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1. Near Field Cosmology: Translating Galaxy Properties to Lyman-alpha and Lyman-continuum escape fractions

   Olivieri Villalvazo, Mario A.; Pilon, Andrew; Venkatesan, Aparna; Rosenberg, Jessica; Gronke, Max; Salzer, John; Cannon, John M.; Janowiecki, Steven (January 2019, American Astronomical Society, AAS Meeting)

   We present our analyses of 39 selected star-forming low- to intermediate-mass low-redshift galaxies from the KISSR survey. These galaxies were selected as being representative in the local volume of the kinds of early galaxies that might have hosted the first stars, and span a range of galaxy properties (EWHA, reddening, metallicity, stellar mass). The KISSR systems contain a population, in appearance resembling "purple peas", with potentially steep UV slopes and high equivalent widths in H-alpha. Using archival GALEX data and theoretical models of radiation transport in dusty galaxies with clumpy gas media, we translate measurements of the UV slopes of these low-mass low-z KISSR galaxies to their escape fractions in Ly-alpha (LyA) and Ly-continuum (LyC) radiation, confirming a relationship between a galaxy's steep UV spectral slope and a significant (> 0.1) LyA escape fraction. This relationship is seen in existing data of low- to intermediate-mass galaxies in the local volume (please see accompanying poster by Pilon et al. at this meeting). We also translate measured LyA escape fractions in the literature for 14 LARS galaxies and a few dozen green pea galaxies to their LyC escape fractions using similar modeling. This work was supported by the University of San Francisco (USF) Faculty Development Fund, the USF Student Travel Fund, and by the Undergraduate ALFALFA Team through NSF grant AST-1637339. 

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2. Lyman continuum escape fraction in Ly α emitters at z ≃ 3.1

   https://doi.org/10.1093/mnrasl/slaa007  

   Bian, Fuyan; Fan, Xiaohui (March 2020, Monthly Notices of the Royal Astronomical Society: Letters)

   ABSTRACT We measure the Lyman continuum (LyC) escape fraction in 54 faint Lyman-alpha emitters (LAEs) at $$z$$ ≃ 3.1 in the GOODS-South field. With the average magnitude of R = 26.7 AB (MUV = −18.8 and L ≃ 0.1L*), these galaxies represent a population of compact young dwarf galaxies. Their properties are likely to resemble those in the galaxies responsible for reionizing the Universe at $$z$$ > 6. We do not detect LyC emission in any individual LAEs in the deep HST F336W images, which covers the rest-frame 820 Å. We do not detect the LyC emission of these LAEs in the stacked F336W images either. The 3σ upper limit of LyC escape fractions is $$f_{\rm esc}\lt 14\!-\!32{{\ \rm per\ cent}}$$. However, the high Ly α rest-frame equivalent width (EW), low stellar mass, and UV luminosity of these LAEs suggest that they should have $$f_{\rm esc}\gt 50{{\ \rm per\ cent}}$$. The low LyC escape fraction from this work and other stacking analyses suggests that the LyC-leaking galaxies with $$f_{\rm esc}\gt 50{{\ \rm per\ cent}}$$ at $$z$$ = 2–3 do not follow the relation between fesc and UV luminosity and Ly α EW derived from typical galaxies at similar redshifts. Therefore, the UV luminosity and Ly α EW are not the best indicators for the LyC escape fraction. 

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3. Connecting the escape fraction of Lyman-alpha and Lyman-continuum photons in star-forming galaxies at $$\mathbf{z\simeq 4-5}$$

   Begley, R.; Cullen, F.; McLure, R. J.; Shapley, A. E.; Dunlop, J. S.; Carnall, A. C.; McLeod, D. J.; Donnan, C. T.; Hamadouche, M. L.; Stanton, T. M. (January 2023, Monthly notices of the Royal Astronomical Society)
4. Low-redshift Lyman Continuum Survey (LzLCS): Radio continuum properties of low-z Lyman continuum emitters

   https://doi.org/10.1051/0004-6361/202348416  

   Bait, Omkar; Borthakur, Sanchayeeta; Schaerer, Daniel; Momjian, Emmanuel; Sebastian, Biny; Saldana-Lopez, Alberto; Flury, Sophia R; Chisholm, John; Marques-Chaves, Rui; Jaskot, Anne E; et al (August 2024, Astronomy & Astrophysics)

