KPGT Proposals

Water is ubiquitous in the Solar System, being present in gaseous form in all planetary and cometary atmospheres, as ice on the surface and subsurface of Mars, comets, most planetary satellites and distant bodies, and in the liquid phase on Earth. Water plays an important or dominant role in the chemistry of planetary and cometary atmospheres. Comets are sources of water for planets through episodic collisions and continuous production of ice-dust grains. This proposal addresses the broad topic of water and its isotopologues in planetary and cometary atmospheres. The nature of cometary activity and the thermodynamics of cometary comae will be investigated by studying water excitation in a sample of comets. The D/H ratio, the key for constraining the origin and evolution of Solar System species, will be measured for the first time in a Jupiter- family comet. A comparison with existing and new measurements of D/H in Oort-cloud comets will constrain the composition of pre-solar cometary grains and possibly the dynamics of the protosolar nebula. New measurements of D/H in Giant Planets, similarly constraining the composition of proto-planetary ices, will be obtained. The D/H and other isotopic ratios, diagnostic of Mars' atmosphere evolution, will be accurately measured in H2O and CO. The role of water vapor in Mars' atmospheric chemistry will be studied by monitoring vertical profiles of H2O and HDO and by searching for several other species. A detailed study of the source of water in the upper atmosphere of the Giant Planets and Titan will be performed. By monitoring the water abundance, vertical profile, and input fluxes in the various objects, and when possible with the help of mapping observations, we will discriminate between the possible sources of water in the outer planets (interplanetary dust particles, cometary impacts, and local sources). In addition to these inter-connected objectives, serendipitous searches will enhance our knowledge of the composition of planetary and cometary atmospheres.

The scientific motivation for this proposal is to trace the evolution of dust grains in relation to changes of the physical, dynamical and chemical properties of the interstellar medium. This program will provide an unprecedented view of the structure of the ISM at far-infrared and submillimeter wavelengths and will enable us to investigate the impact of dust grains on the ISM physical and chemical state. The program will take full advantage of four unique characteristics of SPIRE and PACS: brightness sensitivity, wavelength coverage, angular resolution, and mapping efficiency. The brightness sensitivity is essential to measure the faint infrared emission from the diffuse regions. The spectrometers will provide the necessary information to derive the physical properties of the atomic and molecular gas and completely characterize dust evolution. The angular resolution is critical for tracing the dominant processes in grain evolution which takes place on all scales down to a few arcseconds. The data statistics will allow us to probe the impact of extreme physical conditions, e.g., high densities, intense vortices or illumination, on the dust evolution. Our goal is to build with Herschel a coherent database on interstellar dust emission extending to much smaller angular scales than the IRAS and DIRBE surveys and covering a wide range of ISM physical conditions, from diffuse clouds to the sites of star formation and protostars. The program is supported by state-of-art modelling of the dust emission and physical processes acting on dust as well as by on-going laboratory measurements of the grains properties at far-infrared and submillimeter wavelengths. The Herschel observations will benefit from ground-based ancillary data (HI and CO) and from Spitzer programs yielding a full description of the spectral energy distribution of interstellar dust from the near-infrared to the submillimeter.

Study of the molecular content of regions far beyond our Solar System has advanced enormously during the last few decades, from the first detections of diatomic molecules to the discovery of polyatomic, complex organic molecules. Nowadays, one major goal of Astrochemistry is to have the most accurate census of the molecular content (and complexity) in Star Forming Regions (SFRs). In the era of the molecular content census, unbiased spectral surveys in the radio to Infrared of SFRs have become a fundamental and necessary tool in modern astrochemistry research. In this context, the frequency range covered by HSO-HIFI, 500-2000 GHz, is of particular importance. It is in this frequency range that light molecules have their ground and low energy transitions, whereas heavier molecules have higher energy transitions. The latter are excited in the warm gas, whereas the former probe the gas at low temperatures as well. It is therefore in the HIFI frequency range that the major gas coolants (notably H$_2$O) and some key components of the chemical composition of SFRs emit. We propose to obtain Spectral Surveys in the HSO-HIFI range of a representative sample of SFRs. To have a meaningful coverage of the different evolutionary stages and different masses requires a large amount of time, about 300 hrs. The proposed observations will provide a large dataset of uttermost interest for the entire astronomical community, and, particularly for the study of star formation processes and of the influence of chemistry on star and planet formation. These two basic aspects, a large requested observing time and an output of high archival value, make the present proposal suitable for a HSO Key Program.

