Context. 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. Aims.We aim to 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. Methods. We used high quality VLT/MUSE optical integral field data to derive the physical properties of the ISM such as ionization, density, shocks, and performed new fitting of the spectral energy distributions of the brightest clusters in ESO 338-IG04 from HST imaging. Results.We find that ESO 338-IG04 has a large ionized halo which we detect to a distance of 9 kpc. We identify four 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 O I/Hα 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. Conclusions. Photoionization 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.
ABSTRACT
We have used the capability of the Multi-Unit Spectroscopic Explorer (MUSE) instrument to explore the impact of stellar feedback at large scales in Haro 11, a galaxy under extreme starburst ...condition and one of the first galaxies where Lyman continuum (LyC) has been detected. Using H α, O iii λ5007, and O i λ6300 emission lines from deep MUSE observations, we have constructed a sequence of velocity-dependent maps of the H α emission, the state of the ionized gas, and a tracer of fast shocks. These allowed us to investigate the ionization structure of the galaxy in 50 km s−1 bins over a velocity range of −400 to 350 km s−1. The ionized gas in Haro 11 is assembled by a rich arrangement of structures, such as superbubbles, filaments, arcs, and galactic ionized channels, whose appearances change drastically with velocity. The central star-forming knots and the star-forming dusty arm are the main engines that power the strong mechanical feedback in this galaxy, although with different impact on the ionization structure. Haro 11 appears to leak LyC radiation in many directions. We found evidence of a kpc-scale fragmented superbubble that may have cleared galactic-scale channels in the ISM. Additionally, the Southwestern hemisphere is highly ionized in all velocities, hinting at a density bound scenario. A compact kpc-scale structure of lowly ionized gas coincides with the diffuse Lyα emission and the presence of fast shocks. Finally, we find evidence that a significant fraction of the ionized gas mass may escape the gravitational potential of the galaxy.
Abstract
Low- and intermediate-mass galaxies are widely discussed as cause of reionization at redshift z ∼ 10–6. However, observational proof of galaxies that are leaking ionizing radiation (Lyman ...continuum; LyC) is a currently ongoing challenge and the list of LyC emitting candidates is still short. Tololo 1247−232 is among those very few galaxies with recently reported leakage. We performed intermediate resolution ultraviolet spectroscopy with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope and confirm ionizing radiation emerging from Tololo 1247−232. Adopting an improved data reduction procedure, we find that LyC escapes from the central stellar clusters, with an escape fraction of 1.5 ± 0.5 per cent only, i.e. the lowest value reported for the galaxy so far. We further make use of far-ultraviolet absorption lines of Si ii and Si iv as a probe of the neutral and ionized interstellar medium (ISM). We find that most of the ISM gas is ionized, likely facilitating LyC escape from density bounded regions. Neutral gas covering as a function of line-of-sight velocity is derived using the apparent optical depth method. The ISM is found to be sufficiently clumpy, supporting the direct escape of LyC photons. We further report on broad-band UV and optical continuum imaging as well as narrow-band imaging of Lyα, Hα and Hβ. Using stellar population synthesis, an Lyα escape fraction of 8 per cent was derived. We also performed Very Large Array 21cm imaging. The hydrogen hyperfine transition was not detected, but a deep upper limit atomic gas mass of ≲109 M⊙ could be derived. The upper limit gas fraction defined as
${M_{\rm H\,\small {I}}}/{M_*}$
is only 20 per cent. Evidence is found that the H i gas halo is relatively small compared to the Lyman Alpha Reference Sample (Hayes et al. 2013, 2014; Östlin et al. 2014).
