ORCID Profile
0000-0002-0930-6466
Current Organisation
The University of Texas at Austin
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Publications
Measurements of the Dust Properties in z ≃ 1–3 Submillimeter Galaxies with ALMA
Publisher: American Astronomical Society
Date: 09-2021
CEERS Key Paper. III. The Diversity of Galaxy Structure and Morphology at z = 3–9 with JWST
Publisher: American Astronomical Society
Date: 03-2023
Abstract: We present a comprehensive analysis of the evolution of the morphological and structural properties of a large s le of galaxies at z = 3–9 using early James Webb Space Telescope (JWST) CEERS NIRCam observations. Our s le consists of 850 galaxies at z 3 detected in both Hubble Space Telescope (HST)/WFC3 and CEERS JWST/NIRCam images, enabling a comparison of HST and JWST morphologies. We conduct a set of visual classifications, with each galaxy in the s le classified three times. We also measure quantitative morphologies across all NIRCam filters. We find that galaxies at z 3 have a wide ersity of morphologies. Galaxies with disks make up 60% of galaxies at z = 3, and this fraction drops to ∼30% at z = 6–9, while galaxies with spheroids make up ∼30%–40% across the redshift range, and pure spheroids with no evidence for disks or irregular features make up ∼20%. The fraction of galaxies with irregular features is roughly constant at all redshifts (∼40%–50%), while those that are purely irregular increases from ∼12% to ∼20% at z 4.5. We note that these are apparent fractions, as many observational effects impact the visibility of morphological features at high redshift. On average, Spheroid-only galaxies have a higher Sérsic index, smaller size, and higher axis ratio than disk or irregular galaxies. Across all redshifts, smaller spheroid and disk galaxies tend to be rounder. Overall, these trends suggest that galaxies with established disks and spheroids exist across the full redshift range of this study, and further work with large s les at higher redshift is needed to quantify when these features first formed.
A REDSHIFT SURVEY OFHERSCHELFAR-INFRARED SELECTED STARBURSTS AND IMPLICATIONS FOR OBSCURED STAR FORMATION
Publisher: American Astronomical Society
Date: 04-12-2012
CEERS Key Paper. II. A First Look at the Resolved Host Properties of AGN at 3 < z < 5 with JWST
Publisher: American Astronomical Society
Date: 03-2023
Abstract: We report on the host properties of five X-ray-luminous active galactic nuclei (AGN) identified at 3 z 5 in the first epoch of imaging from the Cosmic Evolution Early Release Science Survey. Each galaxy has been imaged with the JWST Near-Infrared Camera, which provides rest-frame optical morphologies at these redshifts. We also derive stellar masses and star formation rates for each host by fitting its spectral energy distribution using a combination of galaxy and AGN templates. We find that three of the AGN hosts have spheroidal morphologies, one is a bulge-dominated disk, and one is dominated by pointlike emission. None are found to show strong morphological disturbances that might indicate a recent interaction or merger event. When compared to a s le of mass-matched inactive galaxies, we find that the AGN hosts have morphologies that are less disturbed and more bulge-dominated. Notably, all four of the resolved hosts have rest-frame optical colors consistent with a quenched or poststarburst stellar population. The presence of AGN in passively evolving galaxies at z 3 is significant because a rapid feedback mechanism is required in most semianalytic models and cosmological simulations to explain the growing population of massive quiescent galaxies observed at these redshifts. Our findings show that AGN can continue to inject energy into these systems after their star formation is curtailed, potentially heating their halos and preventing renewed star formation. Additional observations will be needed to determine what role this feedback may play in helping to quench these systems and/or maintain their quiescent state.
