Day 1592

Thursday.  Friday.

1906.10693
Shattering of cosmic sheets due to thermal instabilities: a formation channel for metal-free Lyman Limit Systems
Mandelker, et al

We present a new cosmological zoom-in simulation, where the zoom region consists of two halos with virial mass M_v~5x10^{12}M_{sun} and a ~Mpc long cosmic filament connecting them at z~2. Using this simulation, we study the evolution of the intergalactic medium in between these two halos at unprecedented resolution. At 5>z>3, the two halos are found to lie in a large intergalactic sheet, or "pancake", consisting of multiple co-planar dense filaments along which nearly all halos with M_v>10^9M_{sun} are located. This sheet collapses at z~5 from the merger of two smaller sheets. The strong shock generated by this merger leads to thermal instabilities in the post-shock region, and to a shattering of the sheet resulting in <~kpc scale clouds with temperatures of T>~2x10^4K and densities of n>~10^{-3}cm^{-3}, which are pressure confined in a hot medium with T~10^6K and n>~10^{-5}cm^{-3}. When the sheet is viewed face on, these cold clouds have neutral hydrogen column densities of N_{HI}>10^{17.2}cm^{-2}, making them detectable as Lyman limit systems, though they lie well outside the virial radius of any halo and even well outside the dense filaments. Their chemical composition is pristine, having zero metalicity, similar to several recently observed systems. Since these systems form far from any galaxies, these results are robust to galaxy formation physics, resulting purely from the collapse of large scale structure and radiative cooling, provided sufficient spatial resolution is available.

1906.10697
AGN in dwarf galaxies: frequency, triggering processes and the plausibility of AGN feedback
Kaviraj, et al

While AGN are considered to be key drivers of the evolution of massive galaxies, their potentially significant role in the dwarf-galaxy regime (M*< 10^9 MSun) remains largely unexplored. We combine optical and infrared data, from the Hyper Suprime-Cam (HSC) and the Wide-field Infrared Explorer (WISE) respectively, to explore the properties of ~800 AGN in dwarfs at low redshift (z<0.3). Infrared-selected AGN fractions are ~10-30 per cent in dwarfs, which, for reasonable duty cycles, indicates a high BH-occupation fraction. Visual inspection of the deep HSC images indicates that the merger fraction in dwarf AGN (~6 per cent) shows no excess compared to a control sample of non-AGN, suggesting that the AGN-triggering processes are secular in nature. Energetic arguments indicate that, in both dwarfs and massive galaxies, bolometric AGN luminosities (L_AGN) are significantly greater than supernova luminosities (L_SN). L_AGN/L_SN is, in fact, higher in dwarfs, with predictions from simulations suggesting that this ratio only increases with redshift. Together with the potentially high BH-occupation fraction, this suggests that, if AGN feedback is an important driver of massive-galaxy evolution, the same is likely to be true in the dwarf regime, contrary to our classical thinking.

1906.10744

The angular scale of homogeneity in the Local Universe with the SDSS blue galaxies

Avila, et al

We probe the angular scale of homogeneity in the local Universe using blue galaxies from the SDSS survey as a cosmological tracer. Through the scaled counts in spherical caps, $ \mathcal{N}(<\theta) $, and the fractal correlation dimension, $\mathcal{D}_{2}(\theta)$, we find an angular scale of transition to homogeneity for this sample of $\theta_{\text{H}} = 22.19^{\circ} \pm 1.02^{\circ}$. A comparison of this measurement with another obtained using a different cosmic tracer at a similar redshift range ($z < 0.06$), namely, the HI extragalactic sources from the ALFALFA catalogue, confirms that both results are in excellent agreement (taking into account the corresponding bias correction). We also perform tests to asses the robustness of our results. For instance, we test if the size of the surveyed area is large enough to identify the transition scale we search for, and also we investigate a reduced sample of blue galaxies, obtaining in both cases a similar angular scale for the transition to homogeneity. Our results, besides confirming the existence of an angular scale of transition to homogeneity in different cosmic tracers present in the local Universe, show that the observed angular scale $\theta_{\text{H}}$ agrees well with what is expected in the $\Lambda$CDM scenario. Although we can not prove spatial homogeneity within the approach followed, our results provide one more evidence of it, strengthening the validity of the Cosmological Principle.

1906.11238

First M87 Event Horizon Telescope Results. I. The shadow of the supermassive black hole

The Event Horizon Telescope Collaboration

When surrounded by a transparent emission region, black holes are expected to reveal a dark shadow caused by gravitational light bending and photon capture at the event horizon. To image and study this phenomenon, we have assembled the Event Horizon Telescope, a global very long baseline interferometry array observing at a wavelength of 1.3 mm. This allows us to reconstruct event-horizon-scale images of the supermassive black hole candidate in the center of the giant elliptical galaxy M87. We have resolved the central compact radio source as an asymmetric bright emission ring with a diameter of 42+/-3 micro-as, which is circular and encompasses a central depression in brightness with a flux ratio ~10:1. The emission ring is recovered using different calibration and imaging schemes, with its diameter and width remaining stable over four different observations carried out in different days. Overall, the observed image is consistent with expectations for the shadow of a Kerr black hole as predicted by general relativity. The asymmetry in brightness in the ring can be explained in terms of relativistic beaming of the emission from a plasma rotating close to the speed of light around a black hole. We compare our images to an extensive library of ray-traced general-relativistic magnetohydrodynamic simulations of black holes and derive a central mass of M = (6.5+/-0.7) x 10^9 Msun. Our radio-wave observations thus provide powerful evidence for the presence of supermassive black holes in centers of galaxies and as the central engines of active galactic nuclei. They also present a new tool to explore gravity in its most extreme limit and on a mass scale that was so far not accessible.

1906.11260

Dragonfly imaging of the galaxy NGC5907: a revised view of the iconic stellar stream

van Dokkum, et al

In 2008 it was reported that the stellar stream of the edge-on spiral NGC5907 loops twice around the galaxy, enveloping it in a giant corkscrew-like structure. Here we present imaging of this iconic object with the Dragonfly Telephoto Array, reaching $1\sigma$ surface brightness levels of $\mu_g\approx 30.5$ mag/arcsec$^2$ on arcminute scales. We find that the stream has a qualitatively different morphology from that reported in the 2008 study. The Dragonfly data do not show two loops but a single curved stream with a total length of 45' (220 kpc). The surface brightness of the stream ranges from $\mu_g \approx 27.6$ mag/arcsec$^2$ to $\mu_g\approx 28.8$ mag/arcsec$^2$, and it extends significantly beyond the region where tidal features had previously been detected. We find a density enhancement near the luminosity-weighted midpoint of the stream which we identify as the likely remnant of a nearly-disrupted progenitor galaxy. A restricted N-body simulation provides a qualitative match to all detected features with little fine-tuning. In terms of its spatial extent and stellar mass the stream is similar to Sagittarius, and our results demonstrate the efficacy of low surface brightness-optimized telescopes for obtaining maps of such large streams outside the Local Group. The census of these rare, relatively high mass events complements the census of common, low mass ones that is provided by studies of streams in the Milky Way halo.

1906.11628

Baryon Acoustic Oscillations and the Hubble Constant: past, present and future

Cuceu, et al

We investigate constraints on the Hubble constant ($H_0$) using Baryon Acoustic Oscillations (BAO) and baryon density measurements from Big Bang Nucleosynthesis (BBN). We start by investigating the tension between galaxy BAO measurements and those using the Lyman-$\alpha$ forest, within a Bayesian framework. Using the latest results from eBOSS DR14 we find that the probability of this tension being statistical is $\simeq6.3\%$. We measure $H_0 = 67.6\pm1.1$ km s$^{-1}$ Mpc$^{-1}$, with a weak dependence on the BBN prior used, in agreement with results from Planck Cosmic Microwave Background (CMB) results and in strong tension with distance ladder results. Finally, we forecast the future of BAO $+$ BBN measurements of $H_0$, using the Dark Energy Spectroscopic Instrument (DESI). We find that the choice of BBN prior will have a significant impact when considering future BAO measurements from DESI.

1906.11814

Cosmology-independent local determination of $H_0$ in strong tension with CMB

Camarena, Marra

The determination of the Hubble constant $H_0$ from the well-understood physics of the Cosmic Microwave Background is in tension at $4.4\sigma$ with respect to the model-independent determination of $H_0$, which uses local supernovas calibrated via the cosmic distance ladder. Here, we present a new method to obtain the effective calibration prior on the absolute magnitude of Supernovas Ia by performing a backward analysis on the cosmic distance ladder, and we determine $H_0$ in a cosmology-independent way, assuming only large-scale homogeneity and isotropy. We find that $H_0^{\rm loc} = 75.66 \pm 1.69 \text{ km s}^{-1} {\rm Mpc}^{-1}$, featuring the very low uncertainty of 2.2%, which is very close to the 1.9% error obtained by the SH0ES Collaboration. We also constrain the deceleration parameter to $q_0^{\rm loc} = -1.08 \pm 0.29$, which clearly deviates from the standard-model value of $q_0 \simeq -0.55$. Our determination is in tension at $4.7\sigma$ with the latest results from the Planck Collaboration that assume the standard model of cosmology.

