The Herschel Multi-tiered Extragalactic Survey: HerMES

Abstract: The Herschel Multi-tiered Extragalactic Survey, HerMES, is a legacy program designed to map a set of nested fields totalling ~380 deg^2. Fields range in size from 0.01 to ~20 deg^2, using Herschel-SPIRE (at 250, 350 and 500 \mu m), and Herschel-PACS (at 100 and 160 \mu m), with an additional wider component of 270 deg^2 with SPIRE alone. These bands cover the peak of the redshifted thermal spectral energy distribution from interstellar dust and thus capture the re-processed optical and ultra-violet radiation from star formation that has been absorbed by dust, and are critical for forming a complete multi-wavelength understanding of galaxy formation and evolution. The survey will detect of order 100,000 galaxies at 5\sigma in some of the best studied fields in the sky. Additionally, HerMES is closely coordinated with the PACS Evolutionary Probe survey. Making maximum use of the full spectrum of ancillary data, from radio to X-ray wavelengths, it is designed to: facilitate redshift determination; rapidly identify unusual objects; and understand the relationships between thermal emission from dust and other processes. Scientific questions HerMES will be used to answer include: the total infrared emission of galaxies; the evolution of the luminosity function; the clustering properties of dusty galaxies; and the properties of populations of galaxies which lie below the confusion limit through lensing and statistical techniques. This paper defines the survey observations and data products, outlines the primary scientific goals of the HerMES team, and reviews some of the early results.

• The paper presents a comprehensive legacy survey using Herschel’s SPIRE and PACS instruments to map 380 square degrees and detect roughly 100,000 galaxies at a 5-sigma significance.
• The paper employs a multi-tiered observational strategy that combines deep and shallow fields with extensive multi-wavelength ancillary data to explore infrared properties of galaxies.
• The paper unveils early insights into the evolution of galaxy luminosity functions and star formation rates, setting a robust foundation for future investigations with new observatories like ALMA.

Overview of the Herschel Multi-tiered Extragalactic Survey (HerMES) Paper

The paper presents a detailed overview of the Herschel Multi-tiered Extragalactic Survey (HerMES), conducted using the Herschel Space Observatory's SPIRE and PACS instruments. HerMES represents an extensive legacy program aimed at mapping various celestial fields to support the understanding of galaxy formation and evolution across cosmic epochs. The survey covers approximately 380 square degrees of the sky in multiple bands at 100, 160, 250, 350, and 500 microns. This comprehensive wavelength coverage is selected to capture the peak of the redshifted thermal spectral energy distributions from interstellar dust, providing critical insights into the re-processed optical and ultraviolet radiation from star formation absorbed by dust.

Survey Design and Objectives

HerMES is designed as a multi-tiered survey that includes fields of varying sizes, from deeply observed smaller fields to expansive shallow ones. The survey aims to detect around 100,000 galaxies at a 5-sigma significance in well-studied sky regions. It is closely coordinated with the PACS Evolutionary Probe (PEP) survey to maximize scientific output from the combined data. The fields were selected based on their extensive multi-wavelength ancillary data availability, from radio to X-ray coverage, facilitating redshift determination, the identification of unusual objects, and investigations into the associations between thermal dust emissions and other astronomical processes.

Scientific Questions and Goals

HerMES seeks to address several key scientific questions:

• Determining the total infrared emission and luminosity function of galaxies through cosmic time.
• Understanding the clustering properties of dusty galaxies to probe the large-scale structure of the universe.
• Investigating the properties of galaxy populations below the traditional confusion limit through innovative approaches like gravitational lensing and statistical methodologies.

Early Scientific Insights and Legacy Value

The initial findings and data from HerMES are expected to provide substantial insights into star formation rates, galaxy evolution, and clustering dynamics. Early results have demonstrated strong evolution in the galaxy luminosity function to redshifts of about 1, implying active star formation during these epochs. By leveraging the extensive ancillary data available for these fields, HerMES facilitates comprehensive multi-wavelength investigations of galaxy properties across different cosmic epochs and environments.

The data products from HerMES are expected to have significant archival value, laying the groundwork for future astronomic research. The suite of deliverables will include SPIRE and PACS maps and catalogs, along with cross-identifications with other available data catalogs. These will be invaluable for follow-up investigations with new facilities like ALMA, supporting a wide array of astrophysical research.

Conclusion

HerMES represents a pivotal legacy survey using the Herschel Space Observatory, aimed at unraveling the complexities of galaxy formation and evolutionary processes. Through its extensive and coordinated observational strategy, it provides a rich dataset poised to answer fundamental questions about our universe and set the stage for future astronomical discoveries. The systematic and archival-ready approach ensures that HerMES will continue to support scientific exploration long after its initial data release.