Hasil untuk "astro-ph.CO"

Digvijay Wadekar, Javier Roulet, Tejaswi Venumadhav et al.

Nearly all of the previous gravitational wave (GW) searches in the LIGO-Virgo data included GW waveforms with only the dominant quadrupole harmonic, i.e., omitting higher-order harmonics which are predicted by general relativity. We improved the IAS pipeline by efficiently introducing higher harmonics in the GW templates using the techniques in Wadekar et al. [1, 2]. Using the IAS-HM pipeline on the public LIGO-Virgo data from the O3 run, we find 11 new candidate BBH mergers with $0.52\leq p_\mathrm{astro}\leq 0.88$ (we use the detection threshold as the astrophysical probability, $p_\mathrm{astro}$, being over 0.5, following the approach of other pipelines). We broadly recover the high-significance events from earlier catalogs, except a few which were vetoed. We also find that including higher harmonics in our search raises the significance of a few previously reported marginal events (e.g., GW190711_030756). A few notable properties of our new candidate events are as follows. At $>95$% credibility, 4 candidates have primary masses in the intermediate-mass black hole (IMBH) range (i.e., above $\sim$100 $M_\odot$). 5 candidates have median mass ratio $q \leq 0.5$. 5 candidates have median redshift $z \geq 0.8$. 3 candidates have non-zero $χ_{\rm eff}$ at $>95\%$ credibility. While our new candidate events have modest false alarm rates ($\gtrsim 1.5 $/yr), a population inference study including these can better inform the parameter space of BHs corresponding to the pair instability mass gap, high redshifts and asymmetric mass ratios.

Benjamin R. Safdi

These lecture notes on the particle physics and astrophysics of dark matter (DM) were delivered at TASI 2022 ``Ten Years After the Higgs Discovery: Particle Physics Now and Future." The focus of these lecture notes, aimed at the level of advanced graduate students and beginning postdocs, is on indirect (i.e., astrophysical and cosmological) probes of particle DM models. While DM models and indirect detection are broadly discussed, the examples of weakly interacting massive particles (WIMPs) and axions are worked out in detail. The topics covered include: the role of DM in the cosmology and astrophysics of structure formation, including DM density profiles in galaxies, general constraints on particle DM models, the theory of minimal DM, with the higgsino as a relevant and illustrative example, indirect detection with gamma-rays, including with the upcoming Cherenkov Telescope Array, axions as a solution to the strong-CP problem and a DM candidate, including discussions of possible ultraviolet completions and of axion string cosmology, and astrophysical probes of axions such as with isocurvature perturbations, $N_{\rm eff}$, black hole superradiance, radio telescopes, spectral modulations, stellar polarization, and stellar cooling, amongst other topics. Example Jupyter notebooks are provided that walk the reader through relevant analyses, including an example statistical analysis of a DM annihilation search towards the Segue I dwarf galaxy with gamma-ray data from the Fermi Large Area Telescope that is relevant for DM explanations of the Fermi Galactic Center Excess. We also provide an introduction to frequentist statistics for particle and astro-particle physics. These lecture notes are meant to be pedagogical, with the focus on explaining the underlying physical principles and analysis techniques that are set to play crucial roles in the search for particle DM in the coming decade.

Adrian E. Bayer, Uros Seljak

When searching over a large parameter space for anomalies such as events, peaks, objects, or particles, there is a large probability that spurious signals with seemingly high significance will be found. This is known as the look-elsewhere effect and is prevalent throughout cosmology, (astro)particle physics, and beyond. To avoid making false claims of detection, one must account for this effect when assigning the statistical significance of an anomaly. This is typically accomplished by considering the trials factor, which is generally computed numerically via potentially expensive simulations. In this paper we develop a continuous generalization of the Bonferroni and Sidak corrections by applying the Laplace approximation to evaluate the Bayes factor, and in turn relating the trials factor to the prior-to-posterior volume ratio. We use this to define a test statistic whose frequentist properties have a simple interpretation in terms of the global $p$-value, or statistical significance. We apply this method to various physics-based examples and show it to work well for the full range of $p$-values, i.e. in both the asymptotic and non-asymptotic regimes. We also show that this method naturally accounts for other model complexities such as additional degrees of freedom, generalizing Wilks' theorem. This provides a fast way to quantify statistical significance in light of the look-elsewhere effect, without resorting to expensive simulations.

Francesco D'Eramo, Kevin Hambleton, Stefano Profumo et al.

