分类： 天文学 >> 天文学 提交时间： 2023-02-19
Xinfeng Xu
Alaina Henry
Timothy Heckman
John Chisholm
Rui Marques-Chaves
Floriane Leclercq
Danielle A. Berg
Anne Jaskot
Daniel Schaerer
Gábor Worseck
Ricardo O. Amorín
Hakim Atek
Matthew Hayes
Zhiyuan Ji
Göran Östlin
Alberto Saldana-Lopez
Trinh Thuan
摘要： The Mg II 2796, 2803 doublet has been suggested to be a useful indirect indicator for the escape of Ly-alpha 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 probing 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, and to pure absorption. We find there is a significant trend (with a possibility of spurious correlations of ~ 2%) that galaxies detected as strong LyC Emitters (LCEs) also show larger equivalent widths of Mg II emission, and non-LCEs tend to show evidence of more scattering and absorption features in Mg II We then find Mg II strongly correlates with Ly-alpha in both equivalent width and escape fraction, regardless of whether the emission or absorption dominates the Mg II profiles. Furthermore, we present that, for galaxies categorized as Mg II emitters (MgE), one can adopt 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 to select galaxies as LCEs and to serve as an indirect indicator for the escape of Ly-alpha and LyC.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Maxime Trebitsch
Pratika Dayal
John Chisholm
Steven L. Finkelstein
Anne Jaskot
Sophia Flury
Daniel Schaerer
Hakim Atek
Sanchayeeta Borthakur
Harry Ferguson
Fabio Fontanot
Mauro Giavalisco
Andrea Grazian
Matthew Hayes
Floriane Leclercq
Göran Östlin
Alberto Saldana-Lopez
Trinh X. Thuan
Bingjie Wang
Gábor Worseck
摘要： The fraction of ionizing photons escaping from galaxies, $f_{esc}$, is at the same time a crucial parameter in modelling reionization and a very poorly known quantity, especially at high redshift. Recent observations are starting to constrain the values of $f_{esc}$ in low-z star-forming galaxies, but the validity of this comparison remains to be verified. Applying at high-z the empirical relation between $f_{esc}$ and the UV slope trends derived from the Low-z Lyman Continuum Survey, we use the DELPHI semi-analytical galaxy formation model to estimate the global ionizing emissivity of high-z galaxies, which we use to compute the resulting reionization history. We find that both the global ionizing emissivity and reionization history match the observational constraints. Assuming that the low-z correlations hold during the epoch of reionization, we find that galaxies with $-16 \lesssim M_{UV} \lesssim -13.5$ are the main drivers of reionization. We derive a population-averaged $\langle f_{esc} \rangle \simeq 8\%, 10\%, 20\%$ at z=4.5, 6, 8.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Bingjie Wang
Timothy M. Heckman
Ricardo Amorín
Sanchayeeta Borthakur
John Chisholm
Harry Ferguson
Sophia Flury
Mauro Giavalisco
Andrea Grazian
Matthew Hayes
Alaina Henry
Anne Jaskot
Zhiyuan Ji
Kirill Makan
Stephan McCandliss
M. S. Oey
Göran Östlin
Alberto Saldana-Lopez
Daniel Schaerer
Trinh Thuan
摘要： 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 onboard 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 Lyman-$\alpha$ emission and high [O III]/[O II]). Our results verify an additional technique by which reionization-era galaxies could be studied.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Xinfeng Xu
Alaina Henry
Timothy Heckman
John Chisholm
Gábor Worseck
Max Gronke
Anne Jaskot
Stephan R. McCandliss
Sophia R. Flury
Mauro Giavalisco
Zhiyuan Ji
Ricardo O. Amorín
Danielle A. Berg
Sanchayeeta Borthakur
Nicolas Bouche
Cody Carr
Dawn K. Erb
Harry Ferguson
Thibault Garel
Matthew Hayes
摘要： Star-forming galaxies are considered the likeliest source of the H I ionizing Lyman Continuum (LyC) photons that reionized the intergalactic medium at high redshifts. However, above z >~ 6, the neutral intergalactic medium prevents direct observations of LyC. Therefore, recent years have seen the development of indirect indicators for LyC that can be calibrated at lower redshifts and applied in the Epoch of Reionization. Emission from Mg II \ly\ly 2796, 2803 doublet has been proposed as a promising LyC proxy. In this paper, we present new Hubble Space Telescope/Cosmic Origins Spectrograph observations for 8 LyC emitter candidates, selected to have strong Mg II emission lines. We securely detect LyC emission in 50% (4/8) galaxies with 2$\sigma$ significance. This high detection rate suggests that strong Mg II emitters might be more likely to leak LyC than similar galaxies without strong Mg II. Using photoionization models, we constrain the escape fraction of Mg II as ~ 15 -- 60%. We confirm that the escape fraction of Mg II correlates tightly with that of Lyman-alpha (LyA), which we interpret as an indication that the escape fraction of both species is controlled by resonant scattering in the same low column density gas. Furthermore, we show that the combination of the Mg II emission and dust attenuation can be used to estimate the escape fraction of LyC statistically. These findings confirm that Mg II emission can be adopted to estimate the escape fraction of LyA and LyC in local star-forming galaxies and may serve as a useful indirect indicator at the Epoch of Reionization.
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