ABSTRACT
Star formation is a clustered process that regulates the structure and evolution of galaxies. We investigate this process in the dwarf galaxy Haro 11, forming stars in three knots (A, B, and ...C). The exquisite resolution of HST imaging allows us to resolve the starburst into tens of bright star clusters. We derive masses between 105 and $10^7\, \rm M_{\odot }$ and ages younger than 20 Myr, using photometric modelling. We observe that the clustered star formation has propagated from knot C (the oldest) through knot A (in between) towards knot B (the youngest). We use aperture-matched ultraviolet and optical spectroscopy (HST + MUSE) to independently study the stellar populations of Haro 11 and determine the physical properties of the stellar populations and their feedback in 1-kpc diameter regions. We discuss these results in light of the properties of the ionized gas within the knots. We interpret the broad blue-shifted components of the optical emission lines as outflowing gas (vmax ∼ 400 km/s). The strongest outflow is detected in knot A with a mass rate of $\dot{M}_{\mathrm{ out}}\sim 10\, \rm M_{\odot }/yr$, 10 times higher than the star formation in the same region. Knot B hosts a young and not fully developed outflow, whereas knot C has likely been already evacuated. Because Haro 11 has properties similar to high-redshift unresolved galaxies, our work can additionally aid the understanding of star formation at high redshift, a window that will be opened by upcoming facilities.
ABSTRACT
We use high quality VLT/MUSE data to study the kinematics and the ionized gas properties of Haro 11, a well-known starburst merger system and the closest confirmed Lyman continuum leaking ...galaxy. We present results from integrated line maps, and from maps in three velocity bins comprising the blueshifted, systemic, and redshifted emission. The kinematic analysis reveals complex velocities resulting from the interplay of virial motions and momentum feedback. Star formation happens intensively in three compact knots (knots A, B, and C), but one, knot C, dominates the energy released in supernovae. The halo is characterized by low gas density and extinction, but with large temperature variations, coincident with fast shock regions. Moreover, we find large temperature discrepancies in knot C, when using different temperature-sensitive lines. The relative impact of the knots in the metal enrichment differs. While knot B is strongly enriching its closest surrounding, knot C is likely the main distributor of metals in the halo. In knot A, part of the metal enriched gas seems to escape through low density channels towards the south. We compare the metallicities from two methods and find large discrepancies in knot C, a shocked area, and the highly ionized zones, that we partially attribute to the effect of shocks. This work shows, that traditional relations developed from averaged measurements or simplified methods, fail to probe the diverse conditions of the gas in extreme environments. We need robust relations that include realistic models where several physical processes are simultaneously at work.
Context.
The kinematics of galaxies provide valuable insights into their physics and assembly history. Kinematics are governed not only by the gravitational potential, but also by merger events and ...stellar feedback processes such as stellar winds and supernova explosions.
Aims.
We aim to identify what governs the kinematics in a sample of SDSS-selected nearby starburst galaxies, by obtaining spatially resolved measurements of the gas and stellar kinematics.
Methods.
We obtained near-infrared integral-field
K
-band spectroscopy with VLT/SINFONI for 15 compact starburst galaxies. We derived the integrated as well as spatially resolved stellar and gas kinematics. The stellar kinematics were derived from the CO absorption bands, and Pa
α
and Br
γ
emission lines were used for the gas kinematics.
Results.
Based on the integrated spectra, we find that the majority of galaxies have gas and stellar velocity dispersion that are comparable. A spatially resolved comparison shows that the six galaxies that deviate show evidence for a bulge or stellar feedback. Two galaxies are identified as mergers based on their double-peaked emission lines. In our sample, we find a negative correlation between the ratio of the rotational velocity over the velocity dispersion (
v
rot
/
σ
) and the star formation rate surface density.
Conclusions.
We propose a scenario where the global kinematics of the galaxies are determined by gravitational instabilities that affect both the stars and gas. This process could be driven by mergers or accretion events. Effects of stellar feedback on the ionised gas are more localised and detected only in the spatially resolved analysis. The mass derived from the velocity dispersion provides a reliable mass even if the galaxy cannot be spatially resolved. The technique used in this paper is applicable to galaxies at low and high redshift with the next generation of infrared-focussed telescopes (JWST and ELT).