As a GT Key Program we propose to perform full HIFI and PACS line surveys of 5 sources in the giant molecular clouds Orion and Sagittarius B2. These extraordinary star-forming regions contain the best studied examples of physical and chemical processes prevalent in the interstellar medium, including gravitational compression, thermal and turbulent pressure support, photodissociation, gas and grain chemistry in dense and diffuse quiescent gas, and shocks. With high excitation, rich chemistry, and large molecular column they give the highest chance for new detections in a sensitive search for new molecules. Line surveys of sources (Orion KL, Orion S, Orion Bar, Sgr B2 N+M) defined by these phenomena form the backbone of this proposed program. Herschel offers unprecedented sensitivity and relative calibration accuracy, as well as continuous spectral coverage across the gaps imposed by the atmosphere, opening up a largely unexplored wavelength regime to high resolution spectroscopy. These data will take line surveys to a new level and we will use them to comprehensively characterize the physics (density, thermal balance, kinematics, radiation field) and chemistry (chemical assay, ionization, deuterium fractionation, water ortho/para ratio) of star-forming molecular gas in a manner not previously possible. The opening of this spectral range is also an opportunity to detect the bending transitions of carbon chains and polycyclic aromatic hydrocarbons, along with the rotational transitions of complex organics. Given that these sources have the richest emission spectra seen for star-forming regions in the Galaxy, we anticipate that the proposed observations will define the sub-millimeter/far infrared region of the spectrum and that these data will form a lasting Herschel legacy.

Water is a key molecule for determining the physical and chemical structure of star-forming regions because of its large abundance variations --both in the gas and in the ice-- between warm and cold regions. In this HIFI-led Key Program, we propose a comprehensive set of water observations toward a large sample of well-characterized protostars, covering a wide range of masses and luminosities -- from the lowest to the highest mass protostars -- and a large range of evolutionary stages -- from the first stages represented by the pre-stellar cores to the last stages represented by the pre-main sequence stars surrounded only by their protostellar disks. Lines of H2O, H218O, H217O and chemically related hydrides will be observed. In addition, selected high-frequency lines of CO isotopes, [O I] as well as dust continuum maps will be obtained with HIFI and PACS, and will be complemented by ground-based HDO, CO and continuum maps to ensure a self-consistent data set for analysis. Limited mapping information on arcmin scale provides information on local variations due to outflows and clustered star formation. Together, the data will elucidate the physical processes responsible for the warm gas, probe dynamical processes associated with forming stars and planets, reveal the chemical evolution of water and the oxygen-reservoir, and test basic gas-grain chemical interactions. They will form an unique legacy for the community as a complement to future ground-based programs and for planning future space missions.

With its unprecedented spatial resolution in the critical 75-500 microns wavelength range, Herschel will provide a unique opportunity to determine, for the first time, the fundamental properties of the precursors of OB stars at distances out to a few kpc. The imaging speed of SPIRE and PACS in the parallel mode will enable us to map the entire extent of massive cloud complexes and detect the massive young stellar objects which have been overlooked by IRAS and Spitzer, i.e. the high-mass infrared-quiet protostars and pre-stellar cores. We propose to use SPIRE and PACS to image essentially all of the regions forming OB-type stars at distances < 3 kpc from the Sun (total area of 22~deg^2). To complement this imaging survey, we propose to take smaller photometric and spectroscopic maps with PACS toward a handful of isolated regions that display triggered star formation. The 75/110/170 micronsPACS and 250/350/500 microns SPIRE images of this project will provide an unbiased census of both massive pre-stellar cores and massive Class~0-like protostars, and will trace the large-scale emission of the surrounding clouds. This survey will yield for the first time accurate far-infrared photometry, and thus good luminosity and mass estimates, for a comprehensive, homogeneous sample of OB-type young stellar objects at all evolutionary stages. The multi-wavelength imaging will also reveal spatial variations of the cloud temperature close to HII regions and OB associations. These data, along with the detailed photometric and spectroscopic study of a few prototypical regions of induced star formation, will allow us to determine the importance of external triggers for high-mass star formation in the nearest massive molecular cloud complexes. This Herschel Key Programme is crucially needed to better understand the formation of OB-type stars and will provide the basis for many follow-up studies. In addition, the data will provide templates for galactic studies of star formation, both in our Galaxy and others.

