Star formation efficiency across large-scale galactic environments

Environmental effects on the evolution of galaxies have been one of the leading questions in galaxy studies for decades. In this work, we investigate the relationship between the star formation activity of galaxies and their environmental matter density using the cosmological hydrodynamic simulation Simba. The star formation activity indicators we explore include the star formation efficiency (SFE), specific star formation rate (sSFR) and molecular hydrogen mass fraction ($f^*_{H_2}$) and the environment is considered as the large-scale environmental matter density, calculated based on the stellar mass of nearby galaxies on a 1 Mpc/h grid using the cloud in cell (CIC) method. Our sample includes galaxies with $9<\log(M_*/M_{\odot})$ at $0<z<4$, divided into three mass bins to disentangle the effects of mass and environment on the galactic star formation activity. For low- to intermediate-mass galaxies at low-redshifts ($z<1.5$), we find that the star formation efficiency of those in high-density regions are $\sim 0.3$ dex lower than those in low-density regions. However, there is no significant environmental dependence of the star formation efficiency for massive galaxies over all our redshift range, and low- to intermediate-mass galaxies at high redshifts ($z > 1.5$). We present a scaling relation for the depletion time of molecular hydrogen (${t_{depl}}=1/SFE$) as a function of galaxy parameters including environmental density. Our findings provide a framework for quantifying the environmental effects on the star formation activities of galaxies as a function of stellar mass and redshift. The most significant environmental dependence is seen at later cosmic times ($z<1.5$) and towards lower stellar masses ($9<\log(M_*/M_{\odot})<10$). Future large galaxy surveys can use this framework to look for the environmental dependence of the star formation activity and examine our predictions.Comment: 17 pages, 6 figure

Star-formation driven outflows in local dwarf galaxies as revealed from [CII] observations by Herschel

We characterize the physical properties of star-formation driven outflows in a sample of 29 local dwarf galaxies drawn from the Dwarf Galaxy Survey. We make use of Herschel/PACS archival data to search for atomic outflow signatures in the wings of individual [CII] 158 um spectra and in their stacked line profile. We find a clear excess of emission in the high-velocity tails of 11 sources which can be explained with an additional broad component in the modeling of their spectra. The remaining objects are likely hosts of weaker outflows that can still be detected in the average stacked spectrum. In both cases, we estimate the atomic mass outflow rates which result to be comparable with the star-formation rates of the galaxies, implying mass-loading factors of the order of unity. Outflow velocities in all the 11 galaxies with individual detection are larger than (or compatible with) the escape velocities of their dark matter halos, with an average fraction of 40% of gas escaping into the intergalactic medium (IGM). Depletion timescales due to outflows are lower than those due to gas consumption by star formation in most of our sources, ranging from hundred million to a few billion years. Our outflows are mostly consistent with momentum-driven winds generated by the radiation pressure of young stellar populations on dust grains, although the energy-driven scenario is not excluded if considering a coupling efficiency up to 20% between the energy injected by supernova (SN) and the interstellar medium. Our results suggest that galactic outflows can regulate the star formation history of dwarf galaxies as they are able to enrich with metals the circumgalactic medium of these sources, bringing on average a non-negligible amount of gas into the IGM. Our findings are suitable for tuning chemical evolution models attempting to describe the physical processes shaping the evolution of dwarf galaxies.Comment: Accepted for publication in A&

Molecular outflow in the reionization-epoch quasar J2054-0005 revealed by OH 119 μ\mum observations

Molecular outflows are expected to play a key role in galaxy evolution at high redshift. To study the impact of outflows on star formation at the epoch of reionization, we performed sensitive ALMA observations of OH 119 $\mu$m toward J2054-0005, a luminous quasar at $z=6.04$. The OH line is detected and exhibits a P-Cygni profile that can be fitted with a broad blue-shifted absorption component, providing unambiguous evidence of an outflow, and an emission component at near-systemic velocity. The mean and terminal outflow velocities are estimated to be $v_\mathrm{out}\approx670~\mathrm{km~s}^{-1}$ and $1500~\mathrm{km~s}^{-1}$, respectively, making the molecular outflow in this quasar one of the fastest at the epoch of reionization. The OH line is marginally spatially resolved for the first time in a quasar at $z>6$, revealing that the outflow extends over the central 2 kpc region. The mass outflow rate is comparable to the star formation rate ($\dot{M}_\mathrm{out}/\mathrm{SFR}\sim2$), indicating rapid ($\sim10^7~\mathrm{yr}$) quenching of star formation. The mass outflow rate in a sample star-forming galaxies and quasars at $4<z<6.4$ exhibits a positive correlation with the total infrared luminosity, although the scatter is large. Owing to the high outflow velocity, a large fraction (up to $\sim50\%$) of the outflowing molecular gas may be able to escape from the host galaxy into the intergalactic medium.Comment: Accepted to Ap

