Fabio Bresolin

Honolulu University, Honolulu, Hawaii, United States

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Publications (222)811.08 Total impact

  • Fabio Bresolin · Robert C. Kennicutt
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    ABSTRACT: We acquired spectra of 141 H ii regions in 10 late-type low surface 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.
    No preview · Article · Sep 2015 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We present high S/N spectroscopy of 15 emission-line galaxies (ELGs) cataloged in the KPNO International Spectroscopic Survey (KISS), selected for their possession of high equivalent width [O III] lines. The primary goal of this study was to attempt to derive direct-method ($T_e$) abundances for use in constraining the upper-metallicity branch of the $R_{23}$ relation. The spectra cover the full optical region from [O II]{\lambda}{\lambda}3726,3729 to [S III]{\lambda}{\lambda}9069,9531 and include the measurement of [O III]{\lambda}4363 in 13 objects. From these spectra, we determine abundance ratios of helium, nitrogen, oxygen, neon, sulfur, and argon. We find these galaxies to predominantly possess oxygen abundances in the range of 8.0 $\lesssim$ 12+log(O/H) $\lesssim$ 8.3. We present a comparison of direct-method abundances with empirical SEL techniques, revealing several discrepancies. We also present a comparison of direct-method oxygen abundance calculations using electron temperatures determined from emission lines of O$^{++}$ and S$^{++}$, finding a small systematic shift to lower $T_e$ (~1184 K) and higher metallicity (~0.14 dex) for sulfur-derived $T_e$ compared to oxygen-derived $T_e$. Finally, we explore in some detail the different spectral activity types of targets in our sample, including regular star-forming galaxies, those with suspected AGN contamination, and a local pair of low-metallicity, high-luminosity compact objects.
    Preview · Article · Jul 2015 · The Astronomical Journal
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    ABSTRACT: We present a dynamical analysis of the galaxy cluster AC114 based on a catalogue of 524 velocities. Of these, 169 (32 per cent) are newly obtained at European Southern Observatory (Chile) with the Very Large Telescope and the VIsible MultiObject spectrograph. Data on individual galaxies are presented and the accuracy of the measured velocities is discussed. Dynamical properties of the cluster are derived. We obtain an improved mean redshift value z = 0.31665 ± 0.0008 and velocity dispersion $\sigma = 1893^{+73}_{-82}\ {\rm km\,s^{-1}}$. A large velocity dispersion within the core radius and the shape of the infall pattern suggests that this part of the cluster is in a radial phase of relaxation with a very elongated radial filament spanning 12 000 km s−1. A radial foreground structure is detected within the central 0.5 h−1 Mpc radius, recognizable as a redshift group at the same central redshift value. We analyse the colour distribution for this archetype Butcher–Oemler galaxy cluster and identify the separate red and blue galaxy sequences. The latter subset contains 44 per cent of confirmed members of the cluster, reaching magnitudes as faint as Rf= 21.1 (1.0 mag fainter than previous studies). We derive a mass M200 = (4.3 ± 0.7) × 1015 M⊙ h−1. In a subsequent paper, we will utilize the spectral data presented here to explore the mass–metallicity relation for this intermediate redshift cluster.
    Preview · Article · Jul 2015 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We report the first results of a programme aimed at studying the properties of high-redshift galaxies with ongoing massive and dominant episodes of star formation (H ii galaxies). We use the L(Hβ)–σ distance estimator based on the correlation between the ionized gas velocity dispersions and Balmer emission line luminosities of H ii galaxies and Giant H ii regions to trace the expansion of the Universe up to z ∼ 2.33. This approach provides an independent constraint on the equation of state of dark energy and its possible evolution with look-back time. Here we present high-dispersion (8000 to 10 000 resolution) spectroscopy of H ii galaxies at redshifts between 0.6 and 2.33, obtained at the Very Large Telescope (VLT) using XShooter. Using six of these H ii galaxies we obtain broad constraints on the plane Ωm–w0. The addition of 19 high-z H ii galaxies from the literature improves the constraints and highlights the need for high-quality emission line profiles, fluxes and reddening corrections. The 25 high-z H ii galaxies plus our local compilation of 107 H ii galaxies up to z = 0.16 were used to impose further constraints. Our results are consistent with recent studies, although weaker due to the as yet small sample and low quality of the literature data of high-z H ii galaxies. We show that much better and competitive constraints can be obtained using a larger sample of high-redshift H ii galaxies with high quality data that can be easily obtained with present facilities like K-band Multi Object Spactrograph (KMOS) at the VLT.
