Intermediate Epochs Research Articles

Cosmology in modified f (𝒢) gravity: a late-time cosmic phenomena

ABSTRACT In this work, we present a method for numerically solving the Friedmann equations of modified $f(\mathcal {G})$ gravity in the presence of pressureless matter. This method enables us to predict the redshift behaviour of the Hubble expansion rate. To evaluate the credibility of the model, we applied a Bayesian MCMC technique using late-time cosmic observations to impose limitations on the free parameters of the Gauss–Bonnet model. Our results suggest that the $f(\mathcal {G})$ model can reproduce the low-redshift behaviour of the standard Lambda cold dark matter ($\Lambda$CDM) model, but there are significant differences at high redshifts, leading to the absence of a standard matter-dominated epoch. We also examined the profiles of cosmographic parameters using the model parameter values from the standard range to verify the intermediate epochs. Our analysis shows that the highly promising $f(\mathcal {G})$ model is a feasible candidate for explaining the current epochs. We presented a dynamical system analysis framework to examine the stability of the model. Our study identified critical points depicting various phases of the Universe and explained the evolutionary epochs. We demonstrated that the model effectively captures the evolution of energy components over cosmic time, supporting its validity as an alternate explanation for the observed acceleration of the Universe.

United We Stand: Using Epoch-Wise Agreement of Ensembles to Combat Overfit

Deep neural networks have become the method of choice for solving many classification tasks, largely because they can fit very complex functions defined over raw data. The downside of such powerful learners is the danger of overfit. In this paper, we introduce a novel ensemble classifier for deep networks that effectively overcomes overfitting by combining models generated at specific intermediate epochs during training. Our method allows for the incorporation of useful knowledge obtained by the models during the overfitting phase without deterioration of the general performance, which is usually missed when early stopping is used. To motivate this approach, we begin with the theoretical analysis of a regression model, whose prediction - that the variance among classifiers increases when overfit occurs - is demonstrated empirically in deep networks in common use. Guided by these results, we construct a new ensemble-based prediction method, where the prediction is determined by the class that attains the most consensual prediction throughout the training epochs. Using multiple image and text classification datasets, we show that when regular ensembles suffer from overfit, our method eliminates the harmful reduction in generalization due to overfit, and often even surpasses the performance obtained by early stopping. Our method is easy to implement and can be integrated with any training scheme and architecture, without additional prior knowledge beyond the training set. It is thus a practical and useful tool to overcome overfit.

Circumventing the challenges in the choice of the nonconformal coupling function in inflationary magnetogenesis

[Abridged] As is well known, in order to generate magnetic fields of observed amplitudes during inflation, the conformal invariance of the electromagnetic field has to be broken by coupling it either to the inflaton or to the scalar curvature. Couplings to scalar curvature pose certain challenges even in slow roll inflation and it seems desirable to consider couplings to the inflaton. It can be shown that, in slow roll inflation, to generate nearly scale invariant magnetic fields of adequate strengths, the non-conformal coupling to the inflaton has to be chosen specifically depending on the inflationary model at hand. In a recent work, we had found that, when there arise sharp departures from slow roll inflation leading to strong features in the scalar power spectra, there inevitably arise sharp features in the spectra of the electromagnetic fields, unless the non-conformal coupling functions are extremely fine tuned. In particular, we had found that, if there occurs an epoch of ultra slow roll inflation, then the strength of the magnetic field over large scales can be severely suppressed. In this work, we examine whether these challenges can be circumvented in models of inflation involving two fields. We show that the presence of the additional scalar field allows us to construct coupling functions that lead to magnetic fields of required strengths even when there arise intermediate epochs of ultra slow roll inflation. However, we find that the features in the spectra of the magnetic fields that are induced due to the departures from slow roll inflation cannot be completely ironed out. We make use of the code MagCAMB to calculate the effects of the magnetic fields on the anisotropies in the cosmic microwave background and investigate if the spectra with features are broadly consistent with the current constraints.

