skip to main content

Search for: All records

Creators/Authors contains: "Whitaker, Katherine E."

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Abstract

    In this paper, we present the Heavy Metal Survey, which obtained ultradeep medium-resolution spectra of 21 massive quiescent galaxies at 1.3 <z< 2.3 with Keck/LRIS and MOSFIRE. With integration times of up to 16 hr per band per galaxy, we observe numerous Balmer and metal absorption lines in atmospheric windows. We successfully derive spectroscopic redshifts for all 21 galaxies, and for 19 we also measure stellar velocity dispersions (σv), ages, and elemental abundances, as detailed in an accompanying paper. Except for one emission-line active galactic nucleus, all galaxies are confirmed as quiescent through their faint or absent Hαemission and evolved stellar spectra. For most galaxies exhibiting faint Hα, elevated [Nii]/Hαsuggests a non-star-forming origin. We calculate dynamical masses (Mdyn) by combiningσvwith structural parameters obtained from the Hubble Space Telescope COSMOS(-DASH) survey and compare them with stellar masses (M*) derived using spectrophotometric modeling, considering various assumptions. For a fixed initial mass function (IMF), we observe a strong correlation betweenMdyn/M*andσv. This correlation may suggest that a varying IMF, with high-σvgalaxies being more bottom heavy, was already in place atz∼ 2. When implementing theσv-dependent IMF found in the cores of nearby early-type galaxiesandcorrecting for biases in our stellar mass and size measurements, we find a low scatter inMdyn/M*of 0.14 dex. However, these assumptions result in unphysical stellar masses, which exceed the dynamical masses by 34%. This tension suggests that distant quiescent galaxies do not simply grow inside-out into today’s massive early-type galaxies and the evolution is more complicated.

    more » « less
  2. Abstract

    The James Webb Space Telescope is revealing a new population of dust-reddened broad-line active galactic nuclei (AGN) at redshiftsz≳ 5. Here we present deep NIRSpec/Prism spectroscopy from the Cycle 1 Treasury program Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionization (UNCOVER) of 15 AGN candidates selected to be compact, with red continua in the rest-frame optical but with blue slopes in the UV. From NIRCam photometry alone, they could have been dominated by dusty star formation or an AGN. Here we show that the majority of the compact red sources in UNCOVER are dust-reddened AGN: 60% show definitive evidence for broad-line Hαwith a FWHM > 2000 km s−1, 20% of the current data are inconclusive, and 20% are brown dwarf stars. We propose an updated photometric criterion to select redz> 5 AGN that excludes brown dwarfs and is expected to yield >80% AGN. Remarkably, among allzphot> 5 galaxies with F277W – F444W > 1 in UNCOVER at least 33% are AGN regardless of compactness, climbing to at least 80% AGN for sources with F277W – F444W > 1.6. The confirmed AGN have black hole masses of 107–109M. While their UV luminosities (−16 >MUV> −20 AB mag) are low compared to UV-selected AGN at these epochs, consistent with percent-level scattered AGN light or low levels of unobscured star formation, the inferred bolometric luminosities are typical of 107–109Mblack holes radiating at ∼10%–40% the Eddington limit. The number densities are surprisingly high at ∼10−5Mpc−3mag−1, 100 times more common than the faintest UV-selected quasars, while accounting for ∼1% of the UV-selected galaxies. While their UV faintness suggests they may not contribute strongly to reionization, their ubiquity poses challenges to models of black hole growth.

