Shim, Hyunjin and Im, Myungshin and Lee, Hyung Mok and Lee, Myung Gyoon and Kim, Seong Jin and Hwang, Ho Seong and Hwang, Narae and Ko, Jongwan and Lee, Jong Chul and Lim, Sungsoon and Matsuhara, Hideo and Seo, Hyunjong and Wada, Takehiko and Goto, Tomotsugu (2011) Merging Galaxy Cluster A2255 in Mid-infrared. Astrophysical Journal, 727 (1). Art. No. 14. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20110321-142311601
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We present the mid-infrared (MIR) observation of a nearby galaxy cluster, A2255, by the AKARI space telescope. Using AKARI's continuous wavelength coverage between 3 and 24 μm and the wide field of view, we investigate the properties of cluster member galaxies to see how the infall of the galaxies, the cluster substructures, and the cluster-cluster merger influence their evolution. We show that the excess of MIR (~11 μm) flux is a good indicator for discriminating galaxies at different evolutionary stages and for dividing galaxies into three classes accordingly: strong MIR-excess (N3 – S11 > 0.2) galaxies that include both unobscured and obscured star-forming galaxies; weak MIR-excess (–2.0 < N3 – S11 < –1.2) galaxies that are quiescent, old (> 5 Gyr) galaxies where the MIR emission arises mainly from the circumstellar dust around AGB stars; and intermediate MIR-excess (–1.2 < N3 – S11 < 0.2) galaxies in between the two classes that are less than a few Gyr old past the prime star formation activity. With the MIR-excess diagnostics, we investigate how local and cluster-scale environments affect the individual galaxies. We derive the total star formation rate (SFR) and the specific SFR of A2255 using the strong MIR-excess galaxies. The dust-free, total SFR of A2255 is ~130 M_⊙ yr^(–1), which is consistent with the SFRs of other clusters of galaxies at similar redshifts and with similar masses. We find no strong evidence that supports enhanced star formation either inside the cluster or in the substructure region, suggesting that the infall or the cluster merging activities tend to suppress star formation. The intermediate MIR-excess galaxies, representing galaxies in transition from star-forming galaxies to quiescent galaxies, are located preferentially at the medium density region or cluster substructures with higher surface density of galaxies. Our findings suggest that galaxies are being transformed from star-forming galaxies into red, quiescent galaxies from the infall region through near the core which can be explained well by ram-pressure stripping as previous simulation results suggest. We conclude that the cluster merging and the group/galaxy infall suppress star formation and transform galaxies from star-forming galaxies into quiescent galaxies, most likely due to ram-pressure stripping.
|Additional Information:||© 2011 American Astronomical Society. Received 2009 August 14; accepted 2010 November 4; published 2010 December 23. We thank L. Piovan for providing his SED model. We thank R. Gobat and J. H. Lee for helpful discussions. This work is based on observations with AKARI, a JAXA project with the participation of ESA. The AKARI images are obtained from a Mission Program CLEVL (CLusters of galaxies EVoLution studies). This work was supported by the Korea Science and Engineering Foundation (KOSEF) grant No. 2009-0063616, funded by the Korea government (MEST).|
|Subject Keywords:||galaxies: clusters: individual (A2255) – galaxies: photometry – infrared: galaxies|
|Classification Code:||PACS: 98.65.Cw, 98.62.Mw, 95.85.Hp, 98.62.Lv, 98.62.Ai|
|Official Citation:||Hyunjin Shim et al. 2011 ApJ 727 14 doi: 10.1088/0004-637X/727/1/14|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Benjamin Perez|
|Deposited On:||21 Mar 2011 21:52|
|Last Modified:||26 Dec 2012 13:05|
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