Modelling and analysis of D-BMAP/D-MSP/1 queue using RG-factorization

ABSTRACT The current investigation of our paper is concentrated on an infinite-buffer single-server queueing model with discrete-time batch Markovian arrival process and Markovian service process. The steady-state behaviour of this discrete-time queueing system at various significant time epochs are presented. We first analyze the system-length distribution at outside observer’s epoch using the -factorization technique combined with the spectral expansion method to compute the stochastic matrix . For the purpose of comparative study, a comprehensive analysis of the system-length distribution at outside observer’s epoch is also carried out using the roots method. Next, we obtain the explicit closed-form expressions of the system-length distributions at pre-arrival, intermediate, post-departure and random epochs by developing the relations among them in equilibrium state. The analysis of waiting-time distribution in the queue measured in slots of an arbitrary customer in an arriving batch is also discussed. Computational experiences with adequate numerical results are conferred in the structure of tables and graphs. Finally, we suggest that our queueing model seems to be fitted for outpatient service of any specialized hospital in a smart city.

Stationary Analysis of an Infinite-Buffer D-MAP/D-MSP/1 Queueing System

This paper deals with the analysis of an infinite-buffer single-server D-MAP/D-MSP/1 queueing system. This queueing system can be analyzed by representing level-independent quasi-birth-and-death process in tridiagonal structure. The proposed analysis is based on the use of matrix-geometric method in conjunction with the spectral method to obtain the system-length distribution at outside observer’s epoch. We derive the stationary system-length distributions at random, prearrival, intermediate and post-departure epochs using the system-length distribution at outside observer’s epoch. The waiting-time distribution in the queue measured in slots of an arriving customer is also carried out. Computational procedures along with numerical results are provided to confirm the correctness of our analytical results.

STRUCTURE FEATURES AND HISTORY OF DEVELOPMENT OF THE NORTHWESTERN PART OF THE PACIFIC OCEAN BOTTOM

According to results of interpretation of data of high (120–150 Hz) frequency SCP (seismic continuous profiling), CDP1 (common depth point method) profile and drilling it was found that the NW Pacific abyssal floor is composed by marine and continental series of Late Precambrian-Phanerozoic (sedimentary-trappean cover). Facies of three oceans (earley epicontinental Tethys of Riphean-Paleozoic, late epicontinental Tethys of Late Mesozoic, deep-sea Pacific ocean of Neogene-Quaternary) and intermediate subaerial epochs (Pacifida paleolands) were eliminated. Boundaries of Layers 1–5 and Meso-Cenozoic cover are parallels and gentle incline to the SE from outer rise that is typically for platforms with long inherited development. The cover of old platform break divergent gravitational glide of Layers 1–4 on outer rise slopes in the Neogene-Quaternary. Mesozoic history is connected with mainly land traps, transgression of late Tethys in Jurassic-Early Cretaceous and shallow accumulation of carbonate strata A. Then the sea step back to SE with formation of seacoast series B and draining of region in the Uppermost Early-Late Cretaceous-Paleogene, partly Early Miocene, when here accumulate loesses of Pacifida paleoland (horizon C), fl ooded waters of the young Pacific ocean. Its facieses (strata D1,2) are composed the abyssal fl oor and present of canyon fans on the outer rise and Kamchatka contour megacone in the Tuskarora basin. Fan outbuilding continues before Middle Pleistocene (Japan and Kuril-Kamchatka trench formation as turbidite traps).

THE RECENT STELLAR ARCHEOLOGY OF M31—THE NEAREST RED DISK GALAXY

We examine the star-forming history (SFH) of the M31 disk during the past few hundred Myr. The luminosity functions (LFs) of main sequence stars at distances R_GC > 21 kpc (i.e. > 4 disk scale lengths) are matched by models that assume a constant star formation rate (SFR). However, at smaller R_GC the LFs suggest that during the past ~10 Myr the SFR was 2 - 3 times higher than during the preceding ~100 Myr. The rings of cool gas that harbor a significant fraction of the current star-forming activity are traced by stars with ages ~100 Myr, indicating that (1) these structures have ages of at least 100 Myr, and (2) stars in these structures do not follow the same relation between age and random velocity as their counterparts throughout the disks of other spiral galaxies, probably due to the inherently narrow orbital angular momentum distribution of the giant molecular clouds in these structures. The distribution of evolved red stars is not azimuthally symmetric, in the sense that their projected density along the north east segment of the major axis is roughly twice that on the opposite side of the galaxy. The north east arm of the major axis thus appears to be a fossil star-forming area that dates to intermediate epochs. Such a structure may be the consequence of interactions with a companion galaxy.

