Abstract The Balmer decrement (H α /H β ) provides a constraint on attenuation, the cumulative effects of dust grains in the ISM. The ratio is a reliable spectroscopic tool for deriving the dust ...properties of galaxies that determine many different quantities such as star formation rate, metallicity, and SED models. Here, we measure independently both the attenuation and H α /H β of an occulting galaxy pair: VV 191. Attenuation measurements in the visible spectrum ( A V ,stars ) from dust maps derived from the F606W filter of HST and the F090W filter of JWST are matched with spaxel-by-spaxel H α /H β observations from the George and Cynthia Mitchell Spectrograph of the McDonald Observatory. The 0.5–0.7 μ m bandpass covers the Balmer lines for VV 191. The dust maps of JWST and HST provide the high sensitivity necessary for comparisons and tracking trends of the geometrically favorable galaxy. We present maps and plots of the Balmer lines for the VV 191 galaxy pair and for a specific region highlighting dust lanes for VV 191b in the overlap region. We compute A V ,H II from H α /H β and plot both quantities against A V ,stars . Our results show that regions with higher dust content, residing closer to the spiral center, dominate ionized gas attenuation, leading to an overestimation of A V ,H II by a factor of 2. Further out in the spiral arms, the lower dust content leads to more agreement between the attenuations, indicating a lower star formation rate and larger contribution from older stars to the stellar continuum outside the Petrosian radius.
Abstract James Webb Space Telescope NIRCam images have revealed 154 reliable globular cluster (GC) candidates around the z = 0.0513 elliptical galaxy VV 191a after subtracting 34 likely interlopers ...from background galaxies inside our search area. NIRCam broadband observations are made at 0.9–4.5 μ m using the F090W, F150W, F356W, and F444W filters. Using point-spread-function-matched photometry, the data are analyzed to present color–magnitude diagrams and color distributions that suggest a relatively uniform population of GCs, except for small fractions of reddest (5%–8%) and bluest (2%–4%) outliers. GC models in the F090W versus (F090W–F150W) diagram fit the NIRCam data well and show that the majority of GCs detected have a mass of ∼10 6.5 M ⊙ , with metallicities Fe/H spanning the typical range expected for GCs (−2.5 ≲ Fe/H≲ 0.5). However, the models predict ∼0.3–0.4 mag bluer (F356W–F444W) colors than the NIRCam data for a reasonable range of GC ages, metallicities, and reddening. Although our data do not quite reach the luminosity function turnover, the measured luminosity function is consistent with previous measurements, suggesting an estimated peak at m AB ∼ −9.4 ± 0.2 mag in the F090W filter.
Abstract
The diffuse, unresolved sky provides most of the photons that the Hubble Space Telescope (HST) receives, yet remains poorly understood. The HST Archival Legacy program SKYSURF aims to ...measure the 0.2–1.6
μ
m sky surface brightness (sky-SB) from over 140,000 HST images. We describe a sky-SB measurement algorithm designed for SKYSURF that is able to recover the input sky-SB from simulated images to within 1% uncertainty. We present our sky-SB measurements estimated using this algorithm on the entire SKYSURF database. Comparing our sky-SB spectral energy distribution (SED) to measurements from the literature shows general agreements. Our SKYSURF SED also reveals a possible dependence on the Sun angle, indicating either nonisotropic scattering of solar photons off interplanetary dust or an additional component to zodiacal light. Finally, we update the diffuse light limits in the near-IR based on the methods from Carleton et al., with values of 0.009 MJy sr
−1
(22 nW m
−2
sr
−1
) at 1.25
μ
m, 0.015 MJy sr
−1
(32 nW m
−2
sr
−1
) at 1.4
μ
m, and 0.013 MJy sr
−1
(25 nW m
−2
sr
−1
) at 1.6
μ
m. These estimates provide the most stringent all-sky constraints to date in this wavelength range. SKYSURF sky-SB measurements are made public on the official SKYSURF website and will be used to constrain diffuse light in future papers.
