148 research outputs found
Conditions for detecting lensed Population III galaxies in blind surveys with the James Webb Space Telescope, the Roman Space Telescope and Euclid
Dark matter halos that reach the HI-cooling mass without prior star formation
or external metal pollution represent potential sites for the formation of
small Population III galaxies at high redshifts. Such objects are expected to
attain total stellar masses of at most solar masses and will therefore
typically be extremely faint. Gravitational lensing may in rare cases boost
their fluxes to detectable levels, but to find even a small number of such
objects requires very large sky areas to be surveyed. Because of this, a small,
wide-field telescope can in principle offer better detection prospects than a
large telescope with a smaller field of view. Here, we derive the Pop III
galaxy properties - in terms of comoving number density, stellar initial mass
function and total stellar mass - required to allow gravitational lensing to
lift such objects at redshift z = 5-16 above the detection thresholds of blind
surveys carried out with the James Webb space telescope (JWST), the Roman space
telescope (RST) or Euclid. We find that the prospects for photometric
detections of Pop III galaxies are promising, and that they are better for RST
than for JWST and Euclid. However, the Pop III galaxies favoured by current
simulations have number densities too low to allow spectroscopic detections
based on the strength of the HeII1640 emission line in any of the considered
surveys unless very high star formation efficiencies (10 per cent) are envoked.Comment: 13 pages, 4 figure
Nitrogen substitutional defects in silicon. A quantum mechanical investigation of the structural, electronic and vibrational properties
RD and FSG acknowledges the CINECA award (HP10CTG8YY) under the ISCRA initiative, for the availability of high performance
computing resources and support.The vibrational infrared (IR) and Raman spectra of seven substitutional defects in bulk silicon are computed, by using the quantum mechanical CRYSTAL code, the supercell scheme, an all electron Gaussian type basis set and the B3LYP functional. The relative stability of various spin states has been evaluated, the geometry optimized, the electronic structure analyzed. The IR and Raman intensities have been evaluated analitically. In all cases the IR spectrum is dominated by a single N peak (or by two or three peaks with very close wavenumbers), whose intensity is at least 20 times larger than the one of any other peak. These peaks fall in the 645â712 cmâ1 interval, and a shift of few cmâ1 is observed from case to case. The Raman spectrum of all defects is dominated by an extremely intense peak at about 530 cmâ1, resulting from the (weak) perturbation of the peak of pristine silicon.ISCRA initiative CINECA award (HP10CTG8YY); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Unionâs Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART
The stellar populations of the bluest low surface brightness galaxies
Using optical/near-IR broadband photometry together with Halpha emission line
data, we attempt to constrain the star formation histories, ages, total stellar
masses and stellar mass-to-light ratios for a sample of extremely blue low
surface brightness galaxies. We find that, under standard assumptions about the
stellar initial mass function, the Halpha equivalent widths of these objects
appear inconsistent with recently suggested scenarios including constant or
increasing star formation rates over cosmological time scales. In a critical
assessment of the prospects of obtaining ages from integrated broadband
photometry, we conclude that even with near-IR data, the ages are poorly
constrained and that current observations cannot rule out the possibility that
these objects formed as recently as 1-2 Gyr ago. Methods which could
potentially improve the age estimates are discussed. The stellar masses of
these galaxies are inferred to lie below 10^10 solar masses. This, in
combination with low ages, could constitute a problem for current hierarchical
models of galaxy formation, which predict objects of this mass to form
predominantly early in the history of the universe. The possibility to use the
ages of the bluest low surface brightness galaxies as a test of such models is
demonstrated.Comment: 13 pages, 14 figures, accepted for publication in A&
I Zw 18 as morphological paradigm for rapidly assembling high-z galaxies
IZw18, ever since regarded as the prototypical blue compact dwarf (BCD)
galaxy, is, quite ironically, the most atypical BCD known. This is because its
large exponential low-surface brightness envelope is not due to an old stellar
host but entirely due to extended nebular emission (ne) (Papaderos et al. 2002;
P02). We study IZw18 and IZw18C down to an unprecedently faint surface
brightness level using HST ACS data.
We argue that the properties of IZw18C can be consistently accounted for by
propagating star formation over the past ~100 Myr, in combination with stellar
diffusion and the associated radial stellar mass filtering effect (P02).
As for IZw18, we find that ne extends out to ~16 stellar scale lengths and
provides at least 1/3 of the total optical emission.
The case of IZw18 suggests caution in studies of distant galaxies in dominant
stages of their evolution, rapidly assembling their stellar mass at high
specific star formation rates (SSFRs). It calls attention to the fact that ne
is not necessarily cospatial with the underlying ionizing and non-ionizing
stellar background, neither has to scale with its surface density. The
prodigious energetic output during dominant phases of galaxy evolution may
result in large exponential ne envelopes, extending much beyond the still
compact stellar component, just like in IZw18. Therefore, the morphological
paradigm of IZw18, while probably unique in the nearby Universe, may be
ubiquitous among high-SSFR galaxies at high redshift. Using IZw18 as reference,
we show that extended ne may introduce substantial observational biases and
significantly affect fundamental galaxy relations. Among others, we show that
the surface brightness profiles of distant morphological analogs to IZw18 may
be barely distinguishable from Sersic profiles with an exponent 2<n<5, thus
mimicking the profiles of massive galaxy spheroids. (abridged)Comment: 22 pages, 15 figures, Accepted for publication in Astronomy and
Astrophysic
Dark matter dominated dwarf disc galaxy Segue 1
Several observations reveal that dwarf galaxy Segue 1 has a dark matter (DM)
halo at least ~ 200 times more massive than its visible baryon mass of only ~
103 solar masses. The baryon mass is dominated by stars with perhaps an
interstellar gas mass of < 13 solar masses. Regarding Segue 1 as a dwarf disc
galaxy by its morphological appearance of long stretch, we invoke the dynamic
model of Xiang-Gruess, Lou & Duschl (XLD) to estimate its physical parameters
for possible equilibria with and without an isopedically magnetized gas disc.
