This paper reviews those properties of normal galaxies most relevant to the estimation of the extragalactic infrared background, in particular: (1) their infrared emission spectrum and its variation among galaxies; (2) their morphological properties, and their infrared size distribution in comparison to their apparent visible-light sizes; and (3) other properties such as the infrared-to-radio ratio and color-luminosity relations. Even a simple comparison of those properties to those of the extragalactic infrared background leads to constraints on the fluctuations in time and the secular evolutionary behavior of the infrared luminosity of galaxies.

The Infrared Space Observatory (ISO) has for the first time made possible mid- and far-infrared spectroscopic studies of nearby and moderate redshift, dusty ultraluminous infrared galaxies (ULIRGs). We discuss recent SWS, LWS, ISOPHOT-S and ISOCAM (CVF) results on ULIRGs, addressing the following topics: What powers ULIRGs? What is the AGN-starburst connection? How do ULIRGs evolve? What is the connection of the local ULIRG population to the recently discovered population of mid-IR to submillimeter sources?

The ultraluminous infrared galaxies (ULIRGs) are strong interacting or merging galaxies. Statistical study shows that about ten percent of ULIRGs are QSOs or Seyfert 1 galaxies, and high–resolution HST images suggest that they are likely to be at the post merger stage. We investigate the optical spectroscopic properties for a complete sample of 28 QSOs/Seyfert 1s selected mainly from the IRAS galaxy redshift survey QDOT and 1.2 Jy catalogs. The optical spectra were obtained with the 2.16 m optical telescope of the Beijing Astronomical Observatory between October 1998 and the end of 1999. Statistical results for both continuum and emission lines show the following:

1. Most of our sample galaxies are strong or extremely strong FeII emitters with a ratio of FeII/Hβ larger than 2. There also exists an anti-correlation of the ratio of FeII/Hβ with EW(OIII) and FWHM(Hβ).

2. We fit the continuum for all sample galaxies. Aside from a few objects which could be fitted well by a power-law model, the continuum for most sample Seyfert 1 galaxies can be fitted well by a blackbody model or by composites of power–law and blackbody models. For Seyfert 1 galaxies which fit a power–law, E(B-V) is small and in the range of optically selected Seyfert 1 galaxies. However, for Seyfert 1 galaxies fitting a blackbody model, the temperature increases as E(B-V) increases. This is strong observational evidence to support the evolutionary scenario from starbursts to optical QSOs/Seyfert 1s.

3. We also discuss the possible mechanism for strong FeII emission from the point of view of evolution of mergers to AGNs.

We present the near–infrared (H–band: λ = 1.65 μm) κ–space (κ1 ∝ log M, κ2 ∝ log Ie, κ3 ∝ log M/L) of high surface–brightness early and late type galaxies, based on a sample of 419 objects optically selected in regions of the A262, Cancer, and Virgo clusters and of the Coma Supercluster. We discuss the distribution of the pressure–supported and rotationally–supported systems within this space and the ensuing scaling relations. We analyze the link between galaxy structure and star formation history through a comparison of the loci occupied by galaxies of the Local Universe in both the near–infrared (this work) and optical κ–spaces. Our results support scenarios of galaxy formation and evolution with the following fundamental ingredients: collapsing proto–galactic systems are characterized by i) a bimodal distribution in mass and angular momentum; and by ii) a mass–dependent characteristic star formation time scale.

We introduce the properties of the Two Micron All-Sky Survey (2MASS) for IAU Symposium 204. 2MASS is a near-infrared survey of the entire sky characterized by high reliability and completeness. Catalogs and images for 47% of the sky are now available online. This data release has been used by Wright (2000) and Cambrésy et al. (2000) to subtract the stellar foreground at 1.25 and 2.2 microns from COBE DIRBE data, revealing the cosmological near-infrared background.

The Sloan Digital Sky Survey (SDSS) is an imaging and spectroscopic survey of 104 deg2 in the North Galactic Cap, currently underway with the 2.5-m SDSS Telescope at the Apache Point Observatory in New Mexico. The data products will include u, g, r, i and z-band imaging of several 108 sources and R = 2000 spectra of 106 galaxies. The imaging will have 10-sigma limiting (AB) magnitudes of (u, g, r, i, z) = (21.4, 22.6, 22.3, 21.7, 20.1). The “Main” sample of 9 x 105 galaxies, selected to have r < 17.7 mag, will have spectra with signal-to-noise ratio on the order of ~ 10 per resolution element, and median redshift z ~ 0.1. There will also be a sample of 105 luminous elliptical galaxies, selected on the basis of apparent color and magnitude, which will extend out to redshift z ~ 0.4. The data will be released steadily over the next five years.

