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Monday.
1601.07905
The eating habits of Milky Way mass halos: destroyed dwarf satellites and the metallicity distribution of accreted stars
Season, Mao, Wechsler
Study the mass spectrum of destroyed dwarfs that contribute to the accreted stellar mass of MW mass M_vir~1e12.1 Msun halos using a suite of 45 zoom-in, dissipation-less simulations. Empirical models are employed to relate (peak) sub halo mass to dwarf stellar mass, and use constraints from z=0 observations and hydrodynamical simulations to estimate the metallicity distribution of the accreted stellar material. The dominant contributors to the accreted stellar mass are relatively massive dwarfs with M*~1e8-10 Msun. Halos with more quiescent accretion histories tend to have lower mass progenitors (1e8-9 Msun), and lower overall accreted stellar masses. Ultra-faint mass (M*<1e5 Msun) swarfs contribute a negligible amount (<<1%) to the accreted stellar mass and, despite having low average metallicities, supply a small fraction (~2-5%) of the very metal-poor stars with [Fe/H] < -2. Dwarfs with masses 1e5 < M*/Msun < 1e8 provide a substantial amount of the very metal-poor stellar material (~40-80%), and even relatively metal-rich dwarfs with M*>1e8 Msun can contribute a considerable fraction (~20-60%) of metal-poor stars if their metallicity distributions have significant metal-poor tails. Finally, find that the generic assumption of a quiescent assembly history for the MW halo seems to be in tension with the mass spectrum of its surviving dwarfs. Suggest that the MW could be a "transient fossils", a quiescent halo wit ha recent accretion event(s) that disguises the preceding formation history of the halo.
1601.07967
IDCS J1426.5+3508: weak lensing analysis of a massive galaxy cluster at $z=1.75$
Mo, Gonzalez, Jee, Massey, Rhodes, et al
Present a WL study of the galaxy cluster IDCS at z=1.75, which is the highest redshift SL cluster known and the most distant cluster for which a WL analysis has been undertaken. Using F160W, F814W, and F606W observations with the HST, detect tangential shear at 2 sigma significance. Fitting a NFW mass profile to the shear with a theoretical median mass-concentration relation, derive a mass M_200,crit = (2.3-1.4+2.1)e14 Msun. This mass is consistent with previous mass estimates from the SZ effect, X-ray, and SL. The cluster lies on the local SZ-WL mass scaling relation observed at low redshift, indicative of minimal evolution in this relation.
1601.08228
The void galaxy survey: star formation properties
Beygu, et al
Study the SF properties of 59 void galaxies as part of the Void Galaxy Survey (VGS). Current SFRs are derived from Ha and recent SFRs from near-UV imaging. In addition, IR 3.4/4.6/12/22 um WISE emission is used as SF and mass indicator. IR and optical colors show that the VGS sample displays a wide range of dust and metallicity properties. Combine these measurements with stellar and HI masses to measure the sSFRs (SFR/M*) and SF efficiencies (SFR/M_HI). Compare the SF properties of the sample with galaxies in the more moderate density regions of the cosmic web, 'the field'. Find that sSFRs of the VGS galaxies as a function of stellar and HI mass are similar to those of the galaxies in these field regions. Their SFRa is slightly elevated than the galaxies in the field for a given total HI mass. In the global SF picture presented by Kennicutt-Schmidt, VGS galaxies fall into the region of low average SF and correspondingly low HI surface density. Their mean SFRa/M_HI and SFRa/M* are of the order of 1e-9.9 yr^-1. Conclude that while the large scale underdense environment must play some role in galaxy formation and growth through accretion, find that even with respect to other galaxies in the more mildly underdense regions, the increase in star formation rate is only marginal.
Friday.
1601.07559
Binary stars can provide the "missing photons" needed for reionizaton
Ma, Hopkins, Kasen, Quataert, Faucher-Giguere, Keres, Murray
Empirical constraints on reionization require galactic ionizing photon escape fractions fesc>20%, but recent high-res radiation-hydrodynamic calculations have consistently found much lower values ~1-5%. While these models have included strong stellar feedback and additional processes such as runaway stars, they have almost exclusively considered stellar evolution models based on single (isolated) stars, despite the fact that most massive stars are in binaries. Re-visit these calculations, combining radiative transfer and high-res cosmo sims of galaxies with detailed models for stellar feedback from the Feedback in Realistic Environments (FIRE) project. For the first time, use a stellar evolution model that includes a physically and observationally motivated treatment of binaries (the BPASS model). Binary mass transfer and mergers enhance the population of massive stars at late times (>3 Myr) after SF, which in turn strongly enhances the late-time ionizing photon production (especially at low metallicities). These photons are produced after feedback from massive stars has carved escape channels in the ISM, and so efficiently leak out of galaxies. As a result, the time-averaged "effective" escape fraction (ratio of escaped ionizing photons to observed 1500 A photons) increases by factors 4-10, sufficient to explain reionization. While important uncertainties remain, conclude that binary evolution may be critical for understanding the ionization of the Universe.
1601.07694
Searching for filaments are large-scale structure around DAFT/FADA clusters
Durret, et al
Search for extensions and filaments around the 30 clusters of DAFT/FADA (0.4<z<0.9). Previous detections have been limited until now to relatively low redshifts (z<0.3). Based on a color-magnitude diagram, select red-sequence galaxies, and hence at the cluster redshift, and build density maps, then draw density contours (3 sigma). Find clear elongations in 12 clusters, with sizes reaching up to 7.6 Mpc. 11 other clusters have neighboring structures, but the zones linking them are not detected in the density maps at 3 sigma. 3 clusters show no extended structure and no neighbors, and 4 clusters are of too low contrast to be clearly visible on the density map. Plan to apply to a larger photometric survey such as CFHTLS and SDSS-Stripe82.
