338 research outputs found
Characterizing Bars at z~0 in the optical and NIR: Implications for the Evolution of Barred Disks with Redshift
Critical insights on galaxy evolution stem from the study of bars. With the
advent of HST surveys that trace bars in the rest-frame optical out to z~1, it
is critical to provide a reference baseline for bars at z~0 in the optical
band. We present results on bars at z~0 in the optical and NIR bands based on
180 spirals from OSUBSGS. (1) The deprojected bar fraction at z~0 is ~60% +/-6%
in the NIR H-band and ~44% +/-6% in the optical B-band. (2) The results before
and after deprojection are similar, which is encouraging for high-redshift
studies that forego deprojection. (3) Studies of bars at z~0.2-1.0 (lookback
time of 3-8 Gyr) have reported an optical bar fraction of ~30% +/-6%, after
applying cutoffs in absolute magnitude (M_V = 1.5
kpc), and bar ellipticity (e_bar >= 0.4). Applying these exact cutoffs to the
OSUBSGS data yields a comparable optical B-band bar fraction at z~0 of ~
34%+/-6%. This rules out scenarios where the optical bar fraction in bright
disks declines strongly with redshift. (4) Most (~70%) bars have moderate to
high strentgh or ellipticity (0.50 <= e_bar <= 0.75). There is no bimodality in
the distribution of e_bar. The H-band bar fraction and e_bar show no
substantial variation across RC3 Hubble types Sa to Scd. (5) RC3 bar types
should be used with caution. Many galaxies with RC3 types "AB" turn out to be
unbarred and RC3 bar classes "B" and "AB" have a significant overlap in e_bar.
(6) Most bars have sizes below 5 kpc. Bar and disk sizes correlate, and most
bars have a_bar/R_25~0.1-0.5. This suggests that the growths of bars and disks
are intimately tied.Comment: 11 pages, 17 figures, 3 tables, ApJ accepted, abridged abstract
below. Minor changes and shortened paper for ApJ limits. For high resolution
figures see http://www.as.utexas.edu/~marinova/paper1-highres.pd
Influence of plasma treatment on SiO2/Si and Si3N4/Si substrates for large-scale transfer of graphene
One of the limiting factors of graphene integration into electronic, photonic, or sensing devices is the unavailability of large-scale graphene directly grown on the isolators. Therefore, it is necessary to transfer graphene from the donor growth wafers onto the isolating target wafers. In the present research, graphene was transferred from the chemical vapor deposited 200 mm Germanium/Silicon (Ge/Si) wafers onto isolating (SiO2/Si and Si3N4/Si) wafers by electrochemical delamination procedure, employing poly(methylmethacrylate) as an intermediate support layer. In order to influence the adhesion properties of graphene, the wettability properties of the target substrates were investigated in this study. To increase the adhesion of the graphene on the isolating surfaces, they were pre-treated with oxygen plasma prior the transfer process of graphene. The wetting contact angle measurements revealed the increase of the hydrophilicity after surface interaction with oxygen plasma, leading to improved adhesion of the graphene on 200 mm target wafers and possible proof-of-concept development of graphene-based devices in standard Si technologies
Author Correction: Influence of plasma treatment on SiO2/Si and Si3N4/Si substrates for large-scale transfer of graphene
The original version of this Article omitted an affiliation for M. Lisker. The correct affiliations for M. Lisker are listed below: IHP- Leibniz Institut für innovative Mikroelektronik, Im Technologiepark 25, 15236, Frankfurt (Oder), Germany Technical University of Applied Science Wildau, Hochschulring 1, 15745, Wildau, Germany The original Article and accompanying Supplementary Information file have been corrected
The young stellar population at the center of NGC 205
Context. NGC 205 is a peculiar dwarf elliptical galaxy hosting in its center
a population of young blue stars. Their origin is still matter of debate, the
central fresh star formation activity possibly being related to dynamical
interactions between NGC 205 and M31. Aims. The star formation history in the
central 30\arcsec (120 pc) around the NGC 205 central nucleus is
investigated in order to obtain clues to the origin of the young stellar
population. Methods. Deep HST/ACS CCD photometry is compared with theoretical
isochrones and luminosity functions to characterize the stellar content of the
region under study and compute the recent SF rate. Results. Our photometry
reveals a previously undetected blue plume of young stars clearly
distinguishable down to I26. Our analysis suggests that 1.9
M were produced between approximately 62 Myr and 335 Myr ago in the NGC
205 inner regions, with a latest minor episode occurring 25 Myr ago. This
implies a star formation rate of M/yr over this
period. Conclusions. The excellent fit of the observed luminosity function of
young main sequence stars obtained with a model having a constant star
formation rate argues against a tidally triggered star formation activity over
the last 300 Myr. Rather, a constant SF may be consistent with NGC 205
being on its first interaction with M 31.Comment: 5 pages, 2 figures, accepted for publication in A&A letter
