arXiv subjects

Scott A. Tompkins

Publications and source records attributed to Scott A. Tompkins.

6 recordsLinked to original sources

arXiv2026

We Must Preserve Hubble given its Unique Complementarity to Webb, Roman, and Euclid

We present compelling arguments -- focusing on galaxy science -- for preserving the main imagers and operational modes of the Hubble Space Telescope (HST) for as long as is technically feasible, to assure maximum complementarity to the James Webb Space Telescope (JWST), Roman, and Euclid. HST was designed to work well over the 0.1-1.6 $μ$m wavelength range, and its unique UV-optical performance has fundamentally contributed to our understanding of galaxy assembly and the Cosmic Star Formation History (CSFH). While star-formation started at redshifts $z \gtrsim 10$, when the universe was less than 500 Myr old, the CSFH did not peak until $z \simeq 1.9$ (i.e., about 10 Gyr ago), and has steadily declined since that time. Hence, at least half of all stars in the universe formed it in the last 10 Gyrs where HST provides its unique rest-frame UV view of unobscured young, massive stars tracing cosmic star-formation, as well as unobscured Active Galactic Nuclei (AGN). HST thus uniquely probes (unobscured) young, hot, massive stars and AGN in galaxies, while JWST, Euclid and Roman reveal more advanced stages of older stellar populations, as well as relatively short-lived phases where galaxies produce and shed a lot of dust from intense star-formation, dusty AGN, and the very high redshift universe ($z \gtrsim 10$) not accessible by HST. HST is thus highly complementary to these other facilities, all of which took decades to build to ensure decades of operation. To maximize return on investment in these facilities, ways will need to be found to operate HST imaging instruments in all relevant modes for as long as possible into the JWST and Roman missions.

astro-ph.GA↗

arXiv2026

SKYSURF-11: A New Zodiacal Light Model Optimized for Optical Wavelengths

We present an improved zodiacal light model, optimized for optical wavelengths, using archival Hubble Space Telescope (HST) imaging from the SKYSURF program. The Kelsall et al. 1998 model used infrared imaging from the Diffuse Infrared Background Experiment (DIRBE) on board the Cosmic Background Explorer to create a 3D structure of the interplanetary dust cloud. However, this model cannot accurately represent zodiacal light emission outside of DIRBE's nominal wavelength bandpasses, the bluest of which is 1.25 micron. We present a revision to this model (called ZodiSURF) that incorporates analytical forms of both the scattering phase function and albedo as a function of wavelength, which are empirically determined across optical wavelengths (0.3-1.6 micron) from over 5,000 HST sky surface brightness (sky-SB) measurements. This refined model results in significantly improved predictions of zodiacal light emission at these wavelengths and for Sun angles greater than 80 deg. Fits to HST data show an uncertainty in the model of ~4.5%. Remarkably, the HST sky-SB measurements show an excess of residual diffuse light (HST Sky - ZodiSURF - Diffuse Galactic Light) of 0.013 +/- 0.006 MJy/sr. We suggest that a very dim spherical dust cloud may need to be included in the zodiacal light model, which we present here as a toy model.

astro-ph.CO↗

arXiv2026

SKYSURF. X. A Novel Method for Measuring Integrated Galaxy Light

We describe the drizzling pipeline and contents of the drizzled database for Hubble Space Telescope Cycle 27-29 Archival Legacy project "SKYSURF," the largest archival project ever approved for Hubble. SKYSURF aims to investigate the extragalactic background light using all 143,914 ACSWFC, WFC3UVIS, and WFC3IR images that have been taken by Hubble since its launch in 2002. SKYSURF has produced 38,027 single-visit mosaics and 7,893 multi-visit mosaics across 28 ACSWFC, WFC3UVIS, and WFC3IR filters using nonstandard drizzling methods, which include preserving the lowest sky-level of each visit/group in the drizzled products, applying wider apertures for cosmic-ray rejection, correcting effects caused by charge transfer efficiency degradation, and removing potential light gradients from input images via sky-map subtraction. We generate source catalogs for all drizzled products with SExtractor and provide updated star-galaxy separation parameters and integrated galaxy light (IGL) estimates for 25 of the 28 SKYSURF filters (wavelength range 0.2-1.7 um) using a novel IGL fitting method made possible by the vast SKYSURF dataset. We discuss the data processing and data analysis challenges encountered, detail our solutions, and offer suggestions that may facilitate future large-scale IGL investigations with Webb, SPHEREx, and Roman.

astro-ph.IM↗

arXiv2026

SKYSURF IX -- The Cosmic Optical and Infrared Background from Integrated Galaxy Light Measurements