1906.11823

Anisotropic halo assembly bias and redshift-space distortions

Obuljen, Dalal, Percival

We study the effect of large-scale tidal fields on internal halo properties using a set of N-body simulations. We measure significant cross-correlations between large-scale tidal fields and several non-scalar halo properties: shapes, velocity dispersion, and angular momentum. Selection effects that couple to these non-scalar halo properties can produce anisotropic clustering even in real-space. We investigate the size of this effect and show that it can produce a non-zero quadrupole similar in size to the one generated by linear redshift-space distortions (RSD). Finally, we investigate the clustering properties of halos identified in redshift-space and find enormous deviations from the standard linear RSD model, again caused by anisotropic assembly bias. These effects could contaminate the values of cosmological parameters inferred from the observed redshift-space clustering of galaxies, groups, or 21cm emission from atomic hydrogen, if their selection depends on properties affected by halo assembly bias. We briefly discuss ways in which this effect can be measured in existing and future large-scale structure surveys.

Day 1591

Wednesday.

1906.10126
Evidence for sub-Chandrasekhar Type Ia Supernovae from stellar abundances in Dwarf Galaxies
Kirby, et al

There is no consensus on the progenitors of Type Ia supernovae (SNe Ia) despite their importance for cosmology and chemical evolution. We address this question by using our previously published catalogs of Mg, Si, Ca, Cr, Fe, Co, and Ni abundances in dwarf galaxy satellites of the Milky Way to constrain the mass at which the white dwarf explodes during a typical SN Ia. We fit a simple bi-linear model to the evolution of [X/Fe] with [Fe/H], where X represents each of the elements mentioned above. We use the evolution of [Mg/Fe] coupled with theoretical supernova yields to isolate what fraction of the elements originated in SNe Ia. Then, we infer the [X/Fe] yield of SNe Ia for all of the elements except Mg. We compare these observationally inferred yields to recent theoretical predictions for two classes of Chandrasekhar-mass (M_Ch) SN Ia as well as sub-M_Ch SNe Ia. Most of the inferred SN Ia yields are consistent with all of the theoretical models, but [Ni/Fe] is consistent only with sub-M_Ch models. We conclude that the dominant type of SN Ia in ancient dwarf galaxies is the explosion of a sub-M_Ch white dwarf. The Milky Way and dwarf galaxies with extended star formation histories have higher [Ni/Fe] abundances, which could indicate that the dominant class of SN Ia is different for galaxies where star formation lasted for at least several Gyr.

1906.10136

Hints of sterile neutrinos in recent measurements of the Hubble parameter

Gelmini, et al

Local Universe observations find a value of the Hubble constant $H_0$ that is larger than the value inferred from the Cosmic Microwave Background and other early Universe measurements, assuming known physics and the $\Lambda$CDM cosmological model. We show that additional radiation in active neutrinos produced just before Big Bang Nucleosynthesis by an unstable sterile neutrino with mass $m_s=$ O(10) MeV can alleviate this discrepancy. The necessary masses and couplings of the sterile neutrino, assuming it mixes primarily with $\nu_{\tau}$ and/or $\nu_{\mu}$ neutrinos, are within reach of Super-Kamiokande as well as upcoming laboratory experiments such as NA62.

Day 1590

Tuesday.

1906.09277
The dust-to-gas and dust-to-metals ratio in galaxies from z=0-6
Li, et al

We present predictions for the evolution of the galaxy dust-to-gas (DGR) and dust-to-metal (DTM) ratios from z=0 to 6, using a model for the production, growth, and destruction of dust grains implemented into the \simba\ cosmological hydrodynamic galaxy formation simulation. In our model, dust forms in stellar ejecta, grows by the accretion of metals, and is destroyed by thermal sputtering and supernovae. Our simulation reproduces the observed dust mass function at z=0, but modestly under-predicts the mass function by ~x3 at z ~ 1-2. The z=0 DGR vs metallicity relationship shows a tight positive correlation for star-forming galaxies, while it is uncorrelated for quenched systems. There is little evolution in the DGR-metallicity relationship between z=0-6. We use machine learning techniques to search for the galaxy physical properties that best correlate with the DGR and DTM. We find that the DGR is primarily correlated with the gas-phase metallicity, though correlations with the depletion timescale, stellar mass and gas fraction are non-negligible. We provide a crude fitting relationship for DGR and DTM vs. the gas-phase metallicity, along with a public code package that estimates the DGR and DTM given a set of galaxy physical properties.

1906.09797

Origin of the chromospheric three-minute oscillations in sunspot umbrae

Felipe

Sunspot umbrae show a change in the dominant period of their oscillations from five minutes in the photosphere to three minutes in the chromosphere. In this paper, we explore the two most popular models proposed to explain the three-minute oscillations: the chromospheric acoustic resonator and the propagation of waves with frequency above the cutoff value directly from lower layers. We employ numerical simulations of wave propagation from the solar interior to the corona. Waves are driven by a piston at the bottom boundary. We have performed a parametric study of the measured chromospheric power spectra in a large number of numerical simulations with differences in the driving method, the height of the transition region (or absence of transition region), the strength of the vertical magnetic field, and the value of the radiative cooling time. We find that both mechanisms require the presence of waves with period in the three-minute band at the photosphere. These waves propagate upward and their amplitude increases due to the drop of the density. Their amplification is stronger than that of evanescent low-frequency waves. This effect is enough to explain the dominant period observed in chromospheric spectral lines. However, waves are partially trapped between the photosphere and the transition region, forming an acoustic resonator. This chromospheric resonant cavity strongly enhances the power in the three-minute band. The chromospheric acoustic resonator model and the propagation of waves in the three-minute band directly from the photosphere can explain the observed chromospheric three-minute oscillations. They are both important in different scenarios. Resonances are produced by waves trapped between the temperature minimum and the transition region. Strong magnetic fields and radiative losses remove energy from the waves inside the cavity, resulting in weaker amplitude resonances.

Day 1589

Monday.

1906.09022
The Gaia mission and significance
Mignard

I provide a summary of the ESA space astrometry mission Gaia regarding its main objectives and current status following the 2nd data release (Gaia DR2) in April 2018. The Gaia achievements in astrometry are assessed with a historical perspective by comparing the DR2 content to sky surveys or parallax searches over the last two centuries. One shows that Gaia sounds more like a big leap into a new world than an incremental progress in this field.

1906.09130

Evolution of lithium in the Milky Way halo, discs and bulge

Grisoni, et al

In this work, we study the Galactic evolution of lithium by means of chemical evolution models in the light of the most recent spectroscopic data from Galactic stellar surveys. We consider detailed chemical evolution models for the Milky Way halo, discs and bulge, and we compare our model predictions with the most recent spectroscopic data for these different Galactic components. In particular, we focus on the decrease of lithium at high metallicity observed by the AMBRE Project, the Gaia-ESO Survey, and other spectroscopic surveys, which still remains unexplained by theoretical models. We analyse the various lithium producers and confirm that novae are the main source of lithium in the Galaxy, in agreement with other previous studies. Moreover, we show that, by assuming that the fraction of binary systems giving rise to novae is lower at higher metallicity, we can suggest a novel explanation to the lithium decline at super-solar metallicities: the above assumption is based on independent constraints on the nova system birthrate, that have been recently proposed in the literature. As regards to the thick disc, it is less lithium enhanced due to the shorter timescale of formation and higher star formation efficiency with respect to the thin disc and, therefore, we have a faster evolution and the "reverse knee" in the A(Li) vs. [Fe/H] relation is shifted towards higher metallicities. Finally, we present our predictions about lithium evolution in the Galactic bulge, that, however, still need further data to be confirmed or disproved.

1906.09189

CMB tensions with low-redshift $H_0$ and $S_8$ measurements: impact of a redshift-dependent type-Ia supernovae intrinsic luminosity

Martineli, Tutusaus

Given the recent increase in precision of our cosmological datasets, significant tensions between high- and low-redshift observations started to appear in the measurements of $\Lambda$CDM model parameters. In this work we tackle the tension on the value of the Hubble parameter, $H_0$, and the weighted amplitude of matter fluctuations, $S_8$, obtained from local or low-redshift measurements and from cosmic microwave background (CMB) observations. We combine the main approaches previously used in the literature by extending the cosmological model and accounting for extra systematic uncertainties. In more detail, we reconstruct the Dark Energy equation of state as a function of redshift, while we study the impact of type-Ia supernovae (SNIa) redshift-dependent astrophysical systematic effects on these tensions. We consider a SNIa intrinsic luminosity dependence on redshift due to the star formation rate in its environment, or the metallicity of the progenitor. We find that the $H_0$ and $S_8$ tensions can be significantly alleviated, or even removed, if we account for varying Dark Energy for SNIa and CMB data. However, the tensions remain when we add baryon acoustic oscillations data into the analysis, even after the addition of extra SNIa systematic uncertainties. This points towards the need of either new physics beyond late-time Dark Energy, or other unaccounted systematic effects (particulary in BAO measurements), to fully solve the present tensions.

1906.09262

KiDS+VIKING-450 and DES-Y1 combined: cosmology with cosmic shear

Joudaki, et al

We present a combined tomographic weak gravitational lensing analysis of the Kilo Degree Survey (KV450) and the Dark Energy Survey (DES-Y1). We homogenize the analysis of these two public cosmic shear datasets by adopting consistent priors and modeling of nonlinear scales, and determine new redshift distributions for DES-Y1 based on deep public spectroscopic surveys. Adopting these revised redshifts results in a $0.8 \sigma$ reduction in the DES-inferred value for $S_8$. The combined KV450 + DES-Y1 constraint on $S_8 = 0.762^{+0.025}_{-0.024}$ is in tension with the Planck 2018 constraint from the cosmic microwave background at the level of $2.5\sigma$. This result highlights the importance of developing methods to provide accurate redshift calibration for current and future weak lensing surveys.

