arXiv subjects

C. G. Lacey

Publications and source records attributed to C. G. Lacey.

At least 19 recordsLinked to original sources

arXiv2021

Modelling emission lines in star forming galaxies

We present a new model to compute the luminosity of emission lines in star forming galaxies and apply this in the semi-analytical galaxy formation code GALFORM. The model combines a pre-computed grid of HII region models with an empirical determination of how the properties of HII regions depend on the macroscopic properties of galaxies based on observations of local galaxies. The new model gives a very good reproduction of the locus of star-forming galaxies on standard line ratio diagnostic diagrams. The new model shows evolution in the locus of star forming galaxies with redshift on this line ratio diagram, with a good match to the observed line ratios at $z=1.6$. The model galaxies at high redshift have gas densities and ionisation parameters that are predicted to be $\approx 2-3$ times higher than in local star forming galaxies, which is partly driven by the changing selection with redshift to mimic the observational selection. Our results suggest that the observed evolution in emission line ratios requires other HII region properties to evolve with redshift, such as the gas density, and cannot be reproduced by HII model grids that only allow the gas metallicity and ionisation parameter to vary.

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arXiv2020

Are Lyα emitters segregated in protoclusters regions?

The presence of neutral hydrogen in the inter-stellar medium (ISM) and inter-galactic medium (IGM) induces radiative transfer (RT) effects on Lyα photons which affect the observability of Lyα emitters (LAEs). We use the GALFORM semi-analytic model of galaxy formation and evolution to analyse how these effects shape the spatial distribution of LAEs with respect to Hα emitters (HAEs) around high density regions at high redshift. We find that when a large sample of protoclusters is considered, HAEs showing also Lyα emission (HAEs+LAEs) populate the same regions as those that do not display the Lyα line at $z=2.2$. We compare against the protocluster USS1558-003, one of the most massive protoclusters located at $z=2.53$. Our results indicate that the strong depletion of HAEs+LAEs present in the high density regions of USS1558-003 may be due to cosmic variance. We find that at $z=2.2$ and $z=3.0$, RT of the ISM produces a strong decline ($30$-$50$ per cent) of the clustering amplitude of HAEs+LAEs with respect to HAEs towards the protoclusters centre. At $z=5.7$, given the early evolutionary state of protoclusters and galaxies, the clustering of HAEs+LAEs has a smaller variation ($10$-$20$ per cent) towards the protoclusters centre. Depending on the equivalent width and luminosity criteria of the emission-line galaxy sample, the IGM can have a mild or a null effect on galaxy properties and clustering in high density regions.

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arXiv2017

The VLA-COSMOS 3~GHz Large Project: AGN and host-galaxy properties out to z$\lesssim$6

We explore the multiwavelength properties of AGN host galaxies for different classes of radio-selected AGN out to z$\lesssim$6 via a multiwavelength analysis of about 7700 radio sources in the COSMOS field. The sources were selected with the Very Large Array (VLA) at 3 GHz (10 cm) within the VLA-COSMOS 3 GHz Large Project, and cross-matched with multiwavelength ancillary data. This is the largest sample of high-redshift (z$\lesssim$6) radio sources with exquisite photometric coverage and redshift measurements available. We constructed a sample of moderate-to-high radiative luminosity AGN (HLAGN) via spectral energy distribution (SED) decomposition combined with standard X-ray and mid-infrared diagnostics. Within the remainder of the sample we further identified low-to-moderate radiative luminosity AGN (MLAGN) via excess in radio emission relative to the star formation rates in their host galaxies. We show that AGN power in HLAGN occurs predominantly in radiative form, while MLAGN display a substantial mechanical AGN luminosity component. We found significant differences in the host properties of the two AGN classes, as a function of redshift. At z$<$1.5, MLAGN appear to reside in significantly more massive and less star-forming galaxies compared to HLAGN. At z$>$1.5, we observed a reversal in the behaviour of the stellar mass distributions with the HLAGN populating the higher stellar mass tail. We interpret this finding as a possible hint of the downsizing of galaxies hosting HLAGN, with the most massive galaxies triggering AGN activity earlier than less massive galaxies, and then fading to MLAGN at lower redshifts. Our conclusion is that HLAGN and MLAGN samples trace two distinct galaxy and AGN populations in a wide range of redshifts, possibly resembling the radio AGN types often referred to as radiative- and jet-mode (or high- and low-excitation), respectively.

