ABSTRACT The "main sequence of galaxies"-defined in terms of the total star formation rate versus the total stellar mass M*-is a well-studied tight relation that has been observed at several ...wavelengths and at different redshifts. All earlier studies have derived this relation from integrated properties of galaxies. We recover the same relation from an analysis of spatially resolved properties, with integral field spectroscopic (IFS) observations of 306 galaxies from the CALIFA survey. We consider the SFR surface density in units of log(M yr−1 Kpc−2) and the stellar mass surface density in units of log(M Kpc−2) in individual spaxels that probe spatial scales of 0.5-1.5 Kpc. This local relation exhibits a high degree of correlation with small scatter ( = 0.23 dex), irrespective of the dominant ionization source of the host galaxy or its integrated stellar mass. We highlight (i) the integrated star formation main sequence formed by galaxies whose dominant ionization process is related to star formation, for which we find a slope of 0.81 0.02; (ii) for the spatially resolved relation obtained with the spaxel analysis, we find a slope of 0.72 0.04; and (iii) for the integrated main sequence, we also identified a sequence formed by galaxies that are dominated by an old stellar population, which we have called the retired galaxies sequence.
ABSTRACT
According to their specific star formation rate (sSFR), galaxies are often divided into ‘star-forming’ and ‘passive’ populations. It is argued that the former define a narrow ‘main sequence ...of star-forming galaxies’ (MSSF) of the form sSFR(M*), whereas ‘passive’ galaxies feature negligible levels of star formation activity. Here we use data from the Sloan Digital Sky Survey and the Galaxy And Mass Assembly survey at z < 0.1 to constrain the conditional probability of the sSFR at a given stellar mass. We show that the whole population of galaxies in the local Universe is consistent with a simple probability distribution with only one maximum (roughly corresponding to the MSSF) and relatively shallow power-law tails that fully account for the ‘passive’ population. We compare the quality of the fits provided by such unimodal ansatz against those coming from a double lognormal fit (illustrating the bimodal paradigm), finding that both descriptions are roughly equally compatible with the current data. In addition, we study the physical interpretation of the bidimensional distribution across the M*–sSFR plane and discuss potential implications from a theoretical and observational point of view. We also investigate correlations with metallicity, morphology, and environment, highlighting the need to consider at least an additional parameter in order to fully specify the physical state of a galaxy.
ABSTRACT
Dust plays an important role in the evolution of a galaxy, as it is one of the main ingredients for efficient star formation. Dust grains are also a sink/source of metals when they are ...created/destroyed, and, therefore, a self-consistent treatment is key in order to correctly model chemical evolution. In this work, we discuss the implementation of dust physics in our current multiphase model, which also follows the evolution of atomic, ionized and molecular gas. Our goal is to model the conversion rates among the different phases of the interstellar medium, including the creation, growth and destruction of dust, based, as far as possible, on physical principles rather than on phenomenological recipes. We first present the updated set of differential equations and then discuss the results. We calibrate our model against observations of the Milky Way Galaxy and compare its predictions with extant data. Our results are broadly consistent with the observed data for intermediate and high metallicities, but the models tend to produce more dust than is observed in the low-metallicity regime.
ABSTRACT
This work investigates the fundamental mechanism(s) that drive galaxy evolution in the local Universe. By comparing two proxies of star formation sensitive to different time-scales, such as ...EW($\rm H\,\alpha$) and colours like g − r, one may distinguish between smooth secular evolution (ageing) and sudden changes (quenching) in the recent star formation history of galaxies. Building upon the results obtained from a former study based on 80 000 Sloan Digital Sky Survey (SDSS) single-fibre measurements, we now focus on spatially resolved (on kpc scales) galaxies, comparing with a sample of 637 nearby objects observed by the Calar Alto Legacy Integral-Field Area survey. In general, galaxies cannot be characterized in terms of a single ‘evolutionary stage’. Individual regions within galaxies arrange along a relatively narrow ageing sequence, with some intrinsic scatter possibly due to their different evolutionary paths. These sequences, though, differ from one galaxy to another, although they are broadly consistent with the overall distribution found for the (central) SDSS spectra. We find evidence of recent quenching episodes (relatively blue colours and strong $\rm H\,\alpha$ absorption) in a small fraction of galaxies (most notably, low-mass ellipticals), on global scales and individual regions (particularly at high metallicity). However, we argue that most of the systems, over their entire extent, are compatible with a secular inside-out scenario, where the evolutionary stage correlates with both global (mass, morphology, and environment) and local (surface brightness and metallicity) properties.
Context.
There are typically two different approaches to inferring the mass formation history (MFH) of a given galaxy from its luminosity in different bands. Non-parametric methods are known for ...their flexibility and accuracy, while parametric models are more computationally efficient.
Aims.
