Day 1531

Thursday.  Friday.  Monday.

1902.01972

The Zwicky Transient Facility: data processing, products, and archive
Masci, et al

[...]  ...600 megapixel camera to scan the entire northern visible sky at rates of ~3760 sq deg/hour to median depths pf g~20.8 and r~20.6 mag (AB, 5 sigma in 30 sec).  [...] The products support a broad range of scientific applications: fast and young SNe, rare flux transients, variable stars, eclipsing binaries, variability from AGN, counterparts to gravitational wave sources, a more complete census of Type Ia SNe, and Solar System objects.


1902.02305
Interacting galaxies on FIRE-2: the connection between enhanced star formation and interstellar gas content
Moreno, et al

We present a comprehensive suite of high-resolution (parsec-scale), idealised (non-cosmological) galaxy merger simulations (24 runs, stellar mass ratio ~2.5:1) to investigate the connection between interaction-induced star formation and the evolution of the interstellar medium (ISM) in various temperature-density regimes. We use the GIZMO code and the second version of the 'Feedback in Realistic Environments' model (FIRE-2), which captures the multi-phase structure of the ISM. Our simulations are designed to represent galaxy mergers in the local Universe. In this work, we focus on the 'galaxy-pair period' between first and second pericentric passage. We split the ISM into four regimes: hot, warm, cool and cold-dense, motivated by the hot, ionised, atomic and molecular gas phases observed in real galaxies. We find that, on average, interactions enhance the star formation rate of the pair (~30%, merger-suite sample average) and elevate their cold-dense gas content (~18%). This is accompanied by a decrease in warm gas (~11%), a negligible change in cool gas (~4% increase), and a substantial increase in hot gas (~400%). The amount of cold-dense gas with densities above 1000 cm^3 (the cold ultra-dense regime) is elevated significantly (~240%), but only accounts for 0.15% (on average) of the cold-dense gas budget.

1902.02340

Satellite dwarf galaxies: stripped but not quenched

Hausammann, et al

In the Local Group, quenched gas-poor dwarfs galaxies are most often found close to the Milky Way and Andromeda, while star forming gas-rich ones are located at greater distances. This so-called morphology-density relation is often interpreted as the consequence of the ram pressure stripping of the satellites during their interaction with the Milky Way hot halo gas. While this process has been often investigated, self-consistent high resolution simulations were still missing. In this study, we have analysed the impact of both the ram pressure and tidal forces induced by a host galaxy on dwarf models as realistic as possible emerging from cosmological simulations. These models were re-simulated using both a wind tunnel and a moving box technique. The secular mass growth of the central host galaxy, as well as the gas density and temperature profiles of its hot halo have been taken into account. We show that while ram pressure is very efficient at stripping the hot and diffuse gas of the dwarf galaxies, it can remove their cold gas ($T < 10^3$~[K]) only in very specific conditions. Depending on the infall time of the satellites relatively to the build-up stage of the massive host, star formation can thus be prolonged instead of being quenched. This is the direct consequence of the clumpy nature of the cold gas and the thermal pressure the hot gas exerts onto it. We discuss the possibility that the variety in satellite populations among Milky Way-like galaxies reflects their accretion histories.

1902.02349
Transition of BH feeding from the quiescent regime into star-forming cold disk regime
Inayoshi, Ichikawa, Ostriker, Kuiper

We study the properties of rotating accretion flows onto supermassive black holes (SMBHs) using axisymmetric two-dimensional hydrodynamical simulations with radiative cooling and BH feedback. The simulations resolve the accretion dynamics of gas outside from the BH influence radius through an inner accretion disk. For lower Bondi accretion rates in units of the Eddington rate ($\dot{M}_{\rm B}\ll 10^{-3}~\dot{M}_{\rm Edd}$), the BH feeding is suppressed due to turbulent motion by several orders of magnitudes from the Bondi rate. Thus, the radiative luminosity results in as low as $\sim 10^{-10}-10^{-7}~L_{\rm Edd}$, where $L_{\rm Edd}$ is the Eddington luminosity. For higher rates of $\dot{M}_{\rm B}> 10^{-3}~\dot{M}_{\rm Edd}$, the optically-thin accreting gas cools via free-free emission and forms a geometrically-thin disk, which feeds the BH efficiently and increases the radiative luminosity to $> 10^{-3}~L_{\rm Edd}$. The transitional behavior of accreting BHs in galactic nuclei from radiatively inefficient phases to cold disk accretion naturally explains (1) the reason for the offset between the observed luminosities and theoretical predictions for nearby quiescent SMBHs, and (2) the conditions to fuel gas into the nuclear SMBH. In addition, the cold disk formed in galactic nuclei tends to be gravitationally unstable and leads to star formation when the Bondi rate is as high as $ \dot{M}_{\rm B} > 10^{-2}~M_\odot~{\rm yr}^{-1}$. This is a plausible explanation of the correlation observed between star formation rates and BH feeding rates in Seyfert galaxies.

1902.02374

Photometric biases in modern surveys

Portillo, Speagle, Finkbeiner

Most surveys use maximum-likelihood (ML) methods to fit models when extracting photometry from images. We show these ML estimators systematically overestimate the flux as a function of the signal-to-noise ratio (SNR) and the number of model parameters involved in the fit. This bias is substantially worse for galaxies: while a 1% bias is expected for a 10-sigma point source, a 10-sigma galaxy with a simplified Gaussian profile suffers a 2.5% bias. This bias also behaves differently depending how multiple bands are used in the fit: simultaneously fitting all bands leads the flux bias to become roughly evenly distributed between them, while fixing the position in `non-detection' bands (i.e. forced photometry) gives flux estimates in those bands that are biased low, compounding a bias in derived colors. We show that these effects are present in idealized simulations, outputs from the HSC fake object pipeline (SynPipe), and observations from SDSS Stripe 82. Prescriptions to correct for these biases are provided along with more detailed results related to biases in ML error estimation.

1902.02535

Magnetic field and ISM in the local Galactic disc

Sofue, Nakanishi, Ichiki

Correlation analysis is obtained among Faraday rotation measure, HI column density, thermal and synchrotron radio brightness using archival all-sky maps of the Galaxy. A method is presented to calculate the magnetic strength and its line-of-sight (LOS) component, volume gas densities, effective LOS depth, effective scale height of the disk) from these data in a hybrid way. Applying the method to archival data, all-sky maps of the local magnetic field strength and its parallel component are obtained, which reveal details of local field orientation.

1902.02786
The mean H$\alpha$ EW and Lyman-continuum photon production efficiency for faint $z\approx4-5$ galaxies
Lam, et al

We present the first measurements of the Lyman-continuum photon production efficiency $\xi_{\textrm{ion,0}}$ at $z\sim4$-5 for galaxies fainter than 0.2 $L^*$ ($-$19 mag). $\xi_{\textrm{ion,0}}$ quantifies the production rate of ionizing photons with respect to the UV luminosity density assuming a fiducial escape fraction of zero. Extending previous measurements of $\xi_{\textrm{ion,0}}$ to the faint population is important, as ultra-faint galaxies are expected to contribute the bulk of the ionizing emissivity. We probe $\xi_{\textrm{ion,0}}$ to such faint magnitudes by taking advantage of 200-hour depth Spitzer/IRAC observations from the GREATS program and $\approx$300 3<$z$<6 galaxies with spectroscopic redshifts from the MUSE GTO Deep + Wide programs. Stacked IRAC [3.6]$-$[4.5] colors are derived and used to infer the H$\alpha$ rest-frame equivalent widths, which range from 403\r{A} to 2818\r{A}. The derived $\xi_{\textrm{ion,0}}$ is $\log_{10}(\xi_{\textrm{ion,0}} / \textrm{Hz erg}^{-1}) = 25.36 \pm 0.08$ over $-$20.5 < M$_{\textrm{UV}}$ < $-$17.5, similar to those derived for brighter galaxy samples at the same redshift and therefore suggesting that $\xi_{\textrm{ion}}$ shows no strong dependence on $M_{UV}$. The $\xi_{\textrm{ion,0}}$ values found in our sample imply that the Lyman-continuum escape fraction for $M_{\textrm{UV}} \approx -19$ star-forming galaxies cannot exceed $\approx$8-20\% in the reionization era.