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arXiv2016

The SCUBA-2 Cosmology Legacy Survey: 850um maps, catalogues and number counts

We present a catalogue of nearly 3,000 submillimetre sources detected at 850um over ~5 square degrees surveyed as part of the James Clerk Maxwell Telescope (JCMT) SCUBA-2 Cosmology Legacy Survey (S2CLS). This is the largest survey of its kind at 850um, probing a meaningful cosmic volume at the peak of star formation activity and increasing the sample size of submillimetre galaxies selected at 850um by an order of magnitude. We describe the wide 850um survey component of S2CLS, which covers the key extragalactic survey fields: UKIDSS-UDS, COSMOS, Akari-NEP, Extended Groth Strip, Lockman Hole North, SSA22 and GOODS-North. The average 1-sigma depth of S2CLS is 1.2 mJy/beam, approaching the SCUBA-2 850um confusion limit, which we determine to be ~0.8 mJy/beam. We measure the single dish 850um number counts to unprecedented accuracy, reducing the Poisson errors on the differential counts to approximately 4% at S_850~3mJy. With several independent fields, we investigate field-to-field variance, finding that the number counts on 0.5-1 degree scales are generally within 50% of the S2CLS mean for S_850>3mJy, with scatter consistent with the Poisson and estimated cosmic variance uncertainties, although there is a marginal (2-sigma) density enhancement in the GOODS-North field. The observed number counts are in reasonable agreement with recent phenomenological and semi-analytic models. Finally, the large solid angle of S2CLS allows us to measure the bright-end counts: at S_850>10mJy there are approximately ten sources per square degree, and we detect the distinctive up-turn in the number counts indicative of the detection of local sources of 850um emission and strongly lensed high-redshift galaxies. Here we describe the data collection and reduction procedures and present calibrated maps and a catalogue of sources; these are made publicly available.

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arXiv2016

The clustering and halo occupation distribution of Lyman-break galaxies at $z\sim4$

We investigate the clustering of Lyman-break galaxies (LBGs) at $z\sim4$. Using the hierarchical galaxy formation model GALFORM, we predict, for the first time using a semi-analytical model with feedback from active galactic nuclei (AGN), the angular correlation function (ACF) of LBGs and find agreement within $3\,σ$ with new measurements of the ACF from surveys including the Hubble eXtreme Deep Field (XDF) and CANDELS field. Our simulations confirm the conclusion reached using independent models that although the predicted ACFs reproduce the trend of increased clustering with luminosity, the dependence is less strong than observed. We find that for the detection limits of the XDF field central LBGs at $z\sim 4$ predominantly reside in haloes of mass $\sim 10^{11}-10^{12}h^{-1}M_{\rm \odot}$ and that satellites reside in larger haloes of mass $\sim 10^{12}-10^{13}h^{-1}M_{\rm \odot}$. The model predicts fewer bright satellite LBGs at $z\sim4$ than is inferred from measurements of the ACF at small scales. By analysing the halo occupation distribution (HOD) predicted by the model, we find evidence that AGN feedback affects the HOD of central LBGs in massive haloes. This is a new high-redshift test of this important feedback mechanism. We investigate the effect of photometric errors in the observations on the ACF predictions. We find that the observational uncertainty in the galaxy luminosity reduces the clustering amplitude and that this effect increases towards faint galaxies, particularly on small scales. To compare properties of model with observed LBGs this uncertainty must be considered.

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arXiv2015

A hybrid multi resolution scheme to efficiently model the structure of reionization on the largest scales

Redshifted 21cm measurements of the structure of ionised regions that grow during reionization promise to provide a new probe of early galaxy and structure formation. One of the challenges of modelling reionization is to account both for the sub-halo scale physics of galaxy formation and the regions of ionization on scales that are many orders of magnitude larger. To bridge this gap we first calculate the statistical relationship between ionizing luminosity and Mpc-scale overdensity using detailed models of galaxy formation computed using relatively small volume - ($\sim$100Mpc/$h$)$^{3}$, high resolution dark matter simulations. We then use a Monte-Carlo technique to apply this relationship to reionization of the intergalactic medium within large volume dark matter simulations - ($>$1Gpc/$h$)$^{3}$. The resulting simulations can be used to address the contribution of very large scale clustering of galaxies to the structure of reionization, and show that volumes larger than 500Mpc/$h$ are required to probe the largest reionization features mid-way through reionization. As an example application of our technique, we demonstrate that the predicted 21cm power spectrum amplitude and gradient could be used to determine the importance of supernovae feedback for early galaxy formation.