    Full-text · Article · Jun 2015 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We present a quantitative spectroscopic study of twenty-seven red supergiants in the Sculptor Galaxy NGC 300. J-band spectra were obtained using KMOS on the VLT and studied with state of the art synthetic spectra including NLTE corrections for the strongest diagnostic lines. We report a central metallicity of [Z]= -0.03 +/- 0.05 with a gradient of -0.083 +/- 0.014 [dex/kpc], in agreement with previous studies of blue supergiants and H II-region auroral line measurements. This result marks the first application of the J-band spectroscopic method to a population of individual red supergiant stars beyond the Local Group of galaxies and reveals the great potential of this technique.
    Full-text · Article · May 2015 · The Astrophysical Journal
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    ABSTRACT: The radially averaged metallicity distribution of the ISM and the young stellar population of a sample of 20 disk galaxies is investigated by means of an analytical chemical evolution model which assumes constant ratios of galactic wind mass loss and accretion mass gain to star formation rate. Based on this model the observed metallicities and their gradients can be described surprisingly well by the radially averaged distribution of the ratio of stellar mass to ISM gas mass. The comparison between observed and model predicted metallicity is used to constrain the rate of mass loss through galactic wind and accretion gain in units of the star formation rate. Three groups of galaxies are found: galaxies with either mostly winds and only weak accretion, or mostly accretion and only weak winds, and galaxies where winds are roughly balanced by accretion. The three groups are distinct in the properties of their gas disks. Galaxies with approximately equal rates of mass-loss and accretion gain have low metallicity, atomic hydrogen dominated gas disks with a flat spatial profile. The other two groups have gas disks dominated by molecular hydrogen out to 0.5 to 0.7 isophotal radii and show a radial exponential decline, which is on average steeper for the galaxies with small accretion rates. The rates of accretion (<1.0 x SFR) and outflow (<2.4 x SFR) are relatively low. The latter depend on the calibration of the zero point of the metallicity determination from the use of HII region strong emission lines.
    Full-text · Article · Mar 2015 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We present metallicity gradients in 49 local field star-forming galaxies. We derive gas-phase oxygen abundances using two widely adopted metallicity calibrations based on the [O iii]/Hβ, [N ii]/Hα, and [N ii]/[O ii] line ratios. The two derived metallicity gradients are usually in good agreement within $\pm 0.14\ {\rm dex} R_{25}^{-1}$ (R25 is the B-band iso-photoal radius), but the metallicity gradients can differ significantly when the ionization parameters change systematically with radius. We investigate the metallicity gradients as a function of stellar mass ($8 {<} \log (M_\ast /M_\odot) {<} 11$) and absolute B-band luminosity (−16 > MB > −22). When the metallicity gradients are expressed in dex kpc−1, we show that galaxies with lower mass and luminosity, on average, have steeper metallicity gradients. When the metallicity gradients are expressed in ${\rm dex} R_{25}^{-1}$, we find no correlation between the metallicity gradients, and stellar mass and luminosity. We provide a local benchmark metallicity gradient of field star-forming galaxies useful for comparison with studies at high redshifts. We investigate the origin of the local benchmark gradient using simple chemical evolution models and observed gas and stellar surface density profiles in nearby field spiral galaxies. Our models suggest that the local benchmark gradient is a direct result of the coevolution of gas and stellar disc under virtually closed-box chemical evolution when the stellar-to-gas mass ratio becomes high (≫0.3). These models imply low current mass accretion rates ( ≲ 0.3 × SFR), and low-mass outflow rates ( ≲ 3 × SFR) in local field star-forming galaxies.
