We have detected the CO(2-1) transition from the submillimetre galaxy (SMG) LESSJ033229.4-275619 at z=4.755 using the new Compact Array Broadband Backend system on the Australian Telescope Compact Array. These data have identified a massive gas reservoir available for star formation for the first time in an SMG at z~5. We use the luminosity and velocity width (FWHM of 160 km/s) of the CO(2--1) line emission to constrain the gas and dynamical mass of Mgas~1.6x10^10 Msun and Mdyn(<2kpc)~5x10^10 (0.25/sin^2(i)) Msun, respectively, similar to that observed for SMGs at lower redshifts of z~2-4, although we note that our observed CO FWHM is a factor of ~3 narrower than typically seen in SMGs. Together with the stellar mass we estimate a total baryonic mass of Mbary~1x10^11 Msun, consistent with the dynamical mass for this young galaxy within the uncertainties. Dynamical and baryonic mass limits of high-redshift galaxies are useful tests of galaxy formation models: using the known z~4-5 SMGs as examples of massive baryonic systems, we find that their space density is consistent with that predicted by current galaxy formation models. In addition, these observations have helped to confirm that z~4-5 SMGs possess the baryonic masses and gas consumption timescales necessary to be the progenitors of the luminous old red galaxies seen at z~3. Our results provide a preview of the science that ALMA will enable on the formation and evolution of the earliest massive galaxies in the Universe.
We study resolution effects in numerical simulations of gas-rich and gas-poor major mergers, and show that the formation of slowly-rotating elliptical galaxies often requires a resolution that is beyond the present-day standards to be properly modelled. Our sample of equal-mass merger models encompasses various masses and spatial resolutions, ranging from about 200pc and 10^5 particles per component, typical of some recently published major merger simulations, to up to 32pc and 10^3 M_sun in simulations using 2.4 x 10^7 collisionless particles and 1.2 x 10^7 gas particles, among the highest resolutions reached so far for gas-rich major merger of massive disc galaxies. We find that the formation of fast-rotating early-type galaxies, that are flattened by a significant residual rotation, is overall correctly reproduced at all such resolutions. However, the formation of slow-rotating early-type galaxies, which have a low residual angular momentum and are supported mostly by anisotropic velocity dispersions, is strongly resolution-dependent. The evacuation of angular momentum from the main stellar body is largely missed at standard resolution, and systems that should be slow rotators are then found to be fast rotators. The effect is most important for gas-rich mergers, but is also witnessed in mergers with an absent or modest gas component. The effect is robust with respect to our initial conditions and interaction orbits, and originates in the physical treatment of the relaxation process during the coalescence of the galaxies. Our findings show that a high-enough resolution is required to accurately model the global properties of merger remnants and the evolution of their angular momentum. The role of gas-rich mergers of spiral galaxies in the formation of slow-rotating ellipticals may therefore have been underestimated.
We report the discovery of HI 21-cm absorption towards the well-studied GHz Peaked-Spectrum source CTA 21 (4C 16.09) using the Arecibo Telescope on 2009 September 20 and 21. Recently, the frequency band between 700 and 800 MHz was temporarily opened up to radio astronomy when US TV stations were mandated to switch from analog to digital transmissions, with new frequency allocations. The redshifted HI frequency for CTA 21 falls within this band. CTA 21 has a complex radio structure on a range of scales. The innermost prominent components are separated by ~12 mas while weak diffuse emission extends for up to ~300 mas. The HI absorption profile that we find has two main components, one narrow, the other wider and blue-shifted. The total HI column density is 7.9 x 10^20 cm^-2, assuming a covering factor of unity and a spin temperature of 100 K. This HI absorption confirms the recently determined optical redshift of this faint galaxy of z ~ 0.907. We discuss this new detection in the light of HI absorption studies towards compact radio sources, and also the possibility that CTA 21 may be exhibiting multiple cycles of nuclear activity. This new detection in CTA 21 is consistent with a strong trend for detection of HI absorption in radio galaxies with evidence of episodic nuclear/jet activity.
We use N-body simulations to find the effect of neutrino masses on halo properties, and investigate how the density profiles of both the neutrino and the dark matter components change as a function of the neutrino mass. We compare our neutrino density profiles with results from the N-one-body method and find good agreement. We also show and explain why the Tremaine-Gunn bound for the neutrinos is not saturated. Finally we study how the halo mass function changes as a function of the neutrino mass and compare our results with the Sheth-Tormen semi-analytic formulae. Our results are important for surveys which aim at probing cosmological parameters using clusters, as well as future experiments aiming at measuring the cosmic neutrino background directly.
The mechanisms giving rise to diffuse radio emission in galaxy clusters, and in particular their connection with cluster mergers, are still debated. We aim to obtain new insights into the internal dynamics of the cluster Abell 2294, recently shown to host a radio halo. Our analysis is mainly based on redshift data for 88 galaxies acquired at the Telescopio Nazionale Galileo. We also use new photometric data acquired at the Isaac Newton Telescope and X-ray data from the Chandra archive. We re-estimate the redshift of the large, brightest cluster galaxy (BCG) obtaining <z>=0.1690. We estimate a quite large LOS velocity dispersion sigma_V about 1400 km/s and X-ray temperature T_X about 10 keV. Our optical and X-ray analysis detects evidence for substructure. Our results are consistent with the presence of two massive subclusters separated by a LOS rest frame velocity difference V_rf about 2000 km/s, very closely projected in the plane of sky along the SE-NW direction. The observational picture, interpreted through the analytical two-body model, suggests that Abell 2294 is a cluster merger elongated mainly in the LOS direction and catched during the bound outgoing phase, a few fractions of Gyr after the core crossing. We find Abell 2294 is a very massive cluster with a range of M=2-4 10E15 M_sun. Moreover, contradicting previous findings, our new data do exclude the presence of the H$\alpha$ emission in the spectrum of the BCG galaxy. The outcoming picture of Abell 2294 is that of a massive, quite "normal" merging cluster, as found for many clusters showing diffuse radio sources.
Motivated by the possible extension into a supersymmetric Randall-Sundrum (RS) model, we investigate the properties of the vacuum expectation value (VEV) of the stress-energy tensor for a quantized bulk Dirac spinor field in the RS geometry and compare it with that for a real scalar field. This is carried out via the Green function method based on first principles without invoking the degeneracy factor, whose validity in a warp geometry is a priori unassured. In addition, we investigate the local behavior of the Casimir energy near the two branes. One salient feature we found is that the surface divergences near the two branes have opposite signs. We argue that this is a generic feature of the fermionic Casimir energy density due to its parity transformation in the fifth dimension. Furthermore, we investigate the self-consistency of the RS metric under the quantum correction due to the stress-energy tensor. It is shown that the VEV of the stress-energy tensor and the classical one become comparable near the visible brane if k ~ M ~ M_Pl (the requirement of no hierarchy problem), where k is the curvature of the RS warped geometry and M the 5-dimensional Planck mass. In that case the self-consistency of RS model that includes bulk ?elds is in doubt. If, however, k <~ M, then an approximate self-consistency of the RS-type metric may still be satisfied.
We propose an explicit non-linear realization of massive gravity, which relies on the introduction of a spurious compact extra dimension, on which we impose half-Newmann and half-Dirichlet boundary conditions. At the linearized level, we recover the expected gravitational exchange amplitude between two sources mediated by a massive Fierz-Pauli spin-2 field, while cubic interactions in the additional helicity-0 mode give rise to the expected Vainsthein mechanism. We also show that this framework can accommodate for a flat four-dimensional geometry in the presence of a cosmological constant, putting this framework on a good footing for the study of degravitation.
The CDMS Collaboration has reported two candidate events for dark matter. If the events are due to the elastic scattering of dark matter, the dark matter would be a WIMP dark matter with its mass of the order of 10-100GeV and its scattering cross section with a nucleon is about 10^-43cm^2. We show that such a dark matter is properly realized as a neutralino dark matter in the light higgs boson scenario of the MSSM. The lightest higgs boson mass can be lighter than 114.4GeV in the scenario because of a suppressed interaction between higgs boson and Z bosons. As a result, a large scattering cross section between the dark matter and ordinary matter is obtained.
Generic cosmological models derived from higher dimensional theories with warped extra dimensions have a nonzero cosmological constant-like term induced on the 3+1 space-time, or a physical 3-brane. In the scenario where this 3+1 space-time is an inflating de Sitter "brane" embedded in a higher-dimensional space-time, described by warped geometry, the 4D cosmological term is determined in terms of two length scales: one is a scale associated with the size of extra dimension(s) and the other is a scale associated with the warping of extra space(s). The existence of this term in four dimensions provides a tantalizing possibility of explaining the observed accelerating expansion of the universe from fundamental theories of gravity, e.g. string theory.
We study the classical and quantum models of a Friedmann-Robertson-Walker (FRW) cosmology, coupled to a perfect fluid, in the context of the scalar-metric gravity. Using the Schutz' representation for the perfect fluid, we show that, under a particular gauge choice, it may lead to the identification of a time parameter for the corresponding dynamical system. It is shown that the evolution of the universe based on the classical cosmology represents a late time power law expansion coming from a big-bang singularity in which the scale factor goes to zero while the scalar field blows up. Moreover, this formalism gives rise to a Schr\"{o}dinger-Wheeler-DeWitt (SWD) equation for the quantum-mechanical description of the model under consideration, the eigenfunctions of which can be used to construct the wave function of the universe. We use the resulting wave function in order to investigate the possibility of the avoidance of classical singularities due to quantum effects by means of the many-worlds and ontological interpretation of quantum cosmology.
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We present new measurements of dark matter distributions in 25 X-ray luminous clusters by making a full use of the two-dimensional (2D) weak lensing signals obtained from high-quality Subaru/Suprime-Cam imaging data. Our approach to directly compare the measured lensing shear pattern with elliptical model predictions allows us to extract new information on the mass distributions of individual clusters, such as the halo ellipticity and mass centroid. We find that these parameters on the cluster shape are little degenerate with cluster mass and concentration parameters. By combining the 2D fitting results for a subsample of 18 clusters, the elliptical shape of dark matter haloes is detected at 7\sigma significance level. The mean ellipticity is found to be e = 0.46 \pm 0.04 (1\sigma), which is in excellent agreement with the standard collisionless CDM model prediction. The mass centroid can be constrained with a typical accuracy of ~20" (~50 kpc/h) in radius for each cluster with some significant outliers, enabling to assess one of the most important systematic errors inherent in the stacked cluster weak lensing technique, the mass centroid uncertainty. In addition, the shape of the dark mass distribution is found to be only weakly correlated with that of the member galaxy distribution. We carefully examine possible sources of systematic errors in our measurements, finding none of them to be significant. Our results demonstrate the power of high-quality imaging data for exploring the detailed spatial distribution of dark matter (Abridged).