We explore the phenomenology of a class of models where the dark matter particle can inelastically up-scatter to a heavier excited state via off-diagonal dipolar interactions with the interstellar plasma (gas or free electrons). The heavier particle then rapidly decays back to the dark matter particle plus a quasi-monochromatic photon. For the process to occur at appreciable rates, the mass splitting between the heavier state and the dark matter must be comparable to, or smaller than, the kinetic energy of particles in the plasma. As a result, the predicted photon line falls in the soft X-ray range, or, potentially, at arbitrarily lower energies. We explore experimental constraints from cosmology and particle physics, and present accurate calculations of the dark matter thermal relic density and of the flux of monochromatic X-rays from thermal plasma excitation. We find that the model provides a natural explanation for the observed 3.5 keV line from clusters of galaxies and from the Galactic center, and is consistent with null detections of the line from dwarf galaxies. The unique line shape, which will be resolved by future observations with the Hitomi (formerly Astro-H) satellite, and the predicted unique morphology and target-temperature dependence will enable easy discrimination of this class of models versus other scenarios for the generation of the 3.5 keV line or of any other unidentified line across the electromagnetic spectrum.

Tamara M. Davis

It has been only ~15 years since the discovery of dark energy (although some may argue there were strong indications even earlier). In the short time since measurements of type Ia supernovae indicated an accelerating universe, many other techniques have now confirmed the acceleration is real. The variety of ways in which dark energy has been confirmed is one of the reasons we are so confident in the statement that most of the energy in the universe is in a form we can not see except through its gravitational influence. This review aims to summarise briefly the many varied ways we now have measured dark energy. The fact that these different techniques all indicate that the simplest model remains the best -- that dark energy contributes a constant background acceleration -- is remarkable, since each of these different types of measurements represented opportunities for this simplest model to fail. Although we currently lack a compelling theoretical explanation for this acceleration, any explanation will have to explain the wide variety of complementary observations that we review here. This is an informal presentation, following the lines of the talk I presented at the General Relativity and Gravitation (GR20) conference in Warsaw in July 2013.

R. Essig, J. A. Jaros, W. Wester et al.

Dark sectors, consisting of new, light, weakly-coupled particles that do not interact with the known strong, weak, or electromagnetic forces, are a particularly compelling possibility for new physics. Nature may contain numerous dark sectors, each with their own beautiful structure, distinct particles, and forces. This review summarizes the physics motivation for dark sectors and the exciting opportunities for experimental exploration. It is the summary of the Intensity Frontier subgroup "New, Light, Weakly-coupled Particles" of the Community Summer Study 2013 (Snowmass). We discuss axions, which solve the strong CP problem and are an excellent dark matter candidate, and their generalization to axion-like particles. We also review dark photons and other dark-sector particles, including sub-GeV dark matter, which are theoretically natural, provide for dark matter candidates or new dark matter interactions, and could resolve outstanding puzzles in particle and astro-particle physics. In many cases, the exploration of dark sectors can proceed with existing facilities and comparatively modest experiments. A rich, diverse, and low-cost experimental program has been identified that has the potential for one or more game-changing discoveries. These physics opportunities should be vigorously pursued in the US and elsewhere.

A. de Lorenzo-Cáceres, J. Falcón-Barroso, A. Vazdekis

Numerical simulations of double-barred galaxies predict the build-up of different structural components (e.g., bulges, inner discs) in the central regions of disc galaxies. In those simulations, inner bars have a prominent role in the internal secular evolution of their host galaxies. The development of bulges and inner discs is, however, poorly understood observationally due to the small number of studies focusing on the stellar populations of these systems. In order to provide constraints on the relevant processes inducing the creation of these components in the presence of inner bars, we have carried out a detailed kinematical and stellar population analysis in a sample of four double-barred galaxies, ranging from SB0 to SBb, observed with integral-field spectroscopy. We find that the inner bars present distinct stellar population properties, being younger and more metal-rich than the surrounding bulges and outer bars. While we detect signatures of gas inflow through the inner bars, we find no evidence of associated star-forming regions or newly-formed structures around them. This result suggests that, regardless of their formation scenario, at present these inner bars are playing a moderate or even a minor role in the morphological evolution of this sample of double-barred galaxies.

Alyssa B. Drake, Chris Simpson, Chris A. Collins et al.