Day 1588

Friday.

1906.08263
Unified lensing and kinematic analysis for any elliptical mass profile
Shajib

We demonstrate an efficient method to compute the strong-gravitational-lensing deflection angle and magnification for any elliptical surface-density profile. This method solves a numerical hurdle in lens modelling that has lacked a general solution for nearly three decades. The hurdle emerges because it is prohibitive to derive analytic expressions of the lensing quantities for most elliptical mass profiles. In our method, we first decompose an elliptical mass profile into Gaussian components. We introduce an integral transform that provides us with a fast and accurate algorithm for the Gaussian decomposition. We derive analytic expressions of the lensing quantities for a Gaussian component. As a result, we can compute these quantities for the total mass profile by adding up the contributions from the individual components. This lensing analysis self-consistently completes the kinematic description in terms of Gaussian components presented by Cappellari (2008). Our method is general without extra computational burden unlike other methods currently in use.

1906.08264

Directly testing gravity with Proxima Centauri

Banik, Kroupa

The wide binary orbit of Proxima Centauri around $\alpha$ Centauri A and B differs significantly between Newtonian and Milgromian dynamics (MOND). By combining previous calculations of this effect with mock observations generated using a Monte Carlo procedure, we show that this prediction can be tested using high precision astrometry of Proxima Centauri. This requires ${\approx 10}$ years of observations at an individual epoch precision of $0.5 \, \mu$as, within the design specifications of the proposed Theia mission. In general, the required duration should scale as the 2/5 power of the astrometric precision. A long-period planet could produce a MOND-like astrometric signal, but only if it has a particular ratio of mass to separation squared and a sky position close to the line segment connecting Proxima Centauri with $\alpha$ Centauri. Uncertainties in perspective effects should be small enough for this test if the absolute radial velocity of Proxima Centauri can be measured to within ${\approx 10}$ m/s, better than the present accuracy of 32 m/s. We expect the required improvement to become feasible using radial velocity zero points estimated from larger samples of close binaries, with the Sun providing an anchor. We demonstrate that possible astrometric microlensing of Proxima Centauri is unlikely to affect the results. We also discuss why it should be possible to find sufficiently astrometrically stable reference stars. Adequately addressing these and other issues would enable a decisive test of gravity in the currently little explored low acceleration regime relevant to the dynamical discrepancies in galactic outskirts.

1906.08327

The influence of the void environment on the rate of dark matter halo mass to stellar mass in SDSS MaNGA galaxies

Douglass, et al

We study how the void environment affects the formation and evolution of galaxies in the universe by comparing the ratio of dark matter halo mass to stellar mass of galaxies in voids with galaxies in denser regions. Using spectroscopic observations from the SDSS MaNGA DR15, we estimate the dark matter halo mass of 641 void galaxies and 937 galaxies in denser regions. We use the velocity from the H-alpha emission line to measure the rotation curve of the galaxies since the kinematics of the interstellar medium is smoother than the stellar kinematics. We find that neither the stellar-to-halo-mass relation nor the relationship between the gas-phase metallicity and the ratio of dark matter halo mass to stellar mass is affected by the void environment. We also observe no difference in the distribution of the ratio of dark matter halo mass to stellar mass between void galaxies and galaxies in denser regions, implying that the shape of the dark matter halo profile is independent of a galaxy's environment.

1906.08349

Foreword to the focus issue on machine learning in astronomy and astrophysics

Longo, Merényi, Tino

Astronomical observations already produce vast amounts of data through a new generation of telescopes that cannot be analyzed manually. Next-generation telescopes such as the Large Synoptic Survey Telescope and the Square Kilometer Array are planned to become operational in this decade and the next, and will increase the data volume by many orders of magnitude. The increased spatial, temporal and spectral resolution afford a powerful magnifying lens on the physical processes that underlie the data but, at the same time, generate unprecedented complexity hard to exploit for knowledge extraction. It is therefore imperative to develop machine intelligence, machine learning (ML) in particular, suitable for processing the amount and variety of astronomical data that will be collected, and capable of answering scientific questions based on the data. Astronomical data exhibit the usual challenges associated with 'big data' such as immense volumes, high dimensionality, missing or highly distorted observations. In addition, astronomical data can exhibit large continuous observational gaps, very low signal-to-noise ratio and the need to distinguish between true missing data and non-detections due to upper limits). There are strict laws of physics behind the data production which can be assimilated into ML mechanisms to improve over general off-the-shelf state-of-the-art methods. Significant progress in the face of these challenges can be achieved only via the new discipline of Astroinformatics: a symbiosis of diverse disciplines, such as ML, probabilistic modeling, astronomy and astrophysics, statistics, distributed computing and natural computation. This editorial summarizes the contents of a soon to appear Focus Issue of the PASP on Machine Learning in Astronomy and Astrophysics (with contributions by 69 authors representing 15 countries, from 6 continents).

1906.08680

New perspectives on the BOSS small-scale lensing discrepancy for the Planck $\Lambda$CDM cosmology

Lange, et al

We investigate the abundance, small-scale clustering and galaxy-galaxy lensing signal of galaxies in the Baryon Oscillation Spectroscopic Survey (BOSS). To this end, we present new measurements of the redshift and stellar mass dependence of the lensing properties of the galaxy sample. We analyse to what extent models assuming the Planck18 cosmology fit to the number density and clustering can accurately predict the small-scale lensing signal. In qualitative agreement with previous BOSS studies at redshift $z \sim 0.5$ and with results from the Sloan Digital Sky Survey, we find that the expected signal at small scales ($0.1 < r_{\rm p} < 3 \, h^{-1} \mathrm{Mpc}$) is higher by $\sim 25\%$ than what is measured. Here, we show that this result is persistent over the redshift range $0.1 < z < 0.7$ and for galaxies of different stellar masses. If interpreted as evidence for cosmological parameters different from the Planck CMB findings, our results imply $S_8 = \sigma_8 \sqrt{\Omega_{\rm m} / 0.3} = 0.744 \pm 0.015$, whereas $S_8 = 0.832 \pm 0.013$ for Planck18. However, in addition to being in tension with CMB results, such a change in cosmology alone does not accurately predict the lensing amplitude at larger scales. Instead, other often neglected systematics like baryonic feedback or assembly bias are likely contributing to the small-scale lensing discrepancy. We show that either effect alone, though, is unlikely to completely resolve the tension. Ultimately, a combination of the two effects in combination with a moderate change in cosmological parameters might be needed.

1906.08758

Primordial features from linear to nonlinear scales

Beutler, et al

Sharp features in the primordial power spectrum are a powerful window into the inflationary epoch. To date, the cosmic microwave background (CMB) has offered the most sensitive avenue to search for these signatures. In this paper, we demonstrate the power of large-scale structure observations to surpass the CMB as a probe of primordial features. We show that the signatures in galaxy surveys can be separated from the broadband power spectrum and are as robust to the nonlinear evolution of matter as the standard baryon acoustic oscillations. As a result, analyses can exploit a significant range of scales beyond the linear regime available in the datasets. We develop a feature search for large-scale structure, apply it to BOSS DR12 data and find new bounds on oscillatory features that exceed the sensitivity of Planck for a significant range of frequencies. Moreover, we forecast that the next generation of galaxy surveys, such as DESI and Euclid, will be able to improve current constraints by up to an order of magnitude over an expanded frequency range.

Day 1587

Thursday.

1906.07724
The assembly of the Virgo cluster, traced by its galaxy halos
Taylor, et al

Kinematic studies have produced accurate measurements of the total dark matter mass and mean dark matter density within the optical extent of galaxies, for large samples of objects. Here we consider theoretical predictions for the latter quantity, $\bar{\rho}_{dm}$, measured within the isophotal radius $R_{23.5}$, for isolated halos with universal density profiles. Through a combination of empirical scaling relations, we show that $\bar{\rho}_{dm}$ is expected to depend weakly on halo mass and strongly on redshift. When galaxy halos fall into larger groups or clusters they become tidally stripped, reducing their total dark matter mass, but this process is expected to preserve central density until an object is close to disruption. We confirm this with collisonless simulations of cluster formation, finding that subhalos have values of $\bar{\rho}_{dm}$ close to the analytic predictions. This suggests that $\bar{\rho}_{dm}$ may be a useful indicator of infall redshift onto the cluster. We test this hypothesis with data from the SHIVir survey, which covers a reasonable fraction of the Virgo cluster. We find that galaxies with high $\bar{\rho}_{dm}$ do indeed trace the densest regions of the cluster, with a few notable exceptions. Samples selected by environment have higher densities at a significance of 3.5-4$\sigma$, while samples selected by density are more clustered at 3-3.5$\sigma$ significance. We conclude that halo density can be a powerful tracer of the assembly history of clusters and their member galaxies.

