"DARK  AGES" OF  THE  UNIVERSE

Y.Parijskij, A.Kopylov, N.Soboleva, O.Verkhodanov, A.Temirova, O.Zhelenkova, P.Tcibulev, A.Chepurnov, V.Stolyarov and N.Bursov

Special Astrophysical Observatory
Nizhnij Arkhyz, Karachai-Cherkess Republic, 357147 Russia   

1.Introduction
2.Very HZ Objects: how far they can be?
3.Flux density estimation from Very High Zet (VHZ) objects.
4.Universe transparency problem.
 5.Future activity.
5.1.VHZ objects.
5.2.CMB anisotropy.
 
 6. "Sakharov Oscillation" project.
 6.1.Project SUMMARY. "Sakharov Oscillations"
Russian Low Frequency High Resolution Project
 
References

                At the end of the Century, gross deformation of our understanding of the surrounding Universe  took place and we realised that there are big lagoons in our knowledge. There is some hope, that observational astronomy and particularly radio astronomy may be useful in escaping from the "pagan" state. Today, we are celebrating 100 Years anniversary (using Russian chronology:  "Thunderstorm marker"(Popov, 1896) of the first radio telescope with collecting area about 400 sq.m. dedicated for the receiving of the electromagnetic radiation in radio domain from the lightning in the atmosphere, that is from the Natural source of radiation. In fact, at the end of the last Century, two radio communication windows were opened - let us call them People-to-People  window and People-to Nature window. Both windows are of the great importance but some problems with their interaction exist.
        We shall demonstrate the fantastic break through in the second window, and how Radio may be used in the next generation fundamental experiments, connected with Early Universe.
        Last  1996 Year demonstrated the triumph of Radio Astronomy. It was shown that remote sensing by Radio waves of essentially  whole Universe is quit possible. Three steps were equally important in the firm establishing of this statement.
        1.Exponentially great growth of the sensitivity of radio facilities.
        2.Detection of small scale CMB anisotropy.
        3.Discovery that Thomson depth up to the recombination epoch is less than 1 and at least the most powerful radio population of the Universe may be visible at any distances up to the  recombination epoch; epoch from the Singularity to the Recombination may be traced by careful mapping of the CMB.

2.Very HZ Objects: how far they can be?

 There are more than 100 QSR at 3<z4.46 on the Sky but here we  shall try to estimate the density of much more distant population. We shall use HZ USS FRII RG method of selection very distant but very old stellar  system. Stellar population in QSO practically invisible due to strong gas emmission. In z>1 list of about 250 galaxies most of them are RG. Every year we have new records  and it is demonstrated by Fig.1

 Now radio galaxies are ahead of QSR- most distant RG  has z=4.71, most distant radio loud QSO has z=4.46. But even with smaller z, we can penetrate into the "pre-QSO" epoch using classical stellar evolution models of estimation of the age of the stars in the parent galaxies, connected with the RG. Ultra- steep spectrum population of FRII RG are most popular- they happend to be the most distant. It was demonstrated by Holland group, that about 30% of RG with spectral index more than 1.3 have z>3.

How many USS RG on the SKY? We used well defined RATAN-600 selected area, 0h < R.A. < 24h, DEC=5 deg. were we have now about  500 dayly records at 5-7 fequencies from 22GHz to 1 GHz. The width of the strip depends on the frequency and effective width at the most sensitive frequency, 3.9 GHz was about 0.15 deg. In this 100 sq.deg. area  we discovered  1147 radio sources (that is, about 10 per sq.deg)  with limiting flux density  of few mJy (RC Catalog) and they were used in the BIG TRIO project (RATAN-600, world largest radio telescope, VLA, world best radio imaging system, and 6m. Russian optical telescope, up to now- biggest single mirror instrument, for deep optical identifications). We were the first  users of the most sensitive at long wavelengths  UTRAO catalog before formal publication and 100% of UTRAO objects were visible at 3.9 GHz at RATAN-600. We selected USS objects with alfa > 1 and realized, that the surface density of the USS objects is by factor 100 greater, (about 1 per sq.deg.) than it was believed earlier. This statesment well visible from the FIG.2

 High density region on this all sky map- RATAN-600 selected area. We can compare  our result with results from other groups, see FIG.3 

 