AbstractIn a collaboration between the HSC, P. Harvey (Mission Scientist) and the three instrument consortia we propose to apply the full power of Herschel to investigate the properties of circum-stellar disks. The versatility of Herschel allows us to address several key questions: How do the disks evolve with time? Planets clearly form out of circum-stellar disks and there is growing evidence that the time scale is short, 1 - 10 Myr, for the main accretion phase. During this time period, the stellar radiation and stellar winds clean the disks from most of their dust and gas, eventually making them transparent. However, collisions and evaporation from comet- like bodies will continue to produce dust and gas. This activity declines with time, and we will pursue this scenario by observing a sample of IR excess stars of known age, ranging from a few million years to the age of the sun. Are there analogues to our Kuiper belt around nearby stars? The Kuiper belt is a dust belt surrounding the Sun, located outside the orbit of Neptune, which has a key role in stabilizing orbits of the KE-objects and this dynamical aspect makes it particularly interesting to search for stars that may host KE-belt analogues. Herschel offers a unique sensitivity beyond 100 µm and we propose an extensive survey of nearby stars seeking cold dust emission. What will a closer IR look at the "Fabulous Four" (and some other resolved disks) reveal? Several nearby MS stars with IR excesses have circumstellar dust structures that can be resolved by Herschel. Imaging these structures in the six PACS+SPIRE bands will enable us to explore the dust properties, notably the size distribution and albedo.. What is the composition of young disks? We propose a detailed spectroscopic investigation of four bright disks, including a full spectral scan with PACS, an FTS scan at full resolution and HIFI observations of selected frequencies. The aim is to constrain the properties of both the dust and gas components.

We will carry out a comprehensive spectroscopic study of key molecular line carriers, probing interstellar hydrides and carbon chains. Our investigation will entail high-resolution HIFI spectroscopy of some 25 molecules towards 8 sources, and full spectral scans with PACS. The target hydrides contain the elements H, D, C, N, O, F and Cl. We will take advantage of the strong dust emission from massive star forming regions to detect multiple absorption components from foreground clouds of diverse properties that are known to intersect the selected sight-lines, along with emission and absorption intrinsic to the background sources. Our investigation will provide a wealth of new information about interstellar hydrides -- addressing key puzzles posed by previous observations from the ground since the 1940's, and recently with ISO, SWAS, and ODIN -- and leaving an important Herschel legacy to astrochemistry and ISM science. We will address the role of high temperature chemical reactions in the formation of interstellar molecules, and the question of how such reactions might be driven. We will also investigate the role of grain surface reactions in interstellar chemistry, and the growth of carbon molecules, bridging the gap between molecules and aggregates, as unique spectroscopic signatures of carbon chains and rings, are accessible in the FIR. Many of the lines that are detectable with Herschel in the local Universe become accessible to ground-based observatories for redshifted sources. Our programme will provide an unique benchmark for the studies of molecular gas at high redshift with ALMA.

Present-day star formation starts in the coldest and densest cores of molecular clouds. Still, our knowledge about the very early stages of star formation is limited. Objects at these stages emit most of their luminosity at FIR wavelengths, which is not observable from the ground. Hence, our view in this wavelength range to date remains fuzzy at best, since all available information from the FIR is generally obtained from small aperture satellites severely lacking spatial resolution. Therefore, data are strongly affected by source blending, especially within protoclusters, where the density of potential protostars is very high. This limits the derivation of core masses and density profiles which is a major drawback for detailed studies of young low-mass cores. In addition, it has severely hampered progress in characterising young and cold high-mass cores which are, on average, far more distant. Nevertheless, detailed knowledge about these pre- and protostellar stages is indispensable for answering fundamental questions about the physics of the early collapse phase, the core fragmentation and the general ways to finally form stars of all masses. With Herschel we have the unique opportunity to deeply scrutinise such cold cradles of stars with unprecedented sensitivity and angular resolution in the FIR. We therefore propose to use the PACS and SPIRE instruments to perform deep and directed FIR mapping of confined regions. We have compiled a unique sample of low and high-mass targets that we identified based on careful preparatory studies (including ISO and Spitzer observations) as very promising sources for the study of initial conditions of star formation. The Herschel data will allow us to reconstruct the (3D) density and temperature structure and assess the energy budget of the cores. Furthermore, Herschel will for the first time enable us to perform an advanced modelling of such cold cores that is not affected by simplifications and parameter ambiguities.

