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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

The maximum extent of the filaments and sheets in the cosmic web: an analysis of the SDSS DR17

Filaments and sheets are striking visual patterns in cosmic web. The maximum extent of these large-scale structures are difficult to determine due to their structural variety and complexity. We construct a volume-limited sample of galaxies in a cubic region from the SDSS, divide it into smaller subcubes and shuffle them around. We quantify the average filamentarity and planarity in the 3D galaxy distribution as a function of the density threshold and compare them with those from the shuffled realizations of the original data. The analysis is repeated for different shuffling lengths by varying the size of the subcubes. The average filamentarity and planarity in the shuffled data show a significant reduction when the shuffling scales are smaller than the maximum size of the genuine filaments and sheets. We observe a statistically significant reduction in these statistical measures even at a shuffling scale of $\sim 130 \, {{\, \rm Mpc}}$, indicating that the filaments and sheets in three dimensions can extend up to this length scale. They may extend to somewhat larger length scales that are missed by our analysis due to the limited size of the SDSS data cube. We expect to determine these length scales by applying this method to deeper and larger surveys in future.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

The High Fraction of Thin Disk Galaxies Continues to Challenge ΛCDM Cosmology

Any viable cosmological framework has to match the observed proportion of early- and late-type galaxies. In this contribution, we focus on the distribution of galaxy morphological types in the standard model of cosmology (Lambda cold dark matter, ΛCDM). Using the latest state-of-the-art cosmological ΛCDM simulations known as Illustris, IllustrisTNG, and EAGLE, we calculate the intrinsic and sky-projected aspect ratio distribution of the stars in subhalos with stellar mass M * > 10 10 M ⊙ at redshift z = 0. There is a significant deficit of intrinsically thin disk galaxies, which however comprise most of the locally observed galaxy population. Consequently, the sky-projected aspect ratio distribution produced by these ΛCDM simulations disagrees with the Galaxy And Mass Assembly (GAMA) survey and Sloan Digital Sky Survey at ≥12.52σ (TNG50-1) and ≥14.82σ (EAGLE50) confidence. The deficit of intrinsically thin galaxies could be due to a much less hierarchical merger-driven build-up of observed galaxies than is given by the ΛCDM framework. It might also arise from the implemented sub-grid models, or from the limited resolution of the above-mentioned hydrodynamical simulations. We estimate that an 8 5 times better mass resolution realization than TNG50-1 would reduce the tension with GAMA to the 5.58σ level. Finally, we show that galaxies with fewer major mergers have a somewhat thinner aspect ratio distribution. Given also the high expected frequency of minor mergers in ΛCDM, the problem may be due to minor mergers. In this case, the angular momentum problem could be alleviated in Milgromian dynamics because of a reduced merger frequency arising from the absence of dynamical friction between extended dark matter halos.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1988

A particle astrophysics magnet facility: ASTROMAG

The primary scientific objectives of ASTROMAG are to: examine cosmological models by searching for antimatter and dark matter candidates; study the origin and evolution of matter in the galaxy by direct sampling of galactic matter; and study the origin and acceleration of the relativistic particle plasma in the galaxy and its effects on the dynamics and evolution of the galaxy. These general scientific objectives will be met by ASTROMAG with particle detection instruments designed to make the following observations: search, for anti-nuclei of helium and heavier element; measure the spectra of anti-protons and positrons; measure the isotopic composition of cosmic ray nuclei at energies of several GeV/amu; and measure the energy spectra of cosmic ray nuclei to very high energies.

Ormes, Jonathan F.↗
NASA NTRS1989

Gravitational instability in a primordial collapsing gas cloud

This paper presents an analysis of the linear evolution of short-wavelength perturbations in a background fluid flow which is undergoing gravitational collapse on large scales. Local evolution equations for perturbations to an arbitrary flow are derived in the linear regime and the short-wavelength limit. Local perturbation behavior in an inhomogeneous flow is found to be the same as that in a homogeneous anisotropic flow having the same local velocity field. Background flows in which the scale factors vary as power laws in time are considered to illustrate the relative effects of self-gravity, pressure and kinematics of the background flow on the density perturbation evolution. Perturbation analyses are then presented for more realistic background flows arising from the evolution into the nonlinear regime of initially small density perturbations in an isotropically expanding cosmological model. For low-pressure, inhomogeneous collapses, kinematic effects tend to dominate over self-gravity in driving perturbation growth as the collapse proceeds.

