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Santa Cruz de la Palma, Spain

Ferre-Mateu A.,Subaru Telescope | Mezcua M.,Harvard - Smithsonian Center for Astrophysics | Mezcua M.,Institute of Astrophysics of Canarias | Mezcua M.,University of La Laguna | And 4 more authors.
Astrophysical Journal | Year: 2015

We study a sample of eight massive galaxies that are extreme outliers (3-5σ) in the - Mbulge local scaling relation. Two of these galaxies are confirmed to host extremely large super-massive black holes (SMBHs), whereas the virial mass estimates for the other six are also consistent with having abnormally large SMBHs. From the analysis of their star formation histories and their structural properties, we find that all of these extreme outliers can be considered to be relic galaxies from the early (z ∼ 2) universe: i.e., they are compact (R kpc) and have purely old stellar populations ( Gyr). In order to explain the nature of such deviations from the local relations, we propose a scenario in which the hosts of these über-massive SMBHs are galaxies that have followed a different evolutionary path than the two-phase growth channel assumed for massive galaxies. Once the SMBH and the core of the galaxy are formed at z ∼ 2, the galaxy skips the second phase, remaining structurally untouched and without further mass and size increase. We show that if the outliers had followed the normal evolutionary path by growing in size via merger activity, the expected (mild) growth in mass would place them closer to the observed local relations. Our results suggest that the SMBH growth epoch for the most massive galaxies stopped ∼10 Gyr ago. © 2015. The American Astronomical Society. All rights reserved..

Fuhrmann K.,Ruhr University Bochum | Fuhrmann K.,Isaac Newton Group of Telescopes | Chini R.,Ruhr University Bochum | Chini R.,Catolica del Norte University
Astrophysical Journal | Year: 2015

In continuation of our previous study we present an updated census of new companions and model atmosphere analyses for some 50 southern dwarfs, mostly in the mass range 0.90 ≤ M ≤ 1.10 M⊙. For the common-ropermotion companions μ Vir B, HR 2225 B, HD 67199 B, and HD 114853 B, we confirm their physical association from their radial velocities. We report the discovery of the F-type visual binary α For as a field blue straggler and confirm (ζ Ret, HR 5864) or identify (HD 67199, HR 4013, HR 8843) another five mass transfer systems or candidates. For the F stars T1 Eri and 111 Tau, we present 10σ and 7σ cases for astrometric binaries by virtue of the very accurate van Leeuwen Hipparcos parallaxes. Following the work of Shaya and Olling, we suggest the F-type star ι Vir to be a wide (0.37 pc) hierarchical quadruple system. We confirm the visual binary NLTT 23781/2 as a common-proper-motion object to the very wide (0.54 pc) F star 40 Leo, but discard the G star HD 128987 as an ultra-wide (1.01 pc) physical companion to the α Lib quadruple system on account of a diverse metallicity. The improved statistics of our sample establishes the previously discovered positive correlation of stellar multiplicities with primary mass. For the F star multiplicity census in the mass range 1.10 ≤ M ≤ 1.70 M⊙, we find that at least a quarter consists of triple or higher level systems and at least two out of three F stars are non-single. © 2015. The American Astronomical Society. All rights reserved.

Fuhrmann K.,Ruhr University Bochum | Fuhrmann K.,Isaac Newton Group of Telescopes | Chini R.,Ruhr University Bochum | Chini R.,Catolica del Norte University
Astrophysical Journal, Supplement Series | Year: 2012

As part of a homogeneous all-sky volume-complete sample of half a thousand solar-type stars within 25pc we present a census for the subset of the 150 - mostly F-type stars - in the mass range 1.1 M ≤ M ≤ 1.7 M in terms of their observed multiplicities. The major obstacle, as expected, arises from the onset of stellar rotation in this mass range for it continues to support many hidden companions. Yet, a solid increase of the fraction of binary and higher level systems as a function of the primary mass is manifest. There is even the prospect that on account of many companion candidates the single-star fraction may already converge to zero at the transition to the A-type stars. © 2012. The American Astronomical Society. All rights reserved..