As part of the SKYSURF Hubble Space Telescope (HST) Legacy Archival program we present galaxy number counts which yield measurements of the extragalactic background light (EBL) at 15 different wavelengths. We have processed 82,752 HST images across 23 filters into 16,686 mosaics using the same software and processing pipeline throughout. Using 17/23 filters that give reliable galaxy counts, we constrain the integrated galaxy light (IGL) with a 1.5-9\% error between 0.3 and 1.6 $μ$m in combination with 8 bands from WAVES (Wide Area VISTA Extragalactic Survey) and DEVILS (Deep Extragalactic Visible Legacy Survey). While HST was never intended to undertake large area surveys, through extensive quality control and filtering, we were able to extract a reliable and representative sample of fields distributed across the sky. Our final catalogs cover a combined $\approx 19.6 °^2$, with individual filters covering areas ranging from $\approx 0.16-7.0 °^2$. The combination of numerous independent sight-lines and area coverage allows us to reduce cosmic variance uncertainties in deep number counts to 0.06\%-1.8\%. For the first time we are able to establish a measurement of the IGL, $\mathrm{9.07 \pm 0.35 nW m^{-2} sr^{-1}}$, at 0.59 $μ$m using HST data. We obtain a cosmic optical background value of $ 24.45 \pm 0.50 \mathrm{nW m^{-2} sr^{-1}}$. Different techniques used to measure the COB, both directly and indirectly, have recently converged indicating that the COB arises almost exclusively from processes within galaxies. This in combination with the recent values reported from New Horizons and very high energy (VHE) constraints leaves very little room for any diffuse emission coming from outside the Milky Way.

astro-ph.CO↗

arXiv2024

Modelling the galaxy radio continuum from star formation and active galactic nuclei in the Shark semi-analytic model

We present a model of radio continuum emission associated with star formation (SF) and active galactic nuclei (AGN) implemented in the Shark semi-analytic model of galaxy formation. SF emission includes free-free and synchrotron emission, which depend on the free-electron density and the rate of core-collapse supernovae with a minor contribution from supernova remnants, respectively. AGN emission is modelled based on the jet production rate, which depends on the black hole mass, accretion rate and spin, and includes synchrotron self-absorption. Shark reproduces radio luminosity functions (RLFs) at 1.4 GHz and 150 MHz for 0 $\leq$ z $\leq$ 4, and scaling relations between radio luminosity, star formation rate and infrared luminosity of galaxies in the local and distant universe in good agreement with observations. The model also reproduces observed number counts of radio sources from 150 MHz to 8.4 GHz to within a factor of two on average, though larger discrepancies are seen at the very bright fluxes at higher frequencies. We use this model to understand how the radio continuum emission from radio-quiet AGNs can affect the measured RLFs of galaxies. We find current methods to exclude AGNs from observational samples result in large fractions of radio-quiet AGNs contaminating the "star-forming galaxies" selection and a brighter end to the resulting RLFs. We investigate how this effects the infrared-radio correlation (IRRC) and show that AGN contamination can lead to evolution of the IRRC with redshift. Without this contamination our model predicts a redshift- and stellar mass-independent IRRC, except at the dwarf-galaxy regime.

astro-ph.GA↗

arXiv2023

The cosmic radio background from 150 MHz--8.4 GHz, and its division into AGN and star-forming galaxy flux

We present a revised measurement of the extra-galactic background light (EBL) at radio frequencies based on a near complete compendium of radio source counts. We present the radio-EBL at 150 MHz, 325 MHz, 610 MHz, 1.4 GHz, 3 GHz, 5 GHz, and 8.4 GHz. In all cases the contribution to the radio-EBL, per decade of flux, exhibits a two-humped distribution well matched to the AGN and star-forming galaxy (SFG) populations, and with each population contributing roughly equal energy. Only at 3 GHz are the source count contributions to the EBL fully convergent, and hence we report empirical lower limits to the radio-EBL in the remaining bands. Adopting predictions from the SHARK semi-analytic model for the form of the SFG population, we can fit the fainter source counts providing measurements of the total contribution to the radio-EBL for the SFG and the AGN populations separately. This constitutes an empirically constrained model-dependent measurement for the SFG contribution, but a fully empirical measurement of the AGN contribution. Using the {\sc ProSpect} spectral energy distribution code we can model the UV-optical-infrared-mm-radio SFG EBL at all frequencies from the cosmic star-formation history and the adoption of a Chabrier initial mass function. However, significant discrepancy remains ($5\times$) between our source-count estimates of the radio-EBL and the direct measurements reported from the ARCADE-2 experiment. We can rule out a significant missing discrete source radio population and suggest that the cause of the high ARCADE-2 radio-EBL values may need to be sought either in the foreground subtraction or as a yet unknown diffuse component in the radio sky.

astro-ph.GA↗