THE STELLAR ARCHEOLOGY OF THE M33 DISK: RECENT STAR-FORMING HISTORY AND CONSTRAINTS ON THE TIMING OF AN INTERACTION WITH M31,

Images recorded with MegaCam are used to investigate the recent (t ⩽ 0.25 Gyr) star-forming history (SFH) of the Local Group Sc galaxy M33. The data sample the entire star-forming disk, as well as areas immediately to the north and south of the galaxy. The properties of the stellar disk change near RGC = 8 kpc. Within this radius the luminosity function of main-sequence stars indicates that the star formation rate (SFR) has been constant with time during at least the past 250 Myr, while at larger radii the SFR has declined during this same time period. That the recent SFR in the inner disk has been constant suggests that M33 has evolved in isolation for at least the past ∼0.5 Gyr, thereby providing a constraint on the timing of any recent interaction with M31. The color of the main-sequence ridgeline changes with radius, suggesting a gradient in extinction of size ΔAV/ΔRGC = −0.05 mag kpc−1. The fractional contribution that young stars make to the total mass of the stellar disk changes with radius, peaking near 8 kpc. Evidence is also presented of systematic spatial variations in the SFH of the disk, such that the SFR during the past 100 Myr in the southern half of the galaxy has been ∼0.4 dex higher than in the northern half. Finally, structures with sizes spanning many kpc that contain blue objects—presumably main-sequence stars that formed during intermediate epochs—are identified near the disk boundary. It is argued that these are tidal features that were pulled from the main body of M33 and—in some cases—are the fossil remnants of star formation that occurred in an extended disk during intermediate epochs.

Archimedean-type force in a cosmic dark fluid. II. Qualitative and numerical study of a multistage universe expansion

In this (second) part of the work we present the results of numerical and qualitative analysis, based on a new model of the Archimedean-type interaction between dark matter and dark energy. The Archimedean-type force is linear in the four-gradient of the dark energy pressure and plays a role of self-regulator of the energy redistribution in a cosmic dark fluid. Because of the Archimedean-type interaction the cosmological evolution is shown to have a multistage character. Depending on the choice of the values of the model guiding parameters,the Universe's expansion is shown to be perpetually accelerated, periodic or quasiperiodic with finite number of deceleration/acceleration epochs. We distinguished the models, which can be definitely characterized by the inflation in the early Universe, by the late-time accelerated expansion and nonsingular behavior in intermediate epochs, and classified them with respect to a number of transition points. Transition points appear, when the acceleration parameter changes the sign, providing the natural partition of the Universe's history into epochs of accelerated and decelerated expansion. The strategy and results of numerical calculations are advocated by the qualitative analysis of the instantaneous phase portraits of the dynamic system associated with the key equation for the dark energy pressure evolution.

AND THE REST: THE STELLAR ARCHEOLOGICAL RECORD OF M82 OUTSIDE THE CENTRAL STARBURST

Deep images obtained with MegaCam and WIRCam on the Canada-France-Hawaii Telescope are used to probe the stellar content outside of the central star-forming regions of M82. Stars evolving on the asymptotic giant branch (AGB) are traced along the major axis out to projected distances of 12 kpc, which corresponds to 13 disk scale lengths. The numbers of red supergiants (RSGs) and AGB stars normalized to local surface brightness (the specific frequency or SF) is constant when R GC > 4 kpc, indicating that RSGs and AGB stars are well mixed throughout the disk. Moreover, the SF of bright AGB stars in the outer disks of M82 and the Sc galaxy NGC 2403 are identical, suggesting that the specific star-formation rates (SFRs) in these galaxies during intermediate epochs were similar. This similarity in stellar content, coupled with the presence of an extended stellar disk, is consistent with M82 having been a late-type disk galaxy prior to interacting with M81. Still, there is a paucity of RSGs in the outer disk of M82 when compared with NGC 2403, indicating that the SFR in the outer regions of M82 during the past ~0.1 Gyr has declined dramatically with respect to that in isolated late-type galaxies. The stellar content of the M82 disk plane is also investigated. A mixture of bright main-sequence stars, RSGs, and AGB stars is detected out to minor-axis distances of 7 kpc. These stars, which span a range of ages, are concentrated along the outflow. The brightest extraplanar AGB stars define a system with an exponential scale height of 1.8 ± 0.2 kpc, as measured along the minor axis. It is suggested that the young- and intermediate-aged stars in the extraplanar regions formed in structures similar to M82 South, and that these were subsequently disrupted by the tidal action of M82.

