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We study the young star cluster populations in 23 dwarf and irregular galaxies observed by the Hubble Space Telescope (HST) Legacy ExtraGalactic Ultraviolet Survey (LEGUS), and examine relationships between the ensemble properties of the cluster populations and those of their host galaxies: star formation rate (SFR) density (ΣSFR). A strength of this analysis is the availability of SFRs measured from temporally resolved star formation histories that provide the means to match cluster and host galaxy properties on several time-scales (1–10, 1–100, and 10–100 Myr). Nevertheless, studies of this kind are challenging for dwarf galaxies due to the small numbers of clusters in each system. We mitigate these issues by combining the clusters across different galaxies with similar ΣSFR properties. We find good agreement with a well-established relationship (⁠|$M_{V}^{\mathrm{ brightest}}$| –SFR), but find no significant correlations between ΣSFR and the slopes of the cluster luminosity function, mass function, nor the age distribution. We also find no significant trend between the fraction of stars in bound clusters at different age ranges (Γ1–10, Γ10–100, and Γ1–100) and ΣSFR of the host galaxy. Our data show a decrease in Γ over time (from 1–10 to 10–100 Myr) suggesting early cluster dissolution, though the presence of unbound clusters in the youngest time bin makes it difficult to quantify the degree of dissolution. While our data do not exhibit strong correlations between ΣSFR and ensemble cluster properties, we cannot rule out that a weak trend might exist given the relatively large uncertainties due to low number statistics and the limited ΣSFR range probed. [ABSTRACT FROM AUTHOR]

Scaling laws of dust, H  i gas, and metal mass with stellar mass, specific star formation rate, and metallicity are crucial to our understanding of the build-up of galaxies through their enrichment with metals and dust. In this work, we analyse how the dust and metal content varies with specific gas mass (M H  i / M ⋆) across a diverse sample of 423 nearby galaxies. The observed trends are interpreted with a set of Dust and Element evolUtion modelS (DEUS) – including stellar dust production, grain growth, and dust destruction – within a Bayesian framework to enable a rigorous search of the multidimensional parameter space. We find that these scaling laws for galaxies with −1.0 ≲ log  M H  i / M ⋆ ≲ 0 can be reproduced using closed-box models with high fractions (37–89  |${{\ \rm per\ cent}}$|⁠) of supernova dust surviving a reverse shock, relatively low grain growth efficiencies (ϵ = 30–40), and long dust lifetimes (1–2 Gyr). The models have present-day dust masses with similar contributions from stellar sources (50–80  |${{\ \rm per\ cent}}$|⁠) and grain growth (20–50  |${{\ \rm per\ cent}}$|⁠). Over the entire lifetime of these galaxies, the contribution from stardust (>90  |${{\ \rm per\ cent}}$|⁠) outweighs the fraction of dust grown in the interstellar medium (<10  |${{\ \rm per\ cent}}$|⁠). Our results provide an alternative for the chemical evolution models that require extremely low supernova dust production efficiencies and short grain growth time-scales to reproduce local scaling laws, and could help solving the conundrum on whether or not grains can grow efficiently in the interstellar medium. [ABSTRACT FROM AUTHOR]

We present a study correlating the spatial locations of young star clusters with those of molecular clouds in NGC 5194, in order to investigate the time-scale over which clusters separate from their birth clouds. The star cluster catalogues are from the Legacy ExtraGalactic UV Survey (LEGUS) and the molecular clouds from the Plateau de Bure Interefrometer Arcsecond Whirpool Survey (PAWS). We find that younger star clusters are spatially closer to molecular clouds than older star clusters. The median age for clusters associated with clouds is 4 Myr, whereas it is 50 Myr for clusters that are sufficiently separated from a molecular cloud to be considered unassociated. After ∼6 Myr, the majority of the star clusters lose association with their molecular gas. Younger star clusters are also preferentially located in stellar spiral arms where they are hierarchically distributed in kpc-size regions for 50–100 Myr before dispersing. The youngest star clusters are more strongly clustered, yielding a two-point correlation function with α = −0.28 ± 0.04, than the giant molecular cloud (GMCs) (α = −0.09 ± 0.03) within the same PAWS field. However, the clustering strength of the most massive GMCs, supposedly the progenitors of the young clusters for a star formation efficiency of a few per cent, is comparable (α = −0.35 ± 0.05) to that of the clusters. We find a galactocentric dependence for the coherence of star formation, in which clusters located in the inner region of the galaxy reside in smaller star-forming complexes and display more homogeneous distributions than clusters further from the centre. This result suggests a correlation between the survival of a cluster complex and its environment. [ABSTRACT FROM AUTHOR]