  It is the lower limit of USS RG in our SA, because there were no long wavelength surveys sensitive enough  to pick up all USS objects above our sensitivity limit. We hope to use new generation (NVSS, FIRST type) cataloges to get complete spectral information.  All USS RC objects were mapped by VLA with resolution up to 0.2 arcsec, morphologically classified and identified optically at 6m. telescope. Using all information on the 250 HZ RG with knownredshifts, we estimated redshifts of our USS objects and it was found, that mean redshift for our list is about Z =2 , but 6 have R mag greater than that for the most distant radio objects, discoverded up to now (z=4.71).  Moreover, we have found few objects with radio luminosity greater by factor 10, than optical luminosity of the parent galaxy. Looking at the z>1 list of RG with measured z and with measured R, we could not find any object with radio luminosity greated then optical luminosity even by 1 mag. It well may be, that these pecular objects belong to new exremely distant  LBO (Lyman-Break-Objects) population with z>6, with 912A break redshifted from the R filter band. If it is the case, we may hope, that there are about 1000 objects on the sky with well developed FRII structure and giant black holes in the parent stellar systems at z=6.

 We have now multi-color measurements for about 30 objects of our list and estimated "color redshifts" and ages of stellar systems, responsible for the formation of out FRII radio sources. This age have to be substructed from the age of the Universe, corresponding to the photometric or color redshift of the object to estimate the cosmic time of the first massive stars formation process. Preliminary resuls are shown in the FIG.4

 It is clear, that the MODE of age distribution appearing in the 1 Gy bin, "negative", that is before Big Bang, cases just demonstrate the accuracy of our estimates. At the same time, we should remind, that for the radio loud objects this approach can give us only the lower limit of the stellar system age, because it is generally accepted, that the merging and tidiel disturbancies may be of a great importance in the formation of the FRII objects, the same may be trigger the secondary stars burst events. Even more, for FRII objects we should find time for formation of the dense galactic core stellar claster and (only then) for  erection of the billion solar mass black hole to feed the most energetical in the Universe radio structure. In classical picture, it will take just 1 Gy. If we add to that the time for the formation of the 10^12  solar mass giant ellipticals (normally connected with FRII RG) from the less massive objects, we have to think about alternative ways of formation FRII gE and giant Black Holes inside, e.g. (Rees, 1984). Alternatives include  quick formation of these objects just after separation of matter from radiation field. pom s the  in the
    Let us summarise this part: present day observation indicates, that Universe has galaxy  population at z>>1 and ( may be) even at z>100-300. Is it possible to observe them? In the next 2 parts we are going to give answer to this question.
 

3.Flux density estimation from Very High Zet (VHZ) objects.

Let us put well studied HZ RG at different Z up to recombination epoch and calculate the flux density from this RG without any other assumptions using standard cosmology corrections, e.g. (Longair, 1974).  Object like 1425+635 with z=4.25  will give us FIG.5

     This objects belong to the classical FRII Cygnus-A population or the Radio Sky. We can see, that even with present day sensitivity records (VLA, 1-2 micro-Jy) it is possible to observe this object at any redshift up to recombination epoch if
a)there are objects at these redshifts and
b)the Universe is transparent up to recombination epoch.
     The situation may be even better if we take into account two important processes, which can operate at VHZ: dust emmission and Inverse Compton (I.C.) effect (scattering of the relict photons by the relativistic particles in the radio structures). First process was considered in (Parijskij, Korol'kov, 1986) and many times later. Both processes results in the strong positive K- correction (flux density increases with z instead of decreasing). We demonstrate this effect for Cyg-A object were 100- micron peak of the dust emmission was discovered, see FIG.6

     Even with 1mJy sensitivity this object may be observed up to recombination epoch.  IC effect may very important in XRAY and optical domains. It is easy to show, that for z>4-6 IC luminosity dominates over the radio luminosity if the size of the radio structure is as big as normal for the FRII RG population. Again, due to (1+z)^4 factor in the photon energy density, sky may be covered by new population of XRAY objects if sensitivity of the observations will be comparable with AXAF observatory. In optical domain we shall see "turnover" effect-at Z> Zmax brightness of the object will increase s with Z. We demonstrate  this effect in FIG.7

    We can see, that, again, this type of VHZ objects may be observed with present day optical facilities (with the same "If's" as above).
    Exponential growth of the sensitivity of the radio facilities well established, and all attempts to predict the "saturation" effects failed. We demonstrate this by FIG.8
 

 

 We had 1mJy records only 10 years, now we have 1 microJy record (VLA, 1996) and nano-Jy level is visible with 1 sq.km. array (SKAI project) In the first quarter of the next millenium our "Horoscope" predict pico-Jy level (but no real projects of that kind). We may notice, that communication industry predict the number of personal radio communication facilities comparable with the total population level (more than 10 billion). They will be interconnected through computer network  and may be used as the new generation amature aperture synthesis array with collecting surface about billion sq.m. if civilization will be interested in the Science more than now.
    It is interesting, that in all domains there are great number of projects for new generation facilities, including 1 km 900 sq.m optical ground based adaptive array.
 This part may be also easely summarized: even  present day instrumentation adequates to the sensitivity requirements to pick up at least some kind of the Early Universe population. New generation instruments can extend the size of the visible up to recombination epoch population greatly.