The stellar content of young massive star clusters emit large amounts of Lyman continuum photons and inject momentum into the inter stellar medium (ISM) by the strong stellar winds of the most ...massive stars in the cluster. When the most massive stars explode as supernovae, large amounts of mechanical energy are injected in the ISM. A detailed study of the ISM around these massive cluster provides insights on the effect of cluster feedback. We present high quality integral field spectroscopy taken with VLT/MUSE of two starburst galaxies: ESO 338-IG04 and Haro 11. Both galaxies contain a significant number of super star clusters. The MUSE data provide us with an unprecedented view of the state and kinematics of the ionized gas in the galaxy allowing us to study the effect of stellar feedback on small and large spatial scales. We present our recent results on studying the ISM state of these two galaxies. The data of both galaxies show that the mechanical and ionization feedback of the super star clusters in the galaxy modify the state and kinematics of the ISM substancially by creating highly ionized bubbles around the cluster, making the central part of the galaxy highly ionized. This shows that the HII regions around the individual clusters are density bounded, allowing the ionizing photons to escape and ionize the ISM further out.
The Ly$\alpha$ emission line is one of the main observables of galaxies at
high redshift, but its output depends strongly on the neutral gas distribution
and kinematics around the star-forming ...regions where UV photons are produced.
We present observations of Ly$\alpha$ and 21-cm HI emission at comparable
scales with the goal to qualitatively investigate how the neutral interstellar
medium (ISM) properties impact Ly$\alpha$ transfer in galaxies. We have
observed 21-cm HI at the highest angular resolution possible (~ 3" beam) with
the VLA in two local galaxies from the Lyman Alpha Reference Sample. We
contrast this data with HST Ly$\alpha$ imaging and spectroscopy, and MUSE and
PMAS ionized gas observations. In LARS08, high intensity Ly$\alpha$ emission is
co-spatial with high column density HI where dust content is the lowest. The
Ly$\alpha$ line is strongly redshifted, consistent with velocity redistribution
which allows Ly$\alpha$ escape from high column density neutral medium with low
dust content. In eLARS01, high intensity Ly$\alpha$ emission is located in
regions of low column density HI, below the HI data sensitivity limit
($<2\times10^{20}\,$cm$^{-2}$). The perturbed ISM distribution with low column
density gas in front of the Ly$\alpha$ emission region plays an important role
in the escape. In both galaxies, the faint Ly$\alpha$ emission ($\sim
1\times10^{-16}$erg.s$^{-1}$cm$^{-2}$arcsec$^{-2}$) traces intermediate
H$\alpha$ emission regions where HI is found, regardless of the dust content.
Dust seems to modulate, but not prevent, the formation of a faint Ly$\alpha$
halo. This study suggests the existence of scaling relations between dust,
H$\alpha$, HI, and Ly$\alpha$ emission in galaxies.
Star formation is a clustered process that regulates the structure and evolution of galaxies. We investigate this process in the dwarf galaxy Haro 11, forming stars in three knots (A, B, C). The ...exquisite resolution of HST imaging allows us to resolve the starburst into tens of bright star clusters. We derive masses between \(10^5\) and \(10^7\,\rm M_{\odot}\) and ages younger than 20 Myr, using photometric modeling. We observe that the clustered star formation has propagated from knot C (the oldest) through knot A (in between) towards knot B (the youngest). We use aperture-matched ultraviolet and optical spectroscopy (HST + MUSE) to independently study the stellar populations of Haro 11 and determine the physical properties of the stellar populations and their feedback in 1 kpc diameter regions. We discuss these results in light of the properties of the ionised gas within the knots. We interpret the broad blue-shifted components of the optical emission lines as outflowing gas (\(v_{max} \sim 400\) km/s). The strongest outflow is detected in knot A with a mass-rate of \(\dot{M}_{out}\sim 10\,\rm M_{\odot}/yr\), ten times higher than the star-formation in the same region. Knot B hosts a young and not fully developed outflow, whereas knot C has likely been already evacuated. Because Haro 11 has properties similar to high-redshift unresolved galaxies, our work can additionally aid the understanding of star formation at high redshift, a window that will be opened by upcoming facilities.
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