Examining the evidence for dust destruction in GRB 980703

Aims. The effects that gamma-ray bursts have on their environments is an important and outstanding issue. Dust destruction in particular has long been predicted while observational evidence is difficult to obtain. We examine the evidence for dust destruction by GRB 980703, in which various inconsistent measurements of the host galaxy extinction have been made using the GRB afterglow emission. Methods. We construct a spectral energy distribution from nIR to X-ray to measure the extinction at early times and compare this with previous findings. We also construct nIR/optical SEDs at intermediate epochs to examine a previously reported decrease in extinction. Results. The extinction is very high for a GRB host galaxy. The earliest extinction measurement is likely to be lower than previously estimated, and consistent with most later measurements. In a series of SEDs we do not find any evidence of variable extinction. We therefore conclude that there is no clear evidence of dust destruction in this case.

THE STELLAR CONTENT OF THE POST-STARBURST S0 GALAXY NGC 5102

The stellar content of the S0 galaxy NGC 5102 is investigated using deep r' and i' images obtained with GMOS-S. A modest population of bright main-sequence stars and red supergiants is detected throughout the western portion of the disk. Based on the numbers of main-sequence stars, the star-formation rate (SFR) in NGC 5102 during the past ten million years is estimated to have been 0.02 M ? year. The majority of red giant branch (RGB) stars in the disk of NGC 5102 have [M/H] between ?0.9 and ?0.1, and the metallicity distribution of RGB stars at intermediate galactocentric radii peaks near [M/H] ~?0.6. RGB stars are traced out to galactocentric distances of 10 kpc, which corresponds to ~14 disk scale lengths. A large population of bright asymptotic giant branch stars is seen throughout the western portion of the disk, and the youngest of these have log(t yr) ~ 8.1. It is concluded that (1) stars that formed within the past Gyr comprise ~20% of the total stellar disk mass and (2) the SFR during intermediate epochs in the disk of NGC 5102 was at least 1.4 M ? year. Thus, large-scale star formation occurred throughout the disk of NGC 5102 at approximately the same time that similar elevated levels of star formation occurred in the bulge. It is suggested that NGC 5102 was a spiral galaxy that experienced a galaxy-wide episode of star formation that terminated a few hundred Myr in the past, and that much of its interstellar medium was ejected in an outflow.

