arXiv:0904.1742 [ps, pdf, other] Title: Detection of PAH and Far-Infrared Emission from the Cosmic Eye: Probing the Dust and Star Formation of Lyman Break Galaxies Authors: Brian Siana (1), Ian Smail (2), A. Mark Swinbank (2), Johan Richard (2), Harry I. Teplitz (3), Kristen E. K. Coppin (2), Richard S. Ellis (1), Daniel P. Stark (4), Jean-Paul Kneib (5), Alistair C. Edge (2) ((1) Caltech, (2) Durham, (3) Spitzer Science Center, (4) IoA Cambridge, (5) Marseille) Comments: Accepted for publication in ApJ. 9 pages, 7 figures Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA) We report the results of a Spitzer infrared study of the Cosmic Eye, a strongly lensed, L*_UV Lyman Break Galaxy (LBG) at z=3.074. We obtained Spitzer IRS spectroscopy as well as MIPS 24 and 70 micron photometry. The Eye is detected with high significance at both 24 and 70 microns and, when including a flux limit at 3.5 mm, we estimate an infrared luminosity of L_IR = 8.3 (+4.7-4.4) x10^11 L_sun assuming a magnification of 28+-3. This L_IR is eight times lower than that predicted from the rest-frame UV properties assuming a Calzetti reddening law. This has also been observed in other young LBGs, and indicates that the dust reddening law may be steeper in these galaxies. The mid-IR spectrum shows strong PAH emission at 6.2 and 7.7 microns, with equivalent widths near the maximum values observed in star-forming galaxies at any redshift. The L_PAH-to-L_IR ratio lies close to the relation measured in local starbursts. Therefore, L_PAH or L_MIR may be used to estimate L_IR and thus, star formation rate, of LBGs, whose fluxes at longer wavelengths are typically below current confusion limits. We also report the highest redshift detection of the 3.3 micron PAH emission feature. The PAH ratio, L_6.2/L_3.3=5.1+- 2.7, and the PAH-to-L_IR ratio, L_3.3/L_IR = 8.5 +- 4.7 x10^-4, are both in agreement with measurements in local starbursts and ULIRGs, suggesting that this line may serve as a good proxy for L_PAH or L_IR at z > 3 with the James Webb Space Telescope. [30] arXiv:0904.2365 [ps, pdf, other] Title: A Comparison of Galaxy Merger History Observations and Predictions from Semi-Analytic Models Authors: Serena Bertone (UC Santa Cruz), Christopher J. Conselice (Nottingham University) Comments: 15 pages, 9 figures. Accepted for publication in MNRAS Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO) We present a detailed analysis of predicted galaxy-galaxy merger fractions and rates in the Millennium simulation and compare these with the most up to date observations of the same quantities up to z~3. We carry out our analysis by considering the predicted merger history in the Millennium simulation within a given time interval, as a function of stellar mass. This method, as opposed to pair fraction counts, considers mergers that have already taken place, and allows a more direct comparison with the observed rates and fractions measured with the concentration-asymmetry-clumpiness (CAS) method. We examine the evolution of the predicted merger fraction and rate in the Millennium simulation for galaxies with stellar masses M_* ~ 10^9 - 10^12 M_sun. We find that the predicted merger rates and fractions match the observations well for galaxies with M_* > 10^11 M_sun at z<2, while significant discrepancies occur at lower stellar masses, and at z>2 for M_* > 10^11 M_sun systems. At z>2 the simulations underpredict the observed merger fractions by a factor of 4-10. The shape of the predicted merger fraction and rate evolutions are similar to the observations up to z~2, and peak at 1 10^11 M_sun. We discuss possible reasons for these discrepancies, and compare different realisations of the Millennium simulation to understand the effect of varying the physical implementation of feedback. We conclude that the comparison is potentially affected by a number of issues, including uncertainties in interpreting the observations and simulations in terms of the assumed merger mass ratios and merger time-scales. (abridged) arXiv:0904.2379 [ps, pdf, other] Title: Major Dry-Mergers In Early-Type Brightest Cluster Galaxies Authors: F. S. Liu (1,2), Shude Mao (3), Z. G. Deng (4), X. Y. Xia (5), Z. L. Wen (2) ((1) College of Physics Science and Technology, Shenyang Normal University, China;(2) NAOC, China;(3) Jodrell Bank Centre for Astrophysics, University of Manchester, UK;(4) GUCAS, China;(5) Tianjin Astrophysics Center, Tianjin Normal University, China) Comments: 9 pages, 5 figures and 1 table; Accepted for publication in MNRAS Subjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO) We search for ongoing major dry-mergers in a well selected sample of local Brightest Cluster Galaxies (BCGs) from the C4 cluster catalogue. 18 out of 515 early-type BCGs with redshift between 0.03 and 0.12 are found to be in major dry-mergers, which are selected as pairs (or triples) with $r$-band magnitude difference $\dm<1.5$ and projected separation $\rp<30$ kpc, and showing signatures of interaction in the form of significant asymmetry in residual images. We find that the fraction of BCGs in major dry-mergers increases with the richness of the clusters, consistent with the fact that richer clusters usually have more massive (or luminous) BCGs. We estimate that present-day early-type BCGs may have experienced on average $\sim 0.6 (\tmerge/0.3\Gyr)^{-1}$ major dry-mergers and through this process increases their luminosity (mass) by $15% (\tmerge/0.3\Gyr)^{-1} (\fmass/0.5)$ on average since $z=0.7$, where $\tmerge$ is the merging timescale and $\fmass$ is the mean mass fraction of companion galaxies added to the central ones. We also find that major dry-mergers do not seem to elevate radio activities in BCGs. Our study shows that major dry-mergers involving BCGs in clusters of galaxies are not rare in the local Universe, and they are an important channel for the formation and evolution of BCGs.