1902.02792

Conditions for recognizing the universe with a low galaxy ionizing photon escape fraction

Finkelstein, et al

We explore scenarios for reionizing the intergalactic medium with low galaxy ionizing photon escape fractions. We combine simulation-based halo-mass dependent escape fractions with an extrapolation of the observed galaxy rest-ultraviolet luminosity functions to solve for the reionization history from z=20 to z=4. We explore the posterior distributions for key unknown quantities, including the limiting halo mass for star-formation, the ionizing photon production efficiency, and a potential contribution from active galactic nuclei (AGN). We marginalize over the allowable parameter space using a Markov Chain Monte Carlo method, finding a solution which satisfies the most model-independent constraints on reionization. Our fiducial model can match observational constraints with an average escape fraction of <5% throughout the bulk of the epoch of reionization if: i) galaxies form stars down to the atomic cooling limit before reionization and a photosuppression mass of log(M_h/Msol)~9 during/after reionization (-13<M_UV,lim<-11); ii) galaxies become more efficient producers of ionizing photons at higher redshifts and fainter magnitudes, and iii) there is a significant, but sub-dominant, contribution by AGN at z < 7. In this model the faintest galaxies (M_UV>-15) dominate the ionizing emissivity, leading to an earlier start to reionization and a smoother evolution of the ionized volume filling fraction than models which assume a single escape fraction at all redshifts and luminosities. The ionizing emissivity from this model is consistent with observations at z=4-5 (and below, when extrapolated), in contrast to some models which assume a single escape fraction. Our predicted ionized volume filling fraction at z=7 of Q_HII=78% (+\- 8%) is in ~1-2 sigma tension with observations of Lya emitters at z~7 and the damping wing analyses of the two known z>7 quasars, which prefer Q_HII,z=7~40-50%.

1902.02820

Quenching low-mass satellite galaxies: evidence for a threshold ICM density

Roberts, et al

We compile a sample of SDSS galaxy clusters with high-quality Chandra X-ray data to directly study the influence of the dense intra-cluster medium (ICM) on the quenching of satellite galaxies. We study the quenched fractions of satellite galaxies as a function of ICM density for low- ($10^9 \lesssim M_\star \lesssim 10^{10}\,\mathrm{M_\odot}$), intermediate- ($10^{10} \lesssim M_\star \lesssim 10^{10.5}\,\mathrm{M_\odot}$), and high-mass ($M_\star \gtrsim 10^{10.5}\,\mathrm{M_\odot}$) satellite galaxies with $>\!3000$ satellite galaxies across 24 low-redshift ($z < 0.1$) clusters. For low-mass galaxies we find evidence for a broken powerlaw trend between satellite quenched fraction and local ICM density. The quenched fraction increases modestly at ICM densities below a threshold before increasing sharply beyond this threshold toward the cluster center. We show that this increase in quenched fraction at high ICM density is well matched by a simple, analytic model of ram pressure stripping. These results are consistent with a picture where low-mass cluster galaxies experience an initial, slow-quenching mode driven by steady gas depletion, followed by rapid quenching associated with ram pressure of cold-gas stripping near (one quarter of the virial radius, on average) the cluster center.

Day 1530

Monday.  Tuesday.  Wednesday.

1902.00030
The three causes of low-mass assembly bias
Mansfield, Kravtsov

We present a detailed analysis of the physical processes that cause halo assembly bias -- the dependence of halo clustering on proxies of halo formation time. We focus on the origin of assembly bias in the mass range corresponding to the hosts of typical galaxies and use halo concentration as our chief proxy of halo formation time. We also repeat our key analyses across a broad range of halo masses and for alternative formation time definitions. We show that splashback subhaloes are responsible for two thirds of the assembly bias signal, but do not account for the entire effect. After splashback subhaloes have been removed, we find that the remaining assembly bias signal is due to a relatively small fraction ($\lesssim 10\%$) of haloes in dense regions. We test a number of additional physical processes thought to contribute to assembly bias and demonstrate that the two key processes are the slowing of mass growth by large-scale tidal fields and by the high velocities of ambient matter in sheets and filaments. We also rule out several other proposed physical causes of halo assembly bias. Based on our results, we argue that there are three processes that contribute to assembly bias of low-mass halos: large-scale tidal fields, gravitational heating due to the collapse of large-scale structures, and splashback subhaloes located outside the virial radius.

1902.00044

Euclid prepration IV. Impact of undetected galaxies on weak lensing shear measurements

Euclid Collaboration, Martinet, Schrabback, Hoekstra, Tewes, et al

In modern weak lensing surveys, shape measurement algorithms are calibrated using simulations in order to correct for any residual systematic bias in the shear. These simulations must fully capture the complexity of the observations to avoid introducing any additional bias. In this paper we study the importance of faint galaxies below the observational detection limit of a survey. We simulate simplified Euclid VIS images with and without including this faint population, and measure the shift in the multiplicative shear bias between the two sets of simulations. We measure the shear with three different algorithms: a moment-based approach, model fitting, and machine learning. We find that for all methods, a spatially uniform random distribution of faint galaxies introduces a shear multiplicative bias of the order of a few times $10^{-3}$. This value increases to the order of $10^{-2}$ when including the clustering of the faint galaxies, as measured in the Hubble Space Telescope Ultra Deep Field. The magnification of the faint background galaxies due to the brighter galaxies along the line of sight is found to have a negligible impact on the multiplicative bias. We conclude that the undetected galaxies must be included in the calibration simulations with proper clustering properties down to magnitude 28 in order to reach a residual uncertainty on the multiplicative shear bias calibration of a few times $10^{-4}$, in line with the $2\times10^{-3}$ total accuracy budget required by the scientific objectives of the Euclid survey. We propose two complementary methods for including faint galaxy clustering in the calibration simulations.

1902.00354

Rare cosmological events recorded in muscovite mica

Russel

A study of fossil tracks of charged particles recorded in crystals of muscovite has revealed evidence of rare events of cosmological origin. The events are not compatible with known particle interactions with matter. They were recorded during a period when the crystals were in a metastable state during cooling after growth 13km water equivalent underground. In this state a phase transition can be triggered by low energy events in the range 1eV to 10keV, when the crystals effectively behave as solid-state bubble chambers. At higher energies the chemical etching technique can be used to reveal massive damage to the lattice. The rare events show evidence of interaction with the crystal over a great range of energies. They leave a distinctive record that is easily recognised.

