The Close Environment of 24 μm Galaxies at 0.6 < z < 1.0 in the Cosmos Field

K. I. Caputi , K. Kovač , M. Bolzonella (1) , S. J. Lilly , G. Zamorani (1) , H. Aussel , D. Sanders , S. Bardelli , A. Bongiorno , T. Contini (2) , G. Coppa , O. Cucciati , S. de La Torre (3) , L. de Ravel , P. Franzetti , D. Frayer , B. Garilli , A. Iovino , P. Kampczyk , J.-P. Kneib (3) , C. Knobel , F. Lamareille (2) , J. F. Leborgne (2) , V. Lebrun (3) , O. Lefèvre (3) , E. Lefloc'H , A. Leauthaud (3) , C. Maier , V. Mainieri , M. Mignoli , R. Pellò (2) , Y. Peng , E. Pérez-Montero (2) , E. Ricciardelli , M. Salvato , M. Scodeggio , N. Scoville (4) , J. Silverman , J. Surace , M. Tanaka , L. Tasca (3) , L. Tresse (3) , D. Vergani , E. Zucca , U. Abbas , D. Bottini , P. Capak (4, 5) , A. Cappi , C. M. Carollo , P. Cassata , Alessandro Cimatti , M. Fumana , O. Ilbert , J. Kartaltepe , D. Maccagni , Christian Marinoni (3) , H. Mccracken (6) , P. Memeo , B. Meneux , P. Oesch , C. Porciani , L. Pozzetti , A. Renzini , R. Scaramella , C. Scarlata

1 OABO - INAF - Osservatorio Astronomico di Bologna
2 LATT - Laboratoire Astrophysique de Toulouse-Tarbes
3 LAM - Laboratoire d'Astrophysique de Marseille
4 CALTECH - California Institute of Technology
5 MPIA - Max-Planck-Institut für Astronomie
6 IAP - Institut d'Astrophysique de Paris

We investigate the close environment of 203 Spitzer 24 μm -selected sources at 0.6 < z < 1.0 using zCOSMOS-bright redshifts and spectra of I < 22.5 AB mag galaxies, over 1.5 deg2 of the COSMOS field. We quantify the degree of passivity of the luminous and ultra-luminous IR galaxy (LIRG and ULIRG, respectively) environments by analyzing the fraction of close neighbors with Dn(4000)>1.4. We find that LIRGs at 0.6 < z < 0.8 live in more passive environments than those of other optical galaxies that have the same stellar mass distribution. Instead, ULIRGs inhabit more active regions (e.g., LIRGs and ULIRGs at 0.6 < z < 0.8 have, respectively, (42.0 ± 4.9)% and (24.5 ± 5.9)% of neighbors with Dn(4000)>1.4 within 1 Mpc and ±500 km s–1). The contrast between the activities of the close environments of LIRGs and ULIRGs appears especially enhanced in the COSMOS field density peak at z ~ 0.67, because LIRGs on this peak have a larger fraction of passive neighbors, while ULIRGs have as active close environments as those outside the large-scale structure. The differential environmental activity is related to the differences in the distributions of stellar mass ratios between LIRGs/ULIRGs and their close neighbors, as well as in the general local density fields. At 0.8 < z < 1.0, instead, we find no differences in the environment densities of ULIRGs and other similarly massive galaxies, in spite of the differential activities. We discuss a possible scenario to explain these findings.

Mots clés: galaxies: evolution; infrared: galaxies

Domaines: Astrophysique galactique [astro-ph.GA]

K. I. Caputi, K. Kovač, M. Bolzonella, S. J. Lilly, G. Zamorani, et al.. The Close Environment of 24 μm Galaxies at 0.6 < z < 1.0 in the Cosmos Field. The Astrophysical journal letters, 2009, 691, pp.91-97. ⟨10.1088/0004-637X/691/1/91⟩. ⟨hal-00391625⟩