James Webb Space Telescope Feed Post

Date: 7/9/2024

Harvard ADS: Dust in Little Red Dots

Paper abstract: JWST has revealed a ubiquitous population of "little red dots" (LRDs) at z\gtrsim4, selected via their red rest-frame optical emission and compact morphologies. They are thought to be reddened by dust, whether in tori of active galactic nuclei or the interstellar medium (ISM), though none have direct dust detections to date. Informed by the average characteristics of 675 LRDs drawn from the literature, we provide ballpark constraints on the dust characteristics of the LRD population and estimate they have average dust masses of \langle M_{dust}\rangle=(1.6^{+4.8}_{-0.9})\times10^{4} M_\odot, luminosities of \langle L_{IR}\rangle = (8^{+3}_{-5})\times10^{10} L_\odot and temperatures of \langle T_{dust}\rangle = 110^{+21}_{-36} K. Notably, the spectral energy distributions are thought to peak at ~100 K (rest-frame 20-30\mu m) regardless of heating mechanism, whether AGN or star formation. Our predictions likely mean LRDs have, on average, submillimeter emission a factor of ~100\times fainter than current ALMA limits provide. If one assumes LRDs' rest-optical light is dominated by stars, the star-to-dust ratio is a factor of ~100\times larger than expected from dust formation models; this suggests LRDs' stellar masses may be significantly overestimated. Despite their high apparent volume density, LRDs contribute negligibly (0.1%) to the cosmic dust budget at z\gtrsim4 due to their low dust masses.