We have fit the far-ultraviolet (FUV) to sub-millimeter (850 μm) spectral energy distributions (SEDs) of the 61 galaxies from the Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel (KINGFISH). The fitting has been performed using three models: the Code for Investigating GALaxy Evolution (CIGALE), the GRAphite-SILicate approach (GRASIL), and the Multiwavelength Analysis of Galaxy PHYSical properties (MAGPHYS). We have analyzed the results of the three codes in terms of the SED shapes, and by comparing the derived quantities with simple "recipes" for stellar mass (Mstar), star-formation rate (SFR), dust mass (Mdust), and monochromatic luminosities. Although the algorithms rely on different assumptions for star-formation history, dust attenuation and dust reprocessing, they all well approximate the observed SEDs and are in generally good agreement for the associated quantities. However, the three codes show very different behavior in the mid-infrared regime: in the 5–10 μm region dominated by PAH emission, and also between 25 and 70 μm where there are no observational constraints for the KINGFISH sample. We find that different algorithms give discordant SFR estimates for galaxies with low specific SFR, and that the standard recipes for calculating FUV absorption overestimate the extinction compared to the SED-fitting results. Results also suggest that assuming a "standard" constant stellar mass-to-light ratio overestimates Mstar relative to the SED fitting, and we provide new SED-based formulations for estimating Mstar from WISE W1 (3.4 μm) luminosities and colors. From a principal component analysis of Mstar, SFR, Mdust, and O/H, we reproduce previous scaling relations among Mstar, SFR, and O/H, and find that Mdust can be predicted to within ∼0.3 dex using only Mstar and SFR. [ABSTRACT FROM AUTHOR]

We present an investigation of the relationship between giant molecular cloud (GMC) properties and the associated stellar clusters in the nearby flocculent galaxy NGC 7793. We combine the star cluster catalogue from the HST LEGUS (Legacy ExtraGalactic UV Survey) programme with the 15 pc resolution ALMA CO(2–1) observations. We find a strong spatial correlation between young star clusters and GMCs such that all clusters still associated with a GMC are younger than 11 Myr and display a median age of 2 Myr. The age distribution increases gradually as the cluster–GMC distance increases, with star clusters that are spatially unassociated with molecular gas exhibiting a median age of 7 Myr. Thus, star clusters are able to emerge from their natal clouds long before the time-scale required for clouds to disperse. To investigate if the hierarchy observed in the stellar components is inherited from the GMCs, we quantify the amount of clustering in the spatial distributions of the components and find that the star clusters have a fractal dimension slope of −0.35 ± 0.03, significantly more clustered than the molecular cloud hierarchy with slope of −0.18 ± 0.04 over the range 40–800 pc. We find, however, that the spatial clustering becomes comparable in strength for GMCs and star clusters with slopes of −0.44 ± 0.03 and −0.45 ± 0.06, respectively, when we compare massive (>105 M⊙) GMCs to massive and young star clusters. This shows that massive star clusters trace the same hierarchy as their parent GMCs, under the assumption that the star formation efficiency is a few per cent. [ABSTRACT FROM AUTHOR]

Context. The relative abundance of the dust grain types in the interstellar medium is directly linked to physical quantities that trace the evolution of galaxies. Because of the poor spatial resolution of the infrared and submillimetre data, we are able to study the dependence of the resolved infrared spectral energy distribution (SED) across regions of the interstellar medium (ISM) with different physical properties in just a few objects. Aims. We aim to study the dust properties of the whole disc of M 33 at spatial scales of ~170 pc. This analysis allows us to infer how the relative dust grain abundance changes with the conditions of the ISM, study the existence of a submillimetre excess and look for trends of the gas-to-dust mass ratio (GDR) with other physical properties of the galaxy. Methods. For each pixel in the disc of M 33 we have fitted the infrared SED using a physically motivated dust model that assumes an emissivity index β close to two. We applied a Bayesian statistical method to fit the individual SEDs and derived the best output values from the study of the probability density function of each parameter. We derived the relative amount of the different dust grains in the model, the total dust mass, and the strength of the interstellar radiation field (ISRF) heating the dust at each spatial location. Results. The relative abundance of very small grains tends to increase, and for big grains to decrease, at high values of Hα luminosity. This shows that the dust grains are modified inside the star-forming regions, in agreement with a theoretical framework of dust evolution under different physical conditions. The radial dependence of the GDR is consistent with the shallow metallicity gradient observed in this galaxy. The strength of the ISRF derived in our model correlates with the star formation rate in the galaxy in a pixel by pixel basis. Although this is expected, it is the first time that a correlation between the two quantities has been reported. We have produced a map of submillimetre excess in the 500 μm SPIRE band for the disc of M 33. The excess can be as high as 50% and increases at large galactocentric distances. We further studied the relation of the excess with other physical properties of the galaxy and find that the excess is prominent in zones of diffuse ISM outside the main star-forming regions, where the molecular gas and dust surface density are low. [ABSTRACT FROM AUTHOR]

We acquired spectra of 141HII regions in 10 late-type lowsurface brightness galaxies (LSBGs). The analysis of the chemical abundances obtained from the nebular emission lines shows that metallicity gradients are a common feature of LSBGs, contrary to previous claims concerning the absence of such gradients in this class of galaxies. The average slope, when expressed in units of the isophotal radius, is found to be significantly shallower in comparison to galaxies of high surface brightness. This result can be attributed to the reduced surface brightness range measured across their discs, when combined with a universal surface mass density-metallicity relation. With a similar argument we explain the common abundance gradient observed in high surface brightness galaxy (HSBG) discs and its approximate dispersion. This conclusion is reinforced by our result that LSBGs share the same common abundance gradient with HSBGs, when the slope is expressed in terms of the exponential disc scalelength. [ABSTRACT FROM AUTHOR]