1902.00522
Deep learning for multi-messenger astrophysics: a gateway for discovery in the big data era
Allen, et al

This report provides an overview of recent work that harnesses the Big Data Revolution and Large Scale Computing to address grand computational challenges in Multi-Messenger Astrophysics, with a particular emphasis on real-time discovery campaigns. Acknowledging the transdisciplinary nature of Multi-Messenger Astrophysics, this document has been prepared by members of the physics, astronomy, computer science, data science, software and cyberinfrastructure communities who attended the NSF-, DOE- and NVIDIA-funded "Deep Learning for Multi-Messenger Astrophysics: Real-time Discovery at Scale" workshop, hosted at the National Center for Supercomputing Applications, October 17-19, 2018. Highlights of this report include unanimous agreement that it is critical to accelerate the development and deployment of novel, signal-processing algorithms that use the synergy between artificial intelligence (AI) and high performance computing to maximize the potential for scientific discovery with Multi-Messenger Astrophysics. We discuss key aspects to realize this endeavor, namely (i) the design and exploitation of scalable and computationally efficient AI algorithms for Multi-Messenger Astrophysics; (ii) cyberinfrastructure requirements to numerically simulate astrophysical sources, and to process and interpret Multi-Messenger Astrophysics data; (iii) management of gravitational wave detections and triggers to enable electromagnetic and astro-particle follow-ups; (iv) a vision to harness future developments of machine and deep learning and cyberinfrastructure resources to cope with the scale of discovery in the Big Data Era; (v) and the need to build a community that brings domain experts together with data scientists on equal footing to maximize and accelerate discovery in the nascent field of Multi-Messenger Astrophysics.

1902.00534

The neutrino puzzle: anomalies, interactions, and cosmological tensions

Kreisch, Cyr-Racing, Doré

New physics in the neutrino sector might be necessary to address anomalies between different neutrino oscillation experiments. Intriguingly, it also offers a possible solution to the discrepant cosmological measurements of $H_0$ and $\sigma_8$. We show here that delaying the onset of neutrino free-streaming until close to the epoch of matter-radiation equality can naturally accommodate a larger value for the Hubble constant $H_0=72.3 \pm 1.4$ km/s/Mpc and a lower value of the matter fluctuations $\sigma_8=0.786\pm 0.020$, while not degrading the fit to the cosmic microwave background (CMB) damping tail. We achieve this by introducing neutrino self-interactions in the presence of a non-vanishing sum of neutrino masses. This strongly interacting neutrino cosmology prefers $N_{\rm eff} = 4.02 \pm 0.29$, which has interesting implications for particle model-building and neutrino oscillation anomalies. We show that the absence of the neutrino free-streaming phase shift on the CMB can be compensated by shifting the value of other cosmological parameters, hence providing an important caveat to the detections made in the literature. Due to their impact on the evolution of the gravitational potential at early times, self-interacting neutrinos and their subsequent decoupling leave a rich structure on the matter power spectrum. In particular, we point out the existence of a novel localized feature appearing on scales entering the horizon at the onset of neutrino free-streaming. While the interacting neutrino cosmology provides a better global fit to current cosmological data, we find that traditional Bayesian analyses penalize the model as compared to the standard cosmological. Our analysis shows that it is possible to find radically different cosmological models that nonetheless provide excellent fits to the data, hence providing an impetus to thoroughly explore alternate cosmological scenarios.

1902.00709

Debiasing inference with approximate covariance matrices and other unidentified biases

Sellentin, Starck

When a posterior peaks in unexpected regions of parameter space, new physics has either been discovered, or a bias has not been identified yet. To tell these two cases apart is of paramount importance. We therefore present a method to indicate and mitigate unrecognized biases: Our method runs any pipeline with possibly unknown biases on both simulations and real data. It computes the coverage probability of posteriors, which measures whether posterior volume is a faithful representation of probability or not. If found to be necessary, the posterior is then corrected. This is a non-parametric debiasing procedure which complies with objective Bayesian inference. We use the method to debias inference with approximate covariance matrices and redshift uncertainties. We demonstrate why approximate covariance matrices bias physical constraints, and how this bias can be mitigated. We show that for a Euclid-like survey, if a traditional likelihood exists, then 25 end-to-end simulations suffice to guarantee that the figure of merit deteriorates maximally by 22 percent, or by 10 percent for 225 simulations. Thus, even a pessimistic analysis of Euclid-like data will still constitute an 25-fold increase in precision on the dark energy parameters in comparison to the state of the art (2018) set by KiDS and DES. We provide a public code of our method.

1902.01260

Turning gravitationally lensed supernovae into cosmological probes

Pierre, Rodney

Recently, there have been two landmark discoveries of gravitationally lensed supernovae: the first multiply-imaged SN, ``Refsdal'', and the first Type Ia SN resolved into multiple images, SN iPTF16geu. Fitting the multiple light curves of such objects can deliver measurements of the lensing time delays, which are the difference in arrival times for the separate images. These measurements provide precise tests of lens models or constraints on the Hubble constant and other cosmological parameters that are independent of the local distance ladder. Over the next decade, accurate time delay measurements will be needed for the tens to hundreds of lensed SNe to be found by wide-field time-domain surveys such as LSST and WFIRST. We have developed an open source software package for simulations and time delay measurements of multiply-imaged SNe, including an improved characterization of the uncertainty caused by microlensing. We describe simulations using the package that suggest a before-peak detection of the leading image enables a more accurate time delay measurement by ~4 days compared to an after-peak detection. We also conclude that fitting the effects of microlensing without an accurate prior often leads to biases in the time delay measurement and over-fitting to the data, but that employing a Gaussian Process Regression (GPR) technique is sufficient for determining the uncertainty due to microlensing.

1902.01274
The golden era of neutron stars: from hadrons to quarks
Baym

Neutron stars were first posited in the early thirties, and discovered as pulsars in late sixties; however, only recently are we beginning to understand the matter they contain. This talk describes the continuing development of a consistent picture of the liquid interiors of neutron stars, driven by four advances: observations of two heavy neutron stars with masses $\simeq$ 2.0 solar masses; inferences of masses and radii simultaneously for an increasing number of neutron stars in low mass X-ray binaries, and future determinations via the NICER observatory; the observation of the binary neutron star merger, GW170817, through gravitational waves as well as across the electromagnetic spectrum; and an emerging understanding in QCD of how nuclear matter can turn into deconfined quark matter in the interior. We describe the modern quark-hadron crossover equation of state, QHC18, and the corresponding neutron stars, which agree well with current observations.

1902.01366

Reconstructing gravity on cosmological scales

Raveri

We present the data-driven reconstruction of gravitational theories and Dark Energy models on cosmological scales. We showcase the power of present cosmological probes at constraining these models and quantify the knowledge of their properties that can be acquired through state of the art data. This reconstruction exploits the power of the Effective Field Theory approach to Dark Energy and Modified Gravity phenomenology, which compresses the freedom in defining such models into a finite set of functions that can be reconstructed across cosmic times using cosmological data. We consider several model classes described within this framework and thoroughly discuss their phenomenology and data implications. We find that some models can alleviate the present discrepancy in the determination of the Hubble constant as inferred from the cosmic microwave background and as directly measured. This results in a statistically significant preference for the reconstructed theories over the standard cosmological model.