Herschel provides a unique opportunity to study the earliest stages of star formation. What is the origin of the stellar initial mass function (IMF)? This issue is central in local star formation research and for understanding whether the IMF is truly universal or is likely to depend on metallicity, pressure, or temperature. As prestellar cores and young (Class 0) protostars emit the bulk of their luminosity at ~80-400 microns, the Herschel imaging instruments SPIRE and PACS are ideal for taking a census of such objects down to ~0.01-0.1 Msun in the nearby (<0.5 kpc) molecular cloud complexes. We propose an extensive imaging survey of the densest portions of the Gould Belt with SPIRE at 250-500 and PACS at 110-170 microns down to a 5-sigma column sensitivity NH2~10^21 cm^-2 or Av~1. Our goal is to make a complete, homogeneous mapping of the Av>3 regions with SPIRE and of the Av>6 regions with PACS, and representative areas at Av~1-3 levels with both instruments. The survey sensitivity is well matched to the expected cirrus confusion limit, so we should detect structures throughout the maps. The target clouds span a range of physical conditions, from active, cluster-forming complexes to quiescent regions with lower star formation activity. We should detect hundreds Class 0 protostars and thousands prestellar condensations in the entire ~145 deg^2 SPIRE survey, i.e. ~10 times more cold objects than already identified from the ground. These numbers should allow us to derive an accurate prestellar core mass function. The temperature and density structures of the nearest (< 0.2 kpc) cores will be resolved, revealing the initial conditions for individual protostellar collapse. The large spatial dynamic range of the proposed survey will probe the link between diffuse cirrus-like structures and compact self-gravitating cores. Our main scientific goal is to elucidate the physical mechanisms for the formation of prestellar cores out of the diffuse medium, crucial for understanding the origin of stellar masses.

We propose to perform FIR spectroscopy of the warm and dense ISM (WADI) using the unique observational opportunities of Herschel to improve our understanding of the physical and chemical processes controlling the interaction between stars and their environment. The program will focus on four core topics, energy balance of photon-dominated regions (PDRs), photo-induced chemistry, PDR dynamics and kinematics, shock structures. Both radiative (FUV) and dynamical (shocks) processes will be probed, as key factors in the evolution of the ISM. They regulate star formation and may even govern galaxy evolution on large scales. Most of the energy input in star-forming regions is released as FIR radiation, either as dust continuum or as gas cooling lines. The bright cooling lines from these regions are natural tracers of star formation activity throughout the history of the cosmos; detailed understanding of their origin thus provides the basis for proper interpretation of the observations both of the Milky Way, as well as of nearby and distant galaxies. Herschel's unprecedented spectral coverage at high spatial resolution combined with the spectral resolution of the HIFI instrument allows a detailed study of many key tracers of PDRs and shocks. This allows to deeply probe the interaction of stars with their surrounding through radiation (PDRs) and shocks (SNRs). Observing a proper selection of prototype sources and key lines, will give insight into the details of the physical and chemical processes controlling each of the four core topics above, and will thus allow to model the FIR emission of star forming regions.

Mass loss is one of the most fundamental properties of post-main sequence evolution. The mass-loss process leads to the formation of circumstellar shells containing dust and molecules. Although the mass-loss phenomenon has been studied since the 1960s, and important results have been obtained with the IRAS, ISO and Spitzer space missions, the details of the mass-loss process and the formation and evolution of the circumstellar shells are still not well understood. With its improved spatial resolution compared to ISO and Spitzer, better sensitivity, the extension to longer and unexplored wavelength regions, and medium resolution spectrometers, the combination of PACS and SPIRE observations will lead to a significant improvement in our understanding of the phenomena of mass loss and dust formation. The main aims of this programme are three-fold: (1) to study the time dependence of the mass loss process, via a search for shells and multiple shells around a wide range of evolved objects, in order to quantify the total amounts of mass lost at the various evolutionary stages of low to high-mass stars, (2) to study the dust and gas chemistry as a function of progenitor mass, and (3) to study the properties and asymmetries of evolved star envelopes. To this end, a sample of 103 Asymptotic Giant Branch and Red Super Giants, post-AGB and Planetary Nebulae, Luminous Blue Variables and Wolf-Rayet stars, and 5 Supernovae remnants will be imaged with PACS at 70+170 micron, and a sub-set of 32 stars will be imaged at all 3 wavelengths with SPIRE. In spectroscopy, a sample of 55 stars will be observed over the full wavelength range of PACS and, 23 stars will be observed with the SPIRE FTS. The sample of AGB stars has been selected to cover all chemical types (M-, S-, C-stars), variability types (irregular, semi-regular, Miras) and periods, and mass-loss rates. Stars have been selected to have high IRAS fluxes and low background levels. The spectroscopic targets are typically the brightest of the mapping targets