1906.07737

Cooling flow solutions for the circumgalactic medium

Stern, et al

In several models of galaxy formation feedback occurs in cycles or mainly at high redshift. At times and in regions where feedback heating is ineffective, hot gas in the galaxy halo is expected to form a cooling flow, where the gas advects inward on a cooling timescale. Cooling flow solutions can thus be used as a benchmark for observations and simulations to constrain the timing and extent of feedback heating. Using analytic calculations and idealized 3D hydrodynamic simulations, we show that for a given halo mass and cooling function, steady-state cooling flows form a single-parameter family of solutions, while initially hydrostatic gaseous halos converge on one of these solutions within a cooling time. The solution is thus fully determined once either the mass inflow rate $\dot{M}$ or the total halo gas mass are known. In the Milky Way (MW) halo, a cooling flow with $\dot{M}$ equal to the star formation rate predicts a ratio of the cooling time to the free-fall time of ~10, similar to some feedback-regulated models. This solution also correctly predicts observed OVII and OVIII absorption columns, and the gas density profile implied by OVII and OVIII emission. These results suggest ongoing heating by feedback may be negligible in the inner MW halo. Extending similar solutions out to the cooling radius however underpredicts observed OVI columns around the MW and around other low-redshift star-forming galaxies. This can be reconciled with the successes of the cooling flow model with either a mechanism which preferentially heats the OVI-bearing outer halo, or alternatively if OVI traces cool photoionized gas beyond the accretion shock. We also demonstrate that the entropy profiles of some of the most relaxed clusters are reasonably well described by a cooling flow solution.

1906.07750

The Breakthrough Listen search for intelligent life: Observations of 1327 nearby stars over 1.10-3.45 GHz

Price, et al

Breakthrough Listen (BL) is a ten-year initiative to search for signatures of technologically capable life beyond Earth via radio and optical observations of the local Universe. A core part of the BL program is a comprehensive survey of 1702 nearby stars at radio wavelengths (1-10 GHz). Here, we report on observations with the 64-m CSIRO Parkes radio telescope in New South Wales, Australia, and the 100-m Robert C. Byrd Green Bank radio telescope in West Virginia, USA. Over 2016 January to 2019 March, a sample of 1138 stars was observed at Green Bank using the 1.10-1.90 GHz and 1.80-2.80 GHz receivers, and 189 stars were observed with Parkes over 2.60{3.45 GHz. We searched these data for the presence of engineered signals with Doppler-acceleration drift rates between -4 to 4 Hz/s. Here, we detail our data analysis techniques and provide examples of detected events. After excluding events with characteristics consistent with terrestrial radio interference, we are left with zero candidates. Given the sensitivity of our observations, we can put an upper limit on the power of potential radio transmitters at these frequencies at 2x10^12 W, and 9x10^12 W for GBT and Parkes respectively. These observations constitute the most comprehensive search over 1.10-3.45 GHz for technosignatures to date for Kardashev Type I civilizations. All data products, totalling ~219 TB, are available for download as part of the first BL data release (DR1), as described in a companion paper (Lebofsky et. al., 2019)

1906.08174

Optical follow-up study of 32 high-redshift galaxy cluster candidates from Planck with the William Herschel Telescope

Zohren, Schrabback, et al

The Planck satellite has detected cluster candidates via the Sunyaev Zel'dovich (SZ) effect, but the optical follow-up required to confirm these candidates is still incomplete, especially at high redshifts and for SZ detections at low significance. In this work we present our analysis of optical observations obtained for 32 Planck cluster candidates using ACAM on the 4.2-m William Herschel Telescope. These cluster candidates were preselected using SDSS, WISE, and Pan-STARRS images to likely represent distant clusters at redshifts $z \gtrsim 0.7$. We obtain photometric redshift and richness estimates for all of the cluster candidates from a red-sequence analysis of $r$-, $i$-, and $z$-band imaging data. In addition, long-slit observations allow us to measure the redshifts of a subset of the clusters spectroscopically. The optical richness is often lower than expected from the inferred SZ mass when compared to scaling relations previously calibrated at low redshifts. This likely indicates the impact of Eddington bias and projection effects or noise-induced detections, especially at low SZ-significance. Thus, optical follow-up not only provides redshift measurements, but also an important independent verification method. We find that 18 (7) of the candidates at redshifts $z > 0.5$ ($z > 0.8$) are at least half as rich as expected from scaling relations, thereby clearly confirming these candidates as massive clusters. While the complex selection function of our sample due to our preselection hampers its use for cosmological studies, we do provide a validation of massive high-redshift clusters particularly suitable for further astrophysical investigations.

Day 1586

Wednesday.

1906.07280
Spitzer albedos of Near-Earth Objects
Gustafsson, et al

Thermal infrared observations are the most effective way to measure asteroid diameter and albedo for a large number of near-Earth objects. Major surveys like NEOWISE, NEOSurvey, ExploreNEOs, and NEOLegacy find a small fraction of high albedo objects that do not have clear analogs in the current meteorite population. About 8% of Spitzer-observed near-Earth objects have nominal albedo solutions greater than 0.5. This may be a result of lightcurve variability leading to an incorrect estimate of diameter or inaccurate absolute visual magnitudes. For a sample of 23 high albedo NEOs we do not find that their shapes are significantly different from the McNeill et al. (2019) near-Earth object shape distribution. We performed a Monte Carlo analysis on 1505 near-Earth objects observed by Spitzer, sampling the visible and thermal fluxes of all targets to determine the likelihood of obtaining a high albedo erroneously. Implementing the McNeill shape distribution for near-Earth objects, we provide an upper-limit on the geometric albedo of 0.5+/-0.1 for the near-Earth population.

1906.07431

AGN-driven quenching of satellite galaxies

Dashyan, et al

We explore the effect of active galactic nucleus (AGN) feedback from central galaxies on their satellites by comparing two sets of cosmological zoom-in runs of 27 halos with masses ranging from $10^{12}$ to $10^{13.4}$ solar masses at z=0, with (wAGN) and without (noAGN) AGN feedback. Both simulations include stellar feedback from multiple processes, including powerful winds from supernovae, stellar winds from young massive stars, AGB stars, radiative heating within Str\"omgren spheres and photoelectric heating. Our wAGN model is identical to the noAGN model except that it also includes a model for black hole seeding and accretion, as well as AGN feedback via high-velocity broad absorption line winds and Compton/photoionization heating. We show that the inclusion of AGN feedback from the central galaxy significantly affects the star formation history and the gas content of the satellite galaxies. AGN feedback starts to affect the gas content and the star formation of the satellites as early as z=2. The mean gas rich fraction of satellites at z=0 decreases from 15% in the noAGN simulation to 5% in the wAGN simulation. The difference between the two sets extends as far out as five times the virial radius of the central galaxy at z=1. We investigate the quenching mechanism by studying the physical conditions in the surroundings of pairs of satellites matched across the wAGN and noAGN simulations and find an increase in the temperature and relative velocity of the intergalactic gas.

1906.07676

Euclid: non-parametric point spread function field recovery through interpolation on a Graph Laplacian

Schimtz, et al

Context. Future weak lensing surveys, such as the Euclid mission, will attempt to measure the shapes of billions of galaxies in order to derive cosmological information. These surveys will attain very low levels of statistical error and systematic errors must be extremely well controlled. In particular, the point spread function (PSF) must be estimated using stars in the field, and recovered with high accuracy. Aims. This paper's contributions are twofold. First, we take steps toward a non-parametric method to address the issue of recovering the PSF field, namely that of finding the correct PSF at the position of any galaxy in the field, applicable to Euclid. Our approach relies solely on the data, as opposed to parametric methods that make use of our knowledge of the instrument. Second, we study the impact of imperfect PSF models on the shape measurement of galaxies themselves, and whether common assumptions about this impact hold true in a Euclid scenario. Methods. We use the recently proposed Resolved Components Analysis approach to deal with the undersampling of observed star images. We then estimate the PSF at the positions of galaxies by interpolation on a set of graphs that contain information relative to its spatial variations. We compare our approach to PSFEx, then quantify the impact of PSF recovery errors on galaxy shape measurements through image simulations. Results. Our approach yields an improvement over PSFEx in terms of PSF model and on observed galaxy shape errors, though it is at present not sufficient to reach the required Euclid accuracy. We also find that different shape measurement approaches can react differently to the same PSF modelling errors.

Day 1585

Tuesday.

1906.06780
The origin of parity changes in the Solar Cycle
Hazra, Nandy

Although sunspots have been systematically observed on the Sun's surface over the last four centuries, their magnetic properties have been revealed and documented only since the early 1900s. Sunspots typically appear in pairs of opposite magnetic polarities which have a systematic orientation. This polarity orientation is opposite across the equator -- a trend that has persisted over the last century over which magnetic field observations exist. Taken together with the configuration of the global poloidal field of the Sun -- that governs the heliospheric open flux and cosmic ray flux at Earth -- this phenomenon is consistent with the dipolar parity state of an underlying magnetohydrodynamic dynamo. Although hemispheric asymmetry in the emergence of sunspots is observed in the Sun, a parity shift has never been observed. We simulate hemispheric asymmetry through the introduction of random fluctuations in a computational dynamo model of the solar cycle and demonstrate that changes in parity are indeed possible in long-term simulations covering thousands of years. Quadrupolar modes are found to exist over a significant fraction of the simulated time. In particular, we find that a parity shift in the underlying nature of the sunspot cycle is more likely to occur when sunspot activity dominates in any one hemisphere for a time which is significantly longer than the cycle period. We establish causal pathways connecting hemispheric asymmetry and cross-equatorial phase-shifts to parity flips in the underlying dynamo mechanism. Our findings indicate that the solar cycle may have resided in quadrupolar parity states in the distant past, and provides a possible pathway for predicting parity flips in the future.

