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Post Info TOPIC: Edge-on spiral galaxies
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RE: Edge-on spiral galaxies
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Title: Breaks in thin and thick discs of edge-on galaxies imaged in the Spitzer Survey Stellar Structure in Galaxies (S4G)
Authors: Sébastien Comerón, Bruce G. Elmegreen, Heikki Salo, Eija Laurikainen, E. Athanassoula, Albert Bosma, Johan H. Knapen, Dimitri A. Gadotti, Kartik Sheth, Joannah L. Hinz, Michael W. Regan, Armando Gil de Paz, Juan-Carlos Muńoz-Mateos, Karín Menéndez-Delmestre, Mark Seibert, Taehyun Kim, Trisha Mizusawa, Jarkko Laine, Luis C. Ho, Benne Holwerda

Breaks in the radial luminosity profiles of galaxies have been until now mostly studied averaged over discs. Here we study separately breaks in thin and thick discs in 70 edge-on galaxies using imaging from the Spitzer Survey of Stellar Structure in Galaxies. We built luminosity profiles of the thin and the thick discs parallel to midplanes and we found that thin discs often truncate (77%). Thick discs truncate less often (31%), but when they do, their break radius is comparable with that in the thin disc. This suggests either two different truncation mechanisms - one of dynamical origin affecting both discs simultaneously and another one only affecting the thin disc - or a single mechanism that creates a truncation in one disc or in both depending on some galaxy property. Thin discs apparently antitruncate in around 40% of galaxies. However, in many cases, these antitruncations are an artefact caused by the superposition of a thin disc and a thick disc with the latter having a longer scale length. We estimate the real thin disc antitruncation fraction to be less than 15%. We found that the ratio of the thick and thin stellar disc mass is roughly constant (0.2120 km/s, but becomes much larger at smaller velocities. We hypothesize that this is due to a combination of a high efficiency of supernova feedback and a slower dynamical evolution in lower-mass galaxies causing stellar thin discs to be younger and less massive than in higher-mass galaxies.

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Blobrana


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Title: Evolution in the Dust Lane Fraction of Edge-on L* Spiral Galaxies since z=0.8
Authors: B.W. Holwerda (ESA), J. J. Dalcanton (University of Washington), D. Radburn-Smith (University of Washington), R. S. de Jong (AIP), P. Guhathakurta (Santa Cruz), A. Koekemoer (STSCI), R. J. Allen (STSCI), T. Böker (ESA)

The presence of a well-defined and narrow dust lane in an edge-on spiral galaxy is the observational signature of a thin and dense molecular disk, in which gravitational collapse has overcome turbulence. Using a sample of galaxies out to z~1 extracted from the COSMOS survey, we identify the fraction of massive disks that display a dust lane. Our goal is to explore the evolution in the stability of the molecular ISM disks in spiral galaxies over a cosmic timescale. We check the reliability of our morphological classifications against changes in restframe wavelength, resolution, and cosmic dimming with (artificially redshifted) images of local galaxies from SDSS. We find that the fraction of L* disks with dust lanes in COSMOS is consistent with the local fraction (~80%) out to z~0.7. At z=0.8, the dust lane fraction is only slightly lower. A somewhat lower dust lane fraction in starbursting galaxies tentatively supports the notion that a high specific star formation rate can efficiently destroy or inhibit a dense molecular disk. A small subsample of higher redshift COSMOS galaxies display low internal reddening (E[B-V]), as well as a low incidence of dust lanes. These may be disks in which the growth of the dusty ISM disk lags behind that of the stellar disk. We note that at z=0.8, the most massive galaxies display a lower dust lane fraction than lower mass galaxies. A small contribution of recent mergers or starbursts to this most massive population may be responsible. The fact that the fraction of galaxies with dust lanes in COSMOS is consistent with little or no evolution implies that models to explain the Spectral Energy Distribution or the host galaxy dust extinction of supernovae based on local galaxies are still applicable to higher redshift spirals. It also suggests that dust lanes are long lived phenomena or can be reformed over very short time-scales.

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