Context. Over the past decade, 3D optical spectroscopy has become the preferred tool for understanding the properties of galaxies and is now increasingly used to carry out galaxy surveys. Low redshift surveys include SAURON, DiskMass, ATLAS3D, PINGS, and VENGA. At redshifts above 0.7, surveys such as MASSIV, SINS, GLACE, and IMAGES have targeted the most luminous galaxies to study mainly their kinematic properties. The on-going CALIFA survey (z ~ 0.02) is the first of a series of upcoming integral field spectroscopy (IFS) surveys with large samples representative of the entire population of galaxies. Others include SAMI and MaNGA at lower redshift and the upcoming KMOS surveys at higher redshift. Given the importance of spatial scales in IFS surveys, the study of the effects of spatial resolution on the recovered parameters becomes important. Aims. We explore the capability of the CALIFA survey and a hypothetical higher redshift survey to reproduce the properties of a sample of objects observed with better spatial resolution at lower redshift. Methods. Using a sample of PINGS galaxies, we simulated observations at different redshifts. We then studied the behaviour of different parameters as the spatial resolution degrades with increasing redshift. Results. We show that at the CALIFA resolution, we are able to measure and map common observables in a galaxy study: the number and distribution of Hii regions (Ha flux structure), the gas metallicity (using the O3N2 method), the gas ionization properties (through the [Nii]/Ha and [O iii]/Hß line ratios), and the age of the underlying stellar population (using the D4000 index). This supports the aim of the survey to characterise the observable properties of galaxies in the Local Universe. Our analysis of simulated IFS data cubes at higher redshifts highlights the importance of the projected spatial scale per spaxel as the most important figure of merit in the design of an integral field survey. [ABSTRACT FROM AUTHOR]

Context. Galaxies, which often contain ionised gas, sometimes also exhibit a so-called low-ionisation nuclear emission line region (LINER). For 30 years, this was attributed to a central mass-accreting supermassive black hole (more commonly known as active galactic nucleus, AGN) of low luminosity, making LINER galaxies the largest AGN sub-population, which dominate in numbers over higher luminosity Seyfert galaxies and quasars. This, however, poses a serious problem. While the inferred energy balance is plausible, many LINERs clearly do not contain any other independent signatures of an AGN. Aims. Using integral field spectroscopic data from the CALIFA survey, we compare the observed radial surface brightness profiles with what is expected from illumination by an AGN. Methods. Essential for this analysis is a proper extraction of emission lines, especially weak lines, such as Balmer Hβ lines, which are superposed on an absorption trough. To accomplish this, we use the GANDALF code, which simultaneously fits the underlying stellar continuum and emission lines. Results. For 48 galaxies with LINER-like emission, we show that the radial emission-line surface brightness profiles are inconsistent with ionisation by a central point-source and hence cannot be due to an AGN alone. Conclusions. The most probable explanation for the excess LINER-like emission is ionisation by evolved stars during the short but very hot and energetic phase known as post-AGB. This leads us to an entirely new interpretation. Post-AGB stars are ubiquitous and their ionising effect should be potentially observable in every galaxy with the gas present and with stars older than ∼1 Gyr unless a stronger radiation field from young hot stars or an AGN outshines them. This means that galaxies with LINER-like emission are not a class defined by a property but rather by the absence of a property. It also explains why LINER emission is observed mostly in massive galaxies with old stars and little star formation [ABSTRACT FROM AUTHOR]

When combined with infrared observations with the Spitzer telescope (3 to 160 μm), the Herschel Space Observatory now fully samples the thermal dust emission up to 500 μm and enables us to better estimate the total infrared-submm energy budget (LTIR) of nearby galaxies. We present new empirical calibrations to estimate resolved and integrated total infrared luminosities from Spitzer and Herschel bands used as monochromatic or combined tracers. We base our calibrations on resolved elements of nearby galaxies (3 to 30 Mpc) observed with Herschel. We perform a resolved spectral energy distribution (SED) modelling of these objects using the Draine & Li dust models and investigate the influence of the addition of Spectral and Photometric Imaging Receiver (SPIRE) measurements in the estimation of LTIR. We find that using data up to 250 μm leads to local LTIR values consistent with those obtained with a complete coverage (up to 500 μm) within ±10 per cent for most of our resolved elements. We then study the distribution of energy in the resolved SEDs of our galaxies. The bulk of energy (30–50 per cent) is contained in the [70–160 μm] band. The [24–70 μm] fraction decreases with increasing metallicity. The [160–1100 μm]submillimetre band can account for up to 25 per cent of the LTIR in metal-rich galaxies. We investigate the correlation between the total infrared (TIR) surface brightnesses/luminosities and monochromatic Spitzer and Herschel surface brightnesses/luminosities. The three Photodetector Array Camera and Spectrometer (PACS) bands can be used as reliable monochromatic estimators of the LTIR, the 100 μm band being the most reliable monochromatic tracer. There is also a strong correlation between the SPIRE 250 μm and LTIR, although with more scatter than for the PACS relations. We also study the ability of our monochromatic relations to reproduce integrated LTIR of nearby galaxies as well as LTIR of z ∼ 1–3 sources. Finally, we provide calibration coefficients that can be used to derive TIR surface brightnesses/luminosities from a combination of Spitzer and Herschel surface brightnesses/fluxes and analyse the associated uncertainties. [ABSTRACT FROM AUTHOR]

