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studies of galaxy populations much benefit from the coordinated efforts of multiwavelength observations , which allow for a deeper insight into different galaxy properties and evolution .
one of the best examples of these coordinated efforts is the _ great observatories origins deep survey ( goods ) _
( p.i . : m. giavalisco ) , with 320 arcmin@xmath0 of the sky fully covered with deep observations from x - rays through radio wavelengths .
both north and south goods fields have been designed to be a unique case of _ hst _ coverage : they have deep and homogeneous maps in four broad - band _ advanced camera for surveys ( acs ) _ filters @xmath1 and @xmath2 .
the large amount of science produced over the last years using goods data demonstrates the importance of _ hst _ treasury and other major - telescope legacy programs .    near and mid - ir selected galaxies constitute quite unbiased tracers of two different astrophysical properties : stellar mass and star - formation / agn activity , respectively .
although , in general , these galaxies populations are studied separately , a joint analysis of results allows to better understand the interplay between star formation , agn activity and stellar - mass growth at different cosmic times . in the study of near- and mid - ir - selected galaxies , deep
data have had a major role in the following aspects : 1 ) the determination of optical spectral energy distributions ( seds ) , 2 ) the computation of precise ( @xmath3 ) photometric redshifts , as a complement to existing spectroscopic redshifts and 3 ) galaxy morphology .
the two former aspects have been of key importance to conduct complete studies of galaxy luminosity evolution and stellar mass assembly .
an important landmark in the study of near - ir - selected galaxies has been the k20 survey @xcite , which included part of the goods - south among their fields .
the first science results obtained by the k20 survey have soon been extended after the progressive public releases of the deeper _ isaac - vlt _ @xmath4 and @xmath5-band data in the goods - south ( p.is . : c. cesarsky , e. giallongo ) . finally , after the launch of _ spitzer _ in 2003 ( p.i .
: m. werner ) , both goods fields have been observed with _ irac _ at 3.6 , 4.5 , 5.8 and 8.0 @xmath6 ( p.i .
: m. dickinson ) .    at the typical depths of the goods data ( 21 - 22 vega mag ) ,
@xmath5-selected galaxies mostly span the redshift range @xmath7 , but @xmath8 of these galaxies are found at higher @xmath9 redshifts @xcite@xcite@xcite .
the latter include extremely red galaxies ( ergs ) , which have been the subject of many studies looking for the progenitors of present - day massive ellipticals @xcite@xcite@xcite@xcite@xcite
.    the evolution of the rest - frame @xmath5-band luminosity function ( lf ) has been studied up to @xmath10 with the k20 survey @xcite , and then extended up to redshift @xmath11 using goods and other datasets @xcite @xcite @xcite@xcite .
all these works agree in a mild but still significant increase of the bright end of this lf from @xmath12 to @xmath13 . at the same time , the overall number density of galaxies decreases , making the near - ir luminosity density to be nearly constant with redshift ( cf .
figure [ fig1 ] ) .
multiwavelength sed modelling has also allowed to obtain stellar - mass estimates for near - ir - selected galaxies .
the redshift evolution of galaxy number densities is differential with stellar mass : while the density of moderately massive galaxies ( @xmath14 ) continuosly increases from redshift @xmath15 down to @xmath16 , virtually all of the most massive ( @xmath17 ) galaxies appear to be in place by @xmath18 @xcite@xcite@xcite@xcite@xcite@xcite .
the formation epoch of the most massive galaxies seems to be constrained to the redshift range @xmath19 , as no evidence of such galaxies has been found at @xmath20 in the goods - south field , indicating that these objects must be very rare ( if any exists ) at very high redshifts @xcite .
moreover , during the last years , a general consensus has been achieved on the redshift evolution of the total stellar mass density : half of the stellar mass has been assembled in galaxies before the universe was 30 - 40% of its present age @xcite@xcite@xcite .    ) and with on - going star formation ( @xmath21 ) .
the cosmology adopted has @xmath22 , @xmath23 and @xmath24.,width=340 ]
the study of mid - ir selected galaxies has been a subject of major interest in european astronomy since the launch of the _ infrared space observatory ( iso ) _
e.g. @xcite@xcite@xcite .
the amount of energy contained in the extragalactic ir background ( @xmath25 ) is comparable to that in the optical background @xcite , which emphasizes the importance of understanding the role of mid- and far - ir galaxy populations in the general context of galaxy evolution .
after _ iso _ set the first constraints on the mid - ir universe up to redshift @xmath26 , _ spitzer _ has allowed us to prove that mid - ir galaxies have in fact a significant contribution up to higher @xmath27 redshifts , e.g.@xcite .
a sort of ` downsizing ' effect is observed in the typical stellar masses of the galaxies hosting the bulk of ir activity : at @xmath28 , most of the ir activity is found in @xmath29 $ \sim$}}~}10^{11 } \ , \rm m_\odot$ ] galaxies , while at @xmath30 , an important fraction of the ir activity is concentrated in intermediate - mass galaxies , with @xmath31 @xcite@xcite .    a result that might have come as a surprise is the large fraction of massive galaxies that are experiencing an ultra - luminous ir phase at high redshifts @xcite@xcite .
very recent results suggest that the agn contribution to this ir phase at @xmath28 might be much more important than previously thought @xcite .
the mid - ir lf strongly evolves from @xmath32 to 1 @xcite@xcite .
but , after removing to our best current knowledge the agn contribution at high redshifts , the mid - ir lf associated with star formation shows only a modest evolution from @xmath33 to @xmath34 @xcite .
this is reflected in the observed evolution of the bolometric ir ( @xmath21 ) luminosity density , as shown in figure [ fig1 ] . from this figure ,
it is clear that the amount of energy associated with on - going star formation is significantly larger than the light produced by the stars already locked in galaxies at @xmath35 $ \sim$}}~}0.6 - 0.7 $ ] , while the balance is reversed at lower redshifts .
the @xmath36 luminosity related to star formation can be interpreted as the gradient of the evolution of the assembled stellar mass . by @xmath37 ,
80% of the present - day stellar mass is already in place @xcite , so there is only a minor amount of star formation still needed afterwards to finish assembling our local universe .
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because of their unique quality , 
 _ hubble space telescope ( hst ) _ data have played an important complementary role in studies of infrared ( ir ) galaxies conducted with major facilities , as _ vlt _ or _ 
 spitzer _ , and will be as well very valuable for future telescopes as _ 
 herschel _ and _ 
 alma_. i review here some of the most recent works led by european astronomers on ir galaxies , and discuss the role that _ hst _ has had in the study of different ir galaxy populations . 
 i particularly focus the analysis on the goods fields , where the multiwavelength data and unique _ hst _ coverage have enabled to jointly put constraints on the evolution of star formation activity and stellar - mass growth with cosmic time .