The Evolved Stellar Content of NGC 147, NGC 185, and NGC 205*

Broadband near-infrared images are used to probe the photometric properties of the brightest asymptotic giant branch (AGB) stars within 2' of the centers of the dwarf elliptical galaxies NGC 147, NGC 185, and NGC 205. Sequences originating from oxygen-rich M giants and C stars are clearly distinguished on the (K, H - K) and (K, J - K) color-magnitude diagrams. Based on the peak brightness and color of the M giant sequences, ages of 1 and 0.1 Gyr are predicted for the most recent significant star-forming events in NGC 185 and NGC 205, respectively. The bolometric luminosity function of M giants in NGC 205 is flatter than in NGC 185, in agreement with studies at wavelengths shortward of 1 μm. The most luminous AGB stars in NGC 147 are well mixed with fainter stars throughout the area surveyed in this galaxy, and the peak brightness of the M giant sequence indicates that the most recent significant star-forming activity occurred ~3 Gyr in the past. The C star contents of the three galaxies are compared in two ways. First, the notion of a specific frequency measurement for C stars, in which C star counts per unit magnitude are normalized to a common integrated K-band brightness using published surface photometry, is introduced. The specific frequencies of C stars outside the areas of most recent star formation agree in all three galaxies. Second, comparisons are made using the integrated brightness from C stars, which is normalized to the integrated light from M giants and the integrated light from all stars. The fractional contribution made by C stars to the total AGB light in the K-band is found to be highest in NGC 147 and lowest in the central regions of NGC 205, which is qualitatively consistent with model predictions. The fractional contribution that C stars make to the total K-band light is found to be constant both within and between galaxies, with C stars contributing 2% of the total K-band light. We conclude that, when averaged over timescales of a few gigayears, these galaxies have turned similar fractions of gas and dust, normalized according to total galaxy mass, into stars. We argue that the material for star formation likely originated in well-regulated reservoirs and demonstrate that the mass of gas needed to fuel star formation during intermediate epochs could have been supplied by winds from evolved stars. Finally, multiepoch data are used to investigate the incidence of long-period variables (LPVs) in NGC 185 and NGC 205. While tight constraints cannot be placed on the LPV content of NGC 205, roughly 70% of the stars with MK between -7.5 and -8.0 in the central regions of NGC 185 appear to be LPVs with amplitudes similar to those of LPVs in the LMC.

The Disk and Extraplanar Regions of NGC 55

The stellar content of the nearby SB(s)m galaxy NGC 55 is investigated using images obtained with the Gemini South and Canada-France-Hawaii telescopes. The (K, H - K) and (K, J - K) color-magnitude diagrams (CMDs) of stars near the plane of the disk reveal signatures of large-scale star formation during recent and intermediate epochs in the form of red supergiants (RSGs) with MK = -11.5, and an asymptotic giant branch (AGB) that peaks near MK = -10. Comparisons with stellar evolution models suggest that the brightest RSGs have an age near 8 Myr. A well-defined plume, which stellar evolution models suggest contains stars with masses near the RSG-AGB transition, is detected in CMDs constructed both from infrared and visible wavelength observations. It is concluded that star formation in the thin disk of NGC 55 has occurred at a significant rate for at least the past 0.1-0.2 Gyr, and this is consistent with other indicators. The near-infrared spectral energy distribution of the integrated light near the center of the galaxy is consistent with that in other Magellanic irregular galaxies, indicating that the star-forming history of NGC 55, when averaged over timescales of 0.1-1 Gyr, has likely not been peculiar when compared with other late-type systems. Evidence is also presented that the disk contains a large population of old [log(tyr) ~ 10] stars, and it is argued that a stable disk has been in place in NGC 55 for a significant fraction of the age of the universe. At projected distances in excess of 2 kpc off of the disk plane, the brightest AGB stars have ages 10 Gyr. Thus, despite indications that dust and gas are present in the envelope surrounding the NGC 55 disk, the AGB content suggests that recently formed stars do not occur in large numbers in the extraplanar region. The (r' - i') colors of the RGB in the extraplanar region are consistent with [Fe/H] between -2.2 and -0.7, with the majority of stars having [Fe/H] > -1.2, and the mean metallicity inferred from the RGB color does not change with distance above the disk plane. Thus, the stellar component in the extraplanar envelope is well mixed, at least in terms of metallicity. The mean metallicity of RGB stars is in excellent agreement with that measured in the extraplanar H II regions EHR 1 and 2, suggesting that the age-metallicity relation in this part of NGC 55 has been flat for at least a few Gyr. Finally, the RGB tip occurs near i' = 23.1 in the extraplanar region, and a distance modulus of 26.5 is computed from this feature.

A near infrared view of Local Group dwarf galaxies

We present the results of near-infrared imaging of the dwarf spheroidal galaxies Fornax and Leo I as part of a photometric survey of stellar populations in Local Group dwarf galaxies. Wide-field observations in the J, H, and bands have been obtained with the SOFI camera at the ESO NTT at La Silla, Chile. The aim of this project is to study the evolution of Local Group dwarf spheroidal galaxies, with special regard to star formation at intermediate epochs. The near-infrared data, together with optical catalogs from the Padova Local Group wide-field survey, provide a very large color baseline ideal to study the properties of red giant branch (RGB) and asymptotic giant branch (AGB) stars.

