Search for: All records

We present high-cadence photometric and spectroscopic observations of SN 2023axu, a classical Type II supernova with an absoluteV-band peak magnitude of –17.2 ± 0.1 mag. SN 2023axu was discovered by the Distance Less Than 40 Mpc (DLT40) survey within 1 day of the last nondetection in the nearby galaxy NGC 2283 at 13.7 Mpc. We modeled the early light curve using a recently updated shock cooling model that includes the effects of line blanketing and found the explosion epoch to be MJD 59971.48 ± 0.03 and the probable progenitor to be a red supergiant. The shock cooling model underpredicts the overall UV data, which point to a possible interaction with circumstellar material. This interpretation is further supported by spectral behavior. We see a ledge feature around 4600 Å in the very early spectra (+1.1 and +1.5 days after the explosion), which can be a sign of circumstellar interaction. The signs of circumstellar material are further bolstered by the presence of absorption features blueward of Hαand Hβat day >40, which is also generally attributed to circumstellar interaction. Our analysis shows the need for high-cadence early photometric and spectroscopic data to decipher the mass-loss history of the progenitor.

 

We analyze a sample of 25 [Nev] (λ3426) emission-line galaxies at 1.4 <z< 2.3 using Hubble Space Telescope/Wide Field Camera 3 G102 and G141 grism observations from the CANDELS LyαEmission at Reionization (CLEAR) survey. [Nev] emission probes extremely energetic photoionization (creation potential of 97.11 eV) and is often attributed to energetic radiation from active galactic nuclei (AGNs), shocks from supernovae, or an otherwise very hard ionizing spectrum from the stellar continuum. In this work, we use [Nev] in conjunction with other rest-frame UV/optical emission lines ([Oii]λλ3726, 3729, [Neiii]λ3869, Hβ, [Oiii]λλ4959, 5007, Hα+[Nii]λλ6548, 6583, [Sii]λλ6716, 6731), deep (2–7 Ms) X-ray observations (from Chandra), and mid-infrared imaging (from Spitzer) to study the origin of this emission and to place constraints on the nature of the ionizing engine. The majority of the [Nev]-detected galaxies have properties consistent with ionization from AGNs. However, for our [Nev]-selected sample, the X-ray luminosities are consistent with local (z≲ 0.1) X-ray-selected Seyferts, but the [Nev] luminosities are more consistent with those fromz∼ 1 X-ray-selected QSOs. The excess [Nev] emission requires either reduced hard X-rays or a ∼0.1 keV excess. We discuss possible origins of the apparent [Nev] excess, which could be related to the “soft (X-ray) excess” observed in some QSOs and Seyferts and/or be a consequence of a complex/anisotropic geometry for the narrow-line region, combined with absorption from a warm, relativistic wind ejected from the accretion disk. We also consider implications for future studies of extreme high-ionization systems in the epoch of reionization (z≳ 6) with the James Webb Space Telescope.

 

We present an overview of the CANDELS LyαEmission At Reionization (CLEAR) survey. CLEAR is a 130 orbit program of the Hubble Space Telescope using the Wide Field Camera 3 (WFC3) IR G102 grism. CLEAR targets 12 pointings divided between the GOODS-N and GOODS-S fields of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). Combined with existing spectroscopic data from other programs, the full CLEAR data set includes spectroscopic imaging of these fields over 0.8–1.7μm. In this paper, we describe the CLEAR survey, the survey strategy, the data acquisition, reduction, processing, and science products and catalogs released alongside this paper. The catalogs include emission line fluxes and redshifts derived from the combination of the photometry and grism spectroscopy for 6048 galaxies, primarily ranging from 0.2 ≲z≲ 3. We also provide an overview of CLEAR’s science goals and results. In conjunction with this paper we provide links to electronic versions of the data products, including 1D+2D extracted spectra and emission line maps.

 

