Concentrations of matter, such as galaxies and galactic clusters, originated as very small density fluctuations in the early universe. The existence of galaxy clusters and super-clusters suggests that a natural scale for the matter distribution may not exist. A point of controversy is whether the distribution is fractal and, if so, over what range of scales. One-dimensional models demonstrate that the important dynamics for cluster formation occurs in the position-velocity plane. Here we investigate the development of scaling behavior and multifractal geometry for a family of one dimensional models for three different, scale-free, initial conditions. We show that hierarchical cluster formation depends sensitively on the initial power spectrum. Under special circumstances we confirm a simple relation between the power spectrum, correlation function, and correlation dimension.
We compare current and forecasted constraints on dynamical dark energy models from Type Ia supernovae and the cosmic microwave background using figures of merit based on the volume of the allowed dark energy parameter space. For a two-parameter dark energy equation of state that varies linearly with the scale factor, and assuming a flat universe, the area of the error ellipse can be reduced by a factor of ~10 relative to current constraints by future space-based supernova data and CMB measurements from the Planck satellite. If the dark energy equation of state is described by a more general basis of principal components, the expected improvement in volume-based figures of merit is much greater. While the forecasted precision for any single parameter is only a factor of 2-5 smaller than current uncertainties, the constraints on dark energy models bounded by -1<w<1 improve for approximately 6 independent dark energy parameters resulting in a reduction of the total allowed volume of principal component parameter space by a factor of ~100. Typical quintessence models can be adequately described by just 2-3 of these parameters even given the precision of future data, leading to a more modest but still significant improvement. In addition to advances in supernova and CMB data, percent-level measurement of absolute distance and/or the expansion rate is required to ensure that dark energy constraints remain robust to variations in spatial curvature.
We study the effect of noise in the density field, such as would arise from a finite number density of tracers, on reconstruction of the acoustic peak within the context of Lagrangian perturbation theory. Reconstruction performs better when the density field is determined from denser tracers, but the gains saturate at n~1e-4(h/Mpc)^3. For low density tracers it is best to use a large smoothing scale to define the shifts, but the optimum is very broad.
To investigate the black hole mass vs. stellar velocity dispersion (\msigma) relation of active galaxies, we measured the velocity dispersions of a sample of local Seyfert 1 galaxies, for which we have recently determined black hole masses using reverberation mapping. For most objects, stellar velocity dispersions were measured from high signal-to-noise ratio optical spectra centered on the \ion{Ca}{2} triplet region ($\sim 8500$ \AA), obtained at the Keck, Palomar, and Lick Observatories. For two objects, in which the \ion{Ca}{2} triplet region was contaminated by nuclear emission, the measurement was based on high-quality $H$-band spectra obtained with the OH-Suppressing Infrared Imaging Spectrograph at the Keck-II Telescope. Combining our new measurements with data from the literature, we assemble a sample of 24 active galaxies with stellar velocity dispersions {\it and} reverberation-based black hole mass measurements in the range of black hole mass $10^{6}< \mbh/\msun < 10^{9}$. We use this sample to obtain reverberation mapping constraints on the slope and intrinsic scatter of the \msigma\ relation of active galaxies. Assuming a constant virial coefficient $f$ for the reverberation mapping black hole masses, we find a slope $\beta=3.55\pm0.60$ and the intrinsic scatter $\sigma_{\rm int}=0.43\pm0.08$ dex in the relation $\log (M_{\rm BH} / M_{\odot}) = \alpha + \beta \log (\sigma_{\ast} / {200}$ \kms), which are consistent with those found for quiescent galaxies. We derive an updated value of the virial coefficient $f$ by finding the value which places the reverberation masses in best agreement with the \msigma\ relation of quiescent galaxies; using the quiescent \msigma\ relation determined by G\"ultekin et al.\ we find $\log f=0.72^{+0.09}_{-0.10}$ with an intrinsic scatter of $0.44\pm0.07$ dex. No strong correlations between $f$ and parameters connected to the physics of accretion (such as the Eddington ratio or line-shape measurements) are found. The uncertainty of the virial coefficient remains one of the main sources of the uncertainty in black hole mass determinations using reverberation mapping, and therefore also in single-epoch spectroscopic estimates of black hole masses in active galaxies.
We study the gravitational fragmentation of cold accretion streams flowing into a typical first galaxy. We use a one-zone hydrodynamical model to examine the thermal evolution of the gas entering a 10^8 M_sun DM halo at z=10. The goal is to find the expected fragmentation mass scale and thus a characteristic mass of the first population of stars to form by shock fragmentation at high redshift. Our model accurately describes the chemical and thermal evolution of the gas as we are specifically concerned with how the cooling of the gas alters its fragmentation properties. We find there to be a sharp drop in the fragmentation mass at a metallicity of ~10^-4 Z_sun when a strong molecule destroying, LW background is present. However, If molecules can efficiently form, they dominate the cooling at T < 10^4 K, demonstrating no 'critical metallicity'. We also find that this physical scenario allows for the formation of a cluster of solar mass fragments, or a single 10^4 M_sun fragment, possibly the precursors to primeval clusters and SMBHs. Lastly, we conclude that the usual assumption of isobaricity for galactic shocks breaks down in gas of sufficiently high metallicity, suggesting that metal cooling may lead to thermal instabilities.
We model the time variability of ~9,000 spectroscopically confirmed quasars in SDSS Stripe 82 as a damped random walk. Using 2.7 million photometric measurements collected over 10 years, we confirm the results of Kelly et al. (2009) and Koz{\l}owski et al. (2010) that this model can explain quasar light curves at an impressive fidelity level (0.01-0.02 mag). The damped random walk model provides a simple, fast [O(N) for N data points], and powerful statistical description of quasar light curves by a characteristic time scale (tau) and an asymptotic rms variability on long time scales (SF_inf). We searched for correlations between these two variability parameters and physical parameters such as luminosity and black hole mass, and rest-frame wavelength. We find that tau increases with increasing wavelength with a power law index of 0.17, remains nearly constant with redshift and luminosity, and increases with increasing black hole mass with power law index of 0.21+/-0.07. The amplitude of variability is anti-correlated with the Eddington ratio, which suggests a scenario where optical fluctuations are tied to variations in the accretion rate. The radio-loudest quasars have systematically larger variability amplitudes by about 30%, when corrected for the other observed trends, while the distribution of their characteristic time scale is indistinguishable from that of the full sample. We do not detect any statistically robust differences in the characteristic time scale and variability amplitude between the full sample and the small subsample of quasars detected by ROSAT. Our results provide a simple quantitative framework for generating mock quasar light curves, such as currently used in LSST image simulations. (abridged)
We extend the concept of galaxy environment from the local galaxy number density to the gravitational potential and its functions like the shear tensor. For this purpose we examine whether or not one can make an accurate estimation of the gravitational potential from an observational sample which is finite in volume, biased due to galaxy biasing, and subject to redshift space distortion. Dark halos in a $\Lambda$CDM simulation are used in this test. We find that one needs to stay away from the sample boundaries by more than 30$h^{-1}$Mpc to reduce the error within 20% of the root mean square values of the potential or the shear tensor. The error due to the galaxy biasing can be significantly reduced by using the galaxy mass density field instead of the galaxy number density field. The error caused by the redshift space distortion can be effectively removed by correcting galaxy positions for the peculiar velocity effects. We inspect the dependence of dark matter halo properties on four environmental parameters; local density, gravitational potential, and the ellipticity and prolateness of the shear tensor. We find the local density has the strongest correlation with halo properties. This is evidence that the internal physical properties of dark halos are mainly controlled by small-scale physics. In high density regions dark halos are on average more massive and spherical, and have higher spin parameter and velocity dispersion. In high density regions dark halos are on average more massive and spherical, and have higher spin parameter and velocity dispersion. We also study the relation between the environmental parameters and the subtypes of dark halos. The spin parameter of satellite halos depends only weakly on the local density for all mass ranges studied while that of isloated or central halos depends more sensitively on the local density. (abridged)
We present a sample of 68 low-z MgII low-ionization broad absorption-line (loBAL) quasars. The sample is uniformly selected from the SDSS5 according to the following criteria: (1) 0.4<z<0.8, (2) median S/N>7, and (3) MgII absorption-line width > 1600 \kms. The last criterion is a trade-off between the completeness and consistency with respect to the canonical definition of BAL quasars that have the `balnicity index' BI>0 in CIV BAL. We adopted such a criterion to ensure that ~90% of our sample are classical BAL quasars and the completeness is ~80%, based on extensive tests using high-z quasar samples with measurements of both CIV and MgII BALs. We found (1) MgII BAL is more frequently detected in quasars with narrower Hbeta emission-line, weaker [OIII] emission-line, stronger optical FeII multiplets and higher luminosity. In term of fundamental physical parameters of a black hole accretion system, loBAL fraction is significantly higher in quasars with a higher Eddington ratio than those with a lower Eddington ratio. The fraction is not dependent on the black hole mass in the range concerned. The overall fraction distribution is broad, suggesting a large range of covering factor of the absorption material. (2) [OIII]-weak loBAL quasars averagely show undetected [NeV] emission line and a very small line ratio of [NeV] to [OIII]. However, the line ratio in non-BAL quasars, which is much larger than that in [OIII]-weak loBAL quasars, is independent of the strength of the [OIII] line. (3) loBAL and non-loBAL quasars have similar colors in near-infrared to optical band but different colors in ultraviolet. (4) Quasars with MgII absorption lines of intermediate width are indistinguishable from the non-loBAL quasars in optical emission line properties but their colors are similar to loBAL quasars, redder than non-BAL quasars. We also discuss the implication of these results.
We provide a physical interpretation and explanation of the morphology-density relation for galaxies, drawing on stellar masses, star-formation rates, axis ratios and group halo masses from the Sloan Digital Sky Survey (SDSS). We first re-cast the classical morphology-density relation in more quantitative terms, using low-star formation rate (quiescence) as a proxy for early-type morphology and dark matter halo mass from a group catalog as a proxy for environmental density: for galaxies of a given stellar mass the quiescent fraction is found to increase with increasing dark matter halo mass. Our novel result is that - at a given stellar mass - quiescent galaxies are significantly flatter in dense environments, implying a higher fraction of disk galaxies. Supposing that the denser environments differ simply by a higher incidence of quiescent disk galaxies that are structurally similar to star-forming disk galaxies of similar mass, explains simultaneously and quantitatively these quiescence-environment and shape-environment relations. Our findings add considerable weight to the slow removal of gas as the main physical driver of the morphology-density relation, at the expense of other explanations.
Results are presented from NIR spectroscopy of a sample of BzK-selected, massive star-forming galaxies (sBzKs) at 1.5<z<2.3 that were obtained with OHS/CISCO at Subaru and with SINFONI at VLT. Among the 28 sBzKs observed, Ha emission was detected in 14 objects, and for 11 of them the [NII]6583 was also measured. Multiwavelength photometry was also used to derive stellar masses and extinction parameters, whereas Ha and [NII] have allowed us to estimate SFR, metallicities, ionization mechanisms, and dynamical masses. In order to enforce agreement between SFRs from Ha with those derived from rest-frame UV and MIR, additional obscuration for the emission lines (that originate in HII regions) was required compared to the extinction derived from the slope of the UV continuum. We have also derived the stellar mass-metallicity relation, as well as the relation between stellar mass and specific SFR, and compared them to the results in other studies. At a given stellar mass, the sBzKs appear to have been already enriched to metallicities close to those of local star-forming galaxies of similar mass. The sBzKs presented here tend to have higher metallicities compared to those of UV-selected galaxies, indicating that NIR selected galaxies tend to be a chemically more evolved population. The sBzKs show specific SFRs that are systematically higher, by up to ~2 orders of magnitude, compared to those of local galaxies of the same mass. The empirical correlations between stellar mass and metallicity, and stellar mass and specific SFR are then compared with those of population synthesis models constructed either with the simple closed-box assumption, or within an infall scenario. Within the assumptions that are built-in such models, it appears that a short timescale for the star-formation (~100 Myr) and large initial gas mass appear to be required if one wants to reproduce both relations simultaneously.
It has been proposed that the gamma ray burst - supernova connection may manifest itself in a significant fraction of core collapse supernovae possessing mildly relativistic jets that do not break out of the stellar envelope. Neutrinos would provide proof of the existence of these jets. In the present letter we calculate the event rate of ~100 GeV neutrino-induced cascades in km^3 detectors. We also calculate the event rate for ~10 GeV neutrinos of all flavors with the DeepCore low energy extension of IceCube. The added event rate significantly improves the ability of km^3 detectors to search for these gamma-ray dark bursts. For a core collapse supernova at 10 Mpc we find ~4 events expected in DeepCore and ~6 neutrino-induced cascades in IceCube/KM3Net. Observations at ~10 GeV are mostly sensitive to the pion component of the neutrino production in the choked jet, while the ~100 GeV depends on the kaon component. Finally we discuss extensions of the on-going optical follow-up programs by IceCube and Antares to include neutrinos of all flavors at ~10 GeV and neutrino-induced cascades at ~100 GeV energies.
