75 research outputs found
New insights to the photometric structure of Blue Compact Dwarf Galaxies from deep Near-Infrared studies: II. The sample of northern BCDs
This paper is part of a series of publications which present a systematic
study of Blue Compact Dwarf (BCD) Galaxies in the Near Infrared (NIR). Compared
to the visible light, NIR data allow a better separation of the starburst
emission from the light distribution of the old stellar low-surface brightness
(LSB) host galaxy. We analyze deep NIR broad band images of a sample of 11
BCDs, observed with the Calar Alto 3.6m telescope. This work enlarges the
samples presented in preceding papers of this study (Noeske et al. 2003, Cairos
et al. 2003) by BCDs of the most common morphological type, displaying a
regular elliptical LSB host galaxy. The data presented here allow the detection
and quantitative study of the extended stellar LSB host galaxy in all sample
BCDs. The NIR surface brightness profiles (SBPs) of the LSB host galaxies agree
at large galactocentric radii with those from optical studies, showing also an
exponential intensity decrease and compatible scale lengths. Similar to Noeske
et al. (2003), we find centrally flattening exponential (type V) SBPs of the
host galaxy for several BCDs. Such SBPs remain mostly undetected in optical
bands, due to the comparatively stronger starburst emission at these
wavelengths. We apply a modified exponential distribution to decompose and
quantitatively analyze SBPs of LSB hosts with a type V intensity distribution.
We present the results of the surface photometry and the decomposition of SBPs,
and discuss individual objects with respect to morphological details of their
star-forming regions.Comment: 18 pages, 11 figures; accepted for publication in Astronomy &
Astrophysics; postscript file with full resolution images available at
http://www.ucolick.org/~kai/PUB/noeske_nirbcds_2.ps.g
Limits on the Transverse Velocity of the Lensing Galaxy in Q2237+0305 from the Lack of Strong Microlensing Variability
We present a method for the determination of upper limits on the transverse
velocity of the lensing galaxy in the quadruple quasar system Q2237+0305, based
on the lack of strong microlensing signatures in the quasar lightcurves. The
limits we derive here are based on four months of high quality monitoring data,
by comparing the low amplitudes of the lightcurves of the four components with
extensive numerical simulations. We make use of the absence of strong
variability of the components (especially components B and D) to infer that a
"flat" time interval of such a length is only compatible with an effective
transverse velocity of the lensing galaxy of v_bulk <=630 km/s for typical
microlenses masses of M_microlens=0.1 M_solar (or v_bulk <=2160 km/s for
M_microlens=1.0 M_solar) at the 90% confidence level. This method may be
applicable in the future to other systems.Comment: 7 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
Measuring transverse velocities in gravitationally lensed extragalactic systems using an annual parallax effect
A parallax method to determine transverse velocity in a gravitationally
lensed system is described. Using the annual motion of the Earth around the Sun
allows us to probe the local structure of the magnification map that, under
certain assumptions, can be used to infer the effective transverse velocity.
