arXiv subjects

George Smoot

Publications and source records attributed to George Smoot.

At least 19 recordsLinked to original sources

arXiv2025

Explaining JWST counts with galaxy formation models

A distinct power-law break is apparent m_AB approximately 21 in the deep Near-Infrared PEARLS-JWST galaxy counts. The break becomes more pronounced at longer wavelengths, with the counts slope flattening smoothly with apparent magnitude in the shortest band used at 0.9 microns, trending towards an increasingly broken slope by the longest wavelength passband of JWST NIRCam, 4.4 microns. This behaviour is remarkably well predicted by the GALFORM semi-analytical model of galaxy formation. We use the model to diagnose the origin of this behaviour. We find that the features that are responsible for the break are: 1) the inherent break in the luminosity function; 2) the change in the volume element with redshift and 3) the redshift-dependent nature of the k-correction. We study the contribution to these effects by early and late-type galaxies, using as a proxy for morphology the bulge-to-total stellar mass ratio. We find that the way in which ellipticals populate the bright end of the luminosity function while spirals dominate the faint end is preserved in the galaxy number counts, with a characteristic stellar mass at the break of approximately 10^10 M_sun. We also find that the shape of the number counts is mainly driven by galaxies with relatively low redshift (z < 2) for the PEARLS observational limit of m_AB < 28. We give a comprehensive description of why the galaxy number counts in the near-infrared PEARLS-JWST observation look the way they do and which population of galaxies is dominant at each apparent magnitude.

astro-ph.GA↗

arXiv2024

PASO -- Astronomy and Space Situational Awareness in a Dark Sky Destination

The Pampilhosa da Serra Space Observatory (PASO) is located in the center of the continental Portuguese territory, in the heart of a certified Dark Sky destination by the Starlight Foundation (Aldeias do Xisto) and has been an instrumental asset to advance science, education and astrotourism certifications. PASO hosts astronomy and Space Situational Awareness (SSA) activities including a node of the Portuguese Space Surveillance \& Tracking (SST) infrastructure network, such as a space radar currently in test phase using GEM radiotelescope, a double Wide Field of View Telescope system, a EUSST optical sensor telescope. These instruments allow surveillance of satellite and space debris in LEO, MEO and GEO orbits. The WFOV telescope offers spectroscopy capabilities enabling light curve analysis and cosmic sources monitoring. Instruments for Space Weather are being considered for installation to monitor solar activities and expand the range of SSA services.

astro-ph.IM↗

arXiv2023

Galaxy formation with wave/fuzzy dark matter: The core-halo structure and the solitonic imprint

Dark matter-dominated cores have long been claimed for the well-studied local group dwarf galaxies. More recently, extended stellar halos have been uncovered around several of these dwarfs through deeper imaging and spectroscopy. Such core-halo structures are not a feature of conventional cold dark matter (CDM). In contrast, smooth and prominent dark matter cores are predicted for wave/fuzzy dark matter ($\psi$DM). The question arises as to what extent the visible stellar profiles should reflect this dark matter core structure. Here we compare cosmological hydrodynamical simulations of CDM, ``WDM'' (model used as a proxy for $\psi$DM) \& $\psi$DM, aiming to predict the stellar profiles for these three DM scenarios. We show that cores surrounded by extended halos are distinguishable for $\psi$DM, where the stellar density is enhanced in the core due to the presence of the relatively dense soliton. Our analysis demonstrates that, in our simulations, a distinctive core-halo structure does not appear in the case of CDM in the DM, gas, or stars. Whereas we do find a core-halo transition for DM, gas, and stars for $\psi$DM, and the scale of this transition is in line with the predicted core radius set by the soliton scale anticipated for the adopted boson mass of 2.5$\times10^{-22}$eV. The presence of a core-halo structure in the stellar profile for Galaxy 1 for $\psi$DM is visible for the most massive and the first galaxy to form in the simulation. Clearly, further simulations are needed to establish how strict this possible relationship is between the DM and stellar core-halo profile as a potential observational discriminator. Furthermore, we observe the anticipated asymmetry for $\psi$DM due to the soliton's motion (jumping and random walk), a distinctive characteristic not found in the symmetric distributions of stars in the warm and CDM models.

