177,453 research outputs found
Toward a tomographic analysis of the cross-correlation between planck cmb lensing and h-atlas galaxies
No full textINAF PRIN; ASI/INAF [2014-024-R.0]; INFN-INDARK initiative; Spanish MINECOBianchini, F., Lapi, A., Calabrese, M., Bielewicz, P., Gonzalez-Nuevo, J., Baccigalupi, C., Danese, L., Zotti, G.D., Bourne, N., Cooray, A., Dunne, L., Eales, S., Valiante, E
High-redshift quasars host galaxies: is there a stellar mass crisis?
No full textWe investigate the evolutionary properties of a sample of quasars (QSOs) at 5 <z <6.4 using the semi-analytical hierarchical model GAMETE/QSODUST. We find that the observed properties of these QSOs are well reproduced by a common formation scenario in which stars form according to a standard initial mass function, via quiescent star formation and efficient merger-driven bursts, while the central black hole (BH) grows via gas accretion and BH-BH mergers. Eventually, a strong active galactic nuclei-driven wind starts to clear up the interstellar medium of dust and gas, damping the star formation and un-obscuring the line of sight towards the QSO. In this scenario, all the QSOs hosts have final stellar masses in the range (4-6) × 1011 M⊙, a factor of 3-30 larger than the upper limits allowed by the observations. We discuss alternative scenarios to alleviate this apparent tension: the most likely explanation resides in the large uncertainties that still affect dynamical mass measurements in these high-z galaxies. In addition, during the transition between the starburst-dominated and the active QSO phase, we predict that ˜40 per cent of the progenitor galaxies can be classified as Submillimetre Galaxies, although their number rapidly decreases with redshift
Theoretical cosmic Type Ia supernova rates
No full textThe purpose of this work is the computation of the cosmic Type Ia supernova rates, namely the frequency of Type Ia supernovae per unit time in a unitary volume of the Universe. Our main goal in this work is to predict the Type Ia supernova rates at very high redshifts and to check whether it is possible to select the best delay time distribution model, on the basis of the available observations of Type Ia supernovae. We compute the cosmic Type Ia supernova rates in different scenarios for galaxy formation and predict the expected number of explosions at high redshift (z⩾2). Moreover, we adopt various progenitor models in order to compute the Type Ia supernova rate in typical elliptical galaxies of initial luminous masses of 1010Msun,1011Msun and 1012Msun, and compute the total amount of iron produced by Type Ia supernovae in each case. In this analysis we assume that Type Ia supernovae are caused by thermonuclear explosions of C-O white dwarfs in binary systems and we consider the most popular frameworks: the single degenerate and the double degenerate scenarios. The two competing schemes for the galaxy formation, namely the monolithic collapse and the hierarchical clustering, are also taken into account, by considering the histories of star formation increasing and decreasing with redshift, respectively. We calculate the Type Ia supernova rates through an analytical formulation which rests upon the definition of the SN Ia rate following an instantaneous burst of star formation as a function of the time elapsed from the birth of the progenitor system to its explosion as a Type Ia supernova (i.e. the delay time). What emerges from this work is that: (i) we confirm the result of previous papers that it is not easy to select the best delay time distribution scenario from the observational data and this is because the cosmic star formation rate dominates over the distribution function of the delay times; (ii) the monolithic collapse scenario for galaxy formation predicts an increasing trend of the SN Ia rate at high redshifts (mainly due to the contribution by massive spheroids), whereas the predicted rate in the framework of a decreasing cosmic star formation rate, more in agreement with the hierarchical scenario, drops dramatically at high redshift; (iii) for the elliptical galaxies we note that the predicted maximum of the Type Ia supernova rate depends on the initial galactic mass. The maximum occurs earlier (at about 0.3 Gyr) in the most massive ellipticals, as a consequence of the assumed downsizing in star formation. In addition, we find that the Type Ia supernova rate per unit mass at the present time is higher in bluer ellipticals (i.e. the less massive ones)
A biphasic role of nuclear transcription factor (NF)-kB in the islet beta-cell apoptosis induced by interleukin (IL)-1beta
