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Buat V.,Aix - Marseille University | Giovannoli E.,Aix - Marseille University | Takeuchi T.T.,Nagoya University | Heinis S.,Aix - Marseille University | And 5 more authors.
Astronomy and Astrophysics | Year: 2011

Context. The nearby universe remains the best laboratory to understand the physical properties of galaxies and is a reference for any comparison with high redshift observations. The all sky (or very large) surveys that have been performed from the ultraviolet (UV) to the far-infrared (far-IR) provide us with large datasets of very large wavelength coverage to perform a reference study. Aims. We investigate the dust attenuation characteristics, as well as the star formation rate (SFR) calibrations of a sample of nearby galaxies observed over 13 bands from 0.15 to 160 μm. Methods. A sample of 363 galaxies is built from the AKARI /FIS all sky survey cross-correlated with the SDSS and GALEX surveys. Broad-band spectral energy distributions are fitted with the CIGALE code optimized to analyse variations in the dust attenuation curves and SFR measurements and based on an energetic budget between the stellar and dust emission. Results. Our galaxy sample is primarily selected in far-IR and mostly constituted of massive, actively star-forming galaxies. There is some evidence for a dust attenuation law that is slightly steeper than that used for starburst galaxies but we are unable to constrain the presence or not of a bump at 220 nm. We confirm that a time-dependent dust attenuation is necessary to perform the best fits. Various calibrations of the dust attenuation in the UV as a function of UV-optical colours are discussed. A calibration of the current SFR combining UV and total IR emissions is proposed with an accurate estimate of dust heating by old stars. For the whole sample, 17% of the total dust luminosity is unrelated to the recent star formation. © 2011 ESO.

Rosales-Ortega F.F.,University of Cambridge | Kennicutt R.C.,University of Cambridge | Sanchez S.F.,Centro Astronomico Hispano Aleman | Diaz A.I.,Autonomous University of Madrid | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present the PPAK Integral Field Spectroscopy (IFS) Nearby Galaxies Survey (PINGS), a two-dimensional spectroscopic mosaicking of 17 nearby disc galaxies in the opticalwavelength 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 arcmin2. 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. © 2010 The Authors. Journal compilation © 2010 RAS.

Miralles-Caballero D.,Autonomous University of Madrid | Diaz A.I.,Autonomous University of Madrid | Rosales-Ortega F.F.,National Institute of Astrophysics, Optics and Electronics | Perez-Montero E.,Institute Astrofisica Of Andalucia | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

Numerical simulations of minor mergers predict little enhancement in the global star formation activity. However, it is still unclear the impact they have on the chemical state of the whole galaxy and on the mass build-up in the galaxy bulge and disc. We present a two-dimensional analysis of NCG 3310, currently undergoing an intense starburst likely caused by a recent minor interaction, using data from the PPAK Integral Field Spectroscopy Nearby Galaxies Survey (PINGS). With data from a large sample of about a hundred HII regions identified throughout the disc and spiral arms, we derive, using strong-line metallicity indicators and direct derivations, a rather flat gaseous abundance gradient. Thus, metal mixing processes occurred, as in observed galaxy interactions. Spectra from PINGS data and additional multiwavelength imaging were used to perform a spectral energy distribution fitting to the stellar emission and a photoionization modelling of the nebulae. The ionizing stellar population is characterized by single populations with a narrow age range (2.5-5 Myr) and a broad range of masses (104-6 × 106 M Ȯ). The effect of dust grains in the nebulae is important, indicating that 25-70 per cent of the ultraviolet photons can be absorbed by dust. The ionizing stellar population within the HII regions represents typically a few per cent of the total stellar mass. This ratio, a proxy to the specific star formation rate, presents a flat or negative radial gradient. Therefore, minor interactions may indeed play an important role in the mass build-up of the bulge. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Sanchez S.F.,Centro Astronomico Hispano Aleman | Rosales-Ortega F.F.,University of Cambridge | Kennicutt R.C.,University of Cambridge | Johnson B.D.,University of Cambridge | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

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 ~2.4 M07dot; yr-1. 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 ii 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. © 2010 The Authors. Journal compilation © 2010 RAS.