We estimate the range of DM mass and compare it with available observational
inferences. Due to the relatively high stellar velocity dispersion compared to
the stellar surface mass density, we find that a massive DM halo would be
necessary to sustain disc equilibria. The required DM halo mass agrees grossly
with observational inferences so far. For an isopedic magnetic field in a gas
disc, the ratio f between the DM and baryon potentials depends strongly on the
magnetic field strength. Therefore, a massive DM halo is needed to counteract
either the strong stellar velocity dispersion and rotation of the stellar disc
or the magnetic Lorentz force in the gas disc. By the radial force balances,
the DM halo mass increases for faster disc rotation.Comment: 5 pages, 2 figures, accepted for publication in MNRA
Study of galaxies in the Lynx-Cancer void. -- III. New extreme LSB dwarf galaxies
(Abridged) We present the results of the complex study of the low surface
brightness dwarf (LSBD) gas-rich galaxies J0723+3621, J0737+4724 and
J0852+1350, which reside in the nearby Lynx-Cancer void. Their ratios
M(HI)/L_B, according to HI data obtained with the NRT, are respectively ~3.9,
~2, ~2.6. For the two latter galaxies, we derived oxygen abundance
corresponding to the value of 12+log(O/H) <~7.3, using spectra from the Russian
6m telescope and from the SDSS database. We found two additional blue LSB
dwarfs, J0723+3622 and J0852+1351, which appear to be physical companions of
J0723+3621 and J0852+1350 situated at the projected distances of ~12--13 kpc.
The companion relative velocities, derived from the BTA spectra, are dV = +89
km/s and +30 km/s respectively. The geometry and the relative orientation of
orbits and spins in these pairs indicate, respectively, prograde and polar
encounters for J0723+3621 and J0852+1350. The NRT HI profiles of J0723+3621 and
J0723+3622 indicate a sizable gas flow in this system. The SDSS u,g,r,i images
of the five dwarfs are used to derive the photometric parameters and the
exponential or Sersic disc model fits. For three of them, the (u-g),(g-r),(r-i)
colours of the outer parts, being compared with the PEGASE evolutionary tracks,
evidence for the dominance of the old stellar populations with ages of T
~(8-10)+-3 Gyr. For J0723+3622 and J0737+4724, the outer region colours appear
rather blue, implying the ages of the oldest visible stars of T <~1-3 Gyr. The
new LSB galaxies complement the list of the known most metal-poor and
`unevolved' dwarfs in this void, including DDO 68, SDSS J0926+3343 and others.
This unique concentration of 'unevolved' dwarf galaxies in a small cell of the
nearby Universe implies a physical relationship between the slow galaxy
evolution and the void-type global environment.Comment: 16 pages, 5 tables, 9 figures. MNRAS, in pres
Disentangling genetic and epigenetic determinants of ultrafast adaptation
A major rationale for the advocacy of epigenetically mediated adaptive responses is that they facilitate faster adaptation to environmental challenges. This motivated us to develop a theoreticalâexperimental framework for disclosing the presence of such adaptationâspeeding mechanisms in an experimental evolution setting circumventing the need for pursuing costly mutationâaccumulation experiments. To this end, we exposed clonal populations of budding yeast to a whole range of stressors. By growth phenotyping, we found that almost complete adaptation to arsenic emerged after a few mitotic cell divisions without involving any phenotypic plasticity. Causative mutations were identified by deep sequencing of the arsenicâadapted populations and reconstructed for validation. Mutation effects on growth phenotypes, and the associated mutational target sizes were quantified and embedded in dataâdriven individualâbased evolutionary population models. We found that the experimentally observed homogeneity of adaptation speed and heterogeneity of molecular solutions could only be accounted for if the mutation rate had been near estimates of the basal mutation rate. The ultrafast adaptation could be fully explained by extensive positive pleiotropy such that all beneficial mutations dramatically enhanced multiple fitness components in concert. As our approach can be exploited across a range of model organisms exposed to a variety of environmental challenges, it may be used for determining the importance of epigenetic adaptationâspeeding mechanisms in general.publishedVersio
Bubble mapping with the Square Kilometer Array - I. Detecting galaxies with Euclid, JWST, WFIRST and ELT within ionized bubbles in the intergalactic medium at z>6
Genetically controlled mtDNA deletions prevent ROS damage by arresting oxidative phosphorylation
Deletion of mitochondrial DNA in eukaryotes is currently attributed to rare accidental events associated with mitochondrial replication or repair of double-strand breaks. We report the discovery that yeast cells arrest harmful intramitochondrial superoxide production by shutting down respiration through genetically controlled deletion of mitochondrial oxidative phosphorylation genes. We show that this process critically involves the antioxidant enzyme superoxide dismutase 2 and two-way mitochondrial-nuclear communication through Rtg2 and Rtg3. While mitochondrial DNA homeostasis is rapidly restored after cessation of a short-term superoxide stress, long-term stress causes maladaptive persistence of the deletion process, leading to complete annihilation of the cellular pool of intact mitochondrial genomes and irrevocable loss of respiratory ability. This shows that oxidative stress-induced mitochondrial impairment may be under strict regulatory control. If the results extend to human cells, the results may prove to be of etiological as well as therapeutic importance with regard to age-related mitochondrial impairment and disease
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