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arXiv2015

Galaxy And Mass Assembly (GAMA): end of survey report and data release 2

The Galaxy And Mass Assembly (GAMA) survey is one of the largest contemporary spectroscopic surveys of low-redshift galaxies. Covering an area of ~286 deg^2 (split among five survey regions) down to a limiting magnitude of r < 19.8 mag, we have collected spectra and reliable redshifts for 238,000 objects using the AAOmega spectrograph on the Anglo-Australian Telescope. In addition, we have assembled imaging data from a number of independent surveys in order to generate photometry spanning the wavelength range 1 nm - 1 m. Here we report on the recently completed spectroscopic survey and present a series of diagnostics to assess its final state and the quality of the redshift data. We also describe a number of survey aspects and procedures, or updates thereof, including changes to the input catalogue, redshifting and re-redshifting, and the derivation of ultraviolet, optical and near-infrared photometry. Finally, we present the second public release of GAMA data. In this release we provide input catalogue and targeting information, spectra, redshifts, ultraviolet, optical and near-infrared photometry, single-component Sérsic fits, stellar masses, H$α$-derived star formation rates, environment information, and group properties for all galaxies with r < 19.0 mag in two of our survey regions, and for all galaxies with r < 19.4 mag in a third region (72,225 objects in total). The database serving these data is available at http://www.gama-survey.org/.

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arXiv2015

Constraining the properties of AGN host galaxies with Spectral Energy Distribution modeling

[abridged] We use the latest release of CIGALE, a galaxy SED fitting model relying on energy balance, to study the influence of an AGN in estimating both the SFR and stellar mass in galaxies, as well as the contribution of the AGN to the power output of the host. Using the galaxy formation SAM GALFORM, we create mock galaxy SEDs using realistic star formation histories (SFH) and add an AGN of Type 1, Type 2, or intermediate type whose contribution to the bolometric luminosity can be variable. We perform an SED fitting of these catalogues with CIGALE assuming three different SFHs: a single- and double-exponentially-decreasing, and a delayed SFH. Constraining thecontribution of an AGN to the LIR (fracAGN) is very challenging for fracAGN<20%, with uncertainties of ~5-30% for higher fractions depending on the AGN type, while FIR and sub-mm are essential. The AGN power has an impact on the estimation of $M_*$ in Type 1 and intermediate type AGNs but has no effect for galaxies hosting Type 2 AGNs. We find that in the absence of AGN emission, the best estimates of $M_*$ are obtained using the double-exponentially-decreasing model but at the expense of realistic ages of the stellar population. The delayed SFH model provides good estimates of $M_*$ and SFR, with a maximum offset of 10% as well as better estimates of the age. Our analysis shows that the underestimation of the SFR increases with fracAGN for Type 1 systems, as well as for low contributions of an intermediate AGN type, but it is quite insensitive to the emission of Type 2 AGNs up to fracAGN~45%. Similarly the UV emission is critical in accurately retrieving the $M_*$ for Type 1 and intermediate type AGN, and the SFR of all of the three AGN types. We show that the presence of AGN emission introduces a scatter to the SFR-$M_*$ main sequence relation derived from SED fitting, which is driven by the uncertainties on $M_*$.

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arXiv2015

Galaxy Formation & Dark Matter Modelling in the Era of the Square Kilometre Array

Theoretical galaxy formation models are an established and powerful tool for interpreting the astrophysical significance of observational data, particularly galaxy surveys. Such models have been utilised with great success by optical surveys such as 2dFGRS and SDSS, but their application to radio surveys of cold gas in galaxies has been limited. In this chapter we describe recent developments in the modelling of the cold gas properties in the models, and how these developments are essential if they are to be applied to cold gas surveys of the kind that will be carried out with the SKA. By linking explicitly a galaxy's star formation rate to the abundance of molecular hydrogen in the galaxy rather than cold gas abundance, as was assumed previously, the latest models reproduce naturally many of the global atomic and molecular hydrogen properties of observed galaxies. We review some of the key results of the latest models and highlight areas where further developments are necessary. We discuss also how model predictions can be most accurately compared with observational data, what challenges we expect when creating synthetic galaxy surveys in the SKA era, and how the SKA can be used to test models of dark matter.

