Rest-frame UV Luminosity Function Research Articles

Global preventive feedback of powerful radio jets on galaxy formation

Firmly anchored on observational data, giant radio lobes from massive galaxies hosting supermassive black holes can exert a major negative feedback effect, by endowing the intergalactic gas with significant magnetic pressure hence retarding or preventing gas accretion onto less massive halos in the vicinity. Since massive galaxies that are largely responsible for producing the giant radio lobes, this effect is expected to be stronger in more overdense large-scale environments, such as protoclusters, than in underdense regions, such as voids. We show that by redshift [Formula: see text] halos with masses up to [Formula: see text] are significantly hindered from accreting gas due to this effect for radio bubble volume filling fraction of [Formula: see text], respectively. Since the vast majority of the stars in the universe at [Formula: see text][Formula: see text] 2 to 3 form precisely in those halos, this negative feedback process is likely one major culprit for causing the global downturn in star formation in the universe. It also provides a natural explanation for the rather sudden flattening of the slope of the galaxy rest-frame UV luminosity function around [Formula: see text]. A cross-correlation between protoclusters and Faraday rotation measures may test the predicted magnetic field. Inclusion of this external feedback process in the next generation of cosmological simulations may be imperative.

Constraints on the z ∼ 5 Star-forming Galaxy Luminosity Function From Hubble Space Telescope Imaging of an Unbiased and Complete Sample of Long Gamma-Ray Burst Host Galaxies

We present rest-frame UV Hubble Space Telescope imaging of the largest and most complete sample of 23 long-duration gamma-ray burst (GRB) host galaxies between redshifts 4 and 6. Of these 23, we present new WFC3/F110W imaging for 19 of the hosts, which we combine with archival WFC3/F110W and WFC3/F140W imaging for the remaining four. We use the photometry of the host galaxies from this sample to characterize both the rest-frame UV luminosity function (LF) and the size–luminosity relation of the sample. We find that when assuming the standard Schechter-function parameterization for the UV LF, the GRB host sample is best fit with α=−1.30−0.25+0.30 and M*=−20.33−0.54+0.44 mag, which are consistent with results based on z ∼ 5 Lyman-break galaxies. We find that ∼68% of our size–luminosity measurements fall within or below the same relation for Lyman-break galaxies at z ∼ 4. This study observationally confirms expectations that at z ∼ 5 Lyman-break and GRB host galaxies should trace the same population and demonstrates the utility of GRBs as probes of hidden star formation in the high-redshift Universe. Under the assumption that GRBs unbiasedly trace star formation at this redshift, our nondetection fraction of 7/23 is consistent at the 95% confidence level with 13%–53% of star formation at redshift z ∼ 5 occurring in galaxies fainter than our detection limit of M 1600Å ≈ −18.3 mag.

Bright z ∼ 9 Galaxies in Parallel: The Bright End of the Rest-frame UV Luminosity Function from HST Parallel Programs

The abundance of bright galaxies at z > 8 can provide key constraints on models of galaxy formation and evolution, as the predicted abundance varies greatly when different physical prescriptions for gas cooling and star formation are implemented. We present the results of a search for bright z ∼ 9–10 galaxies selected from pure parallel Hubble Space Telescope (HST) imaging programs. We include 132 fields observed as part of the Brightest of Reionizing Galaxies survey, the Hubble Infrared Pure Parallel Imaging Extragalactic Survey, and the WFC3 Infrared Spectroscopic Parallel survey. These observations cover a total of 620 arcmin2, about 70% of which is also covered with Spitzer Space Telescope infrared imaging. We identify 13 candidate galaxies in the range 8.3 < z < 11 with 24.5 < m H < 26.5 (−22.9 < M UV < −21.2), 11 of which constitute new discoveries. This sample capitalizes on the uncorrelated nature of pure parallel observations to overcome cosmic variance and leverages a full multiwavelength selection process to minimize contamination without sacrificing completeness. We perform detailed completeness and contamination analyses, and present measurements of the bright end of the UV luminosity function using a pseudobinning technique. We find a number density consistent with results from Finkelstein et al. and other searches in HST parallel fields. These bright candidates likely reside in overdensities, potentially representing some of the earliest sites of cosmic reionization. These new candidates are excellent targets for follow up with JWST, and four of them will be observed with the NIRSpec prism in Cycle 1.

