200 research outputs found
CALIFA reveals Prolate Rotation in Massive Early-type Galaxies: A Polar Galaxy Merger Origin?
We present new evidence for eight early-type galaxies (ETGs) from the CALIFA
Survey that show clear rotation around their major photometric axis ("prolate
rotation"). These are LSBCF560-04, NGC 0647, NGC 0810, NGC 2484, NGC 4874, NGC
5216, NGC 6173 and NGC 6338. Including NGC 5485, a known case of an ETG with
stellar prolate rotation, as well as UGC 10695, a further possible candidate
for prolate rotation, we report ten CALIFA galaxies in total that show evidence
for such a feature in their stellar kinematics. Prolate rotators correspond to
~9% of the volume-corrected sample of CALIFA ETGs, a fraction much higher than
previously reported. We find that prolate rotation is more common among the
most massive ETGs. We investigate the implications of these findings by
studying N-body merger simulations, and show that a prolate ETG with rotation
around its major axis could be the result of a major polar merger, with the
amplitude of prolate rotation depending on the initial bulge-to-total stellar
mass ratio of its progenitor galaxies. Additionally, we find that prolate ETGs
resulting from this formation scenario show a correlation between their stellar
line-of-sight velocity and higher order moment h_3, opposite to typical oblate
ETGs, as well as a double peak of their stellar velocity dispersion along their
minor axis. Finally, we investigate the origin of prolate rotation in polar
galaxy merger remnants. Our findings suggest that prolate rotation in massive
ETGs might be more common than previously expected, and can help towards a
better understanding of their dynamical structure and formation origin.Comment: accepted for publication in A&
MRK 1216 & NGC 1277 - An orbit-based dynamical analysis of compact, high velocity dispersion galaxies
We present a dynamical analysis to infer the structural parameters and
properties of the two nearby, compact, high velocity dispersion galaxies
MRK1216 & NGC1277. Combining deep HST imaging, wide-field IFU stellar
kinematics, and complementary long-slit spectroscopic data out to 3 R_e, we
construct orbit-based models to constrain their black hole masses, dark matter
content and stellar mass-to-light ratios. We obtain a black hole mass of
log(Mbh/Msun) = 10.1(+0.1/-0.2) for NGC1277 and an upper limit of log(Mbh/Msun)
= 10.0 for MRK1216, within 99.7 per cent confidence. The stellar mass-to-light
ratios span a range of Upsilon_V = 6.5(+1.5/-1.5) in NGC1277 and Upsilon_H =
1.8(+0.5/-0.8) in MRK1216 and are in good agreement with SSP models of a single
power-law Salpeter IMF. Even though our models do not place strong constraints
on the dark halo parameters, they suggest that dark matter is a necessary
ingredient in MRK1216, with a dark matter contribution of 22(+30/-20) per cent
to the total mass budget within 1 R_e. NGC1277, on the other hand, can be
reproduced without the need for a dark halo, and a maximal dark matter fraction
of 13 per cent within the same radial extent. In addition, we investigate the
orbital structures of both galaxies, which are rotationally supported and
consistent with photometric multi-S\'ersic decompositions, indicating that
these compact objects do not host classical, non-rotating bulges formed during
recent (z <= 2) dissipative events or through violent relaxation. Finally, both
MRK 1216 and NGC 1277 are anisotropic, with a global anisotropy parameter delta
of 0.33 and 0.58, respectively. While MRK 1216 follows the trend of
fast-rotating, oblate galaxies with a flattened velocity dispersion tensor in
the meridional plane of the order of beta_z = delta, NGC 1277 is highly
tangentially anisotropic and seems to belong kinematically to a distinct class
of objects.Comment: 27 pages, 15 figures and 4 tables. Accepted for publication in MNRA
A New Approach to the Study of Stellar Populations in Early-Type Galaxies: K-band Spectral Indices and an Application to the Fornax Cluster
New measurements of K-band spectral features are presented for eleven
early-type galaxies in the nearby Fornax galaxy cluster. Based on these
measurements, the following conclusions have been reached: (1) in galaxies with
no signatures of a young stellar component, the K-band Na I index is highly
correlated with both the optical metallicity indicator [MgFe]' and central
velocity dispersion; (2) in the same galaxies, the K-band Fe features saturate
in galaxies with sigma > 150 km/s while Na I (and [MgFe]') continues to
increase; (3) [Si/Fe] (and possibly [Na/Fe]) is larger in all observed Fornax
galaxies than in Galactic open clusters with near-solar metallicity; (4) in
various near-IR diagnostic diagrams, galaxies with signatures of a young
stellar component (strong Hbeta, weak [MgFe]') are clearly separated from
galaxies with purely old stellar populations; furthermore, this separation is
consistent with the presence of an increased number of M-giant stars (most
likely to be thermally pulsating AGB stars); (5) the near-IR diagrams discussed
here seem as efficient for detecting putatively young stellar components in
early-type galaxies as the more commonly used age/metallicity diagnostic plots
using optical indices (e.g Hbeta vs. [MgFe]').Comment: 47 pages, 16 figures, ApJ accepte
Resolving the age bimodality of galaxy stellar populations on kpc scales
Galaxies in the local Universe are known to follow bimodal distributions in
the global stellar populations properties. We analyze the distribution of the
local average stellar-population ages of 654,053 sub-galactic regions resolved
on ~1-kpc scales in a volume-corrected sample of 394 galaxies, drawn from the
CALIFA-DR3 integral-field-spectroscopy survey and complemented by SDSS imaging.