1601.07857
Overconfidence in photometric redshift estimation
Wittman, Bhaskar, Tobin
Describe a new test of photo-z performance given a spectro-z sample. This test complements the traditional comparison of z differences by testing whether the probability density functions p(z) have the correct width. Test two photo-z codes, BPZ and EAZY, on each of 2 data sets and find that BPZ is consistently overconfident (the p(z) are too narrow) while EAZY produces approximately the correct level of confidence. Show that this is because EAZY models the uncertainty in its spectral energy distribution templates, and that post-hoc smoothing of the BPZ p(z) provides a reasonable substitute for detailed modeling of template uncertainties. Either remedy still leaves a small surplus of galaxies with spectroscopic redshift very far from the peaks. Thus, better modeling of low-probability tails will be needed for high-precision work such as DE constraints with the LSST and other large surveys.
Thursday.
Nature 529 484-489
Mastering the game of Go with deep neural networks and tree search
Silver et al
The game of Go has long been viewed as the most challenging of classic games for artificial intelligence owing to its enormous search space and the difficulty of evaluating board positions and moves. Introduce a new approach to computer Go that uses 'value networks' to evaluate board positions and 'policy networks' to select moves. These deep neural networks are trained by a novel combination of supervised learning from human expert games, and reinforcement learning from games of self-play. Without any lookahead search, the neural networks play Go at the level of state-of-the-art Monte Carlo tree search programs that simulate thousands of random games of self-play. Also introduce a new search algorithm that combines Monte Carlo sim with value and policy networks. Using this search algorithm, the program AlphaGo achieved a 99.8% winning rate against other Go programs, and defeated the human European Go champion by 5 games to 0. This is the first time that a computer program has defeated a human professional pleaser in the full-sized game of Go, a feat previously thought to be at least a decade away.
1601.07178
The feeble giant. Discovery of a large and diffuse Milky Way dwarf galaxy in the constellation of Crater
Torrealba et al
Discovery of the Crater 2 dwarf galaxy, identified in imaging data of the VST ATLAS survey. Half-light radius ~1100 pc, 4th largest dwarf in the MW, surpassed only by the LMC, SMC nd the Sgr dwarf. With a total luminosity of M_V~-8, this satellite galaxy is also is one of the lowest surface brightness dwarfs. Falling under the nominal detection boundary of 30 mag arcsec^-2, it compares in nebulosity to the recently discovered Tuc 2 and Tuc IV and UMa II. Crater 2 is located ~120 kpc from the Sun and appears to be aligned in 3D with the enigmatic globular cluster Crater, the pair of ultra-faint dwarfs Leo IV and Leo V and the classical dwarf Leo II. Argue that such arrangement is probably not accidental and, in fact, can be viewed as the evidence for the accretion of the Crater-Leo group.
1601.07182
Detection and removal of artifacts in astronomical images
Desai, Mohr, Bertin, Kummel, Wetzstein
Astronomical images from topical photometric surveys are typically contaminated with transient artifacts such as CRs, satellite trails and scattered light. Developed and tested an algorithm that removes these artifacts using a deep, artifact free, static sky coadd image built up through the median combination of PSF homogenized, overlapping single epoch images. Transient artifacts are detected and based in each single epoch image through comparison with an artifact free, PSF-matched simulated image that is constructed using the PSF-corrected, model fitting catalog from the artifact free coadd image together with the position variable PSF model of the single epoch image. This approach works well not only for cleaning single epoch images with worse seeing than the PSF homogenized coadd, but also the traditionally much more challenging problem of cleaning single epoch images with better seeing. In addition to masking transient artifacts, developed an interpolation approach that uses the local PSF and performs well in removing artifacts whose widths are smaller than the PSF full width at half maximum, including CRs, the peaks of saturated stars and bleed trails. Tested this algorithm on DES SV data and present performance metrics. More generally, algorithm can be applied to any survey which images the same part of the sky multiple times.
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.
Tuesday.
1601.06434
Subhalo accretion through filaments
Gonzalez, Padilla
Track sub halo orbits of galaxy and group sized haloes in cosmo sims. Identify filamentary structures around haloes and use these to define a sample of sub haloes accreted from filaments as well as a control sample of sub haloes accreted from other directions. Use these samples to study difference in satellite orbits produced by filamentary accretion. The results depend on host halo mass. Find that for low masses, sub halos accreted from filaments show ~10% shorter lifetimes compared to the control sample, they have more radial orbits, reach halo central regions earlier, and are more likely to merge with the host. For higher mass haloes this lifetime difference dissipates and even reverses for cluster sized halos. This behavior appears to be connected to the fact that more massive hosts are connected to stronger filaments with higher velocity coherence and density, with more radial sub halo orbits. Because sub haloes tend to follow the coherent flow of the filament, it is possible that such thick filaments are enough to shield the sub halo from the effect of dynamical friction at least during their first infall. Also identify sub halo pairs/clumps which merge with one another after accretion. They survive as a clump for only a very short time, which is even shorter for higher sub halo masses. There is a 50% and 90% chance they were accreted in the last 0.8 Gyr and 2.3 Gyr respectively. This suggests that the Magellanic Clouds and other local group satellite associations, may have entered the MW viral radius very recently and probably are in their first infall -- or at least still in their first full orbit. Filaments boost the accretion of satellite associations.