Day 1584

Friday.  Monday.

1906.05297
Variations in $\alpha$-element ratios trace the chemical evolution of the disk
Blancato, et al

It is well established that the chemical structure of the Milky Way exhibits a bimodality with respect to the $\alpha$-enhancement of stars at a given [Fe/H]. This has been studied largely based on a bulk $\alpha$ abundance, computed as a summary of several individual $\alpha$-elements. Inspired by the expected subtle differences in their nucleosynthetic origins, here we probe the higher level of granularity encoded in the inter-family [Mg/Si] abundance ratio. Using a large sample of stars with APOGEE abundance measurements, we first demonstrate that there is additional information in this ratio beyond what is already apparent in [$\alpha$/Fe] and [Fe/H] alone. We then consider Gaia astrometry and stellar age estimates to empirically characterize the relationships between [Mg/Si] and various stellar properties. We find small but significant trends between this ratio and $\alpha$-enhancement, age, [Fe/H], location in the Galaxy, and orbital actions. To connect these observed [Mg/Si] variations to a physical origin, we attempt to predict the Mg and Si abundances of stars with the galactic chemical evolution model Chempy. We find that we are unable to reproduce abundances for the stars that we fit, which highlights tensions between the yield tables, the chemical evolution model, and the data. We conclude that a more data-driven approach to nucleosynthetic yield tables and chemical evolution modeling is necessary to maximize insights from large spectroscopic surveys.

1906.05311

The energetics of starburst-driven outflows at z=1 from KMOS

Swinbank, et al

We present an analysis of the gas outflow energetics of 529 main-sequence star-forming galaxies at z~1 using KMOS observations of the broad, underlying H-alpha and forbidden lines of [N II] and [S II]. Based on the stacked spectra for a sample with median star-formation rates and stellar masses of SFR ~ 7 Mo/yr and M* = (1.0+/-0.1)x10^10 Mo respectively, we derive a typical mass outflow rate of dM/dt = 1-4 Mo/yr and a mass loading of dM/dt/SFR = 0.2--0.4. The mass loading of the wind does not show a strong trend with star-formation rate over the range SFR ~ 2--20 Mo/yr, although we identify a trend with stellar mass such that dM/dt/SFR ~ M*^(0.26+/-0.07). Finally, we find that the line width of the broad H-alpha increases with disk circular velocity with a sub-linear scaling relation FWHM_broad ~ v^(0.21+/-0.05). As a result of this behavior, in the lowest mass galaxies (M* < 10^10 Mo), a significant fraction of the outflowing gas should have sufficient velocity to escape the gravitational potential of the halo whilst in the highest mass galaxies (M* > 10^10 Mo) most of the gas will be retained, flowing back on to the galaxy disk at later times.

1906.05800

Paleo-detectors for galactic supernova neutrinos

Baum, et al

Paleo-detectors are a proposed experimental technique in which one would search for traces of recoiling nuclei in ancient minerals. Natural minerals on Earth are as old as $\mathcal{O}(1)$ Gyr and, in many minerals, the damage tracks left by recoiling nuclei are also preserved for time scales long compared to $1\,$Gyr once created. Thus, even reading out relatively small target samples of order $100\,$g, paleo-detectors would allow one to search for very rare events thanks to the large exposure, $\varepsilon \sim 100\;{\rm g\;Gyr} = 10^5\;{\rm t\;yr}$. Here, we explore the potential of paleo-detectors to measure nuclear recoils induced by neutrinos from galactic core collapse supernovae. We find that they would not only allow for a direct measurement of the average core collapse supernova rate in the Milky Way, but would also contain information about the time-dependence of the local supernova rate over the past $\sim 1$ Gyr. Since the supernova rate is thought to be directly proportional to the star formation rate, such a measurement would provide a determination of the local star formation history. We investigate the sensitivity of paleo-detectors to both a smooth time evolution and an enhancement of the core collapse supernova rate on relatively short time scales, as would be expected for a starburst period in the local group.

1906.05835

Global energetics of solar flares: VIII. The low-energy cutoff

Aschwanden, et al

One of the key problems in solar flare physics is the determination of the low-energy cut-off; the value that determines the energy of nonthermal electrons and hence flare energetics. We discuss different approaches to determine the low-energy cut-off in the spectrum of accelerated electrons: (i) the total electron number model, (ii) the time-of-flight model (based on the equivalence of the time-of-flight and the collisional deflection time); (iii) the warm target model of Kontar et al.~(2015), and (iv) the model of the spectral cross-over between thermal and nonthermal components. We find that the first three models are consistent with a low-energy cutoff with a mean value of $\approx 10$ keV, while the cross-over model provides an upper limit for the low-energy cutoff with a mean value of $ \approx 21$ keV. Combining the first three models we find that the ratio of the nonthermal energy to the dissipated magnetic energy in solar flares has a mean value of $q_E=0.57\pm0.08$, which is consistent with an earlier study based on the simplified approximation of the warm target model alone ($q_E=0.51\pm0.17$). This study corroborates the self-consistency between three different low-energy cutoff models in the calculation of nonthermal flare energies.

1906.05866

Proper Fourier decomposition formalism for cosmological fields in spherical shells

Samushia

Cosmological random fields are often analysed in spherical Fourier-Bessel basis. Compared to the Cartesian Fourier basis this has an advantage of properly taking into account some of the relevant physical processes (redshift-space distortions, redshift evolution). The observations usually come in redshift slices and have a partial sky coverage. These masking effects strongly correlate Fourier-Bessel modes that are meant for a perfect spherical geometry and result in a lot of redundant measurements. This work proposes a new Fourier basis that is better suited for measurements in redshift shells and results in fewer Fourier modes, with the radial modes strictly uncorrelated on large scales and the angular modes with significantly reduced redundancy. I argue that the spherical Fourier analysis of cosmological fields should always use these new modes instead of the historically established Fourier-Bessel eigenfunctions. The new angular modes on the other hand have number of practical advantages and disadvantages and whether or not to adopt them for a particular analysis should be made on a case by case basis.

1906.05874

Anomaly in the opacity of the post-deionization intergalactic medium in the Ly$\alpha$ and Ly$\beta$ Forest

Eilers, hennawi, Davies, Oñorbe

We measure the intergalactic medium (IGM) opacity in the Ly$\alpha$ as well as in the Ly$\beta$ forest along $19$ quasar sightlines between $5.5\lesssim z_{\rm abs}\lesssim 6.1$, probing the end stages of the reionization epoch. Owing to its lower oscillator strength the Ly$\beta$ transition is sensitive to different gas temperatures and densities than Ly$\alpha$, providing additional constraints on the ionization and thermal state of the IGM. A comparison of our measurements to different inhomogeneous reionization models, derived from post-processing the Nyx cosmological hydrodynamical simulation to include spatial fluctuations in the ultraviolet background (UVB) or the gas temperature field, as well as to a uniform reionization model with varying thermal states of the IGM, leads to two primary conclusions: First, we find that including the effects of spectral noise is key for a proper data to model comparison. Noise effectively reduces the sensitivity to high opacity regions, and thus even stronger spatial inhomogeneities are required to match the observed scatter in the observations than previously inferred. Second, we find that models which come close to reproducing the distribution of Ly$\alpha$ effective optical depths nevertheless underpredict the Ly$\beta$ opacity at the same spatial locations. The origin of this disagreement is not entirely clear but models with an inversion in the temperature-density relation of the IGM just after reionization is completed match our measurements best, although they still do not fully capture the observations at $z\gtrsim 5.8$.

1906.05876

Galaxy-galaxy lensing in HSC: Validation tests and the impact of heterogeneous spectroscopic training sets

Speagle, et al

Although photometric redshifts (photo-z's) are crucial ingredients for current and upcoming large-scale surveys, the high-quality spectroscopic redshifts currently available to train, validate, and test them are substantially non-representative in both magnitude and color. We investigate the nature and structure of this bias by tracking how objects from a heterogeneous training sample contribute to photo-z predictions as a function of magnitude and color, and illustrate that the underlying redshift distribution at fixed color can evolve strongly as a function of magnitude. We then test the robustness of the galaxy-galaxy lensing signal in 120 deg$^2$ of HSC-SSP DR1 data to spectroscopic completeness and photo-z biases, and find that their impacts are sub-dominant to current statistical uncertainties. Our methodology provides a framework to investigate how spectroscopic incompleteness can impact photo-z-based weak lensing predictions in future surveys such as LSST and WFIRST.