   Context.Sources that leak Lyman continuum (LyC) photons and lead to the reionisation of the universe are an object of intense study using multiple observing facilities. Recently, the Low-redshift LyC Survey (LzLCS) has presented the first large sample of LyC emitting galaxies at low redshift (z ∼ 0.3) with theHubbleSpace Telescope Cosmic Origins Spectrograph. The LzLCS sample contains a robust estimate of the LyC escape fraction (f_esc^LyC) for 66 galaxies, spanning a wide range off_esc^LyCvalues. Aims.Here, we aim to study the dependence off_esc^LyCon the radio continuum (RC) properties of LzLCS sources. Overall, RC emission can provide unique insights into the role of supernova feedback, cosmic rays (CRs), and magnetic fields from its non-thermal emission component. RC emission is also a dust-free tracer of the star formation rate (SFR) in galaxies. Methods.In this study, we present Karl G. Jansky Very Large Array (VLA) RC observations of the LzLCS sources at gigahertz (GHz) frequencies. We performed VLAC(4−8 GHz) andS(2−4 GHz) band observations for a sample of 53 LzLCS sources. We also observed a sub-sample of 17 LzLCS sources in theL(1−2 GHz) band. We detected RC from bothC- andS-bands in 24 sources for which we are able to estimate their radio spectral index across 3−6 GHz, denoted asα_6 GHz^3 GHz. We also used the RC luminosity to estimate their SFRs. Results.The radio spectral index of LzLCS sources spans a wide range, from flat (≥ − 0.1) to very steep (≤ − 1.0). They have a steeper meanα_6 GHz^3 GHz(≈ − 0.92) compared to that expected for normal star-forming galaxies (α_6 GHz^3 GHz ≈ −0.64). They also show a larger scatter inα_6 GHz^3 GHz(∼0.71) compared to that of normal star-forming galaxies (∼0.15). The strongest leakers in our sample show flatα_6 GHz^3 GHz, weak leakers haveα_6 GHz^3 GHzclose to normal star-forming galaxies and non-leakers are characterized by steepα_6 GHz^3 GHz. We argue that a combination of young ages, free-free absorption, and a flat cosmic-ray energy spectrum can altogether lead to a flatα_6 GHz^3 GHzfor strong leakers. Non-leakers are characterized by steep spectra which can arise due to break or cutoff at high frequencies. Such a cutoff in the spectrum can arise in a single injection model of CRs characteristic of galaxies which have recently stopped star-formation. The dependence off_esc^LyConα_6 GHz^3 GHz(which is orientation-independent) suggests that the escape of LyC photons is not highly direction-dependent at least to the first order. The radio-based SFRs (SFR^RC) of LzLCS sources show a large offset (∼0.59 dex) from the standard SFR^RCcalibration. We find that addingα_6 GHz^3 GHzas a second parameter helps us to calibrate the SFR^RCwith SFR_UVand SFR_Hβwithin a scatter of ∼0.21 dex. Conclusions.For the first time, we have found a relation betweenα_6 GHz^3 GHzandf_esc^LyC. This hints at the interesting role of supernovae feedback, CRs, and magnetic fields in facilitating the escape (alternatively, and/or the lack) of LyC photons. 

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5. The physics of Lyman α escape from high-redshift galaxies

   https://doi.org/10.1093/mnras/sty3483  

   Smith, Aaron; Ma, Xiangcheng; Bromm, Volker; Finkelstein, Steven L; Hopkins, Philip F; Faucher-Giguère, Claude-André; Kereš, Dušan (December 2018, Monthly Notices of the Royal Astronomical Society)