Search

The UltraViolet Imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey Fields (UVCANDELS) survey is a Hubble Space Telescope (HST) Cycle-26 Treasury Program, allocated in total 164 orbits of primary Wide-Field Camera 3 Ultraviolet and VISible light F275W imaging with coordinated parallel Advanced Camera for Surveys F435W imaging, on four of the five premier extragalactic survey fields: GOODS-N, GOODS-S, EGS, and COSMOS. We introduce this survey by presenting a comprehensive analysis of the absolute escape fraction ( ${f}_{{\rm{esc}}}^{{\rm{abs}}}$ ) of Lyman continuum radiation through stacking the UV images of a population of star-forming galaxies with secure redshifts at 2.4 ≤ z ≤ 3.0. Our stacking benefits from the catalogs of high-quality spectroscopic redshifts compiled from archival ground-based data and HST slitless spectroscopy, carefully vetted by dedicated visual inspection efforts. We develop a robust stacking method to apply to 10 samples of in total 56 galaxies, and perform detailed Monte Carlo simulations of the intergalactic medium (IGM) attenuation, to take into account the sample variance of the mean IGM transmission when measuring ${f}_{{\rm{esc}}}^{{\rm{abs}}}$ . The full stack at z ≈ 2.44 from 28 galaxies places a stringent 1 σ upper limit of ${f}_{{\rm{esc}}}^{{\rm{abs}}}\lesssim 5 \% $ , whereas the full stack at z ≈ 2.72 of an equal number of galaxies gives an upper limit of ${f}_{{\rm{esc}}}^{{\rm{abs}}}\lesssim 26 \% $ at 1 σ confidence level. These new F275W and F435W imaging mosaics from UVCANDELS have been made publicly available on the Barbara A. Mikulski Archive for Space Telescopes.

Gravitational lensing is a general relativistic (GR) phenomenon where a massive object redirects light, deflecting, magnifying, and sometimes multiplying its source. We use reaction-diffusion (RD) Belousov-Zhabotinsky (BZ) chemistry to study this astronomical effect in a table-top experiment. We experimentally observe BZ waves passing through non-planar, quasi-two-dimensional molds and reproduce the waveforms in computer simulations using planar RD waves propagating with variable diffusion. We tune the variable diffusion to match the Schwarzschild-coordinate light speed near a spherical mass so the RD propagation approximates Einstein’s famous light deflection relation. We discuss varying the diffusion or reaction rates with a gel matrix or with illumination, electric field, or temperature gradients.

We use the Ultraviolet Imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey fields (UVCANDELS) to measure half-light radii in the rest-frame far-UV for ∼16,000 disk-like galaxies over 0.5 ≤ z ≤ 3. We compare these results to rest-frame optical sizes that we measure in a self-consistent way and find that the stellar mass–size relation of disk galaxies is steeper in the rest-frame UV than in the optical across our entire redshift range. We show that this is mainly driven by massive galaxies (≳10 ^10 M _⊙ ), which we find to also be among the most dusty. Our results are consistent with the literature and have commonly been interpreted as evidence of inside-out growth wherein galaxies form their central structures first. However, they could also suggest that the centers of massive galaxies are more heavily attenuated than their outskirts. We distinguish between these scenarios by modeling and selecting galaxies at z = 2 from the VELA simulation suite in a way that is consistent with UVCANDELS. We show that the effects of dust alone can account for the size differences we measure at z = 2. This indicates that, at different wavelengths, size differences and the different slopes of the stellar mass–size relation do not constitute evidence for inside-out growth.