ABSTRACT Taking advantage of the unprecedented combination of sensitivity and angular resolution afforded by the Herschel Space Observatory at far-infrared and submillimetre wavelengths, we aim to characterize the physical properties of cold dust within nearby galaxies, as well as the associated uncertainties, namely the robustness of the parameters we derive using different modified blackbody models. For a pilot subsample of the KINGFISH (Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel) key programme, we perform two-temperature fits of the Spitzer and Herschel photometric data (from 24 to 500 μm), with a warm and a cold component, both globally and in each resolution element. We compare the results obtained from different analysis strategies. At global scale, we observe a range of values of the modified blackbody fit parameters βc (0.8-2.5) and Tc (19.1-25.1 K). We compute maps of our modelling parameters with βc fixed or treated as a free parameter to test the robustness of the temperature and dust surface density maps we deduce. When the emissivity is fixed, we observe steeper temperature gradients as a function of radius than when it is allowed to vary. When the emissivity is fitted as a free parameter, barred galaxies tend to have uniform fitted emissivities. Gathering the parameters obtained in each resolution element in a Tc-βc diagram underlines an anticorrelation between the two parameters. It remains difficult to assess whether the dominant effect is the physics of dust grains, noise, or mixing along the line of sight and in the beam. We finally observe in both cases that the dust column density peaks in central regions of galaxies and bar-ends (coinciding with molecular gas density enhancements usually found in these locations). We also quantify how the total dust mass varies with our assumptions about the emissivity index as well as the influence of the wavelength coverage used in the fits. We show that modified blackbody fits using a shallow emissivity (β < 2.0) lead to significantly lower dust masses compared to the β < 2.0 case, with dust masses lower by up to 50 per cent if βc = 1.5, for instance. The working resolution affects our total dust mass estimates: masses increase from global fits to spatially resolved fits. [ABSTRACT FROM AUTHOR]

We present observational evidence that leakage of ionizing photons from star-forming regions can affect the quantification of the star formation rate (SFR) in galaxies. This effect could partially explain the differences between the SFR estimates using the far-ultraviolet (FUV) and the Hα emission. We find that leakage could decrease the SFR(Hα)/SFR(FUV) ratio by up to 25 per cent. The evidence is based on the observation that the SFR(Hα)/SFR(FUV) ratio is lower for objects showing a shell Hα structure than for regions exhibiting a much more compact morphology. The study has been performed on three object samples: low-luminosity dwarf galaxies from the Local Volume Legacy survey, star-forming regions in the Large Magellanic Cloud and the nearby Local Group galaxy M33. For the three samples we find differences (1.1σ–1.4σ) between the SFR(Hα)/SFR(FUV) for compact and shell objects. Although leakage cannot entirely explain the observed trend of SFR(Hα)/SFR(FUV) ratios for systems with low SFR, we show that the mechanism can lead to different SFR estimates when using Hα and FUV luminosities. Therefore, further study is needed to constrain the contribution of leakage to the low SFR(Hα)/SFR(FUV) ratios observed in dwarf galaxies and its impact on the Hα flux as an SFR indicator in such objects. [ABSTRACT FROM AUTHOR]