1601.06770
Dust grains from the heart of supernovae
Bocchio, et al
Dust grains are classically thought to form in the winds of AGB stars. However, there is increasing evidence for dust formation in SNe. In order to establish the relative importance of these two classes os stellar sources of dust, it is important to know what is the fraction of fretting formed dust in SN ejecta that is able to survive the passage of the reverse shock and be injected in the ISM. With this aim, developed a new code, CRASH_Rev, that allows to follow the dynamics of dust grains in the shocked SN ejecta and to compute the time evolution of the mass, composition and size distribution of the grains. Consider four well studied SNe ind the MW and LMC: SN 1987a, Cas A, the Crab Nebula, and N49. For all the simulated models, find good agreement with observations. Study suggests that SN 1987A is too young for the reverse shock to have affected the dust mass. Conversely, in the other three SNe, the reverse shock has already destroyed between 10 and 40% of the initial dust mass. However, the largest dust mass destruction is predicted to occur between 1e3 and 1e5 yr after the explosions. Since the oldest SN in the sample has and estimated age of 4800 yr, current observations can only provide an upper limit to the mass of SN dust that will enrich the ISM, the so-called effective dust yields. Find that only between 1 and 8% of the currently observed mass will survive. This is in good agreement with the values adopted in chemical evolution models which consider the effect of the NS reverse shock. Discuss the astrophysical implications of the realists for dust enrichment in local galaxies and at high redshift.
Monday.
1601.06063
Detection of the splashback radius and halo assembly bias of massive galaxy clusters
More, Miyatake, Takada, et al
Show that the projected number of density profiles of SDSS photometric galaxies around galaxy clusters displays strong evidence for the splashback radius, a sharp halo edge corresponding to the location of the first orbital epicenter of satellite galaxies after their infall. Split the clusters into two subsamples with different mean projected radial distances of their members, <Rmem>, at fixed richness and redshift, and show that the sample with smaller <Rmem> has a smaller ratio of the splash back radius to the traditional halo boundary R_200m, than the subsample with larger <Rmem>, indicative of different mass accretion rates for the two subsamples. The same cluster samples were recently used by Miyatake+ to show that their large-scale clustering differs despite their similar weak lensing masses, demonstrating strong evidence for halo assembly bias. Expand on this result by presenting a 6.6sigma detection of halo assembly bias using the cluster-photometric galaxy cross-correlations. The measured splash back radii are smaller, while the strength of the assembly bias signal is stronger, than expectations from N-body simulations based on the Lambda-dominated, CDM structure formation model. Dynamical friction or cluster-finding systematics such as miscentering or projection effects are not likely to be the sole source of these discrepancies.
Friday.
1601.05417
Quantifying environmental and line-of-sight effects in models of strong gravitational lens systems
McCully, Keeton, Wong, Zabludoff
Matter near a gravitational lens galaxy or projected along the LoS can affect SL observables by more than contemporary measurement errors. Simulate lens fields with realistic 3d mass configurations (self-consistently including kids), and then use lens models to quantify biases and uncertainties associated with different ways of treating the lens environment (ENV) and LoS. Identify the combination of mass, projected offset, and redshift that determines the importance of a perturbing galaxy for lensing. Foreground structures have a stronger effect on the lens potential than background structures, due to non-linear effects in the foreground and downweighting in the background. There is dramatic variation in the net strength of ENV/LoS effects across different lens fields; modeling fields individually yields stronger priors on H0 than ray tracing through N-body simulations. Lens systems in groups tend to have stronger ENV/LoS contributions than non-group lenses. In models, ignoring mass outside the lens yields poor fits and biased results. Adding external shear can account for tidal stretching from galaxies at redshifts z>=z_lens, but it requires corrections for external convergence and cannot reproduce non-linear effects from foreground galaxies. Using the tidal approximation is reasonable for most perturbers as long as non-linear redshift effects are included. Yet even then, the scatter in H0 is limited by the lens profile degeneracy. Asymmetric image configurations produced by highly elliptical lens galaxies are less sensitive to the lens profile degeneracy, so they offer appealing targets for precision lensing analyses in future surveys like LSST.
1601.05720
Constraining multiplicative bias in CFHTLenS weak lensing shear data
Liu, Ortiz-Vazquez, Hill
Several recent cosmo analyses found tension between constraints derived from CFHTLenS data and this derived from other data sets, such as Planck CMB. Similarly, a direct cross-correlation of the CFHTLenS data with Planck CMB lensing data yielded an anomalously low amplitude compared to expectations based on Planck or WMAP-derived cosmo parameters (Liu + Hill 2015). One potential explanation for these results is a multiplicative bias afflicting the CFHTLenS galaxy shape measurements, from which shears are inferred. Simulations are used in the CFHTLenS pipeline to calibrate such biases, but no data-drive constraints have been presented to date. In this paper, cross-correlate CFHTLenS galaxy density maps with CFHTLenS shear maps and Planck CMB lensing maps to independently calibrate the multiplicative shear bias in CFHTLenS, m, following methods suggested by Vallinotto (2012) and Das+2013. Analyze three magnitude-limited galaxy samples, finding 2-4 sigma evidence for m<1 using the deepest sample (i<24), while the others are consistent with m=1 (no bias). This matches the expectation that the shapes of faint galaxies are the most difficult to measure. The results for m are essentially independent of the assumed cosmology, and only weakly sensitive to assumptions about the galaxy bias. Consider 3 galaxy bias models, finding in all cases that the best-fit multiplicative shear bias is less than unity. A value of m~0.9 would suffice to reconcile the amplitude of density fluctuations inferred from CFHTLenS shear 2pt statistics with that inferred from Planck CMB temperature data. This scenario is consistent with the results.
