CDROM/AJ/V106/P0530 LSB Disk Galaxies (Bothun+ 1993) ================================================================================ The Small Scale Environment of Low Surface Brightness Disk Galaxies Gregory D. Bothun, James M. Schombert, Christopher D. Impey, David Sprayberry, & Stacy S. McGaugh <1993, AJ, 106, 530> =1993AJ....106..530B ================================================================================ Abstract: We use a sample of approximately 340 low surface brightness (LSB) disk galaxies with measured redshifts in combination with the Center for Astrophysics redshift survey to test the hypothesis that LSB galaxies have a deficit of nearby companion galaxies compared to high surface brightness (HSB) disk galaxies. We find a very strong statistical deficit of galaxies located within a projected radius of 0.5 Mpc and within a velocity of 500 km/s around LSB disk galaxies compared to HSB ones. Further, comparing LSB and HSB disk galaxies which are located in the same portion of the sky indicates that the average distance to the nearest neighbor is 1.7 times farther for LSB disk galaxies. A Komologorov-Smirnoff test rules out, at greater than the 99% confidence level, the hypothesis that the distribution of nearest-neighbor distances is the same for HSB and LSB disk galaxies. We speculate that LSB disk galaxies have relatively long formation time scales and therefore must form in relative isolation. In addition, the lack of tidal interactions over a Hubble time serves to suppress the overall star-formation rate as no external trigger is available to help clump the gas. The observed low surface densities of HI in combination with the low probability of tidal interactions effectively prevents these disk galaxies from evolving very rapidly. File Summary: -------------------------------------------------------------------------------- File Name Lrecl Records Explanations -------------------------------------------------------------------------------- table1.dat 43 86 Summary of counts table2.dat 75 12 Difference in mean counts table3.dat 50 15 Nearest-neighbor summary table4.dat 69 38 The most isolated LSB galaxies table5.dat 80 37 The most popular LSB galaxies tables.tex 109 310 TeX version of tables format.tex 85 365 Formatting macros needed by tables.tex -------------------------------------------------------------------------------- Comments for file: table1.dat -------------------------------------------------------------------------------- Table 1 contains the results of raw counts of companions out to a specified radius of approximately 2.4 Mpc. While this statistic carries virtually no spatial information, it does provide a rough test of the hypothesis that LSB galaxies have on average, fewer nearby galaxies than HSB disk galaxies. The first 6 rows refer to all companions contained within a projected radius of 2.4 Mpc and the means are formed without any rejection. Error bars on these means represent root N counting noise. For the remaining entries mean counts are given in annuli of width 0.5 Mpc. Error bars are sigma/N^(-0.5). -------------------------------------------------------------------------------- Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 8 A8 --- Sample Sample designation 9-10 2X --- --- Blank 11-17 A7 km/s Vrange Velocity range 18-22 F5.1 Mpc Rad Projected radius to which counts were made 23-28 I6 --- Ngal Number of galaxies forming the sample mean 29-32 I4 --- Nrej Number of rejected galaxies 33-38 F6.2 --- Counts *Sample mean 39-43 F5.2 --- e_Counts Error in sample mean. -------------------------------------------------------------------------------- Notes for file: table1.dat -------------------------------------------------------------------------------- Counts: Sample mean. In general, mean quantities are calculated after one cycle of 2.5 sigma projection. -------------------------------------------------------------------------------- Comments for file: table2.dat -------------------------------------------------------------------------------- Table 2 summarizes the differences between the means, in units of sigma, in the comparison of various LSB and HSB samples. The POSS and APM samples are compared at radii of 0.5, 1.0, 1.5, and 2.0 Mpc to the total HSB sample as well as to the respective HSB sample that covers the equivalent area of sky. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 8 A8 --- Sample Sample designation 9-10 2X --- --- Blank 11-17 A7 km/s Vrange Velocity range 18-23 F6.1 --- POSS_05 []? POSS comparison at 0.5 Mpc radius 24-27 F4.1 --- POSS_05B *[]? POSS at 0.5 Mpc considering subset B 28-32 F5.1 --- POSS_10 []? POSS comparison at 1.0 Mpc radius 33-36 F4.1 --- POSS_10B *[]? POSS at 1.0 Mpc considering subset B 37-41 F5.1 --- POSS_15 []? POSS comparison at 1.5 Mpc radius 42-45 F4.1 --- POSS_15B *[]? POSS at 1.5 Mpc considering subset B 46-50 F5.1 --- POSS_20 []? POSS comparison at 2.0 Mpc radius 51-54 F4.1 --- POSS_20B *[]? POSS at 2.0 Mpc considering subset B 55-60 F6.1 --- APM_05 []? APM comparison at 0.5 Mpc radius 61-65 F5.1 --- APM_10 []? APM comparison at 1.0 Mpc radius 66-70 F5.1 --- APM_15 []? APM comparison at 1.5 Mpc radius 71-75 F5.1 --- APM_20 []? APM comparison at 2.0 Mpc radius -------------------------------------------------------------------------------- Notes for file: table2.dat -------------------------------------------------------------------------------- POSS_05B, POSS_10B, POSS_15B, POSS_20B: POSS at 0.5, 1.0, 1.5, and 2.0 Mpc obtained by considering subset B in comparison to the POSS HSB sample -------------------------------------------------------------------------------- Comments for file: table3.dat -------------------------------------------------------------------------------- Table 3 summarizes the results of another statistical test for investigating differences in the small scale environment between HSB and LSB samples, which involves determining the mean projected distance to the closest galaxy. However, in addition to noting the mean difference one can also apply the KS test on the respective cumulative distribution functions. This was done by binning the distance to the nearest projected galaxy in bins of width 0.2 Mpc from 0 to 2.4 Mpc. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table3.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 8 A8 --- Sample Sample designation 9-10 2X --- --- Blank 11-14 I4 --- Ngal No. galaxies with 1+ companion within 2.0 Mpc 15-16 2X --- --- Blank 17-23 A7 km/s Vrange Velocity range 24-29 F6.2 Mpc Dist Mean projected distance to nearest companion 30-34 F5.2 Mpc e_Dist Error in mean projected distance 35-39 F5.2 --- POSS_KS []? KS statistic, Dmax, for the POSS sample 40-42 I3 --- c_POSS_KS []? The confidence level that Dmax exceeds 43-47 F5.2 --- APM_KS []? KS statistic, Dmax, for the APM sample 48-50 I3 --- c_APM_KS []? The confidence level that Dmax exceeds -------------------------------------------------------------------------------- Comments for file: table4.dat -------------------------------------------------------------------------------- Table 4 lists the most isolated LSBs. An isolated LSB is one defined as having zero companions in the CfA Redshift Catalog (ZCAT) out to a projected radius of 2 Mpc. Of course, there could be nearby projected galaxies that are not in ZCAT and therefore the authors performed a visual inspection of the plate material for all the galaxies listed in Table 4. The results of the inspection are listed in the comments. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table4.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 7 A7 --- Name Galaxy name 8- 9 2X --- --- Blank 10-13 A4 --- Sample Sample designation (POSS or APM) 14-15 2X --- --- Blank 16-17 F2.0 h RAh Right ascension 1950 18 1X --- --- ':' 19-20 F2.0 min RAm R.A. 1950 21 1X --- --- ':' 22-25 F4.1 s RAs R.A. 1950 26 1X --- --- Blank 27 A1 --- DE- Sign of Declination 1950 28-29 F2.0 deg DEd Declination 1950 30 1X --- --- ':' 31-32 F2.0 arcmin DEm Dec. 1950 33 1X --- --- ':' 34-35 F2.0 arcsec DEs Dec. 1950 36-41 I5 km/s Vel Velocity 42-43 2X --- --- Blank 44-69 A26 --- Comments Comments -------------------------------------------------------------------------------- Comments for file: table5.dat -------------------------------------------------------------------------------- Table 5 lists the most populous LSB galaxies. A populous LSB is defined as one having either 3 or more companions within a projected radius of 0.5 Mpc or 8 or more companions with a projected radius of 2 Mpc. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table5.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 7 A7 --- Name Galaxy name 8- 9 2X --- --- Blank 10-13 A4 --- Sample Sample designation (POSS or APM) 14-15 2X --- --- Blank 16-17 F2.0 h RAh Right ascension 1950 18 1X --- --- ':' 19-20 F2.0 min RAm R.A. 1950 21 1X --- --- ':' 22-25 F4.1 s RAs R.A. 1950 26 1X --- --- Blank 27 A1 --- DE- Sign of Declination 1950 28-29 F2.0 deg DEd Declination 1950 30 1X --- --- ':' 31-32 F2.0 arcmin DEm Dec. 1950 33 1X --- --- ':' 34-35 F2.0 arcsec DEs Dec. 1950 36-41 I5 km/s Vel Velocity 42-43 2X --- --- Blank 44-51 A8 --- Nearby *Name of brightest galaxy within 2 Mpc 52-53 2X --- --- Blank 54-80 A27 --- Comments Comments -------------------------------------------------------------------------------- Notes for file: table5.dat -------------------------------------------------------------------------------- Nearby: Name of the brightest galaxy within 2 Mpc or a known structure near the galaxy -------------------------------------------------------------------------------- ================================================================================ (End) Lee Brotzman [ADS] 09-Mar-1995