The final product of galaxy evolution through cosmic time is the population of galaxies in the local universe. These galaxies are also those that can be studied in most detail, thus providing a stringent benchmark for our understanding of galaxy evolution. Through the huge success of spectroscopic single-fiber, statistical surveys of the Local Universe in the last decade, it has become clear, however, that an authoritative observational description of galaxies will involve measuring their spatially resolved properties over their full optical extent for a statistically significant sample. We present here the Calar Alto Legacy Integral Field Area (CALIFA) survey, which has been designed to provide a first step in this direction. We summarize the survey goals and design, including sample selection and observational strategy. We also showcase the data taken during the first observing runs (June/July 2010) and outline the reduction pipeline, quality control schemes and general characteristics of the reduced data. This survey is obtaining spatially resolved spectroscopic information of a diameter selected sample of ∼600 galaxies in the Local Universe (0.005 < z < 0.03). CALIFA has been designed to allow the building of two-dimensional maps of the following quantities: (a) stellar populations: ages and metallicities; (b) ionized gas: distribution, excitation mechanism and chemical abundances; and (c) kinematic properties: both from stellar and ionized gas components. CALIFA uses the PPAK integral field unit (IFU), with a hexagonal field-of-view of ∼1.3', with a 100% covering factor by adopting a three-pointing dithering scheme. The optical wavelength range is covered from 3700 to 7000 Å, using two overlapping setups (V500 and V1200), with different resolutions: R ∼ 850 and R ∼ 1650, respectively. CALIFA is a legacy survey, intended for the community. The reduced data will be released, once the quality has been guaranteed. The analyzed data fulfill the expectations of the original observing proposal, on the basis of a set of quality checks and exploratory analysis: (i) the final datacubes reach a 3σ limiting surface brightness depth of ∼23.0 mag/arcsec2 for the V500 grating data (∼22.8 mag/arcsec2 for V1200); (ii) about ∼70% of the covered field-of-view is above this 3σ limit; (iii) the data have a blue-to-red relative flux calibration within a few percent in most of the wavelength range; (iv) the absolute flux calibration is accurate within ∼8% with respect to SDSS; (v) the measured spectral resolution is ∼85 km s-1 for V1200 (∼150 km s-1 for V500); (vi) the estimated accuracy of the wavelength calibration is ∼5 km s-1 for the V1200 data (∼10 km s-1 for the V500 data); (vii) the aperture matched CALIFA and SDSS spectra are qualitatively and quantitatively similar. Finally, we show that we are able to carry out all measurements indicated above, recovering the properties of the stellar populations, the ionized gas and the kinematics of both components. The associated maps illustrate the spatial variation of these parameters across the field, reemphasizing the redshift dependence of single aperture spectroscopic measurements. We conclude from this first look at the data that CALIFA will be an important resource for archaeological studies of galaxies in the Local Universe. [ABSTRACT FROM AUTHOR]

Aims. The core collapse supernova rate provides a strong lower limit for the star formation rate (SFR). Progress in using it as a cosmic SFR tracer requires some confidence that it is consistent with more conventional SFR diagnostics in the nearby Universe. This paper compares standard SFR measurements based on Hα, far ultraviolet (FUV) and total infrared (TIR) galaxy luminosities with the observed core collapse supernova rate in the same galaxy sample. The comparison can be viewed from two perspectives. Firstly, by adopting an estimate of the minimum stellar mass to produce a core collapse supernova one can determine a SFR from supernova numbers. Secondly, the radiative SFR can be assumed to be robust and then the supernova statistics provide a constrain on the minimum stellar mass for core collapse supernova progenitors. Methods. The novel aspect of this study is that Hα, FUV and TIR luminosities are now available for a complete galaxy sample within the local 11 Mpc volume and the number of discovered supernovae in this sample within the last 13 years is high enough to perform a meaningful statistical comparison. We exploit the multi-wavelength dataset from 11 HUGS, a volume-limited survey designed to provide a census of SFR in the Local Volume. There are 14 supernovae discovered in this sample of galaxies within the last 13 years. Although one could argue that this may not be complete, it is certainly a robust lower limit. Results. Assuming a lower limit for core collapse of 8 M☉ (as proposed by direct detections of SN progenitor stars and white dwarf progenitors), the core-collapse supernova rate matches the SFR from the FUV luminosity. However, the SFR based on Hα luminosity is lower than these two estimates by a factor of nearly 2. If we assume that the FUV or Hα based luminosities are a true reflection of the SFR, we find that the minimum mass for core collapse supernova progenitors is 8 ±1 M☉ and 6 ±1 M☉, respectively. Conclusions. The estimate of the minimum mass for core collapse supernova progenitors obtained exploiting FUV data is in good agreement with that from the direct detection of supernova progenitors. The concordant results by these independent methods point toward a constraint of 8 ±1 M☉ on the lower mass limit for progenitor stars of core collapse supernovae. [ABSTRACT FROM AUTHOR]

ABSTRACT In this second paper of the series, we present the two-dimensional (2D) emission line abundance analysis of NGC 628, the largest object within the PPAK Integral Field Spectroscopy (IFS) Nearby Galaxies Survey, PINGS. We introduce the methodology applied to the 2D IFS data in order to extract and deal with large spectral samples, from which a 2D abundance analysis can be later performed. We obtain the most complete and reliable abundance gradient of the galaxy up to date, by using the largest number of spectroscopic points sampled in the galaxy, and by comparing the statistical significance of different strong-line metallicity indicators. We find features not previously reported for this galaxy that imply a multimodality of the abundance gradient consistent with a nearly flat distribution in the innermost regions of the galaxy, a steep negative gradient along the disc and a shallow gradient or nearly constant metallicity beyond the optical edge of the galaxy. The N/O ratio seems to follow the same radial behaviour. We demonstrate that the observed dispersion in metallicity shows no systematic dependence with the spatial position, signal-to-noise ratio or ionization conditions, implying that the scatter in abundance for a given radius is reflecting a true spatial physical variation of the oxygen content. Furthermore, by exploiting the 2D IFS data, we were able to construct the 2D metallicity structure of the galaxy, detecting regions of metal enhancement and showing that they vary depending on the choice of the metallicity estimator. The analysis of axisymmetric variations in the disc of NGC 628 suggest that the physical conditions and the star formation history of different symmetric regions of the galaxy have evolved in a different manner. [ABSTRACT FROM AUTHOR]