Early Growth of the Star Formation Rate Function in the Epoch of Reionization: An Approach with Rest-frame Optical Emissions

We present a star formation rate function (SFRF) at z ∼ 6 based on star formation rates (SFRs) derived by spectral energy distribution fitting on data from rest-frame UV to optical wavelengths of galaxies in the CANDELS GOODS-South and North fields. The resulting SFRF shows an excess compared to the previous estimations by using rest-frame UV luminosity functions (LFs) corrected for the dust attenuation and is comparable to that estimated from a far-infrared LF. This suggests that the number density of dust-obscured intensively star-forming galaxies at z ∼ 6 has been underestimated in the previous approach based only on rest-frame UV observations. We parameterize the SFRF using the Schechter function and obtain the best-fit parameter of the characteristic SFR (SFR*) when the faint-end slope and characteristic number density are fixed. The best-fit SFR* at z ∼ 6 is comparable to that at z ∼ 2, when the cosmic star formation activity reaches its peak. Together with SFRF estimations with a similar approach using rest-frame UV to optical data, the SFR* is roughly constant from z ∼ 2 to ∼6 and may decrease above z ∼ 6. Since the SFR* is sensitive to the high-SFR end of the SFRF, this evolution of SFR* suggests that the high-SFR end of the SFRF grows rapidly during the epoch of reionization and reaches a similar level observed at z ∼ 2.

Are the ultra-high-redshift galaxies at z &amp;gt; 10 surprising in the context of standard galaxy formation models?

ABSTRACT A substantial number of ultra-high redshift (8 ≲ z ≲ 17) galaxy candidates have been detected with JWST, posing the question: Are these observational results surprising in the context of current galaxy formation models? We address this question using the well-established Santa Cruz semi-analytic models, implemented within merger trees from the new suite of cosmological N-body simulations gureft, which were carefully designed for ultra-high redshift studies. Using our fiducial models calibrated at z = 0, we present predictions for stellar mass functions, rest-frame UV luminosity functions, and various scaling relations. We find that our (dust-free) models predict galaxy number densities at z ∼ 11 (z ∼ 13) that are an order of magnitude (a factor of ∼30) lower than the observational estimates. We estimate the uncertainty in the observed number densities due to cosmic variance, and find that it leads to a fractional error of ∼20–30 per cent at z = 11 (∼30–80 per cent at z = 14) for a 100 arcmin2 field. We explore which processes in our models are most likely to be rate-limiting for the formation of luminous galaxies at these early epochs, considering the halo formation rate, gas cooling, star formation, and stellar feedback, and conclude that it is mainly efficient stellar-driven winds. We find that a modest boost of a factor of ∼4 to the UV luminosities, which could arise from a top-heavy stellar initial mass function, would bring our current models into agreement with the observations. Adding a stochastic component to the UV luminosity can also reconcile our results with the observations.

The UV luminosity functions of bright z &amp;gt; 8 galaxies: determination from ∼0.41 deg2 of HST observations along ∼300 independent sightlines

ABSTRACT We determine the bright end of the rest-frame UV luminosity function (UVLF) at z = 8–10 by selecting bright z ≳ 8 photometric candidates from the largest systematic compilation of HST (pure-)parallel observations to date, the Super-Brightest-of-Reionizing-Galaxies (SuperBoRG) data set. The data set includes ∼300 independent sightlines from WFC3 observations, totalling 800–1300 arcmin2 (depending on redshift). We identify 31 z ≳ 8 candidates via colour selection and photo-z analysis with observed magnitude (24.1 &amp;lt; H160 &amp;lt; 26.6) and 1σ range probability of $58\!-\!95~{{\ \rm per\ cent}}$ of being true high-z galaxies. Following detailed completeness and source recovery simulations, as well as modelling of interloper contamination, we derive rest-frame UVLFs at z = 8–10 down to MUV ≃ −23. We find that the bright end of the galaxy luminosity function can be described both by a Schechter and by a double power-law function, with our space-based large area determination showing some tentative discrepancies with the luminosity functions derived from ground-based observations at the same redshifts. We identify two possible explanations. The first is that the UVLF includes a substantial contribution from AGNs at magnitudes MUV &amp;lt; −22. The UVLF we derive at z = 8 is consistent with no evolution of the bright end from z = 6–7 UVLFs that include AGNs. An alternative (and non-exclusive) possibility is that the dust content of the observed galaxies decreases with redshift, thereby countering the naturally expected decrease in the UV luminosity functions because of a decreased star-formation rate with increasing redshift. Both scenarios raise interesting prospects to further understand galaxy formation in extreme objects during the epoch of reionization.

