Browsing by Author "Bacon, R."

Rest-frame ultraviolet (UV) emission lines probe electron densities, gas-phase abundances, metallicities, and ionization parameters of the emitting star-forming galaxies and their environments. The strongest main UV emission line, Ly α , has been instrumental in advancing the general knowledge of galaxy formation in the early universe. However, observing Ly α emission becomes increasingly challenging at z  ≳ 6 when the neutral hydrogen fraction of the circumgalactic and intergalactic media increases. Secondary weaker UV emission lines provide important alternative methods for studying galaxy properties at high redshift. We present a large sample of rest-frame UV emission line sources at intermediate redshift for calibrating and exploring the connection between secondary UV lines and the emitting galaxies’ physical properties and their Ly α emission. The sample of 2052 emission line sources with 1.5 <  z  < 6.4 was collected from integral field data from the MUSE-Wide and MUSE-Deep surveys taken as part of Guaranteed Time Observations. The objects were selected through untargeted source detection (i.e., no preselection of sources as in dedicated spectroscopic campaigns) in the three-dimensional MUSE data cubes. We searched optimally extracted one-dimensional spectra of the full sample for UV emission features via emission line template matching, resulting in a sample of more than 100 rest-frame UV emission line detections. We show that the detection efficiency of (non-Ly α ) UV emission lines increases with survey depth, and that the emission line strength of He  II λ 1640 Å, [O  III ] λ 1661 + O  III ] λ 1666, and [Si  III ] λ 1883 + Si  III ] λ 1892 correlate with the strength of [C  III ] λ 1907 + C  III ] λ 1909. The rest-frame equivalent width (EW 0 ) of [C  III ] λ 1907 + C  III ] λ 1909 is found to be roughly 0.22 ± 0.18 of EW 0 (Ly α ). We measured the velocity offsets of resonant emission lines with respect to systemic tracers. For C  IV λ 1548 + C  IV λ 1551 we find that Δ v C  IV ≲ 250 km s −1 , whereas Δ v Ly α falls in the range of 250−500 km s −1 which is in agreement with previous results from the literature. The electron density n e measured from [Si  III ] λ 1883 + Si  III ] λ 1892 and [C  III ] λ 1907 + C  III ] λ 1909 line flux ratios is generally < 10 5 cm −3 and the gas-phase abundance is below solar at 12 + log 10 (O/H)≈8. Lastly, we used “PhotoIonization Model Probability Density Functions” to infer physical parameters of the full sample and individual systems based on photoionization model parameter grids and observational constraints from our UV emission line searches. This reveals that the UV line emitters generally have ionization parameter log 10 (U) ≈ −2.5 and metal mass fractions that scatter around Z  ≈ 10 −2 , that is Z  ≈ 0.66  Z ⊙ . Value-added catalogs of the full sample of MUSE objects studied in this work and a collection of UV line emitters from the literature are provided with this paper.

We have conducted a two-layered spectroscopic survey (10 10 ultra deep and 30 30 deep regions) in the Hubble Ultra Deep Field (HUDF) with the Multi Unit Spectroscopic Explorer (MUSE). The combination of a large field of view, high sensitivity, and wide wavelength coverage provides an order of magnitude improvement in spectroscopically confirmed redshifts in the HUDF; i.e., 1206 secure spectroscopic redshifts for Hubble Space Telescope (HST) continuum selected objects, which corresponds to 15% of the total (7904). The redshift distribution extends well beyond z > 3 and to HST/F775W magnitudes as faint as 30 mag (AB, 1 ). In addition, 132 secure redshifts were obtained for sources with no HST counterparts that were discovered in the MUSE data cubes by a blind search for emission-line features. In total, we present 1338 high quality redshifts, which is a factor of eight increase compared with the previously known spectroscopic redshifts in the same field.We assessed redshifts mainly with the spectral features [O ii] at z < 1:5 (473 objects) and Ly at 2:9 < z < 6:7 (692 objects). With respect to F775W magnitude, a 50% completeness is reached at 26:5 mag for ultra deep and 25:5 mag for deep fields, and the completeness remains &20% up to 28–29 mag and 27 mag, respectively.We used the determined redshifts to test continuum color selection (dropout) diagrams of high-z galaxies. The selection condition for F336W dropouts successfully captures 80% of the targeted z 2:7 galaxies. However, for higher redshift selections (F435W, F606W, and F775W dropouts), the success rates decrease to 20–40%. We empirically redefine the selection boundaries to make an attempt to improve them to 60%. The revised boundaries allow bluer colors that capture Ly emitters with high Ly equivalent widths falling in the broadbands used for the color-color selection. Along with this paper, we release the redshift and line flux catalog.

We tested the performance of photometric redshifts for galaxies in the Hubble Ultra Deep field down to 30th magnitude. We compared photometric redshift estimates from three spectral fitting codes from the literature (EAZY, BPZ and BEAGLE) to high quality redshifts for 1227 galaxies from the MUSE integral field spectrograph. All these codes can return photometric redshifts with bias j(zMUSE 􀀀 pz)=(1 + zMUSE)j < 0:05 down to F775W = 30 and spectroscopic incompleteness is unlikely to strongly modify this statement. We have, however, identified clear systematic biases in the determination of photometric redshifts: in the 0:4 < z < 1:5 range, photometric redshifts are systematically biased low by as much as (zMUSE 􀀀 pz)=(1 + zMUSE) = 􀀀0:04 in the median, and at z > 3 they are systematically biased high by up to (zMUSE 􀀀 pz)=(1 + zMUSE) = 0:05, an o set that can in part be explained by adjusting the amount of intergalactic absorption applied. In agreement with previous studies we find little di erence in the performance of the di erent codes, but in contrast to those we find that adding extensive ground-based and IRAC photometry actually can worsen photo-z performance for faint galaxies.We find an outlier fraction, defined through j(zMUSE 􀀀 pz)=(1 + zMUSE)j > 0:15, of 8% for BPZ and 10% for EAZY and BEAGLE, and show explicitly that this is a strong function of magnitude. While this outlier fraction is high relative to numbers presented in the literature for brighter galaxies, they are very comparable to literature results when the depth of the data is taken into account. Finally, we demonstrate that while a redshift might be of high confidence, the association of a spectrum to the photometric object can be very uncertain and lead to a contamination of a few percent in spectroscopic training samples that do not show up as catastrophic outliers, a problem that must be tackled in order to have su ciently accurate photometric redshifts for future cosmological surveys.