Abstract We use Paschen- β (Pa β ; 1282 nm) observations from the Hubble Space Telescope G141 grism to study the star formation and dust-attenuation properties of a sample of 29 low-redshift ( z < 0.287) galaxies in the CANDELS Ly α Emission at Reionization survey. We first compare the nebular attenuation from Pa β /H α with the stellar attenuation inferred from the spectral energy distribution, finding that the galaxies in our sample are consistent with an average ratio of the continuum attenuation to the nebular gas of 0.44, but with a large amount of excess scatter beyond the observational uncertainties. Much of this scatter is linked to a large variation between the nebular dust attenuation as measured by (space-based) Pa β to (ground-based) H α to that from (ground-based) H α /H β . This implies there are important differences between attenuation measured from grism-based/wide-aperture Pa β fluxes and the ground-based/slit-measured Balmer decrement. We next compare star formation rates (SFRs) from Pa β to those from dust-corrected UV. We perform a survival analysis to infer a census of Pa β emission implied by both detections and nondetections. We find evidence that galaxies with lower stellar mass have more scatter in their ratio of Pa β to attenuation-corrected UV SFRs. When considering our Pa β detection limits, this observation supports the idea that lower-mass galaxies experience “burstier” star formation histories. Together, these results show that Pa β is a valuable tracer of a galaxy’s SFR, probing different timescales of star formation and potentially revealing star formation that is otherwise missed by UV and optical tracers. 

We present findings of the detection of Magnesium II (Mgii,λ= 2796, 2803 Å) absorbers from the early data release of the Dark Energy Spectroscopic Instrument (DESI). DESI is projected to obtain spectroscopy of approximately 3 million quasars (QSOs), of which over 99% are anticipated to be at redshifts greater thanz> 0.3, such that DESI would be able to observe an associated or intervening Mgiiabsorber illuminated by the background QSO. We have developed an autonomous supplementary spectral pipeline that detects these systems through an initial line-fitting process and then confirms the line properties using a Markov Chain Monte Carlo sampler. Based upon a visual inspection of the resulting systems, we estimate that this sample has a purity greater than 99%. We have also investigated the completeness of our sample in regard to both the signal-to-noise properties of the input spectra and the rest-frame equivalent width (W₀) of the absorber systems. From a parent catalog containing 83,207 quasars, we detect a total of 23,921 Mgiiabsorption systems following a series of quality cuts. Extrapolating from this occurrence rate of 28.8% implies a catalog at the completion of the five-year DESI survey that will contain over eight hundred thousand Mgiiabsorbers. The cataloging of these systems will enable significant further research because they carry information regarding circumgalactic medium environments, the distribution of intervening galaxies, and the growth of metallicity across the redshift range 0.3 ≤z< 2.5.

 

Cells possess a multiplicity of non-membrane-bound compartments, which form via liquid-liquid phase separation. These condensates assemble and dissolve as needed to enable central cellular functions. One important class of condensates is those composed of two associating polymer species that form one-to-one specific bonds. What are the physical principles that underlie phase separation in such systems? To address this question, we employed coarse-grained molecular dynamics simulations to examine how the phase boundaries depend on polymer valence, stoichiometry, and binding strength. We discovered a striking phenomenon – for sufficiently strong binding, phase separation is suppressed at rational polymer stoichiometries, which we termed the magic-ratio effect. We further developed an analytical dimer-gel theory that confirmed the magic-ratio effect and disentangled the individual roles of polymer properties in shaping the phase diagram. Our work provides new insights into the factors controlling the phase diagrams of biomolecular condensates, with implications for natural and synthetic systems. 

We introduce the DESI LOW-ZSecondary Target Survey, which combines the wide-area capabilities of the Dark Energy Spectroscopic Instrument (DESI) with an efficient, low-redshift target selection method. Our selection consists of a set of color and surface brightness cuts, combined with modern machine-learning methods, to target low-redshift dwarf galaxies (z< 0.03) between 19 <r< 21 with high completeness. We employ a convolutional neural network (CNN) to select high-priority targets. The LOW-Zsurvey has already obtained over 22,000 redshifts of dwarf galaxies (M_*< 10⁹M_⊙), comparable to the number of dwarf galaxies discovered in the Sloan Digital Sky Survey DR8 and GAMA. As a spare fiber survey, LOW-Zcurrently receives fiber allocation for just ∼50% of its targets. However, we estimate that our selection is highly complete: for galaxies atz< 0.03 within our magnitude limits, we achieve better than 95% completeness with ∼1% efficiency using catalog-level photometric cuts. We also demonstrate that our CNN selectionsz< 0.03 galaxies from the photometric cuts subsample at least 10 times more efficiently while maintaining high completeness. The full 5 yr DESI program will expand the LOW-Zsample, densely mapping the low-redshift Universe, providing an unprecedented sample of dwarf galaxies, and providing critical information about how to pursue effective and efficient low-redshift surveys.