Is Dark Energy justified as an alternative to the cosmological constant $\Lambda$ in order to explain the acceleration of the cosmic expansion ? It turns out that a straightforward dimensional analysis of Einstein equation provides us with clear evidences that the geometrical nature of $\Lambda$ is the only viable source to this phenomenon, in addition of the application of Ockham's razor principle. This contribution is primarily a review of the main stream in the interpretation of $\Lambda$ because it is at the origin of such a research program.
This paper presents light curves and the first systematic characterization of variability of the 106 objects in the Fermi Large Area Telescope (LAT) Bright AGN Sample (LBAS). Weekly light curves obtained during the first 11 months of survey (August 04, 2008 - July 04, 2009), are tested for variability, and their properties are quantified through autocorrelation and structure function analysis. For the brightest sources power density spectra (PDS) and fit of the temporal structure of major flares is performed. More than 50% of the sources are variable, where high states do not exceed 1/4 of the total observation range. Variation amplitudes are larger for FSRQs and low/intermediate synchrotron peaked (LSP/ISP) BL Lac objects. Autocorrelation time scales vary from 4 to a dozen of weeks. Variable sources of the sample have 1/(f^{a}) PDS and show two modes: (1) rather constant baseline with sporadic flaring activity characterized by flatter PDS slopes resembling flickering and red-noise with occasional intermittence, and (2) - measured for a few blazars showing strong activity - complex and structured temporal profiles characterized by longer-term memory and steeper PDS slopes typical of a random-walk underlying mechanism. The average PDS slope of the brightest 22 FSRQs and the 6 brightest BL Lacs is 1.5 and 1.7 respectively. The study of temporal profiles of well resolved flares shows that they generally have symmetric profiles and that their total duration vary between 10 and 100 days.
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The new Wide Field Camera 3/IR observations on the Hubble Ultra-Deep Field started investigating the properties of galaxies during the reionization epoch. To interpret these observations, we present a novel approach inspired by the conditional luminosity function method. We calibrate our model to observations at z=6 and assume a non-evolving galaxy luminosity versus halo mass relation. We first compare model predictions against the luminosity function measured at z=5 and z=4. We then predict the luminosity function at z>=7 under the sole assumption of evolution in the underlying dark-matter halo mass function. Our model is consistent with the observed z>6.5 galaxy number counts in the HUDF survey and suggests a possible steepening of the faint-end slope of the luminosity function: alpha(z>8)< -1.9 compared to alpha=-1.74 at z=6. Although we currently see only the brightest galaxies, a hidden population of lower luminosity objects (L/L_{*}> 10^{-4}) might provide >75% of the total reionizing flux. Assuming escape fraction f_{esc}~0.2, clumping factor C~5, top heavy-IMF and low metallicity, galaxies below the detection limit produce complete reionization at z>8. For solar metallicity and normal stellar IMF, reionization finishes at z>6, but a smaller C/f_{esc} is required for an optical depth consistent with the WMAP measurement. Our model highlights that the star formation rate in sub-L_* galaxies has a quasi-linear relation to dark-matter halo mass, suggesting that radiative and mechanical feedback were less effective at z>6 than today.
We present Hubble Space Telescope UV and optical imaging of the radio galaxy 3C 236, whose relic 4 Mpc radio jet lobes and inner 2 kpc CSS radio source are evidence of multiple epochs of AGN activity. Our data confirm the presence of four bright knots of FUV emission in an arc along the edge of the inner circumnuclear dust disk in the galaxy's nucleus, as well as FUV emission cospatial with the nucleus itself. We interpret these to be sites of recent or ongoing star formation. We present photometry of these knots, as well as an estimate for the internal extinction in the source using the Balmer decrement from SDSS spectroscopy. We estimate the ages of the knots by comparing our extinction-corrected photometry with stellar population synthesis models. We find the four knots cospatial with the dusty disk to be young, of order 10^7 yr old. The FUV emission in the nucleus is likely due to an episode of star formation triggered ~10^9 yr ago. We argue that the young 10^7 yr old knots stem from an episode of star formation that was roughly coeval with the event resulting in reignition of radio activity, creating the CSS source. The 10^9 yr old stars in the nucleus may be associated with the previous epoch of activity that generated the 4 Mpc relic source, before it was cut off by exhaustion or interruption. The ages of the knots, considered in context with the disturbed morphology of the nuclear dust and the double-double morphology of the "old" and "young" radio sources, present evidence for an episodic AGN/starburst connection. We suggest that the AGN fuel supply was interrupted for ~10^7 yr due to a minor merger event and has now been restored, and the resultant non-steady flow of gas toward the nucleus is likely responsible for both the new episode of infall-induced star formation and also the multiple epochs of radio activity.
An initial state for the observable universe consisting of a finite region with a large vacuum energy will break-up due to near horizon quantum critical fluctuations. This will lead to a Freidman-like early universe consisting of an expanding cloud of dark energy stars and radiation. In this note we point out that this scenario provides a simple explanation for the present day density of dark matter as well as the level of CMB temperature flucuations. It is also predicted that all dark matter will be clumped on mass scales ~ 10E3 solar masses.
We study a class of early dark energy (EDE) models, in which, unlike in standard dark energy models, a substantial amount of dark energy exists in the matter-dominated era. We self-consistently include dark energy perturbations, and show that these models may be successfully constrained using future observations of galaxy clusters, in particular the redshift abundance, and the Sunyaev-Zel'dovich (SZ) power spectrum. We make predictions for EDE models, as well as $\Lambda$CDM for incoming X-ray (eROSITA) and microwave (South Pole Telescope) observations. We show that galaxy clusters' mass function and the SZ power spectrum will put strong constraints both on the equation of state of dark energy today and the redshift at which EDE transits to present-day $\Lambda$CDM like behavior for these models, thus providing complementary information to the geometric probes of dark energy. Not including perturbations in EDE models leads to those models being practically indistinguishable from $\Lambda$CDM.
We show an analytic method to construct a bivariate distribution function (DF) with given marginal distributions and correlation coefficient. We introduce a convenient mathematical tool, called a copula, to connect two DFs with any prescribed dependence structure. If the correlation of two variables is weak (Pearson's correlation coefficient $|\rho| <1/3 $), the Farlie-Gumbel-Morgenstern (FGM) copula provides an intuitive and natural way for constructing such a bivariate DF. When the linear correlation is stronger, the FGM copula cannot work anymore. In this case, we propose to use a Gaussian copula, which connects two given marginals and directly related to the linear correlation coefficient between two variables. Using the copulas, we constructed the BLFs and discuss its statistical properties. Especially, we focused on the FUV--FIR BLF, since these two luminosities are related to the star formation (SF) activity. Though both the FUV and FIR are related to the SF activity, the univariate LFs have a very different functional form: former is well described by the Schechter function whilst the latter has a much more extended power-law like luminous end. We constructed the FUV-FIR BLFs by the FGM and Gaussian copulas with different strength of correlation, and examined their statistical properties. Then, we discuss some further possible applications of the BLF: the problem of a multiband flux-limited sample selection, the construction of the SF rate (SFR) function, and the construction of the stellar mass of galaxies ($M_*$)--specific SFR ($SFR/M_*$) relation. The copulas turned out to be a very useful tool to investigate all these issues, especially for including the complicated selection effects.
We calculate the quadra-spectrum and quint-spectrum, corresponding to five and six point correlation functions of the curvature perturbation. For single field inflation with standard kinetic term, the quadra-spectrum and quint-spectrum are small, which are suppressed by slow roll parameters. The calculation can be generalized to multiple fields. When there is no entropy perturbation, the quadra-spectrum and quint-spectrum are suppressed as well. With the presence of entropy perturbation, the quadra-spectrum and quint-spectrum can get boosted. We illustrate this boost in the multi-brid inflation model. For the curvaton scenario, the quadra-spectrum and quint-spectrum are also large in the small r limit. We also calculate representative terms of quadra-spectrum and quint-spectrum for inflation with generalized kinetic terms, and estimate their order of magnitude for quasi-single field inflation.
The origin of life and the origin of the universe represent two of the most important problems of science. Both are resolved by hydro-gravitational dynamics (HGD) cosmology (Gibson 1996, Schild 1996, Gibson 2009ab), which predicts frozen primordial hydrogen-helium gas planets in clumps as the dark matter of galaxies. Merging Earth-mass planets formed stars, moons and comets to incubate and cosmically seed the first life. Cometary panspermia (Hoyle and Wickramasinghe 1981, 1982; Wickramasinghe et al. 2009) occurs naturally by HGD mechanisms. Comets and moons are fragments from mergers of stardust covered frozen gas planets in their step-wise growth to star mass. Supernovae from stellar over-accretion of planets produce stardust (C, N, O, P etc.) chemical fertilizer. Planets collect this infected radioactive dust gravitationally, to provide liquid water domains in contact with life nutrients seeded with life prototypes. The first mutating, evolving, life from HGD likely occurred promptly, following the plasma to gas transition 300,000 years after the big bang when high densities of galaxies and a superabundance of hot primordial soup kitchens first overcame enormous odds against spontaneous creation (Wickramasinghe 2010, Joseph 2000). Images from optical, radio, and infrared space telescopes suggest life on Earth was neither first nor inevitable.
We present UV broadband photometry and optical emission-line measurements for a sample of 32 Brightest Cluster Galaxies (BCGs) in clusters of the Representative XMM-Newton Cluster Structure Survey (REXCESS) with z = 0.06-0.18. The REXCESS clusters, chosen to study scaling relations in clusters of galaxies, have X-ray measurements of high quality. The trends of star formation and BCG colors with BCG and host properties can be investigated with this sample. The UV photometry comes from the XMM Optical Monitor, supplemented by existing archival GALEX photometry. We detected H\alpha and forbidden line emission in 7 (22%) of these BCGs, in optical spectra. All of the emission-line BCGs occupy clusters classified as cool cores, for an emission-line incidence rate of 70% for BCGs in cool core clusters. Significant correlations between the H\alpha equivalent widths, excess UV production in the BCG, and the presence of dense, X-ray bright intracluster gas with a short cooling time are seen, including the fact that all of the H\alpha emitters inhabit systems with short central cooling times and high central ICM densities. Estimates of the star formation rates based on H\alpha and UV excesses are consistent with each other in these 7 systems, ranging from 0.1-8 solar masses per year. The incidence of emission-line BCGs in the REXCESS sample is intermediate, somewhat lower than in other X-ray selected samples (-35%), and somewhat higher than but statistically consistent with optically selected, slightly lower redshift BCG samples (-10-15%). The UV-optical colors (UVW1-R-4.7\pm0.3) of REXCESS BCGs without strong optical emission lines are consistent with those predicted from templates and observations of ellipticals dominated by old stellar populations. We see no trend in UV-optical colors with optical luminosity, R-K color, X-ray temperature, redshift, or offset between X-ray centroid and X-ray peak (<w>).
We compute the one-point probability distribution function (pdf) of small-angle CMB temperature fluctuations due to curved cosmic (super-)strings with a simple model of string network by performing Monte Carlo simulations. Taking into account of the correlation between the curvature and the velocity of string segments, there appear non-Gaussian features, specifically non-Gaussian tails and a skewness, in the one-point pdf. The obtained sample skewness for the intercommuting probability P=1 is $g_1\approx -0.14$, which is consistent with the result reported by Fraisse et al.. We also discuss the dependence of the pdf on $P$. We find that the standard deviation of the Gaussian part increases and non-Gaussian features are suppressed as $P$ decreases. For sufficiently small $P$, the skewness is given by $\lesssim \text{(a\ few)}\times 10^{-2}$.
We use the first compilation of 72 core-collapse supernovae (SNe) from the Palomar Transient Factory (PTF) to study their observed subtype distribution in dwarf galaxies compared to giant galaxies. The nature of the PTF survey provides a minimally biased sample, rich in SNe from dwarf hosts, with spectroscopic classifications. With 15 events detected in dwarf galaxies, our results are still limited by small-number statistics. However, several interesting trends emerge. We find more core-collapse SNe in dwarf galaxies than expected, with a similar N(Ib/c)/N(II) ratio in dwarf and giant hosts (0.25_{-0.15}^{+0.3} and 0.23_{-0.08}^{+0.11}, respectively), although our uncertainties (1 sigma) are still too large to distinguish between these results and those of previous studies and theoretical predictions. We use detailed subclassifications of stripped-envelope core-collapse SNe and find that all Type I core-collapse events occurring in dwarf galaxies are either SNe Ib or broad-lined SNe Ic (SNe Ic-BL), while "normal" SNe Ic dominate in giant galaxies. We also see a significant excess of SNe IIb in dwarf hosts. We hypothesize that in lower metallicity hosts, metallicity-driven mass loss is reduced, allowing massive stars that would have appeared as "normal" SNe Ic in metal-rich galaxies to retain some He and H, exploding as Ib/IIb events. At the same time, another mechanism allows some stars to undergo extensive stripping and explode as SNe Ic-BL (and presumably also as long-duration gamma-ray bursts). As additional PTF data accumulate, more robust statistical analyses will be possible, allowing the evolution of massive stars to be probed via the dwarf-galaxy SN population.