astro-ph.CO↗

arXiv2021

Evidence for lensing of gravitational waves from LIGO-Virgo

Recently, the LIGO-Virgo Collaboration (LVC) concluded that there is no evidence for lensed gravitational waves (GW) in the first half of the O3 run, claiming "We find the observation of lensed events to be unlikely, with the fractional rate at $μ>2$ being $3.3\times 10^{-4}$". While we agree that the chance of an individual GW event being lensed at $μ>2$ is smaller than $10^{-3}$, the number of observed events depends on the product of this small probability times the rate of mergers at high redshift. Observational constraints from the stochastic GW background indicate that the rate of conventional mass BBH mergers (8 < M (M$_{\odot}$) < 15) in the redshift range 1<z< 2 could be as high as O($10^7$) events per year, more than sufficient to compensate for the intrinsically low probability of lensing. To reach the LVC trigger threshold these events require high magnification, but would still produce up to 10 to 30 LVC observable events per year. Thus, all the LVC observed ordinary stellar mass BBH mergers from this epoch must be strongly lensed. By adopting low-rates at high redshift, LVC assumes that lensed events can not be taking place, thus incorrectly assigning them a closer distance and higher masses by a factor of a few (typically 2 to 5). The LVC adopted priors on time delay are in tension with the distribution of observed time delays in lensed quasars. Pairs of events like GW190421-GW190910 and GW190424-GW190910, which are directly assigned a probability of zero by LVC, should be instead considered as prime candidates to be strongly lensed GW pairs, since their separation in time is consistent with observations of time delays in lensed quasars. Correcting for the LVC wrong Bayesian priors, maximum merger rate of conventional mass BBH in 1<z<2, and gravitational lensing time-delay model, reverses the LVC conclusions and supports the strong gravitational lensing hypothesis.

gr-qc↗

arXiv2021

Constraining HeII Reionization Detection Uncertainties via Fast Radio Bursts

Context. The increased detection rate of Fast Radio Bursts (FRBs) makes it likely to get samples of sizes $\mathcal{O}(10^2)$ to $\mathcal{O}(10^3)$ in the near future. Because of their extragalactic origin can help us in understanding the epoch of helium reionization. Aims. We try to identify the epoch of Helium II (HeII) reionization, via the observations of early FRBs in range of $z=3$ to $4$. Methods. We build a model of FRB Dispersion Measure following the HeII reionization model, density fluctuation in large scale structure, host galaxy interstellar medium and local environment of FRB contribution. The model is fit to the ideal intergalactic medium (IGM) dispersion measure model to check the goodness of constraining the HeII reionization via FRB measurement statistics. Conclusion. We report our findings under two categories, accuracy in detection of HeII reionization via FRBs assuming no uncertainty in the redshift measurement and alternatively assuming a varied level of uncertainty in redshift measurement of the FRBs. We show that under the first case, a detection of $N\sim\mathcal{O} (10^2)$ FRBs give an uncertainty of $σ(z_{r, fit})\sim0.5$ from the fit model, and a detection of $N\sim\mathcal{O} (10^3)$ gives an uncertainty of $σ(z_{r, fit})\sim0.1$. While assuming a redshift uncertainty of level $5-20\%$, changes the $σ(z_{r, fit})\sim0.5$ to $0.6$ for $N\sim 100$ and $σ(z_{r, fit})\sim0.1$ to $0.15$ for $N \sim 1000$ case.

astro-ph.HE↗

arXiv2020

A Soliton Solution for the Central Dark Masses in 47- Tuc Globular Cluster and Implications for the Axiverse

We offer a standing wave explanation for the rising proper motions of stars at the center of the globular cluster 47-Tucanae, amounting to $\simeq 0.44\%$ of the total mass. We show this can be explained as a solitonic core of dark matter composed of light bosons, $ m \geq 10^{-18} eV $, corresponding to $ \leq 0.27 pc$, as an alternative to a single black hole (BH) or a concentration of stellar BH remnants proposed recently. This is particularly important as having a concentrated stellar BH remnant with the above radii is very challenging without the heavy core since the three body encounters would prevent the BHs to be that concentrated. We propose this core develops from dark matter captured in the deep gravitational potential of this globular cluster as it orbits the dark halo of our galaxy. This boson may be evidence for a second light axion, additional to a lighter boson of $10^{-22} eV$, favored for the dominant dark matter implied by the large dark cores of dwarf spheroidal galaxies. The identification of two such light bosonic mass scales favors the generic string theory prediction of a wide, discrete mass spectrum of axionic scalar fields.

