The 5th edition of the
Roma-BZCAT
Multifrequency Catalogue of Blazars is available in a printed version and online at the ASDC website (
http://www.asdc.asi.it/bzcat
); it is also in the NED ...database. It presents several relevant changes with respect to the past editions which are briefly described in this paper.
Aims. The development of a general code for 3D Ly\alpha radiation transfer in galaxies to understand the diversity of Ly\alpha line profiles observed in star-forming galaxies and related objects. ...Methods. Using a Monte Carlo technique, we developed a 3D Ly\alpha radiation transfer code that allows for prescribed arbitrary hydrogen density, ionisation, temperature structures, dust distributions, arbitrary velocity fields, and UV photon sources. As a first test and application we examined the Ly\alpha line profiles predicted for several simple geometrical configurations and their dependence on the main input parameters. Results. Overall, we find line profiles reaching from doubly peaked symmetric emission to symmetric Voigt (absorption) in static configurations with increasing dust content, and asymmetric red- (blue-) shifted emission lines with a blue (red) counterpart ranging from absorption to emission (with increasing line/continuum strength) in expanding (infalling) media. In particular we find the following results to be interesting for the interpretation of Ly\alpha profiles from galaxies. 1) Standard Ly\alpha absorption line fitting of global spectra of galaxies may lead to an underestimation of the true hydrogen column density in certain geometrical conditions; 2) Normal (inverted) P-Cygni-like Ly\alpha profiles can be obtained in expanding (infalling) media from objects without any intrinsic Ly\alpha emission, as a natural consequence of radiation transfer effects; 3) The formation and the detailed shape of Ly\alpha profiles resulting from expanding shells has been thoroughly revised. In particular we find that, for sufficiently large column densities ( N_{\rm H} \ga 10cm super(-2)), the position of the main Ly\alpha emission peak is quite generally redshifted by approximately twice the expansion velocity. This is in excellent agreement with the observations of z \sim 3 LBGs, which show that Ly\alpha is redshifted by similar to 2V_{\rm exp}, where V_{\rm exp} is the expansion velocity measured from the interstellar absorption lines blueshifted with respect to the stellar redshift. This finding also indicates that large- scale, fairly symmetric shell structures must be a good description of the outflows in LBGs.
Context.
Coalescences of binary white dwarfs represent a copious source of information for gravitational wave interferometers operating in the decihertz band. Moreover, according to the double ...degenerate scenario, they have been suggested to be possible progenitors of supernovae (SNe) Type Ia events.
Aims.
In this paper we discuss the detectability of gravitational waves emitted by the inspiral of double white dwarfs. We focus on the constraints that can be derived on the source’s luminosity distance, and on other binary’s parameters, such as the angular momentum orientation.
Methods.
We explore the possibility of coincident detections of gravitational and electromagnetic signals; the latter comes from the observation of the supernova counterpart. Confirmation of the double degenerate scenario would allow one to use distances inferred in the gravitational wave channel to consistently calibrate SNe as standard candles.
Results.
We find that decihertz gravitational wave interferometers can measure the luminosity distance with relative accuracy better than 1% for binaries at 100 Mpc. We show how multimessenger observations can put strong constraints on the Hubble constant, which are tighter than current bounds at low redshift, and how they can potentially shed new light on the differences with early-universe measurements.
Here we introduce crash3, the latest release of the 3D radiative transfer code crash. In its current implementation, crash3 integrates into the reference algorithm the code cloudy to evaluate the ...ionization states of metals, self-consistently with the radiative transfer through H and He. The feedback of the heavy elements on the calculation of the gas temperature is also taken into account, making crash3 the first 3D code for cosmological applications which treats self-consistently the radiative transfer through an inhomogeneous distribution of metal-enriched gas with an arbitrary number of point sources and/or a background radiation. The code has been tested in idealized configurations, as well as in a more realistic case of multiple sources embedded in a polluted cosmic web. Through these validation tests, the new method has been proven to be numerically stable and convergent. We have studied the dependence of the results on a number of physical quantities such as the source characteristics (spectral range and shape, intensity), the metal composition, the gas number density and metallicity.
We investigate the effect of primordial helium on hydrogen reionization using a hydrodynamical simulation combined with the cosmological radiative transfer code crash. The radiative transfer ...simulations are performed in a 35.12 h
−1 comoving Mpc box using a variety of assumptions for the amplitude and power-law extreme-ultraviolet (EUV) spectral index of the ionizing emissivity at z > 6. We use an empirically motivated prescription for ionizing sources which, by design, ensures all of the models are consistent with constraints on the Thomson scattering optical depth and the metagalactic hydrogen photoionization rate at z∼ 6. The inclusion of helium slightly delays reionization due to the small number of ionizing photons which reionize neutral helium instead of hydrogen. However, helium has a significant impact on the thermal state of the intergalactic medium (IGM) during hydrogen reionization. Models with a soft EUV spectral index, α= 3, produce IGM temperatures at the mean density at z∼ 6, T
0≃ 10 500 K, which are ∼20 per cent higher compared to models in which helium photoheating is excluded. Harder EUV indices produce even larger IGM temperature boosts by the end of hydrogen reionization. A comparison of these simulations to recent observational estimates of the IGM temperature at z∼ 5-6 suggests that hydrogen reionization was primarily driven by Population II stellar sources with a soft EUV index,
. We also find that faint, as yet undetected galaxies, characterized by a luminosity function with a steepening faint-end slope (αLF≤−2) and an increasing Lyman continuum escape fraction (f
esc∼ 0.5), are required to reproduce the ionizing emissivity used in our simulations at z > 6. Finally, we note there is some tension between recent observational constraints which indicate the IGM is >10 per cent neutral by volume z∼ 7, and estimates of the ionizing emissivity at z= 6 which indicate only 1-3 ionizing photons are emitted per hydrogen atom over a Hubble time at z= 6. This tension may be alleviated by either a lower neutral fraction at z∼ 7 or an IGM which still remains a few per cent neutral by volume at z= 6.