(Abridged) We performed a multiwavelength analysis of a sample of starburst galaxies that show the presence of a substantial population of very young massive (WR) stars. Here we present the global analysis of the derived photometric and chemical properties. We compare optical/NIR colours and the physical properties (reddening coefficient, equivalent widths of the emission and underlying absorption lines, ionization degree, electron density, and electron temperature) and chemical properties with previous observations and galaxy evolution models. Attending to their absolute B-magnitude many of them are not dwarf galaxies, but they should be during their quiescent phase. We found that both C(Hb) and Wabs increase with increasing metallicity. We detected a high N/O ratio in objects showing strong WR features. The ejecta of the WR stars may be the origin of the N enrichment in these galaxies. We compared the abundances provided by the direct method with those obtained using empirical calibrations, finding that (i) the Pilyugin method is the best suitable empirical calibration, (ii) the relations between the oxygen abundance and the N2 or the O3N2 parameters provided by Pettini & Pagel (2004) give acceptable results for objects with 12+log(O/H)>8.0, and (iii) the results provided by empirical calibrations based on photoionization models are systematically 0.2-0.3 dex higher than the values derived from the direct method. The O and N abundances and the N/O ratios are related to the optical/NIR luminosity; the dispersion is consequence of the differences in the star-formation histories. Galaxies with redder colours tend to have higher oxygen and nitrogen abundances. Our detailed analysis is fundamental to understand the nature of galaxies showing strong starbursts, as well as to know their star formation history and the relationships with the environment.
Observations made during the last ten years with the Chandra X-ray Observatory have shed much light on the cooling gas in the centers of clusters of galaxies and the role of active galactic nucleus (AGN) heating. Cooling of the hot intracluster medium in cluster centers can feed the supermassive black holes found in the nuclei of the dominant cluster galaxies leading to AGN outbursts which can reheat the gas, suppressing cooling and large amounts of star formation. AGN heating can come in the form of shocks, buoyantly rising bubbles that have been inflated by radio lobes, and the dissipation of sound waves.
We present the McMaster Unbiased Galaxy Simulations (MUGS), the first 9 galaxies of an unbiased selection ranging in total mass from 5$\times10^{11}$ M$_\odot$ to 2$\times10^{12}$ M$_\odot$ simulated using n-body smoothed particle hydrodynamics (SPH) at high resolution. The simulations include a treatment of low temperature metal cooling, UV background radiation, star formation, and physically motivated stellar feedback. Mock images of the simulations show that the simulations lie within the observed range of relations such as that between color and magnitude and that between brightness and circular velocity (Tully-Fisher). The greatest discrepancy between the simulated galaxies and observed galaxies is the high concentration of material at the center of the galaxies as represented by the centrally peaked rotation curves and the high bulge-to-total ratios of the simulations determined both kinematically and photometrically. This central concentration represents the excess of low angular momentum material that long has plagued morphological studies of simulated galaxies and suggests that higher resolutions and a more accurate description of feedback will be required to simulate more realistic galaxies. Even with the excess central mass concentrations, the simulations suggest the important role merger history and halo spin play in the formation of disks.
Spitzer Space Telescope observations revealed powerful mid-infrared (mid-IR) H2 rotational line emission from the Stephan's Quintet (SQ) X-ray emitting large scale shock associated with a collision between two galaxies. Because H2 forms on dust grains, the presence of H2 is physically linked to the survival of dust, and we expect some dust emission to come from the molecular gas. To test this interpretation, IR observations and dust modeling are used to identify and characterize the thermal dust emission from the shocked molecular gas. The spatial distribution of the IR emission allows us to isolate the faint PAH and dust continuum emission associated with the molecular gas in the SQ shock. We model the spectral energy distribution (SED) of this emission, and fit it to Spitzer observations. Faint PAH and dust continuum emission are detected in the SQ shock, outside star-forming regions. The 12/24um flux ratio in the shock is remarkably close to that of the diffuse Galactic interstellar medium, leading to a Galactic PAH/VSG abundance ratio. However, the properties of the PAH emission spectrum in the shock differ from that of the Galaxy, which may suggest an enhanced fraction of large and neutrals PAHs. The IR SED is consistent with the expected emission from dust associated with the warm (>150K) H2 gas, heated by a UV radiation field of intensity comparable to that of the solar neighborhood, in agreement with GALEX UV observations. The presence of PAHs and dust grains in the high-speed (1000km/s) galaxy collision suggests that dust survives. We propose that the dust that survived destruction was in pre-shock gas at densites larger than a few 0.1cm-3, which was not shocked at velocities larger than 200km/s. [abridged]
We investigate the stellar masses of strongly barred spiral galaxies. Our analysis is based on a sample of ~14000 visually-classified nearby galaxies given in Nair & Abraham 2010(a). The fraction of barred spiral galaxies is found to be a strong function of stellar mass and star formation history, with a minimum near the characteristic mass at which bimodality is seen in the stellar populations of galaxies. We also find bar fractions are very sensitive to the central concentration of galaxies below the transition mass but not above it. This suggests that whatever process is causing the creation of the red and blue sequences is either influencing, or being influenced by, structural changes which manifest themselves in the absence of bars. As a consequence of strong bar fractions being sensitive to the mass range probed, our analysis helps resolve discrepant results on the reported evolution of bar fractions with redshift.
Previous studies of the active galactic nuclei (AGN) contribution to the cosmic X-ray background (CXB) consider only observable parameters such as luminosity and absorbing column. Here, for the first time, we extend the study of the CXB to physical parameters including the Eddington ratio of the sources and the black hole mass. In order to calculate the contribution to the CXB of AGN accreting at various Eddington ratios, an evolving Eddington ratio space density model is calculated. In particular, Compton thick (CT) AGN are modeled as accreting at specific, physically motivated Eddington ratios instead of as a simple extension of the Compton thin type 2 AGN population. Comparing against the observed CT AGN space densities and log N-log S relation indicates that CT AGN are likely a composite population of AGN made up of sources accreting either at >90% or <1% of their Eddington rate.
The collisions of cosmic strings loops and the dynamics of junctions formations in expanding backgrounds are studied. The key parameter controlling the dynamics of junctions formation, the cosmic strings zipping and unzipping is the relative size of the loops compared to the Hubble expansion rate at the time of collision. We study analytically and numerically these processes for large super-horizon size loops, for small sub-horizon size loops as well as for loops with the radii comparable to the Hubble expansion rate at the time of collision.
We study how well the mass of the graviton can be constrained from gravitational-wave (GW) observations of coalescing binary black holes. Whereas the previous investigations employed post-Newtonian (PN) templates describing only the inspiral part of the signal, the recent progress in analytical and numerical relativity has provided analytical waveform templates coherently describing the inspiral-merger-ringdown (IMR) signals. We show that a search for binary black holes employing IMR templates will be able to constrain the mass of the graviton much more accurately (about an order of magnitude) than a search employing PN templates. The best expected bound from GW observatories (lambda_g > 7.8 x 10^13 km from Adv. LIGO, lambda_g > 7.1 x 10^14 km from Einstein Telescope, and lambda_g > 5.9 x 10^17 km from LISA) are several orders-of-magnitude better than the best available model-independent bound (lambda_g > 2.8 x 10^12 km, from Solar system tests). Most importantly, GW observations will provide the first constraints from the highly dynamical, strong-field regime of gravity.
In this work, we consider the cosmological constraints on the interacting dark energy models. We generalize the models considered previously by Guo {\it et al.}, Costa and Alcaniz, and try to discuss two general types of models: type I models are characterized by $\rho_{_X}/\rho_m=f(a)$ and $f(a)$ can be any function of scale factor $a$, whereas type II models are characterized by $\rho_m=\rho_{m0}\,a^{-3+\epsilon(a)}$ and $\epsilon(a)$ can be any function of $a$. We obtain the cosmological constraints on the type I and II models with power-law, CPL-like, logarithmic $f(a)$ and $\epsilon(a)$ by using the latest observational data.
We provide a geometric explanation for the existence of magnification relations for the A, D, E family of caustic singularities, which were established in recent work. In particular, it was shown that for families of general mappings between planes exhibiting any of these caustic singularities, and for any non-caustic target point, the total signed magnification of the corresponding pre-images vanishes. As an application to gravitational lensing, it was also shown that, independent of the choice of a lens model, the total signed magnification vanishes for a light source anywhere in the four-image region close to elliptic and hyperbolic umbilic caustics. This is a more global and higher-order analog of the well-known fold and cusp magnification relations. We now extend each of these mappings to weighted projective space, which is a compact orbifold, and show that magnification relations translate into a statement about the behavior of these extended mappings at infinity. This generalizes multi-dimensional residue techniques developed in previous work, and introduces weighted projective space as a new tool in the theory of caustic singularities and gravitational lensing.
In a large class of models we show that the light scalar field responsible for the Sommerfeld enhancement in the annihilation of dark matter leads to observable direct detection rates, due to its mixing with the standard model Higgs. As a result the large annihilation cross-section of dark matter at present epoch, required to explain the observed cosmic ray anomalies, can be strongly constrained by direct searches. In particular Sommerfeld boost factors of order of a few hundred are already out of the CDMS-II upper bound at 90% confidence level for reasonable values of the model parameters.
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Scaling relations of observed galaxy cluster properties are useful tools for constraining cosmological parameters as well as cluster formation histories. One of the key cosmological parameters, sigma8, is constrained using observed clusters of galaxies, although current estimates of sigma8 from the scaling relations of dynamically relaxed galaxy clusters are limited by the large scatter in the observed cluster mass-temperature (M-T) relation. With a sample of eight strong lensing clusters at 0.3 < z <0.8, we find that the observed cluster concentration-mass relation can be used to reduce the M-T scatter by a factor of 6. Typically only relaxed clusters are used to estimate sigma8, but combining the cluster concentration-mass relation with the M-T relation enables the inclusion of unrelaxed clusters as well. Thus, the resultant gains in the accuracy of sigma8 measurements from clusters are twofold: the errors on sigma8 are reduced and the cluster sample size is increased. Therefore, the statistics on sigma8 determination from clusters are greatly improved by the inclusion of unrelaxed clusters. Exploring cluster scaling relations further, we find that the correlation between brightest cluster galaxy (BCG) luminosity and cluster mass offers insight into the assembly histories of clusters. We find preliminary evidence for a steeper BCG luminosity - cluster mass relation for strong lensing clusters than the general cluster population, hinting that strong lensing clusters may have had more active merging histories.
We update cosmological hot dark matter constraints on neutrinos and hadronic axions. Our most restrictive limits use 7-year data from the Wilkinson Microwave Anisotropy Probe for the cosmic microwave background anisotropies, the halo power spectrum (HPS) from the 7th data release of the Sloan Digital Sky Survey, and the Hubble constant from Hubble Space Telescope observations. We find 95% C.L. upper limits of \sum m_\nu<0.44 eV (no axions), m_a<0.91 eV (assuming \sum m_\nu=0), and \sum m_\nu<0.41 eV and m_a<0.72 eV for two hot dark matter components after marginalising over the respective other mass. CMB data alone yield \sum m_\nu<1.19 eV (no axions), while for axions the HPS is crucial for deriving m_a constraints. This difference can be traced to the fact that for a given hot dark matter fraction axions are much more massive than neutrinos.
