The chemical enrichment in the interstellar medium (ISM) of galaxies is regulated by several physical processes: stellar evolution, grain formation and destruction, galactic inflows and outflows. ...Understanding such processes is essential to follow the chemical enrichment of galaxies through the cosmic epochs, and to interpret the observations. Despite the importance of such topics, the efficiency of the different processes driving the evolution of baryons in galaxies, remain controversial. We revise the current description of metal and dust evolution in local low-metallicity dwarf galaxies and we develop a description for Lyman Break Galaxies. Our main goal is to reproduce i) the peak in the mass of dust over the mass of stars (sMdust) observed within few hundred Myrs; ii) the decrease of the sMdust at later time. The spectral energy distribution of the galaxies is fitted with the "Code Investigating GALaxies Emission" (CIGALE), through which the stellar and dust masses, and the star formation rate are estimated. For some of the dwarf galaxies, the metal and gas content are also available. We run different calculations of chemical evolution in galaxies, and we fit the observed properties through the model predictions. We show that i) a top-heavy initial mass function that favours massive stars and a dust condensation fraction for Type II Supernovae (SNe II) of 50% or more help to reproduce the peak of sMdust observed after 100 Myrs since the beginning of the cycle; ii) galactic outflows play a crucial role in reproducing the decline in sMdust with age, and they are more efficient than grain destruction from SNe II; iii) a star formation efficiency (mass of gas converted into stars) of few per cent is required to explain the metallicity of local dwarf galaxies; iv) dust growth in the ISM is not necessary to reproduce the sMdust and, if present, its effect is erased by galactic outflows.
Background: Most of the stars in the Universe will end their evolution by losing their envelope during the thermally pulsing asymptotic giant branch (TP-AGB) phase, enriching the interstellar medium ...of galaxies with heavy elements, partially condensed into dust grains formed in their extended circumstellar envelopes. Among these stars, carbon-rich TP-AGB stars (C-stars) are particularly relevant for the chemical enrichment of galaxies. We here investigated the role of the metallicity in the dust formation process from a theoretical viewpoint. Methods: We coupled an up-to-date description of dust growth and dust-driven wind, which included the time-averaged effect of shocks, with FRUITY stellar evolutionary tracks. We compared our predictions with observations of C-stars in our Galaxy, in the Magellanic Clouds (LMC and SMC) and in the Galactic Halo, characterised by metallicity between solar and 1/10 of solar. Results: Our models explained the variation of the gas and dust content around C-stars derived from the IRS Spitzer spectra. The wind speed of the C-stars at varying metallicity was well reproduced by our description. We predicted the wind speed at metallicity down to 1/10 of solar in a wide range of mass-loss rates.
Quantifying changes in galaxies' interstellar medium (ISM) abundance after quenching star formation is an important aspect of galaxy evolution, but it is poorly constrained beyond the local universe. ...We characterise the dust-related properties in 548 quiescent galaxies observed at \(0.1<z<0.6\) as part of the hCOSMOS spectroscopic survey. This is the largest sample of quiescent galaxies at intermediate redshifts, for which the co-evolution of dust, metals and stars have been estimated. We reveal the complex relations between the key markers of galaxies' dust life-cycles, such as specific dust mass (\(M_{\rm dust}\)/\(M_{\rm \star}\)), with gas-metallicity (\(Z_{\rm gas}\)), time since quenching (\(t_{\rm quench}\)), stellar age and size. We find morphology to be important factor of a large scatter (\(\sim2\) orders of magnitude) in \(M_{\rm dust}/M_{\rm \star}\). Through modelling the star formation histories of our objects, we derive a broad dynamical range of post-quenching timescales (\(60\:\rm Myr<t_{\rm quench}<3.2\:\rm Gyr\)). We find that \(M_{\rm dust}/M_{\rm \star}\) is the highest in recently quenched systems (\(t_{\rm quench}<500\) Myr), but its further evolution is non-monotonic as a consequence of diverse pathways for prolonged dust formation, or removal on various timescales. Our data are well reproduced by the SIMBA cosmological simulation and chemical models that include dust growth in the ISM. While this process is prevalent in dusty quiescent galaxies, \(\sim15\%\) of objects show signs of external dust acquisition, most likely via minor mergers. Our results strongly suggest that prolonged dust production on a timescale \(0.5-1\:\rm Gyr\) since quenching may be common in dusty quiescent galaxies at intermediate redshifts, even if their gas reservoirs are heavily exhausted (i.e., cold gas fraction \(<1-5\%\)).
