Attention:The NSF Public Access Repository (PAR) system and access will be unavailable from 5:00 PM ET until 8:00 PM ET on Friday, September 11 due to maintenance. We apologize for the inconvenience.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: JWST’s PEARLS: Improved Flux Calibration for NIRCam
Abstract The Prime Extragalactic Areas for Reionization and Lensing Science, a James Webb Space Telescope (JWST) GTO program, obtained a set of unique NIRCam observations that have enabled us to significantly improve the default photometric calibration across both NIRCam modules. The observations consisted of three epochs of 4-band (F150W, F200W, F356W, and F444W) NIRCam imaging in the Spitzer IRAC Dark Field (IDF). The three epochs were six months apart and spanned the full duration of Cycle 1. As the IDF is in the JWST continuous viewing zone, we were able to design the observations such that the two modules of NIRCam, modules A and B, were flipped by 180° and completely overlapped each other’s footprints in alternate epochs. We were therefore able to directly compare the photometry of the same objects observed with different modules and detectors, and we found significant photometric residuals up to ∼0.05 mag in some detectors and filters, for the default version of the calibration files that we used (jwst_1039.pmap). Moreover, there are multiplicative gradients present in the data obtained in the two long-wavelength bands. The problem is less severe in the data reduced using the latest pmap (jwst_1130.pmapas of 2023 September), but it is still present, and is non-negligible. We provide a recipe to correct for this systematic effect to bring the two modules onto a more consistent calibration, to a photometric precision better than ∼0.02 mag.  more » « less
Award ID(s):
2307448
PAR ID:
10538404
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more » ; ; ; ; ; ; « less
Publisher / Repository:
IOP science
Date Published:
Journal Name:
Publications of the Astronomical Society of the Pacific
Volume:
136
Issue:
2
ISSN:
0004-6280
Page Range / eLocation ID:
024501
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; ; et al (, The Astrophysical Journal Supplement Series)
    Abstract We present NIRCam and NIRISS modules for DOLPHOT, a widely used crowded-field stellar photometry package. We describe details of the modules including pixel masking, astrometric alignment, star finding, photometry, catalog creation, and artificial star tests. We tested these modules using NIRCam and NIRISS images of M92 (a Milky Way globular cluster), Draco II (an ultrafaint dwarf galaxy), and Wolf–Lundmark–Mellote (a star-forming dwarf galaxy). DOLPHOT’s photometry is highly precise, and the color–magnitude diagrams are deeper and have better definition than anticipated during original program design in 2017. The primary systematic uncertainties in DOLPHOT’s photometry arise from mismatches in the model and observed point-spread functions (PSFs) and aperture corrections, each contributing ≲0.01 mag to the photometric error budget. Version 1.2 of WebbPSF models, which include charge diffusion and interpixel capacitance effects, significantly reduced PSF-related uncertainties. We also observed minor (≲0.05 mag) chip-to-chip variations in NIRCam’s zero-points, which will be addressed by the JWST flux calibration program. Globular cluster observations are crucial for photometric calibration. Temporal variations in the photometry are generally ≲0.01 mag, although rare large misalignment events can introduce errors up to 0.08 mag. We provide recommended DOLPHOT parameters, guidelines for photometric reduction, and advice for improved observing strategies. Our Early Release Science DOLPHOT data products are available on MAST, complemented by comprehensive online documentation and tutorials for using DOLPHOT with JWST imaging data. 
    more » « less
  2. ; ; ; ; ; ; ; ; ; ; et al (, The Astrophysical Journal)
    Abstract We present 21 transients from our three-epoch, four-band NIRCam observations covering 14.16 arcmin2in the Spitzer IRAC Dark Field (IDF), taken by the JWST Prime Extragalactic Areas for Reionization and Lensing Science program with a time cadence of ∼6 months. A separate Hubble Space Telescope program provided Advanced Camera for Surveys optical imaging contemporaneous with the second and third epochs of the NIRCam observations. The NIRSpec spectroscopy on three transients confirmed a Type Ia supernova atz= 1.63 and the host galaxies of the other two atz= 2.64 and 1.90, respectively. Combining these with the photometric redshifts (zph) of the host galaxies in the rest of the sample, we find that the transients are in either a “mid-z” group atz > 1.6 withMV ≲ − 16.0 mag or a “low-z” group atz < 0.4 withMH ≳ − 14.0 mag. The mid-ztransients are consistent with supernovae. In contrast, the low-ztransients’ luminosities fall in the range of the so-called “gap transients” between supernovae and novae. However, this latter conclusion is only tentative due to possible catastrophic failures inzphthat could bias them to low-z. Conversely, if they are indeed atz < 0.4, it would be worth studying similar transients in the future. Our work further demonstrates the power of NIRCam in transient science and also shows that it would be more fruitful to carry out a long-term monitoring program with more passbands, a higher cadence, and prompt follow-up spectroscopy. Being in the continuous viewing zone of the JWST, the IDF is an ideal field for this purpose. 