Internal convection in thermoelectric generator models
Coupling between heat and electrical currents is at the heart of
thermoelectric processes. From a thermal viewpoint this may be seen as an
additional thermal flux linked to the appearance of electrical current in a
given thermoelectric system. Since this additional flux is associated to the
global displacement of charge carriers in the system, it can be qualified as
convective in opposition to the conductive part associated with both phonons
transport and heat transport by electrons under open circuit condition, as,
e.g., in the Wiedemann-Franz relation. In this article we demonstrate that
considering the convective part of the thermal flux allows both new insight
into the thermoelectric energy conversion and the derivation of the maximum
power condition for generators with realistic thermal coupling.Comment: 8 pages, 3 figure
Formation and evolution of dwarf early-type galaxies in the Virgo cluster I. Internal kinematics
We present new medium resolution kinematic data for a sample of 21 dwarf
early-type galaxies (dEs) mainly in the Virgo cluster, obtained with the WHT
and INT telescopes at the Roque de los Muchachos Observatory (La Palma, Spain).
These data are used to study the origin of the dwarf elliptical galaxy
population inhabiting clusters. We confirm that dEs are not dark matter
dominated galaxies, at least up to the half-light radius. We also find that the
observed galaxies in the outer parts of the cluster are mostly rotationally
supported systems with disky morphological shapes. Rotationally supported dEs
have rotation curves similar to those of star forming galaxies of similar
luminosity and follow the Tully-Fisher relation. This is expected if dE
galaxies are the descendant of low luminosity star forming systems which
recently entered the cluster environment and lost their gas due to a ram
pressure stripping event, quenching their star formation activity and
transforming into quiescent systems, but conserving their angular momentum.Comment: 24 pages, 15 figures and 7 tables. Replaced to match the journal
versio
Young, metal-enriched cores in early-type dwarf galaxies in the Virgo cluster based on colour gradients
Early-type dwarf galaxies are not simply featureless, old objects, but were
found to be much more diverse, hosting substructures and a variety of stellar
population properties. To explore the stellar content of faint early-type
galaxies, and to investigate in particular those with recent central star
formation, we study colours and colour gradients within one effective radius in
optical (g-r) and near-infrared (i-H) bands for 120 Virgo cluster early types
with -19 mag < < -16 mag. Twelve galaxies turn out to have blue cores,
when defined as g-r colour gradients larger than 0.10 mag/, which
represents the positive tail of the gradient distribution. For these galaxies,
we find that they have the strongest age gradients, and that even outside the
blue core, their mean stellar population is younger than the mean of ordinary
faint early types. The metallicity gradients of these blue-cored early-type
dwarf galaxies are, however, in the range of most normal faint early types,
which we find to have non-zero gradients with higher central metallicity. The
blue central regions are consistent with star formation activity within the
last few 100 Myr. We discuss that these galaxies could be explained by
environmental quenching of star formation in the outer galaxy regions, while
the inner star formation activity has continued
The Fornax Deep Survey with VST. I. The extended and diffuse stellar halo of NGC~1399 out to 192 kpc
[Abrigded] We have started a new deep, multi-imaging survey of the Fornax
cluster, dubbed Fornax Deep Survey (FDS), at the VLT Survey Telescope. In this
paper we present the deep photometry inside two square degrees around the
bright galaxy NGC1399 in the core of the cluster. We found a very extended and
diffuse envelope surrounding the luminous galaxy NGC1399: we map the surface
brightness out to 33 arcmin (~ 192 kpc) from the galaxy center and down to
about 31 mag/arcsec^2 in the g band. The deep photometry allows us to detect a
faint stellar bridge in the intracluster region between NGC1399 and NGC1387. By
analyzing the integrated colors of this feature, we argue that it could be due
to the ongoing interaction between the two galaxies, where the outer envelope
of NGC1387 on its east side is stripped away. By fitting the light profile, we
found that it exists a physical break radius in the total light distribution at
R=10 arcmin (~58 kpc) that sets the transition region between the bright
central galaxy and the outer exponential stellar halo. We discuss the main
implications of this work on the build-up of the stellar halo at the center of
the Fornax cluster. By comparing with the numerical simulations of the stellar
halo formation for the most massive BCGs, we find that the observed stellar
halo mass fraction is consistent with a halo formed through the multiple
accretion of progenitors with a stellar mass in the range 10^8 - 10^11 M_sun.