astro-ph.CO↗

arXiv2019

Evidence of Neutrino Enhanced Clustering in a Complete Sample of Sloan Survey Clusters, Implying $\sum m_ν= 0.119 \pm 0.034$ eV

The clustering amplitude of 7143 clusters from the Sloan Digital Sky Survey (SDSS) is found to increase with cluster mass, closely agreeing with the Gaussian random field hypothesis for structure formation. The amplitude of the observed cluster correlation exceeds the predictions from pure cold dark matter (CDM) simulation by $\simeq 6\%$ for the standard Planck-based values of the cosmological parameters. We show that this excess can be naturally accounted for by free streaming of light neutrinos, which opposes gravitational growth, so clusters formed at fixed mass are fewer and hence more biased than for a pure CDM density field. An enhancement of the cluster bias by 7\% matches the observations, corresponding to a total neutrino mass, $m_ν = 0.119 \pm 0.034$ eV at 67\% confidence level, for the standard relic neutrino density. If ongoing laboratory experiments favor a normal neutrino mass hierarchy then we may infer a somewhat larger total mass than the minimum oscillation based value, $\sum m_ν \simeq 0.056eV$, with 90\% confidence. Much higher precision can be achieved by applying our method to a larger sample of more distant clusters with weak lensing derived masses.

astro-ph.CO↗

arXiv2019

Mergers of black hole-neutron star binaries and rates of associated electromagnetic counterparts

Black hole-neutron star (BHNS) binaries are amongst promising candidates for the joint detection of electromagnetic (EM) signals with gravitational waves (GWs) and are expected to be detected in the near future. Here we study the effect of the BHNS binary parameters on the merger ejecta properties and associated EM signals. We estimate the remnant disk and unbound ejecta masses for BH mass and spin distributions motivated from the observations of transient low-mass X-ray binaries (LMXBs) and specific NS equation of state (EoS). The amount of r-process elements synthesised in BHNS mergers is estimated to be a factor of $\sim 10^{2}-10^{4}$ smaller than BNS mergers, due to the smaller dynamical ejecta and merger rates for the former. We compute the EM luminosities and light curves for the early- and late-time emissions from the ultra-relativistic jet, sub-relativistic dynamical ejecta and wind, and the mildly-relativistic cocoon for typical ejecta parameters. We then evaluate the low-latency EM follow-up rates of the GW triggers in terms of the GW detection rate $\dot{N}_{GW}$ for current telescope sensitivities and typical BHNS binary parameters to find that most of the EM counterparts are detectable for high BH spin, small BH mass and stiffer NS EoS when NS disruption is significant. Based on the relative detection rates for given binary parameters, we find the ease of EM follow-up to be: ejecta afterglow $>$ cocoon afterglow $\gtrsim$ jet prompt $>$ ejecta macronova $>$ cocoon prompt $>$ jet afterglow $>>$ wind macronova $>>$ wind afterglow.

astro-ph.HE↗

arXiv2019

Detecting Axion-like Dark Matter with Linearly Polarized Pulsar Light

Non-relativistic QCD axions or axion-like particles are among the most popular candidates for cold Dark Matter (DM) in the universe. We proposed to detect axion-like DM, using linearly polarized pulsar light as a probe. Because of birefringence effect potentially caused by an oscillating galactic axion DM background, when pulsar light travels across the galaxy, its linear polarization angle may vary with time. With a soliton+NFW galactic DM density profile, we show that this strategy can potentially probe an axion-photon coupling as small as $\sim 10^{-13}$ GeV$^{-1}$ for axion mass $m_a \sim 10^{-22}-10^{-20}$ eV, given the current measurement accuracy. An exclusion limit stronger than CAST ($ \sim 10^{-10}$ GeV$^{-1}$) and SN1987A ($ \sim 10^{-11}$ GeV$^{-1}$) could be extended up to $m_a \sim 10^{-18}$ eV and $\sim 10^{-19}$ eV, respectively.