We propose to carry out a comprehensive study of circumstellar envelopes (CSEs) around evolved stars, as a HIFI GTKP. The main scientific aims are to gain deeper insight into the structure, thermodynamics, kinematics and chemistry of CSEs and into the mass-loss history of evolved stars, thereby advancing our understanding on the final stages of stellar evolution of the majority of stars and their resultant impact on the interstellar medium and the cosmic cycle. We will use the unique capabilities of HIFI to probe the inner regions of CSEs, by means of spectrally-resolved observations of the principal cooling transitions: thermal transitions of H2O, and high-excitation rotational transitions of CO and HCN. Such observations provide unique information about the shells where the gas temperatures are 100 - 2000 K and the material is being accelerated. We propose to observe a set of 38 objects, chosen to sample the parameter space of relevance for evolved stars and their circumstellar material. For every star, 3 lines of both 12CO and 13CO will be observed to unravel the mass-loss history. To further unveil the inner structure in the CSEs, observations of different H2O lines are crucial, since H2O is a key molecule to understand the chemistry, the thermodynamics and the dynamics of the inner CSE. We propose to observe a carefully-selected list of H2O transitions covering different excitation degrees, including para- and ortho-H2O lines and a few isotopic lines. The high spectral resolution observations will allow us to determine the velocity field in the warm acceleration regions. With HCN being a major coolant in C-rich CSEs, 2 high-excitation lines will be observed in C-rich AGBs to probe the temperature structure. To further study the oxygen chemistry, we will obtain OH and [OI] lines from PACS GT data. Finally, we will address the puzzling question of the origin of water vapor observed previously in the extreme carbon star IRC+10216, and survey 9 additional C-rich stars for evidence of water.

We propose to use the SPIRE and PACS instruments on Herschel to measure the emission spectrum from dust as well as important cooling lines from the gaseous interstellar medium in sample of 13 very nearby galaxies (M51, M81, NGC2403, NGC891, M83, M82, Arp220, NGC4038/39, NGC1068, NGC4151, CenA, NGC4125, and NGC205). These galaxies have been chosen to probe as wide a region in galaxy parameter space as possible while maximizing the achievable spatial resolution and are already well-studied from X-ray and optical through to radio wavelengths. The far-infrared and submillimeter wavelengths probed by Herschel are absolutely crucial for understanding the physical processes and properties of the interstellar medium,the interplay between star formation and the interstellar medium in galaxies, and how they may depend on the wider galaxian environment.

We will perform a comprehensive far-infrared spectroscopic and photometric survey of infrared bright galaxies at local and intermediate redshifts. Our goal is to use the superior sensitivity, spatial and spectral resolution of Herschel to study these galaxies with minimal extinction effects. We aim to obtain a comprehensive view of the physical processes at work in the interstellar medium of local galaxies ranging from objects with moderately enhanced star formation to the most dense, energetic, and obscured environments in ultra-luminous infrared galaxies (ULIRGs) and around AGN. The objects cover a wide parameter range in luminosity, activity level, and metal enrichment, and will be complemented by a few objects at intermediate redshifts, i.e. at a more active epoch of star formation. In particular we plan to - study the obscuration and physical conditions of the central regions of infrared galaxies by obtaining full PACS and SPIRE spectra of five template starbursts, AGN and ULIRGs. - characterise for a larger local sample the state of the ionised medium and of photo-dissociation and X-ray dominated regions through PACS observations of key diagnostic fine-structure and molecular lines. The densest and warmest region near AGN will also be probed for highly excited CO emission, - determine the role of metallicity in star formation processes of low metallicity galaxies from the nearby LMC/SMC to more distant galaxies, - search for evolution from the intermediate redshift population close to the peak of cosmic star formation till the present time, - study the triggering mechanisms and temporal evolution of infrared activity by photometric mapping of a large sample of interacting galaxies, - determine the structure of a few local templates by spectroscopic mapping along characteristic axes. These PACS line maps will establish the physical conditions of nuclear region, spiral arms/disk, and wind regions.