The bright end of the galaxy luminosity function at z ≃ 7 from the VISTA VIDEO survey

ABSTRACT We have conducted a search for z ≃ 7 Lyman-break galaxies over 8.2 deg2 of near-infrared imaging from the Visible and Infrared Survey Telescope for Astronomy (VISTA) Deep Extragalactic Observations (VIDEO) survey in the XMM–Newton-Large Scale Structure (XMM-LSS) and the Extended Chandra Deep Field-South (ECDF-S) fields. Candidate galaxies were selected from a full photometric redshift analysis down to a Y + J depth of 25.3 (5σ), utilizing deep auxiliary optical and Spitzer/Infrared Array Camera (IRAC) data to remove brown dwarf and red interloper galaxy contaminants. Our final sample consists of 28 candidate galaxies at 6.5 ≤ z ≤ 7.5 with −23.5 ≤ MUV ≤ −21.6. We derive stellar masses of 9.1 ≤ log10(M⋆/M⊙) ≤ 10.9 for the sample, suggesting that these candidates represent some of the most massive galaxies known at this epoch. We measure the rest-frame ultraviolet (UV) luminosity function (LF) at z ≃ 7, confirming previous findings of a gradual decline in number density at the bright end (MUV &amp;lt; −22) that is well described by a double power law (DPL). We show that quasar contamination in this magnitude range is expected to be minimal, in contrast to conclusions from recent pure-parallel Hubble studies. Our results are up to a factor of 10 lower than previous determinations from optical-only ground-based studies at MUV ≲ −23. We find that the inclusion of YJHKs photometry is vital for removing brown dwarf contaminants, and z ≃ 7 samples based on red optical data alone could be highly contaminated (≳50 per cent). In comparison with other robust z &amp;gt; 5 samples, our results further support little evolution in the very bright end of the rest-frame UV LF from z = 5–10, potentially signalling a lack of mass quenching and/or dust obscuration in the most massive galaxies in the first Gyr.

A Lower Bound of Star Formation Activity in Ultra-high-redshift Galaxies Detected with JWST: Implications for Stellar Populations and Radiation Sources

Early results of James Webb Space Telescope observations have delivered bright z ≳ 10 galaxy candidates in greater numbers than expected, enabling construction of rest-frame UV luminosity functions (LFs). The LFs contain key information on the galaxy assembly history, star formation activity, and stellar population of the distant universe. Given an upper bound of the total baryonic mass inflow rate to galaxies from their parent halos estimated from abundance matching, we derive a lower bound on the product of the star formation and UV photon production efficiency in galaxies at each redshift. This stringent constraint requires a high efficiency (≳10%–30%) converting gas into stars, assuming a normal stellar population with a Salpeter-like mass distribution. The efficiency is substantially higher than those of typical nearby galaxies, but is consistent with those seen in starburst galaxies and super-star clusters observed in the nearby universe. Alternatively, the star formation efficiency may be as low as a few percent, which is the average value for the entire galaxy population at z ≃ 6, if the stellar population is metal-free and drawn from a top-heavy mass distribution that produces more intense UV radiation. We discuss several other possible scenarios to achieve the constraint, for instance, energetic radiation produced from compact stellar remnants and quasars, and propose ways to distinguish the scenarios by forthcoming observations.