On the order of one percent of the eventual data volume has been assembled at the time of this meeting, with a few hundred square degrees of survey-quality 5-band imaging, and over 104 survey-quality spectra. In the refereed literature there are detailed descriptions of the survey design, goals and hardware (York et al 2000; Gunn et al. 1998) and first scientific results (e.g., Ivezic et al 2000; Fischer et al. 2000; Leggett et al. 2000; Yanny et al. 2000).

Relevant to measures of the extragalactic background emission, the survey has found many z > 4 quasars and has measured the evolution in their space density (e.g., Fan et al. 2000). Measures of bright galaxy counts, the local galaxy luminosity function, and the evolution of elliptical galaxies are in preparation.

The counts derived from the five mid-IR 15 μm (12–18μm LW3 band) ISOCAM Guaranteed Time Extragalactic Surveys performed in the regions of the Lockman Hole and Marano Field, the HDF-North and South (plus flanking fields), together with those of the lensing cluster A2390 at low fluxes and those of IRAS at high fluxes, cover four decades in flux from 50 μJy to ~0.3 Jy. The roughly 1000 sources detected with ISOCAM, 600 of which have a flux above the 80 % completeness limit, guarantee a very high statistical significance for the integral and differential source counts from 0.1 mJy up to ~5 mJy. The slope of the differential counts is very steep (α = −3.0) in the flux range 0.4-4 mJy, hence much above the Euclidean expectation of α = −2.5. When compared with no-evolution models based on IRAS, our counts show a factor ~ 10 excess at 400 μJy, and a fast convergence, with α = −1.6 at lower fluxes.

Multiwavelength studies of a subsample of the ISOCAM sources in HDF and CFRS fields indicate that they are intrinsically bright galaxies (Luminous Infrared Galaxies, LIRGs), with median redshift 0.7. These galaxies, despite their low surface density, are responsible for a large part of star formation at z < 1 and contribute substantially to the cosmic infrared background at 140 μm.

This paper presents a global analysis of the first 2MASS (Two Micron All Sky Survey) data as observed in seven fields at different Galactic latitudes. These new data lead to strong constraints on the radial structure of the Galactic thin and thick disks. The interpretation of star counts and color distributions of stars in the near-infrared with a synthetic stellar population model provides strong evidence that the Galactic thin disk density scale length, hR, is rather short (2.8±0.3 kpc). The Galactic thick disk population is revisited in the light of new data. We find the thick disk to have a local density of 3.5 ± 2.0% of the thin disk, exponential scale height, hz, of 860±200 pc and exponential scale length, hR, of

We present new medium-deep wide field galaxy counts at J- and K-bands, performed in the ELAIS fields. The source detection limits are at J = 19.5 and K = 18.0 magnitudes. The sky coverage is 1 degree2, making our survey the largest to date at these wavelengths and magnitudes. Counts in this brightness range are critical for normalization of models when explaining the deepest galaxy counts. In our survey fields we find evidence for a higher than expected local galaxy density. If normalized to our counts, galaxy models do not need strong brightness evolution or exotic populations to be explained even at the faintest levels. We measure clearly sub-Euclidean slopes of d log N(m)/dm ~ 0.45 to 0.50 at 13 < K < 17.5 and 14.5 < J < 19. Normal, passively evolving stellar populations along with a high normalization of the local luminosity function and an open cosmological model best fit both the slope and amplitude of our number counts. We report a preliminary value, ~ 30 n Wm−2sr−1, for the K-band extragalactic background light using zodi-subtracted DIRBE-data and our observed star counts. The value is consistent with, e.g., Matsumoto (these Proceedings 2001) and Gorjian, V., Wright, E. L., & Chary, R. R. 2000, ApJ, 536, 550, but is considerably higher than extrapolations from faint galaxy counts.

