Very high energy (VHE ≳0.1 TeV) gamma-rays from extragalactic sources, interacting by γ-γ collisions with diffuse intergalactic radiation fields, provide an alternative way to constrain the diffuse background light, completely independent of direct measurements. The limits depend however on our knowledge of the physics of the gamma-ray sources. After clarifying the interplay between background light and VHE spectra, I summarize the extent and validity of the obtainable limits, and where future improvements can be expected.

The Extragalactic Background Light (EBL) at UV, optical and NIR wavelengths consists of the integrated light of all unresolved galaxies along the line of sight plus any contributions by intergalactic matter including hypothetical decaying relic particles. The measurement of the EBL has turned out to be a tedious problem. This is because of the foreground components of the night sky brightness, much larger than the EBL itself: the Zodiacal Light (ZL), Integrated Starlight (ISL), Diffuse Galactic Light (DGL) and, for ground-based observations, the Airglow (AGL) and the tropospheric scattered light. We have been developing a method for the EBL measurement which utilises the screening effect of a dark nebula on the EBL. A differential measurement in the direction of a high-latitude dark nebula and its surrounding area provides a signal that is due to two components only, i.e. the EBL and the diffusely scattered ISL from the cloud. We present a progress report of this method where we are now utilising intermediate resolution spectroscopy with ESO's VLT telescope. We detect and remove the scattered ISL component by using its characteristic Fraunhofer line spectral signature. In contrast to the ISL, in the EBL spectrum all spectral lines are washed out. We present a high quality spectrum representing the difference between an opaque position within our target cloud and several clear OFF positions around the cloud. We derive a preliminary EBL value at 400 nm and an upper limit to the EBL at 520 nm. These values are in the same range as the EBL lower limits derived from galaxy counts.

Unit: We will use in this paper the abbreviation 1 cgs = 10−9erg s−1cm−2sr−1Å−1

We present the new constraints on the cosmic optical background (COB) obtained from an analysis of the Pioneer 10/11 Imaging Photopolarimeter (IPP) data. After careful examination of data quality, the usable measurements free from the zodiacal light are integrated into sky maps at the blue (~0.44 μm) and red (~0.64 μm) bands. Accurate starlight subtraction is achieved by referring to all-sky star catalogs and a Galactic stellar population synthesis model down to 32.0 mag. We find that the residual light is separated into two components: one component shows a clear correlation with thermal 100 μm brightness, while another betrays a constant level in the lowest 100 μm brightness region. Presence of the second component is significant after all the uncertainties and possible residual light in the Galaxy are taken into account, thus it most likely has the extragalactic origin (i.e., the COB). The derived COB brightness is (1.8 ± 0.9) × 10−9 and (1.2 ± 0.9) × 10−9 erg s−1 cm−2 sr−1 Å−1 at the blue and red band, respectively, or 7.9 ± 4.0 and 7.7 ± 5.8 nW m−2 sr−1. Based on a comparison with the integrated brightness of galaxies, we conclude that the bulk of the COB is comprised of normal galaxies which have already been resolved by the current deepest observations. There seems to be little room for contributions of other populations including “first stars” at these wavelengths. On the other hand, the first component of the IPP residual light represents the diffuse Galactic light (DGL)---scattered starlight by the interstellar dust. We derive the mean DGL-to-100 μm brightness ratios of 2.1 × 10−3 and 4.6 × 10−3 at the two bands, which are roughly consistent with the previous observations toward denser dust regions. Extended red emission in the diffuse interstellar medium is also confirmed.

The extragalactic background light (EBL) is of fundamental importance both for understanding the entire process of galaxy evolution and for γ-ray astronomy. However, the overall spectrum of the EBL between 0.1 and 1000 μm has never been determined directly, neither from observed luminosity functions (LFs), over a wide redshift range, nor from any multiwavelength observation of galaxy spectral energy distributions (SEDs). The evolving overall spectrum of the EBL is derived here utilizing a novel method based on observations only. It is emphasized that the local EBL seems already well constrained from the UV up to the mid-IR. Different independent methodologies such as direct measurement, galaxy counts, γ-ray attenuation and realistic EBL modelings point towards the same EBL intensity level. Therefore, a relevant contribution from Pop III stars to the local EBL seems unlikely.

