| 1. |
- Flury, Sophia R., et al.
(författare)
-
The Low-redshift Lyman Continuum Survey. I. New, Diverse Local Lyman Continuum Emitters
- 2022
-
Ingår i: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 260:1
-
Tidskriftsartikel (refereegranskat)abstract
- The origins of Lyman continuum (LyC) photons responsible for the reionization of the universe are as of yet unknown and highly contested. Detecting LyC photons from the Epoch of Reionization is not possible due to absorption by the intergalactic medium, which has prompted the development of several indirect diagnostics to infer the rate at which galaxies contribute LyC photons to reionize the universe by studying lower-redshift analogs. We present the Low-redshift Lyman Continuum Survey (LzLCS) comprising measurements made with the Hubble Space Telescope Cosmic Origins Spectrograph for a z = 0.2-0.4 sample of 66 galaxies. After careful processing of the far-UV spectra, we obtain a total of 35 Lyman continuum emitters (LCEs) detected with 97.725% confidence, nearly tripling the number of known local LCEs. We estimate escape fractions from the detected LyC flux and upper limits on the undetected LyC flux, finding a range of LyC escape fractions up to 50%. Of the 35 LzLCS LCEs, 12 have LyC escape fractions greater than 5%, more than doubling the number of known local LCEs with cosmologically relevant LyC escape.
|
|
| 2. |
- Flury, Sophia R., et al.
(författare)
-
The Low-redshift Lyman Continuum Survey. II. New Insights into LyC Diagnostics
- 2022
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 930:2
-
Tidskriftsartikel (refereegranskat)abstract
- The Lyman continuum (LyC) cannot be observed at the epoch of reionization (z greater than or similar to 6) owing to intergalactic H i absorption. To identify LyC emitters (LCEs) and infer the fraction of escaping LyC, astronomers have developed various indirect diagnostics of LyC escape. Using measurements of the LyC from the Low-redshift Lyman Continuum Survey (LzLCS), we present the first statistical test of these diagnostics. While optical depth indicators based on Ly alpha, such as peak velocity separation and equivalent width, perform well, we also find that other diagnostics, such as the [O iii]/[O ii] flux ratio and star formation rate surface density, predict whether a galaxy is an LCE. The relationship between these galaxy properties and the fraction of escaping LyC flux suggests that LyC escape depends strongly on H i column density, ionization parameter, and stellar feedback. We find that LCEs occupy a range of stellar masses, metallicities, star formation histories, and ionization parameters, which may indicate episodic and/or different physical causes of LyC escape.
|
|
| 3. |
- Rasekh, Armin, et al.
(författare)
-
A Lyman alpha imaging study of green pea galaxies
-
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.
|
|
| 4. |
- Saldana-Lopez, Alberto, et al.
(författare)
-
The Low-Redshift Lyman Continuum Survey Unveiling the ISM properties of low-z Lyman-continuum emitters
- 2022
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 663
-
Tidskriftsartikel (refereegranskat)abstract
- Aims. Combining 66 ultraviolet (UV) spectra and ancillary data from the recent Low-Redshift Lyman Continuum Survey (LzLCS) and 23 LyC observations by earlier studies, we form a statistical sample of star-forming galaxies at z similar to 0.2-0.4 with which we study the role of cold interstellar medium (ISM) gas in the leakage of ionizing radiation. We also aim to establish empirical relations between the H I neutral and low-ionization state (LIS) absorption lines with different galaxy properties.Methods. We first constrain the massive star content (stellar ages and metallicities) and UV attenuation by fitting the stellar continuum with a combination of simple stellar population models. The models, together with accurate LyC flux measurements, allow us to determine the absolute LyC photon escape fraction for each galaxy (f(esc)(abs)). We then measure the equivalent widths and residual fluxes of multiple H I and LIS lines, and the geometrical covering fraction of the UV emission, adopting the picket-fence model.Results. The LyC escape fraction spans a wide range, with a median f(esc)(abs) (0.16, 0.84 quantiles) of 0.04 (0.02, 0.20), and 50 out of the 89 galaxies detected in the LyC (1 sigma upper limits of f(esc)(abs) less than or similar to 0.01 for non-detections, typically). The H I and LIS line equivalent widths scale with the UV luminosity and attenuation, and inversely with the residual flux of these lines. Additionally, Ly alpha equivalent widths scale with both the H I and LIS residual fluxes, but anti-correlate with the corresponding H I or LIS equivalent widths. The H I and LIS