HerMES: CANDIDATE GRAVITATIONALLY LENSED GALAXIES AND LENSING STATISTICS AT SUBMILLIMETER WAVELENGTHS
Publisher: American Astronomical Society
Date: 14-12-2012
Dusty Starbursts Masquerading as Ultra-high Redshift Galaxies in JWST CEERS Observations
Publisher: American Astronomical Society
Date: 25-01-2023
Abstract: Lyman-break galaxy (LBG) candidates at z ≳ 10 are rapidly being identified in James Webb Space Telescope (JWST)/NIRCam observations. Due to the (redshifted) break produced by neutral hydrogen absorption of rest-frame UV photons, these sources are expected to drop out in the bluer filters while being well detected in redder filters. However, here we show that dust-enshrouded star-forming galaxies at lower redshifts ( z ≲ 7) may also mimic the near-infrared (near-IR) colors of z 10 LBGs, representing potential contaminants in LBG candidate s les. First, we analyze CEERS-DSFG-1, a NIRCam dropout undetected in the F115W and F150W filters but detected at longer wavelengths. Combining the JWST data with (sub)millimeter constraints, including deep NOEMA interferometric observations, we show that this source is a dusty star-forming galaxy (DSFG) at z ≈ 5.1. We also present a tentative 2.6 σ SCUBA-2 detection at 850 μ m around a recently identified z ≈ 16 LBG candidate in the same field and show that, if the emission is real and associated with this candidate, the available photometry is consistent with a z ∼ 5 dusty galaxy with strong nebular emission lines despite its blue near-IR colors. Further observations on this candidate are imperative to mitigate the low confidence of this tentative submillimeter emission and its positional uncertainty. Our analysis shows that robust (sub)millimeter detections of NIRCam dropout galaxies likely imply z ∼ 4–6 redshift solutions, where the observed near-IR break would be the result of a strong rest-frame optical Balmer break combined with high dust attenuation and strong nebular line emission, rather than the rest-frame UV Lyman break. This provides evidence that DSFGs may contaminate searches for ultra-high redshift LBG candidates from JWST observations.
An Analysis of ALMA Deep Fields and the Perceived Dearth of High-z Galaxies
Publisher: American Astronomical Society
Date: 25-07-2018
SuperCLASS – II. Photometric redshifts and characteristics of spatially resolved μJy radio sources
Publisher: Oxford University Press (OUP)
Date: 02-04-2020
Abstract: We present optical and near-infrared imaging covering a ∼1.53 deg2 region in the Super-Cluster Assisted Shear Survey (SuperCLASS) field, which aims to make the first robust weak lensing measurement at radio wavelengths. We derive photometric redshifts for ≈176 000 sources down to $i^\\prime _{\\rm AB}\\sim 24$ and present photometric redshifts for 1.4 GHz expanded Multi-Element Radio Linked Interferometer Network (e-MERLIN) and Karl G. Jansky Very Large Array (VLA) detected radio sources found in the central 0.26 deg2. We compile an initial catalogue of 149 radio sources brighter than S1.4 & 75 μJy and find their photometric redshifts span 0 & zphot & 4 with radio luminosities between 1021 and 1025 W Hz−1, with medians of $\\langle z \\rangle \\, =0.55$ and $\\langle L_{1.4}\\rangle \\, =1.9\\times 10^{23}$ W Hz−1, respectively. We find 95 per cent of the μJy radio source s le (141/149) have spectral energy distributions (SEDs) best fit by star-forming templates while 5 per cent (8/149) are better fit by active galactic nuclei (AGN). Spectral indices are calculated for sources with radio observations from the VLA and Giant Metrewave Radio Telescope (GMRT) at 325 MHz, with an average spectral slope of α = 0.59 ± 0.04. Using the full photometric redshift catalogue, we construct a density map at the redshift of the known galaxy clusters, z = 0.20 ± 0.08. Four of the five clusters are prominently detected at $\\gt 7\\, \\sigma$ in the density map and we confirm the photometric redshifts are consistent with previously measured spectra from a few galaxies at the cluster centres.
