ORCID Profile
0000-0002-2200-9845
Current Organisation
Association of Public and Land-grant Universities
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Publisher: American Astronomical Society
Date: 2023
Abstract: We investigate the relationship between environment, morphology, and the star formation rate (SFR)–stellar mass relation derived from a s le of star-forming (SF) galaxies (commonly referred to as the “star formation main sequence”, SFMS) in the COSMOS field from 0 z 3.5. We constructed and fit the far-UV–far-IR spectral energy distributions of our stellar-mass-selected s le of 111,537 galaxies with stellar and dust emission models using the public packages MAGPHYS and SED3FIT . From the best-fit parameter estimates, we construct the SFR–stellar mass relation as a function of redshift, local environment, NUVrJ color diagnostics, and morphology. We find that the shape of the main sequence derived from our color–color and specific-star-formation-rate-selected SF galaxy population, including the turnover at high stellar mass, does not exhibit an environmental dependence at any redshift from 0 z 3.5. We investigate the role of morphology in the high-mass end of the SFMS to determine whether bulge growth is driving the high-mass turnover. We find that SF galaxies experience this turnover independent of bulge-to-total ratio, strengthening the case that the turnover is due to the disk component’s specific SFR evolving with stellar mass rather than bulge growth.
Publisher: American Astronomical Society
Date: 11-2022
Abstract: Observations and simulations of interacting galaxies and mergers in the local universe have shown that interactions can significantly enhance the star formation rates (SFRs) and fueling of active galactic nuclei (AGN). However, at higher redshift, some simulations suggest that the level of star formation enhancement induced by interactions is lower due to the higher gas fractions and already increased SFRs in these galaxies. To test this, we measure the SFR enhancement in a total of 2351 (1327) massive ( M * 10 10 M ⊙ ) major (1 M 1 / M 2 4) spectroscopic galaxy pairs at 0.5 z 3.0 with Δ V 5000 km s −1 (1000 km s −1 ) and projected separation kpc selected from the extensive spectroscopic coverage in the COSMOS and CANDELS fields. We find that the highest level of SFR enhancement is a factor of 1.23 − 0.09 + 0.08 in the closest projected separation bin ( kpc) relative to a stellar mass-, redshift-, and environment-matched control s le of isolated galaxies. We find that the level of SFR enhancement is a factor of ∼1.5 higher at 0.5 z 1 than at 1 z 3 in the closest projected separation bin. Among a s le of visually identified mergers, we find an enhancement of a factor of 1.86 − 0.18 + 0.29 (∼3 σ ) for coalesced systems. For this visually identified s le, we see a clear trend of increased SFR enhancement with decreasing projected separation (2.40 − 0.37 + 0.62 versus 1.58 − 0.20 + 0.29 for 0.5 z 1.6 and 1.6 z 3.0, respectively). The SFR enhancements seen in our interactions and mergers are all lower than the level seen in local s les at the same separation, suggesting that the level of interaction-induced star formation evolves significantly over this time period.
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.
Publisher: American Astronomical Society
Date: 02-2023
Abstract: The study of galaxy evolution hinges on our ability to interpret multiwavelength galaxy observations in terms of their physical properties. To do this, we rely on spectral energy distribution (SED) models, which allow us to infer physical parameters from spectrophotometric data. In recent years, thanks to wide and deep multiwave band galaxy surveys, the volume of high-quality data have significantly increased. Alongside the increased data, algorithms performing SED fitting have improved, including better modeling prescriptions, newer templates, and more extensive s ling in wavelength space. We present a comprehensive analysis of different SED-fitting codes including their methods and output with the aim of measuring the uncertainties caused by the modeling assumptions. We apply 14 of the most commonly used SED-fitting codes on s les from the CANDELS photometric catalogs at z ∼ 1 and z ∼ 3. We find agreement on the stellar mass, while we observe some discrepancies in the star formation rate (SFR) and dust-attenuation results. To explore the differences and biases among the codes, we explore the impact of the various modeling assumptions as they are set in the codes (e.g., star formation histories, nebular, dust and active galactic nucleus models) on the derived stellar masses, SFRs, and A V values. We then assess the difference among the codes on the SFR–stellar mass relation and we measure the contribution to the uncertainties by the modeling choices (i.e., the modeling uncertainties) in stellar mass (∼0.1 dex), SFR (∼0.3 dex), and dust attenuation (∼0.3 mag). Finally, we present some resources summarizing best practices in SED fitting.
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.
Location: United States of America
Location: United States of America
No related grants have been discovered for Kevin Cooke.