Using a combined analysis of strong lensing and galaxy dynamics, we characterize the mass distributions and M/L ratios of galaxy groups, which form an important transition regime in Lambda-CDM cosmology. By mapping the underlying mass distribution, we test whether groups are dark matter dominated as hypothesized by the standard cosmogony, or isothermal as observed in baryon rich field galaxies. We present our lensing + galaxy dynamics formalism built around the dark matter dominant NFW and Hernquist distributions, compared against the Isothermal Sphere observed in galaxy scale objects. We show that mass measurement in the core of the group (r ~ 0.2 r_{vir}), determined jointly from a lens model and from differential velocity dispersion estimates, may effectively distinguish between these density distributions. We apply our method to MOS observations of two groups, SL2SJ1430+5546 and SL2SJ1431+5533, drawn from our CFHTLS lens catalog. With the measured lensing and dynamical masses, combined with a maximum likelihood estimator built around our model, we estimate the concentration index characterizing each density distribution and the corresponding virial mass of each group. Our results indicate that both groups are dark matter dominant, and reject the Isothermal distribution at >>3 sigma level. For both groups, the estimated i-band M/L ratios of ~260 Msun/Lsun, are similar to other published values for groups. The Gaussian distributions of the velocities of their member galaxies support a high degree of virialization. The differences in their virial masses, 2.8 and 1.6 x 10^14 Msun, and velocity dispersions, 720 and 560 km/s respectively, may indicate however that each group is at a different stage of transition to a cluster. We aim to populate this important transition regime with additional results from ongoing observations of the remaining lensing groups in our catalog.
Low-ionization broad absorption line quasars probe the relatively obscured quasar population, and could be at the early evolutionary stage for quasars. We study the intrinsic fraction of low-ionization (MgII, FeII) broad absorption quasars (LoBALs) using the SDSS, 2MASS, and FIRST surveys. We find that the LoBAL fractions of near infra-red (NIR) and radio samples are 4.0\pm0.5%, 7.2\pm0.6%, and 3.6\pm1.0%, respectively, for Bi-LoBALs, Ai-LoBALs, and FeLoBALs, approximately 5-7 times higher than those measured in the optical sample. This suggests that the fractions measured in the NIR and radio bands are the intrinsic fractions of the populations, and that the optical fractions are significantly biased due to the obscuration effects, similar to high-ionization broad absorption line quasars (HiBALs). We also find that the LoBAL fractions decrease with increasing radio luminosity, again, similar to the HiBALs. The similarity between LoBALs and HiBALs in their NIR and radio properties suggests that the majority of LoBALs and HiBALs can be unified under the same physical scheme. Using a geometric model, we are able to reproduce the NIR, radio properties, and the intrinsic fractions for the majority of broad absorption line quasars including the low-ionization ones. In addition, we find tentative evidence for high fractions of LoBALs at high NIR luminosities, especially for FeLoBALs with a fraction of ~18% for M_K_s < -31 mag. This population of most NIR luminous low-ionization broad absorption line quasars may be at an early evolutionary stage of quasar evolution.
We report results from a survey of MgII absorbers in the spectra of background QSOs that are within close angular distances to a foreground galaxy at z<0.5, using the Magellan Echellette Spectrograph. We have established a spectroscopic sample of 94 galaxies at a median redshift of <z> = 0.24 in fields around 70 distant background QSOs (z_QSO>0.6), 71 of which are in an 'isolated' environment with no known companions and located at rho <~ 120 h^-1 kpc from the line of sight of a background QSO. The rest-frame absolute B-band magnitudes span a range from M_B-5log h=-16.4 to M_B-5log h=-21.4 and rest-frame B_AB-R_AB colors range from B_AB-R_AB~0 to B_AB-R_AB~1.5. Of these 'isolated' galaxies, we find that 47 have corresponding MgII absorbers in the spectra of background QSOs and rest-frame absorption equivalent width W_r(2796)=0.1-2.34 A, and 24 do not give rise to MgII absorption to sensitive upper limits. Our analysis shows that (1) Wr(2796) declines with increasing distance from 'isolated' galaxies but shows no clear trend in 'group' environments; (2) more luminous galaxies possess more extended MgII absorbing halos with the gaseous radius scaled by B-band luminosity according to R_gas=75x(L_B/L_B*)^(0.35+/-0.03) h^{-1} kpc; (3) there is little dependence between the observed absorber strength and galaxy intrinsic colors; and (4) within R_gas, we find a mean covering fraction of <kappa_0.3>~70% for absorbers of Wr(2796)>=0.3 A and <kappa_0.1>~80% for absorbers of Wr(2796)>=0.1 A. The lack of correlation between Wr(2796) and galaxy colors suggests a lack of physical connection between the origin of extended MgII halos and recent star formation history of the galaxies. Finally, we discuss the total gas mass in galactic halos as traced by MgII absorbers. We also compare our results with previous studies.
Semi-analytic models are a powerful tool for studying the formation of galaxies. However, these models inevitably involve a significant number of poorly constrained parameters that must be adjusted to provide an acceptable match to the observed universe. In this paper, we set out to quantify the degree to which observational data-sets can constrain the model parameters. By revealing degeneracies in the parameter space we can hope to better understand the key physical processes probed by the data. We use novel mathematical techniques to explore the parameter space of the GALFORM semi-analytic model. We base our investigation on the Bower et al. 2006 version of GALFORM, adopting the same methodology of selecting model parameters based on an acceptable match to the local bJ and K luminosity functions. The model contains 16 parameters that are poorly constrained, and we investigate this parameter space using the Model Emulator technique, constructing a Bayesian approximation to the GALFORM model that can be rapidly evaluated at any point in parameter space. By combining successive waves of emulation, we show that only 0.26% of the initial volume is of interest for further exploration. However, within this region we show that the Bower et al. 2006 model is only one choice from an extended sub-space of model parameters that can provide equally acceptable fits. We explore the geometry of this region and begin to explore the physical connections between parameters that are exposed by this analysis. We also consider the impact of adding additional observational data to further constrain the parameter space.
From multi-wavelength observations of LAEs,we know that while many LAEs appear to be young and less massive,a noticeable fraction of LAEs possess much older populations of stars and larger stellar mass.How these two classes of LAEs are concordant with the hierarchical galaxy formation scenario has not been understood clearly so far.In this paper,we model LAEs by three-dimensional cosmological simulations of dark halo merger in a CDM universe.As a result,it is shown that the age of simulated LAEs can spread over a wide range from 2*10^6yr to 9*10^8yr.Also,we find that there are two types of LAEs, in one of which the young half-mass age is comparable to the mean age of stellar component,and in the other of which the young half-mass age is appreciably shorter than the mean age.We define the former as Type 1 LAEs and the latter as Type 2 LAEs.A Type 1 corresponds to early starburst in a young galaxy,whereas a Type 2 does to delayed starburst in an evolved galaxy,as a consequence of delayed accretion of a subhalo onto a larger parent halo.Thus,the same halo can experience a Type 2 LAE-phase as well as a Type 1 LAE-phase in the merger history.Type 1s are expected to be younger than 1.5*10^8yr,less dusty,and less massive with stellar mass M*<10^8 Msun,while Type 2s are older than 1.5*10^8yr,even dustier,and as massive as M*~10^8-10^10Msun.The fraction of Type 2s in all LAEs is a function of redshift.Type 2s discriminated clearly from Type 1s in two color diagram of z'-H vs J-K.We find that the brightness distribution of LyA in Type 2s is more extended than the main stellar component,in contrast to Type 1s.This is not only because delayed starbursts tend to occur in the outskirts of a parent galaxy,but also because LyA photons are effectively absorbed by dust in an evolved galaxy.Hence,the extent of LyA emission may be an additional measure to distinguish Type 2s from Type 1s
(Abridged) A procedure is suggested to explore the value of F = alpha^2/mu, where mu = m_e/m_p is the electron-to-proton mass ratio, and alpha is the fine-structure constant. The fundamental physical constants, which are measured in different physical environments of high (terrestrial) and low (interstellar) densities of baryonic matter are supposed to vary in chameleon-like scalar field models, which predict that both masses and coupling constant may depend on the local matter density. The parameter Delta F/F = (F_obs - F_lab)/F_lab can be estimated from the radial velocity offset, Delta V = V_rot-V_fs, between the low-laying rotational transitions in carbon monoxide 13CO and the fine-structure transitions in atomic carbon [CI]. A model-dependent constraint on Delta alpha/alpha can be obtained from Delta F/F using Delta mu/mu independently measured from the ammonia method. Currently available radio astronomical datasets provide an upper limit on |Delta V| < 110 m/s (1sigma). When interpreted in terms of the spatial variation of F, this gives |Delta F/F| < 3.7*10^-{7}. An order of magnitude improvement of this limit will allow us to test independently a non-zero value of Delta mu/mu = (2.2 +/- 0.4_stat +/- 0.3_sys)*10^{-8} recently found with the ammonia method. Taking into account that the ammonia method restricts the spatial variation of mu at the level of |Delta mu/mu| <= 3*10^{-8} and assuming that Delta F/F is the same in the entire interstellar medium, one obtains that the spatial variation of alpha does not exceed the value |Delta alpha/alpha| < 2*10^{-7}. Since extragalactic gas clouds have densities similar to those in the interstellar medium, the bound on Delta alpha/alpha is also expected to be less than 2*10^{-7} at high redshift if no significant temporal dependence of alpha is present.
We calculate the trispectrum in ghost inflation where both the contact diagram and scale-exchange diagram are taken into account. The shape of trispectrum is discussed carefully and we find that the local form is absent in ghost inflation. In general, for the non-local shape trispectrum there are not analogous parameters to $\tau_{NL}^{loc.}$ and $g_{NL}^{loc.}$ which can completely characterize the size of local form trispectrum.
The non-Gaussian distribution of primordial perturbations has the potential to reveal the physical processes at work in the very early Universe. Local models provide a well-defined class of non-Gaussian distributions that arise naturally from the non-linear evolution of density perturbations on super-Hubble scales starting from Gaussian field fluctuations during inflation. I describe the delta-N formalism used to calculate the primordial density perturbation on large scales and then review several models for the origin of local primordial non-Gaussianity, including the cuvaton, modulated reheating and ekpyrotic scenarios. I include an appendix with a table of sign conventions used in specific papers.
We present SHARC-2 350 micron data on 20 luminous z~2 starbursts with S(1.2mm) > 2 mJy from the Spitzer-selected samples of Lonsdale et al. 2009 and Fiolet et al. 2009. All the sources were detected, with S(350um) > 25 mJy for 18. With the data we determine precise dust temperatures and luminosities for these galaxies, using on both single-temperature fits and models with powerlaw mass--temperature distributions. We derive appropriate formulae to use when optical depths are non-negligible. Our models provide an excellent fit to the 6um -- 2mm measurements of local starbursts. We find characteristic single-component temperatures T1 ~ 35.5 +- 2.2 K and integrated IR luminosities around 10^(12.9+-0.1) Lsun for the SWIRE-selected sources. Molecular gas masses are estimated at ~4*10^(10) Msun, assuming kappa(850um)=0.15 m^2/kg and an SMG-like gas-to-dust mass ratio. The best-fit models imply >~2 kpc emission scales. We also note a tight correlation between rest-frame 1.4 GHz radio and IR luminosities confirming star-formation as the predominant power source. The far-infrared properties of our sample are indistinguishable from the purely submillimeter-selected galaxy (SMG) populations from current surveys. We therefore conclude that our original selection criteria, based on mid-infrared IRAC colors and 24 micron flux densities, provides an effective means for the study of SMGs at z ~ 1.5--2.5.
Force balance considerations put a limit on the rate of AGN radiation momentum output, $L/c$, capable of driving galactic superwinds. We show that this condition is insufficient: black holes obeying the observed $\mbh -\sigma $ relation cannot supply enough energy in radiation which can drive the gas out by pressure alone. The shortfall is by up to an order of magnitude in most, but not all, cases. We propose that outflow-triggering of star formation by enhancing the intercloud medium turbulent pressure and squeezing clouds can supply the necessary boost, and suggest possible tests of this hypothesis. We further point out that the time-scales for Bondi accretion and for orbital decay of merging clumps by dynamical friction in the nuclear disk around a central black hole both follow a similar scaling with mass, favoring the most massive black holes, but the latter process is up to two orders of magnitude more rapid at $z\gtsim 10.$ The combination of accretion and coalescence results in earlier formation of more massive black holes, and, in particular, can account for the masses of the black holes inferred to power AGN at $z\sim 6.$
We compute the contribution of kinks on cosmic string loops to stochastic background of gravitational waves (SBGW).We find that kinks contribute at the same order as cusps to the SBGW.We discuss the accessibility of the total background due to kinks as well as cusps to current and planned gravitational wave detectors, as well as to the big bang nucleosynthesis (BBN), the cosmic microwave background (CMB), and pulsar timing constraints. As in the case of cusps, we find that current data from interferometric gravitational wave detectors, such as LIGO, are sensitive to areas of parameter space of cosmic string models complementary to those accessible to pulsar, BBN, and CMB bounds.
The methods of effective field theory are used to study generic theories of inflation with a single inflaton field and to perform a general analysis of the associated non-Gaussianities. We investigate the amplitudes and shapes of the various generic three-point correlators, the bispectra, which may be generated by different classes of single-field inflationary models. Besides the well-known results for the DBI-like models and the ghost inflationary theories, we point out that curvature-related interactions may give rise to large non-Gaussianities in the form of bispectra characterized by a flat shape which is rather uncommon in single-field models of inflation. In a subsequent work, we will perform a similar general analysis for the non-Gaussianities generated by the generic four-point correlator, the trispectrum.