New Determinations of the UV Luminosity Functions from z ∼ 9 to 2 Show a Remarkable Consistency with Halo Growth and a Constant Star Formation Efficiency

Abstract Here we provide the most comprehensive determinations of the rest-frame UV luminosity function (LF) available to date with the Hubble Space Telescope (HST) at z ∼ 2–9. Essentially all of the noncluster extragalactic legacy fields are utilized, including the Hubble Ultra Deep Field, the Hubble Frontier Fields parallel fields, and all five CANDELS fields, for a total survey area of 1136 arcmin2. Our determinations include galaxies at z ∼ 2–3 leveraging the deep HDUV, UVUDF, and ERS WFC3/UVIS observations available over an ∼150 arcmin2 area in the GOODS-North and GOODS-South regions. All together, our collective samples include &gt;24,000 sources, &gt;2.3× larger than previous selections with HST. We identify 5766, 6332, 7240, 3449, 1066, 601, 246, and 33 sources at z ∼ 2, 3, 4, 5, 6, 7, 8, and 9, respectively. Combining our results with an earlier z ∼ 10 LF determination by Oesch et al., we quantify the evolution of the UV LF. Our results indicate that there is (1) a smooth flattening of the faint-end slope α from α ∼ −2.4 at z ∼ 10 to α ∼ −1.5 at z ∼ 2, (2) minimal evolution in the characteristic luminosity M* at z ≥ 2.5, and (3) a monotonic increase in the normalization log 10 ϕ * from z ∼ 10 to 2, which can be well described by a simple second-order polynomial, consistent with an “accelerated” evolution scenario. We find that each of these trends (from z ∼ 10 to 2.5 at least) can be readily explained on the basis of the evolution of the halo mass function and a simple constant star formation efficiency model.

The evolution of the UV luminosity and stellar mass functions of Lyman-α emitters from z ∼ 2 to z ∼ 6

ABSTRACT We measure the evolution of the rest-frame UV luminosity function (LF) and the stellar mass function (SMF) of Lyman-α (Ly α) emitters (LAEs) from z ∼ 2 to z ∼ 6 by exploring ∼4000 LAEs from the SC4K sample. We find a correlation between Ly α luminosity (LLy α) and rest-frame UV (MUV), with best fit M$_{\rm UV}=-1.6_{-0.3}^{+0.2}\log _{10} (\rm L_{Ly\,\alpha }/erg\, s^{-1})+47_{-11}^{+12}$ and a shallower relation between LLy α and stellar mass (M⋆), with best fit $\log _{10} (\rm M_\star /{\rm M}_\odot)=0.9_{-0.1}^{+0.1}\log _{10} (\rm L_{Ly\,\alpha }/erg\, s^{-1})-28_{-3.8}^{+4.0}$. An increasing LLy α cut predominantly lowers the number density of faint MUV and low M⋆ LAEs. We estimate a proxy for the full UV LFs and SMFs of LAEs with simple assumptions of the faint end slope. For the UV LF, we find a brightening of the characteristic UV luminosity (M$_{\rm UV}^*$) with increasing redshift and a decrease of the characteristic number density (Φ*). For the SMF, we measure a characteristic stellar mass (${\rm M_\star ^*/{\rm M}_\odot }$) increase with increasing redshift, and a Φ* decline. However, if we apply a uniform luminosity cut of $\log _{10} (\rm L_{Ly\,\alpha }/erg\, s^{-1}) \ge 43.0$, we find much milder to no evolution in the UV and SMF of LAEs. The UV luminosity density (ρUV) of the full sample of LAEs shows moderate evolution and the stellar mass density (ρM) decreases, with both being always lower than the total ρUV and ρM of more typical galaxies but slowly approaching them with increasing redshift. Overall, our results indicate that both ρUV and ρM of LAEs slowly approach the measurements of continuum-selected galaxies at z &amp;gt; 6, which suggests a key role of LAEs in the epoch of reionization.