Lacey, Cedric G.↗
NASA NTRS1993

The consistency of standard cosmology and the BATSE number versus brightness relation

The integrated number-peak-flux relation measured by the Burst and Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory is compared with several standard cosmological distributions for gamma-ray bursts (GRBs). Friedmann-Robertson-Walker models were used along with the assumption that the bursts are standard candles and have no number or luminosity evolution. For a given Omega spectral shape, we used a free parameter, essentially the comoving number density of bursts, to generate a best fit between the cosmology and the measured relation. Our results are shown for a subsample of the first 260 GRBs recorded by BATSE. We find acceptable fits between simple cosmological models and the brightness distribution data, as determined by the Kolmogorov-Smirnov one-distribution statistical test. One cannot distinguish a single best cosmological model from the goodness of the fits. The best fit implies that BATSE GRBs are complete out to a redshift of about unity. However, significantly higher and lower redshifts, by as much as a factor of 2, are possible for other marginally acceptable fits.

Wickramasinghe, W. A. D. T.↗
NASA NTRS1993

Angular diameters as a probe of a cosmological constant and Omega

The lensing effect of curved space, which can cause the angular diameter of a fixed reference length seen on the sky to reach a minimum and then increase with redshift, has recently been claimed to provide evidence, using compact radio sources, for a q sub 0 = 1/2 expansion. We show here that this relation, in particular the position of the observed minimum, depends sensitively on the value of the cosmological constant, Lambda, in a flat universe. The sensitivity to a nonzero Lambda in a flat universe is compared to the sensitivity to q sub 0 in an open universe without a cosmological constant. The reported results could provide the strongest available limit on the cosmological constant in a flat universe (and on Omega in an open universe) and so we explore how uncertainties in distance measures and evolution of the sources can affect the results. Evolution of less than 30 percent in source size for z of less than 2 can completely alter the results, and so must be convincingly ruled out if this technique is to provide a new tool for cosmology.

Krauss, Lawrence M.↗
DOE OSTI2023

A semi-analytic study of self-interacting dark-matter haloes with baryons

ABSTRACT We combine the isothermal Jeans model and the model of adiabatic halo contraction into a semi-analytic procedure for computing the density profile of self-interacting dark-matter (SIDM) haloes with the gravitational influence from the inhabitant galaxies. The model agrees well with cosmological SIDM simulations over the entire core-forming stage up to the onset of gravothermal core-collapse. Using this model, we show that the halo response to baryons is more diverse in SIDM than in CDM and depends sensitively on galaxy size, a desirable feature in the context of the structural diversity of bright dwarfs. The fast speed of the method facilitates analyses that would be challenging for numerical simulations – notably, we quantify the SIDM halo response as functions of the baryonic properties, on a fine mesh grid spanned by the baryon-to-total-mass ratio, Mb/Mvir, and galaxy compactness, r1/2/Rvir; we show with high statistical precision that for typical Milky-Way-like systems, the SIDM profiles are similar to their CDM counterparts; and we delineate the regime of core-collapse in the Mb/Mvir − r1/2/Rvir space, for a given cross section and concentration. Finally, we compare the isothermal Jeans model with the more sophisticated gravothermal fluid model, and show that the former yields faster core formation and agrees better with cosmological simulations. We attribute the difference to whether the target CDM halo is used as a boundary condition or as the initial condition for the gravothermal evolution, and thus comment on possible improvements of the fluid model. We have made our model publicly available at https://github.com/JiangFangzhou/SIDM.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1996

Cosmological Implications of the Effects of X-Ray Clusters on the Cosmic Microwave Background

We have been carrying forward a program to confront X-ray observations of clusters and their evolution as derived from X-ray observatories with observations of the cosmic microwave background radiation (CMBR). In addition to the material covered in our previous reports (including three published papers), most recently we have explored the effects of a cosmological constant on the predicted Sunyaev-Zel'dovich effect from the ensemble of clusters. In this report we summarize that work from which a paper will be prepared.