    Full-text · Article · Jan 2015 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: Abstract Our research on the age-metallicity and mass-metallicity relations of galaxies is presented and compared to the most popular investigations in the field.
    Full-text · Conference Paper · Oct 2014
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    ABSTRACT: We have determined C abundances in two Galactic ring nebulae. The C enrichment patterns are really puzzling, showing C overabundances that do not fit the predictions of stellar evolution models.
    No preview · Article · Oct 2014
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    ABSTRACT: Superluminous supernovae (SLSNe) of Type Ic have a tendency to occur in faint host galaxies which are likely to have low mass and low metallicity. PTF12dam is one of the closest and best-studied superluminous explosions that has a broad and slowly fading light curve similar to SN 2007bi. Here we present new photometry and spectroscopy for PTF12dam from 200–500 d (rest frame) after peak and a detailed analysis of the host galaxy (SDSS J142446.21+461348.6 at z = 0.107). Using deep templates and image subtraction we show that the light curve can be fit with a magnetar model if escape of high-energy gamma rays is taken into account. The full bolometric light curve from −53 to +399 d (with respect to peak) cannot be fit satisfactorily with the pair-instability models. An alternative model of interaction with a dense circumstellar material (CSM) produces a good fit to the data although this requires a very large mass (∼13 M⊙) of hydrogen-free CSM. The host galaxy is a compact dwarf (physical size ∼1.9 kpc) and with Mg = −19.33 ± 0.10, it is the brightest nearby SLSN Ic host discovered so far. The host is a low-mass system (2.8 × 108 M⊙) with a star formation rate (5.0 M⊙ yr−1), which implies a very high specific star formation rate (17.9 Gyr−1). The remarkably strong nebular emission provide detections of the [O iii] λ4363 and [O ii] λλ7320, 7330auroral lines and an accurate oxygen abundance of 12 + log (O/H) = 8.05 ± 0.09. We show here that they are at the extreme end of the metallicity distribution of dwarf galaxies and propose that low metallicity is a requirement to produce these rare and peculiar SNe.
    Full-text · Article · Sep 2014 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: In a LCDM universe, disk galaxies' outer regions are the last to form. Characterizing their contents is critical for understanding the ongoing process of disk formation, but observing outer disk stellar populations is challenging due to their low surface brightness. We present extremely deep 3.6 micron observations (Spitzer IRAC) of NGC 4625, a galaxy known for its radially extended ultraviolet emitting stellar population. We combine the new imaging with archival UV imaging from the GALEX mission to derive multiwavelength radial profiles for NGC 4625 and compare them to stellar populations models. The colors can be explained by the young stellar population that is responsible for the UV emission and indicate that the current star formation rates in the outermost disk are recent. Extended star formation in NGC 4625 may have been initiated by an interaction with neighboring galaxies NGC 4618 and NGC 4625a, supporting speculation that minor interactions are a common trigger for outer disk star formation and late stage disk growth.
    Preview · Article · Sep 2014 · The Astrophysical Journal
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    ABSTRACT: The validity of the emission-line luminosity versus ionized gas velocity dispersion (L–σ) correlation for H ii galaxies (HIIGx) and its potential as an accurate distance estimator are assessed. For a sample of 128 local (0.02 ≲ z ≲ 0.2) compact HIIGx with high equivalent widths of their Balmer emission lines, we obtained the ionized gas velocity dispersion from high signal-to-noise ratio (S/N) high-dispersion spectroscopy (Subaru High Dispersion Spectrograph (HDS) and European Southern Observatory (ESO) Very Large Telescope Ultraviolet and Visual Echelle Spectrograph (VLT–UVES)) and integrated Hβ fluxes from low-dispersion wide aperture spectrophotometry. We find that the L(Hβ)–σ relation is strong and stable against restrictions in the sample (mostly based on the emission-line profiles). The ‘Gaussianity’ of the profile is important for reducing the root-mean-square (rms) uncertainty of the distance indicator, but at the expense of substantially reducing the sample. By fitting other physical parameters into the correlation, we are able to decrease the scatter significantly without reducing the sample. The size of the star-forming region is an important second parameter, while adding the emission-line equivalent width or the continuum colour and metallicity produces the solution with the smallest rms scatter=δlog L(Hβ) = 0.233. The derived coefficients in the best L(Hβ)–σ relation are very close to what is expected from virialized ionizing clusters, while the derived sum of the stellar and ionized gas masses is similar to the dynamical mass estimated using the Hubble Space Telescope (HST) corrected Petrosian radius. These results are compatible with gravity being the main mechanism causing the broadening of the emission lines in these very young and massive clusters. The derived masses range from about 2 × 106 M⊙ to 109 M⊙ and their ‘corrected’ Petrosian radius ranges from a few tens to a few hundred pc.