A lack of evolution in the very bright end of the galaxy luminosity function from z ≃ 8 to 10

ABSTRACT We utilize deep near-infrared survey data from the UltraVISTA fourth data release (DR4) and the VIDEO survey, in combination with overlapping optical and Spitzer data, to search for bright star-forming galaxies at z ≳ 7.5. Using a full photometric redshift fitting analysis applied to the ∼6 $\, {\rm deg}^2$ of imaging searched, we find 27 Lyman break galaxies (LBGs), including 20 new sources, with best-fitting photometric redshifts in the range 7.4 &amp;lt; z &amp;lt; 9.1. From this sample, we derive the rest-frame UV luminosity function at z = 8 and z = 9 out to extremely bright UV magnitudes (MUV ≃ −23) for the first time. We find an excess in the number density of bright galaxies in comparison to the typically assumed Schechter functional form derived from fainter samples. Combined with previous studies at lower redshift, our results show that there is little evolution in the number density of very bright (MUV ∼ −23) LBGs between z ≃ 5 and z ≃ 9. The tentative detection of an LBG with best-fitting photometric redshift of z = 10.9 ± 1.0 in our data is consistent with the derived evolution. We show that a double power-law fit with a brightening characteristic magnitude (ΔM*/Δz ≃ −0.5) and a steadily steepening bright-end slope (Δβ/Δz ≃ −0.5) provides a good description of the z &amp;gt; 5 data over a wide range in absolute UV magnitude (−23 &amp;lt; MUV &amp;lt; −17). We postulate that the observed evolution can be explained by a lack of mass quenching at very high redshifts in combination with increasing dust obscuration within the first ${\sim}1 \, {\rm Gyr}$ of galaxy evolution.

UV and Lyα luminosity functions of galaxies and star formation rate density at the end of HI reionization from the VIMOS UltraDeep Survey (VUDS)

Context. The star formation rate density (SFRD) evolution presents an area of great interest in the studies of galaxy evolution and reionization. The current constraints of SFRD at z &gt; 5 are based on the rest-frame UV luminosity functions with the data from photometric surveys. The VIMOS UltraDeep Survey (VUDS) was designed to observe galaxies at redshifts up to ∼6 and opened a window for measuring SFRD at z &gt; 5 from a spectroscopic sample with a well-controlled selection function. Aims. We establish a robust statistical description of the star-forming galaxy population at the end of cosmic HI reionization (5.0 ≤ z ≤ 6.6) from a large sample of 49 galaxies with spectroscopically confirmed redshifts. We determine the rest-frame UV and Lyα luminosity functions and use them to calculate SFRD at the median redshift of our sample z = 5.6. Methods. We selected a sample of galaxies at 5.0 ≤ zspec ≤ 6.6 from the VUDS. We cleaned our sample from low redshift interlopers using ancillary photometric data. We identified galaxies with Lyα either in absorption or in emission, at variance with most spectroscopic samples in the literature where Lyα emitters (LAE) dominate. We determined luminosity functions using the 1/Vmax method. Results. The galaxies in this redshift range exhibit a large range in their properties. A fraction of our sample shows strong Lyα emission, while another fraction shows Lyα in absorption. UV-continuum slopes vary with luminosity, with a large dispersion. We find that star-forming galaxies at these redshifts are distributed along the main sequence in the stellar mass vs. SFR plane, described with a slope α = 0.85 ± 0.05. We report a flat evolution of the specific SFR compared to lower redshift measurements. We find that the UV luminosity function is best reproduced by a double power law, while a fit with a Schechter function is only marginally inferior. The Lyα luminosity function is best fitted with a Schechter function. We derive a logSFRDUV(M⊙ yr−1 Mpc−3) = −1.45+0.06−0.08 and logSFRDLyα(M⊙ yr−1 Mpc−3) = −1.40+0.07−0.08. The SFRD derived from the Lyα luminosity function is in excellent agreement with the UV-derived SFRD after correcting for IGM absorption. Conclusions. Our new SFRD measurements at a mean redshift of z = 5.6 are ∼0.2 dex above the mean SFRD reported in Madau &amp; Dickinson (2014, ARA&amp;A, 52, 415), but in excellent agreement with results from Bouwens et al. (2015a, ApJ, 803, 34). These measurements confirm the steep decline of the SFRD at z &gt; 2. The bright end of the Lyα luminosity function has a high number density, indicating a significant star formation activity concentrated in the brightest LAE at these redshifts. LAE with equivalent width EW &gt; 25 Å contribute to about 75% of the total UV-derived SFRD. While our analysis favors low dust content in 5.0 &lt; z &lt; 6.6, uncertainties on the dust extinction correction and associated degeneracy in spectral fitting will remain an issue, when estimating the total SFRD until future surveys extending spectroscopy to the NIR rest-frame spectral domain, such as with JWST.