1601.05779
CosmoLike - cosmological likelihood analyses for photometric galaxy surveys
Krause, Eifler
Explore strategies to extract cosmo constraints from joint analysis of cosmic shear, gg lensing, galaxy clustering, cluster number counts and cluster WL. Utilize the CosmoLike software to simulate results from an LSST like data set, specifically, (1) compare individual and joint analyses of the different probes, (2) vary the selection criteria for lens and source galaxies, (3) investigate the impact of blending, (4) investigate the impact of the assumed cosmo model in multi-probe covariances, (6) quantify information content as a function of scales, and (7) explore the impact of intrinsic galaxy alignment in a multi-probe context. The analyses account for all cross correlations within and across probes and include the higher-order (non-Gaussian) terms in the multi-probe covariance matrix. Simultaneously model cosmo parameters and a variety of systematics, e.g., uncertainties arising from shear and photo-z calibration, cluster mass-observable relation, galaxy intrinsic alignment, and galaxy bias (up to 54 parameters altogether). Highlight 2 results: (1) increasing the number density of source galaxies by ~30% which corresponds to solving blending for LSST, only gains little information. (2) Including small scales in clustering and gg lensing, by utilizing HODs, can substantially boost cosmo constraining power. The CosmoLike modules used to compute the results in this paper at github.com/elikrause/CosmoLike_Forecasts.
1601.05786
CFHTLenS revisited: assessing concordance with Planck including astrophysical systematics
Joudaki, Blake, Heymans, Choi, Harnos-Deraps, Hildebrandt, Joachimi, Johnson, Mead, Parkinson, Viola, van Waerbeke
Investigate the impact of astrophysical systematics on cosmic shear cosmo param constraints from CFHTLenS, and the concordance with CMB measurements by Planck. Present updated CFHTLenS cosmic shear tomography measurements extended to degree scales using a covariance calibrated by a new suite of N-body sims. Analyze these measurements with a new model fitting pipeline, accounting for key systematic uncertainties arising from intrinsic galaxy alignments, baryonic effects in the NL matter PS, and photo-z uncertainties. Examine the impact of the systematic degrees of freedom on the cosmo param constraints, both independently and jointly. When the systematic uncertainties are considered independently, the IA amplitude is the only degree of freedom that is substantially preferred by the data. When the sys uncertainties are considered jointly, there is no consistently strong preference in favor of the more complex models. Quantify the level of concordance between the CFHTLenS and Planck datasets by employing two distinct data concordance tests, grounded in Bayesian evidence and information theory. Find that the two data concordance tests largely agree with one another, and that the level of concordance between CFHTLenS and Planck datasets is sensitive to the exact details of the systematic uncertainties included in the analysis, ranging from decisive discordance to substantial concordance as the treatment of the systematic uncertainties becomes more conservative. The least conservative scenario is the one most favored by the cosmic shear data, but it is also the one that shows the greatest degree of discordance with Planck. The data and analysis code are public at github.com/sjoudaki/cfhtlens-revisited.
Tuesday. Wednesday. Thursday.
1601.04226
Observational evidence of a slow downfall of star formation efficiency in massive galaxies during the last 10 Gyr
Schreiber, et al
Study the causes of the reported mass-dependence of the slope of SFR-M* relation, the so-called "Main Sequence" of SF galaxies, and discuss its implication on the physical processes that shaped the SF history of massive galaxies over cosmic time. Make use of the NIR high-res imaging from HST in the CANDELS fields to perform a careful bulge-to-disk decomposition of distant galaxies and measure for the first time the slope of the SFR-Mdisk relation at z=1. Find that this relation follows very closely the shape of the nominal SFR-M* correlation, still with a pronounced flattening at the high-mass end. This is clearly excluding, at least at z=1, the secular growth of quiescent stellar bulges in SF galaxies as the main driver for the change of slope of the MS. Then, by stacking the Herschel data available in the CANDELS field, estimate the gas mass (Mgas) and the star formation efficiency SFE=SFR/Mgas at different positions on the SFR-M* relation. Find that the relatively low SFRs observed in massive galaxies (M*>5e10 Msun) are caused by a decreased SFE, by up to a factor of 3 as compared to lower stellar mass galaxies, and not by a reduced gas content. Argue that this stellar-mass-dependent SFE can explain the varying slope of the MS since z=1.5, hence over 70% of the Hubble time. The drop of SFE occurs at lower masses in the local Universe (M*>2e10 Msun) and is not present at z=2. Altogether this provides evidence for a slow downfall of the SFE in massive MS galaxies. The resulting loss of SF is found to be rising starting from z=2 to reach a level comparable to the mass growth of the quiescent population by z=1. Finally discuss the possible physical origin of this phenomenon.
1601.04414
On the origin of flux ratio anomaly in quadruple lens systems
Inoue
Use SAM based on N-body sims to study the origin of flux ratio anomaly. Estimate the effect of possible magnification perturbation caused by sub haloes with a mass scale of <~1e9 Msun/h in lensing galaxy haloes. Expected change to the flux ratios per a multiply lensed image is just a few percent and the mean of the expected convergence perturbation at the effective Einstein radius of the lensing galaxy halo is <delta kappa_sub>=0.003, corresponding to the mean of the ratio of a projected DM mass fraction in sub haloes <f_sub>=0.006 for observed 11 quadruple lens systems. In contrast, the expected change to the flux ratio caused by LoS structures in intergalactic spaces is typically ~10% and the mean of the convergence perturbation is <|detla kappa_los|>=0.008, corresponding to <f_los>=0.017. The contribution of magnification perturbation cased by sub haloes is ~40% of the total at a source redshift z_s=0.7 and decreases monotonically in z_s to ~20% at z_s=3.6. Assuming statistical isotropy, the convergence perturbation estimated from the 11 systems has a positive correlation with the source redshift z_s, which is much stronger than that with the lens redshift z_L. This feature also supports the idea that the flux ratio anomaly is caused mainly by LoS structures rather than sub haloes. Also discuss about a possible imprint of LoS structures in demagnification of minimum images due to locally underdense structures in the LoS.
