Day 1635

Monday.  Tuesday.

1910.01644

Constraining star formation histories of blue galaxies using the scatter between stellar mass and halo mass

Hahn, Tinker, Wetzel

We present constraints on the timescale of star formation variability and the correlation between star formation and host halo accretion histories of star-forming (SF) central galaxies from the scatter of the stellar-to-halo mass relation (SHMR). SF galaxies are found to have a tight relationship between their star formation rates and stellar masses on the so-called "star-forming sequence" (SFS), which characterizes their SF histories and $M_*$ growths. Meanwhile, observed SHMR constraints connect $M_*$ growth to halo accretion history. Combining these observed trends with a cosmological $N$-body simulation, we present flexible models that track the SF, $M_*$, and halo accretion histories of SF central galaxies at $z<1$ while reproducing the observed stellar mass function and SFS in SDSS DR7. We find that the scatter in SHMR at $M_h=10^{12}M_\odot$, $\sigma_{M_*|M_h=10^{12}M_\odot}$, is sensitive to the timescale of star formation variability, $t_{\rm duty}$, and the correlation coefficient, $r$, between SF and halo accretion histories: shorter $t_{\rm duty}$ and higher $r$ both result in tighter $\sigma_{M_*|M_h=10^{12}M_\odot}$. To reproduce a constant 0.2 dex scatter over $z=1-0$, our models require $t_{\rm duty}\leq1.5$ Gyr for $r=0.99$ or $r>0.6$ for $t_{\rm duty}=0.1$ Gyr. For $r\sim0.6$, as found in the literature, $t_{\rm duty}<0.2$ Gyr is necessary. Meanwhile, to reproduce the tightening of $\sigma_{M_*|M_h=10^{12}M_\odot}=0.35$ to 0.2 dex from $z=1-0$ in hydrodynamical simulations, our models require $t_{\rm duty}=0.1$ Gyr for $r>0.5$. Although, the lack of consensus on $\sigma_{M_*|M_h=10^{12}M_\odot}$ at $M_h=10^{12}M_\odot$ and at $z=1$ from observations and galaxy formation models remains the main bottleneck in precisely constraining $r$ and $t_{\rm duty}$, we demonstrate that SHMR can be used to constrain the SF and host halo accretion histories of SF central galaxies.

1910.01745

Sensitivity analysis of a galaxy formation model

Oeskiewicz, Baugh

We present the first application of a variance-based sensitivity analysis (SA) to a model that aims to predict the evolution and properties of the whole galaxy population. SA is a well-established technique in other quantitative sciences, but is a relatively novel tool for the evaluation of astrophysical models. We perform a multi-parameter exploration of the GALFORM semi-analytic galaxy formation model, to compute how sensitive the present-day K-band luminosity function is to varying different model parameters. The parameter space is scanned using a low-discrepancy sampling technique proposed by Saltelli. We first demonstrate the usefulness of the SA approach by varying just two model parameters, one which controls supernova feedback and the other the heating of gas by AGN. The SA analysis matches our physical intuition regarding how these parameters affect the predictions for different parts of the galaxy luminosity function. We then use SA to compute Sobol' sensitivity indices varying seven model parameters, connecting the variance in the model output to the variance in the input parameters. The sensitivity is computed in luminosity bins, allowing us to probe the origin of the model predictions in detail. We discover that the SA correctly identifies the least- and most important parameters. Moreover, the SA also captures the combined responses of varying multiple parameters at the same time. Our study marks a much needed step away from the traditional "one-at-a-time" parameter variation often used in this area and improves the transparency of multi-parameter models of galaxy formation.

