Based on a combined analysis of SDSS imaging and CALIFA integral field spectroscopy data, we report on the detection of faint (24 <μr mag/□″< 26) star-forming spiral-arm-like features in the ...periphery of three nearby early-type galaxies (ETGs). These features are of considerable interest because they document the still ongoing inside-out growth of some local ETGs and may add valuable observational insight into the origin and evolution of spiral structure in triaxial stellar systems. A characteristic property of the nebular component in the studied ETGs, classified i+, is a two-radial-zone structure, with the inner zone that displays faint (EW(Hα) ≃ 1 Å) low-ionization nuclear emission-line region (LINER) properties, and the outer one (3 Å <EW(Hα)≲ 20 Å) Hii-region characteristics. This spatial segregation of nebular emission in two physically distinct concentric zones calls for an examination of aperture effects in studies of type i+ ETGs with single-fiber spectroscopic data.
We present the first public data release (DR1) of the Calar Alto Legacy Integral Field Area (CALIFA) survey. It consists of science-grade optical datacubes for the first 100 of eventually 600 nearby ...(0.005 < z < 0.03) galaxies, obtained with the integral-field spectrograph PMAS/PPak mounted on the 3.5 m telescope at the Calar Alto observatory. The galaxies in DR1 already cover a wide range of properties in color–magnitude space, morphological type, stellar mass, and gas ionization conditions. This offers the potential to tackle a variety of open questions in galaxy evolution using spatially resolved spectroscopy. Two different spectral setups are available for each galaxy, (i) a low-resolution V500 setup covering the nominal wavelength range 3745–7500 Å with a spectral resolution of 6.0 Å (FWHM), and (ii) a medium-resolution V1200 setup covering the nominal wavelength range 3650–4840 Å with a spectral resolution of 2.3 Å (FWHM). We present the characteristics and data structure of the CALIFA datasets that should be taken into account for scientific exploitation of the data, in particular the effects of vignetting, bad pixels and spatially correlated noise. The data quality test for all 100 galaxies showed that we reach a median limiting continuum sensitivity of 1.0 × 10-18 erg s-1 cm-2 Å-1 arcsec-2 at 5635 Å and 2.2 × 10-18 erg s-1 cm-2 Å-1 arcsec-2 at 4500 Å for the V500 and V1200 setup respectively, which corresponds to limiting r and g band surface brightnesses of 23.6 mag arcsec-2 and 23.4 mag arcsec-2, or an unresolved emission-line flux detection limit of roughly 1 × 10-17 erg s-1 cm-2 arcsec-2 and 0.6 × 10-17 erg s-1 cm-2 arcsec-2, respectively. The median spatial resolution is 3\hbox{$\farcs$}.″7, and the absolute spectrophotometric calibration is better than 15% (1σ). We also describe the available interfaces and tools that allow easy access to this first publicCALIFA data at http://califa.caha.es/DR1.
We use optical integral field spectroscopy (IFS) of nearby supernova (SN) host galaxies (0.005 <z< 0.03) provided by the Calar Alto Legacy Integral Field Area (CALIFA) Survey with the goal of finding ...correlations in the environmental parameters at the location of different SN types. In this first study of a series we focus on the properties related with star formation (SF). We recover the sequence in association of different SN types to the star-forming regions by using several indicators of the ongoing and recent SF related to both the ionized gas and the stellar populations. While the total ongoing SF is on average the same for the three SN types, SNe Ibc/IIb tend to occur closer to star-forming regions and in higher SF density locations than SNe II and SNe Ia; the latter shows the weakest correlation. SNe Ia host galaxies have masses that are on average ~0.3−0.8 dex higher than those of the core collapse (CC) SNe hosts because the SNe Ia hosts contain alarger fraction of old stellar populations. Using the recent SN Ia delay-time distribution and the SFHs of the galaxies, we show that the SN Ia hosts in our sample are expected to produce twice as many SNe Ia as the CC SN hosts. Since both types occur in hosts with a similar SF rate and hence similar CC SN rate, this can explain the mass difference between the SN Ia and CC SN hosts, and reinforces the finding that at least part of the SNe Ia originate from very old progenitors. By comparing the mean SFH of the eight least massive galaxies with that of the massive SF SN Ia hosts, we find that the low-mass galaxies formed their stars during a longer time (0.65%, 24.46%, and 74.89% in the intervals 0–0.42 Gyr, 0.42–2.4 Gyr, and >2.4 Gyr, respectively) than the massive SN Ia hosts (0.04%, 2.01%, and 97.95% in these intervals). We estimate that the low-mass galaxies produce ten times fewer SNe Ia and three times fewer CC SNe than the high-mass group. Therefore the ratio between the number of CC SNe and SNe Ia is expected to increase with decreasing galaxy mass. CC SNe tend to explode at positions with younger stellar populations than the galaxy average, but the galaxy properties at SNe Ia locations are one average the same as the global galaxy properties.