Observing inversion lines of ammonia (NH3), complemented by rotational lines of NH3 and other molecular species, provides stringent constraints on potential variations of the proton-to-electron mass ratio. While a limit of one part per million is derived for a lookback time of 7 billion years, nearby dark clouds might show a statistically significant variation of order 20-30 parts per billion, possibly being related to chameleon fields. The detection of radio-loud quasars with strong molecular absorption lines at redshifts z > 1 as well as the identification of a larger sample of nearby dark clouds with exceptionally narrow lines (<0.2 km/s) would be essential to improve present limits and to put the acquired results onto a firmer statistical basis.
We have used the Spitzer satellite to monitor the mid-IR evolution of SN 1987A over a 5 year period spanning the epochs between days 6000 and 8000 since the explosion. The supernova (SN) has evolved into a supernova remnant (SNR) and its radiative output is dominated by the interaction of the SN blast wave with the pre-existing equatorial ring (ER). The mid-IR spectrum is dominated by emission from ~180 K silicate dust, collisionally-heated by the hot X-ray emitting gas with a temperature and density of ~5x10^6 K and 3x10^4 cm-3, respectively. The mass of the radiating dust is ~1.2x10^(-6) Msun on day 7554, and scales linearly with IR flux. The infrared to soft-X-ray flux ratio is roughly constant with a value of 2.5. Gas-grain collisions therefore dominate the cooling of the shocked gas. The constancy of of this ratio suggests that very little grain processing or gas cooling have occurred throughout this epoch. The shape of the dust spectrum remained unchanged during the observations while the total flux increased with a time dependence of t^(0.87), t being the time since the first encounter between the blast wave and the ER. These observations are consistent with the transitioning of the blast wave from free expansion to a Sedov phase as it propagates into the main body of the ER.
By the application of the generalized Israel junction conditions we derive cosmological equations for the fourth-order $f(R)$ brane gravity and study their cosmological solutions. We show that there exists a solution which describes a four-dimensional de-Sitter $(dS_4)$ brane embedded in a five-dimensional anti-de-Sitter $(AdS_5)$ bulk for a vanishing Weyl tensor contribution. On the other hand, for the case of a non-vanishing Weyl tensor contribution, there exists a static Einstein universe brane. We claim that in order to get some more general non-static $f(R)$ brane configurations, one needs to admit a dynamical matter energy-momentum tensor in the bulk rather than just a bulk cosmological constant.
TeV-mass dark matter charged under a new GeV-scale gauge force can explain electronic cosmic-ray anomalies. We propose that the CoGeNT and DAMA direct detection experiments are observing scattering of light stable states -- "GeV-Matter" -- that are charged under this force and constitute a small fraction of the dark matter halo. Dark higgsinos in a supersymmetric dark sector are natural candidates for GeV-Matter that scatter off protons with a universal cross-section of 5 x 10^{-38} cm^2 and can naturally be split by 10-30 keV so that their dominant interaction with protons is down-scattering. As an example, down-scattering of an O(5) GeV dark higgsino can simultaneously explain the spectra observed by both CoGeNT and DAMA. The event rates in these experiments correspond to a GeV-Matter abundance of 0.2-1% of the halo mass density. This abundance can arise directly from thermal freeze-out at weak coupling, or from the late decay of an unstable TeV-scale WIMP. Our proposal can be tested by searches for exotics in the BaBar and Belle datasets.
We present a complete explicit N=1, d=4 supergravity action in an arbitrary Jordan frame with non-minimal scalar-curvature coupling of the form $\Phi(z, \bar z)\, R$. The action is derived by suitably gauge-fixing the superconformal action. The theory has a modified Kaehler geometry, and it exhibits a significant dependence on the frame function $\Phi (z, \bar z)$ and its derivatives over scalars, in the bosonic as well as in the fermionic part of the action. Under certain simple conditions, the scalar kinetic terms in the Jordan frame have a canonical form. We consider an embedding of the Next-to-Minimal Supersymmetric Standard Model (NMSSM) gauge theory into supergravity, clarifying the Higgs inflation model recently proposed by Einhorn and Jones. We find that the conditions for canonical kinetic terms are satisfied for the NMSSM scalars in the Jordan frame, which leads to a simple action. However, we find that the gauge singlet field experiences a strong tachyonic instability during inflation in this model. Thus, a modification of the model is required to support the Higgs-type inflation.
We carefully analyze how the abundance of Nitrogen over Oxygen evolves when dependent on metallicity stellar yields with a primary component of N proceeding from AGBs stars are used. We show the results obtained with a chemical evolution models grid, calculated with variable star formation efficiencies, which produce different star formation histories. Finally we see how the N/O abundance is related on the evolutionary history.
We consider spherically symmetric inhomogeneous dust models with a positive cosmological constant, $\Lambda$, given by the Lemaitre-Tolman-Bondi metric. These configurations provide a simple but useful generalization of the Lambda-CDM model describing cold dark matter (CDM) and a Lambda term, which seems to fit current cosmological observations. The dynamics of these models can be fully described by scalar evolution equations that can be given in the form of a proper dynamical system associated with a 4-dimensional phase space whose critical points and invariant subspaces are examined and classified. The phase space evolution of various configurations is studied in detail by means of two 2-dimensional subspaces: a projection into the invariant homogeneous subspace associated with Lambda-CDM solutions with FLRW metric, and a projection into a subspace generated by suitably defined fluctuations that convey the effects of inhomogeneity. We look at cases with perpetual expansion, bouncing and loitering behavior, as well as configurations with "mixed" kinematic patters, such as a collapsing region in an expanding background. In all cases, phase space trajectories emerge from and converge to stable past and future attractors in a qualitatively analogous way as in the case of the FLRW limit. However, we can identify in both projections of the phase space various qualitative features absent in the FLRW limit that can be useful in the construction of toy models of astrophysical and cosmological inhomogeneities.
This is a summary of presentations delivered at the OC1 parallel session "Primordial Gravitational Waves and the CMB" of the 12th Marcel Grossmann meeting in Paris, July 2009. The reports and discussions demonstrated significant progress that was achieved in theory and observations. It appears that the existing data provide some indications of the presence of gravitational wave contribution to the CMB anisotropies, while ongoing and planned observational efforts are likely to convert these indications into more confident statements about the actual detection.
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We present a statistical characterization of the carbon-star to M-giant (C/M) ratio in the halo of M31. Based on application of pseudo-filter band passes to our Keck/DEIMOS spectra we measure the 81-77-color index of 1288 stars in the giant stellar stream and in halo fields out to large distances. From this well-established narrow-band system, supplemented by V-I colors, we find only a low number (five in total) of C-star candidates. The resulting low C/M ratio of 10% is consistent with the values in the M31 disk and inner halo from the literature. Although our analysis is challenged by small number statistics and our sample selection, there is an indication that the oxygen-rich M-giants occur in similar number throughout the entire halo. We also find no difference in the C-star population of the halo fields compared to the giant stream. The very low C/M ratio is at odds with the observed low metallicities and the presence of intermediate-age stars at large radii. Our observed absence of a substantial carbon star population in the these regions indicates that the (outer) M31 halo cannot be dominated by the debris of disk-like or SMC-type galaxies, but rather resemble the dwarf elliptical NGC 147.
We study the coherent temperature and polarization patterns produced in homogeneous but anisotropic cosmological models. We show results for all Bianchi types with a Friedman-Robertson-Walker limit (i.e. Types I, V, VII$_{0}$, VII$_{h}$ and IX) to illustrate the range of possible behaviour. We discuss the role of spatial curvature, shear and rotation in the geodesic equations for each model and establish some basic results concerning the symmetries of the patterns produced. We also give examples of the time-evolution of these patterns in terms of the Stokes parameters $I$, $Q$ and $U$.
We use the Om statistic and the Genetic Algorithms (GA) in order to derive a null test on the spatially flat cosmological constant model $\Lambda$CDM. This is done in two steps: first, we apply the GA to the Constitution SNIa data in order to acquire a model independent reconstruction of the expansion history of the Universe $H(z)$ and second, we use the reconstructed $H(z)$ in conjunction with the Om statistic, which is constant only for the $\Lambda$CDM model, to derive our constraints. We find that while $\Lambda$CDM is consistent with the data at the $2\sigma$ level, some deviations from $\Lambda$CDM model at low redshifts seems to be mildly preferred.
We investigate the stellar populations of Lyman alpha emitters (LAEs) at z=5.7 and 6.6 in a 0.65 deg^2 sky of the Subaru/XMM-Newton Deep Survey (SXDS) Field, using deep images from the SXDS, UKIDSS/UDS, and Spitzer/SpUDS programs. We produce stacked multiband images at each redshift from 165 (z=5.7) and 91 (z=6.6) objects, to derive typical spectral energy distributions (SEDs) of z~6-7 LAEs for the first time. The stacked LAEs have as blue UV continua as the HST/WFC3 z-dropout galaxies of similar Muv, with a spectral slope beta-3, but at the same time they have red UV-to-optical colors with detection in the 3.6um bnd. Using SED fitting we find that the stacked LAEs have low stellar masses of ~(3-10)*10^7 Msun, very young ages of ~1-3 Myr, negligible dust extinction, and strong nebular emission from the ionized ISM, although the z=6.6 object is fitted similarly well with high-mass models without nebular emission; inclusion of nebular emission reproduces the red UV-to-optical color while keeping the UV color sufficiently blue. We infer that typical LAEs at z~6-7 are building blocks of normal galaxies seen gt lower redshifts. We find a tentative decrease in the Lyman alpha escape fraction from z=5.7 to 6.6, which may implyn increase in the IGM neutral fraction. From the minimum contribution of nebular emission required to fit the observed SEDs, we place an upper limit on the escape fraction of ionizing photons to be f_esc~0.6 at z=5.7 and ~0.9 at z=6.6. We also compare the stellar populations of our LAEs with that of stacked HST/WFC3 z-dropout galaxies.
A detection or nondetection of primordial non-Gaussianity in the CMB data is essential not only to test alternative models of the physics of the early universe but also to discriminate among classes of inflationary models. Given this far reaching consequences of such a non-Gaussianity detection for our understanding of the physics of the early universe, it is important to employ alternative indicators in order to have further information about the Gaussianity features of CMB that may be helpful for identifying their origins. In this way, a considerable effort has recently gone into the design of non-Gaussianity indicators, and in their application in the search for deviation from Gaussianity in the CMB data. Recently we have proposed two new large-angle non-Gaussianity indicators which provide measures of the departure from Gaussianity on large angular scales. We have used these indicators to carry out analyses of Gaussianity of the single frequency bands and of the available foreground-reduced {\it five-year} maps with and without the KQ75 mask. Here we extend and complement these studies by performing a new analysis of deviation from Gaussianity of the {\it three-year} harmonic ILC (HILC) foreground-reduced full-sky and KQ75 masked maps obtained from WMAP data. We show that this full-sky foreground-reduced maps presents a significant deviation from Gaussianity, which is brought down to a level of consistency with Gaussianity when the KQ75 mask is employed.
Recent cosmic ray, gamma ray, and microwave signals observed by Fermi, PAMELA, and WMAP indicate an unexpected primary source of e+e- at 10-1000 GeV. We fit these data to "standard backgrounds" plus a new source, assumed to be a separable function of position and energy. For the spatial part, we consider three cases: annihilating dark matter, decaying dark matter, and pulsars. In each case, we use GALPROP to inject energy in log-spaced energy bins and compute the expected cosmic-ray and photon signals for each bin. We then fit a linear combination of energy bins, plus backgrounds, to the data. We use a non-parametric fit, with no prior constraints on the spectrum except smoothness and non-negativity. In addition, we consider arbitrary modifications to the energy spectrum of the "ordinary" primary source function, fixing its spatial part, finding this alone to be inadequate to explain the PAMELA or WMAP signals. We explore variations in the fits due to choice of magnetic field, primary electron injection index, spatial profiles, propagation parameters, and fit regularization method. Dark matter annihilation fits well, where our fit finds a mass of ~1 TeV and a boost factor times energy fraction of ~70. While it is possible for dark matter decay and pulsars to fit the data, unconventionally high magnetic fields and radiation densities are required near the Galactic Center to counter the relative shallowness of the assumed spatial profiles. We also fit to linear combinations of these three scenarios, though the fit is much less constrained.