Acquisition of typical EEG waveforms during fMRI: SSVEP, LRP, and frontal theta

Recent work has demonstrated the feasibility of simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). Virtually no systematic comparisons between EEG recorded inside and outside the MR scanner have been conducted, and it is unknown if different kinds of frequency mix, topography, and domain-specific processing are uniformly recordable within the scanner environment. The aim of the study was to investigate several typical EEG waveforms in the same subjects inside the magnet during fMRI and outside the MR examination room. We examined whether uniform artifact subtraction allows the extraction of these different EEG waveforms inside the scanner during EPI scanning to the same extent as outside the scanner. Three well-established experiments were conducted, eliciting steady state visual evoked potentials (SSVEP), lateralized readiness potentials (LRP), and frontal theta enhancement induced by mental addition. All waveforms could be extracted from the EEG recorded during fMRI. Substantially no differences in these waveforms of interest were found between gradient-switching and intermediate epochs during fMRI (only the SSVEP-experiment was designed for a comparison of gradient—with intermediate epochs), or between waveforms recorded inside the scanner during EPI scanning and outside the MR examination room (all experiments). However, non-specific amplitude differences were found between inside and outside recorded EEG at lateral electrodes, which were not in any interaction with the effects of interest. The source of these differences requires further exploration. The high concordance of activation patterns with published results demonstrates that EPI-images could be acquired during EEG recording without significant distortion.

Deep Near‐Infrared Imaging of a Field in the Outer Disk of M82 with the Altair Adaptive Optics System on Gemini‐North

ABSTRACTDeep H and K′ images recorded with the Altair adaptive optics system and Near‐Infrared Imager on Gemini‐North are used to probe the red stellar content in a field with a projected distance of 1 kpc above the disk plane of the starburst galaxy M82. The data have an angular resolution of 008 FWHM, and individual asymptotic giant branch (AGB) and red giant branch (RGB) stars are resolved. The AGB extends to at least 1.7 mag in K above the RGB tip, which occurs at K = 21.7. The relative numbers of bright AGB stars and RGB stars are consistent with stellar evolution models, and one of the brightest AGB stars has an H−K color and K brightness that is consistent with it being a C star. The brightnesses of the AGB stars suggest that they formed during intermediate epochs, possibly after the last major interaction with M81. Therefore, star formation in M82 during intermediate epochs may not have been restricted to the plane of the disk.

What can we learn on the thermal history of the Universe from future cosmic microwave background spectrum measurements at long wavelengths

We analyse the implications of future observations of the cosmic microwave background (CMB) absolute temperature at centimetre and decimetre wavelengths, where both ground, balloon and space experiments are currently under way to complement the accurate COBE/FIRAS data available at λ? 1 cm. Our analysis shows that forthcoming ground and balloon measurements will allow a better understanding of free-free distortions but will not be able to significantly improve the constraints already provided by the FIRAS data on the possible energy exchanges in the primeval plasma. The same holds even for observations with sensitivities up to ∼10 times better than those of forthcoming experiments. Thus, we have studied the impact of very high-quality data, such as those, in principle, achievable with a space experiment such as the Diffuse Microwave Emission Survey (DIMES) planned to measure the CMB absolute temperature at 0.5? λ ∼ 15 cm with a sensitivity of ∼0.1 mK, close to that of FIRAS. We have demonstrated that such high-quality data would improve by a factor of ∼50 the FIRAS results on the fractional energy exchanges, Δ∈/∈ i , associated with dissipation processes possibly occurred in a wide range of cosmic epochs, at intermediate and high redshifts (y h ? 1), and that the energy dissipation epoch could also be significantly constrained. By jointly considering two dissipation processes occurring at different epochs, we demonstrated that the sensitivity and frequency coverage of a DIMES-like experiment would allow one to accurately recover the epoch and the amount of energy possibly injected into the radiation field at early and intermediate epochs even in the presence of a possible late distortion, while the constraints on the energy possibly dissipated at late epochs can be improved by a factor of ≃2. In addition, such measurements can provide an independent and very accurate cross-check of FIRAS calibration. Finally, a DIMES-like experiment will be able to provide indicative independent estimates of the baryon density: the product Ω b H 2 0 can be recovered within a factor of ∼2-5 even in the case of (very small) early distortions with Δ∈/∈ i ∼ (5-2) x 10 - 6 . On the other hand, for Ω b (H 0 /50) 2 ? 0.2, an independent baryon density determination with an accuracy at ∼ per cent level, comparable to that achievable with CMB anisotropy experiments, would require an accuracy of ∼1 mK or better in the measurement of possible early distortions but up to a wavelength from ∼ few x dm to ∼7 dm, according to the baryon density value.