We study a composition of normal and exotic matter which is required for a flat Emergent Universe scenario permitted by the equation of state (EOS)($p=A\rho-B\rho^{1/2}$) and predict the range of the permissible values for the parameters $A$ and $B$ to explore a physically viable cosmological model. The permitted values of the parameters are determined taking into account the $H(z)-z$ data obtained from observations, a model independent BAO peak parameter and CMB shift parameter (WMAP7 data). It is found that although $A$ can be very close to zero, most of the observations favours a small and negative $A$. As a consequence, the effective Equation of State parameter for this class of Emergent Universe solutions remains negative always. We also compared the magnitude ($\mu (z)$) vs. redshift($z$) curve obtained in the model with that obtained from the union compilation data. According to our analysis the class of Emergent Universe solutions considered here is not ruled out by the observations.
We present rest-frame optical images and spectra of the gravitationally lensed, star-forming galaxy J0900+2234 (z=2.03). The observations were performed with the newly commissioned LUCIFER1 near-infrared instrument mounted on the Large Binocular Telescope (LBT). We fit lens models to the rest-frame optical images and find the galaxy has an intrinsic effective radius of 7.4 kpc with a lens magnification factor of about 5 for the A and B components. We also discovered a new arc belonging to another lensed high-z source galaxy, which makes this lens system a potential double Einstein ring system. Using the high S/N rest-frame spectra covering H+K band, we detected Hbeta, OIII, Halpha, NII and SII emission lines. Detailed physical properties of this high-z galaxy were derived. The extinction towards the ionized HII regions (E_g(B-V)) is computed from the flux ratio of Halpha and Hbeta and appears to be much higher than that towards stellar continuum (E_s(B-V)), derived from the optical and NIR broad band photometry fitting. The metallicity was estimated using N2 and O3N2 indices. It is in the range of 1/5-1/3 solar abundance, which is much lower than the typical z~2 star-forming galaxies. From the flux ratio of SII 6717 and 6732, we found that the electron number density of the HII regions in the high-z galaxy were >1000 cm^-3, consistent with other z~2 galaxies but much higher than that in local HII regions. The star-formation rate was estimated via the Halpha luminosity, after correction for the lens magnification, to be about 116\pm16 Msun/yr. Combining the FWHM of Halpha emission lines and the half-light radius, we found the dynamical mass of the lensed galaxy is 7.2x10^10 Msun.
We study the star formation histories (SFH) and stellar populations of 213 red and 226 blue nearly face-on low surface brightness disk galaxies (LSBGs), which are selected from the main galaxy sample of Sloan Digital Sky Survey (SDSS) Data Release Seven (DR7). We also want to compare the stellar populations and SFH between the two groups. The sample of both red and blue LSBGs have sufficient signal-to-noise ratio in the spectral continua. We obtain their absorption-line indices (e.g. Mg_2, H\delta_A), D_n(4000) and stellar masses from the MPA/JHU catalogs to study their stellar populations and SFH. Moreover we fit their optical spectra (stellar absorption lines and continua) by using the spectral synthesis code STARLIGHT on the basis of the templates of Simple Stellar Populations (SSPs). We find that red LSBGs tend to be relatively older, higher metallicity, more massive and have higher surface mass density than blue LSBGs. The D_n(4000)-H\delta_A plane shows that perhaps red and blue LSBGs have different SFH: blue LSBGs are more likely to be experiencing a sporadic star formation events at the present day, whereas red LSBGs are more likely to form stars continuously over the past 1-2 Gyr. Moreover, the fraction of galaxies that experienced recent sporadic formation events decreases with increasing stellar mass. Furthermore, two sub-samples are defined for both red and blue LSBGs: the sub-sample within the same stellar mass range of 9.5 <= log(M_\star/M_\odot) <= 10.3, and the surface brightness limiting sub-sample with \mu_0(R) <= 20.7 mag arcsec^{-2}. They show consistent results with the total sample in the corresponding relationships, which confirm that our results to compare the blue and red LSBGs are robust.
We consider large-scale collective motion of flat edge-on spiral galaxies from the Revised Flat Galaxy Catalogue (RFGC) taking into account the curvature of space-time in the Local Universe at the scale 100h^{-1} Mpc. We analyse how the relativistic model of collective motion should be modified to provide the best possible values of parameters, the effects that impact these parameters and ways to mitigate them. Evolution of galactic diameters, selection effects, and difference between isophotal and angular diameter distances are inadequate to explain this impact. At the same time, measurement error in HI line widths and angular diameters can easily provide such an impact. This is illustrated in a toy model, which allows analytical consideration, and then in the full model using Monte Carlo simulations. The resulting velocity field is very close to that provided by the non-relativistic model of motion. The obtained bulk flow velocity is consistent with {\Lambda}CDM cosmology.
The cosmological model of dark energy interacting with cold dark matter without coupling to the baryonic matter, is studied in the background of both classical Einstein and loop quantum cosmology. We consider two types of interacting models. In the former model, the interaction is a linear combination of the densities of two dark sectors, while in the latter model, the interaction with a constant transfer rate depends only on the density of cold dark matter. It is shown that the dynamical results in loop quantum cosmology are different from those in classical Einstein cosmology for both two kinds of interacting models. Moreover, the form of the interaction affects significantly the dynamical results in both kinds of cosmology.
ALMA will become fully operational in a few years and open a new window on primordial galaxies. The mm and submm domain is privileged, since the peak of dust emission between 60 and 100 microns is redshifted there for z= 5-10, and the continuum benefits from a negative K-correction. At least 100 times more sources than with present instruments could be discovered, so that more normal galaxies, with lower luminosities than huge starbursts and quasars will be surveyed. The high spatial resolution will suppress the confusion, which plagues today single dish bolometer surveys. Several CO lines detected in broad-band receivers will determine the redshift of objects too obscured to be seen in the optical. With the present instrumentation, only the most massive and gas rich objects have been detected in CO at high z, most of them being ultra-luminous starbursts with an extremely high star formation efficiency. However, selection biases are omni-present in this domain, and ALMA will statistically clarify the evolution of star formation efficiency, being fully complementary to JWST and ELTs.
We present the results of a baryonic Tully-Fisher relation (BTFR) study for a local sample of relatively isolated disk galaxies. We derive a BTFR with a slope near 3 measured over about 4 dex in baryon mass for our combined \textrm{H\,\scriptsize{I}} and bright spiral disk samples. This BTFR is significantly flatter and has less scatter than the TFR (stellar mass only) with its slope near 4 reported for other samples and studies. A BTFR slope near 3 is in better agreement with the expected slope from simple $\Lambda$CDM cosmological simulations that include both stellar and gas baryons. The scatter in the TFR/BTFR appears to depend on $W_{20}$: galaxies that rotate slower have more scatter. The atomic gas--to--stars ratio shows a break near $W_{20} = 250$ \kms\, probably associated with a change in star formation efficiency. In contrast the absence of such a break in the BTFR suggests that this relation was probably set at the main epoch of baryon dissipation rather than as a product of later galactic evolution.
We present the results of our stellar photometry and spectroscopy for the new Local Group galaxy VV 124 (UGC 4879) obtained with the 6-m BTA telescope. The presence of a few bright supergiants in the galaxy indicates that the current star formation process is weak. The apparent distribution of stars with different ages in VV 124 does not differ from the analogous distributions of stars in irregular galaxies, but the ratio of the numbers of young and old stars indicates that VV 124 belongs to the rare Irr/Sph type of galaxies. The old stars (red giants) form the most extended structure, a thick disk with an exponential decrease in the star number density to the edge. Definitely, the young population unresolvable in images makes a great contribution to the background emission from the central galactic regions. The presence of young stars is also confirmed by the [O III] emission line visible in the spectra that belongs to extensive diffuse galactic regions. The mean radial velocity of several components (two bright supergiants, the unresolvable stellar population, and the diffuse gas) is v_h = -70+/-15 km/s and the velocity with which VV 124 falls into the Local Group is v_LG = -12+/-15 km/s. We confirm the distance to the galaxy D = 1.1+/-0.1 Mpc and the metallicity of red giants ([Fe/H] = -1.37) found by Kopylov et al. (2008).VV 124 is located on the periphery of the Local Group approximately at the same distance from M 31 and our Galaxy and is isolated from other galaxies. The galaxy LeoA nearest to it is 0.5 Mpc away.
[Abridged]. We present SEDs for single-age, single-metallicity stellar populations (SSPs) covering the optical range at resolution 2.3A (FWHM). These SEDs constitute our base models, as they combine scaled-solar isochrones with MILES empirical stellar library, which follows the chemical evolution pattern of the solar neighbourhood. The models rely as much as possible on empirical ingredients, not just on the stellar spectra, but also on extensive photometric libraries. The unprecedented stellar parameter coverage of MILES allowed us to safely extend our optical SSP SED predictions from intermediate- to very-old age regimes, and the metallicity coverage of the SSPs from super-solar to [M/H]=-2.3. SSPs with such low metallicities are particularly useful for globular cluster studies. Observed spectra can be studied by means of full spectrum fitting or line-strengths. For the latter we propose a new Line Index System (LIS) to avoid the intrinsic uncertainties associated with the popular Lick/IDS system and provide more appropriate, uniform, spectral resolution. Apart from constant resolution as function of wavelength the system is also based on flux-calibrated spectra. Data can be analyzed at three different resolutions: 5A, 8.4A and 14A (FWHM), which are appropriate for studying globular cluster, low and intermediate-mass galaxies, and massive galaxies, respectively. Polynomials to transform current Lick/IDS line index measurements to the new system are provided. A web-page with a suite of on-line tools to facilitate the handling and transformation of the spectra is available at this http URL
We report sub-arcsecond scale radio continuum observations of a field of 35 by 22 arcmin centred in NGC3351 obtained with the Multi-Element Radio Linked Interferometer Network (MERLIN). We found 23 radio sources in this field, 6 of which are projected within the D$_{25}$ isophote of the galaxy, and 3 are located inside the central 100 arcsec in radius. Two of these three are significantly extended, while the third one is relatively compact. This one is the only source with a previously detected counterpart at other wavelengths and could constitute the radio counterpart of a young supernova remnant. The other two are probably related to jets from a background AGN. We are not able to detect individual supernovae or SNRs in the central region ($r<600$ pc) of the galaxy. This could imply that the ionising populations of the circumnuclear star-forming regions (CNSFRs) are too young (less than a few Myr) to host supernovae. Also the diffusion length of the relativistic electrons in the ISM associated with the SN from previous events of star formation seems to be larger than our maximum resolution of 50 pc in radius. Detecting the thermal bremsstrahlung emission from the circumnuclear HII regions probably requires deeper observations.
