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).
We present rest-frame ultraviolet and optical spectroscopy of the brightest lensed galaxy yet discovered, at redshift z = 2.4. The source reveals a characteristic triple-peaked Lyman α profile that ...has been predicted in various theoretical works, but to our knowledge has not been unambiguously observed previously. The feature is well fit by a superposition of two components: a double-peak profile emerging from substantial radiative transfer, and a narrow, central component resulting from directly escaping Lyman α photons, but it is poorly fit by either component alone. We demonstrate that the feature is unlikely to contain contamination from nearby sources, and that the central peak is unaffected by radiative transfer effects except for very slight absorption. The feature is detected at signal-to-noise ratios exceeding 80 per pixel at line center, and bears strong resemblance to synthetic profiles predicted by numerical models.
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.
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.
We present high-resolution far-UV spectroscopy of the 14 galaxies of the Ly alpha Reference Sample; a sample of strongly star-forming galaxies at low redshifts (0.028 <z<.0.18). We compare the ...derived properties to global properties derived from multi-band imaging and 21 cm H I interferometry and single-dish observations, as well as archival optical SDSS spectra. Besides the Ly alpha line, the spectra contain a number of metal absorption features allowing us to probe the kinematics of the neutral ISM and evaluate the optical depth and and covering fraction of the neutral medium as a function of line of sight velocity. Furthermore, we show how this, in combination with the precise determination of systemic velocity and good Ly alpha spectra, can be used to distinguish a model in which separate clumps together fully cover the background source, from the "picket fence" model named by Heckman et al. We find that no one single effect dominates in governing Ly alpha radiative transfer and escape. Ly alpha escape in our sample coincides with a maximum velocity-binned covering fraction of <, ~0.9 and bulk outflow velocities of > ~50 km s super(-1), although a number of galaxies show these characteristics and yet little or no Ly alpha escape. We find that Ly alpha peak velocities, where available, are not consistent with a strong backscattered component, but rather with a simpler model of an intrinsic emission line overlaid by a blueshifted absorption profile from the outflowing wind. Finally, we find a strong anticorrelation between H alpha equivalent width and maximum velocity-binned covering factor, and propose a heuristic explanatory model.
Abstract As the nearest confirmed Lyman continuum (LyC) emitter, Haro 11 is an exceptional laboratory for studying LyC escape processes crucial to cosmic reionization. Our new Hubble Space ...Telescope/Cosmic Origins Spectrograph G130M/1055 observations of its three star-forming knots now reveal that the observed LyC originates in Knots B and C, with 903–912 Å luminosities of 1.9 ± 1.5 × 10 40 erg s −1 and 0.9 ± 0.7 × 10 40 erg s −1 , respectively. We derive local escape fractions f esc,912 = 3.4% ± 2.9% and 5.1% ± 4.3% for Knots B and C, respectively. Our Starburst99 modeling shows dominant populations on the order of ∼1–4 Myr and 1–2 × 10 7 M ⊙ in each knot, with the youngest population in Knot B. Thus, the knot with the strongest LyC detection has the highest LyC production. However, LyC escape is likely less efficient in Knot B than in Knot C due to higher neutral gas covering. Our results therefore stress the importance of the intrinsic ionizing luminosity, and not just the escape fraction, for LyC detection. Similarly, the Ly α escape fraction does not consistently correlate with LyC flux, nor do narrow Ly α red peaks. High observed Ly α luminosity and low Ly α peak velocity separation, however, do correlate with higher LyC escape. Another insight comes from the undetected Knot A, which drives the Green Pea properties of Haro 11. Its density-bounded conditions suggest highly anisotropic LyC escape. Finally, both of the LyC-leaking Knots, B and C, host ultraluminous X-ray sources (ULXs). While stars strongly dominate over the ULXs in LyC emission, this intriguing coincidence underscores the importance of unveiling the role of accretors in LyC escape and reionization.