Forman, William R.↗
DOE OSTI2023

No redshift evolution in the rest-frame ultraviolet emission line properties of quasars from z = 1.5 to z = 4.0

We analyse the rest-frame ultraviolet (UV) spectra of 2531 high-redshift (3.5 < z < 4.0) quasars from the Sloan Digital Sky Survey DR16Q catalogue. In combination with previous work, we study the redshift evolution of the rest-frame UV line properties across the entire redshift range, 1.5 < z < 4.0. We improve the systemic redshift estimates at z > 3.5 using a cross-correlation algorithm that employs high signal-to-noise template spectra spanning the full range in UV emission line properties. We then quantify the evolution of C iv and He ii emission line properties with redshift. The increase in C iv blueshifts with cosmological redshift can be fully explained by the higher luminosities of quasars observed at high redshifts. We recover broadly similar trends between the He ii equivalent width and C iv blueshift at both 1.5 < z < 2.65 and 3.5 < z < 4.0 suggesting that the blueshift depends systematically on the spectral energy density (SED) of the quasar and there is no evolution in the SED over the redshift range 1.5 < z < 4.0. C iv blueshifts are highest when L/L Edd ≥ 0.2 and M BH ≥ 10 9 M ⊙ for the entire 1.5 < z < 4.0 sample. We find that luminosity matching samples as a means to explore the evolution of their rest-frame UV emission line properties is only viable if the samples are also matched in the M BH –L/L Edd plane. Quasars at z ≥ 6 are on average less massive and have higher Eddington-scaled accretion rates than their luminosity-matched counterparts at 1.5 < z < 4.0, which could explain the observed evolution in their UV line properties.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

The large scale polarization explorer (LSPE) for CMB measurements: performance forecast

The measurement of the polarization of the Cosmic Microwave Background (CMB) radiation is one of the current frontiers in cosmology. In particular, the detection of the divergence-free component of the polarization field, the B-mode component, reveals the presence of gravitational waves in the early Universe. The detection of such component is at the moment the most promising technique to probe the inflationary theory describing the very early evolution of the Universe. The measurement of the polarization of the Cosmic Microwave Background (CMB) radiation is one of the current frontiers in cosmology. In particular, the detection of the primordial divergence-free component of the polarization field, the B-mode, could reveal the presence of gravitational waves in the early Universe. The detection of such a component is at the moment the most promising technique to probe the inflationary theory describing the very early evolution of the Universe. We present the updated performance forecast of the Large Scale Polarization Explorer (LSPE), a program dedicated to the measurement of the CMB polarization. LSPE is composed of two instruments: LSPE-Strip, a radiometer-based telescope on the ground in Tenerife-Teide observatory, and LSPE-SWIPE (Short-Wavelength Instrument for the Polarization Explorer) a bolometer-based instrument designed to fly on a winter arctic stratospheric long-duration balloon. The program is among the few dedicated to observation of the Northern Hemisphere, while most of the international effort is focused into ground-based observation in the Southern Hemisphere. Measurements are currently scheduled in Winter 2022/23 for LSPE-SWIPE, with a flight duration up to 15 days, and in Summer 2022 with two years observations for LSPE-Strip. In this work, we describe the main features of the two instruments, identifying the most critical aspects of the design, in terms of impact on the performance forecast. We estimate the expected sensitivity of each instrument and propagate their combined observing power to the sensitivity to cosmological parameters, including the effect of scanning strategy, component separation, residual foregrounds and partial sky coverage. We also set requirements on the control of the most critical systematic effects and describe techniques to mitigate their impact. LSPE will reach a sensitivity in tensor-to-scalar ratio of σr < 0.01, set an upper limit r < 0.015 at 95% confidence level, and improve constraints on other cosmological parameters.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