I review work on modelling the infrared and submillimetre SEDs of galaxies. The underlying physical assumptions are discussed and spherically symmetric, axisymmetric, and 3-dimensional radiative transfer codes are reviewed. Models for galaxies with Spitzer IRS data and for galaxies in the Herschel-Hermes survey are discussed. Searches for high redshift infrared and submillimetre galaxies, the star formation history, the evolution of dust extinction, and constraints from source-counts, are briefly discussed.

Using extensive mid-IR datasets from AKARI, i.e. 9 band photometry covering the wavelength range from 2 μm to 24 μm and the unbiased spectroscopic survey for sources with Sν (9μm)>0.3 mJy, we investigated the PAHs emission features in distant starburst galaxies. PAH-selected galaxies, selected with an extremely red mid-IR colour due to PAHs, are found to have a peculiar rest-frame 11-to-8 μm flux ratio, which is systematically smaller than nearby starburst/AGN spectral templates. This may indicate a systematic difference in the physical condition of the ISM between nearby and distant starburst galaxies.

We summarise recent progress in understanding the star formation activity in early-type galaxies (ETGs), using recent studies that leverage photometry in the rest-frame ultraviolet (UV) wavelengths. While classically thought to be old, passively-evolving systems, recent UV studies have revealed widespread star formation in ETGs, with ~20% of the stellar mass in today's ETGs forming at late epochs (z < 1). A strong correlation is found between the presence of morphological disturbances and blue UV colours, suggesting that the star formation is merger-driven. However, the major merger rate at late epochs is far too low to satisfy the number of disturbed ETGs, indicating that minor mergers drive the star formation in these galaxies over the latter half of cosmic time. Together with the recent literature which suggests that minor mergers may drive the size evolution of massive ETGs, these results highlight the significant role of minor mergers in driving the evolution of massive galaxies in the low and intermediate-redshift Universe.

Detailed studies of the stellar populations of intermediate-redshift galaxies can shed light onto the processes responsible for the significant evolution of the massive galaxy population since z < 1. We have undertaken such a study by means of deep rest-frame optical spectroscopy with IMACS on Magellan on a sample of ~80 galaxies selected from CDFS to have stellar masses > 1010M⊙ and redshift 0.65 < z < 0.75. We analyse stellar absorption line strengths and interpret them with a Monte Carlo library of star formation histories to derive constraints on mean stellar ages, metallicities and stellar masses. We present here the first characterization of the stellar mass–metallicity and stellar mass–age relations at z~0.7 and their evolution to the present-day.

We stack FIRST survey cutout images of 811 K+A galaxies to derive a mean 1.4 GHz radio image of our sample from which we measure a mean K+A flux density of 56 μJy. We carry out Monte Carlo simulations by randomly selecting radio-quiet white dwarfs to create 10,000 stacks equivalent to our K+A stack. From the measured fluxes of these stacks, we establish a 5σ detection limit of 43 μJy for stacked images. For the average redshift of our sample, we find an mean star formation rate of ~1.7 M⊙ yr−1. We split the sample by age and find a mean radio flux of 60 μJy, which corresponds to a star formation rate of 1.6 M⊙ yr−1, for galaxies with starburst ages less than 250 Myr.

We present preliminary results on Submillimeter Array (SMA) observations of three Luminous Infrared Galaxies (LIRGs) and one infrared Quasi Stellar Object (IR QSO). The galaxies were observed at sub-kpc spatial resolution in lines of CO and 13CO, as well as in the continuum at 1.3mm. The moment maps show that the molecular gas in these galaxies is distributed in rotating disks with velocity gradients ranging from ~30 to 120 km s−1 kpc−1. Combined with archival CO J=3-2 data, the spatial distributions of the CO J=3-2/J=2-1 ratios shows clear variations across the galaxies. The brightness temperature of the overlap region in VV 114 is found to be lower than that in the nuclear region of VV 114E, suggesting that that the bulk of molecular gas in this region is sub-thermalized.

I summarise recent results on multi-wavelength properties of distant lensed galaxies, with a particular focus on Herschel. Submm surveys have already resulted in a breakthrough discovery of an extremely efficient selection technique for strong gravitational lenses. Benefitting from the gravitational magnification boost, blind mm-wave redshifts have been demonstrated on IRAM, SMA and GBT, and follow-up emission line detections have been made of water, [Oiii], [Cii] and other species, revealing the PDR/XDR/CRDR conditions. I also discuss HST imaging of submm lenses, lensed galaxy reconstruction, the prospects for ALMA and e-Merlin and the effects of differential magnification. Many emission line diagnostics are relatively unaffected by differential magnification, but SED-based estimates of bolometric fractions in lensed infrared galaxies are so unreliable as to be useless, unless a lens mass model is available to correct for differential amplification.