We describe an smooth particle hydrodynamics (SPH) model for chemical enrichment and radiative cooling in cosmological simulations of structure formation. This model includes: (i) the delayed gas ...restitution from stars by means of a probabilistic approach designed to reduce the statistical noise and, hence, to allow for the study of the inner chemical structure of objects with moderately high numbers of particles; (ii) the full dependence of metal production on the detailed chemical composition of stellar particles by using, for the first time in SPH codes, the Qij matrix formalism that relates each nucleosynthetic product to its sources and (iii) the full dependence of radiative cooling on the detailed chemical composition of gas particles, achieved through a fast algorithm using a new metallicity parameter ζ(T) that gives the weight of each element on the total cooling function. The resolution effects and the results obtained from this SPH chemical model have been tested by comparing its predictions in different problems with known theoretical solutions. We also present some preliminary results on the chemical properties of elliptical galaxies found in self-consistent cosmological simulations. Such simulations show that the above ζ-cooling method is important to prevent an overestimation of the metallicity-dependent cooling rate, whereas the Qij formalism is important to prevent a significant underestimation of the α/Fe ratio in simulated galaxy-like objects.
This is the second paper of a series reporting the results from the popstar evolutionary synthesis models. Here, we present synthetic emission-line spectra of H ii regions photoionized by young star ...clusters, for seven values of cluster masses and for ages between 0.1 and 5.2 Myr. The ionizing spectral energy distributions (SEDs) are those obtained by the popstar code for six different metallicities, with a very low-metallicity set, Z= 0.0001, not included in previous similar works. We assume that the radius of the H ii region is the distance at which the ionized gas is deposited by the action of the mechanical energy of the winds and supernovae from the central ionizing young cluster. In this way, the ionization parameter is eliminated as free argument, since now its value is obtained from the cluster physical properties (mass, age and metallicity) and from the gaseous medium characteristics (density and abundances). We discuss our results and compare them with those from previous models and also with a large data set of giant H ii regions for which abundances have been derived in a homogeneous manner. The values of the O iii lines (at λλ 4363, 4959, 5007 Å) in the lowest metallicity nebulae are found to be very weak and similar to those coming from very high-metallicity regions (solar or oversolar). Thus, the sole use of the oxygen lines is not enough to distinguish between very low and very high metallicity regions. In these cases, we emphasize the need of the additional support of alternative metallicity tracers, like the S iii lines in the near-infrared.