In this work we propose an alternative, based on a polynomial expansion around the present time, that combines the advantages of both techniques.
Methods.
In our approach, the MFH is decomposed through an orthonormal basis of
N
polynomials in lookback time. To test the proposed framework, synthetic observations are generated from models based on common analytical approximations (exponential, delayed-
τ
, and Gaussian star formation histories), as well as cosmological simulations for the Illustris-TNG suite. A normalized distance is used to measure the quality of the fit, and the input MFH is compared with the polynomial reconstructions both at the present time and through cosmic evolution. Our polynomial expansion is also compared with widely used parametric and non-parametric methods such as C
IGALE
and P
ROSPECTOR
.
Results.
The observed luminosities are reproduced with an accuracy of around 10 per cent for a constant star formation rate (
N
= 1) and better for higher-order polynomials. Our method provides good results on the reconstruction of the total stellar mass, the star formation rate, and even its first derivative for smooth star formation histories, but it has difficulties in reproducing variations on short timescales and/or star formation histories that peak at the earliest times of the Universe.
Conclusions.
The polynomial expansion appears to be a promising alternative to other analytical functions used in parametric methods, combining both speed and flexibility.
ABSTRACT
We carry out 1D hydrodynamical simulations of the evolution of a spherically symmetric supernova remnant (SNR) subject to an external radiation field (ERF) that influences the cooling and ...heating rates of the gas. We consider homogeneous media with ambient hydrogen number densities nH, 0 of 0.1 and 1 cm−3 permeated by an average radiation field including the cosmic microwave, extragalactic, and Galactic backgrounds, attenuated by an effective column density NH, eff from 1018 to 1021 cm−2. Our results may be classified into two broad categories: at low NH, eff, the ERF presents little absorption in the ultraviolet (ionizing) regime, and all the ’unshielded’ cases feature an equilibrium temperature Teq ∼ 7000 K below which the ambient gas cannot cool further. In this scenario, the SNR develops a nearly isothermal shock profile whose shell becomes thicker over time. At higher NH, eff, the ERF is heavily absorbed in the UV range, yielding a roughly constant heating function for temperatures ≲ 104 K. These ‘shielded’ cases develop a thin, cold and dense shell throughout their evolution. Energy and momentum injection to the medium do not change significantly between both scenarios, albeit luminosity is higher and more uniformly distributed over the shell for unshielded SNR.
We investigate the production of electrons and positrons in the Milky Way within the context of dark matter annihilation. Upper limits on the relevant cross-section are obtained by combining ...observational data at different wavelengths (from Haslam, WMAP and Fermi all-sky intensity maps) with recent measurements of the electron and positron spectra in the solar neighbourhood by PAMELA, Fermi and HESS. We consider synchrotron emission in the radio and microwave bands, as well as inverse Compton scattering and final-state radiation at gamma-ray energies. According to our results, the dark matter annihilation cross-section into electron-positron pairs should not be higher than the canonical value for a thermal relic if the mass of the dark matter candidate is smaller than a few GeV. In addition, we also derive a stringent upper limit on the inner logarithmic slope α of the density profile of the Milky Way dark matter halo (α < 1 if m
dm < 5 GeV, α < 1.3 if m
dm < 100 GeV and α < 1.5 if m
dm < 2 TeV) assuming that σv e± =3 × 10-26 cm3 s−1. A logarithmic slope steeper than α ∼ 1.5 is hardly compatible with a thermal relic lighter than ∼1 TeV, regardless of the dominant annihilation channel.
We measured the gas abundance profiles in a sample of 122 face-on spiral galaxies observed by the CALIFA survey and included all spaxels whose line emission was consistent with star formation. This ...type of analysis allowed us to improve the statistics with respect to previous studies, and to properly estimate the oxygen distribution across the entire disc to a distance of up to 3−4 disc effective radii (re). We confirm the results obtained from classical H ii region analysis. In addition to the general negative gradient, an outer flattening can be observed in the oxygen abundance radial profile. An inner drop is also found in some cases. There is a common abundance gradient between 0.5 and 2.0 re of αO / H = − 0.075 dex /re with a scatter of σ = 0.016 dex /re when normalising the distances to the disc effective radius. By performing a set of Kolmogorov-Smirnov tests, we determined that this slope is independent of other galaxy properties, such as morphology, absolute magnitude, and the presence or absence of bars. In particular, barred galaxies do not seem to display shallower gradients, as predicted by numerical simulations. Interestingly, we find that most of thegalaxies in the sample with reliable oxygen abundance values beyond ~2 effective radii (57 galaxies) present a flattening of the abundance gradient in these outer regions. This flattening is not associated with any morphological feature, which suggests that it is a common property of disc galaxies. Finally, we detect a drop or truncation of the abundance in the inner regions of 27 galaxies in the sample; this is only visible for the most massive galaxies.
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