Star formation and quenching among the most massive galaxies at z~1.7

We have conducted a detailed object-by-object study of a mass-complete (M*>10^11 M_sun) sample of 56 galaxies at 1.4 < z < 2 in the GOODS-South field, showing that an accurate de-blending in MIPS/24um images is essential to properly assign to each galaxy its own star formation rate (SFR), whereas an automatic procedure often fails. This applies especially to galaxies with SFRs below the Main Sequence (MS) value, which may be in their quenching phase. After that, the sample splits evenly between galaxies forming stars within a factor of 4 of the MS rate (~45%), and sub-MS galaxies with SFRs ~10-1000 times smaller (~55%). We did not find a well defined class of intermediate, transient objects below the MS, suggesting that the conversion of a massive MS galaxy into a quenched remnant may take a relatively short time (<1 Gyr), though a larger sample should be analyzed in the same way to set precise limits on the quenching timescale. X-ray detected AGNs represent a ~30% fraction of the sample, and are found among both star-forming and quenched galaxies. The morphological analysis revealed that ~50% of our massive objects are bulge-dominated, and almost all MS galaxies with a relevant bulge component host an AGN. We also found sub-MS SFRs in many bulge-dominated systems, providing support to the notion that bulge growth, AGN activity and quenching of star formation are closely related to each other.Comment: 27 pages, 19 figures, accepted for publication by MNRA

Psychiatric Disorders and Oxidative Injury: Antioxidant Effects of Zolpidem Therapy disclosed In Silico

Zolpidem (N,N-Dimethyl-2-[6-methyl-2-(4-methylphenyl)imidazo[1,2-a]pyridin-3-yl]acetamide) is a well-known drug for the treatment of sleeping disorders. Recent literature reports on positive effects of zolpidem therapy on improving renal damage after cisplatin and on reducing akinesia without sleep induction. This has been ascribed to the antioxidant and neuroprotective capacity of this molecule, and tentatively explained according to a generic structural similarity between zolpidem and melatonin. In this work, we investigate in silico the antioxidant potential of zolpidem as scavenger of five ROSs, acting via hydrogen atom transfer (HAT) mechanism; computational methodologies based on density functional theory are employed. For completeness, the analysis is extended to six metabolites. Thermodynamic and kinetic results disclose that indeed zolpidem is an efficient radical scavenger, similarly to melatonin and Trolox, supporting the biomedical evidence that the antioxidant potential of zolpidem therapy may have a beneficial effect against oxidative injury, which is emerging as an important etiopathogenesis in numerous severe diseases, including psychiatric disorders

ALMA reveals the molecular gas properties of five star-forming galaxies across the main sequence at 3

International audienceWe present the detection of CO(5-4) with S/N> 7 - 13 and a lower CO transition with S/N > 3 (CO(4-3) for 4 galaxies, and CO(3-2) for one) with ALMA in band 3 and 4 in five main sequence star-forming galaxies with stellar masses 3-6x10^10 M/M_sun at 3 < z < 3.5. We find a good correlation between the total far-infrared luminosity LFIR and the luminosity of the CO(5-4) transition L'CO(5-4), where L'CO(5-4) increases with SFR, indicating that CO(5-4) is a good tracer of the obscured SFR in these galaxies. The two galaxies that lie closer to the star-forming main sequence have CO SLED slopes that are comparable to other star-forming populations, such as local SMGs and BzK star-forming galaxies; the three objects with higher specific star formation rates (sSFR) have far steeper CO SLEDs, which possibly indicates a more concentrated episode of star formation. By exploiting the CO SLED slopes to extrapolate the luminosity of the CO(1-0) transition, and using a classical conversion factor for main sequence galaxies of alpha_CO = 3.8 M_sun(K km s^-1 pc^-2)^-1, we find that these galaxies are very gas rich, with molecular gas fractions between 60 and 80%, and quite long depletion times, between 0.2 and 1 Gyr. Finally, we obtain dynamical masses that are comparable with the sum of stellar and gas mass (at least for four out of five galaxies), allowing us to put a first constraint on the alpha_CO parameter for main sequence galaxies at an unprecedented redshift

