We have conducted an archival Spitzer study of 38 early-type galaxies (ETGs) in order to determine the origin of the dust in approximately half of this population. Our sample galaxies generally have good wavelength coverage from 3.6um to 160um, as well as visible-wavelength HST images. We use the Spitzer data to estimate dust masses, or establish upper limits, and find that all of the ETGs with dust lanes in the HST data are detected in all of the Spitzer bands and have dust masses of ~10^{5-6.5} Msun, while galaxies without dust lanes are not detected at 70um and 160um and typically have <10^5 Msun of dust. The apparently dust-free galaxies do have 24um emission that scales with the shorter wavelength flux, yet substantially exceeds the expectations of photospheric emission by approximately a factor of three. We conclude this emission is dominated by hot, circumstellar dust around evolved stars that does not survive to form a substantial interstellar component. The order of magnitude variations in dust masses between galaxies with similar stellar populations rules out a subtantial contribution from continual, internal production in spite of the clear evidence for circumstellar dust. We demonstrate that the interstellar dust is not due to purely external accretion, unless the product of the merger rate of dusty satellites and the dust lifetime is at least an order of magnitude higher than expected. We propose that dust in ETGs is seeded by external accretion, yet the accreted dust is maintained by continued growth in externally-accreted cold gas beyond the nominal lifetime of individual grains. The several Gyr depletion time of the cold gas is long enough to reconcile the fraction of dusty ETGs with the merger rate of gas-rich satellites. As the majority of dusty ETGs are also low-luminosity AGN and likely fueled by this cold gas, their lifetime should similarly be several Gyr.
Hot versus Cold: the Dichotomy in Spherical Accretion of Cooling Flows onto Supermassive Black Holes in Elliptical Galaxies, Galaxy Groups and Clusters
Self-regulated growth of supermassive black holes by a dual jet/heating AGN feedback mechanism: methods, tests and implications for cosmological simulations
Supermassive Dark Stars and their remnants as a possible solution to three recent cosmic dawn puzzles
Colgate University（科尔盖特大学）；University of Pennsylvania（宾夕法尼亚大学）；Space Telescope Science Institute (STScI)（太空望远镜科学研究所）；Johns Hopkins University（约翰斯·霍普金斯大学）；University of Texas（德克萨斯大学）；Stockholm University（斯德哥尔摩大学）；Nordic Institute for Theoretical Physics (NORDITA)（北欧理论物理研究所）
JWST Reveals a Candidate Supermassive Black Hole Binary at z=4.3 in the Brightest Sub-millimeter Galaxy in COSMOS-Web
The University of Texas at Austin（德克萨斯大学奥斯汀分校）；University of California Santa Barbara（加州大学圣塔芭芭拉分校）；University of Colorado, Boulder（科罗拉多大学博尔德分校）；NASA-Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）