Recently Kashlinsky et al.(2008), Kashlinsky et al.(2010) discovered a $\sim 10^3$ km/$s$ bulk flow of the universe out to $z\simeq 0.3$, through the dark flow induced CMB dipole in directions of clusters. We point out that this dark flow also induces CMB temperature fluctuations at much smaller angular scales, through modulation of the inhomogeneous electron distribution on the uniform dark flow. This dark flow induced small scale kinetic Sunyaev Zel'dovich (SZ) effect is a non-negligible component of the CMB sky, only a factor of $\sim 2$ smaller than the conventional kinetic SZ effect at $\ell\sim 10^3-10^4$. Its existence worsens the low SZ problem recently found by the South Pole Telescope (Lueker et al. 2009), although no conclusive constraints can be drawn. It is also correlated with the large scale structure (LSS) and its correlation with 2MASS galaxy distribution reaches $0.3 \mu$K at $\ell=10^3$, under a directional dependent optimal weighting scheme. We estimate that, WMAP plus 2MASS is already able to detect this dark flow induced small scale kinetic SZ effect with $\sim 6\sigma$ confidence. Deeper galaxy surveys such as SDSS can further improve the measurement. Planck plus existing galaxy surveys can reach $\ga 14\sigma$ detection. Existing CMB-LSS cross correlation measurements shall be reanalyzed to probe the dark flow and to eliminate possible bias on the integrated Sachs-Wolfe effect measurement through the CMB-LSS cross correlation.
We present the correlations between the spectroscopic metallicities and ninety-three different intrinsic colors of M31 globular clusters, including seventy-eight BATC colors and fifteen SDSS and near infrared ugrizK colors. The BATC colors were derived from the archival images of thirteen filters (from c to p), which were taken by Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey with a 60/90 cm f/3 Schmidt telescope. The spectroscopic metallicities adopted in our work were from literature. We fitted the correlations of seventy-eight different BATC colors and the metallicities for 123 old confirmed globular clusters, and the result implies that correlation coefficients of twenty-three colors r>0.7. Especially, for the colors $(f-k)_0$, $(f-o)_0$, and $(h-k)_0$, the correlation coefficients are r>0.8. Meanwhile, we also note that the correlation coefficients (r) approach zero for $(g-h)_0$, $(k-m)_0$, $(k-n)_0$, and $(m-n)_0$, which are likely to be independent of metallicity. Similarity, we fitted the correlations of metallicity and ugrizK colors for 127 old confirmed GCs. The result indicates that all these colors are metal-sensitive (r>0.7), of which $(u-K)_0$ is the most metal-sensitive color. Our work provides an easy way to simply estimate the metallicity from colors.
We study the problem of searching for cosmic string signal patterns in the present high resolution and high sensitivity observations of the Cosmic Microwave Background (CMB). This article discusses a technique capable of recognizing Kaiser-Stebbins effect signatures in total intensity anisotropy maps, and shows that the biggest factor that produces confusion is represented by the acoustic oscillation features of the scale comparable to the size of horizon at recombination. Simulations show that the distribution of null signals for pure Gaussian maps converges to a $\chi^2$ distribution, with detectability threshold corresponding to a string induced step signal with an amplitude of about 100 $\muK$ which corresponds to a limit of roughly $G\mu < 1.5\times 10^{-6}$. We study the statistics of spurious detections caused by extra-Galactic and Galactic foregrounds. For diffuse Galactic foregrounds, which represents the dominant source of contamination, we derive sky masks outlining the available region of the sky where the Galactic confusion is sub-dominant, specializing our analysis to the case represented by the frequency coverage and nominal sensitivity and resolution of the Planck experiment.
We study the excitation of fine structure levels of C I, II and O I by ultraviolet (UV) photons around strong UV sources which are also ionizing sources of the cosmological reionization at redshift of $\sim$ 10. The evolutions of ionized regions around a point source are calculated by solving rate equations for non-equilibrium chemistry. Signals of UV photons through the fine structure lines are considered to be stronger at locations of more abundant chemical species of C I, II and O I. Such environments would be realized where strong fluxes of non-ionizing UV line photons available for the pumping up of fine structure levels exist, and simultaneously ionizing UV photons are effectively shielded by dense H I regions. Signals from H I regions of moderately large densities induced by redshifted UV photons emitted at the point sources are found to be dominantly large over those of others. We discuss the detectability of the signals, and show that signals from idealized environments will be possibly detected by radio observations with the Atacama Large Millimeter/submillimeter Array (ALMA) under construction or next-generation arrays.
We present the results of our investigation into the stellar populations of 24 radio galaxies at z~0.5 drawn from four complete, low-frequency selected radio surveys. We use the strength of the 4000A break as an indicator of recent star formation, and compare this with radio luminosity, optical spectral classification and morphological classification. We find evidence of different star formation histories for high- and low-luminosity radio sources; our group of low radio luminosity sources (typically FRI-type sources) has systematically older stellar populations than the higher radio luminosity group. Our sample is also fairly well divided by optical spectral classification. We find that galaxies classified as having low excitation spectra (LEGs) possess older stellar populations than high excitation line objects (HEGs), with the HEGs showing evidence for recent star formation. We also investigate the link between radio morphology, as used by Owen & Laing (1989), and the stellar populations. We find that there is a preference for the "fat-double" sources to have older stellar populations than the "classical double" sources, although this is also linked to these sources lying predominantly in the LEG and HEG categories respectively. These results are consistent with the hypothesis that HEGs are powered by accretion of cold gas, which could be supplied, for example, by recent mergers, secular instabilities, or filamentary cold flows. These processes could also trigger star formation in the host galaxy. The host galaxies of the LEGs do not show evidence for recent star formation and an influx of cold gas, and are consistent with being powered by the accretion of the hot phase of the inter-stellar medium.
We have examined the luminosity-size relationship as a function of environment for 12150 SDSS galaxies with precise visual classifications from the catalog of Nair & Abraham (2010a). Our analysis is subdivided into investigations of early-type galaxies and late-type galaxies. Early-type galaxies reveal a surprisingly tight luminosity-size relation. The dispersion in luminosity about the fiducial relation is only ~0.14 dex (0.35 mag), even though the sample contains galaxies which differ by a factor of almost 100 in luminosity. The dispersion about the luminosity-size relation is comparable to the dispersion about the fundamental plane, even though the luminosity-size relation is fundamentally simpler and computed using purely photometric parameters. The key contributors to the dispersion about the luminosity-size relation are found to be color and central concentration. Expanding our analysis to the full range of morphological types, we show that the slope, zero point, and scatter about the luminosity-size relation is independent of environmental density. Our study thus indicates that whatever process is building galaxies is doing so in a way that preserves fundamental scaling laws even as the typical luminosity of galaxies changes with environment. However, the distribution of galaxies along the luminosity-size relation is found to be strongly dependent on galaxy environment. This variation is in the sense that, at a given morphology, larger and more luminous galaxies are rarer in sparser environments. Our analysis of late-type galaxy morphologies reveals that scatter increases towards later Hubble types. Taken together, these results place strong constraints on conventional hierarchical models in which galaxies are built up in an essentially stochastic way.
Dwarf galaxies provide opportunities for drawing inferences about the processes in the early universe by observing our "cosmological backyard"-the Local Group and its vicinity. This special issue of the open-access journal Advances in Astronomy is a snapshot of the current state of the art of dwarf-galaxy cosmology.
A generic expectation for gas accreted by high mass haloes is that it is shock heated to the virial temperature of the halo. In low mass haloes, or at high redshift, however, the gas cooling rate is sufficiently rapid that an accretion shock is unlikely to form. Instead, gas can accrete directly into the centre of the halo in a `cold mode' of accretion. Although semi-analytic models have always made a clear distinction between hydrostatic and rapid cooling they have not made a distinction between whether or not an accretion shock forms. Starting from the well-established Galform code, we investigate the effect of explicitly accounting for cold mode accretion using the shock stability model of Birnboim & Dekel. When we modify the code so that there is no effective feedback from galaxy formation, we find that cold mode accretion is the dominant channel for feeding gas into the galaxies at high redshifts. However, this does not translate into a significant difference in the star formation history of the universe compared to the previous code. When effective feedback is included in the model, we find that the the cold mode is much less apparent because of the presence of gas ejected from the galaxy. Thus the inclusion of the additional cold mode physics makes little difference to basic results from earlier semi-analytic models which used a simpler treatment of gas accretion. For more sophisticated predictions of its consequences, we require a better understanding of how the cold mode delivers angular momentum to galaxies and how it interacts with outflows.
In Lyman-alpha forest measurements it is generally assumed that quasars are mere background light sources which are uncorrelated with the forest. Gravitational lensing of the quasars violates this assumption. This effect leads to a measurement bias, but more interestingly it provides a valuable signal. The lensing signal can be extracted by correlating quasar magnitudes with the flux power spectrum and with the flux decrement. These correlations will be challenging to measure but their detection provides a direct measure of how features in the Lyman-alpha forest trace the underlying mass density field. Observing them will test the fundamental hypothesis that fluctuations in the forest are predominantly driven by fluctuations in mass, rather than in the ionizing background, helium reionization or winds. We discuss ways to disentangle the lensing signal from other sources of such correlations, including dust, continuum and background residuals. The lensing-induced measurement bias arises from sample selection: one preferentially collects spectra of magnified quasars which are behind overdense regions. This measurement bias is ~0.1-1% for the flux power spectrum, optical depth and the flux probability distribution. Since the effect is systematic, quantities such as the amplitude of the flux power spectrum averaged across scales should be interpreted with care.
Recent work on the engines of active galactic nuclei jets suggests their power depends strongly and perhaps counter-intuitively on black hole spin. We explore the consequences of this on the radio-loud population of active galactic nuclei and find that the time evolution of the most powerful radio galaxies and radio-loud quasars fits into a picture in which black hole spin varies from retrograde to prograde with respect to the accreting material. Unlike the current view, according to which jet powers decrease in tandem with a global downsizing effect, we argue for a drop in jet power resulting directly from the paucity of retrograde accretion systems at lower redshift $z$ caused by a continuous history of accretion dating back to higher $z$. In addition, the model provides simple interpretations for the basic spectral features differentiating radio-loud and radio-quiet objects, such as the presence or absence of disk reflection, broadened iron lines and signatures of disk winds. We also briefly describe our models' interpretation of microquasar state transitions. We highlight our result that the most radio-loud and most radio-quiet objects both harbor highly spinning black holes but in retrograde and prograde configurations, respectively.
We present the fifth edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog, which is based upon the SDSS Seventh Data Release. The catalog, which contains 105,783 spectroscopically confirmed quasars, represents the conclusion of the SDSS-I and SDSS-II quasar survey. The catalog consists of the SDSS objects that have luminosities larger than M_i = -22.0 (in a cosmology with H_0 = 70 km/s/Mpc Omega_M = 0.3, and Omega_Lambda = 0.7) have at least one emission line with FWHM larger than 1000 km/s or have interesting/complex absorption features, are fainter than i > 15.0 and have highly reliable redshifts. The catalog covers an area of 9380 deg^2. The quasar redshifts range from 0.065 to 5.46, with a median value of 1.49; the catalog includes 1248 quasars at redshifts greater than four, of which 56 are at redshifts greater than five. The catalog contains 9210 quasars with i < 18; slightly over half of the entries have i< 19. For each object the catalog presents positions accurate to better than 0.1" rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3800-9200 Ang. at a spectral resolution R = 2000 the spectra can be retrieved from the SDSS public database using the information provided in the catalog. Over 96% of the objects in the catalog were discovered by the SDSS. We also include a supplemental list of an additional 207 quasars with SDSS spectra whose archive photometric information is incomplete.
We study the general properties of fluid spheres satisfying the heuristic assumption that their areas and proper radius are equal (the Euclidean condition). Dissipative and non-dissipative models are considered. In the latter case, all models are necessarily geodesic and a subclass of the Lemaitre-Tolman-Bondi solution is obtained. In the dissipative case solutions are non-geodesic and are characterized by the fact that all non-gravitational forces acting on any fluid element produces a radial three-acceleration independent on its inertial mass.
In this work, we explore the "degenerate gravitino" scenario where the mass difference between the gravitino and the lightest MSSM particle is much smaller than the gravitino mass itself. In this case, the energy released in the decay of the next to lightest sypersymmetric particle (NLSP) is reduced. Consequently the cosmological and astrophysical constraints on the gravitino abundance, and hence on the reheating temperature, become softer than in the usual case. On the other hand, such small mass splittings generically imply a much longer lifetime for the NLSP. We find that, in the constrained MSSM (CMSSM), for neutralino LSP or NLSP, reheating temperatures compatible with thermal leptogenesis are reached for small splittings of order 10^{-2} GeV. While for stau NLSP, temperatures of 4x10^9 GeV can be obtained even for splittings of order of tens of GeVs. This "degenerate gravitino" scenario offers a possible way out to the gravitino problem for thermal leptogenesis in supersymmetric theories.
