[en] We present GalMC, a Markov Chain Monte Carlo (MCMC) algorithm designed to fit the spectral energy distributions (SEDs) of galaxies to infer physical properties such as age, stellar mass, dust reddening, metallicity, redshift, and star formation rate. We describe the features of the code and the extensive tests conducted to ensure that our procedure leads to unbiased parameter estimation and accurate evaluation of uncertainties. We compare its performance to grid-based algorithms, showing that the efficiency in CPU time is ∼100 times better for MCMC for a three-dimensional parameter space and increasing with the number of dimensions. We use GalMC to fit the stacked SEDs of two samples of Lyman alpha emitters (LAEs) at redshift z = 3.1. Our fit reveals that the typical LAE detected in the IRAC 3.6 μm band has age = 0.67 [0.37-1.81] Gyr and stellar mass = 3.2 [2.5-4.2] x 10⁹ M_sun, while the typical LAE not detected at 3.6 μm has age = 0.06 [0.01-0.2] Gyr and stellar mass = 2 [1.1-3.4] x 10⁸ M_sun. The SEDs of both stacks are consistent with the absence of dust. The data do not significantly prefer exponential with respect to constant star formation history. The stellar populations of these two samples are consistent with the previous study by Lai et al., with some differences due to the improved modeling of the stellar populations. A constraint on the metallicity of z = 3.1 LAEs from broadband photometry, requiring Z < Z_sun at 95% confidence, is found here for the first time.

[en] Lyα emitting (LAE) galaxies are thought to be progenitors of present-day L* galaxies. Clustering analyses have suggested that LAEs at z ∼ 3 might evolve into LAEs at z ∼ 2, but it is unclear whether the physical nature of these galaxies is compatible with this hypothesis. Several groups have investigated the properties of LAEs using spectral energy distribution (SED) fitting, but direct comparison of their results is complicated by inconsistencies in the treatment of the data and in the assumptions made in modeling the stellar populations, which are degenerate with the effects of galaxy evolution. By using the same data analysis pipeline and SED fitting software on two stacked samples of LAEs at z = 3.1 and z = 2.1, and by eliminating several systematic uncertainties that might cause a discrepancy, we determine that the physical properties of these two samples of galaxies are dramatically different. LAEs at z = 3.1 are found to be old (age ∼1 Gyr) and metal-poor (Z < 0.2 Z_☉), while LAEs at z = 2.1 appear to be young (age ∼50 Myr) and metal-rich (Z > Z_☉). The difference in the observed stellar ages makes it very unlikely that z 3.1 LAEs evolve directly into z = 2.1 LAEs. Larger samples of galaxies, studies of individual objects, and spectroscopic measurements of metallicity at these redshifts are needed to confirm this picture, which is difficult to reconcile with the effects of 1 Gyr of cosmological evolution.

[en] Population III (Pop III) galaxies are predicted to exist at high redshifts and may be rendered sufficiently bright for detection with current telescopes when gravitationally lensed by a foreground galaxy cluster. Pop III galaxies that exhibit strong Lyα emission should furthermore be identifiable from broadband photometry because of their unusual colors. Here, we report on a search for such objects at $z\gtrsim <!--\; ???\; -->6$ in the imaging data from the Cluster Lensing And Supernova survey with Hubble (CLASH), covering 25 galaxy clusters in 16 filters. Our selection algorithm returns five singly imaged candidates with Lyα-like color signatures, for which ground-based spectroscopy with current 8–10 m class telescopes should be able to test the predicted strength of the Lyα line. None of these five objects have been included in previous CLASH compilations of high-redshift galaxy candidates. However, when large grids of spectral synthesis models are applied to the study of these objects, we find that only two of these candidates are significantly better fitted by Pop III models than by more mundane, low-metallicity stellar populations.

