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while there exist quite deep and high - resolution wfpc2 and nicmos images at the hdf - n , it has been desired to have the ground - base @xmath4-band data at the field with comparable depth and image quality in order to study more rest - frame optical properties of high - redshift galaxies . for the purpose
, we obtained the very deep @xmath0-band image using the subaru telescope equipped with a nir camera , cisco . with about 10 hours of net integration under the condition of 0.3 - 0.6 arcsec seeing
, we reached to the depth of @xmath5 as the peak of the counts of the detected galaxies .    using the data , combined with the archived hst data taken in the wfpc2 @xmath6 as well as nicmos @xmath7 bands
, we studied the ( i ) rest - frame optical morphology of the galaxies at @xmath8 , ( 2 ) stellar mass distribution of high - redshift galaxies , and ( 3 ) correlation between galaxy properties with the stellar mass .
figure 1 shows the subaru @xmath0-band image together with the hst @xmath9-band images .
there is no clear hubble sequence for galaxies at @xmath10 .
the morphological feature seen in the hst wfpc2 images are well recognized in the subaru @xmath0-band image .
figure 2 shows the obtained stellar mass distribution for the @xmath0-band selected galaxies between @xmath11 and 4.5 .
this is obtained by fitting the hst @xmath12 and subaru @xmath0-band photometric data by the stellar evolutionary synthesis models ( gissel96 ; buruzual and charlot 1993 ) changing the star - formation history , imf , age , extinction , etc ( papovich et al .
2001 , shapley et al .
the filled circles show the galaxies with spectroscopic redshift and those only with photometric redshift are by the open circles .
we note that the stellar mass of the hdf - n @xmath0-selected galaxies are typically very small , in the range between @xmath13-@xmath14 @xmath15 .    in figure 3 , we present the possible correlation between stellar - mass and the rest - frame @xmath16 color for the galaxies
there are few massive ( in stellar mass ) galaxies with t he bluest color and the massive galaxies tend to have redder @xmath16 color .
if the rest @xmath16 color represents the age difference , then massive objects tend to have rather old average age , which may imply that the star - formation in these galaxies have been occurred rather successively , may be through the merging or assembly process .
we also obtained moderately deep @xmath17 and @xmath0-band images at the field of a radio galaxy 53w002 at z=2.4 where pascarelle et al .
( 1996 ) discovered a dozen of emission - line objects and candidates using the hst wfpc2 intermediate - band image .
keel et al .
( 1999 ) also discovered that the field lies in the high - density region of strong emission line objects from the ground - base narrow - band images .
we studied ( i ) the rest - frame optical properties of the emission - line selected objects and ( ii ) surface density of old quiescent galaxies at the redshift in the field using the subaru data combined with the hst wfpc2 and nicmos archive data .
the detailed results are presented in yamada et al .
( 2001 ) . in brief summary
, many of the emission - line objects are faint in nir wavelength and so they are intrinsically compact and small objects dominated by the on - going star formation , and there are few developed quiescent galaxies that are older than @xmath18 gyr in the field .
the detailed discussion about the mass of the radio galaxy 53w002 itself based on the subaru ohs and cisco spectra is presented in motohara et al .
( 2001 ) .
figure 4 shows the @xmath19 color - magnitude diagram of the @xmath0-selected galaxies in the field of 53w002 ( filled circles ) .
we also noticed a somewhat conspicuous change of the color distribution at @xmath20 . while the brighter objects show the colors distributed over the expected color rang for old and young galaxies at @xmath21 , below @xmath20 ,
most of the galaxies have blue colors ( @xmath22 ) and a small fraction have further red colors ( @xmath23 ) .
there are few galaxies with intermediate color range and thus there is a conspicuous color gap or void in the diagram .
this trend is also seen in the @xmath24 vs @xmath4 diagram ( yamada et al .
then we compare the color - magnitude distribution on these two fields .
the data for the objects in hdf - n are shown by the open squares in figure 4 , and strikingly , the color - magnitude distributions in the two fields are quite similar , although faint red population is not seen in hdf - n .
it suggests that this kind of color - magnitude distribution is a typical aspect of the universe if not an average .    what causes the conspicuous bluing of the @xmath25 colors ?
similar trend has in fact been reported by previous authors ( cowie et al .
1995 , mccraken et al .
2000 , gardner 1995 , sarraco et al .