We present new results on the cosmic star formation history in the SXDS-UDS field out to z=1.6. We compile narrow-band data from the Subaru Telescope and the Visible and Infrared Survey Telescope for Astronomy (VISTA) in conjunction with broad-band data from the SXDS and UDS, to make a selection of 5725 emission-line galaxies in 12 redshift slices, spanning 10 Gyr of cosmic time. We determine photometric redshifts for the sample using 11-band photometry, and use a spectroscopically confirmed subset to fine tune the resultant redshift distribution. We use the maximum-likelihood technique to determine luminosity functions in each redshift slice and model the selection effects inherent in any narrow-band selection statistically, to obviate the retrospective corrections ordinarily required. The deep narrow-band data are sensitive to very low star formation rates (SFRs), and allow an accurate evaluation of the faint end slope of the Schechter function, alpha. We find that alpha is particularly sensitive to the assumed faintest broadband magnitude of a galaxy capable of hosting an emission line, and propose that this limit should be empirically motivated. For this analysis we base our threshold on the limiting observed equivalent widths of emission lines in the local Universe. We compute the characteristic SFR of galaxies in each redshift slice, and the integrated SFR density, rho_{SFR}. We find our results to be in good agreement with the literature and parametrize the evolution of the SFR density as rho_{SFR} proportional to (1 + z)^{4.58} confirming a steep decline in star formation activity since z = 1.6.

Stefano Profumo

Can we learn about New Physics with astronomical and astro-particle data? Understanding how this is possible is key to unraveling one of the most pressing mysteries at the interface of cosmology and particle physics: the fundamental nature of dark matter. I will discuss some of the recent puzzling findings in cosmic-ray electron-positron data and in gamma-ray observations that might be related to dark matter. I will argue that recent cosmic-ray data, most notably from the Pamela and Fermi satellites, indicate that previously unaccounted-for powerful sources in the Galaxy inject high-energy electrons and positrons. Interestingly, this new source class might be related to new fundamental particle physics, and specifically to pair-annihilation or decay of galactic dark matter. This exciting scenario is directly constrained by Fermi gamma-ray observations, which also inform us on astrophysical source counterparts that could also be responsible for the high-energy electron-positron excess. Observations of gamma-ray emission from the central regions of the Galaxy as well as claims on a gamma-ray line at around 130 GeV also recently triggered a wide-spread interest: I will address the question of whether we are really observing signals from dark matter annihilation, how to test this hypothesis, and which astrophysical mechanisms constitute the relevant background.

D. Guidetti, R. A. Laing, A. H. Bridle et al.

We present detailed imaging of Faraday rotation and depolarization for the radio galaxies 0206+35, 3C 270, 3C 353 and M 84, based on Very Large Array observations at multiple frequencies in the range 1365 to 8440 MHz. This work suggests a more complex picture of the magneto-ionic environments of radio galaxies than was apparent from earlier work. All of the sources show spectacular banded rotation measure (RM) structures with contours of constant RM perpendicular to the major axes of their radio lobes. We give a comprehensive description of the banded RM phenomenon and present an initial attempt to interpret it as a consequence of interactions between the sources and their surroundings. We show that the material responsible for the Faraday rotation is in front of the radio emission and that the bands are likely to be caused by magnetized plasma which has been compressed by the expanding radio lobes. A two-dimensional magnetic structure in which the field lines are a family of ellipses draped around the leading edge of the lobe can produce RM bands in the correct orientation for any source orientation. We also report the first detections of rims of high depolarization at the edges of the inner radio lobes of M 84 and 3C 270. These are spatially coincident with shells of enhanced X-ray surface brightness, in which both the field strength and the thermal gas density are likely to be increased by compression.

Steven Janowiecki, J. Christopher Mihos, Paul Harding et al.

We use deep V-band surface photometry of five of the brightest elliptical galaxies in the Virgo cluster to search for diffuse tidal streams, shells, and plumes in their outer halos (r > 50 kpc). We fit and subtract elliptical isophotal models from the galaxy images to reveal a variety of substructure, with surface brightnesses in the range mu_V= 26-29 mag/arcsec^2. M49 possesses an extended, interleaved shell system reminiscent of the radial accretion of a satellite companion, while M89's complex system of shells and plumes suggests a more complicated accretion history involving either multiple events or a major merger. M87 has a set of long streamers as might be expected from stripping of low luminosity dwarfs on radial orbits in Virgo. M86 also displays a number of small streams indicative of stripping of dwarf companions, but these comprise much less luminosity than those of M87. Only M84 lacks significant tidal features. We quantify the photometric properties of these structures, and discuss their origins in the context of each galaxy's environment and kinematics within the Virgo cluster.