[en] We present MIPS 24 μm observations of the Hubble Deep Field South taken with the Spitzer Space Telescope. The resulting image is 254 arcmin² in size and has a sensitivity ranging between ∼12 and ∼30 μJy rms, with a median sensitivity of ∼20 μJy rms. A total of 495 sources have been cataloged with a signal-to-noise ratio greater than 5σ. The source catalog is presented as well as source counts which have been corrected for completeness and flux boosting. The IR sources are then combined with MUSYC optical/NIR and ATHDFS radio observations to obtain redshifts and radio flux densities of the sample. We use the IR/radio flux density ratio (q₂₄) to explore the IR-radio correlation for this IR sample and find q₂₄ = 0.71 ± 0.31 for sources detected in both IR and radio. The results are extended by stacking IR sources not detected in the radio observations and we derive an average q₂₄ for redshift bins between 0 < z < 2.5. We find that the high-redshift (z>1) sources have an average q₂₄ ratio which is better fit by local LIRG SEDs rather than local ULIRG SEDs, indicating that high-redshift ULIRGs differ in their IR/radio properties. So, ULIRGs at high-redshift have SEDs different from those found locally. Infrared-faint radio sources are examined, and while nine radio sources do not have an MIPS detection and are therefore radio-loud active galactic nuclei (AGNs), only one radio source has an extreme IRAC 3.6 μm to radio flux density ratio indicating it is a radio-loud AGN at z>1.

[en] We present a rest-frame ultraviolet morphological analysis of 108 z ≅ 2.1 Lyα emitters (LAEs) in the Extended Chandra Deep Field South and compare it to a similar sample of 171 LAEs at z ≅ 3.1. Using Hubble Space Telescope images from the Galaxy Evolution from Morphology and SEDs survey, Great Observatories Origins Deep Survey, and Hubble Ultradeep Field, we measure size and photometric component distributions, where photometric components are defined as distinct clumps of UV-continuum emission. At both redshifts, >80% of LAEs have observed half-light radii <2 kpc, but the median half-light radius rises from 0.95 ± 0.04 kpc at z 3.1 to 1.41 ± 0.14 kpc at z = 2.1. A similar evolution is seen in the sizes of individual rest-UV components, but there is no evidence for evolution in the number of multi-component systems. In the z = 2.1 sample, we see clear correlations between the size of an LAE and other physical properties derived from its spectral energy distribution (SED). LAEs are found to be larger for galaxies with higher stellar mass, star formation rate, and dust obscuration, but there is no evidence for a trend between equivalent width and half-light radius at either redshift. The presence of these correlations suggests that a wide range of objects are being selected by LAE surveys at z ∼ 2, including a significant fraction of objects for which a massive and moderately extended population of old stars underlies the young starburst giving rise to the Lyα emission.

[en] Highlights: • Detailed study to quantify microplastics (MP) on Caribbean beaches • On average 261 MP were detected per kg of sand (dry weight). • A difference was found among islands, with a range of 130 to 239 MP/kg sand. • Over 95% of particles identified were fibers. • No difference was found between lee- and windward side of islands. - Abstract: Here we investigate microplastics contamination on beaches of four islands of the Lesser Antilles (Anguilla, St. Barthélemy, St. Eustatius and St. Martin/Maarten). These islands are close to the North Atlantic subtropical gyre, which contains high levels of microplastics. On average 261 ± 6 microplastics/kg of dry sand were found, with a maximum of 620 ± 96 microplastics on Grandes Cayes, Saint Martin. The vast majority of these microplastics (>95%) were fibers. Levels of microplastics differed among islands, with significantly lower levels found in St. Eustatius compared to the other Islands. No difference in microplastic levels was found between windward and leeward beaches. Our research provides a detailed study on microplastics on beaches in the Lesser Antilles. These results are important in developing a deeper understanding of the extent of the microplastic challenge within the Caribbean region, a hotspot of biodiversity.