Science
Evidence for a distant giant planet in the solar system
Batygin, Brown
Analysis show, within the scattered disk population of Kuiper Belt exhibit an unexpected clustering in their respective arguments of perihelion. Show that the orbits of KBOs cluster not only in argument of perihelion, but also in physical space. Demonstrate that the perihelion positions and orbital planes of the objects are tightly confined and that such a clustering has only a probability of 0.007% to be due to chance, thus requiring a dynamical origin. Find that the observed orbital alignment can be maintained by a distant eccentric planet with mass >~10 M_earth whose orbit lies in approximately the same plane as those of the distant KBOs, but whose perihelion is 180 deg away from the perihelia of the minor bodies. In addition to accounting for the observed orbital alignment, the existence of such a plant naturally explains the presence of high-perihelion Sedna-like objects, as well as the known collection of high semimajor axis objects with inclinations between 60 and 150 deg whose origin was previously unclear. Continued analysis of both distant and highly include outer solar system objects provides the opportunity for testing the hypothesis as well as further constraining the orbital elements and mass of the distant planet.
Science
ASASSN-15lh: a highly super-luminous supernova
Dong, et al
Discovery of SN 2015L: the most luminous SN yet found. At z=0.2326, ASASSN-15lh reached an absolute magnitude of M_u,AB=-23.5±0.1 and bolometric luminosity L_bol=(2.2±0.2)e45 ergs/s, which is more than twice as luminous as any previously known SN. It as several major features characteristic of the H-poor super-luminous SNe (SLSNe-I), whose energy sources and progenitors are currently pool understood. In contrast to most previously known SLSNe-I that reside in SF dwarf galaxies ASASSN-15lh appears to be hosted by a luminous galaxies (MK~-25.5) with litter SF. In the 4 months since first detection, ASASSN-15lh radiated (1.1±0.2)e52 ergs, challenging the magnetar model for its engine.
1601.04704
The formation of massive, quiescent galaxies at cosmic noon
Feldmann, Hopkins, Quataert, Faucher-Giguere, Keres
The cosmic noon (z~1.5-3) marked a period of vigorous SF for most galaxies. However, about a 1/3 of the more massive galaxies at those times were quiescent in the sense that their observed stellar populations are inconsistent with rapid SF. The reduced SF activity is often attributed to gaseous outflows driven by feedback from SMBHs, but the impact of BH feedback on galaxies in the young Universe is not yet definitively established. Analyze the origin of quiescent galaxies with the help of ultra-high resolution, cosmo sims that include feedback from stars but do not model the uncertain consequences of BH feedback. Show that DM haloes with specific accretion rates below ~0.25-0.4 per Gyr preferentially host galaxies with reduced SFRs and red broadband colors. The fraction of such haloes in large dark matter only simulations matches the observed fraction of massive quiescent galaxies (~1e10-11 Msun). This strongly suggests that halo accretion rate is the key parameter determining which massive galaxies at z~1.5-3 become quiescent. Empirical models that connect galaxy and halo evolution, such as HOD or abundance matching models assume a tight link between galaxy properties and the masses of their parent haloes. These models will benefit from adding the specific accretion rate of haloes as a second model parameter.
1501.04947
The morphologies and alignments of gas, mass and the central galaxies of CLASH clusters of galaxies
Donahue, et al
Because morphology is often used to infer the state of relaxation of galaxy clusters, analyze and present a uniformly estimated X-ray morphological statistics for quantitative characterization of all 25 clusters in CLASH. Compare X-ray morphologies of CLASH cluster with those identically measured for a large sample of simulated clusters for the MUSIC-2 sims, selected by mass. Confirm a threshold in X-ray surface brightness concentration of C>0.4 for cool-core clusters, where C is the ratio of X-ray emission inside 100kpc/h70 compared to inside 500 kpc/h70. Report and compare morphologies of these clusters inferred from SZE maps of he hot gas and in from projected mass maps based on SL and WL. Find a strong agreement in alignments of the orientation of major axis for the lensing ,X-ray and SZE maps of nearly all of the CLASH clusters at radii of 500 kpc (approximately 0.5 R500 for these clusters). Also find a striking alignment of clusters shapes at the 500 kpc scale, as measured with X-ray, SZE, and lensing, with that of the NIR stellar light a 10 kpc scales for the 20 "relaxed" clusters. This strong alignment indicates a powerful coupling between the cluster- and galaxy-scale galaxy formation processes.
Friday. Monday.
1601.03391
Galaxy and mass assembly (GAMA): stellar mass growth of spiral galaxies in the cosmic web
Alpaslan et al
Look for correlated changes in stellar mass and SFR along filaments in the cosmic web by examining the stellar masses and UV-derived SFR of 1799 ungrouped and unpaired spiral galaxies that reside in filaments. Devise multiple distance metrics to characterize the complex geometry of filaments, and find that galaxies closer to the cylindrical centre of a filament have higher stellar masses than their counterparts near the periphery of filaments, on the edges of voids. In addition, these peripheral spiral galaxies have higher sSFR at a given mass. Complementing the sample of filament spiral galaxies with spiral galaxies in tendrils and voids, find that the average SFR of these objects in different large scale environments are similar to each other with the primary discriminant in SFR being stellar mass, in line with previous works. However, the distributions of SFRs are found to vary with LS environment. Results thus suggest a model in which in addition to stellar mass as the primary discriminant, the LS environment is imprinted in the SFR as a second order effect. Furthermore, the detailed results for filament galaxies suggest a model in which gas accretion from voids onto filaments is primarily in an orthogonal direction. Overall, find the results to be in line with theoretical expectations of the thermodynamic properties of the IGM in different LS environments.
