.7663 THE ASTRONOMICAL JOURNAL VOLUME 98, NUMBER 3 SEPTEMBER 1989 98. THE IRAS BRIGHT GALAXY SAMPLE. IV. COMPLETE IRAS OBSERVATIONS B. T. Soifer, L. Boehmer, G. Neugebauer, and D. B. Sanders Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, California 91125 1989AJ Received 15 March 1989; revised 15 May 1989 ABSTRACT Total flux densities, peak flux densities, and spatial extents, are reported at 12, 25, 60, and 100 /¿m for all sources in the IRAS Bright Galaxy Sample. This sample represents the brightest examples of galaxies selected by a strictly infrared flux-density criterion, and as such presents the most complete description of the infrared properties of infrared bright galaxies observed in the IRAS survey. Data for 330 galaxies are reported here, with 313 galaxies having 60 fim flux densities >5.24 Jy, the completeness limit of this revised Bright Galaxy sample. At 12 /¿m, 300 of the 313 galaxies are detected, while at 25 pm, 312 of the 313 are detected. At 100 pm, all 313 galaxies are detected. The relationships between number counts and flux density show that the Bright Galaxy sample contains significant subsamples of galaxies that are complete to 0.8, 0.8, and 16 Jy at 12, 25, and 100 pm, respectively. These cutoffs are determined by the 60 pm selection criterion and the distribution of infrared colors of infrared bright galaxies. The galaxies in the Bright Galaxy sample show significant ranges in all parameters measured by IRAS. All correla- tions that are found show significant dispersion, so that no single measured parameter uniquely defines a galaxy’s infrared properties. Galaxies selected to be “warm” and “cold” in the observed ratio of flux densities at 25 and 60 pm can be distinguished in several of the infrared properties. For the galaxies in the Bright Galaxy sample both the ratio of flux densities ^(60 pm)/Sv(\0D pm) and 5^(12 pm)/ Sv{25 pm) correlate with infrared luminosity, and more significantly with the ratio of infrared-to- visible flux. The relation between these two ratios of flux densities, found previously by several workers, holds for the sample, with different slopes appearing to exist for the warmer and colder galaxies in the sample. It is suggested that single photon heating of small grains, often the dominant source of 12 and 25 pm radiation from galaxies, significantly affects the emission of some galaxies at 60 pm, while optical depth effects appear to alter the emergent radiation at 12 and 25 pm. The warmer galaxies generally have less dust mass at a given infrared luminosity than do the cold galaxies. I. INTRODUCTION source with color corrected 60 pm flux density >5.4 Jy (roughly ten times the lowest measurable flux density of the The IRAS Bright Galaxy Sample (hereafter referred to as IRAS Point Source Catalog at 60 pm) in an area of the BG sample) was chosen as a representative sample of the —14,500° sq. with declination, <5 > — 30°, and Galactic lati- brightest extragalactic sources in the IRAS survey. The sam- tude, I > 30°. Sources were taken from the IRAS Point ple consists of all extragalactic sources brighter than 5.24 Jy Source Catalog Version 1.0 (PSC), the IRAS Catalog of at 60 pm, in an area of sky at high Galactic latitude. Soifer et Small Scale Structures (SSS), and a preliminary version of al. (1986) derived the far-infrared luminosity function for 10 the Catalog of IRAS Observations of Large Optical Galaxies the BG sample for far-infrared luminosities Z, > 10 L0. In (Rice et al. 1988). Analysis of the relationship between Paper I ( Soifer et a/. 1987 ), the full sample was described, 60 number counts and flux density, hereafter called the “log N- and 100 pm flux densities were reported for these galaxies, logS” relation, for this sample indicated that the sample is and the far-infrared luminosity function was derived for the complete to the flux density cutoff of 5.4 Jy. entire sample. This paper completes our examination of the The best flux density estimates at 60 and 100 pm for the IRAS observed properties of the BG sample. BG sample taken from the PSC, SSS, and Rice et al. ( 1988) Because the BG sample represents the brightest extraga- were reported in Paper I. No attempt was made in that paper lactic sources at 60 pm, it presents the best opportunity to to report data at 12 and 25 pm because the objects were often study the infrared properties of infrared bright galaxies. Fur- extended at these wavelengths, and in many cases no detec- thermore, the only selection criteria applied were area con- tions were reported in the aforementioned IRAS catalogs. straints and a flux-density limit at 60 pm. This sample thus In order to provide flux measurements for the sources in