Constraining the Volume Density of Dusty Star-forming Galaxies through the First 3 mm Number Counts from ALMA
Publisher: American Astronomical Society
Date: 13-12-2018
Large-scale Structure around a z=2.1 Cluster
Publisher: American Astronomical Society
Date: 27-07-2016
HerMES: deep number counts at 250 μm, 350 μm and 500 μm in the COSMOS and GOODS-N fields and the build-up of the cosmic infrared background
Publisher: EDP Sciences
Date: 06-2012
The Physical Conditions of Emission-line Galaxies at Cosmic Dawn from JWST/NIRSpec Spectroscopy in the SMACS 0723 Early Release Observations
Publisher: American Astronomical Society
Date: 03-2023
Abstract: We present rest-frame optical emission-line flux ratio measurements for five z 5 galaxies observed by the James Webb Space Telescope Near-Infared Spectrograph (NIRSpec) in the SMACS 0723 Early Release Observations. We add several quality-control and post-processing steps to the NIRSpec pipeline reduction products in order to ensure reliable relative flux calibration of emission lines that are closely separated in wavelength, despite the uncertain absolute spectrophotometry of the current version of the reductions. Compared to z ∼ 3 galaxies in the literature, the z 5 galaxies have similar [O iii ] λ 5008/H β ratios, similar [O iii ] λ 4364/H γ ratios, and higher (∼0.5 dex) [Ne III ] λ 3870/[O II ] λ 3728 ratios. We compare the observations to MAPPINGS V photoionization models and find that the measured [Ne III ] λ 3870/[O II ] λ 3728, [O iii ] λ 4364/H γ , and [O iii ] λ 5008/H β emission-line ratios are consistent with an interstellar medium (ISM) that has very high ionization ( log ( Q ) ≃ 8 − 9 , units of cm s −1 ), low metallicity ( Z / Z ⊙ ≲ 0.2), and very high pressure ( log ( P / k ) ≃ 8 − 9 , units of cm −3 ). The combination of [O iii ] λ 4364/H γ and [O iii ] λ (4960 + 5008)/H β line ratios indicate very high electron temperatures of 4.1 log ( T e / K ) 4.4 , further implying metallicities of Z / Z ⊙ ≲ 0.2 with the application of low-redshift calibrations for “ T e -based” metallicities. These observations represent a tantalizing new view of the physical conditions of the ISM in galaxies at cosmic dawn.
The Evolution of the IR Luminosity Function and Dust-obscured Star Formation over the Past 13 Billion Years
Publisher: American Astronomical Society
Date: 03-2021
Abstract: We present the first results from the Mapping Obscuration to Reionization with ALMA (MORA) survey, the largest Atacama Large Millimeter/submillimeter Array (ALMA) blank-field contiguous survey to date (184 arcmin 2 ) and the only at 2 mm to search for dusty star-forming galaxies (DSFGs). We use the 13 sources detected above 5 σ to estimate the first ALMA galaxy number counts at this wavelength. These number counts are then combined with the state-of-the-art galaxy number counts at 1.2 and 3 mm and with a backward evolution model to place constraints on the evolution of the IR luminosity function and dust-obscured star formation in the past 13 billion years. Our results suggest a steep redshift evolution on the space density of DSFGs and confirm the flattening of the IR luminosity function at faint luminosities, with a slope of . We conclude that the dust-obscured component, which peaks at z ≈ 2–2.5, has dominated the cosmic history of star formation for the past ∼12 billion years, back to z ∼ 4. At z = 5, the dust-obscured star formation is estimated to be ∼35% of the total star formation rate density and decreases to 25%–20% at z = 6–7, implying a minor contribution of dust-enshrouded star formation in the first billion years of the universe. With the dust-obscured star formation history constrained up to the end of the epoch of reionization, our results provide a benchmark to test galaxy formation models, to study the galaxy mass assembly history, and to understand the dust and metal enrichment of the universe at early times.
