Professor Andrew Bunker

Abstract:

Recently, a large number of compact sources at z > 4 with blue UV slopes and extremely red rest-frame optical slopes have been found in James Webb Space Telescope (JWST) extragalactic surveys. As a subsample of these sources, commonly called “little red dots” (LRDs), have been spectroscopically observed to host a broad-line active galactic nucleus (AGN), they have been the focus of multiple recent studies in an attempt to understand the origin of their UV and optical emission. Here, we assemble a sample of 123 LRDs from the literature along with spectroscopic and photometric JWST-identified samples of AGNs to compare their colors and spectral slopes. We find that while obscured AGNs at z < 6 have highly dissimilar colors to LRDs, unobscured AGNs at z < 6 span a wide range of colors, with only a subsample showing colors similar to LRDs. At z > 6, the majority of the unobscured AGNs that have been found in these samples are LRDs, but this may be related to the fact that these sources are at large bolometric luminosities. Because LRDs occupy a unique position in galaxy color space, they are more straightforward to target, and the large number of broad-line AGNs that do not have LRD colors and slopes are therefore underrepresented in many spectroscopic surveys because they are more difficult to preselect. Current LRD selection techniques return a large and disparate population, including many sources having 2–5 μm colors impacted by emission-line flux boosting in individual filters.

Abstract:

Over the past two decades, tight correlations between black hole masses (M•) and their host galaxy properties have been firmly established for massive galaxies (with stellar mass log(M*/M⊙)≳10 ) at low-z (z < 1), indicating coevolution of supermassive black holes and galaxies. However, the situation at high-z, especially beyond cosmic noon (z ≳ 2.5), is controversial. With a combination of JWST Near Infrared Camera (NIRCam)/wide field slitless spectroscopy (WFSS) from FRESCO, CONGRESS and deep multiband NIRCam/image data from JADES in the GOODS fields, we study the black-hole-to-galaxy mass relation at z ∼ 1–4. After identifying 18 broad-line active galactic nuclei (AGNs) at 1 < z < 4 (with 8 at z > 2.5) from the WFSS data, we measure their black hole masses based on broad near-infrared lines (Paα, Paβ, and He i λ10833 Å), and constrain their stellar masses from AGN-galaxy image decomposition or spectral energy distribution decomposition. Taking account of the observational biases, the intrinsic scatter of the M•−M* relation, and the errors in mass measurements, we find no significant difference in the M•/M* ratio for 2.5 < z < 4 compared to that at lower redshifts (1 < z < 2.5), suggesting no evolution of the M•−M* relation at log(M*/M⊙)≳10 up to z ∼ 4.