About 70-80% of the previously estimated WMAP CMB quadrupole signal would be an artefact of incorrect Doppler dipole subtraction if the hypothesis of a small timing interpolation error were correct. Observations of bright foreground objects constitute part of the time-ordered-data (TOD). Scans of an object in different directions should be shifted by the would-be timing error, causing a blurring effect. Three half-years of the calibrated, filtered WMAP TOD are compiled individually for the four W band differencing assemblies (DA's), with no masking of bright objects, giving 12 maps for each timing offset. Percentiles of the temperature-fluctuation distribution in each map at HEALPix resolution N_side=2048 are used to determine the dependence of all-sky image sharpness on the timing offset. In the W band, the 99.999% percentile, i.e. the temperature fluctuation in the approx 503-rd brightest pixel, is the least noisy percentile. Using this statistic, the hypothesis that a -25.6 ms offset relative to the timing adopted by the WMAP collaboration gives a focus at least as sharp as the uncorrected timing is rejected at 4.6\sigma significance. The Q and V band maps also reject the -25.6 ms offset hypothesis at high statistical significance. The requirement that the correct choice of timing offset must maximise image sharpness implies that the hypothesis of a timing error in the WMAP collaboration's compilation of the WMAP calibrated, filtered TOD is rejected at high statistical significance in each of the Q, V and W wavebands. However, the hypothesis that a timing error was applied during calibration of the raw TOD, inducing a dipole difference signal, is not excluded by this method.
We discuss the formation of supermassive black holes in the early universe, and how to probe their subsequent evolution with the upcoming mm/sub-mm telescope ALMA. We first focus on the chemical and radiative conditions for black hole formation, in particular considering radiation trapping and molecular dissociation effects. We then turn our attention towards the magnetic properties in the halos where the first black holes form, and show that the presence of turbulence may lead to a magnetic dynamo, which could support the black hole formation process by providing an efficient means of transporting the angular momentum. We finally focus on observable properties of high-redshift black holes with respect to ALMA, and discuss how to distinguish between chemistry driven by the starburst and chemistry driven by X-rays from the black hole.
I highlight the synergies of the Wide Field X-ray Telescope (WFXT) with the next generation radio surveys, including those to be obtained with the Australian Square Kilometre Array Pathfinder and the Square Kilometre Array, and discuss the overlap between the X-ray and radio source populations. WFXT will benefit greatly from the availability of deep radio catalogues with very high astrometric precision, while on the other hand WFXT data will be vital for the identification of faint radio sources down to ~ 50 microJy.
Fitting synthetic spectral energy distributions (SED) to the multi-band photometry of galaxies to derive their star formation rates (SFR), stellar masses, ages, etc. requires making a priori assumptions about their star formation histories (SFH). A widely adopted parameterization of the SFH, the so-called tau-models where SFR goes as e^{-t/tau) is shown to lead to unrealistically low ages when applied to star forming galaxies at z ~ 2, a problem shared by other SFHs when the age is left as a free parameter in the fitting. This happens because the SED of such galaxies, at all wavelengths, is dominated by their youngest stellar populations, which outshine the older ones. Thus, the SED of such galaxies conveys little information on the beginning of star formation. To cope with this problem, we explore a variety of SFHs, such as constant SFR and inverted-tau models - with SFR as e^{+t/tau) - along with various priors on age, including assuming that star formation started at high redshift in all the galaxies. We find that inverted-tau models with such latter assumption give SFRs and extinctions in excellent agreement with the values derived using only the UV part of the SED. These models are also shown to accurately recover the SFRs and masses of mock galaxies at z ~ 2 constructed from semi-analytic models. All other explored SFH templates do not fulfil these two test. In particular, direct-tau models with unconstrained age in the fitting procedure overstimate SFRs and underestimate stellar mass, and would exacerbate an apparent mismatch between the cosmic evolution of the volume densities of SFR and stellar mass. We conclude that for high-redshift star forming galaxies an exponentially increasing SFR with a high formation redshift is preferable to other forms of the SFH so far adopted in the literature.
In this work Gamma Ray Burst (GRB) data is used to place constraints on a putative coupling between dark energy and dark matter. Type Ia supernovae (SNe Ia) constraints from the Sloan Digital Sky Survey II (SDSS-II) first-year results, the cosmic microwave background radiation (CMBR) shift parameter from WMAP seven year results and the baryon acoustic oscillation (BAO) peak from the Sloan Digital Sky Survey (SDSS) are also discussed. The prospects for the field are assessed, as more GRB events become available.
A new harassment model is presented that models the complex, and dynamical tidal field of a Virgo like galaxy cluster. The model is applied to small, late-type dwarf disc galaxies (of substantially lower mass than in previous harassment simulations) as they infall into the cluster from the outskirts. These dwarf galaxies are only mildly affected by high speed tidal encounters with little or no observable consequences; typical stellar losses are $<10\%$, producing very low surface brightness streams ($\mu_B > 31$ mag arcsec$^{-2}$), and a factor of two drop in dynamical mass-to-light ratio. Final stellar discs remain disc-like, and dominated by rotation although often with tidally induced spiral structure. By means of Monte-Carlo simulations, the statistically likely influences of harassment on infalling dwarf galaxies are determined. The effects of harassment are found to be highly dependent on the orbit of the galaxy within the cluster, such that newly accreted dwarf galaxies typically suffer only mild harassment. Strong tidal encounters, that can morphologically transform discs into spheroidals, are rare occurring in $<15 \%$ of dwarf galaxy infalls for typical orbits of sub-structure within $\Lambda$CDM cluster mass halos. For orbits with small apocentric distances ($<$250 kpc), harassment is significantly stronger resulting in complete disruption or heavy mass loss ($>90 \%$ dark matter and $> 50 \%$ stellar), however, such orbits are expected to be highly improbable for newly infalling galaxies due to the deep potential well of the cluster.
The Rastall's theory is a modification of the General Relativity theory leading to a different expression for the conservation law in the matter sector compared with the usual one. It has been argued recently that such a theory may have applications to the dark energy problem, since a pressureless fluid may lead to an accelerated universe. In the present work we confront the Rastall's theory with the power spectrum data. The results indicate a configuration that essentially reduces the Rastall's theory to General Relativity, unless the non-usual conservation law refers to a scalar field, situation where other configurations are eventually possible.
Light gravitinos, with mass in the eV to MeV range, are well-motivated in particle physics, but their status as dark-matter candidates is muddled by early-Universe uncertainties. We investigate how upcoming data from colliders may clarify this picture. Light gravitinos are produced primarily in the decays of the next-to-lightest supersymmetric particle, resulting in spectacular signals, including di-photons, delayed and non-pointing photons, kinked charged tracks, and heavy metastable charged particles. We find that the Tevatron with 20/fb and the 7 TeV LHC with 1/fb may both see evidence for hundreds of light-gravitino events. Remarkably, this collider data is also well suited to distinguish between currently viable light-gravitino scenarios, with striking implications for structure formation, inflation, and other early-Universe cosmology.
A small fraction of core collapse supernovae (SNe) show evidence that the outgoing blast wave has encountered a substantial mass ~ 1-10 M_sun of circumstellar matter (CSM) at radii ~100-1000 AU, much more than can nominally be explained by pre-explosion stellar winds. In extreme cases this interaction may power the most luminous, optically-energetic SNe yet discovered. Interpretations for the origin of the CSM have thus far centered on explosive eruptions from the star just ~ years to decades prior to the core collapse. Here we consider an alternative possibility that the inferred CSM is a relic disk left over from stellar birth. We investigate this hypothesis by calculating the evolution of proto-stellar disks around massive stars following their early embedded phase using a self-similar accretion model. We identify an initial gravitationally-unstable ("gravito-turbulent") phase, followed by a much longer period of irradiation-supported accretion during which less effective non-gravitational forms of angular momentum transport dominate. Although external influences, such as the presence of a wide binary companion, may preclude disk survival in many systems, we find that massive (~1-10 M_sun) disks can preferentially survive around the most massive stars. Reasons for this perhaps counterintuitive include (1) the shorter stellar lifetimes and (2) large photo-evaporation radii (~ 1000 AU) of very massive stars; (3) suppression of the magneto-rotational instability due to the shielding from external sources of ionization; and (4) relative invulnerability of massive disks to lower mass stellar collisions and luminous blue variable eruptions. Because very luminous SNe are rare, testing the relic disk model requires constraining the presence of long-lived disks around a small fraction of very massive stars.
Nonsingular cosmologies are investigated in the framework of f(R) gravity within the first order formalism. General conditions for bounces in isotropic and homogeneous cosmology are presented. It is shown that only a quadratic curvature correction is needed to predict a bounce in a flat or to describe cyclic evolution in a curved dust-filled universe. Formalism for perturbations in these models is set up. In the simplest cases, the perturbations diverge at the turnover. Conditions to obtain smooth evolution are derived.
The viability of a possible cosmological scenario is investigated. The theoretical framework is the constrained next-to-minimal supersymmetric standard model (cNMSSM), with a gravitino playing the role of the lightest supersymmetric particle (LSP) and a neutralino acting as the next-to-lightest supersymmetric particle (NLSP). All the necessary constraints from colliders and cosmology have been taken into account. For gravitino we have considered the two usual production mechanisms, namely out-of equillibrium decay from the NLSP, and scattering processes from the thermal bath. The maximum allowed reheating temperature after inflation, as well as the maximum allowed gravitino mass are determined.
Effects of quantized free scalar fields in cosmological spacetimes with Big Rip singularities are investigated. The energy densities for these fields are computed at late times when the expansion is very rapid. For the massless minimally coupled field it is shown that an attractor state exists in the sense that, for a large class of states, the energy density of the field asymptotically approaches the energy density it would have if it was in the attractor state. Results of numerical computations of the energy density for the massless minimally coupled field and for massive fields with minimal and conformal coupling to the scalar curvature are presented. For the massive fields the energy density is seen to always asymptotically approach that of the corresponding massless field. The question of whether the energy densities of quantized fields can be large enough for backreaction effects to remove the Big Rip singularity is addressed.
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Using estimates of dark halo masses from satellite kinematics, weak gravitational lensing, and halo abundance matching, combined with the Tully-Fisher and Faber-Jackson relations, we derive the mean relation between the optical, V_opt, and virial, V_200, circular velocities of early- and late-type galaxies at redshift z~0. For late-type galaxies V_opt ~ V_200 over the velocity range V_opt=90-260 km/s, and is consistent with V_opt = V_maxh (the maximum circular velocity of NFW dark matter haloes in the concordance LCDM cosmology). However, for early-type galaxies V_opt \ne V_200, with the exception of early-type galaxies with V_opt simeq 350 km/s. This is inconsistent with early-type galaxies being, in general, globally isothermal. For low mass (V_opt < 250 km/s) early-types V_opt > V_maxh, indicating that baryons have modified the potential well, while high mass (V_opt > 400 km/s) early-types have V_opt < V_maxh. Folding in measurements of the black hole mass - velocity dispersion relation, our results imply that the supermassive black hole - halo mass relation has a logarithmic slope which varies from ~1.4 at halo masses of ~10^{12} Msun/h to ~0.65 at halo masses of 10^{13.5} Msun/h. The values of V_opt/V_200 we infer for the Milky Way and M31 are lower than the values currently favored by direct observations and dynamical models. This offset is due to the fact that the Milky Way and M31 have higher V_opt and lower V_200 compared to typical late-type galaxies of the same stellar masses. We show that current high resolution cosmological hydrodynamical simulations are unable to form galaxies which simultaneously reproduce both the V_opt/V_200 ratio and the V_opt-M_star (Tully-Fisher/Faber-Jackson) relation.