Searching Far and Long. I. Pilot ALMA 2 mm Follow-up of Bright Dusty Galaxies as a Redshift Filter
Publisher: American Astronomical Society
Date: 05-2022
Abstract: A complete census of dusty star-forming galaxies (DSFGs) at early epochs is necessary to constrain the obscured contribution to the cosmic star formation rate density (CSFRD) however, DSFGs beyond z ∼ 4 are both rare and hard to identify from photometric data alone due to degeneracies in submillimeter photometry with redshift. Here, we present a pilot study obtaining follow-up Atacama Large Millimeter Array (ALMA) 2 mm observations of a complete s le of 39 850 μ m-bright dusty galaxies in the SSA22 field. Empirical modeling suggests 2 mm imaging of existing s les of DSFGs selected at 850 μ m—1 mm can quickly and easily isolate the “needle in a haystack” DSFGs that sit at z 4 or beyond. Combining archival submillimeter imaging with our measured ALMA 2 mm photometry (1 σ ∼ 0.08 mJy beam −1 rms), we characterize the galaxies’ IR spectral energy distributions (SEDs) and use them to constrain redshifts. With available redshift constraints fit via the combination of six submillimeter bands, we identify 6/39 high- z candidates each with % likelihood to sit at z 4, and find a positive correlation between redshift and 2 mm flux density. Specifically, our models suggest the addition of 2 mm to a moderately constrained IR SED will improve the accuracy of a millimeter-derived redshift from Δ z /(1 + z ) = 0.3 to Δ z /(1 + z ) = 0.2. Our IR SED characterizations provide evidence for relatively high-emissivity spectral indices (〈 β 〉 = 2.4 ± 0.3) in the s le. We measure that especially bright ( S 850 μ m 5.55 mJy) DSFGs contribute ∼10% to the cosmic-averaged CSFRD from 2 z 5, confirming findings from previous work with similar s les.
The fine line between normal and starburst galaxies
Publisher: Oxford University Press (OUP)
Date: 14-07-2017
A Long Time Ago in a Galaxy Far, Far Away: A Candidate z ∼ 12 Galaxy in Early JWST CEERS Imaging
Publisher: American Astronomical Society
Date: 12-2022
Abstract: We report the discovery of a candidate galaxy with a photo- z of z ∼ 12 in the first epoch of the James Webb Space Telescope (JWST) Cosmic Evolution Early Release Science Survey. Following conservative selection criteria, we identify a source with a robust z phot = 11.8 − 0.2 + 0.3 (1 σ uncertainty) with m F200W = 27.3 and ≳7 σ detections in five filters. The source is not detected at λ 1.4 μ m in deep imaging from both Hubble Space Telescope (HST) and JWST and has faint ∼3 σ detections in JWST F150W and HST F160W, which signal a Ly α break near the red edge of both filters, implying z ∼ 12. This object (Maisie’s Galaxy) exhibits F115W − F200W 1.9 mag (2 σ lower limit) with a blue continuum slope, resulting in 99.6% of the photo- z probability distribution function favoring z 11. All data-quality images show no artifacts at the candidate’s position, and independent analyses consistently find a strong preference for z 11. Its colors are inconsistent with Galactic stars, and it is resolved ( r h = 340 ± 14 pc). Maisie’s Galaxy has log M * / M ⊙ ∼ 8.5 and is highly star-forming (log sSFR ∼ −8.2 yr −1 ), with a blue rest-UV color ( β ∼ −2.5) indicating little dust, though not extremely low metallicity. While the presence of this source is in tension with most predictions, it agrees with empirical extrapolations assuming UV luminosity functions that smoothly decline with increasing redshift. Should follow-up spectroscopy validate this redshift, our universe was already aglow with galaxies less than 400 Myr after the Big Bang.
HerMES: CANDIDATE HIGH-REDSHIFT GALAXIES DISCOVERED WITHHERSCHEL/SPIRE,
Publisher: American Astronomical Society
Date: 13-12-2013
Erratum: “The Brightest Galaxies in the Dark Ages: Galaxies’ Dust Continuum Emission during the Reionization Era” (2018, ApJ, 862, 77)
Publisher: American Astronomical Society
Date: 30-03-2020
The Molecular Gas Reservoirs of z ∼ 2 Galaxies: A Comparison of CO(1−0) and Dust-based Molecular Gas Masses
Publisher: American Astronomical Society
Date: 18-07-2019
A POPULATION OFz> 2 FAR-INFRAREDHERSCHEL-SPIRE-SELECTED STARBURSTS
Publisher: American Astronomical Society
Date: 04-12-2012
SPITZERIMAGING OF STRONGLY LENSEDHERSCHEL-SELECTED DUSTY STAR-FORMING GALAXIES
Publisher: American Astronomical Society
Date: 12-11-2015
HerMES: COSMIC INFRARED BACKGROUND ANISOTROPIES AND THE CLUSTERING OF DUSTY STAR-FORMING GALAXIES
Publisher: American Astronomical Society
Date: 08-07-2015
