| 1. |
- Adamo, Angela, et al.
(författare)
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Star cluster formation in the most extreme environments: Insights from the HiPEEC survey
- 2020
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 499:3, s. 3267-3294
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Tidskriftsartikel (refereegranskat)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.
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| 2. |
- Hayes, Matthew J., et al.
(författare)
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Spectral Shapes of the Lyα Emission from Galaxies. : II. The influence of stellar properties and nebular conditions on the emergent line profiles
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We demonstrate how the stellar properties and nebular conditions in star-forming galaxies modulate the emission and spectral profile of HI Lyman-alpha (Lyα) emission line. In this second paper in a series, we examine the net Lyα output, kinematics, and in particular emission of blue-shifted Lyαradiation. We use intermediate resolution spectroscopy obtained with the Cosmic Origins Spectrograph on HST, giving a sample of 87 galaxies at redshift (z) between 0.05 and 0.44. We contrast the Lyα spectral measurements with properties of the ionized gas (from optical spectroscopy) and stars(from stellar spectral modeling). We demonstrate correlations of unprecedented strength between the Lyα escape fraction (or equivalent width) and properties correlating with ionization parameter(p ≈ 10−15). The same data reveal evolution in the relative contribution of blue-shifted emission to the total Lyα, which varies from ≈ 0 to ≈ 40 % on average (p ≈ 10−6). We also find particularly strong correlations with estimators of stellar evolutionary stage, nebular abundance, and weaker correlations regarding thermodynamic variables. Analysis of the low ionization stage absorption lines suggests the net emission and line profile is predominantly governed by the column of absorbing gas close to zero velocity. Multi-parametric analysis of the many variables presented here reveals that we can reliably predict up to 80 % of the Lyα luminosity variance, and ∼ 50 % of the variance on the EW. We also analyze the most crucial predictive variables, finding that for tracers of the high and low ionization gas and Hβ luminosity dominate the luminosity prediction whereas the Lyα EW is most well predicted by Hβ EW and the Hα/Hβ ratio. We discuss our results with reference to high redshift observations, with particular focus upon the use of Lyα to probe the nebular conditions in star forming galaxies and the reionization of the universe.
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| 3. |
- Hayes, Matthew J., et al.
(författare)
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Spectral Shapes of the Lyα Emission from Galaxies. I. Blueshifted Emission and Intrinsic Invariance with Redshift*
- 2021
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 908:1, s. 1-17
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the redshift evolution of the spectral profile of H i Lyα emission from star-forming galaxies. In this first study we pay special attention to the contribution of blueshifted emission. At redshift z = 2.9–6.6, we compile spectra of a sample of 229 Lyα-selected galaxies identified with the Multi-Unit Spectroscopic Explorer at the Very Large Telescope, while at low z ( < 0.44) we use a sample of 74 ultraviolet-selected galaxies observed with the Cosmic Origin Spectrograph on board the Hubble Space Telescope. At low z, where absorption from the intergalactic medium (IGM) is negligible, we show that the ratio of Lyα luminosity blueward and redward of line center (LB/R) increases rapidly with increasing equivalent width (WLyα). This correlation does not, however, emerge at z = 3–4, and we use bootstrap simulations to demonstrate that trends in LB/R should be suppressed by variations in IGM absorption. Our main result is that the observed blueshifted contribution evolves rapidly downward with increasing redshift: LB/R ≈ 30% at z ≈ 0, but dropping to 15% at z ≈ 3, and to below 3% by z ≈ 6. Applying further simulations of the IGM absorption to the unabsorbed COS spectrum, we demonstrate that this decrease in the blue-wing contribution can be entirely attributed to the thickening of intervening Lyα absorbing systems, with no need for additional H i opacity from local structure, companion galaxies, or cosmic infall. We discuss our results in light of the numerical radiative transfer simulations, the evolving total Lyα and ionizing output of galaxies, and the utility of resolved Lyα spectra in the reionization epoch.
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| 4. |
- Hayes, Matthew J., et al.
(författare)
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Spectral shapes of the Ly α emission from galaxies – II. The influence of stellar properties and nebular conditions on the emergent Ly α profiles
- 2023
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 520:4, s. 5903-5927
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate how the stellar and nebular conditions in star-forming galaxies modulate the emission and spectral profile of H I Ly α emission line. We examine the net Ly α output, kinematics, and in particular emission of blueshifted Ly α radiation, using spectroscopy from with the Cosmic Origins Spectrograph on Hubble Space Telescope (HST), giving a sample of 87 galaxies at redshift z = 0.05−0.44. We contrast the Ly α spectral measurements with properties of the ionized gas (from optical spectra) and stars (from stellar modelling). We demonstrate correlations of unprecedented strength between the Ly α escape fraction (and equivalent width) and the ionization parameter (p ≈ 10−15). The relative contribution of blueshifted emission to the total Ly α also increases from ≈0 to ≈40 per cent over the range of O32 ratios (p ≈ 10−6). We also find particularly strong correlations with estimators of stellar age and nebular abundance, and weaker correlations regarding thermodynamic variables. Low ionization stage absorption lines suggest the Ly α emission and line profile are predominantly governed by the column of absorbing gas near zero velocity. Simultaneous multiparametric analysis over many variables shows we can predict 80 per cent of the variance on Ly α luminosity, and ∼50 per cent on the EW. We determine the most crucial predictive variables, finding that for tracers of the ionization state and H β luminosity dominate the luminosity prediction whereas the Ly α EW is best predicted by H β EW and the H α/H β ratio. We discuss our results with reference to high-redshift observations, focussing upon the use of Ly α to probe the nebular conditions in high-z galaxies and cosmic reionization.