We present new results from our search for Giant H\,{\sc ii} Regions in galaxies visible from the southern hemisphere. In this work we study two galaxies: NGC\,7479 and NGC\,6070. Using high-resolution spectra, obtained with different instruments at Las Campanas Observatory, we are able to resolve the emission-line profile widths and determine the intrinsic velocity dispersion of the ionised gas. We detect profile widths corresponding to supersonic velocity dispersions in the six observed H\,{\sc ii} regions. We find that all of them show at least two distinct kinematical components: a relatively narrow feature (between ~11 and ~22\kms) and a broader (between ~31 and ~77\kms) component. Two of the regions show a complex narrow profile in all ion lines, which can be further split into two components with different radial velocities. Whereas the wing broadening of the overall profile can be fitted with a low-intensity broad component for almost all profiles, in one region it was better reproduced by two separate shell-like wings. We have analysed the impact that the presence of multiple components has on the location of the H{\sc ii} regions in the $\log(L) - \log(\sigma)$ plane. Although the overall distribution confirms the presence of a regression, the precise location of the regions in the plane is strongly dependent on the components derived from the profile fitting.
Near future cosmology will see the advent of wide area photometric galaxy surveys, like the Dark Energy Survey (DES), that extent to high redshifts (z ~ 1 - 2) but with poor radial distance resolution. In such cases splitting the data into redshift bins and using the angular correlation function $w(\theta)$, or the $C_{\ell}$ power spectrum, will become the standard approach to extract cosmological information or to study the nature of dark energy through the Baryon Acoustic Oscillations (BAO) probe. In this work we present a detailed model for $w(\theta)$ at large scales as a function of redshift and bin width, including all relevant effects, namely nonlinear gravitational clustering, bias, redshift space distortions and photo-z uncertainties. We also present a model for the full covariance matrix characterizing the angular correlation measurements, that takes into account the same effects as for $w(\theta)$ and also the possibility of a shot-noise component and partial sky coverage. Provided with a large volume N-body simulation from the MICE collaboration we built several ensembles of mock redshift bins with a sky coverage and depth typical of forthcoming photometric surveys. The model for the angular correlation and the one for the covariance matrix agree remarkably well with the mock measurements in all configurations. The prospects for a full shape analysis of $w(\theta)$ at BAO scales in forthcoming photometric surveys such as DES are thus very encouraging.
In this work, we present results for the photometric and clustering properties of galaxies that arise in a LambdaCDM hydrodynamical simulation of the local Universe. The present-day distribution of matter was constructed to match the observed large scale pattern of the IRAS 1.2-Jy galaxy survey. Our simulation follows the formation and evolution of galaxies in a cosmological sphere with a volume of ~130^3 (Mpc/h)^3 including supernova feedback, galactic winds, photoheating due to an uniform meta-galactic background and chemical enrichment of the gas and stellar populations. However, we do not consider AGNs. In the simulation, a total of ~20000 galaxies are formed above the resolution limit, and around 60 haloes are more massive than ~10^14 M_sun. Luminosities of the galaxies are calculated based on a stellar population synthesis model including the attenuation by dust, which is calculated from the cold gas left within the simulated galaxies. Environmental effects like colour bi-modality and differential clustering power of the hydrodynamical galaxies are qualitatively similar to observed trends. Nevertheless, the overcooling present in the simulations lead to too blue and overluminous brightest cluster galaxies (BCGs). To overcome this, we mimic the late-time suppression of star formation in massive halos by ignoring recently formed stars with the aid of a simple post-processing recipe. In this way we find luminosity functions, both for field and group/cluster galaxies, in better agreement with observations. Specifically, the BCGs then follow the observed luminosity-halo mass relation. However, in such a case, the colour bi-modality is basically lost, pointing towards a more complex interplay of late suppression of star formation than what is given by the simple scheme adopted.
One of the great endeavors of the past decade has been the evaluation of different observational techniques for measuring dark energy properties and of theoretical techniques for constraining models of cosmic acceleration given cosmological data. This chapter reviews a few of the key developments, promises, and cautions for revealing dark energy. We also present a few new calculations, on direct detection of acceleration through redshift drift, the minimum uncertainty in the equation of state, and testing gravity.
Through a detailed numerical investigation in three spatial dimensions, we demonstrate that long-lived time-dependent field configurations emerge dynamically during symmetry breaking in an expanding de Sitter spacetime. We investigate two situations: a single scalar field with a double-well potential and the bosonic sector of an SU(2) non-Abelian Higgs model. For the single scalar, we show that large-amplitude oscillon configurations emerge spontaneously and persist to contribute about 1.2% of the energy density of the universe. We also show that for a range of parameters, oscillon lifetimes are enhanced by the expansion and that this effect is a result of parametric resonance. For the SU(2) case, we see about 3% of the final energy density in oscillons.
The inner mass-profile of the relaxed cluster Abell 1703 is analysed by two very different strong-lensing techniques applied to deep ACS and WFC3 imaging. Our parametric method has the accuracy required to reproduce the many sets of multiple images, based on the assumption that mass approximately traces light. We test this assumption with a fully non-parametric, adaptive grid method, with no knowledge of the galaxy distribution. Differences between the methods are seen on fine scales due to member galaxies which must be included in models designed to search for lensed images, but on the larger scale the general distribution of dark matter is in good agreement, with very similar radial mass profiles. We add undiluted weak-lensing measurements from deep multi-colour Subaru imaging to obtain a fully model-independent mass profile out to the virial radius and beyond. Consistency is found in the region of overlap between the weak and strong lensing, and the full mass profile is well-described by an NFW model of a concentration parameter, $c_{\rm vir}\simeq 7.15\pm0.5$ (and $M_{vir}\simeq 1.22\pm0.15 \times 10^{15}M_{\odot}/h$). Abell 1703 lies above the standard $c$--$M$ relation predicted for the standard $\Lambda$CDM model, similar to other massive relaxed clusters with accurately determined lensing-based profiles.
We present 1D numerical simulations, which consider the effects of radiative
cooling and gravity on the hydrodynamics of the matter reinserted by stellar
winds and supernovae within young nuclear starbursts with a central
supermassive black hole (SMBH). The simulations confirm our previous
semi-analytic results for low energetic starbursts, evolving in a
quasi-adiabatic regime, and extend them to more powerful starbursts evolving in
the catastrophic cooling regime. The simulations show a bimodal hydrodynamic
solution in all cases. They present a quasi-stationary accretion flow onto the
black hole, defined by the matter reinserted by massive stars within the
stagnation volume and a stationary starburst wind, driven by the high thermal
pressure acquired in the region between the stagnation and the starburst radii.
In the catastrophic cooling regime, the stagnation radius rapidly approaches
the surface of the starburst region, as one considers more massive starbursts.
This leads to larger accretion rates onto the SMBH and concurrently to powerful
winds able to inhibit interstellar matter from approaching the nuclear
starburst.
Our self-consistent model thus establishes a direct physical link between the
SMBH accretion rate and the nuclear star formation activity of the host galaxy
and provides a good upper limit to the accretion rate onto the central black
hole.
We present a statistically complete sample of very X-ray luminous galaxy clusters detected in the MAssive Cluster Survey (MACS). This second MACS release comprises all 34 MACS clusters with nominal X-ray fluxes in excess of 2x10^(-12) erg/s/cm^2 (0.1-2.4 keV) in the ROSAT Bright Source Catalogue; two thirds of them are new discoveries. Extending over the redshift range from 0.3 to 0.5, this subset complements the complete sample of the 12 most distant MACS clusters (z>0.5) published in 2007 and further exemplifies the efficacy of X-ray selection for the compilation of samples of intrinsically massive galaxy clusters. Extensive follow-up observations with Chandra/ACIS led to three additional MACS cluster candidates being eliminated as (predominantly) X-ray point sources. For another four clusters --- which, however, remain in our sample of 34 --- the point-source contamination was found to be about 50%. The median X-ray luminosity of 1.3x10^45 erg/s (0.1-2.4 keV, Chandra, within r_500) of the clusters in this subsample demonstrates the power of the MACS survey strategy to find the most extreme and rarest clusters out to significant redshift. A comparison of the optical and X-ray data for all clusters in this release finds a wide range of morphologies with no obvious bias in favour of either relaxed or merging systems.
We investigate the performance of the parametric Maximum Likelihood component separation method in the context of the CMB B-mode signal detection and its characterization by small-scale CMB suborbital experiments. We consider high-resolution (FWHM=8') balloon-borne and ground-based observatories mapping low dust-contrast sky areas of 400 and 1000 square degrees, in three frequency channels, 150, 250, 410 GHz, and 90, 150, 220 GHz, with sensitivity of order 1 to 10 micro-K per beam-size pixel. These are chosen to be representative of some of the proposed, next-generation, bolometric experiments. We study the residual foreground contributions left in the recovered CMB maps in the pixel and harmonic domain and discuss their impact on a determination of the tensor-to-scalar ratio, r. In particular, we find that the residuals derived from the simulated data of the considered balloon-borne observatories are sufficiently low not to be relevant for the B-mode science. However, the ground-based observatories are in need of some external information to permit satisfactory cleaning. We find that if such information is indeed available in the latter case, both the ground-based and balloon-borne experiments can detect the values of r as low as ~0.04 at 95% confidence level. The contribution of the foreground residuals to these limits is found to be then subdominant and these are driven by the statistical uncertainty due to CMB, including E-to-B leakage, and noise. We emphasize that reaching such levels will require a sufficient control of the level of systematic effects present in the data.
