Day 810

Tuesday.

1501.00500
When did round disk galaxies form?
Takeuchi et al

When and how galaxy morphology such as disk and bulge seen in the present-day universe emerged is still not clear.  In the universe at z>2, galaxies with various morphology are seen, and SF galaxies at z~2 show an intrinsic shape of bar-like structure.  Then when did round disk structure form?   Take a simple and straightforward approach to see the epoch when the round disk galaxy population emerged, by constraining the intrinsic shape statistically based on apparent axial ratio distribution of galaxies.  Derived the distributions of the apparent axial ratios in the rest-frame optical light (~5000 A) of SF main sequence galaxies at 2.5>z>1.4, 1.4>z>0.85, and 0.85>z>0.5, and found that the apparent axial ratios of them show peaky distributions at z>0.85, while a rather flat distribution at the lower redshift.  By using a triaxial model for the intrinsic shape (A>B>C), find the best-fit models give the peaks of the B/A distribution of 0.81pm0.04, 0.84pm0.04, and 0.92pm0.05 at 2.5>z>1.4, 1.4>z>0.85, and 0.85>z>0.5, respectively.  The last value is close to the local value of 0.95.  Thickness (C/A) is ~0.25 at all the z and is close to the local value (0.21).  The results indicate the shape of the SF galaxies in the MS changes gradually, and the round disk is established at around z~0.9.  Establishment of the round disk may be due to a cease of violent interaction of galaxies or a growth of a bulge and/or a super-massive BH resides at the center of a galaxy which dissolves the bar structure.

1501.00690
Galactic magnetic fields and hierarchical galaxy formation
Rodrigues, ... Baugh, et al

A framework is introduced for coupling the evolution of galactic magnetic fields sustained by the mean-field dynamo with the formation and evolution of galaxies in the cold dark matter cosmology.  Estimates of the steady-state strength of the large-scale and turbulence B-fields from mean-field and fluctuation dynamo models are used together with galaxy properties predicted by SAM of galaxy formation for a population of spiral galaxies.  Find that the field strength is mostly controlled by the evolving gas content of the galaxies.  Thus, because of the differences in the implementation of the SF law, feedback from SNe and ram-pressure stripping, each of the galaxy formation models considered predicts a distribution of field strengths with unique features.  The most prominent of them is the difference in typical B-fields strengths obtained for the satellite and central galaxies populations as well as the typical strength of the large-scale B-field in galaxies of different mass.

1501.00963
The eleventh and twelfth data releases of the Sloan Digital Sky Survey: final data from SDSS-III
Alam et al

SDSS-III: data from 2008 to 2014.  Lots of data.

1410.4345
HOPE: a Python Just-In_time compiler for astrophysical computations
Akeret, Gamper, Amara, Refregier

In order to combine the ease of Python and the speed of C++, developed HOPE, a specialized Python just-in-time (JIT) compiler designed for numerical astrophysical applications.  HOPE focuses on a subset of the language and is able to translate Python code into C++ while performing numerical optimisation on mathematical expressions at runtime.  To enable the JIT compilation, the user only needs to adda a decorator to the function definition.  Assess the performance of HOPE by performing a series of benchmarks and compare its execution speed with that of plain Python, C++ and the other existing frameworks.  Find that HOPE improves the performance compared to plain Python by a factor of 2 to 120, achieves speeds comparable to that of C++ and often exceeds the speed of the existing solutions.  Discuss the differences between HOPE and the other frameworks, as well as future extensions of its capabilities.  The fully documented HOPE packages is available on the web.