Incremental Value of Cardiac Biomarkers in Mid-term Prognosis of Patients with Acute Coronary Syndrome

BACKGROUND: Given the number of prognostic studies, both short- and long-termed, in patients with myocardial infarction (MI), the data on predictors of major adverse cardiac events (MACE) following discharge still remains limited. Assessment of left ventricular (LV) function, combined with the use of cardiac biomarkers, such as NT-proBNP can help in the early identification of patients at risk of developing heart failure and/or other MACE in acute MI (AMI) survivors. AIM: The aim of the study was to identify early predictors of MACE in MI patients, that underwent primary percutaneous coronary intervention, with special emphasis on cardiac biomarkers. MATERIALS AND METHODS: We analyzed clinical, LV functional, angiographic variables, as well cardiac troponin (hsTn), a marker of myocardial necrosis, natriuretic peptide (NT-proBNP), a marker of myocardial stress, and white blood cells (WBC), as a marker of inflammation. The study was designed as longitudinal, prospective observational cohort study undertaken on 150 AMI patients hospitalized at University Clinic of Cardiology over the period of September 2018 to March 2019. Inclusion criteria: All incomers hospitalized for AMI over the aforementioned period who were willing to participate in the study and gave signed informed consent. Exclusion criteria: Patients who were not consented to participate in the study, patients who suffered in-hospital mortality over the index hospitalization and those with the previous HF and/or AMI. IBM SPSS statistical software version 22 was used for statistical analysis. Descriptive and comparative statistical methods were applied. Continuous variables were presented as means, while categorical as frequencies and percentages. Comparative statistic tests: Chi-square test, for variables with dichotomous distribution, t-test and one-way ANOVA for continuous variables with two or more categories were applied. Risk ratios with 95% confidence intervals were calculated, and the significance was determined using Cochran and Mantel-Haenszel test (at the level of <0.05). Receiver operator characteristic curves (ROC) were used for prediction capability. Correlations, uni- and multivariate linear, and logistic regression analysis were undertaken to identify significantly associated variables. RESULTS: The average follow-up period was 31 months. In total, 26 patients suffered from at least one MACE. Multivariate logistic regression analysis identified several independent predictors: NT-proBNP (p = 0.007), number of diseased vessels (p = 0.027), and need for loop diuretic therapy (p = 0.050). ROC curve demonstrated excellent discriminatory function for MACE of NT-proBNP and WBC (area under the curve 0.640, and 0.658, p = 0.025 and 0.011, respectively). CONCLUSION: The combination of biomarkers for myocardial stress and inflammation improves the prediction of MACE in MI survivors

Detection and characterisation of distant, dusty star-forming galaxies in Herschel cosmological surveys

La population de galaxies poussiéreuses ayant un fort taux de formation stellaire (Dusty Star Forming Galaxies, DSFGs) joue un rôle très important dans l’histoire de l’univers, avec des taux de formation d’étoiles allant de quelques centaines à quelques milliers de masses solaires par an. Les sondages infrarouges, comme ceux entrepris à l’aide du satellite Herschel, nous offrent l’opportunité de recenser de manière approfondie ces DSFGs jusqu’à de grands décalages spectraux. Cependant, jusqu’à présent seul un petit nombre de DSFG détecté par Herschel ont été confirmés pour être à des décalages spectraux supérieurs à 4. Les modèles de formation et d’évolution des galaxies stipulent généralement que la population de DSFG à z > 4 sont les progéniteurs des galaxies elliptiques, observées dans les amas les plus massifs de l’univers local. L’abondance des DSFGs à z > 4 se révèle donc être décisive pour contraindre ces modèles ainsi que pour vérifier notre compréhension globale de l’univers lointain. Le premier objectif de mon travail de recherche est d’identifier les candidates galaxies à z > 4 détectées sur des champs les plus larges possibles observés par Herschel et l’instrument SPIRE et d’examiner les propriétés statistiques de celles-ci. A cette fin, j’ai créé un nouvel algorithme de sélection dans le but d’augmenter substantiellement le nombre de candidates et de comprendre leur nature.Over the last few decades, great progress has been made in our understanding of the star formation history of the Universe. With the discovery of distant, dusty star-forming galaxies (DSFGs) it has become apparent that observing at rest-frame UV and optical wavelengths is insufficient as a large fraction of the star formation is dust obscured. Thanks to the extensive observational studies carried out during the last two decades, we learn that DSFGs have a redshift peak at z ∼ 2, matching the cosmic time where galaxies have formed most of their young, massive stars. However, it remains extremely challenging to use the Herschel space observatory for identifying a tail extending towards much higher redshifts (z > 4). As a result, until recently only a small number of infrared-selected DSFGs at z > 4 were known, most of them strongly gravitationally lensed. One of the main goals of this Thesis is to assemble candidate z > 4 galaxies detected in a large area survey observed by Herschel-SPIRE and to examine the statistical properties and environments of these systems