Abridged. The feedback between massive stars and the interstellar medium is one of the most important processes in the evolution of dwarf galaxies. This interaction results in numerous neutral and ionised gas structures that have been found both in the disc and in the halo of these galaxies. However, their origin and fate are still poorly understood. We here present new HI and optical data of two nearby irregular dwarf galaxies: IC 4662 and NGC 5408. The HI line data were obtained with the ATCA and are part of the Local Volume HI Survey. They are complemented by optical images and spectroscopic data obtained with the ESO NTT and the ESO 3.6m telescope. Our main aim is to study the kinematics of the neutral and ionised gas components in order to search for outflowing gas structures and to make predictions about their fate. We find the HI gas envelopes of both galaxies to extend well beyond the optical discs. The optical disc is embedded into the central HI maximum in both galaxies. However, higher resolution HI maps show that the HI intensity peaks are typically offset from the prominent HII regions. While NGC 5408 shows a fairly regular HI velocity field, which allows us to derive a rotation curve, IC 4662 reveals a rather twisted HI velocity field, possibly caused by a recent merger event. We detect outflows with velocities between 20 and 60 km/s in our Halpha spectra of both galaxies, sometimes with HI counterparts of similar velocity. We suggest the existence of expanding superbubbles, especially in NGC 5408. This is also supported by the detection of FWHMs as high as 70 km/s in Halpha. In case of NGC 5408, we compare our results with the escape velocity of the galaxy, which shows that the measured expansion velocities are in all cases too low to allow the gas to escape from the gravitational potential of NGC 5408. This result is consistent with studies of other dwarf galaxies.
We examine the temperature structure of the intergalactic medium IGM) surounding a hard radiation source, such as a Quasi-Stellar Object (QSO), as it responds to the onset of helium reionization by the source. We model the reionization using a radiative transfer (RT) code coupled to a particle-mesh (PM) N-body code. Neutral hydrogen and helium are initially ionized by a starburst spectrum, which is allowed to gradually evolve into a power law spectrum (fnu ~ nu^(-0.5)). Multiple simulations were performed with different times for the onset and dominance of the hard spectrum, with onset redshifts ranging from z = 3.5 to 5.5. The source is placed in a high-density region to mimic the expected local environment of a QSO. Simulations with the source placed in a low-density environment were also performed as control cases to explore the role of the environment on the properties of the surrounding IGM. We find in both cases that the IGM temperature within the HeIII region produced exceeds the IGM temperature before full helium reionization, resulting in a "thermal proximity effect", but that the temperature in the HeIII region increases systematically with distance from the source. With time the temperature relaxes with a reduced spread as a function of impact parameter along neighbouring lines of sight, although the trend continues to persist until z = 2. Such a trend could be detected using the widths of intervening metal absorption systems using high resolution, high signal-to-noise ratio spectra.
Two new luminosity functions of galaxies can be built starting from three and four parameter generalized gamma distributions. In the astrophysical conversion, the number of parameters increases by one, due to the addition of the overall density of galaxies. A third new galaxy luminosity function is built starting from a three parameter generalized gamma distribution for the mass of galaxies once a simple nonlinear relationship between mass and luminosity is assumed; in this case the number of parameters is five because the overall density of galaxies and a parameter that regulates mass and luminosity are added. The three new galaxy luminosity functions were tested on the Sloan Digital Sky Survey (SDSS) in five different bands; the results always produce a "better fit" than the Schechter function. The formalism that has been developed allows to analyze the Schechter function with a transformation of location. A test between theoretical and observed number of galaxies as a function of redshift was done on data extracted from a two-degree field galaxy redshift survey.
In this paper we summarise the status of single field models of inflation in light of the WMAP 7 data release. We find little has changed since the 5 year release, and results are consistent with previous findings. The increase in the upper bound on the running of the spectral index impacts on the status of the production of Primordial Black Holes from single field models. The lower bound on the equilateral configuration of the non-gaussianity parameter is reduced and thus the bounds on the theoretical parameters of (UV) DBI single brane models are weakened. In the case of multiple coincident branes the bounds are also weakened and the two, three or four brane cases will produce a tensor-signal that could possibly be observed in the future.
One of the most pressing issues in cosmology is whether general relativity (GR) plus a dark sector is the underlying physical theory or whether a modified gravity model is needed. Upcoming dark energy experiments designed to probe dark energy with multiple methods can address this question by comparing the results of the different methods in constraining dark energy parameters. Disagreement would signal the breakdown of the assumed model (GR plus dark energy). We study the power of this consistency test by projecting constraints in the w_0-w_a plane from the four different techniques of the Dark Energy Survey in the event that the underlying true model is modified gravity. We find that the standard technique of looking for overlap has some shortcomings, propose as an alternative the Multi-dimensional Consistency Test, and introduce the methodology for projecting whether a given experiment will be able to distinguish a modified gravity model from GR.
We present a survey of the mass surface-density of spiral disks, motivated by outstanding uncertainties in rotation-curve decompositions. Our method exploits integral-field spectroscopy to measure stellar and gas kinematics in nearly face-on galaxies sampled at 515, 660, and 860 nm, using the custom-built SparsePak and PPak instruments. A two-tiered sample, selected from the UGC, includes 146 nearly face-on galaxies, with B<14.7 and disk scale-lengths between 10 and 20 arcsec, for which we have obtained H-alpha velocity-fields; and a representative 46-galaxy subset for which we have obtained stellar velocities and velocity dispersions. Based on re-calibration of extant photometric and spectroscopic data, we show these galaxies span factors of 100 in L(K) (0.03 < L/L(K)* < 3), 8 in L(B)/L(K), 10 in R-band disk central surface-brightness, with distances between 15 and 200 Mpc. The survey is augmented by 4-70 micron Spitzer IRAC and MIPS photometry, ground-based UBVRIJHK photometry, and HI aperture-synthesis imaging. We outline the spectroscopic analysis protocol for deriving precise and accurate line-of-sight stellar velocity dispersions. Our key measurement is the dynamical disk-mass surface-density. Star-formation rates and kinematic and photometric regularity of galaxy disks are also central products of the study. The survey is designed to yield random and systematic errors small enough (i) to confirm or disprove the maximum-disk hypothesis for intermediate-type disk galaxies, (ii) to provide an absolute calibration of the stellar mass-to-light ratio well below uncertainties in present-day stellar-population synthesis models, and (iii) to make significant progress in defining the shape of dark halos in the inner regions of disk galaxies.
Coalescing binary systems, consisting of two collapsed objects, are among the most promising sources of high frequency gravitational waves signals detectable, in principle, by ground-based interferometers. Binary systems of Neutron Star or Black Hole/Neutron Star mergers should also give rise to short Gamma Ray Bursts, a subclass of Gamma Ray Bursts. Short-hard-Gamma Ray Bursts might thus provide a powerful way to infer the merger rate of two-collapsed object binaries. Under the hypothesis that most short Gamma Ray Bursts originate from binaries of Neutron Star or Black Hole/Neutron Star mergers, we outline here the possibility to associate short Gamma Ray Bursts as electromagnetic counterpart of coalescing binary systems.
A precise electromagnetic measurement of the sky coordinates and redshift of a coalescing black hole binary holds the key for using its gravitational wave (GW) signal to constrain cosmological parameters and to test general relativity. Here we show that the merger of ~10^{6-8}M_sun black holes is generically followed over a period of years by multiple electromagnetic flares from tidally disrupted stars. The sudden recoil imparted to the merged black hole by GW emission results promptly in a tidal disruption rate of stars as high as ~0.1-1 per year. The sequential disruption of stars within a single galaxy over a short period provides a unique electromagnetic flag of a recent black hole coalescence event, and can be used on its own to calibrate the expected rate of GW sources for pulsar timing arrays or the proposed Laser Interferometer Space Antenna (LISA).
Using the method of integral-field (3D) spectroscopy, we have investigated the kinematics and distribution of the gas and stars at the center of the early-type spiral galaxy with a medium scale bar NGC 7177 as well as the change in the mean age of the stellar population along the radius. A classical picture of radial gas inflow to the galactic center along the shock fronts delineated by dust concentration at the leading edges of the bar has been revealed. The gas inflow is observed down to a radius R = 1".5 -- 2", where the gas flows at the inner Lindblad resonance concentrate in an azimuthally highly inhomogeneous nuclear star formation ring. The bar in NGC 7177 is shown to be thick in z coordinate; basically, it has already turned into a pseudo-bulge as a result of secular dynamical evolution. The mean stellar age inside the star formation ring, in the galactic nucleus, is old, ~10 Gyr. Outside, at a distance R = 6" - 8" from the nucleus, the mean age of the stellar population is ~2 Gyr. If we agree that the bar in NGC 7177 is old, then, obviously, the star formation ring has migrated radially inward in the last 1-2 Gyr, in accordance with the predictions of some dynamical models.
We present an analytical model which reproduces measured galaxy number counts from surveys in the wavelength range of 500 micron to 2 mm. The model involves a single high-redshift galaxy population with a Schechter luminosity function which has been gravitationally lensed by galaxy clusters in the mass range 10^13 to 10^15 Msun. This simple model reproduces both the low flux and the high flux end of the number counts reported by the BLAST, SCUBA, AzTEC and the SPT surveys. In particular, our model accounts for the most luminous galaxies detected by SPT as the result of high magnifications by galaxy clusters (magnification factors of 10-30). This interpretation implies that submillimeter and millimeter surveys of this population may prove to be a useful addition to ongoing cluster detection surveys. The model also implies that the bulk of submillimeter galaxies detected at wavelengths larger than 500 micron lie at redshifts greater than 2.
The study of the hydrodynamics of bubble growth in first-order phase transitions is very relevant for electroweak baryogenesis, as the baryon asymmetry depends sensitively on the bubble wall velocity, and also for predicting the size of the gravity wave signal resulting from bubble collisions, which depends on both the bubble wall velocity and the plasma fluid velocity. We perform such study in different bubble expansion regimes, namely deflagrations, detonations, hybrids (steady states) and runaway solutions (accelerating wall), without relying on a specific particle physics model. We compute the efficiency of the transfer of vacuum energy to the bubble wall and the plasma in all regimes. We clarify the condition determining the runaway regime and stress that in most models of strong first-order phase transitions this will modify expectations for the gravity wave signal. Indeed, in this case, most of the kinetic energy is concentrated in the wall and almost no turbulent fluid motions are expected since the surrounding fluid is kept mostly at rest.
If dark matter in the galactic halo is composed of bosons that form a Bose-Einstein condensate then it is likely that the rotation of the halo will lead to the nucleation of vortices. After a review of the Gross-Pitaevskii equation, the Thomas-Fermi approximation and vortices in general, we consider vortices in detail. We find strong bounds for the boson mass, interaction strength, the shape and quantity of vortices in the halo, the critical rotational velocity for the nucleation of vortices and, in the Thomas-Fermi regime, an exact solution for the mass density of a single, axisymmetric vortex.
We show that the inclusion of simple anisotropic pressures stops the isotropic Friedmann universe being a stable attractor as an initial or final singularity is approached when pressures can exceed the energy density. This shows that the situation with isotropic pressures, studied earlier in the context of cyclic and ekpyrotic cosmologies, is not generic, and Kasner-like behaviour occurs when simple pressure anisotropies are present. We find all the asymptotic behaviours and determine the dynamics when the anisotropic principal pressures are proportional to the density. We expect distortions and anisotropies to be significantly amplified through a simple cosmological bounce in cyclic or ekpyrotic cosmologies when ultra-stiff pressures are present.