1910.02906
A framework for measuring weak-lensing magnification using the fundamental plane
Freudenburg, Huff, Hirata

Galaxy-galaxy lensing is an essential tool for probing dark matter halos and constraining cosmological parameters. While galaxy-galaxy lensing measurements usually rely on shear, weak-lensing magnification contains additional constraining information. Using the fundamental plane (FP) of elliptical galaxies to anchor the size distribution of a background population is one method that has been proposed for performing a magnification measurement. We present a formalism for using the FP residuals of elliptical galaxies to jointly estimate the foreground mass and background redshift errors for a stacked lens scenario. The FP residuals include information about weak-lensing magnification $\kappa$, and therefore foreground mass, since to first order, nonzero $\kappa$ affects galaxy size but not other FP properties. We also present a modular, extensible code that implements the formalism using emulated galaxy catalogs of a photometric galaxy survey. We find that combining FP information with observed number counts of the source galaxies constrains mass and photo-z error parameters significantly better than an estimator that includes number counts only. In particular, the improvement in the constraint on the mass is an order of magnitude better if FP residuals are included. Furthermore, we find that the mass estimator is robust to selection effects. The effective size noise for a foreground lens of mass $M_H=10^{14}M_\odot$, with a conservative selection function in size and surface brightness applied to the source population, is $\sigma_{\kappa,\mathrm{eff}}=0.183$. We discuss the improvements to our FP model necessary to make this formalism a practical companion to shear analyses in weak lensing surveys.

Day 1634

Tuesday.  Wednesday.  Thursday.  Friday.

1909.12854
Hawaii Two-0: high-redshift galaxy clustering and bias
Beck, et al

We perform an analysis of two-point galaxy clustering and galaxy bias using Subaru Hyper-Suprime Cam (HSC) data taken jointly by the Subaru Strategic Program and the University of Hawaii in the COSMOS field. The depth of the data is similar to the ongoing Hawaii Two-0 (H20) optical galaxy survey, thus the results are indicative of future constraints from tenfold area. We measure the angular auto-power spectra of the galaxy overdensity in three redshift bins, defined by dropouts from the g-, r- and i-bands, and compare them to the theoretical expectation from concordance cosmology with linear galaxy bias. We determine the redshift distribution of each bin using a standard template-based photometric redshift method, coupled with a self-organizing map (SOM) to quantify colour space coverage. We also investigate sources of systematic errors to inform the methodology and requirements for Hawaii Two-0. The linear galaxy bias fit results are $b_{\mathrm{gal,g}} = 3.90 \pm 0.33 (\mathrm{stat}) \substack{ +0.64 \\ -0.24 } (\mathrm{sys})$ at redshift $z \simeq 3.7$, $b_{\mathrm{gal,r}} = 8.44 \pm 0.63 (\mathrm{stat}) \substack{ +1.42 \\ -0.72 } (\mathrm{sys})$ at $z \simeq 4.7$, and $b_{\mathrm{gal,i}} = 11.94 \pm 2.24 (\mathrm{stat}) \substack{ +1.82 \\ -1.27 } (\mathrm{sys})$ at $z \simeq 5.9$.

1910.00483
A detailed description of the CamSpec likelihood pipeline and a reanalysis of the Planck high frequency maps
Efstathiou, Gratton

This paper presents a detailed description of the CamSpec likelihood which has been used to analyse Planck temperature and polarization maps of the cosmic microwave background since the first Planck data release. We have created a number of likelihoods using a range of Galactic sky masks and different methods of temperature foreground cleaning. Our most powerful likelihood uses 80 percent of the sky in temperature and polarization. Our results show that the six-parameter LCDM cosmology provides an excellent fit to the Planck data. There is no evidence for statistically significant internal tensions in the Planck TT, TE and EE spectra computed for different frequency combinations. We present evidence that the tendencies for the Planck temperature power spectra to favour a lensing amplitude A_L>1 and positive spatial curvature are caused by statistical fluctuations in the temperature power spectra. Using our statistically most powerful likelihood, we find that the A_L parameter differs from unity at no more than the 2.2 sigma level. We find no evidence for anomalous shifts in cosmological parameters with multipole range. In fact, we show that the combined TTTEEE likelihood over the restricted multipole range 2-800 gives cosmological parameters for the base LCDM cosmology that are very close to those derived from the full multipole range 2-2500. We present revised constraints on a few extensions of the base LCDM cosmology, focussing on the sum of neutrino masses, number of relativistic species and the tensor-scalar ratio. The results presented here show that the Planck data are remarkably consistent between detector-sets, frequencies and sky area. We find no evidence in our analysis that cosmological parameters determined from the CamSpec likelihood are affected to any significant degree by systematic errors in the Planck data (abridged).