Herschel/HIFI’s unique spectroscopic capabilities will allow us to make a representative velocity-resolved inventory of important cooling lines in nearby galaxies, AGN and starburst nuclei. Such observations explore the physical conditions within regions of active star formation in low and high metallicity environments, shedding light on the physics of large scale star formation in the contemporary and, by extension, the early universe. Multi-line data combined with numerical radiative transfer and chemical network models quantitatively constrain the various phases of the interstellar medium (ISM). Key lines in Herschel/HIFI’s spectral range include the bright fine-structure lines of neutral and ionized atomic carbon, nitrogen and oxygen, a unique set of water lines, and the high-excitation CO transitions. The far-infrared spectra of many galaxies reflect the gas energy balance through atomic and molecular cooling lines from photo-dissociation regions (PDRs) and forbidden fine-structure lines from HII-regions. Within the beam of an extragalactic observation, any of the ISM components (dense warm PDRs on the surfaces of UV-exposed molecular clouds, low-density warm atomic clouds will contribute to the brightness of the molecular or fine-structure lines. Our high spectral resolution studies will unravel the structure of the ISM by analysis of their main cooling lines. Velocity information provides sub-beam spatial resolution and ties HIFI observations of different species to complementary PACS line integrated intensity maps on larger scales. In addition, water is a key molecule for our understanding of the chemistry and energy balance in the denser ISM. Herschel/HIFI will measure the brightness of the ground-state transitions to determine the gas temperature of the ISM via line ratios.

Despite IRAS, ISO and Spitzer, there is still much we do know about dust in galaxies, partly because of sensitivity limitations and partly because previous telescopes were insensitive to dust colder than about 15 K. Our knowledge is especially poor for ellipticals which have barely been detected by previous telescopes. As part of the SPIRE GT programme, we propose to obtain images at 250, 350 and 520 microns of a sample of 323 galaxies selected to be useful both for studying the dust in individual galaxies and for drawing statistical conclusions about the role of dust in galaxies in general. The Herschel Reference Survey will be the first survey sensitive to all the dust in galaxies and which will detect dust in galaxies of all Hubble types. Apart from its legacy value, we intend to use the survey for the following projects: 1) We will make a comprehensive study of dust along the Hubble sequence, investigating how the dust mass varies with Hubble type. mass of stars, current star formation rate, past star formation rate, and the masses of molecular and atomic gas. 2) We will investigate within individual galaxies the connections between the star formation rate and the different phases of the ISM, from the nucleus to the HI outside the optical disk. 3) We will investigate how the mass and distribution of dust depend on a galaxy's environment. 4) We will investigate whether there is an intergalactic dust cycle by looking for dusty halos, dusty superwinds and tidally-stripped dust around galaxies. 5) We will investigate the origin of dust in ellipticals, and the evolution of the galaxies themselves, by looking for dust disks and dust shells and by looking for correlations between the mass and distribution of the dust and the other properties of the galaxy. 6) We will measure the local luminosity and dust-mass functions, which will be necessary to interpret the results of the deep surveys, another part of the proposed GT programme. The total time required for the survey is 112.6 hours.

While much of what we have gleaned of the details of dust and gas properties and the processes of dust recycling and heating and cooling in galaxies has been limited to Galactic studies, with Herschel we will be able to explore these issues in low metallicity dwarf galaxies which are known by now to exhibit dust and gas properties different from more metal-rich galaxies. Because these objects are relatively nearby, it is possible to relate the observed variations in the SEDs to the actual physical phenomena occuring within the ISM of the galaxy, allowing the construction of a rich interpretative framework for unresolved, more distant galaxies in the early universe. Using the SPIRE and PACS instruments on Herschel, we propose to map the dust and gas in a 51 dwarf galaxies, sampling a broad metallicity range of 1/50 to 1/3 solar. These data, in conjunction with other ancillary data, will be used to construct the emission spectrum of the dust plus that of the gas in the most important cooling lines. The combination of these instruments onboard Herschel will provide the first opportunity to study the dust and gas in extremely low metallicity environments that have not yet experienced repeated recycling through the ISM. The interpretation of this data will open the door to comprehending primordial ISM conditions and star formation in the young universe.