The method is applied to OGLE data for QSO2237+0305 and the velocity value is
estimated to be about (15 +/- 10) km/s if attributed to the lensing galaxy or
about (420 +/- 300) km/s if attributed to the quasar. We find this estimate
unreasonably small and conclude that we have not measured a parallax effect. We
give a short list of properties that a system should possess to allow a
successful implementation of this method.Comment: v2: journal reference update
Dynamics of Starbursting Dwarf Galaxies: I Zw 18
I Zw 18 is a prototype Blue Compact Dwarf (BCD), characterized by a strong
starburst and extremely low metallicity (Z ~ 0.02 Zsun). It has long been
considered a candidate young galaxy in the Local Universe, but recent studies
indicate the presence of old stars. We analysed archival VLA observations of
the 21 cm line and found that the HI associated to the starburst region forms a
compact fast-rotating disk. The HI column densities are very high, up to
~50-100 Msun/pc^2 (~0.6-1.2 x 10^22 atoms/cm^2). The rotation curve is flat
with a steep rise in the inner parts, indicating the presence of a strong
central concentration of mass. Mass models with a dark matter halo show that
baryons may dominate the gravitational potential in the inner regions. A radial
inflow/outflow motion of ~15 km/s is also present. I Zw 18 appears structurally
different from typical dwarf irregulars in terms of gas distribution, stellar
distribution and dynamics. It may be considered as a "miniature"
high-surface-brightness disk galaxy. These dynamical properties must be tightly
related to the starburst. They also shed new light on the question of the
descendants of BCDs. There is also extended HI emission towards the outlying
stellar complex I Zw 18 C and a ~13.5 kpc HI tail. An interaction/merger
between gas-rich dwarfs is the most likely explanation for the starburst.Comment: 13 pages, 10 figures, to be published in Astronomy & Astrophysic
Weak lensing reconstruction through cosmic magnification I: a minimal variance map reconstruction
We present a concept study on weak lensing map reconstruction through the
cosmic magnification effect in galaxy number density distribution. We propose a
minimal variance linear estimator to minimize both the dominant systematical
and statistical errors in the map reconstruction. It utilizes the distinctively
different flux dependences to separate the cosmic magnification signal from the
overwhelming galaxy intrinsic clustering noise. It also minimizes the shot
noise error by an optimal weighting scheme on the galaxy number density in each
flux bin. Our method is in principle applicable to all galaxy surveys with
reasonable redshift information. We demonstrate its applicability against the
planned Square Kilometer Array survey, under simplified conditions. Weak
lensing maps reconstructed through our method are complementary to that from
cosmic shear and CMB and 21cm lensing. They are useful for cross checking over
systematical errors in weak lensing reconstruction and for improving
cosmological constraints.Comment: 12 pages, 9 figures, published in MNRA
Embryonic Pig Pancreatic Tissue Transplantation for the Treatment of Diabetes
BACKGROUND: Transplantation of embryonic pig pancreatic tissue as a source of insulin has been suggested for the cure of diabetes. However, previous limited clinical trials failed in their attempts to treat diabetic patients by transplantation of advanced gestational age porcine embryonic pancreas. In the present study we examined growth potential, functionality, and immunogenicity of pig embryonic pancreatic tissue harvested at different gestational ages. METHODS AND FINDINGS: Implantation of embryonic pig pancreatic tissues of different gestational ages in SCID mice reveals that embryonic day 42 (E42) pig pancreas can enable a massive growth of pig islets for prolonged periods and restore normoglycemia in diabetic mice. Furthermore, both direct and indirect T cell rejection responses to the xenogeneic tissue demonstrated that E42 tissue, in comparison to E56 or later embryonic tissues, exhibits markedly reduced immunogenicity. Finally, fully immunocompetent diabetic mice grafted with the E42 pig pancreatic tissue and treated with an immunosuppression protocol comprising CTLA4-Ig and anti–CD40 ligand (anti-CD40L) attained normal blood glucose levels, eliminating the need for insulin. CONCLUSIONS: These results emphasize the importance of selecting embryonic tissue of the correct gestational age for optimal growth and function and for reduced immunogenicity, and provide a proof of principle for the therapeutic potential of E42 embryonic pig pancreatic tissue transplantation in diabetes
Gas Metallicities in the Extended Disks of NGC 1512 and NGC 3621. Chemical Signatures of Metal Mixing or Enriched Gas Accretion?