1910.00725
Cosmic microwave background anisotropy numerical solutions (CMBAns) I: An introduction to $C_l$ calculation
Das, Phan

Cosmological Boltzmann codes are often used by researchers for calculating the CMB angular power spectra from different theoretical models, for cosmological parameter estimation, etc. Therefore, the accuracy of a Boltzmann code is of utmost importance. Different Markov Chain Monte Carlo based parameter estimation algorithms typically require 10^3 - 10^4 iterations of Boltzmann code. This makes the time complexity of such codes another critical factor. In the last two decades, several Boltzmann packages, such as CMBFAST, CAMB, CMBEasy, CLASS etc., have been developed. In this paper, we present a new cosmological Boltzmann code, CMBAns, that can be used for accurate calculation of the CMB power spectrum. At present, CMBAns is developed for a flat background matrix. It is mostly written in the C language. However, we borrowed the concept of class from C++. This gives researchers the flexibility to develop their own independent package based on CMBAns, without an in-depth understanding of the source code. We also develop multiple stand-alone facilities which can be directly compiled and run on a given parameter set. In this paper, we discuss all the mathematical formulation, approximation schemes, integration methods etc., that are used in CMBAns. The package will be made available through github for public use in the near future.

1910.01163

Evolution of giant molecular clouds across cosmic time

Guszejnov, et al

Giant molecular clouds (GMCs) are well-studied in the local Universe, however, exactly how their properties vary during galaxy evolution is poorly understood due to challenging resolution requirements, both observational and computational. We present the first time-dependent analysis of giant molecular clouds in a Milky Way-like galaxy and an LMC-like dwarf galaxy of the FIRE-2 (Feedback In Realistic Environments) simulation suite, which have sufficient resolution to predict the bulk properties of GMCs in cosmological galaxy formation self-consistently. We show explicitly that the majority of star formation outside the galactic center occurs within self-gravitating gas structures that have properties consistent with observed bound GMCs. We find that the typical cloud bulk properties such as mass and surface density do not vary more than a factor of 2 in any systematic way after the first Gyr of cosmic evolution within a given galaxy from its progenitor. While the median properties are constant, the tails of the distributions can briefly undergo drastic changes, which can produce very massive and dense self-gravitating gas clouds. Once the galaxy forms, we identify only two systematic trends in bulk properties over cosmic time: a steady increase in metallicity produced by previous stellar populations and a weak decrease in bulk cloud temperatures. With the exception of metallicity we find no significant differences in cloud properties between the Milky Way-like and dwarf galaxies. These results have important implications for cosmological star and star cluster formation and put especially strong constraints on theories relating the stellar initial mass function to cloud properties.

1910.01172

Test particle simulations of cosmic rays

Mertsch

Modelling of cosmic ray transport and interpretation of cosmic ray data ultimately rely on a solid understanding of the interactions of charged particles with turbulent magnetic fields. The paradigm over the last 50 years has been the so-called quasi-linear theory, despite some well-known issues. In the absence of a widely accepted extension of quasi-linear theory, wave-particle interactions must also be studied in numerical simulations where the equations of motion are directly solved in a realisation of the turbulent magnetic field. The applications of such test particle simulations of cosmic rays are manifold: testing transport theories, computing parameters like diffusion coefficients or making predictions for phenomena beyond standard quasi-linear theory, e.g. for cosmic ray small-scale anisotropies. In this review, we seek to give a low-level introduction to test particle simulations of cosmic rays, enabling readers to run their own test particle simulations. We start with a review of quasi-linear theory, highlighting some of its issues and suggested extensions. Next, we summarise the state-of-the-art in test particle simulations and give concrete recipes for generating synthetic turbulence. We present a couple of examples for applications of such simulations and comment on an important conceptual detail in the backtracking of particles.