Rosales-Ortega F.F.,University of Cambridge | Rosales-Ortega F.F.,Autonomous University of Madrid | Diaz A.I.,Autonomous University of Madrid | Kennicutt R.C.,University of Cambridge | Sanchez S.F.,Centro Astronomico Hispano Aleman
Monthly Notices of the Royal Astronomical Society | Year: 2011

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. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Hernandez-Fernandez J.D.,Institute Astrofisica Of Andalucia | Vilchez J.M.,Institute Astrofisica Of Andalucia | Iglesias-Paramo J.,Institute Astrofisica Of Andalucia | Iglesias-Paramo J.,Centro Astronomico Hispano Aleman
Astrophysical Journal | Year: 2012

In this work, we present the results of a novel approach devoted to disentangling the role of the environmental processes affecting galaxies in clusters. This is based on the analysis of the near-UV (NUV) - r′ distributions of a large sample of star-forming galaxies in clusters spanning more than four absolute magnitudes. The galaxies inhabit three distinct environmental regions: virial regions, cluster infall regions, and field environment. We have applied rigorous statistical tests to analyze both the complete NUV - r′ distributions and their averages for three different bins of the r′-band galaxy luminosity down to , throughout the three environmental regions considered. We have identified the environmental processes that significantly affect the star-forming galaxies in a given luminosity bin by using criteria based on the characteristics of these processes: their typical timescales, the regions where they operate, and the galaxy luminosity range for which their effects are more intense. We have found that the high-luminosity () star-forming galaxies do not show significant signs in their star formation activity of being affected by: (1) the environment in the last 108yr, or (2) a sudden quenching in the last 1.5Gyr. The intermediate-luminosity () star-forming galaxies appear to be affected by starvation in the virial regions and by the harassment in the virial and infall regions. Low-luminosity () star-forming galaxies seem to be affected by the same environmental processes as intermediate-luminosity star-forming galaxies in a stronger way, which would be expected for their lower luminosities. © 2012. The American Astronomical Society. All rights reserved.

Petropoulou V.,Institute Astrofisica Of Andalucia Csic | Vilchez J.,Institute Astrofisica Of Andalucia Csic | Iglesias-Paramo J.,Institute Astrofisica Of Andalucia Csic | Iglesias-Paramo J.,Centro Astronomico Hispano Aleman
Astrophysical Journal | Year: 2012

In this paper, we study the chemical history of low-mass star-forming (SF) galaxies in the local universe clusters Coma, A1367, A779, and A634. The aim of this work is to search for the imprint of the environment on the chemical evolution of these galaxies. Galaxy chemical evolution is linked to the star formation history, as well as to the gas interchange with the environment, and low-mass galaxies are well known to be vulnerable systems to environmental processes affecting both these parameters. For our study we have used spectra from the SDSS-III DR8. We have examined the spectroscopic properties of SF galaxies of stellar masses 108-1010 M ⊙, located from the core to the cluster's outskirts. The gas-phase O/H and N/O chemical abundances have been derived using the latest empirical calibrations. We have examined the mass-metallicity relation of cluster galaxies, finding well-defined sequences. The slope of these sequences, for galaxies in low-mass clusters and galaxies at large cluster-centric distances, follows the predictions of recent hydrodynamic models. A flattening of this slope has been observed for galaxies located in the core of the two more massive clusters of the sample, principally in Coma, suggesting that the imprint of the cluster environment on the chemical evolution of SF galaxies should be sensitive to both the galaxy mass and the host cluster mass. The H I gas content of Coma and A1367 galaxies indicates that low-mass SF galaxies, located at the core of these clusters, have been severely affected by ram-pressure stripping (RPS). The observed mass-dependent enhancement of the metal content of low-mass galaxies in dense environments seems plausible, according to hydrodynamic simulations. This enhanced metal enrichment could be produced by the combination of effects such as wind reaccretion, due to pressure confinement by the intracluster medium (ICM), and the truncation of gas infall, as a result of the RPS. Thus, the properties of the ICM should play an important role in the chemical evolution of low-mass galaxies in clusters. © 2012. The American Astronomical Society. All rights reserved.

Hernandez-Fernandez J.D.,Institute Astrofisica Of Andalucia | Iglesias-Paramo J.,Institute Astrofisica Of Andalucia | Iglesias-Paramo J.,Centro Astronomico Hispano Aleman | Vilchez J.M.,Institute Astrofisica Of Andalucia
Astrophysical Journal, Supplement Series | Year: 2012

In this paper, we present a sample of cluster galaxies devoted to study the environmental influence on the star formation activity. This sample of galaxies inhabits in clusters showing a rich variety in their characteristics and have been observed by the SDSS-DR6 down to M B ∼ -18, and by the Galaxy Evolution Explorer AIS throughout sky regions corresponding to several megaparsecs. We assign the broadband and emission-line fluxes from ultraviolet to far-infrared to each galaxy performing an accurate spectral energy distribution for spectral fitting analysis. The clusters follow the general X-ray luminosity versus velocity dispersion trend of L X σ 4.4 c. The analysis of the distributions of galaxy density counting up to the 5th nearest neighbor Σ 5 shows: (1) the virial regions and the cluster outskirts share a common range in the high density part of the distribution. This can be attributed to the presence of massive galaxy structures in the surroundings of virial regions. (2) The virial regions of massive clusters (σ c > 550kms -1) present a Σ 5 distribution statistically distinguishable (∼96%) from the corresponding distribution of low-mass clusters (σ c < 550kms -1). Both massive and low-mass clusters follow a similar density-radius trend, but the low-mass clusters avoid the high density extreme. We illustrate, with ABELL 1185, the environmental trends of galaxy populations. Maps of sky projected galaxy density show how low-luminosity star-forming galaxies appear distributed along more spread structures than their giant counterparts, whereas low-luminosity passive galaxies avoid the low-density environment. Giant passive and star-forming galaxies share rather similar sky regions with passive galaxies exhibiting more concentrated distributions. © 2012. The American Astronomical Society. All rights reserved.