    more » « less
  3. ; ; ; ; ; ; ; ; ; ; et al (, The Astrophysical Journal Supplement Series)
    Abstract We present the early data release of the multicycle JWST-NEXUS treasury program (2024–2028), which includes NIRCam imaging and WFSS observations from the first (partial) NEXUS-Wide epoch covering the central 100 arcmin2of the NEXUS field, located near the north ecliptic pole and within the Euclid Ultra-Deep Field. We release reduced NIRCam mosaics (F090W, F115W, F150W, F200W, F356W, and F444W), photometric source catalogs, as well as preliminary WFSS spectra (in F322W2 and F444W) for the subset of bright sources (F356W <21 mag or F444W <21 mag). These observations fully cover the NEXUS-Deep area, and anchor the long-term baseline of the program. These data will be used for initial target selection for the NIRSpec/Multi-Object Spectroscopy (MOS) starting from 2025 June. The NIRCam imaging reaches depths of 27.4–28.2 (AB) mag in F090W–F444W. Upcoming NEXUS-Wide epochs will expand the area to the full ∼400 arcmin2, and improve the NIRCam exposure depths in the Wide tier by a factor of 3. In addition, this central region will be repeatedly covered by the NEXUS-Deep observations (NIRCam imaging and NIRSpec/MOS PRISM spectroscopy) over 18 epochs with a ∼2 month cadence. We demonstrate the data quality of the first NEXUS observations, and showcase some example science cases enabled by these data. 
    more » « less
  4. ; ; ; ; ; ; ; ; ; ; et al (, The Astrophysical Journal Supplement Series)
    Abstract We present the JWST Resolved Stellar Populations Early Release Science (ERS) program. We obtained 27.5 hr of NIRCam and NIRISS imaging of three targets in the Local Group (Milky Way globular cluster M92, ultrafaint dwarf galaxy DracoII, and star-forming dwarf galaxy WLM), which span factors of ∼105in luminosity, ∼104in distance, and ∼105in surface brightness. We describe the survey strategy, scientific and technical goals, implementation details, present select NIRCam color–magnitude diagrams (CMDs), and validate the NIRCam exposure time calculator (ETC). Our CMDs are among the deepest in existence for each class of target. They touch the theoretical hydrogen-burning limit in M92 (<0.08M⊙;MF090W∼ +13.6), include the lowest-mass stars observed outside the Milky Way in Draco II (0.09M⊙;MF090W∼ +12.1), and reach ∼1.5 mag below the oldest main-sequence turnoff in WLM (MF090W∼ +4.6). The PARSEC stellar models provide a good qualitative match to the NIRCam CMDs, though they are ∼0.05 mag too blue compared to M92 F090W − F150W data. Our CMDs show detector-dependent color offsets ranging from ∼0.02 mag in F090W – F150W to ∼0.1 mag in F277W – F444W; these appear to be due to differences in the zero-point calibrations among the detectors. The NIRCam ETC (v2.0) matches the signal-to-noise ratios based on photon noise in uncrowded fields, but the ETC may not be accurate in more crowded fields, similar to what is known for the Hubble Space Telescope. We release the point-source photometry package DOLPHOT, optimized for NIRCam and NIRISS, for the community. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al (, The Astrophysical Journal Supplement Series)
    Abstract With its unprecedented sensitivity and spatial resolution, the James Webb Space Telescope (JWST) has opened a new window for time-domain discoveries in the infrared. Here we report observations in the only field that has received four epochs (spanning 126 days) of JWST NIRCam observations in Cycle 1. This field is toward MACS J0416.1−2403, which is a rich galaxy cluster at redshiftz= 0.4 and is one of the Hubble Frontier Fields. We have discovered 14 transients from these data. Twelve of these transients happened in three galaxies (withz= 0.94, 1.01, and 2.091) crossing a lensing caustic of the cluster, and these transients are highly magnified by gravitational lensing. These 12 transients are likely of a similar nature to those previously reported based on the Hubble Space Telescope (HST) data in this field, i.e., individual stars in the highly magnified arcs. However, these 12 could not have been found by HST because they were too red and too faint. The other two transients are associated with background galaxies (z= 2.205 and 0.7093) that are only moderately magnified, and they are likely supernovae. They indicate a demagnified supernova surface density, when monitored at a time cadence of a few months to a ∼3–4μm survey limit of AB ∼28.5 mag, of ∼0.5 arcmin−2integrated toz≈ 2. This survey depth is beyond the capability of HST but can be easily reached by JWST. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Text Encoded Conversion
  • XML
  • Save / Share this Record
  • Send to Email