    Full-text · Article · Aug 2014 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We present deep echelle spectrophotometry of the brightest emission-line knots of the star-forming galaxies He 2−10, Mrk 1271, NGC 3125, NGC 5408, POX 4, SDSS J1253−0312, Tol 1457−262, Tol 1924−416 and the H ii region Hubble V in the Local Group dwarf irregular galaxy NGC 6822. The data have been taken with the Very Large Telescope Ultraviolet-Visual Echelle Spectrograph in the 3100–10420 Å range. We determine electron densities and temperatures of the ionized gas from several emission-line intensity ratios for all the objects. We derive the ionic abundances of C2+ and/or O2+ from faint pure recombination lines in several of the objects, permitting to derive their C/H and C/O ratios. We have explored the chemical evolution at low metallicities analysing the C/O versus O/H, C/O versus N/O and C/N versus O/H relations for Galactic and extragalactic H ii regions and comparing with results for Galactic halo stars and damped Lyα systems. We find that H ii regions in star-forming dwarf galaxies occupy a different locus in the C/O versus O/H diagram than those belonging to the inner discs of spiral galaxies, indicating their different chemical evolution histories, and that the bulk of C in the most metal-poor extragalactic H ii regions should have the same origin than in halo stars. The comparison between the C/O ratios in H ii regions and in stars of the Galactic thick and thin discs seems to give arguments to support the merging scenario for the origin of the Galactic thick disc. Finally, we find an apparent coupling between C and N enrichment at the usual metallicities determined for H ii regions and that this coupling breaks in very low metallicity objects.
    Full-text · Article · Jun 2014 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We demonstrate how the metallicities of young super star clusters (SSC) can be measured using novel spectroscopic techniques in the J-band. The near-infrared flux of SSCs older than ~6 Myr is dominated by tens to hundreds of red supergiant stars. Our technique is designed to harness the integrated light of that population and produces accurate metallicities for new observations in galaxies above (M83) and below (NGC 6946) solar metallicity. In M83 we find [Z] = +0.28 ± 0.14 dex using a moderate resolution (R ~ 3500) J-band spectrum and in NGC 6496 we report [Z] = -0.32 ± 0.20 dex from a low resolution spectrum of R ~ 1800. Recently commissioned low resolution multiplexed spectrographs on the Very Large Telescope (KMOS) and Keck (MOSFIRE) will allow accurate measurements of SSC metallicities across the disks of star-forming galaxies up to distances of 70 Mpc with single night observation campaigns using the method presented in this paper.
    No preview · Article · May 2014 · The Astrophysical Journal
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    ABSTRACT: Low resolution (~4.5 ?) ESO VLT/FORS spectra of blue supergiant stars are analyzed to determine stellar metallicities (based on elements such as iron, titanium, and magnesium) in the extended disk of the spiral galaxy, NGC?3621. Mildly subsolar metallicity (?0.30?dex) is found for the outer objects beyond 7?kpc, independent of galactocentric radius and compatible with the absence of a metallicity gradient, confirming the results of a recent investigation of interstellar medium H II region gas oxygen abundances. The stellar metallicities are slightly higher than those from the H II regions when based on measurements of the weak forbidden auroral oxygen line at 4363 ? but lower than the ones obtained with the R 23 strong line method. It is shown that the present level of metallicity in the extended disk cannot be the result of chemical evolution over the age of the disk with the present rate of in situ star formation. Additional mechanisms must be involved. In addition to metallicity, stellar effective temperatures, gravities, interstellar reddening, and bolometric magnitudes are determined. After the application of individual reddening corrections for each target, the flux-weighted gravity-luminosity relationship of blue supergiant stars is used to obtain a distance modulus of 29.07 ? 0.09?mag (distance D = 6.52 ? 0.28?Mpc). This new distance is discussed in relation to Cepheid and the tip of the red giant branch distances.