1910.01194

ESA Voyage 2050 white paper: Unvailing the faint ultraviolet Universe

Zanella, et al

New and unique science opportunities in several different fields of astrophysics are offered by conducting spectroscopic studies of the Universe in the ultraviolet (UV), a wavelength regime that is not accessible from the ground. We present some of the scientific challenges that can be addressed with a space-based mission in 2035 - 2050. (1) By detecting the intergalactic medium in emission it will be possible to unveil the cosmic web, whose existence is predicted by current theories of structure formation, but it has not been probed yet. (2) Observations of the neutral gas distribution (by mapping the Lyman-alpha emission) in low-redshift galaxy cluster members will clarify the efficiency with which ram-pressure stripping removes the gas from galaxies and the role of the environment in quenching star formation. (3) By observing statistical samples of supernovae in the UV it will be possible to characterize the progenitor population of core-collapse supernovae, providing the initial conditions for any forward-modeling simulation and allowing the community to progress in the understanding of the explosion mechanism of stars and the final stages of stellar evolution. (4) Targeting populations of accreting white dwarfs in globular clusters it will be possible to constrain the evolution and fate of these stars and investigate the properties of the most compact systems with the shortest orbital periods which are expected to be the brightest low frequency gravitational wave sources. A UV-optimized telescope (wavelength range ~ 90 - 350 nm), equipped with a panoramic integral field spectrograph with a large field of view (FoV ~ 1 x 1 arcmin^2), with medium spectral (R = 4000) and spatial (~ 1" - 3") resolution will allow the community to simultaneously obtain spectral and photometric information of the targets, and tackle the science questions presented in this paper.

1910.01209

Element abundances of Solar energetic particles and the photosphere, the corona, and the Solar wind

Reames

From a turbulent history, the study of abundances of elements in solar energetic particles (SEPs) has grown into an extensive field that probes the solar corona and the physical processes of SEP acceleration and transport. Underlying SEPs are the abundances of the solar corona, which differ from photospheric abundances as a function of the first ionization potentials (FIPs) of the elements. The FIP-dependence of SEPs also differs from that of the solar wind; each has a different magnetic environment where low-FIP ions and high-FIP neutral atoms rise toward the corona. Two major sources generate SEPs: The small "impulsive" SEP events are associated with magnetic reconnection in solar jets that produce 1000-fold enhancements from H to Pb as a function of mass-to-charge ratio A/Q, and also 1000-fold enhancements in 3He/4He produced by resonant wave-particle interactions. In large "gradual" events, SEPs are accelerated at shock waves driven out from the Sun by wide, fast coronal mass ejections (CMEs). A/Q dependence of ion transport allows us to estimate Q and hence the source plasma temperature T. Weaker shock waves favor reacceleration of suprathermal ions accumulated from earlier impulsive SEP events, along with protons from the ambient plasma. In strong shocks the ambient plasma dominates. Ions from impulsive sources have T ~ 3 MK; those from ambient coronal plasma have T = 1 - 2 MK. These FIP- and A/Q-dependences explore complex new interactions in the corona and in SEP sources.

1910.01259

Joint survey processing of LSST, Euclid and WFIRST: enabling a broad array of astrophysics and cosmology through pixel level combinations of datasets

Chary, et al

Joint survey processing (JSP) is the pixel level combination of LSST, Euclid, and WFIRST datasets. By combining the high spatial resolution of the space-based datasets with deep, seeing-limited, ground-based images in the optical bands, systematics like source confusion and astrometric mismatch can be addressed to derive the highest precision optical/infrared photometric catalogs. This white paper highlights the scientific motivation, computational and algorithmic needs to build joint pixel level processing capabilities, which the individual projects by themselves will not be able to support. Through this white paper, we request that the Astro2020 decadal committee recognize the JSP effort as a multi-agency project with the natural outcome being a collaborative effort among groups which are normally supported by a single agency. JSP will allow the U.S. (and international) astronomical community to manipulate the flagship data sets and undertake innovative science investigations ranging from solar system object characterization, exoplanet detections, nearby galaxy rotation rates and dark matter properties, to epoch of reionization studies. It will also result in the ultimate constraints on cosmological parameters and the nature of dark energy, with far smaller uncertainties and a better handle on systematics than by any one survey alone.