astro-ph.CO↗

arXiv2018

Thermal and non-thermal emission from the cocoon of a gamma-ray burst jet

We present hydrodynamic simulations of the hot cocoon produced when a relativistic jet passes through the gamma-ray burst (GRB) progenitor star and its environment, and we compute the lightcurve and spectrum of the radiation emitted by the cocoon. The radiation from the cocoon has a nearly thermal spectrum with a peak in the X-ray band, and it lasts for a few minutes in the observer frame; the cocoon radiation starts at roughly the same time as when $γ$-rays from a burst trigger detectors aboard GRB satellites. The isotropic cocoon luminosity ($\sim 10^{47}$ erg s$^{-1}$) is of the same order of magnitude as the X-ray luminosity of a typical long-GRB afterglow during the plateau phase. This radiation should be identifiable in the Swift data because of its nearly thermal spectrum which is distinct from the somewhat brighter power-law component. The detection of this thermal component would provide information regarding the size and density stratification of the GRB progenitor star. Photons from the cocoon are also inverse-Compton (IC) scattered by electrons in the relativistic jet. We present the IC lightcurve and spectrum, by post-processing the results of the numerical simulations. The IC spectrum lies in 10 keV--MeV band for typical GRB parameters. The detection of this IC component would provide an independent measurement of GRB jet Lorentz factor and it would also help to determine the jet magnetisation parameter.

astro-ph.HE↗

arXiv2017

Observational Constraints on the Primordial Curvature Power Spectrum

CMB observations provide a precise measurement of the primordial power spectrum on large scales, corresponding to wavenumbers $10^{-3}$ Mpc$^{-1}$ < k < 0.1 Mpc$^{-1}$, [1-8]. Luminous red galaxies and galaxy clusters probe the matter power spectrum on overlapping scales (0.02 Mpc$^{-1}$ < k < 0.7 Mpc$^{-1}$ [9-18]), while the Lyman-alpha forest reaches slightly smaller scales (0.3 Mpc$^{-1} < k < 3$ Mpc$^{-1}$; [19]). These observations indicate that the primordial power spectrum is nearly scale-invariant with amplitude close to $2 \times 10^{-9}$, [5, 20-25]. They also strongly support Inflation and motivate us to obtain constraints reaching to smaller scales on the primordial curvature power spectrum and by implication on Inflation. One could obtain limits to much higher values of $k < 10^5$ Mpc$^{-1}$ and with less sensitivity even higher to $k < 10^{19}- 10^{23}$ Mpc$^{-1}$ using limits from CMB spectral distortions(SD)and on ultracompact minihalo objects(UCMHs)and Primordial Black Holes(PBHs). In this paper, we revisit and collect all the known constraints on both PBHs and UCMHs. We show that unless one uses SD, PBHs give us very relaxed bounds on the primordial curvature perturbations. UCMHs are very informative over a reasonable $k$ range($3 < k < 10^6$ Mpc$^{-1}$)and lead to significant upper-bounds on the curvature spectrum. We review the conditions under which the tighter constraints on the UCMHs could imply extremely strong bounds on the fraction of Dark Matter that could be PBHs. Failure to satisfy these conditions would lead to over production of the UCMHs, which is inconsistent with the observations. Therefore, we can almost rule out PBH within their overlap scales with the UCMHs. We consider the UCMH bounds from experiments such as $γ$-rays, Neutrinos, Reionization, pulsar-timing and SD. We show that they lead to comparable results independent of the form of DM.

astro-ph.CO↗

arXiv2011

Cosmology today-A brief review

This is a brief review of the standard model of cosmology. We first introduce the FRW models and their flat solutions for energy fluids playing an important role in the dynamics at different epochs. We then introduce different cosmological lengths and some of their applications. The later part is dedicated to the physical processes and concepts necessary to understand the early and very early Universe and observations of it.

astro-ph.CO↗

arXiv2010

Design of an IF section for C band polarimetry

In the context of the Galactic Emission Mapping, a new receiver at 5GHz was developed to characterize the galactic foreground to the Cosmic Microwave Background Radiation. This is a 5GHz super heterodyne polarimeter with double down conversion, with a high gain IF chain using the latest RF technology working at 600MHz central frequency that feeds a four channel digital correlator. This paper describes the receiver and its current status. Design options and constraints are presented with some simulations and experimental results of a circuit prototype.

