Catching galaxies in the act of quenching star formation

Detecting galaxies when their star-formation is being quenched is crucial to understand the mechanisms driving their evolution. We identify for the first time a sample of quenching galaxies selected just after the interruption of their star formation by exploiting the [O III]5007/Halpha ratio and searching for galaxies with undetected [O III]. Using a sample of ~174000 star-forming galaxies extracted from the SDSS-DR8 at 0.04 < z < 0.21,we identify the ~300 quenching galaxy best candidates with low [O III]/Halpha, out of ~26000 galaxies without [O III] emission. They have masses between 10^9.7 and 10^10.8 Mo, consistently with the corresponding growth of the quiescent population at these redshifts. Their main properties (i.e. star-formation rate, colours and metallicities) are comparable to those of the star-forming population, coherently with the hypothesis of recent quenching, but preferably reside in higher-density environments.Most candidates have morphologies similar to star-forming galaxies, suggesting that no morphological transformation has occurred yet. From a survival analysis we find a low fraction of candidates (~0.58% of the star-forming population), leading to a short quenching timescale of tQ~50Myr and an e-folding time for the quenching history of tauQ~90Myr, and their upper limits of tQ<0.76 Gyr and tauQ<1.5Gyr, assuming as quenching galaxies 50% of objects without [O III] (~7.5%).Our results are compatible with a 'rapid' quenching scenario of satellites galaxies due to the final phase of strangulation or ram-pressure stripping. This approach represents a robust alternative to methods used so far to select quenched galaxies (e.g. colours, specific star-formation rate, or post-starburst spectra).Comment: 22 pages, 23 figures, accepted for publication in MNRA

A methodology to select galaxies just after the quenching of star formation

We propose a new methodology aimed at finding star-forming galaxies in the phase which immediately follows the star-formation (SF) quenching, based on the use of high- to low-ionization emission line ratios. These ratios rapidly disappear after the SF halt, due to the softening of the UV ionizing radiation. We focus on [O III] $\lambda$5007/H$\alpha$ and [Ne III] $\lambda$3869/[O II] $\lambda$3727, studying them with simulations obtained with the CLOUDY photoionization code. If a sharp quenching is assumed, we find that the two ratios are very sensitive tracers as they drop by a factor $\sim$ 10 within $\sim$ 10 Myr from the interruption of the SF; instead, if a smoother and slower SF decline is assumed (i.e. an exponentially declining star-formation history with $e$-folding time $\tau=$ 200 Myr), they decrease by a factor $\sim$ 2 within $\sim$ 80 Myr. We mitigate the ionization -- metallicity degeneracy affecting our methodology using pairs of emission line ratios separately related to metallicity and ionization, adopting the [N II] $\lambda$6584/[O II] $\lambda$3727 ratio as metallicity diagnostic. Using a Sloan Digital Sky Survey galaxy sample, we identify 10 examples among the most extreme quenching candidates within the [O III] $\lambda$5007/H$\alpha$ vs. [N II] $\lambda$6584/[O II] $\lambda$3727 plane, characterized by low [O III] $\lambda$5007/H$\alpha$, faint [Ne III] $\lambda$3869, and by blue dust-corrected spectra and $(u-r)$ colours, as expected if the SF quenching has occurred in the very recent past. Our results also suggest that the observed fractions of quenching candidates can be used to constrain the quenching mechanism at work and its time-scales.Comment: Accepted for publication in MNRAS; 19 pages, 21 figures, 1 tabl

Investigating the conclusive phases of galaxy evolution: from star formation to quiescence