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| 5. |
- Melinder, Jens, et al.
(författare)
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Lyman alpha escape from 45 star forming galaxies– the Lyα Reference Sample XIV
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present Lyα 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 using FUVluminosity and Hα equivalent width criteria, but no constraints on Lyα luminosity have been applied. We employ a pixel SED fitting code to obtain accurate continuum subtracted Lyα, Hα and Hβ maps. We find that Lyα is less concentrated than FUV and optical line emission in almost all galaxies with significant Lyα emission. We present global measurements of Lyα and other quantities measured in apertures designed to capture all of the Lyα emission. We then show how the escape fraction ofLyα relates to a number of other measured quantities (mass, metallicity, star formation, ionization parameter, and extinction). We find that the escape fraction is strongly anti-correlated with both nebular and stellar extinction, weakly anti-correlated with stellar mass, but no conclusive evidence for correlations to other quantities. We show that Lyα 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 a star formation rate calibration based on Lyαluminosity, where the equivalent width of Lyα is used to correct for non-unity escape fraction, and show that this relation provides a reasonably accurate calibration but with a large scatter. We also show stacked growth curves of Lyα for the galaxies that can be used to find aperture loss fractions at a given physical radius
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| 6. |
- Melinder, Jens, 1977-, et al.
(författare)
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The Lyα Reference Sample. XIV. Lyα Imaging of 45 Low-redshift Star-forming Galaxies and Inferences on Global Emission
- 2023
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Ingår i: Astrophysical Journal Supplement Series. - 0067-0049 .- 1538-4365. ; 266:1
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Tidskriftsartikel (refereegranskat)abstract
- We present Lyα 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 Hα equivalent width criteria, but no constraints on Lyα luminosity. We employ a pixel stellar continuum fitting code to obtain accurate continuum-subtracted Lyα, Hα, and Hβ maps. We find that Lyα is less concentrated than FUV and optical line emission in almost all galaxies with significant Lyα emission. We present global measurements of Lyα and other quantities measured in apertures designed to capture all of the Lyα emission. We then show how the escape fraction of Lyα 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 Lyα 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 Lyα luminosity, where the equivalent width of Lyα 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 Lyα for the galaxies that can be used to find aperture loss fractions at a given physical radius.
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| 7. |
- Rasekh, Armin, et al.
(författare)
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A Lyman alpha imaging study of green pea galaxies
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Aims. We present Hubble space telescope (HST) imaging data of six green pea (GP) galaxies (two of which are confirmed Lymancontinuum leakers, and a third is a probable leaker). We investigate their Lyα photometric properties by measuring their Lyα global observables, study their Lyα halos, and how their compactness is related to some of the primary diagnostics used to predict whether a galaxy is a Lyman continuum (LyC) leaker.Methods. We constructed Lyα images from multi-filter HST imaging from the far UV to the red and Hα, using a continuum subtraction method from the literature. In the resulting Lyα images, we measured global observables: Lyα luminosity, Lyα equivalent width and Lyα escape fraction by estimating a global aperture for each galaxy and measured these quantities within this aperture. To study the Lyα morphology of these galaxies, we studied their Lyα surface brightness (SB) using two different methods i) a method devised to study the Lyα SB of high−z Lyα emitters and ii) a method used to study more nearby star-forming galaxies. Moreover, we measured the concentration parameter for each galaxy. We studied the fraction of Lyα emission recovered within the COS/HST field-of-view compared to the global aperture we derived in our analysis. We also looked at how O32 and the red/blue peak separation of the Lyα line profile relate to Lyα compactness and the Lyα escape fraction.Results. We detect Lyα emission (> 10σ) for all galaxies. Despite their compactness (far UV Petrosian radii rp20 ∼ 1 kpc), all galaxies show extended Lyα emission detected out to radii 13 to 34 kpc. Our analysis suggests that the known correlation between fLyαesc and EWLyα in nearby SFGs holds for GPs, too. We also see that the method used to study the Lyα SB profiles of high−z LAEs is not applicable to low-redshift galaxies. Our analysis shows that (except for one galaxy) the majority of the total measured Lyα flux is emitted within the HST/COS aperture. Furthermore, we found that O32 does not correlate with the quantities related to the Lyα compactness or the Lyα escape fraction. However, the peak separation strongly anti-correlates with the Lyα escape fraction and strongly correlates with the Lyα halo fraction. Finally, our findings suggest that one additional galaxy is a good candidate for being a significant LyC emitter.