UVCANDELS is a Hubble Space Telescope Cycle-26 Treasury Program awarded 164 orbits of primary ultraviolet (UV) F275W imaging and coordinated parallel optical F435W imaging in four CANDELS fields—GOODS-N, GOODS-S, EGS, and COSMOS—covering a total area of ∼426 arcmin ^2 . This is ∼2.7 times larger than the area covered by previous deep-field space UV data combined, reaching a depth of about 27 and 28 ABmag (5 σ in 0.”2 apertures) for F275W and F435W, respectively. Along with new photometric catalogs, we present an analysis of the rest-frame UV luminosity function (LF), relying on our UV-optimized aperture photometry method, yielding a factor of 1.5 increase over H-isophot aperture photometry in the signal-to-noise ratios of galaxies in our F275W imaging. Using well-tested photometric redshift measurements, we identify 5810 galaxies at redshifts 0.6 < z < 1, down to an absolute magnitude of M _UV = −14.2. In order to minimize the effect of uncertainties in estimating the completeness function, especially at the faint end, we restrict our analysis to sources above 30% completeness, which provides a final sample of 4726 galaxies at −21.5 < M _UV < −15.5. We performed a maximum likelihood estimate to derive the best-fit parameters of the UV LF. We report a best-fit faint-end slope of $\alpha =-{1.359}_{-0.041}^{+0.041}$ at z ∼ 0.8. Creating subsamples at z ∼ 0.7 and z ∼ 0.9, we observe a possible evolution of α with redshift. The unobscured UV luminosity density at M _UV < −10 is derived as ${\rho }_{{\rm{U}}{\rm{V}}}={1.339}_{-0.030}^{+0.027}\,(\times {10}^{26}\,{\rm{e}}{\rm{r}}{\rm{g}}\,{{\rm{s}}}^{-1}\,{{\rm{H}}{\rm{z}}}^{-1}\,{{\rm{M}}{\rm{p}}{\rm{c}}}^{-3})$ using our best-fit LF parameters. The new F275W and F435 photometric catalogs from UVCANDELS have been made publicly available on the Barbara A. Mikulski Archive for Space Telescopes.

The UltraViolet imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey Fields (UVCANDELS) program provides deep Hubble Space Telescope (HST) F275W and F435W imaging over four CANDELS fields (GOODS-N, GOODS-S, COSMOS, and Extended Groth Strip). We combine this newly acquired UV imaging with existing HST imaging from CANDELS as well as existing ancillary data to obtain robust photometric redshifts and reliable estimates for galaxy physical properties for over 150,000 galaxies in the ∼430 arcmin ^2 UVCANDELS area. Here, we leverage the power of the new UV photometry to not only improve the photometric redshift measurements in these fields, but also constrain the full redshift probability distribution combining multiple redshift-fitting tools. Furthermore, using the full UV-to-IR photometric data set, we measure the galaxy physical properties by fitting templates from population synthesis models with two different parameterizations (flexible and fixed form) of the star formation histories (SFHs). Compared to the flexible SFH parameterization, we find that the fixed-form SFHs systematically underestimate the galaxy stellar masses, both at the low-mass (≲10 ^9 M _⊙ ) and high-mass (≳10 ^10 M _⊙ ) end, by as much as ∼0.5 dex. This underestimation is primarily due the limited ability of fixed-form SFH parameterization to simultaneously capture the chaotic nature of star formation in these galaxies.

We present results from the MOSFIRE Deep Evolution Field survey on broad flux from the nebular emission lines Hα, [N ii], [O iii], Hβ, and [S ii]. The sample consists of 127 star-forming galaxies at 1.37 < z < 2.61 and 84 galaxies at 2.95 < z < 3.80. We decompose the emission lines using narrow and broad Gaussian components that we define as having FWHM < 275 km s−1 and FWHM > 300 km s−1, respectively, for both individual galaxies and stacks. For individual galaxies, broad emission is detected at >3σ in <10% of galaxies and the broad flux accounts for 10%–70% of the total flux. In the stacks, we find a slight increase in broad to narrow flux ratio with mass but note that we cannot reliably detect broad emission with FWHM < 275 km s−1, which may be significant at low masses. When placed on the N2-BPT diagram ([O iii]/Hβ versus [N ii]/Hα), the broad components of the stacks are shifted toward higher [O iii]/Hβ and [N ii]/Hα ratios compared to the narrow component. We compare the location of the broad components to shock models and find that the broad component could be explained as a shocked outflow, but we do not rule out other possibilities, such as the presence of an AGN. We discuss the possible consequences of shocked emission on the galaxy location in emission line diagnostic diagrams and calculation of SFR. We attempt to estimate the mass outflow rate/star formation rate, but caution that our results strongly rely on the assumptions regarding the physical properties of the outflow. [ABSTRACT FROM AUTHOR]