282 research outputs found
Dynamics of blue compact galaxies, as revealed by their H-alpha velocity fields I. The data, velocity fields and rotation curves
Observations of six luminous blue compact galaxies (BCGs) and two star
forming companion galaxies were carried out with the CIGALE scanning
Fabry-Perot interferometer attached to the ESO 3.6m telescope on La Silla. The
observations were made in the H-alpha emission line which is prominent in BCGs.
A velocity sampling of 5 km/s and a pixel size of 0.9 arcseconds were used. In
this paper we present the observations and the data together with the velocity
fields and the derived rotation curves. In addition we provide rough estimates
of the total dynamical mass and of the ionised gas mass for each galaxy. All
galaxies display rotation, but while the companion galaxies have regular
velocity fields, those of the BCGs are complex and appear perturbed. This is
the most extensive study to date of the optical velocity fields of BCGs. The
interpretation of these results will be presented in a forthcoming paper (Paper
II).Comment: 26 pages, 14 figures. Accepted for publication in A&AS. The paper
(with figures in slightly higher resolution) and an electronic table is also
available at ftp://ftp.iap.fr/pub/from_users/ostlin/Articles/ . Replaced
version, figure captions fixe
VLT/MUSE view of the highly ionized outflow cones in the nearby starburst ESO338-IG04
The Ly line is an important diagnostic for star formation at high
redshift, but interpreting its flux and line profile is difficult because of
the resonance nature of Ly. Trends between the escape of Ly
photons and dust and properties of the interstellar medium (ISM) have been
found, but detailed comparisons between Ly emission and the properties
of the gas in local high-redshift analogs are vital for understanding the
relation between Ly emission and galaxy properties. For the first time,
we can directly infer the properties of the ionized gas at the same location
and similar spatial scales of the extended Ly halo around ESO 338-IG04.
We obtained VLT/MUSE integral field spectra. We used ionization parameter
mapping of the [SII]/[OIII] line ratio and the kinematics of H to study
the ionization state and kinematics of the ISM of ESO338-IG04. The velocity map
reveals two outflows. The entire central area of the galaxy is highly ionized
by photons leaking from the HII regions around the youngest star clusters.
Three highly ionized cones have been identified, of which one is associated
with an outflow. We propose a scenario where the outflows are created by
mechanical feedback of the older clusters, while the highly ionized gas is
caused by the hard ionizing photons emitted by the youngest clusters. A
comparison with the Ly map shows that the (approximately bipolar)
asymmetries observed in the Ly emission are consistent with the base of
the outflows detected in H. No clear correlation with the ionization
cones is found. The mechanical and ionization feedback of star clusters
significantly changes the state of the ISM by creating ionized cones and
outflows. The comparison with Ly suggests that especially the outflows
could facilitate the escape of Ly photons [Abridged].Comment: Accepted for publication in A&A Letters, 4 pages, 2 figure
MUSE Illuminates Channels for Lyman Continuum Escape in the Halo of SBS 0335-52E
We report on the discovery of ionised gas filaments in the circum-galactic
halo of the extremely metal-poor compact starburst SBS 0335-052E in a 1.5h
integration with the MUSE integral-field spectrograph. We detect these features
in H and [OIII] emission down to surface-brightness levels of erg scmarcsec. The filaments have
projected diameters of 2.1 kpc and extend more than 9 kpc to the north and
north-west from the main stellar body. We also detect extended nebular HeII
4686 emission that brightens towards the north-west at the rim of a
star-burst driven super-shell, suggestive of a locally enhanced UV radiation
field due to shocks. We also present a velocity field of the ionised gas. The
filaments appear to connect seamlessly in velocity space to the kinematical
disturbances caused by the shell. Similar to high- star-forming galaxies,
the ionised gas in this galaxy is dispersion dominated. We argue that the
filaments were created via feedback from the starburst and that these ionised
structures in the halo may act as escape channels for Lyman continuum radiation
in this gas-rich system.Comment: Revised version after peer review. Accepted for publication in A&A
letter
Local starburst galaxies and their descendants
Despite strong interest in the starburst (hereafter SB) phenomenon, the
concept remains ill-defined. We use a strict definition of SB to examine the
statistical properties of local SB and post-starburst (hereafter PB) galaxies.
