Day 1068

Friday.


1603.05249
On the feasibility of characterizing free-floating planets with current and future space-based microlensing surveys
Henderson, Shvartzvald

Simultaneous space- and ground-based microlensing surveys, such as K2's Campaign 9 (K2C9) and WFIRST, facilitate measuring the masses and distances of free-floating planet (FFP) candidates.  FFPs are identified as single-lens events with a short timescale, of order 1 day.  Measuring the mass of the lensing object requires determining the finite size of the source star rho, as well as the microns parallax pi_E.  A planet that is bound to but widely separated from a host star can produce a light curve similar to that of an FFP.  This tension can be resolved with high-resolution imaging of the microlensing target to search for the lens flux F_l from a possible host star.  Here, investigate the accessible parameter space for each of these components --- pi_E, rho and F_l -- considering different satellites for a range of FFP masses, Galactic distances, and source star properties.  Find that at the beginning of K2C9, when its projected separation from the Earth (as viewed from the center of its survey field) is <~0.2 AU, it will be able to measure pi_E for Jupiter-mass FFP candidates at distances lager than ~2 kpc and to Earth-mass lenses at ~8 kpc.  At the end of its campaign, when D_perp=0.81 AU, it is sensitive to planetary-mass lenses for distances >~3.5 kpc, and even then only to those with mass >~ M_Jup.   From lens flux constraints, find that it will be possible to exclude all stellar-mass host stars (down to the deuterium-burning limit) for events within ~2kpc.  Together these indicate that the ability to characterize FFPs detected during K2C9 is optimized for events occurring toward the beginning of the campaign.   WFIRST, on the other hand, will be able to detect and characterize FFPs with masses at least as low as super-Earths throughout the Galaxy during its entire microlensing survey.


1603.05253
Cosmological $N$-body simulations with suppressed variance
Angulo, Pontzen

Present and test a method that dramatically reduces variance arising from the sparse sampling of wave modes in cosmo sims.  The method uses two sims which are fixed (the initial Fourier mode amplitudes are fixed to the ensemble average PS) and paired (with initial modes exactly out of phase).  Measure the PS, monopole and quadrupole z-space correlation functions, halo mass function and reduced bispectrum at z=1.  By these measures, predictions from a fixed pair can be as precise on non-linear scales as an average over 50 traditional simulations.  The fixing procedure introduces a non-Gaussian correction to the initial conditions; give an analytic argument showing why the simulations are still able to predict the mean properties of the Gaussian ensemble. Anticipate that the method will drive down the computational time requirements for accurate large-scale explorations of galaxy bias and clustering statistics, enabling more precise comparisons with theoretical models, and facilitating the use of numerical simulations in cosmo data interpretation.


1603.05275
Local analogs for high-redshift galaxies: resembling the physical conditions of the interstellar medium in high-redshift galaxies
Bian, et al

The sample of local analogs for high-z galaxies in SDSS, selected based on their positions in the [OIII]/Hbeta versus [NII]/Halpha nebular emission-line diagram, resemble the physical conditions of the ISM to those in high-z galaxies.  Physical properties such as sSFRs, flat UV continuum and compact galaxy sizes are found to also be similar.  In particular, the ionization parameters and electron densities in these analogs are comparable to those in z~2-3 galaxies, but higher than those in normal SDSS galaxies by ~0.6 dex and ~0.9 dex, respectively.  The mass-metallicity relation (MZR) in these local analogs shows -0.2 dex offset from that in SDSS SF galaxies at the low mass end, which is consistent with the MZR of the z~2-3 galaxies.  Compare the local analogs in this study with those in other studies, including Lyman break analogs (LBA) and green pea (GP) galaxies.  The analogs in this study share a similar SF surface density with LBAs, but the ionization parameters and electron densities in the analogs are higher than those in LBAs by factors of 1.5 and 3, respectively.  The analogs in this study have comparable ionization parameter and electron density to the GP galaxies, but the method can select galaxies in a wider z range.  Find the high sSFR and SFR surface density can increase the electron density and ionization parameters, but still cannot fully explain the difference in ISM condition between nearby galaxies and the local analogs/high-z galaxies.