Deep Spitzer 24 μm COSMOS Imaging. I. The Evolution of Luminous Dusty Galaxies—Confronting the Models

We present the first results obtained from the identification of ~30,000 sources in the Spitzer/24 μm observations of the COSMOS field at S_(24 μm) ≳ 80 μJy. Using accurate photometric redshifts (σ_ z ~ 0.12 at z ~ 2 for 24 μm sources with i ^+ ≳ 25 mag AB) and simple extrapolations of the number counts at faint fluxes, we resolve with unprecedented detail the buildup of the mid-infrared background across cosmic ages. We find that ~50% and ~80% of the 24 μm background intensity originate from galaxies at z ≳ 1 and z ≳ 2, respectively, supporting the scenario where highly obscured sources at very high redshifts (z ≳ 2) contribute only marginally to the cosmic infrared background. Assuming flux-limited selections at optical wavelengths, we also find that the fraction of i ^+-band sources with 24 μm detection strongly increases up to z ~ 2 as a consequence of the rapid evolution that star-forming galaxies have undergone with look-back time. Nonetheless, this rising trend shows a clear break at z ~ 1.3, probably due to k-correction effects implied by the complexity of spectral energy distributions in the mid-infrared. Finally, we compare our results with the predictions from different models of galaxy formation. We note that semianalytical formalisms currently fail to reproduce the redshift distributions observed at 24 μm. Furthermore, the simulated galaxies at S _(24 μm) > 80 μJy exhibit R–K colors much bluer than observed and the predicted K-band fluxes are systematically underestimated at z ≳ 0.5. Unless these discrepancies mainly result from an incorrect treatment of extinction in the models they may reflect an underestimate of the predicted density of high-redshift massive sources with strong ongoing star formation, which would point to more fundamental processes and/or parameters (e.g., initial mass function, critical density to form stars, feedback,...) that are still not fully controlled in the simulations. The most recent backward evolution scenarios reproduce reasonably well the flux/redshift distribution of 24 μm sources up to z ~ 3, although none of them is able to exactly match our results at all redshifts

Role of ubiquitination in retro-translocation of cholera toxin and escape of cytosolic degradation

Cholera toxin travels from the cell surface of affected mammalian cells to the endoplasmic reticulum (ER), where the A1 chain is released and retro-translocated across the ER membrane into the cytosol. We have tested whether, as in other cases, retro-translocation requires poly-ubiquitination. We show that an A1 chain mutant that lacks lysines and has a blocked N-terminus, and therefore cannot be ubiquitinated, remains active in vivo. The A1 chain is not degraded in the cytosol, as demonstrated by the fact that proteasome inhibitors do not stimulate its activity. When additional lysines are introduced into the A1 chain, moderate degradation by the proteasome is observed. The unfolded A1 chain rapidly refolds in vitro. These results show that poly-ubiquitination is not required for retro-translocation of all proteins across the ER membrane and indicate that the reason why the toxin escapes degradation in the cytosol may be both its paucity of lysines and its rapid refolding

Retrograde transport of cholera toxin from the plasma membrane to the endoplasmic reticulum requires the trans-Golgi network but not the Golgi apparatus in Exo2-treated cells

Cholera toxin (CT) follows a glycolipid-dependent entry pathway from the plasma membrane through the trans-Golgi network (TGN) to the endoplasmic reticulum (ER) where it is retro-translocated into the cytosol to induce toxicity. Whether access to the Golgi apparatus is necessary for transport to the ER is not known. Exo2 is a small chemical that rapidly blocks anterograde traffic from the ER to the Golgi and selectively disrupts the Golgi apparatus but not the TGN. Here we use Exo2 to determine the role of the Golgi apparatus in CT trafficking. We find that under the condition of complete Golgi ablation by Exo2, CT reaches the TGN and moves efficiently into the ER without loss in toxicity. We propose that even in the absence of Exo2 the glycolipid pathway that carries the toxin from plasma membrane into the ER bypasses the Golgi apparatus entirely