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We analyze the color gradients (CGs) of ~50000 nearby SDSS galaxies. From synthetic spectral models based on a simplified star formation recipe, we derive the mean spectral properties, and explain the observed radial trends of the color as gradients of the stellar population age and metallicity (Z). The most massive ETGs (M_* > 10^{11} Msun) have shallow CGs in correspondence of shallow (negative) Z gradients. In the stellar mass range 10^(10.3-10.5) < M_* < 10^(11) Msun, the Z gradients reach their minimum of ~ -0.5 dex^{-1}. At M_* ~ 10^{10.3-10.5} Msun, color and Z gradient slopes suddenly change. They turn out to anti-correlate with the mass, becoming highly positive at the very low masses. We have also found that age gradients anti-correlate with Z gradients, as predicted by hierarchical cosmological simulations for ETGs. On the other side, LTGs have gradients which systematically decrease with mass (and are always more negative than in ETGs), consistently with the expectation from gas infall and SN feedback scenarios. Z is found to be the main driver of the trend of color gradients, especially for LTGs, but age gradients are not negligible and seem to play a significant role too. We have been able to highlight that older galaxies have systematically shallower age and Z gradients than younger ones. Our results for high-mass galaxies are in perfect agreement with predictions based on the merging scenario, while the evolution of LTGs and younger and less massive ETGs seems to be mainly driven by infall and SN feedback. (Abridged)
We report new cm-wave measurements at five frequencies between 15 and 18GHz of the continuum emission from the reportedly anomalous "region 4" of the nearby galaxy NGC6946. We find that the emission in this frequency range is significantly in excess of that measured at 8.5GHz, but has a spectrum from 15-18GHz consistent with optically thin free-free emission from a compact HII region. In combination with previously published data we fit four emission models containing different continuum components using the Bayesian spectrum analysis package radiospec. These fits show that, in combination with data at other frequencies, a model with a spinning dust component is slightly preferred to those that possess better-established emission mechanisms.
We conduct numerical experiments by evolving gaseous/stellar disks embedded in live dark matter halos aiming at quantifying the effect of gas spatial resolution and gas content on the bar evolution. Model sequences have been constructed using different resolution, and gas fraction has been varied along each sequence within fgas=0%-50%, keeping the disk and halo properties unchanged. We find that the spatial resolution becomes important with an increase in `fgas'. For the higher resolution model sequences, we observe a bimodal behavior in the bar evolution with respect to the gas fraction, especially during the secular phase of this evolution. The switch from the gas-poor to gas-rich behavior is abrupt and depends on the resolution used. The diverging evolution has been observed in nearly all basic parameters characterizing bars, such as the bar strength, central mass concentration, vertical buckling amplitude, size, etc. We find that the presence of the gas component severely limits the bar growth and affects its pattern speed evolution. Gas-poor models display rapidly decelerating bars, while gas-rich models exhibit bars with constant or even slowly accelerating tumbling. The gas-rich models have bar corotation (CR) radii within the disk at all times, in constrast with gas-poor and purely stellar disks. The CR-to-bar size ratio is less than 2 for gas rich-models. We have confirmed that the disk angular momentum within the CR remains unchanged in the gas-poor models, as long as the CR stays within the disk, but experiences a sharp drop before leveling off in the gas-rich models. Finally, we discuss a number of observed correlations between various parameters of simulated bars, e.g., bar sizes and gas fractions, bar strength and buckling amplitude, bar strength and its size, etc.
We revisit the growth of perturbations in scalar-tensor (ST) cosmologies. We show that on large subhorizon scales, in the Newtonian gauge, the usual subhorizon growth equation does not describe the growth of perturbations accurately, as a result of scale-dependent relativistic corrections to the Poisson equation. We derive a scale-dependent version of the growth equation which is in excellent agreement with exact numerical results. Based on this equation, we propose an accurate scale dependent parameterization for the growth of perturbations in these models.
We have investigated the oxygen and nitrogen chemical abundances in extremely compact star-forming galaxies with redshifts between $\sim$0.11-0.35, popularly referred to as "green peas". Direct and strong-line methods sensitive to the N/O ratio applied to their SDSS spectra reveals that these systems are genuine metal-poor galaxies, with mean oxygen abundances 20% solar. At a given metallicity these galaxies display systematically large N/O ratios compared to normal galaxies, which can explain the strong difference between our metallicities measurements and previous ones. While their N/O ratios follow the relation with stellar mass of local star-forming galaxies in the SDSS, we find that the mass--metallicity relation of the "green peas" is offset $\ga$0.3 dex to lower metallicities. We argue that recent interaction-induced inflow of gas, possibly coupled with a selective metal-rich gas loss, driven by supernova winds, may explain our findings and the known galaxy properties, namely high specific star formation rates, extreme compactness, and disturbed optical morphologies. The "green pea" galaxy properties seem to be not common in the nearby Universe, suggesting a short and extreme stage of their evolution. Therefore, these galaxies may allow us to study in great detail many processes, such as starburst activity and chemical enrichment, under physical conditions approaching those in galaxies at higher redshifts.
In the present work, by the help of the newly released Union2 compilation which consists of 557 Type Ia supernovae (SNIa), we calibrate 109 long Gamma-Ray Bursts (GRBs) with the well-known Amati relation, using the cosmology-independent calibration method proposed by Liang {\it et al.}. We have obtained 59 calibrated high-redshift GRBs which can be used to constrain cosmological models without the circularity problem (we call them "Hymnium" GRBs sample for convenience). Then, we consider the joint constraints on 7 cosmological models from the latest observational data, namely, the combination of 557 Union2 SNIa dataset, 59 calibrated Hymnium GRBs dataset (obtained in this work), the shift parameter $R$ from the WMAP 7-year data, and the distance parameter $A$ of the measurement of the baryon acoustic oscillation (BAO) peak in the distribution of SDSS luminous red galaxies. We also briefly consider the comparison of these 7 cosmological models.
We present a performance analysis of the DiskMass Survey. The survey uses collisionless tracers in the form of disk stars to measure the surface-density of spiral disks, to provide an absolute calibration of the stellar mass-to-light ratio, and to yield robust estimates of the dark-matter halo density profile in the inner regions of galaxies. We find a disk inclination range of 25-35 degrees is optimal for our measurements, consistent with our survey design to select nearly face-on galaxies. Uncertainties in disk scale-heights are significant, but can be estimated from radial scale-lengths to 25% now, and more precisely in the future. We detail the spectroscopic analysis used to derive line-of-sight velocity dispersions, precise at low surface-brightness, and accurate in the presence of composite stellar populations. Our methods take full advantage of large-grasp integral-field spectroscopy and an extensive library of observed stars. We show that the baryon-to-total mass fraction (F_b) is not a well-defined observational quantity because it is coupled to the halo mass model. This remains true even when the disk mass is known and spatially-extended rotation curves are available. In contrast, the fraction of the rotation speed supplied by the disk at 2.2 scale lengths (disk maximality) is a robust observational indicator of the baryonic disk contribution to the potential. We construct the error-budget for the key quantities: dynamical disk mass surface-density, disk stellar mass-to-light ratio, and disk maximality (V_disk / V_circular). Random and systematic errors in these quantities for individual galaxies will be ~25%, while survey precision for sample quartiles are reduced to 10%, largely devoid of systematic errors outside of distance uncertainties.
NGC 2903 is a nearby barred spiral with an active starburst in the center and Hii regions distributed along its bar. We aim to analyse the star formation properties in the bar region of NGC 2903 and study the links with the typical bar morphological features. A combination of space and ground-based data from the far-ultraviolet to the sub-millimeter spectral ranges is used to create a panchromatic view of the NGC 2903 bar. We produce two catalogues: one for the current star formation regions, as traced by the halpha compact emission, and a second one for the ultraviolet (UV) emitting knots, containing positions and luminosities. From them we have obtained ultraviolet colours, star formation rates, dust attenuation and halpha EWs, and their spatial distribution have been analysed. Stellar cluster ages have been estimated using stellar population synthesis models (Starburst99). NGC 2903 is a complex galaxy, with a very different morphology on each spectral band. The CO(J=1-0) and the 3.6 micron emission trace each other in a clear barred structure, while the halpha leads both components and it has an s-shape distribution. The UV emission is patchy and does not resemble a bar. The UV emission is also characterised by a number of regions located symmetrically with respect to the galaxy center, almost perpendicular to the bar, in a spiral shape covering the inner ~2.5 kpc. These regions do not show a significant halpha nor 24 micron emission. We have estimated ages for these regions ranging from 150 to 320 Myr, being older than the rest of the UV knots, which have ages lower than 10 Myr. The SFR calculated from the UV emission is ~0.4 M$_{\odot}$/yr, compatible with the SFR as derived from halpha calibrations (M$_{\odot}$/yr).
We consider models of inflection point inflation. The main drawback of such models is that they suffer from the overshoot problem. Namely the initial condition should be fine tuned to be near the inflection point for the universe to inflate. We show that stringy realizations of inflection point inflation are common and offer a natural resolution to the overshoot problem.
It was recently realized that matter modeled by the scalar field sector of the Lee-Wick Standard Model yields, in the context of a homogeneous and isotropic cosmological background, a bouncing cosmology. However, bouncing cosmologies induced by pressure-less matter are in general unstable to the addition of relativistic matter (i.e. radiation). Here we study the possibility of obtaining a bouncing cosmology if we add not only radiation, but also its Lee-Wick partner, to the matter sector. We find that, in general, no bounce occurs. The only way to obtain a bounce is to choose initial conditions with very special phases of the radiation field and its Lee-Wick partner.
We study a noninteracting supersymmetric model in de Sitter spacetime. Supersymmetry breaking induces a nonzero vacuum energy density. A short distance cut-off of the order of Planck length provides a matching between the vacuum energy density and the cosmological constant related to the de Sitter expansion parameter.
A variant of the accelerating cosmology reconstruction program is developed for $f(R)$ gravity and for a modified Yang-Mills/Maxwell theory. Reconstruction schemes in terms of e-foldings and by using an auxiliary scalar field are developed for the two theories. An example of a model with a transient phantom behavior without real matter is explicitly discussed in both schemes. Further, the two reconstruction procedures are applied to the more physically interesting case of a Yang-Mills/Maxwell theory, again with explicit examples. Detailed comparison of the two schemes for reconstruction is presented in all these cases. It seems to support physical non-equivalence of the two frames.
