Star formation along the Hubble sequence Delgado, R M Gonzalez; Fernandes, R Cid; Perez, E ...
Astronomy and astrophysics (Berlin),
6/2016, Letnik:
590
Journal Article
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The spatially resolved stellar population content of today's galaxies holds important information for understanding the different processes that contribute to the star formation and mass assembly ...histories of galaxies. The aim of this paper is to characterize the radial structure of the star formation rate (SFR) in galaxies in the nearby Universe as represented by a uniquely rich and diverse data set drawn from the CALIFA survey. The sample under study contains 416 galaxies observed with integral field spectroscopy, covering a wide range of Hubble types and stellar masses ranging from M sub(?)~ 10 super(9) to 7 x 10 super(11)M sub(?). Spectral synthesis techniques are applied to the datacubes to derive 2D maps and radial profiles of the intensity of the star formation rate in the recent past (Sigma sub(SFR)), as well as related properties, such as the local specific star formation rate (sSFR), defined as the ratio between Sigma sub(SFR) and the stellar mass surface density (mu sub(*)). To emphasize the behavior of these properties for galaxies that are on and off the main sequence of star formation (MSSF), we stack the individual radial profiles in seven bins of galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd), and several stellar masses. Our main results are: (a) the intensity of the star formation rate shows declining profiles that exhibit very small differences between spirals with values at R= 1 half light radius (HLR) within a factor two of Sigma sub(SFR)~ 20 M sub(?) Gyr super(-1) pc super(-2). The dispersion in the Sigma sub(SFR)(R) profiles is significantly smaller in late type spirals (Sbc, Sc, Sd). This confirms that the MSSF is a sequence of galaxies with nearly constant Sigma sub(SFR). (b) sSFR values scale with Hubble type and increase radially outward with a steeper slope in the inner 1 HLR. This behavior suggests that galaxies are quenched inside-out and that this process is faster in the central, bulge-dominated part than in the disks. (c) As a whole and at all radii, E and S0 are off the MSSF with SFR much smaller than spirals of the same mass. (d) Applying the volume corrections for the CALIFA sample, we obtain a density of star formation in the local Universe of rho sub(SFR)= (0.0105 + or - 0.0008) M sub(?) yr super(-1) Mpc super(-3), in agreement with independent estimates. Most of the star formation is occurring in the disks of spirals. (e) The volume-averaged birthrate parameter, which measures the current SFR with respect to its lifetime average, b? = 0.39 + or - 0.03, suggests that the present day Universe is forming stars a about one-third of its past average rate. E, S0, and the bulge of early type spirals (Sa, Sb) contribute little to the recent SFRof the Universe, which is dominated by the disks of Sbc, Sc, and Sd spirals. (f) There is a tight relation between Sigma sub(SFR) and mu sub(*), defining a local MSSF relation with a logarithmic slope of 0.8, similar to the global MSSF relation between SFR and M sub(?). This suggests that local processes are important in determining the star formation in disks, probably through a density dependence of the SFR law. The scatter in the local MSSF is driven by morphology-related offsets, with Sigma sub(SFR)/mu sub(*)(the local sSFR) increasing from early to late type galaxies, indicating that the shut down of the star formation is more related to global processes, such as the formation of a spheroidal component.
Various different physical processes contribute to the star formation and stellar mass assembly histories of galaxies. One important approach to understanding the significance of these different ...processes on galaxy evolution is the study of the stellar population content of today's galaxies in a spatially resolved manner. The aim of this paper is to characterize in detail the radial structure of stellar population properties of galaxies in the nearby universe, based on a uniquely large galaxy sample, considering the quality and coverage of the data. The sample under study was drawn from the CALIFA survey and contains 300 galaxies observed with integral field spectroscopy. To study mean trends with overall galaxy properties, the individual radial profiles are stacked in seven bins of galaxy morphology (E, SO,Sa, Sb, Sbc, Sc, and Sd). The galaxies from the sample have decreasing-outward stellar extinction; all spirals show similar radial profiles, independent from the stellar mass, but redder than E and SO. Overall, we conclude that quenching processes act in manners that are independent of mass, while metallicity and galaxy structure are influenced by mass-dependent processes.
The main objective of this work is to check if the star formation efficiency plays a relevant role in the evolution of the relative abundance N/O. In order to explore this idea, we analyse the ...evolution of the nitrogen-to-oxygen ratio as predicted by a set of computed theoretical models. These models consist of simulated galaxies with different total masses which are evolved assuming different collapse time-scales and different star formation efficiencies. The combinations of these two parameters produce different star formation histories, which in turn have, as we show, an important impact on the resulting N/O ratio. Since we want to check the effect of variations in these efficiencies on our model results, the same stellar yield sets are used for all of them. The selected yields have an important primary nitrogen contribution coming from low- and intermediate-mass stars, which implies that N is ejected with a certain delay with respect to O. It allows us to obtain, as we demonstrate, a dispersion of results in the N/O–O/H plane when star formation efficiencies vary which is in general agreement with observations. The model results for the N/O abundance ratio are in good agreement with most observational data trends. In particular, the behaviour shown by the extragalactic H ii regions is well reproduced with present-time resulting abundances. Furthermore, the low N/O values estimated for high-redshift objects, such as those obtained for damped Lyman α galaxies, as well as the higher (and constant) values of N/O observed for irregular and dwarf galaxies or halo stars, can be simultaneously obtained with our models at the same low oxygen abundances 12 + log(O/H) ∼ 7. We therefore conclude that, even though there seems to be a general belief that abundance ratios depend mostly on stellar yields, these are not the only parameter at work when both elements are ejected by stars of different mass ranges, and that differences in the star formation history of galaxies and regions within them are a key factor to explain the data in the N/O–O/H plane.