residual fluxes are correlated, indicating that the neutral gas is spatially traced by the low-ionization transitions. We find that the observed trends of the absorption lines and the UV attenuation are primarily driven by the geometric covering fraction of the gas. The observed nonuniform gas coverage also demonstrates that LyC photons escape through low-column-density channels in the ISM. The equivalent widths and residual fluxes of both the H I and LIS lines strongly correlate with f(esc)(abs): strong LyC leakers (highest f(esc)(abs)) show weak absorption lines, low UV attenuation, and large Ly alpha equivalent widths. We provide several empirical calibrations to estimate f(esc)(abs) from UV absorption lines. Finally, we show that simultaneous UV absorption line and dust attenuation measurements can, in general, predict the escape fraction of galaxies. We apply our method to available measurements of UV LIS lines of 15 star-forming galaxies at z similar to 4 6 (plus 3 high-z galaxy composites), finding that these high-redshift, UV-bright galaxies (M-UV less than or similar to 21) may have low escape fractions, f(esc)(abs) less than or similar to 0.1.Conclusions. UV absorption lines trace the cold ISM gas of galaxies, which governs the physics of the LyC escape. We show that, with some assumptions, the absolute LyC escape can be statistically predicted using UV absorption lines, and the method can be applied to study galaxies across a wide redshift range, including in the epoch of cosmic reionization.
|
|
| 5. |
- Wang, Bingjie, et al.
(författare)
-
The Low-redshift Lyman-continuum Survey : [S ii] Deficiency and the Leakage of Ionizing Radiation
- 2021
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 916:1
-
Tidskriftsartikel (refereegranskat)abstract
- The relationship between galaxy characteristics and the reionization of the universe remains elusive, mainly due to the observational difficulty in accessing the Lyman continuum (LyC) at these redshifts. It is thus important to identify low-redshift LyC-leaking galaxies that can be used as laboratories to investigate the physical processes that allow LyC photons to escape. The weakness of the [S ii] nebular emission lines relative to typical star-forming galaxies has been proposed as a LyC predictor. In this paper, we show that the [S ii] deficiency is an effective method to select LyC-leaking candidates using data from the Low-redshift LyC Survey, which has detected flux below the Lyman edge in 35 out of 66 star-forming galaxies with the Cosmic Origins Spectrograph on board the Hubble Space Telescope. We show that LyC leakers tend to be more [S ii] deficient and that the fraction of their detections increases as [S ii] deficiency becomes more prominent. Correlational studies suggest that [S ii] deficiency complements other LyC diagnostics (such as strong Lyα emission and high [O iii]/[O ii]). Our results verify an additional technique by which reionization-era galaxies could be studied.
|
|
| 6. |
- Xu, Xinfeng, et al.
(författare)
-
The Low-redshift Lyman Continuum Survey : Optically Thin and Thick Mg II Lines as Probes of Lyman Continuum Escape
- 2023
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 943:2
-
Tidskriftsartikel (refereegranskat)abstract
- The Mg II λλ2796, 2803 doublet has been suggested as a useful indirect indicator for the escape of Lyα and Lyman continuum (LyC) photons in local star-forming galaxies. However, studies to date have focused on small samples of galaxies with strong Mg II or strong LyC emission. Here, we present the first study of Mg II to probe a large dynamic range of galaxy properties, using newly obtained high-signal-to-noise, moderate-resolution spectra of Mg II, for a sample of 34 galaxies selected from the Low-redshift Lyman Continuum Survey. We show that the galaxies in our sample have Mg II profiles ranging from strong emission to P-Cygni profiles to pure absorption. We find that there is a significant trend (with a possibility of spurious correlations of ∼2%) that galaxies that are detected as strong LyC emitters (LCEs) show larger equivalent widths of Mg II emission, while non-LCEs tend to show evidence of more scattering and absorption features in Mg II. We then find that Mg II strongly correlates with Lyα in both equivalent width and escape fraction, regardless of whether emission or absorption dominates the Mg II profiles. Furthermore, we show that, for galaxies that are categorized as Mg II emitters, one can use the information of Mg II, metallicity, and dust to estimate the escape fraction of LyC within a factor of ∼3. These findings confirm that Mg II lines can be used as a tool for selecting galaxies as LCEs and thus serve as an indirect indicator for the escape of Lyα and LyC.
|
|