Inferring the astrophysics of reionization and cosmic dawn from galaxy luminosity functions and the 21-cm signal

The properties of the first galaxies, expected to drive the Cosmic Dawn (CD) and the Epoch of Reionization (EoR), are encoded in the 3D structure of the cosmic 21-cm signal. Parameter inference from upcoming 21-cm observations promises to revolutionize our understanding of these unseen galaxies. However, prior inference was done using models with several simplifying assumptions. Here we introduce a flexible, physically-motivated parametrization for high-$z$ galaxy properties, implementing it in the public code 21cmFAST. In particular, we allow their star formation rates and ionizing escape fraction to scale with the masses of their host dark matter halos, and directly compute inhomogeneous, sub-grid recombinations in the intergalactic medium. Combining current Hubble observations of the rest-frame UV luminosity function (UV LFs) at high-$z$ with a mock 1000h 21-cm observation using the Hydrogen Epoch of Reionization Arrays (HERA), we constrain the parameters of our model using a Monte Carlo Markov Chain sampler of 3D simulations, 21CMMC. We show that the amplitude and scaling of the stellar mass with halo mass is strongly constrained by LF observations, while the remaining galaxy properties are constrained mainly by 21-cm observations. The two data sets compliment each other quite well, mitigating degeneracies intrinsic to each observation. All eight of our astrophysical parameters are able to be constrained at the level of $\sim 10\%$ or better. The updated versions of 21cmFAST and 21CMMC used in this work are publicly available.

Semi-analytic forecasts forJWST– I. UV luminosity functions atz = 4–10

In anticipation of the upcoming deployment of the James Webb Space Telescope (JWST), we present high-redshift predictions by the well-established Santa Cruz semi-analytic model. We update the models by re-calibrating them after adopting cosmological parameters consistent with recent constraints from Planck. We provide predictions for rest-frame UV luminosity functions for galaxy populations over a wide range of MUV from ∼−6 to ∼−24 between |$z$| = 4–10. In addition, we present the corresponding predictions for observed-frame galaxy number counts in different redshift bins in the full set of NIRCam filters. We provide predictions of the quantitative effect on these observables of varying the physical recipes implemented in the models, such as the molecular gas depletion time (star formation efficiency), scalings or the scalings of outflow rates driven by stars, and supernovae with galaxy circular velocity. Based on these results, we discuss what may be learned about the physical processes that shape galaxy formation from JWST observations of galaxy number densities at different intrinsic luminosities. All data tables for the results presented in this work are available at https://www.simonsfoundation.org/semi-analytic-forecasts-for-jwst/.

Obscured star formation in bright z ≃ 7 Lyman-break galaxies

We present Atacama Large Millimeter/Submillimeter Array observations of the rest-frame far-infrared (FIR) dust continuum emission of six bright Lyman-break galaxies (LBGs) at $z \simeq 7$. One LBG is detected ($5.2\sigma$ at peak emission), while the others remain individually undetected at the $3\sigma$ level. The average FIR luminosity of the sample is found to be $L_{\rm FIR} \simeq 2 \times 10^{11}\,{\rm L}_{\odot}$, corresponding to an obscured star-formation rate (SFR) that is comparable to that inferred from the unobscured UV emission. In comparison to the infrared excess (IRX$\,=L_{\rm FIR}/L_{\rm UV}$)-$\beta$ relation, our results are consistent with a Calzetti-like attenuation law (assuming a dust temperature of T = 40-50 K). We find a physical offset of 3 kpc between the dust continuum emission and the rest-frame UV light probed by Hubble Space Telescope imaging for galaxy ID65666 at $z = 7.17^{+0.09}_{-0.06}$. The offset is suggestive of an inhomogeneous dust distribution, where 75% of the total star formation activity (SFR$ \,\simeq 70\,{\rm M}_{\odot}/{\rm yr}$) of the galaxy is completely obscured. Our results provide direct evidence that dust obscuration plays a key role in shaping the bright-end of the observed rest-frame UV luminosity function at $z \simeq 7$, in agreement with cosmological galaxy formation simulations. The existence of a heavily-obscured component of galaxy ID65666 indicates that dusty star-forming regions, or even entire galaxies, that are "UV-dark" are significant even in the $z \simeq 7$ galaxy population.