James Webb Space Telescope NIRCam images have revealed 154 reliable globular cluster (GC) candidates around the \(z = 0.0513\) elliptical galaxy VV~191a after subtracting 34 likely interlopers from ...background galaxies inside our search area. NIRCam broadband observations are made at 0.9-4.5 \(\mu\)m using the F090W, F150W, F356W, and F444W filters. Using PSF-matched photometry, the data are analyzed to present color-magnitude diagrams (CMDs) and color distributions that suggest a relatively uniform population of GCs, except for small fractions of reddest (5-8%) and bluest (2-4%) outliers. GC models in the F090W vs. (F090-F150W) diagram fit the NIRCam data well and show that the majority of GCs detected have a mass of approximately $\sim$$10^{6.5}$$M_{\odot}\(, with metallicities Fe/H spanning the typical range expected for GCs (-2.5\)\le\( Fe/H\)\le\( 0.5). However, the models predict \)\sim\(0.3-0.4 mag bluer (F356W-F444W) colors than the NIRCam data for a reasonable range of GC ages, metallicities, and reddening. Although our data does not quite reach the luminosity function turnover, the measured luminosity function is consistent with previous measurements, suggesting an estimated peak at \)m_{\rm AB}$$\sim\(-9.4 mag, \)\pm$0.2 mag in the F090W filter.
We give an overview and describe the rationale, methods, and testing of the Hubble Space Telescope (HST) Archival Legacy project "SKYSURF." SKYSURF uses HST's unique capability as an absolute ...photometer to measure the ∼0.2–1.7 μm sky-surface brightness (sky-SB) from 249,861 WFPC2, ACS, and WFC3 exposures in ∼1400 independent HST fields. SKYSURF's panchromatic data set is designed to constrain the discrete and diffuse UV to near-IR sky components: Zodiacal Light (ZL), Kuiper Belt Objects (KBOs), Diffuse Galactic Light (DGL), and the discrete plus diffuse Extragalactic Background Light (EBL). We outline SKYSURF's methods to: (1) measure sky-SB levels between detected objects; (2) measure the discrete EBL, most of which comes from AB≃17–22 mag galaxies; and (3) estimate how much truly diffuse light may exist. Simulations of HST WFC3/IR images with known sky values and gradients, realistic cosmic ray (CR) distributions, and star plus galaxy counts were processed with nine different algorithms to measure the "Lowest Estimated Sky-SB" (LES) in each image between the discrete objects. The best algorithms recover the LES values within 0.2% when there are no image gradients, and within 0.2%–0.4% when there are 5%–10% gradients. We provide a proof of concept of our methods from the WFC3/IR F125W images, where any residual diffuse light that HST sees in excess of zodiacal model predictions does not depend on the total object flux that each image contains. This enables us to present our first SKYSURF results on diffuse light in Carleton et al.
We present the first results from the HST Archival Legacy project "SKYSURF." As described in Windhorst et al., SKYSURF utilizes the large HST archive to study the diffuse UV, optical, and near-IR ...backgrounds and foregrounds in detail. Here, we utilize SKYSURF's first sky-surface-brightness measurements to constrain the level of near-IR diffuse Extragalactic Background Light (EBL) in three near-IR filters (F125W, F140W, and F160W). This is done by comparing our preliminary sky measurements of >30,000 images to zodiacal light models, carefully selecting the darkest images to avoid contamination from stray light. Our sky-surface-brightness measurements have been verified to an accuracy of better than 1%, which when combined with systematic errors associated with HST, results in sky-brightness uncertainties of ∼ 2%–4% ≃ 0.005 MJy sr−1 in each image. When compared to the Kelsall et al. zodiacal model, an isotropic diffuse background of ∼30 nW m−2 sr−1 remains, whereas using the Wright zodiacal model results in no discernible diffuse background. Based primarily on uncertainties in the foreground model subtraction, we present limits on the amount of diffuse EBL of 29, 40, and 29 nW m−2 sr−1, for F125W, F140W, and F160W, respectively. While this light is generally isotropic, our modeling at this point does not distinguish between a cosmological origin or a solar system origin (such as a dim, diffuse, spherical cloud of cometary dust).