1906.05892

Was the Sun a slow rotator? -- Sodium and Potassium constraints from the Lunar regolith

Saxena, et al

While the Earth and Moon are generally similar in composition, a notable difference between the two is the apparent depletion in moderately volatile elements in lunar samples. This is often attributed to the formation process of the Moon and demonstrates the importance of these elements as evolutionary tracers. Here we show that paleo space weather may have driven the loss of a significant portion of moderate volatiles, such as sodium and potassium from the surface of the Moon. The remaining sodium and potassium in the regolith is dependent on the primordial rotation state of the Sun. Notably, given the joint constraints shown in the observed degree of depletion of sodium and potassium in lunar samples and the evolution of activity of solar analogues over time, the Sun is highly likely to have been a slow rotator. Since the young Sun's activity was important in affecting the evolution of planetary surfaces, atmospheres, and habitability in the early Solar System, this is an important constraint on the solar activity environment at that time. Finally, since solar activity was strongest in the first billion years of the Solar System, when the Moon was most heavily bombarded by impactors, evolution of the Sun's activity may also be recorded in lunar crust and would be an important well-preserved and relatively accessible record of past Solar System processes.

1906.06041

Cosmological constraints from cosmic shear two-point correlation functions with HSC survey first-year data

Hamana, et al

We present measurements of cosmic shear two-point correlation functions (TPCFs) from Hyper Suprime-Cam Subaru Strategic Program (HSC SSP) first-year data, and derived cosmological constraints based on a blind analysis. The HSC first-year shape catalog is divided into four tomographic redshift bins ranging from $z=0.3$ to 1.5 with equal widths of $\Delta z =0.3$. The unweighted galaxy number densities in each tomographic bin are 5.9, 5.9, 4.3, and 2.4 arcmin$^{-2}$ from lower to higher redshifts, respectively. We adopt the standard TPCF estimators, $\xi_\pm$, for our cosmological analysis, given that we find no evidence of the significant B-mode shear. The TPCFs are detected at high significance for all ten combinations of auto- and cross-tomographic bins over a wide angular range, yielding a total signal-to-noise ratio of 19 in the angular ranges adopted in the cosmological analysis, $7'<\theta<56'$ for $\xi_+$ and $28'<\theta<178'$ for $\xi_-$. We perform the standard Bayesian likelihood analysis for cosmological inference from the measured cosmic shear TPCFs, including contributions from intrinsic alignment of galaxies as well as systematic effects from PSF model errors, shear calibration uncertainty, and source redshift distribution errors. We adopt a covariance matrix derived from realistic mock catalogs constructed from full-sky gravitational lensing simulations that fully account for survey geometry and measurement noise. For a flat $\Lambda$ cold dark matter model, we find $S_8 \equiv \sigma_8\sqrt{\Omega_m/0.3}=0.804_{-0.029}^{+0.032}$, and $\Omega_m=0.346_{-0.100}^{+0.052}$. We carefully check the robustness of the cosmological results against astrophysical modeling uncertainties and systematic uncertainties in measurements, and find that none of them has a significant impact on the cosmological constraints.

1906.06130

The HI velocity function: a test of cosmology or baryon physics?

Chauhan, et al

Accurately predicting the shape of the HI velocity function of galaxies is regarded widely as a fundamental test of any viable dark matter model. Straightforward analyses of cosmological $N$-body simulations imply that the LCDM model predicts an overabundance of low circular velocity galaxies when compared to observed HI velocity functions, but more nuanced analyses that account for the relationship between galaxies and their host haloes suggest that how we model the influence of baryonic processes has a significant impact on HI velocity function predictions. We explore this in detail by modeling HI emission lines of galaxies in the SHARK semi-analytic galaxy formation model, built on the SURFS suite of LCDM N-body simulations. We create a simulated ALFALFA survey, in which we apply the survey selection function and account for effects such as beam confusion, and compare simulated and observed HI velocity width distributions, finding differences of < 50%, orders of magnitude smaller than the discrepancies reported in the past. This is a direct consequence of our careful treatment of survey selection effects and, importantly, how we model the relationship between galaxy and halo circular velocity - the HI mass-maximum circular velocity relation of galaxies is characterized by a large scatter. These biases are complex enough that building a velocity function from the observed HI line widths cannot be done reliably.

Day 1583

Thursday.

1906.05079
A thousand earths: a very large aperture, ultralight space telescope array for atmospheric biosignature surveys
Asai, et al

An outstanding, multi-disciplinary goal of modern science is the study of the diversity of potentially Earth-like planets and the search for life in them. This goal requires a bold new generation of space telescopes, but even the most ambitious designs yet hope to characterize several dozen potentially habitable planets. Such a sample may be too small to truly understand the complexity of exo-earths. We describe here a notional concept for a novel space observatory designed to characterize 1,000 transiting exo-earth candidates. The Nautilus concept is based on an array of inflatable spacecraft carrying very large diameter (8.5m), very low-weight, multi-order diffractive optical elements (MODE lenses) as light-collecting elements. The mirrors typical to current space telescopes are replaced by MODE lenses with a 10 times lighter areal density that are 100 times less sensitive to misalignments, enabling light-weight structure. MODE lenses can be cost-effectively replicated through molding. The Nautilus mission concept has a potential to greatly reduce fabrication and launch costs, and mission risks compared to the current space telescope paradigm through replicated components and identical, light-weight unit telescopes. Nautilus is designed to survey transiting exo-earths for biosignatures up to a distance of 300 pc, enabling a rigorous statistical exploration of the frequency and properties of life-bearing planets and the diversity of exo-earths.

1906.05167

Effect of star rotation rates on the characteristics of energetic particle events

Fu, et al

Recent detection of superflares on solar-type stars by Kepler mission raised a possibility that they can be associated with energetic coronal mass ejections (CMEs) and energetic particle events (SEPs). These space weather events can impact habitability of exoplanets around these stars. Here we use the improved Particle Acceleration and Transport in the Heliosphere (iPATH) model, to model the time intensity profile and spectrum of SEPs accelerated at CME-driven shocks from stars of different ages traced by their rotation rates. We consider a solar-like (G-type) star with 6 different rotation rates varying from 0.5 to 3.0 times rotation speed of the sun. In all 6 cases, a fast CME is launched with the same speed of 1500 km/sec and the resulting time intensity profiles at 3 locations and energy spectra at 5 locations at 1 AU are obtained. The maximum particle energy at the shock front as a function of r is also shown. Our results suggest that within 0.8 AU the maximum particle energy at the shock front increases with the rotation rate of the star. However, event integrated spectra for the five selected locations along the CME path show complicated patterns. This is because the Parker magnetic field for rapidly rotating stars is more tightly winded. Our results can be used in estimating the radiation environments of terrestrial-type exoplanets around solar-type stars.

1906.05184

A model for micro quasars of population III

Checa, Romero

Current simulations indicate that the first stars were formed predominantly in binary systems. The study of the contribution of the first accreting binary systems to the reionization and heating of the intergalactic medium requires the formulation of a concrete model for microquasars of Population III. We aim at constructing a complete model for microquasars where the donor star is of Population III. We consider that the mas-loss of the star is caused exclusively by the spill of matter through the Roche lobe towards the black hole. We calculate the spectral energy distribution of the radiation produced by the accretion disk, the radiation-pressure driven wind, and the relativistic particles in the jets, within the framework of a lepto-hadronic model. In addition, we estimate the impact on the reionization by the first microquasars. We determine that Population III microquasars are powerful sources of ultraviolet radiation produced by the winds of their super-critical disks, and generate a broadband non-thermal emission in jets. Our results indicate that microquasars in the early Universe could have been important for the reionization and heating of the intergalactic medium.

Day 1582

Wednesday.

1906.04180
Characterizing the infall times and quenching timescales of Milky Way satellites with $Gaia$ proper motions
Fillingham, et al

Observations of low-mass satellite galaxies in the nearby Universe point towards a strong dichotomy in their star-forming properties relative to systems with similar mass in the field. Specifically, satellite galaxies are preferentially gas poor and no longer forming stars, while their field counterparts are largely gas rich and actively forming stars. Much of the recent work to understand this dichotomy has been statistical in nature, determining not just that environmental processes are most likely responsible for quenching these low-mass systems but also that they must operate very quickly after infall onto the host system, with quenching timescales $\lesssim 2~ {\rm Gyr}$ at ${M}_{\star} \lesssim 10^{8}~{\rm M}_{\odot}$. This work utilizes the newly-available $Gaia$ DR2 proper motion measurements along with the Phat ELVIS suite of high-resolution, cosmological, zoom-in simulations to study low-mass satellite quenching around the Milky Way on an object-by-object basis. We derive constraints on the infall times for $37$ of the known low-mass satellite galaxies of the Milky Way, finding that $\gtrsim~70\%$ of the `classical' satellites of the Milky Way are consistent with the very short quenching timescales inferred from the total population in previous works. The remaining classical Milky Way satellites have quenching timescales noticeably longer, with $\tau_{\rm quench} \sim 6 - 8~{\rm Gyr}$, highlighting how detailed orbital modeling is likely necessary to understand the specifics of environmental quenching for individual satellite galaxies. Additionally, we find that the $6$ ultra-faint dwarf galaxies with publicly available $HST$-based star-formation histories are all consistent with having their star formation shut down prior to infall onto the Milky Way -- which, combined with their very early quenching times, strongly favors quenching driven by reionization.

