Auto-consistent metallicity and star formation history of the nearest blue compact dwarf galaxy NGC 6789

We present a detailed auto-consistent study of the nearest blue compact dwarf galaxy NGC 6789 by means of optical and UV archive photometry data and optical long-slit ISIS-WHT spectroscopy observations of the five brightest star-forming knots. The analysis of the spectra in all knots allowed the derivation of ionic chemical abundances of oxygen, nitrogen, sulphur, argon and neon using measures of both the high- and low-excitation electron temperatures, leading to the conclusion that NGC 6789 is chemically homogeneous with low values of the abundance of oxygen in the range 12+log(O/H) = 7.80-7.93, but presenting at the same time higher values of the nitrogen-to-oxygen ratio than expected for its metal regime. We used archival HST/WFPC2 F555W and F814W observations of NGC 6789 to perform a photometric study of the colour-magnitude diagram (CMD) of the resolved stellar populations and derive its star formation history (SFH), which is compatible with the presence of different young and old stellar populations whose metallicities do not necessarily increase with age. We fit the observed optical spectrum in all the five knots using the STARLIGHT code and a combination of single stellar populations following the SFH obtained from the CMD. We compare the resulting stellar masses and the relative fractions of the ionising populations with a non-constrained SFH case. The properties of the younger populations were obtained using CLOUDY photoionisation models, giving similar ages in all the knots in the range 3-6 Myr and the estimation of the dust absorption factor, which correlates with the observed GALEX FUV-NUV colour indices. The total photometric extinction and dust-absorption corrected H\alpha\ fluxes were finally used to derive the star formation rates.Comment: 18 pages, 6 figures, 10 tables; accepted by MNRA

A spatially resolved study of ionized regions in galaxies at differet scales

Tesis doctoral inédita. Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Teórica. Fecha de lectura: 11-09-200

IMF shape constraints from stellar populations and dynamics from CALIFA

M. Lyubenova et. al.In this paper, we describe how we use stellar dynamics information to constrain the shape of the stellar initial mass function (IMF) in a sample of 27 early-type galaxies from the CALIFA survey. We obtain dynamical and stellar mass-to-light ratios, ¿dyn and ¿*, over a homogenous aperture of 0.5 Re. We use the constraint ¿dyn¿¿* to test two IMF shapes within the framework of the extended MILES stellar population models. We rule out a single power-law IMF shape for 75 per cent of the galaxies in our sample. Conversely, we find that a double power-law IMF shape with a varying high-mass end slope is compatible (within 1¿) with 95 per cent of the galaxies. We also show that dynamical and stellar IMF mismatch factors give consistent results for the systematic variation of the IMF in these galaxies. © 2016, Published by Oxford University Press on behalf of the Royal Astronomical Society.This Paper is based on data obtained by the CALIFA survey, funded by the Spanish Ministry of Science under grant ICTS-2009-10, and the CAHA. IMN and JFB acknowledge funding from grant AYA2013-48226-C3-1-P from the Spanish Ministry of Economy and Competitiveness (MINECO) and, together with and GvdV, from the FP7 Marie Curie Actions via the ITN DAGAL (grant 289313). CJW acknowledges support through the Marie Curie Career Integration Grant 303912. Support for LG is provided by the Ministry of Economy, Development, and Tourism's Millennium Science Initiative through grant IC120009 awarded to The Millennium Institute of Astrophysics (MAS), and CONICYT through FONDECYT grant 3140566. RGD acknowledges support from AyA2014-57490-P. JMA acknowledges support from the ERC Starting Grant (SEDmorph; P.I. V. Wild).Peer Reviewe