We investigate the variation in the mid-infrared spectral energy distributions of 373 low-redshift (\(z<0.4\)) star-forming galaxies, which reflects a variety of polycyclic aromatic hydrocarbon (PAH) ...emission features. The relative strength of PAH emission is parameterized as \(q_\mathrm{PAH}\), which is defined as the mass fraction of PAH particles in the total dust mass. With the aid of continuous mid-infrared photometric data points covering 7-24\(\mu\)m and far-infrared flux densities, \(q_\mathrm{PAH}\) values are derived through spectral energy distribution fitting. The correlation between \(q_\mathrm{PAH}\) and other physical properties of galaxies, i.e., gas-phase metallicity (\(12+\mathrm{log(O/H)}\)), stellar mass, and specific star-formation rate (sSFR) are explored. As in previous studies, \(q_\mathrm{PAH}\) values of galaxies with high metallicity are found to be higher than those with low metallicity. The strength of PAH emission is also positively correlated with the stellar mass and negatively correlated with the sSFR. The correlation between \(q_\mathrm{PAH}\) and each parameter still exists even after the other two parameters are fixed. In addition to the PAH strength, the application of metallicity-dependent gas-to-dust mass ratio appears to work well to estimate gas mass that matches the observed relationship between molecular gas and physical parameters. The result obtained will be used to calibrate the observed PAH luminosity-total infrared luminosity relation, based on the variation of MIR-FIR SED, which is used in the estimation of hidden star formation.
The vast majority (>=90%) of presolar SiC grains identified in primitive meteorites are relics of ancient asymptotic giant branch (AGB) stars, whose ejecta were incorporated into the Solar System ...during its formation. Detailed characterization of these ancient stardust grains has revealed precious information on mixing processes in AGB interiors in great detail. However, the mass and metallicity distribution of their parent stars still remains ambiguous, although such information is crucial to investigating the slow neutron capture process, whose efficiency is mass- and metallicity-dependent. Using a well-known Milky Way chemo-dynamical model, we follow the evolution of the AGB stars that polluted the Solar System at 4.57 Gyr ago and weighted the stars based on their SiC dust productions. We find that presolar SiC in the Solar System predominantly originated from AGB stars with M~2 Msun and Z~Zsun. Our finding well explains the grain-size distribution of presolar SiC identified in situ in primitive meteorites. Moreover, it provides complementary results to very recent papers dealing with the characterization of parent stars of presolar SiC.
A&A 653, A107 (2021) In this work we study how to employ the upcoming Legacy Survey of Space and
Time (LSST) data to constrain physical properties of normal, star forming
galaxies. We use simulated ...LSST data and existing real observations to test the
estimations of the physical properties of galaxies, such as star formation rate
(SFR), stellar mass ($M_{star}$), and dust luminosity ($L_{dust}$). We focus on
normal star-forming galaxies, as they form the majority of the galaxy
population in the universe and therefore are more likely to be observed by the
LSST. We perform a simulation of LSST observations and uncertainties of 50,385
real galaxies within redshift range $0<z<2.5$. In order to achieve this goal,
we used the unique multi-wavelength data from the Herschel Extragalactic Legacy
Project (HELP) survey. Our analysis focus on two fields: ELAIS-N1 and COSMOS.
To obtain galaxy physical properties we fit their Spectral Energy Distributions
(SEDs) using the Code Investigating GALaxy Emission (CIGALE). We compare the
main galaxy physical properties obtained from the fit of the observed
multi-wavelength photometry of galaxies (from UV to FIR) to the ones obtained
from the simulated LSST optical measurements only. The stellar masses estimated
based on the LSST measurements are in agreement with the full UV-FIR SED
estimations, as they depend mainly on the UV and optical emission, well covered
by LSST in the considered redshift range. We obtain a clear overestimation of
SFR, $L_{dust}$, $M_{dust}$ estimated with LSST only, highly correlated with
redshift. We investigate the cause of this overestimation and we conclude that
it is related to an overestimation of the dust attenuation, both UV and NIR. We
find that it is necessary to employ auxiliary rest-frame mid-infrared
observations, simulated UV observations, or FUV attenuation (AFUV)- Mstar
relation, to correct the overestimation.
We have computed a grid of hydrostatic spherical COMARCS models for C stars covering metallicities from Z/H=0 to -2 and values of the carbon excess C-O from 6.41 to 9.15, plus some temperature ...sequences, where the amount of oxygen and nitrogen is increased relative to a scaled solar element mixture. Such abundance variations may appear during the late stages of stellar evolution. Our study covers changes of O/Z and N/Z going up to +0.5. Based on the atmospheric structures we have calculated synthetic spectra and photometry for all of the models in a consistent way. The sequences with changed O/Z and N/Z can be used to derive correction terms, which are applied to the colours predicted for a certain combination of effective temperature, surface gravity, metallicity and carbon excess. If one neglects these shifts in case of a variable oxygen amount, taking C-O instead of C/O gives much better results, since the first quantity dominates the formation of many important molecular species. For the warmer C giants with weaker pulsation it is in principle possible to determine C-O, O/Z or N/Z from high resolution spectra, when the opacities in the radiative transfer calculations for the models and observable properties are treated consistently. The corresponding changes due to the abundances often become significantly larger than the deviations caused by uncertainties of the stellar parameters or by a optically thin dust shell. Photometric data and low or medium resolution spectra are not sufficient to derive the mentioned quantities.