ISO's infrared camera was used to make deep mid-infrared (MIR) images through three gravitationally lensing clusters of galaxies. Observations were made at 7 μm and 15 μm covering more than 50 square arcminutes, with the lensing increasing the sensitivity to background sources significantly.

A large number of MIR sources were detected behind the lenses and provide source counts, corrected for cluster contamination and lensing distortion effects, which exceed by a factor of 10 the expectation from local counts assuming a no-evolution model. The results are consistent with larger-area surveys and the detected population resolves a substantial fraction (of order 60%) of the background MIR radiation intensity into discrete sources.

We discuss the evidence, in large part derived from lensing cluster observations, for overlap of the ISO 15 μm faint galaxy population with the 850 μm submillimetre and the 0.5 to 7 keV X-ray populations. We find that the ISO data shows substantial overlap with both the submillimetre and the X-ray source populations, with roughly 25% of ISO sources being detected at submillimetre wavelengths and a significant number of Chandra X-ray sources being detected in the ISO data.

The cosmic far-infrared background is now well measured from 140 μm to 1 mm. Uncertainties remain at 100 μm (and even more at 60 μm). These are dominated by limitations of the zodiacal model. The nature of sources dominating the background near its maximum are beginning to be studied through deep surveys carried out with ISOPHOT. These surveys show very steep number counts and fluctuations of the background due to unresolved sources.

The higher spatial resolution and sensitivity of ISO allowed several extragalactic surveys to be extended to greater depth than obtained with IRAS. With the extended wavelength range deep surveys were performed for the first time at wavelengths up to ~ 200 μm. They favour galaxy models with strong evolution. With ISO's new capabilities the spectral energy distributions of larger samples of ULIRGs in the local universe and those of quasars and radio galaxies were determined. These data are applicable as templates to the more distant universe. Foreground components from zodiacal light and cirrus to the intracluster dust emission were studied in connection with their separation from the extragalactic background radiation.

We have searched for point-like sources in eight fields mapped at two or three wavelengths between 90 μm and 180 μm with the ISOPHOT instrument aboard the ISO satellite. Most of the 55 sources detected are suspected to be extragalactic and cannot be associated with previously known objects. It is probable, also from the far-infrared (FIR) spectral energy distributions, that dust-enshrouded, distant galaxies form a significant fraction of the sources.

We present a tentative list of the detected extragalactic FIR-sources. Based on the analyzed data we estimate the number density of extragalactic sources at wavelengths 90 μm, 150 μm and 180 μm and at flux density levels down to 100 mJy to be 1 x 105 sr−1, 2x105 sr−1, and 3xl05 sr−1, respectively.

Models of strong galaxy evolution are in best agreement with our results, although the number of detections exceeds predictions of most models. No-evolution models can be rejected at a high confidence level. Comparison with COBE results indicates that at 90 μm the detected sources correspond to >20% of the extragalactic background light. At longer wavelengths the corresponding fraction is ~ 10%.

We have used the Far-InfraRed BACKground (FIRBACK) field observations with ISOPHOT at 170 μm to search for the Cosmic Far-InfraRed Background (CFIRB) fluctuations. Our study is based on power spectra analyses which allow us to statistically separate each of the background components (Galactic and extragalactic). We show that the extragalactic background fluctuations in FIRBACK fields lie well above the instrumental noise and the cirrus confusion noise. The observed power spectra show a flattening at high spatial frequencies which is due to unresolved extragalactic sources. The level of the extragalactic power spectrum fluctuations is nearly the same in all FIRBACK fields. This is the first time that fluctuations due to unresolved extragalactic sources have been isolated at far-infrared wavelengths. In the two largest FIRBACK fields, the power spectra clearly reveal the presence of correlated extragalactic fluctuations, which we are currently analyzing. However, if 3σ detected sources are cleaned from the maps, the CFIRB fluctuations appear at this time to be compatible with a Poissonian distribution. We would need an independent cirrus template (like for the HI gas) to more incisively remove the Galactic contribution to see whether additional correlations are present.

A simple and versatile parametrized approach to the star formation history allows a quantitative investigation of the constraints from far infrared and submillimetre counts and background intensity measurements.