This paper, the first of two, introduces an observational study of spiral structure in galaxies chosen from the Spitzer Infrared Nearby Galaxies Survey (SINGS). Near-infrared (NIR) and optical data are used to produce mass surface density maps, and from these the morphology of the disc is examined. The aim of this work is to characterize the prevalence of spiral structure in this sample and, in the cases where a clear spiral pattern is found, include the findings in a comparative study (reported in Paper II). A two-armed ('grand design') spiral pattern is found in approximately half of the galaxies studied, including all those that are designated as grand design in the optical, but also including some, but not all, optically flocculent galaxies. It is found that the level of non-axisymmetric structure in the galaxies' mass distributions is only modestly higher in those galaxies that are classified as 'grand design' compared with those that are not, implying that non-grand design galaxies possess significant power in higher order modes. There is no evidence that bars preferentially trigger the spirals, but they do appear to stir up non-axisymmetric structure in the disc. In contrast, there is evidence that strong/close tidal interactions with companion galaxies are associated with strong two-armed spiral structure in the IR, though there are a number of galaxies with relatively weak IR spiral structure that do not possess such companions. [ABSTRACT FROM AUTHOR]

We present a study of the variation of spatial structure of stellar populations within dwarf galaxies as a function of the population age. We use deep Hubble Space Telescope/Advanced Camera for Surveys imaging of nearby dwarf galaxies in order to resolve individual stars and create composite colour-magnitude diagrams (CMDs) for each galaxy. Using the obtained CMDs, we select blue helium burning stars, which can be unambiguously age-dated by comparing the absolute magnitude of individual stars with stellar isochrones. Additionally, we select a very young () population of OB stars for a subset of the galaxies based on the tip of the young main sequence. By selecting stars in different age ranges, we can then study how the spatial distribution of these stars evolves with time. We find, in agreement with previous studies, that stars are born within galaxies with a high degree of substructure which is made up of a continuous distribution of clusters, groups and associations from parsec to hundreds of parsec scales. These structures disperse on time-scales of tens to hundreds of Myr, which we quantify using the two-point correlation function and the Q-parameter developed by Cartwright & Whitworth. On galactic scales, we can place lower limits on the time it takes to remove the original structure (i.e. structure survives for at least this long), t, which varies between (NGC 2366) and (DDO 165). This is similar to what we have found previously for the Small Magellanic Cloud () and the Large Magellanic Cloud (). We do not find any strong correlations between t and the luminosity of the host galaxy. [ABSTRACT FROM AUTHOR]

Using deep Subaru/Faint Object Camera And Spectrograph (FOCAS) spectra of 34 H regions in both the inner and outer parts of the extended ultraviolet (XUV) disc galaxy NGC 4625 we have measured an abundance gradient out to almost 2.5 times the optical isophotal radius. We applied several strong line abundance calibrations to determine the H region abundances, including , [N ]/[O ], [N ]/H as well as the [O ]4363 auroral line, which we detected in three of the H regions. We find that at the transition between the inner and outer disc the abundance gradient becomes flatter. In addition, there appears to be an abundance discontinuity in proximity of this transition. Several of our target H regions appear to deviate from the ionization sequence defined in the [N ]/H versus [O ]/H diagnostic diagram by bright extragalactic H regions. Using theoretical models we conclude that the most likely explanations for these deviations are either related to the time evolution of the H regions or stochastic variations in the ionizing stellar populations of these low-mass H regions, although we are unable to distinguish between these two effects. Such effects can also impact on the reliability of the strong line abundance determinations. [ABSTRACT FROM AUTHOR]

We present a wide-field Integral Field Spectroscopy (IFS) survey on the nearby face-on Sbc galaxy NGC 628, comprising 11094 individual spectra, covering a nearly circular field-of-view of ∼6 arcmin in diameter, with a sampling of ∼2.7 arcsec per spectrum in the optical wavelength range (3700-7000 Å). This galaxy is part of the PPAK IFS Nearby Galaxies Survey (PINGS). To our knowledge, this is the widest spectroscopic survey ever made in a single nearby galaxy. A detailed flux calibration was applied, granting a spectrophotometric accuracy of ∼0.2 mag. The spectroscopic data were analysed both as a single integrated spectrum that characterizes the global properties of the galaxy and using each individual spectrum to determine the spatial variation of the stellar and ionized gas components. The spatial distribution of the luminosity-weighted ages and metallicities of the stellar populations was analysed. Using typical strong emission-line ratios we derived the integrated and 2D spatial distribution of the ionized gas, the dust content, star formation rate (SFR) and oxygen abundance. The age of the stellar populations shows a negative gradient from the inner (older) to the outer (younger) regions. We found an inversion of this gradient in the central ∼1 kpc region, where a somewhat younger stellar population is present within a ring at this radius. This structure is associated with a circumnuclear star-forming region at ∼500 pc, also found in similar spiral galaxies. From the study of the integrated and spatially resolved ionized gas, we found a moderate SFR of . The oxygen abundance shows a clear gradient of higher metallicity values from the inner part to the outer part of the galaxy, with a mean value of 12 + log(O/H) ∼ 8.7. At some specific regions of the galaxy, the spatially resolved distribution of the physical properties shows some level of structure, suggesting real point-to-point variations within an individual H region. Our results are consistent with an inside-out growth scheme, with stronger star formation at the outer regions, and with evolved stellar populations in the inner ones. [ABSTRACT FROM AUTHOR]