1902.01401

AGN all the way down?  AGN-like line ratios are common in the lowest-mass isolated quiescent galaxies

Dickey, Geha, Wetzel, El-Badry

We investigate the lowest-mass quiescent galaxies known to exist in isolated environments ($\mathrm{M^* = 10^{9.0-9.5} \ M_\odot}$; 1.5 Mpc from a more massive galaxy). This population may represent the lowest stellar mass galaxies in which internal feedback quenches galaxy-wide star formation. We present Keck/ESI long-slit spectroscopy for 27 isolated galaxies in this regime: 20 quiescent galaxies and 7 star-forming galaxies. We measure emission line strengths as a function of radius and place galaxies on the Baldwin Phillips Terlevich (BPT) diagram. Remarkably, 16 of 20 quiescent galaxies in our sample host central AGN-like line ratios. Only 5 of these quiescent galaxies were identified as AGN-like in SDSS due to lower spatial resolution and signal-to-noise. We find that many of the quiescent galaxies in our sample have spatially-extended emission across the non-SF regions of BPT-space. When considering only the central 1$^{\prime\prime}$, we identify a tight relationship between distance from the BPT star-forming sequence and host galaxy stellar age as traced by $\mathrm{D_n4000}$, such that older stellar ages are associated with larger distances from the star-forming locus. Our results suggest that the presence of hard ionizing radiation (AGN-like line ratios) is intrinsically tied to the quenching of what may be the lowest-mass self-quenched galaxies.

1902.01417

Occurrence rates of planets orbiting FGK stars: combining Kepler DR25, Gaia DR2 and Bayesian inference

Hsu, et al

We characterize the occurrence rate of planets, ranging in size from 0.5-16 R$_\oplus$, orbiting FGK stars with orbital periods from 0.5-500 days. Our analysis is based on results from the `DR25' catalog of planet candidates produced by NASA's Kepler mission and stellar radii from Gaia `DR2'. We incorporate additional Kepler data products to accurately characterize the the efficiency of planets being recognized as a `threshold crossing events' (TCE) by Kepler's Transiting Planet Search pipeline and labeled as a planet candidate by the robovetter. Using a hierarchical Bayesian model, we derive planet occurrence rates for a wide range of planet sizes and orbital periods. For planets with sizes 1-1.75 R$_\oplus$ and orbital periods of 237-500 days, we find a rate of planets per FGK star of $ 0.24^{+0.11}_{-0.10}$ ($68.3\%$ credible interval). While the true rate of such planets could be lower by a factor of $\sim~2$ (primarily due to potential contamination of planet candidates by false alarms), the upper limits on the occurrence rate of such planets are robust to $\sim~10\%$. We recommend that mission concepts aiming to characterize potentially rocky planets in or near the habitable zone of sun-like stars prepare compelling science programs that would be robust for a true rate in the range $f_{R,P} = 0.05-0.51$ for $1-1.75$ R$_\oplus$ planets with orbital periods in 237-500 days, or a differential rate of $\Gamma_\oplus \equiv (d^2 f)/[d(\ln P)~d(\ln R_{p})] = 0.11-1.2$.

1902.01503

Environmental effects on halo abundance and weak lensing peak statistics toward large underdone regions

Higuchi, Inoue

The cosmic microwave background (CMB) contains an anomalous cold spot with a surrounding hot ring, known as the Cold Spot. Inoue & Silk (2006) proposed that this feature could be explained by postulating a supervoid: if such a large underdense region exists, then the growth of matter perturbing around the spot might differ from the average value in the Universe and the differences might affect weak lensing analysis of peak statistics. To investigate environmental effects on halo number count and peak statistics, we used a publicly available ray-tracing simulation for a box size of 2250$h^{-1}$Mpc on a side (Takahashi et al. 2017). We found that the number counts for massive haloes toward the largest underdense region in the simulation decreases and the corresponding significance of the difference, based on a cosmic average, is $\geq3\sigma$. On the basis of the results of peak statistics analysis, the number of high peaks decreases with the decrement of massive haloes, but the number of low peaks increases with the lack of matter in the line of sight. The highest significance of the decrement in peak counts in large underdense regions is $10\sigma$ in the total signal-to-noise ratio. Our result implies that environmental effects on halo abundance and weak lensing peak statistic can be used to probe the presence and properties of supervoids.

1902.01665
What shapes a galaxy? - Unraveling the role of mass, environment and star formation in forming galactic structure
Bluck, et al

We investigate the dependence of galaxy structure on a variety of galactic and environmental parameters for ~500,000 galaxies at z<0.2, taken from the Sloan Digital Sky Survey data release 7 (SDSS-DR7). We utilise bulge-to-total stellar mass ratio, (B/T)_*, as the primary indicator of galactic structure, which circumvents issues of morphological dependence on waveband. We rank galaxy and environmental parameters in terms of how predictive they are of galaxy structure, using an artificial neural network approach. We find that distance from the star forming main sequence (Delta_SFR), followed by stellar mass (M_*), are the most closely connected parameters to (B/T)_*, and are significantly more predictive of galaxy structure than global star formation rate (SFR), or any environmental metric considered (for both central and satellite galaxies). Additionally, we make a detailed comparison to the Illustris hydrodynamical simulation and the LGalaxies semi-analytic model. In both simulations, we find a significant lack of bulge-dominated galaxies at a fixed stellar mass, compared to the SDSS. This result highlights a potentially serious problem in contemporary models of galaxy evolution.

1902.01775
Low-redshift lowest-metallicity star-forming galaxies in the SDSS DR14
Izotov, Guseva, Fricke, Henkel

We present a sample of low-redshift (z<0.133) candidates for extremely low-metallicity star-forming galaxies with oxygen abundances 12+logO/H<7.4 selected from the Data Release 14 (DR14) of the Sloan Digital Sky Survey (SDSS). Three methods are used to derive their oxygen abundances. Among these methods two are based on strong [OII]3727, [OIII]4959, and [OIII]5007 emission lines, which we call strong-line and semi-empirical methods. These were applied for all galaxies. We have developed one of these methods, the strong-line method, in this paper. This method is specifically focused on the accurate determination of metallicity in extremely low-metallicity galaxies and may not be used at higher metallicities with12+logO/H>7.5. The third, the direct Te method, was applied for galaxies with detected [OIII]4363 emission lines. All three methods give consistent abundances and can be used in combination or separately for selection of lowest-metallicity candidates. However, the strong-line method is preferable for spectra with a poorly detected or undetected [OIII]4363 emission line. In total, our list of selected candidates for extremely low-metallicity galaxies includes 66 objects.

Day 1529

Wednesday, Thursday, Friday.

1901.09925

Testing the impact of satellite anisotropy on large and small scale intrinsic alignments sing hydrodynamical simulations

Samuroff, Mandelbaum, Di Matteo

Galaxy intrinsic alignments (IAs) have long been recognised as a significant contaminant to weak lensing-based cosmological inference. In this paper we seek to quantify the impact of a common modelling assumption in analytic descriptions of intrinsic alignments: that of spherically symmetric dark matter halos. Understanding such effects is important as the current generation of intrinsic alignment models are known to be limited, particularly on small scales, and building an accurate theoretical description will be essential for fully exploiting the information in future lensing data. Our analysis is based on a catalogue of 113,560 galaxies between $z=0.06-1.00$ from MassiveBlack-II, a hydrodynamical simulation of box length $100 h^{-1}$ Mpc. We find satellite anisotropy contributes at the level of $\geq 30-40\%$ to the small scale alignment correlation functions. At separations larger than $1 h^{-1}$ Mpc the impact is roughly scale-independent, inducing a shift in the amplitude of the IA power spectra of $\sim20\%$. These conclusions are consistent across the redshift range and between the MassiveBlack-II and Illustris simulations. The cosmological implications of these results are tested using a simulated likelihood analysis. Synthetic cosmic shear data is constructed with the expected characteristics (depth, area and number density) of a future LSST-like survey. Our results suggest that modelling alignments using a halo model based upon spherical symmetry could potentially induce cosmological parameter biases at the $\sim 1.5\sigma$ level for $S_8$ and $w$.