ABSTRACT
We describe the observations of the low metallicity nearby galaxy AGC 198691 (Leoncino Dwarf) obtained with the Integral Field Unit of the instrument MEGARA at the Gran Telescopio Canarias. ...The observations cover the wavelength ranges 4304–5198 Å and 6098–7306 Å with a resolving power R ≈ 6000. We present 2D maps of the ionized gas, deriving the extension of the H ii region and gas kinematics from the observed emission lines. We have not found any evidence of recent gas infall or loss of metals by means of outflows. This result is supported by the closed-box model predictions, consistent with the oxygen abundance found by other authors in this galaxy and points towards Leoncino being a genuine XMD galaxy. We present for the first time spatially resolved spectroscopy allowing the detailed study of a star-forming region. We use popstar + cloudy models to simulate the emission-line spectrum. We find that the central emission-line spectrum can be explained by a single young ionizing cluster with an age of ≈ 3.5 ± 0.5 Myr and a stellar mass of ≈ 2 $\times \, 10^{3}$ M⊙. However, the radial profiles of ${\rm O\, {\small III}}$ λ 5007Å and the Balmer lines in emission demand photoionization by clusters of different ages between 3.5 and 6.5 Myr that might respond either to the evolution of a single cluster evolving along the cooling time of the nebula (≈ 3 Myr at the metallicity of Leoncino, Z≈ 0.0004) or to mass segregation of the cluster, being both scenarios consistent with the observed equivalent widths of the Balmer lines.
Context. The study of the integrated properties of star-forming galaxies is central to understand their formation and evolution. Some of these properties are extensive and therefore their analysis ...require totally covering and spatially resolved observations. Among these properties, metallicity can be defined in spiral discs by means of integral field spectroscopy (IFS) of individual H ii regions. The simultaneous analysis of the abundances of primary elements, as oxygen, and secondary, as nitrogen, also provides clues about the star formation history and the processes that shape the build-up of spiral discs. Aims. Our main aim is to analyse simultaneously O/H and N/O abundance ratios in H ii regions in different radial positions of the discs in a large sample of spiral galaxies to obtain the slopes and the characteristic abundance ratios that can be related to their integrated properties. Methods. We analysed the optical spectra of individual selected H ii regions extracted from a sample of 350 spiral galaxies of the CALIFA survey. We calculated total O/H abundances and, for the first time, N/O ratios using the semi-empirical routine Hii-Chi-mistry, which, according to Pérez-Montero (2014, MNRAS, 441, 2663), is consistent with the direct method and reduces the uncertainty in the O/H derivation using N ii lines owing to the dispersion in the O/H-N/O relation. Then we performed linear fittings to the abundances as a function of the de-projected galactocentric distances. Results. The analysis of the radial distribution both for O/H and N/O in the non-interacting galaxies reveals that both average slopes are negative, but a non-negligible fraction of objects have a flat or even a positive gradient (at least 10% for O/H and 4% for N/O). The slopes normalised to the effective radius appear to have a slight dependence on the total stellar mass and the morphological type, as late low-mass objects tend to have flatter slopes. No clear relation is found, however, to explain the presence of inverted gradients in this sample, and there is no dependence between the average slopes and the presence of a bar. The relation between the resulting O/H and N/O linear fittings at the effective radius is much tighter (correlation coefficient ρs = 0.80) than between O/H and N/O slopes (ρs = 0.39) or for O/H and N/O in the individual H ii regions (ρs = 0.37). These O/H and N/O values at the effective radius also correlate very tightly (less than 0.03 dex of dispersion) with total luminosity and stellar mass. The relation with other integrated properties, such as star formation rate, colour, or morphology, can be understood only in light of the found relation with mass.
