334 research outputs found
An IFU investigation of possible Lyman continuum escape from Mrk 71/NGC 2366
Mrk 71/NGC 2366 is the closest Green Pea (GP) analog and candidate Lyman
Continuum (LyC) emitter. Recently, 11 LyC-leaking GPs have been detected
through direct observations of the ionizing continuum, making this the most
abundant class of confirmed LyC-emitters at any redshift. High resolution,
multi-wavelength studies of GPs can lead to an understanding of the method(s),
through which LyC escapes from these galaxies. The proximity of Mrk 71/NCG 2366
offers unprecedented detail on the inner workings of a GP analog, and enables
us to identify the mechanisms of LyC escape. We use 5825-7650{\AA} integral
field unit PMAS observations to study the kinematics and physical conditions in
Mrk 71. An electron density map is obtained from the [S II] ratio. A fortuitous
second order contamination by the [O II]3727 doublet enables the construction
of an electron temperature map. Resolved maps of sound speed, thermal
broadening, "true" velocity dispersion, and Mach number are obtained and
compared to the high resolution magneto-hydrodynamic SILCC simulations. Two
regions of increased velocity dispersion indicative of outflows are detected to
the north and south of the super star cluster, knot B, with redshifted and
blueshifted velocities, respectively. We confirm the presence of a faint broad
kinematical component, which is seemingly decoupled from the outflow regions,
and is fainter and narrower than previously reported in the literature. Within
uncertainties, the low- and high-ionization gas move together. Outside of the
core of Mrk 71, an increase in Mach numbers is detected, implying a decrease in
gas density. Simulations suggest this drop in density can be as high as ~4 dex,
down to almost optically thin levels, which would imply a non-zero LyC escape
fraction along the outflows... [abridged]Comment: Accepted for publication in A&A. 17 pages, 16 figures, 4 table
Mapping Lyman Continuum escape in Tololo 1247-232
Low redshift, spatially resolved Lyman continuum (LyC) emitters allow us to
clarify the processes for LyC escape from these starburst galaxies. We use
Hubble Space Telescope (HST) WFC3 and ACS imaging of the confirmed low-redshift
LyC emitter Tol 1247-232 to study the ionization structure of the gas and its
relation to the ionizing star clusters. We perform ionization parameter mapping
(IPM) using [O III]4959, 5007 and [O II]3727 imaging as the high- and
low-ionization tracers, revealing broad, large-scale, optically thin regions
originating from the center, and reaching the outskirts of the galaxy,
consistent with LyC escape. We carry out stellar population synthesis modeling
of the 26 brightest clusters using our HST photometry. Combining these data
with the nebular photometry, we find a global LyC escape fraction of f_esc =
0.12, with uncertainties also consistent with zero escape and with all measured
f_esc values for this galaxy. Our analysis suggests that, similar to other
candidate LyC emitters, a two-stage starburst has taken place in this galaxy,
with a 12 Myr old, massive, central cluster likely having pre-cleared regions
in and around the center, and the second generation of 2 - 4 Myr old clusters
dominating the current ionization, including some escape from the galaxy.Comment: Accepted for publication in Ap
Recommended from our members
Multifaceted Changes in Synaptic Composition and Astrocytic Involvement in a Mouse Model of Fragile X Syndrome.
Fragile X Syndrome (FXS), a common inheritable form of intellectual disability, is known to alter neocortical circuits. However, its impact on the diverse synapse types comprising these circuits, or on the involvement of astrocytes, is not well known. We used immunofluorescent array tomography to quantify different synaptic populations and their association with astrocytes in layers 1 through 4 of the adult somatosensory cortex of a FXS mouse model, the FMR1 knockout mouse. The collected multi-channel data contained approximately 1.6 million synapses which were analyzed using a probabilistic synapse detector. Our study reveals complex, synapse-type and layer specific changes in the neocortical circuitry of FMR1 knockout mice. We report an increase of small glutamatergic VGluT1 synapses in layer 4 accompanied by a decrease in large VGluT1 synapses in layers 1 and 4. VGluT2 synapses show a rather consistent decrease in density in layers 1 and 2/3. In all layers, we observe the loss of large inhibitory synapses. Lastly, astrocytic association of excitatory synapses decreases. The ability to dissect the circuit deficits by synapse type and astrocytic involvement will be crucial for understanding how these changes affect circuit function, and ultimately defining targets for therapeutic intervention
UM 462, a local Green Pea galaxy analog under the MUSE magnifying glass
[ABRIGED] Stellar feedback in high-redshift galaxies plays an important role
in the re-ionization epoch of the Universe. Green Pea galaxies (GPs) postulate
as favorite local laboratories. However, at their typical redshift of
, the most intimate interaction between stars and surrounding ISM
cannot be disentangled. Detailed studies of Blue Compact Dwarf galaxies (BCDs)
are necessary to anchor our investigations on them. We present here a study in
detail UM 462, a BCD with similar properties to GPs uisng high quality optical
IFS data with MUSE. Total oxygen abundance by means of the direct method is
12+(O/H)8.02 and homogenous all over the galaxy, in stark contrast
with the metallicities derived from several strong line methods. The velocity
field for the ionised gas presents a velocity stratification in the area
towards the north with redder velocities in the high ionisation lines and bluer
velocities in the low ionisation lines. This is the only area with velocity
dispersions clearly above the MUSE instrumental width, and it is surrounded by
two 1 kpc-long structures nicknamed \emph{the horns}. We interpret the
observational evidence in that area as a fragmented super-bubble fruit of the
stellar feedback and it may constitute a preferred channel for LyC photons from
the youngest generation of stars to escape. The most recent SF seems to
propagate from the outer to the inner parts of the galaxy, and then from east
to west. We identified a supernova remnant and Wolf-Rayet stars - as traced by
the red bump - that support this picture. The direction of the propagation
implies the presence of younger Wolf-Rayet stars at the maximum in H.