This thesis will try to contribute to the understanding of open issues in
cosmology by considering f(R) and brane-world theories. In Chapter 1, we shall
summarise the main features of f(R) gravities in the metric formalism and we
shall introduce both the notion of brane excitations, the branons and the
brane-skyrmions. We shall finish the chapter by providing some insight about
the possibility of mini black holes detection in the LHC as a signature for the
validity of these modified gravity theories.
The Chapter 2 will deal with f(R) theories able to mimic Einstein-Hilbert
plus cosmological constant solutions and f(R) theories will be shown to be able
to mimic the cosmological evolution generated by any perfect fluid with
constant equation of state.
The Chapter 3 will be devoted to the computation of cosmological
perturbations for f(R) theories. Special attention will be paid here to obtain
a completely general differential equation for the evolution of perturbations
and its particularization for the so-called sub-Hubble scales will be
explicitly shown.
In the Chapter 4 we shall focus on the study of black holes in f(R) gravities
in an arbitrary number of dimensions. With this purpose we shall study constant
curvature solutions for f(R) theories as well as perturbative solutions around
the standard SAdS geometry. An important part of this chapter will be then
devoted to the thermodynamics of SAdS black holes in f(R) theories.
In the Chapter 5 we will thoroughly study brane-skyrmions. In this context,
the recent claim of detection of an unexpected feature in the CMB, referred to
as the cold spot, will be explained as a topological defect on the brane in
complete agreement with those calculations in the literature that tried to
explain that cold spot as a texture of a NLSM.
Main conclusions are summarized all together in Chapter 6 .
We discuss a possible generation of radio bursts preceding final stages of binary neutron star mergings which can be accompanied by short gamma-ray bursts. Detection of such bursts appear to be advantageous in the low-frequency radio band due to a time delay of ten to several hundred seconds required for radio signal to propagate in the ionized intergalactic medium. This delay makes it possible to use short gamma-ray burst alerts to promptly monitor specific regions on the sky by low-frequency radio facilities, especially by LOFAR. To estimate the strength of the radio signal, we assume a power-law dependence of the radio luminosity on the total energy release in a magnetically dominated outflow, as found in millisecond pulsars. Based on the planned LOFAR sensitivity at 120 MHz, we estimate that the LOFAR detection rate of such radio transients could be about several events per month from redshifts up to $z\sim1.3$ in the most optimistic scenario. The LOFAR ability to detect such events would crucially depend on exact efficiency of low-frequency radio emission mechanism.
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We present HST/WFPC2 observations across the disk of the nearby isolated dwarf S0 galaxy NGC 404, which hosts an extended gas disk. Our deepest field reaches the red clump and main-sequence stars with ages <500 Myr. Although we detect trace amounts of star formation at times more recent than 10 Gyr for all fields, the proportion of red giant stars to asymptotic giants and main sequence stars suggests that the disk is dominated by an ancient (>10 Gyr) population. Detailed modeling of the color-magnitude diagram suggests that ~70% of the stellar mass in the NGC 404 disk formed by z~2 (10 Gyr ago) and at least ~90% formed prior to z~1 (8 Gyr ago). These results indicate that the stellar populations of the NGC 404 disk are on average significantly older than those of other nearby disk galaxies, suggesting that early and late type disks may have different long-term evolutionary histories, not simply differences in their recent star formation rates. Comparisons of the spatial distribution of the young stellar mass and FUV emission in GALEX images show that the brightest FUV regions contain the youngest stars, but that some young stars (<160 Myr) lie outside of these regions. FUV luminosity appears to be strongly affected by both age and stellar mass within individual regions. Finally, we use our measurements to infer the relationship between the star formation rate and the gas density of the disk at previous epochs. We find that most of the history of the NGC 404 disk is consistent with star formation that has decreased with the gas density according to the Schmidt law. However, 0.5-1 Gyr ago, the star formation rate was unusually low for the inferred gas density, consistent with the possibility that there was a gas accretion event that reignited star formation ~0.5 Gyr ago. Such an event could explain why this S0 galaxy hosts an extended gas disk.
We combine new high sensitivity ultraviolet (UV) imaging from the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) with existing deep HST/Advanced Camera for Surveys (ACS) optical images from the Great Observatories Origins Deep Survey (GOODS) program to identify UV-dropouts, which are Lyman break galaxy (LBG) candidates at z~1-3. These new HST/WFC3 observations were taken over 50 sq.arcmin in the GOODS-South field as a part of the Early Release Science program. The uniqueness of these new UV data is that they are observed in 3 UV/optical (WFC3 UVIS) channel filters (F225W, F275W and F336W), which allows us to identify three different sets of UV-dropout samples. We apply Lyman break dropout selection criteria to identify F225W-, F275W- and F336W-dropouts, which are z~1.7, 2.1 and 2.7 LBG candidates, respectively. We use multi-wavelength imaging combined with available spectroscopic and photometric redshifts to carefully access the validity of our UV-dropout candidates. Our results are as follows: (1) these WFC3 UVIS filters are very reliable in selecting LBGs with z~2.0, which will reduce the gap between the well studied z~>3 and z~0 regimes, (2) the combined number counts agrees very well with the observed evolution in number counts when compared with higher redshift LBG samples, and (3) the best-fit Schechter function parameters from the rest-frame UV luminosity functions at three different redshifts fit very well with the evolutionary trend of the characteristic absolute magnitude, and the faint-end slope, as a function of redshift. This is the first study to illustrate the usefulness of the WFC3 UVIS channel observations to select z<3 LBGs. The addition of the new WFC3 on the HST has made it possible to uniformly select LBGs from z~1 to z~9, and significantly enhance our understanding of these galaxies using HST sensitivity and resolution.
Scalar fields with a "chameleon" property, in which the effective particle mass is a function of its local environment, are common to many theories beyond the standard model and could be responsible for dark energy. If these fields couple weakly to the photon, they could be detectable through the "afterglow" effect of photon-chameleon-photon transitions. The ADMX experiment was used in the first chameleon search with a microwave cavity to set a new limit on scalar chameleon-photon coupling excluding values between 2*10^9 and 5*10^14 for effective chameleon masses between 1.9510 and 1.9525 micro-eV.
Several independent cosmological tests have shown evidences that the energy density of the Universe is dominated by a dark energy component, which cause the present accelerated expansion. The large scale structure formation can be used to probe dark energy models, and the mass function of dark matter haloes is one of the best statistical tools to perform this study. We present here a statistical analysis of mass functions of galaxies under a homogeneous dark energy model, proposed in the work of Percival (2005), using an observational flux-limited X-ray cluster survey, and CMB data from WMAP. We compare, in our analysis, the standard Press-Schechter (PS) approach (where a Gaussian distribution is used to describe the primordial density fluctuation field of the mass function), and the PL (Power Law) mass function (where we apply a nonextensive q-statistical distribution to the primordial density field). We conclude that the PS mass function cannot explain at the same time the X-ray and the CMB data (even at 99% confidence level), and the PS best fit dark energy equation of state parameter is $\omega=-0.58$, which is distant from the cosmological constant case. The PL mass function provides better fits to the HIFLUGCS X-ray galaxy data and the CMB data; we also note that the $\omega$ parameter is very sensible to modifications in the PL free parameter, $q$, suggesting that the PL mass function could be a powerful tool to constrain dark energy models.
We have performed a comprehensive multiwavelength analysis of a sample of 20 starburst galaxies that show a substantial population of very young massive stars, most of them classified as Wolf-Rayet (WR) galaxies. We have analysed optical/NIR colours, physical and chemical properties of the ionized gas, stellar, gas and dust content, star-formation rate and interaction degree (among many other galaxy properties) of our galaxy sample using multi-wavelength data. We compile 41 independent star-forming regions --with oxygen abundances between 12+log(O/H) = 7.58 and 8.75--, of which 31 have a direct estimate of the electron temperature of the ionized gas. This paper, only submitted to astro-ph, compiles the most common empirical calibrations to the oxygen abundance, and presents the comparison between the chemical abundances derived in these galaxies using the direct method with those obtained through empirical calibrations, as it is published in Lopez-Sanchez & Esteban (2010b). We find that (i) the Pilyugin method (Pilyugin 2001a,b; Pilyugin & Thuan 2005) which considers the R23 and the P parameters, is the best suited empirical calibration for these star-forming galaxies, (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 (McGaugh, 1991; Kewley & Dopita, 2002; Kobulnicky & Kewley, 2004) are systematically 0.2 -- 0.3 dex higher than the values derived from the direct method. These differences are of the same order that the abundance discrepancy found between recombination and collisionally excited lines. This may suggest the existence of temperature fluctuations in the ionized gas, as exists in Galactic and other extragalactic HII regions.
We compare mid-infrared emission-line properties, from high-resolution Spitzer spectra of a hard X-ray (14 -- 195 keV) selected sample of nearby (z < 0.05) AGN detected by the Burst Alert Telescope (BAT) aboard Swift. The luminosity distribution for the mid-infrared emission-lines, [O IV] 25.89 micron, [Ne II] 12.81 micron, [Ne III] 15.56 micron and [Ne V] 14.32/24.32 micron, and hard X-ray continuum show no differences between Seyfert 1 and Seyfert 2 populations, however six newly discovered BAT AGNs are under-luminous in [O IV], most likely the result of dust extinction in the host galaxy. The overall tightness of the mid-infrared correlations and BAT fluxes and luminosities suggests that the emission lines primarily arise in gas ionized by the AGN. We also compare the mid-infrared emission-lines in the BAT AGNs with those from published studies of ULIRGs, PG QSOs, star-forming galaxies and LINERs. We find that the BAT AGN sample fall into a distinctive region when comparing the [Ne III]/[Ne II] and the [O IV]/[Ne III] ratios. These line ratios are lower in sources that have been previously classified in the mid-infrared/optical as AGN than those found for the BAT AGN, suggesting that, in our X-ray selected sample, the AGN represents the main contribution to the observed line emission. These ratios represent a new emission line diagnostic for distinguishing between AGN and star forming galaxies.
We calculate the most massive object in the Universe, finding it to be a cluster of galaxies with total mass M_200=3.8e15 Msun at z=0.22, with the 1 sigma marginalized regions being 3.3e15 Msun<M_200<4.4e15 Msun and 0.12<z<0.36. We restrict ourselves to self-gravitating bound objects, and base our results on halo mass functions derived from N-body simulations. Since we consider the very highest mass objects, the number of candidates is expected to be small, and therefore each candidate can be extensively observed and characterized. If objects are found with excessively large masses, or insufficient objects are found near the maximum expected mass, this would be a strong indication of the failure of LambdaCDM. The expected range of the highest masses is very sensitive to redshift, providing an additional evolutionary probe of LambdaCDM. We find that the three most massive clusters in the recent SPT 178 deg^2 catalog match predictions, while XMMU J2235.3--2557 is roughly 3 sigma inconsistent with LambdaCDM. These results are robust; 15% errors in the mass measurements do not qualitatively alter our conclusions. Our findings motivate further observations of the highest mass end of the mass function. Future surveys will explore much larger volumes, and the most massive object in the Universe may be identified within the next decade. The mass distribution of the largest objects in the Universe is a potentially powerful test of LambdaCDM, probing non-Gaussianity and the behavior of gravity on large scales.