Day 1633

Thursday, Friday, Monday.

1909.11333
The dust mass function from z~0 to z~2
Pozzi, et al

We derive for the first time the dust mass function (DMF) in a wide redshift range, from z~0.2 up to z~2.5. In order to trace the dust emission, we start from a far-IR (160-um) Herschel selected catalogue in the COSMOS field. We estimate the dust masses by fitting the far-IR data (lam_rest>50um) with a modified black body function and we present a detailed analysis to take into account the incompleteness in dust masses from a far-IR perspective. By parametrizing the observed DMF with a Schechter function in the redshift range 0.1<z<0.25, where we are able to sample faint dust masses, we measure a steep slope (alpha~1.48), as found by the majority of works in the Local Universe. We detect a strong dust mass evolution, with M_d^star at z~2.5 almost one dex larger than in the local Universe, combined with a decrease in their number density. Integrating our DMFs we estimate the dust mass density (DMD), finding a broad peak at z~1, with a decrease by a factor of ~3 towards z~0 and z~2.5. In general, the trend found for the DMD mostly agrees with the derivation of Driver et al. (2018), another DMD determination based also on far-IR detections, and with other measures based on indirect tracers.

1909.11742
Active galactic nuclei winds as the origin of the H2 emission excess in nearby galaxies
Riffel, Zakamska, Riffel

In most galaxies, the fluxes of rotational H2 lines strongly correlate with star formation diagnostics (such as polycyclic aromatic hydrocarbons, PAH), suggesting that H2 emission from warm molecular gas is a minor byproduct of star formation. We analyse the optical properties of a sample of 309 nearby galaxies derived from a parent sample of 2,015 objects observed with the Spitzer Space Telescope. We find a correlation between the [OI]6300 emission-line flux and kinematics and the H2 S(3)9.665um/PAH11.3um. The [OI]6300 kinematics in Active Galactic Nuclei (AGN) can not be explained only by gas motions due to the gravitational potential of their host galaxies, suggesting that AGN driven outflows are important to the observed kinematics. While H2 excess also correlates with the fluxes and kinematics of ionized gas (probed by [OIII]), the correlation with [OI] is much stronger, suggesting that H2 and [OI] emission probe the same phase or tightly coupled phases of the wind. We conclude that the excess of H2 emission seen in AGN is produced by shocks due to AGN driven outflows and in the same clouds that produce the [OI] emission. Our results provide an indirect detection of neutral and molecular winds and suggest a new way to select galaxies that likely host molecular outflows. Further ground- and space-based spatially resolved observations of different phases of the molecular gas (cold, warm and hot) are necessary to test our new selection method.

1909.12248

Direct measurement of the Kepler space telescope CCD's intra-pixel response function

Vorobiev, et al

Space missions designed for high precision photometric monitoring of stars often under-sample the point-spread function, with much of the light landing within a single pixel. Missions like MOST, Kepler, BRITE, and TESS, do this to avoid uncertainties due to pixel-to-pixel response nonuniformity. This approach has worked remarkably well. However, individual pixels also exhibit response nonuniformity. Typically, pixels are most sensitive near their centers and less sensitive near the edges, with a difference in response of as much as 50%. The exact shape of this fall-off, and its dependence on the wavelength of light, is the intra-pixel response function (IPRF). A direct measurement of the IPRF can be used to improve the photometric uncertainties, leading to improved photometry and astrometry of under-sampled systems. Using the spot-scan technique, we measured the IPRF of a flight spare e2v CCD90 imaging sensor, which is used in the Kepler focal plane. Our spot scanner generates spots with a full-width at half-maximum of $\lesssim$3 microns across the range of 400 nm - 850 nm. We find that Kepler's CCD shows similar IPRF behavior to other back-illuminated devices, with a decrease in responsivity near the edges of a pixel by $\sim$50%. The IPRF also depends on wavelength, exhibiting a large amount of diffusion at shorter wavelengths and becoming much more defined by the gate structure in the near-IR. This method can also be used to measure the IPRF of the CCDs used for TESS, which borrows much from the Kepler mission.