The Cosmic Infrared Background ExpeRiment (CIBER) is a rocket-borne absolute photometry imaging and spectroscopy experiment optimized to detect signatures of first-light galaxies present during reionization in the unresolved IR background. CIBER-I consists of a wide-field two-color camera for fluctuation measurements, a low-resolution absolute spectrometer for absolute EBL measurements, and a narrow-band imaging spectrometer to measure and correct scattered emission from the foreground zodiacal cloud. CIBER-I was successfully flown in February 2009 and July 2010 and four more flights are planned by 2014, including an upgrade (CIBER-II). We propose, after several additional flights of CIBER-I, an improved CIBER-II camera consisting of a wide-field 30 cm imager operating in 4 bands between 0.5 and 2.1 microns. It is designed for a high significance detection of unresolved IR background fluctuations at the minimum level necessary for reionization. With a FOV 50 to 2000 times larger than existing IR instruments on satellites, CIBER-II will carry out the definitive study to establish the surface density of sources responsible for reionization.

EMU is a wide-field radio continuum survey planned for the new Australian Square Kilometre Array Pathfinder (ASKAP) telescope, due to be completed in 2012. The primary goal of EMU is to make a deep (~10μJy/bm rms) radio continuum survey of the entire Southern Sky at 1.4 GHz, extending as far North as +30° declination, with a 10 arcsec resolution. EMU is expected to detect and catalog about 70 million galaxies, including typical star-forming galaxies up to z = 1, powerful starbursts to even greater redshifts, and AGNs to the edge of the Universe. EMU will undoubtedly discover new classes of object. Here I present the science goals and survey parameters.

The Atacama Large Millimeter/submillimeter Array (ALMA) is a telescope comprising 66 antennas that is located in the Atacama Desert in Chile, one of the driest locations on Earth. When the telescope is fully operational, it will perform observations over ten receiver bands at wavelengths from 9.5-0.32 mm (31-950 GHz) with unprecedented sensitivities to continuum emission from cold (<20 K) dust, Bremsstrahlung, and synchrotron emission as well as submillimetre and millimetre molecular lines. With baselines out to 16km and dynamic reconfiguration, ALMA will achieve spatial resolutions ranging from 3″ to 0.010″, allowing for detailed imaging of continuum or molecular line emission from 0.1-1 kpc scale gas and dust discs in high-redshift sources or 10-100 pc scale molecular clouds and substructures within nearby galaxies. Science observations started on 30 September 2011 with 16 antennas and four receiver bands on baselines up to 400 m. The telescope's capabilities will steadily improve until full operations begin in 2013.

The MeerKAT (64 x 13.5m dish radio interferometer) is South Africa's precursor instrument for the Square Kilometre Array (SKA), exploring dish design, instrumentation, and the characteristics of a Karoo desert site and is projected to be on sky in 2016. One of two top-priority, Key Projects is a single deep field, integrating for 5000 hours total with the aim to detect neutral atomic hydrogen through its 21 cm line emission out to redshift unity and beyond. This first truly deep HI survey will help constrain fueling models for galaxy assembly and evolution. It will measure the evolution of the cosmic neutral gas density and its distribution over galaxies over cosmic time, explore evolution of the gas in galaxies, measure the Tully-Fisher relation, measure OH maser counts, and address many more topics. Here we present the observing strategy and envisaged science case for this unique deep field, which encompasses the Chandra Deep Field-South (and the footprints of GOODS, GEMS and several other surveys) to produce a singular legacy multi-wavelength data-set.

If galaxies consisted only of stars, and some early-type systems in general and dwarf spheroidal galaxies in particular fit this prescription, then the calculation of the SED in principle is straightforward. The emergent luminosity at any wavelength simply is the sum over all the luminosities of all the stars in the system. This can be calculated, of course provided that one has a complete understanding of stellar populations, which remains a non-trivial issue. Most galaxies, however, also contain an interstellar medium (ISM). The ISM absorbs, scatters and reprocesses the radiation and relativistic particles from sources within galaxies, primarily stars and AGN. That the ISM is neither isotropic nor homogeneous adds to the challenge of how to properly account for its influence on the luminosity emerging from galaxies.