    more » « less

    We present the results of a search for high-redshift (z > 9) galaxy candidates in the JWST UNCOVER survey, using deep NIRCam and NIRISS imaging in seven bands over ∼45 arcmin2 and ancillary Hubble Space Telescope (HST) observations. The NIRCam observations reach a 5σ limiting magnitude of ∼29.2 AB. The identification of high-z candidates relies on a combination of a dropout selection and photometric redshifts. We find 16 candidates at 9 < z < 12 and three candidates at 12 < z < 13, eight candidates are deemed very robust. Their lensing amplification ranges from μ = 1.2 to 11.5. Candidates have a wide range of (lensing corrected) luminosities and young ages, with low stellar masses [6.8 < log(M⋆/M⊙) < 9.5] and low star formation rates (SFR = 0.2–7 M⊙ yr−1), confirming previous findings in early JWST observations of z > 9. A few galaxies at z ∼ 9−10 appear to show a clear Balmer break between the F356W and F444W/F410M bands, which helps constrain their stellar mass. We estimate blue UV continuum slopes between β = −1.8 and −2.3, typical for early galaxies at z > 9 but not as extreme as the bluest recently discovered sources. We also find evidence for a rapid redshift-evolution of the mass-luminosity relation and a redshift evolution of the UV continuum slope for a given range of intrinsic magnitude, in line with theoretical predictions. These findings suggest that deeper JWST observations are needed to reach the fainter galaxy population at those early epochs, and follow-up spectroscopy will help better constrain the physical properties and star formation histories of a larger sample of galaxies.

    more » « less
  4. Abstract

    The James Webb Space Telescope is now detecting early black holes (BHs) as they transition from “seeds” to supermassive BHs. Recently, Bogdan et al. reported the detection of an X-ray luminous supermassive BH, UHZ-1, with a photometric redshift atz> 10. Such an extreme source at this very high redshift provides new insights on seeding and growth models for BHs given the short time available for formation and growth. Harnessing the exquisite sensitivity of JWST/NIRSpec, here we report the spectroscopic confirmation of UHZ-1 atz= 10.073 ± 0.002. We find that the NIRSpec/Prism spectrum is typical of recently discoveredz≈ 10 galaxies, characterized primarily by star formation features. We see no clear evidence of the powerful X-ray source in the rest-frame UV/optical spectrum, which may suggest heavy obscuration of the central BH, in line with the Compton-thick column density measured in the X-rays. We perform a stellar population fit simultaneously to the new NIRSpec spectroscopy and previously available photometry. The fit yields a stellar-mass estimate for the host galaxy that is significantly better constrained than prior photometric estimates (M1.40.4+0.3×108M). Given the predicted BH mass (MBH∼ 107–108M), the resulting ratio ofMBH/Mremains 2 to 3 orders of magnitude higher than local values, thus lending support to the heavy seeding channel for the formation of supermassive BHs within the first billion years of cosmic evolution.

    more » « less
  5. Abstract

    Over the past decade, rest-frame color–color diagrams have become popular tools for selecting quiescent galaxies at high redshift, breaking the color degeneracy between quiescent and dust-reddened star-forming galaxies. In this work, we study one such color–color selection tool—the rest-frameUVversusVJdiagram—by employing mock observations of cosmological galaxy formation simulations. In particular, we conduct numerical experiments assessing both trends in galaxy properties inUVJspace and the color–color evolution of massive galaxies as they quench at redshiftsz∼ 1–2. We find that our models broadly reproduce the observedUVJdiagram atz= 1–2, including (for the first time in a cosmological simulation) reproducing the population of extremely dust-reddened galaxies in the top right of theUVJdiagram. However, our models primarily populate this region with low-mass galaxies and do not produce as clear a bimodality between star-forming and quiescent galaxies as is seen in observations. The former issue is due to an excess of dust in low-mass galaxies and relatively gray attenuation curves in high-mass galaxies, while the latter is due to the overpopulation of the green valley insimba. When investigating the time evolution of galaxies on theUVJdiagram, we find that the quenching pathway on theUVJdiagram is independent of the quenching timescale, and instead dependent primarily on the average specific star formation rate in the 1 Gyr prior to the onset of quenching. Our results support the interpretation of different quenching pathways as corresponding to the divergent evolution of post-starburst and green valley galaxies.