The ensemble of results exemplifies the potential of 2D detailed spectroscopic
studies of dwarf star-forming galaxies at high spatial resolution as key
reference for similar studies on primeval galaxies.Comment: 29 pages, 25 figures; resubmitted to A&A after taking the referee's
comments and suggestions into accoun
Super star clusters in Haro 11: properties of a very young starburst and evidence for a near-infrared flux excess
We have used multiband imaging to investigate the nature of an extreme starburst environment in the nearby Lyman break galaxy analogue Haro 11 (ESO 350−IG038) by means of its stellar cluster population. The central starburst region has been observed in eight different high-resolution Hubble Space Telescope (HST) wavebands, sampling the stellar and gas components from UV to near-infrared. Photometric imaging of the galaxy was also carried out at 2.16 μm by NaCo AO instrument at the ESO Very Large Telescope. We constructed integrated spectral energy distributions (SEDs) for about 200 star clusters located in the active star-forming regions and compared them with single stellar population models (suitable for physical properties of very young cluster population) in order to derive ages, masses and extinctions of the star clusters. The cluster age distribution we recover confirms that the present starburst has lasted for 40 Myr, and shows a peak of cluster formation only 3.5 Myr old. With such an extremely young cluster population, Haro 11 represents a unique opportunity to investigate the youngest phase of the cluster formation process and evolution in starburst systems. We looked for possible relations between cluster ages, extinctions and masses. Extinction tends to diminish as a function of the cluster age, but the spread is large and reaches the highest dispersion for clusters in partial embedded phases (8000 Å which cannot be explained by simple stellar evolutionary models. Fitting SED models over all wavebands leads to systematic overestimates of cluster ages and incorrect masses for the stellar population supplying the light in these clusters. We show that the red excess affects also the HST F814W filter, which is typically used to constrain cluster physical properties. The clusters which show the red excess are younger than 40 Myr; we discuss possible physical explanations for the phenomenon. Finally, we estimate that Haro 11 has produced bound clusters at a rate almost a factor of 10 higher than the massive and regular spirals, like the Milky Way. The present cluster formation efficiency is ∼38 per cent of the galactic star formation rat
Precision spectrophotometry for PNLF distances: the case of NGC 300
The Multi-Unit Spectroscopic Explorer (MUSE) has enabled a renaissance of the
planetary nebula luminosity function (PNLF) as a standard candle. In the case
of NGC 300, we learned that the precise spectrophotometry of MUSE was crucial
to obtain an accurate PNLF distance. We present the advantage of the integral
field spectrograph compared to the slit spectrograph in delivering precise
spectrophotometry by simulating a slit observation on integral field
spectroscopy data. We also discuss the possible systematic shift in measuring
the PNLF distance using the least-square method, especially when the PNLF
cutoff is affected by small number statistics.Comment: 5 pages, 4 figures, Submitted to the Proceedings of IAU Symposium
384: Planetary Nebulae: a Universal Toolbox in the Era of Precision
Astrophysic
The Red Halo Phenomenon
Optical and near-IR observations of the halos of disk galaxies and blue
compact galaxies have revealed a very red spectral energy distribution, which
cannot easily be reconciled with a normal, metal-poor stellar population like
that in the stellar halo of the Milky Way. Here, spectral evolutionary models
are used to explore the consequences of these observations. We demonstrate that
a stellar population of low to intermediate metallicity, but with an extremely
bottom-heavy initial mass function, can explain the red halos around both types
of objects. Other previously suggested explanations, like nebular emission or
very metal-rich stars, are shown to fail in this respect. This indicates that,
if the reported halo colours are correct, halo populations dominated by
low-mass stars may be a phenomenon common to galaxies of very different Hubble
types. Potential tests of this hypothesis are discussed, along with its
implications for the baryonic dark matter content of galaxies.Comment: 6 pages, 3 figures, Accepted for publication in Ap
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