330 research outputs found
Recent star formation in clusters of galaxies: extreme compact starbursts in A539 and A634
We report on the detection of two Halpha-emitting extreme compact objects
from deep images of the Abell 634 and Abell 539 clusters of galaxies at z ~
0.03. Follow up long slit spectroscopy of these two unresolved sources revealed
that they are members of their respective clusters showing HII type spectra.
The luminosity and the extreme equivalent width of Halpha+[NII] measured for
these sources, together with their very compact appearance, has raised the
question about the origin of these intense starbursts in the cluster
environment. We propose the compact starburst in Abell 539 resulted from the
compression of the interstellar gas of a dwarf galaxy when entering the cluster
core; while the starburst galaxy in Abell 634 is likely to be the result of a
galaxy-galaxy interaction, illustrating the preprocessing of galaxies during
their infall towards the central regions of clusters. The contribution of these
compact star-forming dwarf galaxies to the star formation history of galaxy
clusters is discussed, as well as a possible link with the recently discovered
early-type ultra-compact dwarf galaxies. We note that these extreme objects
will be rarely detected in normal magnitude-limited optical or NIR surveys,
mainly due to their low stellar masses (of the order of 10^6 solar masses),
whereas they will easily show up in dedicated Halpha surveys given the high
equivalent width of their emission lines.Comment: Accepted for publication in the Astronomical Journal. 31 pages, 10
fig
Absence of quantum-confined Stark effect in GaN quantum disks embedded in (Al,Ga)N nanowires grown by molecular beam epitaxy
Several of the key issues of planar (Al,Ga)N-based deep-ultraviolet light
emitting diodes could potentially be overcome by utilizing nanowire
heterostructures, exhibiting high structural perfection and improved light
extraction. Here, we study the spontaneous emission of GaN/(Al,Ga)N nanowire
ensembles grown on Si(111) by plasma-assisted molecular beam epitaxy. The
nanowires contain single GaN quantum disks embedded in long (Al,Ga)N nanowire
segments essential for efficient light extraction. These quantum disks are
found to exhibit intense emission at unexpectedly high energies, namely,
significantly above the GaN bandgap, and almost independent of the disk
thickness. An in-depth investigation of the actual structure and composition of
the nanowires reveals a spontaneously formed Al gradient both along and across
the nanowire, resulting in a complex core/shell structure with an Al deficient
core and an Al rich shell with continuously varying Al content along the entire
length of the (Al,Ga)N segment. This compositional change along the nanowire
growth axis induces a polarization doping of the shell that results in a
degenerate electron gas in the disk, thus screening the built-in electric
fields. The high carrier density not only results in the unexpectedly high
transition energies, but also in radiative lifetimes depending only weakly on
temperature, leading to a comparatively high internal quantum efficiency of the
GaN quantum disks up to room temperature.Comment: This document is the unedited Author's version of a Submitted Work
that was subsequently accepted for publication in Nano Letters (2019),
copyright (C) American Chemical Society after peer review. To access the
final edited and published work see
https://doi.org/10.1021/acs.nanolett.9b01521, the supporting information is
available (free of charge) under the same lin
Chemical abundances in spiral and irregular galaxies. O and N abundances derived from global emission--line spectra
The validity of oxygen and nitrogen abundances derived from the global
emission-line spectra of galaxies via the P-method has been investigated using
a collection of published spectra of individual HII regions in irregular and
spiral galaxies. The conclusions of Kobulnicky, Kennicutt & Pizagno (1999) that
global emission-line spectra can reliably indicate the chemical properties of
galaxies has been confirmed. It has been shown that the comparison of the
global spectrum of a galaxy with a collection of spectra of individual HII
regions can be used to distinguish high and low metallicity objects and to
estimate accurate chemical abundances in a galaxy. The oxygen and nitrogen
abundances in samples of UV-selected and normal nearby galaxies have been
determined. It has been found that the UV-selected galaxies occupy the same
area in the N/O -- O/H diagram as individual HII regions in nearby galaxies.
