THE CLOSE ENVIRONMENT OF 24 μm GALAXIES AT 0.6 < 1.0 IN THE COSMOS FIELD

Caputi, K. I.; Kovač, K.; Bolzonella, M.; Lilly, S. J.; Zamorani, G.; Aussel, H.; Sanders, D.; Bardelli, S.; Bongiorno, A.; Contini, T.; Coppa, G.; Cucciati, O.; de la Torre, S.; de Ravel, L.; Franzetti, P.; Frayer, D.; Garilli, B.; Iovino, A.; Kampczyk, P.; Kneib, J. -P.; Knobel, C.; Lamareille, F.; Le Borgne, J. F.; Le Brun, V.; Le Fèvre, O.; Le Floc'h, E.; Leauthaud, A.; Maier, C.; Mainieri, V.; Mignoli, M.; Pellò, R.; Peng, Y.; Pérez-Montero, E.; Ricciardelli, E.; Salvato, M.; Scodeggio, M.; Scoville, N.; Silverman, J.; Surace, J.; Tanaka, M.; Tasca, L.; Tresse, L.; Vergani, D.; Zucca, E.; Abbas, U.; Bottini, D.; Capak, P.; Cappi, A.; Carollo, C. M.; Cassata, P.; Cimatti, A.; Fumana, M.; Ilbert, O.; Kartaltepe, J.; Maccagni, D.; Marinoni, C.; Mccracken, H.; Memeo, P.; Meneux, B.; Oesch, P.; Porciani, C.; Pozzetti, L.; Renzini, A.; Scaramella, R.; Scarlata, C.

doi:10.1088/0004-637X/691/1/91

We investigate the close environment of 203 Spitzer 24 mu m-selected sources at 0.6 < z < 1.0 using zCOSMOS-bright redshifts and spectra of I < 22.5 AB mag galaxies, over 1.5 deg(2) 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 D-n (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 D-n (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 similar to 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.

THE CLOSE ENVIRONMENT OF 24 μm GALAXIES AT 0.6 < 1.0 IN THE COSMOS FIELD / Caputi, K. I.; Kovač, K.; Bolzonella, M.; Lilly, S. J.; Zamorani, G.; Aussel, H.; Sanders, D.; Bardelli, S.; Bongiorno, A.; Contini, T.; Coppa, G.; Cucciati, O.; de la Torre, S.; de Ravel, L.; Franzetti, P.; Frayer, D.; Garilli, B.; Iovino, A.; Kampczyk, P.; Kneib, J. -P.; Knobel, C.; Lamareille, F.; Le Borgne, J. F.; Le Brun, V.; Le Fèvre, O.; Le Floc'h, E.; Leauthaud, A.; Maier, C.; Mainieri, V.; Mignoli, M.; Pellò, R.; Peng, Y.; Pérez-Montero, E.; Ricciardelli, E.; Salvato, M.; Scodeggio, M.; Scoville, N.; Silverman, J.; Surace, J.; Tanaka, M.; Tasca, L.; Tresse, L.; Vergani, D.; Zucca, E.; Abbas, U.; Bottini, D.; Capak, P.; Cappi, A.; Carollo, C. M.; Cassata, P.; Cimatti, A.; Fumana, M.; Ilbert, O.; Kartaltepe, J.; Maccagni, D.; Marinoni, C.; Mccracken, H.; Memeo, P.; Meneux, B.; Oesch, P.; Porciani, C.; Pozzetti, L.; Renzini, A.; Scaramella, R.; Scarlata, C.. - In: THE ASTROPHYSICAL JOURNAL. - ISSN 0004-637X. - 691:1(2009), pp. 91-97. [10.1088/0004-637X/691/1/91]