The Bolocam Galactic Plane Survey (BGPS) is a 1.1 mm continuum survey of the Galactic Plane made using Bolocam on the Caltech Submillimeter Observatory. Millimeter-wavelength thermal dust emission reveals the repositories of the densest molecular gas, ranging in scale from cores to whole clouds. By pinpointing these regions, the connection of this gas to nascent and ongoing star formation may be explored. The BGPS coverage totals 170 square degrees (with 33" FWHM effective resolution). The survey is contiguous over the range -10.5 ≤ l ≤ 90.5, |b| ≤ 0.5. Towards the Cygnus X spiral arm, the coverage was flared to |b| ≤ 1.5 for 75.5 ≤ l ≤ 87.5. In addition, cross-cuts to |b| ≤ 1.5 were made at l = 3, 15, 30 and 31. The total area of this section is 133 square degrees. With the exception of the increase in latitude, no pre-selection criteria were applied to the coverage in this region. In addition to the contiguous region, four targeted regions in the outer Galaxy were observed: IC1396 (9 square degrees, 97.5 ≤ l ≤ 100.5, 2.25 ≤ l ≤ 5.25), a region towards the Perseus Arm (4 square degrees centered on l = 111, b=0 near NGC7538), W3/4/5 (18 square degrees, 132.5 ≤ l ≤ 138.5) and Gem OB1 (6 square degrees, 187.5 ≤ l ≤ 193.5). The survey has detected approximately 8,400 sources, to an rms noise level in the maps ranging from 30 to 60 mJy beam^-1. The BGPS survey and catalog provide an important database for future sub/millimeter observations with the Herschel Space Observatory, ALMA, SCUBA-2, APEX, and others.

The Caltech Submillimeter Observatory is operated by Caltech under a contract from the NSF. We would like to acknowledge the staff and day crew of the CSO for their assistance over the many years of this project.

For a detailed description of the BOLOCAM GPS survey observations and methods, please refer to the BGPS paper. Important caveats are as follows. The effective resolution of the survey is that of a Gaussian PSF of 33" FWHM (corresponding to an area of 2.9×10^-8 ster). The positional uncertainty of the maps is 6" RMS. The maps are calibrated into Jy beam^-1 using Mars as a primary flux standard, and accounting for atmosphere opacity variations in real time. The processing of the maps removes more than 90% of flux for features with extents larger than 5.9', and attenuates the aperture flux of structures extending to 3.8' by 50%. We have compared our flux densities to those of Motte et al 2007 and Matthews et al 2009 and find that we need to multiply our flux densities up by a factor of 1.5 to match. We have investigated possible sources for the discrepancy, but do not currently understand the source of the difference. For now, we recommend multiplying the flux densities in the maps and catalogs presented here by the factor 1.5+0.15 to obtain consistency with other data sets. We are continuing to explore the source of this discrepancy, particularly in the calibration and filtering stages of the data pipeline. The latest data releases should be obtained from this website.

The BGPS image data are cataloged with a custom algorithm, Bolocat, designed to identify bright, compact sources as well as filamentary structure. Bolocat operates on maps in a three step process:

1. Significant emission is identified relative to a background noise level.
2. Regions of significant emission are divided into sources using a seeded watershed algorithm, similar to Clumpfind or Source Extractor, assigning each pixel to a single catalog source.
3. The properties of sources are determined using moments of the emission distribution with respect to the coordinate axes.

Bolocat sources are usually extended asymmetric structures. The Bolocam catalog reports source positions based on the maximum of emission in each source, which are likely the best targets for follow-up observations of these millimeter continuum sources. Source centroids, sizes and flux densities are also reported. The catalog release includes pixel maps of the catalog sources that indicate which positions in the original maps are included in a specific catalog source. Full details of the cataloging methods are available in a companion paper.

The BGPS team:

John Bally, James Aguirre, Eric Todd Bradley, Richard Chamberlin, Claudia Cyganowski, Meredith Drosback, Neal Evans, Adam Ginsburg, Jason Glenn, Paul Harvey, Miranda Nordhaus, Erik Rosolowsky, Josh Walawender, Jonathan Williams, Guy Stringfellow, Yancy Shirley, Wayne Schlingman, Cara Battersby, and Darren Dowell

The BGPS project is supported by the National Science Foundation through NSF grant AST-0708403. J.A. was supported by a Jansky Fellowship from the National Radio Astronomy Observatory (NRAO). The first observing runs for BGPS were supported by travel funds provided by NRAO. Team support was provided in part by NSF grant AST-0607793 to the University of Texas at Austin.

The Bolocam team:

Peter A.R. Ade, Mihail Amarie, James J. Bock, Samantha F. Edgington, Jason Glenn, Alexey Goldin, Sunil Golwala, Douglas Haig, Andrew E. Lange, Glenn Laurent, Philip D. Mauskopf, Minhee Yun, and Hien Nguyen

Support for the development of Bolocam was provided by NSF grants AST-9980846 and AST-0206158.