We report new results regarding the Ly alpha output of galaxies, derived from the Lyman Alpha Reference Sample, and focused on Hubble Space Telescope imaging. For 14 galaxies we present intensity ...images in Ly alpha , H alpha , and UV, and maps of H alpha /H beta , Ly alpha equivalent width (EW), and Ly alpha /H alpha . We present Ly alpha and UV radial light profiles and show they are well-fitted by Sersic profiles, but Ly alpha profiles show indices systematically lower than those of the UV (n approximately 1-2 instead of gap4). This reveals a general lack of the central concentration in Ly alpha that is ubiquitous in the UV. Photometric growth curves increase more slowly for Ly alpha than the far ultraviolet, showing that small apertures may underestimate the EW. For most galaxies, however, flux and EW curves flatten by radii approximately 10 kpc, suggesting that if placed at high-z only a few of our galaxies would suffer from large flux losses. We compute global properties of the sample in large apertures, and show total Ly alpha luminosities to be independent of all other quantities. Normalized Ly alpha throughput, however, shows significant correlations: escape is found to be higher in galaxies of lower star formation rate, dust content, mass, and nebular quantities that suggest harder ionizing continuum and lower metallicity. Six galaxies would be selected as high-z Ly alpha emitters, based upon their luminosity and EW. We discuss the results in the context of high-z Ly alpha and UV samples. A few galaxies have EWs above 50 A, and one shows f super(Ly) alpha sub(esc) of 80%; such objects have not previously been reported at low-z.
A comprehensive set of optical and near-infrared (NIR) photometry and spectroscopy is presented for the faint and fast 2008ha-like supernova (SN) 2010ae. Contingent on the adopted value of host ...extinction, SN 2010ae reached a peak brightness of −13.8 > MV > −15.3 mag, while modeling of the UVOIR light curve suggests it produced 0.003–0.007 M⊙ of 56Ni, ejected 0.30−0.60 M⊙ of material, and had an explosion energy of 0.04–0.30 × 1051 erg. The values of these explosion parameters are similar to the peculiar SN 2008ha –for which we also present previously unpublished early phase optical and NIR light curves – and places these two transients at the faint end of the 2002cx-like SN population. Detailed inspection of the post-maximum NIR spectroscopic sequence indicates the presence of a multitude of spectral features, which are identified through SYNAPPS modeling to be mainly attributed to Co ii. Comparison with a collection of published and unpublished NIR spectra of other 2002cx-like SNe, reveals that a Co ii footprint is ubiquitous to this subclass of transients, providing a link to Type Ia SNe. A visual-wavelength spectrum of SN 2010ae obtained at +252 days past maximum shows a striking resemblance to a similar epoch spectrum of SN 2002cx. However, subtle differences in the strength and ratio of calcium emission features, as well as diversity among similar epoch spectra of other 2002cx-like SNe indicates a range of physical conditions of the ejecta, highlighting the heterogeneous nature of thispeculiar class of transients.
Abstract
We present Ly
α
imaging of 45 low-redshift star-forming galaxies observed with the Hubble Space Telescope. The galaxies have been selected to have moderate to high star formation rates ...(SFRs) using far-ultraviolet (FUV) luminosity and H
α
equivalent width criteria, but no constraints on Ly
α
luminosity. We employ a pixel stellar continuum fitting code to obtain accurate continuum-subtracted Ly
α
, H
α
, and H
β
maps. We find that Ly
α
is less concentrated than FUV and optical line emission in almost all galaxies with significant Ly
α
emission. We present global measurements of Ly
α
and other quantities measured in apertures designed to capture all of the Ly
α
emission. We then show how the escape fraction of Ly
α
relates to a number of other measured quantities (mass, metallicity, star formation, ionization parameter, and extinction). We find that the escape fraction is strongly anticorrelated with nebular and stellar extinction, weakly anticorrelated with stellar mass, but no conclusive evidence for correlations with other quantities. We show that Ly
α
escape fractions are inconsistent with common dust extinction laws, and discuss how a combination of radiative transfer effects and clumpy dust models can help resolve the discrepancies. We present an SFR calibration based on Ly
α
luminosity, where the equivalent width of Ly
α
is used to correct for nonunity escape fraction, and show that this relation provides a reasonably accurate SFR estimate. We also show stacked growth curves of Ly
α
for the galaxies that can be used to find aperture loss fractions at a given physical radius.
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 characterised 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.
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