Despite the progress made towards a more comprehensive knowledge of galaxy evolution, a global picture of the mechanisms regulating the formation of stars in galaxies, of how galaxy evolutionary properties correlate with stellar masses and star formation rates (SFRs) and of the processes suppressing the star formation in galaxies and their timescales is still lacking. In this thesis work, we attempt to address some of these open questions, inspecting galaxy evolution back in cosmic time. In particular, we start from the archaeological analysis of passive local galaxies (1), reconstructing their past star formation histories. Then we take a step back towards the phase in which galaxies quench their star formation (2), defining a new methodology able to identify the quenching progenitors of passive galaxies. Finally, we move back to the star-forming phase (3), investigating the properties of high-redshift galaxies which could be the star-forming progenitors of the passive local ones. Our investigations mainly rely on the spectral analysis of galaxies. In particular, we study both the passive and star-forming phase by exploiting the information contained in the galaxy full-spectrum, whose shape depends on the properties of the underlying stellar populations. The quenching phase is instead investigated by means of emission line ratios, which are associated to the Interstellar Medium (ISM) and its ionization state during or just after the star formation has stopped.Nonostante i progressi fatti verso una più profonda comprensione dell’evoluzione delle galassie, manca ancora una visione completa di quali siano i meccanismi che regolano la formazione sellare nelle galassie, di come le proprietaà evolutive delle galassie correlino con le loro masse e tassi di formazione stellare e quali processi siano respons- abili dello spegnimento della formazione stellare e i loro tempi-scala. In questo lavoro di tesi, si è cercato di rispondere ad alcune di queste domande aperte, studiando l’evoluzione delle galassie a ritroso nel tempo. In particolare, siamo partiti dallo studio archeologico di galassie passive locali (1), ricostruendo le loro storie di formazione stellare. Abbiamo poi fatto un passo indietro verso la fase in cui le galassie spengono la loro formazione stellare (2), definendo una nuova metodologia che ci permetta di identificare i progenitori delle galassie passive nella fase immediatamente successiva all’interruzione della formazione stellare. Infine, siamo andati ancora più indietro nel tempo, studiando la fase in cui le galassie formano stelle (3), analizzando le proprietà di galassie ad alto redshift che potrebbero essere i progenitori delle galassie passive locali. I nostri studi si sono basati sull’analisi spettrale delle galassie. In particolare, abbiamo studiato la fase passiva e quella star-forming sfruttando l’informazione contenuta nella totalità degli spettri delle galassie analizzate, la cui forma dipende dalle caratteristiche delle popolazioni stellari. La fase di spegnimento della formazione stellare è stata in- vece analizzata usando rapporti tra righe di emissione, che sono collegate al mezzo interstellare e al suo stato di ionizzazione durante o subito dopo lo spegnimento della formazione stellare

Setting the Stage for Cosmic Chronometers. I. Assessing the Impact of Young Stellar Populations on Hubble Parameter Measurements

The expansion history of the Universe can be constrained in a cosmology-independent way by measuring the differential age evolution of cosmic chronometers. This yields a measurement of the Hubble parameter $H(z)$ as a function of redshift. The most reliable cosmic chronometers known so far are extremely massive and passively evolving galaxies. Age-dating these galaxies is, however, a difficult task, and even a small contribution of an underlying young stellar population could, in principle, affect the age estimate and its cosmological interpretation. We present several spectral indicators to detect, quantify and constrain such contamination in old galaxies, and study how their combination can be used to maximize the purity of cosmic chronometers selection. In particular, we analyze the CaII H/K ratio, the presence (or absence) of H$\alpha$ and [OII] emission lines, higher order Balmer absorption lines, and UV flux; each indicator is especially sensitive to a particular age range, allowing us to detect young components ranging between 10 Myr and 1 Gyr. The combination of these indicators minimizes the contamination to a level below 1% in the case of ideal data. More importantly, it offers a way to control the systematic error on $H(z)$ as a function of the contamination by young stellar populations. We show that for our previous measurements of the Hubble parameter, the possible bias induced by the presence of a younger component is well below the current errors. We envision that these indicators will be instrumental in paving the road for a robust and reliable dating of the old population and its cosmological interpretation.Comment: 18 pages, 8 figures. Accepted for publication in the Astrophysical Journa

Monitoring for cytomegalovirus and Epstein-Barr virus infection in chronic lymphocytic leukemia patients receiving i.v. fludarabine-cyclophosphamide combination and alemtuzumab as consolidation therapy.

The combination of fludarabine and cyclophosphamide (FC) has become the standard of care in chronic lymphocytic leukemia (CLL) patients. Due to the well-recognized F-related immunosuppression,[1][1] a higher risk of opportunistic infections could be expected by adding another immunosuppressive agen

A 6% measurement of the Hubble parameter at z~0.45: direct evidence of the epoch of cosmic re-acceleration