1601.03455
Globular clusters as cradles of life and advanced civilizations
Stefano, Ray
Globular clusters are ancient stellar populations with no SF or core-collapse SNe. Several lines of evidence suggest that globular clusters are rich in planets. If so, and if advanced civilizations can develop there, then the distances between these civilizations and other stars would be far smaller than typical distances between stars in the Galactic disk. The relative proximity would facilitate interstellar communication and travel. However, the vary proximity that promotes interstellar travel also beings danger, wince stellar interactions can destroy planetary systems. However, by molding globular clusters and their stellar populations, find that large regions of many globular clusters can be thought of as "sweet spots" where habitable-zone planetary orbits can be stable for long times. Also compute the ambient densities and fluxes in the regions within which habitable-zone planets can survive. Globular clusters are among the best targets for searches for extraterrestrial intelligence (SETI). Use the Drake equation to compare globular clusters to the Galactic disk, in terms of the likelihood of housing advanced communicating civilizations. Also consider free-floating planets, since wide-orbit planets can be ejected and travel freely through the clusters. A civilization spawned in a globular cluster may have opportunities to establish self-sustaining outposts, thereby reducing the probability that a single catastrophic event will destroy the civilization or its descendants. Although individual civilizations within a cluster may follow different evolutionary paths, or even be destroyed, the cluster may always host some advanced civilization, once a small number of them have managed to jump across interstellar space.
1601.03740
Turnaround overdensity as cosmological observable: the case for a local measurement of $\Lambda$
Tanoglidis et al
Demonstrate that, in the context of the LCDM model, it is in principle possible to measure the value of the cosmological constant by tracing, across cosmic time, the evolution of the turnaround radius of cosmic structures. The novelty of the presented method is that it is local, in the sense that it uses the effect of the cosmo constant on the relatively short scales of cosmic structures and not on the dynamics of the universe at its largest scales. In this way, it can provide an important consistency check for the standard cosmological model and can give signs of new physics, beyond LCDM.
1601.03741
Probing dark energy via galaxy cluster outskirts
Morandi, Sun
Present a Bayesian approach to combine Planck data and the X-ray physical properties of the intracluster medium in the virialization region of a sample of 320 galaxy clusters (0.056<z<1.24, kT>3 keV) observed with Chandra. Exploit the high-level of similarity of the emission measure in the cluster outskirts as cosmo proxy. The cosmo parameters are thus constrained assuming that the emission measure profiles at different redshift are weakly self-similar, that is their shape is universal, explicitly allowing for temperature and redshift dependences of the gas fraction. This cosmo test, in combination with Planck+SNIa data, allows putting a tight constraint on the DE models. For a constant-w model, have w=-1.010±0.030 and Omegam=0.311±0.014, while for a time-evolving EoS DE w(z), have Omega_m=0.308±).017, w0=-0.993±0.046 and wa=-0.123±0.400. Constraints on the cosmology are further improved by adding priors on the gas fraction evolution from hydrodynamic sims. Current data favor the cosmo constant with w=-1, with no evidence for dynamic DE. Checked that the method is robust towards different sources of systematics, including background modeling, outlier measurements, selection effects, inhomogeneities of the gas distribution and cosmic filaments. Also provided for the first time constraints on which definition of cluster boundary radius is more tenable, namely based on a fixed overdensity with respect to the critical density of the Universe. This novel cosmo test has the capacity to provide a generational leap forward in the understanding of the EoS of DE.
1601.03947
SKA weak lensing I: cosmological forecasts and the power of radio-optical cross-correlations
Harrison Camera, Zuntz, Brown
Construct forecasts for cosmo prometter constraints from WL surveys involving SKA. Considering matter content, DE and modified gravity parameters, show that the first phase of the SKA can be competitive with other Stage III experiments such as DES, and full SKA can potentially form tighter constraints than Stage IV optical WL experiments, such as those that will be constructed with LSST or Euclid-like facilities. Using WL alone, going from SKA1 to SKA2 represents improvements by factors of ~10 in matter, ~8 in DE and ~5 in modified gravity parameters. Also show, for the first time, the powerful result that comparably tight constrains (within ~5%) for both Stage III and IV experiments, can be gained from cross-correlating shear maps between the optical and radio wavebands, a process which will also eliminate a number of potential sources of systematic errors which can otherwise greatly limit the utility of WL cosmology.
Tuesday. Wednesday. Thursday.
1601.02023
Cluster mass profile reconstruction with size and flux magnification on the HST STAGES survey
Duncan, Heymans, Heavens, Joachimi
Present the first measurement of individual cluster mass estimates using WL size and flux magnification. Using data from the HST-STAGES survey of the A901/902 supercluster, detect the 4 known groups in the supercluster at high significance using magnification alone. Discuss the application of a fully Bayesian inference analysis, and investigate a broad range of potential systematics in the application of the method. Compare the results to a previous WL shear analysis of the same field finding the recovered signal-to-noise of the magnification-only analysis to range from 45% o 110% of the S/N in the shear-only analysis. On a case-by-case basis find consistent magnification and shear constraints on cluster viral radius, and find magnification constraints to be a factor 0.77±0.18 lower than the shear measurements for the the full sample.
1601.02091
AGN host galaxy mass function in COSMOS: is AGN feedback responsible for the mass-quenching of galaxies?