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arXiv2015

The origin of the atomic and molecular gas contents of early-type galaxies. II. Misaligned gas accretion

We study the origin of the wide distribution of angles between the angular momenta of the stellar and gas components, $α_{\rm G,S}$, in early-type galaxies (ETGs). We use the GALFORM model of galaxy formation, set in the $Λ$ cold dark matter framework, and coupled it with a Monte-Carlo simulation to follow the angular momenta flips driven by matter accretion onto haloes and galaxies. We consider a gas disk to be misaligned with respect to the stellar body if $α_{\rm G,S}>30$~degrees. By assuming that the only sources of misaligments in galaxies are galaxy mergers, we place a lower limit of $2-5$ per cent on the fraction of ETGs with misaligned gas/stellar components. These low fractions are inconsistent with the observed value of $\approx 42\pm 6$ per cent in ATLAS$^{\rm 3D}$. In the more general case, in which smooth gas accretion in addition to galaxy mergers can drive misalignments, our calculation predicts that $\approx 46$ per cent of ETGs have $α_{\rm G,S}>30$~degrees. In this calculation, we find correlations between $α_{\rm G,S}$ and stellar mass, cold gas fraction and star formation rate, such that ETGs with high masses, low cold gas fractions and low star formation rates are more likely to display aligned cold gas and stellar components. We confirm these trends observationally for the first time using ATLAS$^{\rm 3D}$ data. We argue that the high fraction of misaligned gas discs observed in ETGs is mostly due to smooth gas accretion (e.g. cooling from the hot halo of galaxies) which takes place after most of the stellar mass of the galaxy is in place and comes misaligned with respect to the stellar component. Galaxies that have accreted most of their cold gas content prior to the time where most of the stellar mass was in place show aligned components.

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arXiv2014

The origin of the atomic and molecular gas contents of early-type galaxies. I. A new test of galaxy formation physics

We study the atomic (HI) and molecular hydrogen (H2) contents of early-type galaxies (ETGs) and their gas sources using the GALFORM model of galaxy formation. This model uses a self-consistent calculation of the star formation rate (SFR), which depends on the H2 content of galaxies. We first present a new analysis of HIPASS and ATLAS3D surveys, with special emphasis on ETGs. The model predicts HI and H2 contents of ETGs in agreement with the observations from these surveys only if partial ram pressure stripping of the hot gas is included, showing that observations of neutral gas in `quenched' galaxies place stringent constraints on the treatment of the hot gas in satellites. We find that ~90% of ETGs at z=0 have neutral gas contents supplied by radiative cooling from their hot halos, 8% were supplied by gas accretion from minor mergers that took place in the last 1Gyr, while 2% were supplied by mass loss from old stars. The model predicts neutral gas fractions strongly decreasing with increasing bulge fraction. This is due to the impeded disk regeneration in ETGs, resulting from both active galactic nuclei feedback and environmental quenching by partial ram pressure stripping of the hot gas.

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arXiv2014

Which galaxies dominate the neutral gas content of the Universe?

We study the contribution of galaxies with different properties to the global densities of star formation rate (SFR), atomic (HI) and molecular hydrogen (H2) as a function of redshift. We use the GALFORM model of galaxy formation, which is set in the LCDM framework. This model includes a self-consistent calculation of the SFR, which depends on the H2 content of galaxies. The predicted SFR density and how much of this is contributed by galaxies with different stellar masses and infrared luminosities are in agreement with observations. The model predicts a modest evolution of the HI density at z<3, which is also in agreement with the observations. The HI density is predicted to be always dominated by galaxies with SFR<1Msun/yr. This contrasts with the H2 density, which is predicted to be dominated by galaxies with SFR>10Msun/yr. Current high-redshift galaxy surveys are limited to detect carbon monoxide in galaxies with SFR>30Msun/yr, which in our model make up, at most, 20% of the H2 in the universe. In terms of stellar mass, the predicted H2 density is dominated by massive galaxies, Mstellar>10^10Msun, while the HI density is dominated by low mass galaxies, Mstellar<10^9Msun. In the context of upcoming neutral gas surveys, we suggest that the faint nature of the galaxies dominating the HI content of the Universe will hamper the identification of optical counterparts, while for H2, we expect follow up observations of molecular emission lines of already existing galaxy catalogues to be able to uncover the H2 density of the Universe.

astro-ph.CO↗

arXiv2014

A new model of galaxy formation: How sensitive are predicted galaxy luminosities to the choice of SPS model?