Covey K.R.,Harvard - Smithsonian Center for Astrophysics | Covey K.R.,Cornell University | Lada C.J.,Harvard - Smithsonian Center for Astrophysics | Roman-Zuniga C.,Centro Astronomico Hispano Aleman | And 4 more authors.
Astrophysical Journal | Year: 2010

We have investigated the stellar content of Barnard 59 (B59), the most active star-forming core in the Pipe Nebula. Using the SpeX spectrograph on the NASA Infrared Telescope Facility, we obtained moderate resolution, nearinfrared (NIR) spectra for 20 candidate young stellar objects (YSOs) in B59 and a representative sample of NIR and mid-IR bright sources distributed throughout the Pipe. Measuring luminosity and temperature sensitive features in these spectra, we identified likely background giant stars and measured each star's spectral type, extinction, and NIR continuum excess. To measure B59's age, we place its candidate YSOs in the Hertzsprung-Russell diagram and compare their location to YSOs in several well-studied star-forming regions, as well as predictions of pre-main-sequence (PMS) evolutionary models. We find that B59 is composed of late-type (K4-M6) low-mass (0.9-0.1 M⊙) YSOs whose median stellar age is comparable to, if not slightly older than, that of YSOs within the ρ Oph, Taurus, and Chameleon star-forming regions. Deriving absolute age estimates from PMS models computed by D'Antona et al., and accounting only for statistical uncertainties, we measure B59's median stellar age to be 2.6 ± 0.8 Myr. Including potential systematic effects increases the error budget for B59's median (DM98) stellar age to 2.6+4.1 -2.6 Myr. We also find that the relative age orderings implied by PMS evolutionary tracks depend on the range of stellar masses sampled, as model isochrones possess significantly different mass dependences. The maximum likelihood median stellar age we measure for B59, and the region's observed gas properties, suggests that the B59 dense core has been stable against global collapse for roughly six dynamical timescales and is actively forming stars with a star formation efficiency per dynamical time of ∼6%. While the ∼150% uncertainties associated with our age measurement propagate directly into these derived star formation timescales, the maximum likelihood values nonetheless agree well with recent star formation simulations that incorporate various forms of support against collapse, such as subcritical magnetic fields, outflows, and radiative feedback from protostellar heating. Copyright is not claimed for this article. All rights reserved. Printed in the U.S.A.

Neumayer N.,European Southern Observatory | Neumayer N.,TU Munich | Walcher C.J.,European Space Agency | Walcher C.J.,Leibniz Institute for Astrophysics Potsdam | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present two-dimensional Hα velocity fields for 20 late-type, disc-dominated spiral galaxies, the largest sample to date with high-resolution Hα velocity fields for bulgeless discs. From these data, we derive rotation curves and the location of the kinematic centres. The galaxy sample was selected to contain nucleated and non-nucleated galaxies (as determined from prior Hubble Space Telescope imaging), which allows us to investigate what impact the gas kinematics in the host disc have on the presence (or absence) of a nuclear star cluster. In general, we find that the velocity fields span a broad range of morphologies. While some galaxies show regular rotation, most have some degree of irregular gas motions, which in nearly all cases either can be attributed to the presence of a bar or is connected to a rather patchy distribution of the Hα emission and the stellar light. There appears to be no systematic difference in the kinematics of nucleated and non-nucleated discs. Due to the large fields of view of the integral field units we use, we are able to observe the flattening of the rotation curve in almost all of our sample galaxies. This makes modelling of the velocity fields relatively straightforward. Due to the complexities of the velocity fields, we obtain reliable determinations of the kinematic centre for only six of our 20 sample galaxies. For all of these, the locations of the nuclear star cluster/photometric centre and the kinematic centre agree within the uncertainties. These locations also agree for seven more objects, despite considerably larger uncertainties as to the accuracy of the kinematic centre. If we disregard all kinematically irregular galaxies, our study concludes that nuclear star clusters truly occupy the nuclei, or dynamical centres, of their hosts. Our results are thus consistent with in situ formation of nuclear star clusters. Yet, many well-motivated formation scenarios for nuclear clusters invoke off-centre cluster formation and subsequent sinking of clusters due to dynamical friction. In that case, our results imply that dynamical friction in the centres of bulgeless galaxies must be very effective in driving massive clusters to the kinematic centre. © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS.

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