astro-ph.IM↗

arXiv2010

Digital Complex Correlator for a C-band Polarimetry survey

The international Galactic Emission Mapping project aims to map and characterize the polarization field of the Milky Way. In Portugal it will cartograph the C-band sky polarized emission of the Northern Hemisphere and provide templates for map calibration and foreground control of microwave space probes like ESA Planck Surveyor mission. The receiver system is equipped with a novel receiver with a full digital back-end using an Altera Field Programmable Gate Array, having a very favorable cost/performance relation. This new digital backend comprises a base-band complex cross-correlator outputting the four Stokes parameters of the incoming polarized radiation. In this document we describe the design and implementation of the complex correlator using COTS components and a processing FPGA, detailing the method applied in the several algorithm stages and suitable for large sky area surveys.

astro-ph.IM↗

arXiv2009

BigBOSS: The Ground-Based Stage IV Dark Energy Experiment

The BigBOSS experiment is a proposed DOE-NSF Stage IV ground-based dark energy experiment to study baryon acoustic oscillations (BAO) and the growth of structure with an all-sky galaxy redshift survey. The project is designed to unlock the mystery of dark energy using existing ground-based facilities operated by NOAO. A new 4000-fiber R=5000 spectrograph covering a 3-degree diameter field will measure BAO and redshift space distortions in the distribution of galaxies and hydrogen gas spanning redshifts from 0.2<z<3.5. The Dark Energy Task Force figure of merit (DETF FoM) for this experiment is expected to be equal to that of a JDEM mission for BAO with the lower risk and cost typical of a ground-based experiment. This project will enable an unprecedented multi-object spectroscopic capability for the U.S. community through an existing NOAO facility. The U.S. community would have access directly to this instrument/telescope combination, as well as access to the legacy archives that will be created by the BAO key project.

astro-ph.CO↗

arXiv2007

Design of an IF section for a Galactic Emission Mapping experiment

In the context of the Galactic Emission Mapping collaboration, a galactic survey at 5GHz is in preparation to properly characterize the galactic foreground to the Cosmic Microwave Background Radiation (CMBR). For the North sky survey, a new receiver is being developed. This 5GHz heterodyne polarimeter has a high gain IF (intermediate frequency) chain using the latest RF technology and microstrip design that we describe in the present article. Working at 600MHz central frequency, it consists of a pre-amplifier with an integral band-pass filter followed by an amplifier with digitally controlled gain and a frequency converter to zero-IF that feeds the ADC of a four channel digital correlator (outside the scope of the present article). This paper focuses the design options and constraints and presents the simulations and experimental results of a circuit prototype.

astro-ph↗

arXiv2006

Cosmic Microwave Background Mini-Review

A compact overview of the status of CMB anisotropy results and their cosmological interpretation up until the end of 2005. Sections headings: Introduction; Description of CMB Anisotropies; Cosmological Parameters; Physics of Anisotropies; Current Anisotropy Data; CMB Polarization; Complications; Constraints on Cosmologies; Particle Physics Constraints; Fundamental Lessons; and Future Directions.

astro-ph↗

arXiv2004

The large-scale polarization of the microwave background and foreground

The DASI discovery of CMB polarization has opened a new chapter in cosmology. Most of the useful information about inflationary gravitational waves and reionization is on large angular scales where Galactic foreground contamination is the worst, so a key challenge is to model, quantify and remove polarized foregrounds. We use the POLAR experiment, COBE/DMR and radio surveys to provide the strongest limits to date on the TE cross power spectrum of the CMB on large angular scales and to quantify the polarized synchrotron radiation, which is likely to be the most challenging polarized contaminant for the MAP satellite. We find that the synchrotron E- and B-contributions are equal to within 10% from 408-820 MHz with a hint of E-domination at higher frequencies. We quantify Faraday Rotation and Depolarization effects in the two-dimensional (l,nu)-plane and show that they cause the synchrotron polarization percentage to drop both towards lower frequencies and towards lower multipoles.

astro-ph↗