We present a new release of the GALFORM semi-analytical model of galaxy formation and evolution, which exploits a Millennium Simulation-class N-body run performed with the WMAP7 cosmology. We use this new model to study the impact of the choice of stellar population synthesis (SPS) model on the predicted evolution of the galaxy luminosity function. The semi-analytical model is run using seven different SPS models. In each case we obtain the rest-frame luminosity function in the far-ultra-violet, optical and near-infrared (NIR) wavelength ranges. We find that both the predicted rest-frame ultra-violet and optical luminosity function are insensitive to the choice of SPS model. However, we find that the predicted evolution of the rest-frame NIR luminosity function depends strongly on the treatment of the thermally pulsating asymptotic giant branch (TP-AGB) stellar phase in the SPS models, with differences larger than a factor of 2 for model galaxies brighter than $M_{\rm AB}(K)-5$log$h<-22$ ($\sim$L$_*$ for $0\leq z\leq 1.5$). We have also explored the predicted number counts of galaxies, finding remarkable agreement between the results with different choices of SPS model, except when selecting galaxies with very red optical-NIR colours. The predicted number counts of these extremely red galaxies appear to be more affected by the treatment of star formation in disks than by the treatment of TP-AGB stars in the SPS models.

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arXiv2013

The cross-power spectrum between 21cm emission and galaxies in hierarchical galaxy formation models

The correlation between 21cm fluctuations and galaxies is sensitive to the astrophysical properties of the galaxies that drove reionization. Thus, detailed measurements of the cross-power spectrum and its evolution could provide a powerful measurement both of the properties of early galaxies and the process of reionization. In this paper, we study the evolution of the cross-power spectrum between 21cm emission and galaxies using a model which combines the hierarchical galaxy formation model GALFORM implemented within the Millennium-II dark matter simulation, with a semi-numerical scheme to describe the resulting ionization structure. We find that inclusion of different feedback processes changes the cross-power spectrum shape and amplitude. In particular, the feature in the cross-power spectrum corresponding to the size of ionized regions is significantly affected by supernovae feedback. We calculate predicted observational uncertainties of the cross-correlation coefficient based on specifications of the Murchison Widefield Array (MWA) combined with galaxy surveys of varying area and depth. We find that the cross-power spectrum could be detected over several square degrees of galaxy survey with galaxy redshift errors less than 0.1.

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arXiv2013

How well can we really estimate the stellar masses of galaxies from broadband photometry?

The estimated stellar masses of galaxies are widely used to characterize how the galaxy population evolves over cosmic time. If stellar masses can be estimated in a robust manner, free from any bias, global diagnostics such as the stellar mass function can be used to constrain the physics of galaxy formation. We explore how galaxy stellar masses, estimated by fitting broad-band spectral energy distributions (SEDs) with stellar population models, can be biased as a result of commonly adopted assumptions for the star-formation and chemical enrichment histories, recycled fractions and dust attenuation curves of galaxies. We apply the observational technique of broad-band SED fitting to model galaxy SEDs calculated by the theoretical galaxy formation model GALFORM, isolating the effect of each of these assumptions. We find that, averaged over the entire galaxy population, the common assumption of exponentially declining star-formation histories does not adversely affect stellar mass estimation. We show that fixing the metallicity in SED fitting or using sparsely sampled metallicity grids can introduce mass dependent systematics into stellar mass estimates. We find that the common assumption of a star-dust geometry corresponding to a uniform foreground dust screen can cause the stellar masses of dusty model galaxies to be significantly underestimated. Finally, we show that stellar mass functions recovered by applying SED fitting to model galaxies at high redshift can differ significantly in both shape and normalization from the intrinsic mass functions predicted by a given model. Given these differences, our methodology of using stellar masses estimated from model galaxy SEDs offers a new, self-consistent way to compare model predictions with observations.