Deriving the expansion history of the Universe is a major goal of modern cosmology. To date, the most accurate measurements have been obtained with Type Ia Supernovae (SNe) and Baryon Acoustic Oscillations (BAO), providing evidence for the existence of a transition epoch at which the expansion rate changes from decelerated to accelerated. However, these results have been obtained within the framework of specific cosmological models that must be implicitly or explicitly assumed in the measurement. It is therefore crucial to obtain measurements of the accelerated expansion of the Universe independently of assumptions on cosmological models. Here we exploit the unprecedented statistics provided by the Baryon Oscillation Spectroscopic Survey (BOSS, [1-3]) Data Release 9 to provide new constraints on the Hubble parameter H(z) using the cosmic chronometers approach. We extract a sample of more than 130000 of the most massive and passively evolving galaxies, obtaining five new cosmology-independent H(z) measurements in the redshift range 0.3 < z < 0.5, with an accuracy of ~11-16% incorporating both statistical and systematic errors. Once combined, these measurements yield a 6% accuracy constraint of H(z = 0.4293) = 91.8 ± 5.3 km/s/Mpc. The new data are crucial to provide the first cosmology-independent determination of the transition redshift at high statistical significance, measuring zt = 0.4 ± 0.1, and to significantly disfavor the null hypothesis of no transition between decelerated and accelerated expansion at 99.9% confidence level. This analysis highlights the wide potential of the cosmic chronometers approach: it permits to derive constraints on the expansion history of the Universe with results competitive with standard probes, and most importantly, being the estimates independent of the cosmological model, it can constrain cosmologies beyond and including the ΛCDM model

Two Different Therapeutic Approaches for SARS-CoV-2 in hiPSCs-Derived Lung Organoids

The global health emergency for SARS-CoV-2 (COVID-19) created an urgent need to develop new treatments and therapeutic drugs. In this study, we tested, for the first time on human cells, a new tetravalent neutralizing antibody (15033-7) targeting Spike protein and a synthetic peptide homologous to dipeptidyl peptidase-4 (DPP4) receptor on host cells. Both could represent powerful immunotherapeutic candidates for COVID-19 treatment. The infection begins in the proximal airways, namely the alveolar type 2 (AT2) cells of the distal lung, which express both ACE2 and DPP4 receptors. Thus, to evaluate the efficacy of both approaches, we developed three-dimensional (3D) complex lung organoid structures (hLORGs) derived from human-induced pluripotent stem cells (iPSCs) and resembling the in vivo organ. Afterward, hLORGs were infected by different SARS-CoV-2 S pseudovirus variants and treated by the Ab15033-7 or DPP4 peptide. Using both approaches, we observed a significant reduction of viral entry and a modulation of the expression of genes implicated in innate immunity and inflammatory response. These data demonstrate the efficacy of such approaches in strongly reducing the infection efficiency in vitro and, importantly, provide proof-of-principle evidence that hiPSC-derived hLORGs represent an ideal in vitro system for testing both therapeutic and preventive modalities against COVID-19

A 6% measurement of the Hubble parameter at z~0.45 : direct evidence of the epoch of cosmic re-acceleration

MM, LP and AC acknowledge financial contributions by grants ASI/INAF I/023/12/0 and PRIN MIUR 2010-2011 "The dark Universe and the cosmic evolution of baryons: from current surveys to Euclid". RJ and LV thank the Royal Society for financial support and the ICIC at Imperial College for hospitality while this work was being completed. LV is supported by the European Research Council under the European Community's Seventh Framework Programme FP7-IDEAS-Phys.LSS 240117. Funding for this work was partially provided by the Spanish MINECO under projects AYA2014-58747-P and MDM-2014-0369 of ICCUB (Unidad de Excelencia "Maria de Maeztu") Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science.Deriving the expansion history of the Universe is a major goal of modern cosmology. To date, the most accurate measurements have been obtained with Type Ia Supernovae (SNe) and Baryon Acoustic Oscillations (BAO), providing evidence for the existence of a transition epoch at which the expansion rate changes from decelerated to accelerated. However, these results have been obtained within the framework of specific cosmological models that must be implicitly or explicitly assumed in the measurement. It is therefore crucial to obtain measurements of the accelerated expansion of the Universe independently of assumptions on cosmological models. Here we exploit the unprecedented statistics provided by the Baryon Oscillation Spectroscopic Survey (BOSS, [1-3]) Data Release 9 to provide new constraints on the Hubble parameter H(z) using the cosmic chronometers approach. We extract a sample of more than 130000 of the most massive and passively evolving galaxies, obtaining five new cosmology-independent H(z) measurements in the redshift range 0.3 < z < 0.5, with an accuracy of ~11–16% incorporating both statistical and systematic errors. Once combined, these measurements yield a 6% accuracy constraint of H(z = 0.4293) = 91.8 ± 5.3 km/s/Mpc. The new data are crucial to provide the first cosmology-independent determination of the transition redshift at high statistical significance, measuring zt = 0.4 ± 0.1, and to significantly disfavor the null hypothesis of no transition between decelerated and accelerated expansion at 99.9% confidence level. This analysis highlights the wide potential of the cosmic chronometers approach: it permits to derive constraints on the expansion history of the Universe with results competitive with standard probes, and most importantly, being the estimates independent of the cosmological model, it can constrain cosmologies beyond—and including—the ΛCDM model.PostprintPeer reviewe

