Day 811

Wednesday.

1412.6501
Confirmation of a star formation bias in type Ia supernova distances and its effect on measurement of the Hubble Constant
Rigault, et al

Previously, used the Nearby Supernova Factory sample to show that SNeIa having locally SF environments are dimmer than SNeIa having locally passive environments.  Here, use the constitution sample together with host galaxy data from GALEX to independently confirm that result.  The effect is seen using both the SALT2 and MLCS2k2 light curve fitting and standardization methods, with brightness differences of 0.094pm0.037 mag for SALT2 and 0.155pm0.041 mag for MLCS2k2 with R_V=2.5  When combined with previous measurement the effect is 0.094pm0.037 mag for SALT2.  If the ratio of these local SNIa environments changes with redshift or sample selection, this can lead to a bias in cosmological measurements.  Explore this issue further, using as an example the direct measurement of H0.    GALEX observations show that the SNeIa having standardized absolute magnitudes calibrated via the Cepheid period-luminosity relation using HST originate in predominantly SF environments, where as only ~50% of the Hubble flow comparison sample have locally SF environments.  As a consequence, the H0 measurement using SNeIa is currently overestimated.  Correcting for this bias, find a value of H0^corr=70.6pm2.6 km/s/Mpc when using the LMC distance, MW parallaxes and the NGC4258 megamaser as the Cepheid zero point, and 68.8pm3.3km/s/Mpc when only using NGC4258.  The correction brings the direct measurement of N0 within 1sigma of recent indirect measurements based on the CMB PS.

1501.00996
Using atomic clocks to detect gravitational waves
Loeb, Maoz

Atomic clocks have recently reached a rational timing precision of <1e-18.  Point out that an array of atomic clocks, distributed along the Earth's orbit around the Sun, will have the sensitivity needed to detect the time dilation effect of mHz GWs, such as those emitted by SMBH binaries at cosmological distances.  Simultaneous measurement of clock-rates at different phases of a passing GW provides an attractive alternative to the interferometric detection of temporal variations in distance between test masses separated by less than a GW wavelength, cruelty envisioned for the eLISA mission.

1501.01002
The first galaxies: simulating their feedback-regulated assembly
Jeon, et al

Investigate the formation of a galaxy reaching a virial mass of 1e8 at z~10 by carrying out a zoomed radiation-hydrodynamical cosmo sim.  This sim traces Pop III SF, characterized by a modestly top-heavy IMF, and considers stellar feedback such as photoionization heating from Pop III and Pop II stars, mechanical and chemical feedback from SNe, and X-ray feedback from accreting BHs and high-mass X-ray binaries.  Self-consistently impose a transition in SF mode from top-heavy Pop III to low-mass Pop II at the critical metallicity Zcrit=1e-3.5 Zsun.  Find that the SFR in the computational box is dominated by Pop III until z~13, and by Pop II thereafter.  The IGM is metal-enriched to an average of Zavg=1e-4 Zsun at z~10, mainly by pair-instability SNe, while 70% of the produced Pop II stars die in core-collapse SNe.  The simulated galaxy experiences bursty SF, with a substantially reduced gas content due to photoionization heating form Pop III and Pop II stars, together with SN feedback.  Specifically, this gives rise to a baryon fraction of fbar=0.05 at z~10.  All the gas within the simulated galaxy is metal-enriched above 1e-5 Zsun, such that there are no remaining pockets of primordial gas.  Further estimate the intrinsic luminosity of the simulated galaxy to be Lbol~5e6 Lsun, corresponding to an observed flux of 1e-3 nJy, which is too low to be detected by the JWST.  Also show that the simulated galaxy falls below the observed relation between mean stellar metallicity and total stellar mass for local dwarf galaxies by ~1 dex, although this may be an artifact of having missed any subsequent SF at z<10. 

1501.01048
The SKA as a doorway to angular momentum
Obreschkow et al

The SKA has a unique opportunity to become the world-leading facility for angular momentum studies due to its ability to measure the resolved and/or global HI kinematics in very large and well-characterised galaxy samples.