1901.10129
Effect of lensing magnification on type Ia supernova cosmology
Sakakibara, et al

Effect of gravitational magnification on the measurement of distance modulus of type Ia supernovae is presented. We investigate a correlation between magnification and Hubble residual to explore how the magnification affects the estimation of cosmological parameters. We estimate magnification of type Ia supernovae in two distinct methods: one is based on convergence mass reconstruction under the weak lensing limit and the other is based on the direct measurement from galaxies distribution. Both magnification measurements are measured from Subaru Hyper Suprime-Cam survey catalogue. For both measurements, we find no significant correlation between Hubble residual and magnification. Furthermore, we correct for the apparent supernovae fluxes obtained by Supernova Legacy Survey 3-year sample using direct measurement of the magnification. We find $\Omega_{\rm m0} = 0.287 ^{+0.104} _{-0.085}$ and $w = -1.161 ^{+0.595}_{-0.358}$ for supernovae samples corrected for lensing magnification when we use photometric redshift catalogue of Mizuki, while $\Omega_{\rm m0} = 0.253 ^{+0.113} _{-0.087}$ and $w = -1.078 ^{+0.498} _{-0.297}$ for DEmP photo-z catalogue. Therefore, we conclude that the effect of magnification on the supernova cosmology is negligibly small for the current surveys; however, it has to be considered for the future supernova survey like LSST.

1901.10294

The kinematics of local thick discs do not support an accretion origin

Comerón, et al

Thick discs are nearly ubiquitous components of the discs of present-day galaxies. It has been proposed that a fraction of their stars has been accreted. Here, we aim to find whether accretion of satellites is the main thick disc formation mechanism. To do so, we observed a sample of eight nearby edge-on galaxies with the MUSE integral field unit at the VLT. Six of the galaxies have a distinct thick disc. We derived thick disc velocities and velocity dispersions for the galaxies in our sample. We devise a formalism to estimate the fractions of retrograde material in the thick discs by using kinematical maps and thin/thick disk decompositions. None of the galaxies in our sample shows strong evidence for retrograde material at large distances from the centre. Including those found in the literature, there are seventeen thick discs with studied kinematics, with only one showing unambiguous signatures of retrograde material. Literature numerical studies of dynamical friction allow us to estimate that at the current cosmic time about one in six mergers for which the stars of the accreted galaxy ended in a thick disc were retrograde. This is in tension with the observed fraction of 1/17 of galaxies with a partly retrograde thick disc. We conclude that satellite accretion is not favoured by observations to be the main thick disk formation mechanism.

1901.10460

Lessons from the curious case of the 'fastest' star in Gaia DR2

Boubert, et al

Gaia DR2 5932173855446728064 was recently proposed to be unbound from the Milky Way based on the $-614.3\pm2.5\;\mathrm{km}\;\mathrm{s}^{-1}$ median radial velocity given in Gaia DR2. We obtained eight epochs of spectroscopic follow-up and find a very different median radial velocity of $-56.5 \pm 5.3\;\mathrm{km}\;\mathrm{s}^{-1}$. If this difference were to be explained by binarity, then the unseen companion would be an intermediate-mass black hole; we therefore argue that the Gaia DR2 radial velocity must be in error. We find it likely that the spectra obtained by Gaia were dominated by the light from a star $4.3\;\mathrm{arcsec}$ away, and that, due to the slitless, time delay integration nature of Gaia spectroscopy, this angular offset corresponded to a spurious $620\;\mathrm{km}\;\mathrm{s}^{-1}$ shift in the calcium triplet of the second star. We argue that such unanticipated alignments between stars may account for 105 of the 202 stars with radial velocities faster than $500\;\mathrm{km}\;\mathrm{s}^{-1}$ in Gaia DR2 and propose a quality cut to exclude stars that are susceptible. We propose further cuts to remove stars where the colour photometry is suspect and stars where the radial velocity measurement is based on fewer than four transits, and thus produce an unprecedentedly clean selection of Gaia RVS stars for use in studies of Galactic dynamics.

1901.10481

The fate of AGB wind in massive galaxies and the ICM

Li, Bryan, Quataert

Asymptotic Giant Branch (AGB) winds from evolved stars not only provide a non-trivial amount of mass and energy return, but also produce dust grains in massive elliptical galaxies. Due to the fast stellar velocity and the high ambient temperature, the wind is thought to form a comet-like tail, similar to Mira in the Local Bubble. Many massive elliptical galaxies and cluster central galaxies host extended dusty cold filaments. The fate of the cold dusty stellar wind and its relation to cold filaments are not well understood. In this work, we carry out both analytical and numerical studies of the interaction between an AGB wind and the surrounding hot gas. We find that the cooling time of the tail is inversely proportional to the ambient pressure. In the absence of cooling, or in low pressure environments (e.g., the outskirts of elliptical galaxies), AGB winds are quickly mixed into the hot gas, and all the AGB winds have similar appearance and head-to-tail ratio. In high pressure environments, such as the Local Bubble and the central regions of massive elliptical galaxies, some of the gas in the mixing layer between the stellar wind and the surrounding hot gas can cool efficiently and cause the tail to become longer. Our simulated tail of Mira itself has similar length and velocity to that observed, and appears similar to the simulated AGB tail in the central regions of massive galaxies. We speculate that instead of thermal instability, the induced condensation at the mixing layer of AGB winds may be the origin of cold filaments in massive galaxies and galaxy clusters. This naturally explains the existence of dust and PAH in the filaments.

1901.10522
Coping with selection effects: a primer on regression with Truncated data
Mantz

The finite sensitivity of instruments or detection methods means that data sets in many areas of astronomy, for example cosmological or exoplanet surveys, are necessarily systematically incomplete. Such data sets, where the population being investigated is of unknown size and only partially represented in the data, are called "truncated" in the statistical literature. Truncation can be accounted for through a relatively straightforward modification to the model being fitted in many circumstances, provided that the model can be extended to describe the population of undetected sources. Here I examine the problem of regression using truncated data in general terms, and use a simple example to show the impact of selecting a subset of potential data on the dependent variable, on the independent variable, and on a second dependent variable that is correlated with the variable of interest. Special circumstances in which selection effects are ignorable are noted. I also comment on computational strategies for performing regression with truncated data, as an extension of methods that have become popular for the non-truncated case, and provide some general recommendations.

1901.10690

Effects of massive neutrinos and dynamical dark energy on the cluster mass function

Biswas, et al

The presence of massive neutrinos affects the growth of large-scale structure in the universe, leaving a potentially observable imprint on the abundance and properties of massive dark matter-dominated halos. Cosmological surveys detect large numbers of these halos in the form of rich groups and clusters, using the information as an input to constraining the properties of dark energy. We use a suite of N-body simulations that include the effects of massive neutrinos as well as of dynamical dark energy to study the properties of the mass function. As in our previous work, we follow an approach valid at low neutrino mass, where the neutrino overdensities are assumed to be too small to act as a significant nonlinear source term for gravity. We study how well a universal form for the halo mass function describes our numerical results, finding that the use of an appropriate linear power spectrum within the formalism yields a good match to the simulation results, correctly accounting for the (neutrino mass-dependent) suppression of the mass function.

