Tuesday, 07/02/13

Two papers today, the first compares [CII] and PAH emission in RCW 38. In at least one direction, Kaneda et al. see the [CII] drop as the CO emission picks up, just as we expect. Another point is the good correlation between [CII] and PAH, again as expected if both are good tracers of PDRs. The second paper claims that early-type galaxies of the same mass are 30-50% larger in clusters than in the field at intermediate redshifts. This is kind of interesting, because the same isn’t found for galaxies in the present day universe, so would mean some differential evolution of these galaxies from then until now.

Title: Large-scale mapping of the massive star-forming region RCW38 in the [CII] and PAH emission
Authors: Kaneda, H.; Nakagawa, T.; Ghosh, S. K.; Ojha, D. K.; Ishihara, D.; Kondo, T.; Ninan, J. P.; Tanabe, M.; Fukui, Y.; Hattori, Y.; Onaka, T.; Torii, K.; Yamagishi, M.
Publication: eprint arXiv:1307.0263
Publication Date: 06/2013
Origin: ARXIV
Keywords: Astrophysics – Galaxy Astrophysics
Comment: 10 pages, 7 figures, accepted for publication in A&A
Bibliographic Code: 2013arXiv1307.0263K


We investigate the large-scale structure of the interstellar medium (ISM) around the massive star cluster RCW38 in the [CII] 158 um line and polycyclic aromatic hydrocarbon (PAH) emission. We carried out [CII] line mapping of an area of ~30’x15′ for RCW~38 by a Fabry-Perot spectrometer on a 100 cm balloon-borne telescope with an angular resolution of ~1′.5. We compared the [CII] intensity map with the PAH and dust emission maps obtained by the AKARI satellite. The [CII] emission shows a highly nonuniform distribution around the cluster, exhibiting the structure widely extended to the north and the east from the center. The [CII] intensity rapidly drops toward the southwest direction, where a CO cloud appears to dominate. We decompose the 3-160 um spectral energy distributions of the surrounding ISM structure into PAH as well as warm and cool dust components with the help of 2.5-5 um spectra. We find that the [CII] emission spatially corresponds to the PAH emission better than to the dust emission, confirming the relative importance of PAHs for photo-electric heating of gas in photo-dissociation regions. A naive interpretation based on our observational results indicates that molecular clouds associated with RCW38 are located both on the side of and behind the cluster.

Title: Larger sizes of massive quiescent early-type galaxies in clusters than in the field at 0.8 < z < 1.5
Authors: Delaye, L.; Huertas-Company, M.; Mei, S.; Lidman, C.; Licitra, R.; Newman, A.; Raichoor, A.; Shankar, F.; Barrientos, F.; Bernardi, M.; Cerulo, P.; Couch, W.; Demarco, R.;Muñoz, R.; Sanchez-Janssen, R.; Tanaka, M.
Publication: eprint arXiv:1307.0003
Publication Date: 06/2013
Origin: ARXIV
Keywords: Astrophysics – Cosmology and Extragalactic Astrophysics
Comment: submitted to MNRAS
Bibliographic Code: 2013arXiv1307.0003D


[abridged] The mass-size relation of early-type galaxies (ETGs) has been largely studied in the last years to probe the mass assembly of the most massive objects in the Universe. In this paper, we focus on the mass-size relation of quiescent massive ETGs (Mstar/Msol > 3*10^10) living in massive clusters (M200 ~ 10^14 Mstar) at 0.8< z <1.5, as compared to those living in the field at the same epoch. Our sample contains ~ 400 ETGs in clusters and the same number in the field. Therefore, our sample is approximately an order of magnitude larger than previous studies in the same redshift range for galaxy clusters. We find that ETGs living in clusters are between ~30-50% larger than galaxies with the same stellar mass residing in the field. We parametrize the size using the mass-normalized size, gamma=Re/Mstar^0.57. The gamma distributions in both environments peak at the same position but the distributions in clusters are more skewed towards larger sizes. Since this size difference is not observed in the local Universe, the size evolution at fixed stellar mass from z~1.5 of cluster galaxies is less steep ((1+z)-0.53pm0.04) than the evolution of field galaxies ((1+z)-0.92pm0.04). The size difference seems to be essentially driven by the galaxies residing in the clusters cores (R<0.5*R200). If part of the size evolution is due to mergers, the difference we see between cluster and field galaxies could be due to higher merger rates in clusters at higher redshift, probably during the formation phase of the clusters when velocity dispersions are lower. We cannot exclude however that the difference is driven by newly quenched galaxies which are quenched more efficiently in clusters. The implications of these results for the hierarchical growth of ETGs will be discussed in a companion paper.

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