1906.04262

Tests of acoustic scale shifts in halo-based mock galaxy catalogues

Yutong, Eisenstein

We utilise mock catalogues from high-accuracy cosmological $N$-body simulations to quantify shifts in the recovery of the acoustic scale that could potentially result from galaxy clustering bias. The relationship between galaxies and dark matter halos presents a complicated source of systematic errors in modern redshift surveys, particularly when aiming to make cosmological measurements to sub-percent precision. Apart from a scalar, linear bias parameter accounting for the density contrast ratio between matter tracers and the true matter distribution, other types of galaxy bias, such as assembly and velocity biases, may also significantly alter clustering signals from small to large scales. We create mocks based on generalised halo occupation populations of 36 periodic boxes from the \abacuscosmos release with. In a total volume of $48 \, h^{-3} \mathrm{Gpc}^3$, we test various biased models along with an unbiased base case. Two reconstruction methods are applied to galaxy samples and the apparent acoustic scale is derived by fitting the two-point correlation function multipoles. With respect to the baseline, we find a $0.3\%$ shift in the line-of-sight acoustic scale for one variation in the satellite galaxy population, and we find an $0.7\%$ shift for an extreme level of velocity bias of the central galaxies. All other bias models are consistent with zero shift at the $0.2\%$ level after reconstruction. We note that the bias models explored are relatively large variations, producing sizeable and likely distinguishable changes in small-scale clustering, the modelling of which would further calibrate the BAO standard ruler.

1906.04290

No signs of star formation being regulated in the most luminous quasars at z~2 with ALMA

Schulze, et al

We present ALMA Band~7 observations at $850\mu$m of 20 luminous ($\log\, L_{\rm bol}>46.9$ [erg s$^{-1}$]) unobscured quasars at $z\sim2$. We detect continuum emission for 19/20 quasars. After subtracting an AGN contribution, we measure the total far-IR luminosity for 18 quasars, assuming a modified blackbody model, and attribute the emission as indicative of the star formation rate (SFR). Our sample can be characterized with a log-normal SFR distribution having a mean of 140 $M_\odot$ yr$^{-1}$ and a dispersion of 0.5 dex. Based on an inference of their stellar masses, the SFRs are similar, in both the mean and dispersion, with star-forming main-sequence galaxies at the equivalent epoch. Thus, there is no evidence for a systematic enhancement or suppression (i.e., regulation or quenching) of star formation in the hosts of the most luminous quasars at $z\sim2$. These results are consistent with the Magneticum cosmological simulation, while in disagreement with a widely recognized phenomenological model that predicts higher SFRs than observed here based on the high bolometric luminosities of this sample. Furthermore, there is only a weak relation between SFR and accretion rate onto their supermassive black holes both for average and individual measurements. We interpret these results as indicative of star formation and quasar accretion being fed from the available gas reservoir(s) in their host with a disconnect due to their different physical sizes, temporal scales, and means of gas processing.

Day 1581

Thursday.  Friday.  Monday. Tuesday.

1906.01638
KiDS-SQuaD II: Machine learning selection of bright extragalactic objects to search for new gravitationally lensed quasars
Khramtsov, et al

The KiDS Strongly lensed QUAsar Detection project (KiDS-SQuaD) aims at finding as many previously undiscovered gravitational lensed quasars as possible in the Kilo Degree Survey. This is the second paper of this series where we present a new, automatic object classification method based on machine learning technique. The main goal of this paper is to build a catalogue of bright extragalactic objects (galaxies and quasars), from the KiDS Data Release 4, with a minimum stellar contamination, preserving the completeness as much as possible, to then apply morphological methods to select reliable gravitationally lensed (GL) quasar candidates. After testing some of the most used machine learning algorithms, decision trees based classifiers, we decided to use CatBoost, that was specifically trained with the aim of creating a sample of extragalactic sources as clean as possible from stars. We discuss the input data, define the training sample for the classifier, give quantitative estimates of its performances, and finally describe the validation results with Gaia DR2, AllWISE, and GAMA catalogues. We have built and make available to the scientific community the KiDS Bright EXtraGalactic Objects catalogue (KiDS-BEXGO), specifically created to find gravitational lenses. This is made of $\approx6$ millions of sources classified as quasars ($\approx 200\,000$) and galaxies ($\approx 5.7$M), up to $r<22^m$. From this catalog we selected 'Multiplets': close pairs of quasars or galaxies surrounded by at least one quasar, presenting the 12 most reliable gravitationally lensed quasar candidates, to demonstrate the potential of the catalogue, which will be further explored in a forthcoming paper. We compared our search to the previous one, presented in the first paper from this series, showing that employing a machine learning method decreases the stars-contaminators within the GL candidates.

1906.01846
Brighter-fatter effect in near-infrared detectors -- I. Theory of flat auto-correlations
Hirata, Choi

Weak gravitational lensing studies aim to measure small distortions in the shapes of distant galaxies, and thus place very tight demands on the understanding of detector-induced systematic effects in astronomical images. The Wide-Field Infrared Survey Telescope (WFIRST) will carry out weak lensing measurements in the near infrared using the new Teledyne H4RG-10 detector arrays, which makes the range of possible detector systematics very different from traditional weak lensing measurements using optical CCDs. One of the non-linear detector effects observed in CCDs is the brighter-fatter effect (BFE), in which charge already accumulated in a pixel alters the electric field geometry and causes new charge to be deflected away from brighter pixels. Here we describe the formalism for measuring the BFE using flat field correlation functions in infrared detector arrays. The auto-correlation of CCD flat fields is often used to measure the BFE, but because the infrared detector arrays are read out with the charge "in place," the flat field correlations are dominated by capacitive cross-talk between neighboring pixels (the inter-pixel capacitance, or IPC). We show that because the infrared detector arrays can be read out non-destructively, one can compute numerous cross-correlation functions between different time slices of the same flat exposures, and that correlations due to IPC and BFE leave distinct imprints. We generate a suite of simulated flat fields and show that the underlying IPC and BFE parameters can be extracted, even when both are present in the simulation. There are some biases in the BFE coefficients up to 12%, which are likely caused by higher order terms that are dropped from this analysis. The method is applied to laboratory data in the companion Paper II.

1906.01847

Brighter-Fatter effect in near-infrared detectors -- II. Auto-correlation analysis of H4RG-10 flats

Choi, Hirata

The Wide Field Infrared Survey Telescope (WFIRST) will investigate the origins of cosmic acceleration using weak gravitational lensing at near infrared wavelengths. Lensing analyses place strict constraints on the precision of size and ellipticity measurements of the point spread function. WFIRST will use hybrid complementary metal oxide semiconductor (CMOS) detector arrays, which must be fully characterized to inform data reduction and calibration procedures such that unbiased cosmological results can be achieved. Hirata & Choi 2019 introduces formalism to connect the cross-correlation signal of different flat field time samples to non-linear detector behaviors such as the brighter fatter effect (BFE) and non-linear inter-pixel capacitance (NL-IPC), and this paper applies that framework to a WFIRST development detector, SCA 18237. We find a residual correlation signal after accounting for classical non-linearity. This residual correlation contains a combination of the BFE and NL-IPC; however, further tests suggest that the BFE is the dominant mechanism. If interpreted as a pure BFE, it suggests that the effective area of a pixel is increased by $(2.87\pm0.03)\times 10^{-7}$ (stat.) for every electron in the 4 nearest neighbors, with a rapid $\sim r^{-5.6\pm0.2}$ fall-off of the effect for more distant neighbors. We show that the IPC inferred from hot pixels contains the same large-scale spatial variations as the IPC inferred from auto-correlations, albeit with an overall offset of $\sim 0.06\%$. The NL-IPC inferred from hot pixels is too small to explain the cross-correlation measurement, further supporting the BFE hypothesis. This work presents the first evidence for the BFE in an H4RG-10 detector, demonstrates some of the useful insights that can be gleaned from flat field statistics, and represents a significant step towards calibration of WFIRST data.

1906.01967

Local monitoring of atmospheric transparency from the NASA MERRA-2 global assimilation system

Guyonnet, et al

Ground-based astronomy has to correct astronomical observations from the impact of the atmospheric transparency and its variability. The current objective of several observatories is to achieve a sub-percent level monitoring of atmospheric transmission. A promising approach has been to combine internal calibration of the observations with various external meteorological probes, upon availability and depending on quality. In this paper we investigate the use of the NASA Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) which is a global climate monitoring project that renders freely available for any given site, at any time, all the parameters constraining atmospheric transmission. This paper demonstrates the extraction of the relevant atmospheric parameters for optical astronomy at two sites: Mauna Kea in Hawaii and Cerro Tololo International Observatory in Chile. The temporal variability for the past eight years (annual, overnight and hourly), as well as the spatial gradients of ozone, precipitable water vapor, and aerosol optical depth is presented and their respective impacts on the atmospheric transparency is analyzed.

1906.02214

A pathfinder for imaging extrasolar Earths from the ground

Currie

The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) project is an instrument on the Subaru telescope that is pushing the frontiers of what is possible with ground-based high-contrast imaging of extrasolar planets. The system features key breakthroughs in wavefront sensing and coronagraphy to yield extremely high Strehl ratio corrections and deep planet-to-star contrasts, even for optically faint stars. SCExAO is coupled to a near-infrared integral field spectrograph -- CHARIS -- yielding robust planet spectral characterization. In its first full year of operations, SCExAO has already clarified the properties of candidate companions around $\kappa$ And, LkCa 15, and HD 163296, showing the former to be a likely low-gravity, planet-mass object and the latter two to be misidentified disk signals. SCExAO's planet imaging capabilities in the near future will be further upgraded; the system is emerging as a prototype of the kind of dedicated planet-imaging system that could directly detect an Earth-like planet around a nearby low-mass star with Extremely Large Telescopes like the Thirty Meter Telescope.