1901.11031

Probing dark matter structure down to $10^7$ solar masses: flux ratio statistics in gravitational lenses with line of sight halos

Gilman, et al

Strong lensing provides a powerful means of investigating the nature of dark matter as it probes the mass function and density profiles of halos on sub-galactic scales. We present an extension of a forward modeling framework that uses flux ratios from quadruply imaged quasars (quads) to measure the shape and amplitude of the halo mass function, including line of sight (LOS) halos and main deflector subhalos. We apply this machinery to 50 mock lenses --- roughly the number of known quads --- with mass functions exhibiting a free-streaming cutoff parameterized by the half-mode mass $m_{\rm{hm}}$. Assuming cold dark matter (CDM), we forecast bounds on $m_{\rm{hm}}$ and the corresponding thermal relic particle masses for scenarios with a range of tidal destruction severity. With significant tidal destruction, at $2 \sigma$ we constrain $m_{\rm{hm}}<10^{7.9} \left(10^{8.4}\right) M_{\odot}$, or a 4.4 (3.1) keV thermal relic, with image flux uncertainties from measurements and lens modeling of $2\% \left(6\%\right)$. With less severe tidal destruction we constrain $m_{\rm{hm}}<10^{7} \left(10^{7.4}\right) M_{\odot}$, or an 8.2 (6.2) keV thermal relic. If dark matter is warm, with $m_{\rm{hm}} = 10^{7.7} M_{\odot}$ (5.1 keV), we would favor WDM with $m_{\rm{hm}} > 10^{7.7} M_{\odot}$ over CDM with relative likelihoods of 22:1 and 8:1 with flux uncertainties of $2\%$ and $6\%$, respectively. These bounds improve over those obtained by modeling only main deflector subhalos because LOS objects produce additional flux perturbations, especially for high redshift systems. These results indicate that $\sim 50$ quads can conclusively differentiate between warm and cold dark matter.

1901.11353

Intensive monitoring survey of nearby galaxies (IMSNG)

Im, et al

Intensive Monitoring Survey of Nearby Galaxies (IMSNG) is a high cadence observation program monitoring nearby galaxies with high probabilities of hosting supernovae (SNe). IMSNG aims to constrain the SN explosion mechanism by inferring sizes of SN progenitor systems through the detection of the shock-heated emission that lasts less than a few days after the SN explosion. To catch the signal, IMSNG utilizes a network of 0.5-m to 1-m class telescopes around the world and monitors the images of 60 nearby galaxies at distances D < 50 Mpc to a cadence as short as a few hours. The target galaxies are bright in near-ultraviolet (NUV) with M_NUV < -18.4 AB mag and have high probabilities of hosting SNe (0.06 SN/yr per galaxy). With this strategy, we expect to detect the early light curves of 3.4 SNe per year to a depth of R ~ 19.5 mag, enabling us to detect the shock-heated emission from a progenitor star with a radius as small as 0.1 R_sun. The accumulated data will be also useful for studying faint features around the target galaxies and other science projects. So far, 18 SNe have occurred in our target fields (16 in IMSNG galaxies) over 5 years, confirming our SN rate estimate of 0.06 SN/yr per galaxy.

Day 1528

Monday.  Tuesday.

1901.08595
Weak lensing effect on CMB in the presence of a dipole anisotropy
Agarwal, et al

Investigate weak lensing effect on CMB in the presence of dipole anisotropy.  The approach of fiat-sky approximation is considered.  Determine the functions sigma_0^2 and sigma_2^2 that appear in expressions of the lensed CMB power spectrum in the presence of a dipole anisotropy.  Determine the correction to B-mode PS which is found to be appreciable at low multipoles.  However, the temperature and E-mode power spectrum are not altered significantly.


1901.08605
Investing for discovery and sustainability in Astronomy in the 2020s
Najita

This report, created to aid NAOA in its planning for the 2020 Decadal Survey on A+A, review the outcome of the previous Astro2010; describes the themes that emerged from the 2018 NAOA community planning workshop "NOAO Community needs for Science in the 2020s"; and based on the above, offers thoughts for the coming review.  Find that a balanced set of investments in small-to-large-scale initiatives is essential to a sustainable future, based on the experience of previous decades.  While large facilities are the "value" investments that are guaranteed to produce compelling science and discoveries, smaller facilities are the "growth stocks" that are likely to deliver the biggest science bang per buck, sometimes with outsize returns.  Investments in data-intensive missions also have benefits to society beyond the science they deliver.  By training scientists who are well equipped to use their data science skills to solve problems in the public or private sector, astronomy can provide a valuable service to society by contributing to a data-capable workforce.


1901.08679
Fourier series expansion of the dark energy equation of state
Tamayo, Vazquez

The DE component of the universe still remains as a mystery, however, several papers based on observational data have shown that its equation of state may have an oscillatory behavior.  In this paper, provide a general description for the DE EoS w(z) in the form of Fourier series.  This description generalizes some previous dynamical DE models and is in agreement with the w(z) reconstructions.  Make use of a modified version of a simple and fast MCMC code to constrain the model parameters.  For the analysis, use data from SN Ia, BAO, H(z) measurements and CMB.  Provide a comparison of the proposed model with LCDM, wCDM and the standard Taylor approximation.  The Fourier series expansion of w(z) is preferred from LCDM at more than 3 sigma significant level based on the improvement in the fit alone.  Use the Akaike criteria to perform the model comparison and found that, even though there are extra parameters, there is a slight preference of the Fourier series compared with the LCDM model.  The preferred shape of  w(z) found here puts in jeopardy the single scalar field models, as they cannot reproduce the crossing the phantom divide line w=-1.


1901.08681
The Local Perspective on the Hubble Tension: Local structures does not impact measurement of the Hubble Constant
Kenworthy, Scolnic, Riess

Use the largest sample to date of spectro-SN Ia distances and redshifts to look for evidence in the Hubble diagram of LS outflows caused by local voids suggested to exist at z<0.15.  The sample combines data from the Pantheon sample with the Foundation survey and the most recent release of light curves from the Carnegie Supernova Project to create a sample of 1295 SNe over a redshift range of 0.01<z<2.26.  Make use of an inhomogeneous and isotropic Lemaitre-Tolman-Bondi metric to model a void in the SN Ia distance-z relation.  Conclude that the SN luminosity distance-z relation is inconsistent at the 4-5 sigma confidence level with large local under densities (|delta|>20%, where the density contrast delta = Delta-rho/rho) proposed in some galaxy count studies, and find no evidence of a change in the Hubble constant corresponding to a void with a sharp edge in the z range 0.023<z<0.15.  Conclude that the distance latter value of H0, with a current precision of sigma H0=2.2%, is not significantly affected by local density contrasts, with an empirical precision of sigma H0~0.60%, in agreement with cosmic variance in the Hubble constant of sigma H0=0.42% predicted from simulations of LSS.  Derive a 5 sigma constraint on local density contrasts on scales larger than 69 Mpc/h of |delta|<27%.  The presence of local structure does not appear to impede the possibility of measuring the Hubble constant to 1% precision.