The Outer Regions of the Nearby Sc Galaxies NGC 2403 and M33: Evidence for an Intermediate-Age Population at Large Radii

Deep g'r'i'z' images obtained with the Gemini Multiobject Spectrograph (GMOS) on Gemini North are used to investigate the stellar content in the outer regions of the nearby Sc galaxies NGC 2403 and M33. The field observed in NGC 2403 covers galactocentric distances between 5 and 11 kpc perpendicular to the line of sight (R) and 7 and 19 kpc along the plane of the disk (R). The red giant branch (RGB) tip occurs at i' = 23.6 ? 0.1, and the Cepheid and RGB-tip distance scales for NGC 2403 are in good agreement. The number density of bright main-sequence stars in this field experiences a steep cutoff at R ~ 10 kpc, which is consistent with the expected truncation radius of the disk predicted from studies of edge-on spiral galaxies. While very young stars are restricted to R < 10 kpc, a population of bright asymptotic giant branch (AGB) stars is present throughout the entire GMOS field, indicating that star formation occurred outside of the present-day star-forming disk of NGC 2403 during intermediate epochs. The AGB stars are not in a tidal stream; in fact, the ratio of AGB stars above the RGB tip to those below the RGB tip does not change with radius, indicating that the bright AGB stars are uniformly mixed with the fainter stellar content throughout the field. The AGB luminosity function (LF) scales with r-band surface brightness over a wide range of radii throughout the main body of NGC 2403, indicating that the age distribution of stars in the outer regions of the present-day star-forming disk is not skewed to younger values than in the inner disk. Based on the color of stars on the upper portions of the RGB, it is concluded that metallicity changes across the field, with [Fe/H] = -0.8 ? 0.1(random) ? 0.3(systematic) at R = 5 kpc, and [Fe/H] = -2.2 ? 0.2(random) ? 0.8(systematic) at R = 11 kpc. The M33 field samples R between 8 and 10 kpc and R between 14 and 17 kpc. Bright AGB stars are detected in this field, and the ratio of bright AGB stars to stars on the upper RGB is at least as large as that measured in the outer regions of NGC 2403; thus, an intermediate-age population occurs well outside of the young star-forming disk of M33. The color of stars on the upper RGB suggests that [Fe/H] = -1.0 ? 0.3(random) ? 0.3(systematic) in this field. The globular cluster systems of both NGC 2403 and M33 contain objects that formed during intermediate epochs, and it is suggested that the luminous AGB stars detected in the current study are the field counterparts of these clusters. The detection of intermediate-age stars in the outer regions of these galaxies is consistent with models in which late-type spiral galaxies formed more slowly than earlier-type systems.

CMB temperature and polarization anisotropy fundamentals

The tremendous experimental progress in cosmic microwave background (CMB) temperature and polarization anisotropy studies over the last few years has helped establish a standard paradigm for cosmology at intermediate epochs and has simultaneously raised questions regarding the physical processes at the two opposite ends of time. What is the physics behind the source of structure in the universe and the dark energy that is currently accelerating its expansion? We review the acoustic phenomenology that forms the cornerstone of the standard cosmological model and discuss internal consistency relations which lend credence to its interpretation. We discuss future milestones in the study of CMB anisotropy that have implications for inflationary and dark energy models. These include signatures of gravitational waves and gravitational lensing in the polarization fields and secondary temperature anisotropy from the transit of CMB photons across the large-scale structure of the universe.