2001 , but see sarraco et al .
we found that at least two phenomena are responsible for the distribution , namely , ( i ) deficit of intrinsically faint ( @xmath26 ) red galaxies at intermediate redshift ( z > 0.5 - 1 ) , and ( ii ) deficit of red galaxies including luminous ones at @xmath27 .
this can be well recognized by comparing the data with the passive evolutionary models for the color - magnitude relation in the coma cluster ( kodama et al .
1998 ) that are also shown if figure 4 .
three lines represent the tracks of passively - evolving galaxies that are formed at @xmath28 and have @xmath29 at present epoch .
the cosmology is @xmath30=1 , @xmath31=0.3 , @xmath32=0.7 , and @xmath33=70 km s@xmath34 mpc@xmath34 .    for the galaxies in hdf - n , we have the data of spectroscopic and photometric redshift .
we can see clear deficit of faint red galaxies for those between @xmath35 and @xmath36 as shown in figure 5 .
this is quite puzzling and interesting phenomena , since it can not be explained by simple field - to - field variation effects because there are a certain number of luminous red galaxies at the same redshift .
the number density of low - mass objects are expected to be larger than that of the luminous objects since the local luminosity function have exponential cut - off at the luminous end at any band .
our result may imply that we rarely see the less massive galaxies that are dominated by old - stellar population at the intermediate redshift where old massive galaxies exist .
it may be related to the negative faint - end of the local e / s0 luminosity function .
kajisawa and yamada ( 2001 ) investigated a complete volume - limited sample of galaxies with @xmath37 up to z=2 in the hdf - n . based on their careful morphological classification as well as evaluation of the possible uncertainty in photometric redshift , they concluded that the number density of early - type galaxies in hdf - n have very conspicuous decrease above z=1 .
so the deficit of red galaxies at @xmath38 seen in figure 4 may not be surprising although we still do not fully understand why such rapid change of the number density is observed at @xmath39 after considering the possible effects of field - to - field variation and dust extinction , etc .
we are planning to conduct more extended deep nir and optical survey with subaru to fully resolve these questions .
bruzual a. , g.  & charlot , s.  1993 , apj , 405 , 538 cowie , l.  l. , hu , e.  m. , & songaila , a.  1995 , aj , 110 , 1576 dickinson , m.  2000 , royal society of london philosophical transactions series , 358 , 2001 gardner , j.  p. , cowie , l.  l. , & wainscoat , r.  j.  1993 , apjl , 415 , l9 kajisawa , m.  & yamada , t.  2001 , pasj , 53 , 833 keel , w.  c. , cohen , s.  h. , windhorst , r.  a. , & waddington , i.  1999 , aj , 118 , 2547 kodama , t. , arimoto , n. , barger , a.  j. , & aragon - salamanca , a.  1998 , a$a , 334 , 99 mccracken , h.  j. , metcalfe , n. , shanks , t. , campos , a. , gardner , j.  p. , & fong , r.  2000 , mnras , 311 , 707 motohara , k.  et al .
2001 , pasj , 53 , 459 pascarelle , s.  m. , windhorst , r.  a. , keel , w.  c. , scoville , n. , & armus , l.  1996 , american astronomical society meeting , 189 , 8302 papovich , c. , dickinson , m. , & ferguson , h.  c.  2001 , apj , 559 , 620 saracco , p. , giallongo , e. , cristiani , s. , dodorico , s. , fontana , a. , iovino , a. , poli , f. , & vanzella , e.  2001 , a&a , 375 , 1 saracco , p. , dodorico , s. , moorwood , a. , buzzoni , a. , cuby , j .-
g . , & lidman , c.  1999 , a&a , 349 , 751 shapley , a.  e. , steidel , c.  c. , adelberger , k.  l. , dickinson , m. , giavalisco , m. , & pettini , m.  2001 , apj , 562 , 95 yamada , t. et al .
2001 , pasj , 53 , 1119 .
we present the results of the deep nir imaging observations using the subaru telescope . at the hubble deep field north , we obtained the new and deepest @xmath0-band image ( 10 hours ) to study the rest - frame optical morphology of galaxies at z@xmath1 and the stellar mass distribution of galaxies at @xmath2 . 
 we also study the rest - frame optical properties of the building blocks in the field of 53w002 and overall color distribution there . 
 we then combined these data to compare the color and magnitude distribution in these two fields . 
 the opt - nir color - magnitude distributions in the two fields looks very similar and we report the conspicuous color change below @xmath3 and discuss the cause of the feature .