1901.08875
Laser communication and coordination control of spacecraft swarms
Kalita, et al

Swamis of small spacecraft offer whole new capabilities in earth observation, global positioning and communications compared to a large monolithic spacecraft.  These small spacecrafts can provide bigger apertures that increase gain in communication antennas, increase area coverage of effective resolution of distributed cameras and enable persistent observation of ground or space targets.  However, there remain important challenges in operating large number of spacecrafts at once.  Current methods would require a large number of ground operators monitor and actively control these spacecrafts which poses challenges in terms of coordination and control which prevents the technology from scaled up in cost-effective manner.  Technologies are required to enable one ground operator to manage tens if not hundred os spacecrafts.  Propose to utilize laser beams directed from the ground or from a command and control spacecraft to organize and manage a large swarm.  Each satellite in the swarm will have a customized "smart skin" containing solar panels, power and control circuitry and an embedded secondary propulsion unit.  A secondary propulsion unit may include electrospray propulsion, solar radiation pressure-based system, photonics laser thrusters an Lorentz force thrusters.  Solar panels typically occupy the largest surface area on an earth orbiting satellite.  A laser beam from another spacecraft or from the ground would interact with solar panels of the spacecraft swarm.  The laser beam would be used to select a 'leader' amongst a group of spacecrafts, set parameters for formation-flight, including separation distance, local if-then rules and coordinated changes in attitude and position.


1901.08878
The cosmic spectral energy distribution in the EAGLE simulation
Baes, et al

The cosmic spectral energy distribution (CSED) is the total emissivity as a function of wavelength of galaxies in a given cosmic volume. We compare the observed CSED from the UV to the submm to that computed from the EAGLE cosmological hydrodynamical simulation, post-processed with stellar population synthesis models and including dust radiative transfer using the SKIRT code. The agreement with the data is better than 0.15 dex over the entire wavelength range at redshift $z=0$, except at UV wavelengths where the EAGLE model overestimates the observed CSED by up to a factor 2. Global properties of the CSED as inferred from CIGALE fits, such as the stellar mass density, mean star formation density, and mean dust-to-stellar-mass ratio, agree to within better than 20 per cent. At higher redshift, EAGLE increasingly underestimates the CSED at optical-NIR wavelengths with the FIR/submm emissivity underestimated by more than a factor of 5 by redshift $z=1$. We believe that these differences are due to a combination of incompleteness of the EAGLE-SKIRT database, the small simulation volume and the consequent lack of luminous galaxies, and our lack of knowledge on the evolution of the characteristics of the interstellar dust in galaxies. The impressive agreement between the simulated and observed CSED at lower $z$ confirms that the combination of EAGLE and SKIRT dust processing yields a fairly realistic representation of the local Universe.

1901.08885

Modeling the large-scale power deficit

Vitenti, Peter, Valentini

We investigate a set of cosmological models for which the primordial power spectrum has a large-scale power deficit. The standard power-law spectrum is subject to long-wavelength modifications described by some new parameters, resulting in corrections to the anisotropies in the cosmic microwave background. The new parameters are fitted to different data sets: temperature only, temperature and polarization, the low-redshift determination of $H_0$, and baryonic acoustic oscillations. We discuss the statistical significance of the modified spectra, from both frequentist and Bayesian perspectives. Our analysis suggests motivations for considering models that break scalar-tensor consistency, or models with negligible power in the far super-Hubble limit. We present what appears to be substantial evidence for a new scale around 350 Mpc above which the primordial (scalar) power spectrum is sharply reduced by about 20%.

1901.08994

Global radiation signature from early structure formation

Liu, et al

We use cosmological hydrodynamic zoom-in simulations to study early structure formation in two dark matter (DM) cosmologies, a standard CDM model, and a warm DM (WDM) model with a particle mass of $m_{\chi}c^{2}=3$ keV. We focus on DM haloes with virial masses $M\sim 10^{10}\ M_{\odot}$. We find that the first star formation activity is delayed by $\sim 200$ Myr in the WDM model, with similar delays for metal enrichment and the formation of the second generation of stars. However, the differences between the two models in globally-averaged properties, such as star formation rate density and mean metallicity, decrease towards lower redshifts ($z\lesssim 10$). Metal enrichment in the WDM cosmology is restricted to dense environments, while low-density gas can also be significantly enriched in the CDM case. We calculate the free-free contribution from early structure formation at redshifts $z>6$ to the cosmic radio background (CRB), and find that it is $3.8_{-1.7}^{+15.8}$% ($10.4_{-4.6}^{+43.3}$%) of the total signal inferred from radio experiments such as ARCADE 2, in the WDM (CDM) model. We find that the direct detection of the $\mathrm{H_{2}}$ emission from early structure formation ($z\gtrsim 7.2$), originating from the low-mass haloes explored here, will be challenging even with the next generation of planned far-infrared space telescopes, unless the signal is magnified by at least a factor of 10 via gravitational lensing. However, more massive haloes with $M\gtrsim 10^{12}\ M_{\odot}$ may be observable for $z\gtrsim 10$, even without lensing, provided that our extrapolation from the scale of our simulated haloes is valid.

1901.09001

Constraining the neutral fraction of hydrogen in the IGM at redshift 7.5

Hoag, Bradac, et al

We present a large spectroscopic campaign with Keck/MOSFIRE targeting Lyman-alpha emission (Ly$\alpha$) from intrinsically faint Lyman-break Galaxies (LBGs) behind 12 efficient galaxy cluster lenses. Gravitational lensing allows us to probe the more abundant faint galaxy population to sensitive Ly$\alpha$ equivalent width limits. During the campaign we targeted 70 LBG candidates with MOSFIRE Y-band, selected photometrically to cover Ly$\alpha$ over the range $7<z<8.2$. We detect $S/N>5$ emission lines in 2 of these galaxies and find that they are likely Ly$\alpha$ at $z=7.148\pm0.001$ and $z=7.161\pm0.001$. We present new lens models for 4 of the galaxy clusters, using our previously published lens models for the remaining clusters to determine the magnification factors for the source galaxies. Using a Bayesian framework that employs large scale reionization simulations of the intergalactic medium (IGM) as well as realistic properties of the interstellar medium and circumgalactic medium, we infer the volume-averaged neutral hydrogen fraction, $\overline{x}_{\mathrm{HI}}$, in the IGM during reionization to be $\overline{x}_{\mathrm{HI}}=0.88^{+0.05}_{-0.10}$ at $z=7.6\pm0.6$. Our result is consistent with a late and rapid reionization scenario inferred by Planck.

1901.09039

The galaxy - halo connection in low mass haloes

Feldmann, et al

Properties of galaxies vary systematically with the mass of their parent dark matter halos. This basic galaxy - halo connection shows a fair amount of scatter whose origin is not fully understood. Here, we study how differences in the halo assembly history affect central galaxies in low mass (M_halo < 10^12 M_sun) halos at z=2-6 with the help of the MassiveFIRE suite of cosmological simulations. In contrast to previous works that tie galaxy properties to halo concentration and halo formation redshift, we focus on halo growth rate as a measure of assembly history. We find that, at fixed halo mass, faster growing halos tend to have lower stellar masses and higher SFRs per unit stellar mass but similar overall SFRs. We provide a simple explanation for these findings with the help of an analytic model that captures approximately the behavior of our hydrodynamical simulations. Specifically, among halos of a given current mass, quickly growing halos have lower stellar masses (and thus higher sSFRs) because they were less massive and had comparably lower cold gas masses and SFRs in the past than slowly growing halos. By combining these findings with estimates for the scatter of the halo growth rate, we show that variations in growth rate at fixed halo mass may largely explain the scatter of the stellar mass - halo mass relation. In contrast, halo growth variations likely play only a minor role in the scatter of the star forming sequence in low mass galaxies.