Here we introduce GAMESH, a novel pipeline that implements self-consistent radiative and chemical feedback in a computational model of galaxy formation. By combining the cosmological ...chemical-evolution model GAMETE with the radiative transfer code CRASH, GAMESH can post-process realistic outputs of a N-body simulation describing the red-shift evolution of the forming galaxy. After introducing the GAMESH implementation and its features, we apply the code to a low-resolution N-body simulation of the formation of the Milky Way and we investigate the combined effects of self-consistent radiative and chemical feedback. Many physical properties, which can be directly compared with observations in the Galaxy and its surrounding satellites, are predicted by the code along with the merger-tree assembly. The resulting red-shift evolution for the Local Group of star-formation rates, reionization and metal enrichment along with the predicted metallicity distribution function of halo stars are critically compared with observations. We discuss the merits and limitations of the first release of gamesh, which also opens new directions to a full implementation of feedback processes in galaxy-formation models by combining semi-analytic and numerical methods.
Aims. We investigated the X-ray emission properties of the powerful radio galaxy 3C 459 revealed by a recent Chandra follow-up observation carried out in October 2014 with a 62 ks exposure. Methods. ...We performed an X-ray spectral analysis from a few selected regions on an image obtained from this observation and also compared the X-ray image with a 4.9 GHz VLA radio map available in the literature. Results. The dominant contribution comes from the radio core but significant X-ray emission is detected at larger angular separations from it, surrounding both radio jets and lobes. According to a scenario in which the extended X-ray emission is due to a plasma collisionally heated by jet-driven shocks and not magnetically dominated, we estimated its temperature to be ∼0.8 keV. This hot gas cocoon could be responsible for the radio depolarization observed in 3C 459, as recently proposed also for 3C 171 and 3C 305. On the other hand, our spectral analysis and the presence of an oxygen K edge, blueshifted at 1.23 keV, cannot exclude the possibility that the X-ray radiation originating from the inner regions of the radio galaxy could be intercepted by some outflow of absorbing material intervening along the line of sight, as already found in some BAL quasars.
Two new high-energy γ-ray blazar candidates Campana, R; Maselli, A; Bernieri, E ...
Monthly Notices of the Royal Astronomical Society,
03/2017, Volume:
465, Issue:
3
Journal Article
Peer reviewed
Open access
We report the detection of two new gamma -ray sources in the Fermi-Large Area Telescope sky (Pass 8) at energies higher than 20 GeV and confirmed at lower energies, using a source detection tool ...based on the Minimum Spanning Tree algorithm. One of these sources, at a Galactic latitude of about -4 degree , is a new discovery, while the other was previously reported above 50 GeV in the 2FHL catalogue. We searched for archival multiwavelength data of possible counterparts and found interesting candidates. Both objects are radio sources and their Wide-field Infrared Survey Explorer infrared colours are typical of blazars. While, for the former source, no optical spectra are available, for the latter, a puzzling optical spectrum corresponding to a white dwarf star is found in the 6dF data base. We discuss the spectral energy distributions of both sources and possible interpretations.
ABSTRACT Here we investigate how LyC-opaque systems present in the intergalactic medium at $z$ ≈ 3 can distort the spectral shape of a uniform UV background (UVB) through radiative transfer (RT) ...effects. With this aim in mind, we perform a multifrequency RT simulation through a cosmic volume of 10 h−1 cMpc scale polluted by metals, and self-consistently derive the ions of all the species. The UVB spatial fluctuations are traced by the ratio of He $\,\small {II}$ and H $\,\small {I}$ column density, η, and the ratio of C $\, \small {IV}$ and Si $\, \small {IV}$ optical depths, ζ. We find that: (i) η spatially fluctuates through overdense systems (Δ) with statistically significant deviations δη > 25 per cent in 18 per cent of the volume; (ii) same fluctuations in ζ are also present in 34 per cent of the enriched domain (only 8 per cent of the total volume) and derive from a combination of RT induced effects and in-homogeneous metal enrichment, both effective in systems with Δ > 1.5.
Agrin is a large extracellular matrix protein whose isoforms differ in their tissue distribution and function. Motoneuron-derived y+z+ agrin regulates the formation of the neuromuscular junction ...(NMJ), while y-z- agrin is widely expressed and has diverse functions. Previously we identified a missense mutation (V1727F) in the second laminin globular (LG2) domain of agrin that causes severe congenital myasthenic syndrome. Here, we define pathogenic effects of the agrin V1727F mutation that account for the profound dysfunction of the NMJ. First, by expressing agrin variants in heterologous cells, we show that the V1727F mutation reduces the secretion of y+z+ agrin compared to wild type, whereas it has no effect on the secretion of y-z- agrin. Second, we find that the V1727F mutation significantly impairs binding of y+z+ agrin to both heparin and the low-density lipoprotein receptor-related protein 4 (LRP4) coreceptor. Third, molecular modeling of the LG2 domain suggests that the V1727F mutation primarily disrupts the y splice insert, and consistent with this we find that it partially occludes the contribution of the y splice insert to agrin binding to heparin and LRP4. Together, these findings identify several pathogenic effects of the V1727F mutation that reduce its expression and ability to bind heparan sulfate proteoglycan and LRP4 coreceptors involved in the muscle-specific kinase signaling pathway. These defects primarily impair the function of neural y+z+ agrin and combine to cause a severe CMS phenotype, whereas y-z- agrin function in other tissues appears preserved.
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