Wednesday.
1601.06783
Properties of interstellar medium in star-forming galaxies at z~1.4 revealed with ALMA
Seko, et al
Conduct observations of 12CO(J=5-4) and dust thermal continuum emission toward 20 star-forming galaxies on the main sequence at z~1.4 using ALMA to investigate the properties of the ISM. The sample of galaxies are chosen to trace the distributions of star-forming galaxies in diagrams of M*-SFR and stellar mass-metallicity. Detected CO emission lines from 11 galaxies. The molecular gas mass is derived by adopting a metallicity-dependent CO-toH2 conversion factor and assuming a CO(5-4)/CO(1-0) luminosity ratio of 0.23. Molecular gas masses and its fractions (molecular gas mass/(molecular gas mass + stellar mass)) for the detected galaxies are in the ranges of (3.9-12)e10Msun and 0.25-0.94, respectively; these values are significantly larger than those in local spiral galaxies. The molecular gas mass fraction decreases with increasing stellar mass; the relation holds for 4 times lower stellar mass than that covered in previous studies, and that the molecular gas mass fraction decreases with increasing metallicity. Stacking analyses also show the same trends. The dust thermal emissions were clearly detected from 2 galaxies and marginally detected from 5. Dust masses of the detected galaxies are (3.9-38)e7 Msun. Derived gas-to-dust ratios and found they are 3-4 times larger than this in local galaxies. The depletion times of molecular gas for the detected galaxies are (1.4-36)e8 yr while the results of the stacking analysis show ~3e8 yr. The depletion time tends to decrease with increasing stellar mass and metallicity though the trend is not so significant, which contrasts with the trends in local galaxies.
1601.06787
Tidal disruption event (TDE) demographics
Kochanek
Survey the properties of stars destroyed in TDEs as a function of BH mass, stellar mass and evolutionary state, SFH and redshift. For Mbg<1e7 Msun, the typical TDE is due to a dwarfs (M*~0.3Msun), although the MF is relatively flat for M*<Msun. Contribution from older MS stars and sub-giants is small but not negligible. From Mbh~1e7.5-8.5 Msun, the balance rapidly shifts to higher mass stars and a larger contribution from evolved stars, and is ultimately dominated by evolved stars at higher BH masses. The SFH has little effect until the rates are dominated by evolved stars. TDE rates should decline very rapidly towards higher z. The volumetric rate of TDEs is very high because the BH mass function diverges for low masses. However, any emission mechanism which is largely Eddington-limited for low BH masses suppresses this divergence in any observed sample and leads to TDE samples dominated by Mbh~1e6.0-7.5 Msun BHs with roughly Eddington peak accretion rates. The typical fall back times is relatively long, with 16% having Tfb<1e-1 years (37 days), and 84% having longer time scales. Many residual rate discrepancies can be explained if surveys are biased against TDEs with these longer Tfb, which seems very plausible if Tfb has any relation to the transient rise time. For almost any BH mass function, systematic searches for fainter, faster time scale TDEs in smaller galaxies, and longer time scale TDEs in more massive galaxies are likely to be rewarded.
1601.06791
The stellar-to-halo mass relation of GAMA galaxies from 100 square degrees of KiDS weak lensing data
van Uitert, Cacciato, et al
KiDS + GAMA: lensing aloe results in poor constraints on the stellar-to-halo mass relation due to a degeneracy between the satellite fraction and the halo mass, which is lifted when simultaneously fitting the stellar mass function. At M*>5e10 Msun/h^2, the stelar mass increases with halo mass as ~Mh^0.25. The ratio of DM to stellar mass has a minimum at a halo mass of 8e11 Msun/h with a value of Mh/M*=56±15[h]. Also use the GAMA group catalogue to select centrals and satellites in groups with 5 or more members, which trace retcons in space where the local matter density is higher than average, and determine for the first time the stellar-to-halo mass relation in these denser environments. Find no significant differences compared to the relation from the full sample, which suggests that the stellar-to-halo mass relation does not vary strongly with local density. Furthermore, find that the stellar-to-halo mass relation of central galaxies can also be obtained by modeling the lensing signal and stellar mass function of satellite galaxies only, which shows that the assumptions to model the satellite contribution in the halo model do not significantly bias the stellar-tohalo mass relation. Finally, show that the combination of WL with the stellar MF can be used to test the purity of group catalogs.
1601.06792
Sample variance in weak lensing: how many simulations are required?
Petri, Haiman, May
Constraining cosmology using WL consists of comparing a measured feature vector of dimension Nb with its simulated counterpart. An accurate estimate of the NbxNb feature covariance matrix C is essential to obtain accurate parameter confidence intervals. When C is measured from a set of simulations, an important question is how large this set should be. To answer this question, construct different ensembles of Nr realizations of the shear field, using a common randomization procedure that recycles the outputs from a smaller number Ns<Nr of independent ray-tracing N-body sims. Study parameter confidence intervals as a function of (Ns,Nr) in the range 1<=Ns<=200 and 1<=Nr<~1e5. Previous work has shown that Gaussian noise in the feature vectors (from which the covariance is estimated) lead, at quadratic order, to an O(1/Nr) degradation of the parameter confidence intervals. Using a variety of lensing features measured in the simulations, including shear-shear power spectra and peak counts, show that cubic and quartic covariance fluctuations lead to additional O(1/Nr^2) error degradation that is not negligible when Nr is only a factor of few larger than Nb. Study the large Nr limit, and find that a single, 240Mpc/h sized 512^3 particle N-body sim (Ns=1) can be repeatedly recycled to produce as many as Nr=few e4 shear mass whose power spectra and high-significance peak counts can be treated as statistically independent. As a result, a small number of sims (Ns=1 or 2) is sufficient to forecast parameter confidence intervals at percent accuracy.
1601.06793
Systematic or signal? How dark mater misalignments can bias strong lensing models of galaxy clusters
Harvey, Kneib, Jauzac
Explore how assuming that mass traces light in SL models can lead to systematic errors in the predicted position of multiple images. Use a model based on MACSJ0416 (z=0.397), split each galactic halo into a baryonic and DM component, then shift the DM halo such that it no longer aligners with the baryonic halo and investigate how this affects the resulting position of multiple images. For physically motivated misalignments in dark halo position, ellipticity, position angle and density profile, and that multiple images can move on average by more than 0.2" with individual images moving greater than 1". Estimate the full error induced by assuming that light traces mass and find that this assumption leads to an expected RMS error of 0.5", almost the entire error budget observed in the Frontier Fields. Given the large potential contribution from the assumption that light traces mass to the error budget in mass reconstructions, predict that it should be possible to make a first significant detection and characterization of dark halo misalignments in HFF with SL. Find that it may be possible to detect ~1kpc offsets between DM and baryons, the smoking gun for self-interacting DM, should the correct alignment of multiple images be observed.
1601.06990
Shifting milestones of natural sciences: the ancient Egyptian discovery of Algol's period confirmed
Jets, Porceddu
Cairo Calendar (1255-1163 BC) show a 2.85 day cycle in the lucky prognosis, corresponding to that of the eclipsing binary Algol. Similarly, the period of the Moon, 29.6 days, also strongly regulated the teams described as lucky for Heaven and for Earth. Discover the actual rules in the appearance and behavior of deities during the whole year.
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