1909.12371
The SAMI galaxy survey: first detection of a transition in spin orientation with respect to cosmic filaments in the stellar kinematics of galaxies
Welker, et al

We present the first detection of mass dependent galactic spin alignments with local cosmic filaments with over 2 sigma confidence using IFS kinematics. The 3D network of cosmic filaments is reconstructed on Mpc scales across GAMA fields using the cosmic web extractor DisPerSe. We assign field galaxies from the SAMI survey to their nearest filament segment in 3D and estimate the degree of alignment between SAMI galaxies kinematic spin axis and their nearest filament in projection. Low-mass galaxies align their spin with their nearest filament while higher mass counterparts are more likely to display an orthogonal orientation. The stellar transition mass from the first trend to the second is bracketed between log stellar masses 10.4 and 10.9, with hints of an increase with filament scale. Consistent signals are found in the HorizonAGN cosmological hydrodynamic simulation. This supports a scenario of early angular momentum build-up in vorticity rich quadrants around filaments at low stellar mass followed by progressive flip of spins orthogonal to the cosmic filaments through mergers at high stellar mass. Conversely, we show that dark-matter only simulations post-processed with a semi-analytic model treatment of galaxy formation struggles to reproduce this alignment signal. This suggests that gas physics is key in enhancing the galaxy-filament alignment.

Day 1632

Friday.  Monday.  Tuesday.


1909.08624
ALMACAL VI: Molecular gas mass density across cosmic time via a blind search for intervening molecular absorbers
Klitsch, et al

We are just starting to understand the physical processes driving the dramatic change in cosmic star-formation rate between $z\sim 2$ and the present day. A quantity directly linked to star formation is the molecular gas density, which should be measured through independent methods to explore variations due to cosmic variance and systematic uncertainties. We use intervening CO absorption lines in the spectra of mm-bright background sources to provide a census of the molecular gas mass density of the Universe. The data used in this work are taken from ALMACAL, a wide and deep survey utilizing the ALMA calibrator archive. While we report multiple Galactic absorption lines and one intrinsic absorber, no extragalactic intervening molecular absorbers are detected. However, thanks to the large redshift path surveyed ($\Delta z=182$), we provide constraints on the molecular column density distribution function beyond $z\sim 0$. In addition, we probe column densities of N(H$_2$) > 10$^{16}$ atoms~cm$^{-2}$, five orders of magnitude lower than in previous studies. We use the cosmological hydrodynamical simulation IllustrisTNG to show that our upper limits of $\rho ({\rm H}_2)\lesssim 10^{8.3} \text{M}_{\odot} \text{Mpc}^{-3}$ at $0 < z \leq 1.7$ already provide new constraints on current theoretical predictions of the cold molecular phase of the gas. These results are in agreement with recent CO emission-line surveys and are complementary to those studies. The combined constraints indicate that the present decrease of the cosmic star-formation rate history is consistent with an increasing depletion of molecular gas in galaxies compared to $z\sim 2$.

1909.08791
Prospects for line on temperate planets around brown dwarfs
Lingam, Ginsburg, Loeb

There is growing evidence that brown dwarfs may be comparable to main-sequence stars in terms of their abundance. In this paper, we explore the prospects for the existence of life on Earth-like planets around brown dwarfs. We consider the following factors: (i) the duration planets can exist in the temporally shifting habitable zone, (ii) the minimum photon fluxes necessary for oxygenic photosynthesis, and (iii) the lower limits on the fluxes of ultraviolet radiation to drive prebiotic reactions ostensibly necessary for the origin of life. By taking these effects into consideration, we find that it is unlikely for brown dwarfs with masses $\lesssim 30 M_J$ to host habitable planets over geologically significant timescales. We also briefly discuss some of the major biosignatures that might arise on these planets, assess the likelihood of their detection, and highlight some avenues for further study.

