Brought to Light II: Revealing the Origins of Cloaked Spiral Features in Cluster Passive Dwarf Galaxies

Abstract

In our companion paper (Brought to Light I: Michea et al. 2021), we reveal spectacular spiral galaxy-like features in deep optical imaging of nine Virgo early-type dwarf galaxies, hidden beneath a dominating smooth stellar disk. Using a new combination of approaches, we find that bar- and spiral-like features contribute 2.2-6.4% of the total flux within 2 R${}_{\mathrm{eff}}$. In this study, we conduct high resolution simulations of cluster harassment of passive dwarf galaxies. Following close pericenter passages of the cluster core, tidal triggering generates features in our model disks that bear a striking resemblance to the observed features. However, we find the disks must be highly rotationally supported (V${}_{\mathrm{peak}}/{\sigma }_0\sim 3$), much higher than typically observed. We propose that some early-type dwarfs may contain a few percent of their mass in a cold, thin disk which is buried in the light of a hot, diffuse disk, and only revealed when they undergo tidal triggering. The red optical colors of our sample do not indicate any recent significant star formation, and our simulations show that very plunging pericenter passages (r${}_{\mathrm{peri}}<0.25$r${}_{\mathrm{vir}}$) are required for tidal triggering. Thus, many cluster early-type dwarfs with less plunging orbits may host a yet undetected cold stellar disk component. We discuss possible origin scenarios and consider why similar mass star-forming galaxies in the field are significantly more thin disk dominated than in our cluster sample.

20 pages, 12 figures, 2 tables. Accepted to ApJ. Companion paper: Brought to Light I (Michea et al. 2021) accepted to AJ, also listed on arXiv today (1st of April, 2021)

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• The First Fall is the Hardest: The Importance of Peculiar Galaxy Dynamics at Infall Time for Tidal Stripping Acting at the Centers of Groups and Clusters
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• The Galaxy Replacement Technique (GRT): a New Approach to Study Tidal Stripping and Formation of Intracluster Light in a Cosmological Context
• Brought to Light I: Quantification of Disk Substructure in Dwarf Early-Type Galaxies
• Evidence for globular cluster collapse after a dwarf-dwarf merger: A potential nuclear star cluster in formation
• Probing the Low-mass End of the Black Hole Mass Function via a Study of Faint Local Spiral Galaxies
• Identification of Intermediate-mass Black Hole Candidates Among a Sample of Sd Galaxies
• New observational recipes for measuring dynamical state of galaxy clusters
• Early-type Dwarf Galaxies in the Local Universe. Evidence of Ex-situ Growth
• Brought to Light III: Colors of Disk and Clump Substructures in Dwarf Early-Type Galaxies of the Fornax Cluster