[en] We present properties of individual and composite rest-UV spectra of continuum- and narrowband-selected star-forming galaxies (SFGs) at a redshift of 2 < z < 3.5 discovered by the MUSYC collaboration in the Extended Chandra Deep Field-South. Among our sample of 81 UV-bright SFGs, 59 have R < 25.5, of which 32 have rest-frame equivalent widths of W_Lyα > 20 Å, the canonical limit to be classified as an Lyα-emitting galaxy. We divide our data set into subsamples based on properties that we are able to measure for each individual galaxy: Lyα equivalent width, rest-frame UV colors, and redshift. Among our subsample of galaxies with R < 25.5, those with rest frame W_Lyα > 20 Å have bluer UV continua, weaker low-ionization interstellar absorption lines, weaker C IV absorption, and stronger Si II* nebular emission than those with W_Lyα < 20 Å. We measure a velocity offset of Δv ∼ 600 km s^–1 between Lyα emission and low-ionization absorption, which does not vary substantially among any of our subsamples. We find that the interstellar component, as opposed to the stellar component, dominates the high-ionization absorption line profiles. We find that the low- and high-ionization Si ionization states have similar kinematic properties, yet the low-ionization absorption is correlated with Lyα emission and the high-ionization absorption is not. These trends are consistent with outflowing neutral gas being in the form of neutral clouds embedded in ionized gas as previously suggested by Steidel et al. Moreover, our galaxies with bluer UV colors have stronger Lyα emission, weaker low-ionization absorption, and more prominent nebular emission line profiles. From a redshift of 2.7 < z < 3.5 to 2.0 < z < 2.7, our subsample of galaxies with W_Lyα < 20 Å shows no significant evolution in their physical properties or the nature of their outflows. Among our data set, UV-bright galaxies with W_Lyα > 20 Å exhibit weaker Lyα emission at lower redshifts, although we caution that this could be caused by spectroscopic confirmation of low Lyα equivalent width galaxies being harder at z ∼ 3 than z ∼ 2.

[en] We study the physical properties of 216 z ≅ 2.1 Lyα-emitting galaxies (LAEs) discovered in an ultra-deep narrow- MUSYC image of the ECDF-S. We fit their stacked spectral energy distribution (SED) using Charlot and Bruzual templates. We consider star formation histories (SFHs) parameterized by the e-folding time parameter τ, allowing for exponentially decreasing (τ > 0), exponentially increasing (τ < 0), and constant star formation rates (SFRs). We estimated the average flux at 5015 A of our LAE sample, finding a non-detection, which translates into negligible He II line emission at z ≅ 2.1. In addition to this, the lack of high equivalent width (EW) Lyα line objects ruled out the hypothesis of a top-heavy initial mass function in LAEs. The typical LAEs of our sample are characterized by best-fit parameters and 68% confidence intervals of log(M_*/M_sun) = 8.6[8.4-9.1], E(B - V) = 0.22[0.00-0.31], τ = -0.02[(- 4)-18] Gyr, and age_SF = 0.018[0.009-3] Gyr. Thus, we obtain robust measurements of low stellar mass and dust content, but we cannot place meaningful constraints on the age or SFH of the LAEs. We also calculate the instantaneous SFR to be 35[0.003-170] M_sun yr^-1, with its average over the last 100 Myr before observation giving (SFR)₁₀₀ = 4[2-30] M_sun yr^-1. When we compare the results for the same SFH, typical LAEs at z ≅ 2.1 appear dustier and show higher instantaneous SFRs than z ≅ 3.1 LAEs, while the observed stellar masses of the two samples seem consistent. Because the majority are low-mass galaxies, our typical LAEs appear to occupy the low-mass end of the distribution of star-forming galaxies at z ∼ 2. We perform SED fitting on several sub-samples selected based on photometric properties and find that LAE sub-samples at z ≅ 2.1 exhibit heterogeneous properties. The typical IRAC-bright, UV-bright, and red LAEs have the largest stellar mass and dust reddening. The typical UV-faint, IRAC-faint, and high EW LAE sub-samples appear less massive (<10⁹ M_sun) and less dusty, with E(B - V) consistent with zero.