Finally, we show that intermediate-redshift galaxies systematically deviate
from the metallicity -- luminosity trend of local galaxies.Comment: 15 pages, 17 figures, accepted for publication in Astronomy and
Astrophysic
Determining efficacy of monitoring devices on ceramic bond to resin composite
Objectives: This paper aims to assess the effectiveness of 3D nanoroughness and 2D microroughness evaluations, by their correlation with contact angle measurements and shear bond strength test, in order to evaluate the effect of two different acids conditioning on the bonding efficacy of a leucite-based glass-ceramic to a composite resin. Study Design: Ceramic (IPS Empress) blocks were treated as follows: 1) no treatment, 2) 37% phosphoric acid (H 3 PO 4 ), 15 s, 3) 9% hydrofluoric acid (HF), 5 min. Micro- and nano-roughness were assessed with a profilometer and by means of an atomic force microscopy (AFM). Water contact angle (CA) measurements were determined to assess wettability of the ceramic surfaces with the asixymetric drop shape analysis contact diameter technique. Shear bond strength (SBS) was tested to a resin composite (Z100) with three different adhesive systems (Scotch bond Multipurpose Plus, Clearfil New Bond, ProBOND). Scanning electron microscopy (SEM) images were performed. Results: Nanoroughness values assessed in 50x50 ?m areas were higher for the HF group, these differences were not detected by profilometric analysis. HF treatment created the nano- roughest surfaces and the smallest CA (p<0.05), producing the highest SBS to the composite resin with all tested adhesive systems (p<0.05). No diffe- rences existed between the SBS produced by the adhesive systems evaluated with any of the surface treatments tested. Conclusions: Nano-roughness obtained in a 50x50 ?m scan size areas was the most reliable data to evaluate the topographical changes produced by the different acid treatments on ceramic surfaces
Nearby supernova host galaxies from the CALIFA Survey: II. SN environmental metallicity
The metallicity of a supernova (SN) progenitor, together with its mass, is
one of the main parameters that rules their outcome. We present a metallicity
study of 115 nearby SN host galaxies (0.005<z<0.03) which hosted 142 SNe using
Integral Field Spectroscopy (IFS) from the CALIFA survey. Using O3N2 we found
no statistically significant differences between the gas-phase metallicities at
the locations of the three main SN types (Ia, Ib/c and II) all having
~8.500.02 dex. The total galaxy metallicities are also very similar and we
argue that this is because our sample consists only of SNe discovered in
massive galaxies (log(M/Msun)>10 dex) by targeted searches. We also found no
evidence that the metallicity at the SN location differs from the average
metallicity at the GCD of the SNe. By extending our SN sample with published
metallicities at the SN location, we studied the metallicity distributions for
all SN subtypes split into SN discovered in targeted and untargeted searches.
We confirm a bias toward higher host masses and metallicities in the targeted
searches. Combining data from targeted and untargeted searches we found a
sequence from higher to lower local metallicity: SN Ia, Ic, and II show the
highest metallicity, which is significantly higher than SN Ib, IIb, and Ic-BL.
Our results support the picture of SN Ib resulting from binary progenitors and,
at least part of, SN Ic being the result of single massive stars stripped of
their outer layers by metallicity driven winds. We studied several proxies of
the local metallicity frequently used in the literature and found that the
total host metallicity allows for the estimation of the metallicity at the SN
location with an accuracy better than 0.08 dex and very small bias. In
addition, weak AGNs not seen in total spectra may only weakly bias (by 0.04
dex) the metallicity estimate from integrated spectra. (abridged)Comment: 24 pages, 16 Figures, 13 Tables, Accepted in A&
Isolation, Characterization and Antitumour Propirties of the 1,2-Popylenediaminetetraacetate trans-Diaqua-Copper (II)
A trans-diaquacomplex formed by copper(II) sulphate and the sequestering polyamminopolycarboxylic
ligand 1,2-propylenediaminetetraacetic acid (PDTA) has been isolated and characterized by
chemical analysis, titrimetry, FT-IR and electronic spectroscopy, Potentiometric and electronic
measurements identified the ligand as tetradentate, two nitrogen and two oxygen atoms being bonded to the
Cu(II) in planar positions. This octahedral monomeric soluble compound, is an unusual example of a copper
(II) substance showing significant in vitro antitumour activity against the human ovarian tumour cells TG
(ID50 = 2.29 μM at 48 h) and important in vivo antitumour activity against solid Sarcoma 180 with
complete regression of the tumour at a dose of 12.5 mg/Kg body weight
The impact of environmental effects on AGN: a decline in the incidence of ionized outflows
AGN have been generally considered to be less frequent in denser environments
due to the lower number of galaxy-galaxy interactions and/or the removal of
their gas-rich reservoirs by the dense intergalactic medium. However, recent
observational and theoretical works suggest that the effect of ram-pressure
stripping might reduce the angular momentum of their gas, causing it to infall
towards the super massive black hole (SMBH) at their centre, activating the AGN
phase. In this work we explore the connection between environment and nuclear
activity by evaluating the variation in the incidence of ionized outflows in
AGN across different environments. We select a sample of optical AGN
from the Sloan Digital Sky Survey Data Release 13 that we match with the group
catalogue from Lim et al. 2017. We further probe their environment through the
projected distance to the central galaxy of the group/cluster and the projected
surface density to the 5th neighbour (). We find that at lower masses
(M), the fraction of ionized outflows is significantly
lower in satellite (%) than in isolated (%) AGN. The fraction of
outflows in all satellite AGN decreases towards closer distances to the
central, whereas only the lower-mass ones display a significant decline with
. Although this study does not include AGN in the densest regions of
galaxy clusters, our findings suggest that AGN in dense environments accrete
less gas than those in the field potentially due to the removal of the gas
reservoirs via stripping or starvation, consistent with a negative connection
between environment and AGN activity. We propose that the observed change in
the incidence of outflows towards denser regions of groups and clusters could
contribute to the higher gas metallicities of cluster galaxies compared to
field ones, especially at lower masses.Comment: 9 pages, 6 figures, Accepted for publication in Astronomy and
Astrophysic
The interplay between ionized gas and massive stars in the HII galaxy IIZw70: integral field spectroscopy with PMAS
We performed an integral field spectroscopic study for the HII galaxy IIZw70
in order to investigate the interplay between its ionized interstellar medium
(ISM) and the massive star formation (SF). Observations were taken in the
optical spectral range (3700-6800 A) with the Potsdam Multi-Aperture
Spectrophotometer (PMAS) attached to the 3.5 m telescope at CAHA. We created
and analysed maps of spatially distributed emission-lines, continuum emission
and properties of the ionized ISM (e.g. physical-chemical conditions, dust
extinction, kinematics). We investigated the relation of these properties to
the spatial distribution and evolutionary stage of the massive stars. For the
first time we have detected the presence of Wolf-Rayet (WR) stars in this
galaxy. The peak of the ionized gas emission coincides with the location of the
WR bump. The region of the galaxy with lower dust extinction corresponds to the
region that shows the lowest values of velocity dispersion and radial velocity.
