Thursday January 10th, 2012

he evolution of galaxies resolved in space and time: an inside-out growth view from the CALIFA survey

E. Pérez, R. Cid Fernandes, R. M. González Delgado, R. García-Benito, S. F. Sánchez, B. Husemann, D. Mast, J. R. Rodón, D. Kupko, N. Backsmann, A. L. de Amorim, G. van de Ven, J. Walcher, L. Wisotzki, C. Cortijo-Ferrero, CALIFA Collaboration
(Submitted on 8 Jan 2013)

The growth of galaxies is one of the key problems in understanding the structure and evolution of the universe and its constituents. Galaxies can grow their stellar mass by accretion of halo or intergalactic gas clouds, or by merging with smaller or similar mass galaxies. The gas available translates into a rate of star formation, which controls the generation of metals in the universe. The spatially resolved history of their stellar mass assembly has not been obtained so far for any given galaxy beyond the Local Group. Here we demonstrate how massive galaxies grow their stellar mass inside-out. We report the results from the analysis of the first 105 galaxies of the largest to date three-dimensional spectroscopic survey of galaxies in the local universe (CALIFA). We apply the fossil record method of stellar population spectral synthesis to recover the spatially and time resolved star formation history of each galaxy. We show, for the first time, that the signal of downsizing is spatially preserved, with both inner and outer regions growing faster for more massive galaxies. Further, we show that the relative growth rate of the spheroidal component, nucleus and inner galaxy, that happened 5-7 Gyr ago, shows a maximum at a critical stellar mass ~10^10 Msun. We also find that galaxies less massive than ~10^10 Msun show a transition to outside-in growth, thus connecting with results from resolved studies of the growth of low mass galaxies.

Comments: ApJ Letters in press; 5 pages, 5 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
DOI: 10.1088/2041-8205/763/1/L1
Cite as: arXiv:1301.1679 [astro-ph.CO]
(or arXiv:1301.1679v1 [astro-ph.CO] for this version)

Modeling The Molecular Composition in an AGN Disk

Nanase Harada, Todd A. Thompson, Eric Herbst
(Submitted on 9 Jan 2013)

We use a high-temperature chemical network to derive the molecular abundances in axisymmetric accretion disk models around active galactic nuclei (AGNs) within 100 pc using simple radial and vertical density and temperature distributions motivated by more detailed physical models. We explore the effects of X-ray irradiation and cosmic ray ionization on the spatial distribution of the molecular abundances of CO, CN, CS, HCN, HCO+, HC3N, C2H, and c-C3H2 using a variety of plausible disk structures. These simple models have molecular regions with a layer of X-ray dominated regions, a midplane without the strong influence of X-rays, and a high-temperature region in the inner portion with moderate X-ray flux where families of polyynes (C$_{\rm n}$H$_{2}$) and cyanopolyynes can be enhanced. For the high midplane density disks we explore, we find that cosmic rays produced by supernovae do not significantly affect the regions unless the star formation efficiency significantly exceeds that of the Milky Way. We highlight molecular abundance observations and ratios that may distinguish among theoretical models of the density distribution in AGN disks. Finally, we assess the importance of the shock crossing time and the accretion time relative to the formation time for various chemical species. Vertical column densities are tabulated for a number of molecular species at both the characteristic shock crossing time and steady state. Although we do not attempt to fit any particular system or set of observations, we discuss our models and results in the context of the nearby AGN NGC 1068.

Comments: Accepted for publication in ApJ
Subjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1301.1955 [astro-ph.GA]
(or arXiv:1301.1955v1 [astro-ph.GA] for this version)
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