[en] We discovered a sample of 250 Lyα emitting (LAE) galaxies at z ≅ 2.1 in an ultra-deep 3727 A narrow-band MUSYC image of the Extended Chandra Deep Field-South. The LAEs were selected to have rest-frame equivalent widths (EWs) >20 A and emission-line fluxes F_Lyα>2.0 x 10^-17 erg cm^-2 s^-1, after carefully subtracting the continuum contributions from narrow-band photometry. The median emission-line flux of our sample is F_Lyα = 4.2 x 10^-17 erg cm^-2 s^-1, corresponding to a median Lyα luminosity L_Lyα = 1.3 x 10⁴² erg s^-1 at z ≅ 2.1. At this flux, our sample is ≥90% complete. Approximately 4% of the original NB-selected candidates were detected in X-rays by Chandra, and 7% were detected in the rest-frame far-UV by the Galaxy Evolution Explorer; these objects were eliminated to minimize contamination by active galactic nuclei and low-redshift galaxies. At L_Lyα ≥ 1.3 x 10⁴² erg s^-1, the EW distribution is unbiased and is represented by an exponential with scale-length 83 ±10 A. Above this same luminosity threshold, we find a number density of 1.5 ± 0.5 x 10^-3 Mpc^-3. Neither the number density of LAEs nor the scale-length of their EW distribution show significant evolution from z ≅ 3 to z ≅ 2. We used the rest-frame UV luminosity to estimate a median star formation rate of 4 M_sun yr^-1. The median rest-frame UV slope, parameterized by the color B - R, is typical of dust-free, 0.5-1 Gyr old or moderately dusty, 300-500 Myr old population. Approximately 30% of our sample is consistent with being very young (age <100 Myr) galaxies without dust. Approximately 40% of the sample occupies the z ∼ 2 star-forming galaxy locus in the UVR two-color diagram, but the true percentage could be significantly higher taking into account photometric errors. Clustering analysis reveals that LAEs at z ≅ 2.1 have r₀ = 4.8 ± 0.9 Mpc, corresponding to a bias factor b = 1.8 ± 0.3. This implies that z ≅ 2.1 LAEs reside in dark matter halos with median masses log(M/M_sun) = 11.5^+0.4_-0.5, which are among the lowest mass halos yet probed at this redshift. We used the Sheth and Tormen conditional mass function to study the descendants of these LAEs and found that their typical present-day descendants are local galaxies with L* properties, like the Milky Way.

[en] We have co-added the X-ray flux of all known Lyα emitters (LAEs) in the 4 Ms Chandra Deep Field South (CDF-S) region, achieving the tightest upper limits yet on the X-ray to Lyα ratio. We use the X-ray data to place sensitive upper limits on the average unobscured star formation rate (SFR_X) in these galaxies. A very small fraction of Lyα galaxies in the field are individually detected in the X-rays, implying a low fraction of active galactic nucleus activity. After excluding the few X-ray-detected LAEs, we stack the undetected LAEs located in the 4 Ms CDF-S data and 250 ks Extended CDF-S (ECDF-S) data, and compute a 1σ upper limit on SFR_X < 1.6, 14, 28, 28, 140, 440, 880 M_☉ yr^–1 for LAEs located at z ∼ 0.3 and z = 2.1, 3.1, 3.2, 4.5, 5.7, and 6.5, respectively. The upper limit of SFR_X in LAEs can be then compared to SFR_Lyα derived from Lyα line and thus can constrain on the Lyα escape fraction (f^Esc_Lyα). The f^Esc_Lyα from X-ray at z ∼ 0.3 is substantially larger than that from UV or Hα. Three X-ray-detected LAE galaxies at z ∼ 0.3 show f^Esc_Lyα ∼ 3%-22%, and the average Lyα escape fraction from stacking the X-ray-undetected LAEs show f^Esc_Lyα > 28% at 3σ significance level at the same redshift. We derive a lower limit on f^Esc_Lyα > 14% (84% confidence level, 1σ lower limit) for LAEs at redshift z ∼ 2.1 and z ∼ 3.1-3.2. At z > 4, the current LAE samples are not of sufficient size to constrain SFR_X well. By averaging all the LAEs at z > 2, the X-ray non-detection constrains f^Esc_Lyα > 17% (84% confidence level, 1σ lower limit), and rejects f^Esc_Lyα < 5.7% at the 99.87% confidence level from 2.1 < z < 6.5.