UVUDF: UV Luminosity Functions at the Cosmic High Noon

Abstract We present the rest-1500 Å UV luminosity functions (LF) for star-forming galaxies during the cosmic high noon—the peak of cosmic star formation rate at . We use deep NUV imaging data obtained as part of the Hubble Ultra-Violet Ultra Deep Field (UVUDF) program, along with existing deep optical and NIR coverage on the HUDF. We select F225W, F275W, and F336W dropout samples using the Lyman break technique, along with samples in the corresponding redshift ranges selected using photometric redshifts, and measure the rest-frame UV LF at , respectively, using the modified maximum likelihood estimator. We perform simulations to quantify the survey and sample incompleteness for the UVUDF samples to correct the effective volume calculations for the LF. We select galaxies down to and fit a faint-end slope of at , , and , respectively. We compare the star formation properties of galaxies from these UV observations with results from Hα and UV+IR observations. We find a lack of high-SFR sources in the UV LF compared to the Hα and UV+IR, likely due to dusty SFGs not being properly accounted for by the generic relation used to correct for dust. We compute a volume-averaged UV-to-Hα ratio by abundance matching the rest-frame UV LF and Hα LF. We find an increasing UV-to-Hα ratio toward low-mass galaxies ( ). We conclude that this could be due to a larger contribution from starbursting galaxies compared to the high-mass end.

Unveiling the nature of brightz ≃ 7galaxies with theHubble Space Telescope

We present new Hubble Space Telescope/Wide Field Camera 3 imaging of 25 extremely luminous (-23.2 < M_ UV < -21.2) Lyman-break galaxies (LBGs) at z ~ 7. The sample was initially selected from 1.65 deg^2 of ground-based imaging in the UltraVISTA/COSMOS and UDS/SXDS fields, and includes the extreme Lyman-alpha emitters, `Himiko' and `CR7'. A deconfusion analysis of the deep Spitzer photometry available suggests that these galaxies exhibit strong rest-frame optical nebular emission lines (EW_0(H_beta + [OIII]) > 600A). We find that irregular, multiple-component morphologies suggestive of clumpy or merging systems are common (f_multi > 0.4) in bright z ~ 7 galaxies, and ubiquitous at the very bright end (M_UV < -22.5). The galaxies have half-light radii in the range r_1/2 ~ 0.5-3 kpc. The size measurements provide the first determination of the size-luminosity relation at z ~ 7 that extends to M_UV ~ -23. We find the relation to be steep with r_1/2 ~ L^1/2. Excluding clumpy, multi-component galaxies however, we find a shallower relation that implies an increased star-formation rate surface density in bright LBGs. Using the new, independent, HST/WFC3 data we confirm that the rest-frame UV luminosity function at z ~ 7 favours a power-law decline at the bright-end, compared to an exponential Schechter function drop-off. Finally, these results have important implications for the Euclid mission, which we predict will detect > 1000 similarly bright galaxies at z ~ 7. Our new HST imaging suggests that the vast majority of these galaxies will be spatially resolved by Euclid, mitigating concerns over dwarf star contamination.