We have compared far-ultraviolet (FUV), near-ultraviolet (NUV) and Hα measurements for star-forming regions in 21 galaxies, in order to characterize the properties of their discs at radii beyond the main optical radius ( R25). In our representative sample of extended and non-extended ultraviolet (UV) discs, we find that half of the extended UV discs also exhibit extended Hα emission. We find that extended UV discs fall into two categories: those with a sharp truncation in the Hα disc close to the optical edge ( R25), and those with extended emission in Hα as well as in the UV. Although most galaxies with strong Hα truncations near R25 show a significant corresponding falloff in UV emission (a factor of 10–100), the transition tends to be much smoother than in Hα, and significant UV emission often extends well beyond this radius, confirming earlier results by Thilker et al. and others. After correcting for dust attenuation the median fraction of total FUV emission from regions outside of R25 is 1.7 per cent, but it can be as high as 35 per cent in the most extreme cases. The corresponding fractions of Hα emission are approximately half as large on average. This difference reflects both a slightly lower ratio of Hα to UV emission in the H ii regions in the outer discs and a lower fraction of star clusters showing H ii regions. Most H ii regions in the extended disc have fluxes consistent with small numbers of ionizing O-type stars, and this poor sampling of the upper initial mass function (IMF) in small clusters can probably account for the differences in the emission properties, consistent with earlier conclusions by Zaritsky & Christlein, without needing to invoke a significant change in the stellar IMF itself. Consistent Hα/FUV ratios and brightest H ii region to total Hα fluxes in the inner and extended discs across our whole galaxy sample demonstrate no evidence for a change in the cluster luminosity function or the IMF in the low gas density outer disc. [ABSTRACT FROM AUTHOR]

We present the PPAK Integral Field Spectroscopy (IFS) Nearby Galaxies Survey (PINGS), a two-dimensional spectroscopic mosaicking of 17 nearby disc galaxies in the optical wavelength range. This project represents the first attempt to obtain continuous coverage spectra of the whole surface of a galaxy in the nearby Universe. The final data set comprises more than 50 000 individual spectra, covering in total an observed area of nearly 80 arcmin . The observations will be supplemented with broad-band and narrow-band imaging for those objects without publicly available images in order to maximize the scientific and archival values of the data set. In this paper we describe the main astrophysical issues to be addressed by the PINGS project, present the galaxy sample and explain the observing strategy, the data reduction process and all uncertainties involved. Additionally, we give some scientific highlights extracted from the first analysis of the PINGS sample. A companion paper will report on the first results obtained for NGC 628: the largest IFS survey on a single galaxy. [ABSTRACT FROM AUTHOR]

In this paper we derive ages and masses for 276 clusters in the merger galaxy NGC 3256. This was achieved by taking accurate photometry in four wavebands from archival Hubble Space Telescope images. Photometric measurements are compared to synthetic stellar population (SSP) models to find the most probable age, mass and extinction. The cluster population of NGC 3256 reveals an increase in the star formation rate (SFR) over the last 100 Myr and the initial cluster mass function (ICMF) is best described by a power-law relation with slope . Using the observed cluster population for NGC 3256 we calculate the implied mass of clusters younger than 10-Myr old, and convert this to a cluster formation rate over the last 10 Myr. Comparison of this value with the SFR indicates the fraction of stars found within bound clusters after the embedded phase of cluster formation, , is per cent for NGC 3256. We carried out an in-depth analysis into the errors associated with such calculations showing that errors introduced by the SSP fitting must be taken into account and an unconstrained metallicity adds to these uncertainties. Observational biases should also be considered. Using published cluster population data sets we calculate for six other galaxies and examine how varies with environment. We show that increases with the SFR density and can be described as a power-law type relation of the form . [ABSTRACT FROM AUTHOR]

We present Integral Field Spectroscopy (IFS) of NGC 595, one of the most luminous H ii regions in M33. This type of observations allows us to study the variation of the principal emission-line ratios across the surface of the nebula. At each position of the field of view, we fit the main emission-line features of the spectrum within the spectral range of 3650–6990 Å and create maps of the principal emission-line ratios for the total surface of the region. The extinction map derived from the Balmer decrement and the absorbed Hα luminosity show good spatial correlation with the 24 μm emission from Spitzer. We also show here the capability of the IFS to study the existence of Wolf–Rayet (WR) stars, identifying the previously catalogued WR stars and detecting a new candidate towards the north of the region. The ionization structure of the region nicely follows the Hα shell morphology and is clearly related to the location of the central ionizing stars. The electron density distribution does not show strong variations within the H ii region nor any trend with the Hα emission distribution. We study the behaviour within the H ii region of several classical emission-line ratios proposed as metallicity calibrators: while [N ii]/Hα and [N ii]/[O iii] show important variations, the index is substantially constant across the surface of the nebula, despite the strong variation of the ionization parameter as a function of the radial distance from the ionizing stars. These results show the reliability in using the index to characterize the metallicity of H ii regions even when only a fraction of the total area is covered by the observations. [ABSTRACT FROM AUTHOR]

