ABSTRACT
We present the Hubble imaging Probe of Extreme Environments and Clusters (HiPEEC) survey. We fit HST NUV to NIR broad-band and H α fluxes to derive star cluster ages, masses, and extinctions ...and determine the star formation rate (SFR) of six merging galaxies. These systems are excellent laboratories to trace cluster formation under extreme gas physical conditions, rare in the local Universe, but typical for star-forming galaxies at cosmic noon. We detect clusters with ages of 1–500 Myr and masses that exceed 107 M⊙. The recent cluster formation history and their distribution within the host galaxies suggest that systems such as NGC 34, NGC 1614, and NGC 4194 are close to their final coalescing phase, while NGC 3256, NGC 3690, and NGC 6052 are at an earlier/intermediate stage. A Bayesian analysis of the cluster mass function in the age interval 1–100 Myr provides strong evidence in four of the six galaxies that an exponentially truncated power law better describes the observed mass distributions. For two galaxies, the fits are inconclusive due to low number statistics. We determine power-law slopes β ∼ −1.5 to −2.0 and truncation masses, Mc, between 106 and a few times 107 M⊙, among the highest values reported in the literature. Advanced mergers have higher Mc than early/intermediate merger stage galaxies, suggesting rapid changes in the dense gas conditions during the merger. We compare the total stellar mass in clusters to the SFR of the galaxy, finding that these systems are among the most efficient environments to form star clusters in the local Universe.
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).
Context.
When studying the production and escape of Lyman continuum (LyC) from galaxies, it is standard to rely on an array of indirect observational tracers in the preselection of candidate leakers.
...Aims.
In this work, we investigate how much ionizing radiation might be missed due to these selection criteria by completely removing them and performing a search selected purely from rest-frame LyC emission; and how that affects our estimates of the ionizing background.
Methods.
We inverted the conventional method and performed a bottom-up search for LyC leaking galaxies at redshifts 2 ≲
z
≲ 3.5. Using archival data from HST and VLT/MUSE, we ran source finding software on UV-filter HST images from the
Hubble
Ultra Deep Field (HUDF), and subjected all detected sources to a series of tests to eliminate those that are inconsistent with being ionizing sources.
Results.
We find six new and one previously identified candidate leakers with absolute escape fractions ranging from 36% to ∼100%. Our filtering criteria eliminate one object previously reported as a candidate ionizing emitter in the literature, and we report non-detections in the rest-frame Lyman continuum of two other previously reported sources. We find that our candidates make a contribution to the metagalactic ionizing field of log
10
(
ϵ
ν
) = 25.32
−0.21
+0.25
and 25.29
−0.22
+0.27
erg s
−1
Hz
−1
cMpc
−3
for the full set of candidates and for the four strongest candidates only; both values are higher than but consistent with other recent figures in the literature.
Conclusions.
Our findings suggest that galaxies that do not meet the usual selection criteria may make a non-negligible contribution to the cosmic ionizing field. We recommend that similar searches be carried out on a larger scale in well-studied fields with both UV and large ancillary data coverage, for example in the full set of CANDELS fields.
We estimate the fraction of core-collapse supernovae (CCSNe) that remain undetected by optical SN searches due to obscuration by large amounts of dust in their host galaxies. This effect is ...especially important in luminous and ultraluminous infrared galaxies, which are locally rare but dominate the star formation at redshifts of z ~ 1-2. We perform a detailed investigation of the SN activity in the nearby luminous infrared galaxy Arp 299 and estimate that up to 83% of the SNe in Arp 299 and in similar galaxies in the local universe are missed by observations at optical wavelengths. For rest-frame optical surveys we find the fraction of SNe missed due to high dust extinction to increase from the average local value of ~19% to ~38% at z ~ 1.2 and then remain roughly constant up to z ~ 2. It is therefore crucial to take into account the effects of obscuration by dust when determining SN rates at high redshift and when predicting the number of CCSNe detectable by future high-z surveys such as LSST, JWST, and Euclid. For a sample of nearby CCSNe (distances 6-15 Mpc) detected during the last 12 yr, we find a lower limit for the local CCSN rate of (ProQuest: Formulae and/or non-USASCII text omitted) x 10 super(-4) yr super(-1) Mpc super(-3), consistent with that expected from the star formation rate. Even closer, at distances less than ~6 Mpc, we find a significant increase in the CCSN rate, indicating a local overdensity of star formation caused by a small number of galaxies that have each hosted multiple SNe.
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 1.5 h integration with the MUSE integral-field ...spectrograph. We detect these features in Hα and O iii emission down to a limiting surface-brightness of 5 × 10-19 erg s-1 cm-2 arcsec-2. 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 He ii λ4686 emission that brightens towards the north-west at the rim of a starburst driven super-shell. 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-z 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.
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 Lyα 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 Lyα. Trends between ...the escape of Lyα photons and dust and properties of the interstellar medium (ISM) have been found, but detailed comparisons between Lyα emission and the properties of the gas in local high-redshift analogs are vital for understanding the relation between Lyα emission and galaxy properties. Aims. 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 Lyα halo around the local Lyα emitter and Lyman-break galaxy analog ESO 338-IG04. Methods. We obtained VLT/MUSE integral field spectra. We used ionization parameter mapping of the S ii/O iii line ratio and the kinematics of Hα to study the ionization state and kinematics of the ISM of ESO 338-IG04. Results. The velocity map reveals two outflows, one toward the north, the other toward the south of ESO 338. The ionization parameter mapping shows that the entire central area of the galaxy is highly ionized by photons leaking from the H ii regions around the youngest star clusters. Three highly ionized cones have been identified, of which one is associated with an outflow detected in the Hα. 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 Lyα map shows that the (approximately bipolar) asymmetries observed in the Lyα emission are consistent with the base of the outflows detected in Hα. No clear correlation with the ionization cones is found. Conclusions. The mechanical and ionization feedback of star clusters significantly changes the state of the ISM by creating ionized cones and outflows. The comparison with Lyα suggests that especially the outflows could facilitate the escape of Lyα photons.
The Lyman alpha reference sample Guaita, L; Melinder, J; Hayes, M ...
Astronomy and astrophysics (Berlin),
04/2015, Letnik:
576
Journal Article
Recenzirano
Odprti dostop
The transport of Ly alpha photons in galaxies is a complex process and the conditions under which Ly alpha photons manage to escape from certain galaxies is still under investigation. The Lyman alpha ...reference sample (LARS) is a sample of 14 local starforming galaxies, designed to study Ly alpha in detail and relate it to restframe UV and optical emission. With the aim of identifying restframe UV and optical properties, which are typical of Ly alpha emitters at both low and high redshift, we investigated the morphological properties of the LARS galaxies, in particular the ones that exhibit intense Ly alpha radiation. We measured sizes and morphological parameters in the continuum, Ly alpha , and H alpha images. We studied morphology by using the Gini coefficient vs. M20 and asymmetry vs. concentration diagrams. The stack of LARSLAE Ly alpha images is peaked in the centre, indicating that the conditions, which make a galaxy an LAE, tend to produce a concentrated surface brightness profile. On the other hand, the stack of all LARS galaxies is shallower and more extended.
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