1909.09230

Determining the composition of relativistic jets from polarization maps

Anantua, Emami, Loeb

We present a stationary, axisymmetric, self-similar semi-analytic model of magnetically dominated jet plasma based on force-free regions of a relativistic magnetohydrodynamic simulation. We use this model to illustrate how the composition of relativistic jet plasma can be determined, with special attention to the example of M87. In particular, we compute synthetic Stokes maps in e-e+p plasmas with various positron-to-proton ratios using synchrotron emission models scaling the partial pressure of electrons and positrons emitting at the observed frequency to the magnetic pressure, taking into account Faraday rotation and conversion. The lepton-dominated models produce bilaterally asymmetric radio intensity profiles with strong linear polarization and Stokes Q and U maps that are bilaterally asymmetric (but strongly up-down correlated) and antisymmetric (and sometimes up-down anticorrelated), respectively. The hadronic models produce more centrally brightened intensity and polarization maps. Circular polarization provides the cleanest observational tool for distinguishing the plasmas, as it increases outward from the jet core and central axis for highly ionic plasma, and is suppressed for pair dominated plasma. We find a measurable degree of circular polarization V/I of O(10e-3) for sub-equipartition hadronic jet plasmas. Our stationary model predicts that the intensity-normalized autocorrelation functions of Q and U increase and decrease with frequency, respectively. On the other hand, the autocorrelation of V is less sensitive to the frequency. Multi-band polarimetric observations could therefore be used as a novel probe of the composition of jet plasma.

1909.09632

Photometric redshift calibration with self organizing maps

Wright, Hildebrandt, van den Busch, Heymans

Accurate photometric redshift calibration is central to the robustness of all cosmology constraints from cosmic shear surveys. Analyses of the Kilo-Degree Survey, KiDS, re-weighted training samples from all overlapping spectroscopic surveys to provide a direct redshift calibration. Using self-organising maps (SOMs) we demonstrate that this spectroscopic compilation is sufficiently complete for KiDS, representing $99\%$ of the effective 2D cosmic shear sample. We use the SOM to define a $100\%$ represented `gold' cosmic shear sample, per tomographic bin. Using mock simulations of KiDS and the spectroscopic training set, we demonstrate that the mean redshift of the `gold' sample can be recovered by the SOM with an accuracy better than $| \Delta \langle z \rangle | < 0.004$, with the exception of the $0.7 < z_B < 0.9$ tomographic bin with $ |\Delta \langle z \rangle | = 0.011$. Photometric noise, sample variance, and spectroscopic selection effects induce a combined maximal scatter of $\sigma_{\Delta \langle z \rangle} < 0.007$ in all tomographic bins. We demonstrate that the previous direct redshift calibration method applied to the full cosmic shear sample is accurate to $| \Delta \langle z \rangle | < 0.025$. We find that photometric noise dominates the calibration dispersion, and that neither sampling variance nor a realistic fraction of spectroscopic misidentifications in the training set introduce significant bias.

1909.10314

Leadership and participation in NASA's explorer-class missions

Centrella, et al

We have conducted a data study of leadership and participation in NASA's Astrophysics Explorer-class missions for the nine solicitations issued during the period 2008-2016, using gender as a marker of diversity. During this time, 102 Principal Investigators (PIs) submitted Explorer-class proposals; only four of these PIs were female. Among the 102 PIs, there were 61 unique PIs overall; of these, just three were female. The percentage of females in science teams in these proposals ranges from a low of 10% to a high of 19% across the various solicitations. Combining data from all these Explorer-class proposals, we find that the overall participation by females in science teams is 14%. Eighteen of the Explorer-class proposals had zero females in science roles, and this includes science teams with as many as 28 members. These results demonstrate that participation by women in the leadership of and, in many cases, on the science teams of proposals for Explorer-class missions is well below the representation of women in astronomy and astrophysics as a whole. In this white paper, we present our data and a discussion of our results, their context, and the ramifications for consideration by Astro2020 in its study of the state of the profession.