4.Universe transparency problem.

 We were involved in the attempts to see the objects at recombination epoch, z=1000, directly in the radio window from 1967, just after Silk suggestion to observe protogalxies. As usual, we had only upper limit on the CMB anisotropy at all scales, from 18 arcsec to several degrees, greater than the horizon scale at the epoch of recombination. We began with Big Pulkovo Radio Telescope (130m strip) and working up to now with RATAN-600, using the same strip survey, which we used for the detection of the distant radio sources. At the end of 1996 we had about 400 dayly records iat several frequencies and in the different modes of observations (and in different azimuths), see FIG.9
 

 

 Only at the sub-degrees scales we had seen some extra  noise above simple power low spectrum, which can be easely atributed to the small scale Galactic noise and confusion effects due to the unresolved background radio sources. We demonstrate this noise at 3.9 GHz in the FIG.10.,
 

 

 It should be mentioned here, that signal-noise ratio was much greater than 1 everywere, reaching more than 10 (more than 100 in energetical units, Cl, Legendre polinom terminology). It is demonstrated by FIG.11
 

We can try to convert our one- dimentional Fourie spectrum into the  standard Cl values, see FIG.12

 

Error bars here reflect only random errors, connected with receiver and atmospherical noise. It is just the noise, visible in the difference between two independent sets of observations. Extra noise above COBE power spectrum (2<l<<10) well visible in the  region 250 < l < 850  with effective amplitude about up to 40 micro K. The main uncertainties were connected with the interpretation of this extra noise. Galactic synchrotron and free-free emmission and confusion effect were the main alternatives of the the CMB anisotropy. The systematic errors connected with "cosmic variance" limitation should also large- less then 100 pixels were used in FIG.12. The very fact of extra noise at these scale was established in early 80th and was published in 1984 (see (Parijskij, Korol'kov, 1986) for references), but only now we may reject all alternatives exept CMB anisotropy. Indeed, there are now great progress in mm and  submm observatioins of the sky anisotropy and only last, 1996 resulted in the acknowlegment of the reality of the extra noise at the sub-deg. scales, in 200<l<800 region and with amplitude about 30 micro-K above COBE level, see FIG.13.

  The main alternative of CMB anisotropy in this frequency region  was Galactic dust emmission. Now we can reject it also as very unprobable- at submm, mm and at long cm wavelengths we have extra noise in the same 200< l < 800 interval and of the same amplitude. Even with 30%  errors in both groups of measurments we can proof the black body spectrum of the extra noise at the sub-horizon scales; it is demonstrated by FIG.14.

  If we compare the observed amplitudes and scales with predictions of practically all variants of the Theory of Early Universe, we unescapable came to conclusion, that we really see recombination epoch; moreover, the Tompson depth of the whole part of the Universe from the  observer to the recombination epoch is much less then 1. At present,  we estimate it as less then 0.1 just from comparison of present day observations with most popular variants of the Theory.
    It is interesting, that from  part 1  and part 3 results we can eliminate the epoch of the secondary reheating in the Early Universe. Indeed, we have shown, that there is population of very active objects at z> 6 and may be even at z>>6. These population  has very powerfull ability in ionization of intergalactic medium; in the very popular unified model, FRII RG are QSO objects with "wrong" orientation. We can calculate the Stremgren sphere for our USS RG and, using our space density estimation from part 1 consideration, find redshift at which Stremgren radius will be smaller then the distance between our USS FRII RG objects if there no strong evolution effects. The result will be model- dependent, but we cannot extrapolate the estimated space density of VHZ object too far due to the high transparency of the universe (part 3). It means, that we have upper and lower limit on the epoch of secondary ionization. At present , we think it is somewhere inside  6 <z< 30 interval, see FIG.15.