We make use of a 500ks Chandra HRC-S/LETG spectrum of the blazar H2356-309, combined with a lower S/N spectrum of the same target, to search for the presence of warm-hot absorbing gas associated with two Large-Scale Structures (LSSs) crossed by this sightline at z=0.062 (the Pisces-Cetus Supercluster, PCS) and at z=0.128 ("Farther Sculptor Wall", FSW). No statistically significant (>=3sigma) individual absorption is detected from any of the strong He- or H-like transitions of C, O and Ne at the redshifts of the structures. However we are still able to constrain the physical and geometrical parameters of the associated putative absorbing gas, by performing joint spectral fit of marginal detections and upper limits of the strongest expected lines with our self-consistent hybrid ionization WHIM spectral model. At the redshift of the PCS we identify a warm phase with logT=5.35_-0.13^+0.07 K and log N_H =19.1+/-0.2 cm^-2 possibly coexisting with a hotter and less significant phase with logT=6.9^+0.1_-0.8 K and log N_H=20.1^+0.3_-1.7 cm^-2 (1sigma errors). For the FSW we estimate logT=6.6_-0.2^+0.1 K and log N_H=19.8_-0.8^+0.4 cm^-2. Our constraints allow us to estimate the cumulative number density per unit redshifts of OVII WHIM absorbers. We also estimate the cosmological mass density obtaining Omega_b(WHIM)=(0.021^+0.031_-0.018) (Z/Z_sun)^-1, consistent with the mass density of the intergalactic 'missing baryons' for high metallicities.
We study the statistical descriptors for some cosmological inflationary models that allow us to get large levels of non-gaussianity and violations of statistical isotropy. Basically, we study two different class of models: a model that include only scalar field perturbations, specifically a subclass of small-field slow-roll models of inflation with canonical kinetic terms, and models that admit both vector and scalar field perturbations. We study the former to show that it is possible to attain very high, including observable, values for the levels of non-gaussianity f_{NL} and \tao_{NL} in the bispectrum B_\zeta and trispectrum T_\zeta of the primordial curvature perturbation \zeta respectively. Such a result is obtained by taking care of loop corrections in the spectrum P_\zeta, the bispectrum B_\zeta and the trispectrum T_\zeta . Sizeable values for f_{NL} and \tao_{NL} arise even if \zeta is generated during inflation. For the latter we study the spectrum P_\zeta, bispectrum B_\zeta and trispectrum $T_\zeta of the primordial curvature perturbation when \zeta is generated by scalar and vector field perturbations. The tree-level and one-loop contributions from vector field perturbations are worked out considering the possibility that the one-loop contributions may be dominant over the tree level terms. The levels of non-gaussianity f_{NL} and \tao_{NL}, are calculated and related to the level of statistical anisotropy in the power spectrum, g_\zeta . For very small amounts of statistical anisotropy in the power spectrum, the levels of non-gaussianity may be very high, in some cases exceeding the current observational limit.
We present the Bayesian analysis of four different types of backreation models, which are based on the Buchert equations. In this approach, one considers a solution to the Einstein equations for a general matter distribution and then an average of various observable quantities is taken. Such an approach became of considerable interest when it was shown that it could lead to agreement with observations without resorting to dark energy. In this paper we compare the LambdaCDM model and the backreation models with SNIa, BAO, and CMB data, and find that the former is favoured. However, the tested models were based on some particular assumptions about the relation between the average spatial curvature and the backreaction, as well as the relation between the curvature and curvature index. In this paper we modified the latter assumption, leaving the former unchanged. We find that, by varying the relation between the curvature and curvature index, we can obtain a better fit. Therefore, some further work is still needed -- in particular the relation between the backreaction and the curvature should be revisited in order to fully determine the feasibility of the backreaction models to mimic dark energy.
The standard model of elementary particle physics and the theory of general relativity can be extended by the introduction of a vacuum variable which is responsible for the near vanishing of the present cosmological constant (vacuum energy density). The explicit realization of this vacuum variable can be via a three-form gauge field, an aether-type velocity field, or any other field appropriate for the description of the equilibrium state corresponding to the Lorentz-invariant quantum vacuum. The extended theory has, without fine-tuning, a Minkowski-type solution of the field equations with spacetime-independent fields and provides, therefore, a possible solution of the main cosmological constant problem.
We give an explicit realization of the "String Axiverse" discussed in Arvanitaki et. al \cite{Arvanitaki:2009fg} by extending our previous results on moduli stabilization in $M$ theory to include axions. We extend the analysis of \cite{Arvanitaki:2009fg} to allow for high scale inflation that leads to a moduli dominated pre-BBN Universe. We demonstrate that an axion which solves the strong-CP problem naturally arises and that both the axion decay constants and GUT scale can consistently be around $2\times 10^{16}$ GeV with a much smaller fine tuning than is usually expected. Constraints on the Axiverse from cosmological observations, namely isocurvature perturbations and tensor modes are described. Extending work of Fox et. al \cite{Fox:2004kb}, we note that {\it the observation of tensor modes at Planck will falsify the Axiverse completely.} Finally we note that Axiverse models whose lightest axion has mass of order $10^{-15}$ eV and with decay constants of order $5\times 10^{14}$ GeV require no (anthropic) fine-tuning, though standard unification at $10^{16}$ GeV is difficult to accommodate.
We propose a non-local scalar-tensor model of gravity with pseudo-differential operators inspired by the effective action of p-adic string and string field theory on flat spacetime. An infinite number of derivatives act both on the metric and scalar field sector. The system is localized via the diffusion equation approach and its cosmology is studied. We find several exact dynamical solutions which are stationary in the diffusion flow. In particular, and contrary to standard general relativity, there exist de Sitter and power-law solutions also in an open universe, as well as solutions with sudden future singularities. Also, from the point of view of quantum field theory, spontaneous symmetry breaking can be naturally realized in the class of actions we consider.
The primary goal of this paper is to provide the evidence that can either
prove or falsify the hypothesis that dark matter in the Galactic halo can clump
into stellar-mass compact objects. If such objects existed, they would act as
lenses to external sources in the Magellanic Clouds, giving rise to an
observable effect of microlensing. We present the results of our search for
such events, based on the data from the second phase of the OGLE survey
(1996-2000) towards the SMC. The data set we used is comprised of 2.1 million
monitored sources distributed over an area of 2.4 square degrees. We found only
one microlensing event candidate, however its poor quality light curve limited
our discussion on the exact distance to the lensing object.
Given a single event, taking the blending (crowding of stars) into account
for the detection efficiency simulations, and deriving the HST-corrected number
of monitored stars, the microlensing optical depth is tau=(1.55+-1.55)10e-7.
This result is consistent with the expected SMC self-lensing signal, with no
need of introducing dark matter microlenses. Rejecting the unconvincing event
leads to the upper limit on the fraction of dark matter in the form of MACHOs
to f<20 per cent for deflectors' masses around 0.4 Msun and f<11 per cent for
masses between 0.003 and 0.2 Msun (95 per cent confidence limit). Our result
indicates that the Milky Way's dark matter is unlikely to be clumpy and form
compact objects in the sub-solar-mass range.
X-ray Flash (XRF) 100316D, a nearby super-long under-luminous burst with a peak energy E_p \sim 20 keV, was detected by Swift and was found to be associated with an energetic supernova SN 2010bh. Both the spectral and the temporal behavior of this burst are rather similar to that of XRF 060218, except that the latter was associated with a "less energetic" SN 2006aj and had a prominent soft thermal emission component in the spectrum. We analyze the spectral and temporal properties of this burst, and interpret the prompt gamma-ray emission and the early X-ray plateau emission as synchrotron emission from a dissipating Poynting-flux-dominated outflow, probably powered by a magnetar with a spin period of $P \sim 10$ ms and the polar cap magnetic field $B_{\rm p} \sim 3\times 10^{15}$ G. The energetic supernova SN 2010bh associated with this burst is, however, difficult to interpret within the slow magnetar model, which implies that the nascent magnetar may spin much faster with an initial rotation period $\sim 1$ ms, and thus suggests a delay between the core collapse and the emergence of the relativistic magnetar wind from the star. The diverse behaviors of low-luminosity GRBs and their associated SNe may be understood within a unified picture that invokes different initial powers of the central engine and different delay times between the core collapse and the emergence of the relativistic jet from the star.
Astronomical observations toward Sagittarius B2(M) as well as other sources with APEX have recently suggested that the rest frequency of the J = 1 - 0 transitions of 13CH+ is too low by about 80 MHz. Improved rest frequencies of isotopologs of methylidynium should be derived to support analyses of spectral recording obtained with the ongoing Herschel mission or the upcoming SOFIA. Laboratory electronic spectra of four isotopologs of CH+ have been subjected to one global least-squares fit. Laboratory data for the J = 1 - 0 ground state rotational transitions of CH+, 13CH+, and CD+, which became available during the refereeing process, have been included in the fit as well. An accurate set of spectroscopic parameters has been obtained together with equilibrium bond lengths and accurate rest frequencies for six CH+ isotopologs: CH+, 13CH+, 13CD+, CD+, 14CH+, and CT+. The present data will be useful for the analyses of $Herschel$ or SOFIA observations of methylidynium isotopic species.
In paper the closed Friedmann-Robertson-Walker model with quantization in presence of the positive cosmological constant, radiation and Chaplygin gas is studied. For analysis of tunneling probability for birth of an asymptotically deSitter, inflationary Universe as a function of the radiation energy a new definition of a "free" wave propagating inside strong fields is introduced. Vilenkin's tunneling boundary condition is corrected, penetrability and reflection are calculated in fully quantum stationary approach.
Primordial black hole (PBH) abundance limits constrain the primordial power spectrum, and hence models of inflation, on scales far smaller than those probed by cosmological observations. Single field inflation models which are compatible with all cosmological data can have large enough perturbations on small scales to overproduce PBHs, and hence be excluded. The standard formulae for the amplitude of perturbations do not hold for modes that exit the horizon close to the end of inflation however. We use a modified flow analysis to identify models of inflation where the amplitude of perturbations on small scales is large. For these models we then carry out a numerical evolution of the perturbations and use the PBH constraints on the power spectrum to eliminate models which overproduce PBHs. Significant PBH formation can occur in models in which inflation can continue indefinitely and is ended via a secondary mechanism. We demonstrate that PBHs constrain these types of inflation models and show that a numerical evaluation of the power spectrum decreases the number of otherwise viable models of inflation.
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