(Abridged) We have obtained spectra of 135 HII regions located in the inner
and extended disks of the spiral galaxies NGC 1512 and NGC 3621, spanning the
range of galactocentric distances 0.2-2 x R25 (from 2-3 kpc to 18-25 kpc). We
find that the excitation properties of nebulae in the outer (R>R25) disks are
similar to those of the inner disks, but on average younger HII regions tend to
be selected in the bright inner disks. Reddening by dust is not negligible in
the outer disks, and subject to significant large-scale spatial variations. For
both galaxies the radial abundance gradient flattens to a constant value
outside of the isophotal radius. The outer disk O/H abundance ratio is highly
homogeneous, with a scatter of only ~0.06 dex. Based on the excitation and
chemical (N/O ratio) analysis we find no compelling evidence for variations in
the upper initial mass function of the ionizing clusters of extended disks. The
O/H abundance in the outer disks of the target galaxies corresponds to 35% of
the solar value (or higher, depending on the metallicity diagnostic). This
conflicts with the notion that metallicities in extended disks of spiral
galaxies are necessarily low. The observed metal enrichment cannot be produced
with the current level of star formation. We discuss the possibility that metal
transport mechanisms from the inner disks lead to metal pollution of the outer
disks. Gas accretion from the intergalactic medium, enriched by outflows,
offers an alternative solution.Comment: Accepted for publication in the Astrophysical Journa
Luminosity-Metallicity Relation for dIrr Galaxies in the Near-Infrared
(abridged) The present work is a first step to collect homogeneous abundances
and near-infrared (NIR) luminosities for a sample of dwarf irregular (dIrr)
galaxies, located in nearby groups. The use of NIR luminosities is intended to
provide a better proxy to mass than the blue luminosities commonly used in the
literature; in addition, selecting group members reduces the impact of
uncertain distances. Accurate abundances are derived to assess the galaxy
metallicity. Optical spectra are collected for Hii regions in the dIrrs,
allowing the determination of oxygen abundances by means of the
temperature-sensitive method. For each dIrr galaxy H-band imaging is performed
and the total magnitudes are measured via surface photometry. This high-quality
database allows us to build a well-defined luminosity-metallicity relation in
the range -13 >= M(H) >= -20. The scatter around its linear fit is reduced to
0.11 dex, the lowest of all relations currently available. There might exist a
difference between the relation for dIrrs and the relation for giant galaxies,
although a firm conclusion should await direct abundance determinations for a
significant sample of massive galaxies. This new dataset provides an improved
luminosity-metallicity relation, based on a standard NIR band, for dwarf
star-forming galaxies. The relation can now be compared with some confidence to
the predictions of models of galaxy evolution. Exciting follow-ups of this work
are (a) exploring groups with higher densities, (b) exploring nearby galaxy
clusters to probe environmental effects on the luminosity-metallicity relation,
and (c) deriving direct oxygen abundances in the central regions of
star-forming giant galaxies, to settle the question of a possible dichotomy
between the chemical evolution of dwarfs and that of massive galaxies.Comment: 23 pages, 10 figures, accepted by A&
Two phase galaxy formation: The Gas Content of Normal Galaxies
We investigate the atomic (HI) and molecular (H_2) Hydrogen content of normal
galaxies by combining observational studies linking galaxy stellar and gas
budgets to their host dark matter (DM) properties, with a physically grounded
galaxy formation model. This enables us to analyse empirical relationships
between the virial, stellar, and gaseous masses of galaxies and explore their
physical origins. Utilising a semi-analytic model (SAM) to study the evolution
of baryonic material within evolving DM halos, we study the effects of baryonic
infall and various star formation and feedback mechanisms on the properties of
formed galaxies using the most up-to-date physical recipes. We find that in
order to significantly improve agreement with observations of low-mass galaxies
we must suppress the infall of baryonic material and exploit a two-phase
interstellar medium (ISM), where the ratio of HI to H_2 is determined by the
galactic disk structure. Modifying the standard Schmidt-Kennicutt star
formation law, which acts upon the total cold gas in galaxy discs and includes
a critical density threshold, and employing a star formation law which
correlates with the H_2 gas mass results in a lower overall star formation
rate. This in turn, allows us to simultaneously reproduce stellar, HI and H_2
mass functions of normal galaxies.Comment: 16 pages, 12 figures, 1 table. Moderate revision to match version
accepted for publication in MNRA
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