This might suggest that the halo of NGC1399 has also gone through a major
merging event. The absence of a significant number of luminous stellar streams
and tidal tails out to 192 kpc suggests that the epoch of this strong
interaction goes back to an early formation epoch. Therefore, differently from
the Virgo cluster, the extended stellar halo around NGC1399 is characterised by
a more diffuse and well-mixed component, including the ICL.Comment: Accepted for publication in ApJ; 25 pages and 14 figures. An higher
resolution file is available at the following link
https://www.dropbox.com/s/fvltppduysdn6pb/NGC1399_fin_2c.pdf?dl=
Stellar Kinematics and Structural Properties of Virgo Cluster Dwarf Early-Type Galaxies from the SMAKCED Project. I. Kinematically Decoupled Cores and Implications for Infallen Groups in Clusters
We present evidence for kinematically decoupled cores (KDCs) in two dwarf
early-type (dE) galaxies in the Virgo cluster, VCC 1183 and VCC 1453, studied
as part of the SMAKCED stellar absorption-line spectroscopy and imaging survey.
These KDCs have radii of 1.8'' (0.14 kpc) and 4.2'' (0.33 kpc), respectively.
Each of these KDCs is distinct from the main body of its host galaxy in two
ways: (1) inverted sense of rotation; and (2) younger (and possibly more
metal-rich) stellar population. The observed stellar population differences are
probably associated with the KDC, although we cannot rule out the possibility
of intrinsic radial gradients in the host galaxy. We describe a statistical
analysis method to detect, quantify the significance of, and characterize KDCs
in long-slit rotation curve data. We apply this method to the two dE galaxies
presented in this paper and to five other dEs for which KDCs have been reported
in the literature. Among these seven dEs, there are four significant KDC
detections, two marginal KDC detections, and one dE with an unusual central
kinematic anomaly that may be an asymmetric KDC.The frequency of occurence of
KDCs and their properties provide important constraints on the formation
history of their host galaxies. We discuss different formation scenarios for
these KDCs in cluster environments and find that dwarf-dwarf wet mergers or gas
accretion can explain the properties of these KDCs. Both of these mechanisms
require that the progenitor had a close companion with a low relative velocity.
This suggests that KDCs were formed in galaxy pairs residing in a poor group
environment or in isolation whose subsequent infall into the cluster quenched
star formation.Comment: 14 pages, accepted for publication in Ap
Stellar age versus mass of early-type galaxies in the Virgo Cluster
The flux excess of elliptical galaxies in the far-ultraviolet can be
reproduced by population synthesis models when accounting for the population of
old hot helium-burning subdwarf stars. This has been achieved by Han and
coworkers through a quantitative model of binary stellar evolution. Here, we
compare the resulting evolutionary population synthesis model to the GALEX
far-near ultraviolet colors (FUV-NUV) of Virgo cluster early-type galaxies that
were published by Boselli and coworkers. FUV-NUV is reddest at about the
dividing luminosity of dwarf and giant galaxies, and becomes increasingly blue
for both brighter and fainter luminosities. This behavior can be easily
explained by the binary model with a continuous sequence of longer duration and
later truncation of star formation at lower galaxy masses. Thus, in contrast to
previous conclusions, the GALEX data do not require a dichotomy between the
stellar population properties of dwarfs and giants. Their apparently opposite
behavior in FUV-NUV occurs naturally when the formation of hot subdwarfs
through binary evolution is taken into account.Comment: 8 pages, 4 figures. Accepted for publication in Ap
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