The metallicity of a supernova progenitor, together with its mass, is one of the main parameters that can rule the progenitor's fate. We present the second study of nearby supernova (SN) host ...galaxies (0.005 < z< 0.03) using integral field spectroscopy (IFS) from the CALIFA survey. We analyze the metallicity of 115 galaxies, which hosted 132 SNe within and 10 SNe outside the field of view (FoV) of the instrument. Another 18 galaxies, which hosted only SNe outside the FoV, were also studied. Using the O3N2 calibrator that was described elsewhere, we found no statistically significant differences between the gas-phase metallicities at the locations of the three main SN types - Ia, Ib/c and II; they all have 12 + log(O/H) = 8.50 within 0.02 dex. The total galaxy metallicities are also very similar, and we argue that the reason is that our sample only consists of SNe discovered in massive galaxies (log(M/M sub(middot in circle)) > 10 dex) by targeted searches. We neither found evidence that the metallicity at the SN location differs from the average metallicity at the galactocentric distance of the SNe. By extending our SN sample with published metallicities at the SN location, we are able to study the metallicity distributions for all SN subtypes split into SN discovered in targeted and untargeted searches. We confirm a bias toward higher host masses and metallicities in the targeted searches. By combining data from targeted and untargeted searches, we found a sequence from higher to lower local metallicity: SN Ia, Ic, and II show the highest metallicity, which is significantly higher than those of SN Ib, IIb, and Ic-BL. Our results support the scenario according to which SN Ib result from binary progenitors. Additionally, at least part of the SN Ic are the result of single massive stars that were stripped of their outer layers by metallicity-driven winds. We studied several proxies of the local metallicity that are frequently used in the literature and found that the total host metallicity allows estimating the metallicity at the SN location with an accuracy better than 0.08 dex and very small bias. In addition, weak AGNs that cannot be seen in the total spectrum may weakly bias (by 0.04 dex) the metallicity estimate that is derived from the galaxy-integrated spectrum.
Spiral arms are the most singular features in disc galaxies. These structures can exhibit different patterns, namely grand design and flocculent arms, with easily distinguishable characteristics. ...However, their origin and the mechanisms shaping them are unclear. The overall role of spirals in the chemical evolution of disc galaxies is another unsolved question. In particular, it has not been fully explored if the H ii regions of spiral arms present different properties from those located in the interarm regions. Here we analyse the radial oxygen abundance gradient of the arm and interarm star forming regions of 63 face-on spiral galaxies using CALIFA Integral Field Spectroscopy data. We focus the analysis on three characteristic parameters of the profile: slope, zero-point, and scatter. The sample is morphologically separated into flocculent versus grand design spirals and barred versus unbarred galaxies. We find subtle but statistically significant differences betweenthe arm and interarm distributions for flocculent galaxies, suggesting that the mechanisms generating the spiral structure in these galaxies may be different to those producing grand design systems, for which no significant differences are found. We also find small differences in barred galaxies, not observed in unbarred systems, hinting that bars may affect the chemical distribution of these galaxies but not strongly enough as to be reflected in the overall abundance distribution. In light of these results, we propose bars and flocculent structure as two distinct mechanisms inducing differences in the abundance distribution between arm and interarm star forming regions.
MEGARA-GTC stellar spectral library: I García-Vargas, M L; Carrasco, E; Mollá, M ...
Monthly notices of the Royal Astronomical Society,
03/2020, Letnik:
493, Številka:
1
Journal Article
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ABSTRACT
MEGARA (Multi Espectrógrafo en GTC de Alta Resolución para Astronomía) is an optical (3650–9750 Å), fibre-fed, medium-high spectral resolution (R = 6000, 12 000 and 20 000) instrument for ...the Gran Telescopio CANARIAS (GTC) 10.4-m telescope, commissioned in the summer of 2017, and currently in operation. The scientific exploitation of MEGARA requires a stellar spectra library to interpret galaxy data and to estimate the contribution of the stellar populations. In this paper, we introduce the MEGARA-GTC spectral library, detailing the rationale behind the building of this catalogue. We present the spectra of 97 stars (21 individual stars and 56 members of the globular cluster M15, which are both subsamples taken during the commissioning runs, and 20 stars from our ongoing GTC Open-Time programme). The spectra have R = 20 000 in the HR-R and HR-I set-ups, centred at 6563 and 8633 Å, respectively. We describe the procedures to reduce and analyse the data. Then, we determine the best-fitting theoretical models to each spectrum through a χ2 minimization technique, to derive the stellar physical parameters, and we discuss the results. We have also measured some absorption lines and indices. Finally, we introduce our project to complete the library and the data base in order to make the spectra available to the community.
Abstract
Planetary nebulae (PNe) constitute an important tool to study the chemical evolution of the Milky Way and other galaxies, probing the nucleosynthesis processes, abundance gradients and the ...chemical enrichment of the interstellar medium. In particular, Galactic bulge PNe (GBPNe) have been extensively used in the literature to study the chemical properties of this Galactic structure. However, the presently available GBPN chemical composition studies are strongly biased, since they were focused on brighter objects, predominantly located in Galactic regions of low interstellar reddening. In this work, we report physical parameters and abundances derived for a sample of 17 high-extinction PNe located in the inner 2° of the Galactic bulge, based on low-dispersion spectroscopy secured at the Southern Astrophysical Research telescope using the Goodman spectrograph. The new data allow us to extend our data base including faint objects, providing chemical compositions for PNe located in this region of the bulge and an estimation for the masses of their progenitors to explore the chemical enrichment history of the central region of the Galactic bulge. The results show that there is an enhancement in the N/O abundance ratio in the Galactic Centre PNe compared with PNe located in the outer regions of the Galactic bulge. This may indicate recent episodes of star formation occurring near the Galactic Centre.
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