1909.10540

Quiescent galaxies 1.5 billion years after the big bang and their progenitors

Valenetino, et al

We report two secure ($z=3.775,4.012$) and one tentative ($z\approx3.767$) spectroscopic confirmations of massive and quiescent galaxies close to their quenching epoch through $K$-band observations with Keck/MOSFIRE and VLT/X-Shooter. The stellar continuum emission, the absence of strong nebular emission lines and the lack of significant far-infrared detections confirm the passive nature of these objects, disfavoring the alternative solution of low-redshift dusty star-forming interlopers. We derive stellar masses of $\mathrm{log}(M_\star/M_\odot)\sim11$ and star formation rates placing these galaxies $\gtrsim1-2$ dex below the main sequence at their redshifts. The adopted parametrization of the star formation history suggests that these sources experienced a strong ($\langle\rm SFR\rangle\sim1200-3500\,M_\odot$yr$^{-1}$) and short ($\sim50$ Myr) burst of star formation, peaking $\sim 150-500$ Myr before the time of observation, all properties reminiscent of the characteristics of sub-millimeter galaxies (SMGs) at $z>4$. We investigate this connection by comparing the comoving number densities and the properties of these two populations. We find a fair agreement only with the deepest sub-mm surveys detecting not only the most extreme starbursts, but also more normal galaxies. We support these findings by further exploring the Illustris-TNG cosmological simulation, retrieving populations of both fully quenched massive galaxies at $z\sim3-4$ and SMGs at $z\sim4-5$, with number densities and properties in broad agreement with the observations at $z\sim3$, but in increasing tension at higher redshift. Nevertheless, as suggested by the observations, not all the progenitors of quiescent galaxies at these redshifts shine as bright SMGs in their past and, similarly, not all bright SMGs quench by $z\sim3$, both fractions depending on the threshold assumed to define the SMGs themselves. [Abridged]

1909.11006

Cosmology from large-scale structure: constraining $\Lambda$CDM with BOSS

Tröster, et al

We reanalyse the anisotropic galaxy clustering measurement from the Baryon Oscillation Spectroscopic Survey (BOSS), demonstrating that using the full shape information provides cosmological constraints that are comparable to other low-redshift probes. We find $\Omega_\mathrm{m} = 0.317^{+0.015}_{-0.019}$, $\sigma_8 = 0.710\pm 0.049$, and $h = 0.704\pm 0.024$ for flat $\Lambda$CDM cosmologies using uninformative priors on $\Omega_\mathrm{c}h^2$, $100\theta_\mathrm{MC}$, $\ln 10^{10} A_{s}$, and $n_{s}$, and a prior on $\Omega_\mathrm{b}h^2$ that is much wider than current constraints. We quantify the agreement between the Planck 2018 constraints from the cosmic microwave background and BOSS, finding the two data sets to be consistent within a flat $\Lambda$CDM cosmology using the Bayes factor as well as the prior-insensitive suspiciousness statistic. Combining two low-redshift probes, we jointly analyse the clustering of BOSS galaxies with weak lensing measurements from the Kilo-Degree Survey (KV450). The combination of BOSS and KV450 improves the measurement by up to 45%, constraining $\sigma_8 = 0.702\pm 0.029$ and $S_8 = \sigma_8\sqrt{\Omega_\mathrm{m}/0.3} = 0.728\pm 0.026$. Over the full 5D parameter space, the odds in favour of single cosmology describing galaxy clustering, lensing, and the cosmic microwave background are $7\pm2$. The suspiciousness statistic signals a $2.1\pm0.3\sigma$ tension between the combined low-redshift probes and measurements from the cosmic microwave background.