should be unbiased except for the specific 60 pm selection the BG sample at 12 and 25 pm, as well as to improve the 60 criterion, and thereby should present a well-defined view of and 100 pm flux estimates, improved IRAS measurements the infrared properties of infrared bright galaxies. for the BG sample were obtained from two sources. For gal- In this paper we report the 12, 25, 60, and 100 pm flux axies with large angular diameters, the IRAS flux densities densities for all the galaxies in the BG sample, using the most were taken from the Catalog of IRAS Observations of Large accurate reductions of the IRAS observations presently Optical Galaxies (Rice et al. 1988). For all other galaxies in available. The study of how the infrared properties of these the BG sample the IRAS data were reprocessed by the galaxies relate to their optical morphology is the subject of a addscan/scanpi processing (Helou et al. 1988) at the In- subsequent paper (Sanders cía/. 1989). frared Processing and Analysis Center. All the measure- IL THE SAMPLE AND DATA REDUCTION ments were brought onto the calibration scale of the PSC, Version 2.0. The selection criteria for the BG sample were described in After projecting the individual detector tracks onto a Paper I. Briefly, the original criteria were: any extragalactic “mean track” for the source, the addscan processing 766 Astron. J. 98 (3), September 1989 0004-6256/89/030766-32$00.90 © 1989 Am. Astron. Soc. 766 © American Astronomical Society • Provided by the NASA Astrophysics Data System .7663 767 SOIFER ETAL. : IRAS BRIGHT GALAXY SAMPLE 767 98. coadds in one-dimensional data from all IRAS detectors found to meet the 60 /zm flux-density criterion based on its crossing the position of the source. The data are coadded extended emission while searching for galaxies with low ra- after subtracting a second-order baseline fitted to the data tios of Sv (60i¿m)/Sv ( 100 /¿m). The sources that fall below within + of the central position (but excluding the data the new selection limit are listed in Table 1(b). Thus there 1989AJ within + 4 min). The result of this coaddition is a one di- are 313 sources with flux density at 60/zm Sv (60/zm) >5.24 mensional “drift scan” of flux density versus position along Jy in the statistically complete BG sample. the mean track. For all sources included in Paper I, the posi- For those sources that show evidence of extended emis- tion taken for the source was the position reported in Paper sion, i.e., those classified as marginally resolved (U + ) or I. For the large galaxies, the optical position of the galaxy resolved (R), additional data are included in Table II. The (de Vaucouleurs, de Vaucouleurs, and Corwin 1976) was contents of this table are described in Appendix B. For refer- assumed. For the three sources added from the PSC Version ence, the average values of the full widths at 25% and 50% of 2.0, the position was taken from that catalog. Analysis of the peak flux density are given in Table III as a function of wave- positional uncertainties of known sources (IRAS Explana- length for an unresolved source (Helou and Kopan 1988, tory Supplement 1988) suggests that the best positions for private communication). the infrared emission from the galaxies detected are those Table IV shows the distribution among the extent codes measured directly by IRAS. for the sources at each wavelength. Table IV reflects the The flux density of the source was estimated in several changing angular resolution of the IRAS instrument as a ways based on the coadded one-dimensional data. A “point- function of wavelength. While nearly § of the sources in the source template” was fitted to the source, to derive both the BG sample are resolved or marginally resolved at 12 and 25 “Point Source Catalog” equivalent flux density and the cor- /zm, with a detector width of more than half the sources relation coefficient of the fit. In addition, the total flux den- are unresolved at 60 /zm with a detector width of 1.5', and sity within + 4' of the source position was determined by more than | of the sources are unresolved at 100 /zm with integrating the flux density versus position data. The point- detector width of 3' (IRAS Explanatory Supplement 1988). source flux density and total flux density were derived for all four IRAS bands for all sources. After processing the data, the output was inspected for each source at all wavelengths IV. RESULTS to determine if the source was adequately fit by the point- a) Completeness of the Bright Galaxy Sample source template. If this was adequate, only the flux density from the point-source template fit was retained as the best estimator of the IRAS flux density.