Ten years ago our team completed the Hubble Space Telescope Key Project on the extragalactic distance scale. Cepheids were detected in some 25 galaxies and used to calibrate four secondary distance indicators that reach out into the expansion field beyond the noise of galaxy peculiar velocities. The result was H0 = 72 ± 8 km s−1 Mpc−1 and put an end to galaxy distances uncertain by a factor of two. This work has been awarded the Gruber Prize in Cosmology for 2009. [ABSTRACT FROM PUBLISHER]

We use Spitzer IRAC 3.6 and 4.5 μm near-infrared data from the Spitzer Infrared Nearby Galaxies Survey (SINGS), optical B, V and I and Two-Micron All-Sky Survey Ks-band data to produce mass surface density maps of M81. The IRAC 3.6- and 4.5-μm data, whilst dominated by emission from old stellar populations, are corrected for small-scale contamination by young stars and polycyclic aromatic hydrocarbon emission. The I-band data are used to produce a mass surface density map by a colour correction, following the method of Bell and de Jong. We fit a bulge and exponential disc to each mass map, and subtract these components to reveal the non-axisymmetric mass surface density. From the residual mass maps, we are able to extract the amplitude and phase of the density wave, using azimuthal profiles. The response of the gas is observed via dust emission in the 8-μm IRAC band, allowing a comparison between the phase of the stellar density wave and gas shock. The relationship between this angular offset and radius suggests that the spiral structure is reasonably long-lived and allows the position of corotation to be determined. [ABSTRACT FROM AUTHOR]

This is the second part of an Hα kinematics follow-up survey of the Spitzer Infrared Nearby Galaxies Survey (SINGS) sample. The aim of this paper is to shed new light on the role of baryons and their kinematics and on the dark/luminous matter relation in the star-forming regions of galaxies, in relation with studies at other wavelengths. The data for 37 galaxies are presented. The observations were made using Fabry–Perot interferometry with the photon-counting camera FaNTOmM on four different telescopes, namely the Canada–France–Hawaii 3.6-m, the ESO La Silla 3.6-m, the William Herschel 4.2-m and the Observatoire du mont Mégantic 1.6-m telescopes. The velocity fields are computed using customidl routines designed for an optimal use of the data. The kinematical parameters and rotation curves are derived using thegipsy software. It is shown that non-circular motions associated with galactic bars affect the kinematical parameters fitting and the velocity gradient of the rotation curves. This leads to incorrect determinations of the baryonic and dark matter distributions in the mass models derived from those rotation curves. [ABSTRACT FROM AUTHOR]

We have found the peculiar galaxy NGC 922 to be a new drop-through ring galaxy using multiwavelength (ultraviolet–radio) imaging and spectroscopic observations. Its ‘C’-shaped morphology and tidal plume indicate a recent strong interaction with its companion which was identified with these observations. Using numerical simulations we demonstrate that the main properties of the system can be generated by a high-speed off-axis drop-through collision of a small galaxy with a larger disc system, thus making NGC 922 one of the nearest known collisional ring galaxies. While these systems are rare in the local Universe, recent deep Hubble Space Telescope images suggest they were more common in the early Universe. [ABSTRACT FROM AUTHOR]

The Kennicutt-Schmidt law (Schmidt 1959; Kennicutt 1998, hereafter K-S law) is a power law correlation between area averaged star formation rate (ΣSFR) and gas surface density (Σgas). Despite its importance, the physics that underlie this correlation has remained unclear. The power law index, N, is a prime discriminator of the mechanisms that regulate star formation and form the K-S law (e.g. Leroy et al. 2008; Tan 2010). We present a study of the resolved K-S law for 10 nearby disk galaxies using our new CO(1-0) data at 750 and 500 pc resolutions. The CO(1-0) line emission is established as a tracer of the molecular gas column density, and results in a super-linear correlation (N = 1.3 and 1.8). We discuss the cause of the discrepancy between previous studies, and the mechanism of star formation indicated from our new results. [ABSTRACT FROM PUBLISHER]

We present a multiwavelength analysis of a compact group infalling at high speed (~1700 km s−1) into the dynamically young cluster Abell 1367. Peculiar morphologies and unusually high Halpha emission are associated with two giant galaxies and at least ten dwarfs/extragalactic HII regions, making this group the region with the highest density of star formation activity ever observed in the local clusters. Moreover Halpha imaging observations reveal extraordinary complex trails of ionized gas behind the galaxies, with projected lengths exceeding 100 kpc. These unique cometary trails mark the gaseous trajectory of galaxies, witnessing their dive into the hot cluster intergalactic medium. Under the combined action of tidal forces among group members and the ram-pressure by the cluster ambient medium, the group galaxies were fragmented and the ionized gas was blown out. The properties of this group suggest that environmental effects within infalling groups may have represented a preprocessing step of the galaxy evolution during the high redshift cluster assembly phase. [ABSTRACT FROM PUBLISHER]