1906.02217

A null test to probe the scale-dependence of the growth of structure as a test of General Relativity

Franco, et al

The main science driver for the coming generation of cosmological surveys is understanding dark energy which relies on testing General Relativity on the largest scales. Once we move beyond the simplest explanation for dark energy of a cosmological constant, the space of possible theories becomes both vast and extremely hard to compute realistic observables. A key discriminator of a cosmological constant, however, is that the growth of structure is scale-invariant on large scales. By carefully weighting observables derived from distributions of numbers of galaxies and a dipole pattern in their apparent sizes, we construct a null test which vanishes for any model of gravity or dark energy where the growth of structure is scale-independent. It relies only on very few assumptions about cosmology, and does not require any modelling of the growth of structure at late times. We show that with a survey like the Dark Energy Spectroscopic Instrument a scale-dependence of the order of 10-20 percent can be detected with 3 standard deviations with the null test, which will drop by a factor of 2 for a survey with a larger number of galaxies and volume, like the Square Kilometre Array will be capable of. We also show that the null test is very insensitive to typical uncertainties in other cosmological parameters including massive neutrinos and scale-dependent bias, making this a key null test for the cosmological constant.

1906.02747
The relationship between black hole mass and galaxy properties: examining the black hole feedback model in IllustrisTNG
Terrazas, et al

Supermassive black hole feedback is thought to be responsible for the lack of star formation, or quiescence, in a significant fraction of galaxies. We explore how observable correlations between the specific star formation rate (sSFR), stellar mass (M$_{\rm{star}}$), and black hole mass (M$_{\rm{BH}}$) are sensitive to the physics of black hole feedback in a galaxy formation model. We use the IllustrisTNG simulation suite, specifically the TNG100 simulation and ten model variations that alter the parameters of the black hole model. Focusing on central galaxies at $z = 0$ with M$_{\rm{star}} > 10^{10}$ M$_{\odot}$, we find that the sSFR of galaxies in IllustrisTNG decreases once the energy from black hole kinetic winds at low accretion rates becomes larger than the gravitational binding energy of gas within the galaxy stellar radius. This occurs at a particular M$_{\rm{BH}}$ threshold above which galaxies are found to sharply transition from being mostly star-forming to mostly quiescent. As a result of this behavior, the fraction of quiescent galaxies as a function of M$_{\rm{star}}$ is sensitive to both the normalization of the M$_{\rm{BH}}$-M$_{\rm{star}}$ relation and the M$_{\rm{BH}}$ threshold for quiescence in IllustrisTNG. Finally, we compare these model results to observations of 91 central galaxies with dynamical M$_{\rm{BH}}$ measurements with the caveat that this sample is not representative of the whole galaxy population. While IllustrisTNG reproduces the observed trend that quiescent galaxies host more massive black holes, the observations exhibit a broader scatter in M$_{\rm{BH}}$ at a given M$_{\rm{star}}$ and show a smoother decline in sSFR with M$_{\rm{BH}}$.

1906.02787

The B-star exoplanet abundance study: a co-moving 16-25 Mjup companion to the young binary system HIP 79098

Janson, et al

Wide low-mass substellar companions are known to be very rare among low-mass stars, but appear to become increasingly common with increasing stellar mass. However, B-type stars, which are the most massive stars within ~150 pc of the Sun, have not yet been examined to the same extent as AFGKM-type stars in that regard. In order to address this issue, we launched the ongoing B-star Exoplanet Abundance Study (BEAST) to examine the frequency and properties of planets, brown dwarfs, and disks around B-type stars in the Scorpius-Centaurus (Sco-Cen) association; we also analyzed archival data of B-type stars in Sco-Cen. During this process, we identified a candidate substellar companion to the B9-type spectroscopic binary HIP 79098 AB, which we refer to as HIP 79098 (AB)b. The candidate had been previously reported in the literature, but was classified as a background contaminant on the basis of its peculiar colors. Here we demonstrate that the colors of HIP 79098 (AB)b are consistent with several recently discovered young and low-mass brown dwarfs, including other companions to stars in Sco-Cen. Furthermore, we show unambiguous common proper motion over a 15-year baseline, robustly identifying HIP 79098 (AB)b as a bona fide substellar circumbinary companion at a 345+/-6 AU projected separation to the B9-type stellar pair. With a model-dependent mass of 16-25 Mjup yielding a mass ratio of <1%, HIP 79098 (AB)b joins a growing number of substellar companions with planet-like mass ratios around massive stars. Our observations underline the importance of common proper motion analysis in the identification of physical companionship, and imply that additional companions could potentially remain hidden in the archives of purely photometric surveys.

1906.03035

The impact of the fiducial cosmology assumption on BAO cosmological parameter inference

Carter, et al

Standard analysis pipelines for measurements of Baryon Acoustic Oscillations (BAO) in galaxy surveys make use of a fiducial cosmological model to guide the data compression required to transform from observed redshifts and angles to the measured angular and radial BAO peak positions. In order to remove any dependence on the fiducial cosmology from the results, all models compared to the data should mimic the compression and its dependence on the fiducial model. In practice, approximations are made when testing models: (1) There is assumed to be no residual dependence on the fiducial cosmology after reconstruction, (2) differences in the distance--redshift relationship are assumed to match a linear scaling, and (3) differences in clustering between true and fiducial models are assumed to be removed by the free parameters used to null the non-BAO signal. We test these approximations using the current standard measurement procedure with a set of halo catalogs from the {\sc Aemulus} suite of $N$-body simulations, which span a range of $w\mathrm{CDM}$ cosmological models. We focus on reconstruction of the primordial BAO and locating the BAO. For the range of $w\mathrm{CDM}$ cosmologies covered by the {\sc Aemulus} suite, we find no evidence for systematic errors in the measured BAO shift parameters $\alpha_{\parallel}$ and $\alpha_{\bot}$ to $< 0.1\%$. However, the measured errors $\sigma_{\alpha_{\parallel}}$ and $\sigma_{\alpha_{\bot}}$ show a notable absolute increase by up to $+0.001$ and $+0.002$ respectively in the case that the fiducial cosmology does not match the truth. These effects on the inferred BAO scale will be important given the precision of measurements expected from future surveys including DESI, Euclid, and WFIRST.

1906.03156

Cosmological constraints with deep learning from KiDS-450 weak lensing maps

Fluri, et al

Convolutional Neural Networks (CNN) have recently been demonstrated on synthetic data to improve upon the precision of cosmological inference. In particular they have the potential to yield more precise cosmological constraints from weak lensing mass maps than the two-point functions. We present the cosmological results with a CNN from the KiDS-450 tomographic weak lensing dataset, constraining the total matter density $\Omega_m$, the fluctuation amplitude $\sigma_8$, and the intrinsic alignment amplitude $A_{\rm{IA}}$. We use a grid of N-body simulations to generate a training set of tomographic weak lensing maps. We test the robustness of the expected constraints to various effects, such as baryonic feedback, simulation accuracy, different value of $H_0$, or the lightcone projection technique. We train a set of ResNet-based CNNs with varying depths to analyze sets of tomographic KiDS mass maps divided into 20 flat regions, with applied Gaussian smoothing of $\sigma=2.34$ arcmin. The uncertainties on shear calibration and $n(z)$ error are marginalized in the likelihood pipeline. Following a blinding scheme, we derive constraints of $S_8 = \sigma_8 (\Omega_m/0.3)^{0.5} = 0.777^{+0.038}_{-0.036}$ with our CNN analysis, with $A_{\rm{IA}}=1.398^{+0.779}_{-0.724}$. We compare this result to the power spectrum analysis on the same maps and likelihood pipeline and find an improvement of about $30\%$ for the CNN. We discuss how our results offer excellent prospects for the use of deep learning in future cosmological data analysis.

1906.03673

The ssos Pipeline: identification of Solar System Objects in Astronomical images

Mahlke, et al

Observatories and satellites around the globe produce tremendous amounts of imaging data to study many different astrophysical phenomena. The serendipitous observations of Solar System objects are a fortunate by-product which have often been neglected due to the lack of a simple yet efficient identification algorithm. Meanwhile, the determination of the orbit, chemical composition, and physical properties such as rotation period and 3D-shape of Solar System objects requires a large number of astrometry and multi-band photometry observations. Such observations are hidden in current and future astrophysical archives, and a method to harvest these goldmines is needed. This article presents an easy-to-implement, light-weight software package which detects bodies of the Solar System in astronomical images and measures their astrometry and photometry. The ssos pipeline is versatile, allowing for application to all kinds of observatory imaging products. The sole principle requirement is that the images observe overlapping areas of the sky within a reasonable time range. Both known and unknown Solar System objects are recovered, from fast-moving near-Earth asteroids to slow objects in the Kuiper belt. The high-level pipeline design and two test applications are described here, highlighting the versatility of the algorithm with both narrow-field pointed and wide-field survey observations. In the first study, 2,828 detections of 204 SSOs are recovered from publicly available images of the GTC OSIRIS Broad Band DR1. The false-positive ratio of SSO detections ranges from 0%-23% depending on the pipeline setup. The second test study utilizes the images of the first data release of J-PLUS, a 12-band optical survey. 4,606 SSO candidates are recovered, with a false-positive ratio of (2.0 +- 0.2)%.