 

Abstract We report on the gas-phase metallicity gradients of a sample of 238 star-forming galaxies at 0.6 < z < 2.6, measured through deep near-infrared Hubble Space Telescope slitless spectroscopy. The observations include 12 orbit depth Hubble/WFC3 G102 grism spectra taken as a part of the CANDELS Ly α Emission at Reionization (CLEAR) survey, and archival WFC3 G102+G141 grism spectra overlapping the CLEAR footprint. The majority of galaxies in this sample are consistent with having a zero or slightly positive metallicity gradient ( dZ / dR ≥ 0, i.e., increasing with radius) across the full mass range probed (8.5 < log M * / M ⊙ < 10.5). We measure the intrinsic population scatter of the metallicity gradients, and show that it increases with decreasing stellar mass—consistent with previous reports in the literature, but confirmed here with a much larger sample. To understand the physical mechanisms governing this scatter, we search for correlations between the observed gradient and various stellar population properties at fixed mass. However, we find no evidence for a correlation with the galaxy properties we consider—including star formation rates, sizes, star formation rate surface densities, and star formation rates per gravitational potential energy. We use the observed weakness of these correlations to provide material constraints for predicted intrinsic correlations from theoretical models. 

Using spatially resolved Hαemission line maps of star-forming galaxies, we study the spatial distribution of star formation over a wide range in redshift (0.5 ≲z≲ 1.7). Ourz∼ 0.5 measurements come from deep Hubble Space Telescope (HST) Wide Field Camera 3 G102 grism spectroscopy obtained as part of the CANDELS LyαEmission at Reionization Experiment. For star-forming galaxies with log(M_*/M_⊙) ≥ 8.96, the mean Hαeffective radius is 1.2 ± 0.1 times larger than that of the stellar continuum, implying inside-out growth via star formation. This measurement agrees within 1σwith those measured atz∼ 1 andz∼ 1.7 from the 3D-HST and KMOS^3Dsurveys, respectively, implying no redshift evolution. However, we observe redshift evolution in the stellar mass surface density within 1 kpc (Σ_1kpc). Star-forming galaxies atz∼ 0.5 with a stellar mass of log(M_*/M_⊙) = 9.5 have a ratio of Σ_1kpcin Hαrelative to their stellar continuum that is lower by (19 ± 2)% compared toz∼ 1 galaxies. Σ_1kpc,Hα/Σ_1kpc,Contdecreases toward higher stellar masses. The majority of the redshift evolution in Σ_1kpc,Hα/Σ_1kpc,Contversus stellar mass stems from the fact that log(Σ_1kpc,Hα) declines twice as much as log(Σ_1kpc,Cont) fromz∼ 1 to 0.5 (at a fixed stellar mass of log(M_*/M_⊙) = 9.5). By comparing our results to the TNG50 cosmological magneto-hydrodynamical simulation, we rule out dust as the driver of this evolution. Our results are consistent with inside-out quenching following in the wake of inside-out growth, the former of which drives the significant drop in Σ_1kpc,Hαfromz∼ 1 toz∼ 0.5.

 

In most environments, organisms compete for limited resources. The number and relative abundance of species that an ecosystem can host is referred to as ‘species diversity’. The competitive-exclusion principle is a hypothesis which proposes that, in an ecosystem, competition for resources results in decreased diversity: only species best equipped to consume the available resources thrive, while their less successful competitors die off. However, many natural ecosystems foster a wide array of species despite offering relatively few resources. Researchers have proposed many competing theories to explain how this paradox can emerge, but they have mainly focused on ecosystems where nutrients are steadily supplied. By contrast, less is known about the way species diversity is maintained when nutrients are only intermittently available, for example in ecosystems that have seasons. To address this question, Erez, Lopez et al. modeled communities of bacteria in which nutrients were repeatedly added and then used up. Depending on conditions, a variety of relationships between the amount of nutrient supplied and community diversity could emerge, suggesting that ecosystems do not follow a simple, universal rule that dictates species diversity. In particular, the resulting communities displayed a higher diversity of microbes than the limit imposed by the competitive-exclusion principle. Further observations allowed Erez, Lopez et al. to suggest guiding principles for when diversity in ecosystems will be maintained or lost. In this framework, ‘early-bird’ species, which rapidly use a subset of the available nutrients, grow to dominate the ecosystem. Even though ‘late-bird’ species are more effective at consuming the remaining resources, they cannot compete with the increased sheer numbers of the ‘early-birds’, leading to a ‘rich-get-richer’ phenomenon. Oceanic plankton, arctic permafrost and many other threatened, resource-poor ecosystems across the world can dramatically influence our daily lives. Closer to home, shifts in the microbe communities that live on the surface of the human body and in the digestive system are linked to poor health. Understanding how species diversity emerges and changes will help to protect our external and internal environments.