Day 605

Wednesday.

1403.2379
A study of the shortest-peroid planets found with Kepler
Sanchis-Ojeda et al

Present the results of a survey aimed at discovering and studying transiting planets with orbital periods shorter than 1 day (ultra-short period, or USP, planets), using data from Kepler.  Computed FTs of the photometric time series for all 200k target stars, and detected transit signals based on the presence of regularly spaced sharp peaks in the Fourier spectrum.  Present a list of 106 USP candidates, of which 18 have not previously been described in the literature.  In addition, among the objects studied, there are 26 USP candidates that had been previously reported in the literature which do not pass the various tests.  All 106 of the candidates have passed several standard tests to rule out false positives doe to eclipsing stellar systems.  A low false positive rate is also implied by the relatively high fraction of candidates for which more than one transiting planet signal was detected.  By assuming these multi-transit candidates represent coplanar multi-planet systems, able to infer that the USP planets are typically accompanied by other planets with periods in the range 1-50 days, in contrast with hot Jupiters which very rarely have companions in that same period range.  Another clear pattern is that almost all USP planets are smaller than 2 R_Earth, possibly because gas giants in very tight orbits would lose their atmospheres by photo vaporization when subject to extremely strong stellar irradiation.  Based on the survey statistics, USP planets exist around approximately 0.51pm0.07% of G-dwarf stars, and 0.83pm0.18% of K-dwarf stars.  [that's a small fraction.]

1403.2389
A thousand shadows of Andromeda: rotating planes of satellites in the Millennium-II cosmological simulation
Ibata et al

Bahl & Baumgardt investigated the incidence of planar alignments of satellite galaxies in the Millennium-II simulation, and concluded that vast thin planes of dwarf galaxies, similar to that observed in M31, occur frequently by chance in LCDM cosmology.  However, their analysis did not capture the essential fact that the observed alignment is simultaneously radially extended, yet thin, and kinematically unusual.  With the caveat that the Millennium-II simulation may not have sufficient mass resolution to identify confidently simulacra [i.e., analogues] of low-luminosity dwarf galaxies, reexamine that simulation for planar structures, using the same methods as employed by Ibata+2013 on the real M31 satellites.  Find that 0.04% of host galaxies display satellite alignments that are at least as extreme as the observations, when considering their extent, thickness and number of members rotating in the same sense.  Further instigate the angular momentum properties of the coplanar satellites, and find that the median of the specific angular momentum derived from the LoS velocities in the real M31 structure (1.3e4 km/s kpc) is very high compared to systems drawn from the simulations.  Analysis confirms that it is highly unlikely that the observed structure around Andromeda galaxy is due to a chance occurrence.  Interestingly, the few extreme systems that are similar to M31 arise from the accretion of a massive sub-halo with its own spatially-concentrated entourage of orphan satellites.  [I don't understand the logic...]

1403.2409
Satellite abundances around bright isolated galaxies II: radial distribution and environmental effects
Wang, Sales, Henriques, White

Use SDSS-DR8 to study the radial distribution of satellite galaxies around isolated primaries, comparing to SAM of galaxy formation based on Millennium and Millennium-II sims.  SDSS satellites behave differently around high-and low-mass primaries: those orbiting objects with M*>1e11 Msun are mostly red and are less concentrated towards their host than the inferred DM halo, an effect that is very pronounced for the few blue satellites.  On the other hand, less massive primaries have steeper satellite profiles that agree quite well with the expected DM distribution and are dominated by blue satellites, even in the inner regions where strong environmental effects are expected.  In fact, such effects appear to be strong only for primaries with M*>1e11 Msun.  This behavior is not reproduced by current SAMs, where satellite profiles always parallel those of the DM and satellite populations are predominantly red for primaries of all masses.  The disagreement with SDSS suggests that environmental effects are too efficient in the models.  Modifying the treatment of environmental and SF processes can substantially increase the fraction of blue satellites, but their radial distribution remains significantly shallower than observed.  It seems that most satellites of low-mass primaries can continue to form stars even after orbiting within their joint halo for 5 Gyr or more.

1403.2475
Star forming filaments in warm dark models
Gao, Theuns, Springel

15% of the stars of the z=0 galaxy formed in filaments.  At higher redshift, these stars give galaxies a stringy appearance, which, if observed, might be a strong indication that the DM is warm.