Blood ammonia levels in liver cirrhosis: a clue for the presence of portosystemic collateral veins

<p>Abstract</p> <p>Background</p> <p>Portal hypertension leads to the formation of portosystemic collateral veins in liver cirrhosis. The resulting shunting is responsible for the development of portosystemic encephalopathy. Although ammonia plays a certain role in determining portosystemic encephalopathy, the venous ammonia level has not been found to correlate with the presence or severity of this entity. So, it has become partially obsolete. Realizing the need for non-invasive markers mirroring the presence of esophageal varices in order to reduce the number of endoscopy screening, we came back to determine whether there was a correlation between blood ammonia concentrations and the detection of portosystemic collateral veins, also evaluating splenomegaly, hypersplenism (thrombocytopenia) and the severity of liver cirrhosis.</p> <p>Methods</p> <p>One hundred and fifty three consecutive patients with hepatic cirrhosis of various etiologies were recruited to participate in endoscopic and ultrasonography screening for the presence of portosystemic collaterals mostly esophageal varices, but also portal hypertensive gastropathy and large spontaneous shunts.</p> <p>Results</p> <p>Based on Child-Pugh classification, the median level of blood ammonia was 45 mcM/L in 64 patients belonging to class A, 66 mcM/L in 66 patients of class B and 108 mcM/L in 23 patients of class C respectively (p < 0.001).</p> <p>The grade of esophageal varices was concordant with venous ammonia levels (rho 0.43, p < 0.001). The best area under the curve was given by ammonia concentrations, i, e., 0.78, when comparing areas of ammonia levels, platelet count and spleen longitudinal diameter at ultrasonography. Ammonia levels predicted hepatic decompensation and ascites presence (Odds Ratio 1.018, p < 0.001).</p> <p>Conclusion</p> <p>Identifying cirrhotic patients with high blood ammonia concentrations could be clinically useful, as high levels would lead to suspicion of being in presence of collaterals, in clinical practice of esophageal varices, and pinpoint those patients requiring closer follow-up and endoscopic screening.</p

Extracting evolutionary information from the spectral decomposition of early-type galaxies.

Holding the major share of stellar mass in galaxies and being also old and passively evolving, early-type galaxies (ETGs) are the primary probes in investigating these various evolution scenarios, as well as being useful means to provide insights on cosmological parameters. In this thesis work I focused specifically on ETGs and on their capability in constraining galaxy formation and evolution; in particular, the principal aims were to derive some of the ETGs evolutionary parameters, such as age, metallicity and star formation history (SFH) and to study their age-redshift and mass-age relations. In order to infer galaxy physical parameters, I used the public code STARLIGHT: this program provides a best fit to the observed spectrum from a combination of many theoretical models defined in user-made libraries. the comparison between the output and input light-weighted ages shows a good agreement starting from SNRs of ∼ 10, with a bias of ∼ 2.2% and a dispersion 3%. Furthermore, also metallicities and SFHs are well reproduced. In the second part of the thesis I performed an analysis on real data, starting from Sloan Digital Sky Survey (SDSS) spectra. I found that galaxies get older with cosmic time and with increasing mass (for a fixed redshift bin); absolute light-weighted ages, instead, result independent from the fitting parameters or the synthetic models used. Metallicities, instead, are very similar from each other and clearly consistent with the ones derived from the Lick indices. The predicted SFH indicates the presence of a double burst of star formation. Velocity dispersions and extinctiona are also well constrained, following the expected behaviours. As a further step, I also fitted single SDSS spectra (with SNR∼ 20), to verify that stacked spectra gave the same results without introducing any bias: this is an important check, if one wants to apply the method at higher z, where stacked spectra are necessary to increase the SNR. Our upcoming aim is to adopt this approach also on galaxy spectra obtained from higher redshift Surveys, such as BOSS (z ∼ 0.5), zCOSMOS (z 1), K20 (z ∼ 1), GMASS (z ∼ 1.5) and, eventually, Euclid (z 2). Indeed, I am currently carrying on a preliminary study to estabilish the applicability of the method to lower resolution, as well as higher redshift (z 2) spectra, just like the Euclid ones