Jun-Hwan Choi, Kentaro Nagamine

We develop a new ``Multicomponent and Variable Velocity'' (MVV) galactic outflow model for cosmological smoothed particle hydrodynamic (SPH) simulations. The MVV wind model reflects the fact that the wind material can arise from different phases in the interstellar medium (ISM), and the mass-loading factor in the MVV model is a function of galaxy stellar mass. We find that the simulation with the MVV outflow has the following characteristics: (i) the intergalactic medium (IGM) is hardly heated up, and the mean IGM temperature is almost the same as in the no-wind run; (ii) it has lower cosmic star formation rates (SFRs) compared to the no-wind run, but higher SFRs than the constant velocity wind run; (iii) it roughly agrees with the observed IGM metallicity, and roughly follows the observed evolution of Omega(Civ); (iv) the lower mass galaxies have larger mass-loading factors, and the low-mass end of galaxy stellar mass function is flatter than in the previous simulations. Therefore, the MVV outflow model mildly alleviates the problem of too steep galaxy stellar mass function seen in the previous SPH simulations. In summary, the new MVV outflow model shows reasonable agreement with observations, and gives better results than the constant velocity wind model.

A. Shahmoradi, R. J. Nemiroff

GRB satellites are relatively inefficient detectors of dim hard bursts because they trigger on photon counts, which are number-biased against hard photons. Therefore, for example, given two bursts of identical peak luminosity near the detection threshold, a dim soft burst will be preferentially detected over a dim hard burst. This detector bias can create or skew an apparent correlation where increasingly hard GRBs appear increasingly bright. Although such correlations may be obfuscated by a middle step where GRBs need to be bright enough to have their actual redshifts determined, it is found that the bias is generally pervasive. This result is derived here through simulations convolving a wide variety of possible GRB brightnesses and spectra with the BATSE Large Area Detectors (LAD) detection thresholds. The presented analyses indicate that the rest-frame $νF_ν$ spectrum peak energy of long-duration GRBs, $\epi$, is not a good cosmological standard candle without significant corrections for selection effects. Therefore, the appearance of $\epi$ in seeming correlations such as the Amati ($E_{iso}-\epi$), Ghirlanda ($E_γ-\epi$), and $L_{iso}-\epi$ relations is statistically real but strongly influenced by so far uncalibrated GRB detector thresholds.

Robert C. Fletcher

This paper presents a compelling argument for the physical light speed in the Friedman-Lemaitre-Robertson-Walker (FLRW) universe to vary with the cosmic time coordinate "t" of FLRW. It must be variable when the radial comoving differential coordinates of FLRW is interpreted as physical and therefore transformable by a Lorentz transform locally to differentials of stationary physical coordinates. Because the FLRW differential radial distance has a time varying coefficient a(t), integration of the transformed differentials to obtain stationary coordinates for a short radial distance requires the light speed c(t) to be proportional to the square root of da/dt. Since we assume homogeneity of space, this derived c(t) is the physical light speed on all points of the FLRW universe. This impacts the interpretation of all astronomical observations of distant phenomena that are sensitive to light speed. A world transform from FLRW that has a Minkowski metric close to the origin is shown to have a physical radius out to all points of the visible universe. In order to obtain numerical values for c(t), the general relativity (GR) field equation is extended by using a variable gravitational constant and rest mass that keeps constant the gravitational and particle rest energies. This also keeps constant the proportionality constant between the GR tensors of the field equation and conserves the rest stress-energy tensor of the ideal fluid used in the FLRW GR field equation. In the same way all of special and general relativity is extended to include a variable light speed.

C. L. Carilli, S. Myers, P. Appleton et al.

When, and how, did the first galaxies and supermassive black holes (SMBH) form, and how did they reionization the Universe? First galaxy formation and cosmic reionization are among the last frontiers in studies of cosmic structure formation. We delineate the detailed astrophysical probes of early galaxy and SMBH formation afforded by observations at centimeter through submillimeter wavelengths. These observations include studies of the molecular gas (= the fuel for star formation in galaxies), atomic fine structure lines (= the dominant ISM gas coolant), thermal dust continuum emission (= an ideal star formation rate estimator), and radio continuum emission from star formation and relativistic jets. High resolution spectroscopic imaging can be used to study galaxy dynamics and star formation on sub-kpc scales. These cm and mm observations are the necessary compliment to near-IR observations, which probe the stars and ionized gas, and X-ray observations, which reveal the AGN. Together, a suite of revolutionary observatories planned for the next decade from centimeter to X-ray wavelengths will provide the requisite panchromatic view of the complex processes involved in the formation of the first generation of galaxies and SMBHs, and cosmic reionization.

Hongsheng Zhang, Hyerim Noh, Zong-Hong Zhu et al.