We also seek relationships to active galaxies. Potential SB galaxies are
selected from the SDSS DR7 and their stellar content is analysed. We apply an
age dependent dust attenuation correction and derive star formation rates
(SFR), ages and masses of the young and old populations. The photometric masses
nicely agree with dynamical masses derived from the H-alpha emission line
width. To select SB galaxies, we use the birthrate parameter b=SFR/,
requiring b>=3. The PB sample is selected from the citerion EW(Hdelta_abs)>=6
A. Only 1% of star-forming galaxies are found to be SB galaxies. They
contribute 3-6% to the stellar production and are therefore unimportant for the
local star formation activity. The median SB age is 70 Myr, roughly independent
of mass. The b-parameter strongly depends on burst age. Values close to b=60
are found at ages ~10 Myr, while almost no SBs are found at ages >1 Gyr. The
median baryonic burst mass fraction of sub-L* galaxies is 5%, decreasing slowly
with mass. The median mass fraction of the recent burst in the PB sample is
5-10%. The age-mass distribution of the progenitors of the PBs is bimodal with
a break at log(M)~10.6 above which the ages are doubled. The SB and PB
luminosity functions (hereafter LFs) follow each other closely until M_r~-21,
when AGNs begin to dominate. The PB LF continues to follow the AGN LF while SB
loose significance. This suggests that the number of luminous SBs is
underestimated by about one dex at high luminosities, due to large amounts of
dust and/or AGN blending. It also indicates that the SB phase preceded the AGN
phase. We also discuss the conditions for global gas outflow caused by stellar
feedback.Comment: Accepted for publication in Astronomy and Astrophysics. This is an
extended, substantially revised and corrected version with partly modified
conclusion
Super star cluster feedback driving ionization, shocks and outflows in the halo of the nearby starburst ESO 338-IG04
Stellar feedback strongly affects the interstellar medium (ISM) of galaxies.
Stellar feedback in the first galaxies likely plays a major role in enabling
the escape of LyC photons, which contribute to the re-ionization of the
Universe. Nearby starburst galaxies serve as local analogues allowing for a
spatially resolved assessment of the feedback processes in these galaxies. We
characterize the feedback effects from the star clusters in the local
high-redshift analogue ESO 338-IG04 on the ISM and compare the results with the
properties of the most massive clusters. We use high quality VLT/MUSE optical
integral field data to derive the physical properties of the ISM such as
ionization, density, shocks, and perform new fitting of the spectral energy
distributions of the brightest clusters in ESO 338-IG04 from HST imaging. ESO
338-IG04 has a large ionized halo which we detect to a distance of 9 kpc. We
identify 4 Wolf-Rayet (WR) clusters based on the blue and red WR bump. We
follow previously identified ionization cones and find that the ionization of
the halo increases with distance. Analysis of the galaxy kinematics shows two
complex outflows driven by the numerous young clusters in the galaxy. We find a
ring of shocked emission traced by an enhanced [OI]/H ratio surrounding
the starburst and at the end of the outflow. Finally we detect nitrogen
enriched gas associated with the outflow, likely caused by the WR stars in the
massive star clusters. Photo-ionization dominates the central starburst and
sets the ionization structure of the entire halo, resulting in a density
bounded halo, facilitating the escape of LyC photons. Outside the central
starburst, shocks triggered by an expanding super bubble become important. The
shocks at the end of the outflow suggest interaction between the hot outflowing
material and the more quiescent halo gas.Comment: Accepted for publication in Astronomy and Astrophysics, 22 pages, 15
figure
The temporal and spatial evolution of the starburst in ESO 338-IG04 as probed by its star clusters
In this paper we use ultra-violet (UV) and optical HST photometry in five
bands, and an extensive set of spectral evolutionary synthesis scenarios to
investigate the age and masses of 124 star clusters in the luminous blue