Integral field spectroscopy of HII regions in M33

Integral field spectroscopy (IFS) is presented for star forming regions in M33. A central area of 300 x 500 pc^2 and the external HII region IC 132, at a galactocentric distance {\sim} 19arcmin (4.69 kpc) were observed with the Potsdam Multi Aperture Spectrophotometer (PMAS) instrument at the 3.5 m telescope of the Calar Alto Hispano- Alem\'an observatory (CAHA). The spectral coverage goes from 3600 A to 1{\mu}m to include from [OII]{\lambda}3727 A to the near infrared lines required for deriving sulphur electron temperature and abundance diagnostics. Local conditions within individual HII regions are presented in the form of emission line fluxes and physical conditions for each spatial resolution element (spaxel) and for segments with similar H{\alpha} surface brightness. A clear dichotomy is observed when comparing the central to outer disc HII regions. While the external HII region has higher electron temperature plus larger H{\beta} equivalent width, size and excitation, the central region has higher extinction and metal content. The dichotomy extends to the BPT diagnostic diagrams that show two orthogonal broad distributions of points. By comparing with pseudo-3D photoionization models we conclude that the bulk observed differences are probably related to a different ionization parameter and metallicity. Wolf-Rayet features are detected in IC 132, and resolved into two concentrations whose integrated spectra were used to estimate the characteristic number of WR stars. No WR features were detected in the central HII regions despite their higher metallicity.Comment: 72 pages, 37 figure

Disentangling the metallicity and star formation history of H ii galaxies through tailor-made models

We present a self-consistent study of the stellar populations and the ionized gas in a sample of 10 H ii galaxies with, at least, four measured electron temperatures and a precise determination of ionic abundances following the 'direct method'. We fitted the spectral energy distribution of the galaxies using the program starlight and starburst99 libraries in order to quantify the contribution of the underlying stellar population to the equivalent width of Hβ [EW(Hβ)], which amounts to about 10 per cent for most of the objects. We then studied the Wolf-Rayet (WR) stellar populations detected in seven of the galaxies. The presence of these populations and the EW(Hβ) values, once corrected for the continuum contribution from underlying stars and ultravoilet dust absorption, indicate that the ionizing stellar populations were created following a continuous star formation episode of 10 Myr duration, hence WR stars may be present in all of objects even if they are not detected in some of them.The derived stellar features, the number of ionizing photons and the relative intensities of the most prominent emission lines were used as input parameters to compute tailored models with the photoionization code cloudy. Our models are able to adequately reproduce the thermal and ionization structure of these galaxies as deduced from their collisionally excited emission lines. This indicates that ionic abundances can be derived following the 'direct method' if the thermal structure of the ionized gas is well traced, hence no abundance discrepancy factors are implied for this kind of objects. Only the electron temperature of S+ is overestimated by the models, with the corresponding underestimate of its abundance, pointing to the possible presence of outer shells of diffuse gas in these objects that have not been taken into account in our models. This kind of geometrical effects can affect the determination of the equivalent effective temperature of the ionizing cluster using calibrators which depend on low-excitation emission lines.Facultad de Ciencias Astronómicas y Geofísica

Disentangling the metallicity and star formation history of H ii galaxies through tailor-made models

We present a self-consistent study of the stellar populations and the ionized gas in a sample of 10 H ii galaxies with, at least, four measured electron temperatures and a precise determination of ionic abundances following the 'direct method'. We fitted the spectral energy distribution of the galaxies using the program starlight and starburst99 libraries in order to quantify the contribution of the underlying stellar population to the equivalent width of Hβ [EW(Hβ)], which amounts to about 10 per cent for most of the objects. We then studied the Wolf-Rayet (WR) stellar populations detected in seven of the galaxies. The presence of these populations and the EW(Hβ) values, once corrected for the continuum contribution from underlying stars and ultravoilet dust absorption, indicate that the ionizing stellar populations were created following a continuous star formation episode of 10 Myr duration, hence WR stars may be present in all of objects even if they are not detected in some of them.The derived stellar features, the number of ionizing photons and the relative intensities of the most prominent emission lines were used as input parameters to compute tailored models with the photoionization code cloudy. Our models are able to adequately reproduce the thermal and ionization structure of these galaxies as deduced from their collisionally excited emission lines. This indicates that ionic abundances can be derived following the 'direct method' if the thermal structure of the ionized gas is well traced, hence no abundance discrepancy factors are implied for this kind of objects. Only the electron temperature of S+ is overestimated by the models, with the corresponding underestimate of its abundance, pointing to the possible presence of outer shells of diffuse gas in these objects that have not been taken into account in our models. This kind of geometrical effects can affect the determination of the equivalent effective temperature of the ionizing cluster using calibrators which depend on low-excitation emission lines.Facultad de Ciencias Astronómicas y Geofísica