New constraints on warm dark matter from the Lyman- α forest power spectrum

The forest of Lyman-α absorption lines detected in the spectra of distant quasars encodes information on the nature and properties of dark matter and the thermodynamics of diffuse baryonic material. Its main observable—the 1D flux power spectrum (FPS)—should exhibit a suppression on small scales and an enhancement on large scales in warm dark matter (WDM) cosmologies compared to standard Λ⁢CDM. Here, we present an unprecedented suite of 1080 high-resolution cosmological hydrodynamical simulations run with the graphics processing unit-accelerated code cholla to study the evolution of the Lyman-α forest under a wide range of physically motivated gas thermal histories along with different free-streaming lengths of WDM thermal relics in the early Universe. A statistical comparison of synthetic data with the forest FPS measured down to the smallest velocity scales ever probed at redshifts 4.0≲z≲5.2 [E. Boera et al., Revealing reionization with the thermal history of the intergalactic medium: New constraints from the Ly⁢α flux power spectrum, Astrophys. J. 872, 101 (2019)] yields a lower-limit m WDM >3.1 keV (95% C.L.) for the WDM particle mass and constrains the amplitude and spectrum of the photoheating and photoionizing background produced by star-forming galaxies and active galactic nuclei at these redshifts. Interestingly, our Bayesian inference analysis appears to weakly favor WDM models with a peak likelihood value at the thermal relic mass of m WDM =4.5 keV. In conclusion, we find that the suppression of the FPS from free-streaming saturates at k≳0.1 s km -1 because of peculiar velocity smearing, and this saturated suppression combined with a slightly lower gas temperature provides a moderately better fit to the observed small-scale FPS for WDM cosmologies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Supernova Cosmology with the Dark Energy Survey

This proposal requests supplemental funds to addresses our continued effort to carry out a Type Ia supernova (SN Ia) cosmology analysis with the Dark Energy Survey (DES) data. DES is well underway to discovering and identifying thousands of SN Ia out to a cosmological redshift of z =1.2 over its 5-year survey, and will obtain the best constraints on dark energy and its possible evolution with redshift. We propose to develop two key analysis algorithms and tools that are critical for this achieving the goals: 1) a final photometry pipeline that uses novel techniques to extract unbiased SN fluxes from the images and 2) a robust statistical framework for measuring cosmological parameters from SN Ia light curves with well-characterized systematic uncertainties.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Perturbation theory for modeling galaxy bias: validation with simulations of the Dark Energy Survey

We describe perturbation theory (PT) models of galaxy bias for applications to photometric galaxy surveys. We model the galaxy-galaxy and galaxy-matter correlation functions in configuration space and validate against measurements from mock catalogs designed for the Dark Energy Survey (DES). We find that an effective PT model with five galaxy bias parameters provides a good description of the 3D correlation functions above scales of 4 Mpc/$h$ and $z < 1$. Our tests show that at the projected precision of the DES-Year 3 analysis, two of the non-linear bias parameters can be fixed to their co-evolution values, and a third (the $k^2$ term for higher derivative bias) set to zero. The agreement is typically at the 2 percent level over scales of interest, which is the statistical uncertainty of our simulation measurements. To achieve this level of agreement, our {\it fiducial} model requires using the full non-linear matter power spectrum (rather than the 1-loop PT one). We also measure the relationship between the non-linear and linear bias parameters and compare them to their expected co-evolution values. We use these tests to motivate the galaxy bias model and scale cuts for the cosmological analysis of the Dark Energy Survey; our conclusions are generally applicable to all photometric surveys.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Anisotropic Satellite Galaxy Quenching: A Unique Signature of Energetic Feedback by Supermassive Black Holes?

