A Comprehensive Photometric Selection of “Little Red Dots” in MIRI Fields: An Infrared-Bright Little Red Dot at <i>z</i> = 3.1386 with Warm Dust Emission

Abstract JWST has revealed a population of compact “Little Red Dots” (LRDs) at z ≳ 4, with red rest-frame optical and blue UV colors. These objects are likely compact dusty starbursts or heavily reddened AGNs, playing a pivotal role in early black hole growth, dust production, and stellar assembly. We introduce a new photometric selection to identify LRDs over a broad range in redshifts and rest-frame UV to near-IR (NIR) colors enabling a more complete census of the population. This method identifies 248 LRDs with F444W &lt; 27 mag over 263 arcmin 2 in the JADES, PRIMER-COSMOS, and PRIMER-UDS fields with MIRI coverage, increasing the number density by 1.7× compared to previous samples, suggesting that previous censuses were underestimated. Most LRDs are detected in MIRI/F770W but only 7% (17) are detected in F1800W. We use MIRI-based rest-frame [1 – 3 μ m] colors to trace dust emission. F1800W-detected LRDs have a median [1 – 3 μ m] = 1.5 mag, with a broad scatter indicative of diverse dust emission properties. About 20% exhibit colors [1 – 3 μ m] &lt; 1 mag consistent with negligible dust emission, but the majority show significant dust emission at 3 μ m ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>f</mml:mi> <mml:mrow> <mml:mn>3</mml:mn> <mml:mi>μ</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> <mml:mi>dust</mml:mi> </mml:msubsup> <mml:mo>≲</mml:mo> <mml:mn>0.8</mml:mn> </mml:math> ) from the galaxy’s interstellar medium or a hot-dust-deficient active galactic nucleus torus. The correlation between bluer UV to NIR colors and stronger IR emission suggests that the bluest LRDs may resemble unobscured QSOs. We report an LRD at z spec = 3.1386, detected by MIRI, Spitzer/MIPS, and Herschel/PACS. Its IR spectral energy distribution rises steeply at λ rest &gt; 6 μ m and peaks near ∼40 μ m, providing the first direct evidence of warm dust emission ( T = 50–100 K) in an LRD.