    more » « less
  6. Abstract

    In 2022 November, the James Webb Space Telescope (JWST) returned deep near-infrared images of A2744—a powerful lensing cluster capable of magnifying distant, incipient galaxies beyond it. Together with existing Hubble Space Telescope (HST) imaging, this publicly available data set opens a fundamentally new discovery space to understand the remaining mysteries of the formation and evolution of galaxies across cosmic time. In this work, we detect and measure some 60,000 objects across the 49 arcmin2JWST footprint down to a 5σlimiting magnitude of ∼30 mag in 0.″32 apertures. Photometry is performed using circular apertures on images matched to the point-spread function (PSF) of the reddest NIRCam broad band, F444W, and cleaned of bright cluster galaxies and the related intracluster light. To give an impression of the photometric performance, we measure photometric redshifts and achieve aσNMAD≈ 0.03 based on known, but relatively small, spectroscopic samples. With this paper, we publicly release our HST and JWST PSF-matched photometric catalog with optimally assigned aperture sizes for easy use, along with single aperture catalogs, photometric redshifts, rest-frame colors, and individual magnification estimates. These catalogs will set the stage for efficient and deep spectroscopic follow up of some of the first JWST-selected samples in summer of 2023.

    more » « less
  7. Abstract Observations of cold molecular gas reservoirs are critical for understanding the shutdown of star formation in massive galaxies. While dust continuum is an efficient and affordable tracer, this method relies upon the assumption of a “normal” molecular-gas to dust mass ratio, δ GDR , typically of order 100. Recent null detections of quiescent galaxies in deep dust continuum observations support a picture where the cold gas and dust have been rapidly depleted or expelled. In this work, we present another viable explanation: a significant fraction of galaxies with low star formation per unit stellar mass are predicted to have extreme δ GDR ratios. We show that simulated massive quiescent galaxies at 0 < z < 3 in the simba cosmological simulations have δ GDR values that extend >4 orders of magnitude. The dust in most simulated quiescent galaxies is destroyed significantly more rapidly than the molecular gas depletes, and cannot be replenished. The transition from star-forming to quiescent halts dust formation via star formation processes, with dust subsequently destroyed by supernova shocks and thermal sputtering of dust grains embedded in hot plasma. After this point, the dust growth rate in the models is not sufficient to overcome the loss of >3 orders of magnitude in dust mass to return to normal values of δ GDR despite having high metallicity. Our results indicate that it is not straight forward to use a single observational indicator to robustly preselect exotic versus normal ratios. These simulations make strong predictions that can be tested with millimeter facilities. 
    more » « less
  8. null (Ed.)
  9. ABSTRACT We compare the star-forming main sequence (SFMS) of galaxies – both integrated and resolved on 1 kpc scales – between the high-resolution TNG50 simulation of IllustrisTNG and observations from the 3D-HST slitless spectroscopic survey at z ∼ 1. Contrasting integrated star formation rates (SFRs), we find that the slope and normalization of the star-forming main sequence in TNG50 are quantitatively consistent with values derived by fitting observations from 3D-HST with the Prospector Bayesian inference framework. The previous offsets of 0.2–1 dex between observed and simulated main-sequence normalizations are resolved when using the updated masses and SFRs from Prospector. The scatter is generically smaller in TNG50 than in 3D-HST for more massive galaxies with M*> 1010 M⊙, by ∼10–40 per cent, after accounting for observational uncertainties. When comparing resolved star formation, we also find good agreement between TNG50 and 3D-HST: average specific star formation rate (sSFR) radial profiles of galaxies at all masses and radii below, on, and above the SFMS are similar in both normalization and shape. Most noteworthy, massive galaxies with M*> 1010.5 M⊙, which have fallen below the SFMS due to ongoing quenching, exhibit a clear central SFR suppression, in both TNG50 and 3D-HST. In contrast, the original Illustris simulation and a variant TNG run without black hole kinetic wind feedback, do not reproduce the central SFR profile suppression seen in data. In TNG, inside-out quenching is due to the supermassive black hole (SMBH) feedback model operating at low accretion rates. 
    more » « less