We describe a key programme using the unprecedented sensitivity and spatial resolution of Herschel for a comprehensive far-infrared photometric survey of the extragalactic sky. Blank field surveys using PACS at 170, 110 and 75micron are supplemented with targeted observations of massive z~1 clusters and lensing clusters. We will resolve the bulk of the Cosmic Infrared Background, determine the nature of its constituent sources and trace the evolution of dust-obscured star formation. Our survey will study the evolution of galaxies and AGN over a wide range of redshifts and in environments of different density, and provide the crucial far-infrared measurements lacking for a full understanding of intermediate and high redshift galaxy populations previously identified at other wavelengths. We have chosen fields with excellent multi-wavelength coverage enabling both rapid science results and a lasting legacy value. This survey is coordinated with Herschel/SPIRE observations of the same fields in a Key programme submitted by the SPIRE SAG 1.

The detection of a significant fraction of the highest redshift quasars (z > 5) in the (sub-)mm wavelength range indicates that a substantial amount of dust has been synthesized already during the first billion year since the Big Bang. Recent 24 micron observations with Spitzer have shown that very hot dust is present close to the QSO core in most z >5 quasars. However, both the (sub-)mm and MIR observations can only catch tails of the dust emission spectrum, at lambda_rest > 200 µm, and at lambda_rest < 5 µm, respectively. Measuring the peak of the dust emission, expected to reach 10 ... 30 mJy around lambda_rest ~ 50 µm (120µm < lambda_obs < 700µm), has been beyond the capabilities of FIR satellites or ground-based sub-mm telescopes. Thus, critical properties, such as FIR luminosity, dust temperatures and mass, remain unconstrained. To improve on this situation, we propose a Herschel Guaranteed Time Key Programme (GT KP) to collect far-infrared and sub-millimeter photometry of more than 100 high redshift quasars using the PACS and SPIRE instruments. We plan to determine the SEDs of three samples of QSOs: (i) all z > 5 quasars known to date, (ii) a dozen radio loud quasars and galaxies at the highest redshifts, and (iii) 29 Broad Absorption Line (BAL) quasars together with a comparison sample of 17 non-BAL QSOs at matching redshifts. In addition, we plan to obtain PACS spectroscopy of four very dust-rich and lensed high-redshift QSOs and galaxies for spectral line diagnostics, which will help to disentangle the contributions of AGN- and starburst-heated dust and thus complement the SED-based study. We will spend in total 165 hours of PACS GT in this key programme, 115 hours for the photometry with PACS and SPIRE, and 50 hours for the FIR spectroscopy.

A central challenge in astrophysics today is to understand the complex processes of galaxy formation: the development of galactic structure, the conversion of gas into stars, and the growth of supermassive black holes. The far-infrared / submillimetre waveband is of particular importance for studying these processes because roughly half of the cosmic energy density produced by galaxies arises from optical/UV starlight that has been absorbed by dust and reradiated at these wavelengths. Existing surveys are already presenting a serious challenge for theorists, revealing many more luminous, massive galaxies at high redshifts than are predicted by simple prescriptions within the hierarchical merging paradigm. Submillimetre surveys however have been extremely limited but have already provided tantalizing clues to a strongly evolving population of infrared-luminous galaxies. We propose HerMES, the Herschel Multi-tiered Extragalactic Survey, to chart the formation and evolution of infrared galaxies throughout cosmic history. HerMES consists of a nested set of fields that will bring unprecedented depth and breadth to the study of infrared galaxies. We will use HerMES to measure the bolometric emission of infrared galaxies, study the evolution of the luminosity function, measure their clustering properties, and probe populations of galaxies below the confusion limit through lensing and statistical techniques. HerMES is closely coordinated with the PACS Evolutionary Probe survey. We will make maximum use of ancillary surveys from radio to X-ray wavelengths to facilitate redshift determination, rapidly identify unusual objects, and understand the relationships between thermal dust emission and other emission mechanisms. HerMES will provide a rich data set legacy for the greater astronomical community to mine for years to come.