Missing Giants: Predictions on Dust-obscured Galaxy Stellar Mass Assembly Throughout Cosmic Time
Publisher: American Astronomical Society
Date: 28-07-2023
Abstract: Due to their extremely dust-obscured nature, much uncertainty still exists surrounding the stellar mass growth and content in dusty, star-forming galaxies (DSFGs) at z 1. In this work, we present a numerical model built using empirical data on DSFGs to estimate their stellar mass contributions across the first ∼10 Gyr of cosmic time. We generate a dust-obscured stellar mass function that extends beyond the mass limit of star-forming stellar mass functions in the literature, and predict that massive DSFGs constitute as much as 50%–100% of all star-forming galaxies with M ≥10 11 M ⊙ at z 1. We predict the number density of massive DSFGs and find general agreement with observations, although more data is needed to narrow wide observational uncertainties. We forward-model mock massive DSFGs to their quiescent descendants and find remarkable agreement with observations from the literature demonstrating that, to first order, massive DSFGs are a sufficient ancestral population to describe the prevalence of massive quiescent galaxies at z 1. We predict that massive DSFGs and their descendants contribute as much as 25%–60% to the cosmic stellar mass density during the peak of cosmic star formation, and predict an intense epoch of population growth during the ∼1 Gyr from z = 6 to 3 during which the majority of the most massive galaxies at high- z grow and then quench. Future studies seeking to understand massive galaxy growth and evolution in the early universe should strategize synergies with data from the latest observatories (e.g., JWST and the Atacama Large Millimeter/submillimeter Array) to better include the heavily dust-obscured galaxy population.
On the Gas Content, Star Formation Efficiency, and Environmental Quenching of Massive Galaxies in Protoclusters at z ≈ 2.0–2.5
Publisher: American Astronomical Society
Date: 18-12-2019
An ALMA Survey of Submillimeter Galaxies in the ExtendedChandraDeep Field South: Spectroscopic Redshifts
Publisher: American Astronomical Society
Date: 09-05-2017
The Brightest Galaxies in the Dark Ages: Galaxies’ Dust Continuum Emission during the Reionization Era
Publisher: American Astronomical Society
Date: 25-07-2018
Physical Characterization of an Unlensed, Dusty Star-forming Galaxy at z = 5.85
Publisher: American Astronomical Society
Date: 11-12-2019
CEERS Key Paper. I. An Early Look into the First 500 Myr of Galaxy Formation with JWST
Publisher: American Astronomical Society
Date: 03-2023
Abstract: We present an investigation into the first 500 Myr of galaxy evolution from the Cosmic Evolution Early Release Science (CEERS) survey. CEERS, one of 13 JWST ERS programs, targets galaxy formation from z ∼ 0.5 to using several imaging and spectroscopic modes. We make use of the first epoch of CEERS NIRCam imaging, spanning 35.5 arcmin 2 , to search for candidate galaxies at z 9. Following a detailed data reduction process implementing several custom steps to produce high-quality reduced images, we perform multiband photometry across seven NIRCam broad- and medium-band (and six Hubble broadband) filters focusing on robust colors and accurate total fluxes. We measure photometric redshifts and devise a robust set of selection criteria to identify a s le of 26 galaxy candidates at z ∼ 9–16. These objects are compact with a median half-light radius of ∼0.5 kpc. We present an early estimate of the z ∼ 11 rest-frame ultraviolet (UV) luminosity function, finding that the number density of galaxies at M UV ∼ −20 appears to evolve very little from z ∼ 9 to 11. We also find that the abundance (surface density [arcmin −2 ]) of our candidates exceeds nearly all theoretical predictions. We explore potential implications, including that at z 10, star formation may be dominated by top-heavy initial mass functions, which would result in an increased ratio of UV light per unit halo mass, though a complete lack of dust attenuation and/or changing star formation physics may also play a role. While spectroscopic confirmation of these sources is urgently required, our results suggest that the deeper views to come with JWST should yield prolific s les of ultrahigh-redshift galaxies with which to further explore these conclusions.
Related Organisations
University Of Cambridge
Location: United Kingdom of Great Britain and Northern Ireland
Related Funding Activities
No related grants have been discovered for Caitlin Casey.