J/A+A/560/A9 AMIGA. Revision of the isolation degree (Argudo-Fernandez+, 2013) ================================================================================ The AMIGA sample of isolated galaxies. XII. Revision of the isolation degree for AMIGA galaxies using the SDSS. Argudo-Fernandez M., Verley S., Bergond G., Sulentic J., Sabater J., Fernandez Lorenzo M., Leon S., Espada D., Verdes-Montenegro L., Santander-Vela J.D., Ruiz J.E., Sanchez-Exposito S. =2013A&A...560A...9A (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Galaxies, photometry ; Spectroscopy Keywords: galaxies: general - galaxies: fundamental parameters - galaxies: formation - galaxies: evolution Abstract: To understand the evolution of galaxies, it is necessary to have a reference sample where the effect of the environment is minimized and quantified. In the framework of the AMIGA project (Analysis of the interstellar Medium of Isolated GAlaxies), we present a revision of the environment for galaxies in the Catalogue of Isolated Galaxies (CIG, Karachentseva 1973, Cat. VII/82) using the ninth data release of the Sloan Digital Sky Survey (SDSS-DR9). The aims of this study are to refine the photometric-based AMIGA sample of isolated galaxies and to provide an improvement of the quantification of the isolation degree with respect to previous works, using both photometry and spectroscopy. We developed an automatic method to search for neighbours within a projected area of 1Mpc radius centred on each primary galaxy to revise the CIG isolation criteria introduced by Karachentseva (1973, Cat. VII/82). The local number density at the fifth nearest neighbour and the tidal strength affecting the CIG galaxy were estimated to quantify the isolation degree. Of the 636 CIG galaxies considered in the photometric study, 426 galaxies fulfil the CIG isolation criteria within 1Mpc, taking into account projected neighbours. Of the 411 CIG galaxies considered in the spectroscopic study, 347 galaxies fulfil the CIG isolation criteria when a criterion about redshift difference is added. The available redshifts allow us to reject background neighbours and thus improve the photometric assessment. On average, galaxies in the AMIGA sample show lower values in the local number density and the tidal strength parameters than galaxies in denser environments such as pairs, triplets, compact groups, and clusters. For the first time, the environment and the isolation degree of AMIGA galaxies are quantified using digital data. The use of the SDSS database permits one to identify fainter and smaller-size satellites than in previous AMIGA works. The AMIGA sample is improved by this study, because we reduced the sample of isolated galaxies used in previous AMIGA works by about 20%. The availability of the spectroscopic data allows us to check the validity of the CIG isolation criteria, which is not fully efficient. About 50% of the neighbours considered as potential companions in the photometric study are in fact background objects. We also find that about 92% of the neighbour galaxies that show recession velocities similar to the corresponding CIG galaxy are not considered by the CIG isolation criteria as potential companions, which may have a considerable influence on the evolution of the central CIG galaxy. Description: Result of the revision of the CIG isolation criteria and quantification of the isolation degree for 636 CIG galaxies in the photometric study, and 411 CIG galaxies in the spectroscopic study, using data from the Ninth Data Release of the Sloan Digital Sky Survey. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table2.dat 30 636 Revision of the isolation degree using photometric database table4.dat 50 411 Revision of the isolation degree using spectroscopic database -------------------------------------------------------------------------------- See also: J/A+A/411/391 : AMIGA project Revised positions for CIG galaxies (Leon+ 2003) J/A+A/436/443 : AMIGA I. Velocities of CIG galaxies (Verdes-Montenegro+ 2005) J/A+A/449/937 : AMIGA II. Morphological refinement (Sulentic+, 2006) J/A+A/462/507 : AMIGA III. IRAS data (Lisenfeld+, 2007) J/A+A/470/505 : AMIGA IV. Neighbours around CIG galaxies (Verley+, 2007) J/A+A/472/121 : AMIGA V. Isolation parameters (Verley+, 2007) J/A+A/485/475 : AMIGA VI. Radio fluxes of the isolated galaxies (Leon+ 2008) J/A+A/486/73 : AMIGA VII. FIR and radio study (Sabater+, 2008) J/A+A/532/A117 : AMIGA VIII. Flux ratio asymmetry parameter (Espada+, 2011) J/A+A/534/A102 : AMIGA IX. Molecular gas properties (Lisenfeld+, 2011) J/A+A/540/A47 : AMIGA X. Isolated galaxy colors (Fernandez Lorenzo+, 2012) J/A+A/545/A15 : AMIGA XI. Optical nuclear activity (Sabater+, 2012) J/MNRAS/397/1756 : Fourier-derived parameters of CIG sample (Durbala+, 2009) J/MNRAS/434/325 : 452 AMIGA galaxies physical param. (Fernandez Lorenzo+, 2013) http://amiga.iaa.es : AMIGA Home Page Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 4 I4 --- CIG CIG (VII/82) number, in Simbad 6- 11 F6.2 arcmin r1Mpc Projected angular radius equal to the adopted distance at 1 Mpc 14- 17 F4.2 --- r1Mpc/r80Dp Ratio between projected angular radius at 1 Mpc over the original field radius used in the CIG isolation criteria 19 I1 --- isol [0/1] Result of the CIG isolation criteria: "1" if the galaxy passes, "0" if it fails 21- 25 F5.2 --- QKarp Tidal strength estimate of similar-size neighbours 27- 30 F4.2 --- etakp Local number density of similar-size neighbours -------------------------------------------------------------------------------- Byte-by-byte Description of file: table4.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 4 I4 --- CIG CIG (VII/82) number, in Simbad 6 I1 --- isol [0/1] Result of the CIG isolation criteria for neighbours within 1Mpc and |{Delta}v|<=500km/s (1) 8- 9 I2 --- k500 Number of neighbours within 1Mpc and |{Delta}v|<=500km/s 11- 15 F5.2 --- Q500 ?=- Tidal strength estimation using neighbours within 1Mpc and |{Delta}v|<=500km/s 17 I1 --- f_Q500 [0/2] Flag in Q500 (2) 19- 23 F5.2 --- etak500 ?=- Local number density using neighbours within 1Mpc and |{Delta}v|<=500km/s 25 I1 --- f_etak500 [0/2] Flag in etak500 (3) 27- 31 F5.2 --- zcomp Redshift completeness in the field 33- 34 I2 --- k500ul Number of neighbours within 1Mpc and |{Delta}v|<=500km/s using upper limits 36- 40 F5.2 --- Q500ul ?=- Tidal strength upper limit estimation using neighbours within 1Mpc and |{Delta}v|<=500km/s 42 I1 --- f_Q500ul [0/2] Flag in Q500ul (4) 44- 48 F5.2 --- etak500ul ?=- Local number density upper limit using neighbours within 1Mpc and |{Delta}v|<=500km/s 50 I1 --- f_etak500ul [0/2] Flag in etak500ul (5) -------------------------------------------------------------------------------- Note (1): isol flag as follows: 1 = the galaxy passes 0 = it fails Note (2): f_Q500 flag as follows: 0 = if k500>=1 2 = if k500=0 Note (3): f_etak500 flag as follows: 0 = if k500>=2 1 = if k500=1 2 = if k500=0 Note (4): f_Q500ul flag as follows: 0 = if k500ul>=1 2 = if k500ul=0 Note (5): f_etak500ul flag as follows: 0 = if k500ul>=2 1 = if k500ul=1 2 = if k500ul=0 -------------------------------------------------------------------------------- Acknowledgements: Maria del Carmen Argudo Fernandez, margudo(at)iaa.es ================================================================================ (End) Patricia Vannier [CDS] 27-Nov-2013