We present a novel mechanism for the present acceleration of the universe. We find that the temperature of the Unruh radiation perceived by the brane is not equal to the inherent temperature (Hawking temperature at the apparent horizon) of the brane universe in the frame of Dvali-Gabadadze-Porrati (DGP) braneworld model. The Unruh radiation perceived by a dust dominated brane is always warmer than the brane measured by the geometric temperature, which naturally induces an energy flow between bulk and brane based on the most sound thermodynamics principles. Through a thorough investigation to the microscopic mechanism of interaction between bulk Unruh radiation and brane matter, we put forward that an energy influx from bulk Unruh radiation to the dust matter on the brane accelerates the universe.

Chris A. Collins, John P. Stott, Matt Hilton et al.

The current consensus is that galaxies begin as small density fluctuations in the early Universe and grow by in situ star formation and hierarchical merging. Stars begin to form relatively quickly in sub-galactic sized building blocks called haloes which are subsequently assembled into galaxies. However, exactly when this assembly takes place is a matter of some debate. Here we report that the stellar masses of brightest cluster galaxies, which are the most luminous objects emitting stellar light, some 9 billion years ago are not significantly different from their stellar masses today. Brightest cluster galaxies are almost fully assembled 4-5 Gyrs after the Big Bang, having grown to more than 90% of their final stellar mass by this time. Our data conflict with the most recent galaxy formation models based on the largest simulations of dark matter halo development. These models predict protracted formation of brightest cluster galaxies over a Hubble time, with only 22% of the stellar mass assembled at the epoch probed by our sample. Our findings suggest a new picture in which brightest cluster galaxies experience an early period of rapid growth rather than prolonged hierarchical assembly.

Daniel A. Evans, James N. Reeves, Martin J. Hardcastle et al.

We present results from a new 100-ks Suzaku observation of the nearby radio galaxy 3C 33, and investigate the nature of absorption, reflection, and jet production in this source. We model the 2-70 keV nuclear continuum with a power law that is absorbed either through one or more layers of pc-scale neutral material, or through a modestly ionized pc-scale obscurer. The expected signatures of reflection from a neutral accretion disk are absent in 3C 33: there is no evidence of a relativistically blurred Fe K$α$ emission line, and no Compton reflection hump above 10 keV. We discuss the implications of this for the nature of jet production in 3C 33.

Fabio Gastaldello, Stefano Ettori, Italo Balestra et al.

Recent work based on a global measurement of the ICM properties find evidence for an increase of the iron abundance in galaxy clusters with temperature around 2-4 keV. We have undertaken a study of the metal distribution in nearby clusters in this temperature range, aiming at resolving spatially the metal content of the ICM. The XMM observation of the first object of the sample, the cluster Abell 2028, reveals a complex structure of the cluster over scale of ~ 300 kpc, showing an interaction between two sub-clusters in a ``cometary'' configuration. We show that a naive one-component fit for the core of Abell 2028 returns a biased high metallicity. This is due to the inverse iron-bias, which is not related to the presence in the spectrum of both Fe-L and Fe-K emission lines but to the behavior of the fitting code in shaping the Fe-L complex of a one temperature component to adjust to the multi-temperature structure of the projected spectrum.

Emma V. Ryan-Weber, Max Pettini, Piero Madau et al.

We present the results of the largest survey to date for intergalactic metals at redshifts z > 5, using near-IR spectra of nine QSOs with emission redshifts z(em) > 5.7. We find, for the first time, a change in the comoving mass density of C IV ions as we look back to redshifts z > 5. At a mean <z> = 5.76, we deduce Omega(C IV)=(4.4+/-2.6)x10^(-9) which implies a drop by a factor of about 3.5 compared to the value at z < 4.7, after accounting for the differing sensitivities of different surveys. The observed number of C IV doublets is also lower by a similar factor, compared to expectations for a non-evolving column density distribution of absorbers. These results point to a rapid build-up of intergalactic C IV over a period of only 300 Myr; such a build-up could reflect the accumulation of metals associated with the rising levels of star formation activity from z = 9 indicated by galaxy counts, and/or an increasing degree of ionisation of the intergalactic medium (IGM), following the overlap of ionisation fronts from star-forming regions. If the value of Omega(C IV) we derive is typical of the IGM at large, it would imply a metallicity Z(IGM) = 10^(-4) Z(Sun). The early-type stars responsible for synthesising these metals would have emitted only about one Lyman continuum photon per baryon prior to z = 5.8; such a background is insufficient to keep the IGM ionised and we speculate on possible factors which could make up the required shortfall.