Following the discovery of SAGE0536AGN (\(z \sim\) 0.14), with the strongest 10-\(\mu\)m silicate emission ever observed for an Active Galactic Nucleus (AGN), we discovered SAGE0534AGN (\(z \sim\) ...1.01), a similar AGN but with less extreme silicate emission. Both were originally mistaken as evolved stars in the Magellanic Clouds. Lack of far-infrared emission, and therefore star-formation, implies we are seeing the central engine of the AGN without contribution from the host galaxy. They could be a key link in galaxy evolution. We used a dimensionality reduction algorithm, t-SNE (t-distributed Stochastic Neighbourhood Embedding) with multi-wavelength data from Gaia EDR3, VISTA survey of the Magellanic Clouds, AllWISE and the Australian SKA Pathfinder to find these two unusual AGN are grouped with 16 other objects separated from the rest, suggesting a rare class. Our spectroscopy at SAAO/SALT and literature data confirm at least 14 of these objects are extragalactic (\(0.13 < z < 1.23\)), all hosting AGN. Using spectral energy distribution fitter CIGALE we find that the majority of dust emission (\(> 70 \%\)) in these sources is due to the AGN. Host galaxies appear to be either in or transitioning into the green valley. There is a trend of a thinning torus, increasing X-ray luminosity and decreasing Eddington ratio as the AGN transition through the green valley, implying that as the accretion supply depletes, the torus depletes and the column density reduces. Also, the near-infrared variability amplitude of these sources correlates with attenuation by the torus, implying the torus plays a role in the variability.
We present a map of the total intrinsic reddening across ~90 deg\(^{2}\) of the Large Magellanic Cloud (LMC) derived using optical (ugriz) and near-infrared (IR; YJKs) spectral energy distributions ...(SEDs) of background galaxies. The reddening map is created from a sample of 222,752 early-type galaxies based on the LEPHARE \(\chi^{2}\) minimisation SED-fitting routine. We find excellent agreement between the regions of enhanced intrinsic reddening across the central (4x4 deg\(^2\)) region of the LMC and the morphology of the low-level pervasive dust emission as traced by far-IR emission. In addition, we are able to distinguish smaller, isolated enhancements that are coincident with known star-forming regions and the clustering of young stars observed in morphology maps. The level of reddening associated with the molecular ridge south of 30 Doradus is, however, smaller than in the literature reddening maps. The reduced number of galaxies detected in this region, due to high extinction and crowding, may bias our results towards lower reddening values. Our map is consistent with maps derived from red clump stars and from the analysis of the star formation history across the LMC. This study represents one of the first large-scale categorisations of extragalactic sources behind the LMC and as such we provide the LEPHARE outputs for our full sample of ~2.5 million sources.
Precise studies on the Galactic bulge, globular cluster, Galactic halo and Galactic thick disk require stellar models with alpha enhancement and various values of helium content. These models are ...also important for extra-Galactic population synthesis studies. For this purpose, we complement the existing PARSEC models, which are based on the solar partition of heavy elements, with alpha-enhanced partitions. We collect detailed measurements on the metal mixture and helium abundance for the two populations of 47 Tuc (NGC 104) from the literature, and calculate stellar tracks and isochrones with these alpha-enhanced compositions. By fitting the precise color-magnitude diagram with HST ACS/WFC data, from low main sequence till horizontal branch, we calibrate some free parameters that are important for the evolution of low mass stars like the mixing at the bottom of the convective envelope. This new calibration significantly improves the prediction of the RGB bump brightness. Comparison with the observed RGB and HB luminosity functions also shows that the evolutionary lifetimes are correctly predicted. As a further result of this calibration process, we derive the age, distance modulus, reddening, and the red giant branch mass loss for 47 Tuc. We apply the new calibration and alpha-enhanced mixtures of the two 47 Tuc populations ( alpha/Fe ~0.4 and 0.2) to other metallicities. The new models reproduce the RGB bump observations much better than previous models. This new PARSEC database, with the newly updated alpha-enhanced stellar evolutionary tracks and isochrones, will also be part of the new stellar products for Gaia.