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arXiv2013

Constraints on black hole fuelling modes from the clustering of X-ray AGN

We present a clustering analysis of X-ray selected AGN by compiling X-ray samples from the literature and re-estimating the dark matter (DM) halo masses of AGN in a uniform manner. We find that moderate luminosity AGN (Lx(2-10 keV)=10^42-10^44 erg/sec) in the z=0-1.3 Universe are typically found in DM haloes with masses of ~10^13 Msun. We then compare our findings to the theoretical predictions of the coupled galaxy and black hole formation model GALFORM. We find good agreement when our calculation includes the hot-halo mode of accretion onto the central black hole. This type of accretion, which is additional to the common cold accretion during disk instabilities and galaxy mergers, is tightly coupled to the AGN feedback in the model. The hot-halo mode becomes prominent in DM haloes with masses greater than ~10^12.5 Msun, where AGN feedback typically operates, giving rise to a distinct class of moderate luminosity AGN that inhabit rich clusters and superclusters. Cold gas fuelling of the black hole cannot produce the observationally inferred DM halo masses of X-ray AGN. Switching off AGN feedback in the model results in a large population of luminous quasars (Lx(2-10 keV) > 10^44 erg/sec) in DM haloes with masses up to ~10^14 Msun, which is inconsistent with the observed clustering of quasars. The abundance of hot-halo AGN decreases significantly in the z~3-4 universe. At such high redshifts, the cold accretion mode is solely responsible for shaping the environment of moderate luminosity AGN. Our analysis supports two accretion modes (cold and hot) for the fuelling of supermassive black holes and strongly underlines the importance of AGN feedback in cosmological models both of galaxy formation and black hole growth.

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arXiv2013

The most luminous quasars do not live in the most massive dark matter haloes at any redshift

Quasars represent the brightest Active Galactic Nuclei (AGN) in the Universe and are thought to indicate the location of prodigiously growing Black Holes (BHs), with luminosities as high as 10^48 erg/sec. It is often expected though that such an extremely energetic process will take place in the most massive bound structures in the dark matter (DM) distribution. We show that in contrast to this expectation, in a galaxy formation model which includes AGN feedback, quasars are predicted to live in average DM halo environments with typical masses of a few times 10^12 Msun. This fundamental prediction arises from the fact that quasar activity (i.e., BH accretion with luminosity greater than 10^46 erg/sec) is inhibited in DM haloes where AGN feedback operates. The galaxy hosts of quasars in our simulations are identified with over massive (in gas and stars) spheroidal galaxies, in which BH accretion is triggered via a galaxy merger or secular processes. We further show that the z=0 descendants of high redshift (z~6) QSOs span a wide range of morphologies, galaxy and halo masses. The z~6 BHs typically grow only by a modest factor by the present day. Remarkably, high redshift QSOs never inhabit the largest DM haloes at that time and their descendants are very seldom found in the most massive haloes at z=0. We also show that observationally it is very likely to find an enhancement in the abundance of galaxies around quasars at z~5. However, these enhancements are considerably weaker compared to the overdensities expected at the extreme peaks of the DM distribution. Thus, it is very unlikely that a quasar detected in the $z\gtrsim5$ Universe pinpoints the location of the progenitors of superclusters in the local Universe.

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arXiv2013

Variation in the escape fraction of ionising photons from galaxies and the redshifted 21-cm power spectrum during reionization

The observed power spectrum of redshifted 21cm fluctuations is known to be sensitive to the astrophysical properties of the galaxies that drove reionization. Thus, detailed measurements of the 21cm power spectrum and its evolution could lead to measurements of the properties of early galaxies that are otherwise inaccessible. In this paper, we study the effect of mass and redshift dependent escape fractions of ionizing radiation on the ability of forthcoming experiments to constrain galaxy formation via the redshifted 21cm power spectrum. We use a model for reionization which combines the hierarchical galaxy formation model GALFORM implemented within the Millennium-II dark matter simulation, with a semi-numerical scheme to describe the resulting ionization structure. Using this model we show that the structure and distribution of ionised regions at fixed neutral fraction, and hence the slope and amplitude of the 21 cm power spectrum, is dependent on the variation of ionising photon escape fraction with galaxy mass and redshift. However, we find that the influence of the unknown escape fraction and its evolution is smaller than the dominant astrophysical effect provided by SNe feedback strength in high redshift galaxies. The unknown escape fraction of ionizing radiation from galaxies is therefore unlikely to prevent measurement of the properties of high redshift star formation using observations of the 21cm power spectrum.

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