    Preview · Article · Apr 2014 · The Astrophysical Journal
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    ABSTRACT: We demonstrate how the metallicities of young super star clusters can be measured using novel spectroscopic techniques in the J-band. The near-infrared flux of super star clusters older than ~6 Myr is dominated by tens to hundreds of red supergiant stars. Our technique is designed to harness the integrated light of that population and produces accurate metallicities for new observations in galaxies above (M83) and below (NGC 6946) solar metallicity. In M83 we find [Z]= +0.28 +/- 0.14 dex using a moderate resolution (R~3500) J-band spectrum and in NGC 6496 we report [Z]= -0.32 +/- 0.20 dex from a low resolution spectrum of R~1800. Recently commissioned low resolution multiplexed spectrographs on the VLT (KMOS) and Keck (MOSFIRE) will allow accurate measurements of super star cluster metallicities across the disks of star-forming galaxies up to distances of 70 Mpc with single night observation campaigns using the method presented in this letter.
    Full-text · Article · Apr 2014
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    ABSTRACT: We present new results on the chemical composition of the Galactic ring nebula NGC 6888 surrounding the WN6(h) star WR136. The data are based on deep spectroscopical observations taken with the High Dispersion Spectrograph at the 8.2 m Subaru Telescope. The spectra cover the optical range from 3700 to 7400 Å. The effect of the CNO cycle is well-identified in the abundances of He, N, and O, while elements not involved in the synthesis such as Ar, S, and Fe present values consistent with the solar vicinity and the ambient gas. The major achievement of this work is the first detection of the faint C II λ4267 recombination line in a Wolf-Rayet nebula. This allows us to estimate the C abundance in NGC 6888 and therefore investigate for the first time the trace of the CNO cycle in a ring nebula around a Wolf-Rayet star. Although the detection of the C II line has a low signal-to-noise ratio, the C abundance seems to be higher than the predictions of recent stellar evolution models of massive stars. The Ne abundance also shows a puzzling pattern with an abundance of about 0.5 dex lower than the solar vicinity, which may be related to the action of the NeNa cycle. Attending to the constraints imposed by the dynamical timescale and the He/H and N/O ratios of the nebula, the comparison with stellar evolution models indicates that the initial mass of the stellar progenitor of NGC 6888 is between 25 M ☉ and 40 M ☉.
    Full-text · Article · Feb 2014 · The Astrophysical Journal
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    ABSTRACT: We present a quantitative analysis of the low-resolution (~4.5 Å) spectra of 12 late-B and early-A blue supergiants (BSGs) in the metal-poor dwarf galaxy NGC 3109. A modified method of analysis is presented which does not require use of the Balmer jump as an independent T eff indicator, as used in previous studies. We determine stellar effective temperatures, gravities, metallicities, reddening, and luminosities, and combine our sample with the early-B-type BSGs analyzed by Evans et al. to derive the distance to NGC 3109 using the flux-weighted gravity-luminosity relation (FGLR). Using primarily Fe-group elements, we find an average metallicity of = –0.67 ± 0.13, and no evidence of a metallicity gradient in the galaxy. Our metallicities are higher than those found by Evans et al. based on the oxygen abundances of early-B supergiants ( = –0.93 ± 0.07), suggesting a low α/Fe ratio for the galaxy. We adjust the position of NGC 3109 on the BSG-determined galaxy mass-metallicity relation accordingly and compare it to metallicity studies of H II regions in star-forming galaxies. We derive an FGLR distance modulus of 25.55 ± 0.09 (1.27 Mpc) that compares well with Cepheid and tip of the red giant branch distances. The FGLR itself is consistent with those found in other galaxies, demonstrating the reliability of this method as a measure of extragalactic distances.
