KINGFISH -- Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel: Survey Description and Image Atlas

Abstract: The KINGFISH project (Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel) is an imaging and spectroscopic survey of 61 nearby (d < 30 Mpc) galaxies, chosen to cover a wide range of galaxy properties and local interstellar medium (ISM) environments found in the nearby Universe. Its broad goals are to characterize the ISM of present-day galaxies, the heating and cooling of their gaseous and dust components, and to better understand the physical processes linking star formation and the ISM. KINGFISH is a direct descendant of the Spitzer Infrared Nearby Galaxies Survey (SINGS), which produced complete Spitzer imaging and spectroscopic mapping and a comprehensive set of multi-wavelength ancillary observations for the sample. The Herschel imaging consists of complete maps for the galaxies at 70, 100, 160, 250, 350, and 500 microns. The spectal line imaging of the principal atomic ISM cooling lines ([OI]63um, [OIII]88um, [NII]122,205um, and [CII]158um) covers the subregions in the centers and disks that already have been mapped in the mid-infrared with Spitzer. The KINGFISH and SINGS multi-wavelength datasets combined provide panchromatic mapping of the galaxies sufficient to resolve individual star-forming regions, and tracing the important heating and cooling channels of the ISM, across a wide range of local extragalactic ISM environments. This paper summarizes the scientific strategy for KINGFISH, the properties of the galaxy sample, the observing strategy, and data processing and products. It also presents a combined Spitzer and Herschel image atlas for the KINGFISH galaxies, covering the wavelength range 3.6 -- 500 microns. All imaging and spectroscopy data products will be released to the Herschel user generated product archives.

• The paper presents a detailed far-infrared survey with Herschel that maps the interstellar medium properties of 61 nearby galaxies.
• It employs multi-wavelength imaging and spectroscopy to analyze dust heating and cooling mechanisms associated with star formation.
• The study calibrates FIR cooling lines as tracers for star formation rates, advancing our understanding of galaxy evolution.

Overview of the KINGFISH Project

The KINGFISH project, or "Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel," represents a significant astronomical endeavor aimed at understanding the interstellar medium (ISM) of nearby galaxies. Utilizing the Herschel Space Observatory, the project encompasses an extensive survey of 61 galaxies within 30 Mpc, meticulously chosen to cover a broad spectrum of galaxy properties and ISM environments.

Scientific Objectives and Methodology

The research aims to thoroughly characterize the ISM in present-day galaxies by examining the thermal properties of both gaseous and dust components, and to explore the complex relationship between star formation and the ISM. The survey builds upon previous groundwork laid by the Spitzer Infrared Nearby Galaxies Survey (SINGS), combining its rich dataset with new infrared observations taken with Herschel. The observational strategy involves imaging at multiple wavelengths (70, 100, 160, 250, 350, and 500 microns) and spectroscopic mapping of key atomic cooling lines within the ISM, such as [OI]63 µm and [CII]158 µm.

Key Findings and Results

The combination of these high-resolution FIR and submillimeter observations with ancillary multiwavelength data enables detailed mapping of ISM processes across different environments. Notably, KINGFISH data facilitate the spatial resolution of star-forming regions, providing vital insights into the dust heating mechanisms and ISM cooling processes that occur within these galaxies. The extensive wavelength coverage permits a more nuanced dissection of dust temperature distributions and heating sources, ranging from intense star-forming regions to more diffuse interstellar environments.

Among the numerous findings, two key observations stand out:

1. Dust Heating and Cooling: Through the detailed SED maps covering the UV to FIR range, the researchers have been able to analyze the dust heating across different scales and correlate this with star formation activities. Importantly, the combination of Herschel’s spatial resolution with existing Spitzer data offers significant enhancements in probing the thermal structure of dust emissions within these galaxies.
2. ISM Cooling Lines as SFR Tracers: The project also explores the applicability of FIR cooling lines as tracers for star formation rates (SFR) based on their detection in high-redshift galaxies. KINGFISH provides essential local calibrations needed to understand the utility and limitations of employing such lines in SFR diagnostics for various galaxy types.

Implications and Future Directions

Practically, the KINGFISH dataset serves as an invaluable resource for calibrating star formation diagnostics, offering detailed baseline information against which high-redshift observations can be compared. Such data are crucial for understanding galaxy evolution across cosmic time. Theoretically, this work advances models of galaxy formation and dynamics by linking observable ISM properties with underlying processes of star formation, enhancing our understanding of galaxy evolution mechanisms.

Looking forward, the interrelated study of dust properties, gas dynamics, and star formation as facilitated by KINGFISH will continue to enrich our astrophysical paradigms. Potential future lines of inquiry may involve deeper exploration into the variations in ISM properties across different environments, especially in relation to metallicity and galactic structure, or extending these methodologies to more distant or less-resolved galaxy samples.

Overall, the KINGFISH project exemplifies a meticulous effort in mapping the intricate relationships between star formation and the ISM, setting a pivotal foundation for future explorations in galaxy astrophysics.