THE EVOLUTION OF THE FAINT END OF THE UV LUMINOSITY FUNCTION DURING THE PEAK EPOCH OF STAR FORMATION *

ABSTRACT We present a robust measurement of the rest-frame UV luminosity function (LF) and its evolution during the peak epoch of cosmic star formation at . We use our deep near-ultraviolet imaging from WFC3/UVIS on the Hubble Space Telescope and existing Advanced Camera for Surveys (ACS)/WFC and WFC3/IR imaging of three lensing galaxy clusters, Abell 2744 and MACS J0717 from the Hubble Frontier Field survey and Abell 1689. Combining deep UV imaging and high magnification from strong gravitational lensing, we use photometric redshifts to identify 780 ultra-faint galaxies with AB mag at . From these samples, we identified five new, faint, multiply imaged systems in A1689. We run a Monte Carlo simulation to estimate the completeness correction and effective volume for each cluster using the latest published lensing models. We compute the rest-frame UV LF and find the best-fit faint-end slopes of , , and at , , and , respectively. Our results demonstrate that the UV LF becomes steeper from to with no sign of a turnover down to AB mag. We further derive the UV LFs using the Lyman break “dropout” selection and confirm the robustness of our conclusions against different selection methodologies. Because the sample sizes are so large and extend to such faint luminosities, the statistical uncertainties are quite small, and systematic uncertainties (due to the assumed size distribution, for example) likely dominate. If we restrict our analysis to galaxies and volumes above completeness in order to minimize these systematics, we still find that the faint-end slope is steep and getting steeper with redshift, though with slightly shallower (less negative) values ( , −1.69 ± 0.07, and −1.79 ± 0.08 for , 1.9, and 2.6, respectively). Finally, we conclude that the faint star-forming galaxies with UV magnitudes of covered in this study produce the majority (55%–60%) of the unobscured UV luminosity density at .

The minimum halo mass for star formation atz = 6–8

Recent analysis of strongly-lensed sources in the Hubble Frontier Fields indicates that the rest-frame UV luminosity function of galaxies at $z=$6--8 rises as a power law down to $M_\mathrm{UV}=-15$, and possibly as faint as -12.5. We use predictions from a cosmological radiation hydrodynamic simulation to map these luminosities onto physical space, constraining the minimum dark matter halo mass and stellar mass that the Frontier Fields probe. While previously-published theoretical studies have suggested or assumed that early star formation was suppressed in halos less massive than $10^9$--$10^{11} M_\odot$, we find that recent observations demand vigorous star formation in halos at least as massive as (3.1, 5.6, 10.5)$\times10^9 M_\odot$ at $z=(6,7,8)$. Likewise, we find that Frontier Fields observations probe down to stellar masses of (8.1, 18, 32)$\times10^6 M_\odot$; that is, they are observing the likely progenitors of analogues to Local Group dwarfs such as Pegasus and M32. Our simulations yield somewhat different constraints than two complementary models that have been invoked in similar analyses, emphasizing the need for further observational constraints on the galaxy-halo connection.

“Observing and Analyzing” Images from a Simulated High-Redshift Universe

We investigate the high-redshift evolution of the rest-frame UV-luminosity function (LF) of galaxies via hydrodynamical cosmological simulations, coupled with an emulated observational astronomy pipeline that provides a direct comparison with observations. We do this by creating mock images and synthetic galaxy catalogs of ≈100 arcmin-2 fields from the numerical model at redshifts ≈4.5 to 10.4. We include the effects of dust extinction and the point-spread function (PSF) for the Hubble WFC3 camera for comparison with space observations. We also include the expected zodiacal background to predict its effect on space observations, including future missions such as the James Webb Space Telescope (JWST). When our model catalogs are fitted to Schechter function parameters, we predict that the faint-end slope (α) of the LF evolves as α = -1.16–0.12z over the redshift range z ≈ 4.5–7.7, in excellent agreement with observations from, e.g., Hathi and coworkers. However, for redshifts z ≈ 6–10.4, α(z) appears to display a shallower evolution, α = -1.79–0.03z. Augmenting the simulations with more detailed physics—specifically stellar winds and supernovae (SN)—produces similar results. The model shows an overproduction of galaxies, especially at faint magnitudes, compared with the observations, although the discrepancy is reduced when dust extinction is taken into account.