The quenched fraction of satellite galaxies is aligned with the orientation of the halo's central galaxy, such that on average, satellites form stars at a lower rate along the major axis of the central. This effect, called anisotropic satellite galaxy quenching (ASGQ), has been found in observational data and cosmological simulations. Analyzing the IllustrisTNG simulation, Martín-Navarro et al. recently argued that ASGQ is caused by anisotropic energetic feedback and constitutes "compelling observational evidence for the role of black holes in regulating galaxy evolution." In this Letter, we study the causes of ASGQ in state-of-the-art galaxy formation simulations to evaluate this claim. We show that cosmological simulations predict that on average, satellite galaxies along the major axis of the dark matter halo tend to have been accreted at earlier cosmic times and are hosted by subhalos of larger peak halo masses. As a result, a modulation of the quenched fraction with respect to the major axis of the central galaxy is a natural prediction of hierarchical structure formation. We show that ASGQ is predicted by the UniverseMachine galaxy formation model, a model without anisotropic feedback. Furthermore, we demonstrate that even in the IllustrisTNG simulation, anisotropic satellite accretion properties are the main cause of ASGQ. Ultimately, we argue that ASGQ is not a reliable indicator of supermassive black hole feedback in galaxy formation simulations and, thus, should not be interpreted as such in observational data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) – XV. Constraining the cosmic reionization at 5.5 < z < 7

ABSTRACT Revealing the cosmic hydrogen reionization history is one of the main goals of the modern cosmology. z > 5 quasars (QSOs) have been used as back-lights to investigate the evolution of the intervening intergalactic medium (IGM) during the cosmic reionization since their first discovery. However, due to the small population of luminous QSOs (∼130 QSOs known to date), a tight constraint on the reionization history has not yet been placed. In this work, we aim to tighten the constraint using the 93 QSOs (5.5 < z < 7.1) recently discovered in the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQS) project. This is the largest QSO sample used to constrain the epoch of reionization. We measure the mean IGM Ly α transmission and the QSO near-zone size using the UV spectra of these QSOs. The mean IGM Ly α transmission rises above zero at z ≲ 6, indicating the end of the reionization. The near-zone sizes of the SHELLQs QSOs are consistent with sizes spanned by QSOs of lifetime tq ∼ 1–100 Myr in simulations. Due to the scatter created by the low signal-to-noise spectra and large Ly α redshift uncertainty, we cannot conclude whether the redshift evolution of the near-zone size is affected by the reionization effect.

Lu, Ting-Yi (ORCID:0000000249656524)↗
DOE OSTI2024

Predictions for a Low-mass Cutoff for the Primordial Black Hole Mass Spectrum

In this note, we outline how a modest violation in the conservation of mass during the merger of two PBHs affects the PBH mass spectrum that we previously obtained using a Boltzmann equation model for the evolution of the mass spectrum with no mass loss. We find that if the initial cosmological redshift is of the order of 10 12 , then the fraction of primordial holes with masses greater than 10 3 solar masses appears to be close to what is required to provide the seeds for galaxies. In addition, we note that as a result of rapid collisions and strong coupling to electromagnetic radiation for temperatures > GeV, there will be an effective low-mass cutoff in the mass spectrum for PBH masses less than a certain PBH mass less than 0.1M ⊙ . We also point out that this cutoff in the mass spectrum below ~ 0.1M ⊙ can be confirmed by combining future microlensing observations from the Roman Space Telescope and the Vera C. Rubin Observatory with astrometric observations.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1977

Dirac cosmology

The large numbers hypothesis (LNH) linking the magnitude of large dimensionless ratios in physics (on the order of 10 to the 40th power) to cosmic time is examined. The LNH is checked against evidence on 3K background radiation of the universe and the (log N, log S)-relation for radio galaxies. Earlier criticisms of LNH by Gamow and Teller are examined, and alternative hypotheses put forth by Dicke and Carter (1974) are discussed. The discussion covers: continuous (additive or multiplicative) creation of matter, the Einstein metric and the atomic metric, and general cosmological and local astronomical implications of LNH. LNH is also viewed in relation to solar evolution and pulsar physics.

Canuto, V.↗
NASA NTRS2003

Physics of Galaxy Clusters and How it Affects Cosmological Tests

We have worked on the analysis of the Chandra observations of the distant clusters of galaxies, and on exploring new ways to obtain cosmological constraints from the cluster data. Some of the scientific results are discussed below: (1) Evolution of the cluster scaling relations at z is approximately 0.5; (2) Using gas mass as a proxy for the total cluster mass.

Vikhlinin, Alexey↗