compact galaxy ESO338-IG04 (Tololo 1924-416). The very small internal reddening
makes ESO 338-IG04 an excellent laboratory for studying the formation of
massive star clusters. We have used the star clusters to trace the temporal and
spatial evolution of the starburst, and to put constraints on the star
formation activity over a cosmological time-scale. The present starburst has
been active for about 40 Myr. A standard Salpeter initial mass function (IMF)
extending up to 120 solar masses provides the best fit to the data, although a
flatter IMF cannot be excluded. The compact star clusters provide 30-40 percent
of the UV luminosity and star formation activity. We find no evidence for dust
obscuration even among the youngest (< 1 Myr) clusters. The fraction of stellar
mass contained in compact star clusters is found to be several percent, which
is an unusually high value. The intermediate age clusters show a flattened
space distribution which agrees with the isophotal shape of the galaxy, whereas
the oldest clusters seem to have a spherical distribution.(abridged)Comment: Accepted for publication in A&
Neutral gas in Lyman-alpha emitting galaxies Haro 11 and ESO 338-IG04 measured through sodium absorption
Context. The Lyman alpha emission line of galaxies is an important tool for
finding galaxies at high redshift, and thus probe the structure of the early
universe. However, the resonance nature of the line and its sensitivity to dust
and neutral gas is still not fully understood.
Aims. We present measurements of the velocity, covering fraction and optical
depth of neutral gas in front of two well known local blue compact galaxies
that show Lyman alpha in emission: ESO 338-IG 04 and Haro 11. We thus test
observationally the hypothesis that Lyman alpha can escape through neutral gas
by being Doppler shifted out of resonance.
Methods. We present integral field spectroscopy from the GIRAFFE/Argus
spectrograph at VLT/FLAMES in Paranal, Chile. The excellent wavelength
resolution allows us to accurately measure the velocity of the ionized and
neutral gas through the H-alpha emission and Na D absorption, which traces the
ionized medium and cold interstellar gas, respectively. We also present
independent measurements with the VLT/X-shooter spectrograph which confirm our
results.
Results. For ESO 338-IG04, we measure no significant shift of neutral gas.
The best fit velocity is -15 (16) km/s. For Haro 11, we see an outflow from
knot B at 44 (13) km/s and infalling gas towards knot C with 32 (12) km/s.
Based on the relative strength of the Na D absorption lines, we estimate low
covering fractions of neutral gas (down to 10%) in all three cases.
Conclusions. The Na D absorption likely occurs in dense clumps with higher
column densities than where the bulk of the Ly-alpha scattering takes place.
Still, we find no strong correlation between outflowing neutral gas and a high
Lyman alpha escape fraction. The Lyman alpha photons from these two galaxies
are therefore likely escaping due to a low column density and/or covering
fraction.Comment: 9 pages, 3 figure
The starburst phenomenon from the optical/near-IR perspective
The optical/near-IR stellar continuum carries unique information about the
stellar population in a galaxy, its mass function and star-formation history.
Star-forming regions display rich emission-line spectra from which we can
derive the dust and gas distribution, map velocity fields, metallicities and
young massive stars and locate shocks and stellar winds. All this information
is very useful in the dissection of the starburst phenomenon. We discuss a few
of the advantages and limitations of observations in the optical/near-IR region
and focus on some results. Special attention is given to the role of
interactions and mergers and observations of the relatively dust-free starburst
dwarfs. In the future we expect new and refined diagnostic tools to provide us
with more detailed information about the IMF, strength and duration of the
burst and its triggering mechanisms.Comment: 6 pages, 3 figures, to appear in "Starbursts: from 30 Doradus to
Lyman Break Galaxies" 2005, eds. R. de Grijs and R. M. Gonzalez Delgado
(Kluwer
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