Bongiorno, et al
Investigate the role of SMBH in the global context of galaxy evolution by measuring the host galaxy stellar mass function (HGMF) and the specific accretion rate i.e., lambda_SAR, distribution function (SARDF) up to z~2.5 with ~1000 X-ray selected AGN from XMM-COSMOS. Using a maximum likelihood approach, jointly fit the stellar mass function and specific accretion rate distribution function, with the X-ray luminosity function as an additional constraint. The best fit model characterizes the SARDF as a double power-law with mass dependent but z independent break whose low lambda_SAR slope flattens with increasing redshift while the normalization increases. This implies that, for a given stellar mass, higher lambda_SAR objects have a peak in their space density at earlier epoch compared to the lower lambda_SAR ones, following and mimicking the well known AGN cosmic downsizing as observed in the AGN luminosity function. The mass function of active galaxies is described by a Schechter function with an almost constant Mstar* and a low mass slope alpha that flattens with redshift. Compared to the stellar MF, find that the HGMF has a similar shape and that, up to log(Mstar/Msun)~11.5 the ratio of AGN host galaxies to star forming galaxies is basically constant (~10%). Finally, the comparison of the AGN HGMF for different luminosity and specific accretion ratio sub-classes with the phenomenological model prediction by Peng+2010 for the "transient" population, i.e., galaxies in the process of being mass-quenched, reveals that low-luminosity AGN do not appear to be able to contribute significantly to the quenching and that at least at higher masses, i.e., Mstar>1e10.7 Msun, feedback from luminous AGN (log(Lbol) >~46 [erg/s]) may be responsible for the quenching of SF in the host galaxy.
1601.02266
The most luminous H$\alpha$ emitters at z~0.8-2.23 from HiZELS: evolution of AGN and star-forming galaxies
Sorbet et al
Find little to no evolution in the AGN fraction with redshift within errors, but the AGN fraction increases strongly with Ha luminosity and correlates best with L_Ha/L*_Ha(z). While L_Ha<L*_Ha(z) Ha emitters are largely dominated by SF galaxies (>80%), the most luminous Ha emitters (L_Ha>10 L*_Ha(z)) at any cosmic time are essentially all BL-AGN. Using the AGN-decontaminated sample of luminous SF galaxies, and integrating down to a fixed Ha luminosity, find a factor of ~1300x evolution in the SFR density from z=0 to z=2.23. This is much stronger than the evolution from typical Ha SF galaxies and in line with the evolution seen for constant luminosity cuts used to select "Ultra-luminous" infrared galaxies and/or sub-millietre galaxies. By taking in to account the evolution in the typical Ha luminosity, show that the most strongly SF Ha-selected galaxies at any epoch contribute the same fractional amount of 15% to the total SFR density, at least up to z=2.23.
1601.02611
Is there a maximum mass for black holes in galactic nuclei?
Inayoshi, Haiman
The largest observed SMBHs have mass of M_BH~1e10 Msun, nearly independent of redshift, from the local (z~0) to the early (z>6) universe. Suggest that the growth of SMBHs above a few 1e10 Msun is prevented by small scale accretion physics, independent of the properties of their host galaxies or of cosmology. Growing more massive BHs requires a gas supply rate from galactic scales onto a nuclear region as high as >1e3Msun/yr. At such a high accretion rate, most of the gas converts to stars at large radii (~10-100 pc), well before reaching the BH. Adopt a simple model (Thompson+ 2005) for a SF accretion disk, and find that the accretion rate in the sub-pc nuclear region is reduced to the smaller value of at most a few Msun/yr. This prevents SMBHs from growing above ~1e11 Msun in the age of the Universe. Furthermore, once a SMBH recaches a sufficiently high mass, this rate falls below the critical value at which the accretion flow becomes advection dominated. Once this transition occurs, BH feeding can be suppressed by strong outflows and jets from hot gas near the BH. Find that the maximum SMBH mass, given by this transition, is between M_BH,max ~ (1-6)e10 Msun, depending primarily on the efficiency of angular momentum transfer inside the galactic disk and not on other properties of the host galaxy.
1510.02618
Spectral distortion of the CMB by the cumulative CO emission from galaxies throughout cosmic history
Mashian, Loeb, Sternberg
Cumulative CO emission from galaxies throughout cosmic history distorts the spectrum of the CMB at a level that is well above the detection limit of future instruments, such as PIXIE (Primordial Inflation Explorer). Most of the CO foreground originates from modest redshifts z~2-5, and needs to be efficiently removed for more subtle distortions from the earlier universe to be detected.
1601.02624
The mass-concentration-redshift relation of cold and warm dark matter haloes
Ludlow, ... Navarro, Cole, Frenk, et al
Sims with standard LCDM models, as well as several additional simulations with sharply truncated density fluctuation power spectra, such as those expected in WDM scenario. The c(M,z) relation of CDM haloes is monotonic: concentrations decrease with increasing viral mass at tied redshift, and decrease with increasing redshift at fixed mass. The main-progenitor mass accretion histories (MAHs) of CDM haloes are also scale-free, a result that has been used to infer halo concentrations directly from MAHs. These results do not apply to WDM haloes: their MAHs are not scale-free because of the characteristic scale imposed by the PS suppression. Further, the WDM c(M,z) relation is not monotonic: concentrations peak at a halo mass scale dictated by the truncation scale, and decrease at higher and lower masses. Show that the assembly history of a halo can still be used to infer its concentration, provided that the total mass of its collapsed progenitors is considered (the "collapsed mass history"; CMH), rather than just that of its main ancestor. This follows the original NFW proposal, and exploits the scale-free nature of CMHs to derive a simple scaling that reproduces the mass-concentration-redshift relation of both CDM and WDM haloes in sims over a vast range of halo masses and cosmic time The model therefore provides a robust account of the mass, redshift, cosmo and PS dependence of the concentrations of DM haloes assembled hierarchically.