The models include four spectral components: infrared cirrus, an M 82-like starburst, an Arp 220-like starburst and an AGN dust torus. The 60 μm luminosity function is determined for each chosen rate of evolution using the PSCz redshift data for 15000 galaxies. The proportions of each spectral type as a function of 60 μm luminosity are chosen for consistency with IRAS and SCUBA colour-luminosity relations, and with the fraction of AGN as a function of luminosity found in 12 μm samples.

A good fit to the observed counts at 0.44, 2.2, 15, 60, 90, 175 and 850 μm can be found with pure luminosity evolution in all 3 cosmological models investigated: Ω0 = 1, Ω0 = 0.3 (Λ = 0), and Ω0 = 0.3, Λ = 0.7. All 3 models also give an acceptable fit to the integrated background spectrum. The total mass-density of stars generated in all 3 cosmological models is consistent with that observed.

I review the emerging picture of galaxy formation and evolution that is coming from observations in the optical waveband and in the submillimeter waveband. In the former I look at the work of several groups but in the latter I focus on the results from the Canada-UK Deep Submillimeter Survey (CUDSS), an 850 micron survey of about 100 square arcmin of sky carried out with SCUBA to a limiting flux of 3 mJy. I discuss what we do and do not know about the sources responsible for emitting a significant fraction of the extragalactic background at 850 microns.

Deep surveys performed with millimetric telescopes and with the Infrared Space Observatory have partly resolved the Cosmic IR Background (CIRB) into a population of IR sources characterized by extremely high rates of cosmological evolution (comparable to or higher than those observed for quasars). We report in this paper on early attempts to study these sources and to understand their physics. The IR multi-wavelength galaxy statistics can be explained by assuming, for the bulk of the IR population, spectra typical of starbursts, an indication that stellar more than quasar activity produces the IR emission by faint galaxies. From our fits to the observed optical-IR SEDs, the latter appear to mostly include massive galaxies hosting violent starbursts (SFR ~ 100 M⊙/yr). We interpret the strong redshift-evolution as an increase with z of the rate of interactions between galaxies (density evolution) and an increase of their IR luminosity due to the more abundant fuel available in the past (luminosity evolution). Our evolutionary scheme considers a bimodal star formation (SF) in galaxies, including long-lived quiescent SF, and enhanced SF taking place during transient events triggered by interactions and merging. The large energy content in the CIRB may possibly require a top-heavy stellar IMF associated with the starburst phase. The observed evolution of galaxy IR emissivity is so strong from z=0 to z ~ 1 that the CIRB spectral shape imposes a fast turnover to the evolution at z > 1: scenarios in which a relevant fraction of stellar formation occurs at very high-z (e.g., the bulk of stars in spheroids) are not supported by our analysis.

We present the characteristics of far-infrared (FIR) brightness fluctuations at 90 μm and 170 μm in the Lockman Hole, which were surveyed with the ISOPHOT instrument aboard the Infrared Space Observatory (ISO), and give constraints on the galaxy number counts down to 30 mJy at 90 μm and 50 mJy at 170 μm. The fluctuation power spectra of the FIR images are not dominated by IR cirrus, and are instead most likely due to star-forming galaxies. This analysis indicates the existence of strong evolution in the counts. Especially at 90 μm, the source density is much larger than that expected from the currently available galaxy count models. The galaxies responsible for the fluctuations also significantly contribute to the cosmic infrared background radiation recently derived from an analysis of the COBE data.

Recently reported infrared galaxy number counts and cosmic infrared background (CIRB) measures all suggest that galaxies have experienced a strong evolutionary phase. We statistically estimated the galaxy evolution history from these data. We treated the evolution of galaxy luminosity as a stepwise nonparametric form, in order to explore the most suitable evolutionary history which satisfies the constraint from the CIRB. We found that an order of magnitude increase of the far infrared luminosity at redshift z = 0.75 - 1.0 was necessary to reproduce the very high CIRB intensity at ~ 150 μm reported by Hauser et al. (1998). We note that too large an evolutionary factor at high z overpredicts the CIRB intensity around 1 mm. The evolutionary history also satisfies the constraints from galaxy number counts obtained by IRAS, ISO and SCUBA. The rapid evolution of the IR luminosity density required from the CIRB well reproduces the very steep slope of galaxy number counts obtained by ISO. Based on this result and the evolution of optical luminosity density, we quantitatively discuss the contribution of starburst galaxies. In addition, we present the performance of the Japanese IRIS galaxy survey.