This is the third paper of a series reporting the results from the popstar evolutionary synthesis models. The main goal of this work is to present and discuss the synthetic photometric properties of ...single stellar populations resulting from our popstar code. Colours in the Johnson and Sloan Digital Sky Survey (SDSS) systems, Hα and Hβ luminosities and equivalent widths, and ionizing region size, have been computed for a wide range of metallicity (Z = 0.0001-0.05) and age (0.1 Myr to 20 Gyr). We calculate the evolution of the cluster and the region geometry in a consistent manner. We demonstrate the importance of the contribution of emission lines to broader band photometry when characterizing stellar populations, through the presentation of both contaminated and non-contaminated colours (in both the Johnson and SDSS systems). The tabulated colours include stellar and nebular components, in addition to line emission. The main application of these models is the determination of physical properties of a given young ionizing cluster, when only photometric observations are available; for an isolated star-forming region, the young star cluster models can be used, free from the contamination of any underlying background stellar population. In most cases, however, the ionizing population is usually embedded in a large and complex system, and the observed photometric properties result from the combination of a young star-forming burst and the underlying older population of the host. Therefore, the second objective of this paper is to provide a grid of models useful in the interpretation of mixed regions where the separation of young and old populations is not sufficiently reliable. We describe the set of popstar spectral energy distributions (SEDs), and the derived colours for mixed populations where an underlying host population is combined in different mass-ratios with a recent ionizing burst. These colours, together with other common photometric parameters, such as the Hα radius of the ionized region, and Balmer line equivalent widths and luminosities, allow one to infer the physical properties of star-forming regions even in the absence of spectroscopic information.
Context. The oxygen and nitrogen-to-oxygen abundances relation is characterized by a plateau around log(N/O) = –1.6 at metallicities lower than 12+log(O/H) ~ 8.25. However, there is a subset of blue ...compact dwarf galaxies (BCDs) with unexpectedly high N/O values. Aims. We want to study the spatial distribution of the physical properties and of oxygen and nitrogen abundances in three BCDs (HS 0128+2832, HS 0837+4717, and Mrk 930) with a reported excess of N/O in order to investigate the nature of this excess and, particularly, its association with Wolf-Rayet (WR) stars. Methods. We observed these BCDs by using PMAS integral field spectroscopy in the optical spectral range (3700–6900 Å) and mapping the brightest emission lines, hence their interstellar medium (ISM) physical-chemical properties (reddening, excitation, electron density and temperature, and O and N chemical abundances), using both the direct method and appropriate strong-line methods. We made a statistical analysis of the resulting distributions and compared them with the integrated properties of the galaxies. Results. Outer parts of the three galaxies are placed in the “AGN-zone” of the Nii/Hα vs. Oiii/Hβ diagnostic diagram most likely due to a high N/O combined with the excitation structure in these regions. From the statistical analysis, it is assumed that a certain property can be considered as spatially homogeneous (or uniform) if a normal Gaussian function fits its distribution in several regions of the galaxy. Moreover, a disagreement between the integrated properties and the mean values of the distribution usually appears when a Gaussian does not fit the corresponding distribution. We find that 1) for HS 0128+2832, only the N/O ratio as derived from the direct method is uniform; 2) for HS 0837+4717, all properties are uniform; and 3) for Mrk 930, the uniformity is found for all parameters, except for electron density and reddening. The rotation curve, the Hα map, and UV images reveal a perturbed morphology and possible interacting processes in Mrk 930. Finally, if the N/O is constant on spatial scales of several kpc, as our analysis indicates, we conclude that there are not enough WR stars estimated from spectroscopy to pollute the ISM and to produce the observed N/O excess in these objects.
We present an analysis of the gas-phase oxygen abundances of a sample of 28 galaxies in the local Universe (z < 0.02) hosting Type Ia supernovae (SNe Ia). The data were obtained with the 4.2 m ...William Herschel Telescope. We derive local oxygen abundances for the regions where the SNe Ia exploded by calculating oxygen gradients through each galaxy (when possible) or assuming the oxygen abundance of the closest H ii region. The sample selection only considered galaxies for which distances not based on the SN Ia method are available. Then, we use a principal component analysis to study the dependence of the absolute magnitudes on the colour of the SN Ia, the oxygen abundances of the region where they exploded and the stretch of the SN light curve. We demonstrate that our previous result suggesting a metallicity dependence on the SN Ia luminosity for non-reddened SNe Ia can be extended to our whole sample. These results reinforce the need of including a metallicity proxy, such as the oxygen abundance of the host galaxy, to minimize the systematic effect induced by the metallicity dependence of the SN Ia luminosity in future studies of SNe Ia at cosmological distances.
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