Positive outcomes from undergraduate research experiences (UREs) have resulted in calls to broaden and diversify participation in research. However, we have little understanding of what demographics ...are reported and considered in the analyses of student outcomes from UREs. Without this information, it is impossible to assess whether participation in UREs has been diversified and how outcomes may vary by participant identity. Through a comprehensive literature search, we systematically identified 147 peer-reviewed research articles on student participation in UREs in the natural sciences, published between 2014 and 2020. We coded each paper to document which student demographic variables are reported and considered in analyses. The majority (88%) of articles on UREs reported at least one demographic variable and 62% incorporate demographics into their analyses, but demographics beyond gender and race/ethnicity were infrequently considered. Articles on independent research apprenticeships included demographics in their analyses more frequently than studies on course-based undergraduate research experiences (CUREs). Trends in reporting and analyzing demographics did not change from 2014 to 2020. Future efforts to collect these data will help assess whether goals to diversify UREs are being met and inform how to design UREs to meet the needs of diverse student groups.
Undergraduate research is one of the most valuable activities an undergraduate can engage in because of its benefits, and studies have shown that longer experiences are more beneficial. However, ...prior research has illuminated that undergraduates encounter challenges that may cause them to exit research prematurely. These studies have been almost exclusively conducted at research-intensive (R1) institutions, and it is unclear whether such challenges are generalizable to other institution types. To address this, we extended a study previously conducted at public R1 institutions. In the current study, we analyze data from 1262 students across 25 public R1s, 12 private R1s, 30 master's-granting institutions, and 20 primarily undergraduate institutions (PUIs) to assess: (1) to what extent institution type predicts students' decisions to persist in undergraduate research; and (2) what factors affect students' decisions to either stay in or consider leaving their undergraduate research experiences (UREs) at different institution types. We found students at public R1s are more likely to leave their UREs compared with students at master's-granting institutions and PUIs. However, there are few differences in why students enrolled at different institution types consider leaving or choose to stay in their UREs. This work highlights the importance of studying undergraduate research across institutions.
We present a new lens model for the $z=0.396$ galaxy cluster MACS
J0416.1$-$2403 based on a previously known set of 77 spectroscopically
confirmed, multiply imaged galaxies plus an additional set of ...42 candidate
multiply imaged galaxies from past HST and new JWST data. The new galaxies lack
spectroscopic redshifts but have geometric and/or photometric redshift
estimates that are presented here. The new model predicts magnifications and
time delays for all multiple images. The full set of constraints totals 343,
constituting the largest sample of multiple images lensed by a single cluster
to date. Caustic-crossing galaxies lensed by this cluster are especially
interesting. Some of these galaxies show transient events, most of which are
interpreted as micro-lensing of stars at cosmological distances. These
caustic-crossing arcs are expected to show similar events in future, deeper
JWST observations. We provide time delay and magnification models for all these
arcs. The time delays and the magnifications for different arcs are generally
anti-correlated, as expected from $N$-body simulations.
In the major sub-halos of the cluster, the dark-matter mass from our lens
model correlates well with the observed number of globular clusters. This
confirms earlier results, derived at lower redshifts, which suggest that
globular clusters can be used as powerful mass proxies for the halo masses when
lensing constraints are scarce or not available.
The diffuse, unresolved sky provides most of the photons that the Hubble Space Telescope (HST) receives, yet remains poorly understood. HST Archival Legacy program SKYSURF aims to measure the 0.2-1.6 ...\(\mu\)m sky surface brightness (sky-SB) from over 140,000 HST images. We describe a sky-SB measurement algorithm designed for SKYSURF that is able to recover the input sky-SB from simulated images to within 1% uncertainty. We present our sky-SB measurements estimated using this algorithm on the entire SKYSURF database. Comparing our sky-SB spectral energy distribution (SED) to measurements from the literature shows general agreements. Our SKYSURF SED also reveals a possible dependence on Sun angle, indicating either non-isotropic scattering of solar photons off interplanetary dust or an additional component to Zodiacal Light. Finally, we update Diffuse Light limits in the near-IR based on the methods from Carleton et al. (2022), with values of 0.009 MJy sr\(^{-1}\) (22 nW m\(^{-2}\) sr\(^{-1}\)) at 1.25 \(\mu\)m, 0.015 MJy sr\(^{-1}\) (32 nW m\(^{-2}\) sr\(^{-1}\)) at 1.4 \(\mu\)m, and 0.013 MJy sr\(^{-1}\) (25 nW m\(^{-2}\) sr\(^{-1}\)) at 1.6 \(\mu\)m. These estimates provide the most stringent all-sky constraints to date in this wavelength range. SKYSURF sky-SB measurements are made public on the official SKYSURF website and will be used to constrain Diffuse Light in future papers.
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