1901.09041

The occurrence of compact groups of galaxies through cosmic time

Wiens, et al

We use the outputs of a semi-analytical model of galaxy formation run on the Millennium Simulation to investigate the prevalence of three-dimensional compact groups (CGs) of galaxies from $z = 11$ to 0. Our publicly available code identifies CGs using the 3D galaxy number density, the mass ratio of secondary+tertiary to the primary member, mass density in a surrounding shell, the relative velocities of candidate CG members, and a minimum CG membership of three. We adopt "default" values for the first three criteria, representing the observed population of Hickson CGs at $z = 0$. The percentage of non-dwarf galaxies ($M > 5 \times 10^{8}h^{-1}\ M_{\odot}$) in CGs peaks near $z \sim 2$ for the default set, and between $z \sim 1 - 3$ for other parameter sets. This percentage declines rapidly at higher redshifts ($z \gtrsim 4$), consistent with the galaxy population as a whole being dominated by low-mass galaxies excluded from this analysis. According to the most liberal criteria, $\lesssim 3\%$ of non-dwarf galaxies are members of CGs at the redshift where the CG population peaks. Our default criteria result in a population of CGs at $z < 0.03$ with number densities and sizes consistent with Hickson CGs. Tracking identified CG galaxies and merger products to $z = 0$, we find that $\lesssim 16\%$ of non-dwarf galaxies have been CG members at some point in their history. Intriguingly, the great majority ($96\%$) of $z = 2$ CGs have merged to a single galaxy by $z= 0$. There is a discrepancy in the velocity dispersions of Millennium Simulation CGs compared to those in observed CGs, which remains unresolved.

1901.09083

What the sudden death of solar cycles can tell us about the nature of the solar interior

McIntosh, et al

We observe the abrupt end of solar activity cycles at the Sun's equator by combining almost 140 years of observations from ground and space. These "terminator" events appear to be very closely related to the onset of magnetic activity belonging to the next sunspot cycle at mid-latitudes and the polar-reversal process at high-latitudes. Using multi-scale tracers of solar activity we examine the timing of these events in relation to the excitation of new activity and find that the time taken for the solar plasma to communicate this transition is of the order of one solar rotation, but could be shorter. Utilizing uniquely comprehensive solar observations from the Solar Terrestrial Relations Observatory (STEREO), and Solar Dynamics Observatory (SDO) we see that this transitional event is strongly longitudinal in nature. Combined, these characteristics imply that magnetic information is communicated through the solar interior rapidly. A range of possibilities exist to explain such behavior: the presence of magnetic reconnection in the deep interior, internal gravity waves on the solar tachocline, or that the magnetic fields present in the Sun's convection zone could be very large, with a poloidal field strengths reaching 50k - considerably larger than conventional explorations of solar and stellar dynamos estimate. Regardless of mechanism responsible, the rapid timescales demonstrated by the Sun's global magnetic field reconfiguration present strong constraints on first-principles numerical simulations of the solar interior and, by extension, other stars.

1901.09144

Probing cosmic acceleration by strong gravitational lensing systems

Tu, Hu, Wang

Recently, some divergent conclusions about cosmic acceleration were obtained using type Ia supernovae (SNe Ia), with opposite assumptions on the intrinsic luminosity evolution. In this paper, we use strong gravitational lensing systems to probe the cosmic acceleration. Since the theory of strong gravitational lensing is established certainly, and the Einstein radius is determined by stable cosmic geometry. We study two cosmological models, $\Lambda$CDM and power-law models, through 152 strong gravitational lensing systems, incorporating with 30 Hubble parameters $H(z)$ and 11 baryon acoustic oscillation (BAO) measurements. Bayesian evidence are introduced to make a one-on-one comparison between cosmological models. Basing on Bayes factors $\ln B$ of flat $\Lambda$CDM versus power-law and $R_{h}=ct$ models are $\ln B>5$, we find that the flat $\Lambda$CDM is strongly supported by the combination of the datasets. Namely, an accelerating cosmology with non power-law expansion is preferred by our numeration.

1901.09488

Mock galaxy shape catalogs in the Subaru Hyper Suprime-Cam Survey

Shirasaki, Hamana, Takada, Takahashi, Miyatake

We use the full-sky ray-tracing weak lensing simulations to generate 2268 mock catalogs for the Subaru Hyper Suprime-Cam (HSC) survey first-year shear catalog in Mandelbaum et al. (2018). Our mock catalogs take into account various effects as in the real data: the survey footprints, inhomogeneous angular distribution of source galaxies, statistical uncertainties in photometric redshift (photo-z) estimate, variations in the lensing weight due to observational conditions and galaxy's properties, and the statistical noise in galaxy shape measurements due to both intrinsic shapes and the measurement errors. We then utilize our mock catalogs to evaluate statistical uncertainties expected in measurements of cosmic shear two-point correlations $\xi_{\pm}$ with tomographic redshift information for the HSC survey. First we develop a quasi-analytical formula for the Gaussian sample variance properly taking into account the number of source pairs in the survey footprints. The standard Gaussian formula significantly overestimates or underestimates the mock results by 50\% level. Secondly we show that different photo-z catalogs or the six disconnected fields, rather than a consecutive geometry for the same area, cause variations in the covariance by ~5\%. Thirdly, we study the chi-square distribution for $\xi_{\pm}$ among the mock catalogs and find the wider distribution than that naively expected for the distribution with the degrees-of-freedom of data vector used. Finally, we propose a method to include non-zero multiplicative bias in mock shape catalog and show the non-zero multiplicative bias can change the effective shape noise term in cosmic shear analyses. Our results suggest an importance of estimating an accurate form of the likelihood function (and therefore the covariance) for robust cosmological parameter inference from the precise measurements.

1901.09737

Implications of the lens redshift distribution of strong lensing systems: cosmological parameters and the global properties of early-type galaxies

Ma, et al

In this paper, we assemble a well-defined sample of early-type gravitational lenses extracted from a large collection of 158 systems, and use the redshift distribution of galactic-scale lenses to test the standard cosmological model ($\Lambda$CDM) and the modified gravity theory (DGP). Two additional sub-samples are also included to account for possible selection effect introduced by the detectability of lens galaxies. Our results show that independent measurement of the matter density parameter ($\Omega_m$) could be expected from such strong lensing statistics. Based on future measurements of strong lensing systems from the forthcoming LSST survey, one can expect $\Omega_m$ to be estimated at the precision of $\Delta\Omega_m\sim 0.006$, which provides a better constraint on $\Omega_m$ than \textit{Planck} 2015 results. Moreover, use the lens redshift test is also used to constrain the characteristic velocity dispersion of the lensing galaxies, which is well consistent with that derived from the optical spectroscopic observations. A parameter $f_E$ is adopted to quantify the relation between the lensing-based velocity dispersion and the corresponding stellar value. Finally, the accumulation of detectable galactic lenses from future LSST survey would lead to more stringent fits of $\Delta f_E\sim10^{-3}$, which encourages us to test the global properties of early-type galaxies at much higher accuracy.