1601.02664
A comparative study of knots of star formation in interacting vs. spiral galaxies
Smith, et al
Interacting galaxies are known to have higher global rates of SF on average than normal galaxies, relative to their stellar masses. Using UV and IR photometry combined with new and published H-alpha images, compare the SFRs of ~700 SF complexes in 46 nearby interacting galaxy pairs with those of regions in 39 normal spiral galaxies. The interacting galaxies have proportionally more regions with high SFRs than the spirals. The most extreme regions in the interacting systems lie at the intersections of spiral/tidal structures, where gas is expected to pile up and trigger SF. Published HST images show unusually large and luminous star clusters in the highest luminosity regions. The SFRs of the clumps correlate with measures of the dust attenuation, consistent with the idea that regions with more interstellar gas have more SF. For the clumps with the highest SFRs, the apparent dust attenuation is consistent with the Calzetti starburst dust attenuation law. This suggests that the high luminosity regions are dominated by a central group of young stars surrounded by a shell of clumpy interstellar gas. In contrast, the lower luminosity clumps are bright in the UV relative to H-alpha, suggesting either a high differential attenuation between the ionized gas and the stars, or a post-starburst population bright in the UV but faded in Ha. The fraction of the global light of the galaxies in the clumps is higher on average for the interacting galaxies than for the spirals. Thus the SF regions in interacting galaxies are more luminous, dustier, or younger on average.
1601.02693
The effects of assembly bias on cosmological inference from galaxy-galaxy lensing and galaxy clusters
McEwen, Weinberg
The combination of GGL and galaxy clustering is a promising route to measuring the amplitude of matter clustering and testing modified gravity theories of cosmic acceleration. HOD modeling can extend the approach down to nonlinear scales, but galaxy assembly bias could introduce systematic errors by causing the HOD to vary with large scale environment at fixed halo mass. Investigate this problem using the mock galaxy catalogs created by Hearin+Watson (2013), which exhibit significant assembly bias because galaxy luminosity is tied to halo peak circular velocity and galaxy color is tied to halo formation time. The preferential placement of galaxies (especially red galaxies) in older haloes affects the cutoff of the mean occupation function <N_cen(M_min)> for central galaxies, with haloes in overdense regions more likely to host galaxies. The effect of assembly bias on the satellite galaxy HOD is minimal. Introduce an extended, environment dependent HOD (EDHOD) prescription to describe these results and fit galaxy correlation measurements. Crucially, find that the galaxy-matter cross-correlation coefficient, r_gm==xi_gm/sqrt(xi_mm xi_gg), is insensitive to assembly bias on scales r>~1Mpc/h, even though xi_gm and xi_gg are both affected individually. Can therefore recover the correct xi_mm from the HW13 gg and gm correlations using either a standard HOD or EDHOD fitting method. For Mr<-19 or Mr<-20 samples, the recovery of xi_mm is accurate to 2% or better. For a sample of red Mr<-20 galaxies, achieve 2% recovery at r>2 Mpc/h with EDHOD modeling but lower accuracy at smaller scales or with a standard HOD fit.
1601.03042
When the Milky Way turnoff the lights: APOGEE provides evidence of star formation "quenching" in our Galaxy
Haywood, et al
Show the first evidence that the MW experienced a generalized quenching of its SF at the end of its thick disk formation ~9 Gyr ago. Elemental abundances of stars studied as part of the APOGEE survey reveal indeed that in less than ~2 Gyr the SFR in the Galaxy dropped by an order-of-magnitude. Because of the tight correlation between age and alpha abundance, this event reflects in the dearth of stars along the inner disk sequence the [Fe/H]-[a/Fe] plane. Before this phase, which lasted about 1.5 Gyr, the MW was actively forming stars. Afterwards, the SF resumed at a much lower level to form the thin disk. These events are very well matched by the latest observation of MW-type progenitors at high redshifts. In late type galaxies, quenching is believed to be related to a long and secure exhaustion of gas. In our Galaxy, it occurred on a much shorter time scale, while the chemical continuity before and after the quenching indicates that it was not due to the exhaustion of the gas. While quenching is generally associated with spheroids, the results show that it also occurs in galaxies like the MW, possibly when they are undergoing a morphological transition from thick to thin disks. Given the demographics of late type galaxies in the local universe, in which classical bulges are rare, suggest further that this may hold true generally in galaxies with mass lower than or approximately M*, where quenching could be directly a consequence of thick disk formation. Emphasize that the quenching phase in MW could be contemporaneous with, and related to, the formation of the bar. Sketch a scenario on how a strong bar may inhibit SF.
1601.03051
Gravitational lensing by ring-like structures
Lake, Zheng
Study a class of gravitational lensing systems consisting of an inclined ring/belt, with and without an added point mass at the centre. Show that a common property of such systems is the so-called "pseudo-caustic", across which the magnification of a point source changes discontinuously and yet remains finite. Such a magnification change can be associated with either a change in image multiplicity or a sudden change in the size of one of the images. The existence of pseudo-caustics and the complex interplay between them and the formal caustics (corresponding to points of infinite magnification) can lead to interesting consequences, such as truncated or open caustics and the violation of Burke's theorem. The origin of the pseudo-caustics is found to be the discontinuity in the solutions to the lens equation across the ring/belt boundaries, and the pseudo-caustics correspond to these boundaries in the image (lens) plane. Provide a few illustrative examples to understand the pseudo-caustic features, and in a separate paper, consider a specific astronomical application of microlensing by extrasolar asteroid belts.
1601.03052
Detecting extrasolar asteroid belts through their microlensing signatures
Lake, Zheng, Dong
(see abstract directly above) Astroid belt + star lens systems create "pseudo-caustics", where the magnification exhibits a finite but discontinuous jump. These features allow such systems to generate distinctive microlensing light curves across a wide region of belt parameter space and possess remarkably large using cross-sections. Sample light curves for a range of mastoid bel parameters are presented. In the near future, space-based microlensing surveys (e.g., WFIRST) may be able t discover extrasolar asteroid belts with masses of the order of 0.1 M_earth.