The cosmic web influences the rapid evolution of the cold interstellar medium in SIMBA galaxies

Understanding the relationship between the cosmic web and the galaxy's cold interstellar medium (ISM; gas, dust, and metals) is one of the key steps towards understanding galaxy evolution. However, the exploration of key ISM properties with respect to cosmic web environments beyond the local universe is still in its infancy, both due to various observational and theoretical challenges. Here I present the results of the study that explores, for the first time, how the structural properties of environments in which dusty galaxies reside influence their ISM. We use SIMBA cosmological simulation in order to track the cosmic evolution of some of the evolutionary markers of the ISM (such as the gas-to-dust mass ratio and dust-to-metal ratio) as a function of their distances to the 3D cosmic web features. I will demonstrate how the proximity of a galaxy to a filament shapes the rapid cosmic evolution of the galaxy ISM, but differently for star-forming and quiescent galaxies. Particular attention will be given to the role of the cosmic web in shaping excess gas-to-dust mass ratios in galaxies within the first 1 Gyr since their quenching

Preparing for LSST Data: in Search of Main Physical Properties of the Main Sequence Galaxies

International audienceThe main goal of the Vera C. Rubin observatory is to perform the 10 year Legacy Survey of Space and Time (LSST). This future state-of-art observatory will open the new window to study billions of galaxies from Local Universe as well as the high redshift objects. To get ready to work with the petabytes of data collected by the LSST we performed a simulation of future observations and uncertainties based on the 50,385 real galaxies within the redshift range 0<z<2.5, from the EN and COSMOS fields of the Herschel Extragalactic Legacy Project (HELP) survey. We obtain the main physical properties of the galaxies (such as SFR, \mstar, and \ldust) using the Code Investigating GALaxy Emission (CIGALE) by modelling their spectral energy distributions. To test the performance of the fit on the LSST observations, we compared the main galaxy physical properties obtained from the SED fitting performed on the real galaxies (with UV to the far-IR coverage) with the one obtained with the simulated LSST optical measurements alone

Preparing for LSST Data: in Search of Main Physical Properties of the Main Sequence Galaxies

International audienceThe main goal of the Vera C. Rubin observatory is to perform the 10 year Legacy Survey of Space and Time (LSST). This future state-of-art observatory will open the new window to study billions of galaxies from Local Universe as well as the high redshift objects. To get ready to work with the petabytes of data collected by the LSST we performed a simulation of future observations and uncertainties based on the 50,385 real galaxies within the redshift range 0<z<2.5, from the EN and COSMOS fields of the Herschel Extragalactic Legacy Project (HELP) survey. We obtain the main physical properties of the galaxies (such as SFR, \mstar, and \ldust) using the Code Investigating GALaxy Emission (CIGALE) by modelling their spectral energy distributions. To test the performance of the fit on the LSST observations, we compared the main galaxy physical properties obtained from the SED fitting performed on the real galaxies (with UV to the far-IR coverage) with the one obtained with the simulated LSST optical measurements alone

Molecular Outflow in the Reionization-epoch Quasar J2054-0005 Revealed by OH 119 μm Observations

Molecular outflows are expected to play a key role in galaxy evolution at high redshift. To study the impact of outflows on star formation at the epoch of reionization, we performed sensitive Atacama Large Millimeter/submillimeter Array observations of OH 119 μ m toward J2054-0005, a luminous quasar at z = 6.04. The OH line is detected and exhibits a P-Cygni profile that can be fitted with a broad blueshifted absorption component, providing unambiguous evidence of an outflow, and an emission component at near-systemic velocity. The mean and terminal outflow velocities are estimated to be v _out ≈ 670 and 1500 km s ^−1 , respectively, making the molecular outflow in this quasar one of the fastest at the epoch of reionization. The OH line is marginally spatially resolved for the first time in a quasar at z > 6, revealing that the outflow extends over the central 2 kpc region. The mass outflow rate is comparable to the star formation rate ( ${\dot{M}}_{\mathrm{out}}/\mathrm{SFR}\sim 2$ ), indicating rapid (∼10 ^7 yr) quenching of star formation. The mass outflow rate in a sample of star-forming galaxies and quasars at 4 < z < 6.4 exhibits a positive correlation with the total infrared luminosity, although the scatter is large. Owing to the high outflow velocity, a large fraction (up to ∼50%) of the outflowing molecular gas may be able to escape from the host galaxy into the intergalactic medium