The physical properties of S0 galaxy PGC 26218: the origin of starburst and star formation

We present 2D-spectroscopic observations from Centro Astron\'omico Hispano Alem\'an (CAHA) 3.5 m telescope and the millimetre observation from NOrthern Extended Millimeter Array (NOEMA) of the nearby S0 galaxy PGC 26218, which shows central star-formation activity and post-starburst outside in the disk. We estimate the star formation rate (SFR = $0.28\pm0.01$ $M_{\odot} \rm yr^{-1}$) and molecular gas mass ($\rm log\$$M_{\rm H_{2}}=7.60\pm0.15\ M_{\odot}$) of PGC 26218 based on the extinction-corrected H$\alpha$emission line and the CO-$\rm H_{2}$conversion factor ($\alpha_{\rm CO}$) of the Milky Way, respectively. We find that PGC 26218 follows the star forming main sequence (SFMS) and the Kennicutt-Schmidt law. Comparing the kinematics of CO($J$=1-0), stars and H$\alpha$, we find that the rotational axis of CO($J$=1-0) is 45$^{\circ}$different from that of H$\alpha$. In addition, the profile of the CO($J$=1-0) emission line shows asymmetry and has an inflow component of$\sim$46$\rm km\ s^{-1}$. With the decomposition of the optical image, we confirm that PGC 26218 shows multiple nuclear structures. The projected offset between the most luminous optical center and the center of CO($J$=1-0) is$5.2\arcsec$($\sim$ 0.6 kpc) and the latter overlaps with one of the optical cores. These results support that PGC 26218 may have experienced a gas-rich minor merger, extending its star formation and locating it in the SFMS.Comment: accepted for publication in ApJ, 16 page, 12 figure

Sociology and hierarchy of voids: A study of seven nearby CAVITY galaxy voids and their dynamical CosmicFlows-3 environment

The present study addresses a key question related to our understanding of the relation between void galaxies and their environment: the relationship between luminous and dark matter in and around voids. Aims. To explore the extent to which local Universe voids are empty of matter, we study the full (dark+luminous) matter content of seven nearby cosmic voids that are fully contained within the CosmicFlows-3 volume. Methods. We obtained the matter-density profiles of seven cosmic voids using two independent methods. These were built from the galaxy redshift space two-point correlation function in conjunction with peculiar velocity gradients from the CosmicFlows-3 dataset. Results. The results are striking, because when the redshift survey is used, all voids show a radial positive gradient of galaxies, while based on the dynamical analysis, only three of these voids display a clear underdensity of matter in their center. Conclusions. This work constitutes the most detailed observational analysis of voids conducted so far, and shows that void emptiness should be derived from dynamical information. From this limited study, the Hercules void appears to be the best candidate for a local Universe pure “pristine volume”, expanding in three directions with no dark matter located in that void.Institut Universitaire de FranceCentre National D'etudes SpatialesInstituto de Salud Carlos III Spanish GovernmentEuropean Commission PID2020-224414GB-I00 PID2020-113689GB-I00Spanish Ministerio de Ciencia e Innovacion (MCIN)Agencia Estatal de Investigacion (AEI)European Social Fund (ESF) 20215AT016 CEX2020-001058-MCentro Superior de Investigaciones Cientificas (CSIC) under the PIE project KR4598/2-1German Research Foundation (DFG) PID2019-105602GBI00Junta de AndaluciaSpanish Government FQM108MCIN/AEIEuropean Union NextGenerationEUAgencia Estatal de Investigacion Espanola (AEI)Center for Forestry Research & Experimentation (CIEF) CEX2021-001131-SEuropean Union-Next Generation EU FundsState Research Agency (AEI-MCINN) of the Spanish Ministry of Science and Innovation under the grant "The structure and evolution of galaxies and their central regions" - Ministry of Universitie