No full textIL-1 beta is an important mediator in the pathogenesis of type I diabetes both in vivo and in vitro and it has been shown to induce islet beta-cell apoptosis. Most of the IL-1 beta effects seem to be mediated by NF-kappa B transcription factor activation, but its role in the induction of islet beta-cell apoptosis has not yet been clarified. Taking advantage of the protease inhibitor TPCK (N-tosyl-L-phenylalanine chloromethyl ketone), which specifically inhibits the nuclear transcription factor NF-kappa B activation, we studied the role of NF-kappa B in the rIL-1 beta treated rat pancreatic islets. Our results show that TPCK blocked rlL-1 beta-mediated early increase of MnSOD activity and beta-cell defence/repair protein expression, suggesting a protective role for NF-kappa B at the beginning of IL-1 beta treatment; but, in a second phase, NF-kappa B induces a sustained decrease of specific beta-cell proteins like insulin, GLUT-2 and PDX-1 with a concomitant increase of aspecific proteins and iNOS transcription. The appearance of iNOS expression correlates with increased levels of nitrite + nitrate levels and appearance of mitochondrial damage detected either at morphological and biochemical level. After 36 h of IL-1 beta treatment islet beta-cells begin to undergo apoptosis. Since IL-1 beta induction of apoptosis is completely prevented by TCPK treatment, this finding underscores the central role of NF-kappa B in this process. Thus, our results clearly indicate that NF-kappa B regulates MnSOD genes expression and MnSOD activity, which protects islet beta-cells by IL-1 beta damage. Furthermore, when the IL-1 beta stress impairs islet beta-cell function, NF-kappa B activation regulates the entrance of islet beta-cell into the cell death program
Super-Eddington growth of the first black holes
No full textThe assembly of the first super massive black holes (SMBHs) at z ≳ 6 is still a subject of intense debate. If black holes (BHs) grow at their Eddington rate, they must start from ≳104 M⊙ seeds formed by the direct collapse of gas. Here, we explore the alternative scenario where ̃100 M⊙ BH remnants of the first stars grow at super-Eddington rate via radiatively inefficient slim accretion discs. We use an improved version of the cosmological, data-constrained semi-analytic model GAMETE/QSODUST, where we follow the evolution of nuclear BHs and gas cooling, disc and bulge formation of their host galaxies. Adopting SDSS J1148+5251 (J1148) at z = 6.4 as a prototype of luminous z ≳ 6 quasars, we find that ̃80 per cent of its SMBH mass is grown by super-Eddington accretion, which can be sustained down to z ̃ 10 in dense, gas-rich environments. The average BH mass at z ̃ 20 is MBH ≳ 104 M⊙, comparable to that of direct collapse BHs. At z = 6.4 the AGN-driven mass outflow rate is consistent with the observations and the BH-to-bulge mass ratio is compatible with the local scaling relation. However, the stellar mass in the central 2.5 kpc is closer to the value inferred from CO observations. Finally, ̃20 per cent of J1148 progenitors at z = 7.1 have BH luminosities and masses comparable to ULAS J1120+0641, suggesting that this quasar may be one of the progenitors of J1148
Endothelin 1 (ET-1) control on the adrenal gland activity of the lizard Podarcis sicula.
No full textAppropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
The effect of different type Ia supernova progenitors on Galactic chemical evolution
No full textAims. Our aim is to show how different hypotheses about type Ia supernova progenitors can affect Galactic chemical evolution.
Supernovae Ia are believed to be the main producers of Fe and the
timescale with which Fe is restored into the interstellar medium depends on the assumed supernova progenitor
model. This is a way of selecting the most appropriate progenitor model for supernovae Ia, a still debated
issue.
Methods. We include different type Ia SN progenitor models, identified by their distribution of time delays, in a very detailed
chemical
evolution model for the Milky Way which follows the evolution of several chemical species. We test the single degenerate
and the double
degenerate models for supernova Ia progenitors, as well as other more empirical models based on differences in the time delay
distributions.
Results. We find that assuming the single degenerate or the double degenerate scenario produces negligible differences in the predicted [O/Fe] vs. [Fe/H] relation. On the other hand, assuming a percentage of prompt (exploding in the first 100 Myr) type Ia supernovae of 50%, or that the maximum type Ia rate is reached after 3–4 Gyr from the beginning of star formation, as suggested by several authors, produces more noticeable effects on the [O/Fe] trend. However, given the spread still existing in the observational data, no model can be firmly excluded on the basis of only the [O/Fe]
ratios. On the other hand, when the predictions of the different models are compared with the G-dwarf metallicity distribution, the scenarios with very few prompt type Ia supernovae can be excluded.
Conclusions. Models including the single degenerate or double degenerate scenario with a percentage of 10–13% of prompt type Ia supernovae produce results in very good agreement with the observations. A fraction of prompt type Ia supernovae larger than 30% worsens the agreement with observations and the same occurs if no prompt type Ia supernovae are allowed. In particular, two empirical models for the type Ia SN progenitors can be excluded:
the one without prompt type Ia supernovae and the one assuming a delay time distribution that is t-0.5. We conclude that the typical timescale for the Fe enrichment in the Milky Way is around 1–1.5 Gyr and that type Ia supernovae already should appear during the halo phase
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