    Full-text · Article · Feb 2014 · The Astrophysical Journal
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    ABSTRACT: The Pan-STARRS1 (PS1) survey has obtained imaging in five bands (griz yP1) over 10 Medium Deep Survey (MDS) fields covering a total of 70 square degrees. This paper describes the search for apparently hostless supernovae (SNe) within the first year of PS1 MDS data with an aim of discovering superluminous supernovae (SLSNe). A total of 249 hostless transients were discovered down to a limiting magnitude of MAB ∼ 23.5, of which 76 were classified as Type Ia supernovae (SNe Ia). There were 57 SNe with complete light curves that are likely core-collapse SNe (CCSNe) or type Ic SLSNe and 12 of these have had spectra taken. Of these 12 hostless, non-Type Ia SNe, 7 were SLSNe of type Ic at redshifts between 0.5 and 1.4. This illustrates that the discovery rate of type Ic SLSNe can be maximized by concentrating on hostless transients and removing normal SNe Ia. We present data for two possible SLSNe; PS1-10pm (z = 1.206) and PS1-10ahf (z = 1.1), and estimate the rate of type Ic SLSNe to be between $3^{+3}_{-2}\times 10^{-5}$ and $8^{+2}_{-1}\times 10^{-5}$ that of the CCSN rate within 0.3 ≤ z ≤ 1.4 by applying a Monte Carlo technique. The rate of slowly evolving, type Ic SLSNe (such as SN2007bi) is estimated as a factor of 10 lower than this range.
    Full-text · Article · Feb 2014 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: Our research on the age-metallicity and mass-metallicity relations of galaxies is presented and compared to the most recent investigations in the field. We have been able to measure oxygen abundances using the direct method for objects spanning four orders of magnitude in mass, and probing the last 4 Gyr of galaxy evolution. We have found preliminary evidence that the metallicity evolution is consistent with expectations based on age-metallicity relations obtained with low resolution stellar spectra of resolved Local Group galaxies.
    Full-text · Article · Jan 2014

Publication Stats

5k Citations
811.08 Total Impact Points

Institutions

  • 2002-2015
    • Honolulu University
      Honolulu, Hawaii, United States
  • 2014
    • Universidad Nacional Autónoma de México
      • Institute of Astronomy
      Ciudad de México, The Federal District, Mexico
  • 2002-2014
    • University of Hawaiʻi at Mānoa
      • Institute for Astronomy
      Honolulu, Hawaii, United States
  • 2013
    • Queen's University Belfast
      • Astrophysics Research Centre (ARC)
      Béal Feirste, N Ireland, United Kingdom
  • 2006-2013
    • University of Concepción
      • • Departamento de Astronomía
      • • Departamento de Física
      Ciudad de Concepcion, Biobío, Chile
    • Liverpool John Moores University
      Liverpool, England, United Kingdom
  • 2009
    • University of Cambridge
      • Institute of Astronomy
      Cambridge, England, United Kingdom
  • 2004-2009
    • Space Telescope Science Institute
      Baltimore, Maryland, United States
  • 1999-2009
    • European Southern Observatory
      Arching, Bavaria, Germany
  • 1998-2009
    • The University of Arizona
      • Department of Astronomy
      Tucson, Arizona, United States
  • 2008
    • University of Hawai'i System
      Honolulu, Hawaii, United States
    • Northern Arizona University
      • Department of Physics and Astronomy
      Flagstaff, Arizona, United States
  • 1990-2005
    • University of Padova
      • Department of Physics and Astronomy "Galileo Galilei"
      Padua, Veneto, Italy
  • 2001
    • University Hospital München
      München, Bavaria, Germany
  • 1992
    • University of Alabama
      Tuscaloosa, Alabama, United States