 

  As far as very early collapsed object concerned, we can also eliminate the fraction of that type  of object; during collapse of one barion about 5000 UV photons appearing and, again, small optical depth up to recombination epoch strongly eliminates the number of such events. FRII RG  may be just exception which does not change the transparency of the very Early Universe (z>100-300).
  We can resume this part: we are sure now, that Universe is transparent up to recombination epoch. We are also sure now, that  Universe was neutral, non-ionized from z=1000 up to z<30 in the small barion content Universe consistent with primordial He/H ratio (Omega barion about 0.01) and up to z<3 in the Universe with Omega barion=1. Last variant seems disagrees with observation of z>5 objects and do not agrees  with our estimation of the density of USS FRII RG at z>>1.
  Small Tomson depth means big depth in the neutral hydrogen Universe. Objects with z>6-30 cannot be observed and new method of redshifts estimates have to be used. Two variants are visible from the discussion in part 2 (100 micron peak, IC effect;  the ratio of Radio to IC fluxes are proportional to the (1+z)^4 ). Dubrovich suggested to use He and Li instead of H many years ago, see Dubrovich 1997 for referencies.

 5.Future activity

5.1.VHZ objects.

We hope to have multi- color photometry for all objects in the RATAN-600 USS FRII RG list and direct spectroscopy of the most interesting objects. We shall try to trace the efficiency of this approach at the lower level of flux density using at least NVSS data for our strip. With surface density about few per the horison scale (2 deg.) we can check the LSS predictions, which are very different at z>3 for different scenaria. FRII RG very often connected with galactic clusters (70%) and this population may be used for mapping of the LSS. Resolution of the RATAN-600 just enough for observation of
S-Z effects in the distant clusters, marked by the distant RG. In fact,  first observation S-Z decrement was done with RATAN-600 type radio telescope in 1971 (Parijskij, 1972). This effect does not changes under Lorents transformation in the Reley-Jeans region (amplitude of the decrement is the same at any z). At the same time, multi-frequency detection at both side of the Planck spectrum can be used for determination of the redshift of the cluster without spectroscopy. It is clear now, that there is new class of sky objects- S-Z "dark spots" without optical and XRAY counterparts (Lasensby, this volume) and for them only radio measurments are possible.

5.2.CMB anisotropy.

 We are going to concentrate ourself on the "Sakharov Oscillations" scales (1deg- 0.1deg) and on the secondary
effects at smaller scales, up to the RATAN-600 resolution limit (few arcsec). The main limitation for the ground based experiments are connected with the atmosphere noise. We shall show here, that it is not the case when the scales under investigations are small enough and (or) the size of the dish is big enough.
There are at least 2 well known ways to eliminate the atmospheric noise: beam switching and multi-frequencies observations are among the most popular one. The problem is , that very often even the residial noise is much greater, then the receiver noise alone. Without any atmospheric filtration best modern receiver has noise by 100- 1000 times less, then atmospheric one, see FIG.16 
 

 

 Here we present bad weather case at 1.38cm with RATAN-600 radio telescope, simple  single beam scan in the transit mode. Below-receiver noise only after integration on the time scale, corresponding to the polinom Legendre scale. Even for very small scales  atmospheric noise dominates.
 CMB anisotropy has spectrum very different from the atmosheric one and  using even 2- frequencies method we can subtruct the atmoshere. For small dishes it can help but not greatly. For big dish suppression is much greater. We demonstrate the difference by FIG.17 and FIG.18

 

 Due to the same reason simple beam switching is much more effective for the near field zone case. Appropriate formalism was developed for both cases many years ago by Pulkovo group, see,  e.g., Kaidanovski et al, 1982 and early referencies there. Using this approach and much more accurate measurments of the atmospheric noise structural function (see, e.g., FIG.20)

it is easy to predict the residial noise if different scales we  observe with different dishes, see FIG.21
 

 

 From this type of consideration we can find the boundary between Ground based and Space based experiments on the plane "scales-telescope dimentions", see FIG.22.

 

    Unusual requirements for the Ground based observations- it  is much better to have telescope size much greater, than you need to just to resolve the scale under investigations. From the last  figure it is clear, that all scales greater then about 1 deg. may studied from the Space only, but all scales smaller than 1 deg. may be studied from the Ground as well as from the Space!
    That important result was used to clearify the role of the RATAN-600, world biggest reflector type radio telescope, in the future CMB anisotropy measurements: high l part of the space spectrum at the wavelengths, which penetrates through the atmosphere.
    How far we can be from the "optimum frequency" for CMB anisotropy  measurements with highest sensitivity? Greatest unsertainties  connected w