Fuhrmann K.,Ruhr University Bochum | Fuhrmann K.,Isaac Newton Group of Telescopes
Monthly Notices of the Royal Astronomical Society | Year: 2011

This fifth in a series of papers finishes the model atmosphere analyses of an unbiased, volume-complete sample of more than 300 nearby solar-type stars. The sample first disintegrates into thick-disc and thin-disc stars on account of their different distributions in the [Mg/H]-[Fe/Mg] chemical abundance plane. Detailed stellar age-datings of the locally few, but very relevant, subgiants show this map to be the sequel of a major star formation gap and hence the legacy for the two stellar populations. Among the stars of the thin disc the subgiant 70 Vir with τ= 8.1 ± 0.6Gyr remains the best case to constrain the age of this comparatively young population. Uncertainties for the existing thick-disc subgiants are about twice as much, but they consistently promote ages of 12-13Gyr. The unbiased thin-disc metallicity distribution functions of magnesium and iron average at 〈[Mg/H]〉=-0.009 ± 0.012 dex and 〈[Fe/H]〉=-0.034 ± 0.015dex, thereby demonstrating that the Sun is a typical thin-disc star in terms of these two elements. The small but likewise unbiased sample of thick-disc stars leads to 〈[Mg/H]〉=-0.207 ± 0.049 dex and 〈[Fe/H]〉=-0.584 ± 0.057 dex, which implies that about two-thirds of the α-element magnesium was already synthesized in the early Milky Way. Similarly, the age-metallicity relations for the thin disc result in Δ[Mg/H]=+0.006dexGyr-1 and Δ[Fe/H]=+0.017dexGyr-1 and lead to the conclusion that a similar percentage of iron was synthesized before the birth of the thin disc. In comparison with the considerable metallicity dispersions σ[Mg/H]= 0.151dex and σ[Fe/H]= 0.191dex for the stars of the thin disc, this immediately explains the coexistence of old, metal rich as well as young, fairly metal poor stars within this stellar population. The stellar multiplicities of the solar-type thin-disc stars show a minority of less than 47per cent to be single and at least 15per cent to belong to triple and higher level systems. More concisely, in terms of the primary masses there is a clear correlation with mass with a cross-over of preferentially single to binary stars at M≃ 1.25M⊙ and a fraction of 21per cent of triple and higher level systems at this particular mass. The steady record of new discoveries of nearby companion stars renders these numbers, however, as yet provisional, with an ever-decreasing fraction of single objects. For the thick disc the multiplicity statistics are necessarily weak, yet tentatively imply even less single stars and eventually more triple or higher level systems. Most importantly, and as already addressed in the previous papers of this series, the rigorous census of the long-lived stars of the sample uncovers the thick disc as a massive, dark population with a 20per cent local normalization, and, on account of its larger scaleheight, a mass comparable to that of the thin disc. With the ages of its stars at or above 12 Gyr the thick-disc epoch then leads to a very different star formation rate and qualifies this stellar population as a single-burst component, much at variance with the thin disc whose stars cover the complete stellar age range of 1Myr up to 8 Gyr. Such information conveyed by the stars of the solar neighbourhood then clearly do not support a gradual build-up scenario, a hierarchical cold-dark-matter-dominated formation picture for our parent spiral. Provided the Milky Way is not an unusual spiral galaxy, it implies that this paradigm is also challenged in a much broader context. © 2011 The Author Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Leitherer C.,US Space Telescope Science Institute | Otalvaro P.A.O.,University of Antioquia | Bresolin F.,University of Hawaii at Manoa | Kudritzki R.-P.,University of Hawaii at Manoa | And 5 more authors.
Astrophysical Journal, Supplement Series | Year: 2010

We computed a comprehensive set of theoretical ultraviolet spectra of hot, massive stars with the radiationhydrodynamics code WM-Basic. This model atmosphere and spectral synthesis code is optimized for computing the strong P Cygni type lines originating in the winds of hot stars, which are the strongest features in the ultraviolet spectral region. The computed set is suitable as a spectral library for inclusion in evolutionary synthesis models of star clusters and star-forming galaxies. The chosen stellar parameters cover the upper left Hertzsprung-Russell diagram at L ≳ 102.75 L ≳ and Teff ≳ 20,000 K. The adopted elemental abundances are 0.05 Z⊙, 0.2 Z⊙, 0.4 Z⊙, Z⊙, and 2 Z ⊙,. The spectra cover the wavelength range from 900 to 3000Åand have a resolution of 0.4 Å We compared the theoretical spectra to data of individual hot stars in the Galaxy and the Magellanic Clouds obtained with the International Ultraviolet Explorer and Far Ultraviolet Spectroscopic Explorer satellites and found very good agreement. We built a library with the set of spectra and implemented it into the evolutionary synthesis code Starburst99 where it complements and extends the existing empirical library toward lower chemical abundances. Comparison of population synthesis models at solar and near-solar composition demonstrates consistency between synthetic spectra generated with either library. We discuss the potential of the new library for the interpretation of the rest-frame ultraviolet spectra of starforming galaxies. Properties that can be addressed with the models include ages, initial mass function, and heavy-element abundance. The library can be obtained both individually or as part of the Starburst99 package. © 2010. The American Astronomical Society. All rights reserved.

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