Recently a mechanism to generate mass from gravitational interaction, based on Mach principle, according to which the inertia of a body is a property of matter as well as of the background provided by the rest-of-the-universe was presented in \cite{novello} \cite{novello2}. In these papers such an idea was realized for scalar and spinor fields treating the rest-of-the-universe in its vacuum state. In the present paper, using an extended version of Mach principle, the same strategy will be applied to show how the Heisenberg-Nambu-Jona-Lasinio non-linear equation for fermions $\Psi$ arises as a consequence of the gravitational interaction of $ \Psi$ with the rest-of-the-universe.
The quantum theory of cosmological perturbations in single field inflation is formulated in terms of a path integral, starting from first principles and a canonical formulation. The free propagators are obtained from the well known gauge-invariant quadratic action for both scalar and tensor perturbations and the interaction terms are given in a form which allows the determination of vertices to arbitrary order. Any correlation function can be calculated by a diagrammatic expansion which, apart from the propagating physical degrees of freedom, also contains various commuting and anti-commuting auxiliary fields in internal lines and loops. We briefly discuss the tree-level 3-point and 4-point functions of the inflaton perturbations.
We propose a novel mechanism for dark matter to explain the observed annual modulation signal at DAMA/LIBRA which avoids existing constraints from every other dark matter direct detection experiment including CRESST, CDMS, and XENON10. The dark matter consists of at least two light states with mass ~few GeV and splittings ~5 keV. It is natural for the heavier states to be cosmologically long-lived and to make up an O(1) fraction of the dark matter. Direct detection rates are dominated by the exothermic reactions in which an excited dark matter state down-scatters off of a nucleus, becoming a lower energy state. In contrast to (endothermic) inelastic dark matter, the most sensitive experiments for exothermic dark matter are those with light nuclei and low threshold energies. Interestingly, this model can also naturally account for the observed low-energy events at CoGeNT. The only significant constraint on the model arises from the DAMA/LIBRA unmodulated spectrum but it can be tested in the near future by a low-threshold analysis of CDMS-Si and possibly other experiments including CRESST, COUPP, and XENON100.
We present 2323 High-Amplitude \delta-Scuti (HADS) candidates discovered in the Large Magellanic Cloud (LMC) by the SuperMACHO survey (Rest et al. 2005). Frequency analyses of these candidates reveal that several are multimode pulsators, including 119 whose largest amplitude of pulsation is in the fundamental (F) mode and 19 whose largest amplitude of pulsation is in the first overtone (FO) mode. Using Fourier decomposition of the HADS light curves, we find that the period-luminosity (PL) relation defined by the FO pulsators does not show a clear separation from the PL-relation defined by the F pulsators. This differs from other instability strip pulsators such as type c RR Lyrae. We also present evidence for a larger amplitude, subluminous population of HADS similar to that observed in Fornax (Poretti et al. 2008).
The Great Observatories All-sky LIRG Survey (GOALS) consists of a complete sample of 202 Luminous Infrared Galaxies (LIRGs) selected from the IRAS Revised Bright Galaxy Sample (RBGS). The galaxies span the full range of interaction stages, from isolated galaxies to interacting pairs to late stage mergers. We present a comparison of the UV and infrared properties of 135 galaxies in GOALS observed by GALEX and Spitzer. For interacting galaxies with separations greater than the resolution of GALEX and Spitzer (2-6"), we assess the UV and IR properties of each galaxy individually. The contribution of the FUV to the measured SFR ranges from 0.2% to 17.9%, with a median of 2.8% and a mean of 4.0 +/- 0.4%. The specific star formation rate of the GOALS sample is extremely high, with a median value (3.9*10^{-10} yr^{-1}) that is comparable to the highest specific star formation rates seen in the Spitzer Infrared Nearby Galaxies Survey sample. We examine the position of each galaxy on the IR excess-UV slope (IRX-beta) diagram as a function of galaxy properties, including IR luminosity and interaction stage. The LIRGs on average have greater IR excesses than would be expected based on their UV colors if they obeyed the same relations as starbursts with L_IR < 10^{11}L_0 or normal late-type galaxies. The ratio of L_IR to the value one would estimate from the IRXg-beta relation published for lower luminosity starburst galaxies ranges from 0.2 to 68, with a median value of 2.7. A minimum of 19% of the total IR luminosity in the RBGS is produced in LIRGs and ULIRGs with red UV colors (beta > 0). Among resolved interacting systems, 32% contain one galaxy which dominates the IR emission while the companion dominates the UV emission. Only 21% of the resolved systems contain a single galaxy which dominates both wavelengths.
We consider a class of late-decaying dark-matter models, in which a dark matter particle decays to a heavy stable daughter of approximately the same mass, together with one or more relativistic particles which carry away only a small fraction of the parent rest mass. Such decays can affect galactic halo structure and evolution, and have been invoked as a remedy to some of the small scale structure-formation problems of cold dark matter. There are existing stringent limits on the dark matter lifetime if the decays produce photons. By considering examples in which the relativistic decay products instead consist of neutrinos or electron-position pairs, we derive stringent limits on these scenarios for a wide range of dark matter masses. We thus eliminate a sizable portion of the parameter space for these late decay models if the dominant decay channel involves Standard Model final states.
Several recent studies have considered the implications for astrophysics and cosmology of some possible nonclassical properties of spacetime at the Planck scale. The new effects, such as a Planck-scale-modified energy-momentum (dispersion) relation, are often inferred from the analysis of some quantum versions of Minkowski spacetime, and therefore the relevant estimates depend heavily on the assumption that there could not be significant interplay between Planck-scale and curvature effects. We here scrutinize this assumption, using as guidance a quantum version of de Sitter spacetime with known Inonu-Wigner contraction to a quantum Minkowski spacetime. And we show that, contrary to common (but unsupported) beliefs, the interplay between Planck-scale and curvature effects can be significant. Within our illustrative example, in the Minkowski limit the quantum-geometry deformation parameter is indeed given by the Planck scale, while in the de Sitter picture the parameter of quantization of geometry depends both on the Planck scale and the curvature scalar. For the much-studied case of Planck-scale effects that intervene in the observation of gamma-ray bursts we can estimate the implications of "quantum spacetime curvature" within robust simplifying assumptions. For cosmology at the present stage of the development of the relevant mathematics one cannot go beyond semiheuristic reasoning, and we here propose a candidate approximate description of a quantum FRW geometry, obtained by patching together pieces (with different spacetime curvature) of our quantum de Sitter. This semiheuristic picture, in spite of its limitations, provides rather robust evidence that in the early Universe the interplay between Planck-scale and curvature effects could have been particularly significant.
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In this paper we show expectations on the radio--X-ray luminosity correlation of radio halos at 120 MHz. According to the "turbulent re-acceleration scenario", low frequency observations are expected to detect a new population of radio halos that, due to their ultra-steep spectra, are missed by present observations at ~ GHz frequencies. These radio halos should also be less luminous than presently observed halos hosted in clusters with the same X-ray luminosity. Making use of Monte Carlo procedures, we show that the presence of these ultra-steep spectrum halos at 120 MHz causes a steepening and a broadening of the correlation between the synchrotron power and the cluster X-ray luminosity with respect to that observed at 1.4 GHz. We investigate the role of future low frequency radio surveys, and find that the upcoming LOFAR surveys will be able to test these expectations.
We use Shen et al.'s (2009) measurements of luminosity-dependent clustering in the SDSS Data Release 5 Quasar Catalog, at redshifts 0.4 < z < 2.5, to constrain the relation between quasar luminosity and host halo mass and to infer the duty cycle f_opt, the fraction of black holes that shine as optically luminous quasars at a given time. We assume a monotonic mean relation between quasar luminosity and host halo mass, with log-normal scatter \Sigma. For specified f_opt and \Sigma, matching the observed quasar space density determines the normalization of the luminosity-halo mass relation, from which we predict the clustering bias. The data show no change of bias between the faint and bright halves of the quasar sample but a modest increase in bias for the brightest 10%. At the mean redshift z=1.45 of the sample, the data can be well described either by models with small intrinsic scatter (\Sigma=0.1 dex) and a duty cycle f_opt=6*10^(-4) or by models with much larger duty cycles and larger values of the scatter. "Continuity equation" models of the black hole mass population imply f_opt > 2*10^(-3) in this range of masses and redshifts, and the combination of this constraint with the clustering measurements implies scatter \Sigma > 0.4 dex. These findings contrast with those inferred from the much stronger clustering of high-luminosity quasars at z~4, which require minimal scatter between luminosity and halo mass and duty cycles close to one.
We have carried out a redshift survey using the VIMOS spectrograph on the VLT towards the Cosmic Microwave Background cold spot. A possible cause of the cold spot is the Integrated Sachs-Wolfe effect imprinted by an extremely large void (hundreds of Mpc in linear dimension) at intermediate or low redshifts. The redshift distribution of over seven hundred z<1 emission-line galaxies drawn from an I-band flux limited sample of galaxies in the direction of the cold spot shows no evidence of a gap on scales of Delta-z> 0.05 as would be expected if such a void existed at 0.35<z<1. There are troughs in the redshift distribution on smaller scales (Delta-z ~0.01) indicating that smaller scale voids may connect regions separated by several degrees towards the cold spot. A comparison of this distribution with that generated from similarly-sized subsamples drawn from widely-spaced pointings of the VVDS survey does not indicate that the redshift distribution towards the cold spot is anomalous or that these small gaps can be uniquely attributed to real voids.
There is a strong decrease in scatter in the black hole mass versus bulge luminosity relationship with increasing luminosity and very little scatter for the most luminous galaxies. It is shown that this is a natural consequence of the substantial initial dispersion in the ratio of black hole mass to total stellar mass and of subsequent galaxy growth through hierarchical mergers. "Fine-tuning" through feedback between black hole growth and bulge growth is neither necessary nor desirable.
In order for a white dwarf (WD) to achieve the Chandrasekhar mass, M_C, and explode as a Type Ia supernova (SNIa), it must interact with another star, either accreting matter from or merging with it. The failure to identify the types of binaries which produce SNeIa is the "progenitor problem". Its solution is required if we are to utilize the full potential of SNeIa to elucidate basic cosmological and physical principles. In single-degenerate models, a WD accretes and burns matter at high rates. Nuclear-burning WDs (NBWDs) with mass close to M_C are hot and luminous, potentially detectable as supersoft x-ray sources (SSSs). In previous work we showed that > 90-99% of the required number of progenitors do not appear as SSSs during most of the crucial phase of mass increase. The obvious implication is that double-degenerate (DD) binaries form the main class of progenitors. We show in this paper, however, that many binaries that later become DDs must pass through a long-lived NBWD phase during which they are potentially detectable as SSSs. The paucity of SSSs is therefore not a strong argument in favor of DD models. Those NBWDs that are the progenitors of DD binaries are likely to appear as symbiotic binaries for intervals > 10^6 years. In fact, symbiotic pre-DDs should be common, whether or not the WDs eventually produce SNeIa. The key to solving the progenitor problem lies in understanding the appearance of NBWDs. Most do not appear as SSSs most of the time. We therefore consider the evolution of NBWDs to address the question of what their appearance may be and how we can hope to detect them.
We present a method that we developed to discern where the optical microvariability (OM) in quasars originates: in the accretion disk (related to thermal processes) or in the jet (related to non-thermal processes). Analyzing nearly simultaneous observations in three different optical bands of continuum emission, we are able to determine the origin of several isolated OM events. In particular, our method indicates that from nine events reported by Ramirez et al. (2009), three of them are consistent with a thermal origin, three to non-thermal, and three cannot be discerned. The implications for the emission models of OM are briefly discussed.
The first stars to form in the Universe may be powered by the annihilation of weakly interacting dark matter particles. These so-called dark stars, if observed, may give us a clue about the nature of dark matter. Here we examine which models for particle dark matter satisfy the conditions for the formation of dark stars. We find that in general models with thermal dark matter lead to the formation of dark stars, with few notable exceptions: heavy neutralinos in the presence of coannihilations, annihilations that are resonant at dark matter freeze-out but not in dark stars, some models of neutrinophilic dark matter annihilating into neutrinos only and lighter than about 50 GeV. In particular, we find that a thermal DM candidate in standard Cosmology always forms a dark star as long as its mass is heavier than about 50 GeV and the thermal average of its annihilation cross section is the same at the decoupling temperature and during the dark star formation, as for instance in the case of an annihilation cross section with a non-vanishing s-wave contribution.
I present a simple, and hopefully convincing, discussion of a solution to the dark energy problem, which arises because the visible universe is well approximated by a black hole.