We find a bimodal local-age distribution, with an old and a young peak
primarily due to regions in early-type galaxies and star-forming regions of
spirals, respectively. Within spiral galaxies, the older ages of bulges and
inter-arm regions relative to spiral arms support an internal age bimodality.
Although regions of higher stellar-mass surface-density, mu*, are typically
older, mu* alone does not determine the stellar population age and a bimodal
distribution is found at any fixed mu*. We identify an "old ridge" of regions
of age ~9 Gyr, independent of mu*, and a "young sequence" of regions with age
increasing with mu* from 1-1.5 Gyr to 4-5 Gyr. We interpret the former as
regions containing only old stars, and the latter as regions where the relative
contamination of old stellar populations by young stars decreases as mu*
increases. The reason why this bimodal age distribution is not inconsistent
with the unimodal shape of the cosmic-averaged star-formation history is that
i) the dominating contribution by young stars biases the age low with respect
to the average epoch of star formation, and ii) the use of a single average age
per region is unable to represent the full time-extent of the star-formation
history of "young-sequence" regions.Comment: 17 pages, 11 figures, MNRAS accepte
SĂntesis de kesterita Cu2ZnSn(S,Se)4 mediante mĂ©todos de hot-injection y solvotermal
En el presente trabajo se han sintetizado compuestos con estructura de kesterita Cu2ZnSn(S,Se)4 mediante mĂ©todos de sĂntesis “hot-injection” y solvotermal. Se ha analizado la efectividad de ambos procedimientos sobre las propiedades fĂsico-quĂmicas del material. Paralelamente, se ha estudiado la influencia de precursores y disolventes sobre la reactividad y la morfologĂa del sistema. Los materiales desarrollados se han caracterizado estructural y microestructuralmente.Kesterite solid solution of Cu2ZnSn(S,Se)4 have been synthesized by “hot-injection” and solvothermal methods. The procedure effectiveness that affect to the physical and chemical properties of the final material have been analyzed. The influence of different raw materials and solvents has been investigated in order to improve the preparation procedure. The materials have been characterized structurally and morphologically
The space density distribution of galaxies in the absolute magnitude - rotation velocity plane: a volume-complete Tully-Fisher relation from CALIFA stellar kinematics
The space density distribution of galaxies in the absolute magnitude -
rotation velocity plane: a volume-complete Tully-Fisher relation from CALIFA
stellar kinematicsComment: Accepted to A&
Easy and low-cost aqueous precipitation method to obtain Cu2ZnSn(S, Se)4 thin layers
An easy method to obtain kesterite Cu2ZnSn(Se1-x,Sx)4 (CZTSSe) solid solution as an absorber for thin film photovoltaic solar cells is discussed in this report. Particular emphasis is directed toward the procedure´s steps of the CZTSSe preparation, as well as its structure and properties. For the preparation of CZTSSe an easy, low-cost and sustainable aqueous precipitation method that included chemical transformations of metal selenite precipitate, its reduction to metal selenides and further crystallization of kesterite, is applied. This procedure is more viable as avoids the use of selenization treatment and thus generation of toxic vapors and employs water as a solvent instead of organic compounds. In addition, the proposed procedure is very attractive way of preparation for industrial large-scale fabrication of the most promising absorber candidates for photovoltaic thin film solar cells.