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| 8. |
- Rasekh, Armin, et al.
(författare)
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The Lyman Alpha Reference Sample XII. Morphology of extended Lyman alpha emission in star-forming galaxies
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 662
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We use Hubble Space Telescope data of 45 nearby star-forming galaxies to investigate properties of Lyman-alpha (Lyα) halos, Lyα morphology, and the star-forming characteristics of galaxies. We study how the morphology of Lyα emission is related to other Lyα observables. Furthermore, we study the interdependencies of Lyα morphological quantities.Methods. We studied the spatial extent of Lyα using surface brightness profiles in the following two ways (i) using circular apertures and (ii) within faint Lyα isophotes. We also measured the average intensity and the size of the regions with a high star formation rate density. The morphology of the galaxies was quantified by computing centroid position, axis ratio, and position angle in the Lyα, ultraviolet continuum, and I band maps.Results. We found that galaxies with more extended star-forming regions possess larger Lyα halos. Furthermore, galaxies with more elongated Lyα morphology are also more extended in Lyα. Our data suggest that Lyα bright galaxies appear rounder in their Lyα morphology, and there is less of a contribution from their Lyα halo to their overall luminosity. We compared our results with studies at high redshift and found that whilst the Lyα extent in the inner regions of the galaxies in our sample are similar to the high-z Lyα emitters (LAEs), Lyα halos are more extended in high-z LAEs.Conclusions. Our analysis suggests that the Lyα morphology affects the measurement of other observable quantities concerning Lyα emission, and some of the conclusions drawn from high redshift LAEs might be biased towards galaxies with specific Lyα shapes. In particular, faint Lyα emitters have larger Lyα scale lengths and halo fractions. This implies that faint Lyα emitters are harder to detect at high redshift than previously believed.
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| 9. |
- Runnholm, Axel, 1992-, et al.
(författare)
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On the evolution of the size of Lyman alpha haloes across cosmic time : no change in the circumgalactic gas distribution when probed by line emission
- 2023
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Ingår i: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 522:3, s. 4275-4293
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Tidskriftsartikel (refereegranskat)abstract
- Lyman alpha (Ly alpha) is now routinely used as a tool for studying high-redshift galaxies, and its resonant nature means it can trace neutral hydrogen around star-forming galaxies. Integral field spectrograph measurements of high-redshift Ly alpha emitters indicate that significant extended Ly alpha halo emission is ubiquitous around such objects. We present a sample of redshift 0.23 to 0.31 galaxies observed with the Hubble Space Telescope selected to match the star formation properties of high-z samples while optimizing the observations for detection of low surface brightness Ly alpha emission. The Ly alpha escape fractions range between 0.7 and 37 per cent, and we detect extended Ly alpha emission around six out of seven targets. We find Ly alpha halo to UV scale length ratios around 6:1, which is marginally lower than high-redshift observations, and halo flux fractions between 60 and 85 per cent - consistent with high-redshift observations - when using comparable methods. However, our targets show additional extended stellar UV emission: we parametrize this with a new double exponential model. We find that this parametrization does not strongly affect the observed Ly alpha halo fractions. We find that deeper H alpha data would be required to firmly determine the origin of Ly alpha halo emission; however, there are indications that H alpha is more extended than the central FUV profile, potentially indicating conditions favourable for the escape of ionizing radiation. We discuss our results in the context of high-redshift galaxies, cosmological simulations, evolutionary studies of the circumgalactic medium in emission, and the emission of ionizing radiation.
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| 10. |
- Runnholm, Axel, et al.
(författare)
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On the evolution of the size of Lyman alpha halos across cosmic time: no change in the circumgalactic gas distribution when probed by line emission
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Lyman ? (Ly?) is now routinely used as a tool for detecting high redshift galaxies and its resonant nature means it can trace neutral hydrogen around star-forming galaxies. Integral field spectrograph measurements of high-? Ly? emitters indicate that significant extended Ly? halo emission is ubiquitous around such objects. We present a sample of redshift 0.23 to 0.32 galaxies observed with the Hubble Space Telescope selected to match the star formation properties of high-? samples while optimizing the observations for detection of low surface brightness Ly? emission. All seven targets show Ly? emission, with total escape fractions between 0.7% and 37%, and extended Ly? emission. We find Ly? halo to UV scale length ratios around 10:1, and halo flux fractions between 60% and 85% —consistent with high redshift observations—when using comparable methods. However, our targets show additional extended stellar UV emission which we parametrize with a new three exponential component model for Ly? emission. Halo fractions become much smaller with this methodology and some become consistent with zero. Comparing UV and H? emission reveals that H? is also extended and can partially explain the origin of diffuse Ly?. We interpret this as evidence that the creation of Ly? halos cannot be attributed to one single process but rather a combination of in-situ recombination and spatial scattering or possibly collisional excitation. We discuss our results in the context of high-redshift galaxies, evolutionary studies of the circumgalactic medium in emission, and inferences concerning the emission of ionizing radiation.
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