.
CMB anisotropy measurements
on the 0.5 - 1.0 degree scale.
Improvements in ground based and balloon borne instruments is now
detecting anisotropy on this scale but with some uncertainty
in the overall amplitude. Measures of the
power spectrum reveal large scale power on the 100-200
H-1 Mpc
scale which corresponds to an angular scale of 0.5 - 1.0 degree
at z 
1000. This data
should effectively discriminate between
the various exotic fixes to CDM theory as well as the alternate
theories such as explosions, PBI, or topological defects.
Keck 10-meter observations
of QSO absorption line systems.
As demonstrated previously, these observations reflect the metal
production history of the Universe over the range z = 1-5. The
use of a large aperture allows fainter systems to be probed at
higher resolution resulting in much more secure line identification
(see Lu et al. 1996).
The Hubble Deep field (e.g.,
Figure 5.3). This deep survey
has produced 2000 interesting galaxies that are at various stages
of formation at various redshifts. Already it has been claimed on the basis
of color analysis of objects in the HDF that the very reddest galaxies
likely are at z 
4 (see
Clements and Couch 1996). A candidate very red object is shown
in Figure 7.1. This object is purported to be
at z 6 (Lanzetta
et al. 1996).
Obviously this awaits spectroscopic confirmation
but in general the HDF is the first true extragalactic gold mine of
information produced by HST and its the subject of much new analysis
(see references in Appendix). The redshift distribution of some of these
HDF galaxies obtained recently with the Keck telescope in shown in
Figure 7.2.
Most of these are at low redshift (a manifestation of the FBG problem
discussed in chapter 6) with a handful
between redshifts 2 and 3.5.
|
Figure 7-1: Filter photometry of a very red galaxy in the Hubble Deep Field. From left to right filters are 3000, 4500, 6000 and 8100 angstroms. The object appears strongest in the 8100 angstrom filter. Under the assumption that this increase in brightness is due to redshift Lyman-alpha radiation, the redshift of this object would be z > 6. Figure courtesy of Ken Lanzetta. |
Surveys for weak
gravitational lensing: In essence
this is a survey to paint a gravity map of the Universe via lensing
distortions. The space density of lensed systems as a function of
redshift is a direct reflection of the volume per unit redshift.
It is surveys like these that will ultimately either produce a positive
detection of 
or a strong
upper limit and hence will rank
as one of the most important cosmological observations ever made.
|
Figure 7-2: Distribution of redshifts of objects in the Hubble Deep Field obtained with the Keck 10-m telescope. The majority of objects with measured redshifts to date have relatively low redshift. This is consistent with the hypothesis that galaxy formation occurs over a long period and there are rather few very high redshift galaxies in the HDF (see Cohen etal 1996 for details). |
The continued quest for
H0 and 
: Clearly if
distance estimation techniques continue to improve, we may one day
look forward to direct measures of these parameters to an accuracy
of a few percent. While past history suggests that this level of
accuracy isn't going to be achieved any time soon in a manner that is
accepted (unless some new physical technique emerges) by most, it is
clear that our techniques are getting better. If and when these
parameters are measured at this level, it will slam the door on a number
of cosmological models. The most interesting aspect of all of this would
be a reliable determination that
is low meaning either
dominates or the Universe is
very open. This
would send theorists scrambling for new structure formation models.
Particle Physics and
Cosmology: Clearly the detection of
a supersymmetric particle and/or a definitive measurement of neutrino
mass would elevate experimental particle physics to observational
cosmology. Direct detection of the DM , by any means, is probably
the single most important new cosmological observation that can be made.
The Advanced X-ray
Astronomical Facility (AXAF): Like HST
and CGRO, AXAF is the third of the great observatories program of
NASA. AXAF will be significantly more sensitive than any previous
X-ray mission and should provide the observations necessary to construct
the X-ray luminosity function of galaxies and its evolution with
redshift. The detection of X-ray clusters with z
2 would
be rather unexpected in CDM structure formation scenarios.
Shuttle Infrared Telescope
Facility (SIRTF): This is the
last of the great observatories. SIRTF will have the sensitivity to make
a better determination of the character of the diffuse extragalactic
infrared light and determine, once and for all, if dusty shrouds
around protogalaxies are that which have prevented their detection.
Peering through dusty curtains
into the heart of a forming galaxy is akin to witnessing
a primal birth and may have spiritual ramifications that transcend
our cosmological model.
This array of new observations will provide a clear test of the validity and usefulness of this book. How much of what we have described here will be valid when the new data comes in? Do we have the basic framework correct but just lack the details or have we missed something fundamental? Will our fervor for a non-zero cosmological constant survive the test of these new observations? Whichever is the case, it seems that our grand and insatiable curiosity about the nature of the Universe will continue to grow and as our observational and theoretical knowledge base expands, we can look forward to new and more complex challenges in the near future. The quest for knowledge seems to have sufficient momentum to strongly propel us into the next millennium in search of better cosmological models that ultimately forge the connection between human beings and the Cosmos.