The overall picture suggests that the ISM of this region is being disrupted via
photoionization and stellar winds, leading to a spatial decoupling between
gas+stars and dust clouds. The bulk of dust appears to be located at the
boundaries of the region occupied by the probable ionizing cluster. We also
found that this region is associated to the nebular emission in HeII4686 and to
the intensity maximum of most emission lines. This indicates that the hard
ionizing radiation responsible for the HeII4686 nebular emission can be related
to the youngest stars. Within 0.4 x 0.3 kpc^2 in the central burst, we
derived O/H using direct determinations of Te[OIII]. We found abundances in the
range 12+log(O/H)=7.65-8.05, yielding an error-weighted mean of
12+log(O/H)=7.86 0.05.Comment: 10 pages, 10 figures, accepted for publication in A&A, minor changes
adde
Integral field spectroscopy of M1-67. A Wolf-Rayet nebula with LBVN appearance
This work aims to disentangle the morphological, kinematic, and chemical
components of the nebula M1-67 to shed light on its process of formation around
the central Wolf-Rayet (WR) star WR124. We have carried out integral field
spectroscopy observations over two regions of M1-67, covering most of the
nebula in the optical range. Maps of electron density, line ratios, and radial
velocity were created to perform a detailed analysis of the two-dimensional
structure. We studied the physical and chemical properties by means of
integrated spectra selected over the whole nebula. Photoionization models were
performed to confirm the empirical chemical results theoretically. In addition,
we analysed infrared spectroscopic data and the MIPS 24micron image of M1-67
from Spitzer. We find that the ionized gas of M1-67 is condensed in knots
aligned in a preferred axis along the NE-SW direction, like a bipolar
structure. Both electron density and radial velocity decrease in this direction
when moving away from the central star. From the derived electron temperature,
Te~8200 K, we have estimated chemical abundances, obtaining that nitrogen
appears strongly enriched and oxygen depleted. From the last two results, we
infer that this bipolarity is the consequence of an ejection of an evolved
stage of WR124 with material processed in the CNO cycle. The infrared study has
revealed that the bipolar axis is composed of ionized gas with a low ionization
degree that is well mixed with warm dust and of a spherical bubble surrounding
the ejection at 24micron. Taking the evolution of a 60 Mo star and the temporal
scale of the bipolar ejection into account, we propose that the observed gas
was ejected during an eruption in the luminous blue variable. The star has
entered the WR phase recently without apparent signs of interaction between
WR-winds and interstellar material.Comment: Accepted for publication in section 6 of Astronomy and Astrophysics.
The official date of acceptance is 15/03/2013. 17 pages, 14 figures and 8
table
Abundance determination in HII regions from spectra without the [OII]3727+3729 line
We suggest an empirical calibration for determination of oxygen and nitrogen
abundances and electron temperature in HII regions where the [OII]3727+3729
line (R_2) is not available. The calibration is based on the strong emission
lines of OIII, NII, and SII (NS calibration) and derived using the spectra of
HII regions with measured electron temperatures as calibration datapoints. The
NS calibration makes it possible to derive abundances for HII regions in nearby
galaxies from the SDSS spectra where R_2 line is out of the measured wavelength
range, but can also be used for the oxygen and nitrogen abundances
determinations in any HII region independently whether the nebular oxygen line
[OII]3727+3729 is available or not. The NS calibration provides reliable oxygen
and nitrogen abundances for HII regions over the whole range of metallicities.Comment: 6 pages, 4 figures, accepted for publication in the MNRA
- …