Tuesday 10/09/12

Title: Properties of Molecular Gas in Galaxies in Early and Mid Stage of the Interaction: I. Distribution of Molecular Gas
Authors: Kaneko, Hiroyuki; Kuno, Nario; Iono, Daisuke; Tamura, Yoichi; Tosaki, Tomoka; Nakanishi, Koichiro; Sawada, Tsuyoshi
Publication: eprint arXiv:1210.2217
Publication Date: 10/2012
Origin: ARXIV
Keywords: Astrophysics – Galaxy Astrophysics, Astrophysics – Cosmology and Extragalactic Astrophysics
Comment: 28 pages, 10 figures, accepted for publication in PASJ
Bibliographic Code: 2012arXiv1210.2217K


We present the results of 12CO(J = 1-0) mapping observations toward four interacting galaxies in early and mid stages of the interaction to understand the behavior of molecular gas in galaxy-galaxy interaction. The observations were carried out using the 45-m telescope at Nobeyama Radio Observatory (NRO). We compared our CO total flux to those previously obtained with single-dish observations and found that there are no discrepancy between them. Applying a typical CO-H2 conversion factor, all constituent galaxies have molecular gas mass more than 10^9 M_sun. Comparisons to HI, Ks and tracers of SF such as Halpha, FUV, 8 um and 24 um revealed that the distribution of molecular gas in interacting galaxies in the early stage of the interaction differs from atomic gas, stars and star-forming regions. These differences are not explained without the result of the interaction. Central concentration of molecular gas of interacting galaxies in the early stage of the interaction is lower than that of isolated galaxies, which suggests molecular gas is distributed off-centre and/or extends in the beginning of the interaction.

Title: Cosmic Evolution of Star-Formation Enhancement in Close Major-Merger Galaxy Pairs Since z = 1
Authors: Xu, C. K.; Shupe, D. L.; B’ethermin, M.; Aussel, H.; Berta, S.; Bock, J.; Bridge, C.; Conley, A.; Cooray, A.; Elbaz, D.; Franceschini, A.; Le Floc’h, E.; Lu, N.;Lutz, D.; Magnelli, B.; Marsden, G.; Oliver, S. J.; Pozzi, F.; Riguccini, L.; Schulz, B.; Scoville, N.; Vaccari, M.; Vieira, J. D.; Wang, L.; Zemcov, M.
Publication: eprint arXiv:1210.2362
Publication Date: 10/2012
Origin: ARXIV
Keywords: Astrophysics – Cosmology and Extragalactic Astrophysics
Comment: 7 pages, 4 figures; accepted by ApJ
Bibliographic Code: 2012arXiv1210.2362X


The infrared (IR) emission of M_* galaxies (10^{10.4} < M_{star} < 10^{11.0} M_\sun) in galaxy pairs, derived using data obtained in Herschel (PEP/HerMES) and Spitzer (S-COSMOS) surveys, is compared to that of single disk galaxies in well matched control samples to study the cosmic evolution of the star-formation enhancement induced by galaxy-galaxy interaction. Both the mean IR SED and mean IR luminosity of star-forming galaxies (SFGs) in SFG+SFG (S+S) pairs in the redshift bin of 0.6 < z < 1 are consistent with no star-formation enhancement. SFGs in S+S pairs in a lower redshift bin of 0.2 < z < 0.6 show marginal evidence for a weak star-formation enhancement. Together with the significant and strong sSFR enhancement shown by SFGs in a local sample of S+S pairs (obtained using previously published Spitzer observations), our results reveal a trend for the star-formation enhancement in S+S pairs to decrease with increasing redshift. Between z=0 and z=1, this decline of interaction-induced star-formation enhancement occurs in parallel with the dramatic increase (by a factor of ~10) of the sSFR of single SFGs, both can be explained by the higher gas fraction in higher z disks. SFGs in mixed pairs (S+E pairs) do not show any significant star-formation enhancement at any redshift. The difference between SFGs in S+S pairs and in S+E pairs suggests a modulation of the sSFR by the inter-galactic medium IGM in the dark matter halos (DMH) hosting these pairs.

Title: Star formation laws and thresholds from ISM structure and turbulence
Authors: Renaud, Florent; Kraljic, Katarina; Bournaud, Frédéric
Publication: eprint arXiv:1210.2355
Publication Date: 10/2012
Origin: ARXIV
Keywords: Astrophysics – Cosmology and Extragalactic Astrophysics, Astrophysics – Galaxy Astrophysics
Comment: 6 pages, re-submitted to ApJL after referee report
Bibliographic Code: 2012arXiv1210.2355R


We present an analytical model of the relation between the surface density of gas and star formation rate in galaxies and clouds, as a function of the presence of supersonic turbulence and the associated structure of the interstellar medium. The model predicts a power-law relation of index 3/2, flattened under the effects of stellar feedback at high densities or in very turbulent media, and a break at low surface densities when ISM turbulence becomes too weak to induce strong compression. This model explains the diversity of star formation laws and thresholds observed in nearby spirals and their resolved regions, the Small Magellanic Cloud, high-redshift disks and starbursting mergers, as well as Galactic molecular clouds. While other models have proposed interstellar dust content and molecule formation to be key ingredients to the observed variations of the star formation efficiency, we demonstrate instead that these variations can be explained by interstellar medium turbulence and structure in various types of galaxies.

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