(Abridged) We study the predictions of various annihilating Dark Matter (DM) models in order to interpret the origin of non-thermal phenomena in galaxy clusters. We consider three neutralino DM models with light (9 GeV), intermediate (60 GeV) and high (500 GeV) mass. The secondary particles created by neutralino annihilation produce a multi-frequency Spectral Energy Distribution (SED), as well as heating of the intracluster gas, that are tested against the observations available for the Coma cluster. The DM produced SEDs are normalized to the Coma radio halo spectrum. We find that it is not possible to interpret all non-thermal phenomena observed in Coma in terms of DM annihilation. The DM model with 9 GeV mass produces too small power at all frequencies, while the DM model with 500 GeV produces a large excess power at all frequencies. The DM model with 60 GeV and $\tau^{\pm}$ composition is consistent with the HXR and gamma-ray data but fails to reproduce the EUV and soft X-ray data. The DM model with 60 GeV and $b{\bar b}$ composition is always below the observed fluxes. The radio halo spectrum of Coma is well fitted only in the $b{\bar b}$ or light and intermediate mass DM models. The heating produced by DM annihilation in the center of Coma is always larger than the intracluster gas cooling rate for an NFW DM density profile and it is substantially smaller than the cooling rate only for a cored DM density profile in DM model with 9 GeV. We conclude that the possibility of interpreting the origin of non-thermal phenomena in galaxy clusters with DM annihilation models requires a low neutralino mass and a cored DM density profile. If we then consider the multimessenger constraints to the neutralino annihilation cross-section, it turns out that such scenario would also be excluded unless we introduce a substantial boost factor due to the presence of DM substructures.
The kinetic Sunyaev Zel'dovich effect (kSZ) effect is a potentially powerful probe to the missing baryons. However, the kSZ signal is overwhelmed by various contaminations and the cosmological application is hampered by loss of redshift information due to the projection effect. We propose a kSZ tomography method to alleviate these problems, with the aid of galaxy spectroscopic redshift surveys. We propose to estimate the large scale peculiar velocity through the 3D galaxy distribution, weigh it by the 3D galaxy density and adopt the product projected along the line of sight with a proper weighting as an estimator of the true kSZ temperature fluctuation $\Theta$. We thus propose to measure the kSZ signal through the $\Hat{\Theta}$-$\Theta$ cross correlation. This approach has a number of advantages (see details in the abstract of the paper). We test the proposed kSZ tomography against non-adiabatic and adiabatic hydrodynamical simulations. We confirm that $\hat{\Theta}$ is indeed tightly correlated with $\Theta$ at $k\la 1h/$Mpc, although nonlinearities in the density and velocity fields and nonlinear redshift distortion do weaken the tightness of the $\hat{\Theta}$-$\Theta$ correlation. We further quantify the reconstruction noise in $\Hat{\Theta}$ from galaxy distribution shot noise. Based on these results, we quantify the applicability of the proposed kSZ tomography for future surveys. We find that, in combination with the BigBOSS-N spectroscopic redshift survey, the PLANCK CMB experiment will be able to detect the kSZ with an overall significance of $\sim 50\sigma$ and further measure its redshift distribution at many redshift bins over $0<z<2$.
TeV photons from blazars at relatively large distances, interacting with the optical-IR cosmic background, are efficiently converted into electron-positron pairs. The produced pairs are extremely relativistic (Lorentz factors of the order of 1e6 1e7 and promptly loose their energy through inverse Compton scatterings with the photons of the microwave cosmic background, producing emission in the GeV band. The spectrum and the flux level of this reprocessed emission is critically dependent on the intensity of the intergalactic magnetic field, B, that can deflect the pairs diluting the intrinsic emission over a large solid angle. We derive a simple relation for the reprocessed spectrum expected from a steady source. We apply this treatment to the blazar 1ES 0229+200, whose intrinsic very hard TeV spectrum is expected to be approximately steady. Comparing the predicted reprocessed emission with the upper limits measured by the Fermi/Large Area Telescope, we constrain the value of the intergalactic magnetic field to be larger than B ~5e-15 Gauss.
We present deep Keck spectroscopy for 12 morphologically-selected field spheroidals in the redshift range 1.05<z<1.41 in order to investigate the continuity in physical properties between the claimed massive compact red galaxies ("nuggets") at z~2 and well-established data for massive spheroidal galaxies below z~1. By combining Keck-based stellar velocity dispersions with HST-based sizes, we find that the most massive systems (Mdyn > 10^11 Msol) grew in size over 0<z<1.4 as (1+z)^(-0.70 +- 0.11) whereas intermediate mass systems (10^11 Msol > Mdyn > 10^10 Msol) did not grow significantly. These trends are consistent with a picture in which more massive spheroidals formed at higher redshift via "wetter" mergers involving greater dissipation. To examine growth under the favored "dry" merger hypothesis, we also examine size growth at a fixed velocity dispersion. This test, uniquely possible with our dynamical data, allows us to consider the effects of "progenitor bias." Above our completeness limit (sigma > 200 km/s), we find size growth consistent with that inferred for the mass-selected sample, thus ruling out strong progenitor bias. To maintain continuity in the growth of massive galaxies over the past 10 Gyr, our new results imply that size evolution over 1.4<z<2.3, a period of 1.7 Gyr, must have been even more dramatic than hitherto claimed if the red sources at z>2 are truly massive and compact.
We present optical emission-line spectra for outlying HII regions in the extended neutral gas disk surrounding the blue compact dwarf galaxy NGC 2915. Using a combination of strong-line R23 and direct oxygen abundance measurements, we report a flat, possibly increasing, metallicity gradient out to 1.2 times the Holmberg radius. We find the outer-disk of NGC 2915 to be enriched to a metallicity of 0.4 Z_solar. An analysis of the metal yields shows that the outer disk of NGC 2915 is overabundant for its gas fraction, while the central star-foming core is similarly under-abundant for its gas fraction. Star formation rates derived from very deep ~14 ks GALEX FUV exposures indicate that the low-level of star formation observed at large radii is not sufficient to have produced the measured oxygen abundances at these galactocentric distances. We consider 3 plausible mechanisms that may explain the metal-enriched outer gaseous disk of NGC 2915: radial redistribution of centrally generated metals, strong galactic winds with subsequent fallback, and galaxy accretion. Our results have implications for the physical origin of the mass-metallicity relation for gas-rich dwarf galaxies.
We present an analytical derivation of the Sachs Wolfe effect sourced by a primordial magnetic field. In order to consistently specify the initial conditions, we assume that the magnetic field is generated by a causal process, namely a first order phase transition in the early universe. As for the topological defects case, we apply the general relativistic junction conditions to match the perturbation variables before and after the phase transition which generates the magnetic field, in such a way that the total energy momentum tensor is conserved across the transition and Einstein's equations are satisfied. We further solve the evolution equations for the metric and fluid perturbations at large scales analytically including neutrinos, and derive the magnetic Sachs Wolfe effect. We find that the relevant contribution to the magnetic Sachs Wolfe effect comes from the metric perturbations at next-to-leading order in the large scale limit. The leading order term is in fact strongly suppressed due to the presence of free-streaming neutrinos. We derive the neutrino compensation effect dynamically and confirm that the magnetic Sachs Wolfe spectrum from a causal magnetic field behaves as l(l+1)C_l^B \propto l^2 as found in the latest numerical analyses.
We present chemical evolution models with different Z-dependent yields to reproduce the O/H gradient of the Galactic disk. We find that moderate Z-dependent yields for massive stars produce an excellent fit to the observed C/H, and O/H gradients of the disk of the Galaxy derived from HII regions. The best model also fits: the H, He, C, and O abundances derived from recombination lines of the HII region M17, the protosolar H, He, O, and C abundances, the C/O versus O/H relationship derived from stars of the solar vicinity, and the C/H and O/H values for young F and G stars of the solar vicinity. The agreement of the model with the protosolar abundances at the Sun-formation time implies that the Sun originated at a galactocentric distance similar to that of the solar vicinity. The simultaneous fit of the HII regions and the protosolar abundances supports the method to derive abundances based on HII regions recombination lines. We obtain a good agreement between our model for the present day abundances and the C/O versus O/H relationship derived from extragalactic HII regions in nearby spiral galaxies.
An extension of the MSSM called the munuSSM does not allow a conventional thermal leptogenesis scenario because of the low scale seesaw that it utilizes. Hence, we investigate the possibility of electroweak baryogenesis. Specifically, we identify a parameter region for which the electroweak phase transition is sufficiently strongly first order to realize electroweak baryogenesis. In addition to transitions that are similar to those in the NMSSM, we find a novel class of phase transitions in which there is a rotation in the singlet vector space.
Analyses have found a "haze" of anomalous microwave emission surrounding the Galactic Center in the WMAP sky maps. A recent study using Fermi data detected a similar haze in the gamma-ray. Several studies have modeled these hazes as radiation from the leptonic byproducts of dark matter annihilations, and arguably no convincing astrophysical alternative has been suggested. We discuss the characteristics of astrophysical cosmic ray sources that could potentially explain this microwave and gamma-ray emission. The most promising astrophysical scenarios involve cosmic ray sources that are clustered such that many fall within ~1 kpc of the Galactic Center. For example, we show that several hundred Galactic Center supernovae in the last million years plus a diffusion-hardened electron spectrum may be consistent with present constraints on this emission. Alternatively, it could be due to a burst of activity probably associated with Sagittarius A* occurring ~1 Myr ago and producing >10^51 erg in cosmic ray electrons. Different models predict different trends for the spectral index of the microwave and gamma-ray spectrum as a function of angle from the Galactic Center that should be robust to cosmic ray propagation uncertainties. In particular, if the haze is from dark matter annihilations, it should have a very hard microwave and gamma-ray spectrum for which the spectral shape does not change significantly with angle, which we argue would be difficult to achieve with any astrophysical mechanism. Observations with the Planck and Fermi satellites can distinguish between viable haze models using these signatures.
Non-Gaussianities of the primordial density perturbations have emerged as a very powerful possible signal to test the dynamics that drove the period of inflation. While in general the most sensitive observable is the three-point function in this paper we show that there are technically natural inflationary models where the leading source of non-Gaussianity is the four-point function. Using the recently developed Effective Field Theory of Inflation, we are able to show that it is possible to impose an approximate parity symmetry and an approximate continuous shift symmetry on the inflaton fluctuations that allow for a unique quartic operator, while approximately forbidding all the cubic ones. The resulting four-point function can have only two shapes depending on the two possible dispersion relations for the fluctuations: either $\omega\sim c_s k$ or $\omega\sim k^2/M$.
SN 2007od exhibits characteristics that have rarely been seen in a Type IIP supernova (SN). Optical V band photometry reveals a very steep brightness decline between the plateau and nebular phases of ~4.5 mag, likely due to SN 2007od containing a low mass of 56Ni. The optical spectra show an evolution from normal Type IIP with broad Halpha emission, to a complex, four component Halpha emission profile exhibiting asymmetries caused by dust extinction after day 232. This is similar to the spectral evolution of the Type IIn SN 1998S, although no early-time narrow (~200 km s-1) Halpha component was present in SN 2007od. In both SNe, the intermediate-width Halpha emission components are thought to arise in the interaction between the ejecta and its circumstellar medium (CSM). SN 2007od also shows a mid-IR excess due to new dust. The evolution of the Halpha profile and the presence of the mid-IR excess provide strong evidence that SN 2007od formed new dust before day 232. Late-time observations reveal a flattening of the visible lightcurve. This flattening is a strong indication of the presence of a light echo, which likely accounts for much of the broad, underlying Halpha component seen at late-times. We believe the multi-peaked Halpha emission is consistent with the interaction of the ejecta with a circumstellar ring or torus (for the inner components at \pm1500 km s-1), and a single blob or cloud of circumstellar material out of the plane of the CSM ring (for the outer component at -5000 km s-1). The most probable location for the formation of new dust is in the cool dense shell created by the interaction between the expanding ejecta and its CSM. Monte Carlo radiative transfer modeling of the dust emission from SN 2007od implies that up to 4x 10-4Msun of new dust has formed. This is similar to the amounts of dust formed in other CCSNe such as SNe 1999em, 2004et, and 2006jc.
The work is an attempt to model a scenario of inflation in the framework of Anti de Sit- ter/Conformal Field theory (AdS/CFT) duality, a potentially complete nonperturbative description of quantum gravity via string theory. We look at bubble geometries with de Sitter interiors within an ambient Schwarzschild anti-de Sitter black hole spacetime and obtain a characterization for the states in the dual CFT on boundary of the asymptotic AdS which code the expanding dS bubble. These can then in turn be used to specify initial conditions for cosmology. Our scenario naturally interprets the entropy of de Sitter space as a (logarithm of) subspace of states of the black hole microstates. Consistency checks are performed and a number of implications regarding cosmology are discussed including how the key problems or paradoxes of conventional eternal inflation are overcome.
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