Kesterite CZTSSe solid solution has been prepared and characterized in terms of chemical composition, structural and morphological transformations, as well as optical and electrical properties, confirming the viability and effectiveness of the applied process. The optimal electrical parameters obtained of the device are 21.5 mA/cm2, 532 mV, 42.8%., and 4.9% to short circuit current (Jsc), open circuit voltage (Voc), fill factor (FF), and efficiency (Eff.) respectively. Detailed description of each procedure steps and full characterization of the products, starting from as-prepared, intermediate and final compound is also exposed that could be very useful for any experimental scientist.The authors would like to acknowledge the financial support of the Spanish Ministry of Economy and Competitiveness under the programs RETOS-COLABORACION (RTC-2014–2294-3) and RETOS-INVESTIGACIÓN (ENE2013-49136-C4-2-R). We also appreciate the characterization assistance of Central Service of Scientific Instrumentation (SCIC) at the University Jaume I and Catalonia Institute for Energy Research (IREC) for them help in the Raman measurements and solar cell asembly. R. Martà would like to acknowledge the economic support of the FPI-UJI grand (Formación del personal investigator-Universidad Jaume I)
Preparation of Cu(In,Ga)Se2 photovoltaic absorbers by an aqueous metal selenite co-precipitation route
In this paper, we report a novel and simple solution-based approach for the fabrication of chalcopyrite Cu(In,Ga)Se2 thin film solar cells. An aqueous co-precipitation method based on metal selenites, M2(SeO3)x (M = Cu, In, Ga) precursors was investigated. The resulting powder, dispersed in a binder to form an ink, was coated on a substrate by doctor blade technique. A soft annealing treatment allowed the reduction of metal selenites into selenides. Further rapid thermal processing (RTP) achieved crystalline chalcopyrite absorber. The obtained layer provides good compositional control and adequate morphology for solar cell applications. The water-based synthesis is a sustainable and simple procedure, and together with doctor blade printing, provides a potential cost-effective advantage over conventional fabrication processes (vacuum-based deposition techniques). The short circuit current (JSC), open circuit voltage (VOC), fill factor (FF), and total area power conversion efficiency (Eff.) of the device are 26 mA/cm2, 450 mV, 62%, and 7.2%, respectively. The effective band gap of 1.12 eV confirmed Ga-incorporation in the CIGS crystal lattice.This work was supported by the Spanish Ministry of Science and
Competiveness under INNPACTO Program (IPT-2011-0913-
920000). The authors would like to thanks to Manuel Ocana Jurado ~
(ICMS-CISC) for his help in the XPS measurements. L. Oliveira
would like to thank the support of the National Council for Scientific
and Technological Development (CNPq) e Brazil
Integrated J- and H-band spectra of globular clusters in the LMC: implications for stellar population models and galaxy age dating
(Abridged) The rest-frame near-IR spectra of intermediate age (1-2 Gyr)
stellar populations are dominated by carbon based absorption features offering
a wealth of information. Yet, spectral libraries that include the near-IR
wavelength range do not sample a sufficiently broad range of ages and
metallicities to allow for accurate calibration of stellar population models
and thus the interpretation of the observations. In this paper we investigate
the integrated J- and H-band spectra of six intermediate age (1-3 Gyr) and old
(>10 Gyr) globular clusters in the Large Magellanic Cloud, using observations
obtained with the SINFONI IFU at the VLT. H-band C2 and K-band 12CO(2-0)
feature strengths are compared to the models of Maraston (2005). C2 is
reasonably well reproduced by the models at all ages, while 12CO(2-0) shows
good agreement for older (age>2 Gyr) populations, but the younger (1.3 Gyr)
globular clusters do not follow the models. We argue that this is due to the
fact that the empirical calibration of the models relies on only a few Milky
Way carbon star spectra, which show different 12CO(2-0) index strengths than
the LMC stars. The C2 absorption feature strength correlates strongly with age.
It is present essentially only in populations that have 1-2 Gyr old stars,
while its value is consistent with zero for older populations. The distinct
spectral energy distribution observed for the intermediate age globular
clusters in the J- and H-bands agrees well with the model predictions of
Maraston for the contribution from the thermally pulsing asymptotic giant
branch phase (TP-AGB). We show that the H-band C2 absorption feature and the
J-, H-band spectral shape can be used as an age indicator for intermediate age
stellar populations in integrated spectra of star clusters and galaxies.Comment: 10 pages, 6 figures, abstract abridged, accepted for publication in
A&
The nature of LINER galaxies: Ubiquitous hot old stars and rare accreting black holes
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 (AGN) of low
luminosity, making LINER galaxies the largest AGN-sub-population, dominating 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. Using
integral field spectroscopic data from the CALIFA survey, we aim at comparing
the observed radial surface brightness profiles with what is expected from
illumination by an AGN. Essential for this analysis is a proper extraction of
emission-lines, especially weak lines such as the Balmer Hb line which is
superposed on an absorption trough. To accomplish this, we use the GANDALF code
which simultaneously fits the underlying stellar continuum and emission lines.
We show for 48 galaxies with LINER-like emission, 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. 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 gas
present and 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 in fact 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.Comment: 8 pages, 7 figure
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