1210.7807
Spectroscopi evidence of distinct stellar populations in the counter-rotating stellar disks of NGC 3593 and NGC 4550
Coccato, et al
Both galaxies known to host 2 counter-rotating stellar disks; ionized gas co-rotating with one of them. Secondary stellar disk is younger, more metal poor, and more alpha-enhanced than the main galaxy stellar disk. Rule out internal origin of secondary stellar component; favor a scenario where it formed from gas accreted on retrograde orbits from the environment fueling an in situ outside-in rapid star formation. Binary galaxy merger scenario cannot be ruled out; large sample is required to statistically determine which is the most efficient mechanism to build counter-rotating stellar disks.
1210.7808
On the evolution of the HI column density distribution in cosmological simulations
Rahmati, ... Schaye et al
The predicted NI column density distributions agree very well with observations: in particular, the simulations reproduce the remarkable lack of evolution in the column density distribution of Lyman limit and weak damped Lya systems below z=3. The evlution of the low column density end is affected by the increasing importance of collisional ionization with decreasing redshift. The simulations predict the abundance of strong damped Lya systems to broadly track the cosmic SFR density.
1210.7814
Formation and evolution of dwarf early-type galaxies in the Virgo cluster II. kinematic scaling relations
Toloba ... van de Ven, ... et al
Virgo dwarf early-type galaxies (dEs): scaling relations show that dEs are different from early-type galaxies (Es), and that they further strengthen the previous findings that dEs are closer to and likely formed from late-type galaxies.
1210.7820
The galactic magnetic field
Jansson, Farrar
B-field from WMAP7 22 GHz synchrotron intensity map together with other results to obtain a 13-parameter model of the Galactic random field, and to determine the strength of the striated random field. Obtain very good fit to WMAP7 polarized and total intensity emission maps; as well as faraday rotation measures (RM). Data calls for striated component to the random field whose orientation is aligned with the regular field, having zero mean and rms strength @20% larger than the regular field. In the new model: the regular field has a significant out-of-plane component, which had not been considered earlier. The new GMF model gives a much better description of the totality of data than previous models in the literature.
1210.7829
Diversity of type Ia supernovae imprinted in chemical abundances
Tsujimoto, Shigeyama
A time delay of SNIa explosions hinders the imprint of their nucleosynthesis on stellar abundances. Some cases give birth to stars that avoid enrichment of their chemical compositions by massive stars and thereby exhibit a SNIa-like elemental feature including a very low [Mg/Fe]~-1. Propose: presence of a class of SNIa that yield the low abundance ratios of [Cr, Mn, Ni/Fe]; new model of chemical evolution reveal that the proposed class of SNIa (slow SNIa) associated with ones exploding on a long timescale after stellar birth, and gives a significant impact on the chemical enrichment on LMC. In MW, effect unseen due to the overwhelming enrichment by the major class of SNIa that explode promptly and eject a large amount of Fe-group elements. This nicely explains the different metal features between the two galaxies as well as the puzzling feature seen in the LMC stars exhibiting very low Ca but normal Mg abundances. The corresponding channel of slow SNIa is exemplified by performing detailed nucleosynthesis calculations in the scheme of SNIa resulting from a 0.8+0.6 solar mass white dwarf merger. [why would LMC have more slow SNIa?]
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